Comparisons of the different definitions of the western Pacific pattern and associated winter climate anomalies in Eurasia and North America

摘要

The western Pacific pattern (WP), characterized by a meridional dipole structure in geopotential height anomalies centred at approximately 50 degrees N over the North Pacific, is one of the most prominent teleconnection patterns over the Northern Hemisphere (NH) in boreal winter. Several methods to identify the WP exist in the literature. Based on eight WP indices defined by different methods, this study analyses their dominant frequencies, spatial structures, climatic impacts, and relations to the Arctic Oscillation (AO) and El Nino-Southern Oscillation (ENSO). The correlation coefficients of the eight WP indices show a considerable spread, but most of them are statistically significant. Most of the WPIs capture a pronounced power peak at approximately 5 years. The meridional dipole structure of the WP can be captured by all the WPIs, but it shows a large spread in the location of the centre. Several WPIs are significantly correlated with the winter AO, with marked signals of atmospheric anomalies over the Arctic region. The connections of the WP with the simultaneous winter ENSO depend largely on their definitions. The impacts of the WP on the surface air temperature over many parts of Eurasia and North America are also sensitive to its definition. Differences in surface air temperature anomalies are related to differences in the spatial structure of the WP as captured by the range of WPIs.