Abstract
By the Nobeyama Radioheliograph,
evolution of radio features in flare
productive active region
NOAA7321 was observed. Delay of emergence of radio feature was detected
comparing with soft
X-ray feature observed by Yohkoh, which implied that coronal region
above NOAA7321 had
weak magnetic field strength and high temperature at initial phase of
evolution. During evolution of
this region, many radio bursts are observed by the radioheliograph and
the radio polarimeters at
Nobeyama and Toyokawa. These bursts showed radio spectra with high
turnover frequency and
steep lower frequency cutoff. Negative bursts were observed during
entire observation period of
NOAA7321. These results suggest that the radio bursts in NOAA7321 were
caused by
continuous appearance of strong magnetic field regions to lower corona.