Energy-Casimir方法在中尺度扰动稳定性研究中的应用  

Application of Energy-Casimir method to the study of mesoscale disturbance stability

作　　者：冉令坤[1] 楚艳丽[2] 高守亭[1] 

机构地区：[1]中国科学院大气物理研究所,北京100029 [2]北京城市气象研究所,北京100089

出　　处：《气象学报》2009年第4期530-539,共10页Acta Meteorologica Sinica

基　　金：国家自然科学基金面上项目(40405011和40875032);国家自然科学基金重点项目(2004CB418301)

摘　　要：考虑湿空气中的水汽效应,引进Casimir函数(它是虚位温的单值函数),在x方向动量方程和总能量方程的基础上,采用Energy-Casimir方法建立了三维非地转平衡和非静力平衡的拟能量波作用方程,由于该方程建立在非地转平衡和非静力平衡的动力框架下,因此可用于讨论层结稳定大气内中尺度扰动系统的发展演变。理论分析表明,拟能量波作用方程具有非守恒形式,其中的拟能量波作用密度主要由扰动动能、有效位能和浮力能三部分组成;拟能量波作用密度局地变化除了受拟能量波作用通量散度影响之外,纬向基本气流切变、科氏力作功以及由非绝热加热和水汽相变所构成的波作用源汇项对其也都有贡献。诊断分析结果表明,对流层中低层的拟能量波作用密度与观测的6 h累积地面降水在水平空间分布和时间演变趋势上比较接近,说明拟能量波作用密度能够较好地抓住强降水区上空对流层中低层动力场和热力场的扰动特征,并在一定程度上可以有效地表征降水系统的发展演变,因而与地面降水量存在紧密联系。波作用方程各项的计算分析表明,波作用通量散度与拟能量波作用密度局地变化的倾向以及强降水区的变化比较一致,并且在强度上强于纬向基本气流切变项和科氏力作功项,因此波作用通量散度对拟能量波作用密度的局地变化具有重要贡献。Taking into account the effect of moisture, we derive a three-dimensional pseudoenergy wave-activity relation for moist atmosphere from the primitive zonal momentum and total energy equations in Cartesian coordinates by using Energy-Casimir method. In the derivation, a Casimir function is introduced which is a single-value function of virtual potential temperature. Since the pseudoenergy wave-activity relation is constructed in the ageostrophic and nonhydrostatic dynamical framework, it may be applicable to diagnosing the stability of mesoscale disturbance systems in a steady-stratification atmosphere. The theoretical analysis shows that the wave-activity relation presented a nonconservative form in which the pseudoenergy wave-activity density is composed of disturbance kinetic energy, available potential energy and buoyant energy. The local change of pseudoenergy wave-activity density depends on the combination of shear of zonal basic flow, Coriolis force work and wave-activity source or sink as well as wave-activity flux divergence. The diagnosis shows that horizontal distribution and temporal trend of pseudoenergy wave-activity density are similar to that of the observation of 6-hour accumulated surface rainfall, which indicates that the pseudoenergy wave-activity density in the middle and low levels is capable of representing the dynamical and thermodynamic typical vertical feature of precipitable mesoscale systems so that the pseudoenergy wave-activity density is closely related to the observed surface rainfall. The calculation of the terms in wave-activity relation reveals that the wave-activity flux divergence shares a similar temporal trend with the locale change of pseudoenergy wave-activity density and the observed surface rainfall. Although the terms associated with the shear of zonal basic flow and the Coriolis force make contribution to the local change of pseudoenergy wave-activity density, the contribution coming from wave-activity flux divergence is much more noticeable.

关 键 词：拟能量波作用密度 波作用通量 层结稳定 不稳定 

分 类 号：P456.7[天文地球—大气科学及气象学] P458.1