- Angell, J.K. ERL/Air Resources Laboratory
- Flynn, L.T. NESDIS/Climate Research and Applications Division
- Gelman, M.E. NWS/Climate Prediction Center
- Hofmann, D. ERL/Climate Monitoring and Diagnostic Lab.
- Long, C.S. NWS/Climate Prediction Center
- Miller, A.J. NWS/Climate Prediction Center
- Nagatani, R.M. NWS/Climate Prediction Center
- Oltmans, S. ERL/Climate Monitoring and Diagnostic Lab.
- Zhou, S. RS Information Systems
Concerns of possible global ozone depletion (e.g., WMO/UNEP, 1994) have led to
major international programs to monitor and explain the observed ozone variations in the
stratosphere. In response to these, and other long-term climate concerns, NOAA has
established routine monitoring programs using both ground-based and satellite measurement
techniques (OFCM, 1988).
Selected indicators of stratospheric climate are presented in each Summary from
information contributed by NOAA personnel. A Summary for the Northern Hemisphere is issued
each April, and, for the Southern Hemisphere, each December. These Summaries are available
on the World-Wide-Web at the site:
Further information may be obtained from:
Melvyn E. Gelman
NOAA, Climate Prediction Center
5200 Auth Road
Camp Springs, MD 20746-4304
Telephone: (301) 763-8000 ext.7558
Fax: (301) 763-8125
For the Northern Hemisphere winter of 2002-2003,
low total ozone values were again observed over the Arctic region. The Arctic area experiencing very low ozone was larger
than for the previous two years, but not as large as in the 1990s. During December, January , February and March, of
2002-2003, there were portions of the Arctic region where average values of total ozone were up to 45 percent lower
than comparable values during the early 1980s. At the same time, total ozone values over middle latitudes and portions of the
Arctic region had much higher than average values. Minimum temperatures observed in the lower stratosphere over the Arctic region in
December and early January were below minus 78 C, allowing the formation of polar stratospheric clouds which promote the chemical
destruction of ozone. Stratosphere temperatures in mid January rose dramatically, with significant warming throughout the Arctic
stratosphere, with a splitting in two of the stratospheric polar vortex, and associated circulation effects. These stratospheric
warming conditions were also associated with movement of high ozone into the Aleutian Arctic region during January, and a splitting
in two of the region of low total ozone values. From 1979 to the early 1990s, total ozone had generally decreased over the
middle latitudes of the Northern Hemisphere at the rate of 2 to 4 percent per decade, but the downward trend has not continued
in recent years. The amounts of chlorine and other ozone destroying chemicals in the stratosphere have been reported to have
reached peak values around 1997-98, and have remained at high levels. Much of the recent year-to-year differences in north polar
winter-spring stratospheric ozone destruction may be explained as being due to the varying conditions associated with interannual
meteorological variability. The low total ozone values in the Arctic region in the winter of 2002-2003 are attributed to meteorological
conditions which were favorable for ozone destruction, with the continued presence of ozone destroying chemicals in the stratosphere.
I. DATA RESOURCES
The data available are listed below. This combination of complementary
data, from different platforms and sensors, provides a strong capability to monitor global
ozone and temperature.
|METHOD OF OBSERVATION
||Balloon - Ozonesonde
||Balloon - Radiosonde
We have used total column ozone data from the NASA Nimbus-7 SBUV instrument from 1979 through
February1985; NOAA-9 SBUV/2 from March 1985 to December 1988; NOAA-11 SBUV/2 from January 1989
to December 1993; NOAA-9 SBUV/2 from January 1994 to December 1995; NOAA-14 SBUV/2 from January
1996 to June 1998; NOAA-11 SBUV/2 from July 1998 to September 2000; and NOAA-16 SBUV/2 from October
2000. Solar Backscatter Ultra-Violet (SBUV) instruments can produce data only for daylight-viewing
conditions, so SBUV/2 data are not available at polar latitudes during winter darkness. Increasing
loss of NOAA-11 data at sub-polar latitudes from 1989 to1993 was caused by satellite precession,
resulting in SBUV/2 viewing high latitudes only in darkness.
The maps in
Figure 1a and 1b show Northern Hemisphere monthly mean total ozone
amounts for December 2002 and March 2003. High ozone extends over northern latitudes in the western hemisphere,
while low total ozone values prevail over the eastern hemisphere Arctic region. Figure 2a
shows the monthly mean total ozone percent difference of the December 2002 monthly mean for eight December
monthly means, 1979-1986 (Nagatani et al., 1988). The 1979 to 1986 base period is chosen
because 1979-1986 average values are indicative of the early data record. For December 2002,
negative anomalies of greater than 30 percent are evident extending from North America to Europe,
but with positive anomalies of more than 45 percent centered over the Aleutian Arctic region.
The persistence and movement of areas of low and high total ozone anomaly are shown in the maps
for January (Figure 2b), February (Figure 2c)
and March 2003 (Figure 2d). Figure 3a, b, c, and d
show maps of temperature anomaly at the lower stratospheric level of 50 hPa for December 2002 to
March 2003, respectively. The areas of low and high ozone anomaly correspond quite closely with
the regions of low and high temperature anomaly.
Figure 4 shows
monthly mean temperature anomalies at 50 hPa for three latitude regions, 65N-90N, 25N-65N,
and 25S-25N. The temperature anomalies for middle and high latitudes for December 2002 and
January to March 2003 were slightly negative, but strongly below average for the equatorial
Extremely low temperatures
(lower than -78 C) over the Arctic region in the lower stratosphere are linked to depletion of ozone.
Temperatures in the lower stratosphere are closely coupled to ozone through dynamics and photochemistry.
Very low temperatures contribute to the presence of polar stratospheric clouds (PSCs). PSCs enhance the
production and lifetime of reactive chlorine, leading to ozone depletion in the presence of sunlight
(WMO, 1999). Daily minimum temperatures over the polar region, 65N to 90N at 50 hPa (approximately 19 km)
are shown in Figure 5 . During November, December and early January, daily
minimum temperatures were lower than -78 C. Temperatures increased markedly in association with stratospheric
warming in mid January and then again in February and March.
Figure 6 compares
the average 100 hPa temperature in the polar region for each March of the last 24 years with the date the
stratospheric polar vortex diminished below a specific threshold size. The size of the vortex was defined
by the maximum in the gradient of potential vorticity contours at the 450 K isentropic surface, based on the
NCEP/NCAR reanalyses. March 2003 was close to average in the temperatures and duration of the polar vortex.
Figure 7 shows the relationship between the persistence of the polar vortex and the persistence of high latitude
total ozone values of less than 300 DU. In the winter of 2002-2003 there was close to average persistence of
both the Arctic polar vortex and region of anomalously low ozone.
Figure 8 shows the average area,
during February and March for each year since 1979, of low ozone (lower than 300 DU). For 2003, the area of
anomalously low total ozone was greater than conditions in 4 out of the last 5 years. But not as great as
most of the years in the 1990s.
A time series, from December 2002 to
March 2003, of normalized height anomalies from 1000 to 30 hPa, for the north polar region 65-90N, is shown in
Figure 9. The strong positive anomaly in January, associated with strong stratospheric warming, appears to
propagate from the stratosphere downward to the surface, resulting in a negative Arctic Oscillation phase.
However, relatively weak positive or negative height anomalies in other periods do not propagate down to the
surface (Zhou et al., 2002 and Baldwin and Dunkerton, 1999).
Figure 10 shows monthly average
anomalies of zonal mean total ozone, as a function of latitude and time, from January 1979 to March 2003.
The percent anomalies are derived relative to each month's 1979-2003 average. SBUV/2 data (in this figure
only) have been adjusted for long term consistency (Miller et al., 2002). The largest anomalies occur in
winter and spring months for the polar region of the Southern Hemisphere. In the north polar region,
positive anomalies prevailed in 1979 and the early 1980s, but mostly negative anomalies predominated
in the 1990s. However, during the winter of 2002-2003, positive zonal mean total ozone anomalies are
shown over the Northern Hemisphere. The Scientific Assessment of Ozone: 1998 (WMO, 1999) reported that
total column ozone decreased at northern midlatitudes (25-60N) between 1979 and 1991, with estimated linear
trend downward of 4 percent per decade. However, since the recovery after 1993 from the 1991 Mt. Pinatubo
volcanic eruption, the downward trend of total ozone has not continued.
The NOAA Climate Monitoring and
Diagnostics Laboratory (CMDL) operates a 16-station global Dobson spectrophotometer network for total ozone
trend studies. Figure 11 shows the total ozone data for four mid-latitude U.S. stations from1979 through 2002.
The large annual variation is a result of ozone transport processes which cause a winter-spring maximum and
summer-fall minimum at northern mid-latitudes. Figure 12 shows the four-station average percent deviation
from their long-term monthly means. These anomalies, derived from ground-based measurements, are consistent
with the anomalies from SBUV/2 satellite ozone measurements, shown in Figure 10. Middle latitude total ozone
values in the years since 1993 have not continued to decline as they had declined from 1979 to 1993. However
ozone values have also not recovered to their higher 1980 values. The implication of these changes needs to be
examined in the context of changes in amounts of ozone depleting gases in the atmosphere and varying meteorological
III. CONCLUDING REMARKS
In the winter of 2002-2003, negative
and positive anomalies of total ozone were prevalent in the high latitudes of the Northern Hemisphere. The low
and high anomalies in total ozone were associated with the meteorological conditions of low and high anomalies
of lower stratosphere temperature. Arctic temperatures were sufficiently low for the formation of polar stratospheric
clouds and consequent chemical ozone depletion within the polar vortex. Chlorine and other ozone destroying chemicals
in the lower stratosphere reached peak values around 1997-98, and have remained at high levels. As a consequence, lower
stratosphere ozone destruction is strong when meteorological conditions of a strong polar vortex and cold polar
Total ozone declined over mid-latitudes
of the Northern Hemisphere at the rate of about 2 to 4 percent per decade from 1979 to 1993. In recent years the
strong rate of decline of Northern Hemisphere total ozone has not continued, but current stratospheric ozone amounts
continue to be below the amounts measured before the early 1980s. A full explanation of ozone and temperature anomalies
must include all aspects of ozone photochemistry and meteorological dynamics. Continued monitoring and measurements are
essential toward this end.
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Nagatani, R.N., A.J. Miller, K.W. Johnson,
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OFCM, 1988: National Plan for Stratospheric
Monitoring 1988-1997. FCM-P17-1988. Federal Coordinator for Meteorological Services and Supporting Research, U.S. Dept.
WMO, 1999: Scientific assessment of ozone
depletion: 1998. World Meteorological Organization Global Ozone Research and Monitoring Project - Report No. 44.
Zhou, S., A.J. Miller, J. Wang, and J.K.
Angell, 2002: Downward-propagating temperature anomalies in the preconditioned polar stratosphere. J. Climate,