The Interdecadal Variation Characteristics of Arctic Sea Ice Cover-ENSO-East Asian Monsoon and Their Interrelationshipat Quasi-Four Years Time Scale

Interdecadal and quasi-four years variation characterstics of Arctic sea for cover, ENSO and East Asian monsoon index(EAMI) are analyzed based on Singular Spectrum Analys. (SSA), lead-lag correlation and EOF for the past four decades. Results show that the Arctic sea for cover decreased in the early 1970s, several years earlier than that of global SSTA increase in the mid 1970s, which indicates that recent warming over the Northern Hemisphere firstly begins in the Arctic region in the 1970s. Great change of the East Asian monsoon intensity from stronger to weaker in summer (from weaker to stronger in winter) took place in the mid 1970s response to the abrupt modulation of SSTA particularly in the tropical eastern Pacific.Focus on the quasi-four years oscillation,close relationship is found among the sea ice cover, ENSO and EAMI based on lead-lag correlation. In which, the correlation coefficient reaches its maximum when the index of NINO3 SSTA variation takes 6 and 9 months lead of the western Pacific subtropical high and sea for cover index in Section-Ⅲ. Their interaction can be explained in the framework of asymmetric Walker circulation anomaly and Western Pacific Northern Pole (WPN) teleconnection pattern in the context of quasi-four years oscillation.

STUDY ON THE QUASI-FOUR YEAR OSCILLATION OF AIR-SEA INTERACTION

Complex Singular Value Decomposition(CSVD)analysis technique was applied to study the Quasi Four year Oscillation(QFO)of air sea interaction and its coupled pattern evolution during different phases.Results show that:(1)CSVD method can better reveal phase relation between two physical fields:(2)Not only northerly anomalies from Northern Hemisphere but also southerly anomalies from Southern Hemisphere contribute to EI Nino.They converge in western equatorial Pacific,leading to outburst of strong equatorial westerly anomalies,and result in strong El Nino event onset:(3)An abnormal subtropical anticyclone circulation appears over northwestern Pacific while El Nino developing.It favors transitions from the warm SST(EI Nino)to the cold SST(La Nina),just as the tropical westerly anomalies produced by abnormal cyclone during a decaying La Nina.which encourage the development of El Nino:(4)The westerly anomalies in equatorial Pacific are mainly induced by eastward abnormal subtropical cyclone pairs,which are located in north and south Pacific respectively,and are not the eastward westerly anomalies from equatorial Indian Ocean.