Rw. Smith et al., OBSERVATION AND SIMULATIONS OF WINDS AND TEMPERATURES IN THE ANTARCTIC THERMOSPHERE FOR AUGUST 2-10, 1992, J GEO R-S P, 103(A5), 1998, pp. 9473-9480
Optically derived upper thermospheric wind and temperature data, colle
cted at Antarctic stations at South Pole (L=14), Mawson (L=9.3), and H
alley (L=4.6), and averaged over the low-activity period August 2-10,
1992, have been interpreted with the help of simulation by the Nationa
l Center for Atmospheric Research thermosphere ionosphere electrodynam
ic general circulation model (TIEGCM) with inputs matching the average
conditions of observation. The simulation provides a global backgroun
d context upon which the widely-separated optical observations can be
placed. The simulation shows three large-scale structures in the polar
wind field: the morning vortex, the evening vortex, and the cross-pol
ar wind jet. Each of these came within view of the group of observing
stations during the diurnal cycle, providing arrival time observations
and signatures which were examined relative to the TIEGCM simulation.
Reasonable correspondence was found, indicating the capability of the
model to agree simultaneously with observations at three widely space
d stations representative of the subauroral and auroral zones, as well
as the polar cap. Simulated wind directions were in excellent agreeme
nt with observation, although wind magnitudes frequently exceeded meas
ured values by up to 30%, Apparent divergent flows in the data from Ha
lley and Mawson were explained as signatures of vortices from their pr
esence in the simulated wind fields. Observed diurnal mean temperature
s compared well with the simulation, confirming that heat inputs and t
he distribution of thermal energy in the model are, on average, reason
able, A significant and persistent difference between experimental and
modeled temperatures was that the diurnal temperature variation obser
ved at South Pole peaked at the nightside crossing of the jet and was
minimum a few hours before noon magnetic local time, whereas the simul
ation indicated minimum temperatures on the nightside, in antiphase to
the measurements. A simple calculation indicates that the observed te
mperature difference between the air parcels entering the polar cap, e
ncountered on the dayside, and those leaving the polar cap on the nigh
tside is reasonably matched to the heating due to the ion-drag acceler
ation process. No explanation of the lack of this temperature rise in
the TIEGCM simulation is presently available.