Occurrence of sporadic-E layer over the ionospheric station of Rome: Analysis of data for thirty-two years

Hourly systematic measurements of the highest frequency reflected by the sporadic-E layer (foEs) recorded at the Rome ionospheric observatory (Italy, 41.8° N, 12.5° E), were considered during the period January 1976–December 2007, to calculate the percentage of occurrence of sporadic-E layer with frequencies foEs greater than a given threshold value fT, P(foEs > fT).To study possible influences from solar activity, measurements of foEs recorded near the periods of minimum and maximum solar activity, were also considered. Measurements of foEs recorded for the period January 2000–December 2007 were analysed to study the influence of magnetic activity on foEs occurrence frequency. The results are provided as maps showing P(foEs > fT) with foEs above the selected level (fT = 3, 4, 5, 6, 7, 8, and 9 MHz), for each hour from 00.00 L.T. to 23.00 L.T. and for each month.The results reveal a relatively low P(foEs > fT) before sunrise and after sunset in all seasons; the most significant P(foEs > fT) occur during daytime in summer months; intense formations of sporadic-E layer occur rarely during the year; P(foEs > fT) does not depend significantly on solar and geomagnetic activity.