Merge pull request #514 from NCAR/mom6-time

Bug-fix: Mom6 time

Author: hkershaw-brown

CHANGELOG.rst

@@ -22,6 +22,21 @@ individual files.
 
 The changes are now listed with the most recent at the top.
 
+**July 27 2023 :: Bug-fixes for MOM6 and WRF. Tag v10.8.1**
+
+- bug-fixes:
+
+  - MOM6 read_model_time converts to dart time to match observation sequences.
+  - MOM6 salinity units converted to MSU during model_interpolate.
+  - WRF get_dist calculation fixed for observations with VERTISUNDEF.
+
+- doc-fixes:
+
+  - WOD and GTSPP converter documentation notes about salinity units.
+  - MOM6 documentation for setting the Gregorian calendar in CESM.
+  - comment fix in filter_mod.f90
+
+
 **June 27 2023 :: CAM-DART observation preprocessor. Tag v10.8.0**
 
 - Tool to remove observations above a given CAM level from an obs sequence file

assimilation_code/modules/assimilation/filter_mod.f90

@@ -1711,7 +1711,7 @@ subroutine obs_space_sync_QCs(obs_fwd_op_ens_handle,  &
 io_task = map_pe_to_task(obs_fwd_op_ens_handle, 0)
 my_task = my_task_id()
 
-! write the obs_seq.final file
+! create temp space for QC values
 if (my_task == io_task) then
    allocate(obs_temp(num_obs_in_set))
 else 

conf.py

@@ -21,7 +21,7 @@
 author = 'Data Assimilation Research Section'
 
 # The full version, including alpha/beta/rc tags
-release = '10.8.0'
+release = '10.8.1'
 master_doc = 'README'
 
 # -- General configuration ---------------------------------------------------

models/MOM6/model_mod.f90

@@ -950,14 +950,21 @@ 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
 

models/MOM6/readme.rst

@@ -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
+---------
+
+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
 ------------------------------