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In 2023 April, a low-latitude aurora observed by the all-sky camera at Hanle, Ladakh, India (33°14’N geographic latitude), generated significant interest. This was the first such aurora recorded from the Indian region in the space era and occurred during a moderate solar storm. This study explores this low-latitude auroral sighting, which happened during the sheath-region passage of an interplanetary coronal mass ejection. We analyze in situ multispacecraft particle measurements and geomagnetic field observations from both ground-based and satellite-based magnetometers. The auroral observations at Hanle coincided with intense substorm activity. Our findings indicate that the aurora did not actually reach India; the equatorward boundary was beyond 50°N geographic latitude. Enhanced electron fluxes with energies below 100 eV were detected at 54°N geographic latitude at about 830 km altitude in the predawn sector (4–5 hr local time). In the midnight sector, the equatorward boundary is estimated to be around 52°N geographic latitude, based on Hanle observations and considering emission altitudes of 600–650 km due to low-energy electrons. Thus, the low-latitude red aurora observed from India resulted from the emissions at higher altitudes due to low-energy electron precipitation in the auroral oval and a slight equatorward expansion of the auroral oval. The low-energy electrons likely originated from the plasma sheet and were precipitated due to enhanced wave–particle interactions from strong magnetosphere compression during high solar wind pressure. This study is crucial in understanding low-latitude auroras in the modern space era.

Gradual solar proton events are thought to consist of solar components originating near the Sun and interplanetary components associated with interplanetary shocks, and the role of interplanetary shocks is considered to be crucial in supplying particles to regions that are not magnetically connected to the solar source region. We calculate the ratios of the peak intensities for the four energy channels (13–16, 20–25, 32–40, and 40–64 MeV) and compare the ratios observed by multiple spacecraft at different locations. We often find that the ratio of peak intensities observed at different locations in the same event remains almost constant as the energy varies. In other words, the ratio of peak intensities from the different energy channels remains almost constant as the position of the spacecraft changes. The phenomenon implies that in many gradual events, energetic particles observed at different locations are mainly composed of solar components that undergo perpendicular diffusion in both the vicinity of the Sun and the interplanetary space, and that perpendicular diffusion is the main factor enabling energetic particles to be observed in regions without magnetic connection to the solar source region.

Unusual explosive activity occasionally occurs from the Sun, releasing large amounts of solar energetic particles. Extreme solar particle ejection events in the past 11,000 yr have been detected by sharp increases of cosmogenic isotopes in annual tree rings and ice cores. However, quantitative estimation of the event magnitudes is not straightforward, as the cosmogenic isotopes are indirect records of solar particles. Similar solar particle ejection events may also accumulate records in surface materials of airless bodies such as the Moon and asteroids. Samples from the asteroid 25143 Itokawa have been irradiated by solar winds for tens to hundreds of years at some points in the last few million years. Here, we report implantation profiles of solar particle He from an Itokawa regolith grain that trace an extreme solar particle ejection event. The implantation profiles indicate that the fluences of suprathermal solar particles were 250–1300 times larger than that expected from the current normal solar activity. Since the degrees of excesses are inversely related to the solar wind irradiation periods, the high-energy particle fluence would have been derived from a single event. The event was approximately 40 times larger than the 2003 Halloween solar storms, which is one of the largest solar particle ejection events observed since the space-based measurement of solar activity began. The event magnitude is similar to the largest events inferred from the cosmogenic isotope records in terrestrial samples. Our result provides direct evidence of an extreme solar particle ejection event in the last few million years.

A new daily composite of the solar flare index (SFI) and the hemispherically‐resolved versions (hSFI) are presented for 1937 to 2024. The data set confirms that the northern hemisphere (NH) dominated solar flare activity during Solar Cycles 17 to 21, but that the southern hemisphere has dominated from Solar Cycle 22 to present. That said, the highest SFI value occurred in the NH during the recent superstorm of May 2024. In sunspot activity, the “Gnevyshev‐Ohl rule” shows that the sum of sunspot numbers during even‐numbered cycles is related to those of adjacent odd‐numbered cycles. A similar rule appears to apply to SFI. The “Gnevyshev gap” phenomenon where solar maximum activity sometimes has two peaks separated by up to 1–2 years of a gap is confirmed for SFI. Although our data set represents the longest continuous daily data set for solar flare activity to‐date, it is known that stronger solar flare events occurred before 1937. Therefore, a brief discussion of earlier solar flare events in the historical record is also provided for context. The statistics of the SFI and hSFI series are compared to other solar and geomagnetic activity indices, including the May and October 2024 solar storms. Statistical analysis of past geomagnetic storms confirms they are more frequent during active cycles and less frequent during solar minima. Strong geomagnetic storms are also more likely to occur during the positive phase of a 1.7 year's quasi‐biennial oscillation in solar activity. The likelihood of low‐magnetic latitude aurorae seems to have a 30 year periodicity component.

Multiple interplanetary coronal mass ejections (ICMEs) erupted from AR 13664 during 2024 May 8–13. On 2024 May 10, after the arrival of the ICME shock at 17:04 UT, a Forbush Decrease (FD) was seen in various Neutron Monitor (NM) stations located worldwide. This paper presents a comprehensive analysis of neutron data from 28 NM stations and gamma-ray data obtained from the NaI(Tl) detector at Maitri, Antarctica. The present paper reports for the first time about an ICME shock-sheath related enhancement of ∼3%–5% magnitude in the neutron flux at stations with geomagnetic rigidity between 4 and 7 GV, located at higher altitudes (≥1000 m). For these stations, the high-rigidity ends of the asymptotic trajectories are confined to the midnight to the postmidnight region. It appears that the increase may be associated with magnetospheric particle precipitation triggered by the passage of the ICME shock-sheath. The variation of FD amplitude with rigidity shows a decreasing trend in general, with a minimum amplitude at 5–7 GV, which we attribute to the location of field-aligned currents (FACs). The FD amplitude is found to have the effects of storm-time westward ring current, FACs, and magnetospheric dynamics, in addition to the ICME parameters. During the recovery phase of FD, enhancement is observed between 01:50 and 03:00 UT on 2024 May 11, which coincided with Ground Level Enhancement (GLE#74). The GLE#74 was coeval with the strong SYM-H index and the sudden recovery of the FD due to reduced interplanetary magnetic field, which might be responsible for the observed enhancement at high rigidity stations.

The extreme solar storm of 2024 May 10, during the 25th solar cycle, which recorded a symmetric H component index (Sym-H) reaching −500 nT, was the strongest since the 2003 Halloween storm. This event offered a unique opportunity for unprecedented multipoint observation of the complex interaction of interplanetary coronal mass ejections (ICMEs) from different vantage points. Utilizing NASA’s Wind, ACE, DSCOVR, THEMIS-C, STEREO-A, MMS, and ISRO’s recently launched Aditya-L1 spacecraft, we comprehensively investigated the spatiotemporal variations in interplanetary plasma and magnetic field parameters. Our study reveals large-scale quasi-steady magnetic reconnection within the interior of the ICME flux rope, possibly triggered by interactions between multiple ICMEs. A current sheet (CS) forms within the flux rope, enabling internal magnetic reconnection between concentric magnetic surfaces, which leads to a sharp reversal of the interplanetary magnetic field (IMF) By component, as observed at the L1 point. Concurrently, reconnection exhaust and enhanced electron and ion fluxes were detected with the CS, extending over 200 RE (1.3 million kilometers) along the geocentric solar ecliptic y-direction. This finding sheds new light on the role of internal reconnection in ICME evolution, highlighting its pivotal role in modifying the morphology of the ICME magnetic structure and exerting severe space weather effects on Earth.

Geomagnetic storms are disorders in Earth’s magnetic field triggered by solar activity. This research attempts to foretell the total electron content (TEC) using the Kriging and AI model in both low and mid-latitude stations during strong geomagnetic storms that happened on March 17, 2015 and February 3, 2022. This research paper focuses on predicting and analysing TEC anomalies in the ionosphere during the solar storm by using three models: ordinary kriging (OK), cokriging (CoK) and recurrent neural network (RNN). The predicted TEC values by the models are justified with the TIEGCM and KMPCA models. Parameters like RMSE, CC, MAE, and MAPE were applied to assess the execution of predictive models and to quantify the accuracy of predictions. The average RMSE for TEC predicted in the low-latitude region ranges from 4.90 to 5.41, 5.85 to 6.26 and 8.50 to 9.90 for the OK, CoK, and RNN models, respectively. Likewise, the average RMSE for TEC predicted in the mid-latitude region ranges from 1.81 to 4.04, 1.91 to 4.24 and 2.77 to 5.38 for the OK, CoK, and RNN models, respectively. The performance evaluation parameters show that the OK performs better than the CoK and RNN models.

— The aim of the paper is to assess the energy parameters of physical processes starting from the solar storm of April 21, 2023, and ending with the perturbations of the Earth’s lithosphere on April 23–24, 2023. The energy of processes in all subsystems of the Sun–interplanetary medium–magnetosphere–ionosphere–atmosphere–lithosphere system is analyzed. A comparative analysis of this storm with an extreme storm is performed. The storm of April 23–24, 2023, was unique due to the shift of the auroral zone to the midlatitudes to 50°. The international auroral brightness scale is improved. The auroral energy scale is proposed.

Modern civilization relies on a complex, globally interconnected industrial agriculture system to produce food. Its unprecedented yields hinge on external inputs like machinery, fertilizers, and pesticides, rendering it vulnerable to disruptions in production and international trade. Such a disruption could be caused by large‐scale damage to the electrical grid. Solar storms, nuclear detonations in the upper atmosphere, pandemics, or cyber‐attacks, could cause this severe damage to electrical infrastructure. To assess the impact of such a global catastrophic infrastructure loss on major food crops (corn, rice, soybean, wheat), we employ a generalized linear model. The predictions show a crop‐specific yield reduction between 15% and 37% in phase 1, the year after the catastrophe, assuming rationed use of fertilizers, pesticides, and fuel stocks. In phase 2, when all stocks are depleted, yields decrease by 35%–48%. Soybean is less affected in phase 1, while all crops experience strong declines in phase 2. Europe, North and South America, and parts of India, China, and Indonesia face major yield reductions, potentially up to 75%, while most African countries are less affected. These findings underscore the necessity for preparation by highlighting the vulnerability of the food system. Modern farming, dependent on machinery, fertilizer and pesticides, is at risk from electrical grid disruptions due to various catastrophes. Yields may drop 15%–37% in the first year and 35%–48% after industrial inputs run out, varying by crop. Europe, the Americas, and parts of Asia can see up to 75% yield reductions. Preparation is crucial.

The Near-Earth space environment is impacted by various radiation sources like galactic cosmic rays, solar storms, geomagnetic storms, etc. In the present paper, we have estimated the impact of space radiation observed during the last four cycles. We have observed that during solar cycle 24, there were fewer solar radiation storms than during its three preceding solar cycles. In terms of solar radiation storm strength, solar cycle 22 recorded a maximum intensity of S4 (severe radiation storm) of ~ 43000 pfu. In comparison, the maximum intensity of solar cycle 24 was ~ 6530 pfu (S3 type). We have concluded that the intensity of an X-class flare did not predict the intensity of the ensuing geomagnetic activity. The flares with less intensity in X-rays, e.g. M-class and C-class flares, can give rise to stronger radiation storms. Using the NOAA scales, we have compared the data of intense radiation storms with geomagnetic storms of higher intensity. This analysis has revealed that there were only 11 days during solar cycles 23 and 24 where the maximum solar radiation storm (solar particle event) coincided with a period of severe geomagnetic storming. On comparison of monthly neutron count (cosmic ray intensity) relative to the average of the last 20 years, we also deduced that the neutron count was 7.12% greater than usual during the most recent solar low, which was nearly as high as the last solar cycle lowest (8.20%). We have observed the lower probability rate of Solar Particle Events during the 3 or so years cantered on solar minimum, and the probability does not necessarily peak within a few years of solar maximum. The intensity of relativistic electrons observed by GOES in geostationary orbit was relatively low during periods of low geomagnetic activity and low solar wind speed, and the outer belt 2 MeV electrons flux appears to be highly associated with the Dst index.