Abstract
Abstract. One of the major sources of uncertainty in model estimates of the global sea-salt aerosol distribution is the emission parameterization. We evaluate a new sea-salt aerosol life cycle module coupled to the online multiscale chemical transport model NMMB/BSC-CTM. We compare 5 yr global simulations using five state-of-the-art sea-salt open-ocean emission schemes with monthly averaged coarse aerosol optical depth (AOD) from selected AERONET sun photometers, surface concentration measurements from the University of Miami's Ocean Aerosol Network, and measurements from two NOAA/PMEL cruises (AEROINDOEX and ACE1). Model results are highly sensitive to the introduction of sea-surface-temperature (SST)-dependent emissions and to the accounting of spume particles production. Emission ranges from 3888 Tg yr−1 to 8114 Tg yr−1, lifetime varies between 7.3 h and 11.3 h, and the average column mass load is between 5.0 Tg and 7.2 Tg. Coarse AOD is reproduced with an overall correlation of around 0.5 and with normalized biases ranging from +8.8% to +38.8%. Surface concentration is simulated with normalized biases ranging from −9.5% to +28% and the overall correlation is around 0.5. Our results indicate that SST-dependent emission schemes improve the overall model performance in reproducing surface concentrations. On the other hand, they lead to an overestimation of the coarse AOD at tropical latitudes, although it may be affected by uncertainties in the comparison due to the use of all-sky model AOD, the treatment of water uptake, deposition and optical properties in the model and/or an inaccurate size distribution at emission.
Highlights
Sea salt is one of the most abundant aerosol species globally
Lewis and Schwartz (2004) estimate the total sea-salt emission to vary from 0.3 Tg yr−1 to 30 Tg yr−1 and estimates from models involved in the AEROCOM project range from 3 Tg yr−1 to 18 Tg yr−1 for year 2000 (Textor et al, 2006)
The model coarse aerosol optical depth (AOD) is calculated from the dust and sea-salt components allowing the use of AEROsol RObotics NETwork (AERONET) stations affected by dust to be included in the evaluation
Summary
Sea salt is one of the most abundant aerosol species globally. It perturbs the radiative fluxes directly by interacting with shortwave and longwave radiation, and indirectly by acting as cloud condensation nuclei (CCN) and altering marine cloud brightness and lifetime. We shortly recall the parameterizations involved in the sea-salt aerosol cycle, i.e., surface layer, gridscale cloud microphysics, convective adjustment and precipitation, and radiation schemes. Given the strong uncertainties on the activation properties of dust, solubility is obtained by applying an intermediate hypothesis between pure hydrophobic and pure hydrophilic aerosol Both global and regional simulations of dust optical depth have been exhaustively evaluated in Pérez et al (2011) and Haustein et al (2012). In this contribution, the model coarse AOD is calculated from the dust and sea-salt components allowing the use of AERONET stations affected by dust to be included in the evaluation.
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