热带气旋路径预报概率圆应用

Application of Probability Circle Radius in Forecasting Tropical Cyclones

热带气旋路径预报采用预报概率圆可以有效减少不可避免的预报错误,在2004～2007年中央气象台主观路径预报资料的基础上,使用统计方法并根据预报误差与热带气旋预报移动速度和移动方向的相关关系分类,分别计算了相应的24、48、72 h路径预报的70%概率圆半径,修改了原来业务中使用的概率圆半径,以期替代原来在业务中使用的概率圆半径。同时应用修改后的概率圆半径对近5年的路径主观预报进行了分析,给出了2004～2007年预报误差分布特点以及较大预报误差热带气旋个例的误差产生原因,并讨论了该方法改进的可能性。

A cone is used to represent the probable track of the center of a tropical cyclone,which is formed by enclosing the area swept out by a set of circles along the forecast track（at 24,48 hours,etc）.The size of each circle is set so that the entire track of the tropical cyclone can be expected to remain within the cone roughly 60% to 70% of the time.Based on forecasts over the previous 4 years（from 2004 to 2007）,the relationship between tropical cyclone track forecast error and their forecast movement speed and direction is used in classification,and the probability circle radiuses are calculated by means of the statistical method as for the forecast valid time of 24,48,72 hours,respectively.The old data used operationally since 2007 are replaced with the new results calculated for the western North Pacific basin in order to reduce the forecast uncertainty.Meantime,the subjective forecasts in the recent five years are analyzed in terms of the modified probability circle radius.The characteristics of forecast errors and the causes of great errors in some tropical cyclone forecasting cases are also given from 2004 to 2007.Possibility of improving the calculation method of radius is also discussed.