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| 2. |
- Erell, Evyatar, et al.
(författare)
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The effect of stability on estimated variations of advected moisture in the Canyon Air Temperature (CAT) model
- 2010
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Ingår i: Ninth Symposium on the Urban Environment. ; :J4C.4
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Konferensbidrag (refereegranskat)abstract
- CAT (Canyon Air Temperature) is a parametric model that predicts site-specific air temperature in an urban street canyon for extended periods on the basis of data from a reference station in the region. A method is described for incorporating spatial and temporal variations in advected moisture, allowing application of the model with no prior knowledge of moisture availability in the area. The revised model is tested against data from field experiments in Gothenburg and Adelaide, in all seasons and in a variety of atmospheric conditions. Moisture availability is determined by site surface cover only in super-stable conditions and in the absence of wind. In other weather conditions, the effect of stability on advection from more distant source areas is weak.
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| 3. |
- Johansson, Erik, et al.
(författare)
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The influence of urban design on outdoor thermal comfort in the hot, humid city of Colombo, Sri Lanka
- 2006
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Ingår i: International Journal of Biometeorology. - : Springer Science and Business Media LLC. - 1432-1254 .- 0020-7128. ; 51:2, s. 119-133, s. 217-220
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Tidskriftsartikel (refereegranskat)abstract
- The outdoor environment is deteriorating in many tropical cities due to rapid urbanization. This leads to a number of problems related to health and well-being of humans and also negatively affects social and commercial outdoor activities. The creation of thermally comfortable microclimates in urban environments is therefore very important. This paper discusses the influence of street-canyon geometry on outdoor thermal comfort in Colombo, Sri Lanka. Five sites with different urban geometry, ground cover, and distance from the sea were studied during the warmest season. The environmental parameters affecting thermal comfort, viz. air temperature, humidity, wind speed, and solar radiation, were measured, and the thermal comfort was estimated by calculating the physiologically equivalent temperature (PET). The thermal comfort is far above the assumed comfort zone due to the combination of intense solar radiation, high temperatures, and low wind speeds, especially on clear days. The worst conditions were found in wide streets with low-rise buildings and no shade trees. The most comfortable conditions were found in narrow streets with tall buildings, especially if shade trees were present, as well as in areas near the coast where the sea breeze had a positive effect. In order to improve the outdoor comfort in Colombo, it is suggested to allow a more compact urban form with deeper street canyons and to provide additional shade through the use of trees, covered walkways, pedestrian arcades, etc. The opening up of the city's coastal strip would allow the sea breeze to penetrate further into the city.
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| 4. |
- Kent, Christoph W., et al.
(författare)
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Evaluation of Urban Local-Scale Aerodynamic Parameters: Implications for the Vertical Profile of Wind Speed and for Source Areas
- 2017
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Ingår i: Boundary-Layer Meteorology. - : Springer Science and Business Media LLC. - 0006-8314 .- 1573-1472. ; 164:2, s. 183-213
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Tidskriftsartikel (refereegranskat)abstract
- © 2017 The Author(s)Nine methods to determine local-scale aerodynamic roughness length (Formula presented.) and zero-plane displacement (Formula presented.) are compared at three sites (within 60 m of each other) in London, UK. Methods include three anemometric (single-level high frequency observations), six morphometric (surface geometry) and one reference-based approach (look-up tables). A footprint model is used with the morphometric methods in an iterative procedure. The results are insensitive to the initial (Formula presented.) and (Formula presented.) estimates. Across the three sites, (Formula presented.) varies between 5 and 45 m depending upon the method used. Morphometric methods that incorporate roughness-element height variability agree better with anemometric methods, indicating (Formula presented.) is consistently greater than the local mean building height. Depending upon method and wind direction, (Formula presented.) varies between 0.1 and 5 m with morphometric (Formula presented.) consistently being 2–3 m larger than the anemometric (Formula presented.). No morphometric method consistently resembles the anemometric methods. Wind-speed profiles observed with Doppler lidar provide additional data with which to assess the methods. Locally determined roughness parameters are used to extrapolate wind-speed profiles to a height roughly 200 m above the canopy. Wind-speed profiles extrapolated based on morphometric methods that account for roughness-element height variability are most similar to observations. The extent of the modelled source area for measurements varies by up to a factor of three, depending upon the morphometric method used to determine (Formula presented.) and (Formula presented.).
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| 5. |
- Kokkonen, Tom V., et al.
(författare)
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Simulation of the radiative effect of haze on the urban hydrological cycle using reanalysis data in Beijing
- 2019
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 19:10, s. 7001-7017
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Tidskriftsartikel (refereegranskat)abstract
- Although increased aerosol concentration modifies local air temperatures and boundary layer structure in urban areas, little is known about its effects on the urban hydrological cycle. Changes in the hydrological cycle modify surface runoff and flooding. Furthermore, as runoff commonly transports pollutants to soil and water, any changes impact urban soil and aquatic environments. To explore the radiative effect of haze on changes in the urban surface water balance in Beijing, different haze levels are modelled using the Surface Urban Energy and Water Balance Scheme (SUEWS), forced by reanalysis data. The pollution levels are classified using aerosol optical depth observations. The secondary aims are to examine the usability of a global reanalysis dataset in a highly polluted environment and the SUEWS model performance. We show that the reanalysis data do not include the attenuating effect of haze on incoming solar radiation and develop a correction method. Using these corrected data, SUEWS simulates measured eddy covariance heat fluxes well. Both surface runoff and drainage increase with severe haze levels, particularly with low precipitation rates: runoff from 0.06 to 0.18 mm d(-1) and drainage from 0.43 to 0.62 mm d(-1) during fairly clean to extremely polluted conditions, respectively. Considering all precipitation events, runoff rates are higher during extremely polluted conditions than cleaner conditions, but as the cleanest conditions have high precipitation rates, they induce the largest runoff. Thus, the haze radiative effect is unlikely to modify flash flooding likelihood. However, flushing pollutants from surfaces may increase pollutant loads in urban water bodies.
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| 6. |
- Mitraka, Zina, et al.
(författare)
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Towards discriminating between zones with different thermal behaviour in cities
- 2017
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Ingår i: 2017 Joint Urban Remote Sensing Event, JURSE 2017. Dubai, United Arab Emirates; 6-8 March 2017.. - 9781509058082
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Konferensbidrag (refereegranskat)abstract
- The advances in satellite sensor technology, the launch of new satellites and the continuous development of remote sensing technology constantly increase the opportunities for monitoring the thermal behaviour of cities from space. Not only the surface temperature, but several other parameters related to the urban climate can be quantified from Earth Observation (EO) data. In this study, remote sensing techniques are applied to derive EO data products and a methodology is proposed that combines this information to discriminate between zones with different thermal behaviour in cities. Information on the building, pervious and paved surface cover, the surface albedo, the mean building/tree height and the sky view factor is quantified in local scale and then used to identify possible zones with homogeneous thermal characteristics.
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