中-β尺度干线的形成与局地强对流暴雨

THE FORMATION OF A MESO-β DRY LINE AND LOCAL CONVECTIVE RAINSTORM

本文用地面中尺度资料分析了北京地区一次强对流暴雨过程,发现本次过程的影响系统为中-β尺度的干线。它的两侧分别为干热空气和暖湿气流。干热空气是由边界层向下逐渐扩展的,在其下沉过程中受到山地下坡的增幅作用,使减湿增温的过程特别强烈。这种系统与我国常见的露点锋结构很不一样。本文用逐时资料计算了中尺度地面物理量场,给出它的发展过程及演变特征,并与影响美国强对流天气的干线系统进行了比较研究。

Using meso-scale data at the surface, the characteristics of a meso-β scale system causing a heavy rainstorm in Beijing area is studied. It is discovered that there is a dry line with the hot, dry air and cool, moisture air at its two sides respectively. The hot and dry air layer extends downward from the top of boundry layer, and is enhanced by downglide motion at the lee side of mountain. The increase of temperature and decrease of moisture become more drastic in that situation. The formation and structure of this system is different from the so called 'dew-point front' commonly seen in China, even though they are all characterized by a zone of moisture discontinuity. However, it seems similar to the dry line occurring at the east side of the Rocky Mountains. The evolutions of the pressure, temperature and dew point depression during the whole life cycle of the dry line are given hourly. And the features of the stratification and radar echoes are also illustrated.