Do recent emission trends imply higher emissions forever?     

Detlef P. van Vuuren  Keywan Riahi 《Climatic change》2008,91(3-4):237-248

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基于ENVISAT/ASAR资料的土壤湿度反演方法   总被引：3，自引：0，他引：3  

张堂堂  文军  韦志刚  刘蓉  刘远永  李振朝 《高原气象》2008,27(2):279-285

提出了利用ENVISAT/ASAR/AP模式VV极化的低入射角数据和黄土高原陆面过程试验资料对黄土高原平凉试验区表层土壤湿度进行反演的方法。结果表明:在相对平坦的混合地表类型区域,反演的土壤湿度与地面实测值平均误差<0.02 cm3.cm-3,绝对误差均在0.04 cm3.cm-3范围内,该结果能较好地对黄土高原塬区土壤湿度进行干旱监测;但在陡峭山坡及塬边等地形起伏较大的区域,结果较差。  相似文献   

The Turbulent Lagrangian Time Scale in Forest Canopies Constrained by Fluxes,Concentrations and Source Distributions   总被引：1，自引：1，他引：0  

Vanessa Haverd  Ray Leuning  David Griffith  Eva van Gorsel  Matthias Cuntz 《Boundary-Layer Meteorology》2009,130(2):209-228

One-dimensional Lagrangian dispersion models, frequently used to relate in-canopy source/sink distributions of energy, water and trace gases to vertical concentration profiles, require estimates of the standard deviation of the vertical wind speed, which can be measured, and the Lagrangian time scale, T _L , which cannot. In this work we use non-linear parameter estimation to determine the vertical profile of the Lagrangian time scale that simultaneously optimises agreement between modelled and measured vertical profiles of temperature, water vapour and carbon dioxide concentrations within a 40-m tall temperate Eucalyptus forest in south-eastern Australia. Modelled temperature and concentration profiles are generated using Lagrangian dispersion theory combined with source/sink distributions of sensible heat, water vapour and CO₂. These distributions are derived from a multilayer Soil-Vegetation-Atmospheric-Transfer model subject to multiple constraints: (1) daytime eddy flux measurements of sensible heat, latent heat, and CO₂ above the canopy, (2) in-canopy lidar measurements of leaf area density distribution, and (3) chamber measurements of CO₂ ground fluxes. The resulting estimate of Lagrangian time scale within the canopy under near-neutral conditions is about 1.7 times higher than previous estimates and decreases towards zero at the ground. It represents an advance over previous estimates of T _L , which are largely unconstrained by measurements.  相似文献   

The importance of three centuries of land-use change for the global and regional terrestrial carbon cycle   总被引：4，自引：0，他引：4  

Jelle G. Van Minnen  Kees Klein Goldewijk  Elke Stehfest  Bas Eickhout  Gerard van Drecht  Rik Leemans 《Climatic change》2009,97(1-2):123-144

Large amounts of carbon (C) have been released into the atmosphere over the past centuries. Less than half of this C stays in the atmosphere. The remainder is taken up by the oceans and terrestrial ecosystems. Where does the C come from and where and when does this uptake occur? We address these questions by providing new estimates of regional land-use emissions and natural carbon fluxes for the 1700–2000 period, simultaneously considering multiple anthropogenic (e.g. land and energy demand) and biochemical factors in a geographically explicit manner. The observed historical atmospheric CO₂ concentration profile for the 1700 to 2000 period has been reproduced well. The terrestrial natural biosphere has been a major carbon sink, due to changes in climate, atmospheric CO₂, nitrogen and management. Due to land-use change large amounts of carbon have been emitted into the atmosphere. The net effect was an emission of 35 Pg C into the atmosphere for the 1700 to 2000 period. If land use had remained constant at its distribution in 1700, then the terrestrial C uptake would have increased by 142 Pg C. This overall difference of including or excluding land-use changes (i.e. 177 Pg C) comes to more than half of the historical fossil-fuel related emissions of 308 Pg C. Historically, global land-use emissions were predominantly caused by the expansion of cropland and pasture, while wood harvesting (for timber and fuel wood) only played a minor role. These findings are robust even when changing some of the important drivers like the extent of historical land-use changes. Under varying assumptions, land-use emissions over the past three centuries could have increased up to 20%, but remained significantly lower than from other sources. Combining the regional land-use and natural C fluxes, North America and Europe were net C sources before 1900, but turned into sinks during the twentieth century. Nowadays, these fluxes are a magnitude smaller than energy- and industry-related emissions. Tropical regions were C neutral prior to 1950, but then accelerated deforestation turned these regions into major C sources. The energy- and industry-related emissions are currently increasing in many tropical regions, but are still less than the land-use emissions. Based on the presented relevance of the land-use and natural fluxes for the historical C cycle and the significance of fossil-fuel emissions nowadays, there is a need for an integrated approach for energy, nature and land use in evaluating possible climate change mitigation policies.  相似文献   

Spatial and temporal variation in climate change: a bird’s eye view     

Joseph J. Fontaine  Karie L. Decker  Susan K. Skagen  Charles van Riper III 《Climatic change》2009,97(1-2):305-311

Recent changes in global climate have dramatically altered worldwide temperatures and the corresponding timing of seasonal climate conditions. Recognizing the degree to which species respond to changing climates is therefore an area of increasing conservation concern as species that are unable to respond face increased risk of extinction. Here we examine spatial and temporal heterogeneity in the rate of climate change across western North America and discuss the potential for conditions to arise that may limit the ability of western migratory birds to adapt to changing climates. Based on 52 years of climate data, we show that changes in temperature and precipitation differ significantly between spring migration habitats in the desert southwest and breeding habitats throughout western North America. Such differences may ultimately increase costs to individual birds and thereby threaten the long-term population viability of many species.  相似文献   

Annual variation of the southern boundary current in the Banda Sea   总被引：1，自引：0，他引：1  

Fadli Syamsudin  Hendrik M. van Aken  Arata Kaneko 《Dynamics of Atmospheres and Oceans》2010

ADCP measurements in the southern Banda Sea, obtained with the bulk carrier “MS First Jupiter” from 1997 until 2000, have been analysed. The observations reveal the presence of an eastward flowing southern boundary current, bringing water from the Indonesian throughflow towards the connections with the Indian Ocean in Ombai Strait and the Timor Sea. The mean transport in the upper 300 m is estimated to be about 5 Sv, over 50% of the outflow towards the Indian Ocean in this layer through the eastern passages near Timor. The velocity in the boundary current shows a clear annual variation, more or less in phase with the annually varying inflow through Makassar Strait and the outflow near Timor. The phase of the annual variation cannot be explained by the monsoonal variation of the local winds. Therefore this annual variation of the throughflow is probably generated by large-scale forcing. A considerable reduction of the strength of the boundary current was observed in 1998, following the 1997–1998 El Niño with a delay of about half a year. On shorter time scales, Kelvin waves, entering the Banda Sea from the Indian Ocean, cause flow reversals of the boundary current.  相似文献   

Diurnal and Seasonal Trends in Convective Mixed-Layer Heights Estimated from Two Years of Continuous Ceilometer Observations in Vancouver,BC     

Derek van der Kamp  Ian McKendry 《Boundary-Layer Meteorology》2010,137(3):459-475

Twenty-six months of continuous ceilometer data are used to estimate the convective mixed-layer height for 710 days by identifying backscatter gradients associated with the entrainment zone. To accomplish this, a semi-automatic procedure is developed that removes all non-applicable data before applying a mixed-layer height algorithm to the backscatter profiles. Two different algorithms for estimating the mixed-layer height are assessed: the minimum-gradient method and the ideal-profile method. The latter of these two algorithms is found to be more robust. Comparisons of mixed-layer height values estimated from the ceilometer agree with previous observations with slightly higher estimates in the mornings and evenings. For clear days with no cumulus cloud formation, the seasonal cycle in mixed-layer heights peaks in late June to early July. Daily maximum values are suppressed by the site’s coastal location, remaining below 800 m for all but a few days. The mean daily maximum mixed-layer height increases by 384 m for days with boundary-layer clouds. The mean summer diurnal trend is found not to differ greatly from that in spring on clear days, while days with boundary-layer clouds have higher spring values than in summer. Net surface heat flux and synoptic stability likely have the largest influence on the mixed-layer heights. Additionally, large intra-monthly variability suggests a strong influence from regional dynamics.  相似文献   

Study of the total lightning activity in a hailstorm   总被引：1，自引：0，他引：1  

Joan Montany  Serge Soula  Nicolau Pineda  Oscar van der Velde  Pere Clapers  Glria Sol  Joan Bech  D. Romero 《Atmospheric Research》2009,91(2-4):430-437

A thunderstorm that developed over northeastern Spain on 16 June 2006 is analyzed. This severe thunderstorm produced hailstones as large as 40 mm and had a lifetime of 3 h and 30 min. Radar cross-sections show strong vertical development with cloud echo tops reaching an altitude of 13 km. The specific characteristics of the lightning activity of this storm were: (i) a large amount (81%) of negative cloud-to-ground (−CG) flashes with very low peak currents (< 10 kA in absolute value), (ii) a very large proportion of intra-cloud (IC) flashes with an IC/CG ratio reaching about 400, (iii) a large number of “short” IC flashes (with only 1-VHF source according to SAFIR detection), (iv) a large increase of the −CG flash rate and of the CG proportion near the end of the storm. The rate of −CG flashes with a low peak current were observed to evolve similarly to the rates of IC flashes. Most of them have been assumed to be IC flashes misclassified by the Spanish Lightning Detection Network (SLDN). They have been filtered as it is usually done for misclassified +CG flashes. After this filtering, CG flash rates remained very low (< 1 min^− 1) with +CG flashes sometimes dominant. All the particular lightning activity characteristics similar to those observed in the Severe Thunderstorm Electrification and Precipitation Study (STEPS) campaigns support the hypothesis that this thunderstorm could have had an inverted-polarity or complex charge structure. The maximum IC flash rate (67 min^− 1) peaked 24 min before the presence of reflectivity higher than 60 dBZ. The IC activity abruptly decreased during the period when reflectivity was dramatically increasing. The time of maximum reflectivity observed by radar was consistent with the times of reported hail at the ground.  相似文献   

Identification, definition and quantification of goods and services provided by marine biodiversity: implications for the ecosystem approach     

Beaumont NJ  Austen MC  Atkins JP  Burdon D  Degraer S  Dentinho TP  Derous S  Holm P  Horton T  van Ierland E  Marboe AH  Starkey DJ  Townsend M  Zarzycki T 《Marine pollution bulletin》2007,54(3):253-265

This paper identifies and defines ecosystem goods and services provided by marine biodiversity. Case studies have been used to provide an insight into the practical issues associated with the assessment of marine ecosystem goods and services at specific locations. The aim of this research was to validate the definitions of goods and services, and to identify knowledge gaps and likely difficulties of quantifying the goods and services. A validated theoretical framework for the assessment of goods and services is detailed, and examples of the goods and services at a variety of case study areas are documented. These results will enable future assessments of marine ecosystem goods and services. It is concluded that the utilisation of this goods and services approach has the capacity to play a fundamental role in the Ecosystem Approach, by enabling the pressures and demands of society, the economy and the environment to be integrated into environmental management.  相似文献   

PQLI measure of development: A study of literacy and basic resources in India   总被引：1，自引：0，他引：1  

B. K. Roy Ph. D. 《GeoJournal》1985,10(1):75-81

There are various tools to measure infrastructural development as applied with considerations of statistical data and geographical phenomena. As example, the Physical Quality of Life Index (PQLI) measure has been tested on death and birth statistics and some consciousness has been reached of being reasonably acceptable tool to measure awareness of dynamism of such phenomena. An attempt has been made to consider some special data on resources and literacy in population independently and tested some issues to examine the gaps in the contemporary situation of India's development. This is the central theme outlined in this experiment to focus intensive research modifications on the concept developed by Morris D. Morris. It is essential that this research may be viewed critically by all concerned to further investigate on the issues for application on other sets of data and regions.The views expressed in the paper are of author's own and have no relation to his service in the Government of India's Office of the Registrar General, India.  相似文献