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Simulation of the energy distribution of relativistic electron precipitation caused by quasi-linear interactions with EMIC waves.

Li Z, Millan RM, Hudson MK - J Geophys Res Space Phys (2013)

Bottom Line: The precipitating flux, on the other hand, first rapidly increases and then gradually decreases.We also show that increasing wave frequency can lead to the occurrence of a second peak.In both single- and double-peak cases, increasing wave frequency, cold plasma density or decreasing background magnetic field strength lowers the energies of the peak(s) and causes the precipitation to increase at low energies and decrease at high energies at the start of the precipitation.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Astronomy, Dartmouth College Hanover, New Hampshire, USA.

ABSTRACT

[1]Previous studies on electromagnetic ion cyclotron (EMIC) waves as a possible cause of relativistic electron precipitation (REP) mainly focus on the time evolution of the trapped electron flux. However, directly measured by balloons and many satellites is the precipitating flux as well as its dependence on both time and energy. Therefore, to better understand whether pitch angle scattering by EMIC waves is an important radiation belt electron loss mechanism and whether quasi-linear theory is a sufficient theoretical treatment, we simulate the quasi-linear wave-particle interactions for a range of parameters and generate energy spectra, laying the foundation for modeling specific events that can be compared with balloon and spacecraft observations. We show that the REP energy spectrum has a peaked structure, with a lower cutoff at the minimum resonant energy. The peak moves with time toward higher energies and the spectrum flattens. The precipitating flux, on the other hand, first rapidly increases and then gradually decreases. We also show that increasing wave frequency can lead to the occurrence of a second peak. In both single- and double-peak cases, increasing wave frequency, cold plasma density or decreasing background magnetic field strength lowers the energies of the peak(s) and causes the precipitation to increase at low energies and decrease at high energies at the start of the precipitation.

No MeSH data available.


Related in: MedlinePlus

Evolution of the pitch angle distribution of the trapped flux of 4 MeV electrons in the simulation time 0 to 5 min. B0, N0, ω1, and ω2 are the same as Figure 1(c). At B0=200 nT (L∼6.7), the loss cone is ∼2.3°. At 0 min, the trapped flux distribution is the initial Maxwellian flux distribution equation 3.
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fig03: Evolution of the pitch angle distribution of the trapped flux of 4 MeV electrons in the simulation time 0 to 5 min. B0, N0, ω1, and ω2 are the same as Figure 1(c). At B0=200 nT (L∼6.7), the loss cone is ∼2.3°. At 0 min, the trapped flux distribution is the initial Maxwellian flux distribution equation 3.

Mentions: [9]Applying the results for the diffusion coefficients from section 3, we solve equation 2 for the trapped equatorial electron flux j0(α0,E,t). An example is shown in Figure 3. As we can see, the loss cone fills up quickly (e.g., the first ∼60 s in Figure 3) before gradually being depleted as the total flux drops due to loss to the loss cone.


Simulation of the energy distribution of relativistic electron precipitation caused by quasi-linear interactions with EMIC waves.

Li Z, Millan RM, Hudson MK - J Geophys Res Space Phys (2013)

Evolution of the pitch angle distribution of the trapped flux of 4 MeV electrons in the simulation time 0 to 5 min. B0, N0, ω1, and ω2 are the same as Figure 1(c). At B0=200 nT (L∼6.7), the loss cone is ∼2.3°. At 0 min, the trapped flux distribution is the initial Maxwellian flux distribution equation 3.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4497461&req=5

fig03: Evolution of the pitch angle distribution of the trapped flux of 4 MeV electrons in the simulation time 0 to 5 min. B0, N0, ω1, and ω2 are the same as Figure 1(c). At B0=200 nT (L∼6.7), the loss cone is ∼2.3°. At 0 min, the trapped flux distribution is the initial Maxwellian flux distribution equation 3.
Mentions: [9]Applying the results for the diffusion coefficients from section 3, we solve equation 2 for the trapped equatorial electron flux j0(α0,E,t). An example is shown in Figure 3. As we can see, the loss cone fills up quickly (e.g., the first ∼60 s in Figure 3) before gradually being depleted as the total flux drops due to loss to the loss cone.

Bottom Line: The precipitating flux, on the other hand, first rapidly increases and then gradually decreases.We also show that increasing wave frequency can lead to the occurrence of a second peak.In both single- and double-peak cases, increasing wave frequency, cold plasma density or decreasing background magnetic field strength lowers the energies of the peak(s) and causes the precipitation to increase at low energies and decrease at high energies at the start of the precipitation.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Astronomy, Dartmouth College Hanover, New Hampshire, USA.

ABSTRACT

[1]Previous studies on electromagnetic ion cyclotron (EMIC) waves as a possible cause of relativistic electron precipitation (REP) mainly focus on the time evolution of the trapped electron flux. However, directly measured by balloons and many satellites is the precipitating flux as well as its dependence on both time and energy. Therefore, to better understand whether pitch angle scattering by EMIC waves is an important radiation belt electron loss mechanism and whether quasi-linear theory is a sufficient theoretical treatment, we simulate the quasi-linear wave-particle interactions for a range of parameters and generate energy spectra, laying the foundation for modeling specific events that can be compared with balloon and spacecraft observations. We show that the REP energy spectrum has a peaked structure, with a lower cutoff at the minimum resonant energy. The peak moves with time toward higher energies and the spectrum flattens. The precipitating flux, on the other hand, first rapidly increases and then gradually decreases. We also show that increasing wave frequency can lead to the occurrence of a second peak. In both single- and double-peak cases, increasing wave frequency, cold plasma density or decreasing background magnetic field strength lowers the energies of the peak(s) and causes the precipitation to increase at low energies and decrease at high energies at the start of the precipitation.

No MeSH data available.


Related in: MedlinePlus