Statistical state dynamics of weak jets in barotropic beta-plane turbulence

TitleStatistical state dynamics of weak jets in barotropic beta-plane turbulence
Publication TypeJournal Article
Year of Publication2019
AuthorsBakas N.A, Constantinou N.C, Ioannou P.J
JournalJournal of the Atmospheric Sciences
Date Published2019/03
Type of ArticleArticle
ISBN Number0022-4928
Accession NumberWOS:000461635100001
Keywords2-dimensional turbulence; atmosphere; atmospheric dynamics; Barotropic flows; emergence; flows; generation; jets; Meteorology & Atmospheric Sciences; nonlinear dynamics; Planetary atmospheres; stability; turbulence; waves; zonal jets

Zonal jets in a barotropic setup emerge out of homogeneous turbulence through a flow-forming instability of the homogeneous turbulent state (zonostrophic instability), which occurs as the turbulence intensity increases. This has been demonstrated using the statistical state dynamics (SSD) framework with a closure at second order. Furthermore, it was shown that for small supercriticality the flow-forming instability follows Ginzburg-Landau (G-L) dynamics. Here, the SSD framework is used to study the equilibration of this flow-forming instability for small supercriticality. First, we compare the predictions of the weakly nonlinear G-L dynamics to the fully nonlinear SSD dynamics closed at second order for a wide range of parameters. A new branch of jet equilibria is revealed that is not contiguously connected with the G-L branch. This new branch at weak supercriticalities involves jets with larger amplitude compared to the ones of the G-L branch. Furthermore, this new branch continues even for subcritical values with respect to the linear flow-forming instability. Thus, a new nonlinear flow-forming instability out of homogeneous turbulence is revealed. Second, we investigate how both the linear flow-forming instability and the novel nonlinear flow-forming instability are equilibrated. We identify the physical processes underlying the jet equilibration as well as the types of eddies that contribute in each process. Third, we propose a modification of the diffusion coefficient of the G-L dynamics that is able to capture the evolution of weak jets at scales other than the marginal scale (side-band instabilities) for the linear flow-forming instability.

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