Medium energy pitch angle distribution during substorm injected electron clouds

Abstract

[1] An investigation of pitch angle resolved electron data of energy <47 keV made by the MPA instrument on LANL geosynchronous satellites reveals a signature of symmetric peaks in the pitch angle distributions, observed to expand from being nearly at perpendicular pitch angles ($90°) to nearly field aligned at lower energies. This feature is seen in almost every interval of increased fluxes at geosynchronous orbit. A closer examination reveals the expansion of the peak in pitch angle to be such that the corresponding parallel velocity (along B) is constant. In some time intervals there are simultaneous symmetric peaks in more than one energy band and the parallel energy corresponding to the symmetric peaks is seen to vary as function of time. The observations might be explained by particles interacting with whistler mode chorus through Landau resonance, diffusing particles with parallel velocity near the phase velocity of the waves.

Modeling the propagation characteristics of chorus using CRRES suprathermal electron fluxes

“…This assumption is consistent with past work which has indicated that suprathermal fluxes are generally isotropic , and even if some anisotropy is present, it does not affect the Landau damping rates appreciably [Thorne and Horne, 1994]. The assumption of suprathermal flux isotropy is particularly valid during active times (which are of most interest to us in the present study) when the presence of intense waves tends to isotropise the electron distribution [Asnes et al, 2005] at lower energies.…”

Coherent nonlinear scattering of energetic electrons in the process of whistler mode chorus generation

“… Meredith et al [1999] have reported the observations of characteristic distributions in the restricted region at the equator outside the plasmapause, where the pitch angle distributions are formed with sharply peaked at 90° in the relatively low energy range below a few keV, which is known as a pancake distribution [ Wrenn et al , 1979]. Similar types of pitch angle distributions in keV combined with butterfly distributions were reported [ Åsnes et al , 2005]. It has been suggested that ECH (Electron Cyclotron Harmonic) waves are responsible for the formation of pancake distributions [ Meredith et al , 2000].…”

Pancake-like and tablet-like distribution functions of energetic electrons in the middle magnetosphere

“…Other particle distributions with a considerably greater spread along the longitudinal velocity were also obtained in the RB (Bell et al, 2000;Asnes et al, 2005). Actually, whistler waves exist in a certain frequency band, which is determined by the mean distribution function anisotropy, frequency dependence of the magnetospheric resonator quality, and special features of the wave ray tracing.…”

“…1) near the magnetic equator plane in the RB has recently been obtained in the space experiments. Asnes et al (2005) give experimental data obtained using the Magnetospheric Plasma Analyser (MPA) instrument onboard the LANL geosynchronous satellites, according to which pancake-like distributions of the energetic electrons with energies less than 47 keV can exist. The authors consider such distributions as resulting from the wave-particle interaction with chorus emissions outside the plasmasphere due to the Cherenkov resonance.…”

“…If V 2 zL is not so large, then there will be one point of interaction at the magnetic equator, and for even smaller V 2 zL this point disappears, too. Therefore, there is a minimum value of V 2 zL , which corresponds to the boundary of the wave-particle interaction in the magnetic equatorial plane even at the maximum possible frequency (11) (Goldstein and Tsurutani, 1984;Bespalov and Trakhtengerts, 1986;Asnes et al, 2005):…”