Simultaneous observations of atmospheric summer tides at Grahamstown (South Africa) and Adelaide (Australia)

Observations of atmospheric tides and the prevailing wind in the mesosphere , made simultaneously during summer months with meteor radar at Grahamstown (South Africa) and MF radar at Adelaide (South Australia) between 1987-199 3, are presented and compared. After allowing for differences in observing technique it is found that the results generally show similar month-to-mont h and interannual trends. The amplitudes at both centres show considerable variability but phases are generally fairly stable, apart from a noteworthy deviation in the phase of the semidiurnal tide at Grahamstown during one s ummer season. The prevailing wind is found to be significantly stronger at Grahamstown, particularly in the case of the zonal component. The amplitude of the zonal component of the diurnal tide appears to be larger at Grahams town, particularly during January, whereas the amplitudes of the meridional diurnal tide and of both components of the semidiurnal tide are generally similar at each centre. The phase of the diurnal tide at Grahamstown is con sistently earlier than at Adelaide by a few hours, but the semidiurnal phas es are closer and can be earlier or later. For both tides the phases of the zonal and meridional components are fairly close to quadrature at both cen tres, resulting in anticlockwise rotation of the tidal wind vectors in each case. The overall results suggest some contamination of the main migrating modes with non-migrating components, especially in the ease of the diurnal tide. (C) 1998 Elsevier Science Ltd. All rights reserved.