基于WRF的高原低涡内波动特征及空心结构的初步研究

本文采用美国新一代非静力中尺度数值模式WRFV3.1.1版本对2006年8月14日的1次高原低涡过程进行了3重嵌套的数值模拟,分析模拟输出的高时空分辨率资料,发现涡度散度在各层次上均存在着正负值区域的相临交替分布,体现出一定的波动性,并随时间的变化而旋转,由此对高原低涡中的涡旋波的产生和发展进行详细分析,发现高原低涡中同时具有产生涡旋Rossby波与惯性重力波的条件,进一步粗略计算了涡旋波切向的移速介于涡旋Rossby波与惯性重力波的理论移速之间。由分析结果得出结论认为,在低涡中心区域,由于较高的涡度径向梯度,同时有较强的辐合辐散,波动表现出以涡旋Rossby波与惯性重力波混合的特性为主;低涡外围区域中涡度径向梯度大大减弱,失去了产生涡旋Rossby的条件,显现为惯性重力波的特性。同时高原低涡生命期相对较短,波动在圆周上的传播条件不均匀,这说明可能大多高原低涡螺旋形态的发展并不均匀或并不完整,较难形成如同海上热带气旋般比较均匀和完整的螺旋云带。另外,模拟也发现,在低涡成熟阶段,低涡呈现暖心结构,中心区域垂直运动较弱,表现为相对平静的眼区域。

The Analyses of Wave and Eye Region in Tibetan Plateau Vortex

In this study, the process of a Tibet plateau vortex at August 14, 2006 was simulated with triple nested using the new generation of the mesoscale numerical model WRFV3.1.1 which was developed by NCAR/NCEP.The high resolution model output data shows that at the developing and mature stage of the vortex, the distribution of velocity divergence and vorticity both showing a certain degree of fluctuant, which alternating between the distribution of positive and negative values.By analyzing the wave in the Tibet plateau vortex, finding out that there are both generation conditions for Vortex-Rossby (VR) waves and Inertial Gravity (IG) wave.The moving speed of the wave in the vortex is between the theory speed of VR wave and IG wave.In the center region of the vortex, the radial gradient of vorticity and divergence are both high, so the wave shows mixed features of VR and IG wave.At the outer region of the vortex, the radial gradient of vorticity is too weak to support VR wave, so the wave in the vortex shows the feature of IG wave.Further more, Tibetan Plateau Vortex has a very short life cycle compared to Tropical Cyclone, and the wave propagation conditions in the ring are uneven, so the tangential spread of wave can be fracture at somewhere of the circle.This may inferred that it is difficult for the Tibetan Plateau Vortex to form the perfect spiral shape as Tropical Cyclone.In addition, the simulation also found that at the mature stage of Tibet plateau vortex, it has very weak vertical motion in the center compared to the outer area, and there is a warm core in the center like an eye which is calm.