Fig. 4
Susceptibilities for different CCN proxies. Susceptibilities based on aerosol optical depth (AOD), aerosol index (AI), and cloud condensation nuclei (CCN) column number (\({N}_{{\rm{ccn}}}\)) for global ocean data and for the regions defined by Quaas et al.39: North Pacific Ocean (NPO), Tropical Pacific Ocean (TPO), South Pacific Ocean (SPO), Southern Indian Ocean (SIO), South Atlantic Ocean (SAO), Tropical Indian Ocean (TIO), Tropical Atlantic Ocean (TAO), and North Atlantic Ocean (NAO). Solid bars are based on the full range of \({N}_{{\rm{ccn}}}\), AI, and AOD values while transparent bars only use the ranges \({N}_{{\rm{ccn}}}\,> \, 1{0}^{7}{\rm{cm}}^{-2}\), AI \(> \) 0.05, and AOD \(> \) 0.07, respectively. Error bars indicate the standard error (2\(\sigma\)) of the linear regression and do not include the systematic error term of (+0.06 for \({S}_{{\rm{ccn}}}^{{\rm{opt}}}\)) that follows from the simulator. The number of aerosol-\({N}_{{\rm{d}}}\) pairs are indicated for proxy above the bars.
