Rapid intensification of a tropical hurricane as self-organized development of open dissipative system

Forecasting of rapid intensification of a tropical hurricane (TH) still remains as challenging problem [1-3]. High emphasis is placed also on vital problem of clarification of potential influence of global warming [4-5]. A new approach, based at so-called equilibrium translation model (ETM) [6-8], links the intricate phenomenon of rapid intensification to certain type of conformity of dynamical and thermal fields in the system TH-ocean-atmosphere (alignment effect). The same model leads to new insight into the problem influence of global warming.

ETM considers TH as self-organized dissipative system internally geared to maximum intensification. Realization of this internal tendency depends on two external factors: heat inflow from an ocean and dynamical influence of surrounding atmosphere. When the main dynamical driver (environmental wind) is found to be in tune with TH internal driving mechanism, this natural heat engine becomes mostly efficient in terms of conversion of oceanic heat potential into cyclonic motion of atmosphere. As a result TH intensifies rapidly.

The main outcome of ETM is disclosure of non-dimensional alignment number (Nal) (incorporating main integral thermal and dynamical parameters of the system) serving as a criteria of aforementioned systemic conformity.

The second approximation of ETM [7-8] (covering general case of TH of non-circular outer boundary) determines the condition of establishment of equilibrium translation as Nal approximately equal to 30.

The key role of Nal in TH rapid intensification is demonstrated through correlation of rather wide field data [6-8].

At the same time, in the part of cases, insufficient accuracy of procedures of evaluation of Nal manifests itself [6-8]. The problem mainly is connected with calculation of TH local translation speed through discrete data on geographical coordinates of TH centre specified in regular forecast advisories [3]. According [6-8] in such a case the local translation speed may be evaluated through several equations, however each of them may result tangible uncertainty (for instance, when TH translates through curved trajectory or with variable speed).

As in terms of the theory of complex adaptive systems Nal represents the main aggregated parameter of TH development, it gains significant importance working out of adequate aggregation procedure.

By this goal, a new aggregation procedure is developed including a new approach to determination of local transition speed of TH through the data specified in regular forecast advisories [3]. Corresponding new correlation demonstrates improvement of interpretation of the available field data on rapid intensification of TH.

Important potential implication of ETM is revealed also in terms of clarification of vital problem of influence of global warming on tropical cyclonic activity. The model prejudices widely discussed concept about simple intensifying influence of an ocean warming on TH intensity.

According to ETM, in certain zones of World Ocean, gradual elevation of HHP may result even hindering of TH development by mistuning of existed currently rough correlation of TH equilibrium translation speeds with prevailing regional winds. The most unwanted scenarios may take place in the zones where long-term changes are accompanied by favorable for such a correlation transformation of the fields of prevailing winds and HHP.

In this context rather unexpected level of tropical cyclonic activity in 2006-2007 is examined in the framework of ETM.

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