PNNL

Abstract

The abundance and sources of ice nucleating particles (INPs), particles required for heterogeneous ice nucleation, are long-standing sources of uncertainty in quantifying aerosol-cloud interactions and the resulting radiative feedbacks. In this study, data from two observation campaigns dedicated to characterizing INPs associated with sea spray aerosol (SSA) and other sources were used to evaluate the current capabilities for numerically estimating number concentrations of INPs (nINPs) in remote marine environments in a global model. Aerosols simulated by the Community Atmospheric Model (CAM5) with constrained meteorology successfully reconstructed observed aerosol mass and surface area concentrations during field studies conducted at the Mace Head Research Station (MHD, North Atlantic) and over the Southern Ocean to the south of Tasmania (CAPRICORN). Accounting only for SSA and mineral dust contributions via existing parameterizations, simulated nINPs were within a factor of 10 of nINPs observed with an offline ice spectrometer at MHD and CAPRICORN, for 93% and 69% of observations, respectively, demonstrating model-observation closure for both studies. Exploring annual simulated vertical profiles of nINPs over MHD and CAPRICORN revealed that mineral dust INPs may be critical to INP populations above 3-5 km in remote locations, particularly during non-winter months. The interplay between mineral dust and SSA demonstrated by these experiments indicates a need for future studies dedicated to constraining INP abundance and composition at altitudes relevant for mixed-phase clouds in remote marine regions.