3-D solar atmospheric model over active regions

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European Space Agency, (Special Publication) ESA SP
Citações (Scopus)
Seihorst C.L.
Costa J.E.R.
Silva A.V.R.
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We present here the first results of our 3-D solar atmospheric model over active regions based on radio observations. Intense magnetic fields take place in active regions, which may result in a gyro-resonance emission contribution to the brightness temperature observed at radio frequencies. This model considers the temperature and densities (electrons and ions) distributions, as well as the local magnetic 3-D structure. The location of the magnetic field lines was obtained from force-free extrapolation of MDI (SOHO) magnetograms. This procedure yields three cubes with magnetic field intensities, one for each vector component. Magnetic loops are simulated by filling the region around each magnetic field line with densities and temperature values distinct from the quiet solar atmosphere. Thus, the atmospheric region changes where these flux tubes are present. The model, represented by a volume of 500×500×200 arcsec3, has as free parameters: the flux tube distributions of temperature and density, as well the width. For each column of the cube representing the atmosphere, the equations of radiative transport (including bremsstrahlung and gyro-resonance emission) were solved for the brightness temperature at 17 GHz. These brightness temperature of 500×500 arcsec2 were compared with high spatial resolution solar maps at 17 GHz observed by the Nobeyama Radioheliograph (NoRH). The free parameters are varied so as to obtain the best match to the observations. As a result, the observations are repoduced by an active region model with maximum brightness temperature of 5.2×104 K, magnetic flux tubes with 10 times the local density and 4 times the local temperature below the transition region, and above it, 6 and 2 times the local densities and temperatures, respectively. For this same region, the gyro-resonance emission is negligible compared to the bremsstrahlung contribution, even though the photospheric magnetic field intensities reach 1800 G. The magnetic field contributed mainly for the geometry of the problem.
Assuntos Scopus
Astronomical observations: radio emission , Photospheric magnetic field intensities , Solar physics: Electric and magnetic fields