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HYCOM and the need for overflow/entrainment parameterizations.

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Presentation on theme: "HYCOM and the need for overflow/entrainment parameterizations."— Presentation transcript:

1 HYCOM and the need for overflow/entrainment parameterizations

2 Overflow Representation in Numerical Models Strongly dependent on the choice of the vertical coordinate Strongly dependent on the choice of the vertical coordinate In fixed coordinate models (z and σ), the numerically induced entrainment (i.e. mixing) is larger than observed => no need for parameterization, the focus is on reducing the numerically-induced mixing to below observations (DYNAMO, Griffies et al. (2000), …) In fixed coordinate models (z and σ), the numerically induced entrainment (i.e. mixing) is larger than observed => no need for parameterization, the focus is on reducing the numerically-induced mixing to below observations (DYNAMO, Griffies et al. (2000), …) In density coordinate models, the densest fluid will sink to the bottom => need for an entrainment parameterization In density coordinate models, the densest fluid will sink to the bottom => need for an entrainment parameterization

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

4 HYCOM Investigation in HYCOM 2º global configuration for the NCAR CCSM and OMIP Investigation in HYCOM 2º global configuration for the NCAR CCSM and OMIPglobal configuration global configuration Investigation in the 1/12º North Atlantic Ocean prediction system (U.S. GODAE) Investigation in the 1/12º North Atlantic Ocean prediction system (U.S. GODAE) What are the targets? One needs to define the metrics. What are the targets? One needs to define the metrics.

5 U.S. GODAE: Global Ocean Prediction with the Hybrid Coordinate Ocean Model (HYCOM) Representation of the Mediterranean Outflow and Dennmark Straits Overflow

6 Objectives and Goals A broad partnership of institutions that will collaborate in developing and demonstrating the performance and application of eddy- resolving, real-time global and basin-scale ocean prediction systems using HYCOM A broad partnership of institutions that will collaborate in developing and demonstrating the performance and application of eddy- resolving, real-time global and basin-scale ocean prediction systems using HYCOM To be transitioned for operational use To be transitioned for operational use

7 Opportunities Global high resolution (1/12º) model outputs available to the community at large Global high resolution (1/12º) model outputs available to the community at large Strong participation of the coastal ocean modeling community in using and evaluating boundary conditions from the global and basin-scale ocean modeling prediction systems Strong participation of the coastal ocean modeling community in using and evaluating boundary conditions from the global and basin-scale ocean modeling prediction systems

8 HYCOM HYCOM is the result of a very effective collaboration between the U. of Miami, NRL/Stennis, and the Los Alamos National Laboratory. HYCOM is the result of a very effective collaboration between the U. of Miami, NRL/Stennis, and the Los Alamos National Laboratory. HYCOM has been configured globally (up to 3/4º ~60km mid-latitude resolution) and basin-scale (up to 1/12º ~7km mid- latitude resolution – North Atlantic and Pacific) HYCOM has been configured globally (up to 3/4º ~60km mid-latitude resolution) and basin-scale (up to 1/12º ~7km mid- latitude resolution – North Atlantic and Pacific)

9 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.

10 1/25° HYCOM East Asian Seas Model Boundary conditions via one-way nesting and 6 hrly ECMWF 10 m atmospheric forcing Nested inside 1/6° HYCOM Pacific Basin Model

11 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 front associated with sharp topographic feature (cannot be resolved with fixed coordinates) red=eastward flowblue=westward flow East China Sea Yellow Sea flow reversal with depth Isopycnals over shelf region z-levels and sigma-levels over shelf and in mixed layer Snapshot on 12 April Yellow Sea

12 Configuration of the Prediction Systems Basin-scale (NRL/Miami and NOAA) Basin-scale (NRL/Miami and NOAA) Basin-scale

13 Configuration of the Prediction Systems Global Global – Sea Ice Options Energy loan Energy loan 4-layer thermodynamic (Russel et al., 2000) 4-layer thermodynamic (Russel et al., 2000) Los Alamos CICE Los Alamos CICE –Target 1/12º for NAVOCEANO 1/12º for NAVOCEANO 1/4º (~20 km) for FNMOC (ocean component of coupled ocean-atmosphere) 1/4º (~20 km) for FNMOC (ocean component of coupled ocean-atmosphere)

14 Denmark Straits Overflow Along 31°W Temperature Salinity Results from 1/12° Atlantic HYCOM Colder fresher water forms over the shelf in the Nordic Seas and spills over the Denmark Strait and entrains more saline Irminger Sea water

15 Results from 1/12° Atlantic HYCOM

16 More on Dennmark Straits plans in Xiaobiao Xu’s presentation

17 Representation of the Mediterranean Outflow in MICOM and HYCOM Entrainment parameterization in MICOM => Papadakis et al. (2003) Entrainment parameterization in MICOM => Papadakis et al. (2003) Outflow representation in MICOM and HYCOM Outflow representation in MICOM and HYCOM Entrainment parameterization in HYCOM vs. MICOM Entrainment parameterization in HYCOM vs. MICOM Discussion Discussion

18 Entrainment Parameterization in MICOM (Papadakis et al., 2003) Based in the implicit diapycnal mixing scheme of Hallberg (2000) Based in the implicit diapycnal mixing scheme of Hallberg (2000) Uses a Richardson number dependent entrainment parameterization of Turner (1986) based on laboratory experiments Uses a Richardson number dependent entrainment parameterization of Turner (1986) based on laboratory experiments Evaluated in a realistic MICOM regional model (1/12º grid) with imposed boundary conditions at the Strait of Gibraltar Evaluated in a realistic MICOM regional model (1/12º grid) with imposed boundary conditions at the Strait of Gibraltar

19 Domain Configuration

20 Boundary Conditions at the Strait of Gibraltar Inflow/outflow =.8 Sv

21 Sensitivity to Entrainment Parameterization (Turner, 1986)

22 Outflow Representation

23

24 Sensitivity to Mixing Frequency

25 Implementation in 1/12º North Atlantic MICOM Layer 10 thickness Salinity Layer Meddies dissipate quickly, outflow too shallow

26 MICOM 1/12º Transport ~.7 Sv

27 MICOM 1/12º

28 HYCOM 1/12º Transport ~ 1 Sv

29 HYCOM 1/12º

30 KPP vs. Turner (1986) The K-Profile parameterization (Large et al., 1994) is widely used in ocean models The K-Profile parameterization (Large et al., 1994) is widely used in ocean models KPP is derived from observations while Turner (1986) is primarily derived from laboratory experiments KPP is derived from observations while Turner (1986) is primarily derived from laboratory experiments There are non-oceanic aspect aspects in Turner (1986), i.e. lack of rotation, … There are non-oceanic aspect aspects in Turner (1986), i.e. lack of rotation, … KPP is however a broad representation of the processes and may not be very relevant to overflows KPP is however a broad representation of the processes and may not be very relevant to overflows

31 Present Strategy Evaluation of KPP and Turner (1986) [possibly other parameterizations as they are developed => CPTs on overflows] Evaluation of KPP and Turner (1986) [possibly other parameterizations as they are developed => CPTs on overflows] –Idealized configurations –Comparison to 2D non-hydrostatic configurations (i.e. Ozgokmen and Chassignet, 2002) Document the sensitivity to numerical choices such as stratification, mixing frequency,….. Document the sensitivity to numerical choices such as stratification, mixing frequency,…..


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