New Saharan wind observations reveal substantial biases in analysed dust‐generating winds

摘要

The Sahara is the largest source of airborne mineral dust on Earth. New data from the Fennec field campaign from remote Sahara allow evaluation of ECMWF ERA‐Interim analysed winds. High winds and diurnal variation are under‐represented in analyses, which perform less well during the summer monsoon (even in the isolated central Sahara). Analyses do not capture the seasonal cycle, missing the summertime maximum in winds in the central Sahara summer time dust hotspot. Abstract For the remote Sahara, the Earth's largest dust source, there has always been a near‐absence of data for evaluating models. Here, new observations from the Fennec project are used along with Sahelian data from the African Monsoon Multidisciplinary Analysis (AMMA) to give an unprecedented evaluation of dust‐generating winds in the European Centre for Medium‐Range Weather Forecasts ERA‐Interim reanalysis (ERA‐I). Consistent with past studies, near‐surface, high‐speed winds are lacking in ERA‐I and the diurnal variability is under‐represented. During the summer monsoon season, correlations of ERA‐I with observed wind‐speed are low (～0.35 in Sahel and 0.25–0.4 in the Sahara). Fennec data show for the first time that: (1) correlations are reduced even in the Sahara, not directly influenced by the monsoon, (2) the systematic underestimation of observed winds by ERA‐I in the summertime Sahel extends into the central Sahara: potentially explaining the failure of global models to capture the observed global dust maximum that occurs over the summertime Sahara (such as CMIP5), and demonstrates that modelled winds must be improved if they are to capture this key feature of the climatology.