Seasonal and Long-Term Variations in Atmospheric CO_2 and ^<85>Kr in Tsukuba, Central Japan

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Since February 1992, measurements of atmospheric CO_2 at 200m above the ground have been taken from a meteorological tower (lat 36.1°N, long 140.1°E, 25m a.s.l.) in Tsukuba, central Japan. We have examined seasonal/long-term variations in atmospheric CO_2, based on atmospheric ^<85>Kr, a noble gas with well-known source and sink terms, monitored continuously at weekly intervals in Tsukuba since May 1995. During the annual cycle, the daily mean values of atmospheric CO_2 in the afternoons (1300-1600 JST) showed maximum in late April, except in 2002, and minimum in late August or early September. The seasonal variations in atmospheric ^<85>Kr, which is low in summer and high in winter, were caused by the seasonal variations in the large-scale atmospheric circulation, and latitudinal distribution of atmospheric ^<85>Kr. Compared with seasonal variations in atmospheric ^<85>Kr, the draw-down (DD) and buildup (BU) for atmospheric CO_2 occurred about 1 week and 3 weeks later, respectively. The peak-to-trough amplitude of de-trended seasonal variations in atmospheric CO_2 concentrations ranged from 11 to 14 ppm. A decrease in the seasonal CO_2 minimum occurred with a decrease in the ^<85>Kr concentration, showing the effect of air mass transport from different origins. Unlike the minimum, the maximum CO_2 did not vary as expected from the air mass transport. The daily mean values of atmospheric CO_2 increased at an average rate of 2.0 ppm yr^<-1>, with a range from -0.5 to 4 ppm yr^<-1>. While both CO_2 and ^<85>Kr are emitted into the atmosphere, due to energy consumption, the growth rate of atmospheric CO_2 showed a pattern different from that of atmospheric ^<85>Kr (0.03 Bq m^<-3> yr^<-1>).
社団法人日本気象学会の論文
2006-12-25

Seasonal and Long-Term Variations in Atmospheric CO_2 and ^<85>Kr in Tsukuba, Central Japan

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