Evidence for the coincident long period oscillations in the Equatorial Ionization Anomaly with the zonal neutral wind in the mesosphere

Abstract

The day-to-day variations of the f 0 F2 values in the north crest region (Okinawa 26°N, 128°E) of the Equatorial Ionization Anomaly (EIA) are studied in both temporal and frequency domain. Then, the long period (2–20 days) oscillations that appeared in the EIA are compared with the concurring planetary-scale waves in the neutral wind in the mesosphere observed in both hemispheres, at Kyoto (35°N, 136°E) and Adelaide (35°S, 138°E), that are located at nearly the same longitude as Okinawa. The contrast shows that for a short period wave (2–5 day), especially during the summer time of the two hemispheres (around July and August for the northern, January and February for the other), the variations of strength and period in the EIA and the zonal neutral wind are in line with each other; for a longer period wave, if the wind amplitude is rather large, there is also correspondence in the EIA's variation. Further studies show that the seasonal variations of the strength of the two kinds of oscillations are in good agreement as well. This gives direct observational evidence to interpret the long period oscillations in the neutral wind as probably being the driving source of the same period oscillations in the EIA. It will also support the mechanism of the electrodynamic coupling between the equatorial ionosphere and the mesosphere which had been suggested before.