| Structure of Thunderstorm Gust Fronts with Topographic Effects |
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| 作者姓名： | A. A. Bidokhti T. Bani-Hashem |
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| 作者单位： | A. A. Bidokhti and T. Bani-Hashem Institute of Geophysics，Tehran University，P.O，Box 14155-6466，Tehran，LR. Iran |
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| 摘 要： | Surface meteorological observations, associated with gust fronts produced by thunderstorm outflows over Tehran, an area surrounded by mountains, have been analyzed. Distinctive features are sudden drop in air temperature, up to 10℃, sharp increase in wind speed, up to 30 m s-1, with wind shift, to northwesterly, ressure jump, up to 4 hPa, humidity increase, up to 40%, and rain after some 20 min. Gust fronts which often occur in spring time, have a typical thickness of about 1.5 km and produce vertical wind shear of the order of 10-2s-1. Although these features seem to be common for most of the events, their intensities differ from one event to another, indicating that the gust fronts may occur in different sizes and shapes. Apart from a dominant effect on the formation of the original thunderstorms, topography appears to break up the frontal structure of the gust fronts. The internal Rossby radius of deformation for these flows is small enough (～ 100 km) for rotational effects to be minor.A laboratory model of the gust front (gravity current) also shows that it initially has a distinctive head with a turbulent wake, and can be broken up by topography. It is shown that when the environment is stratified, turbulence due to lobes and clefts instabilities near the nose of the current is suppressed. When the ground is rough, these instabilities are highly amplified and the internal Froude number of the flow is reduced. The bottom slope in the presence of rough topography leads to the break up of the current head and produces a broad and highly non-uniform head, recognized in the density signals.
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| 收稿时间： | 9 January 2001 |
Structure of thunderstorm gust fronts with topographic effects |
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| A. A. Bidokhti,T. Bani-Hashem.Structure of Thunderstorm Gust Fronts with Topographic Effects[J].Advances in Atmospheric Sciences,2001,18(6):1161-1174. |
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| Authors: | A A Bidokhti T Bani-Hashem |
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| Institution: | Institute of Geophysics, Tehran University, P.O. Box 14155-6466, Tehran. I.R. Iran,Institute of Geophysics, Tehran University, P.O. Box 14155-6466, Tehran. I.R. Iran |
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| Abstract: | Surface meteorological observations, associated with gust fronts produced by thunderstorm outflows over Tehran, an area surrounded by mountains, have been analyzed, Distinctive features are sudden drop in air temperature, up to 10 C, sharp increase in wind speed, up to 30 m s-1, with wind shift, to northwesterly, pressure jump, up to 4 hPa, humidity increase, up to 40%, and rain after some 20 min. Gust fronts which of ten occur in spring time, have a typical thickness of about 1.5 km and produce vertical wind shear of the or der of 10-2s-1. Although these features seem to be common for most of the events, their intensities differ from one event to another, indicating that the gust fronts may occur in different sizes and shapes. Apart from a dominant effect on the formation of the original thunderstorms, topography appears to break up the frontal structure of the gust fronts. The internal Rossby radius of deformation for these flows is small enough (~ 100 km) for rotational effects to be minor. A laboratory model of the gust front (gravity current) also shows that it initially has a distinctive head with a turbulent wake, and can be broken up by topography. It is shown that when the environment is strati- fled, turbulence due to lobes and clefts instabilities near the nose of the current is suppressed. When the ground is rough, these instabilities are highly amplified and the internal Froude number of the now is re- duced. The bottom slope in the presence of rough topography leads to the break up of the current head and produces a broad and highly non-uniform head, recognized in the density signals. |
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| Keywords: | Frontal structure Gravity current Meteorological data Outflows |
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