Estimates of large‐scale divergence in the lower troposphere over the western equatorial Pacific

Abstract

A network of 915‐MHz wind profilers measured half‐hourly lower‐tropospheric winds over the western equatorial Pacific with vertical resolutions as high as 100 m during November 1992 through February 1993, the intensive observing period (IOP) of the Tropical Ocean Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment (TOGA COARE). These wind data are used in conjunction with collocated surface wind measurements to examine the near‐surface divergent flow over the western Pacific warm pool during austral summer as well as the synoptic‐scale variability of divergence in both time and space. The synoptic‐scale wind field estimated from profiler data exhibits stronger near‐surf ace divergence than sonde‐based estimates from the same time period. Temporal variations of the lower‐tropospheric divergence profiles are described by three vertical structure functions derived from Varimax‐rotated eigenvector analysis. One vertical mode appears to be associated with deep convection, one with near‐surface processes, and one with shallower convection. These structure functions vary zonally across the COARE region, with the convective modes having convergence maxima at lower elevations to the west of the intensive flux array (IFA) than over and east of it.