Magnetosphere Seminars

April 30, 2013 – “Estimating magnetic field power spectrum and the magnetic diffusion coefficients using CRRES magnetometer data”

Speaker:Ashar Ali (LASP)
Date:Tuesday, Apr 30, 2013
Time:4:00 PM
Location:LASP Space Science Building, room N248 upstairs. Map

Seminar Abstract:

Radial diffusion has been established as one of the acceleration mechanisms responsible for populating and depleting the Van Allen radiation belts with high energy charged particles. Random perturbations in the fields energize particles over ULF time scales by conserving the first and second adiabatic invariants of a particle while violating the third adiabatic invariant which then causes diffusion. In this presentation, we use the magnetometer data from the Combined Release and Radiation Effects Satellite (CRRES) to estimate the magnetic component of the diffusion coefficient. We estimate the power spectral density (PSD) of the compressional component of the geomagnetic field in the 0.8 mHz to 16.3 mHz range containing the Pc-5 interval. First, we present different methodologies to estimate the magnetic field spectrum and their potential pitfalls. Second we investigate the dependence of the magnetic PSD on radial distance L, measure of geomagnetic disturbance Kp, and magnetic local time. Most diffusion coefficient formulations assume uniform power in azimuth and we present evidence to the contrary. We see a clear local time dependence in the magnetic PSD. Third, we recompute the PSDs averaging over all local times and then obtain the magnetic component of the diffusion coefficient using the relativistically corrected formulation of Fei et al. (2006). The results will then be compared with previous work, notably Brautigam and Albert (2000), Brautigam et al. (2005) along with more recent efforts of Ozeke et al. (2012), and Tu et al. (2012).