冷空气大风过程中动量下传特征

利用NCEP再分析资料,对中国西北地区一次大范围冷空气大风过程中的动量下传特征进行了分析。结果表明:动量下传大风是高低空风场辐合辐散的环流运动强迫所造成的大风,发生的区域一般在高空急流南部整层垂直速度接近零的地方;动量下传大风起风前后,垂直速度在高空急流两侧存在明显的反转,且下沉气流区较早接地,大风风速比冷锋大风略小,但持续时间较长;地面冷锋过境之后,高层高位涡区在高空槽持续影响的情况下有明显的向下传递作用,表示具有高位涡特征大气的侵入;高空槽是造成动量下传的主要原因,高空槽的形状及强度对于预报动量下传大风具有较大的意义,槽过境及槽后强西北气流可造成大风的持续。

The Characteristics of Momentum Transfer during a Cold Strong Wind Process

In this paper, the cold wind momentum transfer characteristics at a large scale in northwest China are on analyzed using the NCEP reanalysis data. The results show that the momentum transfer during the wind process is caused by convergence and divergence of air at high and low height field. The convergence takes place at the entrance of jet with strong pressure at surface pressure field. as a compensation, updrafts appear at the downstream of the jet , and strong wind occurs generally in the south of jet , where vertical velocity of the whole layer is close to zero. The velocity in the jet stream has an obvious reverse when the strong wind occurs, and sinking airflow lands earlier. Its speed is smaller than the cold wind, but it's longer. The potential vorticity has a downward transportation after a cold vortex area, meaning an invasion of high potential vorticity. The strong northwest currents after upper trough can cause sustained wind, and the upper through is main reason of momentum transfer. The research results can enhance understanding on momentum characteristics, and gather experience for accurate prediction of strong wind.