地面加热对沙尘暴数值模拟结果的影响研究

Effects of Surface Heating Flux on the Numerical Simulation Results of Dust Storm

利用沙尘数值预报模式并针对2002年3月18—20日典型沙尘暴过程,模拟研究了地面热通量对沙尘暴的影响及其机制。结果发现,沙尘天气数值预报模式较准确地模拟了本次沙尘暴过程。模式对白天地面加热强度和夜间地面冷却强度均有一定程度的高估。地面热通量能够使沙尘暴明显增强,同时也通过导致地面风速、层结稳定度、地面摩擦速度产生明显的日变化,进而导致沙尘暴强度的日变化。地面热通量影响地面风速的方式是导致混合层形成,从而有利于产生高空动量下传。另外,沙尘暴发生时地面热通量主要影响地面和行星边界层中的天气要素,随时间推移地面热通量能够持续影响上升运动强度,且这一影响从边界层逐渐向上扩展到自由大气,并达到500hPa以上。

A dusty weather numerical prediction model was used to simulate the effects of the surface heating flux on the dust storm.The case is a super severe dust storm process occurred in eastern Asia from Mar.18 to Mar.20,2002.This dust storm process was successfully simulated by the model.The simulated dusty weather regions corresponded to the observational regions.But the simulated intensity of surface heating in daytime and the surface cooling at night was overrated.In the desert region of Inner Mongolia the surface sensitive heating flux brought a net heating to the atmosphere.The surface heating flux enhanced the intensity of dust storm.Meanwhile,it enhanced the daily change of intensity of dust storm seriously through enhancing the daily change of surface wind speed,the stratification instability in lower atmosphere and the surface friction velocity.The main mechanism of surface heating flux influencing the surface wind speed is that it can lead a mixed layer（ML）in the lower atmosphere and so the downward transportation of momentum was enhanced.Through this mechanism the strength of surface wind speed and the friction velocity are enhanced.In addition,the advection of air in ML contributed to the sustaining and expanding of ML.The influencing process of surface heating flux can be divided to two phases.In the dust storm formation phase,the surface heat flux mainly affected the weather elements in the PBL（planetary boundary layer）and at surface,such as the surface wind speed,the stratification stability and surface friction velocity discussed above.In the second phase,the surface heating flux enhanced the ascending motion from the lower troposphere up to the middle troposphere according with the time processing.This influence can touch the height above 500 hPa.