Zonally uniform tidal oscillations in the tropical middle atmosphere

Abstract:

Atmospheric tides have an important role in the vertical coupling of the atmosphere. Since tides are mainly excited in the lower atmosphere, it is necessary to understand the tidal characteristics in these altitude regions. Of all tidal components, this study focuses on the non-Sun-synchronous components, i.e., nonmigrating tides.

Sakazaki et al. (2015, J.G.R.) extracted nonmigrating tides using a composite as a function of universal time in physical space, without performing a zonal wave-number decomposition. With this method, it was demonstrated that tropical nonmigrating tides from the troposphere to the lower mesosphere were regarded as gravity waves excited by diabatic heating enhanced over two major continents, specifically Africa and South America.

The present study discovered that as well the above mentioned gravity-wave patterns, zonally uniform tidal signals are clearly seen in the tropical middle atmosphere particularly during the Northern Hemisphere summer, by using data from climate chemistry models (CCMs), reanalyses, and satellite measurements (SABER and GPS-RO). Antisymmetric components with respect to the equator are dominant and are characterized by a vertical wavelength of ~15 km and a diurnal frequency. The observed latitudinal and vertical structures can be explained by the second, propagating, antisymmetric Hough mode.