Diurnal nonmigrating tides in the tropical lower thermosphere

A comparison is performed between monthly-mean nonmigrating diurnal tide wind components at 95 km derived from Upper Atmosphere Research Satellite (UARS) wind observations, the Middle Atmosphere Circulation Model at Kyushu University (MACMKU), and the Global Scale Wave Model (GSWM) driven by latent heating due to deep tropical convection. A degree of overall agreement is obtained in the sense that annual-mean spectra at 95 km indicate that the UARS data, MACMKU and GSWM all share the same nonmigrating tide components (eastward-propagating with zonal wavenumber s = -3; westward-propagating with s = 2; standing or zonally-symmetric with s = 0; DE3, DW2, DO) at about the same power level. In combination with the migrating tide these wave components give rise to significant longitude variability in the total diurnal tidal fields. Beyond the above model/measurement agreements, significant discrepancies remain between the latitudinal-seasonal structures delineated by models and observation. For MACMKU, some of these discrepancies may be related to the specifics of the convective parameterization that is employed. Significant work remains to better delineate tropospheric forcing mechanisms and nonlinear wave-wave interactions as sources for nonmigrating tides.