Diagnosis And Numerical Simulation Of Dust Weather Occurred In April 2006 In Henan Province

On the basis of NCEP global spectral model, surface and upper-air conventional observationdata, the synoptic climate background and physical parameter fields are diagnosed and analyzedin a dust weather process during April 11-13,2006 in Henan Province. Results show that theprocess results from the strong cold air and Mongolia cyclone under the climate background ofdrought in the early time. According to the analysis results of the thermal advection, on one hand,strong cold advection promote the development of Mongolia cyclone with help of the warmadvection; one the other hand, the strong cold advection make the trough and the cold front moveeast and south, which lead to the synoptic process featuring high wind, dust and cold wave. Wecan get the results through the analysis of air stratified atmosphere that the stratification isinstable at the time of the outbreak of the dust weather but stable during the strongest period ofthe process. It is found by the analysis of the helicity that the vertical distribution of the holicityappears negative value in the upper layer and positive value in the low value. There are certaincorresponding relation between positive helicity evolution and the occurrence time of dustweather. The occurrence time of the strongest dust weather is almost in coincidence with themaximum positive helicity of the medium and low layer of troposphere and the 400-500hPa. It isalso suggested by second circulation that the sinking motion of the north bifurcation of the directcirculation of the second circulation help high jet stream move down, promote the wind speed toincrease in the medium and low layer of troposphere, make cold front move south, lead to theinstability of stratified atmosphere and drive the outbreak of the dust weather.The process is simulated and diagnosed by the meso-scale numerical model MM5 and theNCEP globe spectral model data. Results show that both coarse and fine mesh model cansimulate the occurrence and evolution of the front area and ground cold high in the process. Thedust weather process is diagnosed and analyzed by adopting the coarse mesh dynamic consistent data exported by the model. The result is that dry air incursion phenomenon appears obviouslyand plays an important role during the process. On one hand, high potential vorticity and lowhumidity air slips south down along the dense belt of potential equivalent temperature, whichlead to little disturbance of potential vorticity distributing from the medium and low layer oftroposphere, induce the temperature disturbance in low level, these disturbance of high and lowtemperature and potential vorticity, induce the circulation interaction and then lead to the genesisand development of cyclone. On the other hand, dry intrusion not only induce temperaturedisturbance in low level, make the strong cold advection move south and low trough east andcold front south, trigger instable weather, but also work with the lapping stream field of lowlevel convergence and high divergence to produce the weather process in Henan featuring dust,high wind and dust. It is also found that momentum moving down because of high level jet windspeed decreasing is the primary dynamic factor of the outbreak of the ground high wind and dustin the dust weather process. Finally, terrain sensitivity test is done and the contribution of theHuangtu plateau is discussed in the process.Based on the analysis of the thermo and dynamic process research in the dust weather, thecharacters of meso-scale system outbreak, development and structure evolution are initiallyrevealed in the dust weather process which makes us know better the mechanism of dust weatherin Henan province and then provides scientific theory basis for disaster prevention and reduction.