摘要
利用高空、地面观测资料和NCEP 0.5°×0.5°分辨率的CFSR资料,对华东地区冷锋后和静止锋前两个高架对流个例的天气类型、环境背景、生成与发展机理进行分析,并对比异同点。分析结果表明:安徽、江苏冷锋后高架对流最大可能的机制是动力抬升触发对流不稳定后产生的,浙江舟山的对流很有可能是在条件稳定性近于中性情况下,由锋生过程强迫的锋面垂直环流产生。浙北静止锋前高架对流可能是在条件对称不稳定条件下,850 hPa急流风速辐合和暖平流的共同作用的结果,850~700 hPa地转绝对动量调整触发条件对称不稳定是其增强机制。共同特点是雷暴都发生在850 hPa等温线密集的锋区,850 hPa都有很强的西南急流,有逆温和强的垂直风切变。不同点在于冷锋后型逆温由西南暖湿气流和冷锋共同形成,逆温幅度更大,为10~15℃,而静止锋前型只有6~7℃;850 hPa西南急流风速更大,为25 m·s^-1以上,静止锋前型为20 m·s^-1;静止锋前型0~6 km高度垂直风切变达40 m·s^-1,冷锋型只有30 m·s^-1。冷锋后型850 hPa受明显切变线影响,静止锋前型只有风速的切变。用雷达产品对高架对流系统的结构分析结果表明:1)冷锋后型回波范围大,比较连续,最强中心55 dBZ,850 hPa切变线位置引导整体回波移动。2)静止锋前型回波比较分散,呈多条平行窄带状,单体的生成比较随机,但移动比较规律,随环境气流平移,没有传播现象。单体最强中心60 dBZ,生命史达2 h左右,有小尺度气旋性辐合、中层径向辐合、低层辐散等强对流特征。单体倾斜度比地面对流单体的大,上升气流和下沉气流距离比较远。当气旋性辐合强度减弱,低层辐散区逐渐远离主体回波时,单体将减弱,可作为临近预报的线索。短期预报关注重点是850 hPa西南暖湿气流的强度(20~30 m·s^-1),风向、风速的分布,锋区位置,暖平流强度(3×10-4~5×10-4℃/s),θse的垂直分布及风随高度的变化(风向随高度顺转角度大于180°,0~6 km高度垂直风切变达30~40 m·s^-1)等。
Based on high and surface observation data and NCEP 0.5°×0.5°CFSR data,two elevated convection processes occurring after the cold front and before the stationary front in Eastern China were analyzed.The weather types,environmental background,genesis and development mechanisms were analyzed,while the similarities and differences were revealed.The results showed that the most possible mechanism for case occurred in Anhui and Jiangsu provinces was that the convective instability triggered by dynamic lifting caused convection.The convection in Zhoushan,Zhejiang,was more likely generated in the neutral stability,from vertical circulation forced by frontogenesis.The case occurred in the north part of Zhejiang province was formed in conditional symmetric instability before the surface stationary front.This elevated convection was triggered by wind speed convergence and warm advection at 850 hPa level.Moreover,its enhancement mechanism was conditional symmetric instability caused by geostrophic absolute momentum at 850-700 hPa level.The common features of the two cases were the thunderstorm occurred in frontal zone where isotherms were dense at 850 hPa,and there were strong southwesterly flow,temperature inversion,and strong vertical wind shear at 850 hPa.The differences were as follows.In the convection after cold front,the temperature inversion was caused by southwesterly warm and wet flow,was 10-15℃,before stationary front,it was 6-7℃.In cold front,the wind speed of southwesterly flow at 850 hPa was greater,which was over 25 m·s^-1,while it was 20 m·s^-1 before stationary front.The 0-6 km vertical wind shear was 40 m·s^-1 before stationary front,while it was 30 m·s^-1 in cold front.The convection after cold front was significantly affected by shear line at 850 hPa,while there was only wind speed shear before stationary front.The structure characteristics of two elevated convection processes were investigated using radar data,and the results were as follows.1)The elevated convection occurred after the cold front had continuous radar echoes with large range and the maximum reflectivity around 55 dBZ.The movement of strong centers was guided by shear line at 850 hPa.2)The elevated convection occurred before stationary front had scattered radar echoes with a number of parallel narrow band.The movement of echoes was guided by environment air regularly,while they generated randomly.The convective cells,with the maximum reflectivity around 60 dBZ,lasted for 2 hours,with the strong convective characteristics as small scale cyclone convergence,middle layer radial convergence,low-level divergence and so on.However,the gradient was larger than convection cell on ground,the distance between updraft and downdraft was longer.When the intensity of cyclonic convergence weakened and the low-level divergence zone kept away from main echo,the cell would recede,which could provide a clue for short-term forecast.The emphases on short-term forecast were the intensity of southwest warm moist flow at 850 hPa(20-30 m·s^-1),the distribution of wind direction and wind speed,the position of frontal zone,the intensity of warm advection(3×10-4-5×10-4℃·s^-1),the vertical distribution of potential pseudo-equivalent temperature,the variation of wind with height(the clockwise rotation angle of wind direction with height was bigger than 180°,the 0-6 km vertical wind shear reached 30-40 m·s^-1)and so on.
作者
陈淑琴
章丽娜
曹宗元
刘菡
Chen Shuqin;Zhang Li’na;Cao Zongyuan;Liu Han(Zhoushan Meteorological Office,Zhoushan 306021,China;China Meteorological Administration Training Centre,Beijing 100081,China)
出处
《气象与环境科学》
2019年第4期63-73,共11页
Meteorological and Environmental Sciences
基金
国家自然科学基金青年科学基金项目(41705031)
中国气象局预报员专项(CMAYBY2017029)
关键词
高架对流
条件对称不稳定
地转绝对动量调整
倾斜对流结构特征
elevated convection
conditional symmetric instability
geostrophic absolute momentum adjustment
slantwise convection feature
