New Zealand Journal of Marine and Freshwater Research abstracts

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Circulation within the Wairarapa Eddy, New Zealand

Stephen M. Chiswell

National Institute of Water and Atmospheric
 Research Limited
P.O. Box 14 901
Wellington, New Zealand
email: s.chiswell@niwa.cri.nz

Abstract  The Wairarapa Eddy appears as a permanent anticyclonic eddy situated off the east coast of the North Island, New Zealand. In April 2001 a spatial survey of the eddy was made on a ship equipped with an Acoustic Doppler Current Profiler (ADCP). The absolute circulation at 100 m was estimated by objective mapping of the ADCP-derived velocities to produce a velocity field that has enforced non-divergence. Assuming that enforcing non-divergence produces the best estimate of the geostrophic flow, this velocity field can be used as a “level of known motion” to reference geostrophic velocities at other depths. In particular, it can be used to estimate the velocity at 2000 dbar, which is otherwise used in this region as a level of no motion. The resulting flow at 2000 dbar has a mean speed of 0.07 m s^-1, and appears to be well correlated with the surface flow.

Keywords  geostrophic circulation; level of no motion; eddy

M02052 Received 27 June 2002; accepted 27 June 2003; Online publication date 31 October 2003
New Zealand Journal of Marine and Freshwater Research, 2003, Vol. 37: 691-704
0028-8330/03/3704-0691 $7.00 © The Royal Society of New Zealand 2003

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