On the Forced Tangentially-Averaged Radial-Vertical Circulation within Vortices. Part II: The Transformation of Tropical Storm Haima (2004)

A real case study for the transformation of Tropical Storm (TS)Haima (2004) into an extratropical cyclone (EC) is carried out numerically since, afterlandfall, Haima (2004) (as an EC) brought severe weather to a large area(from the south to the north) in China during 13--16 September 2004. Withthe linear diagnostic model (derived in a previous study) for thetangentially-averaged radial-vertical circulation within vortices moving onthe spherical Earth, Haima's (2004) life cycle is reconstructed noticeablywell. Therefore, the major contributor could be identified confidently forHaima's (2004) extratropical transition based on the diagnostic modeloutputs. The quantitative comparison shows that up to a 90% contributionto the inner-region updraft and a 55% contribution to the upper-layeroutflow come from latent heating during Haima's (2004) TS stage. Up to a90% contribution to the inner-region updraft and nearly a 100%contribution to the upper-layer outflow come from the upper-layer eddyangular momentum advection (EAMA) during Haima's (2004) EC stage.Representing the asymmetric structure of the storm, the predominantlypositive contribution of the upper-layer EAMA to Haima's (2004)transformation is closely associated with the S-shaped westerlies in theupper layer with two jets. One jet in the cyclonic-curvature area carriescyclonic angular momentum into the storm, and the other jet in theanticyclonic-curvature area carries anticyclonic angular momentum out of thestorm. Consequently, the newly-increased cyclonic tangential wind isdeflected by the Coriolis force to the right to form the upper-layer outflowaccompanied by the central-area rising motion, leading to Haima's (2004)extratropical transition after its landfall.