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- Author or Editor: Y. Wakata x
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Abstract
The Lagrangian motions of floating matter on the sea surface were simulated by using the surface current data based on shipdrift data produced by Meehl. The validity of the simulation was confirmed by comparing the results of the model with the trajectories of satellite tracked drift in the eastern North Pacific observed by Kirwan et al. Some cases which originated in the western North Pacific Ocean were investigated. It was found that drifters set in the ocean during spring quickly migrated to North America on the strong eastward North Pacific currents of the summer season. Trajectories started during autumn showed a loop in the western North Pacific and took more time to arrive in the eastern area of the North Pacific Ocean. Each trajectory that arrived in the eastern area of the North Pacific Ocean, showing a large loop, traveled over a one year interval owing to the large surface current vortex. This vortical sea surface current was driven by the clockwise winds around the atmospheric subtropical high pressure region located in the North Pacific.
Numerous calculations with initial positions randomly scattered in space and time were performed, and the accumulated matter density was obtained. High density areas where the debris concentrated were found at several places (i.e., near Berinuda, west of Australia, the center of the South Atlantic, and north of the Hawaiian Wands). In focussing on the North Pacific, it was found that three identifiable high density areas circulate with three year periods. It is emphasized that the instantaneous strong convergence areas do not always agree with the high accumulation density areas owning to the hysteresis or memory of the floating debris.
Abstract
The Lagrangian motions of floating matter on the sea surface were simulated by using the surface current data based on shipdrift data produced by Meehl. The validity of the simulation was confirmed by comparing the results of the model with the trajectories of satellite tracked drift in the eastern North Pacific observed by Kirwan et al. Some cases which originated in the western North Pacific Ocean were investigated. It was found that drifters set in the ocean during spring quickly migrated to North America on the strong eastward North Pacific currents of the summer season. Trajectories started during autumn showed a loop in the western North Pacific and took more time to arrive in the eastern area of the North Pacific Ocean. Each trajectory that arrived in the eastern area of the North Pacific Ocean, showing a large loop, traveled over a one year interval owing to the large surface current vortex. This vortical sea surface current was driven by the clockwise winds around the atmospheric subtropical high pressure region located in the North Pacific.
Numerous calculations with initial positions randomly scattered in space and time were performed, and the accumulated matter density was obtained. High density areas where the debris concentrated were found at several places (i.e., near Berinuda, west of Australia, the center of the South Atlantic, and north of the Hawaiian Wands). In focussing on the North Pacific, it was found that three identifiable high density areas circulate with three year periods. It is emphasized that the instantaneous strong convergence areas do not always agree with the high accumulation density areas owning to the hysteresis or memory of the floating debris.
Abstract
In order to test certain aspects of the ENSO mechanism proposed by Suarez and Schopf and by Battisti and Hirst, we force a shallow water ocean with 28 years of observed (FSU) winds and decompose both the atmospheric forcing and ocean response into equatorial modes.
The proposed mechanism was verified in the following sense. For each warm phase of the cycle, a downwelling Kelvin mode directly forced by the weakening of the trade winds in the central Pacific was found. The same wind anomaly forces an upwelling gravest Rossby mode which propagates freely westward and reflects as a freely propagating Kelvin mode at the western boundary. This Kelvin mode returns to the scene of the original warming and acts as a retarded forcing (of opposite sign) eventually switching the phase of the oscillation from warm to cold. The cold phase then proceeds by the same mechanism but with modes of opposite signs, to eventually switch to the warm phase.
The contribution of the higher Rossby modes to this process is estimated. It is found that almost all the Kelvin response in the western Pacific results from the reflection of the gravest symmetric equatorial Rossby mode so that the ENSO cycle is defined by the interaction of only two ocean modes, the Kelvin and lowest Rossby mode. These modes are sometimes forced directly by the wind as part of an intrinsic coupled atmosphere–ocean mode and sometimes propagate freely where the wind forcing is negligible. The distinction between these two manifestations of the ocean modes is of the greatest importance and is stressed throughout the paper.
The case of the warm event of 1976 is an interesting example of the failure of the switching mechanism, and is discussed in the conclusion.
Abstract
In order to test certain aspects of the ENSO mechanism proposed by Suarez and Schopf and by Battisti and Hirst, we force a shallow water ocean with 28 years of observed (FSU) winds and decompose both the atmospheric forcing and ocean response into equatorial modes.
The proposed mechanism was verified in the following sense. For each warm phase of the cycle, a downwelling Kelvin mode directly forced by the weakening of the trade winds in the central Pacific was found. The same wind anomaly forces an upwelling gravest Rossby mode which propagates freely westward and reflects as a freely propagating Kelvin mode at the western boundary. This Kelvin mode returns to the scene of the original warming and acts as a retarded forcing (of opposite sign) eventually switching the phase of the oscillation from warm to cold. The cold phase then proceeds by the same mechanism but with modes of opposite signs, to eventually switch to the warm phase.
The contribution of the higher Rossby modes to this process is estimated. It is found that almost all the Kelvin response in the western Pacific results from the reflection of the gravest symmetric equatorial Rossby mode so that the ENSO cycle is defined by the interaction of only two ocean modes, the Kelvin and lowest Rossby mode. These modes are sometimes forced directly by the wind as part of an intrinsic coupled atmosphere–ocean mode and sometimes propagate freely where the wind forcing is negligible. The distinction between these two manifestations of the ocean modes is of the greatest importance and is stressed throughout the paper.
The case of the warm event of 1976 is an interesting example of the failure of the switching mechanism, and is discussed in the conclusion.
