hi - When there's a modulo axis, you can give Ferret ranges of I or X
beyond the values on the grid. You can do this:
let at2m = t2m[i=60:69@AVE]
This average will cross the branch cut. Try this as well, to see what
the values are
LIST/i=60:69 t2m
Ansley
Ming Yang wrote:
HI, Ansley
Thank you for your help. I used show grid t2m to check the longitude
axis and it turned out a modulo axis. But I still don't know how to do the
average. Suppose I want to calculate the mean t2m of grids where I=1:5, I
should use the command
yes? let at2m=t2m[I=1:5@AVE]
But if I want to calculate the mean from I=1:5 plut I=60:64, should I use
the command like this
yes? let at2m=t2m[I=60:5@AVE]
Thank you again for your help.
Ming
On Wed, 11 May 2005, Ansley Manke wrote:
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
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