Stormtime Electron PSD Radial Profiles for Small and Large K Values: SCATHA Observations

A critical piece of information that is needed to help understand the transport and acceleration of electrons in the inner magnetosphere is the radial gradient of the phase space density (PSD) at constant first and second invariants. We use the detailed energetic electron angular and spectral data combined with the magnetic field from SCATHA and a field model to obtain the PSD radial profile evolution through a small magnetic storm (2 May, 1986; Dst >-95 nT). We examine the pre storm PSD radial profiles and compare the changes that occur through the storm recovery period. SCATHA provides electron observations covering the M range 200 - 2500 MeV/G and K range 0.06 - 0.65 Re G^{1/2} over an L* range of 5.2 - 7.3 Re. Thus SCATHA provides the PSD radial profiles both near and off the magnetic equator for a range of M values. We used data only from the dayside magnetosphere to avoid the night side region where field models generally match the observed field more poorly. The PSD radial profiles show a range of features from peaked in L* at small K and M during the pre storm period to relatively flat for much of K and L* late in the post storm recovery. During the electron PSD enhancement period, 6-10 May, the PDS radial profiles ranged from those with relative minima in the L* = 5.2-7 range to those that had peaks in the L* = 5.2-6.5 range depending on the value of K. There are significant differences in the radial profiles for small and intermediate K values at constant M. This indicates the importance of being able to measure the near equatorial pitch angle distributions. For example, during the early recovery period the PSD profiles were flat or decreasing for K=0.06 for M > 1200 MeV/G while they are peaked near L*=5.75 for K > 0.2. After the post storm PSD's maximized, within the L* range of the observations, the radial profiles were relatively flat or slightly falling with increasing L*. The results will be discussed in terms of what they imply for the electron transport and acceleration processes.