Response of North Pacific ocean circulation in a Kuroshio-resolving ocean model to an Arctic Oscillation (AO)-like change in Northern Hemisphere atmospheric circulation due to greenhouse-gas forcing

Abstract

Time-slice experiments are performed using a high-resolution North Pacific ocean general circulation model (NPOGCM) resolving the strong currents near Japan, such as the Kuroshio and the Oyashio, to investigate the effect of global warming on the North Pacific ocean circulation. The NPOGCM is forced by heat, momentum, and fresh-water fluxes obtained from a global warming projection using a global climate model (MRI-CGCM2.2). The annual mean sea-level pressure trend exhibits an annular pattern similar to the positive phase of the Arctic Oscillation in a global warming projection by MRI-CGCM2.2 based on the Intergovernmental Panel on Climate Change (IPCC) SRES A2 emission scenario. Associated with this trend, the anticyclonic atmospheric circulation is intensified over the mid-latitude North-Pacific, leading to a northward shift of the oceanic subtropical wind-driven gyre boundary, where extensions of the Kuroshio exist in MRI-CGCM2.2. Under these forcing changes, NPOGCM projects that in the future climate warm core eddies are more frequently pinched off from the Kuroshio off the eastern coast of Japan, leading to an annual mean SST rise over 5 K at its maximum, compared with the present climate. The projected annual mean sea-level rise ranges from 12 to 18 cm along the coasts of Japan, and about 40 cm over the ocean east of Japan. © 2006, Meteorological Society of Japan.