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<p>This study characterizes the atmospheric circulation patterns and forcings driving wet periods across various regions in Southern South America (SSA) from 1979 to 2022. Wet periods were identified using the Standardized Precipitation Evapotranspiration Index (SPEI) and large-scale patterns were analyzed based on the stream function anomalies at 500&#xa0;hPa, vertically integrated moisture flux divergence (VIMFD), and evapotranspiration (ET). The stream function anomalies were classified into two circulation clusters, Cl 1 and Cl 2, to distinguish associated circulation types. Cl 1 is characterized by Rossby wave trains from the western tropical Pacific and is likely influenced by negative phases of the Indian Ocean Dipole (IOD) and the South Atlantic Ocean Dipole (SAOD), both forcings with a predominant influence in the Andean Altiplano; and Cl 2, a more coherent pattern resembling the negative phase of the Southern Annular Mode (SAM) and a Pacific-South American wave train, possibly influenced by El Niño events, which strongly affected wet conditions in eastern SSA, particularly in summer and spring, or by positive IOD phases which showed influence in part of this region as well. High VIMFD values in eastern regions highlight the role of circulation in moisture balance, while local factors and ET show greater significance in Patagonia and mountainous areas. These findings reveal that wet periods in SSA result from an interplay between multiple remote and local forcings, highlighting their varied contributions across regions.</p>

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Assessing wet events in southern South America: tropospheric circulation features and main forcings

  • 期刊论文

  • 发表日期：

    2025年8月6日

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  • María Eugenia Pérez de Mendiola,
  • Josefina Blázquez,
  • Silvina A. Solman

摘要

This study characterizes the atmospheric circulation patterns and forcings driving wet periods across various regions in Southern South America (SSA) from 1979 to 2022. Wet periods were identified using the Standardized Precipitation Evapotranspiration Index (SPEI) and large-scale patterns were analyzed based on the stream function anomalies at 500 hPa, vertically integrated moisture flux divergence (VIMFD), and evapotranspiration (ET). The stream function anomalies were classified into two circulation clusters, Cl 1 and Cl 2, to distinguish associated circulation types. Cl 1 is characterized by Rossby wave trains from the western tropical Pacific and is likely influenced by negative phases of the Indian Ocean Dipole (IOD) and the South Atlantic Ocean Dipole (SAOD), both forcings with a predominant influence in the Andean Altiplano; and Cl 2, a more coherent pattern resembling the negative phase of the Southern Annular Mode (SAM) and a Pacific-South American wave train, possibly influenced by El Niño events, which strongly affected wet conditions in eastern SSA, particularly in summer and spring, or by positive IOD phases which showed influence in part of this region as well. High VIMFD values in eastern regions highlight the role of circulation in moisture balance, while local factors and ET show greater significance in Patagonia and mountainous areas. These findings reveal that wet periods in SSA result from an interplay between multiple remote and local forcings, highlighting their varied contributions across regions.