PARTITIONING THE NORTH ATLANTIC INTO REGIONS OF SIMILAR SEASONAL SEA‐SURFACE TEMPERATURE ANOMALIES

Mean sea‐surface temperatures were computed within 127 6°×4° longitude‐by‐latitude cells comprising most of the North Atlantic for 171 three‐month seasons from 1950 to 1992, the mean seasonal cycle was removed, and cells with correlated seasonal anomalies were clustered into regions of coherent thermal behaviour. Clustering algorithms consistently produced smaller thermal regions in the vicinity of the Gulf Stream, and while the regions were generally contiguous, a disjoint region was consistently found near the Grand Banks. Examining within‐region variability as a function of the number of regions revealed no obvious ‘best’ number of regions. For 26 regions, correlations between pairs of cells within a common region were typically 0ċ7; for 13 regions, a sizeable fraction were less than 0ċ5; and for only seven regions, within‐region correlations were distributed fairly uniformly between 0ċ2 and 0ċ8. © 1997 by the Royal Meteorological Society.