Abstract
Abstract. The monsoon system and westerly circulation, to which climate change responds differently, are two important components of global atmospheric circulation interacting with each other in the middle to low latitudes. Relevant research on global millennial-scale climate change in monsoon and westerly regions is mostly devoted to multi-proxy analyses of lakes, stalagmites, ice cores, and marine and eolian sediments. Different responses from these proxies to long-term environmental change make understanding climate change patterns in monsoon and westerly regions difficult. Accordingly, we disaggregated global closed basins into areas governed by monsoon and westerly winds, unified paleoclimate indicators, and added lake models and paleoclimate simulations to emphatically track millennial-scale evolution characteristics and mechanisms of East Asian summer monsoon and westerly winds since the Last Glacial Maximum (LGM). Our results reveal that millennial-scale water balance change exhibits an obvious boundary between global monsoon and westerly regions in closed basins, particularly in the Northern Hemisphere. The effective moisture in most closed basins of the midlatitude Northern Hemisphere mainly exhibits a decreasing trend since the LGM, while that of the low latitudes shows an increasing trend. In the monsoon-dominated closed basins of Asia, a humid climate prevails in the early to mid-Holocene, and a relatively dry climate appears in the LGM and late Holocene. In the westerly-wind-dominated closed basins of Asia, the climate is characterized by a humid LGM and mid-Holocene (MH) compared with the dry early and late Holocene, which is likely to be connected to precipitation brought by the westerly circulation. This study provides insight into the long-term evolution and synergy of westerly winds and monsoon systems as well as a basis for the projection of future hydrological balance.
Highlights
As important components of atmospheric circulation systems, the midlatitude westerly winds and low-latitude monsoon systems play key roles in global climate change
According to the climate records, we comprehensively considered the determinants that have controlled the trend of climate change in the Northern Hemisphere westerlies and East Asian summer monsoon regions since the Last Glacial Maximum (LGM)
The PI period, which is considered a typical period of the late Holocene, is mainly used to measure the changes in hydroclimate conditions during the LGM and MH periods relative to the late Holocene, as well as verify the feasibility of the lake models by comparing the lake-level simulations with the lake status records among the three periods
Summary
As important components of atmospheric circulation systems, the midlatitude westerly winds and low-latitude monsoon systems play key roles in global climate change. Closed basins with a relatively independent hydrological cycle system have plenty of terminal lake records that provide more evidence for retrospecting climate change (Li et al, 2017), and these can be regarded as ideal regions to study the spatiotemporal difference between monsoons and westerly winds. By constructing virtual lake systems, here we applied lake models and a transient climate evolution model to continuously simulate water balance change since the LGM in global closed basins. In the midlatitude closed basins of the Northern Hemisphere, the good match between a water balance simulation and a reconstructed moisture index from 27 paleoclimate records verifies the reliability of the simulation results. We disaggregated the Northern Hemisphere midlatitude closed basins into areas dominated by monsoons and westerly winds and emphatically explored the temporal evolution of the East Asian summer monsoon and westerly winds since the LGM. This study reveals millennial-scale climate change from the perspective of water balance, and provides a new method for studying the synergy of the westerly winds and monsoons
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