Spread-F/sporadic e coupling at Chung-Li, especially for postsunset periods of sunspot maximum years

Abstract

Using ionogram-recorded data, the coupling between spread-F occurrence and enhanced Es blanketing frequencies (fbEs) (indicative of foEs changes), has been investigated for an equatorial-ionospheric-anomaly crest station, Chung-Li, for the postsunset periods of sunspot-maximum years. Apart from the evidence for coupling from inspections of the f-plots alone, for the years analyzed (1981, 1982, 1988, and 1989), statistical results of more significance were found from superposed-epoch analyses. Isolated spread-F events of duration of 2 hours or less which started at or before 2200 LT were used as controls on time series. These series were made up of comparisons between 15-min f-plot fbEs values and interpolated monthly median fbEs values. Evidence for coupling was found for the analyses which involved 97 controls. The evidence in the f-plots for three events involving Es patches, which investigators have examined in some detail using the VHF radar at Chung-Li, suggests that these, events are also coupled to isolated spread-F occurrence. Copyright 2003 by the American Geophysical Union.