Contrails and volcanic ash

This Envisat image, acquired on 24 May 2011, shows a large cloud of ash north-east of Scotland that has been carried by winds from Iceland’s Grímsvötn volcano about 1000 km away. The Grímsvötn volcano, located in southeast Iceland about 200 km east of Reykjavik, began erupting on 21 May for the first time since 2004.

About 800 km south of the ash cloud, numerous aircraft condensation trails, or 'contrails', are visible south of Ireland. Exhaust emissions from jet aircraft contain large amounts of water vapour, which, under certain atmospheric states, will condense to form ice crystals. These act as condensation nuclei around which even more water vapour in the surrounding air condenses. The end result is the formation of an elongated cloud-like condensation trail in the sky.