Plotting x-y-sigma data on a x,y pressure section

[Jeremy S Pal <jpal@xxxxxxx>]

  Hi -

I have 4D (x-y-z-t) model output data that are stored on a sigma vertical
coordinate.  I want to plot the data (say temperature) on a pressure
vertical grid.  I have successfully created a contour map of temperature
on a latitude-pressure grid using zaxreplace.  However, when I attempt to
create a contour map of temperature for a specified pressure section on a
lat-lon grid, I get an error (see below).  When running the demo
sigma_coordinate_demo.jnl, I also get a similar error.

Does anyone know how to fix this problem?  Also is zaxreplace the best
thing to use to plot sigma coordinate data on a pressure grid?  (I am
running Ferret V500beta1.1 on CompaqTru64 (Digital Unix V4.0F).)


  Thank you in advance,

  - Jeremy


Here is the script:

set data OTMAPCTL_93.des"   ! Open dataset
define axis/z=1:14:1 zz     ! Clone z-axis since I can't figure out how to
                            ! extract sigma values from above data
define grid/z=zz zgrid
file/var=sigma/grid=zgrid sigma.txt  ! Put sigma data onto zgrid
let pres=sigma[d=2]*(ps[d=1]-50)+50  ! Convert sigma to pressure
define axis/Z=50:1000:1/unit=millibars/depth plev
let t_on_p = ZAXREPLACE(tk[d=1,l=5],pres[l=5],z[gz=plev])

shade t_on_p[i=90]    ! This works very nicely
shade t_on_p[z=900]   ! Here it seems to get confused
 **ERROR: illegal limits: TK is not in the range Z=0.995
          Axis extremes are Z=0.995
shade t_on_p[z=0.5]   ! More confusion
 **ERROR: illegal limits: T_ON_P is not in the range Z=0.5
          Axis extremes are Z=49.5:1001