Aerosol, Cloud, and Precipitation Interactions over the Eastern North Atlantic

With their extensive coverage, marine low clouds greatly impact global climate. Presently, marine low clouds are poorly represented in global climate models (GCMs), and the response of marine low clouds to changes in atmospheric greenhouse gases and aerosols remains the major source of uncertainty in climate simulations. The Eastern North Atlantic (ENA) is a region of persistent but diverse subtropical marine boundary layer (MBL) clouds, whose albedo and precipitation are highly susceptible to perturbations in aerosol properties. Downwind of the North American continent, ENA is periodically impacted by anthropogenic aerosol, making it an excellent location to study the cloud condensation nuclei (CCN) budget in a remote marine region periodically perturbed by anthropogenic emissions, and to investigate the impacts of long-range transport of aerosols on remote marine clouds.

The Aerosol and Cloud Experiments in Eastern North Atlantic (ACE-ENA), supported by the DOE Atmospheric Radiation Measurement (ARM) program, are designed to improve the understanding of the MBL CCN budget, cloud and drizzle microphysics, and the impact of aerosol on marine low cloud and precipitation over the ENA by combining airborne observations and long term surface based measurements. The study involved two airborne deployments with the ARM Aerial Facility G-1 aircraft: Summer (June 15 to July 25, 2017); Winter (January 10 to February 20, 2018). A total of 39 flights were carried out in the Azores, near the ARM ENA site on Graciosa Island. The long term measurements at the ENA site provide important seasonal context for the airborne observations during the two deployments, and the cloud structures provided by the scanning radars at the ENA site put the detailed in-situ measurements into mesoscale and cloud lifecycle contexts. Another important aspect for this study is to provide high quality in-situ measurements for validating and improving ground-based retrieval algorithms at the ENA site.

This presentation will describe preliminary analysis of observations from the ACE-ENA deployments, focusing on vertical structures and horizontal variabilities of aerosol properties, cloud and drizzle microphysics, and insights into the processes that drive the properties and interactions of aerosol and marine low clouds.