Sandstorm In Northwest Process Mesoscale Numerical Simulation And Diagnostic Analysis

Using the actual data as initial field, this paper simulates numerically the weatherpattern , wind field and temperature of the strong sandstorm in Northwest area duringApril 8-9 ,2001 and the simulation results are very good. The diagnostic analysis for thesandstorm process on the base of height, temperature, pressure and wind etc output fromthe model shows that the upper cold trough, low-level wind shear, surface coldanticyclonic ridge, mesoscale cyclone and cold front are the main synoptic systems,surface cold anticyclonic ridge and cold front provide condition of wind force tooccurrence of the sandstorm weather, the strong mesoscale cyclone before front makespressure gradient before and after cold front obviously strengthen, moreover, and itincreases obviously the temperature of the controlled area, as a result , the updraftmovement caused by convergence before front strengthens. Through the thermodynamicanalysis for the sandstorm weather according to the simulated potential temperature,potential vorticity field, it is found that this sandstorm weather occurred in the conditionof the atmospheric stratification stability, the area of the high potential temperature valueand the potential temperature gradient have a good corresponding relationship with thesurface cold air and cold front, so are the strength of potential vorticity and the differentdeveloping stage of sandstorm. The contrast analysis for the vertical distribution featureof the simulated physical quantities such as vorticity, divergence, vertical velocity .spiraldegree etc suggests that there are a good disposal among the various physical quantitiesfields in the different stage during the period of sandstorm development, and reveals thatthe dynamic mechanism of the forming, developing, decreasing of the sandstorm weatherand trigger and indication effects of the micro-mesoscale systems and secondary verticalcirculation to the occurring and developing of sandstorm in Northwest area. The analysisfor the evolution of the upper westerly field, north-south wind field show that the upperjet stream is a good indication to sandstorm-occurring areas, the strong sandstorm appearsat the right side of the entry domain of the jet stream and the ascension domain ofsecondary circulation. The narrow effect and the hampering, lifting, rounding effect ofcurrent of orography provide advantageous geographical conditions.