Investigations of high-density urban boundary layer under summer prevailing wind conditions with Doppler LiDAR: A case study in Hong Kong

Abstract

The high-density urban boundary layer (UBL) is one of the most complex atmospheric conditions, while the field data of UBL is limited due to the lack of suitable measurement methods. To better understand the UBL structures in high-density cities, a pioneering investigation is conducted in Hong Kong by Doppler wind LiDAR. Vertical wind speed profiles are measured at three locations: Cape D'Aguilar (upwind), University of Hong Kong (downtown), and Hong Kong University of Science and Technology (downwind). To address the weak wind conditions in summer, the prevailing southwest wind condition is selected as the subject of investigation. Based on the observations, the gradient height over Hong Kong is approximately 1.0–1.2 km. Below this height, the vertical wind speed profiles are significantly modified by surface morphologies. The power-law equation appropriately parametrizes the upwind (α = 0.1–0.15) and downwind (α = 0.27) profiles, but it has limitations when parametrizing the downtown profile. Deficiencies of the vertical wind speed profiles predicted by conventional meso-scale simulations and wind-tunnel experiments are revealed. These results provide researchers and engineers benchmarking data to refine their urban climate predictions. They generalize a better understanding of the UBL climates, which can be shared with other high-density cities.