Abstract
African dust intrusions in the marine mixing layer of the Eastern North Atlantic subtropical region (23.5°N to 35°N) are favoured in winter when the eastern edge of the Azores High covers Southwestern Europe and North Africa. In situ ground pressure observations and reanalysis from National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) and European Centre for Medium-Range Weather Forecasts (ECMWF) indicate that the Azores High has strengthened and shifted eastward in winter over the last three decades. This is evidenced by the increase over time of the Madrid–Tenerife Index which is defined as the geopotential height anomaly difference at 1000 mb between Tenerife (28.5°N; 16.3°W) and Madrid (40.5°N; 3.5°W) in winter and of the African Index which is defined as the residence time over Africa of air mass trajectories entering the subtropical Eastern North Atlantic Ocean. Barcelona Supercomputing Center/Dust Regional Atmospheric Model (BSC-DREAM) dust regional model simulations from 1958 to 2006 were performed, assuming that the soil characteristics of dust sources remained unchanged over time. Simulated winter dust concentration levels are well correlated (0.67) with the available background observations for the 1998–2004 period. The model results show a two-fold increase in winter dust concentrations over the 1980–2006 period with respect to the 1958–1979 period, corresponding to the strengthening and eastward shift of the Azores High. DOI: 10.1111/j.1600-0889.2010.00524.x
Highlights
African air mass intrusions exert a significant impact on background aerosol levels over the subtropical Eastern North Atlantic Ocean
Analyses based on surface dust concentrations measured at Barbados since 1965 (Prospero and Nees, 1986; Prospero and Lamb, 2003; Chiapello et al, 2005), as well as other studies (Moulin et al, 1997; Prospero, 1999; Mahowald et al, 2002; Ginoux et al, 2004; Foltz and McPhaden, 2008; Mahowald et al, 2010), suggest that dust load trends at tropical latitudes could be driven by drought periods in the Sahel, and that there is a significant correlation with the North Atlantic Oscillation (NAO) index in winter
According to Moulin et al (1997), interannual variations in dust transport over the Atlantic Ocean are well correlated with the climatic variability defined by the NAO because this large-scale climatic control on the dust export is affected through changes in precipitation and atmospheric circulation over the regions of dust mobilization and transport
Summary
African air mass intrusions exert a significant impact on background aerosol levels over the subtropical Eastern North Atlantic Ocean (from the Tropic of Cancer, 23.5◦N to 35◦N, see Fig. 1a). Analyses based on surface dust concentrations measured at Barbados since 1965 (Prospero and Nees, 1986; Prospero and Lamb, 2003; Chiapello et al, 2005), as well as other studies (Moulin et al, 1997; Prospero, 1999; Mahowald et al, 2002; Ginoux et al., 2004; Foltz and McPhaden, 2008; Mahowald et al, 2010), suggest that dust load trends at tropical latitudes could be driven by drought periods in the Sahel, and that there is a significant correlation with the North Atlantic Oscillation (NAO) index in winter. The Canary Islands constitute an excellent site to study the impact of African dust over the subtropical Eastern North Atlantic region (Torres-Padron et al, 2002; Viana et al, 2002; Alonso-Perez et al, 2007). We have performed long-term simulations with the Barcelona Supercomputing Center/Dust Regional Atmospheric Model (BSC-DREAM) regional dust model to quantify the impact of atmospheric circulation changes, associated to the Azores High, on dust concentrations over the region
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