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Impact of thermophysical data and roughness length on the local scale flow, temperatures and heat fluxes in South-eastern European urban areas

Surface properties have a significant impact on the surface energy balance. Thus, they may have an influence on ground temperatures, which affect vertical temperature profiles. Temperature profiles influence other meteorological fields, such as atmospheric heat fluxes, boundary layer depths, pressures and velocities. So, surface properties also affect the cloud and precipitation formation (Romero et al., 1995 ; Xue et al., 1996 ; De Ridder, 1998 ; Friedrich and Mölders, 2000 ; Thielen et al., 2000) and the air quality (Taha, 1996, 1997 ; Yoshikado and Tsuchida, 1996, Jacobson, 1999). On the large time-scale land surface changes can also induce changes in radiative energy balance at the top of the atmosphere (Ackerman and Inoue, 1994). This paper examines the sensitivity of the core model of the European Zooming Model, namely the non-hydrostatic mesoscale model MEMO (Moussiopoulos, 1994, 1995 ; Kunz and Moussiopoulos, 1995) to parameters that affect the nonlinear heat balance equation. In particular, the effect of varying parameters (such as short-wave albedo, evaporation parameter, volumetric heat capacity and thermal soil conductivity and roughness lengths) on mesoscale wind flow patterns, surface temperature, air humidity as well as surface turbulent sensible and latent heat fluxes are studied. Above mentioned parameters strongly depend on the surface characteristics. Although numerous studies suggest a wide variety of values for these parameters (among others Pielke, 1984 ; Oke, 1987 ; Romero et al., 1995 ; Sailor, 1995, 1998 ; Grimmond and Oke, 1999 ; Friedrich and Mölders, 2000 ; Thielen et al., 2000), it is well known that they may substantially differ from one region to another. The more so, the need of such an investigation was indicated by some of the previous studies (Klaić and Nitis, 2000). In the present study a number of sensitivity tests are performed with an aim to establish thermophysical parameter values applicable for southeastern Europe. Specifically, MEMO is applied to the Greater Zagreb area (GZA), the Greater Athens area (GAA) and the Greater Thessaloniki area (GTA) for various meteorological conditions favouring the formation of photochemical smog. A further objective is to validate the model, since until now a correlation between the modeled and measured variables for above areas has not been examined.

short-wave albedo; evaporation parameter; volumetric heat capacity; thermal soil conductivity; roughness length; local scale flow; temperature; heat flux

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