Ruth H. Preller

Wind-driven effects on the Yellow Sea Warm Current

The Yellow Sea is a shallow basin writh an average depth of 44 m located between China and the Korean Peninsula. One of the dominant ocean circulation features of the Yellow Sea is a warm wrater intrusion known as the Yellow Sea Warm Current. This feature is present throughout the year but reaches its farthest northward extension in winter. The circulation of the Yellow, East China, and Bohai Seas was modeled using the Princeton Ocean Model to better understand the dynamics of the Yellow Sea Warm Current. The horizontal resolution of the model varies from 8 km in the Yellow Sea to 25 km in the East China Sea. Twenty-four sigma levels are used to define the vertical structure. The model uses daily atmospheric forcing from the Navy Operational Global Atmospheric Prediction System for 1993. Open boundary conditions are applied at the Taiwan Strait, the Tsushima (Korea) Strait, an area south of Taiwan, and the Tokara Strait, with a closed boundary south of the Ryukyu Islands. The model results are examined to determine the effect of the wind on the northward extension of the warm water intrusion, using both water mass characteristics and northward velocity components. Sensitivity tests and spectrum analyses, performed to study the influence of the wind on the Yellow Sea Warm Current, show that winds modify the pathway and extent of the Yellow Sea Warm Current. The currents origin, however, appears to be due to external forcing from the current systems developed in the East China Sea.

Transport reversals at Taiwan Strait during October and November 1999

[1] The observed transport reversals at Taiwan Strait during October and November 1999 are examined by analytic solutions, a numerical ocean model, and the prediction from a real-time, North Pacific Ocean, data-assimilating model. Wind stress explains a majority of the transport reversals. The reversals are forced by a combination of the local wind and the remote wind in the Yellow and East China Seas. The connection between the Yellow and East China Seas wind stress and transport reversals at Taiwan Strait is provided by coastally trapped waves. The waves are generated by the northerly winter wind bursts in the Yellow Sea and are enhanced in the East China Sea by alongshore northerly wind.

The Influence of Bottom Topography on Upwelling off Peru

Abstract The x-y-t, two-layer β-plane numerical model developed by Hurlburt (1974) is used to examine the upwelling system off Peru. The region off Peru from 14 to 15°30s is one of strong and persistent upwelling. The most distinctive feature of the Peruvian upwelling circulation is a predominant poleward flow. A local area model, when forced by wind stress only, cannot account for the observed Peruvian circulation. When an additional barotropic forcing is applied in the model, a dominating poleward flow results. The effects of wind stress are felt on the upper layer and by the third day of integration an equatorward flow develops near the coast. Two functional representations of the actual topography are used in the model and compared to a flat-bottom case. Model results, when compared to observations, show that the observed upwelling maximum ∼40 km south of 15°S is the result of a mesoscale topographic feature, a seamount. Variations of longshore and cross-shelf flow in cases with sloping topography ar...

The development of a coupled ice-ocean model for forecasting ice conditions in the Arctic

A coupled ice-ocean model has been developed to investigate how a better simulation of ice-ocean interaction can improve sea ice forecasting capabilities. The coupling of the ice and ocean results in improved temporal variability of ocean circulation and heat and salt exchange between ice and ocean. The U.S. Navys Polar Ice Prediction System is coupled to a diagnostic version of the Bryan-Cox three-dimensional ocean circulation model. A horizontal grid spacing of 127 km was used in the coupled model with 17 vertical levels from the surface to the ocean bottom. Atmospheric data from the Naval Operational Global Atmospheric Prediction System (NOGAPS) for 1986 were used to force the model. The ice-ocean model simulation yielded realistic ice thickness distributions, ice drifts, and ocean currents. The model predicted accurate seasonal trends in ice growth and decay. Excess ice is often grown in the Greenland and Barents seas in fall and winter. This is due, in part, to the models grid resolution which does not accurately resolve narrow currents, such as the West Spitsbergen Current. A sensitivity study of the heat transfer coefficients used in the ice model showed that the ice edge could be improved by using different coefficient values for thick ice, thin ice, and open water. Other sensitivity studies examined the effect of removing the “distorted” physics frequently used in the Bryan-Cox ocean circulation model and the effect of the vertical eddy momentum coefficient on the surface ocean circulation. An additional simulation was made using 1989 NOGAPS forcing to examine what type of variability could occur when using different years of NOGAPS forcing in the diagnostic ocean model. Significant differences occurred between the 1989 and 1986 ice thickness distributions as well as the oceanic heat fluxes. These differences show that the forecast system, which presently uses an ocean “climatology,” can benefit from the variability allowed by the diagnostic ocean model.

Coastal wave generation in the Bohai Bay and propagation along the Chinese coast

The Bohai Bay and Yellow Sea experience sea surface height (SSH) changes of 20 cm and larger during wintertime northerly and southerly wind bursts that have a time scale of a few days. These large SSH changes give rise to coastal shelf waves that subsequently propagate southward along the Chinese coast. Two models provide observations of these waves. The first one is a statistical model based on four years of TOPEX/POSEIDON (T/P) altimeter SSH observations and Navy Operational Global Atmospheric Prediction System (NOGAPS) wind stress fields. The second model is a numerical model forced by the wind stress. The numerical model provides an objective interpretation of the wind stress response based on dynamical equations. The statistical model is based on observations with a linear response to the wind forcing and thus complements the numerical model. The observed waves closely resemble gravest mode shelf waves derived by analytical solutions.

An ice‐ocean coupled model for the Northern Hemisphere

Abstract : The Polar Ice Prediction System (PIPS), based on the Hibler ice model, has been reformulated into spherical coordinates for the Northern Hemisphere. These spherical coordinates help to avoid a numerical singularity at the North Pole and numerical instabilities in high latitudes. Further, a coordinate transformation was chosen so that a new equator coincides with the 170 deg W - 10 deg E great circle, and a new north pole is located at the intersection of the 100 deg E meridian and the true Equator. The spherical coordinate PIPS model has been extended southward in a version of the model called PlPS2.0. In another development, the Cox ocean model has been transformed into the same spherical coordinate system as PIPS and then coupled with the sea ice model. The coupling technique of the ice and ocean models is conceptually similar to that described in Hibler and Bryan, but the heat and momentum exchanges have been modified. The two models are coupled by exchanging daily information of ice and ocean. The coupled model has been tested using the 1986 monthly forcing of the Navy Operational Global Atmospheric Prediction System (NOGAPS), as well as other inputs describing river runoff, bottom topography, and climatological water temperature and salinity. Preliminary results have been published. This report describes the coordinate transformation referred to above, the physics of the heat and momentum exchanges, model parameters, variable ice-water drag coefficients, and a test case using the 1986 monthly NOGAPS forcing fields. For the discussions in this report, the model domain was divided into seven subregions: the Sea of Okhotsk, the Bering Sea, the central Arctic, the Barents Sea, Hudson Bay, the Labrador Sea/Baffin Bay, and the Norwegian/East Greenland Seas.

Sea surface height variations in the Yellow and East China Seas: 2. SSH variability in the weekly and semiweekly bands

Two types of models are used to examine the sea surface height (SSH) variability at the principle short time frequency bands in the Yellow and East China Seas. The models are a primitive equation numerical model and a statistical model based on TOPEX/POSEIDON altimeter data. In situ pressure gauge measurements at two mooring locations are first used to evaluate each model. In addition, a comparison of the numerical and statistical models is made through duplicate analysis of the response to the main extended empirical orthogonal function wind stress modes. In the northern Yellow Sea the wind stress, pressure gauge data, numerical model, and statistical model all indicate local spectral maxima in bands centered on the weekly and semiweekly periods. The coherence of the two models with the in situ data is significant down to 3-day periods at the northern mooring and down to 5-day periods at the southern mooring. The meridional wind stress variability in the semiweekly band is higher than the weekly band energy in the northern Yellow Sea and Bohai Bay and lower than the weekly band energy across the East China Sea. The SSH variability contained in the weekly and semiweekly bands is largest in the Bohai Bay and northern Yellow Sea with a region of high energy along the Chinese coast. The spatial structure of the weekly and semiweekly SSH variability is similar to the wind stress variability at these bands with semiweekly variability higher in the Bohai Bay and northern Yellow Sea and weekly variability dominant in the East China Sea.

Short‐term sea ice forecasting: An assessment of ice concentration and ice drift forecasts using the U.S. Navy's Arctic Cap Nowcast/Forecast System

In this study the forecast skill of the U.S. Navy operational Arctic sea ice forecast system, the Arctic Cap Nowcast/Forecast System (ACNFS), is presented for the period Feb 2014 – June 2015. ACNFS is designed to provide short term, 1-7 day forecasts of Arctic sea ice and ocean conditions. Many quantities are forecast by ACNFS; the most commonly used include ice concentration, ice thickness, ice velocity, sea surface temperature, sea surface salinity, and sea surface velocities. Ice concentration forecast skill is compared to a persistent ice state and historical sea ice climatology. Skill scores are focused on areas where ice concentration changes by ±5% or more, and are therefore limited to primarily the marginal ice zone. We demonstrate that ACNFS forecasts are skillful compared to assuming a persistent ice state, especially beyond 24 hours. ACNFS is also shown to be particularly skillful compared to a climatologic state for forecasts up to 102 hours. Modeled ice drift velocity is compared to observed buoy data from the International Arctic Buoy Programme. A seasonal bias is shown where ACNFS is slower than IABP velocity in the summer months and faster in the winter months. In February 2015 ACNFS began to assimilate a blended ice concentration derived from Advanced Microwave Scanning Radiometer 2 (AMSR2) and the Interactive Multisensor Snow and Ice Mapping System (IMS). Preliminary results show that assimilating AMSR2 blended with IMS improves the short-term forecast skill and ice edge location compared to the independently derived National Ice Center Ice Edge product. This article is protected by copyright. All rights reserved.

Integrated Modeling of the Battlespace Environment

The goal of the Battlespace Environments Institute (BEI) is to integrate Earth and space modeling capabilities into a seamless, whole-Earth common modeling infrastructure that facilitates interservice development of multiple, mission-specific environmental simulations and supports battlefield decisions, improves interoperability, and reduces operating costs.

Validation of the Global Relocatable Tide/Surge Model PCTides

The Naval Research Laboratory (NRL) has developed a global, relocatable, tide/surge forecast system called PCTides. This system was designed in response to a U.S. Navy requirement to rapidly produce tidal predictions anywhere in the world. The system is composed of a two-dimensional barotropic ocean model driven by tidal forcing only or in conjunction with surface wind and pressure forcing. PCTides is unique in its ability to forecast tidal parameters for a user-specified latitude/longitude domain easily and quickly, and is especially useful in areas where observations are nonexistent. PCTides provides short-term (daily to weekly) predictions of water-level elevation and depth-averaged ocean currents. The system has been tested in numerous regions and validated against observations collected in conjunction with several navy exercises.