Microphysical Characteristics of Biomass Burning Aerosol Impacted Southeast Atlantic Marine Stratocumulus from the FPDR - PDI

Aerosol-cloud interactions in the southeastern Atlantic (SEA) region were investigated during three filed deployments (September 2016, August 2017, and October 2018) during the ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) EV-2 campaign. This region is of interest due to seasonally persistent marine stratocumulus (MSc) cloud decks that are an important component of the climate system due to their radiative and hydrologic impacts. The SEA deck is unique due to the interactions between these clouds and transported biomass burning aerosol during the July-October fire season. These biomass burning aerosol play multiple roles in modifying the cloud deck through interactions with radiation as absorbing aerosol and through modifications to cloud microphysical properties as cloud condensation nuclei. This work uses in situ cloud data obtained with a Flight Probe Dual Range - Phase Doppler Interferometer (FPDR - PDI), to characterize the microphysical characteristics of observed MSc clouds.

The combination of the FPDR - PDI and the suite of aerosol instrumentation on board the NASA P-3 allows for a thorough analysis of aerosol-cloud interactions in the SEA. The FPDR - PDI provides unique cloud microphysical observations of individual cloud drop arrivals allowing for the computation of a variety of microphysical cloud properties including individual drop size, cloud drop number concentration, cloud drop size distributions, liquid water content, and cloud thickness. The FPDR - PDI measurement technique also provides droplet spacing and drop velocity information which is used to investigate turbulence and entrainment mixing processes. These observations were made via sawtooth legs (providing vertical structure) and horizontal level legs (providing information on the cellular size and structure) of the SEA MSc deck. Here we present a statistically summary of cloud properties (thickness, cloud drop size distribution, liquid water content, effective radius, total cloud drop number concentration, and more) over the SEA for the full ORACLES project. Cloud microphysical properties are then sorted by aerosol observations (below and/or in-cloud CCN, CO and CO₂ in cloud, above cloud AOD, and more) to investigate aerosol-cloud interactions.