一次高空急流增强过程中的中尺度扰动和动量输送特征

Characteristics of the meso-scale perturbations and momentum transportation associated with an intensification process of upper-level jet

本文利用中尺度数值模式的高分辨率模拟结果,研究了夏季东亚副热带西风急流一次短时间尺度强度变化过程中的中尺度西风扰动特征和相应的动量输送特征。结果表明,此次急流强度短时间尺度变化以急流轴线为界,北侧增强,南侧减弱。急流整体增强和急流内部中尺度西风扰动的积累效应有关。急流入口区(出口区)南侧主要为西风动量水平通量辐散区(辐合区),北侧为辐合区(辐散区),西风动量水平辐合辐散区的水平尺度只有百公里左右,也属于中尺度范围,并且辐合辐散区一般位于地形坡度较大区域上空。西风动量的垂直输送与西风动量水平通量散度分布几乎一致,但数值小一个量级以上。

In this paper,the numerical simulation data at high-resolution conducted with meso-scale nonhydrostatic model MM5 are used to investigate the characteristics of the meso-scale perturbations and momentum transportation associated with a short-term intensification process of East Asian subtropical westerly jet.The results show that the jet intensification process can be divided into two aspects along with the jet axis,namely,the intensification north to the axis and weakening south to the axis.The large-scale intensification of the jet is related to the accumulation of positive meso-scale westerly perturbations.The divergence（convergence） of westerly momentum horizontal flux is mainly located in the south part of the jet entrance（exit） region,whereas the convergence（divergence） is mainly located in the north part of the jet entrance（exit） region,and the divergence（convergence） area,which corresponds to the large topographic gradient,is at the horizontal scale of about 100 km,belonging to the meso-scale perturbation.The distribution of the vertical transportation of westerly momentum is similar to that of the horizontal flux basically,but it is over one order less in magnitude.