Using satellite data, we detected a wind wake trailing westward behind the Hawaiian Islands for 3000 kilometers, a length many times greater than observed anywhere else on Earth. This wind wake drives an eastward ocean current that draws warm water from the Asian coast 8000 kilometers away, leaving marked changes in surface and subsurface ocean temperature. Standing in the path of the steady trade winds, Hawaii triggers an air-sea interaction that provides the feedback to sustain the influence of these small islands over a long stretch of the Pacific Ocean.
Low-frequency variability of the Kuroshio Extension (KE) is studied using observations and a multidecadal hindcast by a high-resolution (0.1°), eddy-resolving, global ocean general circulation model for the Earth Simulator (OFES). In both the OFES hindcast and satellite altimeter observations, low-frequency sea surface height (SSH) variability in the North Pacific is high near the KE front. An empirical orthogonal function (EOF) analysis indicates that much of the SSH variability in the western North Pacific east of Japan is explained by two modes with meridional structures tightly trapped along the KE front. The first mode represents a southward shift and to a lesser degree, an acceleration of the KE jet associated with the 1976/77 shift in basin-scale winds. The second mode reflects quasi-decadal variations in the intensity of the KE jet. Both the spatial structure and time series of these modes derived from the hindcast are in close agreement with observations.A linear Rossby wave model forced by observed wind successfully reproduces the time series of the leading OFES modes but fails to explain why their meridional structure is concentrated on the KE front and inconsistent with the broadscale wind forcing. Further analysis suggests that KE variability may be decomposed into broad-and frontal-scale components in the meridional direction-the former following the linear Rossby wave solution and the latter closely resembling ocean intrinsic modes derived from an OFES run forced by climatological winds. The following scenario is suggested for low-frequency KE variability: basin-scale wind variability excites broadscale Rossby waves, which propagate westward, triggering intrinsic modes of the KE jet and reorganizing SSH variability in space.
Summary An eddy-resolving hindcast experiment forced by daily mean atmospheric reanalysis data covering the second half of the twentieth century was completed successfully on the Earth Simulator. The domain covers quasiglobal from 75 • S to 75 • N excluding arctic regions, with horizontal resolution of 0.1 • and 54 • vertical levels. Encouraged by high performance of the preceding spin-up integration in capturing the time-mean and transient eddy fields of the world oceans, the hindcast run is executed to see how well the observed variations in the low-and midlatitude regions spanning from intraseasonal to decadal timescales are reproduced in the simulation. Our report presented here covers, among others, the El Niño and the Indian Ocean Dipole events, the Pacific and the Pan-Atlantic decadal oscillations, and the intraseasonal variations in the equatorial Pacific and Indian Oceans, which are represented well in the hindcast simulation, comparing with the observations. The simulated variations in not only the surface but also subsurface layers are compared with observations, for example, the decadal subsurface temperature change with narrow structures in the Kuroshio Extension region. Furthermore, we focus on the improved aspects of the hindcast simulation over the spin-up run, possibly brought about by realistic high-frequency daily mean forcing.
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