An intercomparison of medium-scale waves in the Northern and Southern Hemispheres

Characteristic features of medium-scale waves (zonal wavenumbers 4-7) are investigated for the Southern and Northern Hemispheres by the use of two global data sets from the troposphere to stratosphere for the period July 1982 through April 1986. In the Southern Hemisphere, the medium-scale waves with a regularly spaced distribution about latitude circles are frequently observed throughout the year with relatively small zonal wavenumbers in the winter season. From various aspects obtained in this study such as the vertical wave structure and eastward migration, these are considered to be baroclinically unstable waves. On the other hand, in the Northern Hemisphere, the medium-scale waves with the zonally homogeneous property are observed only in the summer season. They are stationary and considered to be topographically unstable waves. In other seasons, medium-scale disturbances are longitudinally localized and do not have the zonally homogeneous nature.