An improved parameterisation of ozone dry deposition to the ocean and its impact in a global climate–chemistry model

• Published in: Atmospheric Chemistry and Physics
• Main Authors: A. K. Luhar, I. E. Galbally, M. T. Woodhouse, M. Thatcher
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2017
• Subjects: Physics; QC1-999; Chemistry; QD1-999; Southern Ocean
• Online Access: https://doi.org/10.5194/acp-17-3749-2017; https://doaj.org/article/0b3a9f465b1742c7981553bca826d96a

Schemes used to parameterise ozone dry deposition velocity at the oceanic surface mainly differ in terms of how the dominant term of surface resistance is parameterised. We examine three such schemes and test them in a global climate–chemistry model that incorporates meteorological nudging and monthly-varying reactive-gas emissions. The default scheme invokes the commonly used assumption that the water surface resistance is constant. The other two schemes, named the one-layer and two-layer reactivity schemes, include the simultaneous influence on the water surface resistance of ozone solubility in water, waterside molecular diffusion and turbulent transfer, and a first-order chemical reaction of ozone with dissolved iodide. Unlike the one-layer scheme, the two-layer scheme can indirectly control the degree of interaction between chemical reaction and turbulent transfer through the specification of a surface reactive layer thickness. A comparison is made of the modelled deposition velocity dependencies on sea surface temperature (SST) and wind speed with recently reported cruise-based observations. The default scheme overestimates the observed deposition velocities by a factor of 2–4 when the chemical reaction is slow (e.g. under colder SSTs in the Southern Ocean). The default scheme has almost no temperature, wind speed, or latitudinal variations in contrast with the observations. The one-layer scheme provides noticeably better variations, but it overestimates deposition velocity by a factor of 2–3 due to an enhancement of the interaction between chemical reaction and turbulent transfer. The two-layer scheme with a surface reactive layer thickness specification of 2.5 µm, which is approximately equal to the reaction-diffusive length scale of the ozone–iodide reaction, is able to simulate the field measurements most closely with respect to absolute values as well as SST and wind-speed dependence. The annual global oceanic deposition of ozone determined using this scheme is approximately half of the original ...