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ACCIMA ROMS issues

Mike Dinniman John Klinck Center for Coastal Physical Oceanography Old Dominion University December 16, 2011. ACCIMA ROMS issues. Outline. Test ocean only circum-Antarctic simulation Code version? Grid questions Things to add Ocean analysis metrics. Ocean Test Simulation.

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ACCIMA ROMS issues

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  1. Mike Dinniman John Klinck Center for Coastal Physical Oceanography Old Dominion University December 16, 2011 ACCIMA ROMS issues

  2. Outline • Test ocean only circum-Antarctic simulation • Code version? • Grid questions • Things to add • Ocean analysis metrics

  3. Ocean Test Simulation • ROMS: ~10 km horizontal resolution (800x800) on a polar stereographic grid, 32 vertical levels • Ice shelves (mechanical and thermodynamic) • Initial θ and S from 18-km ECCO2 • Lateral boundary conditions from ECCO2 (θ, S) and SODA (Ū and SSH) • ECMWF-Interim daily winds for 2010 • No sea ice, no tides, no surface heat or fresh water fluxes in open ocean, simple relaxation of surface θ (30d) and S (120d)

  4. Ocean Test Simulation (cont.) • Timmermann et al. bathymetry (1 min resolution bedrock and ice surfaces) • Grid is not large enough to include all the ACC fronts (does cover maximum sea ice extent) • 1 year simulation takes 71 hours on 32 cores (should scale well: 31 hours on 64 cores) • Is ocean “only” run going to be coupled w/ LANL CICE (i.e. should we wait for the coupling)? If not, do an ocean “only” run w/ built in Budgell sea ice?

  5. ACC Fronts (STF, SAF, PF, SACCF, SB) and Test Domain

  6. 5 day averages of model sea surface height

  7. 5 day averages of model sea surface temperature

  8. ROMS Version? • Test model is modified v3.4 • Latest version with Budgell (not LANL CICE) sea ice and ice shelf code is modified v3.5 (Kate Hedström’s “semi-official” branch) • Latest “official” version from Rutgers is v3.6 (does not include ice shelves or sea ice) • Related: Are we still setting up a CVS Repository?

  9. ROMS grid? • What horizontal resolution? Proposal said we would start with 10 km. Dream would be eddy resolving on shelf (1.5 km?) • Doesn’t have to cover same area as the atmosphere (should be same grid for sea ice), but that would be nice. If not, what gets used for forcing? • What lateral extent? We would like to at least cover out to the Subantarctic Front (45% increase in grid points from present)

  10. ROMS things to add • Tides (said we would in the proposal)? • Updated equation of state (Jackett and McDougall, 2006: valid down to -10 °C) • Ice shelf thickness respond to basal melt/freeze (if no lateral movement or calving, this is easy) • Frazil ice? (available but computationally expensive) • Artificial tracers (e.g. dyes explicitly representing CDW, ISW, AABW)

  11. (courtesy Scott Springer, ESR)

  12. Dye concentration at depth (model level 13) vs. observations showing presence or absence of MCDW

  13. ROMS metrics (with constraints) • ACC transport (observations and ocean reanalyses) • Frontal positions (in-situ observations and altimetry) • Water mass census (ARGO floats, obs climatologies and reanalyses) • Selected cross sections (esp. repeat sections like Drake Passage; also WOCE lines, ANSLOPE, SOGLOBEC) • SST and sea ice extent and drift (satellite obs) • SSH variability (altimetry) • Ice shelf basal melt estimates

  14. ROMS metrics (less sure about constraints) • Heat flux across the shelf break • CDW volume flux across the shelf break • Freshwater content in the ocean mixed layer • Sea ice production in coastal polynyas • AABW formation

  15. DICE DICE+ IICE Clim 300m mean salinity

  16. Difference mostly due to higher friction velocities under ice shelf, but also some effect from changes in water masses on open shelf (courtesy Scott Springer, ESR)

  17. Ice Shelf Modeling • Ice Shelf does not change in time in model • Three equation viscous sub-layer model for heat and salt fluxes (Holland and Jenkins, 1999) • Conservation of Heat • Conservation of Salt • Freezing point of sea water (function of pressure and salinity) • PGF calculation assumes the ice shelf has no flexural rigidity and pressure at the base comes from the floating ice

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