title: How to calculate daily average from ERA5 hourly netCDF data?
body: <p>Hi dear all,</p>
  <p>I do apologize for repeating the question. I have downloaded and merged the ERA5 hourly dew-point temperature data (d2m_wb.nc) from the Copernicus web platform. Now, I want to calculate the daily mean from the hourly d2m_wb.nc data. The timestamps are 00, 01, 02...23. The ECMWF provided an example for the calculation of daily total precipitation (<a href="https://confluence.ecmwf.int/display/CKB/ERA5%3A+How+to+calculate+daily+total+precipitation" rel="nofollow noreferrer">https://confluence.ecmwf.int/display/CKB/ERA5%3A+How+to+calculate+daily+total+precipitation</a>). It said to cover total precipitation for 1st January 2017, we need two days of data.
  (a) 1st January 2017 time = 01 - 23 will give you total precipitation data to cover 00 - 23 UTC for 1st January 2017
  (b) 2nd January 2017 time = 00 will give you total precipitation data to cover 23 - 24 UTC for 1st January 2017</p>
  <p>That means I need to shift the <code>-1hour</code> timestamp to account for step (b). Accordingly, I did it using Climate Data Operators (CDO).</p>
  <pre><code>cdo daymean -shifttime,-1hour in.nc out.nc
  </code></pre>
  <p>and got the following result.</p>
  <pre><code>cdo sinfo d2m_wb.nc
     File format : NetCDF2
      -1 : Institut Source   T Steptype Levels Num    Points Num Dtype : Parameter ID
       1 : unknown  unknown  v instant       1   1       475   1  F64  : -1
     Grid coordinates :
       1 : lonlat                   : points=475 (19x25)
                                lon : 85.5 to 90 by 0.25 degrees_east
                                lat : 21.5 to 27.5 by 0.25 degrees_north
     Vertical coordinates :
       1 : surface                  : levels=1
     Time coordinate :  25904 steps
       RefTime =  1900-01-01 00:00:00  Units = hours  Calendar = gregorian  Bounds = true
    YYYY-MM-DD hh:mm:ss  YYYY-MM-DD hh:mm:ss  YYYY-MM-DD hh:mm:ss  YYYY-MM-DD hh:mm:ss
    1949-12-31 23:00:00  1950-01-01 11:00:00  1950-01-02 11:00:00  1950-01-03 11:00:00
    1950-01-04 11:00:00  1950-01-05 11:00:00  1950-01-06 11:00:00  1950-01-07 11:00:00
    1950-01-08 11:00:00  1950-01-09 11:00:00  1950-01-10 11:00:00  1950-01-11 11:00:00
    1950-01-12 11:00:00  1950-01-13 11:00:00  1950-01-14 11:00:00  1950-01-15 11:00:00
    1950-01-16 11:00:00  1950-01-17 11:00:00  1950-01-18 11:00:00  1950-01-19 11:00:00
    1950-01-20 11:00:00  1950-01-21 11:00:00  1950-01-22 11:00:00  1950-01-23 11:00:00
    1950-01-24 11:00:00  1950-01-25 11:00:00  1950-01-26 11:00:00  1950-01-27 11:00:00
    1950-01-28 11:00:00  1950-01-29 11:00:00  1950-01-30 11:00:00  1950-01-31 11:00:00
    1950-02-01 11:00:00  1950-02-02 11:00:00  1950-02-03 11:00:00  1950-02-04 11:00:00
    1950-02-05 11:00:00  1950-02-06 11:00:00  1950-02-07 11:00:00  1950-02-08 11:00:00
    1950-02-09 11:00:00  1950-02-10 11:00:00  1950-02-11 11:00:00  1950-02-12 11:00:00
    1950-02-13 11:00:00  1950-02-14 11:00:00  1950-02-15 11:00:00  1950-02-16 11:00:00
    1950-02-17 11:00:00  1950-02-18 11:00:00  1950-02-19 11:00:00  1950-02-20 11:00:00
    1950-02-21 11:00:00  1950-02-22 11:00:00  1950-02-23 11:00:00  1950-02-24 11:00:00
    1950-02-25 11:00:00  1950-02-26 11:00:00  1950-02-27 11:00:00  1950-02-28 11:00:00
     ................................................................................
     ................................................................................
     ................................................................................
     .................
    2020-10-03 11:00:00  2020-10-04 11:00:00  2020-10-05 11:00:00  2020-10-06 11:00:00
    2020-10-07 11:00:00  2020-10-08 11:00:00  2020-10-09 11:00:00  2020-10-10 11:00:00
    2020-10-11 11:00:00  2020-10-12 11:00:00  2020-10-13 11:00:00  2020-10-14 11:00:00
    2020-10-15 11:00:00  2020-10-16 11:00:00  2020-10-17 11:00:00  2020-10-18 11:00:00
    2020-10-19 11:00:00  2020-10-20 11:00:00  2020-10-21 11:00:00  2020-10-22 11:00:00
    2020-10-23 11:00:00  2020-10-24 11:00:00  2020-10-25 11:00:00  2020-10-26 11:00:00
    2020-10-27 11:00:00  2020-10-28 11:00:00  2020-10-29 11:00:00  2020-10-30 11:00:00
    2020-10-31 11:00:00  2020-11-01 11:00:00  2020-11-02 11:00:00  2020-11-03 11:00:00
    2020-11-04 11:00:00  2020-11-05 11:00:00  2020-11-06 11:00:00  2020-11-07 11:00:00
    2020-11-08 11:00:00  2020-11-09 11:00:00  2020-11-10 11:00:00  2020-11-11 11:00:00
    2020-11-12 11:00:00  2020-11-13 11:00:00  2020-11-14 11:00:00  2020-11-15 11:00:00
    2020-11-16 11:00:00  2020-11-17 11:00:00  2020-11-18 11:00:00  2020-11-19 11:00:00
    2020-11-20 11:00:00  2020-11-21 11:00:00  2020-11-22 11:00:00  2020-11-23 11:00:00
    2020-11-24 11:00:00  2020-11-25 11:00:00  2020-11-26 11:00:00  2020-11-27 11:00:00
    2020-11-28 11:00:00  2020-11-29 11:00:00  2020-11-30 11:00:00  2020-12-31 23:00:00
  cdo    sinfo: Processed 1 variable over 25904 timesteps [6.03s 37MB
  </code></pre>
  <p>In this case, the timestep shows 11:00:00 (from 1950-01-01 onwards). I guess it should be 12:00:00. What wrong I've done here? Any suggestions will highly be appreciated? Thank you.</p>