Enhanced emission of Alfvén waves from sunspots during proton flares
✍ Scribed by D. J. Mullan
- Publisher
- Springer
- Year
- 1981
- Tongue
- English
- Weight
- 749 KB
- Volume
- 70
- Category
- Article
- ISSN
- 0038-0938
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✦ Synopsis
has shown that, if Alfv6n waves exist in a sunspot umbra, they are normally reflected so strongly by the temperature minimum as to be essentially undetectable in the upper solar atmosphere. However, it is known that in many proton flares, chromospheric emission overlies the umbra of a sunspot, indicating that the transition region (TR) between chromosphere and corona in the umbral flux tube has moved down to lower altitudes. As a result of this lowering, umbral Alfv6n waves have readier access to the corona: the coronal leakage depends exponentially on the altitude of the TR. We find that the Alfv6n wave flux which leaks out of the umbra into the corona can exceed 107 ergs cm -2 s 1. A flux of this magnitude is expected to dissipate rapidly in the corona, thereby contributing to a positive feedback loop which ensures prolonged (~ 1 hr) leakage of the umbral Alfv6n waves into the corona. We propose that these Alfv6n waves may contribute significantly to prolonged energization of proton flares in which umbral coverage occurs.