Coupling aerosols to (cirrus) clouds in the global EMAC-MADE3 aerosol–climate model

• Published in: Geoscientific Model Development 2020-03, Vol.13 (3), p.1635-1661
• Main Authors: Righi, Mattia, Hendricks, Johannes, Lohmann, Ulrike, Beer, Christof Gerhard, Hahn, Valerian, Heinold, Bernd, Heller, Romy, Krämer, Martina, Ponater, Michael, Rolf, Christian, Tegen, Ina, Voigt, Christiane
• Format: Article
• Language: English
• Subjects: Aerosol dynamics; Aerosol effects; Aerosol models; Aerosol particles; Aerosols; Analysis; Anthropogenic factors; Atmosphere; Atmospheric chemistry; Atmospheric models; Aviation; Carbon; Cirrus clouds; Climate change; Climate models; Cloud droplet concentration; Cloud droplets; Cloud formation; Cloud microphysics; Clouds; Clouds (Meteorology); Computer simulation; Configurations; Crystals; Droplets; Environmental assessment; Estimates; Freezing; Global aerosols; Global temperature changes; Humidity; Ice; Ice clouds; Ice crystals; Ice formation; In situ measurement; Intergovernmental Panel on Climate Change; Laboratories; Northern Hemisphere; Nucleation; Oceans; Parameterization; Prejudice; Radiation; Radiation (Physics); Radiation standards; Radiative forcing; Ratios; Satellite observation; Stratiform clouds; Tropical climate; Water; Water vapor; Water vapour
• ISSN: 1991-9603; 1991-959X; 1991-962X; 1991-9603; 1991-962X
• DOI: 10.5194/gmd-13-1635-2020

A new cloud microphysical scheme including a detailed parameterization for aerosol-driven ice formation in cirrus clouds is implemented in the global ECHAM/MESSy Atmospheric Chemistry (EMAC) chemistry–climate model and coupled to the third generation of the Modal Aerosol Dynamics model for Europe adapted for global applications (MADE3) aerosol submodel. The new scheme is able to consistently simulate three regimes of stratiform clouds – liquid, mixed-, and ice-phase (cirrus) clouds – considering the activation of aerosol particles to form cloud droplets and the nucleation of ice crystals. In the cirrus regime, it allows for the competition between homogeneous and heterogeneous freezing for the available supersaturated water vapor, taking into account different types of ice-nucleating particles, whose specific ice-nucleating properties can be flexibly varied in the model setup. The new model configuration is tuned to find the optimal set of parameters that minimizes the model deviations with respect to observations. A detailed evaluation is also performed comparing the model results for standard cloud and radiation variables with a comprehensive set of observations from satellite retrievals and in situ measurements. The performance of EMAC-MADE3 in this new coupled configuration is in line with similar global coupled models and with other global aerosol models featuring ice cloud parameterizations. Some remaining discrepancies, namely a high positive bias in liquid water path in the Northern Hemisphere and overestimated (underestimated) cloud droplet number concentrations over the tropical oceans (in the extratropical regions), which are both a common problem in these kinds of models, need to be taken into account in future applications of the model. To further demonstrate the readiness of the new model system for application studies, an estimate of the anthropogenic aerosol effective radiative forcing (ERF) is provided, showing that EMAC-MADE3 simulates a relatively strong aerosol-induced cooling but within the range reported in the Intergovernmental Panel on Climate Change (IPCC) assessments.