Department of Meteorology and Centre for Past Climate Change, University of Reading, Reading, United Kingdom.
Bristol Research Initiative for the Dynamic Global Environment (BRIDGE), School of Geographical Sciences, University of Bristol, University Road, Bristol, United Kingdom.
Sci Rep. 2017 Aug 24;7(1):9382. doi: 10.1038/s41598-017-09816-8.
The latitude of the tropical rainbelt oscillates seasonally but has also varied on millennial time-scales in response to changes in the seasonal distribution of insolation due to Earth's orbital configuration, as well as climate change initiated at high latitudes. Interpretations of palaeoclimate proxy archives often suggest hemispherically coherent variations, some proposing meridional shifts in global rainbelt position and the 'global monsoon', while others propose interhemispherically symmetric expansion and contraction. Here, we use a unique set of climate model simulations of the last glacial cycle (120 kyr), that compares well against a compilation of precipitation proxy data, to demonstrate that while asymmetric extratropical forcings (icesheets, freshwater hosing) generally produce meridional shifts in the zonal mean rainbelt, orbital variations produce expansion/contractions in terms of the global zonal mean. This is primarily a dynamic response of the rainbelt over the oceans to regional interhemispheric temperature gradients, which is opposite to the largely local thermodynamic terrestrial response to insolation. The mode of rainbelt variation is regionally variable, depending on surface type (land or ocean) and surrounding continental configuration. This makes interpretation of precipitation-proxy records as large-scale rainbelt movement challenging, requiring regional or global data syntheses.
雨带的纬度随季节呈季节性波动，但也会因地球轨道配置引起的太阳辐射季节性分布变化以及高纬度地区引发的气候变化，在千年时间尺度上发生变化。对古气候代用记录的解释常常表明存在半球间一致的变化，有些提出全球雨带位置和“全球季风”的经向移动，而另一些则提出跨半球对称的扩张和收缩。在这里，我们使用了一组独特的末次冰期（120 千年前）气候模型模拟结果，这些结果与降水代用数据的汇编进行了很好的比较，证明了尽管非对称的中纬度强迫作用（冰盖、淡水喷洒）通常会导致纬向平均雨带的经向移动，但轨道变化会导致全球纬向平均的扩张/收缩。这主要是海洋上雨带对区域跨半球温度梯度的动态响应，与太阳辐射对陆地的主要局部热力学响应相反。雨带变化的模式因地区而异，取决于地表类型（陆地或海洋）和周围大陆的配置。这使得对降水代用记录的解释变得具有挑战性，因为这些记录代表了大规模雨带的移动，需要进行区域或全球数据综合。
