电离层加热实验中超强电子密度增强特征

2011年11月利用欧洲非相干散射雷达协会(EISCAT)的大功率加热设备和诊断设施开展了挪威高纬度地区电离层加热实验. 在此次加热实验中, UHF雷达探测到了十分明显的电子密度增强现象, 反射高度附近电子密度最大增幅可达269.3%, 而在远离谐振区的300~500 km及以上高度的增幅也可达30%~50%. 通过对加热前后离子线谱和数据残差的对比分析, 表明300~500 km的电子密度增强是真实可信的, 在如此大的空间范围出现增幅如此大的电子密度增强特征实属罕见. 另外通过对等离子体线谱的分析, 得到了等离子体线双谐振峰结构, 本文利用电子的速度分布函数和等离子体线谱之间的关系, 对加热实验中观测到的等离子体线谱进行了仿真, 提出了超热电子是引起本次电子密度增强的可能机制. 并利用仿真中所使用的超热电子速度参数对超热电子的电离能力、横向和纵向自由程进行了计算, 最终验证了所提出的物理机制的合理性.

A large increase of electron density in ionospheric heating experiment

The high latitude ionospheric heating experiment was carried out with the EISCAT high power heating and diagnosing facilities in November 2011 in Norway. An obviously increased electron density was observed by UHF radar. The increase is up to 269.3% above the background level around the reflection height, and it could reach 30%~50% at the altitude range of 300~500 km far away from the heater interaction region. The increased electron density observed at 300~500 km is verified by the analysis of ion lines and residual error in this experiment. To the authors' knowledge, the large increase of electron density in such a large range of space is extremely rare. In addition, a double-peaked spectrum is observed in plasma lines. The plasma lines are simulated based on the relationship between the electron velocity distribution function and the plasma line spectrum, and the large increase of electron density in this experiment may be caused by suprathermal electrons. The ionization ability, horizontal and vertical free path of suprathermal electrons are calculated using the velocity parameters used in the plasma lines simulation, and the hypothesis is proved to be reliable.