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Although, wind turbines have traditionally been sited in open terrain, there is a growing trend of installing turbines in non-homogeneous terrain, such as urban areas. Recorded urban turbine failures suggest that turbine design has been inadequate for the turbulence experienced at these sites and hence a better understanding of the turbine-loading issues in the built environment is required. This paper compares turbine blade load statistics for inflow turbulence fields based on the open terrain standard Kaimal spectra, as suggested in the standard IEC61400-2 that covers the design and safety standard of small wind turbines, and measured turbulence spectra from a built environment site. The findings show that for extreme, high turbulent intensity winds, the measured spectra predict isolated loading events around twice the magnitude of loads predicted by use of the standard spectra. The work suggests the need for improvements to the standard in order to model the non-Gaussian wind statistics that occur in extreme events such as sudden strong gusts.

The use of small grid-connected wind turbines is increasing within the built environment, yet atmospheric turbulence in this environment is more complex than the open terrain sites on which the turbine design standards are based. The current IEC61400-2 design standard uses stochastic turbulence models adapted from the von Karman and Kaimal power spectra in order to simulate flow fields that are used by designers to predict structural loading on small wind turbines. Both spectra are based on observations in the atmospheric surface layer developed over flat, smooth and uniform terrain yet IEC61400-2 does not offer any modifications of the spectra for more complex terrain such as that which exists in the built environment. This paper investigates the extent to which the von Karman and Kaimal models, as presented in IEC61400-2, are appropriate for use in the design of SWTs installed on the rooftop of a warehouse in the built environment. In particular the paper attempts to gauge how different the turbulence spectra currently used for turbine design are from the actual inflow conditions experienced by the turbines on the roof. The power spectra of all three wind components in neutral and slightly unstable atmospheric conditions at four heights above the rooftop are considered. A degree of misfit function was used to compare von Karman, Kaimal and measured power spectra, as an indicator of model suitability. A sensitivity study was carried out to assess the influence of turbulence length scale and wind direction on the results. The Kaimal spectral function was the better of the existing models in predicting the trends of all wind components and was used as a starting point in developing an approach to modelling turbulence power spectra for a rooftop site in the built environment by incorporating typical length scales at the site.

The authors evaluate a 30-yr (1981–2010) Weather Research and Forecast (WRF) Model regional climate simulation over the southwest of Western Australia (SWWA), a region with a Mediterranean climate, using ERA-Interim boundary conditions. The analysis assesses the spatial and temporal characteristics of climate extremes, using a selection of climate indices, with an emphasis on metrics that are relevant for forestry and agricultural applications. Two nested domains at 10- and 5-km resolution are examined, with the higher-resolution simulation resolving convection explicitly. Simulation results are compared with a high-resolution, gridded observational dataset that provides daily rainfall, minimum temperatures, and maximum temperatures. Results show that, at both resolutions, the model is able to simulate the daily, seasonal, and annual variation of temperature and precipitation well, including extreme events. The higher-resolution domain displayed significant performance gains in simulating dry-season convective precipitation, rainfall around complex terrain, and the spatial distribution of frost conditions. The high-resolution domain was, however, influenced by grid-edge effects in the southwestern margin, which reduced the ability of the domain to represent frontal rainfall along the coastal region. On the basis of these results, the authors feel confident in using the WRF Model for regional climate simulations for the SWWA, including studies that focus on the spatial and temporal representation of climate extremes. This study provides a baseline climatological description at a high resolution that can be used for impact studies and will also provide a benchmark for climate simulations driven by general circulation models.

The south-west of Western Australia has experienced significant land-cover change as well as a decline in rainfall. Given that most precipitation in the region results from frontal passages, the impact of land-cover change on the dynamics of cold fronts is explored using the Regional Atmospheric Modeling System version 6.0. Frontal simulations are evaluated against high resolution atmospheric soundings, station observations, and gridded rainfall analyses and shown to reproduce the qualitative features of cold fronts. Land-cover change results in a decrease in total frontal precipitation through a decrease in boundary-layer turbulent kinetic energy and vertically integrated moisture convergence, and an increase in wind speed within the lower boundary layer. Such processes contribute to reduced convective rainfall under current vegetation cover.

A sea-breeze event in south-west Western Australia is simulated using the Regional Atmospheric Modelling System (RAMS) version 6.0. The model is evaluated against high resolution soundings as well as station observations and is shown to reproduce the qualitative features of the sea breeze well. Sensitivity tests are carried out to investigate the effects of historical land-cover change and changes in soil moisture on the dynamics of the sea breeze. It is found that land-cover change alone, i.e., a change from wooded grasslands to bare soil, with no change in soil moisture initialisation, does not significantly alter the overall structure of the sea breeze but results in higher surface winds due to the reduced vegetation roughness length, which leads to enhanced surface moisture advection inland. On the other hand, land-cover change in conjunction with increased soil moisture results in a considerably weaker, shallower, and less penetrative sea breeze, and delays its onset and duration. A sea-breeze scaling analysis highlights the impact of increasing soil moisture on reducing the sea-breeze volume flux scale.

A two-layer steady-state resistance model is compared with routine meteorological data collected from the Western Australian wheat belt during 2000–06. Major difficulties in implementing such a model are the correct parameterization for the incoming longwave radiation and estimation of daily soil moisture, neither of which are routinely measured. These difficulties are addressed by testing parameterizations for incoming longwave radiation calibrated to local conditions and incorporating a soil–water balance model based on routine weather data. The modified model has RMSE and biases ranging from 2.4° to 3.1°C and −0.2° to 0.8°C, respectively, across the wheat belt when comparing all minimum nocturnal temperatures. The model is shown to predict frost events approximately 55% of the time and illustrates that frost damage to foliage may occur when screen temperatures are < 2°C.

An integral scale of surface heterogeneity is defined in terms of the structure function of surface properties (surface temperature and albedo) and related to flux measurements taken during the NOPEX experiment. The spatial variation of the sensible and latent heat fluxes is shown to be related to this structure function. Although the surface heterogeneity clearly influences the spatial variation of the fluxes, the variance of the fluxes scales under mixed layer scaling and not the heterogeneity of the underlying surface.

Regional turbulent fluxes of momentum, sensible and latent heat collected over both agricultural and native vegetation in the south west of Australia are presented. Analysis of the energy spectrum illustrates that the most energetic eddies are between scales of 20 metres to 5 kilometres and highlights the spatial distance required to obtain representative regional fluxes. For the sensible heat flux, this distance is a function of measurement height whereas the latent flux is also influenced by surface variability. Statistics of these fluxes highlight that for the unstable surface layer, despite marked differences in the underlying vegetation and the corresponding sources of heat and moisture, heat is transported more efficiently than water vapour from the ground surface.

The development and movement of sea breezes under the influence of a thermally induced synoptic coastal trough and coastal terrain are simulated. These simulations are analyzed in the context of an extensive observational data set. The synoptic trough acts to determine the presence and intensity of the sea breeze through the advection of warm air in the surface layer whereas local topography acts to enhance the breeze and turn the low-level flow. Interaction between the sea breeze circulation and the trough assists trough movement across the coastline.

A modified soil-canopy-boundary layer model based on Ek and Mahrt is presented to simulate surface heat fluxes on a daily basis. The model is validated against independent published bare soil data from Agassiz, Canada, and observations taken over sparse and dense vegetation as part of the HAPEX-MOBILHY (Hydrological Atmospheric Pilot Experiment-Modelisation du Bilan Hydrique) experiment. Simulated surface energy components are shown to be in close agreement with the observations, and the sensitivity of the parameterization is evaluated.

A regional air pollution model, based on the solution of the Langevin equation, is developed and validated for both point and area sources. By incorporating the spatial and temporal variations in motor vehicle emissions for Perth, Western Australia, the model is able to reproduce the observed magnitude and spread of the urban plume.

Observations show that the urban heat island in the atmospheric layer below roof level is most strongly developed during calm, cloudless conditions at night. This paper outlines two versions of a numerical model to describe the cooling of rural and street canyon surfaces under these conditions using surface thermal and radiative properties and the radiative geometry of the canyons. One version uses a full system of differential equations and the other the simpler force-restore approach. The two approaches are shown to be in general agreement and the output of the simpler model is shown to give a faithful representation of cooling of rural and urban surfaces, and therefore heat islands, when compared with field observations.

A comparison between a numerical mesoscale model and the computationally simpler flow model developed as part of the European wind atlas is presented. Despite observed horizontal variations in topographically induced mesoscale forcing which is not incorporated in the simpler model, there is general agreement on an order of magnitude assessment of the wind energy variations. The range of applicability of such simpler wind energy assessment models is shown to be limited to regions where the mesoscale forcing inherent in the base observations has not varied appreciably.

Hydrostatically dominated forced flow over the asymmetric topography of the Darling Scarp, Western Australia, is modelled using a hydrostatic numerical mesoscale model and compared with observations. Simulations reproduce the essential features of wave overturning and the development of a shooting hydraulic flow. This response is dependent on the wind profile but not on the existence of a critical level. the high backsheared environment leads to a high ratio of the Brunt-Vaisala frequency to wind speed throughout the profile, resulting in short wavelengths, high nonlinearity and overturning. With the ratio of the halfwidth of the topography to the boundary-layer depth being small, the flow fields are shown to be sensitive to the boundary layer.

Previous studies have suggested that mesoscale processes are important in determining available wind energy potential in southern Australia. These effects are quantified by application of a numerical mesoscale model to the Swan coastal plain of Western Australia, illustrating that the wind power potential in this area is dominated by the sea breeze circulation and topographical influences. While sea breezes are a common feature of the summer climate, they are a significant source of wind energy only under weak synoptic flows, whereas mesoscale topographical effects are significant under all synoptic conditions.

The development and application of a three dimensional regional air dispersion model to the Kwinana industrial area is described. Spatial variation in the flow and variations in surface roughness are incorporated and the model results are shown to be in close agreement with visual observations.

Statistical models based on persistence and climatology are used to forecast tropical cyclone tracks off the northwest coast of Australia. A comparison based on the 1980–81 season shows that a first order least squares fit of the eight primary predictors has a higher level of statistical significance and comparable mean forecast errors to predictions based on higher order regression equations.

Attenuation of solar radiation at Adelaide is estimated by a comparison of simultaneous readings taken at an urban and semi-rural site. These show that the city contributes over one-third of the total turbidity and the role of the aerosol layer is to scatter rather than absorb solar radiation.

The Kwinana Air Modelling Study has been initiated by the State Government of Western Australia to investigate the meteorology of the coastal region of Kwinana and assess its implications for air pollution dispersion. Wind data from this study has been analysed following the methods outlined by Lyons [4, 6] to describe the mesoscale variations within the flow across this region.

Within the numerical mesoscale model described by McNider and Pielke (1981) the eddy exchange coefficients are estimated from either a local or nonlocal scheme. Switching between these is dependent on the sign of the surface heat flux. In inhomogeneous regions this switching is shown to be sensitive to the height of the stable planetary boundary layer. By defining the boundary layer height as the height to which turbulence generated by the wind shear falls to zero, a more realistic estimate can be obtained and the model is able to simulate observed potential temperature fields.

Observations of mesoscale variations in temperature and wind fields in a desert environment are presented and discussed. In particular the influence of low relief under conditions of strong stability is highlighted and stagnant flow is shown to occur below a critical Froude number of 1.5. Sudden nocturnal temperature increases are also analysed and possible mechanisms for their formation discussed.

Observations of forced flow over the highly asymmetric topography of the Darling Scarp, Western Australia, are presented. These are typified by shallow surface gradient winds of 10-20 m s-1 with an inherent critical level aloft and a stable layer produced through nocturnal radiational cooling. The observations highlight a topographically induced hydraulic jump, lee waves or vertically propagating hydrostatic waves depending on the upwind stability and wind profile. The vertically propagating waves and hydraulic jump are observed to produce accelerated flow down the escarpment.

The non-uniformity of the wind field over an approximately 500 km 2 area of urban and suburban Adelaide, South Australia, which has a relatively simple topography, was investigated and the data from a twelve month monitoring period used to compute air-flow trajectories. By superimposing the maps of annual wind field climatology and the likely source locations, a map showing the potential distribution of possible pollutants has been constructed.

A comparison between observed and modelled wind profiles at an operational wind turbine site highlights the inability of a neutral flow model to accurately predict the flow under low to moderate wind speeds. The importance of these flow conditions to power generation is demonstrated.

The Southwest Australian region has large homogeneous tracts of differing vegetation types separated by a sharp transition called the vermin or bunny fence which runs for almost 750 km. Seasonal winter agriculture is found to the west of the fence, whereas to the east native perennial vegetation grows. Geostationary Meteorological Satellite-5 imagery are used to construct monthly cumulus cloud frequency of occurrence maps for the region 0800 to 1500 LT in hourly increments for 1999 and 2000. Moderate Resolution Imaging Spectroradiometer (MODIS) imagery are used to retrieve regional values of surface temperature, albedo, Normalized Difference Vegetation Index, fractional soil moisture availability, sensible and latent heat fluxes. High spatial resolution Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imagery are used to retrieve detailed values along the fence. MODIS imagery also is utilized to retrieve cloud optical thickness, droplet sizes, and liquid water paths. This study shows that higher soil moisture availability is found over agricultural areas during winter (September) and over native vegetation areas during summer (December). Latent heat fluxes are higher over native vegetation than over agricultural areas during summer, while sensible heat fluxes are lower. Cumulus clouds occur with higher frequency and have higher optical thicknesses, cloud liquid water contents, and effective radii over agricultural areas during the winter and over native perennial vegetation during the dry summer. This is due to higher latent heat fluxes and available energy over agriculture during winter and over native vegetation during summer. We conclude that land use differences result in differences in available soil moisture and surface energy fluxes, which in turn lead to the observed preferential enhancement of cumulus cloudiness and cumulus cloud properties.

A feedback loop between regional scale deforestation and climate change was investigated in an experiment using novel, small size airborne platforms and instrument setups. Experiments were performed in a worldwide unique natural laboratory in Western Australia, characterized by two adjacent homogeneous observation areas with distinctly different land use characteristics. Conversion of several ten thousand square km of forests into agricultural land began more than a century ago. Changes in albedo and surface roughness and the water budget of soil and the planetary boundary layer evolved over decades. Besides different meteorology we found a significant up to now overseen source of aerosol over the agriculture. The enhanced number of cloud condensation nuclei is coupled through the hydrological groundwater cycle with deforestation. Modification of surface properties and aerosol number concentrations are key factors for the observed reduction of precipitation. The results document the importance of aerosol indirect effects on climate due to nanometer size biogenic aerosol and human impact on aerosol sources.