Aerosol–Radiation–Cloud Interactions over the Southeast Atlantic: Preliminary Results from Recent Aircraft and Surface-Based Measurements (Invited Presentation)

The remote southeast Atlantic seasonally hosts expansive shortwave-absorbing aerosol layers overlying and sometimes mixing into an equally expansive low cloud deck. The climatically-significant region is home to intriguing aerosol-cloud-radiation interactions with unique impacts on our planet, interactions that have until recently been poorly observed. This changed in 2016 with the NASA ORACLES (ObseRvations of Aerosols Above Clouds and Their IntEractionS) deployment of two aircraft to Namibia in September, and the 17-month-long DOE LASIC (Layered Atlantic Smoke Interactions with Clouds) ARM Mobile Facility deployment to Ascension Island, approximately midway between continental Africa and South America at 8S, beginning in June. In August of 2017, ORACLES based itself in Sao Tome, in the Gulf of Guinea, the UK CLARIFY aircraft project on Ascension Island, and the French AeroClo-SA project in Namibia. An early finding is significant synoptic-scale oscillations in the presence and amount of absorbing aerosols within the boundary layer, with increased boundary-layer loadings present to the north at Ascension Island. The boundary-layer loading is clearly elevated in August relative to September. Free-tropospheric aerosol, when present, is often clearly touching the cloudy boundary layer top at Ascension, and less so to the south in September, although more than initially anticipated. Conditions between the September, 2016 and August, 2017 aircraft deployments will be contrasted and put into context with the 17-month-long LASIC measurements. A model-observational comparison exercise will also be discussed. This presentation reflects the work of the entire ORACLES and LASIC Science Teams.