Moderate Storm Research Articles

A comparative Analytical Investigation of Different Geomagnetic Storms During Solar Cycles 23 and 24

Abstract In this work, the geomagnetic storms that occurred during solar cycles 23 and 24 were classified based on the value of the Disturbance Storm Time index (Dst), which was considered an indicator of the strength of geomagnetic conditions. The special criterion of Dst >-50 nT was adopted in the classification process of the geomagnetic storms based on the minimum daily value of the Dst-index. The number of geomagnetic storms that occurred during the study period was counted according to the adopted criteria, including moderate storms with (Dst >-50 nT), strong storms with (Dst >-100 nT), severe storms with (Dst >-200 nT), and great storms with (Dst >-350 nT). The statistical results showed that the total number of geomagnetic storms identified during solar cycle 23 was 571 storms, while during solar cycle 24, the number of storms decreased to 282 storms. Depending on the minimum value of Dst-index, the geomagnetic storms identified during Cycle 23 were classified into: 446 moderate, 101 strong, 19 severe, and 5 great storms. During Cycle 24, it was classified into: 247 moderate, 34 strong, and 1 severe storm. Also, the results of the study indicated that no storm of either a severe or great type was recorded during the solar cycle 24, given that this cycle witnessed low solar activity. This indicates that solar activity associated with sunspot number (SSN) corresponds to the rate of occurrence and strength of geomagnetic storms of all categories.

Statistical Analysis of the Correlation between Geomagnetic Storm Intensity and Solar Wind Parameters from 1996 to 2023

The occurrence of space weather events, notably geomagnetic storms driven by various solar wind structures, can significantly alter Earth’s electromagnetic environment. In this study, we examined the interplanetary origins and statistical distribution of 384 geomagnetic storms (Dstmin ≤ −50 nT) that occurred from September 1996 to December 2023. We statistically analyzed the correlations between storm intensity and solar wind parameters (SWPs) across different subsets. The results indicate that (1) the solar activity level, indicated by the sunspot number (SSN), and the number of geomagnetic storms during the first four years of the 25th solar cycle were intermediate, compared to the first four years of the 23rd and 24th solar cycles. Specifically, ICME-related structures caused 80% of the strong storms (Dstmin ≤ −100 nT) and 34% of the moderate storms (−100 nT < Dstmin ≤ −50 nT) from 2020 to 2023. (2) The storm intensity correlated with the peak and/or time-integral values of the southward interplanetary magnetic field (IMF Bs), the dawn–dusk electric field (Ey), the Akasofu’s function (ε), and dynamic pressure (Psw) to varying extents. Strong storms exhibited higher correlation levels than moderate ones and ICME-related storms showed larger correlation levels compared to those driven by other sources. (3) Compared with the storms from 1996-09 to 2000-08, the storms that occurred from 2020 to 2023 had lower correlations with the peak values of the IMF Bs and Ey but higher correlations with the peak value of ε and the time-integral values of the IMF Bs, Ey, Psw, and ε. (4) Among the 174 events that featured continuous southward IMF during the storm’s main phase, the duration of southward IMF during about 66.7% of moderate storms and 51.5% of strong storms were less than 13 h. Continuous southward IMF resulted in more direct and efficient energy coupling, enhancing the correlation between the peak values of SWPs and storm intensity but weakening the relationships with the time-integral values of SWPs. Notably, when the southward IMF persisted for a longer duration (e.g., ∆t > 13 h), the continuous energy input further enhanced correlations with both peak and integral values of SWPs, leading to stronger overall correlations with storm intensity. This analysis sheds light on the intricate relationships between geomagnetic storms and their solar wind drivers, emphasizing the significant influence of ICME-related structures and the duration of southward IMF on storm intensity.

Magnetic Storm‐Time Red Aurora as Seen From Hokkaido, Japan on 1 December 2023 Associated With High‐Density Solar Wind

AbstractWe report a citizen science‐motivated study on the cause of an unusually bright red aurora as witnessed from Hokkaido, Japan during a magnetic storm on 1 December 2023. The auroral brightness of 5 kR is unusual for the Dst index peak of only −107 nT. In spite of the moderate storm amplitude, the extremely high solar wind density of >50/cc and dynamic pressure of >25 nPa caused the aurora oval extension to 53 magnetic latitudes (L = 2.8). We discuss that the drift loss of the ring current particles across the small‐size magnetopause is important, and Hokkaido was at the right position to see the direct effect of the large particle injection of the storm‐time substorm.

The effect of continuous geomagnetic storms on enhancements of ultrarelativistic electrons in the Earth’s outer radiation belt

The effect of continuous geomagnetic storms on enhancements of ultrarelativistic electrons in the Earth’s outer radiation belt

Effects of major storms over a spit-tidal flat interaction system (Punta Rasa-Samborombón, Argentina)

Sandy coastal areas are very dynamic systems in which morphological changes occur over different time scales from hours to decades. However, it has been widely reported that major storms are the main responsible of the most significant changes in short to medium time scales. Major storms have been defined using a variety of environmental variables, but they are normally associated with high values of wave height, duration, return period and direction.Here, we aim to characterize types of major storms and to categorize associated morphological impacts over a complex coastal system. The study site, known as Punta Rasa, is located in the Samborombón bay in the outer part of the Río de La Plata estuary (Argentina) and corresponds to a zone of interaction between a large sandy spit and a backwash tidal flat system. Methods combine statistics of wave climate time-series, analysis of wave energy using nearshore numerical modelling (SWAN) and comparison of pre- and post-storm morphological changes by means of shoreline change detection and satellite images derived indexes (CoastSat Toolkit and NDWI index respectively).Results allowed to characterize four types of major storms impacting the study area: High-Energy Storms (HES), defined by an average storm wave below the 1 % exceedance (>2.6 m), Long-Lived Storms (LLS) represented by an exceedance of the 1 % of Du (>60 h), Storm Groups (SG) in which storm return period is <6 days and Northeastern moderate storms (NMS) defined by their eastern, onshore oriented direction. Under HES and NMS storms erosional areas are dominant over depositional, causing shoreline retreat, a growth of the end-spit and the increase on sand deposition on the back-barrier areas. Under LLS and SG storms, the morphological impact varies alongshore, with multiple erosional hotspots found along the shoreline accompanied by a general flattens of the end-spit system.

Distribution and recovery phase of geomagnetic storms during solar cycles 23 and 24

Abstract Coronal mass ejections (CMEs) and Stream Interaction Regions (SIRs) are the main drivers of intense geomagnetic storms. We study the distribution of geomagnetic storms associated with different drivers during solar cycles 23 and 24 (1996-2019). Although the annual occurrence rate of geomagnetic storms in both cycles tracks the sunspot cycle, the second peak in storm activity lags the second sunspot peak. SIRs contribute significantly to the second peak in storm numbers in both cycles, particularly for moderate to stronger-than-moderate storms. We note semiannual peaks in storm numbers much closer to equinoxes for moderate storms, and slightly shifted from equinoxes for intense and stronger-than-intense storms. We note a significant fraction of multiple-peak storms in both cycles due to isolated ICMEs/SIRs, while single-peak storms from multiple interacting drivers, suggesting a complex relationship between storm steps and their drivers. Our study focuses on investigating the recovery phases of geomagnetic storms and examining their dependencies on various storm parameters. Multiple-peak storms in both cycles have recovery phase duration strongly influenced by slow and fast decay phases with no correlation with the main phase buildup rate and Dst peak. However, the recovery phase in single-peak storms for both cycles depends to some extent on the main phase buildup rate and Dst peak, in addition to slow and fast decay phases. Future research should explore recovery phases of single and multiple-peak storms incorporating in-situ solar wind observations for a deeper understanding of storm evolution and decay processes.

Investigation of the Physical Mechanisms of the Formation and Evolution of Equatorial Plasma Bubbles During a Moderate Storm on 17 September 2021

AbstractWe investigate in detail the occurrence and evolution of ionospheric equatorial plasma bubbles (EPBs) during a moderate storm on 17 September 2021, using Global‐scale Observations of the Limb and Disk (GOLD) observations and Whole Atmosphere Community Climate Model‐eXtended (WACCM‐X) simulations. GOLD observations show that there were no EPBs on 16 September before the storm but EPBs occurred after the storm commencement on 17 September. The EPBs extended to ∼30° magnetic latitude. A diagnostic analysis of WACCM‐X simulations reveals that the rapid enhancement of prompt penetration electric fields (PPEFs) after the sudden storm commencement is the main reason that triggered the occurrence of the EPBs. Further quantitative analysis shows that vertical plasma drifts, which are enhanced by the PPEF, played a dominant role in strengthening the Rayleigh‐Taylor instability, leading to the occurrence of the EPBs and the large latitudinal extension of the EPBs to ∼30° magnetic latitude during the night of 17 September.

The Distribution and Evolution of Storm Time Pc3‐5 ULF Wave Power Based on Satellite and Ground Observations

AbstractThe geomagnetic storm is an intense geomagnetic activity, and one important research aspect is the storm time ultralow frequency (ULF) waves, which can resonate with injected particles and impact particle dynamics in the inner magnetosphere. This study focuses on analyzing ULF wave power during geomagnetic storms on the ground, in the magnetosphere and in the solar wind. During the Van Allen Probe era from year 2012–2019, we identified 94 geomagnetic storm events with 25 as strong storms and 69 as moderate storms based on the variation of SYM‐H index. The analysis revealed that for both satellite and ground‐based measurements during storms with different intensity, the ULF wave power was dramatically enhanced in the main phase. In addition, the ULF wave power of strong storms was significantly stronger than that of moderate storms within the magnetosphere and on the ground. While the finding is opposite in the solar wind. Furthermore, the ULF wave power of strong storms exhibited a higher intensity at higher L shell values and in some cases, it can last up to ∼2 days. Besides, the ULF wave power displayed a linear correlation with the absolute value of the SYM‐H index during the storm main phase while it exhibited an exponential association with the absolute value of the SYM‐H index during the recovery phase. This comprehensive analysis offers valuable insights into the evolution of ULF waves in the inner magnetosphere during geomagnetic storm events, shedding light on plasma waves and wave‐particle interactions in this region.

Comparison of wave overtopping estimation models for urban beaches. Towards an early warning system on the Basque coast

This study compares the performance of different wave overtopping estimation models at urban beaches. The models selected for comparison are the Mase et al. (2013) and EurOtop parametric models and the XBeach process-based model in surfbeat and non-hydrostatic mode. Seven energetic storms are selected between 2015 and 2022 with offshore significant wave height ranging between 3 m and 8 m and peak period between 12 s and 20 s to perform the model comparison. The information required to run and validate the models (beach slope, shoreface shape, absence/presence of overtopping) was collected for each storm from coastal videometry. To account for the uncertainties derived from the incident waves randomness and the bathymetry shape when using the process-based model, a series of simulations with random seed boundary conditions were run over two different realistic profile shapes for each storm. The present study is a pilot study on the beach of Zarautz; however, it can be extended to other beaches of the Basque coast. Results indicate that while Mase et al. (2013) and EurOtop tend to reasonably predict the absence or presence of overtopping events, they tend to underestimate the hazard level at the beach of Zarautz. Additionally, the beach underwater profile shape can affect the process-based model performance at intermediate intensity storms and to a lesser extend during moderate storms. Finally, the hazard level at the beach of Zarautz varies significantly alongshore due to the configuration of the seawall, highlighting the need for local adaptation measures. Considering that there is no model that systematically performs better than others, it might be reasonable to use model assemble techniques to draw conclusions from a probabilistic perspective.

Comparison of the first four weak and moderate geomagnetic storms of the 2022 using artificial neural networks

Solar wind parameters (SWP) and geomagnetic indices act as defining factors between the Earth's magnetosphere-ionosphere and the Sun. Models between SWP and indices should be examined seriously to better interpret the dynamics of geomagnetic storms (GSs). This work touches on the first two weak (25 January and 22 February) and moderate (14 January and 13 March) GSs of the 2022 year with an artificial neural network (ANN) model. The models are based on SWP (E, v, P, T, N, Bz) and geomagnetic indices (Dst, Kp, ap). The ANN employs SWP as inputs and indices as outputs, predicting the indices via SWP. The Scaled Conjugate Gradient (trainscg) algorithm is used for the back-propagation iteration. Four different geomagnetic storms, which are weak; Dst = -35 nT (25 January), Dst = –32 nT (22 February), and moderate storms; Dst = -91 (14 January) nT, Dst = -85 nT (13 March), are considered as case studies. The results of the estimations have acceptable accuracy. While the model is trained with mean square error (MSE) loss function, the accuracy of the model is evaluated by both mean square error (MSE) and mean error (ME).

The Variation of Ionospheric O+ and H+ Outflow on Storm Timescales

AbstractGeomagnetic storms are primarily driven by stream interaction regions (SIRs) and coronal mass ejections (CMEs). Since SIR and CME storms have different solar wind and magnetic field characteristics, the magnetospheric response may vary accordingly. Using FAST/TEAMS data, we investigate the variation of ionospheric O+ and H+ outflow as a function of geomagnetic storm phase during SIR and CME magnetic storms. The effects of storm size and solar EUV flux, including solar cycle and seasonal effects, on storm time ionospheric outflow, are also investigated. The results show that for both CME and SIR storms, the O+ and H+ fluences peak during the main phase, and then declines in the recovery phase. However, for CME storms, there is also significant increase during the initial phase. Because the outflow starts during the initial phase in CME storms, there is time for the O+ to reach the plasma sheet before the start of the main phase. Since plasma is convected into the ring current from the plasma sheet during the main phase, this may explain why more O+ is observed in the ring current during CME storms than during SIR storms. We also find that outflow fluence is higher for intense storms than moderate storms and is higher during solar maximum than solar minimum.

Morphological Performance of Vegetated and Non-Vegetated Coastal Dunes with Rocky and Geotextile Tube Cores under Storm Conditions

Coastal dune restoration projects are increasingly seen as a means of protecting the coast against storms, especially with the use of natural (plants), artificial (geotextile tube cores) and hybrid (plants and geotextile tube) elements. As geotextile tube cores have been found to negatively affect dune and beach natural morphodynamics, rocky cores are thus seen as a potential alternative. We carried out laboratory experiments to compare the performance of dunes with rocky cores, geotextile cores, and both types when coupled with planted vegetation. We investigated these elements in the context of scaled mild, moderate, and intense storm conditions. The results showed that dunes with either type of core lost more sand than dunes without cores. The addition of plants generally reduced the erosion across the various options, but most strongly for rocky cores under mild and moderate storm conditions. We also found that dunes with a high density of plants were best for intense conditions. Overall, the use of rocky dune cores, when coupled with plants, is the most suitable and sustainable alternative option in hybrid engineering projects.

Comparison of Empirical and Theoretical Models of the Thermospheric Density Enhancement During the 3–4 February 2022 Geomagnetic Storm

AbstractOn 3 February 2022, at 18:13 UTC, SpaceX launched and a short time later deployed 49 Starlink satellites at an orbit altitude between 210 and 320 km. The satellites were meant to be further raised to 550 km. However, the deployment took place during the main phase of a moderate geomagnetic storm, and another moderate storm occurred on the next day. The resulting increase in atmospheric drag led to 38 out of the 49 satellites reentering the atmosphere in the following days. In this work, we use both observations and simulations to perform a detailed investigation of the thermospheric conditions during this storm. Observations at higher altitudes, by Swarm‐A (∼438 km, 09/21 Local Time [LT]) and the Gravity Recovery and Climate Experiment Follow‐On (∼505 km, 06/18 LT) missions show that during the main phase of the storms the neutral mass density increased by 110% and 120%, respectively. The storm‐time enhancement extended to middle and low latitudes and was stronger in the northern hemisphere. To further investigate the thermospheric variations, we used six empirical and first‐principle numerical models. We found the models captured the upper and lower thermosphere changes, however, their simulated density enhancements differ by up to 70%. Further, the models showed that at the low orbital altitudes of the Starlink satellites (i.e., 200–300 km) the global averaged storm‐time density enhancement reached up to ∼35%–60%. Although such storm effects are far from the largest, they seem to be responsible for the reentry of the 38 satellites.

A New Method for Predicting Non‐Recurrent Geomagnetic Storms

AbstractPredicting non‐recurrent geomagnetic storms caused by Coronal Mass Ejection (CME) is important and necessary for space weather forecasting. Previous studies have shown that it is feasible to predict non‐recurrent geomagnetic storms by reconstructing precursors from cosmic ray intensity (CRI) in the frequency domain. However, the difficulty lies in predicting the minor storms, the moderate storms, and the storms accompanying ground level enhancement (GLE). This study proposes a new method that includes the spectral whitening method and CEEMDAN‐CWT for predicting non‐recurrent geomagnetic storms. The method was applied to 229 CME‐driven events, including 166 events with Kp ≥ 5 and 63 events with Kp &lt; 5, during the solar cycles 23 and 24. This study analyzed 166 geomagnetic storm events and found that 129 of them were accurately predicted, resulting in a recall rate of 77.7%. Additionally, the study found that as the Kp index increased, the amplitude of the precursor detected by this method also increased, while the time interval between the onset of CME and the maximum amplitude of the precursor decreased.

Performance analysis of four PPP service software under different intensity geomagnetic storms

Currently, many precise point positioning (PPP) services provide through software or online websites for GNSS positioning studies and applications. Various PPP service software has different positioning performances due to their respective algorithms and versions. In addition, the positioning accuracy and reliability of PPP services lack systematic evaluation, especially in the case of geomagnetic storms. This study presents the PPP performance analysis of the common GNSS PPP software as CSRS-PPP (https://www.geod.nrcan.gc.ca/), APPS (https://apps.gdgps.net/), Net_Diff (http://center.shao.ac.cn/shao_gnss_ac/), and GAMP (https://www.ngs.noaa.gov/gps-toolbox/GAMP) under different geomagnetic storm intensities. The PPP experiments involve data from 916, 885, and 676 GPS stations data on 17 March 2015 (severe), 26 August 2018 (strong), and 15 January 2022 (moderate), respectively. The results showed that the positioning performance of the four PPP software is different in the magnetic storm environment. We found that during geomagnetic storms, the CSRS-PPP software has the highest positioning accuracy and reliability, while the APPS software shows the worst positioning performance. The performance of Net_Diff and GAMP during geomagnetic storms are comparable but are better than that of APPS. Statistical results indicate that the average values of 3D RMS of CSRS-PPP, APPS, Net_Diff, and GAMP under severe storm are 0.14 m, 0.60 m, 0.40 m, and 0.33 m, under strong storm are 0.18 m, 0.65 m, 0.27 m, and 0.33 m, and under moderate storm are 0.25 m, 1.66 m, 0.26 m, and 0.34 m, respectively. The main reason why the CSRS-PPP has the best positioning accuracy under different intensity storms is that it uses the ambiguity-fixed PPP solution, while the other three software use float solution.

Geomagnetic storm-induced perturbations over Indian equatorial ionosphere

This study reveals the geomagnetic storm-induced ionospheric perturbations observed over the near-equatorial Indian stations - Cochin and Changanacherry in 2021. The 205 MHz VHF radar at Cochin University of Science and Technology (CUSAT) detected the storm-induced E- and F- region echoes during the moderate (28th February − 6th March 2021) and weak (19th − 25th March 2021) storm events. The fast-fluctuating northward interplanetary magnetic field (IMF BZ) and inhibition of the equatorial ionization anomaly (EIA) observed on 1st March indicate the suppression of daytime eastward electric field by the westward electric field associated with the counter electrojet (CEJ). Concurrent equatorward shift in the EIA crest and minor positive storm enhancement in the vertical total electron content were observed. The CEJ could have helped in the accumulation of photo-generated plasma at the near-equatorial region by pushing the daytime F-layer downward. During the moderate storm phase, post-sunset E-region echoes were detected during 1st − 3rd March, attributed to the disturbance dynamo electric field (DDEF). Nevertheless, during the main phase of the weak storm, a poleward shifting of the EIA crest occurred on 20th March, indicating the presence of a prompt penetration electric field (PPEF), which enhanced the upwardE×Bdrift. A major positive ionospheric storm enhancement that lasted for 7 h occurred on 20th March due to the DDEF. Bottom-type F-region echoes were observed over Cochin during the recovery phase of the weak storm. This work highlights the observation of equatorward and poleward shifting of the EIA using a 205 MHz radar.

Koudougou (Burkina Faso, Africa), GPS-TEC Response to Recurrent Geomagnetic Storms during Solar Cycle 24 Declining Phase

In this paper, we presented the effect of moderate geomagnetic storms on the TEC variation at the Koudougou station (Geo Lat 12° 15′N; Geo Long: -2° 20′E) in Burkina Faso (Africa) during the descending phase of solar cycle 24. For this purpose, four moderate geomagnetic storms without storm sudden commencement (SSC) or sudden impulse (SI) that occurred on May 13, 2015 (Dst: -76 nT), June 08, 2015 (Dst: -73 nT), September 11, 2015 (Dst: -80 nT), and May 08-09, 2016 (Dst: -88nT), were considered. These moderate storms were found to be associated with transients induced by fast solar winds. At the Koudougou station, TEC variation shows a positive response to the different moderate geomagnetic storms studied, with increases of order of 2-21 TECU around 1300-1500 UT except for September 11, 2015, TEC variation which shows sometimes negative responses at a few hours (mainly at night). TEC increases observed are a function of geomagnetic parameter (magnitude and polarity) variation. Storm-induced electric field and neutral winds are the main drivers of TEC changes observed during the selected geomagnetic storms. In addition, it was found that the TEC peak on storm day behaves differently compared to the days before and after the storm depending on whether Dst is positive or negative before southward inversion. Indeed, a TEC small peak relative to the days before and after the storm is observed when Dst is negative before southward inversion, and a larger peak occurs in the opposite case. The reasons for these differences are not investigated in this paper.

Extreme storm events shift DOC export from transport-limited to source-limited in a typical flash flood catchment

Dissolved organic carbon (DOC) export regimes are co-determined by DOC source supply and hydrological transport. Field studies have indicated that catchment DOC export is a single regime (source- or transport-limited, or chemostatic). If a shift between DOC export regimes exists, as has been rarely reported before based on low-frequency observation, then conceptual paradigms regarding lateral carbon export need to be revised. DOC dynamics of a flash flood catchment were investigated in this study with high-frequency observations during flood seasons. A three-phase DOC concentration and discharge relationship (n = 713) was observed, i.e., slow increase, rapid increase, and flat phases that occurred during the inter-storm, moderate storm, and extreme storm periods, respectively. Further hysteresis analysis showed that the anticlockwise pattern observed during moderate storms shifted to a clockwise pattern during extreme storms. These transitions suggest that extreme storm events shifted DOC export from transport-limited to source-limited. Failure to consider such a shift can cause significant overestimation of DOC yield in flash flood catchments where DOC yield is largely driven by storms.

Analysis of storm surge events along the Norwegian coast

Observed extreme sea levels are caused by a combination of extreme astronomical tide and extreme storm surge, or by an extreme value in one of these variables and a moderate value in the other. We analyzed measurements from the Norwegian tide gauge network together with storm track data to assess cases of extreme sea level and storm surges. At most stations the highest storm surges only coincided with moderate astronomical tides and vice versa. Simultaneously the extreme storm surges often only coincided with moderate storm intensities. This opens for the possibility of flooding events, where extreme tides and storm surges co-occur, and which could exceed existing sea level records and national building standards. This study also raises the possibility to assess extreme sea level return values as a three-variable system, treating separately the astronomical tide, storm location and storm intensity, instead of the one- or two-variable approach currently used.

Study of Ionosphere Irregularities over the Iberian Peninsula during Two Moderate Geomagnetic Storms Using GNSS and Ionosonde Observations

Studies on the irregularities of the ionosphere during disturbed geomagnetic conditions are fundamental to understanding the complex dynamics taking place in the upper atmosphere. In this work, different data sources are used to study the ionosphere effects of two moderate geomagnetic storms, 26–27 February 2014 and 17–18 September 2021, over the Iberian Peninsula. Data are obtained from digital ionosondes in Spain, Italy and Greece; the Global Navigation Satellite System (GNSS) derived Total Electron Content (TEC) and Rate Of TEC Index (ROTI) from several receiver stations in Spain, Portugal and Morocco; and the UPC Quarter-of-an-hour time resolution Rapid GIM (UQRG), vertical TEC global ionosphere maps (GIMs), produced at 15 min intervals by the Universitat Politecnica de Catalunya (UPC, Spain). This analysis showed that, during the two moderate storms, spread-F and high values of ROTI, indicating the presence of irregularities, are found in a very localized area (Southern Iberian Peninsula and northwest Africa) and local times (night-time). However, no irregularities are found eastwards and northwards of the location indicated. We propose some possible explanations for these observations for both the storms, one of them related to the position of the Equatorial Ionosphere Anomaly (EIA) and the other one attributed to the Perkins’ instabilities.