梅雨期一次黄淮气旋发展的干侵入特征分析

THE ANALYSIS OF DRY INTRUSION FEATURE OF A HUANGHUAI CYCLONE DEVELOPMENT IN MEIYU PERIOD

利用水汽图像、等熵气流、θse等物理量,对2003年梅雨期的一次黄淮气旋发展过程进行了分析,试图揭示干侵入在黄淮气旋发展中的作用。分析结果表明:与干侵入相联系的水汽图像暗区的移动、发展变化与黄淮气旋的发展、加强、减弱对应关系较好。水汽图像暗区前部依气旋的发展加强、维持、减弱而主要出现在黄淮气旋西侧、南侧和东侧。分析垂直环流表明,干侵入来自对流层中上层,与水汽图像暗区有较好的对应关系,在气旋发展强盛期下沉气流区自西向东、自南向北推进。高空动量下传促使地面气旋发展,从而使中、低层大气变得非常干燥。335K等熵面上的流场特征、等熵面陡峭处与水汽图像暗区的对应关系较好。θse的垂直剖面能反映干侵入特征。等熵面在垂直方向的折叠可使对流层中下层出现潜在对流不稳定区。θse=335K位温舌能较好地反映天气系统的三维结构和干侵入特征。自高层向下传递、加强的位涡变化能反映干侵入的动力特征。

In this paper, by using water vapor imagery, the physical quantity of isentropic airflow and θse etc., a process of a Huanghuai cyclone development in the Meiyu period of 2003 is analyzed to reveal the effect of dry intrusion on the development of Huanghuai cyclone. The result of the analysis indicates that the change of the movement and development of the‘dark zone＇ associated with dry intrusion in water-vapor imagery correspond well to the development, enhancement and weakening of Huanghuai cyclones. The leading edge of‘dark zone＇ in water vapor imagery appeared at the west, south and east of Huanghuai cyclone in the three stages of developing enhancing and weakening of the cyclone. The flows in vertical showed that dry intrusion moved downward from the middle or high levels. They relate well with dry intrusion coming down from the middle or high levels and‘dark zone＇ in water-vapor imagery. The downdraft zone of the dry intrusion moves northward d eastward during the development of the cyclone. The air momentum down from high levels developed the cyclone and cooled the air in middle and low troposphere. The flows and steep terrain on θse =335 K isentropic surface correspond well to the ＇dark zone＇ in water vapor imagery. The vertical profile of θse in any direction can show the feature of dry intrusion. The folding of isentropic surface in the vertical can generate potential convective instability in the middle or low levels. The tongue of θse=335 K can reflect 3D structure of synoptic systems and the feature of dry intrusion. High PV moves down from high levels to low levels and enhanced high PV can show dynamical features of dry intrusion.