Declining Aerosols in CMIP5 Projections: Effects on Atmospheric Temperature Structure and Midlatitude Jets
Declining Aerosols in CMIP5 Projections: Effects on Atmospheric Temperature Structure and Midlatitude Jets
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DOI：
10.1175/jcli-d-14-00258.1
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发表时间：
2014-09
影响因子：
4.9
通讯作者：
L. Rotstayn;Emily L. Plymin;M. Collier;O. Boucher;J. Dufresne;Jing‐Jia Luo;K. Salzen;S. Jeffrey;M. Foujols;Y. Ming;L. Horowitz
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作者：
L. Rotstayn;Emily L. Plymin;M. Collier;O. Boucher;J. Dufresne;Jing‐Jia Luo;K. Salzen;S. Jeffrey;M. Foujols;Y. Ming;L. Horowitz
利用耦合模式比对项目（CMIP5）第5阶段的4个模式评估了代表性浓度路径4.5 （RCP4.5）上人为气溶胶减少的影响，重点关注了年、纬向平均大气温度结构和纬向风。对于每个模式，除了人为气溶胶固定在21世纪初的水平外，根据2006 - 2100年RCP4.5强迫的预估与具有相同强迫的预估之间的差异来诊断气溶胶减少的影响。对气溶胶减少的响应可以用气溶胶辐射强迫的经向结构来解释，气溶胶辐射强迫在408N附近达到峰值，在南极消失。温室气体的增加导致热带对流层上层的变暖加剧，并加强了两个半球的中纬度气流。然而，对于下降气溶胶，垂直平均对流层温度响应在408N附近达到峰值，而不是在热带。这表明，对于减少的气溶胶，对流层经向温度梯度在南半球（SH）普遍增加，而在北半球（NH）在热带和亚热带则减少。与热风平衡一致，北半球急流向极地方向增强，向赤道方向减弱，而北半球急流的增强程度大于北半球急流。因此，喷流的不对称响应与气溶胶辐射强迫的经向结构和相关的对流层变暖是一致的：在北半球，最大变暖的纬度与喷流大致重合，而在北半球，变暖在热带地区最强，在高纬度地区最弱。
The effects of declining anthropogenic aerosols in representative concentration pathway 4.5 (RCP4.5) are assessed in four models from phase 5 the Coupled Model Intercomparison Project (CMIP5), with a focus on annual, zonal-mean atmospheric temperature structure and zonal winds. For each model, the effect of declining aerosols is diagnosed from the difference between a projection forced by RCP4.5 for 2006‐2100 and another that has identical forcing, except that anthropogenic aerosols are fixed at early twenty-first-century levels. The response to declining aerosols is interpreted in terms of the meridional structure of aerosol radiative forcing, which peaks near 408N and vanishes at the South Pole. Increasing greenhouse gases cause amplified warming in the tropical upper troposphere and strengthening midlatitude jets in both hemispheres. However, for declining aerosols the vertically averaged tropospheric temperature response peaks near 408N, rather than in the tropics. This implies that for declining aerosols the tropospheric meridional temperature gradient generally increases in the Southern Hemisphere (SH), but in the Northern Hemisphere (NH) it decreases in the tropics and subtropics. Consistent with thermal wind balance, the NH jet then strengthens on its poleward side and weakens on its equatorward side, whereas the SH jet strengthens more than the NH jet. The asymmetric response of the jets is thus consistent with the meridional structure of aerosol radiative forcing and the associated tropospheric warming: in the NH thelatitudeofmaximumwarmingis roughlycollocatedwith thejet, whereasin theSH warmingisstrongestin the tropics and weakest at high latitudes.