Mass conservation upon restart

[yuanjianz]

Your name

Yuanjian Zhang

Your affiliation

WashU

What happened? What did you expect to happen?

Both GC-Classics and GCHP are not able to conserve mass upon restart.

@lizziel:

Initial global mass change upon startup and then stabilizes. Mass conservation is better after a short spin-up period. Issues with unit conversion during restart handling? In theory, passive tracer mass in restart should be conserved upon startup and across a run.

Also, see #2014 and @lizziel's work for bit-of-bit reproducibility in #2521

This could be the result of not properly scaling mixing ratios based on DELP_DRY_RESTART and DELP_DRY_MET.

Mixing ratios should be scaled based on scaled_MR = MR_restart * DELP_DRY_RESTART / DELP_DRY_MET when everything is first read into the model. Then all processes including transport, convection, and chemistry, etc can be executed.

GC-Classics

geos-chem/GeosCore/hco_interface_gc_mod.F90

Lines 4415 to 4419 in bef56c6

	! Call AIRQNT to compute initial air mass quantities
	! Do not update initial tracer concentrations since not read
	! from restart file yet (ewl, 10/28/15)
	CALL AirQnt( Input_Opt, State_Chm, State_Grid, State_Met, &
	RC, update_mixing_ratio=.FALSE. )

Currently, the above snippet in Get_Met_Fields is not updating mixing ratios since Get_Met_Fields is right before Get_GC_Restart:

geos-chem/GeosCore/hco_interface_gc_mod.F90

Lines 1010 to 1033 in bef56c6

	!=======================================================================
	! Get met fields from HEMCO (GEOS-Chem "Classic" only)
	!=======================================================================
	IF ( ( Phase == 0 .or. PHASE == 1 ) .and. notDryRun ) THEN
	CALL Get_Met_Fields( Input_Opt, State_Chm, State_Grid, State_Met, &
	Phase, RC )
	IF ( RC /= HCO_SUCCESS ) THEN
	ErrMsg = 'Error encountered in "Get_Met_Fields"!'
	CALL GC_Error( ErrMsg, RC, ThisLoc )
	RETURN
	ENDIF
	ENDIF
	!=======================================================================
	! Get fields from GEOS-Chem restart file (GEOS-Chem "Classic" only)
	!=======================================================================
	IF ( Phase == 0 .and. notDryRun ) THEN
	CALL Get_GC_Restart( Input_Opt, State_Chm, State_Grid, State_Met, RC )
	IF ( RC /= HCO_SUCCESS ) THEN
	ErrMsg = 'Error encountered in "Get_GC_Restart"!'
	CALL GC_Error( ErrMsg, RC, ThisLoc )
	RETURN
	ENDIF
	ENDIF

It is recommended to either move Get_Met_Fields after Get_GC_Restart or move the reading of DELP_DRY_RESTART into Get_GC_Restart and complete the AirQnt-update_mixing_ratio there.

GCHP

GCHP advection is executed before geos-chem module, so it would be necessary to read DELP_DRY_RESTART in ChemComp Initialization state and do the scaling before AdvComp Run state.