African dust emission and transport exhibits variability on diurnal to decadal time scales, and is known to influence processes such as Amazon productivity, Atlantic climate modes, the regional atmospheric composition and radiative balance and Sahelian precipitation. In order to determine the relevance of African dust in the coupled climate system it is necessary to understand the factors governing its emission and transport. However, African dust is correlated with seemingly disparate atmospheric phenomena, including the El Niño/Southern Oscillation, the North Atlantic Oscillation, the meridional position of the intertropical convergence zone (ITCZ), rainfall in the Sahel and the depth of the Saharan Heat Low, obfuscating the connection between dust and climate. Here we show that variability in North African dust is reflected in the second Empirical Orthogonal Function (EOF) of 10m winds over the Sahara, and that the correlations between dust and various climate phenomena likely result from these phenomena’s ability to excite this orographically-forced EOF. A 161-year time series of dust (1851–2011) created by projecting this EOF onto 10m winds from a historical reanalysis shows that the highest concentrations of dust occurred during the 1910s through the 1940s and 1970s through the 1980s, and there have been three periods of persistent anomalously low dust concentrations, the 1860s, 1950s and the 2000s. Projections of the EOF pattern onto winds from climate models give a statistically significant downward trend in African dust with 21st century increases in greenhouse gasses, potentially due to a slow-down of the tropical circulation.
Amato Evan - The Past, Present and Future of African Dust