Regional and Global Land Data Assimilation Systems: Innovations,Challenges, and Prospects

Since the North American and Global Land Data Assimilation Systems(NLDAS and GLDAS) were established in2004, significant progress has been made in development of regional and global LDASs. National, regional, projectbased, and global LDASs are widely developed across the world. This paper summarizes and overviews the development, current status, applications, challenges, and future prospects of these LDASs. We first introduce various regional and global LDASs including their development history and innovations, and then discuss the evaluation, validation, and applications(from numerical model prediction to water resources management) of these LDASs. More importantly, we document in detail some specific challenges that the LDASs are facing: quality of the in-situ observations, satellite retrievals, reanalysis data, surface meteorological forcing data, and soil and vegetation databases; land surface model physical process treatment and parameter calibration; land data assimilation difficulties; and spatial scale incompatibility problems. Finally, some prospects such as the use of land information system software, the unified global LDAS system with nesting concept and hyper-resolution, and uncertainty estimates for model structure,parameters, and forcing are discussed.     

生物泵在海洋碳循环中的作用

生物过程在海洋碳的自然分布中起着重要的作用,它使海洋中碳的储量大大增加.作者用包含海洋化学过程和一个简单生物过程的三维碳循环模式模拟了生物泵在海洋碳循环中的作用.模式计算的结果表明:生物过程产生的海-气通量的量级非常大;在高纬度和赤道它的量级与因溶解度泵产生的碳的海-气通量差不多.在高纬度地区这两个通量符号相反,使组合模式中的通量大小比只有溶解度泵时的通量小,而在赤道两者的符号相同,使组合模式在赤道的通量大于只有溶解度泵时的通量.在稳态条件下生物泵对海洋吸收人为CO2的直接影响很小.     

节能减排与中国经济的低碳发展

 自1978年实行改革开放以来,中国走的是一条赶超型或压缩型的工业化道路。伴随着经济的高速增长,发达国家上百年工业化过程中分阶段出现的种种资源和环境问题在中国集中显现。面对资源短缺、环境污染和气候变化对经济增长的瓶颈性约束,国家在"十一五"规划纲要中提出了节能减排的具体目标。文章概述了"十一五"规划提出节能减排目标的背景,分析了其对控制温室气体排放的重要意义,总结了目前节能减排工作取得的成绩和存在的困难,提出了中国发展低碳经济的政策建议。     

节能减排与中国经济的低碳发展

自1978年实行改革开放以来,中国走的是一条赶超型或压缩型的工业化道路。伴随着经济的高速增长,发达国家上百年工业化过程中分阶段出现的种种资源和环境问题在中国集中显现。面对资源短缺、环境污染和气候变化对经济增长的瓶颈性约束,国家在"十一五"规划纲要中提出了节能减排的具体目标。文章概述了"十一五"规划提出节能减排目标的背景,分析了其对控制温室气体排放的重要意义,总结了目前节能减排工作取得的成绩和存在的困难,提出了中国发展低碳经济的政策建议。     

Uncertainty of Climate Response to Natural and Anthropogenic Forcings Due to Different Land Use Scenarios

The A.M.Obukhov Institute of Atmospheric Physics,Russian Academy of Sciences (IAP RAS) climate model (CM) of intermediate complexity is extended by a spatially explicit terrestrial carbon cycle module.Numerical experiments with the IAP RAS CM are performed forced by the reconstructions of anthropogenic and natural forcings for the 16th to the 20th centuries and by combined SRES (Special Report on Emission Scenarios) A2-LUH (Land Use Harmonization) anthropogenic scenarios for the 21st century.Hereby,the impact of uncertainty in land-use scenarios on results of simulations with a coupled climate-carbon cycle model is tested.The simulations of the model realistically reproduced historical changes in carbon cycle characteristics.In the IAP RAS CM,climate warming reproduced in the 20th and 21st centuries enhanced terrestrial net primary production but terrestrial carbon uptake was suppressed due to an overcompensating increase in soil respiration.Around year 2100,the simulations the model forced by different land use scenarios diverged markedly,by about 70 Pg (C) in terms of biomass and soil carbon stock but they differed only by about 10 ppmv in terms of atmospheric carbon dioxide content.     

Numerical Simulation Study on the Impacts of Tropospheric and CO_2 Concentration Changes on Winter Wheat. Part I: Model Description

Ozone is well documented as the air pollutant most damaging to agricultural crops and other plants. It is reported that tropospheric O3 concentration increases rapidly in recent 20 years. Evaluating and predicting impacts of ozone concentration changes on crops are drawing great attention in the scientific community. In China, main study method about this filed is controlled experiments, for example, Open Top Chambers. But numerical simulation study about impacts of ozone on crops with crop model was developed slowly, what is more, the study about combined impacts of ozone and carbon dioxide has not been reported. The improved agroecosystem model is presented to evaluate simultaneously impacts of tropospheric O3 and CO2 concentration changes on crops in the paper by integrating algorithms about impacts of ozone on photosynthesis with an existing agroecosystem biogeochemical model (named as DNDC). The main physiological processes of crop growth (phenology, leaf area index, photosynthesis, respiration, assimilated allocation and so on) in the former DNDC are kept. The algorithms about impacts of ozone on photosynthesis and winter wheat leaf are added in the modified DNDC model in order to reveal impacts of ozone and carbon dioxide on growth, development, and yield formation of winter wheat by coupling the simulation about impacts of carbon dioxide on photosynthesis of winter wheat which exists in the former DNDC. In the paper, firstly assimilate allocation algorithms and some genetic parameters (such as daily thermal time of every development stage) were modified in order that DNDC can be applicable in North China. Secondly impacts of ozone on crops were simulated with two different methods- one was impacts of ozone on light use efficiency, and the other was direct effects of ozone on leaves photosynthesis. The latter simulated results are closer to experiment measurements through comparing their simulating results. At last the method of direct impacts of ozone on leaf growth is adopted and the coefficients about impacts of ozone on leaf growth and death are ascertained. Effects of climate changes, increasing ozone, and carbon dioxide concentration on agroecosystem are tried to be simulated numerically in the study which is considered to be advanced and credible.     

Numerical Simulation Study on the Impacts of Tropospheric O3 and CO2 Concentration Changes on Winter Wheat.Part I: Model Description

Ozone is well documented as the air pollutant most damaging to agricultural crops and other plants.It is reported that tropospheric O3 concentration increases rapidly in recent 20 years. Evaluating and predicting impacts of ozone concentration changes on crops are drawing great attention in the scientific community. In China, main study method about this filed is controlled experiments, for example, Open Top Chambers. But numerical simulation study about impacts of ozone on crops with crop model was developed slowly, what is more, the study about combined impacts of ozone and carbon dioxide has not been reported.The improved agroecosystem model is presented to evaluate simultaneously impacts of tropospheric O3 and CO2 concentration changes on crops in the paper by integrating algorithms about impacts of ozone on photosynthesis with an existing agroecosystem biogeochemical model (named as DNDC). The main physiological processes of crop growth (phenology, leaf area index, photosynthesis, respiration, assimilated allocation and so on) in the former DNDC are kept. The algorithms about impacts of ozone on photosynthesis and winter wheat leaf are added in the modified DNDC model in order to reveal impacts of ozone and carbon dioxide on growth, development, and yield formation of winter wheat by coupling the simulation about impacts of carbon dioxide on photosynthesis of winter wheat which exists in the former DNDC. In the paper, firstly assimilate allocation algorithms and some genetic parameters (such as daily thermal time of every development stage) were modified in order that DNDC can be applicable in North China. Secondly impacts of ozone on crops were simulated with two different methods-one was impacts of ozone on light use efficiency , and the other was direct effects of ozone on leaves photosynthesis. The latter simulated results are closer to experiment measurements through comparing their simulating results. At last the method of direct impacts of ozone on leaf growth is adopted and the coe cients about impacts of ozone on leaf growth and death are ascertained. Effects of climate changes, increasing ozone, and carbon dioxide concentration on agroecosystem are tried to be simulated numerically in the study which is considered to be advanced and credible.     

二维能量平衡模式对若干气候问题的研究

Based on a two-dimensional energy balance model, the studies on some climatic issues such as the re- lationship between ice cap latitude and solar constant, desertifieation, and the warming effect of carbon dioxide, have been reviewed and discussed. The phenomenon that a fixed solar constant might correspond to different equilibrium ice cap latitudes is determined by the continuity of albedo distribution. The disconti- nuity in albedo distribution increases the number of equilibrium ice cap latitudes. Desert would expand both northward and southward when desert surface albedo is increasing. This would deteriorate the ecological environment in border regions, and then threaten the existence of local inhabitants. Melting of the polar ice would not be accelerated, with increasing carbon dioxide concentration. The ice cap latitude would move northward slowly, with some “hiatus” periods, under the slowly increasing global average surface tempera- ture. According to the current research, future development of the two-dimensional energy balance model and possible progress are also forecasted.     

Modelling long-term HFC emissions from India's residential air-conditioning sector: exploring implications of alternative refrigerants,best practices,and a sustainable lifestyle within an integrated assessment modelling framework

India's growing role in the global climate debate makes it imperative to analyse emission reduction policies and strategies across a range of GHGs, especially for under-researched non-CO₂ gases. Hydrofluorocarbons' (HFCs) usage in cooling equipment and subsequent emissions are expected to increase dramatically in India with the phase-out of hydrochlorofluorocarbons (HCFCs) as coolants in air-conditioning equipment. We focus on the residential air-conditioning sector in India and analyse a suite of HFC and alternative coolant gas scenarios for understanding the implications for GHG emissions from this sector within an integrated assessment modelling framework. We find that, if unabated, HFC410A emissions will contribute to 36% of the total global warming impact from the residential air-conditioner sector in India in 2050, irrespective of the future economic growth trajectory, and the remaining 64% is from energy to power residential air-conditioners. A move towards more efficient, low global warming potential (GWP) alternative refrigerants will significantly reduce the cumulative global warming footprint of this sector by 37% during the period 2010–2050, due to gains both from energy efficiency as well as low GWP alternatives. Best practices for reducing direct emissions are important, but only of limited utility, and if a sustainable lifestyle is adopted by consumers with lower floorspace, low GWP refrigerants, and higher building envelope efficiencies, cumulative emissions during 2010–2050 can be reduced by 46% compared to the Reference scenario.

Policy relevance

Our analysis has important implications for Indian climate policy. We highlight that the Indian government's amendment proposal to the Montreal Protocol is a strong signal to the Indian market that the transition away from high GWP refrigerants towards low/zero GWP alternatives will happen sooner or later. The Bureau of Energy Efficiency should extend building energy conservation code policy to residential buildings immediately, and the government should mandate it. Government authorities should set guidelines and mandate reporting of data related to air-conditioner coolant recharge frequency and recovery of scrapped air-conditioner units. For contentious issues like flammability where there is no consensus within the industry, the government needs to undertake an independent technical assessment that can provide unbiased and reliable information to the market.     

Carbon taxes: a review of experience and policy design considerations

State and local governments in the USA are evaluating a wide range of policies to reduce carbon emissions, including carbon taxes, which have existed internationally for nearly 20 years. In this article, existing carbon tax policies, both internationally and in the USA, are reviewed, and carbon policy design and effectiveness are analysed. Design considerations include which sectors to tax, where to set the tax rate, how to use tax revenues, what the impact will be on consumers, and how to ensure that emissions reduction goals are achieved. Emissions reductions that are due to carbon taxes can be difficult to measure, although some jurisdictions quantify reductions in overall emissions, others examine impacts that are due to programmes funded by carbon tax revenues.     

Atmospheric Effects of the Emerging Mainland Chinese Transportation System at and Beyond the Regional Scale

Local surface travel needs in the Peoples Republic of China (mainlandChina) have traditionally been met largely by nonpolluting bicycles. A majorautomobile manufacturing/importing effort has begun in the country over thelast decade, and planning documents indicate that the Chinese may strive toacquire more than 100 million vehicles early in the next century. By analogywith large automotive fleets already existing in the western world, bothregional and global scale pollution effects are to be expected from theincrease. The present work adopts the latest projections of Chinese automobilemanufacture and performs some quantitative assessments of the extent ofpollution generation.Focus for the investigation is placed upon the oxidant ozone. Emissions of theprecursor species nitrogen oxides and volatile organics are constructed basedon data for the current automotive sector in the eastern portion of the UnitedStates. Ozone production is first estimated from measured values forcontinental/oceanic scale yields relative to precursor oxidation. Theestimates are then corroborated through idealized two dimensional modeling ofthe photochemistry taking place in springtime air flow off the Asian land massand toward the Pacific Ocean. The projected fleet sizes could increase coastaland remote oceanic ozone concentrations by tens of parts per billion (ppb)in the lower troposphere. Influences on the tropospheric aerosol system andon the major greenhouse gas carbon dioxide are treated peripherally. Nitrogenoxides created during the vehicular internal combustion process willcontribute to nitrate pollution levels measured in the open Pacific. Thepotential for soot and fugitive dust increases should be considered as theautomotive infrastructure develops. Since the emerging Chinese automotivetransportation system will represent a substantial addition to the globalfleet and all the carbon in gasoline is eventually oxidized completely, asignificant rise in global carbon dioxide inputs will ensue as well.Some policy issues are treated preliminary. The assumption is made thatalterations to regional oxidant/aerosol systems and to terrestrial climate areconceivable. The likelihood that the Chinese can achieve the latest vehiclefleet goals is discussed, from the points of view of new production, positivepollution feedbacks from a growing automobile industry, and known petroleumreserves. Vehicular fuel and maintenance options lying before the Chinese areoutlines and compared. To provide some perspective on the magnitude of theenvironmental changes associated with an Asian automotive buildup, recentestimates of the effects of future air traffic over the Pacific Rim aredescribed.     

中国农业温室气体减排交易的机遇与挑战

 在介绍国际碳市场情况的基础上,总结潜在的农业温室气体减排交易项目类型,探讨中国如何在国际碳市场前景不明朗、自愿碳市场刚刚起步,以及国内实现节能减排目标和实施生态补偿机制的机遇中,克服农业温室气体减排项目所面临的单位减排量小、交易成本高、方法学和独立的第三方认证机构缺乏,以及国内交易平台尚不规范的困难,积极探索利用市场机制控制农业温室气体排放的方法。     

改进的UD模式及其在海洋碳循环中的应用

针对政府间气候变化专业委员会历次报告中"表层—深层"海水间碳通量的差异,利用改进的"上升—扩散"(upwelling-diffusion,UD)模式模拟海洋碳循环状态。除了改进模式结构外,还建立了直接计算海洋溶解无机碳(dissolved inorganic carbon,DIC)δ13C分布的控制方程。区别于目前广泛采用的深度参数的方法,直接利用沉积物捕获器的观测计算分解流量,减少了参数的引用。为更加符合海洋生物地球化学循环,采用地球化学海洋断面研究计划GEOSECS(Geochemical Ocean Sections Study)的海洋磷酸盐分布来标定两个深海动力参数:垂直扩散系数3 000 m2/a和上涌速率3.5 m/a,从而得到温跃层平均深度为860 m,这些参数都在直接观测和其他模式标定的结果之间。通过复原稳定状态下DIC分布并与GEOSECS的观测进行对比,得出自产业革命到20世纪70年代中期的海洋吸收大气CO2约为78 Gt C(Gigatonnes Carbon,1 Gt=1×1015g),与其他的模式估计及观测计算结果相吻合。模式模拟的"混合层—深层"海水间的碳通量为46 Gt C/a,远小于IPCC第四次报告(101 Gt C/a)而与第三次报告(42 Gt C/a)的估算相一致,但仍小于δ13C质量守恒法确定的范围(60~80 Gt C/a)。     

广州番禺地区草地陆气相互作用观测研究

介绍了2004年在广州番禺进行的陆气相互作用观测试验。观测研究表明:新型的超声风温仪虽然带有雨滴防护沙网, 但雨滴对超声观测的误差影响显著, 尤其是对u, w方向。雨天情况下与z/L相关系数很低, 湍流强度与稳定度不存在1/3次方关系。涡动相关法和能量平衡法计算的感热通量及潜热通量比较接近, 感热、潜热通量相关系数分别达到0.8699和0.8633, 两种方法带来的误差主要发生在近地层稳定度发生明显变化的时刻, 即在午间热通量的峰值或傍晚或晚间热通量的低值, 其中能量平衡法计算的感热、潜热普遍具有较大的正负峰值。涡动相关法计算的Q_h+Q_e普遍偏小, 与可用能量R_n-Q_g多数情况下存在能量不平衡, 说明了忽略热存储项的地表能量平衡方程的局限性。番禺夏、秋季近地层各能量具有与太阳辐射相似的日变化特征, 但夏季的潜热大于感热, 而秋季则相反。近地面二氧化碳从5—8月是一个减低过程, 尔后上升到12月份浓度最高, 总体浓度值在350×10-6~400×10-6之间变化。     

弱光层异养过程对海洋储碳的影响:进展、挑战和展望

海洋是地表系统最大的碳库和重要碳汇区。海洋生物泵通过一系列复杂的生物地球化学过程将CO₂转化成颗粒有机碳（Particulate Organic Carbon,POC）并输送到深海,是海洋储碳的重要途径。弱光层（真光层底部到1 000 m）的生物异养过程消耗了超过70%从真光层输出的POC通量,决定了生物泵的储碳效率,因此准确定量弱光层的再矿化速率对评估海洋碳汇有重要意义。本文针对海洋生物泵储碳问题,聚焦弱光层异养过程对海洋储碳的影响机制,对全球弱光层再矿化定量工作进行评述,综合分析弱光层POC的衰减、再矿化等问题,并展望了相关新技术的应用。     

The Rose Spit Eddy in Dixon Entrance: Evidence for its existence and underlying dynamics

Abstract

The existence and dynamics of the so‐called “Rose Spit Eddy” in Dixon Entrance, British Columbia, are investigated by (i) analysing published observations of low‐frequency Eulerian and Lagrangian currents in the region; (ii) interpreting tidal residuals produced by the Hecate Model (a non‐rotating hydraulic model of Hecate Strait and Dixon Entrance); and (iii) running a barotropic, non‐linear numerical tidal model over simplified topography to investigate residuals produced over the Rose Spit sill.

Observations have consistently revealed persistent basin‐wide, surface‐intensified cyclonic shears within central and eastern Dixon Entrance. The Hecate hydraulic tidal model also produced a tidal residual cyclonic gyre in central Dixon Entrance, but with velocities considerably larger than those observed. Barotropic numerical simulations of tidal streams flowing over a representation of the Rose Spit sill produced residual flows along the sill in reasonable agreement with observations and theory. A southward‐directed jet flow was produced off Cape Chacon. Elsewhere, tidal rectification was weak. Run without the Coriolis force, organized flow along the sill broke down, although the headland jet off Cape Chacon persisted.

We submit that the observed Rose Spit eddy results from interactions between buoyancy‐driven coastal currents and tidally rectified flows generated over the Rose Spit sill, and near Cape Chacon, and perhaps indirectly, over the western flank of Learmonth Bank (which although west of the Rose Spit eddy, contributes to the cross‐channel flow across the Entrance). These regions of localized tidal stress will each favour recirculation of a portion of the coastal current within the Entrance, helping to form the eddy.

We believe that the Hecate hydraulic model eddy was generated to a significant degree by phase errors introduced at the northern open boundary, where a rocking barrier was used to force currents. A second rocking barrier also produced a large cyclonic gyre, not supported by observations, near the model's southern boundary.     

Northern Canadian Wetlands: Net Ecosystem CO2 Exchange and Climatic Change

Northern Canadian peatlands represent a long term sink for atmospheric carbon dioxide (CO2), however there is concern they may become a net source of CO2 due to climatic change. Climatic change is expected to result in significant changes in regional hydrology in boreal and subarctic regions of Canada. A hydrologic model predicted a summer water table drop of 0.14 m in northern Canadian fens given an increase in summer temperature and rainfall of 3°C and 1 mm d-1, respectively. Moreover, surface peat temperature increased by 2.3°C. Net ecosystem exchange of CO2 was modelled using these modelled hydrologic and thermal changes with respiration:peat temperature and water table:net ecosystem production relationships developed from measurements at wetlands in northern Sweden and near Churchill, Manitoba. Model results indicate that the net atmospheric CO2 sink function of fens may be enhanced under future 2 × CO2 scenarios, while bogs may become a net source of atmospheric CO2. If the net ecosystem productivity response to the new hydrologic conditions was ignored then the model predicts a decrease in summer carbon storage for all peatland types.     

Global transport and inter-reservoir exchange of carbon dioxide with particular reference to stable isotopic distributions

A two-dimensional model of global atmospheric transport is used to relate estimated air-to-surface exchanges of carbon dioxide (CO₂) to spatial and temporal variations of atmospheric CO₂ concentrations and isotopic composition. The atmospheric model coupled with models of the biosphere and mixed layer of the ocean describes the gross features of the global carbon cycle. In particular this paper considers the change in isotopic composition due to interreservoir exchanges and thus the potential application and measurement requirements of new isotopic observational programs.A comparison is made between the model-generated CO₂ concentration variation and those observed on secular, interannual and seasonal time scales and spatially through the depth of the troposphere and meridionally from pole-to-pole.The relationship between isotopic and concentration variation on a seasonal time-scale is discussed and it is shown how this can be used to quantitatively estimate relative contributions of biospheric and oceanic CO₂ exchange. Further, it is shown that the interhemispheric gradient of concentration and isotopic ratio results primarily from the redistribution of fossil fuel CO₂. Both isotopic and concentration data indicate that tropical deforestation contributes less than 2 Gt yr^-1 of carbon to the atmosphere.The study suggests that changes in the rate of change of the ratio of ¹³C to ¹²C in the atmosphere of less than 0.03 yr^-1 might be expected if net exchanges with the biosphere are the cause of interannual variations of CO₂ concentrations.     

Measuring correlations between atmospheric oxygen and carbon dioxide mole fractions: A preliminary study in urban air

On 25 and 26 October 1986 the air in Cambridge, Massachusetts was monitored for O₂ and CO₂ mole fraction. O₂ concentrations were detected from changes in the relative refractivity of dried air between two lines of ¹⁹⁸Hg at 2537.269 and 4359.562 Å using dual-wavelength interferometry. Changes in oxygen mole fraction were resolved with two-minute time resolution to a precision of ±2.0 ppm. Changes in O₂ were shown to be strongly anticorrelated with changes in CO₂ as expected for combustion processes. The demonstrated instrumental capabilities are appropriate for measuring changes in O₂ mole fraction in background air which could be of importance to a broad range of biogeochemical studies.