Atmosphere Ocean Science Friday Seminar

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A few balanced models for frontogenesis

Speaker: Ryan Shìjié Dù, CAOS

Location: Warren Weaver Hall 1314

Date: Friday, March 24, 2023, 4 p.m.

Synopsis:

Frontogenesis is a crucial process active in the submesoscale ocean that creates asymmetries in vertical vorticity (\zeta) and velocity (w). Capturing the correct frontogenesis behavior in an evolving model depends on incorporating the ageostrophic vertical restratifying circulation in the advection of momentum and buoyancy. In this informal pedagogical style talk, we will first look at what frontogenesis and the associated ageostrophic circulation looks like in the classic 2D (in y-z) frontogenesis situation using the primitive equations system. In comparison, quasi-geostrophy (QG), a balanced model, does not use the ageostrophic circulation for advection. Therefore it misses crucial qualitative features. However, balanced models are attractive because they filter out the waves, which are mostly irrevalvant for coherent advection of tracers. We thus look at two balanced models of intermediate complexity: semi-geostrophic model and QG+1. We see that they could diagnose the ageostrophic circulation from a single prognostic variable; and more crucially, they use the ageostrophic circulation in the advection of that prognostic variable. As a final example we will move to "3D" and show some SQG(+1) simulations, where qualitative features of frontogenesis are captured by SQG+1 while not by regular SQG.

After all this, if there is ample time and audience interest, we could talk about QG+1 in the shallow water system, or do a quick showcase of the Dedalus solver, which is a versatile tool that solved most of the PDEs shown in this talk.