Tuesday, November 18, 2008

2008 - Ozone hole

The ozone hole does not persist year round. It forms every spring in the Southern Hemisphere (August and September), when sunlight begins to return to Antarctica after the months of polar darkness.

During the cold, dark winter, a vortex of winds encircles Antarctica.

This vortex isolates the air in the stratosphere from mixing with warmer air at higher latitudes.

In the extreme cold, unusual clouds, called polar stratospheric clouds, form, even though the air is very dry.

Within these clouds, chemically stable forms of chlorine and bromine (put into the atmosphere by people) are converted into less stable gases.

When the sunlight returns in the spring, ultraviolet light breaks the less-stable chlorine and bromine gases into free chlorine and bromine atoms that catalyze ozone destruction.

Ozone concentrations thin throughout August and into September or October.

As Southern Hemisphere spring progresses, temperatures climb, and the vortex of winds that isolated the Antarctic stratosphere weakens.

Ozone-destroying chlorine and bromine gases disperse into the rest of the atmosphere.

Ozone destruction ceases for the year, and ozone levels begin to rebuild throughout the summer.

Although the ozone hole is not the cause of global warming, the two man-made climate changes are related in other ways.

The destruction of ozone has caused the Antarctic stratosphere to be cooler than it would normally be in the summer and fall.

Models and observations indicate that the cooling intensifies the vortex of winds that isolate frigid Antarctic air from warmer air from higher latitudes.

Ozone-hole-related cooling may be the reason why interior Antarctica has not warmed up as fast as most of the rest of the planet due to global warming.

NASA scientists are using data from satellites like Aura along with computer simulations of atmospheric chemistry and global climate to predict how recovery of the ozone hole could accelerate Antartic warming


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