Global distributions of diurnal and semidiurnal tides: observations from HRDI-UARS of the MLT region and comparisons with GSWM-02 (migrating, nonmigrating components)

Abstract

Abstract. HRDI (High Resolution Doppler Interferometer-UARS) winds data have been analyzed in 4• -latitude by 10 • -longitude cells at 96 km 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 (12 h) and diurnal (24 h) 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 (94 km) 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, Correspondence to: A. H. Manson (manson@dansas.usask.ca) 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.

Arctic tidal characteristics at Eureka (80° N, 86° W) and Svalbard (78° N, 16° E) for 2006/07: seasonal and longitudinal variations, migrating and non-migrating tides

“…Their study confirms the presence of diurnal NMT s=0, +2, −3 and semidiurnal NMT s=+1 and +3; the s=0 and +2 diurnal tides were not resolvable earlier from HRDI winds data, although the spectra were wide and their presence was suspected (Manson et al, 2004a). Although these NMT are tides in the temperature-field, their presence confirms their production processes as being SPW and/or latent heat release with wave numbers S=1 and 2.…”

“…There are factors of nearly ten between the March amplitudes, with the zonal component providing the larger differences. The tidal variations with longitude near 40 • N for the CUJO network (Manson et al, 2004c were much smaller; and the hemispheric zonal patterns of amplitude and phase seen in HRDI satellite data from 96 km (Manson et al, 2004a), also for these lower latitudes, were significant but smaller. The hodographs of Figs.…”

“…The elliptical patterns will then depart from circularity. We have noted this in 96 km-tides from satellite data (Manson et al, 2004a), earlier radar data and tidal models for northern Scandinavia (Manson et al, 2004b), and in MFR data from Saskatoon .…”

“…Such satellite data are most useful in providing information on migrating tides (MT), which are the zonal (longitudinal) mean tides, and also nonmigrating-tides (NMT) from equator to medium-high latitudes (40-70 • ); e.g. Manson et al (2004a), Forbes and Wu (2006), Zhang et al (2006). The temporal resolution of satellite systems is also generally quite restricted, with seasonal means tending to dominate the results.…”

Maps of <I>fo</I>F2, <I>hm</I>F2, and plasma frequency above F2-layer peak in the night-time low-latitude ionosphere derived from Intercosmos-19 satellite topside sounding data

“…This supposition seems quite reasonable, as there is experimental evidence that higher harmonics of these parameters at low latitudes are rather strong (e.g. Mayr et al, 1979;Herrero and Spenser, 1982;Manson et al, 2004), but this problem requires further study.…”