| HRDI (High Resolution Doppler Interferometer-UARS) winds data have been
analyzed in 4°-latitude by 10°-longitude cells at 96km to obtain the global distribution
of the solar-tidal amplitudes and phases. The solstices June–July (1993), December–January
(1993–1994), and one equinox (September–October, 1994) are analyzed.
In an earlier paper (Manson et al., 2002b) the emphasis was solely upon the
longitudinal and latitudinal variations of the amplitudes and phases of the semidiurnal
(12h) and diurnal (24h) tides. The longitudinal structures were shown to be quite
distinctive, and in the case of the EW component of the diurnal tide there were typically
four maxima/perturbations of amplitudes or phases around a latitude circle. In this case
they tended to be associated with the locations of the major oceans. Here, a spatial
complex spectral analysis has been applied to the data set, to obtain the zonal wave
numbers for the tides as functions of latitude. For the diurnal tide the dominant s=1
migrating component and nonmigrating tides with wave numbers s=–3, –2, 0, 2 are
identified; and for the semidiurnal tide, as well as the dominant s=2 migrating
component, the spectra indicate the presence of nonmigrating tides with wave numbers
s=–2, 0, 4. These wave numbers are also simply related to the global longitudinal
structures in the tidal amplitudes and phases.
Comparisons are made with the Global Scale Wave Model (GSWM-02), which
now incorporates migrating and nonmigrating tides associated with tropospheric latent
heat processes, and offers monthly outputs. For the diurnal tide the dominant nonmigrating
tidal spectral feature (94km) is for wave number s=–3; it is relatively stronger
than in the HRDI winds, and produces quite consistent structures in the global tidal fields
with four longitudinal maxima. Overall, the modelled 24-h tidal amplitudes are larger than
observed during the equinox beyond 40° latitude. For the semidiurnal tide, nonmigrating
tides are frequently indicated in the spectra with wave numbers s=–2, 0, 6; and
there are complementary longitudinal structures in the global tidal fields with two and
four maxima evident. Modelled 12-h tidal amplitudes are much smaller than observed
during non-winter months beyond 30°. There is a detailed discussion of the spectral
features, their seasonal variations, and the similarities with the HRDI tidal data. This
discussion is in the context of the inherent limitations of the model.
Key words. Meteorology and atmospheric dynamics (middle
atmosphere dynamics; thermospheric dynamics; waves
and tides) |