The ambipolar diffusion coefficient (D) of the atmosphere, obtained from the experimental amplitude decay of 62,081 underdense ratio meteor trails, recorded by the meteor wind radar operated at Trivandrum, was analyzed to obtain the annual (AO) and semiannual oscillations (SAO) of the monthly mean ''D.''

The amplitudes of AO and SAO of the mean D were interpreted in terms of AO and SAO of the mesopause temperature. The results show excellent agreement with the AO and SAO of mesopause temperature reported earlier using rocket data in low latitudes. While the COSPAR International Reference Atmosphere (CIRA) 1972 models reproduce the SAO observed in the present study, the more recent CIRA 1986 models do not reproduce AO of mesopause temperature at low latitudes. It is of significance to note that AO of mesopause temperature is much stronger than SAO. ¿ American Geophysical Union 1993