Hi Tony,
Yes, if the grid is defined with units of degrees longitude and
latitude, then Ferret does compute with weighted averages. A way to
compare with the nco computation is to set the units of the X and Y
axis to something else
yes? set axis/units=" " `temperature,return=xaxis`
yes? set axis/units=" " `temperature,return=yaxis`
And then compute the average - this will treat the units of the axes as
just numbers, and might compare with the nco computation.
Ansley
Tony Jolibois wrote:
Hi Ansley,
You're right for the correction, nco do not compute weighted average,
ferret yes, I think this is the difference (I tested average on
longitude only I have the same result with nco and ferret).
Thanks for your reponse,
Tony
Ansley Manke wrote:
Hi Tony,
Could you send us the grid information, that is the output of:
ncdump -h mercatorPsy3v1R1v_med_levitus_1998_M01.nc
One thing that could make a difference is whether the averaging
computes the area for each grid cell based on the latitude correction
for the location of each cell. Also, whether the grid is
irregularly-spaced might have some impact.
Ansley
Tony Jolibois wrote:
Hi all,
I have to compute averages on longitude and latitude axes to have a one
value result, data are ocean model outputs (depth=0).
When I use ferret and nco to compute these averages, I don't find the
same result, I don't understand why. With nco I find a
temperature_averaged = 14.06548 and with ferret I find 14.38.
Source file : mercatorPsy3v1R1v_med_levitus_1998_M01.nc (levitus
climatology over Mediterranean sea)
ncwa -a
latitude,longitude -d depth,0,0
mercatorPsy3v1R1v_med_levitus_1998_M01.nc
mercatorPsy3v1R1v_med_levitus_1998_M01_averaged.nc
result : temperature_averaged = 14.06548
yes? use
mercatorPsy3v1R1v_med_levitus_1998_M01.nc
yes? define variable/unit="degC"/title="Temperature (degC)"
temperature_averaged = temperature[x=@AVE,y=@AVE,z=0]
yes? list temperature_averaged
VARIABLE : Temperature (degC) (degC)
DATA SET : MERCATOR PSY3V1R1 VITRINE CLIM (with bathy mask)
FILENAME : mercatorPsy3v1R1v_med_levitus_1998_M01.nc
LONGITUDE: 6.1W(-6.1) to 45.1E(45.1)
LATITUDE : 30N to 48N
DEPTH (m): 0
14.38
yes?
Can someone help me ?
Tony
--
Tony Jolibois
CLS - Direction Océanographie Spatiale
8-10 rue hermès - 31520 Ramonville Saint-Agne
tjolibois@cls.fr
Tél : +33 (0) 561 393 797
Fax : +33 (0) 561 393 782
Click here
to report this email as spam.
--
Tony Jolibois
CLS - Direction Océanographie Spatiale
8-10 rue hermès - 31520 Ramonville Saint-Agne
tjolibois@cls.fr
Tél : +33 (0) 561 393 797
Fax : +33 (0) 561 393 782
|