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Code 7320: Ocean Dynamics and Prediction Branch

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Surface boundary layer thermal stability and its relationship to significant wave height errors obtained from WAVEWATCH III
Posted on June 4, 2019
Significant wave height (Hs) calculated with the WAVEWATCH III® model deviates from the in-situ measurements from moored buoys. We hypothesize that this deviation would be smaller if the model used a well-calibrated method to account for stability variations within the surface boundary layer (SBL). This research determines a relationship between such errors and the SBL thermal stability. It can be exploited to create an empirical correction to wind speed, an “effective wind speed”. (Read more)     
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Posted on May 23, 2019
Researchers have found a new way to use satellites to monitor the Great Whirl, a massive whirlpool the size of Colorado that forms each year off the coast of East Africa, they report in a new study. Using 23 years of satellite data, the new findings show the Great Whirl is larger and longer-lived than scientists previously thought. At its peak, the giant whirlpool is, on average, 275,000 square kilometers (106,000 square miles) in area and persists for about 200 days out of the year. (Read more)     
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Parameterization of the Inverse Error Covariances for SWOT Altimetry
Posted on May 9, 2019
High-resolution (swath) altimeter missions scheduled to monitor the ocean surface in the near future have observation error covariances (OECs) with slowly decaying off-diagonal elements. This property presents a challenge for the majority of the data assimilation (DA) algorithms which were designed under the assumption of the diagonal OECs being easily inverted. We present a method of approximating the inverse of a dense OEC by a sparse matrix represented by the polynomial of spatially inhomogeneous differential operators, whose coefficients are optimized to fit the target OEC by minimizing a quadratic cost function. (Read more)     
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Regional Ocean Data Assimilation using the Local Ensemble Transform Kalman Filter (LETKF) with the Navy Coastal Ocean Model
Posted on April 22, 2019
A globally relocatable regional ocean nowcast/forecast system developed at the Naval Research Laboratory is modified to use the Local Ensemble Transform Kalman Filter (LETKF) for data assimilation. We present initial results using the LETKF with the NCOM/NCODA forecast system in a regional model in comparison with a perturbed-observation ensemble. (Read more)     
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Assimilating Inferred Velocity Observations from Float Positions to Improve an Ocean Model’s Prediction Skill
Posted on March 13, 2019
The Navy Coupled Ocean 3D Variational Data Assimilation (NCODA-VAR) system is one of the primary tools that the Navy uses operationally to ingest, process, quality and control, and assimilate ocean observations in near-real time in order to regularly update and improve the forecast skill of several different operational ocean prediction systems. One of the current deficiencies of NCODA, however, is its inability to properly assimilate velocity observations. It lacks the mechanism to correlate velocities with temperature and salinity, which the analysis needs in order to be dynamically stable. (Read more)     
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Validation of Sentinel-1 Synthetic Aperture Radar Spectra Against Buoy and Global WAVEWATCH III Spectra
Posted on March 6, 2019
We developed a validation procedure for Sentinel-1 SAR wave spectra that includes quality control measures. The current routine for validating SAR wave spectra against buoy wave spectra is shown (center panel). Pairs of SAR and buoy wave spectra are spatially and temporally colocated (within 1°and 0.5 hours, respectively). Bulk parameters (e.g., significant wave height, various wave periods, measures of spectral bandwidth, and the fourth spectral moment) calculated from the SAR spectra are compared graphically and statistically to those calculated from the buoy spectra. (Read more)     
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The Intra-Americas Sea Nowcast/Forecast System for Hypoxia Modeling on the Louisiana Continental Shelf
Posted on February 1, 2019
Recurrence of extensive hypoxia on the Louisiana continental shelf in the summer has a strong impact on the marine life and ecosystems. The formation of hypoxia depends on nutrient enhanced primary production and subsequent respiration in the water and sediment. It also depends on the physical processes of stratification, transport, mixing and air-sea exchanges. All these processes are spatially and temporally variable. Several coastal circulation models based on NCOM, ROMS, FVCOM, in conjunction with hypoxia models in various degree of sophistication have been applied to better understand the processes of hypoxia formation in the region. (Read more)     
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Modeled Air-Sea Heat Flux vs IN-SITU DATA: Statistical Comparison
Posted on January 24, 2019
Many physical phenomena occurring at or near the ocean surface (such as upwelling, dense water formation, hurricanes, etc.) are particularly sensitive to small variations in air-sea heat flux. The parameterization of these fluxes in coupled models is then crucial to obtain accurate forecasts in both surface and subsurface events. In our case, differences in the horizontal resolution and pixel position between the NAVGEM (atmospheric) and the HYCOM (oceanic) components of the Earth System Prediction Capability System (ESPC) makes this comparison a rare challenge. Here we present a validation of global heat fluxes derived from the ESPC through a comparison with heat fluxes obtained from in-situ data during two months of 2015 as an example. (Read more)     
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Nordic Seas Water Property Evolution
Posted on January 3, 2019
Cold fresh water from the Arctic and warm salty water from the Atlantic oceans meet in the Nordic Seas where the vertical structure has been evolving in recent decades. Because water properties are changing and seawater non-linearities are stronger at low temperatures and salinities making dynamics subject to thermobaricity and cabbeling, numerical ocean forecasting is more complex. Using the Modular Ocean Model version 6 (MOM6) with both isopycnal layer and z-level coordinates and MIT General Circulation Model (MITgcm) in both hydrostatic and non-hydrostatic mode, we demonstrate a mechanism for water mass formation or modification. (Read more)     
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Anomalous circulation in the Pacific Sector of the Arctic Ocean in July-December 2008
Posted on December 27, 2018
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)     
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Exploring Fine-Scale Ocean Fronts in the Mississippi Bight Coastal Zone
Posted on December 17, 2018
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)     
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Impact of Freshwater from Arctic Rivers in a High-Resolution Model
Posted on December 13, 2018
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)     
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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
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)     
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Automated system and method for vertical gradient correction
Posted on October 23, 2018
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)     
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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
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)     
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