Synoptics of dust intrusion days from the African continent into the Atlantic Ocean

The phenomenon of dust intrusion from north Africa into the Atlantic Ocean was examined on daily bases for the month of July from 1983 to 1988 (184 cases). Composite patterns of wind flows and geopotential heights for the intrusion versus no-intrusion cases as well as the difference between them (intrusion minus no intrusion), in the area (60°W-25°E, 0°-60°N), were analyzed. For both intrusion and no-intrusion days a closed high pressure, centered at approximately (45°W, 32°N), was found, with a ridge northeastward. East of the ridge was a trough located to the west of the European and the north African coast. Further east was a closed high in the western Sahara with a ridge northeastward. Each of the maps presenting the difference between the two aforementioned variables shows two highs: one over western Europe and the other, quite strong, west of the African coast on the 24°N-25°N latitudes. Between them, centered about (15°W, 37°N), there is a low-pressure area. As a result of the higher pressure at the African anticyclone in the intrusion cases, an easterly-northeasterly flow dominates at the latitudes 18°N-22°N, which presumably causes the dust intrusion from the continent into the Atlantic. Correlation between the Total Ozone Mapping Spectrometer aerosol index on the one hand and the wind magnitude and the u and v components on the other hand was also analyzed for the entire data set. Correlation coefficients of r = 0.52, r = -0.46, and r = -0.27 were found. Analysis of two extreme intrusion and no-intrusion cases in July 1983 demonstrates the synoptic situation that allows the Saharan dust to reach England and NW Europe.