The Dynamics of Westerly Jets

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The dynamics of westerly jetsWesterly jets are ubiquitous in the circulations of atmospheres and oceans on rotating planets. In Earth's atmosphere westerly jets organize the weather and they mediate the transport of important trace gases. Lee will investigate the dynamical mechanisms that determine the structure of jets and their responses to climate change. The research will focus on three aspects of jets: They are associated with "staircases" in the distributions of conserved quantities, most notably the potential vorticity. There are flat regions of conserved quantities - the "steps" - between jets. This implies that mixing is effective in these regions. The centers of jets feature sharp gradients in conserved quantities, implying that jets are barriers to mixing. Lee will generate an inventory of model runs with different parameter settings and with different jet configurations. These will be analyzed to determine the mechanisms that control mixing and thus set the structures of the staircasesJets are self-maintaining and self-sharpening. This leads to the possibility that there can be more than one possible arrangement of jets for a given set of climate parameters. As the climate changes, the circulation may jump from one configuration to another. Lee will develop a theory for the fluid-dynamical fluxes that maintain the jets. Predictions of multiple equilibria from this theory will be tested in numerical models.Jets in the Southern Hemisphere, within hurricanes, and in idealized simulations of turbulence on a rotating sphere, all exhibit spiral structures. Lee will use her catalog of simulations, along with additional simulations with tropical heating, to test hypotheses about the conditions that permit spiral jets to exist as stable structures.Broader impacts include training graduate students and incorporating research results in a course in climate dynamics taught by the PI. She also plans to involve undergraduates in her research.