Study of the low and mid-latitude ionospheric response to the geomagnetic storm of 20th December 2015

The ionospheric response over the low and mid-latitudes along the 78∘±3∘\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$78^{\circ}\pm 3^{\circ}$\end{document}E longitude sector is studied for the 20th December 2015 geomagnetic storm. The global positioning system (GPS) derived total electron content (TEC) over mid & low-latitude stations and also an ionosonde observation of the F2 layer critical frequency over a mid-latitude station are analyzed. On the day of storm (20th December) the interplanetary magnetic field turned southward around 0330 UT and reached to its minimum value around −20 nT. SYM-H index started to decline at the same time and attained to its minimum value of about −180 nT at around 2330 UT after a very long main-phase duration (∼20 hours). During the storm’s main phase, a large TEC variation is observed for both the locations which have been attributed to the prompt penetration electric field (PPEF). The uniqueness of the observed TEC variation lies in the fact that while over the mid-latitude the TEC returned to its quiet time variations after the recovery phase, the enhancement in TEC over low-latitude has been observed even after two days (anomalous increase on 22nd December) of the storm which indicates the absence of disturb dynamo electric field (DDEF) for low-latitude over 78°E longitude. The thermospheric O/N2 data obtained both from, observations as well as CTIPe model simulation are in good agreement with the observed TEC variation except for the 22nd December over the mid-latitude location. This anomalous behavior on 22nd December over low-latitude could be due to some local dynamics or the transport of plasma by the background seasonal and storm time meridional winds over the studied region.