基于降水目标的主雨带识别及预报误差空间检验

Identification and spatial verification of the forecasting bias of the main rain belts based on precipitation objectives

利用2014-2018年4-6月福建省及周边地区实测降水量和ECMWF模式降水量预报产品资料,采用目标识别方法,设定降水量阈值α,选取合适的特征尺度D0和邻近度阈值β,分别识别实况降水场的主雨带和预报降水场的所有雨带,并选取匹配度阈值进行目标配对,确定与实况降水场主雨带最匹配的预报降水场主雨带。改进SAL空间检验方法,将模式主雨带预报误差用主雨带的强度(指降水极值和降水量阈值)、位置(指重心点位置)、形态(指主轴、次轴特征长度和轴向角度)属性的预报误差来表示。结果表明:预报主雨带的降水极值比实况小,但降水量阈值比实况大;预报主雨带的重心点位置与实况相比,4月偏西、偏南,5月、6月偏西、偏北,预报主雨带的重心位置多是滞后于实况,位于实况主雨带的上游;主雨带大都呈窄长带状分布,预报主雨带比实况更窄长,且预报时效越长越窄长。预报主雨带轴向角度比实况略小,总体均呈东偏北走向。以上分析结果可为模式主雨带预报误差的订正提供依据。

Based on precipitation data from observations and predictions from the ECMWF(European Centre for Medium-Range Weather Forecasts)model in Fujian and surrounding areas from April to June in 2014-2018,the main rain belts from the observations and all of the rain belts from predictions were determined using an object identification method,in which a rainfall threshold,an appropriate characteristic spatial scale,and a close degree were set.Through pairing objects with the observations,the threshold of matching degree was selected to determine the predicted main rain belts.The SAL(Structure,Amplitude,and Location)spatial verification method was improved and accounted for the biases associated with the intensity,position,and morphology of the predicting main rain belts.The results show that,compared with the observations,the maximum amount in precipitation for the main rain belts prediction by the model is smaller,but the threshold one is larger.The position of main rain belts lies more westward and southward in April,but more westward and northward in May and June.The position of the main rain belts predictions by the model lags behind the observations and tends to be located in the upstream of the moving direction of the observations.The main rain belts have a stripe shape.The morphology of the predicted main rain belts is narrower and longer,and this tendency intensifies with the forecast lead time.The predicted axial angle of main rain belts is slightly smaller and tends to oriented north-eastwards.This work provides guidance for the bias correction of the main rain belts forecasting by the model.