Atmosphere Ocean Science Colloquium

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Lower-Tropospheric Eddy Momentum Fluxes in Idealized Models and Reanalysis Data

Speaker: Nicholas Lutsko, MIT

Location: Warren Weaver Hall 1302

Date: Wednesday, February 21, 2018, 3:30 p.m.

Synopsis:

Abstract: In Earth’s atmosphere eddy momentum fluxes (EMFs) are largest in the upper troposphere, but EMFs in the lower troposphere, although modest in amplitude, have an intriguing structure. To document this structure, the EMFs in the lower tropospheres of a two-layer quasigeostrophic model, a primitive equation model, and the Southern Hemisphere of a reanalysis dataset are investigated. The lower-tropospheric EMFs are very similar in the cores of the jets in both models and the reanalysis data, with EMF divergence (opposing the upper-tropospheric convergence) due to relatively long waves with slow eastward phase speeds and EMF divergence (as in the upper troposphere) due to shorter waves with faster eastward phase speeds. As the two-layer model is able to capture the EMF divergence by long waves, a qualitative picture of the underlying dynamics is proposed that relies on the negative potential vorticity gradient in the lower layer of the model. Finally, scenarios in which lower tropospheric EMFs can become larger relative to upper tropospheric EMFs are discussed, including configurations with reduced surface friction and with altered potential vorticity gradients in each layer.