Ten years of aeolian dust dynamics in a desert region (Negev desert, Israel): analysis of airborne dust concentration, dust accumulation and the high-magnitude dust events

At Sede Boqer (northern Negev desert, Israel), aeolian dust dynamics have b een measured since 1986. The data are somewhat preliminary for the first 2 years, bur from 1988 onward, the data set is nearly complete and contains a mple information with respect to northern Negev dust. In this paper, severa l dynamic aspects of the Negev dust are investigated for the decade 1988-19 97. Airborne dust concentration, which was measured by total particulate ul trahigh-volume sampling at 1-m height, was of the order of 120 mug m (-3) ( based on 24-h measuring intervals) as an average, with higher values during the day than at night. Concentration was also higher during spring and aut umn compared to summer and winter. In the decade 1988-1997, dust concentrat ion decreased from 1988 to 1992 and increased from 1992 to 1997. Systematic oscillations with a periodicity of 30 months occur in the concentration cu rves. Dust accumulation, which was measured in marble collectors installed at ground level, was of the order of 10-25 gm (-2) month (-1), with an aver age value of 17.1 gm (-2) month (1). The accumulation rate was higher durin g the day hours than during the night. There was a tendency for the accumul ation to be highest in February and then gradually decrease until the follo wing January, but considerable scatter occurs in this trend. During 1988-19 97, dust accumulation at Sede Boqer sharply decreased in the first 2 years, increased during the next 4 years, and more or less stabilized from 1995 o nward. There was no agreement between the temporal evolution of the velocit y of accumulation v(a) and the temporal evolutions of dust concentration, d ust accumulation or wind speed. Most high-magnitude dust events (defined in this study as events with an average airborne dust concentration greater t han or equal to 400 mug m (-3)) occurring at Sede Boqer are true dust storm s, which occur predominantly during the day hours. During the period 1988-1 991, dust storms and dust hazes were equally abundant, but from 1992 onward the high-magnitude dust events were nearly exclusively dust storms. The di stribution of dust storms and dust hazes over the year is different: the fo rmer are mainly concentrated in the period November-May, whereas the latter occur anywhere in the year. True dust storms are usually associated with l ocal cyclonic activity, but may also be connected to local thunderstorm cel ls (haboob-type dust storms). At Sede Boqer, there is no correlation in the wet season between rainfall and dust activity. A significant correlation e xists between rainfall (in the wet season) and dust activity in the next dr y season: wet seasons with low rainfall are followed by dry seasons with hi gh dust activity, and wet seasons with high rainfall are followed by dry se asons with low dust activity. The time lag between rainfall intensity and d ust activity is most probably caused by the dust crust on the desert floor, which is much stronger after rain seasons with high precipitation than aft er rain seasons with low precipitation. (C) 2001 Academic Press.