Multi-frequency heliograph observations of type II bursts

Details Multi-frequency heliograph observations of type II bursts Multi-frequency heliograph observations of type II bursts

Oct 1975

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1975pasau...2..370n&link_type=abstract

(Astronomical Society of Australia, Annual General Meeting, 9th, Parkes, New South Wales, Australia, May 14-16, 1975.) Astronomi

Astronomy and Astrophysics

Astronomy

14

Fine Structure, Harmonic Radiation, Spectroheliographs, Spectrum Analysis, Type 2 Bursts, Brightness Temperature, Plasma Frequencies, Radio Transmission, Shock Wave Propagation, Solar Corona

Scientific paper

Results are presented for analysis of multifrequency observations of five solar type II bursts which were made with a radioheliograph at frequencies of 160, 80, and 43.25 MHz. The spectra of all five bursts are found to exhibit split-banded harmonic structure. It is shown that (1) fundamental sources are, on the average, twice as large and twice as bright as harmonic sources; (2) fundamental sources are much higher than harmonic ones; (3) both types of sources increase in size with decreasing frequency; (4) the sizes of related upper and lower fundamental and harmonic sources are essentially equal, but the lower sources are twice as bright; (5) the observed sources are nearly circular and only slightly elongated; and (6) the maximum observed brightness temperature increases with decreasing frequency in the present frequency range. These results indicate that the portion of a wide-angle MHD disturbance which becomes a type II-emitting shock wave does not generally propagate radially or along the local density gradient; instead, it tends to move away from large sunspots. It is concluded that the large sizes and source separations observed in this study are incompatible with the predictions made by current scattering theories.

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