Aerosol-Aware Bulk Microphysics Scheme: A sensitivity study of Hurricane Earl

Aerosols-cloud-microphysical processes are largely unknown in their influence on tropical cyclone evolution and intensification; aerosols possess the largest uncertainty. Field, laboratory and modeling studies strongly suggest the importance of aerosols in tropical cyclone clouds properties but there is still an ongoing discussion of whether aerosols have a positive or negative effect on intensification.

To address some of the existing questions, high resolution numerical simulations of hurricane Earl were performed using the Weather Research and Forecasting (WRF-ARW) model with the new Aerosol-Aware bulk microphysics scheme. This new and implemented version of Thompson microphysics scheme incorporate number concentration of aerosols available for ice nucleation through the addition of explicit activation of nuclei from a major CCN aerosol source (i.e. sulfates, organics and sea salt) and the addition of explicit nucleation of ice crystals from the most dominant IN source (i.e. mineral dust).

Three simulations are performed: (1) Control Case, Thompson (2008) scheme with no aerosols included, (2) Aerosol-Aware Case, new scheme with aerosols concentration from GOCART and (3) Sensitivity Case, increase GOCART aerosols concentration (10 times).

Results of model simulations reveal that the injection of aerosols into the storm can impact the structure, size and intensity of the system. Significance changes are shown in terms of cloud water and snow number concentration (increase tendency) while the ice number concentration presented a decrease tendency.