ANALYSIS OF THE SEASONAL BEHAVIOR OF TROPOSPHERIC OZONE AT HONG-KONG

Ozonesondes have been launched at Hong Kong (22.2 degrees N, 114.3 deg rees E) since 1993. The results of data analysis of the ozone profiles are presented, with a focus on the seasonal cycle in tropospheric ozo ne. The results show that the tropospheric ozone column has an obvious maximum in spring and a minimum in summer. The former is a common fea ture at many locations in the Northern Hemisphere. The summer minimum is attributed to the onset of the summer monsoon when air flow from th e Asian continent is replaced by air from the South China Sea or the t ropical Pacific. The tropospheric ozone has an important influence on the seasonal cycle of total ozone at Hong Kong. The seasonal cycle of ozone mixing ratio below 2 km is bimodal with ozone peaks in spring an d autumn. A frequently observed feature in late autumn and winter is a relative minimum of ozone mixing ratio (as low as 30-40 ppbv) in the upper troposphere (from about 9 to 16 km). Trajectory analysis shows t his relative minimum of ozone is associated with air masses coming fro m the tropical region. It is proposed that the East Asia local Hadley circulation is responsible for this feature. (C) 1977 Elsevier Science Ltd.