Ship trails and ship induced cloud dynamics

A combination of satellite image analysis and numerical cloud modeling has provided new insight into how ship trails are formed and why they occur where they do. The cold ocean waters and shallow marine boundary layers in the East Pacific, and in the North Atlantic make these regions particularly sensitive to cloud formation triggered by heat releases over the ocean. This heat may be released directly from the ships engines and by latent heat released from the cloud condensation nuclei (CCN) to cloud droplet formation process. Detailed image analysis of an exceptionally high resolution photograph of ship trails observed by the Apollo-Soyuz mission in July 1975 shows that these ship trails began as a brightening of background marine stratocumulus and eventually grew to a point where the ship trails generated a plume like structure with clear regions on both sides. A numerical cloud model was constructed with initial meteorological conditions similar to those observed by ships in a nearby region of the ocean. A heat input of 30 MW produced a similar ship-trail cloud behavior to that observed in the photograph after a 1-h simulation time.