Thornton, Joel AWright, Christopher J2024-09-092024-09-092024Wright_washington_0250O_26777.pdfhttps://hdl.handle.net/1773/51787Thesis (Master's)--University of Washington, 2024Aerosol interactions with clouds represent a significant uncertainty to our understanding of the Earth system. Deep convective clouds, in particular, can have complex responses to aerosol that have proven difficult to elucidate. Here, we leverage the two busiest shipping lanes in the world, which carve a narrow path of pollution through a pristine marine bound- ary layer, to make headway on the influence of aerosol on deep convective clouds. We use the recent change in allowable fuel sulfur by the International Maritime Organization to test the sensitivity of the lightning to shifting aerosol size distributions. We find that, across a range of thermodynamic conditions, the enhancement of lightning over the shipping lanes has fallen by over 30%. Retrievals of cloud droplet number show a similar decline. The enhancement is therefore at least partially aerosol-mediated, a conclusion that is supported by observations of droplet number at cloud base. These results have fundamental implica- tions for our understanding of aerosol-cloud interactions, suggesting that deep clouds show sensitivity to the shifts in aerosol number distribution in the remote marine environment.application/pdfen-USnoneLightningAtmospheric sciencesAtmospheric sciencesThesis