A summary of data on the occurrence of flares and the development of active regions, based on cinematographic data is given. It is shown that flare frequency is determined by the orientation of the magnetic axis relative to the direction of solar rotation and the morphology of the magnetic field as seen in Hα. In particular, flares are most numerous in simple round spots with reversed polarity nearby, although they may also be frequent in complex spots with polarity reversal. Important solar active regions are shown to evolve principally along two lines; typically they appear as bright regions with loops and grow rapidly to stable bipolar magnetic form. Important activity will occur as the result of later growth of following polarity ahead of the main spots, or some other source of reversal. However, some groups appear as reversed polarity regions and grow rapidly to a level of extreme activity. A series of papers giving case histories is promised.

© 1970 Kluwer Academic Publishers. Provided by the NASA Astrophysics Data System. Received 21 April 1970; Issue Date October 1970. I thank the various people who have cooperated in operating the Caltech and Tel Aviv Photoheliographs - David Bohlin, Spencer Weart, David Lambert, Ernest Lorenz, James Pederson, Uri Feldman and Reuven Zach, as well as Gail Pruss for help with the prints. This work was supported by NASA Grant No. 05-002-034 and by the NSF Atmospheric Science Section Grants 1472 and 13642.

<p>Published - <a href="/records/3vtm5-qqc59/files/1970SoPh___14__328Z.pdf?download=1">1970SoPh___14__328Z.pdf</a></p>