Near-real time ozone forecasting made possible ...( Up in the stratosphere about 25 km abov...),Health

Up in the stratosphere about 25 km above our heads is the ozone layer. Stratospheric ozone absorbs up to 98% of the Sun's harmful ultraviolet light making the difference between a suntan and sunburn, and safeguarding all life on Earth. But chemical activity in the stratosphere ultimately due to the presence of manmade gases such as chlorofluorocarbons (CFCs) can thin the ozone layer.

The Brussels-based Belgian Institute for Space Aeronomy (BIRA-IASB from its initials in Flemish and French) has developed a service called the Belgian Assimilation System of Chemical Observations from Envisat (BASCOE) that maps and forecasts not only the concentration of ozone in the stratosphere but also 56 other chemical species, including those responsible for ozone depletion.

BASCOE relies on an instrument aboard Envisat called the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). It works day and night to measure infrared emissions from the Earth's 'limb' the narrow band of atmosphere between the planetary surface and empty space. Emissions along certain wavelengths work like signatures, indicating the presence of specific atmospheric chemicals.

MIPAS has the capability to measure up to 30 trace gas species, but for the time being only a subset of them is provided by the ESA ground segment operationally to the user community. The others whose concentrations are forecast by BASCOE have their presence calculated indirectly, by assimilating MIPAS level 2 products into a complex computer model of stratospheric chemistry processes developed by BIRA-IASB. The resultant analyses are available within a day.

"The stratosphere is one of the best-understood areas of atmospheric chemistry, a fact which makes the BASCOE model possible," explained Dominique Fonteyn of BIRA-IASB. "In fact this model predates the launch of Envisat, and was originally intended simply as a summary of our existing understanding of stratospheric chemistry. But the l
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Contact: Claus Zehner
claus.zehner@esa.int
39-069-418-0544
European Space Agency
3-Nov-2003

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