Fernando Simões

Comment on "An analysis of VLF electric field spectra measured in Titan's atmosphere by the Huygens probe" by J. A. Morente et al.

Citation: Grard, R., S. Berthelin, C. Beghin, M. Hamelin, J.‐J. Berthelier, J. J. Lopez‐Moreno, and F. Simoes (2011), Commenton “An analysis of VLF electric field spectra measured in Titan’s atmosphere by the Huygens probe” by J. A. Morente et al.,J. Geophys. Res., 116, E05005, doi:10.1029/2009JE003555.

Monitoring D-region variability from lightning measurements

In situ measurements of ionospheric D-region characteristics are somewhat scarce and rely mostly on sounding rockets. Remote sensing techniques employing Very Low Frequency (VLF) transmitters can provide electron density estimates from subionospheric wave propagation modeling. Here we discuss how lightning waveform measurements, namely sferics and tweeks, can be used for monitoring the D-region variability and day-night transition, and for local electron density estimates. A brief comparison among D-region aeronomy models is also presented.

Observations of 50/60 Hz power line radiation in the low latitude ionosphere detected by the electric field instrument on the C/NOFS satellite

One of the most ubiquitous forms of EM radiation emanating from the earths surface is that of power line radiation. Associated with the generation of AC electric power, such emissions are typically launched along conducting power lines that may travel hundreds, or even thousands of km, from generating stations. The fundamental frequencies of such emissions are characteristically 50 Hz or 60 Hz, depending on the regional standards for power generation/consumption. The frequency of this radiation is well below that of the plasma frequency of the ionosphere (typically several MHz) and hence is expected to reflect back to the earth and propagate in the waveguide formed by the earths surface and the bottom ledge of the ionosphere, typically near 100 km. Given that such power lines are widespread on the exposed lithosphere, the leakage of some ELF emissions associated with electric power generation might nevertheless be expected in the ionosphere, in the same manner in which a small fraction of the power associated with ELF Schumann resonances and lightning sferics have been shown to penetrate into the ionosphere. Despite their known frequency signatures and source locations, the direct detection in space (i.e., in the ionosphere) of 50/60 Hz waves associated with terrestrial power line emissions is, to our knowledge, not commonly observed.