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Sample records for vlf ionospheric soundings

  1. Models of ionospheric VLF absorption of powerful ground based transmitters

    Science.gov (United States)

    Cohen, M. B.; Lehtinen, N. G.; Inan, U. S.

    2012-12-01

    Ground based Very Low Frequency (VLF, 3-30 kHz) radio transmitters play a role in precipitation of energetic Van Allen electrons. Initial analyses of the contribution of VLF transmitters to radiation belt losses were based on early models of trans-ionospheric propagation known as the Helliwell absorption curves, but some recent studies have found that the model overestimates (by 20-100 dB) the VLF energy reaching the magnetosphere. It was subsequently suggested that conversion of wave energy into electrostatic modes may be responsible for the error. We utilize a newly available extensive record of VLF transmitter energy reaching the magnetosphere, taken from the DEMETER satellite, and perform a direct comparison with a sophisticated full wave model of trans-ionospheric propagation. Although the model does not include the effect of ionospheric irregularities, it correctly predicts the average total power injected into the magnetosphere within several dB. The results, particularly at nighttime, appear to be robust against the variability of the ionospheric electron density. We conclude that the global effect of irregularity scattering on whistler mode conversion to quasi-electrostatic may be no larger than 6 dB.

  2. VLF emissions from ionospheric/magnetospheric plasma

    Indian Academy of Sciences (India)

    R P Patel; R P Singh

    2001-05-01

    VLF emissions such as hiss, chorus, oscillating tones, hiss-triggered chorus and whistler triggered emissions have been observed at low latitude Indian stations. In this paper we present dynamic spectra of these emissions and discuss their various observed features. It is argued that most of the emissions are generated during Doppler shifted cyclotron resonance interaction between the whistler mode wave and counter streaming energetic electrons. Resonance energy of the participating electron and interaction length are evaluated to explain the generation mechanism of some of these emissions observed at Indian stations.

  3. PRECURSORS OF EARTHQUAKES: VLF SIGNALSIONOSPHERE IONOSPHERE RELATION

    Directory of Open Access Journals (Sweden)

    Mustafa ULAS

    2013-01-01

    Full Text Available lot of people have died because of earthquakes every year. Therefore It is crucial to predict the time of the earthquakes reasonable time before it had happed. This paper presents recent information published in the literature about precursors of earthquakes. The relationships between earthquakes and ionosphere are targeted to guide new researches in order to study further to find novel prediction methods.

  4. Excitation of VLF quasi-electrostatic oscillations in the ionospheric plasma

    Directory of Open Access Journals (Sweden)

    B. Lundin

    Full Text Available A numerical solution of the dispersion equation for electromagnetic waves in a hot magnetized collisionless plasma has shown that, in a current-free ionospheric plasma, the distortion of the electron distribution function reproducing the downward flow of a thermal electron component and the compensating upward flow of the suprathermal electrons, which are responsible for the resulting heat flux, can destabilize quasi-electrostatic ion sound waves. The numerical analysis, performed with ion densities and electron temperature taken from the data recorded by the Interkosmos-24 (IK-24, Aktivny satellite, is compared with a VLF spectrum registered at the same time on board. This spectrum shows a wide frequency band emission below the local ion plasma frequency. The direction of the electron heat flux inherent to the assumed model of VLF emission generation is discussed

  5. VLF observations of ionospheric disturbances in association with TLEs from the EuroSprite-2007 campaign

    DEFF Research Database (Denmark)

    NaitAmor, S.; AlAbdoadaim, M. A.; Cohen, M. B.

    2010-01-01

    Two Very Low Frequency (VLF) AWESOME remote sensing systems located at Algiers, Algeria (36.45°N, 3.28°E) and Sebha, Libya (27.02°N, 14.26°E) monitor VLF signal perturbations for evidence of ionospheric disturbances. During the EuroSprite-2007 campaign a number of Transient Luminous Events (TLEs...

  6. Multi Station Frequency Response and Polarization of ELF/VLF Signals Generated via Ionospheric Modification

    Science.gov (United States)

    Maxworth, Ashanthi; Golkowski, Mark; University of Colorado Denver Team

    2013-10-01

    ELF/VLF wave generation via HF modulated ionospheric heating has been practiced for many years as a unique way to generate waves in the ELF/VLF band (3 Hz - 30 kHz). This paper presents experimental results and associated theoretical modeling from work performed at the High Frequency Active Auroral Research Program (HAARP) facility in Alaska, USA. An experiment was designed to investigate the modulation frequency dependence of the generated ELF/VLF signal amplitudes and polarization at multiple sites at distances of 37 km, 50 km and 99 km from the facility. While no difference is observed for X mode versus O mode modulation of the heating wave, it is found that ELF/VLF amplitude and polarization as a function of modulated ELF/VLF frequency is different for each site. An ionospheric heating code is used to determine the primary current sources leading to the observations.

  7. ELF/VLF wave generation from the beating of two HF ionospheric heating sources

    Science.gov (United States)

    Cohen, M. B.; Moore, R. C.; Golkowski, M.; Lehtinen, N. G.

    2012-12-01

    It is well established that Extremely Low Frequency (ELF, 0.3-3 kHz) and Very Low Frequency (VLF, 3-30 kHz) radio waves can be generated via modulated High Frequency (HF, 3-10 MHz) heating of the lower ionosphere (60-100 km). The ionospheric absorption of HF power modifies the conductivity of the lower ionosphere, which in the presence of natural currents such as the auroral electrojet, creates an `antenna in the sky.' We utilize a theoretical model of the HF to ELF/VLF conversion and the ELF/VLF propagation, and calculate the amplitudes of the generated ELF/VLF waves when two HF heating waves, separated by the ELF/VLF frequency, are transmitted from two adjacent locations. The resulting ELF/VLF radiation pattern exhibits a strong directional dependence (as much as 15 dB) that depends on the physical spacing of the two HF sources. This beat wave source can produce signals 10-20 dB stronger than those generated using amplitude modulation, particularly for frequencies greater than 5-10 kHz. We evaluate recent suggestions that beating two HF waves generates ELF/VLF waves in the F-region (>150 km), and conclude that those experimental results may have misinterpreted, and can be explained strictly by the much more well established D region mechanism.

  8. Ionospheric disturbances in D-layer recorded by VLF receiver at Tashkent IHY station

    Science.gov (United States)

    Ahmedov, Bobomurat

    Tashkent International Heliophysical Year (IHY) station is a member of Atmospheric Weather Electromagnetic System for Observation, Modeling and Education (AWESOME) network being operated globally to study the ionosphere and the magnetosphere with the help of electromagnetic waves in Very Low Frequency (VLF) band. Regular monitoring of the D- and F-layers of ionosphere over Central Asia territory is being performed on the permanent basis starting year 2008. Solar flare events are permanently observed and the analysis showed that there is simultaneous correlation between the times of change of amplitude of the waves and the Solar flares. Features of the lightning discharge generated by radio atmospherics are studied and its effectiveness in D-region ionosphere diagnostics is explained. We have studied VLF amplitude anomalies related to the earthquakes (EQs) occurred in the recent years with magnitude more than 5 on the path way from the VLF transmitters to the Tashkent station assuming that propagation of VLF ground-based transmitters signals can be perturbed by EQ preparation can be detectable from the ground-based measurements in the VLF bands. For analyzing narrowband data we have used the Nighttime Fluctuation (NF) method paying attention to the data obtained during the local nighttime (20:00 LT-04:00 LT). The mean nighttime amplitude (or trend) and nighttime fluctuation are found to increase significantly before the EQ occurred on the path way from the transmitters to the receiver. The obtained results have revealed an agreement with VLF amplitude anomalies observed in Tashkent VLF station during the strong EQs occurred on the path way from the transmitters to the receiver. Some results are presented to show the probing potentiality of VLF waves to predict short term EQs with high magnitude.

  9. Catalogue of x-ray solar flare induced variations in sub-ionospheric very low frequency (VLF) waveguides

    Science.gov (United States)

    Eichelberger, Hans; Schwingenschuh, Konrad; Boudjada, Mohammed Y.; Besser, Bruno P.; Wolbang, Daniel; Rozhnoi, Alexander; Solovieva, Maria; Biagi, Pier F.; Stachel, Manfred; Prattes, Gustav; Aydogar, Özer; Muck, Cosima; Grill, Claudia; Jernej, Irmgard; Stachel, Thomas; Moro, Florian

    2017-04-01

    In this study we present a catalogue of solar flare induced very low frequency (VLF) variations along sub-ionospheric paths between several transmitters and the Graz seismo-electromagnetic UltraMSK receiving station. These measurements of non-seismic disturbances are important in order to carefully characterise the Earth-ionosphere VLF waveguide and disentangle possible earthquake related phenomena from natural and man-made ambient VLF amplitude and phase modifications. The period of investigation is from Jan. 2010 to April 2016, i.e. largely covers the sunspot cycle 24. In total we've 373 VLF amplitude and phase fluctuations related with C/M/X-class solar flare events (the data are from NOAA GOES x-ray flux measurements). We obtain the statistics (dependence on VLF signal vs. x-ray flux variations) for high signal-to-noise ratio VLF links under consideration of the zenith angle. We conclude, that with the mid-latitude Graz VLF knot, a part of the European receiver network, a reliable service for solar flare induced variations of the VLF waveguide can be established. In addition to complementary region-wide network multi-parameter observations this could be a crucial step towards a full characterisation of the behaviour of sub-ionospheric VLF paths including modifications related to seismic activity.

  10. Extended lateral heating of the nighttime ionosphere by ground-based VLF transmitters

    OpenAIRE

    İnan, Umran Savaş; Graf, K. L.; Spasojevic, M.; Marshall, R. A.; Lehtinen, N. G.; Foust, F. R.

    2013-01-01

    JOURNAL OF GEOPHYSICAL RESEARCH: SPACE PHYSICS, VOL. 118, 7783–7797, doi:10.1002/2013JA019337, 2013 Extended lateral heating of the nighttime ionosphere by ground-based VLF transmitters K. L. Graf,1 M. Spasojevic,1 R. A. Marshall,2 N. G. Lehtinen,1 F. R. Foust,1 and U. S. Inan1,3 Received 16 August 2013; revised 9 October 2013; accepted 11 November 2013; published 3 December 2013. [1] The effects of ground-based very low frequency (VLF) transmitters on the lower ionospher...

  11. Modeling of the lower ionospheric response and VLF signal modulation during a total solar eclipse using ionospheric chemistry and LWPC

    Science.gov (United States)

    Chakraborty, Suman; Palit, Sourav; Ray, Suman; Chakrabarti, Sandip K.

    2016-02-01

    The variation in the solar Extreme Ultraviolet (EUV) radiation flux by any measure is the most dominant natural source to produce perturbations or modulations in the ionospheric chemical and plasma properties. A solar eclipse, though a very rare phenomenon, is similarly bound to produce a significant short time effect on the local ionospheric properties. The influence of the ionizing solar flux reduction during a solar eclipse on the lower ionosphere or, more precisely, the D-region, can be studied with the observation of Very Low Frequency (VLF) radio wave signal modulation. The interpretation of such an effect on VLF signals requires a knowledge of the D-region ion chemistry, which is not well studied till date. Dominant parameters which govern the ion chemistry, such as the recombination coefficients, are poorly known. The occurrence of events such as a solar eclipse provides us with an excellent opportunity to investigate the accuracy of our knowledge of the chemical condition in this part of Earth's atmosphere and the properties which control the ionospheric stability under such disturbances. In this paper, using existing knowledge of the lower ionospheric chemical and physical properties we carry out an interpretation of the effects obtained during the total solar eclipse of 22 of July 2009 on the VLF signal. Data obtained from a week long campaign conducted by the Indian Centre for Space Physics (ICSP) over the Indian subcontinent has been used for this purpose. Both positive and negative amplitude changes during the eclipse were observed along various receiver locations. In this paper, data for a propagation path between a Indian Navy VLF transmitter named VTX3 and a pair of receivers in India are used. We start from the observed solar flux during the eclipse and calculate the ionization during the whole time span over most of the influenced region in a range of height. We incorporate a D-region ion-chemistry model to find the equilibrium ion density over

  12. Cluster observations of ELF/VLF signals generated by modulated heating of the lower ionosphere with the HAARP HF transmitter

    OpenAIRE

    Platino, M.; Inan, U.S.; Bell, T. F.; Pickett, J; Kennedy, E J; Trotignon, J. G.; Rauch, J. L.; Canu, P.

    2004-01-01

    It is now well known that amplitude modulated HF transmissions into the ionosphere can be used to generate ELF/VLF signals using the so-called "electrojet antenna". Although most observations of the generated ELF/VLF signals have been made on the ground, several low and high-altitude satellite observations have also been reported (James et al., 1990). One of the important unknowns in the physics of ELF/VLF wave generation by ionospheric heating is the volume of the magnetosphere ill...

  13. Cluster observations of ELF/VLF signals generated by modulated heating of the lower ionosphere with the HAARP HF transmitter

    OpenAIRE

    Platino, M.; U. S. Inan; Bell, T.F.; Pickett, J.; Kennedy, E.J.; J. G. Trotignon; Rauch, J.L.; P. Canu

    2004-01-01

    It is now well known that amplitude modulated HF transmissions into the ionosphere can be used to generate ELF/VLF signals using the so-called "electrojet antenna". Although most observations of the generated ELF/VLF signals have been made on the ground, several low and high-altitude satellite observations have also been reported (James et al., 1990). One of the important unknowns in the physics of ELF/VLF wave generation by ionospheric heating is the volume of the magnetosphere ill...

  14. Study of Ionospheric Perturbations in D-Layer Using Awesome VLF Receiver Data at Tashkent Station

    Science.gov (United States)

    Ahmedov, Bobomurat

    2012-07-01

    One VLF receiver and two SuperSID receivers were provided to Uzbekistan IHY cite by Stanford University and are operating in Tashkent, under the International Heliophysical Year (IHY). The results obtained at Tashkent IHY station are applied to earthquake electromagnetic precursors, lightning, and solar flares and to ionospheric disturbances originating from gamma ray flares of Soft Gamma-Ray Repeaters connected with evolution of strongly magnetized neutron stars believed as magnetars. Regular monitoring of the D-layer of ionosphere over Central Asia territory has been performed on the permanent basis. Few Solar flare events are observed during February in 2010-2011 years and the analysis showed that there is simultaneous correlation between the times of change of amplitude of the waves and the Solar flares. Features of the lightning discharge generated by radio atmospherics are studied and its effectiveness in D-region ionosphere diagnostics is explained. Assuming that earthquakes (EQs) can be preceded by the electromagnetic signals in the VLF bands detectable from ground-based measurements we have studied VLF amplitude anomalies related to the earthquakes occurred in 2009-2010 years with magnitude more than 5 on the path way from the VLF transmitters to the Tashkent station. For analysing narrowband data we have used the Nighttime Fluctuation (NF) method paying attention to the data obtained during the local nighttime (18:00 LT-06:00 LT). The amplitude data are analysed only for the reason that perturbations are identified more clearly in the amplitude data than in phase data. The mean nighttime amplitude (or trend) and normalized trend are found to increase significantly before the EQ with the same tendency as the NF and normalized NF. The obtained results have revealed a fine agreement with VLF amplitude anomalies observed in Tashkent VLF station during the strong earthquakes occurred on the path way from the transmitters to the receiver. Some of the initial

  15. Numerical modelling of VLF radio wave propagation through earth-ionosphere waveguide and its application to sudden ionospheric disturbances

    CERN Document Server

    Pal, Sujay

    2015-01-01

    In this thesis, we theoretically predict the normal characteristics of Very Low Frequency (3~30 kHz) radio wave propagation through Earth-ionosphere waveguide corresponding to normal behavior of the D-region ionosphere. We took the VLF narrow band data from the receivers of Indian Centre for Space Physics (ICSP) to validate our models. Detection of sudden ionospheric disturbances (SIDs) are common to all the measurements. We apply our theoretical models to infer the D-region characteristics and to reproduce the observed VLF signal behavior corresponding to such SIDs. We develop a code based on ray theory to simulate the diurnal behavior of VLF signals over short propagation paths (2000~3000 km). The diurnal variation from this code are comparable to the variation obtained from a more general Long Wave Propagation Capability (LWPC) code which is based on mode theory approach. We simulate the observational results obtained during the Total Solar Eclipse of July 22, 2009 in India. We also report and simulate a h...

  16. Study of Ionospheric Perturbations in D-Layer Using VLF Receiver at Tashkent IHY Station

    Science.gov (United States)

    Ahmedov, Bobomurat

    2016-07-01

    Tashkent International Heliophysical Year (IHY) station is a member of Atmospheric Weather Electromagnetic System for Observation, Modeling and Education (AWESOME) network being operated globally to study the ionosphere and the magnetosphere with the help of electromagnetic waves in Very Low Frequency (VLF) band. Regular monitoring of the D- and F-layers of ionosphere over Central Asia territory is being performed on the permanent basis starting year 2008 when one VLF receiver and two SuperSID receivers were provided to Uzbekistan IHY cite by Stanford University. The results obtained at Tashkent IHY station are applied to earthquake electromagnetic precursors, lightning, and Solar flares and to ionospheric disturbances originating from gamma ray flares of Soft Gamma-Ray Repeaters connected with evolution of strongly magnetized neutron stars believed as magnetars. Regular monitoring of the D-layer of ionosphere over Central Asia territory has been performed on the permanent basis. Several Solar events are observed and the analysis has shown that there is simultaneous correlation between the times of change of amplitude of the waves and the Solar flares. Features of the lightning discharge generated by radio atmospherics are studied and its effectiveness in D-region ionosphere diagnostics is examined.

  17. Statistical study of seismo-ionospheric perturbations around Japan by using VLF/LF transmitters with a focal mechanism

    Science.gov (United States)

    Kawano, Tomoki; Hobara, Yasuhide; Tatsuta, Kenshin

    2016-04-01

    In this paper we perform the statistical analysis to study the response of the lower ionosphere prior to major seismic activities focusing on different earthquake types. The lower ionospheric condition is represented by daily averaged nighttime electric amplitude from various VLF/LF transmitter signals received in Japan by UEC team. Six-year record of ionospheric conditions are used for our data analysis. Over 200 earthquakes occurred around the VLF/LF transmitter - receiver paths during the time period of analysis. They are characterized into three different groups based on the Centroid-Moment-Tensor (CMT) solution such as reverse fault type, normal fault type and stress slip type. The ionospheric anomaly is identified by a large change (2 sigma criteria) in the VLF/LF daily nighttime amplitude. As a result, the highest occurrence rate of ionospheric anomaly is obtained for reverse type fault for both sea and ground earthquakes. The occurrence rate for these earthquakes are statistically significant because they are significantly large in comparison to those calculated from random test. The difference of occurrence rate of the ionospheric perturbations may indicate the coupling efficiency of seismic activity into the overlaying ionosphere originated from the pre-seismic condition of earth's crust. We also perform the trend-based earthquake prediction. Alarm threshold in nighttime VLF amplitude with -3.5 sigma is found to be most effective and significant for the earthquake prediction by using lower ionospheric perturbations.

  18. Active Ionospheric Generation of ELF/VLF Waves.

    Science.gov (United States)

    1985-08-15

    extensions. 2. NONLINEAR INTERACTION OF TWO HF WAVE PACKETS WITH AN ELF WAVE IN THE LOWER IONOSPHERE We assume first that the two interactins hish... matter , besides its intrinsic scientific merit, has a broad spectrum of applications, ransins from ionospheric and magnetospheric probing to low...initial wave envelopes are rectansular and the decay waves have small amplitudes; specifically, we let 1a 2 1/1aL=O.O1, la 3 l=O.0. Because we have in mind

  19. Ionospheric Oblique Incidence Soundings by Satellites

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The oblique incidence sweep-frequency ionospheric sounding technique uses the same principle of operation as the vertical incidence sounder. The primary difference...

  20. Ionosphere-magnetosphere studies using ground based VLF radio propagation technique: an Indian example

    Science.gov (United States)

    Chakravarty, Subhas

    Since IGY period (1957-58), natural and artificially produced Very Low Frequency (VLF) elec-tromagnetic radiations are being recorded at large number of ground stations all over the world and on-board satellites to study various radio wave-thermal/energetic plasma interactive pro-cesses related to earth's ionosphere-plasmasphere-magnetosphere environment. The terrestrial propagation of these VLF radio waves are primarily enabled through the earth ionosphere wave guide (EIWG) mode to long horizontal distances around the globe and ducted along the ge-omagnetic field lines into the conjugate hemisphere through the plasmasphere-magnetosphere regions. The time frequency spectra of the received signals indicate presence of dispersion (wave/group velocities changing with frequency) and various cut-off frequencies based on the width of the EIWG, electron gyro and plasma frequencies etc., providing several types of received signals like whistlers, chorus, tweeks, hiss and hisslers which can be heard on loud-speakers/earphones with distinguishing audio structures. While the VLF technique has been a very effective tool for studying middle and high latitude phenomena, the importance of the similar and anomalous observations over the Indian low latitude stations provide potentially new challenges for their scientific interpretation and modelling. The ducted and non-ducted magnetospheric propagation, pro-longitudinal (PL) mode, low latitude TRIMPI/TLE (Tran-sient Luminous Emissions) or other effects of wave-particle/wave-wave interactions, effects due to ionospheric irregularities and electric fields, full wave solutions to D-region ionisation per-turbations due to solar and stellar energetic X-and γ ray emissions during normal and flaring conditions are a few problems which have been addressed in these low latitude studies over India. Since the conjugate points of Indian stations lie over the Indian oceanic region, the VLF propagation effects would be relatively free from

  1. Cluster observations of ELF/VLF signals generated by modulated heating of the lower ionosphere with the HAARP HF transmitter

    Directory of Open Access Journals (Sweden)

    M. Platino

    2004-07-01

    Full Text Available It is now well known that amplitude modulated HF transmissions into the ionosphere can be used to generate ELF/VLF signals using the so-called "electrojet antenna". Although most observations of the generated ELF/VLF signals have been made on the ground, several low and high-altitude satellite observations have also been reported (James et al., 1990. One of the important unknowns in the physics of ELF/VLF wave generation by ionospheric heating is the volume of the magnetosphere illuminated by the ELF/VLF waves. In an attempt to investigate this question further, ground-satellite conjunction experiments have recently been conducted using the four Cluster satellites and the HF heater of the High-Frequency Active Auroral Research Program (HAARP facility in Gakona, Alaska. Being located on largely closed field lines at L≈4.9, HAARP is currently also being used for ground-to-ground type of ELF/VLF wave-injection experiments, and will be increasingly used for this purpose as it is now being upgraded for higher power operation. In this paper, we describe the HAARP installation and present recent results of the HAARP-Cluster experiments. We give an overview of the detected ELF/VLF signals at Cluster, and a possible explanation of the spectral signature detected, as well as the determination of the location of the point of injection of the HAARP ELF/VLF signals into the magnetosphere using ray tracing.

  2. Solar flare induced D-region ionospheric perturbations evaluated from VLF measurements

    Science.gov (United States)

    Singh, Ashutosh K.; Singh, A. K.; Singh, Rajesh; Singh, R. P.

    2014-03-01

    The results of very low frequency (VLF) wave amplitude measurements carried out at the low latitude station Varanasi (geom. lat. 14∘55'N, long. 154∘E), India during solar flares are presented for the first time. The VLF waves (19.8 kHz) transmitted from the NWC-transmitter, Australia propagated in the Earth-ionosphere waveguide to long distances and were recorded at Varanasi. Data are analyzed and the reflection height H' and the sharpness factor β are evaluated. It is found that the reflection height decreases whereas sharpness factor increases with the increase of solar flare power. The H' is found to be higher and β smaller at low latitudes than the corresponding values at mid and high latitudes. The sunspot numbers were low during the considered period 2011-2012, being the rising phase of solar cycle 24 and as a result cosmic rays may impact the D-region ionosphere. The increased ionization from the flare lowers the effective reflecting height, H', of the D-region roughly in proportion to the logarithm of the X-ray flare intensity from a typical mid-day unperturbed value of about 71-72 km down to about 65 km for an X class flare. The sharpness ( β) of the lower edge of the D-region is also significantly increased by the flare but reaches a clear saturation value of about 0.48 km-1 for flares of magnitude greater than about X1 class.

  3. Lightning and ionospheric remote sensing using VLF/ELF radio atmospherics

    Science.gov (United States)

    Cummer, Steven Andrew

    Lightning discharges radiate the bulk of their electromagnetic energy in the Very Low Frequency (VLF, 3- 30 kHz) and Extremely Low Frequency (ELF, 3-3000 Hz) frequency ranges. This energy, contained in impulse-like signals called radio atmospherics or sferics, is guided for long distances by multiple reflections from the ground and lower ionosphere. These two facts suggest that observed sferic waveforms radiated from lightning contain a great deal of information about both the state of the ionosphere along the propagation path and the dynamics of the current in the lightning return stroke. The aim of this dissertation is to develop and implement the necessary techniques to use sferic observations to determine the characteristics of the ionosphere and lightning. In this work, a quantitative model of sferic propagation is developed, and with it the spectral characteristics of VLF (> 1.5 kHz) sferics are shown to depend primarily on the propagation-path-averaged ionospheric D region electron density profile. Using this propagation model, a parameterized ionosphere is iteratively varied to find the theoretical sferic spectrum that agrees best with an observed sferic spectrum composed of the average of many individual sferic spectra. In most nighttime cases, the quality of the agreement allows the height of an exponentially-varying electron density profile to be inferred with a precision of 0.2 km. Since the general sferic waveform depends on the source current-moment waveform as well as the ionospherically- controlled propagation, the former quantity can be measured for individual discharges from observed sferics. Of particular interest are those lightning discharges associated with mesospheric optical emissions known as sprites. By using a robust deconvolution technique, source current-moment waveforms are extracted from individual observed ELF (< 1.5 kHz) sferics. The cases studied in detail show that optical emissions are sometimes produced with a smaller vertical

  4. Cone structure and focusing of VLF and LF electromagnetic waves at high altitudes in the ionosphere

    Science.gov (United States)

    Alpert, Ya. L.; Green, J. L.

    1994-01-01

    The frequency and angle dependencies of the electric field radiated by an electric dipole E = E(sub 0) cos omega(t) are studied through numerical calculations of absolute value of E in the VLF and LF frequency bands where F is less than or equal 0.02 to 0.05 f(sub b) in a model ionosphere over an altitude region of 800-6000 km where the wave frequency and electron gyrofrequency varies between F approximately 4-500 kHz and f(sub b) is approximately equal (1.1 to 0.2) MHz respectively. It is found that the amplitudes of the electric field have large maxima in four regions: close to the direction of the Earth magnetic field line B(sub 0) (it is called the axis field E(sub 0), in the Storey E(sub St), reversed Storey E(sub RevSt), and resonance E(sub Res) cones. The maximal values of E(sub 0), E(sub Res), and E(sub RevSt) are the most pronounced close to the lower hybrid frequency, F approximately F(sub L). The flux of the electric field is concentrated in very narrow regions, with the apex angles of the cones Delta-B is approximately (0.1-1) deg. The enhancement and focusing of the electric field increases with altitude starting at Z greater than 800 km. At Z greater than or equal to 1000 up to 6000 km, the relative value of absolute value of E, in comparison with its value at Z = 800 km is about (10(exp 2) to 10(exp 4)) times larger. Thus the flux of VLF and LF electromagnetic waves generated at high altitudes in the Earth's ionosphere are trapped into very narrow conical beams similar to laser beams.

  5. Cone structure and focusing of VLF and LF electromagnetic waves at high altitudes in the ionosphere

    Science.gov (United States)

    Alpert, Ya. L.; Green, J. L.

    1994-01-01

    The frequency and angle dependencies of the electric field radiated by an electric dipole E = E(sub 0) cos omega(t) are studied through numerical calculations of absolute value of E in the VLF and LF frequency bands where F is less than or equal 0.02 to 0.05 f(sub b) in a model ionosphere over an altitude region of 800-6000 km where the wave frequency and electron gyrofrequency varies between F approximately 4-500 kHz and f(sub b) is approximately equal (1.1 to 0.2) MHz respectively. It is found that the amplitudes of the electric field have large maxima in four regions: close to the direction of the Earth magnetic field line B(sub 0) (it is called the axis field E(sub 0), in the Storey E(sub St), reversed Storey E(sub RevSt), and resonance E(sub Res) cones. The maximal values of E(sub 0), E(sub Res), and E(sub RevSt) are the most pronounced close to the lower hybrid frequency, F approximately F(sub L). The flux of the electric field is concentrated in very narrow regions, with the apex angles of the cones Delta-B is approximately (0.1-1) deg. The enhancement and focusing of the electric field increases with altitude starting at Z greater than 800 km. At Z greater than or equal to 1000 up to 6000 km, the relative value of absolute value of E, in comparison with its value at Z = 800 km is about (10(exp 2) to 10(exp 4)) times larger. Thus the flux of VLF and LF electromagnetic waves generated at high altitudes in the Earth's ionosphere are trapped into very narrow conical beams similar to laser beams.

  6. Deconvolving the lightning sferic VLF source waveform from its temporally-superposed ionospheric reflections

    Science.gov (United States)

    Jacobson, A. R.; Holzworth, R. H.; Shao, X.

    2010-12-01

    Powerful sferic signals can be used for ionospheric sounding. We have recently applied sferics from Narrow Bipolar Events (NBEs) to studying the ionospheric D-regions’ electron-density profile. The NBE sferic’s narrow temporal support allows the ionospheric reflection signal to be easily separated from the source sferic waveform, at least for ranges up to several-hundred km. Both NBEs and cloud-to-ground (CG) sferics are sufficiently powerful for practical use in ionospheric sounding of this sort. Unfortunately, the incidence of NBEs is small compared to CGs (perhaps on the order of 1:100). The Duke University group has benefited from use of CG sferics in D-region monitoring. The Duke approach does not require separation of the “source” waveform from the ionospheric reflections. By contrast, our approach relies on separating these two signal components. CG sferics observed at ranges up to several-hundred km present their own challenge. The CG source waveform is quite long compared to NBEs. Thus much of the CG source waveform is confounded by partial temporal overlap of signals reflected from the ionospheric D-region. This is especially true at night, when D-region attenuation is minimal, causing the strongest reflection amplitudes. How then can we separate the source waveform from the confounding ionospheric reflections? We will present a formal solution to this problem, based on using simultaneous sferic recordings at two or more sensor stations. The approach will be illustrated with CG recordings from multiple stations of the Los Alamos Sferic Array. Potentially the method will allow copious CG recordings to be exploited for D-region sounding as well as for gaining better “ground truth” on the CG source function.

  7. Statistical correlation of spectral broadening in VLF transmitter signal and low-frequency ionospheric turbulence from observation on DEMETER satellite

    Directory of Open Access Journals (Sweden)

    A. Rozhnoi

    2008-10-01

    Full Text Available In our earlier papers we have found the effect of VLF transmitter signal depression over epicenters of the large earthquakes from observation on the French DEMETER satellite that can be considered as new method of global diagnostics of seismic influence on the ionosphere. At present paper we investigate a possibility VLF signal-ionospheric turbulence interaction using additional characteristic of VLF signal-spectrum broadening. This characteristic is important for estimation of the interaction type: linear or nonlinear scattering. Our main results are the following:
    – There are two zones of increased spectrum broadening, which are centered near magnetic latitudes Φ=±10° and Φ=±40°. Basing on the previous case study research and ground ionosonde registrations, probably it is evidence of nonlinear (active scattering of VLF signal on the ionospheric turbulence. However occurrence rate of spectrum broadening in the middle-latitude area is higher than in the near-equatorial zone (~15–20% in comparison with ~100% in former area that is probably coincides with the rate of ionospheric turbulence.
    – From two years statistics of observation in the selected 3 low-latitude regions and 1 middle-latitude region inside reception area of VLF signal from NWC transmitter we find a correlation of spectrum broadening neither with ion-cyclotron noise (f=150–500 Hz, which possibly means poor representation of the turbulence by the noise due to its mixture with natural ELF emission (which correlates with whistler, nor with magnetic storm activity.
    – We find rather evident correlation of ion-cyclotron frequency noise, VLF signal depression and weak correlation of spectrum broadening with seismicity in the middle-latitude region over Japan. But in the low-latitude regions we do not find such a correlation. Statistical decrease of VLF signal supports our previous case study results. However rather weak spectrum broadening

  8. ELF/VLF Perturbations Above the Haarp Transmitter Recorded by the Demeter Satellite in the Upper Ionosphere

    Science.gov (United States)

    Titova, E. E.; Demekhov, A. G.; Mochalov, A. A.; Gvozdevsky, B. B.; Mogilevsky, M. M.; Parrot, M.

    2015-08-01

    In the studies of the data received from DEMETER (orbit altitude above the Earth is about 700 km), we detected for the first time electromagnetic perturbations, which are due to the ionospheric modification by HAARP, a high-power high-frequency transmitter, simultaneously in the extremely low-frequency (ELF, below 1200 Hz) and very low-frequency (VLF, below 20 kHz) ranges. Of the thirteen analyzed flybys of the satellite above the heated area, the ELF/VLF signals were detected in three cases in the daytime (LT = 11-12 h), when the minimum distance between the geomagnetic projections of the satellite and the heated area center on the Earth's surface did not exceed 31 km. During the nighttime flybys, the ELF/VLF perturbations were not detected. The size of the perturbed region was about 100 km. The amplitude, spectrum, and polarization of the ELF perturbations were analyzed, and their comparison with the characteristics of natural ELF noise above the HAARP transmitter was performed. In particular, it was shown that in the daytime the ELF perturbation amplitude above the heated area can exceed by a factor of 3 to 8 the amplitude of natural ELF noise. The absence of the nighttime records of artificial ELF/VLF perturbations above the heated area can be due to both the lower frequency of the heating signal, at which the heating occurs in the lower ionosphere, and the higher level of natural noise. The spectrum of the VLF signals related to the HAARP transmitter operation had two peaks at frequencies of 8 to 10 kHz and 15 to 18 kHz, which are close to the first and second harmonics of the lower-hybrid resonance in the heated area. The effect of the whistler wave propagation near the lower-hybrid resonance region on the perturbation spectrum recorded in the upper ionosphere for these signals has been demonstrated. In particular, some of the spectrum features can be explained by assuming that the VLF signals propagate in quasiresonance, rather than quasilongitudinal, regime

  9. Atmospheric effects assessment program: Ionospheric sounding

    Science.gov (United States)

    Sprague, R. A.

    1994-02-01

    This document reports efforts on two main goals: to study the short-term ionospheric variability and to study the effects of this variability on high frequency (HF) skywave field strength. To achieve the first goal, ionospheric soundings are being done at 5-minute intervals at San Diego, CA, and at Logan, UT. This time interval was chosen to adequately resolve variations produced by locally generated gravity waves. To study the effects of short-term ionospheric variability on high frequency communications, a circuit is being established to measure the variability of the received HF signal strength. The chosen circuit will have the transmitter located in Forsyth, MT, and the receiver in Imperial Beach, CA (approximately 20 miles south of NRaD).

  10. VLF Remote -Sensing of the Lower Ionosphere with AWESOME Receivers: Solar Flares, Lightning-induced Electron Precipitation, Sudden Ionospheric Disturbances, Sprites, Gravity Waves and Gamma-ray Flares

    Science.gov (United States)

    Inan, U. S.; Cohen, M.; Scherrer, P.; Scherrer, D.

    2006-11-01

    Stanford University Very Low Frequency (VLF) radio receivers have been used extensively for remote sensing of the ionosphere and the magnetosphere. Among the phenomena that can be uniquely measured via VLF receivers are radio atmospherics, whistlers, electron precipitation, solar flares, sudden ionospheric disturbances, gravity waves, sprites, and cosmic gamma-ray flares. With the use of simple square air-core magnetic loop antennas of a couple of meters in size, the sensitivity of these instruments allows the measurement of magnetic fields as low as several tens of femtoTesla per root Hz, in the frequency range of ~300 Hz to 50 kHz. This sensitivity well exceeds that required to detect any event above the ambient atmospheric noise floor, determined by the totality of lightning activity on this planet. In recent years, as cost of production, timing accuracy (due to low cost GPS cards), and data handling flexibility of the systems has improved, it has become possible to distribute many of these instruments in the form of arrays, to perform interferometric and holographic imaging of the lower ionosphere. These goals can be achieved using the newest version of the Stanford VLF receiver, known as AWESOME: Atmospheric Weather Educational System for Observation and Modeling of Electromagnetics. In the context of the IHY/UNBSS program for 2007, the AWESOME receivers can be used extensively as part of the United Nations initiative to place scientific instruments in developing countries. Drawing on the Stanford experiences from setting up arrays of VLF receivers, including an interferometer in Alaska, the Holographic Array for Ionospheric and Lightning research (HAIL) consisting of instruments at 13 different high schools in mid-western United States, a broader set of ELF/VLF receivers in Alaska, and various receivers abroad, including in France, Japan, Greece, Turkey, and India, a global network of ELF/VLF receivers offer possibilities for a wide range of scientific topics

  11. A Probe of magnetosphere-ionosphere coupling using Very Low Frequency (VLF) Radio Signal from North-West Cape (Australia) to Kolkata (India)

    Science.gov (United States)

    Nwankwo, Victor U. J.; Chakrabarti, Sandip Kumar

    Very low frequency (VLF) radio waves has been employed for the detection and study of various terrestrial and extra-terrestrial high energy phenomena such as solar flares, solar eclipse, gamma ray burst, lightning induced electron precipitation etc., and the subsequent variations in the lower ionosphere driven by these events. In this study, we exploit the propagation characteristics of VLF signal through the Earth-ionosphere waveguide, to probe changes in ionospheric signatures, induced by solar driven variations in magnetospheric conditions. Our study is based on the VLF signal (amplitude and phase) received at the Ionospheric and Earthquake Research Centre (IERC), Sitapur, under Indian Centre for Space Physics (ICSP), which is transmitted by the Australian NWC station at about 19.8kHz.

  12. VLF Remote Sensing of the Lower Ionosphere: Solar Flares, Electron Precipitation, Sudden Ionospheric Disturbances, Sprites, Gravity Waves and Gamma-ray Flares

    Science.gov (United States)

    Tan, J. H.; Cohen, M.; Inan, U. S.; Scherrer, P. H.; Scherrer, D.

    2005-12-01

    Stanford University Very Low Frequency (VLF) and Extremely Low Frequency (ELF) radio receivers have been used extensively for remote sensing of the ionosphere and the magnetosphere. Among the phenomena that can be uniquely measured via ELF/VLF receivers are radio atmospherics, whistlers, electron precipitation, solar flares, sudden ionospheric disturbances, gravity waves, sprites, and cosmic gamma-ray flares. With the use of simple square air-core magnetic loop antennas of a couple of meters in size, the sensitivity of these instruments allows the measurement of magnetic fields as low as several tens of femtoTesla per root-Hz, in the frequency range of ~30 Hz to 50 kHz. This sensitivity well exceeds that required to detect any event above the ambient atmospheric noise floor, determined by the totality of lightning activity on the planet. In recent years, as cost of production, timing accuracy (due to low cost GPS clocks), and data handling flexibility of the systems has improved, it has become possible to distribute many of these instruments in the form of arrays, to perform interferometric and holographic imaging of the lower ionosphere. In the context of the IHY in 2007, the ELF/VLF receiver can used extensively as part of the United Nations initiative to place scientific instruments in developing countries. Stanford University's past experiences setting up arrays of ELF/VLF receivers include an interferometer in Alaska, the Holographic Array for Ionospheric and Lightning research (HAIL) consisting of instruments at 13 different high schools in mid-western United States, a broader set of ELF/VLF receivers in Alaska, and various receivers abroad, including in France, Japan, Greece, Turkey, Ireland, and India. A global network of ELF/VLF receivers offer possibilities for a wide range of scientific topics, as well as serving as a means for educational outreach. These goals will be achieved using the newest version of the Stanford VLF receiver, known as AWESOME

  13. Multiple-Station Observation of Frequency Dependence and Polarization Characteristics of ELF/VLF waves generated via Ionospheric Modification

    Science.gov (United States)

    Maxworth, A. S.; Golkowski, M.; Cohen, M.; Moore, R. C.

    2014-12-01

    Generation of Extremely Low Frequency (ELF) and Very Low Frequency (VLF) signals through ionospheric modification has been practiced for many years. Heating the lower ionosphere with high power HF waves allows for modulation of natural current systems. Our experiments were carried out at the High Frequency Active Auroral Research Program (HAARP) facility in Alaska, USA. In this experiment, the ionosphere was heated with a vertical amplitude modulating signal and the modulation frequency was changed sequentially within an array of 40 frequencies followed by a frequency ramp. The observed magnetic field amplitude and polarization of the generated ELF/VLF signals were analyzed for multiple sites and as a function of modulation frequency. Our three observation sites: Chistochina, Paxson and Paradise are located within 36km (azimuth 47.7°), 50.2km (azimuth -20°) and 99km (azimuth 80.3°) respectively. We show that the peak amplitudes observed as a function of frequency result from vertical resonance in the Earth-ionosphere waveguide and can be used to diagnose the D-region profile. Polarization analysis showed that out of the three sites Paxson shows the highest circularity in the magnetic field polarization, compared to Chistochina and Paradise which show highly linear polarizations. The experimental results were compared with a theoretical simulation model results and it was clear that in both cases, the modulated Hall current dominates the observed signals at Chistochina and Paradise sites and at Paxson there is an equal contribution from Hall and Pedersen currents. The Chistochina site shows the highest magnetic field amplitudes in both experimental and simulation environments. Depending upon the experimental and simulation observations at the three sites, a radiation pattern for the HAARP ionospheric heater can be mapped

  14. Electromagnetic Wave-filled Cavities Observed by the GEODESIC Sounding Rocket: A Direct Encounter with VLF Saucer Source Regions

    Science.gov (United States)

    Kabirzadeh, Rasoul

    The GEODESIC sounding rocket encountered hundreds of localized, VLF-wave-filled density depletions in an auroral return current region at altitudes between 900--1000 km. While these are similar to well-studied lower-hybrid "spikelets", which are electrostatic, many of the GEODESIC events exhibited strong VLF magnetic field enhancements as well. In the present study we show that these magnetic field fluctuations can be interpreted as the result of geomagnetic field-aligned electron currents driven by fluctuating electric fields parallel to the geomagnetic field lines. This observation suggests that the electromagnetic wave-filled cavities are signatures of unstable filaments of return current fluctuating at VLF frequencies. We argue that the cavities' spatial dimensions, their location inside the return current region and their total radiated power are consistent with the properties of VLF saucer source regions inferred from earlier satellite observations taken at higher altitudes.

  15. Horizontal Ionospheric Electron Density Gradients Observed by FORMOSAT-3/COSMIC TIP: Spatial Distributions and Effects on VLF Wave Propagation at Mid-Latitudes

    Directory of Open Access Journals (Sweden)

    Damien H. Chua

    2009-01-01

    Full Text Available We investigate the spatial variability of electron densities in the nightside ionosphere and its effects on very-low frequency (VLF wave propagation using a suite of instruments from the FORMOSAT-3/Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC spacecraft.We use observations from the Tiny Ionospheric Photometer (TIP instruments to infer the horizontal electron density gradients along each satellite track. We demonstrate that the OI 1356 _ radiance measured by the TIP instruments tracks the horizontal electron density structure well with high spatial resolution and unprecedented sensitivity. Accurate measurements of the horizontal electron density gradients are important for improving retrieved electron density profiles from GPS occultation and other tomographic remote sensing techniques. The processes underlying the variability in the large-scale, nightside electron density gradients are the main drivers of ionospheric weather. TIP observations reveal significant variability in both the small and large scale structure of the nightside ionosphere. The relative intensities, relative widths, and latitudinal separation of the northern and southern ionization crests of the Appleton anomalies show a high degree of longitudinal variation.We demonstrate how the TIP observations can be used to measure the horizontal gradient of the refractive index of whistler-mode VLF waves propagating in a cold, collisionless plasma. These measurements are critical for understanding how gradients in electron density associated with ionospheric structure such as depletions and the Appleton anomalies affect VLF wave propagation through the equatorial and mid-latitude ionosphere.

  16. Ionospheric perturbations in possible association with the 2010 Haiti earthquake, as based on medium-distance subionospheric VLF propagation data

    Directory of Open Access Journals (Sweden)

    M. Hayakawa

    2011-02-01

    Full Text Available Ionospheric perturbations in possible association with the 2010 Haiti earthquake occurred on 12 January 2010 (with a magnitude of 7.0 and depth of 10 km are investigated on the basis of subionospheric propagation data from the NAA transmitter on the east coast of the USA to a VLF receiving station in Peru. The local nighttime VLF amplitude data are extensively investigated during the period from the beginning of October 2009 to the end of March 2010, in which the trend (nighttime average amplitude, dispersion and nighttime fluctuation are analysed. It is found that a clear precursory ionosphere perturbation is detected just around New Years day of 2010, about 12 days before the main shock, which is characterised by the simultaneous decrease in the trend and the increases in dispersion and nighttime fluctuation. An additional finding might be the presence of the effect of the Earth's tide one and two months before the main shock, which can only be seen for a huge EQ.

  17. Modeling of very low frequency (VLF radio wave signal profile due to solar flares using the GEANT4 Monte Carlo simulation coupled with ionospheric chemistry

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    S. Palit

    2013-09-01

    Full Text Available X-ray photons emitted during solar flares cause ionization in the lower ionosphere (~60 to 100 km in excess of what is expected to occur due to a quiet sun. Very low frequency (VLF radio wave signals reflected from the D-region of the ionosphere are affected by this excess ionization. In this paper, we reproduce the deviation in VLF signal strength during solar flares by numerical modeling. We use GEANT4 Monte Carlo simulation code to compute the rate of ionization due to a M-class flare and a X-class flare. The output of the simulation is then used in a simplified ionospheric chemistry model to calculate the time variation of electron density at different altitudes in the D-region of the ionosphere. The resulting electron density variation profile is then self-consistently used in the LWPC code to obtain the time variation of the change in VLF signal. We did the modeling of the VLF signal along the NWC (Australia to IERC/ICSP (India propagation path and compared the results with observations. The agreement is found to be very satisfactory.

  18. Investigations of natural and artificial disturbances in the Earth-ionosphere cavity via VLF radio links for the time span 2009-2015 (sunspot cycle 24)

    Science.gov (United States)

    Eichelberger, Hans; Schwingenschuh, Konrad; Besser, B. P.; Prattes, Gustav; Aydogar; Wolbang, Daniel; Rozhnoi, Alexander; Solovieva, Maria; Biagi, Pier Francesco; Boudjada, Mohammed

    2016-07-01

    We focus on natural disturbances of the sub-ionospheric VLF waveguide in the time span 2009 to 2015 (sunspot cycle 24), i.e. variations in amplitude and phase measurements of the radio paths are considered. In particular we're investigating numerous solar flares (up to X-class), geomagnetic storms and substorms, therefore discuss how to discriminate natural from artificial variations between different transmitters and receivers. Meteorological effects could be important [1] and we estimate the possibility to detect the influence of lithospheric sources in the VLF radio links. As part of the VLF multistation network we're using the single receiver mid-latitude station in Graz, Austria. This facility receives up to 12 transmitter simultaneously (frequency range 10-50 kHz), has 20 sec temporal resolution, and is running continuously since 2009 [2]. We obtain the statistics relating VLF amplitude and phase fluctuations with C/M/X-class solar flares, and characterise night time fluctuations in connection with enhanced particle precipitation in the northern latitude path (Iceland transmitter). The statistics is important to improve the quality of seismo-electromagnetic studies. We conclude that for ionospheric perturbations (D-layer), e.g. solar flares, a reliable real time monitoring service can be established. Atmospheric and lithospheric variations are generally difficult to characterise, it's harder to distinguish between natural and man made signals, therefore - as a future outlook - complementary ground and satellite based measurements can deliver valuable additional information for environmental monitoring. References: [1] A. Rozhnoi et al.: Meteorological effects in the lower ionosphere as based on VLF/LF signal observations, Nat. Hazards Earth Syst. Sci., 14, 2671-2679, 2014. [2] K. Schwingenschuh et al.: The Graz seismo-electromagnetic VLF facility, Nat. Hazards Earth Syst. Sci., 11, 1121-1127, 2011.

  19. Excitation of earth-ionosphere waveguide in the ELF and lower VLF bands by modulated ionospheric current. Technical report

    Energy Technology Data Exchange (ETDEWEB)

    Field, E.C.; Bloom, R.M.

    1993-05-21

    In this report the authors use the principal of reciprocity in conjunction with a full-wave propagation code to calculate ground-level fields excited by ionospheric currents modulated at frequencies between 50 and 100 Hz with HF heaters. Their results show the dependence on source orientation, altitude, and dimension and therefore pertain to experiments using the HIPAS or HAARP ionospheric heaters. In the end-fire mode, the waveguide excitation efficiency of an ELF HED in the ionosphere is up to 20 dB greater than for a ground-based antenna, provided its altitude does not exceed 80-to-90 km. The highest efficiency occurs for a source altitude of around 70 km; if that altitude is raised to 100 km, the efficiency drops by about 20 dB in the day and 10 dB at night. That efficiency does not account for the greater conductivity modulation that might be achieved at altitudes greater than 70 km, however. The trade-off between the altitude dependencies of the excitation efficiency and maximum achievable modulation depends on the ERP of the HF heater, the optimum altitude increasing with increasing ERP. For HIPAS the best modulation altitude is around 70 km, whereas for HAARP there might be marginal value in modulating at attitudes as high as 100 Km. Ionospheric modification, Ionospheric currents, Ionospheric heating.

  20. Ionospheric perturbations related to the earthquake in Vrancea area on November 22, 2014, as detected by electromagnetic VLF/LF frequency signals

    Directory of Open Access Journals (Sweden)

    Maria Solovieva

    2015-11-01

    Full Text Available Data from the European network of very low/ low frequency (VLF/LF receivers has been used to study the response of the lower ionosphere to the earthquake of magnitude 5.5 in Vrancea area on November 22, 2014. Negative amplitude anomalies have been observed during 3 days before the earthquake and two days after, on the LF (45.9 kHz signal passed above the seismic area. No perturbations have been found for the same signal in control paths during this period. Other possible influences both from above and below which can produce perturbations in the ionosphere have been taken into consideration.

  1. The combined study of the middle atmosphere meteorological parameters and lower ionosphere dynamics over Europe by means of remote VLF-LF measurements

    Science.gov (United States)

    Zetzer, J. I.; Lyakhov, A.; Yakymenko, K.

    2012-12-01

    The results of comprehensive analysis of long-term records of VLF-LF European transmitters by means of Mikhnevo geophysical observatory (Institute of Geospheres Dynamics), SID station A118 (France) and a number of AWESOM receivers are presented. In the previous study (A.A.Egoshin et al., Izvestiya, Physics of the Solid Earth, 2012, Vol. 48, No. 3, pp. 275-286) the results obtained under the minimum solar activity were presented that have shown the link between the lower ionosphere parameters and meteorological fields of the middle atmosphere. The current study expands the evidence to the increased solar activity level as well as the number of receivers, thus allowing more dense coverage of the Europe by the radio paths. Middle atmosphere data under study were provided by the EOS Aura Microwave Limb Sounder. These asynoptic data, in turn, were processed by the space-time spectral analysis on various pressure levels for various window lengths. The results are presented for the spatial structure of wave-like perturbations in the VLF-LF signal strength, which result from the lower ionosphere disturbances on various radio paths. Special short-windowed space-time study was evaluated for the periods of anomalous temporal behavior of the VLF-LF signals and the results of the altitude-latitude mode structures of the geopotential height, neutral temperature, water and ozone constituents are presented. It is shown that the spatial properties of the lower ionosphere can vary significantly at relatively small scale. Moreover, the altitude-latitude mode structures do not coincide in space as well as in time, thus, complicating the lower ionosphere response to the meteorological variations of the middle atmosphere. The analysis of all assembled data proves two main points. At first, it is possible to evaluate synoptic long-term monitoring of the middle atmosphere via the lower ionosphere perturbations as seen by VLF-LF receivers. At second, the theoretical models of the lower

  2. Description of ionospheric disturbances observed by Vertical Ionospheric Sounding at 3 MHz

    Directory of Open Access Journals (Sweden)

    James Arokiasami Baskaradas

    2014-03-01

    Full Text Available High Frequency radio waves reflected by the ionosphere can provide a relevant amount of information within the composite received signal. The ionosphere is indeed a frequency dispersive, bi-refractive, absorbing medium, in which multipath propagation occurs due to disturbance on a varied time-spatial scale. On the time-spatial level of Small Scale Disturbances (SSD the ionosphere dynamics, detectable by Vertical Ionospheric Sounding (VIS, is mainly dependent on wrinkled layers acting as multi-reflectors. The present paper discusses different aspects of the effects of multipath fading suffered by the wave along the propagation path and potentially associated with SSD. To achieve these objectives, a VIS campaign at a fixed frequency of 3.0 MHz was conducted at the ionospheric observatory in Rome (Latitude 41.8 N; Longitude 12.5 E, by collecting a series of measurements of the power variations in received echo signals recorded between two consecutive ionograms whose sounding repetition rate was set to 15 min. The obtained results show that: 1 the fading suffered by the wave follows either a Rayleigh trend or a Nakagami-Rice trend, or a mix of them, the mixed case being the most frequent (about 65 % of the analysed cases; 2 the predominant periodicities characterizing the power variation are less than 25 s; such values are compatible with the small scale ionospheric disturbances; 3 for all the 24 hours of the day the ionospheric reflector is pretty stable and for time intervals of 10-30 s the periods of stability occur with a percentage of occurrence ranging between 55% and 95 %; for time intervals of 190- 210 s the periods of stability occur instead with a percentage of occurrence ranging between 5% and 54 %.

  3. Further study on the role of atmospheric gravity waves on the seismo-ionospheric perturbations as detected by subionospheric VLF/LF propagation

    Directory of Open Access Journals (Sweden)

    F. Muto

    2009-07-01

    Full Text Available As the target earthquake we have taken a huge earthquake (EQ named Miyagi-oki earthquake on 16 August 2005 (with magnitude of 7.2 and we have analyzed the 4 month period including the date of this EQ. In addition to our previous analysis on the nighttime average amplitude (trend and nighttime fluctuation, we have proposed the use of fluctuation power spectra in the frequency rage of atmospheric gravity waves (period=10 min to 100 min as a third parameter of subionospheric VLF/LF propagation characteristics. Then it is found that this third parameter would be of additional importance in confirming the presence of seismo-ionospheric perturbations. Finally, we have discovered an important role of lunar tidal effect in the VLF/LF data, which appears one and two months before this large EQ.

  4. Ranking of Sudden Ionospheric Disturbances by Means of the Duration of Vlf Perturbed Signal in Agreement with Satellite X-Ray Flux Classification

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    Ammar Ahmed

    2016-12-01

    Full Text Available Ionosphere undergoes permanently solar flares that quickly change its properties inducing sometime unwanted effects. These changes, or events, are known as Sudden Ionospheric Disturbances (SIDs and the knowledge of their magnitude may be of great interest to anticipate probable damages. Currently, there does not exist any classification of these ionospheric changes based on their amplitude due to the wide variability of its responses. The only way to surmise their importance is to study them indirectly, throughout the classification of the X-ray flux intensity recorded by satellites. An attempt of classification based on their duration was proposed by the American Association of Variable Star Observers (AAVSO but it is not very accurate because SID’s duration is measured directly from the raw signal of the Very Low Frequency (VLF signal and/or the Low Frequency (LF signal. The aim of this work is to investigate, through a set of simple mathematical techniques applied to VLF/LF signals recorded by ground based receivers, the best method to estimate SIDs durations and then propose a new classification based on these durations.

  5. A multiple-mode three-dimensional model of VLF propagation in the earth-ionosphere waveguide in the presence of localized D region disturbances

    Science.gov (United States)

    Poulsen, William L.; Inan, Umran S.; Bell, Timothy F.

    1993-01-01

    Transient localized D region disturbances, such as those associated with lightning discharges, affect the characteristics of VLF waves propagating in the Earth-ionosphere waveguide. In particular, both phase and amplitude changes in the subionospheric signal can be observed at receiving sites as a result of the wave scattering that takes place in the disturbed region. In the present paper we present a multiple-mode three-dimensional model of VLF propagation in the Earth-ionosphere waveguide in the presence of localized D region disturbances. The model takes into account great circle (GC) propagation paths with realistic ground and ionospheric conductivity changes that result in mode conversion along the path. It is assumed that conductivity changes transverse to the GC paths are negligible except in the vicinity of the D region disturbance and that mode coupling is negligible within the disturbed region. This new model is applied to experimental observations and is found to be in general agreement. The diagnostics potential of the model for characterizing energetic particle precipitation events is discussed.

  6. Response of low latitude D-region ionosphere to the Total Solar Eclipse of 22 July 2009, deduced from ELF/VLF analysis

    Science.gov (United States)

    Singh, A. K.; Singh, R.; Singh, A. K.

    2011-12-01

    Response of the D-region of the ionosphere to the total solar eclipse of 22 July 2009 at low latitude, Varanasi (geomagnetic lat = 140 55'N, longitude = 1540 E, dip. angle = 37.30) was investigated using ELF/VLF radio signal. The solar eclipse started at 05:30:04.4 hrs IST and lasted up to 07:27 hrs IST with totally from 6.25 IST to 6.27 IST.The changes in D-region ionospheric VLF reflection heights and electron density during eclipse have been estimated from tweek analysis. The reflection height increased from ~90 km from the first occurrence of tweek to about 93-94 km at the totality and then decreased to ~89 km at the end of the eclipse. The reflection heights are lower by 2-3 km as compared to the usual nighttime tweek reflection heights. The electron density is found to vary between 25-27 cm-3 at the reflection heights. The significant increase in tweek reflection height of about 15 km during the eclipse as compared to the daytime (morning) reflection heights of ~ 78 km is observed. Observations suggest that about 30-40% obscuration of solar disc can lead to the tweeks occurrence which otherwise occur only in the nighttime. A significant increase of 3dB in the strength of the amplitude of VLF signal is observed around the time of TSE as compared to a control day. These low latitude ionospheric perturbations on the eclipse day are discussed and compared with other normal days. During a solar eclipse, the decrease in solar flux due to moon's shadow causes sudden change in the D-region physical and chemical processes. During the totality due to blocking of Lyman-α 1215Å (major D-region ionizing radiation) by moon's umbral shadow, the electron density decreases drastically towards the nighttime values [Smith, 1972]. During the TSE, there was no production of ionization in the ionosphere and the ions and electrons in the lowest part of it recombined at a rapid rate resulting a depletion in the electron density in the 'D' region of the Ionosphere and hence an

  7. Investigation of VLF and HF waves showing seismo-ionospheric anomalies induced by the 29 September 2009 Samoa earthquake (Mw=8.1

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    M. Parrot

    2010-05-01

    Full Text Available In Samoa Islands, a powerful earthquake took place at 17:48:10.99 UTC (06:48:10.99 LT on 29 September 2009 with a magnitude Mw=8.1. Using ICE (Instrument Champ Electrique and IMSC (Instrument Magnetic Search Coil experiments onboard the DEMETER (Detection of Electromagnetic Emissions Transmitted from Earthquake Regions satellite we have surveyed possible variations in electromagnetic signals transmitted by the ground-based VLF transmitter NPM in Hawaii and in HF plasma waves close to the Samoa earthquake during the seismic activity. The indices Dst and Kp were used to distinguish pre-earthquake anomalies from the other anomalies related to the geomagnetic activities. In a previous study we have shown that anomalies in IAP (plasma analyzer and ISL (Langmuir probe experiments onboard the DEMETER and also TEC (Total Electron Content data appear 1 to 5 days before the Samoa earthquake. In this paper we show that the anomalies in the VLF transmitter signal and in the HF range appear with the same time scale. The lack of significant geomagnetic activities indicates that these anomalous behaviors could be regarded as seismo-ionospheric precursors. It is also shown that comparative analysis is more effective in seismo-ionospheric studies.

  8. Studies on different geophysical and extra-terrestrial events within the Earth-ionosphere cavity in terms of ULF/ELF/VLF radio waves

    Science.gov (United States)

    Sanfui, Minu; Haldar, D. K.; Biswas, Debasish

    2016-10-01

    The space between the two spherical conducting shells, Earth surface and the lower boundary of the ionosphere, behaves as a spherical cavity in which some electromagnetic signals can propagate a long distance and is called Earth-ionosphere waveguide. Through this waveguide ultra low frequency (ULF), extremely low frequency (ELF) and very low frequency (VLF) signals can propagate efficiently with low attenuation. Resonances which occur for ELF waves due to round-the-world propagation interfering with 2n π phase difference are called Schumann resonances. Lightnings are the main sources of energy continuously producing these electromagnetic radiations from the troposphere. Some fixed frequency signals are also transmitted through the waveguide from different stations for navigation purposes. The intensity and phase of these signals at a particular position depend on the waveguide characteristics which are highly influenced by different natural events. Thus the signatures of different geophysical and extra-terrestrial events may be investigated by studying these signals through proper monitoring of the time series data using suitable techniques. In this article, we provide a review on ULF, ELF and VLF signals within the waveguide in terms of different geophysical and extra-terrestrial events like lightning, earthquakes, Leonid meteor shower, solar flares, solar eclipse, geomagnetic storms, and TLEs etc.

  9. Resistivity soundings and VLF profiles for siting groundwater wells in a fractured basement aquifer in the Arabian Shield, Saudi Arabia

    Science.gov (United States)

    Ammar, A. I.; Kruse, S. E.

    2016-04-01

    Seasonal shortages of groundwater are common in parts of the Arabian Shield, where complex basement hydrogeology can make siting of water wells difficult. To identify optimal production well locations, six 200-400 m-long Very Low Frequency (VLF) electromagnetic traverses and ten Vertical Electrical Soundings (VESes) were run at the western edge of the Arabian Shield near At-Taif town, Saudi Arabia. Here wadi sediments overlie fractured Precambrian basement, which in turn overlies unfractured basement. The fractured basement forms the water supply aquifer. Both VLF and VES data indicate significant lateral heterogeneity in the electrical conductivity of both wadi and basement deposits over lengths scales as small as ∼100 m. VES results correlate closely with data from two wells in the study area. The change in resistivity at the wadi-to-fractured basement contact is relatively subtle, but the transition from low resistivity fractured basement to high resistivity unfractured basement is well resolved. Inferred wadi thicknesses range from 0 to 14 m; the electrically conductive fractured basement extends from wadi down to 12-32 m depth. VES data indicate the fractured basement aquifer thickens progressively to the south in this area. A production well, sited on the basis of the VES analysis, successfully yielded 70m3/day. The relationship between VLF and VES data is complex, suggesting that the terrain is heterogeneous on the scale of the different effective sampling volumes of the two methods, and/or that fracture azimuth is locally heterogeneous. Overall resistivities in this study are similar to those observed at other locations in Saudi Arabia, suggesting these methods may be widely applicable for siting of groundwater wells in the complex basement of the Arabian Shield.

  10. Ionospheric turbulence from TEC variations and VLF/LF transmitter signal observations before and during the destructive seismic activity of August and October 2016 in Central Italy

    Science.gov (United States)

    Contadakis, Michael E.; Arabelos, Demetrios N.; Vergos, George; Spatala, Spyrous; Skeberis, Christos; Xenos, Tomas D.; Biagi, Pierfrancesco; Scordilis, Emmanuel M.

    2017-04-01

    In this paper we investigate the ionospheric turbulence from TEC variations and VLF/LF transmitter signal observations before and during the disastrous seismic activity of August and October 2016 in Central Italy . The Total Electron Content (TEC) data of 8 Global Positioning System (GPS) stations of the EUREF network, which are being provided by IONOLAB (Turkey), were analysed using Discrete Fourier Analysis in order to investigate the TEC variations (Contadakis et al. 2009, Contadakis et al. 2012, Contadakis et al. 2015). The data acquired for VLF/LF signal observations are from the receiver of Thessaloniki(40.59N, 22,78E), Greece (Skeberis et al. 2015) which monitor the VLF/LF transmitters of the International Network for Frontier Research on Earthquake Precursors (INFREP). A method of normalization according to the distance between the receiver and the transmitter is applied on the above data and then they are processed by the Hilbert Huang Transform (HHT) to produce the corresponding spectra for visual analysis. The results of this investigation indicate that the High- Frequency limit fo, of the ionospheric turbulence content, increases as the site and the moment of the earthquake occurrence is approaching, pointing to the earthquake locus. In accordence ,the analyzed data from the receiver of INFREP network in Thessaloniki, Greece show that the signals from the two VLF European transmitters, Tavolara ( Italy) and Le Blanc (France), for wich the transmission path crosses the epicentral zones, indicate enhanced high frequency variations, the last ten days before the moment of the earthquake occurrence. We conclude that the LAIC mechanism through acoustic or gravity wave could explain this phenomenology. Reference Contadakis, M.E., Arabelos, D.N., Asteriadis, G., Spatalas, S.D., Pikridas, C. TEC variations over the Mediterranean during the seismic activity period of the last quarter of 2005 in the area of Greece, Nat. Hazards and Earth Syst. Sci., 8, 1267

  11. 电离层人工调制激发的下行ELF/VLF波辐射%The downward ELF/VLF waves radiation excited by ionospheric artificial modulation

    Institute of Scientific and Technical Information of China (English)

    常珊珊; 赵正予; 汪枫

    2011-01-01

    By heating the ionosphere with large ELF/VLF-modulated HF wave, a virtual antenna is produced in the ionosphere, which is an effective means to radiate ELF/VLF waves. This paper uses the modulated-heating models of Wang Feng (2009) to calculate the strength of the LF radiation source produced by HF heating, uses full-wave model to analyze attenuation and reflection of the LF wave transmitting downward, and with HAARP experiment parameter, simulates magnetic field of the LF signals on the sea, which is in PT order, according with the experimental data.%通过大功率ELF/VLF调幅高频波对电离层进行加热,形成电离层虚拟天线,可以作为发射ELF/VLF波的一种有效手段.本文使用汪枫(2009)的调制加热模型,计算高频加热电离层产生的低频辐射源强度,采用全波解算法分析辐射的低频波向下传播过程中的衰减和反射问题,并采用HAARP实验参数,模拟出在海面上接收到的低频信号强度为PT量级,与实验数据一致.模拟结果表明,加热泵波功率、低频调制波频率、以及加热纬度位置是影响ELF/VLF波辐射和传播的三个主要因素.

  12. Short period ionospheric perturbations from continuous Doppler sounding

    Science.gov (United States)

    Fiser, Jiri; Chum, Jaroslav; Lastovicka, Jan; Buresova, Dalia

    2017-04-01

    Results of recent observations of ionospheric perturbations on short time scales obtained by international network (Czech Republic, Argentina, Taiwan and South Africa) of multipoint continuous Doppler sounders with time resolution about 10 s are presented. Examples of observation and analysis of propagation of gravity waves (GWs), equatorial spread F (ESF), infrasound from earthquake and large convective systems, as well as ionospheric perturbations caused by solar flares will be shown. It is documented that roughly poleward propagation of GWs dominates in the local summer, whereas mainly equatorward propagation is observed in the local winter. The analysis of occurrences and zonal drifts of ESF based on Doppler sounding are consistent with optical and satellite measurements. The observations of co-seismic perturbations by Doppler sounders in the vicinity of ionosondes and seismic sensors proved that the co-seismic perturbations are caused by approximately vertically propagating infrasound waves triggered by vertical motion of the ground surface. Numerical simulations and Doppler measurements confirmed that in the vicinity (up to about 1000 km) from epicenters of strong earthquake, the infrasound propagates in nonlinear regime in the upper atmosphere, which results in the formation of N-shaped pulse. Solar flares are observed both as sudden frequency deviations and amplitude attenuations of Doppler signal.

  13. A multiple receiver - multiple transmitter VLF high-order differential analysis evaluation network for near real-time detection and discrimination of seismic-ionospheric precursor phenomena

    Science.gov (United States)

    Skeberis, Christos; Zaharis, Zaharias; Xenos, Thomas; Spatalas, Spyridon; Stratakis, Dimitrios; Maggipinto, Tommaso; Biagi, Pier francesco

    2016-04-01

    This study provides an evaluation of the application of high-order differential analysis on VLF signals on a multiple-receiver multiple-transmitter network. This application provides a method for near-real-time detection of disturbances that can be attributed to seismic-ionospheric precursor phenomena and can discriminate disturbances that could be classified as false positives and thus should be attributed to other geomagnetic influences. VLF data acquired in Thessaloniki, Greece (40.59N, 22,78E) Herakleion, Greece (35.31N, 25.10E), Nicosia, Cyprus (35.17N, 33.35E), Italy (42.42N, 13.08E) and transmitted by the VLF station in Tavolara, Italy (ICV station 40.923N, 9.731E) and the station in Keflavik, Iceland (ICE 64.02N, 22.57W) from January 2015 to January 2016 were used for the purpose of this paper. The receivers have been developed by Elettronika Srl and are part of the International Network for Frontier Research on Earthquake Precursors (INFREP). The process applied for this study has been further developed and is based on differential analysis. The signals undergo transformation using an enhanced version of the Hilbert Huang Transform, and relevant spectra are produced. On the product of this process, differential analysis is applied. Finally, the method produces the correlation coefficient of signals that are on the same path over an earthquake epicenter in order to highlight disturbances, and on the opposite can make comparisons with unrelated transmitted signals of different paths to eliminate disturbances that are not localized to the area of interest. This improvement provides a simple method of noise cancellation to signals that would otherwise be considered as false positives. A further evaluation of the method is provided with the presentation and discussion of sample results. The method seems to be a robust tool of analysis of VLF signals and also an automatic detection tool with built-in noise cancellation of outside disturbances.

  14. Application of an Automated System for the Processing of VLF signals to Detect, Analyze and Classify Seismic-Ionospheric Precursor Phenomena

    Science.gov (United States)

    Skeberis, Christos; Xenos, Thomas; Contadakis, Michael; Arabelos, Dimitrios; Biagi, Pier Francesco; Maggipinto, Tommaso

    2013-04-01

    This paper studies the development and application of an automated system based on Predictive Modular Neural Networks (PREMONNs) and Self Organizing Maps (SOMs) along with the necessary backend development of database classification required to provide a fully integrated system for detecting disturbances that can be attributed to seismic-ionospheric precursor phenomena using VLF radio signals. The aforementioned system can analyze all the relevant data and bring forth and adaptively discriminate different characteristics in the received signals, in real time in order to provide data segments of interest that can be correlated to subsequent seismic phenomena and can be classified with respect to pre-recorded samples of previous points of interest (POIs). PREMONNs as it was demonstrated in previous studies can be used for time-series switching detection and can be applied to the detection of POIs , whereas SOMs have been extensively used in unsupervised pattern recognition and classification of datasets. For the purpose of this paper, data acquired in Thessaloniki (40.59N, 22,78E) from the VLF station in Tavolara, Italy (ICV station Lat 40.923, Lon. 9.731) for over two years (December 2010 - December 2012) are used. The receiver was developed by Elettronika Srl, and is part of the International Network for Frontier Research on Earthquake Precursors (INFREP). The received VLF signal is normalized and then processed using the Empirical Mode Decomposition Method (EMD). The resulting data are passed to an Artificial Neural Network (ANN) based on PREMONNs trained specifically for this purpose and the output from that stage is passed onto a classifier based on SOMs to compare and classify points of interest based on a current database of received signals and identifying and storing new ones for future reference. The efficacy of the detection and the results of the aforementioned process is then discussed and results are presented. Therefore, based on the results it may be

  15. Penetration Characteristics of VLF Wave From Atmosphere Into the Lower Ionosphere%VLF波从大气层到低电离层的传输特性分析

    Institute of Scientific and Technical Information of China (English)

    赵庶凡; 申旭辉; 潘威炎; 张学民

    2011-01-01

    Many papers have indicated that earthquake happens associated with a width frequency band of VLF (Very Low Frequency), ULF (Ultra Low Frequency), ELF (Extremely Low Frequency)electromagnetic radiation, which have been recorded by satellites in the ionosphere and low magnetosphere.In this paper, the reflection and transmission coefficient of the homogeneous half-space ionosphere has been calculated using propagation matrix method.Simultaneously the Booker quartic equation is solved to get the refractive index in the ionosphere.The analysis of the factors which influence the reflection and transmission coefficient of the ionosphere and the propagation characteristics in the ionosphere of VLF wave have been performed, such as wave frequency, incident angle, geomagnetic inclination, electron density and collision frequency in the ionosphere to provide fundamental basis for further studies on numerical calculation of propagation of ULF/VLF waves in the stratified ionosphere and support the study of seismo-ionosphere coupling mechanism.The results show that it is easier for the TE (Traverse Electric) wave radiated by vertical electric dipole to penetrate into the ionosphere, but the TM (Traverse Magnetic) wave radiated by horizontal electric dipole is reflected again and again in the ground-ionosphere waveguide.It is easier to observe the VLF wave anomaly when the electron density is lower or at the high-latitude region.The O wave experiences severer attenuation than X wave, so X wave is a penetration mode whereas O wave is a non penetration mode in the ionosphere.The attenuation of the two characteristic wave decrease as the decrease of the angle between the geomagnetic field and wave vector, that is to say the attenuation is the smallest when longitudinal propagation.When the geomagnetic field is considered, the ULF/VLF wave related with earthquake can penetrate into the ionosphere which is confirmed by the satellite observation.But the further physical mechanism will

  16. Dual-Spacecraft Observation of Density Features in the Near-Terminator Martian Ionosphere: Mars Express Ionospheric Sounding and MAVEN

    Science.gov (United States)

    Morgan, D. D.; Gurnett, D. A.; Mahaffy, P. R.; Halekas, J. S.; Frahm, R. A.; Connerney, J. E. P.

    2015-12-01

    The Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS), on the Mars Express spacecraft, incorporates the Active Ionospheric Sounding (AIS) mode, which is used to sound the topside of the Martian ionosphere. This instrument has been used over the last ten years to identify and study a wide variety of ionospheric features. The advent of the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, inserted into Mars orbit in September 2014, allows us to look at the ionosphere with two spacecraft. In this study, we find density features, primarily depressions with one apparent ionopause, identifiable within a few hours and a few tens of degrees in solar zenith angle in the MARSIS AIS and MAVEN Neutral Gas and Ion Mass Spectrometer (NGIMS) data, and study them with a variety of instruments from both spacecraft. Most of the features identified occur in the vicinity of weak crustal magnetic fields and are slowly migrating toward higher solar zenith angles. During these events, MARSIS scalar magnetic fields are slightly elevated above the model crustal fields. Two of the three depressions are coincident with abrupt increases in the solar wind density, as measured by the MAVEN Solar Wind Ion Analyzer (SWIA), and with abrupt changes in the solar wind magnetic field clock angle, from MAVEN Magnetometer (MAG). We believe that both changes in the solar wind and proximity to crustal field anomalies are related to the existence of these dropouts.

  17. Brief communication "Monitoring ionospheric variations before earthquakes using the vertical and oblique sounding network over China"

    Directory of Open Access Journals (Sweden)

    Z. Wu

    2011-04-01

    Full Text Available The problem of earthquake prediction has stimulated the research for correlation between seismic activity and ionospheric anomaly. Many observations have shown the existence of anomaly of critical frequency of ionospheric F-region, foF2, before earthquake onset. Ionospheric sounding has been conducted routinely for more than 60 years in China by the China Research Institute of Radiowave Propagation (CRIRP, and deveoloped a very powerful ability to observe the ionosphere. In this paper, we briefly describe the anomalous variation of the foF2 before Ms8.0 Wenchuan earthquake (occurred on 12 May 2008 at 14:28 LT; 31.00° N, 103.40° E, which is a sign of the great interest arising in the seismo-ionospheric investigation of Chinese researchers. Furthermore, we introduce the routine work on seismo-ionospheric anomaly by the ground based high-resolution ionospheric observation (GBHIO network comprising 5 vertical and 20 oblique sounding stations.

  18. A new campaign for oblique-incidence ionospheric sounding over Europe and its data application

    Science.gov (United States)

    Zolesi, B.; Fontana, G.; Perrone, L.; Pietrella, M.; Romano, V.; Tutone, G.; Belehaki, A.; Tsagouri, I.; Kouris, S. S.; Vallianatos, F.; Makris, J. P.; Angling, M. J.

    2008-04-01

    New systematic oblique ionospheric radio sounding measurements over Central Europe, concerning the radio links between Inskip (UK, 53.5°N, 2.5°W) and Rome (Italy, 41.8°N, 12.5°E) and between Inskip and Chania (Greece, 35.7°N, 24.0°E), have been performed since November 2003. Different long-term (i.e. monthly median) ionospheric predictions and nowcasting techniques have been applied and compared with the oblique-incidence radio sounding measurements. The MUF (basic maximum usable frequency) measurements observed during the early part of the experiment have been used to compare the performances of different methods. The preliminary analysis has shown good performances for the long-term prediction models, in particular in winter months for ICEPAC (ionospheric communications enhanced profile analysis and circuit) and in equinox/summer months for ASAPS (advanced stand-alone prediction system) and SIRM&LKW (simplified ionospheric regional model lockwood). The nowcasting methods SIRMUP&LKW (SIRM updating method lockwood) and ISWIRM (instantaneous space weighted ionospheric regional model) reveal good results for moderate and disturbed geomagnetic conditions when compared with the long-term prediction methods.

  19. Data verification of a hardware-software complex of sounding an ionosphere and ionosonde DPS-4

    Science.gov (United States)

    Smirnov, Vladimir; Ruzhin, Yuri; Smirnova, Elena; Skobelkin, Vladimir; Tynyankin, Sergey

    Appeared in recent years, opportunities to use as a source of signals used to determine the parameters of the ionosphere, the spacecraft global navigation satellite systems GLONASS and GPS are not currently in widespread use practices ionospheric wave frequency and radio centers and dispatch services. Given the urgency of the discussed areas of research, long experiment whose purpose is to conduct a comparative analysis of the results of determining the critical frequency of F2-layer of the ionosphere in two ways - vertical sounding (ionosonde DPS-4) and radio translucence track "satellite-the Earth" with signals using GLONASS satellites and GPS was started in 2013. For a comparative analysis of the results the hardware-software complex ionospheric soundings (HSCIS) was located at territory of the Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of the Russian Academy of Sciences. HSCIS product includes a personal computer with it specialized software, a dual-frequency navigation receiver and small receiving antenna. Used in the product receiver developed by NovAtel allows us to receive the signals of the navigation systems GPS/GLONASS and maintain their processing in real time. Location receiver determined autonomously: antenna position - 55.76o N, 37.94o E, coordinates ionosonde DPS-4 - 55.5o N, 37.3o E. In fact, both devices were in close proximity, which it allows for the identity conditions of observation. Both devices operate in real time. Ionosonde DPS- 4 gave the ionosphere parameters every 15 minutes, HSCIS - every minute. Information from both instruments displayed on the screen monitors, and recorded in the memory used by computers. Along with the numerical parameters on the monitor products HSCIS displayed time course of the critical frequency F2- layer of the ionosphere obtained from observations of the nearest navigation satellite. When limiting elevation observations 15o simultaneous use of navigation satellites can

  20. Ionospheric Sounding Opportunities Using Signal Data From Preexisting Amateur Radio And Other Networks

    Science.gov (United States)

    Cushley, A. C.; Noel, J. M. A.

    2015-12-01

    Amateur radio and other transmissions used for dedicated purposes, such as the Automatic Packet Reporting System (APRS) and Automatic Dependent Surveillance Broadcast (ADS-B), are signals that exist for another reason, but can be used for ionospheric sounding. Whether mandated and government funded or voluntarily constructed and operated, these networks provide data that can be used for scientific and operational purposes which rely on space weather data. Given the current state of the global economic environment and fiscal consequences to scientific research funding in Canada, these types of networks offer an innovative solution with preexisting hardware for more real-time and archival space-weather data to supplement current methods, particularly for data assimilation, modelling and forecasting. Furthermore, mobile ground-based transmitters offer more flexibility for deployment than stationary receivers. Numerical modelling has demonstrated that APRS and ADS-B signals are subject to Faraday rotation (FR) as they pass through the ionosphere. Ray tracingtechniques were used to determine the characteristics of individual waves, including the wave path and the state of polarization. The modelled FR was computed and converted to total electron content (TEC) along the raypaths. TEC data can be used as input for computerized ionospheric tomography (CIT) in order to reconstruct electron density maps of the ionosphere.

  1. A new type of daytime high-frequency VLF emissions at auroral latitudes ("bird emissions")

    Science.gov (United States)

    Manninen, J.; Turunen, T.; Kleimenova, N. G.; Gromova, L. I.; Kozlovskii, A. E.

    2017-01-01

    This paper is concerned with a new, previously unknown type of high-frequency (above 4 kHz) VLF emissions that were detected during winter VLF campaigns in Kannuslehto ( L 5.5), Finland. These previously unknown emissions have been discovered as a result of the application of special digital filtering: it clears the VLF records from pulse signals of intensive atmospherics, which prevent other kinds of VLF emissions in the same frequency range from being seen on spectrograms. As it appears, aside from wellknown bursts of auroral hisses and discrete quasiperiodic emissions, a previously unknown type of daytime right-hand polarized VLF waves is also present at frequencies above 4 kHz. These emissions can persist for several hours as series of separate short discrete wideband (from 4 to 10 kHz and higher) signals, each with a duration between one and several minutes. It has been found that such signals can be observed almost daily in winter. These emissions sound like bird's chirping to a human ear; for that reason, they were called "bird emissions." The dynamic spectra of individual signals often resemble flying birds. The signals are observed during daytime, more often in magnetically quiet conditions preceded by geomagnetic disturbances. As a rule, the occurrence of these bird emissions is accompanied by a slight increase in electron density in the lower ionosphere, which is evidence of the precipitation of energetic (>30 keV) electrons. This raises a number of questions as to where and how the VLF bird emissions are generated and how such emissions, at frequencies greatly exceeding half the electron equatorial gyrofrequency at L 5.5, can reach the Earth's surface.

  2. Design and Application of Wuhan Ionospheric Oblique Backscattering Sounding System with the Addition of an Antenna Array (WIOBSS-AA).

    Science.gov (United States)

    Cui, Xiao; Chen, Gang; Wang, Jin; Song, Huan; Gong, Wanlin

    2016-06-15

    The Wuhan Ionospheric Oblique Backscattering Sounding System with the addition of an antenna array (WIOBSS-AA) is the newest member of the WIOBSS family. It is a multi-channel radio system using phased-array antenna technology. The transmitting part of this radio system applies an array composed of five log-periodic antennas to form five beams that span an area to the northwest of the radar site. The hardware and the antenna array of the first multi-channel ionosonde in the WIOBSS family are introduced in detail in this paper. An ionospheric detection experiment was carried out in Chongyang, Hubei province, China on 16 March 2015 to examine the performance of WIOBSS-AA. The radio system demonstrated its ability to obtain ionospheric electron density information over a wide area. The observations indicate that during the experiment, the monitored large-area ionospheric F2-layer was calm and electron density increased with decreasing latitude.

  3. Engineering aspect of the microwave ionosphere nonlinear interaction experiment (MINIX) with a sounding rocket

    Science.gov (United States)

    Nagatomo, Makoto; Kaya, Nobuyuki; Matsumoto, Hiroshi

    The Microwave Ionosphere Nonlinear Interaction Experiment (MINIX) is a sounding rocket experiment to study possible effects of strong microwave fields in case it is used for energy transmission from the Solar Power Satellite (SPS) upon the Earth's atmosphere. Its secondary objective is to develop high power microwave technology for space use. Two rocket-borne magnetrons were used to emit 2.45 GHz microwave in order to make a simulated condition of power transmission from an SPS to a ground station. Sounding of the environment radiated by microwave was conducted by the diagnostic package onboard the daughter unit which was separated slowly from the mother unit. The main design drivers of this experiment were to build such high power equipments in a standard type of sounding rocket, to keep the cost within the budget and to perform a series of experiments without complete loss of the mission. The key technology for this experiment is a rocket-borne magnetron and high voltage converter. Location of position of the daughter unit relative to the mother unit was a difficult requirement for a spin-stabilized rocket. These problems were solved by application of such a low cost commercial products as a magnetron for microwave oven and a video tape recorder and camera.

  4. Ionospheric turbulence from ground-based and satellite VLF/LF transmitter signal observations for the Simushir earthquake (November 15, 2006

    Directory of Open Access Journals (Sweden)

    Pier Francesco Biagi

    2012-04-01

    Full Text Available

    Signals from very low frequency (VLF/ low frequency (LF transmitters recorded on the ground station at Petropavlovsk-Kamchatsky and on board the French DEMETER satellite were analyzed for the Simushir earthquake (M 8.3; November 15, 2006. The period of analysis was from October 1, 2006, to January 31, 2007. The ground and satellite data were processed by a method based on the difference between the real signal at night-time and the model signal. The model for the ground observations was the monthly averaged signal amplitudes and phases, as calculated for the quiet days of every month. For the satellite data, a two-dimensional model of the signal distribution over the selected area was constructed. Preseismic effects were found several days before the earthquake, in both the ground and satellite observations.

     

  5. An Artificial Particle Precipitation Technique Using HAARP-Generated VLF Waves

    Science.gov (United States)

    2006-11-02

    AFRL-VS-HA-TR-2007-1021 An Artificial Particle Precipitation Technique Using HAARP -Generated VLF Waves O o o r- Q M. J. Kosch T. Pedersen J...Artificial Particle Precipitation Technique Using HAARP Generated VLF Waves. 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 62101F...model. The frequency-time modulated VLF wave patterns have been successfully implemented at the HAARP ionospheric modification facility in Alaska

  6. Effects of solar eclipse on the ionosphere observed by the Doppler sounding

    Science.gov (United States)

    Sindelarova, Tereza; Mosna, Zbysek; Chum, Jaroslav

    2017-04-01

    The Doppler sounding of the ionosphere is based on measurements of the frequency shift between the transmitted and received radio wave of a stable known frequency. The frequency shift is related to changes of the phase path of the radio wave and can be influenced by the vertical motion of the reflecting layer due to gravity waves, by compression and rarefaction of gas at a fixed height owing to infrasound waves or by changes of electron density due to changes of ionization rate e.g. during the solar eclipse or solar flares. We studied effects of total solar eclipses on 20 March 2015 in the Czech Republic and on 9 March 2016 on Taiwan. In both events, the Doppler sounding was located in the area of partial eclipse. Distinct disturbance was observed around the time of the maximum eclipse. We assume that it is related to processes at the site of measurements rather than to waves propagating from the region of total eclipse.

  7. Possibility of Earthquake-prediction by analyzing VLF signals

    Science.gov (United States)

    Ray, Suman; Chakrabarti, Sandip Kumar; Sasmal, Sudipta

    2016-07-01

    Prediction of seismic events is one of the most challenging jobs for the scientific community. Conventional ways for prediction of earthquakes are to monitor crustal structure movements, though this method has not yet yield satisfactory results. Furthermore, this method fails to give any short-term prediction. Recently, it is noticed that prior to any seismic event a huge amount of energy is released which may create disturbances in the lower part of D-layer/E-layer of the ionosphere. This ionospheric disturbance may be used as a precursor of earthquakes. Since VLF radio waves propagate inside the wave-guide formed by lower ionosphere and Earth's surface, this signal may be used to identify ionospheric disturbances due to seismic activity. We have analyzed VLF signals to find out the correlations, if any, between the VLF signal anomalies and seismic activities. We have done both the case by case study and also the statistical analysis using a whole year data. In both the methods we found that the night time amplitude of VLF signals fluctuated anomalously three days before the seismic events. Also we found that the terminator time of the VLF signals shifted anomalously towards night time before few days of any major seismic events. We calculate the D-layer preparation time and D-layer disappearance time from the VLF signals. We have observed that this D-layer preparation time and D-layer disappearance time become anomalously high 1-2 days before seismic events. Also we found some strong evidences which indicate that it may possible to predict the location of epicenters of earthquakes in future by analyzing VLF signals for multiple propagation paths.

  8. The CuSPED Mission: CubeSat for GNSS Sounding of the Ionosphere-Plasmasphere Electron Density

    Science.gov (United States)

    Gross, Jason N.; Keesee, Amy M.; Christian, John A.; Gu, Yu; Scime, Earl; Komjathy, Attila; Lightsey, E. Glenn; Pollock, Craig J.

    2016-01-01

    The CubeSat for GNSS Sounding of Ionosphere-Plasmasphere Electron Density (CuSPED) is a 3U CubeSat mission concept that has been developed in response to the NASA Heliophysics program's decadal science goal of the determining of the dynamics and coupling of the Earth's magnetosphere, ionosphere, and atmosphere and their response to solar and terrestrial inputs. The mission was formulated through a collaboration between West Virginia University, Georgia Tech, NASA GSFC and NASA JPL, and features a 3U CubeSat that hosts both a miniaturized space capable Global Navigation Satellite System (GNSS) receiver for topside atmospheric sounding, along with a Thermal Electron Capped Hemispherical Spectrometer (TECHS) for the purpose of in situ electron precipitation measurements. These two complimentary measurement techniques will provide data for the purpose of constraining ionosphere-magnetosphere coupling models and will also enable studies of the local plasma environment and spacecraft charging; a phenomenon which is known to lead to significant errors in the measurement of low-energy, charged species from instruments aboard spacecraft traversing the ionosphere. This paper will provide an overview of the concept including its science motivation and implementation.

  9. Ionospheric E–F valley observed by a sounding rocket at the low-latitude station Hainan

    Directory of Open Access Journals (Sweden)

    J. K. Shi

    2013-08-01

    Full Text Available According to the sounding rocket experiment conducted at Hainan ionospheric observatory (19.5° N, 109.1° E, a valley between the E layer and F layer in the ionospheric electron density profile is observed and presented. The sounding rocket was launched in the morning (06:15 LT on 7 May 2011, and the observed electron density profile outside the valley agrees with the simultaneous observation by the DPS-4 digisonde at the same station. The width of the observed valley was about 42 km, the depth almost 50%, and the altitude of the electron density minimum 123.5 km. This is the first observation of the E–F valley in the low-latitude region in the East Asian sector. The results are also compared with models, and the physical mechanism of the observed valley is discussed in this paper.

  10. INSPIRE: A VLF Radio Project for High School Students

    Science.gov (United States)

    Marshall, Jill A.; Pine, Bill; Taylor, William W. L.

    2007-01-01

    Since 1988 the Interactive NASA Space Physics Ionospheric Radio Experiment, or INSPIRE, has given students the opportunity to build research-quality VLF radio receivers and make observations of both natural and stimulated radio waves in the atmosphere. Any high school science class is eligible to join the INSPIRE volunteer observing network and…

  11. Sounding-Rocket Studies of Langmuir-Wave Microphysics in the Auroral Ionosphere

    Science.gov (United States)

    Dombrowski, Micah P.

    Since their discovery in laboratory plasmas in the 1920s, Langmuir waves have been observed to be ubiquitous in plasma environments, particularly in space plasmas. From the greater solar wind to planetary foreshocks and the auroral ionosphere, Langmuir waves are a key factor mediating electron temperature, and controlling electron beam propagation and beam-plasma energy transfer. Because they are so important, Langmuir waves in the space environment have been intensively investigated; however, there remain two challenging types of experiments that are relatively lacking: three-dimensional measurements of Langmuir-wave fields, and measurements of Langmuir wave-electron correlations. This thesis works on filling these two gaps, plus development of new Langmuir-wave instrumentation. The CHARM-II wave-particle Correlator instrument was designed to study the energy transfer between electron beams and plasmas via the sorting of incoming particles by concurrent Langmuir-wave phase, allowing for direct observation of electron bunching. Data from the CHARM-II sounding rocket comprises the first such observations with statistical levels of events, revealing an association between the polarity of the resistive component of the electron phase-bunching and changes in the electron flux at the associated energy, such that a negative resistive component goes with an increase in electron flux, and vice versa, effectively showing energy flow from the beam to the waves, and subsequent enhancements of wave damping. Surprisingly, the results also show comparable amounts of resistive and reactive activity. A test-particle simulation was developed to confirm the details of the theoretical explanation for the observed effect. A three-dimensional Langmuir-wave receiver flown on the TRICE sounding rocket mission reveals the beat signature of the amplitude-modulated 'bursty' form of Langmuir waves which has been observed in many environments. An analysis of the three-dimensional data shows

  12. Phase compensation of MARSIS subsurface sounding data and estimation of ionospheric properties: New insights from SHARAD results

    Science.gov (United States)

    Campbell, Bruce A.; Watters, Thomas R.

    2016-02-01

    Subsurface radar sounding observations by the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) and Shallow Radar (SHARAD) instruments are affected by ionospheric phase distortions that lead to image blurring and delay offsets. Based on experience with SHARAD image correction, we propose that ionospheric blurring in MARSIS radargrams may be compensated with a model of smoothly varying quadratic phase errors along the track. This method yields well-focused radargrams for geologic interpretation and allows analysis of the validity range for models used to derive total electron content (TEC) from phase distortion terms in previous MARSIS studies. The quadratic term appears to be a good proxy for TEC at solar zenith angles >65° for MARSIS Band 4 (5 MHz) and >75° for Band 3 (4 MHz). Comparison of MARSIS- and SHARAD-derived TEC values from 2007 to 2014 reveals correlations in seasonal behavior and in the characterization of ionospheric activity due to coronal mass ejections. We also present SHARAD and MARSIS evidence for a persistent region of anomalous radar scattering south of Arsia Mons. These echoes have been previously suggested to arise from refraction of the radar signal by electron density variations. There are no strong signatures, however, in the quadratic image compensation term correlated with the anomalous scattering, suggesting either that electron density variations responsible for refracted signal paths occur primarily in regions offset from the spacecraft track or that these density changes have a minimal impact on the integrated phase distortion of the subspacecraft footprint. We suggest observations and analyses to better constrain the mechanism and timing of such echoes.

  13. VLF Science at Indian Centre for Space Physics

    Science.gov (United States)

    Chakrabarti, Sandip Kumar

    2016-07-01

    Indian Centre for Space Physics has been monitoring VLF signals from stations around the world at its laboratories at Kolkata and Sitapur (Ionospheric and Earthquake Research Centre) as well as at several places throughout India when in a campaign mode. We have been interested to study high energy events from space, such as solar flares and gamma ray bursts. We have made studies during multiple solar eclipses and most importantly made substantial progress in the problem of lithosphere-ionosphere coupling while understanding various types of anomalies prior to major earthquakes. Other effects such as AGWs and LEPs are being studied. We have experience of two antarctic expedition and obtained VLF data from both Maitri and Bharati stations of India, which revealed, among other things, how the signal attenuation can indicate the extent of ice mass in Antarctica. We have been able to reproduce various VLF perturbation events using Atmospheric Chemical evolution model coupled with LWPC code. For instance we have reproduced solar flare induced VLF amplitude perturbation pattern by completely ab initio calculation. We also targeted the inverse problem, namely, deduction of the injected radiation spectra from space from the VLF signal alone, thereby establishing that the Earth can be used as a gigantic detector. These interesting results would be presented in my review talk.

  14. Study of the effect of solar flares on VLF signals during D-layer preparation or disappearance time

    Science.gov (United States)

    Ray, Suman; Chakrabarti, Sandip Kumar; Palit, Sourav

    2016-07-01

    "Very Low Frequency" (VLF) is one of the bands of the Radio waves having frequency 3-30 KHz, which propagates through the Earth-ionosphere wave-guide. In relation to propagation of radio waves through ionosphere, low mass and high mobility cause electrons to play a vital role. Electrons are not distributed uniformly in the ionosphere and depending on this factor, ionosphere has different layers namely D, E and F. Different ionospheric layers generally exist during day and night time. During day-time when the main source of the ionization of the ionosphere is Sun, the lower most layer of ionosphere is D-layer. But during the night-time when Sun is absent and cosmic ray is the main source of the ionization of the ionosphere, this D-layer disappears and E-layer becomes the lower most region of the ionosphere. Normally, patterns of VLF signal depend on regular solar flux variations. However, during solar flares extra energetic particles are released from Sun, which makes the changes in the ionization of the ionosphere and these changes can perturb VLF signal amplitude. Usually if a solar flare occurs during any time of day, it only affects the amplitude and phase of the VLF signals. But in the present work, we found the if the flare occurs during D-layer preparation / disappearance time, then it will not only affect to amplitude and phase of the VLF signals but also to terminator times of VLF signals. We have observed that the sun set terminator time of the VLF signals shifted towards night time due to the effect of a M-class solar flare which occurred during the D-layer disappearance time. The shift is so high that it crossed 5σ level. We are now trying to a make model using the ion-chemistry and LWPC code to explain this observed effect.

  15. Transionospheric Propagation of VLF Transmitter Signals

    Science.gov (United States)

    Cohen, M.; Inan, U. S.; Lehtinen, N. G.

    2012-12-01

    Ground based Very Low Frequency (VLF, 3-30 kHz) radio transmitters may play a significant role in precipitation of inner belt (L<2.5) energetic Van Allen electrons. Initial analyses of the total contribution of VLF transmitters utilized models of transionospheric propagation, but some recent studies have suggested that those models may overestimate (by 20-100 dB) the VLF energy reaching the magnetosphere. One possible cause of this discrepancy was suggested to be conversion of wave energy into electrostatic modes in the D, E, and F regions, from ionospheric density irregularities, either natural or generated by the transmitter heating itself. The DEMETER satellite built a six year history of continuous and global survey mode data which, when combined, yields detailed pictures of the radiation pattern from many transmitters into space at 680 km, with 25 km resolution, and clear features like the interference pattern on the ground mapped upwards. With both E and B survey mode data, we can also directly approximate the total power injected into the magnetosphere from each transmitter, separately for day and night, as well as the power arriving at the conjugate region. We find no detectable variation of signal intensity with geomagnetic conditions. We find evidence of transmitter heating affecting the transionospheric propagation of other transmitters. We find that the power reaching the conjugate region is a large fraction of the power injected above the transmitter. We then employ a full wave model to simulate VLF transmitter transionospheric propagation, calculating the electromagnetic fields and power flux injected into the magnetosphere. Although the model does not include ionospheric irregularities, the radiation pattern largely matches the observed one, and the total power calculated is within 6 dB of observations for every transmitter, both day and night, and across a range of low to middle latitudes and transmitter powers. We thus conclude that the effect of

  16. Seismo-electromagnetic VLF link calibration in Europe

    Science.gov (United States)

    Eichelberger, Hans; Schwingenschuh, Konrad; Wolbang, Daniel; Besser, Bruno P.; Rozhnoi, Alexander; Solovieva, Maria; Biagi, Pier Francesco; Stachel, Manfred; Prattes, Gustav; Boudjada, Mohammed Y.; Aydogar, Özer; Zehetleitner, Sigrid; Grill, Claudia; Jernej, Irmgard

    2015-04-01

    The general background is the investigation of seismic activity with electromagnetic signals, i.e. to disentangle amplitude and phase modifications from a variety of sources. This work focus on characterisation of very low frequency (VLF) radio links between several transmitters and the Graz receiver in the current active solar cycle. Particular emphasis is on solar flares related disturbances in the Earth-ionosphere waveguide, an important dayside non-seismic influence on the VLF paths. These variations can serve as a calibration tool of the facility even for nighttime periods when different seismo-electromagnetic (SEM) methods are applied, e.g. terminator time or nighttime amplitude. Supporting data are the GOES X-ray flux measurements. As immediate objective we study individual C/M/X-class solar flare events in the sub-ionospheric VLF waveguide (amplitude fluctuations) and calculate statistical parameters with the C-class population. The used system, which is part of a broader network of receiving stations, is primarily dedicated to investigate earthquake related phenomena and associated lithospheric atmospheric ionospheric coupling mechanisms. We receive simultaneously 12 VLF transmitters (amplitude and phase measurements) from the northern hemisphere with a selected temporal resolution of 20 seconds. We conclude that the numerous C/M/X-class solar flare events, together with the the high signal-to-noise ratio of the facility, are a valuable combination for short-term VLF path characterisation in a robust manner. As outlook, due to the steady VLF measurements, a monitoring service for certain lower atmospheric variations can be envisaged.

  17. Ionospheric disturbances caused by long period sound waves generated by Saturn-Apollo launches

    Science.gov (United States)

    Rao, G. L.

    1972-01-01

    Wavelike disturbances were observed in the ionosphere following several nuclear explosions in early 1960's. Supersonic shock waves within the atmosphere generated by large rockets can cause ionospheric electron density perturbations. A CW phase path Doppler array in the New York area was operated during the Saturn-Apollo 12 and 13 launches and recorded Doppler frequency fluctuations due to rocket launchings. Cross correlation and power spectral analyses of the phase path-path Doppler frequency variation records showed that the phase velocities of the signal arrivals were from south of the array with 700 - 800 m/sec corresponding to periods in the range of 2 to 4 minutes. Ionograms taken every 60 seconds from Wallops Islands showed clearly ionospheric disturbances due to rockets. The group velocities were estimated to be of the order of 450 m/sec 1 obtained from the earliest visible disturbances seen on CW phase path Doppler records and ionograms together with the rocket trajectory data.

  18. The VLF fingerprint of elves: Step-like and long-recovery early VLF perturbations caused by powerful ±CG lightning EM pulses

    Science.gov (United States)

    Haldoupis, Christos; Cohen, Morris; Arnone, Enrico; Cotts, Benjamin; Dietrich, Stefano

    2013-08-01

    Subionospheric VLF recordings are investigated in relation with intense cloud-to-ground (CG) lightning data. Lightning impacts the lower ionosphere via heating and ionization changes which produce VLF signal perturbations known as early VLF events. Typically, early events recover in about 100 s, but a small subclass does not recover for many minutes, known as long-recovery early events (LORE). In this study, we identify LORE as a distinct category of early VLF events, whose signature may occur either on its own or alongside the short-lived typical early VLF event. Since LORE onsets coincide with powerful lightning strokes of either polarity (±), we infer that they are due to long-lasting ionization changes in the uppermost D region ionosphere caused by electromagnetic pulses emitted by strong ± CG lightning peak currents of typically > 250 kA, which are also known to generate elves. The LORE perturbations are detected when the discharge is located within ~250 km from the great circle path of a VLF transmitter-receiver link. The probability of occurrence increases with stroke intensity and approaches unity for discharges with peak currents ≥ ~300 kA. LOREs are nighttime phenomena that occur preferentially, at least in the present regional data set, during winter when strong ± CG discharges are more frequent and intense. The evidence suggests LORE as a distinct signature representing the VLF fingerprint of elves, a fact which, although was predicted by theory, it escaped identification in the long-going VLF research of lightning effects in the lower ionosphere.

  19. Monitoring of the velocity field of the plasma motion under sounding of F ionospheric region by the probe waves

    Science.gov (United States)

    Sergeev, Evgeny; Komrakov, G. P.; Smyshlyaev, Sergey E.

    Results of investigations of the motions in F region of the ionosphere by means of the method of the space-frequency diversity reception are presented. Measurements of the vertical and horizontal plasma drift velocities have been performed over SURA facility (Russia) using of multifrequency dopler station for vertical sounding and diversity three point reception of the reflected radiosignals. Possibilities of a day (15 hours) monitoring of the drift velocity space at different altitudes were studied by using of the three fixed probe frequencies 4353 kHz, 5853 kHz and 7353 kHz. For another experimental series complex investigations of the pumped ionospheric volume were performed by its diagnostics at different frequencies with the short (¡ 200 mks) wide frequency band (˜ 500 kHz) and powerful (˜ 20 - 150 MW ERP) pulses. Data about a fine distribution structure of the vertical and horizontal plasma drift velocities in the turbulence plasma range were first obtained with a high frequency (˜ 1 kHz) and temporal (˜ 20 ms) resolution. The work was supported by RFBR grants 07-02-00464 and 06-02-17334.

  20. ULF fluctuations of the geomagnetic field and ionospheric sounding measurements at low latitudes during the first CAWSES campaign

    Directory of Open Access Journals (Sweden)

    U. Villante

    2006-07-01

    Full Text Available We present an analysis of ULF geomagnetic field fluctuations at low latitudes during the first CAWSES campaign (29 March-3 April 2004. During the whole campaign, mainly in the prenoon sector, a moderate Pc3-4 pulsation activity is observed, clearly related to interplanetary upstream waves. On 3 April, in correspondence to the Earth's arrival of a coronal mass ejection, two SIs are observed whose waveforms are indicative of a contribution of the high-latitude ionospheric currents to the low-latitude ground field. During the following geomagnetic storm, low frequency (Pc5 waves are observed at discrete frequencies. Their correspondence with the same frequencies detected in the radial components of the interplanetary magnetic field and solar wind speed suggests that Alfvénic solar wind fluctuations may act as direct drivers of magnetospheric fluctuations. A cross-phase analysis, using different pairs of stations, is also presented for identifying field line resonant frequencies and monitoring changes in plasmaspheric mass density. Lastly, an analysis of ionospheric vertical soundings, measured at the Rome ionosonde station (41.8° N, 12.5° E, and vertical TEC measurements deduced from GPS signals within an European network shows the relation between the ULF resonances in the inner magnetosphere and thermal plasma density variations during geomagnetically quiet conditions, in contrast to various storm phases at the end of the CAWSES campaign.

  1. Optical Observation of the Ionospheric-Magnetospheric Outflowing Oxygen Ions by XUV Onboard Sounding Rocket SS-520-2

    Science.gov (United States)

    Tashiro, S.; Yamazaki, A.; Yoshikawa, I.; Takizawa, Y.; Miyake, W.; Endo, M.; Nakamura, M.

    2001-12-01

    We built the Extreme ultraviolet scanner (XUV) for imaging oxygen ions to outflow from the polar ionosphere into the magnetosphere. The XUV onboard a sounding rocket SS-520-2 imaged the oxygen ions above 1000 km altitude near the polar cusp on December 4, 2000. The XUV is a normal incidence telescope that has a peak sensitivity at the wavelength 83.4 [nm] of OII emission and consists of a Mo coated mirror, a band pass filter and a channel electron multiplier. The band pass filter selectively transmits OII emission and eliminates background emissions such as HeI emission at the 30.4 [nm], HeII emission at the 58.4 [nm], and HI emission at the 121.6 [nm]. The observed OII emission intensity is proportional to the ion density integrated along the line of sight. Therefore The observed OII emission intensity distribution makes possible to determine the oxygen ion distribution. We will present the oxygen ion distribution and discuss the process and quantity of that ionospheric oxygen ions outflow into the magnetosphere.

  2. Optimizing an ELF/VLF Phased Array at HAARP

    Science.gov (United States)

    Fujimaru, S.; Moore, R. C.

    2013-12-01

    The goal of this study is to maximize the amplitude of 1-5 kHz ELF/VLF waves generated by ionospheric HF heating and measured at a ground-based ELF/VLF receiver. The optimization makes use of experimental observations performed during ELF/VLF wave generation experiments at the High-frequency Active Auroral Research Program (HAARP) Observatory in Gakona, Alaska. During these experiments, the amplitude, phase, and propagation delay of the ELF/VLF waves were carefully measured. The HF beam was aimed at 15 degrees zenith angle in 8 different azimuthal directions, equally spaced in a circle, while broadcasting a 3.25 MHz (X-mode) signal that was amplitude modulated (square wave) with a linear frequency-time chirp between 1 and 5 kHz. The experimental observations are used to provide reference amplitudes, phases, and propagation delays for ELF/VLF waves generated at these specific locations. The presented optimization accounts for the trade-off between duty cycle, heated area, and the distributed nature of the source region in order to construct a "most efficient" phased array. The amplitudes and phases generated by modulated heating at each location are combined in post-processing to find an optimal combination of duty cycle, heating location, and heating order.

  3. Oblique-incidence ionospheric soundings over Central Europe and their application for testing now casting and long term prediction models

    Science.gov (United States)

    Pietrella, M.; Perrone, L.; Fontana, G.; Romano, V.; Malagnini, A.; Tutone, G.; Zolesi, B.; Cander, Lj. R.; Belehaki, A.; Tsagouri, I.; Kouris, S. S.; Vallianatos, F.; Makris, J.; Angling, M.

    2009-06-01

    After a first oblique-incidence ionospheric sounding campaign over Central Europe performed during the period 2003-2004 over the radio links between Inskip (UK, 53.5°N, 2.5°W) and Rome (Italy, 41.8°N, 12.5°E) and between Inskip and Chania (Crete, 35.7°N, 24.0°E), new and more extensive analysis of systematic MUF measurements from January 2005 to December 2006 have been performed. MUF measurements collected during moderately disturbed days (17 ⩽ Ap ⩽ 32), disturbed days (32 50), have been used to test the long term prediction models (ASAPS, ICEPAC and SIRM&LKW), and the now casting models (SIRMUP&LKW and ISWIRM&LKW). The performances of the different prediction methods in terms of r.m.s are shown for selected range of geomagnetic activity and for each season.

  4. A Global Survey of ELF/VLF Radio Noise

    Science.gov (United States)

    2002-09-30

    Smith, 2002]. Finally, our participation in one of the HAARP experimental programs, during which we made much use of the ELF/VLF radio noise data...Porrat, Teague, and Fraser-Smith, 1999]. Our objective was to make the first long-distance detection of ELF signals generated by the HAARP ...ionospheric heater; we did not succeed, but the continuing improve- ments to the HAARP heating facility in Alaska will ultimately lead to the routine

  5. VLF signal anomalies dues to TS and Hurricanes

    Science.gov (United States)

    Nait Amor, Samir

    2017-04-01

    VLF signal propagates by multiples reflection in the Earth-Ionosphere wave guide. It constitutes a powerful tool to study the lower region of the ionosphere, the D region. This technique was applied to study perturbations related to the solar flares effect, TGF, the connection between TLEs and Early events.... In this contribution I will present a new results on the evidence of signal perturbations associated with TS and Hurricanes. A wavelet spectral analysis is applied to the signal amplitude to search for eventual Atmospheric Gravity wave which may be the origin of the signal perturbations.

  6. Ionospheric Effects of a Solar Eclipse of March 20, 2015 on Oblique Sounding Paths in the Eurasian Longitudinal Sector

    Science.gov (United States)

    Uryadov, V. P.; Kolchev, A. A.; Vybornov, F. I.; Shumaev, V. V.; Egoshin, A. I.; Chernov, A. G.

    2016-11-01

    The results of measuring HF signals on oblique chirp sounding paths in the Eurasian region during a solar eclipse of March 20, 2015 and the neighboring days are presented. The solar eclipse took place against the background of a strong magnetic storm. It was established that during the solar eclipse on oblique sounding paths of different length and orientation the decrease in the maximum observable frequency for the F mode (MOF-F) and the lowest observable frequency for the F mode (LOF-F) was 8-14% and 22-33%, respectively. During the eclipse, the signal amplitude increased by 3-5 dB. On the Lovozero—Nizhny Novgorod path in the maximum phase of the solar eclipse, the electron density decrease in the ionospheric E and F2 layers at the midpoint of the path reached 37% and 22%, respectively. According to the MOF and LOF variation measurements for various modes, the group delay time of radio signals, and the results of spectral analysis, it was found that in the eclipse there were wave disturbances with a period of 25 to 50 min. However, quasi-periodic variations of MOF-F and LOF-F having a a period of 50 to 80 min but which started before the eclipse were detected on some paths. Probably, in these cases, the variations were a result of the superposition of disturbances from two sources, namely, the magnetic storm and the solar eclipse.

  7. Combined operation of two ground transmitters for enhanced ionospheric heating

    Science.gov (United States)

    Lee, M. C.; Groves, K. M.; Liao, C. P.; Rivas, D. R.; Kuo, S. P.

    1988-01-01

    The combined operation of a high or medium frequency ground transmitter and a VLF transmitter for enhanced ionospheric heating is examined. The high or medium frequency transmitter operating in a pulsed mode produce short-scale density striations that can render the nonlinear mode conversion of the subsequently launched VLF waves into lower hybrid waves. Also if the VLF waves are intense enough, they can excite meter-scale density striations and lower hybrid waves via parametric instabilities. The expected ionospheric effects of the system are discussed.

  8. Test particle simulation of resonant interaction between energetic electrons in the magnetosphere and ELF/VLF waves generated by ionospheric modification%基于试验粒子模拟的电离层人工调制激发的极低频和甚低频波对磁层高能电子的散射效应

    Institute of Scientific and Technical Information of China (English)

    常珊珊; 倪彬彬; 赵正予; 汪枫; 李金星; 赵晶晶; 顾旭东; 周晨

    2014-01-01

    电离层调制加热能够有效激发极低频和甚低频(ELF/VLF)波,其中向上传播进入磁层的ELF/VLF波能够与高能电子发生共振相互作用,具有人工沉降高能电子、消除辐射带等潜在实际用途.本文综合运用射线追踪和试验粒子方法模拟电离层人工激发的单频ELF/VLF波在电离层和磁层的传播,以及在外辐射带层与高能电子的共振相互作用过程,通过投掷角和能量散射系数评估人工ELF/VLF波对磁层高能电子的共振散射效应.研究表明,电离层人工ELF/VLF波传播到磁层后呈现高倾斜性,传播所能跨域的空间范围主要取决于加热的纬度位置和调制频率.在内辐射带,与∼100 keV到几个MeV高能电子发生一阶共振相互作用的为>10 kHz的VLF波段;在外辐射带,为几百Hz到1 kHz的ELF波段.对于L=4.5的外辐射带,试验粒子模拟结果显示,单个粒子在人工ELF波作用下投掷角和能量(α, E )的改变具有随机性,而所有试验粒子平均化的∆α2和∆E2随时间呈现出近似线性的增大,说明波粒共振散射过程体现出整体性.基于试验粒子模拟得到的共振散射系数表明,幅度为10 pT的人工ELF波可在外辐射带的磁赤道局地对1 MeV电子产生较强的投掷角散射效应,进而影响高能电子的损失、沉降等动力学过程.当人工ELF/VLF波在传播过程中变得高度倾斜,不仅最基本的一阶共振十分重要,高阶共振散射也具有较大效应.这些定量分析结果表明,通过电离层加热激发人工ELF/VLF哨声波来沉降、消除辐射带高能电子具有可行性.%Ionospheric modulation can artificially trigger ELF/VLF whistler waves, which can leak into the inner magneto-sphere and contribute to resonant interactions with energetic electrons. Combining the ray tracing method and test particle simulations, we investigate the propagation of these artificially generated ELF/VLF waves

  9. Decrease of VLF transmitter signal and Chorus-whistler waves before l'Aquila earthquake occurrence

    Directory of Open Access Journals (Sweden)

    M. Y. Boudjada

    2010-07-01

    Full Text Available We investigate the VLF emissions observed by the Instrument Champ Electrique (ICE experiment onboard the DEMETER micro-satellite. We analyze intensity level variation 10 days before and after the occurrence of l'Aquila earthquake (EQ. We found a clear decrease of the VLF received signal related to ionospheric whistler mode (mainly Chorus emission and to signal transmitted by the DFY VLF station in Germany, few days (more than one week before the earthquake. The VLF power spectral density decreases of more than two orders of magnitude until the EQ, and it recovers to normal levels just after the EQ occurrence. The geomagnetic activity is principally weak four days before EQ and increases again one day before l'Aquila seismic event. Our results are discussed in the frame of short- and long-terms earthquakes prediction focusing on the crucial role of the magnetic field of the Earth.

  10. Prediction of the Nighttime VLF Subionospheric Signal Amplitude by Using Nonlinear Autoregressive with Exogenous Input Neural Network Model

    Science.gov (United States)

    Santosa, H.; Hobara, Y.; Balikhin, M. A.

    2015-12-01

    Very Low Frequency (VLF) waves have been proposed as an approach to study and monitor the lower ionospheric conditions. The ionospheric perturbations are identified in relation with thunderstorm activity, geomagnetic storm and other factors. The temporal dependence of VLF amplitude has a complicated and large daily variabilities in general due to combinations of both effects from above (space weather effect) and below (atmospheric and crustal processes) of the ionosphere. Quantitative contributions from different external sources are not known well yet. Thus the modelling and prediction of VLF wave amplitude are important issues to study the lower ionospheric responses from various external parameters and to also detect the anomalies of the ionosphere. The purpose of the study is to model and predict nighttime average amplitude of VLF wave propagation from the VLF transmitter in Hawaii (NPM) to receiver in Chofu (CHO) Tokyo, Japan path using NARX neural network. The constructed model was trained for the target parameter of nighttime average amplitude of NPM-CHO path. The NARX model, which was built based on daily input variables of various physical parameters such as stratosphere temperature, cosmic rays and total column ozone, possessed good accuracies. As a result, the constructed models are capable of performing accurate multistep ahead predictions, while maintaining acceptable one step ahead prediction accuracy. The results of the predicted daily VLF amplitude are in good agreement with observed (true) value for one step ahead prediction (r = 0.92, RMSE = 1.99), multi-step ahead 5 days prediction (r = 0.91, RMSE = 1.14) and multi-step ahead 10 days prediction (r = 0.75, RMSE = 1.74). The developed model indicates the feasibility and reliability of predicting lower ionospheric properties by the NARX neural network approach, and provides physical insights on the responses of lower ionosphere due to various external forcing.

  11. 100 Days of ELF/VLF Generation via HF Heating with HAARP (Invited)

    Science.gov (United States)

    Cohen, M.; Golkowski, M.

    2013-12-01

    ELF/VLF radio waves are difficult to generate with conventional antennas. Ionospheric HF heating facilities generate ELF/VLF waves via modulated heating of the lower ionosphere. HF heating of the ionosphere changes the lower ionospheric conductivity, which in the presence of natural currents such as the auroral electrojet, creates an antenna in the sky when heating is modulated at ELF/VLF frequencies. We present a summary of nearly 100 days of ELF/VLF wave generation experiments at the 3.6 MW HAARP facility near Gakona, Alaska, and provide a baseline reference of ELF/VLF generation capabilities with HF heating. Between February 2007 and August 2008, HAARP was operated on close to 100 days for ELF/VLF wave generation experiments, at a variety of ELF/VLF frequencies, seasons and times of day. We present comprehensive statistics of generated ELF/VLF magnetic fields observed at a nearby site, in the 500-3500 Hz band. Transmissions with a specific HF beam configuration (3.25 MHz, vertical beam, amplitude modulation) are isolated so the data comparison is self-consistent, across nearly 5 million individual measurements of either a tone or a piece of a frequency-time ramp. There is a minimum in the average generation close to local midnight. It is found that generation during local nighttime is on average weaker, but more highly variable, with a small number of very strong generation periods. Signal amplitudes from day to day may vary by as much as 20-30 dB. Generation strengthens by ~5 dB during the first ~30 minutes of transmission, which may be a signature of slow electron density changes from sustained HF heating. Theoretical calculations are made to relate the amplitude observed to the power injected into the waveguide and reaching 250 km. The median power generated by HAARP and injected into the waveguide is ~0.05-0.1 W in this base-line configuration (vertical beam, 3.25 MHz, amplitude modulation), but may have generated hundreds of Watts for brief durations

  12. DC electric field measurement in the mid-latitude ionosphere by S-520-26 sounding rocket in Japan

    Science.gov (United States)

    Ishisaka, K.; Suda, K.; Sugai, M.; Takahashi, T.; Yamamoto, M.; Abe, T.; Watanabe, S.

    2012-12-01

    S-520-26 sounding rocket experiment was carried out at Uchinoura Space Center (USC) in Japan at 5:51 JST on 12 January, 2012. The purpose of this experiment is the investigation of the bonding process between the atmospheres and the plasma in the thermosphere. S-520-26 sounding rocket reached to an altitude of 298 km 278 seconds after a launch. The S-520-26 payload was equipped with Electric Field Detector (EFD) with a two set of orthogonal double probes to measure both DC and AC less than 200 Hz electric fields in the spin plane of the payload by using the double probe method. One of the probes is the inflatable tube structure antenna, called the ITA, with a length of 5 m (tip-to-tip). And ITA is very lightweight (12.5g per one boom). The ITA extended and worked without any problems. It was the first successful use of an inflatable structure as a flight antenna. Another one is the ribbon antenna with a length of 2 m (tip-to-tip). The electrodes of two double probe antennas were used to gather the potentials which were detected with high impedance pre-amplifiers using the floating (unbiased) double probe technique. The potential differences on the two main orthogonal axes were digitized on-board using 16-bit analog-digital converter, sampled at 800 samples/sec with low pass filter at cut-off frequency of 200 Hz. Results of DC electric fields measured by the EFD have the large sine waves that result from the payload rotation at the spin period. The largest contribution to the electric field measurements by double probes moving through the ionosphere at mid-latitudes is that due to the v x B fields created by their motion across the ambient magnetic field, where v is the rocket velocity in the Earth-fixed reference frame and B is the ambient magnetic field. The sum of the squares of the two components represents the magnitude of the DC electric field in the spin plane of the payload. These data reveal abrupt, large-scale variations which can immediately be attributed

  13. Artificial Aurora and Ionospheric Heating by HAARP

    Science.gov (United States)

    Hadavandkhani, S.; Nikouravan, Bijan; Ghazimaghrebi, F.

    2016-08-01

    A recent experiment was achieved at HAARP to study the scaling of the ionospherically generated ELF signal with power transmitted from the high frequency (HF) array. The results were in excellent agreement with computer simulations. The outcomes approving that the ELF power increases with the square of the incident HF power. This paper present a review on the situation of the ionized particles in Ionospheric layer when stimulated by artificial an ELF and VLF external high energy radio waves.

  14. ELF/VLF wave disturbances detected by the DEMETER satellite over the HAARP transmitter

    Science.gov (United States)

    Titova, Elena; Demekhov, Andrei; Parrot, Michel; Mogilevsky, Mikhail; Mochalov, Alexey; Pashin, Anatoly

    We report observations of electromagnetic the ELF/VLF wave disturbances by the DEMETER satellite (670 km altitude) overflying the HAARP heating facility (62.39(°) N, 145.15(°) W, L = 4.9). The HAARP HF transmitter operated at the maximum available power of 3.6 MW, O-mode polarization, and the beam directed towards the magnetic zenith. ELF/VLF waves caused by the HAARP heating are detected by the DEMETER satellite when the HF radio wave frequency was close to the critical frequency (foF2) of the ionospheric F2 layer but below it. ELF/VLF wave disturbances observed above the HAARP transmitter were detected by electrical antennas in an area with characteristic size 10 (2) km. We analyze amplitude and polarization spectra of the ELF disturbances and compare them with the characteristics of natural ELF hiss above HAARP. The VLF wave disturbances in the topside ionosphere above the HAARP transmitter were detected in the frequency ranges 8-17 kHz and 15-18 kHz which are close to the lower hybrid resonance frequency f _LHR in the heating region and its second harmonic (2f _LHR), respectively. In the case where the HAARP HF power was modulated, the detected VLF waves were also modulated with the same frequency whereas in the ELF frequency range the modulation period of the HAARP power was not observed. Possible mechanisms of generation of the ELF/VLF disturbances produced by the HAARP transmitter in the topside ionosphere are discussed.

  15. One day prediction of nighttime VLF amplitudes using nonlinear autoregression and neural network modeling

    Science.gov (United States)

    Santosa, H.; Hobara, Y.

    2017-01-01

    The electric field amplitude of very low frequency (VLF) transmitter from Hawaii (NPM) has been continuously recorded at Chofu (CHF), Tokyo, Japan. The VLF amplitude variability indicates lower ionospheric perturbation in the D region (60-90 km altitude range) around the NPM-CHF propagation path. We carried out the prediction of daily nighttime mean VLF amplitude by using Nonlinear Autoregressive with Exogenous Input Neural Network (NARX NN). The NARX NN model, which was built based on the daily input variables of various physical parameters such as stratospheric temperature, total column ozone, cosmic rays, Dst, and Kp indices possess good accuracy during the model building. The fitted model was constructed within the training period from 1 January 2011 to 4 February 2013 by using three algorithms, namely, Bayesian Neural Network (BRANN), Levenberg Marquardt Neural Network (LMANN), and Scaled Conjugate Gradient (SCG). The LMANN has the largest Pearson correlation coefficient (r) of 0.94 and smallest root-mean-square error (RMSE) of 1.19 dB. The constructed models by using LMANN were applied to predict the VLF amplitude from 5 February 2013 to 31 December 2013. As a result the one step (1 day) ahead predicted nighttime VLF amplitude has the r of 0.93 and RMSE of 2.25 dB. We conclude that the model built according to the proposed methodology provides good predictions of the electric field amplitude of VLF waves for NPM-CHF (midlatitude) propagation path.

  16. Ground-based acoustic parametric generator impact on the atmosphere and ionosphere in an active experiment

    Science.gov (United States)

    Rapoport, Yuriy G.; Cheremnykh, Oleg K.; Koshovy, Volodymyr V.; Melnik, Mykola O.; Ivantyshyn, Oleh L.; Nogach, Roman T.; Selivanov, Yuriy A.; Grimalsky, Vladimir V.; Mezentsev, Valentyn P.; Karataeva, Larysa M.; Ivchenko, Vasyl. M.; Milinevsky, Gennadi P.; Fedun, Viktor N.; Tkachenko, Eugen N.

    2017-01-01

    We develop theoretical basics of active experiments with two beams of acoustic waves, radiated by a ground-based sound generator. These beams are transformed into atmospheric acoustic gravity waves (AGWs), which have parameters that enable them to penetrate to the altitudes of the ionospheric E and F regions where they influence the electron concentration of the ionosphere. Acoustic waves are generated by the ground-based parametric sound generator (PSG) at the two close frequencies. The main idea of the experiment is to design the output parameters of the PSG to build a cascade scheme of nonlinear wave frequency downshift transformations to provide the necessary conditions for their vertical propagation and to enable penetration to ionospheric altitudes. The PSG generates sound waves (SWs) with frequencies f1 = 600 and f2 = 625 Hz and large amplitudes (100-420 m s-1). Each of these waves is modulated with the frequency of 0.016 Hz. The novelty of the proposed analytical-numerical model is due to simultaneous accounting for nonlinearity, diffraction, losses, and dispersion and inclusion of the two-stage transformation (1) of the initial acoustic waves to the acoustic wave with the difference frequency Δf = f2 - f1 in the altitude ranges 0-0.1 km, in the strongly nonlinear regime, and (2) of the acoustic wave with the difference frequency to atmospheric acoustic gravity waves with the modulational frequency in the altitude ranges 0.1-20 km, which then reach the altitudes of the ionospheric E and F regions, in a practically linear regime. AGWs, nonlinearly transformed from the sound waves, launched by the two-frequency ground-based sound generator can increase the transparency of the ionosphere for the electromagnetic waves in HF (MHz) and VLF (kHz) ranges. The developed theoretical model can be used for interpreting an active experiment that includes the PSG impact on the atmosphere-ionosphere system, measurements of electromagnetic and acoustic fields, study of

  17. Characterisation of very low frequency (VLF) fluctuations at the Graz receiver knot in the INFREP system

    Science.gov (United States)

    Eichelberger, H. U.; Prattes, G.; Schwingenschuh, K.; Wolbang, D.; Boudjada, M. Y.; Rozhnoi, A.; Solovieva, M.; Biagi, P. F.; Maggipinto, T.; Stachel, M.; Jernej, I.; Aydogar, Ö.; Besser, B. P.

    2012-04-01

    In the frame of the European VLF/LF radio receiver network (International Network for Frontier Research on Earthquake Precursors - INFREP) we investigate radio paths between several transmitters and receivers, among them the Graz VLF facility. For this knot the data coverage spans more than two years of continuous samples from 11 transmitters with a network wide 20 seconds temporal resolution. The main scientific objective is the characterisation of VLF fluctuations in amplitude and phase related with artificial and natural sources, e.g. disturbances due to seismic phenomena. Examples of VLF disturbances due to seismic activity are given by Rozhnoi et al. (2009) and complementary investigations are carried out by Prattes et al. (2011). For VLF usually the (i) nighttime amplitude variations and (ii) terminator time methods are used. They have been regularly applied in data analysis of seismic events mainly in Asian area. Paths crossing the earthquake preparation zone and control links are used for earthquake events. Various VLF waveguide properties are important, e.g. the length of the individual paths, the lower lithospheric-surface boundary and the upper {day, night}-time ionospheric {D, E}-layer physics. Beside the nominal diurnal and seasonal behaviour we are measuring natural variations, e.g. solar flare effects and manmade noise, i.e. local disturbances related with the urban environment of the receiver location. Measurements indicate that above a threshold of magnitude M 5 the methods are successful applicable. We show for a time span of more than two years how VLF fluctuations and their seasonal variations relate with atmospheric parameters, e.g. temperatures, zonal wind, and heat- and momentum-fluxes and discuss the impact on seismic event detection via VLF methods. Complementary ground- and satellite-based investigations, e.g. in nearby ULF or LF frequency ranges, are useful.

  18. The investigation of ionospheric response to total eclipses on 29th March, 2006 and on 20th March, 2015 based on HF oblique sounding data

    Science.gov (United States)

    Vertogradov, G. G.; Vertogradova, E. G.

    2016-09-01

    The investigation of ionosphere response to solar eclipses was carried out. Maximum observable frequencies were analyzed during two eclipses on 29th March, 2006 and on 20th March, 2015 on several oblique sounding paths which were within the range of solar flux obscuration. The model describing local changes in the ionosphere, caused by the obscuration of solar flux during eclipse, is suggested. The computer simulation of HF radiowave propagation during the eclipses was carried out on the basis of this model, while quiet ionosphere was described by IRI-2012 model. It is shown that this approach gives adequate description of HF channel during eclipses for all propagation paths under consideration while the parameters of the model were the same for all paths. As the result of computer simulation time delays of ionosperic responses during eclipses were obtained (~1800-2000 s). It was found that maximum depletion of electron concentration reached 85% in D-region for both eclipses. The electron density depletions at height of F2-peak were 48% and 34% for eclipse on 29th March, 2006 and on 20th March, 2015 respectively.

  19. Stochastic properties of lower ionosphere as earthquake precursor

    Science.gov (United States)

    Šlégr, Jan; Váňová, Kamila

    2017-01-01

    Lower portion of the ionosphere known as the D-layer has properties of Gaussian random plane affecting very low frequency waves. This is manifested by stochastic properties of reflected VLF waves as their auto-correlation function (ACF) in time is the Bessel function of the first kind and zero order. In this paper, we show that the properties of this Bessel function are connected with the seismic activity in the area near the great circle path of VLF waves.

  20. Multifractal variability of Very Low Frequency (VLF) signal during Earthquakes (M greater than 5) occurred at Greece during the year 2011-2012

    Science.gov (United States)

    Sondhiya, Deepak Kumar; Gwal, Ashok Kumar; Verma, Shivali; Kasde, Satish Kumar; Sonakia, Anjana

    In this work Wavelet Transform Modulus Maxima (WTMM) based multifractal analysis method is used to extracts the earthquake precursory signatures from scaling characteristics of subionospheric Very Low Frequency (VLF) signals. We found specific dynamics of their fractal characteristics before the earthquake, appearance of the spike in the signal and increase of the fractal dimension. We analyze VLF signals of famous Turkey Bafa transmitter (N 370 24’, E 27019’) recorded by sudden Ionospheric Disturbance (SID) monitoring station located at South of France during the Earthquake occurred at Greece during the year 2011-2012. The analysis of VLF signal during some days before and after the occurrence of earthquake has been done. Keywords: Multifractal analysis, VLF signal, Sudden Ionospheric disturbances

  1. ELF and VLF radio waves

    Science.gov (United States)

    Barr, R.; Jones, D. L.; Rodger, C. J.

    2000-11-01

    This review covers developments in ELF and VLF radio-wave propagation research over the last 50 years of the Journal of Atmospheric and Solar-Terrestrial Physics. A review of such a large field, over such a long period, cannot be fully comprehensive and the authors have therefore covered important areas which have they themselves have found interesting. The survey begins with a review of work on natural and man made sources of ELF and VLF radiation. This is followed by sections on experimental and theoretical studies of unperturbed (ambient) ELF and VLF radio propagation. Schumann resonance research, which is currently undergoing a renaissance, is then reviewed. A review of research into transient perturbations of ELF and VLF propagation follows, extending from the early work on nuclear explosions up to the current work on sprites. The review concludes with a brief summary of the VLF navigation systems of the USSR and USA, (Alpha and Omega) whose development and life-span covered most of the last 50 years.

  2. The impact of PMSE and NLC particles on VLF propagation

    Directory of Open Access Journals (Sweden)

    D. Nunn

    2004-04-01

    Full Text Available PMSE or Polar Mesosphere Summer Echoes are a well-known phenomenon in the summer northern polar regions, in which anomalous VHF/UHF radar echoes are returned from heights ~85km. Noctilucent clouds and electron density biteouts are two phenomena that sometimes occur together with PMSE. Electron density biteouts are electron density depletion layers of up to 90%, which may be several kms thick. Using the NOSC Modefndr code based on Wait's modal theory for subionospheric propagation, we calculate the shifts in received VLF amplitude and phase that occur as a result of electron density biteouts. The code assumes a homogeneous background ionosphere and a homogeneous biteout layer along the Great Circle Path (GCP corridor, for transmitter receiver path lengths in the range of 500–6000km.

    For profiles during the 10h about midnight and under quiet geomagnetic conditions, where the electron density at 85km would normally be less than 500el/cc, it was found that received signal perturbations were significant, of the order of 1–4dB and 5–40° of phase. Perturbation amplitudes increase roughly as the square root of frequency. At short range perturbations are rather erratic, but more consistent at large ranges, readily interpretable in terms of the shifts in excitation factor, attenuation factor and v/c ratios for Wait's modes. Under these conditions such shifts should be detectable by a well constituted experiment involving multiple paths and multiple frequencies in the north polar region in summer. It is anticipated that VLF propagation could be a valuable diagnostic for biteout/PMSE when electron density at 85km is under 500el/cc, under which circumstances PMSE are not directly detectable by VHF/UHF radars.

    Key words. Electromagnetism (wave propagation – Ionosphere (polar ionosphere – Radioscience (ionospheric propagation

  3. 100 days of ELF/VLF generation via HF heating with HAARP

    Science.gov (United States)

    Cohen, M. B.; Gołkowski, M.

    2013-10-01

    Extremely low frequency/very low frequency (ELF/VLF) radio waves are difficult to generate with conventional antennas. Ionospheric high frequency (HF) heating facilities generate ELF/VLF waves via modulated heating of the lower ionosphere. HF heating of the ionosphere changes the lower ionospheric conductivity, which in the presence of natural currents such as the auroral electrojet creates an antenna in the sky when heating is modulated at ELF/VLF frequencies. We present a summary of nearly 100 days of ELF/VLF wave generation experiments at the 3.6 MW High Frequency Active Auroral Research Program (HAARP) facility near Gakona, Alaska, at a variety of ELF/VLF frequencies, seasons, and times of day. We present comprehensive statistics of generated ELF/VLF magnetic fields observed at a nearby site, in the 500-3500 Hz band. Transmissions with a specific HF beam configuration (3.25 MHz, vertical beam, amplitude modulation) are isolated so the data comparison is self-consistent, across nearly 5 million individual measurements of either a tone or a piece of a frequency-time ramp. There is a minimum in the average generation close to local midnight. It is found that generation during local nighttime is on average weaker but more highly variable, with a small number of very strong generation periods. Signal amplitudes from day to day may vary by as much as 20-30 dB. Generation strengthens by ˜5 dB during the first ˜30 min of transmission, which may be a signature of slow electron density changes from sustained HF heating. Theoretical calculations are made to relate the amplitude observed to the power injected into the waveguide and reaching 250 km. The median power generated by HAARP and injected into the waveguide is ˜0.05-0.1 W in this baseline configuration (vertical beam, 3.25 MHz, amplitude modulation) but may have generated hundreds of watts for brief durations. Several efficiency improvements have improved the ELF/VLF wave generation efficiency further.

  4. Comparative Analysis of VLF Signal Variation along Trajectory Induced by X-ray Solar Flares

    Indian Academy of Sciences (India)

    A. Kolarski; D. Grubor

    2015-12-01

    Comparative qualitative analysis of amplitude and phase delay variations was carried out along the trajectory of GQD/22.1 kHz and NAA/24.0 kHz VLF signal traces, propagating from Skelton (UK) and Maine (USA) toward Belgrade, induced by four isolated solar X-ray flare events occurred during the period from September 2005 to December 2006. For monitoring, recording and for storage of VLF data at the Institute of Physics in Belgrade, Serbia, the AbsPAL system was used. For modeling purposes of propagating conditions along GQD and NAA signal propagation paths, LWPCv21 program code was used. Occurred solar flare events induced lower ionosphere electron density height profile changes, causing perturbations in VLF wave propagation within Earth-ionosphere waveguides. As analyzed VLF signals characterize by different propagation parameters along trajectories from their transmitters to the Belgrade receiver site, their propagation is affected in different ways for different solar flare events and also for the same solar flare events.

  5. Comparative Analysis of VLF Signal Variation along Trajectory Induced by X-ray Solar Flares

    Science.gov (United States)

    Kolarski, A.; Grubor, D.

    2015-12-01

    Comparative qualitative analysis of amplitude and phase delay variations was carried out along the trajectory of GQD/22.1 kHz and NAA/24.0 kHz VLF signal traces, propagating from Skelton (UK) and Maine (USA) toward Belgrade, induced by four isolated solar X-ray flare events occurred during the period from September 2005 to December 2006. For monitoring, recording and for storage of VLF data at the Institute of Physics in Belgrade, Serbia, the AbsPAL system was used. For modeling purposes of propagating conditions along GQD and NAA signal propagation paths, LWPCv21 program code was used. Occurred solar flare events induced lower ionosphere electron density height profile changes, causing perturbations in VLF wave propagation within Earth-ionosphere waveguides. As analyzed VLF signals characterize by different propagation parameters along trajectories from their transmitters to the Belgrade receiver site, their propagation is affected in different ways for different solar flare events and also for the same solar flare events.

  6. Sound

    CERN Document Server

    Robertson, William C

    2003-01-01

    Muddled about what makes music? Stuck on the study of harmonics? Dumbfounded by how sound gets around? Now you no longer have to struggle to teach concepts you really don t grasp yourself. Sound takes an intentionally light touch to help out all those adults science teachers, parents wanting to help with homework, home-schoolers seeking necessary scientific background to teach middle school physics with confidence. The book introduces sound waves and uses that model to explain sound-related occurrences. Starting with the basics of what causes sound and how it travels, you'll learn how musical instruments work, how sound waves add and subtract, how the human ear works, and even why you can sound like a Munchkin when you inhale helium. Sound is the fourth book in the award-winning Stop Faking It! Series, published by NSTA Press. Like the other popular volumes, it is written by irreverent educator Bill Robertson, who offers this Sound recommendation: One of the coolest activities is whacking a spinning metal rod...

  7. Sound

    CERN Document Server

    2013-01-01

    Sound has the power to soothe, excite, warn, protect, and inform. Indeed, the transmission and reception of audio signals pervade our daily lives. Readers will examine the mechanics and properties of sound and provides an overview of the "interdisciplinary science called acoustics." Also covered are functions and diseases of the human ear.

  8. Lightning impact on micro-second long ionospheric variability

    Science.gov (United States)

    Koh, Kuang Liang; Liu, Zhongjian; Fullekrug, Martin

    2017-04-01

    Lightning discharges cause electron heating and enhanced ionisation in the D region ionosphere which disturb the transmission of VLF communications [Inan et al., 2010]. A disturbance of such nature was measured in a VLF transmission with a sampling rate of 1 MHz, enabling much faster ionospheric variability to be observed when compared to previous studies which typically report results with a time resolution >5-20ms. The disturbance resembles "Long Recovery Early VLF" (LORE) events [Haldoupis et al. 2013, Cotts & Inan 2007]. LOREs exhibit observable ionospheric effects that last longer (>200s) than other lightning related disturbances. It was proposed that the mechanism behind the long-lasting effects of LOREs is different to shorter events [Gordillo-Vázquez et al. 2016]. The ionospheric variability inferred from the transmitted signal is seen to change dramatically after the lightning onset, suggesting that there are fast processes in the ionosphere affected or produced which have not been considered in previous research. The ionospheric variability inferred from the main two frequencies of the transmission is different. A possible explanation is a difference in the propagation paths of the two main frequencies of the transmission [Füllekrug et al., 2015]. References Inan, U.S., Cummer, S.A., Marshall, R.A., 2010. A survey of ELF and VLF research on lightning-ionosphere interactions and causative discharges. J. Geophys. Res. 115, A00E36. doi:10.1029/2009JA014775 Cotts, B.R.T., Inan, U.S., 2007. VLF observation of long ionospheric recovery events. Geophys. Res. Lett. 34, L14809. doi:10.1029/2007GL030094 Haldoupis, C., Cohen, M., Arnone, E., Cotts, B., Dietrich, S., 2013. The VLF fingerprint of elves: Step-like and long-recovery early VLF perturbations caused by powerful ±CG lightning EM pulses. J. Geophys. Res. Space Physics 118, 5392-5402. doi:10.1002/jgra.50489 Gordillo-Vázquez, F.J., Luque, A., Haldoupis, C., 2016. Upper D region chemical kinetic modeling of

  9. Coordinated study of non-seismic and weak seismic events (magnitude M less than 5) using VLF radio links

    Science.gov (United States)

    Wolbang, Daniel; Biernat, Helfried K.; Friedrich, Martin; Schwingenschuh, Konrad; Besser, B. P.; Eichelberger, Hans; Prattes, Gustav; Rozhnoi, Alexander; Solovieva, Maria; Biagi, Pier Francesco; Boudjada, Mohammed Y.

    In this study we analyze low seismicity earthquakes (EQs) with magnitudes M earthquake precursor phenomena generated in the lithosphere and then propagating in the atmosphere / ionosphere [1]. The major challenge of this seismo-electromagnetic (SEM) method is to differentiate parameter variations and disentangle seismic from non-seismic sources. In the course of the European radio receiver network (International Network for Frontier Research on Earthquake Precursors, INFREP) radio signals in the VLF/LF frequency range are continuously recorded by dedicated, distributed transmitters. The major VLF receiving station for this study (10-50 kHz, Graz, Austria) operates continuously throughout the year, the selected network-wide temporal resolution is 20 sec, 12 transmitters, located mainly in Europe, are received (amplitude and phase). The facility has a proven high reliability and availability. The VLF links from the transmitters to the receivers are sometimes more, sometimes less influenced by various disturbances. In case the signal is crossing an EQ preparation zone, we are in principle able to detect seismic activity if the signal to noise ratio is high enough [2]. Generally we distinguish between ionospheric or atmospheric disturbances, influences which depend on the EQ properties, and transmitter variations itself. Ionospheric / Atmospheric variations can be generated, e.g. by geomagnetic storms, solar flares or waves in the troposphere. The properties of the sub-ionospheric VLF waveguide are affected by the length of the radio path, the distance to the EQ preparation zone, the parameters of the earthquake (magnitude, depth, type), and daytime / nighttime disturbances. In order to minimize ionospheric influences on the radio path we are considering mainly nighttime periods. Beside the terminator time method, where only the VLF sunrise and sunset period is analyzed, we are using the residual method (2 hours before and after local midnight), where the difference

  10. Dynamics and structure of the vertical ionospheric disturbances caused by Tohoku earthquake according to Irkutsk bistatic CHIRP-sounding

    Science.gov (United States)

    Berngardt, Oleg; Kotovich, Galina; Podlesnyi, Alexey

    In the work we present results of observation of the mid-scale vertical ionospheric irregularities caused by Tohoku earthquake with 1 minute temporary resolution. Their spatial and temporary dynamics is also investigated. The main instrument used in the analysis is bistatic CHIRP-sounder of own development of ISTP SB RAS. The CHIRP-sounder provides frequency change speed up to 1000 kHz/sec, and provides 1 minute temporal resolution, comparable with SuperDARN radars and GPS receivers network. The receiver and the transmitter of the sounder are located close to Irkutsk (52N,104E) at distance 120 km between each other. Synchronization of time and frequency is provided by GPS. As showed the analysis of the experimental data, the main response of the ionosphere was observed at Irkutsk from 06:10 to 07:00UT. Short-term variations of the electron density profile were also observed from 06:00UT. This corresponds to the main horizontal speed of disturbances about 2500 m/s and below. The vertical scale of the irregularities was 10-20 km. Irregularities practically weren't observed at heights above 200km. The obtained data don't contradict the data obtained by other researchers. Work was done under financial support of IV.12.2 OFN Russian Academy of Sciences program.

  11. Monitoring of Sudden Ionospheric Disturbances (SID) from Kolkata (INDIA)

    CERN Document Server

    Chakrabarti, S K; Bose, B; Mandal, S; Chatterjee, A; Nandi, N M; Pal, S; Khan, R; Chakrabarti, Sandip K.

    2003-01-01

    We report our first results of monitoring sudden ionospheric disturbances (SID). We present data taken continuously for two weeks during 20th Sept. 2002 and 4th Oct. 2002. We compare the effects of solar flares of the VLF signal with those obtained by GOES Satellite of NASA monitoring in X-rays and found excellent agreement.

  12. Global effects on Ionospheric Weather over the Indian subcontinent at Sunrise and Sunset

    Science.gov (United States)

    Basak, Tamal; Chakrabarti, S. K.; Pal, S.

    2010-10-01

    Study of Very Low Frequency (VLF) electromagnetic wave is very important for knowing the behavior of the Ionospheric layers due to Sunrise-Sunset, Earthquakes, Solar flares, Solar eclipses and other terrestrial and extra terrestrial radiations. We study the properties of the variation of the VLF signal strength theoretically all over Indian sub-continent. As an example, we concentrate on the VLF signal transmitted by Indian Naval Transmitter VTX at Vijayanarayanam (Latitude 08°23', Longitude 77°45') near the southern tip of Indian subcontinent. As has been noticed, several receiving stations placed during the VLF campaign in all over India, the VLF signal strength varies significantly with place and time. To understand the diurnal and seasonal variation of the received signal, a complete knowledge of physics of intensity distribution of the VLF signal is essential. The spatial variation of VLF signal plays an important role in selecting future VLF stations. In the wave-hop theoretical model presented here, horizontally stratified ionospheric layers have been considered. The VLF wave emitted by the transmitter has both the ground wave and the sky wave components. The ground wave attenuates during propagation. The sky wave component experiences reflections by the ionosphere on its way to the receiver and its attenuation depends on the degree of ionization. Intensity variation occurs at a given receiver location for interference among singly and multiply reflected waves. This has been simulated considering some simplified and justifiable assumptions. This spatial variation wave-hop theoretical model developed here has been compared with LWPC code generated results.

  13. Development of ground-based ELF/VLF receiver system in Wuhan and its first results

    Science.gov (United States)

    Chen, Yanping; Yang, Guobin; Ni, Binbin; Zhao, Zhengyu; Gu, Xudong; Zhou, Chen; Wang, Feng

    2016-05-01

    A new digital low-frequency receiver system has been developed at Wuhan University for sensitive reception of low-latitude broadband Extremely Low Frequency (ELF) and Very Low Frequency (VLF) radio waves originating from either natural or artificial sources. These low-frequency radio waves are useful for ionospheric remote sensing, geospace environment monitoring, and submarine communications. This paper presents the principle and architecture of the system framework, including magnetic loop antenna design, low-noise analog front-end and digital receiver with data sampling and transmission. A new structure is adopted in the analog front end to provide high common-mode rejection and to reduce interference. On basis of field programmable gate array (FPGA) device and Universal Serial Bus (USB) architecture, the digital receiver is developed along with time keeping and synchronization module. The validity and feasibility of the self-developed ground-based ELF/VLF receiver system is evaluated by first results of experimental data that show the temporal variation of broadband ELF/VLF wave spectral intensity in Wuhan (30.54 °N, 114.37 °E). In addition to the acquisition of VLF transmitter signals at various frequencies, tweek atmospherics are also clearly captured to occur at multiple modes up to n = 6.

  14. Lightning Location With Single-Station Observation of VLF Spherics

    Science.gov (United States)

    Nagano, I.; Yagitani, S.; Komonmae, H.; Takezono, N.

    2001-12-01

    Most of the lightning location systems recently available require the simultaneous reception of lightning-generated radio pulses (spherics) at multiple stations. In this work, we develop a lightning location system to determine both the direction and range of a lightning stroke with a single-station observation of VLF spherics. The technique used here is a rather classical one, but we try to improve the ranging accuracy by applying sophisticated signal processing techniques, and our final goal is to develop a portable lightning locator. We observe wave forms of two horizontal magnetic fields and one vertical electric field of VLF spherics, each of which usually consists of a couple of sequential pulses. The first pulse comes directly from a lightning return stroke, and is used for the direction finding of the stroke. On the other hand, the second and later pulses are the multiple reflections of the first pulse inside the Earth-ionosphere waveguide. Since the time-of-arrival (ToA) of each pulse is determined by its propagation path length in the waveguide, by using the observed difference in ToA of two or more pulses, we can inversely estimate not only the reflection height at the ionosphere but also the range of the lightning stroke. By installing the developed system at Kanazawa University, we have been observing lightning-generated spherics since April, 2000. Compared with the lightning location data provided by a local power company, preliminary analysis shows that this system can locate each lightning stroke within several hundred km with a sufficient accuracy.

  15. ELF/VLF/LF Radio Propagation and Systems Aspects (La Propagation des Ondes Radio ELF/VLF/LF et les Aspects Systemes)

    Science.gov (United States)

    1993-05-01

    Umime 11uld sb’ngft R11111M fgM 7-1 INVESTIGATIONS OF EQUATORIAL IONOSPHERE NIGHTTIME MODE CONVERSION AT VLF* Verne Hildebrand IWG Corporation, 1940 Fifth...uniform, Symposium), supposing that has an length equal to Ŗa" and it is MIT, Cambridge oriented on the zz direction (fig.8). USA, Julio 1991 Let us...about 10 to 14 years. My from the floor, would someone like to start off? own experience as a systems engineer is that Verne Hildebrand the systems have

  16. A comparative study of measured amplitude and phase perturbations of VLF and LF radio signals induced by solar flares

    Directory of Open Access Journals (Sweden)

    Šulić D.M.

    2014-01-01

    Full Text Available Very Low Frequency (VLF and Low Frequency (LF signal perturbations were examined to study ionospheric disturbances induced by solar X-ray flares in order to understand processes involved in propagation of VLF/LF radio signals over short paths and to estimate specific characteristics of each short path. The receiver at the Belgrade station is constantly monitoring the amplitude and phase of a coherent and subionospherically propagating LF signal operated in Sicily NSC at 45.90 kHz, and a VLF signal operated in Isola di Tavolara ICV at 20.27 kHz, with the great circle distances of 953 km and 976 km, respectively. A significant number of similarities between these short paths is a direct result of both transmitters and the receiver’s geographic location. The main difference is in transmitter frequencies. From July 2008 to February 2014 there were about 200 events that were chosen for further examination. All selected examples showed that the amplitude and phase of VLF and LF signals were perturbed by solar X-ray flares occurrence. This six-year period covers both minimum and maximum of solar activity. Simultaneous measurement of amplitude and phase of the VLF/LF signals during a solar flare occurrence was applied to evaluate the electron density profile versus altitude, to carry out the function of time over the middle Europe. [Projekat Ministarstva nauke Republike Srbije, br. 176002 i br. III4402

  17. Ionospheric response over Europe during the solar eclipse of March 20, 2015

    Science.gov (United States)

    Hoque, Mohammed Mainul; Wenzel, Daniela; Jakowski, Norbert; Gerzen, Tatjana; Berdermann, Jens; Wilken, Volker; Kriegel, Martin; Sato, Hiroatsu; Borries, Claudia; Minkwitz, David

    2016-10-01

    The solar eclipse on March 20, 2015 was a fascinating event for people in Northern Europe. From a scientific point of view, the solar eclipse can be considered as an in situ experiment on the Earth's upper atmosphere with a well-defined switching off and on of solar irradiation. Due to the strong changes in solar radiation during the eclipse, dynamic processes were initiated in the atmosphere and ionosphere causing a measurable impact, for example, on temperature and ionization. We analyzed the behavior of total ionospheric ionization over Europe by reconstructing total electron content (TEC) maps and differential TEC maps. Investigating the large depletion zone around the shadow spot, we found a TEC reduction of up to 6 TEC units, i.e., the total plasma depletion reached up to about 50%. However, the March 20, 2015 eclipse occurred during the recovery phase of a strong geomagnetic storm and the ionosphere was still perturbed and depleted. Therefore, the unusual high depletion is due to the negative bias of up to 20% already observed over Northern Europe before the eclipse occurred. After removing the negative storm effect, the eclipse-induced depletion amounts to about 30%, which is in agreement with previous observations. During the solar eclipse, ionospheric plasma redistribution processes significantly affected the shape of the electron density profile, which is seen in the equivalent slab thickness derived by combining vertical incidence sounding (VS) and TEC measurements. We found enhanced slab thickness values revealing, on the one hand, an increased width of the ionosphere around the maximum phase and, on the other, evidence for delayed depletion of the topside ionosphere. Additionally, we investigated very low frequency (VLF) signal strength measurements and found immediate amplitude changes due to ionization loss at the lower ionosphere during the eclipse time. We found that the magnitude of TEC depletion is linearly dependent on the Sun's obscuration

  18. Ionospheric response over Europe during the solar eclipse of March 20, 2015

    Directory of Open Access Journals (Sweden)

    Hoque Mohammed Mainul

    2016-01-01

    Full Text Available The solar eclipse on March 20, 2015 was a fascinating event for people in Northern Europe. From a scientific point of view, the solar eclipse can be considered as an in situ experiment on the Earth’s upper atmosphere with a well-defined switching off and on of solar irradiation. Due to the strong changes in solar radiation during the eclipse, dynamic processes were initiated in the atmosphere and ionosphere causing a measurable impact, for example, on temperature and ionization. We analyzed the behavior of total ionospheric ionization over Europe by reconstructing total electron content (TEC maps and differential TEC maps. Investigating the large depletion zone around the shadow spot, we found a TEC reduction of up to 6 TEC units, i.e., the total plasma depletion reached up to about 50%. However, the March 20, 2015 eclipse occurred during the recovery phase of a strong geomagnetic storm and the ionosphere was still perturbed and depleted. Therefore, the unusual high depletion is due to the negative bias of up to 20% already observed over Northern Europe before the eclipse occurred. After removing the negative storm effect, the eclipse-induced depletion amounts to about 30%, which is in agreement with previous observations. During the solar eclipse, ionospheric plasma redistribution processes significantly affected the shape of the electron density profile, which is seen in the equivalent slab thickness derived by combining vertical incidence sounding (VS and TEC measurements. We found enhanced slab thickness values revealing, on the one hand, an increased width of the ionosphere around the maximum phase and, on the other, evidence for delayed depletion of the topside ionosphere. Additionally, we investigated very low frequency (VLF signal strength measurements and found immediate amplitude changes due to ionization loss at the lower ionosphere during the eclipse time. We found that the magnitude of TEC depletion is linearly dependent on the

  19. Building and Testing a Portable VLF Receiver

    Science.gov (United States)

    McLaughlin, Robert; Krause, L.

    2014-01-01

    Unwanted emissions or signal noise is a major problem for VLF radio receivers. These can occur from man made sources such as power line hum, which can be prevalent for many harmonics after the fundamental 50 or 60 Hz AC source or from VLF radio transmissions such as LORAN, used for navigation and communications. Natural emissions can also be detrimental to the quality of recordings as some of the more interesting natural emissions such as whistlers or auroral chorus may be drowned out by the more common sferic emissions. VLF receivers must selectively filter out unwanted emissions and amplify the filtered signal to a record-able level without degrading the quality.

  20. Diagnostics of plasma in the ionospheric D-region: detection and study of different ionospheric disturbance types

    Science.gov (United States)

    Nina, Aleksandra; Čadež, Vladimir M.; Popović, Luka Č.; Srećković, Vladimir A.

    2017-07-01

    Here we discuss our recent investigations of the ionospheric plasma by using very low and low frequency (VLF/LF) radio waves. We give a review of how to detect different low ionospheric reactions (sudden ionospheric disturbances) to various terrestrial and extra-terrestrial events, show their classification according to intensity and time duration, and present some methods for their detections in time and frequency domains. Investigations of detection in time domain are carried out for intensive long-lasting perturbations induced by solar X-ray flares and for short-lasting perturbations caused by gamma ray bursts. We also analyze time variations of signals used in the low ionospheric monitoring after earthquake events. In addition, we describe a procedure for the detection of acoustic and gravity waves from the VLF/LF signal analysis in frequency domain. The research of the low ionospheric plasma is based on data collected by the VLF/LF receivers located in Belgrade, Serbia. Contribution to the Topical Issue "Physics of Ionized Gases (SPIG 2016)", edited by Goran Poparic, Bratislav Obradovic, Dragana Maric and Aleksandar Milosavljevic.

  1. On the occurrence of ground observations of ELF/VLF magnetospheric amplification induced by the HAARP facility

    OpenAIRE

    İnan, Umran Savaş; Golkowski, M.; Cohen, M. B.; Carpenter, D. L.

    2011-01-01

    The ionospheric heating facility of the High Frequency Active Auroral Research Program (HAARP) has been used extensively in the last 3 years for injection of ELF/VLF waves into the magnetosphere via modulated heating of the overhead auroral electrojet currents. Of particular interest are waves that are observed to be nonlinearly amplified after interaction with hot plasma electrons in the Earth's radiation belts. Past results have shown HAARP to be an effective platform for controlled studies...

  2. VLF/LF Reflectivity of the Polar Ionosphere.

    Science.gov (United States)

    1980-06-01

    APPROVED: dk EDW1AD A. LEWIS Propagation Branch Electromagnetic Sciences Division APPROVED: ALLAN ~ C. SCHELL, Chief Electromagnetic Sciences Division...o0o o.s D ’ o~oo, 0l0 C’~3JI~0J .OIC U3 ’. - C,~jJ~jO~ .0t~]~3~ (0,cc 0 0 C? * v ocl )JI Cno f -oi i on i idw0 P Pt pop Poe e P-p. opt d73 S * A K A

  3. Microprocessor implementation of an FFT for ionospheric VLF observations

    Science.gov (United States)

    Elvidge, J.; Kintner, P.; Holzworth, R.

    1984-01-01

    A fast Fourier transform algorithm is implemented on a CMOS microprocessor for application to very low-frequency electric fields (less than 10 kHz) sensed on high-altitude scientific balloons. Two FFT's are calculated simultaneously by associating them with conjugate symmetric and conjugate antisymmetric results. One goal of the system was to detect spectral signatures associated with fast time variations present in natural signals such as whistlers and chorus. Although a full evaluation of the system was not possible for operational reasons, a measure of the system's success has been defined and evaluated.

  4. Modulation of auroral electrojet currents using dual modulated HF beams with ELF phase offset, a potential D-region ionospheric diagnostic

    Science.gov (United States)

    GołKowski, M.; Cohen, M. B.; Moore, R. C.

    2013-05-01

    Experiments at the ionospheric heating facility of the High Frequency Active Auroral Research Program (HAARP) are performed employing dual HF beams amplitude modulated at ELF/VLF with a phase offset between the two modulation waveforms. The amplitude of the observed ELF/VLF waves is strongly dependent on the imposed ELF/VLF phase offset, the modulation waveform, and the orientation of the HF beams. Data from two ground stations are interpreted using simulations of modulated heating power envelopes as well as a comprehensive model of ionospheric ELF/VLF generation. It is found that two colocated vertical beams HF beams excite a single ionospheric ELF/VLF source, but independent ELF/VLF sources can be induced in the ionospheric region above the heater if the HF beams are offset from zenith to intersect at their 3 dB points. Furthermore, the use of two vertical HF beams with ELF phase offset is found to be a potential diagnostic method for the ionospheric D region.

  5. Whistler propagation in ionospheric density ducts: Simulations and DEMETER observations

    Science.gov (United States)

    Woodroffe, J. R.; Streltsov, A. V.; Vartanyan, A.; Milikh, G. M.

    2013-11-01

    On 16 October 2009, the Detection of Electromagnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite observed VLF whistler wave activity coincident with an ionospheric heating experiment conducted at HAARP. At the same time, density measurements by DEMETER indicate the presence of multiple field-aligned enhancements. Using an electron MHD model, we show that the distribution of VLF power observed by DEMETER is consistent with the propagation of whistlers from the heating region inside the observed density enhancements. We also discuss other interesting features of this event, including coupling of the lower hybrid and whistler modes, whistler trapping in artificial density ducts, and the interference of whistlers waves from two adjacent ducts.

  6. Production of Ionospheric Perturbations by Cloud-to-Ground Lightning and the Recovery of the Lower Ionosphere

    Science.gov (United States)

    Liu, Ningyu; Dwyer, Joseph; Rassoul, Hamid

    2013-04-01

    The fact that lightning/thunderstorm activities can directly modify the lower ionosphere has long been established by observations of the perturbations of very low frequency (VLF) signals propagating in the earth-ionosphere waveguide. These perturbations are known as early VLF events [Inan et al., 2010, JGR, 115, A00E36, 2010]. More recently discovered transient luminous events caused by the lightning/thunderstorm activities only last ~1-100 ms, but studies of the early VLF events show that the lightning ionospheric effects can persist much longer, >10s min [Cotts and Inan, GRL, 34, L14809, 2007; Haldoupis et al., JGR, 39, L16801, 2012; Salut et al., JGR, 117, A08311, 2012]. It has been suggested that the long recovery is caused by long-lasting conductivity perturbations in the lower ionosphere, which can be created by sprites/sprite halos which in turn are triggered by cloud-to-ground (CG) lightning [Moore et al., JGR, 108, 1363, 2003; Haldoupis et al., 2012]. We recently developed a two-dimensional fluid model with simplified ionospheric chemistry for studying the quasi-electrostatic effects of lightning in the lower ionosphere [Liu, JGR, 117, A03308, 2012]. The model chemistry captures major ion species and reactions in the lower ionosphere. Additional important features of the model include self-consistent background ion density profiles and full description of electron and ion transport. In this talk, we present the simulation results on the dynamics of sprite halos caused by negative CG lightning. The modeling results indicate that electron density around 60 km altitude can be enhanced in a region as wide as 80 km. The enhancement reaches its full extent in ~1 s and recovers in 1-10 s, which are on the same orders as the durations of slow onset and post-onset peaks of some VLF events, respectively. In addition, long-lasting electron and ion density perturbations can occur around 80 km altitude due to negative halos as well as positive halos, which can explain

  7. Terrestrial VLF transmitter injection into the magnetosphere

    OpenAIRE

    2012-01-01

    Terrestrial VLF transmitter injection into the magnetosphere M. B. Cohen1 and U. S. Inan1,2 Received 1 June 2012; revised 15 June 2012; accepted 18 June 2012; published 9 August 2012. [1] Very Low Frequency (VLF, 3–30 kHz) radio waves emitted from ground sources (transmitters and lightning) strongly impact the radiation belts, driving electron precipitation via whistler-electron gyroresonance, and contributing to the formation of the slot region. However, calculations of the...

  8. C/NOFS-VEFI results on magnetic-latitude control over coupling of lightning-generated VLF into zero-hop whistlers

    Science.gov (United States)

    Jacobson, A. R.; Holzworth, R.; Pfaff, R. F., Jr.; Heelis, R. A.

    2016-12-01

    The C/NOFS satellite had a low-inclination (13 deg) orbit and provided multi-year observations (2008 - 2015) of the innermost plasmasphere within 26 deg of the magnetic equator. We report on VEFI (Vector Electric Field Instrument) recordings of zero-hop whistler-wave electric fields in this low-latitude region. We describe evidence regarding the VLF coupling variabilities, in particular versus magnetic latitude. We rely critically on data provided by the CINDI (C/NOFS Ion and Neutral Drift Investigation) measurements of the ion-composition, and by WWLLN (World-Wide Lightning-Location Network) groundtruthing of lightning-VLF source location, energy, and time. This low-latitude region has been predicted to permit only reduced VLF coupling, due essentially to a Snell's Law total reflection from the underside of the ionosphere. Nonetheless various studies of VLF coupling at discrete frequencies (from naval VLF transmitters) indicate that there is some intermittent, anomalous coupling not predicted by a simple Snell's Law. We address this problem using broadband illumination by lightning-generated VLF.

  9. Characteristics of VLF wave propagation in the Earth's magnetosphere in the presence of an artificial density duct

    Science.gov (United States)

    Pasmanik, Dmitry; Demekhov, Andrei

    We study the propagation of VLF waves in the Earth's ionosphere and magnetosphere in the presence of large-scale artificial plasma inhomogeneities which can be created by HF heating facilities like HAARP and ``Sura''. A region with enhanced cold plasma density can be formed due to the action of HF heating. This region is extended along geomagnetic field (up to altitudes of several thousand km) and has rather small size across magnetic field (about 1 degree). The geometric-optical approximation is used to study wave propagation. The plasma density and ion composition are calculated with the use of SAMI2 model, which was modified to take the effect of HF heating into account. We calculate ray trajectories of waves with different initial frequency and wave-normal angles and originating at altitudes of about 100 km in the region near the heating area. The source of such waves could be the lightning discharges, modulated HF heating of the ionosphere, or VLF transmitters. Variation of the wave amplitude along the ray trajectories due to refraction is considered and spatial distribution of wave intensity in the magnetosphere is analyzed. We show that the presence of such a density disturbances can lead to significant changes of wave propagation trajectories, in particular, to efficient guiding of VLF waves in this region. This can result in a drastic increase of the VLF-wave intensity in the density duct. The dependence of wave propagation properties on parameters of heating facility operation regime is considered. We study the variation of the spatial distribution of VLF wave intensity related to the slow evolution of the artificial inhomogeneity during the heating.

  10. Observation of Sudden Ionospheric Disturbances over Istanbul in Response to X-Ray Flare Events

    Science.gov (United States)

    Ceren Kalafatoglu Eyiguler, Emine; Kaymaz, Zerefsan; Ceren Moral, Aysegul

    2016-07-01

    Sudden ionospheric disturbances (SID) are the enhanced electron density structures in the D region ionosphere which occur in response to the increase in X-ray flares and EUV flux. SIDs can be monitored using Very Low Frequency (VLF) radio signals (3-30 kHz) which travel between the D-region and the surface of the Earth. In this study, we use SID monitors obtained from the Stanford University Solar Center and two antennas which were built at the Istanbul Technical University to track the ionospheric disturbances in the VLF range. Our antennas are capable of capturing signals from several VLF transmitting stations. In this work, we focus on the variations in the signal strength of the closest VLF transmitting station 'TBB' which is operating at 26.7 kHz frequency at BAFA, Turkey (37.43N, 27.15E). We present ITU SID observations from both antennas; show the daily variation, general structure and the typical patterns we observe as well as case studies of significant events. Our initial analysis shows close relationship between observed X-ray flares from geosynchronous GOES 13 and GOES 15 satellites and VLF station signal strength received by the monitors.

  11. Unusually high frequency natural VLF radio emissions observed during daytime in Northern Finland

    Science.gov (United States)

    Manninen, Jyrki; Turunen, Tauno; Kleimenova, Natalia; Rycroft, Michael; Gromova, Liudmila; Sirviö, Iina

    2016-12-01

    Geomagnetic field variations and electromagnetic waves of different frequencies are ever present in the Earth’s environment in which the Earth’s fauna and flora have evolved and live. These waves are a very useful tool for studying and exploring the physics of plasma processes occurring in the magnetosphere and ionosphere. Here we present ground-based observations of natural electromagnetic emissions of magnetospheric origin at very low frequency (VLF, 3-30 kHz), which are neither heard nor seen in their spectrograms because they are hidden by strong impulsive signals (sferics) originating in lightning discharges. After filtering out the sferics, peculiar emissions are revealed in these digital recordings, made in Northern Finland, at unusually high frequencies in the VLF band. These recently revealed emissions, which are observed for several hours almost every day in winter, contain short (˜1-3 min) burst-like structures at frequencies above 4-6 kHz, even up to 15 kHz; fine structure on the 1 s time scale is also prevalent. It seems that these whistler mode emissions are generated deep inside the magnetosphere, but the detailed nature, generation region and propagation behaviour of these newly discovered high latitude VLF emissions remain unknown; however, further research on them may shed new light on wave-particle interactions occurring in the Earth’s radiation belts.

  12. ALTAIR Radar Plasma Drifts and in situ Electric and Magnetic Field Measurements on Two Sounding Rockets and the C/NOFS Satellite in the Low Latitude Ionosphere at Sunset

    Science.gov (United States)

    Kudeki, Erhan; Pfaff, Robert; Rowland, Douglas; Klenzing, Jeffrey; Freudenreich, Henry

    2016-07-01

    We present ALTAIR incoherent scatter radar plasma drifts and in situ electric field, magnetic field, and plasma density measurements made simultaneously with probes on two sounding rockets and the C/NOFS satellite in the low latitude ionosphere in the vicinity of Kwajalein Atoll. The coincident data were gathered during sunset conditions prior to a spread-F event during the NASA EVEX Campaign. The sounding rocket apogees were 180 km and 330 km, while the C/NOFS altitude in this region was ~ 390 km. Electric field data from all three platforms display upwards vertical plasma drifts, while the zonal drifts change direction as a function of altitude and/or local time. The variable drifts provide evidence of a dynamic plasma environment which may contribute to the unstable conditions necessary for spread-F instabilities to form.

  13. Full-wave model of D-region upward VLF coupling to whistlers in the plasmasphere

    Science.gov (United States)

    Jacobson, A. R.; Shao, X.; Lay, E. H.

    2012-12-01

    Atmospheric-lightning-to-plasmasphere VLF coupling via whistlers is key to understanding the problem of radiation-belt losses and the slot region. In the lowermost ionosphere, the "D-region" (roughly 60 - 100 km altitude), the coupling occurs between the VLF incident from the "vacuum" below, to the electron whistler capable of transiting upward through the E- and F-regions above. We have modified our successful and data-validated D-region VLF downward-reflection model to predict upward-coupled whistler waveforms recorded on topside satellites. The model has been run in production mode for predicting downward-reflected waveforms recorded at ground stations, but the model's internal calculation also fully describes the "penetrating" solution that merges into the oblique electron whistler. We have begun to test the model against VLF, three-dimensional electric-field recordings from the Vector Electric Field Instrument (VEFI) [Pfaff et al., 2010] on the C/NOFS satellite. VEFI's broadband recording and large on-board memory serendipitously provide an excellent platform for studying lightning whistlers in the plasmasphere. We have already demonstrated [Jacobson et al., 2011] that VEFI is superbly suited for testing transionospheric propagation, in conjunction with the World Wide Lightning Location Network (WWLLN; see www.wwlln.net) to provide groundtruth location/time of the lightning strokes. This poster will describe latest results. Jacobson, A. R., R. H. Holzworth, R. F. Pfaff, and M. P. McCarthy (2011), Study of oblique whistlers in the low-latitude ionosphere, jointly with the C/NOFS satellite and the World-Wide Lightning Location Network, Annales Geophysicae, 29, 851-863. Pfaff, R., D. Rowland, H. Freudenreich, K. Bromund, K. Le, M. Acuna, J. Klenzing, C. Liebrecht, S. Martin, W. J. Burke, N. C. Maynard, D. E. Hunton, P. A. Roddy, J. O. Ballenthin, and G. R. Wilson (2010), Observations of DC electric fields in the low-latitude ionosphere and their variations with

  14. Characteristics of VLF/LF Sferics from Elve-producing Lightning Discharges

    Science.gov (United States)

    Blaes, P.; Zoghzoghy, F. G.; Marshall, R. A.

    2013-12-01

    Lightning return strokes radiate an electromagnetic pulse (EMP) which interacts with the D-region ionosphere; the largest EMPs produce new ionization, heating, and optical emissions known as elves. Elves are at least six times more common than sprites and other transient luminous events. Though the probability that a lightning return stroke will produce an elve is correlated with the return stroke peak current, many large peak current strokes do not produce visible elves. Apart from the lightning peak current, elve production may depend on the return stroke speed, lightning altitude, and ionospheric conditions. In this work we investigate the detailed structure of lightning that gives rise to elves by analyzing the characteristics of VLF/LF lightning sferics in conjunction with optical elve observations. Lightning sferics were observed using an array of six VLF/LF receivers (1 MHz sample-rate) in Oklahoma, and elves were observed using two high-speed photometers pointed over the Oklahoma region: one located at Langmuir Laboratory, NM and the other at McDonald Observatory, TX. Hundreds of elves with coincident LF sferics were observed during the summer months of 2013. We present data comparing the characteristics of elve-producing and non-elve producing lightning as measured by LF sferics. In addition, we compare these sferic and elve observations with FDTD simulations to determine key properties of elve-producing lightning.

  15. Characteristic of Tweek Atmospherics Observed in Mid-latitude using AWESOME VLF Receiver

    Directory of Open Access Journals (Sweden)

    Norbayah Yusop

    2014-03-01

    Full Text Available This study presents the analysis of tweek atmospherics received by AWESOME VLF receiver at station of Gakona (62.71°N, 143.99°W during four months observation from January to April 2011. Tweek which originates from lightning discharge are used to monitor the nighttime D-region ionosphere using the fundamental cut-off frequency to measure the variations of the lower ionosphere’s reflection height, the equivalent electron density at the reflection height and the propagation distance travel by tweeks. In this study, a total of 1316 tweeks are analyzed and from the analysis, it shows that equinox’s season has the highest tweek occurrence compared to winter season in March and April. The maximum harmonic (m of t weeks is found to be up to fourth ( m = 4 and tweeks with mode number one (m = 1 are more dominantly occurred. Our observations indicate that the equivalent electron densities for tweeks varies from 22-27 eL/cm3 in the altitude ranged of 75 to 91 km and demonstrate that these ELF/VLF signals travel considerable distances up to 6700 km from the causative lightning discharges. The ionospheric parameters for three locations (high, middle and low latitude respectively were compared and the results show that they are almost consistent for all the locations.

  16. Tilt - ellips and rho - phase modelling of VLF EM and VLF R in Candi Umbul Magelang

    Science.gov (United States)

    Affanti, Adella Putri; Niasari, Sintia Windhi

    2017-07-01

    A research for geothermal energy is increased due to the need of green energy. The presence of geothermal manifestations indicate the existence of geothermal system. One of the geothermal manifestations is warm spring. CandiUmbul area which located in Telomoyo, Magelang has warm spring as the geothermal manifestation. Very Low Frequency (VLF) is one of geophysical method that can be used to map the subsurface in Candi Umbul, Telomoyo. VLF is a method using electromagnetic field that powered and transferred by the transmitter. The receiver read the electromagnetic signal which induce the rock and give information about the conductivity as the physical property measurred. In this research, after collecting and processing data, we modeled tilt-ellips data of VLF-EM and rho-phase data of VLF-R to explain the geothermal system of Candi Umbul. Both VLF-EM and VLF-R model were correlated for the interpretation. The model showed an anomalous conductive feature beneath the research area. The result of this research showed that the anomaly is oriented in NW-SE direction. This direction is assumed as a fluid path way of Candi Umbul which became the outflow of Telomoyo geothermal system. To prove the early deduction this research is still on going.

  17. A study of VLF signals variations associated with the changes of ionization level in the D-region in consequence of solar conditions

    CERN Document Server

    Sulic, D M; Mihajlov, A A

    2016-01-01

    In this paper we confine our attention to the analysis of amplitude and phase data acquired by monitoring VLF/LF radio signals emitted by four European transmitters during a seven-year period (2008-2014). All the data were recorded at a Belgrade site (44.85$^{0}$ N, 20.38$^{0}$ E) by the Stanford University ELF/VLF receiver AWESOME. Propagation of VLF/LF radio signal takes place in the Earth-ionosphere waveguide and strongly depends on ionization level of the D-region, which means that it is mainly controlled by solar conditions. Some results of amplitude and phase variations on GQD/22.10 kHz, DHO/23.40 kHz, ICV/20.27 kHz and NSC/45.90 kHz radio signals measurements at short distances ($D < 2$ Mm) over Central Europe and their interpretation are summarized in this paper. Attention is restricted to regular diurnal, seasonal and solar variations including sunrise and sunset effects on propagation characteristics of four VLF/LF radio signals. We study VLF/LF propagation over short path as a superposition of d...

  18. Ionosperic anomaly due to seismic activities – Part 1: Calibration of the VLF signal of VTX 18.2 KHz station from Kolkata and deviation during seismic events

    OpenAIRE

    Sasmal, S.; Chakrabarti, S. K.

    2009-01-01

    VLF signals are long thought to give away important information about the lithosphere-ionosphere coupling. In order to establish co-relations, if any, between the ionospheric activities and the earthquakes, we need to understand what the reference signals are, throughout the year. The best opportunity to do this is during the period of solar minimum where the number of flares and sunspots are negligible and the data would be primarily affected by the sun and variation would be due to normal s...

  19. Exploiting LF/MF signals of opportunity for lower ionospheric remote sensing

    Science.gov (United States)

    Higginson-Rollins, Marc A.; Cohen, Morris B.

    2017-08-01

    We introduce a method to diagnose and track the D region ionosphere (60-100 km). This region is important for long-distance terrestrial communication and is impacted by a variety of geophysical phenomena, but it is traditionally very difficult to detect. Modern remote sensing methods used to study the D region are predominately near the very low frequency (VLF, 3-30 kHz) band, with some work also done in the high-frequency and very high frequency bands (HF/VHF, 3-300 MHz). However, the frequency band between VLF and HF has been largely ignored as a diagnostic tool for the ionosphere. In this paper, we evaluate the use of 300 kHz radio reflections as a diagnostic tool for characterizing the D region of the ionosphere. We present radio receiver data, analyze diurnal trends in the signal from these transmitters, and identify ionospheric disturbances impacting LF/MF propagation. We find that 300 kHz remote sensing may allow a unique method for D region diagnostics compared to both the VLF and HF/VHF frequency bands, due to a more direct ionospheric reflection coefficient calculation method with high temporal resolution without the use of forward modeling.

  20. Propagation of a whistler wave incident from above on the lower nighttime ionosphere

    Directory of Open Access Journals (Sweden)

    P. Bespalov

    2017-05-01

    Full Text Available The problems of reflection and transmission of a whistler wave incident in the nighttime ionosphere from above are considered. Numerical solution of the wave equations for a typical condition of the lower ionosphere is found. The solution area comprises both the region of strong wave refraction and a sharp boundary of the nighttime ionosphere (∼ 100 km. The energy reflection coefficient and horizontal wave magnetic field on the ground surface are calculated. The results obtained are important for analysis of the extremely low-frequency and very low-frequency (ELF–VLF emission phenomena observed from both the satellites and the ground-based observatories.

  1. New Generation of ELF/VLF Wave Injection Experiments for HAARP

    Science.gov (United States)

    Sonwalkar, V. S.; Reddy, A.; Watkins, B. J.

    2016-12-01

    We present a ray tracing study to investigate the feasibility of a new generation of wave injection experiments from HAARP transmitter (L 4.9). Highly successful whistler mode wave injection experiments from SIPLE station, Antarctica, have established the importance of such experiments to study magnetospheric wave-particle interactions, and for cold and hot plasma diagnostics [Helliwell and Katsufrakis, 1974; Carpenter and Miller, 1976; Sonwalkar et al., 1997]. Modulated heating experiments from HAARP have shown that it is possible to launch ELF/VLF waves into the magnetosphere that can be observed on the ground after one-, two-, and multi-hop ducted propagation [Inan et al., 2004]. Recent research has also shown that ionospheric heating experiments using HAARP can lead to the formation of magnetospheric ducts [e.g. Milikh et al., 2010; Fallen et al., 2011]. Collectively, these results indicate that the HAARP (or similar) transmitter can be used first to form ducts on nearby L shells, and then to inject and trap transmitter generated ELF/VLF waves in those ducts. Ray tracing studies using a model magnetosphere shows that ELF/VLF waves in a few kilohertz range can be trapped in ducts with L shells near the HAARP transmitter. For example, 1.5 kHz waves injected from L shell = 4.9 and altitude = 200 km can be trapped in ducts located within 0.3 L of the transmitter L-shell. The duct parameters needed for ray-trapping are typically duct width dL 0.1-0.3 and duct enhancement factor dNe/Ne 10-20% or more. The location of plasmapause with respect to transmitter plays a role in the nature of trapping. The duct locations and parameters required for trapping ELF/VLF waves inside the ducts are consistent with past observations of ducts generated by the HAARP transmitter. Ray tracing calculations provide trapped wave normal angles, time delays, resonant energetic electron energy, estimates of wave intensity inside the duct, on the ground, and on satellites such DEMETER, Van

  2. Observation of Long Ionospheric Recoveries from Lightning-induced Electron Precipitation Events

    Science.gov (United States)

    Mohammadpour Salut, M.; Cohen, M.

    2015-12-01

    Lightning strokes induces lower ionospheric nighttime disturbances which can be detected through Very Low Frequency (VLF) remote sensing via at least two means: (1) direct heating and ionization, known as an Early event, and (2) triggered precipitation of energetic electrons from the radiation belts, known as Lightning-induced Electron Precipitation (LEP). For each, the ionospheric recover time is typically a few minutes or less. A small class of Early events have been identified as having unusually long ionospheric recoveries (10s of minutes), with the underlying mechanism still in question. Our study shows for the first time that some LEP events also demonstrate unusually long recovery. The VLF events were detected by visual inspection of the recorded data in both the North-South and East-West magnetic fields. Data from the National Lightning Detection Network (NLDN) are used to determine the location and peak current of the lightning responsible for each lightning-associated VLF perturbation. LEP or Early VLF events are determined by measuring the time delay between the causative lightning discharges and the onset of all lightning-associated perturbations. LEP events typically possess an onset delay greater than ~ 200 msec following the causative lightning discharges, while the onset of Early VLF events is time-aligned (events are distinguished from ducted events based on the location of the causative lightning relative to the precipitation region. From 15 March to 20 April and 15 October to 15 November 2011, a total of 385 LEP events observed at Indiana, Montana, Colorado and Oklahoma VLF sites, on the NAA, NLK and NML transmitter signals. 46 of these events exhibited a long recovery. It has been found that the occurrence rate of ducted long recovery LEP events is higher than nonducted. Of the 46 long recovery LEP events, 33 events were induced by ducted whistlers, and 13 events were associated with nonducted obliquely propagating whistler waves. The occurrence

  3. Meteor fireball sounds identified

    Science.gov (United States)

    Keay, Colin

    1992-01-01

    Sounds heard simultaneously with the flight of large meteor fireballs are electrical in origin. Confirmation that Extra/Very Low Frequency (ELF/VLF) electromagnetic radiation is produced by the fireball was obtained by Japanese researchers. Although the generation mechanism is not fully understood, studies of the Meteorite Observation and Recovery Project (MORP) and other fireball data indicate that interaction with the atmosphere is definitely responsible and the cut-off magnitude of -9 found for sustained electrophonic sounds is supported by theory. Brief bursts of ELF/VLF radiation may accompany flares or explosions of smaller fireballs, producing transient sounds near favorably placed observers. Laboratory studies show that mundane physical objects can respond to electrical excitation and produce audible sounds. Reports of electrophonic sounds should no longer be discarded. A catalog of over 300 reports relating to electrophonic phenomena associated with meteor fireballs, aurorae, and lightning was assembled. Many other reports have been cataloged in Russian. These may assist the full solution of the similar long-standing and contentious mystery of audible auroral displays.

  4. IMPACT OF CYCLONES OVER KAMCHATKA ON ELECTRON DISTRIBUTION IN THE IONOSPHERE

    Directory of Open Access Journals (Sweden)

    Bogdanov, V.V.

    2016-11-01

    Full Text Available The paper presents the results of investigation of cyclone impact on ionosphere parameters. Ionosphere state was observed by the automatic sounding equipment applying low-orbital navigational spacecrafts in the conditions of low seismicity

  5. Interplanetary Radio Transmission Through Serial Ionospheric and Material Barriers

    Energy Technology Data Exchange (ETDEWEB)

    Fields, David [ORNL; Kennedy, Robert G [ORNL; Roy, Kenneth I [ORNL; Vacaliuc, Bogdan [ORNL

    2013-01-01

    A usual first principle in planning radio astronomy observations from the earth is that monitoring must be carried out well above the ionospheric plasma cutoff frequency (~5 MHz). Before space probes existed, radio astronomy was almost entirely done above 6 MHz, and this value is considered a practical lower limit by most radio astronomers. Furthermore, daytime ionization (especially D-layer formation) places additional constraints on wave propagation, and waves of frequency below 10-20 MHz suffer significant attenuation. More careful calculations of wave propagation through the earth s ionosphere suggest that for certain conditions (primarily the presence of a magnetic field) there may be a transmission window well below this assumed limit. Indeed, for receiving extraterrestrial radiation below the ionospheric plasma cutoff frequency, a choice of VLF frequency appears optimal to minimize loss. The calculation, experimental validation, and conclusions are presented here. This work demonstrates the possibility of VLF transmission through the ionosphere and various subsequent material barriers. Implications include development of a new robust communications channel, communications with submerged or subterranean receivers / instruments on or offworld, and a new approach to SETI.

  6. VLF Perturbations Associated with Solar Eclipses of November 2012 and may 2013 IN the South Pacific Region

    Science.gov (United States)

    Kumar, S.; Kumar, A.

    2015-12-01

    Sub-ionospheric VLF signals from the NWC (19.8 kHz), NPM (21.4 kHz) and NLK (24.8 kHz) MSK VLF transmitters are monitored at Suva, Fiji, with a time resolution of 0.1s using GPS based timing and SoftPAL VLF system. Here one minute averaged amplitude and phase data have been used for analysis. We present perturbations in VLF propagation and D-region changes associated with 13 November 2012 total solar eclipse (SE) and 9-10 May 2013 annular SE using VLF observations at Suva, Fiji. During 13-14 November 2012 total SE, the totality shadow intercepted NWC-Suva path and NWC signal amplitude and phase decreased by about 0.70 dB and 23°, respectively. NPM signal amplitude during 9-10 May 2013 SE decreased by about 2.0 dB. The amplitude perturbation of ~1.8 dB on NLK signal was measured from the unperturbed level associated with 9-10 May 2013 SE. The decrease in the amplitude at the site can be understood in terms of destructive interference of modes converted at the discontinuity created by the eclipse intercepting the different Transmitter-receiver great circle paths (TRGCPs) and changes in the propagation conditions along TRGCPs. The decrease in the amplitude and phase of NWC signal for 13-14 November 2012 SE has been modeled using Long Wave Propagation Capability code to estimate the changes in D-region reflection height (H') and sharpness factor (β) which shows that H' and β were increased by 0.95 km and 0.01 km-1, respectively. The phase changes on NWC signal associated with 9-10 May 2013 SE have been used to estimate the recombination coefficient value, for 75 km height where electron density reduction due to SE was about 40%. The changes in the D-region parameters and the electron density are due to sudden decrease of the photo-ionization creating nighttime like conditions in the D-region ionosphere.

  7. Long-term and transient forcing of the low ionosphere monitored by SAVNET

    Science.gov (United States)

    Raulin, Jean-Pierre; Bertoni, Fernando C. P.; Gavilán, Hernan R.; Samanes, Jorge C.

    2010-10-01

    In this paper we present the main findings obtained by the South America VLF NETwork since its installation in the South America territory. In particular we show the capability of the VLF technique to monitor the long-term solar activity and transient solar and geomagnetic disturbances. On long timescales they are indices on the possibility of monitoring the Lyman-α solar radiation. On shorter timescales we show that the VLF technique is a very sensitive mean of detecting solar X-ray flares. Those small events with a peak power ⩾5×10-7 W/m2 are detected with a 100% probability. A lower limit for the X-ray power of ˜2.7 10-7 W/m2 has been found in order to produce a ionospheric disturbance, and we confirm the important role of the Lyman-α radiation to form and maintain the low ionospheric D-region. SAVNET has also observed for the first time the ionospheric disturbances produced by outbursts from the magnetar SGR 1550-5408. This genuine detection suggests the possibility of monitoring on a routine basis these objects of fundamental importance in high-energy astrophysics. Finally, we show that SAVNET is well suited for participating to the search for seismo-ionospheric disturbances in order to study the possibility of earthquake events prediction.

  8. Effect of the total solar eclipse of March 20, 2015, on VLF/LF propagation

    Science.gov (United States)

    Solovieva, M. S.; Rozhnoi, A. A.; Fedun, V.; Schwingenschuh, K.

    2016-05-01

    The analyzed amplitude and phase variations in electromagnetic VLF and LF signals at 20-45 kHz, received in Moscow, Graz (Austria), and Sheffield (UK) during the total solar eclipse of March 20, 2015, are considered. The 22 analyzed paths have lengths of 200—6100 km, are differently oriented, and cross 40-100% occultation regions. Fifteen paths crossed the region where the occultation varied from 40 to 90%. Solar eclipse effects were found only on one of these paths in the signal phase (-50°). Four long paths crossed the 90-100% occultation region, and signal amplitude and phase anomalies were detected for all four paths. Negative phase anomalies varied from-75° to-90°, and the amplitude anomalies were both positive and negative and were not larger than 5 dB. It was shown that the effective height of the ionosphere varied from 6.5 to 11 km during the eclipse.

  9. A Study On The Final Phase Of The Bardarbunga Volcano Of 2015 Using Vlf Wave Of Nrk Signal Of Iceland Received At Kiel Longwave Monitor

    Directory of Open Access Journals (Sweden)

    Govinda Sharma

    2015-08-01

    Full Text Available Seismo-ionospheric changes often affect the VLF waves resulting in possible changes in the terminator times and often lead to night time fluctuations. The Bardarbunga volcano which started on 2014 ended on the last days of February of 2015. In this paper we present the results of the VLF analysis of the first three months of 2015 using a signal of 37.50 KHz where an analysis on the sunset terminator time D-layer dissipation time daytime fluctuation and night time fluctuation of the VLF amplitude was done. We contrasted the values of these parameters for the first two months of 2015 where the volcano was active with third month of 2015 when the volcano had completely subsided. The Sunset terminator time and the daytime fluctuations in the VLF amplitude for the first two months showed no major anomalies. The anomaly in the D-layer disappearance time and night time fluctuation count reached its peak values for the volcanically active months.

  10. Preprocessing of ionospheric echo Doppler spectra

    Institute of Scientific and Technical Information of China (English)

    FANG Liang; ZHAO Zhengyu; WANG Feng; SU Fanfan

    2007-01-01

    The real-time information of the distant ionosphere can be acquired by using the Wuhan ionospheric oblique backscattering sounding system(WIOBSS),which adopts a discontinuous wave mechanism.After the characteristics of the ionospheric echo Doppler spectra were analyzed,the signal preprocessing was developed in this paper,which aimed at improving the Doppler spectra.The results indicate that the preprocessing not only makes the system acquire a higher ability of target detection but also suppresses the radio frequency interference by 6-7 dB.

  11. EUV measurement of ionospheric oxygen ions

    Science.gov (United States)

    Nakasaka, Y.; Yamazaki, A.; Yoshikawa, I.; Tashiro, S.; Miyake, W.; Nakamura, M.

    2001-12-01

    We have measured the OII emission from the F-layer ionosphere by the sounding rocket SS-520-2, which was launched from the Svalbard Rocket Experiment Site, Ny Aalesund in Norway, last December. This was the first in situ EUV observation of the ionospheric Oxygen ions. Oxygen ion is the main component of the ionospheric F layer. We have studied the oxygen ions distribution in the ionosphere by means of optical observation. Oxygen ions resonantly scatter the solar OII(83.4nm) line. We have built an extreme ultraviolet (XUV) scanner, which is sensitive to the OII 83.4-nm emission and contamination free from the Lyman-alpha line, especially for the sounding rocket SS-520-2. The rocket flew along the magnetospheric cusp region, and 600 sec after the launch it reached its apex at 1108 km in altitude, and its total operation time was 1100sec. In the downleg of the flight, below 350 km in altitude (900-1100sec after the launch), XUV observed very high intensity (200~300 Rayleigh) of OII emissions from the ionospheric F layer. We have estimated the column density of the oxygen ion along the XUV_fs line-of-sight from the measured OII intensity. In this presentation, we will discuss the density profile of the oxygen ions in the ionospheric F region, i.e., the dependence on the altitude, longitude and latitude. We will compare the obtained distribution with the model of the ionosphere.

  12. Generation of whistler waves by continuous HF heating of the upper ionosphere

    Science.gov (United States)

    Vartanyan, A.; Milikh, G. M.; Eliasson, B.; Najmi, A. C.; Parrot, M.; Papadopoulos, K.

    2016-07-01

    Broadband VLF waves in the frequency range 7-10 kkHz and 15-19 kHz, generated by F region CW HF ionospheric heating in the absence of electrojet currents, were detected by the DEMETER satellite overflying the High Frequency Active Auroral Research Program (HAARP) transmitter during HAARP/BRIOCHE campaigns. The VLF waves are in a frequency range corresponding to the F region lower lybrid (LH) frequency and its harmonic. This paper aims to show that the VLF observations are whistler waves generated by mode conversion of LH waves that were parametrically excited by HF-pump-plasma interaction at the upper hybrid layer. The paper discusses the basic physics and presents a model that conjectures (1) the VLF waves observed at the LH frequency are due to the interaction of the LH waves with meter-scale field-aligned striations—generating whistler waves near the LH frequency; and (2) the VLF waves at twice the LH frequency are due to the interaction of two counterpropagating LH waves—generating whistler waves near the LH frequency harmonic. The model is supported by numerical simulations that show good agreement with the observations. The (Detection of Electromagnetic Emissions Transmitted from Earthquake Regions results and model discussions are complemented by the Kodiak radar, ionograms, and stimulated electromagnetic emission observations.

  13. On the ionospheric perturbation for the 1995 Kobe earthquake: revisited

    Directory of Open Access Journals (Sweden)

    Masashi Hayakawa

    2016-01-01

    Full Text Available The presence of seismo-lower ionospheric perturbation for the Kobe earthquake (EQ has been revisited with a relatively new phenomenon of ULF (ultra-low-frequency magnetic field depression effect. By using the ULF data in Japan only at Kakioka belonging to Japan Meteorological Agency (because data from Memambetsu and Kanoya were not available, we have found that a very clear ULF depression was observed at Kakioka on 14 January 1995. A comparison with our former result on subionospheric VLF (very low frequency propagation anomaly indicates that the occurrence of ULF depression exhibits a temporal coincidence (synchronization with that of subionospheric VLF anomaly. This may be acceptable because the ULF depression can be explained in terms of enhanced absorption of magnetospheric ULF waves through the disturbed lower ionosphere prior to an EQ. The result of ULF magnetic field depression in this paper is likely to provide a further support to the presence of the lower ionospheric perturbation before the Kobe EQ.

  14. Testing Plasma Physics in the Ionosphere

    Science.gov (United States)

    Papadopoulos, Konstantinos

    TESTING PLASMA PHYSICS IN THE IONOSPHERE K. Papadopoulos University of Maryland College Park, MD 20742 Ionospheric heaters supplemented by ground and space based diagnostic instruments, such as radars, optical cameras and photometers, HF/VLF/ELF/ULF receivers and magnetometers, radio beacons, riometers and ionosondes have for a long time being used to conduct plasma physics, geophysical and radio science investigations. The latest entry to ionospheric heating, the HF transmitter associated with the High Frequency Active Ionospheric Research Program (HAARP), was completed in February 2007. The transmitter consists of 180 antenna elements spanning 30.6 acres and can radiate 3.6 MW of HF power in the 2.8-10.0 MHz frequency range. With increasing frequency the beam-width varies from 15-5 degrees, corresponding to 20-30 dB gain and resulting in Effective Radiating Power (ERP) between .36 - 4.0 GW. The antenna can point to any direction in a cone of 30 degrees from the vertical, with a reposition time of 15 degrees in 15 microseconds resulting in super-luminous scanning speeds. The transmitter can synthesize essentially any desired waveform within the regulatory allowed bandwidth in linear and circular polarization. These capabilities far exceed those of previous ionospheric heaters and allow for new frontier research in plasma physics, geophysics and radio science. Following a brief discussion of the relationship of the new capabilities of the facility with thresholds of physical processes that could not be achieved previously, the presentation will discuss recent results in the areas of ULF/ELF/VLF generation and propagation and wave-particle interactions in the magnetosphere acquired with the completed facility. The presentation will conclude with a detailed discussion of possible frontier science experiments in the areas of Langmuir turbulence, parametric instabilities, electron acceleration, optical emissions and field aligned striations and duct generation, made

  15. VLF signal modulations during the total solar eclipse of 22nd July, 2009: model using D region ion chemistry and LWPC

    Science.gov (United States)

    Chakraborty, Suman; Chakrabarti, Sandip Kumar; Palit, Sourav; Ray, Suman

    2016-07-01

    One of the major sources of ionospheric perturbations is variations in solar Extreme Ultraviolet (EUV) radiation flux. Solar eclipse is a phenomenon which is capable of producing significant effects on the physical and chemical properties of the ionospheric plasma. During a solar eclipse, the solar radiation flux reduces considerably for a limited period of time over specific locations on the Earth. This induces certain changes within the ionosphere or more precisely, in the D-region which can be studied with the observation of Very Low Frequency (VLF) radio signal modulations. The parameters which mainly govern the ion-chemistry, such as the recombination coefficients are poorly known till date. Solar eclipse provides us with an excellent opportunity to study these parameters as its time of occurrence is known beforehand and thus we can equip ourselves accordingly. In the present study we considered the Total Solar Eclipse (TSE) that occurred on 22nd July, 2009 within the Indian subcontinent. Indian Centre for Space Physics (ICSP) conducted a week long campaign during the eclipse and data were recorded from dozens of places within India and abroad. Both positive and negative changes in VLF signal amplitude were observed. In this paper, data for a propagation path between Indian Navy VLF transmitter named VTX3 and a pair of receivers in India, namely Malda and Kolkata are used. We start with calculating the obscuration function for these two places to find the variations in ionization flux within the period of the eclipse. After this, we incorporated the D region ion chemistry model to find the equilibrium ion density over the region and employ the LWPC code to find the VLF signal amplitude. We varied the values of recombination coefficients to achieve desired accuracy in our results. In doing so, we achieved two goals: First, we have been able to reproduce the trend of variation in VLF signal amplitude (both positive and negative) at both the receiving locations

  16. Bispectrum Analysis of Non-linear wave-wave Interaction between VLF Transmitter signal and ELF emission on the Basis of DEMETER satellite observations

    Science.gov (United States)

    Sondhiya, Deepak Kumar; Gwal, Ashok Kumar; Kasde, Satish Kumar

    2016-07-01

    Symmetric sidebands are observed in the ionosphere by the DEMETER (Detection of Electromagnetic Radiation Transmitted through Earthquake Region) satellite, when it passes above the Indian VLF transmitter, named VTX (18.2 kHz), located near Kanyakumari, India. The spectral boarding phenomena may be divided into two types: (1) spectrally broadened components occurring without any association with ELF/VLF emissions under disturbed ionospheric condition, (2) Spectrally broadened components with predominant side band structure in association with ELF emission. Generally spectral analysis at second order (Power spectrum) is used to analyze the frequency component of signal, but it losses the phase information among the different Fourier components. To retain this information the bispectrum (third order) and/or the bicoherence (normalized bispectrum) are used. Results suggest a non-linear mode coupling between the transmitter signal and ELF emission which produces sidebands that are quasi-electrostatic in nature. However, faint spectral broadened components in both types 1 and 2 may be connected with Doppler shift of quasi-electrostatic, whistler mode waves with a broad spectrum near resonance cone, due to scattering of the transmitter signals from ionospheric irregularities in the F-region. Keywords: spectral boarding, wave-wave Interaction, whistler mode waves and Doppler shift

  17. Global and Seasonal Assessments of Magnetosphere / Ionosphere Coupling via Lightning-Induced Electron Precipitation

    Science.gov (United States)

    Sousa, Austin; Marshall, Robert; Close, Sigrid

    2016-07-01

    Pitch-angle scattering by radio waves in the VLF (~3-30kHz) band is thought to be a major loss mechanism for energetic radiation-belt electrons. Resonant interactions with Whistler-mode VLF waves can alter the reflection altitude of trapped electrons ~100keV - 1MeV; when a particle reflects at a low enough altitude, it can be removed from the magnetosphere through collisions with ionospheric constituents. Terrestrial lightning provides a natural and constantly-occurring source of VLF waves. Here we present a global assessment of lightning-induced electron precipitation (LEP) due to resonant pitch-angle scattering from whistler-mode waves, which represent a coupling process between the magnetosphere and ionosphere. We combine an end-to-end model of the LEP process with terrestrial lightning activity data from the GLD360 sensor network to construct a realtime geospatial model of LEP-driven energy deposition into the ionosphere. We explore global and seasonal statistics, provide precipitation estimates across a variety of magnetospheric conditions, and compare the total impact to other magnetospheric loss processes. Additionally, we use our model to optimize event selection from the energetic-particle detectors on board the FIREBIRD CubeSats, in order to download data over the satellite's low-bandwidth downlink. Ultimately, FIREBIRD data will be used to validate our model, and to provide one-to-one correlative measurements of lightning strokes and subsequent precipitation.

  18. HAARP-based Investigations of Lightning-induced Nonlinearities within the D-Region Ionosphere

    Science.gov (United States)

    Moore, R. C.

    2015-12-01

    It is well-documented that energetic lightning can produce fantastical events with the lower ionosphere. Although the High-frequency Active Auroral Research Program (HAARP) transmitter is not as powerful as lightning, it can be used to investigate the nonlinear interactions that occur within the lower ionosphere, many of which also occur during lightning-induced ionospheric events. This paper presents the best experimental results obtained during D-region modification experiments performed by the University of Florida at the HAARP observatory between 2007 and 2014, including ELF/VLF wave generation experiments, wave-wave mixing experiments, and cross-modulation experiments. We emphasize the physical processes important for lightning-ionosphere interactions that can be directly investigated using HAARP.

  19. Design of a flexible and low-power ionospheric sounder

    Science.gov (United States)

    Morris, Alex

    Characterizing the structure of the ionosphere has practical applications for telecommunications and scientific applications for studies of the near-Earth space environment. Among several methods for measuring parameters of the ionosphere is ionospheric sounding, a radar technique that determines the electron content of the ionosphere as a function of height. Various research, military, and commercial institutions operate hundreds of ground-based ionosondes throughout the globe, and new ionosondes continue to be deployed in increasingly remote and distant locations. This thesis presents the design of an ionospheric sounder that reduces the power, size, and cost compared to existing systems. Key improvements include the use of an open-source software-defined radio platform and channel-aware dynamic sounding scheduling.

  20. Nonlinear Interactions within the D-Region Ionosphere

    Science.gov (United States)

    Moore, Robert

    2016-07-01

    This paper highlights the best results obtained during D-region modification experiments performed by the University of Florida at the High-frequency Active Auroral Research Program (HAARP) observatory between 2007 and 2014. Over this period, we saw a tremendous improvement in ELF/VLF wave generation efficiency. We identified methods to characterize ambient and modified ionospheric properties and to discern and quantify specific types of interactions. We have demonstrated several important implications of HF cross-modulation effects, including "Doppler Spoofing" on HF radio waves. Throughout this talk, observations are compared with the predictions of an ionospheric HF heating model to provide context and guidance for future D-region modification experiments.

  1. Solution uniquity of an inverse VLF problem: A case-study of the polar, ground-based, VLF radio signal disturbances caused by the ultra-energetic relativistic electron precipitations and of their southern boundaries

    Science.gov (United States)

    Remenets, G. F.; Astafiev, A. M.

    2016-09-01

    Here we present the results of a case study of the rare, abnormal, qualitatively specific behavior of Aldra (northern Norway) and GBR (UK) VLF transmitter signals (10-16 kHz) received at Kola Peninsula. The abnormal amplitude and the phase disturbances of signals were used as a proxy for ultra-energetic relativistic (solar?) electron precipitation (URE, ∼100 MeV) into the middle polar atmosphere. The disturbances have been observed under quiet or moderately disturbed geomagnetic activity. Based on bearing results, it was established that the abnormal variations of the electric conductivity of ionized middle atmosphere (of a sporadic Ds layer under the regular ionosphere D layer) were characterized by the following: (i) the time function of height h(t) of an effective spherical waveguide between the Earth surface and the sporadic Ds layer shows a minimum value equal to ∼30 km and (ii) the reflection coefficient R(t) of radio wave with a grazing angle of incidence from a virtual boundary with height h(t) has a minimum value equal to ∼0.4. The southern boundaries of the ultra-energetic relativistic electron precipitations have been found as well. They turned out to be not southerly than 61 degree of magnetic latitude and similar to the ones obtained in our previous study of the events for other dates under the similar geophysical conditions although we do not know anything definite about the rigidity and density of the electron fluxes. A used calculation method of analysis is based on a necessary condition that a number n of input data should be greater than a number m of output parameter-functions. We have stated by numerical testing that a decrease of n from 6 to 4 generates a lack of uniqueness of an inverse VLF problem solution for m = 2. It is important for future VLF ground-based monitoring of the URE precipitation events.

  2. High-resolution ionospheric observations and modeling over Belgium during the solar eclipse of 20 March 2015 including first results of ionospheric tilt and plasma drift measurements

    Science.gov (United States)

    Verhulst, Tobias G. W.; Sapundjiev, Danislav; Stankov, Stanimir M.

    2016-06-01

    The ionospheric behavior over Belgium during the partial solar eclipse of 20 March 2015 is analyzed based on high-resolution solar radio flux, vertical incidence sounding, and GPS TEC measurements. First results of ionosonde-based ionospheric plasma drift and tilt observations are presented and analyzed, including some traveling ionospheric disturbances caused by the eclipse. Also, collocated ionosonde and GPS measurements are used to reconstruct the time evolution of the vertical electron density distribution using the Royal Meteorological Institute (RMI) ionospheric specification system, called Local Ionospheric Electron Density profile Reconstruction (LIEDR).

  3. Nonlinear phenomena arising from radio wave heating of the lower ionosphere

    Science.gov (United States)

    Tomko, A. A.

    1981-08-01

    This document describes a theoretical and experimental study of the interaction of high power, high frequency radio waves with the lower ionosphere. The theoretical calculations presented here show that the electron temperature of the ionospheric plasma can be greatly enhanced when the plasma is irradiated by a powerful groundbased HF transmitter with an effective radiated power of the order of 100 MW. If this plasma heating is maintained for times exceeding a few seconds, the composition of the plasma can also be altered. These temperature and composition modifications cause significant changes in the plasma conductivity and wave absorption in the medium. Two experiments were conducted in order to test for the predicted absorption and conductivity modifications: a vertical incidence plus absorption experiment and a nonlinear demodulation experiment. Data from the absorption experiment clearly show a large (9 dB) increase in wave absorption at 2.4 MHz due to a high power (60 MW ERP) HF heating of the ionosphere. The nonlinear demodulation experiment generated strong VLF radiation when the ionosphere was irradiated by a powerful modulated HF wave. These VLF signals are believed to be due to HF heating induced conductivity modulation of the dynamo current system.

  4. Harmonic H sup + gyrofrequency structures in auroral hiss observed by high-altitude auroral sounding rockets

    Energy Technology Data Exchange (ETDEWEB)

    Kintner, P.M.; Vago, J. (Cornell Univ., Ithaca, NY (USA)); Scales, W. (Naval Research Lab., Washington, DC (USA)); Yau, A.; Whalen, B. (National Research Council of Canada, Ottwawa, Ontario (Canada)); Arnoldy, R. (Univ. of New Hampshire, Durham (USA)); Moore, T. (Marshall Space Flight Center, Huntsville, AL (USA))

    1991-06-01

    Two recent sounding rocket experiments have yielded VLF wave data with spectral structures ordered by the hydrogen gyrofrequency. The spectral structures occur near and above the lower hybrid frequency in association with auroral hiss. These structures are observed within and near regions of auroral electron precipitation and transverse ion acceleration. They are accompanied by auroral hiss but are anticorrelated with spectral peaks at the lower hybrid frequency. They are typically found above 500 km altitude, have no measureable magnetic component, and are at least occasionally short wavelength (k{rho}{sub i}{ge}1). Because the spectral structures appear to be electrostatic, are ordered by the hydrogen gyrofrequency, and are short wavelength, the authors interpret the structures as modes which connect the lower hybrid mode with the hydrogen Bernstein modes. A study of the plasma wave mode structure in the vicinity of the lower hybrid frequency is presented to substantiate this interpretation. The results imply that these waves are a common feature of the auroral zone ionosphere above 500 km altitude and exist any time that auroral hiss exists. The absence of previous satellite abservations of this phenomenon can be explained by Doppler broadening.

  5. Periodic and quiescent solar activity effects in the low ionosphere, using SAVNET data

    Science.gov (United States)

    Bertoni, F. C. P.; Raulin, J.-P.; Gavilan, H. R.; Kaufmann, P.; Raymundo, T. E.

    2010-10-01

    Important results have been acquired using the measurements of VLF amplitude and phase signals from the South America VLF Network (SAVNET) stations. This network is an international project coordinated by CRAAM, Brazil in cooperation with Peru and Argentina. It started operating in April 2006, and now counts on eight stations (Atibaia, Palmas, Santa Maria and Estaça~o Antártica Comandante Ferraz in Brazil; Piura, Punta-Lobos and Ica, in Peru; CASLEO, in Argentina). Researches, through the last decades, have demonstrated the versatility of the VLF technique for many scientific and technological purposes. In this work, we summarize some recent results using SAVNET data base. We have obtained daily maximum diurnal amplitude time series that exhibited behavior patterns in different time scales: 1) 1ong term variations indicating the solar activity level control of the low ionosphere; 2) characteristic periods of alternated slow and fast variations, the former being related to solar illumination conditions, and the latter that have been associated with the winter anomaly at high latitudes; 3) 27-days period related to the solar rotation and consequently associated to the solar Lyman-α radiation flux variations, reinforcing earlier theories about the importance of this spectral line for the D-region formation. Finally, we conclude presenting preliminary results of simulation using LWPC, which showed very good agreement at times of observed modal amplitude minima for a given VLF propagation path.

  6. The Search for VLF Precursors to Major Earthquakes: A Case Study with the M9.0 Earthquake of 11-Mar-2011 (Invited)

    Science.gov (United States)

    Cohen, M.; Kosovichev, P.; Marshall, R. A.; Droscoll, A.; Scherrer, D. K.

    2013-12-01

    It has been proposed that Very Low Frequency (VLF, 3-30 kHz) radio remote sensing may be used to detect ionospheric changes which may precede major earthquakes by hours or days. We report the results of a search for VLF precursors to the M9.0 Tohoku earthquake of 11-Mar-2011, the fifth most powerful earthquake in recorded history. Broadband and narrowband radio recordings were made at a site in Onagawa, Japan located ~102 km from the epicenter. The receiver operated for about two minutes after the start of the earthquake, after which the receiver lost power. Examination of the VLF data shows no radio emissions preceding or coincident with the onset of the earthquake. However, once the secondary seismic waves reached the receiver, a number of impulses and diffuse noise bands arose which may result from the entire power grid shaking or from radio emissions from compressing or fracturing rocks. Examination of the ELF data (0.2-1 kHz) shows no precursor effect in the hours preceding the seismic activity. We also examine the amplitudes of VLF subionospherically propagating transmitter signals going back months before the earthquake. We apply previously proposed techniques to extract properties of the diurnal amplitude profile that have been thought to correlate with earthquake precursors, but find no anomalous effect despite the remarkable intensity of the earthquake and proximity of the receiver to the epicenter. In general there are anomalous deviations but they cannot be reliably correlated with seismic activity. We also report the results of a global search for a lightning precursor effect on lightning flash rates, using the GLD360 network.

  7. Ionospheric Digital Database

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The ionosphere is that part of the Earth's atmosphere that results mainly from the photo ionization of the upper atmosphere. Traditionally, the following ionospheric...

  8. Building and the analysis of two radio antennas (SSRT) in vlf zone

    Science.gov (United States)

    Marbouti, Marjan; Khakian Ghomi, Mehdi; Salmanpour Paeen Afrakati, Mohammad Reza; Riahi, Jahad; Ghanbari, Keyvan; Moradi Khanghahi, Abolfazl; Nahavandi, Behzad

    interesting results in this regard. The first result is that the time difference between SRT (time of rise end across ionosphere) and the sunrise as well as the SST (time of set beginning in ionosphere) and the sunset in the geographical location of signal encounter from ionosphere during summer is more as compared to winter season. And the second result is that we could measure a height of ionosphere by means of some calculations; during this period the signal had the maximum absorption. This is called the effective annihilation height and this effective annihilation height was secured for 8 VLF receivers. The results indicated that the effective annihilation height during autumn and winter seasons is higher and more than spring and summer seasons

  9. Retrieval of ionospheric profiles from the Mars Express MARSIS experiment data and comparison with radio occultation data

    Directory of Open Access Journals (Sweden)

    B. Sánchez-Cano

    2012-05-01

    Full Text Available Since 2005 the Mars Advanced Radar and Ionospheric Sounding experiment (MARSIS aboard Mars Express has acquired a unique dataset on the ionosphere of Mars made up of ionospheric soundings taken by the instrument working in its active ionospheric sounding (AIS mode. These soundings play a role similar to those of modern Terrestrial digisondes in the analysis of our planet ionosphere and have allowed us to dramatically improve our knowledge about the Martian ionosphere. This paper describes this kind of data, which are available from the public Planetary Science Archive, and introduces the MAISDAT tool developed by the European Space Agency to analyze and derive the vertical profile of electron density. Comparisons with radio occultation profiles obtained from Mars Express Radio Science instrument are performed to validate the procedure used in this study.

  10. Retrieval of ionospheric profiles from the Mars Express MARSIS experiment data and comparison with radio-occultation data

    Directory of Open Access Journals (Sweden)

    B. Sánchez-Cano

    2012-01-01

    Full Text Available Since 2005 the Mars Advanced Radar and Ionospheric Sounding experiment (MARSIS aboard Mars Express has acquired a unique data set on the ionosphere of Mars made up of ionospheric soundings taken by the instrument working in its Active Ionospheric Sounding (AIS mode. These soundings play a role similar to those of modern Terrestrial digisondes in the analysis of our planet ionosphere and have allowed us to dramatically improve our knowledge about the Martian ionosphere. This paper describes this kind of data, which are available from the public Planetary Science Archive, and introduces the MAISDAT tool developed by the European Space Agency to analyze and derive the vertical profile of electron density. Comparisons with radio-occultation profiles obtained from Mars Express Radio Science instrument are performed to validate the procedure used in this study.

  11. Remote Sensing of the Night-time Lower Ionosphere from Lightning Generated Sferics Recorded in the South Pacific Region

    Science.gov (United States)

    Sushil, K.; Ramachandran, V.

    The lightning generated Extremely Low Frequency ELF and Very Low Frequency VLF radio signals tweeks recorded using the lightning detection system under Word Wide Lightning Location WWLL Network at Suva 18 2 o S 178 3 o E Fiji a low latitude ground wave station in the South Pacific region are used to determine the lower ionospheric electron content and its variation during night-time Due to its least relative inaccessibility the lower ionosphere consisting of D-region is among the least studied regions of the Earth s atmosphere The lightning generated sferics which are short pulses typically of 1-10 ms with significant spectral contents over the ELF VLF can be used in the study of the lower ionosphere A total of 400 tweeks recoded in the time period of 1800-0600 hrs FST during 2003- 2004 have been analysed Matlab codes are used to analyse the data files recorded using lightning software and each of data file is of 11 MB with one minute duration The value of ionospheric reflecting height h calculated using waveguide mode theory of electromagnetic wave propagation in the spherical cell Earth-ionosphere waveguide having perfectly conducting boundaries is found to vary from 80-95 km in the night-time To estimate the electron density at the ionospheric reflection heights i e lower ionosphere we perform a qualitative analysis based on the propagation theory of radio waves in an infinite collisionless anisotropic ionospheric plasma Shvets and Hayakawa J Atmos Sol -Terr Phys 60 461

  12. An aerostat-supported ELF/VLF transmitter

    Science.gov (United States)

    Field, E. C., Jr.; Kies, L. R.; Bannister, P. R.; Ingram, R. F.; Hopkins, W. D.; Roberts, M. A.

    1989-03-01

    A demonstration of an aerostat-supported extremely low frequency/very low frequency (ELF/VLF) transmitting antenna was performed. At ELF the vertical electric dipole (VED) antenna radiated at least 100,000 times more power than would a horizontal electric dipole having the same moment. That efficiency was achieved with an altitude of 12,500 feet (3810 m). Calculations show that the radiated power will increase as the fourth power of aerostat altitude. The tether antenna exhibited a corona onset voltage of 180 kV and was resistant to the degrading effects of ELF corona. Prolonged in-corona operation is therefore possible. The antenna was continuously tuned, despite changes in height and capacitance caused by the aerostat flight dynamics. The huge 300-H ELF tuning inductor posed no problem. Enhanced VED moments were achieved at ELF by operation at voltages up to 260 kV, 40% above the corona onset voltage. At VLF the antenna emulated a monopole that had a radiation efficiency greater than 90%. The measured bandwidths were large: 1.5 kHz at 23 kHz and 3.5 kHz at 34 kHz. The antenna height exceeded one-quarter wavelength at VLF, so the antenna could be tuned capacitively and required relatively low base voltages. At both VLF and ELF the measured fields agreed closely with predictions.

  13. The European VLF/LF radio network: current status

    Science.gov (United States)

    Biagi, Pier Francesco; Maggipinto, Tommaso; Ermini, A.

    2014-11-01

    For several years researches about correlation between seismicity and disturbances in radio broadcasting are being carried out: in particular, the Japanese Pacific VLF radio network and the European VLF-LF radio network have been developed during the last years. The European network has been developed starting from two LF receivers located in central Italy in 1996. Up to now, 11 receivers of a new type, able to sample the VLF and LF intensity of ten radio signals, are being into operation in different European countries. The daily updating of data is effective and the data bank is located at the Department of Physics of the University of Bari (Italy) which is the central node of the network. In order to discover anomalies, the software able to carry out automatically a daily data analysis by the Wavelet spectra method has been planned and realized. At the moment, the software operates on four signals (two LF and two VLF) collected by one of the receiver located in Italy. If the anomaly is particularly strong a warning system gives an advise on the work station into operation in the central node of the Network. In any case, before assuming an anomaly as a seismic anomaly, geomagnetic and meteorological data must be checked as well as any possible instrumental malfunction. At present these controls are carried out only discontinuously by the researchers of the Bari Team.

  14. Modeling the variations of reflection coefficient of Earth's lower ionosphere using very low frequency radio wave data by artificial neural network

    Science.gov (United States)

    Ghanbari, Keyvan; Khakian Ghomi, Mehdi; Mohammadi, Mohammad; Marbouti, Marjan; Tan, Le Minh

    2016-08-01

    The ionized atmosphere lying from 50 to 600 km above surface, known as ionosphere, contains high amount of electrons and ions. Very Low Frequency (VLF) radio waves with frequencies between 3 and 30 kHz are reflected from the lower ionosphere specifically D-region. A lot of applications in long range communications and navigation systems have been inspired by this characteristic of ionosphere. There are several factors which affect the ionization rate in this region, such as: time of day (presence of sun in the sky), solar zenith angle (seasons) and solar activities. Due to nonlinear response of ionospheric reflection coefficient to these factors, finding an accurate relation between these parameters and reflection coefficient is an arduous task. In order to model these kinds of nonlinear functionalities, some numerical methods are employed. One of these methods is artificial neural network (ANN). In this paper, the VLF radio wave data of 4 sudden ionospheric disturbance (SID) stations are given to a multi-layer perceptron ANN in order to simulate the variations of reflection coefficient of D region ionosphere. After training, validation and testing the ANN, outputs of ANN and observed values are plotted together for 2 random cases of each station. By evaluating the results using 2 parameters of pearson correlation coefficient and root mean square error, a satisfying agreement was found between ANN outputs and real observed data.

  15. Sound and sound sources

    DEFF Research Database (Denmark)

    Larsen, Ole Næsbye; Wahlberg, Magnus

    2017-01-01

    There is no difference in principle between the infrasonic and ultrasonic sounds, which are inaudible to humans (or other animals) and the sounds that we can hear. In all cases, sound is a wave of pressure and particle oscillations propagating through an elastic medium, such as air. This chapter...... is about the physical laws that govern how animals produce sound signals and how physical principles determine the signals’ frequency content and sound level, the nature of the sound field (sound pressure versus particle vibrations) as well as directional properties of the emitted signal. Many...... of these properties are dictated by simple physical relationships between the size of the sound emitter and the wavelength of emitted sound. The wavelengths of the signals need to be sufficiently short in relation to the size of the emitter to allow for the efficient production of propagating sound pressure waves...

  16. Ionospheric phenomena before strong earthquakes

    Directory of Open Access Journals (Sweden)

    A. S. Silina

    2001-01-01

    Full Text Available A statistical analysis of several ionospheric parameters before earthquakes with magnitude M > 5.5 located less than 500 km from an ionospheric vertical sounding station is performed. Ionospheric effects preceding "deep" (depth h > 33 km and "crust" (h 33 km earthquakes were analysed separately. Data of nighttime measurements of the critical frequencies foF2 and foEs, the frequency fbEs and Es-spread at the middle latitude station Dushanbe were used. The frequencies foF2 and fbEs are proportional to the square root of the ionization density at heights of 300 km and 100 km, respectively. It is shown that two days before the earthquakes the values of foF2 averaged over the morning hours (00:00 LT–06:00 LT and of fbEs averaged over the nighttime hours (18:00 LT–06:00 LT decrease; the effect is stronger for the "deep" earthquakes. Analysing the coefficient of semitransparency which characterizes the degree of small-scale turbulence, it was shown that this value increases 1–4 days before "crust" earthquakes, and it does not change before "deep" earthquakes. Studying Es-spread which manifests itself as diffuse Es track on ionograms and characterizes the degree of large-scale turbulence, it was found that the number of Es-spread observations increases 1–3 days before the earthquakes; for "deep" earthquakes the effect is more intensive. Thus it may be concluded that different mechanisms of energy transfer from the region of earthquake preparation to the ionosphere occur for "deep" and "crust" events.

  17. Current methods for studying dynamic processes in the ionosphere

    Science.gov (United States)

    Filipp, Nikolai D.; Blaunshtein, Natan Sh.; Erukhimov, Lev M.; Ivanov, Vladimir A.; Uriadov, Valerii P.

    Current experimental and theoretical data relevant to the study of dynamic processes in the ionospheric plasma using state-of-the-art methods are summarized. The methods used include linear FM sounding, partial radio wave reflection, oblique-incidence radio wave scattering, radio wave heating of the ionosphere, plasma injection, and computer simulation of physical processes. For each specific method, experimental data are compared against theoretical predictions and numerical calculations.

  18. Physics based model of D-region variability related to VLF propagation effects

    Science.gov (United States)

    Chakravarty, S. C.

    2012-07-01

    D-region (~60-85 km) electron density profiles measured using large number of sounding rocket experiments carried out from two Indian low latitude stations show large variations with solar zenith angle, season and solar activity. Similarly the ground based multi frequency radio wave absorption technique has provided continuous data on the morphology of the hourly electron density variations. However suitable models of the D-region electron density profile variations both during quiet and disturbed solar conditions over the Indian region are lacking. The renewed interest in the study of the VLF/LF propagation anomalies taking place through perturbations in the D-region electron densities due to various geophysical phenomena requires the availability of a baseline D-region model over low latitudes. The purpose of this paper is to critically review the physical processes of D-region production and loss of free electrons, dynamical coupling due to variety of vertically propagating atmospheric waves, sudden changes brought about by the solar energetic events like CMEs and different categories of X-ray flares. Low latitude region is not likely to be affected by the PMSE or PCA type of events but the changes due to lightning induced mesospheric red sprites and LEPs need to be considered. Based on this analysis, a preliminary low latitude D-region electron density profile model development is proposed. Sample results would illustrate key requirements from such a model in terms of its effectiveness to simulate the low latitude observations of VLF/LF amplitude and phase variations using waveguide propagation models like LWPC.

  19. Effects of solar and geomagnetic activities on the sub-ionospheric very low frequency transmitter signals received by the DEMETER micro-satellite

    Directory of Open Access Journals (Sweden)

    Günter Stangl

    2012-04-01

    Full Text Available

    In the framework of seismic precursor electromagnetic investigations, we analyzed the very low frequency (VLF amplitude signals recorded by the Instrument Champ Electrique (ICE experiment on board the DEMETER micro-satellite. The sun-synchronous orbits of the micro-satellite allowed us to cover an invariant latitude of between –65° and +65° in a time interval of about 40 min. We considered four transmitter signals emitted by stations in Europe (France, FTU, 18.3 kHz; Germany, DFY, 16.58 kHz, Asia (Japan, JP, 17.8 kHz and Australia (Australia, NWC, 19.8 kHz. We studied the variations of these VLF signals, taking into consideration: the signal-to-noise ratio, sunspots, and the geomagnetic activity. We show that the degree of correlation in periods of high geomagnetic and solar activities is, on average, about 40%. Such effects can be fully neglected in the period of weak activity. We also find that the solar activity can have a more important effect on the VLF transmitter signal than the geomagnetic activity. Our data are combined with models where the coupling between the lithosphere, atmosphere and ionosphere is essential to explain how ionospheric disturbances scatter the VLF transmitter signal.


  20. Sound Hole Sound

    CERN Document Server

    Politzer, David

    2015-01-01

    The volume of air that goes in and out of a musical instrument's sound hole is related to the sound hole's contribution to the volume of the sound. Helmholtz's result for the simplest case of steady flow through an elliptical hole is reviewed. Measurements on multiple holes in sound box geometries and scales relevant to real musical instruments demonstrate the importance of a variety of effects. Electric capacitance of single flat plates is a mathematically identical problem, offering an alternate way to understand the most important of those effects. The measurements also confirm and illuminate aspects of Helmholtz's "bottle" resonator model as applied to musical instrument sound boxes and sound holes.

  1. VLF/LF (Very Low Frequency/Low Frequency) Reflection Properties of the Low Latitude Ionosphere

    Science.gov (United States)

    1988-02-04

    pleasure for the U.S. personnel. Although it is virtually impossible to mention all the individuals who contributed, we wish to especially ... Educacional da Regiao de Blumenau (FURB), who planned the day-to-day experimental efforts and who provided valuable technical Insight and guidance to all...or more grazing incidence angle, with the trend being especially pronounced in the daytime. Figure 23 shows 20 kHz reflectiont coefficients derived

  2. Detection of ionospheric perturbations associated with Japanese earthquakes on the basis of reception of LF transmitter signals on the satellite DEMETER

    Directory of Open Access Journals (Sweden)

    F. Muto

    2008-02-01

    Full Text Available There have been recently reported a lot of electromagnetic phenomena associated with earthquakes (EQs. Among these, the ground-based reception of subionospheric waves from VLF/LF transmitters, is recognized as a promising tool to investigate the ionospheric perturbations associated with EQs. This paper deals with the corresponding whistler-mode signals in the upper ionosphere from those VLF/LF transmitters, which is the counterpart of subionospheric signals. The whistler-mode VLF/LF transmitter signals are detected on board the French satellite, DEMETER launched on 29 June 2004. We have chosen several large Japanese EQs including the Miyagi-oki EQ (16 August 2005; M=7.2, depth=36 km, and the target transmitter is a Japanese LF transmitter (JJY whose transmitter frequency is 40 kHz. Due to large longitudinal separation of each satellite orbit (2500 km, we have to adopt a statistical analysis over a rather long period (such as 3 weeks or one month to have reliable data set. By analyzing the spatial distribution of JJY signal intensity (in the form of signal to noise ratio SNR during a period of 4 months including the Miyagi-oki EQ, we have found significant changes in the intensity; generally the SNR is significantly depleted before the EQ, which is considered to be a precursory ionospheric signature of the EQ. This abnormal effect is reasonably explained in terms of either (1 enhanced absorption of whistler-mode LF signals in the lower ionosphere due to the lowering of the lower ionosphere, or (2 nonlinear wave-wave scattering. Finally, this analysis suggests an important role of satellite observation in the study of lithosphere-atmosphere-ionosphere coupling.

  3. Application of lightning discharge generated radio atmospherics/tweeks in lower ionospheric plasma diagnostics

    Energy Technology Data Exchange (ETDEWEB)

    Maurya, A K; Singh, R; Veenadhari, B [Indian Institute of Geomagnetism, New Panvel, Navi Mumbai - 410 218 (India); Pant, P [Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak, Nainital - 263129, Uttrakhand (India); Singh, A K, E-mail: ajeet.iig@gmail.co, E-mail: akmaurya@iigs.iigm.res.i [Physics Department, Banaras Hindu University, Varanasi - 221005 (India)

    2010-02-01

    Lightning discharges during thunderstorm are the significant natural source of electromagnetic waves. They generate electromagnetic pulses, which vary from few Hz to tens of MHz, but the maximum radiated energy is confined in extremely low (ELF: 3-3000Hz) and very low (VLF: 3-30 KHz) frequency band. These pulsed signals with frequency dispersion are known as radio atmospherics or tweeks. These waves propagate through the process of multiple reflections in the earth-ionosphere waveguide over long distances with very low attenuation (2-3 dB/1000km). Since these waves are reflected by lower boundary of ionosphere, these are used extensively for probing the D-region ionosphere. D-region is important to the space weather, as well as the submarine communication and navigational aid. In this perspective the measurement of electron density profiles of the D-region is undoubtedly of great interest to both the development of reliable models and radio wave propagation. Earlier work on the tweeks is mainly focused to the theoretical considerations related to polarization, waveform analysis, and occurrence time and propagation mechanism. In this study we investigate tweeks to determine the equivalent night time electron densities at reflection height of the D-region. Distance traveled by the VLF waves from the causative lightning discharges to the receiving station has also been calculated. Tweeks recorded at a low latitude ground station of Allahabad (Geomag. lat. 16.05{sup 0} N) during the night of 23 March 2007 have been used in the present analysis. Based on the analysis of the fundamental cut-off frequency of tweeks, the estimated equivalent electron density of the D-region has been found to be in the range of {approx}20 to 25 el/cm{sup 3} at ionospheric reflection height of {approx}80 to 95 km respectively. Propagation distance in Earth-Ionosphere wave guide (EIWG) from causative lightning source to experimental site varies from {approx}1500 to 8000 km.

  4. VLF wave injection experiments from Siple Station, Antarctica

    OpenAIRE

    R.A., Helliwell

    1987-01-01

    The background of VLF wave-particle experiments from Siple Station, Antarctica, including wave-induced precipitation is briefly reviewed. Single frequency ducted signals that exceed a certain 'threshold' intensity are observed at the conjugate point (Roberval, Quebec) to be amplified 30-50dB, with temporal growth rates of 30-200dB/s. Following saturation, variable frequency emissions are triggered. When a second signal is added to the first, with a frequency spacing Df

  5. VLF Tan Delta Measurement for Used XLPE Power Cables

    Energy Technology Data Exchange (ETDEWEB)

    Lim, Woo Sang; Ha, Che Wung; Joo, Kwang Ho [Korea Hydro and Nuclear Power Co., Daejeon (Korea, Republic of)

    2011-05-15

    Medium voltage power cables in nuclear power plants are currently managed through the visual inspection or by monitoring environmental factors such as the temperature and radiation levels. However, these methods are insufficient to monitor aging degradation of power cables. The NRC requires an additional monitoring program to detect the aged degradation, especially for safety-related power cables which are inaccessible or installed underground. EPRI suggested that very low frequency (VLF) tan {delta} test be included in MV power cable diagnostic programs. In addition, the VLF tan {delta} test was recently adopted for domestic submarine distribution cable diagnostics. KEPRI suggested that the impacts of leakage current should be controlled in VLF tan {delta} test for the submarine cables. As a pre-process to develop such a program, tan {delta} tests have been performed for 4.16 kV cables which were removed from the domestic nuclear power plant after approximate 30 years of service to analyze the degradation of long time serviced cables and the effect of leakage current from the both ends of cables

  6. Source locations for impulsive electric signals seen in the night ionosphere of Venus

    Science.gov (United States)

    Russell, C. T.; Von Dornum, M.; Scarf, F. L.

    1989-01-01

    A mapping of the rate of occurrence of impulsive VLF noise bursts in Venus' dark low altitude ionosphere, which increases rapidly with decreasing altitude, as a function of latitude and longitude indicates enhanced occurrence rates over Atla. In a 30-sec observing period, there are impulsive signals 70 percent of the time at 160 km in the region of maximum occurrence; the occurrence rates, moreover, increase with decreasing latitude, so that the equatorial rate is of the order of 1.6 times that at 30 deg latitude. These phenomena are in keeping with lightning-generated wave sources.

  7. The physical principles of the combined ELF/VLF method for single-station global location of lightning

    Science.gov (United States)

    Mushtak, V.; Price, C.; Williams, E.

    Single -station electromagnetic methods for global lightning location are based on specific features of ELF wave propagation. First, ELF waves propagate with an extremely low attenuation not exceeding 1.5 dB/Mm up to 100 Hz. For this reason, the propagation has a resonant character (the Schumann resonance phenomena) imparting a unique pattern to the spectrum of a lightning waveform depending on the parent lightning's location relative to the given observer. The wave impedance technique realized by Kemp and Jones (1971) and widely adopted afterwards eliminates any need for the frequency dependence of the spectral density of the source's current moment for the location purpose. At the same time, an adequate single-mode propagation model can be applied for recovering this dependence and providing additional information about the source. As the only shortcoming of ELF location procedure, considerable error in estimates of the arrival directions of lightning waveforms was revealed by means of the satellite (OTD) identification of parent lightning events. These azimuthal deviations result in global location accuracies of 1-2 Mm (Boccippio et al, 1998) hardly acceptable in many geophysical problems. Price et al. (2002) found similar azimuthal errors in the ELF technique by means of the ground-truth (NLDN) identification of sprite-producing thunderstorms in Colorado when observing atmospherics in the Negev Desert, Israel. The location accuracy had been essentially improved - to better than 0.2 Mm on this 11 Mm path - by combining ELF distance estimates with VLF direction finding. Theoretical considerations show that this improvement is to be explained by a distinction between the ELF and VLF refraction effects at the day-night boundary of the Earth- ionosphere waveguide. While the difference between the day-time and night-time values of the phase velocity in the ELF range reaches 15%, it does not exceed 1% in the VLF range, with a corresponding diminishment of azimuthal

  8. Altitude distribution of electron concentration in ionospheric D-region in presence of time-varying solar radiation flux

    Energy Technology Data Exchange (ETDEWEB)

    Nina, A., E-mail: sandrast@ipb.ac.rs [Institute of Physics, University of Belgrade, P.O. Box 57, Belgrade (Serbia); Cadez, V. [Astronomical Observatory, Volgina 7, 11060 Belgrade (Serbia); Sreckovic, V. [Institute of Physics, University of Belgrade, P.O. Box 57, Belgrade (Serbia); Sulic, D. [Faculty of Ecology and Environmental Protection, Union - Nikola Tesla University, Cara Dusana 62, 11000 Belgrade (Serbia)

    2012-05-15

    In this paper, we study the influence of solar flares on electron concentration in the terrestrial ionospheric D-region by analyzing the amplitude and phase time variations of very low frequency (VLF) radio waves emitted by DHO transmitter (Germany) and recorded by the AWESOME receiver in Belgrade (Serbia) in real time. The rise of photo-ionization rate in the ionospheric D-region is a typical consequence of solar flare activity as recorded by GOES-15 satellite for the event on March 24, 2011 between 12:01 UT and 12:11 UT. At altitudes around 70 km, the photo-ionization and recombination are the dominant electron gain and electron loss processes, respectively. We analyze the relative contribution of each of these two processes in the resulting electron concentration variation in perturbed ionosphere.

  9. Resonance between coherent whistler mode waves and electrons in the topside ionosphere

    Science.gov (United States)

    Neubert, T.; Bell, T. F.; Storey, L. R. O.

    1987-01-01

    Landau resonance and cyclotron resonance of coherent whistler mode waves and energetic electrons are explored for magnetoplasmas with appreciable gradients in the plasma density and magnetic field strength. It is shown that in the topside ionosphere of the earth near the ion transition height the gradients in plasma density and magnetic field strength along a magnetic field line may match in a way which enhances both Landau and cyclotron interactions between waves and electrons at the loss cone pitch angle. The pitch angle scattering induced by a signal from a ground-based VLF transmitter in the ionosphere above the transmitter has been estimated and compared to the pitch angle scattering induced by naturally occurring ELF hiss through cyclotron resonance. It is found that the expected scattering due to plasmapheric hiss is an order of magnitude larger than that due to Landau resonance in the topside ionosphere. Pitch angle scattering due to cyclotron resonance in the topside ionosphere, however, may be larger by a factor of 2. It is suggested that the 'fast Trimpi' effect may be caused by a cyclotron resonance interaction in the topside ionosphere.

  10. High time resolution observations of HF cross-modulation within the D region ionosphere

    Science.gov (United States)

    Langston, J.; Moore, R. C.

    2013-05-01

    High-frequency cross-modulation is employed to probe the D region ionosphere during HF heating experiments at the High-frequency Active Auroral Research Program (HAARP) observatory. We have adapted Fejer's well-known cross-modulation probing method to determine the extent of ionospheric conductivity modification in the D region ionosphere with high (5 μsec) time resolution. We demonstrate that the method can be used to analyze D region conductivity changes produced by HF heating both during the initial stages of heating and under steady state conditions. The sequence of CW probe pulses used allow the separation of cross-modulation effects that occur as the probe pulse propagates upward and downward through the heated region. We discuss how this probing technique can be applied to benefit ELF/VLF wave generation experiments and ionospheric irregularities experiments at higher altitudes. We demonstrate that large phase changes equivalent to Doppler shift velocities >60 km/s can be imposed on HF waves propagating through the heated D region ionosphere.

  11. Analyzing the characteristics of phase-shift keyed signals applied to the measurement of an electron concentration profile using the radiophysical model of the ionosphere

    Science.gov (United States)

    Alsatkin, S. S.; Medvedev, A. V.; Kushnarev, D. S.

    2009-12-01

    The radiophysical model of the ionosphere, which can approximately imitate the ionospheric response to a sounding signal, is presented. The model mathematical description and input parameters are given. The results of modeling the ionospheric response to different types of sounding signals are presented. The methods for estimating the quality of restoration of an initial power profile are described. The optimal characteristics of the signal, which allows for a high-quality restoration of an initial power profile, and the modeling results are presented.

  12. Fine structure in the ionospheric D-region

    Science.gov (United States)

    Thrane, E. V.; Grandal, B.; Fla, T.; Brekke, A.

    1981-07-01

    The 'partial reflection' method developed by Gardner and Pawsey (1953) turned out to be a useful tool for studies of the ionospheric D-region. A comparison is conducted of the observations of weak radio echoes from the ionospheric D-region, with model computations of radio wave scattering. The model computations are based on volume scattering from irregular ionospheric structures measured in situ in a sounding rocket. The experimental data were obtained from a rocket-borne electrostatic ion-current probe combined with simultaneous recordings of partial reflections. It is found that the intensity and height variation of partial reflections measured during the rocket flight are consistent with volume scattering from the ionospheric irregularities measured by the electrostatic probe in the rocket. The power spectra of ion density fluctuations derived from the rocket data indicate that these fluctuations are caused by turbulence in the neutral air. It is, therefore, concluded that such turbulence is an important source of partial reflections.

  13. Diffuse spreading of inhomogeneities in the ionospheric dusty plasma

    Energy Technology Data Exchange (ETDEWEB)

    Shalimov, S. L., E-mail: pmsk7@mail.ru [Russian Academy of Sciences, Schmidt Institute of Physics of the Earth (Russian Federation); Kozlovsky, A. [Sodankylä Geophysical Observatory (Finland)

    2015-08-15

    According to results of sounding of the lower ionosphere at altitudes of about 100 km, the duration of radio reflections from sufficiently dense ionized meteor trails, which characterizes their lifetime, can reach a few tens of seconds to several tens of minutes. This is much longer than the characteristic spreading time (on the order of fractions of a second to several seconds) typical in meteor radar measurements. The presence of dust in the lower ionosphere is shown to affect the ambipolar diffusion coefficient, which determines the spreading of plasma inhomogeneities. It is found that the diffusion coefficient depends substantially on the charge and size of dust grains, which allows one to explain the results of ionospheric sounding.

  14. High Power Radio Wave Interactions within the D-Region Ionosphere

    Science.gov (United States)

    Moore, R. C.

    2014-12-01

    This paper highlights the best results obtained during D-region modification experiments performed by the University of Florida at the High-frequency Active Auroral Research Program (HAARP) observatory between 2007 and 2014. Over this period, we have seen a tremendous improvement in ELF/VLF wave generation efficiency. We have identified methods to characterize ambient and modified ionospheric properties and to discern and quantify specific types of interactions. We have demonstrated several important implications of HF cross-modulation effects, including "Doppler Spoofing" on HF radio waves. Throughout this talk, observations are compared with the predictions of an ionospheric HF heating model to provide context and guidance for future D-region modification experiments.

  15. Ionosphere and Radio Communication

    Indian Academy of Sciences (India)

    Saradi Bora

    2017-02-01

    The Earth's ionosphere consists of plasma produced by thephotoionization of thin upper atmospheric gases by UV raysand photons of short wavelength from the sun. The upperionosphere is used for radio communication and navigationas it reflects long, medium, as well as short radio waves. Sincesolar radiation is the main cause of the existence of ionosphere,any variation in the radiations can affect the entireradio communication system. This article attempts to brieflyintroduce the readers to the study of ionosphere in the contextof its use as a radio reflector, with particular reference toIndia.

  16. Role of the magnetospheric and ionospheric currents in the generation of the equatorial scintillations during geomagnetic storms

    Directory of Open Access Journals (Sweden)

    L. Z. Biktash

    2004-09-01

    Full Text Available The equatorial ionosphere parameters, Kp, Dst, AU and AL indices characterized contribution of different magnetospheric and ionospheric currents to the H-component of geomagnetic field are examined to test the geomagnetic activity effect on the generation of ionospheric irregularities producing VLF scintillations. According to the results of the current statistical studies, one can predict near 70% of scintillations from Aarons' criteria using the Dst index, which mainly depicts the magnetospheric ring current field. To amplify Aarons' criteria or to propose new criteria for predicting scintillation characteristics is the question. In the present phase of the experimental investigations of electron density irregularities in the ionosphere new ways are opened up because observations in the interaction between the solar wind - magnetosphere - ionosphere during magnetic storms have progressed greatly. According to present view, the intensity of the electric fields and currents at the polar regions, as well as the magnetospheric ring current intensity, are strongly dependent on the variations of the interplanetary magnetic field. The magnetospheric ring current cannot directly penetrate the equatorial ionosphere and because of this difficulties emerge in explaining its relation to scintillation activity. On the other hand, the equatorial scintillations can be observed in the absence of the magnetospheric ring current. It is shown that in addition to Aarons' criteria for the prediction of the ionospheric scintillations, models can be used to explain the relationship between the equatorial ionospheric parameters, h'F, foF2, and the equatorial geomagnetic variations with the polar ionosphere currents and the solar wind.

  17. Sudden Ionospheric Disturbances (SID)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Sudden ionospheric disturbances (SID) are caused by solar flare enhanced X-rays in the 1 to 10 angstrom range. Solar flares can produce large increases of ionization...

  18. The response of the lower ionosphere driven by the chain of the meteotsunamis in the Mediterranean Sea during 23 - 28 June 2014

    Science.gov (United States)

    Solovieva, Maria; Rozhnoi, Alexander; Levin, Boris; Biagi, Pier Francesco; Maggipinto, Tommaso; Fedun, Viktor

    2016-04-01

    The tsunamis are long waves originated in the seas and oceans from different reasons. The basic contribution to tsunami formation is created by the earthquakes, however there are another sources of the tsunamis. Among them some part of the tsunamis are formed due to the meteorological reasons. Such tsunamis formed under the influence of atmospheric processes are named the meteotsunamis. Jumps of the atmospheric pressure, typhoons, hurricanes, storms, cold fronts, etc. can be the meteotsunamis reasons. The meteotsunamis are observed at many locations around the world: in oceans, seas and even lakes. Tsunamis and meteotsunamis have the same periods, same spatial scales and they also generate internal gravity waves (IGWs) propagating upward into the ionosphere where they dissipate and produce perturbations in the plasma density. These perturbations can be detected by electromagnetic waves such as sub-ionospheric very low and low-frequencies (VLF/LF) signals. A chain of meteotsunamis was observed in the Mediterranean and the Black Sea during 23 - 28 June 2014. These events were caused by a unique synoptic system that traveled above the Mediterranean Sea from Spain to Turkey and into the Black Sea. The system produced sharp atmospheric pressure changes (more than 2 hPa in 5 min), which caused tsunami waves in the open waters of 2-3 cm. The waves traveled in the open sea in different directions and intensified topographically close to the coast. The measurements from the VLF/LF ground based network of receiver stations in the South Europe "The International Network For Frontier Research on Earthquake Precursors" (INFREP) were used to study the response of the lower ionosphere to the meteotsunamis in the Mediterranean Sea. Revealed VLF/LF anomalies coincided in time with meteotsunami events. The nighttime anomalies in low-frequency signal were observed on 23-24 June in the region between Spain and Sicily. The next VLF/LF anomalies were registered on 25-26 June near Italy

  19. 电离层人工调制在水平分层电离层中所激发的ELF波辐射%Radiation of ELF waves by ionospheric artificial modulation into a stratified ionosphere

    Institute of Scientific and Technical Information of China (English)

    汪枫; 赵正予; 常珊珊; 赵光欣; 青海银

    2012-01-01

    通过大功率ELF/VIF调幅高频波能有效地扰动低电离层,形成等效的ELF/VLF电离层虚拟天线,用来辐射ELF/VLF波,所辐射出的低频信号可以进入中性大气层形成地球-电离层波导.本文基于调制加热模型,采用全波有限元算法计算由人工调制电离层所形成的电偶极矩所辐射出的ELF波在水平分层电离层中的波场,计算结果将与地面观测结果进行比较.模拟结果表明,所辐射出的ELF波在电离层中形成一个窄的准直波束,海面所能接收到的ELF信号强度为pT量级,并且频率越低,海面所接收到的场强就越小,与HAARP实验数据一致.结果还表明,低纬电离层对低频信号的传播衰减较大,并且所能透射出电离层的角度小,因此高纬地区更适合地球-电离层波导的激发.%Using powerful high-frequency radio waves modulated at ELF/VLF can efficiently modify the lower ionosphere which can act as an equivalent ELF/VLF virtual antenna for the generation of ELF/VLF waves which can propagate in the Earth-ionosphere waveguide. In this paper, based on the modulation model, a full-wave finite element method is used to calculate the field of the ELF waves radiated by the dipole moment which is produced by ionospheric artificial modulation in the stratified ionosphere and the calculated values are compared to the ground observation. The numerical modeling shows that these waves form a narrow collimated beam and the magnitude of field intensity of low frequency signals received on the sea is -pT which will become smaller when the frequency is lower and this result is in accordance with the laboratory data from HAARP. The result also shows that it has stronger attenuation and small angel penetrating the ionosphere for the low signal at low latitude, so that the excitation of the Earth-ionosphere waveguide is easier at high latitude.

  20. Ionospheric Perturbations Possibly Caused by Preseismic Electromagnetic Emissions

    Science.gov (United States)

    Sgrigna, V.; Conti, L.; Corsi, M.; Galper, A. M.; Malvezzi, V.; Picozza, P.; Scrimaglio, R.; Stagni, L.; Zilpimiani, D.

    2001-05-01

    The seismicity is one of the main manifestations of the dynamical processes into the lithosphere. Electromagnetic emissions (EME) in the ULF/ELF/VLF/LF/HF range, that are related to the seismic activity, are known since a long time, but their generation mechanisms are not well understood. Two types of emissions can be considered. First, precursory emissions observed in a large frequency range, from some fraction of Hz up to several MHz, which occur a few hours before earthquakes and related to the rock microfracturing in the preparation focal area. Second, emissions observed after a shock and generally attributed to the propagation of acoustic-gravity waves. Several mechanisms have been proposed for the ionospheric perturbations caused by EME: ionospheric motion; Joule heating; plasma instabilities; precipitations of high energy charged particles (particle bursts) from the radiation belt. The explanation of the last phenomenon is connected with a disturbance of the particle flux in the lower radiation belt caused by the ULF EME waves generated in the forthcoming earthquake hypocenter and propagated upwards into the near Earth space. ULF EME interact with charged particles trapped by the Geomagnetic field modifying their pitch angle and provoking the precipitation of such particles from the radiation belt. The precipitated particle bursts (PB) drift around the Earth along the L-shell which corresponds to the earthquake epicenter. The results of correlations between PBs and earthquakes will be reported.

  1. Electric and VLF-MT survey of Tegatayama tunnel; Tegatayama tunnel no denki tansa oyobi VLF tansa

    Energy Technology Data Exchange (ETDEWEB)

    Nishitani, T. [Akita University, Akita (Japan). Mining College

    1997-05-27

    To survey the structure at the depth between 20 and 30 m, field tests were conducted by means of vertical electric and VFL-MT (magnetotelluric) survey. Tegatayama tunnel has a total length of 276 m, width of 7.5 m, and height of 4.7 m, and the depth from the surface is about 28 m near the top of mountain. Near the tunnel, the thickness of surface soil is about 60 cm, which consists of clay soil including soft mudstone gravel. It was found that terrace deposit is distributed up to the depth of 8 m, and that mudstone is distributed below the depth of 8 m. Weighted four-electrode method was adopted for the vertical electrical survey. Measurements were conducted at the immediately above the tunnel, 10 m apart from the center of tunnel in the right and left, and 20 m apart from the center in the east. For the VLF-MT method, component of frequency 22.2 kHz was used. As a result of the tests, it was difficult to illustrate the existence of tunnel from the vertical electrical survey only at one point. Feature of the tunnel could be well illustrated by means of the VLF-MT method. 3 refs., 9 figs.

  2. Martian ionosphere response to solar wind variability during solar minimum

    Science.gov (United States)

    Sanchez-Cano, Beatriz; Lester, Mark; Witasse, Olivier; Mays, M. Leila; Hall, Benjamin E. S.; Milan, Stephen E.; Cartacci, Marco; Blelly, Pierre-Louis; Andrews, David; Opgenoorth, Hermann; Odstrcil, Dusan

    2016-04-01

    Solar cycle variations in solar radiation create notable density changes in the Martian ionosphere. In addition to this long-term variability, there are numerous short-term and non-recurrent solar events that hit Mars which need to be considered, such as Interplanetary Coronal Mass Ejections (ICMEs), Co-Rotation Interaction Regions (CIRs), solar flares, or solar wind high speed streams. The response of the Martian plasma system to each of these events is often unusual, especially during the long period of extreme low solar activity in 2008 and 2009. This work shows the long-term solar cycle impact on the ionosphere of Mars using data from The Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS), and The Analyzer of Space Plasma and Energetic Atoms (ASPERA-3), and with empirical and numerical models on Mars Express. Particular attention is given to the different ionospheric responses observed during the last, extended solar minimum. Mars' ionospheric response followed a similar pattern to the response observed in the Earth's ionosphere, despite the large differences related to the inner-origin of the magnetic field of both planets. The ionospheric temperature was cooler, the topside scale height was smaller and almost constant with altitude, the secondary ionospheric layer practically disappeared and the whole atmospheric total electron content (TEC) suffered an extreme reduction of about 30-40%, not predicted before by models. Moreover, there is a larger probability for the induced magnetic field to be present in the ionosphere, than in other phases of the solar cycle. The short-term variability is also addressed with the study of an ICME followed by a fast stream that hit Mars in March 2008, where solar wind data are provided by ACE and STEREO-B and supported by simulations using the WSA-ENLIL Model. The solar wind conditions lead to the formation of a CIR centred on the interface of the fast and the slow solar wind streams. Mars' system reacted to

  3. Preseismic Lithosphere-Atmosphere-Ionosphere Coupling

    Science.gov (United States)

    Kamogawa, Masashi

    [Liu et al, JGR, 2006], nighttime decrease of background intensity of VLF electromagnetic waves possibly attributed to ionospheric disturbance in D region [Nemec et al., GRL, 2008; Nemec et al., JGR, 2009; Pisa et al, JGR, 2013]. Although these reported anomalies are plausible from a statistical correlation mostly satisfying the above criteria. In this presentation, I review recent studies of preseismic atmospheric-ionospheric coupling and introduce the plausible mechanisms.

  4. Disturbance in the lower ionosphere that accompanied the reentry of the Chelyabinsk cosmic body

    Science.gov (United States)

    Chernogor, L. F.

    2017-09-01

    The paper describes quasi-periodic and aperiodic variations in the phase and amplitude of radio waves of LF and VLF ranges, which accompanied the flight and explosion of the Chelyabinsk meteoroid. Quasi-periodic variations in the phase have been explained by the generation of acoustic-gravity waves in the atmosphere, which modulate the electron density in the ionosphere and the phase of radio waves. Aperiodic variations in the phase and amplitude of radio waves are associated with an increase in the electron density in the lower ionosphere (at altitudes of 65-70 km). This increase was most likely caused by the interactions of subsystems in the Earth-atmosphere-ionosphere-magnetosphere system or, more correctly, by the precipitation of high-energy electrons from the magnetosphere into the lower ionosphere, which was stimulated by the flight and explosion of a cosmic body. According to the estimates, the density of the flux of electrons with energies of 100 KeV should be on the order of 106 m-2 s-1.

  5. Interpretation of VLF-EM & VLF-R data using tipper and impedance analyses: A case study from Candi Umbul-Telomoyo, Magelang, Indonesia

    Science.gov (United States)

    Prastyani, Erina; Niasari, Sintia Windhi

    2017-07-01

    The goal of all geophysical survey techniques is to image the properties of the Earth's subsurface. Very Low Frequency (VLF) is one of the geophysical survey technique that has been commonly used for ore exploration and mapping faults or fracture zones. Faults or fracture zones are necessary components in providing the fluid pathway in geothermal systems. The Candi Umbul-Telomoyo is one of the geothermal prospect sites in Indonesia, which is located in Magelang, Central Java. Recent studies hypothesized that this site was an outflow area of Telomoyo volcano geothermal complex. We used the VLF-EM and VLF-R techniques to infer faults or fracture zones that might be a path for geothermal fluids in the Candi Umbul-Telomoyo. From the measurements, we got tilt angle, ellipticity, primary and secondary magnetic fieldfor VLF-EM data; and apparent resistivity, phase angle, electric and magnetic field for VLF-R data. To interpret the data, we used tipper and impedance analyses. The result of both analyses show similarities in the directions and positions of anomalous current concentrations. We conclude these anomalous current concentrations as faults. Our interpretation is agreeing with the Geologic Map of the Semarang and Magelang Quadrangles that shows the expected fault beneath the Mt. Telomoyo.

  6. Nowcasting, forecasting and warning for ionospheric propagation: supporting databases

    Directory of Open Access Journals (Sweden)

    N. Jakowski

    2004-06-01

    Full Text Available The use of data is essential in the context of nowcasting, forecasting and warning of ionospheric propagation conditions, with roles to play in the development, evaluation and operation of models and services. Descriptions are given of three databases that have been established in the course of the COST 271 Action: a database of prompt ionospheric soundings, an extension to a database generated by the EISCAT incoherent scatter radars, and a database intended to facilitate evaluation of TEC estimation methods. Each database includes some background information, a description of the contents and interface, and instructions as to how to gain access to it.

  7. The cause of small scale disturbances in the lower ionosphere of Mars

    Science.gov (United States)

    Peter, Kerstin Susanne; Pätzold, Martin; González-Galindo, Francisco; Molina-Cuberos, Gregorio; Lillis, Robert J.; Dunn, Patrick A.; Witasse, Olivier; Tellmann, Silvia; Häusler, Bernd

    2016-10-01

    The radio-science experiment MaRS (Mars Express Radio Science) on the Mars Express spacecraft sounds the neutral atmosphere and ionosphere of Mars since 2004. Approximately 800 vertical profiles of the ionospheric electron density have been acquired until today. A subset of these MaRS dayside observations contains small scale disturbances in the lower part of the ionosphere. Those electron density profiles show unusual small scale features in the M1 altitude range which appear either merged with or completely detached from the M1 layer. Possible explanations for this additional ionospheric electron density may be ionospheric NO+, enhanced solar X-ray fluxes, solar energetic particle events (SEPs) or meteoroid influx. A 1D photo-chemical model of the Mars dayside ionosphere (IonA-2) is used to investigate the behavior of planetary NO+ in the lower dayside ionosphere. The influence of variable solar X-ray on the ionospheric electron density is estimated with IonA-2 and the influence of SEPs is discussed. A possible correlation between the meteoroid influx in the Mars atmosphere and the small scale disturbances is investigated based on a model of the ablation/chemical reactions of meteoroids with the atmosphere/ionosphere (MSDM) and on MAVEN IUVS magnesium ion observations.

  8. More evidence for a one-to-one correlation between Sprites and Early VLF perturbations

    DEFF Research Database (Denmark)

    Haldoupis, C.; Amvrosiadi, N.; Cotts, B. R. T.;

    2010-01-01

    Past studies have shown a correlation between sprites and early VLF perturbations, but the reported correlation varies widely from ∼50% to 100%. The present study resolves these large discrepancies by analyzing several case studies of sprite and narrowband VLF observations, in which multiple...... for this option to be resolved we need more studies using highly sensitive optical systems capable of detecting weaker sprites, sprite halos and elves....

  9. Large-Scale Ionospheric Effects Related to Electron-Gyro Harmonics: What We Have Learned from HAARP.

    Science.gov (United States)

    Watkins, B. J.; Fallen, C. T.; Secan, J. A.

    2014-12-01

    The HAARP ionospheric modification facility has unique capabilities that enable a wide range of HF frequencies with transmit powers ranging from very low to very high values. We will review a range of experiment results that illustrate large-scale ionospheric effects when the HF frequencies used are close to electron gyro-harmoncs and we focus mainly on the 3rd and 4th harmonics. The data are primarily from the UHF diagnosticc radar and total electron content (TEC) observations through the heated topside ionosphere. Radar data for HF frequencies just above and just below gyro harmoncs show significant differences in radar scatter cross-section that suggest differing plasma processes, and this effect is HF power dependent with some effects only observable with full HF power. For the production of artificial ionization in the E-region when the HF frequency is near gyro-harmoncs the results differ significantly for relatively small (50 kHz) variations in the HF frequency. We show how slow FM scans in conjunction with gyro-harmonic effects are effective in producing artificial ionization in the lower ionosphere.In the topside ionosphere enhanced density and upward fluxes have been observed and these may act as effective ducts for the propagation of VLF waves upward into the magneosphere. Experimental techniques have been developed that may be used to continuously maintain these effects in the topside ionossphere.

  10. Ionosphere monitoring and forecast activities within the IAG working group "Ionosphere Prediction"

    Science.gov (United States)

    Hoque, Mainul; Garcia-Rigo, Alberto; Erdogan, Eren; Cueto Santamaría, Marta; Jakowski, Norbert; Berdermann, Jens; Hernandez-Pajares, Manuel; Schmidt, Michael; Wilken, Volker

    2017-04-01

    Ionospheric disturbances can affect technologies in space and on Earth disrupting satellite and airline operations, communications networks, navigation systems. As the world becomes ever more dependent on these technologies, ionospheric disturbances as part of space weather pose an increasing risk to the economic vitality and national security. Therefore, having the knowledge of ionospheric state in advance during space weather events is becoming more and more important. To promote scientific cooperation we recently formed a Working Group (WG) called "Ionosphere Predictions" within the International Association of Geodesy (IAG) under Sub-Commission 4.3 "Atmosphere Remote Sensing" of the Commission 4 "Positioning and Applications". The general objective of the WG is to promote the development of ionosphere prediction algorithm/models based on the dependence of ionospheric characteristics on solar and magnetic conditions combining data from different sensors to improve the spatial and temporal resolution and sensitivity taking advantage of different sounding geometries and latency. Our presented work enables the possibility to compare total electron content (TEC) prediction approaches/results from different centers contributing to this WG such as German Aerospace Center (DLR), Universitat Politècnica de Catalunya (UPC), Technische Universität München (TUM) and GMV. DLR developed a model-assisted TEC forecast algorithm taking benefit from actual trends of the TEC behavior at each grid point. Since during perturbations, characterized by large TEC fluctuations or ionization fronts, this approach may fail, the trend information is merged with the current background model which provides a stable climatological TEC behavior. The presented solution is a first step to regularly provide forecasted TEC services via SWACI/IMPC by DLR. UPC forecast model is based on applying linear regression to a temporal window of TEC maps in the Discrete Cosine Transform (DCT) domain

  11. Characterizing Extreme Ionospheric Storms

    Science.gov (United States)

    Sparks, L.; Komjathy, A.; Altshuler, E.

    2011-12-01

    Ionospheric storms consist of disturbances of the upper atmosphere that generate regions of enhanced electron density typically lasting several hours. Depending upon the storm magnitude, gradients in electron density can sometimes become large and highly localized. The existence of such localized, dense irregularities is a major source of positioning error for users of the Global Positioning System (GPS). Consequently, satellite-based augmentation systems have been implemented to improve the accuracy and to ensure the integrity of user position estimates derived from GPS measurements. Large-scale irregularities generally do not pose a serious threat to estimate integrity as they can be readily detected by such systems. Of greater concern, however, are highly localized irregularities that interfere with the propagation of a signal detected by a user measurement but are poorly sampled by the receivers in the system network. The most challenging conditions have been found to arise following disturbances of large magnitude that occur only rarely over the course of a solar cycle. These extremely disturbed conditions exhibit behavior distinct from moderately disturbed conditions and, hence, have been designated "extreme storms". In this paper we examine and compare the behavior of the extreme ionospheric storms of solar cycle 23 (or, more precisely, extreme storms occurring between January 1, 2000, and December 31, 2008), as represented in maps of vertical total electron content. To identify these storms, we present a robust means of quantifying the regional magnitude of an ionospheric storm. Ionospheric storms are observed frequently to occur in conjunction with magnetic storms, i.e., periods of geophysical activity as measured by magnetometers. While various geomagnetic indices, such as the disturbance storm time (Dst) and the planetary Kp index, have long been used to rank the magnitudes of distinct magnetic storms, no comparable, generally recognized index exists for

  12. On the effectiveness of the vlf-em method For ground water prospecting in the Basement terrains, Sinai, Egypt

    OpenAIRE

    Shendi, El-Arabi Hendi [العربيى هندي شندي

    1997-01-01

    The VLF-EM method is proved to be an effective, fast and inexpensive tool for ground water prospecting in the basement terrains of Southern Sinai. The resistive shallow alluvial deposits increase the penetration depth of the received VLF waves to as deep as 40 meters which is very reasonable to detect the water bearing alluvium in the studied areas. The measured horizontal and vertical components of the resultant VLF-EM field were used to calculate the apparent resistivities of the conductive...

  13. Investigation of the Earth Ionosphere using the Radio Emission of Pulsars

    CERN Document Server

    Ulyanov, O M; Mukha, D V; Seredkina, A A

    2013-01-01

    The investigation of the Earth ionosphere both in a quiet and a disturbed states is still desirable. Despite recent progress in its modeling and in estimating the electron concentration along the line of sight by GPS signals, the impact of the disturbed ionosphere and magnetic field on the wave propagation still remains not sufficiently understood. This is due to lack of information on the polarization of GPS signals, and due to poorly conditioned models of the ionosphere at high altitudes and strong perturbations. In this article we consider a possibility of using the data of pulsar radio emission, along with the traditional GPS system data, for the vertical and oblique sounding of the ionosphere. This approach also allows to monitor parameters of the propagation medium, such as the dispersion measure and the rotation measure using changes of the polarization between pulses. By using a selected pulsar constellation it is possible to increase the number of directions in which parameters of the ionosphere and ...

  14. 3 dimensional ionospheric electron density reconstruction based on GPS measurements

    Science.gov (United States)

    Stolle, C.; Schlüter, S.; Jacobi, C.; Jakowski, N.

    When radio waves as sended by the naviagtion system GPS are passing through the ionosphere they are subject to delays in phase, travel time and polarisation which is an effect of the free electrons. The measured integrated value of Total Electron Content can be utilised for three-dimensional reconstruction of electron density patterns in the ionosphere. Here a tomographic approach is represented. Scince the distribution of data is very sparse and patchy we decided for an algebraic iterative algorithm. The ground based GPS data collected by IGS receivers can be combined by space based GPS of radio limb sounding, incoherent scatter radar and ionosondes data. Hereby, radio occultation data improve beside the amount of available data especially the vertical resolution of electron density distribution. Ionosonde peack electron densities are taken as stop criteria determination for iteration. Reconstructed ionospheric scenarios and validations of the system by independent measurements are presented.

  15. Global scale ionospheric irregularities associated with thunderstorm activity

    CERN Document Server

    Pulinets, S A

    2002-01-01

    The potential difference near 280 kV exists between ground and ionosphere. This potential difference is generated by thunderstorm discharges all over the world, and return current closes the circuit in the areas of fair weather (so-called fair weather current). The model calculations and experimental measurements clearly demonstrate non-uniform latitude-longitude distribution of electric field within the atmosphere. The recent calculations show that the strong large scale vertical atmospheric electric field can penetrate into the ionosphere and create large scale irregularities of the electron concentration. To check this the global distributions of thunderstorm activity obtained with the satellite monitoring for different seasons were compared with the global distributions of ionosphere critical frequency (which is equivalent to peak electron concentration) obtained with the help of satellite topside sounding. The similarity of the obtained global distributions clearly demonstrates the effects of thunderstor...

  16. Effective electron recombination coefficient in ionospheric D-region during the relaxation regime after solar flare from February 18, 2011

    Energy Technology Data Exchange (ETDEWEB)

    Nina, A. [Institute of Physics, University of Belgrade, P.O. Box 57, Belgrade (Serbia); Cadez, V. [Astronomical Observatory, Volgina 7, 11060 Belgrade (Serbia); Sulic, D., E-mail: dsulic@ipb.ac.rs [Faculty of Ecology and Environmental Protection, Union - Nikola Tesla University, Cara Dusana 62, 11000 Belgrade (Serbia); Sreckovic, V. [Institute of Physics, University of Belgrade, P.O. Box 57, Belgrade (Serbia); Zigman, V. [University of Nova Gorica, Vipavska 13, Rona Dolina, SI-5000 Nova Gorica (Slovenia)

    2012-05-15

    In this paper, we present a model for determination of a weakly time dependent effective recombination coefficient for the perturbed terrestrial ionospheric D-region plasma. We study consequences of a class M1.0 X-ray solar flare, recorded by GOES-15 satellite on February 18, 2011 between 14:00 and 14:15 UT, by analyzing the amplitude and phase real time variations of very low frequency (VLF) radio waves emitted by transmitter DHO (located in Germany) at frequency 23.4 kHz and recorded by the AWESOME receiver in Belgrade (Serbia). Our analysis is limited to ionospheric perturbations localized at altitudes around 70 km where the dominant electron gain and electron loss processes are the photo-ionization and recombination, respectively.

  17. Current methods for studying dynamic processes in the ionosphere. Sovremennye metody issledovaniia dinamicheskikh protsessov v ionosfere

    Energy Technology Data Exchange (ETDEWEB)

    Filipp, N.D.; Blaunshtein, N.SH.; Erukhimov, L.M.; Ivanov, V.A.; Uriadov, V.P.

    1991-01-01

    Current experimental and theoretical data relevant to the study of dynamic processes in the ionospheric plasma using state-of-the-art methods are summarized. The methods used include linear FM sounding, partial radio wave reflection, oblique-incidence radio wave scattering, radio wave heating of the ionosphere, plasma injection, and computer simulation of physical processes. For each specific method, experimental data are compared against theoretical predictions and numerical calculations. 251 refs.

  18. Ionospheric Effects from the superbolid exploded over the Chelyabinsk area

    Science.gov (United States)

    Ruzhin, Yuri; Smirnov, Vladimir; Kuznetsov, Vladimir; Smirnova, Elena

    The Chelyabinsk meteorite fall is undoubtedly the most documented in history. Its passage through the atmosphere was recorded by video and photographers, visual observers, infrasonic microphones, seismographs on the ground, and by satellites in orbit. The data of transionospheric sounding by signals from the GPS cluster satellites carried out in the zone of explosion of the Chelyabinsk meteoroid have been analyzed. The analysis has shown that the explosion had a very weak effect on the ionosphere. The observed ionospheric disturbances were asymmetric with respect to the explosion epicenter. The signals obtained were compared both in shape and in amplitude with the known surface explosions for which the diagnostics of the ionospheric effects had been made by radio techniques. Ionospheric effects in the form of acoustic-gravity waves (AGW) produced by 500-600 tons TNT explosions on the ground are detected with confidence both by vertical sounding and by GPS techniques. This allows us to suggest that the reported equivalent of the meteoroid explosion was obviously overestimated. The experiments on the injection of barium vapor (3.3 kg) carried out under similar conditions in the terminator zone revealed the response of the ionosphere in variations of the critical frequencies of the layer at a distance of 1500-2000 km (AGW with a period of 5-10 min). The absence of such ionospheric effects in the remote zone at 1500-1700 km from the epicenter of the bolide explosion in the case under discussion also makes us feel doubtful about the estimated explosion equivalent.

  19. Saturn's ionosphere and plasmasphere

    Science.gov (United States)

    Moore, Luke Edward

    2008-01-01

    A number of puzzling phenomena were revealed when the Voyager spacecraft flew past Saturn in 1981 to measure the ionized portions (ionosphere) of its upper atmosphere (thermosphere). Most of these issues have remained unexplained in the intervening 25 years due to a lack of conclusive observational data. With the arrival of Cassini at Saturn in July 2004, however, a new era of observations began, providing the promise of fresh evidence and demanding the development of a contemporary theoretical framework in order to re-examine old mysteries and understand new discoveries. This dissertation presents studies of Saturn's ionosphere and inner plasmasphere based on new time-dependent photochemical and diffusive transport models that solve the ion equations of continuity in one dimension. Calculations are conducted within the overall framework of a self-consistent, three-dimensional general circulation model (GCM) of Saturn's thermosphere, and the results of these studies are combined with GCM results to provide the building blocks of a new comprehensive model, the Saturn-Thermosphere- Ionosphere-Model (STIM). The one-dimensional model calculations are used to constrain and investigate a number of unresolved issues and to make testable predictions based on those investigations. Five primary topics are addressed: (1) the additional loss processes required to bring predicted electron densities into agreement with observations, (2) the discrepancy between theory and observations regarding the diurnal variation of peak electron density, (3) the effects of shadowing by Saturn's rings on its ionosphere, (4) the yet unknown electron and ion temperatures at Saturn, and (5) the ionospheric contribution to Saturn's plasmasphere. The models show that a steady influx of water into Saturn's atmosphere--from its rings or icy satellites--is required to explain observed electron densities. Additionally, the time-variability of the water source may be the cause of frequently observed

  20. Foley Sounds vs Real Sounds

    DEFF Research Database (Denmark)

    Trento, Stefano; Götzen, Amalia De

    2011-01-01

    This paper is an initial attempt to study the world of sound effects for motion pictures, also known as Foley sounds. Throughout several audio and audio-video tests we have compared both Foley and real sounds originated by an identical action. The main purpose was to evaluate if sound effects...

  1. Effects of Martian crustal magnetic field on its ionosphere

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The effect of the Martian crustal magnetic field is one of the hot topics of the study of Martian ionosphere.The studies on this topic are summarized in this paper.Main data of the Martian ionosphere were resulted from radio occultation experiments.According to the observations,the electron density scale height and the peak electron density of the Martian ionosphere are influenced by its crustal magnetic field.The strong horizontal magnetic field prevents the vertical diffusion of the plasma and makes the electron density scale height in the topside ionosphere close to that in the photo equilibrium region.In the cusp-like regions with strong vertical magnetic field,the enhanced vertical diffusion leads to a larger electron density scale height in the diffusion equilibrium region.The observation of radio occultation experiment onboard Mars Global Surveyor (MGS) showed that the averaged peak electron density observed in the southern hemisphere with strong crustal magnetic field was slightly larger than that in the northern hemisphere with weak crustal magnetic field.The Mars advanced radar for subsurface and ionosphere sounding (MARSIS) onboard Mars Express (MEX) was the first topside sounder to be used to observe Martian ionosphere.The MARSIS results confirmed that the enhancement of the peak electron density occurred in cusp-like regions with open field lines,and the amount of the enhancement was much larger than that observed by the radio occultation experiment.There are two possible mechanisms for the peak electron density enhancement in the cusp-like crustal magnetic field regions:One is the precipitation of the energetic particles and the other is the heating by the waves excited by plasma instabilities.It’s difficult to determine which one is the key mechanism for the peak electron density enhancement.Based on these studies,several interesting problems on the Martian ionosphere and plasma environment are presented.

  2. Variation properties of ionospheric eclipse factor and ionospheric influence factor

    Institute of Scientific and Technical Information of China (English)

    ZHAO Chunmei; YUAN Yunbin; OU Jikun; CHEN Jinping

    2005-01-01

    The concepts and calculation methods of ionospheric eclipse factor (IEF) and ionospheric influence factor (IFF) are further illustrated. The temporal and spacial variation properties of IEF and IFF are studied, which shows that the properties are influenced by the geographic position and season. The possibility of improving the precision of using GPS data to determine ionospheric delay based on the above variation properties is also analysed.

  3. Field aligned current observations in the polar cusp ionosphere

    Science.gov (United States)

    Ledley, B. G.; Farthing, W. H.

    1973-01-01

    Vector magnetic field measurements made during a sounding rocket flight in the polar cusp ionosphere show field fluctuations in the lower F-region which are interpreted as being caused by the payload's passage through a structured field aligned current system. The field aligned currents have a characteristic horizontal scale size of one kilometer. Analysis of one large field fluctuation gives a current density of 0.0001 amp/m sq.

  4. Field-aligned current observations in the polar cusp ionosphere

    Science.gov (United States)

    Ledley, B. G.; Farthing, W. H.

    1974-01-01

    Vector magnetic field measurements made during a sounding rocket flight in the polar cusp ionosphere show field fluctuations in the lower F region that are interpreted as being caused by the passage of the payload through a structured field-aligned current system. The field-aligned currents have a characteristic horizontal scale size of about 1 km. Analysis of one large field fluctuation gives a current density of .001 A/sq m.

  5. Ionospheric Feedback Instability in the Coupling of Magnetosphere-Ionosphere

    Institute of Scientific and Technical Information of China (English)

    王旭宇; 曹晋滨

    2003-01-01

    The ionospheric feedback instability is discussed by using the conductivity argument. We give an exact quantitative description to show that the free energy for this instability comes from the reduction of the Joule dissipation produced by the pre-existing convection electric field through self-consistent changes in ionization and conducactive ionosphere is pumped into the magnetosphere, wlich is contrary to the usual case whereby energy carried electron E × B drift. The electron conductivity is controlled by the ion Perdersen conductivity rather than by the electrons Pedersen conductivity. We also provide a qualitative theoretical explanation to the intense aurora favoured by a lower ambient ionospheric conductivity in the ionospheric feedback instability.

  6. The Sounds of Space

    Science.gov (United States)

    Gurnett, Donald

    2009-11-01

    The popular concept of space is that it is a vacuum, with nothing of interest between the stars, planets, moons and other astronomical objects. In fact most of space is permeated by plasma, sometimes quite dense, as in the solar corona and planetary ionospheres, and sometimes quite tenuous, as is in planetary radiation belts. Even less well known is that these space plasmas support and produce an astonishing large variety of waves, the ``sounds of space.'' In this talk I will give you a tour of these space sounds, starting with the very early discovery of ``whistlers'' nearly a century ago, and proceeding through my nearly fifty years of research on space plasma waves using spacecraft-borne instrumentation. In addition to being of scientific interest, some of these sounds can even be described as ``musical,'' and have served as the basis for various musical compositions, including a production called ``Sun Rings,'' written by the well-known composer Terry Riley, that has been performed by the Kronos Quartet to audiences all around the world.

  7. TLEs and early VLF events: Simulating the important impact of transmitter-disturbance-receiver geometry

    Science.gov (United States)

    NaitAmor, S.; Ghalila, H.; Cohen, M. B.

    2017-01-01

    Early very low frequency (VLF) events are perturbations to subionospherically propagating VLF radio transmitters which sometimes occur when lightning activity is near the transmitter-receiver path. They are often correlated to Transient Luminous Events (TLEs). Recent analysis have focused on a new type of early events whose recovery time persists for many minutes, called LOng Recovery Events (LOREs). The underlying cause of these events is still unclear. Curiously, LOREs sometimes appear on only one path, while the same event observed on a different transmitter-receiver path does not indicate a LORE. In this paper we observe and simulate two cases of early signal perturbations: The first is a typical early VLF event, and the second is a LORE. Both were recorded by two AWESOME VLF receivers in North Africa on 12 December 2009, during the EuroSprite campaign. We combine observations with theoretical modeling to infer the electron density change that most closely reproduces the observed perturbation. Our results explain the cases where LOREs are detected on only one path as resulting from transmitter-receiver geometry significantly which impacts the modal content and therefore the observed VLF recovery time.

  8. Ionospheric Turbulence and the Evolution of Artificial Irregularities Excited by RF Interactions at HAARP

    Science.gov (United States)

    Sheerin, J. P.; Rayyan, N.; Watkins, B. J.; Bristow, W. A.; Bernhardt, P. A.

    2015-12-01

    The HAARP phased-array HF transmitter at Gakona, AK delivers up to 3.6 GW (ERP) of HF power in the range of 2.8 - 10 MHz to the ionosphere with millisecond pointing, power modulation, and frequency agility. HAARP's unique features have enabled the conduct of a number of nonlinear plasma experiments in the interaction region of overdense ionospheric plasma including stimulated electromagnetic emissions (SEE), artificial aurora, artificial ionization layers, VLF wave-particle interactions in the magnetosphere, strong Langmuir turbulence (SLT) and suprathermal electron acceleration. Diagnostics include the Modular UHF Ionospheric Radar (MUIR) sited at HAARP, the SuperDARN-Kodiak HF radar, spacecraft radio beacons, HF receivers to record stimulated electromagnetic emissions (SEE) and telescopes and cameras for optical emissions. We report on short timescale ponderomotive overshoot effects, artificial field-aligned irregularities (AFAI), the aspect angle dependence of the intensity of the plasma line, and suprathermal electrons. For a narrow range of HF pointing between Spitze and magnetic zenith, a reduced threshold for AFAI is observed. Applications are made to the study of irregularities relevant to spacecraft communication and navigation systems.

  9. Studies of High Power RF-induced Turbulence in the Ionosphere over HAARP

    Science.gov (United States)

    Sheerin, J. P.; Watkins, B. J.; Bristow, W. A.; Bernhardt, P. A.

    2016-12-01

    The HAARP phased-array HF transmitter at Gakona, AK delivers up to 3.6 GW (ERP) of HF power in the range of 2.8 - 10 MHz to the ionosphere with millisecond pointing, power modulation, and frequency agility. HAARP's unique features have enabled the conduct of a number of nonlinear plasma experiments in the interaction region of overdense ionospheric plasma including stimulated electromagnetic emissions (SEE), artificial aurora, artificial ionization layers, VLF wave-particle interactions in the magnetosphere, strong Langmuir turbulence (SLT) and suprathermal electron acceleration. Diagnostics include the Modular UHF Ionospheric Radar (MUIR) sited at HAARP, the SuperDARN-Kodiak HF radar, spacecraft radio beacons, HF receivers to record stimulated electromagnetic emissions (SEE) and telescopes and cameras for optical emissions. We report on short timescale ponderomotive overshoot effects, artificial field-aligned irregularities (AFAI), the aspect angle dependence of the intensity of the plasma line, and production of suprathermal electrons. For a narrow range of HF pointing between Spitze and magnetic zenith, a reduced threshold for AFAI is observed. Recent results of simulations of these experiments enable interpretation of many observed features. Applications are made to the study of irregularities relevant to spacecraft communication and navigation systems.

  10. Imagining Sound

    DEFF Research Database (Denmark)

    Grimshaw, Mark; Garner, Tom Alexander

    2014-01-01

    We make the case in this essay that sound that is imagined is both a perception and as much a sound as that perceived through external stimulation. To argue this, we look at the evidence from auditory science, neuroscience, and philosophy, briefly present some new conceptual thinking on sound...... that accounts for this view, and then use this to look at what the future might hold in the context of imagining sound and developing technology....

  11. Imagining Sound

    DEFF Research Database (Denmark)

    Grimshaw, Mark; Garner, Tom Alexander

    2014-01-01

    We make the case in this essay that sound that is imagined is both a perception and as much a sound as that perceived through external stimulation. To argue this, we look at the evidence from auditory science, neuroscience, and philosophy, briefly present some new conceptual thinking on sound...... that accounts for this view, and then use this to look at what the future might hold in the context of imagining sound and developing technology....

  12. The European VLF/LF Radio Network: the current status

    Science.gov (United States)

    Biagi, Pier Francesco; Maggipinto, Tommaso; Schiavulli, Luigi; Ligonzo, Teresa; Colella, Roberto; Ermini, Anita; Martinelli, Giovanni; Palangio, Paolo; Moldovan, Iren; Silva, Hugo; Contadakis, Michael; Frantzis, Xenophon; Katzis, Konstantinos; Buyuksarac, Aydin; D'Amico, Sebastiano

    2014-05-01

    Since 2009 a network of VLF (20-60 kHz) and LF (150-300 kHz) radio receivers has been put into operation in Europe in order to study earthquakes precursors. At the moment the network consists of eleven receivers four of which are located in Italy, two in Greece and one in Portugal, Romania, Malta, Cyprus and Turkey. The data (sampling rate of 1min) are downloaded automatically at the end of each day and they are stored in the server located at the Department of Physics of the University of Bari (Italy), that is the central node of the network. Still, in some case, problems of connection exist. The different trends are open and visible on the web site: http://beta.fisica.uniba.it/infrep/Hom.aspx. The data files can be downloaded by the same web site but they are protected by username and password. Among the different methods of data analysis the Wavelet spectra appear to be the most sensitive ones. The software able to apply this technique on the radio data automatically at the end of each day has been planned and realized. At the moment it operates on four signals collected by one of the Italian receivers; if an anomaly stands up and it is over a fixed threshold a warning advise appears. In the web site, this activity is protected by a specific username and password.

  13. Local Ionospheric Scintillation Analysis

    Science.gov (United States)

    2017-03-14

    WORK UNIT NUMBER 7.  PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) ASIAN INSTITUTE OF TECHNOLOGY MOO 9 PHAHOLYOTHIN RD KM.42 KLONG NUNG PATHUM 12120...carried out as part of the densification and maintenance of the SCINDA network in South East Asia. 15.  SUBJECT TERMS Ionosphere, AOARD 16...Theoretical Physics (ICTP), International Civil Aviation Organization (ICAO), Boston College, University of California Los Angeles and AMBER projects

  14. Probing geomagnetic storm-driven magnetosphere-ionosphere dynamics in D-region via propagation characteristics of very low frequency radio signals

    Science.gov (United States)

    Nwankwo, Victor U. J.; Chakrabarti, Sandip K.; Ogunmodimu, Olugbenga

    2016-07-01

    The amplitude and phase of VLF/LF radio signals are sensitive to changes in electrical conductivity of the lower ionosphere which imprints its signature on the Earth-ionosphere waveguide. This characteristic makes it useful in studying sudden ionospheric disturbances, especially those related to prompt X-ray flux output from solar flares and gamma ray bursts (GRBs). However, strong geomagnetic disturbance and storm conditions are known to produce large and global ionospheric disturbances, which can significantly affect VLF radio propagation in the D region of the ionosphere. In this paper, using the data of three propagation paths at mid-latitudes (40-54°), we analyse the trend in variation of aspects of VLF diurnal signal under varying solar and geomagnetic space environmental conditions in order to identify possible geomagnetic footprints on the D region characteristics. We found that the trend of variations generally reflected the prevailing space weather conditions in various time scales. In particular, the 'dipping' of mid-day signal amplitude peak (MDP) occurs after significant geomagnetic perturbed or storm conditions in the time scale of 1-2 days. The mean signal amplitude before sunrise (MBSR) and mean signal amplitude after sunset (MASS) also exhibit storm-induced dipping, but they appear to be influenced by event's exact occurrence time and the highly variable conditions of dusk-to-dawn ionosphere. We also observed few cases of the signals rise (e.g., MDP, MBSR or MASS) following a significant geomagnetic event. This effect may be related to storms associated phenomena or effects arising from sources other than solar origin. The magnitude of induced dipping (or rise) significantly depends on the intensity and duration of event(s), as well as the propagation path of the signal. The post-storm day signal (following a main event, with lesser or significantly reduced geomagnetic activity) exhibited a tendency of recovery to pre-storm day level. In the

  15. VLF/LF EM emissions as main precursor of earthquakes and their searching possibilities for Georgian s/a region

    Science.gov (United States)

    Kachakhidze, Manana; Kachakhidze, Nino

    2016-04-01

    Authors of abstract have created work which offers model of earth electromagnetic emissions generation detected in the process of earthquake preparation on the basis of electrodynamics. The model gives qualitative explanation of a mechanism of generation of electromagnetic waves emitted in the earthquake preparation period. Besides, scheme of the methodology of earthquake forecasting is created based on avalanche-like unstable model of fault formation and an analogous model of electromagnetic contour, synthesis of which, is rather harmonious. According to the authors of the work electromagnetic emissions in radiodiapason is more universal and reliable than other anomalous variations of various geophysical phenomena in earthquake preparation period; Besides, VLF/LF electromagnetic emissions might be declared as the main precursor of earthquake because it might turn out very useful with the view of prediction of large (M ≥5) inland earthquakes and to govern processes going on in lithosphere-atmosphere - ionosphere coupling (LAIC) system. Since the other geophysical phenomena, which may accompany earthquake preparation process and expose themselves several months, weeks or days prior to earthquakes are less informative with the view of earthquake forecasting, it is admissible to consider them as earthquake indicators. Physical mechanisms of mentioned phenomena are explained on the basis of the model of generation of electromagnetic emissions detected before earthquake, where a process of earthquake preparation and its realization are considered taking into account distributed and conservative systems properties. Up to these days electromagnetic emissions detection network did not exist in Georgia. European colleagues helped us (Prof. Dr. PF Biagi, Prof. Dr. Aydın BÜYÜKSARAÇ) and made possible the installation of a receiver. We are going to develop network and put our share in searching of earthquakes problem. Participation in conference is supported by financial

  16. Observations of the impenetrable barrier, the plasmapause, and the VLF bubble during the 17 March 2015 storm

    Science.gov (United States)

    Foster, J. C.; Erickson, P. J.; Baker, D. N.; Jaynes, A. N.; Mishin, E. V.; Fennel, J. F.; Li, X.; Henderson, M. G.; Kanekal, S. G.

    2016-06-01

    Van Allen Probes observations during the 17 March 2015 major geomagnetic storm strongly suggest that VLF transmitter-induced waves play an important role in sculpting the earthward extent of outer zone MeV electrons. A magnetically confined bubble of very low frequency (VLF) wave emissions of terrestrial, human-produced origin surrounds the Earth. The outer limit of the VLF bubble closely matches the position of an apparent barrier to the inward extent of multi-MeV radiation belt electrons near 2.8 Earth radii. When the VLF transmitter signals extend beyond the eroded plasmapause, electron loss processes set up near the outer extent of the VLF bubble create an earthward limit to the region of local acceleration near L = 2.8 as MeV electrons are scattered into the atmospheric loss cone.

  17. Subionospehric VLF perturbations of red sprites: 3D FDTD modeling and experimental results

    Science.gov (United States)

    Iwamoto, M.; Hobara, Y.; Ohta, K.; Minatohara, T.; Otsuyama, T.; Hayakawa, M.

    2012-04-01

    Majority of red sprites occurs in association with large positive cloud to ground discharges. Although the red sprite consists of highly ionized structure, physical properties of the ionization columns such as electron density and spatial extent have not understood well. In this paper 3D finite-difference time-domain (FDTD) method carried out to compute the subionospheric VLF signal perturbations due to the sprite ionization columns. Spatial scales of columns are determined by the sprite images obtained from our optical observations during winter lightning activities over the sea of Japan. Numerical results indicate that the multiple sprites generate the complicated scattering pattern of the VLF transmitter waves depending on special orientation and extent of sprite ionization columns. Spatial dependence of the scattered amplitude are compared with those from the experimental results of VLF observation network.

  18. Combined ULF and VLF observations of seismo-electro-magnetic phenomena in Europe

    Science.gov (United States)

    Schwingenschuh, Konrad; Eichelberger, Hans; Wolbang, Daniel; Prattes, Gustav; Besser, Bruno; Boudjada, Mohammed Y.; Stangl, Günter; Magnes, Werner; Berghofer, Gerhard; Aydogar, Özer; Rozhnoi, Alexander; Solovieva, Maria; Vellante, Massimo; Villante, Umberto; Biagi, Pier F.

    2014-05-01

    A combined analysis of magnetic ultra-low-frequency (ULF) and electromagnetic very-low-frequency (VLF) fluctuations before, during and after earthquakes in south and south-east Europe is presented. The magnetic fluctuations are studied in the frame of the South European Geomagnetic Array (SEGMA) network. The fluxgate and searchcoil magnetometers, located in Italy, Bulgaria and Hungary perform measurements of fluctuations in the pico-Tesla and nano-Tesla range from milli-Hertz to 100 Hz. The properties of VLF radio links (10 kHz - 50 kHz) are studied in the frame of the European VLF/LF radio receiver network (INFREP). Single parameter studies of ULF and VLF variations in the vicinity of earthquakes in Europe have been performed in the last decade (Villante et al. 2010, Rozhnoi et al. 2009). We present the first results of a dual parameter study based on single parameter ULF and VLF observations. The proposed method provides the opportunity to decrease the number of false alerts. A dual parameter seismo-electro-magnetic reliability number is developed and compared with single parameter quality numbers. References: Rozhnoi, A., Solovieva, M., Molchanov, O., Schwingenschuh, K., Boudjada, M., Biagi, P. F., Maggipinto, T., Castellana, L., Ermini, A., and Hayakawa, M.: Anomalies in VLF radio signals prior the Abruzzo earthquake (M=6.3) on 6 April 2009, Nat. Hazards Earth Syst. Sci., 9, 1727-1732, doi:10.5194/nhess-9-1727-2009, 2009. Villante, U., De Lauretis, M., De Paulis, C., Francia, P., Piancatelli, A., Pietropaolo, E., Vellante, M., Meloni, A., Palangio, P., Schwingenschuh, K., Prattes, G., Magnes, W., and Nenovski, P.: The 6 April 2009 earthquake at L'Aquila: a preliminary analysis of magnetic field measurements, Nat. Hazards Earth Syst. Sci., 10, 203-214, doi:10.5194/nhess-10-203-2010, 2010.

  19. Quasi-periodic VLF emissions observed during daytime at a low latitude Indian ground station Jammu

    Indian Academy of Sciences (India)

    K K Singh; J Singh; R P Patel; A K Singh; R P Singh; Rejesh Singh; P A Ganai

    2009-06-01

    This paper reports quasi-periodic pulsing hiss emissions recorded during daytime in the frequency range of 50 Hz –15 kHz at low latitude station Jammu (geomag.lat.=22° 26′N; =1.17). It is noted that pulsing VLF emissions are a rare phenomena at low latitudes.The various spectrograms of pulsing VLF hiss emissions presented in this paper clearly show band limited spectrums regularly pulsing with almost equal period of the order of few seconds in the frequency range of ∼3-8 kHz. Generation and propagation mechanism of these emissions are briefly discussed.

  20. Subionospheric VLF signatures and their association with sprites observed during EuroSprite 2003

    DEFF Research Database (Denmark)

    Mika, A.; Haldoupis, C.; Marshall, R.A.

    2005-01-01

    to sprites. Bandpass filtering of the broadband VLF signal revealed that only about 5% of the sprites were escorted by early VLF perturbations, possibly due to backscatter. Finally, by using all 131 sprites captured during EuroSprite-2003, the time lags of the sprites to the preceding +/- CG discharges were...... computed and analyzed. The time-lag distribution had a well defined tail suggesting that at least one third of the sprites observed were lagging the +/- CG discharges by more than 30 up to 300 ms. In addition these "long-delayed" sprites were not accompanied by any radio-sferics during the sprite...

  1. Similar Data Retrieval from Enormous Datasets on ELF/VLF Wave Spectrum Observed by Akebono

    Directory of Open Access Journals (Sweden)

    Y Kasahara

    2010-02-01

    Full Text Available As the total amount of data measured by scientific spacecraft is drastically increasing, it is necessary for researchers to develop new computation methods for efficient analysis of these enormous datasets. In the present study, we propose a new algorithm for similar data retrieval. We first discuss key descriptors that represent characteristics of the VLF/ELF waves observed by the Akebono spacecraft. Second, an algorithm for similar data retrieval is introduced. Finally, we demonstrate that the developed algorithm works well for the retrieval of the VLF spectrum with a small amount of CPU load.

  2. Ionospheric response to the entry and explosion of the South Ural superbolide

    Science.gov (United States)

    Ruzhin, Yu. Ya.; Kuznetsov, V. D.; Smirnov, V. M.

    2014-09-01

    The South Ural meteoroid (February 15, 2013; near the city of Chelyabinsk) is undoubtedly the best documented meteoroid in history. Its passage through the atmosphere has been recorded on videos and photographs, visually by observers, with ground-based infrasound microphones and seismographs, and by satellites in orbit. In this work, the results are presented of an analysis of the transionospheric GPS sounding data collected in the vicinity of the South Ural meteoroid site, which show a weak ionospheric effect. The ionospheric disturbances are found to be asymmetric about the explosion epicenter. The received signals are compared, both in shape and amplitude, with the reported ionospheric effects of ground level explosions with radio diagnostics. It is shown that the confident registration of ionospheric effects as acoustic gravity waves (AGWs) by means of vertical sounding and GPS technologies for ground explosions in the range of 0.26-0.6 kt casts doubt on the existing TNT equivalent estimates (up to 500 kt) for the Chelyabinsk event. The absence of effects in the magnetic field and in the ionosphere far zone at distances of 1500-2000 km from the superbolide explosion epicenter also raises a question about the possibility of an overestimated TNT equivalent. An alternative explanation is to consider the superposition of a cylindrical ballistic wave (due to the hypersonic motion of the meteoroid) with spherical shock waves caused by the multiple time points of fragmentation (multiple explosions) of the superbolide as a resulting source of the AGW impact on ionospheric layers.

  3. Study of the mid-latitude ionospheric response to geomagnetic storms in the European region

    Science.gov (United States)

    Berényi, Kitti Alexandra; Barta, Veronika; Kis, Arpad

    2016-07-01

    Geomagnetic storms affect the ionospheric regions of the terrestrial upper atmosphere through different physical and atmospheric processes. The phenomena that can be regarded as a result of these processes, generally is named as "ionospheric storm". The processes depend on altitude, segment of the day, the geomagnetic latitude and longitude, strength of solar activity and the type of the geomagnetic storm. We examine the data of ground-based radio wave ionosphere sounding measurements of European ionospheric stations (mainly the data of Nagycenk Geophysical Observatory) in order to determine how and to what extent a geomagnetic disturbance of a certain strength affects the mid-latitude ionospheric regions in winter and in summer. For our analysis we used disturbed time periods between November 2012 and June 2015. Our results show significant changing of the ionospheric F2 layer parameters on strongly disturbed days compared to quiet ones. We show that the critical frequencies (foF2) increase compared to their quiet day value when the ionospheric storm was positive. On the other hand, the critical frequencies become lower, when the storm was negative. In our analysis we determined the magnitude of these changes on the chosen days. For a more complete analysis we compare also the evolution of the F2 layer parameters of the European ionosonde stations on a North-South geographic longitude during a full storm duration. The results present the evolution of an ionospheric storm over a geographic meridian. Furthermore, we compared the two type of geomagnetic storms, namely the CME caused geomagnetic storm - the so-called Sudden impulse (Si) storms- and the HSS (High Speed Solar Wind Streams) caused geomagnetic storms -the so-called Gradual storms (Gs)- impact on the ionospheric F2-layer (foF2 parameter). The results show a significant difference between the effect of Si and of the Gs storms on the ionospheric F2-layer.

  4. Swarm GPS Receiver Performance under the Influence of Ionospheric Scintillation

    Science.gov (United States)

    Ren, Le; Schön, Steffen

    2016-04-01

    The Swarm mission launched on 22 November 2013 is ESA's first constellation of satellites to study the dynamics of the Earth's magnetic field and its interaction with the Earth system. This mission consists of three identical satellites in near-polar orbits , two flying almost side-by-side at an initial altitude of 460 km, the third flying in a higher orbit of about 530 km. Each satellite is equipped with a high precision 8-channels dual-frequency receiver for the precise orbit determination, which is also the essential fundament in order to take full advantage of the data information provided by this constellation, e.g. for the recovery of gravity field. The quality of the final orbit determination depends on the observation data from the receivers. In this contribution, we will analyze the performance of the Swarm on-board receivers, especially under the influence of ionospheric scintillation caused by ionospheric irregularities. This is a prerequisite for high quality satellite positioning as well as a sound study of the ionosphere. Ionospheric scintillation can lead to the phase disturbances, cycle slips or even loss of signal tracking. The RINEX observation data from Swarm Level 1b products are used to analyze the Swarm receiver performance. We will demonstrate the signal strength, code and phase noise, different linear combinations (geometry free, ionosphere free), as well as GDOP values for the 3 Swarm satellites. The first results show that the observation data are severely disturbed and the signals could be lost around the geomagnetic equator and geomagnetic poles where the ionosphere is active. The results also show that the receivers are more stable in those areas after the update in October 2015.

  5. Ionospheric effects of whistler waves from rocket-triggered lightning

    Science.gov (United States)

    Cotts, B. R. T.; Gołkowski, M.; Moore, R. C.

    2011-12-01

    Lightning-induced electron precipitation (LEP) is one of the primary mechanisms for energetic electron loss from Earth's radiation belts. While previous works have emphasized lightning location and the return stroke peak current in quantifying lightning's role in radiation belt electron loss, the spectrum of the lightning return stroke has received far less attention. Rocket-triggered lightning experiments performed at the International Center for Lightning Research and Testing (ICLRT) at Camp Blanding, Florida, provide a means to directly measure the spectral content of individual lightning return strokes. Using an integrated set of numerical models and directly observed rocket-triggered lightning channel-base currents we calculate the latitudinal dependence of the precipitation signature. Model results indicate that rocket-triggered lightning may produce detectable LEP events and that return strokes with higher ELF (3 Hz-3 kHz) content cause proportionally more ionospheric ionization and precipitate more electrons at higher latitudes than return strokes with proportionally higher VLF (3 kHz-30 kHz) content. The predicted spatio-temporal signature of the induced electron precipitation is highly dependent upon the return stroke spectral content. As a result, we postulate that rocket-triggered lightning experiments enable us to the estimate the spectral profile of energetic electrons precipitated from the Earth's radiation belts.

  6. On the numerical modelling of VLF chorus dynamical spectra

    Directory of Open Access Journals (Sweden)

    D. Nunn

    2009-06-01

    Full Text Available This paper presents a study of the use of a one-dimensional Vlasov Hybrid Simulation (VHS computer code to simulate the dynamical spectra (i.e. frequency versus time spectrograms of ELF/VLF chorus signals (from ~a fraction to ~10 kHz. Recently excellent measurements of chorus have been made in the source region close to the geomagnetic equator aboard the four spacecraft Cluster mission. Using Cluster data for wave amplitude, which is up to 300 pT, local gyrofrequency, cold plasma density, and L-shell, observed chorus signals are reproduced with remarkable fidelity and, in particular, sweep rates in the range 1–10 kHz result as observed. Further, we find that the sweep rate is a falling function of increasing cold plasma density, again in accord with observations. Finally, we have satisfactorily simulated the rather rare falling frequency elements of chorus which are sometimes observed aboard Cluster in the generation region. For both rising and falling chorus we have presented detailed structural analyses of the generation regions. The main contributor to the frequency sweep rate is primarily the establishment of wave number/frequency gradients across the generation region by the out of phase component of the resonant particle current. The secondary contributor is the shortening of the wavelength of resonant particle current relative to that of the wave field. In view of the close agreement between observation and simulation, we conclude that nonlinear electron cyclotron resonance is indeed the mechanism underlying the generation of chorus signals just outside the plasmasphere.

  7. Model of traveling ionospheric disturbances

    Directory of Open Access Journals (Sweden)

    Fedorenko Yury P.

    2013-10-01

    Full Text Available A multiscale semi-empirical model of traveling ionospheric disturbances (TIDs is developed. The model is based on the following assumptions: (1 TIDs are generated by acoustic-gravity waves (AGWs and propagate as pressure waves; (2 time intervals between adjacent extrema of atmospheric pressure oscillations in a disturbance source are constant; (3 the pressure extrema propagate from the source up to ~14 000 km at a constant horizontal velocity; (4 the velocity of each extremum is determined only by its number in a TID train. The model was validated using literature data on disturbances generated by about 20 surface and high-altitude nuclear explosions, two volcano explosions, one earthquake and by energetic proton precipitation events in the magnetospheric cusp of the northern hemisphere. Model tests using literature data show that the spatial and temporal TID periods may be predicted with an accuracy of 12%. Adequacy of the model was also confirmed by our observations collected using transionospheric sounding. The following TID parameters: amplitudes, horizontal spatial periods, and a TID front inclination angle in a vertical plane are increasing as the distance between an AGW and the excitation source is increasing. Diurnal and seasonal variability of the TID occurrence, defined as ratio of TID events to the total number of observations for the corresponding period, is not observed. However, the TID occurrence was growing from ~50% in 1987 to ~98% in 2010. The results of other studies asserting that the TID occurrence does not depend on the number of sunspots and magnetic activity are confirmed. The TID occurrence has doubled over the period from 1987 to 2010 indicating increasing solar activity which is not associated with sunspot numbers. The dynamics of spatial horizontal periods was studied in a range of 150–35 000 km.

  8. Unsound Sound

    DEFF Research Database (Denmark)

    Knakkergaard, Martin

    2016-01-01

    This article discusses the change in premise that digitally produced sound brings about and how digital technologies more generally have changed our relationship to the musical artifact, not simply in degree but in kind. It demonstrates how our acoustical conceptions are thoroughly challenged...... by the digital production of sound and, by questioning the ontological basis for digital sound, turns our understanding of the core term substance upside down....

  9. Compact way of the ionosphere layers critical frequency detection using A-map

    Science.gov (United States)

    Yusupov, Kamil; Akchurin, Adel

    2016-07-01

    The critical frequency of the ionosphere layer characterizes the electron density of the ionosphere layers and it is an important parameter for ionosphere observation. So, it has long been established that the critical frequencies have correlation with the solar activity, the geomagnetic activity, the neutral atmosphere and others. Based on the analysis of the critical frequency of the ionosphere the empirical models was based (e.g. IRI). Critical frequencies detection is complex due to the inhomogeneous properties of the ionosphere, which leads to the nonlinearity of reflection traces in ionogram at vertical sounding. This paper describes ionogram processing algorithm using the A-maps [Akchurin, 2011; Yusupov, 2014] for ionosphere layers critical frequency detection. For A-map construction, the reflected signal amplitude is allocated. Our ionosonde has not magnetoionic modes polarization separation; therefore, A-map has signal amplitude failures (due to interference). Also, ionosphere traces have amplitude failures associated with the signal focusing as a result of the effects of the TID and others. An important is the noise presence from the other HF radio system. To decrease the influence of these effects in critical frequency detection it is used several filtering stages that smooth A-map amplitude oscillation. Next is searching amplitude threshold, which mark the boundary of the critical frequency. The resulting F-plot easily compared with A-map, which have high precision visually noticeable critical frequency. This algorithm is well suited for the E- and F-regions critical frequency detection.

  10. Signatures of mesospheric particles in ionospheric data

    Directory of Open Access Journals (Sweden)

    M. Friedrich

    2009-02-01

    Full Text Available The state of the ionosphere during the 2007 ECOMA/MASS campaign is described by in-situ observations by three sounding rockets launched from the Andøya Rocket Range and by ground based observations. The ground based measurements included the incoherent scatter radar EISCAT near Tromsø (both on UHF and VHF, as well as an MF radar, a meteor radar and an imaging riometer all located in the close vicinity of the rocket range. The pronounced electron density bite-outs seen by two of the rockets could not be detected from the ground, but the associated PMSE (Polar Mesospheric Summer Echoes provide indirect evidence of pronounced perturbations of mesospheric electron densities.

  11. Sound Absorbers

    Science.gov (United States)

    Fuchs, H. V.; Möser, M.

    Sound absorption indicates the transformation of sound energy into heat. It is, for instance, employed to design the acoustics in rooms. The noise emitted by machinery and plants shall be reduced before arriving at a workplace; auditoria such as lecture rooms or concert halls require a certain reverberation time. Such design goals are realised by installing absorbing components at the walls with well-defined absorption characteristics, which are adjusted for corresponding demands. Sound absorbers also play an important role in acoustic capsules, ducts and screens to avoid sound immission from noise intensive environments into the neighbourhood.

  12. Ionospheric response to the partial solar eclipse of March 29, 2006, according to the observations at Nizhni Novgorod and Murmansk

    Science.gov (United States)

    Belikovich, V. V.; Vyakhirev, V. D.; Kalinina, E. E.; Tereshchenko, V. D.; Chernyakov, S. M.; Tereshchenko, V. A.

    2008-02-01

    The results of observations of the solar eclipse ionospheric effects on March 29, 2006, are presented. The observations were conducted using the partial reflection method near Nizhni Novgorod and the vertical sounding method at the automatic ionospheric station near Murmansk. It has been obtained that the electron density at altitudes of 77 and 91 km decreases by a factor of more than 4; in this case the response of the ionosphere at an altitude of 91 km lags behind the eclipse maximum phase on the Earth by approximately 20 min. It has been established that the eclipse in the E and F1 regions of the polar ionosphere causes a change in the electron density by 15-20%. The delay time of this effect varies from 12 to 24 min depending on the altitude. It has been registered that the reflection virtual altitude at altitudes of the ionospheric F region increases in Murmansk and Nizhni Novgorod.

  13. A review of GPS/GLONASS studies of the ionospheric response to natural and anthropogenic processes and phenomena

    Science.gov (United States)

    Afraimovich, Edward L.; Astafyeva, Elvira I.; Demyanov, Vladislav V.; Edemskiy, Ilya K.; Gavrilyuk, Nadezhda S.; Ishin, Artem B.; Kosogorov, Eugene A.; Leonovich, Lyudmila A.; Lesyuta, Oleg S.; Palamartchouk, Kirill S.; Perevalova, Natalia P.; Polyakova, Anna S.; Smolkov, Gennadyi Y.; Voeykov, Sergey V.; Yasyukevich, Yury V.; Zhivetiev, Ilya V.

    2013-08-01

    The article is a review of studies of ionospheric effects carried out in ISTP SB RAS. The main results of GPS/GLONASS radio sounding of ionospheric disturbances of natural and anthropogenic origin are presented. The article is devoted to ionospheric effects of solar eclipses, solar flares, solar terminator, earthquakes, tropical cyclones, large-scale ionospheric disturbances of auroral origin, rocket launches. Dynamics of global electron content analysis is also presented. The special attention is paid on the influence of solar flares and ionospheric irregularities on GPS and GLONASS performance. The work is a tribute to the leader of GNSS-monitoring workgroup Prof. E.L. Afraimovich (12 March 1940-8 November 2009).

  14. Three-dimensional FDTD Modeling of Earth-ionosphere Cavity Resonances

    Science.gov (United States)

    Yang, H.; Pasko, V. P.

    2003-12-01

    Resonance properties of the earth-ionosphere cavity were first predicted by W. O. Schumann in 1952 [Schumann, Z. Naturforsch. A, 7, 149, 1952]. Since then observations of extremely low frequency (ELF) signals in the frequency range 1-500 Hz have become a powerful tool for monitoring of global lightning activity and planetary scale variability of the lower ionosphere, as well as, in recent years, for location and remote sensing of sprites, jets and elves and associated lightning discharges [e.g., Sato et al., JASTP, 65, 607, 2003; Su et al., Nature, 423, 974, 2003; and references cited therein]. The simplicity and flexibility of finite difference time domain (FDTD) technique for finding first principles solutions of electromagnetic problems in a medium with arbitrary inhomogeneities and ever-increasing computer power make FDTD an excellent candidate to be the technique of the future in development of realistic numerical models of VLF/ELF propagation in Earth-ionosphere waveguide [Cummer, IEEE Trans. Antennas Propagat., 48, 1420, 2000], and several reports about successful application of the FDTD technique for solution of related problems have recently appeared in the literature [e.g., Thevenot et al., Ann. Telecommun., 54, 297, 1999; Cummer, 2000; Berenger, Ann. Telecommun., 57, 1059, 2002, Simpson and Taflove, IEEE Antennas Wireless Propagat. Lett., 1, 53, 2002]. In this talk we will present results from a new three-dimensional spherical FDTD model, which is designed for studies of ELF electromagnetic signals under 100 Hz in the earth-ionosphere cavity. The model accounts for a realistic latitudinal and longitudinal variation of ground conductivity (i.e., for the boundaries between oceans and continents) by employing a broadband surface impedance technique proposed in [Breggs et al., IEEE Trans. Antenna Propagat., 41, 118, 1993]. The realistic distributions of atmospheric/lower ionospheric conductivity are derived from the international reference ionosphere model

  15. Ionosperic anomaly due to seismic activities – Part 1: Calibration of the VLF signal of VTX 18.2 KHz station from Kolkata and deviation during seismic events

    Directory of Open Access Journals (Sweden)

    S. Sasmal

    2009-08-01

    Full Text Available VLF signals are long thought to give away important information about the lithosphere-ionosphere coupling. In order to establish co-relations, if any, between the ionospheric activities and the earthquakes, we need to understand what the reference signals are, throughout the year. The best opportunity to do this is during the period of solar minimum where the number of flares and sunspots are negligible and the data would be primarily affected by the sun and variation would be due to normal sunset and sunrise effects. In this paper, we present the result of the sunrise and sunset terminators as a function of the day of the year for a period of four years, viz, 2005–2008 when the solar activity was very low. The terminators are for the 18.2 KHz VTX signal of the Indian Navy as observed from Indian Centre for Space Physics receiving station located in Kolkata. A total of 624 days of data have been used to obtain the mean plot. Any deviation of observations from this so-called the standardized calibration curve would point to influences by terrestrial (such as earthquakes and extra-terrestrial events (such as solar activities. We present examples of deviations which occur in a period of 16 months and show that the correlation with seismic events is significant and typically the highest deviation takes place up to a couple of days prior to the seismic event. Simultaneous observations of such deviations from more than one station could improve the predictability of earthquakes.

  16. Ionosperic anomaly due to seismic activities - Part 1: Calibration of the VLF signal of VTX 18.2 KHz station from Kolkata and deviation during seismic events

    Science.gov (United States)

    Sasmal, S.; Chakrabarti, S. K.

    2009-08-01

    VLF signals are long thought to give away important information about the lithosphere-ionosphere coupling. In order to establish co-relations, if any, between the ionospheric activities and the earthquakes, we need to understand what the reference signals are, throughout the year. The best opportunity to do this is during the period of solar minimum where the number of flares and sunspots are negligible and the data would be primarily affected by the sun and variation would be due to normal sunset and sunrise effects. In this paper, we present the result of the sunrise and sunset terminators as a function of the day of the year for a period of four years, viz, 2005-2008 when the solar activity was very low. The terminators are for the 18.2 KHz VTX signal of the Indian Navy as observed from Indian Centre for Space Physics receiving station located in Kolkata. A total of 624 days of data have been used to obtain the mean plot. Any deviation of observations from this so-called the standardized calibration curve would point to influences by terrestrial (such as earthquakes) and extra-terrestrial events (such as solar activities). We present examples of deviations which occur in a period of 16 months and show that the correlation with seismic events is significant and typically the highest deviation takes place up to a couple of days prior to the seismic event. Simultaneous observations of such deviations from more than one station could improve the predictability of earthquakes.

  17. The ionospheric response in the Brazilian sector during the super geomagnetic storm on 20 November 2003

    Science.gov (United States)

    Becker-Guedes, F.; Sahai, Y.; Fagundes, P. R.; Espinoza, E. S.; Pillat, V. G.; Lima, W. L. C.; Basu, Su.; Basu, Sa.; Otsuka, Y.; Shiokawa, K.; MacKenzie, E. M.; Pi, X.; Bittencourt, J. A.

    2007-05-01

    A very intense geomagnetic storm (superstorm) began with storm sudden commencement (SSC) at 08:03 UT on 20 November 2003, as a result of the coronal mass ejection (CME) by sunspot 484 hurled into space on 18 November 2003. The geomagnetic storm attained |Dst|max=472 nT at 20:00 UT (20 November). In this paper we present the simultaneous ionospheric sounding observations, using the Canadian Advanced Digital Ionosondes (CADIs), carried out from Palmas (PAL; 10.2° S, 48.2° W; dip latitude 5.5° S; a near equatorial station) and São José dos Campos (SJC; 23.2° S, 45.9° W; dip latitude 17.6° S; station located under the crest of equatorial ionospheric anomaly), Brazil. In addition, total electron content (TEC) measurements from several GPS receiving stations in the Brazilian sector during this storm are presented. The simultaneous ionospheric sounding observations carried out at SJC and PAL, and TEC observations on 3 consecutive days viz., 19 November (quiet), 20 November (disturbed) and 21 November (recovery phase) are presented. Salient features from the ionospheric observations in the Brazilian sector during the superstorm are discussed. The difference in the observed ionospheric response at the two stations (PAL and SJC) is considerable. This is not surprising given that PAL is close to the magnetic equator and SJC is near the crest of the equatorial ionospheric anomaly (EIA). It should be pointed out that soon after the SSC (about 4 h later), the F-region critical frequency (foF2), the F-region peak height (hpF2), and variations of virtual heights at different frequencies (iso-frequency plots) all show wavelike oscillations of the F-region during daytime at both the ionospheric sounding stations. Unusual rapid uplifting of F-region at PAL was observed during both the main and recovery phases of the storm.

  18. Investigation of TEC and VLF space measurements associated to L'Aquila (Italy earthquakes

    Directory of Open Access Journals (Sweden)

    G. Stangl

    2011-04-01

    Full Text Available In this study, we report on Total Electron Content (TEC and Very Low Frequency (VLF space measurements derived from Global Positioning System (GPS and DEMETER satellites, respectively. These measurements are associated with the earthquake (EQ of a magnitude of 6.3, which occurred on 6 April 2009, in L'Aquila (Italy. Anomaly features are derived from the analysis of TEC and VLF observations recorded two weeks before and after the seismic event occurrence. A TEC map with an interpolated regional pixel resolution of 1° × 1° × 15 min in latitude, longitude and time was generated, allowing for the checking of a possible presence of disturbances over the L'Aquila region. This analysis is combined with the study of the time profile associated to the VLF flux density variations recorded by the Instrument Champ Electrique (ICE experiment on-board DEMETER satellite. We discuss, on the one hand, the combination efficiency of the electronic density and the VLF electromagnetic measurements and, on the other hand, the difficulty to distinguish between global effects and regional ones related to the earthquake.

  19. Study of latitudinal effects on VLF transmitter signals recorded by DEMETER/ICE experiment

    Science.gov (United States)

    Boudjada, M. Y.; Schwingenschuh, K.; Berthelier, J. J.; Döller, R.; Galopeau, P. H. M.; Parrot, M.; Stangl, G.; Biernat, H.; Voller, W.; Besser, B.

    2010-05-01

    We report on VLF transmitter signals observed by the ‘Instrument Capteur Electrique' (ICE) experiment onboard the DEMETER micro-satellite. The DEMETER polar and circular sun-synchronous orbits lead to cover an invariant latitude range between -65° and +65° where up- and down-going half-orbits correspond to night-time (22:00 LT) and day-time (10:00 LT), respectively. The DEMETER orbit features permit to record signals emitted by some VLF ground-stations and detected by ICE experiment. We consider three transmitter signals emitted by stations in Europe (Germany, DFY, 16.58 kHz), in Asia (Japan, JP, 17.8 kHz) and in Australia (Australia, NWC, 19.8 kHz). We study the variation of these VLF signals taking into consideration the DEMETER satellite latitudes .We emphasis on latitudes where the satellite is close to the Earth's sub-auroral regions. We discuss particularly the presence, or not, of auroral magnetic activity effect on the VLF transmitter signals.

  20. Long-term analysis of ionospheric polar patches based on CHAMP TEC data

    DEFF Research Database (Denmark)

    Noja, M.; Stolle, Claudia; Park, J.

    2013-01-01

    Total electron content (TEC) from LEO satellites offers great possibility to sound the upper ionosphere and plasmasphere. This paper describes a method to derive absolute TEC observations aboard CHAMP considering multipath effects and receiver differential code bias. The long-term data set of 9...

  1. The study of the midlatitude ionospheric response to geomagnetic activity at Nagycenk Geophysical Observatory

    Science.gov (United States)

    Berényi, Kitti; Kis, Árpád; Barta, Veronika; Novák, Attila

    2016-04-01

    Geomagnetic storms affect the ionospheric regions of the terrestrial upper atmosphere, causing several physical and chemical atmospheric processes. The changes and phenomena, which can be seen as a result of these processes, generally called ionospheric storm. These processes depend on altitude, term of the day, and the strength of solar activity, the geomagnetic latitude and longitude. The differences between ionospheric regions mostly come from the variations of altitude dependent neutral and ionized atmospheric components, and from the physical parameters of solar radiation. We examined the data of the ground-based radio wave ionosphere sounding instruments of the European ionospheric stations (mainly the data of Nagycenk Geophysical Observatory), called ionosonde, to determine how and what extent a given strength of a geomagnetic disturbance affect the middle latitude ionospheric regions in winter. We chose the storm for the research from November 2012 and March 2015. As the main result of our research, we can show significant differences between the each ionospheric (F1 and F2) layer parameters on quiet and strong stormy days. When we saw, that the critical frequencies (foF2) increase from their quiet day value, then the effect of the ionospheric storm was positive, otherwise, if they drop, they were negative. With our analysis, the magnitude of these changes could be determined. Furthermore we demonstrated, how a full strong geomagnetic storm affects the ionospheric foF2 parameter during different storm phases. It has been showed, how a positive or negative ionospheric storm develop during a geomagnetic storm. For a more completed analysis, we compared also the evolution of the F2 layer parameters of the European ionosonde stations on a North-South geographic longitude during a full storm duration. Therefore we determined, that the data of the ionosonde at Nagycenk Geophysical Observatory are appropriate, it detects the same state of ionosphere like the

  2. Ionospheric Signatures of North Korean Nuclear Test on 12 February 2013

    Science.gov (United States)

    Yoon, M.; Kim, D.; Yang, Y. M.; Lee, J.; Komjathy, A.

    2014-12-01

    Previous studies on interactions between the atmospheric waves and ionospheric perturbations concluded that the acoustic-gravity waves triggered by solid earth events such as earthquakes, tsunamis and underground nuclear tests may be used in detecting the ionospheric perturbations. Ionospheric perturbations have been observed using sounding radars and GPS remote sensing techniques since 1970s. As primary examples, ionospheric disturbances associated with 2006 and 2009 North Korean underground nuclear tests were observed using GPS measurements. In this work, we processed GNSS stations in South Korea and Japan and analyzed traveling ionospheric disturbances that were coincident with the 2013 North Korean underground test. North Korea conducted the third underground nuclear test at 2:57 UTC on February 12, 2013. The magnitude of earthquake generated by this event was registered to be an Mw 5.1 event. After analyzing GPS measurements from nearby stations, strong ionospheric perturbations were observed 15-30 minutes after the reported event, and the disturbances were shown to have primarily two different wave trains. The maximum VTEC perturbations turned out to be between 0.4 to 0.7 TECU. Five stations located in the northwest-to-southeast direction were also scrutinized for the propagation direction and amplitude variation related to ionospheric wave structures. The results clearly showed that the maximum amplitude of the waves may be higher as the stations are closer to the epicenter indicating that the waveforms may propagate away from the epicenter. In this research, we will analyze the characteristics of the detected ionospheric perturbations associated with the underground nuclear test. These findings are expected to verify our modeling results. We hope to get a better understanding of the influence of man-made hazards on the temporal and spatial variability of the global ionosphere.

  3. Experimentally investigate ionospheric depletion chemicals in artificially created ionosphere

    Energy Technology Data Exchange (ETDEWEB)

    Liu Yu; Cao Jinxiang; Wang Jian; Zheng Zhe; Xu Liang; Du Yinchang [CAS Key Laboratory of Basic Plasma Physics, Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

    2012-09-15

    A new approach for investigating ionosphere chemical depletion in the laboratory is introduced. Air glow discharge plasma closely resembling the ionosphere in both composition and chemical reactions is used as the artificially created ionosphere. The ionospheric depletion experiment is accomplished by releasing chemicals such as SF{sub 6}, CCl{sub 2}F{sub 2}, and CO{sub 2} into the model discharge. The evolution of the electron density is investigated by varying the plasma pressure and input power. It is found that the negative ion (SF{sub 6}{sup -}, CCl{sub 2}F{sub 2}{sup -}) intermediary species provide larger reduction of the electron density than the positive ion (CO{sub 2}{sup +}) intermediary species. The negative ion intermediary species are also more efficient in producing ionospheric holes because of their fast reaction rates. Airglow enhancement attributed to SF{sub 6} and CO{sub 2} releases agrees well with the published data. Compared to the traditional methods, the new scheme is simpler to use, both in the release of chemicals and in the electron density measurements. It is therefore more efficient for investigating the release of chemicals in the ionosphere.

  4. Radar sounding of Mars from the orbit of the Mars-Express automatic interplanetary station

    Science.gov (United States)

    Smirnov, V. M.; Chernaya, L. F.; Yushkova, O. V.; Rykov, K. N.

    2006-07-01

    On the base of the laser altimetry results obtained using the orbital altimeter MOLA (the MGS mission) and the data of radio occultation experiments of transionospheric sounding of the Mars ionosphere, a method for interpretation of the planet radar sounding data is developed. The proposed method includes a program package for numerical simulation of the process of radiowave propagation through the media under study.

  5. Ionospheric precursors to scintillation activity

    Directory of Open Access Journals (Sweden)

    Paul S.J. Spencer

    2014-03-01

    Full Text Available Ionospheric scintillation is the rapid fluctuation of both phase and amplitude of trans-ionospheric radio waves due to small scale electron density irregularities in the ionosphere. Prediction of the occurrence of scintillation at L band frequencies is needed to mitigate the disruption of space-based communication and navigation systems. The purpose of this paper is to present a method of using tomographic inversions of the ionospheric electron density obtained from ground-based GPS data to infer the location and strength of the post-sunset plasma drift vortex. This vortex is related to the pre-reversal enhancement in the eastwards electric field which has been correlated to the subsequent occurrence of scintillation.

  6. Models of Titan's Ionosphere

    Science.gov (United States)

    Robertson, I. P.; Cravens, T. E.; Waite, J. H.; Wahlund, J.; Yelle, R. V.; Vuitton, V.; Coates, A.; Magee, B.; Gell, D. A.

    2007-12-01

    During the TA and T18 encounters with Titan, in situ measurements were made of Titan's atmosphere and ionosphere by several instruments on board the Cassini Orbiter, including the Ion and Neutral Mass Spectrometer (INMS), the Langmuir probe on the Cassini Radio and Plasma Wave Experiment (RPWS), and the Cassini Plasma Spectrometer Subsystem (CAPS). Both of these encounters were on the day as well as the night side of Titan. The model uses neutral densities measured by the INMS instrument and the electron temperature was measured by the RPWS instrument. The model also includes energetic electron fluxes measured by the CAPS instrument, which act as an important source of ionization on the night side. The modeled ion densities are compared with densities measured by INMS in its Open Source mode.

  7. Intra-plasmaspheric wave power density deduced from long-term DEMETER measurements of terrestrial VLF transmitter wave amplitudes

    Science.gov (United States)

    Lauben, D.; Cohen, M.; Inan, U.

    2012-12-01

    We deduce the 3d intra-plasmaspheric distribution of VLF wave power between conjugate regions of strong VLF wave amplitudes as measured by DEMETER for high-power terrestrial VLF transmitters during its ~6-yr lifetime. We employ a mixed WKB/full-wave technique to solve for the primary and secondary electromagnetic and electrostatic waves which are transmitted and reflected from strong cold-plasma density gradients and posited irregularities, in order to match the respective end-point measured amplitude distributions. Energy arriving in the conjugate region and also escaping to other regions of the magnetosphere is note. The resulting 3d distribution allows improved estimates for the long-term average particle scattering induced by terrestrial VLF transmitters.

  8. Van Allen Probes observations of prompt MeV radiation belt electron acceleration in nonlinear interactions with VLF chorus

    Science.gov (United States)

    Foster, J. C.; Erickson, P. J.; Omura, Y.; Baker, D. N.; Kletzing, C. A.; Claudepierre, S. G.

    2017-01-01

    Prompt recovery of MeV (millions of electron Volts) electron populations in the poststorm core of the outer terrestrial radiation belt involves local acceleration of a seed population of energetic electrons in interactions with VLF chorus waves. Electron interactions during the generation of VLF rising tones are strongly nonlinear, such that a fraction of the relativistic electrons at resonant energies are trapped by waves, leading to significant nonadiabatic energy exchange. Through detailed examination of VLF chorus and electron fluxes observed by Van Allen Probes, we investigate the efficiency of nonlinear processes for acceleration of electrons to MeV energies. We find through subpacket analysis of chorus waveforms that electrons with initial energy of hundreds of keV to 3 MeV can be accelerated by 50 keV-200 keV in resonant interactions with a single VLF rising tone on a time scale of 10-100 ms.

  9. Diagnostics of the ionospheric turbulence by wide band radio signals

    Science.gov (United States)

    Sergeev, Evgeny; Shindin, Alexey; Grach, Savely

    Results of the investigations of the time-space structure of the HF-pumped ionospheric volume above the SURA heating facility are presented. The method of investigations is based on mea-surements of the amplitude and phase of pulsed (pulse duration diagnostics, technical capabilities of SURA transmitter-receiver system, specially elaborated time-frequency modes of transmitter operation, space diversity three point reception, wide band signal recording, digital filtering, spectral and correlation analysis of the short radio pulses reflected from ionosphere were used. As a result of numerically solved in-verse problem of vertical sounding of the HF-perturbed ionosphere, dynamic behavior of the electron plasma density variations was obtained in the regions close to plasma resonance and upper hybrid resonance of the pump wave. In our experiments the pumping usually leaded to plasma expulsion from the resonance regions. A magnitude of artificial plasma density pertur-bations achieved 0.8% from the background density for pump power about P 60 MW ERP. The methods of a similarity and full correlation analysis were used for pulse signal amplitude processing, which were obtained by diversity three point reception with the receiving aerial separation of 84 m. As a result, novel data on fine structure of the space field of the vertical and horizontal velocities of plasma in the perturbed ionosphere volume with high time (up to 20 ms) and frequency (˜ 1 kHz) resolution are obtained. This frequency resolution can be translated into altitude resolution (˜ 50-100 m) in the ionosphere. The work was supported by RFBR grants 10-02-00642, 09-02-01150 and Federal Special-purpose Program "Scientific and pedagogical personnel of innovative Russia".

  10. Sound Intensity

    DEFF Research Database (Denmark)

    Crocker, M.J.; Jacobsen, Finn

    1997-01-01

    This chapter is an overview, intended for readers with no special knowledge about this particular topic. The chapter deals with all aspects of sound intensity and its measurement from the fundamental theoretical background to practical applications of the measurement technique....

  11. Sound Intensity

    DEFF Research Database (Denmark)

    Crocker, M.J.; Jacobsen, Finn

    1997-01-01

    This chapter is an overview, intended for readers with no special knowledge about this particular topic. The chapter deals with all aspects of sound intensity and its measurement from the fundamental theoretical background to practical applications of the measurement technique.......This chapter is an overview, intended for readers with no special knowledge about this particular topic. The chapter deals with all aspects of sound intensity and its measurement from the fundamental theoretical background to practical applications of the measurement technique....

  12. Sound intensity

    DEFF Research Database (Denmark)

    Crocker, Malcolm J.; Jacobsen, Finn

    1998-01-01

    This chapter is an overview, intended for readers with no special knowledge about this particular topic. The chapter deals with all aspects of sound intensity and its measurement from the fundamental theoretical background to practical applications of the measurement technique.......This chapter is an overview, intended for readers with no special knowledge about this particular topic. The chapter deals with all aspects of sound intensity and its measurement from the fundamental theoretical background to practical applications of the measurement technique....

  13. VLF Source Localization with a Freely Drifting Sensor Array

    Science.gov (United States)

    1992-09-01

    and the performance of the MFP is degraded and leads to errors in the es- timation of the source location [ Tolstoy , 1989; Feuillade et. al., 1989...EOFs), for measured physical quantities such as temperature, salinity, or sound speed as a function of depth [Davis, 1976; Tolstoy et. al., 19911. In an...4050 EOFCef~ lEO ~ref~lEOF~oef#I Figure 5.13 Joint trajectories of the wave number BOF coefficients for different annealing runs. 113

  14. Ionospheric Response during the Equinox and the Solstice Periods over Turkey

    Science.gov (United States)

    Cinar, Ali; Arikan, Feza; Karatay, Secil

    2016-07-01

    Ionosphere is a layer of the atmosphere which is an integral part of whole geomagnetic and geological framework. Ionosphere responds to solar EUV radiation by varying within the diurnal 24-hour period, seasonal periods and annually and over the 11-year cycle of solar activity. Therefore, relying on the evidence that there have been variations observed in the VLF, LF and HF signals, magnetic field of the earth and in the local electric field, a unified theory, that would explain the mechanism and cause of the disturbance in the layers of atmosphere, is a widely investigated research topic. In this study, the behavior of the IONOLAB- Total Electron Content (TEC) estimates obtained from dual frequency ground-based GPS receivers are examined using Symmetric Kullback Leibler Distance (SKLD) and L2 Norm (L2N) methods both for the periods that include the equinox and solstice between 2010 and 2012 for Turkey. The solstice and equinox periods within the same year and the solstice periods and the equinox periods from 2010 to 2012 are compared with each other for 18 Turkish National Permanent GPS Network (TNPGN-Active) stations. It is observed that the difference between solstice and equinox periods increases related to the upgrading geomagnetic activity. SKLD and L2N values in the solstice are larger than those in the equinox. This study is supported by TUBITAK EEEAG 114E541 a part of the Scientific and Technological Research Projects Funding Program.

  15. Comparison of ionospheric parameters calculated with UAM and measured at Voeykovo observatory

    Science.gov (United States)

    Rybakov, M. V.; Namgaladze, A. A.; Karpov, M. I.

    2016-09-01

    The measurements of the critical frequencies of the ionospheric F2 layer based on vertical radiosounding, which was performed with a CADI digital ionosonde at the Voeykovo magnetic-ionospheric observatory in February 2013, have been considered. The observations have been compared with the upper atmosphere numerical model (UAM) data for three days that differ in the amplitude and the character of solar and magnetic activity and correspond to quiet and moderately disturbed states of the ionosphere. The work was performed in order to improve the methods for determining the ionospheric state by vertical sounding ionograms. The time variations in the F2 layer critical frequency, electric field vector zonal component, and thermospheric wind velocity meridional component have been analyzed. Calculations were performed with three UAM variants. The UAM version providing the best agreement with the CADI ionosonde data was the version in which the neutral temperature, neutral composition, and pressure gradients are calculated according to the MSIS empirical model and the horizontal neutral wind velocity is determined by the equation of motion with pressure gradients from MSIS. The calculated values corresponded to the measurements, except those for the evening, because the electron density at the ionospheric F2 layer maximum depends more strongly on electric fields and thermospheric wind velocities during this period. Thus, the indicated UAM version with the above limitations can be used to determine the state of the subauroral ionosphere.

  16. The ionospheric eclipse factor method (IEFM) and its application to determining the ionospheric delay for GPS

    DEFF Research Database (Denmark)

    Yuan, Y.; Tscherning, C.C.; Knudsen, Per

    2006-01-01

    A new method for modeling the ionospheric delay using global positioning system (GPS) data is proposed, called the ionospheric eclipse factor method (IEFM). It is based on establishing a concept referred to as the ionospheric eclipse factor (IEF) lambda of the ionospheric pierce point (IPP...

  17. Satellite Observations of Ionospheric Earthquake Precursors

    Science.gov (United States)

    Grimal'Skij, V. V.; Ivchenko, V. N.; Lizunov, G. V.

    The authors review satellite observations of seismogenic phenomena in the ionosphere. Based on literature data, hypothetical patterns of seismogenic phenomena were reconstructed. The authors discuss the reasons which allow the ionospheric "anomalies" to be correlated with eartquake precursors.

  18. Latest progress on interactions between VLF/ELF waves and energetic electrons in the inner magnetosphere

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Interactions between very/extremely low frequency (VLF/ELF) waves and energetic electrons play a fundamental role in dynamics occurring in the inner magnetosphere. Here, we briefly discuss global properties of VLF/ELF waves, along with the variability of the electron radiation belts associated with wave-particle interactions and radial diffusion. We provide cases of electron loss and acceleration as a result of wave-particle interactions primarily due to such waves, and particularly some preliminary results of 3D evolution of phase space density from our currently developing 3D code. We comment on the existing mechanisms responsible for acceleration and loss, and identify several critical issues that need to be addressed. We review latest progress and suggest open questions for future investigation.

  19. Prediction Capabilities of VLF/LF Emission as the Main Precursor of Earthquake

    CERN Document Server

    Kachakhidze, Manana

    2013-01-01

    Recent satellite and ground-based observations proved that in earthquake preparation period in the seismogenic area we have VLF/LF and ULF electromagnetic emissions. According to the opinion of the authors of the present paper this phenomenon is more universal and reliable than other earthquake indicators. Hypothetically, in case of availability of adequate methodological grounds, in the nearest future, earth VLF/LF electromagnetic emission might be declared as the main precursor of earthquake. In particular, permanent monitoring of frequency spectrum of earth electromagnetic emission generated in the earthquake preparation period might turn out very useful with the view of prediction of large (M 5) inland earthquakes. The present paper offers a scheme of the methodology according to which the reality of the above given hypothesis can be checked up. To prove the prediction capabilities of earth electromagnetic emission we have used avalanche-like unstable model of fault formation and an analogous model of ele...

  20. Study the Broadband Very Low Frequency Data Received from Different Places and Observe the Possible Ionospheric Events

    Science.gov (United States)

    Sasmal, Sudipta; Chakrabarti, Sandip Kumar; Mondal, Sushanta Kumar; Ray, Suman

    2012-07-01

    We present the broad band data received from Stanford AWESOME VLF receiver at different places. We record the data from Kolkata, Ionospheric and Earthquake Research Center (IERC), Sitapur and Maitri Station, Antarctica. The broadband data contains data in the frequency range of 0-50kHz. This is in reality the Fourier transform of the magnetic field variation recorded from the magnetic cross loop antenna. The Antarctica data contains the signature of sferics but the signals do not have a strong signature of whistlers because the lightning effect is minimum at the conjugate points. Antarctica data is also dotted with massive precipitation of charged particles. For other baselines we try to observe the effect of the solar flares if any and try to compare it with quiet days.

  1. Ionospheric heating for radiation belt control

    Science.gov (United States)

    Burke, William J.; Villalon, Elena

    1990-10-01

    Pitch-angle scattering interactions of electromagnetic waves in the ELF/VLF bands with trapped electrons describe the dynamics of the freshly filled radiation belts flux tubes. The natural existence of a 'slot' region with electron fluxes below the Kennel-Petschek limit requires non-local wave sources. A set of planned, active experiments is described in which VLF radiation is injected from ground and space band transmitters in conjunction with the Combined Release and Radiation Effects Satellite in the radiation belts. These experiments can measure the intensity if waves driving pitch-angle diffusion and the electron energies in gyroresonance with the waves.

  2. Ionospheric Signatures of the Earthquake in South Korea on 31 March 2014

    Science.gov (United States)

    Choi, P. H.; Yoon, M.; Yang, Y. M.; Lee, J.; Komjathy, A.

    2015-12-01

    Previous studies on interactions between the atmospheric waves and ionospheric perturbations concluded that the acoustic-gravity waves triggered by solid earth events such as earthquakes, tsunamis and underground nuclear tests may be used in detecting the ionospheric perturbations. Ionospheric perturbations have been observed using sounding radars and GPS remote sensing techniques since 1970s. As primary examples, ionospheric disturbances associated with the Tohoku earthquake and tsunami on March 11, 2011 were observed and analyzed using GPS measurements. In this work, we processed GPS stations in South Korea and analyzed traveling ionospheric disturbances that were coincident with the 2014 South Korean earthquake. The 31 March 2014 earthquake occurred at 19:48 UTC and the magnitude of this event was registered to be 5.0 Mw. This earthquake is the fourth strongest in South Korea since records began. After analyzing GPS measurements from nearby stations, strong ionospheric perturbations were observed about 20 minutes after the reported event, and the disturbances were shown to have primarily a wave train with periods of 60-120 minutes. The maximum VTEC perturbations turned out to be between 0.6 to 1.3 TECU. In this research, we will analyze the characteristics of the detected ionospheric perturbations associated with the earthquake and compare these results with those from man-made earthquakes such as underground nuclear tests. These findings are expected to verify our modeling results. We also hope to get a better understanding of the influence of both natural hazards and man-made hazards on the temporal and spatial variability of the global ionosphere

  3. Electron dispersion events in the morningside auroral zone and their relationship with VLF emissions

    Science.gov (United States)

    Hardy, David A.; Burke, William J.; Villalon, Elena

    1990-05-01

    This paper reports on observations of electron precipitation bursts observed in the morningside auroral zone with the J sensor, an electron detector aboard the Hilat satellite. The characteristics of these precipitation events are documented, and a theoretical explanation that could account for the observed properties is presented. According to this model, the dispersion events result from impulsive interactions of the electrons with intense asymmetric packets of VLF waves via the nonlinear ponderomotive force.

  4. Unidentified Sounds

    DEFF Research Database (Denmark)

    Kreutzfeldt, Jacob

    2015-01-01

    This article investigates how urban spaces and its noises are approached by radio reporters in the first decades of public radio production in Denmark. Focussing on the period before reel tape was incorporated in production by late 1940es, I ask how urban space and urban sounds are heard...... in Danish radio until early post-war years. Yet I trace early attempts at managing noisy urban conditions and demonstrate how reporters experimented with available technological repositories and developed techniques in order to make sense in and through urban environments. Inspired by Michel Serres idea...... of the parasite I analyse such techniques as ways of distinguishing between noise and meaningful sounds, and ultimately show how such ventures constituted auditory responses to modernity and let organised sound enter the public sphere....

  5. Low-latitude ionospheric effects on SBAS

    Science.gov (United States)

    Arenas, J.; Sardón, E.; Sainz, A.; Ochoa, B.; Magdaleno, S.

    2016-06-01

    Satellite-based augmentation systems (SBAS) provide augmentation to Global Navigation Satellite Systems (GNSS) users in three areas: (1) broadcasting accurate corrections to GNSS satellite ephemeris, (2) providing a real-time empirical ionospheric model in the service area, and (3) providing integrity information in the form of estimates of the confidence of the ephemeris corrections and ionospheric delays. Ionospheric effects on SBAS are twofold: (a) the input data used by the SBAS will be affected by ionospheric effects, and (b) the more perturbed the ionosphere is, the more difficult it will be to provide accurate and reliable ionospheric information to the users. The ionosphere at low latitudes presents larger variability and more intense phenomena than at midlatitudes. Therefore, SBAS providing service to low-latitude regions will be more affected than those at other latitudes. From the different low-latitude ionospheric effects, this paper will focus on those having the largest impact on SBAS, which are total electron content temporal and spatial gradients, ionospheric scintillations, and depletions. This paper will present the impact of these effects on EGNOS (European Global Navigation Overlay System), the European SBAS. Although EGNOS can be considered as a midlatitude SBAS, it has to provide coverage down to rather low latitudes, so sometimes low-latitude ionospheric effects are observed in the EGNOS data. It will be shown how EGNOS performs under nominal conditions and how its performance is degraded when low-latitude ionospheric phenomena occur. Real EGNOS data affected by low-latitude ionospheric phenomena will be used.

  6. Study of long path VLF signal propagation characteristics as observed from Indian Antarctic station, Maitri

    Science.gov (United States)

    Sasmal, Sudipta; Pal, Sujay; Chakrabarti, Sandip K.

    2014-10-01

    To examine the quality and propagation characteristics of the Very Low Frequency (VLF) radio waves in a very long propagation path, Indian Centre for Space Physics, Kolkata, participated in the 27th Indian scientific expedition to Antarctica during 2007-2008. One Stanford University made AWESOME VLF receiving system was installed at the Indian Antarctic station Maitri and about five weeks of data were recorded successfully from the Indian transmitter VTX and several other transmitting stations worldwide. The quality of the signal from the VTX transmitter was found to be very good, consistent and highly stable in day and night. The signal shows the evidences of the presence of the 24 h solar radiation in the Antarctic region during local summer. Here we report the both narrow band and broadband VLF observations from this site. The diurnal variations of VTX signal (18.2 kHz) are presented systematically for Antarctica path and also compared the same with the variations for a short propagation path (VTX-Kolkata). We compute the spatial distribution of the VTX signal along the VTX-Antarctica path using the most well-known LWPC model for an all-day and all-night propagation conditions. The calculated signal amplitudes corresponding to those conditions relatively corroborate the observations. We also present the attenuation rate of the dominant waveguide modes corresponding to those propagation conditions where the effects of the Antarctic polar ice on the attenuation of different propagating waveguide modes are visible.

  7. Initial Results from SQUID Sensor: Analysis and Modeling for the ELF/VLF Atmospheric Noise

    Directory of Open Access Journals (Sweden)

    Huan Hao

    2017-02-01

    Full Text Available In this paper, the amplitude probability density (APD of the wideband extremely low frequency (ELF and very low frequency (VLF atmospheric noise is studied. The electromagnetic signals from the atmosphere, referred to herein as atmospheric noise, was recorded by a mobile low-temperature superconducting quantum interference device (SQUID receiver under magnetically unshielded conditions. In order to eliminate the adverse effect brought by the geomagnetic activities and powerline, the measured field data was preprocessed to suppress the baseline wandering and harmonics by symmetric wavelet transform and least square methods firstly. Then statistical analysis was performed for the atmospheric noise on different time and frequency scales. Finally, the wideband ELF/VLF atmospheric noise was analyzed and modeled separately. Experimental results show that, Gaussian model is appropriate to depict preprocessed ELF atmospheric noise by a hole puncher operator. While for VLF atmospheric noise, symmetric α-stable (SαS distribution is more accurate to fit the heavy-tail of the envelope probability density function (pdf.

  8. Sound Settlements

    DEFF Research Database (Denmark)

    Mortensen, Peder Duelund; Hornyanszky, Elisabeth Dalholm; Larsen, Jacob Norvig

    2013-01-01

    Præsentation af projektresultater fra Interreg forskningen Sound Settlements om udvikling af bæredygtighed i det almene boligbyggerier i København, Malmø, Helsingborg og Lund samt europæiske eksempler på best practice......Præsentation af projektresultater fra Interreg forskningen Sound Settlements om udvikling af bæredygtighed i det almene boligbyggerier i København, Malmø, Helsingborg og Lund samt europæiske eksempler på best practice...

  9. Fluid Sounds

    DEFF Research Database (Denmark)

    2016-01-01

    are tempo, time, voice, sound and music. Our goal is to bring analytical and performative awareness to academic means of expression, and the audio paper provides us with a new and experimental platform to do so. Our thoughts about and definition of the audio paper is explained in the first text of the issue...... by introducing a new format: The Audio Paper. The purpose of the audio paper is to extend the written academic text: to present discussions and explorations of a certain argument or problem in sound. The audio paper is an extension of expressive means: Not only words and syntax are means of expression – so...

  10. Resonant scattering of energetic electrons in the outer radiation belt by HAARP-induced ELF/VLF waves

    Science.gov (United States)

    Chang, Shanshan; Zhu, Zhengping; Ni, Binbin; Cao, Xing; Luo, Weihua

    2016-10-01

    Several extremely low-frequency (ELF)/very low-frequency (VLF) wave generation experiments have been performed successfully at High-Frequency Active Auroral Research Program (HAARP) heating facility and the artificial ELF/VLF signals can leak into the outer radiation belt and contribute to resonant interactions with energetic electrons. Based on the artificial wave properties revealed by many of in situ observations, we implement test particle simulations to evaluate the effects of energetic electron resonant scattering driven by the HAARP-induced ELF/VLF waves. The results indicate that for both single-frequency/monotonic wave and multi-frequency/broadband waves, the behavior of each electron is stochastic while the averaged diffusion effect exhibits temporal linearity in the wave-particle interaction process. The computed local diffusion coefficients show that, the local pitch-angle scattering due to HARRP-induced single-frequency ELF/VLF whistlers with an amplitude of ∼10 pT can be intense near the loss cone with a rate of ∼10-2 rad2 s-1, suggesting the feasibility of HAARP-induced ELF/VLF waves for removal of outer radiation belt energetic electrons. In contrast, the energy diffusion of energetic electrons is relatively weak, which confirms that pitch-angle scattering by artificial ELF/VLF waves can dominantly lead to the precipitation of energetic electrons. Moreover, diffusion rates of the discrete, broadband waves, with the same amplitude of each discrete frequency as the monotonic waves, can be much larger, which suggests that it is feasible to trigger a reasonable broadband wave instead of the monotonic wave to achieve better performance of controlled precipitation of energetic electrons. Moreover, our test particle scattering simulation show good agreement with the predictions of the quasi-linear theory, confirming that both methods are applied to evaluate the effects of resonant interactions between radiation belt electrons and artificially generated

  11. Atmospheric Gravity Waves (AGWs) as the driver of seismo-ionospheric coupling: recent major earthquakes of Nepal and Imphal - case study

    Science.gov (United States)

    Chakraborty, Suman; Chakrabarti, Sandip Kumar; Sasmal, Sudipta

    2016-07-01

    An important channel of the lithosphere-atmosphere-ionosphere coupling (LAIC) is the acoustic and gravity wave channel where the atmospheric gravity waves (AGW) play the most important part. Atmospheric waves are excited due to seismic gravitational vibrations before earthquakes and their effects on the atmosphere are the sources for seismo-ionospheric coupling which are manifested as perturbations in Very Low Frequency (VLF)/Low Frequency (LF) signal (amplitude/phase). For our study, we chose the recent major earthquakes that took place in Nepal and Imphal. The Nepal earthquake occurred on 12th May, 2015 at 12:50 pm local time (07:05 UTC) with Richter scale magnitude of M = 7.3 and depth 10 km (6.21 miles) at southeast of Kodari. The Imphal earthquake occurred on 4th January, 2016 at 4:35 am local time (23:05 UTC , 3rd January, UTC) with Richter scale magnitude of M = 6.7 and depth 55 km (34.2 miles). The data has been collected from Ionospheric and Earthquake Research Centre (IERC) of Indian Centre for Space Physics (ICSP) transmitted from JJI station of Japan. We performed both Fast Fourier Transform (FFT) and wavelet analysis on the VLF data for a couple of days before and after the major earthquakes. For both earthquakes, we observed wave like structures with periods of almost an hour before and after the earthquake day. The wave like oscillations after the earthquake may be due to the aftershock effects. We also observed that the amplitude of the wave like structures depends on the location of the epicenter between the transmitting and the receiving points and also on the depth of the earthquake.

  12. Sound Settlements

    DEFF Research Database (Denmark)

    Mortensen, Peder Duelund; Hornyanszky, Elisabeth Dalholm; Larsen, Jacob Norvig;

    2013-01-01

    Præsentation af projektresultater fra Interreg forskningen Sound Settlements om udvikling af bæredygtighed i det almene boligbyggerier i København, Malmø, Helsingborg og Lund samt europæiske eksempler på best practice...

  13. Use of Southern California Integrated GPS Network (SCIGN) to image post-seismic perturbations of the ionosphere.

    Science.gov (United States)

    Artru, J.; Ducic, V.; Lognonné, P.

    2002-12-01

    Post-seismic perturbations in the atmosphere and ionosphere are induced by solid earth-atmosphere coupling, and can be monitored systematically after large earthquakes, e.g. using Doppler sounding. We will focus here on the capacity of short-scale imagery of the ionosphere offered by dense GPS networks. SCIGN is composed of 250 receivers in Southern California that provide continuous measurements of Total Electron Content along each receiver-satellite. A reconstruction of 2-D vertical electron content maps is performed, with a special attention paid on the accuracy and resolution achieved. We applied our technique to the detection of post-seismic ionospheric perturbations by the Hector Mine Earthquake in Southern California on October 16th, 1999. Two regimes of seismic perturbations are found, the first one related to seismic waves traveling in the ionosphere at about 3 km/s whereas the second regime would be induced by the onset of a gravity wave.

  14. What in situ measurements of thermal electrons tell us about electron heating in the high-latitude ionosphere

    Science.gov (United States)

    Lund, E. J.; Lessard, M.; Cohen, I. J.; Lynch, K. A.

    2012-12-01

    The transfer of energy from precipitating particles and incoming photons to ionospheric plasma is a key issue in the physics of the high-latitude ionosphere. However, in situ measurements of electron temperature in the ionosphere have historically been difficult to make. Over the past decade, we have flown several rockets equipped with an electron retarding potential analyzer (ERPA), an instrument designed to measure thermal electrons in the ionosphere. These missions include launches into the cusp (SERSIO, SCIFER-2) and nightside aurora (CASCADES-2, ACES, MICA). In the cusp, the soft electron precipitation which is found in regions of ion outflow leads to increases in electron temperature due to energy deposition in the E and lower F region. The electron temperature increase at sounding rocket altitudes (500--1500~km) is delayed by ˜100~s with respect to the precipitation. By contrast, the higher energy of precipitating electrons in the nightside aurora makes them less effective at heating ionospheric electrons at these altitudes, while in downward current regions ionospheric electrons are found to be cooler than in upward current regions. We discuss the implications of these results for the ionospheric ion outflow problem as well as future prospects for in situ electron temperature measurements.

  15. Stratospheric Sudden Warming Effects on the Ionospheric Migrating Tides during 2008-2010 observed by FORMOSAT-3/COSMIC

    Science.gov (United States)

    Lin, J.; Lin, C.; Chang, L. C.; Liu, H.; Chen, W.; Chen, C.; Liu, J. G.

    2013-12-01

    In this paper, ionospheric electron densities obtained from radio occultation soundings of FORMOSAT-3/COSMIC are decomposed into their various constituent tidal components for studying the stratospheric sudden warming (SSW) effects on the ionosphere during 2008-2010. The tidal analysis indicates that the amplitudes of the zonal mean and major migrating tidal components (DW1, SW2 and TW3) decrease around the time of the SSW, with phase/time shifts in the daily time of maximum around EIA and middle latitudes. Meanwhile consistent enhancements of the SW2 and nonmigrating SW1 tides are seen after the stratospheric temperature increase. In addition to the amplitude changes of the tidal components, well matched phase shifts of the ionospheric migrating tides and the stratospheric temperatures are found for the three SSW events, suggesting a good indicator of the ionospheric response. Although the conditions of the planetary waves and the mean winds in the middle atmosphere region during the 2008-2010 SSW events may be different, similar variations of the ionospheric tidal components and their associated phase shifts are found. Futher, these ionospheric responses will be compared with realistic simulations of Thermosphere-Ionosphere-Mesophere-Electrodynamics General Circulation Model (TIME-GCM) by nudging Modern-Era Retrospective analysis for Research and Applications (MERRA) data.

  16. The Effects of the Ionosphere on Ground-based Detection of the Global 21 cm Signal from the Cosmic Dawn and the Dark Ages

    Science.gov (United States)

    Datta, Abhirup; Bradley, Richard; Burns, Jack O.; Harker, Geraint; Komjathy, Attila; Lazio, T. Joseph W.

    2016-11-01

    Detection of the global H i 21 cm signal from the Cosmic Dawn and the Epoch of Reionization is the key science driver for several ongoing ground-based and future ground-/space-based experiments. The crucial spectral features in the global 21 cm signal (turning points) occur at low radio frequencies ≲ 100 {{MHz}}. In addition to the human-generated radio frequency interference, Earth’s ionosphere drastically corrupts low-frequency radio observations from the ground. In this paper, we examine the effects of time-varying ionospheric refraction, absorption, and thermal emission at these low radio frequencies and their combined effect on any ground-based global 21 cm experiment. It should be noted that this is the first study of the effect of a dynamic ionosphere on global 21 cm experiments. The fluctuations in the ionosphere are influenced by solar activity with flicker noise characteristics. The same characteristics are reflected in the ionospheric corruption to any radio signal passing through the ionosphere. As a result, any ground-based observations of the faint global 21 cm signal are corrupted by flicker noise (or 1/f noise, where f is the dynamical frequency) which scales as {ν }-2 (where ν is the frequency of radio observation) in the presence of a bright galactic foreground (\\propto {ν }-s, where s is the radio spectral index). Hence, the calibration of the ionosphere for any such experiment is critical. Any attempt to calibrate the ionospheric effects will be subject to the inaccuracies in the current ionospheric measurements using Global Positioning System (GPS) ionospheric measurements, riometer measurements, ionospheric soundings, etc. Even considering an optimistic improvement in the accuracy of GPS-total electron content measurements, we conclude that Earth’s ionosphere poses a significant challenge in the absolute detection of the global 21 cm signal below 100 MHz.

  17. Characterising the Ionosphere (La caracterisation de l’ionosphere)

    Science.gov (United States)

    2009-01-01

    Astronomical Journal, 76, 2, pp. 123-140, 1971. Garcia-Fernandez, M., M. Hernandez-Pajares, J.M. Juan , J. Sanz, Improvement of ionospheric electron density...Katlenburg- Lindau , ProduServ GmbH Verlagsservice, Berlin, pp. 371-390, 1996. Jakowski, N., A. Wehrenpfennig, S. Heise, C. Reigber, H. Luehr, L

  18. Effects of Crustal Fields on the Ionosphere of Mars as seen by MAVEN

    Science.gov (United States)

    Vogt, Marissa F.; Withers, Paul; Flynn, Casey L.; Andersson, Laila; Brain, David; Mitchell, David; Connerney, Jack; Espley, Jared R.

    2016-10-01

    Mars lacks a global intrinsic magnetic field but possesses regions of strong crustal magnetic field that are concentrated in the southern hemisphere. Previous studies have used Mars Global Surveyor or Mars Express data to show that these crustal fields influence the electron densities in the Martian ionosphere. However, many of these studies relied on remote radio occultation or radar sounding measurements and therefore relied on models to infer the crustal magnetic field strength and direction. In fall 2015 the MAVEN spacecraft passed through these crustal field regions at low altitudes, on the day side, and collected comprehensive measurements of the local plasma and magnetic field properties. The MAVEN observations therefore provide an excellent dataset with which to examine the effects of crustal fields on the ionosphere. We report on the MAVEN electron density measurements in the southern crustal field regions and discuss the influence of the magnetic field direction and topology on the dayside Martian ionosphere.

  19. Ionosphere correction algorithm for spaceborne SAR imaging

    Institute of Scientific and Technical Information of China (English)

    Lin Yang; Mengdao Xing; Guangcai Sun

    2016-01-01

    For spaceborne synthetic aperture radar (SAR) ima-ging, the dispersive ionosphere has significant effects on the pro-pagation of the low frequency (especial y P-band) radar signal. The ionospheric effects can be a significant source of the phase error in the radar signal, which causes a degeneration of the image quality in spaceborne SAR imaging system. The background ionospheric effects on spaceborne SAR through modeling and simulation are analyzed, and the qualitative and quantitative analysis based on the spatio-temporal variability of the ionosphere is given. A novel ionosphere correction algorithm (ICA) is proposed to deal with the ionospheric effects on the low frequency spaceborne SAR radar signal. With the proposed algorithm, the degradation of the image quality caused by the ionosphere is corrected. The simulation re-sults show the effectiveness of the proposed algorithm.

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

    Directory of Open Access Journals (Sweden)

    D. P. Grubor

    2008-06-01

    Full Text Available 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.

  1. Daytime Ionosphere Retrieval Algorithm for the Ionospheric Connection Explorer (ICON)

    Science.gov (United States)

    Stephan, Andrew W.; Korpela, Eric J.; Sirk, Martin M.; England, Scott L.; Immel, Thomas J.

    2017-07-01

    The NASA Ionospheric Connection Explorer Extreme Ultraviolet spectrograph, ICON EUV, will measure altitude profiles of the daytime extreme-ultraviolet (EUV) OII emission near 83.4 and 61.7 nm that are used to determine density profiles and state parameters of the ionosphere. This paper describes the algorithm concept and approach to inverting these measured OII emission profiles to derive the associated O+ density profile from 150-450 km as a proxy for the electron content in the F-region of the ionosphere. The algorithm incorporates a bias evaluation and feedback step, developed at the U.S. Naval Research Laboratory using data from the Special Sensor Ultraviolet Limb Imager (SSULI) and the Remote Atmospheric and Ionospheric Detection System (RAIDS) missions, that is able to effectively mitigate the effects of systematic instrument calibration errors and inaccuracies in the original photon source within the forward model. Results are presented from end-to-end simulations that convolved simulated airglow profiles with the expected instrument measurement response to produce profiles that were inverted with the algorithm to return data products for comparison to truth. Simulations of measurements over a representative ICON orbit show the algorithm is able to reproduce hmF2 values to better than 5 km accuracy, and NmF2 to better than 12% accuracy over a 12-second integration, and demonstrate that the ICON EUV instrument and daytime ionosphere algorithm can meet the ICON science objectives which require 20 km vertical resolution in hmF2 and 18% precision in NmF2.

  2. Features of discrete VLF emissions observed at Gulmarg, India during the magnetic storm of 6–7 March, 1986

    Indian Academy of Sciences (India)

    R Singh; A K Singh; D Siingh; R P Singh

    2007-12-01

    During the analysis of archived VLF data from Indian low latitude ground stations, some discrete VLF emissions recorded at the low latitude ground station Gulmarg (geomagnetic latitude 24°26′N; geomagnetic longitude 147° 09′E, L = 1.28) during moderate magnetic storm activity ( $K^{−}_{P}$} = 32, index varies from 4 to 6 during the observation period) on 6/7 March, 1986 are presented in this paper. The dynamic spectra of these discrete VLF emissions were observed along with tweeks and its harmonics, which is interesting and complex to explain. In most of the events the harmonic frequency of tweeks correlates with the starting frequency of harmonics of discrete emissions. In order to explain the observed features of discrete VLF emissions, we propose cyclotron resonance interaction between whistler mode wave and energetic electrons of inner radiation belt as possible generation mechanism. An attempt is also made to determine parallel energy, anisotropy and wave growth relevant to the generation process of VLF emissions.

  3. Global scale comparison of simultaneous ionospheric potential measurements

    Science.gov (United States)

    Markson, R.; Ruhnke, L. H.; Williams, E. R.

    A unique series of simultaneous ionospheric potential ( VI) balloon soundings were obtained every 3 h over 2 full days at Weston, MA and Darwin, Australia, on the other side of the earth. These comparisons were to test the assumption that the ionosphere at sub-auroral latitudes is an equipotential and that a single measurement can provide a globally representative number. Another objective was to evaluate meteorological conditions affecting the measurements in a clean dry continental atmosphere (Darwin) compared with a more variable moist less clean atmosphere (Weston). The results indicate that for the Darwin data the VI measurements were within 10% of the classic Carnegie curve diurnal variation while the Weston data were more variable and often too large. The major source of error appears to be due to hydrated aerosol at Weston causing high electric fields in the exchange layer that were not fully compensated by electric fields above the inversion. The prototype instrumentation also contributed some error. The major finding of this experiment is that a layer of low conductivity air near the ground can have an unexpectedly large effect on electric field sounding data leading to error in the estimates of VI magnitude. This finding would not have been possible if simultaneous measurements in different airmasses had not been made since the individual electric field profiles appeared normal.

  4. Ionospheric redistribution during geomagnetic storms.

    Science.gov (United States)

    Immel, T J; Mannucci, A J

    2013-12-01

    [1]The abundance of plasma in the daytime ionosphere is often seen to grow greatly during geomagnetic storms. Recent reports suggest that the magnitude of the plasma density enhancement depends on the UT of storm onset. This possibility is investigated over a 7year period using global maps of ionospheric total electron content (TEC) produced at the Jet Propulsion Laboratory. The analysis confirms that the American sector exhibits, on average, larger storm time enhancement in ionospheric plasma content, up to 50% in the afternoon middle-latitude region and 30% in the vicinity of the high-latitude auroral cusp, with largest effect in the Southern Hemisphere. We investigate whether this effect is related to the magnitude of the causative magnetic storms. Using the same advanced Dst index employed to sort the TEC maps into quiet and active (Dststorm strength that corresponds closely to the TEC variation but follows it by 3-6h. For this and other reasons detailed in this report, we conclude that the UT-dependent peak in storm time TEC is likely not related to the magnitude of external storm time forcing but more likely attributable to phenomena such as the low magnetic field in the South American region. The large Dst variation suggests a possible system-level effect of the observed variation in ionospheric storm response on the measured strength of the terrestrial ring current, possibly connected through UT-dependent modulation of ion outflow.

  5. Calibrating for Ionospheric Phase Delays

    Science.gov (United States)

    Macdoran, P. F.

    1985-01-01

    Technique determines ionospheric phase delay on real-time universally applicable basis in terms of electrons per meter squared by coherently modulating two L-band carrier frequencies received from two Global Positioning System satelites. Two pseudorandom number sequences cross-correlated to derive delay time.

  6. Fluid Sounds

    DEFF Research Database (Denmark)

    Explorations and analysis of soundscapes have, since Canadian R. Murray Schafer's work during the early 1970's, developed into various established research - and artistic disciplines. The interest in sonic environments is today present within a broad range of contemporary art projects and in arch...... are tempo, time, voice, sound and music. Our goal is to bring analytical and performative awareness to academic means of expression, and the audio paper provides us with a new and experimental platform to do so....... by introducing a new format: The Audio Paper. The purpose of the audio paper is to extend the written academic text: to present discussions and explorations of a certain argument or problem in sound. The audio paper is an extension of expressive means: Not only words and syntax are means of expression – so...

  7. Radio occultation measurements of the lunar ionosphere.

    Science.gov (United States)

    Pluchino, S.; Schillirò, F.; Salerno, E.; Pupillo, G.; Maccaferri, G.; Cassaro, P.

    Radio occultation measurements by using interplanetary probes is a well known technique to obtain information on planetary atmospheres. To further understand the morphology of the lunar ionosphere we performed radio occultation experiments by using the radio sounding technique. This method mainly consists in the analisys of the effects produced on the radio wave transmitted from the spacecraft to the Earth when it crosses the atmosphere. The wave amplitude and phase undergo modifications that are correlated to the physical parameters - i.e. electron density - of the crossed medium. The first data set was obtained during the lunar occultations of the European probe SMART-1 shortly before impacting the lunar soil on September 3rd, 2006. During this experiment several radio occultation measurements of the signal transmitted by the spacecraft were performed in S and X band by using the 32 meters radiotelescopes (at Medicina and Noto) of the Istituto di Radioastronomia - Istituto Nazionale di Astrofisica. Further experiments were performed during lunar occultations of Saturn and Venus. On May 22nd and June 18th 2007 the Cassini spacecraft, orbiting Saturn, and the Venus Express spacecraft, orbiting Venus, respectively were occulted by the Moon. The variation of the Total Electron Content (TEC) measured by our instruments (˜ 1013 el/m2) on this occasion is in agreement with values of the electron number density acquired by in situ measuments of the US Apollo missions and the USSR Luna 19 and 22 probes.

  8. A two-dimensional global simulation study of inductive-dynamic magnetosphere-ionosphere/thermosphere coupling

    Science.gov (United States)

    Tu, J.; Song, P.

    2016-12-01

    We have developed a new numerical simulation model of the ionosphere/thermosphere by using an inductive-dynamic approach (including self-consistent solutions of Faraday's law and retaining inertia terms in ion momentum equations), that is, based on magnetic field B and plasma velocity v (B, v paradigm), which is distinctive from the conventional modeling based on electric field E and current j. The model solves self-consistently time-dependent continuity, momentum, and energy equations for multiple species of ions and neutrals including photochemistry, and Maxwell's equations. The governing equations solved in the model are a set of multifluid-collisional-Hall MHD equations which are one of unique features of our ionosphere/thermosphere model. With such an inductive-dynamic approach, not only sound wave mode but also all possible MHD wave modes are retained in the solutions of the governing equations so that the dynamic coupling between the magnetosphere and ionosphere and among different regions of the ionosphere can be self-consistently investigated. In the present study, we demonstrate dynamic propagation of field-aligned currents and ionospheric electric field carried by Alfven waves, as well as formation of closure horizontal currents (Pedersen currents in the E-region), indicating that the M-I coupling is via the Alfven waves instead of the field-aligned currents or electric field mapping. The simulation results also show that the Poynting flux and strongest energy dissipation in the ionosphere/thermosphere is in the regions of the largest ion velocities and not necessarily in the auroral oval where the field-aligned currents reside. The frictional heating increases plasma temperature and thus drives ion upflows. The frictional heating also increase neutral temperature and produces neutral upflows but in a much longer time scale. Furthermore, the coupling of high-to-low latitude ionosphere is investigated in terms of propagation of fast MHD waves.

  9. Responses of the Ionosphere to the Great Sumatra Earthquake and Volcanic Eruption of Pinatubo

    Institute of Scientific and Technical Information of China (English)

    HAO Yong-Qiang; XIAO Zuo; ZHANG Dong-He

    2006-01-01

    @@ A sudden ionospheric disturbance was detected by the Doppler shift sounding equipment at Beijing, about 25min later after the outbreak of the Sumatra earthquake on 26 December 2004. This ionospheric disturbance appeared less than 10min after the earthquake was first recorded at Beijing seismological station by the arrival of the seismic Rayleigh wave. The analysis shows that about 18 min is the time necessary for the seismic Rayleigh wave to propagate from the epicentre to Beijing and then about 5-10min for acoustic waves to propagate from the surface of the Beijing area to the altitude of the ionosphere. Also, a report was made as another example to show the ionospheric response of Doppler shift observation at Beijing area during the Mount Pinatubo eruption of 1991.These two examples show clear evidence of the lithosphere-atmosphere-ionosphere coupling. The former case is in the frequency domain of infrasonic waves of the Earth surface oscillation due to the Rayleigh waves caused by the earthquake, while the latter is in the acoustic-gravity wave category directly excited in the atmosphere by the mass and energy eruptions of Mount Pinatubo.

  10. Ionospheric Modelling using GPS to Calibrate the MWA. II: Regional ionospheric modelling using GPS and GLONASS to estimate ionospheric gradients

    CERN Document Server

    Arora, B S; Ord, S M; Tingay, S J; Bell, M; Callingham, J R; Dwarakanath, K S; For, B -Q; Hancock, P; Hindson, L; Hurley-Walker, N; Johnston-Hollitt, M; Kapinska, A D; Lenc, E; McKinley, B; Offringa, A R; Procopio, P; Staveley-Smith, L; Wayth, R B; Wu, C; Zheng, Q

    2016-01-01

    We estimate spatial gradients in the ionosphere using the Global Positioning System (GPS) and GLONASS (Russian global navigation system) observations, utilising data from multiple GPS stations in the vicinity of Murchison Radio-astronomy Observatory (MRO). In previous work the ionosphere was characterised using a single-station to model the ionosphere as a single layer of fixed height and this was compared with ionospheric data derived from radio astronomy observations obtained from the Murchison Widefield Array (MWA). Having made improvements to our data quality (via cycle slip detection and repair) and incorporating data from the GLONASS system, we now present a multi-station approach. These two developments significantly improve our modelling of the ionosphere. We also explore the effects of a variable-height model. We conclude that modelling the small-scale features in the ionosphere that have been observed with the MWA will require a much denser network of Global Navigation Satellite System (GNSS) statio...

  11. Application of gamma ray spectrometric measurements and VLF-EM data for tracing vein type uranium mineralization

    Directory of Open Access Journals (Sweden)

    Ibrahim Gaafar

    2015-12-01

    Full Text Available This study is an attempt to use the gamma ray spectrometric measurements and VLF-EM data to identify the subsurface structure and map uranium mineralization along El Sela shear zone, South Eastern Desert of Egypt. Many injections more or less mineralized with uranium and associated with alteration processes were recorded in El Sela shear zone. As results from previous works, the emplacement of these injections is structurally controlled and well defined by large shear zones striking in an ENE–WSW direction and crosscut by NW–SE to NNW–SSE fault sets. VLF method has been applied to map the structure and the presence of radioactive minerals that have been delineated by the detection of high uranium mineralization. The electromagnetic survey was carried out to detect the presence of shallow and deep conductive zones that cross the granites along ENE–WSW fracturing directions and to map its spatial distribution. The survey comprised seventy N–S spectrometry and VLF-EM profiles with 20 m separation. The resulted data were displayed as composite maps for K, eU and eTh as well as VLF-Fraser map. Twelve profiles with 100 m separation were selected for detailed description. The VLF-EM data were interpreted qualitatively as well as quantitatively using the Fraser and the Karous–Hjelt filters. Fraser filtered data and relative current density pseudo-sections indicate the presence of shallow and deep conductive zones that cross the granites along ENE–WSW shearing directions. High uranium concentrations found just above the higher apparent current-density zones that coincide with El-Sela shear zone indicate a positive relation between conductivity and uranium minerals occurrence. This enables to infer that the anomalies detected by VLF-EM data are due to the highly conductive shear zone enriched with uranium mineralization extending for more than 80 m.

  12. Localized Ionospheric Particle Acceleration and Wave Acceleration of Auroral Ions: Amicist Data Set

    Science.gov (United States)

    Lynch, Kristina A.

    1999-01-01

    Research supported by this grant covered two main topics: auroral ion acceleration from ELF-band wave activity, and from VLF-spikelet (lower hybrid solitary structure) wave activity. Recent auroral sounding rocket data illustrate the relative significance of various mechanisms for initiating auroral ion outflow. Two nightside mechanisms are shown in detail. The first mechanism is ion acceleration within lower hybrid solitary wave events. The new data from this two payload mission show clearly that: (1) these individual events are spatially localized to scales approximately 100 m wide perpendicular to B, in agreement with previous investigations of these structures, and (2) that the probability of occurrence of the events is greatest at times of maximum VLF wave intensity. The second mechanism is ion acceleration by broadband, low frequency electrostatic waves, observed in a 30 km wide region at the poleward edge of the arc. The ion fluxes from the two mechanisms are compared and it is shown that while lower hybrid solitary structures do indeed accelerate ions in regions of intense VLF waves, the outflow from the electrostatic ion wave acceleration region is dominant for the aurora investigated by this sounding rocket, AMICIST. The fluxes are shown to be consistent with DE-1 and Freja outflow measurements, indicating that the AMICIST observations show the low altitude, microphysical signatures of nightside auroral outflow. In this paper, we present a review of sounding rocket observations of the ion acceleration seen nightside auroral zone lower hybrid solitary structures. Observations from Topaz3, Amicist, and Phaze2 are presented on various spatial scales, including the two-point measurements of the Amicist mission. From this collection of observations, we will demonstrate the following characteristics of transverse ion acceleration (TAI) in LHSS. The ion acceleration process is narrowly confined to 90 degrees pitch angle, in spatially confined regions of up to a

  13. Detecting leachate plumes and groundwater pollution at Ruseifa municipal landfill utilizing VLF-EM method

    Science.gov (United States)

    Al-Tarazi, E.; Abu Rajab, J.; Al-Naqa, A.; El-Waheidi, M.

    2008-09-01

    A Very Low Frequency-Electromagnetic (VLF-EM) survey was carried out in two sites of domestic waste of old and recent landfills. The landfill structures lie on a major highly fractured limestone aquifer of shallow groundwater less than 30 m, which is considered as the main source of fresh water in Amman-Zarqa region. A total of 18 VLF-EM profiles were conducted with length ranges between 250 and 1500 m. Hydrochemical and biochemical analysis of water samples, taken from wells in the region, has also been conducted. The integrated results of previous DC resistivity method of the same study area and the outcomes of the 2-D tipper inversion of VLF-EM data proved the efficiency of this method in locating shallow and deep leachate plume with resistivity less than 20 Ω m, and enabling the mapping of anomalous bodies and their extensions down to 40 m depth. The sign of groundwater contamination was noticed in many surrounding wells resulting in the high number of fecal coliform bacteria and total coliform bacteria and the increase in inorganic parameters such as chloride (Cl). The pollution of groundwater wells in the landfill area is attributed to the leachate bodies which flow through the upper part of Wadi Es Sir (A7) or Amman-Wadi Es Sir Aquifer (B2/A7). Furthermore, several structural features were detected and the direction of local groundwater movement has been determined. The structural features have been found to have critical effects on the flowing of leachate plume towards north-northeast and west-southwest of the potable aquifer in the area.

  14. SNR changes of VLF radio signals detected onboard the DEMETER satellite and their possible relationship to the Wenchuan earthquake

    Institute of Scientific and Technical Information of China (English)

    M.; Parrot

    2009-01-01

    Here we used the VLF signal data received by the DEMETER satellite, transmitted from various ground VLF transmitters which are located around China, to study the changes in the signal to noise ratio (SNR) before and after the Wenchuan earthquake, which had a magnitude of 8.0. We also found that the SNRs of different frequency signals decreased significantly over the epicenter region before the earthquake, and reverted to their original levels after the earthquake. This phenomenon may be related to the earthquake.

  15. The ionosphere disturbances observation on the Kharkiv incoherent scatter radar

    Science.gov (United States)

    Cherniak, Iu.; Lysenko, V.

    2009-04-01

    he ionosphere plasma characteristics are responding on variations of solar and magnetic activity. The research of an ionosphere structure and dynamics is important as for understanding physics of processes and for radiophysical problems solution. The method incoherent scatter (IS) of radio waves allows determining experimentally both regular variations of the basic parameters ionosphere, and their behavior during perturbation. The equipment and measurement technique, developed by authors, are allows obtaining certain data about behavior of an ionosphere during various origin and intensity ionosphere perturbations. The Institute of Ionsphere IS radar located near Kharkiv, Ukraine (geographic coordinates: 49.6oN, 36.3oE, geomagnetic coordinates: 45.7oN, 117.8oE) was used to observe the processes in the ionosphere. The radar is operate with 100-m zenith parabolic antenna at 158 MHz with peak transmitted power of ~2.0 MW. The double-frequency measuring channel mode with compound sounding signal was employed for experiments. That provided ~ 20-km resolution in range ~100-400 km and ~100-km in range ~200-1100 km. Over a period of series of experiment are obtained data about variations of electron density simultaneous in the heights interval 100-1000 km, including three sun eclipses, two superstrong and a few moderate magnetic storms, as well as disturbance, is caused by powerful rockets starts. During strong geomagnetic storm on November 8-12, 2004 was observed night time increasing of electronic temperature up to 3000 Љ and ions temperature up to 2000K. Usually at this time temperature of ions is equal to temperature of electrons. During negative ionosphere storm was observed decreasing of electronic density at maximum F2 layer. The height of a F2 layer maximum was increased by 150 km and 70 km at daytime. The interesting phenomenon - high-power backscatter signal coherent backscatter was observed first time during geogeomagnetic storm 29-30 may 2003. A usually

  16. Preface: International Reference Ionosphere - Progress in Ionospheric Modelling

    Science.gov (United States)

    Bilitza Dieter; Reinisch, Bodo

    2010-01-01

    The international reference ionosphere (lRI) is the internationally recommended empirical model for the specification of ionospheric parameters supported by the Committee on Space Research (COSPAR) and the International Union of Radio Science (URSI) and recognized by the International Standardization Organization (ISO). IRI is being continually improved by a team of international experts as new data become available and better models are being developed. This issue chronicles the latest phase of model updates as reported during two IRI-related meetings. The first was a special session during the Scientific Assembly of the Committee of Space Research (COSPAR) in Montreal, Canada in July 2008 and the second was an IRI Task Force Activity at the US Air Force Academy in Colorado Springs in May 2009. This work led to several improvements and additions of the model which will be included in the next version, IRI-201O. The issue is divided into three sections focusing on the improvements made in the topside ionosphere, the F-peak, and the lower ionosphere, respectively. This issue would not have been possible without the reviewing efforts of many individuals. Each paper was reviewed by two referees. We thankfully acknowledge the contribution to this issue made by the following reviewers: Jacob Adeniyi, David Altadill, Eduardo Araujo, Feza Arikan, Dieter Bilitza, Jilijana Cander, Bela Fejer, Tamara Gulyaeva, Manuel Hermindez-Pajares, Ivan Kutiev, John MacDougal, Leo McNamara, Bruno Nava, Olivier Obrou, Elijah Oyeyemi, Vadym Paznukhov, Bodo Reinisch, John Retterer, Phil Richards, Gary Sales, J.H. Sastri, Ludger Scherliess, Iwona Stanislavska, Stamir Stankov, Shin-Yi Su, Manlian Zhang, Y ongliang Zhang, and Irina Zakharenkova. We are grateful to Peggy Ann Shea for her final review and guidance as the editor-in-chief for special issues of Advances in Space Research. We thank the authors for their timely submission and their quick response to the reviewer comments and humbly

  17. Numerical simulation of whistler-triggered VLF emissions observed in Antartica

    Energy Technology Data Exchange (ETDEWEB)

    Nunn, D. [Southhampton Univ., Southhampton (United Kingdom); Smith, A.J. [British Antarctic Survey, Cambridge (United Kingdom)

    1996-03-01

    The authors have extracted from VLF databases from British Antarctica Survey data taken at Halley and Faraday stations, examples of whistler-triggered emissions (WTE). The WTE are relatively narrow band emissions triggered by natural background whistlers undergoing nonlinear wave particle interactions generally in the equatorial regions. They occur with either rising or falling frequency relative to the triggering waves. Using a Vlasov type code the authors are able to simulate the types of emissions which are observed. 24 refs., 8 figs., 3 tabs.

  18. Circuit Methods for VLF Antenna Couplers. [for use in Loran or Omega receiver systems

    Science.gov (United States)

    Burhans, R. W.

    1977-01-01

    The limitations of different E-field antenna coupler or preamplifier circuits are presented. All circuits were evaluated using actual Loran or Omega signals. Electric field whip or wire antennas are the simplest types which can be used for reception of VLF signals in the 10 to 100 kHz range. JFET or MOSFET transistors provide impedance transformation and some voltage gain in simple circuits where the power for operating the preamplifier uses the same coaxial cable that feeds the signal back to the receiver. The circuit techniques provide useful alternative methods for Loran-Omega receiver system designers.

  19. LINFOMA RELACIONADO AO VÍRUS DA LEUCEMIA FELINA (VLF) – RELATO DE CASO

    OpenAIRE

    Eleutério, Daniela Aparecida Sampaio; Faculdade Dr. Francisco Maeda - FAFRAM

    2014-01-01

    O presente trabalho tem como objetivo relatar um caso de linfoma relacionado ao vírus da leucemia felina (VLF) ocorrido na cidade de Uberlândia-MG. Um felino, macho, de três anos de idade, foi encaminhado ao Hospital Veterinário da Universidade Federal de Uberlândia, apresentando-se apático, dispneico, com alterações oculares, mucosas hipocoradas e linfonodos reativos. O hemograma do animal indicou anemia normocítica. No exame radiográfico observou deslocamento da traquéia dorsalmente e não f...

  20. Developing an ionospheric map for South Africa

    Directory of Open Access Journals (Sweden)

    D. I. Okoh

    2010-07-01

    Full Text Available The development of a map of the ionosphere over South Africa is presented in this paper. The International Reference Ionosphere (IRI model, South African Bottomside Ionospheric Model (SABIM, and measurements from ionosondes in the South African Ionosonde Network, were combined within their own limitations to develop an accurate representation of the South African ionosphere. The map is essentially in the form of a computer program that shows spatial and temporal representations of the South African ionosphere for a given set of geophysical parameters. A validation of the map is attempted using a comparison of Total Electron Content (TEC values derived from the map, from the IRI model, and from Global Positioning System (GPS measurements. It is foreseen that the final South African ionospheric map will be implemented as a Space Weather product of the African Space Weather Regional Warning Centre.

  1. Ionospheric effects of thunderstorms and lightning

    Energy Technology Data Exchange (ETDEWEB)

    Lay, Erin H. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2014-02-03

    Tropospheric thunderstorms have been reported to disturb the lower ionosphere (~65-90 km) by convective atmospheric gravity waves and by electromagnetic field changes produced by lightning discharges. However, due to the low electron density in the lower ionosphere, active probing of its electron distribution is difficult, and the various perturbative effects are poorly understood. Recently, we have demonstrated that by using remotely-detected ?me waveforms of lightning radio signals it is possible to probe the lower ionosphere and its fluctuations in a spatially and temporally-resolved manner. Here we report evidence of gravity wave effects on the lower ionosphere originating from the thunderstorm. We also report variations in the nighttime ionosphere atop a small thunderstorm and associate the variations with the storm’s electrical activity. Finally, we present a data analysis technique to map ionospheric acoustic waves near thunderstorms.

  2. The ionospheric response in the Brazilian sector during the super geomagnetic storm on 20 November 2003

    Directory of Open Access Journals (Sweden)

    F. Becker-Guedes

    2007-05-01

    Full Text Available A very intense geomagnetic storm (superstorm began with storm sudden commencement (SSC at 08:03 UT on 20 November 2003, as a result of the coronal mass ejection (CME by sunspot 484 hurled into space on 18 November 2003. The geomagnetic storm attained |Dst|max=472 nT at 20:00 UT (20 November. In this paper we present the simultaneous ionospheric sounding observations, using the Canadian Advanced Digital Ionosondes (CADIs, carried out from Palmas (PAL; 10.2° S, 48.2° W; dip latitude 5.5° S; a near equatorial station and São José dos Campos (SJC; 23.2° S, 45.9° W; dip latitude 17.6° S; station located under the crest of equatorial ionospheric anomaly, Brazil. In addition, total electron content (TEC measurements from several GPS receiving stations in the Brazilian sector during this storm are presented. The simultaneous ionospheric sounding observations carried out at SJC and PAL, and TEC observations on 3 consecutive days viz., 19 November (quiet, 20 November (disturbed and 21 November (recovery phase are presented. Salient features from the ionospheric observations in the Brazilian sector during the superstorm are discussed. The difference in the observed ionospheric response at the two stations (PAL and SJC is considerable. This is not surprising given that PAL is close to the magnetic equator and SJC is near the crest of the equatorial ionospheric anomaly (EIA. It should be pointed out that soon after the SSC (about 4 h later, the F-region critical frequency (foF2, the F-region peak height (hpF2, and variations of virtual heights at different frequencies (iso-frequency plots all show wavelike oscillations of the F-region during daytime at both the ionospheric sounding stations. Unusual rapid uplifting of F-region at PAL was observed during both the main and recovery phases of the storm.

  3. Ionospheric research for space weather service support

    Science.gov (United States)

    Stanislawska, Iwona; Gulyaeva, Tamara; Dziak-Jankowska, Beata

    2016-07-01

    Knowledge of the behavior of the ionosphere is very important for space weather services. A wide variety of ground based and satellite existing and future systems (communications, radar, surveillance, intelligence gathering, satellite operation, etc) is affected by the ionosphere. There are the needs for reliable and efficient support for such systems against natural hazard and minimalization of the risk failure. The joint research Project on the 'Ionospheric Weather' of IZMIRAN and SRC PAS is aimed to provide on-line the ionospheric parameters characterizing the space weather in the ionosphere. It is devoted to science, techniques and to more application oriented areas of ionospheric investigation in order to support space weather services. The studies based on data mining philosophy increasing the knowledge of ionospheric physical properties, modelling capabilities and gain applications of various procedures in ionospheric monitoring and forecasting were concerned. In the framework of the joint Project the novel techniques for data analysis, the original system of the ionospheric disturbance indices and their implementation for the ionosphere and the ionospheric radio wave propagation are developed since 1997. Data of ionosonde measurements and results of their forecasting for the ionospheric observatories network, the regional maps and global ionospheric maps of total electron content from the navigational satellite system (GNSS) observations, the global maps of the F2 layer peak parameters (foF2, hmF2) and W-index of the ionospheric variability are provided at the web pages of SRC PAS and IZMIRAN. The data processing systems include analysis and forecast of geomagnetic indices ap and kp and new eta index applied for the ionosphere forecasting. For the first time in the world the new products of the W-index maps analysis are provided in Catalogues of the ionospheric storms and sub-storms and their association with the global geomagnetic Dst storms is

  4. Earthquake responses in the high-latitude ionosphere

    Science.gov (United States)

    Sergeeva, N. G.; Turunen, E.; Ogloblina, O. F.; Chernyakov, S. M.

    2009-10-01

    The data, obtained using the methods of partial reflections and ionosphere vertical sounding on the Kola Peninsula and in Scandinavia, at Tumannyi (69.0° N, 35.7° E) and Sodankyla (67.37°N, 26.63°E) observatories, have been analyzed in order to detect earthquake responses. The strong earthquakes have been considered: one earthquake with a magnitude of 7.7 occurred at 0819:25 UT on July 17, 2006, on the western coast of Indonesia (9.33° S, 107.26° E), and another earthquake with a magnitude of 6.2 occurred 2253:59 UT on May 26, 2006, on Yava (7.94° S, 110.32° E). These earthquakes, the epicenters of which were located in the same region and at identical depths (10 km), were observed under quiet conditions in the geomagnetic field (Σ K p = 5.7 and 6.3) and during small solar flares. The response of the ionosphere to these flares was mainly observed in the parameters of the lower ionosphere in the D and E regions. It has been found out that the period of variations in the ordinary component of the partially reflected signal at altitudes of the E region increased before the earthquake that occurred on July 17, 2006. The f min variations at Sodankyla observatory started 20 h before the earthquake. The periods of these variations were 3-6 h. The same periods were found in the variations in other ionospheric parameters ( foEs and h’Es). The variations in the ordinary component of partially reflected signals with periods of 2-5 hours were observed on the day of another earthquake (May 26, 2006). Internal gravity waves with periods of several hours, which can be related to the earthquakes, were detected in the amplitude spectra of the ordinary component of partially reflected signals and in other parameters in the lower ionosphere.

  5. Radar Sounding of Mars with MARSIS

    Science.gov (United States)

    Plaut, J. J.; Picardi, G.; Orosei, R.; Gurnett, D. A.

    2009-12-01

    MARSIS, the Mars Advanced Radar for Subsurface and Ionospheric Sounding, is a radar sounder that has been observing Mars from the Mars Express orbiter since June 2005. MARSIS works in the range of 1.3 to 5.5 MHz, and includes significant onboard data summing. MARSIS also operates in an Active Ionospheric Sounding mode down to 0.1 MHz to capture echoes from the topside of the ionosphere. MARSIS signals easily penetrate the polar layered deposits (PLD), usually to their basal contact with the substrate. The typically strong echo return from the lower interface of the PLD indicates that only minor attenuation of the radar signal is occurring within the PLD, implying a composition of nearly pure water ice. MARSIS data have been used to map the bed of the polar deposits to their maximum depth of over 3.5 km in the south. In the north, MARSIS delineates the extent of the “basal unit,” a sediment-laden icy layer that makes up more than a third of the total volume of the topographic cap. In both polar regions, the bed topography does not display a regional-scale deflection that might be expected from a flexural response to the PLD load, indicating a thick elastic lithosphere in these regions. Subsurface interfaces in the low latitudes of Mars are also being mapped by MARSIS, in the equatorial Medusae Fossae Formation. MARSIS has not detected any unambiguous evidence for sizable shallow aquifers. While it is possible that such features exist, the lack of detection more likely indicates that liquid water is not abundant in the shallow (< several km) subsurface of Mars. However, water ice is abundant in the polar regions, including a large area surrounding the polar layered deposits that is associated with the Dorsa Argentea Formation. In addition, analysis of the MARSIS surface echo strength suggests that a substantial fraction of the upper km of the subsurface of the northern plains may be ice-rich. In its ionospheric mode, MARSIS has characterized the complex structure

  6. Some unusual discrete VLF emissions observed at a low-latitude ground station at Agra

    Directory of Open Access Journals (Sweden)

    B. Singh

    Full Text Available A detailed analysis of the VLF emissions data obtained during occasional whistler campaigns at the low-latitude ground station Agra (geomagnetic latitude 17°1' N, L = 1.15 has yielded some unusual discrete VLF emissions of the rising type. These include (1 emissions occurring at time intervals increasing in ge ommetrical progression, (2 emissions occuring simulta neously in different frequency ranges and (3 emissions observed during daytime. In the present study, the observed characteristics of these emissions are described and interpreted. It is shown that the increasing time delay between different components of the emissions match closely with the propagation time delays between different hops of a whistler of dispersion 19 s1/2, the unusual occurrence of the emissions in two different frequency ranges approximately at the same time may possibly be linked with their generation at two different locations, and the occurrence of emissions during daytime may be due to propagation under the influence of equatorial anomaly.

  7. In connection with identification of VLF emissions before L'Aquila earthquake

    CERN Document Server

    Kachakhidze, M; Kachakhidze, N

    2012-01-01

    The present paper deals with an attempt to check up the theoretical model of self-generated seismo-electromagnetic oscillations of LAI system on the basis of retrospective data. Application of the offered simple model enables one to explain qualitatively the mechanism of VLF electromagnetic emission initiated in the process of an earthquake preparation. It is worth to pay attention to the fact that frequency changes from MHz to kHz in electromagnetic emission spectrum comes to a good agreement with avalanche-like unstable model of fault formation. L'Aquila earthquake taken as an example to isolate reliably the Earth VLF emission from the magnetospheric electromagnetic emission of the same frequency range, MHD criterion is offered together with geomagnetic activity indexes. On the basis of the considered three earthquakes, according to the opinion of authors the model of self-generated seismo-electromagnetic oscillations of the LAI system will enable us to approach the problem of resolution of earthquake predi...

  8. In connection with identification of VLF emissions before L'Aquila earthquake

    Directory of Open Access Journals (Sweden)

    M. K. Kachakhidze

    2012-04-01

    Full Text Available The present paper deals with an attempt to check the theoretical model of self-generated seismo-electromagnetic oscillations of LAI system on the basis of retrospective data.

    Application of the offered simple model enables one to explain qualitatively the mechanism of VLF electromagnetic emission initiated in the process of an earthquake preparation. Besides, the model enables us to associate telluric character geoelectric and geomagnetic perturbations incited by rock polarization and self-generated electromagnetic oscillations of lithosphere-atmosphere system.

    L'Aquila earthquake taken as an example to isolate reliably the Earth VLF emission from the magnetospheric electromagnetic emission of the same frequency range, MHD criterion is offered together with geomagnetic activity indexes.

    On the basis of the considered three earthquakes, according to the opinion of authors the model of self-generated seismo-electromagnetic oscillations of the LAI system will enable us to approach the problem of resolution of earthquake prediction with certain accuracy.

  9. Orbiting transmitter and antenna for spaceborne communications at ELF/VLF to submerged submarines

    Science.gov (United States)

    Bannister, P. R.; Harrison, J. K.; Rupp, C. C.; King, R. W. P.; Cosmo, M. L.; Lorenzini, E. C.; Dyer, C. J.; Grossi, M. D.

    1993-01-01

    An orbital emplacement for the transmitter and the antenna of a communications link at ELF (30 to 300 Hz) and VLF (3 kHz to 30 kHz) to submerged submarines has been considered since the very inception of the space age. However, only recently has space technology reached a sufficient level of maturity for system designers to undertake serious studies of this link configuration. The optimistic outlook stems from recent space technology developments, such as the design and construction by NASA of long orbiting tethers, and the testing, onboard Shuttle Orbiter ATLANTIS, of the first spaceborne 20 km metal wire. This is known as the Tethered Satellite System-1 (TSS-1), a space mission that might be possibly followed by other flights, with tether lengths that could reach 100 km. Once deployed at a height of, say, 300 km, from a Shuttle Orbiter, or from another suitable platform, a long, thin tether aligns itself along the local vertical by virtue of the gradient of the Earth gravity field. If made of metal, the tether can function as a VED (Vertical Electric Dipole) transmitting antenna at ELF and VLF.

  10. Detection of ionospheric Alfvén resonator signatures in the equatorial ionosphere

    Science.gov (United States)

    Simões, Fernando; Klenzing, Jeffrey; Ivanov, Stoyan; Pfaff, Robert; Freudenreich, Henry; Bilitza, Dieter; Rowland, Douglas; Bromund, Kenneth; Liebrecht, Maria Carmen; Martin, Steven; Schuck, Peter; Uribe, Paulo; Yokoyama, Tatsuhiro

    2012-11-01

    The ionosphere response resulting from minimum solar activity during cycle 23/24 was unusual and offered unique opportunities for investigating space weather in the near-Earth environment. We report ultra low frequency electric field signatures related to the ionospheric Alfvén resonator detected by the Communications/Navigation Outage Forecasting System (C/NOFS) satellite in the equatorial region. These signatures are used to constrain ionospheric empirical models and offer a new approach for monitoring ionosphere dynamics and space weather phenomena, namely aeronomy processes, Alfvén wave propagation, and troposphere-ionosphere-magnetosphere coupling mechanisms.

  11. Ionospheric heating for radiation-belt control

    Energy Technology Data Exchange (ETDEWEB)

    Burke, W.J.; Villalon, E.

    1990-10-01

    Pitch-angle scattering interactions of electromagnetic waves in the ELF/VLF bands with trapped electrons, as formulated by Kennel and Petschek 1, describe the dynamics of the freshly filled radiation belts flux tubes. The natural existence of a slot region with electron fluxes below the Kennel-Petschek limit requires non-local wave sources. We describe a set of planned, active experiments in which VLF radiation will be injected from ground and space based transmitters in conjunction with the CRRES satellite in the radiation belts. These experiments will measure the intensity of waves driving pitch-angle diffusion and the electron energies in gyroresonance with the waves. An ability to reduce the flux of energetic particles trapped in the radiation belts by artificial means could improve the reliability of microelectronic components on earth-observing satellites in middle-altitude orbits.

  12. Sound Search Engine Concept

    DEFF Research Database (Denmark)

    2006-01-01

    Sound search is provided by the major search engines, however, indexing is text based, not sound based. We will establish a dedicated sound search services with based on sound feature indexing. The current demo shows the concept of the sound search engine. The first engine will be realased June...

  13. Sound Search Engine Concept

    DEFF Research Database (Denmark)

    2006-01-01

    Sound search is provided by the major search engines, however, indexing is text based, not sound based. We will establish a dedicated sound search services with based on sound feature indexing. The current demo shows the concept of the sound search engine. The first engine will be realased June...

  14. The nighttime winter anomaly (NWA) effect in the american sector as a consequence of interhemispheric ionospheric coupling

    Science.gov (United States)

    Förster, M.; Jakowski, N.

    1988-06-01

    The nighttime winter anomaly (NWA) effect was observed during solar minimum conditions at the American sector by means of ionospheric electron content and vertical sounding measurements in Havana (Cuba). An effective interhemispheric transport of plasma is suggested to explain enhanced northern nighttime ionization during winter solstice. To elucidate this effect, an adequate physicalnumerical model of the coupled system ionosphere-plasmasphere is presented and applied to a corotating tube of plasma at L=1.5 in the American sector. The NWA can be explained by theoretically derived higher tube content during the December solstice and accordingly by more intense nighttime fluxes from the plasmasphere, compared to the June solstice.

  15. Data Assimilation Techniques for Ionospheric Reference Scenarios - project overview and achieved outcomes

    Science.gov (United States)

    Gerzen, Tatjana; Wilken, Volker; Hoque, Mainul; Minkwitz, David; Schlueter, Stefan

    2016-04-01

    generated 3D ionosphere reconstructions as well as the final IRSs are validated with independent GNSS slant TEC (Total Electron Content) data, vertical sounding observations and JASON 1 and 2 derived vertical TEC. This presentation gives an overview about the DAIS project and the achieved results. We outline the assimilation approach, show the reconstruction and the validation results and finally address open questions.

  16. ELF/VLF signatures of sprite-producing lightning discharges observed during the 2005 EuroSprite campaign

    DEFF Research Database (Denmark)

    Greenberg, E.; Price, C.; Yair, Y.

    2009-01-01

    During the summer of 2005, transient luminous events were optically imaged from the French Pyrénées as part of the EuroSprite campaign. Simultaneously, extremely low frequency (ELF: 3–3000 Hz) and broadband very low frequency (VLF: 3–30 kHz) data were recorded continuously at two separate receive...

  17. NASA Space Sounds API

    Data.gov (United States)

    National Aeronautics and Space Administration — NASA has released a series of space sounds via sound cloud. We have abstracted away some of the hassle in accessing these sounds, so that developers can play with...

  18. Effects of a Solar Eclipse on the Propagation of VLF-LF Signals: Observations and Results

    Directory of Open Access Journals (Sweden)

    Barin Kumar De

    2011-01-01

    Full Text Available The results from the measurements of some of the fundamental parameters (amplitude of sferics and transmitted signal, conductivity of lower ionosphere of the ionospheric responses to the 22 July 2009 solar eclipse (partial: 91.7% are shown. This study summarizes our results from sferics signals at 81 kHz and subionospheric transmitted signals at 19.8 and 40 kHz recorded at Agartala, Tripura (latitude: 23¢XN, longitude: 91.4¢XE. We observed significant absorption in amplitude of these signals during the eclipse period compared to their ambient values for the same period during the adjacent 7 days. The signal strength along their propagation paths was controlled by the eclipse associated decrease in ionization in the D-region of the ionosphere. Waveguide mode theory calculations show that the elevation of the height of lower ionosphere boundary of the Earth-ionosphere waveguide to a value where the conductivity parameter was 106 unit. The absorption in 81 kHz sferics amplitude is high compared to the absorption in the amplitude of 40 kHz signal transmitted from Japan. The simultaneous changes in the amplitudes of sferics and in the amplitude of transmitted signals assert some sort of coupling between the upper atmosphere and the Earth¡¦s near-surface atmosphere prevailing clouds during solar eclipse.

  19. Introduction to the Special Issue on Sounding Rockets and Instrumentation

    CERN Document Server

    Christe, Steven; Pfaff, Rob; Garcia, Michael

    2016-01-01

    Rocket technology, originally developed for military applications, has provided a low-cost observing platform to carry critical and rapid-response scientific investigations for over 70 years. Even with the development of launch vehicles that could put satellites into orbit, high altitude sounding rockets have remained relevant. In addition to science observations, sounding rockets provide a unique technology test platform and a valuable training ground for scientists and engineers. Most importantly, sounding rockets remain the only way to explore the tenuous regions of the Earth's atmosphere (the upper stratosphere, mesosphere, and lower ionosphere/thermosphere) above balloon altitudes ($\\sim$40 km) and below satellite orbits ($\\sim$160 km). They can lift remote sensing telescope payloads with masses up to 400 kg to altitudes of 350 km providing observing times of up to 6 minutes above the blocking influence of Earth's atmosphere. Though a number of sounding rocket research programs exist around the world, th...

  20. Ionospheric control of the magnetosphere: conductance

    Directory of Open Access Journals (Sweden)

    A. J. Ridley

    2004-01-01

    Full Text Available It is well known that the ionosphere plays a role in determining the global state of the magnetosphere. The ionosphere allows magnetospheric currents to close, thereby allowing magnetospheric convection to occur. The amount of current which can be carried through the ionosphere is mainly determined by the ionospheric conductivity. This paper starts to quantify the nonlinear relationship between the ionospheric conductivity and the global state of the magnetosphere. It is found that the steady-state magnetosphere acts neither as a current nor as a voltage generator; a uniform Hall conductance can influence the potential pattern at low latitudes, but not at high latitude; the EUV generated conductance forces the currents to close in the sunlight, while the potential is large on the nightside; the solar generated Hall conductances cause a large asymmetry between the dawn and dusk potential, which effects the pressure distribution in the magnetosphere; a uniform polar cap potential removes some of this asymmetry; the potential difference between solar minimum and maximum is ∼11%; and the auroral precipitation can be related to the local field-aligned current through an exponential function.

    Key words. Ionosphere (ionosphere-magnetosphere interactions; modelling and forecasting; polar ionosphere

  1. The fine structure of the ionosphere

    DEFF Research Database (Denmark)

    D'Angelo, N.; Michelsen, Poul

    1967-01-01

    We consider in this note the excitation of ion-acoustic waves by vertical gradients of density in the ionosphere. The conclusion is reached that the fine structure of the ionosphere is probably affected by the resulting instability, as comparison with observations seems to indicate. Recently, Liu...

  2. Ionospheric Modeling for Precise GNSS Applications

    NARCIS (Netherlands)

    Memarzadeh, Y.

    2009-01-01

    The main objective of this thesis is to develop a procedure for modeling and predicting ionospheric Total Electron Content (TEC) for high precision differential GNSS applications. As the ionosphere is a highly dynamic medium, we believe that to have a reliable procedure it is necessary to transfer t

  3. Artificial neural network applications in ionospheric studies

    Directory of Open Access Journals (Sweden)

    L. R. Cander

    1998-06-01

    Full Text Available The ionosphere of Earth exhibits considerable spatial changes and has large temporal variability of various timescales related to the mechanisms of creation, decay and transport of space ionospheric plasma. Many techniques for modelling electron density profiles through entire ionosphere have been developed in order to solve the "age-old problem" of ionospheric physics which has not yet been fully solved. A new way to address this problem is by applying artificial intelligence methodologies to current large amounts of solar-terrestrial and ionospheric data. It is the aim of this paper to show by the most recent examples that modern development of numerical models for ionospheric monthly median long-term prediction and daily hourly short-term forecasting may proceed successfully applying the artificial neural networks. The performance of these techniques is illustrated with different artificial neural networks developed to model and predict the temporal and spatial variations of ionospheric critical frequency, f0F2 and Total Electron Content (TEC. Comparisons between results obtained by the proposed approaches and measured f0F2 and TEC data provide prospects for future applications of the artificial neural networks in ionospheric studies.

  4. Probing ionospheric structure using LOFAR data

    NARCIS (Netherlands)

    Mevius, M.; Van Der Tol, S.; Pandey, V. N.

    2015-01-01

    To obtain high quality images with the Lofar low frequency radio telescope, accurate ionospheric characterization and calibration is essential. The large field of view of LOFAR (several 10s of square degrees) requires good knowledge of the spatial variation of the ionosphere. In this work to probe t

  5. Diagnostics of ionospheric turbulence by pulse wideband signals

    Science.gov (United States)

    Sergeev, E. N.; Grach, S. M.; Komrakov, G. P.; Kotov, P. V.

    New results on diagnostics of HF-pumped ionosphere by means of powerful sim 20 MW ERP and short tau lesssim 200 mu mathrm s pulses are presented The pulse duration tau was chosen to be less than a period of multiple ionospheric reflections sim 2 ms Specially elaborated algorithms of signal processing allowed to analyze amplitude and phase evolution of different spectral components of recorded signal in a bandwidth of order of 200 kHz Experiments were handled at the Sura facility Russia in 2004--2005 One or two Sura transmitters with 20 -- 80 MW ERP radiated the pump wave at a frequency f 0 including a range far from and close to forth electron gyroharmonic 4f ce sim 5390 -- 5440 kHz The third transmitter at a frequency f d approx f 0 pm 0 -- 1150 kHz was used for ionosphere sounding by diagnostic pulses with tau 20 -- 200 mu mathrm s and an interpulse period T 20 -- 40 ms Stable 5 MHz generator was used to synchronize the transmitter and receiver equipment The signal spectral components shifted by 1 kHz were processed using digital mixer and narrow Bessel 10 Hz filter in Labview and Matlab environments As a rule a positive values of the doppler frequency shift Delta f for different spectral components were observed during the pumping This corresponded to an increase of plasma density and can be related to an additional ionization and or temperature dependence of recombination coefficient under diurnal conditions and heights below 220 km Besides a fine structure of the turbulence region

  6. Electrostatic analyzer measurements of ionospheric thermal ion populations

    Science.gov (United States)

    Fernandes, P. A.; Lynch, K. A.

    2016-07-01

    We define the observational parameter regime necessary for observing low-altitude ionospheric origins of high-latitude ion upflow/outflow. We present measurement challenges and identify a new analysis technique which mitigates these impediments. To probe the initiation of auroral ion upflow, it is necessary to examine the thermal ion population at 200-350 km, where typical thermal energies are tenths of eV. Interpretation of the thermal ion distribution function measurement requires removal of payload sheath and ram effects. We use a 3-D Maxwellian model to quantify how observed ionospheric parameters such as density, temperature, and flows affect in situ measurements of the thermal ion distribution function. We define the viable acceptance window of a typical top hat electrostatic analyzer in this regime and show that the instrument's energy resolution prohibits it from directly observing the shape of the particle spectra. To extract detailed information about measured particle population, we define two intermediate parameters from the measured distribution function, then use a Maxwellian model to replicate possible measured parameters for comparison to the data. Liouville's theorem and the thin-sheath approximation allow us to couple the measured and modeled intermediate parameters such that measurements inside the sheath provide information about plasma outside the sheath. We apply this technique to sounding rocket data to show that careful windowing of the data and Maxwellian models allows for extraction of the best choice of geophysical parameters. More widespread use of this analysis technique will help our community expand its observational database of the seed regions of ionospheric outflows.

  7. Unmanned airborne vehicle (UAV): Flight testing and evaluation of two-channel E-field very low frequency (VLF) instrument

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1998-12-01

    Using VLF frequencies, transmitted by the Navy`s network, for airborne remote sensing of the earth`s electrical, magnetic characteristics was first considered by the United States Geological Survey (USGS) around the mid 1970s. The first VLF system was designed and developed by the USGS for installation and operation on a single engine, fixed wing aircraft used by the Branch of Geophysics for geophysical surveying. The system consisted of five channels. Two E-field channels with sensors consisting of a fixed vertical loaded dipole antenna with pre-amp mounted on top of the fuselage and a gyro stabilized horizontal loaded dipole antenna with pre-amp mounted on a tail boom. The three channel magnetic sensor consisted of three orthogonal coils mounted on the same gyro stabilized platform as the horizontal E-field antenna. The main features of the VLF receiver were: narrow band-width frequency selection using crystal filters, phase shifters for zeroing out system phase variances, phase-lock loops for generating real and quadrature gates, and synchronous detectors for generating real and quadrature outputs. In the mid 1990s the Branch of Geophysics designed and developed a two-channel E-field ground portable VLF system. The system was built using state-of-the-art circuit components and new concepts in circuit architecture. Small size, light weight, low power, durability, and reliability were key considerations in the design of the instrument. The primary purpose of the instrument was for collecting VLF data during ground surveys over small grid areas. Later the system was modified for installation on a Unmanned Airborne Vehicle (UAV). A series of three field trips were made to Easton, Maryland for testing and evaluating the system performance.

  8. Density duct formation in the wake of a travelling ionospheric disturbance: Murchison Widefield Array observations

    CERN Document Server

    Loi, Shyeh Tjing; Murphy, Tara; Erickson, Philip J; Bell, Martin E; Rowlinson, Antonia; Arora, Balwinder Singh; Morgan, John; Ekers, Ronald D; Hurley-Walker, Natasha; Kaplan, David L

    2016-01-01

    Geomagnetically-aligned density structures with a range of sizes exist in the near-Earth plasma environment, including 10-100 km-wide VLF/HF wave-ducting structures. Their small diameters and modest density enhancements make them difficult to observe, and there is limited evidence for any of the several formation mechanisms proposed to date. We present a case study of an event on 26 August 2014 where a travelling ionospheric disturbance (TID) shortly precedes the formation of a complex collection of field-aligned ducts, using data obtained by the Murchison Widefield Array (MWA) radio telescope. Their spatiotemporal proximity leads us to suggest a causal interpretation. Geomagnetic conditions were quiet at the time, and no obvious triggers were noted. Growth of the structures proceeds rapidly, within 0.5 hr of the passage of the TID, attaining their peak prominence 1-2 hr later and persisting for several more hours until observations ended at local dawn. Analyses of the next two days show field-aligned structu...

  9. Ionospheric Anomaly before Kyushu|Japan Earthquake

    Directory of Open Access Journals (Sweden)

    YANG Li

    2017-05-01

    Full Text Available GIM data released by IGS is used in the article and a new method of combining the Sliding Time Window Method and the Ionospheric TEC correlation analysis method of adjacent grid points is proposed to study the relationship between pre-earthquake ionospheric anomalies and earthquake. By analyzing the abnormal change of TEC in the 5 grid points around the seismic region, the abnormal change of ionospheric TEC is found before the earthquake and the correlation between the TEC sequences of lattice points is significantly affected by earthquake. Based on the analysis of the spatial distribution of TEC anomaly, anomalies of 6 h, 12 h and 6 h were found near the epicenter three days before the earthquake. Finally, ionospheric tomographic technology is used to do tomographic inversion on electron density. And the distribution of the electron density in the ionospheric anomaly is further analyzed.

  10. Plasma interactions in the Martian Nightside Ionosphere

    Science.gov (United States)

    Andersson, L.; Fowler, C. M.; Ergun, R.; Weber, T. D.; Andrews, D. J.; Morooka, M. W.; Delory, G. T.; Eriksson, A. I.; Mitchell, D. L.; McFadden, J. P.; Connerney, J. E. P.

    2015-12-01

    Based on measurements from a number of missions at Mars the nightside ionosphere is patchy. The new mission MAVEN dedicated to observe the upper atmosphere and the plasma interactions provides the first comprehensive observations of the low altitude nightside ionosphere. Observations show that at density gradients the plasma is unstable and significant wave power, heated/accelerated electrons, and heated ions are co-located. Below 300 km, thermal electrons (>3 eV) are observed at the gradients to low density regions. The nightside ionosphere below 180 km is thought to be maintained by electron impact ionization and therefore these regions with thermal electrons may be the primary energy source for the low altitude ionosphere. Outside of the low density regions the plasma is cold. These observations suggest that the wave heating might be the primary process in the Matrian nightside ionosphere. The characteristics of these regions associated with density gradients will be presented and discussed in this presentation.

  11. Sound Ecologies

    Directory of Open Access Journals (Sweden)

    Michelle Duffy

    2010-02-01

    Full Text Available Discussions about what constitutes ‘the rural’ invariably focus on notions of spatial location – of inhabiting spaces apart from that of the metropolitan. Deeply embedded in our images of what it means to be Australian, nonetheless our intellectual framing of ‘the rural’ as something outback and beyond has significant implications for our relations with these spaces. The relatively recent phenomenon of sea- and tree-changes has struck many unawares, and not simply because a good latté is so hard to find. Although a frivolous remark, such an apparent lack does shift our focus to a bodily scale of the rural; how is rural place re/made through our experiences of it? This article originates out of on-going research that explores the practice of listening and sound and the ways in which the body can draw attention to the intuitive, emotional, and psychoanalytical processes of subjectivity and place-making. Drawing on Nigel Thrift’s concept of an ecology of place, I suggest that contemporary heightened concerns with regards to loss and lack in rural Australia has led to a nascent emotional economy – one in which individual and intimate connections to the rural require a rethinking of how we live community and belonging. In such a terrain, what does it mean to be rural?

  12. Sound ecologies

    Directory of Open Access Journals (Sweden)

    Duffy, Michelle

    2010-01-01

    Full Text Available Discussions about what constitutes ‘the rural’ invariably focus on notions of spatial location – of inhabiting spaces apart from that of the metropolitan. Deeply embedded in our images of what it means to be Australian, nonetheless our intellectual framing of ‘the rural’ as something outback and beyond has significant implications for our relations with these spaces. The relatively recent phenomenon of sea- and tree-changes has struck many unawares, and not simply because a good latté is so hard to find. Although a frivolous remark, such an apparent lack does shift our focus to a bodily scale of the rural; how is rural place re/made through our experiences of it? This article originates out of on-going research that explores the practice of listening and sound and the ways in which the body can draw attention to the intuitive, emotional, and psychoanalytical processes of subjectivity and place-making. Drawing on Nigel Thrift’s concept of an ecology of place, I suggest that contemporary heightened concerns with regards to loss and lack in rural Australia has led to a nascent emotional economy – one in which individual and intimate connections to the rural require a rethinking of how we live community and belonging. In such a terrain, what does it mean to be rural?

  13. Sound Ecologies

    Directory of Open Access Journals (Sweden)

    Michelle Duffy

    2010-02-01

    Full Text Available Discussions about what constitutes ‘the rural’ invariably focus on notions of spatial location – of inhabiting spaces apart from that of the metropolitan. Deeply embedded in our images of what it means to be Australian, nonetheless our intellectual framing of ‘the rural’ as something outback and beyond has significant implications for our relations with these spaces. The relatively recent phenomenon of sea- and tree-changes has struck many unawares, and not simply because a good latté is so hard to find. Although a frivolous remark, such an apparent lack does shift our focus to a bodily scale of the rural; how is rural place re/made through our experiences of it? This article originates out of on-going research that explores the practice of listening and sound and the ways in which the body can draw attention to the intuitive, emotional, and psychoanalytical processes of subjectivity and place-making. Drawing on Nigel Thrift’s concept of an ecology of place, I suggest that contemporary heightened concerns with regards to loss and lack in rural Australia has led to a nascent emotional economy – one in which individual and intimate connections to the rural require a rethinking of how we live community and belonging. In such a terrain, what does it mean to be rural?

  14. Charged particles in Titan's ionosphere

    Science.gov (United States)

    Tripathi, Sachchida

    2010-05-01

    Charged particles in Titan's ionosphere Marykutty Michael1, Sachchida Nand Tripathi1,2,3, Pratima Arya1 1Indian Institute of Technology Kanpur 2Oak Ridge Associated Universities 3NASA Goddard Space Flight Center Observations by two instruments onboard the Cassini spacecraft, Ion Neutral Mass Spectrometer (INMS) and CAssini Plasma Spectrometer (CAPS), revealed the existence of heavy hydrocarbon and nitrile species with masses of several thousand atomic mass units at altitudes of 950 - 1400 km in the atmosphere of Titan (Waite et al., 2007; Crary et al., 2009). Though these particles were believed to be molecules, they are most likely aerosols formed by the clumping of smaller molecules (Waite et al., 2009). These particles were estimated to have a density of 10-3 kg m-3 and a size of up to 256 nm. The existence of very heavy ions has also been observed by the CAPS components with a mass by charge ratio of up to 10000 (Coates et al., 2007, 2009; Sittler et al., 2009). The goal of this paper is to find out whether the so called heavy ions (or charged particles) are generated by the charge transfer of ions and electrons to the particles. The charging of these particles has been studied by using the charge balance equations that include positive ions, negative ions, electrons, neutral and charged particles. Information on the most abundant ion clusters are obtained from Vuitton et al., (2009) and Wilson and Atreya, (2004). Mass by charge ratio thus calculated will be compared with those observed by Coates et al. (2007). References: Coates AJ, et al., Discovery of heavy negative ions in Titan's ionosphere, Geophys. Res. Lett., 34:L22103, 2007. Coates AJ, et al., Heavy negative ions in titan's ionosphere: altitude and latitude dependence. Planet. Space Sci., doi:10.1016/j.pss.2009.05.009, 2009. Crary F.J., et al., Heavy ions, temperatures and winds in titan's ionosphere: Combined cassini caps and inms observations. Planet. Space Sci., doi:10.1016/j.pss.2009.09.006, 2009

  15. Ionospheric observations made by a time-interleaved Doppler ionosonde

    Science.gov (United States)

    Lynn, Kenneth J. W.

    2008-10-01

    Mid-latitude HF observations of ionospheric Doppler velocity as a function of frequency are reported here as observed over a quiet 24-h period by a KEL IPS71 ionosonde operating at a 5-min sampling rate. The unique time-interleaving technique used in this ionosonde provided a Doppler resolution of 0.04 Hz over a Doppler range of ±2.5 Hz at each sounding frequency via FFT processing and is described here for the first time. The time-interleaving technique can be applied to other types of ionosonde as well as to other applications. The measurements described were made at a middle latitude site (Salisbury, South Australia). Doppler variations (rate-of-change of foF2 as predicted by a simple parabolic layer model. The descending cusp in short-period TIDs is shown to mark an abrupt change with increasing frequency from negative towards positive Doppler shift with the greatest change in Doppler shift being observed below the cusp. The “smilergram” is introduced as observed in both F2 and Sporadic E. The characteristic curve in Doppler versus group height at a single frequency is described and related to changes in reflection symmetry, velocity and depth of moving ionospheric inhomogeneities.

  16. Ionospheric data assimilation and forecasting during storms

    Science.gov (United States)

    Chartier, Alex T.; Matsuo, Tomoko; Anderson, Jeffrey L.; Collins, Nancy; Hoar, Timothy J.; Lu, Gang; Mitchell, Cathryn N.; Coster, Anthea J.; Paxton, Larry J.; Bust, Gary S.

    2016-01-01

    Ionospheric storms can have important effects on radio communications and navigation systems. Storm time ionospheric predictions have the potential to form part of effective mitigation strategies to these problems. Ionospheric storms are caused by strong forcing from the solar wind. Electron density enhancements are driven by penetration electric fields, as well as by thermosphere-ionosphere behavior including Traveling Atmospheric Disturbances and Traveling Ionospheric Disturbances and changes to the neutral composition. This study assesses the effect on 1 h predictions of specifying initial ionospheric and thermospheric conditions using total electron content (TEC) observations under a fixed set of solar and high-latitude drivers. Prediction performance is assessed against TEC observations, incoherent scatter radar, and in situ electron density observations. Corotated TEC data provide a benchmark of forecast accuracy. The primary case study is the storm of 10 September 2005, while the anomalous storm of 21 January 2005 provides a secondary comparison. The study uses an ensemble Kalman filter constructed with the Data Assimilation Research Testbed and the Thermosphere Ionosphere Electrodynamics General Circulation Model. Maps of preprocessed, verticalized GPS TEC are assimilated, while high-latitude specifications from the Assimilative Mapping of Ionospheric Electrodynamics and solar flux observations from the Solar Extreme Ultraviolet Experiment are used to drive the model. The filter adjusts ionospheric and thermospheric parameters, making use of time-evolving covariance estimates. The approach is effective in correcting model biases but does not capture all the behavior of the storms. In particular, a ridge-like enhancement over the continental USA is not predicted, indicating the importance of predicting storm time electric field behavior to the problem of ionospheric forecasting.

  17. Whistlers and related ionospheric phenomena

    CERN Document Server

    Helliwell, Robert A

    2006-01-01

    The investigation of whistlers and related phenomena is a key element in studies of very-low-frequency propagation, satellite communication, the outer ionosphere, and solar-terrestrial relationships. This comprehensive text presents a history of the study of the phenomena and includes all the elements necessary for the calculation of the characteristics of whistlers and whistler-mode signals.An introduction and brief history are followed by a summary of the theory of whistlers and a detailed explanation of the calculation of their characteristics. Succeeding chapters offer a complete atlas of

  18. Calculating Speed of Sound

    Science.gov (United States)

    Bhatnagar, Shalabh

    2017-01-01

    Sound is an emerging source of renewable energy but it has some limitations. The main limitation is, the amount of energy that can be extracted from sound is very less and that is because of the velocity of the sound. The velocity of sound changes as per medium. If we could increase the velocity of the sound in a medium we would be probably able to extract more amount of energy from sound and will be able to transfer it at a higher rate. To increase the velocity of sound we should know the speed of sound. If we go by the theory of classic mechanics speed is the distance travelled by a particle divided by time whereas velocity is the displacement of particle divided by time. The speed of sound in dry air at 20 °C (68 °F) is considered to be 343.2 meters per second and it won't be wrong in saying that 342.2 meters is the velocity of sound not the speed as it's the displacement of the sound not the total distance sound wave covered. Sound travels in the form of mechanical wave, so while calculating the speed of sound the whole path of wave should be considered not just the distance traveled by sound. In this paper I would like to focus on calculating the actual speed of sound wave which can help us to extract more energy and make sound travel with faster velocity.

  19. Ionospheric Challenges for GNSS Based Augmentation Systems

    Science.gov (United States)

    Doherty, P.; Valladares, C. E.

    2007-12-01

    The ionosphere is a highly dynamic physical phenomenon that presents a variable source of error for Global Navigation Satellite System (GNSS) signals and GNSS based operational systems. The Federal Aviation Administration's (FAA) Wide-Area Augmentation System (WAAS) was designed to enhance the GNSS standard positioning service by providing additional accuracy, availability and integrity that is sufficient for use in commercial aviation. It is the first of a number of planned regional Satellite Based Augmentation Systems (SBAS). Other systems in development include the European EGNOS system, the MSAS system in Japan and the GAGAN system in India. In addition, the South American countries are investigating the feasibility of operating an SBAS system in this region. Much of the WAAS ionospheric research and development focused on defining and mitigating ionospheric challenges characteristic of the mid-latitude regions, where the ionosphere is well studied and relatively quiescent. The EGNOS and MSAS systems will primarily operate under a similarly quiescent mid-latitude ionosphere. SBAS system development in South America, India and other low-latitude regions, however, will have to contend with much more extreme conditions. These conditions include strong spatial and temporal gradients, plasma depletions and scintillation. All of these conditions have a potential to limit SBAS performance in the low latitude regions. This presentation will review the effects that the ionosphere has on the mid-latitude WAAS system. It will present the techniques that are used to mitigate ionospheric disturbances induced on the system during severe geomagnetic activity and it will quantify the effect that this activity has on system performance. The presentation will then present data from the South American Low-latitude Ionospheric Sensor Network (LISN) that can be used to infer the ionospheric effects on SBAS performance in the most challenging low-latitude ionospheric environment

  20. Seismo-traveling ionospheric disturbances of earthquake and tsunami waves observed by space- and ground-based GPS receivers

    Science.gov (United States)

    Liu, J. Y. G.; Chen, C. Y.; Lin, C. H.

    2015-12-01

    FORMOSAT-3/COSMIC (F3/C) is a constellation of six microsatellites launched on April 15, 2006 and has been orbiting with 72° inclination at 700 to 800 km above the earth since December 2007. The main payload of the F3/C is the GPS Occultation eXperiment (GOX) which carries out probing the radio occultation (RO) total electron content between GPS satellite and F3/C. Therefore, F3/C provides us an excellent opportunity to vertically scan ionospheric electron density from 100 up to 800 km altitude. On the other hand, worldwide ground-based GPS receivers can be employed to observe traveling ionospheric disturbances of the TEC. Here, we present the ionosphere response to seismic and tsunami waves by means of F3/C RO TEC and worldwide ground-based GPS TEC as well as existing data of infrasondes, magnetometers, and Doppler sounding systems during the 11 March 2011 M9.0 Tohoku earthquake.

  1. The mechanism of mid-latitude Pi2 waves in the upper ionosphere as revealed by combined Doppler and magnetometer observations

    Directory of Open Access Journals (Sweden)

    V. A. Pilipenko

    2013-04-01

    Full Text Available The interpretation of simultaneous ionospheric Doppler sounding and ground magnetometer observations of low-latitude Pi2 waves is revised. We compare the theoretical estimates of the ionospheric Doppler velocity for the same amplitude of the ground magnetic disturbances produced by a large-scale compressional mode and an Alfvén mode. The plasma vertical displacement caused by the wave electric field is shown to be the dominating effect. Taking into account the correction of the previous paper, the observations of low-latitude Pi2 in the F layer ionosphere by Doppler sounding and SuperDARN (Super Dual Auroral Radar Network radars give consistent results. We suggest that the Doppler response to Pi2 waves is produced by the Alfvén wave component, but not the fast-mode component, whereas the ground magnetic signal is composed from both Alfvén and fast magnetosonic modes.

  2. VLF signal perturbation due to the total solar eclipse of March 2015

    Science.gov (United States)

    Nait Amor, Samir; Bouderba, Yasmina

    2016-07-01

    On March 20 2015 a total Solar eclipse occurred and covered several regions in north America, Greenland, west of Europe and north Africa with different occultation rates. During this event, many VLF paths recorded at Algiers receiver were perturbed. In this contribution, we will present a qualitative analysis of two paths (GQD and DHO) which were disturbed differently since the occultation rate at the transmitter locations was different. In addition to the qualitative study, we determined the newly formed reference height and β values at different times during the eclipse transit. From these determined parameters the time profile of the electron density is then deduced. The results showed that the new reference height, β and the electron density are different from one transmitter analysis to other due to the occultation rate difference.

  3. Connecting Stratospheric and Ionospheric Anomalies

    Science.gov (United States)

    Spraggs, M. E.; Goncharenko, L. P.; Zhang, S.; Coster, A. J.; Benkevitch, L. V.

    2014-12-01

    This study investigates any relationship between lunar phases and ionospheric anomalies that appear at low latitudes concurrently with sudden stratospheric warmings (SSWs). The study utilizes World-wide GPS Receiver Network Total Electron Content (TEC) data spanning 13 years (2001-2014) and focuses on the changes in the equatorial ionization anomaly the Western hemisphere. TEC is highly variable due to the influences of solar flux, geomagnetic activity, and seasonal variation and these influences are removed by the use of model. This empirical TEC model is a combination of linear dependencies of solar flux (F10.7) and geomagnetic activity (Ap3) with a third degree polynomial dependency for day-of-year (DOY). With such dependencies removed, the remaining TEC variation could be resolved and attributed to an appropriate mechanism. Lunar phase and apside was investigated in particular, especially the new and full moon phases during perigees when tidal forcing would be most powerful. Lunar tidal forcing on planetary waves is also examined as being physically responsible for setting up conditions that may give rise to SSWs and ionospheric anomalies. Preliminary results suggest that such anomalies may be enhanced in intensity during the full or new moon and even more so during perigee by different amounts depending on whether the SSW is a major (40-60%) or minor (20-45%) event.

  4. SPEAR-1: An experiment to measure current collection in the ionosphere by high voltage biased conductors

    Science.gov (United States)

    Raitt, W. John; Myers, Neil B.; Roberts, Jon A.; Thompson, D. C.

    1990-01-01

    An experiment is described in which a high electrical potential difference, up to 45 kV, was applied between deployed conducting spheres and a sounding rocket in the ionosphere. Measurements were made of the applied voltage and the resulting currents for each of 24 applications of different high potentials. In addition, diagnostic measurements of optical emissions in the vicinity of the spheres, energetic particle flow to the sounding rocket, dc electric field and wave data were made. The ambient plasma and neutral environments were measured by a Langmuir probe and a cold cathode neutral ionization gauge, respectively. The payload is described and examples of the measured current and voltage characteristics are presented. The characteristics of the measured currents are discussed in terms of the diagnostic measurements and the in-situ measurements of the vehicle environment. In general, it was found that the currents observed were at a level typical of magnetically limited currents from the ionospheric plasma for potentials less than 12 kV, and slightly higher for larger potentials. However, due to the failure to expose the plasma contactor, the vehicle sheath modified the sphere sheaths and made comparisons with the analytic models of Langmuir-Blodgett and Parker-Murphy less meaningful. Examples of localized enhancements of ambient gas density resulting from the operation of the attitude control system thrusters (cold nitrogen) were obtained. Current measurements and optical data indicated localized discharges due to enhanced gas density that reduced the vehicle-ionosphere impedance.

  5. Inductive ionospheric solver for magnetospheric MHD simulations

    Directory of Open Access Journals (Sweden)

    H. Vanhamäki

    2011-01-01

    Full Text Available We present a new scheme for solving the ionospheric boundary conditions required in magnetospheric MHD simulations. In contrast to the electrostatic ionospheric solvers currently in use, the new solver takes ionospheric induction into account by solving Faraday's law simultaneously with Ohm's law and current continuity. From the viewpoint of an MHD simulation, the new inductive solver is similar to the electrostatic solvers, as the same input data is used (field-aligned current [FAC] and ionospheric conductances and similar output is produced (ionospheric electric field. The inductive solver is tested using realistic, databased models of an omega-band and westward traveling surge. Although the tests were performed with local models and MHD simulations require a global ionospheric solution, we may nevertheless conclude that the new solution scheme is feasible also in practice. In the test cases the difference between static and electrodynamic solutions is up to ~10 V km−1 in certain locations, or up to 20-40% of the total electric field. This is in agreement with previous estimates. It should also be noted that if FAC is replaced by the ground magnetic field (or ionospheric equivalent current in the input data set, exactly the same formalism can be used to construct an inductive version of the KRM method originally developed by Kamide et al. (1981.

  6. Inductive ionospheric solver for magnetospheric MHD simulations

    Science.gov (United States)

    Vanhamäki, H.

    2011-01-01

    We present a new scheme for solving the ionospheric boundary conditions required in magnetospheric MHD simulations. In contrast to the electrostatic ionospheric solvers currently in use, the new solver takes ionospheric induction into account by solving Faraday's law simultaneously with Ohm's law and current continuity. From the viewpoint of an MHD simulation, the new inductive solver is similar to the electrostatic solvers, as the same input data is used (field-aligned current [FAC] and ionospheric conductances) and similar output is produced (ionospheric electric field). The inductive solver is tested using realistic, databased models of an omega-band and westward traveling surge. Although the tests were performed with local models and MHD simulations require a global ionospheric solution, we may nevertheless conclude that the new solution scheme is feasible also in practice. In the test cases the difference between static and electrodynamic solutions is up to ~10 V km-1 in certain locations, or up to 20-40% of the total electric field. This is in agreement with previous estimates. It should also be noted that if FAC is replaced by the ground magnetic field (or ionospheric equivalent current) in the input data set, exactly the same formalism can be used to construct an inductive version of the KRM method originally developed by Kamide et al. (1981).

  7. Electron dispersion events in the morningside auroral zone and their relationship with VLF emissions

    Energy Technology Data Exchange (ETDEWEB)

    Hardy, D.A.; Burke, W.J. (Hanscom Air Force Base, MA (United States)); Villalon, E. (Northeastern Univ., Boston, MA (United States))

    1990-05-01

    Energy/time dispersion events have been observed in the precipitating electron data in the energy range from 630 eV to 20 keV recorded by the J sensor on the low-altitude, polar-orbiting HILAT satellite. The dispersions are such that the higher-energy electrons are observed earlier in time than the lower-energy electrons The time interval for single dispersion event is from 1 to 2 s. Within an auroral pass in which such energy/time dispersion events are observed, there are typically several such events, and they can be spaced within the pass in either a periodic or aperiodic manner. The events are typically observed within and toward the equatorward edge of the region of diffuse auroral electron precipitation. During a given pass the events can be observed over a wide range of L shells. The occurrence of these events maximizes in the interval 0600-1,200 hours MLT. The energy/time dispersion is generally consistent with the electrons originating from a common source. The events are seen at L shells from 3.7 to greater than 15. The source distance for the electrons is inferred to be generally beyond the equator for events at L shells less than approximately 8 and before the equator for events at higher L shells. Because of the low energies at which the dispersions are observed, it is unlikely that their occurrence can be explained by resonant interaction with VLF waves. Based on circumstantial evidence from other reported observations common to the morning sector, and alternative theoretical explanation is presented. According to this model the dispersion events result from impulsive interactions of the electrons with intense, asymmetric packets of VLF waves via the nonlinear, ponderomotive force.

  8. The Sound of Science

    Science.gov (United States)

    Merwade, Venkatesh; Eichinger, David; Harriger, Bradley; Doherty, Erin; Habben, Ryan

    2014-01-01

    While the science of sound can be taught by explaining the concept of sound waves and vibrations, the authors of this article focused their efforts on creating a more engaging way to teach the science of sound--through engineering design. In this article they share the experience of teaching sound to third graders through an engineering challenge…

  9. Sounds Exaggerate Visual Shape

    Science.gov (United States)

    Sweeny, Timothy D.; Guzman-Martinez, Emmanuel; Ortega, Laura; Grabowecky, Marcia; Suzuki, Satoru

    2012-01-01

    While perceiving speech, people see mouth shapes that are systematically associated with sounds. In particular, a vertically stretched mouth produces a /woo/ sound, whereas a horizontally stretched mouth produces a /wee/ sound. We demonstrate that hearing these speech sounds alters how we see aspect ratio, a basic visual feature that contributes…

  10. The Sound of Science

    Science.gov (United States)

    Merwade, Venkatesh; Eichinger, David; Harriger, Bradley; Doherty, Erin; Habben, Ryan

    2014-01-01

    While the science of sound can be taught by explaining the concept of sound waves and vibrations, the authors of this article focused their efforts on creating a more engaging way to teach the science of sound--through engineering design. In this article they share the experience of teaching sound to third graders through an engineering challenge…

  11. Sound reproduction system

    NARCIS (Netherlands)

    Boone, M.M.; De Vries, D.; Horbach, U.

    2002-01-01

    Arrangement of a sound reproduction system (1), including at least one input (2), a sound field generator (4), a loudspeaker panel (10); the at least one input (2) connected to the sound filed generator (4), and the sound filed (4) connected to the loudspeaker panel (10); the at least one input (2)

  12. Testing Ionospheric Faraday Rotation Corrections in CASA

    Science.gov (United States)

    Kooi, Jason E.; Moellenbrock, George

    2015-04-01

    The Earth’s ionosphere introduces direction- and time-dependent effects over a range of physical and temporal scales and so is a major source for unmodeled phase offsets for low frequency radioastronomical observations. Ionospheric effects are often the limiting factor to making sensitive radioastronomical measurements to probe the solar corona or coronal mass ejections at low frequencies (CASA) package. CASA, which was developed to meet the data post-processing needs of next generation telescopes such as the Karl G. Jansky Very Large Array (VLA), did not previously have the capability to mitigate ionospheric effects. This algorithm uses GPS-based global ionosphere maps to mitigate the first and second order ionospheric effects (dispersion delay and Faraday rotation, respectively). We investigated several data centers as potential sources for global ionospheric models and chose the International Global Navigation Satellite System Service data product because data from other sources are generally too sparse to use without additional interpolation schemes. This implementation of ionospheric corrections in CASA has been tested on several sets of VLA observations and all of them showed a significant reduction of the dispersion delay. In order to rigorously test CASA’s ability to mitigate ionospheric Faraday rotation, we made VLA full-polarization observations of the standard VLA phase calibrators J0359+5057 and J0423+4150 in August 2014, using L band (1 - 2 GHz), S band (2 - 4 GHz), and C band (4 - 6 GHz) frequencies in the D array configuration. The observations were 4 hours in duration, beginning near local sunrise. In this paper, we give a general description of how these corrections are implemented as well as discussion of the code’s ability to mitigate the ionospheric effects present in these test observations over a range of times and elevation angles. This work was supported at the University of Iowa by grant ATM09-56901.

  13. Parameters of seismic source as deduced from 1Hz ionospheric GPS data: Ionospheric Seismology or Ionosphere as a natural indicator of numerous geophysical events

    Science.gov (United States)

    Astafyeva, Elvira

    2013-04-01

    The Earth's ionosphere is known to be highly responsive to a large variety of geophysical phenomena coming from above (solar-driven variations, solar flares, magnetospheric events, etc) and from below (earthquakes, tsunamis, volcano eruptions, explosions). Therefore, study of ionospheric response to these events sheds light on the interplanetary/ionosphere and lithosphere/atmosphere/ionosphere couplings. Apart from the pure scientific interests in ionospheric studies, knowledge on the storm-time and quiet-time ionospheric behavior is vitally important for all GNSS users, since the ionosphere changes the amplitude and phase of transionospheric radio signals. The purpose of the ERC Starting Grant project "SIREAL" is to perform a wide spectrum of ionosphere-related research, from ionospheric seismology to ionospheric storms and GNSS/GPS performance during extreme ionospheric and space weather events. The main focus of the project is made on such rare and interdisciplinary subject as ionospheric seismology. Ionospheric seismology is a sufficiently new branch of geophysics, aiming to study ionospheric response to large earthquakes and to investigate the main properties of various ionospheric disturbances generated by quake-like events, including shallow earthquakes, tsunamis and volcano eruptions. Recent work by Astafyeva et al. (2011, Geophys. Res. Lett., L22104, DOI:10.1029/2011GL049623),showed that in some cases, use of high-precision GPS data can provide ionospheric images of seismic fault (its location and dimensions) about ~7-8 min after an earthquake, which opens new opportunities for short-time tsunami warnings. On the example of the Tohoku-oki earthquake on 11 March 2011, here we will show first results of the ERC project, on how the use of 1 Hz ionospheric GPS measurements can provide information on seismic parameters.

  14. Ionosphere Waves Service (IWS) – a problem-oriented tool in ionosphere and Space Weather research produced by POPDAT project

    OpenAIRE

    Ferencz Csaba; Lizunov Georgii; Crespon François; Price Ivan; Bankov Ludmil; Przepiórka Dorota; Brieß Klaus; Dudkin Denis; Girenko Andrey; Korepanov Valery; Kuzmych Andrii; Skorokhod Tetiana; Marinov Pencho; Piankova Olena; Rothkaehl Hanna

    2014-01-01

    In the frame of the FP7 POPDAT project the Ionosphere Waves Service (IWS) has been developed and opened for public access by ionosphere experts. IWS is forming a database, derived from archived ionospheric wave records to assist the ionosphere and Space Weather research, and to answer the following questions: How can the data of earlier ionospheric missions be reprocessed with current algorithms to gain more profitable results? How could the scientific community be provided with a new insight...

  15. Advances in regional ionospheric mapping over europe

    Directory of Open Access Journals (Sweden)

    L. R. Cander

    1998-06-01

    Full Text Available Over the past several years significant advances have been made in all areas of ionospheric modelling and mapping studies. Ionospheric models and maps of varying complexity have been formulated from analytic and simple numerical models that are user friendly" calculations to complete general circulation models that require hours on today’s supercomputers. All have their place and are used in different applications. This review describes progress in regional ionospheric mapping over Europe in the frame of the COST 238 and 251 projects.

  16. Global Three-Dimensional Ionospheric Data Assimilation Model Using Ground-based GPS and Radio Occultation Total Electron Content

    Science.gov (United States)

    Jann-Yenq Liu, Tiger; Lin, Chi-Yen; Matsuo, Tomoko; Lin, Charles C. H.; Tsai, Ho-Fang; Chen, Chao-Yen

    2017-04-01

    An ionospheric data assimilation approach presented here is based on the Gauss-Markov Kalman filter with International Reference Ionosphere (IRI) as the background model and designed to assimilate the total electron content (TEC) observed from ground-based GPS receivers and space-based radio occultation (RO) of FORMOSAT-3/COSMIC (F3/C) or FORMOSAT-7/COSMIC-2 (F7/C2). The Kalman filter consists of the forecast step according to Gauss-Markov process and measurement update step. Observing System Simulation Experiments (OSSEs) show that the Gauss-Markov Kalman filter procedure can increase the accuracy of the data assimilation analysis over the procedure consisting of the measurement update step alone. Moreover, in comparing to F3/C, the dense F7/C2 RO observation can further increase the model accuracy significantly. Validating the data assimilation results with the vertical TEC in Global Ionosphere Maps and that derived from ground-based GPS measurements, as well as the ionospheric F2-peak height and electron density sounded by ionosondes is also carried out. Both the OSSE results and the observation validations confirm that the developed data assimilation model can be used to reconstruct the three-dimensional electron density in the ionosphere satisfactorily.

  17. A comparison of EISCAT and Dynasonde measurements of the auroral ionosphere

    Directory of Open Access Journals (Sweden)

    K. J. F. Sedgemore

    Full Text Available Incoherent-scatter radar and ionospheric sounding are powerful and complementary techniques in the study of the Earth's ionosphere. The work presented here involves the use of the Tromsø Dynasonde as a correlative diagnostic with the EISCAT incoherent-scatter radar. A comparison of electron-density profiles shows how a Dynasonde can be used to calibrate an incoherent-scatter radar and to monitor changes in the system. Skymaps of the direction of Dynasonde echoes are compared with EISCAT-derived density profiles to illustrate how a Dynasonde can be used to measure the drift velocity of auroral features. Vector velocities fitted to Dynasonde echoes are compared with EISCAT-derived plasma velocities. The results show good agreement when the data are taken during quiet to moderately active conditions and averaged over time scales of 30 min or more.

  18. Artificial periodic irregularities in the high-latitude ionosphere excited by the HAARP facility

    Science.gov (United States)

    Bakhmetieva, N. V.; Grach, S. M.; Sergeev, E. N.; Shindin, A. V.; Milikh, G. M.; Siefring, C. L.; Bernhardt, P. A.; McCarrick, M.

    2016-07-01

    We present results of the new observations of artificial periodic irregularities (APIs) in the ionosphere using the High Frequency Active Auroral Research Program (HAARP) heating facility carried out in late May and early June 2014.The objective of this work is to detect API using high-latitude facility and analyze possible differences of the temporal and spatial variations of the API echoes in the high (HAARP) and middle (Sura) latitudes. Irregularities were created by the powerful wave of X mode and were sounded using the short probing pulses signals of X mode. API echoes were observed in the D, E, and F regions of the ionosphere. Amplitudes and characteristic times of the API echoes were measured. The API growth and decay times at HAARP (high latitudes) observed were similar to those at the Sura heating facility (midlatitudes).

  19. Correlation of VLF-EM Data with Radiometric Measurements: Implications for Uranium Exploration around Beldih, South Purulia Shear Zone, India

    Directory of Open Access Journals (Sweden)

    Saurabh Mittal

    2014-01-01

    Full Text Available This study is an attempt to correlate VLF-EM data with the radiometric measurements to decipher the subsurface structure and to locate uranium mineralization in the shear zone. The study area is around Beldih mine which is an open cast apatite mine located on the South Purulia Shear Zone. VLF method has been applied to map the structure and the presence of radioactive minerals has been delineated by the detection of high α and γ counts with respect to the background radiations. High radiation counts and high surface γ activity are found just above the higher apparent current-density zones in all the profiles studied, at various locations, indicating uranium and/or thorium mineralization as well as good correlation between these techniques.

  20. Space weather. Ionospheric control of magnetotail reconnection.

    Science.gov (United States)

    Lotko, William; Smith, Ryan H; Zhang, Binzheng; Ouellette, Jeremy E; Brambles, Oliver J; Lyon, John G

    2014-07-11

    Observed distributions of high-speed plasma flows at distances of 10 to 30 Earth radii (R(E)) in Earth's magnetotail neutral sheet are highly skewed toward the premidnight sector. The flows are a product of the magnetic reconnection process that converts magnetic energy stored in the magnetotail into plasma kinetic and thermal energy. We show, using global numerical simulations, that the electrodynamic interaction between Earth's magnetosphere and ionosphere produces an asymmetry consistent with observed distributions in nightside reconnection and plasmasheet flows and in accompanying ionospheric convection. The primary causal agent is the meridional gradient in the ionospheric Hall conductance which, through the Cowling effect, regulates the distribution of electrical currents flowing within and between the ionosphere and magnetotail.

  1. The magnetohydrodynamic description of Earth's ionosphere

    CERN Document Server

    Pandey, B P

    2016-01-01

    The wave propagation in the partially ionized ionosphere plays an important role in the magnetosphere ionosphere coupling. For example, the ionosphere may supports very low-frequency Alfven wave which can be caused by a balance between the bulk fluid inertia (mostly due to neutrals in the lower and middle E region) and the deformation of the magnetic field. The plasma neutral collisional momentum exchange facilitates the transfer of the magnetic stress (felt directly by the ions) to the neutrals. Therefore, in the low-frequency (with respect to the neutral ion collision frequency) limit, waves through the ionosphere can propagate with very little damping. In the vanishing plasma inertia limit, waves can be excited due to the loading of neutral inertia on the field lines and thus may have very long wavelength and can easily couple to the magnetosphere. The frequency of these waves are below few Hz.

  2. On the Ionospheric Holes of Venus

    Science.gov (United States)

    Collinson, G.; Fedorov, A.; Futaana, Y.; Masunaga, K.; Hartle, R. E.; Stenberg, G.; Budnik, E.; Grebowsky, J. M.; Holmstrom, M.; andre, N.; Barabash, S. V.; Zhang, T.

    2013-12-01

    One of the most intriguing unsolved mysteries that endures from the Pioneer Venus Orbiter is that of ~1000km wide ``Holes" in the nightside Ionosphere. The phenomena remains unexplained, despite their frequent observation during the first three years of the mission, and more than thirty years having elapsed since their first description in the literature. We present new observations by the ESA Venus Express of Ionospheric Holes at very high altitudes, providing us with the opportunity to study this fascinating phenomena with modern instrumentation. We discuss the insight that these new data give us into the effect of Ionospheric Holes on atmospheric escape, and the evidence that suggests that Ionospheric Holes are due to an internal planetary magnetic field.

  3. SHOCK WAVE IN IONOSPHERE DURING EARTHQUAKE

    Directory of Open Access Journals (Sweden)

    V.V. Kuznetsov

    2016-11-01

    Full Text Available Fundamentally new model of the shock wave (SW generation in atmosphere and ionosphere during earthquake is proposed. The model proceeds from the idea of cooperative shock water crystallization in a cloud

  4. Measurement of ionospheric large-scale irregularity

    Institute of Scientific and Technical Information of China (English)

    韩文焌; 郑怡嘉; 张喜镇

    1996-01-01

    Based on the observations of a meter-wave aperture synthesis radio telescope,as the scale length of ionospheric irregularity is greatly larger than the baseline length of interferometer,the phase error induced by the output signal of interferometer due to ionosphere is proportional to the baseline length and accordingly the expressions for extracting the information about ionosphere are derived.By using the ray theory and considering that the antenna is always tracking to the radio source in astronomical observation,the wave motion expression of traveling ionospheric disturbance observed in the total electron content is also derived,which is consistent with that obtained from the conception of thin-phase screen;then the Doppler velocity due to antenna tracking is introduced.Finally the inversion analysis for the horizontal phase velocity of TID from observed data is given.

  5. The Earth's ionosphere plasma physics and electrodynamics

    CERN Document Server

    Kelley, Michael C

    2007-01-01

    Although interesting in its own right, due to the ever-increasing use of satellites for communication and navigation, weather in the ionosphere is of great concern. Every such system uses trans-ionospheric propagation of radio waves, waves which must traverse the commonly turbulent ionosphere. Understanding this turbulence and predicting it are one of the major goals of the National Space Weather program. Acquiring such a prediction capability will rest on understanding the very topics of this book, the plasma physics and electrodynamics of the system. Fully updated to reflect advances in the field in the 20 years since the first edition published Explores the buffeting of the ionosphere from above by the sun and from below by the lower atmosphere Unique text appropriate both as a reference and for coursework.

  6. Remote Sensing of Ionosphere by IONOLAB Group

    Science.gov (United States)

    Arikan, Feza

    2016-07-01

    Ionosphere is a temporally and spatially varying, dispersive, anisotropic and inhomogeneous medium that is characterized primarily by its electron density distribution. Electron density is a complex function of spatial and temporal variations of solar, geomagnetic, and seismic activities. Ionosphere is the main source of error for navigation and positioning systems and satellite communication. Therefore, characterization and constant monitoring of variability of the ionosphere is of utmost importance for the performance improvement of these systems. Since ionospheric electron density is not a directly measurable quantity, an important derivable parameter is the Total Electron Content (TEC), which is used widely to characterize the ionosphere. TEC is proportional to the total number of electrons on a line crossing the atmosphere. IONOLAB is a research group is formed by Hacettepe University, Bilkent University and Kastamonu University, Turkey gathered to handle the challenges of the ionosphere using state-of-the-art remote sensing and signal processing techniques. IONOLAB group provides unique space weather services of IONOLAB-TEC, International Reference Ionosphere extended to Plasmasphere (IRI-Plas) model based IRI-Plas-MAP, IRI-Plas-STEC and Online IRI-Plas-2015 model at www.ionolab.org. IONOLAB group has been working for imaging and monitoring of ionospheric structure for the last 15 years. TEC is estimated from dual frequency GPS receivers as IONOLAB-TEC using IONOLAB-BIAS. For high spatio-temporal resolution 2-D imaging or mapping, IONOLAB-MAP algorithm is developed that uses automated Universal Kriging or Ordinary Kriging in which the experimental semivariogram is fitted to Matern Function with Particle Swarm Optimization (PSO). For 3-D imaging of ionosphere and 1-D vertical profiles of electron density, state-of-the-art IRI-Plas model based IONOLAB-CIT algorithm is developed for regional reconstruction that employs Kalman Filters for state

  7. Ionospheric disturbances in Asian region of Russia during sudden stratospheric warmings

    Science.gov (United States)

    Kurkin, Vladimir; Chernigovskaya, Marina; Medvedeva, Irina; Orlov, Igor

    This paper presents an investigation of the subauroral and mid-latitude ionosphere variations in the Asian region of Russia during stratospheric warmings in 2008, 2009 and 2010. We used the data from network of vertical and oblique-incidence sounding ionosounders of ISTP SB RAS. Irkutsk chirp-sounder (vertical incidence sounding) run every 1 minute on 24-hour basis for 30 days in winter of 2008, 2009 and 2010 to study small-scale and medium-scale distur-bances. The experiments on the radio paths Magadan-Irkutsk, Khabarovsk-Irkutsk and Norilsk -Irkutsk were conducted in order to study large-scale ionospheric disturbances. The frequency range was from 4 to 30 MHz, the sweep rate used 500 kHz/sec. To identify the stratospheric warming events the Berlin Meteorological University data (http://strat-www.met.fu-berlin.de) on stratospheric warming at standard isobaric levels and the atmospheric temperature height profiles measured by the Microwave Limb Sounder (MLS) aboard the EOS Aura spacecraft were used. The increase of wave activity in upper ionosphere over Asian region of Russia has recorded during stratospheric warmings. Spectrums of multi-scale variations were derived from the data obtained during the prolonged experiments. The analysis of experimental data has revealed the amplitudes of planetary waves in ionosphere during stratospheric warmings in 2008 and 2010 larger than ones in winter 2009 as opposed to amplitude variations of temperature in stratosphere. This work was supported by Russian Foundation for Basic Research (grant 08-05-00658).

  8. Modeling Weather in the Ionosphere using the Navy's Highly Integrated Thermosphere and Ionosphere Demonstration System (HITIDES)

    Science.gov (United States)

    McDonald, S. E.; Sassi, F.; Zawdie, K.; McCormack, J. P.; Coker, C.; Huba, J.; Krall, J.

    2016-12-01

    The Naval Research Laboratory (NRL) has recently developed a ground-to-space atmosphere-ionosphere prediction capability, the Highly Integrated Thermosphere and Ionosphere Demonstration System (HITIDES). HITIDES is the U.S. Navy's first coupled, physics-based, atmosphere-ionosphere model, one in which the atmosphere extends from the ground to the exobase ( 500 km altitude) and the ionosphere reaches several 10,000 km in altitude. HITIDES has been developed by coupling the extended version of the Whole Atmosphere Community Climate Model (WACCM-X) with NRL's ionospheric model, Sami3 is Another Model of the Ionosphere (SAMI3). Integrated into this model are the effects of drivers from atmospheric weather (day-to-day meteorology), the Sun, and the changing high altitude composition. To simulate specific events, HITIDES can be constrained by data analysis products or observations. We have performed simulations of the ionosphere during January-February 2010 in which lower atmospheric weather patterns have been introduced using the Navy Operational Global Atmospheric Prediction System-Advanced Level Physics High Altitude (NOGAPS-ALPHA) data assimilation products. The same time period has also been simulated using the new atmospheric forecast model, the NAVy Global Environmental Model (NAVGEM), which has replaced NOGAPS-ALPHA. The two simulations are compared with each other and with observations of the low latitude ionosphere. We will discuss the importance of including lower atmospheric meteorology in ionospheric simulations to capture day-to-day variability as well as large-scale longitudinal structure in the low-latitude ionosphere. In addition, we examine the effect of the variability on HF radio wave propagation by comparing simulated ionograms calculated from the HITIDES ionospheric specifications to ionosonde measurements.

  9. Ionospheric variations during sudden stratospheric warming in the high- and mid-latitude regions

    Science.gov (United States)

    Yasyukevich, Anna; Voeykov, Sergey; Mylnikova, Anna

    2017-04-01

    The ionospheric dynamic in the high- and middle-latitude regions during the periods of sudden stratospheric warmings (SSW) was studied by using the international network of phase dual-frequency GPS/GLONASS receivers and the vertical sounding data. Twelve SSW events that occurred in the Northern Hemisphere 2006 through 2013 were considered. In order to identify the possible response of the ionosphere to SSW events, we carried out the analysis of the total electron (TEC) and the F2-layer maximum electron density (NmF2) deviations from the background level. We have also studied changes of the level of total electron content (TEC) wave-like variations characterized by a special index WTEC. The index reflects the intensity of medium- and large-scale traveling ionospheric disturbances. The dynamics of the high- and middle-latitude ionosphere at the points near the SSW areas was found to differ from the regular. For a large number of events, it is shown that, despite quiet geomagnetic conditions, a noticeable decrease in the NmF2 and TEC values (by 5-10% relative to the background level) is observed during the SSW evolution and maximum stages. On the contrary, for 10-20 days after the SSW maxima, NmF2 and TEC significantly exceed the monthly averaged values. Moreover, these electron density changes are observed for both strong and weak stratospheric warmings, and are recorded mainly during daytime. The observed SSW effects in the polar and mid-latitude ionosphere are assumed to be probably associated with the changes in the neutral composition at the thermospheric heights that affect the F2-layer electron density. The study is supported by the Russian Foundation for Basic Research under Grant No. 16-35-60018, as well as by the RF President Grant of Public Support for RF Leading Scientific Schools (NSh-6894.2016.5).

  10. Ionospheric Weather and Climate—— A Review on Chinese Works From 2004 to 2006

    Institute of Scientific and Technical Information of China (English)

    WAN Weixing; XIAO Zuo

    2006-01-01

    This paper reviews the recent studies on the ionospheric weather and climate. As a national report prepared for COSPAR, the works concerned here are limited to those made by Chinese scientists during 2004-2006. The main contents include the sudden ionospheric disturbances, the ionospheric storms, the traveling ionospheric disturbances, ionospheric variability, the annual and semiannual ionospheric variations, the solar cycle ionospheric variations, and the long term ionospheric changes.

  11. New type of ensemble of quasi-periodic, long-lasting VLF emissions at the auroral zone

    Directory of Open Access Journals (Sweden)

    J. Manninen

    2012-12-01

    Full Text Available A new type of the series of quasi-periodic (QP very low frequency (VLF emissions in frequency range of 1–5 kHz, and not associated with geomagnetic pulsations, has been discovered at auroral latitudes (L = 5.3 during the Finnish VLF campaign (held in December 2011. At least five unusually spectacular events, each with a duration of several hours, have been observed during the night under conditions of quiet geomagnetic activity (Kp = 0–1, although QPs usually occur during the daytime. Contrary to the QP emissions typically occurring during the day, the spectral structure of these QP events represented an extended, complicated sequence of repeated discrete rising VLF signals. Their duration was about 2–3 min each, with the repetition periods ranging from ~1 min to ~10 min. Two such nighttime non-typical events are reported in this paper. The fine structure of the separated QP elements may represent a mixture of the different frequency band signals, which seem to have independent origins. It was found that the periodic signals with lower frequency appear to trigger the strong dispersive upper frequency signals. The temporal dynamics of the spectral structure of the QPs studied were significantly controlled by some disturbances in the solar wind and interplanetary magnetic field (IMF. This finding is very important for future theoretical investigations because the generation mechanism of this new type of QP emissions is not yet understood.

  12. Ionospheric Response Due to Seismic Activity

    Science.gov (United States)

    Sharma, Dinesh Kumar

    2016-07-01

    Signatures of the seismic activity in the ionospheric F2 region have been studied by analyzing the measurement of electron and ion temperatures during the occurrence of earthquake. The ionospheric electron and ion temperatures data recorded by the RPA payload aboard the Indian SROSS-C2 satellite during the period from January 1995 to December 2000 were used for the altitude range 430-630 km over Indian region. The normal day's electron and ion temperatures have been compared to the temperatures recorded during the seismic activity. The details of seismic events were obtained from USGS earthquake data information website. It has been found that the average electron temperature is enhanced during the occurrence of earthquakes by 1.2 to 1.5 times and this enhancement was for ion temperature ranging from 1.1to 1.3 times over the normal day's average temperatures. The above careful quantitative analysis of ionospheric electron and ion temperatures data shows the consistent enhancement in the ionospheric electron and ion temperatures. It is expected that the seismogenic vertical electrical field propagates up to the ionospheric heights and induces Joule heating that may cause the enhancement in ionospheric temperatures.

  13. Computerized ionospheric tomography with the IRI model

    Science.gov (United States)

    Arikan, Orhan; Arikan, Feza; Erol, Cemil B.

    Computerized ionospheric tomography (CIT) is a method to estimate ionospheric electron density distribution by using the global positioning system (GPS) signals recorded by the GPS receivers. Ionospheric electron density is a function of latitude, longitude, height and time. A general approach in CIT is to represent the ionosphere as a linear combination of basis functions. In this study, the model of the ionosphere is obtained from the IRI in latitude and height only. The goal is to determine the best representing basis function from the set of Squeezed Legendre polynomials, truncated Legendre polynomials, Haar Wavelets and singular value decomposition (SVD). The reconstruction algorithms used in this study can be listed as total least squares (TLS), regularized least squares, algebraic reconstruction technique (ART) and a hybrid algorithm where the reconstruction from the TLS algorithm is used as the initial estimate for the ART. The error performance of the reconstruction algorithms are compared with respect to the electron density generated by the IRI-2001 model. In the investigated scenario, the measurements are obtained from the IRI-2001 as the line integral of the electron density profiles, imitating the total electron content estimated from GPS measurements. It has been observed that the minimum error between the reconstructed and model ionospheres depends on both the reconstruction algorithm and the basis functions where the best results have been obtained for the basis functions from the model itself through SVD.

  14. Computerized ionospheric tomography based on geosynchronous SAR

    Science.gov (United States)

    Hu, Cheng; Tian, Ye; Dong, Xichao; Wang, Rui; Long, Teng

    2017-02-01

    Computerized ionospheric tomography (CIT) based on spaceborne synthetic aperture radar (SAR) is an emerging technique to construct the three-dimensional (3-D) image of ionosphere. The current studies are all based on the Low Earth Orbit synthetic aperture radar (LEO SAR) which is limited by long repeat period and small coverage. In this paper, a novel ionospheric 3-D CIT technique based on geosynchronous SAR (GEO SAR) is put forward. First, several influences of complex atmospheric environment on GEO SAR focusing are detailedly analyzed, including background ionosphere and multiple scattering effects (induced by turbulent ionosphere), tropospheric effects, and random noises. Then the corresponding GEO SAR signal model is constructed with consideration of the temporal-variant background ionosphere within the GEO SAR long integration time (typically 100 s to 1000 s level). Concurrently, an accurate total electron content (TEC) retrieval method based on GEO SAR data is put forward through subband division in range and subaperture division in azimuth, obtaining variant TEC value with respect to the azimuth time. The processing steps of GEO SAR CIT are given and discussed. Owing to the short repeat period and large coverage area, GEO SAR CIT has potentials of covering the specific space continuously and completely and resultantly has excellent real-time performance. Finally, the TEC retrieval and GEO SAR CIT construction are performed by employing a numerical study based on the meteorological data. The feasibility and correctness of the proposed methods are verified.

  15. What is sound energy ?

    CERN Document Server

    Loria, Laura

    2017-01-01

    Sounds are all around us, but what makes sound? How does it travel? What can it do? These questions and more will be answered as the science of sound energy is examined in depth. Readers will learn how the physical movement of objects creates sound, as well as the qualities of sound and how they vary, and are received. The uses of sound energy in various fields will be explored. Simple illustrations of sophisticated scientific concepts will enhance the young learner's understanding of the topic.

  16. Artificial ionospheric modification: The Metal Oxide Space Cloud experiment

    Science.gov (United States)

    Caton, Ronald G.; Pedersen, Todd R.; Groves, Keith M.; Hines, Jack; Cannon, Paul S.; Jackson-Booth, Natasha; Parris, Richard T.; Holmes, Jeffrey M.; Su, Yi-Jiun; Mishin, Evgeny V.; Roddy, Patrick A.; Viggiano, Albert A.; Shuman, Nicholas S.; Ard, Shaun G.; Bernhardt, Paul A.; Siefring, Carl L.; Retterer, John; Kudeki, Erhan; Reyes, Pablo M.

    2017-05-01

    Clouds of vaporized samarium (Sm) were released during sounding rocket flights from the Reagan Test Site, Kwajalein Atoll in May 2013 as part of the Metal Oxide Space Cloud (MOSC) experiment. A network of ground-based sensors observed the resulting clouds from five locations in the Republic of the Marshall Islands. Of primary interest was an examination of the extent to which a tailored radio frequency (RF) propagation environment could be generated through artificial ionospheric modification. The MOSC experiment consisted of launches near dusk on two separate evenings each releasing 6 kg of Sm vapor at altitudes near 170 km and 180 km. Localized plasma clouds were generated through a combination of photoionization and chemi-ionization (Sm + O → SmO+ + e-) processes producing signatures visible in optical sensors, incoherent scatter radar, and in high-frequency (HF) diagnostics. Here we present an overview of the experiment payloads, document the flight characteristics, and describe the experimental measurements conducted throughout the 2 week launch window. Multi-instrument analysis including incoherent scatter observations, HF soundings, RF beacon measurements, and optical data provided the opportunity for a comprehensive characterization of the physical, spectral, and plasma density composition of the artificial plasma clouds as a function of space and time. A series of companion papers submitted along with this experimental overview provide more detail on the individual elements for interested readers.

  17. A generalized trigonometric series function model for determining ionospheric delay

    Institute of Scientific and Technical Information of China (English)

    YUAN Yunbin; OU Jikun

    2004-01-01

    A generalized trigonometric series function (GTSF) model, with an adjustable number of parameters, is proposed and analyzed to study ionosphere by using GPS, especially to provide ionospheric delay correction for single frequency GPS users. The preliminary results show that, in comparison with the trigonometric series function (TSF) model and the polynomial (POLY) model, the GTSF model can more precisely describe the ionospheric variation and more efficiently provide the ionospheric correction when GPS data are used to investigate or extract the earth's ionospheric total electron content. It is also shown that the GTSF model can further improve the precision and accuracy of modeling local ionospheric delays.

  18. Synthesized size-sound sound symbolism

    NARCIS (Netherlands)

    Lockwood, G.F.; Hagoort, P.; Dingemanse, M.

    2016-01-01

    Studies of sound symbolism have shown that people can associate sound and meaning in consistent ways when presented with maximally contrastive stimulus pairs of nonwords such as bouba/kiki (rounded/sharp) or mil/mal (small/big). Recent work has shown the effect extends to antonymic words from natura

  19. Measurements of ionospheric TEC in the direction of GPS satellites and comparison with three ionospheric models

    Directory of Open Access Journals (Sweden)

    E. Zuccheretti

    1997-06-01

    Full Text Available The IEN Galileo Ferraris uses GPS for time and frequency synchronization. To obtain high performance it is important to reduce the error due to the ionospheric time-delay in GPS measurements. Evaluations of TEC in the direction of GPS satellites, obtained from three different ionospheric models, have been compared with corresponding measurements by GPS signal.

  20. Characteristics of flux-time profiles, temporal evolution, and spatial distribution of radiation-belt electron precipitation bursts in the upper ionosphere before great and giant earthquakes

    Directory of Open Access Journals (Sweden)

    Sergey Pulinets

    2012-04-01

    Full Text Available

    The analysis of energetic electron observations made by the DEMETER satellite reveals that radiation belt electron precipitation (RBEP bursts are observed in general several (~1-6 days before a large (M > 6.5 earthquake (EQ in the presence of broad band (~1-20 kHz VLF waves. The EBs show in general a relative peak-to-background flux increase usually < 100, they have a time duration of ~0.5 – 3 min, and their energy spectrum reach up to energies <~500 keV. The RBEP activity is observed as one, two or three EBs throughout a semi-orbit, depended on the magnetic field structure above the EQ epicenter. A statistical analysis has been made for earthquakes in Japan, which reveals a standard temporal variation of the number of EBs, which begins with an incremental rate several days before major earthquakes, and after a maximum, decreases so that the electron precipitation ceases above the epicenter. Some earthquake induced EBs were observed not only in the nightside ionosphere, but also in the dayside ionosphere.

     

  1. Early sound symbolism for vowel sounds.

    Science.gov (United States)

    Spector, Ferrinne; Maurer, Daphne

    2013-01-01

    Children and adults consistently match some words (e.g., kiki) to jagged shapes and other words (e.g., bouba) to rounded shapes, providing evidence for non-arbitrary sound-shape mapping. In this study, we investigated the influence of vowels on sound-shape matching in toddlers, using four contrasting pairs of nonsense words differing in vowel sound (/i/ as in feet vs. /o/ as in boat) and four rounded-jagged shape pairs. Crucially, we used reduplicated syllables (e.g., kiki vs. koko) rather than confounding vowel sound with consonant context and syllable variability (e.g., kiki vs. bouba). Toddlers consistently matched words with /o/ to rounded shapes and words with /i/ to jagged shapes (p vowel sound and shape.

  2. DE-1 and COSMOS 1809 observations of lower hybrid waves excited by VLF whistler mode waves

    Science.gov (United States)

    Bell, T. F; Inan, U. S.; Lauben, D.; Sonwalkar, V. S.; Helliwell, R. A.; Sobolev, Ya. P.; Chmyrev, V. M.; Gonzalez, S.

    1994-01-01

    Past work demostrates that strong lower hybrid (LH) waves can be excited by electromagnetic whistler mode waves throughout large regions of the topside ionosphere and magnetosphere. The effects of the excited LH waves upon the suprathermal ion population in the topside ionosphere and magnetosphere depend upon the distribution of LH wave amplitude with wavelength lambda. The present work reports plasma wave data from the DE-1 and COSMOS 1809 spacecraft which suggests that the excited LH wave spectrum has components for which lambda less than or equal to 3.5 m when excitation occurs at a frequency roughly equal to the local lower hybrid resonance frequency. This wavelength limit is a factor of approximately 3 below that reported in past work and suggests that the excited LH waves can interact with suprathermal H(+) ions with energy less than or equal to 6 eV. This finding supports recent work concerning the heating of suprathermal ions above thunderstorm cells.

  3. Sound wave transmission (image)

    Science.gov (United States)

    When sounds waves reach the ear, they are translated into nerve impulses. These impulses then travel to the brain where they are interpreted by the brain as sound. The hearing mechanisms within the inner ear, can ...

  4. Making fictions sound real

    DEFF Research Database (Denmark)

    Langkjær, Birger

    2010-01-01

    This article examines the role that sound plays in making fictions perceptually real to film audiences, whether these fictions are realist or non-realist in content and narrative form. I will argue that some aspects of film sound practices and the kind of experiences they trigger are related...... to basic rules of human perception, whereas others are more properly explained in relation to how aesthetic devices, including sound, are used to characterise the fiction and thereby make it perceptually real to its audience. Finally, I will argue that not all genres can be defined by a simple taxonomy...... of sounds. Apart from an account of the kinds of sounds that typically appear in a specific genre, a genre analysis of sound may also benefit from a functionalist approach that focuses on how sounds can make both realist and non-realist aspects of genres sound real to audiences....

  5. An Antropologist of Sound

    DEFF Research Database (Denmark)

    Groth, Sanne Krogh

    2015-01-01

    PROFESSOR PORTRAIT: Sanne Krogh Groth met Holger Schulze, newly appointed professor in Musicology at the Department for Arts and Cultural Studies, University of Copenhagen, to a talk about anthropology of sound, sound studies, musical canons and ideology....

  6. Modelling Hyperboloid Sound Scattering

    DEFF Research Database (Denmark)

    Burry, Jane; Davis, Daniel; Peters, Brady;

    2011-01-01

    The Responsive Acoustic Surfaces workshop project described here sought new understandings about the interaction between geometry and sound in the arena of sound scattering. This paper reports on the challenges associated with modelling, simulating, fabricating and measuring this phenomenon using...

  7. Large-scale and Medium-scale Traveling Ionospheric Disturbances Registered during Magnetic Storms over North-Eastern Region of Russian Federation

    Science.gov (United States)

    Ivanova, Vera; Kurkin, Vladimir

    2016-07-01

    Earth's ionosphere is dynamical steadily changed medium. On a level with daily and seasonal variations of ionospheric parameters there are irregular components connected with wave motions in neutral atmosphere. F2 ionosphere region disturbances are developed in global scale during geomagnetic storms and characterized considerable variations in F2-region critical frequencies and heights. High frequency oblique-incidence sounding method allows us to diagnose ionospheric parameters variations in regions poorly equipped with vertical sounding stations. In this work we provide the analysis of large-scale and medium-scale traveling ionospheric disturbances (LS and MS TID's accordingly) registered during experiments from 2006 till 2011 which carried out by means of the monthly duration sets with 5-min intervals over oblique-incidence sounding paths located in the north-eastern region of Russian Federation. For the analysis we have been chosen experimental data obtained during minor and moderate geomagnetic storms. After ionograms processing maximum observed frequencies (MOF) deviations from median values were calculated. Using MOF deviations from medians the analysis of LS TID's appearance cases was carried out. Studied MOF deviations from medians can be caused by cusps on ionograms also. These cusps move with the course of time through the sequences of ionograms along upper rays from region with higher delays to region with lower delays. Such cusps on ionograms are caused by MS TID's. In this work the analysis of MS TID events registration by these cusps on ionograms was carried out. Then the comparison between LS and MS TID's appearance probability was performed. It is shown that registered MOF variations are caused by superposition of wave-like processes of different scales taken place in ionosphere during magnetic storms. This work was supported by the RFBR grants No 14-05-00259-a and No 14-05-00578-a.

  8. Longitudinal differences observed in the ionospheric F-region during the major geomagnetic storm of 31 March 2001

    Directory of Open Access Journals (Sweden)

    Y. Sahai

    2004-09-01

    Full Text Available A new ionospheric sounding station using a Canadian Advanced Digital Ionosonde (CADI was established for routine measurements by the "Universidade do Vale do Paraiba (UNIVAP" at São José dos Campos (23.2° S, 45.9° W, Brazil, in August 2000. A major geomagnetic storm with gradual commencement at about 01:00 UT was observed on 31 March 2001. In this paper, we present and discuss salient features from the ionospheric sounding measurements carried out at S. J. Campos on the three consecutive UT days 30 March (quiet, 31 March (disturbed and 1 April (recovery 2001. During most of the storm period, the foF2 values showed negative phase, whereas during the two storm-time peaks, large F-region height variations were observed. In order to study the longitudinal differences observed in the F-region during the storm, the simultaneous ionospheric sounding measurements carried out at S. J. Campos, El Arenosillo (37.1° N, 6.7° W, Spain, Okinawa (26.3° N, 127.8° E, Japan and Wakkanai (45.5° N, 141.7° E, Japan, during the period 30 March-1 April 2001, have been analyzed. A comparison of the observed ionospheric parameters (h'F and foF2 in the two longitudinal zones (1. Japanese and 2. Brazilian-Spanish shows both similarities and differences associated with the geomagnetic disturbances. Some latitudinal differences are also observed in the two longitudinal zones. In addition, global ionospheric TEC maps from the worldwide network of GPS receivers are presented, showing widespread TEC changes during both the main and recovery phases of the storm. The ionospheric sounding measurements are compared with the ASPEN-TIMEGCM model runs appropriate for the storm conditions. The model results produce better agreement during the quiet period. During the disturbed period, some of the observed F-region height variations are well reproduced by the model results. The model foF2 and TEC results differ considerably during the

  9. Characteristic features of topside ionograms in the high-latitude ionosphere.

    Science.gov (United States)

    Panshin, Evgeniy; Danilkin, Nick; Tsybulya, Konstantin; Zhuravliov, Sergey

    Topside ionograms display a multitude of specific features in the high-latitude regions. In this report we present an analysis of these features based upon topside ionograms of the Kosmos-1809 satellite taken in May-June 1987. These ionograms were received onboard icebreaker Sibir during a polar expedition in this time. Since the ionograms were downlinked directly in the time of sounding, they were not strongly curtailed to fit the limited onboard memory and thus were much more informative. Acquiring the data in such way allowed us to see little-studied and even unknown ionogram features. Among them we note traces of a characteristic form which were interpreted earlier as signal reflections from almost vertical walls with increased electron density. Such structures are typical for the auroral oval ionosphere. To interpret this features we used a technique of ray trajectory synthesis. We present a sequence of ionograms with all phases of closing to, flying through and away from a higher-density wall. Quite often one find on the polar ionograms broad-band noise signals in different frequency ranges. On the ionograms they are seen as frequency-limited vertical columns from the very top of the ionogram to its bottom. Low-frequency noise (0.3-0.8 MHz) appear during auroral oval fly-throughs and are interpreted as a result of auroral kilometric radiation (AKR). Narrow bands on the magnetic gyrofrequency and upper hybrid frequency could be understood as an ionospheric plasma resonance response near the radiating antenna. Also, there are strong noises in the 3-5 MHz which we were not able to interpret. During some sounding sessions the transmitter was turned off so it was possible to record only natural and artificial noises and separate them from the ionospheric sounding responses.

  10. An Antropologist of Sound

    DEFF Research Database (Denmark)

    Groth, Sanne Krogh

    2015-01-01

    PROFESSOR PORTRAIT: Sanne Krogh Groth met Holger Schulze, newly appointed professor in Musicology at the Department for Arts and Cultural Studies, University of Copenhagen, to a talk about anthropology of sound, sound studies, musical canons and ideology.......PROFESSOR PORTRAIT: Sanne Krogh Groth met Holger Schulze, newly appointed professor in Musicology at the Department for Arts and Cultural Studies, University of Copenhagen, to a talk about anthropology of sound, sound studies, musical canons and ideology....

  11. Man & Sound Environment 2010.

    OpenAIRE

    2010-01-01

    Proceedings to the conference "Man and Sound Environment 2010" arranged by The sound Envirnment Center at Lund university. Ulf Landström, Swedish Noise Research Network & Frans Mossberg The Sound Environment Centre at Lund university. CONTENTS: Preface – Symposium “Man and Sound Environment 2010” The prevalence of noise problems. Gunn Marit Aasvang, Norwegian Institute of Public Health, Department of Environmental Medicine, Nydalen, Oslo, Norway Effects of ...

  12. Broadcast sound technology

    CERN Document Server

    Talbot-Smith, Michael

    1990-01-01

    Broadcast Sound Technology provides an explanation of the underlying principles of modern audio technology. Organized into 21 chapters, the book first describes the basic sound; behavior of sound waves; aspects of hearing, harming, and charming the ear; room acoustics; reverberation; microphones; phantom power; loudspeakers; basic stereo; and monitoring of audio signal. Subsequent chapters explore the processing of audio signal, sockets, sound desks, and digital audio. Analogue and digital tape recording and reproduction, as well as noise reduction, are also explained.

  13. Researching home through sounds

    DEFF Research Database (Denmark)

    Winther, Ida Wentzel

    2014-01-01

    sounds via the sense of hearing; i.e., by listening. Furthermore, I examine some of the methodological challenges associated with listening to a space (as sound), interpreting what is heard and then representing the sounds in a text. I also discuss the types of knowledge that may be created through...... auditory and visual approaches....

  14. Ionospheric Impacts on UHF Space Surveillance

    Science.gov (United States)

    Jones, J.; Ceron-Gomez, D.; Richards, G.

    2016-09-01

    Earth's atmosphere contains regions of ionized plasma caused by the interaction of highly energetic solar radiation. This region of ionization is called the ionosphere and varies significantly with altitude, latitude, local solar time, season, and solar cycle. Significant ionization begins at about 100 km (E layer) with a peak in the ionization at about 350 km (F2 layer). Above the F2 layer, the atmosphere is mostly ionized but the ion and electron densities are low due to the unavailability of neutral molecules for ionization so the electron density decreases exponentially with height to well over 1000 km. The gradients of these variations in the ionosphere play a significant role in radio wave propagation. These gradients induce variations in the index of refraction and cause some radio waves to refract. The amount of refraction depends on the magnitude and direction of the electron density gradient and the frequency of the radio wave. The refraction is significant at HF frequencies (3-30 MHz) with decreasing effects toward the UHF (300-3000 MHz) range. UHF is commonly used for tracking of space objects in low Earth orbit (LEO). While ionospheric refraction is small for UHF frequencies, it can cause errors in range, azimuth angle, and elevation angle estimation by ground-based radars tracking space objects. These errors can cause significant uncertainty in precise orbit determinations. For radio waves transiting the ionosphere, it is important to understand and account for these effects. Using a sophisticated radio wave propagation tool suite and an empirical ionospheric model, we calculate the errors induced by the ionosphere in a simulation of a notional space surveillance radar tracking objects in LEO. These errors are analyzed to determine correlations with ionospheric variability. Corrections to surveillance radar measurements can be adapted from our simulation capability.

  15. Kinesonde observations of ionosphere modification by intense electromagnetic fields from Platteville, Colorado.

    Science.gov (United States)

    Wright, J. W.

    1973-01-01

    Observations by the Kinesonde (a multifrequency, spaced antenna, digitized complex-amplitude radio sounding system) of ionospheric responses to excitation by the high-power transmitter at Platteville, Colo., are described. Increases of echo scintillation rate and intensity at frequencies reflected near and far from the excitation level are shown. Significant onset delays of these responses suggest disturbance propagation velocities of a few kilometers per second. Calculated echolocations show a time-dependent development toward the excitation region, again with a delayed response. Comments are offered regarding the relative utility of ionogram and Kinesonde observations for study of these phenomena.

  16. Interhemispheric ionospheric coupling at the American sector during low solar activity. I - Observations

    Science.gov (United States)

    Jakowski, N.; Foerster, M.; Lazo, B.; Lois, L.

    Ionospheric electron content and vertical sounding data obtained in Havana during the solar minimum year 1976 indicate a nighttime winter anomaly effect. These experimental data are compared with observations from the ionosonde station Port Stanley (geomagnetically conjugated latitude region) and with total electron content observations from Tucuman/Argentina (geographically conjugated latitude). An effective interhemispheric transport of plasma is suggested to explain the enhanced nighttime ionization in Havana during winter nights. The downward plasma flux has been estimated to lie in the range of 3 x 10 to the 8th/sq cm/s.

  17. Introduction to the Special Issue on Sounding Rockets and Instrumentation

    Science.gov (United States)

    Christe, Steven; Zeiger, Ben; Pfaff, Rob; Garcia, Michael

    2016-03-01

    Rocket technology, originally developed for military applications, has provided a low-cost observing platform to carry critical and rapid-response scientific investigations for over 70 years. Even with the development of launch vehicles that could put satellites into orbit, high altitude sounding rockets have remained relevant. In addition to science observations, sounding rockets provide a unique technology test platform and a valuable training ground for scientists and engineers. Most importantly, sounding rockets remain the only way to explore the tenuous regions of the Earth’s atmosphere (the upper stratosphere, mesosphere, and lower ionosphere/thermosphere) above balloon altitudes (˜40km) and below satellite orbits (˜160km). They can lift remote sensing telescope payloads with masses up to 400kg to altitudes of 350km providing observing times of up to 6min above the blocking influence of Earth’s atmosphere. Though a number of sounding rocket research programs exist around the world, this article focuses on the NASA Sounding Rocket Program, and particularly on the astrophysical and solar sounding rocket payloads.

  18. Modeling of Plasma Irregularities in Expanding Ionospheric Dust Clouds

    Science.gov (United States)

    Fu, H.; Scales, W.; Mahmoudian, A.; Bordikar, M. R.

    2009-12-01

    Natural dust layers occur in the earth’s mesosphere (50km-85km). Plasma irregularities are associated with these natural dust layers that produce radar echoes. Recently, an Ionospheric sounding rocket experiment was performed to investigate the plasma irregularities in upper atmospheric dust layers. The Charged Aerosol Release Experiment (CARE) uses a rocket payload injection of particles in the ionosphere to determine the mechanisms for enhanced radar scatter from plasma irregularities embedded in artificial dusty plasma in space. A 2-D hybrid computational model is described that may be used to study a variety of irregularities in dusty space plasmas which may lead to radar echoes. In this model, the dust and ions are both treated with Particle-In-Cell method while the dust charge varies with time based on the standard dust Orbit Motion Limited charging model. A stochastic model is adopted to remove particle ions due to the dust charging process. Electrons are treated with a fluid model including the parallel dynamics of magnetic fields. Fourier spectral methods with a predictor-corrector time advance are used to solve it. This numerical model will be used to investigate the electrodynamics and several possible plasma irregularity generation mechanisms after the creation of an artificial dust layer. The first is the dust ion-acoustic instability due to the drift of dust relative to the plasma. The instability saturates by trapping some ions. The effects of dust radius and dust drift velocity on plasma irregularities will be analyzed further. Also, a shear- driven instability in expanding dusty clouds is investigated.

  19. Oblique echoes at unusually high frequencies in MARSIS-AIS measurements of the topside ionosphere of Mars

    Science.gov (United States)

    Fallows, Kathryn J.; Withers, Paul; Morgan, David

    2016-10-01

    The topside plasma density measurements from the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument on the Mars Express orbiter have been invaluable for studying the influence of the crustal magnetic fields on the distribution of plasma in the Mars ionosphere. A common feature, especially in the southern crustal field region, is an "oblique echo," or an off-nadir reflection consistent with the spacecraft passing by, or directly above, a localized region with a sharp gradient in electron density. These are often interpreted as regions where the ionosphere is heated by the solar wind fields and plasma which penetrate the ionosphere along vertical field lines.We present a subset of these oblique echoes which are characterized by reflections at frequencies much higher than those from the nadir ionosphere. If these are interpreted in the same way as typical return signals, where the frequency of the reflected signal is assumed to be the plasma frequency at the point of reflection, then these may be the highest plasma densities reported to date at Mars. In two cases, reflections are detected at the maximum sounding frequency of the instrument, 5.5 MHz, which corresponds to electron densities of 3.75x105 cm-3.These features are associated with strong, vertical magnetic fields, as expected for typical oblique echoes. However, they are only observed in regions where there is also an above-average likelihood of the field lines being open to the solar wind. This is consistent with the interpretation that these cusp-like regions can allow for interaction with the solar wind, but it is not yet clear whether these are an extreme case of "typical" oblique echoes, or whether these high-frequency echoes are caused by a unique physical process or observation geometry.

  20. Experimental evidence of electromagnetic pollution of ionosphere

    Science.gov (United States)

    Pronenko, Vira; Korepanov, Valery; Dudkin, Denis

    The Earth’s ionosphere responds to external perturbations originated mainly in the Sun, which is the primary driver of the space weather (SW). But solar activity influences on the ionosphere and the Earth's atmosphere (i.e., the energy transfer in the direction of the Sun-magnetosphere-ionosphere-atmosphere-surface of the Earth), though important, is not a unique factor affecting its state - there is also a significant impact of the powerful natural and anthropogenic processes, which occur on the Earth’s surface and propagating in opposite direction along the Earth’s surface-atmosphere-ionosphere-magnetosphere chain. Numerous experimental data confirm that the powerful sources and consumers of electrical energy (radio transmitters, power plants, power lines and industrial objects) cause different ionospheric phenomena, for example, changes of the electromagnetic (EM) field and plasma in the ionosphere, and affect on the state of the Earth atmosphere. Anthropogenic EM effects in the ionosphere are already observed by the scientific satellites and the consequences of their impact on the ionosphere are not currently known. Therefore, it is very important and urgent task to conduct the statistically significant research of the ionospheric parameters variations due to the influence of the powerful man-made factors, primarily owing to substantial increase of the EM energy production. Naturally, the satellite monitoring of the ionosphere and magnetosphere in the frequency range from tens of hertz to tens of MHz with wide ground support offers the best opportunity to observe the EM energy release, both in the global and local scales. Parasitic EM radiation from the power supply lines, when entering the ionosphere-magnetosphere system, might have an impact on the electron population in the radiation belt. Its interaction with trapped particles will change their energy and pitch angles; as a result particle precipitations might occur. Observations of EM emission by

  1. Sound visualization and manipulation

    CERN Document Server

    Kim, Yang-Hann

    2013-01-01

    Unique in addressing two different problems - sound visualization and manipulation - in a unified way Advances in signal processing technology are enabling ever more accurate visualization of existing sound fields and precisely defined sound field production. The idea of explaining both the problem of sound visualization and the problem of the manipulation of sound within one book supports this inter-related area of study.  With rapid development of array technologies, it is possible to do much in terms of visualization and manipulation, among other technologies involved with the spatial dis

  2. Mesoscale ionospheric tomography at the Auroral region

    Science.gov (United States)

    Luntama, J.; Kokkatil, G. V.

    2008-12-01

    FMI (Finnish Meteorological Institute) has used observations from the dense GNSS network in Finland for high resolution regional ionospheric tomography. The observation system used in this work is the VRS (Virtual Reference Station) network in Finland operated by Geotrim Ltd. This network contains 86 GNSS ground stations providing two frequency GPS and GLONASS observations with the sampling rate of 1 Hz. The network covers the whole Finland and the sampling of the ionosphere is very good for observing mesoscale ionospheric structures at the Auroral region. The ionospheric tomography software used by FMI is the MIDAS (Multi-Instrument Data Analysis System) algorithm developed and implemented by the University of Bath (Mitchell and Spencer, 2003). MIDAS is a 3-D extension of the 2-D tomography algorithm originally presented by Fremouw et al. (1992). The research at FMI is based on ground based GNSS data collected in December 2006. The impacts of the two geomagnetic storms during the month are clearly visible in the retrieved electron density and TEC maps and they can be correlated with the magnetic field disturbances measured by the IMAGE magnetometer network. This is the first time that mesoscale structures in the ionospheric plasma can be detected from ground based GNSS observations at the Auroral region. The continuous high rate observation data from the Geotrim network allows monitoring of the temporal evolution of these structures throughout the storms. Validation of the high resolution electron density and TEC maps is a challenge as independent reference observations with a similar resolution are not available. FMI has compared the 3-D electron density maps against the 2-D electron density plots retrieved from the observations from the Ionospheric Tomography Chain operated by the Sodankylä Geophysical Observatory (SGO). Additional validation has been performed with intercomparisons with observations from the ground based magnetometer and auroral camera network

  3. Radio Sounding Techniques for the Galilean Icy Moons and their Jovian Magnetospheric Environment

    Science.gov (United States)

    Green, James L.; Markus, Thursten; Fung, Shing F.; Benson, Robert F.; Reinich, Bodo W.; Song, Paul; Gogineni, S. Prasad; Cooper, John F.; Taylor, William W. L.; Garcia, Leonard

    2004-01-01

    Radio sounding of the Earth's topside ionosphere and magnetosphere is a proven technique from geospace missions such as the International Satellites for Ionospheric Studies (ISIS) and the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE). Application of this technique to Jupiter's icy moons and the surrounding Jovian magnetosphere will provide unique remote sensing observations of the plasma and magnetic field environments and the subsurface conductivities, of Europa, Ganymede, and Callisto. Spatial structures of ionospheric plasma above the surfaces of the moons vary in response to magnetic-field perturbations from (1) magnetospheric plasma flows, (2) ionospheric currents from ionization of sputtered surface material, and (3) induced electric currents in salty subsurface oceans and from the plasma flows and ionospheric currents themselves. Radio sounding from 3 kHz to 10 MHz can provide the global electron densities necessary for the extraction of the oceanic current signals and supplements in-situ plasma and magnetic field measurements. While radio sounding requires high transmitter power for subsurface sounding, little power is needed to probe the electron density and magnetic field intensity near the spacecraft. For subsurface sounding, reflections occur at changes in the dielectric index, e.g., at the interfaces between two different phases of water or between water and soil. Variations in sub-surface conductivity of the icy moons can be investigated by radio sounding in the frequency range from 10 MHz to 50 MHz, allowing the determination of the presence of density and solid-liquid phase boundaries associated with oceans and related structures in overlying ice crusts. The detection of subsurface oceans underneath the icy crusts of the Jovian moons is one of the primary objectives of the Jupiter Icy Moons Orbiter (JIMO) mission. Preliminary modeling results show that return signals are clearly distinguishable be&een an ice crust with a thickness of

  4. Ionospheric Scintillation Effects on GPS

    Science.gov (United States)

    Steenburgh, R. A.; Smithtro, C.; Groves, K.

    2007-12-01

    . Ionospheric scintillation of Global Positioning System (GPS) signals threatens navigation and military operations by degrading performance or making GPS unavailable. Scintillation is particularly active, although not limited to, a belt encircling the earth within 20 degrees of the geomagnetic equator. As GPS applications and users increases, so does the potential for detrimental impacts from scintillation. We examined amplitude scintillation data spanning seven years from Ascension Island, U.K.; Ancon, Peru; and Antofagasta, Chile in the Atlantic/Americas longitudinal sector at as well as data from Parepare, Indonesia; Marak Parak, Malaysia; Pontianak, Indonesia; Guam; and Diego Garcia, U.K.; in the Pacific longitudinal sector. From these data, we calculate percent probability of occurrence of scintillation at various intensities described by the S4 index. Additionally, we determine Dilution of Precision at one minute resolution. We examine diurnal, seasonal and solar cycle characteristics and make spatial comparisons. In general, activity was greatest during the equinoxes and solar maximum, although scintillation at Antofagasta, Chile was higher during 1998 rather than at solar maximum.

  5. Charge Balance in the Martian Ionosphere

    Science.gov (United States)

    Esman, Teresa; Yelle, Roger V.; Stone, Shane W.; Andersson, Laila; Fowler, Christopher Michael; Benna, Mehdi; Eparvier, Francis; Mahaffy, Paul; Ergun, Bob; Elrod, Meredith K.; MAVEN

    2016-10-01

    We present empirical models of the Martian ionosphere in conjunction with data from the Langmuir Probe and Waves (LPW), Neutral Gas and Ion Mass Spectrometer (NGIMS), and Extreme Ultraviolet Monitor (EUVM) instruments aboard the Mars Atmosphere and Volatile Evolution mission (MAVEN) spacecraft. Among the data provided by MAVEN are electron densities and temperatures, ion and neutral densities, and solar extreme ultraviolet (EUV) flux. We explore a number of contributors to the CO2 photoionization rate, with a specific focus on the role of electron temperatures, which, prior to MAVEN, were not well-known. We compare our results with expectations of the ionospheric structure and behavior to confirm our understanding of the basic structure of the Martian ionosphere in the photochemical region. We show that the ionosphere of Mars is well matched by photochemical equilibrium to within the accuracy of the measurements. These results will aid in the development of more complex ionospheric and escape models and lead to a comprehensive and global scale picture of thermal ion escape on Mars.

  6. Short Time-Scale Enhancements to the Global Thermosphere Temperature and Nitric Oxide Content Resulting From Ionospheric Joule Heating

    Science.gov (United States)

    Weimer, D. R.; Mlynczak, M. G.; Hunt, L. A.; Sutton, E. K.

    2014-12-01

    The total Joule heating in the polar ionosphere can be derived from an empirical model of the electric fields and currents, using input measurements of the solar wind velocity and interplanetary magnetic field (IMF). In the thermosphere, measurements of the neutral density from accelerometers on the CHAMP and GRACE satellites are used to derive exospheric temperatures, showing that enhanced ionospheric energy dissipation produces elevated temperatures with little delay.Using the total ionospheric heating, changes in the global mean exosphere temperature as a function of time can be calculated with a simple differential equation. The results compare very well with the CHAMP and GRACE measurement. A critical part of the calculation is the rate at which the thermosphere cools after the ionospheric heating is reduced. It had been noted previously that events with significant levels of heating subsequently cool at a faster rate, and this cooling was attributed to enhanced nitric oxide emissions. This correlation with nitric oxide has been confirmed with very high correlations with measurements of nitric oxide emissions in the thermosphere, from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite. These measurements were used in a recent improvement in the equations that calculate the thermosphere temperature. The global nitric oxide cooling rates are included in this calculation, and the predicted levels of nitric oxide, derived from the ionosphere heating model, match the SABER measurements very well, having correlation coefficients on the order of 0.9.These calculations are used to govern the sorting of measurements CHAMP and GRACE measurements, on the basis of the global temperature enhancements due to Joule heating, as well as various solar indices, and season. Global maps of the exospheric temperature are produced from these sorted data.

  7. Prediction soft-X-ray spectrum of solar flares from Very Low Frequency observations: an inverse problem in ionospheric science

    Science.gov (United States)

    Palit, Sourav; Chakrabarti, Sandip Kumar; Ray, Suman

    2016-07-01

    Earth's lower ionosphere and upper atmosphere absorb X-rays and gamma-rays from astronomical sources such as solar flares, Short Gamma ray Repeaters (SGRs) or Gamma Ray Bursts (GRBs). The electron-ion production rates due to the ionization of such energetic photons at different heights depend on the intensity and wavelength of the injected spectrum and hence vary from one source to another. Obviously the ion density vs. altitude profile has the imprint of the incident photon spectrum. In this paper, we examine the possibility of inverting the electron density-height profiles uniquely by deconvolution of the VLF amplitude signal to obtain information on the injected spectrum. We have been able to reproduce the soft-X-ray part of the injected spectra from two different classes of solar flares with satisfactory accuracy. With the possibilities of probing even lower parts of the atmosphere, the method presented here is useful to carry out a similar exercise to infer the higher energy part of solar flare spectra and spectra of more energetic events such as the GRBs, SGRs etc. We show that to a certain accuracy, the Earth's atmosphere may be used as a gigantic detector of relatively strong ionizing extra-terrestrial events.

  8. An Initial Investigation of Ionospheric Gradients for Detection of Ionospheric Disturbances over Turkey

    Science.gov (United States)

    Koroglu, Meltem; Arikan, Feza; Koroglu, Ozan

    2015-04-01

    Ionosphere is an ionized layer of earth's atmosphere which affect the propagation of radio signals due to highly varying electron density structure. Total Electron Content (TEC) and Slant Total Electron Content (STEC) are convenient measures of total electron density along a ray path. STEC model is given by the line integral of the electron density between the receiver and GPS satellite. TEC and STEC can be estimated by observing the difference between the two GPS signal time delays that have different frequencies L1 (1575 MHz) and L2 (1227 MHz). During extreme ionospheric storms ionospheric gradients becomes larger than those of quiet days since time delays of the radio signals becomes anomalous. Ionosphere gradients can be modeled as a linear semi-infinite wave front with constant propagation speed. One way of computing the ionospheric gradients is to compare the STEC values estimated between two neighbouring GPS stations. In this so-called station-pair method, ionospheric gradients are defined by dividing the difference of the time delays of two receivers, that see the same satellite at the same time period. In this study, ionospheric gradients over Turkey are computed using the Turkish National Permanent GPS Network (TNPGN-Active) between May 2009 and September 2012. The GPS receivers are paired in east-west and north-south directions with distances less than 150 km. GPS-STEC for each station are calculated using IONOLAB-TEC and IONOLAB-BIAS softwares (www.ionolab.org). Ionospheric delays are calculated for each paired station for both L1 and L2 frequencies and for each satellite in view with 30 s time resolution. During the investigation period, different types of geomagnetic storms, Travelling Ionospheric Disturbances (TID), Sudden Ionospheric Disturbances (SID) and various earthquakes with magnitudes between 3 to 7.4 have occured. Significant variations in the structure of station-pair gradients have been observed depending on location of station-pairs, the

  9. Representation of the Auroral and Polar Ionosphere in the International Reference Ionosphere (IRI)

    Science.gov (United States)

    Bilitza, Dieter; Reinisch, Bodo

    2013-01-01

    This issue of Advances in Space Research presents a selection of papers that document the progress in developing and improving the International Reference Ionosphere (IRI), a widely used standard for the parameters that describe the Earths ionosphere. The core set of papers was presented during the 2010 General Assembly of the Committee on Space Research in Bremen, Germany in a session that focused on the representation of the auroral and polar ionosphere in the IRI model. In addition, papers were solicited and submitted from the scientific community in a general call for appropriate papers.

  10. The ionospheric response to perturbation electric fields during the onset phase of geomagnetic storms

    Energy Technology Data Exchange (ETDEWEB)

    Jakowski, N.; Jungstand, A. (Deutsche Forschungsanstalt fuer Luft- and Raumfahrt, Neustrelitz (Germany)); Schlegel, K.; Kohl, H.; Rinnert, K. (Max-Planck-Institut fuer Aeronomie, Katlenburg-Lindau (Germany))

    1992-07-01

    The generation and propagation of ionospheric storms are studied by analyzing EISCAT radar, and vertical sounding and total electron content data obtained under different geophysical conditions. Both case studies as well as the average storm pattern of percentage deviations of different ionospheric parameters from their corresponding reference values such as total electron content, F2-layer critical frequency, F2 layer critical height, and slab thickness indicate the action of a perturbation electric field during the first few hours of the onset of geomagnetic storms. Considering the onset phase of the storm on July 28-29, 1987 evidence has been found that high latitude electric fields may penetrate to lower latitudes before the ring current has developed. Different mechanisms are assumed to be responsible for daytime and nightime behaviour, respectively. The negative phase propagates equatorward with velocities in the order of 70-350 m/s following a strong heating of the thermosphere and ionosphere due to the auroral electrojet. 24 refs., 10 figs.

  11. GNSS data filtering optimization for ionospheric observation

    Science.gov (United States)

    D'Angelo, G.; Spogli, L.; Cesaroni, C.; Sgrigna, V.; Alfonsi, L.; Aquino, M. H. O.

    2015-12-01

    In the last years, the use of GNSS (Global Navigation Satellite Systems) data has been gradually increasing, for both scientific studies and technological applications. High-rate GNSS data, able to generate and output 50-Hz phase and amplitude samples, are commonly used to study electron density irregularities within the ionosphere. Ionospheric irregularities may cause scintillations, which are rapid and random fluctuations of the phase and the amplitude of the received GNSS signals. For scintillation analysis, usually, GNSS signals observed at an elevation angle lower than an arbitrary threshold (usually 15°, 20° or 30°) are filtered out, to remove the possible error sources due to the local environment where the receiver is deployed. Indeed, the signal scattered by the environment surrounding the receiver could mimic ionospheric scintillation, because buildings, trees, etc. might create diffusion, diffraction and reflection. Although widely adopted, the elevation angle threshold has some downsides, as it may under or overestimate the actual impact of multipath due to local environment. Certainly, an incorrect selection of the field of view spanned by the GNSS antenna may lead to the misidentification of scintillation events at low elevation angles. With the aim to tackle the non-ionospheric effects induced by multipath at ground, in this paper we introduce a filtering technique, termed SOLIDIFY (Standalone OutLiers IDentIfication Filtering analYsis technique), aiming at excluding the multipath sources of non-ionospheric origin to improve the quality of the information obtained by the GNSS signal in a given site. SOLIDIFY is a statistical filtering technique based on the signal quality parameters measured by scintillation receivers. The technique is applied and optimized on the data acquired by a scintillation receiver located at the Istituto Nazionale di Geofisica e Vulcanologia, in Rome. The results of the exercise show that, in the considered case of a noisy

  12. Multi-GNSS for Ionospheric Scintillation Studies

    Science.gov (United States)

    Morton, Y.

    2015-12-01

    GNSS have been widely used for ionospheric monitoring. We anticipate over 160 GNSS satellites broadcasting 400 signals by 2023, nearly double the number today. With their well-defined signal structures, high spatial density and spectral diversity, GNSS offers low cost and distributed passive sensing of ionosphere effects. There are, however, many challenges to utilize GNSS resources to characterize and forecast ionospheric scintillation. Originally intended for navigation purposes, GNSS receivers are designed to filter out nuisance effects due to ionosphere effects. GNSS measurements are plagued with errors from multipath, oscillator jitters, processing artifacts, and neutral atmosphere effects. Strong scintillation events are often characterized by turbulent structures in ionosphere, causing simultaneous deep amplitude fading and abrupt carrier phase changes. The combined weak signal and high carrier dynamics imposes conflicting requirements for GNSS receiver design. Therefore, GNSS receivers often experience cycle slips and loss of lock of signals during strong scintillation events. High quality, raw GNSS signals bearing space weather signatures and robust receiver algorithms designed to capture these signatures are needed in order for GNSS to be a reliable and useful agent for scintillation monitoring and forecasting. Our event-driven, reconfigurable data collection system is designed to achieve this purpose. To date, our global network has collected ~150TB of raw GNSS data during space weather events. A suite of novel receiver processing algorithms has been developed by exploitating GNSS spatial, frequency, temporal, and constellation diversity to process signals experiencing challenging scintillation impact. The algorithms and data have advanced our understanding of scintillation impact on GNSS, lead to more robust receiver technologies, and enabled high spatial and temporal resolution depiction of ionosphere responses to solar and geomagnetic conditions. This

  13. Urban sound ecologies

    Directory of Open Access Journals (Sweden)

    Sanne Krogh Groth

    2013-12-01

    Full Text Available Within recent years, there has been a renewed focus on sound in urban environments. From sound installations in public space to sound festivals in alternative settings, we find a common interest in sound art relating to the urban environment. Artworks or interventions presented in such contexts share the characteristics of site specificity. However, this article will consider the artwork in a broader context by re-examining how sound installations relate to the urban environment. For that purpose, this article brings together ecology terms from acoustic ecology of the sound theories of the 1970s while developing them into recent definitions of ecology in urban studies. Finally, we unfold our framing of urban sound ecologies with three case analyses: a sound intervention in Berlin, a symphony for wind instruments in Copenhagen and a video walk in a former railway station in Kassel. The article concludes that the ways in which recent sound installations work with urban ecologies vary. While two of the examples blend into the urban environment, the other transfers the concert format and its mode of listening to urban space. Last, and in accordance with recent soundscape research, we point to how artists working with new information and media technologies create inventive ways of inserting sound and image into urban environments.

  14. Magnetic zenith effect in ionospheric modifications

    Energy Technology Data Exchange (ETDEWEB)

    Gurevich, A.V.; Zybin, K.P.; Carlson, H.C.; Pedersen, T

    2002-12-09

    The theory of ionospheric modification for the beam of powerful radio emission directed along magnetic field lines is developed. Nonlinear process of beam self-focusing on striations is shown to determine strong amplification of heating and acceleration of plasma electrons. It results in a dramatic enhancement of optic emission from the magnetic zenith region in ionospheric F-layer. An excellent agreement between the theory and recent fundamental observations at HAARP facility (Alaska) [T. Pedersen et al., Geophys. Res. Lett. (2002), in press] is demonstrated.

  15. Sound a very short introduction

    CERN Document Server

    Goldsmith, Mike

    2015-01-01

    Sound is integral to how we experience the world, in the form of noise as well as music. But what is sound? What is the physical basis of pitch and harmony? And how are sound waves exploited in musical instruments? Sound: A Very Short Introduction looks at the science of sound and the behaviour of sound waves with their different frequencies. It also explores sound in different contexts, covering the audible and inaudible, sound underground and underwater, acoustic and electronic sound, and hearing in humans and animals. It concludes with the problem of sound out of place—noise and its reduction.

  16. Plasma heating, electric fields and plasma flow by electron beam ionospheric injection

    Science.gov (United States)

    Winckler, J. R.; Erickson, K. N.

    1990-01-01

    The electric fields and the floating potentials of a Plasma Diagnostics Payload (PDP) located near a powerful electron beam injected from a large sounding rocket into the auroral zone ionosphere have been studied. As the PDP drifted away from the beam laterally, it surveyed a region of hot plasma extending nearly to 60 m radius. Large polarization electric fields transverse to B were imbedded in this hot plasma, which displayed large ELF wave variations and also an average pattern which has led to a model of the plasma flow about the negative line potential of the beam resembling a hydrodynamic vortex in a uniform flow field. Most of the present results are derived from the ECHO 6 sounding rocket mission.

  17. Applications of the VLF-EM method for rapid Sumatran fault identification in Leuser national park, Aceh

    Science.gov (United States)

    Irwandi, Marwan, Muksin, Fashbir

    2017-07-01

    Aceh is an area which is located at volcanically active region and at the meeting point of the Eurasian and the Indo-Australian plates. Many mountain formations and folds are formed as a result of the meeting of these plates. One of the mountains in Aceh is The Gunung Leuser, the highest mountain in the province with altitude of 3,404 m. The active geodynamic conditions could lead to the formation of potentially active faults which produce earthquakes. Due to safety reason, there are few researches done to identify active faults in the LE (Leuser Ecosystem). Therefore, we propose a preliminary study to identify morphological patterns of the fault system from the topography data of SRTM (Shuttle Radar Topography Mission). Having obtained the approximate location of fault, then a Very Low Frequency method is applied to determine the detail characteristic of the fault. This method can determine the subsurface structure to a depth of 50 m without digging or drilling. In this study, we measure three profiles with length of each profile of 12-16 km. Along profile 1, the VLF data fluctuated due to relatively high iron deposition along the line. For profile 2, the results are very consistent with the adjacent to the fault Blangkejeren which is the main part of the Sumatran Fault. Profile 3 Lokop - Kutacane fault also shows the correction of the topography. In general, VLF method is relatively influenced by noise as the consequences of the passive electromagnetic measurement. Thus, it is important to develop an analysis method of VLF data that includes the topographical correction so that better lateral anomaly map can be created.

  18. Characterization and applications of VLF/LF source locations from lightning using the Huntsville Alabama Marx Meter Array

    Science.gov (United States)

    Bitzer, Phillip M.; Christian, Hugh J.; Stewart, Mike; Burchfield, Jeff; Podgorny, Scott; Corredor, David; Hall, John; Kuznetsov, Evgeny; Franklin, Veronica

    2013-04-01

    Arrays that detect and locate the four-dimensional spacetime positions of radiation sources from lightning have largely utilized sensors sensitive to the very high frequency (VHF) regime with ˜ 15 km baselines or very low frequency/low frequency (VLF/LF) regime with ˜ 100 km baselines. This paper details initial results from the newly developed Huntsville Alabama Marx Meter Array (HAMMA), consisting of Marx meters (electric field change meters) sensitive to a frequency band ˜ 1 Hz to 400 kHz. The arrival time of HAMMA waveforms due to radiation sources from lightning are used to determine the spacetime position of these sources. The locations are compared with two well-documented and operational arrays, the National Lightning Detection Network (NLDN) and the North Alabama Lightning Mapping Array (NALMA). The standard deviation of the difference between HAMMA and NLDN locations of return strokes is 305 and 266 m in x and y, respectively, while the standard deviation of the difference between HAMMA and NALMA sources is 237, 226, and 688 m in x, y and z, respectively. We further show that NLDN intracloud locations differ in horizontal distance from the corresponding HAMMA locations by a median value of 479 m. In addition, we use HAMMA source locations to map several lightning flashes in the VLF/LF and show HAMMA sources largely map out the same electrical extent as VHF sources and provide unique insights to the properties of the discharges occurring. Finally, we show that VLF/LF sources can determine the leader polarity in several example flashes but not necessarily whether a flash comes to ground. Copyright 2013 American Geophysical Union. All rights reserved.

  19. Sound Insulation between Dwellings

    DEFF Research Database (Denmark)

    Rasmussen, Birgit

    2011-01-01

    Regulatory sound insulation requirements for dwellings exist in more than 30 countries in Europe. In some countries, requirements have existed since the 1950s. Findings from comparative studies show that sound insulation descriptors and requirements represent a high degree of diversity...... and initiate – where needed – improvement of sound insulation of new and existing dwellings in Europe to the benefit of the inhabitants and the society. A European COST Action TU0901 "Integrating and Harmonizing Sound Insulation Aspects in Sustainable Urban Housing Constructions", has been established and runs...... 2009-2013. The main objectives of TU0901 are to prepare proposals for harmonized sound insulation descriptors and for a European sound classification scheme with a number of quality classes for dwellings. Findings from the studies provide input for the discussions in COST TU0901. Data collected from 24...

  20. Sound insulation between dwellings

    DEFF Research Database (Denmark)

    Rasmussen, Birgit

    2011-01-01

    Regulatory sound insulation requirements for dwellings exist in more than 30 countries in Europe. In some countries, requirements have existed since the 1950s. Findings from comparative studies show that sound insulation descriptors and requirements represent a high degree of diversity...... and initiate – where needed – improvement of sound insulation of new and existing dwellings in Europe to the benefit of the inhabitants and the society. A European COST Action TU0901 "Integrating and Harmonizing Sound Insulation Aspects in Sustainable Urban Housing Constructions", has been established and runs...... 2009-2013. The main objectives of TU0901 are to prepare proposals for harmonized sound insulation descriptors and for a European sound classification scheme with a number of quality classes for dwellings. Findings from the studies provide input for the discussions in COST TU0901. Data collected from 24...

  1. The sound of distance.

    Science.gov (United States)

    Rabaglia, Cristina D; Maglio, Sam J; Krehm, Madelaine; Seok, Jin H; Trope, Yaacov

    2016-07-01

    Human languages may be more than completely arbitrary symbolic systems. A growing literature supports sound symbolism, or the existence of consistent, intuitive relationships between speech sounds and specific concepts. Prior work establishes that these sound-to-meaning mappings can shape language-related judgments and decisions, but do their effects generalize beyond merely the linguistic and truly color how we navigate our environment? We examine this possibility, relating a predominant sound symbolic distinction (vowel frontness) to a novel associate (spatial proximity) in five studies. We show that changing one vowel in a label can influence estimations of distance, impacting judgment, perception, and action. The results (1) provide the first experimental support for a relationship between vowels and spatial distance and (2) demonstrate that sound-to-meaning mappings have outcomes that extend beyond just language and can - through a single sound - influence how we perceive and behave toward objects in the world. Copyright © 2016 Elsevier B.V. All rights reserved.

  2. Study of the Total Electron Content in Mars ionosphere from MARSIS data set

    Science.gov (United States)

    Bergeot, Nicolas; Witasse, Olivier; Kofman, Wlodek; Grima, Cyril; Mouginot, Jeremie; Peter, Kerstin; Pätzold, Martin; Dehant, Véronique

    2016-04-01

    Centimeter level accuracy on the signal delay will be required on X-band radio link for future Mars landers such as InSIGHT, aiming at better determining the interior structure of Mars. One of the main error sources in the estimated signal delay is directly linked to the Total Electron Content (TEC) values at Earth and Mars ionosphere level. While the Earth ionosphere is now well modeled and monitored at regional and global scales, this is not the case concerning the Mars' upper atmosphere. The present paper aims at establishing the basis to model the climatological behavior of the TEC on a global scale in the Mars' ionosphere. For that we analyzed ˜8.5 years of data (mid-2005 to 2014) of the vertical Total Electron Content (vTEC) expressed in TEC units (1 TECu = 1016e-.m-2) from the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) radar. Our study takes advantage of the double data set of EUV solar index and Mars vTEC data to develop an empirical Model of Mars Ionosphere (MoMo). The finality of this model is to predict the vTEC at a given latitude, solar zenith angle and season taking only F10.7P solar index as input. To minimize the differences during the least-square adjustment between the modeled and observed vTEC, we considered (1) a 4th-order polynomial function to describe the vTEC diurnal behavior (2) a discretization with respect to Mars seasons (depending on Ls) and (3) two latitudinal sectors (North and South hemispheres). The mean of the differences between the model and the observations is 0.00±0.07 TECu with an error of the model around 0.1 TECu depending on the Solar Zenith Angle (SZA), season and hemisphere of interest (e.g. rms 0.12 TECu for SZA equal to 50°±5° in the Northern hemisphere during the spring season). Additionally, comparison with 250 Mars Express radio occultation data shows differences with MoMo predictions of 0.02±0.06 TECu for solar zenith angles below 50 degrees. Using the model we (1) highlighted

  3. Chemical release experiments to induce F region ionospheric plasma irregularities at the magnetic equator

    Science.gov (United States)

    Sultan, Peter Jared

    1994-01-01

    The largest-scale plasma instability that occurs naturally in the Earth's ionosphere is a turbulent upwelling of the equatorial F region known as equatorial spread-F (ESF). During an ESF event, high plasma density magnetic fluxtubes at the bottomside of the F region are thought to change places with lower plasma density flux-tubes from below in a Rayleigh-Taylor type (heavy fluid over light fluid) instability. This interchange creates a large-scale (10's of km) density perturbation locally, which rapidly penetrates through to the topside of the F region, creating a plume of cascading smaller-scale (meter to centimeter scale) irregularities from the sharp density gradients at the edges of the rising plasma 'bubble'. In a theoretical test of this overall scenario for ESF, a linear instability growth rate is derived following the magnetic fluxtube formalism of Haerendel. Using realistic atmospheric and ionospheric density model inputs, growth rates are calculated for a range of geophysical conditions. Time/altitude domains having positive growth rates are found to coincide with observed time/altitude patterns of ESF occurrence, thus supporting the fluxtube model. The physics also are tested experimentally by the deliberate creation of plasma bubbles in ambient ionospheres that the fluxtube model predicts are susceptible to the Rayleigh-Taylor instability. Two such artificial seed perturbations were generated during the 1990 NASA/Boston University CRRES-at-Kwajalein campaign, when clouds of sulfur hexafluoride (SF6) were released by sounding rockets to initiate plasma recombinations near the bottomside of the equatorial ionosphere. Multiple diagnostics (incoherent scatter radar, high frequency radar, optics, and satellite polarimeters at several sites) were used to monitor the prelaunch status of the ionosphere and the electron depleted regions that resulted from the chemical releases. Small ESF plumes were observed to form in the region of the artificial perturbation

  4. Modeling of the travelling ionospheric disturbances. Case study of ASG-EUPOS network

    Science.gov (United States)

    Zanimonskiy, Yevgen M.; Nykiel, Grzegorz; Figurski, Mariusz; Yampolski, Yuri M.

    2016-04-01

    Traveling ionospheric disturbances (TIDs) - this is quite established term for a relatively stable spatial structures, which are characterized by a certain distribution of the electron concentration and are moved as a whole, especially in the horizontal direction. In most cases TIDs are associated with atmospheric gravity waves (AGW) and are expected to be a quasi-plane wave. Effective modern method of studying TIDs is the sounding of ionosphere by GNSS signals received by the dense regional network. Method of the orthogonal projection of the ionosphere electronic content variations for the total electron content (TEC) mapping allows visualizing the ionospheric irregularities (Zanimonskiy et. al. 2016). Such maps can be used to detect TIDs, their modeling and determination of model parameters, such as: direction and speed of movement, spatial period and the height of the ionosphere layer, in which TIDs are localized. In this paper traveling ionospheric disturbances detected over Poland are presented for the day of St. Patrick (March 2015). Into the calculation process observational data from dense regional network deployed in Poland (ASG-EUPOS) were used. Estimated TIDs were characterized by relative frequent occurrence, up to several times a day, and were observed from a few tens of minutes to hour. The direction of detected TIDs movement in most cases was opposite to the horizontal wind calculated by Horizontal Wind Model 07 at the height of TID. Furthermore, the amplitudes of estimated TEC variations during the TID passage were proportional to the background TEC values and consequently to the higher level of the geomagnetic activity. The extremely high TEC variations and speed of TIDs were registered during the severe geomagnetic storm are discussed in this paper. Further works are carried out to the investigation of quantitative relation between the parameters of TIDs and horizontal winds, as well as to accumulation of statistics and characteristics of TIDs

  5. Ionospheric plasma density structures associated with magnetopause motion: a case study using the Cluster spacecraft and the EISCAT Svalbard Radar

    Directory of Open Access Journals (Sweden)

    F. Pitout

    2004-07-01

    Full Text Available On 5 January 2003, the footprint of the Cluster spacecraft, then orbiting in the dayside magnetosphere near the magnetopause, was in the close vicinity of the EISCAT Svalbard Radar (ESR in the dayside afternoon sector. This configuration made possible the study of the magnetopause motion and its direct consequences on the ionospheric plasma at high latitude. Cluster observed multiple magnetopause crossings despite its high latitude, while on the ground the magnetic activity was very low, whereas the ionospheric plasma sounded by the ESR exhibited poleward moving plasma density structures. In this paper, we compare the satellite and radar data, in order to show that the plasma density structures are directly related to the magnetopause motion and its associated pulsed ionospheric flow. We propose that the variations in electric field make the convection velocity vary enough to alter the electron population by accelerating the chemistry in the F-region and act as a source of electron depletion. The magnetopause motion is in this case, a source of plasma density structures in the polar dayside ionosphere.

  6. Estimation of energy budget of ionosphere-thermosphere system during two CIR-HSS events: observations and modeling

    Science.gov (United States)

    Verkhoglyadova, Olga; Meng, Xing; Mannucci, Anthony J.; Tsurutani, Bruce T.; Hunt, Linda A.; Mlynczak, Martin G.; Hajra, Rajkumar; Emery, Barbara A.

    2016-04-01

    We analyze the energy budget of the ionosphere-thermosphere (IT) system during two High-Speed Streams (HSSs) on 22-31 January, 2007 (in the descending phase of solar cycle 23) and 25 April-2 May, 2011 (in the ascending phase of solar cycle 24) to understand typical features, similarities, and differences in magnetosphere-ionosphere-thermosphere (IT) coupling during HSS geomagnetic activity. We focus on the solar wind energy input into the magnetosphere (by using coupling functions) and energy partitioning within the IT system during these intervals. The Joule heating is estimated empirically. Hemispheric power is estimated based on satellite measurements. We utilize observations from TIMED/SABER (Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry) to estimate nitric oxide (NO) and carbon dioxide (CO2) cooling emission fluxes. We perform a detailed modeling study of these two similar HSS events with the Global Ionosphere-Thermosphere Model (GITM) and different external driving inputs to understand the IT response and to address how well the model reproduces the energy transport. GITM is run in a mode with forecastable inputs. It is shown that the model captures the main features of the energy coupling, but underestimates NO cooling and auroral heating in high latitudes. Lower thermospheric forcing at 100 km altitude is important for correct energy balance of the IT system. We discuss challenges for a physics-based general forecasting approach in modeling the energy budget of moderate IT storms caused by HSSs.

  7. Profiling of Ionospheric Electron Density Based on FormoSat-3/COSMIC Data: Results from the Intense Observation Period Experiment

    Directory of Open Access Journals (Sweden)

    Lung-Chih Tsai

    2009-01-01

    Full Text Available Multi-channel Global Position System (GPS carrier phase signals received by the FormoSat-3 (FS3/COSMIC program's six low Earth orbiting (LEO satellites were used to undertake active limb sounding of the Earth¡¦s atmosphere and ionosphere via radio occultation (RO. In this study, the effects of large-scale horizontal gradients and/or inhomogeneous ionospheric electron densities (ne were considered by developing an iterative scheme to determine "compensated" total electron content (TEC values through nearby occultation observations. Using an iterative Abel inversion through "compensated" TEC values, more than one-hundred and eighty thousand vertical ionospheric ne profiles were collected during the intense observation period (IOP of 20 June - 27 September (day number 171 to 270 2006. Coincidences of GPS RO observations to ionospheric ne ionosonde data from forty-nine worldwide stations have been examined. It is found that the iterative scheme gives improved retrievals over the standard Abel inversion. From several thousand matches within the IOP experiment, the root mean square (rms foF2 differences between the ionosonde measurements and the FS3/COSMIC retrievals are improved from 1.67 to 1.07 MHz. The results also show improvement in the overestimates (underestimates on low (high retrieved foF2s, while the obtained hmF2s give better agreement with ionosonde observations.

  8. Planetary wave signatures in the equatorial atmosphere ionosphere system, and mesosphere- E- and F-region coupling

    Science.gov (United States)

    Abdu, M. A.; Ramkumar, T. K.; Batista, I. S.; Brum, C. G. M.; Takahashi, H.; Reinisch, B. W.; Sobral, J. H. A.

    2006-02-01

    Upward transport of wave energy and momentum due to gravity, tidal and planetary waves from below and extra-tropics controls the phenomenology of the equatorial atmosphere ionosphere system. An important aspect of this phenomenology is the development of small- and large-scale structures including thin layers in the mesosphere and E-region, and the formation of wide spectrum plasma structures of the equatorial F-region, widely known as equatorial spread F/plasma bubble irregularities (that are known to have significant impact on space application systems based on trans-ionospheric radio waves propagation). It seems that the effects of tidal and gravity waves at mesospheric and thermospheric heights and their control of ionospheric densities, electric fields and currents are relatively better known than are the effects originating from vertical coupling due to planetary waves. Results from airglow, radar and ionospheric sounding observations demonstrate the existence of significant planetary wave influence on plasma parameters at E- and F-region heights over equatorial latitudes. We present and discuss here some results showing planetary wave oscillations in concurrent mesospheric winds and equatorial electrojet intensity variations in the Indian sector as well as in the mesospheric airglow and F-layer height variation in Brazil. Also presented are evidences of planetary wave-scale oscillations in equatorial evening pre-reversal electric field (F-region vertical drift) and their effects on equatorial spread F /plasma bubble irregularity development and day-to-day variability.

  9. Overview of the Equatorial Electrojet and Related Ionospheric Current Systems

    Science.gov (United States)

    2007-11-02

    89-96. 28. D. Papadopoulos, T. Wallace, G. Milikh, and B. Peter, "Equatorial ELF/VLF Generation," presented at the HAARP ELF Measurements Workshop...Indianapolis, IN, 1985, p. 1-3 (chap. 1). 31. HAARP ELF Measurements Workshop, High Frequency Active Auroral Research Program, Arlington, VA

  10. Solar illumination control of ionospheric outflow above polar cap arcs

    CERN Document Server

    Maes, L; De Keyser, J; Dandouras, I; Fear, R C; Fontaine, D; Haaland, S

    2016-01-01

    We measure the flux density, composition, and energy of outflowing ions above the polar cap, accelerated by quasi-static electric fields parallel to the magnetic field and associated with polar cap arcs, using Cluster. Mapping the spacecraft position to its ionospheric foot point, we analyze the dependence of these parameters on the solar zenith angle (SZA). We find a clear transition at SZA between We find a clear transition at SZA between $\\sim$94$^{\\circ}$ and $\\sim$107$^{\\circ}$, with the O$^{+}$ flux higher above the sunlit ionosphere. This dependence on the illumination of the local ionosphere indicates that significant O$^{+}$ upflow occurs locally above the polar ionosphere. The same is found for H$^{+}$, but to a lesser extent. This effect can result in a seasonal variation of the total ion upflow from the polar ionosphere. Furthermore, we show that low-magnitude field-aligned potential drops are preferentially observed above the sunlit ionosphere, suggesting a feedback effect of ionospheric conducti...

  11. InfoSound

    DEFF Research Database (Denmark)

    Sonnenwald, Diane H.; Gopinath, B.; Haberman, Gary O.

    1990-01-01

    The authors explore ways to enhance users' comprehension of complex applications using music and sound effects to present application-program events that are difficult to detect visually. A prototype system, Infosound, allows developers to create and store musical sequences and sound effects...... helped users detect rapid, multiple-event sequences that were difficult to visually detect using text and graphical interfaces. The authors describe the architecture of InfoSound, the use of the system, and the lessons learned....

  12. Comfort in Sound

    Institute of Scientific and Technical Information of China (English)

    KIT GILLET

    2008-01-01

    @@ Drown your winter sorrows in sound with these three top surround-sound systems With winter here, it is time to start considering ways to improve your home entertainment options. While a good DVD or Blu-ray player and games console should keep you happily occupied without needing to leave the warmth of your apartment, investing in a cutting-edge surround sound system wiU ensure that winter passes without you even noticing.

  13. VLF/ELF wave activity in the vicinity of the polar cusp: Cluster observations

    Directory of Open Access Journals (Sweden)

    N. Lin

    2006-08-01

    Full Text Available Observations by the Cluster spacecraft of VLF/ELF wave activity show distinct signatures for different regions in the vicinity of high altitude polar cusps, which are identified by using magnetic field and plasma data along spacecraft trajectories. These waves include: (1 Broad band magnetic noise observed in the polar cusp at frequencies from several Hz to ~100 Hz, below the local electron cyclotron frequency, fce. Similar magnetic noise is also observed in the high latitude magnetosheath and the magnetopause boundary layer. (2 Strong broad band electrostatic emissions observed in the cusp, in the magnetosheath, and in the high latitude magnetopause boundary layer, at frequencies extending from several Hz to tens of kHz, with maximum intensities below ~100 Hz. (3 Narrow-band electromagnetic whistler waves at frequencies ~0.2–0.6 fce, frequently observed in the closed boundary layer (CBL adjacent to the polar cusp. These waves are for the first time observed in this region to be accompanied by counter-streaming electron beams of ~100 eV, which suggests that the waves are excited by these electrons through wave-particle interaction. (4 Narrow-band electrostatic waves observed slightly above the local fce in the CBL. (5 Lion roars, observed in the high latitude magnetosheath, often in magnetic troughs of mirror mode oscillations. The above wave signatures can serve as indicators of the regions in the vicinity of the magnetospheric cusp.

  14. Urban Sound Ecologies

    DEFF Research Database (Denmark)

    Groth, Sanne Krogh; Samson, Kristine

    2013-01-01

    share the characteristics of site specificity. However, this article will consider the artwork in a broader context by re-examining how sound installations relate to the urban environment. For that purpose, this article brings together ecology terms from acoustic ecology of the sound theories...... of the 1970s while developing them into recent definitions of ecology in urban studies. Finally, we unfold our framing of urban sound ecologies with three case analyses: a sound intervention in Berlin, a symphony for wind instruments in Copenhagen and a video walk in a former railway station in Kassel...

  15. Light and Sound

    CERN Document Server

    Karam, P Andrew

    2010-01-01

    Our world is largely defined by what we see and hear-but our uses for light and sound go far beyond simply seeing a photo or hearing a song. A concentrated beam of light, lasers are powerful tools used in industry, research, and medicine, as well as in everyday electronics like DVD and CD players. Ultrasound, sound emitted at a high frequency, helps create images of a developing baby, cleans teeth, and much more. Light and Sound teaches how light and sound work, how they are used in our day-to-day lives, and how they can be used to learn about the universe at large.

  16. Simulated Response of the Magnetosphere-Ionosphere System to Different Forms of Empirically Regulated Ionospheric Outflows

    Science.gov (United States)

    Lotko, W.; Lyon, J.; Melanson, P.; Murr, D.; Wiltberger, M.

    2006-12-01

    Empirically derived power-law relations between the locally measured Poynting flux (S) flowing toward the ionosphere and the number flux of ions (F) flowing away from the ionosphere exhibit significant differences that depend on the choice of satellite data samples (Strangeway et al., 2005; Zheng et al., 2005). Such relations attempt to capture in lumped form the causality of electromagnetic power flows into collisionless ion acceleration in the topside ionosphere and low-altitude magnetosphere and the resulting ion outflows -- effects that are otherwise difficult to treat in first-principles fluid models for the field-aligned mass transport. We have implemented a power-law relation of the form F = A*S**b, where A and b are adjustable parameters ultimately constrained by observation, as a low-altitude boundary condition on the LFM global simulation model. This boundary condition allows ions of ionospheric origin to enter the magnetospheric simulation domain and to mix with plasma of solar wind origin in populating the magnetosphere. According to the empirical relation, more ionospheric ions are causally injected into the simulation domain as the Poynting flux through the low-altitude boundary increases. In this paper, we report results from simulations using different values of the parameters A and b to determine the sensitivity of the magnetospheric response to the form of the empirical relation. Simulation diagnostics for the transpolar potential, field-aligned current, ionospheric conductivity, precipitating electron energy flux, and Joule dissipation rate will be presented.

  17. Early Sound Symbolism for Vowel Sounds

    Directory of Open Access Journals (Sweden)

    Ferrinne Spector

    2013-06-01

    Full Text Available Children and adults consistently match some words (e.g., kiki to jagged shapes and other words (e.g., bouba to rounded shapes, providing evidence for non-arbitrary sound–shape mapping. In this study, we investigated the influence of vowels on sound–shape matching in toddlers, using four contrasting pairs of nonsense words differing in vowel sound (/i/ as in feet vs. /o/ as in boat and four rounded–jagged shape pairs. Crucially, we used reduplicated syllables (e.g., kiki vs. koko rather than confounding vowel sound with consonant context and syllable variability (e.g., kiki vs. bouba. Toddlers consistently matched words with /o/ to rounded shapes and words with /i/ to jagged shapes (p < 0.01. The results suggest that there may be naturally biased correspondences between vowel sound and shape.

  18. Behavior of Parameters of Nighttime Electron Density Enhancements of the Ionospheric F2 Layer

    Science.gov (United States)

    Yakovets, Artur; Gordienko, Galina

    2017-04-01

    There is known a wide class of disturbances of the F2-layer of the ionosphere, which are superimposed on the regular diurnal variations of the electron density. Different types of disturbances are characterized by different mechanisms of their generation. Traveling ionospheric disturbances appear to be the most characteristic features of the inhomogeneous structure of the ionosphere. Another type of ionospheric disturbances presents the nighttime electron density enhancements in the ionospheric F2- layer maximum (NmF2). This type of irregularities is described in numerous papers. There is a concept that, in spite of the various mechanisms of ionospheric disturbances generation a response of F2-layer parameters exhibits similar features associated with the upward lift and the simultaneous expansion of the layer and then its subsequent downward movement, including layer compression, which results in the formation of the electron density peak in the layer maximum at the moment of greatest compression. The aim of this study is a verification of this concept on the example of disturbances related with the nighttime electron density enhancements, and the definition of precise quantitative relationships between the variations of different F2-layer parameters for such disturbances. By using the data of the ionospheric vertical sounding in Almaty, (76° 55'E, 43°15'N) during 2001-2012, analysis of the behavior the F2-layer parameters during the night electron density enhancements was carried out within framework of a single concept of effects of various types of ionospheric plasma perturbations in variations of height and half-thickness of the F2-layer, accompanied by increasing and decreasing NmF2 at moments of maximum compression and expansion of the layer. For a quantitative analysis of the parameters of nighttime enhancements we have selected 20 nights characterized by low magnetic activity (Dst> - 50 nT) and evident manifestations of the nighttime electron density

  19. Ionospheric TEC Weather Map Over South America

    Science.gov (United States)

    Takahashi, H.; Wrasse, C. M.; Denardini, C. M.; Pádua, M. B.; de Paula, E. R.; Costa, S. M. A.; Otsuka, Y.; Shiokawa, K.; Monico, J. F. Galera; Ivo, A.; Sant'Anna, N.

    2016-11-01

    Ionospheric weather maps using the total electron content (TEC) monitored by ground-based Global Navigation Satellite Systems (GNSS) receivers over South American continent, TECMAP, have been operationally produced by Instituto Nacional de Pesquisas Espaciais's Space Weather Study and Monitoring Program (Estudo e Monitoramento Brasileiro de Clima Especial) since 2013. In order to cover the whole continent, four GNSS receiver networks, (Rede Brasileiro de Monitoramento Contínuo) RBMC/Brazilian Institute for Geography and Statistics, Low-latitude Ionospheric Sensor Network, International GNSS Service, and Red Argentina de Monitoreo Satelital Continuo, in total 140 sites, have been used. TECMAPs with a time resolution of 10 min are produced in 12 h time delay. Spatial resolution of the map is rather low, varying between 50 and 500 km depending on the density of the observation points. Large day-to-day variabilities of the equatorial ionization anomaly have been observed. Spatial gradient of TEC from the anomaly trough (total electron content unit, 1 TECU = 1016 el m-2 (TECU) 80) causes a large ionospheric range delay in the GNSS positioning system. Ionospheric plasma bubbles, their seeding and development, could be monitored. This plasma density (spatial and temporal) variability causes not only the GNSS-based positioning error but also radio wave scintillations. Monitoring of these phenomena by TEC mapping becomes an important issue for space weather concern for high-technology positioning system and telecommunication.

  20. Global Assimilation of Ionospheric Measurements (GAIM)

    Science.gov (United States)

    Schunk, R. W.; Scherliess, L.; Sojka, J. J.; Thompson, D. C.; Anderson, D. N.; Codrescu, M.; Minter, C.; Fuller-Rowell, T. J.; Heelis, R. A.; Hairston, M.; Howe, B. M.

    2001-12-01

    The ionosphere is a highly dynamic medium that can vary significantly from day to day and from hour to hour at a given location, and these variations can have detrimental effects on military and civilian systems. In an effort to minimize or circumvent the detrimental effects, a physics-based data assimilation model of the ionosphere and neutral atmosphere is under development with funding from the DoD MURI program. Two university consortia are involved, with USU and USC as the lead institutions. When completed, the GAIM (Global Assimilation of Ionospheric Measurements) model will provide specifications and forecasts on a spatial grid that can be global, regional, or local (50 km x 50 km). GAIM will use a physics-based ionosphere-plasmasphere model and a Kalman filter as a basis for assimilating a diverse set of real-time (or near real-time) measurements. Some of the data to be assimilated include in situ density measurements from satellites, ionosonde electron density profiles, occultation data, ground-based GPS TECs, TECs between ground stations and LEO satellites with radio beacons, and line-of-sight UV emissions from selected satellites. The resulting specifications and forecasts will be in the form of 3-dimensional electron density distributions from 90 km to geosynchronous altitude (35,000 km). An initial form of GAIM already exists and recent results from the USU consortium will be presented.

  1. ionFR: Ionospheric Faraday rotation [Dataset

    NARCIS (Netherlands)

    Sotomayor-Beltran, C.; et al., [Unknown; Hessels, J.W.T.; van Leeuwen, J.; Markoff, S.; Wijers, R.A.M.J.

    2013-01-01

    IonFR calculates the amount of ionospheric Faraday rotation for a specific epoch, geographic location, and line-of-sight. The code uses a number of publicly available, GPS-derived total electron content maps and the most recent release of the International Geomagnetic Reference Field. ionFR can be

  2. Ionospheric error analysis in gps measurements

    Directory of Open Access Journals (Sweden)

    G. Pugliano

    2008-06-01

    Full Text Available The results of an experiment aimed at evaluating the effects of the ionosphere on GPS positioning applications are presented in this paper. Specifically, the study, based upon a differential approach, was conducted utilizing GPS measurements acquired by various receivers located at increasing inter-distances. The experimental research was developed upon the basis of two groups of baselines: the first group is comprised of "short" baselines (less than 10 km; the second group is characterized by greater distances (up to 90 km. The obtained results were compared either upon the basis of the geometric characteristics, for six different baseline lengths, using 24 hours of data, or upon temporal variations, by examining two periods of varying intensity in ionospheric activity respectively coinciding with the maximum of the 23 solar cycle and in conditions of low ionospheric activity. The analysis revealed variations in terms of inter-distance as well as different performances primarily owing to temporal modifications in the state of the ionosphere.

  3. Ionospheric precursors for crustal earthquakes in Italy

    Directory of Open Access Journals (Sweden)

    L. Perrone

    2010-04-01

    Full Text Available Crustal earthquakes with magnitude 6.0>M≥5.5 observed in Italy for the period 1979–2009 including the last one at L'Aquila on 6 April 2009 were considered to check if the earlier obtained relationships for ionospheric precursors for strong Japanese earthquakes are valid for the Italian moderate earthquakes. The ionospheric precursors are based on the observed variations of the sporadic E-layer parameters (h'Es, fbEs and foF2 at the ionospheric station Rome. Empirical dependencies for the seismo-ionospheric disturbances relating the earthquake magnitude and the epicenter distance are obtained and they have been shown to be similar to those obtained earlier for Japanese earthquakes. The dependences indicate the process of spreading the disturbance from the epicenter towards periphery during the earthquake preparation process. Large lead times for the precursor occurrence (up to 34 days for M=5.8–5.9 tells about a prolong preparation period. A possibility of using the obtained relationships for the earthquakes prediction is discussed.

  4. Method for Canceling Ionospheric Doppler Effect

    Science.gov (United States)

    Vessot, R. F. C.

    1982-01-01

    Unified transponder system with hydrogen-maser oscillators at both stations can compensate for both motional and ionospheric components of Doppler shift. Appropriate choices of frequency shift in output of mixer m3. System exploits proportionality between dispersive component of frequency shift and reciprocal of frequency to achieve cancellation of dispersive component at output.

  5. Midday reversal of equatorial ionospheric electric field

    Directory of Open Access Journals (Sweden)

    R. G. Rastogi

    Full Text Available A comparative study of the geomagnetic and ionospheric data at equatorial and low-latitude stations in India over the 20 year period 1956–1975 is described. The reversal of the electric field in the ionosphere over the magnetic equator during the midday hours indicated by the disappearance of the equatorial sporadic E region echoes on the ionograms is a rare phenomenon occurring on about 1% of time. Most of these events are associated with geomagnetically active periods. By comparing the simultaneous geomagnetic H field at Kodaikanal and at Alibag during the geomagnetic storms it is shown that ring current decreases are observed at both stations. However, an additional westward electric field is superimposed in the ionosphere during the main phase of the storm which can be strong enough to temporarily reverse the normally eastward electric field in the dayside ionosphere. It is suggested that these electric fields associated with the V×Bz electric fields originate at the magnetopause due to the interaction of the solar wind and the interplanetary magnetic field.

  6. Ionospheric response to geomagnetic disturbances in the north-eastern region of Asia during the minimum of 23rd cycle of solar activity

    Science.gov (United States)

    Kurkin, V. I.; Pirog, O. M.; Polekh, N. M.; Mikhalev, A. V.; Poddelsky, I. N.; Stepanov, A. E.

    2008-12-01

    We present the results of studies of the subauroral and mid-latitude ionosphere variations in the north-eastern region of Asia. We used the data from network of vertical and oblique-incidence sounding ionosondes and optical measurements. Long-term experiments on the radio paths Magadan-Irkutsk and Norilsk-Irkutsk were carried out within the period 2005-2007. Vertical sounding stations operated in standard regime. Observation of airglow near Irkutsk was provided by the zenith photometer that measured intensities of 557.7 and 630.0 nm atomic oxygen emissions. The results may be summarized as follows. (1) Large daytime negative disturbances are observed during the main and recovery phases mainly at high latitudes, whereas the positive disturbances observed during the main phase at mid latitudes. The disturbances changed their sign between Yakutsk and Irkutsk. (2) During the main and recovery storm phases the fall of foF2 associated with the equatorward wall of the main ionospheric trough is observed in the afternoon and evening. (3) Fluctuations of the electron density more intensive at mid latitudes during the storm main phase are observed during all considered periods. They are classed as traveling ionospheric disturbances (TID). Such sharp gradients of electron density are responsible for the strong changes in the characteristics of the radio wave propagation, particularity MOF. (4) A large-scale ionospheric disturbance is noted at the meridional chain of ionosonds in December 2006 as the sharp increase of foF2. It appears in the evening in the minimum of Dst at high latitude and propagate to equator. (5) A maximum of 630 nm emission above Irkutsk corresponds to the foF2 increase. (6) The obtained experimental data on the net of vertical and oblique-incidence sounding with high time resolution show that such net is the effective facility to study the conditions of the radio wave propagation and can be used for the diagnostic of the ionosphere.

  7. Ionospheric response to particle precipitation within aurora

    Energy Technology Data Exchange (ETDEWEB)

    Wahlund, J.E. (Swedish Inst. of Space Physics, Uppsala (Sweden))

    1992-03-01

    The aurora is just the visible signature of a large number of processes occurring in a planetary ionosphere as a response to energetic charged particles falling in from the near-empty space far above the planetary atmosphere. This thesis, based on measurements using the EISCAT incoherent scatter radar system in northern Scandinavia, discusses ionospheric response processes and especially a mechanism leading to atmospheric gas escape from a planet. One of the most spectacular events in the high latitude atmosphere on earth are the 'auroral arcs' - dynamic rayed sheets of light. An investigation of the conditions of the ionosphere surrounding auroral arcs shows that strong field-aligned bulk ion outflows appear in the topside ionosphere which account for a large fraction of the escape of atmospheric oxygen from earth. Four different additional ionospheric responses are closely related to this ion outflow; 1. enhanced electron temperatures of several thousand Kelvin above an altitude of about 250 km, 2. enhanced ionization around an altitude of 200 km corresponding to electron precipitation with energies of a few hundred eV, 3. the occurrence of naturally enhanced ion acoustic fluctuations seen in the radar spectrum, most likely produced by an ion-ion two-stream instability, and 4. upward directed field-aligned currents partly carried by the outflowing ions. From these observations, it is suggested that the energy dissipation into the background plasma through Joule heating, the production of a few hundred eV energetic run-away electrons, and strong ion outflows are partly produced by the simultaneous presence of ion acoustic turbulence and field-aligned currents above auroral arcs. (20 refs.) (au).

  8. Ionospheric response to particle precipitation within aurora

    Energy Technology Data Exchange (ETDEWEB)

    Wahlund, J.E. [Swedish Inst. of Space Physics, Uppsala (Sweden)

    1992-03-01

    The aurora is just the visible signature of a large number of processes occurring in a planetary ionosphere as a response to energetic charged particles falling in from the near-empty space far above the planetary atmosphere. This thesis, based on measurements using the EISCAT incoherent scatter radar system in northern Scandinavia, discusses ionospheric response processes and especially a mechanism leading to atmospheric gas escape from a planet. One of the most spectacular events in the high latitude atmosphere on earth are the `auroral arcs` - dynamic rayed sheets of light. An investigation of the conditions of the ionosphere surrounding auroral arcs shows that strong field-aligned bulk ion outflows appear in the topside ionosphere which account for a large fraction of the escape of atmospheric oxygen from earth. Four different additional ionospheric responses are closely related to this ion outflow; 1. enhanced electron temperatures of several thousand Kelvin above an altitude of about 250 km, 2. enhanced ionization around an altitude of 200 km corresponding to electron precipitation with energies of a few hundred eV, 3. the occurrence of naturally enhanced ion acoustic fluctuations seen in the radar spectrum, most likely produced by an ion-ion two-stream instability, and 4. upward directed field-aligned currents partly carried by the outflowing ions. From these observations, it is suggested that the energy dissipation into the background plasma through Joule heating, the production of a few hundred eV energetic run-away electrons, and strong ion outflows are partly produced by the simultaneous presence of ion acoustic turbulence and field-aligned currents above auroral arcs. (20 refs.) (au).

  9. GPS, GNSS, and Ionospheric Density Gradients

    Science.gov (United States)

    Kintner, P. M.; O'Hanlon, B.; Humphreys, T. E.

    2009-12-01

    Ionospheric density and density gradients affect GNSS signals in two ways. They can introduce ranging errors or irregularities that form on the density gradients producing scintillation. Here we focus on the issue of ranging errors. There are two approaches to mitigating ranging errors produced by ionospheric density gradients which can be 20-30 m during major magnetic storms. The first approach is to use a reference receiver(s) to determine the ionospheric contribution to ranging errors. The ranging error is then transmitted to the user for correction within the mobile receiver. This approach is frequently referred to as differential GPS and, when multiple reference receivers are used, the system is referred to as an augmentation system. This approach is vulnerable to ionospheric gradients depending on the reference receiver spacing(s) and latency in applying the correction within the mobile receiver. The second approach is to transmit navigation signals at two frequencies and then use the relative delay between the two signals to both estimate the ranging error and calculate the correct range. Currently the dual frequency technique is used by US military receivers with an encryption key and some civilian receivers which must be stationary and average over times long compared to those required for navigation. However, the technology of space based radio navigation is changing. GPS will soon be a system with three frequencies and multiple codes. Furthermore Europe, Russia, and China are developing independent systems to complement and compete with GPS while India and Japan are developing local systems to enhance GPS performance in their regions. In this talk we address two questions. How do density gradients affect augmentation systems including the social consequences and will the new GPS/GNSS systems with multiple civilian frequencies be able to remove ionospheric errors. The answers are not at all clear.

  10. Electrodynamics of ionospheric weather over low latitudes

    Science.gov (United States)

    Abdu, Mangalathayil Ali

    2016-12-01

    The dynamic state of the ionosphere at low latitudes is largely controlled by electric fields originating from dynamo actions by atmospheric waves propagating from below and the solar wind-magnetosphere interaction from above. These electric fields cause structuring of the ionosphere in wide ranging spatial and temporal scales that impact on space-based communication and navigation systems constituting an important segment of our technology-based day-to-day lives. The largest of the ionosphere structures, the equatorial ionization anomaly, with global maximum of plasma densities can cause propagation delays on the GNSS signals. The sunset electrodynamics is responsible for the generation of plasma bubble wide spectrum irregularities that can cause scintillation or even disruptions of satellite communication/navigation signals. Driven basically by upward propagating tides, these electric fields can suffer significant modulations from perturbation winds due to gravity waves, planetary/Kelvin waves, and non-migrating tides, as recent observational and modeling results have demonstrated. The changing state of the plasma distribution arising from these highly variable electric fields constitutes an important component of the ionospheric weather disturbances. Another, often dominating, component arises from solar disturbances when coronal mass ejection (CME) interaction with the earth's magnetosphere results in energy transport to low latitudes in the form of storm time prompt penetration electric fields and thermospheric disturbance winds. As a result, drastic modifications can occur in the form of layer restructuring (Es-, F3 layers etc.), large total electron content (TEC) enhancements, equatorial ionization anomaly (EIA) latitudinal expansion/contraction, anomalous polarization electric fields/vertical drifts, enhanced growth/suppression of plasma structuring, etc. A brief review of our current understanding of the ionospheric weather variations and the

  11. Remote Oxygen Sensing by Ionospheric Excitation (ROSIE

    Directory of Open Access Journals (Sweden)

    K. S. Kalogerakis

    2009-05-01

    Full Text Available The principal optical observable emission resulting from ionospheric modification (IM experiments is the atomic oxygen red line at 630 nm, originating from the O(1D–3P transition. Because the O(1D atom has a long radiative lifetime, it is sensitive to collisional relaxation and an observed decay faster than the radiative rate can be attributed to collisions with atmospheric species. In contrast to the common practice of ignoring O-atoms in interpreting such observations in the past, recent experimental studies on the relaxation of O(1D by O(3P have revealed the dominant role of oxygen atoms in controlling the lifetime of O(1D at altitudes relevant to IM experiments. Using the most up-to-date rate coefficients for collisional relaxation of O(1D by O, N2, and O2, it is now possible to analyze the red line decays observed in IM experiments and thus probe the local ionospheric composition. In this manner, we can demonstrate an approach to remotely detect O-atoms at the altitudes relevant to IM experiments, which we call remote oxygen sensing by ionospheric excitation (ROSIE. The results can be compared with atmospheric models and used to study the temporal, seasonal, altitude and spatial variation of ionospheric O-atom density in the vicinity of heating facilities. We discuss the relevance to atmospheric observations and ionospheric heating experiments and report an analysis of representative IM data.

  12. Hydromagnetic Waves in the Magnetosphere and the Ionosphere

    CERN Document Server

    Alperovich, Leonid S

    2007-01-01

    The book deals with Ultra-Low-Frequency (ULF)-electromagnetic waves observed on Earth and in Space. These are so-called geomagnetic variations or pulsations. Alfvén's discovery related to the influence of the strong magnetic field on the conducting fluids (magnetohydrodynamics) led to development of the concept that the ULF-waves are magnetospheric magnetohydrodynamic (MHD)-waves. MHD-waves at their propagation gather information about the magnetosphere, ionosphere, and the ground. There are two applied aspects based on using the ULF electromagnetic oscillations. The first one is the ground-based diagnostics of the magnetosphere. This is an attempt to monitor in the real time the magnetosphere size, distance to the last closed field-lines, distribution of the cold plasma, etc. The second one is the deep electromagnetic sounding of the Earth. The basis for these studies is the capability of any electromagnetic wave to penetrate a conductor to a finite depth. The ULF-waves can reach the depth of a few hundred ...

  13. Inferring agency from sound

    NARCIS (Netherlands)

    Knoblich, G.K.; Repp, B.H.

    2009-01-01

    In three experiments we investigated how people determine whether or not they are in control of sounds they hear. The sounds were either triggered by participants’ taps or controlled by a computer. The task was to distinguish between self-control and external control during active tapping, and durin

  14. Notes on Sound

    Directory of Open Access Journals (Sweden)

    Bonnie Jones

    2012-08-01

    Full Text Available Bonnie Jones creates improvised and composed text-sound performances that explore the fluidity and function of electronic noise (field recordings, circuit bending and text (poetry, found, spoken. She is interested in how people perceive, “read” and interact with these sounds and texts given our current technological moment.

  15. The sounds of nanotechnology

    Science.gov (United States)

    Campbell, Norah; Deane, Cormac; Murphy, Padraig

    2017-07-01

    Public perceptions of nanotechnology are shaped by sound in surprising ways. Our analysis of the audiovisual techniques employed by nanotechnology stakeholders shows that well-chosen sounds can help to win public trust, create value and convey the weird reality of objects on the nanoscale.

  16. Hamiltonian Algorithm Sound Synthesis

    OpenAIRE

    大矢, 健一

    2013-01-01

    Hamiltonian Algorithm (HA) is an algorithm for searching solutions is optimization problems. This paper introduces a sound synthesis technique using Hamiltonian Algorithm and shows a simple example. "Hamiltonian Algorithm Sound Synthesis" uses phase transition effect in HA. Because of this transition effect, totally new waveforms are produced.

  17. OMNIDIRECTIONAL SOUND SOURCE

    DEFF Research Database (Denmark)

    1996-01-01

    A sound source comprising a loudspeaker (6) and a hollow coupler (4) with an open inlet which communicates with and is closed by the loudspeaker (6) and an open outlet, said coupler (4) comprising rigid walls which cannot respond to the sound pressures produced by the loudspeaker (6). According...

  18. Breaking the Sound Barrier

    Science.gov (United States)

    Brown, Tom; Boehringer, Kim

    2007-01-01

    Students in a fourth-grade class participated in a series of dynamic sound learning centers followed by a dramatic capstone event--an exploration of the amazing Trashcan Whoosh Waves. It's a notoriously difficult subject to teach, but this hands-on, exploratory approach ignited student interest in sound, promoted language acquisition, and built…

  19. Light and sound

    Institute of Scientific and Technical Information of China (English)

    王佩夫

    2002-01-01

    Light travels at a speed which is about a million times faster than the speed of sound.In one second,light travels about 300,000 km,but sound travels only 314m,you can get some idea of this difference(区别) by watching the start of a race.

  20. Waveform analysis of sound

    CERN Document Server

    Tohyama, Mikio

    2015-01-01

    What is this sound? What does that sound indicate? These are two questions frequently heard in daily conversation. Sound results from the vibrations of elastic media and in daily life provides informative signals of events happening in the surrounding environment. In interpreting auditory sensations, the human ear seems particularly good at extracting the signal signatures from sound waves. Although exploring auditory processing schemes may be beyond our capabilities, source signature analysis is a very attractive area in which signal-processing schemes can be developed using mathematical expressions. This book is inspired by such processing schemes and is oriented to signature analysis of waveforms. Most of the examples in the book are taken from data of sound and vibrations; however, the methods and theories are mostly formulated using mathematical expressions rather than by acoustical interpretation. This book might therefore be attractive and informative for scientists, engineers, researchers, and graduat...

  1. InfoSound

    DEFF Research Database (Denmark)

    Sonnenwald, Diane H.; Gopinath, B.; Haberman, Gary O.

    1990-01-01

    The authors explore ways to enhance users' comprehension of complex applications using music and sound effects to present application-program events that are difficult to detect visually. A prototype system, Infosound, allows developers to create and store musical sequences and sound effects...... helped users detect rapid, multiple-event sequences that were difficult to visually detect using text and graphical interfaces. The authors describe the architecture of InfoSound, the use of the system, and the lessons learned....... with application events, and have real-time, continuous auditory control of sounds during application execution. InfoSound has been used to create auditory interfaces for two applications: a telephone network service simulation and a parallel computation simulation. The auditory interfaces in these applications...

  2. IONOSPHERIC CORRECTION METHOD FOR PRECISE POSITIONING WITH GPS ACTIVE NETWORK

    Institute of Scientific and Technical Information of China (English)

    GAOShan; CHENWu; HUCong-wei; CHENYong-qi; DINGXiao-li

    2005-01-01

    The ionospheric delay error is a major error source which degrades the positioning accuracy in network real time kinematic (RTK) positioning over a long distance. Different approaches are proposed to estimate GPS errors based on GPS reference network, such as virtual reference stations (VRSs) and network corrections. A new method is used to model the ionospheric total electronic content (TEC) distribution in space. Unlike most ionospheric models, only the ionospheric delays along the satellite tracks are modelled. Therefore, the models are of high precise resolution of the ionospheric TEC distribution in both spatial and temporal scales. A new algorithm is used to solve the equation singularity problem. Experiments demonstrate that the new ionospheric correction method can be used to describe the ionospheric variation at a low latitude area where ionospheric activities are strong. Also, the accuracy of the ionospheric model is enough to support centimeter-level positioning within the network. As ionospheric models are satellite-based models (each satellite has one model), the model parameters can be easily incorporated with the existing differential GPS Radio Technical Commission for Maritime Service (DGPS RTCM) 104 format.

  3. Modeling of Ionospheric Delay for SBAS Using Spherical Harmonics Functions

    Directory of Open Access Journals (Sweden)

    Deokhwa Han

    2013-06-01

    Full Text Available In SBAS (satellite-based augmentation system, it is important to estimate ionospheric delay accurately to guarantee user's accuracy and integrity. Grid based ionospheric models are generally used to estimate ionospheric delay for SBAS. In grid based model, SBAS broadcasts vertical ionospheric delays at the grid point, and users get their ionospheric delay by interpolating those values. Ionospheric model based on spherical harmonics function is another method to estimate ionospheric delay. This is a function based approach and spherical harmonics function is a 2-D fourier series, containing the product of latitude dependent associated Legendre functions and the sum of the longitude dependent sine and cosine terms. Using ionospheric delay measurements, coefficients for each spherical harmonics functions are estimated. If these coefficients are known, user can reconstruct ionospheric delay. In this paper, we consider the spherical harmonics based model and propose a ionospheric delay estimation strategy for SBAS that can be used to mitigate ionospheric delay estimation error, especially in storm condition. First, coefficients are estimated under initial order and degree. Then residual errors for each measurement are modeled by higher order and degree terms, then coefficients for these terms are estimated. Because SBAS message capacity is limited, in normal condition, initial order terms are only used to estimate ionospheric delay. If ionospheric storm is detected and there is need to mitigate the error, higher order terms are also used and error can be decreased. To compare the accuracy of spherical harmonics based model with grid based model, some post-processing test results are presented. Raw observation data is obtained from RINEX format and the root mean square(RMS and max value of residual errors are presented.

  4. GreenCube and RocketCube: Low-Resource Sensorcraft for Atmospheric and Ionospheric Science

    Science.gov (United States)

    Bracikowski, P. J.; Lynch, K. A.; Slagle, A. K.; Fagin, M. H.; Currey, S. R.; Siddiqui, M. U.

    2009-12-01

    expect to be able to detect atmospheric gravity waves from the GPS-derived position and velocity of the two balloons and the ambient temperature profiles. Preliminary analysis of the temperature data shows indications of atmospheric gravity waves. RocketCube is a graduate student-designed low-resource sensorcraft development project being designed for future ionospheric multi-point missions. The FPGA-based bus system, based on GreenCube’s systems, will be able to control and digitize analog data from any low voltage instrument and telemeter that data. RocketCube contains a GPS and high-resolution magnetometer for position and orientation information. The Lynch Rocket Lab's initial interest in developing RocketCube is to investigate the k-spectrum of density irregularities in the auroral ionosphere. To this end, RocketCube will test a new Petite retarding potential analyzer Ion Probe (PIP) for examining subsonic and supersonic thermal ion populations in the ionosphere. The tentatively planned launch will be from a Wallops Flight Facility sounding rocket test flight in 2011. RocketCube serves as a step toward a scientific auroral sounding rocket mission that will feature an array of subpayloads to study the auroral ionosphere.

  5. Lung Sounds in Bronchial Asthma

    Directory of Open Access Journals (Sweden)

    Yukio Nagasaka

    2012-01-01

    In lung sound analysis, the narrower the airways are, the higher the frequency of breathing sounds is, and, if a patient has higher than normal breathing sounds, i.e., bronchial sounds, he or she may have airway narrowing or airway inflammation. It is sometimes difficult to detect subtle changes in lung sounds; therefore, we anticipate that automated analysis of lung sounds will be used to overcome these difficulties in the near future.

  6. Properties of a Sound Wave

    OpenAIRE

    2003-01-01

    This interactive tutorial covers the following properties of sound wave: frequency, period, amplitude, total pressure, ambient pressure, and peak sound pressure. Students need to have a sound card on their computer and speakers to hear the sounds produced. The interactions in this tutorial include: Mouse over some text for visual explanations., Varying the frequency and amplitude of a sound wave, and be able to listen to the changing pitch of the sound., A short self-check quiz. PH2401 ...

  7. Relationship of dayside main layer ionosphere height to local solar time on Mars and implications for solar wind interaction influence

    Science.gov (United States)

    Zhang, Zhenfei; Orosei, Roberto; Huang, Qian; Zhang, Jie

    2015-08-01

    To understand the influence of solar wind on the daytime main layer ionosphere of Mars, we investigated the local solar time (LST) variations of three characteristic heights of the ionosphere, namely, the heights of the 1 MHz and 1.5 MHz reflection points (i.e., 1.24 × 1010 m-3 and 2.79 × 1010 m-3 isodensity contours, respectively) and the density peak. We used a total of 19,996 Mars Advanced Radar for Subsurface and Ionosphere Sounding observations distributed on the northern hemisphere, with solar zenith angle ≤80°, acquired from June 2005 to October 2013. We exploited the kernel partial least squares regression method to extract the nonlinear relationships of the heights to LST and a few other variables. The average height of the 1 MHz reflection point decreased from ~218 km at 10:00 A.M. to ~206 km at 16:00 P.M. local time; the height of the 1.5 MHz reflection point decreased simultaneously from ~190 km to ~181 km. These decreasing trends are in contrast to the LST variation of the density peak height, which increased from ~128 km to ~137 km over the same LST interval. Based on these findings and previous results, we suggest that the solar wind may penetrate the Martian ionosphere down to altitudes of about 50 km above the main density peak and may, in conjunction with the asymmetric draping of the interplanetary magnetic field, compress the upper part of the main ionosphere layer on the P.M. side ~10 km more than on the A.M. side.

  8. Photoacoustic Sounds from Meteors

    Science.gov (United States)

    Spalding, Richard; Tencer, John; Sweatt, William; Conley, Benjamin; Hogan, Roy; Boslough, Mark; Gonzales, GiGi; Spurný, Pavel

    2017-01-01

    Concurrent sound associated with very bright meteors manifests as popping, hissing, and faint rustling sounds occurring simultaneously with the arrival of light from meteors. Numerous instances have been documented with −11 to −13 brightness. These sounds cannot be attributed to direct acoustic propagation from the upper atmosphere for which travel time would be several minutes. Concurrent sounds must be associated with some form of electromagnetic energy generated by the meteor, propagated to the vicinity of the observer, and transduced into acoustic waves. Previously, energy propagated from meteors was assumed to be RF emissions. This has not been well validated experimentally. Herein we describe experimental results and numerical models in support of photoacoustic coupling as the mechanism. Recent photometric measurements of fireballs reveal strong millisecond flares and significant brightness oscillations at frequencies ≥40 Hz. Strongly modulated light at these frequencies with sufficient intensity can create concurrent sounds through radiative heating of common dielectric materials like hair, clothing, and leaves. This heating produces small pressure oscillations in the air contacting the absorbers. Calculations show that −12 brightness meteors can generate audible sound at ~25 dB SPL. The photoacoustic hypothesis provides an alternative explanation for this longstanding mystery about generation of concurrent sounds by fireballs. PMID:28145486

  9. Sound as artifact

    Science.gov (United States)

    Benjamin, Jeffrey L.

    A distinguishing feature of the discipline of archaeology is its reliance upon sensory dependant investigation. As perceived by all of the senses, the felt environment is a unique area of archaeological knowledge. It is generally accepted that the emergence of industrial processes in the recent past has been accompanied by unprecedented sonic extremes. The work of environmental historians has provided ample evidence that the introduction of much of this unwanted sound, or "noise" was an area of contestation. More recent research in the history of sound has called for more nuanced distinctions than the noisy/quiet dichotomy. Acoustic archaeology tends to focus upon a reconstruction of sound producing instruments and spaces with a primary goal of ascertaining intentionality. Most archaeoacoustic research is focused on learning more about the sonic world of people within prehistoric timeframes while some research has been done on historic sites. In this thesis, by way of a meditation on industrial sound and the physical remains of the Quincy Mining Company blacksmith shop (Hancock, MI) in particular, I argue for an acceptance and inclusion of sound as artifact in and of itself. I am introducing the concept of an individual sound-form, or sonifact , as a reproducible, repeatable, representable physical entity, created by tangible, perhaps even visible, host-artifacts. A sonifact is a sound that endures through time, with negligible variability. Through the piecing together of historical and archaeological evidence, in this thesis I present a plausible sonifactual assemblage at the blacksmith shop in April 1916 as it may have been experienced by an individual traversing the vicinity on foot: an 'historic soundwalk.' The sensory apprehension of abandoned industrial sites is multi-faceted. In this thesis I hope to make the case for an acceptance of sound as a primary heritage value when thinking about the industrial past, and also for an increased awareness and acceptance

  10. Ionospheric effects on repeat-pass SAR interferometry

    Science.gov (United States)

    Feng, Jian; Zhen, Weimin; Wu, Zhensen

    2017-10-01

    InSAR measurements can be significantly affected by the atmosphere when the radar signal propagates through the atmosphere since it varies with space and time. Great efforts have been made in recent years to better understand the properties of the tropospheric effects and to develop methods for mitigating these effects. By using the basic principles of InSAR, the quantitative analysis of ionospheric delay effects on topography and surface deformation have been introduced for the first time. The measurement errors can be related to the vertical ionospheric total electron content (vTEC). By using the ionospheric observations, the effects of temporal ionospheric variations on InSAR have been analyzed. The results indicate that the ionospheric variations with time, season, solar cycle and geomagnetic activities can compromise the effectiveness of InSAR for both the measurement of topography and surface determination. The repeat-pass SAR interferometry errors induced by ionosphere should be corrected by actual measurements.

  11. Low-Frequency Waves in HF Heating of the Ionosphere

    Science.gov (United States)

    Sharma, A. S.; Eliasson, B.; Milikh, G. M.; Najmi, A.; Papadopoulos, K.; Shao, X.; Vartanyan, A.

    2016-02-01

    Ionospheric heating experiments have enabled an exploration of the ionosphere as a large-scale natural laboratory for the study of many plasma processes. These experiments inject high-frequency (HF) radio waves using high-power transmitters and an array of ground- and space-based diagnostics. This chapter discusses the excitation and propagation of low-frequency waves in HF heating of the ionosphere. The theoretical aspects and the associated models and simulations, and the results from experiments, mostly from the HAARP facility, are presented together to provide a comprehensive interpretation of the relevant plasma processes. The chapter presents the plasma model of the ionosphere for describing the physical processes during HF heating, the numerical code, and the simulations of the excitation of low-frequency waves by HF heating. It then gives the simulations of the high-latitude ionosphere and mid-latitude ionosphere. The chapter also briefly discusses the role of kinetic processes associated with wave generation.

  12. A clear link connecting the troposphere and ionosphere: ionospheric reponses to the 2015 Typhoon Dujuan

    Science.gov (United States)

    Kong, Jian; Yao, Yibin; Xu, Yahui; Kuo, Chungyen; Zhang, Liang; Liu, Lei; Zhai, Changzhi

    2017-09-01

    The global navigation satellite system (GNSS) total electron content (TEC) sequences were used to capture the arrival time and location of the ionosphere disturbances in response to the 2015 Typhoon Dujuan. After removing the de-trended TEC variation, the clear ionosphere disturbances on the typhoon landing day could be distinguished, and these disturbances disappeared from the TEC sequences before and after the typhoon landing day. The foF2 data observed by Xiamen ionosonde station also show ionosphere disturbances. Based on the advantages of GNSS multi-point observations, the disturbances horizontal velocity in the ionosphere were estimated according to the linear theory for a dispersion relation of acoustic gravity waves (AGWs) in an isothermal atmosphere. The average horizontal velocity (˜ 240 m/s) and the radial velocity (˜ 287 m/s) were used in the two-dimensional grid search for the origin point on the Earth's surface. The origin area was determined to be on the eastern side of Taiwan. Lastly, a possible physical mechanism is discussed in this study. When typhoons land on Taiwan, the severe convective storms and the drag effect from the Central Mountains create an ideal location for development of AGWs. Topographic conditions, like the high lapse rate, contribute to the formation of AGWs, which then propagates into the ionosphere altitude.

  13. The sound handbook

    CERN Document Server

    Crook, Tim

    2013-01-01

    'Tim Crook has written an important and much-needed book, and its arrival on our shelves has come at a highly appropriate time.' Professor Seán Street, Bournemouth UniversityThe Sound Handbook maps theoretical and practical connections between the creation and study of sound across the multi-media spectrum of film, radio, music, sound art, websites, animation and computer games entertainment, and stage theatre. Using an interdisciplinary approach Tim Crook explores the technologies, philosophies and cultural issues involved in making a

  14. Sound Objects for SVG

    OpenAIRE

    Colbrant, Audrey; Lasorsa, Yohan; Lemordant, Jacques; Liodenot, David; Razafimahazo, Mathieu

    2010-01-01

    International audience; A sound object can be defined as a time structure of audio chunks whose duration is on the time scale of 100 ms to several seconds. Sound objects have heterogeneous and time-varying properties. They are the basic elements of any format for Interactive Audio (IA). We have designed an XML language, A2ML, for Interactive Audio which offers, concerning the sequencing of sounds, a level of capabilities similar to that of iXMF, the interactive audio file format defined by th...

  15. Solar cycle variations in the ionosphere of Mars

    Energy Technology Data Exchange (ETDEWEB)

    Sanchez-Cano, B.; Lester, M.; Witasse, Ol; Blelly, P.L.; Cartacci, M.; Radicella, S.M.; Herraiz, M.

    2016-07-01

    Solar cycle variations in solar radiation create notable changes in the Martian ionosphere, which have been analysed with Mars Express plasma datasets in this paper. In general, lower densities and temperatures of the ionosphere are found during the low solar activity phase, while higher densities and temperatures are found during the high solar activity phase. In this paper, we assess the degree of influence of the long term solar flux variations in the ionosphere of Mars. (Author)

  16. Trans-Ionospheric High Frequency Signal Ray Tracing

    Science.gov (United States)

    Wright, S.; Gillespie, R. J.

    2012-09-01

    All electromagnetic radiation undergoes refraction as it propagates through the atmosphere. Tropospheric refraction is largely governed by interaction of the radiation with bounded electrons; ionospheric refraction is primarily governed by free electron interactions. The latter phenomenon is important for propagation and refraction of High Frequency (HF) through Extremely High Frequency (EHF) signals. The degree to which HF to EHF signals are bent is dependent upon the integrated refractive effect of the ionosphere: a result of the signal's angle of incidence with the boundaries between adjacent ionospheric regions, the magnitude of change in electron density between two regions, as well as the frequency of the signal. In the case of HF signals, the ionosphere may bend the signal so much that it is directed back down towards the Earth, making over-the-horizon HF radio communication possible. Ionospheric refraction is a major challenge for space-based geolocation applications, where the ionosphere is typically the biggest contributor to geolocation error. Accurate geolocation requires an algorithm that accurately reflects the physical process of a signal transiting the ionosphere, and an accurate specification of the ionosphere at the time of the signal transit. Currently implemented solutions are limited by both the algorithm chosen to perform the ray trace and by the accuracy of the ionospheric data used in the calculations. This paper describes a technique for adapting a ray tracing algorithm to run on a General-Purpose Graphics Processing Unit (GPGPU or GPU), and using a physics-based model specifying the ionosphere at the time of signal transit. This technique allows simultaneous geolocation of significantly more signals than an equivalently priced Central Processing Unit (CPU) based system. Additionally, because this technique makes use of the most widely accepted numeric algorithm for ionospheric ray tracing and a timely physics-based model of the ionosphere

  17. COMPARISON OF COSEISMIC IONOSPHERIC DISTURBANCE WAVEFORMS REVISITED: STRIKE-SLIP, NORMAL, AND REVERSE FAULT EARTHQUAKE

    Directory of Open Access Journals (Sweden)

    Mokhamad Nur Cahyadi

    2015-02-01

    Full Text Available Using Total Electron Content (TEC measurements with Global Positioning System we studied ionospheric responses to three large earthquakes with difference focal mechanism that occurred in the Sumatra Andaman 26 December 2004, North off Sumatra 11 April 2012, and North Japan 7 December 2012. These earthquakes have different focal mechanisms, i.e. high-angle reverse, strike-slip, and normal faulting, respectively. TEC responses to the Sumatra Andaman 2004 and north Japan 2012 events initiated with positive changes. On the other hand, the initial TEC changes in the Sumatra 2012 earthquake showed both positive and negative polarities depending on the azimuth around the focal area. Such a variety may reflect differences in coseismic vertical crustal displacements, which are dominated by uplift and subsidence in the Sumatra 2012 event. This phenomena has same characteristic with 1994 Kuril Arch earthquake. There are three different propagation velocity in the Sumatra 2012 earthquake, within the first 300 km until 430 km, the CID propagation velocity was ~3 km/s, which is equal to the secod sound speed at the height of the ionospheric F-layer. Starting from 380 km until 750 km out from the epicenter, the disturbance seems to divide into two separate perturbations, with each propagating at a different velocity, about 1 km/s for the one and about 0.4 m/s for the other. The apparent velocity in the Sumatra Andaman 2004 and Japan 2012 propagated ~ 1 km/s and ~ 0.3 km/s, consistent with the sound speed at the ionospheric F layer height and internal gravity wave respectively. Resonant oscillation of TEC with a frequency of ~ 3.7 mHZ and ~4.4 mHz have been found in the Sumatra 2012 and Sumatra Andaman 2004 events. Those earthquakes, which occurred during a period of quiet geomagnetic activity, also showed clear preseismic TEC anomalies similar to those before the 2011 Tohoku-Oki and 2007 Bengkulu earthquake.   The positive anomalies started 30-60 minutes

  18. Quasiperiodic behavior of electrons in the ionosphere

    Energy Technology Data Exchange (ETDEWEB)

    Lysak, R.L.; Knuth, K.H.; Thompson, B.J. [Univ. of Minnesota, Minneapolis, MN (United States). School of Physics and Astronomy

    1995-12-31

    Electrons traveling in the ionosphere-inner magnetosphere region can become trapped by the quasi-static electric field at auroral altitudes and magnetic mirroring at ionospheric heights. A model is developed to simulate electron trajectories influenced by electric field fluctuations, and a dynamical analysis is performed on the resulting orbits. For fluctuations in the frequency range of 1 Hz, a bounce resonance may develop between electrons with typical travel times of few seconds. These electrons can remain trapped indefinitely, resulting in distinct quasiperiodic behavior. A stroboscopic map (a Poincare map with time as a state variable of the system) is applied, and the results form a 2-Torus in velocity phase space. The poster includes discussions on the acceleration process, the dynamical analysis, behavior in phase space, physical implications of the system, and a statistical summary of electron orbits.

  19. ULF Generation by Modulated Ionospheric Heating

    Science.gov (United States)

    Chang, C.; Labenski, J.; Wallace, T.; Papadopoulos, K.

    2013-12-01

    Modulated ionospheric heating experiments designed to generate ULF waves using the HAARP heater have been conducted since 2007. Artificial ULF waves in the Pc1 frequency range were observed from space and by ground induction magnetometers located in the vicinity of the heater as well as at long distances. Two distinct generation mechanisms of artificial ULF waves were identified. The first was electroject modulation under geomagnetically disturbed conditions. The second was pressure modulation in the E and F regions of the ionosphere under quiet conditions. Ground detections of ULF waves near the heater included both Shear Alfven waves and Magnetosonic waves generated by electrojet and/or pressure modulations. Distant ULF detections involved Magnetosonic wave propagation in the Alfvenic duct with pressure modulation as the most likely source. Summary of our observations and theoretical interpretations will be presented at the meeting. We would like to acknowledge the support provided by the staff at the HAARP facility during our ULF experiments.

  20. Electromagnetically Driven Plasma-Field Dynamics in Modified Ionosphere

    Science.gov (United States)

    Kochetov, Andrey; Terina, Galina

    Under sounding of an artificial ionospheric turbulence by short probing radio pulses of ordinary polarization the two types of scattered signals were observed: a "caviton" signal (CS) and a "plasma" signal (PS), which appeared with the heating transmitter switching on and disap-peared after its switching off (G.I. Terina J. Atm. Terr. Phys, 57, 1995, 273, Izv. VUZov, Radiofizika, 39, 1998, 203). The scattered signal of PS type was revealed also after the heating switching off. It was called an "aftereffect plasma signal" (AEPS) (G.I. Terina Izv .VUZov, Radiofizika, 43, 2000, 958). This signal had large time and spatial delays and appeared mostly when corresponding PS had envelope fluctuations. The aftereffect phenomenon was expressed at time on CS by amplitude increasing at once after the heating transmitter turning off. The theoretical model of this phenomenon is proposed in and some peculiarities of the aftereffect phenomena of the scattered signals in modified ionospheric plasma are considered and discussed. For theoretical interpretation of the characteristics of CS and AEPS the numerical solution of nonlinear Shrüdinger equation (NSE) with driven extension were carried out in inhomogeneous plasma layer with linear electron density profile (A.V. Kochetov, V.A. Mironov, G.I. Terina, Adv. Space Reseacrh, 29, 2002, 1369) and for the one with prescribed density depletion (and A.V. Kochetov, G.I. Terina, Adv. Space Reseacrh, 38, 2006, 2490). The simulation results obtained for linear inhomogeneous plasma layer and for plasma one with density depletion al-low us to interpret the aftereffect of CS and PS qualitatively. The field amplitude increase at relaxation stage displayed at calculations allows us to interpret of CS aftereffect. The large time delays of AEPS can be explained as a result of powerful radio waves trapping in the forming at the plasma resonance regions density depletions (E. Mjøhus, J. Geophys. Res. 103, 1998, 14711; B. Eliasson and L. Stenflo, J