北京城区近地面比湿和风场时空分布特征

利用2008—2012年北京城区平均5 km的高密度自动气象站逐时观测数据,分析了北京城区近地面比湿、风向和风速的时空精细分布特征,初步探究了城市下垫面对局地气象要素的影响机制。研究表明:夏季白天北京城区为干岛,冬季城区表现为弱湿岛特征。受城市效应的影响,北京城区与郊区比湿日变化有明显差异。近地面10 m风受到地形、城市和季节性盛行风的共同影响。当气流经过城区时有明显的绕流现象。夏季05:00—10:00 (北京时,下同),受山风、弱的夏季偏南风和城市热岛共同作用,气流向城市中心辐合。冬季15:00—19:00,受季节盛行风偏北气流和谷风偏南气流的共同作用,在城区形成一条西北—东南走向的辐合线。对风速研究发现:城市粗糙下垫面使北京城区风速减小,二环路和三环路之间存在一条“n”状的风速小值带。由此可见,除已开展较多研究的城市热岛效应外,北京城市效应对近地面湿度和风场亦有显著影响。     

The Influence of Thermally-Induced Mesoscale Circulations on Turbulence Statistics Over an Idealized Urban Area Under a Zero Background Wind

The influence of mesoscale circulations induced by urban-rural differential surface sensible heat flux and roughness on convective boundary-layer (CBL) flow statistics over an isolated urban area has been examined using large-eddy simulation (LES). Results are analyzed when the circulations influence the entire urban area under a zero background wind. For comparison, the CBL flow over an infinite urban area with identical urban surface characteristics under the same background meteorological conditions is generated as a control case (without circulations). The turbulent flow over the isolated urban area exhibits a mix of streaky structure and cellular pattern, while the cellular pattern dominates in the control case. The mixed-layer height varies significantly over the isolated urban area, and can be lower near the edge of the urban area than over the rural area. The vertical profiles of turbulence statistics over the isolated urban area vary horizontally and are dramatically different from the control case. The turbulent kinetic energy (TKE) sources include wind shear, convergence, and buoyancy productions, compared to only buoyancy production in the control case. The normalized vertical velocity variance is reduced compared to the control case except in the central urban area where it is little affected. The low-level flow convergence is mainly responsible for the enhanced horizontal velocity variance in the central urban area, while wind shear is responsible for the additional local maximum of the horizontal velocity variance near the middle of the CBL outside the central area. Parameterizations in the prognostic equation for TKE used in mesoscale models are evaluated against the LES results over the isolated urban area. We also discuss conditions under which the urban-induced circulations occur and when they may affect the entire urban area. Given that urban-induced circulations can influence the entire urban area within hours for an urban area of a realistic size, it is inappropriate to directly apply empirical relations of turbulence statistics derived under horizontally-homogenous flow conditions to an urban area.     

地面风对上海城市热岛影响的观测分析

首先利用上海77个区域站2011—2014年逐时气温和风资料,研究了地面风对上海城市热岛(urban heat island,UHI)的影响及UHI季节性空间分布特征的成因,并从海陆热力差异初步揭示了向岸风对热岛强度(urban heat island intensity,I_(UHI))的影响。其次利用上海7个国家站1961—2014年逐月气温和风资料,研究了上海各季地面风速与I_(UHI)的年际变化关系。结果表明:(1)UHI中心出现的位置与风向、风速有密切的关系,特别是夜间UHI中心有向城市下风方向漂移的特征,其平均漂移风速阈值为2 m·s~(-1),UHI区域随风速增大向城市下风方向延伸,I_(UHI)随风速的增大而减小。(2)上海各季夜间UHI特征明显,尤以秋冬季最为明显,春季次之,夏季最弱。春夏季夜间UHI中心出现在城区西北侧,而秋冬季夜间UHI中心稳定在城区,表现为典型UHI。各季白天均表现为下风方大范围增暖现象。季节地面盛行风决定了UHI季节性空间分布特征。(3)白天向岸风具有抑制升温作用(春夏季最为明显),受其影响气温大值区易出现在内陆地区,春夏季城市偏东区I_(UHI)小于偏西区;夜间向岸风具有抑制降温作用(秋冬季最为明显),受其影响秋冬季东部沿海地区出现明显增暖且城市偏东区I_(UHI)大于偏西区。海陆热力差随季节不同和盛行风风速大小决定了向岸风这种作用的大小及影响范围。(4)各季年平均地面风速与I_(UHI)均呈显著负相关,1961—2014年上海各季风速均表现为递减趋势(春冬季最明显),为I_(UHI)增大提供有利条件。21世纪以来各季I_(UHI)均呈现减缓特征(夏秋季最明显),风速并不是导致I_(UHI)减缓的主要因素。     

Influence of Thermal Effects on the Wind Field Within the Urban Environment

Micrometeorological conditions in the vicinity of urban buildings strongly influence the requirements that are imposed on building heating and cooling. The goal of the present study, carried out within the Advance Tools for Rational Energy Use towards Sustainability (ATREUS) European research network, is the evaluation of the wind field around buildings with walls heated by solar radiation. Two computational fluid dynamics (CFD) codes were validated against extensive wind-tunnel observations to assess the influence of thermal effects on model performance. The code selected from this validation was used to simulate the wind and temperature fields for a summer day in a specific region of the city of Lisbon. For this study, the meteorological data produced by a non-hydrostatic mesoscale atmospheric model (MM5) were used as boundary conditions for a CFD code, which was further applied to analyze the effects of local roughness elements and thermodynamic conditions on the air flow around buildings. The CFD modelling can also provide the inflow parameters for a Heating, Ventilation and Air Conditioning (HVAC) system, used to evaluate the building energy budgets and to predict performance of the air-conditioning system. The main finding of the present three-dimensional analyses is that thermal forcing associated with the heating of buildings can significantly modify local properties of the air flow.     

城市热岛效应对北京夏季高温的影响

应用1998—2002年北京地区自动气象站观测资料,探讨了城市热岛效应对夏季高温的增幅作用。结果表明:北京地区夏季平均热岛指数随着环境温度的升高呈上升趋势,城市热岛效应对高温强度有明显的增幅作用。并应用中尺度MM5模式,对2000年7月一次典型高温天气过程进行了数值模拟。试验表明:模式对于北京地区夏季高温及城市热岛的范围和强度均有较好的模拟能力。     

柳州风的特征在城市规划中的应用

分析了柳州市风的特征，阐明了风与城市规划的关系，并对城市规划中如何考虑风的特征进行了说明。     

柳州风的特征在城市规划中的应用

分析了柳州市风的特征,阐明了风与城市规划的关系,并对城市规划中如何考虑风的特征进行了说明。     

《巴黎协定》适应和损失损害内容的解读和对策

《巴黎协定》基本照顾了各缔约方的核心关切,坚持了《联合国气候变化框架公约》（以下简称《公约》）的原则,基本体现了发达国家和发展中国家的区分。在适应部分,《巴黎协定》设立了与全球温升目标相联系的全球适应目标,明确了对发展中国家的适应支持,并确定了具有一定法律约束力的全球适应信息通报和5年周期的全球盘点。在损失损害部分,《巴黎协定》锁定了《公约》下的华沙损失损害国际机制,并基本确定了一个各国通过可持续发展和国际合作共同解决损失损害问题的框架。但是,《巴黎协定》仍然没有解决很多技术性问题和缔约方之间关键性和实质性的分歧。中国作为发展中大国将继续在适应和损失损害问题中面临着出资压力,应通过增强国内适应行动、强化适应和损失损害相关研究和高效利用气候变化南南合作基金3个方面,为谈判争取主动并为推动全球适应气候变化减少损失损害做出贡献。     

屋顶绿化对城市降温效应的模拟分析——以南京市为例

利用WRF模式耦合单层城市冠层模式,针对屋顶绿化对城市降温效果进行了模拟,结果表明:(1)南京夏季绿化后的屋顶反照率约为0.15,较水泥及其他反光材料的反照率略小,在白天可造成约0.2℃的升温。(2)绿化后的屋顶热容量明显增加,可使白天气温下降0.33℃;在夜间,可使气温升高0.21℃左右。(3)在植被阻挡作用及土壤层阻挡作用下,屋顶的导热率降低。在白天,净辐射能很难向下层传递,从而转化为感热加热大气,造成气温升高。(4)土壤湿度的改变使更多净辐射能转化为潜热释放。在白天可使温度降低1.23℃;在夜间,平均降温幅度为0.44℃。除此之外,模拟不同季节的统计结果表明,屋顶绿化降温效果在夏季最为明显,最大降幅可达1.22℃,春季0.96℃,秋季0.75℃,冬季只有0.38℃。     

Numerical Simulation of Wind and Temperature Fields over Beijing Area in Summer

1. IntroductionThe basic role of urban-rural boundary layer re-search is to study all kinds of physical process changesin the atmosphere boundary layer over urban and itssurrounding areas. Urban heat island (UHI) is a well-known feature of urban-rural climate. Attempts toincrease the understanding of the causes of the UHIand other urban-rural boundary layer phenomena haveused observational, theoretical and modelling methodssince long before. Seaman (1989) used a hydrostaticmodel, with real …     

平流计算方案对一次江淮梅雨暴雨模拟的影响

为对比MM5模式中原中央差平流方案和新型半拉格朗日插值计算方案CIP的模拟差别,针对2006年7月5~6日的江淮流域梅雨暴雨过程进行了模拟,证实了CIP方案对这次暴雨过程具有较好的模拟效果,它更加真实地再现了梅雨锋降水的中尺度结构,改进了模式的模拟结果,特别是对梅雨锋内对流运动结构的模拟,显示了CIP对刻画大梯度分布和强对流运动计算的良好性能。平流的高精度计算对提高这类系统的模拟精度非常重要。     

峡谷区建坝高度对近坝区风场特性的影响

在复杂地形、副热带高压和季风天气等因素共同影响下,高山峡谷区内风场复杂多变,极易形成“狭管效应”,进而导致灾害性大风,对大型工程施工与运行造成较大影响。本文基于流体力学基本原理,采用标准k－ε紊流模型以及PISO（Pressure Implict with Splitting of Operator）算法,以白鹤滩水电站区域发生7级北风为典型计算工况,研究了大坝建坝过程中近坝区风速场变化规律和建坝对风速场的影响范围。成果表明:坝体的阻挡作用使风速场在坝顶处产生绕流分离和风场抬升,在建坝高程以下形成低风速区;建坝高程650 m与750 m时,缆机平台范围内风速约15～16 m/s,大坝下游风速垂直分布显著影响区河道长度分别为4.4H_t和4.5H_t（H_t为建坝高度）;坝顶处风速场显著影响高度分别为2.0H_t和3.0H_t。大坝蓄水至正常蓄水位825 m高度时,大坝下游风场显著影响区河道长度为8.0倍坝高（2.3 km）,最大影响河道区长度为30.4倍坝高（8.8 km）;坝顶影响高度达到1500 m高度左右,约3.5倍坝高。     

重庆城区近百余年旱涝变化

用Z指数作为旱涝等级标准,利用重庆城区百余年降水量资料,分析了历年及四季旱涝出现的频率,采用趋势分析、最大熵谱分析以及小波分析方法,研究了重庆城区年及四季旱涝的变化特征。结果表明:重庆城区年及四季干旱和洪涝发生频率均在25%以上,重庆旱涝灾害较频繁;多项式拟合和周期分析表明,城区年及四季旱涝具有阶段性变化特征,某些阶段年际变化特征也很显著,总体而言,年及夏季旱涝的年代际变化特征较明显,其它三个季节则是年际变化特征较明显。近几年的年旱涝变化处于偏涝阶段;而近几年夏季的旱涝变化,从年代际尺度来看,目前处在偏旱阶段,出现干旱的可能性较大;而其它三季则处于偏涝阶段。     

大风条件下城市冠层流场模拟

发展了基于k-ε湍流闭合方法的城市冠层流场模式,建筑群采用多孔介质来表示,对气流的阻力以形式阻力来描述,采用该模式模拟北京市一个小区的流场,并将模拟结果与北京325 m气象塔观测资料进行比较,结果表明:在大风情况下,计算风廓线与观测拟合风廓线比较吻合.该模式可以用于大风条件下城市冠层流场的模拟.     

Achievability of the Paris Agreement targets in the EU: demand-side reduction potentials in a carbon budget perspective

Limiting global warming to ‘well below’ 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase even further to 1.5°C is an integral part of the 2015 Paris Agreement. To achieve these aims, cumulative global carbon emissions after 2016 should not exceed 940 – 390?Gt of CO₂ (for the 2°C target) and 167 – ?48?Gt of CO₂ (for the 1.5°C target) by the end of the century. This paper analyses the EU’s cumulative carbon emissions in different models and scenarios (global models, EU-focused models and national carbon mitigation scenarios). Due to the higher reductions in energy use and carbon intensity of the end-use sectors in the national scenarios, we identify an additional mitigation potential of 26–37 Gt cumulative CO₂ emissions up to 2050 compared to what is currently included in global or EU scenarios. These additional reductions could help to both reduce the need for carbon dioxide removals and bring cumulative emissions in global and EU scenarios in line with a fairness-based domestic EU budget for a 2°C target, while still remaining way above the budget for 1.5°C.

Key policy insights

• Models used for policy advice such as global integrated assessment models or EU models fail to consider certain mitigation potential available at the level of sectors.

• Global and EU models assume significant levels of CO₂ emission reductions from carbon capture and storage to reach the 1.5°C target but also to reach the 2°C target.

• Global and EU model scenarios are not compatible with a fair domestic EU share in the global carbon budget either for 2°C or for 1.5°C.

• Integrating additional sectoral mitigation potential from detailed national models can help bring down cumulative emissions in global and EU models to a level comparable to a fairness-based domestic EU share compatible with the 2°C target, but not the 1.5°C aspiration.

     

Development of a Multi-Layer Urban Canopy Model for the Analysis of Energy Consumption in a Big City: Structure of the Urban Canopy Model and its Basic Performance

A multilayer one-dimensional canopy model was developed to analyze the relationship between urban warming and the increase in energy consumption in a big city. The canopy model, which consists of one-dimensional diffusion equations with a drag force, has three major parameters: building width, distance between buildings, and vertical floor density distribution, which is the distribution of a ratio of the number of the buildings that are taller than some level to all the buildings in the area under consideration. In addition, a simplified radiative process in the canopy is introduced. Both the drag force of the buildings and the radiative process depend on the floor density distribution. The thermal characteristics of an urban canopy including the effects of anthropogenic heat are very complicated. Therefore, the focus of this research is mainly on the basic performance of an urban canopy without anthropogenic heat. First, the basic thermal characteristics of the urban canopy alone were investigated. The canopy model was then connected with a three-dimensional mesoscale meteorological model, and on-line calculations were performed for 10 and 11 August, 2002 in Tokyo, Japan. The temperature near the ground surface at the bottom of the canopy was considerably improved by the calculation with the canopy model. However, a small difference remained between the calculation and the observation for minimum temperature. Deceleration of the wind was well reproduced for the velocity at the top of the building by the calculation with the canopy model, in which the floor density distribution was considered.     

合肥东南引风口对城区热岛调节作用的评估

通过观测资料分析，认为合肥市东南引风口的夏季通风作用对合肥市夏季城市热岛强度起到一定的调节作用。并通过热量平衡方程的数值模拟，分析了该区域下垫面状况的改变对合肥市区夏季平均温度的可能影响。     

呼和浩特市城区发展对大气环境的影响分析

基于呼和浩特市近50年逐日定时地面气象资料、2002—2006年的逐日07时和19时各标准层探空资料、2001—2006年逐日主要污染物浓度和主要污染源源强、1961—2006年社会经济数据、2002年城区建设现状及1996—2010年城市总体规划资料,利用区域边界层模式模拟方法,研究了呼和浩特市城区建设发展对大气环境的影响。结果表明：（1）呼和浩特市城区发展后（规划后）气温高于现状（规划前）,城区中心气温与周边地区气温差增大,城市热岛效应增强;（2）呼和浩特城区规划后冬季气流汇集辐合区域增多,辐合能力增强,从而使冬季大气污染加剧;（3）呼和浩特市城区扩展后引起的下垫面热力与动力参数变化,将导致气流场发生显著变化,使得污染物的辐合能力增强。总体而言,呼和浩特市城区规划后虽增加了部分绿地等面积,但建筑物的增高增密、下垫面性质的改变,将使大气环境扩散能力减弱,大气污染加重。     

天津城市环境对一次局地降水过程影响的模拟研究

采用中尺度气象模式WRF结合自动站观测资料,对天津城区及附近发生的一次局地降水过程进行数值模拟和敏感性试验,研究了城市环境(城市地表、城市大气污染)对降水发生发展的影响。结果表明:城市地表引起的热岛环流,叠加海风环流后,改变了辐合线的位置和强度,直接影响了对流降水的发生及落区。城市大气污染状况可影响对流发展后的强度及降水量,敏感性试验结果显示气溶胶浓度增大后区域平均降水量增加约25%;气溶胶的增雨效应主要表现在可增进对流云中液态水和冰相物质含量,增多的液态水物质被强的上升气流抬升到较高处冻结形成冰晶,这一过程中增多的凝结潜热又可促进对流发展,最终导致地面总降水量增多,研究个例中气溶胶浓度增加可使潜热加热率最大增加110 K·h~(-1)。     

二维街谷地面加热引起的流场特征的水槽实验研究

利用拖曳式水槽,采用激光粒子成像速度场测量系统(PIV),模拟了街谷存在地面加热时流场特征;讨论了环境风场对其的影响。我们发现在静风条件下,街谷中环流完全由热力驱动,对流活动可伸展至街谷上方;在建筑物层顶以上,也可发现水平和垂直方向的运动。这些对流活动有助于基本风场为零时,街谷内外动量和物质的交换。当街谷较宽时,对流形成的涡旋可能为两个以上,形态较为复杂并随时间变化,当街谷变窄时,涡旋蜕化成只有一个。当有弱环境风场存在时,街谷中的对流呈现为一个主涡旋,随着风速增加,涡旋形状更加规则,其中心并向下风向移动。