Abstract:
Coordinated measurements were made on two nights in December 1992 of thermospheric temperature with a Fabry-Perot Interferometer (FPI) at Kavalur ( dip∼ 9.5° N) and of F-layer height with ionosondes at Trivandrum ( dip∼ 0.6° S), Kodaikanal ( dip 3°N), Sriharikota ( dip∼ 10.5° N) and Ahmedabad (dip 34°N) in India. On both the nights which are geomagnetically quiet (Ap≤9), the FPI measurements revealed a distinct temperature enhancement around midnight over Kavalur. Neutral winds estimated from h'F data of Trivandrum and Sriharikota showed significant poleward winds in association with the temperature increase over Kavalur. At Ahmedabad a clear-cut descent of F-layer followed the temperature enhancement over Kavalur. This pattern is consistently seen on the two nights. The simultaneous thermospheric and ionospheric observations demonstrate for the first time the relationship, in totality, between the equatorial midnight temperature maximum (MTM), poleward reversal of nighttime meridional winds and ‘postmidnight collapse’ of F-layer at low latitudes.
