Josh Kohut

Slocum Gliders: Robust and Ready

Buoyancy driven Slocum Gliders were a vision of Douglas Webb, which Henry Stommel championed in a futuristic vision published in 1989. Slocum Gliders have transitioned from a concept to a technology serving basic research and environmental stewardship. The long duration and low operating costs of Gliders allow them to anchor spatial time series. Large distances, over 600 km, can be covered using a single set of alkaline batteries. Since the initial tests, a wide range of physical and optical sensors have been integrated into the Glider allowing measurements of temperature, salinity, depth averaged currents, surface currents, fluorescence, apparent and inherent optical properties. A command/control center, entitled Dockserver, has been developed that allows users to fly fleets of gliders simultaneously in multiple places around the world via the Internet. Over the last 2.5 years, Rutgers Gliders have logged 27 056 kilometers, and flown 1357 days at sea. Gliders call into the automated Glider Command Center at the Rutgers campus via satellite phone to provide a status update, download data, and receive new mission commands. The ability to operate Gliders for extended periods of time are making them the central in situ technology for the evolving ocean observatories. Off shore New Jersey Gliders have occupied a cross shelf transect and have documented the annual variability in shelf wide stratification on the Mid-Atlantic Bight and the role of storms in sediment resuspension. The sustained data permits scientists to gather regional data critical to addressing if, and how, the oceans are changing.

Improving HF Radar Surface Current Measurements with Measured Antenna Beam Patterns

A high-frequency (HF) radar system is deployed on the New Jersey continental shelf as part of a coastal ocean observatory. The system includes two remote transmit‐receive sites in Brant Beach and Brigantine, New Jersey, and a central processing site in Tuckerton, New Jersey. The system uses radio waves scattered off the ocean to measure the radial velocity, range, and bearing of the scattering surface. Calculation of the bearing for HF radar systems depends on the actual beam pattern of the receive antennas. A series of antenna beam pattern measurements conducted on the New Jersey system shows that these patterns are often distorted when an antenna is deployed in the field. Tests indicate that the local environment, not system hardware, causes the most significant distortion of the pattern from the theoretical shape. Correlation with an in situ acoustic Doppler current profiler (ADCP) indicates that the beam pattern distortion can bias the bearing estimate. It is shown that this bias can be removed if the measured beam patterns are used to estimate the bearing.

Seasonal evolution of hydrographic fields in the central Middle Atlantic Bight from glider observations

[1] The first sustained glider observations in the Middle Atlantic Bight are used to describe the seasonal evolution of hydrographic fields off New Jersey. Near-surface temperatures respond to the seasonal cycle of surface heating, while waters at depth are primarily influenced by advection of cold waters from the north in the cold-pool during spring/summer, and warming due to mixing during fall. The thermocline thickness increases in the offshore direction. Salinity presents seasonal variability due to river discharge and wind variations, with low-salinity waters spanning ∼100 km across the shelf from May to September in a ∼10 m thick surface layer. Stratification intensifies from April/May to late summer, especially within 80 km from the coast. The pycnocline deepens in the water column during late summer, while the passage of storms during fall rapidly reduces the stratification. The glider high-resolution observations allowed for unprecedented detailed characterization of the spatial scales of variability.

Characterizing Observed Environmental Variability With HF Doppler Radar Surface Current Mappers and Acoustic Doppler Current Profilers: Environmental Variability in the Coastal Ocean

A network of high-frequency (HF) radars is deployed along the New Jersey coast providing synoptic current maps across the entire shelf. These data serve a variety of user groups from scientific research to Coast Guard search and rescue. In addition, model forecasts have been shown to improve with surface current assimilation. In all applications, there is a need for better definitions and assessment of the measurement uncertainty. During a summer coastal predictive skill experiment in 2001, an array of in situ current profilers was deployed near two HF radar sites, one long-range and one standard-range system. Comparison statistics were calculated between different vertical bins on the same current profiler, between different current profilers, and between the current profilers and the different HF radars. The velocity difference in the vertical and horizontal directions were then characterized using the observed root-mean-square (rms) differences. We further focused on two cases, one with relatively high vertical variability, and the second with relatively low vertical variability. Observed differences between the top bin of the current profiler and the HF radar were influenced by both system accuracy and the environment. Using the in situ current profilers, the environmental variability over scales based on the HF radar sampling was quantified. HF radar comparisons with the current profilers were on the same order as the observed environmental difference over the same scales, indicating that the environment has a significant influence on the observed differences. Velocity variability in the vertical and horizontal directions both contribute to these differences. When the potential effects of the vertical variability could be minimized, the remaining difference between the current profiler and the HF radar was similar to the measured horizontal velocity difference (~2.5 cm/s) and below the resolution of the raw radial data at the time of the deployment

Seasonal climatology of wind-driven circulation on the New Jersey Shelf

[1] The spatial structure of the mean and seasonal surface circulation in the central region of the Mid‐Atlantic Bight (New Jersey Shelf) are characterized using 6 years of CODAR long‐range HF radar data (2002–2007). The mean surface flow over the New Jersey Shelf is 2–12 cm/s down shelf and offshore to the south. The detided root‐mean‐square (RMS) velocity variability ranges from 11 to 20 cm/s. The variability is on the order of the mean current offshore and several times that of the mean current nearshore. The Hudson Shelf Valley and the shelf break act as dynamical boundaries that define the New Jersey Shelf. The surface flow on the New Jersey Shelf depends on topography, seasonal stratification, and wind forcing. The flow is in the approximate direction of the wind during the unstratified season and more to the right of the wind during the stratified season. During the stratified summer season, the dominant along‐shore upwelling favorable winds from the SW drive cross‐shelf offshore flow. During the unstratified/well‐mixed winter season, the dominant cross‐shore NW winds drive cross‐shelf offshore flows. During the transition seasons of spring and autumn, along‐shore NE winds, often associated with storm events, drive energetic down‐shelf, along‐shelf flows. The surface transport pathways are either cross‐shelf dominated during summer and winter or along‐shelf dominated during the transition seasons. The residence time of surface Lagrangian drifters on the New Jersey Shelf ranged from 1 to 7 weeks with summer and autumn showing faster transport than winter and spring.

The Integrated Ocean Observing System High-Frequency Radar Network: Status and Local, Regional, and National Applications

A national high-frequency radar network has been created over the past 20 years that provides hourly 2-D ocean surface current velocity fields in near real time from a few km offshore out to approximately 200 km. This preoperational network is made up of more than 100 radars from 30 different institutions. The Integrated Ocean Observing System efforts have supported the standards-based ingest and delivery of these velocity fields to a number of applications such as coastal search and rescue, oil spill response, water quality monitoring, and safe and efficient marine navigation. Thus, regardless of the operating institution or location of the radar systems, emergency response managers, and other users, can rely on a common source and means of obtaining and using the data. Details of the history, the physics, and the application of high-frequency radar are discussed with successes of the integrated network highlighted.

Operation and application of a regional high-frequency radar network in the Mid-Atlantic Bight

The Mid-Atlantic Regional Coastal Ocean Observing System (MARCOOS) High-Frequency Radar Network, which comprises 13 long-range sites, 2 medium-range sites, and 12 standard-range sites, is operated as part of the Integrated Ocean Observing System. This regional implementation of the network has been operational for 2 years and has matured to the point where the radars provide consistent coverage from Cape Cod to Cape Hatteras. A concerted effort was made in the MARCOOS project to increase the resiliency of the radar stations from the elements, power issues, and other issues that can disable the hardware of the system. The quality control and assurance activities in the Mid-Atlantic Bight have been guided by the needs of the Coast Guard Search and Rescue Office. As of May 2009, these quality-controlled MARCOOS High-Frequency Radar totals are being served through the Coast Guards Environmental Data Server to the Coast Guard Search and Rescue Optimal Planning System. In addition to the service to U.S. Coast Guard Search and Rescue Operations, this data supports water quality, physical oceanographic, and fisheries research throughout the Mid-Atlantic Bight.

Dispersal of the Hudson River Plume in the New York Bight: Synthesis of Observational and Numerical Studies During LaTTE

characterized the variability of the Hudson River discharge and identified several freshwater transport pathways that lead to cross-shelf mixing of the Hudson plume. The plumes variability is comprised of several different outflow configurations that are related to wind forcing, river discharge, and shelf circulation. The modes are characterized by coastal current formation and unsteady bulge recirculation. Coastal currents are favored during low-discharge conditions and downwelling winds, and represent a rapid downshelf transport pathway. Bulge formation is favored during high-discharge conditions and upwelling winds. The bulge is characterized by clockwise rotating fluid and results in freshwater transport that is to the left of the outflow and opposed to classical coastal current theory. Upwelling winds augment this eastward flow and rapidly drive the freshwater along the Long Island coast. Upwelling winds also favor a midshelf transport pathway that advects fluid from the bulge region rapidly across the shelf on the inshore side of the Hudson Shelf Valley. A clockwise bulgelike recirculation also occurs along the New Jersey coast, to the south of the river mouth, and is characterized by an offshore veering of the coastal current. Modeling results indicate that the coastal transport pathways dominate during the winter months while the midshelf transport pathway dominates during summer months. Finally, because the time scales of biogeochemical transformations in the plume range from hours to weeks or longer, the details of both the near-and far-field plume dynamics play a central role in the fate of material transported from terrestrial to marine ecosystems.

Glider observations and modeling of sediment transport in Hurricane Sandy

Regional sediment resuspension and transport are examined as Hurricane Sandy made landfall on the Mid-Atlantic Bight (MAB) in October 2012. A Teledyne-Webb Slocum glider, equipped with a Nortek Aquadopp current profiler, was deployed on the continental shelf ahead of the storm, and is used to validate sediment transport routines coupled to the Regional Ocean Modeling System (ROMS). The glider was deployed on 25 October, 5 days before Sandy made landfall in southern New Jersey (NJ) and flew along the 40 m isobath south of the Hudson Shelf Valley. We used optical and acoustic backscatter to compare with two modeled size classes along the glider track, 0.1 and 0.4 mm sand, respectively. Observations and modeling revealed full water column resuspension for both size classes for over 24 h during peak waves and currents, with transport oriented along-shelf toward the southwest. Regional model predictions showed over 3 cm of sediment eroded on the northern portion of the NJ shelf where waves and currents were the highest. As the storm passed and winds reversed from onshore to offshore on the southern portion of the domain waves and subsequently orbital velocities necessary for resuspension were reduced leading to over 3 cm of deposition across the entire shelf, just north of Delaware Bay. This study highlights the utility of gliders as a new asset in support of the development and verification of regional sediment resuspension and transport models, particularly during large tropical and extratropical cyclones when in situ data sets are not readily available.

Evaluation of two algorithms for a network of coastal HF radars in the Mid-Atlantic Bight

The National High Frequency (HF) Surface Current Mapping Radar Network is being developed as a backbone system within the U.S. Integrated Ocean Observing System. This paper focuses on the application of HF radar-derived surface current maps to U.S. Coast Guard Search and Rescue operations along the Mid-Atlantic coast of the USA. In that context, we evaluated two algorithms used to combine maps of radial currents into a single map of total vector currents. In situ data provided by seven drifter deployments and four bottom-mounted current meters were used to (1) evaluate the well-established unweighted least squares (UWLS) and the more recently adapted optimal interpolation (OI) algorithms and (2) quantify the sensitivity of the OI algorithm to varying decorrelation scales and error thresholds. Results with both algorithms were shown to depend on the location within the HF radar data footprint. The comparisons near the center of the HF radar coverage showed no significant difference between the two algorithms. The most significant distinction between the two was seen in the drifter trajectories. With these simulations, the weighting of radial velocities by distance in the OI implementation was very effective at reducing both the distance between the actual drifter and the cluster of simulated particles as well as the scale of the search area that encompasses them. In this study, the OI further reduced the already improved UWLS-based search areas by an additional factor of 2. The results also indicated that the OI output was relatively insensitive to the varying decorrelation scales and error thresholds tested.