Constraining the low‐cloud optical depth feedback at middle and high latitudes using satellite observations
Constraining the low‐cloud optical depth feedback at middle and high latitudes using satellite observations
复制标题
DOI：
10.1002/2016jd025233
复制
发表时间：
2016-08
期刊：
影响因子：
--
通讯作者：
C. Terai;S. Klein;M. Zelinka
中科院分区：
文献类型：
--
作者：
C. Terai;S. Klein;M. Zelinka
中高纬度地区变暖导致云光学深度增加，这是所有气候模型中都发现的强大的云反馈响应。这项研究的结果表明，低层云的光学深度对温度的响应是时间尺度不变的。时间尺度不变性允许人们使用卫星观测来约束模型的光学深度反馈。将三个无源传感器卫星检索结果与第五耦合模型比对项目 (CMIP5) 的大气模型比对项目 (AMIP) 的八个模型的模拟进行比较。这项研究证实，低云光学深度响应在 AMIP 模拟中具有时间尺度不变性，通常在纬度高于 40° 的地区。与卫星估计相比，大多数模型高估了每月和年际时间尺度上光学深度随变暖而增加的情况。许多模型也没有捕捉到在所有三颗卫星观测和之前的研究中发现的估计反演强度的光学深度的增加。模型和卫星之间的差异在两个半球和一年中的大部分月份都存在。用卫星的灵敏度简单地替换模型的光学深度灵敏度，可以在 40°–70°S 纬度带中将短波云负反馈减少至少 50%，在 40°–70°N 纬度带中减少至少 65%。根据对卫星观测的分析，我们得出的结论是，中高纬度地区的低云光学深度反馈在气候模型中可能过于负面。
The increase in cloud optical depth with warming at middle and high latitudes is a robust cloud feedback response found across all climate models. This study builds on results that suggest the optical depth response to temperature is timescale invariant for low‐level clouds. The timescale invariance allows one to use satellite observations to constrain the models' optical depth feedbacks. Three passive‐sensor satellite retrievals are compared against simulations from eight models from the Atmosphere Model Intercomparison Project (AMIP) of the 5th Coupled Model Intercomparison Project (CMIP5). This study confirms that the low‐cloud optical depth response is timescale invariant in the AMIP simulations, generally at latitudes higher than 40°. Compared to satellite estimates, most models overestimate the increase in optical depth with warming at the monthly and interannual timescales. Many models also do not capture the increase in optical depth with estimated inversion strength that is found in all three satellite observations and in previous studies. The discrepancy between models and satellites exists in both hemispheres and in most months of the year. A simple replacement of the models' optical depth sensitivities with the satellites' sensitivities reduces the negative shortwave cloud feedback by at least 50% in the 40°–70°S latitude band and by at least 65% in the 40°–70°N latitude band. Based on this analysis of satellite observations, we conclude that the low‐cloud optical depth feedback at middle and high latitudes is likely too negative in climate models.