Estimation of the Threshold Friction Velocities over Various Dust Storm Source Areas in Northwest China

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  • Funds:

    Supported by the National Natural Science Foundation of China under Grant Nos. 41075005 and 40775013, the "973" National Key Basic Research Program of China under Grant No. 2010CB428501, the R&D Special Fund for Public Welfare (meteorology) by the Ministry of Finance and Ministry of Science and Technology of China under Grant No. GYHY200806007, and the National Basic Research and Development Program under Grant No. 2006AA06A306.

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  • The emission of dust particles into the atmosphere is governed by the aerodynamic and resistant factors,which are quantified by the friction velocity u* and the threshold friction velocity u*t, respectively. The threshold friction velocity u*t influences the vertical dust flux and dust transport. Based on the micrometeorological data obtained in the springs of 2004 and 2006 over Hunshandake desert area, Loess Plateau,and Gobi desert area, the relationship between dust concentration and friction velocity for the dust events that occurred over Hunshandake desert area was investigated, and the threshold friction velocities over the three different dust source areas were estimated. The results show that the value of dust concentration is low during the preemission stage of a dust storm event, and the rapid increase of friction velocity provides favorable dynamic conditions for dust emission. During the dust emission stage, the dust concentration increases sharply due to mechanical and thermal turbulent mixing. At the calm-down stage, the dust concentration drops nearly linearly with the decreasing friction velocity, on account of the gravitational deposition of larger dust particles. When the dust concentration is higher than 200 μg m-3, it is considered as a dust emission process. According to the criteria, the values of threshold friction velocity over Hunshandake desert area and Gobi region are 0.6 and 0.45 m s-1, respectively. The threshold friction velocity over Loess Plateau depends on the wind direction, due to the complex terrain and inhomogeneous surface. The northwest wind shows the effects of the Mu Us desert in the northwest. The corresponding u*t is 0.35 m s-1. The south wind exhibits the characteristics of the Loess hilly dunes in the south, and the u*t is 0.7 m s-1.The large roughness length of the Loess hilly dunes and the large inter-particle cohesion for the clay soil texture increases the local friction velocity. Different threshold friction velocities and occurrence frequencies of strong wind account for different dust emission capabilities for various source areas.
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    沈阳化工大学材料科学与工程学院 沈阳 110142

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Estimation of the Threshold Friction Velocities over Various Dust Storm Source Areas in Northwest China

  • 1. Department of Atmospheric and Oceanic Sciences,School of Physics,Peking University,Beijing 100871;
    Department of Atmospheric and Oceanic Sciences,School of Physics,Peking University,Beijing 100871
Funds: Supported by the National Natural Science Foundation of China under Grant Nos. 41075005 and 40775013, the "973" National Key Basic Research Program of China under Grant No. 2010CB428501, the R&D Special Fund for Public Welfare (meteorology) by the Ministry of Finance and Ministry of Science and Technology of China under Grant No. GYHY200806007, and the National Basic Research and Development Program under Grant No. 2006AA06A306.

Abstract: The emission of dust particles into the atmosphere is governed by the aerodynamic and resistant factors,which are quantified by the friction velocity u* and the threshold friction velocity u*t, respectively. The threshold friction velocity u*t influences the vertical dust flux and dust transport. Based on the micrometeorological data obtained in the springs of 2004 and 2006 over Hunshandake desert area, Loess Plateau,and Gobi desert area, the relationship between dust concentration and friction velocity for the dust events that occurred over Hunshandake desert area was investigated, and the threshold friction velocities over the three different dust source areas were estimated. The results show that the value of dust concentration is low during the preemission stage of a dust storm event, and the rapid increase of friction velocity provides favorable dynamic conditions for dust emission. During the dust emission stage, the dust concentration increases sharply due to mechanical and thermal turbulent mixing. At the calm-down stage, the dust concentration drops nearly linearly with the decreasing friction velocity, on account of the gravitational deposition of larger dust particles. When the dust concentration is higher than 200 μg m-3, it is considered as a dust emission process. According to the criteria, the values of threshold friction velocity over Hunshandake desert area and Gobi region are 0.6 and 0.45 m s-1, respectively. The threshold friction velocity over Loess Plateau depends on the wind direction, due to the complex terrain and inhomogeneous surface. The northwest wind shows the effects of the Mu Us desert in the northwest. The corresponding u*t is 0.35 m s-1. The south wind exhibits the characteristics of the Loess hilly dunes in the south, and the u*t is 0.7 m s-1.The large roughness length of the Loess hilly dunes and the large inter-particle cohesion for the clay soil texture increases the local friction velocity. Different threshold friction velocities and occurrence frequencies of strong wind account for different dust emission capabilities for various source areas.

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