|Title||Statistical state dynamics of weak jets in barotropic beta-plane turbulence|
|Publication Type||Journal Article|
|Year of Publication||2019|
|Authors||Bakas N.A, Constantinou N.C, Ioannou P.J|
|Journal||Journal of the Atmospheric Sciences|
|Type of Article||Article|
|Keywords||2-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.