Three Revolutions in Weather Forecasting

回顾过去100多年，天气预报经历了两次跃进：第一次是地面和高空天气图的绘制和应用（空间上的跃进），第二次是数值预报的实施（时间上的跃进）。经过这两次跃进，天气预报已经走过了从经验和定性描述到今天定量计算的一门数理学科。洛伦兹发现大气混沌现象后，天气预报正在经历从单一确定论到多值概率论的第三次跃进（观念上的革命），并试图通过量化或简化不确定因素来提高天气的可预报性和降低预报的不确定性。重点介绍两种现行的量化或简化不确定因素的做法：一是直接面对问题（量化），即用集合预报的方法，定量描述预报的不确定性，使之成为预报的一部分，让用户在决策时科学地应用更全面的预报信息；二是绕开数学上的难题（简化），把大气变量分解为瞬变气候与瞬变扰动两个部分，用瞬变扰动建立与异常天气之间的联系。The scientiifc evolution of weather forecasts is brielfy reviewed from a historical perspective in this paper. During the last 100 years, applications of weather maps (surface and upper air) and numerical weather prediction (NWP) to daily weather forecasts marked two major achievements:weather maps expanded our view from two dimensions to three dimensions in space and NWP brought us ahead of real weather in time. Through these advancements, weather forecasting has gradually evolved from an empirical to a qualitatively-reasoning and further to an exact physical science based on mathematical equations. With the discovery of chaos by Prof. Edward Lorenz, weather forecasting is now undergoing its third philosophical revolution from a deterministic to probabilistic world to facing the reality of its limited predictability. Two different approaches are presented, as the main focus of this paper, to deal with the limitation of predictability and forecast uncertainty: one is using ensemble forecasting technique to directly quantify and include forecast uncertainty information in a forecast which can be utilized by end-users to make better decisions;the other is an attempt to have a workaround of nonlinearity mathematically by decomposing a meteorological ifeld into climatic and anomalous two components. Therefore, weather forecasting could be possibly simpliifed in dealing with the anomalous components only.0613-2