The ECHAM model has been developed from the ECMWF model (cycle 31, November 1988). It contains several changes, mostly in the parameterization, in order to adjust the model for climate simulations. The reference resolution is T42, but the model is set up to use resolutions in the range T21 to T106. Long term integrations have so far only been done for T21, T42 and T63.
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Deutsches Klimarechenzentrum (2009) studied this question.