HYCOM and the need for HYCOM and the need for overflow/entrainment overflow/entrainment

parameterizationsparameterizations

Overflow Representation in Overflow Representation in Numerical ModelsNumerical Models

• Strongly dependent on the choice of the Strongly dependent on the choice of the vertical coordinatevertical coordinate

• In fixed coordinate models (z and In fixed coordinate models (z and σσ), the ), the numerically induced entrainment (i.e. numerically induced entrainment (i.e. mixing) is larger than observed => no mixing) is larger than observed => no need for parameterization, the focus is on need for parameterization, the focus is on reducing the numerically-induced mixing reducing the numerically-induced mixing to below observations (DYNAMO, Griffies to below observations (DYNAMO, Griffies et al. (2000), …)et al. (2000), …)

• In density coordinate models, the densest In density coordinate models, the densest fluid will sink to the bottom => need for fluid will sink to the bottom => need for an entrainment parameterizationan entrainment parameterization

Entrainment Entrainment parameterizationparameterization

• The specific parameterization will depend The specific parameterization will depend on the resolution: large difference on the resolution: large difference between coarse climate models between coarse climate models (horizontal resolution of 1º or lower ) and (horizontal resolution of 1º or lower ) and truly eddy-resolving models (horizontal truly eddy-resolving models (horizontal resolution of ~1/10º). Different viscosity resolution of ~1/10º). Different viscosity => different modeled Ri/Fr numbers=> different modeled Ri/Fr numbers

• How do we address this?How do we address this?

HYCOM HYCOM

• Investigation in HYCOM 2º Investigation in HYCOM 2º global configuration global configuration for the NCAR for the NCAR CCSM and OMIPCCSM and OMIP

• Investigation in the 1/12º North Investigation in the 1/12º North Atlantic Ocean prediction system Atlantic Ocean prediction system (U.S. GODAE)(U.S. GODAE)

• What are the targets? One needs to What are the targets? One needs to define the metrics.define the metrics.

U.S. GODAE: Global Ocean U.S. GODAE: Global Ocean Prediction with the Hybrid Prediction with the Hybrid Coordinate Ocean Model Coordinate Ocean Model

(HYCOM)(HYCOM)

Representation of the Mediterranean Outflow and Dennmark Straits Overflow

Objectives and GoalsObjectives and Goals

• A broad partnership of institutions that A broad partnership of institutions that will collaborate in developing and will collaborate in developing and demonstrating the performance and demonstrating the performance and application of eddy-resolving, real-time application of eddy-resolving, real-time global and basin-scale ocean prediction global and basin-scale ocean prediction systems using HYCOMsystems using HYCOM

• To be transitioned for operational useTo be transitioned for operational use

OpportunitiesOpportunities

• Global high resolution (1/12º) model Global high resolution (1/12º) model outputs available to the community outputs available to the community at largeat large

• Strong participation of the coastal Strong participation of the coastal ocean modeling community in using ocean modeling community in using and evaluating boundary conditions and evaluating boundary conditions from the global and basin-scale from the global and basin-scale ocean modeling prediction systemsocean modeling prediction systems

HYCOMHYCOM

• HYCOM is the result of a very HYCOM is the result of a very effective collaboration between the effective collaboration between the U. of Miami, NRL/Stennis, and the Los U. of Miami, NRL/Stennis, and the Los Alamos National Laboratory. Alamos National Laboratory.

• HYCOM has been configured globally HYCOM has been configured globally (up to 3/4º ~60km mid-latitude (up to 3/4º ~60km mid-latitude resolution) and basin-scale (up to resolution) and basin-scale (up to 1/12º ~7km mid-latitude resolution – 1/12º ~7km mid-latitude resolution – North Atlantic and Pacific)North Atlantic and Pacific)

The hybrid coordinate is one that is isopycnal in the open, stratified ocean, but smoothly reverts to a terrain-following coordinate in shallow coastal regions, and to pressure coordinate in the mixed layer and/or unstratified seas.

1/25° HYCOM East Asian Seas Model

Boundary conditions via one-way nestingand 6 hrly ECMWF 10 m atmospheric forcing

Nested inside 1/6° HYCOM Pacific Basin Model

1/25° East Asian Seas HYCOM (nested inside 1/6° Pacific HYCOM)

North-south velocity cross-section along 124.5°E, upper 400 m

Snapshot on 14 October

density frontassociated with

sharp topographic feature(cannot be resolved with

fixed coordinates)

red=eastward flowblue=westward flow

East China Sea

Yellow Sea flowreversal with depth

Isopycnals overshelf region

z-levels and sigma-levelsover shelf and in mixed layer

Snapshot on 12 April

Yellow Sea

Configuration of the Prediction Configuration of the Prediction SystemsSystems

• Basin-scaleBasin-scale (NRL/Miami and NOAA) (NRL/Miami and NOAA)

Configuration of the Prediction Configuration of the Prediction SystemsSystems

• Global Global – Sea Ice OptionsSea Ice Options

•Energy loanEnergy loan

•4-layer thermodynamic 4-layer thermodynamic (Russel et al., 2000)(Russel et al., 2000)

•Los Alamos CICELos Alamos CICE

– TargetTarget•1/12º for NAVOCEANO 1/12º for NAVOCEANO

•1/4º (~20 km) for FNMOC 1/4º (~20 km) for FNMOC (ocean component of (ocean component of coupled ocean-coupled ocean-atmosphere)atmosphere)

Denmark Straits Overflow Along 31°W

Temperature

Salinity

Results from 1/12° Atlantic HYCOM

Colder fresher water forms over the shelfin the Nordic Seas and spills over the Denmark Strait

and entrains moresaline Irminger Sea water

Results from 1/12° Atlantic HYCOM

Results from 1/12° Atlantic HYCOM

More on Dennmark Straits plans in Xiaobiao Xu’s

presentation

Representation of the Representation of the Mediterranean Outflow in MICOM Mediterranean Outflow in MICOM

and HYCOMand HYCOM

• Entrainment parameterization in Entrainment parameterization in MICOM => Papadakis et al. (2003)MICOM => Papadakis et al. (2003)

• Outflow representation in MICOM and Outflow representation in MICOM and HYCOMHYCOM

• Entrainment parameterization in Entrainment parameterization in HYCOM vs. MICOMHYCOM vs. MICOM

• DiscussionDiscussion

Entrainment Parameterization Entrainment Parameterization in MICOM (Papadakis et al., in MICOM (Papadakis et al.,

2003)2003)• Based in the implicit diapycnal mixing Based in the implicit diapycnal mixing

scheme of Hallberg (2000)scheme of Hallberg (2000)

• Uses a Richardson number dependent Uses a Richardson number dependent entrainment parameterization of Turner entrainment parameterization of Turner (1986) based on laboratory experiments(1986) based on laboratory experiments

• Evaluated in a realistic MICOM regional Evaluated in a realistic MICOM regional model (1/12º grid) with imposed model (1/12º grid) with imposed boundary conditions at the Strait of boundary conditions at the Strait of Gibraltar Gibraltar

Domain Configuration

Boundary Conditions at the Strait of Gibraltar

Inflow/outflow = .8 Sv

Sensitivity to Entrainment Sensitivity to Entrainment Parameterization (Turner, Parameterization (Turner,

1986)1986)

Outflow RepresentationOutflow Representation

Outflow RepresentationOutflow Representation

Sensitivity to Mixing Sensitivity to Mixing FrequencyFrequency

Implementation in 1/12º North Implementation in 1/12º North Atlantic MICOM Atlantic MICOM

Layer 10 thickness1979-1986

Salinity Layer 101979-1986

Meddies dissipate quickly, outflow too shallow

MICOM 1/12ºMICOM 1/12º

Transport ~ .7 Sv

MICOM 1/12ºMICOM 1/12º

HYCOM 1/12ºHYCOM 1/12º

Transport ~ 1 Sv

HYCOM 1/12ºHYCOM 1/12º

KPP vs. Turner (1986)KPP vs. Turner (1986)• The K-Profile parameterization (Large et The K-Profile parameterization (Large et

al., 1994) is widely used in ocean modelsal., 1994) is widely used in ocean models

• KPP is derived from observations while KPP is derived from observations while Turner (1986) is primarily derived from Turner (1986) is primarily derived from laboratory experimentslaboratory experiments

• There are non-oceanic aspect aspects in There are non-oceanic aspect aspects in Turner (1986), i.e. lack of rotation, …Turner (1986), i.e. lack of rotation, …

• KPP is however a broad representation of KPP is however a broad representation of the processes and may not be very the processes and may not be very relevant to overflowsrelevant to overflows

Present StrategyPresent Strategy

• Evaluation of KPP and Turner (1986) Evaluation of KPP and Turner (1986) [possibly other parameterizations as [possibly other parameterizations as they are developed => CPTs on they are developed => CPTs on overflows]overflows]– Idealized configurationsIdealized configurations– Comparison to 2D non-hydrostatic Comparison to 2D non-hydrostatic

configurations (i.e. Ozgokmen and configurations (i.e. Ozgokmen and Chassignet, 2002)Chassignet, 2002)

• Document the sensitivity to numerical Document the sensitivity to numerical choices such as stratification, mixing choices such as stratification, mixing frequency,…..frequency,…..