National Weather Center Colloquium

Quasi-geostrophic diagnosis of the influence of vorticity advection on the development of upper level jet-front systems

Dr. Jonathan Martin

Department of Atmospheric and Oceanic Sciences, University of Wisconsin-Madison

04 October 2016, 4:00 PM

National Weather Center, Room 1313
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

A partition of the geostrophic vorticity into shear and curvature components is employed to consider the influence of differential vorticity advection on the development of upper level jet-front systems in northwesterly flow. The analysis reveals that negative geostrophic shear vorticity advection by the thermal wind, inextricably coincident with regions of geostrophic cold air advection in cyclonic shear, forces subsidence that is distributed in narrow, quasi-linear, frontal-scale bands aligned along the warm edge of the upper baroclinic zone. This component of the quasi-geostrophic (QG) subsidence makes the largest contribution to upper frontogenetical tilting. Since QG omega forced by geostrophic vorticity advection is of the shearwise variety, the analysis shows that the traditional emphasis on the role of laterally displaced transverse circulations is an incomplete description of the upper frontogenetic tilting that arises in such environments. In fact, the results suggest that Mudrick’s emphasis on negative vorticity advection increasing with height combined with Shapiro’s insight regarding the lateral displacement of frontogenetic transverse circulations offers the most comprehensive way to conceptualize the forcings that promote rapid upper level jet-front development in regions of geostrophic cold air advection in cyclonic shear

Speaker bio

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