Fine structure superimposed on mm-wavelength (18-23 GHz) spectra of solar active region

Details Fine structure superimposed on mm-wavelength (18-23 GHz) spectra of solar active region Fine structure superimposed on mm-wavelength (18-23 GHz) spectra of solar active region

Feb 1991

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991ipesprept.....c&link_type=abstract

M.S. Thesis Instituto de Pesquisas Espaciais, Sao Jose dos Campos (Brazil).

Physics

Bremsstrahlung, Chromosphere, Fine Structure, Radiometers, Solar Activity, Temporal Resolution, Calibrating, Current Sheets, Cyclotrons, Frequencies, Neutral Currents

Scientific paper

A mm-lambda, 23-18 GHz, variable frequency radiometer with frequency resolution of 1 GHz and time resolution of 0.6-16 sec. has been developed in conjunction with a 13.7 meter diameter antenna. Here, this new radiometer, the procedures of calibration and observations of active region are described in detail. Observations of active region have been carried out using the mm-lambda radiometer. So far, spectra of four active regions have been observed. Two of these spectra have exhibited frequency fine structures in emission as well as in absorption, of the order of 2 GHz wide in frequency and in amplitude less than or equal to 100 percent of the original flux value, lasting for about half an hour. The spectra of the center of the sun and those of the active region have been interpreted in terms of 'bremsstrahlung' as a process of emission. Fine structure in absorption has been interpreted in terms of presence of a neutral current sheet between the radio source and the observer. The superimposed fine structure in emission has been discussed in terms of two possible mechanisms: (1) the emission of cyclotron line, and (2) the radio signature of a mysterious temperature plateau in the chromosphere.

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