Photospheric Velocity Fields as Indicators of Flare Activity.
Abstract
The photospheric line-of-sight velocity field of 24 active regions was examined in relation to the flare activity of the regions. There is a good correlation between the complexity of the velocity field and the level of flare activity in the active region within plus or minus 12 hours. Specific velocity patterns could be recognized at 55 of 73 flare sites. Failure to detect patterns at all but one of the remaining flare sites can be understood as due to unfavorable geometry for the detection of the patterns. The specific velocity patterns found at flare sites consist of anomalous Evershed flow patterns in sunspot penumbras (12 of 55 sites), small-scale, mulitpolar velocity structures (15 of 55 sites), and apparent horizontal shears of the velocity field (48 of 55 sites). The shears are frequently but not necessarily associated with magnetic polarity reversal lines. There appears to be a better relation between flare activity and the spatial extent of a velocity shear line than with the strength of the shear. As an aid to predicting the level of flare activity, the velocity complexity of an active region appears to be a practical and valuable parameter.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 01, 1979
- Accession Number
- ADA080561
Entities
People
- Judson W. Harvey
- K. L. Harvey