Southern hemisphere climate variability as represented by an ocean-atmosphere coupled model

Abstract

Southern Hemisphere (SH) climate variability has been the focus of several researchers (e.g., Wallace and Hsu, 1983). According to these early studies, the SH is characterized by quasistationary oscillations and zonally propagating waves in the atmospheric circulation. The ability of predicting these modes of climate variability on longer timescales is vital. Potential predictability is usually measured as a signal-to-noise contrast between the slowly evolving and chaotic components of the climate system. Such measures are certainly sensitive to how the variance decomposition is performed. One way of separating the variance is using a temporal filtering technique which assumes that weather noise dominates much shorter timescales (e.g., Basher and Thomosph, 1996). Notwithstanding, weather noise includes not only high-frequency, day to day fluctuations but also low-frequency intraseasonal fluctuations that give rise to chaotic, unpredictable variability through temporal fluctuation. The aim of this study is, therefore, to assess the ability of a coupled global climate model in reproducing observed SH climate variability using a variance decomposition procedure recently suggested by Zheng and Frederiksen (2004) and Zheng et al. (2009).