A Study of the Development of Active Regions on the Sun.

Abstract

The early development of a large number of active regions was studied. Magnetic, photospheric, and chromospheric observations from Mount Wilson were used. It was found that the supergranular pattern of the solar atmosphere plays a very fundamental role in the development of active regions. New regions form in or immediately adjacent to expanding weak old regions that are seen as an enhanced calcium network. The first appearance of the new calcium plage (also of sunspots) takes place in the space between several supergranules, and the subsequent brightening occurs between supergranules, usually filling in several of them. In many cases it appeared that during the first day or two of the development of the group, the magnetic fields did not show zero net flux. Usually the direction of the development of the plage was from following to leading The increase of magnetic flux (the initial growth of the plage) takes place only during the first few days in the life of a region. During this period the boundary of the filamentary structure in Ha increases at the rate of about 200 m/sec. This evidently represents the rapid ordering of magnetic fields around the plage.