EVOLUTION IN SPACE AND TIME OF SUPERPENUMBRAL CHROMOSPHERIC FIBRILS

We have studied the spatial structure and temporal evolution of the intensity and Doppler velocity of dark fibrils forming the superpenumbra of an isolated regular sunspot. The observations were obtained with the Multichannel Subtractive Double Pass (MSDP) spectrograph which operates in Hα and is in...

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Bibliographic Details
Published in:Solar physics 1997-05, Vol.172 (1-2), p.139-149
Main Authors: Tsiropoula, G, Dialetis, D, Alissandrakis, C E, Mein, P, Mein, N
Format: Article
Language:English
Subjects:
Absorption
Density
Doppler effect
Evolution
Intervals
Solar physics
Spectrographs
Temporal logic
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Summary:We have studied the spatial structure and temporal evolution of the intensity and Doppler velocity of dark fibrils forming the superpenumbra of an isolated regular sunspot. The observations were obtained with the Multichannel Subtractive Double Pass (MSDP) spectrograph which operates in Hα and is installed at the focus of the Vacuum Tower Telescope (VTT) at Tenerife (Canary Islands). The fibril pattern shows a remarkable stability during the period of our observations (64 min). Moreover, almost all individual fibrils are identifiable in all frames, but they undergo continual changes in contrast, shape and size. Investigating the temporal evolution of intensity and velocity of individual fibrils, fluctuations were found which have a quasi periodic behavior. As mechanisms for these changes we may suggest (a) change of the Doppler shift due to a wave, (b) periodic changes of the density of the Hα absorbing material, (c) disappearance and reappearance of fibrils, in more or less the same magnetic flux tube, at regular intervals.[PUBLICATION ABSTRACT]
ISSN:0038-0938
1573-093X
DOI:10.1023/A:1004939631975