Southward Intertropical Convergence Zone Shifts and Implications for an Atmospheric Bipolar Seesaw
Southward Intertropical Convergence Zone Shifts and Implications for an Atmospheric Bipolar Seesaw
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DOI：
10.1175/jcli-d-12-00279.1
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发表时间：
2013-06-01
影响因子：
4.9
通讯作者：
Ditlevsen, Peter D.
中科院分区：
文献类型：
--
作者：
Cvijanovic, Ivana;Langen, Peter L.;Ditlevsen, Peter D.
在这项研究中，向南热带辐合带（ITCZ）的变化进行了研究，在三个不同的方案：北方半球冷却，南半球变暖，并结合后两者的两极跷跷板状强迫。实验表明，相互影响，北方和南方高纬度强迫施加热带降水，这表明一个时间尺度依赖的主导地位的北方与南方强迫。据此，提出了热带降水变化的两个阶段，即北半球高纬强迫主导的快分量和南半球高纬强迫主导的慢分量。因此，这些结果可能有助于未来理解和解释高分辨率热带古降水代理及其与高纬度记录的关系（例如，冰芯数据）。实验还表明，南大洋变暖具有全球性影响，影响到热带和北方热带外地区，如ITCZ向南移动以及北大西洋中高纬表面温度和风的变化。在动力学方面的考虑，热带环流对高纬度强迫的响应被发现是非线性的：大气热传输和Hadley环流异常显着不同（在幅度上）时，比较变暖和冷却的实验。这些都与不同的半球间的温度梯度，主要是由水蒸气响应的非线性改变。大气层顶部通量响应分解为大气反馈效应，表明热带地区水汽和云反馈占主导地位，长波云反馈效应控制着整个云响应。
In this study, southward intertropical convergence zone (ITCZ) shifts are investigated in three different scenarios: Northern Hemispheric cooling, Southern Hemispheric warming, and a bipolar seesaw-like forcing that combines the latter two. The experiments demonstrate the mutual effects that northern- and southern-high-latitude forcings exert on tropical precipitation, suggesting a time-scale-dependent dominance of northern versus southern forcings. In accordance with this, two-phase tropical precipitation shifts are suggested, involving a fast component dominated by the high-northern-latitude forcing and a slower component due to the southern-high-latitude forcing. The results may thus be useful for the future understanding and interpretation of high-resolution tropical paleoprecipitation proxies and their relation to high-latitude records (e.g., ice core data). The experiments also show that Southern Ocean warming has a global impact, affecting both the tropics and northern extratropics, as seen in a southward ITCZ shift and mid- and high-latitude North Atlantic surface temperature and wind changes. In terms of dynamical considerations, the tropical circulation response to high-latitude forcing is found to be nonlinear: the atmospheric heat transport and Hadley cell anomalies differ significantly (in magnitude) when comparing the warming and cooling experiments. These are related to different interhemispheric temperature gradients that are altered mainly by nonlinearities in water vapor response. Decomposition of the top-of-the-atmosphere flux response into atmospheric feedback effects shows the dominance of water vapor and cloud feedbacks in the tropics, with the longwave cloud feedback effect governing the overall cloud response.