Ice Sheet Coupling

Overview

Ice sheet coupling with the rest of the model depends on which ice sheet is being modeled, Antarctica or Greenland.

Ice-shelf coupling: (ocn_c2_glcshelf, glcshelf_c2_ocn) Fluxes between the bottom of the ice shelf and the ocean underneath it. The ice-shelf coupling will be used for Antarctica (left side of figure).  Greenland has some small ice shelves, but they are too small to be resolved sufficiently in MPAS-Ocean, so we do not intend to use the ice-shelf coupling for Greenland cases.

Thermal-forcing coupling: (ocn_c2_glctf) Passes thermal forcing at a prescribed ocean depth (300 m) from MPAS-Ocean to MALI, where MALI uses it to calculate grounded marine melting through an existing 'facemelting' parameterization. The thermal-forcing coupling is primarily intended for Greenland where there are primarily vertical cliffs and little floating ice (right side of figure). In that geometry, MPAS-Ocean is not equipped to calculate melt rates, and even if it could, most of the narrow fjords around Greenland would be unresolved so the ocean domain rarely intercepts the Greenland marine termini.  Instead, we make use of marine melting parameterizations that are a function of the thermal forcing (ocean temperature minus in situ freezing temperature).  We also make use of a capability we added to MALI to horizontally extrapolate ocean thermal forcing from wherever on the MALI mesh it’s available to the current terminus positions.  While the thermal-forcing coupling is primarily developed for Greenland, Antarctica also has vertical marine cliffs without ice shelves in some places (and will likely have more in the future), so we do anticipate eventually using the TF coupling in Antarctica at the same time as the ice-shelf coupling. Implemented in https://github.com/E3SM-Project/E3SM/pull/6632

land coupling: (glc_2_lnd and lnd_2_glc) the surface mass balance (SMB) between the ice sheet and the atmosphere is calculated in the land model. The “glc_2_lnd” coupling passes the necessary data to and from that calculation. The land ice passes elevation of the ice sheet in a flexible number of topography classes (10 in the example below) to the SMB routine in the land model.

sea-ice coupling: (glc_2_ice): icebergs. Icebergs form from the ice sheets but are then advected by the sea-ice model.

Attribute strings

General land ice states and fluxes

• g2x_states: Sg_icemask, Sg_icemask_coupled_fluxes, Sg_ice_covered, Sg_topo, Sg_blit, Sg_blis, Sg_lithop, Sg_icemask_grounded, Sg_icemask_floating, Sg_tbot, Sg_dztbot

• g2x_fluxes: Fogg_rofl, Fogg_rofi, Figg_rofi, Flgg_hflx, Fogx_qicelo, Fogx_qiceho

  • g2o_liq_fluxes: Fogg_rofl

  • g2o_iceq_fluxes: Fogg_rofi

• x2g_states: Sl_tsrf, So_blt, So_bls, So_htv, So_stv, So_rhoeff

  • x2g_states_from_lnd: Sl_tsrf

• x2g_fluxes: Flgl_qice, Fogx_qiceli, Fogx_qicehi

  • x2g_fluxes_from_lnd: Flgl_qice

land to glc adds the following coupling fields

• l2x states: Sl_tsrf00 through Sl_tsrf10  and Sl_topo00 through Sl_topo10

• l2x states to glc: Sl_tsrf00 to Sl_tsrf10 AND Sl_topo00 to Sl_topo10

• l2x fluxes: Flgl_qice00 through Flgl_qice10

• l2x_fluxes_to_glc:  Flgl_qice00 to Flgl_qice10

glc to lnd adds the following coupling fields:

• x2l states: Sg_ice_covered00 through Sg_ice_covered10  AND  Sg_topo00 through Sg_topo10

• x2l states from glc: Sg_ice_covered00 through Sg_ice_covered10 AND Sg_topo00 through Sg_topo10

• g2x states to lnd: Sg_icemask:Sg_icemask_coupled_fluxes:Sg_ice_covered:Sg_topo

• x2l fluxes:  Flgg_hflx00 to Flgg_hflx10

• x2l fluxes from glc:  Flgg_hflx00 to Flgg_hflx10