平流涡度方程及其在2006年Bilis台风分析中的应用

推导得到气压坐标中的动量叉乘形式的垂直涡度方程,这个动量叉乘形式的涡度方程包含了水平风的平流旋转效应,可称为平流涡度方程.由于水平风场的平流作用可由等压面天气图直观分析得到,因此平流涡度方程可方便用于实际天气分析.对2006年的Bilis台风移动过程中由经典涡度方程和平流涡度方程计算得到的垂直涡度倾向进行对比分析发现,二者计算得到的垂直涡度倾向变化的分布形式接近,但平流涡度方程计算得到的倾向的数值明显大于经典涡度方程的数值,正负涡度倾向区也更集中.对Bilis移动过程中的垂直涡度方程和平流涡度方程中各项的计算分析表明,水平风场的平流旋转作用是Bilis发展移动过程中垂直涡度变化的一个主要因素,是造成垂直涡度增强并发展的主要原因.因此,当水平风场平流旋转效应较强时,平流作用对垂直涡度倾向变化起主导作用,可直接用平流项来近似分析Bilis台风的涡度变化.而平流涡度方程中地转涡度和散度项的变化趋势与Bilis台风的移动路径有较好的一致性,这一项对台风的移动路径预报有更好的指示意义.

Advective vorticity equation and its application to the vorticity variation of typhoon Bills in 2006

The vorticity equation in the form of momentum cross multiplication is derived in pressure coordinate, in which the divergence term in the classic vorticity equation (CVE) does not appear. This vorticity equation in momentum cross multiplication form involves the rotation effect of the horizontal wind advection, which can be called the advective vorticity equation (AVE). Because the rotational effect of horizontal wind advection can be directly analyzed on the synoptic charts, this equation is easily applied to operational weather analysis. The vorticity and its tendency of typhoon Bills occurred in July 2006, it is analyzed and the results show that the distributions of the vertical vorticity tendencies from the two equations are similar except that the values of AVE is larger than that of CVE, and positive vorticity tendency from AVE is more concentrated than that of CVE. The detailed analyses of the three terms on the right hand side of AVE indicated that the advective term is a leading factor in determining the change of vertical vorticity for the development of the typhoon Bilis. When the vorticity induced by the rotational effect of horizontal wind advection plays a dominant role, AVE shows advantages for the diagnosis and analysis of synoptic systems. Thus, the AVE is useful for analysis of the change of vorticity and diagnosis of the movement for typhoon Bills. Furthermore, the tendency of the term related to geostrophic vortieity and divergence always accords with the track of Bilis, which means this term can be used as an indicator for track prediction of typhoon.