The Phenomenon of Solar TypeⅠNoise Storm in the Short Decimetric Radio Continuum Emission

A decimetric type Ⅳ burst associated with type Ⅲ burst groups and typeⅠnoise storm was observed with the solar radio spectrometers (1.0～2.0GHz and 2.6～3.8 GHz)at National Astronomical Observatories of China (NAOC)on September 23, 1998.The typeⅠnoise storm occurred in the decaying phase of the type Ⅳ burst is emphatically discussed.This noise storm consists of many typeⅠbursts.The duration of each typeⅠburst is of the order of 100-300 ms.The total duration is greater than 11 minutes.Moreover, this noise storm also consists of other fast fine structures, such as single spike or type Ⅲ bursts, spike group, and the pair of type Ⅲ bursts.The durations of these fine structures are in the range about 100-300 ms.Probably, there are some fine structures with durations less than 100ms, but they are not found because of the limitation of the time resolution of the instrument.The circular polarization degree of the typeⅠnoise storm emission is greater than that of the type Ⅳ continuum emission, and with an average value of 64%.The polarization degree of the type Ⅲ bursts are almost 100%, which are week intensity bursts with strong polarization.The typeⅠnoise storm may be attributed to the fundamental plasma radiation similar to the high polarized type Ⅲ noise storm.Because the traditional typeⅠnoise storm is occurred in the range from meter to decameter wavelengths, the decimetric typeⅠnoise storm may be the extension of the metric one, or may be the behavior of the transition region.Because the typeⅠand Ⅲ bursts are occurred simultaneously, this possibly means that they are attributed to the same electron beams.