资源环境科技发展态势分析平台

Previous studies documented that El Nino (EN) events are in general associated with negative phases of the Southern Annular Mode (SAM). EN 2015-2016 (EN15-16) was one of the three strongest events ever recorded. However, it was associated with a SAM positive phase of extreme intensity. Furthermore, while the negative linear relationship between ENSO and SAM during the most recent period (1986-2014) was significant and associated with a narrow uncertainty band, the combined condition of both climate patterns in the EN15-16 event was an outlier. The EN15-16 influence on the austral summer circulation anomalies at the extratropical and polar regions of the Southern Hemisphere was considerably altered by the strong SAM positive phase, which was evident not only at the troposphere but also at the stratosphere. Such circulation changes resulted in unusual regional impacts, such as negative anomalies of surface air temperature in western Antarctic Peninsula and negative precipitation anomalies in southeastern South America, ever recorded for previous strong EN events. Further research is needed to better understand the mechanisms explaining the SAM behaviour during 2015-2016 and its implication for climate predictability on seasonal timescales.