Latitudinal Dependence of the Geomagnetic and Solar Activity Effect on Sporadic-E Layer

Based on the global COSMIC occultation data, the latitudinal dependence of the geomagnetic and solar activity effect on the sporadic-E (Es) layer is statically investigated. At middle geomagnetic latitudes, Es occurrence rates generally decrease with increasing solar activity, except during winter and spring in the Southern Hemisphere. Meteor radar observations show that meteor rates in this region increase under enhanced solar activity, opposite to the observed Es response, suggesting that meteoric input is unlikely to be the dominant factor. Instead, the decrease in Es occurrence is more plausibly associated with weakened tidal forcing near typical Es altitudes, which may reduce the efficiency of vertical wind shear in converging long-lived metallic ions. At low geomagnetic latitudes, Es occurrence also generally shows a negative correlation with solar activity, likely related to the combined effects of reduced meteoric input and tidal modulation. For geomagnetic activity dependence, daytime Es occurrence at middle geomagnetic latitudes generally decreases with increasing geomagnetic activity, whereas the nighttime response is more seasonally dependent. In contrast, at high geomagnetic latitudes, Es occurrence exhibits a positive correlation with geomagnetic activity, particularly at night. The magnetic local time dependence further shows that high-latitude nighttime Es occurrence is significantly higher than that during daytime and increases markedly under disturbed geomagnetic conditions. This pronounced nightside enhancement suggests that storm-time high-latitude electrodynamic forcing, including enhanced convection electric fields and ion convergence, plays an important role in promoting polar Es formation.