青藏高原边坡地形重力波拖曳方案应用的个例研究

本文针对我国西南地区的一次持续性暴雨过程,利用WRF模式引入地形重力波拖曳方案进行120h的模拟,对比结果认为引入地形重力波拖曳的模拟效果总体看来略有优势,并详细分析了不同模拟时段的位势高度场,风场,海平面气压场与降水,其结果认为,引入与未引入地形重力波模拟的差异主要出现在48~72h之后,位势高度场方面,72h之后,在青藏高原主体上引入拖曳方案后的模拟结果相对未引入拖曳方案的结果是正偏差,高原下游地区为负偏差,引入后的模拟相对准确;风场模拟方面同样72h以内的模拟差距较小,72h之后高原上出现一处气旋性涡旋,其中心位置的模拟,引入拖曳方案后的结果相对准确,本次个例中出现的一例西南低涡,两实验都能够较好的模拟出700h Pa的气旋性涡旋;降水模拟的结果表明,在72h之后,对于四川地区降水中心位置的模拟,引入拖曳方案的模拟有所提高,但中心依然过强。这方面主要考虑降水的模拟牵涉模式内部更为复杂的处理过程和其他因素,地形重力波拖曳只是其中一个影响因素而不是核心因素。另外此方案对温度场及海平面气压场模拟的影响不明显。理论上讲引入地形重力波拖曳效应的模拟是物理过程相对更为完善的,在本次个例中模拟效果也略优,但在高原下坡复杂地形处长期应用的模拟效果仍需要更多的测试,将在后续工作中加以完善。

Application of Gravity Wave Drag Scheme at the Sloping Area of Tibet Plateau in a Case Study

In this paper,a case study was carried out to find to what extent the numerical simulation results will be affected by turn on the gravity wave drag scheme in Weather Research and Forecasted Model. The case is a continuous heavy rain process in southwest China,and two numerical simulations lasted 120 hours was done to simulate the process. One with the gravity wave drag scheme turned on and another with the gravity wave drag scheme turned off. The difference between two simulations was getting clearer after 48 ~ 72 hours. Values of geopotential height on Tibet Plateau is higher with gravity wave drag scheme than without it. Values of geopotential height at downstream areas of Tibet Plateau is lower with the scheme than without it. The simulated position of a vortex on Tibet Plateau is more precisely with the scheme. And both simulations can depicted an active southwest vortex in Sichuan basin. The position of maximum precipitation are better characterized by the simulation with the scheme,but value of the precipitation are over too much in both simulations. This may because the precipitation process is so complicated and gravity wave drag scheme is not the key point to influencing the result. Also,the scheme cannot make much influence on temperature and surface pressure. Overall the result with gravity wave drag scheme is slightly better. It need to admit that this is only a case study and have its uncertainty. The applicability of the scheme is sure need to have a long-term test in the in subsequent work.