Ionospheric Response to Anomalous Geomagnetic Storm of 27 October 2021–05 November 2021

This study presents the first results on the ionospheric response and occurrence of ionospheric irregularities to the anomalous geomagnetic storm which occurred during period of 27 October 2021–05 November 2021 that was the first strong anomalous storm occurred in the current solar cycle with symmetric horizontal component (SYM-H) peak value of − 118 nT. Multi-site GPS observations from middle latitude of European longitudinal, equatorial region of American and Asian sector were used to analyze variations of total electron content (TEC) and the occurrence of the ionospheric irregularities during the storm period. The storm caused composite consequences on the terrestrial ionosphere. The remarkable positive ionospheric storm with deviation in TEC (ΔTEC) \(\approx\)(120–200) %  was occurred at equatorial station over American within longitudinal belt of \({\left(65-74\right)}^{^\circ }\)W during the beginning of recovery phase of the storm. In addition, appreciable vertical total electron content enhancement of  ΔTEC \(\approx\)(40–60) % was also noticed during recovery phase over European middle latitude with in longitudinal belt of \({\left(2-20\right)}^{^\circ }\) E. Regarding, occurrence of ionospheric irregularity the present study concluded that, the generation of ionospheric irregularity was completely suppressed during initial, major and recovery phase of the storm over both equatorial regions of American and Indian longitudinal sector. However, there was a moderate occurrence of ionospheric irregularity over both sectors during 27–31 October 2021, which could be attributed to the effect of 28 October solar flare and less intensity of southward-directed Bz component of the interplanetary magnetic field (IMFBz) during this periods. Moreover, the local time at which the maximum excursion of SYM-H may matter for the suppression of irregularities during the anomalous strong storm of 4 November 2021. In future, it may need further study, using additional observations and numerical modeling which may  shed more light on the response of anomalous geomagnetic storm of 4 November 2021. This study is presenting the first result of ionospheric response and the effects of anomalous geomagnetic storm of the current solar cycle on the occurrence of irregularities over low latitude region of South American and Asian sector.