一个六层亚洲有限区域模式及对一次西南涡过程的数值模拟

A NUMERICAL EXPERIMENT ON THE LEE CYCLOGENESIS OF QINGHAI—XIZANG PLATEAU IN A SIX—LEVEL LIMITED AREA MODEL

本文介绍的六层亚洲有限区域模式包含了地形作用和地面摩擦、动量、热量和水汽的水平和垂直方向扩散过程(其中包括了下垫面感热作用)、水汽凝结潜热、云和辐射作用以及积云对流等物理过程。并运用新的有效的计算气压梯度力的方法。为减少青藏高原引起的σ面上的初值(由 p 面到σ面)的插值误差,用了初始时刻的迭代插值方法。另外,利用上述模式,以1981年7月11日12时客观分析为初始场,对青藏高原背风坡地区的西南涡形成过程进行了数值模拟试验,较成功地研究了青藏高原动力作用对西南涡形成和发展过程的影响,模式还较成功地模拟出在西南涡形成过程中在我国西南地区低层西南风急流的迅速形成和维持过程。如果降低模式地形高度(如将青藏高原降至3000m 以下),地形的坡度也变小了,西南涡的模拟就不能成功。本模式所用的新的气压梯度力的计算方法,使预报效果得到了改进。

The present model,including more physical processes,is a six-level primitive equation modelfor Asia area with efficient and accurate numerical techniques for the computations of pressuregradient force and the initial fields in the vicinity of mountains in σ—coordinate.The numericalexperiments on the lee cyclogenesis of Qinghai-Xizang plateau are performed successfully by us-ing the present model with the initial condition based on objective analysis data on 11th July,1981.More interesting simulation results are displayed,and they show that the dynamic influenceof Qinghai-Xizang plateau is an important role to the lee cyclogenesis with low-level south—westerly jet stream in southwestern China.The results also show that unless the consideration ofmountain effects(or reducing the orographic height by the factor of 0.5 in the model)the simu-lations are failure.