Southern Ocean albedo, inter-hemispheric energy transports and the double ITCZ: global impacts of biases in a coupled model
Southern Ocean albedo, inter-hemispheric energy transports and the double ITCZ: global impacts of biases in a coupled model
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DOI：
10.1007/s00382-016-3205-5
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发表时间：
2017-04-01
期刊：
影响因子：
4.6
通讯作者：
Stephens, Graeme
中科院分区：
文献类型：
--
作者：
Hawcroft, Matt;Haywood, Jim M.;Stephens, Graeme
气候模型中的半球间反照率、跨赤道能量传输和双热带辐合带（ITCZ）偏差之间存在因果关系。南大洋云偏差是许多模型中半球间反照率偏差的主要决定因素，包括 HadGEM2-ES（与动态海洋完全耦合的模型）。在这项研究中，在南大洋应用了有针对性的反照率校正，以探索人为减少这些偏差的动态响应。南半球急流的强度随着热带-温带温度梯度的增加而增强，同时增加了向大气中中纬度地区的能量传输，但在双ITCZ偏差或大气跨赤道能量传输方面没有观察到任何改善，这一发现支持了其他最近的研究。热带地区能源运输的大部分调整是在海洋中实现的，而响应进一步仅限于太平洋。因此，经常争论的南大洋和热带降水偏差之间的遥相关性被削弱了。进一步减少热带长波偏差的实验并没有改善热带大气的表现。这些结果表明，先前研究中显示的热带降水的显着改善可能是由于缺乏动力海洋和/或该工作中应用的简化的半球反照率偏差校正的结果。它进一步表明，如果不改进大气过程的表示，在专注于大规模能量控制的耦合模型中纠正双 ITCZ 问题的努力将被证明是徒劳的。
A causal link has been invoked between inter-hemispheric albedo, cross-equatorial energy transport and the double-Intertropical Convergence Zone (ITCZ) bias in climate models. Southern Ocean cloud biases are a major determinant of inter-hemispheric albedo biases in many models, including HadGEM2-ES, a fully coupled model with a dynamical ocean. In this study, targeted albedo corrections are applied in the Southern Ocean to explore the dynamical response to artificially reducing these biases. The Southern Hemisphere jet increases in strength in response to the increased tropical-extratropical temperature gradient, with increased energy transport into the mid-latitudes in the atmosphere, but no improvement is observed in the double-ITCZ bias or atmospheric cross-equatorial energy transport, a finding which supports other recent work. The majority of the adjustment in energy transport in the tropics is achieved in the ocean, with the response further limited to the Pacific Ocean. As a result, the frequently argued teleconnection between the Southern Ocean and tropical precipitation biases is muted. Further experiments in which tropical longwave biases are also reduced do not yield improvement in the representation of the tropical atmosphere. These results suggest that the dramatic improvements in tropical precipitation that have been shown in previous studies may be a function of the lack of dynamical ocean and/or the simplified hemispheric albedo bias corrections applied in that work. It further suggests that efforts to correct the double ITCZ problem in coupled models that focus on large-scale energetic controls will prove fruitless without improvements in the representation of atmospheric processes.