Analysis of Blanketing Sporadic-E Layer and Associated Tidal Periodicities Over a Brazilian Station Undergoing a Transition From Low Latitude to Midlatitude

Analyses on a complete year of Digisonde data are conducted to investigate the sporadic-E (Es) layers over Santa Maria (29.7(degrees)S, 53.8(degrees)W, dip lat.: -37(degrees)), Brazil. This region is undergoing a transition from low latitude to midlatitude within the South American Magnetic Anomaly (SAMA), which provides a key motivation to explore their behavior and the associated tidal periodicities. The Es are classified into four types: flat (Es-f), low (Es-l), high (Es-h), and cusp (Es-c). The diurnal and seasonal variations of their top (ftEs) and blanketing (fbEs) frequencies and virtual height (h'Es) are examined. The frequency parameters show the presence of intense Es during equinoxes besides summer. It is also remarkable that the higher values of mean h'Es during winter compared to the other seasons during daytime. These observations differ from previous theories about midlatitude Es layers. The diurnal occurrence rates of the Es-b types exhibited distinct dependencies on both local time and seasons. The Es-h and Es-c were observed exclusively during the daytime, with the former dominating the occurrences in all seasons. To investigate any tidal periodicities embedded in the ftEs, fbEs, and h'Es time series, the Lomb-Scargle technique was employed. The analysis revealed the presence of 24-, 12-, 8-, and 6-hr periodicities in both fbEs and h'Es when considering the entire year of data. However, when the data are fractioned into seasons, the predominant periodicities were found to be 24- and 12-hr cycles. Furthermore, when considering the different Es-b types, the Lomb-Scargle analysis indicated varying periodicities.