Author Topic: Anemometer Direction  (Read 1228 times)

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Offline SlowModem

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Anemometer Direction
« on: December 19, 2013, 03:06:22 PM »
Asked on another thread:

........could [you] shed some light on a confusion around wind direction reference that seems to be around.

Is the wind direction for surface wind for meteorological use based on magnetic or geographic north? I  expect that it is geographic north, but then at airports the surface wind is always reported in reference to magnetic north, to go together with the magnetic north reference for the runways.

Some weather station instructions simply say to use a compass to line the vane up with north and are mum as to whether or not to compensate for the local variance while others just say to line it up with North and leave it at that.

From the CWOP Weather Station Siting, Performance, and Data Quality Guide:

CWOP requires wind direction reports in degrees from true north. You will have to
locate magnetic north using a compass and rotate and lock in your mast
using installation procedures. Before installing your mast, know the magnetic declination
to correct to true north. The National Geophysical Data Center (NGDC) has a page that
will calculate this for you:
Here’s a link to a declination map for the CONUS (lower 48 states of the U.S.):
Use of a GPS can be very beneficial in determining your precise latitude and longitude;
however, GPS is notoriously inaccurate in determining direction when stationary. GPS
should not be used to determine north; a magnetic compass is a much more accurate tool
for this determination. If unable to point the anemometer to true north during mast
installation, make a direction correction from your weather station console or data
logging software.
« Last Edit: December 19, 2013, 03:10:38 PM by SlowModem »
Greg Whitehead
Ten Mile, TN USA