IONOSPHERIC FOOTPRINT OF MAGNETOSHEATH-LIKE PARTICLE-PRECIPITATION OBSERVED BY AN INCOHERENT-SCATTER RADAR

We have examined Sondrestrom incoherent scatter radar observations of ionospheric plasma density and temperature distributions and measureme nts of F region ion drifts that were made during a prenoon pass of the DMSP-F7 satellite through the radar field of view. The spacecraft tra versed a region of intense electron precipitation with a characteristi c energy below approximately 200 eV. Particles with such low character istic energies are believed to be directly or indirectly of magnetoshe ath origin. The precipitation region had a width of about 2-degrees in variant latitude and covered the low-latitude boundary layer (LLBL), t he cusp, and the equatorward section of the plasma mantle (PM). The co rotating radar observed a patch of enhanced electron density and eleva ted electron temperature in the F2 region between about 10.5 and 12 ma gnetic local time in the same invariant latitude range where DMSP-F7 d etected the soft-electron flux. The ion drift pattern, also obtained b y radar, shows that it is unlikely that the plasma patch was produced by solar radiation and advected into the radar field of view. We sugge st that the radar observed modifications of the ionospheric plasma dis tribution, which resulted from direct entry of magnetosheath electrons into the magnetosphere and down to ionospheric altitudes. Model calcu lations of the ionospheric response to the observed electron precipita tion support our interpretation. The spectral characteristics of the e lectron flux in the LLBL, cusp, and equatorward section of the PM were in this case too similar to allow to distinguish between them by usin g incoherent scatter radar measurements only.