The lower photosphere of active regions of the Sun prior to flares and without flares. II. Physical conditions.
Abstract
The physical conditions have been analysed in lower and middle photospheric layers of active regions prior to and without flares. The temperature, gas pressure and turbulent velocities were determined from intercomparisons of observed and theoretical profiles of several Fraunhofer lines insensitive to magnetic fields. In deep layers, the characteristics obtained for regions without flares agree quite well with the VAL-F model of a facula. In the lower photosphere (m ≥ 2), the difference between physical conditions in flaring and non-flaring regions becomes apparent as long as 10 h prior to flares; in the former, the lines spring from denser (by 5 - 20%) and hotter (by 100 - 150K) layers with turbulent velocities up to 6 - 7 km/s. In the interval from 3 - 4 h to 1 h, the temperature and density excesses decrease with time. Immediately before flares, sharp changes in all medium characteristics are observed, the temperature excess may reach 300K while that of pressure amounts to -25%. As the height grows, in the middle photosphere, the differences diminish.
- Publication:
-
Kinematika i Fizika Nebesnykh Tel
- Pub Date:
- April 1993
- Bibcode:
- 1993KFNT....9...57A
- Keywords:
-
- Atmospheric Composition;
- Photosphere;
- Plasma Turbulence;
- Solar Atmosphere;
- Solar Flares;
- Fraunhofer Lines;
- Gas Pressure;
- Gas Temperature;
- Solar Activity;
- Solar Physics