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Statistical characteristics of two-dimensional and quasigeostrophic turbulence


Respondent	Huvudhandledare	Bihandledare	Datum
Andreas Vallgren	Erik Lindborg	Geert Brethouwer	2010-06-14

Opponent
Johan Nilsson, Meteorologiska Inst. SU

Betygsnämd

Abstract

Two codes have been developed and implemented for use on massively parallel super computers to simulate two-dimensional and quasigeostrophic turbulence. The codes have been found to scale well with increasing resolution and width of the simulations. This has allowed for the highest resolution simulations of two-dimensional and quasigeostrophic turbulence so far reported in the literature. The direct numerical simulations have focused on the statistical characteristicsof turbulent cascades of energy and enstrophy, the role of coherent vortices and departures from universal scaling laws, theoretized more than 40 years ago. In particular, the investigations have concerned the enstrophy and energy cascade in forced and decaying two-dimensional turbulence. Furthermore, the applicability of Charney’s hypotheses on quasigeostrophic turbulence has been tested. The results have shed light on the flow evolution at very large Reynolds numbers. The most important results are the robustness of the enstrophy cascade in forced and decaying two-dimensional turbulence, the unexpected dependency on an infrared Reynolds number in the spectral scaling of the energy spectrum in the inverse energy cascade, and the validation of Charney’s predictions on the dynamics of quasigeostrophic turbulence. It has also been shown that the scaling of the energy spectrum in the enstrophy cascade is insensitive to intermittency in higher order statistics, but that corrections might apply to the ”universal” Batchelor-Kraichnan constant.
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