Contributors:

• 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:
http://www.cpc.ncep.noaa.gov/products/stratosphere/winter_bulletins

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
E-mail: melvyn.gelman@noaa.gov

ABSTRACT

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 years.

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.

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 darkness.

II. DISCUSSION

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.

Figure 3 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.

Monthly 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).

Figure 7 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.

Figure 8 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.

Figure 9 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.

Figure 10 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.

IV. REFERENCES

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., 107(0), doi:10.1029/200,D000853.

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.

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.