Solar atmospheric model over a highly polarized 17 GHz active region

Details Solar atmospheric model over a highly polarized 17 GHz active region Solar atmospheric model over a highly polarized 17 GHz active region

Sep 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008a%26a...488.1079s&link_type=abstract

Astronomy and Astrophysics, Volume 488, Issue 3, 2008, pp.1079-1084

Astronomy and Astrophysics

Astrophysics

2

Sun: Atmosphere, Sun: Magnetic Fields, Sun: Radio Radiation

Scientific paper

Aims: We construct a 3D solar atmospheric model to reproduce active region brightness temperature of radio observations. Methods: A 3D solar atmospheric model was developed to reproduce the radio observations at 17 and 34 GHz from the Nobeyama Radioheliograph. The model included bremsstrahlung and gyro-resonance emission mechanisms. Both potential and force-free magnetic field extrapolations from MDI magnetograms are considered, as well as the changes in the quiet Sun atmosphere (density and temperature distributions) due to the magnetic field interaction. We analyze a highly polarized active region at 17 GHz (85 ± 5% LHCP) observed 2002 June 25 (NOAA 10008). Results: Modeling of this region requires that the whole projected region between the magnetic field footpoints changes its atmospheric density and temperature constitution. The modeling at 17 GHz showed the following results: a) the intensity of the corrected MDI magnetograms is able to account for the emission as gyro-resonance, but, the problem with saturation points still persists; b) for a low number of saturation points, a simple linear correction can change the maximum brightness temperature results in the simulations completely; c) the brightness temperature maxima resulting from the linear correction in the magnetic field intensities reproduced all maxima observed during the day (1.14-1.76 × 105 K); and d) the spatial brightness distribution of the gyro-resonance emission of NOAA 10008 was well-reproduced either by a potential or force-free field extrapolation with low positive α (0.70-1.10 × 10-2 Mm-1). At 34 GHz, the emission was successfully modeled as completely free-free radiation with a brightness temperature maximum in agreement with the observations. Conclusions: In summary the model is able to account for the observations at both frequencies, which are, however, produced by distinct emission mechanisms.

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