PAOC Colloquium: Ryan Abernathey (LDEO)
Monday, April 23, 2018 at 12:00pm to 1:00pm
Building 54, 923
21 AMES ST, Cambridge, MA 02139
Quantifying Transport by Coherent Lagrangian Vortices
Ocean mesoscale eddies contribute significantly to the transport of heat and other tracers in the ocean. However, there is an ongoing debate about how exactly eddies cause transport: is it mostly through stirring on the periphery of the eddy, or is it by “trapping” and transporting fluid inside the eddy core? In this study, we employ recently developed tools from dynamical systems theory to make a comprehensive census of coherent Lagrangian mesoscale eddies in the global ocean. This is the largest-scale Lagrangian eddy census performed to date, with over 100,000 structures identified. The statistics of Lagrangian eddy size and propagation speed are broadly similar to previous eddy tracking results based on sea-surface height anomalies (e.g. Chelton et al. 2011). However, the material nature of our Lagrangian eddies enables a precise quantification of their role in transport. We define a "coherent diffusivity" diagnostic based on the relative meridional dispersion of Lagrangian particles contained within material eddies and show that the the transport due to these structures accounts for less than 1% of the total turbulent meridional transport. We conclude that most of the ocean "eddy flux" is due to incoherent stirring, rather than the bulk translation of coherent structures. Implications for the parameterization of eddy fluxes are discussed.
About the Speaker
My primary research interests are:
- The role of ocean circulation (particularly the Southern Ocean) in the climate system
- Dynamics of the Antarctic Circumpolar Current and its overturning circulation
Mixing and transport by ocean eddies
About this Series
The PAOC Colloquium is a weekly interdisciplinary seminar series that brings together the whole PAOC community. Seminar topics include all research concerning the physics, chemistry, and biology of the atmospheres, oceans and climate, but also talks about e.g. societal impacts of climatic processes. The seminars generally take place on Monday from 12-1pm. Lunch is provided to encourage students and post-docs to meet with the speaker. Besides the seminar and lunch, individual meetings with professors, post-docs, and students are arranged.
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