Abstract
Abstract The present paper provides a rationale for the regeneration stage undergone by surface cyclones when they cross a baroclinic jet from its anticyclonic-shear (warm) side to its cyclonic-shear (cold) side in a two-layer quasigeostrophic model. To do so, the evolution of finite-amplitude synoptic cyclones in various baroclinic zonal flows is analyzed. Baroclinic zonal flows with uniform horizontal shears are first considered. While the anticyclonic shear allows a much more efficient and sustainable extraction of potential energy than the cyclonic shear, the growth of the lower-layer eddy kinetic energy (EKE) is shown to be highly dependent on the choice of the parameter values. An increased vertical shear leads to a more rapid EKE increase in the anticyclonic shear than in the cyclonic shear whereas increasing the vertically averaged potential vorticity gradient or the barotropic shear stabilizes the EKE more in the former shear than in the latter. Finally, vertical velocities arising from the nonlinear interaction between synoptic cyclones are shown to favor EKE growth in the cyclonic shear rather than in the anticyclonic one. The evolution of cyclones initialized on the warm side of a meridionally confined baroclinic jet is then investigated. The lower-layer cyclone crosses the jet axis and undergoes two distinct growth stages. The first growth stage results from the classical baroclinic interaction and is mainly driven by linear interaction between the cyclones and the jet. The second growth stage is mainly a nonlinear process. It is triggered by the vertical velocities created by the three-dimensional structure of the cyclonic disturbances when they reach the cyclonic side of the jet.
Highlights
It is well known that extratropical cyclones develop by extracting energy from the available background potential energy through baroclinic interaction
The present paper systematically compared the impact of both sides of a baroclinic zonal jet in the growth of finite-amplitude surface cyclones using a two-layer quasigeostrophic model
The first step consisted in systematically analyzing the impact of cyclonic and anticyclonic uniform background shears on the eddy kinetic energy budget at the lower layer over a large range of parameters
Summary
It is well known that extratropical cyclones develop by extracting energy from the available background potential energy through baroclinic interaction. The Norwegian cyclone model (Bjerknes and Solberg 1922) is found to appear in the cyclonic-shear case while the model of Shapiro and Keyser (1990) with a T-bone frontal structure dominates in unsheared cases. Despite all this information, it is still unclear which side of a baroclinic zonal jet is the more cyclogenetic. The purpose of the present study is to numerically investigate this aspect within a quasigeostrophic framework by modifying the vertical and horizontal shears of the background flow as well as the scale and intensity of the synoptic disturbances in the initial conditions of the model
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
