Najat M. R. Al-Ubaidi*
Department of Astronomy and Space, Col lege of Science, University of
Baghdad, Baghdad, Iraq
Abstract. Ionosonde data recorded at Kokubunji, Japan (Latitude 35.7 N; Longitude 139.5 E) during a year of low solar activity (1994) and high solar activity (1990) were used in our research work to study the correlation between daily sunspot numbers (R) and the daily mid-latitude F2-region critical frequency (foF2) for four seasons. There is a diurnal variation of (foF2) with (R). Trends found over the year of solar maximum (1990) are more positive in March and December, but negative in June and September. The year of solar minimum (1994) shows positive trends in June and September, but negative trends in March and December.
Keywords: Critical frequency - sunspot number - F2 layer