El Niñoの日本冬季気候への影響

Abstract

Influence of the ENSO (El Niño/Southern Oscillation) on East Asian winter monsoon is examined. It is widely accepted that the El Niño tends to bring warm climate in December-January-February (DJF) winter season in Japan. However, our study reveal that in the DJF-averaged fields the ENSO has little impact on the near-surface temperature anomalies there. In particular, near-surface temperature anomaly fields in the late winter show neutral signals. Simultaneously, the Pacific-Northern American (PNA) pattern is dominant in the upper troposphere while no strong signals are found near Japan. In contrast, in the early winter, the WP pattern with positive phase are dominant so that winter tends to be warm in Western Japan. The opposite is true for La Niña. Dynamical mechanisms of such seasonal evolutions in the upper-level height field from early winter to late winter are not yet clarified yet and thus remain for future work.