EVIDENCE OF THERMAL CONDUCTION SUPPRESSION IN A SOLAR FLARING LOOP BY CORONAL SEISMOLOGY OF SLOW-MODE WAVES

Journal Article · Sun Sep 20 04:00:00 EDT 2015 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/811/1/L13· OSTI ID:22518882

Wang, Tongjiang; Ofman, Leon; Provornikova, Elena ^[1]; Sun, Xudong ^[2]

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1. Department of Physics, Catholic University of America, 620 Michigan Avenue NE, Washington, DC 20064 (United States)
2. W. W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305 (United States)

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{sup −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.

• OSTI ID: 22518882
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 1 Vol. 811; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
DENSITY
DISTURBANCES
ELECTRON DENSITY
EXTREME ULTRAVIOLET RADIATION
MAGNETOHYDRODYNAMICS
OSCILLATIONS
SEISMOLOGY
SOLAR CORONA
SOLAR FLARES
SOUND WAVES
SUN
THERMAL CONDUCTION
THERMAL CONDUCTIVITY
TIME DEPENDENCE
VISCOSITY