An overview of the ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) project: aerosol-cloud-radiation interactions in the Southeast Atlantic basin
Authors: Redemann Jens , Wood Robert , Zuidema Paquita , Doherty Sarah J. , Luna Bernadette , LeBlanc Samuel E. , Diamond Michael S. , Shinozuka Yohei , Chang Ian Y. , Ueyama Rei , Pfister Leonhard , Ryoo Ju-me , Dobracki Amie N. , da Silva Arlindo M. , Longo Karla M. , Kacenelenbogen Meloë S. , Flynn Connor J. , Pistone Kristina , Knox Nichola M. , Piketh Stuart J. , Haywood James M. , Formenti Paola , Mallet Marc , Stier Philip , Ackerman Andrew S. , Bauer Susanne E. , Fridlind Ann M. , Carmichael Gregory R. , Saide Pablo E. , Ferrada Gonzalo A. , Howell Steven G. , Freitag Steffen , Cairns Brian , Holben Brent N. , Knobelspiesse Kirk D. , Tanelli Simone , L'Ecuyer Tristan S. , Dzambo Andrew M. , Sy Ousmane O. , McFarquhar Greg M. , Poellot Michael R. , Gupta Siddhant , O'Brien Joseph R. , Nenes Athanasios , Kacarab Mary E. , Wong Jenny P. S. , Small-Griswold Jennifer D. , Thornhill Kenneth L. , Noone David , Podolske James R. , Schmidt K. Sebastian , Pilewskie Peter , Chen Hong , Cochrane Sabrina P. , Sedlacek Arthur J. , Lang Timothy J. , Stith Eric , Segal-Rozenhaimer Michal , Ferrare Richard A. , Burton Sharon P. , Hostetler Chris A. , Diner David J. , Platnick Steven E. , Myers Jeffrey S. , Meyer Kerry G. , Spangenberg Douglas A. , Maring Hal , Gao Lan 
Published: June 2020

Abstract. Southern Africa produces almost a third of the Earth’s biomass burning (BB) aerosol particles, yet the fate of these particles and their influence on regional and global climate is poorly understood. ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) is a five-year NASA EVS-2 (Earth Venture Suborbital-2) investigation with three Intensive Observation Periods designed to study key atmospheric processes that determine the climate impacts of these aerosols. During the Southern Hemisphere winter and spring (June-October), aerosol particles reaching 3–5 km in altitude are transported westward over the South-East Atlantic, where they interact with one of the largest subtropical stratocumulus subtropical stratocumulus (Sc) cloud decks in the world. The representation of these interactions in climate models remains highly uncertain in part due to a scarcity of observational constraints on aerosol and cloud properties, and due to the parameterized treatment of physical processes. Three ORACLES deployments by the NASA P-3 aircraft in September 2016, August 2017 and October 2018 (totaling ~350 science flight hours), augmented by the deployment of the NASA ER-2 aircraft for remote sensing in September 2016 (totaling ~100 science flight hours), were intended to help fill this observational gap. ORACLES focuses on three fundamental science questions centered on the climate effects of African BB aerosols: (a) direct aerosol radiative effects; (b) effects of aerosol absorption on atmospheric circulation and clouds; (c) aerosol-cloud microphysical interactions. This paper summarizes the ORACLES science objectives, describes the project implementation, provides an overview of the flights and measurements in each deployment, and highlights the integrative modeling efforts from cloud to global scales to address science objectives. Significant new findings on the vertical structure of BB aerosol physical and chemical properties, chemical aging, cloud condensation nuclei, rain and precipitation statistics, and aerosol indirect effects are emphasized, but their detailed descriptions are the subject of separate publications. The main purpose of this paper is to familiarize the broader scientific community with the ORACLES project and the data set it produced.