Influence of buildings and trees on PALM model’s shortwave radiation modeling

The utilization of micrometeorological models for urban planning purposes, mitigation strategies development, and studying the atmospheric boundary layer of densely built urban environments has become ever-increasing. Due to the high complexity and variety of urban structures within the cities (e.g., urban fabric, transit roads, green urban areas, water bodies, sports, and leisure facilities, etc.), a comprehensive assessment of these areas and their interaction with the atmosphere is a complicated task. One of the physical processes strongly influenced by the city’s configuration, presence of trees, and buildings is the radiative transfer within the urban environment (e.g., absorption, scattering, emission, reflections between individual surfaces, etc.). Precise modeling of the radiative transfer processes is of particular importance due to their influence on the surface radiation budget, human energy balance, building energy management, etc. Hence, for a model to be operational for various purposes its validation and assessment of the radiation modeling aspect is necessary for everyday usage.  
In this study, the numerical simulations are performed by the micrometeorological model PALM. The model was configured and run in the spin-up mode, during which LSM, BSM PCM, RTM, BIO, and MESO modules were utilized. The selected domain is located in a realistic and densely built urban area within the city of Prague, has an extent of 800 x 500 m, and is simulated in 1 m resolution. For experiment purposes, we selected two different episodes with clear-sky conditions during the year 2019. The PALM model outputs have been evaluated against three different stations, both quantitatively and qualitatively.
We validate the shortwave radiation modeled by PALM at the height corresponding to the height of the sensor and show how the microscale model modifies direct and reflected shortwave radiation by performing a comparison against measurements collected at three different locations within the simulation domain. The findings of this study show and lead to a better understanding of how trees, buildings, and albedos of different surfaces affect and modify shortwave radiation in urban environments.