The atmosphere general circulation model ECHAM4.L39(DLR) (hereafter referred to as E39) is based on the standard version of the ECHAM4 model. Whereas the standard version of ECHAM4 uses 19 vertical layers, the number of layers has been increased to 39 in E39, with the highest gain of vertical resolution in the upper troposphere and lower stratosphere, while the top model level remains centered at 10 hPa. The vertical resolution in the extra-tropical tropopause region has been enhanced from approximately 2 km to 700 m. Among other effects, the increased number of vertical levels leads to a lifting of the so-called "sponge" layer of the model, i.e., those uppermost layers, in which horizontal diffusion is gradually enhanced to prevent spurious wave reflection at the upper model boundary. Thus, the domain, in which these numerical requirements yield a substantially suppressed model variability (probably the two uppermost layers), is restricted to the region above approximately 25 hPa.
See also homepage of Christine Land.