The weakening of zonal atmospheric circulation, a widely accepted projection of climate change in response to global warming, features a weakening of the Indian Ocean Walker circulation (IWC), with an anomalous ascending motion over the western and anomalous descending motion over the eastern Indian Ocean. The projected IWC weakening has previously been attributed to slower warming in the east than the west, that is, to a positive Indian Ocean Dipole (IOD)-like warming pattern. However, such a warming pattern can also be induced by IWC weakening. As a result, the cause-and-effect relationship cannot be easily determined, and the projected change is poorly constrained and highly uncertain. Here, using a suite of coupled climate model simulations under a high-emission scenario, we find that the IWC slowdown is accompanied by not only a positive IOD-like warming pattern but also anomalous meridional circulation that is associated with anomalous descending motion over the eastern Indian Ocean. We further show that the anomalous local meridional circulation is closely linked to enhanced land-sea thermal contrast and is unlikely to result from the positive IOD-like warming pattern, suggesting that the IWC weakening is in part driven by the anomalous local meridional circulation. Our findings underscore the important role of local meridional circulation changes in modulating future IWC changes.

纬向大气环流减弱是一种广泛接受的气候变化响应全球变暖的预测，其特点是印度洋沃克环流（IWC）减弱，在印度洋西部出现异常上升运动，在东部印度洋出现异常下降运动. 预计 IWC 减弱以前被归因于东部的变暖比西部慢，也就是说，正印度洋偶极子 (IOD) 样变暖模式。然而，这种变暖模式也可能是由 IWC 减弱引起的。因此，因果关系不容易确定，预测的变化约束很差，不确定性很大。在这里，在高排放情景下使用一套耦合气候模型模拟，我们发现，IWC 的减速不仅伴随着类似 IOD 的正变暖模式，而且伴随着与印度洋东部上空异常下降运动相关的异常经向环流。我们进一步表明，异常的局地经向环流与增强的海陆热对比密切相关，不太可能是由正 IOD 样变暖模式引起的，这表明 IWC 减弱部分是由异常的局地经向环流驱动的。我们的研究结果强调了局部经向环流变化在调节未来 IWC 变化中的重要作用。我们进一步表明，异常的局地经向环流与增强的海陆热对比密切相关，不太可能是由正 IOD 样变暖模式引起的，这表明 IWC 减弱部分是由异常的局地经向环流驱动的。我们的研究结果强调了局部经向环流变化在调节未来 IWC 变化中的重要作用。我们进一步表明，异常的局地经向环流与增强的海陆热对比密切相关，不太可能是由正 IOD 样变暖模式引起的，这表明 IWC 减弱部分是由异常的局地经向环流驱动的。我们的研究结果强调了局部经向环流变化在调节未来 IWC 变化中的重要作用。