16:45 〜 17:00
[AAS04-15] C-130H輸送機により観測された北西太平洋上空における大気ポテンシャル酸素の季節および年々変動
キーワード：大気ポテンシャル酸素（APO）、航空機観測
The cargo aircraft C-130H flies once per month from Atsugi Base (35.45°N, 139.45°E), Kanagawa, Japan, to Minamitorishima (MNM; 24.28°N, 153.98°E), and air samples are collected during the level flight (~6 km) and the descent portion at MNM. The air samples have been analyzed for O2/N2and Ar/N2ratios and stable isotopic ratios of N2, O2and Ar since May 2012. The analysis indicated a significant artificial fractionation due to thermal diffusion during the air sample collection. Nevertheless we succeeded to correct the effects of the fractionation on the observed O2/N2ratio precisely by using the observed Ar/N2ratio (Ishidoya et al., 2014). The corrected O2/N2ratio showed a secular decrease accompanied by a prominent seasonal cycle. The average secular change rate of the mid-tropospheric corrected O2/N2ratio was found to be -25.2±0.5 per meg yr-1for the period 2012 – 2018, which agreed well with that observed at La Jolla, USA by Scripps O2program (Keeling and Manning, 2014). As the uncertainty of the change rate, we considered the spatial difference of the rates and the stability of the O2/N2ratio of standard air.
The Atmospheric Potential Oxygen (APO=O2+1.1xCO2), calculated by using the corrected O2/N2ratio, also showed prominent seasonal cycles, and the amplitude of the mid-tropospheric seasonal APO cycle observed at 25.5°N was found to be 55 and 31 % of those observed at 33.5°N and the surface MNM (Ishidoya et al., 2017), respectively. On the other hand, the corresponding seasonal amplitude of CO2at 25.5°N was found to be 72 and 93 % of those at 33.5°N and the surface MNM, respectively. An atmospheric transport model (Niwa et al., 2017) reproduced general features of the observed seasonal APO and CO2cycles, and its tagged simulation suggested that the mid-tropospheric seasonal APO cycle in the northern low latitudes was reduced significantly by the anti-phase seasonal APO cycle from the southern hemisphere. The observed APO showed interannual variations superimposed on secular downward trends, and the temporal change rates take maxima from the end of 2014 to the beginning of the 2015 at the surface MNM and in the mid-troposphere at 29 – 34 °N. A comparison between the observed and simulated interannual variations of APO suggested that an interannual variation of the atmospheric transport contributed about 30 % of the observed variation.
Acknowledgments
We thank the staff of Japan Meteorological Agency for their work to collect the air samples onboard a cargo aircraft C-130H. This study was partly supported by the JSPS KAKENHI Grant Number 15H02814, and the Global Environment Research Coordination System from the Ministry of the Environment, Japan.
References
Ishidoya, S. et al. (2014) New atmospheric O2/N2ratio measurements over the western North Pacific using a cargo aircraft C-130H, SOLA, 10, 23-28.
Ishidoya, S. et al. (2017) Development of a continuous measurement system for atmospheric O2/N2ratio using a paramagnetic analyzer and its application in Minamitorishima Island, Japan, SOLA, 13, 230-234.
Keeling, R. F., and A. C. Manning (2014) Studies of recent changes in atmospheric O2content, in Treatise on Geochemistry,5, 2nd ed., pp. 385–404.
Niwa, Y. et al. (2017) A 4D-Var inversion system based on the icosahedral grid model (NICAM-TM 4D-Var v1.0) – Part 1: Offline forward and adjoint transport models, Geosci. Model Dev., 10, 1157-1174.
The Atmospheric Potential Oxygen (APO=O2+1.1xCO2), calculated by using the corrected O2/N2ratio, also showed prominent seasonal cycles, and the amplitude of the mid-tropospheric seasonal APO cycle observed at 25.5°N was found to be 55 and 31 % of those observed at 33.5°N and the surface MNM (Ishidoya et al., 2017), respectively. On the other hand, the corresponding seasonal amplitude of CO2at 25.5°N was found to be 72 and 93 % of those at 33.5°N and the surface MNM, respectively. An atmospheric transport model (Niwa et al., 2017) reproduced general features of the observed seasonal APO and CO2cycles, and its tagged simulation suggested that the mid-tropospheric seasonal APO cycle in the northern low latitudes was reduced significantly by the anti-phase seasonal APO cycle from the southern hemisphere. The observed APO showed interannual variations superimposed on secular downward trends, and the temporal change rates take maxima from the end of 2014 to the beginning of the 2015 at the surface MNM and in the mid-troposphere at 29 – 34 °N. A comparison between the observed and simulated interannual variations of APO suggested that an interannual variation of the atmospheric transport contributed about 30 % of the observed variation.
Acknowledgments
We thank the staff of Japan Meteorological Agency for their work to collect the air samples onboard a cargo aircraft C-130H. This study was partly supported by the JSPS KAKENHI Grant Number 15H02814, and the Global Environment Research Coordination System from the Ministry of the Environment, Japan.
References
Ishidoya, S. et al. (2014) New atmospheric O2/N2ratio measurements over the western North Pacific using a cargo aircraft C-130H, SOLA, 10, 23-28.
Ishidoya, S. et al. (2017) Development of a continuous measurement system for atmospheric O2/N2ratio using a paramagnetic analyzer and its application in Minamitorishima Island, Japan, SOLA, 13, 230-234.
Keeling, R. F., and A. C. Manning (2014) Studies of recent changes in atmospheric O2content, in Treatise on Geochemistry,5, 2nd ed., pp. 385–404.
Niwa, Y. et al. (2017) A 4D-Var inversion system based on the icosahedral grid model (NICAM-TM 4D-Var v1.0) – Part 1: Offline forward and adjoint transport models, Geosci. Model Dev., 10, 1157-1174.