Simulation And Research Of Boundary Layer Processes In Arid And Semiarid Areas Of Northwest By Mesoscale Meteorological Model

In this paper, we analyzed the Northwest semi-arid, arid boundary layer processes and their characteristics by using both ARPS and WRF mesoscale meteorological model simulation. First from the observation data we concluded variation of sensible heat flux in SACOL; and then stand by the simulation results of sensible heat flux to determine the accuracy of the model in SACOL; then analyzed the boundary layer processes in semi-arid regions by using simulation results; following analyzed the boundary layer processes in arid regions of northwest by using higher resolution simulations of one month integral; finally, the paper proposes a kind of formation mechanism of ultra-high convection boundary layer in northwest arid area and analyzed the role of residual layer in boundary layer processes.Based on the observation and simulation analysis obtained the following conclusions:1. Sensible heat flux in SACOL is bigger in summer than in winter, the fluctuations of sensible heat flux is bigger in summer than in winter under similar weather conditions, there is a lag in the peak of winter diurnal variations of sensible heat flux than in summer.2. Overall ARPS and WRF on SACOL simulated sensible heat flux stations have a certain precision, but they have some differences between the simulation results, the two models simulated sensible heat flux concentrated in the peak at 12 noon-afternoon 13, the day of the ARPS simulated sensible heat flux has a higher accuracy than the WRF, the simulation results are closer to the observations,the simulation results of ARPS are smoother than WRF, night for the ARPS simulated sensible heat flux are significantly larger than the observed values, while the WRF is relatively close to the observations.3. According to the simulation results, boundary layer in semi-arid regions has the following characteristics:stable boundary layer can be divided into the boundary layer-the initial stage of development-rapid uplift stage-stable uplift stage-the maximum height of convective boundary layer and gradually decay Phase-rapid decay stage-stages of stable boundary layer; ARPS simulated maximum boundary layer height in semi-arid regions is 3700m, while WRF's result is 2700m;two models' simulation results of specific humidity profiles are comply with the distribution of the atmospheric boundary layer specific humidity, specific humidity between the simulation results are distributed in 0-10g/kg, near the top of the boundary layer specific humidity has a inversion phenomenon; simulated wind profile of two models in semi-arid regions all comply with the atmospheric boundary layer wind speed distribution.4. According to the simulation results of arid regions, Jiuquan, Linze, Minle, Minqin 4 sites in July 2009 the maximum boundary layer height of the time there was basically Beijing,17,18, the four sites generally have higher maximum boundary layer height, four sites at the maximum boundary layer height ranges of Jiuquan 2500-4200m, Linze 2900-4800m, Minle 2100-4050m, Minqin 3200-5250m.5. The specific humidity of the four sites in common as follow:under the convective boundary layer height, specific humidity was approximately uniform or slowly decreasing trend, over the convective boundary layer height, specific humidity changed rapidly with height, gradient of specific humidity Increased rapidly, rising the specific humidity decreases almost to 0, in the stable boundary layer at night the specific humidity has a inversion phenomenon.6. More arid than in humid region has a residual layer deeper, thus forming a higher maximum boundary layer height.7. If there are no big weather systems, high convective boundary layer in northwest ard regions are not formated in one day, they formated through the residual layer effects and other combined effects in a time scale of about 3-5 days, in arid regions development and changes of the residual layer itself has a period of 3-5 days.8. In the northwestern arid and semi arid areas, deep residual layer at night is the base to form high convective boundary layer height of the next day, convective boundary layer height and thickness of residual layer at night are closely linked, the development of convective boundary layer evolution also closely related with the vertical velocity field.