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- ItemGONG p-Mode Parameters Through Two Solar Cycles(Dordrecht [u.a.] : Springer Science + Business Media B.V, 2018) Kiefer, RenĂ©; Komm, Rudi; Hill, Frank; Broomhall, Anne-Marie; Roth, MarkusWe investigate the parameters of global solar p-mode oscillations, namely damping width Γ, amplitude A, mean squared velocity ⟨v2⟩, energy E, and energy supply rate dE/dt, derived from two solar cycles’ worth (1996 – 2018) of Global Oscillation Network Group (GONG) time series for harmonic degrees l=0--150. We correct for the effect of fill factor, apparent solar radius, and spurious jumps in the mode amplitudes. We find that the amplitude of the activity-related changes of Γ and A depends on both frequency and harmonic degree of the modes, with the largest variations of Γ for modes with 2400 μHz≤ν≤3300 μHz and 31≤l≤60 with a minimum-to-maximum variation of 26.6±0.3% and of A for modes with 2400 μHz≤ν≤3300 μHz and 61≤l≤100 with a minimum-to-maximum variation of 27.4±0.4%. The level of correlation between the solar radio flux F10.7 and mode parameters also depends on mode frequency and harmonic degree. As a function of mode frequency, the mode amplitudes are found to follow an asymmetric Voigt profile with νmax=3073.59±0.18 μHz. From the mode parameters, we calculate physical mode quantities and average them over specific mode frequency ranges. In this way, we find that the mean squared velocities ⟨v2⟩ and energies E of p modes are anticorrelated with the level of activity, varying by 14.7±0.3% and 18.4±0.3%, respectively, and that the mode energy supply rates show no significant correlation with activity. With this study we expand previously published results on the temporal variation of solar p-mode parameters. Our results will be helpful to future studies of the excitation and damping of p modes, i.e., the interplay between convection, magnetic field, and resonant acoustic oscillations.
- ItemVortex Motions in the Solar Atmosphere: Definitions, Theory, Observations, and Modelling(Dordrecht [u.a.] : Springer Science + Business Media B.V, 2023) Tziotziou, K.; Scullion, E.; Shelyag, S.; Steiner, O.; Khomenko, E.; Tsiropoula, G.; Canivete Cuissa, J.R.; Wedemeyer, S.; Kontogiannis, I.; Yadav, N.; Kitiashvili, I. N.; Skirvin, S.J.; Dakanalis, I.; Kosovichev, A.G.; Fedun, V.Vortex flows, related to solar convective turbulent dynamics at granular scales and their interplay with magnetic fields within intergranular lanes, occur abundantly on the solar surface and in the atmosphere above. Their presence is revealed in high-resolution and high-cadence solar observations from the ground and from space and with state-of-the-art magnetoconvection simulations. Vortical flows exhibit complex characteristics and dynamics, excite a wide range of different waves, and couple different layers of the solar atmosphere, which facilitates the channeling and transfer of mass, momentum and energy from the solar surface up to the low corona. Here we provide a comprehensive review of documented research and new developments in theory, observations, and modelling of vortices over the past couple of decades after their observational discovery, including recent observations in Hα, innovative detection techniques, diverse hydrostatic modelling of waves and forefront magnetohydrodynamic simulations incorporating effects of a non-ideal plasma. It is the first systematic overview of solar vortex flows at granular scales, a field with a plethora of names for phenomena that exhibit similarities and differences and often interconnect and rely on the same physics. With the advent of the 4-m Daniel K. Inouye Solar Telescope and the forthcoming European Solar Telescope, the ongoing Solar Orbiter mission, and the development of cutting-edge simulations, this review timely addresses the state-of-the-art on vortex flows and outlines both theoretical and observational future research directions.