New Zealand Journal of Marine and Freshwater Research abstracts
Mean and variability in the Wairarapa and Hikurangi Eddies, 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 mean and variability of the circulation
off the east coast of the North Island, New Zealand are investigated using
shipboard conductivity-temperature-depth (CTD) and satellite altimeter data
collected between 1993 and 2003. The altimeter data are used to adjust the
in situ observations for the mesoscale eddy variability before computing
the 11-year mean in dynamic height. Mean dynamic height shows two anticyclonic
eddies, centred near 178.3°E, 41.2°S and 176.2°E, 42.4°S.
These locations are consistent with previous historical observations of the
Wairarapa and Hikurangi Eddies, respectively. A long-term trend in both in
situ and satellite data shows that dynamic height rose at an average rate
of up to 2 dyn cm year-1 in the centre of the Wairarapa Eddy which is consistent
with a strengthening of the eddy over the 11 years. The satellite data show
periodic shedding of the Wairarapa Eddy from near East Cape at a rate of
between two and three eddies per year. Thus, rather than indicating a permanent
stationary eddy, the mean eddy reflects a region where the eddies tend to
stall out or merge with the previous eddy. Often, the eddies will continue
up the Hikurangi Trough so that the Hikurangi Eddy can be regarded as an
older Wairarapa Eddy.
Keywords Wairarapa eddy; circulation; climatology
M04121; Online publication date 18 February 2005
Received 17 June 2004; accepted 23 November 2004
New Zealand Journal of Marine and Freshwater Research, 2005, Vol. 39:
121–134
0028-8330/05/3901-0121 © The Royal Society of New Zealand 2005
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