Upper Tropospheric Waves in the Tropics. Part I: Dynamical Analysis in the Wavenumber-Frequency Domain

Abstract

Abstract Space and time spectra of large-scale wave disturbances at the 200 mb level in the latitude belt 20°S to 40°N are studied based on wind data for the period June–August 1967. The kinetic energy of the transient waves shows a minimum near 10°N where convective activity attains a maximum. The transient eddies in the zonal wind component have dominant scales of zonal wavenumbers s = 3–6 in most latitudes, while those in the meridional wind component have dominant scales of s = 6–8. By decomposing the wind data into symmetric and antisymmetric components with respect to the equator, three prototype equatorial wave modes are detected: 1) Kelvin waves of zonal wavenumber s = 1 and 2 and a period of 7 days, and s = 1 and periods longer than 20 days; 2) mixed Rossby-gravity waves of s = 4 and a period of 5 days; and 3) Rossby waves (of the lowest meridional nodal number) of s = 2 and a period near 12 days. Westward moving short waves (s = 7–15) gain kinetic energy from the mean easterly flow. Eastward mov...