| Summary: | In this work, we investigate the possible effects of geomagnetic activity on the ionospheric critical frequencies (foF2) in geomagnetic conjugate points. For this purpose, hourly foF2 data measured for the year 1976 from the ionosonde stations Akita, St. John's and Resolute Bay in the Northern hemisphere and their corresponding magnetic conjugate ionosonde stations Brisbane, Halley Bay and Scott Base in the Southern hemisphere are examined. Planetary geomagnetic activity "3h-K-p" indices are used as a geomagnetic activity indicator. foF2 data in the magnetic conjugate points (MCP) are investigated by using a superposed epoch analysis method. This analysis is done depending on the response of foF2 to geomagnetic activity variations in MCP based on geomagnetic stormy days around equinoxes (March 21, September 23) and solstices (June 21, December 21), and the results obtained from these MCP are compared. From these results, it is found that foF2 values in magnetic conjugate pairs give similar reactions to geomagnetic activity variations simultaneously, although this relationship differs according to the seasons and magnetic latitudes of the stations. (C) 2018 COSPAR. Published by Elsevier Ltd. All rights reserved. C1 [Timocin, Erdinc] Mersin Univ, Dept Med Serv & Tech, TR-33343 Mersin, Turkey. [Unal, Ibrahim] Inonu Univ, Dept Sci Teaching, TR-44280 Malatya, Turkey. [Tulunay, Yurdanur] Middle East Tech Univ, Dept Aeronaut Engn, TR-06800 Ankara, Turkey. [Goker, Umit Deniz] Istanbul Gelisim Univ, Dept Aviat Management, TR-34315 Istanbul, Turkey.
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