OS53A-01 13:40h
Using the Gulf of Maine Ocean Observing System for Preliminary Characterization of the Seasonal and Interannual Variability of the Gulf of Maine Coastal Current System
The Gulf of Maine Ocean Observing System (GoMOOS) has been established as a sustained, comprehensive, real-time, observing system that includes an array of moored physical and optical sensors, shore based long-range CODAR for surface current mapping, numerical circulation and wave modeling, satellite observations, and web delivery of data and data products. The GoMOOS moored array presently consists of 10 solar-powered, automated buoy systems that telemeter data hourly via cellular phone, iridium, or GOES satellite transmitters. The buoys are deployed within the major bays and estuaries of the Gulf, along the Continental Shelf from Nova Scotia to Massachusetts, in the Jordan Basin, and in the Northeast Channel, which represents the only pathway of exchange with the North Atlantic at depths exceeding 100 m. The first buoys were deployed in the summer of 2001, and the system is now beginning to provide time series long enough to provide an indication of seasonal and interannual variability of the flow and physical properties of the complex and little understood Gulf of Maine Coastal Current system. Preliminary analysis suggests a strong seasonal cycle and significant interannual variability that combine to produce previously unknown reversals of the typical southwestward flow of the coastal current.
OS53A-02 INVITED 14:10h
The GoMOOS Nowcast/Forecast System
A circulation nowcast/forecast system was developed for the Gulf of Maine as an integral component of the Gulf of Maine Ocean Observing System (GoMOOS) technical program. The system has been used daily to produce short-term forecasts of the circulation and physical properties in the Gulf of Maine. One of the expectations is that the system can provide consistent SST to fill in AVHRR gaps and eventually produce reliable 3D temperature and flow fields for fishery applications. We first present the framework of the nowcast/forecast system, which includes an algorithm to assimilate satellite derived SST. Comparisons between the modeled and the observed temperature and velocity (both in situ and satellite derived) are discussed. In general, the assimilation algorithm is stable and produces SST patterns mimicking the AVHRR. Seasonal variations in temperature and the coastal current are well reproduced. Correlation between the modeled and observed fields in the synoptic band is summarized for individual buoys in monthly bins. Comparisons of spectral characteristics suggest that the system successfully captures the wind-driven events, whereas it is less satisfactory in simulating high frequency variability in summer.
OS53A-03 14:40h
Adjoint Data Assimilative Model Study of the Gulf of Maine Coastal Circulation
Data assimilation (DA) in the coastal ocean can be divided into category of either sequential estimation or variational adjoint. Sequential estimation techniques blend models with observations directly, using a variety of algorithms with which the relative weights of data and model are calculated. Variational adjoint techniques infer model control variables (e.g. parameters, forcing functions, boundary conditions, etc.) that minimize the misfit between observations and predictions. The advantage of the latter techniques over the former is that the resulting model solutions obey model dynamics. In this study, the Gulf of Maine coastal circulation and the material property transport are investigated with the Dartmouth variational adjoint DA modeling system, which assimilates in-situ data via inversion for the unknown sea level elevation at open boundaries. In-situ observations include ADCP currents and coastal sea levels. The adjoint DA model skill is evaluated by the inter-comparisons between modeled and observed drifter trajectories. Excellent model skill is found, demonstrating the utility and effectiveness of the adjoint DA modeling system in bridging in-situ observations with coastal ocean model simulations. Implications of the adjoint DA strategy on the emergent coastal ocean observing systems are discussed.
OS53A-04 14:55h
What Must be Observed to Diagnose & Model the Circulation of the Gulf of Maine on Monthly and Seasonal Timescales?
The Gulf of Maine is, at depth, a semi-enclosed sea off the coast of New England and the Canadian Maritimes. Its circulation is driven by large-scale density gradients formed by winter-time water mass transformations, buoyancy forcing from estuarine and from the deep ocean, and the winds. An analysis of the sources of variability in the six-month mean transport across the central Gulf of Maine finds that that most of variability is caused by large scale hydrographic variability (approximately 50%), with smaller variations forced by changes in transport into the basin from the Scotian Shelf (about 35%) and by winds (15%). Most numerical models of the region are not able to capture the dominant source of variability in the model, changes in the density field. This failure is not due to flaws in the model, but to inadequate observations of the hydrographic structure of the gulf, and of its inflows. Because this data is not routinely obtained, the effects of large scale climate patterns such as the North-Atlantic Oscillation are not reflected in the models. Assimilation of surface temperature does not solve this problem; due to the importance of salinity in the Gulf of Maine and the increase of temperature with depth, surface temperature do not uniquely specify conditions at depth, even in the winter. A surprisingly modest observational program would be adequate to constrain the models, and allow them to capture the dominant source of circulation variability in the Gulf of Maine. The minimum necessary requirements of such an observational program are defined. It is suggested that a similar analysis should be prepared for other coasts where the internal density field is an important factor in driving the circulations on timescales of months or longer, as has been found to be true on the Mid-Atlantic bight and elsewhere.
OS53A-05 15:10h
Nowcast Skill of the New York Harbor Observation and Prediction System
The New York Harbor Observing and Prediction System (NYHOPS) provides nowcasts and forecasts of surface/bottom currents, salinities and temperatures, waves, and water level, for the New York /New Jersey Harbor Estuary including the waters eastward to the continental shelf break of the New York Bight and Long Island Sound in one contiguous fashion. The system has been in operation since the end of 2003. The operations, from the acquisition of oceanographic and meteorological data to the delivery of marine nowcast/forecast information to a wide group of users are now automated. The observational system consists of shore-based and moored platforms at strategic locations inside the harbor, and at four sites along the coast of New Jersey, most of them equipped with both oceanographic and meteorological sensors. Ferry-based conductivity and temperature sensors are also part of the observational network. The Stevens web site imports and serves all available real-time data (www.stevens.edu/maritimeforecast). The prediction system is based on the Princeton Ocean Model and is designed to provide accurate and comprehensive realizations of meteorological and oceanographic conditions. Forcing is based on NOAA/NWS/NCEP's Mesoscale Eta 12km atmospheric forecast model, USGS river flow gauges, NOAA/NOS water level stations and effluents from 110 wastewater treatment plants. The water level at all the open boundary locations is specified by a combination of a reconstructed tidal record using tidal harmonics and by persisting the low frequency observed water level variation at Atlantic City, NJ. Temperature and salinity at the open boundaries are taken from climatology. The system is designed to automatically transfer forcing data and perform forecasts once daily, at 0000 hours. In order to firmly establish the credibility and robustness of NYHOPS, a skill assessment protocol continually runs in the background. This protocol has been implemented to quantify the accuracy of the system products. The first step in the assessment process, to be reported here, involves the nowcast portion of the forecast system. Point measurements and spatial maps of observed water levels, temperature and salinity at ten spatially distributed locations have been used to determine the skill of the system nowcasts. While the analysis indicates that the system skill is quite reasonable, regions have been identified where higher model resolution and better observational coverage are needed. A data assimilation scheme suitable for the highly variable NYHOPS environment is being developed and implemented. The scheme is being guided by the distribution of model errors.
OS53A-06 15:25h
Early Scientific Results From the East Florida Shelf Information System(EFSIS)
As part of the SEA-COOS (Southeast Atlantic-Coastal Ocean Observing System) Program, the Princeton Ocean Model (POM) has been implemented on a curvilinear grid (ca. 2 to 10 km) and in sigma coordinates (25 levels, with concentrations nearsurface and nearbottom), for the East Florida Shelf (EFS), including all of the Straits of Florida, in both a barotropic and a baroclinic mode, which are called EFS-POM. The forcing includes upstream open boundary conditions for the Florida Current in the Gulf of Mexico and downstream open boundary conditions at ca. 32N, climatological monthly surface heating/cooling, synoptic wind-forcing from a NCEP mesoscale numerical weather prediction model (Eta), and eight major tidal constituents. EFS-POM hindcast simulations are used for process and sensitivity studies. EFS-POM is also used as the core of a real-time nowcast/forecast system, called the East Florida Shelf Information System (EFSIS). The observations and observing system elements existing prior to SEA-COOS are used for EFS-POM model validation and EFSIS nowcast/forecast verification, respectively, while awaiting the emergence of new and additional observing system elements as part of SEA-COOS. In the interim, EFS-POM and EFSIS have opened possibilities for examining long-standing scientific issues; e.g., the dynamics of Florida Current frontal meanders and cut-off eddies, internal tides, and cross-shelf exchange.
http://efsis.rsmas.miami.edu