エル・ニーニョ時の対流圏上層の大気応答と日本の冬の寒暖の関係

Abstract

In the Far East, El Niño (La Niña) typically brings warm (cold) winter via the teleconnections excited by the anomalous sea surface temperature (SST) in the tropics. Some ENSO events, however, have the opposite tendencies. To understand the mechanisms of the disparate mid-latitude responses during ENSO, composite analysis has been conducted using long-term reanalysis dataset. Our analysis shows that about 63% (67%) of all El Niño (La Niña) events are classified as typical warm (cold) winter around Japan and about 37% (33%) as atypical events. A Western Pacific (WP)-like pattern appears in typical events. Surprisingly, the Pacific/North American (PNA) pattern, which is a well-known feature during ENSO, is obscure during typical events. In fact, the PNA pattern dominates during atypical events with large amplitudes. In addition, SST distributions differ not only in the eastern Pacific Ocean but also in the western Pacific Ocean. These SST anomalies seem to cause differences divergence wind anomalies to cause different atmospheric responses in the mid-latitudes during ENSO.