The Observation Of Variation Of Meteorological Parameters And Study Of Thermodynamical Structure During Dust-storm

Sandstorms is one of the major natural disasters in north China region. Since 16 centuries BC, sand-dust phenomenon is documented or described in history books. In recent years, frequent sandstorms weather and climate effects, the effects of the ecological environment, the production of socio-economic development and social security, as well as the negative impact on human health effects caused by sandstorms are widely concerned. In this paper we study the character variations of meteorological parameters during the dust-storm and the thermo-dynamical structure.The method and content as following: (1) Helicity were introduced and used to study sandstorms in north-west China , especially Relative Earth Helicity and Relative Storm Helicity were applied to diagnosis the severe dust-storm in summer in Hexi Corridor. (2) Thermal stability during sandstorms were diagnoses by application of "3θ" curve and change characteristics of atmospheric. (3)The vertical parameters distribution of sandstorms are studied by use encryption sounding data. (4)Per minute data in the season of spring and summer sand-storms, which observed by automatic weather station, were used to analysis the meteorological parameters during dust-storm . (5)Basis on the study of sandstorms microscopic characteristics of sandstorms, thermal-dynamical model is used to computer the convective of sandstorms' tangential velocity and vertical velocity . The main results show as following:(1) Relative Earth Helicity and Relative Storm Helicity were applied to diagnosis the severe dust-storm in summer. There is a close relationship between thermal advection and Relative Earth Helicity, but this kind of helicity values closely relates to exactly analysis and diagnosis the intensity of weather system, especially the horizontal temperature gradient. Relative Storm Helicity high values center has a good homologous to the dust-storms severe areas.(2) Using high detective data over Minqin and Jiuquan base station in Hexi corridor of Gansu province, 3~θ variations were analyzed. The results show that the atmosphere stratification is hot and dry before the dust-storm, but cold and wet at the end of the sandstorm. The stratification is also beneficial to occur dust-storm at adjust phases, but adjusts to stable state at the end phases of dust-storm. Before sandstorm happened, the layer of atmospheric humidity is small. With the trough is approaching, humidity is increased in high levels and thehumidity transmission to the lower levels in the following time, the atmospheric layer relative humidity is increased.(3) Using the per minute surface meteorological parameter data of the twice sandstorms cases recorded by sandstorm automatic observation system of Jiuquan base station on March 28 and on July 12 of 2004 , the micro meteorological element change characteristic were analyzed . The result indicated that, the surface humidity and barometric pressure are both quite low before sandstorms explode. Surface pressure increases suddenly in the beginning course of the twice sandstorms, then maintains a period of relatively steady states. But the relatively steady period is longer in the spring sandstorm case than winter's. The surface pressure largely increases once again before sandstorms nearly finished. The surface air temperature is high before sandstorms happened, but decrease quickly at the end of the course. In the spring sandstorm period, Ocm depth earth temperature and surface air temperature change tendency quite consistent. But in summer not only Ocm depth earth temperature but the 5cm depth earth temperature variation is consistent with surface air temperature change tendency. Owning to the difference of the surface characters in different seasons , the horizontal visibility of summer case is bad than the spring courses, although the horizontal wind speed of the spring occurs is obviously bigger than the summer sandstorms.(4) According to the theory of natural convection as a engine proposed by Renn o and Ingersoll in 1996, the thermodynamical structure of a dust-storm were analyzed , which occurred in the Jjiuquan area of Gansu Province at 20 on July 12, 2004. The result shows that the air near the surface is in the dryness and heat condition, and there is extreme low temperature between 200hpa and 300hpa levels. The huge vertical temperature gradient of atmosphere is benefit to dry convection. The intensity of the dust-storm is closely related to the tangential and vertical velocity of the micro-scale and meso-scale convections. The tangential velocity and vertical velocity according to computation are close to the foreign stiu observation results. The tangential velocity is 11.4m/s and vertical velocity is 14m/s according to computation, but the maximal surrounding's velocity, memorized by the dust-storm observational system, is only 9.3m/s.