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Energy storage in a densely-built mediterranean city centre Roberts, Sarah Marie

Abstract

The complex, three-dimensional nature of an urban area and the challenges inherent in directly measuring urban energy storage flux (ΔQs) have led to this heat flux being an understudied component of the urban surface energy balance. The primary goal of this research is to compare the relative ability of several different methods to estimate the magnitude and temporal variation of ΔQs in an urban environment against those obtained as in observed energy balances. The investigation is based on results from a site in the center of Marseille, France. This locale provides an ideal environment for this study, because it has a warm, dry climate (hence sensible heat dominates) and massive urban development (hence a large thermal mass), so that heat storage is likely to be a significant part of the overall surface energy balance. Estimates of ΔQs obtained from tower-mounted instruments (the energy balance residual approach) are compared to results from a parameterization scheme (Objective Hysteresis Model, OHM), a localscale numerical model (Town Energy Balance, TEB), and a bulk heat transfer approach (Thermal Mass Scheme, TMS). Meteorological and urban construction data are used as inputs to the methods. Two-dimensional and three-dimensional formulations of the OHM do not sufficiently handle surface-atmosphere sensible heat exchanges in this highly urbanized and windy environment while TEB shows good agreement with the residual approach. TMS values are comparable to those from the other two methods but the laborious nature of the approach renders it impractical in such a complex setting. TEB's good performance at this site, as well as at other dry urban settings (central Mexico City and a light industrial site in Vancouver, British Columbia), suggest it possesses promise as a basis for further analyses and sensitivity tests designed to better understand the impacts of varying flow regimes, building geometry and materials on local-scale urban surface-atmosphere energy exchanges. Such an analysis was performed and the results reveal that the wind regime plays a dominant role in surface-atmosphere energy partitioning in this environment. Varying urban geometry and surface radiative properties also result in appreciable changes whereas alterations to surface thermal parameters generate the least impact.

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