Ionospheric total electron content (TEC) variations prior and after to the great Gorkha Earthquake in Nepal (Mw = 7.8) on April 25, 2015, were analysed using measurements from widely distributed Global Positioning System (GPS) network. This study has been performed to understand the relationship between ionospheric TEC anomalies and earthquake occurrences. The analysis of vertical TEC (VTEC) time series from different GPS stations shows that the abnormal TEC variations appeared few days up to a few hours before the events. The results indicate that deviation in VTEC observed on the distant GPS station from the epicentre was found less relative to that of the stations near the epicentre, inferring that the variation in ionospheric VTEC nearly inversely relies upon the distance of GPS stations from the epicentre. Moreover, the pre-earthquake ionospheric anomalies were also observed in the geomagnetically conjugated region. In view of the solar-terrestrial environment, the pre-earthquake ionospheric anomalies could be associated with the Nepal earthquake. The VTEC anomaly was identified when it crosses the upper bound or lower bound. The outcomes additionally show that TEC variation was dominant in the vicinity of the earthquake epicentre. We also describe contrast in TEC throughout the globe using global ionospheric maps at regular 2-hour UT intervals, the day before, during and after the earthquake. In addition, we observed that areas heavily influenced by TEC were found to be transposed from eastern sectors to western sectors through the equatorial plane.

Researchers have studied the interplanetary magnetic field (IMF) and solar-wind (SW) parameters that influence the development of geomagnetic storms for more than a decade. This study utilised newly developed tools for investigating the association between solar and interplanetary plasma parameters along with geomagnetic (GM) indices during two different geomagnetic storms of varying intensity that occurred on 20 November 2003 (SYM-H = -490 nT) and 22 June 2015 (SYM-H = -139 nT). As the largest storm in Solar Cycle (SC)-23 and the second largest in SC-24, these events were deliberately chosen to represent extreme space weather activity. The study of these severe geomagnetic events provides a unique opportunity to better understand the coupling nature between the solar wind-magnetosphere-ionosphere system. Cross wavelet analysis (XWT) exposes high common power regions between the solar wind velocity (Vsw) and interplanetary magnetic field component (IMF-Bz), plasma pressure (Psw), plasma density (Nsw), Geomagnetic Auroral Electrojet (AE) index and Symmetrical Ring Current Index (SYM‐H). Another useful tool is wavelet transform coherence (WTC), which we have applied to measure how coherent the XWT is in time-frequency space. Thus, the local correlation between two continuous wavelet transforms (CWTs) can be conceived of as WTC. Moreover, we examined the relationship among the solar wind parameters during storm events using detrended cross-correlation analysis (DXA) with possible explanations. The study’s findings will demonstrate that the suggested methods are a simple, effective, and robust method for gaining deeper insight into the complex spatiotemporal characteristics of time series.