Unraveling impact factors for future changes in the Brewer‐Dobson circulation
Unraveling impact factors for future changes in the Brewer‐Dobson circulation
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DOI：
10.1002/jgrd.50775
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发表时间：
2013-09
期刊：
影响因子：
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通讯作者：
S. Oberländer;U. Langematz;Stefanie Meul
中科院分区：
文献类型：
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作者：
S. Oberländer;U. Langematz;Stefanie Meul
气候模型预测，随着未来温室气体（GHG）浓度的增加，布鲁尔多布森环流（BDC）将增加。本研究通过EMAC化学气候模型的敏感性模拟，通过改变外部强迫，如温室气体浓度，海面温度（SST）和海冰浓度以及臭氧消耗物质（ODS），分别确定了BDC未来变化的原因。热带SST上升的特殊影响进行了评估。不同的波的剩余环流的变化的贡献计算以及平流层空气（AoA）的平均年龄的变化，以占混合过程的影响。我们发现，在北半球冬季，热带向上的质量通量增加约1%/dec在上层平流层和2%/dec在下层平流层，直到世纪结束。平均AoA分别减少60和30天/dec。瞬变行星波和天气波的变化解释了平流层下部BDC的加强，而平流层上部的变化是由于未来气候中重力波传播特性的改善。关于外部强迫，温室气体浓度上升的辐射影响只影响平流层上层，而平流层下层的信号几乎完全是由于海表温度上升。热带海温的变化不仅影响浅，但也深分支的BDC证实，从剩余环流和混合的变化。消耗臭氧层物质的减少将略微抵消南半球生物多样性的增加。
Climate models project an increase in the Brewer‐Dobson circulation (BDC) with increasing future greenhouse gas (GHG) concentrations. This study identifies the causes of future changes in the BDC from sensitivity simulations with the EMAC chemistry‐climate model, by changing the external forcings, like GHG concentrations, sea surface temperatures (SSTs) together with sea ice concentrations, and ozone‐depleting substances (ODS), separately. The particular influence of rising tropical SSTs is assessed. Contributions of different waves to changes in the residual circulation are calculated as well as changes in mean age of stratospheric air (AoA) to account for the effect of mixing processes. We find that in boreal winter the tropical upward mass flux increases by about 1%/dec in the upper and 2%/dec in the lower stratosphere until the end of the 21st century. Mean AoA decreases by up to 60 and 30 days/dec, respectively. Changes in transient planetary and synoptic waves account for the strengthening of the BDC in the lower stratosphere, whereas upper stratospheric changes are due to improved propagation properties for gravity waves in future climate. Regarding the external forcings, the radiative impact of rising GHG concentrations is detected to affect upper stratospheric layers only, whereas lower stratospheric signals are almost entirely due to rising SSTs. Changes in tropical SSTs influence not only the shallow but also the deep branch of the BDC as confirmed from both changes in residual circulation and mixing. Declining ODS will slightly counteract the BDC increase in the Southern Hemisphere.