Daily averaging of variables (SSH)

1

Dear All,

May I clarify on the possibility to output daily averaged variables (i.e. sea surface heights)? Some of the checks I have done on the built-in 25h averaging code:
From dia25h.F90, I see the code performs averaging over 25 hours, which seems to obtain the hourly instantaneous output and averages them over 25 hours (12:00 to 12:00). I verified from my log as well.

 dia_tide : Summed the following number of hourly values so far          25
  1. If we were to require 24 hours averaging, we would be required to change the code?
  2. The code seems to indicate that it uses time steps for the averaging. The namelist_cfg I have specified the rn_rdt = 300 seconds, shouldn’t it use the instantaneous values every 300 seconds to perform the averaging or I have understood this incorrectly?
2

I am not sure to understand your question… dia25h is a very specific routine used to filter out tidal signal by applying 25h averaging.
You must not use this outputs for any another purpose.
For default output files, see chapter 10.2 and more specifically chapters 10.2.4 and 10.2.5 of the NEMO reference documentation available here:

3

Ok I am not aware. I would just like to know if there is a way to output daily averaged variables, preferably over the time steps? Or do we have to use cdo to accomplish that?

4

I would say that is more of an XIOS question. For example, our field_def_nemo-oce.xml file contains such a line (in the beginning):

<field_definition level="1" prec="4" operation="average" enabled=".TRUE." default_value="1.e20" > <!-- time step automaticaly defined -->

which encapsulates all fields. The operation="average" key means that by default, all output fields will be averaged over the desired output frequency. operation="instant" would yield instant values. Unless this “operation” key is overwritten (e.g. in the specific field you’re looking at, or in the file_def XML file), the fields are averaged over time.

P.S.: if you use QCO/VVL, be wary of averaging 3D fields - it is probably more meaningful to weight them with respect to the varying level thicknesses, e.g.:

<field field_ref="toce"     name="thetao"     operation="instant" freq_op="1d" > @toce_e3t / @e3t </field>

as far as I understood, here XIOS will perform the ratio at every time step, and then average the result over the desired period. See section 3.2 of the XIOS user guide.