Relativistic electron events in 2002: Studies of pitch angle isotropization

[1] Energization of electrons to relativistic energies in the Earth's outer radiation belt is not fully understood. Recent renewed interest in the problem has resulted in a number of models which invoke a variety of physical processes ranging from diffusive particle transport to in situ acceleration. Evolution of local pitch angle distributions and global flux isotropization timescales of relativistic electrons may be important discriminators of the underlying physical processes of energization, transport, and loss. Data from SAMPEX, Polar, and LANL suite of satellites were used to study electron isotropization and pitch angle evolution for relativistic electron enhancement events during the year 2002. It was found that during electron energization events there is generally increased precipitation of electrons and rapid electron flux isotropization on a global scale. Case studies using pitch angle resolved data collected at geosynchronous distances suggest an in situ broadening of the local pitch angle distribution in agreement with the corresponding global isotropization measurements. These observations suggest that electron energization in the magnetosphere is intimately associated with rapid pitch angle scattering leading to a flattening of the pitch angle distributions of energized electrons.