Physics
Scientific paper
Mar 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992soph..138...93a&link_type=abstract
Solar Physics (ISSN 0038-0938), vol. 138, March 1992, p. 93-105.
Physics
20
Astronomical Photography, Chromosphere, Sunspots, Umbras, Fine Structure, H Alpha Line, Propagation Velocity, Solar Magnetic Field
Scientific paper
Running penumbral waves, umbral oscillations, umbral flashes, and their interrelations were studied from H-alpha observations of a large isolated sunspot. Using a subtraction image processing technique, the sharp intensity gradient between the umbra and the penumbra was removed, and the low-contrast, fine features were enhanced. Running penumbral waves were observed which started in umbral elements with a size of a few arcseconds, covered the umbra and subsequently propagated through the penumbra. The period of the waves was 190 s, and the mean propagation velocity was about 15 km/s. Intense brightenings were detected, located between umbral elements from where waves started, which had the characteristics of umbral flashes. There are indications that umbral flashes are related to the propagation of the waves through the umbra and their coupling. The subtraction images also show considerable fine structure in the chromospheric umbra, with size between 0.3 and 0.8 arcsec.
Alissandrakis Constantine E.
Dialetis D.
Georgakilas A. A.
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