【中文介绍】

  目前为止，基于大量观测和数值模拟结果，学界对现在和未来热带太平洋沃克环流的长期变化趋势仍然存在较大争议。为了理解沃克环流在不同时间尺度上的变化机理，我们使用国际古气候模拟比较计划资料集中的16个气候模式试验数据，定量分析了热带太平洋沃克环流的强度和位置在末次冰盛期（大约2.1万年前）气候背景下的变化特征。基于纬向质量流函数，大部分模式模拟显示，该时期年平均沃克环流较工业化革命前期减弱，平均减幅为15%；且其西边界和环流中心位置东移，平均分别移动9个和8个经度；上述变化与赤道印度洋和太平洋之间的东西向海平面气压差、赤道太平洋低层信风的减弱紧密相关。季节变化上，热带太平洋沃克环流在全年各季节均减弱东移。进一步分析表明，在末次冰盛期大量冰盖和低温室气体浓度强迫下，北半球大尺度不均匀变冷引起海陆热力对比在北半球冷季增大、暖季减小，使得亚洲和非洲北部季风降水在冷、暖季均减少，进而导致热力驱动的行星尺度东西向环流减弱，使得赤道西太平洋低层信风减弱，从而造成冷、暖季太平洋沃克环流的减弱和东移，最终年平均沃克环流亦减弱东移。

  【英文介绍】

   Based on various observations and model simulations, the long-term changes in the present and future tropical Pacific Walker circulation (PWC) have remained inconclusive. In order to understand the PWC changes at varying time scales, the annual and seasonal changes in the PWC during the last glacial maximum (LGM) are investigated using all available numerical experiments from the Paleoclimate Modelling Intercomparison Project Phases 2 and 3. Compared to the preindustrial period, the annual mean of the PWC intensity weakened by an average of 15%, and both the western edge and center of the PWC cell shifted eastward by an average of 9° and 8°, respectively, as obtained from the ensemble mean of the 16 models used for analysis during the LGM. Those changes were closely linked with an overall weakening of the equatorial Indo-Pacific east–west sea level pressure difference and low-level trade winds over the equatorial west/central Pacific. On the seasonal scale, the LGM PWC generally weakened and shifted eastward throughout the seasons of year. In response to the LGM large ice sheets and lower atmospheric greenhouse gas concentrations, the large-scale uneven surface cooling in the northern hemisphere led to an increased (a decreased) land–sea thermal contrast in boreal cold (warm) seasons. These induced decreases in the North Asian and African monsoon rainfall and hence suppressed a large-scale thermally direct east–west circulation in the two seasons. As a result, the LGM PWC weakened and shifted eastward in both boreal cold and warm seasons, which jointly contributed to the weakening and eastward shift of the annual mean PWC.

  【关键图表】

  【引用格式】       

   Zhiping Tian and Dabang Jiang, 2020: Weakening and eastward shift of the tropical Pacific Walker circulation during the last glacial maximum. Boreas, 49, 200–210, https://doi.org/10.1111/bor.12417.