That is a problem with cdo. The first time step should be considered, the second is just the first timestep of the next month. You should use the average.sh script which is present in the regcm postproc directory, It makes the file with one timestep.<div>
average.sh month 
<a href="http://india_atm.2002010100_pressure.nc/" target="_blank">India_ATM.2002010100_pressure.nc</a> <a href="http://india_atm.200207.nc/" target="_blank">India_ATM.200207.nc</a> <br><br><div class="gmail_quote">On Thu, May 24, 2012 at 8:11 PM, Kanha Pattnayak <span dir="ltr">&lt;<a href="mailto:kcpattnayak@gmail.com" target="_blank">kcpattnayak@gmail.com</a>&gt;</span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Dear All<div><br></div><div>I am using CDO for calculating daily and monthly files for RegCM4.2 outputs i.e. ATM, RAD and SRF files.</div>
<div>After the postprocessing, the monthly files suppose to be of <b>1 time step</b> but the .ctl files shows <b>2 time step </b>and both the time steps shows different values.</div>
<div>I am totally confuse which time step to use whether 1st or 2nd. Please suggest me what to do.</div><div><br></div><div>I am using the following command for monthly average</div><div><br></div><div>cdo monavg <a href="http://India_ATM.2002010100_pressure.nc" target="_blank">India_ATM.2002010100_pressure.nc</a> <a href="http://India_ATM.200207.nc" target="_blank">India_ATM.200207.nc</a></div>

<div><br></div><div>The following is the corresponding .ctl file</div><div><br></div><div><div>dset ^<a href="http://India_ATM.200207.nc" target="_blank">India_ATM.200207.nc</a></div><div>dtype netcdf</div><div>undef -1e+34_FillValue</div>

<div>title ICTP Regional Climatic model V4 ATM output</div><div>pdef  118  99 bilin sequential binary-big ^India.coord</div><div>xdef   258 linear   49.47   0.24</div><div>ydef   197 linear   -5.11   0.24</div><div>zdef   11 levels  1000.0  925.0  850.0  700.0  500.0  400.0  300.0  250.0  200.0  150.0  100.0</div>

<div>tdef        2 linear 18Z31jul2002    6hr</div><div>vectorpairs u,v s01u10m,s01v10m</div><div>vars   14</div><div>xlon=&gt;xlon 0 y,x Longitude at cross points (degrees_east)</div><div>xlat=&gt;xlat 0 y,x Latitude at cross points (degrees_north)</div>

<div>topo=&gt;topo 0 y,x Domain surface elevation (m)</div><div>mask=&gt;mask 0 y,x Domain land/ocean mask (1)</div><div>ps=&gt;ps 0 t,y,x Surface pressure (hPa)</div><div>u=&gt;u   11 t,z,y,x U component (westerly) of wind (m s-1)</div>

<div>v=&gt;v   11 t,z,y,x V component (southerly) of wind (m s-1)</div><div>omega=&gt;omega   11 t,z,y,x Pressure velocity (hPa s-1)</div><div>t=&gt;t   11 t,z,y,x Temperature (K)</div><div>qv=&gt;qv   11 t,z,y,x Water vapor mixing ratio (kg kg-1)</div>

<div>qc=&gt;qc   11 t,z,y,x Cloud water mixing ratio (kg kg-1)</div><div>tpr=&gt;tpr 0 t,y,x Total daily precipitation rate (kg m-2 day-1)</div><div>tgb=&gt;tgb 0 t,y,x Lower groud temperature (K)</div><div>swt=&gt;swt 0 t,y,x Total soil water (kg m-2)</div>

<div>endvars</div></div><div><br></div><div><br></div><div>Thanks in advance</div><span class="HOEnZb"><font color="#888888"><div><div><br></div><div><br></div>-- <br>Kanhu Charan Pattnayak (Research Scholar)<br>Room No.331, Block - VI<br>
Centre for Atmospheric Sciences<br>
IIT Delhi, Hauz Khas<br>New Delhi - 110 016<br>India<br>
</div>
</font></span><br>_______________________________________________<br>
RegCNET mailing list<br>
<a href="mailto:RegCNET@lists.ictp.it">RegCNET@lists.ictp.it</a><br>
<a href="https://lists.ictp.it/mailman/listinfo.cgi/regcnet" target="_blank">https://lists.ictp.it/mailman/listinfo.cgi/regcnet</a><br></blockquote></div><br><br clear="all"><div><br></div>-- <br>Syed Ahsan Ali Bokhari <br>
Electronic Engineer (EE)<div><br>Research &amp; Development Division<br>Pakistan Meteorological Department H-8/4, Islamabad.<br>Phone # off  +92518358714</div><div>Cell # +923155145014<br></div><br>
</div>