Ionospheric irregularities and storm-induced equatorial and high-latitude effects at the anomaly crest region

Abstract

IEC information received through VHF RB measurements has been analyzed over the anomaly crest region of Guwahati (92° E, 26° N, 15° N geo.mag) along with a few low/low-mid latitude observations for understanding the roles of influx of plasma to anomaly crest regions, from equatorward and poleward processes during geomagnetically disturbed situations. The conditions leading to inflow of plasma to equatorial anomaly crest region or inhibition of such processes have been described in the paper through systematic analysis of disturbed day (free from sudden commencements) ionospheric electron content (IEC) variations at different temporal situtions. The storm-induced effects in relation to the development of the above conditions have also been examined for moderate and moderately severe isolated storm cases. Finally the paper deals with a few severe storms. The storm-triggered IEC features indicate inhibition or suppression of plasma dumping process at anomaly crests, through equatorial anomaly phenomenon. During winter and many equinoxial storms, the compression effect pushes this station away from the region where effective dumping of ionization from the equator is expected. Diffusion of plasma from the polar region to the crest area has also been observed through penetration of the eastward electric field during many disturbed situations. Depletion of noontime density during winter and equinoxial months and enhancement of the same during summer geomagnetically active situations are examined through anomaly compression (or inhibition) process as well as plasma replenishment through the equatorward wind.