三相云显式降水方案和高原东部“96.1”暴雪成因的中尺度数值模拟

THREE-PHASE CLOUD EXPLICITY PRECIPITATION SCHEME AND MESOSCALE NUMERICAL SIMULATION FOR GENERATED CAUSE OF THE “96.1” SNOWSTORM

对“96.1”高原暴雪天气过程进行的天气学成因分析指出 ,欧洲阻高崩溃 ,里海—咸海横槽转竖 ,槽后向南入侵青藏高原的干冷偏北气流与槽前来自孟加拉湾和中印半岛向北不断推进的强劲西南暖湿气流 ,在青藏高原东北部交汇而形成、发展并持续的切变线 ,是产生高原暴雪的中尺度天气系统。 通过将冰相云微物理过程参数化和三相云显式降水方案引入MM4而发展的中尺度模式模拟系统 ,在采用常规观测资料的条件下 ,基本上成功地模拟出了“96.1”高原暴雪中尺度切变线的生成、发展和演变结构。结果表明 ,发展和改进的该中尺度模式模拟系统可用于青藏高原复杂地形和下垫面上中尺度系统发生、发展及结构演变的数值模拟研究。 模拟的流场及诸物理场时空演变揭示 :流场辐合线与暴雪切变线时空演变一致表明 ,流场对高原中尺度系统的表征有本质上的重要性 ;散度场和涡度场相互耦合是暴雪切变线发生、发展的重要动力机制 ;垂直上升运动的加强和持续是水汽凝结和冻结成雪的必要条件 ;湿对流不稳定为暴雪提供了热力不稳定条件 ;辐合带、涡度带、上升运动区和深厚湿舌的迭置是产生暴雪的强耦合结构。模拟的暴雪带和降水量与观测分析大体一致 ,表明三相云显式降水方案基本上是合理的。

The analysis of generated cause for the “96.1” snowstorm event over Qinghai Xizang Plateau was conducted using weather observational data. The results indicated that the European blocking high collapsed, the cold trough transformed from transversal into upright, the southwards invading cold and dry air flow behind the trough and the northwards intensive southwest warm wet air flow coming from the Bay of Bengal and the Indian peninsula were converged over northeastern part of Qinghai Xizang Plateau while a mesoscale shear line was formed and persistent developed. This shear line was main mesoscale weather system of producing the “96.1” snowstorm over Qinghai Xizang Plateau. A mesoscale model and simulation system was developed through incorperating an ice phase cloud microphysics process parameterization and a three phase cloud explicity precipitation scheme. The genesis and development as well as evolutive structure of a mesoscale shear line associated with the “96.1” snowstorm over Qinghai Xizang Plateau were basically successful simulated under the condition of using conventional observational data. The results showed that the developed and improved mesoscale model and simulation system is suitable for numerical simulation research of the genesis, development and structural evolution of mesoscale system over Qinghai Xizang Plateau of possessing complex topography and underlying surface. Space time evolution of simulated streamline field and physical fields revealed that the space time evolutive consistence of the convergence line of the streamline field with the shear line associated snowstorm showed the expression of the mesoscale system over Qinghai Xizang Plateau that is essential important by using streamline field possesses. An important mechanism of the genesis and development for the snowstorm shear line was that the divergence on upper levels was more intensive than convergence on lower levels and a dynamic coupling of positive vorticity zone with convergent zone. The intension and persistence of vertical ascending motion was a necessary condition of vapor condensation and snow formed by freezing. The deep, thick, wet tongue and moist convection instability supplied abundant moisture source and thermal instability condition. The superposition of the deep, thick, wet tongue and the convergent zone as well as the ascending motion was an intensive coupling structure for the formation and persistence of the snowstorm. The roughly consistence between the snowstorm zone and precipitation with that of the observational analysis showed the three phase cloud explicity precipitation scheme is basical reasonable.