陈明轩, 王迎春. 2012: 低层垂直风切变和冷池相互作用影响华北地区一次飑线过程发展维持的数值模拟. 气象学报, (3): 371-386. DOI: 10.11676/qxxb2012.033
引用本文: 陈明轩, 王迎春. 2012: 低层垂直风切变和冷池相互作用影响华北地区一次飑线过程发展维持的数值模拟. 气象学报, (3): 371-386. DOI: 10.11676/qxxb2012.033
CHEN Mingxuan, WANG Yingchun. 2012: Numerical simulation study of interactional effects of the low-level vertical wind shear with the cold pool on a squall line evolution in North China. Acta Meteorologica Sinica, (3): 371-386. DOI: 10.11676/qxxb2012.033
Citation: CHEN Mingxuan, WANG Yingchun. 2012: Numerical simulation study of interactional effects of the low-level vertical wind shear with the cold pool on a squall line evolution in North China. Acta Meteorologica Sinica, (3): 371-386. DOI: 10.11676/qxxb2012.033

低层垂直风切变和冷池相互作用影响华北地区一次飑线过程发展维持的数值模拟

Numerical simulation study of interactional effects of the low-level vertical wind shear with the cold pool on a squall line evolution in North China

  • 摘要: 利用三维数值云模式和雷达资料四维变分同化技术,通过对6部新一代多普勒天气雷达观测资料进行快速更新循环同化和云尺度数值模拟,初步分析了2009年7月23日发生在华北地区的一次飑线过程的低层动力和热动力影响机制。结果表明,这次飑线过程处在低层中等强度切变的环境条件下,低层环境垂直风切变和冷池相互作用是本次飑线过程维持发展和传播的关键机制。在飑线发展的初期,低层垂直风切变较强,但冷池偏弱,冷池传播速度(C)和垂直于飑线的低层切变分量(ΔU)的比值C/ΔU<1,飑线回波前倾。而此时环境热力条件(对流有效位能较高和自由对流高度较低)对飑线的发展加强起到了积极作用,克服了这种低层切变和冷池不平衡所形成的不利条件。在飑线的加强和成熟阶段,由于对流降水使冷空气不断下沉,从而导致冷池快速加强,使低层切变和冷池强度逐渐达到近似平衡状态(C/ΔU≈1),低层大气处于最强的垂直抬升状态,飑线发展最为强盛,飑线回波直立。随着时间的推移,降水累积效应导致冷池强度明显大于低层切变强度(C/ΔU>1),不利的形势导致飑线逐渐趋于消散,飑线回波明显变宽、后倾,回波顶高显著下降。对模拟结果的定性分析和定量计算均表明,影响这次飑线过程发展维持的低层垂直风切变和冷池相互作用机制与Rotunno和Weisman等用来解释飑线发展演变的RKW理论一致。另外,模拟结果显示,低层0—3 km风切变对飑线的发展维持最为重要,但是0—6 km的中层风切变也有正面作用,特别是在飑线发展旺盛阶段,应该考虑其影响。

     

    Abstract: A preliminary analysis of low-level dynamical and thermo-dynamical effects on a squall line case occurred in North China on 23 July 2009 is implemented, based on 4DVar assimilation to 6 CINRAD radar observations and numerical simulation with a three-dimensional cloud model under a rapid update cycling mode. The results indicate that the squall line is under the conditions of low-level moderate shear environments and the interaction of the low-level vertical wind shear with the cold pool is the key mechanism for structure and evolution of the squall line. There is strong low level vertical wind shear but weak cold pool during the initial period of squall line development with a ratio of C, the speed of the cold pool propagation, to ΔU, the component of the low-level shear perpendicular to the squall line, less than 1 (i.e., C/ΔU1) causes the squall line to gradually dissipate. The storm line echo observed by radars distinctly broadens and tilts upshear with very low height of strong echo top during the decay period of the squall line. Both the qualitative analysis and quantitative calculation from the simulated results show the influence explanation of the low-level shear and cold pool interaction on the squall line development is accordant to the RKW theory for addressing the squall line structure, evolution, and intensity by the relative balance between the cold pool intensity and the low-level shear magnitude that advanced by Rotunno and Weisman et al. In addition, simulated results indicate low-level 0-3 km shear is most important to squall line development whereas 0-6 km shear has also positive effects on squall line evolution, especially while the squall line is at its best survival state.

     

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