A Model Simulation of the Summer Circulation from the Eastern Mediterranean past Lake Kinneret in the Jordan Valley

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  • 1 The Hebrew University, Jerusalem, Israel
  • | 2 Israel Atomic Energy Commission, Nuclear Research Centre, Negev, Israel
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Abstract

A model is described for the representation and study of air flow from the eastern Mediterranean (on the west side of the model's domain) past Lake Kinneret in the Jordan Valley (about 210 m below MSL) and beyond to the east (on the east side of the model) in the summer months. The primary purpose of the model is to improve our understanding of two striking features of the meteorology of the lake area in summer: 1) the almost daily development of strong winds and an associated storm on the lake in the afternoon, and 2) a nearly 50% drop in wind speed across the lake, from the western to the eastern shore, over a distance of only 10 km, again in the afternoon.

The model is two-dimensional. It uses the sigma coordinate system and is thus hydrostatic. The horizontal grid distance is 4 km. It has 10 levels in the vertical, between the surface and the top at 750 mb. The first level in the vertical is 10 m above the surface and each of the higher levels is at an attitude that is approximately twice the altitude of the next lower level.

In the numerical scheme we apply Machuk's splitting method: a numerical filter is applied in the horizontal which suppresses short waves but leaves the long waves relatively unaffected. The time step is 8 s.

The results indicate the development of strong winds on the west side of the lake in the afternoon. These winds are explained by the model as being the sudden incursion of the cool Mediterranean sea breeze front to the relatively warm Kinneret Valley. The strong intensity is explained by the dynamic effect of the hills with a contribution due to the collapse of an opposing upslope valley breeze. It is also suggested that an important contribution to the downslope acceleration is made by the onset of a density current when relatively cool Mediterranean air penetrates the warm air in the valley. The model needs further improvement since the time of onset of the strong winds is about 1.5 h late compared with observations. The weakening of the winds from the west shore to the east shore is well simulated by the model.

Abstract

A model is described for the representation and study of air flow from the eastern Mediterranean (on the west side of the model's domain) past Lake Kinneret in the Jordan Valley (about 210 m below MSL) and beyond to the east (on the east side of the model) in the summer months. The primary purpose of the model is to improve our understanding of two striking features of the meteorology of the lake area in summer: 1) the almost daily development of strong winds and an associated storm on the lake in the afternoon, and 2) a nearly 50% drop in wind speed across the lake, from the western to the eastern shore, over a distance of only 10 km, again in the afternoon.

The model is two-dimensional. It uses the sigma coordinate system and is thus hydrostatic. The horizontal grid distance is 4 km. It has 10 levels in the vertical, between the surface and the top at 750 mb. The first level in the vertical is 10 m above the surface and each of the higher levels is at an attitude that is approximately twice the altitude of the next lower level.

In the numerical scheme we apply Machuk's splitting method: a numerical filter is applied in the horizontal which suppresses short waves but leaves the long waves relatively unaffected. The time step is 8 s.

The results indicate the development of strong winds on the west side of the lake in the afternoon. These winds are explained by the model as being the sudden incursion of the cool Mediterranean sea breeze front to the relatively warm Kinneret Valley. The strong intensity is explained by the dynamic effect of the hills with a contribution due to the collapse of an opposing upslope valley breeze. It is also suggested that an important contribution to the downslope acceleration is made by the onset of a density current when relatively cool Mediterranean air penetrates the warm air in the valley. The model needs further improvement since the time of onset of the strong winds is about 1.5 h late compared with observations. The weakening of the winds from the west shore to the east shore is well simulated by the model.

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