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 similar to 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. Citation: Simoes, F., J.-J. Berthelier, M. Godefroy, and S. Yahi (2009), Observation and modeling of the Earth-ionosphere cavity electromagnetic transverse resonance and variation of the D-region electron density near sunset, Geophys. Res. Lett., 36, L14816, doi:10.1029/2009GL039286..