OCO-2-based CO₂ flux estimates for Amazonia look much better in the dry than wet season

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Dry Season Soundings

Wet Season Soundings

John B. Miller¹, Giordane Martins, Tim Newberger¹, Kathryn McKain¹

1. NOAA Global Monitoring Laboratory, Boulder, USA

OCO-2 v10 data

OCO-2 v10 data

Thanks to OCO-2 v10 MIP team, OCO-2 data providers, and global in situ measurement groups!!

Amazonia is a critical component of global carbon balance

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• Largest tropical forest region
• High above and below-ground biomass
• High GPP and high respiration; net balance hard to predict.
• High fire fluxes
• Huge area, similar to conterminous USA

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Rough footprint of MANaus aircraft profiles

Amazonia has a complex mixture of sources and sinks that is trending

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Brienen et al., 2015 Nature

Net

Growth

Death

RAINFOR biometry network

• Fluxes from airborne CO₂ data also show trends and spatial gradient (e.g., Gatti et al., 2021 Nature)

Harris et al.,

2021 Nature Comm.

Satellite imagery

We use light aircraft equipped with on-board GHG measurement, and spiral above the forest

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Vertical profiles reveal seasonally changing net CO₂ flux

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• All data from Manaus multi-species ObsPack; v2 available
• > 100 ~twice-monthly vertical profiles 2017 – present; ongoing

Sink

Neutral

Sink

Source

Early Wet

Late Wet

Trans/Dry

~Dry

OCO-2 land data adds information in dry season, but not in wet season.

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• Measurements wrt OCO-2 v10 MIP ensemble mean

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• 25^th, 50^th, and 75^th %ile

Global in situ data adds little information to Amazonian fluxes

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• In situ data corrects the top of the prior profile better than LNLG, but profile shape stays fixed.

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• This indicates that large-scale fluxes and transport are simulated well.

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• But there is little constraint on Amazonian fluxes.

How to get wet season information?

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• More flights and towers – minimal weather bias.
• Also solar-tracking FTSs
• Could active or very high resolution passive satellites improve coverage?
• Biosphere model parameter optimization – parameters should be time-invariant
• Is V11B coverage any better?

Wet

Dry

Final thought

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🡪 We need to be careful in using OCO-2 data when quantifying CO₂ exchange seasonality and La Niño/El Niño contrasts, because these correlate with cloudiness and sounding density.

V10 ocean glint data provides little help…

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