Lower and Middle Atmospheric Electrodynamics
U. S. Inan
Stanford University, Stanford, California, USA (email@example.com)
Electrodynamics of the upper and middle atmosphere is significantly affected by dynamic phenomena in the lower atmosphere, in particular driven by thunderstorm and lightning activity. Precious little is known about the dynamics and chemistry of the altitude range below ~60 km, especially at night, due to the extremely low densities, that preclude any useful radar measurements. Transient disturbances produced by individual lightning discharges, as well as longer lasting effects (e.g., ionization enhancements or elevated electron temperatures) maintained through the duration of intense thunderstorms present windows-of-measurability that may help us better understand the highly complex dynamics of these regions. The measurables become available during brief periods of spectacular optical displays, known as sprites, gigantic blue-jets, elves, as well as in the form of ionization/temperature enhancements, and Terrestrial Gamma-ray Flashes (TGFs). Chemical response of the middle atmosphere to these dynamic disturbances is clearly measurable, and allows the assessment of the rate coefficients of different processes (e.g., attachment, recombination). For example, during clearly measurable ionospheric signatures of lightning-induced electron precipitation events, the energies of the radiation belt electrons involved can be as high as several Me, in which case the disturbances produced are at altitudes as low as ~50-60 km. In recent years, several examples of unusually long lasting (tens of minutes instead of tens of seconds) disturbances have been observed, which defy the predictions of currently available chemistry models.
The electrodynamics of the middle atmospheric phenomena driven by lightning discharges can be highly complex, requiring dynamic solutions of the Boltzmann’s equation together with Maxwell’s Equations, with the myriad of the elastic and inelastic loss processes in air accounted for. The resulting optical, x-ray, and ionization enhancement (or attachment driven depletion) responses are thus equally complex and rich, but thus present the opportunity of extracting heretofore-unavailable information about the many underlying complex processes. Part of the complexity of the responses result from the variability of the driving fields (EMP and quasi-static) that are released in lightning discharges. However, a substantial part of the observed complexity is a result of the highly variable ambient density and conductivity profiles of the night-time lower ionosphere. In this talk, we review the basic electrodynamics of the lower and middle atmosphere, with particular attention to dynamic response of the system to intense fields and sudden disturbances.