Atmospheric oceanic and hydrological contributions to seasonal variations in length of day

In our previous studies, the annual and semiannual residuals derived in the axial angular momentum budget of the solid Earth-atmosphere system reflected significant signals, which must be caused by additional excitation sources. Here, the contribution for the wind term from the atmospheric layer between the 10 hPa and 0.3 hPa levels to the seasonal variations in length of day (LOD) was still missing. Therefore, there is the need to extend the top level into the upper stratosphere up to 0.3 hPa. To investigate the missing wind effects at seasonal time scales, we use the axial atmospheric angular momentum (AAM) data derived for the 10-0.3 hPa layer from 1991 to 1997. Ocean current and mass distribution changes also induce detectable LOD variations. Axial oceanic angular momentum (OAM) functions as generated by oceanic general circulation models (GCMs), namely for the ECHAM3 and the MICOM models, are available from 1975 to 1994 and 1992 to 1994, respectively, to compute the oceanic contributions to LOD changes. Concerning the variations in hydrological angular momentum (HAM) as another excitation source, we use the estimates of the hydrological contribution by Chao and O'Connor (1988). Using the vector representation, we show to what extent the vectors achieve a balance in the global axial angular momentum budget on the seasonal time scales. (orig.)Available from TIB Hannover: RR 6134(2000,5) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman