Thermohaline Circulation in the Coupled Thermohaline Circulation in the Coupled GISS/HYCOM Climate SimulationGISS/HYCOM Climate Simulation

Shan SunShan SunNASA/GISS NASA/GISS

Rainer BleckRainer BleckLos Alamos National LaboratoryLos Alamos National Laboratory

Model SetupModel Setup

GISS AGCM: updated cloud and PBL GISS AGCM: updated cloud and PBL parameterization, 20 layers, 4x5 deg parameterization, 20 layers, 4x5 deg resolutionresolution

HYCOM: Bleck (2002), with a less diffusive HYCOM: Bleck (2002), with a less diffusive grid generator, 16 layers, 2xcos(lat) grid generator, 16 layers, 2xcos(lat) resolutionresolution

Ice model: thermodynamics (Russell et al., Ice model: thermodynamics (Russell et al., 2000) and Hibler dynamics (Zhang and 2000) and Hibler dynamics (Zhang and Rothrock, 2000)Rothrock, 2000)

Model ExperimentsModel ExperimentsControl A: 500 year runControl A: 500 year run

Control B: as Control A, but usingControl B: as Control A, but using

spiciness in place of salinity during advectionspiciness in place of salinity during advection

““brine pump” (poor man’s plume model)brine pump” (poor man’s plume model)

1% CO1% CO2 2 rise per year up to doublingrise per year up to doubling

Con

trol

A

Con

trol

A

Control A

Control A

Control B

2 x CO2

SST and its Drift

Net Heatflux at the Surface (W/m2)

Precipitation (mm/day)

SummarySummary

The density/spiciness advection appears to be The density/spiciness advection appears to be beneficial to coupled GISS/HYCOM model beneficial to coupled GISS/HYCOM model simulationssimulations

Atlantic thermohaline circulation under the global Atlantic thermohaline circulation under the global warming scenario is no longer stable as seen in warming scenario is no longer stable as seen in previous version of GISS/HYCOM (Sun and Bleck previous version of GISS/HYCOM (Sun and Bleck 2002)2002)

The climate sensitivity to surface mixing schemes The climate sensitivity to surface mixing schemes needs to be further examinedneeds to be further examined

The double ITCZ seems to be related to the cold The double ITCZ seems to be related to the cold bias along the equatorial Pacificbias along the equatorial Pacific