In GEOS coupled model with MOM6 and CICE6, we still run BL99 thermodynamics. We recently encountered an issue. Occasionally the run crashed with "(temperature_changes)Thermo iteration does not converge" error because fluxes don't match energy change in all ice layers. The crash happens in grid cells with ice fraction of order 1.e-8 and thickness of 1cm (category 1). At the beginning of the time step when error happens, one or more middle layers have Tin close to or at Tmlt.
Hi all,
In
GEOS
coupled model withMOM6
andCICE6
, we still run BL99 thermodynamics. We recently encountered an issue. Occasionally the run crashed with "(temperature_changes)Thermo iteration does not converge" error because fluxes don't match energy change in all ice layers. The crash happens in grid cells with ice fraction of order 1.e-8 and thickness of 1cm (category 1). At the beginning of the time step when error happens, one or more middle layers haveTin
close to or atTmlt
.I managed to track down the issue is in
init_vertical_profile
. TherezTin
is computed based on enthalpyzqin
andTmlts
. https://github.com/CICE-Consortium/Icepack/blob/66682a877bd902b239b333324f29531b5d117cb3/columnphysics/icepack_therm_vertical.F90#L887 In our case where it crashed,zTin
gets aboveTmlts
, but it then is reset to be equal toTmlts
incalculate_Tin_from_qin
https://github.com/CICE-Consortium/Icepack/blob/66682a877bd902b239b333324f29531b5d117cb3/columnphysics/icepack_therm_shared.F90#L84-L85 However, enthalpy
zqin
is NOT recomputed based on the updatedzTin=Tmlts
, and that results in inconsistent ice temperature and enthalpy which is exactly the flux error intemperature_changes
.I think it is a bug to not update
zqin
whenzTin
is reset toTmlt
. In fact, there are commented code https://github.com/CICE-Consortium/Icepack/blob/66682a877bd902b239b333324f29531b5d117cb3/columnphysics/icepack_therm_vertical.F90#L972-L978 to do the enthalpy correction. After I uncomment the above code, the run went past the crash.I understand BL99 is not the mainstream scheme used by Icepack nowadays, but still want to report it and hopefully it gets addressed. Thanks.