On the forced tangentially-averaged radial-vertical circulation within vortices. Part II: The transformation of Tropical Storm Haima (2004)

Abstract

A real case study for the transformation of Tropical Storm (TS) Haima (2004) into an extratropical cyclone (EC) is carried out numerically since, after landfall, 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. With the linear diagnostic model (derived in a previous study) for the tangentially-averaged radial-vertical circulation within vortices moving on the spherical Earth, Haima’s (2004) life cycle is reconstructed noticeably well. Therefore, the major contributor could be identified confidently for Haima’s (2004) extratropical transition based on the diagnostic model outputs. The quantitative comparison shows that up to a 90% contribution to the innerregion updraft and a 55% contribution to the upper-layer outflow come from latent heating during Haima’s (2004) TS stage. Up to a 90% contribution to the inner-region updraft and nearly a 100% contribution to the upper-layer outflow come from the upper-layer eddy angular momentum advection (EAMA) during Haima’s (2004) EC stage. Representing the asymmetric structure of the storm, the predominantly positive contribution of the upper-layer EAMA to Haima’s (2004) transformation is closely associated with the Sshaped westerlies in the upper layer with two jets. One jet in the cyclonic-curvature area carries cyclonic angular momentum into the storm, and the other jet in the anticyclonic-curvature area carries anticyclonic angular momentum out of the storm. Consequently, the newly-increased cyclonic tangential wind is deflected by the Coriolis force to the right to form the upper-layer outflow accompanied by the central-area rising motion, leading to Haima’s (2004) extratropical transition after its landfall.