Ionosphere-Thermosphere Coupling

The energy released through magnetic field merging and the substorm is distributed in the coupled geospace system via field-aligned currents, particle precipitation, plasma waves and Joule heating of the thermosphere. This energy deposition in the ionosphere and thermosphere greatly modifies their overall large-scale structure and dynamics. SESAME observations will make an important contribution by providing considerable relevant data. For example, the ion and neutral winds can be measured in a common volume, and the flow of energy to lower latitudes (e.g. as gravity waves) can be monitored. These observations should help to resolve key issues such as the relative importance of Joule heating and Lorentz forcing in gravity wave generation, and also the factors affecting the spectrum of waves observed in the thermosphere, both at the source region and in the far-field.

Upward field-aligned ion acceleration from the ionosphere (Jones et al., 1988) occurs frequently where the relative horizontal velocity of the ionic and the neutral components of the ionosphere is large (e.g. near the cusp, the Harang discontinuity, and auroral arcs). This upflow is a significant source of heavy ions for the magnetosphere (Chappell et al., 1987). The combination of SESAME's simultaneous measurements of neutral and ion velocity, and POLAR measurements of these upward fluxes should allow better quantitative assessment of the factors affecting this outflow, and the mechanisms for particle acceleration to be determined for the first time.

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