1948—2001年全球陆地春季降水长期变化的时空特征          下载免费PDF全文

强卫龙  施能 《大气科学学报》2004,27(3):326-335

利用全球陆地月降水资料(PREC/L)中3个月的资料,研究了1948—2001年全球陆地3—5月降水长期变化的时空特征。结果表明,1948—2001年,全球3—5月的降水量以负趋势为主要变化特征,明显减少的区域是:热带非洲、亚洲中西部、中国中东部、俄罗斯东部、南极的恩德比地和威尔克斯地等9个地区;降水量增加的区域是:俄罗斯西北部、美国西北部、加拿大西南部、南美洲南部、加拿大北部等7个地区。还研究了35个纬圈3—5月平均降水量的趋势系数。在分析全球季节降水量与ENSO的关系中,指出春季是春夏秋三季中最不显著的。  相似文献   

The cultural context of forest degradation in adjacent Purépechan communities, Michoacán, Mexico     

Martha A Works  Keith S Hadley 《The Geographical journal》2004,170(1):22-38

Recent changes in the cultural and forest landscapes of the Meseta Purépecha in Michoacán, Mexico as a result of forest degradation underscore the complexity of forest change processes in the tropical highlands of Latin America. Differences in community perception and forest structure and composition between the furniture-making and lumber-producing towns of Pichátaro and Sevina, Purépechan indigenous communities located amidst pine forests on Michoacán's volcanic plateau illustrate the dynamics of this process. We base our comparisons on interviews and field measures of forest structure. Our results show dramatic changes in the forests and cultural landscapes of both communities during the past decade. Following high regional timber exports during the early 1990s, Sevina shifted from a self-sufficient to a timber importation community. By comparison, communal forests and individual parcels in Pichátaro continue to provide wood for approximately 300 wood shops. Field data and forest stand maps confirm the perception of forest degradation in both communities. While Pichátaro has maintained a larger and more diverse forest base to date, stand structure data indicate selective harvesting has led to a shift in dominance toward the less economically desirable pine species and oak. Deforestation and degradation of Sevina and Pichátaro's community forests are symptomatic of both the Meseta Purépecha and Mexico in general. Current forest conditions in both communities justify local, regional, and national concerns regarding declining biodiversity and sustainable economies.  相似文献   

Three-dimensional empirical traveltimes: construction and applications     

T. Nicholson  M. Sambridge  Ó. Gudmundsson 《Geophysical Journal International》2004,156(2):307-328

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Determination of regional stress tensors from fault-slip data   总被引：1，自引：0，他引：1  

Peiliang Xu 《Geophysical Journal International》2004,157(3):1316-1330

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Moscow, the global city? The position of the Russian capital within the European system of metropolitan areas   总被引：1，自引：0，他引：1  

Isolde Brade  Robert Rudolph 《Area》2004,36(1):69-80

During the 1990s, the city of Moscow was subject to an extraordinary transformation in its political, economic and social structures, which had consequences for the position of Moscow within the national and international hierarchy of cities. This article is concerned with the trends that can be discerned regarding the position of Moscow on the national and European scales. Without a doubt, the development of Moscow is characterized by an increasing separation from the national urban system and a growing international orientation. The Russian capital has no competitors on the national level: measured against the relevant economic indicators it is a long way ahead of the remaining Russian cities, which are primarily integrated into national and regional economic flows, and participate in the global economy only to a limited degree. Moscow, in contrast, is increasingly striving to integrate itself into transnational and international economic structures. Although the concept of Moscow as a global city is often instrumentalized in municipal politics, the ability of the Russian capital to act as a global centre is in fact limited. At present Moscow's most important function, from a Central European perspective, is to act as a bridging link between Central and Western Europe and Russia. There is a danger that the spatial disparities between Moscow on the one hand, and the remaining Russian cities and regions on the other, will continue to grow.  相似文献   

Global time variations of hydrological signals from GRACE satellite gravimetry   总被引：10，自引：0，他引：10  

G. Ramillien  A. Cazenave  O. Brunau 《Geophysical Journal International》2004,158(3):813-826

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盐湖环境变化趋势与趋利避害   总被引：4，自引：0，他引：4       下载免费PDF全文

蒋先锋郑绵平  齐文  赵元艺 《中国地质》2004,31(3):294-300

盐湖／湖泊是气候变化的一面镜子本文以国内外典型盐湖区地质灾害为案例。说明自然引起的盐湖地质灾害，人类在事先监测而掌握其变化趋势情况下，可趋利避害，减少损失程度。文中分析在中国西部气候可能由暖干向暖湿转型的情势下，中国盐湖的变化趋势，并就其近期湖水涨缩特点划分3种类型(湖水上涨型区、湖水下降型区和湖水上涨不稳区)。为了适应中国盐湖区气候一湖泊变化，提出在重要盐湖区增建和完善水文、气象观察站，并与遥感监测相结合；建立多学科、跨部门的近期西部盐湖区环境变化的重大基础项目。同时需在重点盐湖区增设防洪防旱水利设施工程、制定湖区生态保护措施等，在筑建盐田和基建工程时应充分考虑洪水泛滥的影响。  相似文献   

地质雷达资料的偏移速度分析和叠前偏移   总被引：2，自引：1，他引：2  

周辉  韩波  邱东玲  裴建新  王兆磊 《吉林大学学报(地球科学版)》2005,35(2):248-252,256

地质雷达资料偏移成像的精度与地下介质介电常数分布的确定精度有直接关系.提出用全局最优化偏移速度分析方法求取介电常数分布.目标函数定义为各共成像点道集零延迟归一化互相关值之和.在假设地下介质是分块的,且每块介质的介电常数可以用有限项的与空间坐标有关的多项式函数来表示的前提下,用遗传算法由浅至深逐块确定使目标函数达到最大的多项式函数的各项系数从而确定介电常数.叠前偏移用时间域有限差分求解麦克斯韦方程组的逆时偏移方法实现.合成雷达记录的偏移速度分析和偏移叠加结果表明,全局最优化偏移速度分析有较高的精度,偏移叠加剖面与实际构造一致.  相似文献   

Influence of the modified global ocean tide model with local tides of East and South China Seas on load gravity in China and its neighbor area     

周江存  孙和平 《地震学报(英文版)》2005,18(3):354-360

Introduction With the development of science and technology, the accuracy of gravity measurement is im-proved. The gravity observation with FG5 gravimeter has reached accuracy of μ magnitude. And the high accurate superconducting gravimeter can detect the tiny signal of 10?2 μ magnitude in frequency domain. With the high-accuracy gravity observation on Earth′s surface, the Earth′s tidal parameters can be determined precisely. And the observations can also be used to invert the struc-ture…  相似文献   

生态水文学与生态水文地质学   总被引：1，自引：0，他引：1  

万力  曹文炳  胡伏生  梁四海  金晓媚 《地质通报》2005,24(8):700-703

在分析生态水文学学科发展过程的基础上，对生态水文地质学的研究对象、内容和方法进行了讨论。生态水文地质学是生态学与水文地质学交叉渗透后形成的学科，是地下水资源可持续利用的理论基础。当前中国生态水文地质学研究的主要任务是生态状况的定量描述、水文地质条件与生态状况的关系、多重界面水分转换机制及其生态效应、含水层中地下水各种物理化学过程的生态效应和气候变化对地下水的影响及其生态响应等问题。生态水文地质学必将在中国实施可持续发展战略的过程中发挥巨大的作用。  相似文献