HIGHLY STRUCTURED IONOSPHERIC CONVECTION FOR NORTHWARD INTERPLANETARYMAGNETIC-FIELD - A CASE-STUDY WITH DE-2 OBSERVATIONS

Dynamics Explorer 2 observed a highly structured plasma convection in the dawn sector of the high-latitude ionosphere on October 25, 1981. A nalyzing the magnetic and electric field and plasma data for the event , we have clarified the relation between the electric field variations and the plasmas. There is a region of spiky electric field variations that create a highly structured convection. This region of spiky elec tric field variations generally coincides with a region having source electrons of low temperature (roughly 60-100 eV) and high density (rou ghly 1-5 cm(-3), sometimes much higher). Ions having energies of sever al hundred to several kilo electron volts precipitate in the region of the spiky electric field variations. Results of the analysis also sug gest that the highly structured plasma drift is detached from the days ide reverse convection, that is, sunward flow at the highest latitudes and antisunward flow at lower latitudes. Thus our results do not agre e with some of the previous studies which suggested that the structure d plasma convection is a continuation of the dayside convection that h as become irregular near the nightside edge and that its source region is the plasma sheet. We suggest that the source for the highly struct ured convection lies in the distant low-latitude boundary layer, and p ropose a source electric field configuration.