A numerical investigation of aerosol effect on cloud microphysics in an idealized tropical cyclone using the WRF piggybacking framework

Efforts were made to separate the effects of aerosol on cloud microphysics in an idealized tropical cyclone (TC) from meteorological effects using a spectral bin microphysics scheme and the piggybacking methodology introduced by Grabowski et al. (2017). Modifying the initial distribution of cloud condensation nuclei (CCN) from maritime to continental condition, the increase of CCN leads to a clear enhancement of mixing ratio and number concentration of cloud droplets and a decrease of number concentration of raindrops especially in the lower atmosphere. Therefore, lower supersaturation can be traced under the continental condition due to the extra consumption of water vapor, leading to more condensation as well as relatively larger buoyancy beneath the freezing layer, which is postulated as condensational invigoration. Although invigoration is identified within a thin layer above the 0 °C isotherm, it is still dominantly attributed to the condensation of water vapor toward supercooled liquid drops with small contributions from riming of snow/graupel. No evidence indicates the mixed-phase invigoration at high layers. In addition, a larger cloud fraction is found in both high and low layers in the continental condition, especially within the inner core of a TC. It is noted that aerosols may also influence the spatial pattern of TC precipitation, although the difference of area-averaged precipitation is less notable. Finally, the experiments are repeated to further examine the aerosol effect on TC with different intensity and quantitatively demonstrate that the impact of aerosol is weaker in stronger TC due to the dominant control of the dynamics.