Differential Rotation and Giant Cell Circulation of the Solar Ca⁺-Network

Extract

High precision computer controlled tracings of bright Ca⁺-mottles were performed during 1974 and 1975 at the Locarno Observatory of Göttingen to study solar differential rotation and to search for giant cell circulation pattern. Details of the observing method and the results from observations during 1974 have been published very recently (Schröter and Wöhl, 1975). Our method consists of measuring the position of 5–15 bright Ca⁺-mottles with respect to the center of the solar disc every 10 to 15 min during 4 h every day. A computer controlled program determines first the center of the disc and immediately afterwards the right ascension and declination of a Ca⁺-mottle which was centered by the observer into a 1′-diameter spectrograph pinhole by watching a TV-monitor displaying a Ca⁺-K-line solar image. From a linear least squares fit of the observed positions the solar latitude and longitude were computed for the beginning and the end of the daily 4 h observation period. From this the components in latitude and longitude of the proper motions were derived which result from the differential rotation, possible giant cell circulation and the small scale random walk of these features.