Interannual variability in the North Pacific meridional overturning circulation

摘要

We analyzed the temporal and spatial variation,and interannual variability of the North Pacific meridional overturning circulation using an empirical orthogonal function method,and calculated mass transport using Simple Ocean Data Assimilation Data from 1958-2008.The meridional streamfunction field in the North Pacific tilts N-S; the Tropical Cell (TC),Subtropical Cell (STC),and Deep Tropical Cell (DTC) may be in phase on an annual time scale; the TC and the STC are out of phase on an interannual time scale,but the interannual variability of the DTC is complex.The TC and STC interannual variability is associated with ENSO (El Ni(n)o-Southem Oscillation).The TC northward,southward,upward,and downward transports all weaken in El Ni(n)os and strengthen in La Ni(n)as.The STC northward and southward transports are out of phase,while the STC northward and downward transports are in phase.Sea-surface water that reaches the middle latitude and is subducted may not completely return to the tropics.The zonal wind anomalies over the central North Pacific,which control Ekman transport,and the east-west slope of the sea level may be major factors causing the TC northward and southward transport interannual variability and the STC northward and southward transports on the interannual time scale.The DTC northward and southward transports decrease during strong E1 Ni(n)os and increase during strong La Ni(n)as.DTC upward and downward transports are not strongly correlated with the Ni(n)o-3 index and may not be completely controlled by ENSO.