PRECURSOR TO EQUATORIAL SPREAD-F IN OI-630.0-NM DAYGLOW

A unique OI 630.0 nm dayglow photometer operated from Waltair (10.0 degrees N dip lat.), a-low-latitude station in India, in a bidirectional mode, i.e., over zenith and at 20 degrees elevation pointing north, has revealed features associated with the evolution of tile Equatorial Ionization Anomaly (EIA). The estimated strength of the EIA on a particular day based on these features reveal that significant differences exist in the EIA contribution to OI 630.0 nm on equatorial spread-F (ESF) and non-ESF days. There exists a precursor in the OI 630.0 nm dayglow which enables the prediction of ESF at least 3 hours prior to its actual occurrence and hence points to the significant control of daytime EIA-related processes in the triggering of the post-sunset ESF.