Abstract
A statistical investigation into the horizontal propagation of ∼8–30 min gravity waves (GWs) in the ionosphere over a 1 year period from June 2010 to May 2011 is presented. The GWs were observed by multipoint continuous Doppler sounding systems installed in the Czech Republic and in the Western Cape, South Africa. Measurements of GW propagation in the ionosphere over South Africa have never been presented before. Simultaneous measurements from nearby ionosondes made it possible to estimate the height of the GW observations and show that the analyzed GWs propagated at altitudes from ∼150 to ∼250 km. The analyzed waves were mainly observed after sunrise and around sunset. Our statistical study shows that the analyzed GWs propagated with horizontal velocities from ∼70 to 250 m/s. The average observed horizontal velocities were ∼100 m/s in the local summer and 125–150 m/s in the local winter. The waves propagated approximately poleward in the local summer, whereas roughly equatorward propagation was observed in the local winter. Westward propagation was rarely observed in the Czech Republic, and eastward (southeast) propagation was seldom observed in South Africa. A comparison with neutral wind velocities shows that the analyzed GWs propagated approximately against the neutral winds calculated by the HWM07 model. The estimated horizontal wavelengths of the analyzed waves were ∼100–300 km.
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