The ionosphere as a whispering gallery

1962 ◽  
Vol 265 (1323) ◽  
pp. 554-569 ◽  
Keyword(s):  
Electron Density ◽  
Spherical Surface ◽  
Low Frequency ◽  
Electron Density Profile ◽  
Whispering Gallery Modes ◽  
Radio Waves ◽  
Sound Waves ◽  
Whispering Gallery ◽  
The Earth ◽  
Reflexion Coefficient

The propagation of radio waves of very low frequency to great distances is conveniently treated by regarding the space between the earth and the ionosphere as a wave-guide. Several authors have found that the least attenuated modes are profoundly affected by the earth’s curvature. This effect is investigated for several models of the ionosphere. It is found, in particular, that for frequencies greater than about 30 kc/s some modes are possible for which the energy is concentrated in a region near the base of the ionosphere, and the field strength near the ground is small. It is useful to think of such modes as being composed of waves repeatedly reflected at the inside spherical surface of the ionosphere, the rays being chords of this sphere. By analogy with sound waves these modes are called ‘whispering gallery modes’. The theory uses wave admittance and reflexion coefficient variables because these satisfy differential equations which are convenient for integration using a digital computer. The curvature of the earth is allowed for by using the method of the modified refractive index, but the earth’s magnetic field is neglected. Formulae for the m ode condition and the excitation of the various modes by a transmitter are given and discussed. A new way of dealing with an ionosphere having a continuous electron density profile is presented. The results of some numerical calculations are given both for a sharply bounded homogeneous ionosphere and for an exponential profile of electron density.

The propagation of very low-frequency radio waves in ducts in the magnetosphere

1971 ◽  
Vol 321 (1544) ◽  
pp. 69-93 ◽  
Keyword(s):  
Electron Density ◽  
Low Frequency ◽  
Electron Density Profile ◽  
Radio Waves ◽  
Order Mode ◽  
Inhomogeneous Wave ◽  
Ionization Density ◽  
Barrier Region ◽  
Uniform Medium ◽  
Whistler Propagation

A method is developed to calculate waveguide modes in a plane stratified duct of enhanced or reduced ionization density in an otherwise uniform magneto-ionic medium. It may in principle be applied to ducts with an arbitrary electron density profile, and with dimensions of the order of the wavelength in the medium. Computations are carried out for one simple model with enhanced ionization density and parameters typical of whistler propagation. The fields inside and outside the duct are discussed. It is shown that the energy flux in the inhomogeneous wave outside the physical boundaries of the duct may in certain circumstances be important. The types of waveguide mode which may occur are discussed. In particular there is one mode called the zero-order mode which always propagates even when the duct is very narrow or when the electron density in the duct differs only infinitesimally from that in the uniform medium outside. In the limit where the duct no longer exists this mode becomes a plane wave. When the axis of the duct is curved and there are transverse gradients of ionization density and of magnetic field in the medium outside the duct, all modes may tunnel through a barrier region, in which the wave is evanescent, to a region where the energy is refracted away from the duct. Consideration of this process leads to a criterion for deciding whether a duct is sufficiently strong to maintain guiding.

scholarly journals Survey of electron density changes in the daytime ionosphere over the Arecibo observatory due to lightning and solar flares

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Caitano L. da Silva ◽  
Sophia D. Salazar ◽  
Christiano G. M. Brum ◽  
Pedrina Terra
Keyword(s):  
Electron Density ◽  
Solar Flares ◽  
Low Frequency ◽  
Lower Ionosphere ◽  
Weather Conditions ◽  
Optical Observations ◽  
Radio Waves ◽  
D Region ◽  
E Region ◽  
Arecibo Observatory

AbstractOptical observations of transient luminous events and remote-sensing of the lower ionosphere with low-frequency radio waves have demonstrated that thunderstorms and lightning can have substantial impacts in the nighttime ionospheric D region. However, it remains a challenge to quantify such effects in the daytime lower ionosphere. The wealth of electron density data acquired over the years by the Arecibo Observatory incoherent scatter radar (ISR) with high vertical spatial resolution (300-m in the present study), combined with its tropical location in a region of high lightning activity, indicate a potentially transformative pathway to address this issue. Through a systematic survey, we show that daytime sudden electron density changes registered by Arecibo’s ISR during thunderstorm times are on average different than the ones happening during fair weather conditions (driven by other external factors). These changes typically correspond to electron density depletions in the D and E region. The survey also shows that these disturbances are different than the ones associated with solar flares, which tend to have longer duration and most often correspond to an increase in the local electron density content.

scholarly journals Precision Pulsar Timing with NASA's Deep Space Network

2015 ◽  
Vol 11 (A29B) ◽  
pp. 367-369
Author(s):  
Lawrence Teitelbaum ◽  
Walid Majid ◽  
Manuel M. Franco ◽  
Daniel J. Hoppe ◽  
Shinji Horiuchi ◽  
...  
Keyword(s):  
Low Frequency ◽  
Radio Waves ◽  
Deep Space ◽  
Radio Pulsars ◽  
Deep Space Network ◽  
Space Network ◽  
The Earth ◽  
Pulsar Timing ◽  
Initial Results ◽  
Stable Rotation

AbstractMillisecond pulsars (MSPs) are a class of radio pulsars with extremely stable rotation. Their excellent timing stability can be used to study a wide variety of astrophysical phenomena. In particular, a large sample of these pulsars can be used to detect low-frequency gravitational waves. We have developed a precision pulsar timing backend for the NASA Deep Space Network (DSN), which will allow the use of short gaps in tracking schedules to time pulses from an ensemble of MSPs. The DSN operates clusters of large dish antennas (up to 70-m in diameter), located roughly equidistant around the Earth, for communication and tracking of deep-space spacecraft. The backend system will be capable of removing entirely the dispersive effects of propagation of radio waves through the interstellar medium in real-time. We will describe our development work, initial results, and prospects for future observations over the next few years.

scholarly journals Classification of X-ray solar flares regarding their effects on the lower ionosphere electron density profile

2008 ◽  
Vol 26 (7) ◽  
pp. 1731-1740 ◽  
Author(s):  
D. P. Grubor ◽  
D. M. Šulić ◽  
V. Žigman
Keyword(s):  
Electron Density ◽  
Solar Flares ◽  
Low Frequency ◽  
Lower Ionosphere ◽  
Electron Density Profile ◽  
Height Range ◽  
X Ray ◽  
Reflection Height ◽  
Single Trace

Abstract. The classification of X-ray solar flares is performed regarding their effects on the Very Low Frequency (VLF) wave propagation along the Earth-ionosphere waveguide. The changes in propagation are detected from an observed VLF signal phase and amplitude perturbations, taking place during X-ray solar flares. All flare effects chosen for the analysis are recorded by the Absolute Phase and Amplitude Logger (AbsPal), during the summer months of 2004–2007, on the single trace, Skelton (54.72 N, 2.88 W) to Belgrade (44.85 N, 20.38 E) with a distance along the Great Circle Path (GCP) D≈2000 km in length. The observed VLF amplitude and phase perturbations are simulated by the computer program Long-Wavelength Propagation Capability (LWPC), using Wait's model of the lower ionosphere, as determined by two parameters: the sharpness (β in 1/km) and reflection height (H' in km). By varying the values of β and H' so as to match the observed amplitude and phase perturbations, the variation of the D-region electron density height profile Ne(z) was reconstructed, throughout flare duration. The procedure is illustrated as applied to a series of flares, from class C to M5 (5×10−5 W/m2 at 0.1–0.8 nm), each giving rise to a different time development of signal perturbation. The corresponding change in electron density from the unperturbed value at the unperturbed reflection height, i.e. Ne(74 km)=2.16×108 m−3 to the value induced by an M5 class flare, up to Ne(74 km)=4×1010 m−3 is obtained. The β parameter is found to range from 0.30–0.49 1/km and the reflection height H' to vary from 74–63 km. The changes in Ne(z) during the flares, within height range z=60 to 90 km are determined, as well.

Comparison of Q-bursts detected near the Earth’s surface and 140 m below ground level

2021 ◽  
Author(s):  
József Bór ◽  
István Lemperger ◽  
Karolina Szabóné André ◽  
Tamás Bozóki ◽  
Janusz Mlynarczyk ◽  
...  
Keyword(s):  
Wave Attenuation ◽  
Low Frequency ◽  
Field Measurements ◽  
Ground Level ◽  
Finite Conductivity ◽  
Radio Waves ◽  
Radio Communication ◽  
Mine Shaft ◽  
Near Surface ◽  
The Earth

<p>Q-bursts are signatures of exceptionally powerful lightning strokes which produce intense radio waves typically in the extremely low frequency band (ELF, 3Hz-3kHz). Due to the finite conductivity of the Earth’s surface, radio waves in this frequency range can be also detected in greater depths. While the penetration of electromagnetic (EM) waves in a conducting half space has been investigated and utilized, e.g., under water for submarine radio communication, very few field measurements consider the subsurface detection of ELF waves in the continental crust.</p><p>In this work, Q-bursts recorded in near surface and corresponding underground ELF band observations are compared in order to characterize the frequency dependent effect of the upper section of the Earth’s crust on the spectrum of the Q-burst signals.</p><p>Practically co-located, but not simultaneous quasi-surface and underground temporal ELF band magnetic field measurements were made near Mátraszentimre, in the Mátra Mountains, Hungary. The underground measurement was carried out inside a mine shaft in the Matra Gravitational and Geophysical Laboratory (MGGL) at a depth of 140 m. ELF observations from two permanent recording stations in the Széchenyi István Geophysical Observatory (NCK, Hungary) and in Hylaty (HYL, Poland), less than 250 km away from MGGL, were involved in the analysis to deduce the transfer function between the unsynchronized quasi-surface and underground measurements in the Mátra.</p><p>The set of Q-bursts, which were parallelly detected at all three locations, was identified using GPS synchronized time stamps. Natural origin of the signals was confirmed by identifying the parent lightning strokes in the database of the World Wide Lightning Location Network (WWLLN) via matching the detection times and the corresponding source directions calculated at NCK station.</p><p>The good agreement of the results from independent Matra-NCK (5-30 Hz) and Matra-HYL (5-140 Hz) station-pairwise analyses confirm that the frequency dependence of the wave attenuation due to overlying rocks is exponential. The deduced integrated local conductivity, 30-40 S/m, of the upper section of the Earth’s crust suggests that probably the soil has prominent role in attenuating ground penetrating EM waves in the ELF band.</p>

scholarly journals Remote sensing planetary waves in the midlatitude mesosphere using low frequency transmitter signals

2011 ◽  
Vol 29 (7) ◽  
pp. 1287-1293 ◽  
Author(s):  
E. D. Schmitter
Keyword(s):  
Electron Density ◽  
Planetary Wave ◽  
Low Frequency ◽  
Lower Ionosphere ◽  
Signal Amplitude ◽  
Propagation Path ◽  
Polar Regions ◽  
Radio Waves ◽  
Good Proxy ◽  
Winter Time

Abstract. Very low and low radio frequency (VLF/LF) propagation responds sensitively to the electron density distribution in the lower ionosphere (upper mesosphere). Whereas propagation paths crossing subpolar and polar regions are frequently affected by forcing from above by particle precipitations, mid- and lowlatitude paths let forcing from below be more prominent. Our observations (2009–2011) show, that the low frequency propagation conditions along the midlatitude path from Sicily to Germany (52° N 8° E) using the NSY 45.9 kHz transmitter (37° N 14° E) prove to be a good proxy of mesosphere planetary wave activity along the propagation path. High absorption events with VLF/LF propagation correlate to the well known winter time D-layer anomaly observed with high frequency (HF) radio waves. VLF/LF propagation calculations are presented which show that the radio signal amplitude variations can be modeled by planetary wave modulated collison frequency and electron density profiles. The other way around wave pressure amplitudes can be inferred from the VLF/LF data.

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