Layer averaging (winds)

[Stephen R McMillan]

Aloha Janon--how's it going?

By convention, as with other variables (lat, lon, time), GrADS considers
pressure levels from low to high (by height, that is), so your second
opton (lev=500,lev=200) should give you the correct result. You've
probably already noticed that 'd u(lev=200);v.2(lev=200)' will give you
the same result as your first option.

I agree with you--seems like the order should not matter, but it does in
GrADS. Of course, someone out there in GrADS-land may know of situations
where the order does not matter.

Good luck from PA--
Steve McMillan



Jason E Patla <patla at HAWAII.EDU>
Sent by: GRADSUSR at LIST.CINECA.IT
09/14/2006 11:27 PM
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Layer averaging (winds)





Aloha Group,
I'm trying to determine the average winds vectors with files of
multi-layered U (u) and V (v.2) wind components.  I am unfortunately
getting mixed results using the AVE and MEAN functions.
For example, when trying to display the layer average for 200mb to 500mb,
the two following commands yield different results (only the order of the
levels are switched):

d ave(u,lev=200,lev=500);ave(v.2,lev=200,lev=500)

and

d ave(u,lev=500,lev=200);ave(v.2,lev=500,lev=200)

I would have guess the average is the average regardless from which layer
you start or finish.  I get the same differing output using the MEAN
command.  Any suggestions?  FYI, the levels in between are 200, 250, 300,
400 and 500mb.
Thanks in advance for your help.
Jason

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