Quantifying Aerosol Indirect Effects on Precipitation on Global Scales
Interactions between clouds, aerosols, and precipitation and the resulting impacts on the global energy and water cycle represent a critical pathway by which human activities can impact the global climate system. Yet aerosol indirect effects are among the least well understood and most hotly debated processes in current climate research. Due to their strong sensitivity to both aerosol composition and the local environment, understanding and ultimately quantifying aerosol-cloud interactions on global scales requires an interdisciplinary approach that includes analysis of multi-sensor datasets and associated modeling activities to establish causality and investigate underlying physical processes.
Our group uses state-of-the-art satellite datasets, many of which we develop ourselves, to examine the ways aerosols influence clouds and precipitation. Our recent research has shown evidence that pollution in the East China Sea suppresses precipitation with sufficient frequency to show up clearly on annual precipitation climatologies from the Tropical Rainfall Measuring Mission. We have also used multi-sensor A-Train observations to demonstrate that clouds in polluted regions tend to be brighter, contain smaller droplets, grow deeper, and rain less efficiently than those in cleaner environments. Through ongoing collaborations with numerical modeling groups we are currently exploring the ability of models to capture these effects, using model output to examine physical processes in more detail, and exploring evidence that larger sea salt aerosols may induce opposite responses in clouds and rainfall. Ultimately this information may help improve aerosol processes in climate models so that we may better represent these effects in predictions of future climate.