Climate Prediction Center - Stratosphere: Winter Bulletins

Concerns about 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 after each April, and for the Southern Hemisphere, after each December. These Summaries are available on the World-Wide-Web, at the site

Further information may be obtained from Craig S Long
W/NP52, RM 806, WWB
NOAA Climate Prediction Center
5200 Auth Road
Camp Springs, MD 20746-4304
Telephone: (301) 763-8071, ext. 7557
Fax: (301) 763-8125
E-mail: Craig.Long at noaa.gov

“Average” sums up the 2009 ozone hole and Southern Hemisphere Winter/Spring seasons. This year’s ozone hole was “average” in peak size and longevity. The sizes of the South Polar vortex and area in which PSC clouds could form were also “average” over the entire SH winter/spring. Directly above the South Pole (SP), NOAA’s ESRL ozonesonde observations indicated that ozone was on the low side of historical observations all year long. As the ozone depletion occurred, from August through September, total ozone values dropped to a minimum ozonesonde-reported value of 99 DU on September 25, 2009. Complete ozone depletion in the entire14-22 km region was not observed this year; however, complete depletion did occur several time in parts of this altitude region. The low ozone value was recorded while the polar circulation was centered over the SP station in September, but in October the polar circulation developed a strong wave 1 pattern displacing the polar vortex toward Africa. Consequently, after September the center of the polar vortex and the ozone hole were not located directly above the SP station. Dynamically, wave activity was slightly above average but without strong episodes to disrupt the circulation. Temperatures were near the 30 year average over the south polar region. The residual Quasi-Biennial Oscillation (QBO) circulation resulted in higher than average ozone values in the surf zone and lower than average ozone values in the tropics.

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 Solar Backscatter UltraViolet (SBUV) instrument from 1979 through 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 December 1998; NOAA-11 SBUV/2 from January 1999 to December 2000; NOAA-16 SBUV/2 from January 2001 to December 2005; NOAA-17 from January 2006 to December 2008; and NOAA-18 from January 2009 to present. Solar-backscatter ultraviolet measurements are not available at polar latitudes during winter darkness.

Figure 1 presents a time series of the size of the Ozone Hole, the size of the south polar vortex, and the size of the south polar area where lower stratospheric temperatures were below -78ºC (polar stratospheric cloud, PSC area). The daily 2009 values are shown, along with the extreme and average daily values for the 10 most recent years. The “Ozone Hole” is defined as the area in which total ozone amounts fall below 220 Dobson Units (DU). The polar vortex is defined as the area within the -32 potential vorticity units on the 450K isentropic surface (This surface is usually near the 70 hPa pressure level). The total ozone in this bulletin is determined from SBUV/2 analyses. The coverage of the SBUV/2 on NOAA polar orbiting satellites increases poleward on a daily basis during August and September as sunlight returns to the southern high latitudes. This is also the same time that ozone depletion occurs. Figure 1a shows that the ozone hole size for this year was very near “average” in terms of the past 10 years. The peak ozone hole size was detected on September 19, 2009 at 23.7 million sq km. Figure 1b and 1c indicate that both the south polar vortex area and the PSC area were “average” compared to the past ten years. The ozone hole filled in rather abruptly in late November as the transition from winter to spring circulation hastened in late November.

Figure 2 shows the average September PSC areas from 1979 to 2009. The September mean PSC area for 2009 was 188 m sq km. This is about 15-20 m sq km smaller than the five largest September PSC areas. The 2009 September PSC area is similar in size (~185 m sq km) to that of 1980, 1999, 2001, and 2007. In September 1980 an area of similarly cold temperatures did exist and PSC probably did form, but the chlorine content in the atmosphere was much less such that heterogeneous ozone depletion did not occur on a massive scale. Figure 3 shows that the peak ozone hole sizes for 1999, 2001, 2007 and 2009 were also similar in size. The figure shows that the 2009 peak ozone hole size ranked 10th largest out of 31 ozone holes periods observed since 1979. (NOTE: the 1979 and 1981 ozone holes were small and unstructured, hence their dates could not be placed in Figure 4.)

Figure 4 shows the relationship between the Vortex Vanishing Date and the Ozone Hole Vanishing Date. The relationship between the ozone hole and vortex vanishing dates is such that the longer the vortex lasts the closer the ozone hole vanishing date is to the vortex vanishing date. Unlike 2008 in which both dates were longer than any previous year, the dates for 2009 are in the “middle of the pack”.

Maps of the Southern Hemisphere monthly mean total ozone analyses from the NOAA-18 SBUV/2 for August, September, October, and November are shown in Figure 5 and their anomalies relative to the mean for the 1979-1986 period are shown in Figure 6. Figure 5a and 5b show that the ozone depletion area was very centered upon the South Pole. The ozone maximum region equatorward of the ozone depletion area is also uniformly distributed around all longitudes. Figure 5c shows that in October a wave 1 pattern existed pushing the ozone hole area towards the African side of Antarctica. The ozone maximum region has also developed its characteristic “crescent” shape with the maximum region directed toward New Zealand. Figure 5d shows the ozone hole retained a wave 1 feature in November, but the central longitude moved westward toward South America. The ozone anomalies in Figure 6 show that ozone depletion of greater than 45% occurred in all four months. The anomaly maps also show that the ozone maximum region is anomalously high by about 20%. The tropical region is characterized by negative anomalies of 10-15%. These later two ozone anomaly features are consistent with the direct and residual circulations of the QBO winds.

The equatorial zonally averaged zonal wind anomalies between 100 and 10 hPa are shown in Figure 7. Oscillations of eastward and westward wind anomalies (aka QBO) are very apparent. In 2009 there were descending easterlies above and descending westerlies below 20 hPa. In this phase the Brewer-Dobson circulation is increased. Characteristically, negative total ozone anomalies exist in the tropics with positive anomalies in the subtropics.

The zonal mean total column ozone anomalies from a cohesive SBUV/2 data set are presented in Figure 8. The latitude regions of positive and negative anomalies are more clearly identified in terms of the total ozone zonal mean anomalies. In association with the transition from westerlies to easterlies in the QBO winds, lower than average tropical ozone values are observed. In the surf region and in the middle latitudes the QBO’s residual circulation results with positive ozone anomalies. These patterns show up again in Figure 9, which are the mean total ozone anomalies for the equatorial zone (10N-10S), the surf zone (10ºS-25ºS) and the southern middle latitudes (30ºS-50ºS). The QBO-like pattern in the equatorial zone is very distinct. There is also no apparent trend in the ozone anomalies with time. Transitioning from the equatorial zone to the middle latitude zone, one begins to see a negative trend in the ozone anomalies. Also apparent is that positive ozone anomalies are present when the equatorial ozone anomalies are negative.

The transport of heat into the polar latitudes dictates the mean temperature of the polar vortex by modulating the Brew-Dobson circulation, and its variability can also dictate the longevity of the polar vortex. Figure 10 shows the eddy heat flux at 100 hPa between 45ºS and 75ºS averaged over a 10 day period. The 2009 eddy heat flux rarely exceeds the daily variability’s one standard deviation, implying that the wave activity in 2009 was “normal”, and thus the polar vortex was not greatly disturbed, and lasted until the end of November. The increased eddy heat flux activity in October coincides with the wave 1 pattern of the polar vortex during this month. The next period of eddy heat flux activity, in the third week of November, coincides with the disruption of the polar vortex and the mixing remnants of the ozone hole with higher ozone concentration air.

A considerable amount of wave activity occurs in the middle and upper stratosphere. It plays a role in the timing of the transition of the winter to spring circulation. Between August and December the wave activity, as stated above, can affect the size and longevity of the ozone hole. We see in Figure 11 , which shows the wave 1 amplitude from 1000 to 0.4 hPa for the latitude zone between 50ºS and 80ºS, that there were short periods of increased wave activity prior to August, the end of August, at the end of September, throughout October, and then in November. This wave amplitude agrees well with the high eddy heat flux periods shown in Figure 10.

Temperatures in the vertical region of the stratosphere where ozone depletion occurs during the austral winter and spring were not as cold as seen in previous years. Figure 12 shows the coldest temperature at 50 hPa poleward of 65ºS. As usual from May through October the temperatures are cold enough (T< 78ºC) to support the formation of Type I PSC clouds. However, the coldest temperatures were closer to the 30 year CPC mean than to the extreme temperatures. Figure 13 shows the zonal mean seasonal average temperature anomalies for September-October-November. The 65ºS-90ºS anomalies for 2009 are below average. The sustained vortex that existed throughout October and most of November may account for the below average temperatures. The near normal temperature anomalies in the mid-latitudes may be associated with the positive ozone anomalies.

The time series of total column ozone derived from ozonesondes launched from the South Pole station are shown in Figure 14 . The 2009 observations shows that during the austral winter months (July and August) the total ozone amounts were below previous years. In September the decline of total ozone was very similar to other years, reaching a minimum value of 95 DU on September 25th. As discussed earlier, it was shortly after this that a wave one pattern developed in the south polar circulation moving the area of maximum depletion away from directly over the South Pole towards the African quadrant. In past years, when the circulation stayed centered over the SP (1993, 1999, and 2006), the total ozone minimum was not achieved until the first or second week of October.

Time series of the integrated partial column ozone amount between 12 and 20 km are shown in Figure 15 ; this is the vertical region of greatest ozone depletion. The time series shows large variability of the ozone amount in this region during the austral winter months. But during the first week of October, the integrated amount of ozone can be very near zero. The 2009 observations show that the ozone depletion over the South Pole was not nearly as great as other years. Again, this can be attributed to the polar circulation pattern moving off of the pole toward Africa.

Several ozonesonde profiles in late September and early October, 2009 are shown in Figure 16 . Although the late September profiles have a lower integrated total ozone, there is much more ozone in the 12-20 km region than in the profiles from a week later. Apparently, low ozone amounts below 12 km in the late September profiles account for the lower total ozone amounts.

The average total ozone amounts for the latter half of October since the early 1960’s at the South Pole taken by the Dobson Spectrophotometer are presented in Figure 17 . The time series shows, with the inclusion of the 2009 observation, that the 2000’s continue to be highly variable in contrast to the late 1990’s which were consistent and had lower total ozone values.

The ozone hole for 2009 was “average” relative to the last 10 years. The size of the polar vortex was smaller than previous years as was the area of temperatures cold enough to support PSC formation. On the other hand, wave activity was not substantially large and as a consequence the polar vortex circulation existed well into November. The minimum total ozone amount measured at the South Pole occurred in late September, which is about a week earlier than most years. The early date is due to the formation of a wave 1 in the polar circulation which moved the area of greatest depletion away from the South Pole towards the African quadrant.

Observations of chlorofluorocarbons 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 impact the atmospheric ozone amounts for many decades to come. The Antarctic Ozone Hole is expected to continue for decades. Antarctic ozone abundances are projected to return to pre-1980 levels around 2060-2075, roughly 10-25 years later than estimated in the 2002 Assessment. The projection of this later return is primarily due to a better representation of the time evolution of ozone-depleting gases in the Polar Regions. In the next two decades, the Antarctic Ozone Hole is not expected to improve significantly (WMO, 2007). Further, changing conditions (i.e. meteorological, solar, and volcanic aerosols) 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 22 years of South Pole ozone vertical profile measurements, Hofmann et al., (2009) suggested that, according to indicators such as the September ozone loss rate at 14-21 km and ozone loss at the upper limits of the ozone hole (22-24 km), the beginning of recovery of the Antarctic Ozone Hole had not yet begun and may not be detected for some time. An intriguing aspect of recent observations of the Antarctic stratosphere had been the apparent trend towards a later breakup of the vortex in years since 1990, relative to the 1980s. The size and duration and size of the 2008 Ozone Hole 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. Russell 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., 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, 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, 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.

WMO, 2006: Scientific assessment of ozone depletion: 2006. World Meteorological Organization Global Ozone Research and Monitoring Project.

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