Remote and local forcing of Rossby wave variability in the midlatitude Pacific Ocean

Abstract

A reduced-gravity model is used to investigate the low-frequency variability in the eastern mid-latitude Pacific Ocean. The domain covers the eastern North Pacific from 18°N to 500N and from 1550W to the North American coast. In a first experiment the model is forced by the wind stress from COADS. A second experiment consists in forcing the model from its southern boundary using the results of an equatorial reduced-gravity model. The wavenumber-frequency spectrum calculated from the model is consistent with observations. Most of the calculated low-frequency variability in the ocean interior is in the form of westward propagating Rossby waves. Investigation in the wavenumber-frequency domain shows that either mechanism (locally wind-forced and remotely forced coastal disturbances) is capable of generating the westward-traveling waves that determine the ocean interior variability. For the locally forced model a critical latitude at about 350N is observed. The disturbances in the region north and south of this latitude present a clear dichotomy in their propagating characteristics: a strong off-shore decaying factor to the north and off-shore propagation to the south.