Time Axis error

["Bruce W. Ford" <fordville_bruce@xxxxxxxxx>]

Ferreters,
 
I'm getting a strange time axis error when subtracting
CDF files that happen to be for Janaury.  The data are
CDC monthly composite CDFs.

For instance:

SET DATA "intraseasonal/feb97-z200a.nc"
SET DATA "intraseasonal/jan97-z200a.nc"
let z200ad = hgt[d=1]-hgt[d=2]

Gives me:
***Note:  Ambiguous coordinates on T axis: 
HGT[d=1]-HGT[d=2]
**Error:  Illegal limits:  HGT is not in the range
T=01JAN
Axis extremes are T+01-JAN  00:00

Thoughts?  Work-arounds?

Thanks in advance!

Bruce

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