A Numerical Simulation of the Daily Variation of CO2 in the Central Part of Japan —Summer Case

Since 1993, CO2 concentration and its flux between the atmosphere and a temperatre forest ecosystem have been examined in the central part of Japan (the Takayama site). Daily variation of CO2 concentration at the Takayama site during three days in July was compared with the results of a numerical simulation, in which both the CO2 flux of anthropogenic origin and that from the ecosystem were considered. The CO2 flux from the ecosystem was estimated from the data at the Takayama site and extended to all the central part of Japan with the aid of a vegetation map. When the CO2 flux at night estimated from the observation at the top of a 27 m tower at Takayama site was used as the grid average in the model, the amplitude of CO2 variation obtained from the calculation was smaller than the observed amplitude at the Takayama site, which is located at the top of a hill. The anthropogenic contamination of CO2 was also investigated. The simulation suggested the possibility of long-range transport of CO2 from Nagoya and Tokyo, two cities located about 150 km south and 300 km southeast of the Takayama site. The effect of these large cities was greater than that of nearby Takayama City.