Ambipolar diffusion coefficients in the meteor region have been measured using meteor decay times determined with the CLOVAR radar [Hocking, 1997>. This parameter may then be used to infer information about atmospheric temperatures or pressures in that region. In particular, we show annual variations in the parameter T/P. Our procedures, together with the underlying assumptions, are described, and our results are compared to the CIRA (1986) empirical model as well as other experimental data. These successful measurements have been possible because of our use of a new 5-element interferometer which has minimal inter-element coupling and has an angular location accuracy of better than ¿2¿, together with new algorithms which introduce important corrections to the decay time height profile. We concentrate in this paper on monthly averages, but higher temporal resolutions are possible. ¿ 1997 American Geophysical Union