Characteristics of decadal-centennial-scale changes in East Asian summer monsoon circulation and precipitation during the Medieval Warm Period and Little Ice Age and in the present day

Using meteorological observations, proxies of precipitation and temperature, and climate simulation outputs, we synthetically analyzed the regularities of decadal-centennial-scale changes in the summer thermal contrast between land and ocean and summer precipitation over the East Asian monsoon region during the past millennium; compared the basic characteristics of the East Asian summer monsoon (EASM) circulation and precipitation in the present day, the Little Ice Age (LIA) and the Medieval Warm Period (MWP); and explored their links with solar irradiance and global climate change. The results indicate that over the last 150 years, the EASM circulation and precipitation, indicated by the temperature contrast between the East Asian mainland and adjacent oceans, had a significant decadal perturbation and have been weaker during the period of rapid global warming over the past 50 years. On the centennial time scale, the EASM in the MWP was strongest over the past 1000 years. Over the past 1000 years, the EASM was weakest in 1450?C1570. When the EASM circulation was weaker, the monsoon rain belt over eastern China was generally located more southward, with there being less precipitation in North China and more precipitation in the Yangtze River valley; therefore, there was an anomalous pattern of southern flood/northern drought. From the 1900s to 1920s, precipitation had a pattern opposite to that of the southern flood/northern drought, with there being less precipitation in the Yangtze River valley and more precipitation in North China. Compared with the case for the MWP, there was a longer-time-scale southern flood/northern drought phenomenon in 1400?C1600. Moreover, the EASM circulation and precipitation did not synchronously vary with the trend of global temperature. During the last 150 years, although the annual mean surface temperature around the world and in China has increased, the EASM circulation and precipitation did not have strengthening or weakening trends. Over the past 1000 years, the weakest EASM occurred ahead of the lowest Northern Hemispheric temperature and corresponded to the weakest solar irradiance.     

Asian-Pacific Oscillation index and variation of East Asian summer monsoon over the past millennium

To study the long-term variation of the East Asian summer monsoon （EASM）, the Asian-Pacific Oscillation index （IAPO）, representing a zonal thermal contrast between Asia and the North Pacific, is reconstructed over the past millennium. During the Little Ice Age （LIA）, the variability of the reconstructed IAPO is closely linked to dry-wet anomalies in eastern China on the centennial scale. This correlation pattern is consistent with the observation during the current period, which suggests that the reconstructed IAPO may generally represent the centennial-scale variation of the EASM and rainfall anomalies over eastern China during the LIA.     

Simulated analysis of summer climate on centennial time scale in eastern China during the last millennium

Using Lanczos filtered simulation results from the ECHO-G coupled ocean-atmosphere model, this study analyzes the spatiotemporal structure of temperature and precipitation on centennial time scale to examine how climate change in eastern China responded to external forcing during the last millennium. The conclusions are (1) eastern China experienced a warm-cold-warm climate transition, and the transition from the warm period to the cold period was slower than the cold to warm transition which followed it. There was more rainfall in the warm periods, and the transitional peak and valley of precipitation lag those of temperature. The effective solar radiation and solar irradiance have significant impacts on the temporal variation of both temperature and precipitation. Volcanic activity plays an important role in the sudden drop of temperature before the Present Warm Period (PWP). There is a positive correlation between precipitation and volcanic activity before 1400 A.D., and a negative relationship between the two thereafter. The concentration of greenhouse gases increases in the PWP, and the temperature and precipitation increase accordingly. (2) The spatial pattern of the first leading empirical orthogonal function (EOF) mode of temperature on centennial time scale is consistent with that on the inter-annual/inter-decadal (IA-ID) time scales; namely, the entirety of eastern China is of the same sign. This pattern has good coherence with effective solar radiation and the concentrations of greenhouse gases. The first leading EOF mode of precipitation on centennial time scale is totally different from that on the IA-ID time scales. The first leading mode of centennial time scale changes consistently over the entirety of eastern China, while the middle and lower reaches of the Yangtze and Yellow Rivers are the opposite to the rest of eastern China is the leading spatial pattern on IA-ID time scale. The distribution of precipitation on centennial time scale is affected by solar irradiance and greenhouse gas concentrations.     

Events of abrupt change of Indian monsoon recorded in Dasuopu ice core from Himalayas

Three ice cores distributed across Dasuopu glacier in Himalayas were recovered. A 400-year net annual accumulation record reconstructed from one of the cores reflects the major precipitation trend in the central Himalayas. This record is related closely to the Indian monsoon precipitation. Wavelet and moving T-test were applied to the 400-year-long Dasuopu accumulation record, and significant staggered variability and abrupt change of the record on interannual to centennial time scales are identified. Finally the possible reason for abrupt change of the accumulation record is discussed.     

Imprint of solar activity on Nanjing stalagmite annual layer thickness sequence during the Last Glacial Maximum

PREVIOUS STUDIES ON ANNUAL GROWTH LAMINAE IN STA-LAGMITES SUGGESTED THAT IT IS A USEFUL PROXY TO INVESTI-GATE ANNUALLY HIGH-RESOLUTION CLIMATES[1―4].THE VARIA-TION OF ANNUAL LAMINAE THICKNESS HAS BEEN EXPLAINED AS REFLECTING SEASONAL CHANGES EITHER IN DR…     

A comparison of the Medieval Warm Period, Little Ice Age and 20th century warming simulated by the FGOALS climate system model

To compare differences among the Medieval Warm Period (MWP), Little Ice Age (LIA), and 20th century global warming (20CW), six sets of transient and equilibrium simulations were generated using the climate system model FGOALS_gl. This model was developed by the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences. The results indicate that MWP warming is evident on a global scale, except for at mid-latitudes of the North Pacific. However, the magnitude of the warming is weaker than that in the 20th century. The warming in the high latitudes of the Northern Hemisphere is stronger than that in the Southern Hemisphere. The LIA cooling is also evident on a global scale, with a strong cooling over the high Eurasian continent, while the cooling center is over the Arctic domain. Both the MWP and the 20CW experiments exhibit the strongest warming anomalies in the middle troposphere around 200?C300 hPa, but the cooling center of the LIA experiment is seen in the polar surface of the Northern Hemisphere. A comparison of model simulation against the reconstruction indicates that model??s performance in simulating the surface air temperature changes during the warm periods is better than that during the cold periods. The consistencies between model and reconstruction in lower latitudes are better than those in high latitudes. Comparison of the inter-annual variability mode of East Asian summer monsoon (EASM) rainfall during the MWP, LIA and 20CW reveals a similar rainfall anomalies pattern. However, the time spectra of the principal component during the three typical periods of the last millennium are different, and the quasi-biannual oscillation is more evident during the two warm periods. At a centennial time scale, the external mode of the EASM variability driven by the changes of effective solar radiation is determined by the changes of large scale land-sea thermal contrast. The rainfall anomalies over the east of 110°E exhibit a meridional homogeneous change pattern, which is different from the meridional out-of-phase change of rainfall anomalies associated with the internal mode.     

Reconstructed index of summer monsoon dry-wet modes in East Asia for the last millennium

Monthly precipitation datasets collected at 160 stations in China as well as the monthly winds and humidity data derived from the US National Centers for Environmental Prediction (NCEP) were used to construct the relationship between six summer dry-wet modes in eastern China and the summer monsoon airflow northward advance in East Asia. A millennial series of the monsoon dry-wet index (MDWI) was reconstructed based on Wang??s six summer dry-wet modes in eastern China since 950 AD. A high (low) index indicates that the strong (weak) East Asian summer monsoon airflow can reach northern (southern) China and cause above (below) normal precipitation. Interdecadal periodic variations, such as the approximate 70-year oscillation, can be found in the MDWI series. In the last millennium, northern China has experienced persistent decadal wet periods and persistent decadal dry periods. At present, the MDWI is a low period on the interdecadal time scale so above-normal precipitation is observed in southern China and below-normal precipitation in northern China.     

Solar forced transient evolution of Pacific upper water thermal structure during the Holocene in an earth system model of intermediate complexity

Forced by transient solar activities since 7 ka,the thermal structures of the Pacific upper water at boreal winter are featured by an enhanced response of 3-dimensional Western Pacific Warm Pool(WPWP) in an Earth system model of Intermediate Complexity at centennial scales.During solar maximum periods,the magnitude of surface ocean temperature variations is 30% larger in the western tropical Pacific than in the Ni o3 region,while at subsurface,it is 40% larger in the subtropical North Pacific than in the western Equatorial Pacific.They compromise stronger zonal and meridional thermal gradients in surface and subsurface Pacific respectively which are both linearly responded to solar forcing at centennial periods.The surface gradient is most sensitive at 208-year period while the subsurface gradient shows more significance at periods longer than 208-year.Also noteworthy are two differences:(1) the phase lags at these periods of surface gradient are slightly smaller than that of subsurface;(2) the 148-year and 102-year periods in surface gradient are lost in subsurface gradient.These modeled features preliminary confirm the centennial fluctuations of WPWP in paleo-proxies and a potential solar forcing during the Holocene.     

Decadal change of the East Asian summer monsoon and its related surface temperature in Asia-Pacific during 1880–2004

The East Asian summer monsoon （EASM） and its related change of surface temperature in the past century were not clearly ad- dressed due to absence of atmospheric reanalysis data before 1948. On the benchmark of station-observed sea level pressure （SLP） in China, we utilized multiple SLP datasets and evaluated their qualities in measuring the SLP-based EASM index （EASMI）. It is found that the EASMI based on the SLP of the Hadley center version 2 （HadSLP2） has shown the best performance on the inter- annual and decadal time scales. Instead of showing a linear weakening trend pointed out by the previous study, the EASMI has likely exhibited the decadal variability, characterized by weakened trends during 1880-1906, 1921-1936, and 1960-2004, and with enhanced trends during 1906-1921 and 1936-1960, respectively. Corresponding to the weakened and enhanced periods of EASMI since the 1920s, the surface air temperature （SAT） index （SATI） averaged in eastern China has likely shown a warming and a cooling trend, respectively. However, the decadal abrupt transitions between the two indices do not occur concurrently, which results in a weak correlation between two indices on the decadal time scale. Further analysis indicates that there are four key regions where the SAT is significantly correlated with the EASMI, suggesting the joint impact of surface temperature in Asia-Pacific on the EASM during 1880-2004. In which, the decadal change of SAT near the Lake Baikal plays an important role in the linear trends of the EASM before and after 1960.     

How would global-mean temperature change in the 21st century?

The time series of HadCRUT3 global-mean surface air temperature (GSAT) anomaly, Pacific decadal oscillation (PDO) index, and the equatorial Pacific sea surface temperature (SST) were utilized, and their long-term trends and multiple time-scale periodic oscillations were explored in this study. A long-term trend with a warming rate about 0.44°C /century during 1850–2008, two cool floors occurred respectively around 1910 and during 1950–1970, and three warm flats happened in the 1870s, 1940s and since the year 1998 were found in the GSAT. In this duration, the variability of GSAT can be well reconstructed by the quasi-21-year, the quasi-65-year, and century-scale oscillations. The recent decadal warm flat is caused by their positive phase overlapping from these three oscillations. The maximum rising temperature reached 0.26°C was simulated in 2004 by the three oscillations. The quasi-21-year and the quasi-65-year oscillations were possibly caused by solar radiation and internal variability of the ocean-atmosphere system. Therefore, an outlook of GSAT for the 21st century was made based on the long-term trend and these three oscillations. It was expected that a cool floor and a warm flat of the GSAT would appear in the 2030s and 2060s, respectively. However, the highest warming range is predicted about 0.6°C, it is less than the threshold 2°C and IPCC projection.     

Effect of precession on the Asian summer monsoon evolution: A systematic review

Geological climatic records and model simulations on the Asian summer monsoon climate change induced by insolation forcing of the Earth＇s precession are systematically reviewed in this paper. The presentation of the questions on the mechanism of the Asian monsoon evolution at the precession band, currently existing debates and future research directions are discussed. Since the early 1980s, more and more observed evidence and simulated results, especially the absolute-dated stalagmite records and orbital-scale transient model runs in the last few years, have indicated that the quasi-20ka period in the Quaternary monsoon climate change is caused by precession. However, debates still exist on the dynamic mechanism how precession affects the Asian monsoon. The ＂zero phase＂ hypothesis says that the Asian monsoon is merely controlled by summer insolation in the Northern Hemisphere （NH） while the ＂latent heat＂ hypothesis emphasizes the dominant effect of latent heat transport from the Southern Hemisphere （SH） besides the role of the northern insolation. The two hypotheses have separately been supported by some evidence. Although we are cognizant of the importance of northern solar radiation and the remote effect of southern insolation, it has still a long way to go before comprehensively understanding the evolutionary mechanism of the Asian monsoon. In view of the problems existing in present researches of monsoon-dominated climate change at the precession scale, we propose that studies on the environmental significance of geological monsoon proxies, feedback processes in the long-term transient simulations and intercomparisons between observations and modeling results should be strengthened in the future.     

华北夏季降水年代际变化与东亚夏季风、大气环流异常

利用华北夏季降水资料和NCEP/NCAR再分析资料,对华北夏季降水、东亚夏季风年代际变化特征及大气环流异常进行研究,发现一些有意义的结果:华北夏季降水变化存在明显的8a、18a周期,东亚夏季风变化18a、28a周期性比较明显,二者年代际变化特征明显,但华北夏季降水变化和东亚夏季风变化的周期不完全一致.华北夏季降水量变化在60年代中期发生了突变,东亚夏季风变化在70年代中期发生了突变.华北夏季降水与东亚夏季风变化存在很好的相关关系,强夏季风年,华北夏季降水一般偏多,弱夏季风年,华北夏季降水一般偏少,但又不完全一致.东亚夏季风减弱是造成华北夏季降水减少的一个重要因素,但不是唯一因素,华北夏季降水减少还与环流异常密切相关.在地面上,青臧高原地区、华北地区气温下降造成华北低压系统活动减少,不利于降水.在850 hPa层上,东亚中纬度的西南季风和副热带高压南部的偏东风、西北部的西南风异常减弱,使得西南气流输送水汽很多难以到达30°N以北的地区,而副热带高压西部外围偏东南、偏南气流输送到华北地区的水汽也大量减少,水汽不足造成华北夏季降水偏少.在500 hPa高度场上,80年代欧亚遥相关型表现与50年代相反,变为欧洲( )、乌拉尔山(-)、中亚( )形势,这种环流使得乌拉尔山高压脊减弱,贝加尔湖至青藏高原高空槽变浅,纬向环流表现突出,不利于冷暖空气南北交换.同时在500 hPa气温场上,80年代,西伯利亚至青藏高原西北部的冷槽明显东移南压到蒙古至华北地区,锋区位于华北以东以南位置,使得华北地区冷暖空气交汇减少,降水也因此减少.华北夏季降水减少是由于东亚夏季风减弱和大气环流异常造成的.     

Abrupt changes in the Asian southwest monsoon during the Holocene and their links to the North Atlantic Ocean

During the last ice age, the Indian Ocean southwest monsoon exhibited abrupt changes that were closely correlated with millennial-scale climate events in the North Atlantic region, suggesting a mechanistic link. In the Holocene epoch, which had a more stable climate, the amplitude of abrupt changes in North Atlantic climate was much smaller, and it has been unclear whether these changes are related to monsoon variability. Here we present a continuous record of centennial-scale monsoon variability throughout the Holocene from rapidly accumulating and minimally bioturbated sediments in the anoxic Arabian Sea. Our monsoon proxy record reveals several intervals of weak summer monsoon that coincide with cold periods documented in the North Atlantic region--including the most recent climate changes from the Medieval Warm Period to the Little Ice Age and then to the present. We therefore suggest that the link between North Atlantic climate and the Asian monsoon is a persistent aspect of global climate.     

Periodic oscillations in millennial global-mean temperature and their causes

Time series of solar radiation and north Pacific sea surface temperature (SST) index were used to analyze their causality relationship with various periodic oscillations in reconstructed millennial global-mean temperature series. The three long-term periods of the Medieval Warm Period (MWP), Little Ice Age (LIA) and recent Global Warming Period (GWP) were distinct in the temperature series. 21-year, 65-year, 115-year and 200-year oscillations were derived from the temperature series after removing three long-term climatic temperatures. The phases of temperature oscillations significantly lagged behind oceanic SST and solar radiation variability. The recent decadal warm period was caused by the quasi-21-year temperature oscillation. At this century-cross period, the four oscillations reached their peaks simultaneously, which did not occur during the last millennium. Based on the long-term trend during the GWP and the four periodic oscillations, global-mean temperature is expected to drop to a new cool period in the 2030s and then a rising trend would be towards to a new warm period in the 2060s.     

亚欧大陆经向热力差异对亚洲季风的影响Ⅰ:与东亚冬季风的关系

 通过对亚欧大陆不同季节热力变化的对比分析,发现亚欧大陆冬、春季有明显的经向热力差异,夏、秋季存在准纬向的热力差异.进一步分析还发现大陆冬季经向热力差异与东亚冬季风有很好的正相关关系,即热力差异指数越大(小),则东亚冬季风越强(弱);在经向热力异常发生的同时,洋面热力状况也显著不同,从而导致东亚地区不同区域间海陆热力对比发生变化,引起降水分布的不同.     

A signature of cosmic-ray increase in AD 774-775 from tree rings in Japan

Increases in (14)C concentrations in tree rings could be attributed to cosmic-ray events, as have increases in (10)Be and nitrate in ice cores. The record of the past 3,000 years in the IntCal09 data set, which is a time series at 5-year intervals describing the (14)C content of trees over a period of approximately 10,000 years, shows three periods during which (14)C increased at a rate greater than 3‰ over 10 years. Two of these periods have been measured at high time resolution, but neither showed increases on a timescale of about 1 year (refs 11 and 12). Here we report (14)C measurements in annual rings of Japanese cedar trees from ad 750 to ad 820 (the remaining period), with 1- and 2-year resolution. We find a rapid increase of about 12‰ in the (14)C content from ad 774 to 775, which is about 20 times larger than the change attributed to ordinary solar modulation. When averaged over 10 years, the data are consistent with the decadal IntCal (14)C data from North American and European trees. We argue that neither a solar flare nor a local supernova is likely to have been responsible.     

High resolution stalagmite δ18O records over the past 1000 years from Dongge Cave in Guizhou

Based on MC-ICP-MS U-series dating andstable O-isotope analysis results, a 4-5 years resolution monsoon record over the past 1000 years has been established for two stalagmites from Dongge Cave, Guizhou. The high resolution oxygen isotope record serves as a proxy for variations in rainfall of Asian southwest monsoon over the Yunnan-Guizhou Plateau. A close relation of the δ18O record with the A^14C record from tree rings largely reflects impact of centennial-scale solar activity on the monsoon climate changes. The conspicuous decrease in the δ18O value at AD 1720 indicates an abrupt increase in monsoon rainfall, suggesting that an atmospheric-oceanic couple over the tropical Indian Ocean plays an important role in rapid increase of the Northern Hemisphere temperature over the last century.     

High-resolution stalagmite δ 13C record of soil processes from southwestern China during the early MIS 3

Knowledge of the evolution of pedogenic processes in the carbonate area is important to understand the dynamics of rock desertification.A precisely-dated stalagmite δ13C record between 61.3 and 50.5 ka BP from southwestern China,potentially related to soil biogenic CO2 production,shifts within a narrow range between -9‰ and -7‰,and exhibits a prominent cycle of 350-470 a,independent of the Asian monsoon changes.This indicates that a threshold effect might control the amplitude of calcite δ13C variability,likely associated with the vertical soil loss in the carbonate area.The periodic δ13C changes reflect that the loss/recovery of soil cover can operate on centennial scale.Thus,the rock desertification in southwestern China might at least initiate 60 ka ago and should be of natural origin.     

Stalagmite-inferred Holocene precipitation in northern Guizhou Province,China, and asynchronous termination of the Climatic Optimum in the Asian monsoon territory

An absolute-dated, bi-decadal-resolution, stalagmite oxygen-isotopic time series from Shigao Cave reveals the evolution of summer monsoon precipitation over the past 9.9 ka BP in northern Guizhou Province, Southwest China. The  18O-inferred climate conditions are divisible into three distinct stages: (1) a maximum humid era from 9.9-6.6 ka BP; (2) a gradual declining precipitation interval between 6.6-1.6 ka BP; and (3) a relatively low precipitation time window after 1.6 ka BP. Consistency of contemporaneous stalagmite Holocene 18O records between Shigao and other caves in the Indian and East Asian monsoon realms support the effect of primary orbital solar forcings on monsoonal precipitation. However, statistical analysis shows a significant spatial asynchroneity of the Holocene Optimum termination in the Asian monsoon territory. The Holocene Optimum ended at 7.2-7.4 ka BP in Oman, located in the Indian monsoon region, and at 5.6-5.8 ka BP in Central China, in the East Asian monsoon zone. In Southwest China, the termination occurred between these periods, at 6.6-7.0 ka BP, and was influenced by both monsoon systems. We propose that this spatially asynchronous ending of Holocene Optimum in Asia may be attributed to sea surface temperature changes in the western tropical Pacific, which is a primary moisture source for the East Asian monsoon.     

Seasonal cycle of the zonal land-sea thermal contrast and East Asian subtropical monsoon circulation

Based on analysis of the climatic temperature latitudinal deviation on middle troposphere, its seasonal cycle suggests that due to the rapid warming from eastern China continent to the east of Tibetan Plateau and the heating of Tibetan Plateau in spring, seasonal transition of the thermal difference between East Asia continent and West Pacific first takes place in the subtropical region with greatest intensity. On the accompanying low troposphere, the prevailing wind turns from northerly in winter to southerly in summer with the convection precipitation occurring at the same time. This maybe indicates the onset of the East Asian subtropical summer monsoon. Consequently, we advice that the seasonal cycle formed by the zonal thermal contrast between Asian continent and West Pacific may be an independent driving force of East Asian subtropical monsoon.