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<p>The center of Israel presents a relatively simple vertical topographical cross-section: The eastern&#xa0;Mediterranean coast to the west, Judea and Samaria mountains in the center and the deep and steep&#xa0;Jordan valley to the east. Further to the east of the Jordan valley there is a plateau of the Moab&#xa0;mountains.</p><p>This work presents climatological examination of the daytime boundary layer height (BLH a.g.l) variability during non-summer months according to high resolution (3 km) WRF simulations during at least 5 years (2009-2013). Verification against radiosonde measurements at Beit Dagan at the central coastal plain has shown good agreement between predicted and measured variables including the BLH (mean absolute error 200-500 m).</p><p>The shape of monthly BLH histograms varies as a function of season and topography. During December-February the monthly BLH median above the mountain peak and its easterly slope is lower than that over the coastal area (0.3-1.2, 0.9-1.5 km), while during the transitional months September, October, May, the situation is reversed (0.9-1.8, 0.6-1.2 km). In order to track the reason behind the reduction of the BLH over the mountain peak during winter, an examination of the BLH variability during the local afternoon, 10-13 UTC, (12-15 LT) during the various months was performed. As a result, 8 test cases with relatively low (&lt;350 m) BLH were isolated mainly during December. Weak pressure gradients and weak (&lt; 5 m/s) easterly flows were found to be responsible for the low BLH. The synoptic pressure during these events is characterized by a ridge from the south in the middle troposphere and central Red Sea Trough or high to the east or to the north of Israel next to the surface. Foehn winds, which locally reduce the humidity and enhance the temperature, flow over the eastern slope of the Jordan valley and the western slope of the mountain. In such cases, the mild synoptic pressure gradients are responsible for the maintenance of the local cooling over the mountain peak. Limited warm air advection to the mountain peak and close to zero sensible heat flux maintain relatively cold air over the mountain peak and its eastern slope. This examination gives insights into the mechanism of shallow winter day time boundary layer events over the mountain peak and serves as a starting point for further research.</p>

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Spatial variability of non-summer daytime boundary layer height over the Israeli coastal-mountain-valley topography reveals unique shallow boundary layer winter events

  • 期刊论文

  • 发表日期：

    2025年2月26日

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  • Sigalit Berkovic

摘要

The center of Israel presents a relatively simple vertical topographical cross-section: The eastern Mediterranean coast to the west, Judea and Samaria mountains in the center and the deep and steep Jordan valley to the east. Further to the east of the Jordan valley there is a plateau of the Moab mountains.

This work presents climatological examination of the daytime boundary layer height (BLH a.g.l) variability during non-summer months according to high resolution (3 km) WRF simulations during at least 5 years (2009-2013). Verification against radiosonde measurements at Beit Dagan at the central coastal plain has shown good agreement between predicted and measured variables including the BLH (mean absolute error 200-500 m).

The shape of monthly BLH histograms varies as a function of season and topography. During December-February the monthly BLH median above the mountain peak and its easterly slope is lower than that over the coastal area (0.3-1.2, 0.9-1.5 km), while during the transitional months September, October, May, the situation is reversed (0.9-1.8, 0.6-1.2 km). In order to track the reason behind the reduction of the BLH over the mountain peak during winter, an examination of the BLH variability during the local afternoon, 10-13 UTC, (12-15 LT) during the various months was performed. As a result, 8 test cases with relatively low (<350 m) BLH were isolated mainly during December. Weak pressure gradients and weak (< 5 m/s) easterly flows were found to be responsible for the low BLH. The synoptic pressure during these events is characterized by a ridge from the south in the middle troposphere and central Red Sea Trough or high to the east or to the north of Israel next to the surface. Foehn winds, which locally reduce the humidity and enhance the temperature, flow over the eastern slope of the Jordan valley and the western slope of the mountain. In such cases, the mild synoptic pressure gradients are responsible for the maintenance of the local cooling over the mountain peak. Limited warm air advection to the mountain peak and close to zero sensible heat flux maintain relatively cold air over the mountain peak and its eastern slope. This examination gives insights into the mechanism of shallow winter day time boundary layer events over the mountain peak and serves as a starting point for further research.