Coarse particle and derived ice nuclei concentrations in the northern and southern subtropical middle troposphere

Satellite-based climatologies reveal that mineral dust aerosol increases south-to-north across the intertropical convergence zone. The south-to-north aerosol gradient, combined with the propensity of mineral dust to nucleate ice at a relatively warm temperature, indicate that clouds within the subtropics could be impacted. A statistical investigation of the south-to-north aerosol contrast was conducted by analyzing coarse mode aerosol concentration measurements, a surrogate for mineral dust, sampled above a southern hemisphere and a northern hemisphere subtropical marine boundary layer. Coarse mode concentrations were obtained from an optical particle counter operated on the NCAR C-130 during two summer-season projects (VOCALS and ICET). The coarse particle concentration values were also input into the DeMott et al. (2010) parameterization and ice nuclei concentrations were derived. A temperature-dependent ice nuclei spectrum is derived for both regions.