Southern Hemispheric Atmospheric Blocking Patterns in CESM‐LENS2: Effects of Reversal Versus Anomaly Approaches

Abstract Atmospheric blocking is characterized as an anticyclonic flow structure which decelerates movement of weather systems in the mid‐latitudes. This study evaluates for the first time, Southern Hemispheric (SH) blocking representation in the Community Earth System Model Large Ensemble 2 (LENS2) using two blocking detection methods, True‐Reversal (TR) in local westerly and Persistent Positive Anomaly (PPA). We found that PPA blocks are better represented in LENS2 compared to TR, and future changes in the SH blocking patterns are regionally varying and insensitive to blocking detection method. LENS2 suggests hemispheric decline in TR (PPA) blocking frequency by −9% (−1%) and −16% (no change in PPA) for summer and winter seasons, respectively. Both methods agree on the future eastward (summer), and equatorward (winter) shift in the SH blocking patterns. This future shift contributes robust increase in the Antarctic Peninsula by the end of the 21st century.