Satellite imagery can often show us beauty on a grand scale. And some of the most amazing pictures of all are those of human activity. This incredible pattern of cloud trails across the sky was not left by airborne jets but by ships plowing their way across the Atlantic.
This recent NASA photo shows a section of the North Atlantic off the Portuguese coast. Across it, bright, narrow cloud trails of vapor called ship tracks trace the routes of ocean-going vessels as they make their way to distant ports.
Depending on atmospheric conditions, some clouds can be hundreds of miles long, each dissipating out from a fine point to soft, feather-like squiggle as they are dispersed by the wind.
How do the trails form?
Credit: NASA/Jeff Schmaltz, LANCE/EOSDIS Rapid Response
The cloud trails form when tiny water droplets in the air condense around pollution particles called sulfates that ships produce as an exhaust from burning fuel. The droplets of vapor that constitute these trails are much smaller than those in the low-lying ocean clouds, which form around salt particles.
Because of the way sunlight scatters through the smaller drops, ship tracks appear significantly brighter and thicker than ordinary clouds. This makes the network of trails stand out much more vividly against the dark sea.
The Less-Than-Beautiful Truth Behind Cloud Trails
Sadly, a report in 2008 reveals how the picture may not be as pretty as it first appears. Chemists from the University of California San Diego outlined how, on some days, sulfates from ship engines "account ... for nearly one-half of the fine, sulfur-rich particulate matter in the air known to be hazardous to human health."
Certainly then ship tracks are something worth keeping an eye on.
The images were captured by a device called the Moderate Resolution Imaging Spectroradiometer (MODIS) on board the Aqua satellite, which was launched by NASA in 2002. MODIS gathers all kinds of data — from sea level changes and snow cover to deforestation and wild fires — as part of the Earth Observing System, a long-term project that aims to give scientists and the public "an improved understanding of the Earth as an integrated system."