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Re: [ferret_users] Are there changes to @DIN transformation in new FERRET v6.64?

Hi -
Thank you for the report.  The units of the integral should be in meters.  According to the General information about transforms
"When calculating integrals and derivatives (@IIN, @DIN, @DDC, @DDF, and @DDB) Ferret attempts to use standardized units for the grid coordinates. If the underlying axis is in a known unit of length Ferret converts grid box lengths to meters."
So, assuming your grid is in units of Longitude/Latitude, and Meters for depth, then the result would be in meters.  The only code change between v6.1 and v6.64, is the result of this discussion about the latitude correction for computations on the globe,


which applied in particular to irregularly-spaced grids and grids where the coordinate values are not centered in their grid boxes.  The difference for that calculation for fairly small regions such as yours and small grid boxes, should not be significant.

The other thing that occurred before v6.64 is a change in the compilers we use to build Ferret. I do see a difference in Ferret executables built with the previous compiler and the  current one, when I try computing a computation over var[X=@DIN,Z=@DIN] as you are doing.  We'll look into this more.


On 11/21/2010 8:47 PM, Chaojiao.Sun@xxxxxxxx wrote:

We recently upgraded our old FERRET v6.1 to the new v6.64 on a Dell M905 blade server running Suse Linux Enterprise Server 11, with the executables "64-bit Linux  v6.6.4 Linked with NetCDF-4 libraries" downloaded from the FERRET website. 

There was an unexpected change to the volume transport calculation: I used to get m^3 in my transport calculation, and by dividing by 10^6, I would get transport in Sv. Now when I run the same program, the unit seems to be no longer in m^3. What has changed?

Here is an example:

Vortex> ferret
        FERRET v6.64
        Linux(gfortran) 2.6.9-89.0.20.ELsmp - 09/16/10
        22-Nov-10 12:28

yes? use uvw.relax.05.clim.2065-2085.nc
yes? show data
     currently SET data sets:
    1> ./uvw.relax.05.clim.2065-2085.nc  (default)
 name     title                             I         J         K         L
 U        zonal current                    1:1191    1:968     1:47      1:1
 V        meridional current               1:1191    1:968     1:47      1:1
 WT       vertical velocity T-points       1:1191    1:968     1:47      1:1
          Start time for average period    ...       ...       ...       1:1
          End time for average period      ...       ...       ...       1:1
          Length of average period         ...       ...       ...       1:1

yes? list v[x=113.5:116@din,y=-32,z=0:200@din]
             VARIABLE : meridional current (m/sec)
             DATA SET : OFAM Mk3.5 A1B Relax
             FILENAME : uvw.relax.05.clim.2065-2085.nc
             LONGITUDE: 113.5E to 116E (XZ integ.)
             LATITUDE : 32S
             DEPTH (m): 0 to 200 (XZ integ.)
             TIME     : 01-MAY-2065 12:00 NOLEAP

Question: what is the unit of this transport value of -196.3?

Please note: by manual calculation, I should get about -4 Sv.


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