Application of Microwave Spectroscopy to the Study of Coronal Field Changes Associated with a Disappearing Sunspot,
CALIFORNIA INST OF TECH PASADENA
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A critical physical parameter affecting solar activity is the distribution of coronal magnetic fields. Microwave observations provide the only technique for the quantitative measurement of these fields. This report presents the preliminary analysis of high spatial and spectral resolution observations designed to measure the distribution and evolution of the coronal magnetic fields of a disappearing sunspot. Data at 56 frequencies between 1.2 and 14 GHz were acquired with the three-element frequency-agile interferometer. This system directly measured the size of coronal microwave sources at each frequency and polarization. The temperature of the source was determined from the ratio of source flux to area. This yielded the size and brightness temperature spectra of the microwave sources associated with a sunspot as it disappeared over three successive days. On the basis of gyroresonance opacity, the corona would be expected to be opaque at microwave frequencies at surfaces corresponding to specific values of coronal field strength. The overall form of the observed spectra was consistent with such expectations, although there were differences of potential physical significance.