Statistical study on the characterization of ULF Pulsations in the Inner Magnetosphere by THEMIS

ULF pulsations (2~25 mHz) have significant influence on the transport of energetic particles trapped in the outer radiation belt, which have drift frequencies comparable to this range. However recent studies indicate that not all classes of ULF waves are equally important for radiation belt electron acceleration. For example, simulations suggest that electrons could be adiabatically accelerated through a drift-resonance interaction with either azimuthal (toroidal) mode or radial (poloidal) mode ULF waves. THEMIS electric field observations provide a good opportunity to study and fully characterize the features of the ULF pulsations in the inner magnetosphere. The ULF polarization study by Sarris et al [2008] focuses on the observations made by one THEMIS probe during its out-bound pass on September 4th, 2007. Here we will present the statistical studies of the polarizations of ULF pulsations, based on the spin-fit electric and magnetic field data from July 2007 to June 2008, with full local time coverage. Through this global coverage, ULF polarizations are characterized at different regions, in terms of radial distance and local times. Preliminary analysis indicates that the polarizations of electric field pulsation are more radial in dawn/dusk sectors and more azimuthal in noon/midnight sectors.