Three-dimensional structures of tropical nonmigrating tides in a high-vertical-resolution global circulation model

In this paper we investigate nonmigrating tides from the ground to the lower mesosphere using data from a high-resolution global circulation model (KANTO GCM), as well as observational data from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on board the Thermosphere–Ionosphere–Mesosphere Energetics and Dynamics (TIMED) satellite and from GPS radio-occultation measurements obtained with the COSMIC/FORMOSAT-III mission. We extract nonmigrating tides using a composite as a function of universal time in physical space, without performing a zonal wave-number decomposition. The KANTO GCM clearly demonstrates that tropical nonmigrating tides are interpreted as gravity waves excited by diabatic heating enhanced over two major continents, specifically Africa and South America. They propagate zonally, in a direction away from their sources; that is, west- and eastward-propagating waves are dominant on the western and eastern sides of the continents, respectively. These characteristics are observed in two satellite data sets as well, except that the amplitudes in the KANTO GCM are larger than those in the observations. These findings are also discussed in spectral space (i.e., in zonal wave-number space), as in previous studies. It was found that the DW5 (DE3) tide corresponds to the packet of westward (eastward)-propagating waves on the western (eastern) side of the continents. Seasonal variations of nonmigrating tides are also investigated. It is suggested that filtering owing to the stratopause semiannual oscillation (S-SAO), as well as diabatic heating in the troposphere, are important for the seasonal variations of nonmigrating tides in the mesosphere and the lower thermosphere.