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
Jaidev Sharma, Brajesh Kumar, Anil K. Malik, Hari Om Vats
Summary: The study reveals that the solar transition region rotates differentially as a function of latitude, with rotation rates varying according to the solar activity cycle. Interestingly, the rotational differentiality of the transition region is lower than that of the corona.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Yamini K. Rao, Giulio Del Zanna, Helen E. Mason, Roger Dufresne
Summary: Using spectroscopic diagnostics, the study determined various plasma parameters in the transition region of the quiet Sun, with electron number density estimated around 10^(10) cm(-3). The research found center-to-limb variations in path-lengths and compared results from different atomic models, indicating potential overestimation under the isothermal assumption.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
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
Kyuhyoun Cho, Jongchul Chae, Maria S. Madjarska
Summary: The analysis of umbral flashes in merging sunspots suggests that the subsurface of the umbra is an environment where convection can occur more easily than the convergent interface, supporting the cluster model. Further studies based on umbral velocity oscillations in the lower atmosphere are needed for more concrete results.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
Yuto Bekki, Robert H. Cameron, Laurent Gizon
Summary: The study focuses on detecting and characterizing modes present in nonlinear numerical simulations of solar convection, highlighting equatorial Rossby modes and columnar convective modes. These modes are compared to linear models and solar observations, providing insights into their amplitudes and impact on heat and angular momentum transport.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
G. Y. Chen, L. Y. Chen, Y. Guo, M. D. Ding, P. F. Chen, R. Erdelyi
Summary: By applying solar magneto-seismology, this study investigated the characteristics of coronal loop oscillations triggered by solar eruptions. The results revealed that the period of coronal loop oscillations is not only influenced by the density and magnetic field distribution, but also by the shape of the loop geometry.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
Fabian Menezes, Caius L. Selhorst, Carlos Guillermo Gimenez de Castro, Adriana Valio
Summary: Measurements of the radius and limb brightening of the Sun provide important information about the solar atmosphere structure and temperature. The study found that the solar radius increases as the observation at radio frequency decreases, indicating emission sources originating higher in the atmosphere. Using two different methods, the inflection-point method was found to be the least affected by antenna beam size and limb brightening level, and thus should be used for solar radius estimates at radio wavelengths. The measured average radii and limb brightening estimates agree with previous measurements reported in the literature.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
C. E. Alissandrakis, S. Patsourakos, A. Nindos, C. Bouratzis, A. Hillaris
Summary: This study reports the first detection of radio emission from a surge. The radio emission occurred in two phases and consisted of two sources. In addition, the radio emission showed signs of pulsations and spikes. The study discusses possible emission mechanisms for the lower radio source's slow time variability component.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
D. Calchetti, M. Stangalini, S. Jafarzadeh, G. Valori, K. Albert, N. Albelo Jorge, A. Alvarez-Herrero, T. Appourchaux, M. Balaguer Jimenez, L. R. Bellot Rubio, J. Blanco Rodriguez, A. Feller, A. Gandorfer, D. Germerott, L. Gizon, L. Guerrero, P. Gutierrez-Marques, J. Hirzberger, F. Kahil, M. Kolleck, A. Korpi-Lagg, A. Moreno Vacas, D. Orozco Suarez, I. Perez-Grande, E. Sanchis Kilders, J. Schou, U. Schuehle, J. Sinjan, S. K. Solanki, J. Staub, H. Strecker, J. C. del Toro Iniesta, R. Volkmer, J. Woch
Summary: In November 2021, Solar Orbiter began its nominal mission phase and gathered scientific data during three observation windows to study magnetohydrodynamic (MHD) wave modes in an active region using the spectropolarimetric capabilities of its instruments. The paper focuses on the analysis of a high-cadence dataset acquired by the High-Resolution Telescope (HRT) of the Polarimetric and Helioseismic Imager (SO/PHI) on board the Solar Orbiter. Various MHD modes at different frequencies are found to be excited in all studied structures, including sunspots and magnetic pores. The measurements from SO/PHI confirm the presence of magnetic and velocity oscillations consistent with MHD wave modes, but further improvements in modeling are needed to fully understand the relationship between different diagnostic fluctuations.
ASTRONOMY & ASTROPHYSICS
(2023)
Article
Astronomy & Astrophysics
Llorenc Melis, Roberto Soler, Jaume Terradas
Summary: The fine structure of solar prominences consist of thin threads outlining magnetic field lines. Transverse waves of Alfvenic nature are commonly observed in these threads, which are driven at the photosphere and propagate to the coronal prominences. Energy balance between radiative losses, thermal conduction, and Alfven wave heating is explored to construct 1D equilibrium models of prominence threads. Equilibrium profiles of temperature, density, and ionisation fraction are computed along the thread using the energy balance equation, and the wave heating rate is calculated using the Alfven wave equation. The iterative process is repeated until a self-consistent thread model heated by Alfven waves is achieved.
ASTRONOMY & ASTROPHYSICS
(2023)
Article
Astronomy & Astrophysics
Richa N. Jain, R. K. Choudhary, Anil Bhardwaj, T. Imamura, Anshuman Sharma, Umang M. Parikh
Summary: The solar inner corona, a region critical for energizing the solar wind, remains poorly understood due to observational limitations. By utilizing coronal radio-sounding and extreme ultraviolet observations, our study sheds light on the dynamics of the least-explored inner corona. We found that the speed of the solar wind in this region was higher than expected, providing unique insights into the properties and energization of high-velocity plasma streams.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
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
Jagdev Singh, Muthu Priyal, B. Ravindra
Summary: A new methodology was developed to study chromospheric variations by generating uniform time series of Ca-K spectroheliograms, improving the correlation between sunspot and Ca-K line data significantly. Adjusting image contrast using the equal-contrast technique helped compensate for variations in image quality and enabled accurate analysis of enhanced, active, and quiet networks over a century.
ASTROPHYSICAL JOURNAL
(2021)
Article
Astronomy & Astrophysics
D. Vukadinovic, I Milic, O. Atanackovic
Summary: The understanding of the magnetic field structure in the solar atmosphere is crucial for assessing its dynamics and energy balance. This study investigates the applicability of the weak-field approximation (WFA) for retrieving the depth-dependent line-of-sight (LOS) magnetic field. The results show that the WFA provides a reliable estimate of the LOS magnetic field structure, offering a significant advantage over classical spectropolarimetric inversions.
ASTRONOMY & ASTROPHYSICS
(2022)
