Analyses of Virtual Ship-Tracks Systematically Underestimate Aerosol-Cloud Interactions Signals

Abstract

Ship-tracks are important natural/opportunistic experiments to study aerosol-cloud interactions (ACIs). However, detectable ship-tracks are not produced in many instances. Virtual ship-tracks have been conceived to expand the scale of ACIs analyses. Cloud responses in virtual ship-tracks differ strongly from those of detected ones. Here we show that the current approach of virtual ship-tracks can lead to systematic biases and errors and suggest necessary improvements. Errors in trajectory modeling introduce mismatches between areas actually affected by ship-emissions and virtual ship-track locations, that is, positional errors. Positional errors systematically underestimate ACI signals and the underestimate is severe as indicated by analysis of cloud droplet number concentration changes. The assumption of fixed ship-track width also systematically diminishes resulting aerosol effects by more than 10%, which leads to a forcing difference of around 0.1 Wm⁻². We make suggestions to improve the simulation of virtual ship-tracks so that their full potential for studying ACIs can be unleashed.