Abstract: In order to explore the impact of urban canopy effect on forecast of surface meteorological element, the optimized urban single model was coupled into the rapid-refresh multi-scale analysis and prediction system-short term (RMAPS-ST). For this purpose, two contrast experiments were set, they were the coupling urban single model or uncoupling urban single model into the RMAPS-ST denoted as UCM and NOUCM, respectively. In addition, the short-term forecast effects of surface meteorological elements (2 m temperature, 10 m wind speed and 2 m specific humidity) in North China were evaluated in mid-January and mid-July 2017. The results show that UCM test could significantly improve the forecast performance of the RMAPS-ST to surface meteorological elements. Compared with NOUCM test, the prediction of surface meteorological elements in UCM test was closer to the observation in cities of North China. Considering canopy effect could effectively reduce forecast bias of 2 m temperature in most urban stations of North China, and the accuracy of 24-hour temperature forecast improved by 42% and 15% in mid-January and mid-July, respectively. The urban canopy effect could increase friction coefficients, which decreased low-level wind speed significantly and improved the prediction ability of 10 m wind speed, and the forecast accuracy improved by 40% and above. For specific humidity at 2 meters height, the impact of canopy effect on the forecast of specific humidity wasn’t significant. Compared with the observation, the forecasted specific humidity at 2 meters height by two tests was dryer in all day in mid-July, and the canopy effect could significantly improve dryer state in urban areas, the forecast accuracy increased by 17%.

Key words: urban canopy model, numerical simulation, forecast performance comparison, surface meteorological elements

摘要： 将优化冠层参数的城市冠层模式耦合到快速更新循环系统RMAPS-ST中，探究城市冠层效应对地面气象要素预报的影响。设计耦合城市冠层模式（UCM）和未耦合城市冠层模式（NOUCM）两组对比试验，对华北区域2017年1月中旬和7月中旬的地面气象要素（2 m气温、10 m风速和2 m比湿）进行短期预报评估。结果表明：与NOUCM试验相比，UCM试验能够显著提高RMAPS-ST系统对地面气象要素的预报性能，使华北区域城市地面气象要素的预报更接近于观测。考虑冠层效应能够有效减小华北城市站点的2 m气温预报偏差，1月中旬和7月中旬24 h气温预报准确率分别提高42%和15%。冠层效应的引入增加了城市摩擦系数，改善了10 m风速预报偏差明显偏大现象，预报准确率均提高40%以上。对于2 m比湿，两组试验1月中旬的预报偏差均较小，冠层的引入对预报结果无显著影响；两组试验对7月中旬的比湿预报全天偏干，冠层效应能显著改善城区比湿偏干的情况，预报准确率提高17%。

关键词: 城市冠层模式, 数值模拟, 预报性能比较, 地面气象要素