Miguel Canals

Development of an Operational Nearshore Wave Forecast System for Puerto Rico and the U.S. Virgin Islands

Abstract Anselmi-Molina, C.M.; Canals, M.; Morell, J.; Gonzalez, J.; Capella, J., and Mercado, A, 2012. Development of an operational nearshore wave forecast system for Puerto Rico and the U.S. Virgin Islands. An assessment of coastal information needs in Puerto Rico and the U.S. Virgin Islands identified real-time wave data and improved wave forecasts as essential for supporting nearshore operations in the region. After deployment of operational wave-measuring buoys off the north, south, east, and west coasts of the Puerto Rico–Virgin Islands archipelago, the Simulating WAves Nearshore (SWAN) model was implemented for the region. The main purpose of its implementation is to provide for data needs in areas not well represented by the buoys as well as for filling the nearshore gap not addressed by the operational National Oceanic and Atmospheric Administration (NOAA) Multigrid WAVEWATCH III (NMWWIII) model forecast. The model consists of a nesting between WWIII and SWAN where oceanic boundary conditions in the form of two-dimensional wave spectra are supplied by the NMWWIII model. In this study we present results from two model-validation experiments under varying physical-forcing scenarios, one in which swell waves dominate (Rincón) and one in which wind swell dominates (Ponce). The results show good agreement between the observed and the modeled wave field for the Rincón domain, on Puerto Ricos northwest coast and facing the Atlantic Ocean, which indicates that appropriate boundary conditions are being obtained from NMWWIII and propagated correctly by SWAN into nearshore areas. Results for the Ponce domain, in Puerto Ricos southern coast and facing the Caribbean Sea, highlight the need for more accurate high-resolution wind products to properly resolve the wind-driven wave field dominating this area.

Potential Structuring Forces on a Shelf Edge Upper Mesophotic Coral Ecosystem in the US Virgin Islands

Mesophotic coral ecosystems are extensive light-dependent habitats that typically form between 30 – 150 m depth in the tropical oceans. The forces that structure the benthic communities in these ecosystems are poorly understood but this is rapidly changing with technological advances in technical diving and remote observation that allow large-scale scientific investigation. Recent observations of southeastern Puerto Rican Shelf of the US Virgin Islands have shown that this Caribbean mesophotic coral ecosystem has distinct habitats within the same depth ranges and across small horizontal distances (25%. High-resolution bathymetric mapping of the shelf edge revealed a topographically distinct semi-continuous 71 km-long relict barrier reef bank system. The purpose of this study was to characterize the pattern of mesophotic habitat development of the shelf edge and use this data to narrow the potential long-term and large-scale structuring forces of this mesophotic coral ecosystem. We hypothesized from limited preliminary observations that the shelf edge coral cover was limited in shallower portions of the bank and on the seaward orientation. Through stratified random surveys we found that increasing depth and decreasing wave driven benthic orbital velocities were positively related to coral abundance on the shelf edge. In addition, low coral cover habitats of the shelf edge contrasted strongly with adjacent on shelf banks surveyed previously in the same depth range, which had relatively high coral cover (>30%). Predictions of benthic orbital velocities during major storms suggested that mechanical disturbance combined with low rates of coral recovery as a possible mechanism structuring the patterns of coral cover, and these factors could be targets of future research.

Optimizing and validating high-frequency radar surface current measurements in the Mona Passage

Mapping of the ocean surface velocity field of the eastern Mona Passage is important due to the fact that the Passage is a major shipping lane to the Panama Canal, as well as a key route for illegal traffic into the United States. As such, two high-frequency radar (HFR) stations have been emplaced along the west coast of Puerto Rico to allow such mapping and to explore its performance in vessel detection and tracking. Coverage of the south-eastern quadrant of the Passage is provided, extending west to Mona Island and north to Rincon. Results were posted online hourly in near real-time, and to optimize these results, antenna beam patterns were measured twice and corrections applied to the resulting radial returns. Validation measurements were undertaken in order to assess the basic capability of the Mona Passage HFR array to measure surface currents in this tropical environment, including repeated deployment of Lagrangian drifters, as well as an acoustic Doppler current profiler, and compared with modeled tidal currents. The experimental measures demonstrated good agreement to both in situ and modeled data, thus lending confidence to the area-wide surface current maps generated by this system. Demonstrating that these are in large part the product of the surrounding environment, repeated measurements showed limited temporal variability of antenna distortion patterns. Comparing experimental Lagrangian trajectories and a numerical particle tracking algorithm showed mixed results, achieving better agreement during periods of low intrahour variability in current direction than during periods of rapid tidal reversal.

Expanding the Caribbean Coastal Ocean Observing System into the nearshore region

After five years of continued development, the Caribbean Coastal Ocean Observing System (CariCOOS) has reached a major turning point regarding the nature of its ocean observing platforms and numerical modeling efforts. During the design stage of CariCOOS, stakeholder consultations highlighted the need for operational instrumented buoy platforms to provide data on winds, waves, currents and water quality. This led to the deployment of three full data buoys off the coasts of San Juan, Ponce and the United States Virgin Islands (USVI), a directional Datawell Waverider buoy in the Mona Passage, an array of shore based High Frequency Radar antennas for surface current mapping in the Mona Passage, and a network of 13 hurricane-hardened coastal meteorological stations. In addition, a suite of numerical models of winds and waves are currently operational for the region and continuously validated with our observational assets. Although stakeholders have expressed satisfaction with the regional-scale understanding obtained with CariCOOS models and ocean observing assets, recent consultations have highlighted the need for sector focused products to be developed at smaller scales targeting selected ports, highly visited and yet often hazardous tourist beaches, marine protected areas and other locations. Efforts in the current developmental stage are aimed in this direction; our mission consists of a combination of maintaining our suite of buoys, weather stations and numerical models with the development of new observing platforms and models to satisfy the nearshore-specific needs of our stakeholders. Despite being closer to shore, however, observing and predicting the complexity of the wind, wave and current patterns in the nearshore region requires highly specialized sensors and very high resolution numerical models. Stakeholder-driven efforts focused in the nearshore region currently underway at Cari-COOS include the development of a high-resolution jetski-based bathymetric surveying and side scan sonar system, a real-time surfzone currents and beach hazards warning system, and the implementation of a three-dimensional baroclinic circulation model for important ports and nearshore regions. In this paper we describe these and other new initiatives in detail and explain the design and development process.

Characterization of mesoscale eddies and detection of submesoscale eddies derived from satellite imagery and HF radar off the coast of southwestern Puerto Rico

Coherent sub-mesoscale features such as spiral eddies are known to be ubiquitous in the worlds oceans. Yet, due to their complex geometry, they are often difficult to characterize. Sub-mesoscale ocean dynamics with characteristic dimensions on the order of kilometers have been found to play a major role in upper ocean stirring and mixing. Manifestations of these structures all around the Caribbean Coastal Ocean Observing System (CariCOOS) region have been found to influence coastal and oceanic waters impacting upper ocean hydrodynamics and biogeochemistry. CariCOOS modeling efforts in the region have yet to produce reliable forecasts of near coastal ocean dynamics. Owing to the growing demand for coastal ocean models yielding accurate forecast, CariCOOS has proposed the operational deployment of a 1/100 degree Regional Ocean Modelling System (ROMS) nested in the 1/36 degree resolution Navy Coastal Ocean Model (AMSEAS) which itself is nested in the Hybrid Coordinate Ocean Model (HYCOM), a global 1/12 degree data-assimilative hybrid isopycnal-sigma-pressure coordinates forecast system. Although the progression has been consistent, results urge the identification of possible skill performance constraints and phenomenological limitations. An inward approach has been adopted to assess the output of parent models versus observations from satellites, drifters, gliders, sea level measurements, buoys, and HF radars. Part of the adopted approach focuses on the characterization and daily-based detection of sub-mesoscale ocean dynamic features. CariCOOS observational assets and satellite imagery brings forth the ability to characterize quasi-permanent (or periodical) phenomena close to the coast. Thanks to the recent expansion of the CariCOOS High-Frequency (HF) radar network consisting of two long range (5 MHz) antennas on the southwestern coast of Puerto Rico, unprecedented spatial and temporal coverage will be available for this two-part study. For the first part, historical satellite altimetry, as well as other discrete observations, will be used to characterize the quasi-geostrophic mesoscale eddy signatures near the southwestern coast of Puerto Rico. On the second part, satellite imagery and HF radar capabilities to capture sub-mesoscale eddy phenomena will be assessed with the objective of implementing coherent structure detection algorithm based on a vector geometry method. A comparison between detected sub-mesoscale eddies with HF radars and available operational models (AMSEAS & HYCOM) will be qualitatively assessed.

Coupled global wind and tide driven coastal water levels and currents in Puerto Rico and the U.S. Virgin Islands

A high-resolution, unstructured finite element hydrodynamic model was implemented with a focus on the regional dynamics of Puerto Rico and the U.S. Virgin Islands. Spatial resolution of the unstructured mesh is at least 100 m along all the coastlines of Puerto Rico and the U.S. Virgin Islands and reaches a resolution finer than 50 m in selected areas with complex coastlines. The model is forced with a global tide solution (TPXO8) and global atmospheric forcing provided by the NCEP Climate Forecast System (CFSv2) model. Inclusion of the global atmospheric forcing resulted in an increase of the model accuracy in modeling water levels. Atmospheric forcing was a necessary condition for the generation of currents and high frequency water level oscillations such as seiches. This newly developed hydrodynamic model for Puerto Rico and the U.S. Virgin Islands has applications for maritime users as the inclusion of global winds results in more accurate water levels as well as coastal currents, which were not able to be generated previously without the inclusion of atmospheric forcing. In addition, the generation of high frequency oscillations that have been observed in measurements allows for further study of local scale dynamics that have not been able to be previously replicated by numerical models in this region.

Development of novel instrumented Lagrangian drifters to probe the internal structure of breaking surface waves

Understanding wave breaking phenomena, especially the post-breaking turbulent dynamics, is a challenging problem that still lacks satisfactory understanding. The present study is concerned with the development of novel instrumentation adapted to obtain Lagrangian field measurements of essential variables that are intimately related to the physics of wave breaking. The subsequent turbulence generated upon the breaking point evolves into a complex hydrodynamic flow abounded by intense short-lived 3D vortex structures and the presence of air cavities and bubbles. In this article we describe the design, development and testing of miniature Lagrangian drifters equipped with 3-axis accelerometers as well as a High Definiton (HD) video camera. Two types of drifters were developed, one specifically designed to measure acceleration spectra and a larger version capable of measuring acceleration and bubble size distribution. Both versions are equipped with onboard flash memory units to record local quantities of the aforementioned variables. We have conducted lab experiments and also initial field observations in plunging waves with heights of 2 meters breaking over a coral reef. We have observed acceleration signatures which are believed to be the result of drifter entrainment into coherent vortex structures. We expect that after further development of these drifters, and the resulting field observations will likely yield substantial information about the Lagrangian frequency spectra of acceleration, time-dependent bubble size spectra and ultimately energy dissipation, giving us a new perspective on the dynamics of breaking waves. Furthermore, the device also shows promise for advancing our knowledge of the 3D distribution of vortex structures in the surf zone through the reconstruction of particles trajectories via dead reckoning. The authors are not aware of any previous study that reports this type of field measurements.

An Overview of the Caribbean Coastal Ocean Observing System and Data Measurements during Hurricane Irene

The Caribbean Coastal Ocean Observing System (CariCOOS) is the observing arm of the Caribbean Regional Association for Integrated Coastal Ocean Observing (CaRA). This effort, funded by the NOAA Integrated Ocean Observing System (IOOS) office, is one of eleven coastal observing systems and regional associations which along with federal agencies constitute the national coastal component of the US Integrated Ocean Observing System. CariCOOS observational assets provide a real time network to monitor wind, waves and currents and consists of four ocean data buoys and thirteen hurricane-hardened land based weather stations, distributed along the coastal areas of Puerto Rico and the US Virgin Islands. In this paper we present a detailed description of our observational infrastructure and provide analysis of wind and wave observations during the passage of Hurricane Irene over Puerto Rico and the US Virgin Islands during August 21-22, 2011.

Design and Development of an Instrumented Drifter for Lagrangian Measurements of Inertial Particle Dynamics in Breaking Waves

Understanding wave breaking phenomena is a challenging problem that still lacks satisfactory understanding. The present paper is concerned with the development of novel instrumentation adapted to obtain Lagrangian field measurements of essential variables that are intimately related to the physics of wave breaking. These miniature (6.4 cm) Lagrangian drifters are equipped with micro-electromechanical systems (MEMS) inertial measurement units (IMUs) that record acceleration, angular rate and magnetic field data at rapid sampling rates (100 Hz). Using a quaternion-based sensor fusion algorithm, multiple sensor data is filtered in postprocessing procedures to obtain the best possible estimates of particle orientation and acceleration. We show that the developed instrumentation is able to collect meaningful data of inertial particle dynamics in a controlled laboratory flow, where the instrumented particle trajectories are benchmarked against an analytical representation of the flow. Results indicate that dead reckoning errors grow quadratically in time and that for a typical wave overturning event trajectory estimates are expected to remain within a radius r <; 0.7 m with a 95% confidence level. Also, special attention is given to gyroscope reliability during the actual wave breaking process through an empirical evaluation of gyroscope performance in plunging waves. Angular rate measurements from two separate gyroscopes mounted inside the same drifter show high agreement leading to the conclusion that gyroscope errors arising from wave induced vibrations are negligible. Finally, we report on the first ever Lagrangian field observations of inertial particle dynamics in plunging waves with heights on the order of 2 m. We expect that further development of the technology and analysis tools presented herein could revolutionize our understanding of the hydrodynamics of breaking waves.

A nearshore breaker prediction system for Puerto Rico and the United States Virgin Islands in support of beach safety and drowning prevention

More than half of Puerto Ricos population does not know how to swim and, usually, there are no lifeguards at all on Puerto Ricos beaches. In addition, Puerto Rico has a strongly seasonal cycle in wave heights, and marine conditions can change very quickly as intense swell events arrive. Intense surfzone currents caused by wave-induced pressure gradients pose a threat to beachgoers at hundreds of beaches throughout the region. These are the main facts that account for an average of 25 beach drownings per year. The present study describes the development and implementation of a nearshore breaker prediction system for the PR/USVI region. A high-resolution operational wave model, the CariCOOS Nearshore Wave Model, has been developed in order to adequately resolve wave transformation across the PR/USVI archipelago. The performance of the model for offshore and coastal locations was validated using wave observations from four CariCOOS buoys, with very good results. After ensuring that the model performed satisfactorily at the CariCOOS buoy locations, a field validation experiment was conducted to evaluate model performance in the nearshore region and within the surfzone. A field experiment involving bottom-mounted wave sensors was carried out at the Tres Palmas Marine Reserve in Rincn, Puerto Rico in order to evaluate the performance of one of the high-resolution nested grids. The model was shown to be able to resolve wave transformation with very good results up to just seaward of the surf zone. This shows that the model is able to resolve wave transformation including shoaling, diffraction and refraction at this location. After model validation, a simple method was developed to estimate nearshore breaker heights based on the model output at strategically placed virtual buoys. Each virtual buoy was located just outside the surfzone for each beach, so that the available wave energy flux just seaward of the surfzone could be estimated from the SWAN output. Based on this available wave energy flux, an estimate of the maximum expected breaker heights was obtained using a semi-empirical formulation for breaker heights. While a rigorous validation of breaker heights is very difficult due to the complexity of measuring breaker heights in the surfzone, the breaker height predictions were compared to visually estimated breaker heights at a beach in Rincόn, Puerto Rico. While the results of this comparison should be taken with caution, given the subjective nature of visually estimated breaker heights, the results suggest that in general the breaker model can estimate the arrival of high breaker events at this beach with reasonable accuracy. Following this methodology for estimating the range of expected breaker heights, a custom webpage was created in which the range of expected breaker heights as a function of time are provided via a nearshore virtual buoy system at 84 beaches throughout the PR/USVI archipelago.