ECOM模式在丁字湾的应用   总被引：3，自引：3，他引：3  

张越美  孙英兰 《中国海洋大学学报(自然科学版)》2001,31(5):659-665

应用河口、陆架和海洋模式 (ECOM模型 ) ,引入干湿网格法模拟潮滩涨落的改进 ,并建立丁字湾及近岸海域的三维变动边界潮流模型。该模型考虑了湾口拦门沙、湾内水道和人工围海等地形特点。计算结果与实测值比较符合良好 ,较好地刻画出丁字湾 M2 分潮潮流场的时空分布特点。  相似文献   

洞庭盆地两护村孔重矿物特征及其对第四纪构造活动与环境演变的响应   总被引：12，自引：1，他引：11  

柏道远  李长安  陈渡平  周柯军  马铁球  王先辉  彭云益  李纲 《地质论评》2010,56(2):246-260

第四纪洞庭盆地主体自西向东分为安乡凹陷、赤山隆起和沅江凹陷等3个次级构造单元。在安乡凹陷东南部两护村新施工揭穿第四系的ZKC1孔,其地层组成自下而上依次为早更新世华田组、汨罗组,中更新世早期—中期洞庭湖组,晚更新世坡头组以及全新统等。对钻孔岩芯进行了系统的重矿物分析,进而根据特征重矿物来源和含量变化,结合钻孔岩性和岩相变化以及区域地质和地理背景,探讨洞庭盆地南部早—中更新世沉积环境暨河湖变迁以及构造沉降过程。研究表明,洞庭盆地存在幕式断陷活动,早更新世早期、早更新世末期和中更新世中—后期等3个时期强烈断陷沉降,相对湖平面上升,来源于盆地南缘中段的资江河水部分向西注入安乡凹陷,导致ZKC1孔华田组下段下部、汨罗组顶部、洞庭湖组上段等相应层位中的锆石、金红石、锐钛矿和菱铁矿等(主要来源于资江流域)含量显著增高。其它时期断陷作用较弱,河湖水位低,沅水和资江分别沿其主水道于赤山隆起西侧和东侧向北汇入长江,导致ZKC1孔相应沉积层位中锆石、金红石、锐钛矿和菱铁矿的含量明显偏低。对重矿物特征指数变化与孢粉和化学蚀变指数所反映的气候变化的相关性研究,暗示上述3次相对湖平面上升的主要原因不是降水增加,而是构造沉降增强。  相似文献   

我国东北地区降水空间分布及干湿驰豫时间的研究   总被引：8，自引：2，他引：6  

刘会玉  张明阳  林振山 《南京气象学院学报》2004,27(1):97-105

根据东北地区24个典型测站1951—2001年的降水量资料,利用EOF方法分析了我国东北地区的降水空间分布;同时,通过子波诊断技术结合突变点数建模技术,研究了我国东北地区的降水演变周期特征,并对干湿态之间转换的驰豫时间做了定量的研究。结果表明：东北地区的降水空间分布具有整体一致的性质,同时还存在南北及东西的差异;大部分站点都具有干→湿的驰豫时间长于湿→干的驰豫时间的特征,体现了东北地区容易维持干旱状态的特性。  相似文献   

On final evolutions in the restricted planar parabolic three-body problem     

Martha Alvarez  Josep Maria Cors  Joaquin Delgado 《Celestial Mechanics and Dynamical Astronomy》2006,95(1-4):173-200

In this paper, we prove the existence of special type of motions in the restricted planar parabolic three-body problem, of the type exchange, emission–capture, and emission–escape with close passages to collinear and equilateral triangle configuration, among others. The proof is based on a gradient-like property of the Jacobian function when equations of motion are written in a rotating–pulsating reference frame, and the extended phase space is compactified in the time direction. Thus a phase space diffeomorphic to -coordinates (θ, ζ, ζ′) is obtained with the boundary manifolds θ = ± π/2 corresponding to escapes of the binaries when time tends to ± ∞. It is shown there exists exactly five critical points on each boundary, corresponding to classic homographic solutions. The connections of the invariant manifolds associated to the collinear configurations, and stable/unstable sets associated to binary collision on the boundary manifolds, are obtained for arbitrary masses of the primaries. For equal masses extra connections are obtained, which include equilateral configurations. Based on the gradient-like property, a geometric criterion for capture is proposed and is compared with a criterion introduced by Merman (1953b) in the fifties, and an example studied numerically by Kocina (1954).  相似文献   

An Integrated Analysis of Dry-Wet Variability in Western China for the Last 4-5 Centuries     

钱维宏  林祥 《大气科学进展》2009,26(5):951-961

An overview of dry-wet climate variability among monsoon-westerly regions and the monsoon northernmost marginal active zone in China   总被引：7，自引：2，他引：5  

钱维宏  丁婷  胡豪然  林祥  秦爱民 《大气科学进展》2009,26(4):630-641

Climate in mainland China can be divided into the monsoon region in the southeast and the westerly region in the northwest as well as the intercross zone, i.e., the monsoon northernmost marginal active zone that is oriented from Southwest China to the upper Yellow River, North China, and Northeast China. In the three regions, dry-wet climate changes are directly linked to the interaction of the southerly monsoon flow on the east side of the Tibetan Plateau and the westerly flow on the north side of the Plateau from the inter-annual to inter-decadal timescales. Some basic features of climate variability in the three regions for the last half century and the historical hundreds of years are reviewed in this paper. In the last half century, an increasing trend of summer precipitation associated with the enhancing westerly flow is found in the westerly region from Xinjiang to northern parts of North China and Northeast China. On the other hand, an increasing trend of summer precipitation along the Yangtze River and a decreasing trend of summer precipitation along the monsoon northernmost marginal active zone are associated with the weakening monsoon flow in East Asia. Historical documents are widely distributed in the monsoon region for hundreds of years and natural climate proxies are constructed in the non-monsoon region, while two types of climate proxies can be commonly found over the monsoon northernmost marginal active zone. In the monsoon region, dry-wet variation centers are altered among North China, the lower Yangtze River, and South China from one century to another. Dry or wet anomalies are firstly observed along the monsoon northernmost marginal active zone and shifted southward or southeastward to the Yangtze River valley and South China in about a 70-year timescale. Severe drought events are experienced along the monsoon northernmost marginal active zone during the last 5 centuries. Inter-decadal dry-wet variations are depicted by natural proxies for the last 4--5 centuries in several areas over the non-monsoon region. Some questions, such as the impact of global warming on dry-wet regime changes in China, complex interactions between the monsoon and westerly flows in Northeast China, and the integrated multi-proxy analysis throughout all of China, are proposed.  相似文献   

Characteristics of dry-wet abrupt alternation events in the middle and lower reaches of the Yangtze River Basin and the relationship with ENSO   总被引：1，自引：0，他引：1  

Lijie Shan  Liping Zhang  Jiyun Song  Yanjun Zhang  Dunxian She  Jun Xia 《地理学报(英文版)》2018,28(8):1039-1058

During recent decades, more frequent flood-drought alternations have been seen in China as a result of global climate change and intensive human activities, which have significant implications on water and food security. To better identify the characteristics of flood-drought alternations, we proposed a modified dry-wet abrupt alternation index (DWAAI) and applied the new method in the middle and lower reaches of the Yangtze River Basin (YRB-ML) to analyze the long-term spatio-temporal characteristics of dry-wet abrupt alternation (DWAA) events based on the daily precipitation observations at 75 rainfall stations in summer from 1960 to 2015. We found that the DWAA events have been spreading in the study area with higher frequency and intensity since 1960. In particular, the DWAA events mainly occurred in May and June in the northwest of the YRB-ML, including Hanjiang River Basin, the middle reaches of the YRB, north of Dongting Lake and northwest of Poyang Lake. In addition, we also analyzed the impact of El Niño Southern Oscillation (ENSO) on DWAA events in the YRB-ML. The results showed that around 41.04% of DWAA events occurred during the declining stages of La Niña or within the subsequent 8 months after La Niña, which implies that La Niña events could be predictive signals of DWAA events. Besides, significant negative correlations have been found between the modified DWAAI values of all the rainfall stations and the sea surface temperature anomalies in the Nino3.4 region within the 6 months prior to the DWAA events, particularly for the Poyang Lake watershed and the middle reaches of the YRB. This study has significant implications on the flood and drought control and water resources management in the YRB-ML under the challenge of future climate change.  相似文献   

酸性环境干湿循环对泥质砂岩力学特性影响的试验研究   总被引：2，自引：0，他引：2  

刘新荣  张梁  傅晏 《岩土力学》2014,35(Z2):45-52

由于库水位升降及降雨等原因,岩体经常处于干湿交替状态,对岩体工程的长期稳定性不利。以三峡库区泥质砂岩为研究对象,进行了酸性环境干湿循环交替作用后的常规单轴与三轴压缩试验研究,获得了泥质砂岩在酸性溶液浸泡干湿循环后的相关力学参数。相对于没有经过干湿循环作用的干燥试件,经过不同次数的干湿循环作用后,泥质砂岩的弹性模量、单轴抗压强度、黏聚力与内摩擦角都有不同程度的降低。各个力学指标的总体变化趋势是在第一次饱水之后有大幅度的降低,此后随着干湿循环次数的增加其降低的幅度逐渐减小。同时,酸性溶液的pH值对力学指标的影响很大,存在对泥质砂岩力学性能影响较大的一个临界pH值,低于此值酸性溶液对泥质砂岩力学性能影响显著增大,高于此值酸性溶液对其力学性能影响较小。  相似文献   

复合盐与干湿循环双重因素作用下混凝土耐久性试验     

宿晓萍  王清 《吉林大学学报(地球科学版)》2013,43(3):851-857

吉林省大安市是松嫩平原土壤盐渍化最严重的地区之一,以苏打盐渍土为主,境内的土壤与地表水中的易溶盐分量相似。为了研究复合盐与干湿交替环境下混凝土的耐久性,根据大安地区盐渍土中主要易溶盐的含量,配制了4种不同质量分数的复合盐侵蚀溶液,再以水溶液用于试验对比,共制备了5种配合比的混凝土,进行盐浸-热烘试验。结果表明：在干湿循环条件下,复合盐对混凝土材料有较强的腐蚀性,而且盐溶液的质量分数越大,混凝土破坏越严重;干湿循环作用后,混凝土的质量变化规律为先增加后减少,而动弹性模量先呈小幅增长,达到一定干湿循环次数后,呈下降趋势;引气剂与粉煤灰均能够提高混凝土抗盐蚀-干湿循环的破坏能力,但引气混凝土提高效果更显著。  相似文献   

西南地区秋季干湿时空变化特征及其成因分析   总被引：4，自引：2，他引：2  

徐栋夫  李栋梁  曲巧娜  赵晓萌 《热带气象学报》2013,29(4):570-580

利用西南地区97站1960—2009年的日平均气温、降水量资料计算干湿指数,分析了西南地区秋季干湿、降水、气温的时空变化特征,并使用再分析资料探讨其异常的大气环流特征。结果表明:西南地区秋季在1980年代末期出现干旱化趋势,21世纪初干旱化趋势明显,其中以东部干旱化趋势显著。西南地区秋季干湿变化存在全区域一致和东、西部相反变化两个主要异常模态,而且干湿异常的空间模态主要由降水异常决定,其演变则受气温的影响更明显一些。全区域一致变化的模态与前期夏季西太平洋暖池附近海温以及同期西太平洋副高、东亚大槽、南支槽有关,并且此模态对应的偏干年基本上均是高温和少雨共同作用造成的,而偏湿年则有低温偏湿和多雨偏湿两种类型。东、西部相反变化的模态与垂直运动和东部低层的南、北风异常有关。   相似文献