1. SPARC/IGACO-O 3 /IOC Initiative on Understanding Past Changes in the Vertical Distribution of Ozone including Do we need another assessment? Or what? Neil Harris SPARC / IGACO-O3 / IOC Workshop on Past Changes in the Vertical Distribution of Ozone Geneva January 25 th -27 th 2011

2. Outline 1998 SPARC/IOC/GAW Ozone Profile Assessment Motivation and lessons learnt Where do we stand now, 15 years on? Are the measurements good enough? And, for what? Workshop What are ther new issues? What can be done about them? Possible next steps

3. SPARC/IOC/GAW Assessment of Trends in the Vertical Distribution of Ozone May 1998 Edited by N. Harris, R. Hudson and C. Phillips SPARC Report No. 1, and WMO Ozone Research and Monitoring Project Report No. 43 Motivation Difficulties to derive consistent (global) profile ozone trends, esp. ≤ 20 km Disagreements between satellite series SAGE (I and II) and SBUV Large uncertainties, variable coverage Assessment of Trends in Vertical Distribution of Ozone (1998)

4. Profile information available for 1998 Ozone Profile Assessment Ground-based largely northern mid-lats satellite largely global & higher alt 1970199019801960

5. Trends in differences vs SAGE II Figure 1 from 1998 summary Key results: Drifts were pretty large - up to 10% per decade. What is needed for ozone-climate studies? 1 %/ decade (as for column)? 3 %/ decade? 10 %/ decade? Is it helpful to have a target? Or should we just do what we can?

6. Key results: Combined estimate of the mean trend in vertical distribution of ozone over northern mid-latitudes from 1980-1996 (heavy solid line) calculated using the trends derived from SAGE I/II, ozonesondes, SBUV and Umkehr measurements. Combined uncertainties are shown as 1  (light solid lines) and 2  (dashed lines). The combined trends and uncertainties are extended down to 10 km as shown by the light dotted lines. The results below 15 km are a mixture of stratospheric and tropospheric trends and the exact numbers should be viewed with caution. Combined trends have not been extended lower into the troposphere because there are concerns regarding the representativeness of any mean trends derived from the small sample of sonde stations. But much, much more in there….. Figure 2 from 1998 summary

7. Lessons learnt (nearly all positive) Committed team of authors and contributors mix of neutrals and experts (latter on instrument teams) wanting to improve overall understanding of measurements not overly concerned with ‘defending’ their own instruments able to commit real time and effort supported by agencies or institutions Assessment provided (for the first time) the chance to spend enough combined time to sort the problem out the appropriate expert forum a tangible end product (an assessment produced in time for the 1998 UNEP/WMO Assessment) Assessment of Trends in Vertical Distribution of Ozone (1998)

8. Where do we stand now? How does the ozone profile recover as ODS decrease? Recent measurements of the vertical ozone distribution did not say much at all about ODS recovery Effect of climate change Why? No consistent global view of ozone profile measurements after 2005 SAGE (workhorse for 1984-2005) turned off; as was HALOE (1991-2005) Many satellites making profile measurements since 2005, but they have not been well enough assessed to know what has been happening to trends in ozone profile McLinden

9. a Changes in distribution of ozone as climate changes Seidel et al., Nat. Geo., 2008 Change in location of maximum total ozone gradient in sub-tropics Total ozone is stable to 1% / decade

10. Vertical-latitudinal cross-sections of past values (1960–1970, black contours) and long-term changes (differences between 1960–1970 and 2090–2100, colour shading) for (a) annual mean vertical residual velocity; and (b) ozone using an ensemble mean of three simulations from the CMAM. For ozone, the past values are in units of ppmv and the long-term changes as relative changes. a Hegglin and Shepherd, Nat. Geo., 2010 Changes in distribution of ozone as climate changes Ozone

11. Vertical-latitudinal cross-sections of past values (1960–1970, black contours) and long-term changes (differences between 1960–1970 and 2090–2100, colour shading) for (a) annual mean vertical residual velocity; and (b) ozone using an ensemble mean of three simulations from the CMAM. For ozone, the past values are in units of ppmv and the long-term changes as relative changes. a Hegglin and Shepherd, Nat. Geo., 2010 Changes in distribution of ozone as climate changes % change over 130 yrs Ozone

12. Vertical-latitudinal cross-sections of past values (1960–1970, black contours) and long-term changes (differences between 1960–1970 and 2090–2100, colour shading) for (a) annual mean vertical residual velocity; and (b) ozone using an ensemble mean of three simulations from the CMAM. For ozone, the past values are in units of ppmv and the long-term changes as relative changes. a Hegglin and Shepherd, Nat. Geo., 2010 Changes in distribution of ozone as climate changes % change over 130 yrs What stability / precision /accuracy is needed? What is achievable? Does it depend on altitude? What spatial resolution is required? Ozone

13. Available O 3 profile measurements Do not want to enter into “debate” on funding future instruments other than to say they are needed!!!

14. Available O 3 profile measurements ENVISAT & AURA with multiple instruments SCISAT, ODIN with ≥ 1 instrument

15. Available O 3 profile measurements SBUV record 1978-now, but different instruments - low vertical resolution below 25 km A number of other UV-Vis instruments (GOME, SCIAMACHY, OSIRIS...) Is there an occultation record that can extend SAGE? Series of microwave limb-sounders (MLS, ODIN, A-MLS, SMILES) What to use for validation? What for their own trends? Much better geographical spread of ground-based networks in last 10 years SBUV GOME Umkehr Sondes Microwave Lidar Aircraft

16. Goal of new Ozone profile activity Overall goal: reliable knowledge of longterm (stratospheric) ozone profile evolution: involves a)satellite data retrieval, quality and records b)ground-based measurements (ozonesonde, lidars, Umkehr...) retrieval, quality and records c)procedures for homogenizing existing vertically resolved ozone measurements from different sources d)creating databases in different coordinate systems (for different users) Should be used as input for UNEP/WMO O 3 Assessment in 2014, i.e. ready in 2013 How best to proceed? Another assessment? Or is a different mechanism better? More instruments, more people Will need rigour and diplomacy Can electronic means be used more (vs meetings)?

17. First step: Workshop in Geneva: Jan 25-27 2011 Aims Define issues Discuss (a) what is being done and (b) what could be done* (c) how best to coordinate globally? including will there be a core measurement again? is it best to have multiple core measurements? what should be used for validation, what for trends? what are good ways to merge time series? how can this be assessed? Decide how this initiative should be organised leaders, work plan, communication, end product * ESA, NASA, CSA, SSC already have relevant programmes / projects and other groups working on it

18. Programme Satellite How good are the records? How can the recent records be best used to make multi-decadal records? Are measurements by different techniques compatible? Can SAGE be extended? Can we do better? What work is on-going? Chairs: Claus Zehner & Larry Flynn Ground-based How good are the records? Which are suitable for multi-decadal analyses on their own? (Global?) How best to use for validation? What work is on-going? Chairs: Mike Kurylo & Wolfgang Steinbrecht First step: Workshop in Geneva: Jan 25-27 2011

19. Programme Integrated data sets What is there? Instrumentally-based vs combined data sets? Role for full data assimilation? Does using met. data help or hinder? Chair: Bill Randel All chairs have been asked (a) to keep to the timetable (i.e. be brutal and ruthless) and (b) lead the discussion. Posters Will then have ~ 1 day for discussions Mixture of break-out groups and plenary Need to produce a plan of action for next two years Will be looking for interest and commitment Identify topics, leaders, needs Plan will be discussed next week at SPARC Steering Group First step: Workshop in Geneva: Jan 25-27 2011

20. Possible outcomes 1.Assessment 2.Series of papers / focussed reports adding up  could lead to virtual assessment 3.Agree workplan (work and poss. papers) leading to another workshop in a year  then decide re assessment / papers 4Do nothing special In all cases, need to define Issues Studies Sub-groups Leadership Timetable Level of commitment Need to avoid undue ownership (and defence) of instruments ?

21. 1998 Assessment Structure Chapter 1Chapter 1. Characteristics of Ozone Data Sources Used for Trend Identification Lead Authors : David Hofmann, Clive Rodgers Chapter 2Chapter 2. Ozone Data Quality Lead Authors : James M. Russell III, Herman G. J. Smit Chapter 3Chapter 3. Ozone Change as a Function of Altitude Lead Authors : Richard Stolarski, William Randel

22. Possible outcomes 1.Assessment 2.Series of papers / focussed reports adding up could lead to virtual assessment 3.Agree workplan (work and poss. papers) leading to another workshop in a year then decide re assessment / papers 4Do nothing special In all cases, need to define Issues Studies Sub-groups Leadership Timetable Level of commitment

23. Thank you