Anomalous Polarization Profiles in Sunspots: Possible Origin of Umbral Flashes

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Science  26 May 2000:
Vol. 288, Issue 5470, pp. 1396-1398
DOI: 10.1126/science.288.5470.1396

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We present time-series spectropolarimetric observations of sunspots in the Ca II infrared triplet lines, which show a periodic occurrence of anomalous, asymmetric, circular polarization profiles in the umbral chromosphere. The profiles may be caused by the periodic development of an unresolved atmospheric component in a downward flowing magnetized environment. This active component with upward directed velocities as high as 10 kilometers per second is connected to the umbral flash (UF) phenomenon. We can explain the observations with a semiempirical model of the chromospheric oscillation and of the sunspot magnetized atmospheric plasma during a UF event.

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