Analyses on the Characteristics of Beijing Summer Urban Heat Island (UHI)and Its Meteorological Fields

In this paper, the summer meteorological data (from 1998 to 2003) from 10 observatories, 1 auto-observatory and the Beijing 325m tower have been used to study the urban heat island (UHI) and the meteorological fields near the surface in the summer of Beijing. The results show that the UHI in Beijing summer is very obvious, and its average intensity reaches 1.64℃ over the past 6 years; the strong UHI occurs mainly at night (average intensity is 2.62℃ at 02:00 a.m.). In daytime, it becomes weaker quickly, the average intensity is 0.6℃ at 2:00 p.m., and sometimes even an urban cold island (UCI) can be found. With the development of urbanization in Beijing, the number of days with UHI intensity more than 2℃ increases year by year, and the strongest UHI reaches 9℃; when the UHI is very strong, the wind field can show an UHI circulation (convergence) with weak wind in urban areas. Combined with the data of the 325m tower, the results also show that when strong UHI occurs, the inversion in atmospheric boundary layer (ABL) is very obvious, and its top is very high.