Impact of the Winter North Pacific Oscillation on the Surface Air Temperature over Eurasia and North America: Sensitivity to the Index Definition

Abstract

This study analyzes the impact of the winter North Pacific Oscillation (NPO) on the surface air temperature (SAT) variations over Eurasia and North America based on six different NPO indices. Results show that the influences of the winter NPO on the SAT over Eurasia and North America are sensitive to the definition of the NPO index. The impact of the winter NPO on the SAT variations over Eurasia (North America) is significant (insignificant) when the anticyclonic anomaly associated with the NPO index over the North Pacific midlatitudes shifts westward and pronounced northerly wind anomalies appear around Lake Baikal. By contrast, the impact of the winter NPO on the SAT variations over Eurasia (North America) is insignificant (significant) when the anticyclonic anomaly over the North Pacific related to the NPO index shifts eastward and the associated northerly wind anomalies to its eastern flank extend to North America. The present study suggests that the NPO definition should be taken into account when analyzing the impact of the winter NPO on Eurasian and North American SAT variations.

摘 要

基于六种不同的指数定义方法, 本文研究了冬季北太平洋涛动(North Pacific Oscillation, NPO)对欧亚大陆和北美地区地表气温(surface air temperature, SAT)变率的影响. 结果表明, 冬季NPO对欧亚大陆和北美SAT的影响敏感于NPO指数的定义方式. 当与NPO相联系的北太平洋中纬度反气旋异常西移, 贝加尔湖附近出现显著的异常偏北风, 则冬季NPO对欧亚大陆(北美)SAT的影响是显著(不显著)的. 反之, 当与NPO相联系的北太平洋反气旋异常东移, 且其东侧的偏北风异常延伸到北美地区, 则冬季NPO对欧亚大陆(北美)SAT的影响不显著(显著). 本文的研究结果表明, 当分析冬季NPO对欧亚大陆和北美SAT变率的影响时需谨慎考虑NPO指数的定义方法.