南大4 km预报系统对新疆夏季降水预报的评估

南大4 km预报系统(WRF_NJU)是南京大学自2013年起每年夏季每日两次对中国地区进行的4 km分辨率的48 h实时预报。将该系统、欧洲中期天气预报中心(EC)、中国气象局(CMA)和日本气象厅(JMA)在2016—2018年夏季6—8月对新疆北疆和南疆地区降水的预报与自动站观测资料进行对比分析。结果表明:Gilbert技巧评分(GSS)一般EC最高,WRF_NJU次之,JMA最低。空间上,EC在南、北疆的预报都最接近观测,WRF_NJU预报降水平均偏低,CMA和JMA明显偏高。WRF_NJU预报降水的日变化趋势与观测一致,峰值时段基本相同,稍有1~2 h偏差。量级上总体偏高,在峰值时段尤为明显。降水过程发展方面,WRF_NJU对大多数降水过程模拟效果较好。通过个例分析,发现高空急流和低层水汽输送的预报效果直接影响着降水的预报效果。

Evaluation of precipitation forecasts from NJU 4 km forecasting system in Xinjiang during summer

The NJU 4 km forecasting system (WRF_NJU) produce 48 h real-time forecasts at a 4 km grid spacing over China twice daily for the summer seasons at Nanjing University since 2013. The precipitation forecast from June to August in the summer of 2016-2018 in North and South Xinjiang from this model, the European Center for medium range weather forecast (EC), China Meteorological Administration (CMA) and Japan Meteorological Agency (JMA)were compared with the observational data of automatic weather stations. Results show that: generally, Gilbert Skill Score (GSS) of EC is the highest, WRF_NJU is second and JMA is the lowest. In terms of spatial distribution, the forecast in North and South Xinjiang from EC is the closest to observation, and the average precipitation forecast from WRF_NJU is lower, while CMA and JMA are obviously higher. The diurnal variations of precipitation forecast from WRF_NJU is consistent with the observed variations. The peak period is basically consistent, with a slight deviation of 1-2 hours. Forecast is generally higher than observation, especially in peak period. In the aspect of precipitation episodes and propagation, WRF_NJU can simulate most precipitation processes well. After studying selected cases, it is found that the precipitation forecast is directly affected by the forecast of upper-level jet stream and lower-level water vapor transport.