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.     

青藏高原积雪异常对亚洲夏季风气候的影响

为了研究青藏高原积雪异常对亚洲夏季风气候的影响,从季风环流和季风降水等方面综合分析了高原积雪异常对气候的影响,并利用IAP 9L AGCM模式,对高原雪量进行了增加和减少的数值试验。从而提出高原多(少)雪年南亚夏季风偏弱(强),东亚夏季风反而偏强(弱)的新观点。高原积雪异常会导致高原上空大气垂直运动的扰动,扰动传播到下游致使我国长江流域和西太副高所在区域大气对流运动发生变化。高原多(少)雪,夏季我国南方的偏南风增强(减弱),有利于水汽从孟加拉湾和南海向我国大陆输送,但到长江流域时,由于偏南风存在较强(弱)的辐合,江淮流域偏涝(旱)。     

Reconstructed changes in Arctic sea ice over the past 1,450 years

Arctic sea ice extent is now more than two million square kilometres less than it was in the late twentieth century, with important consequences for the climate, the ocean and traditional lifestyles in the Arctic. Although observations show a more or less continuous decline for the past four or five decades, there are few long-term records with which to assess natural sea ice variability. Until now, the question of whether or not current trends are potentially anomalous has therefore remained unanswerable. Here we use a network of high-resolution terrestrial proxies from the circum-Arctic region to reconstruct past extents of summer sea ice, and show that-although extensive uncertainties remain, especially before the sixteenth century-both the duration and magnitude of the current decline in sea ice seem to be unprecedented for the past 1,450 years. Enhanced advection of warm Atlantic water to the Arctic seems to be the main factor driving the decline of sea ice extent on multidecadal timescales, and may result from nonlinear feedbacks between sea ice and the Atlantic meridional overturning circulation. These results reinforce the assertion that sea ice is an active component of Arctic climate variability and that the recent decrease in summer Arctic sea ice is consistent with anthropogenically forced warming.     

Global and China temperature changes associated with the inter-decadal variations of East Asian summer monsoon advances

The modern atmospheric observation and literatural historical drought-flood records were used to extract the inter-decadal signals of dry-wet modes in eastern China and reveal the possible relationship of global and China temperature changes associated with the East Asian summer monsoon advances.A climate pattern of wet-north and dry-south in eastern China and cool period in China and globe are associated with the strong summer monsoon that can advance further to the northernmost part in the East Asian monsoon region.On the contrary,a climate pattern of dry-north and wet-south in eastern China and a warm period in China and globe are associated with the weaker summer monsoon that only reaches the southern part in the region.An interdecadal oscillation with the timescale about 60 years was found dominating in both the dry-wet mode index series of the East Asian summer monsoon and the global temperature series after the secular climate states and long-term trend over inter-centennial timescales have been removed.     

High-resolution multi-proxy records of Asian monsoon activities from terrestrial sediments over the last 75,000 years

Our research group have investigated chronology and sedimentology of terrestrial sediments including loess-paleosols sediments over the last 75 ka at Lanzhou, northwestern China, and over the last 45ka at Tokyo, central Japan. Based on chronology of high resolution dating of ESR, TL, and IRSL and tephrochronology in these sediments, we investigated to reconstruct activities of Asian summer and winter paleomonsoons by using magnetic susceptibility, color reflectance and eolian dust concentrations over the last 75ka. Relations between standard curves of delta ~(18)O in GISP2 and color reflectance in loess-paleosol sediments of Linxia over last 140 ka shows that color reflectances are good proxy records indicating Asian summer paleomonsoon activity in time and are closely related to standard curve of delta ~(18)O in GRIP since the last interglacial. Also, relations between standard curve of delta ~(18)O in GISP2 and eolian dust concentrations over the last 75 ka at Lanzhou shows the Asian winter paleomonsoon activities have coincided with climatic changes in North Atlantic by GISP2 ice cores, and suggests that response of winter monsoon was rapid in global cooling stages, but slow in warming stage. Other results of our research in terrestrial sediments show as follows; 1) Horizons of Heinrich events from H1 to H4 in loess-paleosol sequences at Lanzhou. 2) Magnetic susceptibility and MS frequency dependent are possible to be available as proxy records for pedogenesis of tile Kanto Loam in Japan. 3) 8.2ka cooling event was recognized in Holocene loess-paleosol sequences at Lanzhou.     

Insolation-driven changes in atmospheric circulation over the past 116,000 years in subtropical Brazil

During the last glacial period, large millennial-scale temperature oscillations--the 'Dansgaard/Oeschger' cycles--were the primary climate signal in Northern Hemisphere climate archives from the high latitudes to the tropics. But whether the influence of these abrupt climate changes extended to the tropical and subtropical Southern Hemisphere, where changes in insolation are thought to be the main direct forcing of climate, has remained unclear. Here we present a high-resolution oxygen isotope record of a U/Th-dated stalagmite from subtropical southern Brazil, covering the past 116,200 years. The oxygen isotope signature varies with shifts in the source region and amount of rainfall in the area, and hence records changes in atmospheric circulation and convective intensity over South America. We find that these variations in rainfall source and amount are primarily driven by summer solar radiation, which is controlled by the Earth's precessional cycle. The Dansgaard/Oeschger cycles can be detected in our record and therefore we confirm that they also affect the tropical hydrological cycle, but that in southern subtropical Brazil, millennial-scale climate changes are not as dominant as they are in the Northern Hemisphere.     

Short-term climatic impacts of afforestation in the East Asian monsoon region

The influence of changes in vegetation cover on short-term climate over the East Asian monsoon region is simulated using the Community Climate System Model Version 3.5.The results show the annual mean surface air temperature significantly decreases by 0.93°C in response to afforestation over the East Asian monsoon region.Also,surface air temperature decreases by 1.46 and 0.40°C in summer and winter,respectively.The cooling is caused by enhanced evapotranspiration(ET) produced by increased forest cover.Evapotranspiration is greater in summer than in winter,so summer cooling is greater than winter cooling.The annual mean precipitation increases in response to afforestation,with a maximum of 7% in April.Water vapor increases significantly because of greater latent heat flux release.Meanwhile,afforestation leads to higher surface roughness,which decreases surface wind speed and induces an ascending air motion.These factors can produce more clouds and precipitation.Moreover,the surface albedo and the reflective solar radiation are reduced in response to afforestation.     

近30年海南岛橡胶林时空变化分析

【目的】 海南岛为中国第二大植胶区和仅有的两大热区之一,揭示其橡胶林的时空变化规律,对促进我国天然橡胶产业可持续发展有重要意义。【方法】 在Google Earth Engine(GEE)云计算平台上结合Landsat和Sentinel-2系列时间序列影像和橡胶林物候等信息,以5 a为步长提取了海南岛1990—2020年间7期橡胶林分布图,分析了海南岛橡胶林的时空变化规律。【结果】 ①近30年橡胶林面积增长趋势明显,从1990年的34.44万hm²增长至2020年的58.58万hm²,净增70.11%,且整体上呈现 “北增南减”的空间变化趋势;②在市/县尺度,橡胶林面积最大的主要市/县依次是儋州市、白沙县、澄迈县和琼中县,2020年占全岛橡胶林总面积的51.58%,而三亚市、东方市、文昌市及陵水县的橡胶林面积相对较小,2020年橡胶林总面积占比为5.22%;③近30年来,海南岛91.24%的橡胶林都种植在海拔300 m以下地区,97.75%种植地在25°坡度以下,海拔600 m以上几乎没有橡胶林分布,在海拔50~200 m和坡度0~5°的区域橡胶林增长幅度最大;④海南四大国家级自然保护区的实验区或缓冲区内均有少量橡胶林分布,但面积在逐渐下降。其中,霸王岭保护区内橡胶林面积最大,五指山保护区内面积最小,近30年四大保护区内橡胶林面积累计减少了68.02%,保护效果显著。虽然研究期海南岛的橡胶林面积增长非常显著,但集中在低海拔和相对平缓的区域,没有对位于中高海拔地区的热带雨林造成影响;四大国家级自然保护区内虽均有少量橡胶林分布,但递减趋势明显。【结论】 总体而言,海南橡胶林的发展模式良好,没有以牺牲大量热带森林为代价,尚未对当地的生态环境造成严重影响。     

Influence of the intertropical convergence zone on the East Asian monsoon

The Asian-Australian monsoon is an important component of the Earth's climate system that influences the societal and economic activity of roughly half the world's population. The past strength of the rain-bearing East Asian summer monsoon can be reconstructed with archives such as cave deposits, but the winter monsoon has no such signature in the hydrological cycle and has thus proved difficult to reconstruct. Here we present high-resolution records of the magnetic properties and the titanium content of the sediments of Lake Huguang Maar in coastal southeast China over the past 16,000 years, which we use as proxies for the strength of the winter monsoon winds. We find evidence for stronger winter monsoon winds before the B?lling-Aller?d warming, during the Younger Dryas episode and during the middle and late Holocene, when cave stalagmites suggest weaker summer monsoons. We conclude that this anticorrelation is best explained by migrations in the intertropical convergence zone. Similar migrations of the intertropical convergence zone have been observed in Central America for the period ad 700 to 900 (refs 4-6), suggesting global climatic changes at that time. From the coincidence in timing, we suggest that these migrations in the tropical rain belt could have contributed to the declines of both the Tang dynasty in China and the Classic Maya in Central America.     

The East Asian winter monsoon: re-amplification in the mid-2000s

Based on several reanalysis and observational datasets,this study demonstrates that the East Asian winter monsoon(EAWM)recovered from its weak epoch and reamplified in the mid-2000s.Accordingly,East Asia has experienced more cold winters and significant negative surface air temperature anomalies during the recent strong EAWM epoch spanning the period 2004–2012.The associated cooling was mainly located over inland northern East Asia with a west–east orientation.The cooling generally coincided with negative winter temperature trends in eastern Eurasia in the last two decades,possibly contributing to the observed regional cooling trend when the global mean temperature is still trending up.Enhanced wintertime blocking activity around the Ural mountain region and diminished Arctic sea ice concentration in the previous September are suggested to be the responsible internal atmospheric process and external driver for the recent re-amplification of the EAWM,respectively.     

Anomalous activity of East Asian winter monsoon and the tropical Pacific SSTA

The relationship between the anomalous East Asian winter monsoon (EAWM) activity and the tropical Pacific SST anomalies has been identified using the results of 40-year integration of the IAP CGCM1 model and 10-year observational data. In the strong EAWM year, the western and central Pacific are dominated by positive SST anomalies while the eastern Pacific is negative ones. In the weak EAWM year, the SSTA pattern is quite different and shows El Nino-like SST anomalies. The strong EAWM activity tends to create extra easterly flow to the east and extra westerly flow to the west of the warm SSTA region over the equatorial western and central Pacific, thus leading to the enhancement of convergence and convection of the flow in this region and favorable to the maintenance and development of such an SSTA pattern. On the other hand, the warm SST anomaly over the western and central Pacific, as a forcing, may lead to a specific pattern of the northern extratropical atmosphere, which is favorable to the strong EAWM activity. The tropical Pacific SSTA pattern related closely to the strong EAWM activity differs significantly from that of the La Nina year.     

Sensitivity experiments of impacts of large-scale urbanization in East China on East Asian winter monsoon

By using the global atmospheric general circulation model CAM4.0 including an urban canopy parameterization scheme,the possible impacts of large-scale urbanization in East China on East Asian winter monsoon was investigated via idealized numerical experiments.Results suggest that large-scale urbanization can cause a significant warming effect in both surface temperature and air temperature near the surface over most areas of East China.Meanwhile,large-scale urbanization also alters the surface energy balance,causing evident increases in net surface long-wave radiation and sensible heat flux as well as intensified surface thermal heating to the atmosphere.Forced by the surface thermal heating anomalies induced by the large-scale urban expansion,East Asian winter monsoon circulation exhibits distinct changes.Overall,the extensive urbanization over East China will weaken East Asian winter monsoon,but intensify winter monsoon in northeast China.     

The East Asian summer monsoon circulation anomaly index and its interannual variations

Based on the concept of East Asia-Pacific (EAP) teleconnection which influences East Asian summer monsoon, an index for East Asian summer monsoon circulation anomaly was defined and it was pointed out that this index can describle the interannual variation character of summer climate in East Asia, especially in the Yangtze River and Huaihe River Valley.     

Natural interdecadal weakening of East Asian summer monsoon in the late 20th century

Based on the reanalysis data throughout 1948-2002 as derived from the United States National Centers for Environmental Prediction and National Center for Atmospheric Research, it is revealed that East Asian summer monsoon （EASM） intensity weakens on an interdecadal timescale since the mid-1960s, and twice interdecadal jumps are recorded in the EASM intensity index series in the late 20th century, respectively occurring in the mid-1960s and mid- to late 1970s. Six globally coupled atmosphere-ocean models＇ outputs under the SRES A2 greenhouse gas and aerosol emission scenario, provided by the IPCC Data Distribution Center and the Hadley Center for Climate Prediction and Research, are then systematically examined. It follows that the above EASM weakening is not closely related to synchro- nizing anthropogenic global warming, and, therefore, it should be qualitatively natural change process. Over the 21st century, the EASM intensity is likely increased slightly by continually intensified greenhouse effect relative to the late 20th century.     

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.     

Southern Hemisphere mean zonal wind in upper troposphere and East Asian summer monsoon circulation

1 Introduction Variability of the East Asian summer monsoon (EASM) has been detected by considering roles of El Nino and Southern Oscillation (ENSO) cycle, snow cover over Eurasia and Tibetan Plateau, and signals from the soil (namely, the soil temperatur…     

锶同位素研究在古季风演化研究中的应用研究

自从Rb—Sr同位素体系被应用于地质年龄以来，随着Rb—Sr同位素地球化学理论和测试分析技术的逐步发展和完善，其应用越来越广泛。主要介绍了锶同位素的基本地球化学特征，分析了锶同位素研究进行全球对比的可能性，探讨了锶同位素研究在我国黄土季风演化研究中的应用。众多研究显示Rb／Sr和^87Sr／^86Sr的比值变化受控于风化成壤作用的强弱，与降雨量、磁化率变化有很好的线性相关关系。通过曲线的分析、对比发现Rb／Sr和^87Sr／^86Sr曲线所蕴含的气候信息比磁化率曲线更为丰富和详细，与SPECMAP δ^18O曲线具有同步变化特征和更好的对应关系。这些研究表明Rb／Sr和^87Sr／^86Sr比值极可能是一种东亚夏季风演化更为灵敏的替代性指标，在古气候重建中有着广阔的应用前景。     

锶同位素研究在古季风演化研究中的应用研究

自从Rb-Sr同位素体系被应用于地质年龄以来,随着Rb-Sr同位素地球化学理论和测试分析技术的逐步发展和完善,其应用越来越广泛。主要介绍了锶同位素的基本地球化学特征,分析了锶同位素研究进行全球对比的可能性,探讨了锶同位素研究在我国黄土季风演化研究中的应用。众多研究显示Rb/Sr和87Sr/86Sr的比值变化受控于风化成壤作用的强弱,与降雨量、磁化率变化有很好的线性相关关系。通过曲线的分析、对比发现Rb/Sr和87Sr/86Sr曲线所蕴含的气候信息比磁化率曲线更为丰富和详细,与SPECMAP     

Weakening relationship between East Asian winter monsoon and ENSO after mid-1970s

The East Asian winter monsoon(EAWM) is characterized by the frequent cold surges and associated closely with the Siberia High,East Asian Trough,and high-level westerly jet stream.The ENSO cycle can modulate the EAWM since it has co-variability with the sea surface temperature over the Indo-Western-Pacific which can tune the land-sea thermal contrast for the EAWM.This paper,by analyzing the EAWM,ENSO,and associated atmosphere-ocean variability,documents the weakening of the EAWMENSO relationship after the 1970s.The significant out-of-phase inter-relationship is found to be diminished after the 1970s.Further study in this work suggests that the weakened co-variability of the tropical Indo-Western-Pacific climate associated with ENSO after the 1970s is partly responsible for the weakened inter-relationship.Meanwhile,the reduced EAWM interannual variability and northward retreat of the EAWM-associated climate variability are favorable to the weakened ENSO-EAWM connection.