Possible bug in zaxreplace

[Bill Gustafson <wigustafson@xxxxxxxxxxx>]

Hello Ferreters,

I am trying to regrid data from sigma levels to pressure surfaces using
the zaxreplace method described in the Ferret v5 documentation.  I have
discovered a reproducable bug (at least with my data) and am curious if
others have noticed it too.  Unfortunately, I have been unable to
reproduce the bug with the default datasets that come with Ferret.  One
possible difference between my data and the others is that I am using
netCDF files while they are not.  The problem occurs on both an SGI O200
with Irix6.5 and on a Dec Alpha running OSFv4.0.

In a nutshell, the problem occurs when trying to plot a particular
vertical level of a variable whose vertical level has been redefined using
zaxreplace.  Once I define the new vertical axis and the interpolated
variable, if I try to do a horizontal plot I get an error about illegal
limits for the vertical levels.  But, if I do the same horizontal plot
using all 4 dimensions (and get the resulting error message), and then
repeat the plot I want of shading 3 dimensions for a horizontal plot, I
get the correct result.

If anybody else has had this problem, I would like to know a work-around
because I cannot use the above method in a script.  The error of forcing
too many dimensions causes the script to crash.

For those interested, below are the lines of Ferret commands I type to
make the problem occur:

 use "/w/ivor/wpac/1990sst/out.90070100.nc"  ! A netCDF formatted file
 set region/l=10                         ! Look at one particular time
 define axis/z=100:1050:10/unit=mb/depth newax
 let temp_on_pres=zaxreplace(temp,pres,z[gz=newax])
 shade temp_on_pres[z=850]

This results in the error:
 **ERROR: illegal limits: TEMP is not in the range Z=0.995
          Axis extremes are Z=0.995

Now, by typing:
 shade temp_on_pres  !This results in an error about too many dims
 shade temp_on_pres[z=850]
I get the correct plot of temperature interpolated to the pressure
surface.

Thanks for any help you can offer.

Sincerely,
    Bill
______________________________________________________________
_                       Bill Gustafson                       _
______________Atmospheric Science Ph.D. Candidate_____________
School:                                                  Home:
Land, Air and Water Resources              1431 El Capitan St.
University of California, Davis           Davis, CA 95616-6656
1 Shields Avenue                                 (530)753-8692
Davis, CA 95616-8627                    
U.S.A.
(530)752-1868                                 ivor@ucdavis.edu
______________________________________________________________