Incorporation of the Urban Thermal and Moisture Components into the PX-Land Surface Model (LSM) within the Mesoscale Weather Research and Forecasting (WRF) Model

摘要

In the mesoscale Weather Research and Forecasting (WRF) model, few urban modeling options exist such as Urban Canopy Model (UCM), Building Effect Parameterization (BEP), and Building Energy Model (BEM). These models have certain limitations as far as the choice of land surface models (LSM), planetary boundary layer (PBL) schemes, and computational expenses are concerned. The authors Dy et al., (2019) made an attempt to include the urban momentum drag effect for wind speed modeling by developing a new multilayer model with modifications to the non-local Asymmetric Convective Model Version 2 (ACM2) PBL scheme. The urban-based ACM2 (UACM) model has shown a significant improvement in wind speed reduction near to the urban ground surface along-with an inflection point in the vertical wind profile at roof level. In this study, urban thermal and moisture components are newly introduced in the PX-LSM combined with the UACM model. The urban street-level surface composition includes the impervious, vegetated, and bare ground fractions. The street and roof surface temperature's diurnal variation is modelled using the two layer force-restore algorithm. Simple radiation treatment is considered to account shadowing within the streets based on the solar zenith angle and building morphology. The heat and moisture fluxes are computed at the street and roof levels together with a simple algorithm for anthropogenic heating. The new UACM model has an advantage of minimal urban morphological parameters requirement, simple formulation, and more efficient execution. The upgraded model is tested with the both idealized and real case WRF simulations over the Pearl River Delta (PRD) region in Southern China. The evaluation demonstrated greatly improved wind, moisture and temperature predictions at the urban measurement sites compared to the base ACM2 model.