| description abstract | Zonal harmonic analysis has been carried out on 30-day mean pressure fields of several runs of the NCAR global circulation model (GCM): A January 6-layer case with the earth's orography; a January 6-layer case without orography; a January 12-layer case with orography; and a January 12-layer case without orography. Zonal harmonic mean waves 1, 2, and 3 from each experiment were compared between cases and with observed data. In the Northern Hemisphere below 18 km, neither the mountain (M) nor the no-mountain (NM) versions of the 6-layer January model can simulate the amplitude of waves 1 and 3 correctly when compared with observed data. The 6-layer NM case does better at simulating the amplitude of wave 2 than does the 6-layer M case. For the 12-layer version of the model, on the other hand, the M case simulated the amplitudes of waves 1 and 2 quite well in the stratosphere, while the NM case only does well with wave 2. In the Southern Hemisphere, neither the M nor NM waves in general resemble those observed. The results suggest that the rigid top boundary of the NCAR GCM does influence the structure of the zonal harmonic mean waves by preventing vertical propagation of wave energy through that level. Comparison of amplitudes and phases of zonal harmonic waves in two 30-day periods in the same case shows that in general the waves are in the same positions and have the same amplitudes. The amplitudes and phases of waves 1, 2, and 3 in two January 6-layer cases with slightly different initial conditions were compared and the waves were not significantly different in the two cases. The maximum amplitude of wave 1 in the model stratosphere occurs at about 60'N while the westerly jet has a maximum at 30°N. In this respect the NCAR model apparently is inconsistent with observations or linear theories. | |
