Eddy energetics in the subtropical front over the Chatham Rise, New Zealand

Abstract

The Chatham Rise, which rises to a depth of 400 m immediately to the east of New Zealand, appears to constrain the latitudinal movement of the Subtropical Front (STF). Data from current meters moored over the Chatham Rise are used to estimate the spatial variation of mean and turbulent kinetic energies and Reynolds stresses in and around the STF. Mean currents over 8 months are to the east, and are stronger south of the rise. Mean speeds at 250 m south of the rise are as high as 15 cm s−1 compared to 4.5 cm s−1 north of the rise. In contrast, the eddy kinetic energy is higher to the north at 8.2 J m−3 compared to 3.3 J m−3 to the south. Short‐term current meter moorings over the crest of the rise show no coherence over length scales of 15 km for periods less than 10 days. At 250 m depth, Reynolds stresses are positive north of the rise, and negative south of it, suggesting an export of momentum away from the STF.