South Pacific Convergence Zone driven atmospheric river changes over Dronning Maud Land, Antarctica: Observational and CESM2 LENS2 evidence

Abstract

Atmospheric river (AR) landfalls profoundly impact Antarctic snowfall accumulation, surface melting and ice shelf calving/collapse. However, comprehensive case studies are still required to better understand AR changes and their underlying mechanisms. Here, we use ERA5 reanalysis and Community Earth System Model version 2 (CESM2) ensembles to examine the spatial distribution and long-term trends of Antarctic ARs during 1979–2022, and also investigate the mechanisms behind it by distinguishing between dynamic and thermodynamic effects. Reanalysis shows a strong increase in annual AR frequency over Dronning Maud Land (DML) in Antarctica during 1979–2022, predominantly driven by dynamical processes. Sea surface temperature (SST) anomalies in the South Pacific Convergence Zone (SPCZ) strongly modulate AR intensification over DML by enhancing convection and exciting a Rossby wave train, which deepens the Weddell Sea cyclone anomaly and amplifies downstream high-pressure ridges. Fingerprinting experiments with the 50-member CESM2 ensemble confirm the pivotal role of internal Pacific variability in reproducing observed AR trends. These results highlight the importance of accurately representing SPCZ SST variability for understanding the mechanisms driving Antarctic AR changes.