A high-resolution coupled ice-ocean model of winter circulation on the bering sea shelf. Part I: Ice model refinements and skill assessments

The Bering Sea Shelf transitions from ice-free to mostly ice-covered and back again over each winter. Sea ice coverage and the timing of ice melt play a critical role in determining shelf structure and consequently ecosystem response during the spring transition and summer. In this study, a 2-km resolution ocean model, which is based on the Regional Ocean Modeling System (ROMS) and was initially run and verified against a variety of observational data sources for summer 2009, is augmented with an ice model to study the coupled ice/ocean dynamics of the Bering Sea shelf from fall 2009 to summer 2010. Here we demonstrate that a single-category ice model is appropriate to describe seasonal evolution of the ice. Enhancements are made to the ice thermodynamic module and air/ice stress formulations to improve the match between the model and satellite microwave estimates of ice distribution and extent. The refined model accurately represents the timing and spatial extent of the spread of sea ice over the winter season as well as the ice retreat as it melts in spring and summer. Comparison with satellite products also suggests that the model captures the sea ice response on shorter temporal (similar to O(days)) and spatial scales (similar to O(20 km)). The modification to the drag formulation for example, can improve the modeled sea ice distribution in response to wind events overall and in particular in polynya regions along the coastlines of the Seward and Chukotka peninsulas and St. Lawrence Island

Influence of varying upper ocean stratification on coastal near-inertial currents

The influence of varying horizontal and vertical stratification in the upper layer ( inline image m) associated with riverine waters and seasonal atmospheric fluxes on coastal near-inertial currents is investigated with remotely sensed and in situ observations of surface and subsurface currents and realistic numerical model outputs off the coast of Oregon. Based on numerical simulations with and without the Columbia River (CR) during summer, the directly wind-forced near-inertial surface currents are enhanced by 30%–60% when the near-surface layer has a stratified condition due to riverine water inputs from the CR. Comparing model results without the CR for summer and winter conditions indicates that the directly wind-forced near-inertial surface current response to a unit wind forcing during summer are 20%–70% stronger than those during winter depending on the cross-shore location, which is in contrast to the seasonal patterns of both mixed-layer depth and amplitudes of near-inertial currents. The model simulations are used to examine aspects of coastal inhibition of near-inertial currents, manifested in their spatial coherence in the cross-shore direction, where the phase propagates upward over the continental shelf, bounces at the coast, and continues increasing upward offshore (toward surface) and then downward offshore at the surface, with magnitudes and length scales in the near-surface layer increasing offshore. This pattern exhibits a particularly well-organized structure during winter. Similarly, the raypaths of clockwise near-inertial internal waves are consistent with the phase propagation of coherence, showing the influence of upper layer stratification and coastal inhibition.The data used in the paper will be available from the authors upon request ([email protected]) to comply with the American Geophysical Union Publications Data Policy.Keywords: near-inertial currents, stratification, coastal river plume, wind transfer function, coherence, coastal inhibitio

Evaluation of directly wind-coherent near-inertial surface currents off Oregon using a statistical parameterization and analytical and numerical models

Directly wind-coherent near-inertial surface currents off the Oregon coast are investigated with a statistical parameterization of observations and outputs of a regional numerical ocean model and three one-dimensional analytical models including the slab layer, Ekman, and near-surface averaged Ekman models. The transfer functions and response functions, statistically estimated from observed wind stress at NDBC buoys and surface currents derived from shored-based high-frequency radars, enable us to isolate the directly wind-forced near-inertial surface currents. Concurrent observations of the wind and currents are crucial to evaluate the directly wind-forced currents. Thus, the wind stress and surface current fields obtained from a regional ocean model, which simulates variability of the wind and surface currents on scales comparable to those in observations, are analyzed with the same statistical parameterization to derive the point-by-point transfer functions and response functions. Model and data comparisons show that the regional ocean model describes near-inertial variability of surface currents qualitatively and quantitatively correctly. The estimated response functions exhibit decay time scales in a range of 3-5 days, and about 40% of the near-inertial motions are explained by local wind stress. Among the one-dimensional analytical models, the near-surface averaged Ekman model explains the statistically derived wind-current relationship better than other analytical models.Keywords: wind transfer function, directly wind-coherent near-inertial currents, near-inertial currents, surface current

Advancing coastal ocean modelling, analysis, and prediction for the US Integrated Ocean Observing System

Author Posting. © The Author(s), 2017. This is the author's version of the work. It is posted here by permission of Taylor & Francis for personal use, not for redistribution. The definitive version was published in Journal of Operational Oceanography 10 (2017): 115-126, doi:10.1080/1755876X.2017.1322026.This paper outlines strategies that would advance coastal ocean modeling, analysis and prediction as a complement to the observing and data management activities of the coastal components of the U.S. Integrated Ocean Observing System (IOOS®) and the Global Ocean Observing System (GOOS). The views presented are the consensus of a group of U.S. based researchers with a cross-section of coastal oceanography and ocean modeling expertise and community representation drawn from Regional and U.S. Federal partners in IOOS. Priorities for research and development are suggested that would enhance the value of IOOS observations through model-based synthesis, deliver better model-based information products, and assist the design, evaluation and operation of the observing system itself. The proposed priorities are: model coupling, data assimilation, nearshore processes, cyberinfrastructure and model skill assessment, modeling for observing system design, evaluation and operation, ensemble prediction, and fast predictors. Approaches are suggested to accomplish substantial progress in a 3-8 year timeframe. In addition, the group proposes steps to promote collaboration between research and operations groups in Regional Associations, U.S. Federal Agencies, and the international ocean research community in general that would foster coordination on scientific and technical issues, and strengthen federal-academic partnerships benefiting IOOS stakeholders and end users.2018-05-2

Coastal Ocean Forecasting: science foundation and user benefits

The advancement of Coastal Ocean Forecasting Systems (COFS) requires the support of continuous scientific progress addressing: (a) the primary mechanisms driving coastal circulation; (b) methods to achieve fully integrated coastal systems (observations and models), that are dynamically embedded in larger scale systems; and (c) methods to adequately represent air-sea and biophysical interactions. Issues of downscaling, data assimilation, atmosphere-wave-ocean couplings and ecosystem dynamics in the coastal ocean are discussed. These science topics are fundamental for successful COFS, which are connected to evolving downstream applications, dictated by the socioeconomic needs of rapidly increasing coastal populations

A nested grid model of the Oregon Coastal Transition Zone: Simulations and comparisons with observations during the 2001 upwelling season

The Oregon Coastal Transition Zone (OCTZ) extends several hundred kilometers offshore where shelf flows interact with the northern California Current. A primitive-equation numerical ocean model is used to study the upwelling circulation in this region from 1 May to 1 November 2001. This OCTZ model obtains initial and boundary conditions from a larger-scale model of the California Current System and forcing from a regional atmospheric model product. The model results are compared with extensive in situ and remotely sensed data, and the model is found to provide a realistic representation of flows both over the shelf and in the broader OCTZ. Simulation of coastal sea level and shelf currents over the complex topography of the central Oregon coast is improved quantitatively relative to previous regional models. A particularly significant qualitative improvement is realistic representation of coastal jet separation and eddy formation offshore of Cape Blanco. Three-dimensional Lagrangian analysis of water parcel displacement shows that the surface waters inshore of the separated jet are upwelled from near the bottom along the shelf as far north as 45.5°N. A large eddy, which incorporates some of this upwelled water and carries it farther westward, forms offshore in the late summer. Ensemble simulations show a distinction between the strongly deterministic response to wind forcing over the shelf and the more unstable, less predictable jet separation and offshore eddy formation processes in the region near Cape Blanco

Distant effect of assimilation of moored currents into a model of coastal wind-driven circulation off Oregon

An optimal interpolation (OI) sequential algorithm is implemented for a three-dimensional primitive equation model to assimilate current measurements from acoustic Doppler profilers moored on the Oregon shelf as a part of the Coastal Ocean Advances in Shelf Transport (COAST) upwelling experiment (May–August 2001). A stationary estimate of the forecast error covariance required by the OI is computed based on the error covariance in the model solution not constrained by data assimilation. Lagged model error covariances are used to account for the effect of previously assimilated data. The forecast error covariance has a shorter alongshore spatial scale than the model error covariance unconstrained by the data, as an effect of propagating dynamical modes. Assimilation of currents from one or two of the moorings located on the path of the upwelling jet helps to improve the model data rms error and correlation at the mooring sites located at an alongshore distance of 90 km, south or north from the assimilation sites. The coastal jet is deflected offshore over Heceta Bank, and assimilation of data from an inner-shelf mooring in the jet separation zone does not help to improve prediction in the far field. Larger improvements are obtained for the first part of the study period (yeardays 146–190). In the second part (days 191–237) the geometry of our limited area model possibly limits prediction accuracy. In numerical experiments involving assimilation of data from only one mooring the actual and expected rms error improvements are compared, providing a consistency test for the forecast error covariance.Keywords: upwelling, coastal ocean prediction, data assimilationKeywords: upwelling, coastal ocean prediction, data assimilatio

Assimilation of moored velocity data in a model of coastal wind-driven circulation off Oregon: Multivariate capabilities

Horizontal current measurements from an array of moored acoustic Doppler profilers are assimilated sequentially into a model of coastal wind-driven circulation off Oregon during the upwelling season of May–August 2001. Model results are compared against independent moored and ship survey data to document a positive effect of velocity data assimilation (DA) on other oceanic variables of interest such as the sea surface height (SSH), temperature, potential density, surface salinity, and near-bottom turbulence parameters. Significant improvement is achieved for the nearshore SSH even when data are assimilated from only two moorings at an alongshore distance of 50 km from the SSH verification site. At 45°N, in an area of simple shelf bathymetry with relatively small alongshore variations, the model (even without DA) provides a good description of the isopycnal structure on a cross-shore section. At 44.2°N, over complicated bathymetry, velocity DA may improve the slope of isopycnals but at the same time not necessarily the density values themselves. Data assimilation based on a time-invariant representation of the forecast error covariance may inhibit spatial variability on horizontal scales smaller than the assumed forecast error decorrelation scale. An experiment involving assimilation of both velocity and moored salinity measurements demonstrates that moored velocity DA improves transport of buoyant surface water. The level of improvement in the near-bottom turbulent dissipation and bottom stress found with the DA model indicates that it is suitable for future studies of spatial and temporal variability in the bottom boundary layer off Oregon.Keywords: shelf circulation, modeling, data assimilatio

Better Regional Ocean Observing Through Cross-National Cooperation: A Case Study From the Northeast Pacific

The ocean knows no political borders. Ocean processes, like summertime wind-driven upwelling, stretch thousands of kilometers along the Northeast Pacific (NEP) coast. This upwelling drives marine ecosystem productivity and is modulated by weather systems and seasonal to interdecadal ocean-atmosphere variability. Major ocean currents in the NEP transport water properties such as heat, fresh water, nutrients, dissolved oxygen, pCO2, and pH close to the shore. The eastward North Pacific Current bifurcates offshore in the NEP, delivering open-ocean signals south into the California Current and north into the Gulf of Alaska. There is a large and growing number of NEP ocean observing elements operated by government agencies, Native American Tribes, First Nations groups, not-for-profit organizations, and private entities. Observing elements include moored and mobile platforms, shipboard repeat cruises, as well as land-based and estuarine stations. A wide range of multidisciplinary ocean sensors are deployed to track, for example, upwelling, downwelling, ocean productivity, harmful algal blooms, ocean acidification and hypoxia, seismic activity and tsunami wave propagation. Data delivery to shore and observatory controls are done through satellite and cell phone communication, and via seafloor cables. Remote sensing from satellites and land-based coastal radar provide broader spatial coverage, while numerical circulation and biogeochemical modeling complement ocean observing efforts. Models span from the deep ocean into the inland Salish Sea and estuaries. NEP ocean observing systems are used to understand regional processes and, together with numerical models, provide ocean forecasts. By sharing data, experiences and lessons learned, the regional ocean observatory is better than the sum of its parts