MgE71241:1attf:3(t At-- 0 -3 5t5M I:. N1144±TitoD riziMinliJ VAT .9f 1 ...

4 1. INTRODUCTION
region) neutral circulation for given geophysical situations (solar maximum, near solstice)
can be modeled reasonably using a three-dimensional, time-dependent model with appropri-
ate parameterizations for the energy and momentum inputs. Killeen et al. [19881 extended
the NCAR TGCM to accommodate a time-dependent prescription of auroral particle pre-
cipitation and magnetospheric convection.
The thermospheric neutral winds driven by motion of convecting plasma in turn produce
a dynamo effect. It was noted by Banks [1972] that these winds can generate an electric field
that drives plasma motion, even if magnetospheric electric field is cut off. This phenomenon
is called the 'flywheel' effect. Deng et al. 11991] investigated the flywheel currents by simu-
lating a storm which occurred on 23 November 1982 using the NCAR. TICCM. The resulting
height-integrated Hall currents at high-latitude were dominated by the neutral wind-driven
component for several hours after the end of the storm main phase. The direction of these
currents was reversed from normal. Furthermore, Deng et al. 11993] extended the previ-
ous work to include a comparison between the calculated time-dependent ionospheric Ilall
current system and the field-aligned currents measured by DE-2 satellite in the storm-time
recovery period. As a result, DE-2 measurements demonstrated 'local' (satellite-altitude)
flywheel effects. Richmond [1995] examined the flywheel effect by the NCAR thermosphere-
ionosphere-electrodynamics general circulation model (TIE-CCM) which was an extension
of the NCAR TIGCM. It was found that, after a field-aligned current between the ionosphere
and the outer magnetosphere has been cut off, ion drifts become similar to high-latitude neu-
tral winds at altitude of 145 km, with a total potential drop of 7.5kV, or 25% of originally
imposed one.
1.2.2 Empirical models
The MSIS (mass spectrometer incoherent scatter) model has gone through several revi-
sions. The MSIS-83 model [Hiden, 1983] was based on data from seven satellites, numerous
rocket probes, and five ground-based incoherent scatter (IS) radars. The MSIS-86 model
Widen, 19871 combined these earlier measurements with the DE-2 data and is capable of
providing temperature and densities of N, N2, 02, 0, He, Ar, and H as functions of ex-
°spheric temperature, local time, latitude, longitude, universal time, F10.7, and A. The
MSIS-86 model has been adopted as the new CIRA empirical model Widen et al., 1988],
which is available in a computer compatible form for the first time.