THERMOSPHERIC MERIDIONAL NEUTRAL WINDS ASSOCIATED WITH EQUATORIAL MIDNIGHT TEMPERATURE MAXIMUM (MTM)

Coordinated measurements were made on two nights in December 1992 of t hermospheric temperature with a Fabry-Perot Interferometer (FPI) at Ka valur (dip approximately 9.50 N) and of F-layer height with ionosondes at Trivandrum (dip approximately 0.6-degrees-S), Kodaikanal (dip 3-de grees-N), Sriharikota (dip approximately 10.5-degrees-N) and Ahmedabad (dip 34-degrees-N) in India. On both the nights which are geomagnetic ally quiet (Ap less-than-or-equal-to 9), the FPI measurements revealed a distinct temperature enhancement around midnight over Kavalur. Neut ral winds estimated from h'F data of Trivandrum and Sriharikota showed significant pole-ward winds in association with the temperature incre ase over Kavalur. At Ahmedabad a clear-cut descent of F-layer followed the temperature enhancement over Kavalur. This pattern is consistentl y seen on the two nights. The simultaneous thermospheric and ionospher ic observations demonstrate for the first time the relationship, in to tality, between the equatorial midnight temperature maximum (MTM), pol eward reversal of nighttime meridional winds and 'postmidnight collaps e' of F-layer at low latitudes.