bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dominating active regions in the minima of solar activity
Authors: Suleymanova R. A. , Abramenko V. I. 
Published: December 2024

AbstractDuring minima of solar activity, it is possible to estimate the influence of convection zone turbulence on the magnetic flux tubes forming active regions (ARs), because the toroidal field of the old cycle weakens, and the new toroidal field is still weak. We analyzed ARs of solar minima between 23-24 and 24-25 solar cycles. ARs were classified as regular, irregular and unipolar spots. Regular ARs follow the empirical laws consistent with the Babcock–Leighton dynamo theory. We found that regular ARs dominate by flux and by number during the solar minima. Irregular ARs are mainly represented by bipolar structures of deformed orientation and contribute only one-third in the total flux and one-third in the total number. Very complex multipolar ARs are extremely rare. So, during solar minima the global dynamo still guides the formation of ARs, whereas the turbulence only slightly affects the toroidal flux tubes orientation.
Evolution of a nanoflare-scale magnetic reconnection event in the quiet Sun
Authors: Robinson Rebecca A. 
Published: December 2024

AbstractLow-lying loops in the quiet Sun are a reliable source of energy for atmospheric heating, but the mechanisms by which they evolve are somewhat enigmatic. To address the origins of atmospheric heating events in the quiet Sun, we utilize our stratified, convection-driven, 3D MHD simulation Bifrost to explore the evolution and eventual major reconnection between several magnetic features; one of which is a magnetic flux rope. We zoom in on the buildup of the magnetic flux rope, which self-orders in the corona via an inverse cascade of helicity. We also discover that the flux rope attempts to relax to a linear force-free field according to Taylor’s theory, but cannot do so completely. Finally, we demonstrate that the eventual nanoflare-scale reconnection event could potentially be observed in the 171 Å channels of SDO/AIA and the future MUSE mission. We also determine that the spectral resolution of MUSE is sensitive enough to capture the kinematics of the bi-directional plasma jets emanating from the reconnection region.
Center-to-limb variation of spectral lines and their effect on full-disk observations
Authors: Pietrow Alexander G. M. , Pastor Yabar Adur 
Published: December 2024

AbstractAn accurate description of the center-to-limb variation (CLV) of stellar spectra is becoming an increasingly critical factor in both stellar and exoplanet characterization. In particular, the CLV of spectral lines is extremely challenging as its characterization requires highly detailed knowledge of the stellar physical conditions. To this end, we present the Numerical Empirical Sun-as-a-Star Integrator (NESSI) as a tool for translating high-resolution solar observations of a partial field of view into disk-integrated spectra that can be used to test common assumptions in stellar physics.
The role of nonlinear toroidal flux loss due to flux emergence in the long-term evolution of the solar cycle
Authors: Biswas Akash 
Published: December 2024

AbstractA striking feature of the solar cycle is that at the beginning, sunspots appear around mid-latitudes, and over time the latitudes of emergences migrate towards the equator. The maximum level of activity varies from cycle to cycle. For strong cycles, the activity begins early and at higher latitudes with wider sunspot distributions than for weak cycles. The activity and the width of sunspot belts increase rapidly and begin to decline when the belts are still at high latitudes. However, in the late stages of the cycles, the level of activity, and properties of the butterfly wings all have the same statistical properties independent of the peak strength of the cycles. We have modelled these features using Babcock–Leighton type dynamo model and shown that the toroidal flux loss from the solar interior due to magnetic buoyancy is an essential nonlinearity that leads to all the cycles decline in the same way.
AutoTAB: An Algorithm to Track Bipolar Magnetic Regions and Initial results from the Tracked BMRs
Authors: Sreedevi Anu , Jha Bibhuti Kumar , Karak Bidya Binay , Banerjee Dipankar 
Published: December 2024

AbstractAutoTAB is a state-of-the-art, fully automatic algorithm that tracks the Bipolar Magnetic Regions (BMRs) in magnetogram observations. AutoTAB employs identified BMR regions from Line-of-Sight magnetograms from MDI and HMI (1996–2022) to track the BMRs through their evolution on the nearside of the Sun. AutoTAB enables us to create a comprehensive and unique catalog of tracked information of 9232 BMRs in the mentioned time period. This dataset is used to study the collective statistical properties of BMRs and particularly to identify the correct theory for the BMR formation. Here, we discuss the algorithm’s functionality and the initial findings obtained from the AutoTAB BMRs catalog.
Exploring the Quenching of Bipolar Magnetic Region Tilts using AutoTAB
Authors: Jha Bibhuti Kumar , Sreedevi Anu B. , Karak Bidya Binay , Banerjee Dipankar 
Published: December 2024

AbstractThe tilt of the bipolar magnetic region (BMR) is crucial in the Babcock-Leighton process for the generation of the poloidal magnetic field in the Sun. We extend the work of Jha et al. (2020) and analyze the recently reported tracked BMR catalogue based on AutoTAB (Sreedevi et al. 2023) from Michelson Doppler Imager (1996–2011) and Helioseismic and Magnetic Imager (2010–2018). Using the tracked information of BMRs based on AutoTAB, we confirm that the distribution of Bmax reported by Jha et al. (2020) is not because of the BMRs are picked multiple times at the different phases of their evolution instead it is also present if we consider each BMRs only once. Moreover, we find that the slope of Joy’s law (〈γ0〉) initially increases slowly with the increase of Bmax. However, when Bmax >2.5 kG, γ0 decreases. The decrease of observed γ0 with Bmax provides a hint to a nonlinear tilt quenching in the Babcock-Leighton process.
Thermal instability in the impulsive phase of solar flares with sub-THz component
Authors: Smirnova V. V. , Tsap Yu. T. , Motorina G. G. , Morgachev A. S. , Bárta M. 
Published: December 2024

AbstractCoronal rain is formed in the post-impulsive phase of solar flares due to the thermal instability of coronal plasma in EUV loops. As a result, the sub-terahertz (sub-THz) emission flux in the post-impulsive phase of solar flares can be increased due to the increasing of the optical thickness of the thermal source. This suggests that sub-THz observations can be used as a diagnostic tool for coronal rain.This work is aimed to analyse the relationship between the sub-THz radiation and variations of the temperature and the emission measure of the EUV coronal plasma during the post-impulsive phase of the SOL2022-05-04T08:45 solar flare.Based on the two-dimensional temperature and emission measure distributions obtained from the AIA/SDO EUV intensity data, it was found that the temperature decreases whereas the emission measure reaches the maximum near the sub-THz flare peak. This circumstance and peculiarities of the radiation time profiles in different wave ranges show evidence in favor of the significant contribution of the thermal coronal loop plasma to the flare sub-THz radiation at least for some flare events. The sub-THz emission may be associated with a coronal condensation, accompanied by the formation of coronal rain.
Effects of rotation and surface forcing on deep stellar convection zones
Authors: Käpylä Petri J. 
Published: December 2024

AbstractThe canonical undestanding of stellar convection has recently been put under doubt due to helioseismic results and global 3D convection simulations. This “convective conundrum” is manifested by much higher velocity amplitudes in simulations at large scales in comparison to helioseismic results, and the difficulty in reproducing the solar differential rotation and dynamo with global 3D simulations. Here some aspects of this conundrum are discussed from the viewpoint of hydrodynamic Cartesian 3D simulations targeted at testing the rotational influence and surface forcing on deep convection. More specifically, the dominant scale of convection and the depths of the convection zone and the weakly subadiabatic – yet convecting – Deardorff zone are discussed in detail.
Levels of stabilization of velocity and magnetic induction in the convective zone of the Sun
Authors: Starchenko S. V. 
Published: December 2024

AbstractThe induction and momentum equations of solar dynamo are simplified to a dynamic system for the convective Root-Mean-Square (rms) velocity and the rms magnetic field in the solar convection zone. The study of stable stationary points of this system gives a minor excess of the critical level of the dynamo and, accordingly, moderate magnetic field typically about 1 T (10 kG). A significantly lower rms magnetic field may be possible at some parameters of the system. The stable rms velocity is about 100 m/sec, and the characteristic magnetic times are about the half-period of solar rotation or about an average lifetime of sunspots. Relative magnetic energy is of order 5 kJ/kg that is about the kinetic energy. The unstable stationary points could be near zero magnetic fields as in periods of very lower solar activity similar to the Maunder minimum.
Sub-THz emission from stellar flares and energy release diagnostics
Authors: Tsap Yuriy T. , Stepanov Alexander V. , Melnikov Victor F. 
Published: December 2024

AbstractA comparative analysis of sub-THz emission of stellar flares from red dwarfs has been carried out. ALMA observations indicate that the sub-THz emission flux from stellar flares with a duration of 10 s is an order of magnitude greater than for solar flares. The sub-THz emission is linearly polarized and decreases with frequency. The degree of polarization can reach tens of percent. We show that these types of spectrum slopes and linear polarization can be caused by the synchrotron emission of ultrarelativistic electrons. The origin of the observed relationships between sub-THz, low frequency radio, and X-ray emissions of stellar flares are discussed.
Magnetic field and radial velocity fluxes at the initial stages of the evolution of solar active regions based on measurements at the photospheric level
Authors: Sadykov A. M. , Krasotkin S. A. 
Published: December 2024

AbstractIn this article, the physical processes occurring in the convective layer and the photosphere of the Sun and their connection to the formation of active regions (ARs) and the development of the corresponding magnetic field are explored. Specifically, we test the magnetic flux emergence hypothesis and based on the line-of-sight magnetic field and Doppler shift data obtained from the Global Oscillation Network Group (GONG) observations. The study encompasses the analysis of 24 ARs observed during the period from 2011 to 2022. We find a strong correlation between the magnetic flux and the imbalance of radial velocity fluxes. The results indicate that the magnetic flux emergence hypothesis cannot fully explain the evolution of ARs during their early stages of development.
Convection, rotation, and magnetic activity of solar-like stars from asteroseismology
Authors: Mathur Savita 
Published: December 2024

AbstractDuring the last decade, our understanding of stellar physics and evolution has undergone a tremendous revolution thanks to asteroseismology. Space missions such as CoRoT, Kepler, K2, and TESS have already been observing millions of stars providing high-precision photometric data. With these data, it is possible to study the convection of stars through the convective background in the power spectrum density of the light curves. The properties of the convective background or granulation has been shown to be correlated to the surface gravity of the stars. In addition, when we have enough resolution (so long enough observations) and a high signal-to-noise ratio (SNR), the individual modes can be characterized in particular to study the internal rotational splittings and magnetic field of stars. Finally, the surface magnetic activity also impacts the amplitude and hence detection of the acoustic modes. This effect can be seen as a double-edged sword. Indeed, modes can be studied to look for magnetic activity changes. However, this also means that for stars too magnetically active, modes can be suppressed, preventing us from detecting them.In this talk, I will present some highlights on what asteroseismology has allowed us to better understand the convection, rotation, and magnetism of solar-like stars while opening doors to many more questions.
Nonlinear and stochastic mechanisms of the solar cycle and their implications for the cycle prediction
Authors: Jiang Jie 
Published: December 2024

AbstractSolar activity shows an 11-year (quasi)periodicity with a pronounced, but limited variability of the cycle amplitudes. The properties of active region (AR) emergence play an important role in the modulation of solar cycles and are our central concern in building a model for predicting future cycle(s) in the framework of the Babcock–Leighton (BL)-type dynamo. The emergence of ARs has the property that strong cycles tend to have higher mean latitudes and lower tilt angle coefficients. Their non-linear feedbacks on the solar cycle are referred to as latitudinal quenching and tilt quenching, respectively. Meanwhile, the stochastic properties of AR emergence, e.g., rogue ARs, limit the scope of the solar cycle prediction. For physics-based prediction models of the solar cycle, we suggest that uncertainties in both the observed magnetograms assimilated as the initial field and the properties of the AR emergence should be taken into account.
A Frequency-Dependent Method for Measuring the Sun’s Interior Meridional Circulation
Authors: Chen Ruizhu , Zhao Junwei 
Published: December 2024

AbstractThe Sun’s meridional circulation is a crucial component for understanding the Sun’s dynamo and its interior dynamics. However, the determination of meridional circulation is affected by a systematic center-to-limb (CtoL) effect, which introduces systematic errors 5–10 times stronger than the meridional-flow-induced travel-time shifts in deep-flow measurements. Recently, it was found that the CtoL effect has a significant acoustic-frequency dependence, while flow-induced travel-time shifts show little frequency dependence (Chen & Zhao 2018). This discovery forms the basis for designing a new method to remove the CtoL effect. We therefore propose a frequency-dependent approach to measure the CtoL effect and the flow-induced signals in the Fourier domain. In this work, we present this new method and compare time–distance measurements in different frequency bands with those obtained by previous time-domain methods. The results demonstrate consistency with conventional time-domain fitting methods in the dominant frequency range, promising the potential for conducting meridional flow inversion across a broader frequency spectrum.
Complexity of emerging magnetic flux during lifetime of solar ephemeral regions
Authors: Yang Hanlin 
Published: December 2024

AbstractAs a relatively active region, ephemeral region (ER) exhibits highly complex pattern of magnetic flux emergence. We aim to study detailed secondary flux emergences (SFEs) which we define as bipoles that their locations close to ERs and finally coalesce with ERs after a period. We study the SFEs during the whole process from emergence to decay of 5 ERs observed by the Helioseismic and Magnetic Imager (HMI) aboard Solar Dynamics Observatory (SDO). We find that the maximum unsigned magnetic flux for each of the ERs is around 1020 Mx. All ERs have tens of SFEs with an average emerging magnetic flux of approximately 5×1018 Mx. The frequency of normalized magnetic flux for all the SFEs follows a power law distribution with an index of -2.08. The majority of SFEs occur between the positive and negative polarities of ER, and their growth time is concentrated within one hour. The magnetic axis of SFEs also exhibits a random characteristic. We suggest that the relationship between SFEs and ERs can be understood by regarding the photospheric magnetic field observations as cross-sections of an emerging magnetic structure. Tracking the ERs’ evolution, we propose that the flux emergences are partially emerged Ω-loops, and that the SFEs in ERs may be sequent emergences from the bundle of flux tube of ERs.
Understanding Grand Minima in Solar Activity: Confronting Observations with Dynamo Simulations
Authors: Saha Chitradeep , Nandy Dibyendu 
Published: December 2024

AbstractThe grand minimum in the Sun’s activity is a distinctive mode characterized by a magnetic lull that almost completely lacks the emergence of sunspots on the solar surface for an extended duration. The factors driving this transition of an otherwise magnetically active star into a quiescent phase, the processes occurring within the solar interior and across the heliosphere during this period, and the mechanisms leading to the eventual resurgence of surface magnetic activity remain enigmatic. However, there have been sustained efforts in the past few decades to unravel these mysteries by employing a combination of observation, reconstruction and simulation of solar magnetic variability. Here, we summarize recent research on the solar grand minimum and highlight some outstanding challenges – both intellectual and practical – that necessitate further investigations.
Subsurface Flows Associated with Formation and Flaring Activity of Solar Active Regions
Authors: Kosovichev Alexander G. , Sadykov Viacheslav M. 
Published: December 2024

AbstractWe investigate the evolution of subsurface flows during the emergence and the active phase of sunspot regions using the time–distance helioseismology analysis of the full-disk Dopplergrams from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). We present an analysis of emerging active regions of various types, including delta-type active regions and regions with the reverse polarity order (‘anti-Hale active regions’). The results reveal strong vortical and shearing flows during the emergence of magnetic flux, as well as the process of formation of large-scale converging flow patterns around developing active regions, predominantly in the top 6 Mm deep layers of the convection zone. Our analysis revealed a significant correlation between the flow divergence and helicity in the active regions with their flaring activity, indicating that measuring characteristics of subsurface flows can contribute to flare forecasting.
Krisenfest aufwachsen in Zeiten von Klimawandel, Krieg und Pandemie
Authors: Asbrand Julia , Christiansen Hanna 
Published: December 2024

Zusammenfassung: Das Aufwachsen im 21. Jahrhundert konfrontiert Kinder und Jugendliche mit globalen Herausforderungen wie den Folgen der COVID-19-Pandemie, wirtschaftlichen Krisen, bewaffneten Konflikten und dem Klimawandel. Diese Krisen verstärken sich gegenseitig und betreffen junge Menschen psychisch stärker als Erwachsene. Diese Belastung zeigt sich insbesondere in erhöhten Depressions- und Angstsymptomen. Trotz des wachsenden Bedarfs an psychischer Gesundheitsversorgung mangelt es an adäquaten Angeboten bei einer Verdoppplung der Wartezeiten. Insgesamt zeigen die Erkenntnisse signifikante negative Auswirkungen globaler Krisen auf die gesunde Entwicklung junger Menschen. Der aktuelle Themenschwerpunkt fasst Erkenntnisse zusammen, wie Krisen auf die psychische und somatische Gesundheit wirken und welche Handlungsmöglichkeiten sich für den Erhaltung und die Wiederherstellung der (psychischen) Gesundheit ergeben.
Comparison of the ENSO‐Related Interannual Variability of the ECS‐Kuroshio Before and After 2005
Authors: Liu Zhao‐Jun , Qiao Yu‐Xiang , Nakamura Hirohiko , Zhu Xiao‐Hua , Nishina Ayako , Zhang Chuanzheng , Zhu Ze‐Nan , Xiao Cong 
Published: December 2024

AbstractThe El Niño‐Southern Oscillation (ENSO)‐related interannual variability of the Kuroshio in the East China Sea (ECS) was revisited based on reanalysis outputs during 1993–2018. Unlike the synchronized variations from 2006 to 2018, the period of 1993–2005 showed regional differences in how the ECS‐Kuroshio responded to ENSO events. Specifically, from the upstream region to the midway of the continental slope, the ECS‐Kuroshio exhibited distinct six‐year interannual modulation during 1993–2005. In contrast, downstream Kuroshio variability primarily followed a four‐year cycle, aligning with ENSO variability during the same period. Further analysis suggested that the sea surface height anomaly (SSHA) east of the Kerama Gap, near the midpoint of the Ryukyu Island chain, extended inside the ECS until the southern side of the Tokara Strait along the ECS‐Kuroshio path and was well correlated with the Kuroshio in the Tokara Strait during 1993–2005. The cause of this SSHA signal was attributed to forcing by ENSO‐related wind stress curl changes in the interior region. There was an obvious difference in the ENSO‐related atmospheric circulation before and after 2005. The wind stress curl pattern in the North Pacific during 1993–2005, characterized by a maximum in the Kerama Gap latitude band, shifted northward compared to that during 2006–2018. The relative northward shift of the ENSO‐related wind stress curl, which stimulates the long baroclinic Rossby wave propagating westward and arriving east of the Kerama Gap, affect the interannual variabilities of both the upstream and downstream Kuroshio.