TM5

TM5, or Transport Model 5, is a global three-dimensional chemical transport model used to simulate the distribution and evolution of atmospheric trace gases and aerosols. It is designed for research in atmospheric chemistry and air quality, and it is typically driven by meteorological fields provided by a host general circulation model or reanalysis. The model solves tracer conservation equations for a broad set of species, including ozone, nitrogen oxides, carbon monoxide, methane, and various VOCs, along with inorganic and organic aerosol components. Its chemistry is implemented in modular mechanisms, allowing users to switch between different reaction schemes.

The TM5 framework combines physical transport with chemical processing. Transport processes include horizontal and vertical advection, convection, turbulent diffusion, and dry deposition. Photolysis rates are calculated through a separate module, linking solar radiation to chemical production and loss terms. The model supports multiple horizontal configurations and vertical layouts, enabling both global simulations and regional refinements through nested grids. Typical TM5 setups employ tens of vertical levels and flexible horizontal resolutions, ranging from coarse global grids to finer regional nests.

Applications and usage of TM5 span atmospheric composition studies, model intercomparisons, and policy-relevant assessments. It is frequently employed for sensitivity analyses, scenario testing, and emission inversion studies using adjoint or variational approaches (TM5-4D-Var). These adjoint capabilities support top-down estimation of emissions by assimilating observational data into the model.

Development and community: TM5 has evolved through collaboration among European and international research groups. It is widely used in the atmospheric chemistry and air quality research communities, with multiple groups maintaining and adapting the code for specific studies. Access to TM5 and its documentation is typically coordinated through academic collaborations and project consortia.