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.
DownLoad: