TM5 (Global Chemistry-Transport Model)

TM5 (Global Chemistry-Transport Model)

TM5 is a complex 3-dimensional global atmospheric model which simulates the concentrations of the various atmospheric trace gases, such as long-lived greenhouse gases (carbon dioxide (CO2), methane (CH4), and nitrous oxide (N20)), chemically active species (e.g. ozone (O3)), and aerosols.

The model is run on supercomputers and is driven using analyzed meteorological data, coming from the European Centre for Medium-Range Weather Forecasts (ECMWF), based on more than 10⁶ meteorological observations per day. By using these meteorological fields, TM5 can realistically simulate the transport of the above trace gases. In addition, TM5 simulates the chemical transformation occurring in the atmosphere. Emission data are provided by various databases, such as e.g. EDGAR.

A specific feature of TM5 is that it allows to zoom in over certain regions of interest (e.g. Europe). In this way these zoom regions are simulated at higher horizontal resolution (1ºx1º), but at the same time the zoom simulations are embedded in the global simulations, providing consistent boundary conditions at the borders of the zoom regions.

Simulation for CO on a spatial resolution of 0.5x0.25 degrees over Western Europe.

Use of TM5 for studies of atmospheric greenhouse gases

A major application of TM5 is to better estimate the sources and sinks of long-lived greenhouse gases (CO₂, CH₄, N₂O). While these greenhouse gases have also several natural sources and sinks, their atmospheric concentrations have increased considerably since pre-industrial times (~1700), CO₂ by ~35%, CH₄ by ~150%, N₂O by ~15% (for more details see IPCC 4th assessment report), due to human activities. The increase of these greenhouse gases is the major driving force of Climate Change. Hence, it is crucial to better understand and quantify the major processes and regions of the greenhouse gas emissions.

For these applications TM5 is run in "inverse mode', i.e. backwards in time. Using atmospheric observations (e.g. from global surface measurement networks and satellite data) the inverse TM5 model can identify and quantify the major emission regions or processes.

Surface ozone calculated with the TM5 model for the year 2000.

A recent JRC study had demonstrated the feasibility to use the inverse TM5 model to estimate CH₄ emissions from various European countries, thus allowing to check the consistency with emissions reported under the United Nations Framework Convention on Climate Change (UNFCCC) and the Kyoto protocol. To improve such estimates, however, it is important to further increase the density of atmospheric observations.

An inverse TM5 model version is used at NOAA, USA, to provide estimates of CO₂ fluxes from North America (CarbonTracker).

TM5 calculated NO2 columns with 1x1 zoom regions over Europe, North America.