EVOLUTION IN-SPACE AND TIME OF SUPERPENUMBRAL CHROMOSPHERIC FIBRILS

We have studied the spatial structure and temporal evolution of the in tensity and Doppler velocity of dark fibrils forming the superpenumbra of an isolated regular sunspot. The observations were obtained with t he Multichannel Subtractive Double Pass (MSDP) spectrograph which oper ates in Her and is installed at the focus of the Vacuum Tower Telescop e (VTT) at Tenerife (Canary Islands). The fibril pattern shows a remar kable stability during the period of our observations (64 min). Moreov er, almost all individual fibrils are identifiable in all frames, but they undergo continual changes in contrast, shape and size. Investigat ing the temporal evolution of intensity and velocity of individual fib rils, 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 H alp ha absorbing material, (c) disappearance and reappearance of fibrils, in more or less the same magnetic flux tube, at regular intervals.