Generation of 2–3‐hour oscillations on the east coast of New Zealand

Observed sea‐surface oscillations with periods of about 2.5 hours in New Zealand east coast harbours have previously been regarded as a response to edge waves on the continental shelf and slope, generated by atmospheric forcing and occasionally by tsunamis (Heath 1976, 1979). Calculations of the longshore wavelengths of the edge waves associated with the bathymetry of the east coast continental shelf and slope, and the Chatham Rise (a rise extending 1000 km perpendicular to the east coast of South Island), suggests that the Chatham Rise also takes part in the generation mechanism by acting as a three‐quarter wavelength aerial to double‐sided edge waves.