Lobe Dynamics and Transport in the Stratosphere

Lobe dynamics is a powerful, quantitative, kinematic theory of transport in 2-D Hamiltonian systems (e.g., 2-D incompressible fluid flows). We apply the theory to the large-scale isentropic circulation in the stratosphere, which is 2-D and incompressible to a good approximation. We show that it is possible to compute the underlying geometry of transport (the manifolds and lobes) for real stratospheric flows. The results explain many of the observed transport characteristics of such atmospheric properties as PV and trace constituents. We present case studies and a global analysis of the seasonal variation of mixing barriers in the stratosphere using lobe dynamics.

We suggest some changes to the standard conceptual model of stratospheric transport. It has become common to think of wavebreaking as peeling air from the "edge" of the polar vortex. That view has arisen because the properties being studied (PV or trace constituents) usually have strong gradients near the core of the jet. Lobes that form in this region lead to easily visible filaments or laminae. In fact, the mean property gradients are largely the result of mixing that occurs almost continuously throughout the surf zone (not just during large wavebreaking events). Among other things, these new methods should be very useful in planning and interpreting aircraft and balloon missions.