OCEAN SURFACE CURRENTS .. how to obtain and display Back to Valhalla's Mooring Page
A recent resource for ocean surface currents anywhere in the world is available from the ‘SLOG’ maintained by Eric and Sherrell on SV SARANA. Their procedure for getting the data is at http://www.svsarana.com/oscar/index.php
From the SV SARANA website:
To Retreive current grib information your request should have the following format:
Where LAT1 and LAT2 range between 80N and 80S and LON1 and LON2 are between 180W and 180E
IF you are retrieving data to be used with the OpenCPN program (version 3.2.0) there are some constraints on the requested data.
1) Do not use the equator (0) as a parameter for latitude. Parameters may range from N to S or S to N.
2) Use longitude parameters from W to E (e.g., 120E,130E).
3) Use longitude parameters of multiples of 10 degrees.
An example is shown at the bottom of this page.
If you are retrieving data to be used with the Airmail companion ViewFax program or the Expedition LT program the above restrictions do not apply.
Basically you decide the latitude and longitude limits of the desired data.. This 'box' will look like: 15N,0N,105E,135E
Using any email service, send a blank message to query<at>svsarana.com with the text 'oscar:15N,0N,105E,135E' (using your desired 'box' information. Note that there are no spaces between the text information. Don't overlook the colon after 'oscar').
Within a minute you will receive a reply with an attachment. Save it to your computer.
AIRMAIL/VIEWFAX. If you use the Airmail program the reply will look like:
Double left-clicking on the icon at the bottom left brings up the ViewFax image. Note that the drift (velocity) of the current is displayed wherever the cursor (red arrow) is positioned.
EXPEDITION LT: An alternative display of the information is the Expedition LT program. You can download this program from here.
While the main purpose of this program is to obtain and view GRIB weather files it does display the current files and is a bit better in land detail than the ViewFax program as shown above. A tutorial (in PowerPoint format) on using this program to obtain weather GRIB file can be downloaded from here. (Click on the download icon on the upper right)
Below is the same current file as displayed above in the ViewFax program.. With the 'Current' selected in the window on the right, the drift (velocity) of the current arrows is indicated by the color of the arrow. Also, wherever the cursor (hand with finger) is positioned, the set and drift are displayed in a box.
OpenCPN: Now for an example of using the OpenCPN program version 3.2.0..
The requested current grib file was "OSCAR:10N,1N,120E,140E. The display in OpenCPN is:
Note that the arrows show the direction (set) of the current and, wherever the cursor (red arrow) is positioned the velocity (drift) is shown in the box at the bottom of the GRIP Display Control window. Personally I do not like this display other than it can be overlaid on a planned route for possible changes to take advantage or minimize effects of the current. .
MAX SEA The current display in MaxSea version 10.3.2.1 is done by treating the file as a weather file.
Navigate to where you have saved the OSCAR current GRIB file and open it.
The display shows current arrows with the size proportional to the velocity (drift) of the current.
The symbols for current can be changed by selecting the options for weather.
There are four choices for display of the current. The 'bubbles' choice ...
... gives this display. The velocity (drift) of the current is shown in the bubble and the direction (set) shown with arrows around the bubble.