The global climate model ECHAM has been developed from the ECMWF numerical weather prediction model by the Max-Planck-Institute for Meteorology and the Meteorological Institute of Hamburg University. Several model versions are currently used operationally: ECHAM4 has been used since 1996, ECHAM5 has been made available at the begin of 2004. ECHAM4 has also been available with higher vertical resolution (ECHAM4.L39(DLR)) or with an upward shifted model top at 0.1 hPa (MA-ECHAM4).
ECHAM is used to simulate the development of global weather (temperature, wind, clouds, etc.), using a spatial resolution of between 300 km and 500 km and a time step of between 20 min and 40 min, depending on model version. Besides solar insolation, radiatively active trace gases and sea surface temperatures are usually prescribed. These components determine the simulated global climate. The simulation is not directed to observed individual weather situations but to the reproduction of typical mean characteristics of the atmospheric circulation like Icelandic low, Azores' high, or mean storm tracks.
Based on ECHAM, more complex interactively coupled model systems have been developed, including other components of the climate system: Ocean-Atmosphere models, atmosphere models including the sulfur cycle, etc.. Activities at the DLR-Institute of Atmospheric Physics have been focussed, during the previous years, on the creation and development of interactively coupled climate chemistry models: ECHAM4/CHEM includes chemical reaction in both the troposphere and the stratosphere. It serves to simulate the development of the ozone layer as well as photosmog situations.
In contrast to so-called chemical transport models, the purpose of which is the reproduction of atmospheric chemistry during individual observed meteorological episodes, ECHAM4/CHEM is an appropriate tool to simulate future scenarios of atmospheric chemical composition and its feedback to atmospheric temperature and circulation.