New Zealand wave climate from satellite observations

Abstract Wave data derived from radar altimeters carried on four satellite missions are combined into a wave climatology for New Zealand waters. These data provide extensive observations of wave conditions around New Zealand, where the paucity of measurements has previously hindered definition of the wave climate. The data span the period 1985 to the present with the exception of a 2‐year gap in 1989–91. The spatial distribution of the long‐term mean of significant wave heights (SWH) indicates a strong latitudinal variation in the south‐west Pacific, with values of over 4 m at latitudes of 50–60°S and under 2.5 m towards the tropics. The shadowing of New Zealand is quite marked; a result of the dominant contribution of south‐westerly wave events. The annual range of the mean SWH also varies over the region; within 0.6 m in the north and 1.3 m in the south. A principal component analysis of the monthly anomalies in mean SWH identifies spatial patterns of variation. Some components vary with the local wind more than others suggesting that some anomalies are associated with wind sea and some with swell. Some patterns also appear to vary with the Southern Oscillation Index and can be related to the wind anomalies associated with El Nino events. Frequency distributions of SWH are also determined, and it is noted that in the north of the region the spatial pattern of the high waves differs considerably from the means.

[1]  H. Kaiser.  The varimax criterion for analytic rotation in factor analysis , 1958 .

[2]  P. D. Cotton,et al.  Fifteen years of global wave hindcasts using winds from the European Centre for Medium‐Range Weather Forecasts reanalysis: Validating the reanalyzed winds and assessing the wave climate , 1998 .

[3]  Hiroshi Kawamura,et al.  Validation of wind speeds and significant wave heights observed by the TOPEX altimeter around Japan , 1994 .

[4]  D.J.T. Carter,et al.  An assessment of Geosat wave height and wind speed measurements , 1992 .

[5]  R. Pickrill,et al.  Ocean wave characteristics around New Zealand , 1979 .

[6]  Robert F. Cahalan,et al.  Sampling Errors in the Estimation of Empirical Orthogonal Functions , 1982 .

[7]  Julius Goldhirsh,et al.  Validation of Geosat altimeter‐derived wind speeds and significant wave heights using buoy data , 1987 .

[8]  R. Jennrich,et al.  Rotation for simple loadings , 1966, Psychometrika.

[9]  Ian R. Young.  An intercomparison of GEOSAT, TOPEX and ERS1 measurements of wind speed and wave height , 1998 .

[10]  N. Gordon.  The Southern Oscillation and New Zealand Weather , 1986 .

[11]  G. Forristall,et al.  The Use of Satellite Altimeter Data to Estimate the Extreme Wave Climate , 1997 .

[12]  J. Gower,et al.  Intercalibration of wave and wind data from TOPEX/POSEIDON and moored buoys off the west coast of Canada , 1996 .

[13]  G. Burroughs,et al.  THE ROTATION OF PRINCIPAL COMPONENTS , 1961 .

[14]  Kevin Ewans,et al.  Observations of the Directional Spectrum of Fetch-Limited Waves , 1998 .

[15]  A. Laing.  A spectral model for the sea-state with explicit forcing terms , 1992 .

[16]  Zeki Demirbilek,et al.  Estimation of extreme wave heights using GEOSAT measurements , 1998 .

[17]  K. Ewans,et al.  An Examination of Fetch-Limited Wave Growth off the West Coast of New Zealand by a Comparison with the JONSWAP Results , 1990 .

[18]  R. Preisendorfer,et al.  Principal Component Analysis in Meteorology and Oceanography , 1988 .

[19]  R. Reynolds,et al.  The NCEP/NCAR 40-Year Reanalysis Project , 1996, Renewable Energy.

[20]  Estimates of wave height data for New Zealand waters by numerical modelling , 1993 .

[21]  Greg J. Holland,et al.  Atlas of the Oceans: Wind and Wave Climate , 1996 .

[22]  Roland Romeiser,et al.  Global validation of the wave model WAM over a one-year period using Geosat wave height data , 1993 .

[23]  P. D. Cotton,et al.  Cross calibration of TOPEX, ERS‐I, and Geosat wave heights , 1994 .

[24]  N. Mognard,et al.  Southern Ocean monthly wave fields for austral winters 1985-1988 by Geosat radar altimeter , 1996 .

[25]  Philip S. Callahan,et al.  Comparison of TOPEX/POSEIDON σ0 and significant wave height distributions to Geosat , 1994 .

[26]  A. K. Laing.  An Assessment of Wave Observations from Ships in Southern Oceans , 1985 .