US mapping mask

Hi there

   Could I ask question about the US masking? Say, I have global
atmospheric ptrecipitaion.
I want to calculate the mean precipitation over US. How can I get a US
masking data file.
Is there some US mask data available in NCL or other database?

(I found in NCL, there is a Ncarg4_1 Earth 1 database, but how can I get
the mask data
or build a mask data?)

Thanks a lot!

Best
W

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Received on Wed Apr 3 09:53:41 2013