DYNAMICAL STUDIES ON THE FORMATION OF PLANETARY WAVES.

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Throughout the current study, we have investigated the formation mechanism of stationary and traveling planetary waves on the basis of meteorological reanalysis data along with general circulation model simulations.As regards the traveling planetary waves) interannual variability of the 5-day wave in the stratosphere has been examined by the use of the National Center for Environmental Prediction (NCEP)/ National Center for Atmospheric research (NCAR) reanalysis data. We have found the quasi-biennial variation of the 5-day wave amplitude in the stratosphere. This quasi-biennial variation is closely related to the zonal wind variation associated with the quasi-biennial oscillation (QBO) in the equatorial stratosphere : The 5-day wave amplitude during the easterly shear phase of the QBO is larger than that during the westerly shear phase.On the other hand, the Arctic Oscillation, whose spatial pattern shows a seesaw between the Arctic and mid-latitudes, has been widely discussed concerning the interannual variability of the general circulation. The AO is considered to be closely related to the variability of stationary planetary waves. We have investigated the relationship among the AO, the North Atlantic Oscillation (NAO) and the Pacific and North American (PNA) oscillation pattern on the basis of the NCEP/NCAR reanalysis data. As a result, we have found that the observed AO is almost apparent and two almost independent seesaws, i.e. the NAO and the PNA oscillation pattern, reconstructed from the observed data apparently reproduce the AO.