Ask the Experts: What is the correct wind direction convention to use in EFDC?
While the standard meteorological convention for the wind direction is the compass direction that the wind is coming from (direction from), in EFDC the standard convention is the compass direction that the wind is going towards (direction towards).
If you are given wind direction as the direction from, you can use a simple filter in a spreadsheet program to transform the data to the proper sign convention in EFDC:
=IF(WDIR > 180, WDIR – 180, WDIR + 180)
Alternately, you can use the ISWDINT flag in the EFDCwser.inp file and have EFDC make this correction for you. Here is the explanation of that flag from the wser.inp header:
C ** ISWDINT(NW) = DIRECTION CONVENTION
C ** 0 DIRECTION TOWARDS (EE DEFAULT)
C ** 1 DIRECTION FROM
C ** 2 WINDS IS EAST VELOCITY, WINDD IS NORTH VELOCITY
Note that if you use an ISWDINT other than 0, EFDC will transform your input files to the standard convention of direction towards as soon as the model executable is run.
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