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Sea-Ice in ROMS

Sea-Ice in ROMS. Kate Hedstrom , UAF. Outline. Equations Dynamics Thermodynamics Code cppdefs.h SeaIce directory ice.in Examples Future plans. Dynamics. Momentum equations: Viscous-plastic term:. Ice Strength. Linear with thickness: Quadratic with thickness:. More Dynamics.

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Sea-Ice in ROMS

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  1. Sea-Ice in ROMS Kate Hedstrom, UAF

  2. Outline • Equations • Dynamics • Thermodynamics • Code • cppdefs.h • SeaIce directory • ice.in • Examples • Future plans

  3. Dynamics • Momentum equations: • Viscous-plastic term:

  4. Ice Strength • Linear with thickness: • Quadratic with thickness:

  5. More Dynamics • Rearrange VP: • EVP version:

  6. Solution • Stress tensor equation is timestepped explicitly • Young’s modulus E depends on ice thickness to keep solution close to VP solution • Ice velocities then timestepped with air/water stresses, Coriolis • Since it is all explicit, easy to parallelize (ROMS tiles)

  7. Thermodynamics • Need to compute all the ice growth/melt terms shown

  8. Evolution of Tracers • Ice volume is Ah • Ice concentration is A, • Phi is tunable parameter, value depends on sign of Wao i

  9. Advection of Tracers • Advection uses MPDATA, upwind or full • Ice volume, • Ice concentration • Snow volume • Ice enthalpy • Etc. • Followed by limiter 0 <= A <= 1

  10. More Thermodynamics • Heat fluxes are computed through the ice and snow • Temperature is linear in the ice • FT has an oceanic log layer

  11. Ice cppdefs.h • ICE_MODEL – turn on whole seaice model • ANA_ICE – analytic initial conditions • ICESHELF – ice shelves – something else again entirely • ICE_ADVECT – turn on advection • ICE_SMOLAR • ICE_UPWIND

  12. cppdefs.h • ICE_MOMENTUM – turn on rheology • ICE_EVP • ICE_MOM_BULK • ICE_SHOREFAST – ice slows as it fills water column • FASTICE_CLIMATOLOGY – read in locations where ice doesn’t move • ICE_STRENGTH_QUAD – quadratic ice strength as function of thickness

  13. cppdefs.h • ICE_THERMO – turn on thermodynamics • ICE_MK • ICE_BULK_FLUXES • OUTFLOW_MASK – turn on outflow cells • Reduces ice strength and viscosity in some cells • Cells specified in set_masks.F

  14. Albedo • ROMS default has shortwave radiation being net into the water • Preprocess shortwave to account for albedo • Ice/snow/melt ponds affect albedo, so incoming shortwave must be before albedo corrections • Don’t preprocess shortwave • Various options exist…

  15. Albedo Options • ALBEDO – needs clouds • Water only • ALBEDO_CURVE – function of latitude • Water only • ALBEDO_FILE • Ice and water • ALBEDO_CSIM • Ice only • ICE_ALB_EC92 – Ebert and Curry • Ice only

  16. SeaIce Directory • seaice.F – calls all the rest • Boundary conditions • i2d_bc.F, tibc.F, uibc.F, vibc.F • ice_advect.F – advect the ice tracers • ice_smolar.h • ice_enthalpi.F • ice_thermo.F – compute heat fluxes, melt/freeze rates • ice_mk.h

  17. SeaIce Directory • EVP rheology • ice_evp.F • ice_evp_sig.F • ice_elastic.F • ice_frazil.F • Computes frazil ice formation • Called from step3d_t.F • Checks for negative ice growth and crashes ROMS if found

  18. SeaIce Directory • ice_limit.F • Clamps on ice fields • ice_spdiw.F • Compute shear between ice and water in upper mixed layer • ice_vbc.F • Sets ice-water and ice-air stresses for ice momentum equation

  19. SeaIce Directory • ini_strengthcoef.F • Quadratic ice strength depends on grid spacing • Set 2D coefficient during initialization • ice_flux_rst.F • Timestepping in ROMS calls seaice before output • Seaice computes heat and momentum fluxes for ocean • To get perfect restart, we save the fluxes and use saved fluxes instead of timestepping ice in first step after restart

  20. Boundary Conditions • LBC options • Mix: clamped on inflow, gradient on outflow • Otherwise much like the ocean • Outflow cells • Specify in set_masks.F • Nesting • Offline nesting gives trouble for ice BC • Online nesting is reputed to work

  21. ice.in • Lice – logical for ice (ignored) • dtice – ignored, uses ocean dt • nevp – number of EVP iterations per step • min_h, min_a, max_a – ice limiters for thickness and concentration • Hout, Aout for ice variables • Various things I never change – read about them in the file

  22. Examples • From most mature to least mature • Northeast Pacific (NEP) • Arctic • Arctic2 • Cook Inlet (NWGOA) • All are ice-ocean only, just one grid

  23. Northeast Pacific • 11 km resolution • GLOBEC, BEST, BOEM • Looking at interannual variability • First-year ice only in Bering

  24. Ice Timeseries

  25. Ice Concentration Seth Danielson

  26. Summary of Bering Sea • Ice extent sensitive to incoming solar radiation (including albedo) • Once tuned, the model did a good job • Spring melt is too slow (didn’t use melt pond albedo)

  27. Arctic 1 • Telescoping grid, 5 to 20 km • Boundary at Bering Strait • 20 year hindcast for BOEM • Fastice climatology

  28. Ice Thickness Satellite Model - obs Seth Danielson

  29. Ice Concentration Seth Danielson

  30. Timeseries Seth Danielson

  31. Summary of Chukchi-Beaufort Seas • Ice too mobile, getting too thick off Siberia, too thin off Alaska • Too thin areas grow more ice, making ocean too salty • Excess ice melt in May-June, not enough later in summer • Monthly anomalies have skill except for a few problem summers (1988, 2002, 2003)

  32. Arctic 2 • Includes Bering Sea for looking at Bering Strait flow for NPRB • Includes Canadian archipelago • Quadratic ice strength

  33. Ice Thickness

  34. Northwest Gulf of Alaska • 1.5 km resolution • Includes tides and WET_DRY • Fresh water from land runoff model • Try out CVMix? • For BOEM

  35. Papers • Hunke and Dukowicz, An elastic-viscous-plastic model for sea ice dynamics, JPO, 27, 1849-1867 (1997) • Hunke, Viscous-plastic sea ice dynamics with the EVP model: linearization issues, JCP, 170, 18-38 (2001) • Mellor and Kantha, An ice-ocean coupled model, JGR, 94, 10,937-10,954 (1989)

  36. Papers • Hakkinen and Mellor, Modeling the seasonal variability of a coupled Arctic ice-ocean system, JGR, 97, 20,285-20,304 (1992) • Overland and Pease, Modeling ice dynamics of coastal seas, JGR, 93, 15,619-15,637 (1988) • Steele, Mellor and McPhee, Role of the molecular sublayer in the melting or freezing of sea ice, JPO, 19, 139-147 (1989)

  37. Plans • Eight years ago I wrote: • Replacing Mellor-Kantha with CICE 3.1 • Now aiming for CICE 5. What does it offer? • Multiple ice categories and temperature levels • All the recent sea ice model improvements to melt ponds, rheology, drag, etc. • Still missing fast ice, embedded ice

  38. Random Tips • Circumpolar considerations • GLOBAL_PERIODIC • grid_coords.F(floats, stations) • Beyond ROMS trunk • BIO_UMAINE, aka CoSiNE • ARCTIC in 2012 ROMS manual • BERING coming soon • With WRF

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