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.

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 Data analysis of low frequency transmitter signals received at a midlatitude site with regard to planetary wave activity

2012 ◽  
Vol 10 ◽  
pp. 279-284 ◽  
Author(s):  
E. D. Schmitter
Keyword(s):  
Continuous Monitoring ◽  
Planetary Wave ◽  
Amplitude Ratio ◽  
Low Frequency ◽  
Signal Amplitude ◽  
Wave Activity ◽  
Time Range ◽  
Seasonal Temperature ◽  
Amplitude Data ◽  
Winter Time

Abstract. More than 2 yr of continuously recorded signal amplitude data from the MSK transmitters NRK/TFK (37.5 kHz, Iceland) and NSY (45.9 kHz, Sicily) received at (52° N 8° E) in the time range from August 2009 to September 2011 are analyzed with regard to planetary wave activity. Wavelet analysis of the day/night amplitude ratio reveals clear evidence of quasi 16 day periods mainly during winter time as well as traces of 5 and 10 day periods on both paths. The amplitude ratio is well correlated to the typical stratospheric (10 hPa) seasonal temperature profile – more clearly to be seen on the northern path. The results are in line and an extension of manifold research with regard of ionospheric absorption phenomena caused by atmospheric wave activity. Continuous monitoring of transmitters in the 40 kHz frequency range proved as an inexpensive tool for investigating mesospheric response to forcing from below.

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.

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.

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.

scholarly journals Meteorological effects in the lower ionosphere as based on VLF/LF signal observations

2014 ◽  
Vol 2 (4) ◽  
pp. 2789-2812 ◽  
Author(s):  
A. Rozhnoi ◽  
M. Solovieva ◽  
B. Levin ◽  
M. Hayakawa ◽  
V. Fedun
Keyword(s):  
Gravity Waves ◽  
Atmospheric Pressure ◽  
Low Frequency ◽  
Lower Ionosphere ◽  
Signal Amplitude ◽  
Internal Gravity Waves ◽  
Atmospheric Parameters ◽  
Low Latitudes ◽  
Far Eastern ◽  
Meteorological Effects

Abstract. Very low and low frequency (VLF/LF) data recorded in the Far Eastern stations Petropavlovsk-Kamchatsky (158.92° E, 53.15° N), Yuzhno-Sakhalinsk (142.75° E, 46.95° N) and Yuzhno-Kurilsk (145.861° E, 44.03° N) are investigated to study the meteorological effects in the lower ionosphere. The results demonstrate the sensitivity of the VLF/LF signals to the variations of atmospheric pressure, humidity, wind velocity and temperature, and the VLF/LF record at the station of Yuzhno-Kurilsk is found to be most sensitive to those variations of atmospheric parameters. The region under consideration is characterized by high winter cyclonic activity in midlatitudes and strong summer and autumn typhoon activity in low latitudes. VLF/LF signal variations during 8 tropical cyclones (TCs) with different intensity are considered. Negative nighttime anomalies in the signal amplitude that are most probably caused by TC activity are found for 6 events. Those anomalies are observed during 1–2 days when TCs move inside the sensitivity zones of the subionospheric paths. Perturbations of the VLF signal observed during 2 TCs can be caused by both the TC influence and seismic activity, but no correlation between TC intensity and magnitude of the signal anomalies is found. Spectral analysis of the typhoon-induced disturbed signals revealed the fluctuations with time periods in the range of 7–16 and 15–55 min that corresponds to the range of internal gravity waves periods.

scholarly journals Remote sensing and modeling of energetic electron precipitation into the lower ionosphere using VLF/LF radio waves and field aligned current data

2015 ◽  
Vol 13 ◽  
pp. 233-242
Author(s):  
E. D. Schmitter
Keyword(s):  
Distribution Function ◽  
Energetic Electron ◽  
Lower Ionosphere ◽  
Signal Amplitude ◽  
Reaction Rates ◽  
Current Data ◽  
Electron Precipitation ◽  
Propagation Path ◽  
Satellite Mission ◽  
Field Aligned Current

Abstract. A model for the development of electron density height profiles based on space time distributed ionization sources and reaction rates in the lower ionosphere is described. Special attention is payed to the definition of an auroral oval distribution function for energetic electron energy input into the lower ionosphere based on a Maxwellian energy spectrum. The distribution function is controlled by an activity parameter which is defined proportional to radio signal amplitude disturbances of a VLF/LF transmitter. Adjusting the proportionality constant allows to model precipitation caused VLF/LF signal disturbances using radio wave propagation calculations and to scale the distribution function. Field aligned current (FAC) data from the new Swarm satellite mission are used to constrain the spatial extent of the distribution function. As an example electron precipitation bursts during a moderate substorm on the 12 April 2014 (midnight–dawn) are modeled along the subauroral propagation path from the NFR/TFK transmitter (37.5 kHz, Iceland) to a midlatitude site.

Sunrise effect on 40 kHz signal amplitude and its characteristic variation with respect to geomagnetic storms

2015 ◽  
Vol 93 (12) ◽  
pp. 1574-1582 ◽  
Author(s):  
Apurba Saha ◽  
Anirban Guha ◽  
Barin Kumar De
Keyword(s):  
Geomagnetic Storms ◽  
Low Frequency ◽  
Signal Amplitude ◽  
Type A ◽  
Radio Waves ◽  
Type B ◽  
Type D ◽  
Characteristic Variation ◽  
Sunrise Effect ◽  
Type C

The sunrise effect is a characteristic feature of very low frequency and low frequency radio waves propagated over a large distance. The 40 kHz signal level, transmitted from Miyakoji station (37.4° N, 140.9° E), Japan, and received at Tripura University (23° N, 91.4° E), is found to be attenuated during sunrise with an enhancement before the decrease in the signal level. On the basis of the nature of attenuation of the observed records from 2005 to 2006, those are classified into four different types, namely, type A (three step attenuation), type B (two step attenuation), type C (one step attenuation), and type D (no attenuation). During geomagnetically active days, 84% of type D cases and 31% of type C cases are observed, whereas only 0.9% of type A cases and 7% of type B cases are observed during geomagnetically active days. The fade amplitude of type C fade is also found to maintain a good negative correlation of 77.3% with the geomagnetic Ap indices over the period of 2 years. From the model calculation it is found that in the altitude range from 65 to 80 km, on average the electron density increases by a factor of 5.22 times during geomagnetically active days versus normal days.

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