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Ann. Geophys., 20, 1677-1685, 2002
www.ann-geophys.net/20/1677/2002/
© European Geosciences Union 2002
Solar Cycle variations of ƒoF2 from IGY to 1990
N. K. Sethi, M. K. Goel, and K. K. Mahajan
Radio and Atmospheric Sciences Division, National Physical
Correspondence to: N. K. Sethi (mksethi@csnpl.ren.nic.in)
Abstract. Noontime monthly median values of F2-layer
critical frequency foF2 (m) for some ionospheric stations representing
low- and mid-latitudes are examined for their dependence on solar activity for
the years 1957 (IGY) to 1990. This is the period for which ionospheric data in
digital form is available in two CD-ROMs at the World Data Center, Boulder. It
is observed that at mid-latitudes, foF2 (m) shows nearly a linear
relationship with R12 (the 12-month running average of the Zurich sunspot
number), though this relation is nonlinear for low-latitudes. These results
indicate some departures from the existing information often used in
theoretical and applied areas of space research.
Key words. Ionosphere (equatorial ionosphere;
mid-latitude ionosphere; modelling and forecasting)
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