TOMCAT/SLIMCAT is an off-line

chemical transport model A chemical transport model (CTM) is a type of computer simulation, computer numerical model which typically simulates atmospheric chemistry and may be used for air pollution forecasting. Chemical transport models and general circulation models W ...

(CTM), which models the time-dependent distribution of chemical species in the

troposphere The troposphere is the lowest layer of the atmosphere of Earth. It contains 80% of the total mass of the Atmosphere, planetary atmosphere and 99% of the total mass of water vapor and aerosols, and is where most weather phenomena occur. From the ...

and

stratosphere The stratosphere () is the second-lowest layer of the atmosphere of Earth, located above the troposphere and below the mesosphere. The stratosphere is composed of stratified temperature zones, with the warmer layers of air located higher ...

. It can be used to study topics such as

ozone depletion Ozone depletion consists of two related events observed since the late 1970s: a lowered total amount of ozone in Earth, Earth's upper atmosphere, and a much larger springtime decrease in stratospheric ozone (the ozone layer) around Earth's polar ...

and tropospheric pollution, and was one of the models used the

IPCC The Intergovernmental Panel on Climate Change (IPCC) is an intergovernmental body of the United Nations. Its job is to "provide governments at all levels with scientific information that they can use to develop climate policies". The World M ...

report on Aviation and the Global Atmospher

It incorporates a choice of detailed chemistry schemes for the troposphere or stratosphere, and an optional chemical

data assimilation Data assimilation refers to a large group of methods that update information from numerical computer models with information from observations. Data assimilation is used to update model states, model trajectories over time, model parameters, and ...

scheme. The original model code, called the Toulouse Off-line Model of Chemistry And Transport (TOMCAT), was written by Martyn Chipperfield at

Météo France Météo may refer to: *Weather in French * Météo-France, the French national meteorological service * MétéoMédia, a 24-hour Canadian French-language cable television specialty channel and web site * Météo Suisse, officially the Federal Offic ...

. "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 A general circulation model (GCM) is a type of climate model. It employs a mathematical model of the general circulation of a planetary atmosphere or ocean. It uses the Navier–Stokes equations on a rotating sphere with thermodynamic terms for ...

(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 Ozone () (or trioxygen) is an Inorganic compound, inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , break ...

, can provide feedback on the meteorology via the GCM's radiation scheme. A version called the Single Layer Isentropic Model of Chemistry And Transport (SLIMCAT) was developed in 1995. This used a level of constant

potential temperature The potential temperature of a parcel of fluid at pressure P is the temperature that the parcel would attain if adiabatically brought to a standard reference pressure P_, usually . The potential temperature is denoted \theta and, for a gas well-ap ...

(or equivalently, of constant specific

entropy Entropy is a scientific concept, most commonly associated with states of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodynamics, where it was first recognized, to the micros ...

, 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 allow for multiple isentropic levels with transport between them on longer timescales, although the name "SLIMCAT" has remained despite the multiple levels. The two programs are now maintained as a single code base, which runs in Fortran, and has been parallelised. TOMCAT has been further extended to include a detailed treatment of

aerosol An aerosol is a suspension (chemistry), suspension of fine solid particles or liquid Drop (liquid), droplets in air or another gas. Aerosols can be generated from natural or Human impact on the environment, human causes. The term ''aerosol'' co ...

. GLOMAP (Global Model of Aerosol Processes) simulates a wide range of aerosol species including

black carbon Black carbon (BC) is the light-absorbing refractory form of Chemical_element, elemental carbon remaining after pyrolysis (e.g., charcoal) or produced by incomplete combustion (e.g., soot). Tihomir Novakov originated the term black carbon in ...

sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...

, sea spray, soil dust, and secondary organic aerosol. The primary purpose of TOMCAT/GLOMAP is to simulate aerosol

radiative forcing Radiative forcing (or climate forcing) is a concept used to quantify a change to the balance of energy flowing through a planetary atmosphere. Various factors contribute to this change in energy balance, such as concentrations of greenhouse gases ...

and the impact of aerosol on climate.

References

* 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, 2006. * Spracklen, D.V., Pringle, K.J., Carslaw, K.S., Chipperfield, M.P. and Mann, G.W., A global off-line model of size-resolved aerosol microphysics: I. Model development and prediction of aerosol properties,

Atmospheric Chemistry and Physics ''Atmospheric Chemistry and Physics'' is an open access peer-reviewed scientific journal published by the European Geosciences Union. It covers research on the Earth's atmosphere and the underlying chemical and physical processes, including the al ...

, Vol. 5, 2227–2252, 2005.

External links

TOMCAT/SLIMCAT Project homepage at University of Leeds, UK
(with further published references)
GLOMAP Project page
{{DEFAULTSORT:TOMCAT SLIMCAT Numerical climate and weather models