- Angell, J.K. OAR/Air Resources Laboratory
- Flynn, L.T. NESDIS/Climate Research and Applications Division
- Gelman, M.E. NWS/Climate Prediction Center
- Hofmann, D. OAR/Earth Systems Research Lab.
- Long, C.S. NWS/Climate Prediction Center
- Miller, A.J. NWS/Climate Prediction Center
- Oltmans, S. OAR/Earth Systems Research 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 2005-2006, anomalously high total ozone values predominated over the Arctic region. During December, January,
and February of 2005-2006, 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. 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 lower to middle Arctic stratosphere rose dramatically in January. The
stratospheric warm conditions were associated with a weak polar vortex and the dominance of high ozone in the
Arctic. 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 2005-2006 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. Total ozone values over middle latitudes for 2005-2006 were much
lower than average values, but not as low as some other years during the 1990s. From 1979 to the early 1990s,
total ozone over the middle latitudes of the Northern Hemisphere had generally decreased at the rate of 2 to 4
percent per decade, but the downward trend of middle latitude total ozone has not continued in recent
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; NOAA-16 SBUV/2 from October 2000 to December 2005; and NOAA-17 SBUV/2 from January 2006 to
March 2006. Solar Backscatter Ultra-Violet (SBUV) data are not available at polar latitudes during winter
The four maps in
Figure 1 show increasing prevalence over the Arctic region of high values of monthly mean total
ozone amounts for December 2005 to March 2006. In December, high values of total ozone extended over the
Alaska-Siberian Arctic area, while moderately low values prevailed over the Greenland-Northern Europe Arctic
region. During January, February and March, the region of low ozone diminished, while high ozone intensified
and spread over the entire Arctic region. Figure 2a shows December 2005 monthly mean total ozone percent
difference from the average of eight December monthly means, 1979-1986 (Nagatani et al., 1988). The base period
1979 to1986 average values are indicative of the early data record. For December 2005, maximum positive
anomalies of more than 30 percent extend over the Alaska-Siberia Arctic region, while maximum negative anomalies
of more than 20 percent extend over the Greenland-Northern Europe region. For January
(Figure 2b)and February (Figure 2c)
high total ozone anomalies of greater than 45 percent predominated over the entire Arctic region.
shows the average area, during February and March for each year since 1979, of low Arctic ozone (lower than 300 DU).
For 2006, the Arctic area of anomalously low total ozone was near zero. Lack of very low total Arctic ozone
values in 2005-2006 contrasts strongly with conditions in 2004-2005, when there was a persistence of a large
area of very low total ozone in the Arctic region. Variability in Arctic low total ozone is associated with
variability in the Arctic of very low temperatures in the lower stratosphere.
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 4. During the winter of 2005-2006, daily minimum temperatures in the lower stratosphere were
rarely lower than minus 78 C. The period and location of these low temperatures coincided with the period and
location of low total ozone shown in Figure 1.
temperature anomalies for December 2005 to March 2006 are shown in the latitude versus pressure cross sections
in Figure 5. Positive temperature anomalies are shown in the upper to middle stratosphere in December, with
downward progression of Arctic stratospheric warming shown in January and February. The negative temperature
anomalies overlaying the positive anomalies in February also appear to progress downward from the upper
stratosphere Arctic to lower levels in March.
A time series, from December 2005
to March 2006, of normalized height anomalies from 1000 to 30 hPa, for the north-polar region 65-90N, is shown
in Figure 6. The strong positive anomalies in January and February,
associated with strong stratospheric warming, appear to propagate from the stratosphere downward to the surface,
and were associated with a negative phase of the Arctic Oscillation (Zhou et al., 2002).
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 2005-2006, there was near minimum persistence of both the Arctic polar vortex and region of
anomalously low ozone.
compares the average 100-hPa temperatures in the polar region for each March with the date the stratospheric
polar vortex diminished below a specific threshold size. The apparent relationship in previous years of March
temperature and vortex persistence did not hold in 2006. An explanation can be found in the fact that the
duration of the polar vortex was very limited in 2006, because of warming conditions earlier in the winter.
However the warming subsided and by March north polar temperatures were not especially high.
shows monthly-mean temperature anomalies at 50 hPa for three latitude regions. The high latitude temperature
anomalies for December 2005 to February 2006 were positive, but for March they were negative. For the middle
latitudes and the tropical region, recent temperature anomalies have been strongly below average.
shows monthly anomalies of zonal mean total ozone, as a function of latitude and time. The percent anomalies
are derived relative to each month's 1979-2006 average. SBUV/2 data, in this figure only, have been adjusted
for long-term consistency (Miller et al., 2002). The largest anomalies appear in winter and spring months for
the polar region of the Southern Hemisphere. In the high northern latitude region, positive anomalies prevailed
in the early 1980s, and mostly negative anomalies predominated in the 1990s. However, during the winter of
2005-2006, positive zonal mean total ozone anomalies are shown in northern latitudes. Strong negative anomalies
are shown over middle latitudes.
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 2005. 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. 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 values of the 1980s. 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 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.
III. CONCLUDING REMARKS
In the winter of 2005-2006, 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 2005-2006.
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.
Nagatani, R.N., A.J. Miller, K.W.
Johnson, and M.E. Gelman, 1988: An eight year climatology of meteorological and SBUV ozone data, NOAA Technical
Report NWS 40, 125pp.
Miller, A.J., R.M. Nagatani, L.E. Flynn,
S. Kondragunta, E. Beach, R. Stolarsky, R. McPeters, P.K. Bhartia, M. Deland, C.H. Jackman, D.J.Wuebbles, K.O.Putten,
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, 15, 781-792.