2015/09/22 by Tongjiang Wang, Leon Ofman, L. Ofman +4 · 2 citations
Physics and Astronomy · #Adiabatic process #Astro and Planetary Science #Astrophysics #Computational physics #Coronal loop #Coronal mass ejection #Dissipation #Flare #Ionosphere and magnetosphere dynamics #Magnetic field #Magnetohydrodynamics #Mechanics #Phase (matter) #Physics #Polytropic process #Solar and Space Plasma Dynamics #Solar wind #Thermal conduction #Thermodynamics #astro-ph.SR
paper · pdf · doi:10.1088/2041-8205/811/1/l13
published as 2015, ApJ, 811, L13 · 7 pages, 5 figures, ApJ Lett., 811, L13, 2015
arxiv created 2015/09/22 · openalex publication_date 2015/09/22 · arxiv updated 2015/09/23 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
Analysis of a longitudinal wave event observed by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory is presented. A time sequence of 131 Å images reveals that a C-class flare occurred at one footpoint of a large loop and triggered an intensity disturbance (enhancement) propagating along it. The spatial features and temporal evolution suggest that a fundamental standing slow-mode wave could be set up quickly after meeting of two initial disturbances from the opposite footpoints. The oscillations have a period of ∼12 minutes and a decay time of ∼9 minutes. The measured phase speed of 500 ± 50 km s −1 matches the sound speed in the heated loop of ∼10 MK, confirming that the observed waves are of slow mode. We derive the time-dependent temperature and electron density wave signals from six AIA extreme-ultraviolet channels, and find that they are nearly in phase. The measured polytropic index from the temperature and density perturbations is 1.64 ± 0.08 close to the adiabatic index of 5/3 for an ideal monatomic gas. The interpretation based on a 1D linear MHD model suggests that the thermal conductivity is suppressed by at least a factor of 3 in the hot flare loop at 9 MK and above. The viscosity coefficient is determined by coronal seismology from the observed wave when only considering the compressive viscosity dissipation. We find that to interpret the rapid wave damping, the classical compressive viscosity coefficient needs to be enhanced by a factor of 15 as the upper limit.