Distribution Of Flares Research Articles

Factors That Determine the Power-law Index of an Energy Distribution of Solar Flares

The power-law index of an occurrence frequency distribution of flares as a function of energy is one of the most important indicators to evaluate the contribution of small-scale flares to coronal heating. For a few decades, many studies tried to derive the power-law index using various instruments and methods. However, these results are various and the cause of this uncertainty is unknown due to the variety of observation conditions. Therefore, we investigated the dependence of the index on the solar activity, coronal features, released energy range, and active region properties such as magnetic flux, twist, and size. Our findings are (1) annual power-law index derived from time series of total solar irradiance (Sun-as-a-star observation analysis) has a negative correlation with sunspot number; (2) power-law index in active region is smaller than that of the quiet Sun and coronal holes; (3) power-law index is almost constant in the energy range of 1025 ≲ E ≲ 1030 erg; and (4) active regions that have more magnetic free energy density, unsigned magnetic flux, and shear angle tend to have smaller power-law indices. Based on the results and energy-scaling law of Petschek-type reconnection, we suggest that the power-law index of sunspot-scale events is smaller than that of granule-scale events. Moreover, we indicated that sunspot-scale events follow CSHKP flare model whereas granule-scale events follow Parker’s nanoflare model.

Searching for flaring star–planet interactions in AU Mic TESS observations

ABSTRACT Planets that closely orbit magnetically active stars are thought to be able to interact with their magnetic fields in a way that modulates stellar activity. This modulation in phase with the planetary orbit, such as enhanced X-ray activity, chromospheric spots, radio emission, or flares, is considered the clearest sign of magnetic star–planet interaction (SPI). However, the magnitude of this interaction is poorly constrained, and the intermittent nature of the interaction is a challenge for observers. AU Mic is an early M dwarf, and the most actively flaring planet host detected to date. Its innermost companion, AU Mic b, is a promising target for magnetic SPI observations. We used optical light curves of AU Mic obtained by the Transiting Exoplanet Survey Satellite to search for signs of flaring SPI with AU Mic b using a customized Anderson–Darling test. In the about 50 d of observations, the flare distributions with orbital, rotational, and synodic periods were generally consistent with intrinsic stellar flaring. We found the strongest deviation (p = 0.07, n = 71) from intrinsic flaring with the orbital period of AU Mic b, in the high-energy half of our sample (ED > 1 s). If it reflects the true SPI signal from AU Mic b, extending the observing time by a factor of 2–3 will yield a >3σ detection. Continued monitoring of AU Mic may therefore reveal flaring SPI with orbital phase, while rotational modulation will smear out due to the star’s strong differential rotation.

Estimates of Methane Release From Gas Seeps at the Southern Hikurangi Margin, New Zealand

The highest concentration of cold seep sites worldwide has been observed along convergent margins, where fluid migration through sedimentary sequences is enhanced by tectonic deformation and dewatering of marine sediments. In these regions, gas seeps support thriving chemosynthetic ecosystems increasing productivity and biodiversity along the margin. In this paper, we combine seismic reflection, multibeam and split-beam hydroacoustic data to identify, map and characterize five known sites of active gas seepage. The study area, on the southern Hikurangi Margin off the North Island of Aotearoa/New Zealand, is a well-established gas hydrate province and has widespread evidence for methane seepage. The combination of seismic and hydroacoustic data enable us to investigate the geological structures underlying the seep sites, the origin of the gas in the subsurface and the associated distribution of gas flares emanating from the seabed. Using multi-frequency split-beam echosounder (EK60) data we constrain the volume of gas released at the targeted seep sites that lie between 1,110 and 2,060 m deep. We estimate the total deep-water seeps in the study area emission between 8.66 and 27.21 × 106 kg of methane gas per year. Moreover, we extrpolate methane fluxes for the whole Hikurangi Margin based on an existing gas seep database, that range between 2.77 × 108 and 9.32 × 108 kg of methane released each year. These estimates can result in a potential decrease of regional pH of 0.015–0.166 relative to the background value of 7.962. This study provides the most quantitative assessment to date of total methane release on the Hikurangi Margin. The results have implications for understanding what drives variation in seafloor biological communities and ocean biogeochemistry in subduction margin cold seep sites.

New Time-resolved, Multi-band Flares in the GJ 65 System with gPhoton

Abstract Characterizing the distribution of flare properties and occurrence rates is important for understanding habitability of M-dwarf exoplanets. The Galaxy Evolution Explorer (GALEX) space telescope observed the GJ 65 system, composed of the active, flaring M stars BL Cet and UV Cet, for 15,900 s (∼4.4 hr) in two ultraviolet (UV) bands. The contrast in flux between flares and the photospheres of cool stars is maximized at UV wavelengths, and GJ 65 is the brightest and nearest flaring M-dwarf system with significant GALEX coverage. It therefore represents the best opportunity to measure low-energy flares with GALEX. We construct high-cadence lightcurves from calibrated photon events and find 13 new flare events with near-UV (NUV) energies ranging from 1028.5–1029.5 erg and recover one previously reported flare with an energy of 1031 erg. The newly reported flares are among the smallest M-dwarf flares observed in the UV with sufficient time resolution to discern lightcurve morphology. The estimated flare frequency at these low energies is consistent with extrapolation from the distributions of higher-energy flares on active M dwarfs measured by other surveys. The largest flare in our sample is bright enough to exceed the local nonlinearity threshold of the GALEX detectors, which precludes color analysis. However, we detect quasi-periodic pulsations during this flare in both the far-UV and NUV bands at a period of ∼50 s, which we interpret as a modulation of the flare’s chromospheric thermal emission through periodic triggering of reconnection by external MHD oscillations in the corona.

Localizing flares to understand stellar magnetic fields and space weather in exo‐systems

AbstractStars are uniform spheres, but only to first order. The way in which stellar rotation and magnetism break this symmetry places important observational constraints on stellar magnetic fields, and factors in the assessment of the impact of stellar activity on exoplanet atmospheres. The spatial distribution of flares on the solar surface is well known to be nonuniform, but elusive on other stars. We briefly review the techniques available to recover the loci of stellar flares, and highlight a new method that enables systematic flare localization directly from optical light curves. We provide an estimate of the number of flares we may be able to localize with the Transiting Exoplanet Survey Satellite, and show that it is consistent with the results obtained from the first full sky scan of the mission. We suggest that nonuniform flare latitude distributions need to be taken into account in accurate assessments of exoplanet habitability.

Unified model for orphan and multiwavelength blazar flares

Blazars are a class of active galactic nuclei that host relativistic jets oriented close to the observer's line of sight. Blazars have very complex variability properties. Flares, namely flux variations around the mean value with a well-defined shape and duration, are one of the identifying properties of the blazar phenomenon. Blazars are known to exhibit multiwavelength flares, but also ``orphan'' flares, namely flux changes that appear only in a specific energy range. Various models, sometimes at odds with each other, have been proposed to explain specific flares even for a single source, and cannot be synthesized into a coherent picture. In this paper, we propose a unified model for explaining orphan and multiwavelength flares from blazars in a common framework. We assume that the blazar emission during a flare consists of two components: (i) a quasistable component that arises from the superposition of numerous but comparatively weak dissipation zones along the jet, forming the background (low-state) emission of the blazar, and (ii) a transient component, which is responsible for the sudden enhancement of the blazar flux, forming at a random distance along the jet by a strong energy dissipation event. Whether a multiwavelength or orphan flare is emitted depends on the distance from the base of the jet where the dissipation occurs. Generally speaking, if the dissipation occurs at a small/large distance from the supermassive black hole, the inverse Compton/synchrotron radiation dominates and an orphan $\ensuremath{\gamma}$-ray/optical flare tends to appear. On the other hand, we may expect a multiwavelength flare if the dissipation occurs at an intermediate distance. We show that the model can successfully describe the spectral energy distribution of different flares from the flat spectrum radio quasar 3C 279 and the BL Lacertae object PKS 2155-304.

Simultaneous Multiwavelength Flare Observations of EV Lacertae

Abstract We present the first results of our ongoing project conducting simultaneous multiwavelength observations of flares on nearby active M dwarfs. We acquired data of the nearby dM3.5e star EV Lac using five different observatories: NASA’s Transiting Exoplanet Survey Satellite (TESS), NASA’s Neil Gehrels Swift Observatory (Swift), NASA’s Neutron Interior Composition Explorer (NICER), the University of Hawaii 2.2-meter telescope (UH88), and the Las Cumbres Observatory Global Telescope (LCOGT) Network. During the ∼25 days of TESS observations, we acquired three simultaneous UV/X-ray observations using Swift that total ∼18 ks, 21 simultaneous epochs totaling ∼98 ks of X-ray data using NICER, one observation (∼3 hr) with UH88, and one observation (∼3 hr) with LCOGT. We identified 56 flares in the TESS light curve with estimated energies in the range log E T (erg) = (30.5–33.2), nine flares in the Swift UVM2 light curve with estimated energies in the range log E UV (erg) = (29.3–31.1), 14 flares in the NICER light curve with estimated minimum energies in the range log E N (erg) = (30.5–32.3), and 1 flare in the LCOGT light curve with log E L (erg) = 31.6. We find that the flare frequency distributions (FFDs) of TESS and NICER flares have comparable slopes, β T = −0.67 ± 0.09 and β N = − 0.65 ± 0.19, and the FFD of UVOT flares has a shallower slope (β U = −0.38 ± 0.13). Furthermore, we do not find conclusive evidence for either the first ionization potential (FIP) or the inverse FIP effect during coronal flares on EV Lac.

Open Issues in Statistical Forecasting of Solar Proton Events: A Machine Learning Perspective

AbstractSeveral techniques have been developed in the last two decades to forecast the occurrence of Solar Proton Events (SPEs), mainly based on the statistical association between the 10 MeV proton flux and precursor parameters. The Empirical model for Solar Proton Events Real Time Alert (ESPERTA; Laurenza et al., 2009, https://doi.org/10.1029/2007sw000379) provides a quite good and timely prediction of SPEs after the occurrence of M2 soft x‐ray (SXR) bursts, by using as input parameters the flare heliolongitude, the SXR and the 1 MHz radio fluence. Here, we reinterpret the ESPERTA model in the framework of machine learning and perform a cross validation, leading to a comparable performance. Moreover, we find that, by applying a cut‐off on the M2 flares heliolongitude, the False Alarm Rate (FAR) is reduced. The cut‐off is set to where the cumulative distribution of M2 flares associated with SPEs shows a break which reflects the poor magnetic connection between the Earth and eastern hemisphere flares. The best performance is obtained by using the SMOTE algorithm, leading to probability of detection of 0.83 and a FAR of 0.39. Nevertheless, we demonstrate that a relevant FAR on the predictions is a natural consequence of the sample base rates. From a Bayesian point of view, we find that the FAR explicitly contains the prior knowledge about the class distributions. This is a critical issue of any statistical approach, which requires to perform the model validation by preserving the class distributions within the training and test datasets.

Correlation of the Sunspot Number and the Waiting-time Distribution of Solar Flares, Coronal Mass Ejections, and Solar Wind Switchback Events Observed with the Parker Solar Probe

Abstract Waiting-time distributions of solar flares and coronal mass ejections (CMEs) exhibit power-law-like distribution functions with slopes in the range of α τ ≈ 1.4–3.2, as observed in annual data sets during four solar cycles (1974–2012). We find a close correlation between the waiting-time power-law slope α τ and the sunspot number (SN), i.e., α τ = 1.38 + 0.01 × SN. The waiting-time distribution can be fitted with a Pareto-type function of the form N(τ) = N 0 , where the offset τ 0 depends on the instrumental sensitivity, the detection threshold of events, and pulse pileup effects. The time-dependent power-law slope α τ (t) of waiting-time distributions depends only on the global solar magnetic flux (quantified by the sunspot number) or flaring rate, which is not predicted by self-organized criticality or magnetohydrodynamic turbulence models. Power-law slopes of α τ ≈ 1.2–1.6 were also found in solar wind switchback events, as observed with the Parker Solar Probe during the solar minimum, while steeper slopes are predicted during the solar maximum. We find that the annual variability of switchback events in the heliospheric solar wind and solar flare and CME rates (originating in the photosphere and lower corona) are highly correlated.

A study on flare minimisation in EUV lithography by post‐layout re‐allocation of wire segments

The feature size in Integrated Circuits (ICs) has been scaling down aggressively, thereby posing more challenges in their manufacturability. Conventional immersion lithography using a laser of 193 nm wavelength produces layouts having distortions that degrade performance significantly. To overcome this bottleneck, Next-Generation Lithography (NGL) technologies are being developed. Extreme Ultraviolet Lithography (EUVL), one of the popular NGLs, which uses a light of 13.5 nm wavelength. However, irregularities on the photo reflective surface of clear-field masks used in EUVL, scatter the incident light and cause flare that in turn results in layout pattern distortions and critical dimension (CD) violations. One of the approaches to counter the effect of flare is to utilise dummy metal fills. But this incurs additional mask cost. Herein, a method to reduce the flare variation as well as the average flare distribution for a layout by perturbation of wire segments, without affecting performance at the post-layout phase, is proposed. The results show reductions of 20% and 11% on an average in the flare variation and flare mean, respectively, compared to that for the original layout for two different flare models studied on three standard sets of benchmark suites. Consequently, a reduction in the dummy fill demand of a similar magnitude is thus obtained.

Investigation of Hemispherical Variations of Soft X-Ray Solar Flares during Solar Cycles 21 to 24

In the current investigation we have studied the distribution as well as the asymmetry of solar X-ray flares during the period 1976–2017 which corresponds to solar cycle 21, 22, 23 and the almost complete solar cycle 24. The study of the N–S distribution of soft X-ray flares during solar cycles 21, 22, 23 and 24 reveals that the 10°–20° latitude band produced maximum number of soft X-ray flares and is found to be southern hemisphere dominated during all the considered cycles. The soft X-ray flares events above 40° latitude is very rare. Most of the solar X-ray flare activities are observed to be concentrated in the 8°–30° latitude band. A time-latitude plot has been plotted to graphically represent the soft X-ray flare distribution at various latitudes over the course of solar cycle. Our analysis also reveals that solar cycles 21, 22 and 23 are southern hemisphere dominated and the corresponding probability value is statistically significant. The soft X-ray solar flare activity during solar cycle 24 is also found to be southern hemisphere dominated, similar to cycles 21, 22 and 23. Using cross-correlation analysis, we have found that the smoothed curves of the number of soft X-ray flares in northern hemisphere are ahead of the southern hemisphere by 10 months, 2 months, 8 months and 4 months during solar cycles 21, 22, 23 and 24 respectively. Also, for total time span (1976–2017), the smoothed curve of the frequency of soft X-ray flares in northern hemisphere is ahead of a similar curve from the southern hemisphere by 7 months.

Self-organized Criticality in Stellar Flares

Abstract Power-law size distributions are the hallmarks of nonlinear energy dissipation processes governed by self-organized criticality (SOC). Here we analyze 75 data sets of stellar flare size distributions, mostly obtained from the Extreme-Ultraviolet Explorer and the Kepler mission. We aim to answer the following questions for size distributions of stellar flares. (i) What are the values and uncertainties of power-law slopes? (ii) Do power-law slopes vary with time? (iii) Do power-law slopes depend on the stellar spectral type? (iv) Are they compatible with solar flares? (v) Are they consistent with SOC models? We find that the observed size distributions of stellar flare fluences (or energies) exhibit power-law slopes of α E = 2.09 ± 0.24 for optical data sets observed with Kepler. The observed power-law slopes do not show much time variability and do not depend on the stellar spectral type (M, K, G, F, A, giants). In solar flares, we find that background subtraction lowers the uncorrected value of α E = 2.20 ± 0.22 to α E = 1.57 ± 0.19. Furthermore, most of the stellar flares are temporally not resolved in low-cadence (30 minutes) Kepler data, which causes an additional bias. Taking these two biases into account, the stellar flare data sets are consistent with the theoretical prediction of SOC models, i.e., α E = 1.5. Thus, accurate power-law fits require automated detection of the inertial range and background subtraction, which can be modeled with the generalized Pareto distribution, finite-system size effects, and extreme event outliers.

Моделирование процессов фильтрации технологических растворов при блочном подземном выщелачивании

PAO “Priargunsky Production Mining and Chemical Association” has been working on reserves of uranium deposits of the Streltsovsky ore field for more than 50 years. During this period, most of the rich ores have been worked out by traditional mining and physical technology. The share of poor and ordinary ores remains significant, but traditional technology does not provide the necessary level of profitability. Therefore, the widespread introduction of physicochemical technology: underground block (BPV) and heap leaching (KV) can be a decisive moment in the continuation of the operation of these deposits. The applied technology of underground block leaching has one significant drawback – a low rate of uranium recovery into a productive solution, which significantly reduces the effectiveness of this technology in the development of poor uranium deposits. To increase the yield of uranium into the productive solution, it is necessary to analyze the entire preparation and leaching process and establish the main reasons for the low rates of transition of uranium to a mobile state. For this purpose, it is proposed to simulate the underground leaching process by building visual models of halos spreading of solutions along shrinked ore mining mass accumulated in an underground chamber. During the simulation, it was found that the distribution of the size classes of the broken ore pieces in the chamber can be predicted at the stage of drilling and blasting operations, and when determining the line of least resistance W and the distance between the ends of the wells, take into account the diameter of the controlled crushing zone R_p. At the same time, 3 zones of granulometric compositions are formed: a re-grinding zone, an optimum zone and a non-carbarite exit zone. The flow of solutions through these zones will differ the more significantly, the higher the height of the chamber. In a zone with larger crushing, an almost steep distribution of the solution spreading front is expected. Accordingly, the smaller the fraction, the lower the front to the horizontal is. The following functions are offered to simulate filtering processes: – it is possible to control the flow of working solutions to the fan of irrigation wells in order to achieve optimal leaching parameters, i.e. to quickly control the process; – knowledge of the law of distribution of irrigation flares makes it possible to select the optimal grid of location of single sprinklers

Energy Distribution of Small-scale Flares Derived Using a Genetic Algorithm

Abstract To understand the mechanism of coronal heating, it is crucial to derive the contribution of small-scale flares, the so-called nanoflares, to the heating up of the solar corona. To date, several studies have tried to derive the occurrence frequency distribution of flares as a function of energy to reveal the contribution of small-scale flares. However, there are no studies that derive the distribution with considering the following conditions: (1) evolution of the coronal loop plasma heated by small-scale flares, (2) loops smaller than the spatial resolution of the observed image, and (3) multiwavelength observation. To take into account these conditions, we introduce a new method to analyze small-scale flares statistically based on a one-dimensional loop simulation and a machine-learning technique, that is, the genetic algorithm. First, we obtain six channels of Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) light curves of the active-region coronal loops. Second, we carry out many coronal loop simulations and obtain the SDO/AIA light curves for each simulation in a pseudo-manner. Third, using the genetic algorithm, we estimate the best combination of simulated light curves that reproduce the observation. Consequently, the observed coronal loops are heated by small-scale flares with energy flux larger than that typically required to heat up an active region intermittently. Moreover, we derive the occurrence frequency distribution which has various power-law indices in the range from 1–3, which partially supports the nanoflare heating model. In contrast, we find that 90% of the coronal heating is done by flares that have energy larger than 1025 erg.

Widespread occurrence of methane seeps in deep-water regions of Krishna-Godavari basin, Bay of Bengal

Drilling/coring activities during NGHP-Expeditions 01 and 02 discovered significant gas hydrate deposits in the Krishna-Godavari (KG) basin, a proven petroliferous basin located along the eastern continental margin of India. Active and paleo-cold seeps are also reported from deep waters (>1000 m), indicating methane venting episodes in the KG basin. In the present study, we analyzed geophysical data acquired onboard RV Sindhu Sadhana to study the spatial distribution of gas flares in the KG offshore basin. Twenty-two gas flares were observed in water-column images at seafloor depths ranging from 638 m to 1960 m. All flares except one are detected within the gas hydrate stability zone (GHSZ), which occurs beyond 700–720 m water depths. Most gas flares seem to terminate at these depths, indicating that the bubbles might be coated with a thin methane hydrate skin. Seabed sampling of flare regions shows the presence of chemosynthetic communities and shallow gas hydrates within 2–4 mbsf.The spatial distribution of gas flares is not random and tends to align with the toe-thrust zones and shale diapiric mounds. These compressive structures formed due to shale tectonism in the KG basin have provided an environment conducive for the formation of gas hydrate deposits and gas flares/cold seeps. The analysis of high-resolution seismic data across the flares shows the presence of seismic chimneys and faults, which facilitated migration of deep-seated fluid/gas through the GHSZ. Focused fluid flow along the fault zone and the perturbation of methane + seawater phase curve due to salinity increase owing to the continuous formation of methane hydrate are the most likely mechanisms to explain methane gas migration.

Information Theoretical Approach to Understanding Flare Waiting Times

Abstract There is not currently a consensus on the process responsible for producing the waiting time distribution of solar flares. This study presents an information theoretical approach to determining whether solar flare data are significantly distinguishable from a nonstationary Poisson process. A study of solar flares stronger than C1 class detected by the Geostationary Operational Environmental Satellite from 1975 to 2017 was performed. A sequence of waiting times (time elapsed between adjacent X-ray flare peaks) was constructed from the data. Surrogate waiting time sequences were produced using a time-varying Poisson firing rate from the Bayesian block procedure. Utilizing Shannon entropy, the mutual information of time-lagged waiting time distributions was computed for both the original data and the surrogates using a method of discretization by binning. When the entire period is considered, we see that when compared to carefully constructed surrogates, there is a significant elevation of mutual information on a timescale of approximately 30 hr, demonstrating that flares are confidently related to subsequent flares, contradicting the null hypothesis that flares are produced by a nonstationary Poisson process. When only 4 yr subsets of the data are considered, we see that at relatively small timescales (on the order of 10–30 hr), solar flare waiting times have a significant impact on subsequent flares. When corrected for the number of points in each considered time window, there is no correlation between the magnitude of significance and position in the solar cycle.

Bivariate Number Distribution of Solar Soft X-Ray Flares

Abstract Conventionally, researchers investigated the number distribution of solar flares by univariate analysis using all available data. For the first time, we investigate the bivariate number distribution of peak flux (f) and duration (T) of soft X-ray flares observed by the Geostationary Operational Environmental Satellite during the past 10 years. First, the univariate number distribution of f is found to obey a power law either for each class of flares or for the B or ≥C flares in a certain range of T. But the power-law index of B-class flares is much smaller than those of other higher-class ones. For the ≥C flares, the longer the duration, the smaller the power-law index. The univariate number distribution of T deviates from the power law at shorter durations and is better fitted by a skewed Gaussian function in logarithmic coordinates for almost any given range of f, reflecting the random phenomena in solar flares. Then, based on the univariate analysis, a linear Gaussian function is proposed to describe the bivariate logarithmic number distribution of f and T, from which the local power-law index with respect to either f or T can also be analyzed. The real number distribution of B flares should be in between the observed one and the power-law distribution of stronger flares (≥C). We suggest that nanoflare activity may not be the dominant source of coronal heating.

Accuracy of satellite-derived estimates of flaring volume for offshore oil and gas operations in nine countries

Flaring of natural gas contributes to climate change and wastes a potentially valuable energy resource. Various groups have estimated flaring volumes via remote sensing by nighttime detection of flares using multi-spectral imaging. However, only limited efforts have been made to independently assess the accuracy of these estimation methods. I analyze the accuracy of the VIIRS Nightfire published flare detection results, comparing yearly estimated flaring rates to reported flaring data from governments in 9 countries (Brazil, Canada, Denmark, Mexico, Netherlands, Nigeria, Norway, USA, UK) and 7 years (2012–2018 inclusive). We analyze only flares occurring at offshore oil and gas production platforms and floating production units. A total of 1054 flare volume estimates were compared to volumes reported to government agencies. 80.8% of flare estimates lie within 0.5 orders of magnitude (OM) of reported volumes, which 93.7% fall within 1 OM of the reported volume. Little systematic bias is found except in the smallest size classes (<106 m3 y−1). Relative error ratios are larger for smaller flares. No significant trend was observed across years, and variation by country is in line with that expected by size distribution of flares by country. Wide aggregate estimates for groups of flares will exhibit little bias and dispersion, with the sum of 1000 flares having an expected interquartile range of −6% to +3% of actual reported volumes. Social media blurb: Test of remote sensing for flare detection shows accuracy across 9 countries and 8 years.

Do the solar flares originating from an individual active region follow a random process or a memory-dependent correlation?

ABSTRACT We investigate the waiting time statistics of solar flares both in a flare-productive active region (AR 12673) of the solar cycle 24 and in a three-dimensional magnetohydrodynamic (MHD) simulated AR. The statistical models of a discrete random process and a continuous memory-dependent process are applied to interpret the waiting time distributions (WTDs) of solar flares. Our results indicate that the occurrence of a solar flare in an individual AR maintains a certain amount of memory, and probably arises from MHD turbulence rather than from intermittent avalanches in a self-organized criticality system. It differs from the occurrence of ‘super flares’ when treating the star/Sun as a single non-linear system.

North-South Distribution and Asymmetry of GOES SXR Flares during Solar Cycle 24

Abstract 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 11 to 20 degree latitudes for each hemisphere. Cumulative values of SXR flare count show northern excess during the ascending phase of the cycle. However, in the descending phase of the cycle, southern excess occurred. In the cycle a significant SH dominated asymmetry exists. Near the maximum of the cycle, the asymmetry enhances pronouncedly and reverses in sign.