Based on the tropical cyclone data from the Central Meteorological Observatory of China,Japan Meteorological Agency,Joint Typhoon Warning Center and European Centre for Medium-Range Weather Forecasts(ECMWF)during the period of 2004 to 2009,three consensus methods are used in tropical cyclone(TC)track forecasts.Operational consensus results show that the objective forecasts of ECMWF help to improve consensus skill by 2%,3%-5%and 3%-5%,decrease track bias by 2.5 km,6-9 km and10-12 km for the 24 h,48 h and 72 h forecasts respectively over the years of 2007 to 2009.Analysis also indicates that consensus forecasts hold positive skills relative to each member.The multivariate regression composite is a method that shows relatively low skill,while the methods of arithmetic averaging and composite(in which the weighting coefficient is the reciprocal square of mean error of members)have almost comparable skills among members.Consensus forecast for a lead time of 96 h has negative skill relative to the ECMWF objective forecast.
针对2014年夏末长江中下游地区长时间阴雨寡照天气的成因,利用全国站点观测资料和NCEP再分析资料分析得出:主要由于南亚高压、西太平洋副热带高压和东亚季风等大尺度环流异常所致。200 h Pa南亚高压中心与常年相比位置偏东南,形成有利于该区域降水的动力条件。500 h Pa北半球极涡强度偏强,导致影响中国的冷空气势力也明显偏强。西太平洋副热带高压比常年偏强、偏南、偏西,850 h Pa副高环流明显偏强。8月下半月欧亚中纬度环流形势可分为2个时段:时段1(16—20日)500 h Pa呈现两脊两槽分布,环流经向度明显强于常年,东端的低槽给中国中东部地区带来较强的冷空气。850 h Pa华南的偏西气流偏强,与副高气流共同增强了东海的西南风低空急流。时段2(21—31日)500 h Pa环流变成一脊一槽型,经向度减弱,造成小股冷空气不断到达长江中下游地区。两时段中纬度地区均存在θse锋区、锋生、锋前的垂直上升运动、中低层水汽辐合和由地面往上的湿舌。时段1各物理量表现更清楚,与天气表现相一致。
