Interannual variability in Saharan dust over the North Atlantic Ocean and its relation to meteorological fields during northern winter

Abstract

In this study, we focus on interannual variability in Saharan dust transport over the North Atlantic Ocean during northern winter using the Aerosol Index data from the Total Ozone Mapping Spectrometer (TOMS). Since the TOMS observations provide a long-term global record, they are useful for considering interannual variations of the Saharan dust in relation to the North Atlantic Oscillation (NAO). We calculated correlation coefficients between the NAO Index and the TOMS AI averaged over the northern winter season. Using the correlation map, we defined three regions: Region 1 is in positive correlation over the North Atlantic Ocean, Region 2 is in insignificant correlation over the west Sahara, and Region 3 is in negative correlation over the east Sahara. Focusing on Region 1, we considered the relationship between the regional mean TOMS AI time series and certain meteorological parameters. We used sea level pressure and wind speed fields to represent the synoptic circulation, and virtual temperature and lifting condensation level (LCL) to represent the mixed layer condition. When the TOMS AI in Region 1 is large, the easterly winds over the west Sahara are stronger than usual compared to the NAO, and the virtual temperature is higher than average over the ocean. As a result, the LCL is higher near 20°W–0° and is lower than average over the desert. When dust outflow events are observed over the North Atlantic Ocean, strong winds with a high pressure blow in the west Sahara, and dust containing warm air parcels is carried by these strong winds to ocean through areas near the coast (20°N–30°N, 15°W–10°W) from the west Sahara. We summarized the features of meteorological fields during dust outflow events.