The structure and annual variation of antisymmetric fluctuations of tropical convection and their association with Rossby-gravity waves

Abstract

Antisymmetric fluctuations of tropical convection are shown to exhibit a pronounced spectral peak at a 4-5 day period only during boreal fall and only within about 30° longitude of the date line. The peak amplitude occurs around 7.5° latitude. These fluctuations propagate westward at 15-20 m s-1 with zonal wavelength of about 7000-9000 km. The fluctuations of convection are coherent and out of phase with the equatorial meridional wind, which also exhibits a pronounced spectral peak at a 4-5 day period in the lower troposphere near the date line. The antisymmetric zonal wind also is strongly coherent with the antisymmetric convective fluctuations in this region. The horizontal distributions of the 4-5 day power and coherence of the winds and convection are consistent with that produced by a convectively coupled Rossby-gravity wave that is confined near the date line. -from Authors