| 1. |
- Inagaki, A., et al.
(författare)
-
Thermal Image Velocimetry
- 2013
-
Ingår i: Boundary-Layer Meteorology. - : Springer Science and Business Media LLC. - 0006-8314 .- 1573-1472. ; 149:1, s. 1-18
-
Tidskriftsartikel (refereegranskat)abstract
- A method for measuring the two-dimensional distribution of wind velocity vectors near a surface exposed to solar radiation, by tracking brightness temperature images instead of particle images, is proposed. It is based on time-sequential thermography with the algorithm used for particle image velocimetry. This thermal image velocimetry (TIV) was tested on a full-scale building wall covered by polystyrene boards attached side-by-side over a vertically elongated area measuring 22.2 m by 2.73 m. A thermal infrared camera was installed 8 m from the test wall to capture the wall-surface temperature at 30 Hz frequency. A sonic anemometer was also installed 35 mm from the surface used for validation of the TIV. The advection velocity estimated from thermal infrared imagery had a linear relationship with the wind velocity measured by the sonic anemometer, irrespective of the wind speed and direction. This linear slope was multiplied by the advection velocity of the thermal infrared image to rescale it to the wind velocity, and the term 'TIV velocity' was then used. A histogram and power spectra of the TIV velocity showed quantitatively good agreement with the velocity measured by the sonic anemometer, except for the high-frequency region of the spectra, where the TIV velocity was overestimated compared with that of the sonic anemometer. The method was also tested on ground covered by artificial turf to demonstrate its application to a horizontal plane with a wider area, extending for more than 80 m by 60 m.
|
|
| 2. |
- Johansson, Lars, 1972, et al.
(författare)
-
Statistical modelling of pedestrian wind speed using high‐resolution digital surface models
- 2012
-
Ingår i: The Eight International Conference on Urban Climates. ; :abstract 183
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Spatial variations of near ground wind speed (2magl) within urban areas are simulated by using a statistical model. The model is built upon the statistical relationship between derivatives extracted from digital surface models characterizing urban geometries (sky view factor, fetch, frontal area index) and wind speed, using statistical regression techniques. The geometric parameters are calculated for a number of urban settings in Gothenburg, Sweden. Wind speed patterns are derived using the three-dimensional microclimate model, ENVI-met. The model closely estimate the wind speed within-the major parts of the model domains such as in squares, and narrow streets as well as canyons perpendicular to the incoming wind direction. However, the output wind speed patterns are largely different from the wind speed simulated by ENVI-met in wide streets and around buildings where wind speed is high. Statistical models, as presented here, would be useful for not only climatologist/ meteorologist but also urban designers to consider wind modes depending on urban geometries and also to estimate thermal comfort influenced by wind.
|
|
| 3. |
- Johansson, Lars, et al.
(författare)
-
Towards the modelling of pedestrian wind speed using high-resolution digital surface models and statistical methods
- 2016
-
Ingår i: Theoretical and Applied Climatology. - : Springer Science and Business Media LLC. - 0177-798X .- 1434-4483. ; 124:1, s. 189-203
-
Tidskriftsartikel (refereegranskat)abstract
- Wind is a complex phenomenon and a critical factor in assessing climatic conditions and pedestrian comfort within cities. To obtain spatial information on near-ground wind speed, 3D computational fluid dynamics (CFD) modelling is often used. This is a computationally intensive method which requires extensive computer resources and is time consuming. By using a simpler 2D method, larger areas can be processed and less time is required. This study attempts to model the relationship between near-ground wind speed and urban geometry using 2.5D raster data and variable selection methods. Such models can be implemented in a geographic information system (GIS) to assess the spatial distribution of wind speed at street level in complex urban environments at scales from neighbourhood to city. Wind speed data, 2 m above ground, is obtained from simulations by CFD modelling and used as a response variable. A number of derivatives calculated from high-resolution digital surface models (DSM) are used as potential predictors. A sequential variable selection algorithm followed by all-possible subset regression was used to select candidate models for further evaluation. The results show that the selected models explain general spatial wind speed pattern characteristics but the prediction errors are large, especially so in areas with high wind speeds. However, all selected models did explain 90 % of the wind speed variability (R2 ≈0.90). Predictors adding information on width and height ratio and alignment of street canyons with respect to wind direction are suggested for improving model performance. To assess the applicability of any derived model, the results of the CFD model should be thoroughly evaluated against field measurements.
|
|
| 4. |
- Lindberg, Fredrik, 1974, et al.
(författare)
-
Influence of ground surface characteristics on the mean radiant temperature in urban areas
- 2016
-
Ingår i: International Journal of Biometeorology. - : Springer Science and Business Media LLC. - 0020-7128 .- 1432-1254. ; 60:9, s. 1439-1452
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of variations in land cover on mean radiant temperature (T-mrt) is explored through a simple scheme developed within the radiation model SOLWEIG. Outgoing longwave radiation is parameterised using surface temperature observations on a grass and an asphalt surface, whereas outgoing shortwave radiation is modelled through variations in albedo for the different surfaces. The influence of ground surface materials on T-mrt is small compared to the effects of shadowing. Nevertheless, altering ground surface materials could contribute to a reduction in T-mrt to reduce the radiant load during heat-wave episodes in locations where shadowing is not an option. Evaluation of the new scheme suggests that despite its simplicity it can simulate the outgoing fluxes well, especially during sunny conditions. However, it underestimates at night and in shadowed locations. One grass surface used to develop the parameterisation, with very different characteristics compared to an evaluation grass site, caused T-mrt to be underestimated. The implications of using high temporal resolution (e.g. 15 minutes) meteorological forcing data under partly cloudy conditions are demonstrated even for fairly proximal sites.
|
|
| 5. |
- Lindberg, Fredrik, 1974, et al.
(författare)
-
UMEP - An integrated tool for urban climatology and climate-sensitive planning applications
- 2015
-
Ingår i: ICUC9 – 9 th International Conference on Urban Climate jointly with 12th Symposium on the Environment. 20-24 July, Toulouse, France.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The urban climate is influenced by processes taking place at a range of different scales. Based on application (e.g. land surface or thermal comfort modelling), the appropriate scale has to be considered to make accurate estimation of the phenomena examined. Furthermore, the interaction of processes taking place at different scales makes it important to accurately couple and understand the different scale-dependent processes controlling the urban climate and thus outdoor thermal comfort. In this paper UMEP (Urban Multi-scale Environmental Predictor), an integrated tool for urban climatology and climate sensitive planning applications is presented. The tool can be used for a variety of applications related to outdoor thermal comfort, urban energy consumption, climate change mitigation etc. UMEP combines “state of the art†1D and 2D models related to the processes essential for scale-independent urban climate estimations. The models include SOLWEIG (Lindberg and Grimmond 2011), SUEWS (Järvi et al. 2013), BLUEWS (Onomura et al. 2014) and LUCY (Allen et al. 2011) where each individual model has been extensively evaluated. Here, the new combined system is demonstrated and evaluated. The modelling system is designed to run from the street canyon to city scale (100-105 m) depending on the application. The ranges of scales are those that need to be understood for most urban climate, architectural and/or urban planning projects. The model is able to estimate a number of variables that relate to, for example, spatial variations of urban surface energy exchanges, or boundary layer developments. The ambition is to develop a tool designed for planners and architects, which, at the same time, can be used in more advanced research applications. In order to easily use UMEP a major characteristic is the ability for a user to interact with spatial information to determine model parameters. This requires a dynamic approach where spatial data at different scales and from a variety of sources are needed. This is accomplished by using an existing application programming interface (API) for spatial data. UMEP makes use of QGIS - a cross-platform, free, open source desktop geographic information systems (GIS) application - that provides data viewing, editing and analysis capabilities. QGIS is both extendable by plugins and reducible to only the essential core features needed. Substantial advantages are offered by having GIS-software tightly coupled to the model. These include the ability to read and write a variety of geodata formats, ease of combining geodatasets so issues such as coordinate systems and scale are natively dealt with, visualization of inputs and outputs, and direct calculation of model parameters by pre-processing geodata thus reducing the number of preparation stages required and ensuring consistency between models and users.
|
|
| 6. |
- Lindberg, Fredrik, 1974, et al.
(författare)
-
UMEP - An integrated tool for urban climatology and climate sensitive planning applications
- 2014
-
Ingår i: Towards intergrated modelling of Urban Systems, 15-17 October, Lyon (France).
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The urban climate is influenced by processes taking place at a range of different scales. Based on application (e.g. land surface or thermal comfort modelling), the appropriate scale has to be considered to make accurate estimation of the phenomena examined. Furthermore, the interaction of processes taking place at different scales makes it important to accurately couple and understand the different scale dependent processes controlling the urban climate and thus outdoor thermal comfort. In this paper UMEP (Urban Multi-scale Environmental Predictor), an integrated tool for urban climatology and climate sensitive planning applications is presented. The tool can be used for a variety of applications related to outdoor thermal comfort, urban energy consumption, climate change mitigation etc. The tool consists of a coupled modelling system which combines " state of the art " 1D and 2D models related to the processes essential for scale independent urban climate estimations. MODELLING CONCEPTS The modelling system contained within UMEP is designed to run from the street canyon to city scale (10 0-10 5 m) depending on the application. This is the range of scales that need to be understood in most urban climate, architectural and urban planning projects. The model is able to estimate a number of variables that relate to, for example, spatial variations of urban surface energy exchanges, boundary layer developments. Currently, the following main models that are coupled in UMEP are (Fig. 1): 1. The SOLWEIG-model (SOlar and LongWave Environmental Irradiance Geometry model) which simulates spatial variations of 3D radiation fluxes and mean radiant temperature T mrt in complex urban settings. The model requires a limited number of inputs, such as shortwave radiation, ambient air temperature, humidity, urban geometry and vegetation cover (e.g. Lindberg et al. 2008; Lindberg and Grimmond 2011). SOLWEIG is also able to model shadow patterns which is important information requested by urban planners and architects. A solar energy model, SEBE (Solar Energy on Building Envelopes) will also be incorporated in the modelling system. 2. SUEWS (Surface Urban Energy and Water Balance Scheme), a model able to simulate the urban radiation, energy and water balances using only commonly meteorological variables and information about the surface cover (e.g. Grimmond and Oke 2002; Järvi et al. 2011) and snowmelt (Järvi et al. 2014). 3. BLUEWS (Boundary Layer Urban Energy Water Scheme) is a Convective Boundary Layer (CBL) model (Cleugh and Grimmond 2001) that has been previously coupled to SUEWS (Onomura et al. 2014). From the coupling of the two models it is possible to generate the site-specific input data needed for the calculations made in SOLWEIG i.e. air temperature, radiation and humidity. BLUEWS operates on the local to meso scale (Onomura et al. 2014). 4. LUCY (Large scale Urban Consumption of energY model) simulates all the components of anthropogenic heat flux (Q F) on a global scale which is often ignored or roughly estimated in other energy balance models (Allen et al. 2011; Lindberg et al. 2013). BLUEWS includes options
|
|
| 7. |
- Onomura, Shiho, 1985, et al.
(författare)
-
An intra-urban nocturnal cooling rate model
- 2015
-
Ingår i: ICUC9 – 9 th International Conference on Urban Climate jointly with 12th Symposium on the Urban Environment. 20-24 July 2015, Toulouse, France.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Nocturnal urban heat island (UHI) and intra-urban heat island (IUHI) mainly develop through differences in cooling rates. The cooling process consists of two distinctive phases. In the first phase, around sunset, dense urban areas cool more slowly than more open sites, creating large intra-urban temperature differences that are preserved during the whole night. The intensity of this differential cooling is mainly determined by surface characteristics (geometry and material), prevailing weather conditions and season. On the other hand, the cooling during the rest of night, in the second phase, is independent of the surface characteristics. In this study, we investigated how intra-urban cooling rates in the two phases are statistically related to prevailing weather conditions, season, and sky view factor using observation data from Gothenburg, Sweden. Based on the results, a simple statistical intra-urban nocturnal cooling rate model was developed. The model requires only commonly-used meteorological variables and sky view factor. It was shown that the most intensive cooling rate at an open site, in the first phase, was chiefly dominated by the clearness of the sky and wind speed, i.e. the weather conditions. The cooling rate also had a linear relationship with maximum daily air temperature, which can be treated as the seasonal effect. Under clear sky condition, the magnitude of the cooling rate significantly decreased with lower sky view factor, but, under cloudy conditions, the cooling rate varied less or little. In the second phase, cooling rate seemed to linearly decrease as the night progressed and the slope of the decrease was determined by the clearness of the sky. The model was evaluated using three additional datasets, one from Gothenburg, one from London, UK and one from Ouagadougou, Burkina Faso. Gothenburg and London are classified to have a marine temperate climate (Cfb) and Ouagadougou has a tropical steppe climate (BSh) according to Köppen climate classification. The model simulated cooling rates along a smooth profile statistically determined, while observed cooling rates often fluctuated through night. Nevertheless, the model estimated well the total amount of cooling during the whole night. This resulted in the well-simulated nocturnal air temperature. Modeled cooling rates were deviated from the observation at the sites where the large effects of anthropogenic heat and evapotranspiration were present. The effects were not included in this model yet but were found to be significant. This model can be used for multiple applications such as nocturnal human thermal comfort estimation and climate-sensitive urban planning and design.
|
|
| 8. |
- Onomura, Shiho, 1985, et al.
(författare)
-
Intra-urban nocturnal cooling rates: development and evaluation of the NOCRA model
- 2016
-
Ingår i: Meteorological Applications. - : Wiley. - 1469-8080 .- 1350-4827. ; 23:3, s. 339-352
-
Tidskriftsartikel (refereegranskat)abstract
- A nocturnal cooling rate model (NOCRAM) to simulate nocturnal air temperature at urban sites is presented. The model is designed for urban planners, practitioners and researchers who demand meteorological information for urban planning and research applications. The model is based on the concept of nocturnal cooling, progressing in two distinct phases, i.e. site-dependent cooling around sunset and site-independent cooling from about 1 or 2 h after sunset until sunrise. Cooling rates are usually determined predominantly by prevailing weather conditions (i.e. clearness of the sky and wind speed), followed by maximum daily air temperature and by sky view factors. Second phase cooling is chiefly determined by sky clearness and wind speed. The findings and statistical results from the analysis of observational data during warm months (May–September) from Gothenburg, Sweden, as well as from past studies, were used. The model requires standard meteorological variables (i.e. wind speed, incoming short-wave radiation, air temperature, relative air humidity, air pressure) at a reference station as well as geometrical information (i.e. the sky view factor of the site and the geographical co-ordinates of the reference meteorological station). The model simulates the characteristic development of cooling rates in the two phases at open sites and built-up sites with different sky view factors under a wide range of weather conditions in warm months. Using the modelled cooling rates, nocturnal air temperature is estimated easily with the accuracy of root mean square error (RMSE) ≤1.54°C and R2 ≥0.78.
|
|
| 9. |
- Onomura, Shiho, 1985, et al.
(författare)
-
Meteorological forcing data for urban outdoor thermal comfort models from a coupled convective boundary layer and surface energy balance scheme
- 2015
-
Ingår i: Urban Climate. - : Elsevier BV. - 2212-0955. ; 11, s. 1-23
-
Tidskriftsartikel (refereegranskat)abstract
- Site-specific meteorological forcing appropriate for applications such as urban outdoor thermal comfort simulations can be obtained using a newly coupled scheme that combines a simple slab convective boundary layer (CBL) model and urban land surface model (ULSM) (here two ULSMs are considered). The former simulates daytime CBL height, air temperature and humidity, and the latter estimates urban surface energy and water balance fluxes accounting for changes in land surface cover. The coupled models are tested at a suburban site and two rural sites, one irrigated and one unirrigated grass, in Sacramento, U.S.A. All the variables modelled compare well to measurements (e.g. coefficient of determination = 0.97 and root mean square error = 1.5 °C for air temperature). The current version is applicable to daytime conditions and needs initial state conditions for the CBL model in the appropriate range to obtain the required performance. The coupled model allows routine observations from distant sites (e.g. rural, airport) to be used to predict air temperature and relative humidity in an urban area of interest. This simple model, which can be rapidly applied, could provide urban data for applications such as air quality forecasting and building energy modelling, in addition to outdoor thermal comfort.
|
|
| 10. |
- Onomura, Shiho, 1985
(författare)
-
Modelling of the daytime and night-time urban thermal environment
- 2016
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The world’s urban population is expected to increase over the coming decades. To maintain and improve the health and well-being of urban citizens, it is important to increase our knowledge and develop methods for evaluating the urban thermal environment to support urban planning. The aim of this thesis is to develop and improve the modelling of the urban thermal environment, particularly enabling modelling to be done using readily available data and hardware. The thesis has four parts. The first and second parts describe the development of simplified models for computing day- and night-time urban site-specific air temperatures (Ta) at street level. The third part presents an analysis of nocturnal cooling in the near-surface atmosphere and discusses its implications for modelling the night-time Ta. The final part presents improvements of the SOLWEIG model that allow it to account for different ground cover types when computing the mean radiant temperature (Tmrt). Tmrt is one of important variables governing outdoor human thermal comfort. The daytime model was developed by coupling a convective boundary layer slab model and an urban land surface model. It is used to perturb routinely observed Ta values from a reference site (e.g. rural, airport) to obtain urban site-specific Ta data. The night-time model was developed empirically based on the concept of nocturnal cooling progressing in two distinct phases. It simulates cooling rates at a height of 2 m in urban canyons depending on building density. The modelled cooling rates are then used to estimate the night-time Ta. The models were designed to run on commodity computers and to require only standard meteorological input data and land surface information, all of which are widely available. Both models perform well in terms of temporal development and accuracy. Nocturnal cooling in the lower layer of the near-surface atmosphere (between the ground and a height of 60-70 m) was shown to be more intense and to evolve differently over time compared to cooling in the upper layer (up to 105 m). In addition, two distinct cooling phases were detected in both layers. Around sunset, the rates of cooling diverge decreasing with increasing height in both layers. However, within a few hours after sunset, the cooling rates converge in the lower layer, while the height-dependent cooling rate differences in the upper layer remain largely unchanged over night. The persistent differences in the upper layer are linked to the formation of a stabilized atmospheric layer. The pattern and intensity of cooling depend on the synoptic weather situation (defined in terms of the Lamb weather type) and the season. These results imply that the night-time model can be applied to other heights with a few modifications. A ground cover scheme in the SOLWEIG model was developed based on field observations conducted in Gothenburg. The effects of different ground materials (grass and asphalt) on Tmrt were a few degrees, i.e. about one tenth of the shadowing effect of buildings. This suggests that changing the ground cover type may not be as effective as shadowing at mitigating radiant heat loads during hot days. Nevertheless, it could contribute to a reduction in Tmrt when shadowing is not an option. An evaluation study showed that the model also predicted Tmrt reasonably well over different ground surfaces in London, UK. The models presented in this thesis will be implemented in a climate service tool, which can be used for various scientific and practical applications.
|
|
| 11. |
- Thorsson, Sofia, 1972, et al.
(författare)
-
Present and projected future mean radiant temperature for three European cities
- 2017
-
Ingår i: International Journal of Biometeorology. - : Springer Science and Business Media LLC. - 0020-7128 .- 1432-1254. ; 61:9, s. 1531-1543
-
Tidskriftsartikel (refereegranskat)abstract
- © 2017 The Author(s)Present-day and projected future changes in mean radiant temperature, Tmrt in one northern, one mid-, and one southern European city (represented by Gothenburg, Frankfurt, and Porto), are presented, and the concept of hot spots is adopted. Air temperature, Ta, increased in all cities by 2100, but changes in solar radiation due to changes in cloudiness counterbalanced or exacerbated the effects on Tmrt. The number of days with high Tmrt in Gothenburg was relatively unchanged at the end of the century (+1 day), whereas it more than doubled in Frankfurt and tripled in Porto. The use of street trees to reduce daytime radiant heat load was analyzed using hot spots to identify where trees could be most beneficial. Hot spots, although varying in intensity and frequency, were generally confined to near sunlit southeast-southwest facing walls, in northeast corner of courtyards, and in open spaces in all three cities. By adding trees in these spaces, the radiant heat load can be reduced, especially in spaces with no or few trees. A set of design principles for reducing the radiant heat load is outlined based on these findings and existing literature.
|
|
