Analysis of observations on the urban surface energy balance in Beijing

The 1-year (2009-2010) measurements are analyzed of the urban surface energy balance (SEB) obtained from the sensors located at three vertical layers of a 325-m tower in downtown Beijing. Results show that: (1) The measurements from the 325-m tower represent the SEB characteristics of the cities located in semi-humid warm-temperate continental monsoon climate zone. In a typical hot and rainy summer, cold and dry winter, the measured Bowen ratio is minimum in summer and maximum in winter. The Bowen ratio measured at 140 m for spring, summer, autumn, and winter are 2.86, 0.82, 1.17, and 4.16 respectively. (2) At the height of 140-m (in the constant flux layer), the noontime albedo is similar to 0.10 for summer, similar to 0.12 for spring and autumn, and similar to 0.14 for winter. The ratios of daytime sensible heat flux, latent heat flux, and storage heat flux to net radiation are 0.25, 0.16, and 0.59 for clear-sky days, and 0.33, 0.19, and 0.48 for cloudy days respectively. (3) Under clear-sky days, the nighttime sensible heat flux is almost zero, but the latent heat flux is greater than zero. For cloudy days, the nighttime sensible heat flux is slightly greater than the latent heat flux in winter. The nighttime upward heat flux is presumably due to the anthropogenic release (mainly latent heat for summer, while latent and sensible heat for winter).