The Potential Vorticity Staircase: Formation and Maintenance of Zonal Jets

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This project seeks to improve our understanding of dynamical mechanisms responsible for the formation and maintenance of zonal jets and their implications for atmospheric mixing and transport. The approach is underpinned by the observation that potential vorticity (PV) is a fundamental dynamical quantity that can unify questions of small-scale eddy mixing, wave propagation on jets, and mixing due to wave breaking in their vicinity. In particular, the project will address: (i) fundamental constraints on zonal jets arising from angular momentum conservation (natural, since zonal mean structures such as zonal jets contain most of the atmosphere's angular momentum) and flow stability; (ii) wave dynamics (and associated eddy momentum fluxes) and the role of critical levels; the role also of edge waves propagating on a PV jump in contrast to waves propagating on a smooth background PV gradient; (iii) PV mixing as a route to zonal jet formation, independently of the direction of energy cascade; (iv) tracer mixing and transport and the role of jets as transport barriers; (v) jet evolution and mechanisms of jet merger; (vi) secondary circulations and the development of steep tracer gradients through vertical motions; alignment of tracer and PV gradients. The dynamical processes involved govern zonal structures observed in the terrestrial atmosphere and oceans as well as in the atmospheres of the gas giants. The work will impinge on several areas of climate science, including variability of the mid-latitude storm tracks, subtropical jet, and Arctic oscillation, the hydrological cycle, stratospheric ozone recovery, the dynamical coupling of the stratosphere and troposphere, and transport and mixing across the extratropical tropopause.