北京地区气象环境数值模拟试验

用区域边界层模式RBLM模拟北京地区气象环境特征.数值模拟结果表明(1)北京地区的气象环境很复杂,其主要特点是受昼夜循环的山谷风气流、城市热岛环流以及大尺度系统共同影响.(2)北京市区冬季地面风的日变化较小,主要是偏北气流,城市上游方向在市区的北边,而春夏季地面风的日变化比较明显,市区的进出口气流方向变化很大.(3)北京市城市热岛强度在夏季较强,城市热岛环流明显,城市中心近地面气温比郊区近地面气温高5～6℃左右.(4)数值模拟结果能较好地反映北京地区流场的日变化,与实际观测结果吻合较好.     

北京地区气象环境数据模拟试验

用区域边界层模式RBLM模拟北京地区气象环境特征。数值模拟结果表明：（1）北京地区的气象环境很复杂，其主要特点是受昼夜循环的山谷风气流、城市热岛环流及大尺度系统共同影响。（2）北京市区季地面风的日变化较小，主要是偏北气流，城市上游方向在市区的北边，而春夏季地面风的日变化比较明显，市区的进出口气流方向变化很大。（3）北京市城市热岛强度在夏季较强，城市热岛环流明显，城市中心近地面气温比郊区近地面气温高5－6℃左右。（4）数值模拟结果能较好地反映北京地区流场的日变化，与实际观测结果吻合较好。     

近15年北京夏季城市热岛特征及其演变

根据北京地区20个地面气象观测台站1990-2004年7月的气温资料，分析了最近15年来北京夏季城市热岛的最新特征和变化趋势，也分析了城市热岛与气温，城郊地表温度差与地表温度，气温和地表温度间的关系。结果表明：北京夏季夜间出现了强热岛，郊区城市也出现了热岛现象，但白天城市热岛相对夜间不明显。夜间城市热岛强度呈逐年增强趋势，但白天这种趋势不明显。夜间城市热岛与气温呈正相关，气温高的年份，城市热岛强度相对也大；夜间城郊地表温差与地表温度呈正相关，地表温度越高，城郊地表温差越大；夜间，气温与地表温度呈正相关，气温越高，地表温度也高。白天，这些相关相对夜间来说不那么明显。研究成果对北京城市发展规划和高温灾害的防治有一定的科学参考价值。     

规划建设对深圳夏季城市热岛影响的数值模拟研究

以区域边界层模式RBLM为工具,研究了城市规划建设对深圳夏季城市热岛的影响。分别模拟了当前的城市热岛、高密度建设和能耗增加后的城市热岛、以及布设通风走廊后的城市热岛,得到了以下结论:(1)深圳夏季存在城市热岛现象,且昼间热岛比夜间更为明显,高温中心集中在建设密度较高的南山、福田、罗湖和宝安西部等区;(2)建设密度加大及能源消费增加会导致深圳夏季近地面气温出现大面积的升高,并且夜间升温比昼间更为明显;(3)通风走廊的设置可以在一定程度上抵消高密度建设和能耗增加带来的负面效应。     

地球上的人工气候岛和大气污染源——天气与城市水问题

文章探讨了城市对气温等气象要素的影响规律，指出了城市气候是异于周围农村气候的人工气候岛，例如城市热岛（气温），雨岛（降水量），干岛（相对湿度）等。特殊的城市条件会给城市造成灾害，例如高温灾害，城市洪灾，城市风灾，酸雨，酸雾，光化学烟雾等，城市还有它它自己特有的气象现象，如城市热岛环流（乡村风），城市是地球上的主要大气污染源，在这个人工污染岛中居住，对居民的健康是不利的。     

北京城区热岛环流对山地－平原风的调节作用

利用2002年北京市自动气象站网的逐时资料,采用统计方法对北京城市水平风场的散度、“城市热岛”强度和风向频率的日变化特征进行了分析,并总结归纳出在弱天气系统形势下（地面风速〈3级）北京地区风场的基本形态。结果表明：1）北京“城市热岛”环流是存在的,但只是对区域性的山地-平原风起调节作用。2）在作用相当的因素（如山地-平原风、热岛强度和大气稳定度）控制下,夏季的“城市热岛”环流造成城区风场的辐合特征。3）其他季节的“城市热岛”环流,主要由山地-平原风控制,即刮山地风时,北京城郊的风场表现为向城区的辐合;刮平原风时,北京城区风场表现为辐散特征。     

下垫面对郑州城市边界层风的影响

根据１９９３年１月和７月郑州市中心测点和南郊郑州气象观测站同步观测的地面和边界层气象资料,分析了郑州城市下垫面对边界层风的影响。结果表明,在地面气压梯度比较小且天气晴朗条件下,郑州存在城市热岛环流。受城市热岛环流影响,郊区地面风向指向市区;边界层８００ｍ以下,城市上空吹偏西风时同一高度上南郊风向偏于城市风向左侧,吹偏东风时同一高度上南郊风向偏于市区风向右侧;１２００ｍ以上,城市上空吹偏西风时,同一高度上南郊风向偏于城市风向右侧     

南京地区下垫面变化对城市热岛效应影响的数值模拟

利用新一代中尺度研究和预报模式(Weather Research and Forecasting Model,简称WRF)分别耦合多冠层、单冠层和平板模式三种情况进行南京地区2007年8月1日的天气过程模拟,分析不同城市冠层方案对南京气象场的模拟效果。在此基础上,结合模拟效果最好的城市冠层方案,研究南京城市下垫面的变化对其热岛的影响。结果表明:多冠层方案对近地面气温、10 m风场的模拟效果最好;城区的扩张使南京地区近地面气温升高,主要表现为城市区域夜间升温显著,并且导致热岛强度明显增强;城市扩张后,城区白天风速大范围地减小,同时热岛环流更加显著,且具有明显的城市热岛的"下游效应"。     

城市化对北京单次极端高温过程影响的数值模拟研究

城市化对高温热浪的频次和强度具有重要影响,但目前对于城市化影响高温热浪过程的机理了解还不充分。本文利用WRF模式,对2010年7月2～6日（北京时）北京一次高温过程进行了模拟,分析了城市化对此次高温过程的影响机理。采用优化后的WRF模式,能够模拟出北京连续5日高温的特征和城市热岛强度的变化。城市下垫面的不透水性决定了城区2 m高度处相对湿度低于乡村,削弱了城区通过潜热调节城市气温的能力。日落后,城市感热通量下降缓慢,城区降温速率小于乡村,夜间边界层稳定、高度低,风速小,抑制了城乡之间能量的传输,形成了夜间强的城市热岛强度,造成夜间城市气温明显高于乡村。日出后城乡地面感热通量、潜热通量迅速上升,边界层稳定性下降。午后,城市下垫面分别为地表感热通量和潜热通量的高、低值中心,通过潜热调节气温的能力被削弱;边界层稳定性降低,有利于能量的垂直扩散;此时,城市热岛强度小于夜间。因此,北京城市下垫面形成了明显的城市热岛效应,加重了城区极端高温事件的强度。此外,在这次高温热浪期间,中国东部大部分地区受到大陆暖高压控制,晴空少云,西北气流越山后形成焚风效应,是北京地区高温热浪形成的天气背景。     

长江三角洲夏季海陆风与热岛环流的相互作用及城市化的影响

用三维中尺度模式研究长江三角洲夏季海陆风与城市热岛环流的相互作用,白天由于东海海风和太湖湖风环流与上海市热岛环流相互增强,最大垂直速度可达６．２ｃｍ／ｓ;夜间则相反,由于海风（包括长江江风）与湖风的对撞,因而在上海到江阴市沿江出现一条水平辐合带,如果上海周围地区随着经济发展,大片农田被城市下垫面所取代,而使绿地覆盖率下降到１５％以下,则睡季夜间地面气温可上升３℃,两个增温中心分别在苏州和嘉兴附近,     

Impact of land cover data on the simulation of urban heat island for Berlin using WRF coupled with bulk approach of Noah-LSM

Urban-rural difference of land cover is the key determinant of urban heat island (UHI). In order to evaluate the impact of land cover data on the simulation of UHI, a comparative study between up-to-date CORINE land cover (CLC) and Urban Atlas (UA) with fine resolution (100 and 10 m) and old US Geological Survey (USGS) data with coarse resolution (30 s) was conducted using the Weather Research and Forecasting model (WRF) coupled with bulk approach of Noah-LSM for Berlin. The comparison between old data and new data partly reveals the effect of urbanization on UHI and the historical evolution of UHI, while the comparison between different resolution data reveals the impact of resolution of land cover on the simulation of UHI. Given the high heterogeneity of urban surface and the fine-resolution land cover data, the mosaic approach was implemented in this study to calculate the sub-grid variability in land cover compositions. Results showed that the simulations using UA and CLC data perform better than that using USGS data for both air and land surface temperatures. USGS-based simulation underestimates the temperature, especially in rural areas. The longitudinal variations of both temperature and land surface temperature show good agreement with urban fraction for all the three simulations. To better study the comprehensive characteristic of UHI over Berlin, the UHI curves (UHIC) are developed for all the three simulations based on the relationship between temperature and urban fraction. CLC- and UA-based simulations show smoother UHICs than USGS-based simulation. The simulation with old USGS data obviously underestimates the extent of UHI, while the up-to-date CLC and UA data better reflect the real urbanization and simulate the spatial distribution of UHI more accurately. However, the intensity of UHI simulated by CLC and UA data is not higher than that simulated by USGS data. The simulated air temperature is not dominated by the land cover as much as the land surface temperature, as air temperature is also affected by air advection.     

应用城市地表能量平衡方案研究城市冠层结构对城市热岛的热力影响

用南京大学区域边界层模式NJU-RBLM, 通过对一组理想试验的模拟, 研究了TEB方案 (town energy balance) 和SVAT方案 (soil－vegetation－atmosphere transfer) 模拟城市热岛现象的差异及本质原因, 发现TEB方案对城市热岛 (UHI) 尤其是夜间UHI模拟效果更优, 这是由于TEB方案具备较强模拟城市储热项的能力形成的。此外, 深入探讨UHI对大气边界层热力结构的影响, 发现UHI现象使城市和郊区的近地层位温廓线在清晨和傍晚都存在明显差异, 同时使城市区域气温全天高于郊区, 且日间城乡温差能达到的高度明显高于夜间。分析人为热源和建筑物冠层对UHI的影响时发现: 人为热源对UHI的影响在夜间强于白天, 而建筑物对白天城市湍能的影响强于人为热源的作用。     

Simulation of urban climate with high-resolution WRF model: A case study in Nanjing, China

In this study, urban climate in Nanjing of eastern China is simulated using 1-km resolution Weather Research and Forecasting (WRF) model coupled with a single-layer Urban Canopy Model. Based on the 10-summer simulation results from 2000 to 2009 we find that the WRF model is capable of capturing the high-resolution features of urban climate over Nanjing area. Although WRF underestimates the total precipitation amount, the model performs well in simulating the surface air temperature, relative humidity, and precipitation frequency and inter-annual variability. We find that extremely hot events occur most frequently in urban area, with daily maximum (minimum) temperature exceeding 36°C (28°C) in around 40% (32%) of days. Urban Heat Island (UHI) effect at surface is more evident during nighttime than daytime, with 20% of cases the UHI intensity above 2.5°C at night. However, The UHI affects the vertical structure of Planet Boundary Layer (PBL) more deeply during daytime than nighttime. Net gain for latent heat and net radiation is larger over urban than rural surface during daytime. Correspondingly, net loss of sensible heat and ground heat are larger over urban surface resulting from warmer urban skin. Because of different diurnal characteristics of urban-rural differences in the latent heat, ground heat and other energy fluxes, the near surface UHI intensity exhibits a very complex diurnal feature. UHI effect is stronger in days with less cloud or lower wind speed. Model results reveal a larger precipitation frequency over urban area, mainly contributed by the light rain events (< 10 mm d^?1). Consistent with satellite dataset, around 10?C20% more precipitation occurs in urban than rural area at afternoon induced by more unstable urban PBL, which induces a strong vertical atmospheric mixing and upward moisture transport. A significant enhancement of precipitation is found in the downwind region of urban in our simulations in the afternoon.     

Mesoscale and macroscale aspects of the morning Urban Heat Island around Athens,Greece

Summary This paper examines the characteristics of the morning Urban Heat Island (UHI) in Athens basin, Greece. The study is performed by using and analyzing mesoscale and synoptic data covering the period 1990–2001. The UHI was estimated using the 0600 Local Time (LT) minimum temperature differences between rural and urban areas of the city. The analysis results in 7 UHI classes. A strong UHI was found for the 1/3 of days. The specific meteorological characteristics (surface and upper air, cooling rate) of each UHI class were revealed and examined. The spatial and temporal characteristics of the UHI were also identified. The UHI is largest on nights with clear skies and low relative humidity. In all seasons the UHI switches on rapidly in afternoon. During spring and summer, sea breeze commonly reduces and delays the UHI. Cases documenting the sensitivity and rapidity of changes of the UHI to changes in classes (cloud cover, wind) are also presented. The cooling rate is higher in the urban area under negative and lower under positive UHI conditions. Mesoscale and macroscale phenomena were examined during the different UHI classes through a weather type scheme. It was emerged that high UHI classes are associated with anticyclonic conditions or advection in the lower troposphere, while low UHI classes are associated with strong northeasterly winds. Anticyclonic conditions which frequently occur in spring and early summer, reduce or reverse the UHI to Urban Cooling Island.     

Assessment of urban heat island effect for different land use–land cover from micrometeorological measurements and remote sensing data for megacity Delhi

Urban heat island intensities (UHI) have been assessed based on in situ measurements and satellite-derived observations for the megacity Delhi during a selected period in March 2010. A network of micrometeorological observational stations was set up across the city. Site selection for stations was based on dominant land use–land cover (LULC) classification. Observed UHI intensities could be classified into high, medium and low categories which overall correlated well with the LULC categories viz. dense built-up, medium dense built-up and green/open areas, respectively. Dense urban areas and highly commercial areas were observed to have highest UHI with maximum hourly magnitude peaking up to 10.7 °C and average daily maximum UHI reaching 8.3 °C. UHI obtained in the study was also compared with satellite-derived land surface temperatures (LST). UHI based on in situ ambient temperatures and satellite-derived land surface temperatures show reasonable comparison during nighttime in terms of UHI magnitude and hotspots. However, the relation was found to be poor during daytime. Further, MODIS-derived LSTs showed overestimation during daytime and underestimation during nighttime when compared with in situ skin temperature measurements. Impact of LULC was also reflected in the difference between ambient temperature and skin temperature at the observation stations as built-up canopies reported largest gradient between air and skin temperature. Also, a comparison of intra-city spatial temperature variations based UHI vis-à-vis a reference rural site temperature-based UHI indicated that UHI can be computed with respect to the station measuring lowest temperature within the urban area in the absence of a reference station in the rural area close to the study area. Comparison with maximum and average UHI of other cities of the world revealed that UHI in Delhi is comparable to other major cities of the world such as London, Tokyo and Beijing and calls for mitigation action plans.     

Estimation of urban heat island intensity using biases in surface air temperature simulated by a nonhydrostatic regional climate model

This study demonstrates that urban heat island (UHI) intensity can be estimated by comparing observational data and the outputs of a well-developed high-resolution regional climate model. Such an estimate is possible because the observations include the effects of UHI, whereas the model used does not include urban effects. Therefore, the errors in the simulated surface air temperature, defined as the difference between simulated and observed temperatures (simulated minus observed), are negative in urban areas but 0 in rural areas. UHI intensity is estimated by calculating the difference in temperature error between urban and rural areas. Our results indicate that overall UHI intensity in Japan is 1.5 K and that the intensity is greater in nighttime than in daytime, consistent with the previous studies. This study also shows that root mean square error and the magnitude of systematic error for the annual mean temperature are small (within 1.0 K).     

Urban heat island in a coastal urban area in northern Spain

This work examines the characteristics of the urban heat island (UHI) in a medium-sized city in northern Spain (Bilbao) using 5-year climate data (2005–2009) and the results of three specific measurement campaigns (2009–2010). Urban climate variables are not only compared with those in rural sites but also local climatic differences occurring inside the city are analysed. The findings presented in this paper show the influence of complex topography and sea/land breeze in the urban climate. Spatial characteristics and temporal evolution of UHI is presented. Hourly maximum temperature anomaly (ΔT _{u–r, max}) occurs just after sunrise and an urban cold island (UCI) is developed after midday. Along the year, mean UHI intensity is highest in autumn and the UCI effect increases in spring and summer in relation with sea breeze cooling potential. Diurnal and seasonal variation of air flow patterns appear to influence significantly on UHI intensity.     

Temporal characteristics of the Beijing urban heat island

Summary This paper describes the inter-annual trend, and the seasonal and hourly variation of the near surface urban heat island (UHI) in Beijing. The surface air temperature data (mean, maximum, and minimum) from one urban (downtown Beijing) and one rural (70 km from downtown Beijing) station were used for the period 1977 and 2000. It is found that the temperatures in both urban and rural stations show an increasing tendency. Specifically, minimum temperature shows the greatest tendency at the urban station whereas maximum temperature shows the greatest increase at the rural station. The UHI intensity obtained by calculating the difference in temperatures between the two stations identifies that the intensity is greatest and has the greatest increasing trend for minimum temperature, while the UHI intensity of maximum temperature shows a slow decrease over time. UHI intensity for minimum temperature has a strong positive correlation with the increase in the urban population and the expansion of the yearly construction area. Seasonal analyses showed the UHI intensity is strongest in winter. This seasonal UHI variation tends to be negatively correlated with the seasonal variation of relative humidity and vapor pressure. Hourly variation reveals that the strongest UHI intensity is observed in the late nighttime or evening, while the weakest is observed during the day.     

Temporal variability of the Buenos Aires, Argentina, urban heat island

This paper describes the statistical characteristics and temporal variability of the urban heat island (UHI) intensity in Buenos Aires using 32-year surface meteorological data with 1-h time intervals. Seasonal analyses show that the UHI intensity is strongest during summer months and an “inverse” effect is found frequently during the afternoon hours of the same season. During winter, the UHI effect is in the minimal. The interannual trend and the seasonal variation of the UHI for the main synoptic hours for a longer record of 48?years are studied and associated to changes in meteorological factors as low-level circulation and cloud amount. Despite the population growth, it was found a negative trend in the nocturnal UHI intensity that could be explained by a decline of near clear-sky conditions, a negative trend in the calm frequencies and an increase in wind speed. Urban to rural temperature differences and rural temperatures are negatively correlated for diurnal and nocturnal hours both for annual and seasonal scales. This result is due to the lower interannual variability of urban temperatures in comparison to rural ones.