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Active regions often show S-shaped structures in the corona called sigmoids. These are highly sheared and twisted loops formed along the polarity inversion line. They are considered to be one of the best pre-eruption signatures for CMEs. Here, we investigate the thermodynamic evolution of an on-disk sigmoid observed during December 24-28, 2015. For this purpose, we have employed Emission Measure (EM) and filter-ratio techniques on the observations recorded by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) and X-ray Telescope (XRT) onboard Hinode. The EM analysis showed multi-thermal plasma along the sigmoid and provided a peak temperature of 10-12.5 MK for all observed flares. The sigmoidal structure showed emission from Fe XVIII (93.93 {\AA}) and Fe XXI 128.75 {\AA}) lines in the AIA 94 and 131 {\AA} channels, respectively. Our results show that the hot plasma is often confined to very hot strands. The temperature obtained from the EM analysis was found to be in good agreement with that obtained using the XRT, AIA, and GOES filter-ratio methods. These results provide important constraints for the thermodynamic modeling of sigmoidal structures in the core of active regions. Moreover, this study also benchmarks different techniques available for temperature estimation in solar coronal structures., Comment: 19 pages, 13 figures, Accepted for publication in Monthly Notices of the Royal Astronomical Society

The paper presents a modified version of a previously published 3D model of the solar facular knot (Solov’ev and Kirichek, 2019), which successfully describes the main structural features of the solar facular formations. As in the main model, we use the solution (Schatzman, 1965) in the potential approximation as the basis of the magnetic structure of the facular element. The magnetic profile of the facula, as before, has the shape of a fountain, in which thin streams of plasma rise in the center of the node and flow on its periphery along magnetic field lines. This configuration is very similar to the observed patterns (Lites et al., 2004; Jafarzadeh et al., 2017; Pietarila et al., 2009). In the new modified facula model, we use a different method to introduce force corrections into the potential distribution of the magnetic field, which causes the appearance of additional terms in the formulas for pressure and density. In the new version of the model, a change in only geometric parameters leads to a sharp change in the temperature profiles of the facular knot: instead of a dark central dip in the center of the assembly, a bright, hot formation can occur. An observational example of such a large-scale transformation is found in the Solar Dynamics Observatory data.

—Observations of facular areas of the Sun using the Helioseismic and Magnetic Imager device of the Solar Dynamics Observatory allow detecting long-period oscillations in the magnetic field of facular knots with periods ranging from 30 to 250 minutes. Statistically significant oscillation modes are selected by the method of time series decomposition in empirical modes. During the observation period, which is close to the knot’s lifetime, its parameters (magnetic field, area on the magnetogram, etc.) may change noticeably, although the facular formation retains its structural identity all this time. These changes also affect the effective rigidity of the system (response to external disturbances), which leads to a change in the nature of the oscillations themselves. Based on this, we consider the observed oscillation in the magnetic field of facular knots with periods from 1 to 4 hours as the proper small oscillations of a system whose effective rigidity changes over time. A simple analytical model of the process is presented. It is shown that all three specific modes of low-frequency oscillations detected in facular knots are well described by the proposed model.

Extreme ultraviolet images taken by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory make it possible to use deep vision techniques to forecast solar wind speed—a difficult, high‐impact, and unsolved problem. At a 4 day time horizon, this study uses attention‐based models and a set of methodological improvements to deliver an 11.1% lower RMSE and a 17.4% higher prediction correlation compared to the previous work testing on the period from 2010 to 2018. Our analysis shows that attention‐based models combined with our pipeline consistently outperform convolutional alternatives. Our study shows a large performance improvement by using a 30 min as opposed to a daily sampling frequency. Our model has learned relationships between coronal holes' characteristics and the speed of their associated high‐speed streams, agreeing with empirical results. Our study finds a strong dependence of our best model on the phase of the solar cycle, with the best performance occurring in the declining phase.

Failed filament eruption remains mysterious on its initiation, magnetic environment, and erupting and failing mechanisms. We present multi-wavelength observations of a failed filament eruption and its associated hovered coronal mass ejection (hovered-CME) from limb observations of the Ahead of Solar Terrestrial Relations Observatory. On-disk observations from Solar Dynamics Observatory show the expansion of the anchored leg of an S-shaped filament during the pre-eruption phase. The main eruption starts as a sudden ejection of the erupted leg, which is followed by the appearance of EUV brightening in the S-shaped magnetic field. The brightening is spatio-temporal accompanied with hard X-ray emission enhancement, and cancellation of opposite magnetic polarities, which imply possible reconnection. After reaching the maximum displacement, the erupted material drains back to the Sun along the remaining anchored leg. The non-linear force free magnetic field extrapolation shows an S-shaped magnetic field, formed by two magnetic structures, with a strong enveloped magnetic field. The decay index at the possible apex of the filament is 0.8–1.2. Observations indicate that the failed filament eruption is triggered by tether cutting reconnection and is possibly confined by the upper magnetic field. The hovered-CME, resulting from the failed filament eruption and recording as a coronal mass ejection (CME), may cause the overestimation of the CME count.

Sunquakes (SQs) have been routinely observed in the solar photosphere, but it is only recently that signatures of these events have been detected in the chromosphere. We investigate whether signatures of SQs are common in Ultraviolet (UV) continua, which sample the solar plasma several hundred km above where SQs are typically detected. We analyse observations from the Solar Dynamics Observatory's Atmospheric Imaging Assembly (SDO/AIA) 1600 {\AA} and 1700 {\AA} passbands, for SQ signatures induced by the flares of Solar Cycle 24. We base our analysis on the 62 SQs detected in the recent statistical study presented by Sharykin & Zosovichev (2020). We find that 9 out of 62 SQ candidates produced a response that is clearly detected in running difference images from the AIA 1600 {\AA} and 1700 {\AA} channels. A binary frequency filter with a width of 2 mHz, centred on 6 mHz, was applied to the data. The first signature of each SQ was detected at distances between 5.2 Mm to 25.7 Mm from the associated flare ribbon. Time-distance and regression analysis allowed us to calculate the apparent transverse velocities of the SQs in the UV datasets and found maximum velocities as high as 41 km s-1, 87 Mm away from the SQ source. Our analysis shows that flare induced SQ signatures can be detected in the SDO/AIA 1600 {\AA} and 1700 {\AA} passbands, hinting at their presence in the lower chromosphere. There was no apparent correlation between GOES flare classification, and the appearance of the SQ at these heights.

The combination of immersive virtual reality (VR) environments and distance education has led to a new educational paradigm. In this study, an immersive VR-based distance education system is proposed to enable multiple remote users to send, share, and experience images from the Solar Dynamics Observatory (SDO) via streaming. In contrast to the conventional system in which only experts use SDO data, the proposed system provides a head-mounted-display-based visualization platform that can be easily used by experts and non-experts. Real-time SDO image streaming must be possible to realistically observe changes in the Sun and increase involvement. Thus, multichannel-based SDO image transmission was applied to increase the network bandwidth utilization. To improve the social presence of participants, realistic avatar models controlled by the motions synchronized with the user are provided. In addition, free communication is possible through verbal interactions. This allows multiple remote users to participate simultaneously without having to be physically present. A user study with 20 subjects showed that the participants could observe SDO images in a more immersive manner by using the proposed system. In addition, they experienced social presence because of the user avatar models and an enriched educational experience by conversing with and listening to experts.

Long-term variations of the magnetic field of solitary solar pores with periods in the range of 4–12 h are detected with the Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory (SDO). These long-term oscillations of the pores obviously reflect the movements of these structures as whole magnetic formations around their equilibrium position. In this article, long-period oscillations of the solar pore are studied based on the SDO data for the first time. The results are interpreted with the solution obtained earlier for eigen oscillations of the system with time-varying stiffness.

Automatic detection of solar events, especially uncommon events such as coronal dimming (CD) and coronal wave (CW), is very important in solar physics research. The CD and CW are not only related to the detection of coronal mass ejections (CMEs) but also affect space weather. In this paper, we have studied methods for automatically detecting them. In addition, we have collected and processed a dataset that includes the solar images and event records, where the solar images come from the Atmospheric Imaging Assembly (AIA) of Solar Dynamics Observatory (SDO) and the event records come from Heliophysics Event Knowledgebase (HEK). Different from the methods used before, we introduce the idea of deep learning. We train single-wavelength and multiwavelength models based on Faster R-CNN. In terms of accuracy, the single-wavelength model performs better. The multiwavelength model has a better detection performance on multiple solar events than the single-wavelength model.

Solar magnetograms are important for studying solar activity and predicting space weather disturbances1. Farside magnetograms can be constructed from local helioseismology without any farside data2-4, but their quality is lower than that of typical frontside magnetograms. Here we generate farside solar magnetograms from STEREO/Extreme UltraViolet Imager (EUVI) 304-A images using a deep learning model based on conditional generative adversarial networks (cGANs). We train the model using pairs of Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) 304-A images and SDO/Helioseismic and Magnetic Imager (HMI) magnetograms taken from 2011 to 2017 except for September and October each year. We evaluate the model by comparing pairs of SDO/HMI magnetograms and cGAN-generated magnetograms in September and October. Our method successfully generates frontside solar magnetograms from SDO/AIA 304-A images and these are similar to those of the SDO/HMI, with Hale-patterned active regions being well replicated. Thus we can monitor the temporal evolution of magnetic fields from the farside to the frontside of the Sun using SDO/HMI and farside magnetograms generated by our model when farside extreme-ultraviolet data are available. This study presents an application of image-to-image translation based on cGANs to scientific data. Farside solar magnetograms are generated from STEREO images using deep learning, with Hale-patterned active regions being well reproduced. These images can be used to monitor the temporal evolution of magnetic fields from the farside to the frontside.

We present a study of wave processes occurring in solar active region NOAA 11131 on 2010 December 10, captured by the Solar Dynamics Observatory in the 1600A, 304A, and 171A channels. For spectral analysis we employed pixelised wavelet filtering together with a developed digital technique based on empirical mode decomposition. We studied the 3-minute wave dynamics to obtain relationships with the magnetic structuring of the underlying sunspot. We found that during development of wave trains the motion path occurred along a preferential direction, and that the broadband wavefronts can be represented as a set of separate narrowband oscillation sources. These sources become visible as the waves pass through the umbral inhomogeneities caused by the differing magnetic field inclination angles. We found the spatial and frequency fragmentation of wavefronts, and deduced that the combination of narrowband spherical and linear parts of the wavefronts provide the observed spirality. Maps of the magnetic field inclination angles confirm this assumption. We detect the activation of umbral structures as the increasing of oscillations in the sources along the front ridge. Their temporal dynamics are associated with the occurrence of umbral flashes. Spatial localisation of the sources is stable over time and depends on the oscillation period. We propose that these sources are the result of wave paths along the loops extending outwards from the magnetic bundles of the umbra., 18 pages, 8 figures, accepted to publication in Royal Society Philosophical Transactions A

Coronal loops form the basic building blocks of the magnetically closed solar corona yet much is still to be determined concerning their possible fine-scale structuring and the rate of heat deposition within them. Using an improved multi-stranded loop model to better approximate the numerically challenging transition region, this article examines synthetic NASA Solar Dynamics Observatory’s (SDO) Atmospheric Imaging Assembly (AIA) emission simulated in response to a series of prescribed spatially and temporally random, impulsive and localised heating events across numerous sub-loop elements with a strong weighting towards the base of the structure: the nanoflare heating scenario. The total number of strands and nanoflare repetition times is varied systematically in such a way that the total energy content remains approximately constant across all the cases analysed. Repeated time-lag detection during an emission time series provides a good approximation for the nanoflare repetition time for low-frequency heating. Furthermore, using a combination of AIA 171/193 and 193/211 channel ratios in combination with spectroscopic determination of the standard deviation of the loop-apex temperature over several hours alongside simulations from the outlined multi-stranded loop model, it is demonstrated that both the imposed heating rate and number of strands can be realised.

Earlier studies using extreme-ultraviolet images and line-of-sight magnetograms from the Solar Dynamics Observatory (SDO) have suggested that active region (AR) plages and strong network concentrations often have small, looplike features embedded within them, even though no minority-polarity flux is visible in the corresponding magnetograms. Because of the unexpected nature of these findings, we have searched the SDO database for examples of inverted-Y structures rooted inside "unipolar" plages, with such jetlike structures being interpreted as evidence for magnetic reconnection between small bipoles and the dominant-polarity field. Several illustrative cases are presented from the period 2013--2015, all of which are associated with transient outflows from AR "moss." The triangular or dome-shaped bases have horizontal dimensions of $\sim$2--4 Mm, corresponding to $\sim$1--3 granular diameters. We also note that the spongy-textured Fe IX 17.1 nm moss is not confined to plages, but may extend into regions where the photospheric field is relatively weak or even has mixed polarity. We again find a tendency for bright coronal loops seen in the 17.1, 19.3, and 21.1 nm passbands to show looplike fine structure and compact brightenings at their footpoints. These observations provide further confirmation that present-day magnetograms are significantly underrepresenting the amount of minority-polarity flux inside AR plages and again suggest that footpoint reconnection and small-scale flux cancellation may play a major role in coronal heating, both inside and outside ARs.

Using EUV images and line-of-sight magnetograms from Solar Dynamics Observatory, we examine eight emerging bipolar magnetic regions (BMRs) in central-disk coronal holes for whether the emerging magnetic arch made any noticeable coronal jets directly, via reconnection with ambient open field as modeled by Yokoyama & Shibata. During emergence, each BMR produced no obvious EUV coronal jet of normal brightness, but each produced one or more faint EUV coronal jets that are discernible in AIA 193 Å images. The spires of these jets are much fainter and usually narrower than for typical EUV jets that have been observed to be produced by minifilament eruptions in quiet regions and coronal holes. For each of 26 faint jets from the eight emerging BMRs, we examine whether the faint spire was evidently made a la Yokoyama & Shibata. We find that (1) 16 of these faint spires evidently originate from sites of converging opposite-polarity magnetic flux and show base brightenings like those in minifilament-eruption-driven coronal jets, (2) the 10 other faint spires maybe were made by a burst of the external-magnetic-arcade-building reconnection of the emerging magnetic arch with the ambient open field, with reconnection directly driven by the arch's emergence, but (3) none were unambiguously made by such emergence-driven reconnection. Thus, for these eight emerging BMRs, the observations indicate that emergence-driven external reconnection of the emerging magnetic arch with ambient open field at most produces a jet spire that is much fainter than in previously reported, much more obvious coronal jets driven by minifilament eruptions.

Supra-arcade downflows (SADs) are dark, teardrop-shaped features descending upon flare arcades. They are thought to be the results of magnetic reconnection, but the detailed formation mechanism of SADs and their relationship to flare energy release are still unclear. In this work, we explore the thermodynamical properties of SADs in the 2011 October 22 limb flare using the observations of the Solar Dynamics Observatory/Atmospheric Imaging Assembly and an improved Differential Emission Measure (DEM) technique. Different heating events around SADs are identified and the propagation speeds of plasma heating are calculated. The first heating event starts with the increase of the emission measure at temperatures higher than 5 MK, about 2.8 minutes before the arrival of the first studied SAD. Its propagation speed is about 140 km/s, a little faster than the speed of the SAD. However, the other two events have fast propagation speeds more than 700 km/s. We suspect that the first heating event can be explained by adiabatic compression, but the others may have different causes. Besides, we observed that SADs can push away their surrounding spikes. The formation of SADs is further explained on the basis of patchy and bursty magnetic reconnection that reconnection outflows may push away surrounding plasma and leave dark lanes behind them. The reliability of the DEM results, heating and cooling mechanisms, and other SAD explanations are discussed., 15 pages, 8 figures, accepted for publication in ApJ

We study the recurring jets near AR11176 during the period 2011 March 31 17:00 UT to April 1 05:00 UT using observations from the Atmospheric Imaging Assembly (AIA) on board Solar Dynamics Observatory (SDO). Mini-filaments (mini-filament1 & 2) are found at the base of these recurring jets where mini-filament1 shows the partial signature of eruption in case of Jet1-3. However, the mini-filament2 shows a complete eruption driving a full blow-out jet (Jet4). The eruption of mini-filament2 triggers C-class flare and Jet4 eruption. The eruption of Jet4 triggers a coronal mass ejection (CME). The plane-of-sky velocity of recurring jets (Jet1-4) results in 160 km/s, 106 km/s, 151 km/s and 369 km/s. The estimated velocity of CME is 636 km/s. The continuous magnetic flux cancellation is observed at the base of the jet productive region which could be the cause of the eruption of mini-filaments and recurring jets. In the former case, the mini-filament1 shows partial eruption and first three jets (Jet1-3) are produced, but the rate of cancellation was rather low. However, in the latter case, mini-filament2 fully erupts (perhaps because of a higher cancellation rate), and this triggers a C-class flare and a CME-productive jet. At the base of first three jets (Jet1-3), the mini-filament1 causes to push the overlying dynamic complex thin loops resulting in the reconnection and drives the jet (Jet1-3) eruptions. The formation of the plasma blobs are observed during the eruption of the first jet (Jet1)., 25 Pages, 15 figures, 1 table, Accepted for publication in Solar Physics

The magnetograms of 16 active regions, observed during June–November 2015, were obtained from the Joint Science Operations Center (JSOC) from the Solar Dynamics Observatory (SDO) using the Helioseismic and Magnetic Imager (HMI) and used to determine the fractal dimensions of various magnetic field groups. The fields were divided into strong (positive and negative) and weak (positive and negative) groupings. The area-perimeter method was used to determine the fractal dimensions for the umbral and penumbral regions of the magnetograms. The fractal dimensions were found to be $1.79 \pm 0.49$ and $1.96 \pm 0.29$ for strong and weak magnetic fields, respectively. When compared to the umbral and penumbral fractal dimensions determined by Rajkumar, Haque and Hrudey (Sol. Phys.292, 170, 2017) using white light images, an inverse relationship was found, with the umbra showing lower fractal dimensions than the penumbra for the magnetic field groups compared to the intensity images. This directly implies that there is greater complexity in the penumbral magnetic field groupings than the umbral region. This has implications for models that constrain how the magnetic field groups are contained in the cooler umbral regions.

The SunPy Project developed a 13-question survey to understand the software and hardware usage of the solar-physics community. Of the solar-physics community, 364 members across 35 countries responded to our survey. We found that $99\pm 0.5$99±0.5% of respondents use software in their research and 66% use the Python scientific-software stack. Students are twice as likely as faculty, staff scientists, and researchers to use Python rather than Interactive Data Language (IDL). In this respect, the astrophysics and solar-physics communities differ widely: 78% of solar-physics faculty, staff scientists, and researchers in our sample uses IDL, compared with 44% of astrophysics faculty and scientists sampled by Momcheva and Tollerud (2015). $63\pm 4$63±4% of respondents have not taken any computer-science courses at an undergraduate or graduate level. We also found that most respondents use consumer hardware to run software for solar-physics research. Although 82% of respondents work with data from space-based or ground-based missions, some of which (e.g. the Solar Dynamics Observatory and Daniel K. Inouye Solar Telescope) produce terabytes of data a day, 14% use a regional or national cluster, 5% use a commercial cloud provider, and 29% use exclusively a laptop or desktop. Finally, we found that $73\pm 4$73±4% of respondents cite scientific software in their research, although only $42\pm 3$42±3% do so routinely.

There is no list of bipolar active regions (ARs) with reverse polarity (anti-Hale regions), although statistical investigations of such ARs (bearing the imprint of deep subphotospheric processes) are important for understanding solar-cycle mechanisms. We studied 8606 ARs from 1 January 1989 to 31 December 2018 to detect anti-Hale regions and to compile a catalog. The Solar and Heliospheric Observatory (SOHO) and the Solar Dynamics Observatory (SDO) data, as well as the Debrecen Photoheliographic Data, the Mount Wilson Observatory catalog and drawings, and the USAF/NOAA Solar Region Summary were used. Complex, ambiguous cases related to anti-Hale region identification were analyzed. Two basic and four additional criteria to identify an AR as an anti-Hale region were formulated. The basic criteria assume that: i) dominating features of an AR have to form a bipole of reverse polarity with sunspots/pores of both polarities being present; ii) magnetic connections between the opposite polarities has to be observed. A catalog of anti-Hale regions (275 ARs) is compiled. The catalog contains: NOAA number, date of the greatest total area of sunspots, coordinates, and corrected sunspot area for this date. The tilt and the most complex achieved Mount Wilson magnetic class are also provided. The percentage of anti-Hale groups meeting the proposed criteria is ~3.0% from all studied ARs, which is close to early estimations by authors who had examined each AR individually: ~2.4% by Hale and Nicholson (Ap.J. 62, 270, 1925) and ~3.1% by Richardson (Ap.J. 107, 78, 1948). The enchancement of the anti-Hale percentage in later research might be related to: i) increasing sensitivity of instruments (considering smaller and smaller bipoles); ii) the ambiguities in the anti-Hale region identification., Comment: 18 pages, 9 figures