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TOMCAT Model

Introduction

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 ECMWF) to specify the atmospheric transport and temperatures and then calculate the chemical composition of the troposphere and stratosphere. The model has the option of detailed chemical scheme(s) for the stratosphere and troposphere and is the host model for the GLOMAP aerosol scheme. The model can be used to simulate the past and current atmosphere, to help interpret observations, and to diagnose the extent of environmental issues such as stratospheric ozone depletion or tropospheric pollution.

TOMCAT logo

TOMCAT logo

History

The first version of TOMCAT was written by Martyn Chipperfield (MPC) at Météo-France in Toulouse in 1992 with the help of Pascal Simon. Indeed, TOMCAT was originally an acronym for the Toulouse Offline Model of Chemistry and Transport, reflecting the model's origins. At this stage the model was used for studies of stratospheric chemistry. From 1993 the  development of TOMCAT followed MPC to the Department of Chemistry at the University of Cambridge. At that time 3D models were computationally expensive so, around 1995, MPC wrote SLIMCAT. This was a cheaper, slimmed-down stratosphere-only version of TOMCAT formulated on isentropic levels. SLIMCAT was originally an acronym for Single-Level Isentropic Model of Chemistry and Transport. However, MPC also developed this into a 3D model with vertical motion from diabatic heating rates. Around this time TOMCAT became a 'tropospheric' model and group members in Cambridge helped to add treatments of e.g. convection, boundary layer mixing, and tropospheric chemistry.

MPC moved to Leeds in 2000 where the model development continues. SLIMCAT was 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 library covers all of the applications. Depending on the coordinate employed, the model is still referred to as either TOMCAT or SLIMCAT. Other major developments in Leeds included the addition of aerosol schemes (i.e. GLOMAP).

Because the model is no longer based in Toulouse, and the isentropic coordinate version is not single level, TOMCAT and SLIMCAT are now treated as names and not acronyms.

Main Model Details

  • Variable resolution. Typical resolutions are 2.8 x 2.8 degrees for decadal 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.