Seasonal variability of tropospheric CO 2 over India based on model simulation, satellite retrieval and in-situ observat
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Ó Indian Academy of Sciences (0123456789().,-volV)(0123456789( ).,-volV)
Seasonal variability of tropospheric CO2 over India based on model simulation, satellite retrieval and in-situ observation M KRISHNAPRIYA1,3, RABINDRA K NAYAK1,*, SHAIK ALLAHUDEEN1, A BHUVANACHANDRA1, V K DADHWAL2, C S JHA1, M V R SHESHASAI1, S K SASMAL1 and K V S R PRASAD3 1
National Remote Sensing Center (NRSC), Indian Space Research Organization (ISRO), Balanagar, Hyderabad 500 037, India. 2 Indian Institute of Space Science and Technology (IIST), Thiruvananthapuram, Kerala, India. 3 Department of Meteorology and Physical Oceanography, Andhra University, Visakhapatnam, India. *Corresponding author. e-mail: [email protected] rabindrakumar˙[email protected] MS received 11 February 2020; revised 6 June 2020; accepted 9 July 2020
In this study, investigation of the seasonal cycle of the tropospheric CO2 concentration over India was carried out using the GEOS-Chem atmospheric transport model, Greenhouse gas Observation SATellite (GOSAT) retrievals, and in-situ measurements. The model simulation is highly coherent with the satellite and in-situ datasets, and it shows a distinct seasonal cycle of the tropospheric CO2 tendency over India with a negative phase (decreasing concentration) during April–August and a positive phase (increasing concentration) during September–March. The model diagnostics were analyzed to estimate budgets of the surface layer CO2, up to 650 hPa pressure level, for the two-phases of the seasonal cycle. A mean tendency, equivalent to 0.70 ppmv month1, observed during April–August, which results from the loss of CO2 content in the surface layer through horizontal advection (2.25 ppmv month1) and vertical diffusion (0.20 ppmv month1), that dominates the gain from vertical advection (1.53 ppmv month1). The negative contribution of horizontal advection in this period comes from the transport of CO2 depleted air-parcels over the oceanic region to India by the southwest monsoon winds and the positive contributions of vertical advection comes from upwelling of CO2 enriched air-parcels. The mean tendency, equivalent to 1.01 ppmv month1, during September–March results from the gain through vertical advection (0.78 ppmv month1) and horizontal advection (0.37 ppmv month1) and a small contribution of vertical diffusion (0.15 ppmv month1). In this period, positive contribution of horizontal advection is due to the transport of CO2 enriched air-parcels from the southeast Asian region to India by north-east monsoon winds. At the annual scale, CO2 content of the surface layer over India has a net gain of 0.75 GtC that comes from 14.31 GtC through vertical advection that exceeds the loss due to horizontal advection (11.10 GtC) and vertical diffusion processes (2.46 GtC). This net gain is almost 85% higher than the input of 0.4 GtC through surface Cuxes, which composed of 0.61 GtC anthropogenic emission and 0.21 GtC net terrestrial ecosystem exchanges. Additional sensitivity experiment was carried out to elucidate the
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