Precursor to equatorial spread‐F in OI 630.0 nm dayglow

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Abstract
A unique OI 630.0 nm dayglow photometer operated from Waltair (10.0° N dip lat.), a‐low‐latitude station in India, in a bidirectional mode, i.e., over zenith and at 20° elevation pointing north, has revealed features associated with the evolution of the 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.