Observation and modeling of the Earth‐ionosphere cavity electromagnetic transverse resonance and variation of the D‐region electron density near sunset

In the frame of the African Monsoon Multidisciplinary Analyses campaign, measurements of very low frequency electric fields were performed onboard a stratospheric balloon launched on 7 August 2006 from Niamey, Niger. During flight, numerous sferics were observed associated to lightning from active convective cells a few hundred kilometers from the balloon. Lightning data analysis shows the transverse mode mean frequency of the Earth‐ionosphere cavity decreasing from ∼2.4 to 2 kHz over a period of 1 h about sunset. The observed change of the transverse resonance near dusk can be fairly reproduced by an electromagnetic wave propagation model, which takes into account the D‐region electron density variation predicted by the International Reference Ionosphere model.

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