Fog has recently become a frequent high-impact weather phenomenon along the coastal regions of North China. Accurate fog forecasting remains challenging due to limited understanding of the predictability and mechanism...Fog has recently become a frequent high-impact weather phenomenon along the coastal regions of North China. Accurate fog forecasting remains challenging due to limited understanding of the predictability and mechanism of fog formation associated with synoptic-scale circulation. One frequent synoptic pattern of fog formation in this area is associated with cold front passage(cold-front synoptic pattern, CFSP). This paper explored the predictability of a typical CFSP fog event from the perspective of analyzing key characteristics of synoptic-scale circulation determining fog forecasting performance and the possible mechanism. The event was ensemble forecasted with the Weather Research and Forecasting model. Two groups of ensemble members with good and bad forecasting performance were selected and composited. Results showed that the predictability of this case was largely determined by the simulated strengths of the cold-front circulation(i.e., trough and ridge and the associated surface high). The bad-performing members tended to have a weaker ridge behind a stronger trough, and associated higher pressure over land and a weaker surface high over the sea, leading to an adverse impact on strength and direction of steering flows that inhibit warm moist advection and enhance cold dry advection transported to the focus region. Associated with this cold dry advection, adverse synoptic conditions of stratification and moisture for fog formation were produced, consequently causing failure of fog forecasting in the focus region. This study highlights the importance of accurate synoptic-scale information for improved CFSP fog forecasting, and enhances understanding of fog predictability from perspective of synoptic-scale circulation.展开更多
山区特殊地形下的强降水形成机理复杂、预报难度大,且此类强降水常导致严重的地质灾害。为提升特殊地形下强降水的预报能力,利用常规气象观测资料、欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)ERA...山区特殊地形下的强降水形成机理复杂、预报难度大,且此类强降水常导致严重的地质灾害。为提升特殊地形下强降水的预报能力,利用常规气象观测资料、欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)ERA5再分析资料、FY-4A卫星云图资料、多普勒雷达资料及多模式预报产品,对2022年6月3日夜间至4日清晨发生在陕南汉江盆地的局地短时强降水过程形成原因及模式预报性能进行检验分析。结果表明:(1)本次过程为一次锋面在盆地触发的短时强降水过程,由于对流不稳定层结浅薄、垂直风切变较弱,因此造成的强降水具有明显的局地性,但强度较大,12 h累计降水量多站超过50.0 mm,最大104.8 mm;(2)锋面两端受地形阻挡移动速度较慢并难以翻越高大山脉,因而不断在盆地内触发对流产生强降水,且在盆地近地层形成的次级环流可加强对流活动发展;(3)锋面前部形成的冷池在盆地不断触发新的对流单体后向传播形成列车效应,同时大于50 dBZ的强回波位于0℃层高度以下,具有较高的降水效率,且持续时间较长,因而带来最大62.6 mm·h^(-1)的短时强降水;(4)全球模式对此次短时强降水的预报能力有限,中尺度区域模式能够反映锋面对流的一些特征和降水,尤其是CMA-TRAM(Tropical Regional Atmosphere Model for the South China Sea)和CMA-GD(China Meteorological Administration-Guangdong)模式能较好地反映局地强对流的触发及发展趋势,但对锋前冷池造成的对流系统强度和组织性仍预报偏差较大。展开更多
基金supported by the National Key R&D Program of China (Nos. 2017YFC1404100 and 2017YFC1404104)the National Natural Science Foundation of China (Nos. 41705081 and 41575067)the Global Change Research Program of China (No. 2015CB953904)
文摘Fog has recently become a frequent high-impact weather phenomenon along the coastal regions of North China. Accurate fog forecasting remains challenging due to limited understanding of the predictability and mechanism of fog formation associated with synoptic-scale circulation. One frequent synoptic pattern of fog formation in this area is associated with cold front passage(cold-front synoptic pattern, CFSP). This paper explored the predictability of a typical CFSP fog event from the perspective of analyzing key characteristics of synoptic-scale circulation determining fog forecasting performance and the possible mechanism. The event was ensemble forecasted with the Weather Research and Forecasting model. Two groups of ensemble members with good and bad forecasting performance were selected and composited. Results showed that the predictability of this case was largely determined by the simulated strengths of the cold-front circulation(i.e., trough and ridge and the associated surface high). The bad-performing members tended to have a weaker ridge behind a stronger trough, and associated higher pressure over land and a weaker surface high over the sea, leading to an adverse impact on strength and direction of steering flows that inhibit warm moist advection and enhance cold dry advection transported to the focus region. Associated with this cold dry advection, adverse synoptic conditions of stratification and moisture for fog formation were produced, consequently causing failure of fog forecasting in the focus region. This study highlights the importance of accurate synoptic-scale information for improved CFSP fog forecasting, and enhances understanding of fog predictability from perspective of synoptic-scale circulation.
文摘山区特殊地形下的强降水形成机理复杂、预报难度大,且此类强降水常导致严重的地质灾害。为提升特殊地形下强降水的预报能力,利用常规气象观测资料、欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)ERA5再分析资料、FY-4A卫星云图资料、多普勒雷达资料及多模式预报产品,对2022年6月3日夜间至4日清晨发生在陕南汉江盆地的局地短时强降水过程形成原因及模式预报性能进行检验分析。结果表明:(1)本次过程为一次锋面在盆地触发的短时强降水过程,由于对流不稳定层结浅薄、垂直风切变较弱,因此造成的强降水具有明显的局地性,但强度较大,12 h累计降水量多站超过50.0 mm,最大104.8 mm;(2)锋面两端受地形阻挡移动速度较慢并难以翻越高大山脉,因而不断在盆地内触发对流产生强降水,且在盆地近地层形成的次级环流可加强对流活动发展;(3)锋面前部形成的冷池在盆地不断触发新的对流单体后向传播形成列车效应,同时大于50 dBZ的强回波位于0℃层高度以下,具有较高的降水效率,且持续时间较长,因而带来最大62.6 mm·h^(-1)的短时强降水;(4)全球模式对此次短时强降水的预报能力有限,中尺度区域模式能够反映锋面对流的一些特征和降水,尤其是CMA-TRAM(Tropical Regional Atmosphere Model for the South China Sea)和CMA-GD(China Meteorological Administration-Guangdong)模式能较好地反映局地强对流的触发及发展趋势,但对锋前冷池造成的对流系统强度和组织性仍预报偏差较大。
