Aerosol effects on clouds and their sensitivity to numerical representation of microphysics

This study examined aerosol effects on clouds and their sensitivity to numerical representation of microphysics.; Simulations with high and low CCN numbers were carried out to investigate the role of cloud condensation nuclei (CCN) number in a mesoscale cloud ensemble (MCE) driven by deep convection. Results indicated an increase of precipitation at high CCN due to stronger, more numerous updrafts, initiated by stronger convergence lines around the surface. Stronger convergence lines resulted from interactions between microphysics and dynamics; delayed autoconversion led to larger evaporative cooling of cloud liquid for stronger convergence at high CCN. Precipitation enhancement in deep convective clouds and well-known precipitation suppression in stratiform clouds at high CCN indicated aerosol effects on precipitation depended on cloud-system organization; different cloud-system organizations may have different interactions between dynamics and microphysics. Pairs of numerical experiments, high and low CCN cases, were conducted for different cloud-system organizations. More precipitation resulted from cumulonimbus clouds, but less precipitation from stratocumulus clouds at high CCN.; The effect of aerosol chemical composition on precipitation in the MCE was examined. The increase in organics in aerosol particles lowered critical supersaturation (Sc) for droplet nucleation and led to an increase in cloud droplet number concentration (CDNC), leading to stronger interactions between microphysics and dynamics for larger precipitation. When insoluble substance composed of black carbon (BC) and dust increased by replacing organics in aerosols, larger decrease in precipitation was simulated than when insoluble substance replaced sulfate.; Temporal evolution of precipitation rate of single-moment microphysics was significantly different from that of double-moment microphysics mostly due to different numerical representations of autoconversion, saturation and nucleation. Cloud particle mass and predicted size in double-moment microphysics were significantly different from cloud particle mass and prescribed size in single-moment microphysics, respectively. This led to different cloud radiative forcing (CRF) between double- and single-moment microphysics. Double-moment microphysics showed better agreement between simulated precipitation and radiation and observed counterparts.