Are we 100% sure that the freshwater flux is correctly balanced in the coupled case ?

[patrickscholz]

When did we comment this lines? Which unit has now evap, rain, runoff ... when we do the freshwater balancing. Does the unit of evap, rain, runoff... match the unit of fw

Are we 100% sure that the freshwater is correctly balanced in the coupled case, and there is no drift in the total ocean volume ?

fesom2/src/ice_thermo_cpl.F90

Lines 512 to 520 in b65d289

	!---- convert freshwater mass flux [kg/m**2/s] into sea-water volume flux [m/s]
	fw = fw/rhowat
	! keep in mind that for computation of FW all imposed fluxes were accounted with the ratio rhofwt/rhowat:
	!evap = evap *rhofwt/rhowat
	!rain = rain *rhofwt/rhowat
	!snow = snow *rhofwt/rhowat
	!runo = runo *rhofwt/rhowat
	!subli= subli*rhofwt/rhowat
	!resid= resid*rhofwt/rhowat

Can you check in a recent coupled logfile for the line:

 ___global estimat of eta & hbar____________________
    int(eta), int(hbar)      = -2.787465260128587E-016 -2.787465260128587E-016
     --> error(eta-hbar)     =  0.000000000000000E+000

is int(eta) ~ numerical zero

[JanStreffing]

   0:  ___CHECK GLOBAL OCEAN VARIABLES --> mstep=        6720
   0:    ___global estimat of eta & hbar____________________
   0:     int(eta), int(hbar)      =  -5.3605101156318993E-016  -5.3605101156318993E-016

After 600 years of simulation.

[JanStreffing]

Commenting out happened in:
074602d

[patrickscholz]

@JanStreffing: maybe i missunderstand something here but in ice_therm_cpl.F90 we do ...

fesom2/src/ice_thermo_cpl.F90

Line 322 in 326c029

PmEocn = evap + rain + (1._WP-A)*snow + runo

...

fesom2/src/ice_thermo_cpl.F90

Line 469 in 326c029

fw = PmEocn*rhofwt + fwice + fwsnw

...

fesom2/src/ice_thermo_cpl.F90

Line 524 in 326c029

fw = fw /rhowat

if you set this back into each other

fw    = (PmEocn*rhofwt + fwice + fwsnw)/rhowat
fw    = ( (evap + rain + (1._WP-A)*snow + runo)*rhofwt + fwice + fwsnw)/rhowat
fw    = evap*rhofwt/rhowat + rain*rhofwt/rhowat + ....

so we need to multiply evap, rain ... with factor rhofwt/rhowat to have the same unit as fw. I mean the factor rhofwt/rhowat ~ 1 = 1000/1025 = 0.9756. Nevertheless i see an 3% offset. Or is this scaling of evap, rain, ... done somewhere else?

[JanStreffing]

I think its just done two steps rather than explicitly on each variable.

Freshwater fluxes are combined in m/s (freshwater):

fesom2/src/ice_thermo_cpl.F90

Line 322 in 326c029

PmEocn = evap + rain + (1._WP-A)*snow + runo

Convert to mass flux (kg/m²/s):

fesom2/src/ice_thermo_cpl.F90

Lines 467 to 469 in 326c029

	fwice = - dhgrowth*rhoice
	fwsnw = - dhsngrowth*rhosno
	fw = PmEocn*rhofwt + fwice + fwsnw

Convert to seawater volume flux (m/s of seawater):

fesom2/src/ice_thermo_cpl.F90

Line 524 in 326c029

fw = fw /rhowat

Combining these operations:

fw = (PmEocn * rhofwt) / rhowat
fw = (evap + rain + ...) * (rhofwt/rhowat)
fw = (evap + rain + ...) * (1000/1025)
fw = (evap + rain + ...) * 0.9756

So the ~3% correction factor is applied, just through the combined *rhofwt/rhowat operation rather than on individual variables.