Study Of The Formation And Thermo-dynamical Structures Of Strong Sandstorm

The sandstorm is one of the major natural disasters in northern China. In recent years, especially after2002years, there are some fluctuations of the occurrence frequency of sandstorm, which mean that human have not decrease the sandstorm effectively, so we must face up the problem the of destroy which is brought bf the sandstorm. In this paper, by using observational and NCEP reanalysis data and numerical simulation method, we study the character variations of the strong sandstorm in spring; according to the encryption sounding data, the automatic meteorological observing data and the conventional observing data, we analyzed a case of weather events occurred in the Midwest Inner Mongolia autonomous region on April23-24,2009, the variations of ground meteorological elements and its internal dynamical and thermal changes in event process have been studied. Besides, by using observational and NCEP reanalysis data and through numerical simulation method, the Troposphere-Stratosphere Transportation of dust aerosol in a super dust storm process caused by the Mongolia cyclongenesis was conducted.The method and content as following:(1) The temperature anomaly and the gravity potential height anomaly is negative, and the vector wind anomaly is anti-clockwise over Siberia from850hPa to500hPa, when strong sandstorm occurs more than ever in spring; the updraft area is existing significant, which is good for appearing of Mongolian cyclone repeatedly and south-warding of cold air. The path of cold air is from western Siberia through Central Asia into Mongolia, and then come to the northwest region of China, including Xingjiang and other. The wind speed anomaly is positive in Gansu, Inner Mongolia, Ningxia, northern Shanxi and other places. But the temperature anomaly and the gravity potential height anomaly is positive, and the vector wind anomaly is clockwise over Siberia from850hPa to500hPa, when strong sandstorm occurs less in spring. The downdraft area is developing obviously, cold air can not southward easily and Mongolian cyclone is difficult to appear frequently, the wind field is not conducive to the cold air to invade the sources of sand in China. The climatic characteristic of years in which strong sandstorm occurs more or less than ever in spring is as same as inter-annual’s which is mentioned above. So that, there is inter-annual’s and inter-decadal characteristic of strong sandstorm in spring.(2) The high and low air circulation system configuration and the momentum have been studied. The result showed that:Mongolian cyclone are the main system producing the strong dust storm; The momentum of the high altitude is of great importance for sandstorm development; There is very good corresponding relation between vertical velocity, divergence, vorticity, relative humidity and storm; the distribution of helicity over the sandstorm area was negative at higher levels and positive at lower levels, The distribution of vertical speed over the sandstorm area was negative at higher levels and positive at lower levels, which is good for the taking place of the sandstorm, so the helicity has good indication in the forecasting of sandstorm..(3) The vertical distribution structure of the temperature, humidity and winds is beneficial to the development of the sandstorm’s occur. The pressure drops significantly before the dust storm happens, falls to the lowest while the dust storm occurs, and then rise rapidly; the surface temperature is higher and raise obviously before the dust storm happens, reaches to the highest while the dust storm occurs, and then drop prompt; the wind speed is lesser and the wind direction is east before the dust storm happens, while the dust storm happens the wind attains to the highest and the wind direction is west, and then the wind speed decreases quickly; Thermal stability during sandstorms were diagnoses by application of "30"curve, which will provide a valuable reference data for the monitoring and forecast of dust storms; Relative storm helicity high values center has a good homologous to the dust-storms severe areas; The intensity of the dust-storm is not only closely related to the surrounding velocity, but also the tensity of the micro-scale and meso-scale convections, especially the values of the tangential and vertical velocity.(4) The formation of upper level cut low led the subsiding of upper level jet stream, which induced the tropopause fold and the downward transportation of upper level potential vorticity. The folded tropopause was showing funnel-shaped with its bottom approaching near500hPa. The trajectory analysis shown that the air particles at the lower troposphere in the areas occurring dust weather were raised upward driven by the spiral ascending motion of cyclonic area. The dust aerosol transportation belt split two branches when it got to the upper lever of troposphere. One passed through the folded tropopause into stratosphere and then conducted anticyclonic movement downwards within it. The other retained in the troposphere and maintained cyclonic movement downwards. The process of sand troposphere-to-Stratosphere transport (TST) begins at12:00on the6th, and ends at14:00on the8th, which lasts51hours; the volume is more than ever when the time goes, and there is phenomenon that the dust particle moves upward mainly in the process of the sand TST.