Abstract
The present paper investigates the ionospheric response to the severe geomagnetic storms on St. Patrick’s Day (17 March 2015) and the strong geomagnetic storm (7 October 2015) over the low latitude Saudi Arab region. The GNSS-TEC observations over low latitude RASH station ($28^{\circ}29'\mbox{N}$, $34^{\circ}46'\mbox{E}$) in Saudi Arab confirms that the spatial-temporal alterations over the region not only solely depends on the low latitude electrodynamics but also relies on the high and mid electrodynamics. During the St. Patrick’s Day storm, minimum Dst has reached to −223 nT with AE enhancement up to 2215 nT and VTEC values shown maximum enhancement of 250.16% with comparison to average quiet days VTEC, which is known as the positive effect of geomagnetic storm. The positive response of the VTEC has been observed over the region due to the coexistence of Prompt penetration electric field (PPEF) with the prevailed long duration Disturbance dynamo electric field (DDEF). The F2 layer gets uplifted with the enhanced fountain effect through the equatorial E × B drift, which is observed with the enhancement in hmF2 and enhancement in O/N2 ratio. Concerning the strong geomagnetic storm event on 7 October 2015, minimum Dst has reached to −124 nT with AE enhancement up to 1209.30 nT and VTEC values shown minimum decrement of $-72.14\%$ as compared to the average quiet days VTEC, which is known as the negative effect of geomagnetic storm. The negative response of VTEC has been observed during the main phase of the storm, possibly due to the consequences of suppressed equatorial ionization anomaly (EIA) over the observatory station. The negative response has been described by the downward movement of F2 layer with apparent reduction in hmF2 and depletion in O/N2 ratio over the low latitude region. The results during the storm period also demonstrate that the intensity of amplitude scintillation is enhanced over the low latitude region whose magnitude depends on the severity of the geomagnetic storm.
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