西南区域中心模式SWC-WARMS降水偏差分析

本文利用2014—2015年5—10月12(24)h累积降水资料和西南区域模式(SouthWest Center WRF ADAS Real-time Modeling System,SWC-WARMS)36(72 h)预报时效内降水预报资料,从概率和频次角度分析不同海拔高度地区观测和模式降水在量级及空间分布上的特征差异。结果表明,SWC-WARMS模式各预报时效各量级降水的概率密度均比观测偏大,并向10 mm以下雨量集中,且随预报时效延长偏大更显著;模式与观测降水的概率密度曲线差异在盆地小于高原,地形差异小的区域小于地形差异大的区域。SWC-WARMS模式对四川地区降水预报存在雨日较观测明显偏多,量级偏大,降水频次高值区范围偏大、出现虚假高值区等系统性偏差。此外,模式预报在20—08时比08—20时优,24 h累积降水预报优于12 h降水预报,尤以中雨及以上量级降水落区预报为甚。最后,模式极端强降水预报在20—08、20—20时较实况偏大,08—20时,模式预报在盆地较实况偏小,川西高原和攀西地区偏大。

Deviation analysis of precipitation forecast by SWC-WARMS model

In this paper, using the 12(24 h) cumulative precipitation data from May to October during 2014-2015 and the SWC-WARMS forecast precipitation data within 36(72 h), the characteristic differences in precipitation intensity and spatial distribution between the observed and model precipitations in different altitude areas from the perspective of probability and frequency were analyzed. The results show that the probability density of forecast precipitation by the SWC-WARMS model is higher than that of observations in any forecast time, and the precipitation is concentrated below 10 mm. What''s more, with the extension of forecast time, the wet deviation of model predicts is more significant. The difference of probability density curve in basin is smaller than that in plateau, and the difference of probability density curve in the area with small terrain difference is less than that in the area with large terrain difference. The precipitation forecast by SWC-WARMS model has many deviations, including more rainy days, higher precipitation intensity, large area with high precipitation frequency, and false high value areas. In addition, the SWC-WARMS model forecast at night (20-08) is better than daytime (08-20), and the 24 h cumulative precipitation forecast is superior to the 12 h cumulative precipitation forecast, especially in the forecast of precipitation areas with the moderate rain and above. At last, the extreme heavy precipitation forecasted by the model in the 20-08 period and 20-20 period is heavier than the actual precipitation. In terms of regions, the model predications are lower than the actual situation in basin, but higher in the Western Sichuan Plateau and the Panzhihua-Xichang region.