Solar Radio Pulsation Event Observed by the VLA and OVRO

Details Solar Radio Pulsation Event Observed by the VLA and OVRO Solar Radio Pulsation Event Observed by the VLA and OVRO

May 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...180.4505a&link_type=abstract

American Astronomical Society, 180th AAS Meeting, #45.05; Bulletin of the American Astronomical Society, Vol. 24, p.802

Astronomy and Astrophysics

Astronomy

6

Scientific paper

We investigate interpretational aspects of the radio pulsation event which has been observed by the Very Large Array (VLA) and the Owens Valley Radio Observatory (OVRO) on December 21, 1990, 1930 UT, during the second MAX'91 observing campaign. The VLA was observing with a time resolution of 0.4 s at 0.33, 1.4 and 4.9 GHz, while OVRO used a time resolution of 0.2 s at 1.2, 1.4, 1.6, 1.8 and 2.0 GHz. The radio pulsation event was triggered by a C3.3 class flare in soft X-rays in active region 6412 (NOAA). The time profile of the quasi-periodic radio emission exhibits a period of 8.8 s and shows indications of secondary periodicities with faster periods. We investigate whether these periodicities can be explained in terms of (i) MHD eigen-modes in cylindrical fluxtubes (MHD surface modes and harmonic modes), or (ii) relaxational oscillations of a nonlinear dissipative system. We test these two options by means of Fourier spectra and by reconstruction of the ``strange attractor dimension'' of nonlinear systems. We attempt a three-dimensional reconstruction of the pulsating source by means of magnetic field extrapolation from the photospheric magnetogram and by using the constraints of the radio maps at multiple frequencies. Preliminary analysis indicates that plasma emission as well as gyrosynchrotron emission is coherently modulated in spatially diverging magnetic structures. We investigate whether the pulsating radio emission originates from plasma confined in a pulsating loop structure or whether the radio emission is driven by electron beams which are produced in a pulsating acceleration mechanism. The latter possibility would support a model where the primary energy release itself is governed by a nonlinear dissipative system, e.g. by oscillatory magnetic reconnection.

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