Longitudinal variability of occurrence of ionospheric irregularities over the American, African and Indian regions during geomagnetic storms

This study presents the longitudinal variabilities of occurrence of ionospheric irregularities over the equatorial/low-latitude region of America, Africa and Indian sectors. Five major geomagnetic storms of the equinoctial months of the year 2012-2013 were analyzed for this study. Total Electron Content (TEC) data obtained from Global Navigation Satellite Systems (GNSS) over American, African and Indian longitudinal sectors were used to derive, the rate of change of TEC index (ROTIave), the ionospheric irregularities proxy. Longitudinal variability of occurrence of irregularities were discussed with respect to the local time when the maximum negative of SYM-H index occurs and polarity of IMF Bz in the dusk hours. Almost all of the storms under investigation inhibited the occurrence of irregularities in Indian sector. Out of five storms, two and three storm periods revealed inhibition in the generation of irregularities over the American and African sectors, respectively. Most of the generation of ionospheric irregularities observed in this study were related to post-midnight local time occurrence of the maximum negative excursion of SYM-H index. There were also cases where irregularities are observed when the minimum value of SYM-H occurred in the pre-midnight and daytime period. It appears that the local time at which minimum SYM-H occur is not a sufficient condition to explain the effect of storms on generation/inhibition of ionospheric irregularities. Significant longitudinal variability in the generation of irregularities were also observed over wide longitudinal ranges (South America, Africa and India) during 09 March 2012 and 17 March 2013 storm events. Difference in longitudinal variation of storm-time electric field were a suggested reason. (C) 2019 COSPAR. Published by Elsevier Ltd. All rights reserved.