Role of seasonal transitions and westerly jets in East Asian paleoclimate
Role of seasonal transitions and westerly jets in East Asian paleoclimate
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DOI：
10.1016/j.quascirev.2014.11.009
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发表时间：
2015-01-15
影响因子：
4
通讯作者：
Labrousse, Clothilde A.
中科院分区：
文献类型：
--
作者：
Chiang, John C. H.;Fung, Inez Y.;Labrousse, Clothilde A.
东亚夏季降水气候在过去的气候中经历了巨大的突变，这是对岁差强迫、冰期间冰期旋回以及末次冰期北大西洋突变的响应。然而，目前对上述变化的解释通常是根据夏季风强度的调制来制定的，并且没有考虑到东亚降雨季节演变的已知复杂性，这表现出从春季到梅雨的急剧转变，从梅雨期到夏季，我们探讨了东亚降水气候在夏季经历季节性调制的解释，说古气候变化。根据以前的建议，我们集中在西风急流在亚洲的作用，即它的相对于西藏的纬度是决定东亚降水季节的逐步过渡的关键。为了支持这种联系，我们从观测数据表明，6月的年际协变（7月8日）降雨和对流层上层纬向风显示出与梅雨（夏季）过渡时间改变一致的特性，我们同样认为，东亚古气候的变化是由于急流向北演化的时间改变，季节转换，特别是高原南部急流向北部的转换，决定了春雨向梅雨的季节转换。在一个极端的情况下，我们推测，气候系统倾向于在stadial（冷）阶段的D/O台标和低北方夏季日照期间的急流不跳高原北部，基本上保持东亚在延长的春季conditions.We认为，这一假设提供了一个可行的解释，一个关键的paleoproxy签名的D/O台标在东亚。即洞穴沉积物记录中记录的较重的平均降水Δ O-18。向南的急流位置阻止了同位素较轻的低层季风流渗透到东亚内部;因此，那里的降水将较重，与洞穴沉积物记录一致。这一假说也可以解释东亚古气候变化的其他关键证据，特别是在北大西洋stadials的沙尘条件的发生，以及全新世最佳降雨量的南移。(C)2014爱思唯尔有限公司版权所有。
The summer rainfall climate of East Asia underwent large and abrupt changes during past climates, in response to precessional forcing, glacial interglacial cycles as well as abrupt changes to the North Atlantic during the Last Glacial. However, current interpretations of said changes are typically formulated in terms of modulation of summer monsoon intensity, and do not account for the known complexity in the seasonal evolution of East Asian rainfall, which exhibits sharp transition from the Spring regime to the Meiyu, and then again from the Meiyu to the Summer regime.We explore the interpretation that East Asian rainfall climate undergoes a modulation of its seasonality during said paleoclimate changes. Following previous suggestions we focus on role of the westerly jet over Asia, namely that its latitude relative to Tibet is critical in determining the stepwise transitions in East Asian rainfall seasons. In support of this linkage, we show from observational data that the interannual co-variation of June (July August) rainfall and upper tropospheric zonal winds show properties consistent with an altered timing of the transition to the Meiyu (Summer), and with more northwardshifted westerlies for earlier transitions.We similarly suggest that East Asian paleoclimate changes resulted from an altered timing in the northward evolution of the jet and hence the seasonal transitions, in particular the transition of the jet from south of the Plateau to the north that determines the seasonal transition from Spring rains to the Meiyu. In an extreme scenario which we speculate the climate system tended towards during stadial (cold) phases of D/O stadials and periods of low Northern Hemisphere summer insolation the jet does not jump north of the Plateau, essentially keeping East Asia in prolonged Spring conditions.We argue that this hypothesis provides a viable explanation for a key paleoproxy signature of D/O stadials over East Asia, namely the heavier mean delta O-18 of precipitation as recorded in speleothem records. The southward jet position prevents the low-level monsoonal flow which is isotopically light from penetrating into the interior of East Asia; as such, precipitation there will be heavier, consistent with speleothem records. This hypothesis can also explain other key evidences of East Asian paleoclimate changes, in particular the occurrence of dusty conditions during North Atlantic stadials, and the southward migration of the Holocene optimal rainfall. (C) 2014 Elsevier Ltd. All rights reserved.