Decadal scale changes in the annual cycle of the North Pacific sea‐surface temperature

Climatic variability of the annual cycle of the sea‐surface temperature (SST) is studied in terms of long‐term and pentadal (5 years) anomalies of amplitudes of annual cycle as well as of anomalies of annual, winter, and summer means. Anomalies of annual and seasonal means clearly indicate North Pacific climate shifts. During the 1950s and 1960s, anomalies of annual amplitudes tended to result in anomalies of annual means of the same sign, later (in the 1970s) in anomalies of opposite sign. It was found out that these changes are due principally to different roles of seasonal anomalies in the formation of the annual cycle of SST. Before the North Pacific climate shift of the mid‐1970s, anomalies in amplitudes of annual cycle were generally determined by summer anomalies. In the 1970s, winter anomalies played the leading role in the formation of annual cycle of SST. This switch from the governing role of summer anomalies to that of winter anomalies took place prior to the North Pacific climate shift. In the 1980s summer SST anomalies in the central North Pacific became stronger again. Analysis of time series of spatially averaged and low‐pass filtered summer and winter SST anomalies has revealed that in the southeastern North Pacific (near Baja California), winter and summer anomalies have approximately the same magnitude, though during the 1970s and 1980s winter anomalies were a bit stronger than summer ones. On the contrary, in the central North Pacific, during certain climatic periods (1950s, 1960s and 1980s), summer anomalies were essentially stronger than winter anomalies. Wavelet analysis demonstrated that interdecadal variations in the central North Pacific are much more pronounced in summer SSTs, while in the southeastern North Pacific interdecadal variations are slightly stronger during wintertime. Copyright © 2000 Royal Meteorological Society