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.

Giant pulsations belonging to the Pc5 frequency band were conceived by Rolf (1931). Such pulsations are influenced by magnetospheric processes produced by the solar wind. The purpose of this study is to investigate the Pc5 ULF waves and their relationship to solar parameters and geomagnetic indices, respectively, utilizing data from ground-based magnetometers and data provided by Operating Mission as Nodes on the Internet (OMNI). Magnetic observatories over Earth’s surface reported intense long-period ULF activity on 19 28 February 2014 and 22-23 June 2015. We discovered a highly significant correlation between global Pc5 ULF waves and other interplanetary parameters, as well as a clear peak-to-peak correspondence during storms. We performed continuous wavelet transform (CWT) on the Pc5 integrated power (Ipow) and discovered that the majority of the intense Pc5 spectra are localized within the 64-256 minute Fourier period band. Our results suggest that geomagnetic fluctuations observed at low latitudes do not originate locally but rather are a reflection of global geomagnetic field variations with primary sources in the magnetosphere and high latitude ionosphere, which is consistent with the study of Gupta (1976). We discovered only nominal effects of IMF Bz on Pc5 pulsations, despite its southern counterpart being widely believed to be the principal driver of geomagnetic storms. Additionally, we discovered a moderate effect of solar wind pressure on Pc5 pulsations. A cross-correlation study, on the other hand, indicated a strong and positive association between Pc5 pulsations and solar wind velocity without lag for both geomagnetic activities.

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.