Elemental composition of aerosols collected in the glacier area on Nyainqêntanglha Range, Tibetan Plateau, during summer monsoon season

In order to investigate the elemental composition in atmospheric aerosols and its sources in the glacier area over the Tibetan Plateau (TP), seven totally suspended particle samples were collected continuously at the col of the Zhadang glacier (30°28′N,90°39′E,5800 m a.s.l.), Nyainqêntanglha Range, southern TP, from June to October 2006. Twenty-seven elements (Li, Be, B, Na, Mg, Al, K, Ca, Sc, Ti, V, Fe, Mn, Zn, Ga, As, Rb, Sr, Y, Cd, Cs, Ba, Tl, Pb, Bi, Th, U) were analyzed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The result indicates that the concentrations of most elements (especially crustal elements) are lower than values at the Nam Co Station during the same period of 2005, and also much lower than other sites in the TP such as Wudaoliang and Waliguan. This suggests that elemental compositions of aerosols in the Zhadang glacier area may represent the background levels of the middle/upper troposphere over the TP. Crustal enrichment factors (EFs) reveal that several elements (e.g. B, Zn, As, Cd, Pb and Bi) may have anthropogenic sources. The southern TP is mainly influenced by the summer Indian monsoon during the sampling period. Backward air mass trajectory analysis suggests that air masses in the region may originate from South Asia. Therefore, anthropogenic pollutants from South Asia may be transported by the summer Indian monsoon to the region which clearly affects the atmospheric environment in the southern TP during the summer monsoon season.     

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)     

Arctic dipole anomaly and summer rainfall in Northeast China

A dipole structure anomaly in summer Arctic atmospheric variability is identified in this study, which is characterized by the second mode of empirical orthogonal function （EOF） analysis of summer monthly mean sea level pressure （SLP） north of 70°N, accounting for 12.94% of the variance. The dipole anomaly shows a quasi-barotropic structure with opposite anomalous centers over the Canadian Arctic and the Beaufort Sea and between the Kara Sea and the Laptev Sea. The dipole anomaly reflects alternating variations in location of the polar vortex between the western and eastern Arctic regions. The positive phase of the dipole anomaly corresponds to the center of the polar vortex over the western Arctic, leading to an increase in summer mean rainfall in Northeast China. The dipole anomaly has a predominant 6-year periodicity, and shows interdecadal variations in recent decades.     

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)。     

Statistic characteristics and weather significance of infrared TBB during May―August in Beijing and its vicinity

In order to meet the demand of nowcasting convective storms in Beijing, the climatological characteristics of convective storms in Beijing and its vicinity were analyzed based on the infrared （IR） temperature of black body （TBB） data during May--August of 1997--2004. The climatological probabilities, the diurnal cycle and the spatial distribution of convective storms are given respectively in this paper. The results show that the climatological characteristics of convective storms denoted by TBB≤-52℃ are consistent with those statistic studies based on the surface and lightning observations. Furthermore, the climatological characteristics of May and June are very different from those of July and August, showing that there are two types of convective storms in this region. One occurs in the transient polar air mass on the midlatitude continent during the late spring and early summer. This type of convection arises with thunder, strong wind gust and hail over the mountainous area in the northern part of this region from afternoon to nightfall, the other occurs with heavy rainfall in the warm and moist air mass over the North China Plain and vicinity of Bohai Sea. This study also shows that the long-term data of IR TBB observed by geostationary satellite can complement the temporal and spatial limitation of the weather radar and surface observations.     

The early Holocene optimum inferred from a hish-resolution pollen record of Husuansyan Maar Lake in southern China

A high-resolution pollen record of the past 13000 a from Huguangyan Maar Lake reveals the vegetation and environment changes in southern China during the Holocene. It shows that （i） pollen percentage of trees and shrubs reached 56% during the early Holocene （11600-7800 cal a BP）, of which the pollen percentage of tropical trees reached a maximum at 9500-8000 cal a BP, reflecting a hot and wet environment; （ii） during the mid-Holocene （7800-4200 cal a BP）, the pollen percentage of montane coniferous trees and herbs increased, while the percentage of tropical-subtropical trees decreased, indicating lower temperature and humidity; （iii） in the late Holocene spanning from 4200 to 350 cal a BP, the pollen percentage of herbs and montane conifer increased significantly, indicating a marked decrease of temperature and humidity. Our pollen data reveal that the time period 9500-8000 cal a BP in southern China represents a climatic optimum for the Holocene characterized by hot and wet conditions. This is consistent with the Holocene optimum found in lower latitude regions globally. We speculate that strong insolation might cause the northward migration of the ITCZ and subtropical summer monsoon front, which resulted in an early Holocene optimum in the Huguangyan area. The dry tendency and climate fluctuations of the middle and late Holocene could be associated with a decrease in solar insolation and frequent ENSO event.     

Climatological distribution and diurnal variation of mesoscale convective systems over China and its vicinity during summer

The climatological distribution of mesoscale convective systems （MCSs） over China and its vicinity during summer is statistically analyzed, based on the 10-year （1996-2006, 2004 excluded） June-August infrared TBB （Temperature of black body） dataset. Comparing the results obtained in this paper with the distribution of thunderstorms from surface meteorological stations over China and the distribution of lightning from low-orbit satellites over China and its vicinity in the previous studies, we find that the statistic characteristics of TBB less than -52℃ can better represent the spatiotemporal distribution of MCSs over China and its vicinity during summer. The spreading pattern of the MCSs over this region shows three transmeridional bands of active MCSs, with obvious fluctuation of active MCSs in the band near 30^oN. It can be explained by the atmospheric circulation that the three bands of active MCSs are associated with each other by the summer monsoon over East Asia. We focus on the diurnal variations of MCSs over different underlying surfaces, and the result shows that there are two types of MCSs over China and its vicinity during summer. One type of MCSs has only one active period all day long （single-peak MCSs）, and the other has multiple active periods （multi-peak MCSs）. Single-peak MCSs occur more often over plateaus or mountains, and multi-peak MCSs are more common over plains or basins. Depending on lifetimes and active periods, single-peak MCSs can be classified as Tibetan Plateau MCSs, general mountain MCSs, Ryukyu MCSs, and so on. The diurnal variation of multi-peak MCSs is very similar to that of MCCs （mesoscale convective complexes）, and it reveals that multi-peak MCSs has longer life cycle and larger horizontal scale, becomes weaker after sunset, and develops again after midnight. Tibetan Plateau MCSs and general mountain MCSs both usually develop in the afternoon, but Tibetan Plateau MCSs have longer life cycle and more active MαCSs. Ryukyu MCSs generally develop after     

Meridional seesaw-like distribution of the Meiyu rainfall over the Changjiang-Huaihe River Valley and characteristics in the anomalous climate years

Although Meiyu rainfall has its in-phase spatial variability over the Changjiang-Huaihe River Valley (CHRV) in most years, it is distributed in some years like a seesaw to the north and south of the Changjiang River, when the precipitation tends to be nearly normal throughout the valley, which would inevitably increase difficulties of making short-term prediction of the rainfall. For this reason, EOF analysis is made on 15 related stations’ precipitation from June to July during 1951─2004, revealing that the EOF2 mode shows largely a north-south seesaw-like pattern, and thereby classifying Meiyu patterns into two types: "northern drought and southern flood (NDSF)" and "northern flood and southern drought (NFSD)". Afterwards, the authors investigated ocean-atmospheric characteristics when these two anomalous types occured using the NCEP reanalysis (version 1) and the extended reconstructed SSTs (version 2). The results show that in the NDSF years, the low-level frontal area and moisture convergence center lie more southward, accompanied by weaker subtropical summer mon- soon over East Asia, with the western Pacific subtropical high and 200 hPa South Asia High being more southward. Both the Northern and Southern Hemisphere Annular Modes are stronger than normal in preceding February; SST is higher off China during boreal winter and spring and the opposite happens in the NFSD years. Also, this seesaw-form Meiyu rainfall distribution might be affected to some degree by the previous ENSO event.     

Study on response of ecosystem to the East Asian monsoon in eastern China using LAI data derived from remote sensing information

Based on the leaf area index (LAI) data derived from remote sensing information and eco-climate data, the responses of regional ecosystem variations in seasonal and interannual scales to the East Asian monsoon are studied. It is found that the vegetation ecosystems of eastern China are remarkably correlated with the East Asian monsoon in seasonal and interannual scales. In the seasonal timescale, the obvious variations of the vegetation ecosystems occur with the development of the East Asian monsoon from the south in the spring to the north in the autumn. In the interannual scale, high LAI appears in the strong East Asian monsoon year, whereas low LAI is related to the weak East Asian monsoon year. These further lead to the characteristic of "monsoon-driven ecosystem" in the eastern China monsoon region, which can be revealed by LAI.     

Climatic significance of δ18O records from precipitation on the western Tibetan Plateau

Analysis of daily precipitation samples for stable oxygen isotopes （δ^18O） collected at the Shiquanhe and Gerze （Gaize, Gertse） stations in the Ngari （Ali） region on the western Tibetan Plateau indicates that air temperature affects the δ^18O variations in precipitation at these stations. In summer, Shiquanhe and Gerze show strongly similar trends in precipitation δ^18O, especially in simultaneous precipitation events. Moreover, both stations experienced low δ^18O values in precipitation during the active monsoon period, resulting from the southwest monsoon （the summer phase of the Indian monsoon）. However, during the break monsoon period （during the summer rainy season, when the monsoon circulation is disrupted）, δ^18O values in summer precipitation remain relatively high and local moisture recycling generally controls the moisture sources. Air temperature correlations with δ^18O strengthen during the non-monsoon period （January--June, and October--December） due to continental air masses and the westerlies. In addition, evaporation also influences the δ^18O variations in precipitation. The observed temporal and spatial variations of δ^18O in precipitation on the western Tibetan Plateau and adjacent regions show that the late May and early June-the late August and early September time frame provides an important period for the transportation of moisture from various sources on the Tibetan Plateau, and that the region of the West Kunlun-Tanggula Ranges acts as a significant climatic divide on the Plateau, perhaps for all of western China.     

Meiyu in the middle and lower reaches of the Yangtze River since 1736

＂Yu Xue Fen Cun＂ records during the Qing Dynasty are used to identify the starting and ending dates of Meiyu at the period of 1736-1911. These results, along with the instrumental meteorological records, are used to reconstruct the series of length and precipitation of Meiyu during 1736-2000 over the middle and lower reaches of the Yangtze River. The characteristics of Meiyu are analyzed since 1736. Moreover, the strength of East Asian Summer Monsoon and locations of rainband are discussed, based on the relationship between the length of Meiyu and the Index of East Asian Summer Monsoon. It is found that the starting and ending dates and the length of Meiyu have significant interannual and interdecadal variations. Apart from 7-8 years, 20-30 years and 40 years cycles for the lengths of Meiyu, the centennial oscillation is also presented. The length of Meiyu, monsoon rainband movement over eastern China, and the strength of East Asian Summer Monsoon （EASM） have a very good correlation, which can be expressed in the following： during the periods of 1736-1770, 1821-1870 and 1921-1970, the EASM was stronger, and the monsoon rainband was located in North China and South China easily, corresponding to the decreased length of Meiyu. Whereas during the periods of 1771-1820, 1871-1920 and 1971-2000, the EASM was weaker and monsoon rainband usually stopped at the middle and lower reaches of the Yangtze River, corresponding to the increased length of Meiyu.     

澳大利亚高压对南海夏季风爆发前期的影响

利用NCEP/NCAR的在分析资料,分析了1948～2004年期间澳大利亚（以下简称澳高）的年变化和日变化及其对南海夏季风的影响。结果显示在澳高强弱年这种影响有着不同的结果：在年际变化中,澳高与南海夏季风的相关性在澳高弱年明显大于强澳高年;而日变化中,澳高与南海夏季风的相关性在澳高弱年为正,澳高强年则为负。进一步研究表明,造成这些现象的原因大致可以归为：强弱澳高年,越赤道气流的通道变换;西太平洋副热带高压（以下简称副高）的位置偏向;马斯可林高压（以下简称马高）的作用的叠加效应.这些作用对于南海夏季风的重要组成部分：越赤道气流产生了重要影响,从而影响了南海夏季风的强度。     

Simulation study of China’s net primary production

Spatial and temporal distribution of vegetation net primary production （NPP） in China was studied using three light-use efficiency models （CASA, GLOPEM and GEOLUE） and two mechanistic ecological process models （CEVSA, GEOPRO）. Based on spatial and temporal analysis （e.g. monthly, seasonally and annually） of simulated results from ecological process mechanism models of CASA, GLOPEM and CEVSA, the following conclusions could be made： （1） during the last 20 years, NPP change in China followed closely the seasonal change of climate affected by monsoon with an overall trend of increasing; （2） simulated average seasonal NPP was： 0.571±0.2 GtC in spring, 1.573±0.4 GtC in summer, 0.6±0.2 GtC in autumn, and 0.12±0.1 GtC in winter. Average annual NPP in China was 2.864±1 GtC. All the five models were able to simulate seasonal and spatial features of biomass for different ecological types in China. This paper provides a baseline for China＇s total biomass production. It also offers a means of estimating the NPP change due to afforestation, reforestation, conservation and other human activities and could aid people in using for-mentioned carbon sinks to fulfill China＇s commitment of reducing greenhouse gases.     

Interannual variability of Mascarene high and Australian high and their influences on summer rainfall over East Asia

Based on the reanalysis data from NCEP/NCAR and other observational data,interannual variability of Mascarene high(MH) and Australian high(AH) from 1970 to 1999 is examined.It is shown that interannual variability of MH is dominated by the Antarctic oscillation(AAO),when the circumpolar low in the high southern latitudes deepens,the intensity of MH will be intensified.On the other hand,AH is correlated by AAO as well as EI Nino and South Oscillation(ENSO),the intensity of AH will be intensified when EI Nino occurs.Both correlation analysis and case study demonstrate that summer rainfall over East Asia is closely related to MH and AH.When MH intensifies from boreal spring to summer (i.e.from austral autumn to winter),there is more rainfall over regions from the Yangtze River valley to Japan,in contrast,less rainfall is found over southern China and western Pacific to the east of Taiwan,and most of regions in mid-latitudes of East Asia.Compared with MH,the effect of AH on summer rainfall in East Asia is limited to localized regions,there is more rainfall over southern China with the intensification of AH.The results in this study show that AAO is a strong signal on interannual timescale,which plays an important role in summer rainfall over East Asia.This discovery is of real importance to revealingt the physical mechanism of interannual variability of East Asian summer monsoon and prediction of summer precipitation in China.     

Spatiotemporal vegetation cover variations in the Qinghai-Tibet Plateau under global climate change

Empirical Orthogonal Function （EOF） analysis and the related Principal Components （PC） analysis are used to extract valuable vegetation cover derived information from the National Oceanic and Atmos-pheric Administration （NOAA-AVHRR）＇s Leaf Area Index （LAI） satellite images. Results suggest that from 1982 to 2000 global climate change has contributed to an increase in vegetation cover in the Qinghai-Tibet Plateau. The correlation between rainfall and LAI EOF PC1 and PC2 indicates that rainfall is the major climatic factor influencing interannual variations of average vegetation cover throughout the entire Plateau. However, annual mean vegetation cover trends in the Qinghai-Tibet Plateau are mainly out of phase with air temperature increasing, which is primarily responsible for nonsynchro-nous changes of vegetation cover. In the southern ridge of the Qinghai-Tibet Plateau, recent warming trends contribute to humid weather and favorable conditions for vegetation growth. By contrast, higher temperatures have led to arid conditions and insufficient rainfall in the northern part of the Plateau, leading to drought and other climatic conditions which are not conducive to increased vegetation cover.     

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.     

印度洋海面温度变异与我国西南夏季风的关系

本文根据海-气相互作用的观点,研究了1970～1977年我国西南夏季风的爆发和撤退时间与印度洋海面温度距平的关系。结果表明季风爆发和撤退的早晚,在它们的前期海面温度距平是有差异的,这种差异在一些海区表现得更加明显。这对我们了解我国夏季风的特性是有意义的。     

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.     

Regional characteristics of the interdecadal turning of winter/summer climate modes in Chinese mainland

Tomé and Miranda’s climate trend turning discriminatory model is used to identify the spatial-temporal characteristics of the interdecadal turning of winter/summer climate modes at stations and in eight sub-areas over Chinese mainland based on the 1961–2000 observations. It is found that the stations with close occurrence years of the interdecadal trend turning (ITT) and coincident trends after the ITT exhibit a zonal distribution. A view is accordingly proposed that the interdecadal turnings of climate modes in China have remarkably regional structures. The research results show that after the early 1980s, winter climate over Chinese mainland overall trends towards a “warm-wet” mode, while summer climate had an abrupt change into “warm wet” mode in the late 1980s, suggesting that the time of the “warm-wet” mode turning for winter climate is earlier than that for summer climate. The regional characteristics and test results of the ITTs in eight sub-areas suggest that winter climate exhibits a distinctive “warm-dry” trend in North China after the late 1970s, and a slight “warm-dry” trend in Northeast China, South China, and Southwest China after the late 1980s. A “warm-wet” trend appears in the rest four sub-areas (the middle and lower reaches of the Yangtze River and the Huaihe River Valley, briefly Jianghuai, the east of the Tibetan plateau, and the east and west of Northwest China) after the early 1980s. The summer climate trends towards a “warm-dry” mode in Northeast China, North China and the east of Northwest China after the late 1980s, but a “warm-wet” mode appears in Southwest China and the east of the Tibetan plateau after the middle 1970s, as well as in Jianghuai and the west of Northwest China after the early 1980s. Specially, summer climate in South China started a “cold-wet” trend in 1984.     

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…