An Observational and Modeling Study of Characteristics of Urban Heat Island and Boundary Layer Structures in Beijing

Abstract

In this paper, the characteristics of urban heat island (UHI) and boundary layer structures in the Beijing area, China, are analyzed using conventional and Moderate Resolution Imaging Spectroradiometer (MODIS) observations. The Weather Research and Forecasting (WRF) model coupled with a single-layer urban canopy model (UCM) is used to simulate these urban weather features for comparison with observations. WRF is also used to test the sensitivity of model simulations to different urban land use scenarios and urban building structures to investigate the impacts of urbanization on surface weather and boundary layer structures. Results show that the coupled WRF/Noah/UCM modeling system seems to be able to reproduce the following observed features reasonably well: 1) the diurnal variation of UHI intensity; 2) the spatial distribution of UHI in Beijing; 3) the diurnal variation of wind speed and direction, and interactions between mountain–valley circulations and UHI; 4) small-scale boundary layer convective rolls and cells; and 5) the nocturnal boundary layer lower-level jet. The statistical analyses reveal that urban canopy variables (e.g., temperature, wind speed) from WRF/Noah/UCM compare better with surface observations than the conventional variables (e.g., 2-m temperature, 10-m wind speed). Both observations and the model show that the airflow over Beijing is dominated by mountain–valley flows that are modified by urban–rural circulations. Sensitivity tests imply that the presence or absence of urban surfaces significantly impacts the formation of horizontal convective rolls (HCRs), and the details in urban structures seem to have less pronounced but not negligible effects on HCRs.

Impacts of weather conditions modified by urban expansion on surface ozone: Comparison between the Pearl River Delta and Yangtze River Delta regions

“…According to the same criteria for the 2-m temperature (2 • C) and the 10-m wind speed (1 m s −1 ), the hit rate calculation and the 2 g kg −1 for the 2-m specific humidity, the HR of the 2-m temperature, the 2-m specific humidity, and the 10-m wind speed are 0.78, 0.61, and 0.75, respectively. The HR of the temperature and humidity in Table 1 are close to those above, while the hit rate of the wind speed is much lower than that in Miao et al (2009). Nevertheless, the mean observed 10-m wind speed is only 0.98 m s −1 in that case while 3.2 m s −1 in this.…”

“…As expected from the relatively strict criteria (1 m s −1 ), the HR of the wind speed (0.30) is the lowest among all the variables. In the study of Miao et al (2009), a 24-h WRF/Noah/UCM simulation in relation to the Beijing area on 18-19 August 2005, was conducted. According to the same criteria for the 2-m temperature (2 • C) and the 10-m wind speed (1 m s −1 ), the hit rate calculation and the 2 g kg −1 for the 2-m specific humidity, the HR of the 2-m temperature, the 2-m specific humidity, and the 10-m wind speed are 0.78, 0.61, and 0.75, respectively.…”

Trade-offs and responsiveness of the single-layer urban canopy parametrization in WRF: An offline evaluation using the MOSCEM optimization algorithm and field observations

“…This offline evaluation of the Noah/SLUCM provides an objective assessment and is highly complementary to the evaluation of the coupled WRF/Noah/SLUCM modelling system (e.g. Lin et al, 2008;Miao et al, 2009).…”

Evaluation of Different Urban Microclimate Mitigation Strategies through a PMV Analysis

“…The examination of such phenomenon started in the XIX century [1] and lately it has caught the attention of the international scientific community, as showed by some studies carried out in different countries: Lodz (Poland) [2], Athens (Greece) [3], Beijing (China) [4], Aveiro (Portugal) [5].…”