A profiling float array to assess 3D flow at a front
Abstract
Rationale. Submesoscale activity (with scales <1 day and <10 km) is enhanced where horizontalgradients are strong on the peripheries of mesoscale fronts and eddies (with scales of severaldays and 100 km). Vertical velocity (w) is of order 10 m day~1 and transports properties acrossthe mixed layer base. However, w is challenging to observe amidst an ambient internal wavefieldwith w variability of order 1 cm s~1. Therefore, high spatial and temporal resolution near the frontare needed to understand the 3D flow connecting the surface ocean to the interior.Goals. This DURIP award will add 10 SOLO-II profiling floats equipped with Conductivity-Temperature-Depth instruments (CTD) and chlorophyll (chl) fluorometers to an existing array of8 floats for the Coherent Lagrangian Pathways from the Surface Ocean to Interior (CALYPSO)Departmental Research Initiative. Repeated rapidly-profiling float array deployments and shipbasedsurveys will measure the 3D circulation (w in particular) at a front across a range of scales: at mesoscale by assimilating the float array and ship survey data in a multiscale, numericalmodel and by using a simple diagnostic, quasigeostrophic dynamical model; in submesoscale streamers by tracking tracers, such as salinity (S), spice (T variability alongisopycnals), chl, and potential vorticity; and due to high-frequency internal waves, low-frequency internal tides, and near-inertial internalwaves from each float~s w and density oscillations.Plan. Repeated meso- and submesoscale-resolving surveys with an Underway CTD (UCTD)will follow an array of 18 SOLO-II floats at a mesoscale front between Atlantic and Mediterraneanwaters. A mesoscale UCTD survey and satellite temperature will identify the front. The float arraywill be deployed in a box pattern at a submesoscale streamer along the front. Each float obtainsT, S, and chl fluorescence profiles to 200 m every 100 minutes, which is about 400 profiles over a30-day cruise. A finer resolution submesoscale UCTD survey will follow the float array at the frontwith cross-front sections of 20 km completed every 6 hours with T and S profiles every 4 minutesor 250 m in the horizontal. Once the array strains too much in the alongfront direction and losescross-front coverage, the whole suite of observations will be relocated and repeated every 1~2 days.Anticipated results. To better resolve intense, localized downwelling through the boundarylayer into the interior at the front targeted for CALYPSO, this project will increase the array from8 to 18 rapidly-profiling SOLO-II floats. Repeated deployments of the float array will: (a) measurew directly and by tracking tracers, (b) gather dense hydrographic data to resolve 3D submesoscaleprocesses, (c) aid local prediction via data assimilation, and (d) identify the process(es) producingw, which is enhanced at submesoscales on the edges of fronts and eddies. Graduate students willparticipate in multi-facteted research cruises, learn UCTD survey techniques, and use autonomousinstrumentation. The data from the float array and UCTD will be made available to a future graduatestudent as a component of a PhD program.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jun 13, 2019
- Source ID
- N000141912381
Entities
People
- S. Johnston
Organizations
- Office of Naval Research
- United States Navy
- University of California, San Diego