CLaMS (Chemical Lagrangian Model of the Stratosphere) is a modular chemistry transport model (CTM) system developed at Research Centre Jülich, Germany. CLaMS was first described by McKenna et al (2000a,b) and was expanded into three dimensions by Konopka et al (2004). CLaMS has been employed in recent European field campaigns THESEO, EUPLEX, TROCCINOX and SCOUT-O3 with a focus on simulating ozone depletion and water vapour transport.

Major strengths of CLaMS in comparison to other CTMs are
# its applicability for reverse domain filling studies
# its anisotropic mixing scheme
# its integrability with arbitrary observational data
# its comprehensive chemistry scheme

CLaMS gridding

Unlike other CTMs (e.g. SLIMCAT, REPROBUS), CLaMS operates on a Lagrangian model grid (see section about model grids in general circulation model): an air parcel is described by three space coordinates and a time coordinate. The time evolution path that an air parcels traces in space is called a trajectory. A specialised mixing scheme ensures that physically realistic diffusion is imposed on an ensemble oftrajectories in regions of high wind shear.

CLaMS operates on arbitrarily resolved horizontal grids. The space coordinates are latitude, longitude and potential temperature.

CLaMS Hierarchy

CLaMS is composed of four modules and several preprocessors. The four modules are
# a trajectory module
# a box chemistry module
# a Lagrangian mixing module
# a Lagrangian sedimentation scheme

Trajectory module

Integration of trajectories with 4th order Runge-Kutta method, integration time step 30 minutes. Vertical displacement of trajectories is calculated from radiation budget.

Box chemistry module

Chemistry is based on the ASAD chemistry code of the University ofCambridge. More than 100 chemical reactions involving 40+ chemicalspecies are considered. Integration time step is 10 minutes, speciescan be combined into chemical families to facilitate integration. Themodule includes a radiative transfer model for the determination ofphotolysis rates. The module also includes heterogeneous reactions onNAT, ice and liquid particle surfaces.

Lagrangian mixing

Mixing is based on grid deformation of quasi uniform air parceldistributions. The contraction or elongation factors of the distancesto neighboring air parcels are examined: if a critical elongation(contraction) is reached, new air parcels are introduced (taken away).This way, anisotropic diffusion is simulated in a physically realisticmanner.

Lagrangian sedimentation

Lagrangian sedimentation is calculated by following individual nitricacid trihydrate (NAT) particles that may grow or shrink by the uptakeor release of HNO3 from/to the gas phase. These particle parcels aresimulated independently from the Lagrangian air parcels. Theirtrajectories are determined using the horizontal winds and theirvertical settling velocity that depends on the size of the individualparticles. NAT particles are nucleated assuming a constant nucleationrate and they evaporate where temperatures grow too high. With this,a vertical redistribution of HNO3 (denitrification andrenitrification) is determined.

CLaMS data sets

A chemical transport model does not simulate the dynamics of the atmosphere. For CLaMS, the following meteorological data sets have been used
* European Centre for Medium-Range Weather Forecasts (ECMWF), Predictions, Analyses, ERA-15, ERA40
* United Kingdom Meteorological Office (UKMO)
* European Centre Hamburg Atmospheric Model (ECHAM4), in the DLR version

To initialize the chemical fields in CLaMS, data from a large variety of instruments have provided data.
* on satellite (CRISTA, MIPAS, MLS, HALOE, ILAS, ...),
* on aircraft and balloons (HALOX, FISH, Mark IV, BONBON...)

If no observations are present, the chemical fields can be initialisedfrom two-dimensional chemical models, chemistry-climate models,climatologies, or from correlations between chemical species orchemical species and dynamical variables.

ee also

*Forschungszentrum Jülich
*Ozone depletion

External links

* [ CLaMS at Research Centre Juelich]
* [ Current field campaign SCOUT-O3]


The details of the model CLaMS are well documented and published in the scientific literature.

*Formulation of advection and mixing by [ McKenna et al, 2002a]
*Formulation of chemistry-scheme and initialisation by [ McKenna et al, 2002b]
*Comparison of the chemistry module with other stratospheric models by [ Krämer et al, 2003]
*Calculation of photolysis rates by [ Becker et al, 2000]
*Extension to 3-dimension model version by [ Konopka et al, 2004]
*Lagrangian sedimentation by [ Grooß et al, 2005]

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