Height-resolved cloud condensation nuclei concentrations for bounding aerosol-cloud interactions from spaceborne observations

• Applicant: Dr. Goutam Choudhury
• Subject Area: Atmospheric Science
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 524386224

Clouds in the atmosphere reflect solar radiation and cool the earth. Liquid clouds form when atmospheric water vapour condenses on tiny aerosol particles called cloud condensation nuclei (CCN). Any change in the concentration of CCN modifies the properties of clouds and ultimately alters their reflectivity. For example, an increase in the number of CCN may result in clouds with more liquid droplets, increasing the cloud surface area and thereby increasing cloud reflectivity (cooling effect). However, such aerosol-cloud interactions (ACI) are still not quantified properly, leading to a more uncertain future. A key reason behind our inability to quantify ACI is the lack of global observation of CCN concentrations. Satellite-based ACI studies use aerosol optical properties as proxies for CCN. However, these proxies are often column-integrated and do not guarantee the vertical co-location of the aerosols and clouds that are studied. In addition, they may have retrieval issues over land, restricting the current satellite-based global radiative forcing estimate to oceans only. In light of the aforementioned limitations, I developed a novel algorithm to retrieve height-resolved CCN concentrations from spaceborne lidar measurements, separately for continental, marine, and dust aerosols. Within this project, I plan to apply the algorithm to 15+ years of spaceborne lidar measurements to compile, for the first time, a global height- and type-resolved CCN dataset. The CCN profiles will be further combined with cloud and radiation retrievals from spaceborne radar and radiometers to study the impact of different aerosol types on liquid clouds and to quantify the global instantaneous radiative forcing associated with ACI. The height-resolved measurements will address the vertical co-location issue. As lidars do not have any retrieval-related issues over land, the radiative forcing will be estimated consistently over land and ocean surfaces. This project aims to use the full potential of the spaceborne A-Train sensors, especially the lidar-radar synergetic measurements, which will lead to a step change in satellite-based ACI studies.

• DFG Programme: WBP Fellowship
• International Connection: Israel
• Host: Dr. Tom Goren