Mesoγ-Scale Distribution of Orographic Precipitation: Numerical Study and Comparison with Precipitation Derived from Radar Measurements

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  • 1 Department of Geophysics and Planetary Sciences, Tel Aviv University, Tel Aviv, Israel
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Abstract

On the assumption that moisture convergence due to mechanical uplifting approximately equals the orographic precipitation, the mesoγ-scale rainfall distributions over mountainous regions in Israel are investigated. The simulated distributions are compared to rainfall observations both from raingages and from radar reflectivities. The mean error in the predicted rainfall on scale of 2 km was ±8.4% for mean annual normals and 15%–20% for three case studies. It is suggest that orographic rainfall on the small mesoscale is highly predictable with the adiabatic assumption that the uplifting is determined by V·ΔZs, where V is the horizontal wind encountering the mountain and Zs, is the topographic elevation.

It is also illustrated that the climatological observed rainfall distribution could be complemented by the model at locations where sufficient observations were not available. By comparison of the model simulation with the radar-derived rainfall, the considerable effect that a change in the wind direction has on the orographic rainfall distributions is shown.

Abstract

On the assumption that moisture convergence due to mechanical uplifting approximately equals the orographic precipitation, the mesoγ-scale rainfall distributions over mountainous regions in Israel are investigated. The simulated distributions are compared to rainfall observations both from raingages and from radar reflectivities. The mean error in the predicted rainfall on scale of 2 km was ±8.4% for mean annual normals and 15%–20% for three case studies. It is suggest that orographic rainfall on the small mesoscale is highly predictable with the adiabatic assumption that the uplifting is determined by V·ΔZs, where V is the horizontal wind encountering the mountain and Zs, is the topographic elevation.

It is also illustrated that the climatological observed rainfall distribution could be complemented by the model at locations where sufficient observations were not available. By comparison of the model simulation with the radar-derived rainfall, the considerable effect that a change in the wind direction has on the orographic rainfall distributions is shown.

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