- 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 2003-2004,
anomalously high total ozone values predominated over the Arctic region. During December, January, and February of 2003-2004,
there were portions of the Arctic region where average values of total ozone were greater than 45 percent higher than comparable
values during the early 1980s. At the same time, total ozone values over middle latitudes had much lower than average values.
Minimum temperatures observed in the lower stratosphere over the Arctic region were above average throughout the winter and
only rarely fell below minus 78 C, the temperature below which polar stratospheric clouds form, allowing enhanced chemical
destruction of ozone. Temperatures in the upper stratosphere rose dramatically in December, with subsequent significant warming
throughout the Arctic stratosphere. These stratospheric warming conditions and a weak polar vortex were associated with the
dominance of high ozone in the Arctic. 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 high total ozone values in the Arctic region in the winter of 2003-2004 are
attributed to absence of very low stratospheric temperatures and meteorological conditions not favorable for ozone destruction,
even 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
February 1985; 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. Also, the
NOAA-11 satellite orbit precessed, and SBUV/2 increasingly viewed high latitudes only in darkness, thus
increasing data loss at sub-polar latitudes, especially in 1992 and 1993.
The four maps in
Figure 1 show Northern Hemisphere monthly mean total ozone amounts for December 2003 to March 2004. High ozone
extends over northern latitudes in the western hemisphere, while relatively low total ozone values prevail over the
eastern hemisphere Arctic region. Figure 2a
shows the monthly mean total ozone percent difference of the December 2003 monthly mean from the average of eight
December monthly means, 1979-1986 (Nagatani et al., 1988). The base period is chosen because 1979 to1986 average values
are indicative of the early data record. For December 2003, positive anomalies of greater than 10 percent are shown over
most of North America, with maximum positive anomalies of more than 45 percent extending over the Arctic region.
Persistence of the high total ozone anomaly in the Arctic region is shown in the maps for
January (Figure 2b), and February (Figure 2c).
Strong negative anomalies, predominant over much of the middle to high latitude region in December, January and February,
are also shown in the Arctic region in March 2004 (Figure 2d).
shows the average area, during February and March for each year since 1979, of low Arctic ozone (lower than 300 DU).
For 2004, the area of anomalously low total ozone was near zero. Lack of very low temperatures in the lower stratosphere
(see discussion with Figure 7 and Figure 8) is associated
with the absence in the Arctic of very low total ozone values in 2003-2004.
shows monthly anomalies of zonal mean total ozone, as a function of latitude and time, from January 1979 to March 2004.
The percent anomalies are derived relative to each month's 1979-2004 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 high northern latitude region, positive anomalies prevailed in
1979 and the early 1980s, but mostly negative anomalies predominated in the 1990s. However, during the winter of 2003-2004,
positive zonal mean total ozone anomalies are shown, with negative anomalies over middle latitudes. The Scientific
Assessment of Ozone: 1998 (WMO, 1999) reported that total column ozone decreased at northern mid-latitudes 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 5 shows the total ozone data for four mid-latitude U.S. stations from1979 through 2003. 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 6 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 4 . 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
the 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 conditions.
shows monthly-mean temperature anomalies at 50 hPa for three latitude regions. The temperature anomalies for high
latitudes for December 2003 to February 2004 were positive, but for March they were negative. However, temperature
anomalies were strongly below average for the middle latitudes and the tropical region.
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 8. During the winter of 2003-2004, daily minimum temperatures in
the lower stratosphere were rarely lower than minus 78 C. They were mostly above average from December through
February, and only reached below average in March.
Monthly mean temperature anomalies for
December 2003 to March 2004 are shown in the latitude versus pressure cross sections in Figure 9. Positive temperature
anomalies are shown in the upper to middle stratosphere in December, with downward progression of the Arctic
stratospheric warming shown in January and February. The negative temperature anomalies overlaying the positive
anomalies, associated with strong stratospheric warming, also appear to progress downward from the upper
stratosphere Arctic in January to lower levels in February and March.
A time series, from December 2003
to March 2004, of normalized height anomalies from 1000 to 30 hPa, for the north-polar region 65-90N, is shown
in Figure 10 . The strong positive anomalies in December, January and the first part of February, associated with
strong stratospheric warming, appear to propagate from the stratosphere downward to the surface, associated with
a negative phase of the Arctic Oscillation. In February and March the negative height anomalies also appear to
progress downward (Baldwin and Dunkerton, 1999; Zhou et al., 2002).
compares the average 100-hPa temperatures in the polar region for each March of the last 25 years with the date the
stratospheric polar vortex diminished below a specific threshold size. The apparent relationship in previous years
of March temperature and vortex size did not hold in 2004. An explanation can be found in the fact that the duration
of the polar vortex was very limited in 2004, because of warming conditions earlier in the winter. However the warming
subsided and by March north polar temperatures were not especially high.
shows the relationship between the persistence of the polar vortex and the persistence of high latitude total ozone values
of less than 300 DU for December through March. This relationship holds also for this year. In the winter of 2003-2004,
there was close to minimum in persistence of both the Arctic polar vortex and region of anomalously low ozone.
III. CONCLUDING REMARKS
In the winter of 2003-2004, positive anomalies
of total ozone were prevalent in the high latitudes of the Northern Hemisphere. The positive anomalies in total ozone were
associated with the meteorological conditions of positive anomalies of lower stratosphere temperature. Arctic temperatures
were not 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. Lower stratosphere ozone destruction is strong when meteorological conditions of a strong
polar vortex and cold polar temperatures prevail. Those cold conditions were not present in the lower stratosphere in the
winter of 2003-2004.
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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of the Arctic Oscillation from the stratosphere to the troposphere. .J. Geophys. Res., 107, 30937-30946.
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and R.P. Cebula., 2002, A cohesive total ozone data set from SBUV/(2) satellite system, press, J. Geophys. Res.,
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,