Ultraviolet brightenings in active regions as observed from OSO-8.
Abstract
Repeated raster images of solar active regions taken at the line centers of the Si IV and C IV resonance lines using the University of Colorado (CU) ultraviolet spectrometer aboard OSO-8 reveal dramatic transient brightenings of up to factors of 10. These brightenings last several minutes and frequently show a repetitive character. Inspection of simultaneous Hα flare patrol records show that these transition zone events are often associated with subflare-like brightenings in the chromosphere. These observations indicate that direct excitation or heating of material already at transition zone temperatures caused by non-thermal particle streams is inadequate to explain the degree of brightening of these lines. The measurements suggest that some process that enhances density of material at ∼105 K is occurring during these events.
- Publication:
-
Solar Physics
- Pub Date:
- December 1977
- DOI:
- 10.1007/BF00152578
- Bibcode:
- 1977SoPh...55..347L
- Keywords:
-
- Chromosphere;
- Plasma Spectra;
- Satellite Observation;
- Solar Activity Effects;
- Solar Spectra;
- Ultraviolet Spectra;
- Carbon;
- H Alpha Line;
- High Temperature Plasmas;
- Luminous Intensity;
- Oso-8;
- Plasma Resonance;
- Silicon;
- Spectroheliographs;
- Solar Physics;
- Flare;
- Active Region;
- Transition Zone;
- Line Center;
- Zone Temperature;
- Solar Active Regions:UV Brightening