Long-term aspects of nighttime spread F over a low mid-latitude European station

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Long-term aspects of nighttime spread F over a low mid-latitude European station

Paul, K.S. / Haralambous, H. / Oikonomou, C. / Paul, A.

Abstract In an effort to explore the morphology of nighttime spread F at the lower mid-latitude European station of Nicosia, Cyprus (35°N, 33°E geographic; magnetic dip. 29.38°N), all ionograms recorded by the DPS-4D digisonde during the interval 2009–2016 have been analyzed. Subsequent detailed investigation was performed to establish the possible effect of various triggering mechanisms on spread F within the framework of Perkins instability on a statistical basis by correlating spread F occurrence particular wave pattern signatures (Satellite Trace/Multiple-reflected Echoes), gravity wave signatures, F layer uplift (h'F) and unstable sporadic E layers. The results verify the systematic manifestation and therefore the significance of TIDs and unstable sporadic E layers as triggering factors responsible for seeding spread F development and underline the frequent appearance of multi-reflected echoes and satellite traces as dominant precursors of mid-latitude spread F over European latitudes for the first time. Furthermore clear seasonal characteristics and inverse solar activity dependence of spread F occurrence in lower European mid-latitudes is established similar to southern hemisphere studies undertaken previously.