利用MF雷达对耀斑期间电离层D区电子密度的观测研究

利用MF雷达观测资料对X级别耀斑爆发期间在66—80 km高度之间的电子密度进行了研究,观测到了耀斑爆发期间电子密度的突然增加,在较低高度上的电子密度的时间变化趋势与耀斑的软X射线辐射通量相关.电子密度的变化强度依赖于具体的耀斑参数,有些耀斑引起的电子密度增加高达400 cm^-3,有些仅为100 cm^-3左右.但耀斑期间在这一高度区间增加的总电子含量增量仅占耀斑辐射引起的整个电离层总电子含量增量的千分之一左右.最后,利用恢复阶段电子密度的时间变化过程估算了1997年11月4日耀斑期间部分高度上的有效复合系数.

THE STUDY OF THE ELECTRON DENSITY IN IONOSPHERIC D REGION USING MF RADAR DURING FLARES PERIOD

In this paper, the behavior of the electron density between the height of 66 and 80km observed by MF radar at Waknnai station （45.36°N, 141.81°E） during four X-class flares is studied. The sudden increase of the electron density is observed during all of the flare period. The results show that the MF radar can be used as one routine method to observe electron density of the ionospheric D region. By comparison with the soft X-ray flux, it is found that the temporal variation of the electron density in the lower D region has a good correlation with the soft X-ray flux observed by GOES. Nevertheless, the correlation is not good in the higher altitude because of the atmospheric disturbances in the D region. On the other hand, the increases of electron density depends on the parameters of these four flares, the increase of the electron density for some of flare reach as high as 400 cm-3, some of them is only about 100cm-3. Compared with the increase of the total electron content （TEC） caused by the flare with similar parameters, the total increase of electron density between the height of 66 and 80 km is only about one thousandth of TEC that almost has no effect on the delay time of the radiowave. But, the effect of the Sudden Ionospheric Disturbances caused by the increase of the electron density is very strong due to the very high number density of the atmospheric neutral compositions in the height of D region. In the end, the effective recombination coefficient at different heights is estimated using the electron density at the recovery period during the flare on Nov. 4, 1997.