Two Types of the Western Pacific Pattern, Their Climate Impacts, and the ENSO Modulations

Abstract

The western Pacific (WP) pattern is a major teleconnection pattern that influences the wintertime Northern Hemisphere climate variations. Based on daily NCEP–NCAR reanalysis data, this study examines the climate impacts and the El Niño–Southern Oscillation (ENSO) modulation of two types of the WP pattern. The result shows that the WP patterns may arise from precursory disturbances over Asia and the North Pacific or from the Pacific–North American (PNA) pattern of the same polarity as or opposite polarity to that of the WP patterns. Among these WP patterns, the WP patterns that arise from the PNA pattern of the same polarity are most influential on North American near-surface and polar stratospheric air temperatures; furthermore, their frequency of occurrence, amplitude, and duration can be affected by ENSO phases: the positive WP patterns occur more frequently with larger amplitude and longer duration in El Niño than in La Niña; and the negative WP patterns occur less frequently with smaller amplitude and shorter duration in El Niño than in La Niña. The above findings suggest that the PNA pattern plays a crucial role in the climate impacts and the ENSO modulation of the WP patterns.