New Zealand Journal of Marine and Freshwater Research abstracts
Coherent signals in the temperature and height of the sea surface off North
Cape, New Zealand
ANDREW K. LAING
NILES A. OIEN
RICHARD MURPHY
MICHAEL J. UDDSTROM
National Institute of Water & Atmospheric
Research Ltd
P. O. Box 14 901, Kilbirnie
Wellington, New Zealand
Abstract Dynamic heights of the ocean surface to the
north-east of North Cape, New Zealand are determined from 18 months of
Topex-Poseidon altimeter measurements along a repeat track crossing the East
Auckland current system. The anomalies in the heights and in the cross-track
geostrophic currents derived from these heights both portray strong cyclic
signals with period of c. 140 days travelling towards New Zealand, and a signal
with period of at least 18 months in the opposite sense. Sea-surface
temperature (SST) anomalies and anomalies in the along-track SST gradients
exhibit similar periodicity. The coherence between anomalies in velocity and
temperature gradient and that between anomalies in height and temperature both
reach c. 0.74 at the period of 140 days and 0.88 for the long-period signal. A
correspondence is also shown between the positions of maximum flow in the East
Auckland current and positions of high sea-surface temperature gradient. Winds
are shown to affect the strength of the 140-day signal in the temperature
gradient data, and to impair its coherence with the matching signal in the
velocity anomaly data. In particular, if temperature gradient data are smoothed
through times and places where the recent history of the curl of the
wind-stress is significantly positive (Ekman pumping occurring) the coherence
in the 140-day signal between the velocity and temperature gradient is
increased from 0.74 to 0.92. Similar impacts on the longer period signal are
not found, nor are they evident for either of the two prominent signals in the
coherence between SST and height anomalies.
Keywords altimetry; sea surface temperature; East Auckland
Current; coherence; wind
M97027
Received 1 July 1997; accepted 25 November 1997
PDF file of entire paper: medium quality (3279K); (scanned from paper original: notes about this process)
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