Re: Question about @AVE

[Ansley Manke <ansley.b.manke@xxxxxxxx>]

Hi Ming,
If you make sure that the longitude axes that you are using are defined 
as modulo axes, then Ferret will automatically take care of averaging 
across the branch point where it wraps around the earth.  When you open 
your dataset, you can check whether the input data is on  a modulo axis 
with SHOW GRID varname

 yes? show grid t2m

The first few lines will have something like this

   GRID GNAME
  name     axis        # pts      start         end
  LONAX    LONGITUDE   64mr      

If the m is not present after the number of points in the x axis, then 
the axis is not a modulo axis, and Ferret will not  wrap around when 
making computations.  You can change the setting with a SET AXIS 
command.  If the axis name is LONAX, the command is

 yes? set axis/modulo lonax

Also when you define the longitude axes of your new grids, use the 
/modulo qualifier:

 yes? define axis/x=0:360:10/modulo  xax10

Ansley

Ming Yang wrote:

> Hi, folks
>    I have a Netcdf dateset like this:
> name     title                             I         J         K        L
> T2M      Temperature at 2 Meter           1:64      1:32      ...     1:12000
>
>
> The I coordinate represents longtitude. I would like to use @AVE transfromation
> to compute the average value of the variable T2M over several grids, but
> the problem is the grids I would like average include the 0
> longitude, So that in the @AVE transfromation I have to include I=60:64
> as well as I=1:5. I am wondering what is the easiest way to do this
> calculation in ferret? Thank you in advance.
>
> Best,
> Ming
>
>
>
>