Notes on Ocean Currents (starpath.com/currents)
...always 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, but AVISO stands for Archiving, Validation and Interpretation of Satellite Oceanographic data.)
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We have done a lot of current comparisons with ocean row boats. The results at that time were not very encouraging. This is described here: A comparison of ocean current models. RTOFS is based on GOFS and that was just udated (mid 2017) to v3.1, which shows notable improvements, so all of this eary work is outdated. We did do a recent study comparing RTOFS and NCOM predictions with HF Radar measurements, which had mixed results.
PS. We also routed this same rowboat across the North Atlantic in 2006 from NYC to Falmouth, England. For that work we used the Navy maps (below) augmented by SST data from Johns Hopkins. The models were not much use in those days, and we had no grib versions to work with. This venture deserves a special write up as we were successful in keeping the boat in favorable water and learned a couple tricks. They won the first (and last) Great North Atlantic Rowing Race, setting a new record in the Guinness Book for the first row across the Atlantic that actually arrived at the intended destination. Earlier records just claimed victory crossing a specific longitude, even if they were in the wrong country.
We also have dicussion of current measurements in the work we did with Jacob Adoram row from Seattle to Australia.
VARIOUS OCEAN AND COASTAL CURRENT REFERENCES,
IN NO PARTICULAR ORDER
Keeping Current with Ocean Currents (an overview and update, which ends up coming back to this page!)
For discussion of global currents see Chapter 36 of the latest (2017) Bowditch... or maybe better still find an older version to supplement this one. The coverage seems to be going down. This It has an excellent chart of major current flow patterns and short discussions of each system. PS, as of some point in 2018, NGA discontinued chapter downloads so you need to get the full 109 MB book.
A very informative link on all ocean currents at RSMAS Miami (Please sign their Guest 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.)
Row Boats in Ocean Currents
Summary of Ocean Current Models
HF Radar currents
HF-Radar Coastal Current Measurements
NDBC Presentation of HF radar currents
Global Hf Radar Stations
Limited HF-Radar data for HI Compare with NCOM predictions for HI
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.
Description of RTOFS model with evaluation (pdf)
• RTOFS currents in GRIB format are avilable from Saildocs and Zygrib, and several other sources that offer direct download. (A new version of Zygrib called XyGrib is imrpoved and well maintained, but it does not as of Jan 10, 2019, have direct links to ocean currents. Get RTOFS in GRIB format direct from NOMADS. Get RTOFS in netcdf (.nc) format to open in Panoply and make exports to Google Earth. The data are issued daily starting with h12 and then every 24h to h108. That is 5 forecasts, 24h apart starting on 12z.
Article and Video on the Use of Panoply to View NetCDF Currents
• NCOM is a regional Navy model and considered superior to RTOFS where it is available. NCOM is offered by LuckGrib and there is a direct link to each of the NCOM regions from within Expedition under MyGribs section. You can also get NCOM data by full region direct from NOMADS. These grb2 files can be viewed in OpenCPN. They are about 29 MB.
• OSCAR currents is GRIB format are available from Saildocs. OSCAR are not forecasts, but averages of observed data related to current flow over the past 10 days, issued every 5 days. These valuable current summaries are developed here in Seattle by Kathleen Dohan. Samples are in our comparison link above. We have found that these OSCAR averages are the best way to plan a route across the Equitorial currents and countercurrents. Here is a video note on how to download and view global OSCAR currents for any date. We use Panoply and Google Earth, but these files can be obtained from saildocs. Our text Modern Marine Weather has an extended section on how to obtain various ocean weather relatated products from saildocs as well as from FTPmail. OSCAR currents in netcdf (.nc) format. This data will take Panoply to read.
• Global HYCOM currents in GRIB format are available via Ocens WeatherNet.
• Global Hycom from US Navy
• Archived Global HYCOM (in NetCDF format)
Ocean Model Current Areas
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). This link has many data sources plus a way to get a crude graphic view. The inactive pic below shows the regions you can access online.
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
Copernicus model from Mercator-Ocean in France
Very good global data in this online viewer. Data can be exported to Google Earth.
Select: hourly mean merged surface currents... AND sea_water_velocity. Click a point to get the Time Series option shown below.
REGIONAL NCOM MODEL INFORMATION
The Regional NCOM models produce 4-day forecasts at 3-hour time steps, updated at 00Z daily. FNMOC interpolates the output onto a regular grid with 1/30 degree (~3km) resolution in the horizontal and 40 levels in the vertical; prior to April 5, 2013, the resolution was roughly 1/36 degree. The NetCDF files contain ocean temperature, salinity, eastward and northward currents, and elevation, along with the atmospheric forcing fields provided over the model domain by a 15 km application of the Navy's COAMPS model. The regional NCOM ocean prediction systems assimilate all quality-controlled observations in the region including satellite sea surface temperature and altimetry, as well as surface and profile temperature and salinity data using the Navy Coupled Ocean Data Assimilation (NCODA) system. Boundary conditions are applied from the FNMOC operational 1/12 degree Global HYCOM. Prior to April 2013, boundary conditions were applied from the Navy operational Global NCOM.
Present regional data (grib 2)
Archived global NCOM selected years (2010 to 2013)
Archived Regional data starting and covering various years
New Section on Gulf Stream, in progress...
See super nice presentation by Frank Bohlen at the bermudarace.com site. Includes actual analysis of past races across the current.
NAVO color images. THE STARTING POINT (in our approach) FOR GULF STREAM ANALYSIS: North part color graphic (BW digital) and the South part and GOM color graphic (BW digital )
Save these links they can be hard to find; for a while they were at the OPC, then as of Jul. 2018 they were gone. Compare these with the OPC data: Inshore limit of the southern Gulf Stream
* * * COMPARE RTOFS WITH NCOM (both of these are available in grib format)
Our note on Gulf Stream Sources off the Coast of Florida
Video on importing the Navy Gulf Stream boundaries into echart program as a gpx file.
Sites on the Web for Sea Surface Temperature (SST) and Gulf Stream information.
NAVY SOURCES (these often do not work!.... or you may have to tell your browser to accept pages without valid security certificates.)