Cloud reflectivity is sensitive to atmospheric aerosol concentrations because aerosols provide the condensation nuclei on which water condenses. Increased aerosol concentrations due to human activity affect droplet number concentration, liquid water and cloud fraction, but these changes are subject to large uncertainties. Ship tracks, long lines of polluted clouds that are visible in satellite images, are one of the main tools for quantifying aerosol-cloud-interactions. However, only a small fraction of the clouds polluted by shipping show ship tracks.The invisible tracks project is developing a new method to quantify the effect of shipping on all clouds, showing a significant cloud droplet number increase and a more positive liquid water response when there are no visible tracks.

This project was funded by the EC. Grant no: 860100