摘要
20 0 3年 4月 17日 ,山东省济南地区出现罕见的春季大暴雨过程。卫星云图表明它是由α中尺度对流系统(MαCS)两次连续发展造成的。天气分析结果显示 ,4月中旬这次黄河流域MαCS的发生条件和MCC多发期的盛夏 ( 7,8月份 )相同 ,也产生在大尺度的暖脊中 ,并且有西南风低空急流向MαCS发生区输送暖湿空气。这种条件的出现是和该年春季西太平洋副热带高压异常偏北相关联的。雷达回波分析表明 ,和强对流型风暴相似 ,在MαCS的前沿也存在一条狭窄的对流性强降水带。红外云图黑体辐射温度 (TBB)分析表明 ,这条对流性回波带是和冷云盖的TBB强梯度带或TBB≤ -72℃的特别高耸的云顶相配合。进一步分析还表明 ,MαCS的第 2次发展与来自东面黄、渤海海区强大的低层冷空气回流有关 ,行星边界层风场明显的偏北风、偏南风和偏东风 3股气流结构使得济南附近的辐合特别强 ,导致第 2阶段的雨强更大。低层冷空气的侵入 ,可能是春季MαCS发生条件和流场结构上有别于夏季MCC的独特性。
Based on the operational meteorological data,it is found that as usual MCC appeared in July and August,this MαCS was formed in a macro-scale warm ridge with southwester low level jet (LLJ) transporting warm moist air to the area. The emerging of the conditions was because the western Pacific subtropical high had exceptional northward in that spring. Although in the sense of climate the Yellow River Reaches was in a typical spring, still the synoptic scale condition at that time was quite similar with that in midsummer when MCS(and MCC) emerged, somewhere even stronger (the intensity of LLJ e.g.), so it was very favourable for MαCS. At the profile of the radar echoes, the convections at the first stage were several regularly arranged cells, then they turned into a narrow arc echo band. At last they became a width extended but intensity weaken echo region behind the strong echo band. The second precipitation event lasted from evening to nighttime on 17, April, 2003 with greater intensity. The difference in the infrared images from geostationary meteorological observation satellite was that its major axis was towards northeast-southwest, especially after combining with several convective cells in the southwest at about midnight and became an area cloud band extending from northeast to southwest, the whole cloud system seemed to be a short cold front cloud band. The radar echo presented to be fluctuation. Compared with the first MαCSs heavy precipitation, the divergence of vapor flux and vapor flux vector in the second MαCSs heavy precipitation was even more favourable for MαCS. From the analysis, there was a distinct movement of the cold air in the planetary boundary layer (PBL). The cold air came from the Bo Sea and the north of the Yellow Sea. There were apparently three different air currents in the middle and lower reaches of the Yellow River,i.e southwest air current, southeast air current and northeast air current. The wind shears of these air currents composed a herringbone shear system that was made up of a cold front shear in the west and a warm front type shear in the east. The intersection of these two shears was just the crossing of the three air currents, and it was near Jinan city. The situation that the refluxing of the cold air in the boundary layer led to the strong converging of the three air currents,that is likely to be the special character of the spring MCC in the coastal region of east China.
出处
《气象学报》
CAS
CSCD
北大核心
2004年第4期504-511,F003,共9页
Acta Meteorologica Sinica
基金
国家自然科学基金项目40305004
40233036
40205008
山东省气象局重点科研项目(2004sdqx18)
关键词
暴雨过程分析
雷达回波
中尺度对流系统
红外云图
Heavy rainfall, Mesoscale convective system (MCS), Radar reflectivity factor, Infrared nephogram
