scholarly journals Characterizing the impact of underwater glider observations on the Navy Coastal Ocean Model (NCOM) in the Gulf Stream Region

2021 ◽  
Author(s):  
◽  
Kyle R. Kausch
Keyword(s):  
Gulf Stream ◽  
The United States ◽  
Coastal Ocean ◽  
Ocean Model ◽  
Western Boundary ◽  
Boundary Current ◽  
Argo Data ◽  
Area Of Interest ◽  
Coastal Ocean Model ◽  
The Impact

As the western boundary current of the North Atlantic, the Gulf Stream is a well established area of interest for the United States Navy, predominately due to its proximity to the continental shelf and the associated challenges of acoustic propagation across large property gradients. Autonomous underwater gliders conduct routine, high-resolution surveys along the U.S. East Coast, including within the Gulf Stream. These observations are assimilated into the operational Navy Coastal Ocean Model (NCOM). An investigation of the forecast-to-nowcast changes in the model for 2017 demonstrates the impact of the observations on the model. The magnitude of model change as a function of distance from nearest new observation reveals relatively large impact of glider observations within a radius of 𝒪(100) km. Glider observations are associated with larger local impact than Argo data, likely due to glider sampling focusing on large spatial gradients. Due to the advective nature of the Gulf Stream system, the impact of glider observations in the model is anisotropic with larger impacts extending downstream from observation locations. Forecast-to-nowcast changes in modeled temperature, salinity, and density result in improved agreement between observed and modeled ocean structure within the upper 200 m over the 24 hours between successive model runs.

scholarly journals Local Sensitivities of the Gulf Stream Separation

2017 ◽  
Vol 47 (2) ◽  
pp. 353-373 ◽  
Author(s):  
Joseph Schoonover ◽  
William K. Dewar ◽  
Nicolas Wienders ◽  
Bruno Deremble
Keyword(s):  
Gulf Stream ◽  
General Circulation ◽  
Climate Modeling ◽  
Circulation Model ◽  
Ocean Modeling ◽  
Western Boundary ◽  
Massachusetts Institute Of Technology ◽  
Boundary Current ◽  
Institute Of Technology ◽  
The Impact

AbstractRobust and accurate Gulf Stream separation remains an unsolved problem in general circulation modeling whose resolution will positively impact the ocean and climate modeling communities. Oceanographic literature does not face a shortage of plausible hypotheses that attempt to explain the dynamics of the Gulf Stream separation, yet a single theory that the community agrees on is missing. In this paper, the authors investigate the impact of the deep western boundary current (DWBC), coastline curvature, and continental shelf steepening on the Gulf Stream separation within regional configurations of the Massachusetts Institute of Technology General Circulation Model. Artificial modifications to the regional bathymetry are introduced to investigate the sensitivity of the separation to each of these factors. Metrics for subsurface separation detection confirm the direct link between flow separation and the surface expression of the Gulf Stream in the Mid-Atlantic Bight. It is shown that the Gulf Stream separation and mean surface position are most sensitive to the continental slope steepening, consistent with a theory proposed by Melvin Stern in 1998. In contrast, the Gulf Stream separation exhibits minimal sensitivity to the presence of the DWBC and coastline curvature. The implications of these results to the development of a “separation recipe” for ocean modeling are discussed. This study concludes adequate topographic resolution is a necessary, but not sufficient, condition for proper Gulf Stream separation.

A GPU accelerated finite volume coastal ocean model

2017 ◽  
Vol 29 (4) ◽  
pp. 679-690 ◽  
Author(s):  
Xu-dong Zhao ◽  
Shu-xiu Liang ◽  
Zhao-chen Sun ◽  
Xi-zeng Zhao ◽  
Jia-wen Sun ◽  
...  
Keyword(s):  
Finite Volume ◽  
Coastal Ocean ◽  
Ocean Model ◽  
Coastal Ocean Model

scholarly journals Averaging-Related Biases in Monthly Latent Heat Fluxes

2012 ◽  
Vol 29 (7) ◽  
pp. 974-986 ◽  
Author(s):  
Paul J. Hughes ◽  
Mark A. Bourassa ◽  
Jeremy J. Rolph ◽  
Shawn R. Smith
Keyword(s):  
Latent Heat ◽  
Classical Method ◽  
Surface Flux ◽  
Heat Fluxes ◽  
Western Boundary ◽  
State University ◽  
Boundary Current ◽  
Surface Energy Fluxes ◽  
Temporal Averaging ◽  
The Impact

Abstract Seasonal-to-multidecadal applications that require ocean surface energy fluxes often require accuracies of surface turbulent fluxes to be 5 W m−2 or better. While there is little doubt that uncertainties in the flux algorithms and input data can cause considerable errors, the impact of temporal averaging has been more controversial. The biases resulting from using monthly averaged winds, temperatures, and humidities in the bulk aerodynamic formula (i.e., the so-called classical method) to estimate the monthly mean latent heat fluxes are shown to be substantial and spatially varying in a manner that is consistent with most prior work. These averaging-related biases are linked to nonnegligible submonthly covariances between the wind, temperature, and humidity. To provide additional insight into the averaging-related bias, the methodology behind the third-generation Florida State University monthly mean surface flux product (FSU3) is detailed to highlight additional sources of errors in gridded datasets. The FSU3 latent heat fluxes suffer from this averaging-related bias, which can be as large as 90 W m−2 in western boundary current regions during winter and can exceed 40 W m−2 in synoptically active portions of the tropics. The regional impacts of these biases on the mixed layer temperature tendency are shown to demonstrate that the error resulting from applying the classical method is physically substantial.

Overlooked current estimation biases arising from the Lagrangian Argo trajectory derivation method

2021 ◽  
Author(s):  
Tianyu Wang ◽  
Yan Du ◽  
Minyang Wang
Keyword(s):  
Ocean Model ◽  
Ocean Dynamics ◽  
Western Boundary ◽  
Boundary Current ◽  
Current Estimation ◽  
Quantitative Metrics ◽  
Circumpolar Current ◽  
Derivation Method ◽  
Jet Interactions ◽  
Reference Layer

AbstractAn Argo simulation system is used to provide synthetic Lagrangian trajectories based on the Estimating the Circulation and Climate of the Ocean model, Phase II (ECCO2). In combination with ambient Eulerian velocity at the reference layer (1000 m) from the model, quantitative metrics of the Lagrangian trajectory-derived velocities are computed. The result indicates that the biases induced by the derivation algorithm are strongly linked with ocean dynamics. In low latitudes, Ekman currents and vertically sheared geostrophic currents influence both the magnitude and the direction of the derivation velocity vectors. The maximal shear-induced biases exist near the equator with the amplitudes reaching up to about 1.2 cm s-1. The angles of the shear biases are pronounced in the low latitude oceans, ranging from -8° to 8°. Specifically, the study shows an overlooked bias from the float drifting motions that mainly occurs in the western boundary current and Antarctic circumpolar current (ACC) regions. In these regions, a recently reported horizontal acceleration measured via Lagrangian floats is significantly associated with the strong eddy-jet interactions. The acceleration could induce an overestimation of Eulerian current velocity magnitudes. For the common Argo floats with a 9-day float parking period, the derivation speed biases induced by velocity acceleration would be as large as 3 cm s-1, approximately 12% of the ambient velocity. It might have implications to map the mean mid-depth ocean currents from Argo trajectories, as well as understand the dynamics of eddy-jet interactions in the ocean.

scholarly journals An Unstructured Grid, Finite-Volume Coastal Ocean Model (FVCOM) System

Oceanography ◽  
2006 ◽  
Vol 19 (1) ◽  
pp. 78-89 ◽  
Author(s):  
Changsheng Chen ◽  
Roberet Beardsley ◽  
Geoffrey Cowles
Keyword(s):  
Finite Volume ◽  
Unstructured Grid ◽  
Coastal Ocean ◽  
Ocean Model ◽  
Coastal Ocean Model

Seasonal-to-Decadal Predictability and Prediction of North American Climate—The Atlantic Influence

2006 ◽  
Vol 19 (23) ◽  
pp. 6005-6024 ◽  
Author(s):  
H. M. Van den Dool ◽  
Peitao Peng ◽  
Åke Johansson ◽  
Muthuvel Chelliah ◽  
Amir Shabbar ◽  
...  
Keyword(s):  
North American ◽  
Seasonal Prediction ◽  
Atmospheric Model ◽  
The United States ◽  
Seasonal Forecast ◽  
Ocean Model ◽  
Prediction Skill ◽  
Basic Material ◽  
Atlantic Sector ◽  
The Impact

Abstract The question of the impact of the Atlantic on North American (NA) seasonal prediction skill and predictability is examined. Basic material is collected from the literature, a review of seasonal forecast procedures in Canada and the United States, and some fresh calculations using the NCEP–NCAR reanalysis data. The general impression is one of low predictability (due to the Atlantic) for seasonal mean surface temperature and precipitation over NA. Predictability may be slightly better in the Caribbean and the (sub)tropical Americas, even for precipitation. The NAO is widely seen as an agent making the Atlantic influence felt in NA. While the NAO is well established in most months, its prediction skill is limited. Year-round evidence for an equatorially displaced version of the NAO (named ED_NAO) carrying a good fraction of the variance is also found. In general the predictability from the Pacific is thought to dominate over that from the Atlantic sector, which explains the minimal number of reported Atmospheric Model Intercomparison Project (AMIP) runs that explore Atlantic-only impacts. Caveats are noted as to the question of the influence of a single predictor in a nonlinear environment with many predictors. Skill of a new one-tier global coupled atmosphere–ocean model system at NCEP is reviewed; limited skill is found in midlatitudes and there is modest predictability to look forward to. There are several signs of enthusiasm in the community about using “trends” (low-frequency variations): (a) seasonal forecast tools include persistence of last 10 years’ averaged anomaly (relative to the official 30-yr climatology), (b) hurricane forecasts are based largely on recognizing a global multidecadal mode (which is similar to an Atlantic trend mode in SST), and (c) two recent papers, one empirical and one modeling, giving equal roles to the (North) Pacific and Atlantic in “explaining” variations in drought frequency over NA on a 20 yr or longer time scale during the twentieth century.

scholarly journals The impact of resolving the Rossby radius at mid-latitudes in the ocean: results from a high-resolution version of the Met Office GC2 coupled model

2016 ◽  
Vol 9 (10) ◽  
pp. 3655-3670 ◽  
Author(s):  
Helene T. Hewitt ◽  
Malcolm J. Roberts ◽  
Pat Hyder ◽  
Tim Graham ◽  
Jamie Rae ◽  
...  
Keyword(s):  
High Resolution ◽  
Coupled Model ◽  
Ocean Model ◽  
The Body ◽  
Western Boundary ◽  
Coupled Models ◽  
Technical Developments ◽  
Enhanced Resolution ◽  
Circumpolar Current ◽  
The Impact

Abstract. There is mounting evidence that resolving mesoscale eddies and western boundary currents as well as topographically controlled flows can play an important role in air–sea interaction associated with vertical and lateral transports of heat and salt. Here we describe the development of the Met Office Global Coupled Model version 2 (GC2) with increased resolution relative to the standard model: the ocean resolution is increased from 1/4 to 1/12° (28 to 9 km at the Equator), the atmosphere resolution increased from 60 km (N216) to 25 km (N512) and the coupling period reduced from 3 hourly to hourly. The technical developments that were required to build a version of the model at higher resolution are described as well as results from a 20-year simulation. The results demonstrate the key role played by the enhanced resolution of the ocean model: reduced sea surface temperature (SST) biases, improved ocean heat transports, deeper and stronger overturning circulation and a stronger Antarctic Circumpolar Current. Our results suggest that the improvements seen here require high resolution in both atmosphere and ocean components as well as high-frequency coupling. These results add to the body of evidence suggesting that ocean resolution is an important consideration when developing coupled models for weather and climate applications.

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