Climate Prediction Center - Stratosphere: Winter Bulletins

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

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: mel.gelman@noaa.gov

For the Northern Hemisphere winter of 2004-2005, anomalously low total ozone values predominated over the Arctic region. During December, January, and February of 2004-2005, there were large portions of the Arctic region where average values of total ozone were 30 to 45 percent lower than comparable values during the early 1980s. The size of the Arctic area of anomalously low total ozone in 2004-2005 was among the largest of any year in our record since 1979, and larger than in any year since 1997. Minimum temperatures observed in the lower stratosphere over portions of the Arctic region were near record low values throughout the winter, and through February remained below minus 78 C, the temperature below which polar stratospheric clouds form, allowing enhanced chemical destruction of ozone. The lower stratospheric cold conditions and a very strong polar vortex were associated with the regions of dominance of low ozone in the Arctic. Arctic temperatures in the upper stratosphere rose dramatically in February, with subsequent significant warming in the middle and upper stratosphere, along with the increase in ozone values over the Arctic region. From 1979 to the early 1990s, total ozone had generally decreased over the middle latitudes of the Northern Hemisphere at the rate of 2 to 4 percent per decade, but the downward trend has not continued in recent years. 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 Arctic winter-spring stratospheric ozone destruction may be explained as being due to the varying conditions associated with interannual meteorological variability. The predominance of anomalously low total ozone values in the Arctic region in the winter of 2004-2005 is attributed to the very low stratospheric temperatures and meteorological conditions favorable for ozone destruction, along with the continued presence of ozone destroying chemicals in the stratosphere.

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
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 to March 2005. Solar Backscatter Ultra-Violet (SBUV) data are not available at polar latitudes during winter darkness.

The four maps in Figure 1 show Northern Hemisphere monthly mean total ozone amounts for December 2004 to March 2005. Very low total ozone values prevailed over the Eastern Hemisphere Arctic region, while high ozone extended over middle and high latitudes in the Western Hemisphere. Figure 2a shows the monthly mean total ozone percent difference of the December 2004 monthly mean from the average of eight December monthly means, 1979-1986 (Nagatani et al., 1988). The base period is chosen because 1979 to1986 average values are indicative of the early data record. For December 2004, negative anomalies of greater than 10 percent are shown over most of northern North America, North Atlantic Ocean, Europe, and north Asian Arctic. Persistence of the low total ozone and negative ozone anomalies over most of the Arctic region is shown in the maps for January (Figure 2b), February (Figure 2c), and March (Figure 2d). Negative anomalies of 30 to 45 percent are shown for December through March.

Figure 3 shows the average area, during February and March for each year since 1979, of anomalously low Arctic ozone (lower than 300 DU). For 2005, the size of the area of anomalously low total ozone was among the largest of any year in our record since 1979, and larger than in any year since 1997. Very low lower stratosphere temperatures in 2004-2005 are associated with the presence in the Arctic of very low total ozone values (see discussion with Figure 8).

Figure 4 shows monthly anomalies of zonal mean total ozone, as a function of latitude and time, from January 1979 to March 2005. The percent anomalies are derived relative to each month's 1979-2005 average. SBUV/2 data (in this figure only) have been adjusted for long-term consistency (Miller et al., 2002). The largest anomalies occur in winter and spring months for the polar region of the Southern Hemisphere. In the high northern latitude region, positive anomalies prevailed in 1979 and the early 1980s, but mostly strong negative anomalies predominated in the mid 1990s. During the winter of 2004-2005, negative zonal mean total ozone anomalies are shown in the high northern latitude region, with positive anomalies over middle latitudes. The predominance of average negative anomalies over northern latitudes in Figure 4 is consistent with high latitude areas of strong negative anomalies, along with other high latitude areas of weaker positive anomalies shown in Figure 2.

The NOAA Climate Monitoring and Diagnostics Laboratory (CMDL) operates a 16-station global Dobson spectrophotometer network for total ozone trend studies. Figure 5 shows the total ozone data for four mid-latitude U.S. stations from 1979 through 2004. 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 6 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 4 . At northern mid-latitudes between 1979 and 1991, total column ozone decreased with estimated linear trend downward of 4 percent per decade 1998 (WMO, 1999). However, since the recovery after 1993 from the 1991 Mt. Pinatubo volcanic eruption, the downward trend of total ozone has not continued, but ozone values have not recovered to the higher values of the 1980s. 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.

Figure 7 shows monthly-mean temperature anomalies at 50 hPa for three latitude regions. For the middle latitudes and for the tropical region, monthly average temperature anomalies have been consistently below average since about 1993. The temperature anomalies for high northern latitudes for December 2004 to March 2005 were mostly negative.

Extremely low temperatures (lower than -78 C) over the Arctic region in the lower stratosphere winter and spring are linked to depletion of 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, in the region from 65N to 90N at 50 hPa (approximately 19 km) are shown in Figure 8. During the winter of 2004-2005, daily minimum temperatures over large portions of the Arctic region lower stratosphere were lower than minus 78 C from December through February. Indeed, minimum temperatures in 2004-2005 were near record low values. Moderating of coldest temperatures in the high latitude region was associated with stratospheric warming during late February and March.

Monthly mean temperature anomalies for December 2004 to March 2005 are shown in the latitude versus pressure cross sections in Figure 9. Negative temperature anomalies are shown in the high latitudes of the middle stratosphere in December, January and February. However, positive anomaly associated with a stratospheric warming is evident in the upper stratosphere in February, with downward progression shown in March.

A time series, from December 2004 to April 2005, of normalized height anomalies from 1000 to 10 hPa, for the north-polar region 65-90N, is shown in Figure 10. The strong positive tropospheric height anomalies (and negative Arctic Oscillation Index) in mid January and the first part of February, appear to precede the strong stratospheric warming and positive height anomalies in late February and early March.

Figure 11 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 also holds for this year. In the winter of 2004-2005, despite the very large area of anomalously low ozone in February, because of warming conditions in March, there was only average persistence in duration of the Arctic polar vortex and average persistence of the region of anomalously low ozone.

Figure 12 shows the relationship between temperature and polar vortex persistence by comparing average 100-hPa temperatures in the polar region for each March of the last 26 years with the date the stratospheric polar vortex diminished below a specific threshold size. The relationship in most previous years of March temperature and vortex size is also apparent in 2005. The average March temperature in 2005 was near the average of all years, associated with near average March Arctic vortex persistence.

In the winter of 2004-2005, anomalously low values of total ozone predominated in the high latitudes of the Northern Hemisphere. The size of the area of anomalously low total ozone was among the largest of any year in our record since 1979, and larger than in any year since 1997. The negative anomalies in total ozone were associated with the strong negative temperature anomalies in the lower stratosphere. Arctic temperatures in the lower stratosphere were 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. Stratosphere ozone destruction has been strong in recent years when meteorological conditions of a strong polar vortex and cold polar temperatures prevailed. Those cold conditions were present in the lower stratosphere in the winter of 2004-2005.

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 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., 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.