Thursday, September 6, 2012

Noctilucent clouds indicate more methane in upper atmosphere

Noctilucent clouds [credit: NASA]

The inner solar system is littered with meteoroids of all shapes and sizesfrom asteroid-sized chunks of rock to microscopic specks of dust. Every day Earth scoops up tons of the material, mostly the small stuff. When meteoroids hit our atmosphere and burn up, they leave behind a haze of tiny particles suspended 70 km to 100 km above Earth's surface.

Inside the meteor smoke zone, at a height of 83 km, so-called noctilucent clouds can occur, describes a NASA article. Meteor dust is the nucleating agent around which such clouds form. Specks of meteor smoke act as gathering points where water molecules can assemble themselves and grow into ice crystals to sizes ranging from 20 to 70 nanometers.

While noctilucent clouds appear most often at Arctic latitudes, they have been sighted in recent years as far south as Colorado, Utah and Nebraska. Question is: Why are the clouds brightening and spreading?

Prof. James Russell of Hampton University believes that more in methane in the atmosphere is causing this. Russell explains: "When methane makes its way into the upper atmosphere, it is oxidized by a complex series of reactions to form water vapor. This extra water vapor is then available to grow ice crystals for noctilucent clouds."

In conclusion, this greater occurrence of octilucent clouds is an indication that more methane is escaping into the upper atmosphere.

Graphic prepared by Prof. James Russell of Hampton University showing how methane, a    
greenhouse gas, boosts the abundance of water at the top of Earth's atmosphere. This water
then freezes around "meteor smoke" to form icy noctilucent clouds.              [Credit:  NASA] 

Below, a new ScienceCast video explains how "meteor smoke" seeds noctilucent clouds.