A STUDY OF A DEVELOPING WAVE CYCLONE

Abstract

In the past most diagnostic studies of frontal cyclone development have been carried out through use of quasi-geostrophic models. In this paper we present the results of vertical motions obtained from a 5-level general balance model. Nongeostrophic effects such as deformation and beta term of the balance equations, divergence, vertical advection, and the twisting term of the complete vorticity equation are retained. Advection of thermal and vorticity fields by the divergent part of the wind are also included in this analysis. Diabatic effect through release of latent heat in regions of saturated dynamic ascent, frictional effects at the lower boundary, and sensible heat transfer from the lake waters to the atmosphere are additional features. The results are presented in a partitioned form. The main results of the calculation reveal that: in the initial difluent stage of the upper trough pronounced sinking motions behind the trough are associated with a strong field of convergence in the northwesterly flow in the upper trough. This sinking motion is partitioned to arise primarily from differential vorticity advection by nondivergent part of the wind, Laplacian of thermal advection by nondivergent part of the wind, and the terrain downslope motion. The upper level development is followed by intense surface cyclogenesis during a period of approximately 36 hr. During the latter stages development is found to be associated with intense rising motion arising from differential vorticity advection by the nondivergent part of the wind, Laplacian of thermal advection by the nondivergent part of the wind, latent heat, and surface friction.