Whistler-mode waves
Whistler mode waves are Electromagnetic waves parallel to B with a right hand circular Polarization.
Non-Maxwell - Boltzmann Distribution generate waves thtough Landau damping. They display different dispersions leading to dinstinct spectral characteristics. In @ozakiWhistlermodeWavesMercurys2023 we measure Chorus whistler waves. (remya2016) Whistler waves typically propagate parallel or quasi-parallel (
@remyaPolarizationObliquelyPropagating2016
Papers
Excitation of Whistler‐Mode Waves - @maExcitationWhistlerModeWaves2025
Plasma is created in the laboratory by:
Title: Excitation of Whistler‐Mode Waves by an Electron Temperature Anisotropy in a Laboratory Plasma
Authors: Donglai Ma, Xin An, Jia Han, Shreekrishna Tripathi, Jacob Bortnik, Anton V. Artemyev, Vassilis Angelopoulos, Walter Gekelman, Patrick Pribyl
Zotero link: PDF
Abstract
Naturally occurring whistler‐mode waves in near‐Earth space play a crucial role in accelerating electrons to relativistic energies and scattering them in pitch angle, driving their precipitation into Earth's atmosphere. Here, we report on the results of a controlled laboratory experiment focusing on the excitation of whistler waves via temperature anisotropy instabilities–the same mechanism responsible for their generation in space. In our experiments, anisotropic energetic electrons, produced by perpendicularly propagating microwaves at the equator of a magnetic mirror, provide the free energy for whistler excitation. The observed whistler waves exhibit a distinct periodic excitation pattern, analogous to naturally occurring whistler emissions in space. Particle‐in‐cell simulations reveal that this periodicity arises from a self‐regulating process: whistler‐induced pitch‐angle scattering rapidly relaxes the electron anisotropy, which subsequently rebuilds due to continuous energy injection and further excites wave. Our results have direct implications for understanding the process and characteristics of whistler emissions in near‐Earth space.
,
Plain Language Summary
Whistler‐mode waves govern energetic electron dynamics across diverse plasma systems, while these electrons spontaneously drive wave excitation through velocity‐space micro‐instabilities. Our stable, reproducible experiments demonstrate controlled whistler‐mode wave excitation via a plasma instability. These waves exhibit periodic excitation patterns analogous to natural whistler emissions in space, revealing a repetitive cycle of wave emission and electron anisotropy buildup‐relaxation in both magnetospheric and laboratory driven systems. Our experiments create a new avenue to investigate whistler wave excitation mechanisms highly relevant to near‐Earth space, enhancing our understanding of energetic electron behavior and associated space weather phenomena.
,
Key Points
Whistler waves are excited using temperature‐anisotropic electrons in a magnetic mirror, similar to the inner magnetosphere
Both experiment and particle‐in‐cell simulation reveal that waves exhibit a distinct cyclic excitation pattern similar to waves in space
The periodicity is a self‐regulating process: pitch‐angle scattering relaxes electron anisotropy, which subsequently rebuilds due to continuous energy injection
Blue
the excitation of each wave element corresponds to a rapid reduction in the temperature anisotropy. Additionally, the increase in parallel electron temperature leads to a downshift in wave frequency (Figure 4c), as well as lowering the instability threshold for temperature anisotropy.
[!quote]+ Highlight (Page 6)
strong evidence that the experimentally observed repetitive whistler wave excitation is intrinsically linked to the self‐regulating nature of whistler anisotropy instability in a driven system. Because the time scale for anisotropy relaxation is significantly shorter than its build‐up, the repetition period is primarily controlled by the microwave heating rate, with greater heating power corresponding to a faster repetition rate
Questions
Of particular importance, whistler‐mode chorus waves arise from temperature anisotropic electrons with T⊥/ T‖ >1 injected from the plasma sheet into the inner magnetosphere (T⊥
[!quote]+ Highlight (Page 2)
A 2.45 GHz magnetron heats electrons through electron‐cyclotron‐resonance heating (ECRH). Microwaves propagate in the transverse electric mode with Eˆ microwaves ‖ yˆ see Figure 1 in the waveguide and become evanescent extraordinary (X‐mode) waves as they enter the plasma radially due to the cutoff and resonance conditions.
[!quote]+ Highlight (Page 2)
with ECR heating found to be most efficient when the field minimum is 305 G (fmicrowave ≃3fce)
[!quote]+ Highlight (Page 4)
The assumed instability threshold is plotted as a red dashed line in Figures 3a and 3b (Gary & Wang, 1996).
[!quote]+ Highlight (Page 4)
As the parallel thermal velocity of the electrons increases, unstable waves begin to grow preferentially along the background magnetic field when β‖e >0.025, as shown in Figure 3c (An et al., 2017; Ma et al., 2024; Yue et al., 2016). These parallel whistler waves are then detected by the B‐dot probe located outside the magnetic mirror, with a measured frequency around 0.7 fce. As the parallel electron temperature continues to rise, the wave frequency downshifts, consistent with EXP‐B observations.
[!quote]+ Highlight (Page 5)
microwave penetration depth, inferred from the thermal velocity ratio in Figure 4a, is ∼5 de, in agreement with theoretical predictions and previous experiments
[!quote]+ Highlight (Page 6)
If the parallel thermal velocity in the experiments were to keep increasing throughout each run, simple linear kinetic theory predicts that waves below 0.6fce should appear. Since no such waves were observed, we infer that the parallel thermal velocity saturates at a certain stage in the experiments as shown in Figure 3.
[!quote]+ Highlight (Page 7)
soda straw probes
[!quote]+ Highlight (Page 7)
The heating timescale in the magnetosphere can be roughly estimated by vdrift/inject/dsource, where vdrift/inject—associated with typical whistler wave source energies of 10–30 keV—ranges from 100 to 500 km/s (Gao et al., 2022), and the spatial scale of the whistler wave source is around 500 km (Agapitov et al., 2017). Thus, the heating timescale in the inner magnetosphere is of the same order as the repetition period and significantly longer than the anisotropy relaxation time:Δtrep ≃τdrive ≫ trelax.
[!quote]+ Highlight (Page 7)
Although in the inner magnetosphere the injection of energetic particles provides a continuous source of free energy (e.g., Lu et al., 2021), the underlying principle is the same as in our experiment—both represent continuously driven systems.
Important points
In tokamaks, runaway electrons can drive whistler waves unstable, leading to pitch‐angle scattering that mitigates these runaways
[!quote]+ Highlight (Page 2)
similar to the continuous injection of energetic electrons from the plasma sheet into the inner magnetosphere during geomagnetic activity, our experiments sustain anisotropic electron populations through continuous microwave heating.
[!quote]+ Highlight (Page 2)
an external driver progressively builds up the electron anisotropy until it exceeds the threshold for whistler instability, at which point whistler waves are excited. The waves then rapidly scatter electrons toward the parallel direction, reducing the anisotropy below the threshold, after which the cycle repeats as anisotropy gradually rebuilds.
[!quote]+ Highlight (Page 2)
Thermal electrons emitted from a heated cathode are accelerated by a mesh anode and collide with helium gas in the chamber, producing ionized plasma (Figure 1a). The experiments are performed in the quiescent plasma that remains after the DC discharge is switched off (plasma afterglow).
[!quote]+ Highlight (Page 3)
A photomultiplier tube (PMT) is deployed outside the vacuum chamber at the magnetic equator to detect X‐ray emissions generated when hot electrons strike the metallic surfaces of the plasma chamber. The chamber wall, made of 3/8 inch thick stainless steel, blocks X‐ray transmission below ∼ 100 keV (Wang et al., 2014). X‐ray signals intensify 2–3 ms after microwave initiation, revealing the time required for microwave‐driven electron acceleration to reach 100 keV, and further indicate the high energy tail is not important in whistler‐mode wave excitation.
[!quote]+ Highlight (Page 4)
the frequency remains stable above 0.6 fce during microwave heating suggest that the parallel electron temperature reaches a quasi‐steady state, as indicated by the dashed arrows in Figure 3b. In this state, a balance is established between microwave heating, wave‐driven electron scattering, electron escape through the loss cone, and energy dissipation due to collisions.
[!quote]+ Highlight (Page 7)
observed in the magnetosphere: The anisotropy relaxation time due to whistler wave generation is approximately t ≃50 ω− 1 ce ≃4 × 10− s (An et al., 2017; K. Nishimura et al., 2002), which is much shorter than the typical repetition period Δtrep ∼ 0.1–1 s (Gao et al., 2022; Kandar et al., 2023; Shue et al., 2015).
A static mirror of 3.5m confines the plasma and emulates the magnetosphere. 2.5GHz microwaves heat the electrons through cyclotron resonance in the y direction, maintaining and driving the temperature anisotropy that eventually excites the whistler waves. A magnetic probe measures the magnetic field fluctuations.
EXP-A: Testing different B magnitudes shows that maximum efficiency in heating arises for the 3rd harmonic of the Cyclotron frequency:
The frequency of the exited waves is independent of B value and equal to
EXP-B: Whistler waves get excited 1ms after microwave initiation, while high energy electrons are observed 2-3ms after, indicating that they do not play a role in whistler excitation
Title: Excitation of Whistler‐Mode Waves by an Electron Temperature Anisotropy in a Laboratory Plasma
Authors: Donglai Ma, Xin An, Jia Han, Shreekrishna Tripathi, Jacob Bortnik, Anton V. Artemyev, Vassilis Angelopoulos, Walter Gekelman, Patrick Pribyl
Zotero link: PDF
Abstract
Naturally occurring whistler‐mode waves in near‐Earth space play a crucial role in accelerating electrons to relativistic energies and scattering them in pitch angle, driving their precipitation into Earth's atmosphere. Here, we report on the results of a controlled laboratory experiment focusing on the excitation of whistler waves via temperature anisotropy instabilities–the same mechanism responsible for their generation in space. In our experiments, anisotropic energetic electrons, produced by perpendicularly propagating microwaves at the equator of a magnetic mirror, provide the free energy for whistler excitation. The observed whistler waves exhibit a distinct periodic excitation pattern, analogous to naturally occurring whistler emissions in space. Particle‐in‐cell simulations reveal that this periodicity arises from a self‐regulating process: whistler‐induced pitch‐angle scattering rapidly relaxes the electron anisotropy, which subsequently rebuilds due to continuous energy injection and further excites wave. Our results have direct implications for understanding the process and characteristics of whistler emissions in near‐Earth space.
,
Plain Language Summary
Whistler‐mode waves govern energetic electron dynamics across diverse plasma systems, while these electrons spontaneously drive wave excitation through velocity‐space micro‐instabilities. Our stable, reproducible experiments demonstrate controlled whistler‐mode wave excitation via a plasma instability. These waves exhibit periodic excitation patterns analogous to natural whistler emissions in space, revealing a repetitive cycle of wave emission and electron anisotropy buildup‐relaxation in both magnetospheric and laboratory driven systems. Our experiments create a new avenue to investigate whistler wave excitation mechanisms highly relevant to near‐Earth space, enhancing our understanding of energetic electron behavior and associated space weather phenomena.
,
Key Points
Whistler waves are excited using temperature‐anisotropic electrons in a magnetic mirror, similar to the inner magnetosphere
Both experiment and particle‐in‐cell simulation reveal that waves exhibit a distinct cyclic excitation pattern similar to waves in space
The periodicity is a self‐regulating process: pitch‐angle scattering relaxes electron anisotropy, which subsequently rebuilds due to continuous energy injection
Blue
the excitation of each wave element corresponds to a rapid reduction in the temperature anisotropy. Additionally, the increase in parallel electron temperature leads to a downshift in wave frequency (Figure 4c), as well as lowering the instability threshold for temperature anisotropy.
[!quote]+ Highlight (Page 6)
strong evidence that the experimentally observed repetitive whistler wave excitation is intrinsically linked to the self‐regulating nature of whistler anisotropy instability in a driven system. Because the time scale for anisotropy relaxation is significantly shorter than its build‐up, the repetition period is primarily controlled by the microwave heating rate, with greater heating power corresponding to a faster repetition rate
Questions
Of particular importance, whistler‐mode chorus waves arise from temperature anisotropic electrons with T⊥/ T‖ >1 injected from the plasma sheet into the inner magnetosphere (T⊥
[!quote]+ Highlight (Page 2)
A 2.45 GHz magnetron heats electrons through electron‐cyclotron‐resonance heating (ECRH). Microwaves propagate in the transverse electric mode with Eˆ microwaves ‖ yˆ see Figure 1 in the waveguide and become evanescent extraordinary (X‐mode) waves as they enter the plasma radially due to the cutoff and resonance conditions.
[!quote]+ Highlight (Page 2)
with ECR heating found to be most efficient when the field minimum is 305 G (fmicrowave ≃3fce)
[!quote]+ Highlight (Page 4)
The assumed instability threshold is plotted as a red dashed line in Figures 3a and 3b (Gary & Wang, 1996).
[!quote]+ Highlight (Page 4)
As the parallel thermal velocity of the electrons increases, unstable waves begin to grow preferentially along the background magnetic field when β‖e >0.025, as shown in Figure 3c (An et al., 2017; Ma et al., 2024; Yue et al., 2016). These parallel whistler waves are then detected by the B‐dot probe located outside the magnetic mirror, with a measured frequency around 0.7 fce. As the parallel electron temperature continues to rise, the wave frequency downshifts, consistent with EXP‐B observations.
[!quote]+ Highlight (Page 5)
microwave penetration depth, inferred from the thermal velocity ratio in Figure 4a, is ∼5 de, in agreement with theoretical predictions and previous experiments
[!quote]+ Highlight (Page 6)
If the parallel thermal velocity in the experiments were to keep increasing throughout each run, simple linear kinetic theory predicts that waves below 0.6fce should appear. Since no such waves were observed, we infer that the parallel thermal velocity saturates at a certain stage in the experiments as shown in Figure 3.
[!quote]+ Highlight (Page 7)
soda straw probes
[!quote]+ Highlight (Page 7)
The heating timescale in the magnetosphere can be roughly estimated by vdrift/inject/dsource, where vdrift/inject—associated with typical whistler wave source energies of 10–30 keV—ranges from 100 to 500 km/s (Gao et al., 2022), and the spatial scale of the whistler wave source is around 500 km (Agapitov et al., 2017). Thus, the heating timescale in the inner magnetosphere is of the same order as the repetition period and significantly longer than the anisotropy relaxation time:Δtrep ≃τdrive ≫ trelax.
[!quote]+ Highlight (Page 7)
Although in the inner magnetosphere the injection of energetic particles provides a continuous source of free energy (e.g., Lu et al., 2021), the underlying principle is the same as in our experiment—both represent continuously driven systems.
Important points
In tokamaks, runaway electrons can drive whistler waves unstable, leading to pitch‐angle scattering that mitigates these runaways
[!quote]+ Highlight (Page 2)
similar to the continuous injection of energetic electrons from the plasma sheet into the inner magnetosphere during geomagnetic activity, our experiments sustain anisotropic electron populations through continuous microwave heating.
[!quote]+ Highlight (Page 2)
an external driver progressively builds up the electron anisotropy until it exceeds the threshold for whistler instability, at which point whistler waves are excited. The waves then rapidly scatter electrons toward the parallel direction, reducing the anisotropy below the threshold, after which the cycle repeats as anisotropy gradually rebuilds.
[!quote]+ Highlight (Page 2)
Thermal electrons emitted from a heated cathode are accelerated by a mesh anode and collide with helium gas in the chamber, producing ionized plasma (Figure 1a). The experiments are performed in the quiescent plasma that remains after the DC discharge is switched off (plasma afterglow).
[!quote]+ Highlight (Page 3)
A photomultiplier tube (PMT) is deployed outside the vacuum chamber at the magnetic equator to detect X‐ray emissions generated when hot electrons strike the metallic surfaces of the plasma chamber. The chamber wall, made of 3/8 inch thick stainless steel, blocks X‐ray transmission below ∼ 100 keV (Wang et al., 2014). X‐ray signals intensify 2–3 ms after microwave initiation, revealing the time required for microwave‐driven electron acceleration to reach 100 keV, and further indicate the high energy tail is not important in whistler‐mode wave excitation.
[!quote]+ Highlight (Page 4)
the frequency remains stable above 0.6 fce during microwave heating suggest that the parallel electron temperature reaches a quasi‐steady state, as indicated by the dashed arrows in Figure 3b. In this state, a balance is established between microwave heating, wave‐driven electron scattering, electron escape through the loss cone, and energy dissipation due to collisions.
[!quote]+ Highlight (Page 7)
observed in the magnetosphere: The anisotropy relaxation time due to whistler wave generation is approximately t ≃50 ω− 1 ce ≃4 × 10− s (An et al., 2017; K. Nishimura et al., 2002), which is much shorter than the typical repetition period Δtrep ∼ 0.1–1 s (Gao et al., 2022; Kandar et al., 2023; Shue et al., 2015).
As the anisotropy builds, it exceeds the instability threshold, exciting whistler waves. These waves scatter-accelerate electrons in the parallel direction through cyclotron resonance, lowering the frequency from
This leads to a more isotropic state:
Title: Excitation of Whistler‐Mode Waves by an Electron Temperature Anisotropy in a Laboratory Plasma
Authors: Donglai Ma, Xin An, Jia Han, Shreekrishna Tripathi, Jacob Bortnik, Anton V. Artemyev, Vassilis Angelopoulos, Walter Gekelman, Patrick Pribyl
Zotero link: PDF
Abstract
Naturally occurring whistler‐mode waves in near‐Earth space play a crucial role in accelerating electrons to relativistic energies and scattering them in pitch angle, driving their precipitation into Earth's atmosphere. Here, we report on the results of a controlled laboratory experiment focusing on the excitation of whistler waves via temperature anisotropy instabilities–the same mechanism responsible for their generation in space. In our experiments, anisotropic energetic electrons, produced by perpendicularly propagating microwaves at the equator of a magnetic mirror, provide the free energy for whistler excitation. The observed whistler waves exhibit a distinct periodic excitation pattern, analogous to naturally occurring whistler emissions in space. Particle‐in‐cell simulations reveal that this periodicity arises from a self‐regulating process: whistler‐induced pitch‐angle scattering rapidly relaxes the electron anisotropy, which subsequently rebuilds due to continuous energy injection and further excites wave. Our results have direct implications for understanding the process and characteristics of whistler emissions in near‐Earth space.
,
Plain Language Summary
Whistler‐mode waves govern energetic electron dynamics across diverse plasma systems, while these electrons spontaneously drive wave excitation through velocity‐space micro‐instabilities. Our stable, reproducible experiments demonstrate controlled whistler‐mode wave excitation via a plasma instability. These waves exhibit periodic excitation patterns analogous to natural whistler emissions in space, revealing a repetitive cycle of wave emission and electron anisotropy buildup‐relaxation in both magnetospheric and laboratory driven systems. Our experiments create a new avenue to investigate whistler wave excitation mechanisms highly relevant to near‐Earth space, enhancing our understanding of energetic electron behavior and associated space weather phenomena.
,
Key Points
Whistler waves are excited using temperature‐anisotropic electrons in a magnetic mirror, similar to the inner magnetosphere
Both experiment and particle‐in‐cell simulation reveal that waves exhibit a distinct cyclic excitation pattern similar to waves in space
The periodicity is a self‐regulating process: pitch‐angle scattering relaxes electron anisotropy, which subsequently rebuilds due to continuous energy injection
Blue
the excitation of each wave element corresponds to a rapid reduction in the temperature anisotropy. Additionally, the increase in parallel electron temperature leads to a downshift in wave frequency (Figure 4c), as well as lowering the instability threshold for temperature anisotropy.
[!quote]+ Highlight (Page 6)
strong evidence that the experimentally observed repetitive whistler wave excitation is intrinsically linked to the self‐regulating nature of whistler anisotropy instability in a driven system. Because the time scale for anisotropy relaxation is significantly shorter than its build‐up, the repetition period is primarily controlled by the microwave heating rate, with greater heating power corresponding to a faster repetition rate
Questions
Of particular importance, whistler‐mode chorus waves arise from temperature anisotropic electrons with T⊥/ T‖ >1 injected from the plasma sheet into the inner magnetosphere (T⊥
[!quote]+ Highlight (Page 2)
A 2.45 GHz magnetron heats electrons through electron‐cyclotron‐resonance heating (ECRH). Microwaves propagate in the transverse electric mode with Eˆ microwaves ‖ yˆ see Figure 1 in the waveguide and become evanescent extraordinary (X‐mode) waves as they enter the plasma radially due to the cutoff and resonance conditions.
[!quote]+ Highlight (Page 2)
with ECR heating found to be most efficient when the field minimum is 305 G (fmicrowave ≃3fce)
[!quote]+ Highlight (Page 4)
The assumed instability threshold is plotted as a red dashed line in Figures 3a and 3b (Gary & Wang, 1996).
[!quote]+ Highlight (Page 4)
As the parallel thermal velocity of the electrons increases, unstable waves begin to grow preferentially along the background magnetic field when β‖e >0.025, as shown in Figure 3c (An et al., 2017; Ma et al., 2024; Yue et al., 2016). These parallel whistler waves are then detected by the B‐dot probe located outside the magnetic mirror, with a measured frequency around 0.7 fce. As the parallel electron temperature continues to rise, the wave frequency downshifts, consistent with EXP‐B observations.
[!quote]+ Highlight (Page 5)
microwave penetration depth, inferred from the thermal velocity ratio in Figure 4a, is ∼5 de, in agreement with theoretical predictions and previous experiments
[!quote]+ Highlight (Page 6)
If the parallel thermal velocity in the experiments were to keep increasing throughout each run, simple linear kinetic theory predicts that waves below 0.6fce should appear. Since no such waves were observed, we infer that the parallel thermal velocity saturates at a certain stage in the experiments as shown in Figure 3.
[!quote]+ Highlight (Page 7)
soda straw probes
[!quote]+ Highlight (Page 7)
The heating timescale in the magnetosphere can be roughly estimated by vdrift/inject/dsource, where vdrift/inject—associated with typical whistler wave source energies of 10–30 keV—ranges from 100 to 500 km/s (Gao et al., 2022), and the spatial scale of the whistler wave source is around 500 km (Agapitov et al., 2017). Thus, the heating timescale in the inner magnetosphere is of the same order as the repetition period and significantly longer than the anisotropy relaxation time:Δtrep ≃τdrive ≫ trelax.
[!quote]+ Highlight (Page 7)
Although in the inner magnetosphere the injection of energetic particles provides a continuous source of free energy (e.g., Lu et al., 2021), the underlying principle is the same as in our experiment—both represent continuously driven systems.
Important points
In tokamaks, runaway electrons can drive whistler waves unstable, leading to pitch‐angle scattering that mitigates these runaways
[!quote]+ Highlight (Page 2)
similar to the continuous injection of energetic electrons from the plasma sheet into the inner magnetosphere during geomagnetic activity, our experiments sustain anisotropic electron populations through continuous microwave heating.
[!quote]+ Highlight (Page 2)
an external driver progressively builds up the electron anisotropy until it exceeds the threshold for whistler instability, at which point whistler waves are excited. The waves then rapidly scatter electrons toward the parallel direction, reducing the anisotropy below the threshold, after which the cycle repeats as anisotropy gradually rebuilds.
[!quote]+ Highlight (Page 2)
Thermal electrons emitted from a heated cathode are accelerated by a mesh anode and collide with helium gas in the chamber, producing ionized plasma (Figure 1a). The experiments are performed in the quiescent plasma that remains after the DC discharge is switched off (plasma afterglow).
[!quote]+ Highlight (Page 3)
A photomultiplier tube (PMT) is deployed outside the vacuum chamber at the magnetic equator to detect X‐ray emissions generated when hot electrons strike the metallic surfaces of the plasma chamber. The chamber wall, made of 3/8 inch thick stainless steel, blocks X‐ray transmission below ∼ 100 keV (Wang et al., 2014). X‐ray signals intensify 2–3 ms after microwave initiation, revealing the time required for microwave‐driven electron acceleration to reach 100 keV, and further indicate the high energy tail is not important in whistler‐mode wave excitation.
[!quote]+ Highlight (Page 4)
the frequency remains stable above 0.6 fce during microwave heating suggest that the parallel electron temperature reaches a quasi‐steady state, as indicated by the dashed arrows in Figure 3b. In this state, a balance is established between microwave heating, wave‐driven electron scattering, electron escape through the loss cone, and energy dissipation due to collisions.
[!quote]+ Highlight (Page 7)
observed in the magnetosphere: The anisotropy relaxation time due to whistler wave generation is approximately t ≃50 ω− 1 ce ≃4 × 10− s (An et al., 2017; K. Nishimura et al., 2002), which is much shorter than the typical repetition period Δtrep ∼ 0.1–1 s (Gao et al., 2022; Kandar et al., 2023; Shue et al., 2015).
The periodicity is driven by the heating rate, as the relaxation time is negligible:
Title: Excitation of Whistler‐Mode Waves by an Electron Temperature Anisotropy in a Laboratory Plasma
Authors: Donglai Ma, Xin An, Jia Han, Shreekrishna Tripathi, Jacob Bortnik, Anton V. Artemyev, Vassilis Angelopoulos, Walter Gekelman, Patrick Pribyl
Zotero link: PDF
Abstract
Naturally occurring whistler‐mode waves in near‐Earth space play a crucial role in accelerating electrons to relativistic energies and scattering them in pitch angle, driving their precipitation into Earth's atmosphere. Here, we report on the results of a controlled laboratory experiment focusing on the excitation of whistler waves via temperature anisotropy instabilities–the same mechanism responsible for their generation in space. In our experiments, anisotropic energetic electrons, produced by perpendicularly propagating microwaves at the equator of a magnetic mirror, provide the free energy for whistler excitation. The observed whistler waves exhibit a distinct periodic excitation pattern, analogous to naturally occurring whistler emissions in space. Particle‐in‐cell simulations reveal that this periodicity arises from a self‐regulating process: whistler‐induced pitch‐angle scattering rapidly relaxes the electron anisotropy, which subsequently rebuilds due to continuous energy injection and further excites wave. Our results have direct implications for understanding the process and characteristics of whistler emissions in near‐Earth space.
,
Plain Language Summary
Whistler‐mode waves govern energetic electron dynamics across diverse plasma systems, while these electrons spontaneously drive wave excitation through velocity‐space micro‐instabilities. Our stable, reproducible experiments demonstrate controlled whistler‐mode wave excitation via a plasma instability. These waves exhibit periodic excitation patterns analogous to natural whistler emissions in space, revealing a repetitive cycle of wave emission and electron anisotropy buildup‐relaxation in both magnetospheric and laboratory driven systems. Our experiments create a new avenue to investigate whistler wave excitation mechanisms highly relevant to near‐Earth space, enhancing our understanding of energetic electron behavior and associated space weather phenomena.
,
Key Points
Whistler waves are excited using temperature‐anisotropic electrons in a magnetic mirror, similar to the inner magnetosphere
Both experiment and particle‐in‐cell simulation reveal that waves exhibit a distinct cyclic excitation pattern similar to waves in space
The periodicity is a self‐regulating process: pitch‐angle scattering relaxes electron anisotropy, which subsequently rebuilds due to continuous energy injection
Blue
the excitation of each wave element corresponds to a rapid reduction in the temperature anisotropy. Additionally, the increase in parallel electron temperature leads to a downshift in wave frequency (Figure 4c), as well as lowering the instability threshold for temperature anisotropy.
[!quote]+ Highlight (Page 6)
strong evidence that the experimentally observed repetitive whistler wave excitation is intrinsically linked to the self‐regulating nature of whistler anisotropy instability in a driven system. Because the time scale for anisotropy relaxation is significantly shorter than its build‐up, the repetition period is primarily controlled by the microwave heating rate, with greater heating power corresponding to a faster repetition rate
Questions
Of particular importance, whistler‐mode chorus waves arise from temperature anisotropic electrons with T⊥/ T‖ >1 injected from the plasma sheet into the inner magnetosphere (T⊥
[!quote]+ Highlight (Page 2)
A 2.45 GHz magnetron heats electrons through electron‐cyclotron‐resonance heating (ECRH). Microwaves propagate in the transverse electric mode with Eˆ microwaves ‖ yˆ see Figure 1 in the waveguide and become evanescent extraordinary (X‐mode) waves as they enter the plasma radially due to the cutoff and resonance conditions.
[!quote]+ Highlight (Page 2)
with ECR heating found to be most efficient when the field minimum is 305 G (fmicrowave ≃3fce)
[!quote]+ Highlight (Page 4)
The assumed instability threshold is plotted as a red dashed line in Figures 3a and 3b (Gary & Wang, 1996).
[!quote]+ Highlight (Page 4)
As the parallel thermal velocity of the electrons increases, unstable waves begin to grow preferentially along the background magnetic field when β‖e >0.025, as shown in Figure 3c (An et al., 2017; Ma et al., 2024; Yue et al., 2016). These parallel whistler waves are then detected by the B‐dot probe located outside the magnetic mirror, with a measured frequency around 0.7 fce. As the parallel electron temperature continues to rise, the wave frequency downshifts, consistent with EXP‐B observations.
[!quote]+ Highlight (Page 5)
microwave penetration depth, inferred from the thermal velocity ratio in Figure 4a, is ∼5 de, in agreement with theoretical predictions and previous experiments
[!quote]+ Highlight (Page 6)
If the parallel thermal velocity in the experiments were to keep increasing throughout each run, simple linear kinetic theory predicts that waves below 0.6fce should appear. Since no such waves were observed, we infer that the parallel thermal velocity saturates at a certain stage in the experiments as shown in Figure 3.
[!quote]+ Highlight (Page 7)
soda straw probes
[!quote]+ Highlight (Page 7)
The heating timescale in the magnetosphere can be roughly estimated by vdrift/inject/dsource, where vdrift/inject—associated with typical whistler wave source energies of 10–30 keV—ranges from 100 to 500 km/s (Gao et al., 2022), and the spatial scale of the whistler wave source is around 500 km (Agapitov et al., 2017). Thus, the heating timescale in the inner magnetosphere is of the same order as the repetition period and significantly longer than the anisotropy relaxation time:Δtrep ≃τdrive ≫ trelax.
[!quote]+ Highlight (Page 7)
Although in the inner magnetosphere the injection of energetic particles provides a continuous source of free energy (e.g., Lu et al., 2021), the underlying principle is the same as in our experiment—both represent continuously driven systems.
Important points
In tokamaks, runaway electrons can drive whistler waves unstable, leading to pitch‐angle scattering that mitigates these runaways
[!quote]+ Highlight (Page 2)
similar to the continuous injection of energetic electrons from the plasma sheet into the inner magnetosphere during geomagnetic activity, our experiments sustain anisotropic electron populations through continuous microwave heating.
[!quote]+ Highlight (Page 2)
an external driver progressively builds up the electron anisotropy until it exceeds the threshold for whistler instability, at which point whistler waves are excited. The waves then rapidly scatter electrons toward the parallel direction, reducing the anisotropy below the threshold, after which the cycle repeats as anisotropy gradually rebuilds.
[!quote]+ Highlight (Page 2)
Thermal electrons emitted from a heated cathode are accelerated by a mesh anode and collide with helium gas in the chamber, producing ionized plasma (Figure 1a). The experiments are performed in the quiescent plasma that remains after the DC discharge is switched off (plasma afterglow).
[!quote]+ Highlight (Page 3)
A photomultiplier tube (PMT) is deployed outside the vacuum chamber at the magnetic equator to detect X‐ray emissions generated when hot electrons strike the metallic surfaces of the plasma chamber. The chamber wall, made of 3/8 inch thick stainless steel, blocks X‐ray transmission below ∼ 100 keV (Wang et al., 2014). X‐ray signals intensify 2–3 ms after microwave initiation, revealing the time required for microwave‐driven electron acceleration to reach 100 keV, and further indicate the high energy tail is not important in whistler‐mode wave excitation.
[!quote]+ Highlight (Page 4)
the frequency remains stable above 0.6 fce during microwave heating suggest that the parallel electron temperature reaches a quasi‐steady state, as indicated by the dashed arrows in Figure 3b. In this state, a balance is established between microwave heating, wave‐driven electron scattering, electron escape through the loss cone, and energy dissipation due to collisions.
[!quote]+ Highlight (Page 7)
observed in the magnetosphere: The anisotropy relaxation time due to whistler wave generation is approximately t ≃50 ω− 1 ce ≃4 × 10− s (An et al., 2017; K. Nishimura et al., 2002), which is much shorter than the typical repetition period Δtrep ∼ 0.1–1 s (Gao et al., 2022; Kandar et al., 2023; Shue et al., 2015).
This could potentially be used to estimate injection parameters from the repetition time:
Title: Excitation of Whistler‐Mode Waves by an Electron Temperature Anisotropy in a Laboratory Plasma
Authors: Donglai Ma, Xin An, Jia Han, Shreekrishna Tripathi, Jacob Bortnik, Anton V. Artemyev, Vassilis Angelopoulos, Walter Gekelman, Patrick Pribyl
Zotero link: PDF
Abstract
Naturally occurring whistler‐mode waves in near‐Earth space play a crucial role in accelerating electrons to relativistic energies and scattering them in pitch angle, driving their precipitation into Earth's atmosphere. Here, we report on the results of a controlled laboratory experiment focusing on the excitation of whistler waves via temperature anisotropy instabilities–the same mechanism responsible for their generation in space. In our experiments, anisotropic energetic electrons, produced by perpendicularly propagating microwaves at the equator of a magnetic mirror, provide the free energy for whistler excitation. The observed whistler waves exhibit a distinct periodic excitation pattern, analogous to naturally occurring whistler emissions in space. Particle‐in‐cell simulations reveal that this periodicity arises from a self‐regulating process: whistler‐induced pitch‐angle scattering rapidly relaxes the electron anisotropy, which subsequently rebuilds due to continuous energy injection and further excites wave. Our results have direct implications for understanding the process and characteristics of whistler emissions in near‐Earth space.
,
Plain Language Summary
Whistler‐mode waves govern energetic electron dynamics across diverse plasma systems, while these electrons spontaneously drive wave excitation through velocity‐space micro‐instabilities. Our stable, reproducible experiments demonstrate controlled whistler‐mode wave excitation via a plasma instability. These waves exhibit periodic excitation patterns analogous to natural whistler emissions in space, revealing a repetitive cycle of wave emission and electron anisotropy buildup‐relaxation in both magnetospheric and laboratory driven systems. Our experiments create a new avenue to investigate whistler wave excitation mechanisms highly relevant to near‐Earth space, enhancing our understanding of energetic electron behavior and associated space weather phenomena.
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Key Points
Whistler waves are excited using temperature‐anisotropic electrons in a magnetic mirror, similar to the inner magnetosphere
Both experiment and particle‐in‐cell simulation reveal that waves exhibit a distinct cyclic excitation pattern similar to waves in space
The periodicity is a self‐regulating process: pitch‐angle scattering relaxes electron anisotropy, which subsequently rebuilds due to continuous energy injection
Blue
the excitation of each wave element corresponds to a rapid reduction in the temperature anisotropy. Additionally, the increase in parallel electron temperature leads to a downshift in wave frequency (Figure 4c), as well as lowering the instability threshold for temperature anisotropy.
[!quote]+ Highlight (Page 6)
strong evidence that the experimentally observed repetitive whistler wave excitation is intrinsically linked to the self‐regulating nature of whistler anisotropy instability in a driven system. Because the time scale for anisotropy relaxation is significantly shorter than its build‐up, the repetition period is primarily controlled by the microwave heating rate, with greater heating power corresponding to a faster repetition rate
Questions
Of particular importance, whistler‐mode chorus waves arise from temperature anisotropic electrons with T⊥/ T‖ >1 injected from the plasma sheet into the inner magnetosphere (T⊥
[!quote]+ Highlight (Page 2)
A 2.45 GHz magnetron heats electrons through electron‐cyclotron‐resonance heating (ECRH). Microwaves propagate in the transverse electric mode with Eˆ microwaves ‖ yˆ see Figure 1 in the waveguide and become evanescent extraordinary (X‐mode) waves as they enter the plasma radially due to the cutoff and resonance conditions.
[!quote]+ Highlight (Page 2)
with ECR heating found to be most efficient when the field minimum is 305 G (fmicrowave ≃3fce)
[!quote]+ Highlight (Page 4)
The assumed instability threshold is plotted as a red dashed line in Figures 3a and 3b (Gary & Wang, 1996).
[!quote]+ Highlight (Page 4)
As the parallel thermal velocity of the electrons increases, unstable waves begin to grow preferentially along the background magnetic field when β‖e >0.025, as shown in Figure 3c (An et al., 2017; Ma et al., 2024; Yue et al., 2016). These parallel whistler waves are then detected by the B‐dot probe located outside the magnetic mirror, with a measured frequency around 0.7 fce. As the parallel electron temperature continues to rise, the wave frequency downshifts, consistent with EXP‐B observations.
[!quote]+ Highlight (Page 5)
microwave penetration depth, inferred from the thermal velocity ratio in Figure 4a, is ∼5 de, in agreement with theoretical predictions and previous experiments
[!quote]+ Highlight (Page 6)
If the parallel thermal velocity in the experiments were to keep increasing throughout each run, simple linear kinetic theory predicts that waves below 0.6fce should appear. Since no such waves were observed, we infer that the parallel thermal velocity saturates at a certain stage in the experiments as shown in Figure 3.
[!quote]+ Highlight (Page 7)
soda straw probes
[!quote]+ Highlight (Page 7)
The heating timescale in the magnetosphere can be roughly estimated by vdrift/inject/dsource, where vdrift/inject—associated with typical whistler wave source energies of 10–30 keV—ranges from 100 to 500 km/s (Gao et al., 2022), and the spatial scale of the whistler wave source is around 500 km (Agapitov et al., 2017). Thus, the heating timescale in the inner magnetosphere is of the same order as the repetition period and significantly longer than the anisotropy relaxation time:Δtrep ≃τdrive ≫ trelax.
[!quote]+ Highlight (Page 7)
Although in the inner magnetosphere the injection of energetic particles provides a continuous source of free energy (e.g., Lu et al., 2021), the underlying principle is the same as in our experiment—both represent continuously driven systems.
Important points
In tokamaks, runaway electrons can drive whistler waves unstable, leading to pitch‐angle scattering that mitigates these runaways
[!quote]+ Highlight (Page 2)
similar to the continuous injection of energetic electrons from the plasma sheet into the inner magnetosphere during geomagnetic activity, our experiments sustain anisotropic electron populations through continuous microwave heating.
[!quote]+ Highlight (Page 2)
an external driver progressively builds up the electron anisotropy until it exceeds the threshold for whistler instability, at which point whistler waves are excited. The waves then rapidly scatter electrons toward the parallel direction, reducing the anisotropy below the threshold, after which the cycle repeats as anisotropy gradually rebuilds.
[!quote]+ Highlight (Page 2)
Thermal electrons emitted from a heated cathode are accelerated by a mesh anode and collide with helium gas in the chamber, producing ionized plasma (Figure 1a). The experiments are performed in the quiescent plasma that remains after the DC discharge is switched off (plasma afterglow).
[!quote]+ Highlight (Page 3)
A photomultiplier tube (PMT) is deployed outside the vacuum chamber at the magnetic equator to detect X‐ray emissions generated when hot electrons strike the metallic surfaces of the plasma chamber. The chamber wall, made of 3/8 inch thick stainless steel, blocks X‐ray transmission below ∼ 100 keV (Wang et al., 2014). X‐ray signals intensify 2–3 ms after microwave initiation, revealing the time required for microwave‐driven electron acceleration to reach 100 keV, and further indicate the high energy tail is not important in whistler‐mode wave excitation.
[!quote]+ Highlight (Page 4)
the frequency remains stable above 0.6 fce during microwave heating suggest that the parallel electron temperature reaches a quasi‐steady state, as indicated by the dashed arrows in Figure 3b. In this state, a balance is established between microwave heating, wave‐driven electron scattering, electron escape through the loss cone, and energy dissipation due to collisions.
[!quote]+ Highlight (Page 7)
observed in the magnetosphere: The anisotropy relaxation time due to whistler wave generation is approximately t ≃50 ω− 1 ce ≃4 × 10− s (An et al., 2017; K. Nishimura et al., 2002), which is much shorter than the typical repetition period Δtrep ∼ 0.1–1 s (Gao et al., 2022; Kandar et al., 2023; Shue et al., 2015).
Nonlinear chorus growth @omuraNonlinearWaveGrowth2021
suggested reading:
- @stixWavesPlasmas1992
- https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/JZ071i001p00001
- https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/JA079i001p00118?saml_referrer
- @garyTheorySpacePlasma1993
@ozakiWhistlermodeWavesMercurys2023
Title: Whistler-mode waves in Mercury’s magnetosphere observed by BepiColombo/Mio
Tags: #Mercury
Authors: Mitsunori Ozaki, Satoshi Yagitani, Yasumasa Kasaba, Yoshiya Kasahara, Shoya Matsuda, Yoshiharu Omura, Mitsuru Hikishima, Fouad Sahraoui, Laurent Mirioni, Gérard Chanteur, Satoshi Kurita, Satoru Nakazawa, Go Murakami
Zotero link: PDF
Questions
although finer structures of typical rising-tone elements in the time domain could not be acquired due to telemetry limitations. #Question
- How do you detect this? In the two band paper we have only rising tone ,why? Isn't this signature rising as well?
[!quote]+ Note (Page 3)
The frequency of these broadband waves (that extend from ~10 to over 20 kHz; not shown) is higher than the electron cyclotron frequency and possibly lower than the plasma frequency, and it may play an important role in locally heating the particles at these boundary layers. #Question
- What are broadband waves and what are causes them? Does heating mean that it is an electrostatic process?
[!quote]+ Note (Page 3)
Because Earth’s magnetic moment points southward, Earth’s chorus emission waves also show stronger wave activity in the dawn side3 #Question
- Why is that?
In the flybys isn't this an orbit bias?
[!quote]+ Note (Page 3)
Although chorus wave spectra in Earth’s magnetosphere typically show a power gap at half the electron gyrofrequency33–35, the observed whistler-mode waves at Mercury do not show such a gap. The reason might be related to the characteristics of wave normal angles at Mio’s off-equatorial region. A power gap can be caused by damping of obliquely propagating waves away from the source region34 #Question
- What is this damping process and why it does not exist in mercury?
[!quote]+ Highlight (Page 3)
The propagation distance from the source to the spacecraft location may be different between the night and dawn sides. Figure 1a shows that both flyby paths in the night side were located near the lower magnetic latitudes. This implies that the propagation effects from the source cannot explain the presence of localized whistler-mode waves, and that other physical conditions that impact the wave generation and growth processes are at work. #Question
- ??? hellooo
[!quote]+ Note (Page 3)
to specify regions that grow while propagating from the source region. As a simple assumption, we considered the curvature around a region with Bmin, which maximizes the linear growth rate36
- Look up
[!quote]+ Note (Page 4)
We found that whistler-mode waves can be generated in a region with a lower curvature (below 1.5 × 10−12 m−2) on the day side compared with the wave activity measured at the same distance from Mercury in the night side.
[!quote]+ Highlight (Page 4)
two different magnetic inhomogeneities
[!quote]+ Highlight (Page 4)
In the absence of accurate measurements of the cold and energetic electron densities, it is not possible to compare the wave amplitude observed by Mio with the theoretical amplitude #Question
- What energies would we need and up to which we can reach now?
[!quote]+ Highlight (Page 5)
The quasi-trapped electron ring current develops a temperature anisotropy, in particular on the day side, which is the seed for initial whistler-mode wave growth #Question
- How is the convection E and therefore the ring current generated?
Why temperature anisotropy in the day side?
[!quote]+ Highlight (Page 5)
arge compressional background magnetic fields in the day side take bifurcated background magnetic field minima at northward and southward latitudes above the magnetic equator. Electrons with high equatorial pitch angles are then forced to drift and get reflected at high latitudes without passing through the equatorial plane, the so-called Shabansky orbits
[!quote]+ Highlight (Page 5)
Mercury has no permanent electron radiation belt6,40. If a short-duration quasi-trapped radiation belt could be generated at Mercury, chorus waves would play an important role in generating tentative enhancement of higher energy electron populations.
Important points
However, whistler-mode waves below the electron cyclotron frequency (estimated from an empirical magnetic field model9) were clearly observed in the frequency range 0.6–2 kHz during the first flyby event (23:37 to 23:39 ut). Another wave activity below 1 kHz was observed from 23:20 to 23:22 ut when Mio crossed the magnetic equator (and during 23:29 to 23:31 ut), but it is difficult to determine whether they are natural wave emissions or electromagnetic interference from the spacecraft because of their low signal-to-noise ratio. Similarly, whistler-mode waves were observed in the frequency range 0.6–1.8 kHz during the second flyby event (09:45 to 09:51 ut).
- How do you detect this?
[!quote]+ Note (Page 3)
Mercury’s magnetic fields with highly compressed (day side) and stretched (night side) structures should impact the wave growth rate #Take-aways
[!quote]+ Note (Page 3)
information on wave normal angles and polarisation is not available because of telemetry limitation
[!quote]+ Highlight (Page 4)
The fact that Mio observed an enhancement of whistler-mode wave activity of several tens of picotesla for distances of 1.1 to 1.5RM is consistent with the region containing quasi-trapped moderate-energy (1–10 keV) electrons40,41, as these6,11,16,40,41 can act as seed electrons that feed the instability, leading to the observed whistler-mode waves. #Take-aways
[!quote]+ Highlight (Page 4)
Our observations of dawn whistler-mode waves support the MESSENGER observations of localized high-energy electrons concentrated at the dawn side12 near the equatorial region
[!quote]+ Highlight (Page 5)
The flyby observations strongly support the idea that the background magnetic inhomogeneity has a strong impact on the generation process of planetary chorus waves, which is complemented by the results of simulations in Mercury’s environment #Take-aways
[!quote]+ Highlight (Page 5)
These non-energising (drift shell splitting and Shabansky orbits41) processes based on the background magnetic field structures should play a role in developing the temperature anisotropy of seed electrons.
[!quote]+ Highlight (Page 5)
The observed dawn chorus waves contribute to electron precipitation on the dawn side, which can generate part of the X-ray aurora observed on Mercury #Take-aways
[!quote]+ Highlight (Page 5)
such as probing waveform data during future flybys
Upper band -- above absorption band
Title: Whistler-mode waves in Mercury’s magnetosphere observed by BepiColombo/Mio
Tags: #Mercury
Authors: Mitsunori Ozaki, Satoshi Yagitani, Yasumasa Kasaba, Yoshiya Kasahara, Shoya Matsuda, Yoshiharu Omura, Mitsuru Hikishima, Fouad Sahraoui, Laurent Mirioni, Gérard Chanteur, Satoshi Kurita, Satoru Nakazawa, Go Murakami
Zotero link: PDF
Questions
although finer structures of typical rising-tone elements in the time domain could not be acquired due to telemetry limitations. #Question
- How do you detect this? In the two band paper we have only rising tone ,why? Isn't this signature rising as well?
[!quote]+ Note (Page 3)
The frequency of these broadband waves (that extend from ~10 to over 20 kHz; not shown) is higher than the electron cyclotron frequency and possibly lower than the plasma frequency, and it may play an important role in locally heating the particles at these boundary layers. #Question
- What are broadband waves and what are causes them? Does heating mean that it is an electrostatic process?
[!quote]+ Note (Page 3)
Because Earth’s magnetic moment points southward, Earth’s chorus emission waves also show stronger wave activity in the dawn side3 #Question
- Why is that?
In the flybys isn't this an orbit bias?
[!quote]+ Note (Page 3)
Although chorus wave spectra in Earth’s magnetosphere typically show a power gap at half the electron gyrofrequency33–35, the observed whistler-mode waves at Mercury do not show such a gap. The reason might be related to the characteristics of wave normal angles at Mio’s off-equatorial region. A power gap can be caused by damping of obliquely propagating waves away from the source region34 #Question
- What is this damping process and why it does not exist in mercury?
[!quote]+ Highlight (Page 3)
The propagation distance from the source to the spacecraft location may be different between the night and dawn sides. Figure 1a shows that both flyby paths in the night side were located near the lower magnetic latitudes. This implies that the propagation effects from the source cannot explain the presence of localized whistler-mode waves, and that other physical conditions that impact the wave generation and growth processes are at work. #Question
- ??? hellooo
[!quote]+ Note (Page 3)
to specify regions that grow while propagating from the source region. As a simple assumption, we considered the curvature around a region with Bmin, which maximizes the linear growth rate36
- Look up
[!quote]+ Note (Page 4)
We found that whistler-mode waves can be generated in a region with a lower curvature (below 1.5 × 10−12 m−2) on the day side compared with the wave activity measured at the same distance from Mercury in the night side.
[!quote]+ Highlight (Page 4)
two different magnetic inhomogeneities
[!quote]+ Highlight (Page 4)
In the absence of accurate measurements of the cold and energetic electron densities, it is not possible to compare the wave amplitude observed by Mio with the theoretical amplitude #Question
- What energies would we need and up to which we can reach now?
[!quote]+ Highlight (Page 5)
The quasi-trapped electron ring current develops a temperature anisotropy, in particular on the day side, which is the seed for initial whistler-mode wave growth #Question
- How is the convection E and therefore the ring current generated?
Why temperature anisotropy in the day side?
[!quote]+ Highlight (Page 5)
arge compressional background magnetic fields in the day side take bifurcated background magnetic field minima at northward and southward latitudes above the magnetic equator. Electrons with high equatorial pitch angles are then forced to drift and get reflected at high latitudes without passing through the equatorial plane, the so-called Shabansky orbits
[!quote]+ Highlight (Page 5)
Mercury has no permanent electron radiation belt6,40. If a short-duration quasi-trapped radiation belt could be generated at Mercury, chorus waves would play an important role in generating tentative enhancement of higher energy electron populations.
Important points
However, whistler-mode waves below the electron cyclotron frequency (estimated from an empirical magnetic field model9) were clearly observed in the frequency range 0.6–2 kHz during the first flyby event (23:37 to 23:39 ut). Another wave activity below 1 kHz was observed from 23:20 to 23:22 ut when Mio crossed the magnetic equator (and during 23:29 to 23:31 ut), but it is difficult to determine whether they are natural wave emissions or electromagnetic interference from the spacecraft because of their low signal-to-noise ratio. Similarly, whistler-mode waves were observed in the frequency range 0.6–1.8 kHz during the second flyby event (09:45 to 09:51 ut).
- How do you detect this?
[!quote]+ Note (Page 3)
Mercury’s magnetic fields with highly compressed (day side) and stretched (night side) structures should impact the wave growth rate #Take-aways
[!quote]+ Note (Page 3)
information on wave normal angles and polarisation is not available because of telemetry limitation
[!quote]+ Highlight (Page 4)
The fact that Mio observed an enhancement of whistler-mode wave activity of several tens of picotesla for distances of 1.1 to 1.5RM is consistent with the region containing quasi-trapped moderate-energy (1–10 keV) electrons40,41, as these6,11,16,40,41 can act as seed electrons that feed the instability, leading to the observed whistler-mode waves. #Take-aways
[!quote]+ Highlight (Page 4)
Our observations of dawn whistler-mode waves support the MESSENGER observations of localized high-energy electrons concentrated at the dawn side12 near the equatorial region
[!quote]+ Highlight (Page 5)
The flyby observations strongly support the idea that the background magnetic inhomogeneity has a strong impact on the generation process of planetary chorus waves, which is complemented by the results of simulations in Mercury’s environment #Take-aways
[!quote]+ Highlight (Page 5)
These non-energising (drift shell splitting and Shabansky orbits41) processes based on the background magnetic field structures should play a role in developing the temperature anisotropy of seed electrons.
[!quote]+ Highlight (Page 5)
The observed dawn chorus waves contribute to electron precipitation on the dawn side, which can generate part of the X-ray aurora observed on Mercury #Take-aways
[!quote]+ Highlight (Page 5)
such as probing waveform data during future flybys
Broadband means just that we see various frequencies we cannot explain.
Heating is just acceleration of electrons and does not mean electrostatic (? on wether heat can be described with waves as with phonons)
Title: Whistler-mode waves in Mercury’s magnetosphere observed by BepiColombo/Mio
Tags: #Mercury
Authors: Mitsunori Ozaki, Satoshi Yagitani, Yasumasa Kasaba, Yoshiya Kasahara, Shoya Matsuda, Yoshiharu Omura, Mitsuru Hikishima, Fouad Sahraoui, Laurent Mirioni, Gérard Chanteur, Satoshi Kurita, Satoru Nakazawa, Go Murakami
Zotero link: PDF
Questions
although finer structures of typical rising-tone elements in the time domain could not be acquired due to telemetry limitations. #Question
- How do you detect this? In the two band paper we have only rising tone ,why? Isn't this signature rising as well?
[!quote]+ Note (Page 3)
The frequency of these broadband waves (that extend from ~10 to over 20 kHz; not shown) is higher than the electron cyclotron frequency and possibly lower than the plasma frequency, and it may play an important role in locally heating the particles at these boundary layers. #Question
- What are broadband waves and what are causes them? Does heating mean that it is an electrostatic process?
[!quote]+ Note (Page 3)
Because Earth’s magnetic moment points southward, Earth’s chorus emission waves also show stronger wave activity in the dawn side3 #Question
- Why is that?
In the flybys isn't this an orbit bias?
[!quote]+ Note (Page 3)
Although chorus wave spectra in Earth’s magnetosphere typically show a power gap at half the electron gyrofrequency33–35, the observed whistler-mode waves at Mercury do not show such a gap. The reason might be related to the characteristics of wave normal angles at Mio’s off-equatorial region. A power gap can be caused by damping of obliquely propagating waves away from the source region34 #Question
- What is this damping process and why it does not exist in mercury?
[!quote]+ Highlight (Page 3)
The propagation distance from the source to the spacecraft location may be different between the night and dawn sides. Figure 1a shows that both flyby paths in the night side were located near the lower magnetic latitudes. This implies that the propagation effects from the source cannot explain the presence of localized whistler-mode waves, and that other physical conditions that impact the wave generation and growth processes are at work. #Question
- ??? hellooo
[!quote]+ Note (Page 3)
to specify regions that grow while propagating from the source region. As a simple assumption, we considered the curvature around a region with Bmin, which maximizes the linear growth rate36
- Look up
[!quote]+ Note (Page 4)
We found that whistler-mode waves can be generated in a region with a lower curvature (below 1.5 × 10−12 m−2) on the day side compared with the wave activity measured at the same distance from Mercury in the night side.
[!quote]+ Highlight (Page 4)
two different magnetic inhomogeneities
[!quote]+ Highlight (Page 4)
In the absence of accurate measurements of the cold and energetic electron densities, it is not possible to compare the wave amplitude observed by Mio with the theoretical amplitude #Question
- What energies would we need and up to which we can reach now?
[!quote]+ Highlight (Page 5)
The quasi-trapped electron ring current develops a temperature anisotropy, in particular on the day side, which is the seed for initial whistler-mode wave growth #Question
- How is the convection E and therefore the ring current generated?
Why temperature anisotropy in the day side?
[!quote]+ Highlight (Page 5)
arge compressional background magnetic fields in the day side take bifurcated background magnetic field minima at northward and southward latitudes above the magnetic equator. Electrons with high equatorial pitch angles are then forced to drift and get reflected at high latitudes without passing through the equatorial plane, the so-called Shabansky orbits
[!quote]+ Highlight (Page 5)
Mercury has no permanent electron radiation belt6,40. If a short-duration quasi-trapped radiation belt could be generated at Mercury, chorus waves would play an important role in generating tentative enhancement of higher energy electron populations.
Important points
However, whistler-mode waves below the electron cyclotron frequency (estimated from an empirical magnetic field model9) were clearly observed in the frequency range 0.6–2 kHz during the first flyby event (23:37 to 23:39 ut). Another wave activity below 1 kHz was observed from 23:20 to 23:22 ut when Mio crossed the magnetic equator (and during 23:29 to 23:31 ut), but it is difficult to determine whether they are natural wave emissions or electromagnetic interference from the spacecraft because of their low signal-to-noise ratio. Similarly, whistler-mode waves were observed in the frequency range 0.6–1.8 kHz during the second flyby event (09:45 to 09:51 ut).
- How do you detect this?
[!quote]+ Note (Page 3)
Mercury’s magnetic fields with highly compressed (day side) and stretched (night side) structures should impact the wave growth rate #Take-aways
[!quote]+ Note (Page 3)
information on wave normal angles and polarisation is not available because of telemetry limitation
[!quote]+ Highlight (Page 4)
The fact that Mio observed an enhancement of whistler-mode wave activity of several tens of picotesla for distances of 1.1 to 1.5RM is consistent with the region containing quasi-trapped moderate-energy (1–10 keV) electrons40,41, as these6,11,16,40,41 can act as seed electrons that feed the instability, leading to the observed whistler-mode waves. #Take-aways
[!quote]+ Highlight (Page 4)
Our observations of dawn whistler-mode waves support the MESSENGER observations of localized high-energy electrons concentrated at the dawn side12 near the equatorial region
[!quote]+ Highlight (Page 5)
The flyby observations strongly support the idea that the background magnetic inhomogeneity has a strong impact on the generation process of planetary chorus waves, which is complemented by the results of simulations in Mercury’s environment #Take-aways
[!quote]+ Highlight (Page 5)
These non-energising (drift shell splitting and Shabansky orbits41) processes based on the background magnetic field structures should play a role in developing the temperature anisotropy of seed electrons.
[!quote]+ Highlight (Page 5)
The observed dawn chorus waves contribute to electron precipitation on the dawn side, which can generate part of the X-ray aurora observed on Mercury #Take-aways
[!quote]+ Highlight (Page 5)
such as probing waveform data during future flybys
From simulation it may have more activity there.
Title: Whistler-mode waves in Mercury’s magnetosphere observed by BepiColombo/Mio
Tags: #Mercury
Authors: Mitsunori Ozaki, Satoshi Yagitani, Yasumasa Kasaba, Yoshiya Kasahara, Shoya Matsuda, Yoshiharu Omura, Mitsuru Hikishima, Fouad Sahraoui, Laurent Mirioni, Gérard Chanteur, Satoshi Kurita, Satoru Nakazawa, Go Murakami
Zotero link: PDF
Questions
although finer structures of typical rising-tone elements in the time domain could not be acquired due to telemetry limitations. #Question
- How do you detect this? In the two band paper we have only rising tone ,why? Isn't this signature rising as well?
[!quote]+ Note (Page 3)
The frequency of these broadband waves (that extend from ~10 to over 20 kHz; not shown) is higher than the electron cyclotron frequency and possibly lower than the plasma frequency, and it may play an important role in locally heating the particles at these boundary layers. #Question
- What are broadband waves and what are causes them? Does heating mean that it is an electrostatic process?
[!quote]+ Note (Page 3)
Because Earth’s magnetic moment points southward, Earth’s chorus emission waves also show stronger wave activity in the dawn side3 #Question
- Why is that?
In the flybys isn't this an orbit bias?
[!quote]+ Note (Page 3)
Although chorus wave spectra in Earth’s magnetosphere typically show a power gap at half the electron gyrofrequency33–35, the observed whistler-mode waves at Mercury do not show such a gap. The reason might be related to the characteristics of wave normal angles at Mio’s off-equatorial region. A power gap can be caused by damping of obliquely propagating waves away from the source region34 #Question
- What is this damping process and why it does not exist in mercury?
[!quote]+ Highlight (Page 3)
The propagation distance from the source to the spacecraft location may be different between the night and dawn sides. Figure 1a shows that both flyby paths in the night side were located near the lower magnetic latitudes. This implies that the propagation effects from the source cannot explain the presence of localized whistler-mode waves, and that other physical conditions that impact the wave generation and growth processes are at work. #Question
- ??? hellooo
[!quote]+ Note (Page 3)
to specify regions that grow while propagating from the source region. As a simple assumption, we considered the curvature around a region with Bmin, which maximizes the linear growth rate36
- Look up
[!quote]+ Note (Page 4)
We found that whistler-mode waves can be generated in a region with a lower curvature (below 1.5 × 10−12 m−2) on the day side compared with the wave activity measured at the same distance from Mercury in the night side.
[!quote]+ Highlight (Page 4)
two different magnetic inhomogeneities
[!quote]+ Highlight (Page 4)
In the absence of accurate measurements of the cold and energetic electron densities, it is not possible to compare the wave amplitude observed by Mio with the theoretical amplitude #Question
- What energies would we need and up to which we can reach now?
[!quote]+ Highlight (Page 5)
The quasi-trapped electron ring current develops a temperature anisotropy, in particular on the day side, which is the seed for initial whistler-mode wave growth #Question
- How is the convection E and therefore the ring current generated?
Why temperature anisotropy in the day side?
[!quote]+ Highlight (Page 5)
arge compressional background magnetic fields in the day side take bifurcated background magnetic field minima at northward and southward latitudes above the magnetic equator. Electrons with high equatorial pitch angles are then forced to drift and get reflected at high latitudes without passing through the equatorial plane, the so-called Shabansky orbits
[!quote]+ Highlight (Page 5)
Mercury has no permanent electron radiation belt6,40. If a short-duration quasi-trapped radiation belt could be generated at Mercury, chorus waves would play an important role in generating tentative enhancement of higher energy electron populations.
Important points
However, whistler-mode waves below the electron cyclotron frequency (estimated from an empirical magnetic field model9) were clearly observed in the frequency range 0.6–2 kHz during the first flyby event (23:37 to 23:39 ut). Another wave activity below 1 kHz was observed from 23:20 to 23:22 ut when Mio crossed the magnetic equator (and during 23:29 to 23:31 ut), but it is difficult to determine whether they are natural wave emissions or electromagnetic interference from the spacecraft because of their low signal-to-noise ratio. Similarly, whistler-mode waves were observed in the frequency range 0.6–1.8 kHz during the second flyby event (09:45 to 09:51 ut).
- How do you detect this?
[!quote]+ Note (Page 3)
Mercury’s magnetic fields with highly compressed (day side) and stretched (night side) structures should impact the wave growth rate #Take-aways
[!quote]+ Note (Page 3)
information on wave normal angles and polarisation is not available because of telemetry limitation
[!quote]+ Highlight (Page 4)
The fact that Mio observed an enhancement of whistler-mode wave activity of several tens of picotesla for distances of 1.1 to 1.5RM is consistent with the region containing quasi-trapped moderate-energy (1–10 keV) electrons40,41, as these6,11,16,40,41 can act as seed electrons that feed the instability, leading to the observed whistler-mode waves. #Take-aways
[!quote]+ Highlight (Page 4)
Our observations of dawn whistler-mode waves support the MESSENGER observations of localized high-energy electrons concentrated at the dawn side12 near the equatorial region
[!quote]+ Highlight (Page 5)
The flyby observations strongly support the idea that the background magnetic inhomogeneity has a strong impact on the generation process of planetary chorus waves, which is complemented by the results of simulations in Mercury’s environment #Take-aways
[!quote]+ Highlight (Page 5)
These non-energising (drift shell splitting and Shabansky orbits41) processes based on the background magnetic field structures should play a role in developing the temperature anisotropy of seed electrons.
[!quote]+ Highlight (Page 5)
The observed dawn chorus waves contribute to electron precipitation on the dawn side, which can generate part of the X-ray aurora observed on Mercury #Take-aways
[!quote]+ Highlight (Page 5)
such as probing waveform data during future flybys
E parallel to B to have whistlers
obliquely propagating: k in an angle with
if it was not oblique we wouldnt have Landau damping because E paralllel=0
In order to have Landau damping we need a component of the alternating electric field to be in the direction where electrons can move freely. In a magnetized plasma this is the direction of the ambient magnetic field. For Whistler-mode waves we need
Title: Whistler-mode waves in Mercury’s magnetosphere observed by BepiColombo/Mio
Tags: #Mercury
Authors: Mitsunori Ozaki, Satoshi Yagitani, Yasumasa Kasaba, Yoshiya Kasahara, Shoya Matsuda, Yoshiharu Omura, Mitsuru Hikishima, Fouad Sahraoui, Laurent Mirioni, Gérard Chanteur, Satoshi Kurita, Satoru Nakazawa, Go Murakami
Zotero link: PDF
Questions
although finer structures of typical rising-tone elements in the time domain could not be acquired due to telemetry limitations. #Question
- How do you detect this? In the two band paper we have only rising tone ,why? Isn't this signature rising as well?
[!quote]+ Note (Page 3)
The frequency of these broadband waves (that extend from ~10 to over 20 kHz; not shown) is higher than the electron cyclotron frequency and possibly lower than the plasma frequency, and it may play an important role in locally heating the particles at these boundary layers. #Question
- What are broadband waves and what are causes them? Does heating mean that it is an electrostatic process?
[!quote]+ Note (Page 3)
Because Earth’s magnetic moment points southward, Earth’s chorus emission waves also show stronger wave activity in the dawn side3 #Question
- Why is that?
In the flybys isn't this an orbit bias?
[!quote]+ Note (Page 3)
Although chorus wave spectra in Earth’s magnetosphere typically show a power gap at half the electron gyrofrequency33–35, the observed whistler-mode waves at Mercury do not show such a gap. The reason might be related to the characteristics of wave normal angles at Mio’s off-equatorial region. A power gap can be caused by damping of obliquely propagating waves away from the source region34 #Question
- What is this damping process and why it does not exist in mercury?
[!quote]+ Highlight (Page 3)
The propagation distance from the source to the spacecraft location may be different between the night and dawn sides. Figure 1a shows that both flyby paths in the night side were located near the lower magnetic latitudes. This implies that the propagation effects from the source cannot explain the presence of localized whistler-mode waves, and that other physical conditions that impact the wave generation and growth processes are at work. #Question
- ??? hellooo
[!quote]+ Note (Page 3)
to specify regions that grow while propagating from the source region. As a simple assumption, we considered the curvature around a region with Bmin, which maximizes the linear growth rate36
- Look up
[!quote]+ Note (Page 4)
We found that whistler-mode waves can be generated in a region with a lower curvature (below 1.5 × 10−12 m−2) on the day side compared with the wave activity measured at the same distance from Mercury in the night side.
[!quote]+ Highlight (Page 4)
two different magnetic inhomogeneities
[!quote]+ Highlight (Page 4)
In the absence of accurate measurements of the cold and energetic electron densities, it is not possible to compare the wave amplitude observed by Mio with the theoretical amplitude #Question
- What energies would we need and up to which we can reach now?
[!quote]+ Highlight (Page 5)
The quasi-trapped electron ring current develops a temperature anisotropy, in particular on the day side, which is the seed for initial whistler-mode wave growth #Question
- How is the convection E and therefore the ring current generated?
Why temperature anisotropy in the day side?
[!quote]+ Highlight (Page 5)
arge compressional background magnetic fields in the day side take bifurcated background magnetic field minima at northward and southward latitudes above the magnetic equator. Electrons with high equatorial pitch angles are then forced to drift and get reflected at high latitudes without passing through the equatorial plane, the so-called Shabansky orbits
[!quote]+ Highlight (Page 5)
Mercury has no permanent electron radiation belt6,40. If a short-duration quasi-trapped radiation belt could be generated at Mercury, chorus waves would play an important role in generating tentative enhancement of higher energy electron populations.
Important points
However, whistler-mode waves below the electron cyclotron frequency (estimated from an empirical magnetic field model9) were clearly observed in the frequency range 0.6–2 kHz during the first flyby event (23:37 to 23:39 ut). Another wave activity below 1 kHz was observed from 23:20 to 23:22 ut when Mio crossed the magnetic equator (and during 23:29 to 23:31 ut), but it is difficult to determine whether they are natural wave emissions or electromagnetic interference from the spacecraft because of their low signal-to-noise ratio. Similarly, whistler-mode waves were observed in the frequency range 0.6–1.8 kHz during the second flyby event (09:45 to 09:51 ut).
- How do you detect this?
[!quote]+ Note (Page 3)
Mercury’s magnetic fields with highly compressed (day side) and stretched (night side) structures should impact the wave growth rate #Take-aways
[!quote]+ Note (Page 3)
information on wave normal angles and polarisation is not available because of telemetry limitation
[!quote]+ Highlight (Page 4)
The fact that Mio observed an enhancement of whistler-mode wave activity of several tens of picotesla for distances of 1.1 to 1.5RM is consistent with the region containing quasi-trapped moderate-energy (1–10 keV) electrons40,41, as these6,11,16,40,41 can act as seed electrons that feed the instability, leading to the observed whistler-mode waves. #Take-aways
[!quote]+ Highlight (Page 4)
Our observations of dawn whistler-mode waves support the MESSENGER observations of localized high-energy electrons concentrated at the dawn side12 near the equatorial region
[!quote]+ Highlight (Page 5)
The flyby observations strongly support the idea that the background magnetic inhomogeneity has a strong impact on the generation process of planetary chorus waves, which is complemented by the results of simulations in Mercury’s environment #Take-aways
[!quote]+ Highlight (Page 5)
These non-energising (drift shell splitting and Shabansky orbits41) processes based on the background magnetic field structures should play a role in developing the temperature anisotropy of seed electrons.
[!quote]+ Highlight (Page 5)
The observed dawn chorus waves contribute to electron precipitation on the dawn side, which can generate part of the X-ray aurora observed on Mercury #Take-aways
[!quote]+ Highlight (Page 5)
such as probing waveform data during future flybys
Title: Whistler-mode waves in Mercury’s magnetosphere observed by BepiColombo/Mio
Tags: #Mercury
Authors: Mitsunori Ozaki, Satoshi Yagitani, Yasumasa Kasaba, Yoshiya Kasahara, Shoya Matsuda, Yoshiharu Omura, Mitsuru Hikishima, Fouad Sahraoui, Laurent Mirioni, Gérard Chanteur, Satoshi Kurita, Satoru Nakazawa, Go Murakami
Zotero link: PDF
Questions
although finer structures of typical rising-tone elements in the time domain could not be acquired due to telemetry limitations. #Question
- How do you detect this? In the two band paper we have only rising tone ,why? Isn't this signature rising as well?
[!quote]+ Note (Page 3)
The frequency of these broadband waves (that extend from ~10 to over 20 kHz; not shown) is higher than the electron cyclotron frequency and possibly lower than the plasma frequency, and it may play an important role in locally heating the particles at these boundary layers. #Question
- What are broadband waves and what are causes them? Does heating mean that it is an electrostatic process?
[!quote]+ Note (Page 3)
Because Earth’s magnetic moment points southward, Earth’s chorus emission waves also show stronger wave activity in the dawn side3 #Question
- Why is that?
In the flybys isn't this an orbit bias?
[!quote]+ Note (Page 3)
Although chorus wave spectra in Earth’s magnetosphere typically show a power gap at half the electron gyrofrequency33–35, the observed whistler-mode waves at Mercury do not show such a gap. The reason might be related to the characteristics of wave normal angles at Mio’s off-equatorial region. A power gap can be caused by damping of obliquely propagating waves away from the source region34 #Question
- What is this damping process and why it does not exist in mercury?
[!quote]+ Highlight (Page 3)
The propagation distance from the source to the spacecraft location may be different between the night and dawn sides. Figure 1a shows that both flyby paths in the night side were located near the lower magnetic latitudes. This implies that the propagation effects from the source cannot explain the presence of localized whistler-mode waves, and that other physical conditions that impact the wave generation and growth processes are at work. #Question
- ??? hellooo
[!quote]+ Note (Page 3)
to specify regions that grow while propagating from the source region. As a simple assumption, we considered the curvature around a region with Bmin, which maximizes the linear growth rate36
- Look up
[!quote]+ Note (Page 4)
We found that whistler-mode waves can be generated in a region with a lower curvature (below 1.5 × 10−12 m−2) on the day side compared with the wave activity measured at the same distance from Mercury in the night side.
[!quote]+ Highlight (Page 4)
two different magnetic inhomogeneities
[!quote]+ Highlight (Page 4)
In the absence of accurate measurements of the cold and energetic electron densities, it is not possible to compare the wave amplitude observed by Mio with the theoretical amplitude #Question
- What energies would we need and up to which we can reach now?
[!quote]+ Highlight (Page 5)
The quasi-trapped electron ring current develops a temperature anisotropy, in particular on the day side, which is the seed for initial whistler-mode wave growth #Question
- How is the convection E and therefore the ring current generated?
Why temperature anisotropy in the day side?
[!quote]+ Highlight (Page 5)
arge compressional background magnetic fields in the day side take bifurcated background magnetic field minima at northward and southward latitudes above the magnetic equator. Electrons with high equatorial pitch angles are then forced to drift and get reflected at high latitudes without passing through the equatorial plane, the so-called Shabansky orbits
[!quote]+ Highlight (Page 5)
Mercury has no permanent electron radiation belt6,40. If a short-duration quasi-trapped radiation belt could be generated at Mercury, chorus waves would play an important role in generating tentative enhancement of higher energy electron populations.
Important points
However, whistler-mode waves below the electron cyclotron frequency (estimated from an empirical magnetic field model9) were clearly observed in the frequency range 0.6–2 kHz during the first flyby event (23:37 to 23:39 ut). Another wave activity below 1 kHz was observed from 23:20 to 23:22 ut when Mio crossed the magnetic equator (and during 23:29 to 23:31 ut), but it is difficult to determine whether they are natural wave emissions or electromagnetic interference from the spacecraft because of their low signal-to-noise ratio. Similarly, whistler-mode waves were observed in the frequency range 0.6–1.8 kHz during the second flyby event (09:45 to 09:51 ut).
- How do you detect this?
[!quote]+ Note (Page 3)
Mercury’s magnetic fields with highly compressed (day side) and stretched (night side) structures should impact the wave growth rate #Take-aways
[!quote]+ Note (Page 3)
information on wave normal angles and polarisation is not available because of telemetry limitation
[!quote]+ Highlight (Page 4)
The fact that Mio observed an enhancement of whistler-mode wave activity of several tens of picotesla for distances of 1.1 to 1.5RM is consistent with the region containing quasi-trapped moderate-energy (1–10 keV) electrons40,41, as these6,11,16,40,41 can act as seed electrons that feed the instability, leading to the observed whistler-mode waves. #Take-aways
[!quote]+ Highlight (Page 4)
Our observations of dawn whistler-mode waves support the MESSENGER observations of localized high-energy electrons concentrated at the dawn side12 near the equatorial region
[!quote]+ Highlight (Page 5)
The flyby observations strongly support the idea that the background magnetic inhomogeneity has a strong impact on the generation process of planetary chorus waves, which is complemented by the results of simulations in Mercury’s environment #Take-aways
[!quote]+ Highlight (Page 5)
These non-energising (drift shell splitting and Shabansky orbits41) processes based on the background magnetic field structures should play a role in developing the temperature anisotropy of seed electrons.
[!quote]+ Highlight (Page 5)
The observed dawn chorus waves contribute to electron precipitation on the dawn side, which can generate part of the X-ray aurora observed on Mercury #Take-aways
[!quote]+ Highlight (Page 5)
such as probing waveform data during future flybys
This seems to indicate whistler creation in the day side
Title: Whistler-mode waves in Mercury’s magnetosphere observed by BepiColombo/Mio
Tags: #Mercury
Authors: Mitsunori Ozaki, Satoshi Yagitani, Yasumasa Kasaba, Yoshiya Kasahara, Shoya Matsuda, Yoshiharu Omura, Mitsuru Hikishima, Fouad Sahraoui, Laurent Mirioni, Gérard Chanteur, Satoshi Kurita, Satoru Nakazawa, Go Murakami
Zotero link: PDF
Questions
although finer structures of typical rising-tone elements in the time domain could not be acquired due to telemetry limitations. #Question
- How do you detect this? In the two band paper we have only rising tone ,why? Isn't this signature rising as well?
[!quote]+ Note (Page 3)
The frequency of these broadband waves (that extend from ~10 to over 20 kHz; not shown) is higher than the electron cyclotron frequency and possibly lower than the plasma frequency, and it may play an important role in locally heating the particles at these boundary layers. #Question
- What are broadband waves and what are causes them? Does heating mean that it is an electrostatic process?
[!quote]+ Note (Page 3)
Because Earth’s magnetic moment points southward, Earth’s chorus emission waves also show stronger wave activity in the dawn side3 #Question
- Why is that?
In the flybys isn't this an orbit bias?
[!quote]+ Note (Page 3)
Although chorus wave spectra in Earth’s magnetosphere typically show a power gap at half the electron gyrofrequency33–35, the observed whistler-mode waves at Mercury do not show such a gap. The reason might be related to the characteristics of wave normal angles at Mio’s off-equatorial region. A power gap can be caused by damping of obliquely propagating waves away from the source region34 #Question
- What is this damping process and why it does not exist in mercury?
[!quote]+ Highlight (Page 3)
The propagation distance from the source to the spacecraft location may be different between the night and dawn sides. Figure 1a shows that both flyby paths in the night side were located near the lower magnetic latitudes. This implies that the propagation effects from the source cannot explain the presence of localized whistler-mode waves, and that other physical conditions that impact the wave generation and growth processes are at work. #Question
- ??? hellooo
[!quote]+ Note (Page 3)
to specify regions that grow while propagating from the source region. As a simple assumption, we considered the curvature around a region with Bmin, which maximizes the linear growth rate36
- Look up
[!quote]+ Note (Page 4)
We found that whistler-mode waves can be generated in a region with a lower curvature (below 1.5 × 10−12 m−2) on the day side compared with the wave activity measured at the same distance from Mercury in the night side.
[!quote]+ Highlight (Page 4)
two different magnetic inhomogeneities
[!quote]+ Highlight (Page 4)
In the absence of accurate measurements of the cold and energetic electron densities, it is not possible to compare the wave amplitude observed by Mio with the theoretical amplitude #Question
- What energies would we need and up to which we can reach now?
[!quote]+ Highlight (Page 5)
The quasi-trapped electron ring current develops a temperature anisotropy, in particular on the day side, which is the seed for initial whistler-mode wave growth #Question
- How is the convection E and therefore the ring current generated?
Why temperature anisotropy in the day side?
[!quote]+ Highlight (Page 5)
arge compressional background magnetic fields in the day side take bifurcated background magnetic field minima at northward and southward latitudes above the magnetic equator. Electrons with high equatorial pitch angles are then forced to drift and get reflected at high latitudes without passing through the equatorial plane, the so-called Shabansky orbits
[!quote]+ Highlight (Page 5)
Mercury has no permanent electron radiation belt6,40. If a short-duration quasi-trapped radiation belt could be generated at Mercury, chorus waves would play an important role in generating tentative enhancement of higher energy electron populations.
Important points
However, whistler-mode waves below the electron cyclotron frequency (estimated from an empirical magnetic field model9) were clearly observed in the frequency range 0.6–2 kHz during the first flyby event (23:37 to 23:39 ut). Another wave activity below 1 kHz was observed from 23:20 to 23:22 ut when Mio crossed the magnetic equator (and during 23:29 to 23:31 ut), but it is difficult to determine whether they are natural wave emissions or electromagnetic interference from the spacecraft because of their low signal-to-noise ratio. Similarly, whistler-mode waves were observed in the frequency range 0.6–1.8 kHz during the second flyby event (09:45 to 09:51 ut).
- How do you detect this?
[!quote]+ Note (Page 3)
Mercury’s magnetic fields with highly compressed (day side) and stretched (night side) structures should impact the wave growth rate #Take-aways
[!quote]+ Note (Page 3)
information on wave normal angles and polarisation is not available because of telemetry limitation
[!quote]+ Highlight (Page 4)
The fact that Mio observed an enhancement of whistler-mode wave activity of several tens of picotesla for distances of 1.1 to 1.5RM is consistent with the region containing quasi-trapped moderate-energy (1–10 keV) electrons40,41, as these6,11,16,40,41 can act as seed electrons that feed the instability, leading to the observed whistler-mode waves. #Take-aways
[!quote]+ Highlight (Page 4)
Our observations of dawn whistler-mode waves support the MESSENGER observations of localized high-energy electrons concentrated at the dawn side12 near the equatorial region
[!quote]+ Highlight (Page 5)
The flyby observations strongly support the idea that the background magnetic inhomogeneity has a strong impact on the generation process of planetary chorus waves, which is complemented by the results of simulations in Mercury’s environment #Take-aways
[!quote]+ Highlight (Page 5)
These non-energising (drift shell splitting and Shabansky orbits41) processes based on the background magnetic field structures should play a role in developing the temperature anisotropy of seed electrons.
[!quote]+ Highlight (Page 5)
The observed dawn chorus waves contribute to electron precipitation on the dawn side, which can generate part of the X-ray aurora observed on Mercury #Take-aways
[!quote]+ Highlight (Page 5)
such as probing waveform data during future flybys
Title: Whistler-mode waves in Mercury’s magnetosphere observed by BepiColombo/Mio
Tags: #Mercury
Authors: Mitsunori Ozaki, Satoshi Yagitani, Yasumasa Kasaba, Yoshiya Kasahara, Shoya Matsuda, Yoshiharu Omura, Mitsuru Hikishima, Fouad Sahraoui, Laurent Mirioni, Gérard Chanteur, Satoshi Kurita, Satoru Nakazawa, Go Murakami
Zotero link: PDF
Questions
although finer structures of typical rising-tone elements in the time domain could not be acquired due to telemetry limitations. #Question
- How do you detect this? In the two band paper we have only rising tone ,why? Isn't this signature rising as well?
[!quote]+ Note (Page 3)
The frequency of these broadband waves (that extend from ~10 to over 20 kHz; not shown) is higher than the electron cyclotron frequency and possibly lower than the plasma frequency, and it may play an important role in locally heating the particles at these boundary layers. #Question
- What are broadband waves and what are causes them? Does heating mean that it is an electrostatic process?
[!quote]+ Note (Page 3)
Because Earth’s magnetic moment points southward, Earth’s chorus emission waves also show stronger wave activity in the dawn side3 #Question
- Why is that?
In the flybys isn't this an orbit bias?
[!quote]+ Note (Page 3)
Although chorus wave spectra in Earth’s magnetosphere typically show a power gap at half the electron gyrofrequency33–35, the observed whistler-mode waves at Mercury do not show such a gap. The reason might be related to the characteristics of wave normal angles at Mio’s off-equatorial region. A power gap can be caused by damping of obliquely propagating waves away from the source region34 #Question
- What is this damping process and why it does not exist in mercury?
[!quote]+ Highlight (Page 3)
The propagation distance from the source to the spacecraft location may be different between the night and dawn sides. Figure 1a shows that both flyby paths in the night side were located near the lower magnetic latitudes. This implies that the propagation effects from the source cannot explain the presence of localized whistler-mode waves, and that other physical conditions that impact the wave generation and growth processes are at work. #Question
- ??? hellooo
[!quote]+ Note (Page 3)
to specify regions that grow while propagating from the source region. As a simple assumption, we considered the curvature around a region with Bmin, which maximizes the linear growth rate36
- Look up
[!quote]+ Note (Page 4)
We found that whistler-mode waves can be generated in a region with a lower curvature (below 1.5 × 10−12 m−2) on the day side compared with the wave activity measured at the same distance from Mercury in the night side.
[!quote]+ Highlight (Page 4)
two different magnetic inhomogeneities
[!quote]+ Highlight (Page 4)
In the absence of accurate measurements of the cold and energetic electron densities, it is not possible to compare the wave amplitude observed by Mio with the theoretical amplitude #Question
- What energies would we need and up to which we can reach now?
[!quote]+ Highlight (Page 5)
The quasi-trapped electron ring current develops a temperature anisotropy, in particular on the day side, which is the seed for initial whistler-mode wave growth #Question
- How is the convection E and therefore the ring current generated?
Why temperature anisotropy in the day side?
[!quote]+ Highlight (Page 5)
arge compressional background magnetic fields in the day side take bifurcated background magnetic field minima at northward and southward latitudes above the magnetic equator. Electrons with high equatorial pitch angles are then forced to drift and get reflected at high latitudes without passing through the equatorial plane, the so-called Shabansky orbits
[!quote]+ Highlight (Page 5)
Mercury has no permanent electron radiation belt6,40. If a short-duration quasi-trapped radiation belt could be generated at Mercury, chorus waves would play an important role in generating tentative enhancement of higher energy electron populations.
Important points
However, whistler-mode waves below the electron cyclotron frequency (estimated from an empirical magnetic field model9) were clearly observed in the frequency range 0.6–2 kHz during the first flyby event (23:37 to 23:39 ut). Another wave activity below 1 kHz was observed from 23:20 to 23:22 ut when Mio crossed the magnetic equator (and during 23:29 to 23:31 ut), but it is difficult to determine whether they are natural wave emissions or electromagnetic interference from the spacecraft because of their low signal-to-noise ratio. Similarly, whistler-mode waves were observed in the frequency range 0.6–1.8 kHz during the second flyby event (09:45 to 09:51 ut).
- How do you detect this?
[!quote]+ Note (Page 3)
Mercury’s magnetic fields with highly compressed (day side) and stretched (night side) structures should impact the wave growth rate #Take-aways
[!quote]+ Note (Page 3)
information on wave normal angles and polarisation is not available because of telemetry limitation
[!quote]+ Highlight (Page 4)
The fact that Mio observed an enhancement of whistler-mode wave activity of several tens of picotesla for distances of 1.1 to 1.5RM is consistent with the region containing quasi-trapped moderate-energy (1–10 keV) electrons40,41, as these6,11,16,40,41 can act as seed electrons that feed the instability, leading to the observed whistler-mode waves. #Take-aways
[!quote]+ Highlight (Page 4)
Our observations of dawn whistler-mode waves support the MESSENGER observations of localized high-energy electrons concentrated at the dawn side12 near the equatorial region
[!quote]+ Highlight (Page 5)
The flyby observations strongly support the idea that the background magnetic inhomogeneity has a strong impact on the generation process of planetary chorus waves, which is complemented by the results of simulations in Mercury’s environment #Take-aways
[!quote]+ Highlight (Page 5)
These non-energising (drift shell splitting and Shabansky orbits41) processes based on the background magnetic field structures should play a role in developing the temperature anisotropy of seed electrons.
[!quote]+ Highlight (Page 5)
The observed dawn chorus waves contribute to electron precipitation on the dawn side, which can generate part of the X-ray aurora observed on Mercury #Take-aways
[!quote]+ Highlight (Page 5)
such as probing waveform data during future flybys
Title: Whistler-mode waves in Mercury’s magnetosphere observed by BepiColombo/Mio
Tags: #Mercury
Authors: Mitsunori Ozaki, Satoshi Yagitani, Yasumasa Kasaba, Yoshiya Kasahara, Shoya Matsuda, Yoshiharu Omura, Mitsuru Hikishima, Fouad Sahraoui, Laurent Mirioni, Gérard Chanteur, Satoshi Kurita, Satoru Nakazawa, Go Murakami
Zotero link: PDF
Questions
although finer structures of typical rising-tone elements in the time domain could not be acquired due to telemetry limitations. #Question
- How do you detect this? In the two band paper we have only rising tone ,why? Isn't this signature rising as well?
[!quote]+ Note (Page 3)
The frequency of these broadband waves (that extend from ~10 to over 20 kHz; not shown) is higher than the electron cyclotron frequency and possibly lower than the plasma frequency, and it may play an important role in locally heating the particles at these boundary layers. #Question
- What are broadband waves and what are causes them? Does heating mean that it is an electrostatic process?
[!quote]+ Note (Page 3)
Because Earth’s magnetic moment points southward, Earth’s chorus emission waves also show stronger wave activity in the dawn side3 #Question
- Why is that?
In the flybys isn't this an orbit bias?
[!quote]+ Note (Page 3)
Although chorus wave spectra in Earth’s magnetosphere typically show a power gap at half the electron gyrofrequency33–35, the observed whistler-mode waves at Mercury do not show such a gap. The reason might be related to the characteristics of wave normal angles at Mio’s off-equatorial region. A power gap can be caused by damping of obliquely propagating waves away from the source region34 #Question
- What is this damping process and why it does not exist in mercury?
[!quote]+ Highlight (Page 3)
The propagation distance from the source to the spacecraft location may be different between the night and dawn sides. Figure 1a shows that both flyby paths in the night side were located near the lower magnetic latitudes. This implies that the propagation effects from the source cannot explain the presence of localized whistler-mode waves, and that other physical conditions that impact the wave generation and growth processes are at work. #Question
- ??? hellooo
[!quote]+ Note (Page 3)
to specify regions that grow while propagating from the source region. As a simple assumption, we considered the curvature around a region with Bmin, which maximizes the linear growth rate36
- Look up
[!quote]+ Note (Page 4)
We found that whistler-mode waves can be generated in a region with a lower curvature (below 1.5 × 10−12 m−2) on the day side compared with the wave activity measured at the same distance from Mercury in the night side.
[!quote]+ Highlight (Page 4)
two different magnetic inhomogeneities
[!quote]+ Highlight (Page 4)
In the absence of accurate measurements of the cold and energetic electron densities, it is not possible to compare the wave amplitude observed by Mio with the theoretical amplitude #Question
- What energies would we need and up to which we can reach now?
[!quote]+ Highlight (Page 5)
The quasi-trapped electron ring current develops a temperature anisotropy, in particular on the day side, which is the seed for initial whistler-mode wave growth #Question
- How is the convection E and therefore the ring current generated?
Why temperature anisotropy in the day side?
[!quote]+ Highlight (Page 5)
arge compressional background magnetic fields in the day side take bifurcated background magnetic field minima at northward and southward latitudes above the magnetic equator. Electrons with high equatorial pitch angles are then forced to drift and get reflected at high latitudes without passing through the equatorial plane, the so-called Shabansky orbits
[!quote]+ Highlight (Page 5)
Mercury has no permanent electron radiation belt6,40. If a short-duration quasi-trapped radiation belt could be generated at Mercury, chorus waves would play an important role in generating tentative enhancement of higher energy electron populations.
Important points
However, whistler-mode waves below the electron cyclotron frequency (estimated from an empirical magnetic field model9) were clearly observed in the frequency range 0.6–2 kHz during the first flyby event (23:37 to 23:39 ut). Another wave activity below 1 kHz was observed from 23:20 to 23:22 ut when Mio crossed the magnetic equator (and during 23:29 to 23:31 ut), but it is difficult to determine whether they are natural wave emissions or electromagnetic interference from the spacecraft because of their low signal-to-noise ratio. Similarly, whistler-mode waves were observed in the frequency range 0.6–1.8 kHz during the second flyby event (09:45 to 09:51 ut).
- How do you detect this?
[!quote]+ Note (Page 3)
Mercury’s magnetic fields with highly compressed (day side) and stretched (night side) structures should impact the wave growth rate #Take-aways
[!quote]+ Note (Page 3)
information on wave normal angles and polarisation is not available because of telemetry limitation
[!quote]+ Highlight (Page 4)
The fact that Mio observed an enhancement of whistler-mode wave activity of several tens of picotesla for distances of 1.1 to 1.5RM is consistent with the region containing quasi-trapped moderate-energy (1–10 keV) electrons40,41, as these6,11,16,40,41 can act as seed electrons that feed the instability, leading to the observed whistler-mode waves. #Take-aways
[!quote]+ Highlight (Page 4)
Our observations of dawn whistler-mode waves support the MESSENGER observations of localized high-energy electrons concentrated at the dawn side12 near the equatorial region
[!quote]+ Highlight (Page 5)
The flyby observations strongly support the idea that the background magnetic inhomogeneity has a strong impact on the generation process of planetary chorus waves, which is complemented by the results of simulations in Mercury’s environment #Take-aways
[!quote]+ Highlight (Page 5)
These non-energising (drift shell splitting and Shabansky orbits41) processes based on the background magnetic field structures should play a role in developing the temperature anisotropy of seed electrons.
[!quote]+ Highlight (Page 5)
The observed dawn chorus waves contribute to electron precipitation on the dawn side, which can generate part of the X-ray aurora observed on Mercury #Take-aways
[!quote]+ Highlight (Page 5)
such as probing waveform data during future flybys
whistlers not the same with chirps, omora whistler theory(??)
Title: Whistler-mode waves in Mercury’s magnetosphere observed by BepiColombo/Mio
Tags: #Mercury
Authors: Mitsunori Ozaki, Satoshi Yagitani, Yasumasa Kasaba, Yoshiya Kasahara, Shoya Matsuda, Yoshiharu Omura, Mitsuru Hikishima, Fouad Sahraoui, Laurent Mirioni, Gérard Chanteur, Satoshi Kurita, Satoru Nakazawa, Go Murakami
Zotero link: PDF
Questions
although finer structures of typical rising-tone elements in the time domain could not be acquired due to telemetry limitations. #Question
- How do you detect this? In the two band paper we have only rising tone ,why? Isn't this signature rising as well?
[!quote]+ Note (Page 3)
The frequency of these broadband waves (that extend from ~10 to over 20 kHz; not shown) is higher than the electron cyclotron frequency and possibly lower than the plasma frequency, and it may play an important role in locally heating the particles at these boundary layers. #Question
- What are broadband waves and what are causes them? Does heating mean that it is an electrostatic process?
[!quote]+ Note (Page 3)
Because Earth’s magnetic moment points southward, Earth’s chorus emission waves also show stronger wave activity in the dawn side3 #Question
- Why is that?
In the flybys isn't this an orbit bias?
[!quote]+ Note (Page 3)
Although chorus wave spectra in Earth’s magnetosphere typically show a power gap at half the electron gyrofrequency33–35, the observed whistler-mode waves at Mercury do not show such a gap. The reason might be related to the characteristics of wave normal angles at Mio’s off-equatorial region. A power gap can be caused by damping of obliquely propagating waves away from the source region34 #Question
- What is this damping process and why it does not exist in mercury?
[!quote]+ Highlight (Page 3)
The propagation distance from the source to the spacecraft location may be different between the night and dawn sides. Figure 1a shows that both flyby paths in the night side were located near the lower magnetic latitudes. This implies that the propagation effects from the source cannot explain the presence of localized whistler-mode waves, and that other physical conditions that impact the wave generation and growth processes are at work. #Question
- ??? hellooo
[!quote]+ Note (Page 3)
to specify regions that grow while propagating from the source region. As a simple assumption, we considered the curvature around a region with Bmin, which maximizes the linear growth rate36
- Look up
[!quote]+ Note (Page 4)
We found that whistler-mode waves can be generated in a region with a lower curvature (below 1.5 × 10−12 m−2) on the day side compared with the wave activity measured at the same distance from Mercury in the night side.
[!quote]+ Highlight (Page 4)
two different magnetic inhomogeneities
[!quote]+ Highlight (Page 4)
In the absence of accurate measurements of the cold and energetic electron densities, it is not possible to compare the wave amplitude observed by Mio with the theoretical amplitude #Question
- What energies would we need and up to which we can reach now?
[!quote]+ Highlight (Page 5)
The quasi-trapped electron ring current develops a temperature anisotropy, in particular on the day side, which is the seed for initial whistler-mode wave growth #Question
- How is the convection E and therefore the ring current generated?
Why temperature anisotropy in the day side?
[!quote]+ Highlight (Page 5)
arge compressional background magnetic fields in the day side take bifurcated background magnetic field minima at northward and southward latitudes above the magnetic equator. Electrons with high equatorial pitch angles are then forced to drift and get reflected at high latitudes without passing through the equatorial plane, the so-called Shabansky orbits
[!quote]+ Highlight (Page 5)
Mercury has no permanent electron radiation belt6,40. If a short-duration quasi-trapped radiation belt could be generated at Mercury, chorus waves would play an important role in generating tentative enhancement of higher energy electron populations.
Important points
However, whistler-mode waves below the electron cyclotron frequency (estimated from an empirical magnetic field model9) were clearly observed in the frequency range 0.6–2 kHz during the first flyby event (23:37 to 23:39 ut). Another wave activity below 1 kHz was observed from 23:20 to 23:22 ut when Mio crossed the magnetic equator (and during 23:29 to 23:31 ut), but it is difficult to determine whether they are natural wave emissions or electromagnetic interference from the spacecraft because of their low signal-to-noise ratio. Similarly, whistler-mode waves were observed in the frequency range 0.6–1.8 kHz during the second flyby event (09:45 to 09:51 ut).
- How do you detect this?
[!quote]+ Note (Page 3)
Mercury’s magnetic fields with highly compressed (day side) and stretched (night side) structures should impact the wave growth rate #Take-aways
[!quote]+ Note (Page 3)
information on wave normal angles and polarisation is not available because of telemetry limitation
[!quote]+ Highlight (Page 4)
The fact that Mio observed an enhancement of whistler-mode wave activity of several tens of picotesla for distances of 1.1 to 1.5RM is consistent with the region containing quasi-trapped moderate-energy (1–10 keV) electrons40,41, as these6,11,16,40,41 can act as seed electrons that feed the instability, leading to the observed whistler-mode waves. #Take-aways
[!quote]+ Highlight (Page 4)
Our observations of dawn whistler-mode waves support the MESSENGER observations of localized high-energy electrons concentrated at the dawn side12 near the equatorial region
[!quote]+ Highlight (Page 5)
The flyby observations strongly support the idea that the background magnetic inhomogeneity has a strong impact on the generation process of planetary chorus waves, which is complemented by the results of simulations in Mercury’s environment #Take-aways
[!quote]+ Highlight (Page 5)
These non-energising (drift shell splitting and Shabansky orbits41) processes based on the background magnetic field structures should play a role in developing the temperature anisotropy of seed electrons.
[!quote]+ Highlight (Page 5)
The observed dawn chorus waves contribute to electron precipitation on the dawn side, which can generate part of the X-ray aurora observed on Mercury #Take-aways
[!quote]+ Highlight (Page 5)
such as probing waveform data during future flybys
Title: Whistler-mode waves in Mercury’s magnetosphere observed by BepiColombo/Mio
Tags: #Mercury
Authors: Mitsunori Ozaki, Satoshi Yagitani, Yasumasa Kasaba, Yoshiya Kasahara, Shoya Matsuda, Yoshiharu Omura, Mitsuru Hikishima, Fouad Sahraoui, Laurent Mirioni, Gérard Chanteur, Satoshi Kurita, Satoru Nakazawa, Go Murakami
Zotero link: PDF
Questions
although finer structures of typical rising-tone elements in the time domain could not be acquired due to telemetry limitations. #Question
- How do you detect this? In the two band paper we have only rising tone ,why? Isn't this signature rising as well?
[!quote]+ Note (Page 3)
The frequency of these broadband waves (that extend from ~10 to over 20 kHz; not shown) is higher than the electron cyclotron frequency and possibly lower than the plasma frequency, and it may play an important role in locally heating the particles at these boundary layers. #Question
- What are broadband waves and what are causes them? Does heating mean that it is an electrostatic process?
[!quote]+ Note (Page 3)
Because Earth’s magnetic moment points southward, Earth’s chorus emission waves also show stronger wave activity in the dawn side3 #Question
- Why is that?
In the flybys isn't this an orbit bias?
[!quote]+ Note (Page 3)
Although chorus wave spectra in Earth’s magnetosphere typically show a power gap at half the electron gyrofrequency33–35, the observed whistler-mode waves at Mercury do not show such a gap. The reason might be related to the characteristics of wave normal angles at Mio’s off-equatorial region. A power gap can be caused by damping of obliquely propagating waves away from the source region34 #Question
- What is this damping process and why it does not exist in mercury?
[!quote]+ Highlight (Page 3)
The propagation distance from the source to the spacecraft location may be different between the night and dawn sides. Figure 1a shows that both flyby paths in the night side were located near the lower magnetic latitudes. This implies that the propagation effects from the source cannot explain the presence of localized whistler-mode waves, and that other physical conditions that impact the wave generation and growth processes are at work. #Question
- ??? hellooo
[!quote]+ Note (Page 3)
to specify regions that grow while propagating from the source region. As a simple assumption, we considered the curvature around a region with Bmin, which maximizes the linear growth rate36
- Look up
[!quote]+ Note (Page 4)
We found that whistler-mode waves can be generated in a region with a lower curvature (below 1.5 × 10−12 m−2) on the day side compared with the wave activity measured at the same distance from Mercury in the night side.
[!quote]+ Highlight (Page 4)
two different magnetic inhomogeneities
[!quote]+ Highlight (Page 4)
In the absence of accurate measurements of the cold and energetic electron densities, it is not possible to compare the wave amplitude observed by Mio with the theoretical amplitude #Question
- What energies would we need and up to which we can reach now?
[!quote]+ Highlight (Page 5)
The quasi-trapped electron ring current develops a temperature anisotropy, in particular on the day side, which is the seed for initial whistler-mode wave growth #Question
- How is the convection E and therefore the ring current generated?
Why temperature anisotropy in the day side?
[!quote]+ Highlight (Page 5)
arge compressional background magnetic fields in the day side take bifurcated background magnetic field minima at northward and southward latitudes above the magnetic equator. Electrons with high equatorial pitch angles are then forced to drift and get reflected at high latitudes without passing through the equatorial plane, the so-called Shabansky orbits
[!quote]+ Highlight (Page 5)
Mercury has no permanent electron radiation belt6,40. If a short-duration quasi-trapped radiation belt could be generated at Mercury, chorus waves would play an important role in generating tentative enhancement of higher energy electron populations.
Important points
However, whistler-mode waves below the electron cyclotron frequency (estimated from an empirical magnetic field model9) were clearly observed in the frequency range 0.6–2 kHz during the first flyby event (23:37 to 23:39 ut). Another wave activity below 1 kHz was observed from 23:20 to 23:22 ut when Mio crossed the magnetic equator (and during 23:29 to 23:31 ut), but it is difficult to determine whether they are natural wave emissions or electromagnetic interference from the spacecraft because of their low signal-to-noise ratio. Similarly, whistler-mode waves were observed in the frequency range 0.6–1.8 kHz during the second flyby event (09:45 to 09:51 ut).
- How do you detect this?
[!quote]+ Note (Page 3)
Mercury’s magnetic fields with highly compressed (day side) and stretched (night side) structures should impact the wave growth rate #Take-aways
[!quote]+ Note (Page 3)
information on wave normal angles and polarisation is not available because of telemetry limitation
[!quote]+ Highlight (Page 4)
The fact that Mio observed an enhancement of whistler-mode wave activity of several tens of picotesla for distances of 1.1 to 1.5RM is consistent with the region containing quasi-trapped moderate-energy (1–10 keV) electrons40,41, as these6,11,16,40,41 can act as seed electrons that feed the instability, leading to the observed whistler-mode waves. #Take-aways
[!quote]+ Highlight (Page 4)
Our observations of dawn whistler-mode waves support the MESSENGER observations of localized high-energy electrons concentrated at the dawn side12 near the equatorial region
[!quote]+ Highlight (Page 5)
The flyby observations strongly support the idea that the background magnetic inhomogeneity has a strong impact on the generation process of planetary chorus waves, which is complemented by the results of simulations in Mercury’s environment #Take-aways
[!quote]+ Highlight (Page 5)
These non-energising (drift shell splitting and Shabansky orbits41) processes based on the background magnetic field structures should play a role in developing the temperature anisotropy of seed electrons.
[!quote]+ Highlight (Page 5)
The observed dawn chorus waves contribute to electron precipitation on the dawn side, which can generate part of the X-ray aurora observed on Mercury #Take-aways
[!quote]+ Highlight (Page 5)
such as probing waveform data during future flybys
@liOriginTwobandChorus2019
The rising tone dispersion is reproduced if we take into account the non-linear terms/phenomena.
Look-into
chorus waves exchange energy primarily via two types of resonant interactions: cyclotron resonance, which occurs when the Doppler-shifted wave frequency in the particle’s moving frame matches its gyro-frequency, ω kkvc 1⁄4 ωce, and Landau resonance, which occurs when the wave is stationary in the particle’s frame, ω kkvL 1⁄4 0. #Look-into
It has been well known that chorus waves are generally excited by injected electrons whose perpendicular temperature (with respect to the background magnetic field) exceeds the parallel temperature, and are excited via cyclotron resonant interactions42,4