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 © 2007 Royal Meteorological Society

This study attempts to find a linkage between the interannual variations of the rainfall measured in 12 stations spread over the northern half of Israel (the southern Levant) and atmospheric circulations ranging from regional to global scale. The analysis was done for the midwinter months, December–February, in which two-thirds of the annual rainfall occurs, during the years 1950–2002. The study is based on composite maps for extremely dry/wet seasons and on maps of correlation between atmospheric variables and the rainfall time series. Our results show that an upper-level trough extending from Eastern Europe toward the Eastern Mediterranean (EM) is closely linked with the seasonal rainfall over the study area. This is expressed by a correlation of −0.74 between the 500-hPa geopotential height at 32.5°N, 35°E and the rainfall. This trough has two effects on the southern Levant rainfall: one is the dynamics implied by the upper trough and the other is the cool advection over the EM imparted by the northwesterly flows induced by the trough. The latter presumably enhances the atmospheric instability when it sweeps over the warmer waters of the EM. The upper trough was found to be associated with three global factors: the polar stratospheric jets, in both the Northern and Southern Hemispheres, and the SST variations over the western tropical Pacific Ocean, represented by the ‘Pacific Warm Pool’ index. The EM trough is accompanied by a ridge covering western Europe, so that cold and wet winters in the southern Levant coincide with warm and dry winters over western Europe and vice versa. Copyright © 2005 Royal Meteorological Society.

A 3-yr dataset (February 2000–November 2002) of 30-min averages for particulates, visibility, and meteorological data were analyzed to examine the dependence of particulate matter of less than 10 μm in diameter (PM10) mass concentrations and visibility in Tel Aviv, Israel, on seasonal meteorological conditions, synoptic weather patterns, and airmass history. The persistent nature of the summer synoptic weather pattern in the east Mediterranean (EM) region yielded the highest mean visibility (35 km) and lowest variability in PM10 concentrations, as compared with the higher variance for the other seasons, and spring in particular. The frequent passage of the “Sharav” cyclones during spring causes natural dust outbreaks with extreme values that result in a much higher PM10 annual mean (57 μg m−3) as compared with other larger cities. The history of the air mass dictating the physical and chemical properties of the particulate matter reaching Israel was assessed by back-trajectory analysis from predetermined transport sectors. The west and central European sectors, representing mostly the summer flow regime of European clean air masses that are advected over the Mediterranean, differ significantly in their reduced PM10 loading and high visual range from the Arabian Peninsula and North African sectors, originating from the surrounding deserts. Because the most frequent direction of air masses reaching the EM is from European origins, Tel Aviv experiences most of the time satisfying visibility conditions. Applying the definition “very good visibility” for visibility exceeding 19 km shows that about 90% of the time these conditions were met for this 3-yr period.

The eastern Mediterranean (EM) is one of the regions in the world where elevated concentrations of primary and secondary gaseous air pollutants have been reported frequently, mainly in summer. This review discusses published studies of the atmospheric dispersion and transport conditions characterizing this region during the summer, followed by a description of some essential studies dealing with the corresponding concentrations of air pollutants such as ozone, carbon monoxide, total reactive nitrogen, methane, and sulfate aerosols observed there. The interlaced relationship between the downward motion of the subsiding air aloft induced by global circulation systems affecting the EM and the depth of the Persian Trough, a low-pressure trough that extends from the Asian monsoon at the surface controlling the spatiotemporal distribution of the mixed boundary layer during summer, is discussed. The strength of the wind flow within the mixed layer and its depth affect much the amount of pollutants transported and determine the potential of the atmosphere to disperse contaminants off their origins in the EM. The reduced mixed layer and the accompanying weak westerlies, characterizing the summer in this region, led to reduced ventilation rates, preventing an effective dilution of the contaminants. Several studies pointing at specific local (e.g., ventilation rates) and regional peculiarities (long-range transport) enhancing the build-up of air pollutant concentrations are presented. Tropospheric ozone (O₃) concentrations observed in the summer over the EM are among the highest over the Northern Hemisphere. The three essential processes controlling its formation (i.e., long-range transport of polluted air masses, dynamic subsidence at mid-tropospheric levels, and stratosphere-to-troposphere exchange) are reviewed. Airborne campaigns and satellite-borne initiatives have indicated that the concentration values of reactive nitrogen identified as precursors in the formation of O₃ over the EM were found to be 2 to 10 times higher than in the hemispheric background troposphere. Several factors favor sulfate particulate abundance over the EM. Models, aircraft measurements, and satellite-derived data have clearly shown that sulfate has a maximum during spring and summer over the EM. The carbon monoxide (CO) seasonal cycle, as obtained from global background monitoring sites in the EM, is mostly controlled by the tropospheric concentration of the hydroxyl radical (OH) and therefore demonstrates high concentrations over winter months and the lowest concentrations during summer when photochemistry is active. Modeling studies have shown that the diurnal variations in CO concentration during the summer result from long-range CO transport from European anthropogenic sources, contributing 60 to 80 % of the boundary-layer CO over the EM. The values retrieved from satellite data enable us to derive the spatial distribution of methane (CH₄), identifying August as the month with the highest levels over the EM. The outcomes of a recent extensive examination of the distribution of methane over the tropospheric Mediterranean Basin, as part of the Chemistry-Aerosol Mediterranean Experiment (ChArMEx) program, using model simulations and satellite measurements, are coherent with other previous studies. Moreover, this methane study provides some insight into the role of the Asian monsoon anticyclone in controlling the variability of CH₄ pollutant within mid-to-upper tropospheric levels above the EM in summer.

An opportunity to improve understanding related to the structure of the atmospheric boundary layer (ABL) in Israel along the coastal region environs emerged in April 1997 when the Israel Electric Corporation, Ltd. (IEC), installed and began the operation of a 1290-MHz radar profiler and radio acoustic sounding system (RASS) midway between Haifa and Tel Aviv. This instrument is, in addition to the upper-air measurements carried out routinely by the Israel Meteorological Service (IMS) in Beit-Dagan, at the central coastal plain of Israel. In order to better characterize the spatial variation of the turbulent mixed layer and the stable layer capping it within the ABL, the upper-air measurements from the profiler were compared with the concurrent rawinsonde data from the permanent sounding site in Beit-Dagan. The analysis and simultaneous comparison of both instruments was done for noontime of two consecutive summers (1997–98) and included the following ABL parameters: depth and lapse rate of the mix... Abstract An opportunity to improve understanding related to the structure of the atmospheric boundary layer (ABL) in Israel along the coastal region environs emerged in April 1997 when the Israel Electric Corporation, Ltd. (IEC), installed and began the operation of a 1290-MHz radar profiler and radio acoustic sounding system (RASS) midway between Haifa and Tel Aviv. This instrument is, in addition to the upper-air measurements carried out routinely by the Israel Meteorological Service (IMS) in Beit-Dagan, at the central coastal plain of Israel. In order to better characterize the spatial variation of the turbulent mixed layer and the stable layer capping it within the ABL, the upper-air measurements from the profiler were compared with the concurrent rawinsonde data from the permanent sounding site in Beit-Dagan. The analysis and simultaneous comparison of both instruments was done for noontime of two consecutive summers (1997–98) and included the following ABL parameters: depth and lapse rate of the mix...