Equatorial Atmospheric Waves and Their Association to Convection

Abstract

Equatorial wave systems and their relationships with convective activity are analyzed in the western and central Pacific regions during the Coupled Ocean?Atmosphere Response Experiment (COARE) intensive observation periods. The study uses Geostationary Meteorological Satellite infrared temperature observations and the operational European Centre for Medium-Range Weather Forecasts analyses supplemented with COARE observations. Spectral and complex principal component analysis are applied to the data. Using the linear theory of equatorially trapped waves as a guideline, the existence of three types of waves is detected. In the 7?10-day period range, n = 1 Rossby waves are found to the east of the date line, in a region of weak convective activity. Over the western equatorial Pacific, where intense convection occurs, the 7?10-day waves do not possess the general characteristics of linear Rossby waves, but they are strongly linked to the active phases of westerly wind bursts and of convection. Analysis of the meridional wind reveals intense mixed Rossby?gravity waves with a mean 5-day period and westward phase and eastward group velocities. Over the western Pacific, the convection is found to be strongly correlated with the antisymmetric structure of the divergent field, as predicted by the linear theory. In the 200-hPa divergence field, n = 1 gravity waves are visible, having periods shorter than 2.5 days. They rapidly propagate (about 25 m s?1) both westward and eastward, and have strong correlations with convective clusters.