Westerly Wind Events in the Tropical Pacific, 1986–95*

Based on examination of 10 yr of 10-m winds and wind anomalies from European Centre for Medium-Range Weather Forecasts (ECWMF) analysis, definitions for westerly wind events (WWEs) of eight different types are proposed. The authors construct a composite for each type of event, show that a simple propagating Gaussian model satisfactorily describes the evolution of zonal wind anomaly for each type of event, and determine the scales of each composite event by fitting the model to each composite. The authors discuss the WWEs that occurred during the Tropical Oceans Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE) intensive observing period (IOP) and show the extent to which these composite events are able to reproduce the major westerly wind features of the IOP. The frequency of occurrence of each type of WWE for each year of this record and by calendar month are described; the authors find several types of events are negatively correlated with the annual mean troup Southern Oscillation index (SOI), and that the stronger WWEs often have a statistically significant seasonality. Several instances of widespread westerly wind anomaly are identified and described, but these "mega"-WWEs have few features in common. Although the authors' composites underestimate the peak amplitude of many WWEs and cannot always accurately represent the time evolution of each WWE, the authors believe that they offer a useful framework for representing the sort of westerly wind variability that occurs in the western and central tropical Pacific and can provide a basis for further study of the importance of such winds in the climatological and interannual variability of this part of the World Ocean.