CORE-II HYCOMScience application and test cases

Eric P. Chassignet and Alexandra Bozec

Science application and test case

•In order to validate the code changes and to demonstrate the improvement on HYCOM, one needs to configure a scientifically useful case.

•HYCOM has been implemented as an ESPC ocean component in a standalone configuration on a Parallel Ocean Program (POP) glbx1v6 dipolar grid (320x384) grid and bathymetry. This configuration is a 1-degree climate case from the Community Earth System Model (CESM) also used by CICE in order to provide a direct comparison to simulations performed by the CESM model.

•Several routines of the HYCOM source code (v2.2.86) have been modified to include the proper reading of the CORE-II forcing and a new passive ice component has been added, based on the CESM DICE.

•Several 30-year runs of HYCOM have been performed with the CORE-II (Large and Yeager, 2009) normal year atmospheric fields to assess the sensitivity of the model to several parameters (reference pressure, thermobaricity, and isopycnal smoothing).

Set-up

CCSM3-HYCOM: - CORE-II Atmospheric forcing from 1948 to 2007 through the CCSM coupler (5 Cycles)- Dipole POP gx1v3 grid- Initialization from rest with Levitus PHC2.1 (POPx1v3 initial conditions)- SSS-relaxation:4year/50m everywhere- Normalization of the salt flux at the surface- Bulk Formulation :Large and Yeager- CSIM ice model

FSU-HYCOM: - CORE-II Atmospheric forcing from 1948 to 2007 (5 Cycles) - Tripolar HYCOM GLBt0.72 grid- Initialization from rest with Levitus PHC2.1- SSS-relaxation: 4year/50m everywhere except Antarctic at 6months/50m- Normalization of the salt flux at the surface- Bulk Formulation : Large and Yeager - CICE ice model

Comparison of the grids

GLBt0.72

glbx1v6

Surface BiasesCCSM3-HYCOM FSU-HYCOM

TE

MP

BIA

SS

AL

INIT

Y B

IAS

CC

SM

3-H

YC

OM

FS

U-H

YC

OM

CC

SM

3-H

YC

OM

Ne

w F

SU

-HY

CO

M

Global Drifts

Temperature Salinity

Atlantic DriftsC

CS

M3

-HY

CO

MC

CS

M3

-HY

CO

M F

SU

-HY

CO

MN

ew

FS

U-H

YC

OM

Temperature Salinity

OverturningStreamfunction

CCSM-HYCOM

FSU-HYCOM

Maximum Streamfunction at 26.5ºN

Atlantic heat transport

Mixed Layer depth

New FSU-HYCOMCCSM3-HYCOMPOP-NCAR

MLD 0.125kg/m3 criterium in March average over 1988-2007, last cycle

0. 3.km

Drake Passage

March Mean Arctic Ice Thickness

CCSM-HYCOM FSU-HYCOMPOP-NCAR

Averaged over 1988-2007, cycle 5

HYCOM in CESM implementation

Goal #1: Produce a HYCOM stand-alone baseline run in a C-compset (use of DICE for the ice component) : • based on 1º resolution grid from the POP gx1v6 grid (320x384),• v2.2.86 of the HYCOM source • Initial Conditions Levitus- PHC2• CORE atmospheric forcing Normal Year • Ice component: DICE (new in HYCOM)• Precipitation adjustment (new in HYCOM)• Spatially varying SSS/SST relaxation

For comparison purposes, POP-DICE has been run in its default setting for 30 years (data provided by Caroline Papadopoulos and Julie McClean)

SST & SSS bias after 30 years

POP

POP

REF-HYCOM

REF-HYCOM

Evolution of Global T &S

With precip_adjust:Stabilization of S

REF-POP: eq. to -3% of precipREF-HYCOM: -2% of precip

AMOC Strength

REF-HYCOM AMOC is weaker (12Sv) than in POP (15 Sv).

Drake Passage transport

• Biharmonic Gent-McWilliams more effective at maintaining transport

HYCOM in CESM implementation

Goal #2: Produce a HYCOM-CICE stand-alone baseline run in a G-compset : • based on 1º resolution grid from the POP gx1v6 grid (320x384),• v2.2.86 of the HYCOM source • Initial Conditions Levitus- PHC2• CORE atmospheric forcing Normal Year • Ice component: CICE v4.0 (initial condition: default ice cap provided by CICE)• Precipitation adjustment• Spatially varying SSS/SST relaxation

•Results are compared with HYCOM-DICE (REF-HYCOM)

Evolution of T & S, AMOC strength

HYCOM-CICE (black)REF-HYCOM (Yellow)

HYCOM-CICE (black)REF-HYCOM (yellow)

HYCOM-CICE stabilizes before REF-HYCOM

HYCOM-CICE shows a stronger AMOC at 16Sv than REF-HYCOM (12sv)

HYCOM in CESM implementation

Produce a CESM-HYCOM baseline run in a G-compset : • based on 1º resolution grid from the POP gx1v6 grid (320x384),• v2.2.35 of the HYCOM source (for testing purposes) • Initial Conditions Levitus- PHC2• CORE-II atmospheric forcing provided by DATM• Ice component: CICE v4.0 (CESM version)

(Ice initial condition: ice cap provided by CESM)

Results to be compared with:• CESM-POP• HYCOM-CICE stand-alone

Comparison of the total heat and freshwater fluxF

res

hw

ate

r F

lux

Hea

t F

lux

Comparison of the total heat and freshwater flux (monthly mean Jan/ 1st year)

Questions?

Antarctic Ice Cover/ThicknessCCSM-HYCOM Old FSU-HYCOM New FSU-HYCOM