Time-varying frictional torques, due primarily to changing wind stress over the tropical Pacific associated with the 40- to 50-day tropical oscillation, are computed for the northern summer of 1979. It is shown that they were large enough to cause variations in atmospheric angular momentum equal to one tenth of the annual average atmospheric angular momentum. Further, they are shown to be large enough to explain a considerable fraction of the observed 40- to 50-day variations in atmospheric angular momentum and length of day. ¿ American Geophysical Union 1988