The role of the storm-time prompt penetrating electric field on the net distribution of plasma density over the low latitude ionospheric regions

Abstract

The relative role of the prompt penetration of electric fields and neutral winds in the distribution of ionospheric plasma during geomagnetic storms over the Indian ionosphere region is studied in this paper. Four geomagnetic storms with similar onset times but of varying strengths have been analyzed with the help of data from ground-based magnetometers, and the ACE, GPS, and TIMED satellites. The strength and magnitude of the prompt penetration electric field were inferred from the magnetic field variations of the horizontal component of the magnetic field (ΔH) at Tirunelveli, a dip-equatorial station, using the ground-based magnetometers. The electron density distribution over the Indian ionospheric region was quantified using GPS-derived vertical total electron content (VTEC). Signatures of prompt penetration electric field were present for all the storms considered whose main phase was during the daytime. It is noted that as the strength of the penetration electric field increases, the latitudinal extent to which the electron density gets distributed also increases. The gradient in electron density extends even up to Shimla (a mid-latitude station) during a severe geomagnetic storm. The gradient was less for moderate geomagnetic storms. Since during the geomagnetic storm, a factor that controls electron density modulation is the neutral wind, its contribution is analyzed with the help of the thermospheric O/N2 ratio, measured by the global ultraviolet imager (GUVI) instrument, onboard NASA’s TIMED satellite. The observed increase in the O/N2 ratio does not correspond with the increase in the VTEC. We surmise that during the first day of the storm, the penetrating electric field is an essential factor that controls the electron density distribution in the low-latitude region. Later the plasma density distribution is controlled mainly by the thermospheric wind.