Low‐frequency variability of the North Pacific Ocean: The roles of boundary‐ and wind‐driven baroclinic Rossby waves

Abstract

The effects of the sea level variability along the eastern boundary of the North Pacific Ocean, including those associated with El Niño Southern Oscillation, have been considered an important factor in determining the low‐frequency large‐scale variability of the ocean interior through Rossby waves generated at the eastern boundary. This hypothesis is examined in this study using 8 years worth of the sea surface height observations made by the TOPEX/Poseidon satellite. The timescales of interest are longer than 90 days with the annual cycle removed. The results indicate that the influence of the eastern boundary of the North Pacific Ocean has limited offshore extent, varying from 3000–4000 km at 10°N to 200–300 km at 50°N. The variability in the ocean interior is primarily driven by wind with only a minor influence from the boundary. Simulations of a linear two‐layer model of the ocean driven by wind stress curl are correlated with the observations. The effects of wind forcing accumulate along the characteristics of long nondispersive Rossby waves in the time‐longitude domain. These wind‐driven Rossby waves overwhelm the boundary‐driven waves in the ocean interior, where there are only some small residual effects of the boundary‐driven waves, however. These small effects become clearer after the simulated wind‐driven variability is removed from the observations.