2002 Annual

Tuesday, 15 January 2002: 2:00 PM
Characteristics of African Easterly waves determined by Analses of Gate Observations and an Operational Global Model
Robert W. Burpee, Miami, FL
This article summarizes the publications of Dick Reed and his collaborators aimed at understanding African easterly waves (AEWs). Most of this phase of Reed's research career focused on achieving one of the primary goals of the GARP Atlantic Tropical Experiment (GATE). This goal of GATE, an international meteorological and oceanographic experiment that was conducted from June through September 1974 in northern tropical weather systems (e.g., convection) on synoptic-scale circulations. Reed and his coworkers helped achieve this goal by tracking the AEWs, determining their structure and energetic, identifying their source region, and precipitation. Reed's outstanding GATE achievement was the design of a simple compositing procedure, tested previously in the western Pacific, that enabled Reed and his collaborators to evaluate the significance of various meteorological quantities relative to important features of the AEWs. In the GATE ship array, Reed and collaborators determined the structure of AEWs, their control of convective activity, and their mass, moisture, and heat budgets. Another large-scale effect on convection that they investigated is the diurnal variation of large cirrus cloud cluster and rainfall throughout the region.

Reed and ECMWF collaborators used the ECMWF operational global model of May 1985 to generate a history of AEWs for August and September 1985. They described the verifications of the global model's 48-h forecasts of the 850 hPa vorticity maxima associated with AEWs and determined the forecasts to be quite encouraging. They utilized gridded ECMWF global model data and spectral analyses to resolve the model's characteristics of the AEWs. Analyses identify two regions of African origin of wave vorticity in the 3-5 d frequency band: one to the west of a mountainous region near 22 N, 10 E and the second near the east-west rainfall maximum at 12 N, 10 E. The vorticities in the two areas track westward and merge into a single system near the African coast and then track westward over the tropical Atlantic.

In preparing for a meeting about Sahel drought held at the Vatican, Reed noticed from 1970-85, Sahel was correlated with below-normal tropical cyclone activity in the Atlantic basin.

Neglecting hurricanes, the author believes that the research of Reed and his collaborators is largely responsible for making AEWs the best-documented synoptic disturbances in the tropics.

Supplementary URL: