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Image super-resolution is an important subject in image processing and recognition. Here, we present an attention-aided convolutional neural network for solar image super-resolution. Our method, named SolarCNN, aims to enhance the quality of line-of-sight (LOS) magnetograms of solar active regions (ARs) collected by the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory (SOHO). The ground-truth labels used for training SolarCNN are the LOS magnetograms collected by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. Solar ARs consist of strong magnetic fields in which magnetic energy can suddenly be released to produce extreme space-weather events, such as solar flares, coronal mass ejections, and solar energetic particles. SOHO/MDI covers Solar Cycle 23, which is stronger with more eruptive events than Cycle 24. Enhanced SOHO/MDI magnetograms allow for better understanding and forecasting of violent events of space weather. Experimental results show that SolarCNN improves the quality of SOHO/MDI magnetograms in terms of the structural similarity index measure, Pearson's correlation coefficient, and the peak signal-to-noise ratio. [ABSTRACT FROM AUTHOR]

Solar activity is often caused by the evolution of solar magnetic fields. Magnetic field parameters derived from photospheric vector magnetograms of solar active regions (ARs) have been used to analyze and forecast eruptive events, such as solar flares and coronal mass ejections. Unfortunately, the most recent Solar Cycle 24 was relatively weak with few large flares, though it is the only solar cycle in which consistent time-sequence vector magnetograms have been available through the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) since its launch in 2010. In this work, we look into another major instrument, namely the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory (SOHO) from 1996 to 2010. The data archive of SOHO/MDI covers a more active Solar Cycle 23 with many large flares. However, SOHO/MDI only has line-of-sight (LOS) magnetograms. We propose a new deep learning method, named MagNet, to learn from combined LOS magnetograms, B x and B y , taken by SDO/HMI, along with H α observations collected by the Big Bear Solar Observatory (BBSO), and to generate synthetic vector components B x ′ and B y ′ of ARs. These generated vector components, together with observational LOS data, would form vector magnetograms for SOHO/MDI. In this way, we can expand the availability of vector magnetograms to the period from 1996 to present. Experimental results demonstrate the good performance of the MagNet method. To our knowledge, this is the first time that deep learning has been used to generate photospheric vector magnetograms of ARs for SOHO/MDI using SDO/HMI and H α data. [ABSTRACT FROM AUTHOR]

In December 2020, at the 2-m telescope of the Terskol branch of the Institute of Astronomy, we carried out spectrophotometric observations in the range of ~0.36–0.95 μm of nine asteroids of the Main Belt (19 Fortuna, 52 Europa, 102 Miriam, 177 Irma, 203 Pompeja, 250 Bettina, 266 Aline, 379 Huenna, and 383 Janina), which were near perihelia of their orbits with significant eccentricities, in order to determine the effect of maximum subsolar temperatures on them. The study of the reflecance spectra of asteroids showed that the mineralogy of their matter is low-temperature and basically corresponds to the previously established classification (Tholen, 1989; Bus and Binzel, 2002). But in the spectra of eight asteroids (with the exception of 102 Miriam), for the first time, significant deviations were found that go beyond the spectral boundaries of their taxonomic types in the absence of noticeable changes in the spectral transparency of the Earth's atmosphere at time intervals shorter and longer than the exposure time. Such features can be interpreted as light scattering by a mobile (or inhomogeneous) dusty exosphere that forms near these asteroids near perihelion in the process of ice sublimation at the highest subsolar temperatures. In addition, as follows from the data obtained from the GOES-16 and SOHO satellites, the considered asteroids at the end of November 2020 (10 days before the start of our observations) were affected by a strong solar flare in the X-ray range, and then by a shock wave in solar wind caused by a coronal mass ejection on the Sun, which was quasi-synchronous with the X-ray flare. This probably led to an additional increase in the sublimation activity of the asteroids and manifestations of a derivative dusty exosphere. [ABSTRACT FROM AUTHOR]

In this article, we investigate the formation and disruption of a coronal sigmoid from the active region (AR) NOAA 11909 on 07 December 2013, by analyzing multi-wavelength and multi-instrument observations. Our analysis suggests that the formation of the sigmoid initiated ≈ 1 hour before its eruption through a coupling between two twisted coronal loop systems. This sigmoid can be well regarded as of 'transient' class due to its short lifetime as the eruptive activities started just after ≈ 20 min of its formation. A comparison between coronal and photospheric images suggests that the coronal sigmoid was formed over a simple β -type AR which also possessed dispersed magnetic field structure in the photosphere. The line-of-sight photospheric magnetograms also reveal small-scale flux cancellation events near the polarity inversion line, and overall flux cancellation during the extended pre-eruption phase which suggest the role of tether-cutting reconnection toward the build-up of the flux rope. The disruption of the sigmoid proceeded with a two-ribbon eruptive M1.2 flare (SOL2013-12-07T07:29). In radio frequencies, we observe type III and type II bursts in meter wavelengths during the impulsive phase of the flare. The successful eruption of the flux rope leads to a fast coronal mass ejection (with a linear speed of ≈ 1085 km s−1) in SOHO/LASCO field-of-view. During the evolution of the flare, we clearly observe typical "sigmoid-to-arcade" transformation. Prior to the onset of the impulsive phase of the flare, flux rope undergoes a slow rise (≈ 15 km s−1) which subsequently transitions into a fast eruption (≈ 110 km s−1). The two-phase evolution of the flux rope shows temporal associations with the soft X-ray precursor and impulsive phase emissions of the M-class flare, respectively, thus pointing toward a feedback relationship between magnetic reconnection and early CME dynamics. [ABSTRACT FROM AUTHOR]

Rapidly decaying long-period oscillations often occur in hot coronal loops of active regions associated with small (or micro-) flares. This kind of wave activity was first discovered with the SOHO/SUMER spectrometer from Doppler velocity measurements of hot emission lines, thus also often called "SUMER" oscillations. They were mainly interpreted as global (or fundamental mode) standing slow magnetoacoustic waves. In addition, increasing evidence has suggested that the decaying harmonic type of pulsations detected in light curves of solar and stellar flares are likely caused by standing slow-mode waves. The study of slow magnetoacoustic waves in coronal loops has become a topic of particular interest in connection with coronal seismology. We review recent results from SDO/AIA and Hinode/XRT observations that have detected both standing and reflected intensity oscillations in hot flaring loops showing the physical properties (e.g., oscillation periods, decay times, and triggers) in accord with the SUMER oscillations. We also review recent advances in theory and numerical modeling of slow-mode waves focusing on the wave excitation and damping mechanisms. MHD simulations in 1D, 2D and 3D have been dedicated to understanding the physical conditions for the generation of a reflected propagating or a standing wave by impulsive heating. Various damping mechanisms and their analysis methods are summarized. Calculations based on linear theory suggest that the non-ideal MHD effects such as thermal conduction, compressive viscosity, and optically thin radiation may dominate in damping of slow-mode waves in coronal loops of different physical conditions. Finally, an overview is given of several important seismological applications such as determination of transport coefficients and heating function. [ABSTRACT FROM AUTHOR]

The study of the solar energetic particle events (SEPs) and their association with solar flares and other activities are very crucial to understand the space weather. Keeping this in view, here we present the study of SEPs (intensity ≥ 10 pfu) during the solar cycles 21–24 (1976–2017) in > 10 MeV energy channels associated with solar flares. For our analysis, we have used the data from different instruments onboard SOHO satellite. We have examined the flare size, source location, coronal mass ejections (CMEs) characteristics of associated SEPs. About 31% and 69% of the SEPs were originated from the eastern and western solar hemisphere, respectively. The average CME speed and width were 1238 km s - 1 and 253 ∘ , respectively. About 58% SEPs were associated with halo CMEs and 42% of SEPs associated with CMEs width varying from 10 ∘ to 250 ∘ , respectively. [ABSTRACT FROM AUTHOR]