EPS Colloquium – Morgan O’Neill, University of Toronto

Tropical cyclones act as scrubbers of aerosols in the upper atmosphere

Tropical Cyclones (TCs) loft polluted boundary layer air to the upper atmosphere through deep convective towers in their eyewall and rainbands, changing the distribution of heat, moisture and chemicals in the vicinity of TCs. Aerosols affect TCs, by acting as cloud condensation nuclei (CCN), and are also affected by them, via rainout and washout. In this study we use the output of a global high-resolution atmospheric simulation with interactive chemistry to understand how TC-aerosol interactions change the spatial distribution of different aerosols in the upper troposphere and lower stratosphere. We show that TCs in every region form a large, contiguous clean plume of low hydrophilic aerosol in the TC outflow region (100-300hPa). It extends well beyond the cloud shield and flows equatorward and westward, consistent with the potential vorticity signature of TC outflow. This suggests that aerosol deficit is a robust and smooth tracer of TC exhaust air. The relative deficit of hydrophilic aerosols, including sulfate aerosol relevant to solar radiation management proposals, is found to be a function of TC intensity. Such vast clean plumes are uniquely produced by TCs among all types of tropical convection. The clean plume can serve as a tracer of TC outflow, as it extends far beyond the visible cloud shield. Model results are corroborated by a single airborne flight in the SEAC4RS campaign that was able to measure such aerosols in the vicinity of a TC.

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Dr. Morgan O’Neill is an assistant professor in the Department of Physics at the University of Toronto. She studies the fluid dynamics and moist thermodynamics of severe storms, including hurricanes and supercell thunderstorms. Morgan received a PhD in atmospheric science from the Massachusetts Institute of Technology. She is currently the Chair of the American Physical Society’s Group on the Physics of Climate, and she volunteers extensively for the faculty-led nonprofit Palestinian Students & Scholars At Risk.