The last glacial cycle: transient simulations with an AOGCM
The last glacial cycle: transient simulations with an AOGCM
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DOI：
10.1007/s00382-011-1283-y
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发表时间：
2012-01
期刊：
影响因子：
4.6
通讯作者：
Robin S. Smith;J. Gregory
中科院分区：
文献类型：
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作者：
Robin S. Smith;J. Gregory
使用快速大气-海洋环流模型 (AOGCM) FAMOUS 进行了许多模拟过去 120 公里的瞬态气候运行。这是首次使用完整的 AOGCM 进行此类实验，提供了这一时期大气和海洋的三维模拟。因此，我们的模拟包括从几天到几千年的内部生成的时间变化，以及云和降水等重要过程的物理详细表示。尽管该模型速度很快，但计算限制意味着强迫的变化率增加了 10 倍，使得每个实验的长度为 12 kyr。大气温室气体（GHG）、北半球冰盖以及地球轨道变化引起的太阳辐射变化被视为强迫因素，并在不同的实验中单独或组合应用。南极洲的长期温度变化与冰芯数据的重建非常吻合，时间尺度超过 10 kyr 的变化也是如此。格陵兰岛末次盛冰期（LGM）的冷却得到了相当好的模拟，尽管我们的模拟缺乏冰盖融水强迫，无法重现北半球气候代理或较慢的南半球气候代理中出现的突然的千禧年规模的气候变化。末次盛宴海面冷却的空间模式与代理重建相当吻合。在我们的实验中，在大于 10 kyr 的时间尺度上，大西洋经向翻转环流 (AMOC) 和南极绕极流 (ACC) 的强度存在显着的反相关变化。我们发现，温室气体强迫削弱了 AMOC，增强了 ACC，而北半球冰盖的存在增强了 AMOC，削弱了 ACC。研究发现末次海冰的 AMOC 结构对所使用的冰盖重建的细节很敏感。轨道强迫的进动分量在 AMOC 和 ACC 中引起约 20 kyr 的振荡，其幅度由地球轨道偏心率的变化调节。这些强迫影响以线性方式结合起来，以产生在所有强迫运行中看到的平均气候和海洋变化。
A number of transient climate runs simulating the last 120 kyr have been carried out using FAMOUS, a fast atmosphere–ocean general circulation model (AOGCM). This is the first time such experiments have been done with a full AOGCM, providing a three-dimensional simulation of both atmosphere and ocean over this period. Our simulation thus includes internally generated temporal variability over periods from days to millennia, and physical, detailed representations of important processes such as clouds and precipitation. Although the model is fast, computational restrictions mean that the rate of change of the forcings has been increased by a factor of 10, making each experiment 12 kyr long. Atmospheric greenhouse gases (GHGs), northern hemisphere ice sheets and variations in solar radiation arising from changes in the Earth’s orbit are treated as forcing factors, and are applied either separately or combined in different experiments. The long-term temperature changes on Antarctica match well with reconstructions derived from ice-core data, as does variability on timescales longer than 10 kyr. Last Glacial Maximum (LGM) cooling on Greenland is reasonably well simulated, although our simulations, which lack ice-sheet meltwater forcing, do not reproduce the abrupt, millennial scale climate shifts seen in northern hemisphere climate proxies or their slower southern hemisphere counterparts. The spatial pattern of sea surface cooling at the LGM matches proxy reconstructions reasonably well. There is significant anti-correlated variability in the strengths of the Atlantic meridional overturning circulation (AMOC) and the Antarctic Circumpolar Current (ACC) on timescales greater than 10 kyr in our experiments. We find that GHG forcing weakens the AMOC and strengthens the ACC, whilst the presence of northern hemisphere ice-sheets strengthens the AMOC and weakens the ACC. The structure of the AMOC at the LGM is found to be sensitive to the details of the ice-sheet reconstruction used. The precessional component of the orbital forcing induces ~20 kyr oscillations in the AMOC and ACC, whose amplitude is mediated by changes in the eccentricity of the Earth’s orbit. These forcing influences combine, to first order, in a linear fashion to produce the mean climate and ocean variability seen in the run with all forcings.