Zonal Gradients in the Lower Atmosphere and Upper Ocean across the Windward Antilles during Midsummer 2012

This observational study examines zonal gradients in the lower atmosphere and upper ocean across the windward Antilles during midsummer 2012. While earlier work reported on meridional confluence, here the focus is on the zonal enrichment of trade winds by upstream shallow seas and islands. Intercomparisons along 18.2°N are made between modern reanalysis and satellite estimates, and coastal station, moored buoy, aircraft, and radiosonde observations for one case and as a June–July 2012 average. Mean gradients per 100 km east of Puerto Rico were 0.2 g kg −1 for 925-hPa specific humidity, 0.16°C for SST, 0.01 m for sea level, and 2.0 × 10 −3 g kg −1 for cloud water. Zonal changes in the lower atmosphere occur in three stages: 1) Atlantic, where westward ocean currents, strong trade winds, and subsidence prevail; 2) Antilles, where ocean currents diminish and sea temperatures increase; and 3) island, where trade winds abate [−1 m s −1 (100 km) −1 ] and diurnal evapotranspiration greater than 10 mm day −1 offsets large-scale subsidence producing a localized convection.