THE ROLE OF PLANETARY-WAVES IN THE FORMATION OF INTER-HEMISPHERIC ASYMMETRY IN OZONE DISTRIBUTION

We investigate the formation of inter-hemispheric asymmetry in the meridional circulation induced by planetary waves only and resulting seasonal variation of the total ozone content in wintertime, by overviewing a series of short-range (one month) numerical experiments using observational monthly-averaged zonal mean wind fields as initial conditions in a spherical semi-spectral mechanistic model. It is found that planetary waves induce asymmetric circulations between the Northern Hemisphere (NH) and Southern Hemisphere (SH) and contribute to the formation of an inter-hemispherically distinct distribution of total ozone. Amplification of planetary waves in the SH winter induces a meridional circulation whose downward motion is concentrated to the mid-latitude lower stratosphere, resulting in an ozone increase there. The meridional circulation in the NH extends to the high-latitude stratosphere and contributes to the formation of an ozone maximum in the polar region throughout a winter. During late winter to early spring, the location of maximum increase in ozone content shifts poleward with the movement of the downward region. This suggests that the seasonal variation of the location of the mid-latitude ozone maximum in the SH, known as the subpolar maximum, is controlled by the variation of meridional circulation driven by planetary waves. Diagnoses based on TEM theory show that the asymmetric circulation arises from a difference in the propagation field. Planetary waves in the SH propagate equatorward through a maximum line of refractive index which makes the convergence region of EP flux in the mid-latitude stratosphere. Furthermore, it is found that the degree of asymmetry of the ozone distribution depends on the amplitude, wavenumber and phase velocity of the forced wave, and the asymmetry is most apparent when the stationary wave with wavenumber 1 is forced.