Abstract
Abstract. This first detailed analysis of the mineral dust cycle in the ECHAM5/MESSy Atmospheric Chemistry (EMAC) model system investigates the performance of two dust emission schemes, following the approach of Balkanski et al. (2004) and Tegen et al. (2002), respectively, and the influence of the horizontal model resolution. Here the spectral resolutions T42, T63, T85, and T106 are investigated. A basic sulphur chemistry, enabling the coating of insoluble dust particles to make them soluble, is employed in order to realistically describe the ageing and wet deposition of mineral dust. Independent of the dust emission scheme the five-year simulations with the horizontal resolutions T42 and T63 produce unrealistically high emissions at some grid points in the Tarim Basin in Central Asia, leading to very high dust loads in polar regions. With these coarse resolutions, dust source grid points in the basin and elevated grid points of the Himalayas with high wind speeds cannot be distinguished, causing this overestimation. In T85 and T106 these regions are well separated and considerably less dust is emitted there. With the chosen model setup, the dust emission scheme by Balkanski et al. (2004) places the global maximum of emissions in the Thar Desert in India. This is unrealistic as the Sahara Desert is known to be the largest dust source in the world. This is the main deficiency of this scheme compared to the one by Tegen et al. (2002), which, based on a qualitative comparison to AEROCOM data, produces a very reasonable distribution of emissions and dust loads in simulations with resolutions T85 and T106. For future climate simulations with EMAC focusing on mineral dust, we recommend to use the dust emission scheme by Tegen et al. (2002) and a model resolution of at least T85. Simulations of two selected episodes and comparison to observational data sets show that in this model configuration EMAC is able to realistically simulate also intense, episodic events of dust emission and long-range transport.
Highlights
Airborne mineral dust particles have the potential to influence regional and global climate
Despite the fact that both models, ECHAM5/Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC) and ECHAM5-HAM, are based on the same Global Circulation Models (GCMs) (i.e. ECHAM5) they differ with respect to the implementation of the aerosol modifying processes, e.g., the removal processes and the chemistry
The bias of all simulations using the BK scheme is worse compared to the simulations with the TG scheme but on average they perform better with regard to the mean normalised bias (MNB), the log-mean normalised bias (LMNB), and the normalised root mean square error (NRMS)
Summary
Airborne mineral dust particles have the potential to influence regional and global climate. Due to uncertainties in the source and sink processes of the mineral dust cycle, Global Chemistry Climate Models (GCCMs) cover a very wide range of values for the global dust emission and deposition, the total dust burden and its atmospheric life time. Five-year time slice simulations with four different resolutions (T42 ≈2.8◦, T63 ≈1.9◦, T85 ≈1.4◦, and T106 ≈1.1◦) are considered in this study. With the most reasonable model setup, in terms of reproducing the main climatological aspects, two episodes are simulated and compared with observational data sets. The second episode covers a dust outbreak from the Sahara to Central Europe in May and June 2008. The analysis of the five-year time slice simulations is presented and discussed, followed by the investigation of the two single dust episodes simulated with the most appropriate setup in Sect.
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