Characteristics of solar diurnal variations: A case study based on records from the ground magnetic station at Vassouras, Brazil

► Gapped wavelet technique introduced to isolate diurnal periods in the SAMA region. ► Cross-correlation technique used to compare magnetic stations near/far from the SAMA. ► Correlation coefficients usually larger at equinoxes in years of high solar activity. ► Low correlation coefficients observed where geomagnetic field is particularly high. ► Ionospheric density and geomagnetic intensity may be probable causes of those effects.