第一届未来大气科学论坛

This study investigates the increasing variance of the Southern Annular Mode (SAM) from 1940 to 2020 using state-of-the-art reanalysis products, observational data, climate projections. We first document a substantial increase in the standard deviation of the SAM index around 1980, concurrent with shifts in midlatitude eddy forcing. Composites of precipitation anomalies reveal that positive and negative SAM phases have intensified post-1980, producing more pronounced extreme weather events. Through a simple eddy-jet interaction model, we demonstrate that an increase in eddy forcing is the primary driver of the heightened SAM amplitude. Furthermore, climate model simulations indicate robust future changes in both the mean state and variability of the SAM, suggesting more frequent extremes in Southern Hemisphere weather patterns. This integrated approach, combining reanalysis, observations, simple modeling, and climate projections, clarifies the mechanisms underlying observed and anticipated trends in SAM variability. Our findings highlight the broader implications of intensified jet variability for regional climate and extreme weather.