Interaction with the lower ionosphere of electromagnetic pulses from lightning: Heating, attachment, ionization, and optical emissions.

摘要

A typical lightning discharge produces an intense 20 gigawatt electromagnetic (EM) pulse of 50 to 150 {dollar}mu{dollar}s duration. A significant portion of this energy propagates upward where it interacts with the ambient electrons in the collisional lower ionosphere. In the present work the Boltzmann kinetic equation for electrons and Maxwell's equations for the EM fields are self-consistently solved to simulate the interaction of lightning radiated EM pulses with the lower ionosphere. Results indicate that attachment, ionization, and optical emissions produced in this interaction are sufficient to explain 'early' subionospheric VLF signal perturbations and airglow brightening observed simultaneously with lightning. This model also provides the basis for the quantitative evaluation of a wide variety of electrodynamic and chemical processes in the ionosphere which occur in response to the energy released in lightning discharges. Under nighttime conditions, individual pulses with peak amplitudes of 10-20 V/m (normalized to 100 km free space distance) produce changes in electron density of 1-30% of the ambient while a sequence of such pulses leads to more than 100% modification at altitudes between 85 and 92 km. Among the optical emissions, the most promising for observations are the 1st (red) and 2nd (blue) positive bands of N{dollar}sb2{dollar}, which emit at rates of {dollar}7 times 10sp7{dollar} and {dollar}rm 10sp7{dollar} cm{dollar}rmsp{lcub}-3{rcub}ssp{lcub}-1{rcub}{dollar} at {dollar}sim{dollar}92 km respectively for a 20 V/m EM pulse. The height integrated intensities of the emissions reach {dollar}4 times 10sp7{dollar} and {dollar}6 times 10sp6{dollar} R, last for {dollar}sim{dollar}50 {dollar}mu{dollar}s and produce 1,200 and 200 Rayleigh-seconds for zenith observations.