Low photosphere in active regions of the Sun prior to flares and without flares. I. The Fraunhofer spectrum.
Abstract
A comparative analysis of several photospheric spectral lines has been carried out for 50 active regions prior to flares ("active flocculi") and for 30 regions without flares ("quiet flocculi"). The lines which form in lower photospheric layers (h ≤ 100 km) are found to strengthen in both types of flocculi as compared to the quiet photosphere. On the contrary, the lines which form in higher photospheric layers are weakened. All the lines in flocculi are widened to a various degree. The difference between active and quiet flocculi is noticable already 3 - 10 hours before the onset of flares irrespective of their importance, this difference manifesting itself mainly in a greater widening of deep-forming lines in active flocculi. These lines begin to show a tendency to become weaker 1 - 3 hours before the onset of flares. In some cases, the lines can become stronger and wider again immediately (less than 1 h) before flares. This might be a result of fast-running processes which spread over the lowest photospheric layers as well.
- Publication:
-
Kinematika i Fizika Nebesnykh Tel
- Pub Date:
- February 1993
- Bibcode:
- 1993KFNT....9...24A
- Keywords:
-
- Fraunhofer Lines;
- Photosphere;
- Solar Atmosphere;
- Solar Flares;
- Flocculating;
- H Beta Line;
- Solar Activity;
- Solar Physics