Aircraft and tower measurements of CO2 concentration in the planetary boundary layer and the lower free troposphere over southern taiga in West Siberia: Long-term records from 2002 to 2011
- 著者
- Sasakawa M., Machida T., Tsuda N., Arshinov M.,Davydov D., Fofonov A., Krasnov O.
- 雑誌名
- J. Geophys. Res.-Atmos., 118, 9489-9498
- DOI
- 10.1002/jgrd.50755
- 概要
-
In situ measurements of the vertical distribution of carbon dioxide (CO2) carried out with a light aircraft over a tower site (Berezorechka; 56°08′45″N, 84°19′49″E) in the taiga region of West Siberia from October 2001 to March 2012 document the detailed seasonal and vertical variation of CO2 concentrations during daytime. The variation appears to be controlled mainly by the CO2 flux from taiga ecosystems and the height of the planetary boundary layer (PBL). We calculated average CO2 concentrations in the PBL and the lower free troposphere (LFT), both of which show clear seasonal cycles and an increasing long-term trend. Seasonal amplitude in the PBL had a larger value (29 ppm) than that in the LFT (14 ppm), demonstrating strong CO2 source–sink forcing by the taiga ecosystems. Mean CO2 concentrations during 13:00–17:00 LST observed at the four levels of the tower (5, 20, 40, and 80 m) showed lower CO2 concentrations than that observed in the PBL by aircraft during June–August (growing season). This negative bias decreased with increasing inlet height such that the minimum difference appeared at the 80-m inlet (−2.4 ± 0.8 ppm). No such bias was observed during other months (dormant season). The daytime CO2 flux, based on multiple vertical profiles obtained on a single day, ranged from −36.4 to 3.8 µmol m−2 s−1 during July–September. There was a clear difference in the fluxes between the morning and afternoon, suggesting that these data should be considered examples of fluxes during several daytime hours from the West Siberian taiga.
シベリアには世界最大のタイガが存在するため、全球に及ぼす二酸化炭素フラックスの影響は大きいと予想される。しかしこれまでシベリアにおける温室効果ガス観測は限られたものであった。本研究では、夏季に西シベリアのタイガ上空を航空機で数時間毎に複数回飛行することで、二酸化炭素濃度の鉛直分布の日変動を観測し、タイガの植生による日中の二酸化炭素フラックスを推定した。これまでの報告値より幅広い値（−36.4±0.5〜+3.8±0.5 µmol m−2 s−1）を示した。日照時間が最も長くなる7月の夕方には、これまでに観測されたことの無い非常に大きな負のフラックスが観測され（−32.6±0.6、−36.4±0.5 µmol m−2 s−1）、タイガの植生による吸収量がこれまで予想されていた値より大きく変動する可能性を示した。観測数が限られるため、季節差や年変動を定量的に議論するには更なる観測が必要となる。