Soil Deposition of Atmospheric Hydrogen Constrained using Planetary Scale Observations

Abstract. Quantifying soil deposition fluxes remains the greatest source of uncertainty in the atmospheric H₂ budget. A new method is presented to constrain H₂ deposition schemes in global models using observations of the zonal mean H₂ distribution and seasonality. A "best-fit" scheme that reproduces the observed zonal-mean seasonality of atmospheric H₂ at the planetary scale is found by perturbing a prototype deposition scheme based on soil temperature and moisture dynamics. Comparing the best-fit and prototype schemes provides insight for how the prototype scheme may be improved to better reproduce observed seasonality.

The H₂ signal driven by the prototype scheme is accurate compared to observations in the Northern Hemisphere extra-tropics but shows discrepancies in the Southern Hemisphere, with too high surface mixing ratios and too weak seasonality. A best-fit scheme indicates that the function capturing the soil microbial consumption of H₂ requires a shift of approximately +3 months in the seasonality in the tropics, where the prototype scheme is sensitive to seasonal soil moisture driven by the shifting of the ITCZ. New constraints on the H₂ surface flux at low-latitudes are key to accurately modelling the H₂ cycle in the Southern Hemisphere.