24年11月25日(月)15:00~
- 場所： 616号室
- 発表者：Roger K. Smith(Ludwig-Maximilians University of Munich)
- ＜外部講演＞
- 表題：Early conceptual frameworks for understanding tropical cyclone evolution
- 要旨：In this talk, I will describe recent efforts to reconcile the classical balance theories of tropical cyclone
intensification by Shapiro and Willoughby and Schubert and Hack and the various prognostic balance (or
WISHE-) theories of Emanuel. The WISHE theories have been highly influential and have become widely
accepted as providing a zero-order model for understanding tropical-cyclone behaviour. I will argue that
the classical theories provide a more useful foundation for the development of a conceptual model for
tropical cyclone evolution.
Our endeavour to compare the two theories raised the need to extend the classical theories to account
for explicit latent heat release in slantwise ascending air. While such an effort uncovered enroute a range
of old modelling issues concerning the representation of deep convection in a balance framework, the
analysis provides a new perspective of these issues. The behaviour of the model with explicit latent heat
release is illustrated by a particular calculation starting with a balanced axisymmetric vortex in a
conditionally-unstable atmosphere. As soon as condensation occurs aloft, the moist Eliassen equation for
the overturning circulation becomes hyperbolic in the convectively-unstable region and the model
cannot be advanced forwards beyond this time unless the Eliassen equation is suitably regularized to
remove these hyperbolic regions. However, regularization suppresses deep moist convection, leaving no
mechanism to reverse the frictionally-induced outflow in the lower troposphere required to concentrate
absolute angular momentum there. For this reason, the initial vortex spins down, even following the
formation of elevated cloud with the accompanying latent heat release.
The fact that the flow configuration in the explicit moist version of the classical theories is similar to that
in the WISHE theories raises several fundamental questions concerning the physics of vortex spin up in
the WISHE theories themselves. I will answer these questions in the talk.
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