In this paper the variations of earth rotation parameters, length of day LOD and polar motion, are calculated from integrals of pressure and wind fields over the atmosphere, called atmospheric angular momentum functions.
Input data are from ECMWF (European Centre for Medium-Range Weather Forecasts). 16 ways of calculation are applied, results are compared with geodetic observations of ONT05 (September 2005), C04 series and Bulletin B data of IERS (International Earth rotation and Reference System Service) as well as with similar calculations using NCEP data (National Centers for Environmental Prediction). In terms of polar motion, comparison was done between calculated and observed coordinates (integration approach) as well as between angular momentum functions derived from atmosphere and observation (direct approach). Best RMS deviations are about 30 mas with direct approach and about 0.7 mas with integration approach. Best RMS deviations of LOD are about 22 s. Best results were achieved using C04 series, the high resolution of CONT05 observations was of no advantage due to noise. In terms of polar motion, NCEP data are slightly better, in terms of LOD, ECMWF data are better, because they extend higher up to the atmosphere. In future, advance in calculation of earth rotation parameters from geophysical data should be done for periods longer than one day including influence of oceans too and using longer data series.