Project Funding: 2015 - 2018

NRA: 2014 NASA: OCO-2 Science Team for the OCO-2 Mission   

Funded by NASA

Abstract:
We propose to make calibrated in situ CO2 measurements from aircraft and tower sites in the Amazon Basin to support the validation of total column CO2 retrievals from OCO2. Covering eight million square kilometers and with half the world's remaining undisturbed tropical forests, Amazonia is a critical yet undersampled region within the global carbon cycle. OCO2 column CO2 measurements over Amazônia could rectify the undersampling, but high levels of cloudiness and aerosols from biomass burning will likely make OCO2's job extremely difficult. Moreover, covariances between cloudiness, season, surface flux and convection make clear-sky viewing biases by OCO2 a strong possibility. In situ data from aircraft and towers, which are largely immune to such biases, are therefore required to fully validate OCO2 measurements. In particular, we propose to extend previously funded 0-9 km aircraft profiles above Manaus and combine them with four other aircraft profiling sites throughout the rest of the Basin. Additionally, we seek to support the calibration and continuity of two continuous tower CO2 measurement sites and combine these with another continuous tower CO2 site. Taken together, these eight sites (all consistently calibrated on the WMO CO2 mole fraction scale), in combination with surface flask sites on the coast of Brazil and from the NOAA global network will impose unprecedented constraints on Amazonian surface CO2 fluxes. The fluxes will be estimated by assimilating tower and aircraft data in a global inverse model, which will also yield atmospheric CO2 fields consistent with the calibrated in situ data. These fields will provide an accurate reference against which to evaluate OCO2 clear-sky retrievals and so quantify potential biases in OCO2 CO2. Finally, we propose to use the carbon monoxide (CO) concentrations measured by the aforementioned towers and aircraft profiles, as well as remotely sensed CO from the IASI satellite instrument, to better understand the role of fires and deforestation in the Amazonian carbon balance. Since fire CO2 fluxes also have associated strong CO fluxes, while biome CO2 fluxes do not, a dual tracer assimilation of CO and CO2 will allow us to estimate the net biome CO2 exchange (NBE). We will perform such a joint inversion using IASI CO and OCO2 CO2 validated in the previous stage. Relating the estimated NBE to seasonal and interannual variations in climate (temperature and rainfall, primarily) may then provide insight into the mechanisms driving the variations. At this point, even the seasonality of NBE throughout Amazonian remains controversial, so these flux calculations will represent a significant step forward in our understanding of the Amazonian carbon cycle.