Global climate models indicate that the Southern Hemispheric (SH) jet stream shifts poleward in response to CO2 forcing, but the magnitude of this shift remains highly uncertain. Here we analyse the SH jet stream response to 4×CO2 forcing in Coupled Model Intercomparison Project phase 6 (CMIP6) simulations, and find a substantially muted jet shift during winter compared with CMIP5. We suggest this muted response results from a more poleward mean jet position, consistent with a strongly reduced bias in jet position relative to the reanalysis during 1980--2004. The improved mean jet position cannot be explained by changes in the simulated sea surface temperatures. Instead, we find indications that increased horizontal grid resolution in CMIP6 relative to CMIP5 has contributed to the higher mean jet latitude, and thus to the reduced jet shift under CO2 forcing. These results imply that CMIP6 models can provide more realistic projections of SH climate change.

中文翻译：

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CMIP6 模型中南半球急流对 CO ₂强迫响应的平均状态的作用

全球气候模型表明，南半球 (SH) 急流响应 CO2 强迫向极地移动，但这种移动的幅度仍然高度不确定。在这里，我们分析了耦合模型比对项目第 6 阶段 (CMIP6) 模拟中的 SH 急流对 4×CO2 强迫的响应，并发现与 CMIP5 相比，冬季的急流偏移显着减弱。我们认为这种柔和的响应是由更靠近极地的平均喷流位置造成的，这与 1980--2004 年间相对于再分析的喷流位置偏差大大减少一致。改进的平均射流位置不能用模拟海面温度的变化来解释。相反，我们发现有迹象表明 CMIP6 相对于 CMIP5 的水平网格分辨率增加有助于提高平均急流纬度，从而减少 CO2 强迫下的射流偏移。这些结果意味着 CMIP6 模型可以提供更现实的 SH 气候变化预测。