Urban Surface Layer Research Articles

ПРИМЕНЕНИЕ МНОГОУРОВНЕВОЙ ПАРАМЕТРИЗАЦИИ ГОРОДСКИХ ЛАНДШАФТОВ В КЛИМАТИЧЕСКОЙ МОДЕЛИ WRF-ARW ДЛЯ СОЗДАНИЯ БАЗЫ ДАННЫХ О КЛИМАТЕ МЕГАПОЛИСА И ЕГО ПРИГОРОДОВ: ПЕРВЫЕ РЕЗУЛЬТАТЫ НА ПРИМЕРЕ МОСКОВСКОГО РЕГИОНА

The current development level of urban meteorology as a synthetic science that includes elements of climatology,ecology, urban studies, and computational mathematics requires the creation of adequate databases of meteorological parameters:only in this way can they be properly used for solving problems of both applied sciences and fundamental research.Therefore, obtaining information on the intra-urban distribution of air temperature, relative humidity, and wind speed mustmeet the most stringent quality criteria. The most modern method for obtaining high-resolution databases is hydrodynamic modeling with the use of regional weather and climate forecast models (WRF, COSMO_RU, ENVIRO-HIRLAM, etc.).However, for horizontal resolution of about a kilometer it is already necessary to use so-called multilevel parameterizationsof the urban surface layer of the atmosphere, which take into account the vertical structure within the urban area. For this purpose, it seems promising to adapt the most modern physically based parameterizations of the lower atmosphere, such as Building EnergyParameterization (BEP) and Building Energy Model (BEM), for the popular, freely distributed regional model WRF-ARW, whichhas been used in our study for the Moscow region (Moscow + Moscow Oblast). The article reviews the advantages of this approachand the results of the first computational experiments. We provide estimates of the accuracy of temperature and relative humiditysimulation for a full-fledged experiment on dynamic downscaling of ERA5 reanalysis data within the Moscow region for 2010 (as aperiod with notable seasonal temperature contrasts, including the infamous extreme heat wave over European Russia).

Comparison of Urban Canopy Schemes and Surface Layer Schemes in the Simulation of a Heatwave in the Xiongan New Area

Due to rapid growth and expansion, Xiongan New Area is at risk for heatwaves in the present and future induced by the urban heat island effect. Based on eight combined schemes, including two common WRF surface layer schemes (MM5 and Eta) and urban canopy schemes (SLAB, UCM, BEP and BEP + BEM), simulation performance for 2-m temperature, 2-m relative humidity and 10-m wind during a heatwave in July 2019 was compared and analyzed. The simulation performance is ranked from best to worst: 2-m temperature, 2-m relative humidity, 10-m wind direction and 10-m wind speed. MM5 simulate 2-m temperature and 10-m wind speed better than Eta, but 2-m relative humidity worse. MM5 coupling BEP + BEM provides the highest simulation performance for 2-m air temperature, 10-m wind direction and 10-m wind speed but the worst for 2-m relative humidity. MM5 and Eta produce nearly opposite results for wind direction and wind speed. Due to the Anxin station close to Baiyang Lake, lake-land breeze affects the simulation findings, worsening the correlation between simulated 10-m wind and observation.

Quantifying the coastal urban surface layer structure using distributed temperature sensing in Helsinki, Finland

Abstract. The structure of the urban boundary layer, and particularly the surface layer, displays significant complexity, which can be exacerbated by coastal effects for cities located in such regions. Resolving the complexity of the coastal urban boundary layer remains an important question for many applications such as air quality and numerical weather prediction. One of the most promising new techniques for measuring the structure of the surface layer is fibre-optic distributed temperature sensing (DTS), which has the potential to provide new significant insights for boundary layer meteorology by making it possible to study thermal turbulence with high spatial and temporal resolution. We present 14 weeks of profile measurements with a DTS system at an urban site in Helsinki, Finland, during the winter and spring of 2020. We assess the benefits and drawbacks of using DTS measurements to supplement sonic anemometry for longer measurement periods in varying meteorological conditions, including those found difficult for the DTS method in prior studies. Furthermore, we demonstrate the capabilities of the DTS system using two case scenarios: a study of the erosion of a near-ground cold layer during the passage of a warm front, and a comparison of the near-ground thermal structure with and without the presence of a sea-breeze cell during springtime convective boundary layer development. This study demonstrates the utility of DTS measurements in revealing the internal surface layer structure, beyond the predictions of traditional surface layer theories. This knowledge is important for improving surface layer theories and parametrisations, including those used in numerical weather prediction. The study also highlights the drawbacks of DTS measurements, caused by low signal-to-noise ratios in near-neutral atmospheric conditions, especially when such a system would be used to supplement turbulence measurements over longer periods. Overall, this study presents important considerations for planning new studies or ongoing measurements utilising this exciting and relatively new instrumentation.

High-resolution spatiotemporal patterns of China’s FFCO2 emissions under the impact of LUCC from 2000 to 2015

Fossil fuel carbon dioxide (FFCO2) emissions have become a principal driver behind the increase of atmospheric CO2 concentration and spatiotemporal variations of atmospheric CO2 in the urban surface layer. This study quantifies the 2000–2015 urban high-resolution spatiotemporal patterns of China’s FFCO2 emissions under the impact of the land-use and land-cover change. Multi-source data were used together with various up-to-date geostatistics and spatial analysis methods. FFCO2 emissions were determined to rise over the 15 years in the highest emitting cities in the South and East of China. The high-value clusters inside of all cities expanded outward from their city centers and in some cases transferred to economic development zones or new city centers, while the expansion speeds and variation time were found to differ significantly. We found further that then FFCO2 emissions spatial distribution is interconnected with diverse factors: urbanization, and either croplands (rainfed, irrigated, and post-flooding) or native vegetation, being the two most important. As expected, the increase in urban areas was associated with increased FFCO2 emissions, while the wettability in croplands or the increase in native vegetation have an association with the decrease of FFCO2 emissions. Unlike previous studies, we have found no change associated with changes in water cover. Finally, while the primary source of FFCO2 emissions is still coal, there has been a gradual move to cleaner energy (natural gas in Beijing) or more efficient industrial processes (Wuxi and Dalian), although diverse industrial structures and energy efficiencies exist. Over time, the current spatial patterns of FFCO2 emissions in China will conflict with these trends at the macroscale.

Vertical observations of the atmospheric boundary layer structure over Beijing urban area during air pollution episodes

Abstract. We investigated the interactions between the air pollutants and the structure of the urban boundary layer (UBL) over Beijing by using the data mainly obtained from the 325 m meteorological tower and a Doppler wind lidar during 1–4 December 2016. Results showed that the pollution episodes in this period could be characterized by low surface pressure, high relative humidity, weak wind, and temperature inversion. Compared with a clean daytime episode that took place on 1 December, results also showed that the attenuation ratio of downward shortwave radiation was about 5 %, 24 % and 63 % in afternoon hours (from 12:00 to 14:00 local standard time, LST) on 2–4 December, respectively, while for the net radiation (Rn) attenuation ratio at the 140 m level of the 325 m tower was 3 %, 27 % and 68 %. The large reduction in Rn on 4 December was not only the result of the aerosols, but also clouds. Based on analysis of the surface energy balance at the 140 m level, we found that the sensible heat flux was remarkably diminished during daytime on polluted days and even negative after sunrise (about 07:20 LST) till 14:00 LST on 4 December. We also found that heat storage in the urban surface layer played an important role in the exchange of the sensible heat flux. Owing to the advantages of the wind lidar having superior spatial and temporal resolution, the vertical velocity variance could capture the evolution of the UBL well. It clearly showed that vertical mixing was negatively related to the concentrating of pollutants, and that vertical mixing would also be weakened by a certain quantity of pollutants, and then in turn worsened the pollution further. Compared to the clean daytime on 1 December, the maximums of the boundary layer height (BLH) decreased about 44 % and 56 % on 2–3 December, when the average PM2.5 (PM1) concentrations in afternoon hours (from 12:00 to 14:00 LST) were 44 (48) µg m−3 and 150 (120) µg m−3. Part of these reductions of the BLH was also contributed by the effect of the heat storage in the urban canopy.

Characterizing the State of the Urban Surface Layer Using Radon‐222

AbstractFour years of summertime paired urban‐rural meteorological and radon observations in central Poland are used to assess the relationship between atmospheric stability and urban‐induced changes to the radiation balance and surface energy budget. An existing radon‐based technique for nocturnal stability classification is improved and extended to also infer daytime mixing conditions. The radon‐based scheme is shown to provide a simple, effective, objective means of investigating urban energy budget closure over a range of meteorological conditions, which promises to improve estimates of energy storage and loss terms associated with urban canopies. Special attention is paid to quantifying atmospheric characteristics associated with the arbitrarily assigned radon‐derived stability categories in terms of the more conventional measures: bulk Richardson number and the Monin‐Obukhov stability parameter (z/L). The bulk Richardson number approach is demonstrated to be less effective at grouping periods of similar mean stability, and less selective of extremely stable conditions, than the radon‐based technique. A simple box model is used in conjunction with radon observations and an assumed source function of 15 mBq·m−2·s−1, to show that nocturnal effective mixing heights were deeper and less variable over the urban region. On stable nights hourly median effective mixing heights were 15–20 m over the rural region compared to 40–45 m over the urban region.

Scale Properties of Anisotropic and Isotropic Turbulence in the Urban Surface Layer

The scale properties of anisotropic and isotropic turbulence in the urban surface layer are investigated. A dimensionless anisotropic tensor is introduced and the turbulent tensor anisotropic coefficient, defined as C, where $$C = 3d_{3}\,+\,1 (d_{3}$$ is the minimum eigenvalue of the tensor) is used to characterize the turbulence anisotropy or isotropy. Turbulence is isotropic when $$C \approx 1$$ , and anisotropic when $$C \ll 1$$ . Three-dimensional velocity data collected using a sonic anemometer are analyzed to obtain the anisotropic characteristics of atmospheric turbulence in the urban surface layer, and the tensor anisotropic coefficient of turbulent eddies at different spatial scales calculated. The analysis shows that C is strongly dependent on atmospheric stability $$\xi = (z-z_{\mathrm{d}})/L_{{\textit{MO}}}$$ , where z is the measurement height, $$z_{\mathrm{d}}$$ is the displacement height, and $$L_{{\textit{MO}}}$$ is the Obukhov length. The turbulence at a specific scale in unstable conditions (i.e., $$\xi < 0$$ ) is closer to isotropic than that at the same scale under stable conditions. The maximum isotropic scale of turbulence is determined based on the characteristics of the power spectrum in three directions. Turbulence does not behave isotropically when the eddy scale is greater than the maximum isotropic scale, whereas it is horizontally isotropic at relatively large scales. The maximum isotropic scale of turbulence is compared to the outer scale of temperature, which is obtained by fitting the temperature fluctuation spectrum using the von Karman turbulent model. The results show that the outer scale of temperature is greater than the maximum isotropic scale of turbulence.

Impact of heatwave on a megacity: an observational analysis of New York City during July 2016

More than half of the world’s current population resides in urban areas, and cities account for roughly three-quarters of the total greenhouse gas emissions. Current and future trends in urbanization will have significant impacts on global climate. However, our collective understanding of the climate of urban areas remains deficient, which is mainly related to significant knowledge gaps in observations. The New York City Summer Heat Campaign was initiated to address some of these critical knowledge gaps. As part of the campaign the urban boundary layer over New York City was continuously monitored during July 2016, a period that witnessed three heatwave events. Surface weather stations and indoor sensors were also used to characterize the urban heat island intensity. Our results reveal that during the month, the urban heat island intensity was nearly twice compared to the decadal average. During the heatwave episodes, urban heat island intensities as high as 10 °C were observed. The thermal profiles indicate elevated temperatures in much of the boundary layer between 800–2500 m during the heatwave episodes. The profiles indicate a complex thermal structure and high intra-city variability. Thermal internal boundary layer was observed in neighborhoods populated by tall buildings. Overall the high-pressure system during the heatwave episodes acted as a thermal block and much of the heat generated in the urban surface layer remained within the boundary layer, thereby amplifying the near surface air temperature.

A neighbourhood-scale estimate for the cooling potential of green roofs

Green roofs offer the possibility to mitigate multiple environmental issues in an urban environment. A common benefit attributed to green roofs is the temperature reduction through evaporation. This study focuses on evaluating the effect that evaporative cooling has on outdoor air temperatures in an urban environment. An established urban energy balance model was modified to quantify the cooling potential of green roofs and study the scalability of this mitigation strategy. Simulations were performed for different climates and urban geometries, with varying soil moisture content, green roof fraction and urban surface layer thickness. All simulations show a linear relationship between surface layer temperature reduction ΔTs and domain averaged evaporation rates from vegetation mmW, i.e. ΔTs=eW ⋅ mmW, where eW is the evaporative cooling potential with a value of ∼−0.35 Kdaymm−1. This relationship is independent of the method by which water is supplied. We also derive a simple algebraic relation for eW using a Taylor series expansion.

A new method for measuring the imaginary part of the atmospheric refractive index structure parameter in the urban surface layer

Abstract. The atmospheric refractive index consists of both real and imaginary parts. The intensity of refractive index fluctuations is generally expressed as the refractive index structure parameter, with the real part reflecting the strength of atmospheric turbulence and the imaginary part reflecting absorption in the light path. A large aperture scintillometer (LAS) is often used to measure the structure parameter of the real part of the atmospheric refractive index, from which the sensible and latent heat fluxes can further be obtained, whereas the influence of the imaginary part is ignored or considered noise. In this theoretical analysis study, the relationship between logarithmic light intensity variance and the atmospheric refractive index structure parameter (ARISP), as well as that between the logarithmic light intensity structure function and the ARISP, is derived. Additionally, a simple expression for the imaginary part of the ARISP is obtained which can be conveniently used to determine the imaginary part of the ARISP from LAS measurements. Moreover, these relationships provide a new method for estimating the outer scale of turbulence. Light propagation experiments were performed in the urban surface layer, from which the imaginary part of the ARISP was calculated. The experimental results showed good agreement with the presented theory. The results also suggest that the imaginary part of the ARISP exhibits a different diurnal variation from that of the real part. For the wavelength of light used (0.62 μm), the variation of the imaginary part of the ARISP is related to both the turbulent transport process and the spatial distribution characteristics of aerosols.

Influence of Soil Moisture on Urban Microclimate and Surface-Layer Meteorology in Oklahoma City

AbstractThe influence of soil moisture on the surface-layer atmosphere is examined in this paper by analyzing the outputs of model simulations for different initial soil moisture configurations, with particular emphasis on urban microclimate. In addition to a control case, four different soil moisture distributions within the urban and surrounding rural areas are considered in this study. Outputs from the Global Environmental Multiscale atmospheric model simulations are compared with observations from the Joint Urban 2003 experiment held in Oklahoma City, Oklahoma, and the relevant conclusions drawn in this paper are therefore valid for similar medium-size cities. In general, high soil moisture is found to be associated with colder near-surface temperature and lower near-surface wind speed, whereas drier soil resulted in warmer temperatures and enhanced low-level wind. Relative to urban soil moisture content, rural soil conditions are predicted to have larger impacts on both rural and urban surface-layer meteorological conditions. Dry rural and wet urban soil configurations are shown to have a strong influence on the urban–rural temperature contrast and resulted in city-induced secondary circulations that considerably affect the near-surface wind speed. Dry rural soil in particular is found to intensify the nocturnal low-level jet and significantly affect the thermal stability of nocturnal near-neutral urban surface layer by altering both thermal and mechanical generation of turbulence.

A Multi-layer Radiation Model for Urban Neighbourhoods with Trees

A neighbourhood-scale multi-layer urban canopy model of shortwave and longwave radiation exchange that explicitly includes the radiative effects of tall vegetation (trees) is presented. Tree foliage is permitted both between and above buildings, and mutual shading, emission and reflection between buildings and trees are included. The basic geometry is a two-dimensional canyon with leaf area density profiles and probabilistic variation of building height. Furthermore, the model accounts for three-dimensional path lengths through the foliage. Ray tracing determines the receipt of direct shortwave irradiance by building and foliage elements. View factors for longwave and shortwave diffuse radiation exchange are computed once at the start of the simulation using a Monte Carlo ray tracing approach; for subsequent model timesteps, matrix inversion rapidly solves infinite reflections and interception of emitted longwave between all elements. The model is designed to simulate any combination of shortwave and longwave radiation frequency bands, and to be portable to any neighbourhood-scale urban canopy geometry based on the urban canyon. Additionally, the model is sufficiently flexible to represent forest and forest-clearing scenarios. Model sensitivity tests demonstrate the model is robust and computationally feasible, and highlight the importance of vertical resolution to the performance of urban canopy radiation models. Full model evaluation is limited by the paucity of within-canyon radiation measurements in urban neighbourhoods with trees. Where appropriate model components are tested against analytic relations and results from an independent urban radiation transfer model. Furthermore, system response tests demonstrate the ability of the model to realistically distribute shortwave radiation among urban elements as a function of built form, solar angle and tree foliage height, density and clumping. Separate modelling of photosynthetically-active and near-infrared shortwave bands is shown to be important in some cases. Increased canyon height-to-width ratio and/or tree cover diminishes the net longwave radiation loss of individual canyon elements (e.g., floor, walls), but, notably, has little effect on the net longwave loss of the whole urban canopy. When combined with parametrizations for the impacts of trees on airflow and hydrological processes in the urban surface layer, the new radiation model extends the applicability of urban canopy models and permits more robust assessment of trees as tools to manage urban climate, air quality, human comfort and building energy loads.

The Effects of Inner- and Outer-Layer Turbulence in a Convective Boundary Layer on the Near-Neutral Inertial Sublayer Over an Urban-Like Surface

A large-eddy simulation of the atmospheric boundary layer, large enough to contain both an urban surface layer and a convective mixed layer, was performed to investigate inner-layer and outer-layer scale motions. The objective was to determine the applicability of Monin–Obukhov similarity theory to inner-layer motions, to investigate the influence of outer-layer motions on surface-layer structure, as well as to assess the interaction of the two scales of motion. The urban surface roughness consisted of square-patterned cubic buildings of dimension H (40 m). A spatial filter was used to decompose the two scales in the inertial sublayer. The horizontal square filter of size 10H was effective in separating the inner-layer (surface-layer height ≈ 2 H) and outer-layer scales (boundary-layer height δ ≈ 30H), where the Reynolds stress contribution of the inner layer dominates in the logarithmic layer (depth 2H). Similarity coefficients for velocity fluctuations were successfully determined for inner-layer motions in the surface layer, proving the robustness of Monin–Obukhov similarity for surface-layer turbulence. The inner-layer structures exhibit streaky structures that have similar streamwise length but narrower spanwise width relative to the streamwise velocity fluctuation field, consistent with observations from an outdoor scale model. The outer-layer motions to some extent influence the location of ejections and sweeps through updraft and downdraft motions, respectively, thus, disturbing the homogeneity and similarity of inner-layer motions. Although the horizontal averages of the variances and covariance of motions reveal that the Reynolds stresses are dominated by inner-layer structures, the localized influence of the interaction of outer-layer horizontal and inner-layer vertical motions on the Reynolds stress is not insignificant.

Further Development of the Vegetated Urban Canopy Model Including a Grass-Covered Surface Parametrization and Photosynthesis Effects

The vegetated urban canopy model (VUCM), which includes parametrizations of urban physical processes for artificial surfaces and vegetated areas in an integrated system, has been further developed by including physical processes associated with grass-covered surfaces in urban pervious surfaces and the photosynthesis effects of urban vegetation. Using measurements made from three urban/suburban sites during the BUBBLE field campaign in 2002, the model’s performance in modelling surface fluxes (momentum flux, net radiation, sensible and latent heat fluxes and storage heat flux) and canopy air conditions (canopy air temperature and specific humidity) was critically evaluated for the non-precipitation and the precipitation days. The observed surface fluxes at the urban/suburban sites were significantly altered by precipitation as well as urban vegetation. Especially, the storage heat at urban surfaces and underlying substrates varied drastically depending on weather conditions while having an important role in the formation of a nocturnal urban surface layer. Unlike the nighttime canopy air temperature that was largely affected by the storage-heat release, the daytime canopy air conditions were highly influenced by the vertical turbulent exchange with the overlying atmosphere. The VUCM well reproduced these observed features in surface fluxes and canopy air conditions at all sites while performing well for both the non-precipitation and the precipitation days. The newly implemented parametrizations clearly improved the model’s performance in the simulation of sensible and latent heat fluxes at the sites, more noticeably at the suburban site where the vegetated area fraction is the largest among the sites. Sensitivity analyses for model input parameters in VUCM elucidated the relative importance of the morphological, aerodynamic, hydrological and radiative/thermal properties in modelling urban surface fluxes and canopy air conditions for daytime and nighttime periods. These results suggest that the VUCM has great potential for urban atmospheric numerical modelling for a range of cities and weather conditions in addition to having a better physical basis in the representation of urban vegetated areas and associated physical processes.

Flux measurements of volatile organic compounds by the relaxed eddy accumulation method combined with a GC-FID system in urban Houston, Texas

A tall tower flux measurement setup was established in metropolitan Houston, Texas, to measure trace gas fluxes from emission sources in the urban surface layer. We describe a new relaxed eddy accumulation (REA) system combined with a dual-channel GC-FID used for VOC flux measurements, focusing on benzene, toluene, ethylbenzene and xylenes (BTEX) results. Ambient air sampled from 60 m above the ground next to a sonic anemometer was subsampled by a membrane pump and pushed into an REA valve system with two Teflon bag reservoirs, then transferred to two preconcentration units for thermal desorption. We discuss the performance of our system and the selected BTEX measurement results using approximately 8 weeks of data (May 22–July 22, 2008), presenting diurnal variations of concentrations and fluxes of these traffic tracers. The measured values exhibited diurnal cycles with dominant morning and midday peaks during weekdays related to rush hour traffic and additional weekday daytime toluene and xylenes emissions. Local evaporative emissions, likely from solvent usage, significantly contributed to the measured fluxes. We upscaled measured emissions to the county level using a high resolution land cover data set and compared the results with EPA’s National Emission Inventory (NEI).

Potential risks at an industrial site: A wind tunnel study

A gaseous dispersion over a complex urban area after an accident with a leakage of chlorine in a chemical factory is investigated experimentally in a wind tunnel experiment under neutral conditions by using a Laser Doppler Anemometer and Analyser IREX. Diffusion fields in a turbulent boundary layer are simulated using a model of a landscape surrounding the factory at a scale of 1:1000. The obtained results indicate that morphology is one of the important parameters in studying atmospheric diffusion. The strong turbulent mixing inside the urban surface layer has created a rapid decrease in the surface concentrations. Moreover, the diffusion measured in these experiments may be used to develop and evaluate operational models to predict the dispersion of chlorine in a chemical factory.

An application of the RAMS/FLUENT system on the multi-scale numerical simulation of the urban surface layer—A preliminary study

The Regional Atmospheric Modeling System (RAMS) and the computational fluid dynamics (CFD) codes known as FLUENT are combinatorially applied in a multi-scale numerical simulation of the urban surface layer (USL). RAMS and FLUENT are combined as a multi-scale numerical modeling system, in which the RAMS simulated data are delivered to the computational model for FLUENT simulation in an offline way. Numerical simulations are performed to present and preliminarily validate the capability of the multi-scale modeling system, and the results show that the modeling system can reasonably provide information on the meteorological elements in an urban area from the urban scale to the city-block scale, especially the details of the turbulent flows within the USL.

Local and Global Similarity in Turbulent Transfer of Heat, Water Vapour, And CO 2 in the Dynamic Convective Sublayer Over a Suburban Area

We investigated the ‘local’ and ‘global’ similarity of vertical turbulent transfer of heat, water vapour, and CO2 within an urban surface layer. The results were derived from field measurements in a residential area of Tokyo, Japan during midday on fair-weather days in July 2001. In this study, correlation coefficients and quadrant analysis were used for the evaluation of ‘global’ similarity and wavelet analysis was employed for investigating ‘local’ similarity. The correlation coefficients indicated that the transfer efficiencies of water vapour and CO2 were generally smaller than that of heat. Using wavelet analysis, we found that heat is always efficiently transferred by thermal and organized motions. In contrast, water vapour and CO2, which are passive quantities, were not transferred as efficiently as heat. The quadrant analyses showed that the heat transfer by ejection exceeded that by sweep, and the ratios of ejection to sweep for water vapour and CO2 transfer were less than that for heat. This indicated that heat is more efficiently transferred by upward motions and supported the findings from wavelet analysis. The differences of turbulent transfer between heat and both CO2 and water vapour were probably caused both by the active role of temperature and the heterogeneity in the source distribution of scalars

Experimental and numerical investigation of thermal plume in urban surface layer

A fundamental experiment was conducted to approximately demonstrate the subscale thermal plume over constructions in the urban surface layer. Furthermore, a new subscale modeling for the urban surface layer was proposed. The feasibility of the proposed model was discussed by comparing the two-dimensional numerical simulation results with the experimental one. The present study clarifies, for the first time, subscale thermal plumes with many tiny vortices produced over a simplified model of urban structures. These vortices occur in the thermally stable stratified air layer and strongly promote the ambient temperature rise. The numerical simulation showed a significant temperature increase of more than 5 °C in the region over the urban structures. Information and results collected from this research can be used for future practical applications in planning, redevelopment, and restructuring of urban cities.

Heat, Water Vapor and CO2 Fluxes in an Urban Surface Layer

Heat, Water Vapor and CO2 Fluxes in an Urban Surface Layer