Bridging the data gap in Southern Hemisphere aerosol research

Science

Aerosols are known to affect cloud properties, including their formation, growth, and precipitation, which in turn influences climate over long time scales. Aerosol-cloud-interactions (ACI) depend on how their properties change together, yet few measurements capture this variability, especially in the presence of convective cloud populations that can be observed routinely by satellites. Models are often challenged because they assume aerosols are constant, which potentially leads to erroneous estimates of the impact of ACI. Furthermore, ACI pathways in convective clouds are complex and remain highly uncertain.

To address the data gap and better understand the interactions of convective clouds and the surrounding environment, extensive in situ and remote-sensing measurements were collected during the Cloud, Aerosol, and Complex Terrain Interactions (CACTI) field campaign conducted between October 2018 and April 2019 over the Sierras de Córdoba range of central Argentina. The field campaign aimed to understand how convective clouds interact with environmental conditions, thermodynamics, aerosols, and surface properties. In contrast with previous studies that focused on clouds, this study describes measurements of aerosol number, size, composition, mixing state, and cloud condensation nuclei collected during CACTI.

Impact

This research provides key insights into how aerosols influence convective cloud processes and their implications for weather and climate. By filling significant data gaps in understanding aerosol properties and their variability, the study supports improvements in accurately modeling aerosol-cloud interactions. The findings also highlight the importance of considering the dynamic nature of aerosols in climate models, as traditional assumptions about their uniformity can lead to errors in predicting their effects. Furthermore, this study lays the groundwork for future research in this underexplored region of the Southern Hemisphere. Results from this and future similar studies will inform more precise weather forecasts and climate predictions.

Summary

In addition to measuring aerosol properties in a data-sparse region, the findings from this study will help evaluate predictions over the mid-latitudes of South America and improve parameterization of aerosol processes in local, regional, and global models. Measurements in this study also demonstrate that accounting for the co-variabilities of aerosol properties and convective cloud populations over the Sierras de Córdoba range will be critical. Knowing aerosol properties just below and surrounding clouds is important because aerosols are entrained into the base of clouds by convective updrafts. In addition to cloud base entrainment, aerosols with different properties at higher altitudes are also entrained into the sides of clouds as they grow vertically. As clouds evaporate, the size and composition of aerosol particles that were within cloud droplets can be different than aerosol populations surrounding clouds because of cloud chemistry and coalescence of cloud droplets. Thus, the properties of aerosol populations near the top of the boundary layer and around clouds will change in time as aerosols are cycled through clouds multiple times over several hours. Given the large variations observed in aerosol and cloud properties, and the complexity of these interactions, developing a robust statistical signal of aerosol-cloud interactions from measurements will be challenging and remains an important future research focus.