Energy and radiation balance of a central European city

Abstract

Results from an experimental network of seven energy balance stations in and around a European city are presented. The network of micrometeorological stations was part of the Basel Urban Boundary Layer Experiment (BUBBLE) carried out in the city of Basel, Switzerland. Three urban sites provided turbulent flux densities and radiation data over dense urban surfaces. Together with a suburban site and three rural reference sites, this network allowed the simultaneous comparison of urban, suburban, and rural energy balance partitioning during one month of summertime measurements. The partitioning is analysed together with long-term data to evaluate the magnitude of the urban flux density modification, and to document characteristic values in their diurnal and yearly course. Simple empirical relations between flux densities and surface characteristics are presented. The energy balance partitioning is addressed separately for daytime and nocturnal situations. All four components of the surface radiation budget are analysed. Moreover, the vertical flux density divergences within the urban canopy layer are discussed.

Anthropogenic heat release in an old European agglomeration (Toulouse, France)

“…It is considered to be the largest of the non-measured terms (Q F , Q S and Q A ), and is often approximated by R (Oke and Cleugh, 1987). The basic assumption is that Q S should vanish over longer timescales (one day or multiple of entire days), otherwise it would lead to unrealistic temperature changes of the urban fabric (Christen and Vogt, 2004). Results supporting this hypothesis are presented by Offerle et al (2005).…”

“…This assumption has been used on a one-year time scale by Christen and Vogt (2004) when they found a missing energy source in their energy budget. A potential problem in evaluating Q F as the mean of the residual is that this estimate suffers from the accumulation of the errors on the three measured terms of the SEB.…”

Evaluation of Different Urban Microclimate Mitigation Strategies through a PMV Analysis

“…For what concerns the radiation balance, the differences between urban and rural areas are not that significant [6,7] and the larger nighttime radiative loss determined by the high emissivity [8] compensates for the higher amount of energy input in the daytime in urban areas determined by a low albedo [8]. The increase in temperature in urban areas is so connected to the type of materials used.…”

“…For example, the vegetation tends to cover just a small part of the surface in cities, thus the evapotranspiration is highly reduced and urban areas convert their radiant energy into sensible heat rather than latent heat [6]. The change of urban energy budget determined by a low albedo and the reduced evapotranspiration cause a higher urban energy input in the daytime [8]. Such excess of energy is usually stored: the thermal properties (e.g., heat capacity, thermal conductivity) of the materials used in the cities and the complex and traditional urban morphology increase the heat flux stored in these areas [9][10][11][12][13].…”

“…Such excess of energy is usually stored: the thermal properties (e.g., heat capacity, thermal conductivity) of the materials used in the cities and the complex and traditional urban morphology increase the heat flux stored in these areas [9][10][11][12][13]. The surfaces start releasing the stored energy during the night [8], slowing down the cooling process in the cities and determining a temperature difference between urban and rural areas.…”