Dynamics of the Atmosphere-Ionosphere System

Abstract

The upper atmosphere is the outermost region of a planetary atmosphere where solar radiation leads to formation of an ionosphere with appreciable plasma densities. The upper atmosphere and ionosphere continuously interact with each other in a two-way nonlinear manner. It is therefore increasingly common to refer to them as the atmosphere-ionosphere system. Overall, the state and evolution of the atmotsphere-ionosphere system is influenced by meteorological processes from below, which is called “coupling from below”, and by solar and geomagnetic processes, often defined as “coupling from above” or simply space weather. Meteorological effects include upward propagating gravity waves, planetary waves and tides from the lower atmosphere into the thermosphere. This chapter reviews some elements of energetics and dynamics of the thermosphere-ionosphere system. Gravity waves are shown to play an appreciable role for the energy and momentum budget of the thermosphere, while planetary waves modulate lower thermospheric variability over long time scales. During geomagnetic storms, which are a prominent manifestation of space weather, the thermosphere and ionosphere undergo substantial dynamical and thermal changes due to enhanced ion drag, Joule heating, and particle precipitation. A comprehensive understanding of the response of the atmosphere-ionosphere system to processes of lower atmospheric origin and those originating at Sun require a whole atmosphere approach.