Response Of SST And Subtropical Countercurrent Over The North Pacific To Green-house Gas And Aerosol Forcing

The response of the Sea Surface Temperature (SST) and SubtropicalCountercurrent (STCC) to greenhouse gas (GHG) and aerosol forcing over the NorthPacific is investigated based on the twentieth-century historical and single-forcingexperiments with the Geophysical Fluid Dynamics Laboratory Climate Model version3(GFDL CM3). A number of innovative achievements have been made as follows.The aerosol effect causes the SST to cool in the mid-latitude North Pacific,especially in the Kuroshio-Oyashio-Extension (KOE) region by inducing cyclonicatmosphere circulation anomalies and enhancing thermal advection of subpolar oceancirculation, during the past five decades (1950-2005). The cooling effect exceeds thewarming effect by the GHG increase.SST responses to GHG and aerosol forcing both peak in boreal summer, and thestrongest response of GHG forcing locates in the high-latitude North Pacific, while itlocates in the mid-latitude North Pacific by aerosol forcing. In the aerosol forcingexperiment, the positive feedback among SST, cloud and short-wave radiationcontributes much to the coldest SST response in August over the KOE region. The STCC responses to the GHG and aerosol forcing are also opposite. In theGHG (aerosol) forcing run, the STCC decelerates (accelerates) due to the decreased(increased) Subtropical Mode Water in the North Pacific, resulting from a weaker(stronger) front in the MLD and reduced (increased) subduction in the mode waterformation region. As a result of the aerosol effect exceeds the GHG effect，the NorthPacific SST, Subtropical Mode Water and STCC in response to historical forcing tendto resemble the response to aerosol forcing during the past five decades.