[ferret_users] strange error in climatological zonal average

[jagadish karmacharya <j_karmacharya@xxxxxxxxx>]

Hi all,

I am facing a trouble in zonal averaging that seems strange, atleast to me. The error seems to occur only when condition is just right (or shall I say wrong). Here is my script:

use "/data/erai/erai.ZT.mon.abs.nc"
set region/x=40:110/y=-10:40
set data climatological_axes; can data climatological_axes
let zta=ztemp[t=15-dec-1991:15-nov-2005]
let ztempc=zta[gt=month_reg@mod]
fill/nolab ztempc[x=@ave,z=@ave]

This results in " No valid data " in the plot window. Here is details about data:
sh d
    currently set data sets:
    1> /data/erai/erai.ZT.mon.abs.nc (default)
name        title                        I            J         K        L
ZTEMP    Temperature           1:49     1:38      1:8      1:269   

I tried to trace the source of error without sucess but found that  the error doesn't occur under different scenarios such as:
1) Meridional average ( i.e. fill/nolab ztempc[y=@ave,z=@ave] -> generate plot)
2) use whole time seris used to produce climatology (i.e. let ztempc=ztemp[gt=month_reg@mod]  & then using fill -> generate plot)
3) if zonal average is done ahead of fill command (i.e  replace one of the corresponding line in above script with
    let zta=ztemp[x=@ave,t=15-dec-1991:15-nov-2005]
    or 
    let ztempc=zta[x=@ave,gt=month_reg@mod]
    and then fill/nolab ztempc[z=@ave] -> generate plot)
4) no such problem with one other data I tried:
    (sh d
         currently set data sets:
         1> /data/model/aktica.pm.ztemp.nc (default)
         name        title                        I             J         K        L
        ZTEMP    Temperature T          1:159   1:113    1:17    1:228 )

I am wondering why this error occured in the 1st scenario? does it has to do with data order or something else?

Thank in advice.
 

Jagadish