Sources of Variability in Transport and Deposition of Arctic Aerosols in Changing Climates

Abstract

Light absorbing aerosols affect Arctic climate by reducing the albedo of snow and ice, increasing atmospheric solar heating, and accelerating the melting of the cryosphere. Previous studies have indicated that the reduction of snow and ice albedo caused by light absorbing aerosols is a significant source of Arctic warming and sea ice retreat. Thus, accurate numerical representation of the states and variability of aerosols in the Arctic is important for advancing our understanding of the Arctic and global climate. Although the developments of climate models have led to substantial improvements, notable disagreements still exist between the models and observations.

This thesis assesses sources of uncertainties in aerosol related processes and explores possible improvements to aerosol simulations, with a focus on the Arctic region. Firstly, I evaluate concentrations and radiative effect of black carbon in snow with an ensemble of climate models and ground measurements. Results show the inter-model variation is large and the deposition processes dominate the model variance. Secondly, I investigate how two processes that govern the aerosol distributions may change with future climate warming. I find the changing circulation patterns due to enhanced Arctic warming will promote the transport of aerosol tracers emitted from East Asia and West Europe. Meanwhile, these changes inhibit the poleward transport of aerosol tracers emitted from North America. Another experiment with realistic treatments of aerosol deposition processes reveals that wet removal is the dominant process determining the aerosol distribution in the Arctic. I estimate that the Arctic BC burden may decrease by 13.6% by the end of 21st century due solely to changes in aerosol transport and deposition. Thirdly, I conduct a sensitivity study to explore the influences of physical parameters, model resolution and emission patterns on the modeled Arctic aerosol distributions. Analysis shows that the simulated aerosol fields are most sensitive to the parameters associated with aerosol aging and wet deposition processes. Further comparisons with aircraft measurements indicate that by adjusting these parameters, the biases between models and observations can be reduced substantially. This study provides a comprehensive analysis of aerosol transport and deposition processes in climate models and outlines further improvements.