Impulsive phase explosive dynamics
Abstract
As the result of observational and theoretical research carried out during the last solar cycle, we have seen a dramatic increase in our physical understanding of explosive mass motions during the impulsive phase. One of the major discoveries was the dramatic blueshift of 107 K X-ray lines during the impulsive phase of many solar flares. The temporal and spectral character of these blueshifts is well observed, but their physical interpretation has been quite controversial. Another interesting discovery made during the last solar maximum was strong redshift of 104 K Hα emission during the impulsive phase, which is closely temporally correlated with X-ray and microwave emission. The evidence that redshifts are a consequence of chromospheric explosions is quite strong-stronger, in fact, than that for X-ray blueshifts because of better spatial resolution. Theoretical hydrodynamic simulations of impulsive-phase nonthermal electron transport, spanning the temperature range from 104 to 107 K, show upward-moving 107 K material and downward-moving 104 K material caused by chromospheric evaporation driven by either thermal conduction from a hot flare corona and Coulomb heating by energetic flare electrons of coronal origin. Of the various physical mechanisms that figure in the controversies, only explosive chromospheric evaporation has been shown to explain impulsive-phase Hα redshifts and X-ray blueshifts in a simple and compelling manner.
- Publication:
-
Advances in Space Research
- Pub Date:
- 1986
- DOI:
- 10.1016/0273-1177(86)90140-7
- Bibcode:
- 1986AdSpR...6f.167C
- Keywords:
-
- Solar Flares;
- Stellar Mass Ejection;
- Chromosphere;
- H Alpha Line;
- Red Shift;
- X Ray Spectra;
- Solar Physics