Understanding the vertical transport of aerosols during deep convective events
Atmospheric aerosols affect the global energy budget by scattering and absorbing sunlight (direct effects) and by changing the microphysical structure, lifetime, and coverage of clouds (indirect effects). Globally, free troposphere is a major source of nucleation- and Aitken-mode aerosols due to the enhanced new particle formation rates at high altitudes1. Recent studies have shown deep convective systems are capable of transporting these small aerosols from the free troposphere to the boundary layer by strong convective downdrafts and weaker downward motions in the stratiform regions. These vertically transported aerosols can grow into cloud condensation nuclei (CCN) and play a significant role in the global climate. We are analyzing a multi-year, multi-site measurement record available from the U.S. Department of Energy (DOE) ARM program, including the observations from the 2014/15 Observations and Modeling of the Green Ocean Amazon (GoAmazon) field campaign, the 2018/19 Cloud, Aerosol, and Complex Terrain Interactions (CACTI) field campaign, and the long-term measurements collected at the Southern Great Plains (SGP) atmospheric observatory, where deep convective clouds were frequently observed.
Examining the interaction between boundary layer new particle formation and cloud systems
Atmospheric aerosols affect the earth’s radiation budget directly by scattering solar radiation and indirectly by serving as cloud condensation nuclei (CCN) and affecting cloud properties. Among various atmospheric processes, new particle formation (NPF) is an important source of atmospheric aerosols, contributing almost half of the atmosphere’s CCN. NPF events in the boundary layer are frequently observed and are of great interest, because the new particles can be facilely transported to cloud level and contribute to CCN after they grow to sizes above the Hoppel minimum. Boundary layer NPF events are also ubiquitous around the world, ranging from the high-latitude Arctic and Antarctic regions, through mid-latitude boreal forests, farmlands, cities, and coastal regions, to tropical forests and ocean. Many efforts have been devoted to studying the physio-chemical mechanisms of NPF in the boundary layer and the contribution of newly formed particles to CCN. However, understanding the climate impact of aerosols requires improved knowledge of aerosol-cloud processes. At present, the interactions between NPF and cloud systems are still relatively understudied. Our project will investigate the dependence and impact of boundary layer NPF on cloud systems at the third ARM Mobile Facility (AMF3) in Southeast U.S. The Southeast U.S. region is a warm and humid region with abundant locally forced, atmospheric convection inland and enhanced convection along coasts. The wide range cloud conditions resulted from these shallow to deep convections creates an opportunity to examine their impact and dependence on boundary layer NPF. We propose to analyze aerosol, trace gas, cloud, and meteorological data collected from the early observations at AMF3. This project is aimed at the following objectives: (1) Gaining a quantitative understanding of the impact of cloud systems on NPF occurrence; (2) Examining the impact of boundary layer NPF on CCN population; (3) Investigating the impact of boundary layer NPF on cloud systems.
