日本財団 図書館


Interpentadal Changes of Seasonal Cycle of SST in the North Pacific.

 

lgor Zveryaev (International Pacific Research Center, SOEST, University of Hawaii, 1000 Pope Rd., MSB, Room 227, Honolulu, Hawaii 96822, USA)

e-mail: igorz@soest.hawaii.edu

Konstantin Selemenov (P.P.Shirshov Institute of Oceanology, RAS, Nakhimovsky Ave., 26, Moscow, 117218, Russia)

e-mail: selko@guleve.sio.rssi.ru

 

ABSTRACT

 

Climatic changes in seasonal cycle of sea surface temperature (SST) are studied in terms of pentadal anomalies of amplitude-phase characteristics of seasonal cycle 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.

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 were determined by summer anomalies. Later on, winter anomalies play a 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.

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 semiarmual cycle.

 

INTRODUCTION

 

The North Pacific climate shift of mid 70-ties has been noted and described by a number of investigators (Nitta and Yamada 1989; Tanimoto et al. 1993; Graham 1994; Trenberth and Hurrel 1994; Nakamura et al. 1997) as the most striking manifestation of interdecadal variability in the ocean - atmosphere system. Briefly, this climate shift can be described as a sharp change in polarity of winter SST anomalies in central and south-eastern North Pacific, which occurred in 1976. As a result positive anomalies of SST's in the central North Pacific have been replaced by negative anomalies. Opposite changes have occurred in the south-eastern North Pacific. At the same time strengthening of Aleutian low and related shift of the North Pacific storm track (Nitta and Yamada 1989; Trenberth and Hurrel 1994) can be considered as atmospheric manifestation the North Pacific climate shift.

Most of climatic studies, including above mentioned, are based on analysis of climatic means, i. e. monthly, seasonal and annual means. At the same time it is quite obvious that say different amplitudes can characterize two years having equal annual means, i. e. intensities of seasonal processes during these two years can be quite different. Therefore, positive (negative) trends or anomalies of amplitudes of annual cycle do not necessarily result in positive (negative) trends and amplitudes of annual means. It appears that investigation of long-term changes of intensities of different scale processes and their relationships with ones of climatic means is very reasonable and can improve our understanding of climate variations.

 

 

 

BACK   CONTENTS   NEXT

 






日本財団図書館は、日本財団が運営しています。

  • 日本財団 THE NIPPON FOUNDATION