On the use of high‐resolution satellite data to describe the spatial and temporal variability of sea surface temperatures in the New Zealand region

Abstract

A new high‐resolution (1.1 km) regional data set of satellite‐derived sea surface temperatures (SST) is developed and validated against drifting and moored buoy data. Analysis of 5 years of monthly means and related statistics suggests that there is often a coherent relationship between the SST patterns and oceanographic features. Identifiable relationships are detailed, then used to indicate the temporal and spatial characteristics of watermasses, fronts, and currents. For example, a gradient analysis suggests that the Subtropical Front east of New Zealand (and west of 177°W) is bathymetrically locked to the southern flank of the Chatham Rise (near 44°S). Beyond 177°W it loops southward to a mean position close to 47°S on the northern edge of the Bounty Plateau, adjacent to the Subantarctic Front (near 48°S). Harmonic analysis of the 60 months of data suggests that spatial variability in the amplitude of the SST annual cycle is related to circulation (water mass) features and varies from less than 1°C in Subantarctic Waters to more than 4°C in New Zealand nearshore neritic waters. The Antarctic Circumpolar, East Auckland, and East Cape Currents also display coherent annual cycle amplitude signatures that differ from adjacent water masses. However, the amplitude of the annual cycle in Subantarctic Waters south of the Chatham Rise and north of the Pukaki Rise and Bounty Plateau is significantly different from that of this water mass at other (similar) latitudes. An empirical orthogonal function (EOF) analysis of seasonal anomalies shows that 90% of SST variance can be associated with the annual cycle. However, four EOFs are required to explain 50% of the variance in SST monthly anomalies. The first of these (25.4% of the variance) indicates that anomalies north and east of New Zealand are negatively correlated with those in the Subantarctic. The second EOF represents a Tasman Sea mode and suggests that the Tasman Sea has been in a warming phase since December 1996 (to at least April 1998). This might explain the exceptional size (and sign) of the SST anomaly in New Zealand waters during the 1998 El Niño, where in February 1998 it reached +3.5°C in northern New Zealand waters, similar to the amplitude of the annual cycle.