基于雷达外推和中尺度数值模式的定量降水预报的对比分析

Comparisons of One Hour Precipitation Forecast Between the Radar Extrapolation and the Mesoscale Numerical Model

应用广东2010年出现的4次暴雨过程的气象资料,检验分析了临近预报系统(SWAN)和华南中尺度数值模式(GZMM)中的定量降水产品对晴雨及不同类型降水的预报效果,在此基础上探讨了临近预报系统和数值模式在0～6 h范围内的预报能力的交叉点。结果表明:首先,对于晴雨预报,SWAN系统中降水产品随着预报时效的增加预报效果呈现出减弱的趋势,且高分辨(0.02°)产品的下降速度要快于低分辨率(0.12°);GZMM降水产品(0.12°)在1～3 h预报能力逐步提升,在4～6 h维持相对稳定的水平。对于分辨率同为0.12°的SWAN系统和GZMM模式产品,在第1和第2 h,SWAN产品的CSI评分分别为0.504和0.442,高于GZMM的0.306和0.375,但从第3小时开始GZMM产品CSI评分略高于SWAN产品,表明此后华南中尺度数值模式对晴雨的预报能力优于SWAN系统,交叉点介于2～3 h。其次,进一步检验了上述产品对弱降水(1小时雨量为0.1～2 mm)、一般性降水(2～10 mm)和较强降水(超过10 mm)的预报能力。对于弱降水,GZMM产品CSI评分在0～6 h维持在0.23,高于SWAN产品,表明GZMM模式对于弱降水的预报能力在整体上要强于SWAN系统。对于一般性降水,在0～3 h,分辨率为0.12°的SWAN产品CSI评分高于GZMM产品;两者的CSI评分曲线的交叉点介于3～4 h,即从第4小时开始,GZMM降水产品预报效果更好。对于较强降水,无论是SWAN系统还是GZMM模式,预报能力都呈现出明显的减弱;但SWAN系统在整体上对强降水的预报能力要优于GZMM模式。

Verification results of different precipitation forecast products in the SWAN system and the GZMM model for 4 heavy rain cases in 2010 are discussed.The cross-over point of CSI curves in forecast lead time where the model would perform better than the nowcast,is analyzed in particular.Firstly,the radar nowcast for 1-hour precipitation forecast exceeding 0.1 mm starts with higher scores than the model, but the skill of the nowcast drops as the forecast lead time increases.The GZMM model performs at a fairly steady level over 3—6 hour period with lower scores at 1 and 2 hours.The CSI scores of 1-hour QPF with 0.12°resolution in the SWAN at 1 and 2 hours are 0.504 and 0.442,respectively.At t=3 h,the two CSI curves cross,indicating the skill of the radar extrapolation has decreased to the same level as the model forecast.Secondly,the performance of 1-hour precipitation forecast with 3 graded levels is documented. For the 0.1-2 mm rainfall,the CSI score of the model is about 0.23 over the 6-hour period,and the GZMM model performs better than the SWAN.For rainfall between 2 and 10 mm,the SWAN product with 0.12°resolution performs better than the GZMM model over 0—3 hour period.At t=4 h,the skill of the radar extrapolation has decreased to the same level as the model forecast.For rainfall over 10mm, both the SWAN and the GZMM perform not very good.But the skill of the radar nowcast is higher than that of the GZMM model over the 6-hour period.