The sunspotless flare on April 12, 1991 and the evolution of the neighboring filaments.

Details The sunspotless flare on April 12, 1991 and the evolution of the neighboring filaments. The sunspotless flare on April 12, 1991 and the evolution of the neighboring filaments.

Feb 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26as..109..347l&link_type=abstract

Astronomy and Astrophysics Suppl. 109, 347-353 (1995)

Astronomy and Astrophysics

Astrophysics

1

Sun: Activity, Sun: Flare, Filament

Scientific paper

On April 12, 1991, a 2N sunspotless flare was observed by using the spectra-spectroheliograph at Yunnan Observatory. Halpha_ filtergrams and sequence Halpha_ and Hgamma_ spectra were obtained. In this paper, the morphology of the sunspotless flare and the evolution of the nearby filaments are studied. The results show that the arch-shaped filament which appears on the neutral line to separate the active region from the solar quiet region is activated several days before the onset of the sunspotless flare, and disappears several hours before the onset. It is suggested that the sunspotless flare is associated with the filament, i.e. its activation, disparition brusque and so forth. The sunspotless flare is of unusual long duration (about 80min in the Halpha_ emission) and exhibits a slow rise to maximum intensity (about 20min in the Halpha_ emission) i.e. a `long duration effect' and a `gradual rise-and-fall effect' in both the Halpha_ emission and the soft X-ray radiation, and the flash phase is poorly defined or absent. The energy released by the sunspotless flare may come from the magnetic energy stored in the corresponding plage region. The velocity along the line-of-sight is small for the sunspotless flare (less than several kilometers per second), but rather large for the nearby corridor filament (about a hundred km/s). The horizontal extension velocity of the sunspotless flare is not large. Compared with the general major Halpha_ flare of the same importance, the sunspotless flare is relatively gentle.

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