Observations of wave activity in the ionosphere over South Africa in geomagnetically quiet and disturbed periods

The present paper deals with observations of wave activity in the period range 1–60min at ionospheric heights over the Western Cape, South Africa from May 2010 to July 2010. The study is based on the Doppler type sounding of the ionosphere. The Doppler frequency shift measurements are supplemented with measurements of collocated Digisonde DPS-4D at SANSA Space Sciences, Hermanus. Nine geomagnetically quiet days and nine geomagnetically active days were included in the study. Waves of periods 4–30min were observed during the daytime independent of the level of geomagnetic activity. Amplitudes of 10–30min waves always increased between 14:00 and 16:15 UT (16:00–18:15 LT). Secondary maxima were observed between 06:00 and 07:00 UT (08:00–09:00 LT). The maximum wave amplitudes occurred close to the time of passage of the solar terminator in the studied region which is known to act as a source of gravity waves. Waves of periods 30–50min were observed in the F2 layer during the daytime on five out of the eighteen days analysed, on four geomagnetically active days and on one quiet day. On the geomagnetically active day of 27 July 2010, waves of periods 1–2.5min occurred in the evening and night hours. These waves appeared simultaneously with 1–2.5min fluctuations of horizontal components of the local geomagnetic field. We suppose that the 1–2.5min ionospheric oscillations are a response to the geomagnetic micropulsations.