Evolution and dynamics of equatorial plasma bubbles: Relationships to ExB drift, postsunset total electron content enhancements, and equatorial electrojet strength

The growth in altitude/latitude of equatorial plasma bubbles was monitored, using simultaneous recordings of VHF scintillations at five locations situated between 3degrees and 23degreesN magnetic latitudes along a common meridian (84degreesE) during February 1980. The onsets of postsunset scintillation were mostly abrupt in character, and their occurrence at higher latitudes was conditional on their prior appearance at lower latitudes, indicating a causal link to irregularities associated with rising equatorial plasma bubbles. The day-to-day occurrence and the latitudinal, and effectively altitudinal, growths are examined in relation to the prereversal enhancement in h'F during sunset hours and its rate of rise, the onset of a postsunset secondary maximum (PSSM) in ionospheric electron content (IEC), and equatorial electrojet strength (EEJ) variations. It is observed that the bubble and associated irregularities, after its onset over the magnetic equator, reached the highest altitudes/latitudes only on those days when a prior PSSM in IEC is observed there in addition to high values of h'F, dh'F/dt and bubble rise velocity; otherwise it will be confined to near equatorial latitudes only. Also, the equatorial h'F, dh'F/dt, magnitude of PSSM and intensity of 4 GHz scintillations at low latitude are all showing positive correlation with daytime EEJ strength variations. It is concluded that, after the initial development of a bubble, the ExB drift and the PSSM play an important role in the subsequent growth and evolution, and EEJ is a useful parameter for the prediction of the development.