全球季风：跨越古今探索其机制与难题
The global change across time scales:Mechanisms and outstanding issues
论文是国际“过去全球变化（PAGES）”的工作组十年研讨的总结，于2017年发表在“EarthScienceReviews”上，对现代和古气候学界提出了全球季风的变化机制及存在问题。三百年来，季风历来是作为区域性现象研究的。随着遥感等观测技术的全球覆盖，现代气候学从2000年开始提出“全球季风”的新概念，认为各大洲除了南极都有季风，而且是当今低纬水文循环中最为活跃的因素。这项新认识很快得到古气候学界的响应，2007年PAGES组织建立了“全球季风与低纬过程”工作组，经过多次国际研讨会和反复研讨，汇总了不同时间尺度上的季风记录，四年前的第一篇总结证明了各个区域季风在地质尺度上也存在着对应性 (Wang et al., 2014，发表于“Climate of the Past”)，论证了季风同时具有全球和区域的双重性质。在此基础上，工作组在最终的总结论文中归纳了季风在不同时间尺度上的驱动机制，包括外来因素和气候系统的内部反馈（下图）。
全球季风的变化机制及其时间尺度
论文指出：季风由太阳辐射驱动，其变化对应于“气候赤道（热带辐合带ITCZ）”的南北位移，因而具有全球性； 同时，下垫面的特征如海陆分布、地形、洋流等，又为各大季风系塑造了不同区域特征。季风的演变，一方面受到地球系统的外力驱动，另方面又有气侯系统发的内部反馈。在长时间尺度上，外力驱动常常引起全球性的响应；而在短时间尺度上，内部反馈倾向于造成区域性的变化。文章进一步讨论了季风研究中的争论问题，包括季风作为风和雨的两面性、氧同位素指示水文循环的能力、高纬与低纬过程对季风变化的影响等等。
该篇总结论文由PAGES全球季风工作组组长、同济大学汪品先领衔完成，成员中有著名的华人气侯学家王斌、程海、郭正堂、刘振宇等。作为气侯研究的新课题，全球季风的总结论文在某种程度上反映了华人群落在该领域中的主导地位。
Citation：Wang, P. X., Wang, B., Cheng,H., Fasullo,J., Guo,Z.T., Kiefer,T., Liu,Z.Y., 2017. The global monsoon across time scales: Mechanisms and outstanding issues. Earth-Science Reviews, 173: 84-121
全文链接：http://dx.doi.org/10.1016/j.earscirev.2017.07.006
Abstract：
The present paper addresses driving mechanisms of global monsoon (GM) variability and outstanding issues in GM science. This is the second synthesis of the PAGES GM Working Group following the first synthesis “The Global Monsoon across Time Scales: coherent variability of regional monsoons” published in 2014 (Climate of the Past, 10, 2007–2052). Here we introduce the GM as a planetary scale circulation system and give a brief accounting of why it exhibits regional structure. The primary driver of the GM is solar insolation, and the specificfeatures in the underlying surface, such as land-sea distribution, topography, and oceanic circulations, aremainly responsible for the differences among regional monsoon systems. We then analyze the monsoon formationmechanisms, together with the major processes that drive monsoon variations at various timescales,including external forcings and internal feedbacks. On long time scales, external forcings often induce variability on a global scale, whereas short-term variability in regional monsoon systems is usually caused by internalfeedbacks within the climate system. Finally, a number of debatable issues are discussed, with an emphasis ontime scales beyond the instrumental record. These include the dual nature of the monsoon as wind and rain, themeaning of oxygen isotope in hydrological cycle, in particular of speleothem δ18O, the role of ice-sheet inmonsoon variations, etc. In general, the GM as a system comprises a hierarchy of regional and local monsoonswith various degrees of similarity, though all show coherent variability driven by a common solar forcing. Thegoal of the GM concept, therefore, is by no means to replace or diminish research on the regional monsoons, butto help dissect the mechanisms and controlling factors of monsoon variability at various temporal-spatial scales.
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