Solar atmospheric model over a highly polarized 17 GHz active region
Solar atmospheric model over a highly polarized 17 GHz active region
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高度极化 17 GHz 活动区域上的太阳大气模型
DOI：
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发表时间：
2008
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通讯作者：
J. Costa
中科院分区：
文献类型：
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作者：
C. Selhorst;A. Silva;J. Costa
目标。我们建立了一个三维太阳大气模型来再现射电观测的活动区亮温。方法：研究方法。开发了一个3D太阳大气模型，以再现Nobeama射电日光仪在17 GHz和34 GHz的射电观测。该模型包含了韧致辐射和陀螺共振发射机制。同时考虑了MDI磁图的位势和无力磁场外推，以及由于磁场相互作用而引起的安静太阳大气(密度和温度分布)的变化。我们分析了2002年6月25(美国国家海洋与大气局10008)观测到的17 GHz(85美元，下午5美元)的高极化有源区。结果。对该区域的模拟要求磁场足点之间的整个投影区改变其大气密度和温度构成。17 GHz的模拟结果表明：a)校正后的MDI磁图的强度可以解释为陀螺共振发射，但饱和点的问题仍然存在；b)对于较少的饱和点，简单的线性校正可以完全改变模拟结果的最大亮温；c)由磁场强度线性校正得到的亮温极大值再现了白天观测到的所有极大值(1.14-1.76$，imes，10^5$.K)；用低正α(0.7-1.10imes，10-2 mm-1)的势场和无力场外推都能很好地再现NOAA 10008陀螺共振辐射的空间亮度分布。在34 GHz处，辐射被成功地模拟为完全自由-自由辐射，其最大亮温与观测结果一致。结论。总而言之，该模型能够解释这两个频率下的观测，然而，这两个频率是由不同的发射机制产生的。
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 ($85,pm,5\%$ 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$, imes,10^5$ 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–$1.10, imes,10^{-2}$ 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.