Article
Astronomy & Astrophysics
I. O. I. Virtanen, A. A. Pevtsov, I. I. Virtanen, K. Mursula
Summary: Researchers constructed additional active regions and applied them to the far-side of the Sun in an SFT simulation to assess the possible effects and the magnitude of error that the missing far-side flux causes. The results showed that adding active regions with short lifetimes to the far-side of the Sun results in significantly stronger polar fields in minimum times and slightly delayed polarity reversals.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
I. Poljancic Beljan, R. Jurdana-Sepic, T. Jurkic, R. Brajsa, I. Skokic, D. Sudar, D. Ruzdjak, D. Hrzina, W. Poetzi, A. Hanslmeier, A. M. Veronig
Summary: This study examines the relationship between solar differential rotation and activity, revealing patterns of variation in different phases of the solar cycle and comparing these findings with previous theoretical studies.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
Valentina Abramenko
Summary: The observational evidence suggests that the turbulent component of the solar dynamo has a significant impact on the generation of solar flares, especially during the second peak and descending phase of a solar cycle. These irregular active regions contribute more to the flaring, indicating a pronounced influence of the turbulent component during specific phases of the solar cycle. This is in line with the concept of the essential role of non-linearities and turbulent intermittence in magnetic fields generation inside the convective zone.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
A. Alharbi, I Ballai, V Fedun, G. Verth
Summary: In this study, we investigate the nature and characteristics of partially ionized plasma waves in the weakly ionized limit, which is typical for the lower part of the solar atmosphere. The plasma can be divided into two regions based on the magnitude of collisions between particles and collisional frequencies compared to the gyro-frequency of charged particles. In the non-magnetized solar photosphere, acoustic waves propagate with different damping rates determined by collisions with neutrals. In the weakly ionized chromosphere, only electrons are magnetized, and the two-fluid model is used to describe the dynamics influenced by electric currents created by disassociated charged particles.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
M. Ellwarth, C. E. Fischer, N. Vitas, S. Schmiz, W. Schmidt
Summary: The study focuses on the movement characteristics of exploding granules, revealing that they can form new downflow lanes in interaction with the magnetic field. Additionally, the intensity and velocity oscillations of exploding granules in spectral lines display different temporal and spatial features, contributing to a better understanding of their formation and evolution processes.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
J. Schou, J. Hirzberger, D. Orozco Suarez, K. Albert, N. Albelo Jorge, T. Appourchaux, A. Alvarez-Herrero, J. Blanco Rodriguez, A. Gandorfer, D. Germerott, L. Guerrero, P. Gutierrez-Marques, F. Kahil, M. Kolleck, S. K. Solanki, J. C. del Toro Iniesta, R. Volkmer, J. Woch, B. Fiethe, I. Perez-Grande, E. Sanchis Kilders, M. Balaguer Jimenez, L. R. Bellot Rubio, D. Calchetti, M. Carmona, W. Deutsch, A. Feller, G. Fernandez-Rico, A. Fernandez-Medina, P. Garcia Parejo, J. L. Gasent Blesa, L. Gizon, B. Grauf, K. Heerlein, A. Korpi-Lagg, A. Lopez Jimenez, T. Maue, R. Meller, A. Moreno Vacas, R. Mueller, E. Nakai, W. Schmidt, J. Sinjan, J. Staub, H. Strecker, I. Torralbo, G. Valori
Summary: In order to accurately infer the solar interior, understanding the various physical effects on observations is crucial. This study attempts to measure the complex-valued ratio of the horizontal to vertical displacement of p- and f-modes directly using simultaneous observations from two different instruments. The measured ratio agrees well with the expected value from adiabatic oscillations and indicates that a commonly used approximation should not be used in helioseismic analyses.
ASTRONOMY & ASTROPHYSICS
(2023)
Article
Astronomy & Astrophysics
Andrei A. Plotnikov, Valentina Abramenko, Alexander S. Kutsenko
Summary: In this study, line-of-sight magnetograms obtained by the Helioseismic and Magnetic Imager were used to calculate the decay rate of total unsigned magnetic flux for ephemeral and active regions observed between 2010 and 2017. The findings indicate that most regions follow a power law relationship between peak magnetic flux and flux decay rate, with larger regions losing a smaller fraction of their flux per unit of time than smaller regions. Moreover, there are some regions that exhibit significantly lower decay rates compared to the power law, and these regions are unipolar sunspots with total fluxes in a narrow range.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Yury A. Nagovitsyn, Aleksandra A. Osipova, Alexei A. Pevtsov
Summary: The study revealed that the tilt angles of solar active regions exhibit non-linear changes with latitude, with significant differences between large long-living groups and small short-living groups. This implies potential differences in the physical properties and formation mechanisms of the two populations of solar groups.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
T. Roudier, M. Svanda, J. M. Malherbe, J. Ballot, D. Korda, Z. Frank
Summary: Observations and simulations have shown the existence of long-lasting downflows on the solar surface, which penetrate deep into the Sun, are filled with magnetic fields, and are connected with anchoring coronal loops. This suggests a link between downflows and coronal activity, with EUV cyclones potentially being an effective way to heat the corona.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
Michal Sobotka, Klaus G. Puschmann
Summary: High-resolution observations of horizontal motions in sunspot penumbra have revealed different speeds and directions of granular movements in different regions, shedding light on the structure and evolution of penumbrae.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
A. Prasad, M. Ranganathan, C. Beck, D. P. Choudhary, Q. Hu
Summary: The study found that the inverse Evershed flow is driven along magnetic field lines connecting network elements with the outer penumbra, due to a gas pressure difference resulting from a difference in field strength. The gas pressure difference dominating the pressure force towards the inner foot points is primarily influenced by the difference in field strength.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
Larisa K. Kashapova, Anne-Marie Broomhall, Alena Larionova, Elena G. Kupriyanova, Ilya D. Motyk
Summary: The study investigates the decay phase of solar flares in multiple spectral bands, finding that the average flare profile observed in the 1700 angstrom channel decays more slowly than the average flare profile observed on the M4 dwarf, implying that M dwarf flare emission comes from a more dense layer. The cooling processes in solar flares were best described by the two exponents model, with the broken power-law model providing a good fit to the first decay phase but not to the second.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Anjali J. Kaithakkal, J. M. Borrero, A. Pastor Yabar, J. de la Cruz Rodriguez
Summary: The study aims to quantify the conversion of magnetic to thermal energy during a quiet Sun cancellation event and investigate the resulting dynamics from the interaction of opposite-polarity magnetic features. Observations were made using imaging spectroscopy and spectropolarimetry to study a reconnection-related cancellation event and the appearance of a quiet Sun Ellerman bomb (QSEB). The study confirmed the release of magnetic energy during flux cancellation can support heating in the photosphere and lower chromospheric heights.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
J. S. Castellanos Duran, A. Lagg, S. K. Solanki
Summary: Counter Evershed flows (CEFs) are a common feature in active regions (ARs), occurring in 83.5% of ARs regardless of magnetic complexity, but are observed on average for only 5.9% of the total observation time. The lifetime of CEFs follows a log-normal distribution with a median value of 10.6 hours.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
F. Giannattasio, G. Consolini, F. Berrilli, P. De Michelis
Summary: Studying the dynamic properties of small-scale magnetic fields in the quiet photosphere is important for understanding the dynamic regime of magnetic fields, providing details of magnetic field processes in the solar photosphere, and improving models' ability to represent physical processes. Analysis of magnetic field fluctuations using structure functions revealed persistent magnetic field fluctuations at supergranular boundaries and antipersistent fluctuations within supergranules, highlighting longer-memory processes and short-memory physical processes, respectively.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
Robertus Erdelyi, Marianna B. Korsos, Xin Huang, Yong Yang, Danielle Pizzey, Steven A. Wrathmall, Ifan G. Hughes, Martin J. Dyer, Vikram S. Dhillon, Bernadett Belucz, Roman Brajsa, Piyali Chatterjee, Xuewu Cheng, Yuanyong Deng, Santiago Vargas Dominguez, Raul Joya, Peter Gomory, Norbert G. Gyenge, Arnold Hanslmeier, Ales Kucera, David Kuridze, Faquan Li, Zhong Liu, Long Xu, Mihalis Mathioudakis, Sarah Matthews, James R. T. McAteer, Alexei A. Pevtsov, Werner Potzi, Paolo Romano, Jinhua Shen, Janos Temesvary, Andrey G. Tlatov, Charles Triana, Dominik Utz, Astrid M. Veronig, Yuming Wang, Yihua Yan, Teimuraz Zaqarashvili, Francesca Zuccarello
Summary: SAMM is a future international network that aims to continuously monitor solar activity and provide data for space weather research and forecasting.
JOURNAL OF SPACE WEATHER AND SPACE CLIMATE
(2022)
Article
Astronomy & Astrophysics
Partha Chowdhury, Ravindra Belur, Luca Bertello, Alexei A. Pevtsov
Summary: This study investigates the temporal and periodic variations of the hemispheric Ca-K-index time series in the low-latitude zone using long-term observations from the Kodaikanal Observatory. The study finds significant differences in the temporal evolution of the Ca-K index between the two hemispheres and observes an exponentially decaying distribution for each hemisphere's Ca-K index. Additionally, the study explores midterm periodicities and identifies the presence of the Waldmeier effect and the Gnevyshev gap.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Egor Illarionov, Andrey Tlatov
Summary: This study presents a machine-learning approach to provide a complete and compact description of sunspot groups by mapping their images into a lower-dimensional space. The latent features are considered as an extended description of sunspot groups, which can expand the possibilities for research on sunspot groups.
Article
Astronomy & Astrophysics
I. Tahtinen, I. I. Virtanen, A. A. Pevtsov, K. Mursula
Summary: By studying the relationship between photospheric magnetic fields and ultraviolet radiation, we found that the percentage of bright pixels can explain the variability of 1600 angstrom emission. We developed a model to predict the size of the photospheric magnetic field and found a close correspondence between the magnetic field and bright and dark clusters.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
K. A. Tlatova, V. V. Vasil'eva, I. A. Berezin, E. A. Illarionov, A. G. Tlatov
Summary: The study analyzing the relative number of sunspot groups (A+B) during solar activity cycles found significant variations in the number of groups at different phases of activity cycles.
Article
Astronomy & Astrophysics
Andrey G. Tlatov
Summary: Recent satellite observations and ground-based data have discovered numerous small dark areas with high contrast. The study reveals that most of these dark dots are not associated with magnetic activity, which can significantly affect the calculations of the sunspot index.
Article
Astronomy & Astrophysics
Vladimir M. Lipunov, Viktor G. Kornilov, Kirill Zhirkov, Artem Kuznetsov, Evgenii Gorbovskoy, Nikolai M. Budnev, David A. H. Buckley, Rafael Rebolo Lopez, Miquel Serra-Ricart, Carlos Francile, Nataly Tyurina, Oleg Gress, Pavel Balanutsa, Gleb Antipov, Daniil Vlasenko, Vladislav Topolev, Aristarkh Chasovnikov, Sergei Svertilov, Ricardo Podesta, Federico Podesta, Ekaterina Minkina, Andrei G. Tlatov, Vladimir V. Yurkov, Alexandre Gabovich, Olga Ershova, Viktor Senik, Dmitrii Kuvshinov
Summary: This review discusses the synchronous and follow-up optical observations of high energy astrophysical phenomena conducted by the MASTER Global Robotic Net. The observations include fast radio bursts, gamma-ray bursts, gravitational-wave events, and high energy neutrino sources. The study finds that the ratio of energy released in the optical and radio ranges does not exceed 4 x 105 and identifies a faint optical signal associated with extended afterglow.
Article
Astronomy & Astrophysics
Alexandr Riehokainen, Victoria Smirnova, Alexander Solov'ev, Andrey Tlatov, Ivan Zhivanovich, Firas Al-Hamadani, Polina Strekalova
Summary: In this study, we considered coronal holes as an indication of the Sun's large-scale magnetic field and investigated the periodic variations in the largest areas and longitudinal widths of these coronal holes in different zones. Statistical methods were employed and the results showed periodic changes with periods of 8-9, 13-15, and 26-29 days, most prominently observed in the equatorial region.
Article
Astronomy & Astrophysics
V. M. Lipunov, V. A. Sadovnichy, M. I. Panasyuk, I. V. Yashin, S. I. Svertilov, S. G. Simakov, D. Svinkin, E. Gorbovskoy, G. V. Lipunova, V. G. Kornilov, D. Frederiks, V. Topolev, R. Rebolo, M. Serra, N. Tiurina, E. Minkina, V. V. Bogomolov, A. V. Bogomolov, A. F. Iyudin, A. Chasovnikov, A. Gabovich, A. Tsvetkova, N. M. Budnev, O. A. Gress, G. Antipov, I. Gorbunov, D. Vlasenko, P. Balanutsa, R. Podesta, K. Zhirkov, A. Kuznetsov, V. Vladimirov, F. Podesta, C. Francile, Yu. Sergienko, A. Tlatov, O. Ershova, D. Cheryasov, V. Yurkov, A. V. Krylov
Summary: This article presents the initial findings of synchronous multiwavelength observations of GRB 160625B, including detailed optical photometry and X-ray/gamma-ray emission measurements. The analysis reveals quasi-periodic emission components in the intrinsic optical emission and proposes a three-stage collapse scenario for the GRB. It suggests that these fluctuations may be caused by the forced precession of a rapidly rotating superdense body with a strong magnetic field, ultimately collapsing into a black hole.
ASTROPHYSICAL JOURNAL
(2023)
Article
Astronomy & Astrophysics
Nishtha Sachdeva, Ward B. B. Manchester, Igor Sokolov, Zhenguang Huang, Alexander Pevtsov, Luca Bertello, Alexei A. Pevtsov, Gabor Toth, Bart van der Holst, Carl J. Henney
Summary: We investigate the performance of the Alfven Wave Solar atmosphere Model using near-real-time synoptic maps of the photospheric vector magnetic field. These maps, generated by assimilating data from the Helioseismic Magnetic Imager (HMI), provide contemporary data for numerical models. By applying these maps, we simulate three full Carrington rotations and show that the results reproduce the extreme ultraviolet emission from the low corona, match in situ observations at 1 au, and quantify the total unsigned open magnetic flux from these maps.
ASTROPHYSICAL JOURNAL
(2023)
Article
Astronomy & Astrophysics
Zihan Yu, Jie Chen, Jihong Liu, Alexei A. Pevtsov, Ziyao Hu, Zhike Xue, Jiangtao Su, Yuanyong Deng
Summary: We conducted a statistical study on trans-equatorial loops (TLs) from December 2006 to 2020. Our findings reveal that 160 TLs were identified during this period, with 12% of all active regions being connected by TLs. It was observed that 74% of TLs are connected to regions of preceding magnetic polarity (PTLs), while only 26% are connected to regions of following magnetic polarity (FTLs), which can be attributed to Joy's law. The average length of TLs is 20 degrees, and their lengths decrease during the solar cycle. Furthermore, 88% of the TLs appeared near the solar maximum (2014 ± 2) based on a comparison with the smoothed monthly mean number of sunspots from 2009 to 2018. We also found that TLs are more likely to form when sunspots are closer to the equator, and the tilt angle and latitudinal asymmetry of TL foot-points are independent of the solar cycle.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Yury Nagovitsyn, Alexei Pevtsov, Aleksandra Osipova
Summary: It is found that the average meridional velocities of sunspot groups are linearly related to their average longitudinal velocities, with a high correlation coefficient of -0.95. This relationship differs for different types of sunspot groups. The meridional motions of sunspots do not follow a pronounced global distribution pattern with latitude, but depend on their individual longitudinal velocities in a rotating coordinate system. These findings suggest that the Coriolis force may be responsible for driving the meridional motions of sunspot groups.
Article
Physics, Multidisciplinary
Andrey G. Tlatov, Ivan Berezin
Summary: The magnetic field in the interplanetary medium is formed by the interaction between magnetic field sources on the Sun's photosphere and currents in the expanding atmosphere and solar wind. This three-dimensional problem involves the magnetic field and plasma of the solar wind, where the plasma flow changes the configuration of magnetic field lines. We provide analytical expressions for calculating the total magnetic field vector in spherical coordinates for a radially expanding solar wind flow of finite conductivity and give examples of calculating the magnetic field configuration and structures of the solar corona for the solar eclipse of 21 August 2017.
Article
Astronomy & Astrophysics
V. Lipunov, V. Kornilov, E. Gorbovskoy, N. Tyurina, D. Vlasenko, P. Balanutsa, A. Kuznetsov, O. A. Gress, K. Zhirkov, A. Chasovnikov, V. Topolev, V. Senik, K. Francile, F. Podesta, R. Podesta, D. Buckley, R. Rebolo, M. Serra, N. M. Budnev, A. Tlatov, Ya. Kechin, Yu. Tselik, V. Yurkov, A. Gabovich, D. Dormidontov, D. Kuvshinov, E. Minkina, O. Ershova, D. Cheryasov, V. Vladimirov
Summary: This paper presents the participation and results of the MASTER Global Robotic Network in supporting the aLIGO and LIGO/Virgo gravitational-wave experiments. The main goal of these observations was to perform precise localization of gravitational-wave sources, which resulted in the discovery of kilonova and detection of optical transients unrelated to gravitational waves. The experience gained from these optical localizations is of significant importance for future strategies involving relativistic stars. Furthermore, the analysis of the huge sky areas explored by the MASTER Global Robotic Network led to the discovery and analysis of various explosive phenomena in the Universe.