P97  Study the Effect of Aerodynamic Roughness Length on TaiwanÕs Meteorological Simulation

Cheng, Fang-Yi, Chin-Fang Lin, National Central University, Taiwan and Jeng-Lin Tsi, National Chung-Hsing University, Taiwan

The aerodynamic roughness length (Zo) is essential for simulating wind profile and surface fluxes. The present setup of WRF utilizes a look-up table to provide Z0 that is only dependent on the dominant land use (LU) types. The LU type in Taiwan is composed of forestland (~65%), dry/irrigated cropland (~20%), grassland (~5%), urban (5%) and others (<5%). Specification of Zo from a look-up table would underestimate surface heterogeneity. In this study, Zo was determined based on observed surface fluxes and wind, temperature and humidity profiles for urban, dry and irrigated cropland. For all other LU types, a suggested Z0 from literature was used. An effective Z0 is estimated using the arithmetic mean of the consisted LU type. Two gridded Z0 datasets are derived, Zm and Zt (calculation for momentum and heat flux respectively). The WRF-Z0 (default) overestimated the surface wind speed due to majority of LU type is specified by shorter Z0 elements. WRF-Zm is able to reduce wind speed and agrees better to the observed data due to the enhancement of Zm which increase surface flux exchanging processes. Inclusion of Zt further reduces the diurnal temperature variation. Overall, usage of the updated gridded Z0 improves the model performance.