Influence of Nucleating Aerosols on Tropical Cyclone Initiation and Development

Each year about 1 to 3 Atlantic tropical cyclones (TCs) have been observed to interact with the Saharan Air Layer (SAL), an elevated layer of hot, dry air that drifts from the African continent into the eastern Atlantic Ocean. The SAL is often found to be loaded with aerosols, mainly dust. The impact of aerosols acting as cloud condensation nuclei (CCN), giant CCN (GCCN) and ice nuclei (IN) on the initiation and evolution of a tropical cyclone is examined by conducting a series of numerical simulations using the Regional Atmospheric Modeling System (RAMS) initialized with an idealized pre-TC mesoscale convective vortex (MCV). To highlight the effect of aerosols, the vortex is allowed to develop into a hurricane in a zero wind environment and over an ocean with a constant sea surface temperature. Vertical profiles of CCN, GCCN and IN are constructed using observations from various field campaigns to represent pristine and polluted conditions. The variations in the TC's intensity, wind fields, and precipitation and cloud spatial distributions to the number concentrations and vertical distributions of CCN, GCCN and IN are quantified. Detailed budgets for the nucleation of cloud droplets and ice particles, the diffusion of water vapor, and conversions between hydrometeor categories are calculated to examine the variations of these processes when using different aerosol distributions. Evolution of latent heating and cooling distribution are examined to determine its relationship with storm intensification and distribution of updraft and downdraft.