Physics
Scientific paper
Apr 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993soph..144..349l&link_type=abstract
Solar Physics (ISSN 0038-0938), vol. 144, no. 2, p. 349-360.
Physics
20
Microwave Emission, Solar Physics, Solar Radio Emission, Sunspots, Brightness Distribution, Solar Spectra
Scientific paper
The center-to-limb variation of both the spectral and spatial brightness distributions is investigated using a series of microwave observations of a sunspot in the active region NOAA 4741. Depending on the heliocentric position of the sunspot, the microwave emission appears in two typical profiles: either a ring structure near the center of the disk or a single-peak structure near the limb. Due to the increase of the gyroresonance opacity of the field lines near the spot center as the viewing angle increases, the brightness temperature at high, optically thin frequencies increases slightly as the spot approaches the limb. In addition, a change of effective harmonic, which accompanies a discontinuous change in the degree of polarization, characterizes the center-to-limb variation of the gyroresonance spectrum. Finally, the height of the gyroresonance layer, low in the corona of the active region, is determined from a change of spectrum from gyroresonance to free-free emission as the spot passes over the solar limb.
Gary Dale E.
Hurford Gordon J.
Lee Jeongwoo W.
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