E. J. Metzger

Comparisons of monthly mean 10 m wind speeds from satellites and NWP products over the global ocean

Received 31 December 2008; revised 15 June 2009; accepted 19 June 2009; published 27 August 2009. [1] The accuracy of wind speed at 10 m above the sea surface from two satellite and three numerical weather prediction (NWP) products is investigated over the global ocean. Rain-free equivalent neutral winds from the Quick Scatterometer (QuikSCAT) are converted to stability-dependent winds to be consistent with those from NWP products and are taken as truth in comparisons to winds from other products. Quantitative statistical analyses presented at each grid point over the global ocean reveal that monthly winds from NWP products have almost perfect skill relative to those from QuikSCAT winds during the 3-year common period (September 1999 to August 2002). Exceptions occur in tropical regions and high southern latitudes. Wind speeds adjusted to 10 m at many moored buoys located in different regions of the global ocean further confirm the accuracy of monthly NWP winds, giving RMS difference of 1.0 m s � 1 based on 1281 monthlong time series. The satellite-based QuikSCAT winds agree with buoy winds relatively better than NWP products. While there is good agreement among wind products on monthly timescales, large differences (>3 m s � 1 and more) in NWP winds are found in comparison to QuikSCAT winds on shorter time intervals at high latitudes. Daily means of sensible and latent heat fluxes based on NWP winds can therefore differ as much as 100 W m � 2 in comparison to those based on QuikSCAT winds. In general, NWP wind-based sensible and latent heat fluxes are more similar to their QuikSCATwind-based counterparts in tropical regions and midlatitudes.

Upper-Ocean Processes under the Stratus Cloud Deck in the Southeast Pacific Ocean

Abstract The annual mean heat budget of the upper ocean beneath the stratocumulus/stratus cloud deck in the southeast Pacific is estimated using Simple Ocean Data Assimilation (SODA) and an eddy-resolving Hybrid Coordinate Ocean Model (HYCOM). Both are compared with estimates based on Woods Hole Oceanographic Institution (WHOI) Improved Meteorological (IMET) buoy observations at 20°S, 85°W. Net surface heat fluxes are positive (warming) over most of the area under the stratus cloud deck. Upper-ocean processes responsible for balancing the surface heat flux are examined by estimating each term in the heat equation. In contrast to surface heat fluxes, geostrophic transport in the upper 50 m causes net cooling in most of the stratus cloud deck region. Ekman transport provides net warming north of the IMET site and net cooling south of the IMET site. Although the eddy heat flux divergence term can be comparable to other terms at a particular location, such as the IMET mooring site, it is negligible for the en...

Global Ocean Prediction Using HYCOM

One important aspect of ocean model design is the choice of the vertical coordinate system. Traditional ocean models use a single coordinate type to represent the vertical, but model comparison exercises performed in Europe (DYnamics of North Atlantic MOdels - DYNAMO) (Willebrand et al., 2001) and in the United States (Data Assimilation and Model Evaluation Experiment - DAMEE) (Chassignet et al., 2000) have shown that none of the three main vertical coordinates presently in use (depth [z-levels], density [isopycnal layers], or terrain-following [sigma-levels]) can by itself, be optimal everywhere in the ocean. The HYbrid Coordinate Ocean Model (HYCOM) (Bleck, 2002) is configured to combine all three of these vertical coordinate types. It is isopycnal in the open, stratified ocean, but uses the layered continuity equation to make a dynamically smooth transition to a terrain-following coordinate in shallow coastal regions, and to z-level coordinates in the mixed layer and/or unstratified seas. The hybrid coordinate extends the geographic range of applicability of traditional isopycnic coordinate circulation models toward shallow coastal seas and unstratified parts of the world ocean. It maintains the significant advantages of an isopycnal model in stratified regions while allowing more vertical resolution near the surface and in shallow coastal areas, hence providing a better representation of the upper ocean physics

Southern Bay of Bengal currents and salinity intrusions during the northeast monsoon

Shipboard velocity and hydrographic profiles collected in December 2013 along with drifter observations, satellite altimetry, global ocean nowcast/forecast products, and coupled model simulations were used to examine the circulation in the southern Bay of Bengal as part of ongoing international research efforts in the region. The observations captured the southward flowing East India Coastal Current (EICC) off southeast India and east of Sri Lanka. The EICC was approximately 100 km wide, with speeds exceeding 1 m s−1 in the upper 75 m. East of the EICC, a subsurface-intensified 300 km-wide, northward current was observed, with maximum speeds as high as 1 m s−1 between 50 m and 75 m. The EICC moved low-salinity water out of the bay and the subsurface northward flow carried high-salinity water into the bay during typical northeast monsoon conditions during a time period when the central equatorial Indian Ocean was experiencing a westerly wind burst related to the Madden-Julian Oscillation (MJO) event. While the northward subsurface high-salinity flow has previously been observed during the southwest monsoon, it was observed during the northeast monsoon. The observations are consistent with northward high-salinity subsurface flow in numerical model solutions. The analysis suggests that direct forcing along the equator may play a significant role for high-salinity intrusions east of Sri Lanka.

Real-time ocean modeling systems

The Naval Research Laboratory has developed the worlds first eddy-resolving global ocean nowcast and forecast system. It uses satellite observations and on ocean model running on a high-performance-computing platform to enhance real-time knowledge of the marine environment in which naval submarines and ships must operate.

Real-time Data Assimilation of satellite derived ice concentration into the Arctic Cap Nowcast/Forecast System (ACNFS)

Over the last decade, ice conditions in the Arctic have changed dramatically resulting in the Arctic having a minimum in ice extent during the summers of 2007, 2008 and 2010. With this rapidly changing polar environment, the need for accurate ice forecasts is essential. The Naval Research Laboratory (NRL) has developed the Arctic Cap Nowcast/Forecast System (ACNFS), a two-way coupled ice/ocean system, to forecast ice conditions in the polar regions. This system applies the Los Alamos Community Ice CodE (CICE) coupled via the Earth System Modeling Framework (ESMF) to the HYbrid Coordinate Ocean Model (HYCOM). The Navy Coupled Ocean Data Assimilation (NCODA), a 3-Dimensional VARiational analysis (3DVAR) scheme, is used to assimilate ice and ocean observations into the forecast system. Ice concentration data from two sources: the Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave/Imager (SSM/I) and the Advanced Microwave Scanning Radiometer for Earth Observation System (AMSR-E) are used as observations for the ice analysis. Results from the coupled system using both concentration input datasets will be discussed.

Basin-scale ocean prediction with the hybrid coordinate ocean model

Eddy-resolving simulations of the Atlantic and Pacific Oceans were performed using the hybrid coordinate ocean model (HYCOM) at 1/12/spl deg/ (/spl sim/7 km midlatitude) resolution. HYCOM is isopycnal in the open, stratified ocean, but makes a dynamically smooth transition to a terrain-following coordinate in shallow water and to pressure coordinates in the mixed layer and/or unstratified regions via the layered continuity equation. This approach retains the advantages that each individual vertical coordinate system offers. After a series of free-running simulations, a data assimilative version of the 1/12/spl deg/ Atlantic HYCOM has been developed into a near real-time nowcast/forecast system. Sea surface height analyses of available satellite altimeter data are assimilated into the model. A nowcast and a 10-day forecast are produced each week. Near real-time results are available via the HYCOM consortium for data assimilative ocean modeling web page at http://hycom.rsmas.miami.edu.

An operational real-time eddy-resolving 1/16/spl deg/ global ocean nowcast/forecast system

A real-time eddy-resolving global ocean nowcast/forecast system has been running at the Naval Oceanographic Office (NAVOCEANO) since 18 October 2000 and it became an operational product on 27 September 2001. The system, which was developed at the Naval Research Laboratory (NRL), uses the NRL Layered Ocean Model (NLOM) with 1/16/spl deg/ resolution and seven layers in the vertical. Real-time satellite altimeter sea surface height (SSH) from TOPEX/Poseidon, ERS-2 and Geosat-Follow-On provided by NAVOCEANOs Altimeter Data Fusion Center, are assimilated into the model. The large size of the model grid (4906/spl times/2304/spl times/7) and operational requirements makes it necessary to use a computationally efficient ocean model and assimilation scheme. The assimilation consists of an optimum interpolation (OI) deviation analysis of SSH with the model as a first guess, a statistical inference technique for vertical mass field updates, geostrophic balance for the velocity updates outside the equatorial region and an incremental updating of the model fields to further reduce gravity wave generation. A spatially varying mesoscale covariance function determined from TOPEX/Poseidon and ERS-2 data is used in the OI analysis. The sea surface temperature (SST) assimilation consists of relaxing the NLOM SST to the Modular Ocean Data Assimilation System (MODAS) SST analysis which is performed daily at NAVOCEANO. Real-time and archived results from the model can be viewed at the NRL Website http://www.ocean.nrlssc.navy.mil/global/spl I.bar/nlom. This includes many zoom regions, nowcasts and forecasts of SSH, upper ocean currents and SST, forecast verification statistics, subsurface temperature cross-sections, the amount of altimeter data used for each nowcast from each satellite and nowcast comparisons with unassimilated data. The results show that the model has predictive skill of the mesoscale variability for at least one month.