Eddy flow characteristics and mean flow interactions in the North Pacific

The strength, shape, orientation, mean flow interactions, and propagation characteristics of the time-varying (eddy) flow determined from TOPEX/Poseidon altimeter data in the North Pacific are investigated using equivalent barotropic diagnostic calculations as presented by Hoskins ct al. [1983]. Separate calculations for low- and high-pass flow fields, distinguished by periods greater than and less than 6 months, respectively, are performed and revealed a fundamental difference between the eddy characteristics of the two. The areas with largest values of surface eddy kinetic energy occur in the vicinity of the Kuroshio Extension and the subtropical front. Near the Kuroshio Extension the low-pass surface eddy kinetic energy is gl-eater than the high-pass energy, but in the subtropical frontal area the high-pass eddy Row accounts for more energy than the lowpass flow. For both areas the values of eddy kinetic energy are larger in summer than during winter, Low-pass eddy flow tends to be aligned zonally, and the high-pass eddy flow is aligned meridionally. Near the subtropical front the ratio of major to minor axis length is typically similar to 1.5:1, whereas near the Kuroshio Extension that ratio increases to values near 2:1. Along the southern boundary of the subtropical gyre the high-pass eddy flow tends to propagate eastward relative to the mean flow, tending to decrease the gyre strength. However, the low-pass eddy flow propagates westward relative to the mean flow and tends to increase the gyre strength. An additional computation of surface heat transport is used to deduce vertical propagation tendencies of the eddy flow and indicates that the low-pass flow field transports more heat than the high-pass flow with the largest eddy transports occurring near the coast of Honshu. The sign of the transport indicates a preference for upward energy propagation of the eddy flow there. Many of the characteristics, such as the orientation and propagation tendencies of the eddy flow, are similar to eddy now in the atmosphere: and accentuate a similarity between the general circulations of the atmosphere and ocean.