Re: [ferret_users] Average with ferret vs nco

[Ingo Bethke <Ingo.Bethke@xxxxxxxxxxxxxx>]

Hi Tony,

It seems that your NCO average is just an arithmetic average whereas 
your FERRET average is an area weighted average.

You can achieve the same with NCO using the -w option (but then you need 
to have the grid cell area available as a separate variable).

Cheers,
Ingo

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)
>
>     * With nco :
>
> 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
>
>     * With ferret :
>
> 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
>