26th October 1999
It has been well established that chlorine, put into the atmosphere by the use of chloroflurocarbons (CFCs), causes a large springtime ozone depletion in the southern hemisphere polar `vortex' (the Antarctic Ozone Hole) and a similar, but smaller, depletion in the Arctic. However, many uncertainties remain, especially concerning how this polar depletion contributes to observed ozone decreases at middle latitudes.
International agreements have now phased out the production of these ozone-depleting substances. This is expected to reduce atmospheric chlorine levels over the next 50 years or so, and to lead to a reduction in the size of the springtime Antarctic Ozone Hole on the same timescale. However, climate changes due to the increase in greenhouse gases, which will warm the lower atmosphere and cool the upper atmosphere, may delay this recovery. A more detailed knowledge of the chemistry and dynamics of the Antarctic polar vortex is necessary for accurate predictions of future ozone levels in a colder upper atmosphere.
A new observation platform has been developed with the transformation of the Russian stratospheric aircraft M55-Geophysica (formerly a military reconnaissance plane) into a flying laboratory with twelve complementary scientific instruments that can probe simultaneously the atmosphere. The project started under the auspices of the Italian Programme for Research in Antarctica (PNRA-Programma Nazionale di Ricerche in Antartide), which established in 1995 a collaboration with Myasishchev Design Bureau, the company which built the aircraft for the Russian Defence Ministry in 1988, for the modification of the aircraft and its exploitation in atmospheric research in the Antarctic area. PNRA is a programme of the Italian Ministry of University and Scientific and Technological Research. Since then the project has gained the interest and the contribution of other national and European Research Agencies such as ASI (Agenzia Spaziale Italiana), CNR (Consiglio Nazionale delle Ricerche), BMBF (Bundesministerium für Bildung, Wissenschaft, Forschung and Technologie), NERC (U.K. Natural Environment Research Council), Royal Society (U.K.), Observatory of Neuchatel (Switzerland), ESF (European Science Foundation), EU (European Union), which concurred in the development of new dedicated instrumentation and in the execution of intermediate campaigns.
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The Antarctic campaign of this new observation platform, named APE-GAIA (Airborne Polar Experiment - Geophysica Aircraft In Antarctica), was performed from the 15th of September to the 15th of October from the airport of Ushuaia in Argentina and will be completed in Seville (Spain) on the 28th of October. APE-GAIA was performed with the scientific direction of Dott. Bruno Carli of CNR and the technical direction of Ing. Giuseppe De Rossi of ENEA (Ente Nazionale nuove tecnologie per l’Energia e l’Ambiente).
The M55- Geophysica is an all-weather single seated stratospheric aircraft capable of operating even in severe environmental conditions (e.g. temperatures down to – 90 °C, cross winds at take-off and landing that are strong for such high-altitude aircraft) which reaches for about five hours up to an altitude of 21 km. These characteristics together with the possibility of housing a scientific payload of up to 1,500 kg in a volume of more than 10 m3 with 3 kWatt of power make the M-55 Geophysica an ideal platform for research in the upper troposphere and lower stratosphere.
Significant engineering work was necessary for the modification of the aircraft so that power, navigation data, mechanical interfaces, windows and inlets could be provided to all the instruments. Furthermore, each instrument was built and qualified to operate in the unpressurised aircraft at low temperatures with possible severe accelerations and vibrations.
The payload includes spectrometers for the analysis of the atmospheric chemical composition with remote sensing measurements from the ultraviolet to the far infrared, lidars for detection of the aerosols and in-situ instruments for the measurement of both the main atmospheric constituents for monitoring of depletion processes and tracer species for the identification of dynamical processes.
From Ushuaia the aircraft made five scientific flights. The flights were planned using daily forecasts of winds and temperatures in the atmosphere from 12 - 20 km for the selection of the flight objectives. With these forecasts the scientists predicted the most interesting phenomena within range of the Geophysica and planned the optimum time and path of the flight. In this way the aircraft flew trough the boundaries of the ozone hole several times during the month of operations, was able to sample filaments of air being stripped from the polar vortex and small regions of cold temperature caused at high altitudes by strong winds blowing at low altitudes over mountains on the Antarctic peninsula.
The polar vortex is the area of spiral movement of high altitude air masses that occurs over the polar region in the cold season as a consequence of the collapse of cold air and the gathering of new air from middle latitudes (where the Earth’s rotation has a stronger effect).
Several ground stations both in Latin America and in Antarctica have participated at the campaign with co-ordinated measurements performed during each scientific flight. These localised remote observations provide together with the coarse global picture of satellite measurements the background information for the correct collocation of the detailed measurements obtained with the aircraft instrumentation.
About 70 scientists, engineers and technicians have been operating in Ushuaia during the campaign, and almost as many at other locations have been involved in related activities of modelling, data analysis, auxiliary measurements and logistic organisation from a total of eleven countries (Italy, Russia, Germany, United Kingdom, Switzerland, Finland, Spain, Argentina, United States, Brazil, Chile).
The flights for the transfer of the aircraft from Moscow at 55° N to Ushuaia at 55° S and back have been used in the return leg to perform further scientific measurements that will provide a continuous detailed monitoring over a very wide latitude range.
The operational objectives of the Antarctic campaign have been fully met with accurate forecast of the phenomena, timely operation of both the aircraft and the instruments, and high quality of the acquired data.
Some first scientific results were available in real time during the campaign. These show the occurrence of large ice particles at 20 km altitude in the cold regions generated by orographic waves above the Antarctic mountains. Results from flights performed at the lower altitude of 14 km indicate a greater mixing of the polar vortex at this altitude compared to 18 km, which will allow greater transport of polar air to mid-latitudes.
The majority of the data will require, however, a more elaborate analysis process, and does not allow yet conclusive statements. A complete assessment of the acquired information will involve comparisons between the instruments and testing of consistency of the models with the observations. It is expected that the campaign will provide useful information on the processes controlling ozone in the atmosphere and will improve our estimate of Antarctic ozone recovery time after the phasing out of CFCs .
