Large-Scale Cloud Disturbances Associated with Equatorial Waves

Abstract

Spectral features of large-scale cumulus convective systems over the tropical oceanic area are studied and classified in terms of the atmospheric equatorial waves. Three-hourly GMS infrared data for the period of 1981-1989 are utilized. Some significant features of cloud-atmosphere systems are deduced. As an average feature for the total analysis period, robust signals are identified with Kelvin waves, westward-propagating mixed Rossby-gravity waves (MRGW), n=1 Rossby waves and n=1 westward-propagating inertio-gravity waves (WIGW). Some indications of eastward-propagating n=0 gravity waves and n=2 WIGW are also presented. A common equivalent depth of 15-30m among different wave modes is indicated from the frequency-wavenumber distribution of cloud disturbances. On the other hand, an equatorial radius of deformation of ∼7° is deduced independently from the latitudinal distribution of cloud spectra which shows a good agreement with the above equivalent depth. Seasonal variation of dominant cloud disturbances is also described and discussed in relation to the mean wind profile.