Robust poleward jet shifts in idealised baroclinic-wave life-cycle experiments with noisy initial conditions

Abstract. Idealised baroclinic-wave life-cycle experiments are a widely used tool to study fundamental characteristics of mid-latitude baroclinic instability. A typical life cycle evolves from an initialised baroclinically unstable jet through exponential growth phase particular wave mode, followed by breaking during the mature and wave–mean flow interaction driving shift decay phase. Many authors distinguish between cycles with predominantly anticyclonic (LC1) cyclonic (LC2) breaking, transition two flavours is typically controlled via strength meridional wind shear in initial conditions. While has traditionally been triggered specified perturbation fixed zonal number, this extends concept analysing influence random perturbations without any preferred dependency on evolution. We find that shows robust LC1–LC2 distinction as function shear, while preference for LC1-like observed all non-monochromatic perturbations. In particular, persistent cut-off cyclones form LC2 initialisations found eventually become unstable, onset instability coming sooner larger noise All result poleward their final state, regardless shear. Consistently, tends be predominant phases, even initialisations. Equatorward shifts associated still exist, although purely transient interim state. show wave–wave interactions resulting spectrum play important role phases cycle.