Ionospheric coupling, especially between ionogram‐recorded spread‐F and sporadic‐E enhancements at an equatorial‐anomaly crest station, Chung‐Li

The analysis of ionograms recorded at Chung‐Li, a station situated near the crest of the equatorial ionosphere anomaly, finds that there is coupling between the nighttime F 2 and E s layers at the onset of spread‐F, as is the case in midlatitudes. The results were obtained using isolated patches of spread‐F occurrence of duration 2 hours or less and for sunspot‐minimum years. It is suggested that the medium‐scale traveling ionospheric disturbances (TIDs), which are responsible for the spread‐F occurrence, influence both the F 2 and E s levels almost simultaneously, as their travel is consistent with the evidence from these analyses, as well as that already available for midlatitudes. Some comments are made on the possibility that these medium‐scale TIDs may be responsible directly for some of the small‐scale irregularities observed at these equatorial latitudes.