Arctic Aerosol-Cloud Interactions in Regional and Global Simulations

The pristine conditions in the Arctic make Arctic clouds particularly sensitive to the influence of aerosol-cloud interactions. Global climate models struggle to simulate Arctic clouds because the coarse resolution and parameterisations used are ill-suited for the scale and complexity of aerosol-cloud interactions. This work has used the UK Met Office Unified Model (UM) in both its regional and its global configurations. Comparisons have been made between the global aerosol-climate model and the high-resolution, regional cloud-microphysics model. Observations from ground stations and from the recent MOCCHA campaign have been used to assess the treatment of aerosols and clouds in the UM. Global model output of the seasonal cycle of Arctic aerosol compares poorly to observations, suggesting that the treatment of wet scavenging in the global configuration of the model may need improvement. Output from the regional simulations indicates that cloud drop activation is not accurately represented due to biases in the model vertical wind distribution. It will be shown that improving these parts of the model can lead to more accurate simulations of Arctic aerosol distributions and clouds.