Sensitivity of the northern extratropics hydrological cycle to the changing insolation forcing at 126 and 115 ky BP
Sensitivity of the northern extratropics hydrological cycle to the changing insolation forcing at 126 and 115 ky BP
复制标题
北部温带水文循环对 126 和 115 ky BP 绝缘强迫变化的敏感性
DOI：
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
M. Kageyama
中科院分区：
文献类型：
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作者：
M. Khodri;M. Khodri;G. Ramstein;N. Noblet;M. Kageyama
摘要
在最后一次间冰期结束时，即距今115，000年（115 ky BP）的轨道结构是这样的，即与最后一次间冰期最大值（126 ky BP）相比，北方半球的季节对比度降低了。气候重建认为，在北大西洋的纬度表面温度和盐度梯度增加在115千BP相比，126千BP。根据替代测量，高纬度海洋清新可能是由增强的向北大气水分平流，这将导致减少在北方海的深对流活动。为了评估大气环流对日照强迫变化的这种重新调整，我们用两个AGCM实验探索了大气能量平衡和输送的变化，每个实验针对一种气候。我们表明，在115千年BP至126千年BP的静态热输送的北向增加构成了一个一阶响应的变化的日照。它趋向于平衡大气的热量平衡。尽管海表温度固定（SST）到今天，这一特点是强烈放大的海气热通量交换。通过与同期OAGCM实验的比较，我们发现无论海洋是否允许变化，模拟的表层海洋热通量对太阳辐射强迫的响应都是相似的。潜热输送不经历与干静态相同的变化。在北方高纬度地区，它每年都在减少。这是夏季水汽来源和瞬时活动改变的结果。后者似乎影响潜热输送远远超过干静态之一。冬季的响应，但是，不同于夏季的响应，占主导地位的年平均值。冬季115 kyBP存在一个增强的向北的大气水汽平流，这是高纬海洋在该季节变淡的原因。这一结果似乎证实了从海洋数据中推断出的假设。
Abstract
The orbital configuration at the end of the last interglacial, 115,000 years BP (115 ky BP), was such that the Northern Hemisphere seasonal contrast was decreased when compared to the last interglacial maximum, 126 ky BP. Climatic reconstructions argue for increased latitudinal surface temperature and salinity gradients in the North Atlantic at 115 ky BP compared to 126 ky BP. According to proxy measurements the high-latitude ocean freshening may be explained by enhanced northward atmospheric moisture advection which would have then led to decreased deep convection activity in the northern seas. To evaluate such re-adjustments of the atmospheric circulation to the insolation forcing changes, we have explored the changes in atmospheric energy balance and transport with two AGCM experiments, one for each climate. We show that the northward increase in static heat transport at 115 ky BP to 126 ky BP constitutes a first order response to the changing insolation. It tends to equalise the heat balance of the atmosphere. Despite sea surface temperatures fixed (SSTs) to present-day this feature is strongly amplified by the air–sea heat flux exchanges. By comparing with OAGCM experiments for the same periods, we find that the simulated surface ocean heat flux responses to insolation forcing are similar whether the ocean is allowed to vary or not. The latent heat transport does not undergo the same changes as the dry static one. On an annual basis, it decreases over the high northern latitudes. This is the result of summer modification of moisture sources and transient activity. The latter appears to affect latent heat transport much more than the dry static one. The winter response, however, differs from the summer response which dominates the annual mean. There is an enhanced northward atmospheric moisture advection during winter at 115 ky BP, which is responsible for the freshening of high-latitude ocean during this season. This result seems to confirm the hypothesis inferred from marine data.