Title

The Biophysical Impacts of Aerosols on Surface Climate

Date of Award

Fall 10-1-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Forestry and Environmental Studies

First Advisor

Lee, Xuhui

Abstract

Aerosols, tiny suspended solid or liquid particles in the atmosphere, are important drivers of atmospheric processes. Aerosols affect the climate as well as local weather by modulating the Earth’s energy budget. Previous studies have quantified the impact of aerosols on global climate change, with a focus on the atmospheric radiation budget. However,aerosols have a disproportionately higher impact on the Earth’s surface, where we reside. This dissertation isolated this impact of aerosols on the surface climate to better understand the mechanisms that modulate the overall climate response to aerosol loading. This work developed a surface energy budget perspective to aerosol-climate interactions and quantified the impact of aerosols on surface climate through both radiative and non-radiative pathways. The relative strengths of these pathways depend heavily on both aerosol and land surface properties. Thus, a major emphasis of the dissertation was to investigate the impact of aerosols on the surface energy budget tied to differences in regional aerosol loading and land cover. The research methodology combined data analysis, remote sensing, atmosphere modeling, and land-surface modeling. Both reanalysis datasets with assimilated aerosol observations and atmosphere model runs with radiation diagnostics were used to separate the impact of aerosols on surface climate through the shortwave and longwave radiative effects. To capture the impact of aerosols on surface climate through non-radiative pathways, a global land model was run with and without aerosols. In both cases, a conceptual framework to attribute surface temperature anomalies to its determinants was used to examine the relative impact of each pathway on the local surface temperature.The associated impacts on terrestrial evapotranspiration and land carbon uptake were also quantified on a global scale using land model runs. Finally, given the importance of diffuse radiation of sunlight on surface processes, a comprehensive evaluation of gridded diffuse radiation in current-generation global products was undertaken. To correct some of the observed biases in these gridded products, a supervised machine learning algorithm was trained to develop a global bias-corrected radiation dataset for future land modeling. Aerosols lead to one of the largest uncertainties in both diagnostic and prognostic climate simulations. This dissertation advances our understanding of the biophysical mechanisms through which aerosols can impact surface temperature, terrestrial evapotranspiration, and land carbon uptake. It also provides a broader perspective on the importance of the diffuse radiation fertilization effect and the current uncertainties in its representation in Earth System Models.

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