Variations of solar EUV, UV and ionospheric foF2 related to the solar rotation period

Abstract. Spectral analysis of daily values of various solar indices viz. sunspot number, 10.7-cm flux, H Lyman-α and -β, specific He, Fe and Mg lines and solar X-rays was carried out for two selected intervals. During interval A (May-August 1978, 123 days) the solar indices showed a prominent periodicity near 27 days, while during interval B (January-May 1979, 151 days) the solar indices showed a prominent periodicity near 13 days. For the same intervals, foF2 (max) and foF2 (average) during 1000-1500 LT were similarly analysed for the locations Cachoeira Paulista, SP, Brazil (23°S, 45°W), and Okinawa (26°N, 128°E) and Kokubunji (36°N, 139°E) in Japan. The 27-day and 13-day periodicities in solar indices were reflected in the foF2 series, but in different relative proportions at the three locations, probably due to the interference of local aerodynamical effects. Some other periodicities were common to solar indices and foF2, while some others were present in the solar indices but not in foF2, or vice versa