The urban boundary layer (UBL) is the part of the atmosphere in which most of the planet’s population now lives, and is one of the most complex and least understood microclimates. Given potential climate change impacts and the requirement to develop cities sustainably, the need for sound modelling and observational tools becomes pressing. This review paper considers progress made in studies of the UBL in terms of a conceptual framework spanning microscale to mesoscale determinants of UBL structure and evolution. Considerable progress in observing and modelling the urban surface energy balance has been made. The urban roughness sub-layer is an important region requiring attention as assumptions about atmospheric turbulence break down in this layer and it may dominate coupling of the surface to the UBL due to its considerable depth. The upper 90% of the UBL (mixed and residual layers) remains under-researched but new remote sensing methods and high resolution modelling tools now permit rapid progress. Surface heterogeneity dominates from neighbourhood to regional scales and should be more strongly considered in future studies. Specific research priorities include humidity within the UBL, high-rise urban canopies and the development of long-term, spatially extensive measurement networks coupled strongly to model development.

Progress in observing and modelling the urban boundary layer

Wind energy continues to stand out as a more established and mature technology to offset a large proportion of power. Efforts aimed at improving wind energy use to meet the energy demand in turbulent urban wind environment have been the main technical focus. In previous studies on wind resource and behavior in urban environment, different designs of horizontal axis wind turbines (HAWTs) and vertical axis wind turbines (VAWTs) have been reviewed. This paper vividly captures the fact that wind resource has a great potential to be fully explored and developed in the urban environment. Varying ways of application and application techniques being applied for electrical generation, ventilation and pollution dispersion, onshore cooling and dehumidification of coastal urban cities, and economics and environmental benefits of applying wind energy in urban environments are summarized. Although many new ideas and solutions that factor technical, economical and environmental sustainability in urban areas are coming up every day, challenges in design are gradually being solved to take advantage of urban low and turbulent wind speed characteristics, installation space challenges, vibration and noise reduction, among others. Some of the unique solutions that have been and are being developed in the applications of wind energy technology in urban environments are also reported in this paper.

Advances in wind energy resource exploitation in urban environment: A review

Inter-/intra-zonal seasonal variability of the surface urban heat island based on local climate zones in three central European cities

Doppler wind LiDAR (Light Detection And Ranging) makes use of the principle of optical Doppler shift between the reference and backscattered radiations to measure radial velocities at distances up to several kilometers above the ground. Such instruments promise some advantages, including its large scan volume, movability and provision of 3-dimensional wind measurements, as well as its relatively higher temporal and spatial resolution comparing with other measurement devices. In recent decades, Doppler LiDARs developed by scientific institutes and commercial companies have been well adopted in several real-life applications. Doppler LiDARs are installed in about a dozen airports to study aircraft-induced vortices and detect wind shears. In the wind energy industry, the Doppler LiDAR technique provides a promising alternative to in-situ techniques in wind energy assessment, turbine wake analysis and turbine control. Doppler LiDARs have also been applied in meteorological studies, such as observing boundary layers and tracking tropical cyclones. These applications demonstrate the capability of Doppler LiDARs for measuring backscatter coefficients and wind profiles. In addition, Doppler LiDAR measurements show considerable potential for validating and improving numerical models. It is expected that future development of the Doppler LiDAR technique and data processing algorithms will provide accurate measurements with high spatial and temporal resolutions under different environmental conditions.

A review of progress and applications of pulsed doppler wind LiDARs

A review spanning across a 40-year period (1978–2018) and including a total of 332 applications has been addressed on theoretical and empirical wind resource extrapolation models applied in wind energy, which can be grouped into three main families: (i) the logarithmic models; (ii) the Deaves and Harris (DH) model; (iii) the power law (PL). Applied over 96 very heterogeneous locations worldwide, models have been tested against observations at upper extrapolation height and assessed by location characteristics, extrapolation range skills, and application economical advantages. The logarithmic models can nowadays be considered unsuitable for extrapolating wind resource to hub height of current multi-MW WTs, mainly because exhibiting a limited extrapolation range capability (about 10–50 m median bin). Finer scores in extrapolating wind resource (mean absolute bias of 3.3%) and in predicting energy output (10.1%) were achieved by the DH model, also showing remarkable extrapolation range skills (10–80 m median bin). However, although among the most economical and forward-looking solutions, its need for accurate z0 assessment and u* observations resulted so far in great limitations to its large-scale application for wind energy purposes (less than 1%). Eventually, the PL confirmed the most reliable – and largely most commonly used (73.5%) – approach for wind energy applications. Out of the plethora of PL models developed in the literature, the PL(α)-αlower and the PL(α)-αI were the finest in predicting both extrapolated wind resource (mean absolute error of 4% and 4.4%, respectively) and energy output (8.9% and 5.5%), also exhibiting extrapolation range skills meeting modern WTs requirements. By contrast, the PL using α = 1/7 returned among the worst scores, yet resulting – since the simplest – the solution most frequently applied (19.6%). This study also demonstrated that extrapolation tools requiring the most expensive instrumentation equipment do not necessarily return the finest scores.

A comprehensive review on wind resource extrapolation models applied in wind energy

https://centaur.reading.ac.uk/33064/1/1-s2.0-S0167610513001001-main.pdf

An assessment of a three-beam Doppler lidar wind profiling method for use in urban areas

Wind observations above an urban river using a new lidar technique, scintillometry and anemometry.

https://centaur.reading.ac.uk/33772/1/1-s2.0-S0167610513001645-main.pdf

Observations of wind speed profiles over Greater London, UK, using a Doppler lidar

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An assessment of a three-beam Doppler lidar wind profiling method for use in urban areas

Wind observations above an urban river using a new lidar technique, scintillometry and anemometry.

Observations of wind speed profiles over Greater London, UK, using a Doppler lidar