Structure of Wind and Turbulence below and above a building canopy during the BBMEX–Wind Campaign period in Seoul

A building-block urban meteorological observation experiment – wind (BBMEX-Wind) campaign was carried out to observe vertical profile of 3-dimensional wind speed below and above the building canopy of a street canyon at Gangnam district in Seoul City, Korea for the period of 10 to 24 May 2023. A wind lidar was installed center of the street canyon with a width of 50 m and a height of 70 m, and observed 3-dimensial wind speed and signal-to-noise ratio at around 1 Hz at 25 heights between 40 m and 350 m. Among total 15 days, 7 days were fine (cloud cover < 3/10), while 3 days were cloudy (cloud cover > 7/10). There were 4 rainy days, but total precipitation was as low as 1.5 mm. Skimming flows were observed below the building canopy when lateral winds blow, and channel flows were observed when longitudinal winds blow. In spite of low-speed winds below the building canopy, strong winds above 20 m s⁻¹ above the canopy were observed. Surface roughness length over the building block was calculated as values minimizing the sum of squared error assuming the log-wind profile in the surface layer. It was found that the surface roughness length was about 8 m during the daytime (09 to 16 LST) and about 6 m during the nighttime (22 to 04 LST). Mean values of turbulent kinetic energy (TKE) during the daytime were about 2 times larger than those during the nighttime, while median values of TKE during the daytime were 3 times larger than those during the nighttime. 

 

Key words: BBMEX-Wind, street canyon, surface roughness length, wind lidar

 

Acknowledgements: This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2021R1I1A2052562) and Korea Aerospace Research Institute (KARI).