ANNUAL AND SEMIANNUAL TEMPERATURE OSCILLATIONS AT THE MESOPAUSE LEVELS OVER TRIVANDRUM (8.5-DEGREES-N, 78-DEGREES-E)

The ambipolar diffusion coefficient (D) of the atmosphere, obtained fr om the exponential amplitude decay of 62,081 underdense radio meteor t rails, recorded by the meteor wind radar operated at Trivandrum, was a nalyzed to obtain the annual (AO) and semiannual oscillations (SAO) of the monthly mean ''D''. The amplitudes of AO and SAO of the mean D we re interpreted in terms of AO and SAO of the mesopause temperature. Th e results show excellent agreement with the AO and SAO of mesopause te mperature reported earlier using rocket data in low latitudes. While t he COSPAR International Reference Atmosphere (CIRA) 1972 models reprod uce the SAO observed in the present study, the more recent CIRA 1986 m odels do not reproduce it. Both CIRA 1972 and CIRA 1986 do not reprodu ce AO of mesopause temperature at low latitudes. It is of significance to note that AO of mesopause temperature is much stronger than SAO.