Interdecadal Variability in the Western North Pacific Ocean

Abstract

Low-frequency fluctuations of the ocean and atmosphere over the western North Pacific Ocean (WNPO) on interannual to interdecadal timescales significantly impact the weather and climate of EastAsia, and drive important state transitions observed in marine ecosystems across the Pacific Ocean. In this study, the interdecadal change in air-sea coupled variability is investigated over the WNPOincluding East China Sea (ECS) and Kuroshio Oyashio Extention (KOE) regions during the period 1958/59&#8211 2007/08. Distinct and strong warming of sea surface temperature (SST) occurred in theWNPO during boreal winter around 1988/89 climate transition. This warming is associated with a synchronous change of the subtropical western boundary currents over the North Pacific. Thesecond mode of empirical orthogonal function (EOF) analysis of both Sverdrup volume transport (SVT) and barotropic volume transport (BVT) over the region in December-February explains 25.6%and 29.8% of spatial and temporal variability, respectively. This result shows the westward intensification of North Pacific subtropical gyre on interdecadal time scale. The composite differences ofSVT and BVT between before and after 1988/99 support an increase in the westward intensification of subtropical gyre over the North Pacific. The results of multi-variable EOF shows that thevariability of WNPO SST is associated with the variability of East Asian winterbserved in marine ecosystems across the Pacific Ocean. In this study, the interdecadal change in air-sea coupled variability is investigated over the WNPOincluding East China Sea (ECS) and Kuroshio Oyashio Extention (KOE) regions during the period 1958/59&#8211 2007/08. Distinct and strong warming of sea surface temperature (SST) occurred in theWNPO during boreal winter around 1988/89 climate transition. This warming is associated with a synchronous change of the subtropical western boundary currents over the North Pacific. Thesecond mode of empirical orthogonal function (EOF) analysis of both Sverdrup volume transport (SVT) and barotropic volume transport (BVT) over the region in December-February explains 25.6%and 29.8% of spatial and temporal variability, respectively. This result shows the westward intensification of North Pacific subtropical gyre on interdecadal time scale. The composite differences ofSVT and BVT between before and after 1988/99 support an increase in the westward intensification of subtropical gyre over the North Pacific. The results of multi-variable EOF shows that thevariability of WNPO SST is associated with the variability of East Asian winter