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Nonlinear Processes in Geophysics An interactive open-access journal of the European Geosciences Union
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Volume 9, issue 5/6
Nonlin. Processes Geophys., 9, 497–512, 2002
https://doi.org/10.5194/npg-9-497-2002
© Author(s) 2002. This work is licensed under
the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License.
Nonlin. Processes Geophys., 9, 497–512, 2002
https://doi.org/10.5194/npg-9-497-2002
© Author(s) 2002. This work is licensed under
the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License.

  31 Dec 2002

31 Dec 2002

On the problem of optimal approximation of the four-wave kinetic integral

V. G. Polnikov1,* and L. Farina1 V. G. Polnikov and L. Farina
  • 1Centro de Previsão de Tempo e Estudos Climáticos (CPTEC), Instituto Nacional de Pesquisas Espaciais (INPE), CPTEC/INPE, Cachoeira Paulista, SP, 12630-000, Brazil
  • *permanent address: The State Oceanographic Institute, Moscow, Russia

Abstract. The problem of optimization of analytical and numerical approximations of Hasselmann's nonlinear kinetic integral is discussed in general form. Considering the general expression for the kinetic integral, a principle to obtain the optimal approximation is formulated. From this consideration it follows that the most well-accepted approximations, such as Discrete Interaction Approximation (DIA) (Hasselmann et al., 1985), Reduced Integration Approximation (RIA) (Lin and Perry, 1999), and the Diffusion Approximation proposed recently in Zakharov and Pushkarev (1999) (ZPA), have the same roots. The only difference among them is, essentially, the choice of the 4-wave configuration for the interacting waves. To evaluate a quality of any approximation for the 2-D nonlinear energy transfer, a mathematical measure of relative error is constructed and the meaning of approximation efficiency is postulated. By the use of these features it is shown that DIA has better accuracy and efficiency than ZPA. Following to the general idea of optimal approximation and by using the measures introduced, more efficient and faster versions of DIA are proposed.

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