Improvements in Circumpolar Southern Hemisphere Extratropical Atmospheric Circulation in CMIP6 Compared to CMIP5
Improvements in Circumpolar Southern Hemisphere Extratropical Atmospheric Circulation in CMIP6 Compared to CMIP5
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DOI：
10.1029/2019ea001065
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发表时间：
2020-06-01
影响因子：
3.1
通讯作者：
Rackow, T.
中科院分区：
文献类型：
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作者：
Bracegirdle, T. J.;Holmes, C. R.;Rackow, T.
在前几代气候模式中，与全球相关的主要系统偏差之一是南半球（SII）中纬度对流层涡旋驱动的西风急流的赤道偏倚。这对南大洋热量和碳吸收以及南极陆地和海冰的深远影响是解决这一偏见成为优先事项的关键原因。因此，评估Si的表示是至关重要的。最新一代的全球气候和地球系统模式，包括耦合模式比较计划第6阶段（CMIP6）。本文通过与CMIP5的观测数据和前几代模式的比较，对CMIP5中SH温带大气环流主要指数的代表性进行了评价。评估的指标包括西风急流的纬度和速度、南环模（SAM）的变率以及阿蒙森海低压（ASL）的代表性。这些是根据CMIP5和CMTP6在与现有观测和再分析数据集相匹配的时间段内的历史强迫模拟计算得出的。从目前可用的39个CMIP6模式来看，年平均西风急流的赤道偏倚从CMIP5的1.9度减少到CMIP6的0.4度，从季节角度来看，南方春季和夏季的减少最为明显。与CMIP5相比，SAM去相关时间尺度的偏差减少了一半。然而，对于美国手语来说，没有明显的整体改善。模拟南半球南极大陆周围风的位置、强度和时空行为的计算机模型与实际情况相比经常显示出典型的错误。这可能会影响到非常相关问题的答案，比如海洋吸收了多少热量和碳，或者未来海冰覆盖将如何演变。在这里，我们记录了作为政府间气候变化专门委员会（IPCC）下一份评估报告基础的新一代全球气候模型如何在观测到的南半球风方面发挥作用。我们还分析了与上一代计算机模型相比潜在的改进。总的来说，观测值的一些重要差异（偏差）比以前的模型要小得多（高达50%）。然而，其他诊断几乎没有变化，这表明模型代之间的改进相当有限。然而，我们的研究可以帮助确定剩余偏差的可能原因，并进一步减少即将推出的模型中的错误。
One of the major globally relevant systematic biases in previous generations of climate models has been an equatorward bias in the latitude of the Southern Hemisphere (SII) mid-latitude tropospheric eddy driven westerly jet. The far-reaching implications of this for Southern Ocean heat and carbon uptake and Antarctic land and sea ice are key reasons why addressing this bias is a high priority. It is therefore of primary importance to evaluate the representation of the Si! westerly jet in the latest generation of global climate and earth system models that comprise the Coupled Model Intercomparison Project Phase 6 (CMIP6). In this paper we assess the representation of major indices of SH extratropical atmospheric circulation in CMIP6 by comparison against both observations and the previous generation of CMIP5 models. Indices assessed are the latitude and speed of the westerly jet, variability of the Southern Annular Mode (SAM), and representation of the Amundsen Sea Low (ASL). These are calculated from the historical forcing simulations of both CMIP5 and CMTP6 for time periods matching available observational and reanalysis data sets. From the 39 CMIP6 models available at the time of writing there is an overall reduction in the equatorward bias of the annual mean westerly jet from 1.9 degrees in CMIP5 to 0.4 degrees in CMIP6 and from a seasonal perspective the reduction is clearest in austral spring and summer. This is accompanied by a halving of the bias of SAM decorrelation timescales compared to CMIP5. However, no such overall improvements arc evident for the ASL.Plain Language Summary Computer models that simulate the position, strength, and spatio-temporal behavior of winds in the Southern Hemisphere around the continent of Antarctica often show typical errors when compared to reality. This can impact answers to very relevant questions, such as how much heat and carbon are taken up by the ocean or how the sea ice cover will evolve in the future. Here we document how the newly available next generation of global climate models that form the basis for the next Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) performs with respect to observed Southern Hemisphere winds. We also analyze potential improvements compared to the previous generation of computer models. Overall, some important differences to observations (biases) are much smaller than in the previous models (by up to 50%). Other diagnostics are, however, virtually unchanged, which indicates that the improvements are rather limited between model generations. However, our study could help to identify possible reasons for the remaining biases and to further reduce errors in upcoming models.