Class Solar Flare Research Articles

Electron acceleration and transport in the 2023-03-06 solar flare

We investigated in detail the M5.8 class solar flare that occurred on 2023-03-06. This flare was one of the first strong flares observed by the Siberian Radioheliograph in the microwave range and the Advanced Space-based Solar Observatory in the X-ray range. The flare consisted of two separate flaring events (a “thermal” and a “cooler” ones), and was associated with (and probably triggered by) a filament eruption. During the first part of the flare, the microwave emission was produced in an arcade of relatively short and low flaring loops. During the second part of the flare, the microwave emission was produced by energetic electrons trapped near the top of a large-scale flaring loop; the evolution of the trapped electrons was mostly affected by the Coulomb collisions. Using the available observations and the GX Simulator tool, we created a 3D model of the flare, and estimated the parameters of the energetic electrons in it.

Kink-and-Disconnection Failed Eruption in 3D

We present a case study of a failed eruption that accompanied an M1.5 GOES class solar flare. It was observed by STIX onboard Solar Orbiter, HXI onboard the Advanced Space-based Solar Observatory, AIA onboard Solar Dynamics Observatory, and WAVES onboard the STEREO-A. The important input is from stereoscopic hard X-ray (HXR) observations obtained by HXI and STIX, whose vantage points were separated by 31.5∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$31.5^{\\circ }$\\end{document}, allowing us to unfold the 3D geometry of the event. The eruption was a two-phase event. First, it started with the rope helical kink and then was slowed down, but with the structure still unstable, it erupted two minutes later due to ongoing reconnection in the interacting legs of the kinked structure. A Type III burst was observed in association with the eruption, indicating the acceleration of semirelativistic electrons into the heliosphere. During the second phase, a hot cloud was disconnected and confined in the overlying magnetic field, where the overlying loops connected two adjacent active regions. The estimated and corrected for real geometry velocities are in the range of 385 – 400 km s−1, whereas acceleration reached 4.78 – 6.33 km s−2. These extreme values are much more demanding from a perspective of conditions that are needed to stop the eruption. Images obtained simultaneously by HXI and STIX located in different vantage points showed that flare-related sources are not lying along a normal to the solar surface. The understanding of the eruption analyzed here has been highly enriched thanks to the stereoscopic information about HXR source locations.

Prediction of ionospheric TEC by LSTM and OKSM during M class solar flares occurred during the year 2023

Prediction of ionospheric TEC by LSTM and OKSM during M class solar flares occurred during the year 2023

Observations of Geomagnetic Crochet at High‐Latitudes Due To X1.5 Class Solar Flare on 3 July 2021

AbstractOn 3 July 2021, an X1.5 solar flare from the National Oceanic and Atmospheric Administration solar Active Region AR12838 (24°N, 88°W) occurred at 14:18 UT, peaked at 14:29 UT, and decayed at 14:34 UT. The study of this X1.5 solar flare is significant due to its unique geomagnetic crochet feature at high latitudes and its effective signature on Earth. The study examined X‐rays, the extreme ultraviolet spectrum, ionospheric equivalent current (IEC), and geomagnetic field components. The study reveals a sudden increase in IEC during the X1.5 flare episode, forming a zonal current region and producing a geomagnetic crochet signature in geomagnetic field components at high latitudes (50°–80°N) along the 11°–26°E longitude sector during the flare peak time. All three geomagnetic field components show different sensitivity to the solar flare effect (sfe), and the amplitude and phase of the geomagnetic crochet across latitudes (for a given longitude) are consistent with the variations in the IEC. The present study is the first to appraise geomagnetic crochets of low magnitude (8–40 nT) and short duration (10–15 min) at high latitudes, particularly in the polar cusp region, during the X‐class limb flare.

VLF Signal Variations Seen in the Bucharest Observatory Recordings .

his paper presents a new instrument setup at the Bucharest Observatory of the Astronomical Institute of the Romanian Academy, as well as preliminary results using this setup. It consists of records of VLF (very low frequency) perturbations using a superSID instrument. During March and December 2022 various mounts and settings tests have been performed. Starting October we obtained satisfactory data. We report on detecting the signature of moderate to intense solar flares (M and X–class). In this configuration, the C–class solar flares are less distinguishable from the background noise.

Ionospheric TEC prediction using FFNN during five different X Class solar flares of 2021 and 2022 and comparison with COKSM and IRI PLAS 2017

Abstract The Ionospheric Total Electron Content (TEC) measured in the ray path of the signals directly contributes to the Range Error (RE) of the satellite signals, which affects positioning and navigation. Employing the Co-Kriging-based Surrogate Model (COKSM) to predict TEC and RE correction has proven prolific. This research attempted to test and compare the prediction capability of COKSM with an Artificial Intelligence-based Feed Forward Neural Network model (FFNN) during five X-Class Solar Flares of 2021–22. Also, the results are validated by comparing them with the IRI PLAS 2017 model. TEC, solar, and geomagnetic parameters data for Hyderabad GPS station located at 17.31° N latitude and 78.55° E longitude were collected from IONOLAB & OMNIWEB servers. The COKSM uses six days of input data to predict the 7th day TEC, whereas prediction using the FFNN model is done using 45 days of data before the prediction date. The performance evaluation is done using RMSE, NRMSE, Correlation Coefficient, and sMAPE. The average RMSE for COKSM varied from 1.9 to 9.05, for FFNN it varied from 2.72 to 7.69, and for IRI PLAS 2017 it varied from 7.39 to 11.24. Likewise, evaluation done for three different models over five different X-class solar flare events showed that the COKSM performed well during the high-intensity solar flare conditions. On the other hand, the FFNN model performed well during high-resolution input data conditions. Also, it is notable that both models performed better than the IRI PLAS 2017 model and are suitable for navigational applications.

Low latitude ionospheric TEC response to the solar flares during the peak of solar cycle 24

We describe the newly discovered response of differential vertical total electron content (DVTEC) in the low-equatorial latitude ionosphere to the solar flares during the peak of solar cycle 24 i.e., the year 2014. GPS TEC data for the existing investigation has been acquired from the international GNSS services network station in Bangalore, India (geomagnetic latitude 4.58οN). For the year 2014, we inspected five X-class solar flares, forty-nine M-class solar flares, and three hundred ninety-six C-class solar flares in the current study. To ascertain the relationship between ΔDVTEC and the ΔX-ray and ΔEUV fluxes, the two main ionizing radiation fluxes during flare events are used. Additionally, to identify electron density change in the ionosphere due to solar flares, we used two well-known methodologies, the baseline method and the mean method. The baseline method provides a better correlation between ΔDVTEC and ΔX-ray for X-, M-, and C-class flares. For M- and C- class flares, both methods do not show any meaningful correlation. The Solar disc location effect shows an enhanced (0.573) correlation between ΔDVTEC and ΔX-ray*cos (CMD) for the X-class flares, whereas for M- and C-class flares, no significant change was observed, which indicates feeble or no CMD effect for lower class solar flares while it is opposite for X-class flares. Here we suggest that the high solar activity, and location of the observation station to the EIA trough region might be the possible reason for the observed results.

Formation and Eruption of Hot Channels during an M6.5 Class Solar Flare

We investigate the formation and eruption of hot channels associated with the M6.5 class flare (SOL 2015-06-22T18:23) that occurred in NOAA AR 12371 on 2015 June 22. Two flare precursors are observed before the flare’s main phase. Observations in 94 and 131 Å by SDO/AIA revealed the early morphology of the first hot channel as a group of hot loops, termed the seed hot channel. A few seed hot channels are formed above the polarity inversion line (PIL) and the formation is associated with the parallel motion of the footpoint brightenings along the PIL, which proceeds into the early stage of the flare main phase. During this process, seed hot channels build up and rise slowly, accelerating at the peak of the second precursor. They merge during the process of acceleration, forming a larger hot channel, which then forms an inverted-γ-shape kinking structure. Before the flare peak, the second kinking hot channel with negative crossing appears near the first kinking hot channel that erupted. The eruption of these two hot channels produces two peaks on the main flare's GOES light curve. The propagation of the footpoint brightenings along the PIL indicates that the first kinking hot channel may be formed due to zipper reconnection. The occurrence of merging between seed hot channels observed by AIA is supported by the extrapolated nonlinear force-free field models. The observed writhing motion of the first kinking hot channel may be driven by the Lorentz force.

Analysis of Ionospheric TEC Variations Due to X, M & C Class Solar Flares during the Years 2003 to 2018 and Comparison with IRI Models

Analysis of Ionospheric TEC Variations Due to X, M & C Class Solar Flares during the Years 2003 to 2018 and Comparison with IRI Models

The Mouse That Squeaked: A Small Flare from Proxima Cen Observed in the Millimeter, Optical, and Soft X-Ray with Chandra and ALMA

We present millimeter, optical, and soft X-ray observations of a stellar flare with an energy squarely in the regime of typical X1 solar flares. The flare was observed from Proxima Cen on 2019 May 6 as part of a larger multi-wavelength flare monitoring campaign and was captured by Chandra, the Las Cumbres Observatory Global Telescope, the Iréné du Pont Telescope at Las Campanas Observatory, and the Atacama Large Millimeter Array. Millimeter emission appears to be a common occurrence in small stellar flares that had gone undetected until recently, making it difficult to interpret these events within the current multi-wavelength picture of the flaring process. The May 6 event is the smallest stellar millimeter flare detected to date. We compare the relationship between the soft X-ray and millimeter emission to that observed in solar flares. The X-ray and optical flare energies of 1030.3 ± 0.2 and 1028.9 ± 0.1 erg, respectively, the coronal temperature of T = 11.0 ± 2.1 MK, and the emission measure of 9.5 ± 2.2 × 1049 cm−3 are consistent with M-X class solar flares. We find the soft X-ray and millimeter emission during quiescence are consistent with the Güdel–Benz relation, but not during the flare. The millimeter luminosity is >100× higher than that of an equivalent X1 solar flare and lasts only seconds instead of minutes as seen for solar flares.

One-Minute Quasi-Periodic Pulsations during an M-Class Solar Flare

We study the Quasi-Periodic Pulsations (QPPs) of an M4.4 class solar flare, which occurred in active region NOAA 11165 on 8 March 2011. With the Fast Fourier Transform (FFT) method, we decompose the flare light curve into fast- and slowly-varying components. The 100 s (0.01 Hz) is selected as the cutoff threshold between the fast- and slowly-varying components. One-minute QPPs are found around flare peak at soft X-ray (SXR) and Extreme Ultraviolet (EUV). Using the data from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO), the intermittent jets are detected and the interesting fact is that the jets also display one-minute period. The correlationship between the fast-varying components of SXR or EUV emissions and the jets suggests that the QPPs on light curves and periodic jets could come from the same origination, e.g., the periodic magnetic reconnection in this event.

A study of the characteristic properties of SEP events observed by SOHO ERNE during solar cycle 24

Properties and association of Solar Energetic Particle (SEP) events with their solar sources during the 24th solar cycle were examined. SEPs observed by SOHO ERNE were used. SEP properties include solar release time, peak proton flux and total fluence in different energy channels. Solar release times of SEP events were found out using Velocity Dispersion Analysis (VDA). It is observed that for low Coronal Mass Ejection (CME) velocities, the difference between SEP and CME release times is larger compared to that for high velocities. For SEPs associated with C class Solar Flares (SF), the average time difference in the release times is around 78 min, whereas in M and X class flares the time differences are 38 and 31 min respectively. Correlation analysis of proton peak flux with the CME speed and SF peak flux reveals that the coefficients decrease with increase in particle energy in both the cases. The correlation coefficient between total proton fluence of SEP and the peak flux of SF is moderate and decrease with increase in energy and tends to increase beyond 60 MeV. The correlation between total proton fluence and CME speed is high and it increases initially and then decrease with increase in energy. The analysis of H/He ratio of SEP events shows that the average value of the ratio extends from 16 to 837.

A statistical analysis of X- class solar flares and their association with the super active regions during solar cycles 23- 24

The A statistical distribution function of X-class flares and their association with super-active regions (SARs) during two recent solar cycles 23-24 have been analyzed. The obtained results show that, during solar cycle 23, 57.60 % of the total number of Xclass flares coincides with a set of X1.0 - X1.9 flares, 15.20 % to X2.0 - X2.9, 12.80 % to X3.0 - X4.9, 9.60 % to X5.0 - X9.9, and 4.80 % to ≥ X10 flares. During solar cycle 24, 61.20 % of the total number of X-class flares coincides with a set of X1.0 - X1.9 flares, 22.40 % to X2.0 - X2.9, 8.16 % to both the X3.0 - X4.9 flares, and X5.0 - X9.9 flares. None of the ≥ X10 flares. All X-class flares are found to be in a scattered manner in solar cycles 23 and 24. Among the cycles, solar cycle 24 has been observed relatively very weak cycle and the total number of X-class flares diminished in comparison to previous solar cycles. During solar cycle 23, 29.16% of the X1.0 - X1.9 flares, 36.84 % of the X2.0 - X2.9 flares, 43.75 % of the X3.0 - X4.9 flares, 83.33 % of both the X5.0 - X9.9 flares, and 100.00 % of the ≥ X10 flares were produced by SARs. While during solar cycle 24, 20.00 % of the X1.0 - X1.9 flares, 36.36 % of the X2.0 - X2.9 flares, 25.00 % of the X3.0 - X4.9 flares, 75.00 % of the X5.0 - X9.9 flares, and 0.00 % of the ≥ X10 flares were produced by SARs.

Simulating Properties of “Seasonal” Variability in Solar Activity and Space Weather Impacts

Solar short-term, quasi-annual variability within a decadal sunspot-cycle has recently been observed to strongly correlate with major class solar flares, resulting into quasi-periodic space weather “seasons.” In search for the origin of this quasi-periodic enhanced activity bursts, significant researches are going on. In this article we show, by employing a 3D thin-shell shallow-water type model, that magnetically modified Rossby waves can interact with spot-producing toroidal fields and create certain quasi-periodic spatio-temporal patterns, which plausibly cause a season of enhanced solar activity followed by a relatively quiet period. This is analogous to the Earth’s lower atmosphere, where Rossby waves and jet streams are produced and drive global terrestrial weather. Shallow-water models have been applied to study terrestrial Rossby waves, because their generation layer in the Earth’s lower atmospheric region has a much larger horizontal than vertical scale, one of the model-requirements. In the Sun, though Rossby waves can be generated at various locations, particularly favorable locations are the subadiabatic layers at/near the base of the convection zone where the horizontal scale of the fluid and disturbances in it can be much larger than the vertical scale. However, one important difference with respect to terrestrial waves is that solar Rossby waves are magnetically modified due to presence of strong magnetic fields in the Sun. We consider plausible magnetic field configurations at the base of the convection zone during different phases of the cycle and describe the properties of energetically active Rossby waves generated in our model. We also discuss their influence in causing short-term spatio-temporal variability in solar activity and how this variability could have space weather impacts. An example of a possible space weather impact on the Earth’s radiation belts are presented.

Solar flares and geomagnetic storms of September 2017: Their impacts on the TEC over 75°E longitude sector

• Solar flare effect on TEC at a specific longitude sector is studied. • A special case of co-occurrence of geomagnetic storm and solar flare is examined. • A delayed TEC response is observed during recovery phase of solar flare. This study investigates the ionospheric Total Electron Content (TEC) responses over 75°E longitude to the solar flares and geomagnetic storms of September 6–9, 2017. The results of this study provide the impacts of solely solar flares on the ionosphere and such impact when the effects of solar flares and geomagnetic storm are combined. On September 6, two X class solar flares, namely X2.2 at 0857 UT and X9.3 at 1153 UT, were recorded with quiet geomagnetic conditions. The EUV/X-ray intensity of X9.3 flare was significantly greater than that of X2.2 flare, and the recovery phase of both the flares was slower than their respective impulsive phase. The slower recovery rate in EUV/X-ray intensity is reflected as a delayed TEC response. A nearly 8% higher crest to trough TEC change on flare day than the pre-flare day suggests an enhanced level of the equatorial electrojet. The overall weak TEC response to X9.3 solar flare is attributed to solar zenith angle dependency and shifting of solar flare location from disk center to west limb. The solar flares on September 7–8 were co-occurred with geomagnetic storms and observed large increments in TEC are additionally induced by prompt penetration electric field and the enhanced level of thermospheric compositional changes. On September 9, an increase in TEC is observed during M class solar flares under effect of solar flares and disturbed dynamo electric field.

Possible Associations between Space Weather and the Incidence of Stroke

The aim of our study was to detect the possible association between daily numbers of ischemic strokes (ISs) and hemorrhagic strokes (HSs) and space weather events. The daily numbers of ISs, subarachnoid hemorrhages (SAHs), and intracerebral hemorrhages (ICHs) were obtained from Kaunas Stroke Register during the period of 1986 to 2010. We used time- and season-stratified multivariate Poisson regression. We analyzed data of 597 patients with SAH, 1147 patients with ICH, and 7482 patients with IS. Strong/severe geomagnetic storms (GSs) were associated with an increase in the risk of SAH (by 58%) and HS (by 30%). Only GSs occurring during 6:00–12:00 UT were associated with the risk of IS. Low geomagnetic activity (GMA) was associated with the risk of ICH, HS, and IS (Rate Ratios with 95% CI were 2.51 (1.50–4.21), 2.33 (1.50–3.61), and 1.36 (1.03–1.81), respectively). The days of ≥ X9 class solar flare (SF) were associated with a 39% higher risk of IS. The risk of HS occurrence was greater than two times higher on the day after the maximum of a strong/severe solar proton event (SPE). These results showed that GSs, very low GMA, and stronger SFs and SPEs may be associated with an increased risk of different subtypes of stroke.

Multi-wavelength analysis of CME-driven shock and Type II solar radio burst band-splitting

It is now well established that Coronal Mass Ejections (CMEs) may produce shocks in near Sun and interplanetary medium. A Type-II radio burst is characterized by shock and associated emission with very slow frequency drift rate (∼0.1 MHz/sec). A CME driven shock and their velocity, acceleration/deceleration signature can be observed by a Type-II solar radio burst which drifts with the shock speed and is split in bands of plasma radio emission. These emissions can be seen in radio spectrographs as split bands both in fundamental and harmonic frequencies close to a ratio of 1:2. In this paper, we present an analysis of a CME associated with a band splitting Type-II radio burst observed using multi-instruments in multi-wavelengths. We observed the CME event that occurred in 02 May 2013 (05:24 UT) and is associated with an M1.1 class solar flare from the active region NOAA 11731 located at N10W23 on the solar disk. We use the widely accepted Newkirk coronal density model to estimate the height in the solar atmosphere to compare our results. We conclude that the speed of CME is high enough to produce a Type-II solar radio burst. The analysis of this paper also involved an estimation of the coronal ambient magnetic field and its comparison with the empirical active region magnetic field model (Dulk and McLean in Sol. Phys. 57:279, 1978). This shows the good results. Observations provide sufficient evidence that the unusual patch signature in Type-II solar radio burst is due to the CME–CME interaction.

Statistical analysis of soft X-ray solar flares during solar cycles 22, 23, and 24

This paper presents a statistical analysis of soft X-ray flares during the period January 1986 to June 2017 covering the last three solar cycles (SCs) 22, 23, and 24. We have analyzed the distribution of flare number, the relationship between the occurrence rate of soft X-ray flares and solar activity, and the duration of different intensity class (B, C, M, and X) solar flares during the period of investigation. The total occurrence rates of M and X class flares are 10.33%, 6.77%, and 5.45% in SCs 22, 23, and 24, respectively, which indicates that SC 22 is an SC with frequent large flares. Meanwhile, the M and X class flares are mainly concentrated in solar maximum (71.13%) in SC 22. The correlation coefficients between the annual number of flares and solar F10.7 index, X-ray flux in 0.1–0.8 nm, and EUV flux in 0.1–50 nm in SC 24 (0.91, 0.88, and 0.96) are greater than that in SCs 23 (0.87, 0.85, and 0.86) and 22 (0.88 and 0.81). The median values of the duration of M and X class flares are 39.00 and 71.50 minutes in SC 22, 21.00 and 26.50 minutes in SC 23, and 19.00 and 24.00 minutes in SC 24. The duration of M and X class flares in SC 22 is obviously longer than that in SCs 23 and 24. In addition, the duration of flares increases with the increase of flare intensity.

FEATURES OF THE DEVELOPMENT OF A CIRCULAR SOLAR FLARE

We present the results of the analysis ofmorphology and evolution of the circular solar flare usingH-alpha images. H-alpha filtergrams were obtained withthe Meudon spectroheliograph. The active region NOAA9087 had a complex multipolar magnetic field configura-tion. New magnetic fluxes emerged during the evolution ofthis flare-productive active region. The high flare and surgeactivity was observed in the active region.According to Solar Geophysical Data (SGD) the3N/M6.4 class solar flare occurred on July 19, 2000 at06:37 UT, peaked at 07:23 UT and lasted 2.5 hours. Twobright kernels appeared near large positive-polarity sunspotat the beginning of the flare. In a few minutes bright kernelsoccurred in the center of the active region near polarity in-version line. Space solar observatory Yohkoh detected ahard X-ray (HXR) coronal source in the 13.9-22.7 keV and22.7-32.7 keV energy bands in this location.New kernels appeared in the southern and eastern partsof the active region at the boundaries of the chromosphericnetwork. They brightened sequentially clockwise, whichmay indicate a slipping reconnection. Magnetic reconnec-tion was observed in the main phase of the flare in the east-ern part of the active region. In the late flare phase arcadeof post-reconnection EUV loops connected the main flareribbon with the place of repeated reconnection. Additionalheating may be required for the explanation of the longflare decay phase.Flare ribbons of the circular shape were formed. Thecomplex magnetic configuration of the studied active re-gion and circular shape of the ribbons suggest that it had afan-spine magnetic topology with null points. Possibly,flare ribbons are the locations of intersections of the fanquasi-separatrix layer with the chromosphere. They ap-peared as a result of heating or particle beam moving alonga quasi-separatrix layer from a source in the corona.

Temporal and Periodic Variation of the MCMESI for the Last Two Solar Cycles; Comparison with the Number of Different Class X-ray Solar Flares

In this study we compared the temporal and periodic variations of the Maximum CME Speed Index (MCMESI) and the number of different class (C, M, and X) solar X-Ray flares for the last two solar cycles (Cycle 23 and 24). To obtain the correlation between the MCMESI and solar flare numbers the cross correlation analysis was applied to monthly data sets. Also to investigate the periodic behavior of all data sets the Multi Taper Method (MTM) and the Morlet wavelet analysis method were performed with daily data from 2009 to 2018. To evaluate our wavelet analysis Cross Wavelet Transform (XWT) and Wavelet Transform Coherence (WTC) methods were performed. Causal relationships between datasets were further examined by Convergence Cross Mapping (CCM) method. In results of our analysis we found followings; 1) The C class X-Ray flare numbers increased about 16 % during the solar cycle 24 compared to cycle 23, while all other data sets decreased; the MCMESI decreased about 16 % and the number of M and X class flares decreased about 32 %. 2) All the X-Ray solar flare classes show remarkable positive correlation with the MCMESI. While the correlation between the MCMESI and C class flares comes from the general solar cycle trend, it mainly results from the fluctuations in the data in case of the X class flares. 3) In general, all class flare numbers and the MCMESI show similar periodic behavior. 4) The 546 days periodicity detected in the MCMESI may not be of solar origin or at least the solar flares are not the source of this periodicity. 5) C and M Class solar flares have a stronger causative effect on the MCMESI compared to X class solar flares. However the only bidirectional causal relationship is obtained between the MCMESI and C class flare numbers.