1. Project topic

Recommendation 11: At least two HF radar systems in the inflow area, one looking north (from the Cozumel Island area) and at least one looking across the inflow from the upper Yucatan Peninsula

2. Project title (up to 15 words)

Surface Currents in the Yucatan Channel as Measured with HF Radars

3. Total budget

4. Subaward to FFRDC(s) or UARC(s), if applicable

5. Key personnel

Project Lead:Arnoldo Valle-Levinson, University of Florida, coastal and shelf hydrodynamics

Radar Deployment, Operation and Maintenance:Xavier Flores-Vidal, Universidad Autonoma de Baja California, Instituto de Investigaciones

Oceanologicas, measurements with HF radarsIsmael Mariño-Tapia, CINVESTAV, Merida, Coastal and shelf hydrodynamics in the Yucatan PeninsulaPaulo Salles, UNAM, Sisal, Coastal processes in the Yucatan peninsulaLaura Carrillo, Shelf processes in Quintana Roo

Data Analysis:Francisco Javier Beron-Vera, University of Miami, Dynamical systems – Lagrangian Coherent StructuresMaria Josefina Olascoaga, University of Miami, Dynamical systems – Lagrangian Coherent Structures

Data Validation:Amaia Ruiz de Alegria, Universidad Autonoma de Baja California, Instituto de Investigaciones OceanologicasAlejandro, Universidad Autonoma de Campeche,

6. Project director’s or key personnel’s involvement in other applications

None

7. Project summary (up to 500 words)

This project has the objective of measuring surface currents through the Yucatan Channel, between the Caribbean Sea and the Gulf of Mexico. The Yucatan Channel extends from the northeastern end of the Yucatan peninsula to the western end of Cuba. The objective of this project will be pursued with the installation, operation and maintenance of three High-Frequency (HF) radars. Two radars will be installed in the State of Quintana Roo, Mexico, and one HF radar will be deployed in Cuba. The two radars in Quintana Roo will be ~80 km apart on the eastern coast of the Yucatan Peninsula. This arrangement is optimal, according to simulations of radar distributions in the area. The simulations indicate that a radar in Punta Norte, on the island of Cozumel, yields less than optimal coverage. The radar in Cuba will represent an important bonus for this project, as it would be essential to fulfill recommendation # 11 of the report that motivated this project. This radar will be deployed in La Bajada, ~250 km from the Yucatan peninsula, where the logistics are ideal. A radar at this location ensures complete coverage of the flow spatial structure through the Yucatan Channel.

The radar installation and operation, plus the data dissemination will be made possible by a partnership with Mexican and Cuban colleagues. The main Mexican contact will be Dr. Xavier Flores-Vidal from the Universidad Autonoma de Baja California’s Instituto de Investigaciones Oceanologicas. Xavier is in charge of covering the Mexican part of the Gulf of Mexico with HF radars to produce surface currents. Such coverage, financed by the Mexican Oil Company (PEMEX) through the Mexican Consortium for Research in the Gulf of Mexico (CIGOM), ends in the northern coast of the Yucatan peninsula. The project proposed herein will begin coverage exactly where CIGOM ends. In Cuba, the main contact will be Libertad Rodas, a researcher from the Instituto de Oceanologia de La Habana. Collaboration with Cuban scientists will be pivotal for full coverage of the strait. A crucial aspect of the collaboration with Xavier Flores-Vidal is that the HF radar network in the Mexican Gulf of Mexico already has a permit from the Mexican government through the Mexican Institute of Telecommunications. This permit allows CIGOM and this Project to use HF radio bands for oceanographic research.

Data will be disseminated in near real time through a web portal. This portal will include graphic representations of the data and files with daily packets of data, plus their corresponding metadata. In addition, the portal will have the option of requesting specific periods of data, emulating NOAA’s portal “tidesandcurrents.noaa.gov”. Data dissemination will follow protocols established by the Gulf of Mexcio Research Initiative’s Data Management Program GRIIDC through Dataset Information Forms. Data will also be disseminated through validation and analyses. Validation will consist of comparison to currents measured by moored instrumentation. Analyses will concentrate on a Lagrangian approach that incorporates Stokes drift.

8. Project description (up to 2,000 words)

The Yucatan Channel (Figure 1) is where the Loop Current is preconditioned as the Yucatan current enters the Gulf of Mexico (reference). The understanding of this preconditioning is still clouded by a scarcity of measurements with appropriate spatial resolution. This project will advance understanding of such preconditioning by complementing ongoing observations of the vertical structure of the Yucatan Channel flow. Ongoing observations consist of moored instruments deployed at discrete locations throughout the channel. These observations fall short in providing surface velocities and the spatial resolution needed to elucidate the flow structure throughout the entire channel (reference).

The main objectives of this project are to:

a) measure surface currents in the Yucatan Channel with high frequency (HF) radars;b) validate the surface current fields measured;c) use validated data to calculate coherent structures and diagnose submesoscale features;d) display measurements in near-real time on a web-portal and through the OOS for instant

visualization; ande) provide a web platform, also linked to the OOS, through which archived data will be retrievable

for any period requested.

To address these objectives we will:

1) deploy, operate and maintain 3 HF radars in the Yucatan peninsula and in western Cuba;2) deploy and retrieve bottom mounted ADCPs to validate HF radar measurements near the coast,

at water depths of ~20 m;

3) determine coherent structures in the surface flow with Lagrangian and Eulerian methods;4) calculate spectra of kinetic energy as a function of wavenumber; and5) create a web site to display and access the data being collected.

The project will consist of a team of 3 PIs from Florida (University of Florida – Arnoldo Valle-Levinson; and University of Miami – Josefina Olascoaga and Javier Beron) and 5 PIs from Mexico (Universidad Autonoma de Baja California – Xavier Flores-Vidal and Amaia Ruiz de Alegria; CINVESTAV – Ismael Mariño; Colegio de la Frontera Sur – Laura Carrillo; and University of Campeche – Alejandro Kumicki).

Deployment, operation and maintenance of HF radars

The team will deploy 3 HF radars that will cover the entire Yucatan Channel. Two HF radars will measure from the coast of Quintana Roo and one from western Cuba. Simulations of radar coverage provide strategic locations for the radars and indicate the need for measurements in Cuba (Figure 2).

This approach will require tight collaborations with Mexican colleagues. Collaborators in charge of the deployment, operation and maintenance of HF radars will be Flores, Marino and Valle-Levinson. They will also coordinate with Salles and Carrillo. Also, Mexican collaborators have working relationship with Cubans. Interactions with Cuban scientists will be done jointly with Mexican collaborators. Valle-Levinson has met with Lilliam Arraiza who has participated extensively in studies of the Yucatan Cahnnel with Mexican Researchers from CICESE. Needed to cover the entire channel.

Deployment and retrieval of bottom mounted ADCPs

Amaia and Alejandro. This activity will be carried out with instruments provided by the PIs.

Analysis of radar data collected

The surface vorticity in the Gulf of Mexico, and in particular the Yucatan Channel, exhibits a wealth of structures (Fig. x) spanning mesoscales (50–200 km) and marginally submesoscales (10–25 km). An outstanding mesoscale structure is the anticyclonic ring shed from the Loop Current in the center of the domain. The presence of marginally submesoscale structures is ubiquitous in the gulf and the channel. Note for instance the chain of von Karman-like vortices downstream of Cozumel Island. Similar vortex streets are seen downstream of the western tip of Cuba on other dates. Sequences of vorticity snapshots reveal that a mixture of seemingly coherent vortices and filaments accomplishes the transport across the channel. Satellite-derived ocean color imagery, when available (e.g. Fig. 1), reveals some of these simulated aspects of the surface circulation. With a spatial resolution of O(1) km and a temporal resolution of O(1) hr, radar-derived surface currents will provide a unique opportunity to i) investigate the dynamic relevance of vortices and filaments, and ii) further explore their occurrence down to the submesoscale range.

The analysis of radar-derived surface currents will follow two lines: detection of coherent flow structures and diagnosis of submesoscale features. The first line will use nonlinear dynamics methods designed to reveal coherent flow structures in an observed-independent (or objective) manner. Coherent structures can be revealed objectively with both Lagrangian (Haller and Beron-Vera, 2012; 2014; Haller et al., 2016) and Eulerian (Serra-Haller, 2016) methods. Eulerian methods do not require trajectory integration and thus are particularly well suited to dealing with velocity fields defined on limited spatial domains that are open, such as radar-derived flow. Lagrangian methods, in turn, enable

transport assessments. Recent application of Lagrangian methods (Beron-Vera et al., 2018), to model results, has revealed submesoscale vortices that can coherently transport fluid from the southern coast of Cuba to the Caribbean Sea and then to the Yucatan Channel. We will seek to reveal similar structures that evaluate coherent transport across the channel into the gulf. We will consider novel technology to frame this objectively as well (Karrasch, 2016; Hofherr and Karrasch, 2018). Transport from this application will be limited to two-space dimensions given the nature of the velocity data. However, robust coherent structures in such data are not expected to be confined to the ocean surface. We will seek to verify this expectation with ADCP data that will also validate radar-derived velocity. Transport across the Yucatan Channel is a critical forcing of the Loop Current. Thus, framing the transport reliably is pivotal for informing circulation models.

The second line of analysis will focus on calculations of spectra of kinetic energy (E) as a function of wavenumber (k) and on estimates of mass fluxes. These appraisals diagnose characteristics of the submesoscale surface currents as inferred from the radars. Calculations will shed light on the way that energy is transferred from mesoscales to dissipative scales, which is a subject of debate in oceanography and in particular that of the gulf (Poje et al., 2014; Beron-Vera and LaCasce, 2016). It is well known (cf., e.g., Callies and Ferrari, 2013, for the exposition that follows) that interior quasigeostrophic (QG) turbulence predicts E ~ k−3 , which is below the Rossby deformation scale (about 45 km in the gulf) with a downscale enstrophy cascade. Surface QG turbulence, by contrast, predicts E ~ k−5/3, with energy cascading downscale. Ageostrophic effects leading to frontogenesis can make E flatter (E ~ k−2 ) and, most important, reverse the direction of the energy cascade of a surface QG-like flow from upscale in the QG limit to downscale. The instability of a wintertime deep mixed layer can also make E ~ k−2 but with eddies that are confined between the ocean surface and the mixed-layer base. This distribution of E vs k is different from surface QG, where the eddies are confined toward the surface. Internal waves are another source of submesoscale variability with E ~ k−2 in the short-wave limit and flatten out at scales larger than about 10 km. We will consider relationships between the one-dimensional spectra of longitudinal and transverse components of kinetic energy (Callies and Ferrari, 2013). Also, we will consider recent wave-vortex and Helmholtz decompositions (Buhler et al., 2015; Lindborg, 2015) that help constrain the dominant mechanism of submesoscale energy production.

Web portal

9. Implementation plan (up to 2,000 words)

The implementation plan will include the following activities: deployment and operation of radars; maintenance of the radar infrastructure; data validation; and data analysis. Each one of these activities is outlined first.

Deployment and operation of radars (Xavier, Ismael, Laura, Paulo)

Maintenance of radars (Xavier, Ismael, Laura, Paulo)

Data Validation (Amaia and Alejandro)

Data Analysis (Josefina and Javier)

10. Facilities, equipment and other resources (up to 1,000 words)

11. Data management plan (up to 1,500 words). Please see the Gulf Research Program’s Data Management Policy.

12. References cited

Beron-Vera, F. J., Hadjighasem, A., Xia, Q., Olascoaga, M. J. and Haller, G. (2018a). Coherent Lagrangian swirls among submesoescale motions. Proc. Natl. Acad. Sci. USA, doi:10.1073/pnas.1701392115.

Beron-Vera, F. J. and LaCasce, J. H. (2016). Statistics of simulated and observed pair separations in the Gulf of Mexico. J. Phys. Oceanogr. 46 (7), 2183–2199.

Callies, J. and Ferrari, R. (2013). Interpreting energy and tracer spectra of upper-ocean turbulence in the submesoscale range (1–200 km). J. Phys. Oceanogr. 43, 2456–2474.

Haller, G. (2015). Lagrangian coherent structures. Ann. Rev. Fluid Mech. 47, 137–162.

Haller, G. and Beron-Vera, F. J. (2013). Coherent Lagrangian vortices: The black holes of turbulence. J. Fluid Mech. 731, R4.

Haller, G. and Beron-Vera, F. J. (2012). Geodesic theory of transport barriers in two-dimensional flows. Physica D 241, 1680–1702.

Haller, G., Hadjighasem, A., Farazmand, M. and Huhn, F. (2016). Defining coherent vortices objectively from the vorticity. J. Fluid Mech. 795, 136–173.

Hofherr, F. and Karrasch, D. (2018). Lagrangian transport through surfaces in compressible flows. SIAM Journal on Applied Dynamical Systems 17, 526–546.

Karrasch, D. (2016). Lagrangian transport through surfaces in volume-preserving flows. SIAM J. Appl. Math. 76, 11781190.

Poje, A. C., Ozgokmen, T. M., Lipphart, Jr., B., Haus, B., Ryan, E., Haza, A. C., Jacobs, G., A. Reniers, M. J. O., Novelli, G., Griffa, A., Beron-Vera, F. J., Chen, S., Hogan, P., Coelho, E., Kirwan, Jr., A., Huntley, H. and Mariano, A. (2014). The nature of surface dispersion near the Deepwater Horizon oil spill. Proc. Nat. Acad. Sci. USA 111, 12693–12698.

Serra, M. and Haller, G. (2016). Objective Eulerian coherent structures. Chaos 26, 053110.

Figure 1. A snapshot on 1 July 2013 of sea surface vorticity produced a data-assimilative simulation of the GoM based on the U.S. Navy Coastal Ocean Model (NCOM) at 1-km resolution (for details cf., e.g., Beron-Vera and LaCasce, 2016). Indicated is a domain including the Yucatan Channel where HFR-derived surface currents will be available for analysis. The inset shows a MODIS (Moderate Resolution Imaging Spectroradiometer) derived chlorophyll-a concentration map on 18 February 2014.