Through the application of Fourier and spherical harmonics, analyses are made of the characteristic features of the change with time in amplitudes of the 100mb component ultra-long waves, as well as of their adjustment, in the cold wave occurring in December 1976 in the northern hemisphere, which was characterized by the polar vortex cut-off process with a transverse trough moving around. By making comparison between the activities of the 100mb ultra-long waves and the adjustment of the 500-rob circulation, the authors have achieved some results, which may be helpful to routine medium-range forecasting of cold waves.