Monday, 12 January 2009: 1:45 PM
Interaction of Convection and SST in the Formation and Disappearance of Double ITCZs in the NCAR CCSM3
Room 129A (Phoenix Convention Center)
The role of convection parameterization in the formation of double ITCZ and associated upper ocean biases in the NCAR CCSM3 is investigated by comparing the simulations using the standard and revised Zhang-McFarlane (ZM) convection schemes. 10-year model climatologies show that the simulation with the ZM scheme produces a typical double ITCZ bias, while use of the revised ZM scheme significantly reduces the biases in the precipitation, SST, wind stress, ocean thermocline, upper ocean currents and temperatures in the spurious ITCZ region. Short term simulations from both the stand-alone atmospheric model CAM3 and the coupled model CCSM3 are used to understand why and how the revised ZM scheme helps to alleviate the models' double ITCZ biases. It is found that reduction of precipitation in the southern ITCZ region is primarily a result of different treatment of the interaction between convection and the large-scale circulation in the atmospheric model. The reduction of SST bias in the region in the coupled model is a result of atmosphere-ocean coupling, in which both surface fluxes and ocean heat transport play an equally important role. Details will be presented at the meeting.