Greg Holland and Yuqing Wang

BMRC, Melbourne, Australia.

My purpose in this session (working together with Yuqing Wang), and in other discussion and report preparation leading up to the fourth WMO/CAS International Workshop on Tropical Cyclones, is to try to move away from examination cyclone intensification processes by addressing small components. Having addressed the problem from several view points over many years, I am convinced that this merely introduces confusion, false hopes and misinterpretations. The idea is not new, and there have been a number of talks promoting the idea that an elephant has a rear and a front end and that we, as the proverbial blind people groping in the dark need to move around and examine the whole animal.

Hence, although Hugh has placed me in a lateral interactions section, I choose to try to develop a working hypothesis branching over the full range of potentials. My goal is to generate discussion and to help focus my own muddy thoughts on how to really address the issues. The types of interaction that I include in the hypotheses are indicated schematically in Fig. 1.


There are a number of important and useful clues from experience and previous studies that can help us to formulate an initial hypothesis. The first clues are:

These clues indicate that once a tropical cyclone approaches hurricane intensity the internal dynamics tend to carry it through to the maximum intensity allowed by the environmental conditions. Although transient environmental impulses may change the rate of intensification, an internal adjustment process dictates the time taken to reach maximum intensity. There must be a degree of internal stochasticity, but this is essentially unknown.

The next clues are:

Thus, some process is acting to halt the intensification process that would occur under perfect thermodynamic conditions. It may be that lateral dynamical interactions tend to interrupt the intensification cycle, as suggested by Merrill (1988). However, there also is evidence that the cyclone may change its own thermodynamic environment to reduce the intensification potential (Tonkin 1997).

The final clue is:

Perhaps the response of a tropical cyclone to an imposed lateral interaction or thermodynamic change is determined to some extent by the current (thermodynamic) environment, the presence of other interactions, or the stage of development of the internal dynamics?

This leads us to a working set of hypotheses:

Corollary: It appears that the thermodynamic environment of a developing storm is always
less conducive to development of an intense system than is indicated by the climatological mean, that is: the process of cyclone development inherently reduces the thermodynamic energy potential;

We are testing these hypotheses and will report on the outcome to the meeting. Discussion and argument welcome.


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