In this paper we compare monthly averages of the atmospheric parameter T/p (where T is temperature and p is pressure) derived from the decay of underdense meteor echoes with the CIRA (1986) atmospheric model. The meteor data were collected with the Buckland Park VHF radar situated ~40 km north of Adelaide, Australia. We examine the overall agreement between the meteor observations and CIRA as well as seasonal differences between the two. Comparison is made with the results of Hocking et al. <1997>. Our results are complimentary to those of Hocking et al.; our data were obtained in the Southern Hemisphere as opposed to the Northern Hemisphere. A discussion on the effect of the geomagnetic field on the diffusion of meteor trails and its effect on the measurement of atmospheric parameters is also included. We note that the geomagnetic field is a very important consideration when using meteors for the derivation of atmospheric temperatures and pressures above heights of around 92--93 km. This effect is required to be taken into account above these heights as failure to do so leads to errors in the interpretation of the data. Recent researchers have avoided this problem by restricting their data to below 90 km. ¿ 2000 American Geophysical Union