Tropospheric warming and stratospheric cooling influence the vertical structure of the atmosphere. Numerous studies have analysed the thermal expansion of the troposphere, however, stratospheric cooling reverses the sign of this shift in the middle stratosphere, causing a downward shift in the upper stratosphere and mesosphere. This is a robust feature in transient climate model simulations, but its impact is commonly unappreciated. Here, we quantify the trend difference of the residual mean vertical velocity (), a proxy for diagnosing the advective Brewer–Dobson circulation (BDC) strength, which arises from implicit neglect of the shrinking distance between stratospheric pressure levels in the CCMI‐1 (Chemistry‐Climate Model Initiative part 1) data request. There, a log‐pressure formula with constant scale height is recommended to compute . However, stratospheric cooling in transient climate simulations causes a reduction of the geometrical distance between pressure levels and thereby also the scale height significantly decreases over time. Using the general scale height definition for the transformation, the trends are therefore smaller. In both cases, the units are m·s⁻¹, but in the latter case it is the constant measure of length geopotential metres and not log‐pressure metres. We quantify that, due to the temperature dependence of log‐pressure metres, past studies that based trend analyses on log‐pressure overestimated the advective BDC acceleration by ∼ 20%. This result is consistent among the CCMI‐1 projections over the 1960–2100 period. We highlight that other diagnostics can also be affected by the neglect of the declining stratospheric pressure level distance. A detailed description of the diagnostics is necessary for consistent assessments of trends. Data processing tools should generally not include the constant scale height assumption if the data are used for trend analyses.

中文翻译：

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平流层冷却导致对流Brewer–Dobson循环的高估加速度

对流层变暖和平流层变冷会影响大气的垂直结构。许多研究已经分析了对流层的热膨胀，但是，平流层冷却逆转了平流层中部这种变化的迹象，导致平流层上层和中层中层向下移动。在瞬态气候模型模拟中，这是一个强大的功能，但其影响通常是不为人知的。在这里，我们量化了剩余平均垂直速度（），这是诊断对流Brewer-Dobson循环（BDC）强度的代理，这是由于对CCMI-1（化学-气候模式倡议第1部分）数据请求中平流层压力水平之间的收缩距离的隐式忽略而引起的。在那里，建议使用具有恒定刻度高度的对数压力公式进行计算。但是，瞬态气候模拟中的平流层冷却导致压力水平之间的几何距离减小，从而刻度高度随时间显着减小。因此，使用通用比例尺高度定义进行转换，趋势会更小。在两种情况下，单位均为m · s ^-1，但在后一种情况下，它是长度势能表的常数，而不是对数压力米。由于对数压力米的温度依赖性，我们量化了以往基于对数压力趋势分析的研究高估了对流BDC加速度约20％。这一结果在1960–2100年期间的CCMI-1预测中是一致的。我们着重指出，忽略平流层压力水平距离下降也可能会影响其他诊断。要对趋势进行一致的评估，必须对诊断进行详细说明。如果将数据用于趋势分析，则数据处理工具通常不应包括恒定比例高度假设。