Characteristics of Barolicnic Wave Packets in GCM Data

hPa meridional wind data from a GCM experiment run at GFDL of Princeton University was analyzed to document the characteristics of the baroclinic wave packets in GCM data. By use of the one-point lag correlation and the complex demodulation methods, the wavelength, wavenumber, phase velocity and the group velocity of the wave packets were computed. It is found that the typical wavelengths are around 3?000～6?000?km, the phase velocity is about 10?m/s and the group velocity is about 2～3 times of the phase velocity. It is also found that the downstream development of the baroclinic waves in GCM data is more common than in the observations, and that the wave packets in GCM model are more coherent than in the observations, i.e., the envelopes of the wave packets in model can remain unchanged for a longer period of time. The seasonal variations of the wave packets and the difference between the wave packets in the northern hemisphere and in the southern hemisphere are analyzed in detail. Finally the wave packets in models are compared with wave packets in the observations.