Ionospheric Planetary Wave Activity and Its Role in Equatorial Spread F Day‐to‐Day Variability

A comprehensive analysis on the ionospheric planetary wave activity is undertaken using 8 years of ionosonde data at Trivandrum (8.5°N, 77°E), a dip equatorial station. The study reveals that the dominant planetary wave is of 16‐day type and its strength is maximum in winter solstice/autumnal equinox and minimum in summer solstice in high solar activity conditions. In low solar activity years planetary wave activity strength is more or less comparable in vernal equinox, autumnal equinox, and winter solstice, while it is observed to be least in summer solstice. Further, the planetary wave activity shows direct correlation with solar activity for the different seasons. Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite observations of off‐equatorial E‐region zonal winds confirm the fact that they are strong westward in high solar activity years compared to low solar activity years. The strong westward winds aid the upward propagation of westward propagating planetary waves in high solar activity years. Planetary waves reaching the off‐equatorial E‐region modulate the equatorial F‐region via the coupling along the magnetic field lines. The role of planetary waves in modulating the pre‐reversal enhancement, equatorial spread F duration, and its spread range on a day‐to‐day basis is brought out quantitatively for both high and low solar activity conditions. The study emphasizes the importance of ionospheric planetary wave studies for the prediction of equatorial spread F characteristics. Key Points A quantitative analysis on the seasonal and solar activity variation of ionospheric planetary wave activity is performed The planetary wave modulation of equatorial spread F characteristics is brought out quantitatively on a day‐to‐day basis