Observations of aerosol and cloud structure from the G-1 and the ENA site during ACE-ENA

Description

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. This poster describes statistical analysis of G-1 observations from the ACE-ENA deployments and from concurrent measurements at the ENA site, focusing on vertical structure of aerosol properties, cloud and drizzle microphysics, and the MBL. Although clean by continental standards, we find significantly higher aerosol and cloud droplet concentrations during summer and evidence of frequent ultraclean layers in the upper MBL during winter. Cloud condensation nucleus concentrations and cloud droplet concentrations are quite well correlated in both summer and winter, but the relationships differ. Both summer and winter show variable MBL depths, but there is evidence that deeper MBLs in winter tend to be less decoupled than during summer. Condensate amounts do not show strong seasonality, but precipitation rates from MBL clouds (especially in the intermediate range 0.25-5 mm/day) tend to be higher during winter, which may be reflective of lower wintertime droplet concentrations.