A Climatology of Gravity Wave Motions in the Mesopause Region at Adelaide, Australia

Abstract

A statistical study of gravity wave motions in the mesosphere and lower thermosphere measured with a MF partial reflection radar located at Buckland Park new Adelaide (35°S, 138°E) in the period November 1933 to December 1984 is presented. The analyses am confined to waves with ground based periods between 1 and 24 h. Time-height cross sections show that the mean square amplitudes u?2 and v?2, of the zonal and meridional perturbation velocities, respectively, vary in a predominantly semiannual manner such that the minima in wave activity coincide with the reversals in the zonal circulation in the middle atmosphere. In most instances, v?2 is greater than u?2 which, together with the small but nonzero u?v? fluxes shows that the gravity wave field is partially polarized. A technique similar to that used to analyse partially polarized electromagnetic waves suggests that on a seasonal basis, the wave field is polarized by about 10% to 20% but for shorter periods the degree of polarization may be significantly higher. It is found that the polarized waves with periods greater than 1 h are probably propagating in directions essentially east of south in summer, while in winter the 1?8 h waves are propagating towards the southwest and the 8?24 h waves are propagating towards the northwest.