Critical alignment number and maximum potential intensity of a tropical cyclone

A model of equilibrium translation considers a tropical cyclone (TC) as an open dissipative system geared to maximum self-organized intensification. When large-scale environmental wind favors to this internal tendency of a TC the latter becomes mostly efficient in terms of conversion of oceanic heat into cyclonic motion of atmospheric air (alignment effect). At that the role of main characteristic of development of a TC is gained by non-dimensional alignment number incorporating integral thermal and dynamical parameters of the system cyclone-ocean-atmosphere (COA). In the present study critical value of alignment number (CAN), leading to maximum intensification of a TC, is refined through analysis of comparatively longstanding stages of straightforward near to equilibrium translation with roughly constant TC sizes selected among development histories of around 175 TCs observed during 2003-2009. Possible maximum accuracy of determination of CAN through the set of parameters specified in regular forecast advisories is achieved and linkage of TC rapid intensification through its self-organized development to CAN (the same alignment effect) once again clearly is verified. Selected TCs turn out to be record-breaking intensive at given values of hurricane heat potential (HHP) among all TCs observed during aforementioned period. Supposing that achieved by any selected TC maximum intensity closely approaches maximum potential intensity (MPI) of a TC possible under given conditions of the system COA, the problem of such a maximum is discussed and new empirical equation for MPI is developed. At that it is shown that MPI can be considered as single-valued function of HHP fixed prior to entering of a TC in given area. Taking in account overlooking of alignment effect by existing detailed numerical models, possible interpretation of the effect as an emergent property of the system COA, occurring only at integral scales, is pointed out. Potential specific role of alignment effect also is outlined in the context of clarification of potential influence of global climate change on TCs intensities.