Preprints
https://doi.org/10.5194/amt-2024-167
https://doi.org/10.5194/amt-2024-167
29 Oct 2024
 | 29 Oct 2024
Status: this preprint is currently under review for the journal AMT.

Validation and assessment of satellite-based columnar CO2 and CH4 mixing-ratios from GOSAT and OCO-2 satellites over India

Harish Shivraj Gadhavi, Akanksha Arora, Chaithanya Jain, Mahesh Kumar Sha, Frank Hase, Matthias Frey, Srikanthan Ramachandran, and Achuthan Jayaraman

Abstract. The OCO-2 and GOSAT series of satellites provide near-global coverage of CO2 and CH4 mixing ratios. To accurately derive emission fluxes from the observed mixing ratios, it is crucial that these data meet specific precision and systematic error requirements. In this study, we report validation results for GOSAT and OCO-2 over South Asia, obtained using a portable Fourier Transform infrared Spectrometer (FTS) at a tropical rural site (Gadanki; Latitude: 13.45° N, Longitude: 79.18° E) in Southern India, from November 2015 to July 2016. Biases in CH4 mixing ratios from GOSAT ranged from -9 to -18.5 ppb, depending on the collocation criteria, while CO2 data from OCO-2 demonstrated better accuracy and precision, meeting the requirements of ESA’s Climate Change Initiative (CCI). Using the FLEXPART model, we also show that CH4 emissions from regional sources accounted for only 35 % of the day-to-day observed variability. Both model-derived and observed mixing ratios exhibited the same seasonal variation, with higher values in October–November and lower values in June–July. However, the observed mixing ratios decreased by approximately 100 ppb, while the model-derived values decreased by only 20 ppb, suggesting that atmospheric chemistry and variations in background concentrations play a significant role over South India.

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Harish Shivraj Gadhavi, Akanksha Arora, Chaithanya Jain, Mahesh Kumar Sha, Frank Hase, Matthias Frey, Srikanthan Ramachandran, and Achuthan Jayaraman

Status: open (until 04 Dec 2024)

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Harish Shivraj Gadhavi, Akanksha Arora, Chaithanya Jain, Mahesh Kumar Sha, Frank Hase, Matthias Frey, Srikanthan Ramachandran, and Achuthan Jayaraman
Harish Shivraj Gadhavi, Akanksha Arora, Chaithanya Jain, Mahesh Kumar Sha, Frank Hase, Matthias Frey, Srikanthan Ramachandran, and Achuthan Jayaraman

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Short summary
We used a ground-based Fourier Transform Spectrometer to measure columnar greenhouse gas mixing ratios and validate methane observations from the GOSAT satellite and carbon dioxide observations from GOSAT and OCO-2 over India. Both satellites provide high precision and accuracy, making them suitable for emission flux estimates. Simulations using a Lagrangian dispersion model showed that background mixing ratio variations play a larger role than local source changes.