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.