| 31. |
- Jonsson, P., et al.
(författare)
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Longwave incoming radiation in the Tropics: results from field work in three African cities
- 2006
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Ingår i: Theoretical and Applied Climatology. - : Springer Science and Business Media LLC. - 0177-798X .- 1434-4483. ; 85:3-4, s. 185-201
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates differences in longwave incoming radiation (L down arrow) within and between three African cities, Dar es Salaam (Tanzania), Ouagadougou (Burkina Faso), and Gaborone (Botswana), during the dry season, and evaluates the performance of a model to simulate these fluxes. In each city, direct observations of L down arrow, shortwave incoming radiation (K down arrow), air temperature, air humidity, and total suspended particle (TSP) concentration for three land uses (CBD, green residential, and traditional residential) were taken. The observed L down arrow flux decreases with increasing latitude, and temperature becomes an increasingly important factor in governing L down arrow variations further from the Equator. Humidity, as well as particle loading, differs significantly between the three cities. Differences between observed and modelled epsilon(sky) for rural stations near all cities showed a clear diurnal variation, with maximum differences of 0.08 between day and night. This diurnal difference was incorporated in the model and, for urban areas the model overestimates L down arrow by around 25m(-2). However, this model performs equally well regardless of the land use considered in any of the cities. The residual (difference between observed and modelled urban L down arrow) did not show any correlation with particulate pollution. However, the difference between observed and calculated epsilon(sky) is around 0.05 higher in Ouagadougou compared to the other cities, likely due to the heavy dust load observed here. It is concluded that tropical urban longwave radiation is not dramatically different from the mid latitudes.
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| 32. |
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| 33. |
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| 34. |
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| 35. |
- Lindberg, Fredrik, 1974, et al.
(författare)
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3D modelling of vegetation within a 2D model – evaluation and application
- 2012
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Ingår i: The Eight International Conference on Urban Climates.. ; :abstract nr 180
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The SOlar and LongWave Environmental Irradiance Geometry (SOLWEIG) model simulates spatial variations of 3D radiation fluxes and mean radiant temperature (Tmrt) as well as shadow patterns in complex urban settings. Here, a new vegetation scheme is presented and evaluated. A new shadow casting algorithm for complex vegetation structures makes it possible to obtain continuous images of shadow patterns and sky view factors taking both buildings and vegetation into account. The model is evaluated using 5 days of integral radiation measurements at two sites within a square surrounded by low-rise buildings and vegetation in Göteborg, Sweden (57°N). There is good agreement between modelled and observed values of Tmrt. Furthermore, SOLWEIG is used to examine vegetation and building morphology characteristics through a north-south LiDAR transect across the megacity of London. It is shown that the contribution of vegetation to the shadowing and reduction of Tmrt at ground level is higher during summer than in autumn. The results from these simulations highlight that vegetation can be most effective at reducing heat stress within dense urban environments in summer. The daytime average Tmrt is found to be lowest in the densest urban environments due to shadowing; foremost from buildings but also from trees. It is clearly shown that this method could be used to quantify the influence of vegetation on Tmrt within the urban environment. The results presented in this paper highlight a number of possible climate sensitive planning practices for urban areas at the local scale.
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| 36. |
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| 37. |
- Lindberg, Fredrik, 1974, et al.
(författare)
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Influence of ground surface characteristics on the mean radiant temperature in urban areas
- 2016
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Ingår i: International Journal of Biometeorology. - : Springer Science and Business Media LLC. - 0020-7128 .- 1432-1254. ; 60:9, s. 1439-1452
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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.
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| 38. |
- Lindberg, Fredrik, 1974, et al.
(författare)
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Nature of vegetation and building morphology characteristics across a city: Influence on shadow patterns and mean radiant temperatures in London
- 2011
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Ingår i: Urban Ecosystems. - : Springer Science and Business Media LLC. - 1083-8155 .- 1573-1642. ; 14:4, s. 617-634
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Tidskriftsartikel (refereegranskat)abstract
- Vegetation and building morphology characteristics are investigated at 19 sites on a north-south LiDAR transect across the megacity of London. Local maxima of mean building height and building plan area density at the city centre are evident. Surprisingly, the mean vegetation height (zv3) is also found to be highest in the city centre. From the LiDAR data various morphological parameters are derived as well as shadow patterns. Continuous images of the effects of buildings and of buildings plus vegetation on sky view factor (SVF) are derived. A general reduction of SVF is found, indicating the importance of including vegetation when deriving SVF in urban areas. The contribution of vegetation to the shadowing at ground level is higher during summer than in autumn. Using these 3D data the influence on urban climate and mean radiant temperature (Tmrt) is calculated with SOLWEIG. The results from these simulations highlight that vegetation can be most effective at reducing heat stress within dense urban environments in summer. The daytime average Tmrt is found to be lowest in the densest urban environments due to shadowing, foremost from buildings but also from trees. It is clearly shown that this method could be used to quantify the influence of vegetation on Tmrt within the urban environment. The results presented in this paper highlight a number of possible climate sensitive planning practices for urban areas at the local scale (i.e. 102- 5×10^3 m).
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| 39. |
- Lindberg, Fredrik, 1974, et al.
(författare)
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Sunlit fractions on urban facets – Impact of spatial resolution and approach
- 2015
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Ingår i: Urban Climate. - 2212-0955. ; 12, s. 65-84
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Tidskriftsartikel (refereegranskat)abstract
- The extent of the surface area sunlit is critical for radiative energy exchanges and therefore for a wide range of applications that require urban land surface models (ULSM), ranging from human comfort to weather forecasting. Here a computationally demanding shadow casting algorithm is used to assess the capability of a simple single-layer urban canopy model, which assumes an infinitely long rotating canyon (ILC), to reproduce sunlit areas on roofs, walls and roads over central London. Results indicate that the sunlit road areas are well-represented but somewhat smaller using an ILC, while sunlit roofs areas are consistently larger, especially for dense urban areas. The largest deviations from real world sunlit areas are for roofs during mornings and evenings. Sunlit fractions on walls are overestimated using an ILC during mornings and evenings are found. The implications of these errors are dependent on the application targeted. For example, (independent of albedo) ULSMs used in numerical weather prediction applying ILC representation of the urban form will overestimate outgoing shortwave radiation from roofs due to the overestimation of sunlit fraction of the roofs. Complications of deriving height to width ratios from real world data are also discussed.
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| 40. |
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