S. Yukimoto et al., ENSO-like interdecadal variability in the Pacific Ocean as simulated in a coupled general circulation model, J GEO RES-O, 105(C6), 2000, pp. 13945-13963
Spatial and temporal structures of interdecadal variability in the Pacific
Ocean are investigated using results from an atmosphere-ocean coupled gener
al circulation model (AOGCM). The model shows a basin-wide spatial pattern
of the principal sea surface temperature (SST) variability similar to the o
bserved one. Both interdecadal and interannual temporal structures of the S
ST variability agree well between the observation and the AOGCM. On the oth
er hand, a slab ocean model coupled to the same atmospheric model as the AO
GCM fails to simulate the observed temporal structure. Therefore the timesc
ale of the coupled variability is associated with dynamical processes in th
e ocean. A distinct interdecadal mode of the coupled atmosphere-upper ocean
temperature variability is found in the AOGCM, with a spatiotemporal struc
ture coherent with the SST variability. The mode accompanies an El Nino-Sou
thern Oscillation (ENSO)-like spatial pattern of SST and the surface wind a
nd behaves like a delayed oscillator in ENSO. A wedge-shaped anomaly patter
n of the upper thermocline temperature is formed in the eastern Pacific, an
d its northern subtropical signal propagates westward, enhanced by a subtro
pical wind forcing at the central basin. Arrival of the subtropical signal
at the western Pacific around 20 degrees N switches the anomaly of subsurfa
ce temperature in the equatorial region through anomalous oceanic heat tran
sport along the western boundary. The travel time of the trans-Pacific sign
al in the subtropics appears to be responsible for the timescale of this mo
de. The AOGCM successfully simulated the second mode of SST with a major va
riation in the midlatitude North Pacific as in the observed SST. In the upp
er ocean heat content we found another distinct mode, which is characterize
d by a midlatitude-subtropics dipole pattern migrating around the North Pac
ific subtropical gyre. However, the associated SST variation of this mode s
hows a poor correspondence in the dominant interdecadal modes for the obser
ved SST.