The top of the atmosphere

Atmospheric gases scatter blue wavelength of visible light more than other wavelengths, giving the Earth's visible edge a blue halo. At higher points the atmosphere becomes so thin that it ceases to exist. The image shows the translucent moon emerging from behind the halo.

There is no dividing line as such between Earth's atmosphere and space, but it is useful for the scientist who study the balance of the incoming and outgoing energy of the Earth. They conceptually think of the altitude of 100 kilometers above the Earth as the "top of atmosphere". The top of the atmosphere is the place where solar energy enters the Earth's atmosphere and the thermal radiations from Earth release. So, the balance of incoming and the outgoing energy determines the Earth's temperature. The ability of the Greenhouse gases to change this balance by reducing the amount of thermal energy exiting is called as The Global Warming.

Greenhouse gases are not the only part of the Earth's system that affects the balance. The percent of the incoming sunlight that Earth reflects ( called as 'albedo' ) is also one of the influential factor. Clouds over Earth's surface, snow, ice are highly affected by the Earth's reflection.

Because snow and ice are so reflective, scientists have long expected that melting of snow and ice in the polar regions will accelerate climate warming by reducing the Earth’ albedo. Atmospheric scientist Seiji Kato of NASA’s Langley Research Center and several teammates have used a suite of NASA and NOAA (National Oceanic and Atmospheric Administration) satellite observations to investigate whether this feedback is already underway. The team compared reflected sunlight, clouds, and sea ice and snow cover at polar latitudes from 2000-2004. What they found was a bit of a surprise: while snow and ice in the Arctic declined, the albedo didn’t change.

The above picture was acquired on July 20,2006 with Kodak 760C digital camera having 400 mm lens by the Image Science & Analysis Laboratory, Johnson Space Center. The International Space Station Program supports the astronauts to take the picture of Earth that will be of great value for scientists and for public.