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<p>In<?tk 2?> this study, the possible associations between the Antarctic Oscillation (AAO) and austral summer precipitation in southeastern Africa (10°S–25°S and 25°E–53°E) were investigated for the period from 1979 to 2019. The findings reveal a significant correlation between the AAO index during early austral spring (August to October) and regional mean precipitation over southeastern Africa from December to March. Specifically, the interannual correlations for the CMAP, GPCP, CRU, and GPCC datasets were -0.53, -0.47, -0.48, and -0.45, respectively. These precipitation anomalies are consistent with changes in regional moisture and atmospheric circulation patterns. A persistent upper-level ocean thermal anomaly from spring to summer over the tropical South Indian Ocean is suggested to play a crucial role in the time-lag linkage related to the AAO. Following an active austral spring AAO, surface clockwise wind curl anomalies develop over the central tropical South Indian Ocean. These wind curl anomalies lead to a shallower thermocline and below-normal sea surface height, resulting in cooling of the mixed layer through anomalous upwelling Ekman pumping. This cooling leads to a negative in situ moisture anomaly from spring to summer, which&#xa0;is unfavorable for precipitation over downstream southeastern Africa because of the prevailing easterly winds in austral summer. Moreover, the atmospheric dynamic response to this cooling tends to induce an anomalous anticyclone in the lower troposphere west of southeastern Africa. The anomalous descending air motion, combined with reduced moisture, further suppresses summer precipitation. Thus, the early spring AAO can serve as a useful precursor of summer precipitation over southeastern Africa.<?tk 0?></p>

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Austral spring Antarctic Oscillation modulates summer precipitation over southeastern Africa from 1979 to 2019

  • 期刊论文

  • 发表日期：

    2025年9月15日

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  • Chao-Jie Du,
  • Dao-Yi Gong,
  • Le-Kang Chen

摘要

In this study, the possible associations between the Antarctic Oscillation (AAO) and austral summer precipitation in southeastern Africa (10°S–25°S and 25°E–53°E) were investigated for the period from 1979 to 2019. The findings reveal a significant correlation between the AAO index during early austral spring (August to October) and regional mean precipitation over southeastern Africa from December to March. Specifically, the interannual correlations for the CMAP, GPCP, CRU, and GPCC datasets were -0.53, -0.47, -0.48, and -0.45, respectively. These precipitation anomalies are consistent with changes in regional moisture and atmospheric circulation patterns. A persistent upper-level ocean thermal anomaly from spring to summer over the tropical South Indian Ocean is suggested to play a crucial role in the time-lag linkage related to the AAO. Following an active austral spring AAO, surface clockwise wind curl anomalies develop over the central tropical South Indian Ocean. These wind curl anomalies lead to a shallower thermocline and below-normal sea surface height, resulting in cooling of the mixed layer through anomalous upwelling Ekman pumping. This cooling leads to a negative in situ moisture anomaly from spring to summer, which is unfavorable for precipitation over downstream southeastern Africa because of the prevailing easterly winds in austral summer. Moreover, the atmospheric dynamic response to this cooling tends to induce an anomalous anticyclone in the lower troposphere west of southeastern Africa. The anomalous descending air motion, combined with reduced moisture, further suppresses summer precipitation. Thus, the early spring AAO can serve as a useful precursor of summer precipitation over southeastern Africa.