The global atmospheric angular momentum vector as an indicator of the interactions of atmosphere, ocean and earth

ERA-data are used to calculate time series of the axial and the equatorial components of the global atmospheric angular momentum and the related mountain and friction torques. The torques due to the nonspherical shape of the earth are evaluated invoking a balance condition. The time series are analysed on the basis of the equations for the auto- and crosscovariance functions of the momenta and the torques. The observed covariance functions are inserted in the equations.

It is found that the mountain and friction torques contribute little to the changes of the autocovariance function of the equatorial angular momentum with lag. It is almost exclusively the earth's rotation and its shape which induce these changes. Mass and wind terms are hardly correlated in contrast to predictions of normal mode theories. However there is a strong correlation of mountain torques and wind terms.

As for the axial component it is found that the autocovariance of angular momentum decays rather slowly. The crosscovariance of mountain and friction torques does hardly contribute to the changes of this autocovariance with lag. However the data quality is not sufficiantly high to explain the observed slow decay of the autocovariance in terms of the autocovariances of the torques.