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Abstract:
A detailed description of the third-generation atmospheric general circulation model ECHAM is presen-
ted. The climatology of ECHAM3, as simulated at low and high resolution (T21 and T42, respectively),
is compared with ECMWF analyses (1981-1990) and also with the climatology of two earlier low reso-
lution versions ECHAM 1 and ECHAM2.
At low resolution, the impact of the improved model physics is evident primarily in the simulated time-
mean state which is more successfully reproduced by the more recent model versions, particularly by
ECHAM3. The impact of increased horizontal resolution can be identified not on] v by a generally impro-
ved time-mean circulation, particularly in the Southern Hemisphere, but mosbsignificantly by the incre-
ased level of high-frequency variability. In the low-frequency range, however, the impact of increased
horizontal resolution is modest, and all models fail to reproduce the observed level of low-frequency
intraseasonal variability
