Article
Astronomy & Astrophysics
T. Mehta, K. Jain, S. C. Tripathy, R. Kiefer, D. Kolotkov, A-M Broomhall
Summary: In this study, we investigated the relationship between the solar cycle and the presence and periodicity of the Quasi-Biennial Oscillation (QBO). Using helioseismic techniques and solar activity proxies, we found that the presence of the QBO varied significantly between solar cycles. The QBO presence was reduced in Cycle 24 compared to Cycle 23, and it was not dependent on the depth or frequency of the p-mode.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
K. Mandal, S. M. Hanasoge, L. Gizon
Summary: This study successfully extends the methodology to measure even azimuthal orders of Rossby waves in the Sun, adding credibility to the mode-coupling methodology in helioseismology. The results indicate significant power close to the theoretical dispersion relation for sectoral Rossby modes, with maximum power occurring at mode t = 8.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
J. Philidet, L. Gizon
Summary: This study investigates the impact of turbulent motions on the inertial modes in the Sun's convective zone. The results suggest that the stochastic excitation mechanism by turbulent convection explains the observed mode amplitudes reasonably well. However, the complex power spectra of the modes make the interpretation of the observations challenging.
ASTRONOMY & ASTROPHYSICS
(2023)
Article
Astronomy & Astrophysics
Igor P. Lopin
Summary: The study investigates axisymmetric magnetohydrodynamic wave modes in the model of a coronal magnetic tube, revealing two families of modes and discussing their properties in twisted and untwisted magnetic fields.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
I Lopin
Summary: This study examines the kink oscillations of a curved coronal slab with finite plasma-beta, simulating a loop arcade. The study finds two surface modes, namely the faster mode and slower mode, in the model. As the internal plasma-beta becomes finite and increases, the phase speed of the faster mode increases, while that of the slower mode decreases.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
I Lopin, I Nagorny
Summary: In this work, we study the impact of curvature on slow-mode oscillations in coronal loop arcade using a theoretical approach. By solving a set of magnetohydrodynamic equations, we derive the dispersion relation that governs the compressible MHD modes in a simple model of curved coronal magnetic structures. Our findings reveal the existence of a band of slow body modes and a single hybrid slow mode in coronal loops under typical circumstances, which exhibit radial kink-like displacements and accompanying longitudinal oscillations. These mode properties can explain the observed Doppler shift, intensity oscillations, and spatial displacements in arcade loops.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
K. Kosak, R. Kiefer, A-M Broomhall
Summary: This study investigates the variation of pseudo-mode frequencies with solar activity during the solar cycle. The results show that acoustic oscillation frequencies are correlated with the solar cycle, while pseudo-mode frequencies vary in antiphase. The analysis is based on data from different instruments, and the findings reveal differences in the frequency variations between the instruments.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
David Korda, Michal Svanda
Summary: This study aims to construct a model of flows in average supergranular cells using a consistent time-distance inverse methodology. By analyzing travel-time maps of over 10^4 individual supergranular cells, near-surface divergent horizontal flows and upward vertical flows were discovered. However, systematic errors affected the accuracy of vertical flow estimates, while a longitudinal flow pattern was found to align well with the model of solar rotation in subsurface layers.
ASTRONOMY & ASTROPHYSICS
(2021)
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
David Korda, Michal Svanda, Thierry Roudier
Summary: The study aims to suppress the negative effects of magnetic fields on solar oscillations and measure plasma properties near active regions. This is done through new averaging geometries, a non-linear approach to travel-time measurements, and a consistent inversion method. The new methodology successfully reconstructs surface horizontal flows near active regions and helps understand the depth structure and physical conditions contributing to the evolution of these regions.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
Dan Yang, Laurent Gizon, Helene Barucq
Summary: This study aims to improve helioseismic holography for detecting active regions on the far side of the Sun and enhancing space weather forecasts. By using a clear problem formulation, an accurate forward solver in the frequency domain, and better understanding of noise properties, the method was improved. Active regions on the far side can be detected with high confidence by measuring and averaging phase shifts between the ingression and egression wave fields. The improvements in active region detection rate and false discovery rate are attributed to the use of a complete Green’s function and all available observations on the front side.
ASTRONOMY & ASTROPHYSICS
(2023)
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
Rene Kiefer, Anne-Marie Broomhall
Summary: The study investigates the energy supply rates of solar p modes throughout the solar activity cycle and finds that these rates are anticorrelated with the level of solar activity. Different mode frequency and harmonic degrees show varying strengths of anticorrelation with the solar activity level.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Souvik Das, Ahmed Atteya, Pralay Kumar Karmakar
Summary: A recently developed gravito-electrostatic sheath model is used to study the helioseismic oscillation features in the bi-fluidic solar plasma system. The model reveals the evolution of both dispersive and non-dispersive features of the modified gravito-electrostatic sheath mode fluctuations. Different spectral profiles show important features of the perturbations. The stability of the system depends on various parameters and the dispersive features are more pronounced in the self-gravitational domains.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Laurent Gizon, Robert H. Cameron, Yuto Bekki, Aaron C. Birch, Richard S. Bogart, Allan Sacha Brun, Cilia Damiani, Damien Fournier, Laura Hyest, Kiran Jain, B. Lekshmi, Zhi-Chao Liang, Bastian Proxauf
Summary: The study reports observations of the Sun's toroidal modes, with comparisons made to normal modes of a differentially rotating spherical shell to identify high-latitude inertial modes, critical-latitude inertial modes, and equatorial Rossby modes. The high-latitude and critical-latitude modes exhibit maximum kinetic energy density at the base of the convection zone, with the high-latitude modes being baroclinically unstable due to the latitudinal entropy gradient.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
Zhi-Chao Liang, Aaron C. Birch, Thomas L. Duvall, Laurent Gizon, Jesper Schou
ASTRONOMY & ASTROPHYSICS
(2017)
Article
Astronomy & Astrophysics
Z. -C. Liang, L. Gizon, H. Schunker, T. Philippe
ASTRONOMY & ASTROPHYSICS
(2013)
Article
Astronomy & Astrophysics
Zhi-Chao Liang, Laurent Gizon, Aaron C. Birch, Thomas L. Duvall, S. P. Rajaguru
ASTRONOMY & ASTROPHYSICS
(2018)
Article
Astronomy & Astrophysics
Ming-Hsu Yang, Dean-Yi Chou, Hui Zhao, Zhi-Chao Liang
ASTROPHYSICAL JOURNAL
(2012)
Article
Astronomy & Astrophysics
Dean-Yi Chou, Hui Zhao, Ming-Hsu Yang, Zhi-Chao Liang
ASTROPHYSICAL JOURNAL
(2012)
Article
Astronomy & Astrophysics
Dean-Yi Chou, Zhi-Chao Liang, Ming-Hsu Yang, Ming-Tsung Sun
Article
Astronomy & Astrophysics
Hui Zhao, Dean-Yi Chou, Ming-Hsu Yang, Zhi-Chao Liang, Ming-Tsung Sun
Article
Astronomy & Astrophysics
A. F. Lanza, L. Gizon, T. Zaqarashvili, Z-C Liang, K. Rodenbeck
ASTRONOMY & ASTROPHYSICS
(2019)
Article
Astronomy & Astrophysics
Zhi-Chao Liang, Laurent Gizon, Aaron C. Birch, Thomas L. Duvall
ASTRONOMY & ASTROPHYSICS
(2019)
Article
Multidisciplinary Sciences
Laurent Gizon, Robert H. Cameron, Majid Pourabdian, Zhi-Chao Liang, Damien Fournier, Aaron C. Birch, Chris S. Hanson
Article
Astronomy & Astrophysics
Laurent Gizon, Robert H. Cameron, Yuto Bekki, Aaron C. Birch, Richard S. Bogart, Allan Sacha Brun, Cilia Damiani, Damien Fournier, Laura Hyest, Kiran Jain, B. Lekshmi, Zhi-Chao Liang, Bastian Proxauf
Summary: The study reports observations of the Sun's toroidal modes, with comparisons made to normal modes of a differentially rotating spherical shell to identify high-latitude inertial modes, critical-latitude inertial modes, and equatorial Rossby modes. The high-latitude and critical-latitude modes exhibit maximum kinetic energy density at the base of the convection zone, with the high-latitude modes being baroclinically unstable due to the latitudinal entropy gradient.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
P-L Poulier, Z-C Liang, D. Fournier, L. Gizon
Summary: This study aims to investigate the contribution of inflows into solar active regions to solar cycle variations. The forward-modeling approach suggests that inflows associated with active regions may only partially account for the north-south travel-time measurements seen during the solar cycle.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
Zhi-Chao Liang, Dean-Yi Chou
ASTROPHYSICAL JOURNAL
(2015)
Article
Astronomy & Astrophysics
Zhi-Chao Liang, Dean-Yi Chou
ASTROPHYSICAL JOURNAL
(2015)