一次与西南低涡相联系的低空急流的数值研究

A Mesoscale Numerical Simulation of Low Level Jet Realted with the Southwest Vortex

梅雨期西南低涡的东移发展与长江中下游降水的加强有密切关系 ,作者采用中尺度模式对一次西南低涡及其伴随低空急流的发展演变进行了数值模拟。模拟结果表明 :在长江中下游大巴山地区低空急流先于西南涡东移发展 ;西南低涡及低空急流的生成发展在开始阶段与中层 ( 4 0 0hPa)的弱辐散密切相关 ;南风分量在西南低空急流的演变发展过程中起着更为主动的作用 ;南风分量增大中心位于南风分量中心的前方 ,促使南风分量中心东移 ;南风分量的动量方程收支分析表明水平平流项和产生项是促使南风分量变化的主要作用项 ,水平平流项和垂直平流项大部分相互抵消 ,科里奥利项的作用不可忽视 ,而其他项的值较小 ,在个别阶段和地区行星边界层项的作用在低层也较大。

Using a mesoscale model,a numerical simulation on the low-level jet accompanying the southwest vortex is performed. Results show that the formations and developments of this southwest vortex and the accompanying low-level jet are closely related with the middle level divergence in the beginning;the low-level jet moves eastward and develops prior to the southwest vortex in the west of the Daba Mountain;the south component of horizontal wind contributes more significantly to the evolution of the low-level southwest jet;the strengthen center of south component which locates in front of south component center causes south component center moving eastwerd. Computations of various terms of south wind momentum budget reveal that the horizontal advection and generation term play prominent roles in the strengthen of the south component,and the horizontal and vertical advection have adverse effects;the Coriolis force cannot be ignored with negative effects,the planetary boundary layer term should be considered in some stage and area, the other terms have little effects.