An ongoing investigation of the dynamics of jet streaks in the extratropical upper troposphere provides evidence for interpreting these features in a balanced framework in terms of the superposition of tropopause-based mesoscale coherent vortices (length scale ~500 km) with the enhanced potential vorticity (PV) gradients constituting the extratropical tropopause. Recent studies also have indicated that such vortices may correspond to so-called "short-wave troughs," and as such may be important as upper-level precursor disturbances to synoptic-scale surface cyclogenesis. These investigations suggest that balanced mesoscale vortices not only may be common features of the upper troposphere, but also, through interactions with the synoptic- and planetary-scale flow, may be integral to the dynamics of extratropical weather systems. The primary goal of the current study is to identify issues relevant to the dynamics of these vortices, which will then be addressed in future analytical and numerical investigations.
Several case studies will be presented that describe the evolving three-dimensional structure of observed vortices and their environment, with particular attention devoted to the jet streaks and short-wave troughs associated with these features. These studies will employ model-derived datasets, available from operational numerical weather prediction centres, on scales ranging from regional to global; it is suggested that such a multiscale perspective is necessary, since the interactions between meso-, synoptic-, and planetary-scale flows are likely to be significant for the features of interest. The results of the case studies support the interpretation of jet streaks as the balanced response to the interaction of a coherent vortex with a larger-scale background flow. Such an interpretation leads to the speculation that jet-streak life cycles may be understood more readily in terms of the life cycles of coherent vortices, suggesting a shift in dynamical emphasis from the former to the latter. Of particular interest is whether the observations provide insight into the dynamics of the origin and subsequent evolution of these coherent vortices. In this regard, it appears appropriate to draw from the theories and phenomenological models of turbulence (both quasigeostrophic and rotating stratified) to interpret the observational findings. In addition, since the interactions resulting in jet streaks typically involve the enhanced PV gradients of the tropopause, additional perspectives provided by studies of the stratospheric polar vortex, such as the process of PV gradient intensification, also may aid in the interpretation of the observations.
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12th Conference on Atmospheric and Oceanic Fluid Dynamics