Global distributions of diurnal and semi-diurnal tides: Observations from HRDI-UARS of the MLT region

Abstract

HRDI (High Resolution Doppler Interferometer-UARS) winds data have been analyzed in 4° latitude by 10° longitude cells at 96 km to obtain global contour maps of solar-tidal amplitudes and phases, and also mean winds. The solstices June-July (1993), December-January (1993-1994), and one equinox September-October (1994) are shown. The 24-h diurnal tide that maximizes near the 20-25° latitude has significant seasonal changes with equinoctial maxima, and very clear longitudinal variability. Maxima are very clear over the oceans. In contrast, the 12-h semi-diurnal tides that maximize near the 40-55° latitude have very strong seasonal changes with winter maxima, and more modest longitudinal changes. The similarities with MLT (mesosphere-lower thermosphere) radar observations (90 km) and the GSWM (Global Scale Wave Model) are very satisfactory. The mean winds are consistent with expectations and show clear poleward flow from summer to winter hemispheres in the solstices.