Mean State and Wave Disturbances during Phases I, II, and III of GATE Based on ERA-40

Using ECMWF's second-generation reanalysis, ERA-40, the large-scale mean state and synoptic-scale features associated with African easterly wave disturbances (AEWs) are examined over West Africa and the adjacent eastern Atlantic Ocean during the three 21-day observing periods of the Global Atmospheric Research Program (GARP) Atlantic Tropical Experiment (GATE) in 1974 (Phase I, 26 June-16 July; Phase II, 28 July-17 August; Phase III, 30 August-19 September). Results are partitioned into four geographical boxes, in order to highlight differences among the AEW vortices as they propagate westward along two tracks (northern and southern) over West Africa (land) and the adjacent eastern Atlantic Ocean (water). This marks the first time that a detailed diagnosis of the northerly track AEWs has been conducted. Results are also compared to previous GATE studies and a 30-yr climatology is extracted from ERA-40.