The properties of the North Pacific Intermediate Water from a suite of NOAA/GFDL coupled climate models

Abstract

The properties of the North Pacific Intermediate Waters (NPIW) are investigated using a suite of coupled climate models. It is found that the Kuroshio and the subtropical mode water influence on NPIW as well as high latitude circulations. The coupled models analyzed are NOAA/GFDL CM2.1, which utilized in the IPCC AR4, CM2M, an improved version of CM2.1, and CM2G which utilized an isopycnal ocean model GOLD. All models produce NPIWs (salinity minimum layers). Their properties and formation regions, however, are rather different. NPIW from CM2G is comparable to that of the observed one, but those from CM2M and CM2.1 are saltier and heavier. The distributions of an age tracer show that in CM2M and CM2.1 the low salinity water originates not from the Okhotsk Sea but from the western part of the Kamchatka Sea. The water flows southward the Kamchatka Peninsula and the eastern edge of the Kuril Islands. Upon encountering the Kuroshio Oyashio extension the water penetrates below the subtropical mode water while moving eastward. The penetration occurs away from Japanese coast because of the too strong Kuroshio and thick mode water. In CM2G, the salinity minimum layer starts from the Okhotsk Sea to flow southward along the east coast of Sakhalin and through the Kuril Islands until encountering the Kuroshio Oyashio extension. In this model, the Kuroshio separates at lower latitude and the mode waters. The coupled models analyzed are NOAA/GFDL CM2.1, which utilized in the IPCC AR4, CM2M, an improved version of CM2.1, and CM2G which utilized an isopycnal ocean model GOLD. All models produce NPIWs (salinity minimum layers). Their properties and formation regions, however, are rather different. NPIW from CM2G is comparable to that of the observed one, but those from CM2M and CM2.1 are saltier and heavier. The distributions of an age tracer show that in CM2M and CM2.1 the low salinity water originates not from the Okhotsk Sea but from the wes