The Brewer–Dobson circulation (BDC) is a key feature of the stratosphere that models need to accurately represent in order to simulate surface climate variability and change adequately. For the first time, the Climate Model Intercomparison Project includes in its phase 6 (CMIP6) a set of diagnostics that allow for careful evaluation of the BDC. Here, the BDC is evaluated against observations and reanalyses using historical simulations. CMIP6 results confirm the well-known inconsistency in the sign of BDC trends between observations and models in the middle and upper stratosphere. Nevertheless, the large uncertainty in the observational trend estimates opens the door to compatibility. In particular, when accounting for the limited sampling of the observations, model and observational trend error bars overlap in 40 % of the simulations with available output. The increasing CO₂ simulations feature an acceleration of the BDC but reveal a large spread in the middle-to-upper stratospheric trends, possibly related to the parameterized gravity wave forcing. The very close connection between the shallow branch of the residual circulation and surface temperature is highlighted, which is absent in the deep branch. The trends in mean age of air are shown to be more robust throughout the stratosphere than those in the residual circulation.

中文翻译：

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CMIP6 中的 Brewer-Dobson 环流

布鲁尔-多布森环流 (BDC) 是平流层的一个关键特征，模型需要准确表示以充分模拟地表气候变率和变化。气候模型比对项目第一次在其第 6 阶段 (CMIP6) 中包含了一套诊断方法，可以对 BDC 进行仔细评估。在这里，使用历史模拟根据观察和重新分析对 BDC 进行评估。CMIP6 结果证实了众所周知的在平流层中上层和上层的观测和模型之间的 BDC 趋势符号不一致。然而，观测趋势估计的巨大不确定性为兼容性打开了大门。特别是，当考虑到有限的观察抽样时，模型和观测趋势误差条在 40% 的模拟中与可用输出重叠。不断增加的CO ₂模拟以 BDC 加速为特征，但揭示了平流层中到上层趋势的大范围扩展，这可能与参数化重力波强迫有关。残余环流浅支与地表温度之间的联系非常密切，而深支则没有这种联系。空气平均年龄的趋势在整个平流层中比剩余环流中的趋势更为强劲。