易笑园,李泽椿,姚学祥,王红艳,孙晓磊. 2011. 一个锢囚状中尺度对流系统的多尺度结构分析[J]. 气象学报, 69(2):249-262, doi:10.11676/qxxb2011.021
一个锢囚状中尺度对流系统的多尺度结构分析
An analysis of the multi scale structure and evolution of a meso-scale occluding convective system
投稿时间:2009-04-21  修订日期:2009-06-29
DOI:10.11676/qxxb2011.021
中文关键词:  锢囚状中尺度对流系统, 多尺度结构, 演变, 风场反演
英文关键词:Mesoscale occluding convective system, Multi-scale structure, Evolution, Wind retrieved
基金项目:中国气象局新技术推广项目预报员专项(CMATG2009YB04)、公益性行业专项(GYHY20070604、GYHY200906011)
作者单位
易笑园 南京信息工程大学大气科学学院南京210044天津市气象台,天津300074国家气象中心,北京100081 
李泽椿 南京信息工程大学大气科学学院南京 210044国家气象中心, 北京 100081 
姚学祥 河北省气象局石家庄050002 
王红艳 南京信息工程大学大气科学学院南京210044 
孙晓磊 天津市气象台天津300074 
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中文摘要:
      利用多普勒雷达、气象卫星、自动气象站等监测资料、1°×1° NCEP再分析资料和4DVAR雷达反演低层风场资料,运用雷达拼图图形叠加、剖面和中尺度滤波等分析手段,对2007年7月18日华北东部一个锢囚状α中尺度对流系统(Mα-CS)的多尺度空间、动力结构及其演变进行了细致地分析。结果表明:(1) M-α-CS生命史分为发生发展阶段、成熟阶段和消散阶段。从卫星云图资料看,其冷云盖的形态由条状演变为单一云顶的圆形,再演变成多个云顶的多角形。从雷达资料看,冷云盖下两条交叉的β中尺度强回波带由数个具有独立回波核和生命史的M-γ-CS有组织地排列而成。M-α-CS尚未锢囚时,MγCS非常活跃,造成多处强降水;锢囚时,M-β-CS上的MγCS排列紧密,独立边界模糊,且锢囚点与冷云盖中心正好对应,此时云顶亮温(TBB)达到最低点(-80.16℃);消散时,回波顶和反射率图像上“人”字形结构消失,均呈现出涡旋回波特征,云顶面积达到最大(14.46×104 km2)。(2) MαCS内部有强烈的上升气流,垂直速度中心在600—500 hPa。中尺度滤波后可见,200 hPa上的中尺度反气旋环流影响着冷云盖的形状;700 hPa的中尺度气旋性环流起到将冷空气从其后部卷入MαCS的作用。(3)MαCS内部组织结构与低层气流水平分布关系密切。MαCS发展时,原本与背景主导气流一致的西南入流在大小、方向上均发生变化,而形成辐合线;成熟时,西南暖湿入流减少、西北干冷空气进入;随着气流趋于一致的偏西气流、MαCS内部辐合减弱,且暖湿高能源被干冷气流切断,MαCS进入消散期。(4)对流系统的触发取决于地面 θse等值线密集区内的地面辐合线,其维持和减弱与地面能量分布有关。锢囚状中尺度对流系统与锢囚锋天气系统在尺度上有所不同,但在形态上和形成机理上,却有相似之处。
英文摘要:
      The composite Doppler radar data at the Beijing, Tianjin and Qinhuangdao stations, the satellite data, the automatic meteorological observing stations data and the NCEP 1°×1° reanalysis data were used to analyze the multi-scale structure and evolution of a meso-scale occluding convective system in the east part of the Huabei plain, which caused severe heavy rainfall on 18 July 2007. The methods of the meso-scale filtering, the 4DVAR single Doppler radar retrieval, and the horizontal and vertical section analyses were employed in this paper. The results show that firstly, this MαCS experienced 3 phases including the intialization and developing, the maturation and the dissipation. The cold cloud top of the MαCS changed from an elongated top to a circle one with only single center again to a polygon top with several centers as shown in the satellite images. It is seen from the radar data that a meso-scale convective system under the cold top was a occluding squall line mesoscale convective system, whose two cross meso-β-scale line squall convective systems were composed of several MγCSs arranged in the form of a line with independent strong radar reflectivity center and life-cycle. In the occluding phase of the MαCS the active MγCSs caused local severe rainfall. In the occluded phase, those MγCSs were closely organized together so as to make their edges become obscured with the occluded point corresponding to the cold cloud top center of the MαCS. In the dissipation phase, with the pattern of crossing disappearing and cloud top dropping, the radar echo-top and the reflectivity both showed an eddy feature. Secondly, severe ascending motion existed in the MαCS whose center appears from 600 hPa to 500 hPa.At the height of 200 hPa, an anti cyclonic circulation had an effect on the shape of cold cloud top. At the height of 700 hPa, the cold air flow brought by the cyclonic circulation weakened physically the intensity of MαCS. Thirdly, the structure and intensity in the MαCS closely related to the air flow at the lower troposphere. In the intialization and developing phase of the MαCS, the direction of the southwesterly currents entrancing that is consistant with the background one changed to form a convergence lines. After the mature phase, the dry-cold air flow from the west-north areas entranced into the MαCS instead of the wet-warm air flow, causing the convergence to disappear, the source of high energy to decrease, and the M-α-CS to be dissipated. Finally, the multi-scale convective systems were triggered and organized by the ground-convergence line in the areas of dense potential pseudo equivalent temperature lines. The energy fields concern directly the maintaining or weakening of the multi-scale convective systems. Comparing between the meso-scale occluding convective system and the occluding front weather system, it is found that they had difference in scale but they were resemble in pattern and genesis mechanism.
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