Equatorial ionospheric response to isolated auroral substorms over a solar cycle (1980−85): evidence of longitudinal anomaly

The equatorial ionospheric response to 228isolated, rapid-onset auroral substorms (as defined from the auroral electrojetindex AE) was found from enhancements of the virtual (minimum) height of theF-region (∆h$^prime$F) in the declining phase of asolar cycle (1980–85). The responses, found for three longitudinal sectors atthe equator: Africa (Ouagadougou and Dakar), Asia (Manila) and America (Huancayo),were compared with the response close to the auroral source region at Yakutsk(northern Siberia). The auroral substorm onsets were centered at 17 and 15 UT atsunspot maximum (1980–82) and minimum (1983–85), preceding by 3–5 h the periodof post-sunset height rise in the African sector whereas other sectors were inthe early afternoon (Huancayo) and morning (Manila). The African response,particularly at Ouagadougou, was distinctly different from other sectors. In thesunspot maximum years (1980–81) the auroral surges were followed after about 3 hby a sharp depression (∆h$^prime$F<0) in thepost-sunset height rise, with a period of little or no response (∆h$^prime$F=0)in 1982. A response polarity reversal (∆h$^prime$F>0)was noted in this sector for sunspot minimum (1983–85) when large h$^prime$Fenhancements were observed at the sunset region. The responses in the Asian andAmerican sector were positive except for a case in Huancayo when response wasnegative, following an auroral surge before the sunset at this station. Itappears that the aurorally generated large-scale travelling ionosphericdisturbances (LSTIDs), which first cause positive height enhancements in a sub-aurorallocation (Yakutsk), subsequently affect the unstable post-sunset ionosphere inthe equatorial Africa