Arctic Ozone levels down as much as 66%
4/5/2000-Ozone losses of over 66% have occurred in the Arctic stratosphere near 18km altitude during one of the coldest stratospheric winters on record. These losses are likely to affect the ozone levels over Europe during spring. This is one of the most substantial ozone losses at this altitude in the Arctic.The Arctic ozone hole first appeared in the mid-1990s, more than a decade after the Antarctic hole. Like its southern cousin, it forms as the Sun rises after the midwinter night. Solar radiation triggers reactions between ozone in the stratosphere and chemicals containing chlorine or bromine. These occur fastest on the surface of ice particles in clouds, which only form in the polar stratosphere at temperatures below 80 °C.
"This year is most unusual.
Temperatures have been consistently as low as ever recorded in the Arctic
stratosphere," says Neil Harris, head of the European Ozone Research
Coordinating Unit in Cambridge. "There have been polar stratospheric clouds
since the end of November and we are already seeing ozone destruction."
"These losses are likely to affect the ozone levels over Europe during spring. This is one of the most substantial ozone losses at this altitude in the Arctic," said Scientists taking part in the ozone experiment, a joint initiative by America's National Aeronautics and Space Administration (NASA), the European Ozone Research Coordinating Unit, based in Cambridge, and the European Union's research directorate in a statement issued 4April2000. An Arctic " low ozone event" could easily be blown south by high-altitude winds, and appear over populated areas of The United States, Canada, Europe and the northern regions of Britain.The ozone layer in the upper atmosphere is the key filter for damaging ultraviolet-B (UV-B) radiation in the Sun's rays. Without it, organisms suffer extensive DNA damage, which in humans results in a greater increase in the risk of skin cancer, eye cataracts and defects in the body's immune system.
Ozone losses of over 60% have occurred in the Arctic stratosphere near 18km altitude during one of the coldest stratospheric winters on record. These losses are likely to affect the ozone levels over Europe during spring. This is one of the most substantial ozone losses at this altitude in the Arctic. Measurements from the largest international campaign ever investigating stratospheric ozone depletion have provided more insight into the processes that control stratospheric ozone. They have also reinforced concerns that the Arctic ozone may continue to decline despite the benefits of reductions in stratospheric chlorine levels (a result of the Montreal Protocol), due to the global climate change. Research Commissioner Philippe Busquin points out that "European cooperation within an international team has made it possible to achieve these research results. They will provide the best possible scientific advice to the regulatory process concerning ozone depleting substances in the framework of the Montreal Protocol and, equally important, to the citizens".
During the 1999/2000 winter, the Third European Stratospheric Experiment on Ozone (THESEO 2000) sponsored by European Union and the NASA sponsored SAGE III Ozone Loss and Validation Experiment (SOLVE) obtained measurements of ozone and other atmospheric gases and particles using satellites and aircrafts, large, small and long duration balloons, and ground-based instruments.
Scientists from Europe, the United States, Canada, Russia and Japan joined forces in mounting the biggest field measurement campaign yet to measure ozone amounts and changes in the Arctic stratosphere. The total amount of information collected by the THESEO 2000/SOLVE campaign is more extensive than any information collected by past polar measurement campaigns. Most of the measurements were made near Kiruna, Sweden, with additional measurements being made from satellites and through a network of stations at mid and high northern latitudes.
During the winter of 1999-2000 large ozone losses were observed inside the Arctic stratospheric polar vortex. These ozone losses in the lower stratosphere have been observed by a number of European techniques based on ozonesondes and ground-based measurements developed in the past decade. At altitudes around 18km cumulative losses of over 60% have occurred between January and March. These are among the largest chemical losses at this altitude observed during the 1990s. The effect on column ozone was slightly mitigated by the fact that ozone loss was less dramatic above 20 km altitude. Satellite observations (eg. by the ESA Global Ozone Monitoring Experiment GOME) showed a clear ozone minimum over the polar region during February and March. The average polar column amount of ozone for the first 2 weeks of March was 16% lower than observed in the 1980's.
The mixing of polar air into middle latitudes, both during the winter and as the polar vortex broke down in late March, influences ozone levels over the populated middle latitudes. Dilution of ozone-depleted air into middle latitudes is a major contributor to the long-term mid-latitude ozone decline, along with other chemical and dynamical processes. In March 2000, the World Meteorological Organisation Mapping Centre at the University of Thessaloniki reported that the mean column ozone amounts over Europe were 15 % below the pre-1976 average.
Results from THESEO 2000/SOLVE have reinforced the scientific concern that the recovery of the ozone layer may be delayed. Cooling of the stratosphere could be caused by increasing concentrations of greenhouse gases, by reduced concentrations of ozone in the stratosphere, or by changes in the dynamics of the stratosphere. Even as the stratospheric concentrations of chlorine and bromine decline, such a cooling and, possibly, a more stable Arctic vortex are currently predicted to prolong Arctic ozone depletion.
For further information
More information, including a list of participating institutions, can be found at the Theseo 2000 and Solve web sites:
You may also contact the following people:
NASA Press Release
RELEASE NO: 00-39
NASA-EUROPEAN CAMPAIGN OBSERVES SIGNIFICANT ARCTIC OZONE LOSS
Ozone losses of over 60 percent have occurred in the Arctic stratosphere near 60,000 feet (18 km) in one of the coldest winters on record. This is one of the worst ozone losses at this altitude in the Arctic.
Investigations into the Arctic stratosphere have provided better insights into the processes that control polar ozone. These insights considerably add to our ability to predict ozone levels in the future as chlorine levels decline as a result of the Montreal Protocol, and as greenhouse gases increase. Climate change in the stratosphere will likely enhance ozone losses in the Arctic winter in the coming decades as chlorine levels decrease.
During the 1999/2000 winter, the NASA sponsored SAGE III Ozone Loss and Validation Experiment (SOLVE) and European Union sponsored Third European Stratospheric Experiment on Ozone (THESEO-2000) obtained measurements of ozone, other atmospheric gases, and particles using satellites, airplanes, large, small and long duration balloons, and ground-based instruments. NASA, along with the National Oceanic and Atmospheric Administration (NOAA), the National Science Foundation (NSF), and several universities, worked jointly on the SOLVE mission.
Scientists from the United States joined with scientists from Europe, Canada, Russia and Japan in mounting the biggest field measurement campaign yet to measure ozone amounts and changes in the Arctic stratosphere. The activities were conducted from November 1999 through March 2000. The total amount of information collected by the SOLVE/THESEO 2000 campaign is greater than the information collected in any past polar measurement campaign. Most of the measurements were made near Kiruna, Sweden with additional measurements being made from satellites and a network of stations at mid and high northern latitudes.
During the winter of 1999-2000 large ozone losses were observed in the Arctic stratosphere. These lower stratospheric ozone losses were observed by a number of instruments and techniques, including a National Oceanic and Atmospheric Administration ozone instrument aboard the high altitude NASA ER-2 aircraft. "Measurements from the NASA ER-2 show ozone in the Arctic region decreasing by about 60 percent between January and mid-March," said ER-2 co-project scientist Dr. Paul A. Newman of NASA’s Goddard Space Flight Center, Greenbelt, Md.
These measurements are comparable to the large chemical losses at this altitude observed in several winters in the mid-1990s. The effect on total column ozone was slightly mitigated by the fact that reductions in ozone were smaller above 66,000 feet (20 kilometers). Spacecraft observations by NASA's Total Ozone Mapping Spectrometer-Earth Probe showed a clear ozone minimum over the polar region during February and March. The average polar column amounts of ozone for the first two weeks of March were 16 percent lower than observed in the early 1980's.
Polar stratospheric clouds (PSCs) are necessary for the conversion of chlorine from benign molecular forms into the chlorine monoxide molecule which directly destroy ozone. PSCs were observed over very extensive portions of the Arctic region from early December to early-March. "We were somewhat surprised to see PSCs so early in December," said Dr. Mark Schoeberl, who was the SOLVE co-project scientist for observations made from NASA’s DC-8 aircraft. "Some of the PSC types and their locations which we observed in December did not fit within our current understanding." The last PSCs were observed on March 8 by instruments aboard the DC-8, and on March 15 by satellite.
The polar stratosphere temperatures were extremely low over the course of this last winter. PSCs can only form in these low temperature regions. At 66,000 feet on Jan. 28, the area covered by temperatures low enough to form PSCs was 5.7 million square miles (14.8 million square kilometers), which is larger than the United States. This is the largest area coverage recorded in over 40 years of Northern Hemisphere stratospheric analyses.
"The polar stratospheric clouds covered a larger area, and persisted for a longer period of time, than for any other Arctic winter during the past 20 years. These conditions heighten our concern regarding possible couplings between climate change and stratospheric ozone depletion," said ozone researcher Dr. Ross Salawitch of NASA's Jet Propulsion Laboratory, Pasadena, Calif.
The mixing of polar air into middle latitudes, both during the winter and as the polar circulation broke down in late March, influences ozone levels over the populated middle latitudes. Dilution of ozone depleted air into latitudes is a major contributor to the long-term mid-latitude decline. These mixing processes have been studied during SOLVE/THESEO-2000 and detailed analysis of these processes continues.
For further information visit the
SOLVE web site at: http://cloud1.arc.nasa.gov/solve/
Scientific background information
The ozone loss is directly related to the high concentrations of chlorine compounds that exist in the stratosphere. The principal chlorine compound involved in ozone loss is the chlorine monoxide molecule (ClO). Complementary measurements of ClO were made by instruments on aircraft, balloons, a satellite, and from the ground so that good spatial and temporal coverage was obtained. These instruments showed high ClO concentrations from January to March consistent with the large ozone loss measurements, as did measurements of other important chemical species such as bromine monoxide (BrO).
Polar stratospheric clouds (PSCs) are directly involved in the conversion of chlorine from benign molecular forms into the ClO molecule. PSCs were observed in very extensive portions over the Arctic region from early December to early-March. The last PSCs were observed around 10 March.
The temperatures in the polar stratosphere were extremely low over the course of this last winter, which increases ozone losses. Polar stratospheric clouds can only form in these low temperature regions. At 20 km on January 28, the area covered by temperatures low enough to form these clouds was 14.8 million km2 – as compared with the total surface area of Europe: just over 10 million km2. This is the largest areal coverage recorded in over 40 years of stratospheric analyses. The low temperatures first appeared in mid-November at about 24 km, and persisted at lower altitudes into mid-March. The low temperatures generally resulted from a stratosphere that has been relatively undisturbed by large-scale tropospheric weather systems over the course of the winter.
Measurements in THESEO 2000/SOLVE were made using a large suite of instruments aboard several European aircraft – the German DLR Falcon, the French ARAT and Mystère 20 and a Swiss Air Force Lear Jet - and on NASA's DC-8 and ER-2. Most of these planes were based in Kiruna during the campaign. Nearly 30 research balloons, carrying payloads weighing up to several hundred kilogrammes were launched from Esrange (The Swedish Space Research Centre), Kiruna, by teams from CNES, Esrange and NASA. Atmospheric readings made at the European network of over 30 stations of ground-based instruments have shown how the Arctic stratosphere evolved through the winter and measurements of ozone have been made at the WMO Global Atmospheric Watch network. In addition, ozone losses have been derived from over 600 ozonesondes launched from an international experiment coordinated by the Alfred Wegener Institute in Germany. All these measurements were complemented by observations from a number of satellite instruments including GOME.
In all, more than 500 international scientists, technicians and support workers were involved in the THESEO 2000/SOLVE experiment. The THESEO 2000/SOLVE campaign represents a new level of active cooperation between European, US and other national research scientists. This cooperation will be continued during the analysis of the measurements and there will be a joint science meeting held in Palermo, Italy, in September 2000. Such scientific collaboration has been encouraged under the 1998 European Union/United States Science and Technology Cooperation Agreement.
THESEO 2000 consists of a core of 12 major EU funded projects within the Environment programmes of both Fourth and Fifth Framework programmes for Research and Technological Development. The EU has a major research programme on stratospheric ozone and UV-B which includes laboratory based research into the fundamental principles of stratospheric chemistry, the ozone-climate interactions, the development of new devices to measure the atmosphere’s composition, research into improving atmospheric chemical models and UV-B radiation field measurements. The research funded by the EC Research DG in THESEO 2000 is closely coordinated with, and substantially increased by, the national research programmes. European research on stratospheric ozone and UV-B makes a valuable contribution to the international research which underpins the Montreal Protocol.