Long-term trends in the Southern Annular Mode from transient Mid- to Late Holocene simulation with the IPSL-CM5A2 climate model

Abstract

This study describes time evolution of the Southern Annular Mode (SAM) in Mid- to Late Holocene simulated with a state-of-the-art transient simulation of the last 6000 years carried out with the IPSL-CM5A2 model. Simulated SAM index exhibits significant long-term linear trends of different sign depending on the season that are closely related to multi-millennial changes in insolation which was the main driver of long-term climate change in the study period. Interactions between changes in insolation and the SAM are linked to temperature and pressure changes developed through the entire Southern Hemisphere. In fact, model results suggest that insolation changes produced significant changes in extratropical temperature gradients that, in turn, induced changes in pressure gradients synthesized by significant long-term linear trends in the SAM index from Mid- to Late-Holocene. Considering that changes in the SAM index synthetize changes in hemispheric patterns of temperature, pressure and winds, results exposed in this study should be considered as reference for reconstructions of SAM evolution in the last 6000 years from climate proxy archives.