- Angell, J.K. ERL/Air Resources Laboratory
- 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.
- Planet, W.G. NESDIS/Satellite research Laboratory
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, as well as other long-term climate concerns, NOAA has established
routine monitoring programs utilizing 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: http://www.cpc.ncep.noaa.gov
with location: products/stratosphere/winter_bulletins
Further information may be obtained from:
Alvin J. Miller
NOAA Climate Prediction Center
5200 Auth Road
Washington D. C. 20233
Telephone: (301) 763-8000, ext. 7552
Fax: (301) 763-8125
Very low total column ozone values (near 100 DU, Dobson Units)
were observed over Antarctica during September and October 1995. Ozone
depletion of 20 percent to more than 50 percent was observed over Antarctica in
1995, compared to the ozone amounts previous to the early 1980's. Vertical
soundings over the South Pole during September and October showed nearly
complete destruction of ozone at altitudes between 15 and 20 km. Lower
stratosphere temperatures in the winter and spring of 1995 over the Antarctic
region were below the long-term average, and sufficiently low for ozone
destruction to proceed on polar stratospheric clouds within the polar vortex.
Over mid-latitudes, total ozone has declined by about 4 percent per decade since
I. DATA RESOURCES
The data available and appropriate references are listed below. This
combination of complementary data, from different platforms and sensors,
provides a strong capability to monitor global ozone, temperature and aerosols.
||Komhyr et al., 1986
||Komhyr et al., 1989
||Planet et al. 1994
||Mateer et al., 1971
||Gelman et al., 1986
||Long & Stowe, 1993
We have used the total column ozone data from the NASA Nimbus-7 SBUV instrument
from 1979 through 1988, and the NOAA-11 SBUV/2 from January 1989 to August 1994.
The orbital characteristics of the afternoon NOAA polar orbiting satellites are
such that the equatorial crossing times, over several years, progress to later
in the day. For the SBUV/2 instruments, extremely high solar zenith angles
eventually exceed the diffuser's calibrated range. This happened to the NOAA-11
SBUV/2 in late 1994. Fortunately, the NOAA-9 satellite had migrated back into
the preferred solar zenith angle range. Recent comparisons with available
ground-based observations show that the SBUV/2 NOAA-9 data are, on average,
within two to four percent of Dobson total ozone data. Consequently, we use the
data from the NOAA-9 SBUV/2 beginning in September 1994.
Figure 1 shows monthly average anomaly values (percent) of zonal mean ozone, as
a function of latitude and time, from January 1979 to November 1995. The
anomalies are derived relative to each month's 1979-95 average. Certain aspects
of the long-term global ozone changes may be readily seen. In the extra-tropics
and polar regions, ozone is substantially lower in recent years than in earlier
years. Largest anomalies are shown for the winter-spring months in each
hemisphere, with positive anomalies of more than 10 percent in the earlier years
changing to consistent negative anomalies of greater than 10 percent for recent
years. Stolarski et al. (1992), Hollandsworth et al. (1995) and Miller et al.
(1995), have indicated that the trends in the mid-latitudes are statistically
significant and are about -2 to -4 % per decade. Little or no significant trend
has been found over the equatorial region. Large negative anomalies in the
Northern Hemisphere extra-tropics during 1992-1993 (Gleason et al., 1993) hav e
been related to the Mt. Pinatubo eruption in mid-1991. The anomalies decreased
in 1994 along with the diminishing aerosol loading. However, large negative
anomalies again developed in 1994-95. In the tropical region, a weak positive
anomaly is seen in 1995, as part of a quasi-biennial oscillation of total ozone.
A map of monthly average Southern Hemisphere SBUV/2 total ozone for October 1995
is shown in Figure 2. The region of highest ozone (yellow and red colors) is
seen equatorward of the Antarctic region. Very low total ozone values (less
than 220 DU, blue and purple) are shown over the Antarctic continent. "Ozone
hole" values, below 220 DU , first began to appear over the Antarctic region in
the 1980's (Farman et al., 1985). The most extreme low values of total ozone
are not shown on this map, because of lack of SBUV/2 data for this time period
over the polar region (black area). Figure 3 shows the difference in percent
between the monthly mean total ozone for October 1995 and the eight monthly
means for October 1979-86 (Nagatani et al., 1988). Decreases in total ozone of
greater than 20 percent (green and blue) to more than 50 percent are shown over
a large area of Antarctica. Small positive percent anomalies are shown over
some areas of the tropics and mid-latitudes, associated this year with th e
quasi-biennial increase of total ozone.
Figure 4 shows a comparison of the area covered by ozone values less than 220
DU, the value generally used to denote the "ozone hole". In the Southern
Hemisphere winter-spring of 1995, the area of the "ozone hole" was similar to
recent record setting years, and substantially larger than the earlier years,
such as 1989. There is an uncertainty in the area calculated from the SBUV/2
maps, so small differences in the area for different years may not be
significant. This uncertainty arises because of the lack of SBUV/2 data
poleward of the latitude of sufficient solar illumination for derivation of good
quality SBUV/2 data. Despite uncertainties, the data do indicate that the very
low ozone values in 1995 were as widespread over the Antarctic continent as in
the record low year of 1993.
The extreme low "ozone hole" values moved in late November away from the South
Pole , toward the South America quadrant of Antarctica, and then over the
African quadrant, persisting till early December 1995.
The time series in Figure 5 shows total column ozone at the South Pole
integrated from balloon-borne ozonesondes. Minimum ozone at the South Pole
Station in 1995 occurred on October 5, with a value of 98 DU (+/- 5 DU). This
was slightly lower than the 1994 low (102 DU), but not as low as the record 91
DU in 1993. Total ozone at South Pole Station in 1995 was at or above the
1986-1995 average from July to mid-September, and somewhat below average in
October and November, but not as low as in 1992 and 1993.
Selected ozone profiles measured at the South Pole are shown in Figure 6. The
profile on 5 October 1995, at the time of minimum total column ozone amount at
the South Pole for 1995, is compared with profiles on 12 October 1993 and 23
August 1993. The October profiles show nearly complete destruction of ozone
between 15 and 20 km. Recovery continued during 1995 in the 10-15 km region, as
a result of the diminishing effects of the Pinatubo aerosols. However, ozone
depletion in the 22-24 km region, not seen prior to 1992, continued in 1995.
The extension of the ozone hole to higher altitudes is believed to be related to
increases in chlorine (Hofmann et al., 1995).
Temperatures in the lower stratosphere are closely coupled to ozone through
dynamics and photochemistry. Extremely low stratospheric temperatures (lower
than -78 C) over the Antarctic region are believed to lead to depletion of
ozone, in that low temperatures contribute to the presence of polar
stratospheric clouds (PSCs). PSCs enhance the production and lifetime of
reactive chlorine, leading to ozone depletion (WMO/UNEP, 1994).
Daily minimum temperatures over the polar region, 65S to 90S at 50 mb
(approximately 19 km) are shown in Figure 7. For most of the southern
hemisphere winter and spring of 1995, the minimum temperatures in the polar
region were substantially lower than average. Minimum temperatures were
sufficiently low (lower than -78 C) for polar stratospheric clouds to form and
allow enhanced ozone depletion.
Temperature anomalies for the 100-50 mb layer derived from radiosonde data
(Angell, 1988) are shown in Figure 8 for the Southern Hemisphere and for the
South Polar area. Figure 9 shows temperature anomalies at 50 mb for three
latitude regions, 65S-90S, 25S-65S, and 25N-25S (Gelman et al., 1986). For
these regions, temperature anomalies during 1995 were near record low values.
Aerosol concentration is another potentially important component of
stratospheric variation, and has been suggested as a possible source of ozone
depletion (e.g. Hofmann et al., 1992). Aerosol optical thickness from the
NOAA/AVHRR instrument in 1994 showed that stratospheric aerosol concentrations
continued to diminish from the maximum values observed a few weeks after the
eruption of Mount Pinatubo in June 1991. The NOAA 11 AVHRR instrument failed in
September 1994. Stratospheric aerosols were at such low levels in 1994, that it
was difficult to discern stratospheric aerosols from variations in tropospheric
Total ozone values over Antarctica during September and October 1995 were
extremely low, with the minimum values only slightly higher than the record low
values observed in 1993. The area covered by the lowest total ozone values was
as large in 1995 as in 1993. "Ozone hole" values persisted into early December
1995. Ozone profiles in the 15-20 km region, show nearly complete destruction
of ozone in October 1995, similar to recent years. In 1995 there was some
recovery in the ozone at 10 to 15 km altitude, but some enhanced destruction
evident at 22 to 24 km. We note that the lower stratosphere temperatures over
the Antarctic region in 1995 were below the long-term average, and sufficiently
low (lower than -78 C) for polar stratospheric clouds to form over a large
region. A full explanation of ozone and temperature anomalies must include all
aspects of ozone photochemistry and meteorological dynamics.
Angell, J. K., 1988: Variations and trends in tropospheric and stratospheric
global temperatures. J. Climate, 12, 1296-1313.
Climate Monitoring and Diagnostic Laboratory (CMDL), 1990: Summary Report 1989.
141pp. Available from National Technical Information Service, 5285 Port Royal
Rd., Springfield, Va. 22161.
Farman, J.C., B.G. Gardiner and J.D. Shanklin, 1985: Large losses of total
ozone in Antarctica reveal seasonal CLOx/NOx interaction, Nature, 315, 207-210.
Gelman, M.E., A.J. Miller, K.W. Johnson and R.M. Nagatani, 1986: Detection
of long-term trends in global stratospheric temperature from NMC analyses
derived from NOAA satellite data. Adv. Space Res., 6, 17-26.
Gleason, J., P.K. Bhartia, J.R. Herman, R. McPeters, P. Newman, R.S
Stolarski, L. Flynn, G. Labow, D. Larko, C. Seftor, C. Wellemeyer, W.D.
Komhyr, A. J. Miller, and W. Planet, 1993: Record low global ozone in 1992.
Science, 260, 523-526.
Hofmann, D.J., S.J. Oltmans, J.M. Harris, S. Solomon, T. Deshler, and B.J.
Johnson, 1992: Observation and possible causes of new ozone depletion in
Antarctica in 1991. Nature, 359, 283.
Hofmann, D.J., S.J. Oltmans, B.J. Johnson, J.A. Lathrop, J.M. Harris, and H.
Vomel, 1995: Recovery of ozone in the lower stratosphere of the south pole
during the spring of 1994. Geophys. Res. Lett., 22, 2493-2496.
Hollandsworth S.M., R.D. McPeters, L. Flynn, W.G. Planet, A.J. Miller, and
S. Chandra, 1995: Ozone trends deduced from combined Nimbus 7 SBUV and NOAA-11
SBUV/2 data. Geophys. Res. Lett., 22, 905-908.
Komhyr, W.D., R.D. Gross and R.K. Leonard, 1986: Total ozone decrease at
South Pole, Antarctica, 1964-1985. Geophys. Res. Lett., 13, 1248-1251.
Komyhr, W.D., R.D. Grass, P.J. Reitelbach, S.E. Kuester, P.R. Franchois and
M.L. Fanning, 1989: Total ozone, vertical distributions, and stratospheric
temperatures at South Pole, Antarctica, in 1986 and 1987. J. Geophys. Res.,
Long, C.S. and L.L. Stowe, 1993: Using the NOAA/AVHRR to study stratospheric
aerosol optical thickness following the Mt. Pinatubo eruption. Geophys. Res.
Lett., 21, 2215-2218.
Mateer, C.Y., D. F. Heath and A. J. Krueger, 1971: Estimation of total
ozone from satellite measurements of backscatter ultraviolet earth radiance. J.
Atmos . Sci., 28, 1307-1311.
Miller, A. J., 1989: A review of satellite observations of atmospheric ozone.
Planet. Space Science, 37, 1539-1554.
Miller, A.J., G.C. Tiao, G.C. Reinsel, D. Wuebbles, L.Bishop, J. Kerr, R.M.
Nagatani, J.J. DeLuisi, and C.L. Mateer, 1995: Comparisons of observed ozone
trends in the stratosphere through examination of Umkehr and balloon ozonesonde
data. J. Geophys. Res., 100, 11209-11217.
Nagatani, R.M., 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, 125 pp.
OFCM, 1988: National Plan for Stratospheric Monitoring 1988-1997.
FCM-P17-1988. Federal Coordinator for Meteorological Services and Supporting
Research, U.S. Dept. Commerce, 124pp.
Planet, W. G., J. H. Lienesch, A. J. Miller, R. Nagatani, R, D. McPeters,
E. Hilsenrath, R. P. Cebula, M. T. DeLand, C. G. Wellemeyer, and K. M.
Horvath, 1994: Northern hemisphere total ozone values from 1989-1993 determined
with the NOAA-11 Solar Backscatter Ultraviolet (SBUV/2) instrument. Geophys.
Res. Lett. 21, 205-208.
Stolarski, R., R. Bojkov, L. Bishop, C. Zerefos, J. Staehelin and J Zawodny,
1992: Measured trends in stratospheric ozone, Science, 256, 342-349.
WMO/UNEP, 1994: Scientific assessment of ozone depletion: 1994. Report No.