Cumulus Support

As most of us know when setting up the anemometer we have to set the direction facing NORTH because I live in the northern hemisphere.

Having a compass on my iPhone there are 2 options.

1. Apply............ Magnetic north

2. Normal mode... North

Which of the 2 options is correct ?

Thanks Tony

I don't have any official reference but have read somewhere that it should be true north - and that would likely be your 2. Normal mode... North. Makes sense as magnetic is not a fixed/stationery location.

Paul

Yes, wind direction should be reported relative to true north.

...and just to throw in a bit of confusion, you should take into account 'angle of declination'.
This link describes how it works: http://maps.ngdc.noaa.gov/viewers/histo ... clination/

Although as far as I can see, as amateur weather station operators we really don't need such critical accuracy.

It might be different if we were sailing around the world on a square-rigger - it could make all the difference between finding land or dying of thirst and starving...

Cheers,

GraemeT wrote:...and just to throw in a bit of confusion, you should take into account 'angle of declination'.
This link describes how it works: http://maps.ngdc.noaa.gov/viewers/histo ... clination/

Although as far as I can see, as amateur weather station operators we really don't need such critical accuracy.

It might be different if we were sailing around the world on a square-rigger - it could make all the difference between finding land or dying of thirst and starving...

Cheers,

Applying the angle of (d)eclination to magnetic north gets you true north