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6 1. INTRODUCTION
satellite ion drift measurements, and large-scale background winds derived from a thermo-
spheric general circulation model [Walterscheid and Lyons, 1989]. Their model predicted a
strong jet of eastward wind at the E-region height, and showed modest agreement with the
observed winds.
Fujiwara et al. [1996] performed a numerical simulation of the thermospheric response
to magnetospheric substorm energy injection using a zonal averaged, time-dependent model
of neutral composition, dynamics, and energy budget. In their simulation with an energy
injection of 1 hour, large-scale atmospheric gravity waves (AGWs) generated by substorm
energy via Joule heating of ionospheric currents were clearly identified in the wind field in a
meridional plane as well as in the temporal and spacial variations of the total energy density
of atmosphere above about 130 km height. It was suggested that short-duration energy
injection preferentially generates AGWs which dominate energy oscillations at low latitudes
through adiabatic heating and cooling.
1.3 Satellite observations of the thermospheric neu-
tral wind
Killeen and Roble [1988] reviewed the synopsis of the progress made during the first 5
years of the NASA's Dynamics Explorer (DE) dual-spacecraft mission. The mission plan
was designed involving to companion spacecraft in coplanar orbits: a high-altitude space-
craft (DE-1) instrumented to probe the Earth's inner magnetosphere and plasrnasphere and
a low-altitude spacecraft (DE-2) instrumented to probe the ionosphere and neutral upper
atmosphere simultaneously with the DE-1 measurements. DE-2 has two instruments for
thermospheric wind measurements. They are a Fabry-Perot interferometer (FPI) and a
wind and temperature spectrometer (WATS). Remote sensing measurements of the merid-
ional thermospheric winds using FPI have been combined with in situ measurements of the
zonal component using WATS. The two data sets, with appropriate phasing and averaging,
determined the vector wind along the track of the polar orbiting spacecraft [Killeen et al.,
1982]. The DE-2 satellite has made a significant contribution to our overall understanding
of the thermospheric dynamics at high-latitude and its response to various magnetospheric
and ionospheric disturbances. McComae et al. [1987] used several hundred orbit of DE-
2 over six-month period to investigate quantitatively the dependence of the high-latitude