Meteorological prerequisites of formation of severe wintertime air pollution episodes in Moscow

Large-scale and local weather conditions during severe wintertime air pollution episodes in the Moscow megalopolis are analyzed. Concentrations of CO, NO, and NO₂ obtained from the automated network of the atmosphere pollution control are used as tracers for atmospheric processes in the urban atmospheric boundary layer. It is shown that a high surface air pollution level in the city is formed at a weak wind in the lower atmosphere and only in the presence of a surface or low elevated temperature inversion. Temperature contrasts in the urban heat island generate the circulation that promotes air pollution in megapolis regions remote from large emission sources. It is supposed that in case of severe frosts the amount of anthropogenic heat in the megapolis sharply increases, promoting active turbulent mixing, thus preventing pollution accumulation in the surface air.     

复杂地形条件下城市热岛及局地环流特征的数值模拟

应用基于多层城市冠层方案BEP(Building Environment Parameterization)增加室内空调系统影响的建筑物能量模式BEM(Building Energy Model)方案的WRF模式,模拟研究重庆热岛的特征、成因以及局地环流对热岛形成的影响。文中共有两个算例,一为重庆真实下垫面算例,称之为URBAN算例,二为将城市下垫面替换为耕地下垫面的对比算例,称之为NOURBAN算例。结果表明:1)WRF方案模拟结果与观测2 m气温的对比吻合较好,误差主要出现在正午温度峰值和凌晨温度谷值处,由城市下垫面特性及城市内建筑分布误差引起。2)BEP+BEM方案较好地模拟出了重庆地区的热岛分布的空间和时间特征。重庆市温度的分布受地形和城市下垫面的双重影响,越靠近城区,温度的分布受城市化影响就越大,在海拔低处,温度就越高。3)城区立体三维表面对辐射的陷阱作用导致城市表面总体反射率小,向上短波辐射小于郊区约20 W/m~2。城市表面以感热排放为主,而郊区则表现为潜热的作用占主导。夜间城市地表储热以及空调废热向大气释放,是城市热岛形成的重要原因。4)模拟区域背景风场主要为东南风,局地环流呈现出越靠近山区风速越大、城市区域风速较小的特性,体现了城市密集的建筑群对低层大气流场的空气动力学效应,以及复杂山谷地形的山谷风环流特性。在市区的西侧和东南侧均有高大山脉阻挡,山脉对城市出流的阻碍作用、气流越山与绕流运动对城市热岛的形成有一定影响。     

Numerical simulation of the anthropogenic heat effect on urban boundary layer structure

In this paper, several methods of incorporating anthropogenic heat release into the boundary layer are compared. The best scheme was one that included anthropogenic heat release in both the surface energy balance equation and the thermodynamic equations. In addition, it included diurnal variations and a distribution of heat based on building concentrations. We further investigated the influence of anthropogenic heat release on urban boundary layer structure and the urban heat island, and found that the contribution of anthropogenic heat release to the urban heat island is greatest in the evening and at night, and least at noon. The daily average contribution ratio of anthropogenic heat to urban heat island intensity in the winter is 54.5%, compared with just 43.6% in the summer. Anthropogenic heat strengthens the vertical movement of urban surface air flow, changing the urban heat island circulation. It also makes the urban boundary layer more turbulent and unstable, especially in the morning and evening. The degree of influence of anthropogenic heat release on local boundary layer structure depends on its importance to the surface energy budget.     

重庆市城市热岛效应变化特征及减缓措施

利用1961～2016年重庆市逐日气温资料,分析讨论了重庆市主城区56年城市热岛效应的变化趋势和年变化特征,并利用2009～2016年的逐时气温资料分析讨论了城市热岛效应的日变化特征。结果表明:56年来重庆市城市热岛效应总体呈上升趋势,各季节中盛夏上升最明显;重庆市城市热岛效应存在明显的年变化特征,盛夏的热岛效应最强,初春次之,仲春至初夏的热岛效应最弱;重庆市城市热岛效应具有较明显的日变化特征,各季节热岛效应均表现为白天弱,夜间强。重庆市城市热岛效应的形成及其变化,既受到地理位置、气象条件等自然因素的影响,更由城市下垫面变化(绿地和水体的面积及分布)、大气污染、人为热排放等城市化进程因素所决定。结合重庆城市特点综合运用多种措施可以减缓重庆城市热岛效应。      

Characteristics of the heat island effect in Shanghai and its possible mechanism

The characteristics of the urban heat island effect and the climate change in Shanghai and its possible mechanism are analyzed based on monthly meteorological data from 1961 to 1997 at 16 stations in Shanghai and its adjacent areas. The results indicate that Shanghai City has the characteristics of a heat island of air temperature and maximum and minimum air temperature, a cold island of surface soil temperature, a weak rainy island of precipitation, and a turbid island of minimum visibility and aerosols, with centers at or near Longhua station (the urban station of Shanghai). Besides theses, the characteristics of a cloudy island and sunshine duration island are also obvious, but their centers are located in the southern part of the urban area and in the southern suburbs. A linear trend analysis suggests that all of the above urban effects intensified from 1961 to 1997. So far as the heat island effect is concerned, the heat island index (difference of annual temperature between Longhua and Songjiang stations) strengthens (weakens) as the economic development increases (decreases). The authors suggest that the heating increase caused by increasing energy consumption due to economic development is a main factor in controlling the climate change of Shanghai besides natural factors. On the other hand, increasing pollution aerosols contribute to the enhancement of the turbid island and cooling. On the whole, the heating effect caused by increasing energy consumption is stronger than the cooling effect caused by the turbid island and pollution aerosols.     

Urban heat island diagnosis using ASTER satellite images and ‘in situ’ air temperature

This study demonstrates that thermal satellite images combined with ‘in situ’ ground data can be used to examine models of heat island genesis and thus identify the main causes of urban heat islands (UHIs). The models, although proposed over 30 years ago, have not been thoroughly evaluated due to a combination of inadequate ground data and the low resolution of thermal satellite data. Also there has been limited understanding of the relevance of satellite-derived surface temperatures to local and regional scale air temperatures. A cloud-free ASTER thermal image of urban and rural areas of Hong Kong was obtained on a winter night with a well-developed heat island, accompanied by a 148 km vehicle traverse of air temperatures. Over the whole traverse a high R² of 0.80 was observed between surface and air temperatures, with the two datasets showing a similar amplitude and general trend, but with the surface exhibiting much higher local variability than air temperature. Gradients in both surface and air temperature could be related to differences in land cover, with little evidence of large scale advection, thus supporting the population/physical structure model of UHI causation, rather than the advection model. However, the much higher surface and air temperatures observed over the largest urban area, Kowloon, than over any smaller urban centre with similar physical structure in the New Territories, would seem more indicative of the advection model. The image and ground data suggest that Kowloon's urban canopy layer climate is mainly influenced by local city structure, but it is also modified by a strongly developed, regional scale urban boundary layer which has developed over the largest urban centre of Kowloon, and reinforces heating from both above and below.     

兰州市近50年城市热岛强度变化特征

利用1956-2005年兰州市日平均气温、日最高气温和日最低气温,分析了近50年兰州市城市热岛效应变化,并利用城区和郊区3种气温的倾向率计算了城市热岛强度倾向率和热岛增温贡献率。结果表明：1956-2005年兰州市3种气温的城郊差均呈逐年上升趋势,平均气温、最高气温和最低气温的倾向率分别为每10年0.371℃、0.169℃和0.654℃,其中,最低气温的城郊差上升最明显。近50年兰州市增温主要发生在后25年（1981-2005年）,前25年除城区最低气温外基本上以降温为主。后25年中,城区年平均气温、最高气温和最低气温倾向率分别为每10年0.789℃、0.997℃和0.625℃,郊区则相应为每10年0.493℃、0.790℃和0.077℃,其中最高气温增温最显著,最低气温增温最少;以年平均、最高和最低气温表示的城市热岛强度的倾向率分别为每10年0.395℃、0.188℃和0.674℃,热岛效应对城区增温的贡献率分别达到87.0%、49.6%和100%。冬季城市和郊区的平均气温和最低气温倾向率最大,但热岛增温贡献率最大的是春、夏季气温,而不是冬季气温;这可能主要与兰州市冬季严重的空气污染有关, 因为其对城市热岛有一定的抑制作用。20世纪80年代以后兰州市热岛效应有增强的趋势,但平均气温和最高气温的热岛增温贡献率除个别季节外有所下降。     

2019年沈阳一次凌晨气温骤升过程成因精细分析

2019年12月2日01时沈阳国家基本气象站(沈阳站)气温1 h内异常回升了6.5℃,利用常规和加密地面观测站实况、NCEP再分析及沈阳站逐小时风廓线雷达资料,从系统配置、热力学诊断、城市热岛效应等方面对此次异常升温事件成因进行精细分析。结果表明:沈阳站异常升温阶段,超低空到近地面暖脊过境造成辽宁大部分地区出现气温回升,暖脊过境是引发沈阳站午夜时分异常升温的原因之一;沈阳站位于沈阳市的东南部,当地面风为西北风时,风从温度相对较高的城区吹向郊区,造成沈阳南部郊区各站气温回升,与北部郊区对比得出升温幅度约为3—4℃。城市热岛中心向下风方漂移是沈阳站气温骤升又一原因。值得注意的是,气温回升前的温度基础值对气温回升幅度存在一定程度影响,回升前的基础温度越低,则回升后造成的升温幅度越大。     

济宁市城市化对气温的影响

利用1981—2010年济宁及周边郊区3县台站的气温资料,研究分析了济宁城区、郊区的气温变化趋势和特点,并探讨了城市化发展对济宁城郊温度的影响。研究发现：（1）近30a来,尽管济宁城区、郊区最高气温、年平均气温、最低气温均呈显著增加趋势,且增温幅度依次增大,但城、郊气温增幅有所差异。其中,年平均气温、最低气温增温幅度郊区高于城区,而最高气温增幅二者相差不大,这表明城市化发展对最低气温的影响最大。此外,一年之中城、郊增暖均表现为：冬季、春季增幅最大,秋季次之,夏季最弱,且城、郊温差逐渐缩小;（2）济宁城市热岛强度总体呈上升趋势,但不同年代、不同季节变化趋势不尽相同。其中,1980年代热岛上升微弱,总体低于平均水平,而1990年代维持在一个较高的水平,2000年以后又明显下降;除秋季外,热岛强度均呈现缓慢上升趋势,其中冬季最强,夏季最弱。城市热岛效应具有明显的季节和日变化特征,表现为：冬半年明显高于夏半年,白天明显低于夜间;（3）济宁市区人口和建成区面积与城市热岛具有很大的相关性,两者的相关系数分别为0．81和0．75。     

Numerical study of the nocturnal urban boundary layer

A two-dimensional time-dependent Earth-atmosphere model is developed which can be applied to the study of a class of atmospheric boundary-layer flows which owe their origin to horizontal inhomogeneities with respect to surface roughness and temperature. Our main application of the model is to explore the governing physical mechanisms of nocturnal urban atmospheric boundarylayer flow.A case study is presented in which a stable temperature stratification is assumed to exist in the rural upwind area. It is shown through integration of the numerical model that as this air passes over a city, the heat is redistributed due to increased surface friction (and hence increased turbulent mixing). This redistribution of heat results in the formation of an urban heat island.Additional numerical integrations of the model are conducted to examine the dependence of induced perturbations on: (1) the upwind temperature inversion; (2) the geostrophic wind speed; and (3) urbanization. The results show a linear relationship between heat-island intensity and the rural temperature inversion with the heat island increasing in intensity as the upwind inversion becomes stronger; that the heat-island intensity close to the surface is inversely proportional to the geostrophic wind; and that the effects of anthropogenic heat cause an increase in the perturbation temperature with the perturbation extending to higher altitudes. From this study, we conclude that with an upwind temperature inversion, a city of any size should generate a heat island as a result of increased surface roughness. The heat-island intensity should increase with city size because of two factors: larger cities are usually aerodynamically rougher; and larger cities have a larger anthropogenic heat output.Research supported in part by NSF Grant GA-16822.     

Quantifying the influence of land-use and surface characteristics on spatial variability in the urban heat island

The urban thermal environment varies not only from its rural surroundings but also within the urban area due to intra-urban differences in land-use and surface characteristics. Understanding the causes of this intra-urban variability is a first step in improving urban planning and development. Toward this end, a method for quantifying causes of spatial variability in the urban heat island has been developed. This paper presents the method as applied to a specific test case of Portland, Oregon. Vehicle temperature traverses were used to determine spatial differences in summertime ~2 m air temperature across the metropolitan area in the afternoon. A tree-structured regression model was used to quantify the land-use and surface characteristics that have the greatest influence on daytime UHI intensity. The most important urban characteristic separating warmer from cooler regions of the Portland metropolitan area was canopy cover. Roadway area density was also an important determinant of local UHI magnitudes. Specifically, the air above major arterial roads was found to be warmer on weekdays than weekends, possibly due to increased anthropogenic activity from the vehicle sector on weekdays. In general, warmer regions of the city were associated with industrial and commercial land-use. The downtown core, whilst warmer than the rural surroundings, was not the warmest part of the Portland metropolitan area. This is thought to be due in large part to local shading effects in the urban canyons.     

Interactions between thermal advection in frontal zones and the urban heat island of Wrocław, Poland

Summary This paper deals with variability in the air temperature field of an urban area during thermal advection, associated with frontal zones, and its interaction with an urban heat island (UHI). Thermal changes experienced in Wrocław, Poland form the basis of this case study analysis. The discussion also contributes to questions concerning the definition of the UHI and ways to select UHI episodes from existing data sets. It is shown that changes in temperature generated during periods of advection are of short duration, only a few hours at most, but thermal contrasts between various parts of a city at such times are sometimes large, reaching an intensity of 5–6 K, even as large as 9 K. Thus, their intensity is comparable with that of the UHI occurring on cloudless and windless nights. The thermal influence of advection is often greater than that due to urban factors; it is only on occasions with less dynamic advection, that a concentric temperature field is formed due to the modified physical properties of the city. In the majority of cases, the thermal field is non-concentric and this is linked with the location of a frontal zone at any given time. The thermal effects of advection recorded in a data set might easily be viewed as episodes of UHI existence, especially if analysis is conducted based on the data derived from just two stations – one urban the other rural. On occasions when such ‘quasi-UHI’ occur the role of the location of the rural, reference station is also evaluated. Precise definition of the urban heat island can be of significance when conducting comparative studies of the UHI in cities located in different geographical zones and when making an urban climate synthesis.     

人为热源对城市热岛效应影响的数值模拟试验

利用耦合了单层城市冠层模型UCM的中尺度模式WRF,研究了人为热源对上海区域城市气候的影响。冬季地表温度的模拟结果表明,使用新陆面资料的试验效果要好于使用旧的陆面资料,加入人为热源的试验效果要优于没有加入人为热源的试验,这些反映了热岛效应是不断增加的城市面积和人为热源共同决定的。不同试验模拟的2 m高度上气温的模拟情况时,使用新陆面资料并且加入合理人为热源的试验模拟值明显大于其他试验的模拟值。     

基于TM影响的不同季节北京城市热环境研究

利用2005～2006年4景北京Landsat TM影像,通过热红外波段反演地表温度,揭示不同季节城市热环境分布特征及其空间差异。分别利用遥感反演的地面温度和地面气象站观测的气温数据,计算地表热岛强度和空气热岛强度,并分析其季节变化,结果表明：城区相对近郊区,热岛效应在夏季显著;城区相对于乡村,四季都存在较强的热岛效应。     

低纬高原城市昆明的气候特征

以低纬高原城市昆明为研究对象，利用城市内的实测资料与城郊昆明气象站的资料进行了比较研究，分析了城市内外的气候特征、变化规律及其差异，得到了一些有益的结果，可为探讨低纬高原城市气候特征和形成机制、城市环境污染防治及城市建筑的规划、设计提供依据。     

Towards urbanisation of the non-hydrostatic numerical weather prediction model Lokalmodell (LM)

Numerical weather prediction models are increasingly employed for providing meteorological data for urban air quality applications. Model resolution, physiographic parameters and surface-layer parameterisations need to be adapted to the requirements of the urban boundary layer. The Lokalmodell of the German Weather Service was triple-nested down to a horizontal grid resolution of 1.1 km, urbanised physiographic parameters were implemented, and an additional anthropogenic heat source was introduced. Results of a sensitivity study for a spring dust episode in Helsinki show a clear urbanisation effect of these measures on temperature, humidity and the partitioning of surface fluxes, leading to an increased Bowen ratio and heat storage and an urban heat island effect.     

北京夏季强热岛分析及数值模拟研究

应用北京地区20个常规地面气象站、2个自动气象站和中国科学院大气物理研究所325m气象铁塔的资料，对北京2003年7月热岛状况进行了统计分析，发现北京夏季夜间存在强热岛效应，夏季夜间存在强热岛效应的天数占到了1/3，强弱热岛天数合计占到了大约4/5。进一步分析7月1日强热岛特征及其气象影响因子，结果表明：夜间存在强热岛时，郊区所有测站的地面气温都要低于主城区地面气温，城市强热岛的高温中心在天安门和白家庄连线的主城区；白天日照充足的晴夜，日落后城区320m以下低层大气存在逆温和弱的风速，城区地面气温下降速率和幅度均远小于郊区，城市强热岛因此得以形成和维持。日出后至正午，北京北部郊区日照时间比城区长，郊区地面大气得到来自太阳辐射的能量多于城区，而太阳辐射的加热作用使城区低层大气逆温消失，大气稳定度减弱，并使郊区地面气温上升速率和幅度大于城区，最终导致夜间出现的强热岛减弱、消失。此外，应用MM5模式对强热岛进行了初步数值模拟研究，发现在MM5中考虑城市人为热和热储存，可以改善模式对热岛的数值模拟，表明城市人为热和热储存在夏季强热岛的形成中有重要作用。     

城市热岛效应及对锡林浩特气候变化的影响

利用气候相似性原理和锡林郭勒盟地区气象站站址变迁造成的温度序列变化差异,分析城市热岛效应对城市气温变化的作用,以及对气候变化趋势的影响。选取锡林浩特为代表城市,采用线性趋势分析、相关分析等方法,分析、讨论了城市与郊区气温差异,城市与草原温度历史演变差异,以及城市热岛效应对气候变化的影响等,结果表明:城市热岛效应对城市增温作用明显,使锡林浩特市区年平均气温比周围郊区增高了0.57℃;城市热岛效应对锡林浩特市气候变暖趋势也有一定影响,使锡林浩特相对草原区有0.07℃/10a的增温趋势。     

城市热岛效应监测方法研究进展

城市热岛效应是一种由于城市建筑及人们活动导致的热量在城区空间范围内聚集的现象,是城市气候最明显的特征之一.由于城市热岛影响因素以及相互关系的复杂性,为了精确细致地描述其时空分布,人们采用了多种方法来研究城市热岛现象,主要归纳为：气象站法、定点观测法、运动样带法、遥感测定法以及模拟预测等.最后,认为各种测定方法都存在一定的缺陷,建议多种测定方法综合运用.     

昆明和北京两幢建筑物表面热力效应的观测对比

利用昆明、北京两座城市内建筑物为研究对象, 对其不同朝向外墙壁面、屋顶面表面温度及壁面近旁气温进行了观测, 分析了建筑物外墙壁面表面温度及其近旁气温的垂直分布以及壁面、屋顶对周围大气的热力效应特征, 并对两座城市内建筑物的热力状况进行了比较分析。研究表明:建筑物表面温度受太阳辐射的影响要比近旁气温大得多, 一般说来, 壁面昼间是热源, 夜间是热汇; 受研究对象所在的大区域气候、人类活动等影响, 建筑物外表面的热力效应有许多异同; 建筑物屋顶面与近旁空气间的平均热通量基本为正值, 呈现较强的热源效应, 其热力效应强度与太阳辐射呈现正相关; 城市建筑物的外表面 (壁面、屋顶面) 已成为城市区域内有别于城市地面, 且对城市立体气候的形成具有不可忽视影响的热力作用面。