Numerical simulation of the development of tropical cyclones with a ten-level model. Part II

The importance of some different physical processes and parameters, pertinent to the development of tropical storms, is studied with the aid of the numerical model presented in an earlier paper (Sundqvist, 1970). The developing tropical cyclone exhibited and discussed in detail in the previous paper is used as a reference case for the present experiments.

The results show that the rate of intensification becomes significantly higher when radiational cooling is taken into account. On the other hand, the peak intensity appears to be unaffected.

In another experiment, where a hypothetical poleward movement of the vortex is introduced, it is demonstrated that a mature hurricane may remain quite intense to rather high latitudes, provided other conditions are unchanged.

The decisive role of the sea surface temperature is clearly exhibited in three other applications. For one and the same vertical stratification of the tropical atmosphere the maximum swirling velocity never exceeds 25 m/s when the water temperature is 26°C, while a full-fledged hurricane develops at 27.5°C.

In an attempt to reduce the highest wind speeds of a mature storm by enhancing the heating artificially (cloud seeding), the results indicate that the approach yields the desired tendency in the evolution. However, no changes of significance are observed in the maximum wind during the hypothetical operation that was assumed to last for 40 hours.