A Radio Study of the Evolution of Spatial Structure of an ActiveRegion and Flare

We present the results of a radio study of the evolution of an active region through its are productivity. The radio study was carried out with data obtained by the Nobeyama Radio Heliograph (NoRH) at 17 GHz. We chose the active region AR 7515 which appeared at the east limb on May 23, 1993 and then evolved during its passage across the disk. We followed its evolution until June 2. This region produced many small ares. We consider this region to be a typical active region in the sense that it did not produce any large are, but a large number of weak ares. We investigate the optical and magnetic development of the region and show how this aaects the locations of the aring activity. We discuss a number of events in detail in order to investigate the roles of nonthermal and thermal radio emission in the ares. The nonthermal gyrosynchrotron emission generally occurs in regions of strong magnetic elds, is generally circularly polarized and often varies rapidly in time. On the other hand, gradual radio components tend to be thermal and only weakly polarized if at all. An interesting aspect of the evolution of the ares in this region is that many of the ares in the early phase of the evolution show strong but brief nonthermal radio emission in the impulsive phase followed by gradual thermal emission, whereas in the last 3 days more gradual events without a strong spike of radio emission in the impulsive phase tend to be seen. Correspondingly, the are images suggest that the radio sources { 2 { are more compact during the early phases and more extended in the last half of the period covered. The most dominant component of the preeare region is often not the component which undergoes immediate aring. Sometimes a number of components in the preeare region participate in the are process together. We speculate that these component sources are unresolved compact bipolar loops which are in sequence. Loop{loop interactions occurring at many diierent sites at the same time seems to be a less plausible explanation of these events.