The changes in the East Asian winter monsoon (EAWM) due to the effect of the interaction between the El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) are investigated using long-term surface air temperature (SAT) data and various reanalysis datasets. It is found that when the ENSO and PDO are in-phase (i.e., El Niño/high PDO phase or La Niña/low PDO phase), the EAWM tends to be significantly stronger or weaker. However, when the ENSO and PDO are out-of-phase (i.e., El Niño/low PDO phase or La Niña/high PDO phase), the EAWM does not exhibit distinct features. Hence, the relationship between the EAWM and ENSO on the interannual timescale is not only modulated by interdecadal variations of the PDO but also by the slowly-evolving PDO variations that become a synergistic or dissipative force on the ENSO-related interannual variability according to the phase interferences of ENSO and PDO. The dynamical process through which the EAWM is weakened or strengthened is closely linked to the northerly wind anomalies induced by the strength of Aleutian low variability during the winter season.

Wintertime variations in the magnitude of the western North Pacific subtropical high (WNPSH) and Siberian high are also examined to describe the strength of the EAWM. During the in-phase conditions, the magnitudes of both highs are significantly changed to effect an anomalously warmer and colder East Asian winter climate, but consistent with the above results, no changes are evident during the out-of-phase conditions. Consequently, the results suggest that ENSO-based long-range seasonal climate forecasts for East Asia should be considered with the interdecadal variations of the PDO to obtain more skillful prediction from an operational point of view.

1. INTRODUCTION

2. DATA and METHODOLOGY

2.1 Datasets

2.2 Definitions

2.3 Statistical analyses

3. RESULTS

3.1 Changes in surface air temperature over East Asian continent

3.2 Robustness of the East Asian Winter Monsoon

3.3 Wintertime variations of western North Pacific subtropical high and Siberian high

4. CONCLUDING REMARKS