Characterizing the regional XCO2 variability and its association with ENSO over India inferred from GOSAT and OCO-2 satellite observations

Chiranjit Das; Ravi Kumar Kunchala; Naveen Chandra; Abha Chhabra; Mehul R Pandya

doi:10.1016/j.scitotenv.2023.166176

Characterizing the regional XCO₂ variability and its association with ENSO over India inferred from GOSAT and OCO-2 satellite observations

Sci Total Environ. 2023 Dec 1:902:166176. doi: 10.1016/j.scitotenv.2023.166176. Epub 2023 Aug 9.

Authors

Chiranjit Das¹, Ravi Kumar Kunchala², Naveen Chandra³, Abha Chhabra⁴, Mehul R Pandya⁴

Affiliations

¹ Centre for Atmospheric Sciences, Indian Institute of Technology Delhi, New Delhi, India.
² Centre for Atmospheric Sciences, Indian Institute of Technology Delhi, New Delhi, India. Electronic address: rkkunchala@cas.iitd.ac.in.
³ Research Institute for Global Change, JAMSTEC, Yokohama, Japan.
⁴ Space Applications Centre, Indian Space Research Organisation (ISRO), Ahmedabad, India.

PMID: 37562615
DOI: 10.1016/j.scitotenv.2023.166176

Abstract

India is primarily concerned with comprehending regional carbon source-sink response in the context of changes in atmospheric CO₂ concentrations or anthropogenic emissions. Recent advancements in high-resolution satellite's fine-scale XCO₂ measurements provide an opportunity to understand unprecedented details of source-sink activity on a regional scale. In this study, we investigated the long-term variations of XCO₂ concentration and growth rates as well as its covarying relationship with ENSO and regional climate parameters (temperature, precipitation, soil moisture, and NDVI) over India from 2010 to 2021 using GOSAT and OCO-2 retrievals. The results show since the launch of OCO-2 in 2014, the number of monthly high-quality XCO₂ soundings over India has grown nearly 100-fold compared to GOSAT, launched in 2009. Also, the discrepancy in XCO₂ increase of 2.54(2.43) ppm/yr was observed in GOSAT (OCO-2) retrieval during an overlapping measurement period (2015-2021). Additionally, wavelet analysis indicated that the OCO-2 retrieval is able to capture a better frequency of local-scale XCO₂ variability compared to GOSAT, owing to its high-resolution cloud-free XCO₂ soundings, providing more well-defined regional-scale source-sink features. Furthermore, dominant spatial pattern of XCO₂ variability observed over south and southeast of India in both satellites, with XCO₂ semi-annual and annual variability more distinctly present in OCO-2 compared to GOSAT. A cross-correlation analysis suggested GOSAT XCO₂ growth rate positively correlates with ENSO in different homogeneous monsoon regions of India, with ENSO leading the GOSAT XCO₂ growth rate in all homogeneous regions by 3-9 months. The South Peninsular region sensitive to ENSO changes, especially during 2015-2016 ENSO event, where a decrease in CO₂ uptake was observed is closely linked with precipitation, soil moisture, and temperature anomalies. However, regional climate parameters show a low correlation with XCO₂ growth since CO₂ is a long-lived well-mixed gas primarily having an imprint of large-scale transport in column CO₂.

Keywords: Carbon dioxide; Climate parameters; El Niño-Southern Oscillation (ENSO); Growth rate.