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881.
Anna Maria Jnsson Maj-Lena Linderson Ingrid Stjernquist Peter Schlyter Lars Brring 《Global and Planetary Change》2004,44(1-4):195
In boreal and nemoboreal forests, tree frost hardiness is modified in reaction to cues from day length and temperature. The dehardening processes in Norway spruce, Picea abies, could be estimated to start when the daily mean temperature is above 5 °C for 5 days. Bud burst will occur approximately after 120–170 degree-days above 5 °C, dependent on genetic differences among provenances. A reduced cold hardiness level during autumn and spring and an advanced onset of bud burst are expected impacts of projected future global warming. The aim of this study was to test if this will increase the risk for frost damage caused by temperature backlashes. This was tested for Sweden by comparing output from the Hadley Centre regional climate model, HadRM3H, for the period 1961–1990 with future IPCC scenario SRES A2 and B2 for 2070–2099. Different indices for calculating the susceptibility to frost damage were used to assess changes in frost damage risk. The indices were based on: (1) the start of dehardening; (2) the severity of the temperature backlash; (3) the timing of bud burst; and (4) the cold hardiness level. The start of dehardening and bud burst were calculated to occur earlier all over the country, which is in line with the overall warming in both climate change scenarios. The frequency of temperature backlashes that may cause frost damage was calculated to increase in the southern part, an effect that became gradually less pronounced towards the north. The different timing of the onset of dehardening mainly caused this systematic latitudinal pattern. In the south, it occurs early in the year when the seasonal temperature progression is slow and large temperature variations occur. In the north, dehardening will occur closer to the spring equinox when the temperature progression is faster. 相似文献
882.
. The excess radio-path delay due to the atmospheric water vapor, the wet delay, can be derived from water vapor radiometer
(WVR) measurements. WVR data used for external calibration of space geodetic measurements are not always acquired in the directions
of the space geodetic signal sources, thus extrapolation and interpolation methods for the wet delay are needed. We evaluate
three different methods using approximately 10 days of WVR measurements. Two methods, the gradient method and turbulence method,
use the directional information in the data, while the third method used is linear regression in time regardless of the direction
of the observations. The turbulence method yielded at least 10% less RMS estimation error than the errors from the other two
methods.
Received: 20 May 1997 / Accepted: 15 December 1997 相似文献
883.
A Grid Point Search Algorithm (GRIPSA) for fast integer ambiguity resolution is presented. In the proposed algorithm, after
the orthogonal transformation of the original ambiguity parameters, the confidence ellipsoid of the new parameters is represented
by a rectangular polyhedron with its edges parallel to the corresponding axes. A cubic grid covering the whole polyhedron
is then identified and transformed back to the original coordinate system. The integer values of the corresponding transformed
grid points are obtained by rounding off the transformed values to their nearest integer values. These values are then tested
as to whether they are located inside the polyhedron. Since the identification of the grid points in the transformed coordinate
system greatly reduces the search region of the integer ambiguities, marked improvements are obtained in the computational
effort.
Received: 13 October 1997 / Accepted: 9 June 1998 相似文献
884.
P. Nsombo 《Journal of Geodesy》1998,72(3):144-153
In the determination of the preliminary geoid over Zambia, we compare three methods of the modified Stokes formula: that
of Vincent and Marsh, a modified Wong and Gore method, and a modified spectral weighting method, with the final solution being
estimated by the modified Wong and Gore procedure. The geoid over Zambia (based on GRS80) is rising from north-east to south-west.
It coincides with the reference ellipsoid in the north-western and southern regions of Zambia. The preliminary estimate indicates
maximum and minimum values of about 13.7 and −16.8m, respectively. The mean geoid over the area is −2.8m. Formal analysis
of global root mean square errors for the three models leads us to conclude that for an integration cap radius of about 3
or less, the modified formula using optimal spectral weighting is superior to the Vincent and Marsh method, and to the modified
and unmodified Wong and Gore.
Received: 8 October 1996 / Accepted: 25 June 1997 相似文献
885.
886.
湿大气方程组解的渐近性质 总被引:4,自引:0,他引:4
研究无穷维Hilbert空间中,湿大气运动系统解的长期行为,在导得了湿大气运动方程是Hilbert空间中一个非常特殊的算子方程之后,利用算子的性质讨论了全局吸收集和全局吸引子的存在性,揭示出系统解的渐近行为表现在吸引子的结构上及系统向非绝热加热的非线性适应过程。最后指出了几个简化方程组与原方程组在解的长期行为上的根本不同,从而给出长期天气或气候研究中简化方程组必须遵循的原则。 相似文献
887.
近十五年全球臭氧变化 总被引:16,自引:1,他引:15
利用卫星观测臭氧总含量TOMS(第7版)资料,在剔除季节变化后对全球60°S-60°N范围首先进行了沿纬度分布的线性趋势和周期分析。结果表明:自本世纪70年代末,各纬带上的臭氧总量都呈下降趋势,强度随纬度升高而加剧,并发现总体上北半球臭氧的下降趋势较南半球更加明显;同时证实了准两年振荡是臭氧变化中除年周期外最显著的周期。并对臭氧变化中的准两年振荡作了遥相关分析;发现准两年振荡在强度和位相上基本呈纬向分布并主要表现出赤道对称的特征。135~170°E地区臭氧总量变化所表现出的不同于其它地区的原因可能是这一地区常年频繁出现的对流活动;而臭氧总量下降趋势表现出的北半球同纬度地区均大于南半球的南北半球差异可能是由两半球人类活动的差异引起 相似文献
888.
中国第一个“金钉子”剖面的建立 总被引:17,自引:5,他引:12
中国浙江常山黄泥塘发育了穿越中奥陶统达瑞威尔阶底界的连续地层剖面,笔石和牙形刺的连续演化序列使之得以成为全球对比的标准。经国际地层委员会奥陶系分会、国际地层委员会和国际地科联邮投和批准,已成为达瑞威尔阶的全球层型剖面点。 相似文献
889.
天然气——21世纪的能源 总被引:2,自引:1,他引:1
天然气是一种生态型能源或理想的城市能源。综述了世纪之交的全球天然气工业发展状况,包括储量的增长、输气管道的延长、液化天然气厂的发展和天然气利用技术的进步。介绍了有关国家的天然气利用法规和政策。预测了21世纪全世界天然气供需趋势。论述了为什么说天然气是21世纪的能源。指出了当前和未来全球天然气工业面临的挑战。 相似文献
890.
Small-scale fisheries are becoming a global social and environmental concern. The contribution of marine small-scale fisheries to global food security and coastal livelihoods, coupled with the significant challenges they face, has attracted increasing attention and aid from environmental organizations, philanthropies, and multilateral agencies over recent decades. Our study attends to the understudied role of the World Bank, the largest individual funder shaping present and future sustainability of coastal marine regions, as a key actor shaping global environmental governance paradigms. We asked how funding to the sector has changed over the last 50 years and why, outlining distinct patterns in the flow of small-scale fisheries aid and the underlying intervention models. We contextualize our quantitative analysis of aid patterns over time with qualitative interview data with bank staff, identifying underlying paradigm shifts driven by internal and external factors. More than $2.48 billion was allocated by the World Bank to marine fisheries over the last 50 years, approximately 47% (~$1.17 billion) of which was targeted to marine small-scale fisheries. Three distinct funding periods are identified: rising support to SSF from the 1970s to mid-1980s; a sharp decline in funding in the mid-to-late 1980s and low levels of funding throughout the 1990s; and a steady return to funding SSF in the mid-2000s up to the present. Over time, Bank-funded interventions shifted from pure economic development in the earlier era, to an emphasis on governance and multi-dimensional environmental goals in the recent period. To understand why, we used key-informant interviews to unpack major internal drivers: internal staff changes and presence of key individuals, the decentralization and recentralization of decision-making, and the organization’s shifting emphasis from traditional economic growth to multi-dimensional objectives of poverty reduction, among others. External drivers behind funding and paradigm shifts included pressure from the environmental movement, the rise of sustainable development discourses, key global environmental summits in the 1990s, and rising levels of interest in the fisheries sector by the governments of both donor and recipient countries. Processes of ‘paradigm shifts’ were not swift or singular, rather they were affected by multiple, convergent factors over time. Our findings contribute to the literature on multi-lateral institutions as key actors in environmental governance shaping global development thinking, illustrating the arc of the last half-century of fisheries aid at the Bank while highlighting present dilemmas and future challenges that actors interested in working towards sustainable marine small-scale fisheries face. 相似文献