The Influence of Aerosols on Warm Rain Formation Processes based on A-Train Observations and Global Climate Models

A previous case study by Malavelle et al (2017) revealed an intriguing result during the 2014–2015 Holuhraun Icelandic eruption: a positive liquid water path (LWP) response to aerosol perturbation was clearly detected in the global climate models (GCMs), while LWP response to aerosol perturbation was rather muted in the observations. This new evidence suggests that GCMs excessively estimate the aerosol indirect effect and overestimate cooling effect on the Earth’s climate. Climate simulations in GCMs are extremely sensitive to the threshold particle radius to produce rain, which is a tunable parameter that significantly controls the magnitude of the aerosol-cloud interaction. Therefore, it is critical to compare the warm rain formation processes between the real world and the model simulations. However, this has been an observational challenge. As a result, how aerosols affect warm rain formation processes in the real world has not been explored widely. This study aims to find an answer to the ongoing debate on whether aerosols affect cloud and precipitation formations in liquid clouds, by using Contour Frequency by Optical Depth Diagrams, which gives us an opportunity to monitor the warm rain formation process on both global and regional scales. Moreover, we also examine how environmental parameters affect warm rain formation processes and show how understanding aerosol effects on clouds cannot be done without some understanding of dynamics.