Analysis of the budget of enstrophy during the landing of Typhoon Morakot (2009)

The vorticity enstrophy, divergence energy and deformation energy are introduced in this paper.By deriving their tendency equations which contain both terms of identical signs and those of opposite signs, the interactions between the rotational, divergent and deformational fields can be studied.In the landing process of Typhoon Morakot in Taiwan in 2009, all the three variables and terms in their tendency equations are calculated.The results show that in the stages of development and decay of Morokat, the exchange between vorticity enstrophy and divergence energy and the external forcing of vorticity enstrophy play the most important role in the local change of vorticity enstrophy, while the effect of the exchange between vorticity enstrophy and deformation energy is relatively small.On the whole (both the spatial and time averages), the exchanges between the three variables in the center areas of the typhoon are favorable to the development of vorticity enstrophy.The deformation energy transforms to vorticity enstrophy by the vorticity-deformation transition term, which increases the vorticity enstrophy.In the same time, the deformation energy transforms to the divergence energy by the divergence-deformation transition term, which increases the divergence energy.Then the divergence energy transforms to vorticity enstrophy by the vorticity-divergence transition term, which represents the influence of deformation energy on vorticity enstrophy.