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Dynamic News for 2018 |
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Anomalous circulation in the Pacific Sector of the Arctic Ocean in July-December 2008
Posted on December 27, 2018
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Variability of the mean summer-fall ocean state in the Pacific Sector of the Arctic Ocean (PSAO) is studied using a dynamically constrained synthesis
(4Dvar) of historical in situ observations collected during 1972 to 2008. It is shown that the PSAO circulation during July-December of 2008 was characterized by a pronounced negative
Sea Surface Height (SSH) anomaly along theEurasian shelf break, which caused a significant decline of the transport in the Atlantic Water (AW) inflow
region into the PSAO and increased the sea level difference between the Bering and Chukchi Seas.
(Read more)
For more information contact author.
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Exploring Fine-Scale Ocean Fronts in the Mississippi Bight Coastal Zone
Posted on December 17, 2018
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High-resolution modeling of the Mississippi Bight has allowed for further research and examination of the development of mesoscale frontal
boundaries in the northern Gulf of Mexico. Such high-resolution modeling is necessary to diagnose the development of Lagrangian Coherent
Structures (LCS) which can alter physical, acoustical, and biological processes over short periods of time. The field work to take place
in March and April 2018 will further enhance our knowledge of these frontal boundary structures, and lead to better understanding of these
structures in the coastal zone.
(Read more)
For more information contact author.
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Impact of Freshwater from Arctic Rivers in a High-Resolution Model
Posted on December 13, 2018
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A high-resolution model is run for three years in the Arctic to observe the impact of changing the freshwater input from river discharge.
The model is run with five different river scenarios. The “base case” uses climatological rivers with monthly resolution. A second case
uses daily river discharge values for six major rivers, introducing both shorter-term and interannual variability. In the third case, the
river discharge values are increased by a factor of five, while in the fourth case, the rivers are turned off. These cases allow us to
observe what part of the freshwater variability is fully independent of the rivers, and how both local and large-scale freshwater content
is affected by variations in river discharge.
(Read more)
For more information contact author.
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Improving Arctic sea ice edge forecasts by assimilating
high resolution VIIRS sea ice concentration data into the U.S. Navy’s ice forecast systems
Posted on November 13, 2018
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This study demonstrates the improvement in the ice edge location for both the Arctic and Antarctic regional seas by
assimilating the high resolution VIIRS ice concentration products. This new data source is scheduled to be
implemented into the pre-operational GOFS 3.1 job stream in Spring 2018.
(Read more)
For more information contact author.
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Automated system and method for vertical gradient correction
Posted on October 23, 2018
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System and method for maintaining the observed vertical structure of ocean temperature and salinity in data assimilation
systems that otherwise would produce overly smoothed ocean vertical structure. The present embodiment
uses a multi-layer least squares minimization technique in which the ocean is split into layers with fundamentally
different vertical gradients, and the dynamic ocean layers are constrained by the observed vertical gradients of the layer itself.
(Read more)
For more information contact author.
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System and method for correcting a model-derived vertical structure of ocean temperature and ocean salinity based on velocity observations
Posted on October 23, 2018
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System and method for correcting the vertical structure of the ocean temperature and salinity based on velocity observations.
Three relations that can be precomputed are exploited: (1) the relation between temperature and salinity
throughout a water column, (2) the relation between temperature/salinity and geopotential, and (3) the relation
between geopotential and velocity. The relations are stored in a form that allows efficient application through a crosscorrelation matrix.
(Read more)
For more information contact author.
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Assimilation of Glider Profile Data in a Shelf Ocean via Multi-Scale 4DVAR
Posted on September 17, 2018
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Temperature and salinity profiles from 6 gliders within a roughly 40 km by 40 km region are assimilated into a Relocatable Navy Coastal Ocean Model
(RELO NCOM) with a “multi-scale” four-dimensional variational (4DVAR) approach. Gliders were deployed north of Cape Hatteras (US East Coast) and inshore
of the Gulf Stream in a field experiment from 17 May until 4 June 2017. Gliders were divided into two teams, generally two or three gliders per team.
One team was tasked with station keeping and the other with moving and sampling regions of high variability in temperature and salinity. Data from gliders,
in combination with multi-scale 4DVAR assimilation methods, have the potential to significantly improve model forecasts.
(Read more)
For more information contact author.
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Adapting a Regional Scale Coupled Modeling System to Nearshore Applications
Posted on September 6, 2018
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The Coupled Ocean Atmospheric Modeling System (COAMPS) is a modeling suite of atmospheric, ocean circulation, and wave models that exchange
information using the Earth System Modeling Framework (ESMF). In this system, the Navy Coastal Ocean Model (NCOM) is the circulation model and
Simulating Waves Nearshore (SWAN) is the wave model. In nearshore applications of coupled circulation-wave models, one mechanism for transferring
wave energy to the ocean circulation is via radiation stress gradients.
(Read more)
For more information contact author.
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Impact of Vertical Resolution in Lagrangian Analysis on the Shelf
Posted on August 28, 2018
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Fresh water outflows from the Mississippi River southwest passage strongly affect coastal processes in the Mississippi Bight region. Strong vertical stratification
results that controls the mixing of momentum flux from the atmosphere. This situation presents a challenging problem for numerical models to represent the vertical
structure and associated physics. We use the Consortium for Advanced Research on Transport of Hydrocarbon in the Environment (CARTHE) SubmesoscaleProcesses and
LagrangianAnalysis on the Shelf field experiment in April, May 2017 during which several dense surface drifter deployments were conducted in the area.
(Read more)
For more information contact author.
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Tuning Tidal Perturbations for Augmented State Ensemble Kalman Filter (ASEnKF) Improvements
Posted on August 15, 2018
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The ocean tidal velocity and elevation can be estimated concurrently with the ocean circulation by adding the astronomical tidal forcing, parameterized topographic
internal wave drag, and self-attraction and loading to the general circulation physics. We have previously developed an augmented state ensemble Kalman Filter (ASEnKF)
approach that improves the accuracy of the barotropic tides embedded in a 1/12.5° three-dimensional ocean general circulation model. In the ASEnKF, an extra term,
meant to correct for errors in the tide model due to imperfectly known topography and damping terms, is introduced into the tidal forcing.
(Read more)
For more information contact author.
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Guassianized 2dVar assimilation of ice concentration into CICE model
Posted on August 13, 2018
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Results of numerical experiments assimilating SSMI/IMS data into the HYCOM-driven CICE model are presented. To remove inconsistency between the Gaussian assumptions underlying the 2dVar algorithm and non-Gaussian nature of ice concentration (IC) errors, IC innovations are gaussianized prior to the analysis. The inverse (degaussianization) transform is computed at the analysis step and exploits similarity between the PDFs of IC innovations and increments. Gaussianization uncertainties are taken into account by an additional 2dVar algorithm optimizing the estimate of the background error variance with respect to the innovations obtained after the analysis. Numerical experiments with 2dVar assimilation of SSMI/IMS observations acquired in September-December 2015 in the Beaufort Sea demonstrate 5-10% improvement of the 24-hour forecast skill compared to the operational runs executed without gaussianization.
(Read more)
For more information contact author.
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Science and Engineering Apprentice Program (SEAP) Posters 2018
Posted on July 26, 2018
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The goals of SEAP are to encourage participating high school students to pursue science and engineering careers, to further their education via mentoring by laboratory personnel and their participation in research, and to make them aware of DoN research and technology efforts, which can lead to employment within the DoN.
(View posters)
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4DVAR Assimilation of Glider Teams on the North Carolina Shelf
Posted on July 3, 2018
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We demonstrate a new method to assimilate glider profile data from multiple gliders in close proximity (~10 km or less). Previous work shows assimilating glider data in close proximity (e.g., 1 profile every 10 km or less) super-imposes assimilation updates and over-corrects the background state. The new "boundary control" method was developed using gliders deployed in a field experiment from 17 May until 4 June 2017 near Cape Hatteras
(Read more)
For more information contact author.
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An updated system for guidance of heterogeneous platforms used for multiple gliders in a real-time experiment
Posted on July 3, 2018
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The Guidance of Heterogeneous Observation Systems (GHOST) is a tool designed to sample ocean model outputs to determine a suite of possible path options for unmanned platforms. The system is built around a Runge-Kuttamethod to determine all possible paths, followed by a cost function calculation, an enforcement of safe operating area, and an analysis to determine a top 10% level of cost function and to rank the paths that qualify. A field experiment took place from 16 May until 5 June 2017 aboard the R/V Savannah operating out of the Duke University Marine Laboratory (DUML) in Beaufort, NC. Gliders were deployed in alternating groups with missions defined by one of two possible categories: a station-keeping array and a moving array.
(Read more)
For more information contact author.
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Drag Forces in a Coupled Wave Ice Model: Implementation and Testing
Posted on June 19, 2018
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We are developing a system for modeling the interactions between ocean surface
waves and polar ice floes, which consists of a nonhydrostatic, finite-volume wave
model (NHWAVE) coupled to a discrete element, particle-tracking ice model
(LIGGGHTS). The effects of drag forces between fluid and ice were recently
implemented in the coupled system. The drag formulations assume that the fluid
velocity profile at the interface is logarithmic, leading to a drag coefficient that is a
function of both grid size and a configurable roughness height.
(Read more)
For more information contact author.
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Comparison of Two Global Ocean Reanalyses: NRL Global Ocean Forecast System (GOFS) and U. Maryland Simple Ocean Data Assimilation (SODA)
Posted on June 14, 2018
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The Oceanography Division of the Naval Research Laboratory recently completed a 23-year (1993-2015) coupled ocean-sea ice reanalysis forced by NCEP CFS reanalysis fluxes. The reanalysis uses the Global Ocean Forecast System (GOFS) framework of the HYbrid Coordinate Ocean Model (HYCOM) and the Los Alamos Community Ice CodE (CICE) and the Navy Coupled Ocean Data Assimilation 3D Var system (NCODA). The ocean model has 41 layers and an equatorial resolution of 0.08° (8.8 km) on a tri-polar grid with the sea ice model on the same grid that reduces to ~3.5 km at the North Pole.
(Read more)
For more information contact author.
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Impact of Seawater Nonlinearities on the Nordic Seas Circulation
Posted on May 1, 2018
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The Nordic Seas (Greenland, Iceland, and Norwegian Seas) are important for Arctic-mid-latitude climate linkages. Cold fresh water from the Arctic Ocean and warm salty water from the North Atlantic Ocean meet in the Nordic Seas, where the balance between temperature and salinity variability has been evolving during recent decades. Present Naval Research Laboratory (NRL) ocean forecast systems, however, do not capture the details of this subsurface ocean structure. The goal of this research is to improve NRL ocean forecast capabilities in the Nordic Seas.
(Read more)
For more information contact author.
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Validation of the Fully-Coupled Air-Sea-Wave COAMPS System
Posted on May 1, 2018
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A fully-coupled, air-sea-wave numerical model, COAMPS®, has been developed by the Naval Research Laboratory to further enhance understanding of oceanic, atmospheric, and wave interactions. The fully-coupled air-sea-wave system consists of an atmospheric component with full physics parameterizations, and ocean model, NCOM (Navy Coastal Ocean Model), and two wave components, SWAN (Simulating Waves Nearshore) and WaveWatch III.
(Read more)
For more information contact author.
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Improving Arctic sea ice edge forecasts by assimilating high resolution VIIRS sea ice concentration data into the U.S. Navy’s ice forecast systems
Posted on April 5, 2018
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This study presents the improvement in ice edge error within the U.S. Navy’s sea ice forecast systems gained by assimilating the high horizontal resolution visible/infrared satellite-derived VIIRS ice concentration products. A series of hindcast studies are performed for the period of 1November 2016 - 31October 2017 using the Global Ocean Forecast System (GOFS3.1), a 1/12° HYbrid Coordinate Ocean Model (HYCOM) that is two-way coupled to the Community Ice CodE (CICE) in a daily update cycle with the Navy Coupled Ocean Data Assimilation (NCODA).
(Read more)
For more information contact author.
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Wave Ice Modeling
Posted on March 30, 2018
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NRL's Ocean Dynamics and Prediction Branch performs basic and applied research in computer modeling of ocean circulation and density structure, modeling of ice dynamics, computational numerical techniques, data assimilation, and a mulititude of capabilities related to satellite oceanographic data. This branch translates the results of basic and applied research into accurate, scientifically valid, environmental models and analyses and streamlines these models into operational, data assimilative, nowcast/forecast systems.
(View video)
For more information contact author.
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Anomalous circulation in the Pacific sector of the Arctic Ocean in July-December 2008
Posted on March 2, 2018
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During the last decade, the Pacific sector of the Arctic Ocean (AO) has experienced a pronounced environmental change. The most well-known events have been tremendous ice retreats in 2007 and 2012. The 4Dvar data assimilation approach (DA) allows accurate reconstruction of the circulation through the assimilation of all available observations. We apply a hybrid SIOM-PIOMAS data assimilation approach and reconstruct the circulation during the 2008, and previous decades (1972-1978, 1989-1996, 1997-2006) and for 2003, 2004, 2005 and 2006. Analysis of the reconstructed circulations will allow to analyze interannual variability of the Fresh Water (FW) content and identify the factors responsible for the observed changes.
(Read more)
For more information contact author.
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AGU Ocean Sciences Meeting in Portland, OR
Posted on March 2, 2018
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At the American Geophysical Union (AGU)’s Ocean Sciences Meeting 2018 in Portland, OR with NRL oceanographers Jay Veeramony and Kacey Edwards whose work supports the Navy and Marine Corps through storm surge and inundation prediction.
(Read more)
For more information contact author.
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Coupled Data Assimilation in Navy ESPC
Posted on February 2, 2018
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Data assimilation under global coupled Earth System Prediction Capability (ESPC) presents significantly greater challenges than data assimilation in forecast models of a single earth system like the ocean and atmosphere. In forecasts of a single component, data assimilation has broad flexibility in adjusting boundary conditions to reduce forecast errors; coupled ESPC requires consistent simultaneous adjustment of multiple components within the earth system: air, ocean, ice, and others.
(Read more)
For more information contact author.
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Validation of Heat fluxes Derived from the Earth System Prediction Capability (ESPC) Project
Posted on February 1, 2018
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The numerical representation of physical properties and their exchange at the boundaries in circulation models are the key factors in determining the proper functioning of air-sea coupled models and in defining the accuracy of the output forecast. Given the potential applications of the ESPC coupled models, we have a strong interest in testing the validity of the flux exchange at the surface, and in particular the surface heat fluxes (HF). Here we present an example of the turbulent heat flux global variability during the transition summer-to-fall, 2015 and compare them versus two known data sets, the NFLUX and MERRA heat fluxes.
(Read more)
For more information contact author.
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