uv2dv gives constant field as output.

Dear all,

I'm trying to compute the wind divergence in NCEP-NCAR reanalysis data using cdo uv2dv. I set the variable names to u and v and the codes to 131 and 132. The (global) data were interpolated to a regular gaussian grid, and contain no missing values. The data looked ok until here:

_ cdo info NCEP_uv925_int_T31_wintermeans.nc | head -7

-1 : Date Time Param Level Size Miss : Minimum Mean Maximum
1 : 1948-02-15 00:00:00 131 925 4608 0 : -13.370 0.48458 14.830
2 : 1948-02-15 00:00:00 132 925 4608 0 : -7.3300 -0.048398 7.7100
3 : 1949-02-15 00:00:00 131 925 4608 0 : -13.760 0.11086 12.760
4 : 1949-02-15 00:00:00 132 925 4608 0 : -10.270 -0.065449 7.7700
5 : 1950-02-15 00:00:00 131 925 4608 0 : -12.960 0.14755 13.230
6 : 1950-02-15 00:00:00 132 925 4608 0 : -8.2900 -0.11939 8.2300_

Then I did cdo sp2gp -uv2dv infile outfile. However, my output looks weird, consisting only of one constant value for the whole field.

> cdo info NCEP_dv925_int_T31_wintermeans.nc | head -7
-1 : Date Time Param Level Size Miss : Minimum Mean Maximum
1 : 1948-02-15 00:00:00 155 925 4608 0 : -1.5739e-06 -1.5739e-06 -1.5739e-06
2 : 1948-02-15 00:00:00 138 925 4608 0 : -1.5739e-06 -1.5739e-06 -1.5739e-06
3 : 1949-02-15 00:00:00 155 925 4608 0 : -1.5739e-06 -1.5739e-06 -1.5739e-06
4 : 1949-02-15 00:00:00 138 925 4608 0 : -1.5739e-06 -1.5739e-06 -1.5739e-06
5 : 1950-02-15 00:00:00 155 925 4608 0 : -1.5739e-06 -1.5739e-06 -1.5739e-06
6 : 1950-02-15 00:00:00 138 925 4608 0 : -1.5739e-06 -1.5739e-06 -1.5739e-06

Any idea, why this?

Thanks,
Ralf