Collaborative Research: CMG: Anisotropic Atmospheric Dynamics Across a Wide Range of Scales

University Of Washington, Seattle WA

Investigators

Abstract

Our focus is on the extratropical atmosphere, with special emphasis on the dynamics in highly anisotropic backgrounds, such as is the case near the tropopause. Theoretically, the wave dynamics for a highly-anisotropic background atmosphere has been much less studied than for the homogeneous and isotropic case. Yet it is intrinsic in the atmospheric mixing process that nearly-stepwise environments form in the atmosphere. Furthermore, when the anisotropy is in potential vorticity (PV), the impact on large-scale wave dynamics occurs at leading order, since Rossby wave propagation depends on the presence of PV gradients. The proposed work focuses on the dynamical impact of background anisotropy on cyclone organization, frontogenesis, gravity wave emission and the overall atmospheric energy spectrum. The unifying theme is that it is crucial to study the whole spectrum of scales simultaneously, from energy injection at synoptic scales down to dissipation at frontal scales, because nonlinear interactions affect all scales in between. Hence, the low-frequency variability and predictability of the planetary scales depend significantly, through nonlinear cascades, on the dissipative process at the meso- and frontal scales. A new class of dynamical models take specific advantage of jumps in potential vorticity at a tropopause discontinuity. Exact- and high-resolution solutions provide a testbed to assess the adequacy of current operational models in resolving the dynamical anisotropies. Recognition of the highly-anisotropic nature of tropospheric dynamics redirects previous mathematical efforts on isotropic and homogeneous turbulence to atmospherically more relevant anisotropic problems. The weather over North America is greatly influenced by the pattern of winds near the tropopause, a level of sharp change in the atmospheric conditions found at an altitude of roughly 10 km. Because operational weather models often do not have sufficient resolution to accurately describe the atmospheric motions at these heights, our ability to understand, and thus forecast, the weather and climate throughout the atmosphere is diminished. An example of one of the many issues which will be investigated is why many of the current climate models show a biased error of colder temperatures near the tropopause. The scope of this work seeks to unify the dynamics of the atmosphere from the largest continental-scale (low pressure) cells, through their subsequent collapse to intermediate-scale storm fronts, and the generation of yet smaller-scale (gravity wave) turbulence. The primary focus of new theoretical progress is to account for the important contributions of the tropopause in the evolution of weather patterns. The proposed research lies at the intersection between mathematics and atmospheric science, which is now possible through the synthesis of the investigators' recent advances in tropopause modeling and new results in the numerical computation of the statistics of atmospheric turbulence. The anticipated impact of further understanding of how energy in the lower atmosphere evolves over the full range of thousands down to tens of kilometers would be the elucidation of currently under-resolved features of weather prediction and climate models.