Observational Characteristics of CME Events and Associated Radio Emission

We statistically analyze 76 radio-burst events associated with CME events during the period of 2003~2005,which is in the descending phase of solar activity cycle.The radio data are within the frequency range of 18 MHz to 7 200 MHz and are obtained from the LACSO/SOHO or the spectrometers of Culgoora and NAOC (National Astronomical Observatories of China).Out of the 76 events 50 and 26 are fast and slow,respectively.We find that the fractions of fast and slow CME events decrease and increase in the descending phase of solar activity cycle,respectively.This is possibly because of the correlation of the frequencies of CME events with the variations of structures and positions of solar magnetic fields during the solar activity cycle.Furthermore,we find a trend for types and durations of radio bursts.The durations decrease with the radio frequencies.The trend supports the idea of a unified model about type-II radio bursts associated with CMEs.In addition,we find that type-III bursts or fast fine structures (FS) frequently occur in the wavelength range of centimeters to meters just before or after the CMEs start.The radio FS could be interpreted as precursor phenomena of the CMEs or as the results of small-scale magnetic disturbances in the lower corona caused by magnetic reconnections during the early phases of the CMEs.