A novel approach for deriving the stable boundary layer height and eddy viscosity profiles from the Ekman equations

In this study, we utilize a novel approach to solve the Ekman equations for eddy viscosity profiles in the stable boundary layer. By doing so, a well-known expression for the stable boundary layer height by Zilitinkevich (Boundary-Layer Meteorology, 1972, Vol. 3, 141--145) is rediscovered

Diagnosing evaporative fraction over land from boundary-layer clouds

The potential use of continental fair-weather shallow cumuli as a way to retrieve the daily surface evaporative fraction over land is evaluated in convective conditions. The proposed method utilizes the fact that both the timing of cloud occurrence and the cloud-base height at the time of occurrence provide strong constraints on the surface energy balance and evaporative fraction. The retrieval is especially reliable in the presence of relatively stable and humid-free troposphere profiles. The advantage of the method is that it provides a more direct estimate of the surface evaporative fraction than indirect estimation based on inversion of a highly parameterized land-surface model. In addition, the evaporative fraction is obtained at a scale of a few kilometers, which is more pertinent for weather and climate studies. The retrieval strategy is tested and validated for three contrasting climates: the U.S. southern Great Plains, West Africa, and the Netherlands. We suggest that the use of satellite observations of shallow cumuli can help constrain the retrieval of the surface evaporative fraction within a data assimilation scheme/reanalysis

Surface and atmospheric driven variability of the single‐layer urban canopy model under clear‐sky conditions over London

Urban canopy models (UCMs) are parametrization schemes that are used to improve weather forecasts in urban areas. The performance of UCMs depends on understanding potential uncertainty sources that can generally originate from the (a) urban surface parameters, (b) atmospheric forcing, and (c) physical description. Here, we investigate the relative importance of surface and atmospheric driven model sensitivities of the single‐layer urban canopy model when fully interactive with a 1‐D configuration of the Weather Research and Forecasting model (WRF). The impact of different physical descriptions in UCMs and other key parameterization schemes of WRF is considered. As a case study, we use a 54‐h period with clear‐sky conditions over London. Our analysis is focused on the surface radiation and energy flux partitioning and the intensity of turbulent mixing. The impact of changes in atmospheric forcing and surface parameter values on model performance appears to be comparable in magnitude. The advection of potential temperature, aerosol optical depth, exchange coefficient and roughness length for heat, surface albedo, and the anthropogenic heat flux are the most influential. Some atmospheric forcing variations have similar impact on the key physical processes as changes in surface parameters. Hence, error compensation may occur if one optimizes model performance using a single variable or combinations that have potential for carryover effects (e.g., temperature). Process diagrams help differences to be understood in the physical description of different UCMs, boundary layer, and radiation schemes and between the model and the observations

Determination of complex dielectric functions of ion implanted and implanted‐annealed amorphous silicon by spectroscopic ellipsometry

Measuring with a spectroscopic ellipsometer (SE) in the 1.8–4.5 eV photon energy region we determined the complex dielectric function (ϵ = ϵ1 + iϵ2) of different kinds of amorphous silicon prepared by self‐implantation and thermal relaxation (500 °C, 3 h). These measurements show that the complex dielectric function (and thus the complex refractive index) of implanted a‐Si (i‐a‐Si) differs from that of relaxed (annealed) a‐Si (r‐a‐Si). Moreover, its ϵ differs from the ϵ of evaporated a‐Si (e‐a‐Si) found in the handbooks as ϵ for a‐Si. If we use this ϵ to evaluate SE measurements of ion implanted silicon then the fit is very poor. We deduced the optical band gap of these materials using the Davis–Mott plot based on the relation: (ϵ2E2)1/3 ∼ (E− Eg). The results are: 0.85 eV (i‐a‐Si), 1.12 eV (e‐a‐Si), 1.30 eV (r‐a‐Si). We attribute the optical change to annihilation of point defects

On‐ and off‐line evaluation of the single‐layer urban canopy model in London summertime conditions

Urban canopy models are essential tools in forecasting weather and air quality in cities. However, they require many surface parameters, which are uncertain and can reduce model performance if inappropriately prescribed. Here, we evaluate the model sensitivity of the Single-Layer Urban Canopy Model (SLUCM) in the Weather Research and Forecasting model (WRF) to surface parameters in two different configurations, one coupled to the overlying atmosphere (on-line) in a 1D configuration and one without coupling (off-line). A 2-day summertime period in London is used as a case study, with clear skies and low wind speeds. Our sensitivity tests indicate that SLUCM reacts differently, when coupled to the atmosphere. For certain surface parameters, atmospheric feedback effects can outweigh the variations caused by surface parameter settings. Hence to fully understand model sensitivity atmospheric feedbacks should be considered

Performance of HIRLAM in a semiarid heterogeneous region: evaluation of the land surface and boundary layer description using EFEDA observations

Observations from the European Field Experiment in a Desertification-threatened Area (EFEDA) are used to evaluate the performance of the radiation, land surface, and boundary layer description of the numerical weather prediction (NWP) system High-Resolution Limited Area Model (HIRLAM) in semiarid conditions. Model analysis and 6-h forecast data of the fully coupled three-dimensional model are compared with the comprehensive dataset of a case study representing a sample of 22 days of anticyclonic conditions. Distributed micrometeorological surface stations, radiosondes, flux aircraft, and airborne lidar provide a unique validation dataset of the diurnal cycle of surface and boundary layer processes. The model surface, soil, and boundary layer are found to be too moist and slightly too cold during most of the diurnal cycle. The model radiation and surface energy budgets are biased toward more humid conditions. Model shortcomings are identified essentially in four areas. These are the moisture data assimilation, the land-use and soil classification with its associated physiographic database, the aerosol parameterization in the radiation code, and the boundary layer vertical resolution and entrainment description. Practical steps for immediate improvement of the model performance are proposed. They focus on the use of a land-use and soil classification and physiographic database adapted to Mediterranean landscapes, in combination with the inclusion of aerosol parameters in the radiation scheme, that account for the typically higher aerosol load of arid and semiarid environments.The EFEDA 1991 field phase was cofunded by the European Commission under its Environment Program (Grant EV5VCT93- 0271)

Perceived (In)justice of Public Land Acquisition

Many studies have addressed the justice of public land acquisition, but few studies have addressed the question of what landowners perceive as just. Individual perceptions drive an important part of the social and scientific debates on legitimate and just land acquisition. This article addresses this gap by studying landowners’ and land purchasers’ perceptions of just land acquisition. We did this by uncovering the prevailing discourse on just land acquisition and studying the values that shaped people’s perceptions of just land acquisition. The results showed that perceptions of justice are based on the values of lawfulness, decentness and equality. These values were translated into different norms that resulted in expectations pertaining to just land acquisition. Insight into the different perceptions and the prevailing discourse of just land acquisition and their underlying values increases the understanding of land acquisition processes and land policy strategies. First, it becomes apparent that land acquisition has an essential element of injustice that cannot be avoided by a good process or a just compensation fee. Second, insight in different discourses provides valuable input for debates on just land acquisition. Third, such insight shows that money is not always a sufficient means of indemnification. The combination of sufficient financial compensation, the opportunity of a new location, attractive selling conditions and accurate and open process are all important requisites to ensure that public land acquisition is perceived by the majority of landowners as just.</p

Contribution of cadastral information to climate change policy in the Netherlands

In the challenge to cope with climate change, the importance of urban areas is increasingly acknowledged. This article provides an outline of the use of cadastral information, combined with other spatial datasets in support of climate change policy within the context of the Netherlands. The examples of the municipalities Bussum and Apeldoorn are used to explain and discuss the use of cadastral data to support governments in their climate policies. The paper concludes exploring and discussing the possibilities of implementing this strategy outside the Netherlands and to combine data, experiences and ideas internationall

Cool city mornings by urban heat

The urban heat island effect is a phenomenon observed worldwide, i.e. evening and nocturnal temperatures in cities are usually several degrees higher than in the surrounding countryside. In contrast, cities are sometimes found to be cooler than their rural surroundings in the morning and early afternoon. Here, a general physical explanation for this so-called daytime urban cool island (UCI) effect is presented and validated for the cloud-free days in the BUBBLE campaign in Basel, Switzerland. Simulations with a widely evaluated conceptual atmospheric boundary-layer model coupled to a land-surface model, reveal that the UCI can form due to differences between the early morning mixed-layer depth over the city (deeper) and over the countryside (shallower). The magnitude of the UCI is estimated for various types of urban morphology, categorized by their respective local climate zones

Noble-gas ion bombardment on clean silicon surfaces

Under UHV conditions clean c-Si(111) surfaces have been bombarded at room temperature by noble gases (He,Ne,Ar,Kr). Using spectroscopic ellipsometry, the implantation processes were continuously recorded. A low-dose behavior (amorphization) and a high-dose behavior (dilution) are observed. After termination of the bombardment, a self-anneal behavior appears and some experiments are discussed in order to explain the observed phenomena. After applying a monotonous temperature increase up to 1100 K, the noble gas desorbs and the surface layer returns to the original state, as can be seen from a closed trajectory in the (δψ,δΔ) plane. The low-dose behavior is analyzed in the scope of a simple ellipsometric first-order approximation, and the results obtained are compared with theory. The dilution arising during the high-dose behavior can be explained ellipsometrically by means of microscopic surface roughness, and some complementary measurements are reported to verify this explanation