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.
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 supporting images visit the web site at: http://svs.gsfc.nasa.gov/stories/solve/index.html
For further information visit the SOLVE web site at: http://cloud1.arc.nasa.gov/solve/