Southern Annular Mode Dynamics in Observations and Models. Part II: Eddy Feedbacks
Southern Annular Mode Dynamics in Observations and Models. Part II: Eddy Feedbacks
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DOI：
10.1175/jcli-d-12-00495.1
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发表时间：
2013-07
影响因子：
4.9
通讯作者：
I. Simpson;T. Shepherd;P. Hitchcock;J. Scinocca
中科院分区：
文献类型：
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作者：
I. Simpson;T. Shepherd;P. Hitchcock;J. Scinocca
许多全球气候模式(GCM)很难正确模拟南环型(SAM)变化，特别是在南半球夏季，这种变化往往过于持久。在这项由两部分组成的研究中，分析了一组使用加拿大中层大气模式(CMAM)的实验，以加深对SAM变率的动力学及其在GCM中的不足的理解。在这里，用一种新的方法对涡旋平均流反馈进行了检验，通过量化反馈强度作为纬向尺度和季节的函数，该方法解释了SAM的季节内强迫。在观测到的大气中，夏季，行星尺度波，特别是纬向波数3在西南太平洋局部化区域有很强的负反馈。它取消了一次大的proportionofthepositivefeedbackbysynoptic-andsmaller-scaleeddiesinthezonalmean，，导致对SAM的总体涡流反馈非常弱。CMAM缺乏行星尺度波动的这种负反馈，这对其夏季SAM持续性的偏差有实质性的贡献。此外，这种偏差不能通过人为改善气候环流来缓解，这表明气候环流偏差不是模型中行星波反馈不足的原因。对IntercomparisonProject(CMIP5)confirmsthatthisisindeedacommonproblemamongGCMs，耦合模式第5阶段的夏季涡旋反馈的分析表明，了解这种行星波反馈及其在大气环流模式中不足的原因是提高夏季模拟大气环流变率保真度的关键。
Many global climate models (GCMs) have trouble simulating southern annular mode (SAM) variability correctly, particularly in the Southern Hemisphere summer season where it tends to be too persistent. In this two-part study, a suite of experiments with the Canadian Middle Atmosphere Model (CMAM) is analyzed to improve the understanding of the dynamics of SAM variability and its deficiencies in GCMs. Here, an examination of the eddy‐mean flow feedbacks is presented by quantification of the feedback strength as a function of zonal scale and season using a new methodology that accounts for intraseasonal forcing of the SAM. In the observed atmosphere, in the summer season, a strong negative feedback by planetary-scale waves, in particular zonal wavenumber 3, is found in a localized region in the southwest Pacific. It cancels a large proportionofthepositivefeedbackbysynoptic-andsmaller-scaleeddiesinthezonalmean,resultinginavery weak overall eddy feedback on the SAM. CMAM is deficient in this negative feedback by planetary-scale waves, makingasubstantialcontribution to its bias in summertime SAM persistence. Furthermore, this bias is not alleviated by artificially improving the climatological circulation, suggesting that climatological circulation biases are not the cause of the planetary wave feedback deficiency in the model. Analysis of the summertime eddy feedbacks in the models from phase 5 of the Coupled Model IntercomparisonProject(CMIP5)confirmsthatthisisindeedacommonproblemamongGCMs,suggestingthat understanding this planetary wave feedback and the reason for its deficiency in GCMs is key to improving the fidelity of simulated SAM variability in the summer season.