Formation of Solar Flares without Magnetic Neutral Points.

Abstract

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Formation of Solar Flares without Magnetic Neutral Points. Wentzel, Donat G. Abstract A flare may be caused by the collapse of an unstable chromospheric region, under the action of magnetic forces, toward a surface of minimum but finite magnetic field strength. The compression of the magnetic field during the collapse results in forces which stop the collapse, in a time comparable to the rise time of flare light curves. Turbulence is likely to occur if the velocities of collapse become comparable to Alfv6n speeds. If turbulence occurs, it can cause sufficient Ohmic dissipation of the magnetic fields to explain the rate of optical emission (Wentzel, Astron. J. 68, 299(A), 1963). The dissipation and emission are localized in thin surfaces at eddy boundaries. The total depth of the emitting surfaces crossed by a line of sight through the flare is of the order of 10 km, in agreement with inferences from observations (Suemoto, Hiei, and Hirayama, J. Phys. Soc. Japan 17, Suppl. A-2, 231). if the same kind of collapse which causes an optical flare in the chromosphere occurs at greater heights, the density is insufficient to radiate away the thermal energy derived from Ohmic dissipation. The result is heating, with attendant favorable conditions for the generation of radio, x-ray, and particle events, instead of an optical flare. Depending on the extent of the collapsing region, optical and heating events may occur alone or together. The conditions under which turbulence may occur and the corresponding gas densities have been investigated numerically. Some of the consequences of the theory relate to flare heights and light curves, increases in density before optical flaring starts, rates of expansion of flare areas, homologous flares, and apparently simultaneous flares. Publication: The Astronomical Journal Pub Date: March 1964 DOI: 10.1086/109250 Bibcode: 1964AJ.....69..151W full text sources ADS |