Application of the Radio-Window Concept to the Propagation of
VLF and MF Waves through Night Time Ionosphere Above Powerful
VLF Transmitters
Francois Lefeuvre
LPC2E / CNRS, 3A, Avenue de la Recherche Scientifique, 45071 Orléans cedex 2, France
Keywords: VLF transmitter, MF waves
Abstract: Surprisingly, the propagation of radio waves through the ionosphere is still not completely understood. This
has been recently pointed out from night time observations made by the DEMETER satellite (~700 km
altitude) over powerful VLF ground-based transmitters used for communications with submarines. If it seems
quite reasonable to observe high-power densities of VLF waves over geographical areas located at latitudes
slightly below the ones of the VLF transmitters and their conjugated regions, it is difficult to explain: (i) the
geographical extension of the VLF observations, and (ii) high-power densities of MF waves (lightning-
generated whistlers) observed in the ~2. – 2.5 MHz band, over the same geographical areas than for VLF
waves. The mechanism proposed to explain those observations is based on the radio-windows concept. The
propagation characteristics of radio waves are derived from the Appleton-Hartree formula. The refractive
index n2 is a function of the X = fpe2/f2 and Y= fce/f parameters (with f the wave frequency, fpe the electron
plasma frequency and fce the electron gyrofrequency). Under given conditions for propagation, upgoing rays
which reach the altitude of the X = 1 plasma cut-off are not reflected but converted to another propagation
mode. As an example, for a propagation from below the ionosphere up to the 700 km altitude, assuming a
given night time electron density profile, numerical simulations show that a 25 kHz VLF waves crosses a X
= 1 plasma cut-off at ~ 90 km altitude (the entry into the ionosphere) whereas a 2.2 MHz MF wave crosses a
first X = 1 plasma cut-off at ~ 250 km altitude (entry into the ionosphere) and a second one at ~ 400 km
altitude (output from the ionosphere). The half angles of the transmission cones at the X=1 plasma cut-offs
depend on the level of wave heating at those altitudes and so on the increases in collision frequencies generated
by powerful VLF ground-based transmitters. Numerical simulations show that: (1) in the VLF frequency
range, the wave heating being maximum at the altitude of the Ordinary mode resonance region, i.e. just above
the X = 1 plasma cut-off, the half angle of the transmission cone may reach several dozens degrees, (2) in the
MF frequency range, the wave heating being maximum at the altitude where the product of the electronic
density and the collision frequency is maximum, the opening of the transmission cones strongly depend on
the relative altitudes of the maximum heating and of the X=1 plasma cut-offs.
Brief Bio François Lefeuvre is a CNRS Research Director Emeritus at the LPC2E laboratory (Laboratoire
de Physique et Chimie de l’Environnement et de l’Espace) of the French National Centre for
Scientific Research (CNRS) and the University of Orleans. He is presently Past President of URSI
(International Union of Radio Science). He obtained his first thesis in 1970 at the “Groupe de
Recherche Ionospherique”, Saint-Maur des Fossés, received a fellowship from ESRO (now ESA)
for studying natural ELF and VLF emissions in the magnetosphere at the Physics Department of
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Lefeuvre F.
Application of The Radio-Window Concept to the Propagation of VLF and MF Waves through Night Time Ionosphere Above Powerful VLF.
DOI: 10.5220/0005420400030004
In Proceedings of the Third International Conference on Telecommunications and Remote Sensing (ICTRS 2014), pages 3-4
ISBN: 978-989-758-033-8
Copyright
c
 2014 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved

the Sheffield University in UK (1970), got a permanent position at CNRS in 1972 and obtained is
second thesis (thèse d’état) in 1977 at the University of Orleans. In 1979/1980 he was a visiting
scientist in the Radio Science Group at the Stanford University. He has published scientific papers
in several domains including radio wave propagation within the ionosphere and the magnetosphere,
inverse problems, signal analysis, risk management. He was Co-Investigator for several space
missions (GEOS, AUREOL 3, INTERBALL, DEMETER), Principal Investigator for a wave
experiment on the INTERBALL mission, and PI mission for the TARANIS project. He was
Director of LPCE (Laboratoire de Physique et Chimie de l’Environnement) from 1994 to 2003,
chaired the ESA Space Weather Working Team (2002-2005) and was President of URSI
(International Union of Radio Science) from 2005 to 2008 then from 2009 to 2011
Third International Conference on Telecommunications and Remote Sensing
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