Studying the influence of geomagnetic storms on parameters of the ionospheric F2 layer during solar activity cycle 24

Solar cycles have an asymmetrical shape with a fast rise and a slow decline, which varies from cycle to cycle. This makes it difficult to study the solar cycle phase dependence of the occurrence of intense solar-terrestrial events such as intense geomagnetic storms. In the previous works, differences in the rise and fall time lengths of each solar cycle were not fully considered. We normalized the asymmetric shape of each solar cycle using the rise and fall time lengths and showed the solar cycle phase dependence of occurrence of the intense geomagnetic storms selected using the Dst index for solar cycles 19−24 and using the aa index for solar cycles 12−24. The previous works noted that the occurrence of geomagnetic disturbances shows double peaks before and after solar maximum. Our results showed that the occurrence of the intense geomagnetic storms selected using the Dst and aa indices does not always show clear double peaks and increased more in the earlier half of the fall time than in the other time periods. The Dst and aa indices have been used to select geomagnetic storms in the previous studies. We pointed out that the solar cycle phase dependence of occurrence of the geomagnetic storms selected using the aa index is slightly different from those selected using the Dst index. We showed the geomagnetic storm on 4 August 1972 as an extreme case, which showed difference between Dst and aa. We also showed that intense geomagnetic storms associated with eruptive flares from the active sunspot groups occurred around the solar minima of cycles 17, 19, 20, and 21.Graphical

We examine the solar cycle distribution of major geomagnetic storms (Dst ≤ − 100 nT), including intense storms at the level of −200 nT < Dst ≤ −100 nT, great storms at −300 nT< Dst ≤ −200 nT, and super storms at Dst ≤ −300 nT, which occurred during the period of 1957-2006, based on Dst indices and smoothed monthly sunspot numbers. Statistics show that the majority (82%) of the geomagnetic storms at the level of Dst ≤ −100 nT that occurred in the study period were intense geomagnetic storms, with 12.4% ranked as great storms and 5.6% as super storms. It is interesting to note that about 27% of the geomagnetic storms that occurred at all three intensity levels appeared in the ascending phase of a solar cycle, and about 73% in the descending one. Statistics also show that 76.9% of the intense storms, 79.6% of the great storms and 90.9% of the super storms occurred during the two years before a solar cycle reached its peak, or in the three years after it. The correlation between the size of a solar cycle and the percentage of major storms that occurred, during the period from two years prior to maximum to three years after it, is investigated. Finally, the properties of the multi-peak distribution for major geomagnetic storms in each solar cycle is investigated.

The geoeffectiveness of interplanetary coronal mass ejections (ICMEs) is an important issue in space weather research and forecasting. Based on the ICME catalog that we recently established and the Dst indices from the World Data Center, we study and compare the geoeffectiveness of ICMEs of different in situ signatures and different solar phases from 1995 to 2014. According to different in situ signatures, all ICMEs are divided into three types: isolated ICMEs (I‐ICMEs), multiple ICMEs (M‐ICMEs), and shock‐embedded ICMEs (S‐ICMEs), resulting in a total of 363 group events. The main findings of this work are as follows: (1) Fifty‐eight percent of ICMEs caused geomagnetic storms with Dstmin≤−30 nT. Further, large fraction (87%) of intense geomagnetic storms are caused by ICME groups and their sheath regions. (2) Numbers of ICME groups and the probabilities of ICME groups in causing geomagnetic storms varied in pace with the solar cycle. Meanwhile, the ICME groups and the probabilities of them in causing geomagnetic storms in Solar Cycle 24 are much lower than those in Solar Cycle 23. (3) The maximum value of the intensity of the magnetic field (B), south component of the magnetic field (Bs), and dawn‐dusk electric field vBs are well correlated with the intensity of the magnetic storms. (4) Shock‐embedded ICMEs have a high probability in causing geomagnetic storms, especially intense geomagnetic storms. (5) The compression of shock on the south component of magnetic field is an important factor to enhance the geoeffectiveness of S‐ICMEs structures.

The interplanetary causes of intense geomagnetic storms and their solar dependence occurring during solar cycle 23 (1996–2006) are identified. During this solar cycle, all intense (Dst ≤ −100 nT) geomagnetic storms are found to occur when the interplanetary magnetic field was southwardly directed (in GSM coordinates) for long durations of time. This implies that the most likely cause of the geomagnetic storms was magnetic reconnection between the southward IMF and magnetopause fields. Out of 90 storm events, none of them occurred during purely northward IMF, purely intense IMFByfields or during purely high speed streams. We have found that the most important interplanetary structures leading to intense southwardBz(and intense magnetic storms) are magnetic clouds which drove fast shocks (sMC) causing 24% of the storms, sheath fields (Sh) also causing 24% of the storms, combined sheath and MC fields (Sh+MC) causing 16% of the storms, and corotating interaction regions (CIRs), causing 13% of the storms. These four interplanetary structures are responsible for three quarters of the intense magnetic storms studied. The other interplanetary structures causing geomagnetic storms were: magnetic clouds that did not drive a shock (nsMC), non magnetic clouds ICMEs, complex structures resulting from the interaction of ICMEs, and structures resulting from the interaction of shocks, heliospheric current sheets and high speed stream Alfvén waves. During the rising phase of the solar cycle, sMC and sheaths are the dominant structure driving intense storms. At solar maximum, sheath fields, followed by Sh+MCs and then by sMC were responsible for most of the storms. During the declining phase, sMC, Sh and CIR fields are the main interplanetary structures leading to intense storms. We have also observed that around 70% of the storms follow the interplanetary criteria ofEy≥ 5 mV/m for at least 3 h. Around 90% of the storms used in the study followed a less stringent set of criteria:Ey≥ 3 mV/m for at least 3 h. Finally, we obtain the approximate rate of intense magnetic storms per solar cycle phases: minimum/rising phase 3 storms.year−1, maximum phase 8.5 storms.year−1, and declining/minimum phases 6.5 storms.year−1.

A study of the occurrence of the first intense Geomagnetic storm (G4) to hit the Earth since the start of the Solar Cycle 25 is carried out. This study analyzed the Geomagnetic Storm that occurred between the 28th of October and the 7th of November 2021. The values of the Disturbance storm time (Dst) index of the storm reach -115 nT (G4) which occurred on the 4th of November at 1300UT. The storm is the first intense magnetic storm that occurred in the solar cycle 25. It is also a multiple-step storm with moderate two-step storm occurrence which occurred on the 5th and 6th of November at 1500UT and 0600UT respectively towards the recovery phase after the intense storm. The interplanetary magnetic field (IMF) Bz (nT) during these storm events decreases. Our analysis shows that the rise in solar wind speed, temperature and the enhancement of pressure plays a significant role in the occurrence of the first intense Geomagnetic storm of Solar Cycle 25.

The present investigation is dedicated to the evaluation of GPS performance under disturbed geomagnetic conditions at the equatorial region. When GPS signals encounter the ionospheric irregularities of different size developed during high geomagnetic or solar activity, they undergo rapid changes in their phase and amplitude, known as scintillations. We have studied the occurrence characteristics of scintillation events during geomagnetic storms of different intensity at the crest of equatorial anomaly station Bhopal (23.2N, 77.6E). To accomplish this study we have used two data sets: Disturbed Storm Time (Dst) index and Amplitude Scintillation (S4) index. The geomagnetic storm activity is characterized by the Dst index and the evaluation of GPS performance during disturbed geomagnetic condition is realized through S4 index. We have selected thirty one geomagnetic storms that occurred during the year 2004 and 2005. We then classified these geomagnetic storms and scintillation events into weak, moderate and intense and weak, moderate and strong according to Dst index and S4 index respectively. During all the storm events we observed a good number of scintillation events. We then performed the correlation analysis between the Dst index and S4 index, to find out the impact of storm intensity on the occurrence of scintillation events.

We have investigated the solar wind drivers of magnetic storms during the rising phase of solar cycle 23 from January 1996 to December 1999. We used observations of coronal mass ejections (CMEs) by the Large Angle and Spectrometric Coronagraph instrument on SOHO and in situ solar wind observations by Wind, IMP 8, and ACE spacecraft. The storms were determined from both the Dst and Kp indices, and the study was limited to storms with Dst ≤ −50 nT or Kp ≥ 5. We show examples of different behavior of Dst and Kp indices during magnetic storms caused by different types of solar wind drivers. Furthermore, we have investigated cross‐correlation between peak Dst and Kp values of storms organized according to the associated solar wind driver. It makes a difference whether a sheath region or the following ejecta causes the storm. We found that almost all intense and stronger magnetic storms (Dst ≤ −100 nT, or Kp ≥ 7−) were associated with shocks and CMEs, but for moderate storms, driver statistics were different in different phases of the solar cycle. We found different behavior of the Kp and Dst indices during different types of solar wind drivers. Intense and short‐time disturbances, like postshock streams and sheath regions, generated more Kp storms, and ejecta generated more Dst storms. Thus one should be careful when comparing studies based on any single activity index.

The ionosphere is significantly impacted by disturbed and unfavorable geomagnetic conditions.Geomagnetic disturbances cause changes in the ionosphere, which is the most prominent effects of space weather on the near-earth environment.In October 2011, March 2012, and July 2012, there were three intense geomagnetic storms (Dst index < 100 nT).Over 24 solar cycles, we examined how they affected the ionosphere at low, mid, and high latitude stations in the northern hemisphere.We examined changes in the critical frequency (foF2) of the ionosphere's F2region.During the storms.In these case studies, we investigated the behavior of the ionospheric foF2 delay during each of these geomagnetic storms.We obtained very persuasive results in three cases.An analysis of the previously reported results shows that strong geomagnetic storms primarily negatively impact the ionospheric foF2 at low, mid, and high latitudes in the northern hemisphere.

Coronal mass ejections: a driver of severe space weather

The earth's magnetosphere is an intricate input-output system, where the inputs are the solar wind parameters and the output measure are the geomagnetic. The disturbance storm time (DST) index is one such quantity measure for the intensity of disturbance in the geomagnetic field due to the magnetic storm. The geomagnetic activities have catastrophic effects on several communication networks and harmful for biological livings. Therefore, it is significant to develop a model for the prediction of disturbance in the geomagnetic field. This paper presents linear as well as nonlinear parametric techniques to model the complex magnetosphere dynamics. Neural network (NN)-based modeling techniques, such as feed-forward NN (FFNN), NN integrated with nonlinear autoregression with exogenous (NARX) inputs, adaptive neuro-fuzzy inference system (ANFIS), and recurrent NN are developed for the prediction of the magnetic storm. Global search algorithms, such as particle swarm optimization and genetic algorithm, also train the developed FFNNs. All the models are trained on 15 years' real-time series data of solar wind parameters and DST index on a frequency of 1 h. The accuracy of the predicted DST index for multiple intensity levels of the magnetic storm using all developed linear and nonlinear modeling techniques is presented, compared, and analyzed thoroughly. The performance of NN integrated with NARX inputs and ANFIS is higher than rest of methods developed in the paper. Both techniques have the capability to predict mild, moderate, and intense magnetic storm with high degree of accuracy. The comparative analysis with state of the art shows the enhanced accuracy and robustness of developed models in this paper.

In this work, the impact of different geomagnetic storm events on the plasma-sphere layer (ionosphere layer) over the northern and southern hemisphere regions was investigated during solar cycle 23. To grasp the influence of geomagnetic storms on the behavior and variation of the critical frequency parameter of the F2 ionospheric layer (foF2), five geomagnetic storms (classified as great, severe, and strong), with Disturbance storm time (Dst) values &lt;-100 nT were chosen. Four stations located in different mid-latitude regions in northern and southern hemispheres were designated, the northern stations are: Millstone Hill (42.6° N, 288.50° W) and Rome (41.90° N, 12.50° E) and the southern stations are: Port Stanley (-51.60° S, 302.10° W) and Grahamstown (-33.30° S, 26.50° E). The findings of this study showed that during events of 16 July 2000 and 24 August 2005, the negative storms cause a noticeable reduction in the values of the foF2 parameter at the northern hemisphere stations compared to those at the southern hemisphere. These outcomes are consistent with the results of the examining the variation of D(foF2) and the electron density depletion during the tested event times at all stations except in Rome, where minor enhancements in foF2 value were observed during the August 24 2005 storm. During equinox storm events occurring on March 31 and November 6 2001, a noticeable negative impact of storms was observed across all stations. However, at Millstone Hill and Port Stanley stations, the results showed a slight positive storm impact during the October 21, 2001event.

The Dst (Disturbance storm time) index is a measurement of earth geomagnetic activity and is widely used to characterize the geomagnetic storm. It is calculated on the basis of the average value of the horizontal component of the earth’s magnetic field at four observatories, namely, Hermanus (33.3° south, 80.3° in magnetic dipole latitude and longitude), Kakioka (26.0° north, 206.0°), Honolulu (21.0° north, 266.4°), and San Juan (29.9° north, 3.2°) and is expressed in nano-Teslas. The strength of the low-latitude surface magnetic field is inversely proportional to the energy content of the ring current around earth caused by solar protons and electrons, which increases during geomagnetic storms. Thus a negative Dst index value indicates that the earth’s magnetic field is weakened which is specifically the case during solar storms. Predicting Dst index is a difficult task due to its structural complexity involving a variety of underlying plasma mechanism. For characterizing and forecasting this complex time series, a formal model must be established to identify the specific pattern of the series. Persistent demand for a fool proof model of Geomagnetic Dst index prompted us to investigate the Dst Time Series mechanism with a very recent technique called Visibility Algorithm and it is observed that the Dst time series follows the same model that of a Stochastic Fractional Brownian motion having long range correlation.

We conducted a comprehensive investigation into the relationship between Forbush decreases (FDs), Geomagnetic storms (GS), and Coronal mass ejections (CMEs) during Solar cycles (SC) 23 and 24. GS characterized by the Dst index, do not consistently occur alongside FDs, and conversely. FDs are not always accompanied by GS. Our study analyzed the interdependencies among interplanetary parameters, including FDs, the Dst index, solar wind speed, and the Interplanetary magnetic field (IMF). FDs associated with halo CMEs exhibited a significantly higher correlation compared to those linked with non-halo CME events. Furthermore, halo CMEs play a critical role in triggering larger-amplitude FDs and intense geomagnetic storms, whereas non-halo CMEs tend to result in smaller FD amplitudes. We found that 28.3% were associated with halo CMEs, while the remaining 71.7% were linked to non-halo CMEs. The results indicate that the distribution of FDs and geomagnetic storms varies markedly between the maximum and minimum phases of solar activity.

Geomagnetically Induced Currents (GICs) flowing along electrically conductive infrastructure, such as power transmission lines, are produced by a naturally induced geoelectric field during geomagnetic disturbances, such as magnetic storms. GICs can cause widespread blackouts across power grids, resulting in the loss of electric power. Although GIC intensity is greater in high latitudes, recent studies highlight the importance of considering GIC risks for countries located in the low and middle latitudes, including the Mediterranean region. GIC index is a proxy of the geoelectric field calculated entirely from geomagnetic field variations. Following a recent study where we investigated the GIC index levels for the Mediterranean (i.e., Greece, Italy, France, Spain, Algeria, and Turkey) for the most intense magnetic storms of solar cycle 24 (2008&amp;#8211;2019), here we expand the analysis to encompass solar cycle 25. From the beginning of solar cycle 25 six major magnetic storms occurred with Dst index &amp;#8804; -100 nT. The three most intense magnetic storms (-163 nT &lt; Dst &lt; -212 nT) occurred in March, April and November 2023. We focus on those to compare with previous results showing that GIC index increases are well correlated with Storm Sudden Commencements (SSCs) and shed more light upon the expected GIC activity levels in the Mediterranean region during extreme events.

The intense Geomagnetic Storms (GMSs) with Dst < −100 nT have been investigated for the period from Jan 1996 to Dec 2006. Seven GMSs of doublet and four of triplet nature are observed. Firstly, each GMS has been studied separately as if they are associated with independent Coronal Mass Ejections (CMEs). Secondly, for each doublet and triplet, the accumulated effect on GMS has been investigated and correlated with Dst index so as to understand the geoeffectiveness of Successive Intense GMSs. Majority of the successive intense GMSs have occurred during maximum phase of Solar cycle. During the occurrence of overlapping successive storms Dst falls abruptly. For non-overlapping successive storms, the Dst value falls gradually to minimum, showing a trend of recovery before the geosphere is hit by another storm. It is observed that the combined effect on GMSs is due to the Solar Wind (SW) being complex, having a very high value of SW velocity (Vsw) continuously for a very long period of 2 to 6 days. Further, Bz falls to a much lower value and B rises to a pretty high value for accumulated effect than for isolated GMS. When the GMSs are considered as separate entity, the correlation coefficient of Interplanetary Magnetic Field (IMF) parameters B and Bz and further, their products Vsw.B and Vsw.Bz correlated with Dst index are found to be −0.65, 0.72, −0.66 and 0.77 respectively; whereas, the coefficients are much better with the respective values of −0.7, 0.87, −0.78 and 0.90, for the accumulated effect of GMSs. Thus, it is preferable to investigate the accumulated effect of CMEs causing successive GMSs as compared to their isolated effects.