Evolution of the Indo-Pacific warm pool and Hadley-Walker circulation since the last deglaciation
Gagan, MK; Thompson, LG
发表期刊Hadley Circulation: Present, Past and Future
摘要The Indo-Pacific warm pool (IPWP), East Pacific cold tongue, and deep overturning atmospheric Hadley (meridional) and Walker (zonal) circulations form a tightly coupled system. In this chapter, we explore the concept of the Hadley circulation as the fundamental driver of changes in this system, and examine its possible impact on global climates of the past. Recent modeling studies indicate that the Hadley circulation is sensitive to Milankovitch forcing, dominated by the precession cycle (22,000 years) in the tropics. It is well established that the increasing Northern Hemisphere summer insolation during the post-glacial transition enhanced nor-them summer monsoon rainfall, particularly across the Asian landmass. Based on the results of modeling studies, it is probable that the northward asymmetry in tropical beating led to asymmetrical intensification of the Hadley circulation during the early Holocene. The response of the tropical ocean to the intensification of the Hadley circulation is given by foraminiferal Mg/Ca and coral Sr/Ca sea surface temperature (SST) reconstructions, which show that ocean-atmosphere feedbacks drove the tropical Pacific into a westward-concentrated La Nina-like state (warming in the west, cooling in the east) between similar to 11,000 and similar to 4,000 years ago. At the same time, air temperatures reconstructed from Southern Hemisphere high-altitude tropical ice cores also equal or exceed late Holocene values. The widespread warming of the tropical middle troposphere during the early Holocene suggests that the additional flux of water vapor and heat from the warmer IPWP during the La Nina state overwhelmed any atmospheric cooling brought about by the expansion of the East Pacific cold tongue. However, the expanded cold tongue area could also play a role in the early Holocene warming through enhanced Taken together, the paleoclimate records indicate that a post-glacial strengthening of the Hadley circulation initiated ocean-atmosphere feedbacks that altered the energy budget of the tropics to amplify early Holocene warming. Synchronous warming of the Southern Hemisphere high latitudes, as indicated by Antarctic ice core records, may be the result of southward-directed dynamical heating produced by the asymmetrical Hadley circulation. The demise of the early Holocene warming in the tropics and Southern Hemisphere similar to 4,000 through 7,000 years ago correlates with decreasing Northern Hemisphere summer insolation, a southward migration of the Intertropical Convergence Zone (ITCZ), and the onset of modem El Nino/Southern Oscillation (ENSO) variability.
部门归属Australian Natl Univ, Res Sch Earth Sci, Canberra, ACT 0200, Australia
学科领域Environmental Sciences
GB/T 7714
Gagan, MK,Thompson, LG. Evolution of the Indo-Pacific warm pool and Hadley-Walker circulation since the last deglaciation[J]. Hadley Circulation: Present, Past and Future,2004,21:289-312.
APA Gagan, MK,&Thompson, LG.(2004).Evolution of the Indo-Pacific warm pool and Hadley-Walker circulation since the last deglaciation.Hadley Circulation: Present, Past and Future,21,289-312.
MLA Gagan, MK,et al."Evolution of the Indo-Pacific warm pool and Hadley-Walker circulation since the last deglaciation".Hadley Circulation: Present, Past and Future 21(2004):289-312.
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