- 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 2001-2002, total ozone values observed over the Arctic region were again, as last year, substantially
higher than average. Anomalously low total ozone values were observed over the Arctic region only intermittently
during December. Total ozone values over portions of the Arctic region in December, January and February
averaged from 15 to 25 percent higher than comparable values during the early 1980s. Temperatures observed
in the lower stratosphere over the Arctic region were also above their long term average for most of the winter
of 2001-2002. Only during a few days in December did lower stratosphere temperatures reach below minus 78 C,
allowing the possibility for formation of polar stratospheric clouds which promote the chemical destruction of
ozone. Lower stratosphere temperatures in December and January rose dramatically, with significant warming
throughout the stratosphere and associated circulation effects. These conditions were also associated with the
prevalence of high ozone in the polar region during the winter and the absence of the very low total ozone values.
At middle latitudes of the Northern Hemisphere, total ozone values were predominately lower than average.
Total ozone generally decreased over the midlatitudes of the Northern Hemisphere at the rate of 2 to 4 percent
per decade, from 1979 to the early 1990s, but the downward trend has not continued in recent years. The amounts
of chlorine and other ozone destroying chemicals in the stratosphere in recent years have been reported to have
reached peak values around 1997-98. 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. High total ozone values in the Arctic region in the winter of 2001-2002
are attributed to meteorological conditions which were 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. 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. Recent NOAA-16 total ozone data have
not yet been fully validated. This impacts trends determined for the recent period.
shows monthly average anomalies of zonal mean total ozone, as a function of latitude and time,
from January 1979 to March 2002. The percent anomalies are derived relative to each month's
1979-2002 average. SBUV/2 data (in this figure only) have been adjusted for long term consistency
(Miller et al., 2002, in press). 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 2001-2002, positive zonal mean total ozone anomalies prevailed over the north
polar region, as was also the case in1997-98, 1998-99, and 2000-2001. In middle latitudes, negative
anomalies prevailed in 2001-2002. 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. In the tropics,
a small positive anomaly is seen in 2001-2002, consistent with a quasi-biennial oscillation of total
The NOAA Climate Monitoring and
Diagnostics Laboratory (CMDL) operates a 16-station global Dobson spectrophotometer network for total ozone
trend studies. Figure 2 shows the total ozone data for four mid-latitude U.S. stations from1979 through 2001.
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 3 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 1 . 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
The map in Figure 4
shows Northern Hemisphere monthly mean total ozone amounts for March 2002. High ozone extends
over northern latitudes, with a relative low area extending over the Arctic region. Figure 5a shows
the monthly mean total ozone percent difference of March 2002 from the mean for eight March 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 March 2002, regions of small positive as
well as some negative anomalies are evident over the Arctic region. Negative anomalies appear
throughout middle latitudes. However large positive anomalies of more than 15 to 25 percent are shown
over the Arctic region in the maps for December 2001 (Figure 5b ), January 2002 (Figure 5c ) and
February 2002 (Figure 5d ).
shows monthly mean temperature anomalies at 50 hPa for three latitude regions, 90N-65N, 65N-25N,
and 25S-25N. The temperature anomalies for north polar latitudes for December 2001 and January and
February 2002 were above average values and slightly below average for March 2002. Temperature
anomalies were strongly negative for mid-latitudes and also negative over the equatorial region.
The pattern of zonal mean temperature anomalies in the winter of 2001-2002 closely corresponds to
the pattern of zonal mean ozone anomalies at middle and high latitudes shown in Figure 1 .
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 7 . During November, December and January, daily
minimum temperatures only for a very few days were lower than -78 C. Temperatures increased markedly in
association with stratospheric warmings during each of the months. Without extremely low temperatures,
enhanced ozone destruction does not occur.
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 2002 was among the years with the higher average
temperatures and shorter duration of the polar vortex. Most years in the 1990s had low temperatures,
along with extended persistence of the polar vortex. Figure 9 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 2001-2002 there was low persistence of both the Arctic
polar vortex and no defined region of anomalously low ozone. Meteorological conditions in the winter of
2001-2002 were directly related to the limited ozone destruction and relatively high total ozone over the
shows the average area, during February and March for each year since 1979, of low ozone (lower than 300 DU).
For 2002, there was no area of anomalously low total ozone, comparable to north polar winter conditions in 4
out of the last 5 years.
A time series, from 1979 to
March 2002, of normalized height anomalies from 1000 to 30 hPa, for the north polar region 65-90N, is shown
in Figure 11 . Positive height anomalies were predominant in the 1980s,
while negative anomalies appear in most of the 1990s. The winter height anomalies for 2001-2002 were strongly
positive, consistent with total ozone anomalies. Note that the height anomaly pattern in
Figure 11 is very similar to the downward propagating Arctic Oscillation
signature shown by Baldwin and Dunkerton (1999). Positive height anomalies in 2001-2002, as well as 2000-2001
are consistent with the observed negative phase of the Arctic Oscillation. Investigations are underway
concerning causes and effects of stratospheric variability, as they may be related to tropospheric and surface
changes (Zhou et al., 2002). For example, during the winter of 2001-2002 and 2000-2001, anomalies appear to
propagate to the surface, whereas the 1999-2000 anomalies did not indicate a continuous downward propagation.
III. CONCLUDING REMARKS
In the winter of 2001-2002,
positive anomalies of total ozone were prevalent in the high latitudes of the Northern Hemisphere. Lower
stratosphere temperatures over the Arctic region were also predominantly above average values. Only for
short periods were Arctic temperatures sufficiently low for the formation of polar stratospheric clouds and
consequent chemical ozone depletion within the polar vortex. The conditions in the Arctic region in 2001-2002
and 2000-2001 are in contrast to conditions during 1999-2000, when total ozone in the Arctic region was below
the average. 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 temperatures prevail. High total ozone values
in the Arctic region in the winter of 2001-2002 are attributed to meteorological conditions which were not
favorable for ozone destruction, even with the continued presence of ozone destroying chemicals in the
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.
Baldwin, M.P., X. Cheng, and T.J. Dunkerton, 1994: Observed correlations
between winter-mean tropospheric and stratospheric circulation anomalies. Geophys Res.
Lett., 21, 1141-1144.
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.,
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,
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,