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 2002-2003, low total ozone values were again observed over the Arctic region. The Arctic area experiencing very low ozone was larger than for the previous two years, but not as large as in the 1990s. During December, January , February and March, of 2002-2003, there were portions of the Arctic region where average values of total ozone were up to 45 percent lower than comparable values during the early 1980s. At the same time, total ozone values over middle latitudes and portions of the Arctic region had much higher than average values. Minimum temperatures observed in the lower stratosphere over the Arctic region in December and early January were below minus 78 C, allowing the formation of polar stratospheric clouds which promote the chemical destruction of ozone. Stratosphere temperatures in mid January rose dramatically, with significant warming throughout the Arctic stratosphere, with a splitting in two of the stratospheric polar vortex, and associated circulation effects. These stratospheric warming conditions were also associated with movement of high ozone into the Aleutian Arctic region during January, and a splitting in two of the region of low total ozone values. 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 north polar winter-spring stratospheric ozone destruction may be explained as being due to the varying conditions associated with interannual meteorological variability. The low total ozone values in the Arctic region in the winter of 2002-2003 are attributed to meteorological conditions which were favorable for ozone destruction, 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 February1985; 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.

The maps in Figure 1a and 1b show Northern Hemisphere monthly mean total ozone amounts for December 2002 and March 2003. High ozone extends over northern latitudes in the western hemisphere, while low total ozone values prevail over the eastern hemisphere Arctic region. Figure 2a shows the monthly mean total ozone percent difference of the December 2002 monthly mean for eight December 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 December 2002, negative anomalies of greater than 30 percent are evident extending from North America to Europe, but with positive anomalies of more than 45 percent centered over the Aleutian Arctic region. The persistence and movement of areas of low and high total ozone anomaly are shown in the maps for January (Figure 2b), February (Figure 2c) and March 2003 (Figure 2d). Figure 3a, b, c, and d show maps of temperature anomaly at the lower stratospheric level of 50 hPa for December 2002 to March 2003, respectively. The areas of low and high ozone anomaly correspond quite closely with the regions of low and high temperature anomaly.

Figure 4 shows monthly mean temperature anomalies at 50 hPa for three latitude regions, 65N-90N, 25N-65N, and 25S-25N. The temperature anomalies for middle and high latitudes for December 2002 and January to March 2003 were slightly negative, but strongly below average for the equatorial region.

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 5 . During November, December and early January, daily minimum temperatures were lower than -78 C. Temperatures increased markedly in association with stratospheric warming in mid January and then again in February and March.

Figure 6 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 2003 was close to average in the temperatures and duration of the polar vortex. 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. In the winter of 2002-2003 there was close to average persistence of both the Arctic polar vortex and region of anomalously low ozone.

Figure 8 shows the average area, during February and March for each year since 1979, of low ozone (lower than 300 DU). For 2003, the area of anomalously low total ozone was greater than conditions in 4 out of the last 5 years. But not as great as most of the years in the 1990s.

A time series, from December 2002 to March 2003, of normalized height anomalies from 1000 to 30 hPa, for the north polar region 65-90N, is shown in Figure 9. The strong positive anomaly in January, associated with strong stratospheric warming, appears to propagate from the stratosphere downward to the surface, resulting in a negative Arctic Oscillation phase. However, relatively weak positive or negative height anomalies in other periods do not propagate down to the surface (Zhou et al., 2002 and Baldwin and Dunkerton, 1999).

Figure 10 shows monthly average anomalies of zonal mean total ozone, as a function of latitude and time, from January 1979 to March 2003. The percent anomalies are derived relative to each month's 1979-2003 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 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 2002-2003, positive zonal mean total ozone anomalies are shown over the Northern Hemisphere. 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.

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 2002. 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, shown in Figure 10. 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 meteorological conditions.

In the winter of 2002-2003, negative and positive anomalies of total ozone were prevalent in the high latitudes of the Northern Hemisphere. The low and high anomalies in total ozone were associated with the meteorological conditions of low and high anomalies of lower stratosphere temperature. Arctic temperatures 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. As a consequence, lower stratosphere ozone destruction is strong when meteorological conditions of a strong polar vortex and cold polar temperatures prevail.

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

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.

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.