[P-EM13] Dynamics of the Inner Magnetospheric System

[PEM13-P30] Whistler-Mode Wave Normal Angle Shift and the Related Pitch Angle Distribution of Electrons During Dipolarization

*Kaiti Wang¹, Fumiko Otsuka², Tohru Hada², Ching-Huei Lin³ (1.Tamkang University, 2.Kyushu University, 3.Chien-Hsin University of Science and Technology)

Keywords:whistler-mode waves, wave normal angle shift , pitch angle distribution, dipolarization at tailside

A peculiar wave event was recorded in the whistler frequency range at around a few hundred Hz, at a dipolarization site near the magnetic equator, about 10 Earth radii tailside. The THEMIS mission observed this wave event during an intense decrease in the auroral electrojet index (AL). The wave event is unique, with a shift in the wave normal angle from nearly 160^o to 20^o, right after the dipolarization angle reaches its maximum. The effect of pitch angle scattering on electrons through cyclotron and Landau resonances via this wave event is investigated by performing test particle simulations incorporating the observed wave amplitudes and wave normal angles. The results showed that the primary scattering could occur at nearly 0 and 180 degrees for electrons around 10 keV, similar to the observed changes in electron pitch angle distributions of a similar energy. We will present the observations and computations and show that a wave event with shifted wave normal angles can cause changes in pitch angle distributions in different directions with respect to the ambient magnetic field.