NASA scientists have opened a new window for understanding atmospheric water vapor, its implications for climate change, and ozone depletion. The scientists have created the first detailed map of water containing heavy hydrogen and heavy oxygen atoms in and out of clouds, from the surface of Earth to some 25 miles upward, to better understand the dynamics of how water gets into the stratosphere. Only small amounts of water reach the arid stratosphere, 10 to 50 kilometers (6 to 25 miles) above Earth, so any increase in the water content could potentially lead to destruction of some ozone-shielding capability in this part of the atmosphere. This could produce larger ozone depletions over the North and South Poles as well as at mid-latitudes. Water shapes Earth's climate. The large amount of it in the lower atmosphere, the troposphere, controls how much sunlight gets through to the planet, how much is trapped in our skies, and how much goes back out to space. Higher in the stratosphere, where most of the Earth's ozone shield protects the surface from harmful ultraviolet rays, there is very little water (less than .001 of the surface concentration). Scientists don't fully understand how air is dried before it gets to this region.

In the troposphere, water exists as vapor in air, as liquid droplets in clouds, and as frozen ice particles in high altitude cirrus clouds. Since there is so much water closer to Earth and so few miles above, it is important to understand how water enters and leaves the stratosphere. The "isotopic content," the natural fingerprint left by the heavy forms of water, is key to understanding the process. An isotope is any of two or more forms of an element having the same or very closely related chemical properties and the same atomic number, but different atomic weights. An example is oxygen 16 versus oxygen 18-- both are oxygen, but one is heavier than the other.

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