Contributions of upper ocean stratification over the western North Pacific to ENSO spatial structure

Yoon-Kyoung Lee, KIOST Korea Institute of Ocean Science and Technology, Ansan, Korea, Republic of (South), Sang-Wook Yeh, Hanyang University, Marine Sciences and Convergent Technology, Seoul, Korea, Republic of (South), MinHo Kwon, KIOST Korea Institute of Ocean Science and Technology, Busan, South Korea, Boris Dewitte, LEGOS, Toulouse, France and Byung-Kwon Moon, Jeonbuk National University, Division of Science Education, Jeonju, South Korea
Abstract:
El Niño–Southern Oscillation (ENSO) variability is linked to both wind stress variations and recharge/discharge of oceanic heat content in the equatorial Pacific. The contribution of the surface momentum forcing to the ocean vertical baroclinic mode is important. We examined the changes in the relationship of oceanic vertical baroclinic mode-ENSO, and recent changes in warm pool SST and its linkage with ocean stratification. The mean SST over the western Pacific warm pool, where the wind stress variation is small, has experienced a shift from cool state to warm state in recent decades. Increased SST enhances the vertical stratification at the upper level. The warm pool SST variability is highly correlated with the change in maximum buoyancy frequency which is captured by the wind stress variations projecting onto the first baroclinic mode over the warm pool region. The ocean stratification change over the warm pool region, which is related to the changes in wind stress forcing projecting onto the oceanic baroclinic modes, might contribute to change in El Niño structure in the observation during recent decades.
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