Fig. 11

a The plot shows the equatorial Es OR during autumn in a longitude–local time cross-section. For this plot, we considered Es events from the upper mode (altitude > 105 km). Image b: same as plot a but for Es layers appearing below 105 km. c Comparison of longitudinal variability of eastward EEF (blue) and the upper mode of equatorial sporadic E layers (orange). A clear anticorrelation (R = − 0.69) of both parameters is observed and manifested in the lower right plot d where the Es altitude is mapped against the EEF