Incidence of extensive plasma density depletions in the lower F region

Abstract The Retarding Potential Analyser Payload onboard the Indian satellite SROSS-C recorded a few very steep plasma depletion occurrences near the magnetic equator in the pre-midnight hours during June–July, 1992. These plasma depletions that tantamount to an ionospheric hole in the altitude range from 230 to 300 km, always exist northward of the magnetic equator and extend to latitudes as high as 20°N. However, very adjacent to the magnetic equator on the southern side, a spectacular increase is seen in the ion density sometimes from less than 10 3 to almost 10 6 ions cm −3 within a latitude range of mere 5°, and then tapers off gradually towards southern latitudes. Thus, a peak in ionization which sometimes exceeds in magnitude even the daytime maximum value is seen during nighttime hours at south of the equator. These unusually large depletions and enhancements in plasma density distribution on either side of the magnetic equator, perhaps, can be explained in terms of the plasma transport due to transequatorial meridional winds and the F region electric fields over the equatorial and low latitudes.