Thermohaline Circulation in the Coupled GISS/HYCOM Climate Simulation Shan Sun NASA/GISS Rainer Bleck Los Alamos National Laboratory

Model Setup GISS AGCM: updated cloud and PBL parameterization, 20 layers, 4x5 deg resolution GISS AGCM: updated cloud and PBL parameterization, 20 layers, 4x5 deg resolution HYCOM: Bleck (2002), with a less diffusive grid generator, 16 layers, 2xcos(lat) resolution HYCOM: Bleck (2002), with a less diffusive grid generator, 16 layers, 2xcos(lat) resolution Ice model: thermodynamics (Russell et al., 2000) and Hibler dynamics (Zhang and Rothrock, 2000) Ice model: thermodynamics (Russell et al., 2000) and Hibler dynamics (Zhang and Rothrock, 2000)

Model Experiments Control A: 500 year run Control A: 500 year run Control B: as Control A, but using Control B: as Control A, but using spiciness in place of salinity during advection spiciness in place of salinity during advection “brine pump” (poor man’s plume model) “brine pump” (poor man’s plume model) 1% CO 2 rise per year up to doubling 1% CO 2 rise per year up to doubling

Control A

Control B

2 x CO 2

SST and its Drift

Net Heatflux at the Surface (W/m 2 )

Precipitation (mm/day)

Summary The density/spiciness advection appears to be beneficial to coupled GISS/HYCOM model simulations The density/spiciness advection appears to be beneficial to coupled GISS/HYCOM model simulations Atlantic thermohaline circulation under the global warming scenario is no longer stable as seen in previous version of GISS/HYCOM (Sun and Bleck 2002) Atlantic thermohaline circulation under the global warming scenario is no longer stable as seen in previous version of GISS/HYCOM (Sun and Bleck 2002) The climate sensitivity to surface mixing schemes needs to be further examined The climate sensitivity to surface mixing schemes needs to be further examined The double ITCZ seems to be related to the cold bias along the equatorial Pacific The double ITCZ seems to be related to the cold bias along the equatorial Pacific