Impact of the sensible heat transport modeling in urban canopy models on sea breeze advancement

Thermal and aerodynamic properties derived from urban geometry are crucial in reproducing and evaluating urban climate more accurately in numerical simulations. It has become possible to conduct urban meteorological simulations considering these properties through the parameterizations of physical processes in the urban canopy layer, such as SLUCM (e.g., Kusaka et al., 2001). Many studies have been conducted so far to improve urban canopy models through model refinement and intercomparison experiments, but these studies have mainly conducted in 1D offline simulations focusing on the accuracy on surface heat balance terms. The modification of the surface heat balance can change the weather three dimensionally, which changes the meteorological forcing for the model, too. Thus, 1D offline simulation may lead to misunderstanding the model performance. This study focuses on the sensible heat transport modelling in SLUCM on sea breeze behavior in a 3-D weather field, considering the distribution of the realistic urban aero-thermodynamic parameters in Japan (Kawaura and Nakayoshi, 2023). We evaluated two sensible heat modeling utilized in Kusaka’s SLUCM and Kanda’s SUMM model (Kanda et al. 2005).

The simulation results for the Kanto region of Japan using the regional atmospheric model WRF show that, Kanda’s method, which calculates sensible heat fluxes considering the roughness length of the entire canopy yielded larger sensible heat flux in urban grids thereby forming the stronger pressure gradient from sea to land than Kusaka’s approach did. However, in Kanda method, sea breeze front delayed over Tokyo metropolitan area and after passing Tokyo the front was accelerated toward inland. This is due to the increase in friction velocity, or turbulent mixing, with increasing roughness, indicating the importance of properly considering the urban geometry and incorporating it into the model.