March 17, 2018
The Unbalanced Dynamics of Deep Jet Streaks Above Developing Surface Inverted Troughs
Prof. Michael L. Kaplan (Desert Research Institute)
2018년 3월 21일 (수) 11:00
We will employ high resolution observations and numerical simulations to show how the coupling between low-level and mid-tropospheric largely diabatically-forced frontogenesis results in complex upper-tropospheric jet adjustments in two seemingly radically different phenomena, i.e., 1) a major coastal cyclone and 2) downslope Diablo wind event along the East Coast of North America and West Coast of North America, respectively. As a surface inverted trough develops due to both adiabatic and diabatic forcing in both case studies, the exit regions of the upper-tropospheric jets that are initially not highly accelerative become extremely unbalanced as Lagrangian Rossby numbers >> .5 develop. This occurs in a region that should be decelerating for near thermal wind balance in either straight or curved flows, respectively. As the jet exit regions, one with weak and another with substantial curvature, accelerate, surface mesoscale inverted troughing amplifies in what appears to be a nonlinear feedback cycle in which accelerations aloft produce mass adjustments that strengthen the surface systems which in turn enhance the upper-level exit region accelerations. Extraordinary mesoscale vortices and precipitation swaths develop in the coastal storm case study only observable with GOES-16, visible, and ASCAT scatterometer satellite data, surface observations, and also in numerical simulations. Anticyclonic shear vortices develop in the Diablo wind case study where mesonet surface and wind profilers are compared to simulations. A theory will be presented for how such a breakdown in quasi-geostrophic and quasi-gradient wind balance occurs.