Investigating the Impacts of Aerosol Composition on a Mesoscale Convective System in the Central Great Plains

Concentrations of anthropogenic greenhouse gases, other pollutants and aerosols are magnified in urban areas. Aerosols affect the radiation budget and precipitation in direct (scattering or absorption of incoming light), indirect (cloud processes), and semi-direct (atmospheric stability) ways. The chemical composition of aerosol determines its radiative and hygroscopic properties. In the WRF-Chem model, aerosol activation as cloud condensation nuclei (CCN) is parameterized by a bulk hygroscopicity factor known as kappa. The value of this parameter, when given a specific thermodynamic and dynamic environment including relative humidity, size of the aerosol, and updraft velocity, determines which aerosols will activate as CCN. Previous work has shown that varying the magnitude of emissions leads to changes in phase and size of hydrometeors, which resulted in changing the propagation of a mesoscale convective system (MCS). Here we isolate the effects that aerosol composition has on a severe weather event in the Central Great Plains by examining the dynamical and microphysical changes in deep convective clouds that occur as a result of varying the hygroscopicity of aerosol types. Because the kappa values are the same for sulfate, nitrate and ammonium, we choose a city that has relatively large amounts of organic carbon and black carbon. To isolate the chemical effects on convective cloud dynamics and microphysics, we conduct WRF-Chem simulations that test the sensitivity of precipitation magnitude and hydrometeor phase to the aerosol composition.