Numerical Simulations of Diurnal Variations of Air Temperature and Relative Humidity in the Urban Canopy Layer

도시 캐노피 층 기온과 상대습도의 일변화에 관한 수치 모의

  • Park, Kyeongjoo (School of Earth and Environmental Sciences, Seoul National University) ;
  • Han, Beom-Soon (Department of Biological and Environmental Engineering, Semyung University) ;
  • Jin, Han-Gyul (School of Earth and Environmental Sciences, Seoul National University)
  • 박경주 (서울대학교 지구환경과학부) ;
  • 한범순 (세명대학교 바이오환경공학과) ;
  • 진한결 (서울대학교 지구환경과학부)
  • Received : 2021.07.07
  • Accepted : 2021.08.24
  • Published : 2021.09.30


Diurnal variations of air temperature and relative humidity in the Urban Canopy Layer (UCL) of the Seoul metropolitan area are examined using the Weather Research and Forecasting model coupled with the Seoul National University Urban Canopy Model. The canopy layer air temperature is higher than 2-m air temperature and exhibits a more rapid rise and an earlier peak in the daytime. These result from the multiple reflections of shortwave radiation and longwave radiation trapping due to the urban geometry. Because of the absence of vegetation in the UCL and the higher canopy layer air temperature, the canopy layer relative humidity is lower than 2-m relative humidity. Additional simulations with building height changes are conducted to examine the sensitivities of the canopy layer meteorological variables to the urban canyon aspect ratio. As the aspect ratio increases, net sensible heat flux entering the UCL increases (decreases) in the daytime (nighttime). However, the increase in the volume of the UCL reduces the magnitude of change rate of the canopy layer air temperature. As a result, the canopy layer air temperature generally decreases in the daytime and increases in the nighttime as the aspect ratio increases. The changes in the canopy layer relative humidity due to the aspect ratio change are largely determined by the canopy layer air temperature. As the aspect ratio increases, the canopy layer relative humidity is generally increased in the daytime and decreased in the nighttime, contrary to the canopy layer air temperature.



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