| 天气与气候 |
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| Impacting Factors of Sand-dust Weather Variation over Northwest China and Tibetan Plateau |
| REN Yu-long1,2, WANG Jin-song2,3 |
| 1.Linxia Meteorological Bureau of Gansu Province, Linxia 731100, China; 2.Institute of Arid Meteorology, CMA, Key Open Laboratory of Arid Climate Change and Disaster Reduction of CMA, Key Laboratory of Arid Climatic Change and Reducing Disaster of Gansu Province, Lanzhou 730020, China; 3.Laboratory for Climate Studies, China Meteorological Administration, Beijing 100081, China |
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Abstract The dynamical and thermodynamic factors affecting the variation of the sand-dust weather are analyzed over Northwest China and Tibetan Plateau by using the NCEP(2.5°×2.5°) long-term mean data. The results show: ①The 200 hPa westerly jet stream is the dynamical reason for the change of sand-dust weather. The seasonal changes of position and intensity of upper jet stream are caused by the weather systems at high level. This is just the reason why the sand-dust storms extend to the north and the east from the southern part of Tibetan Plateau. The regional circumfluence is formed by the dynamical structure of upper jet stream, and the down airflow of the circumfluence induces the down-transmission of high momentum, which causes the aggrandizement of wind on surface and the occurrence of sand-dust storms. ②The forming causes are different among the floating dust and the sand-dust storm. The thermodynamic reasons such as surface temperature has immediate influence on the occurrence of floating dust. The dynamical factors such as the upper jet stream affects the intensity of floating dust, but it has feeble influence on the range of the occurrence, whereas it is the immediate reason for the happening of sand-dust storm. The south to north transfer of the 500 hPa frontal belt is also an important reason for the variation of sand-dust storm. ③The edge of the 500 hPa vapour transporting belt is the incidental region for sand-dust storm. When the low level vapour increases within a certain limitation, it can induce the increment of potential instability, which could make the occurring of convection and the sand-dust storm. When the vapour increases to a certain degree, it restrains the occurrence of the sand-dust storm. ④The surface moisture is a factor aggrandizing the happening of sand-dust weather. When the soil was drier, the frequency of the sand-dust weather increases; the soil becomes wetter, the frequency decreases.
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Received: 06 March 2008
Published: 20 July 2009
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2009, Vol. 29 
