Comparing two years of Saharan dust source activation obtained by regional modelling and satellite observations
A regional-scale dust model is used to simulate Saharan dust emissions and atmospheric distributions in the years 2007 and 2008. The model results are compared to dust source activation events compiled from infrared dust index imagery from the geostationary Meteosat Second Generation (MSG) satellite. The observed morning maximum in dust source activation frequencies indicates that the breakdown of nocturnal low-level jets is responsible for a considerable number of dust source activation events in the Sahara. The comparison shows that the time of the day of the onset of dust emission is delayed in the model compared to the observations. Also, the simulated number of dust emission events associated with nocturnal low level jets in mountainous regions is underestimated in the model. The MSG dust index observations indicate a strong increase in dust source activation frequencies in the year 2008 compared to 2007, the difference between the two years is less pronounced in the model. The quantitative comparison of simulated dust optical thicknesses with observations at stations of the sunphotometer network AERONET shows, however, good agreement for both years, indicating that the number of observed dust activation events is only of limited use for estimating actual dust emission fluxes in the Sahara.