OBSERVATION OF 3-6-DAY MERIDIONAL WIND OSCILLATIONS OVER THE TROPICALPACIFIC, 1973-1992 - HORIZONTAL STRUCTURE AND PROPAGATION

Twenty years of rawinsonde data (1973-1992) were examined in conjuncti on with European Centre for Medium-Range Weather Forecasts (ECMWF) ana lyses and outgoing longwave radiation (OLR) in 1980-1989 to determine the horizontal structure, propagation, and convective coupling of 3-6- day meridional wind oscillations over the tropical Pacific. Wave prope rties from ECMWF data, determined by lag correlation with respect to r awinsonde or ECMWF principal components, were consistent with what cou ld be determined from the sparse rawinsonde network alone. Gridded ana lyses allowed a clearer distinction between equatorially trapped Rossb y-gravity waves (RGW) and off-equatorial ''tropical-depression'' (TD) disturbances, so that the contrasting properties of these waves, inclu ding their seasonal and interannual variation, could be studied in bet ter detail. Significant correlations with OLR were found, increasing i n magnitude from eastern to western Pacific. The apparent group propag ation of disturbances was equatorward in the western Pacific, eastward across the central and eastern Pacific, and upward-downward out of th e 150-300-mb layer. Vertical propagation was evident primarily at high er frequencies, implying that only a fraction of the kinetic energy as sociated with Rossby-gravity waves in the upper troposphere was involv ed either in convective coupling to the lower troposphere or vertical momentum transport to the lower stratosphere. It is suggested that in addition to convective and lateral forcings, Rossby-gravity waves are sometimes excited by energetic TD disturbances in the western Pacific.