An idealized model for the eddy-driven Ferrel cell in mid-latitudes

by Woosok Moon (Pukyong National University)

Friday 29 Mar 2024, 14:00 → 15:30 Europe/Stockholm

Albano 3: 6228 - Mega (22 seats) (Albano Building 3)

zoom link : https://stockholmuniversity.zoom.us/j/622224375

Abstract : Conceptual models of the midlatitude atmospheric circulation help greatly to understand its behavior. 

Here, this circulation is described. The poleward heat flux resulting from the baroclinic growth of eddies leads to a decrease in the meridional temperature gradient, which is parameterized through a down-gradient eddy diffusion coefficient D. Similarly, the eddy momentum flux, influenced by barotropic wave breaking, is assumed to be positively proportional with a factor M>0 to the horizontal shear of the zonal mean of the zonal wind, thereby enhancing the intensity of the zonal mean of the zonal wind at upper levels. By incorporating the parameterization of turbulent eddies into the zonal-mean quasi-geostrophic potential vorticity equation, a balance is achieved, resulting in eddy-driven circulations in mid-latitudes akin to the Ferrell cell. The meridional structure of the temperature exhibits two primary features. The first feature is a linear decline in anomalous potential temperature, inducing westerly winds in mid-latitudes. The second feature corresponds to jet streams generated by eddy momentum fluxes. Along with the jet streams, the eddy-driven circulations exhibit the downward (upward) motion at the southern (northern) flank of the jets. The meridional structure of the circulation is influenced by three key factors. The first factor is a structural number denoted as D/SM, where S is the dry static stability affecting the life cycle of synoptic eddies in mid-latitudes. The second factor relates to the planetary size and the third factor is the vertical structure of the atmosphere, associated with eigenvalues of the vertical mode in the main heat equation. The combination of these three factors within the characteristic equation determines the location and number of eddy-driven jets in mid-latitudes.