LOW FREQUENCY WHISTLERS GENERA TED BY INFRASONIC WA YES IN THEIONOSPHERIC E-REGION DURING DISTURBANCES OF DIFFERENT NATURE

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.

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Determine the Physical Mechanism and Source Region of Beat Wave Modulation by Changing the Frequency of HF Waves

Chinese Physics B ◽

10.1088/1674-1056/ac422f ◽

2021 ◽

Author(s):

Zhe Guo ◽

Hanxian Fang ◽

Farideh Honary

Keyword(s):

Physical Mechanism ◽

Source Region ◽

Low Frequency ◽

Signal Amplitude ◽

New Approach ◽

Wave Modulation ◽

F Region ◽

Source Regions ◽

High Modulation ◽

E Region

Abstract This paper introduces a new approach for the determination of the source region of BW (beat wave) modulation. This type of modulation is achieved by transmitting HF continuous waves with a frequency difference of f, where f is the frequency of modulated ELF/VLF (extremely low frequency/very low frequency) waves from two sub-arrays of a high power HF transmitter. Despite the advantages of BW modulation in terms of generating more stable ELF/VLF signal and high modulation efficiency, there exists a controversy on the physical mechanism of BW and its source region. In this paper, the two controversial theories, i.e. BW based on D-E region thermal nonlinearity and BW based on F region ponderomotive nonlinearity are examined for cases where each of these two theories exists exclusively or both of them exist simultaneously. According to the analysis and the simulation results presented in this paper, it is found that the generated VLF signal amplitude exhibits significant variation as a function of HF frequency in different source regions. Therefore, this characteristic can be utilised as a potential new approach to determine the physical mechanism and source location of BW.

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Dispersive changes in magnetic background noise polarization at 0.1 to 6Hz during sunset and sunrise at L=1.3

Annales Geophysicae ◽

10.5194/angeo-22-1989-2004 ◽

2004 ◽

Vol 22 (6) ◽

pp. 1989-2000 ◽

Cited By ~ 6

Author(s):

T. Bösinger ◽

S. L. Shalimov

Keyword(s):

Background Noise ◽

Azimuthal Angle ◽

Low Frequency ◽

Frequency Dispersion ◽

Major Axis ◽

Resonance Structure ◽

Frequency Range ◽

Ionosphere Model ◽

F Region ◽

E Region

Abstract. Polarization properties of the magnetic background noise (MBN) and the spectral resonance structure (SRS) of the ionospheric Alfvén resonator (IAR) below the first Schumann resonance but above 0.1 Hz are measured by a sensitive pulsation magnetometer at the island of Crete (L=1.3) and analyzed using the existing SRS theory by Belyaev et al. (1989b). The focus of the paper is on the systematic changes in the MBN and SRS properties associated with the transition from a sunlit to a dark ionosphere (sunset) and vice versa (sunrise). We are able to pinpoint in observations an E-region and F-region terminator effect and to simulate it by means of a simple ionosphere model, implying the formalism given by Belyaev et al. (1989b). The E-region terminator effect is associated with an apparent control for the SRS presence or absence with no clear frequency dispersion in polarization properties, whereas the F-region terminator effect exhibits strong frequency dispersion, especially in the low frequency range. This yields a change in the ellipticity of MBN, starting as early as 2 to 3h ahead of the "zero-line" of the terminator. In a 24h presentation of the ellipticity versus frequency and time, the sunrise/sunset effect produces a sharp, dispersive boundary between night and day (day and night). Only inside this boundary, during the night hours, is SRS observed, at times accompanied by a large quasi-periodic long period modulation in the azimuthal angle of the major axis of the polarization ellipse. Attention is also paid to peculiarities in the low frequency range (~0.1Hz), where especially large changes in the polarization properties occur in association with the passage of the terminator. The F-region effect is very distinct and well reproduced by our simple model. Changes in the azimuth associated with the E-region terminator effect are of the order of 20&deg.

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A study of seasonal variations of gravity wave intensity in thelower thermosphere using LF D1 wind observations and a numerical model

Annales Geophysicae ◽

10.5194/angeo-22-35-2004 ◽

2004 ◽

Vol 22 (1) ◽

pp. 35-45 ◽

Cited By ~ 9

Author(s):

N. M. Gavrilov ◽

Ch. Jacobi

Keyword(s):

Numerical Model ◽

Drift Velocity ◽

Seasonal Variations ◽

Middle Atmosphere ◽

Low Frequency ◽

Internal Gravity Waves ◽

Short Period ◽

Summer Maximum ◽

E Region ◽

Standard Deviations

Abstract. The data of the regular low-frequency D1 E-region observations at Collm, Germany (52°N, 15°E) in 1983–1999 are used for estimations of the intensity of short-period perturbations of the horizontal drift velocity at 85–110 km altitude. A simple half-hourly-difference numerical filter is used to extract perturbations with time scales of 0.7–3 h. The average monthly standard deviations of short-period perturbations of the zonal velocity near altitude 83 km have a main maximum in summer, a smaller maximum in winter, and minimum values at the equinoxes. At higher altitudes the summer maximum is shifted towards the spring months, and a second maximum of perturbation amplitudes appears in autumn at altitudes near and above 100 km. The seasonal changes in the standard deviations of meridional velocity show the maxima in spring and summer. A numerical model describing the propagation of a set of harmonics modeling a spectrum of internal gravity waves in the atmosphere is used for the interpretation of observed seasonal variations of wind perturbation intensity. Numerical modeling reveals that the observed altitude changes in the seasonal variations of the drift velocity standard deviations may be explained by a superposition of IGWs generated at different levels in the troposphere and middle atmosphere. IGWs generated in the stratospheric and mesospheric jet stream may have substantial amplitudes at altitudes near and above 100 km, where they may modify the seasonal variations, which are typical for IGWs propagating from the troposphere. Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides) – Ionosphere (ionospheric irregularities)

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On the new modes of planetary-scale electromagnetic waves in the ionosphere

Annales Geophysicae ◽

10.5194/angeo-22-1203-2004 ◽

2004 ◽

Vol 22 (4) ◽

pp. 1203-1211 ◽

Cited By ~ 15

Author(s):

G. D. Aburjania ◽

K. Z. Chargazia ◽

G. V. Jandieri ◽

A. G. Khantadze ◽

O. A. Kharshiladze

Keyword(s):

Electromagnetic Waves ◽

Large Scale ◽

Low Frequency ◽

Planetary Scale ◽

Phase Velocities ◽

F Region ◽

E Region ◽

General Dispersion ◽

Fast Waves ◽

The Waves

Abstract. Using an analogy method the frequencies of new modes of the electromagnetic planetary-scale waves (with a wavelength of 103 km or more), having a weather forming nature, are found at different ionospheric altitudes. This method gives the possibility to determine spectra of ionospheric electromagnetic perturbations directly from the dynamic equations without solving the general dispersion equation. It is shown that the permanently acting factor-latitude variation of the geomagnetic field generates fast and slow weakly damping planetary electromagnetic waves in both the E- and F-layers of the ionosphere. The waves propagate eastward and westward along the parallels. The fast waves have phase velocities (1–5)km s–1 and frequencies (10–1–10–4), and the slow waves propagate with velocities of the local winds with frequencies (10–4–10–6)s–1 and are generated in the E-region of the ionosphere. Fast waves having phase velocities (10-1500)km s–1 and frequencies (1–10–3)s–1 are generated in the F-region of the ionosphere. The waves generate the geomagnetic pulsations of the order of one hundred nanoTesla by magnitude. The properties and parameters of the theoretically studied electromagnetic waves agree with those of large-scale ultra-low frequency perturbations observed experimentally in the ionosphere. Key words. Ionosphere (ionospheric disturbances; waves propagation; ionosphere atmosphere interactions)

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Propagation and dispersion of electrostatic waves in the ionospheric E region

Annales Geophysicae ◽

10.1007/s00585-997-0878-4 ◽

1997 ◽

Vol 15 (7) ◽

pp. 878-889 ◽

Cited By ~ 10

Author(s):

K. Iranpour ◽

H. L. Pécseli ◽

J. Trulsen ◽

A. Bahnsen ◽

F. Primdahl ◽

...

Keyword(s):

Hall Current ◽

Low Frequency ◽

Plasma Waves ◽

Electrostatic Waves ◽

Field Fluctuations ◽

E Region ◽

Band Pass ◽

Electrostatic Fluctuations ◽

The Waves ◽

The Rose

Abstract. Low-frequency electrostatic fluctuations in the ionospheric E region were detected by instruments on the ROSE rockets. The phase velocity and dispersion of plasma waves in the ionospheric E region are determined by band-pass filtering and cross-correlating data of the electric-field fluctuations detected by the probes on the ROSE F4 rocket. The results were confirmed by a different method of analysis of the same data. The results show that the waves propagate in the Hall-current direction with a velocity somewhat below the ion sound speed obtained for ionospheric conditions during the flight. It is also found that the waves are dispersive, with the longest wavelengths propagating with the lowest velocity.

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Spectral properties of low-frequency electrostatic waves in the ionospheric E region

Journal of Geophysical Research Atmospheres ◽

10.1029/1999ja900503 ◽

2000 ◽

Vol 105 (A5) ◽

pp. 10585-10601 ◽

Cited By ~ 8

Author(s):

B. Krane ◽

H. L. Pécseli ◽

J. Trulsen ◽

F. Primdahl

Keyword(s):

Spectral Properties ◽

Low Frequency ◽

Electrostatic Waves ◽

E Region

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A discussion on D and E region winds over Europe - The significance and interpretation of ionospheric drift measurements in the low-frequency range

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1972.0017 ◽

1972 ◽

Vol 271 (1217) ◽

pp. 473-484 ◽

Cited By ~ 6

Keyword(s):

Solar Cycle ◽

Seasonal Variations ◽

Democratic Republic ◽

Low Frequency ◽

Frequency Range ◽

Wind Measurements ◽

E Region ◽

Radar Meteor ◽

Ionospheric Drift

Ionospheric drift measurements in the low-frequency range can be shown by comparison with corresponding radar-meteor wind measurements to indicate, in general, very nearly the actual neutral air wind in the 90 to 100 km height region. From m any years of such measurements at two stations in the Germ an Democratic Republic, results have been obtained on both the prevailing and the semidiurnal (tidal) wind components, their seasonal variations, their dependence on the solar cycle and their anomalies during certain major mid-winter stratospheric warmings.

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