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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