MOM6 time - Githubissues

The default in CESM is to run with no leap year. For assimilating with real obs, we need to use the actual time.

Todos:

[x] DART MOM6 documentation, be explicit about the need to set the calendar in CESM. ./xmlchange CALENDAR=GREGORIAN

Note on what happens if you don't set CALENDAR=GREGORIAN mom6 restart file has time in days from year 1. Starting the run at 2015-02-01:

./xmlchange RUN_STARTDATE=2015-02-01

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

 Time = 735151 ;
}

If you don't have leap years switched on you end up with inconstant time information like this: Restart filename has the time 2015-02-11-00000. The Time variable is Time = 735151, which is 2013/10/11

hkershaw@cisl-fisher utilities (main) $ git diff gregorian_time.c 
diff --git a/assimilation_code/modules/utilities/gregorian_time.c b/assimilation_code/modules/utilities/gregorian_time.c
index ee6a72f03..e8fccb87d 100644
--- a/assimilation_code/modules/utilities/gregorian_time.c
+++ b/assimilation_code/modules/utilities/gregorian_time.c
@@ -20,7 +20,7 @@
 #include <stdlib.h>

 /* the start of gregorian numbered days */
-#define BASE_YEAR 1601
+#define BASE_YEAR 1

 enum todo { TO_YMD, TO_DS };
 enum err  { ERROR, OK };
hkershaw@cisl-fisher utilities (main) $ icc gregorian_time.c ; ./a.out  735151 0
735151     0 == 2013/10/11 00:00:00

[x] Convert MOM6 time to DART time for read_model_time read_model_time is used for the move_ahead calculation. MOM6 Model time is days from year 1. This needs to be DART time (days from 1601) since that is what the observation times are.

https://github.com/NCAR/DART/blob/502af7865e258530cba7c7daff6aed4390cbb649/assimilation_code/modules/assimilation/obs_model_mod.f90#L57-L65

Note the model_time for the whole ensemble is from the first ensemble member only: https://github.com/NCAR/DART/blob/502af7865e258530cba7c7daff6aed4390cbb649/assimilation_code/modules/io/state_vector_io_mod.f90#L288-L292

[ ] write_model_time, is used for dart created files: inflation, mean. Should this be MOM6 time (days from year 1) to be consistent with the model restarts? Or DART time (days from 1601) to be consistent with the observations?

NCAR / DART

MOM6 time #494