Effect of geomagnetic storm intensity on the occurrence rate of large-scale ionospheric irregularities across various latitudes

Abstract

In the present study, we have investigated the effect of geomagnetic storms of varying intensity [moderate (−100 nT &lt; disturbance storm time index (Dst) &lt; -70 nT), intense (-150nT &lt; Dst &lt; -100 nT), severe (-150nT &lt; Dst &lt; -250nT), and super (Dst &lt; -250nT)] recorded in the increasing phase of the 25th solar cycle between January 2021 and February 2025 on the occurrence of the large-scale ionospheric irregularities across low latitude to sub-auroral regions [low latitude, IISC (130N, 77.570E; dip latitude: 4.90N); beyond EIA station, Varanasi (25.310N, 82.970E; dip latitude: 16.20N); mid-latitude, POL2 (42.680N, 74.690E; dip latitude: 34.50N); sub auroral, NOVM (550N, 82.900E; dip latitude: 46.20N)] using rate of change of Total electron content (TEC) index (ROTI). At low latitudes, the generation of irregularities was observed when the Dst minimum occurs at local post-midnight hours, irrespective of storm intensity, due to the upward F-layer drift under the influence of the eastward prompt penetration electric field (PPEF). Over mid-latitudes, the irregularities were suppressed during the main phase, which could be associated with the effect of the westward disturbance dynamo electric field (DDEF) induced by the change in the thermospheric O/N<inf>2</inf>ratio. Irregularity generations are more frequent over high latitudes during the main and recovery phases of storms due to the formation of polar patches related to particle precipitation. From the overall analysis, the ROTI occurrence rate shows an increasing pattern with increasing storm intensity levels over IISC, but decreases during highly disturbed geomagnetic conditions (superstorms). Over Varanasi and POL2, the storm intensity does not exhibit significant variation in the ROTI occurrence rate. Contrastingly, the ROTI occurrence rate increases with increasing storm intensity over NOVM. © 2025 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.