Prince William Sound Field Experiment

The evaluation of the NPZ model will be done by comparing model predictions to in situ observations, using profiling instruments and a small number of samples. Profiling instruments added to the CTD will measure oxygen concentrations, nitrate concentrations and in situ chlorophyll fluorescence; water samples will be collected for nutrient analysis (nitrate, phosphate and silicate), extracted chlorophyll, and CHN analysis; net samples will be taken to measure mesozooplankton concentrations.   Dissolved oxygen concentration will be measured with a SeaBird Electronics SBE43 oxygen sensor, and nitrate concentrations will be measured with a Satlantic SUNA (Submersible Underwater Nitrate Analyzer).  Chlorophyll fluorescence will be measured using a WETLabs FLNTU and compared to extracted chlorophyll samples. 

The moorings are installed on an existing oil spill response buoys (with permission from the Alyeska Pipeline Service Company) at Sawmill Bay, Esther Island, and Naked Island.  The mooring instrumentation consists of a Seabird SBE16 (pressure, temperature and conductivity) and a Wetlabs ECO FLNTUSB (fluorescence and turbidity), cage-mounted at 5 meters depth, and the sampling frequency is six times per hour.  The SBE16 also calculates and reports the salinity (PSU), chlorophyll concentration (mg/m3), and turbidity (NTU).

The moorings at Sawmill bay and Esther Island are interfaced through a Campbell Scientific (CS) CR1000 data logger mounted on the buoy in a waterproof enclosure, which also contains batteries, power management hardware and a radio modem (CS RF401).  A 20W solar panel and antenna are mounted on the buoy gantry to keep the batteries charged. Data are telemetered via radio modem from the buoy to a Starband upload center located at nearby hatcheries.  Data will be archived on a CS Loggernet server maintained by Micro Specialties Inc., and made available to AOOS via the internet (http://ambcs.org/SiteViewer.shtml ).  The Naked Island mooring will not have telemetry, and data will be recovered daily by PWSSC staff and supplied for the model runs.  The moorings will be cleaned prior to the beginning of the experiment.

Understanding and modeling ecosystem dynamics is an important component in establishing any ocean observing systems.  The nowcast-forecast modeling program has potential in advancing our understanding of how marine ecosystems respond to climate variability, and these physical and ecological predictions can be used to make better management decisions on marine living resources.  Within the observing system in PWS, the circulation nowcast-forecast system is well underway with a goal to issue predictions of physical conditions.  We are incorporating ecosystem models into the PWS ocean nowcast-forecast system based on the nested ROMS domains. 

The JPL/UCLA group will apply the Regional Ocean Modeling System (ROMS) to PWSOOS.  ROMS has been successfully used for the California coast and it represents an evolution from the family of terrain-following, vertical coordinate models.  ROMS solves the primitive equations under the hydrostatic and Boussinesq approximations. ROMS is discretized in coastline- and terrain-following curvilinear coordinates. A major goal of the observing system in PWS is to develop an operational system that delivers information on physical and biological conditions in real-time to research and application users.  This information includes raw data on environmental conditions, such as wind speed, air temperature, precipitation, ocean currents, ocean temperature, tide height, and water salinity as well as modeled forecasts of anticipated conditions. 

The goal of this observational program is to monitor the long term seasonal and interannual variability of exchange between the Gulf of Alaska and PWS, and to improve our understanding of the magnitude and frequency of water exchange and the forces driving these exchanges.  To provide this information, ADCPs are deployed in the two main entrances of PWS to obtain measurements that allow volume estimates of water transport (Figure 3).  Subsurface moorings are instrumented with one upward looking and one downward looking ADCP mounted on hydrodynamically streamlined buoys at 100 m depth (Figure 4).  Each of the subsurface moorings has three conductivity-temperature recorders (CTDs) mounted at three different depths.  They are nominally at 30 m depth, 100 m depth, and 5 m above the bottom.  These instruments periodically sample temperature and salinity and thus track changes in water properties over time. 

Hydrographic surveys with a conductivity-temperature-depth (CTD) profiler provide oceanographic information for the models to assimilate and to provide the data needed to calculate the mixed layer depth. The PWSSC SeaBird 19+ CTD measures pressure, conductivity, temperature, chlorophyll fluorescence, and turbidity.  Depth, salinity and density (sigma-t) will be derived from the measurements.  A second CTD that includes an oxygen sensor and PAR sensor is being borrowed to allow additional measurements to be collected by the smaller vessels.  A third CTD without any ancillary sensors is also being prepared for use.

Carter Ohlmann,

Art Allen

UCSB;

USCG

Five types of drifters are planned for deployment in 2009.  The PWSSC will deploy Argosphere drifters made by Metocean Data Systems and Surface Velocity Program (SVP) drifters made by Pacific Gyre.  There will be two styles of the SVPs used, one drogued at 10 meters and another at 40 meter.  The 10 meter style use Argos telemetry and the 40 meter style will have Iridium telemetry.  UCSB will deploy Pacific Gyre microstar drifters drogued at one meter.  They will also deploy the Coast Guard self locating data marking buoy (SLDMB) drifters that are also drogued at one meter.

The Argospheres are 28-cm diameter spherical buoys designed to track oil floating on the water.  Position determination is through the Argos satellite system and a GPS receiver.  For the GPS positions, an accuracy of +/- 10 m is normal.  Position updates will be obtained at 0.5-hour intervals.  A hand-held tracking unit will be used to provide location information in the field.

The SVP drifters are 38-cm diameter spherical buoys to which a drogue is attached, and they are expected to drift with the water at the depth of the center of the drogue.  The drogue is a holeysock 2.5 m in height and positioned to be centered at 10 m or 40 m.  Location determination is through the Argos satellite system and GPS receiver.  A Telonics hand held receiver will be used to help guide the recovery of the Argos telemetered units.  Real-time telemetry through the Iridium network and displayed by UCSB will be used to locate the 40 m drogued units.  

The Microstar drifters are drogued at 1 meter and use Iridium telemetry that is updated in near real time and displayed on a UCSB website (http://www.icess.ucsb.edu/drifter/realtime/index.php).  An Iridium receiver on the retrieval boat will help guide the vessel to the drifters.

The Coast Guard SLDMB drifters are drogued at one meter and tracked through the Argos telemetry system.  The drifters transmit a coded signal which will be downloaded by the Coast Guard and made available to the retrieval boat on request.

The Alyeska Tactical Oil Spill Model (ATOM) developed by ASA is a 2D and 3D trajectory and fates model that integrates spatial current data in a variety of formats and surface winds. The Alyeska users typically use tidal hydrodynamics and point observation and forecast winds.

DMAC is charged by IOOS to maintain data and metadata of all data that passes through the system.  DMAC supports the Prince William Sound 2009 field experiment by acquiring, storing, and making available the data from ten PIs and a suite of sampling platforms and models.  DMAC makes available data in formats to reduce time to inject data into the processing and visualization routines.  In general, data formats that are easily readable are: ASCII (flat, CSV), XML, HDF(4, 5, EOS), NetCDF, Grib1 and Grib2.  Files may be compressed using ZIP, Gzip, compress, and Bzip2.  Tar and compressed tar collections are also permitted. PIs may opt to send data as-is, however, the format must be well documented and understood but cannot accept proprietary data that are in formats that cannot be converted without the use of commercial tools. Metadata templates will be made available to participants so that datasets and products are appropriately identified and documented.  This is particularly useful at later stages of the research project (publications). 

HF radars were installed at the Knowles and Shelter Bay sites to measure surface currents in the central Sound.  Our goal was to be operational by 16 July to give three days to test data transmission and give Yi Chao at JPL time to “spin-up” his model and work out any issues with initialization. Each site will report telemeter averages of the radial currents to the University of Alaska Fairbanks on a hourly basis.  The data from the two sites will be combined to provide the N-S and E-W components of the surface currents.  These hourly averaged surface currents will then be made available to modelers and the field personnel. 

Nearly continuous measurements of temperature and salinity are to be collected using two autonomous underwater vehicles (AUV).   The first is a Slocum glider (Figure 6)and the second a REMUS-100 (Figure 7).  The Slocum glider is a 1.8 m long torpedo-shaped winged vehicle built by Webb Research Corporation (WRC) of East Falmouth, MA. It maneuvers through the ocean at a forward speed of 30-40 cm/s in a saw tooth gliding trajectory. The vehicle carries a range of high-quality scientific payloads including a Sea-Bird CTD and a WetLabs ECO puck for chlorophyll and optical backscatter. The primary vehicle navigation system uses an on-board GPS receiver, with backup positioning and communications provided by an Argos transmitter. Two-way communication with the vehicle is maintained by RF modem or global satellite phone service via Iridium.  The operating range using batteries is about 500 km with a maximum depth of 200 m.  The vehicle provides data when it surfaces (approximately every 3 hours), which will then be provided to the modeling groups. 

The PWS Observing System provides for many weather observations within a relatively small area. With over 20 weather stations reporting real time data within an area of 100 square km, PWS has one of the densest networks of marine and terrestrial weather observation platforms in the world. Using this data, the Alaska Experimental Forecast Facility operates two weather models for PWS that have much finer resolution than the current National Weather Service model.  Where the NWS now only has forecasts for areas of about 12 km, the models developed by AEFF allow for forecasts of areas as small as 4 km.

The Weather Research and Forecasting (WRF) system is now being primarily used for the atmospheric modeling in PWS and is compatible with NWS requirements. The WRF modeling system is intended to be a next-generation mesoscale assimilation and numerical model system.

Wave simulations in the Gulf of Alaska now generate relatively coarse scale forecasts that are of little value at the scale of PWS.  Using SWAN (Simulating WAves in the Nearshore) modeling in PWS allows for forecasts that are accurate to within 500 meters.  The SWAN model was developed in Holland and is being used in more than 50 countries to predict wave heights in nearshore and inland waters.  It has been used to accurately predict waves in the Gulf of Maine for nearly two years.

The SWAN model uses data collected from the three NDBC buoys for validation in PWS, as well as the Cape Suckling and Cape Cleare buoys to validate Gulf of Alaska waves.  The model runs every twelve hours to track and predict wave heights. In addition, new technology is being developed by the research group at TAMU that will allow for real-time wave forecasts that are nearly exact for up to six hours at a time.  Once it is fully developed, this technology can easily be added to the SWAN modeling system.

The primary goal will be to generate a GNOME trajectory forecast for the drifters using surface currents input from Yi Chao’s ROMS model for PWS and using winds from Peter Olsson’s WRF high resolution wind forecast model for PWS.   If HF RADAR surface current data becomes available, NOAA will incorporate that into our “oil spill trajectory.”  This GNOME drifter forecast will extend out to 48 hours or as far out as the wind and current models run out to.    The important element here is that the ROMS, WRF, and HF Radar information are rapidly delivered to the Seattle NOAA Hazmat office in GNOME compatible formats.