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It is a work in progress brought to you by Starpath School of Navigation.
Here is the main eye-opener to modern knowledge of currents. It is a fantastic video from NASA called Perpetual Ocean. We reference here the primary source link. It has been placed on YouTube by many folks, but the resolution is compromised in many and most omit the full credits. Click the picture below to go to the NASA source. You can also download a hi-res copy of the video from that link. Watch the dates change in the video to get a rough estimate of time scale. These are model output, but still a good look at what we must deal with in the ocean.
The key word here is mesoscale eddy. They are all over the ocean. They can pass by you in half a day, or they can last for a month. Peak currents in these eddies can reach 5 kts. Two to three knots is not uncommon. Read about mesoscale eddies at the excellent and extensive AVISO web site. (You will have a hard time finding it on their web site, buy AVISO stands for Archiving, Validation and Interpretation of Satellite Oceanographic data.)
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Here is a sample of the state of the art presentation of live ocean current predictions and vessel positions that is possible with modern techniques. Click the pic for latest live data. This is the fine work of Angeline Pendergrass of UW Atmospheric Sciences Dept. We are following a row boat across the tropical Atlantic. Here is the view as they approached Cape Verde Islands having departed from Dakar, Senegal on the way to Miami.
Unfortunately, for the time being at least, we are not at all sure which ocean model might be the best guide for predicting ocean currents. We are still collecting data and studying this. For now here is a first step toward
Keeping Current with Ocean Currents (an overview and update, which ends up coming back to this page!)
For discussion of global currents see Chapter 31 of Bowditch. It has an excellent chart of major current flow patterns and short discussions of each system. (When you select Chapter 31, it will then say you are downloading Chapter 32, but it is indeed 31. And you must accept a warning that this US Gov web site is not safe, although it is. This is how the government supports navigation schools.)
A very informative link on all ocean currents at RSMAS Miami (Please sign their Guess Book if you like their work).
Six-day view of tropical Atlantic in low resolution (Scrolling the pics shows how the mesoscale eddies evolve and move around.)
See also this SUPER NEAT PRESENTATION of Global Hycom Current forecasts from SOEST HI.
(Scroll the left panel to see all the many options there. You can compare their ROMS model predictions with HF-Radar measurements. See this video on how to get to the HYCOM current forecasts.)
• RTOFS currents in GRIB format via latest version of ViewFax Grib Viewer (Ver. 5.0.56) from Jim Corenman. They are requested from and displayed from within ViewFax. Samples are in our comparison link aboveRTOFS currents are now available from many sources.
• OSCAR currents is GRIB format via svsarana.com (from Eric Baicy, while underway on SV Sarana). They display well in the ViewFax viewer, but might not work in all GRIB viewers. OSCAR are not forecasts, but averages over the past 8 days. These valuable current summaries are developed here in Seattle by Kathleen Dohan. Samples are in our comparison link above. They are now (in 2017) available from saildocs, Luckgrib and and others.
• Global HYCOM currents in GRIB format are available via Ocens WeatherNet
[PS. Jim and Eric are both Pacific Northwest sailors, and Ocens is a Pac NW company, and OSCAR is Seattle. So the Pac. NW is doing its part for mariners worldwide, current-wise!]
US Navy NCOM (note special definition of W Lon = 360 - Lon), sample below
OpenDAC software For requesting and viewing ocean data (have not been able to make any of these work yet!).
Ocean Model Current Areas
***Attention*** NAVO's Global NCOM model is expected to be replaced by a 1/12 deg. eddy resolving global HYCOM model in January 2013. Therefore, the global NCOM model data service will be terminated at that time. NCOM data users are advised to switch to the NCEP implementation of the NAVO's global HYCOM, known as RTOFS-Global (Global Real-Time Ocean Forecast System) via the NCEP operational NOMADS server at:
The NCEP Global Real-Time Ocean Forecast System (RTOFS-Global) data is based on the U.S. Navy implementation of Global HYCOM. Regional NCOM data is provided by the Naval Oceanographic Office (NAVO).
(Mouseover and click the desired area to view the valid Global Ocean Model Currents 0-72 hour forecast data)
For NCOM Regional Data via ftp: http://ftp.opc.ncep.noaa.gov/grids/operational/NCOM/regional/
For archived NCOM Data: http://www.ncddc.noaa.gov/ocean-nomads/global-ncom/
For Data via Nomads GDS server: http://nomads.ncep.noaa.gov:9090/dods/ncom
For East Coast images: http://ftp.opc.ncep.noaa.gov/grids/operational/NCOM/images/
For RTOFS Global Data via ftp: http://ftp.opc.ncep.noaa.gov/grids/operational/GLOBALHYCOM/
RTOFS GLOBAL MODEL INFORMATION
The Global Real-Time Ocean Forecast System is based on NAVO's configuration of the 1/12 deg. eddy resolving global HYCOM model and is initialized daily with NAVO generated initial conditions using the NCODA system. RTOFS Global is forced with NCEP's operational GFS winds. For more details see:NOAA/NCEP/MMAB RTOFS Global Web Page
REGIONAL NCOM MODEL INFORMATION
The Regional NCOM models have a resolution of 1/36 deg. (3 km). The U.S. Navy Operational Global Ocean Model (NCOM), developed by the Naval Research Laboratory (Barron et al, 1&2) and maintained by the Naval Oceanographic Office, provides boundary conditions for the regional models. The regional NCOM models found here include the U.S. East Coast (ncom_useast), The Southern California Coast (ncom_socal), Hawaii Coasts (ncom_relo_hawaii) and the Gulf of Mexico and Caribbean Seas (ncom_relo_amseas). The Navy Coupled Ocean Data Assimilation System (NCODA) provides the data assimilation for NCOM including SSH, SST, and in situ observations. For more information about NCOM see:
to be expanded, as it needs more detail to be a practical guide.
...but the short answer is we get the data from NCEP Central Operations and then we analyze it with a remarkable free program called Panoply (there is a learning curve, but tutorials are online). There are other public programs that will read netcdf data, which is needed for this exercise. The data come as N-S (called U) and E-W (called V) components of the current velocities, which must be added as vectors to make the current vectors.
New Section on Gulf Stream, in progress
* * * COMPARE RTOFS WITH NCOM