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-&#x03B1; and -&#x03B2;, 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, <i>foF2</i> (max) and <i>foF2</i> (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 <i>foF</i>2 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 <i>foF</i>2, while some others were present in the solar indices but not in <i>foF</i>2, or vice versa