Institute for Climate and Atmospheric Science (ICAS)

Atmospheric Chemistry Group TOMCAT/SLIMCAT 3D CTM

CTM Description


TOMCAT/SLIMCAT is a three-dimensional (3D) off-line chemical transport model (CTM). The model uses winds and temperatures from meteorological analyses (e.g. from the UK Met Office or ECMWF) to specify the atmospheric transport and temperatures and calculates the abundances of chemical species in the troposphere and stratosphere. The model has the option of detailed chemical scheme(s) for the stratosphere and troposphere. The model can be used to simulate the past and current atmosphere, help interpret observations, and to diagnose the extent of problems such as stratospheric ozone depletion or tropospheric pollution.


The first version of TOMCAT was written by Martyn Chipperfield (MPC) Meteo-France in Toulouse in 1992 with the help of Pascal Simon. At this stage the model was used for stratospheric chemistry studies. From 1993 the use and development of the model followed MPC to the Department of Chemistry at the University of Cambridge. Around 1995 MPC wrote SLIMCAT. This was a stratosphere-only version of TOMCAT formulated on isentropic levels. At this time TOMCAT became a 'tropospheric' model and varrious people in Cambridge helped to add treatments of e.g. convection, boundary layer mixing, and tropospheric chemistry. MPC moved to Leeds in 1999 where the model development continues. Recently, SLIMCAT has been extended downwards to include the troposphere. As the two former models were so similar, it made maintenance/development easier to merge TOMCAT and SLIMCAT into a single library with a choice of vertical coordinate (and other things), so that one model covers all of the applications. Depending on the coordinate use, the model is still referred to as TOMCAT or SLIMCAT.

Main Model Details

  • Variable resolution. Typical resolutions are 5 x 5 degrees for multiannual runs to up to 1 x 1 degree.
  • Forced by meteorological analyses, usually ECMWF and sometimes UKMO.
  • Options of detailed stratospheric or tropospheric chemistry schemes.
  • Options of detailed aerosol microphysics (GLOMAP) and PSCs (DLAPSE).
  • Chemical data assimilation scheme.
  • Embedded trajectory code.
  • Written in Fortran (f77, f90). Runs on most platforms (including vector machines). Parallelised using OpenMP and MPI.

Key Papers

  • Basic model description: (advection, grid, etc)
    Chipperfield, M.P., New Version of the TOMCAT/SLIMCAT Off-Line Chemical Transport Model: Intercomparison of Stratospheric Tracer Experiments
    Q. J. R. Meteorol. Soc., 132, 1179-1203, doi:10.1256/qj.05.51, 2006.
    PDF file
  • Convection scheme:
    Stockwell, D.Z., and M.P. Chipperfield, A tropospheric chemical transport model: Development and validation of the model transport schemes. Q. J. R. Meteorol. Soc. , 125, 1747-1783, 1998.
  • Stratospheric chemistry scheme:
    Chipperfield, M.P., Multiannual Simulations with a Three-Dimensional Chemical Transport Model,
    J. Geophys. Res., 104, 1781-1805, 1999.
  • Tropospheric chemistry scheme:
    Arnold, S.R., M.P. Chipperfield, and M.A. Blitz, A three-dimensional model study of the effect of new temperature-dependent quantum yields for acetone photolysis,
    J. Geophys. Res. , 110 (D22), D22305 doi:10.1029/2005JD005998, 22 November 2005
    PDF file
  • Chemical data assimilation:
    Chipperfield, M.P., B.V. Khattatov, and D.J. Lary, Sequential Assimilation of Stratospheric Chemical Observations in a Three-Dimensional Model,
    J. Geophys. Res., 107(D21), 4585, doi:10.1029/2002JD002110, 2002.
    PDF file

Model Animations

Some animations of TOMCAT/SLIMCAT results are given here.


Technical Reports / Manuals

Here are some documents which describe the model.