雷暴云准静电场和夜间低电离层的电离

用点电荷模型计算雷暴云突然放电后形成的准静电后形成的准静电场随高度的分布，以E/N（E的电场大小，N为大气密度）为输入参量，在一定条件下，对Boltzmann方程数值求解，计算电离层电子数密度的扰动。计算结果表明，在约70-90km之间，在约放电后的10ms内，准静电场大于中性大气的击穿电场，将引起大气的雪崩电离，从而引起夜间低电离层电子密度的显著增加，但这种电子密度的增加是暂的，在很短的时期内就恢复到平静时的水平，恢复时间随高度的变化而不同。

THUNDERSTORM QUASI-ELECTROSTATIC (QE)FIELD AND THE IONIZATION OF NIGHTTIME LOWER IONOSPHERE

Lightning plays an important role not only in the global circuit, but also in the coupling of troposphere-mesosphere-lower ionosphere. It is responsible for some optical phenomena occurring in the upper atmosphere, such as 'sprites', which occur above thunderstorms at altitudes typically ranging from 50 to 90 km. In this paper, a simple point charge model is used to calculate the dependence of amplitude of quasi-electrostatic field on altitude after the thunderstorm discharge completed. By comparison with the disk charge model, we find the point charge model is in good agreement with the former. Since the upper ionospheric boundary are ignored in both models, the calculated thunderstorm QE field is an approximate results. Using the ratio of the electric field to the total atmospheric neutral density as the input parameter, with some reasonable assumption, the Boltzmann equation is solved numerically to decide the disturbance in nighttime lower ionosphere. The results show that the QE field could be greater than the breakdown electric field of the neutral atmosphere between about 70-90km, within about 10ms, which can produce the avalanche ionization of neutrals. As a result, the electron density increases dramatically in these regions. Because the effective time of QE field in ionosphere is very short, the enhancement of electron density will be transient, and the nighttime lower ionospheric disturbance will be recovered to the normal level in a short time. The recovery time depends on the ionospheric altitude due to the different conductivity at different heights in the lower ionosphere.