CDO

I am trying to transform ECMWF monthly averaged fields on model levels into pressure levels. However, the Time stepType "avgd" is apparently unsupported. Is there a workaround?

cdo sinfon era20c_ml_1.grib  

gives

gribapiGetTsteptype: Time stepType avgd unsupported, set to instant!
File format : GRIB2
-1 : Institut Source T Steptype Levels Num Points Num Dtype : Parameter name
1 : ECMWF unknown v instant 91 1 51200 1 P16 : t
2 : ECMWF unknown v instant 91 1 51200 1 P16 : q
3 : ECMWF unknown v instant 91 1 51200 1 P16 : u
4 : ECMWF unknown v instant 91 1 51200 1 P16 : v
5 : ECMWF unknown v instant 1 2 51200 1 P16 : z
6 : ECMWF unknown v instant 1 2 51200 1 P16 : lnsp
Grid coordinates :
1 : gaussian : points=51200 (320x160) np=80
lon : 0 to 358.875 by 1.125 degrees_east circular
lat : 89.14152 to -89.14152 degrees_north
Vertical coordinates :
1 : hybrid : levels=91
lev : 1 to 91 by 1 level
available : vct
2 : hybrid : levels=1
lev : 1 level
available : vct
Time coordinate : 1 step
RefTime = 1900-01-01 00:00:00 Units = hours Calendar = proleptic_gregorian
YYYY-MM-DD hh:mm:ss YYYY-MM-DD hh:mm:ss YYYY-MM-DD hh:mm:ss YYYY-MM-DD hh:mm:ss
1900-01-01 00:00:00
cdo sinfon: Processed 6 variables over 1 timestep [0.64s 88MB]

cdo ml2plx

gives

gribapiGetTsteptype: Time stepType avgd unsupported, set to instant!
!!! failed call to grib_set_long( grib_handle* h, "indicatorOfUnitForTimeRange", 1) !!!
stream_gribapi.c at line 1786: my_grib_set_long(gh, "indicatorOfUnitForTimeRange", unitsOfTime) failed: Key/value not found