摘要
为了研究北京快速更新循环同化预报系统(BJ-RUCv2.0)在北京地区降水日变化的预报偏差特征及其成因,利用2012—2015年夏季BJ-RUCv2.0系统第2重区域(3 km分辨率)预报结果和北京地区122个自动气象站逐时观测数据以及观象台探空观测资料,分析模式对北京地区降水日变化预报偏差的区域性特征和传播特征,研究模式局地环流预报偏差特征及其对降水预报偏差的可能反馈机制。研究结果表明,BJ-RUCv2.0系统多个更新循环的预报在北京平原地区均存在夜间降水漏报问题,降水预报偏差表现为模式预报降水在西部山区降水偏多,预报降水雨带难以在平原地区增强发展,造成了模式降水在傍晚山区偏多而夜间平原地区降水明显偏少。通过分析模式局地环流预报偏差及其响应机制发现,由于白天平原地区近地层偏暖偏干,山区底层偏冷中层偏湿,造成了山区-平原地区间的温度梯度强度偏强且强温差出现时间提前,西部山区午后降水偏多;由于平原地区地面气温预报持续偏高,入夜后偏北风难以到达平原地区,造成了山区-平原间的地形辐合线位置偏北,影响山区降水雨带向平原地区移动,同时平原地区近地层内水汽持续偏低,抑制降水雨带在东移过程中的发展,造成模式在平原地区夜间降水预报容易出现漏报。模式冷启动所用的GFS资料土壤湿度在北京平原地区明显小于实际观测,是模式预报偏暖偏干的可能原因之一。
In order to investigate the characteristic bias in diurnal precipitation variation forecast and the possible reasons in the Rapid Update Cycle Forecast System （BJ-RUCv2.0） in Beijing area, auto-weather station and radiosonde observations were used to evaluate the 3 km resolution forecast of BJ RUCv2.0 over Beijing region during June to August in 2012 and 2015. Re- gional features and propagation characteristics of the bias in diurnal precipitation variation forecast were studied, and the re- sponsive mechanism of bias in local circulation forecast was revealed. Research results show that nighttime precipitation was missing in most cycles of precipitation forecast of BJ-RUCv2.0 in the plain area of Beijing. Specifically, rainfall in the model forecast in western mountainous area was overestimated; it was difficult for precipitation to develop in the plain area in BJ- RUCv2.0 ; precipitation forecasted by the model was too much in mountainous area in the evening but too low in plain area at midnight. The local circulation forecast bias and its responsive mechanism demonstrated that an intense temperature gradient between mountainous and plain area occurred earlier than normal due to the warm and dry forecast bias during the daytime near the surface layer in plain area and moist bias in the middle level in mountainous area, which caused more precipitation in the western mountainous area. The warm bias strengthened after sunset and northerly winds prevailed over plain area, which resul- ted in a northward shift of the topographic convergence between mountainous and plain area and subsequently affected the mov- ing of rain belt from mountain to plain area. There existed a continuous dry bias in plain area, which prohibited the develop- ment of rainfall in plain area and caused the missing forecast of precipitation. Soil moisture of GFS, which was used to provide initial condition for cold start of BJ-RUCv2.0, is noticeably drier than observations, which might contribute to the warm and dry bias in the surface layer.
出处
《气象学报》
CAS
CSCD
北大核心
2017年第2期248-259,共12页
Acta Meteorologica Sinica
基金
公益性行业(气象)科研专项经费项目(GYHY201406012
GYHY201506004)
北京市自然科学基金(8172020)
北京市科技计划项目(Z161100001116098)
关键词
降水日变化
局地环流
温度梯度
地形辐合线
土壤湿度
Diurnal variation of precipitation, Local circulation, Temperature gradient, Topographic convergence, Soil mois-ture
