Interpentadal changes of seasonal cycle of SST in the North Pacific
Igor Zveryaev*1 and Konstantin Selemenov*2
*1 IPRC, SOEST, University of Hawaii
*2 P. P. Shirshov Institute of Oceanology
Climatic changes in seasonal cycle of sea surface temperature (SST) in the North Pacific during 1951-1995 are studied. These changes are discussed in terms of pentadal anomalies of characteristics of annual and semiannual cycles as well as of anomalies of annual, winter and summer means. Anomalies of annual and seasonal means clearly indicate North Pacific climate shift of mid 70-ties. Quasi-decadal changes are more noticeable before climate shift. Before 1971, anomalies of annual amplitudes tend to result in anomalies of annual means of the same sign, later - in anomalies of opposite sign. It is found out that these changes are due principally to different roles of seasonal anomalies in the formation of the annual cycle of SST. Before 1971, anomalies in annual cycle are defined by summer anomalies. Later, winter anomalies play a leading role in the formation of annual cycle. We note that this switch from the governing role of summer anomalies to that of winter anomalies takes place prior to the North Pacific climate shift. Comparative analysis of anomalies of annual and semiannual cycles has revealed that enhanced (reduced) annual cycle does not necessarily result in enhanced (reduced) semiannual cycle. I.e. positive anomalies of semiannual cycle can be related both to positive and negative anomalies of annual cycle. The same is true about negative anomalies of the semiannual cycle.
