Measurements of Aerosol Particle Size Distributions and INPs Over the Southern Ocean in the Late Austral Summer of 2017 on Board the R/V <i>Mirai</i>: Importance of the Marine Boundary Layer Structure

The Southern Ocean (SO) is a unique region with rich ecosystems and minimal anthropogenic terrestrial natural impacts especially during austral summer. We conducted measurements sampling of aerosol particles to investigate the characteristics role in cloud formation on Japanese research vessel Mirai over SO late summer 2017. Observations air masses indicated that bimodal particle size distributions were mostly observed relative abundances two modes varied changes structure marine boundary layer (MBL) such as surface mixing layer. As local minimum diameter between (DH) considered critical for cloud-droplet activation MBL, we analyzed larger than DH (CNAcc) proxy condensation nuclei. Variations concentrations 300 nm accounted by sea-spray source function, whereas it substantially underestimated those CNAcc. This implies significance nonsea-spray sources CNAcc MBL SO. ice nucleating (NINPs) active at −25°C 20–100 m−3, consistent recent observations summertime observational evidence very low NINPs (40–110 cm−3) wide area important predicting effects radiative properties balances using climate models.