Coherent Structures in the Extratropical Atmosphere: A Dynamical Interpretation of Jet Streaks

The objective of this prospectus is to motivate and formulate a research plan to investigate the dynamics of jet streaks, building on recent idealised analytical and numerical work conducted on this topic using barotropic models (Cunningham 1997, hereafter C97). The hypothesis to be investigated is that jet streaks often are associated with the superposition of mesoscale coherent vortices of both monopolar and dipolar nature on a larger-scale westerly background ow. Motivated by observations and guided by theoretical perspectives applicable to coherent structures, geophysical turbulence, and baroclinic-wave life cycles, a hierarchy of idealised dynamical models (nondivergent barotropic; shallow-water; strati ed quasigeostrophic and primitive equation), formulated for f and -plane geometries, will be employed to investigate the following general aspects of jet-streak structure and dynamics: (i) the three-dimensional structure of jet streaks and their representation in terms of coherent structures; (ii) the motion and evolution of jet streaks as represented by coherent structures, both in isolation and in the presence of background ows representative of characteristic synopticand planetary-scale environments in the atmosphere; and (iii) the nature of dynamical balance in jet streaks. Speci c details of this investigation and relevant issues and questions to be addressed regarding these general aspects will be discussed herein. Furthermore, issues requiring investigation that will not be addressed directly by this study, such as the origin of jet streaks and of the associated coherent structures, will be discussed brie y. It is suggested that this study will serve simultaneously to address the limitations of C97 and to provide the next level of generality beyond that study in a hierarchical dynamical explanation of jet streaks.