东江流域枯水期最长连续无降水日数的变化特征   总被引：3，自引：0，他引：3  

王兆礼  覃杰香  陈晓宏 《地理研究》2011,30(9):1693-1701

利用1956-2008年东江流域各降雨站点逐日降雨资料,建立枯水期最长连续无降水日数时间序列（LCDD）,采用经验模态分解（EMD）方法分析该序列的多尺度振荡变化及趋势变化,应用Mann-Kendall法识别突变点,采用R／S分析方法探讨变化趋势的持续性特征,并初步分析LCDD变化的可能原因。结果表明：近53年来,最长...  相似文献   

北京城区城市热岛的多时空尺度变化   总被引：9，自引：1，他引：8  

张佳华  孟倩文  李欣 《地理科学》2011,(11):1349-1354

利用气象台站数据分析北京城郊气温和城市热岛（UHI）强度的年变化及风速对北京UHI的影响;同时分析北京5个城市站点UHI在不同季节的日变化特征。结果表明,近44 a来北京市区与郊区的多年平均气温和UHI强度均呈增加的趋势。风速的降低促进北京城区的UHI出现增加趋势。风速对UHI的季节变化影响也很显著。2005年北京UH...  相似文献   

华南区域降温度日和采暖度日的时空变化特征   总被引：1，自引：0，他引：1  

李艳兰  何如  杜尧东  陆虹 《热带地理》2011,31(1):14-20

利用华南区域110个气象站1961-2008年逐日平均气温资料,计算华南区域各地年降温度日和采暖度日,分析降温度日和采暖度日的时空变化特征,探讨度日与年平均气温的关系.结果表明:华南区域年降温度日具有南部大、北部小,河谷平原大、山区小的地域分布特点;年采暖度日则是由南向北增大.1961-2008年华南区域年降温度日呈现...  相似文献   

西畴县近48年来降水及气温小波分析     

刘云生  黄国平  王顺江 《云南地理环境研究》2011,23(2):90-92

利用连续小波分析1962～2009年西畴县年降水量和年平均气温序列的小波变化特征,揭示了西畴县降水量与平均气温存在多时间尺度的周期变化特征。其中降水有2个明显的特征时间尺度,分别是4年和8年,平均气温存在以准2～4年为周期的周期振荡。此外,也可以看出近48年来,平均气温存在明显升高的趋势,降水也有减少的趋势,为掌握西畴县的气候变化规律及今后的气象预报服务工作提供了一定的参考价值。  相似文献   

http://www.sciencedirect.com/science/article/pii/S167498711300162X     

Fumiko Tajima  Masaki Yoshida  Eiji Ohtani 《地学前缘(英文版)》2015,6(1):79-93

Seismic observations have shown structural variation near the base of the mantle transition zone(MTZ)where subducted cold slabs,as visualized with high seismic speed anomalies(HSSAs),flatten to form stagnant slabs or sink further into the lower mantle.The different slab behaviors were also accompanied by variation of the "660 km" discontinuity depths and low viscosity layers(LVLs) beneath the MTZ that are suggested by geoid inversion studies.We address that deep water transport by subducted slabs and dehydration from hydrous slabs could affect the physical properties of mantle minerals and govern slab dynamics.A systematic series of three-dimensional numerical simulation has been conducted to examine the effects of viscosity reduction or contrast between slab materials on slab behaviors near the base of the MTZ.We found that the viscosity reduction of subducted crustal material leads to a separation of crustal material from the slab main body and its transient stagnation in the MTZ.The once trapped crustal materials in the MTZ eventually sink into the lower mantle within 20-30 My from the start of the plate subduction.The results suggest crustal material recycle in the whole mantle that is consistent with evidence from mantle geochemistry as opposed to a two-layer mantle convection model.Because of the smaller capacity of water content in lower mantle minerals than in MTZ minerals,dehydration should occur at the phase transformation depth,~660 km.The variation of the discontinuity depths and highly localized low seismic speed anomaly(LSSA) zones observed from seismic P waveforms in a relatively high frequency band(~1 Hz) support the hypothesis of dehydration from hydrous slabs at the phase boundary.The LSSAs which correspond to dehydration induced fluids are likely to be very local,given very small hydrogen(H~+) diffusivity associated with subducted slabs.The image of such local LSSA zones embedded in HSSAs may not be necessarily captured in tomography studies.The high electrical conductivity in the MTZ beneath the northwestern Pacific subduction zone does not necessarily require a broad range of high water content homogeneously.  相似文献   

Downstream patterns of bed sediment-borne metals,minerals and organic matter in a stream system receiving acidic mine effluent: A preliminary study   总被引：1，自引：0，他引：1  

Yingqun Ma  Wenzhou Lu  Chuxia Lin 《Journal of Geochemical Exploration》2011

Different downstream variation patterns were observed for a range of bed sediment-borne metals (aqua regia-extractable fraction) in a subtropical stream system receiving acid mine drainage. Mine-originated Fe tended to be deposited in the acidic (mean pH < 4.9) upstream reach in forms of goethite and/or hematite. In contrast, other metals tended to be transported farther downstream and settled in a low-gradient reach with high pH (mean pH > 5.6). The peak of sediment-borne Al, Be, Ca, Cd, Co, Cu, La, Mn, Ni and Zn corresponded very well with the peak of the sediment-borne organic matter, suggesting a close association between the water-borne organic colloids and the inorganic metal oxides/hydroxides during their transport. The marked increase in the sediment-borne Al and Pb started more upstream than the other metals, suggesting that the water-borne Al and Pb were more susceptible to pH rise-induced precipitation, as compared to the other metals. It appeared that the organic colloids played no important role in Pb transport and settlement. The iron precipitates had a limited role to play in affecting the transport and fates of other metals since they were predominantly formed and deposited in the acidic reach, which made them incapable of scavenging cationic metals by co-precipitation or adsorption.  相似文献   

洞庭湖水沙变化分析及影响初探   总被引：4，自引：0，他引：4  

李正最  谢悦波  徐冬梅 《水文》2011,31(1):45-53,40

水沙变化是洞庭湖演变和江湖关系调整的关键因子。综合运用数理统计、小波分析、Mann-Kendall法和累加过滤器等方法,分析1956～2008年洞庭湖入湖和出湖径流和输沙量的变化特征。结果表明:①洞庭湖入湖水量以湘、资、沅、澧四水入流为主,洞庭湖入湖泥沙以荆江三口分沙为主。四水年均入湖水量约占洞庭湖出湖总水量的59.2%;三口入湖沙量约占入湖总沙量的80.9%。②由于荆江裁弯、葛洲坝工程运用、三峡水库拦蓄以及长江上游的水土保持措施的影响,从三口河道进入洞庭湖的水沙呈现明显的衰减趋势,入湖水量所占比重已由荆江裁弯前的42.6%下降到了三峡水库运用初期的21.7%;入湖沙量所占比重已由荆江裁弯前的87.7%下降到了三峡水库运用初期的59.6%。③近50年洞庭湖的泥沙沉积总量达52.9×108t,但泥沙沉积比已由荆江裁弯前的73.3%下降到了三峡水库运用初期的34.0%,洞庭湖泥沙淤积的趋势明显减弱,有利于保持洞庭湖的调洪湖容,延长洞庭湖的寿命;但三峡水库运用初期,三口分流的衰减将加剧洞庭湖区西部地区枯水供水的紧张态势,并使水环境容量下降;同时城陵矶下游长江河道的淤积导致洞庭湖洪水位抬升。  相似文献   

21个气候模式对东亚夏季环流模拟的评估II:年际变化   总被引：4，自引：2，他引：2  

张宏芳  陈海山 《气象科学》2011,31(3):247-257

利用欧洲中期天气预报中心的ERA40再分析资料, 评估了参与政府间气候变化专门委员会第四次评估报告的21个全球海气耦合模式对东亚地区夏季大气环流年际变率的模拟能力,结果表明：（1）模式对东亚地区不同要素的年际变率模拟能力整体偏弱, 500 hPa高度场的模拟能力总体优于海平面气压场及850 hPa风场;（2）两大环流系统年际变率的模拟结果评估表明：就相关系数而言,副高强度、面积的模拟能力优于印度低压,多数模式能正确模拟出副高1970s后期增强的趋势;就标准差来看,模式对印度低压、印度低压东伸槽模拟效果相对较好;（3）评估三种季风指数的模拟能力结果显示,环流异常指数模拟效果略好,但多数模式都不能模拟出海陆气压差、经向风、环流异常季风指数的年际变化。  相似文献   

夏季长三角城市群热岛效应及其对大气边界层结构影响的数值模拟   总被引：12，自引：5，他引：7  

张璐  杨修群  汤剑平  房佳蓓  孙旭光 《气象科学》2011,31(4):431-440

利用WRF/Noah/UCM模拟系统对长三角地区城市群进行了2003—2007年共5个夏季的高分辨率数值模拟,研究了夏季长三角城市群热岛效应及其对大气边界层影响。开展了2组平行的积分试验,控制试验为MODIS遥感资料给出的地表特征分布,敏感性试验将长三角地区的城市表面改为农田类型,其他与控制试验完全相同。两组试验的对比分析表明城市群热岛存在明显的日变化特征,热岛效应白天向上发展较高,夜间地表热岛强度明显增强。城市热岛导致午后城市上空产生强烈的局地上升气流,从而使得低层大气以补偿流的形式向城市辐合,然而在夜间上升运动很微弱。伴随这种热力状况的日变化,大气边界层高度也存在明显的日变化,白天增高,夜间降低。同时,白天城市边界层内风速明显减小,夜间地面风速减小加剧,但夜间边界层顶风速却有所增强。另外,城市化还会导致“城市干岛”现象,且其白天强度大于夜间。  相似文献   

The Seasonal Variations of Aerosols over East Asia as Jointly Inferred from MODIS and OMI          下载免费PDF全文

LIU Qi  DING Wei-Dong  FU Yun-Fei 《大气和海洋科学快报》2011,4(6):330-337

Data on aerosol optical thickness(AOT) and single scattering albedo(SSA) derived from Moderate Resolution Imaging Spectrometer(MODIS) and Ozone Monitoring Instrument(OMI) measurements,respectively,are used jointly to examine the seasonal variations of aerosols over East Asia.The seasonal signals of the total AOT are well defined and nearly similar over the land and over the ocean.These findings indicate a natural cycle of aerosols that originate primarily from natural emissions. In contrast,the small-sized aerosols represented by the fine-mode AOT,which are primarily generated over the land by human activities,do not have evident seasonalscale fluctuations.A persistent maximum of aerosol loadings centered over the Sichuan basin is associated with considerable amounts of fine-mode aerosols throughout the year.Most regions exhibit a general spring maximum. During the summer,however,the aerosol loadings are the most marked over north central China.This occurrence may result from anthropogenic fine particles,such as sulfate and nitrate.Four typical regions were selected to perform a covariation analysis of the monthly gridded AOT and SSA.Over southwestern and southeastern China,if the aerosol loadings are small to moderate they are composed primarily of the highly absorptive aerosols. However,more substantial aerosol loadings probably represent less-absorptive aerosols.The opposite covariation pattern occurring over the coastal-adjacent oceans suggests that the polluted oceanic atmosphere is closely correlated with the windward terrestrial aerosols.North central China is strongly affected by dust aerosols that show moderate absorption.This finding may explain the lower variability in the SSA that accompanies increasing aerosol loadings in this region.  相似文献