Tidal Energetics over the Chatham Rise, New Zealand

Stephen M. Chiswell National Institute of Water and Atmospheric Research, Wellington, New Zealand

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Abstract

Separate one-month current meter deployments in 1996 and 1997 over the Chatham Rise, east of New Zealand, show that tidal phases are both stable in time and close to those derived from a barotropic tidal model, while amplitudes show coefficients of variation as high as 30%. These observations are consistent with the presence of a baroclinic component to the tide that is phase-locked to the barotropic component. The near-zero phase difference between the model and observations suggests local generation of the barotropic tide. As well as the current meter data, two 24-hour time series of CTD casts are used to compute tidal vertical displacements. Vertical displacements up to 40 m lead to estimates of time-averaged potential energy ranging from 75 to 782 J m−2 for the semidiurnal tide and 40 to 147 J m−2 for the diurnal tide. Energy radiated from the Chatham Rise could be as high as 1.1 GW.

Corresponding author address: Dr. Stephen M. Chiswell, National Inst. of Water and Atmos. Res. Ltd., 301 Evans Bay Parade, Greta Point, P.O. Box 14-901, Kilbirnie, Wellington, New Zealand.

s.chiswell@niwa.cr.nz

Abstract

Separate one-month current meter deployments in 1996 and 1997 over the Chatham Rise, east of New Zealand, show that tidal phases are both stable in time and close to those derived from a barotropic tidal model, while amplitudes show coefficients of variation as high as 30%. These observations are consistent with the presence of a baroclinic component to the tide that is phase-locked to the barotropic component. The near-zero phase difference between the model and observations suggests local generation of the barotropic tide. As well as the current meter data, two 24-hour time series of CTD casts are used to compute tidal vertical displacements. Vertical displacements up to 40 m lead to estimates of time-averaged potential energy ranging from 75 to 782 J m−2 for the semidiurnal tide and 40 to 147 J m−2 for the diurnal tide. Energy radiated from the Chatham Rise could be as high as 1.1 GW.

Corresponding author address: Dr. Stephen M. Chiswell, National Inst. of Water and Atmos. Res. Ltd., 301 Evans Bay Parade, Greta Point, P.O. Box 14-901, Kilbirnie, Wellington, New Zealand.

s.chiswell@niwa.cr.nz

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