New Zealand Journal of Marine and Freshwater Research abstracts
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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