The Southern Oscillation and Northern Hemisphere Temperature Variability

Abstract

The Southern Oscillation (SO) is the best defined and understood mode of interannual climate variability. The extreme phases of the SO have been identified with global-scale variations in the atmosphere/ocean circulation system and with the modulation of monsoon precipitation on the global scale. While SO-related precipitation has been the subject of several studies, the magnitude of the SO-related temperature variability on the global scale has not been well documented. In this paper we provide an estimate of the SO-related temperature variability in the context of monitoring global wanning related to the increase in greenhouse gases. This analysis suggested that traditional time series of hemispheric and global temperature anomalies for the calendar year may confuse interannual temperature variability associated with the SO and perceived “climate trend.” Analyses based on calendar-year data are likely to split the effects of the SO-related temperature variability over two years. The Northern Hemisphere cold season (October through March) time series may be more appropriate to separate the SO-related effects on the hemispheric temperature from other modes of variability. Mean interannual temperature anomaly differences associated with the extremes of the SO are estimated to be 0.2°C for the October-to-March season in the Northern Hemisphere. In areas directly linked to the SO, the mean interannual differences amount to over 0.5°C. The SO cannot account for all the variability in the hemispheric times series of surface temperature estimates, but the SO signal must be properly accounted for if these time series are to be understood.