Create test for running cases with cam7 nextsw_cday_calc?

[ekluzek]

Coupled cases are run with nextsw_cday_calc, so maybe we should do the same for offline cases? Just to make things as close as possible to coupled cases? This would just be for clm6_0 physics. We could also make it standard to run with hourly SW radiation to be more similar to coupled cases. Although for the latter that should be turned off certainly for 1PT forcing, and only used for large gridded forcing datasets with temporal frequencies of an hour or more.

[wwieder]

Sorry, I don't know what nextsw_cday_calc is or does. How may this change answers in I-cases?

[ekluzek]

It's a minor change in how the DATM operates. So it's a namelist variable for DATM.

It would only matter if the radiation timestep (set with iradsw) is less frequent than every time-step. For CAM it's hourly. So we'd need to also change iradsw as well.

Here's the description of nextsw_cday_calc from the DATM namelist_definition file:

      Logic to use for calculating nextsw_cday. This variable has no effect when iradsw is
      0 or 1, so by default this only applies in CPLHIST cases.

      For CPLHIST cases, this should agree with the version of CAM (or other atmosphere
      model) used to generate the CPLHIST forcings; the valid values for this variable are
      based on this: 'cam6' is appropriate for cases generated with the driver ordering in
      CAM6 and earlier, and 'cam7' is appropriate for cases generated with the driver
      ordering in CAM7 and later.

      For 'cam6', the next radiation timestep is set to the present time plus 2 timesteps
      when mod(tod+dtime,delta_radsw)==0. For 'cam7', the next radiation timestep is set
      to the present time plus 1 timestep when mod(tod,delta_radsw)==0.

[ekluzek]

Since, it's in DATM, I think the way to do this would be to have it set for the CRJRA2024b forcing with something like this:

diff --git a/datm/cime_config/namelist_definition_datm.xml b/datm/cime_config/namelist_definition_datm.xml
index a77408c..680a0c8 100644
--- a/datm/cime_config/namelist_definition_datm.xml
+++ b/datm/cime_config/namelist_definition_datm.xml
@@ -351,10 +351,11 @@
       Values less than 0 set the next radiation to the present time plus either 1 or 2
       timesteps (depending on the value of nextsw_cday_calc) every -iradsw hours. If
       iradsw is either 0 or 1, the next radiation time is the present time plus 1
-      timestep. (default=1 for non-CPLHIST cases, and -1 for CPLHIST cases.)
+      timestep. (default=1 for non-CPLHIST cases, and -1 for CPLHIST/CLMCRUJRA2024b cases.)
     </desc>
     <values>
       <value>1</value>
+      <value datm_mode="CLMCRUJRA2024b">-1</value>
       <value datm_mode="CPLHIST">-1</value>
     </values>
   </entry>
@@ -381,6 +382,7 @@
     <values>
       <value>cam6</value>
       <value datm_mode="CPLHIST">cam7</value>
+      <value datm_mode="CLMCRUJRA2024b">cam7</value>
     </values>
   </entry>

[wwieder]

Maybe we can discuss this at the next SE meeting? My questions are mainly to try and understand:

1. Background
2. Motivation
3. Impact, (this may require a brief science evaluation)
4. Timeline