Multiyear La Niña Impact on Summer Temperature over Japan
Tomoki Iwakiri, Masahiro Watanabe
Abstract
La Niña is the negative phase of the El Niño-Southern Oscillation (ENSO) cycle. It occurs in the equatorial Pacific, and events known as multiyear La Niña often persists for more than two years. During a conventional La Niña event, the seasonal cycle of surface temperature over Japan is amplified (i.e., hotter summer and colder winter than normal years), but the influence of multiyear events on temperatures over Japan is unclear. In this study, we evaluate the teleconnection associated with multiyear La Niña events. Our research uses composite analyses of observations, reanalysis data, and a large ensemble of atmospheric general circulation model (AGCM) simulations for 1951–2010, driven by observed boundary conditions. We propose two distinct mechanisms involved in multiyear La Niña events that cause hot summers over Japan.