Investigating the Impact of Aerosols on Liquid-Origin Cirrus from Global Observations and Reanalysis Data

Complementarily to their formation mechanism, the origin of cirrus (liquid or in-situ) can substantially affect their microphysical and radiative properties. Liquid-origin cirrus, which stem from the freezing of water droplets at cirrus temperatures, are typically characterised by high ice crystal concentrations and associated with strong cooling effect. However, the global occurence and distribution of this cirrus type as well as the environmental conditions in which they originate. The role of aerosols on liquid-origin cirrus, through their influence on liquid clouds, is also not well understood but can be critical for understanding radiative forcings associated with aerosol-cloud interactions and in implications of potential geo-engineering strategies.

This study investigates cirrus by coupling satellite and reanalysis dataset. Observations from lidar-radar satellite instruments (DARDAR-Nice) provide detailed retrievals of cirrus microphysical properties, such as ice water content and crystal number concentration. To trace the origins of cirrus clouds, we employ Lagrangian air mass trajectories based on ERA5 reanalyses, using FLEXPART. The presence and role of aerosols during the formation phase of these clouds, either in mixed-phase or warm regions, are assessed by integrating these trajectories with aerosol reanalysis products, specifically from CAMS. 

This joint cloud-aerosol dataset from satellite and reanalysis tools is created for one year of satellite observations. The global occurence of liquid-origin cirrus is analysed. The role of aerosols on the formation of liquid-origin clouds is finally investigated, in particular to understand the relevance of low-level aerosols on cirrus properties. Associated radiative effects will also be explored.