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Comparison of the data‐driven top‐down and bottom‐up global terrestrial CO 2 exchanges: GOSAT CO 2 inversion and empirical eddy flux upscaling
Author(s) -
Kondo Masayuki,
Ichii Kazuhito,
Takagi Hiroshi,
Sasakawa Motoki
Publication year - 2015
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2014jg002866
Subject(s) - biosphere , environmental science , southern hemisphere , climatology , biome , inversion (geology) , northern hemisphere , atmospheric sciences , carbon sink , seasonality , subtropics , flux (metallurgy) , boreal , biosphere model , climate change , geology , oceanography , ecosystem , structural basin , ecology , paleontology , materials science , metallurgy , biology
We examined the consistency between terrestrial biosphere fluxes (terrestrial CO 2 exchanges) from data‐driven top‐down (GOSAT CO 2 inversion) and bottom‐up (empirical eddy flux upscaling based on a support vector regression (SVR) model) approaches over 42 global terrestrial regions from June 2009 to October 2011. Seasonal variations of the biosphere fluxes by the two approaches agreed well in boreal and temperate regions across the Northern Hemisphere. Both fluxes also exhibited strong anomalous signals in response to contrasting anomalous spring temperatures observed in North America and boreal Eurasia. This indicates that the CO 2 concentration data integrated in the GOSAT inversion and the meteorological and vegetation data in the SVR models are equally effective in producing spatiotemporal variations of biosphere flux. Meanwhile, large differences in seasonality were found in subtropical and tropical South America, South Asia, and Africa. The GOSAT inversion showed seasonal variations that pivoted around CO 2 neutral, while the SVR model showed seasonal variations that tended toward CO 2 sink. Thus, a large difference in CO 2 budget was identified between the two approaches in subtropical and tropical regions across the Southern Hemisphere. Examination of the integrated data revealed that the large tropical sink of CO 2 by the SVR model was an artifact due to the underrepresented biosphere fluxes predicted by limited eddy flux data for tropical biomes. Because of the global coverage of CO 2 concentration data, the GOSAT inversion provides better estimates of continental CO 2 flux than the SVR model in the Southern Hemisphere.