Storms in the summer of thin ozone layer

About the temperate latitudes of the northern hemisphere, the ozone layer suffers from summer storms. High water vapor penetrates surprisingly flung far into the stratosphere.

Severe summer storms thin the protective ozone layer over the temperate regions of the Northern Hemisphere. The storm systems hurl water vapor up to 20 kilometers altitude and triggering the chain reaction that breaks down the ozone. This has been identified by U.S. researchers of survey flights and models. After a storm, could disappear within a week a quarter to a third of the ozone in the stratosphere. This zone extends then thinned by more than 100 kilometers.


The favorable conditions for this ozone depletion are already surprisingly common: The team led by atmospheric chemist James Anderson had analyzed data on water vapor in the atmosphere, which were collected by the U.S. space agency NASA for flights over the United States. In the researchers report in the journal "Science".

Could be due to climate change, this ozone depletion intensify in the future, the researchers warn. For the warmer atmosphere contains more water vapor. Because a thinner ozone layer allows more harmful ultraviolet rays of the sun, so that could also increase the risk of skin cancer in the densely populated regions of the northern hemisphere.

Sufficient chlorine in the atmosphere

"The idea that the ozone layer will soon be recovered, is a clear error of judgment," say James Anderson of Harvard University in Cambridge and his colleagues. Although we have limited the release of chlorofluorocarbons and other ozone depleting substances halogen compounds become strong. But still sufficient chlorine is available from these compounds in the atmosphere. Water vapor can come to this under certain conditions, the ozone depletion in the stratosphere ahead.

Destroys the ozone, a combination of three oxygen atoms, called by chlorine radicals. This extremely aggressive form of chlorine to the ozone steals an oxygen atom, turning it into ordinary oxygen gas (O 2 microns). The chlorine radicals are formed when precursors attach to tiny, sulfur-containing water droplets in the atmosphere. UV-light and very low temperatures then start a chain reaction destroying ozone.

Favourable conditions to prevail generally above all by the Arctic and Antarctic. Anderson and his colleagues have now found, however, that even in storms over temperate latitudes may arise such chlorine radicals.

Effects of additional water vapor

"The key is the combination of water vapor and temperature," the researchers explain. After starting at about twelve parts of water vapor per million particles of air (parts per million, ppm) of ozone depleting chain reaction run at temperatures that existed in the temperate latitudes of the northern hemisphere summer.

The researchers analyzed the mathematical model could have the consequences of the additional water vapor. Usual for a summer day in the U.S. was 14 hours and 10 hours of sun night and five parts water per million units of volume (ppmv) in the lower stratosphere 15-20 km altitude. "In the case of 12 ppmv were lost 13 percent of ozone during the first four days. At 18 ppmv compared to 21 percent," the researchers write. The affected layer contains about one-fifth of the amount of ozone that is included during a U.S. summer throughout the stratosphere.

Threshold is exceeded regularly

Where does the additional water vapor is, the measurements indicated by research aircraft: Large storm systems of 50 or more kilometers in extent, therefore producing such a large wake that they can hurl water vapor from the lower layers of air up to 20 kilometers altitude. In about 50 percent of survey flights you have registered such a steam-rich conditions.

"Given the measured values is clear that the threshold for the formation of chlorine radicals in the summer across the United States and other temperate regions is also likely to be exceeded on a regular basis," say the researchers. More detailed measurements are now needed to determine the extent and duration of ozone loss in more detail.