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. glcshelf coupling is unique in doing a lot of calculations inside the coupler.  It’s calculating the melt and heat fluxes on the ocean coupling interval (finer than GLC) and the GLC mesh (finer than OCN). 

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_c2_lnd and lnd_c2_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_c2_ice): icebergs. Icebergs form from the ice sheets but are then advected by the sea-ice model.

ocean coupling: (glc_c2_ocn): Sg_icemask, Sg_blit, Sg_blis, Sg_lithop, Sg_icemask_grounded

There is no ocn_c2_glc, ice_c2_glcshelf., ice_c2_glc

Attribute strings

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

  • Sl_tsrf: Surface temperature of glacier (one for each elevation class)

  • Sl_topo: surface height of glacier (one for each elevation class)

• l2x fluxes: Flgl_qice00 through Flgl_qice10

• l2x_fluxes_to_glc:  Flgl_qice00 to Flgl_qice10

  • Flgl_qice: New glacier ice flux

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

  • Sg_ice_covered: Fraction of glacier area

  • Sg_topo: surface height of glacier

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

  • Sg_icemask: Ice sheet grid coverage on global grid

  • Sg_icemask_coupled_fluxes: Ice sheet mask where we are potentially sending non-zero fluxes

  • Sg_ice_covered: Fraction of glacier area

  • Sg_topo

• x2l fluxes:  Flgg_hflx00 to Flgg_hflx10

• x2l fluxes from glc:  Flgg_hflx00 to Flgg_hflx10

  • Flgg_hflx: Downward heat flux from glacier interior.

Resulting 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

  • Sg_blit: Boundary layer interface temperature for ocean

  • Sg_blis: Boundary layer interface salinity for ocean

  • Sg_lithop: Ice sheet lithostatic pressur

  • Sg_icemask_grounded: Grounded ice mask

  • Sg_icemask_floating: Floating ice mask

  • Sg_tbot: Bottom layer ice temperature

  • Sg_dztbot: Bottom layer ice layer half thickness

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

  • Fogg_rofl glc liquid runoff flux to ocean

  • Fogg_rofi glc frozen runoff flux to ocean

  • Figg_rofi: glc frozen runoff_iceberg flux to sea ice

  • Flgg_hflx: Downward heat flux from glacier interior

  • Flgg_qicelo: Subshelf liquid flux for ocean

  • Fogx_qiceho: Subshelf heat flux for the ocean

  • g2o_liq_fluxes: Fogg_rofl

  • g2o_iceq_fluxes: Fogg_rofi

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

  • Sl_tsrf:

  • So_blt: Ice shelf boundary layer ocean temperature

  • So_bls: Ice shelf boundary layer ocean salinity

  • So_htv: Ice shelf ocean heat transfer velocity

  • So_stv: Ice shelf ocean salinity transfer velocity

  • So_rhoeff: Ocean effective pressure

  • x2g_states_from_lnd: Sl_tsrf

• x2g_fluxes: Flgl_qice, Fogx_qiceli, Fogx_qicehi

  • Flgl_qice: New glacier ice flux

  • Fogx_qiceli: Subshelf mass flux for ice sheet

  • Fogx_qicehi: Subshelf heat flux for ice sheet

  • x2g_fluxes_from_lnd: Flgl_qice

Modifications to coupler flow.

Assuming glc_present and glc_prognostic are TRUE so not including.

init

prep_lnd_init (glc_c2_lnd)

if(glc_c2_lnd) init mapper_Sg2l, mapper_Fg2l; derive field lists glc2lnd_non_ec_fields and glc2lnd_ec_extra_fields

prep_ocn_init (glc_c2_ocn, glcshelf_c2_ocn)

if (glc_c2_ocn) init mapper_Rg2o_liq and mapper_Rg2o_ice

if(glcshelf_c2_ocn) init mapper_Sg2o and mapper_Fg2o

prep_ice_init (glc_c2_ice, glcshelf_c2_ice)

if (glc_c2_ice) init mapper_Rg2i

if(glcshelf_c2_ice) init mapper_Sg2i,mapper_Fg2i

prep_glc_init( lnd_c2_glc, ocn_c2_glcshelf)

if ( lnd_c2_glc .or. do_hist_l2x1yrg) initialize l2gacc_lx with seq_flds_l2x_fields_to_glc

if ( lnd_c2_glc) initialize l2x_gx with seq_flds_x2g_fields

if (lnd_c2_glc) init mapper_Sl2g, mapper_Fl2g, mapper_Fg2l; form g2x_lx_fields

if (ocn_c2_glcshelf) init o2x_gx with seq_flds_o2x_fields; init x2gacc_gx

also init mapper_So2g, mapper_Fo2g and arrays for compute_melt_fluxes

if (glc_c2_ocn) do mapping Rg2o_liq, Rg2o_ice; g2x_gx to g2x_ox; seq_flds_g2o_liq/ice_fluxes,

if (glcshelf_c2_ocn) do mapping Sg2o, Fg2o; g2x_gx to g2x_ox MIGHT OVERWRITE ABOVE

if(glc_c2_ice) do mapping Rg2i; g2x_gx to g2x_ix ‘Fixx_rofi’ only

if(glcshelf_c2_ice) do mapping_Sg2i; g2x_gx, g2x_ix, Sg_icemask_coupled_fluxes

if (glc_c2_lnd) do mapping Fg2l, g2x_gx, g2x_lx, glc2lnd_non_ec_fields; do special mapping of elevation class fields with mapper_Fg2l, glc2lnd_ec_extra_fields

in run loop

after land receive

call cime_run_glc_setup_send

if (lnd_c2_glc OR ocn_c2_glcshelf)

if (glcrun_avg_alarm) accumulate for lnd and ocn

if (lnd_c2_glc) call prep_glc_calc_l2x_gc

from seq_flds_x2g_fluxes_from_lnd, special (bilinear with correction) mapping of Flgl_qice See Bilinear lnd to glc prep_glc_map_qice_conservative_lnd2glc, map_lnd2glc (mapper_Sl2g); also if (smb_renormalize) call prep_glc_renormalize_smb; map_glc2lnd_ec

from seq_flds_x2g_states_from_lnd also call special bilinear mapping one state at a time: prep_glc_map_one_state_field_lnd2glc, map_lnd2glc

else prep_glc_zero_flds

At bottom after running atm and ocn

run glc (pass in glc_prognostic)

call cime_run_glc_recv_post

component_exch(glc, flow='c2x')

call cime_run_ocn_recv_post

call cime_run_ocnglc_coupling()

if (glcshelf_to_ocn AND ocn_to_glcshelf)

call prep_glc_calc_o2x_gx: call mapper_So2g; o2x_ox to o2x_gx seq_flds_x2g_states_from_ocn

call prep_glc_calculate_subshelf_boundary_fluxes; compute_melt_fluxes

call prep_ocn_shelf_calc_g2x_ox: map_Sg2o, map_Fg2o; g2x_gx, g2x_ox

prep_glc_accum_ocn (accumulate x2g_g fields)

if ( glcshelf_c2_ice) call mapper map_Sg2i; g2x_gx, g2x_ix; Sg_icemask_coupled_fluxes