Fine structures in solar radio emission at decametre wavelengths

Details Fine structures in solar radio emission at decametre wavelengths Fine structures in solar radio emission at decametre wavelengths

Jun 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...286..597b&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 286, no. 2, p. 597-606

Astronomy and Astrophysics

Astronomy

13

Drift Rate, Electron Cyclotron Heating, Fine Structure, Frequency Shift, Masers, Radio Astronomy, Solar Activity, Solar Corona, Solar Radio Emission, Decametric Waves, High Frequencies, Plasma Oscillations, Very High Frequencies

Scientific paper

Millisecond-duration structures in solar radio emission have been studied at decameter wavelengths using the Acousto-Optic Spectrograph at the Nancay Radio Astronomy Station of the Paris-Meudon Observatory. With this instrument, dynamic spectra can be obtained in left- and right-hand polarization over a 21 MHz band between 20 and 80 MHz with a frequency resolution of 30 kHz and a time resolution down to 42 ms for a single polarization. Observations during 1989 to 1991 have revealed a number of interesting fine structures within the frequency range 26 to 55 MHz. Of particular interest are successions of fine structures a few MHz wide, having durations down to the limit of resolution, which may be superimposed upon some larger outburst. These bursts have negative drift rates of some 10 MHz/s or faster. The envelope of a group of these short-duration bursts may show an overall slow negative drift in frequency. Average values of about 200 and 600 ms are estimated, respectively, for the e-folding decay time and the exciter duration of a burst between 38 and 50 MHz. With a background electron temperature of 106 K, we derive an estimation of the energy of hot electrons (approximately 1 or 2 keV) and of source sizes (less than or equal to 450 km). These emissions seem to be unusual at decametric frequencies although they are quite often observed at higher frequencies. The proposed mechanism is interesting as a possible source of energy exchange and heating in the solar corona. A few solar S-bursts, showing a characteristic negative frequency drift of about 2 MHz/s, were also observed although this type of activity was not profilic.

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