Content - Previous Activities

Previous SPARC activities

Solving the mystery of Carbon Tetrachloride (CCl4)

Carbon tetrachloride (CCl4 or CTC) is a major ozone depleting substance and greenhouse gas: ozone depletion potential (with respect to CFC-11) of 0.72 (WMO, 2015), and a 100-year global warming potential of 1730 (WMO, 2014). Unfortunately, estimated CTC sources and sinks remain inconsistent with abundance observations. The WMO (2014) total global lifetime estimate (26 years) combined with the observed atmospheric trend implies emissions of 57 (40–74) Gg/yr. This emission level cannot be reconciled with emissions from reported net production. Liang et al. (2014) updated (WMO, 2014) by using surface observations of trends and the inter-hemispheric gradient to estimate a 35 (32-37) year global lifetime and 39 (34-45) Gg/yr. The large discrepancy between the near zero UNEP report emissions and 39 Gr/yr top-down emissions suggest that there is a large unknown source of CTC.

This activity brought together science, industry, and technology experts to solve the CTC mystery. The effort involved observation scientists, together with experts in photochemistry, ocean and soil losses, emissions, modeling, and industrial processes. 

As a first step, we brought together experts in all of these areas together for a 2-day workshop. This workshop involved both solicited and submitted presentations related to all aspects of the CTC problem. 

Workshop topics included:

  • Observations of CTC from ground stations, aircraft, balloon, satellite, and ships
  • Photochemistry of CTC loss
  • Ocean and soil losses
  • Global and regional emission estimates
  • CTC consumption and production for both historic and current usage
  • CTC feedstock usage and potential CTC fugitive emissions 
  • Legacy emissions from brown-field sites
  • Reconciling the emission and loss processes of CTC with observations in a global modeling perspective 

The workshop provided information across disciplines and areas that would not necessarily interact with one another. The workshop took place from 5-6 October 2015 in Zurich, Switzerland. For further details please consult:

In 2016, this activity published its final assessment report (SPARC Report No. 7).


Liang, Q. et al. (2014) Constraining the carbon tetrachloride (CCl4) budget using its global trend and inter-hemispheric gradient. Geophys. Res. Lets., 41, 5307-5315.

SPARC (2016) SPARC Report on the Mystery of Carbon tetrachloride. Q. Liang, P.A. Newman, and S. Reimann (Eds.), SPARC Report No. 7, WCRP-13/2016.

WMO (2014) Scientific Assessment of Ozone Depletion: 2010, Global Ozone Research and Monitoring Project. Report No. 52, Geneva, Switzerland, 516 pp.

Activity leaders

Qing Liang, USRA/NASA, USA

Paul Newman, NASA, USA

Stefan Reimann, Empa, Switzerland


Montreal Protocol SAP and TEAP, UNEP, WMO, industry, NGOs, Empa, NASA, NOAA.

Published results

SPARC, 2016: SPARC Report on the Mystery of Carbon tetrachloride. Q. Liang, P.A. Newman, and S. Reimann (Eds.), SPARC Report No. 7, WCRP-13/2016, available at

Ozone Profile (II) – SI2N initiative

Figure 1: Schematic of the five main working groups in the second ozone initiative. The sixth working group looking at the different approaches to combining data sets is led by G. Bodeker and N. Harris. The remit in these six work packages will be re-assessed at the second workshop (from Harris et al., 2011).

Figure 2: Combined ozone profile trends for the periods before 1998 (top row) and after 1998 (bottom row). Click image to enlarge and read the full legend.

A common activity supported by SPARC, the IOC (International Ozone Commission), IGACO-O3/UV (Integrated Global Atmospheric Composition Observations), and NDACC (Network for Detection of Atmospheric Composition Change). The first letters of all partners combined make the activity's acronym: SI2N.

Goals and scientific background: The vertical distribution of stratospheric ozone on a global scale is determined by stratospheric chemistry and transport. The basic features of global vertical distribution of ozone available in the 1970s (see Dütsch, 1979 and Staehelin et al. 2001) were established based on ozone sondes and Umkehr measurements. Since 1972 ozone profiles have been monitored globally and quasi-continuously by satellite instruments, the longest datasets currently existing are the SAGE I and II and SBUV (/2) records.

Beginning around 1970, the emission of anthropogenic ozone depleting substances started to affect the ozone layer. Concentrations of these species (as described by Equivalent Effective Stratospheric Chlorine) peaked in the second part of the 1990s. Stratospheric ozone profile changes, which vary in latitude and season, contain important information about anthropogenic chemical ozone depletion.

During the 1990s information from SAGE I and II, SBUV, and other ground-based measurements revealed partially conflicting results, leading to a SPARC-led investigation and the first SPARC Assessment Report (SPARC Report No. 1, 1998). One key result of this report concerned Northern mid-latitudes: the ozone decrease in the lower stratosphere most strongly contributed to the significant downward trends in total ozone, with an additional maximum in ozone depletion occurring in the upper stratosphere showing a similar relative decrease in ozone mixing ratios (directly attributable to in situ ozone depletion by chlorofluorocarbons and other ozone depleting substances).

Since the beginning of the 21st century, chemical ozone depletion should have slowly been decreasing and information on ozone profile changes is important to document the positive effect of the Montreal Protocol (see WMO, 2014). However, it is also known that stratospheric ozone may also be affected by climate change, e.g. the enhancement of the Brewer Dobson Circulation predicted by state-of-the-art numerical models (see e.g. Harris et al., 2008; Douglas et al., 2011). Reliable information on long-term changes of global ozone profiles from a single instrument does not exist, for example, because the SAGE-II record stopped in 2005 (Douglas et al., 2011). There are, however, several other instrumental records that have been used to obtain observations of vertical ozone changes in the recent past. These have been combined with older records in an attempt to produce homogeneous long-term ozone profile data sets. However, combining such records is challenging because one needs to take into account the small shifts between satellite time series which inevitably occur. At the same time, high quality ground-based ozone profile records, including measurements from NDACC, are becoming longer and include more stations around the globe. These ground-based data provide an excellent complimentary record for long-term profile trend analysis.

Milestones and achievements: The initiative started with a workshop organized in Geneva in January 2011 at which it was decided to promote a new bottom-up activity to coordinate various on-going projects (e.g. supported by national space agencies and ESA (the European Space Agency)) and to stimulate additional efforts. The individual activities began by proving the quality, homogeneity, and consistence of different types of instrumental records (see Figure 1).

In 2012 several meetings were held to discuss and coordinate the activities of the various groups contributing to SI2N. A plenary meeting (with 48 scientists) took place from 16-18 April 2012 near Baltimore, USA, and all groups contributing to the activity participated. This workshop included discussion about the quality of the ozone data sets and the time plan of the activity. It was also decided to publish the SI2N results in a special issue and to summarize the key results in three overview papers (see below). Other meetings were organized for individual groups, such as the ozone-sonde community and the NDACC community. 

In 2013 a SI2N meeting took place in Helsinki, Finland, from 18-20 September (attended by around 40 participants) in which the drafts of the three overview papers that summarize the main SI2N results were intensively discussed. Other papers published in the SI2N special issue and other relevant work was presented in the form of posters to ensure that the main results of the individual contributions were adequately by the three overview papers.
By the end of 2015  the SI2N SPARC activity was formally terminated as decided in the SPARC SSG meeting in Boulder (CO, USA, November 10-13, 2015).

Final results: The relevant results of SI2N are shown in a special issue jointly organized between Atmospheric Chemistry and Physics (ACP), Atmospheric Measurement Techniques (AMT), and Earth System Science Data ESSD): Changes in the vertical distribution of ozone – the SI2N report (see SI2N report by Bhartia et al., 2012). The special issue includes more than 50 published papers. The papers cover a wide variety of studies and deal with important aspects such as data quality and trend analyses of ground-based ozone profile measurements (in relation to NDACC and GAW) and different satellite data sets. 7 merged long-term satellite series (with different lengths) were produced and used as a basis for a quasi-global ozone profile trend analysis (see Tummon et al, ACP, 2015). Three overview papers that summarize the main results of SI2N are being published. One of these papers, describing all relevant measurement systems, was published in by Hassler et al. AMT, 2014. A second paper presenting an analysis of the trends with a particular emphasis on estimating the trend uncertainties was published by Harris et al., ACP, 2015. The third which will summarise the data quality of the ozone records is being prepared. Its production has been overtaken by a paper describing a thorough comparison of the satellite measurements using the ground-based measurements (Hubert et al., AMT, currently under AMT).
Part of the most relevant findings of SI2N are shown in Figure 2 (Harris et al., ACP, 2015).

The work in SI2N has clearly shown the need for on-going, high quality measurements of the vertical distribution of ozone. The absolute importance of stability in being able to produce meaningful ozone trends and credible uncertainties is clear and will require continued observation. Satellite measurements giving a quasi-global view must be complemented by well calibrated ground-based measurements and the production of merged satellite ozone profile data needs further attention. Furthermore, the unquestionable demonstration of positive ozone profile trends as expected from the Montreal Protocol requires longer time series. Important unresolved aspects of SI2N will be incorporated into the work on long-term records developed under the new SPARC Implementation Plan.


Bhartia, P. K., N. Harris, M. van Roozendael, M. Weber, R. Eckman, D. Loyola, J. Urban, C. von Savigny, M. Dameris, S. Godin-Beekmann (eds.), 2012: Changes in the vertical distribution of ozone - the SI2N report. Atmospheric Chemistry and Physics, special issue 284.

Douglass, A., V. E. Fioletov et al., 2010: Stratospheric Ozone and Surface Ultraviolet Radiation, Chapter 2 in Scientific Assessment of Ozone Depletion: 2010, Global Ozone Research and Monitoring Project–Report No. 52, 516 pp., World Meteorological Organization, Geneva, Switzerland, 2010. 

Dütsch, H.-U., 1979: The vertical ozone distribution on a global scale. Pure Appl. Geophys., 116, 511-529. 

Harris, N. R. P., E. Kyrö, J. Staehelin, D. Brunner, S.-B. Andersen, S. Godin-Beekmann, S., Dhomse, P. Hadjinicolaou, G. Hansen, I. Isaksen, A. Jrrar, A. Karpetchko, R. Kivi, B. Knudsen, P. Krizan, J. Lastovicka, J. Maeder, Y. Orsolini, J. A. Pyle, M. Rex, K. Vanicek, M. Weber, I. Wohltmann, P. Zanis and C. Zerefos (2008) Ozone trends at northern mid- and high latitudes – a European perspectiveAnn. Geophys., 26, 1207-1220

Harris, N.R.P., J. Staehelin, and R. Stolarski (2011) The New Initiative on Past Changes in the Vertical Distribution of Ozone, SPARC Newsletters No. 37, July 2011.

Harris, N.R.P., and J. Staehelin (2011) SPARC/IGACO-O3/IOC Initiative on Understanding Past Changes in Vertical Distribution of Ozone. See workshop presentation.

SPARC Report No. 1 (1998) SPARC/IOC/GAW Assessment of Trends in the Vertical Distribution of Ozone. By N. Harris, R. Hudson and C. Phillips (eds.). WMO Ozone Research and Monitoring Project Report No. 43.

Staehelin, J., N.R.P. Harris, C. Appenzeller, and J. Eberhard (2001) Ozone trends: A review. Rev. Geophys., 39, 231-290.

WMO, Scientific Assessment of Ozone Depletion (2010) Global Ozone Research and Monitoring Project–Report No. 52, 516 pp., World Meteorological Organization, Geneva, Switzerland, 2010.

Activity leaders

Neil Harris
European Ozone Research Coordinating Unit, University of Cambridge, UK

Johannes Staehelin
SPARC Office, ETH, Zürich, Switzerland

Richard Stolarski
Johns Hopkins University, Baltimore, MD, USA

Published results

Journal publications:

Bhartia, P. K., N. Harris, M. van Roozendael, M. Weber, R. Eckman, D. Loyola, J. Urban, C. von Savigny, M. Dameris, S. Godin-Beekmann (eds.), 2012: Changes in the vertical distribution of ozone - the SI2N report. Atmospheric Chemistry and Physics, Special issue.

SPARC activity reports:

SPARC Newsletter No. 47, 2016, p. 4: The SI2N Initiative: An Overview of Ozone Profile Trends, by Harris, N.R.P., B. Hassler, D. Hubert, F. Tummon, and J. Staehelin.

SPARC Newsletter No. 39, 2012, p. 21: Progress Report on the SI2N Initiative on Past Changes in the Vertical Distribution of Ozone by Harris, N.R.P., J. Staehelin, and R. Stolarski.

SPARC Newsletter No. 37, 2011, p. 23: The New Initiative on Past Changes in the Vertical Distribution of Ozone, by Harris, N.R.P., J. Staehelin, and R. Stolarski.

Website for further information

SPARC/IO3C/WMO-IGACO-O3/UV activity on Past Changes in the Vertical Distribution of Ozone

See also:
SPARC activity Ozone Profile (I)
SPARC Report No. 1 (1998) Trends in the Vertical Distribution of Ozone

Lifetime of halogen source gases

The Executive Summary of the 2010 WMO/UNEP Ozone Assessment cites lifetime problems and problems associated with lifetimes:

“Evidence is emerging that lifetimes for some important ODSs (e.g., CFC-11) may be somewhat longer than reported in past assessments. In the absence of corroborative studies, however, the CFC-11 lifetime reported in this Assessment remains unchanged at 45 years. Revisions in the CFC-11 lifetime would affect estimates of its global emission derived from atmospheric changes and calculated values for Ozone Depletion Potentials (ODPs) and best-estimate lifetimes for some other halocarbons.”

“A stronger BDC would decrease the abundance of tropical lower stratospheric ozone, increase poleward transport of ozone, and could reduce the atmospheric lifetimes of long-lived ODSs and other trace gases.”

“Carbon tetrachloride (CCl4) tropospheric abundances have declined less rapidly than expected. Emissions derived from data reported to the United Nations Environment Programme (UNEP) are highly variable and on average appear smaller than those inferred from observed abundance trends. Although the size of this discrepancy is sensitive to uncertainties in our knowledge of how long CCl4 persists in the atmosphere (its “lifetime”), the variability cannot be explained by lifetime uncertainties.”

A re-evaluation is needed of the lifetimes of important halogen source gases (e.g., CFC-11, CCl4, Halons, HFCs, HCFCs, and related species), since evidence has emerged that in many cases the actual lifetimes may be considerably longer than those currently assumed in the 2010 WMO/UNEP Ozone Assessment (2010), and in the scenarios used to drive the Chemistry-Climate Models (CCMs). This represents a major uncertainty in reconciling top-down and bottom-up emission estimates, and in model projections.

This SPARC activity on ‘Lifetime of halogen source gases’ will provide a comprehensive review, and include

  • an overview of the theory of estimating lifetimes using models and observations;
  • an update of the kinetic data that determine lifetimes;
  • lifetimes deduced from observed trace-gas distributions;
  • and model estimates of lifetimes, which will require new CCM runs.

Groups that contribute to the validation of CCMs (see CCMVal) will therefore be critical participants in this initiative. The results are expected to be an important input to the next WMO/UNEP Ozone Assessment due to be published in 2014.

This SPARC activity, launched at the 2011 SPARC Scientific Steering Group meeting held in Pune, India, will result in a SPARC science report by spring 2013 to form the basis for the 2014 Ozone Assessment. The scope of the re-evaluation includes:

  1. estimating the numerical values for lifetimes, 
  2. estimating the uncertainties for numerical values for lifetimes, 
  3. assessing the influence/use of different lifetime definitions (e.g. steady-state /instantaneous lifetimes), and 
  4. assessing lifetime changes associated with the changing climate.

Presentation with the outline for the SPARC assessment report (9.1 MB)

Executive committee

Malcolm KoNASA
Langley Research Center, USA

Paul Newman
NASA Goddard Space Flight Center, USA 

Stefan Reimann
Empa, ETH Zurich, Switzerland

Susan E. Strahan
Universities Space Research Association (USRA), USA

Published results

SPARC Science Report:

SPARC Report No. 6 (2013) Lifetimes of Stratospheric Ozone-Depleting Substances, Their Replacements, and Related Species. M.K.W. Ko, P.A. Newman, S. Reimann, S.E. Strahan

SPARC activity report:

SPARC newsletter No. 42 (2014) p. 14: "The SPARC Activity: Lifetime of halogen source gases"

CCMVal - Chemistry-Climate Model Validation

The goal of the SPARC Chemistry-Climate Model Validation Activity (CCMVal) is to improve understanding of coupled chemistry-climate models (CCMs) and their underlying GCMs (General Circulation Models) through process-oriented evaluation, along with discussion and coordinated analysis of science results.

One outcome of this effort is expected to be improvements in how well CCMs represent physical, chemical, and dynamical processes. In addition, this effort will focus on understanding the ability of CCMs to reproduce past trends and variability and providing predictions from ensembles of long model runs. Achieving these goals will involve comparing CCM constituent distributions with (robust) relationships between constituent variables as found in observations. This effort is both a model-model and model-data comparison exercise. Key diagnostics with respect to radiation, dynamics, transport, and stratospheric chemistry and microphysics are defined in the CCMVal Evaluation Table. This approach allows modelers to decide (based on their own priorities and resources) which diagnostics to examine in any particular area. The CCMVal activity helps coordinating and organising CCM model efforts around the world. In this way, the CCM community can provide the maximum amount of useful scientific information for WMO/UNEP and IPCC assessments.

Validation of CCMs is a prerequisite for meaningful prediction, but it is only one aspect. The other aspect is to ensure that model predictions are made under the same conditions. However this is a very challenging and complex issue, because experimental choices (e.g. forcing scenarios, specification of SSTs, experimental strategy) are made by different model groups under various constraints, and it is a challenge to coordinate them.

During phase 1, CCMVal-1, 13 research groups ran CCM simulations and compared their results to process-oriented studies (Eyring et al. 2006, 2007). During the second phase, CCMVal-2, research groups considered a much larger number of CCMs and processes. The major outcome of CCMVal-2 was the SPARC Science Report No. 5 which was published just in time to feed into the 2010 WMO/UNEP Ozone Asssessment.

Activity leaders:

Veronika Eyring, DLR Oberpfaffenhofen, Germany

Darryn Waugh, John Hopkins University, Baltimore MD, USA

Andrew Gettelman, NCAR, Boulder CO, USA

Steven Pawson, NASA Goddard Space Flight Center, Greenbelt MD, USA

Ted G. Shepherd, University of Reading, Reading, UK

Published Results:

SPARC Science Report:

  • SPARC Report No. 5 (2010) Chemistry-Climate Model Validation. Eyring, V., Shepherd, T. and D. Waugh (eds.)

SPARC activity report:

Journal publications:

Find full publication list at

  • Butchart, N., A.J. Chariton-Perez, I. Cionni, S.C. Hardiman, P.H. Hayenes, K. Krüger, P.J. Kushner, P.A. Newman, S.M. Osprey, J. Perlwitz, M. Sigmond, L. Wang, H. Akiyoshi, J. Austin, S. Bekki, A. Baumgaertner, P. Braesicke, C. Brühl, M. Chipperfiled, M. Dameris, S. Dhomse, V. Eyring, R. Garcia, H. Garny, P. Jöckel, J.-F. Mamarque, M. Marchand, M. Michou, O. Morgenstern, T. Nakamura, S. Pawson, D. Plummer, J. Pyle, E. Rozanov, J. Scinocca, T.G. Shepherd, K. Shibata, D. Smale, H. Teyssedre. W. Tian, D. Waugh, and Y. Yamashita (2011)Multimodel climate and variability of the stratosphere. Journal of Geophysical Research - Atmosphere 116, D05102, DOI: 10.1029/2010JD014995.
  • Austin, J., K. Tourpali, E. Rozanov, H. Akiyoshi, S. Bekki, G. Bodeker, C. Brühl, N. Butchart, M. Chipperfield, M. Deushi, V. I. Fomichev, M. A. Giorgetta, L. Gray, K. Kodera, F. Lott, E. Manzini, D. Marsh, K. Matthes, T. Nagashima, K. Shibata, R. S. Stolarski, H. Struthers, and W. Tian (2008) Coupled chemistry climate model simulations of the solar cycle in ozone and temperature. J. Geophys. Res., 113, D11306 
  • Eyring V., N.R.P. Harris, M. Rex, T.G. Shepherd, D.W. Fahey, G.T. Amanatidis, J. Austin, M.P. Chipperfield, M. Dameris, P.M. De F. Forster, A. Gettelman, H.F. Graf, T. Nagashima, P.A. Newman, S. Pawson, M.J. Prather, J.A. Pyle, R.J. Salawitch, B.D. Santer, and D.W. Waugh (2005) A strategy for process-oriented validation of coupled chemistry-climate models. Bull. Am. Meteorol. Soc., 86, 1117–1133
  • Eyring, V., N. Butchart, D. W. Waugh, H. Akiyoshi, J. Austin, S. Bekki, G. E. Bodeker, B. A. Boville, C. Brühl, M. P. Chipperfield, E. Cordero, M. Dameris, M. Deushi, V. E. Fioletov, S. M. Frith, R. R. Garcia, A. Gettelman, M. A. Giorgetta, V. Grewe, L. Jourdain, D. E. Kinnison, E. Mancini, E. Manzini, M. Marchand, D. R. Marsh, T. Nagashima, P. A. Newman, J. E. Nielsen, S. Pawson, G. Pitari, D. A. Plummer, E. Rozanov, M. Schraner, T. G. Shepherd, K. Shibata, R. S. Stolarski, H. Struthers, W. Tian, and M. Yoshiki (2006) Assessment of temperature, trace species and ozone in chemistry-climate model simulations of the recent past. J. Geophys. Res., 111, D22308, doi:10.1029/2006JD007327
  • Eyring, V., D. W. Waugh, G. E. Bodeker, E. Cordero, H. Akiyoshi, J. Austin, S. R. Beagley, B. Boville, P. Braesicke, C. Brühl, N. Butchart, M. P. Chipperfield, M. Dameris, R. Deckert, M. Deushi, S. M. Frith, R. R. Garcia, A. Gettelman, M. Giorgetta, D. E. Kinnison, E. Mancini, E. Manzini, D. R. Marsh, S. Matthes, T. Nagashima, P. A. Newman, J. E. Nielsen, S. Pawson, G. Pitari, D. A. Plummer, E. Rozanov, M. Schraner, J. F. Scinocca, K. Semeniuk, T. G. Shepherd, K. Shibata, B. Steil, R. Stolarski, W. Tian, and M. Yoshiki (2007) Multimodel projections of stratospheric ozone in the 21st century. J. Geophys. Res., 112,  D16303, doi:10.1029/2006JD008332 
  • Gettelman, A., T. Birner, V. Eyring, H. Akiyoshi, S. Bekki, C. Brühl, M. Dameris, D. E. Kinnison, F. Lefevre, F. Lott, E. Mancini, G. Pitari, D. A. Plummer, E. Rozanov, K. Shibata, A. Stenke, H. Struthers, and W. Tian (2009) The Tropical Tropopause Layer 1960–2100. Atmos. Chem. Phys., 9, 1621-1637
  • Son, S.-W., L. M. Polvani, D. W. Waugh, H. Akiyoshi, R. Garcia, D. Kinnison, S. Pawson, E. Rozanov, T. G. Shepherd, and K. Shibata (2008) The Impact of Stratospheric Ozone Recovery on the Southern Hemisphere Westerly Jet. Science, 320, DOI: 10.1126/science.1155939
  • Son, S.-W., L. M. Polvani, D. W. Waugh, T. Birner, H. Akiyoshi, R. R. Garcia, A. Gettelman, D. A. Plummer, and E. Rozanov (2009) Future tropopause trends as simulated by stratosphere-resolving
chemistry-climate models. J. Clim., 22, 429-455
  • Tourpali, K., A. F. Bais, A. Kazantzidis, C. S. Zerefos, H. Akiyoshi, J. Austin, C. Brühl, N. Butchart, M. P. Chipperfield, M. Dameris, M. Deushi, V. Eyring, R. R. Garcia, M. A. Giorgetta, D. E. Kinnison, E. Mancini, E. Manzini, D. R. Marsh, T. Nagashima, G. Pitari, D. A. Plummer, E. Rozanov, J. F. Scinocca, K. Shibata, B. Steil, W. Tian and M. Yoshiki (2009) Clear sky UV simulations in the 21st century based on Ozone and Temperature Projections from Chemistry-Climate Models. Atmos. Chem. Phys., 9, 1165-1172
  • Waugh, D. W. and V. Eyring (2008) Quantitative performance metrics for stratospheric-resolving chemistry-climate models. Atmos. Chem. Phys., 8, 5699-5713.

Website for further information:

SPARC Activity CCMVal

SPARC International Polar Year

In March 2007, the International Council for Science (ICSU) and the World Meteorological Organisation (WMO) launched the International Polar Year (IPY). It ended in March 2009 to encompass full year cycles in the Arctic and the Antarctic.

SPARC was actively involved in the IPY programme with its project: The structure and evolution of the stratospheric polar vortices during IPY and its links to the troposphere.

The goal of this SPARC IPY activity (ID No. 807) was to document the dynamics, chemistry and microphysical processes within the polar vortices during the full IPY cycle, with a focus on the stratosphere-troposphere and stratosphere-mesosphere coupling. One of the key outcomes was the collection of analysis products from several operational centres and several research centres, which were archived at the SPARC Data Center. The analysis products cover the period of IPY (March 2007 to March 2009) and represent the best available self-consistent approximations to the state of the atmosphere during this period.

Project leader:

Dr. Norman McFarlane, Director SPARC Office (2005-2011)

Website for further information:

SPARC-IPY activity

Published results:

SPARC activity reports:

SPARC Newsletter No. 33 (2009), p. 5: SPARC-IPY and beyond, by N. McFarlane et al.

SPARC Newsletter No. 33 (2009), p. 6: Features of the Arctic Stratosphere during IPY, by E. Farahani et al.

SPARC Newsletter No. 33 (2009), p. 14: Studies of the Antarctic Stratosphere during IPY, by A.R. Klekociuk et al.

SPARC Newsletter No. 33 (2009), p. 21: SPARC-IPY Data Archive, by D. Pendlebury

SPARC Newsletter No. 29 (2007), p. 26: SPARC-IPY Update, by S. Polavarapu et al.

Atmospheric chemistry


The Atmospheric Chemistry and Climate (AC&C) initiative was endorsed in March 2006 as a joint effort of WCRP and IGBP, with the SPARC and International Global Atmosphere Chemistry (IGAC) projects tasked to take the lead in its implementation. The initiative was discontinued in 2011.

Within the SPARC project, the focus was on modelling activities in the middle atmosphere, with less emphasis on field experiments of chemistry and chemical processes and the troposphere. Within the IGAC project, efforts focused primarily on constraining atmospheric chemistry components and processes through measurements. 

Published results:

SPARC activity reports:

SPARC Newsletter No. 32 (2009), p. 27: Network for the Detection of Atmospheric Composition Change, by M. Chipperfield and W.J. Randel

SPARC Newsletter No. 29 (2007), p. 5: Atmospheric Chemistry and Climate: A New IGBP-IGAC/WCRP-SPARC Initiative, by Doherty, S., Ravishankara, A.R., and P. Rasch

Websites for further information:

Activity 3 ACC-MIP website

Tropopause Initiative (UTLS)

The SPARC project has, since its inception, tried to stimulate research into the dynamics, transport and chemistry in the Upper Troposphere/Lower Stratosphere  (UTLS) region. One success has been the organization of several multidisciplinary workshops on this topic, starting with the influential Cambridge workshop in 1993 that resulted in the seminal review by Holton et al. in 1995., and the 2009 UTLS workshop in Boulder, Colorado, that resulted in the recent review by Gettelman et al. (2011)., as well as the recent review of the tropical tropopause by Fueglistaler et al (2009).  

The tropopause region and the UTLS is a transition region between the stratosphere and the troposphere. The UTLS includes the Tropical Tropopause Layer (TTL) and the extratropical upper troposphere and lower stratosphere (Ex‐UTLS).

The Tropical Tropopause Layer (TTL) is a transition layer in which the air has mixed stratospheric and tropospheric properties. The TTL has increasing levels of ozone with height, large lapse rates and near its base the net radiative heating changes sign from negative below to positive above. The heat, moisture and chemistry budgets of the TTL ultimately affect the properties of stratospheric air. These budgets are influenced by slow ascent within the upward branch of the Brewer-Dobson circulation and by overshooting deep moist convection, which is an effective transport method from the boundary layer. The relative importance of the contribution of deep moist convection to the heat, moisture and chemistry budgets of the TTL is still uncertain and subject of debate.

The TTL has received attention within the SPARC community from the perspective of its importance for processes in the tropical lower stratosphere, while research on modelling and understanding of deep convection in the tropics has received considerable attention within the GEWEX Cloud System Study (GCSS). The IGAC (International Global Atmospheric Chemistry) community is interested in the role of deep convection in transporting and processing chemical constituents and aerosols. Past activities have aimed at bringing these three groups together to understand the TTL and the role of deep convection in determining the composition of the TTL and the inputs into the stratosphere. The outcome of a workshop was a set of cloud resolving model experiments that aimed at modelling the TWP-ICE experiment over Darwin. Several CRMs were used to allow for a model intercomparison.

The Ex‐UTLS includes the tropopause, a strong static stability gradient and dynamic barrier to transport. The barrier is reflected in tracer profiles. This region exhibits complex dynamical, radiative, and chemical characteristics that place stringent spatial and temporal requirements on observing and modeling systems. The Ex‐UTLS couples the stratosphere to the troposphere through chemical constituent transport (of, e.g., ozone), by dynamically linking the stratospheric circulation with tropospheric wave patterns, and via radiative processes tied to optically thick clouds and clear‐sky gradients of radiatively active gases. A comprehensive picture of the Ex‐UTLS recognizes that thermal gradients and dynamic barriers are necessarily linked, that these barriers inhibit mixing and give rise to spe- cific trace gas distributions, and that there are radiative feedbacks that help maintain this structure.

The current SPARC Tropopause activity has helped facilitate workshops leading to these review papers, and continues to work with a network of scientists interested in the UTLS to further science in this area. Specific foci are to better understand the TTL and the ExUTLS to be able to better understand the impacts of the tropopause region on stratospheric chemistry and tropospheric climate.

Activity leaders:

Juan A. Añel
EPhysLab, Universidade de Vigo, SPAIN

Peter H. Haynes
DAMTP, Centre for Mathematical Sciences, UK

Andrew Gettelman
NCAR, Boulder, CO, USA

Published results:

Science papers:

ARM/GCSS/SPARC TWP-ICE CRM Intercomparison Study. Ann Fridlind, Andrew Ackerman, Jon Petch, Paul Field, Adrian Hill, Greg McFarquhar, Shaocheng Xie

Fueglistaler, S., A. E. Dessler, T. J. Dunkerton, I. Folkins, Q. Fu, and P. W. Mote (2009), The tropical tropopause layer, Rev. Geo- phys., 47, RG1004, doi:10.1029/2008RG000267.

Gettelman, A., P. Hoor, L. L. Pan, W. J. Randel, M. I. Hegglin, and T. Birner (2011), The extratropical upper troposphere and lower stratosphere, Rev. Geophys., 49, RG3003, doi:10.1029/2011RG000355.

Holton, J. R., P. H. Haynes, A. R. Douglass, R. B. Rood, and L. Pfister (1995), Stratosphere‐troposphere exchange, Rev. Geophys., 33(4), 403–439.

SPARC activity reports:

SPARC Newsletter No. 29 (2007), p. 14: A SPARC Tropopause Initiative

SPARC Newsletter No. 28 (2007) p. 7: Modelling of Deep Convection and Chemistry and their Role in the Tropopause Layer: SPARC-GEWEX/GCSS-IGAC Workshop

SPARC Newsletter No. 26 (2006) p. 8: Processes governing the chemical composition of the extratropical UTLS A report from the joint SPARC-IGAC Workshop

SPARC Newsletter No. 21 (2003) p. 2: Highlights from the joint SPARC/IGAC Workshop on Climate-Chemistry Interactions

SPARC Newsletter No. 17 (2002) p. 22: Convection in the Tropical Tropopause Region and Stratosphere-Troposphere Exchange

Halogen chemistry and polar ozone

The report by Pope et al. (2007) of significantly smaller cross sections for the photodissociation of the chlorine monoxide (ClO) dimer, ClOOCl, than previously measured has challenged the quantitative analysis of ozone loss rates in the winter/spring Antarctic and Arctic lower stratosphere. To address these issues, a SPARC initiative had been installed in fall 2007 with the specific objectives of:

  • Evaluating the consequences of the new laboratory data for the ClO dimer photolysis rate on simulations of stratospheric ozone depletion, particularly in winter polar regions.
  • Evaluating old and new laboratory results for the photolysis rate and determining the type of further studies that are necessary to resolve current differences.
  • Assessing qualitative and quantitative evidence from the laboratory, field observations, and models linking polar ozone depletion to stratospheric active chlorine and bromine amounts.

Reference: Pope, F.D., J.C. Hansen, K.D. Bayes, R.R. Friedl, and S.P. Sander (2007) Ultraviolet absorption spectrum of chlorine peroxide, ClOOCl. J. Phys. Chem. 111: 4322-4332.

Activity leaders:

M.J. Kurylo, NASA Goddard Space Flight Center, USA

B.-M. Sinnhuber, University of Bremen, Germany

Published results:

SPARC report:

Kurylo, M.J., B.-M. Sinnhuber et al. (2009) The Role of Halogen Chemistry in Polar Stratospheric Ozone Depletion. SPARC Report.

GRIPS - GCM-Reality Intercomparison Project

The GCM-Reality Intercomparison Project for SPARC (GRIPS) was an initiative in which a comprehensive study of our ability to model the troposphere-stratosphere system with comprehensive general circulation models (GCMs) has been undertaken. This means first our capability of reproducing the current climate and its variability, particularly the links between the troposphere and the middle atmosphere. It also extends to studies of the influence of stratospheric trace gases on climate and an assessment of our ability to predict the impacts of their change. Such effects can only be examined with comprehensive GCMs, which include representations of all physical processes thought to be relevant to the atmospheric circulation.

Many simpler models can be applied to process studies, such as the propagation of planetary waves from the troposphere into the middle atmosphere and their effects on the stratospheric circulation, or the transport of ozone due to these waves and the ensuing chemical effects. While such models are useful for our understanding of individual processes and their likely importance for climate, they were not the focus of GRIPS. This SPARC initiative was concerned with the climate system: the interactions between these individual processes and their relative importance. Two of the most essential questions to answer were:

  1. How well do comprehensive GCMs simulate the current climate of the troposphere and middle atmosphere?
  2. Do these models predictions of the climatic effects of stratospheric change agree with each other?

These two questions essentially defined the short- to long-term objectives of GRIPS.

Activity leader:

Steven Pawson, NASA/GSFC, USA

Published results:

SPARC activity reports:

SPARC Newsletter No. 27 (2006), p. 8: Getting to GRIPS with Climate-Middle Atmosphere Model Validation, by Steven Pawson.

SPARC Newsletter No. 25 (2005), p. 6: Report on GRIPS, by D. Pendlebury and Steven Pawson.

Journal publications:

Butchart, N., A.A. Scaife, M. Bourqui, J. de Grandpre, S.H.E. Hare, J. Kettleborough, U. Langematz, E. Manzini, F. Sassi, K. Shibata, D. Shindell, M. Sigmond (2006) Simulations of anthropogenic change in the strength of the Brewer-Dobson circulation. Climate Dynamics 27, pp. 727-741.

Matthes, K., K. Kodera, J.D. Haigh, D.T. Shindall, K. Shibata, U. Langematz, E. Rozanov, and Y. Kuroda (2003) GRIPS solar experiments intercomparison project: initial results. Meteorology and Geosphysics, 54: 71-90.

Horinouchi, T., S. Pawson, K. Shibata, U. Langematz, E. Manzini, E. Giorgetta, A. Marco, F. Sassi, R.J. Wilson, K. Hamilton, J. de Grandpre, and A.A. Scaife (2003) Tropical cumulus convection and upward-propagating waves in middle-atmospheric GCMs. Journal of the Atmospheric Sciences 60(22), pp. 2765-2782.

Pawson, S., K. Kodera, K. Hamilton, T.G. Shepherd, S.R. Beagley, B.A. Boville, J.D. Farrara, T.D.A. Fairlie, A. Kitoh, W.A. Lahoz, U. Langematz, E. Manzini, D.H. Rind, A.A. Scaife, K. Shibata, P. Simon, R. Swinbank, L. Takacs, R.J. Wilson, J.A. Al-Saasi, M. Amodei, M. Chiba, L. Coly, J. de Grandpre, R.S. Eckman, M. Fiorino, W.L. Grose, H. Koide, J.N. Koshyk, D. Li, J. Lerner, J.D. Mahlman, N.A. McFarlane, C.R. Mechoso, A. Molod, A. O'Neill, R.B. Pierce, W.J. Randel, R.B. Rood, and F. Wu (2000) The GCM-Reality Intercomparison Project for SPARC (GRIPS): Scientific Issues and Initial Results. Bulletin of the American Meteorological Society 81(4), pp. 781-796.

Koshyk, J.N., B.A. Boville, K. Hamilton, E. Manzini, and K. Shibata (1999) Kinetic energy spectrum of horizontal motions in middle-atmopshere models. Journal of Geophysical Research - Atmosphere 104(D22), pp. 27177-27190.

Stratospheric aerosols

Assessments of stratospheric ozone have been conducted for nearly two decades and have evolved from describing ozone morphology to estimating ozone trends, and then to attribution of those trends. Stratospheric aerosol has only been integrated in assessments in the context of their effects on ozone chemistry and has not been critically evaluated. The objective of the SPARC Report No. 4 (2006) was to present a systematic analysis of the state of knowledge of stratospheric aerosols including their precursors. The report included an examination of precursor concentrations and trends, measurements of stratospheric aerosol properties, trends in those properties, and modeling of aerosol formation, transport, and distribution in both background and volcanic conditions. The scope of the report is extensive; however, some aspects of stratospheric aerosol science have been deliberately excluded. For instance, no examination was included of polar stratospheric clouds (PSCs) or other clouds (such as cirrus clouds) occurring at or above the tropopause.

The report produced a gap-free aerosol data base for use beyond this assessment. This required some new analysis that has not previously appeared in the technical literature. Similarly, the trend analysis required the development of a new analysis technique.

Activity leaders:

T. Peter, ETH Zurich, Switzerland

L. Thomason, NASA Langley, USA

Published results:

SPARC report:

SPARC Report No. 4 (2006) Assessment of Stratospheric Aerosol Properties (ASAP). L Thomason and T. Peter (eds.) WCRP-124, WMO/TD- No. 1295.

Middle Atmosphere Climatology

The aim of the SPARC Working Group on Middle Atmosphere Climatology led by David Karoly, Monash University, Australia, was to provide, to the the climate modelling community, the current best estimates of appropriate parameters that determine stratospheric aspects of recent time-varying climate forcing. The approach has been to consolidate existing information and provide estimates of time-varying forcings over the periods since about 1880 associated with stratospheric ozone, stratospheric volcanic aerosols and solar variations.

The activity produced stratospheric climate forcing data sets which were made available to the climate modelling community through the SPARC Data Center and used in the IPCC Third Assessment Report (2001).

Published results:

SPARC Science Report:

SPARC Report No. 3 (2002) Intercomparison of Middle Atmosphere Climatologies. Randel, M.-L. Chanin and C. Michaut (Editors).

SPARC activity report:

SPARC Newsletter No. 14 (2000), p. 15: Stratospheric Aspects of Climate Forcing, by D. Karoly

Journal publication:

Randel, W., P. Udelhofen, E. Fleming, M. Geller, M. Gelman, K. Hamilton, D. Karoly, D. Ortland, S. Pawson, R. Swinbank, F. Wu, M. Baldwin, M.-L. Chanin, P. Keckhut, K. Labitzke, E. Remsberg, A. Simmons, and D. Wu (2004) The SPARC Intercomparison of Middle Atmosphere Climatologies. Journal of Climate 17, p. 987-1003

Water vapour (I)

Considering the fundamental role of water vapour in climate, and the scarcity of information concerning its distribution, variability and long-term evolution, the SPARC Scientific Steering Group recognised the need for a critical review of the knowledge and understanding of the distribution of water vapour and its variability on time scales ranging from the seasonal to the long-term inter-annual. The lack of knowledge on water vapour also led to a large uncertainty in the prediction of climate change. Phase 1 of the SPARC Water Vapour Assessment (WAVAS-I) had been launched in 1998 with the objective to consolidate and review our understanding of the role of water vapour in the climate system and to make this assessment available to support the 2001 IPCC Third Assessment Report on Climate Change (TAR).

The WAVAS Report was published in 2000 as SPARC Report No. 2. In preparation for this report, great effort has been made to prepare the best data sets possible, to retrieve historical data sets, and to make them all available to the assessment team and to the wider community for independent verification of the results (find the data set at the SPARC Data Centre). This report contains an extensive description of the measurements and their associated uncertainties, an assessment of data quality based on comparison studies of the various data sets, and a description of the understanding of the distribution and variability of water vapour in the stratosphere and upper troposphere which ensues from the data. Finally, recommendations are made to ensure that the difficulties met during this work are overcome in order that the remaining uncertainties in our knowledge and understanding can be resolved.

Phase 2 of WAVAS (WAVAS II) will provide an update to this first assessment.

Activity Leaders:

Dieter Kley, Forschungszentrum, Germany
James M. Russell III, Hampton University, USA

Published results:

SPARC report:

SPARC Report No. 2 (2000) Upper Tropospheric and Stratospheric Water Vapour. D. Kley, J.M. Russell III, and C. Philips (eds.). WCRP-113, WMO/TD - No. 1043.

Journal publications:

Rosenlof, K.H., S.J. Oltmans, D. Kley, J.M. Russell III, E.-W. Chiou, W.P. Chu, D.G. Johnson, K.K. Kelly, H.A. Michelsen, G.E. Nedoluha, E.E. Remsberg, G.C. Toon, M.P. McCormick (2001) Stratospheric water vapour increases over the past half-century. Geophysical Research Letters 28(7), pp. 1195-1198, DOI: 10.1029/2000GL012502

Ozone profile (I)

Phase 1 of the SPARC ozone profile activity (ozone profile I) was launched in 1994 to critically examine the underlying research in the existing ozone trends assessment, and to look at plans for the monitoring of ozone (space- and ground-based) to see if the gaps are filled and calibrations ensured. This scientific assessment was carried out jointly by SPARC and the International Ozone Commission (IOC), in close co-operation with WMO’s Global Atmospheric Watch programme (GAW). The assessment led to SPARC Report No. 1 (1998).

The objective of this report was to review critically the measurements and trends of the vertical distribution of ozone and to assess associated uncertainties. Recently revised data were used where appropriate and the time period covered was extended into mid-1996.

This is the first assessment of its kind carried out by SPARC and the IOC. It was stimulated by the WMO/UNEP Scientific Assessment of Ozone Depletion (1994), which found large discrepancies between ozone trends in the lower stratosphere. One of the objectives of this assessment was to ensure continuity in the international effort necessary to prepare the WMO/UNEP Assessments, and the SPARC contribution has been since heavily relied upon in the production of the subsequent ozone  assessment. It was also being used in the preparation of the Special IPCC Report on Aviation and the Global Atmosphere (1999). In addition, this first SPARC-IOC-GAW assessment anticipated the need for precise updated observations of the vertical distribution of stratospheric ozone depletion to be used to assess the impact on climate in the 2001 Third IPCC Assessment Report on Climate Change (TAR).

Phase 2 of the ozone profile activity (Ozone profile II) will provide an update to this first assessment.

Activity leaders:

Neil Harris, European Ozone Research Coordinating Unit, Centre for Atmospheric Science, University of Cambridge, UK
Bob Hudson, Department of Meteorology, University of Maryland, USA

Published results:

SPARC report:

  • SPARC Report No. 1 (1998) SPARC/IOC/GAW Assessment of Trends in the Vertical Distribution of Ozone. By N. Harris, R. Hudson and C. Phillips (eds). WMO Ozone Research and Monitoring Project Report No. 43.