This paper investigates the effects of geomagnetic storms of 25-27 September 2011, 16- 18 March 2013, and 6-8 September 2015 over five mid latitudes stations (Dourbes, Fairford, Moscow, Rome, and Roquetes) and performs a cross correlation analysis of ionospheric and solar parameters during these storms. We observed the highest fluctuations in ionospheric variables during the main phase of storms. In addition, there is strong evidence of pre-storm phenomenon occurring at least a few hours and more than 24 hours prior to the main phase of the geomagnetic storms. We found that the TEC and foF2 parameters have strong dependence with latitudes for the events with Sudden Storm Commencement(SSC) in mid latitude region. Relatively low TEC and foF2 can be observed in Moscow which is at the highest latitude among the five stations because of a decrease in the n(O)/n(N2) ratio through out the storm event. However, for the event with gradual storm commencement, there is no evidence of such dependence. The good correlation of Symmetric-H and Auroral Electrojet Indices with ionospheric parameters indicates that the coupling mechanism between magnetosphere and ionosphere produces intense electric field disturbances in the middle low latitudes.

In this paper, we present the variations of IMF-Bz, Solar wind Parameters (Vsw, Nsw, and Psw), and Geomagnetic Indices (AE and SYM-H), and the variation of Vertical Total Electron Content (VTEC) using simultaneous VTEC data from 12 GPS-TEC stations over the Indian, Australian, Brazilian and South African regions. We describe contrast in Total Electron Content (TEC) throughout the globe using global ionospheric maps at regular 2-hour interval of UT during the three intense geomagnetic storms. Moreover, we observed that heavily TEC influenced areas were found to be transposing through equatorial plane starting from eastern sectors to the western sectors. Indian Ocean, Atlantic Ocean and South Pacific Ocean sectors were affected flowingly. Global Ionospheric Maps evince that Indian and Brazilian sectors were affected heavily explaining the TID and Equatorial Anomaly as seen on those areas. The equatorial and low-latitude regions have been mainly affected by the geomagnetic storms. All these results suggested that the acute disruption of global winds (surging towards the equator from higher latitudes) and electric fields commenced from magnetosphere-ionosphere interaction cause the severe modification in the equatorial, low-latitude region. We checked the cross correlation during the period of high solar and geomagnetic activities; the correlation gradually increased with the near by stations by latitudes in most of the cases which was another intriguing result. the storms were affected globally which is why we believe that variation of TEC over various stations of the globe could turn out to be very helpful in predicting solar wind coupling with magnetosphere-ionospehere.

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.

In this paper, we study the variations of the solar-wind parameters (solar wind velocity, plasma density, and IMF-Bz component) and the Earth’s disturbance storm-time index (Dst), in relation to cosmic ray flux measurements from 8 neutron monitor stations distributed over Canada, Russia, Finland, and Greenland, during 3 intense geomagnetic storms occurred during the 24th solar cycle (March 16-18, 2015, June 21-23, 2015, and September 7-9, 2017). The wavelet analysis of the Forbush decrease seen in the cosmic ray intensity reveals the clear evolution of the classical two-step process, and with a peak period of approximately 2.1 h. The correlation-delay analyses show a very strong correlation (~0.9) between the relative count rate changes cosmic ray intensity and the indices of solar wind velocity and Dst. We obtain similar time-delay responses to the solar wind velocity for all the cases (~4 hours), but large discrepancies are seen for the Dst index between the storms. We therefore recommend not using the Dst index for predicting Forbush decreases. Finally, we employ the resulting delay-times to parameterize the Forbush decreases in terms of solar wind, and we obtain a predictive model with R2 parameter of an approximate value of 0.8. Moreover, we observe a possible dependence on solar wind proton density which modulates the magnitude of Forbush decreases under similar solar wind velocity conditions. Our results verify the suitability of using solar wind parameters to predict Forbush decreases in the cosmic ray flux.

Invasion of solar wind particles inside earth’s magnetosphere induces the distortion of geomagnetic setting of earth. This geomagnetic disturbances be a consequence of energy discharge of solar plasma in different forms such as visible aurora in the polar region, joule heating, ring current energy; momentary fluctuation of earth’s magnetic field (SYM-H), intensification of magnetospheric current system; Field Aligned Current (FAC) and Polar Cap Potential (PCV) and many other phenomena. However, this event can cause some serious calamites, so having better understanding of it and able to be prepared in any severity of such situations is always in good accord. For this, we studied total of nine different intense geomagnetic storms from solar cycle 22, 23 and 24. Events included from solar cycle 22 and 24 were triggered by Stream Interaction Region (SIR) as well as SIR associated with complex structures which were a resultant of interactions between SIRs and Interplanetary Coronal Mass Ejections (ICMEs) respectively. The rest of the selected events which are all from solar cycle 23 were also the responses of solar structures like SIR and ICME along with sheath and magnetic cloud. To understand the impact of the solar wind particles on near earth space, magnetospheric and interplanetary parameters such as IMF-Bz, SYM-H, PCV and FAC are graphed along with total solar input energy and other energy sinks like auroral precipitation, joule heating, and ring current energy. To substantiate result, cross‐correlation technique is used along with pie chart and bar graphing which has helped in statistical investigation.