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1. Coronal Magnetic Field Extrapolation and Topological Analysis of Fine-scale Structures during Solar Flare Precursors

   https://doi.org/10.3847/1538-4357/ad0236  

   He, Wen; Jing, Ju; Wang, Haimin; Nayak, Sushree S.; Prasad, Avijeet (November 2023, The Astrophysical Journal)

   Abstract Magnetic field plays an important role in various solar eruption phenomena. The formation and evolution of the characteristic magnetic field topology in solar eruptions are critical problems that will ultimately help us understand the origin of these eruptions in the solar source regions. With the development of advanced techniques and instruments, observations with higher resolutions in different wavelengths and fields of view have provided more quantitative information for finer structures. It is therefore essential to improve the method with which we study the magnetic field topology in the solar source regions by taking advantage of high-resolution observations. In this study, we employ a nonlinear force-free field extrapolation method based on a nonuniform grid setting for an M-class flare eruption event (SOL2015-06-22T17:39) with embedded vector magnetograms from the Solar Dynamics Observatory (SDO) and the Goode Solar Telescope (GST). The extrapolation results for which the nonuniform embedded magnetogram for the bottom boundary was employed are obtained by maintaining the native resolutions of the corresponding GST and SDO magnetograms. We compare the field line connectivity with the simultaneous GST/Hαand SDO/Atmospheric Imaging Assembly observations for these fine-scale structures, which are associated with precursor brightenings. Then we perform a topological analysis of the field line connectivity corresponding to fine-scale magnetic field structures based on the extrapolation results. The analysis results indicate that when we combine the high-resolution GST magnetogram with a larger magnetogram from the SDO, the derived magnetic field topology is consistent with a scenario of magnetic reconnection among sheared field lines across the main polarity inversion line during solar flare precursors. 

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2. Improving spatial resolution of sunspot HMI images using conditional generative adversarial networks

   https://doi.org/10.1063/5.0181507  

   Prianto, Agus; Wibowo, Ridlo Wahyudi; Putri, Gerhana Puannandra; Huda, Ibnu Nurul; Yurchyshyn, Vasyl; Malasan, Hakim Luthfi (January 2023, American Institute of Physics Conference Series)

   Solar Dynamics Observatory (SDO) spacecraft as a space-based project is able to conduct continuous monitoring of the Sun. The Helioseismic and Magnetic Imager (HMI) instrument on SDO, in particular, provides continuum images and magnetograms with a cadence of under 1 minute. SDO/HMI's spatial resolution is only about 1'', which makes it impossible to perform a good analysis on the subarcsecond scale. On the other hand, larger aperture ground-based telescopes such as the Goode Solar Telescope (GST) at the Big Bear Solar Observatory are able to achieve a better resolution (16 times better than SDO/HMI). However, ground-based telescopes like GST have limitations in terms of observation time, which can only make observations during the day in clearsky condition. The purpose of this study is to make attempts in improving the spatial resolution of images captured by HMI beyond the diffraction limit of the telescope by employing the Conditional Generative Adversarial Networks algorithm (cGAN). The cGAN model was trained using 1800 pairs of HMI and GST sunspot images. This method successfully reconstruct HMI images with a spatial resolution close to GST images, this is supported by \raisebox{-0.5ex}\textasciitilde62\% increase in the peak signal-to-noise ratio (PSNR) value and \raisebox{-0.5ex}\textasciitilde90\% decrease in the mean squared error (MSE) value. The higher resolution sunspot images produced by this model can be useful for further Solar Physics studies. 

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3. A Multimodal Dataset of SDO/HMI Magnetic Polarity Inversions for Solar Flare Forecasting

   https://doi.org/10.7910/DVN/4A7ORF  

   Mansouri, Reza; Khani, Ziba; Aydin, Berkay; Mansouri, Reza (January 2024, Harvard Dataverse)

   Magnetic polarity inversion lines (PILs) in solar active regions are key to triggering flares and eruptions. Recently, engineered PIL features have been used for predicting solar eruptions. Derived from the original PIL dataset, using line-of-sight (LoS) magnetograms provided by the Solar Dynamics Observatory's (SDO) Helioseismic and Magnetic Imager (HMI) Active Region Patches (HARPs), we provide a publicly available comprehensive dataset in a supervised format, where each instance includes a raster of Polarity Inversion Lines (PILs), one of the polarity convex hull, and a multivariate time-series of properties related to PILs. Using SDO-GOES integrated flares historical data covering May 2010 to January 2019, we have assigned each of the instances their corresponding class of flare, FQ, C, M or X. By integrating these diverse data modalities, our approach aims to improve the accuracy of solar flare predictions. Initial findings suggest that the multimodal approach can uncover new patterns and relationships, potentially leading to breakthroughs in predictive accuracy and more effective mitigation strategies against the impacts of solar activities. 

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4. Observation of solar coronal heating powered by magneto-acoustic oscillations in a moss region

   https://doi.org/10.1088/1674-4527/21/4/105  

   Hashim, Parida; Hong, Zhen-Xiang; Ji, Hai-Sheng; Shen, Jin-Hua; Ji, Kai-Fan; Cao, Wen-Da (May 2021, Research in Astronomy and Astrophysics)

   Abstract In this paper, we report the observed temporal correlation between extreme-ultraviolet (EUV) emission and magneto-acoustic oscillations in an EUV moss region, which is the footpoint region only connected by magnetic loops with million-degree plasma. The result is obtained from a detailed multi-wavelength data analysis of the region with the purpose of resolving fine-scale mass and energy flows that come from the photosphere, pass through the chromosphere and finally heat the solar transition region or the corona. The data set covers three atmospheric levels on the Sun, consisting of high-resolution broad-band imaging at TiO 7057 Å and the line of sight magnetograms for the photosphere, high-resolution narrow-band images at helium i 10830 Å for the chromosphere and EUV images at 171 Å for the corona. The 10830 Å narrow-band images and the TiO 7057 Å broad-band images are from a much earlier observation on 2012 July 22 with the 1.6 meter aperture Goode Solar Telescope (GST) at Big Bear Solar Observatory (BBSO) and the EUV 171 Å images and the magnetograms are from observations made by Atmospheric Imaging Assembly (AIA) or Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). We report the following new phenomena: (1) Repeated injections of chromospheric material appearing as 10830 Å absorption are squirted out from inter-granular lanes with a period of ∼ 5 minutes. (2) EUV emissions are found to be periodically modulated with similar periods of ∼ 5 minutes. (3) Around the injection area where 10830 Å absorption is enhanced, both EUV emissions and strength of the magnetic field are remarkably stronger. (4) The peaks on the time profile of the EUV emissions are found to be in sync with oscillatory peaks of the stronger magnetic field in the region. These findings may give a series of strong evidences supporting the scenario that coronal heating is powered by magneto-acoustic waves. 

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5. Analysis of quiet-sun turbulence on the basis of SDO/HMI and goode solar telescope data

   https://doi.org/10.1093/mnras/staa2427  

   Abramenko, Valentina I; Yurchyshyn, Vasyl B (October 2020, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT We analysed line-of-sight magnetic fields and magnetic power spectra of an undisturbed photosphere using magnetograms acquired by the Helioseismic and Magnetic Imager (HMI) on-board the Solar Dynamic Observatory and the Near InfraRed Imaging Spectrapolarimeter (NIRIS) operating at the Goode Solar Telescope of the Big Bear Solar Observatory. In the NIRIS data, we revealed thin flux tubes of 200–400 km in diameter and of 1000–2000 G field strength. The HMI power spectra determined for a coronal hole, a quiet sun, and a plage areas exhibit the same spectral index of −1 on a broad range of spatial scales from 10–20 Mm down to 2.4 Mm. This implies that the same mechanism(s) of magnetic field generation operate everywhere in the undisturbed photosphere. The most plausible one is the local turbulent dynamo. When compared to the HMI spectra, the −1.2 slope of the NIRIS spectrum appears to be more extended into the short spatial range until the cut-off at 0.8–0.9 Mm, after which it continues with a steeper slope of −2.2. Comparison of the observed and Kolmogorov-type spectra allowed us to infer that the Kolmogorov turbulent cascade cannot account for more than 35 per cent of the total magnetic energy observed in the scale range of 3.5–0.3 Mm. The energy excess can be attributed to other mechanisms of field generation such as the local turbulent dynamo and magnetic superdiffusivity observed in an undisturbed photosphere that can slow down the rate of the Kolmogorov cascade leading to a shallower resulting spectrum. 

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