中国东部土壤湿度异常和厄尔尼诺对中国东部夏季降水的作用比较

利用中国气象科学研究院气候系统模式CAMS-CSM中大气和陆面的耦合版本进行了土壤湿度和热带太平洋海温异常影响东亚夏季风的数值模拟,探讨了中国东部从长江中下游到华北(YRNC)春季土壤湿度和厄尔尼诺(El Ni?o)在影响夏季东亚环流和中国东部降水中的作用及其机理.结果表明,中国东部春季土壤湿度和El Ni?o海温异常均对东亚夏季风有显著的影响,其中土壤湿度对中国东部夏季降水的影响略大于海温的作用,然而两者对东亚夏季风环流和中国夏季降水的作用显著不同. YRNC土壤偏湿(干)引起的降水异常模态为中国北部和东南降水偏少(多),而长江流域和东北降水偏多(少),环流上YRNC土壤偏湿(干)能引起西太平洋副热带高压显著偏强(弱)偏西(东)和东亚大槽偏深(浅),表现为弱(强)夏季风形态. El Ni?o对降水的影响显著不同于土壤湿度的作用,在El Ni?o发展期的夏季,中国东北和华北地区为异常反气旋,长江中下游和华南地区为异常气旋,西太平洋副热带高压偏弱,引起长江下游、华南降水偏多,华北降水偏少.在El Ni?o衰减期的夏季,中国东北地区存在一个异常气旋,华南有一个异常反气旋,异常反气旋西部的偏南气流和异常气旋西部的偏北气流在中国中部和北部地区汇合,使得夏季华北和长江中游地区降水增多,其余地区降水偏少.     

影响中国北方强降雪事件年际变化的典型环流背景和水汽收支特征分析

基于1961-2014年中国台站观测资料和NECP/NCAR再分析资料,对影响中国北方强降雪事件（日降雪量5 mm及以上,包括大到暴雪）年际变化的典型大尺度环流特征和水汽条件进行了综合分析.结果表明：中国北方强降雪事件主要集中在新疆北部和东北两个地区,而且强降雪日数和降雪量具有高度一致的年际变化特征.中国北方强降雪事件偏多时,对应北大西洋涛动（NAO）和北极涛动（AO）负位相;贝加尔湖上空维持异常低槽区,有利于冷空气的爆发南下;热带印度洋至热带西太平洋上空维持一条异常反气旋带,有利于暖湿气流向北输送;中国北方及以北区域高空为异常西风气流,提供有利的动力抬升条件,使得强降雪易于在中国北方发生;反之亦然.水汽收支分析显示,中国北方西边界和南边界水汽入流增强在强降雪偏多中起着主要贡献.异常西风水汽输送利于新疆北部大到暴雪偏多,异常西南风水汽输送则利于东北地区大到暴雪的发生.进一步研究揭示：与小雪相比,影响中国北方大到暴雪年际偏多的中高纬环流特征相类似,但环流经向度更大;而且大到暴雪与NAO和AO的关系更密切,并更多的受到来自中低纬地区的水汽输送影响.     

中国北方沙尘暴气候形势的年代际变化

分析了中国北方沙尘气候的时间变化特征, 重点研究与沙尘气侯的年代际变化相应的冬、春季气候和大气环流异常特征. 文章揭示: 在沙尘活动频繁年代(1956~1970)和稀少年代(1985~1999)冬、春季的气候和大气环流有显著差别. 与前一个年代相比, 在后一个年代里冬季极涡异常加深, 50°N附近的西风增强, 东亚极锋锋区位置偏北, 东亚大槽偏弱; 西伯利亚高压北部及中心强度变弱, 阿留申低压明显升压; 东亚季风强度变弱, 影响中国的冷空气势力减弱, 冬、春季大风天气变少. 同时中国北方广大地区冬季温度显著升高, 西北和内蒙古的沙源地区春季降水明显增多. 研究还发现, 在年际尺度上, 中国北方的沙尘活动频次与前冬的西风指数、北极涛动指数呈显著的负相关, 与冬、春季东亚季风指数呈显著的正相关.     

中国东部春季土壤湿度的时空变化特征

利用中国气象局提供的土壤湿度观测资料和欧洲中期天气预报中心（ECMWF）的ERA-40土壤湿度再分析资料,在仔细比较分析两套资料的基础上,研究了100°E以东中国春季土壤湿度的空间分布特征及其在不同时间尺度上的变化特征,结果表明ERA-40资料能很好的再现中国东部春季土壤湿度的时空变化特征,较好地反映出了中国春季土壤存在东北和西南湿、华北和内蒙古干的地理分布及其年际变化．在整个中国东部地区,春季土壤存在不同程度上的干旱化现象;其中西南地区土壤从浅层到深层都存在—致的变干趋势,20世纪80年代后这种变干趋势变得显著;在东部中纬度地区,浅层土壤湿度具有明显的年际变化特征,没有明显的干化趋势,但深层土壤湿度从1988年以后存在较为明显的干化现象;东北地区浅层和深层土壤也存在较明显的变干趋势,其中浅层土壤在20世纪70年代初以后变干趋势减缓,而深层土壤在70年代末以后的变干趋势加剧．     

过去50年中国西部气候和径流变化的区域差异

通过对过去50年中国西部降水和主要河流径流变化的对比分析, 研究降水和径流的区域变化差异, 结果表明, 黄河上游径流和降水与新疆北部和青藏高原南部雅鲁藏布江流域径流、降水呈显著的反相关关系. 中国西部降水变化大体上以青藏高原唐古拉山和天山为界, 表现出南北一致, 中部(西部的喀喇昆仑山除外)相反, 即从南到北呈现出干-湿-干或湿-干-湿的区域变化差异; 在河流径流上表现为北部伊犁河流域和南部雅鲁藏布江流域径流变化的一致性, 而与黄河上游径流变化呈反位相变化; 同时, 新疆和黄河径流的反位相变化表现在年代际上, 而黄河和雅鲁藏布江径流变化表现在年际变化上. 黄河上游径流的变化与西北太平洋季风指数的变化比较一致, 这表明黄河上游径流变化受到较强的东亚季风的影响; 新疆总径流分别与西北太平洋季风指数和西风指数存在显著的正负相关关系, 寻找不同地区径流变化异同对于认识和预测径流未来变化具有重要的指导意义.     

新疆夏季降水年代际转型的归因分析

本研究针对我国内陆新疆地区在20世纪80年代末出现由暖干向暖湿的年代际转型,从大气环流因子进行归因分析.结果显示,位于东亚沿海地区的东亚-太平洋型遥相关波列(EAP)的强度和位置的年代际加强和偏移对于新疆地区此次气候的干湿转型具有重要贡献.转型之前EAP强度偏弱,位置相对偏东,对新疆夏季降水变化没有明显贡献,且影响新疆夏季降水发生的主要环流系统是位于中纬度欧亚大陆上空的异常纬向波列.转型后EAP强度偏强,位置相对前期向西偏移,因此从西北太平洋向我国内陆地区的异常水汽输送显著增强,使得新疆地区大气含水量增加,从而导致20世纪80年代末以后新疆夏季降水的增加.     

现代蒙古高原与中纬度东亚季风区夏季降水一致性变化的空间范围及其成因

蒙古高原地处亚洲中部干旱区东部,受到西风环流的主控,表现出干旱半干旱气候特征,其东部受到季风环流的影响,表现为湿润半湿润气候特征的中纬度东亚季风区.但有研究关注到该地区现代夏季降水的变化与亚洲中部干旱区西部变化并不一致,却与中纬度东亚季风区表现出同相位的降水变化特征.为了查明这种降水一致性的空间范围,文章使用1979～2016年GPCC数据集的逐月降水资料,分别对蒙古高原夏季降水年际和年代际信号进行分析.结果显示:蒙古高原与中纬度东亚季风区在年际和年代际尺度上都呈现出了基本一致的降水变化特征,一致性变化区域主要为蒙古高原、中国东北和华北地区.进一步对蒙古高原与中纬度东亚季风区年代际出现降水一致性变化的物理机制进行研究,发现北大西洋和中亚地区与欧洲和蒙古高原高度场异常反相位配置的欧亚大陆中纬度遥相关波列是导致降水一致性变化的关键因素.当北大西洋和中亚地区为高度场正异常,而蒙古高原出现高度场负异常这种环流配置时,能够将更多的西风和中纬度季风水汽输送到蒙古高原、中国东北和华北地区,并且通过加强东北亚低压来增强东亚夏季风,还可以激发异常上升运动,从而导致主要受西风环流控制的蒙古高原和受季风环流控制的中国东北和华北地区降水出现一致性增加.反之则出现一致性降水减少.这项研究将对理解东亚古降水/湿度重建样点的空间代表性,以及厘清区域气候的一致性背景具有指示性意义.     

中国气候干湿变率与ENSO的关系及其稳定性

利用1951-01~2000-10中国160站气温和降水月平均资料, 计算了自修正PDSI指数. PDSI指数EOF分析第一模态空间场分布和1951~2000年PDSI指数的变化趋势分布十分相似, 第一模态时间系数反映了空间场随时间的演变情况. 研究发现, EOF分析所揭示的中国气候干湿变率和ENSO有着很好的关系. 这种关系表明, 在典型的ENSO暖状态, 中国大部分地区都偏干, 特别是华北地区更易偏干, 长江以南地区和西北容易偏湿, 而长江中下游地区处于变干和湿的过渡区, 变干或湿不明显. 在典型的ENSO冷状态则情况相反. 而中国气候干湿变率年际和年代际变化都对应着强El Niño事件; 反过来当发生强El Niño事件时, 中国气候干湿变率在年际和年代际尺度上有可能发生剧烈变化. 最近20~30 a中国气候干湿的年代际变化, 特别是华北自20世纪70年代末的变干和西北自80年代中期的变湿, 与ENSO朝更暖的状态变化及全球变暖有着紧密的联系. 1951~2000年中国气候干湿变率和ENSO关系的稳定性分析表明, 中国气候干湿变率和ENSO之间在3~8 a变化周期上存着很好的相关关系, 但这种相关关系不稳定, 存在着年代际变化: 1951~1962和1976~1991年两个时间段两者相关关系很高, 而在1963~1975和1992~2000年两时段内, 两者相关关系较差.     

青藏高原春季土壤湿度与我国长江流域夏季降水的联系及其可能机理

土壤湿度作为陆面过程的重要因子,对局地及邻近地区的大气环流和天气气候有重要影响.青藏高原的土壤湿度观测站点稀少,时间较短,鉴于此,本文使用经过部分观测站点检验的卫星反演数据,研究了春季高原土壤湿度的年际变化与后期夏季我国东部降水的联系和可能机理.结果表明:在全球变暖的背景下,高原土壤湿度总体呈现出显著增加的趋势,去除该线性趋势后,我们定义了一个高原土壤湿度指数TPSMI来定量表征高原土壤湿度的年际变化特征,发现表层、中层、深层的土壤湿度年际变率趋于一致,且春季土壤湿度与夏季土壤湿度显著相关(相关系数可达0.56).当TPSMI偏大时,即高原东部土壤湿度偏大,而西部偏小时,夏季在高原东部(西部)存在一个潜热(感热)热源,二者共同作用下,在对流层中高层从高原西部经我国大陆直至东北地区激发出一个气旋—反气旋—气旋波列,该波列呈相当正压结构,有利于东北冷涡的加强及冷空气向南爆发;与此同时,南亚高压加强东伸,西太副高西伸加强,低空南方暖湿气流与北方干冷气流在长江流域汇合,伴随着上升运动加强,从而有利于夏季长江流域降水增多;反之,当TPSMI偏小时,夏季长江流域降水减少.     

南海夏季风爆发与南大洋海温变化之间的联系

利用1979-2009年NCEP第二套大气再分析资料和ERSST海温资料,分析南海夏季风爆发时间的年际和年代际变化特征,考察南海夏季风爆发早晚与南大洋海温之间的联系.主要结果为:(1)南海夏季风爆发时间年际和年代际变化明显,1979-1993年与1994-2009年前后两个阶段爆发时间存在阶段性突变;(2)南海夏季风爆发时间与前期冬季(12-1月)印度洋-南大洋(0-80°E,75°S-50°S)海温、春季(2-3月)太平洋-南大洋(170°E -80°W,75°S-50°S)海温都存在正相关关系,当前期冬、春季南大洋海温偏低(高)时,南海夏季风爆发偏早(晚).南大洋海温信号,无论是年际还是年代际变化,都对南海夏季风爆发具有一定的预测指示作用;(3)南大洋海温异常通过海气相互作用和大气遥相关影响南海夏季风爆发的迟早.当南大洋海温异常偏低(偏高)时,冬季南极涛动偏强(偏弱),同时通过遥相关作用使热带印度洋-西太平洋地区位势高度偏低(偏高)、纬向风加强(减弱),热带大气这种环流异常一直维持到春季4、5月份,位势高度和纬向风异常范围逐步向北扩展并伴随索马里越赤道气流的加强(减弱),从而为南海夏季风爆发偏早(偏晚)提供有利的环流条件.初步分析认为,热带大气环流对南大洋海气相互作用的遥响应与半球际大气质量重新分布引起的南北涛动有关.     

Changes in sediment transport in the Kuye River in the Loess Plateau in China

In this paper, the changes in sediment transport over 51 years from 1955 to 2006 in the Kuye River in the Loess Plateau in China are assessed. Key factors affecting sediment yield and sediment transport, such as precipitation depth, discharge, and human activities are studied. To investigate the changes in sediment yield in this watershed, a trend analysis on sediment concentration, precipitation depth, and discharge is conducted. Precipitation depths at 2 Climate Stations （CSs）, as well as discharge and sediment transport at 3 Gauging Stations （GSs） are used to assess the features of sediment transport in the Kuye River. The rtmoff modulus （defined as the annual average discharge per unit area, L/（s·km^2）） and the sediment transport modulus （defined as the annual suspended sediment transport per unit area, t/（yr km^2）） are introduced in this study to assess the changes in runoff and sediment yield for this watershed. The results show that the highest average monthly discharge during the study period in the Kuye River is 66.23 m^3/s in August with an average monthly sediment concentration of 88.9 kg/m^3. However, the highest average monthly sediment concentration during the study period in the Kuye River is 125.34 kg/m^3 and occurs in July, which has an average discharge of 42.6 m^3/s that is much less than the average monthly discharge in August. It is found that both the runoff modulus and sediment transport modulus at Wenjiachuan GS on the Kuye River has a clear downward trend. During the summer season from July to August, the sediment transport modulus at Wenjiachuan GS is much higher than those at Toudaoguai and Longmen GSs on the Yellow River. The easily erodible loess in the Kuye River watershed and the sparse vegetation are responsible for the extremely high sediment yield from the Kuye River watershed. The analyses of the grain size distribution of suspended load in the Kuye River are presented. The average monthly median grain size of suspended load in the Kuye River is largest in February and then decreases until June. In July, the average monthly median grain size of suspended load approaches another peak and decreases until September. Then, the median grain size of suspended load starts to increase until February of the following year. However, the average monthly median grain size of suspended load in the Yellow River at Toudaoguai and Longmen GSs is the smallest between early summer and late fall The median grain size in the Yellow River starts to increase in November and approaches the largest size in January.     

TritiogenicHe in groundwater in Takaoka

³He/⁴He ratios up to 3.5 times the ratio of atmospheric He were found in groundwater samples. The³He enrichment can be attributed to radiogenic³He produced by in-situ beta-decay of³H. This shows that tritiogenic³He is accumulating in confined waters. From tritiogenic³He and³H concentrations, ages of groundwaters can be calculated. Detection of tritiogenic³He gives a tool to trace a tritium contamination which occurred in the past and cannot be assessed only by the³H counting method.     

Projected changes in flood indices in selected catchments in Poland in the 21st century

The aim of this study is to estimate likely changes in flood indices under a future climate and to assess the uncertainty in these estimates for selected catchments in Poland. Precipitation and temperature time series from climate simulations from the EURO-CORDEX initiative for the periods 1971–2000, 2021–2050 and 2071–2100 following the RCP4.5 and RCP8.5 emission scenarios have been used to produce hydrological simulations based on the HBV hydrological model. As the climate model outputs for Poland are highly biased, post processing in the form of bias correction was first performed so that the climate time series could be applied in hydrological simulations at a catchment-scale. The results indicate that bias correction significantly improves flow simulations and estimated flood indices based on comparisons with simulations from observed climate data for the control period. The estimated changes in the mean annual flood and in flood quantiles under a future climate indicate a large spread in the estimates both within and between the catchments. An ANOVA analysis was used to assess the relative contributions of the 2 emission scenarios, the 7 climate models and the 4 bias correction methods to the total spread in the projected changes in extreme river flow indices for each catchment. The analysis indicates that the differences between climate models generally make the largest contribution to the spread in the ensemble of the three factors considered. The results for bias corrected data show small differences between the four bias correction methods considered, and, in contrast with the results for uncorrected simulations, project increases in flood indices for most catchments under a future climate.     

Variations in trace gas concentrations in different environments in India

Observations of trace gases (SO₂, NH₃, NO₂ and O₃) were made during the period 1981 to 1984 at 6 different locations representative of urban industrial, urban, nonurban, thermal power plant and marine environment. Diurnal variations of the trace gases were studied in an urban environment. Except in the urban industrial environment, the concentration of NH₃ was found in the range of background values. Also, the average concentrations of NO₂ and O₃ at the different environments were in the order of background values. However, the concentrations of SO₂ were substantially higher by about 7 times, in urban industrial and thermal power plant environments. The diurnal variations of SO₂, NH₃ and NO₂ showed anitphase relationship with surface temperature at the urban environment station which is relatively free of industrial pollution. Discussion is centred on trace gas variations in different environments in India together with the values reported for various countries in the world.     

Changes in thermal extremes in Poland

Changes in thermal extremes of the climate of Poland in 1951–2010 are examined. Warm extremes have become more frequent, while cold extremes have become less frequent. In the warming climate of Poland, the increase in the number of extremely warm days in a year and the decrease in the number of extremely cold days in a year have been observed. Also the increase of the maximum number of consecutive hot days in a year and the decrease of the maximum number of consecutive very cold and extremely cold days in a year have been observed. However, the trends are not of ubiquitous statistic significance, as the natural variability is strong.     

Copper in natural waters in Transbaikalia

Cu concentrations in surface (river and lake) and subsurface waters are determined. The geographic pattern of Cu distribution in natural water is identified. This pattern is controlled by the difference between its concentrations in drained rocks and soils and the geochemical redox conditions of its migration. Territories with low, medium, and elevated Cu concentrations in natural waters are identified. The concentrations of Cu in natural waters of the region are found to be generally lower than the Clarke values.     

Hydrological changes in the Ganges system in Bangladesh in the post-Farakka period

Abstract

The basin area of the Ganges River in Bangladesh is extremely dependent on a regular water supply from upstream to meet requirements for agriculture, fisheries, navigation, salinity control, and domestic and industrial sectors. In 1975, India commissioned a barrage on the Ganges River at Farakka to divert a significant portion of the dry season flow in order to make the Calcutta Port navigable. Statistical analyses of discharge and water level data have been carried out to determine if significant changes have occurred in the hydrology of the Ganges system in Bangladesh in the post-Farakka period. Siltation of the Gorai River (an offtake of the Ganges River) has also been examined using the stage-discharge relationship and regression analysis. The analyses show that the diversion has caused considerable hydrological changes in the Ganges system in Bangladesh. The water supply in the dry season has been reduced substantially, while siltation of the Gorai River has increased significantly.     

Applied volcanology in geothermal exploration in Iceland

In an active spreading area like Iceland, where the regional geothermal gradient is in the range 50–150°C/km, it is normally not a problem to find high enough temperature with deep drilling, but the difficulties arise with finding permeable layers at depth within the strata. Various volcanological methods can be applied in the search for aquifers and geothermal reservoir rocks. The flow pattern (as deduced from deuterium studies) indicates that the thermal water flows preferentially along high porosity stratiform horizons and dyke swarms from the recharge areas in the highlands to the hot spring areas in the lowlands. The primary porosity of the volcanic strata is dependent on the chemical composition and the mode of eruption of the volcanic units. Both the reservoir rocks and the flow channels forming the geothermal plumbing system are thought to vary from the Tertiary to the Quaternary provinces due to environmental conditions at the eruptive sites.