7.1 SENSITIVITY OF SURFACE-ATMOSPHERE ENERGY EXCHANGES WITHIN URBAN AREAS DERIVED FROM SIMULATIONS Sarah M. Roberts 1,* , T. R. Oke 1 , A. Lemonsu 2 , C. S. B. Grimmond 3 , and P. Jackson 1 1 University of British Columbia, Vancouver, B.C., Canada; 2 Centre National de Recherches Météorologique, Météo-France, Toulouse, France; 3 Indiana University, Bloomington, IN 1. INTRODUCTION Understanding the nature of energy partitioning at the surface of cities is prerequisite to gaining proper insight and the ability to model their climatic environment. Of particular relevance in the urban setting is the surface-atmosphere exchange of sensible heat. The combined conductive- convective exchange of turbulent sensible heat flux (Q H ) and net storage heat flux (∆Q S ) has been shown to account for over 90% of the daytime net radiation at highly urbanized sites. This sharing depends on surface structure, materials and the degree of surface-atmosphere coupling. Understanding sensible heat exchange is essential in many applications; for example, to assess building climates, and to model evapo- transpiration, the urban heat island, and boundary layer growth. Observational studies, while providing general awareness of urban surface-atmosphere energetic interactions, are often limited in their applicability to other urban sites and/or processes. Numerical models designed to simulate urban climates help overcome the limitations imposed by observations. One such model, the Town Energy Balance (TEB) model of Masson (2000) is implemented here to conduct further analyses to better understand the primary criteria affecting local-scale urban surface- atmosphere energy exchanges. Analyses are performed for a site in Marseille, France. 2. METHODS 2.1 The Site Marseille is situated on the Mediterranean coast in the French region of Provence. The city contains a ________________________________________ *Corresponding author address: Sarah M. Roberts, Dept. of Geography, University of British Columbia, #217 – 1984 West Mall, Vancouver, B.C. Canada V6T 1Z2 E-mail: sroberts@geog.ubc.ca densely built-up center with very little vegetation, constituting about 16% of plan area (Figure 1). Buildings are the highest roughness elements within the study area and are, on average, approximately 16 m in height. The district comprises primarily 19 th century massive limestone and granite administrative, residential and commercial buildings with clay tile or pebble- topped roofs. Streets and sidewalks are asphalt and concrete pavement, respectively, and urban canyons are approximately 7-10 m across. This locale provides an ideal environment for this study, Figure 1 View from the southwest of the city center of Marseille, depicting the densely built-up urban environment of uniform building heights and little greenspace. 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. 2.2 Field Measurements Fast- and slow-response instruments used to conduct energy balance measurements were mounted on a tower which was erected on the roof of a building in the city center of Marseille. Observations were performed in the constant flux layer between 35-44 m above street level, thereby eliminating the influence of individual surface