Storm-Time Response of the Thermosphere\textendashIonosphere System

During a geomagnetic storm, the magnetospheric energy injected into the upper atmosphere increases by at least an order of magnitude, and during these times far exceeds the solar EUV and UV energy input. The energy is initially deposited towards higher latitudes where it heats and expands the thermosphere, increasing temperature and neutral density. Ionospheric plasma at high latitudes accelerates in response to the magnetospheric forcing, and through collisions can drive neutral winds in excess of 1\ km/s. Large scale gravity waves are launched equatorward preceding a change in global circulation. Upwelling at high latitude and equatorward winds transport molecular rich neutral gas towards mid and low latitudes, particularly in the summer hemisphere, where it speeds up recombination and depletes the ionosphere. Additional electrodynamic processes , such as prompt penetration and disturbance dynamo electric fields, accompany the dynamic response to storms and can cause a huge redistribution and increase of ionospheric plasma. The papers following this one will elucidate many of the details in the storm-time response and provide a broader perspective.