There is a great interest to limb flares which show development of flares
in height above the photosphere with emphasis of the coronal part of emission.
An X9 class flare occurred on November 2, 1992 in the active region NOAA 7321
behind the western limb. It was a prominent Long-Duration Event at the decline
of the 22
solar cycle: its decay lasted over 30 hours. The
flare was recorded both by the Nobeyama Radioheliograph (NRH, 17 GHz)
and the Siberian Solar Radio Telescope (SSRT, 5.7 GHz). The interest in this
powerful flare is motivated, first, by the possibility to study microwave
emission mechanisms which manifested themselves in extremely wide range
of four orders of magnitude together with evolution of the spatial structure
of microwave burst sources using two frequencies. Second, sub-second pulses
were observed at both frequencies. So it is possible to estimate the heights
above the photosphere and plasma parameters of sub-second pulse sources
observed in this limb flare.
Some papers have been published devoted to study of different aspects of this
flare: observations of sub-second microwave spikes at 5.7 GHz
(Altyntsev et al. 1995);
acceleration of high-energy electrons
(Nakajima & Metcalf 1995);
long-duration decay stage with large system of ascending H
and soft X-ray (SXR) loops
(Ichimoto et al. 1993;
Feldman et al. 1995).
The most powerful part of the impulsive phase of the flare was studied by
Nakajima et al. (1998)
using mainly hard X-ray Yohkoh and NRH data.
However, some aspects and features of the flare remain obscure. The overall scenario of the flare is still vague. The structure of the magnetic field and the physical conditions in the flaring plasma were not sufficiently investigated. These points constitute the main subject of the present paper.
Some specific issues we would like to address are as follows: observational material (Sect. 2), physical conditions derived from the observations (Sect. 3), the magnetic configuration and the proposed scenario for the flare (Sect. 4).
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