Climate Prediction Center - Stratosphere: Winter Bulletins

Concerns of global ozone depletion (e.g. WMO, 1999) 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

Further information may be obtained from Melvyn E. Gelman
W/NP52, RM 806, WWB
NOAA Climate Prediction Center
5200 Auth Road
Camp Springs, MD 20746-4304
Telephone: (301) 763-8071, ext. 7558
Fax: (301) 763-8125
E-mail: melvyn.gelman@noaa.gov

Extensive ozone depletion was again observed over Antarctica during the Southern Hemisphere winter/spring of 2003, with widespread total ozone anomalies of 30 percent or more below the 1979-1986 base period. The area covered by extremely low total ozone values of less than 220 Dobson Units, defined as the Antarctic "ozone hole" area, was as large as in any previous year. The ozone hole reached maximum size of greater than 27 million square kilometers, with an average size in September of 25.8 million square km, larger than for any previous year.. Vertical profiles of ozone amounts, measured by balloons over the South Pole, showed strongest destruction of ozone in the 15-21 km region. At the South Pole, the minimum total ozone value of 106 Dobson Units, was observed on 26 September 2003, when the center of the ozone hole was nearby. Minimum values were not as low as seen during other recent years. Lower stratosphere temperatures below -78 C (sufficiently low for polar stratospheric cloud formation) in the winter of 2003 occurred again over the Antarctic region, thus promoting chemical ozone loss. However, meteorological conditions of warming over Antarctica in early October limited further severe ozone destruction and also limited the extent and duration of the ozone hole in 2003.

I. DATA RESOURCES

The data used for this report are listed below. This combination of complementary data, from different platforms and sensors, provides a strong capability to monitor global ozone and temperature.

Parameter	Ground-Based	Satellite/Instrument
Total Ozone	Dobson	NOAA/SBUV/2
		Nimbus-7/SBUV
Ozone Profiles	Balloon-Ozonesonde	NOAA/ SBUV/2
		Nimbus-7/SBUV
Temperature Profiles	Balloon - Radiosonde	NOAA/TOVS

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. Precession of the NOAA-11 satellite caused SBUV/2 viewing high latitudes only in darkness and increasing data loss at sub-polar latitudes, especially in 1992 and 1993.

Figure 1 displays monthly average anomaly values (percent) of zonal mean total ozone, as a function of latitude (80N to 80 S) and time (January 1979 to November 2003. The anomalies are derived relative to each month's 1979-2003 average. Certain aspects of long-term global ozone changes may be readily seen. In the polar regions, ozone values were substantially lower in the 1990s than in the 1980s. Largest anomalies are shown for the polar regions in each hemisphere in winter-spring months, with positive anomalies of more than 10 percent in the earlier years changing to negative anomalies of greater than 10 percent for most recent years. In the Antarctic region winter and spring of 2003, average total ozone again reached 10 to 30 percent lower than the long-term average.

Maps of monthly average Southern Hemisphere SBUV/2 total ozone for September and October 2003 are shown in Figure 2a, and Figure 3a. Lowest "ozone hole" values (defined as total ozone values less than 220 DU) appear over Antarctica slightly displaced from the South Pole, and highest total ozone is shown in the Pacific Ocean between Antarctica and Australia. Figure 2b and Figure 3b show the difference in percent between the monthly mean total ozone for September and October 2003 and eight (1979-86) monthly means for those months (Nagatani et al., 1988). Extreme negative anomalies in total ozone of greater than 45 percent are shown over most of Antarctica and adjacent ocean areas, reaching to southern Argentina.

Figure 4a compares, for each year since 1979, the ozone hole area average for all days in October through November. The growth in the ozone hole area from the 1980s through the 1990s is quite apparent. From a very small area in 1982, October/November average values increased dramatically to a maximum in 1998 of 16.4 million square kilometers. The October/November 2003 average ozone hole area was 10.7 million square kilometers, somewhat smaller than most recent years since 1990. Figure 4b, c, and d show the individual monthly average ozone hole size for, respectively, September, October, and November, for years since 1980. There are strong similarities in the progression of ozone hole size in the years 2003 and 2000. The September 2003 ozone hole size was the largest average monthly size ever (25.8 million square km). The size decreased in October, and in November it was substantially diminished.

The center of the ozone hole and associated lowest ozone, and polar vortex are often located close to the South Pole. Figure 5 shows a time series during 2003 of total ozone, measured over the South Pole using balloon-borne ozone instruments, compared with other selected years. Low ozone hole values appeared in August 2003, with lowest values evident in mid-September to October, when the center of the ozone hole was closest to the South Pole. Total ozone values rose in early November, when the ozone hole decreased and was displaced from the South Pole.

On 26 September (Figure 6) a very low total column ozone amount of 106 DU was observed at the South Pole, the minimum value for the year 2003. This profile shows strong destruction of ozone between 15 and 21 km associated with classic ozone hole conditions. The time series in Figure 7 of ozone profiles at the South Pole during 2003 shows the time sequence of dramatic decreases in ozone between 15 and 21 km especially evident in September. Extremely low values of ozone associated with ozone hole conditions continued in October, but moderated thereafter.

One of the longest records of ozone measurements in Antarctica is the total column ozone amount obtained with the Dobson spectrophotometer at South Pole Station. Consistent observations can be obtained beginning on October 15 of each year when sufficient sunlight is available for these optical measurements that use the sun as a light source. This record of average October 15-31 column amounts shown in Figure 8 indicates declines that accelerated in the 1980s and reached consistently low values from 1993-1999. Since 2000 there has been greater variability in this average with the suggestion of a tendency toward greater amounts than seen during the 7-year minimum period.

Ozone amounts in the lower stratosphere are closely coupled to temperatures through dynamics and photochemistry. Extremely low stratospheric temperatures (lower than -78 C) over the Antarctic region contribute to depletion of ozone, in that low temperatures lead to the presence of polar stratospheric clouds (PSCs). PSCs enhance the production and lifetime of reactive chlorine, leading to ozone depletion (WMO, 1999). Daily minimum temperatures at 50 hPa (approximately 19 km) over the polar region, averaged from 65S to 90S are shown in Figure 9. For most of the Southern Hemisphere winter of 2003, minimum temperatures in the south polar region were below -78 C, below long term average minimum values, and indeed near record low temperatures. The rise in temperatures higher than -78 C in October 2003 limited the further formation of polar stratospheric clouds and thus also limited further extreme ozone destruction. Temperatures in the winter and spring of 2003 were much lower than in 2002, and coincided with a much stronger ozone hole in 2003 than in 2002.

Figure 10 shows monthly average temperature anomalies at 50 hPa for three latitude regions, 25S-25N, 65S-25S, and 90S-65S. For the south polar region, winter temperatures were much lower than the long-term average, but positive anomalies were observed in October and November. This was similar to the sequence of events in 2000 and 2002. Negative temperature anomalies predominated over the middle latitudes of the Southern Hemisphere, with very large negative anomalies over tropical latitudes. Both the tropical and middle latitudes of the Southern Hemisphere continue the tendency toward lower temperatures after 1993 relative to higher temperatures in earlier years.

Figure 11 presents time series of the area of the ozone hole, the size of the polar vortex, and the size of the polar area where lower stratosphere temperatures were below -78 C (polar stratospheric cloud, PSC area). The daily 2003 values are shown, along with the extreme and average daily values for the most recent 10 years. During the spring of 2003, the area for all three indicators was larger than average during August, September, and the first part of October. Indeed, the ozone hole was larger in August and several days in September 2003 than for any other recent years. The steady decrease in October of the ozone hole coincided with the decrease in size of the Southern Hemisphere polar vortex and the decrease in size of the area of very low temperatures. The size of the ozone hole correlates well with the size of the PSC area during the formation stages of the ozone hole through the first half of September. Thereafter, the ozone hole size is strongly affected by the size of the polar vortex.

Figure 12 illustrates the direct relationship between the persistence of the ozone hole and the persistence of the Antarctic polar vortex. In years when the winter polar vortex persisted later in the season, the duration into the Spring season of the ozone hole also tended to be extended. For the year 2003, the persistence of the ozone hole and the persistence of the Southern Hemisphere polar vortex extended longer than most years since the ozone hole developed, but shorter than most of the years since 1990.

Very low ozone values were again observed over Antarctica in the winter/spring of 2003. Ozone depletion of more than 40 percent was observed over Antarctica, compared to total ozone amounts observed in the early 1980's. Vertical soundings over the South Pole during August, September and October 2003 again showed strongest destruction of ozone at altitudes between 15 and 21 km. Lower stratosphere temperatures in the winter of 2003 over the Antarctic region were also much lower than average values. Associated with this, the ozone hole area in August and September was among the largest of any previous year. The ozone hole diminished in October and November along with warming stratospheric conditions. So although the Antarctic ozone hole in 2003 reached unprecedented size, the duration of the extremely low ozone conditions was limited by warmer meteorological conditions which developed in October and November.

Observations of chloroflourocarbons and of stratospheric hydrogen chloride support the view that international actions are reducing the use and release of ozone depleting substances (WMO, 1999; Anderson et al., 2000). However, chemicals already in the atmosphere are expected to continue to deplete ozone for many decades to come. Further, changing atmospheric conditions that modulate ozone can complicate the task of detecting the start of ozone layer recovery. The eruption of the Pinatubo volcano provided an example of such a complication in the 1990s. Based on an analysis of 10 years of South Pole ozone vertical profile measurements, Hofmann et al., (1997) estimated that recovery in the Antarctic ozone hole may be detected as early as the coming decade. Indicators include: 1) an end to springtime ozone depletion at 22-24 km, 2) 12-20 km mid-September column ozone loss rate of less than 3 DU per day, and 3) a 12-20 km ozone column of more than 70 DU on September 15. An intriguing aspect of recent observations of the Antarctic stratosphere had been the apparent trend towards a later breakup of the vortex in most recent years. The large size of the August-September 2003 ozone hole but its limited duration in October-November is attributed in part to meteorological conditions. A full explanation of such meteorological anomalies is not yet available. Continued monitoring and measurements, including total ozone and its vertical profile, are essential to achieving the understanding needed to identify ozone recovery.

Anderson, J., J. M. Russel III, S. Solomon, and L. E. Deaver, 2000: Halogen Occultation Experiment confirmation of stratospheric chlorine decreases in accordance with the Montreal Protocol, J. Geophys. Res., 105, 4483-4490.

Hofmann, D.J., S.J. Oltmans, J.M. Harris, B.J. Johnson, and J.A. Lathrop, 1997: Ten years of ozonesonde measurements at the south pole: implications for recovery of springtime Antarctic ozone. J. Geophys. Res., 102, 8931-8943.

Miller, A.J., dt al.,A cohesive total ozone data set from SBUV/(2) satellite system, in press, J.Geophys. Res., 2002.

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, 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.

WMO, 1999: Scientific assessment of ozone depletion: 1998. World Meteorological Organization Global Ozone Research and Monitoring Project - Report No. 44.