CLaMS is a modular chemistry transport model (CTM) system developed at Forschungszentrum Jülich, Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

. 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
Ozone depletion
Ozone depletion describes two distinct but related phenomena observed since the late 1970s: a steady decline of about 4% per decade in the total volume of ozone in Earth's stratosphere , and a much larger springtime decrease in stratospheric ozone over Earth's polar regions. The latter phenomenon...

 and water vapour transport.

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

CLaMS gridding

Unlike other CTMs (e.g. SLIMCAT, REPROBUS), CLaMS operates on a Lagrangian
The Lagrangian, L, of a dynamical system is a function that summarizes the dynamics of the system. It is named after Joseph Louis Lagrange. The concept of a Lagrangian was originally introduced in a reformulation of classical mechanics by Irish mathematician William Rowan Hamilton known as...

 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
Time evolution
Time evolution is the change of state brought about by the passage of time, applicable to systems with internal state . In this formulation, time is not required to be a continuous parameter, but may be discrete or even finite. In classical physics, time evolution of a collection of rigid bodies...

 path that an air parcels traces in space is called a trajectory
A trajectory is the path that a moving object follows through space as a function of time. The object might be a projectile or a satellite, for example. It thus includes the meaning of orbit—the path of a planet, an asteroid or a comet as it travels around a central mass...

. A specialised mixing scheme ensures that physically realistic diffusion
Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...

 is imposed on an ensemble of
trajectories in regions of high wind shear
Wind shear
Wind shear, sometimes referred to as windshear or wind gradient, is a difference in wind speed and direction over a relatively short distance in the atmosphere...


CLaMS operates on arbitrarily resolved horizontal grids. The space coordinates are latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

, longitude
Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees, minutes and seconds, and denoted by the Greek letter lambda ....

 and potential temperature.

CLaMS Hierarchy

CLaMS is composed of four modules and several preprocessors. The four modules are
  1. a trajectory module
  2. a box chemistry module
  3. a Lagrangian mixing module
  4. 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 of Cambridge
University of Cambridge
The University of Cambridge is a public research university located in Cambridge, United Kingdom. It is the second-oldest university in both the United Kingdom and the English-speaking world , and the seventh-oldest globally...

. More than 100 chemical reactions involving 40+ chemical
species are considered. Integration time step is 10 minutes, species
can be combined into chemical families to facilitate integration. The
module includes a radiative transfer model for the determination of
photolysis rates. The module also includes heterogeneous reactions on
NAT, ice and liquid particle surfaces.

Lagrangian mixing

Mixing is based on grid deformation of quasi uniform air parcel
distributions. The contraction or elongation factors of the distances
to 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 realistic

Lagrangian sedimentation

Lagrangian sedimentation is calculated by following individual nitric
acid trihydrate (NAT) particles that may grow or shrink by the uptake
or release of HNO3 from/to the gas phase. These particle parcels are
simulated independently from the Lagrangian air parcels. Their
trajectories are determined using the horizontal winds and their
vertical settling velocity that depends on the size of the individual
particles. NAT particles are nucleated assuming a constant nucleation
rate and they evaporate where temperatures grow too high. With this,
a vertical redistribution of HNO3 (denitrification and
renitrification) is determined.

CLaMS data sets

A chemical transport model
Chemical transport model
A chemical transport model is a type of computer numerical model which typically simulates atmospheric chemistry.- Chemical transport models and general circulation models :...

 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, ERA-40
    ERA-40 is a ECMWF re-analysis of the global atmosphere and surface conditions for 45-years, over the period from September 1957 through August 2002 by ECMWF. Many sources of the meteorological observations were used, including radiosondes, balloons, aircraft, buoyes, satellites, scatterometers....

  • United Kingdom Met Office
    Met Office
    The Met Office , is the United Kingdom's national weather service, and a trading fund of the Department for Business, Innovation and Skills...

  • 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 initialised
from two-dimensional chemical models, chemistry-climate models,
climatologies, or from correlations between chemical species or
chemical species and dynamical variables.

External links

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