New Zealand wave climate from satellite observations

Wave data derived from radar altimeters carried on four satellite missions are combined into a wave climatology for New Zealand waters. These data pro vide extensive observations of wave conditions around New Zealand, where th e paucity of measurements has previously hindered definition of the wave cl imate. 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 s ignificant wave heights (SWH) indicates a strong latitudinal variation in t he south-west Pacific, with values of over 4 m at latitudes of 50-60 degree sS and under 2.5 m towards the tropics. The shadowing of New Zealand is qui te marked; a result of the dominant contribution of south-westerly wave eve nts. 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 patt erns also appear to vary with the Southern Oscillation Index and can be rel ated to the wind anomalies associated with El Nino events. Frequency distri butions of SWH are also determined, and it is noted that in the north of th e region the spatial pattern of the high waves differs considerably from th e means.