下垫面物理过程在一次巴彦淖尔市局地冰雹天气中的作用

Effects of underlying surface physical process on a local hail weather in Bayannaoer City

运用常规气象资料和自动站实测资料，结合2013年7月21日-22日发生的冰雹天气个例，分析下垫面物理过程在巴彦淖尔市强对流天气中的作用。结果表明：①此次降雹的初始雹云是在北部山区的热力和动力强迫下局地触发产生的。由于平原地表受热不均形成的局地热力环流，与边界层南风气流因地形造成的绕流辐合以及山地的动力辐合抬升共同作用使对流云在北部山区形成并发展。低层浅薄的南风气流在山前地区造成迎风坡的上升速度，而且这种上升速度取决于低层最大南风层的风速大小和山体的坡度。降水临近时刻都伴有明显的南风加大并上传现象，南风层次的抬升促进了切变层次的抬高，南风层次的加厚使得水汽输送层次也得到加厚，南风的发展从动力和水汽条件上促进了雹云的发展。②城市下垫面的热力作用对城区及其下风方雹云的发展和降雹的强度、落区等有重要影响。因城市与郊区下垫面的热力差异形成的城市中尺度风场辐合线，以及所造成的强烈上升运动和能量、水汽的聚集，是对流回波在城市中心上空明显增强和东部出现冰雹天气的主要原因。③由惯性重力波在阴山南坡一侧发展、激发对流云带，且越接近平原地区，地形坡度减小，波动发展的程度也减弱，在波峰处对流云带增强。

Using the conventional meteorological data and automatic station data which are combined by a hail event occurred on convective weather sprung locally formation and July 21~22 2005 analyze the effects of such underlying surface physical process on the strong evolution in Bayannaoer City. Results indicate that： （1） The initial hail cloud of this ease are by the thermody development of namic and dynamical forcing induced by the mountainous topography in the north.The convective cloud in the northern mountains is caused by local thermal circulation of plain surface uneven heating flow, convergence of southerly in the boundary layer due to terrain and dynamic convergence uplift of mountain. The rising velocity of windward slope is caused by low layer shallow southerly wind in front of the mountain,and this rate of rise depends on the maximum southerly wind velocity of the lower layer and the slope of the mountain. Precipitation near the moment with southerly significantly increased and upload phenomenon, uplift of the southerly level promotes to elevate shear level and thickening of the southerly level makes water vapor transport level thickened, the development of southerly promotes the development of hail cloud from the dynamic and water vapor conditions. （2）Urban underlying surface thermodynamics effects on the urban area and the downwind have significant influence on the development of the hail cloud and the intensity of hail, failing area etc. The primary factors that intensify the convective radar echoes when it moves over the center city downtown and Hail Weather appears in the east include the surface mesoscaIe wind field convergence line caused by underlying surface thermodynamics differences of city and suburb,as well as the strong upward air and the congregating energy and water vapor. （3） Inertial gravity wave develops and stimulates the convective cloud band on the south side of Mount Yinshan. And the closer to the plain area, the terrain slope decreases, degree of fluctuating development is reduced, the peak of the convective cloud bands enhanced.