This paper presents a statistical analysis of Soft X-ray (SXR) flares during the period January 1976 to December 2007 covering solar cycles (SCs) 21, 22, and 23. We have analysed north-south (N-S) and east-west (E-W) asymmetry of SXR at low (less than equal to 40 degree), high (greater than equal to 50 degree) and total latitudes and center meridian distances (CMDs) respectively. We have also presented the N-S and E-W asymmetry of different intensity classes (B, C, M, and X) during the period of investigation. A slight southern and eastern excess is found after analysis during SC 21, 22, and 23. We found that the annual N-S and E-W hemispheric asymmetry at low latitudes and CMDs is the same as total latitudes and CMDs respectively. E-W asymmetry is different at low and high CMDs. Our statistical result shows that N-S asymmetry is statistically more significant than E-W asymmetry. Total SXR flare activity during SC 23 is high compared to SC 21 and 22. The B class flare activity is higher for SC 23 where as C, M and X class activities are higher for SC 21. We have also analysied the flare evolution parameters, i.e. duration, rise time, decay time and event asymmetry for total SXR as well as for different classes for last three SCs. The duration, rise time and decay time increase with increasing intensity class. On analysing event asymmetry indices, we found more positive values during SC 21 (64.86 per cent) and SC 22 (54.31 per cent), but for SC 23 we have more negative values (48.08 per cent). Our study shows that during SC 23 we have more SXR flare events having shorter decay time as compared to SC 21 and SC 22.
Here we present the results of the study of the north-south (N-S) distribution and asymmetry of GOES soft X-ray (SXR) flares during solar cycle 24. The period of study includes ascending, maximum and descending phases of the cycle. During the cycle double-peaked (2011, 2014) solar maximum has occurred. The cycle peak in the year 2011 is due to B-class flares excess activity in the northern hemisphere (NH) whereas C and M class flares excess activity in the southern hemisphere (SH) supported the second peak of the cycle in 2014. The data analysis shows that the SXR flares are more pronounced in…
Using data from the Geostationary Operational Environmental Satellites (GOES) spacecraft in the 1-8 Å wavelength range for Solar Cycles 23, 24, and part of Cycles 21 and 22, we compare mean temporal parameters (rising, decay times, duration) and the proportion of impulsive short-duration events (SDE) and gradual long-duration events (LDE) among C- and $\geq$M1.0-class flares. It is found that the fraction of the SDE $\geq$M1.0-class flares (including spikes) in Cycle 24 exceeds that in Cycle 23 in all three temporal parameters at the maximum phase and in the decay time during the ascending cyc…
Solar flare activity in cycle 24 is studied. Satellite observations of x-ray fluxes from GOES-15 and UV emission lines from the SDO/EVE experiment are used. The most powerful flares of cycle 24 in classes X9.3 and X8.2 in September 2017 are compared with powerful flares in classes M5-X6.9. The times at which the fluxes in the 30.4 and 9.4 nm lines and in the 0.1-0.8 nm x-ray range begin to increase are compared for 21 of the large flares. The total energies arriving at the earth from flares in the 30.4 and 9.4 nm lines and in the 0.1-0.9 nm x-ray range, $E_{30.4}$, $E_{9.4}$, and $E_{0.1-0.8}$…
Aims. In this paper, we investigate the temporal evolution and north-south (N-S) asymmetry in the occurrence of solar flares during cycle 21, 22, and 23, and compare the results with traditional solar activity indices. Methods. The flare activity is characterized by a soft X-ray (SXR) flare index, which incorporates information about flare occurrences during a selected interval along with the peak intensity of individual events. Results. The SXR flare index correlates well with other conventional parameters of solar activity. Further, it exhibits a significantly higher correlation with sunspot…
The large (X-ray class > M1) and very large (X-ray class >X1) flares (according to the observations of GOES-15 and Preliminary data from Current Catalog of Flare Events) in solar activity cycle 24 were analyzed. The monthly average values of optical Flare Index for 2010 - 2016 were calculated. The values of the total energy of the flare E (J m-2) in the 0.1 -- 0.8 nm range at the level of the earth's atmosphere were estimated. The energy spectrum (the dependence of the number of flares with the full energy E from the value of this full energy) for 115 flares of M5 - X7 classes was built. The c…
The flare activity and the ultraviolet emission of the sun during its 24-th cycle are analysed. As compared to cycles 21-23, where the most powerful flares were observed during the decay phase, in cycle 24 the greatest number of powerful flares (>X2.7) occurred in the rising phase and at the maximum with the exception of the two largest flares of cycle 24 X9.3 and X8.2 in September 2017. We showed that regression fits of solar UV indices to the overall radiation level from the sun are substantially different for cycle 24 compared to cycles 21-23. It is found that for the flare of August 9, 201…
The prediction of the evolution of individual solar cycles is a developing field, faced with divergence of forecasts even for a few years in the future. Specifically for solar flares, long-term modeling is practically absent even in rough terms. In this article a forecast for the evolution of solar cycle 25 in terms of solar flares activity is presented. It is derived from an existing phenomenological model based on the coupling of an internal solar component and a planetary component. In addition to competent temporal resolution, the predictions are characterized by features which both differ…
Cycle Variation in the Occurrence of Great Soft X-ray Solar Flares
Sternberg Astronomical Institute, Lomonosov Moscow State University（列莫诺索夫莫斯科国立大学斯腾伯格天文研究所）；Department of Physics, Lomonosov Moscow State University（列莫诺索夫莫斯科国立大学物理系）
Quasi-periodic pulsations (QPP) are common in solar flares and are now regularly observed in stellar flares. We present the detection of two different types of QPP signals in the thermal emission light curves of the X9.3 class solar flare SOL2017-09-06T12:02, which is the most powerful flare of Cycle 24. The period of the shorter-period QPP drifts from about 12 to 25 seconds during the flare. The observed properties of this QPP are consistent with a sausage oscillation of a plasma loop in the flaring active region. The period of the longer-period QPP is about 4 to 5 minutes. Its properties are…
During 2017, when the Sun was moving toward the minimum phase of solar cycle 24, an exceptionally eruptive active region (AR) NOAA 12673 emerged on the Sun during August 28-September 10. During the highest activity level, the AR turned into a delta-type sunspot region, which manifests the most complex configuration of magnetic fields from the photosphere to the coronal heights. The AR 12673 produced four X-class and 27 M-class flares, along with numerous C-class flares, making it one of the most powerful ARs of solar cycle 24. Notably, it produced the largest flare of solar cycle 24, namely, t…
Automated Solar Flare Statistics in Soft X-rays over 37 Years of GOES Observations - The Invariance of Self-Organized Criticality during Three Solar Cycles
The paper presents results of a search for helioseismic events (sunquakes) produced by M-X class solar flares during Solar Cycle 24. The search is performed by analyzing photospheric Dopplergrams from Helioseismic Magnetic Imager (HMI). Among the total number of 500 M-X class flares, 94 helioseismic events were detected. Our analysis has shown that many strong sunquakes were produced by solar flares of low M class (M1-M5), while in some powerful X-class flares helioseismic waves were not observed or were weak. Our study also revealed that only several active regions were characterized by the m…
The Geostationary Orbital Environmental Satellites (GOES) Soft X-ray (SXR) sensors have provided data relating to, inter alia, the time, intensity and duration of solar flares since the 1970s. The GOES SXR Flare List has become the standard reference catalogue for solar flares and is widely used in solar physics research and space weather. We report here that in the current version of the list there are significant differences between the mean duration of flares which occurred before May 1997 and the mean duration of flares thereafter. Our analysis shows that the reported flare timings for the…
We investigated some properties of coronal mass ejections (CMEs), such as speed, acceleration, polar angle, angular width, and mass, using data acquired by the Large Angle Spectrometric Coronagraph (LASCO) onboard the Solar and Heliospheric Observatory (SOHO) from 31 July 1997 to 31 March 2014, i.e. during the Solar Cycles 23 and 24. We used two CME catalogs: one provided by the Coordinated Data Analysis Workshops (CDAW) Data Center and one obtained by the Computer Aided CME Tracking software (CACTus) detection algorithm. For each dataset, we found that the number of CMEs observed during the p…
The newly revised sunspot number series allows for placing historical geoeffective storms in the context of several hundred years of solar activity. Using statistical analyses of the Geostationary Operational Environmental Satellites (GOES) X-ray observations from the past ~30 years and the Solar and Heliospheric Observatory (SOHO) Large Angle and Spectrometric Coronagraph (LASCO) Coronal Mass Ejection (CME) catalog (1996-present), we present sunspot-number-dependent flare and CME rates. In particular, we present X-ray flare rates as a function of sunspot number for the past three cycles. We a…
We investigate the morphological and magnetic characteristics of solar active region (AR) NOAA 12192. AR 12192 was the largest region of Solar Cycle 24; it underwent noticeable growth and produced 6 X-class flares, 22 M-class flares, and 53 C-class flares in the course of its disc passage. However, the most peculiar fact of this AR is that it was associated with only one CME in spite of producing several X-class flares. In this work, we carry out a comparative study between the eruptive and non-eruptive flares produced by AR 12192. We find that the magnitude of abrupt and permanent changes in …
A deep learning network, Long-Short Term Memory (LSTM) network, is used in this work to predict whether the maximum flare class an active region (AR) will produce in the next 24 hours is class $Γ$. We considered $Γ$ are $\ge M$, $\ge C$ and any flare class. The essence of using LSTM, which is a recurrent neural network, is its capability to capture temporal information of the data samples. The input features are time sequences of 20 magnetic parameters from SHARPs - Space-weather HMI Active Region Patches. We analyzed active regions from June 2010 to Dec 2018, using the Geostationary Operation…
Solar active region (AR) 12673 in 2017 September produced two largest flares in Solar Cycle 24: the X9.3 flare on September 06 and the X8.2 flare on September 10. We attempt to investigate the evolutions of the two great flares and their associated complex magnetic system in detail. Aided by the NLFFF modeling, we identify a double-decker flux rope configuration above the polarity inversion line (PIL) in the AR core region. The north ends of these two flux ropes were rooted in a negative- polarity magnetic patch, which began to move along the PIL and rotate anticlockwise before the X9.3 flare …
The current fleet of space-based solar observatories offers us a wealth of opportunities to study solar flares over a range of wavelengths. Significant advances in our understanding of flare physics often come from coordinated observations between multiple instruments. Consequently, considerable efforts have been, and continue to be made to coordinate observations among instruments (e.g. through the Max Millennium Program of Solar Flare Research). However, there has been no study to date that quantifies how many flares have been observed by combinations of various instruments. Here we describe…
The emergence and magnetic evolution of solar active regions (ARs) of beta-gamma-delta type, which are known to be highly flare-productive, were studied with the SOHO/MDI data in Cycle 23. We selected 31 ARs that can be observed from their birth phase, as unbiased samples for our study. From the analysis of the magnetic topology (twist and writhe), we obtained the following results. i) Emerging beta-gamma-delta ARs can be classified into three topological types as "quasi-beta", "writhed" and "top-to-top". ii) Among them, the "writhed" and "top-to-top" types tend to show high flare activity. ii…
The chromospheric Lyman-alpha line of neutral hydrogen (\lya; 1216Å) is the strongest emission line in the solar spectrum. Fluctuations in \lya\ are known to drive changes in planetary atmospheres, although few instruments have had the ability to capture rapid \lya\ enhancements during solar flares. In this paper we describe flare-associated emissions via a statistical study of 477 M- and X-class flares as observed by the EUV Sensor on board the 15th Geostationary Operational Environmental Satellite, which has been monitoring the full-disk solar \lya\ irradiance on 10~s timescales over the cou…
The heliospheric magnetic field (HMF) is structured into large sectors of positive and negative polarity. The parts of the boundary between these sectors where the change in polarity matches that of the leading-to-following sunspot polarity in that solar hemisphere, are called Hale Sector Boundaries (HSB). We investigate the flare occurrence rate near HSBs and the association between HSBs and active longitudes. Previous work determined the times HSBs were at solar central meridian, using the detection of the HMF sector boundary crossing at the Earth. In addition to this, we use a new approach …
The largest X9.3 solar flare in solar cycle 24 and the preceding X2.2 flare occurred on September 6, 2017, in the solar active region NOAA 12673. This study aims to understand the onset mechanism of these flares via analysis of multiple observational datasets from the Hinode and Solar Dynamics Observatory and results from a non-linear force-free field extrapolation. The most noticeable feature is the intrusion of a major negative-polarity region, appearing similar to a peninsula, oriented northwest into a neighboring opposite-polarity region. We also observe proxies of magnetic reconnection ca…
Solar flare activity is characterised by different classification systems, both in optical and X-ray ranges. The most generally accepted classifications of solar flares describe important parameters of flares such as the maximum of brightness of the flare in the in optical range - $H_α$ flare class (change from F to B), area of the flare in $H_α$ (change from S for areas less than 2 square degrees to 4 for areas more than 24.7 square degrees) and the maximum amplitude of the soft X-ray (SXR-flux) in the band 0.1 -- 0.8 nm ($F_{0.1-0.8}^{max}$) -- X-ray flares of classes from C to X. A new clas…
We present the characteristics of DH type II bursts for the Solar Cycles 23 and 24. The bursts are classified according to their end frequencies into three categories, i.e. Low Frequency Group (LFG; 20 kHz $\leq$ $f$ $\leq$ 200 kHz), Medium Frequency Group (MFG; 200 kHz $<$ $f$ $\leq$ 1 MHz), and High Frequency Group (HFG; 1 MHz $<$ $f$ $\le$ 16 MHz). We find that the sources for LFG, MFG, and HFG events are homogeneously distributed over the active region belt. Our analysis shows a drastic reduction of the DH type II events during Solar Cycle 24 which includes only 35% of the total events (i.…
In this review, we discuss whether the present solar dynamo models can be extrapolated to explain various aspects of stellar activity. We begin with a summary of the following kinds of data for solar-like stars: (i) data pertaining to stellar cycles from Ca H/K emission over many years; (ii) X-ray data indicating hot coronal activity; (iii) starspot data (especially about giant polar spots); and (iv) data pertaining to stellar superflares. Then we describe the current status of solar dynamo modelling---giving an introduction to the flux transport dynamo model, the currently favoured model for …
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 Wav…
A statistical analysis of the relationship between solar energetic particles (SEPs) and properties of solar flares and coronal mass ejections (CMEs) is presented. SEP events during solar cycle 23 are selected which are associated with solar flares originating on the visible hemisphere of the Sun and at least of magnitude M1. Taking into account all flares and CMEs that occurred during this period, the probability for the occurrence of an SEP event near Earth is determined. A strong rise of this probability is observed for increasing flare intensities, more western locations, larger CME speeds …
Studies on the periodic variation and the phase relationship between different solar activity indicators are useful for understanding the long-term evolution of solar activity cycle. Here we report the statistical analysis of grouped solar flare (GSF) and sunspot number (SN) during the time interval from January 1965 to March 2009. We find that, 1) the significant periodicities of both GSF and SN are related to the differential rotation periodicity, the quasi-biennial oscillation (QBO), and the eleven-year Schwabe cycle (ESC), but the specific values are not absolutely identical; 2) the ESC si…
Around the peaks of substantial flares, bright artifact nearly horizontal saturation streaks (B-streaks) corresponding to the brightest parts of the flare sources appear in the STEREO/EUVI 195 A images. We show that the length of such B-streaks can be used for the solution of an actual problem of evaluating the soft X-ray flux and class of far-side flares registered with double STEREO spacecraft but invisible from Earth. For this purpose from data on about 350 flares observed from January 2007 to July 2014 (mainly exceeding the GOES M1.0 level) both with GOES and STEREO, an empirical relation …
The soft X-ray emissions of solar flares come mainly from the bright coronal loops at the highest temperatures normally achieved in the flare process. Their ubiquity has led to their use as a standard measure of flare occurrence and energy, although the overwhelming bulk of the total flare energy goes elsewhere. Recently Dolla et al. (2012) noted quasi-periodic pulsations (QPP) in the soft X-ray signature of the X-class flare SOL2011-02-15, as observed by the standard photometric data from the GOES (Geostationary Operational Environmental Satellite) spacecraft. In this paper we analyze the sui…
University of Michigan（密歇根大学）；Stanford University（斯坦福大学）
We consider the flare prediction problem that distinguishes flare-imminent active regions that produce an M- or X-class flare in the future 24 hours, from quiet active regions that do not produce any flare within $\pm 24$ hours. Using line-of-sight magnetograms and parameters of active regions in two data products covering Solar Cycle 23 and 24, we train and evaluate two deep learning algorithms -- CNN and LSTM -- and their stacking ensembles. The decisions of CNN are explained using visual attribution methods. We have the following three main findings. (1) LSTM trained on data from two solar …
We statistically study the relationship between the Lyman-alpha (\lya) and 1--8 Å soft X-ray (SXR) emissions from 658 M- and X-class solar flares observed by the {\em Geostationary Operational Environmental Satellite} during 2006--2016. Based on the peak times of the two waveband emissions, we divide the flares into three types. Type I (III) has an earlier (a later) peak time in the \lya\ emission than that in the SXR emission, while type II has nearly a same peak time (within the time resolution of 10 s) between the \lya\ and SXR emissions. In these 658 flares, we find that there are 505 (76.…
We present a statistical analysis of properties of Soft X-Ray (SXR) emission, plasma temperature (T), and emission measure (EM), derived from GOES observations of flares in 2002-2017. The temperature and emission measures are obtained using the TEBBS algorithm (Ryan et al. 2012), which delivers reliable results together with uncertainties even for weak B-class flare events. More than 96% of flares demonstrate a sequential appearance of T, SXR, and EM maxima, in agreement with the expected behavior of the chromospheric evaporation process. The relative number of such flares increases with incre…
This paper develops a planetary model to predict the occurrence of intermediate range periodicity in solar activity, in particular the ~155 day Rieger periodicity in flare activity. It is shown that periodicity at half integer multiples of the period of Mercury occurs consistently in indices of solar activity. For this reason the planetary model is based on the triggering of sunspot emergence when planetary tides peak at times of conjunction of Mercury with Venus, Earth and/or Jupiter. The periodicity of components in the planetary model match reasonably well the observed intermediate periodic…
In this paper, we present the multi-wavelength study of a high level of solar activity during which a single active region produced multiple flares/CMEs. According to the sunspot observations, the current solar cycle 24 manifest to be less intense in comparison with the previous recent sunspot cycles. In the course of the current sunspot cycle 24, several small and large sunspot groups have produced various moderate and intense flare/CME events. There are a few active regions with a large number of flaring activities passed across the visible disk of the Sun during 2012-2015. In this study, we…
