OS41A-1198
Predictability of Kuroshio Current Intrusions into the East China Sea.
We use a combination of observations and two fine resolution ocean models to understand the predictability of Kuroshio Current intrusions onto the East China Sea Shelf. The simulations were evaluated for their potential to provide lateral boundary conditions to a real-time regional prediction system whose function is to depict both physical and acoustical properties over the North Taiwan Shelf. Volume transport across the East Taiwan Channel (ETC) as measured by the WOCE PCM-1 moored current meter array was correlated with sea surface height anomaly for the period September 1994 through May 1996. Low transport events were found to be correlated with low sea level off the east coast of Taiwan and surface drifting buoys passing through the ETC were found to encroach the 200 m isobath to the north of Taiwan more often during low rather than during high transport (high sea level) events. We use two models to predict these intrusions: one is the 0.1° global Parallel Ocean Program (POP) and the other is 1/12° global Hybrid Coordinate Ocean Model (HYCOM). The latter model includes the Navy Coupled Ocean Data Assimilation (NCODA) system. Both models are forced with synoptic atmospheric fluxes. Lagrangian particles are released off the southeast coast of Taiwan during high and low ETC transport events. Both models show intrusive behavior during low transport events however those in HYCOM are more realistic in terms of extent and location. Analysis of the equivalent non-assimilative HYCOM simulation will be presented to better understand the role of data assimilation and the vertical coordinate system on the characteristics of these intrusions.
OS41A-1199
Modeling the Interaction of Loop Current Dynamics with Coastal Processes on the Northern Gulf of Mexico
The coastal and shelf areas in the Northern Gulf of Mexico (NGoM) are subject to intense interactions with offshore flows, namely the Loop Current (LC), the Loop Current warm core eddies (LCEs) and the Loop Current frontal eddies (LCFEs). A nesting modeling approach is thus necessary to represent coastal to offshore interactions. Furthermore, the realistic representation of the extension of the Loop Current (and hence its proximity to the NGoM), as well as the position and size of the eddies approaching the shelf-break require boundary conditions from a data assimilative regional model. The Hybrid Coordinate Ocean Model (HYCOM) was employed in the development of a high resolution (1/50 deg resolution) model of the NGoM region, hence called the NGoM-HYCOM model. It is nested within the regional, data assimilative Gulf of Mexico GoM-HYCOM model (1/25 deg resolution), which employs GODAE products for boundary conditions. The study objective is to simulate the NGoM coastal flows and in particular the coastal to offshore interactions. Attention is given to the Mississippi River plume dynamics and the interactions with both the shelf circulation and offshore flows.The numerical simulations employ high frequency, realistic atmospheric forcing (COAMPS 27km). Numerical results demonstrate the impact of LC features over the shelf-break circulation in the vicinity of the Mississippi River Delta. The proximity of LCEs to the shelf-break feeds eastward surface jets that follow the rim of the DeSoto Canyon, and may transport nutrient rich, river derived waters to deeper areas of the Canyon. These surface jets may turn westward when LCFEs impinge over the slope. Cross-shore flows are also generated during this process, which also work as a transport mechanism of river-derived waters to offshore regions. The impact of those features decreases over the shelf and close to the coast, where wind-driven dynamics prevail. Along-shore coastal flows are observed over the shelf in the presence of eastward/westward winds, which is followed by set-up and set-down of sea surface height and also along-shelf transport of Mississippi River waters.
OS41A-1200
Examination of Physical Processes Influencing Coastal Circulation over the Inner Scotian Shelf using a Five-Level Nested-Grid Ocean Circulation Model
A multiply nested-grid ocean circulation modeling system was developed for coastal waters of the Inner Scotian Shelf (ISS) by coupling a limited-area coastal circulation model to an operational shelf circulation model known as Dalcoast. The nested-grid system has five relocatable, dynamically-downscaling five sub- components. The outermost sub-component of the system has a coarse horizontal resolution of (1/12)o for simulating storm surges and two-dimensional barotropic shelf waves over the eastern Canadian shelf (ECS) from Labrador Shelf to the Gulf of Maine, and the innermost sub-component has a fine horizontal resolution of about ~180 m for simulating three-dimensional circulation and hydrographic distributions over Lunenburg Bay of Nova Scotia in the default setup. The nested-grid system is driven by meteorological and astronomical forcing. The meteorological forcing includes sea level air pressures, wind stress and surface heat/freshwater fluxes converted from the 3 hourly weather forecasts produced by the Meteorological Service of Canada. The astronomical forcing is the tidal sea levels and depth-mean currents produced by WebTide based on pre-calculated harmonic constants of five major tidal constitutes over the ECS. In this study, the nested-grid system is used to investigate main physical processes affecting the three-dimensional (3D) circulation and hydrographic distributions over the ISS in June and July 2006. Model results demonstrate that the coastal circulation and hydrographic distributions over the study region are affected significantly by tides, local wind forcing, remotely generated coastal waves during the study period.
OS41A-1201
Near real-time 4DVAR Assimilation and Ensemble Prediction with GODAE Products
We explore the solutions obtained by assimilating separate observational products made available by the Global Ocean Data Assimilation Experiment (GODAE) and other sources in a near real-time incremental, four-dimensional variational data assimilation and ensemble prediction system within the Intra-Americas Sea. We present the results and methods for the assimilation and generating the initial forecast error and ensemble spread during the assimilation procedure. When compared to post-processed science quality observations, the state estimates suffer from our reliance on real-time, quick-look satellite observations of the ocean surface. Despite this problem, the ensemble forecast estimate is often superior to observational persistence.
OS41A-1202
DEVELOPMENT AND APPLICATION OF AN ENKF DATA ASSIMILATION SYSTEM BASED ON MARS-3D: ACHIEVEMENTS AND FUTURE PLANS
This study deals with the development of time-evolving multivariate data assimilation of satellite derived sea surface temperature (SST) and T-S profiles over the continental shelf. This work is being conducted in the framework of the PREVIMER project (www.previmer.org), whose primary objective is the development of an operational forecasting system for the coastal environment along the French coastlines. This presentation discloses a general overview of the project over the period 2008-2012, but it will focus on the results obtained during the initial phase of the project with respect to sequential data assimilation of satellite derived sea surface temperature (SST). This SST data assimilation in the free surface primitive equation model MARS-3D uses Ensemble Kalman Filter (EnKF): it is tested over the Bay of Biscay and the Gulf of Lion. Skill assessment of the data assimilation system is analysed over April-July 2006, a period for which independent temperature and salinity vertical profiles are available over the Biscayan continental shelf. Preliminary results of a similar data assimilation experiment for the Gulf of Lion are also discussed over April-July 2005. The spatial and temporal structure of forecast errors is investigated using an ensemble modelling approach (Monte-Carlo). Multivariate ensemble forecast statistics associated with distinct model error sources (wind forcing, model parameters) are shown to be neither homogeneous over the continental shelf nor stationary. In this large space dynamical system, localization and filtering of small-sized ensemble correlations is needed to provide consistent results through EnKF analysis. The localization used is proportional to the bottom depth. Statistical analysis of the ensemble forecast reliability also reveals that SST forecast errors over the Biscayan continental shelf are season-dependant: during spring, they are mainly governed by the fraction of light lost by scattering and absorption (extinction coefficient) which is due to the Loire and Gironde rivers plumes; during summer, they are dominated by the uncertainties over wind stress and ocean mixing. The potential of sequential data assimilation of SST to improve T-S model predictions over the shelf is investigated, using independent in-situ temperature and salinity profiles over the spring and summer test periods. The data assimilation system provides significant error reduction compared to the non assimilative one, for temperature and salinity over the shelf Finally, the efficiency of combined parameter and state estimation to reduce the SST model forecast biases over the shelf is shown over April-May, a period for which the forecast error is mainly governed by the extinction coefficient.
OS41A-1203
Multivariate Multi-Data Assimilation System in Regional Model With High Resolution
Mercator Ocean has developed a regional North East Shelf forecasting system over the North East Atlantic,
taking advantage of the recent developments in NEMO (1/12). This regional forecasting system uses
boundary conditions from the operational real-time Mercator Ocean North Atlantic high resolution system
(1/12). The assimilation component of the Mercator Ocean system, is based on a reduced-order Kalman filter
(the SEEK or Singular Extended Evolutive Kalman filter). The error statistics are represented in a sub-space
spanned by a small number of dominant 3D error directions. The data assimilation system allows to
constrain the model in a multivariate way with Sea Surface Temperature (RTG-SST), together with all
available satellite Sea Level Anomalies, and with in situ observations from the CORIOLIS database, including
ARGO floats temperature and salinity measurements.At last, we used PALM coupler which provides a
general structure for a modular implementation of a data assimilation system, and makes easier the changes
in the analysis algorithm.
We will confront the results obtained with the regional forecast system (1/12) with IAU (Incremental Analysis
Updates) to the ones obtained with Mercator Ocean North Atlantic high resolution system (1/12).
http://www.mercator-ocean.fr
OS41A-1204
Investigation of Northeastern North America Coastal Circulation Using a Nested Regional Circulation Hindcast Model
A regional coastal circulation model was used to hindcast circulation over the middle Atlantic Bight (MAB) and Gulf of Maine (GOM) shelf from November 2003 to June 2008. Realistic atmospheric forcing, tidal harmonics and real-time river runoff data were used to drive the hindcast. In addition, this regional model was nested inside the data assimilative global HYCOM, which provides dynamically consistent and numerically accurate its initial and open boundary conditions. Model hindcast solutions were gauged against in situ observations, including coastal sea levels, satellite altimeter sea surface height, mooring observed temperature and salinity time series, glider hydrographic transects, and long term means of depth-averaged current analysis. Such data/model comparisons show the nested regional model is skillful in capturing major regional shelf circulation variability, lending confidence for using 4-year of time and space continuous hindcast fields (January 2004-December 2007) to depict shelf- wide circulation dynamics, along- and cross-shelf transport and the associated momentum balances. Model hindcast solutions confirm the existence of the equatorward shelf circulation with gradually decreased alongshore transport from north to south. Mean alongshelf current is characterized by a strong shelf-break jet, whereas the cross-shelf current is characterized by complex convergence and divergence on the shelf. Mean cross-shelf transports were estimated along 200-m isobath. Momentum balance analyses further nonlinear advection, stress and diffusion term all contribute to the ageostrophic circulation in the along- isobath directions, whereas in the across-isobath direction, the nonlinear advection is predominate. Our nested regional circulation model was also coupled with a 11-component ecosystem model. Some preliminary bio-physical modeling result will also be presented.
OS41A-1205
Validation of a Down-Scaled Coastal Ocean Model for Prince William Sound, Alaska
The Princeton Ocean Model (POM) has been implemented and run for several years with mesoscale- resolution in Prince William Sound (PWS), a small (ca.100 km diameter by 400 m deep), two-strait, semi- enclosed sea influenced by highly variable alongshore flows on the external continental shelf. Realistic bottom topography, tidal forcing, and synoptic atmospheric forcing were used together with climatological open boundary conditions to drive PWS-POM. Then, nearly four years ago, the daily updates of three-hourly nowcast/forecast fields of the mesoscale-admitting, data-assimilative Global-Navy Coastal Ocean Model (NCOM) became available to provide synoptic open boundary conditions as an alternative for driving EPWS- POM, where EPWS is an extended PWS domain that includes the external shelf. Hence, a form of downscaling from the ca. 12 km resolution of Global-NCOM to the ca.1 km resolution of EPWS-POM was established. Datasets from coastal tide gauges and moored vertical current profilers are used to form validation metrics for comparison of the performance of EPWS-POM using synoptic versus climatological open boundary conditions.
OS41A-1206
Modeling analysis of the separated jet in the Coastal Transition Zone off Oregon
The three-dimensional time-dependent flow over the shelf and in the Coastal Transition Zone (CTZ) off Oregon has been studied with a circulation model based on the Regional Oceanic Modeling System (ROMS). The model has 3-km resolution and is nested in the 9-km resolution NCOM California Current System model (provided by I. Shulman et al., NRL). The spring-summer 2002 was chosen as a study period, when the GLOBEC field program in Eastern Pacific took place. The observations to be compared with the model results included velocity measurements from mid-shelf moorings, surface velocity measurements from high- frequency (HF) radars in the area of Cape Blanco (43N), surface drifter trajectories, satellite SST maps, and alongtrack SSH altimetry. The comparisons have shown that the model reproduces qualitatively correctly the time-averaged flow structure and variability over the period studied, including the energetic processes associated with separation of the coastal jet off Cape Blanco. Lagrangian analysis of surface particle trajectories has provided information on how the CTZ offshore flow is grouped in filaments and on the location of particular separation zones. The vertical structure of the jet separating from Cape Blanco and flowing westward is strongly affected by the wind blowing southward, e. g. perpendicular to the jet. The jet advects cold, dense upwelled water offshore at the surface. The presence to the north of relatively warmer surface water associated with the offshore eddy field makes the vertical jet structure asymmetric. As a result, the geostrophic component of the flow is weaker on the south and stronger on the north side of the jet. The ageostrophic current component associated with Ekman transport also contributes to the jet asymmetry. The surface current vorticity, negative on the north side of the jet, provides a non-linear addition to the Ekman transport and makes it larger there, compared to that on the south side. The non-linear effect on the Ekman transport results in alternating convergence and divergence zones across the jet.
OS41A-1207
Frontal Structures and Eddy Variability in a 1 km Resolution Model of the Oregon Shelf Flows
Using the Regional Ocean Modeling System (ROMS), a 1-km horizontal resolution ocean model of circulation on the Oregon shelf has been developed, nested in the 3-km resolution ROMS model of the coastal transitition zone (CTZ). The study period is May-August 2002, for when data from the GLOBEC field program are available for model verification. Small-scale eddy variability, resolved in the 1-km solution but not in the 3- km model, affects the upwelling front structure and near-surface cross-shelf heat and salinity transport. In particular, in the 1-km model, the temperature front is more diffused, and qualitatively more similar to the satellite SST. The energy of small-scale eddies apparently cascades to larger scales, with development of mesoscale eddies on the order of 20 km in an abundance not seen in the 3-km model. In August, in the area of a jet separated from Cape Blanco into CTZ, the 1-km solution predicts eddy kinetic energy of surface currents in a better qualitative agreement with long range high frequency (HF) radar observations (using data provided by P. M. Kosro, OSU). Analysis is underway to study the effect of small-scale processes, such as submesoscale eddies and internal tides, on cross-shore momentum and heat transport in the coastal ocean.
OS41A-1208
Simulating coastal to offshore interactions around the South Florida coastal seas and implications on management issues
The South Florida coastal seas include shelf areas and shallow water bodies around ecologically fragile
environments and Marine Protected Areas, such as Florida Bay, the Florida Keys National Marine Sanctuary
(around the largest coral reef system of the continental U.S.) and the Dry Tortugas Ecological Reserve. Man-
made changes in the hydrology of the Everglades have caused dramatic degradation of the coastal
ecosystem through discharge in Florida Bay. New management scenarios are under way to restore historical
flows. The environmental impacts of the management propositions are examined with an inter-disciplinary,
multi-nested modeling system. The HYbrid Coordinate Ocean Model (HYCOM) has been employed for the
Regional Model for South Florida Coastal Seas (SoFLA-HYCOM, 1/25 degree resolution) and for the
embedded, high resolution coastal Florida Keys model (FKEYS- HYCOM, 1/100 degree). Boundary
conditions are extracted from GODAE products: the large scale North Atlantic model (ATL-HYCOM, 1/12
degree) and the intermediate scale Gulf of Mexico model (GOM-HYCOM, 1/25 degree).
The study targets the impacts of large scale oceanic features on the coastal dynamics. Eddies that travel
along the Loop Current/Florida Current front are known to be an important mechanism for the interaction of
nearshore and offshore flows. The high resolution FKEYS simulations reveal both mescoscale and sub-
mesoscale eddy passages during a targeted 2-year simulation period (2004-2005), forced with high
resolution/high frequency atmospheric forcing. Eddies influence sea level changes in the vicinity of Florida
Bay with possible implications on current and future flushing patterns. They also enable upwelling of cooler,
nutrient-rich waters in the vicinity of the Reef Tract and they influence transport and recruitment pathways for
coral fish larvae, as they carry waters of different properties (such as river-borne low-salinity/nutrient-rich
waters from as far as the Mississippi River) and waters containing larvae from upstream sources (such as
from the Dry Tortugas spawning grounds).
http://coastalmodeling.rsmas.miami.edu
OS41A-1209
On the Influence of the Dardanelles Outflow on Biophysical North Aegean Sea Nested Simulations
The Northeastern Aegean Sea, a marginal basin with complex topography, is the part of the Mediterranean where coupling with the Black Sea effectively takes place. The relatively oligotrophic Aegean Sea receives low salinity, eutrophic waters of Black Sea origin that substantially contribute to increased biotic production and to reduction in salinity. The latter has implications on the formation of dense waters that eventually influence the Eastern Mediterranean general circulation. The modified Black Sea waters enter through the Dardanelles Strait and account for lateral fluxes that overwhelm all Aegean river sources combined. Their low density characteristics result on a buoyant plume that exhibits intense seasonal and episodic variability, influenced by seasonal basin stratification, atmospheric forcing and changes in outflow volume and properties. A high resolution (1/50 degree) implementation of the Hybrid Coordinate Ocean Model has been nested within the coarser (1/25 degree), data assimilative Mediterranean HYCOM model to study the plume development and evolution. A coupled hydrodynamic-biogeochemical model, also nested within a 1/10 degree Mediterranean Sea outer model (based on the Princeton Ocean Model and the European Regional Seas Ecosystem Model) has been employed for the study of impacts on ecosystem dynamics associated with the Dardanelles outflow. The assessment of transport pathways of the waters of Black Sea origin in the North Aegean employs simulations with high frequency forcing and satellite derived patterns of SST and chlorophyll-a. Data from recent observational surveys and drifter releases in the Dardanelles plume will be also discussed.
OS41A-1210
The Application of a Limited Domain Unstructured Grid Model: An Evaluation of ADCIRC- HYCOM Coupling
Recent development efforts have added 3D baroclinic dynamics to the coastal model, ADCIRC, which has been successfully, validated using process-oriented tests on simplified domains and laboratory data. Implementation of a model based on unstructured grids, such as ADCIRC, remains attractive due to the flexibility in mapping intricate topography and shorelines and in resolving complex fluid dynamics in shallow straits and near-coastal zones. However, computational demands for high-resolution, 3D, baroclinic simulations increase by an order of magnitude over historical 2D barotropic applications, and thus require the model domain to be restricted to shallow water regions of interest. As a consequence the model open ocean boundary is placed in zones dominated by complex, nonlinear processes, rendering proper specification of offshore forcing even more critical. One solution for the limited domain model is to couple ADCIRC to HYCOM wherein oceanic conditions provided by HYCOM solutions are downscaled as forcing for the coastal dynamics computed within the ADCIRC model. To be presented are details of the ADCIRC- HYCOM coupling along with a preliminary evaluation of the limited domain model approach. Results and discussion are drawn from applications of the coupled model system to coastal regions as diverse as the NE Gulf of Mexico, La Spezia Bay, Italy and the Turkish Strait System.
OS41A-1211
Mechanisms of Sustained Production over Portlock Bank: Modeling and Observations
We use a spatially nested implementation of the Regional Ocean Model System (ROMS) and ocean observations to explore mechanisms responsible for the high primary productivity in the Coastal Gulf of Alaska (CGOA) over Portlock Bank in spring and summer, with a focus on the relationship between mixing, residence time, and productivity. Our CGOA model uses tidal forcing, daily atmospheric forcing, and boundary and initial conditions derived from a larger domain model of the Northeast Pacific. Hydrographic data were collected as part of six surveys undertaken by the GLOBEC/NEP program. Modeling results suggest that primary productivity over the bank in the spring season is dominated by advective losses due to atmospheric conditions; in the summer, high productivity is maintained by tidal mixing, which pumps nutrients onto the bank from the troughs on either side, and from the top of the bank to the sea surface. These modeling results are corroborated by the observational data. It is also found that stronger mixing atop the bank in spring can lead to light limitation and decrease productivity locally. We consider the possible implications of these results as they affect fish survival.
OS41A-1212
Skill Assessment for a Nested and Coupled Biological-Physical Model of Monterey Bay
Results from the Naval Research Laboratory West Coast Modeling Prediction System, a hierarchy of nested and coupled biological-physical models of the Pacific Ocean, are compared to data collected during the Bio- Optical Studies of Predictability and Assimilation for the Coastal Environment (BIOSPACE) project. Specifically, very high-resolution data collected in the Monterey Bay area using the ScanFish MKII platform are compared to the model predicted fields in order to calculate univariate and multivariate model skill metrics. Previously developed summary diagrams are also used to assess the fidelity of the model to both physical and bio-optical fields. The model skill metrics and summary diagrams are further used to distinguish between the spatiotemporal model fidelity to the observed fields and model fidelity to observed patterns in the relationships between physical and bio-optical variables. These preliminary results will serve as a benchmark for further numerical experimentation aimed towards improvement in model forecasting of optical and physical properties for coastal areas.