What drives the mean circulation on the New Zealand west coast continental shelf?

Abstract

A linearised model of Csanady (1976) for the time‐averaged mean flow on a continental shelf is applied to the New Zealand west coast continental shelf. The means are time averages over time scales that are long relative to that of local atmospheric forcing. Forcing of the flow is via the sea surface elevation (specified from deep ocean steric levelling with adjustment for boundary effects), mean winds, and thermohaline forcing (specified by observations and determined by the strong fluctuating flow, the time average of which is the weaker mean flow). The main flow components are found generally to be caused by forcing by the sea surface elevation and local winds. North of latitude 42°30'S the mean sea surface slopes down towards the south, with an associated southward‐directed flow component; south of 42°30'S it slopes down towards the north with an associated northward‐directed flow component. On the northwest coast of the South Island the predominant north‐eastward‐directed wind produces a northeastward along‐shore flow component. On the west coast of the North Island north of Cape Egmont the predominant onshore wind produces a flow towards the north. Thermohaline forcing leads to a southward along‐shore flow decreasing to zero near the sea floor.

Key words:

• winds
• water circulation
• continental shelves
• thermal properties
• sea level
• wind‐driven currents
• mathematical models