PERVASIVE SMALL-SCALE ENHANCEMENTS IN MANTLE AND POLAR RAIN PRECIPITATION

Short duration bursts -- 1-3 s or 0.05-0.15 degrees MLAT -- of 32 eV t o several hundred eV electrons are regularly observed in the polar rai n and mantle precipitation regions by the DMSP satellites. The spacing between bursts is typically 9-12 s (70-90 km) and is sometimes regula r but more often irregular. Sometimes quasi-periodic trains of 4 or 5 evenly spaced bursts occur. Electron spectra in the bursts are variabl e, but typically represent an enhancement of an order of magnitude in the spectral differential energy flux, but without showing signs of fi eld-aligned acceleration. Previous reports of bursty polar cap precipi tation consisted of precipitation with large scale (hundreds of km) sp atial inhomogeneity of plasma sheet origin under northward IMF conditi ons. The bursts described herein occur for southward as well as northw ard IMF B-z, and represent fine structure (7.5 km) within regions that are of magnetosheath origin and which are homogenous over larger spat ial scales (>similar to 100 km). We suggest that the observed phenomen a may be related to the nonstationary processes in the outer high lati tude magnetosphere.