厘米-分米波段Ⅲ型爆发的统计分析

Statistical Analysis of Type Ⅲ Bursts in the Centimetric-Decimetric Wavelength Region

统计分析了太阳第23周期间(2000年7月至2004年9月)在625～1500MHz,2600～3800MHz和5200～7600 MHz范围频谱仪观测到的Ⅲ型射电爆发.给出了Ⅲ型爆发的分布、寿命、频率漂移率、偏振度和频率带宽.结果显示,频率漂移率和频率带宽的平均值随频率的增加而增大,寿命和偏振度的平均值既不是常数也不是在宽频延伸上保持均匀不变的.最多的Ⅲ型爆发分布在625～3800 MHz范围内,且随频率的增加而增多.分析表明,电子加速和能量释放地点主要是在分米波范围内,这个频率范围的特征可能与分米波段上的磁位形有关,并且与主耀斑地点附近磁重联区中的电子加速有关.然而,还有相当数量的Ⅲ型爆发发生在5200～7600 MHz范围内,这个特征表明电子加速的地点是在一个日冕的宽范围中.关于厘米-分米波段Ⅲ型爆发的辐射机制最可能包含相干的等离子体辐射或电子回旋脉泽辐射过程.

A statistical analysis of multi-band type Ⅲ bursts observed with the spectrographes in the ranges of 625-150（MHz, 2600N3800MHz and 5200-7600MHz during the 23rd solar cycle （from July 2000 to September 2004） is carried out in the paper. The main statistical results, e.g., distribution of type Ⅲ bursts, duration, frequency drift rate （normal and reverse slopes）, degree of polarization and frequency bandwidth are given. The results indicate that the average values of the frequency drift rates and frequency bandwidths increase with the frequency. The average values of the durations and degrees of polarization are neither constant nor uniform varying over broad frequency extent. Most of type Ⅲ bursts are distributed within the range from 625 to 3800 MHz, and decrease with the increase in frequency. This distribution result means that the places of electron acceleration and energy release are mainly within the decimetric range, and the characteristic of frequency range is possibly related with the magnetic configuration on decimetric wavelengths, and the position of the electron acceleration in the reconnection region of magnetic field nearby the place of the main flare. However, there are large number type Ⅲ bursts in the range of 5200-7600MHz. This diagnostic means that the place of electron acceleration is in the broad range of the corona. The radiation mechanisms of type Ⅲ bursts on centimetric-decimetric wavelengths most probably include the coherent plasma radiation or the emission processes of electron cyclotron maser.