The annual and seasonal changes in the tropical Pacific Walker circulation (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 0.96×10¹⁴ kg² m⁻² s⁻¹ or 15%, and both the western edge and centre 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's large ice sheets and lower atmospheric greenhouse gas concentrations, 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.

中文翻译：

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最后一次冰川最大期，热带太平洋沃克环流的减弱和东移

使用古气候模拟比对项目第2和第3阶段的所有可用数值实验，研究了最后一次冰期最大值（LGM）期间热带太平洋沃克环流（PWC）的年度和季节性变化。与工业化前时期相比，工业年的年均值PWC强度平均降低0.96×10 ¹⁴  kg ²  m ^-2  s ^-1或15％，并且PWC单元的西边和中心向东平均分别偏移了9°和8°，这是从LGM期间用于分析的16个模型的集合平均值中获得的。这些变化与赤道印度-太平洋东-西海平面压力差的整体减弱和赤道西/中太平洋的低水平贸易风密切相关。在季节尺度上，LGM PWC通常在一年中整个季节减弱并向东移动。为了应对LGM的大冰原和较低的大气温室气体浓度，北半球的大规模不均匀地表降温导致北方（冷）暖季的陆海热反差增加（减少）。这些导致北亚和非洲季风降雨减少，因此抑制了两个季节的大规模热直接东西向环流。结果，在寒冷和温暖的季节，LGM PWC减弱并向东移动，共同导致年均PWC减弱和向东移动。