Long-term changes in summer temperature anomaly patterns in Japan since the early 20th century

The relationship between long-term variations in summer temperature in Japan since the early 20th century and the large-scale atmospheric circulation field was analysed. The combined influence of various circulation predictors on temperarure variations was analysed via a multicomponent canonical correlation analysis(CCA). The positive phase of the first CCA mode is related to a positive temperature anomaly across Japan, characterized by a weak blocking hi gh over the Okhotsk Sea, and a strong North Pac ific subtropical high (NPSH) over Japan. The positive phase of the second CCA mode corresponds to a positive temperature anomaly in southwestern Japan, and a negative anomaly in northern Japan, characterized by an anticyclonic circulation anomaly over eastern China and a cyclonic anomaly over the northwestern Pacific. By investigating the temporal changes in CCA scores, we detected an abrupt increase in the first CCA score in the early 1910s and a long-term increasing trend in the second CCA score since the early 20th centu ry. The abrupt increase in the first CCA score indicates an abrupt increase in temperature throughout Japan . By investigating changes in the circulation field associated with thisabrupt warming, we determined that intensification of zonal flow over the Okhotsk Sea was responsibl e. The increasingtrend of the second CCA score indicates an increase in the regional difference in summer temperatures between northernand somhwestern Japan. After investigating changes in the circulation field before and after the mid-20th century, we suggest that the southwestward shift of the NPSH and the weakening of anticyclonic circulation anomalies over the northwestern Pacific were responsible for this increase in the regional temperature difference