Theory, modeling and observations of 3D transport processes in flows with fronts

Larry Pratt and Irina Rypina

WOODS HOLE OCEANOGRAPHIC INSTITUTION

We propose a combination of filed measurements, theory and modeling, all aimed at contributing to CALYPSO through experimental design, Lagrangian observations, and interpretation of results. A large part of CALYPSO will focus on understanding subduction processes near a western Mediterranean front, and investigating how physical and biological properties are transported from the surface down below the mixed layer. Fronts are often established by a larger scale convergence, but the sinking process might be dominated by the smaller-scale ageostrophic secondary circulations that are established in the vicinity of the front. A number of different frontogenetic and instability processes may contribute to the 3d transport, and our observations and analysis should help to disentangle the relevant processes and to identify which are dominant. We specifically propose novel measurements with drifters drouged at a variety of depths in order to observe the horizontal component associated with subduction of fluid under the front, and to infer the vertical motions. We also plan to release environmentally friendly dye as part of a US trial experiment in order to directly observe the lateral and vertical transport. On the theoretical/modeling side, we want to examine vertical motion associated with spatially-growing meanders of the front, as spatial/convective instability seems important for the Almeria-Oran front. We also want to employ a model of the Alboran Sea (based on the MITgcm) that our graduate student has developed. This will allow us to test our idealized stability calculations in a more realistic setting. We will collaborate closely with Ruth Musgrave on analyzing her non-hydrostatic, ultra-high-resolution model output, focusing on investigation the role of small-scale motions in the resulting 3d processes near a front. Finally, since the transport of surface properties down to depth is an essentially Lagrangian problem, we will apply state-of-the-art analysis from a recent MURI project (OCEAN 3D+1) to both model output and data in order to identify the Lagrangian skeleton of the ageostrophic circulations that cause subduction. In this way, we hope to create a transition between OCEAN 3D+1 and CALYPSO.

You can access the relevant Webpage for CALYPSO here.

You can access the relevant Webpage for the CALYPSO 2019 experiment here.