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Bug-fix: Mom6 time #514

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merged 7 commits into from
Jul 27, 2023
Merged

Bug-fix: Mom6 time #514

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035d4a6
fix misplaced comment about writing an obs_seq file
nancycollins Jun 29, 2023
b2363b7
converts mom6 time (days from year 0) to dart time (from 1601)
hkershaw-brown Jun 22, 2023
9a85fc8
docs for mom6 time
hkershaw-brown Jul 18, 2023
d06220e
Merge pull request #508 from NCAR/filter_comment_fix
hkershaw-brown Jul 27, 2023
f55f44d
bump conf.py and changelog for release
hkershaw-brown Jul 27, 2023
4d50777
Merge branch 'main' into mom6-time
hkershaw-brown Jul 27, 2023
8efab01
Merge branch 'main' into mom6-time
hkershaw-brown Jul 27, 2023
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9 changes: 8 additions & 1 deletion models/MOM6/model_mod.f90
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Expand Up @@ -945,14 +945,21 @@ function read_model_time(filename)
integer :: ncid
character(len=*), parameter :: routine = 'read_model_time'
real(r8) :: days
type(time_type) :: mom6_time
integer :: dart_base_date_in_days, dart_days

dart_base_date_in_days = 584388 ! 1601 1 1 0 0
ncid = nc_open_file_readonly(filename, routine)

call nc_get_variable(ncid, 'Time', days, routine)

call nc_close_file(ncid, routine)

read_model_time = set_time(0,int(days))
! MOM6 counts days from year 1
! DART counts days from 1601
dart_days = int(days) - dart_base_date_in_days

read_model_time = set_time(0,dart_days)

end function read_model_time

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42 changes: 42 additions & 0 deletions models/MOM6/readme.rst
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Expand Up @@ -9,6 +9,48 @@ Instructions for using MOM6 in CESM are available on the `MOM_interface GitHub W

This DART-MOM6 interface was developed for `MOM6 <https://github.com/NCAR/MOM6>`_ within the CESM framework.

MOM6 time
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Documentation is good! Are there other models in CESM that need this info added to their documentation pages? For example, I looked through the CLM documentation, and it doesn't talk about the calendar.

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The dart shell scripts for CLM, POP, CAM set the CALENDAR.

DART/models/clm/shell_scripts/cesm2_2/CLM5_setup_assimilation

Line 128 in 1b76f3a

./xmlchange CALENDAR=GREGORIAN

MOM6 with dart is fairly new (e.g. Robin developing the MOM6-Marble, Alper adding MOM6 multi-instance capability) so I figured it is worth noting in the docs about the calendar.

Maybe it is worth noting about the calendar in the CESM page? @kdraeder what do you think? https://docs.dart.ucar.edu/en/latest/models/CESM/readme.html

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@hkershaw-brown we could move this discussion to email so that we can get this PR approved and released. Especially since the doc changes proposed above could be done in a separate PR. What do you think?

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@mjs2369 sounds like a plan, lets get this one out.

---------

The default in CESM is to run with no leap years.
To assimilate real observations, we need to switch to the Gregorian
calendar to account for leap years.

.. code-block:: text

./xmlchange CALENDAR=GREGORIAN

To illustrate what happens if you do not set CALENDAR=GREGORIAN, here is
an example where the RUN_STARTDATE is set to 2015-02-01 and MOM6 is run for 10 days.

.. code-block:: text

./xmlchange RUN_STARTDATE=2015-02-01

The MOM6 restart file has the following meta data, where Time is days from year 1.

.. code-block:: text

double Time(Time) ;
Time:long_name = "Time" ;
Time:units = "days" ;
Time:axis = "T" ;
...
// global attributes:
:filename = "./c.T62_g16.ens3.mom6.r.2015-02-11-00000._0001.nc" ;
data:

Time = 735151 ;
}


The absence of leap years gives you inconsistent time information when comparing
to observation times in YYYY-MM-DD:

- Restart filename has the time 2015-02-11-00000.
- The Time variable is Time = 735151 days, which is 2013/10/11


MOM6 checksum of restart files
------------------------------

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