Results from a Velocity Transect Along the Equator from 125 to 159°W

Abstract

During March?April 1980, a velocity and CTD transect was made in the Pacific along the equator from 110 to 180°W. The horizontal baroclinic pressure gradient was observed to be primary confined between 160 and 130°W. Direct velocity profiles between 125 and 159°W showed the equatorial undercurrent to be a continuous feature. Maximum eastward transport (per unit width) in the undercurrent was 2.5 ? 108 cm2 s?1 at 150°W and decreased both westward and eastward to about 1.5 ? 108 cm2 s?1 at 159°W and at 125°W. Despite these variations the maximum speeds along the transect remained ?150 cm s?1. Beneath the undercurrent, the velocities decreased and were of the order of 25 cm s?1. They exhibited small-scale variation in the vertical as has recently been observed at other equatorial locations. Above 1600 m, the vertical wavelength of these variations in the zonal component was ?300 m. Small-scale features in these zonal velocities were identifiable over 10° of longitude (1000 km). The small vertical and large horizontal scale suggests that these features might be Kelvin or long Rossby waves. The meridional velocities were primarily confined to the top 1000 m and their structure differed in profiles taken 5° apart.