Coupling and energetics of the equatorial ionosphere-thermosphere system: advances during the STEP period

Abstract

The equatorial ionosphere-thermosphere system (EITS) investigations during the STEP period (1990-1997) were focused on improving our understanding of the dymanic and electrodynamic-coupling process and energetics that govern the climatology of the system, as well as the variabilities of the system arising from forcing by magnetospheric and high latitude processes and by atmospheric waves from below. Thermosphere dynamics and dynamo electric fields serving as drivers of the coupling process are responsible for the major EITS phenomena and their variabilities at different time scales. Especially, the day-to-day variabilities of the equatorial spread F (ESF) have recieved specific attention because of interest in space application areas as well Significant advances were achieved in our understanding and representation of quiet and disturbed electric fields. The STEP period also marked notable improvement in the experimental diagnostic facilities available in the equatorialregions as well as in theoretical modeling of the interactive process that control the major EITS phenomena. Data from coordinated observational campaigns have contributed to a better understanding of the EITS global responses to magnetospheric disturbances. The advances to be briefly discussed in this paper concern most of the major phenomena and the inherent characteristics of the EITS: the equatorial electric field and its sunset enhancement; thermospheric winds and temperature including the MTM (midnight temperature maximum); peculiar features of the ionosphere in the immediate vicinity of the magnetic equator; equatorial spread F/plasma bubble erregularities, including the energy requirement for large scale field aligned irregularities; equatorial anomalies in ion/neutral densities and temperatures. Also presented briefly is an overview of the results on the disturbance characteristics of the key EITS parameters and driving forces under magnetospheric disturbances and atmospheric wave forcing.