基于雷达资料四维变分同化和三维云模式对一次超级单体风暴发展维持热动力机制的模拟分析

陈明轩; 王迎春; 肖现; 高峰

doi:10.3878/j.issn.1006-9895.2012.11132

基于雷达资料四维变分同化和三维云模式对一次超级单体风暴发展维持热动力机制的模拟分析

doi: 10.3878/j.issn.1006-9895.2012.11132

1.
中国气象局北京城市气象研究所,北京 100089
2.
北京市气象局,北京 100089

基金项目: 公益性行业 (气象) 科研专项项目GYHY200706004,国家科技支撑计划课题2008BAC37B03,北京市科技计划课题Z090506016609001

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出版历程
- 收稿日期: 2011-07-25
- 修回日期: 2012-03-16

A Case Simulation Analysis on Thermodynamical Mechanism of Supercell Storm Development Using 3-D Cloud Model and 4-D Variational Assimilation on Radar Data

1.
Institute of Urban Meteorology, China Meteorological Administration, Beijing 100089
2.
Beijing Meteorological Service, Beijing 100089

摘要

摘要: 利用三维云尺度数值模式和雷达资料快速更新循环四维变分同化 (4DVar) 技术,对京津冀地区一次强降水超级单体风暴发展演变的热动力机制进行了数值模拟和结果分析,并结合雷达、加密探空和自动站资料,揭示了快速变化的近风暴大气环境及风暴自身的热动力三维特征对超级单体形成、发展和演变的影响.雷达回波观测分析表明,这是一次由多单体合并加强为“右移”超级单体而后又分裂为多单体的风暴过程.在超级单体形成到发展成熟阶段,风暴前方中低层环境垂直风切变逐渐加强,为超级单体中稳定旋转上升气流和中气旋的形成创造了重要条件.模拟的风矢端图也指示出,风暴前方的低层环境风随高度存在显著的顺时针切变,有利于超级单体风暴的持续发展和右移.与风暴相伴随的冷池以及冷池出流 (阵风锋) 与低层环境风场的辐合均不断增强,风暴前沿的气流上升明显,低层暖湿空气在强的风切变作用下旋转上升进入风暴内,使得超级单体得以维持和加强.在超级单体消散分裂为多单体阶段,模拟的热动力特征均不利于其进一步发展.此时,中低层切变明显减弱,风矢端图具有明显的有利于多单体风暴发展的“直线型”特征.低层扰动温度显示冷池进一步增强并明显扩展,其扩展速度快于风暴的发展移动速度,冷池前沿伸展到风暴前面.低层风场指示冷池出流 (阵风锋) 更加强烈且存在明显的“前冲”特征,并开始“脱离”风暴前沿.风暴前方的辐合上升也明显减弱.基于模拟结果计算了与超级单体发展密切相关的风暴相对环境螺旋度 (SREH) 、风暴整体理查森数 (SBRN) 和风暴强度 (SS).结果显示,在超级单体形成和发展成熟阶段,SREH＞150 m²/s²,SBRN＜45,SS＞0.4,而在超级单体形成之前和接近消散阶段,SREH＜150 m²/s²,SBRN＞45,SS＜0.4.上述结果与前人研究结论基本一致,反映出模拟的SREH、SBRN和SS对该超级单体风暴过程具有明显指示意义.
- 雷达资料 /
- 4DVar /
- 云模式 /
- 超级单体 /
- 热动力机制
Abstract: A numerical simulation on thermodynamical mechanism of a heavy precipitation supercell development in Beijing-Tianjin-Hebei area is implemented by using a three-dimensional cloud-scale numerical model and rapid update cycling 4-D variational assimilation (4DVar) technique of radar data. The analysis on the simulation results and observations of radars, rawinsondes, and Automatic Weather Stations (AWSs) denotes the effects of frequent variational 3-D thermodynamical attribute of storm and storm-relative environment on initiation, intensification, and development of the supercell. The analysis on radar observations indicates the supercell storm with right-moving property evolves from multi-cell storms merging and splits into multi-cell storms again. The simulation results show low-and middle-layer vertical wind shears gradually intensify in the front of the storm that is favorable to form quasi-steady, strongly rotating updraft and mesocyclone in the supercell storm during the period of the supercell initiation and enhancement. The hodographs analyzed by simulated winds indicate the low-level vertical wind shear has significant clockwise-curved attribute in front of storm that is favorable to strengthening and right-moving of the supercell. The simulation also reveals that the cold pool, convergence of outflow (gust front) and low-level wind, and updraft ahead of the supercell continually strengthen along with the storm development, which results in warm and moist low-layer air ascending ahead of the storm continuously. The ascending air revolves into storm under the impact of strong vertical wind shear that maintains and strengthens the supercell storm. During the period of the supercell dissipation and split, the simulation results indicate that all of thermodynamical structures are unfavorable to further development of the supercell. The vertical wind shear weakens evidently and contributes a unidirectional (straight) hodograph that is only conformable to multicell storms. The perturbation temperature shows that the cold pool further intensifies and expands with greater speed than the storm motion during the period. The low-layer winds indicate the outflow boundary (gust front) becomes much intense and forward, and is away from the storm. The low-level convergence and updraft are also weaker during the period than those during the period of the supercell enhancement. The storm-relative environment helicity (SREH), storm bulk Richardson number (SBRN), and storm strength (SS) are calculated by using the simulated data. The results indicate SREH＜150 m²/s², SBRN＜45, and SS＞0.4 during the period of the supercell initiation and enhancement, and the reversed conclusion during the period of the supercell dissipation and split. The coincident conclusion with other investigations implies the simulated SREH, SBRN, and SS are significant to indicate development of the storm case.
- radar data /
- 4DVar /
- cloud model /
- supercell /
- thermodynamical mechanism

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