Enhancement in vertical fluxes at a front by mesoscale-submesoscale coupling
MetadataShow full item record
Oceanic frontal instabilities are of importance for the vertical exchange of properties in the ocean. Submesoscale, O(1) Rossby number, dynamics are particularly relevant for inducing the vertical (and lateral) flux of buoyancy and tracers in the mixed layer, but how these couple with the stratified pycnocline is less clear. Observations show surface fronts often persist beneath the mixed layer. Here we use idealized, three-dimensional model simulations to show how surface fronts that extend deeper into the pycnocline invoke enhanced vertical fluxes through the coupling of submesoscale and mesoscale instabilities. We contrast simulations in which the front is restricted to the mixed layer with those in which it extends deeper. For the deeper fronts, we examine the effect of density stratification on the vertical coupling. Our results show deep fronts can dynamically couple the mixed layer and pycnocline on time scales that increase with the peak stratification beneath the mixed layer. Eddies in the interior generate skew fluxes of buoyancy and tracer oriented along isopycnals, thus providing an adiabatic pathway for the interior to interact with the mixed layer at fronts. The vertical enhancement of tracer fluxes through the mesoscale-submesoscale coupling described here is thus relevant to the vertical supply of nutrients for phytoplankton in the ocean. A further implication for wind-forced fronts is that the vertical structure of the stream function characterizing the exchange between the interior and the mixed layer exhibits significant qualitative differences compared to a linear combination of existing parameterizations of submesoscale eddies in the mixed layer and mesoscale eddies in the interior. The discrepancies are most severe within the mixed layer suggesting a potential role for Ekman-layer dynamics absent in existing submesoscale parameterizations.
Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 119 (2014): 8495–8511, doi:10.1002/2014JC010211.
Suggested CitationArticle: Ramachandran, Sanjiv, Tandon, Amit, Mahadevan, Amala, "Enhancement in vertical fluxes at a front by mesoscale-submesoscale coupling", Journal of Geophysical Research: Oceans 119 (2014): 8495–8511, DOI:10.1002/2014JC010211, https://hdl.handle.net/1912/7169
Showing items related by title, author, creator and subject.
Spiro Jaeger, Gualtiero; Mahadevan, Amala (American Association for the Advancement of Science, 2018-02-28)Salinity, rather than temperature, is the leading influence on density in some regions of the world’s upper oceans. In the Bay of Bengal, heavy monsoonal rains and runoff generate strong salinity gradients that define ...
Spall, Michael A. (American Meteorological Society, 2007-08-01)The influences of strong gradients in sea surface temperature on near-surface cross-front winds are explored in a series of idealized numerical modeling experiments. The atmospheric model is the Naval Research Laboratory ...
Duda, Timothy F. (IEEE, 2004-01)A computational case study of coupled-mode 400-Hz acoustic propagation over the distance 27 km on the continental shelf is presented. The mode coupling reported here is caused by lateral gradients of sound-speed within ...