| Comparisons are made between climatological dynamic fields obtained from
ground-based (GB) and space-based (SB) instruments with a view towards
identifying SB/GB intercalibration issues for TIMED and other future aeronomy
satellite missions. SB measurements are made from the High Resolution Doppler
Imager (HRDI) instrument on the Upper Atmosphere Research Satellite (UARS).
The GB data originate from meteor radars at Obninsk, (55° N,
37° E), Shigaraki (35° N, 136° E) and Jakarta
(6° S, 107° E) and MF spaced-antenna radars at Hawaii
(22° N, 160° W), Christmas I. (2° N, 158° W)
and Adelaide (35° S, 138° E). We focus on monthly-mean
prevailing, diurnal and semidiurnal wind components at 96km, averaged over
the 1991-1999 period. We perform space-based (SB) analyses for 90°
longitude sectors including the GB sites, as well as for the zonal mean.
Taking the monthly prevailing zonal winds from these stations as a whole, on
average, SB zonal winds exceed GB determinations by ~63%, whereas
meridional winds are in much better agreement. The origin of this discrepancy
remains unknown, and should receive high priority in initial GB/SB
comparisons during the TIMED mission.
We perform detailed comparisons between monthly climatologies from Jakarta
and the geographically conjugate sites of Shigaraki and Adelaide, including
some analyses of interannual variations. SB prevailing, diurnal and
semidiurnal tides exceed those measured over Jakarta by factors, on the
average, of the order of 2.0, 1.6, 1.3, respectively, for the eastward wind,
although much variability exists. For the meridional component, SB/GB ratios
for the diurnal and semidiurnal tide are about 1.6 and 1.7. Prevailing and
tidal amplitudes at Adelaide are significantly lower than SB values, whereas
similar net differences do not occur at the conjugate Northern Hemisphere
location of Shigaraki. Adelaide diurnal phases lag SB phases by several
hours, but excellent agreement between the two data sources exists for
semidiurnal tidal phases throughout the year. These results are consistent
with phase retardation effects in the MF radar technique that are thought to
exist above about 90km. Prevailing and tidal amplitudes from Shigaraki
track year-to-year variations in SB fields, whereas in the Southern
Hemisphere poorer agreement exists. The above hemispheric differences are due
in part to MF vs. meteor radar techniques, but zonal asymmetries and
day-to-day variability, combined with inadequate sampling, may also be
playing a role. Based on these results, some obvious recommendations emerge
that are relevant to combined GB/SB studies as part of TIMED and other future
aeronomy missions. |