Modeling the propagation characteristics of chorus using CRRES suprathermal electron fluxes

In the present paper, phase space density functions of the form f(v) = A N /v n are fitted to statistical distributions of suprathermal electron fluxes (E = 0.213–16.5 keV) from the CRRES satellite, parameterized by L-shell, Magnetic Local Time (MLT), and geomagnetic activity. The fitted distributions are used in conjunction with ray tracing to calculate the Landau damping rates of an ensemble of rays representing whistler-mode chorus waves. The modeled propagation characteristics are compared with observations of chorus wave power from the CRRES satellite, as a function of L-shell, MLT, and magnetic latitude, in various frequency bands, and under various geomagnetic conditions. It is shown that the model results are remarkably consistent with many aspects of the observed wave distributions, including frequency, L-shell, MLT, and latitudinal dependence. In addition, the MLT distribution of wave power becomes characteristically asymmetric during active geomagnetic conditions, with small propagation lengths on the nightside which increase with MLT and maximize on the dayside. This asymmetry is shown to be directly related to the dynamics of the Landau resonant suprathermal electrons which drift around the Earth whilst undergoing scattering and loss due to a variety of plasma waves. Consequently, the suprathermal electrons play an important role in radiation belt dynamics, by controlling the distribution of chorus, which in turn contributes to the acceleration and loss of relativistic electrons in the recovery phase of storms

Modeling the wave power distribution and characterisitics of plamaspheric hiss

We simulate the spatial and spectral distributions of plasmaspheric hiss using a technique that involves extensive ray tracing. The rays are injected in the equatorial chorus source region outside the plasmasphere, are power weighted as a function of L-shell, frequency, and wave normal angle, so as to represent the chorus source distribution, and are propagated throughout the simulation domain until the power in each ray is effectively extinguished due to Landau damping. By setting up a large number of virtual observatories, the rays passing each observation location are counted, and a distribution is constructed. Our simulated plasmaspheric hiss spectrum reproduces the main observed features, including the lower and upper frequency cutoffs, the behavior of the bandwidth as a function of L-shell, the spatial extent, and even the two-zone structure of hiss, although the intensity is lower than observed. The wave normal distribution shows that at high latitudes, the wave normals are predominantly oblique, but near the equator, the wave normal distribution can be either predominantly field-aligned (lower L shells), or be bimodal, having a maximum in the field-aligned direction, and another maximum at very oblique angles, comprised of those rays that have broken out of their cyclical trajectories. This distribution of wave normals seems to reconcile the apparently contradictory observations that have been reported previously

Magnetospheric chorus wave simulation with the TRISTAN-MP PIC code

We present the results of particle-in-cell simulations of the whistler anisotropy instability that results in magnetospheric chorus wave excitation. The simulations were carried out using, for the first time for this problem, the 2D TRISTAN-massively parallelized code, widely used before in the modeling of astrophysical shocks. The code has been modified to allow for two populations of electrons: cold electrons (which maintain the wave propagation) and hot electrons (which provide the wave growth). For the hot electrons, the anisotropic form of the relativistic Maxwell-Jüttner distribution is implemented. We adopt the standard approximation of a parabolic magnetic field to simulate the Earth's magnetic field close to the equator. Simulations with different background magnetic field inhomogeneity strengths demonstrate that higher inhomogeneity yields lower frequency chirping rates and, eventually, it suppresses chorus generation. The results are in agreement with other numerical simulations and the theoretical predictions for the frequency chirping rates

Evaluation of whistler mode chorus amplification during an injection event observed on CRRES

The excitation of nightside whistler mode chorus emissions in the low-density region outside the plasmapause is investigated during an injection of plasma sheet electrons into the inner magnetosphere. CRRES data of the electron phase space density (PSD) over the LEPA energy range between 0.1 keV and 30 keV are used to develop an analytical model for the distribution function of injected low-energy electrons. The path-integrated growth of chorus waves is then evaluated with the HOTRAY code by tracing unducted whistler mode chorus waves in a hot magnetized plasma. The results indicate that newly injected electrons are responsible for the intensification of lower-band whistler mode chorus. However, slightly higher electron anisotropy than that obtained from the 5 min-averaged electron PSD data is required to reproduce the observed wave intensity during an injection event. We suggest that the injected electron anisotropy is reduced due to pitch angle scattering by the enhanced chorus waves within the 5-min interval over which the CRRES data are analyzed