cpl(__oifs): coupled-slab ice surface temperature + sea-ice-thickness exchange - #957
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cpl(__oifs): coupled-slab ice surface temperature + sea-ice-thickness exchange#957JanStreffing wants to merge 1 commit into
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… exchange Under OIFS coupled-slab mode (LNEMOLIMTEMP=.false., LNEMOLIMTHK=.true.) the atmosphere solves the ice-tile skin temperature itself, using slab conduction through the coupled ice/snow thickness. This adds the FESOM side of that coupling: - Send the effective sea-ice thickness to the atmosphere as a new coupled field sit_feom (cpl_send slot 8, nsend 7->8 under __oifs) so the atmosphere's slab conduction uses the real ice thickness instead of a fixed nominal. Sent grid-mean (per-ice * concentration), weighted convention like ist/alb. - ist_ref anchor: remember the ice surface temperature as actually transmitted at the OASIS send (the temperature the atmosphere evaluated its ice-tile flux at), captured only on real transmissions. - ice_surftemp: replace the explicit skin update with a dQ/dT-linearized (implicit) solve anchored at ist_ref, zlam = 4*eps*sigma*tref**3 + turbulent sensitivity. This is unconditionally stable regardless of snow/ice insulation and leaves the fixed point unchanged where the surface tracks the coupling temperature. It sets the internal skin temperature used for albedo/melt-pond state only. - Growth budget: the atmosphere owns the surface energy balance in coupled-slab mode, so Qatmice = -a2ihf (the received atmosphere flux) directly. Inert for non-OIFS builds (all changes are #ifdef __oifs / __ifsinterface).
JanStreffing
requested review from
FinnHeu,
dsidoren,
lettie-roach and
patrickscholz
July 23, 2026 10:04
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What
Adds the FESOM side of OIFS coupled-slab sea-ice coupling. Under coupled-slab mode (
LNEMOLIMTEMP=.false.,LNEMOLIMTHK=.true.) the atmosphere solves the ice-tile skin temperature itself, using slab conduction through the coupled ice/snow thickness rather than a fixed nominal slab. This wires FESOM to feed that scheme and to book the growth flux consistently.Changes (all
#ifdef __oifs/__ifsinterface)sit_feom(cpl_sendslot 8,nsend7→8 under__oifs;gen_forcing_couple). Sent grid-mean (per-ice × concentration), weighted convention likeist/alb, so the atmosphere's slab conduction uses the real ice thickness.ist_refanchor — remember the ice surface temperature as actually transmitted at the OASIS send (the temperature the atmosphere evaluated its ice-tile flux at), captured only on real transmissions.ice_surftemp:dQ/dT-linearized (implicit) skin solve anchored atist_ref,zlam = 4·ε·σ·tref³ + turbulent sensitivity. Unconditionally stable regardless of snow/ice insulation; leaves the fixed point unchanged where the surface tracks the coupling temperature. It sets the internal skin temperature used for albedo / melt-pond state only.Qatmice = -a2ihf(received atmosphere flux) directly.Compatibility
Inert for non-OIFS builds. For OIFS builds,
sit_feomis defined viaoasis_def_varas an extra send; OASIS leaves it uncoupled (a no-opput) wherever the namcouple does not reference it, so this does not require a coordinated namcouple change to remain runnable — only a namcouple that addssit_feomneeds a FESOM that provides it.Validation
Multi-year AWI-ESM3 (FESOM2-CORE3-cavity + OIFS-48r1) coupled spin-ups run stably with this + the OIFS receive-side; the implicit solve holds through the polar-night temperature range with no cold runaway.