Spatial and Structural Variation of the Atmospheric Boundary Layer during Summer in Israel—Profiler and Rawinsonde Measurements

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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 mixed layer, depth and virtual temperature gradient of the inversion layer, wind speed and direction at base and top of the inversion layer, and wind speed and direction shears within the inversion. All the sampling days were classified into three modes of the predominant synoptic situation typifying most of the summer days in Israel (i.e., the “Persian trough” synoptic system). Means, standard deviation, and relative standard deviation were calculated and compared between both sites for each of the assigned synoptic category. The analysis shows that (a) a consistently deeper and less unstable mixed layer is observed in the northern coastal site; (b) the interface separating the mixed layer and its capping inversion is sharper at the farther southern and inland site—a feature caused by stronger subsiding conditions above this site; (c) variation in the depth of the mixed layer for the different mode of the Persian trough is more pronounced at the northern site because of the proximity of this site to the cyclonic center of this trough; (d) an anticyclonic veering in horizontal wind direction and speed weakening is observed along the whole ABL profile going inland and south—a finding significant for all synoptic modes except for the shallow Persian trough mode; (e) at the northern coastal site, an anticyclonic shear in horizontal wind direction of 6°–12° (100 m)−1 is observed as ascending from the elevated inversion bottom to its top along the different synoptic modes of the Persian trough; and (f) differences in ABL properties are more affected by distance from shore than by the different modes of the synoptic pattern. This conclusion holds for wind speed and lapse rate within the mixed layer and virtual temperature gradient within the stable layer but not for mixed layer depths that were found to be more affected by the synoptic conditions prevailing over the region.

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