天气预报的理论基础--准地转理论概要及其业务应用
Theoretical Basis of Weather Forecasting:Quasi-Geostrophic Theory Summary and Operational Applications
中文摘要：
准地转理论（quasi-geostrophic theory），是预报员建立清晰的预报思路所必须掌握的动力学基础。从垂直运动和天气系统发展的诊断这两个天气预报的根本问题出发，介绍了准地转理论的来源，指出它是近代大气动力学的正压大气长波理论向现代大气动力学的多层斜压大气数值模式发展的历史必然。准地转方程组的推演过程说明，准地转理论是基于严密数学推导和物理洞察力的、建立在物理学三大定律（动量、能量、质量守恒）之上的完整的大气动力学理论体系，因此是大气动力学的核心。ω方程和位势倾向方程的强迫项表明，温度平流和涡度平流是最基本的预报因子，它们导致地转平衡的破坏，同时又通过所伴随的次级环流使地转平衡得到不断地恢复（即地转适应过程），从而使大尺度环流在缓慢的变化中始终保持准水平和准地转平衡状态。准地转理论还揭示了温度平流是使后倾斜压扰动发展的根本原因，而涡度平流所伴随的垂直环流则导致了大尺度环流系统热力结构的变化。最后给出了一些在常规天气图上可以直接使用的定性规则作为准地转理论在实际预报中应用的参考。
中文关键词：
准地转动力学，大尺度环流系统，斜压发展，次级环流，地转适应
KeyWords：
quasi-geostrophic dynamics,large-scale circulation systems,baroclinic development,secondary circulation,geostrophic adjustment
Abstract：
The quasi-geostrophic (QG) theory is the dynamic basis that forecasters must master to establish a clear idea of weather forecasting. In this paper, from the two fundamental issues of weather forecasting that are the diagnosis of vertical movement and the development of weather systems, the origin of the QG theory is introduced. It is pointed out that it is a historical inevitability of the modern atmospheric dynamics developing from the atmospheric long-wave theory to the multi-level baroclinic atmospheric numerical model. The inference of the QG equations shows that the QG theory is a complete theoretical system of atmospheric dynamics, based on rigorous mathematical derivation and physical insight and built on top of the three laws of physics (conservations of momentum, energy, and mass), so it is the core of the atmospheric dynamics. The forced terms of omega equation and the geopotential tendency equation show that temperature advection and vorticity advection are the most basic predictors, which lead to the destruction of geostrophic balance, and make geostrophic equilbrium restored (ie, geostrophic adjustment process) through the associated secondary circulation, so that large-scale circulation in the slow-changing always maintains the quasi-level and quasi-geostrophic equilibrium. The QG theory also revealed that the temperature advection is the basic reason for the development of backward tilted baroclinic disturbance, yet the vertical circulation associated with the vorticity advection has led to changes in the thermal structure of large-scale circulation systems. Finally, some qualitative rules in conventional weather maps can be used directly as a QG theory application in the operational weather forecasting.