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

•Rearrange VP:

•EVP version:

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)

Thermodynamics

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

Evolution of Tracers

• Ice volume is Ah• Ice concentration is A,• Phi is tunable parameter, value

depends on sign of Wao

i

Advection of Tracers

• Advection uses MPDATA, upwind or full – Ice volume,– Ice concentration– Snow volume– Ice enthalpy– Etc.

• Followed by limiter 0 <= A <= 1

More Thermodynamics

• Heat fluxes are computed through the ice and snow

• Temperature is linear in the ice• FT has an oceanic log layer

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

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

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

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…

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

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

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

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

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

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

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

Examples

• From most mature to least mature– Northeast Pacific (NEP)– Arctic– Arctic2– Cook Inlet (NWGOA)

• All are ice-ocean only, just one grid

Northeast Pacific

• 11 km resolution• GLOBEC, BEST,

BOEM• Looking at

interannual variability

• First-year ice only in Bering

Ice Timeseries

Ice Concentration

Seth Danielson

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)

Arctic 1

• Telescoping grid, 5 to 20 km

• Boundary at Bering Strait

• 20 year hindcast for BOEM

• Fastice climatology

Ice Thickness

Seth Danielson

Satellite Model - obs

Ice Concentration

Seth Danielson

Timeseries

Seth Danielson

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)

Arctic 2

• Includes Bering Sea for looking at Bering Strait flow for NPRB

• Includes Canadian archipelago

• Quadratic ice strength

Ice Thickness

Northwest Gulf of Alaska

• 1.5 km resolution• Includes tides and

WET_DRY• Fresh water from

land runoff model• Try out CVMix?• For BOEM

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)

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)

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

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