Solar Physics Research Articles

Editorial: The Sun seen with the Atacama Large mm and sub-mm array (ALMA)—First results1

et al. comes next, where the results on the temperature structure of the chromosphere, the chromospheric Figure 1. ALMA images of the Sun at 1.3 mm (band 6). Left: Full disk image obtained by scanning with a single dish; the spatial resolution is 30 . Right: High resolution (1 ) image of the region around the sunspot, obtained in interferometric mode with mosaicking. Both images were obtained on December 18, 2015, during the commissioning period and were processed by the authors for better visibility of the disk features.network and spicules are presented, followed by the research article by Tarr et al., which compares the 23 3 mm brightness temperature with the Hα line width in the weak solar network. (Rutten, 2017), with brilliant ideas and acute but constructive criticism. He will be remembered by the 45 entire solar physics community, and we dedicate this Research Topic to his memory.This work makes use of the following ALMA data: ADS/JAO.ALMA.2011.0.00020.SV. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC 48 (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic

A ‘coronal-mass-ejection’ model for flares in Sagittarius A*

ABSTRACT High-resolution near-infrared observations with GRAVITY instrument have revealed rapid orbital motions of a hotspot around Sagittarius A* (Sgr A*), the supermassive black hole in our Galactic Centre, during its three bright flares. The projected distances of the spot to the black hole are measured and seem to increase with time. The values of distance, combined with the measured orbiting time, imply that the spot is rotating with a super-Keplerian velocity. These results are hard to understand if the spot stays within the accretion flow thus provides strong constraints on theoretical models for flares. Previously we have proposed a ‘CME’ model for the flares by analogy with the coronal-mass-ejection model in solar physics. In that model, magnetic reconnection occurred at the surface of the accretion flow results in the formation of flux ropes, which are then ejected out. Energetic electrons accelerated in the current sheet flow into the flux rope region and their radiation is responsible for the flares. In this paper, we apply the model to the interpretation of the GRAVITY results by calculating the dynamics of the ejected flux rope, the evolution of the magnetic field and the energy distribution of accelerated electrons, and the radiation of the system. We find that the model can well explain the observed light curve of the flares, the time-dependent distance, and the super-Keplerian motion of the hotspot. It also explains why the light curve of some flares has double peaks.

Newcomb–Benford Law as a generic flag for changes in the derivation of long-term solar terrestrial physics timeseries

Abstract The Newcomb–Benford Law (NBL) prescribes the probability distribution of the first digit of variables which explore a broad range under conditions including aggregation. Long-term space weather relevant observations and indices necessarily incorporate changes in the contributing number and types of observing instrumentation over time and we find that this can be detected solely by comparison with the NBL. It detects when upstream solar wind magnetic field high resolution OMNI interplanetary magnetic field incorporated new data from the WIND and Advanced Composition Explorer spacecraft after 1995. NBL comparison can detect underlying changes in the geomagnetic auroral electrojet index (activity-dependent background subtraction) and the SuperMAG electrojet index (different station types) that select individual stations showing the largest deflection, but not where station data are averaged, as in the SuperMAG ring-current index. As composite indices become more widespread across the geosciences, the NBL may provide a generic, data processing-independent flag indicating changes in the constituent raw data, calibration, or sampling method.

The case for solar full-disk spectral diagnostics: Chromosphere to corona

In the context of the recent call for white papers for the Decadal Survey for Solar and Space Physics (Heliophysics) 2024–2033, we present the argument that spatially-resolved spectral diagnostics over the full solar disk should be made a high-priority goal in Heliophysics and lead to the development of a mission concept that has the potential to become a cornerstone of the Heliophysics System Observatory (HSO). We claim that a mission providing consistent full-disk sampling of plasma properties (Doppler-shifts, non-thermal velocities, electron densities, elemental composition, etc.) of the chromosphere-corona system at the dynamic timescales of solar eruptive phenomena will revolutionize the field by adding the spectral diagnostics capability to the highly successful concept of full-disk imaging, everywhere, all the time, represented by the Solar Dynamics Observatory (SDO). We argue for it to be developed by the end of the current Decadal Survey cycle around the lessons learned from spectroscopic missions in the current NASA development pipeline, that include innovative strategies for faster integration of large fields-of-view, and comprehensive temperature coverage.

Project Sun Gazers

An actual task of modern solar physics is the prediction of geoeffective phenomena, which include the fast solar wind, flares, and coronal plasma ejections that cause perturbations of the geomagnetic field in near-Earth space. Some of these disturbances are well known as magnetic storms. The goal of the Sun Gazers project is to create a database, three-dimensional visualization and forecast of the events described above. This database will allow us to match initial and boundary conditions for MHD-modeling. Visualization is necessary for visual comparison and analysis of the events of the above database.

On-Orbit Performance of Pd/4H-SiC Schottky UV Detectors in a Low-Earth Orbit

The monitoring of solar ultraviolet radiation from a space platform is now considered essential for a wide range of fieldsincluding solar physics, atmospheric science and astrobiology. 4H-Silicon Carbide (4H-SiC) is a superior alternative toconventional materials like silicon for the fabrication of UV detectors for adverse space conditions due to its inherentradiation hardness and visible-blind nature. This paper describes the space qualification and deployment of indigenouslydeveloped Pd/4H-SiC Schottky UV detectors in a low-earth orbit (LEO) and their on-board performance. Two SiC UVdetectors were flown as a rad-hard sun detection sensor in the nanosatellite INS-2TD. The sensor has carried out solar UVflux observations continuously since its launch in February 2022 and the data gathered during the first seven months offlight is discussed in this paper.

Strategic Study for the Development of Solar Physics in Space

太阳物理学是研究太阳上发生的物理过程及其对行星际空间环境影响的学科。太阳是人类唯一可以进行细致探测的恒星，也是天然的多尺度过程并存的等离子体实验室，同时，太阳活动直接影响日地空间环境和人类地球家园的宜居性，剧烈的太阳活动如耀斑和日冕物质抛射还会影响人类的航天航空、通信导航、电网等高科技活动与设施。因此对太阳物理的研究不仅是理解浩瀚宇宙的基石，也是理解日地联系和行星宜居性的基础，同时还是国家在航天和空间安全领域的战略需求。21世纪以来，随着卫星探测技术发展，太阳物理学进入了全新的发展阶段。本文梳理了近年来太阳物理学在空间探测中的发展态势，凝练中国太阳物理学未来空间探测发展的重点领域，优化学科布局，推进太阳物理的高质量发展。

Asian States and the Arctic Ocean

Asian States and the Arctic Ocean Hide Sakaguchi According to solar physics data, the earth receives 7,400 quadrillion kilojoules (kJ) of energy from the sun each day. From this energy hitting the earth, it is estimated that roughly 80 trillion kJ is available to humans through the food chain from plants and animals. The amount of energy from food that each individual human needs each day is approximately 10 thousand kJ. Thus, solar energy can feed at most 8 billion people through the food chain from plants and animals. According to World Population Prospects 2022, the global population reached 8 billion in November 2022. The populations of China and India are each more than 1.4 billion, and other Asian countries such as Indonesia, Pakistan, Bangladesh, Japan, the Philippines, Vietnam, and Thailand are also among the top twenty largest countries by population. The sum of the populations in these nine countries alone is 3.9 billion. Thus, we should be aware that world population has already reached earth's capacity, and 50% of these people are concentrated in Asia. And yet, world population is projected to continue growing at a high rate for several decades, so we must intensify food production. However, doing so requires huge amounts of energy—in fact, 4% of global electric energy currently consumed is to produce nitrogen fertilizer in support of food production. Consequently, population, food, resources, energy, and the environment are all interrelated global problems, and we are now at a critical point. However, there exists a buffer to alleviate some of the tension of these problems—the oceans. The oceans can work to produce food and energy. At the same time, science has proven that the oceans can support carbon and nitrogen fixation, enabling these elements to support plant life and be used in fertilizers. The Arctic Ocean, especially, has great potential for those purposes. The Arctic Ocean is considered a large polar sea surrounded by the following five coastal states: Canada, Denmark (via Greenland), Norway (via Svalbard), Russia, and the United States (via Alaska). In terms of economic exclusive zones (EEZs), the largest area of Arctic Ocean by country belongs to Canada, 5.3 million square kilometers, while the second-largest belongs to Russia at 4.3 million square kilometers. Therefore, to address the global problems mentioned above, collaboration and cooperation between Asian states, which are largely driving global population growth, and the Arctic states, especially Canada with the largest share of the Arctic Ocean within its EEZ, are essential. International cooperation must be carried out through the development and conservation of the Arctic Ocean. In this context, projects to introduce the [End Page 3] ocean and its development potential to Asian states to attract investment, scientific research, and technological development are of the highest importance. This ocean is truly the last frontier and may be key to our last stand to save the earth. [End Page 4] Hide Sakaguchi President Ocean Policy Research Institute of the Sasakawa Peace Foundation Copyright © 2023 The National Bureau of Asian Research, Seattle, Washington

Effects of solar evolution on finite acquisition time of Fabry–Perot interferometers in high resolution solar physics

Context. The Visible Tunable Filter (VTF) imaging spectropolarimeter will be operated at the Daniel K. Inouye Solar Telescope (DKIST) in Hawaii. Due to its capability in resolving dynamic fine structure of smaller than 0.05 arcsec, the finite acquisition time of typically 11 s affects the measurement process and potentially causes errors in deduced physical parameters. Aims. We estimate these errors and investigate ways of minimising them. Methods. We mimicked the solar surface using a magnetohydrodynamic simulation with a spatially averaged vertical field strength of 200 G. We simulated the measurement process scanning through successive wavelength points with a temporal cadence of 1 s. We synthesised Fe 1617.3 nm for corresponding snapshots. In addition to the classical composition of the line profile, we introduce a novel method where the intensity in each wavelength point is normalised using the simultaneous continuum intensity, and then multiplied by the temporal mean of the continuum intensity. Milne-Eddington inversions were used to infer the line-of-sight velocity, vlos, and the vertical (longitudinal) component of the magnetic field, Blos. Results. We quantify systematic errors, defining the temporal average of the simulation during the measurement as the truth. We find that with the classical composition of the line profiles, errors exceed the sensitivity for vlos, and in filigree regions also for Blos. The novel method that includes normalisation reduces the measurement errors in all cases. Spatial binning without reducing the acquisition time decreases the measurement error slightly. Conclusions. The evolutionary timescale in inter-granular lanes, in particular in areas with magnetic features (filigree), is shorter than the timescale within granules. Hence, depending on the science objective, fewer accumulations could be used for strong magnetic field in inter-granular lanes and more accumulations could be used for the weak granular magnetic fields. As a key result of this investigation, we suggest including the novel method of normalisation in corresponding data pipelines.

Propagating and Stationary Bright Knots in the Quiet Sun

The question of what heats the solar chromosphere and corona remains one of the most important puzzles in solar physics and astrophysics. Up to now, two mechanisms are considered to work in heating the chromosphere and corona: magnetic reconnection and wave (turbulent flow) dissipation. But it is still not understood which mechanism is dominant. To solve the heating problem, one important topic at this stage is that we should understand how much energy is contributing from the two mechanisms respectively to the heating. In the quiet Sun, the thermal energy signal is observed as brightenings. Here we report two kinds of bright knots with a total of 3605 in the chromosphere of the quiet Sun, using the data from the New Vacuum Solar Telescope at Yunnan Observatories. The first kind of 1537 bright knots, which is first detected in chromospheric fibrils where waves and their dissipation are ubiquitous, propagates along these fibrils with velocities from 5 to 69 km s−1. The second kind of 2068 knots keeps stationary, and always appears at the footpoints of these fibrils where network magnetic fields exist, suggesting that magnetic reconnection locally produces these stationary knots. Based on the observations of thousands of bright knots, we display the different distribution patterns of the two kinds of bright knots in the quiet Sun, and deduce that half of the energy for heating the chromosphere is supplied by wave dissipation, and the other half by magnetic reconnection.

Обзор и сравнение особенностей МГД-волн на Солнце и в магнитосфере Земли

Magnetohydrodynamic (MHD) waves play a crucial role in the plasma processes of stellar atmospheres and planetary magnetospheres. Wave phenomena in both media are known to have similarities and unique traits typical of each system.
 MHD waves and related phenomena in magnetospheric and solar physics are studied largely independently of each other, despite the similarity in properties of these media and the common physical foundations of wave generation and propagation. A unified approach to studying MHD waves in the Sun and Earth's magnetosphere opens up prospects for further progress in these two fields.
 The review examines the current state of research into MHD waves in the Sun’s atmosphere and Earth's magnetosphere. It outlines the main features of the wave propagation media: their structure, scales, and typical parameters. We describe the main theoretical models applied to wave behavior studies; discuss their advantages and limitations; compare characteristics of MHD waves in the Sun’s atmosphere and Earth’s magnetosphere; and review observation methods and tools to obtain information on waves in various media.

Review and comparison of MHD wave characteristics at the Sun and in Earth’s magnetosphere

Magnetohydrodynamic (MHD) waves play a crucial role in the plasma processes of stellar atmospheres and planetary magnetospheres. Wave phenomena in both media are known to have similarities and unique traits typical of each system.
 MHD waves and related phenomena in magnetospheric and solar physics are studied largely independently of each other, despite the similarity in properties of these media and the common physical foundations of wave generation and propagation. A unified approach to studying MHD waves in the Sun and Earth's magnetosphere opens up prospects for further progress in these two fields.
 The review examines the current state of research into MHD waves in the Sun’s atmosphere and Earth's magnetosphere. It outlines the main features of the wave propagation media: their structure, scales, and typical parameters. We describe the main theoretical models applied to wave behavior studies; discuss their advantages and limitations; compare characteristics of MHD waves in the Sun’s atmosphere and Earth’s magnetosphere; and review observation methods and tools to obtain information on waves in various media.

Classification of Solar Radio Spectrum Based on Swin Transformer

Solar radio observation is a method used to study the Sun. It is very important for space weather early warning and solar physics research to automatically classify solar radio spectrums in real time and judge whether there is a solar radio burst. As the number of solar radio burst spectrums is small and uneven, this paper proposes a classification method for solar radio spectrums based on the Swin transformer. First, the method transfers the parameters of the pretrained model to the Swin transformer model. Then, the hidden layer weights of the Swin transformer are frozen, and the fully connected layer of the Swin transformer is trained on the target dataset. Finally, parameter tuning is performed. The experimental results show that the method can achieve a true positive rate of 100%, which is more accurate than previous methods. Moreover, the number of our model parameters is only 20 million, which is 80% lower than that of the traditional VGG16 convolutional neural network with more than 130 million parameters.

Deciphering the birth region, formation, and evolution of ambient and transient solar wind using heavy ion observations

This paper outlines key scientific topics that are important for the development of solar system physics and how observations of heavy ion composition can address them. The key objectives include, 1) understanding the Sun’s chemical composition by identifying specific mechanisms driving elemental variation in the corona. 2) Disentangling the solar wind birthplace and drivers of release by determining the relative contributions of active regions (ARs), quiet Sun, and coronal hole plasma to the solar wind. 3) Determining the principal mechanisms driving solar wind evolution from the Sun by identifying the importance and interplay of reconnection, waves, and/or turbulence in driving the extended acceleration and heating of solar wind and transient plasma. The paper recommends complementary heavy ion measurements that can be traced from the Sun to the heliosphere to properly connect and study these regions to address these topics. The careful determination of heavy ion and elemental composition of several particle populations, matched at the Sun and in the heliosphere, will permit for a comprehensive examination of fractionation processes, wave-particle interactions, coronal heating, and solar wind release and energization that are key to understanding how the Sun forms and influences the heliosphere.

MAFIAT: Magnetic field analysis tools

The magnetic twist is one of the key defining parameters of solar flux ropes (FRs). The routine computation of the winding of magnetic field lines, referred to as the twist, has the potential to lead to significant advancement in the field of solar physics and solar—terrestrial research, e.g., by enabling more accurate investigations of FR morphology, stability, and temporal evolution. However, this has been hampered by the axial-dependence of the solution and the availability of simpler, albeit approximate, methods. Here we introduce the Magnetic Field Analysis Tools (MAFIAT) python library and Jupyter notebooks for the computation and exploitation of this quantity. The required axis location is specified manually by the user, either with their own preferred method, or using the twist number calculated from the parallel current by Magnetic Field Analysis Tools. The notebooks allow users to create a variety of novel visualisations of FRs and their twist distributions for scientific study. Magnetic Field Analysis Tools is written in Python and is released under the BSD 3-Clause Licence. Code available at: https://github.com/pricedj/mafiat.

The future of auroral E-region plasma turbulence research

The heating caused by ionospheric E-region plasma turbulence has documented global implications for the energy transfer from space into the terrestrial atmosphere. Traveling atmospheric disturbances, neutral wind motion, energy deposition rates, and ionospheric conductance have all been shown to be potentially affected by turbulent plasma heating. Therefore it is proposed to enhance and expand existing ionospheric radar capabilities and fund research into E-region plasma turbulence so that it is possible to more accurately quantify the solar-terrestrial energy budget and study phenomena related to E-region plasma turbulence. The proposed research funding includes the development of models to accurately predict and model the E-region plasma turbulence using particle-in-cell analysis, fluid-based analysis, and hybrid combinations of the two. This review provides an expanded and more detailed description of the past, present, and future of auroral E-region plasma turbulence research compared to the summary report submitted to the National Academy of Sciences Decadal Survey for Solar and Space Physics (Heliophysics) 2024–2033 (Huyghebaert et al., 2022a).

Self-Supervised Learning for Solar Radio Spectrum Classification

Solar radio observation is an important way to study the Sun. Solar radio bursts contain important information about solar activity. Therefore, real-time automatic detection and classification of solar radio bursts are of great value for subsequent solar physics research and space weather warnings. Traditional image classification methods based on deep learning often require considerable training data. To address insufficient solar radio spectrum images, transfer learning is generally used. However, the large difference between natural images and solar spectrum images has a large impact on the transfer learning effect. In this paper, we propose a self-supervised learning method for solar radio spectrum classification. Our method uses self-supervised training with a self-masking approach in natural language processing. Self-supervised learning is more conducive to learning the essential information about images compared with supervised methods, and it is more suitable for transfer learning. First, the method pre-trains using a large amount of other existing data. Then, the trained model is fine-tuned on the solar radio spectrum dataset. Experiments show that the method achieves a classification accuracy similar to that of convolutional neural networks and Transformer networks with supervised training.

The physics of solar spectral imaging observations in dm-cm wavelengths and the application on space weather

Recently, several new solar radio telescopes have been put into operation and provided spectral-imaging observations with much higher resolutions in decimeter (dm) and centimeter (cm) wavelengths. These telescopes include the Mingantu Spectral Radioheliograph (MUSER, at frequencies of 0.4–15 GHz), the Expanded Owens Valley Solar Array (EOVSA, at frequencies of 1–18 GHz), and the Siberian Radio Heliograph (SRH, at frequencies of 3–24 GHz). These observations offer unprecedented opportunities to study solar physics and space weather, especially to diagnose the coronal magnetic fields, reveal the basic nature of solar eruptions and the related non-thermal energy release, particle accelerations and propagation, and the related emission mechanisms. These results might be the important input to the space weather modeling for predicting the occurrence of disastrous powerful space weather events. In order to provide meaningful reference for other solar physicists and space weather researchers, this paper mainly focus on discussing the potential scientific problems of solar radio spectral-imaging observations in dm-cm wavelengths and its possible applications in the field of space weather. These results will provide a helpful reference for colleagues to make full use of the latest and future observation data obtained from the above solar radio telescopes.

(When) Can Wave Heating Balance Optically Thin Radiative Losses in the Corona?

Why the atmosphere of the Sun is orders of magnitudes hotter than its surface is a long standing question in solar physics. Over the years, many studies have looked at the potential role of magnetohydrodynamic (MHD) waves in sustaining these high temperatures. In this study, we use 3D MHD simulations to investigate (driven) transverse waves in a coronal loop. As the boundary-driven transverse waves propagate along the flux tube, the radial density profile leads to resonant absorption (or mode coupling) and phase mixing in the boundaries of the flux tube and the large velocity shears are subject to the Kelvin–Helmholtz instability (KHI). The combination of these effects leads to enhanced energy dissipation and wave heating. Considering both resonant and nonresonant boundary driving as well as different densities for the flux tube, we show that only wave heating associated with a resonant driver in a lower-density loop (with a loop core density ∼5 × 10−13 kg m−3) is able to balance radiative losses in the loop shell. Changing the model parameters to consider a denser loop or a driver with a nonresonant frequency, or both, leads to cooling of the coronal loop as the energy losses are greater than the energy injection and dissipation rates.

Numerical Modeling of Energetic Electron Acceleration, Transport, and Emission in Solar Flares: Connecting Loop-top and Footpoint Hard X-Ray Sources

The acceleration and transport of energetic electrons during solar flares is one of the outstanding topics in solar physics. Recent X-ray and radio imaging and spectroscopy observations have provided diagnostics of the distribution of nonthermal electrons and suggested that, in certain flare events, electrons are primarily accelerated in the loop top and likely experience trapping and/or scattering effects. By combining the focused particle transport equation with magnetohydrodynamic (MHD) simulations of solar flares, we present a macroscopic particle model that naturally incorporates electron acceleration and transport. Our simulation results indicate that physical processes such as turbulent pitch-angle scattering can have important impacts on both electron acceleration in the loop top and transport in the flare loop, and their influences are highly energy-dependent. A spatial-dependent turbulent scattering with enhancement in the loop top can enable both efficient electron acceleration to high energies and transport of abundant electrons to the footpoints. We further generate spatially resolved synthetic hard X-ray (HXR) emission images and spectra, revealing both the loop-top and footpoint HXR sources. Similar to the observations, we show that the footpoint HXR sources are brighter and harder than the loop-top HXR source. We suggest that the macroscopic particle model provides new insights into understanding the connection between the observed loop-top and footpoint nonthermal emission sources by combining the particle model with dynamically evolving MHD simulations of solar flares.