Satellite instrument helps tackle mysteries of ozone-eating clouds(Forwarded)

ESA News
http://www.esa.int

10 April 2006

Satellite instrument helps tackle mysteries of ozone-eating clouds

Polar stratospheric clouds have become the focus of many research projects
in recent years due to the discovery of their role in ozone depletion, but
essential aspects of these clouds remain a mystery. MIPAS, an instrument
onboard ESA's Envisat, is allowing scientists to gain information about
these clouds necessary for modelling ozone loss.

"The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) is
unique in its possibilities to detect polar stratospheric clouds (PSCs)
since it is the first instrument with the ability to observe these clouds
continuously over the polar regions especially during the polar night,"
Michael Höpfner of Germany's Forschungszentrum Karlsruhe GmbH said.

Using data collected by MIPAS, a German-designed instrument that observes
the atmosphere in middle infrared range, Höpfner and other scientists
discovered a belt of nitric acid trihydrate (NAT) PSCs developing in the
polar night over Antarctica in 2003 about one month after the first PSCs,
which were composed of water crystals, were detected.

There are two classifications of PSCs -- Type I clouds contain hydrated
droplets of nitric acid and sulphuric acid, while Type II clouds consist
of relatively pure water ice crystals.

The presence of NAT was detected because of MIPAS' ability to map the
atmospheric concentrations of more than 20 trace gases, including ozone as
well as the pollutants that attack it.

"This has been the first evidence for the existence of NAT PSCs on a large
scale," Höpfner said. NAT particles, which contain three molecules of
water and one molecule of nitric acid, enhance the potential for ozone
destruction in polar regions.

The thinning of the ozone is caused by the presence of man-made pollutants
in the atmosphere such as chlorine, originating from man-made pollutants
like chlorofluorocarbons (CFCs). During the southern hemisphere winter,
temperatures drop to very low levels causing the chemicals in the
stratosphere, which is in complete darkness during the winter, to freeze
and form PSCs that contain chlorine.

Now banned under the Montreal Protocol, CFCs were once widely used in
aerosol cans and refrigerators -- and have not vanished from the air. CFCs
themselves are inert, but ultraviolet radiation high in the atmosphere
breaks them down into their constituent parts, which can be highly
reactive with ozone.

As the polar spring arrives, sunlight returns and creates chemical
reactions in PSCs responsible for converting benign forms of chlorine into
highly ozone-reactive radicals that spur ozone depletion. A single
molecule of chlorine has the potential to break down thousands of
molecules of ozone.

NAT PSCs enhance the potential for chlorine activation and can also
sediment and irreversibly remove nitrogen from the lower stratosphere,
causing a process known as denitrification, which slows the return of
chlorine to its inactive form and allows for ozone destruction to
continue.

Höpfner and fellow scientists were able to explain the sudden NAT
formation of PSCs in 2003 by temperature disturbances in waves over the
Antarctic Peninsula and the Ellsworth Mountains, suggesting a more
significant role for mountain waves in the formation of Antarctic's PSCs
than previously thought.

According to Höpfner, the presence of PSCs could intensify in the future
due to a globally changing climate where the Earth's surface gets warmer
due to trapped greenhouse gases but the stratosphere gets colder,
providing an environment in which the clouds can form. An increase in PSCs
could counteract the recovery of the ozone layer.

Although scientific efforts have focused on determining PSC composition
and their formation mechanisms, the process causing the ozone depletion is
far from understood. In order to gain a better understanding of ozone
depletion, scientists must continue obtaining data which allows them to
measure the key species involved in the process.

Related news

* South Polar ozone hole makes big comeback
http://www.esa.int/esaCP/SEM712A5QCE_index_0.html
* Envisat witnesses return of the South Polar ozone hole
http://www.esa.int/esaCP/SEM3B90XDYD_index_0.html
* Near-real time ozone forecasting made possible by Envisat
http://www.esa.int/esaCP/SEMR9DWLDMD_index_0.html
* Envisat observes resurgent ozone hole
http://www.esa.int/esaCP/SEMH5K0P4HD_index_0.html

Related missions

* Envisat
http://www.esa.int/esaEO/SEMWYN2VQUD_index_0_m.html

Related links

* Forschungszentrum Karlsruhe GmbH
http://www.fzk.de

[NOTE: Images supporting this release are available at
http://www.esa.int/esaCP/SEMBZNNFGLE_index_1.html ]