MID-LATITUDE AND LOW-LATITUDE PROMPT-PENETRATION IONOSPHERIC ZONAL PLASMA DRIFTS

We have used ion drift observations from the DE-2 satellite to determi ne the latitudinal variation and the temporal evolution of mid- and lo w-latitude prompt penetration zonal plasma drifts driven by magnetosph eric electric fields. Our results indicate that sudden increases in co nvection lead to predominantly westward perturbation drifts which decr ease equartorwards and have largest amplitudes in the dusk-midnight se ctor. The diurnal perturbation drift patterns shift to later local tim es with increasing storm time and decay to new quasiequilibrium values in about 2 hours, as the ring current readjusts to the new polar cap potential. The daily and latitudinal variations and temporal evolution of the DE-2 prompt penetration drifts are generally in good agreement with predictions from the Rice Convection Model, although the experim ental results show larger amplitudes and longer shielding time constan ts.