Chromospheric inhomogeneities in sunspot umbrae |
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| Authors: | Jacques M Beckers Paul E Tallant |
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| Institution: | 1. Sacramento Peak Observatory, Air Force Cambridge Research Laboratories, Sunspot, N.M., U.S.A.
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| Abstract: | The properties of rapidly changing inhomogeneities visible in the H and K lines above sunspot umbrae are described. We find as properties for these ‘Umbral Flashes’: - A lifetime of 50 sec. The light curve is asymmetrical, the increase is faster than the decrease in brightness.
- A diameter ranging from the resolution limit up to 2000 km.
- A tendency to repeat every 145 sec.
- A ‘proper motion’ of 40 km/sec generally directed towards the penumbra.
- A Doppler shift of 6 km/sec.
- A magnetic field of 2100 G.
- A decrease in this field of 12 G/sec. This decrease is probably related to the flash motion.
- At any instant an average of 3–5 flashes in a medium-sized umbra. A weak feature often persists in the umbra after the flash. This post-flash structure initially shows a blue shift, but 100–120 sec after the flash, it shows a rapid red shift just before the flash repeats.
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