Recent Decadal SST Variability in the Northwestern Pacific and Associated Atmospheric Anomalies

Abstract

It has been well known that the North Pacific atmosphere/ocean system fluctuates with periods of 2∼6 years associated with the El Niño/Southern Oscillation (ENSO) events (e.g., Horel and Wallace 1981; Rasmusson and Wallace 1983). Recently evidence has been presented that the system also fluctuates with decadal and even interdecadal timescales (e.g., Nitta and Yamada 1989; Trenberth 1990; Tanimoto et al. 1993; Nakamura et al. 1997 and references therein). A marked decadal and interdecadal climatic event (DICE) occurred around 1976. At that time, sea surface temperature (SST) in the central North Pacific dropped significantly, and SST tended to be lower than the long-term average until the late 1980’s. During that period, the Aleutian low tended to be more intense than before, the Pacific stormtrack was likely to be shifted southward (Trenberth and Hurrel 1994), and the atmospheric intraseasonal fluctuations over the North Pacific including blocking activities tended to be weaker than before (Nakamura 1996). In addition to its own scientific significance, importance of studying North Pacific DICEs lies in their influence upon epipelagic ecosystems (Mantua et al. 1997) and its potential to mask the anthropogenic climatic trend.