New Zealand Journal of Marine and Freshwater Research abstracts
Wave hindcast for the New Zealand region:
deep-water wave climate
Richard M. Gorman
Karin R. Bryan*
National Institute of Water and Atmospheric
Research Limited
P.O. Box 11 115
Hamilton, New Zealand
email: r.gorman@niwa.co’nz
*Present address: Department of Earth Sciences,
University of Waikato, Hamilton, New Zealand.
Andrew K. Laing
National Institute of Water and Atmospheric
Research Limited
P.O. Box 14 901, Kilbirnie
Wellington, New Zealand
Abstract The wave evolution model WAM (WAve Model) has
been implemented for the New Zealand region and used to simulate the generation
and propagation of deep-water waves over a 20-year period (1979-98). The
model extends to include the relevant generation areas of the south-west
Pacific and Southern Oceans. Input winds for the model were derived from
the European Centre for Medium-Range Weather Forecasts (ECMWF). The resulting
synthetic wave climatology will provide a valuable tool for researchers and
coastal planners, as it will help fill gaps in the available wave information
for New Zealand waters. In this paper the hindcasts are described, and comparisons
are made with wave height data from the altimeters flown on the TOPEX/Poseidon
and ERS1 and ERS2 satellite missions. Long-term mean significant wave heights
from the hindcast were generally 0.3-0.5 m lower than values from “buoy-equivalent”
altimeter data throughout the comparison region (150°E-170°W, 60°S-20°S).
Hindcast distributions of significant wave height occurrence matched satellite
data at the lowest wave heights and above the peaks of the distributions,
but tended to overestimate occurrence below the peak and underestimate the
occurrence of the largest wave events. The hindcast was then used to characterise
the wave climate of the New Zealand region. Some prominent features noted
were the large mean heights (3.6 m) in the high latitudes of the Southern
Ocean, associated with strong prevailing westerlies. North of this band,
waves largely propagate towards the north-east, with diminishing mean heights,
further attenuated by the blocking effect of the New Zealand landmasses.
This results in mean wave heights of c. 2 m in offshore waters north-east
of New Zealand. Annual cycles of mean wave height with a range of c. 1 m
were identified throughout the region. These were found to have minima in
summer (December/January), and either unimodal maxima in winter (June/July)
for tropical and temperate latitudes, or bimodal maxima (May and August)
in southern waters. Longer-term variations were also noted in the form of
correlations with the El Niño/Southern Oscillation. Positive correlations
(R Å +0.2) were found off the north-east coast of the North Island,
indicating a moderate tendency for increased wave heights there during La
Niña conditions, whereas negative correlations were found south and
south-west of New Zealand (R Å -0.2), and in the Fiji/Vanuatu region
(R Å +0.4), reflecting wave height enhancements in the El Niño
phase.
Keywords wave modelling; satellite wave data; New Zealand
regional wave hindcast; wave climate
M02078 Received 30 September 2002; accepted 24 March 2003; Published 5
August 2003
New Zealand Journal of Marine and Freshwater Research, 2003, Vol. 37:
589-612
0028-8330/03/3703-0589 $7.00 © The Royal Society of New Zealand
2003
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