1. Introduction: Tasks of SAG Ozone. SAG: Ozone profile information: Ozone Sondes Umkehr

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1 SAG Ozone Geir Braathen (WMO) Johanna Tamminen (IGACO O 3 /UV) Frank Baier, Jack Fishman, Sophie Godin Beekmann, Robert Evans, Ulf Koehler, Takeshi Koide, Ed Hare, Tom McElroy, Alberto Redondas, Herman Smit, Johannes Staehelin (chair), Richard Stolarski, Rene Stuebi, Ronald van der A, Karel Vanicek, Mark Weber

2 1. Introduction: Tasks of SAG Ozone SAG: Ozone profile information: Ozone Sondes Umkehr

3 Total ozone instruments operated by MeteoSwiss at Arosa: 2 Dobson instruments 3 Brewer instruments (2 single and 1 double Brewer) Dobson instrument Earlier version: 1920 th method presently used: IGY: 1958 Brewer spectrophotometer commerc. available: middle of 1980 th completely automated, SO 2 column, UV B

4 Challenge: Total ozone series of Arosa long term changes: small

5 Outline (tasks of SAG Ozone) 2. Dobson network 3. Brewer network 4. Ozone profile measurements (ozone sondes, Umkehr) 5. Capacity building 6. IGACO O3/UV 7. Future 8. Conclusions and outlook

6 Basic measurement principle of ground based measurements of total ozone (most precise measurements: direct sun) Sun photometry, wavelength region: nm I (λ) = I o (λ) exp ( α(λ) X μ β (λ) (p s /p o ) m R δ (λ) m a ) X: total ozone amount (in Dobson units (DU) I (λ): solar irradiance at the wavelength λ measured at the Earth s surface I o (λ): intensity outside the Earth s atmosphere α(λ) is the monochromatic ozone absorption coefficient μ: relative slant path through ozone (air mass factor) β(λ): Rayleigh scattering coefficient p s : station pressure; p o : mean sea level pressure at hpa; m R : relative optical air mass corresp. to Rayleigh scattering (extinction) δ(λ): aerosol optical depth m a : relative optical air mass corresp. to aerosol scattering (extinction)

7 Calibration of total ozone instruments I o (λ): intensity outside the Earth s atmosphere Extrapolation for µ (µ = 0) Langley plot method Requirement: clean atmosphere and stable ozone for one half day Difficult to ensure in extratropics Langley plot calibration for Primary Dobson/Brewer standard instrument in Mauna Loa (Hawaii)

8 2. Dobson network Central Calibration Laboratory: NOAA, Boulder, USA (R. Evans) Calibration of station instruments: Dobson intercomparisons (every 4 years) (Ulf Köhler): Responsibility of Regional Calibration Centers

9 1.0% 1976 scale 1987 scale 1991 scale 1993 scale D065 Abs. Cal at MLO 0.5% 0.0% 0.5% 1.0% Average Percent difference normalized to total ozone=300 DU, averaged over Mu=3, 2, Stability of calibration of World primary Dobson instrument (D083): Percent difference in calculated total ozone based on corrections to D083 A and D tables from Langley plot calibrations at Mauna Loa Observatory, Hawaii (Evans et al., 2004 and Komhyr et al., 1989).

10 Relative differences between standard Dobson instruments and compared station instruments during initial calibrations of the intercomparisons since 1969 (from Köhler et al., 2004). Experience with network: In good shape; because of 3 transfer steps for calibration of station instruments deviations from primary Dobson instrument can amount to (potentially more) ± 2 %; Dobson data quality workshop (Haredc Kralove)

11 WMO/UNEP Dobson Data Quality Workshop Motivation: Comparison with satellite measurements Absolute and relative (in percent from the total number) number of sites with no issues (see text) in the record in 5 bins for Dobson, Brewer, and filter instrument sites located between 60 o S and 60 o N (from Fioletov et al., 2008, workshop prior to SAG ozone meeting in Tenerife) 100 Number of stations Relative number of stations in % Dobson Brewer Filter

12 Hradec Kralove, Czech Republic, February 14 18, 2011, Karel Vanicek), report in prep. Recommendation of the 7 ORMM (Ozone Research Managers Meeting), 2008: A technological workshop should be organized to bring together managers of the archived data sets that require reprocessing and provide guidance on how best to perform this work, following which the reprocessing should then take place. Conveners and Support The Ozone Secretariat of the United Nations Environment Programme The World Meteorological Organization GAW Programme Vienna Convention Trust Fund on Research and Systematic Observations Aims: 1.To bring together managers of the archive data sets from the Dobson stations and provide guidance on how to re evaluate and re process important past data sets 2.To collect the primary (0 level) Dobson data sets and calibration metadata from stations to be saved in the WOUDC data base 3. To present the actual scientific themes and results on operation of the Dobson instruments and data quality assurance at the stations given by invited experts

13 Preliminary Summary of Workshop Station managers representing around 75% of Dobson stations were present Workshop allowed for efficient collaboration between representatives of stations and other experts A detailed template was developed including all critical information Level 0 data of Dobson data need to be archived Digitation of old Dobson data is time consuming Representatives of important stations did not attend (e.g. VR China, India, Kenia)

14 3. Brewer network Central Calibration Laboratory: Environment Canada, Toronto (T. McElroy) : Triad: 3 Brewer instruments, regular Langley plot calibration of one instrument at Mauna Loa Observatory European regional Brewer calibration center: Izaña (Tenerife) (A. Redondas): triad of Brewer spectrophotometers, regularly calibrated by the Langley plot method (redundancy in calibration scale) Calibration of station instruments (every 2 years): Canadian instruments: EC for European instr.: European Brewer calibration center Private companies (needs financing by stations) IOS (International Ozone Service) Kipp and Zonen (company producing Brewer instrument)

15 Experience with Brewer network Brewer instruments: More advanced technology (fully automated, more flexible) Different institutions involved in calibration of station instruments (private companies, funding from stations needed) Biannual Brewer workshop: information of new developments, training of station personnel, exchange in experience Still room for improvements: Highest priority: SOPs for calibration in the Brewer network

16 4. Ozone profile measurements (ozone sondes, Umkehr) Sondes: types: BM, ECC, Japanese and Indian sondes Simulation chamber JOSIE (Jülich Ozone Simulation Experiment) H. Smit ECC ozonesondes different responses: manufacturers (ENSCI Z and SPC 6A) different solute Concentrations (SSTO X) ASOPOS report close to publication

17 Data archieve WOUDC (Ed Hare): Ozone sonde networks Ozonesonde stations: WOUDC, NDACC, SHADOZ NOAA NILU Archives: Different formats and information. Progress underway Homogenisation of (ECC) series WMO/GAW Ozone Sonde Experts Meeting & NDACC Ozone Sonde Workgroup Meeting, Feb. 2009, Jülich, Germany Umkehr: Work in progress

18 5. Capacity building Re use of old Dobson instruments in developing countries including training (K. Vanicek, U. Köhler, R. Evans) (most successful: Partnerships of groups of developing and industrialized countries (Nairobi: Kenia/Switzerland) (WMO/UNEP Dobson Data Quality Workshop, Hradec Kralove)

19 6. IGACO O3/UV Theme Report on Integrated Global Atmospheric Chemistry Observations (IGACO) (2004): Strategy for combing ground based, aircraft and satellite data and modeling Implementation plan for O3 and UV: G. Braathen, A. Mälkki, J. Staehelin, J. Tamminen, and A. Webb: IGACO Ozone and UV radiation Implementation Plan, GAW Report. 182, WMO, Geneva, Main activities (Johanna Tamminen, FMI): Website ( o3.fi/en/index.html) Ozone Theme Meetings, Geneva 2008: Ozone profiles: NDAC and SAG ozone different histories (at least partially) same goals: Discussion of recent results of common interest 2009/2010: ACSO 2011: SPARC/IGACO O 3 /IO3C Initiative on Understanding Past Changes in the Vertical Distribution of Ozone

20 ACSO ("Absorption Cross Sections of Ozone") established in spring 2009 is a joint ad hoc commission of GAW (SAG ozone IGACO O3/UV), International Ozone Commission (IO 3 C, IAMAS). Problem: presently used ozone absorption coefficients (standard): Bass and Paur, 1985 (old, not fulfilling demands of satellite community. Mandate: Review of literature of ozone absorption cross sections (temperature dependencies); first priority: wavelength range of nm (extension?) Impact of changing ozone absorption cross sections for all commonly used (both ground based and satellite) ozone instruments (consistency of records; impact of implementation ). Recommend whether a change should be made to presently used WMO/IO3C standard ozone absorption cross section data (Bass and Paur, 1985). If a change is recommended, provide guidelines and time line for implementing new absorption cross sections, for each instrument type. The findings to be documented in a report. The recommendations to be discussed with the community. The formal mandate ends in two years after the first meeting in 2009 (2011).

21 ACSO results (Dec 2010) Ozone absorption cross sections of the group from Reims (Brion, Daumont, Malicet et al. (BDM (see o3.fmi.fi/acso/): higher quality than Bass and Paur, (denoted as B&P), more suitable for (some) retrieval of atmospheric ozone measurements derived from data in the relevant ultraviolet spectral range. Ozone absorption cross sections in the IR (lower priority at the present time) There seems to be a systematic bias of about 4% between the midinfrared line intensities (around 10 microns) and the ultraviolet crosssections. The effects of a switch of ozone absorption cross sections from B&P to BDM were quantified for the commonly used ground based instruments making use of measurements in the ultraviolet wavelength range (such as Dobson, Brewer and LIDAR instruments).

22 ACSO, cont. The effect of a switch was also quantified for most algorithms used in satellite retrievals; some groups prefer to use other cross sections because of retrieval issues (like using reference spectra recorded with the pre flight instruments). The impact of the switch on TOMS data is expected to be of the order of about 1.5% but the final evaluation of the impact of switching from B&P to DBM in long term TOMS OMI time series requires full reprocessing of the data sets. The impact on SBUV is expected to be very small so it might be possible that in the future, there will be a larger discrepancy between SBUV and TOMS data than before. Further laboratory measurements in order to confirm the ozone absorption cross sections of DBM would be useful, particularly regarding the temperature dependence for the relevant atmospheric conditions. Such experiments are currently underway. It would be very important to perform further measurements in different groups to identify and resolve potential systematic errors or differences. For projects (e.g. GOME, GOME 2, SCIAMACHY) that are presently using cross sections that have been measured with the instrument itself, the impact of using other reference cross sections than the recommended ones needs to be assessed quantitatively

23 New activity for IGACO O3/UV SPARC/IGACO O 3 /IO3C Initiative on Understanding Past Changes in the Vertical Distribution of Ozone Workshop Geneva January 25 th 27 th 2011: Motivation: (i) climate change expected to modify ozone profiles (in addition to ODS); (i) since 2005 (stop of satellite instruments (UARS and SAGE)) ozone profile changes need synthesis (homogenization) from different instruments; Action plan available developed Coordination: Neil Harris, Johannes Staehelin, Rich Stolarski Short Assessment (description of (ground based) instrumental records and their stabilities are expected to provide important scientific papers and/or reports but should not be integral part of the assessment)

24 7. Future

25 Ozone anomalies from model CMAM and measurements; Cly (Shepherd, 2008) more ozone at lower stratosphere: greenhouse gas

26 8. Conclusions and outlook Science Ozone layer will recover from Ozone Depleting Substances (ODS, e.g. CFCs) (Montreal Protocol, 1987) High demand for continuation of high quality stratospheric ozone monitoring in future: (a) Ozone recovery from ODS; (b) comparison with merged satellite data (satellite instruments: limited life times, merged satellite series required for long term trend analysis) ; (c) prediction of super recovery (more O 3 in extratropical tropopause region): relevant for climate change Understanding Past Changes in the Vertical Distribution of Ozone

27 8. Conclusions IGACO O3/UV: Very useful framework for collaboration of satellite and ground based measurements; excellent contribution of FMI (Johanna Tamminen (ACSO, Understanding Past Changes in the Vertical Distribution of Ozone) Ground based measurements: Column ozone: two independent networks Networks: high quality measurements (except in polar regions at low solar elevation): suitable for long term trend analysis and validation of satellite measurements. Dobson network: very good condition, data quality workshop; Brewer network: room for improvement. Ozone sonde network: Challenges with 3 different networks (burden for WOUDC)

28 Outlook Improvements of Brewer network ACSO report and recommendations Introduction of new ozone absorption cross sections (depending on recommendations of ACSO) Homogenization of ozone sonde measurements (also part of Understanding Past Changes in the Vertical Distribution of Ozone ) Further reprocessing of historical total ozone measurements (started with WMO/UNEP Dobson Data Quality Workshop)

29 Acknowledgement: SAG Ozone Geir Braathen (WMO) Johanna Tamminen (IGACO O 3 /UV) 7 Frank Baier 5, Jack Fishman 7, Sophie Godin Beekmann 6, Robert Evans 1, Ulf Koehler 12, Takeshi Koide 12, Ed Hare 4, Tom McElroy 2, Alberto Redondas 2, Herman Smit 3, Rene Stübi 123, Johannes Staehelin (chair), Richard Stolarski 7, Ronald van der A 7, Karel Vanicek 12, Mark Weber 7 1 : Dobson; 2 : Brewer; 3 : ozone sondes 4 : WOUDC; 5 : DLR data base; 6 : NDACC (Lidar) (Umkehr); 7 : satellite;