Showing papers by "Fraunhofer Society published in 1973"

The Hα flare as a secondary product of a coronal instability

Abstract: The assumption that the flare originates in the corona or transition layer, is confronted with the known properties of chromospheric flares It is concluded that the basic mode of the energy transport into chromosphere is heat conduction Only in some flares non-thermal particles contribute to the brightening in lower atmospheric layers: electrons with energy close to 100 keV produce chromospheric bright patches, and protons above 20 MeV cause the photospheric enhancements The particle-produced brightenings are superposed on the basic quasi-thermal flare and involve only small areas as compared with the extensive regions heated through conduction The most probable height of the flare origin appears to be close to the transition layer, between some 4000 and 7000 km above the photosphere The non-thermal acceleration (when present) occurs probably higher than where the flare originates There is no obvious reason why the high electron density in chromospheric flares could not be explained as simply due to increased ionization in the existing plasma, without any flare-induced mass condensations Though there are several facts supporting the flare origin in the corona (or transition layer), one cannot exclude the alternative that the flare instability involves simultaneously a wide (and in different cases different) range of altitudes Energy considerations give some support to such a supposition

Is there horizontal phase propagation of 5-min oscillations at high velocities?

Abstract: New observations of the photospheric 5-min oscillations are presented which prove that the physical reality of the very high horizontal phase propagation velocities observed in connection with the oscillations cannot be maintained. Instead, a statistical model is proposed to explain the observed phase relations.