Linear relationship between the interdecadal and interannual variabilities of North China rainfall in rainy season

Interdecadai and interannuai timescales are dominant in the North China rainfall in rainy season (July and August). On the interdecadai timescale, the North China rainfall exhibited an abrupt decrease at the end of 1970s. In this study, we examined the effect of this abrupt rainfall decrease on the association between rainfall and circulation on the interannuai timescale, and found that the interdecadal variation does not change the physical mechanism responsible for the interannuai variation of North China rainfall.There is a linear relationship between the interdecadai and interannuai variabilities of North China rainfall in rainy season.     

Rainfall spectrum change in North China and its possible mechanism

The seasonal distribution of the rainfall in North China has changed greatly since 1977, with more rainfall in spring and less in July, August, and September (JAS). Wavelet analysis showed that the JAS rainfall underwent an abrupt spectrum change in the mid-1960s. Its interannual variability has declined while the interdecadal component has become the dominant mode, associated with the dry climate. Correlation analysis found that the JAS rainfall is negatively correlated with the departures of the 500 hPa geopotential height significantly over the northwest and southwest of China, and positively correlated with the suer monsoon over eastern China. Therefore, the interdecadal ascending of the air pressure in northwestern China and the monsoon decaying over East Asia in the past 20 years may be the two major causes of North China drought.     

Interannual variation of North China rainfall in rainy season and SSTs in the equatorial eastern Pacific

The rainfall in North China during rainy season （July and August （JA）） exhibits a strong interannual variability. In this study, the atmospheric circulation and SST anomalies associated with the interannual variation of JA North China rainfall are examined. It is found that on the interannual timescale, the JA North China rainfall is associated with significant SST anomalies in the equatorial eastern Pacific, and the North China rainfall and SST anomaly in the equatorial eastern Pacific correspond to the similar variation of the upper-level westerly jet stream over East Asia. A possible mechanism is proposed for the influence of the SST anomalies in the equatorial eastern Pacific on the North China rainfall.     

Origin of summer monsoon rainfall identified by δ18O in precipitation

A negative correlation between δ^18O in monsoon precipitation and f, the ratio of precipitable water in monsoon region to that in water source area, is hypothesized. Using the Rayleigh model, a new method for identifying origin of summer monsoon rainfall is developed based on the hypothesis. In order to validate the method, the isotopic data at New Delhi, a typical station in the southwest monsoon region, and Hong Kong, a typical station in the southeast monsoon region, were collected and analyzed for case studies. The case studies indicate that the water source areas of the monsoon rairdall at the two stations identified by the method are accordant with the general atmosphere circulation patterns. The method developed in this paper is significantly important for tracing the origin of summer monsoon precipitation.     

华北地区1972年和1997年干旱特征及其影响系统分析

利用华北地区实测的月降水量资料,美国NCAR/NCEP 850 hPa的矢量风5、00 hPa和850 hPa的位势高度等再分析资料,分析了华北地区1972年和1997年这2个干旱年干旱的空间分布、强度分布和持续时间,以及西太平洋副热带高压变化、季风进退和欧亚大气环流异常情况.结果表明:1972年是季风正常年,但该年亚洲大陆高压偏强且持续存在、西太平洋副热带高压持续偏弱,导致了干旱的发生与持续;而1997年由于持续偏强的亚洲大陆高压、持续偏弱的季风和西太平洋副热带高压造成该地区严重干旱.     

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.     

叠加马尔可夫链模型在雨季强度指数预测中的应用

根据雨季降水过程中的不确定性和非精确性特点,用有序聚类法(即最优分割法)建立华北地区雨季强度指数的状态分类标准,并以1951~1994年华北地区雨季强度指数所处的状态为依据,用叠加马尔可夫链预测方法来预测1995年和1996年华北地区雨季强度指数所处的状态.结果表明,叠加马尔可夫链预测方法计算方便,结果准确,可为雨季强度指数状态预测分析提供一种新的途径.     

ENSO对东亚夏季风和我国夏季降水的影响研究进展

回顾了最近几年我国学者在ENSO对东亚夏季风和我国夏季降水影响方面的研究成果,通过夏季风时降水的影响分析ENSO对夏季降水的作用,结合1997-1998年的ENSO现象,对前人的理论和统计结果进行了讨论,指出除了ENSO发生的时间、区域、强度外,其增长和衰减率在这一问题的研究中也值得关注。     

Comparison of paleoclimatic characteristics between monsoon and westerly areas, China

For past decades there have been many studies on the climate features during the last interglacial and glacial periods. A comparison between the loess record of western China with that of monsoon areas shows some regional differences. ( i) Generally, the climate of the Yili region since the late Pleistocene was dry, with fluctuations. Late Pleistocene climate change in the study area can be divided into 5 stages, corresponding to 5 marine isotopic stages (MIS 1-MISS), (ii) Evidence from grain size composition, magnetic susceptibility, carbonate content, pollen assemblage and geochemistry shows that the climate during the last glacial period was instable. During MIS4 the westerly winds were strong and the humidity was relatively high. Compared with the early stage, MIS2 was dry. In MIS3, westerly winds were relatively weak; pedogenesis prevailed, forming paleo-sols. (iii) In contrast to the Loess Plateau the deposition rate of dust at the early stage was higher than at the late stage of the last galical in the Yili region. The strongest wind event occurred at about 24 kaBP instead of 18 kaBP. (iv) Variations in the grain size indicate that the westerly winds decreased since the deglaciation, but dust accumulation continued until the late Holocene. High carbonate contents, low ratio of Rb/Sr and lack of soil development imply that the climate was dry during the early and middle Holocene. Since the late Holocene the climate became relatively wet and the soil was developed.     

The onset and advance of the Asian summer monsoon

The transition from the winter monsoon to summer monsoon is characterized by the abrupt change of the atmospheric circulation. Although many studies on the intraseasonal variation of the Asian summer monsoon (ASM) have been made, there are controversial v…     

Synoptic-scale variation of δ18O in summer monsoon rainfall at Lijiang, China

Based on the daily δ~(18)O data in June―September 2003 at Lijiang and the daily mean NCEP/ NCAR reanalysis data, synoptic-scale variation of δ~(18)O in summer monsoon rainfall was investigated. The 'precipitation amount effect' is obvious for the daily δ~(18)O variation, whereas the 'temperature effect' is insignificant. Alternate occurrences of active phase and break phase of the southwest monsoon probably influence the synoptic-scale δ~(18)O variation prominently. Moreover, the isotopic composition in precipitation during the late monsoon months is presumably influenced significantly by recycling of monsoon precipitation. Both the above factors disturb the 'amount effect' of isotopic variation in the monsoon region. This study also indicates that the synoptic-scale rainfall δ~(18)O variation at Lijiang in summer is domi-nated by the Indian monsoon depression (low pressure) system at large scale. These results are important for further studying the 'amount effect' and reconstructing paleoclimate in the monsoon region.     

干旱对华北地区植被变化的影响

利用中分辨率成像光谱仪(moderate-resolutionimagingspectroradiometer,MODIS)归一化植被指数 (normalizeddifferencevegetationindex,NDVI)数据产品和气象站点的帕尔默干旱指数(thepalmerdroughtseverity index,PDSI)数据,分析了2001-2013年华北地区及3个主要地表覆盖类型区植被变化的时空特征和干旱的变化特征, 并以不同时间尺度分析了干旱对植被变化的影响.结果表明:1)华北地区植被NDVI空间分布差异较大,NDVI总体上 呈东南高、西北低的分布特点.2001-2013年,华北地区植被活动呈增强的趋势,其中秋季植被活动的增强趋势最明显. 2)2001-2013年,华北地区的干旱总体上有所减轻,其中秋季干旱减轻的趋势最明显.3)华北地区植被年际变化与干旱 有显著的正相关关系,干旱对植被生长状态有较大影响.北部草原区和中部落叶阔叶林带的植被年际变化与干旱的正相 关性显著;而南部农作物区不显著,干旱对农作物生长状态影响较不明显.4)在季节尺度上,华北地区夏季植被变化与干 旱的正相关性最为显著,夏季植被生长状态最容易受到干旱的影响;以16d的植被数据分析表明,NDVI距平值更适合 表征华北地区植被生长状态与干旱的关系.      

The spring soil moisture and the summer rainfall in eastern China

The relation between the soil moisture in spring and the rainfall in summer in eastern China is investi- gated. Results show that the summer rainfall in eastern China is closely related to the spring soil moisture in the area from North China to the lower reaches of Yangtze River (NCYR). When spring soil moisture anomalies over NCYR are positive, the summer precipitation exhibits positive anomalies in Northeast China and the lower reaches of Yangtze River, and negative anomalies in southern China and North China. The higher soil moisture over NCYR cools land surface and reduces the land-sea tem- perature gradient, which weakens East Asian summer monsoon. The western Pacific Subtropical High (WPSH) is located to the south and shifts westward, resulting in more rainfall in the lower reaches of Yangtze River and less in southern China and North China.     

Interdecadal variation of tropical cyclone activity in association with summer monsoon, sea surface temperature over the western North Pacific

Based on geographic division over the western North Pacific (WNP), the interdecadal relationships between summer monsoon, sea surface temperature (SST) and tropical cyclones activity (including number, track and intensity) are examined. In the past several decades, the western Pacific subtropical high (WPSH) and tropical westerlies contribute to the interdecadal variation of TC number in the northwest and southeast of WNP respectively. The increased TC occurrence density to the east of Philippines related to TC track appears during the 1990s, in terms of both steer flow induced by WPSH and genesis location. From the interdecadal viewpoint, the tendency of TC intensity, measured by averaged accumulated cyclone energy, does well agree with that of SST, implying that SST plays an important role in TC intensity. Supported by Special Scientific Research Project for Public Interest (Grant No. GYHY200806009) and National Basic Research Program of China (Grant No. 2009CB421505)     

亚洲季风区平均雨季起始期的时空分布特征

 利用1961~1990年平均的降水资料,计算了亚洲季风区内91个测站的相对降水指数.在定义相对降水指数大于147作为雨季开始的标志后发现,亚洲季风区中最早进入雨季的地区位于青藏高原东南侧的纵向岭谷北部地区.该地区在3月份进入雨季,即纵向岭谷北部地区著名的“桃花汛”.在此基础上初步讨论了“桃花汛”形成的原因是由于青藏高原大地形作用下,暖湿西南气流沿纵向岭谷向着低纬高原的爬坡抬升作用,结合来自青藏高原的偏北气流带下的冷平流沿纵向河谷的下楔作用最终导致了该地区雨季的开始.     

南华北地区奥陶系古喀斯特特征及其储层前景

南华北地区奥陶系古喀斯特广泛发育,为油气成藏提供了有利条件.通过野外露头剖面观测、钻井岩心观察,奥陶系古喀斯特主要发育于下奥陶统亮甲山组和奥陶系顶部,表现为不整合面(风化壳)残积物、喀斯特角砾、溶蚀孔洞缝等特征.将奥陶系古喀斯特划分为同生期、表生期和埋藏期喀斯特三类,同时讨论了影响和控制奥陶系古喀斯特发育的因素,其中构造、岩性、气候和古地貌为主要因素.研究区受构造隆升控制的表生期喀斯特和同生期喀斯特在横向上分布连续,有利于喀斯特储层发育;另外,奥陶系埋藏期喀斯特广泛发育,也有可能形成有利储层.     

华北鼠李属植物的化学分类学研究

通过对华北鼠李属（ＲｈａｍｎｕｓＬ．）植物的１１个种的化学分析，发现几乎所有的种都含有黄酮类化合物，包括ｍｕｌｔｉｆｌｏｒｉｎＡ，ａｌａｔｅｒｎｉｎ，Ｋａｅｍｐｆｅｒｏｌ－３－０－β－ｒｈａｍｎｉｎｏｓｉｄｅ，其中Ｋａｅｍｐｆｅｒ－ｏｌ－３－０－β－ｒｈａｍｎｉｎｏｓｉｄｅ，普遍存在，为本属的特征性成分．根据黄酮类化合物对部分种的系统地位作了讨论．     

我国北方干旱的时空分布特征分析

通过对北方干旱和半干旱地区时间序列的降雨、径流等资料研究,采用降雨距平百分率和分时段多年降雨空间分布分析方法,进一步了解我国北方降雨,径流与干旱空间变化的全貌,并据此对北方各主要地区的干旱情况进行了分析,为全面掌握、研究和预测北方干旱和生态环境的演变发展奠定基础。     

Evolution of the South China Sea and monsoon history revealed in deep-sea records

As the third summary report of ODP Leg 184 to the South China Sea (SCS), this paper discusses the evolution of the East Asian monsoon and the SCS basin. A multi-proxy approach, involving geochemistry, micropale-ontology, pollen and other analyses, was adopted for reconstructing the evolutionary history of the East Asian monsoon, which was characterized by a series of paleo-climate events especially at 8, 3.2, 2.2 and 0.4 Ma. The new record indicates similar stages in the development of the East and South Asian monsoons, with an enhanced winter monsoon over East Asia being the major difference. The rich spectrums of monsoon variability from the southern SCS also reveal other characteristic features of the low latitude ocean. Evidence for the evolution of the SCS includes the hemipelagic Oligocene sediments, implying the existence of deep water environments during the early seafloor spreading stage of the SCS basin. The four major unconformities and some remarkabl ediagenetic features in upper Oligocene deposits indicate the strongest tectonic events in the region. From a careful comparison of lithologies and sedimentation rates, we conclude that the prominent differences in sedimentary environments between the southern and northern SCS were established only by ～3 Ma.     

1980-2010年华北地区极端高温天气气候事件特征分析

基于1980-2010年共31年NCEP再分析资料和华北地区地面台站资料,采用百分位阈值法研究了华北地区夏季极端高温天气事件的时空特征,并对其环流成因进行了分析.结果表明,1980-2010年华北地区极端高温日数和极端高温事件发生时的日平均、最高温度都有明显的增加趋势,其中极端高温日数的增加趋势尤为显著,线性趋势系数达到0.261,通过了0.01的显著性水平检验.空间分布上,近10年华北地区的极端高温日数显著增加,并且北部地区增加大于南部,极端高温多发区由20世纪80年代的"南多北少"向目前的"北多南少"分布态势转变;合成分析的结果表明,在华北地区极端高温日数偏多年,副高势力较强,且西伸脊点偏西,中高纬度地区为两高一低型,造成华北地区极端高温日数偏多的大气环流系统是其中偏东的深厚大陆高压,此系统强度大且在对流层低层势力尤为强盛,位势高度异常在850 h Pa上超过5 gpm.