Assessing methods to extrapolate the vertical wind-speed profile from surface observations in a city centre during strong winds

Knowledge of the vertical wind-speed profile in cities is important for the construction and insurance industries, wind energy predictions, and simulations of pollutant and toxic gas release. Here, five methods to estimate the spatially- and temporally- averaged wind-speed profile are compared in London: the logarithmic wind law (LOG); the Deaves and Harris equilibrium (DHe) and non-equilibrium (DHv) models; an adaptation of the power law (PL) and the Gryning et al. (GR) profile. Using measurements at 2.5 times the average building height, a source area model is used to determine aerodynamic roughness parameters using two morphometric methods, which assume homogeneous and variable roughness-element heights, respectively. Hourly-averaged wind speeds are extrapolated to 200 m above the canopy during strong wind conditions, and compared to wind speeds observed with Doppler lidar. Wind speeds are consistently underestimated if roughness-element height variability is not considered during aerodynamic parameter determination. Considering height variability, the resulting estimations with the DHe and GR profiles are marginally more similar to observations than the DHv profile, which is more accurate than the LOG and PL methods. An exception is in directions with more homogeneous fetch and a gradual reduction in upwind roughness, where the LOG and PL profiles are more appropriate

Aerodynamic roughness variation with vegetation: analysis in a suburban neighbourhood and a city park

Local aerodynamic roughness parameters (zero-plane displacement, zd, and aerodynamic roughness length, z0) are determined for an urban park and a suburban neighbourhood with a new morphometric parameterisation that includes vegetation. Inter-seasonal analysis at the urban park demonstrates zd determined with two anemometric methods is responsive to vegetation state and is 1 – 4 m greater during leaf-on periods. The seasonal change and directional variability in the magnitude of zd is reproduced by the morphometric methods, which also indicate z0 can be more than halved during leaf-on periods. In the suburban neighbourhood during leaf-on, the anemometric and morphometric methods have similar directional variability for both zd and z0. Wind speeds at approximately 3 times the average roughness-element height are estimated most accurately when using a morphometric method which considers roughness-element height variability. Inclusion of vegetation in the morphometric parameterisation improves wind speed estimation in all cases. Results indicate that the influence of both vegetation and roughness-element height variability are important for accurate determination of local aerodynamic parameters and the associated wind-speed estimation

An arbitrated quantum signature scheme

The general principle for a quantum signature scheme is proposed and investigated based on ideas from classical signature schemes and quantum cryptography. The suggested algorithm is implemented by a symmetrical quantum key cryptosystem and Greenberger-Horne-Zeilinger (GHZ) triplet states and relies on the availability of an arbitrator. We can guarantee the unconditional security of the algorithm, mostly due to the correlation of the GHZ triplet states and the use of quantum one-time pads.Comment: 10 pages, no figures. Phys. Rev. A 65, (In press

Wake characteristics of tall buildings in a realistic urban Canopy

The presence of tall buildings in cities affects momentum and scalar exchange within and above the urban canopy. As wake effects can be important over large distances, they are crucial for urban-flow modelling on and across different spatial scales. We explore the aerodynamic effects of tall buildings on the microscale to local scales with a focus on the interaction between the wake structure, canopy and roughness sublayer (RSL) flow of the surroundings in a realistic urban setting in central London. Flow experiments in a boundary-layer wind tunnel use a 1:200 scale model with two tall buildings (81 m and 134.3 m) for two wind directions. Large changes in mean flow, turbulence statistics and instantaneous flow structure of the wake are evident when tall buildings are part of the complex urban canopy rather than isolated. In the near–wake, the presence of lower buildings displaces the core of the recirculation zone upwards, thereby reducing the vertical depth over which flow reversal occurs. This amplifies vertical shear at the rooftop and enhances turbulent momentum exchange. In the near part of the main–wake, lateral velocity fluctuations and hence turbulence kinetic energy are reduced compared to the isolated building case as eddies generated in the urban canopy and RSL distribute energy down to smaller scales that dissipate more rapidly. Evaluation of a wake model for flow past isolated buildings suggests model refinements are needed to account for such flow-structure changes in tall-building canopies

Implementation of the sectional aerosol module SALSA2.0 into the PALM model system 6.0 : Model development and first evaluation

Urban pedestrian-level air quality is a result of an interplay between turbulent dispersion conditions, background concentrations, and heterogeneous local emissions of air pollutants and their transformation processes. Still, the complexity of these interactions cannot be resolved by the commonly used air quality models. By embedding the sectional aerosol module SALSA2.0 into the large-eddy simulation model PALM, a novel, high-resolution, urban aerosol modelling framework has been developed. The first model evaluation study on the vertical variation of aerosol number concentration and size distribution in a simple street canyon without vegetation in Cambridge, UK, shows good agreement with measurements, with simulated values mainly within a factor of 2 of observations. Dispersion conditions and local emissions govern the pedestrian-level aerosol number concentrations. Out of different aerosol processes, dry deposition is shown to decrease the total number concentration by over 20 %, while condensation and dissolutional increase the total mass by over 10 %. Following the model development, the application of PALM can be extended to local-and neighbourhood-scale air pollution and aerosol studies that require a detailed solution of the ambient flow field.Peer reviewe

Hidden-variable theorems for real experiments

It has recently been questioned whether the Kochen-Specker theorem is relevant to real experiments, which by necessity only have finite precision. We give an affirmative answer to this question by showing how to derive hidden-variable theorems that apply to real experiments, so that non-contextual hidden variables can indeed be experimentally disproved. The essential point is that for the derivation of hidden-variable theorems one does not have to know which observables are really measured by the apparatus. Predictions can be derived for observables that are defined in an entirely operational way.Comment: 4 page

Scanning tunneling spectroscopy of high-temperature superconductors

Tunneling spectroscopy played a central role in the experimental verification of the microscopic theory of superconductivity in the classical superconductors. Initial attempts to apply the same approach to high-temperature superconductors were hampered by various problems related to the complexity of these materials. The use of scanning tunneling microscopy/spectroscopy (STM/STS) on these compounds allowed to overcome the main difficulties. This success motivated a rapidly growing scientific community to apply this technique to high-temperature superconductors. This paper reviews the experimental highlights obtained over the last decade. We first recall the crucial efforts to gain control over the technique and to obtain reproducible results. We then discuss how the STM/STS technique has contributed to the study of some of the most unusual and remarkable properties of high-temperature superconductors: the unusual large gap values and the absence of scaling with the critical temperature; the pseudogap and its relation to superconductivity; the unprecedented small size of the vortex cores and its influence on vortex matter; the unexpected electronic properties of the vortex cores; the combination of atomic resolution and spectroscopy leading to the observation of periodic local density of states modulations in the superconducting and pseudogap states, and in the vortex cores.Comment: To appear in RMP; 65 pages, 62 figure

Urban Multi-scale Environmental Predictor - an extensive tool for climate services in urban areas

The city based climate service tool UMEP (Urban Multi-scale Environmental Predictor) is a coupled modelling system that combines models essential for urban climate processes and is developed as an extensive QGIS plugin. An application is presented to illustrate its potential, specifically of the identification of heat waves and cold waves in cities. The tool has broad utility for applications related to outdoor thermal comfort, urban energy consumption, climate change mitigation etc. It includes tools to: enable users to input atmospheric and surface data from multiple sources, prepare meteorological data for use in urban areas, undertake simulations and consider scenarios, and compare and visualize different combinations of climate indicators

Urban Multi-scale Environmental Predictor (UMEP) : An integrated tool for city-based climate services

UMEP (Urban Multi-scale Environmental Predictor), a city-based climate service tool, combines models and tools essential for climate simulations. Applications are presented to illustrate UMEP's potential in the identification of heat waves and cold waves; the impact of green infrastructure on runoff; the effects of buildings on human thermal stress; solar energy production; and the impact of human activities on heat emissions. UMEP has broad utility for applications related to outdoor thermal comfort, wind, urban energy consumption and climate change mitigation. It includes tools to enable users to input atmospheric and surface data from multiple sources, to characterise the urban environment, to prepare meteorological data for use in cities, to undertake simulations and consider scenarios, and to compare and visualise different combinations of climate indicators. An open-source tool, UMEP is designed to be easily updated as new data and tools are developed, and to be accessible to researchers, decision-makers and practitioners. (C) 2017 The Authors. Published by Elsevier Ltd.Peer reviewe

Aerodynamic roughness parameters in cities: inclusion of vegetation

A widely used morphometric method (Macdonald et al. 1998) to calculate the zero-plane displacement (zd) and aerodynamic roughness length (z0) for momentum is further developed to include vegetation. The adaptation also applies to the Kanda et al. (2013) morphometric method which considers roughness-element height variability. Roughness-element heights (mean, maximum and standard deviation) of both buildings and vegetation are combined with a porosity corrected plan area and drag formulation. The method captures the influence of vegetation (in addition to buildings), with the magnitude of the effect depending upon whether buildings or vegetation are dominant and the porosity of vegetation (e.g. leaf-on or leaf-off state). Application to five urban areas demonstrates that where vegetation is taller and has larger surface cover, its inclusion in the morphometric methods can be more important than the morphometric method used. Implications for modelling the logarithmic wind profile (to 100 m) are demonstrated. Where vegetation is taller and occupies a greater amount of space, wind speeds may be slowed by up to a factor of three