Progress in the quantification of aerosol-cloud interactions estimated from the CALIPSO-CloudSat-Aqua/MODIS record

Abstract. Aerosol-cloud-precipitation interactions are assessed over the non-polar ocean from more than 11 years of combined Aqua-MODIS, CALIPSO-CALIOP, and CloudSat products. The analysis first shows the benefit of incorporating vertically resolved aerosol extinction coefficient (σ_ext) in aerosol-cloud interactions (ACI) assessments, demonstrating that: σ_ext vertically collocated with the cloud layer correlates best with cloud droplet number concentration (N_d), column-integrated aerosol optical depth (AOD) cannot explain the N_d variability in the extratropics, and the S-shape of the AOD-N_d relationship reported in previous studies is an unphysical feature that arises from using AOD as aerosol proxy over oceanic regions.

ACI metric, estimated as the log-scale regression between σ_ext vertically collocated with the cloud layer (σ_exi^CL) and MODIS N_d reveals that the eastern Pacific is the region with the strongest ACI, followed by the Southern Ocean. The susceptibility of clouds to changes in their liquid water path (LWP) and frequency of precipitation followed a 2-step calculation by combining the N_d-σ_exi^CL regression (ACI) with the regression between these macrophysical variables and N_d.LWP susceptibility is negative (LWP decreases with aerosol loading), and statistically significant over the eastern Pacific, eastern Atlantic, and extratropics. In contrast, vast areas of the tropical and subtropical ocean feature negligible changes in LWP with aerosol. Precipitation frequency susceptibility is negative, but the values are only significant over the coastal eastern Pacific and Atlantic. The findings suggest that previous modeling assessments relying on AOD may need to be revisited by taking advantage of the synergy between passive and active sensors.