How do clouds and rainfall adjust the tropical atmosphere?

Atmospheric aerosols are all liquid or solid particles suspended in the air. They are one of the main components of climate due to the role they play as seeds necessary for the formation of cloud droplets, influencing precipitation, as well as the lifetime and opacity of clouds. Aerosols also interact directly with the radiation emitted by the sun, which modulates the amount of solar energy in the atmosphere, cooling it (when the aerosols reflect light back into space) or heating it (when aerosols absorb light). These aerosols' properties depend on their chemical composition, concentration and size. Studying the concentration and size of aerosols also allows us to learn more about the mechanisms through which they were formed and evolved during their lifetimes.

Whilst aerosols influence the properties of clouds and precipitation, clouds can in return, act as a source and sink of aerosols. Indeed, we know that larger aerosols are effectively removed from the atmosphere by clouds and precipitation. Furthermore, observational evidence from the Amazon rainforest suggests that clouds play an important role in the formation of smaller particles there. The main objective of this project is to investigate the processes through which clouds and precipitation influence and regulate the concentration and size of aerosols in the tropical atmosphere.

To do so, we analyse long-term measurements of aerosol size and concentration at three different stations in South America. Using a model, we retrieve the trajectories of the air masses before they are measured at the stations. We combine these trajectories with satellite data on the properties of clouds and precipitation, which allows us to analyse how the concentration and size of aerosols vary according to their interactions with clouds and precipitation over their transport.