The correlation of longitudinal/seasonal variations of evening equatorial pre-reversal drift and of plasma bubbles

摘要

The evening pre-reversal vertical drift velocityenhancement (PRE) constitutes an important seeding mechanism for thegeneration of F region irregularities. Ion density and drift measurementsfrom ROCSAT-1 and DMSP satellites are used to examine the correlation oflongitudinal/seasonal (l/s) variations in the evening pre-reversal verticaldrift velocity at the magnetic equator in the topside ionosphere and theplasma bubble (PB) occurrence probability. The analysis performed for threeyears 2000–2002 (solar maximum), provides consistent evidence as the groundobservations that the equatorial PB occurrence is dependent on and increasesapproximately linearly with PRE, and the l/s variations of PRE play animportant role in the global l/s distribution of PB occurrence. Thesolstitial evening PRE and equatorial PB occurrence show similarlongitudinal variations: During June solstice, two peaks appear in theAfrican and Pacific longitude sectors, and two minimums are observed in theIndian and American regions; During December solstice, the situation isapproximately opposite. The equinoctial longitudinal effects are comparablysmall. It is concluded that the large-scale l/s variations of equatorial PBoccurrence can be closely related to the l/s variations of PRE.