TOMCAT/SLIMCAT

TOMCAT/SLIMCAT is a global three-dimensional off-line chemical transport model (CTM), which models the time-dependent distribution of chemical species in the troposphere and stratosphere. It can be used to study topics such as ozone depletion and tropospheric pollution; it is cited extensively in the WMO/UNEP Scientific Assessments of Ozone Depletion and was one of the models used the IPCC report on Aviation and the Global Atmosphere . It incorporates a choice of detailed chemistry schemes for the troposphere or stratosphere, and an optional chemical data assimilation scheme.

The model, originally called the Toulouse Off-line Model of Chemistry And Transport (TOMCAT), was created by Martyn Chipperfield[1] while working at Météo France. "Off-line" in this sense describes the fact that although the meteorological data (wind components and other fields) which are used as input to the CTM typically derive from a general circulation model (GCM), the CTM is run as a separate program outside of a GCM; this is as distinct from a chemistry simulation scheme which runs within a GCM, in which the simulated chemical distributions, e.g. of ozone, can provide feedback on the meteorology via the GCM's radiation scheme. In practice, the meteorology use to force the model is now taken mainly from meteorological reanalyses so that the model can be compared with real-world observations.[2]

To ease computational costs, Chipperfield developed a stripped-down version called the Single Layer Isentropic Model of Chemistry And Transport (SLIMCAT) in 1995[3]. This used a level of constant potential temperature (or equivalently, of constant specific entropy, hence isentropic), exploiting the fact that due to approximate conservation of energy, atmospheric motions are approximately adiabatic and hence air parcels remain on isentropic levels on short timescales. A diabatic heating scheme was later added, to create a full-stratosphere 3-D model with multiple isentropic levels with transport between them on longer (up to multi-decadal) timescales[4]. The name "SLIMCAT" has remained despite the multiple levels.

The two models were combined into the same library[5] and are now maintained at the University of Leeds as a single code base[6], which runs in Fortran, and has been parallelised using Message Passing Interface (MPI) and OpenMP.

TOMCAT has been further extended to include a detailed treatment of aerosol.[7][8] GLOMAP (Global Model of Aerosol Processes) simulates a wide range of aerosol species including black carbon, sulfate, sea spray, soil dust, and secondary organic aerosol. The primary purpose of TOMCAT/GLOMAP is to simulate aerosol radiative forcing and the impact of aerosol on climate.

TOMCAT is also used in inverse model (INVICAT[9]) to derive surface fluxes of greenhouse gases (GHGs) and halocarbons.

References

  1. ↑ Chipperfield, M. P.; Cariolle, D.; Simon, P.; Ramaroson, R.; Lary, D. J. (1993). "A three-dimensional modeling study of trace species in the Arctic lower stratosphere during winter 1989–1990". Journal of Geophysical Research: Atmospheres. 98 (D4): 7199–7218. doi:10.1029/92JD02977. ISSN 2156-2202.
  2. ↑ Monge-Sanz, B. M.; Chipperfield, M. P.; Simmons, A. J.; Uppala, S. M. (2007). "Mean age of air and transport in a CTM: Comparison of different ECMWF analyses". Geophysical Research Letters. 34 (4). doi:10.1029/2006GL028515. ISSN 1944-8007.
  3. ↑ Chipperfield, M. P.; Santee, M. L.; Froidevaux, L.; Manney, G. L.; Read, W. G.; Waters, J. W.; Roche, A. E.; Russell, J. M. (1996-08-20). "Analysis of UARS data in the southern polar vortex in September 1992 using a chemical transport model". Journal of Geophysical Research: Atmospheres. 101 (D13): 18861–18881. doi:10.1029/96JD00936. ISSN 0148-0227.
  4. ↑ Chipperfield, M. P. (1999). "Multiannual simulations with a three-dimensional chemical transport model". Journal of Geophysical Research: Atmospheres. 104 (D1): 1781–1805. doi:10.1029/98JD02597. ISSN 2156-2202.
  5. ↑ Chipperfield, M. P. (2006). "New version of the TOMCAT/SLIMCAT off-line chemical transport model: Intercomparison of stratospheric tracer experiments". Quarterly Journal of the Royal Meteorological Society. 132 (617): 1179–1203. doi:10.1256/qj.05.51. ISSN 1477-870X.
  6. ↑ "TOMCAT". GitHub. Retrieved 2026-08-30.
  7. ↑ Spracklen, D. V.; Pringle, K. J.; Carslaw, K. S.; Chipperfield, M. P.; Mann, G. W. (2005-08-19). "A global off-line model of size-resolved aerosol microphysics: I. Model development and prediction of aerosol properties". Atmospheric Chemistry and Physics. 5 (8). Copernicus GmbH: 2227–2252. doi:10.5194/acp-5-2227-2005. ISSN 1680-7316.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  8. ↑ Mann, G. W.; Carslaw, K. S.; Ridley, D. A.; Spracklen, D. V.; Pringle, K. J.; Merikanto, J.; Korhonen, H.; Schwarz, J. P.; Lee, L. A.; Manktelow, P. T.; Woodhouse, M. T.; Schmidt, A.; Breider, T. J.; Emmerson, K. M.; Reddington, C. L. (2012-05-22). "Intercomparison of modal and sectional aerosol microphysics representations within the same 3-D global chemical transport model". Atmospheric Chemistry and Physics. 12 (10). Copernicus GmbH: 4449–4476. doi:10.5194/acp-12-4449-2012. ISSN 1680-7316.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  9. ↑ Wilson, C.; Chipperfield, M. P.; Gloor, M.; Chevallier, F. (2014-10-24). "Development of a variational flux inversion system (INVICAT v1.0) using the TOMCAT chemical transport model". Geoscientific Model Development. 7 (5). Copernicus GmbH: 2485–2500. doi:10.5194/gmd-7-2485-2014. ISSN 1991-959X.{{cite journal}}: CS1 maint: unflagged free DOI (link)
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