Influence of wind speed averaging on estimates of dimethylsulfide emission fluxes

[1] The effect of various wind speed averaging periods on calculated dimethylsulfide (DMS) emission fluxes is quantitatively assessed. A global climate model and an emission flux module were run in stand-alone mode for a full year. Twenty-minute instantaneous surface wind speeds and related variables generated by the climate model were archived, and corresponding 1-hour, 6-hour, daily, and monthly averaged quantities were calculated. These various time-averaged, model-derived quantities were used as inputs in the emission flux module, and DMS emissions were calculated using two expressions for the mass transfer velocity commonly used in atmospheric models [Liss and Merlivat, 1986; Nightingale et al., 2000]. Results indicate that the time period selected for averaging wind speeds can affect the magnitude of calculated DMS emission fluxes. A number of individual marine cells within the global grid show DMS emissions fluxes that are 10–60% higher when emissions are calculated using 20-min instantaneous model time step winds rather than monthly averaged wind speeds, and at some locations the differences exceed 200%. Many of these cells are located in the Southern Hemisphere where anthropogenic sulfur emissions are low and changes in oceanic DMS emissions may significantly affect calculated aerosol concentrations and aerosol radiative forcing.

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