Community structure and phenology of chironomids (Insecta: Chironomidae) in a Patagonian Andean stream     

Patricia Elizabeth García  Diego Alejandro An Surez 《Limnologica》2007,37(1):109-117

In this paper, we studied the assemblage of Chironomidae from headwaters of Ñireco stream by recording drifting pupal exuviae caught in the debris close to the shore. Samples were collected in three stations along 18 km of the stream every 2 weeks during spring–summer months and monthly during autumn–winter over a year. A total of 15949 exuviae were collected and 55 taxa were identified. The most abundant taxa were Cricotopus spp. with highest numbers of exuviae recorded in each station over the study period. Subfamily Orthocladiinae was the most abundant taxa, followed by Chironominae and Podonominae. The emergence period in the stream occurred between December 1998 and March 1999. Most of the dominant and frequent species were univoltine. The emergence peaks at each sampling station occurred at the highest temperature of the water recorded.  相似文献   

赣北梅雨期降水异常分析     

舒长根  罗先诚 《热带地理》2002,22(4):367-370

利用天气图和500hPa高度距平资料,对赣北梅雨期多雨年和少雨年中西太平洋副高活动异常进行了对比分析,揭示出赣北梅雨期的长短及降水量的大小,与副高第二次北跳早晚关系密切。在此基础上,进一步研究了副高第二次北跳为什么有早有晚这一关键性问题。结果显示,副高第二次北跳早晚在一定程度上受青藏高原夏季热力状况影响。当青藏高原5月温度偏高时,高原上空的高压偏强,且东移偏早,从而引起副高第二次西伸北跳偏早,赣梅雨期降水偏水。反之,降水偏多。该结合与某些“青藏高原对我国东部天气影响”的研究结果相一致,从而为预测鄱阳湖平原旱涝提供了一条新思路。  相似文献   

海温对辽宁省主汛期降水异常影响的统计分析   总被引：1，自引：0，他引：1  

杨文艳  王谦谦 《南京气象学院学报》2005,28(3):404-409

在对辽宁省主汛期降水异常的时变特征进行分析的基础上，研究了前期海温场对辽宁主汛期(7—8月)降水影响的统计特征。结果表明：1)辽宁省汛期降水异常有明显的年际、年代际变化特征，近44a降水呈减少趋势。小波分析表明存在3～5a的年际周期和10～12a的年代际周期。2)存在2个影响辽宁汛期降水异常的海温关键区及相应的关键时段，它们分别是南大西洋(1—5月)和西太平洋(3—4月)，综合考虑2个关键区可更好地预示辽宁汛期降水的异常。  相似文献   

Comparison between different techniques for evaluation of predominant periods using strong ground motion records and microtremors in Pereira Colombia     

A. Ojeda  J. Escallon 《Soil Dynamics and Earthquake Engineering》2000,20(1-4)

This paper presents a comparison between different techniques for evaluation of predominant periods in soft soil, for the urban area of Pereira city, Western Colombia. In this study we used microtremor and strong ground motion records obtained by a local array of seven accelerographs stations deployed in the city. Response spectra and spectral ratios have been calculated and compared with strong seismic events recorded in solid rock and soft soil stations. These observations allowed the determination of dominant response spectra for several sectors in the urban area. For the microtremor measurements and earthquake data, dominant periods were determined using interpretation of Fourier amplitude spectra and Nakamura's technique. A comparison between dominant periods obtained from strong ground motion records and those obtained from microtremor measurements show similarities, which is in the range 0.2–0.5 s. A preliminary version of a site response map for Pereira city was obtained from this analysis.  相似文献   

岩石磁组构在断裂变形性状与期次研究中的应用——以广西博白-合浦断裂为例   总被引：3，自引：0，他引：3       下载免费PDF全文

阎全人  李增悦  李继亮  熊贤明  唐昌韩 《地质科学》2000,35(3):363-369

岩石磁化率椭球体的三个轴与应变椭球体的三个轴方向相平行,并具有一定的共构关系.变形岩石的磁组构参数P、T、F、L以及磁化率椭球体主张量方向等可以用来定量地表征岩石变形的性状及期次.本文通过实测和计算27个样品的磁组构参数,研究了博白-合浦断裂带的变形性状与期次,结果表明:博白-合浦断裂带大致经历了三期构造变形作用,不同时期具不同性质的构造变形.变形性状分别表现为韧性、韧-脆性及脆性变形,应变行为分别表现为平面、非平面和线性应变.  相似文献   

Changes to flood peaks of a mountain river: implications for analysis of the 2013 flood in the Upper Bow River,Canada          下载免费PDF全文

Paul H. Whitfield  John W. Pomeroy 《水文研究》2016,30(25):4657-4673

The mountain headwater Bow River at Banff, Alberta, Canada, was subject to a large flood in June 2013, over which considerable debate has ensued regarding its probability of occurrence. It is therefore instructive to consider what information long‐term streamflow discharge records provide about environmental change in the Upper Bow River basin above Banff. Though protected as part of Banff National Park, since 1885, the basin has experienced considerable climate and land cover changes, each of which has the potential to impact observations, and hence the interpretations of flood probability. The Bow River at Banff hydrometric station is one of Canada's longest‐operating reference hydrological basin network stations and so has great value for assessing changes in flow regime over time. Furthermore, the station measures a river that provides an extremely important water supply for Calgary and irrigation district downstream and so is of great interest for assessing regional water security. These records were examined for changes in several flood attributes and to determine whether flow changes may have been related to landscape change within the basin as caused by forest fires, conversion from grasslands to forest with fire suppression, and regional climate variations and/or trends. Floods in the Upper Bow River are generated by both snowmelt and rain‐on‐snow (ROS) events, the latter type which include flood events generated by spatially and temporally large storms such as occurred in 2013. The two types of floods also have different frequency characteristics. Snowmelt and ROS flood attributes were not correlated significantly with any climate index or with burned area except that snowmelt event duration correlated negatively to the Pacific Decadal Oscillation. While there is a significant negative trend in all floods over the past 100 years, when separated based on generating process, neither snowmelt floods nor large ROS floods associated with mesoscale storms show any trends over time. Despite extensive changes to the landscape of the basin and in within the climate system, the flood regime remains unchanged, something identified at smaller scales in the region but never at larger scales. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

基于多元分布函数的区域洪水频率分析          下载免费PDF全文

卢韦伟  陈璐  周建中  陈华 《水文》2015,35(5):6-10

极端洪水事件的频率分析往往局限于单个站点,当研究区域内包含多个水文站点时,单变量频率分析方法,会导致低估或高估洪灾风险率。因此,需要进行区域频率分析。传统区域重现期计算方法,同一重现期对应多种设计洪水组合,而基于Kendall分布函数的重现期计算方法(KRP)有效的解决了这一问题。故本文引入三维非对称Copula分布函数拟合区域内各个站点年最大流量的相关关系,利用半参数法估计Copula函数的参数,并采用KRP推求区域洪水发生的重现期。结果表明:区域发生T年一遇的洪水概率远远大于单个站点发生T年一遇的洪水概率;KRP克服了实测序列较短的问题,且能准确估算洪水重现期。本研究为防洪部门制定防洪措施提供一定的科学依据。  相似文献   

Report of the IAU/IAG/COSPAR working group on cartographic coordinates and rotational elements of the planets and satellites: 1991   总被引：1，自引：1，他引：0  

M. E. Dames  V. K. Abalakin  A. Brahic  M. Bursa  B. H. CHovitz  J. H. Lieske  P. K. Seidelmann  A. T. Sinclair  Y. S. Tjuflin 《Celestial Mechanics and Dynamical Astronomy》1992,53(4):377-397

Every three years the IAU/IAG/COSPAR Working Group on Cartographic Coordinates and Rotational Elements of the Planets and Satellites revises tables giving the directions of the north poles of rotation and the prime meridians of the planets and satellites. Also presented are revised tables giving their sizes and shapes.  相似文献   

历史时期伊犁河谷文化遗址时空特征及驱动力分析   总被引：3，自引：2，他引：1  

王芳  张小雷  杨兆萍  栾福明  熊黑钢  王昭国  时卉 《地理学报》2015,70(5)

运用Arc GIS软件对伊犁河谷文化遗址时空分布进行分析,探讨了遗址时空演变特征与人文历史、自然环境的关系。结果表明:1从夏—西周到清—近现代6个时期中,遗址数量及在总数中的比重、出现频率呈倒"V"型变化,从萌芽阶段到巅峰阶段,至衰落阶段。2遗址的空间分布格局由前3个时期的"东高西低"转变为后3个时期的"西高东低",人类活动空间重心发生了转移。3遗址主要分布在1~5级坡度上,其比重由春秋—秦时期的75%增至清—近现代时期的93.75%;而遗址集中分布高程则由春秋—秦和西汉—南北朝时期的4~8级转移到后3个时期的1~4级,且其数量表现出明显的从高海拔的山地丘陵向低海拔平原、从高坡度向低坡度转移。4研究区遗址演变模式与典型干旱区遗址迁移模式相反,表现为特殊的"中上游→下游"迁移的"湿润模式"。5研究区文化遗址分布、时空演变受政治、经济、生产力等人文因素和地貌、海拔、坡度、气候等自然因素的综合影响。由于其气候湿润,水资源丰富,虽然遗址分布和演变表现出一定的河谷谷地、阶地、平原、水资源等"自然因素"指向性规律,但更突出表现为生产力水平、政治稳定、经济发展、商贸交通等"人文力量"指向性规律,这一点在中后期表现得更为明显。  相似文献   

东濮凹陷三叠系砂岩储层构造裂缝特征及形成期次          下载免费PDF全文

王瑞飞  屈艳梅  吕新华  邓瑞健  国殿斌  苏惠  苏琛 《地质科学》2014,49(4):1269-1278

根据露头、 岩心、 薄片、 古地磁、 成像测井、 岩石力学实验等资料;对东濮凹陷北部三叠系砂岩储层构造裂缝特征及形成期次进行分析。东濮凹陷三叠系砂岩储层主要发育北北东、 北东和近东西向3组高角度构造裂缝;裂缝走向近于平行或垂直主断层;倾向为北西和南东。二马营组裂缝较为发育;和尚沟组和刘家沟组裂缝相对不发育。储层裂缝为3期;分别为燕山早期的北西向扩张裂缝和北北西、 北西西向剪切裂缝;燕山晚期形成北东向拉张裂缝;喜马拉雅期形成北北东、 北东向拉张裂缝、 北北东向剪切裂缝和东西向扩张裂缝。古、 今构造应力场和岩石力学性质的各向异性分析表明;现今构造应力场最大水平主应力和岩石抗压强度的各向异性均影响燕山早期北西向裂缝的张开度及有效性。储层裂缝表现为两期;分别为燕山晚期的北东向拉张裂缝、 喜马拉雅期的北北东、 北东向拉张裂缝;北北东向剪切裂缝和东西向扩张裂缝。研究结果阐明了东濮凹陷北部三叠系砂岩储层构造裂缝特征及发育规律。  相似文献