Solar Microflares Observed by SphinX and RHESSI

In 2009, the Russian Complex Orbital Observations Near-Earth of Activity of the Sun (CORONAS-Photon) spacecraft was launched, carrying the Polish Solar PHotometer In X-rays (SphinX). The SphinX was most sensitive in the spectral range 1.2?–?15 keV, thus an excellent opportunity appeared for comparison with the low-energy end of Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spectra. Common spectral measurements with these instruments cover the range where most of the flare energy is accumulated. We have chosen four consecutive small solar events observed on 4 July 2009 at 13:43 UT, 13:48 UT, 13:52 UT, and 13:55 UT (RHESSI flare peak times) and used them to compare the data and results from the two instruments. Moreover, we included Geostationary Operational Environmental Satellite (GOES) records in our analysis. In practice, the range of comparison performed for SphinX and RHESSI is limited roughly to 3?–?6 keV. RHESSI fluxes measured with a use of one, four, and nine detectors in the 3?–?4 keV energy band agree with SphinX measurements. However, we observed that SphinX spectral irradiances are three times higher than those of RHESSI in the 4?–?6 keV energy band. This effect contributes to the difference in obtained emission measures, but the derived temperatures of plasma components are similar. RHESSI spectra were fitted using a model with two thermal components. We have found that the RHESSI hot component is in agreement with GOES, and the RHESSI hotter component fits the SphinX flaring component well. Moreover, we calculated the so-called thermodynamic measure and the total thermal energy content in the four microflares that we studied. The results obtained show that SphinX is a very sensitive complementary observatory for RHESSI and GOES.     

On the Performance of Multi-Instrument Solar Flare Observations During Solar Cycle 24

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 a technique that retrospectively searches archival databases for flares jointly observed by the Ramaty High Energy Solar Spectroscopic Imager (RHESSI), Solar Dynamics Observatory (SDO)/EUV Variability Experiment (EVE – Multiple EUV Grating Spectrograph (MEGS)-A and -B, Hinode/(EUV Imaging Spectrometer, Solar Optical Telescope, and X-Ray Telescope), and Interface Region Imaging Spectrograph (IRIS). Out of the 6953 flares of GOES magnitude C1 or greater that we consider over the 6.5 years after the launch of SDO, 40 have been observed by 6 or more instruments simultaneously. Using each instrument’s individual rate of success in observing flares, we show that the numbers of flares co-observed by 3 or more instruments are higher than the number expected under the assumption that the instruments operated independently of one another. In particular, the number of flares observed by larger numbers of instruments is much higher than expected. Our study illustrates that these missions often acted in cooperation, or at least had aligned goals. We also provide details on an interactive widget (Solar Flare Finder), now available in SSWIDL, which allows a user to search for flaring events that have been observed by a chosen set of instruments. This provides access to a broader range of events in order to answer specific science questions. The difficulty in scheduling coordinated observations for solar-flare research is discussed with respect to instruments projected to begin operations during Solar Cycle 25, such as the Daniel K. Inouye Solar Telescope, Solar Orbiter, and Parker Solar Probe.     

Spatial Size and Plasma Variables of RHESSI Flares

We have analysed 64 flares observed with GOES and RHESSI in the 3.1?–?24.8 keV band (0.5?–?4 Å). Flares were randomly chosen to represent different GOES classes, between B1 and M6. RHESSI was used to image the flaring region on the surface of the Sun. We derived the spatial area of the flare on the surface of the Sun from the imaging observations, scaled it dimensionally to volume, and used the spectroscopically derived emission measure to obtain several flare parameters. We experimented with several imaging methods and selected the use of 50% maximum image photon flux contours to define the flare area (F _50%). Most of the flares showed a single spherical loop-top source. The volume measurement for V, temperature T, and electron density N produced power indices that showed no correlation within the boundaries of error. Larger flares by loop-top source volume are thus neither hotter nor denser. The background-subtracted GOES flux?–?RHESSI Total Emission Measure (TEM _RHESSI) and TEM _GOES?–?TEM _RHESSI dependencies were in agreement with the instrument characteristics and earlier studies. Nonthermal flux was noticed to increase with thermal energy and TEM, which can be said to agree with the “Big Flare Syndrome,” with nonthermal photon flux being considered as one flare manifestation.     

Millimeter and X-Ray Emission from the 5 July 2012 Solar Flare

The 5 July 2012 solar flare SOL2012-07-05T11:44 (11:39?–?11:49 UT) with an increasing millimeter spectrum between 93 and 140 GHz is considered. We use space and ground-based observations in X-ray, extreme ultraviolet, microwave, and millimeter wave ranges obtained with the Reuven Ramaty High-Energy Solar Spectroscopic Imager, Solar Dynamics Observatory (SDO), Geostationary Operational Environmental Satellite, Radio Solar Telescope Network, and Bauman Moscow State Technical University millimeter radio telescope RT-7.5. The main parameters of thermal and accelerated electrons were determined through X-ray spectral fitting assuming the homogeneous thermal source and thick-target model. From the data of the Atmospheric Imaging Assembly/SDO and differential-emission-measure calculations it is shown that the thermal coronal plasma gives a negligible contribution to the millimeter flare emission. Model calculations suggest that the observed increase of millimeter spectral flux with frequency is determined by gyrosynchrotron emission of high-energy (\(\gtrsim 300\) keV) electrons in the chromosphere. The consequences of the results are discussed in the light of the flare-energy-release mechanisms.     

Automated Solar Flare Detection and Feature Extraction in High-Resolution and Full-Disk H$\upalpha$ Images

In this article, an automated solar flare detection method applied to both full-disk and local high-resolution H\(\upalpha\) images is proposed. An adaptive gray threshold and an area threshold are used to segment the flare region. Features of each detected flare event are extracted, e.g. the start, peak, and end time, the importance class, and the brightness class. Experimental results have verified that the proposed method can obtain more stable and accurate segmentation results than previous works on full-disk images from Big Bear Solar Observatory (BBSO) and Kanzelhöhe Observatory for Solar and Environmental Research (KSO), and satisfying segmentation results on high-resolution images from the Goode Solar Telescope (GST). Moreover, the extracted flare features correlate well with the data given by KSO. The method may be able to implement a more complicated statistical analysis of H\(\upalpha\) solar flares.     

Transient Magnetic and Doppler Features Related to the White-Light Flares in NOAA 10486

Rapidly moving transient features have been detected in magnetic and Doppler images of super-active region NOAA 10486 during the X17/4B flare of 28 October 2003 and the X10/2B flare of 29 October 2003. Both these flares were extremely energetic white-light events. The transient features appeared during impulsive phases of the flares and moved with speeds ranging from 30 to 50 km?s^?1. These features were located near the previously reported compact acoustic (Donea and Lindsey, Astrophys. J. 630, 1168, 2005) and seismic sources (Zharkova and Zharkov, Astrophys. J. 664, 573, 2007). We examine the origin of these features and their relationship with various aspects of the flares, viz., hard X-ray emission sources and flare kernels observed at different layers: i) photosphere (white-light continuum), ii) chromosphere (Hα 6563 Å), iii) temperature minimum region (UV 1600 Å), and iv) transition region (UV 284 Å).     

Investigation on M-class Flare-Associated Coronal Mass Ejections with and Without DH Type II Radio Bursts

We perform a statistical analysis on 157 M-class soft X-ray flares observed during 1997?–?2014 with and without deca-hectometric (DH) type II radio bursts aiming at the reasons for the non-occurrence of DH type II bursts in certain events. All the selected events are associated with halo Coronal Mass Ejections (CMEs) detected by the Solar and Heliospheric Observatory (SOHO) / Large Angle Spectrometric and COronograph (LASCO). Out of 157 events, 96 (61%; “Group I”) events are associated with a DH type II burst observed by the Radio and Plasma Wave (WAVES) experiment onboard the Wind spacecraft and 61 (39%; “Group II”) events occur without a DH type II burst. The mean CME speed of Group I is \(1022~\mbox{km}/\mbox{s}\) and that of Group II is \(647~\mbox{km}/\mbox{s}\). It is also found that the properties of the selected M-class flares such as flare intensity, rise time, duration and decay time are greater for the DH associated flares than the non-DH flares. Group I has a slightly larger number (56%) of western events than eastern events (44%), whereas Group II has a larger number of eastern events (62%) than western events (38%). We also compare this analysis with the previous study by Lawrance, Shanmugaraju, and Vr?nak (Solar Phys. 290, 3365L, 2015) concerning X-class flares and confirm that high-intensity flares (X-class and M-class) have the same trend in the CME and flare properties. Additionally we consider aspects like acceleration and the possibility of CME-streamer interaction. The average deceleration of CMEs with DH type II bursts is weaker (\(a = - 4.39\mbox{ m}/\mbox{s}^{2}\)) than that of CMEs without a type II burst (\(a = -12.21\mbox{ m}/\mbox{s}^{2}\)). We analyze the CME-streamer interactions for Group I events using the model proposed by Mancuso and Raymond (Astron. Astrophys. 413, 363, 2004) and find that the interaction regions are the most probable source regions for DH type II radio bursts.     

Measurement of Solar Neutrons on 05 March 2012, Using a Fiber-Type Neutron Monitor Onboard the Attached Payload to the ISS

The solar neutron detector Space Environment Data Acquisition Equipment – Attached Payload (SEDA-FIB) onboard the International Space Station (ISS) detected several events from the solar direction associated with three large solar flares observed on 05 (X1.1), 07 (X5.4), and 09 (M6.3) March 2012. In this study, we focus on the interesting event of 05 March, present the temporal profiles of the neutrons, and discuss the physics that may be related to a possible acceleration scenario for ions above the solar surface. We compare our data with images of the flares obtained by the ultraviolet telescope Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO).     

RHESSI Microflares: I. X-Ray Properties and Multiwavelength Characteristics

We study the general X-ray and multiwavelength characteristics of microflares of GOES class A0.7 to B7.4 (background subtracted) detected by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) on 26 September 2003 comparing them with the properties of regular flares. All the events for which X-ray imaging was feasible originated in one active region and were accumulated in areas with intermixed magnetic polarities. During the events’ rise and peak phase, the RHESSI X-ray spectra show a steep nonthermal power-law component (4?γ?10) for energies ??10 keV. Further evidence for the presence of electron beams is provided by the association with radio type III bursts in 5 out of 11 events where AIP radio spectra were available. The strongest event in our sample shows radio signatures of a type II precursor. The thermally emitting flare plasma observed by RHESSI is found to be hot, 11?T?15 MK, with small emission measures, 10⁴⁶?EM?10⁴⁷ cm^?3, concentrated in the flare loop. In the EUV (TRACE 171 Å), the UV (TRACE 1600 Å) and Kanzelhöhe Solar Observatory Hα, impulsive brightenings at both ends of the RHESSI 3?–?6 keV X-ray loop source are observed, situated in opposite magnetic polarity fields. During the decay phase, a postflare loop at the location of the RHESSI loop source is observed in the TRACE 171 Å? channel showing plasma that is cooled from ??10 MK to ≈?1 MK. Correlations between various thermal and nonthermal parameters derived from the RHESSI microflare spectra compared to the same correlations obtained for a set of small and large flares by Battaglia et al. (Astron. Astrophys. 439, 737, 2005) indicate that the RHESSI instrument gives us a spectrally biased view since it detects only hot (T?10 MK) microflares, and thus the correlations between RHESSI microflare parameters have to be interpreted with caution. The thermal and nonthermal energies derived for the RHESSI microflares are \(\bar{E}_{\mathrm{th}}=7\times 10^{27}\) ergs and \(\bar{E}_{\mathrm{nth}}=2\times 10^{29}\) ergs, respectively. Possible reasons for the order-of-magnitude difference between the thermal and nonthermal microflare energies, which was also found in previous studies, are discussed. The determined event rate of 3.7 h^?1 together with the average microflare energies indicate that the total energy in the observed RHESSI microflares is far too small to account for the heating of the active region corona in which they occur.     

On Flare-CME Characteristics from Sun to Earth Combining Remote-Sensing Image Data with <Emphasis Type="Italic">In Situ</Emphasis> Measurements Supported by Modeling

We analyze the well-observed flare and coronal mass ejection (CME) from 1 October 2011 (SOL2011-10-01T09:18) covering the complete chain of effects – from Sun to Earth – to better understand the dynamic evolution of the CME and its embedded magnetic field. We study in detail the solar surface and atmosphere associated with the flare and CME using the Solar Dynamics Observatory (SDO) and ground-based instruments. We also track the CME signature off-limb with combined extreme ultraviolet (EUV) and white-light data from the Solar Terrestrial Relations Observatory (STEREO). By applying the graduated cylindrical shell (GCS) reconstruction method and total mass to stereoscopic STEREO-SOHO (Solar and Heliospheric Observatory) coronagraph data, we track the temporal and spatial evolution of the CME in the interplanetary space and derive its geometry and 3D mass. We combine the GCS and Lundquist model results to derive the axial flux and helicity of the magnetic cloud (MC) from in situ measurements from Wind. This is compared to nonlinear force-free (NLFF) model results, as well as to the reconnected magnetic flux derived from the flare ribbons (flare reconnection flux) and the magnetic flux encompassed by the associated dimming (dimming flux). We find that magnetic reconnection processes were already ongoing before the start of the impulsive flare phase, adding magnetic flux to the flux rope before its final eruption. The dimming flux increases by more than 25% after the end of the flare, indicating that magnetic flux is still added to the flux rope after eruption. Hence, the derived flare reconnection flux is most probably a lower limit for estimating the magnetic flux within the flux rope. We find that the magnetic helicity and axial magnetic flux are lower in the interplanetary space by ～?50% and 75%, respectively, possibly indicating an erosion process. A CME mass increase of 10% is observed over a range of \({\sim}\,4\,\mbox{--}\,20~\mathrm{R}_{\odot }\). The temporal evolution of the CME-associated core-dimming regions supports the scenario that fast outflows might supply additional mass to the rear part of the CME.     

Interplanetary Coronal Mass Ejections Resulting from Earth-Directed CMEs Using SOHO and ACE Combined Data During Solar Cycle 23

In this work a total of 266 interplanetary coronal mass ejections observed by the Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph (SOHO/LASCO) and then studied by in situ observations from Advanced Composition Explorer (ACE) spacecraft, are presented in a new catalog for the time interval 1996?–?2009 covering Solar Cycle 23. Specifically, we determine the characteristics of the CME which is responsible for the upcoming ICME and the associated solar flare, the initial/background solar wind plasma and magnetic field conditions before the arrival of the CME, the conditions in the sheath of the ICME, the main part of the ICME, the geomagnetic conditions of the ICME’s impact at Earth and finally we remark on the visual examination for each event. Interesting results revealed from this study include the high correlation coefficient values of the magnetic field \(B_{z}\) component against the Ap index (\(r = 0.84\)), as well as against the Dst index (\(r = 0.80\)) and of the effective acceleration against the CME linear speed (\(r = 0.98\)). We also identify a north–south asymmetry for X-class solar flares and an east–west asymmetry for CMEs associated with strong solar flares (magnitude ≥ M1.0) which finally triggered intense geomagnetic storms (with \(\mathrm{Ap} \geq179\)). The majority of the geomagnetic storms are determined to be due to the ICME main part and not to the extreme conditions which dominate inside the sheath. For the intense geomagnetic storms the maximum value of the Ap index is observed almost 4 hours before the minimum Dst index. The amount of information makes this new catalog the most comprehensive ICME catalog for Solar Cycle 23.     

Imaging Spectroscopy of a White-Light Solar Flare

We report observations of a white-light solar flare (SOL2010-06-12T00:57, M2.0) observed by the Helioseismic Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO) and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The HMI data give us the first space-based high-resolution imaging spectroscopy of a white-light flare, including continuum, Doppler, and magnetic signatures for the photospheric Fe i line at 6173.34 Å and its neighboring continuum. In the impulsive phase of the flare, a bright white-light kernel appears in each of the two magnetic footpoints. When the flare occurred, the spectral coverage of the HMI filtergrams (six equidistant samples spanning ±172 mÅ around nominal line center) encompassed the line core and the blue continuum sufficiently far from the core to eliminate significant Doppler crosstalk in the latter, which is otherwise a possibility for the extreme conditions in a white-light flare. RHESSI obtained complete hard X-ray and γ-ray spectra (this was the first γ-ray flare of Cycle 24). The Fe i line appears to be shifted to the blue during the flare but does not go into emission; the contrast is nearly constant across the line profile. We did not detect a seismic wave from this event. The HMI data suggest stepwise changes of the line-of-sight magnetic field in the white-light footpoints.     

Center-to-Limb Variability of Hot Coronal EUV Emissions During Solar Flares

It is generally accepted that densities of quiet-Sun and active region plasma are sufficiently low to justify the optically thin approximation, and this is commonly used in the analysis of line emissions from plasma in the solar corona. However, the densities of solar flare loops are substantially higher, compromising the optically thin approximation. This study begins with a radiative transfer model that uses typical solar flare densities and geometries to show that hot coronal emission lines are not generally optically thin. Furthermore, the model demonstrates that the observed line intensity should exhibit center-to-limb variability (CTLV), with flares observed near the limb being dimmer than those occurring near disk center. The model predictions are validated with an analysis of over 200 flares observed by the EUV Variability Experiment (EVE) on the Solar Dynamics Observatory (SDO), which uses six lines, with peak formation temperatures between 8.9 and 15.8 MK, to show that limb flares are systematically dimmer than disk-center flares. The data are then used to show that the electron column density along the line of sight typically increases by \(1.76 \times 10^{19}~\mbox{cm}^{-2}\) for limb flares over the disk-center flare value. It is shown that the CTLV of hot coronal emissions reduces the amount of ionizing radiation propagating into the solar system, and it changes the relative intensities of lines and bands commonly used for spectral analysis.     

Catalogue of ${>}\,55$ MeV Wide-longitude Solar Proton Events Observed by SOHO,ACE, and the STEREOs at ≈1${\approx}\,1$ AU During 2009 – 2016

Based on energetic particle observations made at \({\approx}\,1\) AU, we present a catalogue of 46 wide-longitude (\({>}\,45^{\circ}\)) solar energetic particle (SEP) events detected at multiple locations during 2009?–?2016. The particle kinetic energies of interest were chosen as \({>}\,55\) MeV for protons and 0.18?–?0.31 MeV for electrons. We make use of proton data from the Solar and Heliospheric Observatory/Energetic and Relativistic Nuclei and Electron Experiment (SOHO/ERNE) and the Solar Terrestrial Relations Observatory/High Energy Telescopes (STEREO/HET), together with electron data from the Advanced Composition Explorer/Electron, Proton, and Alpha Monitor (ACE/EPAM) and the STEREO/Solar Electron and Proton Telescopes (SEPT). We consider soft X-ray data from the Geostationary Operational Environmental Satellites (GOES) and coronal mass ejection (CME) observations made with the SOHO/Large Angle and Spectrometric Coronagraph (LASCO) and STEREO/Coronagraphs 1 and 2 (COR1, COR2) to establish the probable associations between SEP events and the related solar phenomena. Event onset times and peak intensities are determined; velocity dispersion analysis (VDA) and time-shifting analysis (TSA) are performed for protons; TSA is performed for electrons. In our event sample, there is a tendency for the highest peak intensities to occur when the observer is magnetically connected to solar regions west of the flare. Our estimates for the mean event width, derived as the standard deviation of a Gaussian curve modelling the SEP intensities (protons \({\approx}\,44^{\circ}\), electrons \({\approx}\,50^{\circ}\)), largely agree with previous results for lower-energy SEPs. SEP release times with respect to event flares, as well as the event rise times, show no simple dependence on the observer’s connection angle, suggesting that the source region extent and dominant particle acceleration and transport mechanisms are important in defining these characteristics of an event. There is no marked difference between the speed distributions of the CMEs related to wide events and the CMEs related to all near-Earth SEP events of similar energy range from the same time period.     

Detection of Quasi-Periodic Pulsations in Solar EUV Time Series

Quasi-periodic pulsations (QPPs) are intrinsically connected to the mechanism of solar flares. They are regularly observed in the impulsive phase of flares since the 1970s. In the past years, the studies of QPPs regained interest with the advent of a new generation of soft X-ray/extreme ultraviolet radiometers that pave the way for statistical surveys. Since the amplitude of QPPs in these wavelengths is rather small, detecting them implies that the overall trend of the time series needs to be removed before applying any Fourier or wavelet transform. This detrending process is known to produce artificial detection of periods that must then be distinguished from real ones. In this paper, we propose a set of criteria to help identify real periods and discard artifacts. We apply these criteria to data taken by the Extreme Ultraviolet Variability Experiment (EVE)/ESP onboard the Solar Dynamics Observatory (SDO) and the Large Yield Radiometer (LYRA) onboard the PRoject for On-Board Autonomy 2 (PROBA2) to search for QPPs in flares stronger than M5.0 that occurred during Solar Cycle 24.     

Effect of Coulomb collisions on the particle acceleration in collapsing magnetic traps

The problem of particle acceleration in collapsing magnetic traps in the solar corona has been solved by taking into account the particle scattering and braking in the high-temperature plasma of solar flares. The Coulomb collisions are shown to be weak in traps with lifetimes t _l < 10 s and strong for t _l > 100 s. In the approximation of strong collisions, collapsing magnetic traps are capable of confining up to 20% of the injected particles in the corona for a long time. In the collisionless approximation, this value exceeds 90%. The question about the observational manifestations of collisions is examined. For collision times comparable to t _l , the electron spectrumat energies above 10 keV is shown to be a double-power-law one. Such spectra were found by the RHESSI satellite in flares.     

Parameters of superflares on G-Type stars observed with the Kepler space telescope

We continued the analysis of 279 G-type stars with superflares (energies in the range of 10³³–10³⁶ erg). We calculated the SFL parameter (part of the stellar surface which emits in the flare). The SFL estimates were derived from the relation connecting this value with the amplitude of the flare and its radiation on the assumption of the blackbody character of the emission at times close to its maximum. Most SFL values are in the range of 0–0.1, with values of 0.2–0.4 for some strong flares. Dependence of SFL on effective temperature for stars with superflares is similar to that found earlier for the spottedness parameter S. The SFL distribution reaches its maximum in the temperature range of about 5100–5250 K and decreases with the effective temperature increase. We suggested an assumption on the presence of bimodal distribution in the “SFL–rotation period” relation with a gap for objects with rotation periods P of about 10 days. For stars with P less than 10 days, the given data can indicate a decrease in flare areas with the P increase. Our analysis showed that significant changes both in flare energy and in flare areas can be achieved with small changes in spottedness S for one and the same star.     

Pulsations of microwave emission and flare plasma diagnostics

We consider the modulation of nonthermal gyrosynchrotron emission from solar flares by the ballooning and radial oscillations of coronal loops. The damping mechanisms for fast magnetoacoustic modes are analyzed. We suggest a method for diagnosing the plasma of flare loops that allows their main parameters to be estimated from peculiarities of the microwave pulsations. Based on observational data obtained with the Nobeyama Radioheliograph (17 GHz) and using a technique developed for the event of May 8, 1998, we determined the particle density n≈3.7×10¹⁰ cm^?3, the temperature T≈4×10⁷ K, and the magnetic field strength B≈220 G in the region of flare energy release. A wavelet analysis for the solar flare of August 28, 1999, has revealed two main types of microwave oscillations with periods P₁≈7, 14 s and P₂≈2.4 s, which we attribute to the ballooning and radial oscillations of compact and extended flare loops, respectively. An analysis of the time profile for microwave emission shows evidence of coronal loop interaction. We determined flare plasma parameters for the compact (T≈5.3×10⁷ K, n≈4.8≈10¹⁰ cm^?3, B≈280 G) and extended (T≈2.1≈10⁷ K, n≈1.2≈10¹⁰ cm^?3, B≈160 G) loops. The results of the soft X-ray observations are consistent with the adopted model.     

Forecasting Solar Flares Using Magnetogram-based Predictors and Machine Learning

We propose a forecasting approach for solar flares based on data from Solar Cycle 24, taken by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) mission. In particular, we use the Space-weather HMI Active Region Patches (SHARP) product that facilitates cut-out magnetograms of solar active regions (AR) in the Sun in near-realtime (NRT), taken over a five-year interval (2012?–?2016). Our approach utilizes a set of thirteen predictors, which are not included in the SHARP metadata, extracted from line-of-sight and vector photospheric magnetograms. We exploit several machine learning (ML) and conventional statistics techniques to predict flares of peak magnitude \({>}\,\mbox{M1}\) and \({>}\,\mbox{C1}\) within a 24 h forecast window. The ML methods used are multi-layer perceptrons (MLP), support vector machines (SVM), and random forests (RF). We conclude that random forests could be the prediction technique of choice for our sample, with the second-best method being multi-layer perceptrons, subject to an entropy objective function. A Monte Carlo simulation showed that the best-performing method gives accuracy \(\mathrm{ACC}=0.93(0.00)\), true skill statistic \(\mathrm{TSS}=0.74(0.02)\), and Heidke skill score \(\mathrm{HSS}=0.49(0.01)\) for \({>}\,\mbox{M1}\) flare prediction with probability threshold 15% and \(\mathrm{ACC}=0.84(0.00)\), \(\mathrm{TSS}=0.60(0.01)\), and \(\mathrm{HSS}=0.59(0.01)\) for \({>}\,\mbox{C1}\) flare prediction with probability threshold 35%.