Eddy kinetic-energy redistribution within idealized extratropical cyclones using a two-layer quasi-geostrophic model

Eddy kinetic-energy (EKE) redistribution within mid-latitude cyclones is investigated using a two-layer quasi-geostrophic model. The flow is composed of synoptic localized cyclones at both layers interacting with a baroclinic zonal basic flow. The effects of the planetary-vorticity gra dientand the relative-vorticity gradient of the westerly basic flow a re to reduce the upstream ageostrophic geopotential fluxes at the lower laye r and to intensify the downstream fluxes at the upper layer. Furthermore, they a ct to reduce the downward ageostrophic geopotential fluxes and to intens ify the upward ageostrophic fluxes. When cyclones are embedded in a cycloni c shear, EKE rapidly accumulates on the southwestern flank of the lower-l ayer cyclone before being cyclonically redistributed by the rearward cyclonically-oriented ageostrophic fluxes and nonlinear advection. On the contrar y, when cyclones are embedded in an anticyclonic shear, the lower-layer ageostrophic fluxes are mainly westward oriented and the pressure work perfectly combines with nonlinear advection to maintain the EKE increase at the same place upstream or downstream of the lower-layer cyclone, depending on the value of �. Finally, a simulation showing the crossing of a westerly jet by cyclones condenses all the above effects. At the early stages, when cyclones lie on the anticyclonic side of the jet, a strong EKE increase occurs downstream of the lower-layer cyclone. Just after the jet crossing, the EKE is rapidly rearward and cyclonically redistributed by the ageostrophic fluxes and nonlinear adve ction leading to the formation of a lower-layer jet to the south of the cyclone. Copyright c 2013 Royal Meteorological Society