Variations in Sea Surface Temperature and 500 hPa Height over the North Pacific with Reference to the Occurrence of Anomalous Southward Oyashio Intrusion East of Japan

Abstract

The distribution of anomalies of 500 hPa height over the North Pacific is examined with special reference to the occurrence of anomalous southward first Oyashio intrusions east of Japan. EOF analysis of 50O hPa height anomalies over 1967-86 is used to identify the correlation with the occurrence of the anomalous southward Oyashio intrusion. It is shown that the southernmost latitude of the Oyashio has a significant maximum lag correlation of three month to the first EOF component of 500 hPa height anomalies with a southward development of the Aleutian Low. It is also shown that during the period of occurrence of the anomalous southward intrusion of the Oyashio, negative SST anomalies are located in the zonal area over 30°N-50°N in winter. A part of the cooling region is accompanied by the weakened wind stress with the westward direction of the wind stress anomaly, indicating that the cooling can not be attributed to either the sensible/latent heat fluxes or Ekman transport. It is indicated that the southward shift of the subarctic circulation in response to the southward shift of the Aleutian Low results in the negative SST anomalies.