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compositing question



Greetings,

I'm trying to do a composite analysis with ferret and I'm not sure how to 
go about it.  Basically, I have an index file with 15000 days and winds 
with the same time axis.  I want to composite the extreme events with 
extreme defined by some threshold value of the index.  

A rough flow chart should clear up what I'm trying to accomplish:

Open index file
Open data file

define axis/units=day/t=-20:20:1 lag !define a new 41 pt time axis axis 
that goes from 20 days before to 20 days after the extreme.

!now the hard part

scan the index file for values .gt. 2.  for each value greater than 2, get 
the l value.  

for the first such event, then write l-20:l+20 from the data file to a new 
file regridded to the new axis.

for the regridding, could do something like 
let tstamp=t[gz=lag] * 0
let composite = data[l=l=20:l=l+20,d=2] + tstamp !this won't work but 
something like it should.

then for every other event add it to the existing composite file.

At the end I need to divide by the total # of events composited so I need 
a way to count somehow.

I hope this makes sense.  Any help is appreciated.

Cheers,

Brent






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