Maritime Aerosol and CCN Profiles Derived From Ship-Based Measurements Over Eastern North Pacific During MAGIC

Abstract

Atmospheric aerosols are widely recognized to give rise to a substantial radiative forcing to the climate by scattering and absorbing radiation and by modifying the microphysical, lifetime, and radiative properties of clouds. During the Marine ARM GPCI Investigation of Clouds (MAGIC) over the Eastern North Pacific (ENP), the ship-based measured cloud condensation nuclei (CCN) concentration at 0.2% supersaturation (NCCN,0.2) and condensation nuclei concentration (NCN) had mean values of 116.7 and 219.4 cm−3, with the highest concentrations found closest to LA due to an increase in aerosol sources. Moving westward, both NCCN,0.2 and NCN gradually decreased until stabilizing near 100 cm−3 and 200 cm−3, respectively. Using the methods proposed by Ghan and Collins (2004), https://doi.org/10.1175/1520-0426(2004)021<0387:uoisdt>2.0.co;2 and Ghan et al. (2006), https://doi.org/10.1029/2004jd005752, NCCN,0.2 profiles are retrieved using the surface measured NCCN,0.2 as a constraint. For coupled conditions, correlations between the retrieved NCCN,0.2 profiles and cloud-droplet number concentration (NC) increase from 0.26 at the surface to 0.38 near cloud base, particularly true for non-drizzling clouds. Although the correlations are lower than expected, the percentage increase (46.2%) is encouraging. Finally, the relationships between cloud breakup (CB) and the stratocumulus to cumulus transition (SCT) with environmental conditions and associated aerosols are also studied. The decreased NCN trend east of CB is mainly caused by precipitation scavenging, while the increased NCN trend west of CB is strongly associated with the increased surface wind speed and fewer drizzle events. A further study is needed using high-resolution models to simulate these events. © 2022 The Authors.