PIs: Ina Tegen, Johannes Quaas, Bernd Heinold

The project addresses the role of aerosol particles in the Arctic climate and its change in last but also near–future decades. Aerosols transported from different natural and anthropogenic sources modulate the Arctic radiative energy balance directly by interactions with solar and terrestrial radiation, and indirectly by changing cloud properties and atmospheric dynamics. This implies a potentially important contribution of aerosols to positive feedback mechanisms driving the Arctic Amplification. The effects strongly vary in dependence of aerosol transport and transformation processes, which control the optical and cloud nucleation properties of aerosol particles.

The quantification of the aerosol and cloud processes and their effects is, therefore, important to understand the current rapid climate change and to improve predictions of future climate in the Arctic. The quantification of the aerosol direct and indirect climate forcing is particularly challenging in the Arcticdue to specific characteristics of polar regions, such as the dramatic seasonal changes in insolation and surface albedo. Large variations in the distribution and chemical, microphysical, and optical properties of Arctic aerosol further complicate the assessment of the aerosol effects. Current climate model predictions for the Arctic region largely suffer from uncertainties related to the model representation of mixed–phase Arctic clouds, aerosol–cloud interactions, the vertical layering and deposition of aerosol, and the impact of aerosol processing on radiative properties. All these processes also impact the highly uncertain aerosol transport to the Arctic. This study will, therefore, focus on the three main factors of the direct and indirect aerosol radiative effects: (i) the particle mixing/ageing, (ii) the deposition on snow and ice, and(iii) the interaction with clouds.

Using a new–generation general circulation model, the aerosol transport and impact on radiation and clouds will be investigated. Based on the model simulations, the direct radiative forcing and related dynamical feedback mechanisms will be quantified for the Arctic region. This will include considering the impact of ageing and mixing processes on microphysical and optical properties as well as the snow/ice–albedo forcing. A particular focus will be on black carbon (soot) from increasing ship and wildfire emissions. Aerosol–cloud interactions and the aerosol indirect radiative forcing will be studied by applying a comprehensive double–moment cloud microphysical scheme and by evaluating and improving existing cloud parameterizations in the climate model, with particular emphasis on mixed–phase clouds, to explore their role in the Arctic Amplification.

The project will considerably contribute to improve our understanding of the role of aerosols in the Arctic climate. It will provide a model–based assessment of sources and transport pathways of natural and anthropogenic aerosols to the Arctic region, a state–of–the–art estimate of the effective radiative forcing by anthropogenic aerosols, as well as an assessment of the relevance of the aerosol forcing for the observed Arctic climate change.

• D02 provides sptio-temporal context to and interpretation of field observations
• D02 relies on data from (AC)³ as input paramters and for model evaluation