Global modelling of aerosol and aerosol-cloud interactions with EMAC (MADE3)

Simulated near-surface concentration of aerosol sulfate compared with ground-based measurements (circles) from different networks: IMPROVE and CASTNET (North America, left panel); EMEP (Europe, middle) and EANET (East Asia, right). From Kaiser et al. (2018).

A new version of the aerosol submodel MADE3 has been implemented in EMAC v2.54 and coupled to a two-moment cloud scheme including a parametrization for cirrus clouds.

The third version of the aerosol submodel MADE (MADE3) has been implemented in the global climate-chemistry model EMAC v2.54. MADE3 includes a detailed representation of aerosol mixing states by distinguishing purely soluble, purely insoluble and mixed particles. With respect to its predecessors, the new model version also allows simulating the interactions between the fine and coarse aerosol size modes and the aerosol-gas partitioning in the coarse mode in an explicit way.

The ability of the model to simulate global aerosol has been evaluated against a wide range of observational datasets, including ground-based measurements from several station networks around the globe (IMPROVE, CASTNET, EMEP and EANET), in-situ data from various aircraft campaigns, and satellite observations from MODIS and the ESACCI aerosol products. The evaluation showed that EMAC (MADE3) is able to capture the average spatial patterns of aerosol concentrations on the global scale, although it has some bias in the vertical distribution of aerosol mass and number concentrations in the upper troposphere. In general, however, the model performance was found to be in line with other global aerosol models.

MADE3 has been coupled to a two-moment cloud scheme including a parametrization for cirrus clouds. This parametrization considers the main ice formation paths in the cirrus regime, accounting for the competition between homogeneous and heterogeneous freezing processes, also taking into account the deposition of supersaturated water vapor on existing ice crystals. This coupled configuration allows simulating aerosol-cloud interactions at all cloud levels (phases) and has been evaluated against observations and similar (ECHAM5-based) model versions, showing that it is able to reproduce the main cloud and radiation parameters reasonably well. The first estimates of the total anthropogenic aerosol radiative forcing effect with the new model are within the range of the results of the CMIP5 models published in the IPCC AR5. Additional work is currently ongoing to acquire more observational data, in particular in-situ and satellite data of cirrus clouds, in order to extend the model evaluation and further improve the representation of the processes controlling the aerosol-driven ice formation in cirrus clouds.

Reference

Kaiser, J. C., Hendricks, J., Righi, M., Jöckel, P., Tost, H., Kandler, K., Weinzierl, B., Sauer, D., Heimerl, K., Schwarz, J. P., Perring, A. E., and Popp, T.: Global aerosol modeling with MADE3 (v3.0) in EMAC (based on v2.53): model description and evaluation, Geosci. Model Dev. Discuss., doi.org/10.5194/gmd-2018-185, in review, 2018.

Mattia Righi is a research scientist at the Institute for Atmospheric Physics of the German Aerospace Center (DLR) in Oberpfaffenhofen (Germany). His research interests focus on global modelling of aerosol and aerosol-cloud interactions and on the impact of the transport sectors on the global aerosol distribution and on the climate.