Atmospheric carbon dioxide variations at coastal site,Sibukawa, in Seto Inland Sea,Japan. 2. observation from 1980 to 1989

Summary Atmospheric carbon dioxide variations have been studied by using data between May 1980 and July 1989 from Sibukawa in Seto Inland Sea, sited in the western part of Japan. The power spectrum of carbon dioxide shows that the one-day period was predominant and 4 to 5 days period associated with quasiperiodic variation in weather was also significant. The seasonal variation of daily minimum concentration of carbon dioxide shows a maximum in summer months (July–September), and a minimum in winter months (November–December and January–March). The variation pattern seems to be in opposite phase to the carbon dioxide variations expected in the northern hemisphere. This was probably due to reduced vertical mixing under stable stratification of the air layer prevailing during summer months at Sibukawa station. It is noted that the air layer is in lapse conditions during winter months. The annual rate of increase of carbon dioxide concentration is examined using data obtained during winter months. It is 3.1 ppm/year. This value is about twice the increasing rate of increase on a global scale and in the lower troposphere over Japan.With 5 Figures