A comparison analysis between developed and undeveloped depressions over the South China Sea

In this paper, by using two sets of composite data of developed and undeveloped depressions over the South China Sea, we analyze and compare the dynamic structures, the heating fields and the vorticity budget residuals of two different types of depressions. Our conclusions are as follows:
The two types of depressions are similar in thermodynamical and dynamical structures. The main differ ences are:in the high layer of developed depression there is a divergence field, with a center near the zero line of vertical wind shear, and over undeveloped depression, the divergence field is weaker and the vertical wind at its center is greater than 5 m s^-1. The thermodynamical field of the former is asymmetrical and that of the latter is quasi-symmetrical. As far as the dynamics structure is concerned, the convergence in the lower layer and the difference of divergence between the upper and lower layers of developed depression is three tmies larger than that of undeveloped depression. The upward motion and heating field at the center of developed depression is also stronger than that of undeveloped one.
The vorticity budget of the two types of depressions is mainly determined by the divergence term, the vorticity advection term and the vertical transport term. The residual term is also important. The principal contribution comes from the divergence term.This is more significant for developed depression than for undeveloped depression.