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The torsional Alfvén wave is highly regarded as the carrier of the energy from the photosphere to the corona in the solar atmosphere. This paper presents a comprehensive linear analysis of the wave behavior and energy transfer within an open, twisted, divergent magnetic flux tube configuration, considering the impact of wave guide structure on the propagation of these waves using the magneto-hydrodynamic approach. The study shows that waves with frequencies between 0.001 Hz and 1 Hz can effectively penetrate the transition region, with the most efficient energy transfer occurring in the 0.1 Hz to 1 Hz frequency range. The research findings suggest that waves with certain intermediate frequencies are able to transmit energy to the coronal region of the Sun, contributing to its active heating. [ABSTRACT FROM AUTHOR]

The solar cycle is generated by a magnetohydrodynamic dynamo mechanism which involves the induction and recycling of the toroidal and poloidal components of the Sun's magnetic field. Recent observations indicate that the Babcock–Leighton (BL) mechanism – mediated via the emergence and evolution of tilted bipolar active regions – is the primary contributor to the Sun's large-scale dipolar field. Surface flux transport models and dynamo models have been employed to simulate this mechanism, which also allows for physics-based solar cycle forecasts. Recently, an alternative analytic method has been proposed to quantify the contribution of individual active regions to the Sun's dipole moment (DM). Utilizing solar cycle observations spanning a century, here, we test the efficacy of this algebraic approach. Our results demonstrate that the algebraic quantification approach is reasonably successful in estimating DMs at solar minima over the past century – providing a verification of the BL mechanism as the primary contributor to the Sun's dipole field variations. We highlight that this algebraic methodology serves as an independent approach for estimating DMs at the minima of solar cycles, relying on characteristics of bipolar solar active regions. We also show how this method may be utilized for solar cycle predictions; our estimate of the Sun's dipole field at the end of cycle 24 using this approach indicates that solar cycle 25 would be a moderately weak cycle, ranging between solar cycle 20 and cycle 24. [ABSTRACT FROM AUTHOR]

Henri Deslandres initiated imaging spectroscopy of the solar atmosphere in 1892 at Paris Observatory. He developed two kinds of spectrographs: the 'spectrohéliographe des formes', i.e. the monochromatic instrument to reveal chromospheric structures (such as filaments, prominences, plages and active regions); and the 'spectrohéliographe des vitesses', i.e. the spectroheliograph to record line profiles of cross-sections of the Sun, in order to measure the Doppler shifts of dynamic features. Deslandres moved to Meudon and hired Lucien d'Azambuja in 1899; together they built the large quadruple spectroheliograph. CaII K systematic observations of the full Sun started in 1908 and were followed in 1909 by Hα with two dedicated 3-metre spectroheliographs. Daily observations were organized by d'Azambuja who also intensively used the large 7-metre spectroheliograph for his research and thesis (1930). This paper summarizes fifty years of investigations by Mr and Mrs d'Azambuja, who explored various photospheric and chromospheric lines, obtaining special spectroheliograms with the high dispersion 7-metre instrument. They also intensively observed filaments and prominences, reported results in an extensive memoir (1948) and recorded rare solar activity events with the two 3-metre spectroheliographs, until their retirement in 1959. [ABSTRACT FROM AUTHOR]

We analyze the magnetic evolution of solar active region (AR) NOAA 11476 that, between May 9 and 10, 2012, produced a series of surge-type eruptions accompanied by GOES X-ray class-M flares. Using force-free models of the AR coronal structure and observations at several wavelengths, in previous works we studied the detailed evolution of those eruptions, relating them to the characteristic magnetic topology of the AR and reconstructing the involved reconnection scheme. We found that the eruptions were due to the ejection of minifilaments, which were recurrently ejected and reformed at the polarity-inversion line of a bipole that emerged in the middle of the positive main AR magnetic polarity. The bipole was observed to rotate for several tens of hours before the events. In this article we analyze, for the full AR and the rotating bipole, the evolution of a series of magnetic parameters computed using the Helioseismic and Magnetic Imager (HMI) vector magnetograms. We combine this analysis with estimations of the injection of magnetic energy and helicity obtained using the Differential Affine Velocity Estimator for Vector Magnetograms (DAVE4VM) method that determines, from vector magnetograms, the affine velocity field constrained by the induction equation. From our results, we conclude that the bipole rotation was the main driver that provided the magnetic energy and helicity involved in the minifilament destabilizations and ejections. The results also suggest that the observed rotation is probably due to the emergence of a kinked magnetic flux rope with negative writhe helicity. [ABSTRACT FROM AUTHOR]

The orbit of the Solar Orbiter mission carries it and the Polarimetric and Helioseismic Imager (PHI), which is onboard, away from the Sun–Earth line, opening up the first ever possibility of doing stereoscopy of solar photospheric structures. We present a method for a stereoscopic analysis of the height variations in the solar photosphere. This method enables the estimation of relevant quantities, such as the Wilson depression of sunspots and pores. We demonstrate the feasibility of the method using simulated Stokes- I continuum observations of an MHD simulation of the solar-surface layers. Our method estimates the large-scale variations in the solar surface by shifting and correlating two virtual images, mapped from the same surface feature observed from two different vantage points. The resulting vector is then introduced as an initial height estimate in the least-squares Broyden–Fletcher–Goldfarb–Shanno (BFGS) optimization algorithm to reproduce smaller scale structures. The height estimates from the simulated images reproduce well the overall height variations of the MHD simulation. We studied which viewing angles give the best results and found the optimal separation of the view points to be between 10 ∘ and 40 ∘ ; but neither viewing direction should be inclined by more than 30 ∘ from the vertical to the solar surface. The method yields reliable results if the data have a signal-to-noise ratio of 50 or higher. The influence of the spatial resolution of the observed images is considered and discussed. [ABSTRACT FROM AUTHOR]

We consider the M1.1-class solar flare occurred on July 5, 2012, at UT. This event is unique in that a helioseismic perturbation was detected in it despite its low hard X-ray flux in the 25–50 keV energy band and its very soft hard X-ray spectrum. As a rule, most of the known sunquakes have been detected in solar flares with large hard X-ray fluxes at high energies (at least up to 100–300 keV). The event under consideration contradicts the popular hypothesis about the generation of sunquakes by beams of accelerated high-energy electrons. An analysis of the available RHESSI X-ray spectra shows that they can be explained in two ways. The X-ray spectrum in the 25–50 keV energy band is explained by a power-law distribution of accelerated electrons with an power-law index of 7–9 or by the presence of a superhot plasma with a temperature –60 MK. In both cases, we are dealing with electrons of relatively low energies that either were responsible for the sunquake generation or should be considered as a secondary (accompanying) phenomenon with respect to the true cause of the photospheric perturbation. The results of a joint analysis of the X-ray and microwave spectra are presented for the first time for a helioseismically active solar flare. Our analysis shows that the spectra in both ranges can be well explained by the emission of a superhot magnetized plasma and not by accelerated electrons with a soft spectrum. However, the explanation of the spectra when considering partially magnetically trapped accelerated electrons is also possible. We have estimated the parameters of the thermal plasma, accelerated electrons, and energy fluxes of various types. We analyze the dynamics of ultraviolet and X-ray emission sources. We also present an analysis of the magnetic field structure based on vector magnetograms and the nonlinear force-free coronal magnetic field extrapolation. We discuss the mechanisms for the generation of the helioseismic perturbation during the solar flare under consideration. An eruptive process could probably be both primary and secondary causes of the sunquake. The appearance of a superhot plasma in the corona could give rise to propagating thermal fronts into the lower layers of the solar atmosphere, where helioseismic waves are excited. Our analysis does not allow the possibility of the sunquake generation by accelerated electrons with a soft spectrum to be ruled out either. [ABSTRACT FROM AUTHOR]

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]

We used magnetograms acquired with the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) to calculate and analyze spatial correlation functions and the multifractal spectra in solar active regions (ARs). The analysis was performed for two very different types of ARs: i) simple bipolar magnetic structures with regular orientation (the magnetomorphological class A1), and ii) very complex multipolar ARs (the magnetomorphological class B3). All ARs were explored at the developed phase during flareless periods. For correlation functions, the power-law and exponential approximations were calculated and compared. It was found that the exponential law holds for the correlation functions of both types of ARs within spatial scales of 1 – 36 Mm, while the power law failed to approximate the observed correlation functions. The property of multifractality was found in all ARs, being more pronounced for the complex B3-class ARs. Our results might imply that the photospheric magnetic field of an AR is a self-organized system, which, however, does not exhibit properties of self-organized criticality (SOC), and its fractal properties are an attribute of a broader (than SOC only) class of nonlinear systems. [ABSTRACT FROM AUTHOR]

The implementation of automated methods for sunspot detection is essential to obtain better objectivity, efficiency, and accuracy in identifying sunspots and analysing their morphological properties. A desired application is the contouring of sunspots. In this work, we construct sunspot contours from Solar Dynamics Observatory (SDO)/ Helioseismic and Magnetic Imager intensity images by means of an automated method based on development and application of mathematical morphology. The method is validated qualitatively – the resulting contours accurately delimit sunspots. Here, it is applied to high-resolution data (SDO intensitygrams) and validated quantitatively by illustrating a good agreement between the measured sunspot areas and the ones provided by two standard reference catalogues. The method appears to be robust for sunspot identification, and our analysis suggests its application to more complex and irregular-shaped solar structures, such as polarity inversion lines inside delta-sunspots. [ABSTRACT FROM AUTHOR]

We present the results of statistical analysis of various thermal plasma parameters and non-thermal X-ray spectra of helioseismically active (producing "sunquakes") solar flares of the 24th solar cycle up to February 2014. Two samples of flares are compared: with helioseismic activity in the form of sunquakes and a sample of flares without photospheric disturbances. The dependences of the considered flare parameters on the energy of helioseismic disturbances are also investigated. Quantitative parameters of solar flares are taken from the statistical work of the Global Energetics series by Markus Ashwanden in 2014–2019. We consider thermodynamic plasma parameters derived from the analysis of RHESSI X-ray spectra and differential emission measure (from AIA EUV images), as well as the characterization of non-thermal X-ray spectra from RHESSI. Statistical analysis confirmed that helioseismically active solar flares are characterized by significantly larger fluxes of non-thermal X-ray emission compared to flares without photospheric disturbances. A good linear relationship between helioseismic energy and the total flux of non-thermal X-ray radiation and the total energy of accelerated electrons is found. It is shown that the power-law index of the nonthermal X‑ray spectrum is not the parameter by which one can separate the two groups of flares under consideration. The analysis of the X-ray thermal spectra shows a slight difference between the flares with the sunsets. [ABSTRACT FROM AUTHOR]

Abstract The application of machine learning in solar physics has the potential to greatly enhance our understanding of the complex processes that take place in the atmosphere of the Sun. By using techniques such as deep learning, we are now in the position to analyze large amounts of data from solar observations and identify patterns and trends that may not have been apparent using traditional methods. This can help us improve our understanding of explosive events like solar flares, which can have a strong effect on the Earth environment. Predicting hazardous events on Earth becomes crucial for our technological society. Machine learning can also improve our understanding of the inner workings of the sun itself by allowing us to go deeper into the data and to propose more complex models to explain them. Additionally, the use of machine learning can help to automate the analysis of solar data, reducing the need for manual labor and increasing the efficiency of research in this field.

The methods for reducing the observations from the 150-foot tower telescope on Mt. Wilson are reviewed, and a new method for determining the poleward and rotational velocity deviations is described and applied. The flows we study are smaller than global and change with the solar cycle, so we describe them as poleward and rotational deviations rather than meridional circulation when we discuss solar surface flows. Due to a calibration problem with the data prior to 1983, only observations between 1983 and 2013 are presented at this time. After subtraction of latitude-dependent averages over the 30-year period of observation, the residual deviations in both the poleward and the rotational velocity are well synchronized and correspond to what is widely recognized as torsional oscillations. Both flow components need to be included in any model that replicates the torsional oscillations. [ABSTRACT FROM AUTHOR]

Broad-band observations of the solar photosphere began in Meudon in 1875 under the auspices of Jules Janssen. For his part, Henri Deslandres initiated imaging spectroscopy in 1892 at Paris observatory. He invented, concurrently with George Hale in Kenwood (USA), but quite independently, the spectroheliograph designed for monochromatic imagery of the solar atmosphere. Deslandres developed two kinds of spectrographs: the ' spectrohéliographe des formes ', that is, the narrow bandpass instrument to reveal chromospheric structures; and the ' spectrohéliographe des vitesses ', that is, the section spectroheliograph to record line profiles of cross sections of the Sun. This second apparatus was intended to measure the Dopplershifts of dynamic features. Deslandres moved to Meudon in 1898 to build the large quadruple spectroheliograph. The service of Hα and CaII K systematic observations was organized by Lucien d'Azambuja and continues today. The digital technology was introduced in 2002. The collection is one of the longest available: it contains sporadic images from 1893 to 1907 (during the development phase) and systematic observations along 10 solar cycles since 1908. This paper summarizes 130 years of observations, instrumental research and technical advances. [ABSTRACT FROM AUTHOR]

Cosmic rays measured through neutron monitors on Earth's surface have a strong correlation with the number of sunspots on the solar photosphere. Other indices that affect the dynamics of the heliosphere and distortions in the Earth's geomagnetic field also exhibit significant correlations. Typically, studies focus on these indices individually or combine some into a smaller set of estimators. This study uses Structural Equation Modeling to examine relationships between a broad range of parameters of solar dynamics and cosmic ray intensity (measured by the Moscow neutron monitor) across several solar cycles from 1976 to present day. The study also classifies these indices into three distinct contributions: Photosphere, Solar Wind and Terrestrial Geomagnetic Field Distortions. Regression models were built for all solar cycles and the complete cosmic ray series from 1976 to the present, resulting in good estimators with calculated p-values below 0.05 (95% confidence). Relationships among all contributions were determined using their estimators. [ABSTRACT FROM AUTHOR]

The application of machine learning in solar physics has the potential to greatly enhance our understanding of the complex processes that take place in the atmosphere of the Sun. By using techniques such as deep learning, we are now in the position to analyze large amounts of data from solar observations and identify patterns and trends that may not have been apparent using traditional methods. This can help us improve our understanding of explosive events like solar flares, which can have a strong effect on the Earth environment. Predicting hazardous events on Earth becomes crucial for our technological society. Machine learning can also improve our understanding of the inner workings of the sun itself by allowing us to go deeper into the data and to propose more complex models to explain them. Additionally, the use of machine learning can help to automate the analysis of solar data, reducing the need for manual labor and increasing the efficiency of research in this field. [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]

The distribution of magnetic fields of positive and negative polarities over the surface of the Sun was studied on the basis of synoptic maps presented by the NSO/Kitt Peak (1978 – 2016). To emphasize the contribution of weak fields the following transformation of synoptic maps was made: for each synoptic map only magnetic fields with a modulus less than 5 G (| B | ≤ 5 G ) were left unchanged, while larger or smaller fields were replaced by the corresponding threshold values +5 G or − 5 G . Cyclic variations of the magnetic-field polarity have been observed associated with two types of magnetic-field flows in the photosphere. Rush-to-the-poles (RTTP) appear near the maximum of solar activity and have the same sign as the following sunspots. The lifetime of RTTP is ∼ 3 yr, during which time they drift from latitudes 30 – 40 ∘ to the pole, causing the polarity change of the Sun's polar field. Our aim is the study of another type of variation that has the form of series of flows with individual flows of 0.5 – 1 yr with alternating polarity. These flows, called "ripples" by Ulrich and Tran (Astrophys. J.768, 189, 2013), are located in time between two RTTP and drift from the equator to latitudes of ∼ 50 ∘ . The period of variation of ripples was shown to be 1.1 yr for the northern hemisphere and 1.3 yr for the southern hemisphere. It was found that the amplitude of the variation was higher for the time intervals where the polar field had a positive sign. Within the same flow, fields of positive and negative signs developed in antiphase. Two types of flow – RTTP and ripples – together formed a unique structure that had a close connection to the magnetic solar cycle. [ABSTRACT FROM AUTHOR]

The evolution of the global solar magnetic field from the beginning of cycle 21 (mid-1970s) until the currently-ascending cycle 25 is described using photospheric full-disk and synoptic magnetograms from NSO Kitt Peak Vacuum Telescope (KPVT) 512-channel and Spectromagnetograph (SPMG) and the Synoptic Optical Long-term Investigation of the Sun (SOLIS) Vector Spectro-Magnetograph (VSM) and Global Oscillations Network Group (GONG), and Stanford University’s Wilcox Solar Observatory (WSO). The evolving strength and symmetry of the global coronal field are described by potential-field source-surface models decomposed into axisymmetric and non-axisymmetric, and even- and odd-ordered magnetic multipoles. The overall weakness of the global solar magnetic field since cycle 23 splits the 50-year observing window into the stronger, simpler, more hemispherically symmetric cycles 21 and 22 and the weaker, more complex cycles 23 and 24. An anomalously large decrease in the global solar field strength occurred during cycles 23, and an anomalously weak axial/polar field resulted from that cycle, accompanied by an anomalously weak radial interplanetary magnetic field (IMF) during cycle 23 activity minimum and a weakened radial IMF overall since cycle 23. The general long-term decline in solar field strength and the development during cycle 24 of strong swings of hemispheric and polar asymmetry are analyzed in detail, including their transfer through global coronal structural changes to dominate mean in situ interplanetary field measurements for several years. Although more symmetric than cycle 24, the rise phase of cycle 25 began with the southern leading the northern hemisphere, but the north has recovered to lead this cycle’s polar field reversal. The mean polar flux (poleward of ±60°) has reversed at each pole, so far more symmetrically than the cycle 23 and 24 polar reversals.

Recent solar physics missions have shown the definite role of waves and magnetic fields deep in the inner corona, at the chromosphere-corona interface, where dramatic and physically dominant changes occur. HiRISE (High Resolution Imaging and Spectroscopy Explorer), the ambitious new generation ultra-high resolution, interferometric, and coronagraphic, solar physics mission, proposed in response to the ESA Voyage 2050 Call, would address these issues and provide the best-ever and most complete solar observatory, capable of ultra-high spatial, spectral, and temporal resolution observations of the solar atmosphere, from the photosphere to the corona, and of new insights of the solar interior from the core to the photosphere. HiRISE, at the L1 Lagrangian point, would provide meter class FUV imaging and spectro-imaging, EUV and XUV imaging and spectroscopy, magnetic fields measurements, and ambitious and comprehensive coronagraphy by a remote external occulter (two satellites formation flying 375 m apart, with a coronagraph on a chaser satellite). This major and state-of-the-art payload would allow us to characterize temperatures, densities, and velocities in the solar upper chromosphere, transition zone, and inner corona with, in particular, 2D very high resolution multi-spectral imaging-spectroscopy, and, direct coronal magnetic field measurement, thus providing a unique set of tools to understand the structure and onset of coronal heating. HiRISE's objectives are natural complements to the Parker Solar Probe and Solar Orbiter-type missions. We present the science case for HiRISE which will address: i) the fine structure of the chromosphere-corona interface by 2D spectroscopy in FUV at very high resolution; ii) coronal heating roots in the inner corona by ambitious externally-occulted coronagraphy; iii) resolved and global helioseismology thanks to continuity and stability of observing at the L1 Lagrange point; and iv) solar variability and space climate with, in addition, a global comprehensive view of UV variability. [ABSTRACT FROM AUTHOR]

We developed a scan mirror mechanism (SMM) that enable a slit-based spectrometer or spectropolarimeter to precisely and quickly map an astronomical object. The SMM, designed to be installed in the optical path preceding the entrance slit, tilts a folding mirror and then moves the reflected image laterally on the slit plane, thereby feeding a different one-dimensional image to be dispersed by the spectroscopic equipment. In general, the SMM is required to scan quickly and broadly while precisely placing the slit position across the field-of-view (FOV). These performances are in high demand for near-future observations, such as studies on the magnetohydrodynamics of the photosphere and the chromosphere. Our SMM implements a closed-loop control system by installing electromagnetic actuators and gap-based capacitance sensors. Our optical test measurements confirmed that the SMM fulfills the following performance criteria: i) supreme scan-step uniformity (linearity of 0.08 % ) across the wide scan range (± 1005 ″ ), ii) high stability (3 σ = 0.1 ″ ), where the angles are expressed in mechanical angle, and iii) fast stepping speed (26 ms). The excellent capability of the SMM will be demonstrated soon in actual use by installing the mechanism for a near-infrared spectropolarimeter onboard the balloon-borne solar observatory for the third launch, Sunrise III. [ABSTRACT FROM AUTHOR]

Understanding structures and evolutions of the magnetic fields and plasma in multiple layers on the Sun is very important. A force-free magnetic field which is an accurate approximation of the solar corona due to the low plasma β has been widely studied and used to model the coronal magnetic structure. While the force-freeness assumption is well satisfied in the solar corona, the lower atmosphere is not force-free given the high plasma β. Therefore, a magnetohydrostatic (MHS) equilibrium which takes into account plasma forces, such as pressure gradient and gravitational force, is considered to be more appropriate to describe the lower atmosphere. This paper reviews both analytical and numerical extrapolation methods based on the MHS assumption for calculating the magnetic fields and plasma in the solar atmosphere from measured magnetograms. [ABSTRACT FROM AUTHOR]

The Hα line is an important optical line in solar observations containing the information from the photosphere to the chromosphere. To study the mechanisms of solar eruptions and the plasma dynamics in the lower atmosphere, the Chinese Hα Solar Explorer (CHASE) was launched into a Sun-synchronous orbit on October 14, 2021. The scientific payload of the CHASE satellite is the Hα Imaging Spectrograph (HIS). The CHASE/HIS acquires, for the first time, seeing-free Hα spectroscopic observations with high spectral and temporal resolutions. It consists of two observational modes. The raster scanning mode provides full-Sun or region-of-interest spectra at Hα (6559.7–6565.9 Å) and Fe I (6567.8–6570.6 Å) wavebands. The continuum imaging mode obtains full-Sun photospheric images at around 6689 Å. In this paper, we present detailed calibration procedures for the CHASE/HIS science data, including the dark-field and flat-field correction, slit image curvature correction, wavelength and intensity calibration, and coordinate transformation. The higher-level data products can be directly used for scientific research. [ABSTRACT FROM AUTHOR]

The Chinese Hα Solar Explorer (CHASE), dubbed "Xihe"—Goddess of the Sun, was launched on October 14, 2021 as the first solar space mission of China National Space Administration (CNSA). The CHASE mission is designed to test a newly developed satellite platform and to acquire the spectroscopic observations in the Hα waveband. The Hα Imaging Spectrograph (HIS) is the scientific payload of the CHASE satellite. It consists of two observational modes: raster scanning mode and continuum imaging mode. The raster scanning mode obtains full-Sun or region-of-interest spectral images from 6559.7 to 6565.9 Å; and from 6567.8 to 6570.6 Å with 0.024 Å pixel spectral resolution and 1 min temporal resolution. The continuum imaging mode obtains photospheric images in continuum around 6689 Å with the full width at half maximum of 13.4 Å. The CHASE mission will advance our understanding of the dynamics of solar activity in the photosphere and chromosphere. In this paper, we present an overview of the CHASE mission including the scientific objectives, HIS instrument overview, data calibration flow, and first results of on-orbit observations. [ABSTRACT FROM AUTHOR]

This work is part of the applications of neural networks in the study and modeling of the phenomena present in the solar photosphere. The proposed research is based on the network model generative adversaries making use of Pytorch's artificial intelligence modules. Wanted to train a neural network capable of generating groups of images of a high similarity with training images, These images correspond to physical magnitudes of the solar photosphere such as density, field magnetic, plasma speed, temperature, among others, obtained from the MURaM simulation code, although the neural network can be trained to generate images of any physical magnitude. work will focuses on magnetic field imaging in the solar photosphere. The results are presented training of the neural network, the comparison between the training images and the images generated, and the challenges to use these tools in the study of the solar photosphere are proposed, it is achieved demonstrate that GAN-type networks manage to partially recreate physical structures of the solar photosphere, with divergence values close to zero, which allows us to conclusively state that the structure created by the network is in technical terms, physically correct for the laws of magnetism, the following step in the investigation should focus on improving the network so that it can accurately recreate total structures of the solar photosphere that in turn allow evidence of a physical consistency with the MHD equations and have a higher resolution than the one generated in the current project. [ABSTRACT FROM AUTHOR]

The dynamics of the partially ionized solar atmosphere is controlled by the frequent collisions and charge exchange between the predominant neutral hydrogen atoms and charged ions. At signal frequencies below or of the order of either of the collision or charge exchange frequencies, the magnetic stress is felt by both the charged and neutral particles simultaneously. The resulting neutral-mass loading of the ions leads to the rescaling of the effective ion-cyclotron frequency (it becomes the Hall frequency), and the resultant effective Larmor radius becomes of the order of few kms. Thus, the finite Larmor radius effect that manifests as the ion and neutral pressure stress tensors operates over macroscopic scales. Whereas parallel and perpendicular (with respect to the magnetic field) viscous momentum transport competes with the Ohm and Hall diffusion of the magnetic field in the photosphere–chromosphere, the gyroviscous effect becomes important only in the transition region between the chromosphere and corona, where it competes with the ambipolar diffusion. The wave propagation in the gyroviscous effect-dominated medium depends on the plasma β (a ratio of the thermal and magnetic energies). The abundance of free energy makes gyro waves unstable with the onset condition exactly opposite of the Hall instability. However, the maximum growth rate is identical to the Hall instability. For a flow gradient of |${\sim} 0.1 \, \mbox{s}^{-1}$|⁠ , the instability growth time is 1 min. Thus, the transition region may become subject to this fast-growing gyroviscous instability. [ABSTRACT FROM AUTHOR]

We have studied two regions located at the base of a coronal hole. For the K₁ intensity minima and K₂ peaks, which form between the upper photosphere and the lower chromosphere and in the lower chromosphere respectively, a number of Ca II line parameters have been computed. We have improved the determination technique for ∆λᴋ₁ᵥ and ∆λᴋ₁ᵣ, ∆λᴋ₂ᵥ and ∆λᴋ₂ᵣ line profile shifts, including certain cases when their direct determination was complicated. We have determined Iᴋ₁ᵥ, Iᴋ₁ᵣ, Iᴋ₂ᵥ, Iᴋ₂ᵣ intensities, K₁ minima and K₂ peaks separations SEPᴋ₁ = ∆λᴋ₁ᵣ – ∆λᴋ₁ᵥ, SEPᴋ₂ = ∆λᴋ₂ᵣ – ∆λᴋ₂ᵥ, respectively. We have constructed scatter plots and have computed correlation relationships between parameters relating to different levels of atmosphere. We have obtained the following results. The intensities observed in the lower and middle chromosphere are connected closer than intensities related to the upper photosphere and middle chromosphere. The structures with a stronger magnetic field are brighter at the upper photosphere and lower chromosphere levels as compared to the structures with a weaker magnetic field. K₁ minima separations are of greater value for the structures with a stronger magnetic field relative to the structures with a weaker magnetic field, whereas K₂ peaks separations demonstrate the opposite behavior. They are lower for the structures with a stronger magnetic field. It is true not only for the chosen structures belonging to quiet regions but also for the plage, though we need additional statistics for plages. The relation between shifts of K₁ minima and K₂ peak intensities for violet and red wings appeared to be weak. This may be due to the considerable contribution of random movements to the velocity field at the upper photosphere and lower chromosphere levels or due to different forming levels for the profile violet and red wings.

Center to Limb Variations (CLV) or limb darkening allow us to characterize different layers of the solar atmosphere. It is possible to use different wavelengths. These variations give information about the quality of the images observed from ground-based observatories that continuously observe the Sun. Also, a brief description of how the Center to Limb Variations can help to describe the stellar atmospheres, specifically in eclipsing binary stars and stars with exoplanets. [ABSTRACT FROM AUTHOR]

Virtual and augmented reality technology is becoming more commonly available within a plethora of environments in which we exist, including educational environments. With advances in technology, and more exposure to its capabilities, there is a greater expectations and reliance on it. However, much of the hardware (and some of the software) which makes this technology usable is expensive and inaccessible to many. This article introduces a method for capturing and providing cost-effective virtual reality experiences, used here as a tool to give students improved accessory data and context regarding geological lab samples. The method introduced utilises the Google Cardboard camera app and Google Cardboard viewers. The virtual reality environment created is a mini-immersive experience that could be provided to students, or collected by students for their own use. The article reports results from a study of 20 participants who answered a questionnaire outlining their experiences of implementing the method. They responded positively, highlighting the applicability of the method to the task, the ease of use of tool and the accessibility of technology. Image quality of the method was raised as an area for improvement.

The aim of this work is to create a long (410-yr) series of average annual total sunspot areas AR – a physically based index of sunspot activity. We use telescopic observations of the AR index in 1832–1868 and 1875–2020, as well as the relationship between AR and long series of sunspot indices SN (international sunspot numbers, version 2.0) and sunspot groups GN (Svalgaard and Schatten's version of group sunspot numbers). The Royal Greenwich Observatory series after 1976 is extended by the Kislovodsk Mountain Astronomical Station data. When reconstructing AR from SN , it is taken into account that the function AR   =   f (SN) has a non-linear systematic character and uncertainty associated with the heterogeneity of these indices. Therefore, in addition to modelling the most probable AR values, predictive limits of reconstruction uncertainty are determined. In the interval 1610–1699 we carried out the reconstruction on the basis of the GN series using the previously proposed decomposition in pseudo-phase space (DPS) method. The resulting series NO21y is freely available online. We show that for this series the empirical Gnevyshev–Ohl rule and Waldmeier effect are fulfilled. Wavelet analysis reveals periodicities of 8.4–13.8 yr for the main cycle (with a sharp decrease of the period before the global Maunder and Dalton minima) and a two-component Gleissberg cycle with typical periods of 50–60 and 90–110 yr. [ABSTRACT FROM AUTHOR]

In this paper it is shown that rope-rope magnetic reconnection in the solar wind can enhance multifractality in the inertial subrange and drive intermittent magnetic field turbulence. Additionally, it is shown that Lagrangian coherent structures can unveil the transport barriers of magnetic elements in the quiet Sun. [ABSTRACT FROM AUTHOR]

Internal gravity waves have been observed in the Earth's atmosphere and oceans, on Mars and Jupiter, and in the Sun's atmosphere. Despite ample evidence for the existence of propagating gravity waves in the Sun's atmosphere, we still do not have a full understanding of their characteristics and overall role for the dynamics and energetics of the solar atmosphere. Here, we present a new approach to study the propagation of gravity waves in the solar atmosphere. It is based on calculating the threedimensional cross-correlation function between the vertical velocities measured at different heights. We apply this new method to a time series of cospatial and co-temporal Doppler images obtained by SOHO/MDI and Hinode/SOT as well as to simulations of upward propagating gravity wavepackets. We show some preliminary results and outline future developments. [ABSTRACT FROM AUTHOR]

High-resolution observations of polar crown and high-latitude filaments are scarce. We present a unique sample of such filaments observed in high-resolution H α narrow-band filtergrams and broad-band images, which were obtained with a new fast camera system at the Vacuum Tower Telescope (VTT), Tenerife, Spain. The Chromospheric Telescope (ChroTel) provided full-disk context observations in H α , Ca ii K, and He i 10830 Å. The Helioseismic and Magnetic Imager (HMI) and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) provided line-of-sight magnetograms and ultraviolet (UV) 1700 Å filtergrams, respectively. We study filigree in the vicinity of polar crown and high-latitude filaments and relate their locations to magnetic concentrations at the filaments' footpoints. Bright points are a well studied phenomenon in the photosphere at low latitudes, but they were not yet studied in the quiet network close to the poles. We examine size, area, and eccentricity of bright points and find that their morphology is very similar to their counterparts at lower latitudes, but their sizes and areas are larger. Bright points at the footpoints of polar crown filaments are preferentially located at stronger magnetic flux concentrations, which are related to bright regions at the border of supergranules as observed in UV filtergrams. Examining the evolution of bright points on three consecutive days reveals that their amount increases while the filament decays, which indicates they impact the equilibrium of the cool plasma contained in filaments. [ABSTRACT FROM AUTHOR]

Ground-based solar observations are severely affected by Earth's turbulent atmosphere. As a consequence, observed image quality and prevailing seeing conditions are closely related. Partial correction of image degradation is nowadays provided in real time by adaptive optics (AO) systems. In this study, different metrics of image quality are compared with parameters characterizing the prevailing seeing conditions, i.e. Median Filter Gradient Similarity (MFGS), Median Filter Laplacian Similarity (MFLS), Helmli–Scherer mean, granular rms-contrast, differential image motion, and Fried-parameter r 0 . The quiet-Sun observations at disk center were carried out at the Vacuum Tower Telescope (VTT), Observatorio del Teide (OT), Izaña, Tenerife, Spain. In July and August 2016, time series of short-exposure images were recorded with the High-resolution Fast Imager (HiFI) at various wavelengths in the visible and near-infrared parts of the spectrum. Correlation analysis yields the wavelength dependence of the image quality metrics and seeing parameters, and Uniform Manifold Approximation and Projection (UMAP) is employed to characterize the seeing on a particular observing day. In addition, the image quality metrics and seeing parameters are used to determine the field dependence of the correction provided by the AO system. Management of high-resolution imaging data from large-aperture, ground-based telescopes demands reliable image quality metrics and meaningful characterization of prevailing seeing conditions and AO performance. The present study offers guidance on how retrieving such information ex post facto. [ABSTRACT FROM AUTHOR]