2 degree (ne16pg3) out-of-the-box LT and MT functionality

[PeterHjortLauritzen]

What is the feature/what would you like to discuss?

2 degree (ne16pg3) out-of-the-box LT and MT functionality:

• create spun-up initial conditions and add to namelist defaults
• optimized dycore settings and add to namelist defaults

This issue does not concern forcing files etc. (which currently are CMIP6-based as far as I can tell)

Is there anyone in particular you want to be part of this conversation?

No response

Will this change (regression test) answers?

I Don't Know

Will you be implementing this enhancement yourself?

Yes

[PeterHjortLauritzen]

Notes on how I am creating the new initial conditions see (using analytic initial condition):

https://github.com/PeterHjortLauritzen/CAM/wiki/creating-spun%E2%80%90up-2-degree-LT-and-MT-initial-conditions

Namelist default for se_nu_p was not set correctly (fixed)
Reduce se_hypervis_subcycle (for efficiency)

Time-step report from atm.log file with MT (~80km top version):

Estimates for maximum stable and actual time-steps for different aspects of algorithm:
(assume max wind is 240.00000000m/s)
(assume max gravity wave speed is 342m/s)
 
* dt_dyn        (time-stepping dycore  ; u,v,T,dM) <     667.49s     600.00s
* dt_dyn_vis    (hyperviscosity)       ; u,v,T,dM) <     207.43s     200.00s
* dt_tracer_fvm (time-stepping tracers ; q       ) <    1737.48s    1800.00
 WARNING: dt_tracer_fvm theortically unstable
* dt_remap (vertical remap dt)    1800.00
* dt    (del2 sponge           ; u,v,T,dM) <     483.01s    600.00s
 WARNING: theoretically unstable in sponge; increase se_hypervis_subcycle_sponge
  (this WARNING can sometimes be ignored in level 1)
* dt    (del2 sponge           ; u,v,T,dM) <    1449.04s    600.00s
* dt    (del2 sponge           ; u,v,T,dM) <   14490.43s    600.00s
* dt    (del2 sponge           ; u,v,T,dM) <   28980.86s    600.00s

Model was stable in a one year run, i.e. the slightly theoretical instabilities do not seem to materialize!

Time-step report from atm.log file with LT (~42km top version):

Estimates for maximum stable and actual time-steps for different aspects of algorithm:
(assume max wind is 120.00000000m/s)
(assume max gravity wave speed is 342m/s)
 
* dt_dyn        (time-stepping dycore  ; u,v,T,dM) <     667.49s     600.00s
* dt_dyn_vis    (hyperviscosity)       ; u,v,T,dM) <     699.91s     600.00s
* dt_tracer_fvm (time-stepping tracers ; q       ) <    3474.96s    1800.00
* dt_remap (vertical remap dt)    1800.00
* dt    (del2 sponge           ; u,v,T,dM) <    2634.62s    600.00s
* dt    (del2 sponge           ; u,v,T,dM) <    8917.19s    600.00s
* dt    (del2 sponge           ; u,v,T,dM) <    2972.40s    600.00s

Note: of the winds stay below ~100m/s then one could set se_large_Courant_incr=.false. leading to further speed-up.

[PeterHjortLauritzen]

Here are min/max winds in a 1 year simulation with LT in the top 10 layers (see color labeling on the right-hand side of plot):

Here are min/max winds in a 1 year simulation with MT (see color labeling on the right-hand side of plot):