Suspended dust over southeastern Mediterranean and its relation to atmospheric circulations

The Middle East deserts are often subjected to dust, which reduces horizontal visibility to 5 km, and sometimes even to <1 km. The present study examines the annual and inter-annual occurrences of dust events based on 37 years of visibility observations from Hazerim (near Beer Sheba) correlated with PM10 dust concentration. The visibility data was converted to PM10 dust concentration, using concurrent data for three years. We then analyse the linkage between dust and synoptic- to global-scale weather systems. The monthly data indicate that the dust season starts in October and ends in May, with a maximum in March. More than 89% of the total annual dust is accumulated between December and May, the 'high dust season'. The annual totals vary as much as an order of magnitude from year to year. The synoptic system that produces the majority of the dust over the northern Negev is the Cyprus Low, contributing 2/3 of both the total yearly dust yield and of the number of dust observations. This suggests that a positive relationship exists between the dust in the Negev and rainfall in north Israel, both of which are generated by Cyprus Lows. Indeed, a significant (at 0.05 level) correlation of +0.30 was found between the two. Correlation maps evidence that in dust-rich years the cyclonic activity over the Mediterranean is abnormally high and in poor-dust years it is low. A highly significant negative correlation (-0.66) was found between the dust yield and the intensity of the North Atlantic oscillation (NAO), which modulates the cyclonic activity over Europe and the northern Mediterranean. This may also imply that periods in which more dust accumulated as loess in the northern Negev may indicate the existence of negative NAO phase, and concurrently, warmer conditions over the Sahara, colder conditions over Europe and enhanced rainfall over the Mediterranean Basin. Copyright (C) 2007 Royal Meteorological Society.