SIMULATION OF THE TIME-TRANSGRESSIVE NATURE OF EAST ASIAN SUMMER MONSOON PRECIPITATION OVER THE HOLOCENE
East Asian Summer monsoon(EASM),an integral part of the global monsoon circulation system,plays a pivotal role in maintaining regional and global water vapor,heat and momentum transport.Geological records and numerical models have provided insights into the intricate evolution of the EASM during the Holocene.However,it is worth emphasizing that these studies exhibited considerable discrepancies,particularly concerning the"time-transgressive"feature of Holocene EASM precipitation,i.e.,whether the precipitation maxima occurred synchronously across East Asia.By combining reconstruction and simulation approaches,we can gain a profound understanding of the characteristics of paleoclimate change in East Asia.This not only contributes to unraveling the mechanisms governing the East Asian monsoon under natural conditions,but also offers valuable insights into the impact of human activities on climate.In this study,based on a set of full-forcing and single-forcing experiments of Transient Climate Evolution simulations over the last 21000 years(TraCE-21 ka),we investigated the timing of summer precipitation maxima during the Holocene for the regions selected from Northern China(42°N,125°E),Jianghuai Region(30°N,120°E)and Southern China(22°N,115°E).In the full-forcing simulation,the timing of the EASM precipitation maxima and net precipitation maxima during the Holocene initially manifested in North China in the Early Holocene and gradually shifted southwards,eventually reaching South China in the Late Holocene,which aligned with the gradual weakening of the EASM during the Holocene.This receding trend is also confirmed by the East Asian summer monsoon index(EASMI),defined by regional averaged 850 hPa meridional wind between 25° and 40° N,105° and 120° E from June to August.These simulated results are supported by proxy data in Eastern China.For instance,the weakening of precipitation during the Holocene is evident in the lake level records of Northern China.Additionally,the pollen records in southern China suggested a gradual warming and wetter climate.Sensitive experiments further revealed that such EASM evolution was primarily driven by the land-sea thermal contrast variations(refer to the temperature and sea level pressure between the East Asian(20°～60° N,80°～120° E)and the Pacific Ocean(20°～60°N,150°～210°E)),which,in turn,was linked to the reduced boreal summer insolation controlled by changes in Earth's orbital parameters.Furthermore,we employed a simplified moisture budget equation to access the relative contributions of the dynamics(e.g.,the circulation changes)and thermodynamic(e.g.,humidity changes)components to the Holocene EASM precipitation variation.The results indicated that the precipitation changes in northern East Asia were mainly controlled by the dynamical components throughout the Holocene,with the thermodynamic component making a negative contribution in the Early Holocene,and almost negligible impact in the Late Holocene.In Southern China,the dynamical component remained dominant,and the thermodynamic component played a certain contribution.
HoloceneEast Asian summer monsoon precipitation"time-transgressive"nature
万方数据
维普
