Diagnostic Analysis And Research Of "0504" Sand-Dust Storm

The sand-dust weather, unique to semi-arid, arid and desertification areas, formed in specific geographical environment and under underlying surface conditions , is a kind of a small possibility, disastrous weather induced by the particular background of the large-scale circulation and certain a system. It creates heavy losses to the people, causes great harm to the natural ecological environment and speeds up land desertification process. Northern China, especially the northwestern region belongs to one of the global modern sand dust weather high active areas. Therefore, understanding of the sand-dust weather and accurate weather forecasting is still a major scientific problem needed to solve.On the basis of introducing the Ningxia sand-dust storm weather climate background foundation, the sand-dust storm process was analyzed and compared by using the normal observation data of the dust storm which occured on April, 2001 and 2005 in Ningxia. The result shows that (1) Pre- and post- sandstorm, the ground meteorological elements changed greatly, Atmospheric instability significantly increased because of strongest temperature build-up post meridiem, is conducive to high gale under the upper air momentum transportation downward, which provides the dynamic and thermal conditions for the dust weather. (2) Terrain blocking has greater impact on the cold front and the movement of sandstorms.(3) The upper air horizontal and the strong frontal zone are important power mechanism to stimulates this sand-dust storm , the upper air jet stream area formation is essential condition which produces the gale, the sand-dust storm weather , the Mongolian cyclone and the ground cold front is the major effect weather system which creates this sand-dust storm. The analysis result indicated that, two sand-dust storm weather process besides synoptic situation background different, the cold air ways, as well as the dynamic and thermal conditions are basically the same. The sand-dust storm weather formed by the cold air from the western Siberian moves rapidly eastward and forms strong frontal zone over the northern Xinjiang , which corresponding surface cold front moves to such special underlying surface . Upper jet stream was the favorable power condition, the strong ascending motion at low-level and thermal instability induced the sandstorm.The diagnostic of the sand-dust storm process was analyzed which occured on April,2005, found: medium- and low-altitude troughs falling behind the high trough formed this kind of slanting pressure structure, which would deepen this cold trough.The warm advection in front of the trough and 850hPa small-low pressure had a clear indication of the sand-dust storm occurrence. The high and low altitude intense shear on the flow field happened between 500hPa and 700hPa. Strong low-level convergence and height-level divergence coupled with the deep vorticity column is a typical structure which the sand-dust storm generation and development.Vertical velocity generally hollow greatest.The low altitude equivalent potential temperature layer front frontal zone is obvious,the low-level existence unstable thermal energy condition.The distribution of helicity over the sandstorm area was negative at higher levels and positive at lower levels, This vertical distribution of helicity is very conducive to form the development of the sand-dust storms. The K-index analysis indicated that, the atmospheric stratification nearby Ningxia is still relatively stable, the air relatively dry.