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Wind direction - atan2 ?
Added by Bartosz Czernecki about 6 years ago
Hi All,
Does anybody know whether it is possible to calculate wind direction (in degrees) based on the horizontal (U) and vertical (V) wind components?
I have both variables are in one file and I tried to manipulate with the ATAN2 function, but with no success so far..
Best,
Bartek
hi!
atan2 is not available in the expr operators unfortunately. you can create numpy arrays from U and V and use atan2 from there
cheers
ralf
Thanks Ralf,
This is what I thought :/
I would like to avoid python since it would require administrative privilages on a cluster machine, so I'll try to figure out whether is doable in any other way.
In the meantime I found another solution in the Joerg Wenger's slides (https://www.dkrz.de/mms/pdf/klimaforschung/cmip5/Processing_Joerg_Wegner.pdf , slide 16):
cdo mulc,57.3 -atan2 -mulc,-1 U1000.nc -mulc,-1 V1000.nc UV.nc
Unfortunetaly, after creating 2 seperate files for my variables (u10.nc and v10.nc) it still doesn't work...
cdo mulc,57.3 -atan2 -mulc, -1 u10.nc -mulc, -1 v10.nc uv.nc
Operator >1< not found!
Similar operators are:
(not found)
Any ideas what's wrong with that?
Best,
Bartek
I've just figured out a solution with NCO:
ncap2 -v -O -s 'uv10=57.29578*(atan2(U10,V10))+180' input.nc output.nc
.. but I am still willing to get answer to the previous question 
Best,
Bartek
Bartosz Czernecki wrote:
Thanks Ralf,
This is what I thought :/
I would like to avoid python since it would require administrative privilages on a cluster machine, so I'll try to figure out whether is doable in any other way.
In the meantime I found another solution in the Joerg Wenger's slides (https://www.dkrz.de/mms/pdf/klimaforschung/cmip5/Processing_Joerg_Wegner.pdf , slide 16):
cdo mulc,57.3 -atan2 -mulc,-1 U1000.nc -mulc,-1 V1000.nc UV.nc
Unfortunetaly, after creating 2 seperate files for my variables (u10.nc and v10.nc) it still doesn't work...
cdo mulc,57.3 -atan2 -mulc, -1 u10.nc -mulc, -1 v10.nc uv.nc
Operator >1< not found!
Similar operators are:
(not found)
there is a space between mulc, the parameter 1. try this
cdo mulc,57.3 -atan2 -mulc,-1 u10.nc -mulc,-1 v10.nc uv.nc
I think the spaces came from copy/paste from the pdf, this gives funny results sometimes ...
hth
ralf
works like a charm!
thanks a lot! 
best,
bartek