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Sample records for hf produced ionospheric

  1. HF produced ionospheric electron density irregularities diagnosed by UHF radio star scintillations

    Science.gov (United States)

    Frey, A.; Gordon, W. E.

    1982-01-01

    Three observations of radio star intensity fluctuations at UHF are reported for HF ionospheric modification experiments carried out at the Arecibo Observatory. Two observations at 430 MHz and one at 1400 MHz suggest that the the thin phase screen theory is a good approximation to the observed power spectra. It is noted, however, that the theory has to be extended to include antenna filtering. This type of filtering is important for UHF radio star scintillations since the antenna usually has a narrow beamwidth. HF power densities of less than 37 microwatts/sq m incident on the ionosphere give rise to electron density irregularities larger than 13% of the ambient density (at 260 km) having scale sizes of approximately 510 m perpendicular to the geomagnetic field. The irregularities are found to form within 20-25 s after the HF power is turned on. The drift velocities of the irregularities can be estimated from the observed power spectra.

  2. Ionosphere research with a HF/MF cubesat radio instrument

    Science.gov (United States)

    Kallio, Esa; Aikio, Anita; Alho, Markku; Fontell, Mathias; Harri, Ari-Matti; Kauristie, Kirsti; Kestilä, Antti; Koskimaa, Petri; Mäkelä, Jakke; Mäkelä, Miika; Turunen, Esa; Vanhamäki, Heikki; Verronen, Pekka

    2017-04-01

    New technology provides new possibilities to study geospace and 3D ionosphere by using spacecraft and computer simulations. A type of nanosatellites, CubeSats, provide a cost effective possibility to provide in-situ measurements in the ionosphere. Moreover, combined CubeSat observations with ground-based observations gives a new view on auroras and associated electromagnetic phenomena. Especially joint and active CubeSat - ground based observation campaigns enable the possibility of studying the 3D structure of the ionosphere. Furthermore using several CubeSats to form satellite constellations enables much higher temporal resolution. At the same time, increasing computation capacity has made it possible to perform simulations where properties of the ionosphere, such as propagation of the electromagnetic waves in the medium frequency, MF (0.3-3 MHz) and high frequency, HF (3-30 MHz), ranges is based on a 3D ionospheric model and on first-principles modelling. Electromagnetic waves at those frequencies are strongly affected by ionospheric electrons and, consequently, those frequencies can be used for studying the plasma. On the other hand, even if the ionosphere originally enables long-range telecommunication at MF and HF frequencies, the frequent occurrence of spatiotemporal variations in the ionosphere disturbs communication channels, especially at high latitudes. Therefore, study of the MF and HF waves in the ionosphere has both a strong science and technology interests. We introduce recently developed simulation models as well as measuring principles and techniques to investigate the arctic ionosphere by a polar orbiting CubeSat whose novel AM radio instrument measures HF and MF waves. The cubesat, which contains also a white light aurora camera, is planned to be launched in late 2017 (http://www.suomi100satelliitti.fi/eng). The new models are (1) a 3D ray tracing model and (2) a 3D full kinetic electromagnetic simulation. We also introduce how combining of the

  3. Calculating the absorption of HF radio waves in the ionosphere

    Science.gov (United States)

    Zawdie, K. A.; Drob, D. P.; Siskind, D. E.; Coker, C.

    2017-06-01

    It has long been known that the ionospheric absorption of HF radio waves is dependent on the electron density in the ionosphere. This paper examines two aspects of the absorption calculation that have not been as thoroughly investigated. First, the correct method to calculate ionospheric absorption is explored; while the Sen Wyller ray trace formulation is generally cited as the best approximation in the D and E regions of the ionosphere, the Appleton-Hartree formulation is more consistent with the theory in the F region of the ionosphere. It is shown that either ray trace formulation can be used to calculate ionospheric absorption if the correct collision frequencies are utilized. Another frequently overlooked aspect of the attenuation calculation are the variations in the electron-neutral and electron-ion collision frequencies as a function of local time, season, latitude, and solar cycle. These variations result in differences on the order of 30% in the total ionospheric attenuation and should be included in absorption calculations.

  4. HF beacon network for ionospheric specification in Peru

    Science.gov (United States)

    Hysell, D. L.; Milla, M. A.; Vierinen, J.

    2016-12-01

    A growing network of HF beacon transmitters and receivers is being deployed in Peru for specifying the F region ionosphere regionally. The effort is motivated by ionospheric disturbances associated with equatorial spread F (ESF), especially disturbances arising under inauspicious ESF conditions. The beacons use dual frequencies (2.72 and 3.64 MHz). They incorporate PRN coding to afford group-delay measurements. Scatered power, Doppler shift, bearing, and polarization are also measured. An algorithm for inverting the beacon data combined with electron density profiles from Jicamarca is described. Data and representative solutions from recent campaigns will be reviewed.

  5. Generation of ionospheric ducts by the HAARP HF heater

    Energy Technology Data Exchange (ETDEWEB)

    Cohen, J A; Pradipta, R; Burton, L M; Labno, A; Lee, M C [Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Watkins, B J; Fallen, C [University of Alaska Fairbanks, Fairbanks, AK 99775 (United States); Kuo, S P [New York University, Brooklyn, NY 11201 (United States); Burke, W J [Air Force Research Laboratory, Hanscom AFB, MA 01731 (United States); Mabius, D; See, B Z, E-mail: mclee@mit.edu [Boston University, Boston, MA 02215 (United States)

    2010-12-15

    We report an investigation of ionospheric ducts having the shape of large plasma sheets, generated by vertically transmitted HAARP HF heater waves in several experiments conducted in Gakona, Alaska. Theory predicts that O-mode heater wave-created ionospheric ducts form parallel-plate waveguides within the meridional plane, and those generated by the X-mode heater waves are orthogonal to the meridional plane. Our theoretical prediction is supported by measurements of ionosonde data (namely ionograms), range-time-intensity (RTI) plots of UHF and HF backscatter radars, as well as magnetometer data analyses. When these plasma sheets experienced ExB drifts, they were intercepted by the HAARP UHF radar and seen as slanted stripes in the RTI plots. This striking feature was also observed in our earlier experiments using the Arecibo UHF radar.

  6. Magnetospheric injection of ELF/VLF waves with modulated or steered HF heating of the lower ionosphere

    Science.gov (United States)

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

    2011-06-01

    ELF/VLF waves have been generated via steerable HF heating of the lower ionosphere. The temperature-dependent conductivity of the lower ionospheric plasma enables HF heating (and subsequent recovery) to modulate natural current systems such as the auroral electrojet, thus generating an antenna embedded in the ionospheric plasma. We apply a realistic three-dimensional model of HF heating and ionospheric recovery, as well as ELF/VLF wave propagation in and below the ionosphere, to derive the radiation pattern into the magnetosphere as a result of steerable HF heating. It is found that modulated HF heating preferentially directs signals upward into space because of the phasing effect of the upward HF wave propagation. We find that the steering techniques such as the geometric modulation “circle sweep” enhances the total ELF/VLF power injected into the magnetosphere by 5-7 dB compared to amplitude modulated heating, with a few dB enhancement in the peak magnetic field value. Another technique known as beam painting enhances the total injected power by 1-3 dB but produces weaker peak magnetic fields due to the power being spread over a larger area. Observations on the DEMETER spacecraft are presented and compared with theoretical predictions. DEMETER observations show that the signal produced with geometric modulation can be stronger than the signal from AM under the same conditions.

  7. Characterization of Ionosphere Waveguide Propagation by Monitoring HAARP HF Transmissions in Antarctica

    Science.gov (United States)

    2015-04-17

    ionospheric irregularities are of unpredictable character. Their appearance is determined by sporadic factors and depends, specifically, on the enhanced...the ionosphere The effect of ionospheric refraction on the scattering of high frequency (HF) signals by random field-aligned irregularities in the...scattering of high-frequency (HF) (3-30 MHz) and very high- frequency (VHF) (30-300 MHz) waves by field-aligned irregularities of the ionospheric plasma

  8. Probing of medium-scale traveling ionospheric disturbances using HF-induced scatter targets

    Directory of Open Access Journals (Sweden)

    N. F. Blagoveshchenskaya

    2006-09-01

    Full Text Available Experimental results from the Tromsø and Sura heating experiments at high and mid-latitudes are examined. It is shown that the combination of HF-induced target and bi-static HF Doppler radio scatter observations is a profitable method for probing medium-scale traveling ionospheric disturbances (TIDs at high and mid-latitudes. HF ionospheric modification experiments provide a way of producing the HF-induced scatter target in a controlled manner at altitudes where the sensitivity to TIDs is highest. Bi-static HF Doppler radio scatter observations were carried out on the London-Tromsø-St. Petersburg path in the course of a Tromsø heating experiment on 16 November 2004 when the pump wave was reflected from an auroral Es-layer. During Sura heating experiments on 19 and 20 August 2004, when the HF pump wave was reflected from the F2 ionospheric layer, multi-position bi-static HF Doppler radio scatter observations were simultaneously performed at three reception points including St. Petersburg, Kharkov, and Rostov-on-Don. Ray tracing and Doppler shift simulations were made for all experiments. A computational technique has been developed allowing the reconstruction of the TID phase velocities from multi-position bi-static HF Doppler scatters. Parameters of medium-scale TIDs were found. In all experiments they were observed in the evening and pre-midnight hours. TIDs in the auroral E-region with periods of about 23 min were traveling southward at speeds of 210 m/s. TIDs in the mid-latitudinal F-region with periods from 20 to 45 min travelled at speeds between 40 and 150 m/s. During quiet magnetic conditions the waves were traveling in the north-east direction. In disturbed conditions the waves were moving in the south-west direction with higher speeds as compared with quiet conditions. Possible sources for the atmospheric gravity waves at middle and high latitudes are discussed.

  9. Equatorial ionospheric disturbance observed through a transequatorial HF propagation experiment

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    T. Maruyama

    2006-07-01

    Full Text Available A transequatorial radio-wave propagation experiment at shortwave frequencies (HF-TEP was done between Shepparton, Australia, and Oarai, Japan, using the radio broadcasting signals of Radio Australia. The receiving facility at Oarai was capable of direction finding based on the MUSIC (Multiple Signal Classification algorithm. The results were plotted in azimuth-time diagrams (AT plots. During the daytime, the propagation path was close to the great circle connecting Shepparton and Oarai, thus forming a single line in the AT plots. After sunset, off-great-circle paths, or satellite traces in the AT plot, often appeared abruptly to the west and gradually returned to the great circle direction. However, there were very few signals across the great circle to the east. The off-great-circle propagation was very similar to that previously reported and was attributed to reflection by an ionospheric structure near the equator. From the rate of change in the direction, we estimated the drift velocity of the structure to range mostly from 100 to 300 m/s eastward. Multiple instances of off-great-circle propagation with a quasi-periodicity were often observed and their spatial distance in the east-west direction was within the range of large-scale traveling ionospheric disturbances (LS-TIDs. Off-great-circle propagation events were frequently observed in the equinox seasons. Because there were many morphological similarities, the events were attributed to the onset of equatorial plasma bubbles.

  10. Numerical modeling of artificial ionospheric layers driven by high-power HF heating

    Science.gov (United States)

    Eliasson, B.; Shao, X.; Milikh, G.; Mishin, E. V.; Papadopoulos, K.

    2012-10-01

    We present a multi-scale dynamic model for the creation and propagation of artificial plasma layers in the ionosphere observed during high-power high-frequency (HF) heating experiments at HAARP. Ordinary (O) mode electromagnetic (EM) waves excite parametric instabilities and strong Langmuir turbulence (SLT) near the reflection point. The coupling between high-frequency electromagnetic and Langmuir waves and low-frequency ion acoustic waves is numerically simulated using a generalized Zakharov equation. The acceleration of plasma electrons is described by a Fokker-Planck model with an effective diffusion coefficient constructed using the simulated Langmuir wave spectrum. The propagation of the accelerated electrons through the non-uniform ionosphere is simulated by a kinetic model accounting for elastic and inelastic collisions with neutrals. The resulting ionization of neutral gas increases the plasma density below the acceleration region, so that the pump wave is reflected at a lower altitude. This leads to a new turbulent layer at the lower altitude, resulting in a descending artificial ionized layer (DAIL), that moves from near 230 km to about 150 km. At the terminal altitude, ionization, recombination, and ambipolar diffusion reach equilibrium, so the descent stops. The modeling results reproduce artificial ionospheric layers produced for similar sets of parameters during the high-power HF experiments at HAARP.

  11. Assimilative model for ionospheric dynamics employing delay, Doppler, and direction of arrival measurements from multiple HF channels

    Science.gov (United States)

    Fridman, Sergey V.; Nickisch, L. J.; Hausman, Mark; Zunich, George

    2016-03-01

    We describe the development of new HF data assimilation capabilities for our ionospheric inversion algorithm called GPSII (GPS Ionospheric Inversion). Previously existing capabilities of this algorithm included assimilation of GPS total electron content data as well as assimilation of backscatter ionograms. In the present effort we concentrated on developing assimilation tools for data related to HF propagation channels. Measurements of propagation delay, angle of arrival, and the ionosphere-induced Doppler from any number of known propagation links can now be utilized by GPSII. The resulting ionospheric model is consistent with all assimilated measurements. This means that ray tracing simulations of the assimilated propagation links are guaranteed to be in agreement with measured data within the errors of measurement. The key theoretical element for assimilating HF data is the raypath response operator (RPRO) which describes response of raypath parameters to infinitesimal variations of electron density in the ionosphere. We construct the RPRO out of the fundamental solution of linearized ray tracing equations for a dynamic magnetoactive plasma. We demonstrate performance and internal consistency of the algorithm using propagation delay data from multiple oblique ionograms (courtesy of Defence Science and Technology Organisation, Australia) as well as with time series of near-vertical incidence sky wave data (courtesy of the Intelligence Advanced Research Projects Activity HFGeo Program Government team). In all cases GPSII produces electron density distributions which are smooth in space and in time. We simulate the assimilated propagation links by performing ray tracing through GPSII-produced ionosphere and observe that simulated data are indeed in agreement with assimilated measurements.

  12. Numerical modeling of artificial ionospheric layers driven by high-power HF-heating

    Science.gov (United States)

    Milikh, G. M.; Eliasson, B.; Shao, X.; Mishin, E. V.; Papadopoulos, K.

    2012-12-01

    We present a multi-scale dynamic model for the creation and propagation of artificial plasma layers in the ionosphere observed during high-power high frequency heating experiments at HAARP. Ordinary mode electromagnetic waves excite parametric instabilities and strong Langmuir turbulence near the reflection point. The coupling between high frequency electromagnetic and Langmuir waves and low-frequency ion acoustic waves is numerically simulated using a generalized Zakharov equation. The acceleration of plasma electrons is described by a Fokker-Planck model with an effective diffusion coefficient constructed using the simulated Langmuir wave spectrum. The propagation of the accelerated electrons through the non-uniform ionosphere is simulated by a kinetic model accounting for elastic and inelastic collisions with neutrals. The resulting ionization of neutral gas increases the plasma density below the acceleration region, so that the pump wave is reflected at a lower altitude. This leads to a new turbulent layer at the lower altitude, resulting in a descending artificial ionized layer, that moves from near 230 km to about 150 km. At the terminal altitude, ionization, recombination, and ambipolar diffusion reach equilibrium, so the descent stops. The modeling results reproduce artificial ionospheric layers produced for similar sets of parameters during the high-power HF experiments at HAARP.

  13. Radiotomography and HF ray tracing of the artificially disturbed ionosphere above the Sura heating facility

    Science.gov (United States)

    Andreeva, E. S.; Frolov, V. L.; Kunitsyn, V. E.; Kryukovskii, A. S.; Lukin, D. S.; Nazarenko, M. O.; Padokhin, A. M.

    2016-06-01

    We present the results of the radiotomographic imaging of the artificial ionospheric disturbances obtained in the recent experiments on the modification of the midlatitude ionosphere by powerful HF radiowaves carried out at the Sura heater. Radio transmissions from low orbital PARUS beacon satellites recorded at the specially installed network of three receiving sites were used for the remote sensing of the heated ionosphere. We discuss the possibility to generate acoustic-gravity waves (AGWs) with special regimes of ionospheric heating (with the square wave modulation of the effective radiated power at the frequency lower than or of the order of the Brunt-Vaisala frequency of the neutral atmosphere at ionospheric heights during several hours) and present radiotomographic images of the spatial structure of the disturbed volume of the ionosphere corresponding to the directivity pattern of the heater, as well as the spatial structure of the wave-like disturbances, which are possibly heating-induced AGWs, diverging from the heated area of the ionosphere. We also studied the HF propagation of the pumping wave through the reconstructed disturbed ionosphere above the Sura heater, showing the presence of heater-created, field-aligned irregularities that effectively serve as "artificial radio windows."

  14. Geospace ionosphere research with a MF/HF radio instrument on a cubesat

    Science.gov (United States)

    Kallio, E. J.; Aikio, A. T.; Alho, M.; Fontell, M.; van Gijlswijk, R.; Kauristie, K.; Kestilä, A.; Koskimaa, P.; Makela, J. S.; Mäkelä, M.; Turunen, E.; Vanhamäki, H.

    2016-12-01

    Modern technology provides new possibilities to study geospace and its ionosphere, using spacecraft and and computer simulations. A type of nanosatellites, CubeSats, provide a cost effective possibility to provide in-situ measurements in the ionosphere. Moreover, combined CubeSat observations with ground-based observations gives a new view on auroras and associated electromagnetic phenomena. Especially joint and active CubeSat - ground based observation campaigns enable the possibility of studying the 3D structure of the ionosphere. Furthermore using several CubeSats to form satellite constellations enables much higher temporal resolution. At the same time, increasing computation capacity has made it possible to perform simulations where properties of the ionosphere, such as propagation of the electromagnetic waves in the medium frequency, MF (0.3-3 MHz) and high frequency, HF (3-30 MHz), ranges is based on a 3D ionospheric model and on first-principles modelling. Electromagnetic waves at those frequencies are strongly affected by ionospheric electrons and, consequently, those frequencies can be used for studying the plasma. On the other hand, even if the ionosphere originally enables long-range telecommunication at MF and HF frequencies, the frequent occurrence of spatiotemporal variations in the ionosphere disturbs communication channels, especially at high latitudes. Therefore, study of the MF and HF waves in the ionosphere has both a strong science and technology interests. We present computational simulation results and measuring principles and techniques to investigate the arctic ionosphere by a polar orbiting CubeSat whose novel AM radio instrument measures HF and MF waves. The cubesat, which contains also a white light aurora camera, is planned to be launched in 2017 (http://www.suomi100satelliitti.fi/eng). We have modelled the propagation of the radio waves, both ground generated man-made waves and space formed space weather related waves, through the 3D

  15. HF Channel Availability under Ionospheric Disturbances: Model, Method and Measurements as Contributions

    Science.gov (United States)

    Tulunay, E.; Senalp, E. T.; Tulunay, Y.; Warrington, E. M.; Sari, M. O.

    2009-04-01

    A small group at METU has been developing data driven models in order to forecast some critical parameters, which affect the communication and navigation systems, since 1990. The background on the subjects supports new achievements in terms of theoretical and experimental basis contributing the COST 296 WG2 activities. This work mentions the representative contributions. (i) A method has been proposed for the assessment of HF Channel Availability under ionospheric disturbances. Signal to Noise Ratio (SNR), Doppler Spread and Modified Power Delay Spread were considered. The study relates the modem performance to ionospheric disturbances. Ionospheric disturbance was characterised by Disturbance Storm Type (DST) index. Radar data including Effective Multipath Spread, Composite Doppler Spread and SNR values were obtained from the experiment conducted between Leicester UK (52.63° N; 1.08° W) and Uppsala, Sweden (59.92° N; 17.63° E) in the year 2001. First, joint probability density function (PDF) of SNR, Doppler Spread, and Effective Multipath Spread versus DST were considered. It was demonstrated by determining the conditional PDFs, and by using Bayes' Theorem, that there were dependencies between DST and the above mentioned parameters [Sari, 2006]. Thus, it is concluded that the availability of the HF channel is a function of DST. As examples of modem characterizations, Military Standards were considered. Given a magnetic condition, the modem availability was calculated. The model developed represents the ionospheric HF channel, and it is based on a stochastic approach. Depending on the new experimental data, the conditional PDFs could be updated continuously. The HF channel availability under various ionospheric Space Weather (SW) conditions can be determined using the model. The proposed method is general and can include other indices as well. The method can also be applied to a variety of other processes. (ii) The effects of space weather conditions on the

  16. A statistical survey of dayside pulsed ionospheric flows as seen by the CUTLASS Finland HF radar

    Directory of Open Access Journals (Sweden)

    K. A. McWilliams

    Full Text Available Nearly two years of 2-min resolution data and 7- to 21-s resolution data from the CUTLASS Finland HF radar have undergone Fourier analysis in order to study statistically the occurrence rates and repetition frequencies of pulsed ionospheric flows in the noon-sector high-latitude ionosphere. Pulsed ionospheric flow bursts are believed to be the ionospheric footprint of newly reconnected geomagnetic field lines, which occur during episodes of magnetic flux transfer to the terrestrial magnetosphere - flux transfer events or FTEs. The distribution of pulsed ionospheric flows were found to be well grouped in the radar field of view, and to be in the vicinity of the radar signature of the cusp footprint. Two thirds of the pulsed ionospheric flow intervals included in the statistical study occurred when the interplanetary magnetic field had a southward component, supporting the hypothesis that pulsed ionospheric flows are a reconnection-related phenomenon. The occurrence rate of the pulsed ionospheric flow fluctuation period was independent of the radar scan mode. The statistical results obtained from the radar data are compared to occurrence rates and repetition frequencies of FTEs derived from spacecraft data near the magnetopause reconnection region, and to ground-based optical measurements of poleward moving auroral forms. The distributions obtained by the various instruments in different regions of the magnetosphere were remarkably similar. The radar, therefore, appears to give an unbiased sample of magnetopause activity in its routine observations of the cusp footprint.

    Key words: Magnetospheric physics (magnetosphere-ionosphere interactions; plasma convection; solar wind-magnetosphere interactions

  17. A statistical survey of dayside pulsed ionospheric flows as seen by the CUTLASS Finland HF radar

    Directory of Open Access Journals (Sweden)

    K. A. McWilliams

    2000-04-01

    Full Text Available Nearly two years of 2-min resolution data and 7- to 21-s resolution data from the CUTLASS Finland HF radar have undergone Fourier analysis in order to study statistically the occurrence rates and repetition frequencies of pulsed ionospheric flows in the noon-sector high-latitude ionosphere. Pulsed ionospheric flow bursts are believed to be the ionospheric footprint of newly reconnected geomagnetic field lines, which occur during episodes of magnetic flux transfer to the terrestrial magnetosphere - flux transfer events or FTEs. The distribution of pulsed ionospheric flows were found to be well grouped in the radar field of view, and to be in the vicinity of the radar signature of the cusp footprint. Two thirds of the pulsed ionospheric flow intervals included in the statistical study occurred when the interplanetary magnetic field had a southward component, supporting the hypothesis that pulsed ionospheric flows are a reconnection-related phenomenon. The occurrence rate of the pulsed ionospheric flow fluctuation period was independent of the radar scan mode. The statistical results obtained from the radar data are compared to occurrence rates and repetition frequencies of FTEs derived from spacecraft data near the magnetopause reconnection region, and to ground-based optical measurements of poleward moving auroral forms. The distributions obtained by the various instruments in different regions of the magnetosphere were remarkably similar. The radar, therefore, appears to give an unbiased sample of magnetopause activity in its routine observations of the cusp footprint.Key words: Magnetospheric physics (magnetosphere-ionosphere interactions; plasma convection; solar wind-magnetosphere interactions

  18. An MF/HF radio array for radio and radar imaging of the ionosphere

    Science.gov (United States)

    Isham, Brett; Gustavsson, Bjorn; Belyey, Vasyl; Bullett, Terrence

    2016-07-01

    The Aguadilla Radio Array will be installed at the Interamerican University Aguadilla Campus, located in northwestern Puerto Rico. The array is intended for broad-band medium and high-frequency (MF/HF, roughly 2 to 25 MHz) radio and bistatic radar observations of the ionosphere. The main array consists of 20 antenna elements, arranged in a semi-random pattern providing a good distribution of baseline vectors, with 6-meter minimum spacing to eliminate spacial aliasing. A relocatable 6-element array is also being developed, in which each element consists of a crossed pair of active electric dipoles and all associated electronics for phase-coherent radio measurements. A primary scientific goal of the array is to create images of the region of ionospheric radio emissions stimulated by the new Arecibo Observatory high-power high-frequency radio transmitter. A second primary goal is the study of ionospheric structure and dynamics via coherent radar imaging of the ionosphere in collaboration with the University of Colorado / NOAA Versatile Interferometric Pulsed Ionospheric Radar (VIPIR), located at the USGS San Juan Observatory in Cayey, Puerto Rico. In addition to ionospheric research in collaboration with the Cayey and Arecibo Observatories, the goals of the project include the development of radio sounding, polarization, interferometry, and imaging techniques, and training of students at the university and high school levels.

  19. Wavefront Correction of Ionospherically Propagated HF Radio Waves Using Covariance Matching Techniques

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    Y. Zhu

    2017-04-01

    Full Text Available High Frequency (HF radio waves propagating in the ionospheric random inhomogeneous media exhibit a spatial nonlinearity wavefront which may limit the performance of conventional high-resolution methods for HF sky wave radar systems. In this paper, the spatial correlation function of wavefront is theoretically derived on condition that the radio waves propagate through the ionospheric structure containing irregularities. With this function, the influence of wavefront distortions on the array covariance matrix can be quantitatively described with the spatial coherence matrix, which is characterized with the coherence loss parameter. Therefore, the problem of wavefront correction is recast as the determination of coherence loss parameter and this is solved by the covariance matching (CM technique. The effectiveness of the proposed method is evaluated both by the simulated and real radar data. It is shown numerically that an improved direction of arrival (DOA estimation performance can be achieved with the corrected array covariance matrix.

  20. A Cascaded Approach for Correcting Ionospheric Contamination with Large Amplitude in HF Skywave Radars

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    Yajun Li

    2014-01-01

    Full Text Available Ionospheric phase perturbation with large amplitude causes broadening sea clutter’s Bragg peaks to overlap each other; the performance of traditional decontamination methods about filtering Bragg peak is poor, which greatly limits the detection performance of HF skywave radars. In view of the ionospheric phase perturbation with large amplitude, this paper proposes a cascaded approach based on improved S-method to correct the ionospheric phase contamination. This approach consists of two correction steps. At the first step, a time-frequency distribution method based on improved S-method is adopted and an optimal detection method is designed to obtain a coarse ionospheric modulation estimation from the time-frequency distribution. At the second correction step, based on the phase gradient algorithm (PGA is exploited to eliminate the residual contamination. Finally, use the measured data to verify the effectiveness of the method. Simulation results show the time-frequency resolution of this method is high and is not affected by the interference of the cross term; ionospheric phase perturbation with large amplitude can be corrected in low signal-to-noise (SNR; such a cascade correction method has a good effect.

  1. Medium-scale traveling ionospheric disturbances over Taiwan observed with HF Doppler sounding

    Science.gov (United States)

    Fišer, Jiří; Chum, Jaroslav; Liu, Jann-Yenq

    2017-09-01

    We analyzed horizontal velocities of medium-scale traveling ionospheric disturbances using HF Doppler sounding over Taiwan from January 2014 to January 2016. Meridional components of the observed horizontal velocities are in most cases larger than zonal components. In summer, poleward propagation prevails, whereas in winter, disturbances primarily propagate southward. Zonal components of the analyzed events are mostly eastward. Seasonal behaviors of the observed propagation directions are similar at other locations with HF Doppler sounding at middle and low latitudes. Horizontal velocities of the observed events are in the 50-400-ms-1 range. The upper limit is determined using the spacing between reflection points, making the uncertainty in velocity very large for events with velocities larger than this limit. The mean horizontal velocity is 210 ms-1. The range between the 20th and 80th percentile of horizontal velocities is 144-281 ms-1. [Figure not available: see fulltext.

  2. Modelling of optical emissions enhanced by the HF pumping of the ionospheric F-region

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    T. Sergienko

    2012-05-01

    Full Text Available Strong enhancement of the optical emissions with excitation threshold from 1.96 eV (630.0 nm from O(1D up to 18.75 eV (427.8 nm from N2+(1NG have been observed during experiments of the ionosphere modification by high power HF radio waves. Analysis of the optical emission ratios showed clearly that a significant part of the ionospheric electrons have to be accelerated to energies above 30 eV and more in the region where the HF radio wave effectively interacts with the ionospheric plasma. The Monte-Carlo model of electron transport and the optical emission model were used to study the dependence of the optical emission intensity on the acceleration electron parameters. We obtained the following results from analysis of the enhanced intensities of the four optical emissions (630.0, 557.7, 844.6 and 427.8 nm observed in the EISCAT heating experiment on 10 March 2002. The 630.0 emission with an excitation threshold of 1.96 eV is formed predominately by the thermal electrons, where the accelerated electrons play a minor role in the excitation of this emission. In order to explain the experimentally observed intensity ratios, the accelerated electrons must gain energies of more than 60 eV. For accelerated electrons with a power law energy dependence, the efficiency of the optical emission excitation depends on the exponent defining the shape of the electron spectra. However, an agreement with the observed emission intensities is achieved for exponent values not less than zero. Moreover, increasing the exponent to higher values does not affect the emission intensity ratios.

  3. Influence of January 2009 stratospheric warming on HF radio wave propagation in the low-latitude ionosphere

    Science.gov (United States)

    Kotova, Darya; Klimenko, Maksim; Klimenko, Vladimir; Zaharov, Veniamin; Bessarab, Fedor; Korenkov, Yuriy

    2016-12-01

    We have considered the influence of the January 23-27, 2009 sudden stratospheric warming (SSW) event on HF radio wave propagation in the equatorial ionosphere. This event took place during extremely low solar and geomagnetic activity. We use the simulation results obtained with the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) for simulating environmental changes during the SSW event. We both qualitatively and quantitatively reproduced total electron content disturbances obtained from global ground network receiver observations of GPS navigation satellite signals, by setting an additional electric potential and TIME-GCM model output at a height of 80 km. In order to study the influence of this SSW event on HF radio wave propagation and attenuation, we used the numerical model of radio wave propagation based on geometrical optics approximation. It is shown that the sudden stratospheric warming leads to radio signal attenuation and deterioration of radio communication in the daytime equatorial ionosphere.

  4. Generation of ELF waves during HF heating of the ionosphere at midlatitudes

    Science.gov (United States)

    Sharma, A. S.; Eliasson, B.; Shao, X.; Papadopoulos, K.

    2016-07-01

    Modulated high-frequency radio frequency heating of the ionospheric F region produces a local modulation of the electron temperature, and the resulting pressure gradient gives rise to a diamagnetic current. The oscillations of the diamagnetic current excite hydromagnetic waves in the ELF range that propagate away from the heated region. The generation of the waves in the 2-10 Hz range by a modulated heating in the midlatitude ionosphere is studied using numerical simulations of a collisional Hall-magnetohydrodynamic model. To model the plasma processes in the midlatitude ionosphere the Earth's dipole magnetic field and typical ionospheric plasma parameters are used. As the hydromagnetic waves propagate away from the heated region in the F region, the varying plasma conditions lead to changes in their characteristics. Magnetosonic waves generated in the heating region and propagating down to the E region, where the Hall conductivity is dominant, excite oscillating Hall currents that produce shear Alfvén waves propagating along the field lines into the magnetosphere, where they propagate as the electromagnetic ion cyclotron (EMIC) and whistler waves. The EMIC waves propagate to the ion cyclotron resonance layer in the magnetosphere, where they are absorbed.

  5. Investigation into the problem of characterization of the HF ionospheric fluctuating channel of propagation: construction of a physically based HF channel simulator

    Directory of Open Access Journals (Sweden)

    H. J. Strangeways

    2004-06-01

    Full Text Available A wideband HF simulator has been constructed that is based on a detailed physical model. It can generate an output giving a time realization of the HF wideband channel for any HF carrier frequency and bandwidth and for any given transmitter receiver path, time of day, month and year and for any solar activity/geomagnetic conditions. To accomplish this, a comprehensive solution has been obtained to the problem of HF wave propagation for the most general case of a 3D inhomogeneous ionosphere with time-varying electron density fluctuations. The solution is based on the complex phase method (Rytov s method, which has been extended to the case of an inhomogeneous medium and a point source of the field. Results of simulation obtained according to the technique developed have been presented, calculated for a single-hop path 1000 km long oriented to the south from St. Petersburg and including a horizontal electron density gradient present in the IRI model used as the basis of the ionosphere model. The fluctuations of the ionospheric electron density were characterized by an inverse power law anisotropic spatial spectrum. For this model, the random walk of the phasor at the receiver is determined and shown both for paths reflected in the E- and Fregions, being significantly larger for the latter. The oblique sounding ionogram is constructed and reveals three propagation modes: the E-mode and low and high angle F-mode paths. The time-varying field due to each of these paths is then summed at the receiving location enabling the calculation of the scattering function and also the time realization of the received signal shown as a function of both fast and slow time. This is performed both with and without the presence of the geomagnetic field; in the former case the splitting of the F2-mode into both e- and o-modes is seen. It is also shown how the scattering function can be obtained from the time realization of the channel in a way akin to experimental

  6. Global ionospheric effects of geomagnetic storm on May 2-3, 2010 and their influence on HF radio wave propagation

    Science.gov (United States)

    Kotova, Daria; Klimenko, Maxim; Klimenko, Vladimir; Zakharov, Veniamin

    2013-04-01

    In this work we have investigated the global ionospheric response to geomagnetic storm on May 2-3, 2010 using GSM TIP (Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere) simulation results. In the GSM TIP storm time model runs, several input parameters such as cross-polar cap potential difference and R2 FAC (Region 2 Field-Aligned Currents) varied as a function of the geomagnetic activity AE-index. Current simulation also uses the empirical model of high-energy particle precipitation by Zhang and Paxton. In this model, the energy and energy flux of precipitating electrons depend on a 3 hour Kp-index. We also have included the 30 min time delay of R2 FAC variations with respect to the variations of cross-polar cap potential difference. In addition, we use the ground-based ionosonde data for comparison our model results with observations. We present an analysis of the physical mechanisms responsible for the ionospheric effects of geomagnetic storms. The obtained simulation results are used by us as a medium for HF radio wave propagation at different latitudes in quiet conditions, and during main and recovery phase of a geomagnetic storm. To solve the problem of the radio wave propagation we used Zakharov's (I. Kant BFU) model based on geometric optics. In this model the solution of the eikonal equation for each of the two normal modes is reduced using the method of characteristics to the integration of the six ray equation system for the coordinates and momentum. All model equations of this system are solved in spherical geomagnetic coordinate system by the Runge-Kutta method. This model was tested for a plane wave in a parabolic layer. In this study, the complex refractive indices of the ordinary and extraordinary waves at ionospheric heights was calculated for the first time using the global first-principal model of the thermosphere-ionosphere system that describes the parameters of an inhomogeneous anisotropic medium during a

  7. Excitation of Alfvén waves by modulated HF heating of the ionosphere, with application to FAST observations

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    E. Kolesnikova

    Full Text Available During the operation of the EISCAT high power facility (heater at Tromsø, Norway, on 8 October 1998, the FAST spacecraft made electric field and particle observations in the inner magnetosphere at 0.39 Earth radii above the heated ionospheric region. Measurements of the direct current electric field clearly exhibit oscillations with a frequency close to the modulated frequency of heater ( ~ 3 Hz and an amplitude of ~ 2 - 5 mV m-1. Thermal electron data from the electrostatic analyser show the modulation at the same frequency of the downward electron fluxes. During this period the EISCAT UHF incoherent scatter radar, sited also at Tromsø, measured a significant enhancement of the electron density in E-layer up to 2 · 1012 m-3. These observations have prompted us to make quantitative estimates of the expected pulsations in the inner magnetosphere caused by the modulated HF heating of lower ionosphere. Under the conditions of the strong electron precipitation in the ionosphere, which took place during the FAST observations, the primary current caused by the perturbation of the conductivity in the heated region is closed entirely by the parallel current which leaks into the magnetosphere. In such circumstances the conditions at the ionosphere-magnetosphere boundary are most favourable for the launching of an Alfvén wave: it is launched from the node in the gradient of the scalar potential which is proportional to the parallel current. The parallel electric field of the Alfvén wave is significant in the region where the electron inertial length is of order of the transverse wavelength of the Alfvén wave or larger and may effectively accelerate superthermal electrons downward into the ionosphere.

    Key words. Ionosphere (active experiments; ionosphere – magnetosphere interactions; particle acceleration

  8. Excitation of Alfvén waves by modulated HF heating of the ionosphere, with application to FAST observations

    Directory of Open Access Journals (Sweden)

    E. Kolesnikova

    2002-01-01

    Full Text Available During the operation of the EISCAT high power facility (heater at Tromsø, Norway, on 8 October 1998, the FAST spacecraft made electric field and particle observations in the inner magnetosphere at 0.39 Earth radii above the heated ionospheric region. Measurements of the direct current electric field clearly exhibit oscillations with a frequency close to the modulated frequency of heater ( ~ 3 Hz and an amplitude of ~ 2 - 5 mV m-1. Thermal electron data from the electrostatic analyser show the modulation at the same frequency of the downward electron fluxes. During this period the EISCAT UHF incoherent scatter radar, sited also at Tromsø, measured a significant enhancement of the electron density in E-layer up to 2 · 1012 m-3. These observations have prompted us to make quantitative estimates of the expected pulsations in the inner magnetosphere caused by the modulated HF heating of lower ionosphere. Under the conditions of the strong electron precipitation in the ionosphere, which took place during the FAST observations, the primary current caused by the perturbation of the conductivity in the heated region is closed entirely by the parallel current which leaks into the magnetosphere. In such circumstances the conditions at the ionosphere-magnetosphere boundary are most favourable for the launching of an Alfvén wave: it is launched from the node in the gradient of the scalar potential which is proportional to the parallel current. The parallel electric field of the Alfvén wave is significant in the region where the electron inertial length is of order of the transverse wavelength of the Alfvén wave or larger and may effectively accelerate superthermal electrons downward into the ionosphere.Key words. Ionosphere (active experiments; ionosphere – magnetosphere interactions; particle acceleration

  9. Upper atmospheric effects of the hf active auroral research program ionospheric research instrument (HAARP IRI)

    Energy Technology Data Exchange (ETDEWEB)

    Eccles, V.; Armstrong, R.

    1993-05-01

    The earth's ozone layer occurs in the stratosphere, primarily between 10 and 30 miles altitude. The amount of ozone, O3, present is the result of a balance between production and destruction processes. Experiments have shown that natural processes such as auroras create molecules that destroy O. One family of such molecules is called odd nitrogen of which nitric oxide (NO) is an example. Because the HAARP (HF Active Auroral Research Program) facility is designed to mimic and investigate certain natural processes, a study of possible effects of HAARP on the ozone layer was conducted. The study used a detailed model of the thermal and chemical effects of the high power HF beam, which interacts with free electrons in the upper atmosphere above 50 miles altitude. It was found only a small fraction of the beam energy goes into the production of odd nitrogen molecules, whereas odd nitrogen is efficiently produced by auroras. Since the total energy emitted by HAARP in the year is some 200,000 times less than the energy deposited in the upper atmosphere by auroras, the study demonstrates that HAARP HF beam experiments will cause no measurable depletion of the earth's ozone layer.... Ozone, Ozone depletion, Ozone layer, Odd nitrogen, Nitric oxide, HAARP Emitter characteristics.

  10. Observations by the CUTLASS radar, HF Doppler, oblique ionospheric sounding, and TEC from GPS during a magnetic storm

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    D. V. Blagoveshchensky

    2005-07-01

    Full Text Available Multi-diagnostic observations, covering a significant area of northwest Europe, were made during the magnetic storm interval (28–29 April 2001 that occurred during the High Rate SolarMax IGS/GPS-campaign. HF radio observations were made with vertical sounders (St. Petersburg and Sodankyla, oblique incidence sounders (OIS, on paths from Murmansk to St. Petersburg, 1050 km, and Inskip to Leicester, 170 km, Doppler sounders, on paths from Cyprus to St. Petersburg, 2800 km, and Murmansk to St. Petersburg, and a coherent scatter radar (CUTLASS, Hankasalmi, Finland. These, together with total electron content (TEC measurements made at GPS stations from the Euref network in northwest Europe, are presented in this paper. A broad comparison of radio propagation data with ionospheric data at high and mid latitudes, under quiet and disturbed conditions, was undertaken. This analysis, together with a geophysical interpretation, allow us to better understand the nature of the ionospheric processes which occur during geomagnetic storms. The peculiarity of the storm was that it comprised of three individual substorms, the first of which appears to have been triggered by a compression of the magnetosphere. Besides the storm effects, we have also studied substorm effects in the observations separately, providing an improved understanding of the storm/substorm relationship. The main results of the investigations are the following. A narrow trough is formed some 10h after the storm onset in the TEC which is most likely a result of enhanced ionospheric convection. An enhancement in TEC some 2–3 h after the storm onset is most likely a result of heating and upwelling of the auroral ionosphere caused by enhanced currents. The so-called main effect on ionospheric propagation was observed at mid-latitudes during the first two substorms, but only during the first substorm at high latitudes. Ionospheric irregularities observed by CUTLASS were clearly related to the

  11. Influence of geomagnetic storms of September 26-30, 2011, on the ionosphere and HF radiowave propagation. II. radiowave propagation

    Science.gov (United States)

    Kotova, D. S.; Klimenko, M. V.; Klimenko, V. V.; Zakharov, V. E.

    2017-05-01

    A study of HF wave propagation in the three-dimensional inhomogeneous ionosphere has been carried out in an approximation of geometrical optics. The three-dimensional medium of radio wave propagation is considered to be inhomogeneous, absorbing, and anisotropic due to the influence of the geomagnetic field. The parameters of the medium are described by the results of calculations on the basis of the Global Self-Consistent Model of the Thermosphere, Ionosphere, and Protonosphere (GSM TIP). The propagation of radio waves in the equatorial, middle-, and high-latitude ionosphere was studied. Comparisons of the ray trajectories, integral attenuation, deviations of the projection of radio wave trajectories onto the Earth's surface from the great-circle arc, and the behavior of the angle between the wave phase and wave energy directions, as well as the angle between the direction of propagation and the external magnetic field obtained for quiet and disturbed conditions, have been performed. We consider a geomagnetic storm that occurred in 2011, with the main storm phase occurring on September 26, and the day after geomagnetic disturbances, September 29, as disturbed conditions in the ionosphere.

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

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    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.

  13. Generation of the Super Small-Scale Artificial Ionospheric Irregularities in the Ionosphere Pumped by High-Power HF Radio Waves

    Science.gov (United States)

    Frolov, V. L.; Bolotin, I. A.; Vertogradov, G. G.; Vertogradov, V. G.

    2017-11-01

    We present the results of experimental studies of generation of super small-scale plasma-density irregularities in the ionospheric F2 region pumped by a high-power HF O-mode wave at frequencies close to the fourth gyroharmonic in the region of its interaction with the plasma. The experiments were performed using the Sura heating facility. The super small-scale irregularities were sounded by GPS satellite signals. It has been shown that super small-scale irregularities are excited with the most efficiency in the region of the magnetic zenith for the pump wave. The intensity of such irregularities and typical times of their development and decay are determined.

  14. A Statistical study of the Doppler spectral width of high-latitude ionospheric F-region echoes recorded with SuperDARN coherent HF radars

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    J.-P. Villain

    2002-11-01

    Full Text Available The HF radars of the Super Dual Auroral Radar Network (SuperDARN provide measurements of the E × B drift of ionospheric plasma over extended regions of the high-latitude ionosphere. We have conducted a statistical study of the associated Doppler spectral width of ionospheric F-region echoes. The study has been conducted with all available radars from the Northern Hemisphere for 2 specific periods of time. Period 1 corresponds to the winter months of 1994, while period 2 covers October 1996 to March 1997. The distributions of data points and average spectral width are presented as a function of Magnetic Latitude and Magnetic Local Time. The databases are very consistent and exhibit the same features. The most stringent features are: a region of very high spectral width, collocated with the ionospheric LLBL/cusp/mantle region; an oval shaped region of high spectral width, whose equator-ward boundary matches the poleward limit of the Holzworth and Meng auroral oval. A simulation has been conducted to evaluate the geometrical and instrumental effects on the spectral width. It shows that these effects cannot account for the observed spectral features. It is then concluded that these specific spectral width characteristics are the signature of ionospheric/magnetospheric coupling phenomena.Key words. Ionosphere (auroral ionosphere; ionosphere-magnetosphere interactions; ionospheric irregularities

  15. A Statistical study of the Doppler spectral width of high-latitude ionospheric F-region echoes recorded with SuperDARN coherent HF radars

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    J.-P. Villain

    Full Text Available The HF radars of the Super Dual Auroral Radar Network (SuperDARN provide measurements of the E × B drift of ionospheric plasma over extended regions of the high-latitude ionosphere. We have conducted a statistical study of the associated Doppler spectral width of ionospheric F-region echoes. The study has been conducted with all available radars from the Northern Hemisphere for 2 specific periods of time. Period 1 corresponds to the winter months of 1994, while period 2 covers October 1996 to March 1997. The distributions of data points and average spectral width are presented as a function of Magnetic Latitude and Magnetic Local Time. The databases are very consistent and exhibit the same features. The most stringent features are: a region of very high spectral width, collocated with the ionospheric LLBL/cusp/mantle region; an oval shaped region of high spectral width, whose equator-ward boundary matches the poleward limit of the Holzworth and Meng auroral oval. A simulation has been conducted to evaluate the geometrical and instrumental effects on the spectral width. It shows that these effects cannot account for the observed spectral features. It is then concluded that these specific spectral width characteristics are the signature of ionospheric/magnetospheric coupling phenomena.

    Key words. Ionosphere (auroral ionosphere; ionosphere-magnetosphere interactions; ionospheric irregularities

  16. An Ionospheric Es Layer Clutter Model and Suppression in HF Surfacewave Radar

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    Yajun Li

    2013-01-01

    Full Text Available This paper based on a fast implemented multiphase screen method using DFT puts forward an ionospheric Es layer clutter model and uses the newly developed dimensionality reduction space-time adaptive processing- (STAP- JDL algorithm to suppress Es layer clutter, which proves the validity of the proposed model. Firstly, the multiphase screen method was analyzed, and a fast algorithm using DFT was proposed. Then, based on the multiphase screen method and thorough simulation, we reached a conclusion of the high-frequency radio wave propagation’s fluctuation characteristics in the ionosphere. According to the results of the analysis, a new Es layer ionospheric clutter model was established and was compared with the measured data and verification was made. Finally, based on the built clutter model, JDL algorithm was applied to the high-frequency surface wave radar ionospheric clutter suppression, using the measured data to verify the validity of the model and algorithm. The simulation results showed that the built model can show the characteristics of the ionospheric Es layer clutter and that the JDL algorithm can suppress ionospheric Es layer clutter quite effectively.

  17. On the Electric Fields Produced by Dipolar Coulomb Charges of an Individual Thundercloud in the Ionosphere

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    Vitaly P. Kim

    2015-06-01

    Full Text Available In this paper we study the transmission of the electrostatic field due to coulomb charges of an individual thundercloud into the midlatitude ionosphere, taking into account the total geomagnetic field integrated Pedersen conductivity of the ionosphere. It is shown that at ionospheric altitudes, a typical thundercloud produces an insignificant electrostatic field whereas a giant thundercloud can drive the horizontal electrostatic field with a magnitude of ~270 μV/m for nighttime conditions.

  18. X-mode HF Pump-induced Phenomena at High Heater Frequencies in the High Latitude Ionosphere F-region

    Science.gov (United States)

    Blagoveshchenskaya, N. F.; Borisova, T. D.; Kalishin, A. S.; Yeoman, T. K.; Häggström, I.

    2015-12-01

    Experimental results concentrating on X-mode HF-induced phenomena in the high latitude ionosphere F region are discussed. Experiments have been carried out at the HF Heating facility at Tromsø with an effective radiated power of 450 - 650 MW at high heater frequencies of 6.2 - 8.0 MHz. Multi-instriment diagnostics included the European Incoherent Scatter (EISCAT) UHF radar at 931 MHz at Tromsø, the Finland CUTLASS (Co-operative UK Twin Located Auroral Sounding System) radar, the stimulated electromagnetic emission (SEE) equipment at Tromsø, and the HF receiver near St. Petersburg for the observations of narrow band SEE features. The key parameter considered is the ratio between the heater frequency and critical frequency of the F2 layer (fH/foF2). We have analyzed the behaviors of small-scale artificial field-aligned irregularities (FAIs) and HF-enhanced plasma and ion lines (HFPLs and HFILs) depending on the pump proximity to the critical frequency. It was shown that the HFPLs and HFILs coexisted with FAIs throughout the whole heater pulse when fH/foF2 > 1 as well as fH/foF2 ≤ 1. It is indicative that parametric decay instability was not quenched by fully developed FAIs. The comparison between contrasting O/X mode HF-induced phenomena, when the heater frequency is below or near the critical frequency of F2 layer, is made. It was found that an X-mode HF pumping is able to excite different narrow band spectral components in the SEE spectra (within 1 kHz of pump frequency), such as ion acoustic, electrostatic ion cyclotron, and electrostatic ion cyclotron harmonic waves (otherwise known as neutralized ion Bernstein waves) observed at a long distance from the HF Heating facility. It was suggested that these spectral component can be attributed to the stimulated Brillion scatter (SBS) process. The results obtained show that an X-polarized electromagnetic wave scattered by SBS can propagate more than one thousand km without significant attenuation.

  19. The relationship between small-scale and large-scale ionospheric electron density irregularities generated by powerful HF electromagnetic waves at high latitudes

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    E. D. Tereshchenko

    2006-11-01

    Full Text Available Satellite radio beacons were used in June 2001 to probe the ionosphere modified by a radio beam produced by the EISCAT high-power, high-frequency (HF transmitter located near Tromsø (Norway. Amplitude scintillations and variations of the phase of 150- and 400-MHz signals from Russian navigational satellites passing over the modified region were observed at three receiver sites. In several papers it has been stressed that in the polar ionosphere the thermal self-focusing on striations during ionospheric modification is the main mechanism resulting in the formation of large-scale (hundreds of meters to kilometers nonlinear structures aligned along the geomagnetic field (magnetic zenith effect. It has also been claimed that the maximum effects caused by small-scale (tens of meters irregularities detected in satellite signals are also observed in the direction parallel to the magnetic field. Contrary to those studies, the present paper shows that the maximum in amplitude scintillations does not correspond strictly to the magnetic zenith direction because high latitude drifts typically cause a considerable anisotropy of small-scale irregularities in a plane perpendicular to the geomagnetic field resulting in a deviation of the amplitude-scintillation peak relative to the minimum angle between the line-of-sight to the satellite and direction of the geomagnetic field lines. The variance of the logarithmic relative amplitude fluctuations is considered here, which is a useful quantity in such studies. The experimental values of the variance are compared with model calculations and good agreement has been found. It is also shown from the experimental data that in most of the satellite passes a variance maximum occurs at a minimum in the phase fluctuations indicating that the artificial excitation of large-scale irregularities is minimum when the excitation of small-scale irregularities is maximum.

  20. ELF wave generation in the ionosphere using pulse modulated HF heating: initial tests of a technique for increasing ELF wave generation efficiency

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    R. Barr

    1999-06-01

    Full Text Available This paper describes the results of a preliminary study to determine the effective heating and cooling time constants of ionospheric currents in a simulated modulated HF heating, `beam painting' configuration. It has been found that even and odd harmonics of the fundamental ELF wave used to amplitude modulate the HF heater are sourced from different regions of the ionosphere which support significantly different heating and cooling time constants. The fundamental frequency and its odd harmonics are sourced in a region of the ionosphere where the heating and cooling time constants are about equal. The even harmonics on the other hand are sourced from regions of the ionosphere characterised by ratios of cooling to heating time constant greater than ten. It is thought that the even harmonics are sourced in the lower ionosphere (around 65 km where the currents are much smaller than at the higher altitudes around 78 km where the currents at the fundamental frequency and odd harmonics maximise.Key words. Electromagnetics (antennae · Ionosphere (active experiments · Radio science (non linear phenomena

  1. Turbulence characteristics inside ionospheric small-scale expanding structures observed with SuperDARN HF radars

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    R. André

    2003-08-01

    Full Text Available Unusual structures characterized by a very high-velocity divergence have been observed in the high-latitude F-region with SuperDARN radars (André et al., 2000. These structures have been interpreted as due to local demagnetization of the plasma in the ionospheric F-region, during very specific geophysical conditions. In this study, the collective wave scattering theory is used to characterize the decameter-scale turbulence (l approx 15 m inside the structures. The distribution function of the diffusion coefficient is modified when the structures are generated, suggesting that two regimes of turbulence coexist. A temporal analysis decorrelates the two regimes and gives access to the dynamics associated with the structures. It is shown that a high turbulent regime precedes the plasma demagnetization and should be related to an energy deposition. Then a second regime appears when the plasma is demagnetized and disappears simultaneously with the structures. This study is the first application of the collective wave scattering theory to a specific geophysical event.Key words. Ionosphere (auroral ionosphere; ionospheric irregularities – Space plasma physics (turbulence

  2. HF radar detection of infrasonic waves generated in the ionosphere by the 28 March 2005 Sumatra earthquake

    Science.gov (United States)

    Bourdillon, Alain; Occhipinti, Giovanni; Molinié, Jean-Philippe; Rannou, Véronique

    2014-03-01

    Surface waves generated by earthquakes create atmospheric waves detectable in the ionosphere using radio waves techniques: i.e., HF Doppler sounding, GPS and altimeter TEC measurements, as well as radar measurements. We present observations performed with the over-the-horizon (OTH) radar NOSTRADAMUS after the very strong earthquake (M=8.6) that occurred in Sumatra on March 28, 2005. An original method based on the analysis of the RTD (Range-Time-Doppler) image is suggested to identify the multi-chromatic ionospheric signature of the Rayleigh wave. The proposed method presents the advantage to preserve the information on the range variation and time evolution, and provides comprehensive results, as well as easy identification of the waves. In essence, a Burg algorithm of order 1 is proposed to compute the Doppler shift of the radar signal, resulting in sensitivity as good as obtained with higher orders. The multi-chromatic observation of the ionospheric signature of Rayleigh wave allows to extrapolate information coherent with the dispersion curve of Rayleigh waves, that is, we observe two components of the Rayleigh waves with estimated group velocities of 3.8 km/s and 3.6 km/s associated to 28 mHz (T~36 s) and 6.1 mHz (T~164 s) waves, respectively. Spectral analysis of the RTD image reveals anyway the presence of several oscillations at frequencies between 3 and 8 mHz clearly associated to the transfer of energy from the solid-Earth to the atmosphere, and nominally described by the normal modes theory for a complete planet with atmosphere. Oscillations at frequencies larger than 8 mHz are also observed in the spectrum but with smaller amplitudes. Particular attention is pointed out to normal modes 0S29 and 0S37 which are strongly involved in the coupling process. As the proposed method is frequency free, it could be used not only for detection of ionospheric perturbations induced by earthquakes, but also by other natural phenomena as well as volcanic explosions and

  3. Mapping ionospheric backscatter measured by the SuperDARN HF radars – Part 2: Assessing SuperDARN virtual height models

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    T. K. Yeoman

    2008-05-01

    Full Text Available The Super Dual Auroral Radar Network (SuperDARN network of HF coherent backscatter radars form a unique global diagnostic of large-scale ionospheric and magnetospheric dynamics in the Northern and Southern Hemispheres. Currently the ground projections of the HF radar returns are routinely determined by a simple rangefinding algorithm, which takes no account of the prevailing, or indeed the average, HF propagation conditions. This is in spite of the fact that both direct E- and F-region backscatter and 1½-hop E- and F-region backscatter are commonly used in geophysical interpretation of the data. In a companion paper, Chisham et al. (2008 have suggested a new virtual height model for SuperDARN, based on average measured propagation paths. Over shorter propagation paths the existing rangefinding algorithm is adequate, but mapping errors become significant for longer paths where the roundness of the Earth becomes important, and a correct assumption of virtual height becomes more difficult. The SuperDARN radar at Hankasalmi has a propagation path to high power HF ionospheric modification facilities at both Tromsø on a ½-hop path and SPEAR on a 1½-hop path. The SuperDARN radar at Þykkvibǽr has propagation paths to both facilities over 1½-hop paths. These paths provide an opportunity to quantitatively test the available SuperDARN virtual height models. It is also possible to use HF radar backscatter which has been artificially induced by the ionospheric heaters as an accurate calibration point for the Hankasalmi elevation angle of arrival data, providing a range correction algorithm for the SuperDARN radars which directly uses elevation angle. These developments enable the accurate mappings of the SuperDARN electric field measurements which are required for the growing number of multi-instrument studies of the Earth's ionosphere and magnetosphere.

  4. Modification of the high latitude ionosphere F region by X-mode powerful HF radio waves: Experimental results from multi-instrument diagnostics

    Science.gov (United States)

    Blagoveshchenskaya, N. F.; Borisova, T. D.; Yeoman, T. K.; Häggström, I.; Kalishin, A. S.

    2015-12-01

    We present experimental results concentrating on a variety of phenomena in the high latitude ionosphere F2 layer induced by an extraordinary (X-mode) HF pump wave at high heater frequencies (fH=6.2-8.0 MHz), depending on the pump frequency proximity to the ordinary and extraordinary mode critical frequencies, foF2 and fxF2. The experiments were carried out at the EISCAT HF heating facility with an effective radiated power of 450-650 MW in October 2012 and October-November 2013. Their distinctive feature is a wide diapason of critical frequency changes, when the fH/foF2 ratio was varied through a wide range from 0.9 to 1.35. It provides both a proper comparison of X-mode HF-induced phenomena excited under different ratios of fH/foF2 and an estimation of the frequency range above foF2 in which such X-mode phenomena are still possible. It was shown that the HF-enhanced ion and plasma lines are excited above foF2 when the HF pump frequency is lying in range between the foF2 and fxF2, foF2≤fH≤fxF2, whereas small-scale field-aligned irregularities continued to be generated even when fH exceeded fxF2 by up to 1 MHz and an X-polarized pump wave cannot be reflected from the ionosphere. Another parameter of importance is the magnetic zenith effect (HF beam/radar angle direction) which is typical for X-mode phenomena under fH/foF2 >1 as well as fH/foF2 ≤1. We have shown for the first time that an X-mode HF pump wave is able to generate strong narrowband spectral components in the SEE spectra (within 1 kHz of pump frequency) in the ionosphere F region, which were recorded at distance of 1200 km from the HF heating facility. The observed spectral lines can be associated with the ion acoustic, electrostatic ion cyclotron, and electrostatic ion cyclotron harmonic waves (otherwise known as neutralized ion Bernstein waves). The comparison between the O- and X-mode SEE spectra recorded at distance far from HF heating facility clearly demonstrated that variety of the narrowband

  5. Mapping ionospheric backscatter measured by the SuperDARN HF radars – Part 1: A new empirical virtual height model

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    G. Chisham

    2008-05-01

    Full Text Available Accurately mapping the location of ionospheric backscatter targets (density irregularities identified by the Super Dual Auroral Radar Network (SuperDARN HF radars can be a major problem, particularly at far ranges for which the radio propagation paths are longer and more uncertain. Assessing and increasing the accuracy of the mapping of scattering locations is crucial for the measurement of two-dimensional velocity structures on the small and meso-scale, for which overlapping velocity measurements from two radars need to be combined, and for studies in which SuperDARN data are used in conjunction with measurements from other instruments. The co-ordinates of scattering locations are presently estimated using a combination of the measured range and a model virtual height, assuming a straight line virtual propagation path. By studying elevation angle of arrival information of backscatterred signals from 5 years of data (1997–2001 from the Saskatoon SuperDARN radar we have determined the actual distribution of the backscatter target locations in range-virtual height space. This has allowed the derivation of a new empirical virtual height model that allows for a more accurate mapping of the locations of backscatter targets.

  6. Methane Group Ions Produced by Titan's Exosphere and Ionosphere

    Science.gov (United States)

    Sittler, Edward; Hartle, Richard; Simpson, David; Sarantos, Menelaos; Cooper, John; Ali, Ashraf; Lipatov, Alexander

    2014-05-01

    We will be presenting results of methane ions that can be injected into Saturn's magnetosphere as pick up ions from Titan's exosphere and outflowing methonium ions CH5+, the HCNH+ ion and the ethenium ions C2H5+ from Titan's ionosphere. Ionospheric outflows have been seen during the T9 flyby (Sittler et al., 2010), and the T63 and T75 flybys (Coates et al., 2012) where source rates to magnetosphere can be significant ~ 4.0x1024 ions/s. When methane pickup ions are born within Titan's exosphere and convective electric field points outward these ions will populate Saturn's magnetosphere, while inward convective electric field (Saturn side for dipolar magnetospheric fields) will heat the upper atmosphere and exosphere. Using 1D exosphere Westlake et al. (2011) found that the exosphere was hotter and more extended when Titan was within Saturn's sheet, while in lobe like regions of magnetosphere the exosphere is cooler. Using a 3D exosphere model, which can include winds and asymmetric heating at exobase to model methane pickup ion densities; we estimate that when within Saturn's sheet the exobase T ~ 190° K and the estimated density is ~ 2x10-3 ions/cm3 which are observable, while in lobe like regions exosphere T ~ 110° K and densities ~ 10-6 ions/cm3 not observable. The heating from methane pickup ions can be complex depending upon magnetic field geometry, dipolar (heating on Saturn side) and disc geometry (below sheet north polar heating and above sheet south polar heating). This CH4+ pickup ion density difference we estimate can be used by the CAPS ion instruments to determine if the magnetosphere is in the sheet (also plasma sheet usually dominated by water group ions with O+ ions) or lobe state (light ions H+/H2+ dominating the composition). We find CH4+ pickup ions for T36 and T39 flybs when Titan is within Saturn's magntospheric sheet, while during T41 when within lobe regions of Saturn's magnetosphere CH4+ pickup ions were not observed. But for T41 the

  7. Equatorial ionospheric irregularities produced by the Brazilian ionospheric modification experiment (BIME)

    Energy Technology Data Exchange (ETDEWEB)

    Klobuchar, J.A.; Abdu, M.A.

    1989-03-01

    On two separate evenings in September 1982, rockets were launched into the bottomside equatorial F2 region off the coast of Natal, Brazil, to inject chemicals, consisting of mainly H2O and CO2, to create a hole in ionization. The chemicals were injected near the height where the density gradient was steepest, and at a time when the F2 region was rising rapidly, to see whether plasma bubble irregularities could be generated from instabilities triggered by the ionization hole. The eastward drifts of these artificial depletions were observed by the time difference in the TEC features observed at various TEC monitoring stations, and from the changing range of oblique ionosonde echoes observed by an ionosonde located 300 km magnetically east of the chemical release point. Their subsequent evolution into plasma bubble irregularities was demonstrated from the observations of spread F echoes, strong-amplitude scintillation, and TEC depletion at distances of from 300 to 500 km eastward of the release points. The fact that similar behavior of the ionosphere was observed during the evenings of both rocket chemical releases, and on no other nights of the campaign, is strong evidence of successful artificial generation of bubble irregularities by chemical injection into the bottomside F2 region.

  8. Equatorial ionospheric irregularities produced by the Brazilian ionospheric modification experiment (BIME)

    Energy Technology Data Exchange (ETDEWEB)

    Klobuchar, J.A. (Air Force Geophysics Lab., Hanscom Air Force Base, MA (USA)); Abdu, M.A. (Instituto de Pesquisas Espaciais, Sao Jose dos Campos (Brazil))

    1989-03-01

    On two separate evenings in September 1982, rockets were launched into the bottomside equatorial F{sub 2} region off the coast of Natal, Brazil, to inject chemicals, consisting of mainly H{sub 2}O and CO{sub 2}, to create a hole in ionization. The chemicals were injected near the height where the density gradient was steepest, and at a time when the F{sub 2} region was rising rapidly to see whether plasma bubble irregularities could be generated from instabilities triggered by the ionization hole. On both occasions, hole-induced depletions in total electron content (TEC) of more than 10{sup 16} el/m{sup 2} were observed over horizontal distances of at least 60 km from the chemical injection point. The eastward drifts of these artificial depletions were observed by the time difference in the TEC features observed at various TEC monitoring stations, and from the changing range of oblique ionosonde echoes observed by an ionosonde located 300 km magnetically east of the chemical release point. Their subsequent evolution into plasma bubble irregularities was demonstrated from the observations of spread F echoes, strong amplitude scintillation, and TEC depletion at distances of from 300 to 500 km eastward of the release points. The fact that similar behavior of the ionosphere was observed during the evenings of both rocket chemical releases, and on no other nights of the campaign, is strong evidence of successful artificial generation of bubble irregularities by chemical injection into the bottomside F{sub 2} region.

  9. Far-Field Testing Method of Spurious Emission Produced by HF RFID

    Directory of Open Access Journals (Sweden)

    Nikola Gvozdenovic

    2016-01-01

    Full Text Available We present measurements of spurious emission produced by high-frequency radio frequency identification (HF RFID using carrier frequency of 13.56 MHz. HF RFID tags produce unwanted emission due to rectification and more generally due to nonlinearity of analog front end. Depending on the conducting material of an HF RFID coil and surrounding dielectric material, the coil behaves as more or less good antenna on some harmonic frequencies. Exact characterization and analysis of unwanted emission is important from the security perspective as well as from the perspective of interference with other systems. Consequently we measured the harmonics produced in the integrated circuitry and characterized radiation properties of the antenna. Finally we present the measurements of the spurious emission performed in a Gigahertz Transverse Electromagnetic (GTEM cell.

  10. Application of the IRI model to the HF propagation model with optimization of the ionosphere parameters to day-to-day variation

    Science.gov (United States)

    Zaalov, N. Y.; Moskaleva, E. V.; Burmakina, T. S.

    2017-11-01

    The HF propagation model, North Ionospheric Model and Ray Tracing (NIM-RT) was developed and tested for a number of years by comparing measured vertical and oblique ionograms over a number of radio links (especially in high latitude area) with the simulated ionograms. The present paper extends the model in order to include: Implementation of the data retrieved from the International Reference Ionosphere (IRI-2012) model into the software for radio channel modeling. The algorithm for IRI data optimization to the real time condition. Results of comparison between simulated and measured ionograms. Based on these updates, a new software tool called North Ionospheric Model with IRI and Ray Tracing (NIMIRI-RT) was developed, and a number of vertical ionograms corresponding to multiple ionospheric reflections was simulated. The vertical ionograms observed at various ionosondes were compared with the synthesized ionograms, generated by applying NIM-RT in conjunction with initial and optimized IRI data. The ionogram structure simulated by NIMIRI-RT based on the data retrieved from optimized IRI is more reminiscent to the observations than ionograms synthesized with the initial NIMIRI-RT without parameters optimization.

  11. Ionosphere Waves Service (IWS – a problem-oriented tool in ionosphere and Space Weather research produced by POPDAT project

    Directory of Open Access Journals (Sweden)

    Ferencz Csaba

    2014-05-01

    Full Text Available 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 on wave processes that take place in the ionosphere? The answer is a specific and unique data mining service accessing a collection of topical catalogs that characterize a huge number of recorded occurrences of Whistler-like Electromagnetic Wave Phenomena, Atmosphere Gravity Waves, and Traveling Ionosphere Disturbances. IWS online service (http://popdat.cbk.waw.pl offers end users to query optional set of predefined wave phenomena, their detailed characteristics. These were collected by target specific event detection algorithms in selected satellite records during database buildup phase. Result of performed wave processing thus represents useful information on statistical or comparative investigations of wave types, listed in a detailed catalog of ionospheric wave phenomena. The IWS provides wave event characteristics, extracted by specific software systems from data records of the selected satellite missions. The end-user can access targets by making specific searches and use statistical modules within the service in their field of interest. Therefore the IWS opens a new way in ionosphere and Space Weather research. The scientific applications covered by IWS concern beyond Space Weather also other fields like earthquake precursors, ionosphere climatology, geomagnetic storms, troposphere-ionosphere energy transfer, and trans-ionosphere link perturbations.

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

    Directory of Open Access Journals (Sweden)

    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.

  13. How to Recognize and Distinguish Low-Latitude Ionospheric Storms Disturbances Produced by TIDs or PPEFs During Geomagnetic Storms

    Science.gov (United States)

    Fagundes, P. R.; Ribeiro, B. A.; Kavutarapu, V.; Fejer, B. G.; Pillat, V. G.

    2016-12-01

    The effects of geomagnetic storms on ionosphere are one of the important aspects of the space weather and identifying the possible sources of these perturbations is important. Among the possible sources of ionospheric perturbations, the Travelling Ionospheric Disturbance (TID) and Prompt Penetration Electric Field (PPEF) are the most important. In this study, we present and discuss the ionospheric response in the Brazilian sector due to geomagnetic storms occurred during January 2013 and March 2015. These space weather events were investigated using a network of 100 GPS-TEC stations. It has been noticed that the VTEC was disturbed during main phase in both storms. During the first event (January), a positive ionospheric storm peak in TEC is observed first beyond the EIA crest and sometime later at low-latitude and equatorial region. This delayed response at different latitudes could be a signature of TID propagation. In this specific event a TID propagating to northwest direction with a velocity of about 200 m/s. However, during the second event (March), 3 positive ionospheric storm peaks were observed in the VTEC from equator to low latitudes during the storm main phase, but these 3 peaks do not present wave propagation characteristics. Probably, an eastward electric field penetrated at equatorial and low-latitude regions uplifts the F-region where the recombination rates are lower leading to a positive ionospheric storm. To distinguish if the positive ionospheric storm was produced by TID or PPEF, it is important to observe the positive ionospheric storm changes along the meridional direction. In case of TIDs, a meridional propagation of the disturbance wave with a phase and speed will be observed. Therefore, the perturbation occurs first beyond the EIA crest and sometime later at the low latitudes and finally at the equatorial region. In case of PPEF the positive ionospheric storm takes place almost simultaneously from beyond the EIA crest to equatorial region.

  14. Impact of a Strong Magnetic Storm and Two X-Ray Flares on the Ionospheric HF Channel in the Summer Solstice of 2015 According to Oblique Sounding in the Eurasian Region

    Science.gov (United States)

    Uryadov, V. P.; Kolchev, A. A.; Vertogradov, G. G.; Vybornov, F. I.; Egoshin, I. A.; Sklyarevsky, M. S.; Shumaev, V. V.; Chernov, A. G.

    2017-10-01

    We present the results of observations of the impact a strong magnetic storm and two X-ray flares in the summer solstice of 2015 on the HF signal characteristics during oblique sounding of the ionosphere in the Eurasian region. It was found that the negative phase of the magnetic storm led to a strong degradation of the ionospheric channel, up to a long blackout on the paths adjacent to the subauroral latitudes. On the midlatitude paths, a decrease in the maximum observable frequency of the F layer reached 50% with respect to the average values for an undisturbed ionosphere. The propagation velocity of the negative phase of a disturbance from the subauroral to the midlatitude ionosphere is determined (it is equal to about 100 m/s). It is shown that during a magnetic storm the least observable frequency and the average signal-to-noise ratio for the propagation mode via the sporadic E s layer correlate well with the auroral AE index. Anomalous signals were detected in the main phase of the magnetic storm on the Cyprus—Rostov-on-Don path when a chirp ionosonde-radio direction finder was operated in the over-the-horizon HF radar mode. On the basis of modeling and comparison with experimental data, it is shown that the anomalous signals are due to scattering of radio waves by small-scale irregularities located in the subauroral ionospheric F region.

  15. Determination of the electron temperature in the modified ionosphere over HAARP using the HF pumped Stimulated Brillouin Scatter (SBS emission lines

    Directory of Open Access Journals (Sweden)

    P. A. Bernhardt

    2009-12-01

    Full Text Available An ordinary mode electromagnetic wave can decay into an ion acoustic wave and a scattered electromagnetic wave by a process called stimulated Brillouin scatter (SBS. The first detection of this process during ionospheric modification with high power radio waves was reported by Norin et al. (2009 using the HAARP transmitter in Alaska. Subsequent experiments have provided additional verification of this process and quantitative interpretation of the scattered wave frequency offsets to yield measurements of the electron temperatures in the heated ionosphere. Using the SBS technique, electron temperatures between 3000 and 4000 K were measured over the HAARP facility. The matching conditions for decay of the high frequency pump wave show that in addition to the production of an ion-acoustic wave, an electrostatic ion cyclotron wave may also be produced by the generalized SBS processes. Based on the matching condition theory, the first profiles of the scattered wave amplitude are produced using the stimulated Brillouin scatter (SBS matching conditions. These profiles are consistent with maximum ionospheric interactions at the upper-hybrid resonance height and at a region just below the plasma resonance altitude where the pump wave electric fields reach their maximum values.

  16. Ionospheric effects of magnetic storm observed by means of oblique sounding of artificial ionospheric turbulence

    Science.gov (United States)

    Uryadov, V. P.; Vertogradov, G. G.; Vertogradov, V. G.; Ponyatov, A. A.

    Results of experimental studies of the influence of the artificial ionospheric turbulence (AIT) on HF propagation are presented. Ionospheric modification and the creation of a scatterer was produced by powerful radio emission of the SURA heating facility (Nizhny Novgorod region). For diagnostics of the AIT were used the Russian chirp sounders network and HF Doppler radar. The reception of scattered signals was carried out in the Rostov-Don on the oblique V-type antenna oriented to the SURA heating facility. It is investigated ionospheric effects of magnetic storm during August 17-22, 2003 accompanied a period of the experiment. It is shown that ionospheric effects of the magnetic storm observed by means of Doppler frequency shift (DFS) measurements signals scattered from artificial small-scale field-aligned irregularities correlate well with the behavior of the southward component Bz of the interplanetary magnetic field and with variations in the geomagnetic field near the Earth surface. It has been found that at heights of the mid-latitude ionospheric F region under undisturbed conditions the electric field and the drift velocity of irregularities correspond to the typical values about 1 mV m-1 and 20 m s-1, respectively. During magnetic storm these values increase up to values of about 8.6 mV m-1 and 186 m s-1, which better correspond to the values typical for the high-latitude ionosphere. It is found that in the magnetically-disturbed period sporadically appearing trains with quasi-periodical modulation of DFS for the scattered signal with a period of ˜ 40-60 s and amplitude reaching 2 Hz were observed. The relation of the quasi-periodical oscillations of the DFS for the scattered signal to the presence of magnetohydrodynamics waves excited during a magnetic storm is considered. It is concluded that use HF Doppler radar for AIT sounding is of interest for diagnostics of wave processes in the ionosphere and magnetosphere. The conditions of formation of the HF

  17. Response of the convecting high-latitude F layer to a powerful HF wave

    Directory of Open Access Journals (Sweden)

    G. I. Mingaleva

    1997-10-01

    Full Text Available A numerical model of the high-latitude ionosphere, which takes into account the convection of the ionospheric plasma, has been developed and utilized to simulate the F-layer response at auroral latitudes to high-power radio waves. The model produces the time variations of the electron density, positive ion velocity, and ion and electron temperature profiles within a magnetic field tube carried over an ionospheric heater by the convection electric field. The simulations have been performed for the point with the geographic coordinates of the ionospheric HF heating facility near Tromso, Norway, when it is located near the midnight magnetic meridian. The calculations have been made for equinox, at high-solar-activity, and low-geomagnetic-activity conditions. The results indicate that significant variations of the electron temperature, positive ion velocity, and electron density profiles can be produced by HF heating in the convecting high-latitude F layer.

  18. A comparison of satellite scintillation measurements with HF radar backscatter characteristics

    Directory of Open Access Journals (Sweden)

    S. E. Milan

    2005-12-01

    Full Text Available We examine the correspondence between high latitude ionospheric scintillation measurements made at 250MHz with the occurrence of 10MHz HF coherent radar backscatter, on 13 and 14 December 2002. We demonstrate that when the ionospheric intersection point of the scintillation measurements is co-located with significant HF radar backscatter, the observed scintillation, quantified by the S4 index, is elevated. Conversely, when the radar indicates that backscatter is observed away from the intersection point due to movements of the auroral zone, the observed scintillation is low. This suggests that scintillation is highly location-dependent, being enhanced in the auroral zone and being lower at sub-auroral latitudes. The coexistence of scintillation and HF radar backscatter, produced by ionospheric density perturbations with scale sizes of 100s of metres and ~15 m, respectively, suggests that a broad spectrum of density fluctuations is found in the auroral zone.

  19. Angular momentum limit of Hf isotopes produced in three fusion-evaporation reactions

    CERN Document Server

    Domscheit, J; Ernst, J; Fallon, P; Herskind, B; Hübel, H; Korten, W; Lee, I Y; Macchiavelli, A O; Nenoff, N; Siem, S; Ward, D; Wilson, J N

    2001-01-01

    The compound nucleus sup 1 sup 6 sup 8 Hf was populated in three fusion-evaporation reactions with different beam-target mass asymmetries: sup 5 sup 0 Ti+ sup 1 sup 1 sup 8 Sn, sup 6 sup 4 Ni+ sup 1 sup 0 sup 4 Ru and sup 7 sup 4 Ge+ sup 9 sup 4 Zr. Due to the large negative Q values of these reactions the compound nucleus is formed at low excitation energy. At three or four excitation energies for each reaction gamma-ray spectra of the evaporation residues sup 1 sup 6 sup 6 Hf to sup 1 sup 6 sup 3 Hf, corresponding to the 2n to 5n exit channels, respectively, were recorded with the Ge detectors of the 8 pi-spectrometer array. The gamma-ray multiplicity and total energy were measured using the inner ball of BGO detectors. This data was used to determine the maximum angular momentum transferred to each evaporation channel, the gamma-ray decay entry region and the relative cross sections. No differences are observed between the three reactions. This is explained by the very similar dependence of the excitation ...

  20. Metal-assisted chemical etching in HF/Na2S2O8 OR HF/KMnO4 produces porous silicon

    NARCIS (Netherlands)

    Hadjersi, T.; Gabouze, N.; Kooij, Ernst S.; Zinine, A.; Zinine, A.; Ababou, A.; Chergui, W.; Cheraga, H.; Belhousse, S.; Djeghri, A.

    2004-01-01

    A new metal-assisted chemical etching method using Na2S2O8 or KMnO4 as an oxidizing agent was proposed to form a porous silicon layer on a highly resistive p-type silicon. A thin layer of Ag or Pd is deposited on the Si(100) surface prior to immersion in a solution of HF and Na2S2O8 or HF and KMnO4.

  1. Ultralong-range sounding of the ionospheric HF channel using an ionosonde/direction finder with chirp modulation of the signal

    Science.gov (United States)

    G. Vertogradov, G.; Uryadov, V. P.; Vertogradova, E. G.; Ponyatov, A. A.

    2010-08-01

    We present the results of experimental studies of propagation of short radio waves on a long transequatorial path of Laverton (Australia) — Rostov-on-Don, which were obtained with the help of an ionosonde/direction finder with chirp modulation of the signal. It is shown that conditions for propagation of anomalous signals by means of sideband reflection of radio waves from the Himalayan Hills and the Plateau of Iran and also due to scattering of radio waves from the high-latitude ionosphere of the northern hemisphere are realized on the given path. The propagation of radio waves is modeled with allowance for their scattering by anisotropic magnetic field-aligned irregularities of a high-latitude ionosphere, which are located on the northern wall of the main ionospheric trough of the F layer. It is shown that the results of the experiment agree well with the calculated data.

  2. Large-amplitude traveling ionospheric distrubance produced by the May 18, 1980, explosion of Mount St. Helens

    Energy Technology Data Exchange (ETDEWEB)

    Roberts, D.H.; Klobuchar, J.A.; Fougere, P.F.; Hendrickson, D.H.

    1982-08-01

    A remarkable long-lived, large-scale traveling ionospheric disturbance (TID), excited by the May 18, 1980, explosion of Mount St. Helens, has been detected in total electron content monitor data. Oscillatory perturbations in the electron column density of the ionosphere with amplitudes about 10% of the nominal daytime content were detected at three stations whose ionospheric penetration points lie between 1610 and 1890 km from Mount St. Helens. Smaller perturbations were detected at five of six additional stations between 3760 and 4950 km away. The period of the TID increased linearly with great-circle distance from Mount St. Helens, ranging from roughly-equal37 min at the nearest station to roughly-equal116 min at the most distant one. The TID persisted for at least four cycles at the three close stations and three cycles at the more distant stations and was qualitatively similar to TID's produced by the low-altitude thermonuclear detonations of the 1960's. The disturbance front of this TID accelerated from an average velocity of roughly-equal350 m/s between Mt. St. Helens and the close stations to an average velocity of roughly-equal550 m/s to the more distant ones.A model based on the free wave response of an isothermal atmosphere to a point disturbance provides a good fit to the data at the three closest stations, but no such model can account for all of the data. Modeling of the long-distance behavior of the Mount St. Helens TID in terms of upper-atmosphere guided gravity waves is complicated by the requirement of exciting them by a ground-level explosion. There was no evidence for a strong supersonic shock wave in the ionosphere. As a result, the Mount St. Helens disturbance may prove to be a cleaner test of detailed theories of the point excitation and propagation of gravity waves in a realistic atmosphere than were TID's excited by thermonuclear weapons.

  3. Multi-dimensional distribution of near-field ionospheric disturbances produced by the 2015 Mw7.8 Nepal earthquake

    Science.gov (United States)

    Tang, Jun; Yuan, Yunbin

    2017-10-01

    Ionospheric anomalies possibly associated with large earthquakes, particularly coseismic ionospheric disturbances, have been detected by global positioning system (GPS). A large Nepal earthquake with magnitude Mw7.8 occurred on April 25, 2015. In this paper, we investigate the multi-dimensional distribution of near-field coseismic ionospheric disturbances (CIDs) using total electron content (TEC) and computerized ionospheric tomography (CIT) from regional GPS observational data. The results show significant ionospheric TEC disturbances and interesting multi-dimensional structures around the main shock. Regarding the TEC changes, coseismic ionospheric disturbances occur approximately 10-20 min after the earthquake northeast and northwest of epicentre. The maximum ridge-to-trough amplitude of CIDs is up to approximately 0.90 TECU/min. Propagation velocities of the TEC disturbances are 1.27 ± 0.06 km/s and 1.91 ± 0.38 km/s. It is believed that the ionospheric disturbances are triggered by acoustic and Rayleigh waves. Tomographic results show that the three-dimensional distribution of ionospheric disturbances obviously increases at an altitude of 300 km above the surrounding epicentre, predominantly in the entire region between 200 km and 400 km. Significant ionospheric disturbances appear at 06:30 UT from tomographic images. This study reveals characteristics of an ionospheric anomaly caused by the Nepal earthquake.

  4. Influence of magnetospheric processes on winter HF radar spectra characteristics

    Directory of Open Access Journals (Sweden)

    R. André

    2002-11-01

    Full Text Available This study investigates further the relationship between regions of the magnetosphere and the characteristics of HF radar Doppler spectra recorded in the ionospheric projection of those regions. It builds on earlier work, which has reported a relationship between the Doppler spectral width and the ionospheric projection of the magnetospheric cusp region, by introducing novel techniques for classifying the Doppler spectra recorded by the SuperDARN radars. We first review the geophysical factors that can condition the characteristics of the autocorrelation function (ACF data produced by the radars. This leads to a classification scheme of the ACF data which is then applied to a large database compiled from winter data taken by the Northern Hemisphere Super-DARN radars. This statistical study shows that the ACF characteristics are not randomly distributed in space, but rather are spatially organized in the ionosphere. This paper suggests that these regions are ordered primarily by the low energy ( 1 keV electron precipitation region and the presence of intense ULF wave activity.Key words. Ionosphere (auroral ionosphere; ionosphere-magnetosphere interactions; plasma convection

  5. Ionospheric research opportunity

    Science.gov (United States)

    Rickel, Dwight

    1985-05-01

    Ground-based explosions have been exploited successfully in the past as a relatively controlled source for producing ionospheric disturbances. On June 25, the Defense Nuclear Agency will conduct a high explosives test on the northern section of the White Sands Missile Range. Approximately 4,800 tons of ammonium nitrate and fuel oil (ANFO) will be detonated at ground level, producing an acoustic shock wave with a surface pressure change of approximately 20 mbar at a 6 km range. This shock front will have sufficient strength to propagate into the ionosphere with at least a 10% change in the ambient pressure across the disturbance front in the lower F region. Such an ionospheric perturbation will give ionospheric researchers an excellent opportunity to investigate acoustic propagation at ionospheric heights, shock dissipation effect, the ion-neutral coupling process, acoustic-gravity wave (traveling ionospheric disturbance) generation mechanisms, and associated RF phenomena.

  6. Excitation thresholds of field-aligned irregularities and associated ionospheric hysteresis at very high latitudes observed using SPEAR-induced HF radar backscatter

    Directory of Open Access Journals (Sweden)

    D. M. Wright

    2009-07-01

    Full Text Available On 10 October 2006 the SPEAR high power radar facility was operated in a power-stepping mode where both CUTLASS radars were detecting backscatter from the SPEAR-induced field-aligned irregularities (FAIs. The effective radiated power of SPEAR was varied from 1–10 MW. The aim of the experiment was to investigate the power thresholds for excitation (Pt and collapse (Pc of artificially-induced FAIs in the ionosphere over Svalbard. It was demonstrated that FAI could be excited by a SPEAR ERP of only 1 MW, representing only 1/30th of SPEAR's total capability, and that once created the irregularities could be maintained for even lower powers. The experiment also demonstrated that the very high latitude ionosphere exhibits hysteresis, where the down-going part of the power cycle provided a higher density of irregularities than for the equivalent part of the up-going cycle. Although this second result is similar to that observed previously by CUTLASS in conjunction with the Tromsø heater, the same is not true for the equivalent incoherent scatter measurements. The EISCAT Svalbard Radar (ESR failed to detect any hysteresis in the plasma parameters over Svalbard in stark contract with the measurements made using the Tromsø UHF.

  7. Excitation thresholds of field-aligned irregularities and associated ionospheric hysteresis at very high latitudes observed using SPEAR-induced HF radar backscatter

    Directory of Open Access Journals (Sweden)

    D. M. Wright

    2009-07-01

    Full Text Available On 10 October 2006 the SPEAR high power radar facility was operated in a power-stepping mode where both CUTLASS radars were detecting backscatter from the SPEAR-induced field-aligned irregularities (FAIs. The effective radiated power of SPEAR was varied from 1–10 MW. The aim of the experiment was to investigate the power thresholds for excitation (Pt and collapse (Pc of artificially-induced FAIs in the ionosphere over Svalbard. It was demonstrated that FAI could be excited by a SPEAR ERP of only 1 MW, representing only 1/30th of SPEAR's total capability, and that once created the irregularities could be maintained for even lower powers. The experiment also demonstrated that the very high latitude ionosphere exhibits hysteresis, where the down-going part of the power cycle provided a higher density of irregularities than for the equivalent part of the up-going cycle. Although this second result is similar to that observed previously by CUTLASS in conjunction with the Tromsø heater, the same is not true for the equivalent incoherent scatter measurements. The EISCAT Svalbard Radar (ESR failed to detect any hysteresis in the plasma parameters over Svalbard in stark contract with the measurements made using the Tromsø UHF.

  8. First observations of electron gyro-harmonic effects under X-mode HF pumping the high latitude ionospheric F-region

    Science.gov (United States)

    Blagoveshchenskaya, N. F.; Borisova, T. D.; Kalishin, A. S.; Yeoman, T. K.; Häggström, I.

    2017-03-01

    We provide the first experimental evidence of the sensitivity of phenomena induced by extraordinary (X-mode) polarized HF high power radio waves to pump frequency stepping across the fifth electron gyro-harmonic (5fce) from below to above. The results were obtained at the EISCAT (European Incoherent Scatter Scientific Association) HF heater facility near Tromsø under effective radiated powers of 456-715 MW, when the HF pump wave was transmitted into the magnetic zenith. We have analyzed the behavior and intensities of various spectral lines in the narrowband stimulated electromagnetic emission (SEE) spectra observed far from the heater, HF-enhanced plasma and ion lines (HFPL and HFIL) from EISCAT UHF incoherent scatter radar spectra, and artificial field-aligned irregularities from CUTLASS (Co-operative UK Twin Located Auroral Sounding System) observations, depending on the frequency offset of the pump field relative to the 5fce. At pump frequencies below 5fce the narrowband SEE spectra exhibited very intense so-called stimulated ion Bernstein scatter (SIBS), accompanied by other spectral components, associated with stimulated Brillouin scatter (SBS), which are greatly suppressed and disappeared in the vicinity of 5fce and did not reappear at fH>5fce. As the pump frequency reached 5fce, the abrupt enhancements of the HFPL and HFIL power, the appearance of cascade lines in the plasma line spectra, and the onset of increasing CUTLASS backscatter power occurred. That is opposite to the ordinary mode (O-mode) effects in the vicinity of 5fce. The X-mode pumping at frequencies below and in the vicinity of the fifth electron gyro-harmonic clearly demonstrated an ascending altitude of generation of induced plasma and ion lines from the initial interaction height, whereas for O-mode heating the region of interaction descended. The observations are consistent with the coexistence of the electron acceleration along and across the geomagnetic field at fH<5fce, while only very

  9. Initial breakdown and fast leaders in lightning discharges producing long-lasting disturbances of the lower ionosphere

    Science.gov (United States)

    Kotovsky, D. A.; Moore, R. C.; Zhu, Y.; Tran, M. D.; Rakov, V. A.; Pilkey, J. T.; Caicedo, J. A.; Hare, B.; Jordan, D. M.; Uman, M. A.

    2016-06-01

    The recent discovery of long recovery, early VLF scattering events (LOREs) indicates that the electric field changes from lightning discharges are capable of producing long-lasting disturbances (up to tens of minutes) in the upper mesosphere and lower ionosphere. Comparison of lightning mapping array, broadband (up to 10 MHz) electric field, and VLF (˜300 Hz to 42 kHz) magnetic field measurements shows that the field changes produced by initial breakdown (IB) processes and the following leaders in natural, cloud-to-ground lightning discharges are detectable in VLF magnetic field measurements at long distances. IB radiation has been detected in VLF for lightning discharges occurring up to 2630 km away from the VLF observing station. Radio atmospherics associated with 52 LOREs, 51 regular recovery events, and 3098 flashes detected by National Lightning Detection Network and/or GLD360 were examined for IB radiation occurring up to 15 ms before the return stroke. Our analysis reveals that in contrast to regular recovery early VLF events, LOREs are strongly associated with lightning discharges which exhibit an intense IB process and a fast first leader (typical duration <4 ms). These experimental results demonstrate that initial breakdown and leader processes are indicators of discharge properties highly relevant to the total energy transfer between lightning discharges and the middle/upper atmosphere.

  10. 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.

  11. Global Ionosphere Radio Observatory

    Science.gov (United States)

    Galkin, I. A.; Reinisch, B. W.; Huang, X. A.

    2014-12-01

    The Global Ionosphere Radio Observatory (GIRO) comprises a network of ground-based high-frequency vertical sounding sensors, ionosondes, with instrument installations in 27 countries and a central Lowell GIRO Data Center (LGDC) for data acquisition and assimilation, including 46 real-time data streams as of August 2014. The LGDC implemented a suite of technologies for post-processing, modeling, analysis, and dissemination of the acquired and derived data products, including: (1) IRI-based Real-time Assimilative Model, "IRTAM", that builds and publishes every 15-minutes an updated "global weather" map of the peak density and height in the ionosphere, as well as a map of deviations from the classic IRI climate; (2) Global Assimilative Model of Bottomside Ionosphere Timelines (GAMBIT) Database and Explorer holding 15 years worth of IRTAM computed maps at 15 minute cadence;. (3) 17+ million ionograms and matching ionogram-derived records of URSI-standard ionospheric characteristics and vertical profiles of electron density; (4) 10+ million records of the Doppler Skymaps showing spatial distributions over the GIRO locations and plasma drifts; (5) Data and software for Traveling Ionospheric Disturbance (TID) diagnostics; and (6) HR2006 ray tracing software mated to the "realistic" IRTAM ionosphere. In cooperation with the URSI Ionosonde Network Advisory Group (INAG), the LGDC promotes cooperative agreements with the ionosonde observatories of the world to accept and process real-time data of HF radio monitoring of the ionosphere, and to promote a variety of investigations that benefit from the global-scale, prompt, detailed, and accurate descriptions of the ionospheric variability.

  12. A New Inversion Routine to Produce Vertical Electron-Density Profiles from Ionospheric Topside-Sounder Data

    Science.gov (United States)

    Wang, Yongli; Benson, Robert F.

    2011-01-01

    Two software applications have been produced specifically for the analysis of some million digital topside ionograms produced by a recent analog-to-digital conversion effort of selected analog telemetry tapes from the Alouette-2, ISIS-1 and ISIS-2 satellites. One, TOPIST (TOPside Ionogram Scalar with True-height algorithm) from the University of Massachusetts Lowell, is designed for the automatic identification of the topside-ionogram ionospheric-reflection traces and their inversion into vertical electron-density profiles Ne(h). TOPIST also has the capability of manual intervention. The other application, from the Goddard Space Flight Center based on the FORTRAN code of John E. Jackson from the 1960s, is designed as an IDL-based interactive program for the scaling of selected digital topside-sounder ionograms. The Jackson code has also been modified, with some effort, so as to run on modern computers. This modification was motivated by the need to scale selected ionograms from the millions of Alouette/ISIS topside-sounder ionograms that only exist on 35-mm film. During this modification, it became evident that it would be more efficient to design a new code, based on the capabilities of present-day computers, than to continue to modify the old code. Such a new code has been produced and here we will describe its capabilities and compare Ne(h) profiles produced from it with those produced by the Jackson code. The concept of the new code is to assume an initial Ne(h) and derive a final Ne(h) through an iteration process that makes the resulting apparent-height profile fir the scaled values within a certain error range. The new code can be used on the X-, O-, and Z-mode traces. It does not assume any predefined profile shape between two contiguous points, like the exponential rule used in Jackson s program. Instead, Monotone Piecewise Cubic Interpolation is applied in the global profile to keep the monotone nature of the profile, which also ensures better smoothness

  13. 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...

  14. Observations of HF backscatter decay rates from HAARP generated FAI

    Science.gov (United States)

    Bristow, W. A.; Hysell, D. L.

    2016-12-01

    Suitable experiments at the High-frequency Active Auroral Research Program (HAARP) facilities in Gakona, Alaska, create a region of ionospheric Field-Aligned Irregularities (FAI) that produces strong radar backscatter observed by the SuperDARN radar on Kodiak Island, Alaska. Creation of FAI in HF ionospheric modification experiments has been studied by a number of authors who have developed a rich theoretical background. The decay of the irregularities, however, has not been so widely studied yet it has the potential for providing estimates of the parameters of natural irregularity diffusion, which are difficult measure by other means. Hysell, et al. [1996] demonstrated using the decay of radar scatter above the Sura heating facility to estimate irregularity diffusion. A large database of radar backscatter from HAARP generated FAI has been collected over the years. Experiments often cycled the heater power on and off in a way that allowed estimates of the FAI decay rate. The database has been examined to extract decay time estimates and diffusion rates over a range of ionospheric conditions. This presentation will summarize the database and the estimated diffusion rates, and will discuss the potential for targeted experiments for aeronomy measurements. Hysell, D. L., M. C. Kelley, Y. M. Yampolski, V. S. Beley, A. V. Koloskov, P. V. Ponomarenko, and O. F. Tyrnov, HF radar observations of decaying artificial field aligned irregularities, J. Geophys. Res. , 101, 26,981, 1996.

  15. Investigation of ionospheric disturbances and associated diagnostic techniques. Final report, 1 January 1992-31 December 1994

    Energy Technology Data Exchange (ETDEWEB)

    Duncan, L.M.

    1995-12-12

    The objectives of this research and development program were to conduct simulation modeling of the generation and propagation of atmospheric acoustic signals associated with surface and subsurface ground disturbances; to construct an experimental measurement system for exploratory research studies of acoustic generated ionospheric disturbances; to model high power radio wave propagation through the ionosphere, including nonlinear wave plasma interaction effects; and to assist in the assessment of diagnostic systems for observation of ionospheric modification experiments using existing and planned high latitude high power RF transmitting facilities. A computer simulation of ionospheric response to ground launched acoustic pulses was constructed and results compared to observational data associated with HF and incoherent scatter radar measurements of ionospheric effects produced by earthquakes and ground level explosions. These results were then utilized to help define the design, construct and test for an HF Doppler radar system. In addition, an assessment was conducted of ionospheric diagnostic instruments proposed for the Air Force/Navy High Frequency Active Auroral Research Program (HAARP).

  16. Nightside studies of coherent HF Radar spectral width behaviour

    Directory of Open Access Journals (Sweden)

    E. E. Woodfield

    Full Text Available A previous case study found a relationship between high spectral width measured by the CUTLASS Finland HF radar and elevated electron temperatures observed by the EISCAT and ESR incoherent scatter radars in the post-midnight sector of magnetic local time. This paper expands that work by briefly re-examining that interval and looking in depth at two further case studies. In all three cases a region of high HF spectral width (>200 ms-1 exists poleward of a region of low HF spectral width (<200 ms-1. Each case, however, occurs under quite different geomagnetic conditions. The original case study occurred during an interval with no observed electrojet activity, the second study during a transition from quiet to active conditions with a clear band of ion frictional heating indicating the location of the flow reversal boundary, and the third during an isolated sub-storm. These case studies indicate that the relationship between elevated electron temperature and high HF radar spectral width appears on closed field lines after 03:00 magnetic local time (MLT on the nightside. It is not clear whether the same relationship would hold on open field lines, since our analysis of this relationship is restricted in latitude. We find two important properties of high spectral width data on the nightside. Firstly the high spectral width values occur on both open and closed field lines, and secondly that the power spectra which exhibit high widths are both single-peak and multiple-peak. In general the regions of high spectral width (>200 ms-1 have more multiple-peak spectra than the regions of low spectral widths whilst still maintaining a majority of single-peak spectra. We also find that the region of ion frictional heating is collocated with many multiple-peak HF spectra. Several mechanisms for the generation of high spectral width have been proposed which would produce multiple-peak spectra, these are discussed in relation to

  17. Nightside studies of coherent HF Radar spectral width behaviour

    Directory of Open Access Journals (Sweden)

    E. E. Woodfield

    2002-09-01

    Full Text Available A previous case study found a relationship between high spectral width measured by the CUTLASS Finland HF radar and elevated electron temperatures observed by the EISCAT and ESR incoherent scatter radars in the post-midnight sector of magnetic local time. This paper expands that work by briefly re-examining that interval and looking in depth at two further case studies. In all three cases a region of high HF spectral width (>200 ms-1 exists poleward of a region of low HF spectral width (<200 ms-1. Each case, however, occurs under quite different geomagnetic conditions. The original case study occurred during an interval with no observed electrojet activity, the second study during a transition from quiet to active conditions with a clear band of ion frictional heating indicating the location of the flow reversal boundary, and the third during an isolated sub-storm. These case studies indicate that the relationship between elevated electron temperature and high HF radar spectral width appears on closed field lines after 03:00 magnetic local time (MLT on the nightside. It is not clear whether the same relationship would hold on open field lines, since our analysis of this relationship is restricted in latitude. We find two important properties of high spectral width data on the nightside. Firstly the high spectral width values occur on both open and closed field lines, and secondly that the power spectra which exhibit high widths are both single-peak and multiple-peak. In general the regions of high spectral width (>200 ms-1 have more multiple-peak spectra than the regions of low spectral widths whilst still maintaining a majority of single-peak spectra. We also find that the region of ion frictional heating is collocated with many multiple-peak HF spectra. Several mechanisms for the generation of high spectral width have been proposed which would produce multiple-peak spectra, these are discussed in relation to the data presented here. Since the

  18. Use of GPS network data for HF Doppler measurements interpretation

    CERN Document Server

    Petrova, Inna R; Latypov, Ruslan R

    2014-01-01

    The method of measurement of Doppler frequency shift of ionospheric signal - HF Doppler technique - is one of well-known and widely used methods of ionosphere research. It allows to research various disturbances in the ionosphere. There are some sources of disturbances in the ionosphere. These are geomagnetic storms, solar flashes, metrological effects, atmospheric waves. This method allows to find out the influence of earthquakes, explosions and other processes on the ionosphere, which occur near to the Earth. HF Doppler technique has the high sensitivity to small frequency variations and the high time resolution, but interpretation of results is difficult. In this work we make an attempt to use GPS data for Doppler measurements interpretation. Modeling of Doppler frequency shift variations with use of TEC allows to separate ionosphere disturbances of medium scale.

  19. On the Usage of Permanent GPS Stations for the Ionospheric Monitoring in the Zone of RT "URAN-4"

    Science.gov (United States)

    Zanimonskiy, E. M.; Litvinenko, O. A.

    Some results of study of correlation between the ionospheric scintillation index of cosmic radiosources on HF and total electron contents in ionosphere, measured by means of GPS-methods are submitted.

  20. Digital HF communications for the polar regions - a low-cost alternative to satellite?

    Science.gov (United States)

    Prior-Jones, Michael; Warrington, Mike

    2010-05-01

    Digital HF communications for the polar regions - a low-cost alternative to satellite? Prior-Jones, M.R. and Warrington, E. M Communications within the polar regions pose unique technical challenges, due to the physical isolation, lack of infrastructure and extreme weather conditions. Geostationary satellite links are widely used, but they cannot function poleward of 80 degrees due to the curvature of the Earth. Low-earth-orbit systems like Iridium and ARGOS will function all the way to the poles. However, they are expensive, particularly for experiments requiring long time-series. Transferring data by Iridium satellite phone costs of the order of 60USD per megabyte. HF (i.e. 3-30 MHz) radio signals propagate via the ionosphere, allowing long distance transmission beyond the horizon. Ranges of thousands of kilometres can be easily achieved with relatively low transmission powers when propagation is favourable. The polar ionosphere is, however, a challenging environment for radio signals - the signals often reflect from multiple regions of the ionosphere and by multiple hops with intermediate ground reflections producing multipath effects. As the ionosphere is moving, these signals are also subject to very significant Doppler shifts that add to the complexity of the environment. These effects may make data communications at polar latitudes difficult or impossible at times and often only at low data rates. In this paper we discuss our experiments to use modern signal-processing and modulation techniques for digital transmission on HF, offering a similar speed to satellite but without paying the high cost of satellite airtime. Using an HF channel simulator developed by Warrington et al based on measurements of propagation at high latitudes, we have tested the performance of an OFDM-based modem derived from the Digital Radio Mondiale standard used for digital HF broadcasting and found that it outperforms current military modems developed by NATO (STANAG 4285 and 4539

  1. Determining Energy Distributions of HF-Accelerated Electrons at HAARP

    Science.gov (United States)

    2015-11-18

    AFRL-AFOSR-VA-TR-2015-0383 Determining energy distributions of HF -accelerated electrons at HAARP Christopher Fallen University of Alaska Fairbanks...2012 - 11/14/2015 4. TITLE AND SUBTITLE Determining energy distributions of HF -accelerated electrons at HAARP 5a. CONTRACT NUMBER FA9550-12-1-0424...The main project objective was to determine energy distribution of ionosphere electrons accelerated by powerful high-frequency ( HF ) radio waves

  2. Worldwide Hourly Values of Ionospheric Characteristics: foF2, M(3000)F2, hF2,FoF1, M(3000)F1, hF, FoE, hE, foE2, hE2, foEs, fbEs, fmI, and FxI

    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 ionizing effect of Solar electromagnetic radiation. For poleware latitudes, the...

  3. Investigation of Ionospheric Turbulence and Whistler Wave Interactions with Space Plasmas

    Science.gov (United States)

    2012-11-21

    rely on naturally occurring spread F irregularities to serve as ionospheric ducts. We can also use HF wave-created ducts/artificial waveguides, as... ionospheric plasma structures have different configurations. In brief, large-scale sheet- like ionospheric density irregularities can be excited within and...Burke W J, Sulzer M P, Kuo S P and Klien E M C 1998 Generation of large sheet-like ionospheric plasma irregularities at Arecibo Geophys. Res. Lett

  4. Two-dimensional electric field measurements in the ionospheric footprint of a flux transfer event

    Directory of Open Access Journals (Sweden)

    K. A. McWilliams

    2000-12-01

    Full Text Available Line-of-sight Doppler velocities from the SuperDARN CUTLASS HF radar pair have been combined to produce the first two-dimensional vector measurements of the convection pattern throughout the ionospheric footprint of a flux transfer event (a pulsed ionospheric flow, or PIF. Very stable and moderate interplanetary magnetic field conditions, along with a preceding prolonged period of northward interplanetary magnetic field, allow a detailed study of the spatial and the temporal evolution of the ionospheric response to magnetic reconnection. The flux tube footprint is tracked for half an hour across six hours of local time in the auroral zone, from magnetic local noon to dusk. The motion of the footprint of the newly reconnected flux tube is compared with the ionospheric convection velocity. Two primary intervals in the PIF's evolution have been determined. For the first half of its lifetime in the radar field of view the phase speed of the PIF is highly variable and the mean speed is nearly twice the ionospheric convection speed. For the final half of its lifetime the phase velocity becomes much less variable and slows down to the ionospheric convection velocity. The evolution of the flux tube in the magnetosphere has been studied using magnetic field, magnetopause and magnetosheath models. The data are consistent with an interval of azimuthally propagating magnetopause reconnection, in a manner consonant with a peeling of magnetic flux from the magnetopause, followed by an interval of anti-sunward convection of reconnected flux tubes.Key words: Magnetospheric physics (magnetosphere · ionosphere interactions; plasma convection; solar wind · magnetosphere interactions

  5. Two-dimensional electric field measurements in the ionospheric footprint of a flux transfer event

    Directory of Open Access Journals (Sweden)

    K. A. McWilliams

    Full Text Available Line-of-sight Doppler velocities from the SuperDARN CUTLASS HF radar pair have been combined to produce the first two-dimensional vector measurements of the convection pattern throughout the ionospheric footprint of a flux transfer event (a pulsed ionospheric flow, or PIF. Very stable and moderate interplanetary magnetic field conditions, along with a preceding prolonged period of northward interplanetary magnetic field, allow a detailed study of the spatial and the temporal evolution of the ionospheric response to magnetic reconnection. The flux tube footprint is tracked for half an hour across six hours of local time in the auroral zone, from magnetic local noon to dusk. The motion of the footprint of the newly reconnected flux tube is compared with the ionospheric convection velocity. Two primary intervals in the PIF's evolution have been determined. For the first half of its lifetime in the radar field of view the phase speed of the PIF is highly variable and the mean speed is nearly twice the ionospheric convection speed. For the final half of its lifetime the phase velocity becomes much less variable and slows down to the ionospheric convection velocity. The evolution of the flux tube in the magnetosphere has been studied using magnetic field, magnetopause and magnetosheath models. The data are consistent with an interval of azimuthally propagating magnetopause reconnection, in a manner consonant with a peeling of magnetic flux from the magnetopause, followed by an interval of anti-sunward convection of reconnected flux tubes.

    Key words: Magnetospheric physics (magnetosphere · ionosphere interactions; plasma convection; solar wind · magnetosphere interactions

  6. The Ionosphere and Ocean Altimetry

    Science.gov (United States)

    Lindqwister, Ulf J.

    1999-01-01

    The accuracy of satellite-based single-frequency radar ocean altimeters benefits from calibration of the total electron content (TEC) of the ionosphere below the satellite. Data from the global network of Global Positioning System (GPS) receivers provides timely, continuous, and globally well-distributed measurements of ionospheric electron content. We have created a daily automated process called Daily Global Ionospheric Map (Daily-GIM) whose primary purpose is to use global GPS data to provide ionospheric calibration data for the Geosat Follow-On (GFO) ocean altimeter. This process also produces an hourly time-series of global maps of the electron content of the ionosphere. This system is designed to deliver "quick-look" ionospheric calibrations within 24 hours with 90+% reliability and with a root-mean-square accuracy of 2 cm at 13.6 GHz. In addition we produce a second product within 72 hours which takes advantage of additional GPS data which were not available in time for the first process. The diagram shows an example of a comparison between TEC data from the Topographic Experiment (TOPEX) ocean altimeter and Daily-GIM. TEC are displayed in TEC units, TECU, where 5 TECU is 1 cm at 13.6 GHz. Data from a single TOPEX track is shown. Also shown is the Bent climatological model TEC for the track. Although the GFO satellite is not yet in its operational mode, we have been running Daily-GIM reliably (much better than 90%) with better than 2-cm accuracy (based on comparisons against TOPEX) for several months. When timely ephemeris files for the European Remote Sensing Satellite 2 (ERS-2) are available, daily ERS-2 altimeter ionospheric calibration files are produced. When GFO ephemeris files are made available to us, we produce GFO ionosphere calibration files. Users of these GFO ionosphere calibration files find they are a great improvement over the alternative International Reference Ionosphere 1995 (IRI-95) climatological model. In addition, the TOPEX orbit

  7. The high latitudes in the International Reference Ionosphere; Meeting C4 of Commission C, COSPAR Scientific Assembly, 30th, Hamburg, Germany, July 11-21, 1994

    Science.gov (United States)

    Rawer, K.; Bilitza, D.; Singer, W.

    1995-01-01

    An international conference on high-latitude ionospheric modeling produced 27 papers in the areas of ionospheric mapping, electron density and distribution, ion density and distribution, ionospheric storems, ionospheric composition, and ionospheric sounding techniques. Upgrades to the International Reference Ionosphere (IRI) model were proposed in several papers.

  8. Ionizing wave via high-power HF acceleration

    OpenAIRE

    Mishin, Evgeny; Pedersen, Todd

    2010-01-01

    Recent ionospheric modification experiments with the 3.6 MW transmitter at the High Frequency Active Auroral Research Program (HAARP) facility in Alaska led to discovery of artificial ionization descending from the nominal interaction altitude in the background F-region ionosphere by ~60 km. This paper presents a physical model of an ionizing wavefront created by suprathermal electrons accelerated by the HF-excited plasma turbulence.

  9. The WISP/HF system for Spacelab

    Science.gov (United States)

    James, H. G.

    1980-01-01

    The high frequency part of the waves in space plasmas system, WISP/HF, is a flexible shuttle Spacelab instrument for transmitting, receiving, and processing signals in the 0.3 to 30 MHz range. It permits a wide range of plasma wave experiments in the ionosphere including studies of the transmitting antenna, fundamentals of electromagnetic (EM) and electrostatic (ES) waves in magnetoplasmas, instabilities and nonlinearities, and remote sounding of ionospheric structure. Collaborative investigations involving other WISP equipment (e.g., antenna and propagation studies with the WISP/VLF system) or other Spacelab facilities (e.g., beam plasma interactions using charged particle guns) are envisaged. A few specific examples illustrate the relevance of WISP/HF to current scientific interest. The overall goal is to help build a comprehensive understanding of plasmaspheric wave physics through group studies.

  10. 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.

  11. 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.

  12. Effect of Magnetic Activity on Ionospheric Time Delay at Low ...

    Indian Academy of Sciences (India)

    The ionospheric refraction remains a major error source in Global Positioning ... spheric error. This error is negative for carrier phase pseudoranges and positive for the code pseudoranges (Komjathy 1997). The ionospheric delay is ... cause significant changes in the ionospheric morphology, producing large delays of.

  13. A Survey of Ionospheric Models A Preliminary Report on the Development of an Ionospheric Model Thesaurus and Users Guide.

    Science.gov (United States)

    1982-07-13

    H . Sizun , 1979, "The French Short-Term Radio Propagation Predictions in the HF Band" in Solar-Terrestrial...34 Nauka. 117, Moscow (in Russian) Price G. H 1973, "High-Frequency Radio - Wave Propagation Through Plane-Stratified Ionospheric Models," Radio Science...8 (2) 133-138 Price G H .. 1972, "Analytic Ray Solutions for High-Frequency Radio - Wave Propagation Through Plane Stratified ionosphere Models" Ro-

  14. Ionospheric modification by rocket effluents. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Bernhardt, P.A.; Price, K.M.; da Rosa, A.V.

    1980-06-01

    This report describes experimental and theoretical studies related to ionospheric disturbances produced by rocket exhaust vapors. The purpose of our research was to estimate the ionospheric effects of the rocket launches which will be required to place the Satellite Power System (SPS) in operation. During the past year, we have developed computational tools for numerical simulation of ionospheric changes produced by the injection of rocket exhaust vapors. The theoretical work has dealt with (1) the limitations imposed by condensation phenomena in rocket exhaust; (2) complete modeling of the ionospheric depletion process including neutral gas dynamics, plasma physics, chemistry and thermal processes; and (3) the influence of the modified ionosphere on radio wave propagation. We are also reporting on electron content measurements made during the launch of HEAO-C on Sept. 20, 1979. We conclude by suggesting future experiments and areas for future research.

  15. Initial backscatter occurrence statistics from the CUTLASS HF radars

    Directory of Open Access Journals (Sweden)

    S. E. Milan

    Full Text Available A statistical study of the occurrence of ground and ionospheric backscatter within the fields-of-view of the CUTLASS HF radars, at an operating frequency of 10 MHz, during the first 20 months of operation has been undertaken. The diurnal variation of the occurrence of backscatter and the range at which such backscatter is observed is found to be highly dependent on seasonal changes of the ionospheric electron density in both the E and F region, determined from ionosonde observations. In general, ionospheric backscatter is observed at far ranges during the local day in winter months and at near ranges during the local night in summer months. The Iceland radar observes more near-range E region backscatter than the Finland radar as a consequence of its more zonal look-direction. The dependence of the occurrence of backscatter on geomagnetic activity and radar operating frequency are also investigated. The occurrence of ground and ionospheric backscatter is discussed in terms of HF propagation modes and ionospheric electron densities as well as geophysical processes. A brief assessment of the possible impact of solar cycle variations on the observations is made and frequency management is discussed. Such a study, with its focus on the `instrumental' aspect of backscatter occurrence, is essential for a full interpretation of HF coherent radar observations.

  16. Ionosphere-related products for communication and navigation

    Science.gov (United States)

    Tobiska, W.; Schunk, R. W.; Sojka, J. J.; Carlson, H. C.; Gardner, L. C.; Scherliess, L.; Zhu, L.

    2011-12-01

    Space weather's effects upon the near-Earth environment are due to dynamic changes in the energy transfer processes from the Sun's photons, particles, and fields. Of the space environment domains that are affected by space weather, the ionosphere is the key region that affects communication and navigation systems. The Utah State University (USU) Space Weather Center (SWC) is developing and producing commercial space weather applications. A key system-level component for providing timely information about the effects of space weather is the Global Assimilation of Ionospheric Measurements (GAIM) system. GAIM, operated by SWC, improves real-time communication and navigation systems by continuously ingesting up to 10,000 slant TEC measurements every 15-minutes from approximately 500 stations. Ionosonde data from several dozen global stations is ingested every 15 minutes to improve the vertical profiles within GAIM. The global, CONUS, Europe, Asia, South America, and other regional sectors are run with a 15-minute cadence. These operational runs enable SWC to calculate and report the global radio high frequency (HF) signal strengths and near vertical incidence skywave (NVIS) maps used by amateur radio operators and emergency responders, especially during the Japan Great Earthquake and tsunami recovery period. SWC has established its first fully commercial enterprise called Q-up as a result of this activity. GPS uncertainty maps are produced by SWC to improve single-frequency GPS applications. SWC also provides the space weather smartphone app called SpaceWx for iPhone, iPad, iPod, and Android for professional users and public space weather education. SpaceWx displays the real-time solar, heliosphere, magnetosphere, thermosphere, and ionosphere drivers to changes in the total electron content, for example, as well as global NVIS maps. We describe upcoming improvements for moving space weather information through automated systems into final derivative products.

  17. Measurement of cross-sections for produced radionuclide in proton induced reactions on natHf up to 45 MeV

    Science.gov (United States)

    Shahid, Muhammad; Kim, Kwangsoo; Naik, Haladhara; Kim, Guinyun

    2014-03-01

    We measured production cross-sections of Hf, Lu, and Ta radioisotopes from proton-induced reaction of natHf by using a stacked-foil activation and off-line γ-ray spectrometric technique at the MC-50 cyclotron of the Korea Institute of Radiological and Medical Sciences. The results were compared with the reported experimental data as well as the theoretical calculations based on the TALYS 1.4 code. The present results in the energy region from the threshold energy to 45 MeV are in general good agreement with the other experimental data and calculated results. The present experimental results will play an important role in enrichment of the literature data base for proton-induced reactions on natural hafnium leading to various applications. Some of the investigated radionuclides (e.g. 177gLu) have remarkable applications in the field of nuclear medicine, a thin layer activation analysis, and a trace element analysis.

  18. Variable pixel size ionospheric tomography

    Science.gov (United States)

    Zheng, Dunyong; Zheng, Hongwei; Wang, Yanjun; Nie, Wenfeng; Li, Chaokui; Ao, Minsi; Hu, Wusheng; Zhou, Wei

    2017-06-01

    A novel ionospheric tomography technique based on variable pixel size was developed for the tomographic reconstruction of the ionospheric electron density (IED) distribution. In variable pixel size computerized ionospheric tomography (VPSCIT) model, the IED distribution is parameterized by a decomposition of the lower and upper ionosphere with different pixel sizes. Thus, the lower and upper IED distribution may be very differently determined by the available data. The variable pixel size ionospheric tomography and constant pixel size tomography are similar in most other aspects. There are some differences between two kinds of models with constant and variable pixel size respectively, one is that the segments of GPS signal pay should be assigned to the different kinds of pixel in inversion; the other is smoothness constraint factor need to make the appropriate modified where the pixel change in size. For a real dataset, the variable pixel size method distinguishes different electron density distribution zones better than the constant pixel size method. Furthermore, it can be non-chided that when the effort is spent to identify the regions in a model with best data coverage. The variable pixel size method can not only greatly improve the efficiency of inversion, but also produce IED images with high fidelity which are the same as a used uniform pixel size method. In addition, variable pixel size tomography can reduce the underdetermined problem in an ill-posed inverse problem when the data coverage is irregular or less by adjusting quantitative proportion of pixels with different sizes. In comparison with constant pixel size tomography models, the variable pixel size ionospheric tomography technique achieved relatively good results in a numerical simulation. A careful validation of the reliability and superiority of variable pixel size ionospheric tomography was performed. Finally, according to the results of the statistical analysis and quantitative comparison, the

  19. Precise Point Positioning with Ionosphere Estimation and application of Regional Ionospheric Maps

    Science.gov (United States)

    Galera Monico, J. F.; Marques, H. A.; Rocha, G. D. D. C.

    2015-12-01

    The ionosphere is one of most difficult source of errors to be modelled in the GPS positioning, mainly when applying data collected by single frequency receivers. Considering Precise Point Positioning (PPP) with single frequency data the options available include, for example, the use of Klobuchar model or applying Global Ionosphere Maps (GIM). The GIM contains Vertical Electron Content (VTEC) values that are commonly estimated considering a global network with poor covering in certain regions. For this reason Regional Ionosphere Maps (RIM) have been developed considering local GNSS network, for instance, the La Plata Ionospheric Model (LPIM) developed inside the context of SIRGAS (Geocentric Reference System for Americas). The South American RIM are produced with data from nearly 50 GPS ground receivers and considering these maps are generated for each hour with spatial resolution of one degree it is expected to provide better accuracy in GPS positioning for such region. Another possibility to correct for ionosphere effects in the PPP is to apply the ionosphere estimation technique based on Kalman filter. In this case, the ionosphere can be treated as a stochastic process and a good initial guess is necessary what can be obtained from an ionospheric map. In this paper we present the methodology involved with ionosphere estimation by using Kalman filter and also the application of global and regional ionospheric maps in the PPP as first guess. The ionosphere estimation strategy was implemented in the house software called RT_PPP that is capable of accomplishing PPP either for single or dual frequency data. GPS data from Brazilian station near equatorial region were processed and results with regional maps were compared with those by using global maps. Improvements of the order 15% were observed. In case of ionosphere estimation, the estimated coordinates were compared with ionosphere free solution and after PPP convergence the results reached centimeter accuracy.

  20. Surface waves magnitude estimation from ionospheric signature of Rayleigh waves measured by Doppler sounder and OTH radar.

    Science.gov (United States)

    Occhipinti, Giovanni; Aden-Antoniow, Florent; Bablet, Aurélien; Molinie, Jean-Philippe; Farges, Thomas

    2018-01-24

    Surface waves emitted after large earthquakes are known to induce atmospheric infrasonic waves detectable at ionospheric heights using a variety of techniques, such as high frequency (HF) Doppler, global positioning system (GPS), and recently over-the-horizon (OTH) radar. The HF Doppler and OTH radar are particularly sensitive to the ionospheric signature of Rayleigh waves and are used here to show ionospheric perturbations consistent with the propagation of Rayleigh waves related to 28 and 10 events, with a magnitude larger than 6.2, detected by HF Doppler and OTH radar respectively. A transfer function is introduced to convert the ionospheric measurement into the correspondent ground displacement in order to compare it with classic seismometers. The ground vertical displacement, measured at the ground by seismometers, and measured at the ionospheric altitude by HF Doppler and OTH radar, is used here to compute surface wave magnitude. The ionospheric surface wave magnitude (M s iono ) proposed here introduces a new way to characterize earthquakes observing the signature of surface Rayleigh waves in the ionosphere. This work proves that ionospheric observations are useful seismological data to better cover the Earth and to explore the seismology of the Solar system bodies observing the ionosphere of other planets.

  1. HF radar polar patch formation revisited: summer and winter variations in dayside plasma structuring

    Directory of Open Access Journals (Sweden)

    S. E. Milan

    Full Text Available Three intervals of polar patch formation, as observed by the CUTLASS Finland HF coherent radar, are presented. Simultaneous observations from a vertical ionosonde located at Longyearbyen on Svalbard, situated in the dayside convection throat region, allow for F-region plasma structuring, leading to polar cap patch formation to be determined. Solar wind and interplanetary magnetic field (IMF precursors of polar patch formation are investigated with MFI and SWE measurements from the Wind spacecraft. We find that in the cases studied polar cap patches are formed in response to changes in the orientation of the IMF, especially in the By component. The resultant changes in the dayside convection pattern alter the source of plasma drifting through the convection throat region into the polar cap. When the convection flow is directed predominantly polewards, high density sub-auroral or mid-latitude plasma enters the polar cap; when flow is directed zonally, low density plasma entrained in the convection return flow replaces it. This mechanism can act to significantly structure the plasma density at sub-auroral or mid-latitudes as well as in the polar cap. In winter months, polar patches appear to be produced by depletions in an otherwise high plasma density tongue of ionisation. In summer months, patches are enhancements of an otherwise low density tongue of ionisation.

    Key words. Ionosphere (ionospheric irregularities; plasma convection; polar ionosphere

  2. QAPP for Analysis of Data Received from Nine Hydraulic Fracturing (HF) Service Companies

    Science.gov (United States)

    This QAPP provides information concerning the Water Acquisition, Chemical Mixing, Well Injection, and Flowback and Produced Water stages of the HF water cycle as found in Figure 1 of the HF QMP and as described in HF Study Plan.

  3. QAPP for Hydraulic Fracturing (HF) Surface Spills Data Analysis

    Science.gov (United States)

    This QAPP provides information concerning the analysis of spills associated with hydraulic fracturing. This project is relevant to both the chemical mixing and flowback and produced water stages of the HF water cycle as found in the HF Study Plan.

  4. "Twisted Beam" SEE Observations of Ionospheric Heating from HAARP

    Science.gov (United States)

    Briczinski, S. J.; Bernhardt, P. A.; Pedersen, T. R.; Rodriguez, S.; SanAntonio, G.

    2012-12-01

    High power HF radio waves exciting the ionosphere provide aeronomers with a unique space-based laboratory capability. The High-Frequency Active Auroral Research Program (HAARP) in Gakona, Alaksa is the world's largest heating facility, providing effective radiated powers in the gigawatt range. Experiments performed at HAARP have allowed researchers to study many non-linear effects of wave-plasma interactions. Stimulated Electromagnetic Emission (SEE) is of interest to the ionospheric community for its diagnostic purposes. Typical SEE experiments at HAARP have focused on characterizing the parametric decay of the electromagnetic pump wave into several different wave modes such as upper and lower hybrid, ion acoustic, ion-Bernstein and electron-Bernstein. These production modes have been extensively studied at HAARP using traditional beam heating patterns and SEE detection. New results are present from HAARP experiments using a "twisted beam" excitation mode. Unlike traditional heating beams used at HAARP or other heating facilities, the twisted beam attempts to impart orbital angular momentum (OAM) into the heating region. Analysis of twisted beam heating shows that the SEE results obtained are nearly identical to the modes without OAM. One difference in the twisted beam mode is the heating region produced is in the shape of a ring as opposed to the more traditional "solid spot" region. The ring heating pattern may be more conducive to the creation of artificial airglow layers. The results of these runs include artificial layer creation and evolution as pertaining to the twisted beam pattern. The SEE measurements aid the interpretation of the twisted beam interactions in the ionosphere.

  5. 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.

  6. 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...

  7. Measurement of cross-sections for produced radionuclide in proton induced reactions on {sup nat}Hf up to 45 MeV

    Energy Technology Data Exchange (ETDEWEB)

    Shahid, Muhammad; Kim, Kwangsoo [Department of Physics, Kyungpook National University, Daegu 702-701 (Korea, Republic of); Naik, Haladhara [Department of Physics, Kyungpook National University, Daegu 702-701 (Korea, Republic of); Radiochemistry Division, Bhabha Atomic Research Centre, Mumbai 400085 (India); Kim, Guinyun, E-mail: gnkim@knu.ac.kr [Department of Physics, Kyungpook National University, Daegu 702-701 (Korea, Republic of)

    2014-03-01

    We measured production cross-sections of Hf, Lu, and Ta radioisotopes from proton-induced reaction of {sup nat}Hf by using a stacked-foil activation and off-line γ-ray spectrometric technique at the MC-50 cyclotron of the Korea Institute of Radiological and Medical Sciences. The results were compared with the reported experimental data as well as the theoretical calculations based on the TALYS 1.4 code. The present results in the energy region from the threshold energy to 45 MeV are in general good agreement with the other experimental data and calculated results. The present experimental results will play an important role in enrichment of the literature data base for proton-induced reactions on natural hafnium leading to various applications. Some of the investigated radionuclides (e.g. {sup 177g}Lu) have remarkable applications in the field of nuclear medicine, a thin layer activation analysis, and a trace element analysis.

  8. Ionospheric effects on terrestrial communications :Working Group 3 overview

    Directory of Open Access Journals (Sweden)

    A. Bourdillon

    2004-06-01

    Full Text Available Telecommunications via ionospheric reflection of radio signals of ground-based transmitters are a traditional area. However, this technique is still in use in telecommunications, broadcasting, etc. Various problems have not yet been solved and some of them were studied in Working Group 3 (WG3. Structure of WG 3 and the terms of reference of its four working packages are described in the introductory paper by Zolesi and Cander (2004. Here we describe the main results achieved in COST 271 in the following areas: i large-scale fluctuations of planetary and gravity waves; ii development of a new type of HF channel simulator; iii geomagnetic storm effects on the F1-region ionosphere; iv the sporadic E-layer and spread-F phenomena; v the HF radio wave propagation over northerly paths; vi how to increase the bit rate in ionospheric radio links. In general, substantial progress was achieved but some problems remain open for future investigations.

  9. Aspects of HF radio propagation

    Directory of Open Access Journals (Sweden)

    Stephane Saillant

    2009-06-01

    Full Text Available

    radio systems. From the point of view Working Group 2 of the COST 296 Action, interest lies with effects associated

    with propagation via the ionosphere of signals within the HF band. Several aspects are covered in this paper:

    a The directions of arrival and times of flight of signals received over a path oriented along the trough have

    been examined and several types of propagation effects identified. Of particular note, combining the HF observations

    with satellite measurements has identified the presence of irregularities within the floor of the trough that

    result in propagation displaced from the great circle direction. An understanding of the propagation effects that

    result in deviations of the signal path from the great circle direction are of particular relevance to the operation

    of HF radiolocation systems.

    b Inclusion of the results from the above mentioned measurements into a propagation model of the northerly

    ionosphere (i.e. those regions of the ionosphere located poleward of, and including, the mid-latitude trough

    and the use of this model to predict the coverage expected from transmitters where the signals impinge on the

    northerly ionosphere

  10. 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.

  11. Excitation of Artificial Ionospheric Turbulence in the High-Latitude Ionospheric F Region as a Function of the Eiscat/Heating Effective Radiated Power

    Science.gov (United States)

    Borisova, T. D.; Blagoveshchenskaya, N. F.; Yeoman, T. K.; Häggström, I.

    2017-10-01

    We present the results of experimental studies of the parameters of HF-enhanced ion-acoustic and Langmuir plasma waves, as well as small-scale artificial field-aligned irregularities (AFAIs) when the EISCAT/Heating effective radiated power is varied from 10 to 560 MW. In the course of the experiments, a high-power HF radio wave with the alternating ordinary (O-mode) and extraordinary (X-mode) polarizations was radiated towards the magnetic zenith at a frequency of 7.953 MHz lying below the cutoff frequency of the F2 layer. A fundamental difference in the development of artificial ion-acoustic and Langmuir turbulence, which is seen as HF-enhanced ion and plasma lines in the EISCAT spectra, under the O- and X-mode HF pumping was found. The minimum values of the HF pump-wave electric fields in the ionosphere when the HF-enhanced ion and plasma lines, as well as small-scale artificial field-aligned irregularities, start to be excited, were determined from experimental data both for the O- and X-mode HF pumping. Comparison between the experimental and theoretical threshold values of the electric field required for the excitation of artificial ionospheric turbulence in thermal, Langmuir, and ion-acoustic modes in the high-latitude ionospheric F2 layer for the O-mode HF pump wave was made.

  12. Excitation of Artificial Ionospheric Turbulence in the High-Latitude Ionospheric F Region as a Function of the Eiscat/Heating Effective Radiated Power

    Science.gov (United States)

    Borisova, T. D.; Blagoveshchenskaya, N. F.; Yeoman, T. K.; Häggström, I.

    2017-09-01

    We present the results of experimental studies of the parameters of HF-enhanced ion-acoustic and Langmuir plasma waves, as well as small-scale artificial field-aligned irregularities (AFAIs) when the EISCAT/Heating effective radiated power is varied from 10 to 560 MW. In the course of the experiments, a high-power HF radio wave with the alternating ordinary (O-mode) and extraordinary (X-mode) polarizations was radiated towards the magnetic zenith at a frequency of 7.953 MHz lying below the cutoff frequency of the F2 layer. A fundamental difference in the development of artificial ion-acoustic and Langmuir turbulence, which is seen as HF-enhanced ion and plasma lines in the EISCAT spectra, under the O- and X-mode HF pumping was found. The minimum values of the HF pump-wave electric fields in the ionosphere when the HF-enhanced ion and plasma lines, as well as small-scale artificial field-aligned irregularities, start to be excited, were determined from experimental data both for the O- and X-mode HF pumping. Comparison between the experimental and theoretical threshold values of the electric field required for the excitation of artificial ionospheric turbulence in thermal, Langmuir, and ion-acoustic modes in the high-latitude ionospheric F2 layer for the O-mode HF pump wave was made.

  13. Global Ionospheric Structure Imaged by FORMOSAT-3/COSMIC: Early Results

    Directory of Open Access Journals (Sweden)

    Chien-Hung Lin

    2009-01-01

    Full Text Available Anew era of studying the ionospheric space weather effects has come after launch of the innovative satellite constellation, named as Formosa Satellite 3 or Constellation Observing System for Meteorology, Ionosphere, and Climate (abbreviated as FORMOSAT-3/COSMIC or F3/C in short, performing a radio occultation experiment capable of observing the global ionosphere three-dimensionally. This is the first time that a satellite constellation provides instantaneously both the lower and upper parts of the ionospheric electron density up to the satellite altitude. With more than 2500 soundings of the ionospheric vertical electron density profiles every day, ionospheric plasma structures over many continents and most of oceans, where ground-based observation is limited, are now observed continuously. Important ionospheric research topics, such as space weather effects to the ionosphere, variations of ionospheric plasma structure and dynamics produced by solar outputs, and atmosphere-ionosphere coupling processes, can be widely studied and modeled based on the three-dimensional ionospheric images constructed by the F3/C observations. After one year in orbit, a great amount of radio occultation soundings allow us to construct global ionospheric maps to study the ionospheric seasonal effects and atmosphere-ionosphere interactions. Taking advantage of the uniqueness of dense global coverage, the major physical mechanisms of the two studies are given. For study of the seasonal variation during solstice, electron density images of the mid- and low-latitude ionosphere show a clear north-to-south asymmetry which may be affected by the summer-to-winter neutral wind. Meanwhile a significant longitudinal variation at midnight is also seen in the solstitial season. Another interesting result is the four stronger equatorial ionization anomaly (EIA regions located at different longitudes. This four-peaked EIA structure may result from upward propagating nonmigrating

  14. 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.

  15. Kilometer-Spaced GNSS Array for Ionospheric Irregularity Monitoring

    Science.gov (United States)

    Su, Yang

    This dissertation presents automated, systematic data collection, processing, and analysis methods for studying the spatial-temporal properties of Global Navigation Satellite Systems (GNSS) scintillations produced by ionospheric irregularities at high latitudes using a closely spaced multi-receiver array deployed in the northern auroral zone. The main contributions include 1) automated scintillation monitoring, 2) estimation of drift and anisotropy of the irregularities, 3) error analysis of the drift estimates, and 4) multi-instrument study of the ionosphere. A radio wave propagating through the ionosphere, consisting of ionized plasma, may suffer from rapid signal amplitude and/or phase fluctuations known as scintillation. Caused by non-uniform structures in the ionosphere, intense scintillation can lead to GNSS navigation and high-frequency (HF) communication failures. With specialized GNSS receivers, scintillation can be studied to better understand the structure and dynamics of the ionospheric irregularities, which can be parameterized by altitude, drift motion, anisotropy of the shape, horizontal spatial extent and their time evolution. To study the structuring and motion of ionospheric irregularities at the sub-kilometer scale sizes that produce L-band scintillations, a closely-spaced GNSS array has been established in the auroral zone at Poker Flat Research Range, Alaska to investigate high latitude scintillation and irregularities. Routinely collecting low-rate scintillation statistics, the array database also provides 100 Hz power and phase data for each channel at L1/L2C frequency. In this work, a survey of seasonal and hourly dependence of L1 scintillation events over the course of a year is discussed. To efficiently and systematically study scintillation events, an automated low-rate scintillation detection routine is established and performed for each day by screening the phase scintillation index. The spaced-receiver technique is applied to cross

  16. Saturation and hysteresis effects in ionospheric modification experiments observed by the CUTLASS and EISCAT radars

    Directory of Open Access Journals (Sweden)

    D. M. Wright

    2006-03-01

    Full Text Available The results of high latitude ionospheric modification experiments utilising the EISCAT heating facility at Tromsø are presented. As a result of the interaction between the high power pump waves and upper hybrid waves in the ionosphere, field-aligned electron density irregularities are artificially excited. Observations of these structures with the CUTLASS coherent HF radars and the EISCAT incoherent UHF radar exhibit hysteresis effects as the heater output power is varied. These are explained in terms of the two-stage mechanism which leads to the growth of the irregularities. Experiments which involve preconditioning of the ionosphere also indicate that hysteresis could be exploited to maximise the intensity of the field-aligned irregularities, especially where the available heater power is limited.

    In addition, the saturation of the irregularity amplitude is considered. Although, the rate of irregularity growth becomes less rapid at high heater powers it does not seem to fully saturate, indicating that the amplification would continue beyond the capabilities of the Tromsø heater - currently the most powerful of its kind. It is shown that the CUTLASS radars are sensitive to irregularities produced by very low heater powers (effective radiated powers <4 MW. This fact is discussed from the perspective of a new heating facility, SPEAR, located on Spitzbergen and capable of transmitting high frequency radio waves with an effective radiated power ~10% of that of the Tromsø heater (28MW.

  17. Modeling ray tracing through heating perturbed ionosphere with SAMI2

    Science.gov (United States)

    Wu, T.; Huba, J. D.; Bernhardt, P. A.

    2012-12-01

    We present simulations of high frequency (HF) signals/rays tracing through perturbed ionosphere by combining the NRL ionosphere model [Huba, 2000] and the ray tracing program [Jones, 1966]. We show with modeling that by creating artificial disturbances to the ionosphere, i.e. heating-induced geomagnetic-field-aligned density ducts, the radio signal transmission may be deflected out of its original propagation path and may exit the top ionosphere through the density breach at the F2 peak layer. Our results show the possibility to control or disrupt the communication channels in the future.; The solid line shows deviated ray trace due to F2 layer breach created by heat-induced density ducts. The dashed line shows the original ray path when no disturbances present.

  18. Statistical properties of ionospheric stimulated electromagnetic emissions

    Directory of Open Access Journals (Sweden)

    R. L. Karlsson

    2006-08-01

    Full Text Available We have analysed the statistical properties of the stimulated electromagnetic emissions (SEE spectral features in the steady state, reached after a long period of continuous HF pumping of the ionosphere in experiments performed at the Sura ionospheric radio research facility in Russia. Using a digital filter bank method, we have been able to analyse complex valued signals within narrow frequency bands. Each of the SEE spectral features are thereby separated into a number of narrow spectral components. Statistical tests were performed for all these spectral components and the distributions of the spectral amplitudes and phases were evaluated. Also, a test for sinusoidal components was performed. These tests showed that all observed SEE features were indistinguishable from coloured Gaussian noise. The test results exclude that the SEE features can be the result of a single isolated coherent process, but does not rule out that there could be many statistically independent parametric wave-wave processes taking place simultaneously at various parts of the HF-pumped ionosphere, as long as the superposition from all these is incoherent. Furthermore, from the test results, we cannot exclude the possibility that the waveforms of some, or all, of the SEE features may be chaotic.

  19. HF i dag

    DEFF Research Database (Denmark)

    Lindstrøm, Maria Duclos; Simonsen, Birgitte

    2008-01-01

    Notatet er lavet på baggrund af uddannelsesbiografiske dybdeinterviews med kursister på toårigt HF. Indenfor rammerne af en pilotundersøgelse identificerer notatet fire gennemgående profiler: De pragmatiske, de fagligt usikre, second chance-kursisterne, og de HF-kursister, som har HF som first...... choice. Således synliggør undersøgelsen HF som et sammensat uddannelsesmiljø, hvor sammensætningen af kursister i forskellige aldre og med forskellige baggrunde, erfaringer og motivationer er HF's unikke styrke og særpræg - men også rummer udfordringer og konfliktstof....

  20. Study of Ionospheric Indexes T and MF2 related to R12 for Solar Cycles 19-21

    Science.gov (United States)

    Villanueva, Lucia

    2013-04-01

    Modern worldwide communications are mainly based on satellite systems, remote communication networks, and advanced technologies. The most important space weather "meteorological" events produce negative effects on signal transmissions. Magnetic storm conditions that follow coronal mass ejections are particularly of great importance for radio communication at HF frequencies (3-30 MHz range), because the Ionization increase (or decrease), significantly over (or below), the Average Values. Nowadays new technologies make possible to establish Geophysical Observatories and monitor the sun almost in real time giving information about geomagnetic indices. Space Weather programs have interesting software predictions of foF2 producing maps and plots, every some minutes. The Average Values of the ionospheric parameters mainly depend on the position, hour, season and the phase of the 11-year cycle of the solar activity. Around 1990´s several ionospheric indexes were suggested to better predict the state of the foF2 monthly media, as: IF2, G, T and MF2, based on foF2 data from different latitude ionospheric observatories. They really show better seasonal changes than monthly solar indexes of solar flux F10.7 or the international sunspot numbers Ri. The main purpose of this paper is to present an analogic model for the ionospheric index MF2, to establish the average long term predictions of this index. Changes of phase from one cycle to the other of one component of the model is found to fit the data. The usefulness of this model could be the prediction of the ionospheric normal conditions for one entire solar cycle having just the prediction of the maximum of the next smooth sunspot number R12. In this presentation, comparisons of the Australian T index and and the Mikhailov MF2 index show an hysteresis variation with the solar monthly index Ri, such dependence is quite well represented by a polynomial fit of degree 6 for rising and decaying fases for solar cycles 19, 20 and

  1. 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.

  2. Ionospheric manifestations of earthquakes and tsunamis in a dynamic atmosphere

    Science.gov (United States)

    Godin, Oleg A.; Zabotin, Nikolay A.; Zabotina, Liudmila

    2015-04-01

    Observations of the ionosphere provide a new, promising modality for characterizing large-scale physical processes that occur on land and in the ocean. There is a large and rapidly growing body of evidence that a number of natural hazards, including large earthquakes, strong tsunamis, and powerful tornadoes, have pronounced ionospheric manifestations, which are reliably detected by ground-based and satellite-borne instruments. As the focus shifts from detecting the ionospheric features associated with the natural hazards to characterizing the hazards for the purposes of improving early warning systems and contributing to disaster recovery, it becomes imperative to relate quantitatively characteristics of the observed ionospheric disturbances and the underlying natural hazard. The relation between perturbations at the ground level and their ionospheric manifestations is strongly affected by parameters of the intervening atmosphere. In this paper, we employ the ray theory to model propagation of acoustic-gravity waves in three-dimensionally inhomogeneous atmosphere. Huygens' wavefront-tracing and Hamiltonian ray-tracing algorithms are used to simulate propagation of body waves from an earthquake hypocenter through the earth's crust and ocean to the upper atmosphere. We quantify the influence of temperature stratification and winds, including their seasonal variability, and air viscosity and thermal conductivity on the geometry and amplitude of ionospheric disturbances that are generated by seismic surface waves and tsunamis. Modeling results are verified by comparing observations of the velocity fluctuations at altitudes of 150-160 km by a coastal Dynasonde HF radar system with theoretical predictions of ionospheric manifestations of background infragravity waves in the ocean. Dynasonde radar systems are shown to be a promising means for monitoring acoustic-gravity wave activity and observing ionospheric perturbations due to earthquakes and tsunamis. We will discuss

  3. 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.

    2017-10-01

    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.

  4. HF-induced airglow at magnetic zenith: theoretical considerations

    Directory of Open Access Journals (Sweden)

    E. V. Mishin

    2005-01-01

    Full Text Available Observations of airglow at 630nm (red line and 557.7nm (green line during HF modification experiments at the High Frequency Active Auroral Research Program (HAARP heating facility are analyzed. We propose a theoretical framework for understanding the generation of Langmuir and ion acoustic waves during magnetic zenith injections. We show that observations of HF-induced airglow in an underdense ionosphere as well as a decrease in the height of the emitting volume are consistent with this scenario.

  5. Tsunami signature in the ionosphere: A simulation of OTH radar observations

    Science.gov (United States)

    CoïSson, Pierdavide; Occhipinti, Giovanni; Lognonné, Philippe; Molinié, Jean-Philippe; Rolland, Lucie M.

    2011-12-01

    In the last ten years ionospheric anomalies following major earthquakes and tsunamis have been detected. Global Positioning System (GPS) and altimeters have been proven effective for this purpose, through Total Electron Content (TEC) measurement. Most of these ionospheric anomalies are deterministic and reproducible by numerical modeling via the coupling mechanism through ocean, neutral atmosphere and ionosphere. Numerical modeling supplies also useful support in the estimation of expected ionospheric effects and in the exploration and identification of new techniques to detect ionospheric tsunami signatures. We explore here a new ground-based technique, nominally the use of over-the-horizon (OTH) radars, for tsunami detection through ionospheric monitoring. OTH radars operate in High Frequency (HF) band and sounding the bottomside ionosphere they could anticipate the detection of tsunami-driven Internal Gravity Waves (IGW). To validate this hypothesis, we use HF numerical ray-tracing to simulate synthetic OTH radar measurements through a 3D tsunami-driven IGW ionospheric model. Our simulations clearly identify the tsunami signature in the OTH radar measurements one hour and a half before the tsunami arrival on the coast. The large coverage of OTH radar and its sensitivity to plasma anomalies open new perspectives in the oceanic monitoring and future tsunami warning systems.

  6. Toward storm-time ionosphere forecast using GNSS observations

    Science.gov (United States)

    Lin, Charles; Chen, Chia-Hung; Liu, Tiger J. Y.; Chen, Wei-Han

    2016-04-01

    Previous theoretical simulations of the mid- and low-latitude ionospheric responses to space weather events have indicated general features of electron density disturbances. The magnetic storm produced penetration electric field and neutral wind disturbances lead to formation of various storm-time ionospheric electron density structures, such as super plasma fountain, equatorial electron density trough and F3 layer, as well as long-lasting global ionosphere suppression. We attempt to model these storm-related ionospheric electron density structures using the global assimilative ionospheric model that assimilates electron densities taken from FORMOSAT-3/COSMIC and TEC from ground-based GNSS receivers. Using the ensemble Kalman filter with consideration of ion densities, electric potential, thermospheric neutral wind and compositions as update variables, we study the performance and forecast capability of the assimilative model. The assimilative model could be utilized for ionosphere forecast in near future.

  7. TID measurement using oblique transmissions of HF pulses

    Science.gov (United States)

    Galkin, Ivan; Reinisch, Bodo; Huang, Xueqin; Paznukhov, Vadym; Hamel, Ryan; Kozlov, Alexander; Belehaki, Anna

    2017-04-01

    The Traveling Ionospheric Disturbance (TID), a wave-like signature of moving plasma density modulation in the ionosphere, is widely acknowledged for its utility in backtracking the anomalous events responsible for the TID generation, and as a major inconvenience to high-frequency (HF) operational systems because of its deleterious impact on the accuracy of navigation and geolocation. The pilot project "Net-TIDE" for the real-time detection and evaluation of TIDs began its operation in 2016 based on the remote-sensing data from synchronized, network-coordinated HF sounding between pairs of DPS4D ionosondes at five participating observatories in Europe. Measurement of all signal properties (Doppler frequency, angle of arrival, and time-of-flight from transmitter to receiver) proved to be instrumental in detecting the TID and deducing the TID parameters: amplitude, wavelength, phase velocity, and direction of propagation. Processing of the measured HF signal data required a specialized signal processing technique that is capable of consistently extracting different signals that have propagated along different ionospheric paths. The multi-path signal environment proved to be the greatest challenge for the reliable TID specification by Net-TIDE, demanding the development of an intelligent system for "signal tracking". The intelligent system is based on a neural network model of a pre-attentive vision capable of extracting continuous signal tracks from the multi-path signal ensemble. Specific examples of the Net-TIDE algorithm suite operation and its suitability for a fully automated TID warning service are discussed.

  8. Microhardness evaluation alloys Hf-Si-B; Avaliacao de microdureza de ligas Hf-Si-B

    Energy Technology Data Exchange (ETDEWEB)

    Gigolotti, Joao Carlos Janio; Costa, Eliane Fernandes Brasil [Centro Universitario de Volta Redonda (UNIFOA), Volta Redonda, RJ (Brazil); Nunes, Carlos Angelo; Rocha, Elisa Gombio; Coelho, Gilberto Carvalho, E-mail: carlosjanio@uol.com.br, E-mail: eliane-costabrasi@hotmail.com, E-mail: cnunes@demar.eel.usp.br, E-mail: elisarocha@alunos.eel.usp.br, E-mail: coelho@demar.eel.usp.br [Universidade de Sao Paulo (USP), Lorena, SP (Brazil)

    2014-08-15

    The technological advance has generated increasing demand for materials that can be used under high temperature, what includes intermetallic MR-Si-B (MR = refractory metal) alloys with multiphase structures, that can also be applied in oxide environments. Thus, this work had for objective the micro hardness study of the Hf-Si-B system alloys, heat treated at 1600 deg C, in the Hf rich region. Hf-Si-B alloys had been produced with blades of Hf (min. 99.8%), Si (min. 99.998%) and B (min. 99.5%), in the voltaic arc furnace and heat treated at 1600 deg C under argon atmosphere. The relationship of the phases had been previously identified by X-ray diffraction and contrast in backscattered electron imaging mode. The alloys had their hardness analyzed by method Vickers (micro hardness) with load of 0.05 kgf and 0.2 kgf and application time of 20 s. The results, obtained from the arithmetic mean of measurements for each alloy on the heterogeneous region, showed a mean hardness of 11.08 GPA, with small coefficient of variation of 3.8%. The borides HfB2 (19.34 GPa) e HfB - 11.76 GPa, showed the hardness higher than the silicides Hf2Si (8.57 GPa), Hf5Si3 (9.63 GPa), Hf3Si2 (11.66 GPa), Hf5Si4 (10.00 GPa), HfSi (10.02 GPa) e HfSi2 (8.61 GPa). (author)

  9. Incredibly distant ionospheric responses to earthquake

    Science.gov (United States)

    Yusupov, Kamil; Akchurin, Adel

    2015-04-01

    Attempts to observe ionospheric responses to the earthquake has been going on for decades. In recent years, the greatest progress in the study of this question have GPS-measurements with simultaneous HF-measurements. The use of a dense network of GPS-receivers and getting with it sufficiently detailed two-dimensional maps of the total electron content (TEC) greatly clarified the nature of the ionospheric response to strong earthquakes. For ionospheric responses observation, that are remote more than 1000 km from the strong earthquakes epicentres, it is necessary to applying more sensitive methods than GPS. The most experience in the observation of the ionospheric responses to earthquakes accumulated with Doppler sounding. Using these measurements, ionospheric disturbances characteristic features (signature) have been allocated, which associated with the passage of Rayleigh waves on the surface. Particular, this Rayleigh wave signatures allocation is implemented in the Nostradamus coherent backscatter radar. The authors of this method suggest using radar techniques like a sensitive "ionospheric seismometer." The most productive allocation and studying of the vertical structure ionospheric responses could be ionosonde observations. However, their typical 15 minute sounding rate is quite sufficient for observing the regular ionosphere, but it is not enough for studying the ionospheric responses to earthquakes, because ionospheric responses is often seen only in one ionogram and it is absent in adjacent. The decisive factor in establishing the striking ionospheric response to the earthquake was the Tohoku earthquake in 2011, when there was three ionosondes distant at 870-2000 km from the epicentre. These ionosondes simultaneously showed distortion of the F1-layer traces as its multiple stratification (multiple-cusp signature - MCS), which generated by Rayleigh wave. Note that there was another fourth Japanese ionosonde. It is located a little further near boundaries

  10. On Features of the Generation of Artificial Ionospheric Irregularities with Transverse Scales of 50-200 m

    Science.gov (United States)

    Bolotin, I. A.; Frolov, V. L.; Akchurin, A. D.; Zykov, E. Yu.

    2017-05-01

    We consider the features of generation of artificial ionospheric irregularities with transverse (to the geomagnetic field) scales l⊥ ≈ 50-200 m in the ionosphere modified by high-power HF radio waves. It was found that there are at least two mechanisms for generation of these irregularities in the ionospheric F region. The first mechanism is related to the resonant interaction between radio waves and the ionospheric plasma, while the second one takes place even in the absence of the resonant interaction. Different polarization of the high-power radiation was used to separate the mechanisms in the measurements.

  11. Ionospheric modelling for navigation

    Science.gov (United States)

    Aragon Angel, M. A.

    Signals transmitted to and from satellites for communication and navigation purposes must pass through the ionosphere Ionospheric irregularities most common at equatorial latitudes although they could occur anywhere can have a major impact on system performance and reliability and commercial navigation service satellite-based providers need to account for their effects For a GNSS single-frequency receiver the Slant Total Electron Content STEC must be known by the user through broadcast corrections In this context there are several sets of broadcast parameters that can be defined to take into account this ionospheric term The chosen model to generate the ionospheric correction coefficients for the present study is the NeQuick model although with a number of adaptations intended to improve effective ionospheric effect modelling performances The aim of this study is to describe a possible adaptation to the NeQuick model for real time purposes and suitable for single frequency users Therefore it will be necessary to determine the performance of this modified NeQuick model in correcting the ionospheric delay In order to generate the ionospheric corrections for single frequency receivers using the NeQuick model a certain approach should be followed to adapt the performance of NeQuick since this model was originally developed to provide TEC using averaged monthly information of the solar activity and not daily one Thus to use NeQuick for real time applications as an ionospheric broadcasted model such as Klobuchar solar daily information at the user point

  12. Nonlinear interactions of electromagnetic waves with the auroral ionosphere

    Science.gov (United States)

    Wong, Alfred Y.

    1999-09-01

    The ionosphere provides us with an opportunity to perform plasma experiments in an environment with long confinement times, very large-scale lengths, and no confining walls. The auroral ionosphere with its nearly vertical magnetic field geometry is uniquely endowed with large amount of free energy from electron and ion precipitation along the magnetic field and mega-ampere current across the magnetic field. To take advantage of this giant outdoor laboratory, two facilities HAARP and HIPAS, with frequencies ranging from the radio to optical bands, are now available for active probing of and interaction with this interesting region. The ponderomotive pressures from the self-consistent wave fields have produced significant local perturbations of density and particle distributions at heights where the incident EM frequency matches a plasma resonance. This paper will review theory and experiments covering the nonlinear phenomena of parametric decay instability to wave collapse processes. At HF frequencies plasma lenses can be created by preconditioning pulses to focus what is a normally divergent beam into a high-intensity spot to further enhance nonlinear phenomena. At optical wavelengths a large rotating liquid metal mirror is used to focus laser pulses up to a given height. Such laser pulses are tuned to the same wavelengths of selected atomic and molecular resonances, with resulting large scattering cross sections. Ongoing experiments on dual-site experiments and excitation of ELF waves will be presented. The connection of such basic studies to environmental applications will be discussed. Such applications include the global communication using ELF waves, the ozone depletion and remediation and the control of atmospheric CO2 through the use of ion cyclotron resonant heating.

  13. Bottomside Ionospheric Electron Density Specification using Passive High Frequency Signals

    Science.gov (United States)

    Kaeppler, S. R.; Cosgrove, R. B.; Mackay, C.; Varney, R. H.; Kendall, E. A.; Nicolls, M. J.

    2016-12-01

    The vertical bottomside electron density profile is influenced by a variety of natural sources, most especially traveling ionospheric disturbances (TIDs). These disturbances cause plasma to be moved up or down along the local geomagnetic field and can strongly impact the propagation of high frequency radio waves. While the basic physics of these perturbations has been well studied, practical bottomside models are not well developed. We present initial results from an assimilative bottomside ionosphere model. This model uses empirical orthogonal functions based on the International Reference Ionosphere (IRI) to develop a vertical electron density profile, and features a builtin HF ray tracing function. This parameterized model is then perturbed to model electron density perturbations associated with TIDs or ionospheric gradients. Using the ray tracing feature, the model assimilates angle of arrival measurements from passive HF transmitters. We demonstrate the effectiveness of the model using angle of arrival data. Modeling results of bottomside electron density specification are compared against suitable ancillary observations to quantify accuracy of our model.

  14. Electron Acceleration by High Power Radio Waves in the Ionosphere

    Science.gov (United States)

    Bernhardt, Paul

    2012-10-01

    At the highest ERP of the High Altitude Auroral Research Program (HAARP) facility in Alaska, high frequency (HF) electromagnetic (EM) waves in the ionosphere produce artificial aurora and electron-ion plasma layers. Using HAARP, electrons are accelerated by high power electrostatic (ES) waves to energies >100 times the thermal temperature of the ambient plasma. These ES waves are driven by decay of the pump EM wave tuned to plasma resonances. The most efficient acceleration process occurs near the harmonics of the electron cyclotron frequency in earth's magnetic field. Mode conversion plays a role in transforming the ES waves into EM signals that are recorded with ground receivers. These diagnostic waves, called stimulated EM emissions (SEE), show unique resonant signatures of the strongest electron acceleration. This SEE also provides clues about the ES waves responsible for electron acceleration. The electron gas is accelerated by high frequency modes including Langmuir (electron plasma), upper hybrid, and electron Bernstein waves. All of these waves have been identified in the scattered EM spectra as downshifted sidebands of the EM pump frequency. Parametric decay is responsible low frequency companion modes such as ion acoustic, lower hybrid, and ion Bernstein waves. The temporal evolution of the scattered EM spectrum indicates development of field aligned irregularities that aid the mode conversion process. The onset of certain spectral features is strongly correlated with glow plasma discharge structures that are both visible with the unaided eye and detectable using radio backscatter techniques at HF and UHF frequencies. The primary goals are to understand natural plasma layers, to study basic plasma physics in a unique ``laboratory with walls,'' and to create artificial plasma structures that can aid radio communications.

  15. Transient dynamics of secondary radiation from an HF pumped magnetized space plasma

    NARCIS (Netherlands)

    Norin, L.; Grach, S. M.; Thide, B.; Sergeev, E. N.; Leyser, T. B.

    2007-01-01

    In order to systematically analyze the transient wave and radiation processes that are excited when a high-frequency (HF) radio wave is injected into a magnetized space plasma, we have measured the secondary radiation, or stimulated electromagnetic emission ( SEE), from the ionosphere,

  16. Typical disturbances of the daytime equatorial F region observed with a high-resolution HF radar

    Directory of Open Access Journals (Sweden)

    E. Blanc

    1998-06-01

    Full Text Available HF radar measurements were performed near the magnetic equator in Africa (Korhogo 9°24'63''N–5°37'38''W during the International Equatorial Electrojet Year (1993–1994. The HF radar is a high-resolution zenithal radar. It gives ionograms, Doppler spectra and echo parameters at several frequencies simultaneously. This paper presents a comparative study of the daytime ionospheric structures observed during 3 days selected as representative of different magnetic conditions, given by magnetometer measurements. Broad Doppler spectra, large echo width, and amplitude fluctuations revealed small-scale instability processes up to the F-region peak. The height variations measured at different altitudes showed gravity waves and larger-scale disturbances related to solar daytime influence and equatorial electric fields. The possibility of retrieving the ionospheric electric fields from these Doppler or height variation measurements in the presence of the other possible equatorial ionospheric disturbances is discussed.

  17. GLL RPT IONOSPHERE PROFILES

    Data.gov (United States)

    National Aeronautics and Space Administration — The Galileo Radio Propagation Team Ionosphere Profile data set is small number of electron density profiles derived from radio occultation data collected while...

  18. Anomalies in the Ionosphere around the Southern faults of Haiti near the 2010 Earthquake

    Science.gov (United States)

    Cornely, P.; Daniell, R. E.

    2013-12-01

    In the last few decades, research on earthquake prediction has resulted in the recognition that there may exist many earthquake precursors in the lithosphere, atmosphere and ionosphere. The ionosphere is naturally perturbed by solar and geomagnetic disturbances and it is difficult to extract the variations connected with earthquakes particularly for the equatorial and high latitude ionosphere. Several researchers have contending theories on the mechanisms associated with pre-earthquake signals. The basic premise is that a thin layer of particles created before earthquakes due to ions originating from the earth's crust travel to the earth's surface and begin radiating from the earth's surface due to strong electric fields Namgaladze et al., [2009]. The ions can then travel from above earth's surface to the ionosphere where they can create ionospheric disturbances. When solar and geomagnetic disturbances can be ruled out, the effects of pre-seismic activities in the ionosphere can be assessed using fluctuations in the ionospheric electron density in the vicinity of fault lines. The Parameterized Ionospheric Model (PIM) is a fast global ionospheric model which produces electron density profiles (EDPs) between 90 and 25000 km altitude, which corresponds to critical altitudes of the ionosphere Daniell et al., [1995]. Since PIM only simulates a statistical mean ionosphere, sudden variations in ionospheric electron density will not be represented in the models, which make PIM ideal for background electron density predictions. The background predictions can then removed from the actual electron density data which could provide means for identifying pre-seismic electron density perturbations.

  19. HF Radio Angle-of-Arrival Measurements and Ionosonde Positioning

    Directory of Open Access Journals (Sweden)

    Lung-Chih Tsai

    2014-01-01

    Full Text Available Since 2010 a 2nd generation NOAA MF/HF radar, also referred to as the VIPIR ionosonde, has been operated at Hualien, Taiwan (23.8973°N, 121.5503°E. The Hualien VIPIR ionosonde is a modern ionospheric radar, fully digitizing complex signal records and using multiple parallel receiver channels for simultaneous signal measurements from multiple spaced receiving antennas. This paper considers radio direction finding based on interferometric phase measurements from a horizontal antenna array in the Hualien VIPIR ionosonde system. We applied the Hermite normal form method to solve the phase-measurement aliasing and least squares problems and improve the radio angle-of-arrival (AOA measurements. Backward ray-tracing simulation has been proposed to determine radio transmitter position. This paper presents a numerical, step by step ray-tracing method based on the IGRF superimposed onto a phenomenological ionospheric electron density model, the TaiWan Ionospheric Model (TWIM. The proposed methodology is successfully applied to locate two experimental HF radio transmitters at Longquan and Chungli with distance errors within 5 km and less than 5% of the great circle distances.

  20. An Ionospheric Index Model based on Linear Regression and Neural Network Approaches

    Science.gov (United States)

    Tshisaphungo, Mpho; McKinnell, Lee-Anne; Bosco Habarulema, John

    2017-04-01

    The ionosphere is well known to reflect radio wave signals in the high frequency (HF) band due to the present of electron and ions within the region. To optimise the use of long distance HF communications, it is important to understand the drivers of ionospheric storms and accurately predict the propagation conditions especially during disturbed days. This paper presents the development of an ionospheric storm-time index over the South African region for the application of HF communication users. The model will result into a valuable tool to measure the complex ionospheric behaviour in an operational space weather monitoring and forecasting environment. The development of an ionospheric storm-time index is based on a single ionosonde station data over Grahamstown (33.3°S,26.5°E), South Africa. Critical frequency of the F2 layer (foF2) measurements for a period 1996-2014 were considered for this study. The model was developed based on linear regression and neural network approaches. In this talk validation results for low, medium and high solar activity periods will be discussed to demonstrate model's performance.

  1. 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.

  2. Diagnostic study of coupled solar wind-magnetosphere-ionosphere dynamics in D-region ionosphere via VLF signal propagation characteristic

    Science.gov (United States)

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

    2016-07-01

    Geomagnetic disturbances and storms are known to produce significant global disturbances in the ionosphere, including the middle atmosphere and troposphere. There is little understanding about the mechanism and dynamics that drive these processes in lower ionosphere. The ionosphere is also thought to be sensitive to seismic events, and it is believed that it exhibits precursory characteristics as reported in studies via characteristic anomalies in VLF signal. However, distinguishing or separating seismically induced ionospheric fluctuations from those of other origins (e.g., Solar activity, planetary and tidal waves, stratospheric warming etc.) remain vital to robust conclusion, and challenging too. The unique propagation characteristic of VLF radio signal makes it an ideal tool for the study and diagnosis of variability of D-region ionosphere. In this work, we present the analysis of solar wind-magnetosphere-ionosphere coupling dynamics in D-region ionosphere using VLF signal characteristics, and performed an investigation of previously reported 'ionospheric precursors' to understand the true origins of measured anomalies.

  3. Robust detection of ionospheric irregularities

    Science.gov (United States)

    Walter, T.; Hansen, A.; Blanch, J.; Enge, P.; Mannucci, T.; Pi, X.; Sparks, L.; Iijima, B.; El-Arini, B.; Lejeune, R.; hide

    2000-01-01

    The approach outlined in this paper conservatively bounds the ionospheric errors even for the worst observed ionospheric conditions to date, using data sets taken from the operational receivers in the WAAS reference station network.

  4. F-region Magnetospheric ULF Generation by Modulated Ionospheric Heating

    Science.gov (United States)

    Papadopoulos, K.; Tesfaye, B.; Shroff, H.; Shao, X.; Milikh, G.; Chang, C.; Wallace, T.; Inan, U.; Piddyachiy, D.

    2007-12-01

    modulated-HF electromagnetic waves into a stable ionosphere. Ratios of perturbed magnetic field and density to their background values are extracted from simulations. Different radiation patterns from different polarization component of magnetic field perturbation are investigated. Effects of different profiles of non-uniform ionospheric plasma density on ULF wave propagation are also studied through simulation. Preliminary experimental evidence of the process will also be presented. This work was sponsored by ONR MURI Grant 5-28828

  5. Collision-Induced Dissociation Study of Strong Hydrogen-Bonded Cluster Ions Y−(HF)n (Y=F, O2) Using Atmospheric Pressure Corona Discharge Ionization Mass Spectrometry Combined with a HF Generator

    OpenAIRE

    Sakamoto, Kenya; Sekimoto, Kanako; Takayama, Mitsuo

    2017-01-01

    Hydrogen fluoride (HF) was produced by a homemade HF generator in order to investigate the properties of strong hydrogen-bonded clusters such as (HF)n. The HF molecules were ionized in the form of complex ions associated with the negative core ions Y− produced by atmospheric pressure corona discharge ionization (APCDI). The use of APCDI in combination with the homemade HF generator led to the formation of negative-ion HF clusters Y−(HF)n (Y=F, O2), where larger clusters with n≥4 were not dete...

  6. Asymmetry of the Venus nightside ionosphere: Magnus force effects

    Science.gov (United States)

    Pérez-de-Tejada, H.

    2008-11-01

    A study of the dawn-dusk asymmetry of the Venus nightside ionosphere is conducted by examining the configuration of the ionospheric trans-terminator flow around Venus and also the dawn-ward displacement of the region where most of the ionospheric holes and the electron density plateau profiles are observed (dawn meaning the west in the retrograde rotation of Venus and that corresponds to the trailing side in its orbital motion). The study describes the position of the holes and the density plateau profiles which occur at neighboring locations in a region that is scanned as the trajectory of the Pioneer Venus Orbiter (PVO) sweeps through the nightside hemisphere with increasing orbit number. The holes are interpreted as crossings through plasma channels that extend downstream from the magnetic polar regions of the Venus ionosphere and the plateau profiles represent cases in which the electron density maintains nearly constant values in the upper ionosphere along the PVO trajectory. From a collection of PVO passes in which these profiles were observed it is found that they appear at neighboring positions of the ionospheric holes in a local solar time (LST) map including cases where only a density plateau profile or an ionospheric hole was detected. It is argued that the ionospheric holes and the density plateau profiles have a common origin at the magnetic polar regions where plasma channels are formed and that the density plateau profiles represent crossings through a friction layer that is adjacent to the plasma channels. It is further suggested that the dawn-dusk asymmetry in the position of both features in the nightside ionosphere results from a fluid dynamic force (Magnus force) that is produced by the combined effects of the trans-terminator flow and the rotational motion of the ionosphere that have been inferred from the PVO measurements.

  7. Frederiksberg HF kursus

    DEFF Research Database (Denmark)

    Lindstrøm, Maria Duclos

    2008-01-01

    Notatet bygger på et interviewmateriale med dimitterede HF-kursister 3 måneder efter endt eksamen. Notatet undersøger dels, hvad der har hjulpet til at gennemføre, dels hvad der har været negativt og vanskeligt ved uddannelsen. Endvidere belyser notatet hvad kursisterne oplever at tage med fra de...

  8. NICARE I HF propagation experiment results and interpretation

    Science.gov (United States)

    Argo, P.; Fitzgerald, T. J.; Carlos, Robert

    1992-04-01

    The NICARE I chemical release created a large electron density depletion in the nighttime F region of the ionosphere at an altitude of approximately 300 km which persisted for at least 30 min. A three-dimensional ray-tracing code (TRACKER) predicted that the lenslike refractive perturbation would create new off-axis modes in long-distance HF radio paths which reflected in the ionosphere near the depletion. Channel measurements during this experiment bear this out. The multipath created by these new modes induced an increased fading rate on the received signals. Analysis of the time history of the direction of arrival of the new modes indicates that after the initial expansion of the release the western edge continued to move westward while the eastward edge remained stable in location. This behavior is consistent with model predictions of the behavior of the depletion.

  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. 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.

  11. 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.

  12. A warning system for travelling ionospheric disturbances using skywave Doppler frequency and angle-of-arrival measurements

    Science.gov (United States)

    Belehaki, Anna; Reinisch, Bodo; Galkin, Ivan

    2017-04-01

    Travelling ionospheric disturbances (TIDs) constitute a threat for operational systems using groundbased HF and trans-ionospheric VHF-UHF radiowave propagation. TIDs can impose disturbances with amplitudes of up to 20% of the ambient electron density, and a Doppler frequency shifts of the order of 0.5 Hz on HF signals. Therefore their identification and tracking is important for the reliable operation of critical systems using the ionosphere as an essential part or for systems for which the ionosphere is fundamentally a nuisance. The Net-TIDE project has developed a warning system for real-time identification of TIDs using skywave Doppler frequency and angle-of-arrival measurements. Data are collected from network-coordinated HF sounding between pairs of European DPS4D and processed in real-time for the calculation of the angles-of-arrival and Doppler frequencies of ionospherically reflected high-frequency (HF) radio signals. The outcome is provided in real-time to the users to characterise TID activity over Europe based on the measured signal parameters. Complementary methodologies based on the analysis of vertical sounding parameters are currently exploited as verification means to improve the confidence level of the warnings. The resulting map of TID activity is updated every 5 minutes to enable the end-users enabling them to put into action specific mitigation techniques to protect their systems.

  13. Marburg Hemorrhagic Fever (Marburg HF)

    Science.gov (United States)

    ... Submit Search the CDC Marburg hemorrhagic fever (Marburg HF) Note: Javascript is disabled or is not supported ... Fever (VHF) Information for Specific Groups, References... Marburg HF Outbreak Distribution Map Factsheet: Marburg Hemorrhagic Fever [PDF – ...

  14. Computerized ionospheric tomography

    Energy Technology Data Exchange (ETDEWEB)

    Austen, J.R.; Raymund, T.D.; Klobuchar, J.A.; Stalker, J.; Liu, C.H.

    1990-05-03

    In this paper the background of computerized tomography (CT) and its application to the ionosphere is reviewed. CT techniques, using only total electron content (TEC) data, can be used to reconstruct a two-dimensional image of the electron density in the ionosphere. The limitations of this technique are discussed and examples showing the limitations and capabilities are presented. Simulation results for two applications are presented: imaging the high latitude trough, and the correction of tracking radar range rate errors. Some possible extensions of the technique are presented.

  15. Wuhan Ionospheric Oblique Backscattering Sounding System and Its Applications—A Review

    Science.gov (United States)

    Shi, Shuzhu; Yang, Guobin; Jiang, Chunhua; Zhang, Yuannong; Zhao, Zhengyu

    2017-01-01

    For decades, high-frequency (HF) radar has played an important role in sensing the Earth’s environment. Advances in radar technology are providing opportunities to significantly improve the performance of HF radar, and to introduce more applications. This paper presents a low-power, small-size, and multifunctional HF radar developed by the Ionospheric Laboratory of Wuhan University, referred to as the Wuhan Ionospheric Oblique Backscattering Sounding System (WIOBSS). Progress in the development of this radar is described in detail, including the basic principles of operation, the system configuration, the sounding waveforms, and the signal and data processing methods. Furthermore, its various remote sensing applications are briefly reviewed to show the good performance of this radar. Finally, some suggested solutions are given for further improvement of its performance. PMID:28629157

  16. Wuhan Ionospheric Oblique Backscattering Sounding System and Its Applications-A Review.

    Science.gov (United States)

    Shi, Shuzhu; Yang, Guobin; Jiang, Chunhua; Zhang, Yuannong; Zhao, Zhengyu

    2017-06-18

    For decades, high-frequency (HF) radar has played an important role in sensing the Earth's environment. Advances in radar technology are providing opportunities to significantly improve the performance of HF radar, and to introduce more applications. This paper presents a low-power, small-size, and multifunctional HF radar developed by the Ionospheric Laboratory of Wuhan University, referred to as the Wuhan Ionospheric Oblique Backscattering Sounding System (WIOBSS). Progress in the development of this radar is described in detail, including the basic principles of operation, the system configuration, the sounding waveforms, and the signal and data processing methods. Furthermore, its various remote sensing applications are briefly reviewed to show the good performance of this radar. Finally, some suggested solutions are given for further improvement of its performance.

  17. Wuhan Ionospheric Oblique Backscattering Sounding System and Its Applications—A Review

    Directory of Open Access Journals (Sweden)

    Shuzhu Shi

    2017-06-01

    Full Text Available For decades, high-frequency (HF radar has played an important role in sensing the Earth’s environment. Advances in radar technology are providing opportunities to significantly improve the performance of HF radar, and to introduce more applications. This paper presents a low-power, small-size, and multifunctional HF radar developed by the Ionospheric Laboratory of Wuhan University, referred to as the Wuhan Ionospheric Oblique Backscattering Sounding System (WIOBSS. Progress in the development of this radar is described in detail, including the basic principles of operation, the system configuration, the sounding waveforms, and the signal and data processing methods. Furthermore, its various remote sensing applications are briefly reviewed to show the good performance of this radar. Finally, some suggested solutions are given for further improvement of its performance.

  18. Wave and plasma measurements and GPS diagnostics of the main ionospheric trough as a hybrid method used for Space Weather purposes

    Directory of Open Access Journals (Sweden)

    H. Rothkaehl

    2008-02-01

    Full Text Available The region of the main ionospheric trough is a unique region of the ionosphere, where different types of waves and instabilities can be generated. This region of the ionosphere acts like a lens, focusing a variety of indicators from the equator of plasmapause and local ionospheric plasma. This paper reports the results of monitoring the mid-latitude trough structure, dynamics and wave activity. For these purposes, the data gathered by the currently-operating DEMETER satellite and past diagnostics located on IK-19, Apex, and MAGION-3 spacecraft, as well as TEC measurements were used. A global-time varying picture of the ionospheric trough was reconstructed using the sequence of wave spectra registered and plasma measurements in the top-side ionosphere. The authors present the wave activity from ULF frequency band to the HF frequency detected inside the trough region and discuss its properties during geomagnetic disturbances. It is thought that broadband emissions are correlated with low frequency radiation, which is excited by the wave-particle interaction in the equatorial plasmapause and moves to the ionosphere along the geomagnetic field line. In the ionosphere, the suprathermal electrons can interact with these electrostatic waves and excite electron acoustic waves or HF longitudinal plasma waves. Furthermore, the electron density trough can provide useful data on the magnetosphere ionosphere dynamics and morphology and, in consequence, can be used for Space Weather purposes.

  19. Wave and plasma measurements and GPS diagnostics of the main ionospheric trough as a hybrid method used for Space Weather purposes

    Directory of Open Access Journals (Sweden)

    H. Rothkaehl

    2008-02-01

    Full Text Available The region of the main ionospheric trough is a unique region of the ionosphere, where different types of waves and instabilities can be generated. This region of the ionosphere acts like a lens, focusing a variety of indicators from the equator of plasmapause and local ionospheric plasma. This paper reports the results of monitoring the mid-latitude trough structure, dynamics and wave activity. For these purposes, the data gathered by the currently-operating DEMETER satellite and past diagnostics located on IK-19, Apex, and MAGION-3 spacecraft, as well as TEC measurements were used. A global-time varying picture of the ionospheric trough was reconstructed using the sequence of wave spectra registered and plasma measurements in the top-side ionosphere. The authors present the wave activity from ULF frequency band to the HF frequency detected inside the trough region and discuss its properties during geomagnetic disturbances. It is thought that broadband emissions are correlated with low frequency radiation, which is excited by the wave-particle interaction in the equatorial plasmapause and moves to the ionosphere along the geomagnetic field line. In the ionosphere, the suprathermal electrons can interact with these electrostatic waves and excite electron acoustic waves or HF longitudinal plasma waves.

    Furthermore, the electron density trough can provide useful data on the magnetosphere ionosphere dynamics and morphology and, in consequence, can be used for Space Weather purposes.

  20. Global GPS Ionospheric Modelling Using Spherical Harmonic Expansion Approach

    Directory of Open Access Journals (Sweden)

    Byung-Kyu Choi

    2010-12-01

    Full Text Available In this study, we developed a global ionosphere model based on measurements from a worldwide network of global positioning system (GPS. The total number of the international GPS reference stations for development of ionospheric model is about 100 and the spherical harmonic expansion approach as a mathematical method was used. In order to produce the ionospheric total electron content (TEC based on grid form, we defined spatial resolution of 2.0 degree and 5.0 degree in latitude and longitude, respectively. Two-dimensional TEC maps were constructed within the interval of one hour, and have a high temporal resolution compared to global ionosphere maps which are produced by several analysis centers. As a result, we could detect the sudden increase of TEC by processing GPS observables on 29 October, 2003 when the massive solar flare took place.

  1. Collision-Induced Dissociation Study of Strong Hydrogen-Bonded Cluster Ions Y-(HF) n (Y=F, O2) Using Atmospheric Pressure Corona Discharge Ionization Mass Spectrometry Combined with a HF Generator.

    Science.gov (United States)

    Sakamoto, Kenya; Sekimoto, Kanako; Takayama, Mitsuo

    2017-01-01

    Hydrogen fluoride (HF) was produced by a homemade HF generator in order to investigate the properties of strong hydrogen-bonded clusters such as (HF) n . The HF molecules were ionized in the form of complex ions associated with the negative core ions Y - produced by atmospheric pressure corona discharge ionization (APCDI). The use of APCDI in combination with the homemade HF generator led to the formation of negative-ion HF clusters Y - (HF) n (Y=F, O 2 ), where larger clusters with n ≥4 were not detected. The mechanisms for the formation of the HF, F - (HF) n , and O 2 - (HF) n species were discussed from the standpoints of the HF generator and APCDI MS. By performing energy-resolved collision-induced dissociation (CID) experiments on the cluster ions F - (HF) n ( n =1-3), the energies for the loss of HF from F - (HF) 3 , F - (HF) 2 , and F - (HF) were evaluated to be 1 eV or lower, 1 eV or higher, and 2 eV, respectively, on the basis of their center-of-mass energy ( E CM ). These E CM values were consistent with the values of 0.995, 1.308, and 2.048 eV, respectively, obtained by ab initio calculations. The stability of [O 2 (HF) n ] - ( n =1-4) was discussed on the basis of the bond lengths of O 2 H-F - (HF) n and O 2 - H-F(HF) n obtained by ab initio calculations. The calculations indicated that [O 2 (HF) 4 ] - separated into O 2 H and F - (HF) 3 .

  2. Temporal Development of HF-Excited Langmuir and Ion Turbulence at Arecibo

    Science.gov (United States)

    Djuth, F. T.; DuBois, D. F.

    2015-10-01

    The Arecibo high-power, high-frequency (HF) facility and 430 MHz radar are used to examine the temporal development of the HF-induced Langmuir and ion turbulences from 1 ms to many minutes after the turn-on of the HF beam in the F region. All HF observations begin in a smooth, stratified, stable plasma. "Cold start" HF transmissions are employed to avoid remnant irregularities from prior HF transmissions. HF-excited plasma line (HFPL) and ion line echoes are used to monitor the evolution of the turbulence. In the evening/nighttime the HFPL develops in three reproducible stages. Over time scales of 0 to 10-20 ms (possibly 40 ms), the smooth plasma conditions are maintained, and the results are consistent with theoretical models of the excitation of strong Langmuir turbulence near HF reflection. This entails the initiation of the so-called "caviton production cycle." The turbulence from the parametric decay instability is detected at lower altitudes where the radar wave vector matches those of the HF-enhanced waves. The data suggests that the two processes coexist in the region in between. After ~40 ms the "overshoot process" begins and consists of a downward extension of the HFPL from the HF reflection region to heights ~1.1 km below followed by a retreat back to the reflection region. The whole overshoot process takes place over a time scale of ~3 s. Thereafter the echo remains near HF reflection for 20-90 s after HF turn-on. The HFPL echo subsequently breaks up into patches because of the formation of large-scale electron density structures in the plasma. New kinetic models indicate that suprathermal electrons excited in the plasma by, for example, caviton burn-out serve to regulate plasma turbulence in the modified ionospheric volume.

  3. Remote double resonance coupling of radar energy to ionospheric irregularities

    Science.gov (United States)

    Kennel, C. F.

    1971-01-01

    Experimental results indicate that low frequency modulation of a high power radar beam, tuned to one of the critical frequencies of the ionosphere, may produce field-aligned density irregularities when the modulation frequency matches an ionospheric eigenfrequency. By choosing the radar carrier frequency and polarization, a number of interaction layers were selected. The variety of possible excitations shows that the double resonance technique may be adaptable to a number of different objectives.

  4. Formation and detection of high latitude ionospheric irregularities

    Science.gov (United States)

    Lee, M. C.; Buchau, J.; Carlson, H. C., Jr.; Klobuchar, J. A.; Weber, E. J.

    1985-01-01

    Measurements of Total Electron Content (TEC) and airglow variations show that large scale plasma patches appearing in the high-latitude ionsophere have irregular structures evidenced by the satellite phase and amplitude scintillations. Whistler waves, intense quasi-DC electric field, and atmospheric gravity waves can become potential sources of various plamsa instabilities. The role of thermal effects in generating ionospheric irregularities by these sources is discussed. Meter-scale irregularities in the ionospheric E and F regions can be excited parametrically with lower hybrid waves by intense whistler waves. Ohmic dissipation of Pedersen current in the electron gas is able to create ionospheric F region irregularities in plasma blobs or plasma patches (i.e., high ambient plasma density environment) with broad scale lengths ranging from tens of meters to a few kilometers. Through the neutral-charged particle collisions, gravity waves can excite large-scale (less than tens of kilometers) ionospheric irregularities simultaneously with forced ion acoustic modes in the E region. The large-scale ionospheric density fluctuations produced in the E region can extend subsequently alogn the earth's magnetic field to the F region and the topside ionospheric regions. These mechanisms characterized by various thermal effects can contribute additively with other processes to the formation of ionospheric irregularities in the high latitude region.

  5. Ionosphere and Radio Communication

    Indian Academy of Sciences (India)

    spheric winds, solar heating, photoionization, electrical conduc- tivity, and interactions with the magnetic .... GENERAL ARTICLE in satellites to explore the electric field in the neighbourhood of the magnetopause 2. 2 ... that as soon as a space vehicle is sent to the ionosphere, it can dis- turb the neutral atmosphere and the ...

  6. Ionosphere and Radio Communication

    Indian Academy of Sciences (India)

    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 ...

  7. 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.

  8. Ground and Space-Based Measurement of Rocket Engine Burns in the Ionosphere

    Science.gov (United States)

    Bernhardt, P. A.; Ballenthin, J. O.; Baumgardner, J. L.; Bhatt, A.; Boyd, I. D.; Burt, J. M.; Caton, R. G.; Coster, A.; Erickson, P. J.; Huba, J. D.; hide

    2013-01-01

    On-orbit firings of both liquid and solid rocket motors provide localized disturbances to the plasma in the upper atmosphere. Large amounts of energy are deposited to ionosphere in the form of expanding exhaust vapors which change the composition and flow velocity. Charge exchange between the neutral exhaust molecules and the background ions (mainly O+) yields energetic ion beams. The rapidly moving pickup ions excite plasma instabilities and yield optical emissions after dissociative recombination with ambient electrons. Line-of-sight techniques for remote measurements rocket burn effects include direct observation of plume optical emissions with ground and satellite cameras, and plume scatter with UHF and higher frequency radars. Long range detection with HF radars is possible if the burns occur in the dense part of the ionosphere. The exhaust vapors initiate plasma turbulence in the ionosphere that can scatter HF radar waves launched from ground transmitters. Solid rocket motors provide particulates that become charged in the ionosphere and may excite dusty plasma instabilities. Hypersonic exhaust flow impacting the ionospheric plasma launches a low-frequency, electromagnetic pulse that is detectable using satellites with electric field booms. If the exhaust cloud itself passes over a satellite, in situ detectors measure increased ion-acoustic wave turbulence, enhanced neutral and plasma densities, elevated ion temperatures, and magnetic field perturbations. All of these techniques can be used for long range observations of plumes in the ionosphere. To demonstrate such long range measurements, several experiments were conducted by the Naval Research Laboratory including the Charged Aerosol Release Experiment, the Shuttle Ionospheric Modification with Pulsed Localized Exhaust experiments, and the Shuttle Exhaust Ionospheric Turbulence Experiments.

  9. Travelling ionospheric disturbance properties deduced from Super Dual Auroral Radar measurements

    Directory of Open Access Journals (Sweden)

    J. W. MacDougall

    2000-12-01

    Full Text Available Based on modeling of the perturbations in power and elevation angle produced by travelling ionospheric disturbances (TIDs, and observed by the Super Dual Auroral Radar Network, procedures for determining the TID properties are suggested. These procedures are shown to produce reasonable agreement with those properties of the TIDs that can be measured from simultaneous ionosonde measurements. The modeling shows that measurements of angle-of-elevation perturbations by SuperDARN allows for better determination of the TID properties than using only the perturbations of power as is commonly done.Key words: Ionosphere (auroral ionosphere; ionosphere-atmosphere interactions

  10. The CMS HF status

    CERN Document Server

    Rahmat, Rahmat

    2012-01-01

    The experiments at the Large Hadron Collider will have to deal with unprecedented radiation levels. The design of the CMS forward calorimetry detector (HF) is now finalized. The present design of CMS calls for the HF calorimeter to be based on quartz fiber technology. It consists of two modules, located symmetrically at about 11 meters from either side of interaction point. They cover the pseudorapidity range 3-5. The length along the beam is 1.65m or 10 nuclear interaction lenghts. Each calorimeter consists of a large steel block that serves as the absorber. Embedded quartz fibers in the steel absorber run parallel to the beam and constitute the active component of the detector. In order to optimize energy resolution for E and ET flows and forward jets, the calorimeter is effectively segmented longitudinally by using two different fiber lengths. The present status will be discussed.

  11. Survivable HF communications

    Science.gov (United States)

    Randerson, John T.

    Robust HF uses a noncoherent FSK (frequency-shift-keyed) signal. It uses fast pseudorandom frequency hopping and a rugged modulation format which makes it impervious to multipath, atmospheric, and man-made noise. It is optimized as an antijam system. The robust-HF operating frequency range is 2-30 MHz. The pseudorandom frequency hopping uses variable bandwidth and adapts to the best frequencies between the lowest usable frequency and the maximum usable frequency. The system operates skywave (long distance) or ground wave (up to 100 km, or even more over water). Buried hard antennas have been tested and show almost no degradation in system performance. Robust HF uses powerful error coding with variable code rates and code combining, which automatically adapt according to link conditions. The result is exceptional processing gain. A powerful cyclic redundancy check (CRC) is included to prevent delivery of corrupt data. System bit rates run as high as 600 b/s, with average throughput of about 75 b/s, depending on the code rate.

  12. Generation of Acoustic Gravity Waves by Periodic Radio Transmissions from a High-Power Ionospheric Heater

    Science.gov (United States)

    Frolov, Vladimir; Chernogor, Leonid; Rozumenko, Victor

    The Radiophysical Research Institute (Nizhny Novgorod, Russia) and Kharkiv V. N. Karazin National University (Kharkiv, Ukraine) have studied opportunities for the effective generation of acoustic gravity waves (AGWs) in 3 - 180-min period range. The excitation of such waves was conducted for the last several years using the SURA heating facility (Nizhny Novgorod). The detection of the HF-induced AGWs was carried out in the Radiophysical Observatory located near Kharkiv City at a distance of about 960 km from the SURA. A coherent radar for vertical sounding, an ionosonde, and magnetometer chains were used in our measurements. The main results are the following (see [1-5]): 1. Infrasound oscillation trains with a period of 6 min are detected during periodic SURA heater turn-on and -off. Similar oscillation trains are detected after long time pumping, during periodic transmissions with a period of 20 s, as well as after pumping turn-off. The train recordings begin 28 - 54 min after the heater turn-on or -off, and the train propagation speeds are about 300 - 570 m/s, the value of which is close to the sound speed at upper atmospheric altitudes. The amplitude of the Doppler shift frequency is of 10 - 40 mHz, which fits to the 0.1 - 0.3% electron density disturbances at ionospheric altitudes. The amplitude of the infrasound oscillations depends on the SURA mode of operation and the state of the upper atmosphere and ionosphere. 2. High-power radio transmissions stimulate the generation (or enhancement) of waves at ionospheric altitudes in the range of internal gravity wave periods. The HF-induced waves propagate with speeds of 360 - 460 m/s and produce changes in electron density with amplitudes of 2 - 3%. The generation of such periodic perturbations is more preferable with periods of 10 - 60 minutes. Their features depend significantly on the heater mode of operation. It should be stressed that perturbation intensity increases when a pumping wave frequency approaches

  13. GNSS monitoring of the ionosphere for Space Weather services

    Science.gov (United States)

    Krankowski, A.; Sieradzki, R.; Zakharenkova, I. E.; Cherniak, I. V.

    2012-04-01

    The International GNSS Service (IGS) Ionosphere Working Group routinely provides the users global ionosphere maps (GIMs) of vertical total electron content (vTEC). The IGS GIMs are provided with spatial resolution of 5.0 degrees x 2.5 degrees in longitude and latitude, respectively. The current temporal resolution is 2 hours, however, 1-hour maps are delivered as a pilot project. There are three types IGS GIMs: the final, rapid and predicted. The latencies of the IGS ionospheric final and rapid products are 10 days and 1 day, respectively. The predicted GIMs are generated for 1 and 2 days in advance. There are four IGS Associate Analysis Centres (IAACs) that provide ionosphere maps computed with independent methodologies using GNSS data. These maps are uploaded to the IGS Ionosphere Combination and Validation Center at the GRL/UWM (Geodynamics Research Laboratory of the University of Warmia and Mazury in Olsztyn, Poland) that produces the IGS official ionospheric products, which are published online via ftp and www. On the other hand, the increasing number of permanently tracking GNSS stations near the North Geomagnetic Pole allow for using satellite observations to detect the ionospheric disturbances at high latitudes with even higher spatial resolution. In the space weather service developed at GRL/UWM, the data from the Arctic stations belonging to IGS/EPN/POLENET networks were used to study TEC fluctuations and scintillations. Since the beginning of 2011, a near real-time service presenting the conditions in the ionosphere have been operational at GRL/UWM www site. The rate of TEC index (ROTI) expressed in TECU/min is used as a measure of TEC fluctuations. The service provides 2-hour maps of the TEC variability. In addition, for each day the daily map of the ionospheric fluctuations as a function geomagnetic local time is also created. This presentation shows the architecture, algorithms, performance and future developments of the IGS GIMs and this new space

  14. Comparison of Vertical Ionospheric Drifts Obtained by Different Techniques

    Science.gov (United States)

    Kouba, D.

    2016-12-01

    Since 2004 the ionospheric observatory in Pruhonice (Czech Republic, 50N, 14.9E) provides regular ionospheric sounding using Digisonde. In addition to classical ionograms the drift velocities in both E and F region using DDA method are measured routinely. However, vertical component of the drift velocity vector can be estimated by several different methods which can be found in the literature; for example the indirect estimation based on the temporal evolution of measured ionospheric characteristics is often used for calculation of the vertical drift component. The vertical velocity is thus estimated according to the change of characteristics scaled from the classical quarter-hour ionograms. In present paper the direct drift measurement is compared with technique based on measuring of the virtual height at fixed frequency from the F-layer trace on ionogram, technique based on variation of h`F and hmF. The ionospheric observatory in Pruhonice is midlatitudinal station and typicaly provides measurements in 15 minutes cadence. Due to the fact that the most papers use different indirect methods use equatorial data, we also focuse on results of equatorial stations and other stations that carry out measurements with higher cadence (5 minutes). Our comparison shows possibility of using different methods for calculating vertical drift velocity and their relationship to the direct measurement used by Digisondes.

  15. UK Solar System Data Centre: Data Archive for Ionospheric Research

    Science.gov (United States)

    Wild, Matthew; James, Sarah; Bogdanova, Yulia; Crothers, Steve

    2014-05-01

    The UK Solar System Data Centre (UKSSDC) has been working to improve access to its extensive holdings of historical ionospheric data. In our archive, ionospheric data from 200 stations worldwide (1930s-present), such as ionograms and scaled ionospheric parameters (e.g., foF2, fmin, h'F2), is held on both digital and physical media. From the 1990s these data sets are available in digital form and can be downloaded from our web-interface. Thanks to a Natural Environment Research Council grant we are in the process of digitising a selection, 2,200 out of ~27,000, of UK ionosonde film data to be made available via the web interface. It is hoped that more funding will be made available to continue this exercise over the next few years. The UKSSDC also provides real-time ionospheric data retrieval from two RAL Space ionosondes, Chilton and Port Stanley, alongside other European observatories. The UKSSDC is part of RAL Space based at Rutherford Appleton Laboratory with the electronic address: http://www.ukssdc.ac.uk. This is a UK national data archive facility with open data access and can be used by scientists around the globe.

  16. Frequency and power dependency of HF-induced ionization signatures in incoherent scatter radar observations

    Science.gov (United States)

    Gustavsson, Bjorn; Sergienko, Tima; Rietveld, Michael; Brandstrom, Urban; Senior, Andrew; Vickers, Hannah; Kosch, Michael

    Incoherent scatter radar observations of high-power HF radio-wave induced enhancements in backscatter from ion-acoustic and plasma waves have been observed with the EISCAT UHF radar during Heating experiments where the pump-frequency passed through the 3rd and 4th harmonic of the electron gyro-frequency. The altitude-variation of the enhancement indicate an asymmetry in HF-induced ionization between pump-frequencies below and above a gyro-resonance. Models for ionospheric electron density response to ionization from HF-accelerated electrons is compared to the very precise observations of the altitude variation of the matching-altitudes. Optical observations of radio induced optical emissions are used to determine the electron acceleration by HF-radio waves.

  17. HF fiber stuffing in building 186 at CERN

    CERN Multimedia

    Tiziano Camporesi

    2003-01-01

    Each of the 36 HF wedges comprise ca 12000 quartz fibers which are the active element of the calorimeter. The fibers are produced by Polymicro (USA), cleaved and bundled at KFKI, Budapest, Hungary and inserted at CERN.

  18. High frequency based detection of TIDs in the Net-TIDE project: challenges and opportunities for long HF paths

    Science.gov (United States)

    Verhulst, Tobias

    2016-07-01

    Travelling Ionospheric Disturbances (TIDs) are the ionospheric signatures of atmospheric gravity waves. TIDs carry along information about their sources of excitations which may be either natural (energy input from the auroral region, earthquakes/tsunamis, hurricanes, solar terminator, and others) or artificial (ionospheric modification experiments, nuclear explosions, and other powerful blasts like industrial accidents). TIDs contribute to the energy and momentum exchange between different regions of the ionosphere, especially during geomagnetic storms. Their tracking is important because the TIDs affect all services that rely on predictable ionospheric radio wave propagation. Although a number of methods have been proposed to measure TID characteristics, none is able to operate in real time for monitoring purposes. In the framework of a new NATO Science for Peace and Security multi-year project (2014--2017) we are exploiting for the first time the European network of high precision ionospheric DPS4D sounders and the related software to directly identify TIDs over Europe and specify in real-time the gravity wave parameters based on measuring the variations of the angles-of-arrival and Doppler frequencies of ionospherically reflected HF radio signals. The project will run until 2017 and is expected to result in a pilot network of DPS4D ionospheric sounders in Europe, enhanced with a system to process the TID observations for real-time diagnostics and issue warnings for TIDs and the potential disturbance over the area. Based on these warnings the end-users can put in action specific mitigation techniques to protect their systems. The technical challenges of operating long distance ionospheric HF radio links for the detection of TIDs will be discussed.

  19. Collision-Induced Dissociation Study of Strong Hydrogen-Bonded Cluster Ions Y−(HF)n (Y=F, O2) Using Atmospheric Pressure Corona Discharge Ionization Mass Spectrometry Combined with a HF Generator

    Science.gov (United States)

    Sakamoto, Kenya; Sekimoto, Kanako; Takayama, Mitsuo

    2017-01-01

    Hydrogen fluoride (HF) was produced by a homemade HF generator in order to investigate the properties of strong hydrogen-bonded clusters such as (HF)n. The HF molecules were ionized in the form of complex ions associated with the negative core ions Y− produced by atmospheric pressure corona discharge ionization (APCDI). The use of APCDI in combination with the homemade HF generator led to the formation of negative-ion HF clusters Y−(HF)n (Y=F, O2), where larger clusters with n≥4 were not detected. The mechanisms for the formation of the HF, F−(HF)n, and O2−(HF)n species were discussed from the standpoints of the HF generator and APCDI MS. By performing energy-resolved collision-induced dissociation (CID) experiments on the cluster ions F−(HF)n (n=1–3), the energies for the loss of HF from F−(HF)3, F−(HF)2, and F−(HF) were evaluated to be 1 eV or lower, 1 eV or higher, and 2 eV, respectively, on the basis of their center-of-mass energy (ECM). These ECM values were consistent with the values of 0.995, 1.308, and 2.048 eV, respectively, obtained by ab initio calculations. The stability of [O2(HF)n]− (n=1–4) was discussed on the basis of the bond lengths of O2H–F−(HF)n and O2−H–F(HF)n obtained by ab initio calculations. The calculations indicated that [O2(HF)4]− separated into O2H and F−(HF)3. PMID:28966900

  20. Chemistry in the Thermosphere and Ionosphere.

    Science.gov (United States)

    Roble, Raymond G.

    1986-01-01

    An informative review which summarizes information about chemical reactions in the thermosphere and ionosphere. Topics include thermal structure, ultraviolet radiation, ionospheric photochemistry, thermospheric photochemistry, chemical heating, thermospheric circulation, auroral processes and ionospheric interactions. Provides suggested followup…

  1. Considering the potential of IAR emissions for ionospheric sounding

    Science.gov (United States)

    Potapov, A. S.; Polyushkina, T. N.; Tsegmed, B.; Oinats, A. V.; Pashinin, A. Yu.; Edemskiy, I. K.; Mylnikova, A. A.; Ratovsky, K. G.

    2017-11-01

    Knowledge of the ionospheric state allows us to adjust the forecasts of radio wave propagation, specify the environment models, and follow the changes of space weather. At present, probing of the ionosphere is produced by radio sounding with ground ionosondes, as well as by raying signals from satellites. We want to draw attention to the possibility of the diagnosis of the ionospheric parameters by detecting ultra-low frequency (ULF) electromagnetic emission generated in the so-called ionospheric Alfvén resonator (IAR). To do this, we present observations of the IAR emission made simultaneously for the first time at three stations using identical induction magnetometers. The stations are within one-hour difference of local time, two of them are mid-latitudinal; the third one is situated in the auroral zone. We compare frequency and frequency difference between adjacent harmonics of the observed multi-band emission with ionospheric parameters measured at the stations using ionosondes and GPS-observations. Diurnal variations of the ionospheric and ULF emission characteristics are also compared. The results show that there is quite a stable correlation between the resonant frequencies of the resonator bands and the critical frequency of the F2 layer of the ionosphere, namely, the frequency of the IAR emission varies inversely as the critical frequency of the ionosphere. This is due to the fact that the frequency of oscillation captured in the resonator is primarily determined by the Alfvén velocity (which depends on the plasma density) in the ionospheric F2 layer. The correlation is high; it varies at different stations, but is observed distinctly along the whole meridian. However, coefficients of a regression equation that connects the ionosphere critical frequency with DSB frequency vary significantly from day to day at all stations. The reason for such a big spread of the regression parameters is not clear and needs further investigation before we are able to

  2. Local Ionospheric Scintillation Analysis

    Science.gov (United States)

    2017-03-14

    International Conference on Aerospace Electronics, Electrical, Communications & Instrumentation , Vijayawada, India Title: “Ionospheric Impact of Severe...receiver instrumental biases? Radio Sci. 32 (5), 1899–1910, http://dx.doi.org/10.1029/ 97RS01457, 1997. DISTRIBUTION A. Approved for public release...Guarnieni, F.L., Tsuda, T., Saito, A., Yumoto, K., Fejer, B., Fuller -Rowell, T.J., Kozyra, J., Foster, J.C.,Coster, A.J., Vasyliunas, V.M. Global

  3. High latitude ionospheric structure.

    Science.gov (United States)

    Ossakow, S. L.; Burke, W.; Carlson, H. C.; Gary, P.; Heelis, R.; Keskinen, M.; Maynard, N.; Meng, C.; Szuszczewicz, E.; Vickrey, J.

    Contents: 1. Introduction: Ionospheric structure in general. Equatorial spread-F irregularities - a success story and a guide for high latitudes. Focus on high-latitude structure. 2. Sources and observations of high-latitude structure: Electron precipitation structures. Electric fields. Field-aligned currents. Plasma density structure. 3. Plasma instability theory: Macroinstabilities and high latitude structure. Microinstabilities and high latitude structure. 4. An emerging picture. 5. Future studies: Theoretical thrusts. Experimental emphasis.

  4. SEE Observations of Ionospheric Heating from HAARP Using Orbital Angular Momentum

    Science.gov (United States)

    Briczinski, S. J.; Bernhardt, P. A.; Siefring, C. L.

    2013-12-01

    High power HF radio waves exciting the ionosphere provide aeronomers with a unique space-based laboratory capability. The High-Frequency Active Auroral Research Program (HAARP) in Gakona, Alaksa is the world's largest heating facility, providing effective radiated powers in the gigawatt range. Experiments performed at HAARP have allowed researchers to study many non-linear effects of wave-plasma interactions. Stimulated Electromagnetic Emission (SEE) is of interest to the ionospheric community for its diagnostic purposes. Typical SEE experiments at HAARP have focused on characterizing the parametric decay of the electromagnetic pump wave into several different wave modes such as upper and lower hybrid, ion acoustic, ion-Bernstein and electron-Bernstein. These production modes have been extensively studied at HAARP using traditional beam heating patterns and SEE detection. New results are present from HAARP experiments using an excitation mode that attempts to impart orbital angular momentum (OAM) into the heating region. This OAM mode is also referred to as a 'twisted beam.' Previous analysis of twisted beam heating shows that the SEE results obtained are nearly identical to the modes without OAM. Recent twisted beam heating experiments have produced SEE modes not previously characterized. These new modes are presented and discussed. One difference in the twisted beam mode is the heating region produced is in the shape of a ring as opposed to the more traditional 'solid spot' region. The ring heating pattern may be more conducive to the creation of artificial ionization clouds. The results of these runs include artificial ionization creation and evolution as pertaining to the twisted beam pattern.

  5. CDDIS_DORIS_products_ionosphere

    Data.gov (United States)

    National Aeronautics and Space Administration — Ionosphere correction values derived from analysis of Doppler Orbitography by Radiopositioning Integrated on Satellite (DORIS) data. These products are the generated...

  6. Kriging with Unknown Variance Components for Regional Ionospheric Reconstruction

    Directory of Open Access Journals (Sweden)

    Ling Huang

    2017-02-01

    Full Text Available Ionospheric delay effect is a critical issue that limits the accuracy of precise Global Navigation Satellite System (GNSS positioning and navigation for single-frequency users, especially in mid- and low-latitude regions where variations in the ionosphere are larger. Kriging spatial interpolation techniques have been recently introduced to model the spatial correlation and variability of ionosphere, which intrinsically assume that the ionosphere field is stochastically stationary but does not take the random observational errors into account. In this paper, by treating the spatial statistical information on ionosphere as prior knowledge and based on Total Electron Content (TEC semivariogram analysis, we use Kriging techniques to spatially interpolate TEC values. By assuming that the stochastic models of both the ionospheric signals and measurement errors are only known up to some unknown factors, we propose a new Kriging spatial interpolation method with unknown variance components for both the signals of ionosphere and TEC measurements. Variance component estimation has been integrated with Kriging to reconstruct regional ionospheric delays. The method has been applied to data from the Crustal Movement Observation Network of China (CMONOC and compared with the ordinary Kriging and polynomial interpolations with spherical cap harmonic functions, polynomial functions and low-degree spherical harmonic functions. The statistics of results indicate that the daily ionospheric variations during the experimental period characterized by the proposed approach have good agreement with the other methods, ranging from 10 to 80 TEC Unit (TECU, 1 TECU = 1 × 1016 electrons/m2 with an overall mean of 28.2 TECU. The proposed method can produce more appropriate estimations whose general TEC level is as smooth as the ordinary Kriging but with a smaller standard deviation around 3 TECU than others. The residual results show that the interpolation precision of the

  7. Effects of Atmospheric Variability on Ionospheric Manifestations of Earthquakes and Tsunamis

    Science.gov (United States)

    Godin, O. A.; Zabotin, N. A.; Zabotina, L.

    2014-12-01

    There is a large and increasing number of ground-based and satellite-borne instruments, which reliably reveal ionospheric manifestations of natural hazards such as large earthquakes, strong tsunamis, and powerful tornadoes. As the focus shifts from detecting the ionospheric features associated with the natural hazards to characterizing the hazards for the purposes of improving early warning systems and contributing to disaster recovery, it becomes imperative to relate quantitatively characteristics of the observed ionospheric disturbances and the underlying natural hazard. The relation between perturbations at the ground level and their ionospheric manifestations is strongly affected by parameters of the intervening atmosphere. In this paper, we employ the ray theory to model propagation of acoustic gravity waves in three-dimensionally inhomogeneous atmosphere. Huygens' wavefront-tracing and Hamiltonian ray-tracing algorithms are used to simulate wave propagation from an earthquake hypocenter through the earth's crust and ocean to the upper atmosphere as well as the generation of atmospheric waves by seismic surface waves and tsunamis. We quantify the influence of temperature stratification and winds, including their seasonal variability, and air viscosity and thermal conductivity on the geometry and amplitude of ionospheric disturbances. Modeling results are verified by comparing observations of the velocity fluctuations at altitudes of 150-160 km by a coastal Dynasonde HF radar system with theoretical predictions of ionospheric manifestations of background infragravity waves in the ocean. Dynasonde radar systems are shown to be a promising means for monitoring acoustic-gravity wave activity and observing ionospheric perturbations due to earthquakes and tsunamis. The effects will be discussed of background ionospheric disturbances and uncertainty in atmospheric parameters on the feasibility and accuracy of retrieval of open-ocean tsunami heights from observations

  8. Evaluation of six ionospheric models as predictors of TEC

    Energy Technology Data Exchange (ETDEWEB)

    Brown, L.D.; Daniell, R.E.; Fox, M.W.; Klobuchar, J.A.; Doherty, P.H.

    1990-05-03

    The authors have gathered TEC data from a wide range of latitudes and longitudes for a complete range of solar activity. This data was used to evaluate the performance of six ionospheric models as predictors of Total Electron Content (TFC). The TEC parameter is important in correcting modern DOD space systems, which propagate radio signals from the earth to satellites, for the time delay effects of the ionosphere. The TEC data were obtained from polarimeter receivers located in North America, the Pacific, and the East Coast of Asia. The ionospheric models evaluated are: (1) the International Reference Ionosphere (IRI); (2) the Bent model; (3) the Ionospheric Conductivity and Electron Density (ICED) model; (4) the Penn State model; (5) the Fully Analytic Ionospheric Model (FAIM, a modification of the Chiu model); and (6) the Damen-Hartranft model. They will present extensive comparisons between monthly mean TEC at all local times and model TEC obtained by integrating electron density profiles produced by the six models. These comparisons demonstrate that even thought most of the models do very well at representing f0F2, none of them do very well with TEC, probably because of inaccurate representation of the topside scale height. They suggest that one approach to obtaining better representations of TEC is the use of f0E2 from coefficients coupled with a new slab thickness developed at Boston University.

  9. On determining the noon polar cap boundary from SuperDARN HF radar backscatter characteristics

    Directory of Open Access Journals (Sweden)

    M. Pinnock

    2000-12-01

    Full Text Available Previous work has shown that ionospheric HF radar backscatter in the noon sector can be used to locate the footprint of the magnetospheric cusp particle precipitation. This has enabled the radar data to be used as a proxy for the location of the polar cap boundary, and hence measure the flow of plasma across it to derive the reconnection electric field in the ionosphere. This work used only single radar data sets with a field of view limited to ~2 h of local time. In this case study using four of the SuperDARN radars, we examine the boundary determined over 6 h of magnetic local time around the noon sector and its relationship to the convection pattern. The variation with longitude of the latitude of the radar scatter with cusp characteristics shows a bay-like feature. It is shown that this feature is shaped by the variation with longitude of the poleward flow component of the ionospheric plasma and may be understood in terms of cusp ion time-of-flight effects. Using this interpretation, we derive the time-of-flight of the cusp ions and find that it is consistent with approximately 1 keV ions injected from a subsolar reconnection site. A method for deriving a more accurate estimate of the location of the open-closed field line boundary from HF radar data is described.Key words: Ionosphere (ionosphere–magnetosphere interactions; plasma convection · Magnetospheric physics (magnetopause · cusp · and boundary layers

  10. Validation of the CUTLASS HF radar gravity wave observing capability using EISCAT CP-1 data

    Directory of Open Access Journals (Sweden)

    N. F. Arnold

    1998-10-01

    Full Text Available Quasi-periodic fluctuations in the returned ground-scatter power from the SuperDARN HF radars have been linked to the passage of medium-scale gravity waves. We have applied a technique that extracts the first radar range returns from the F-region to study the spatial extent and characteristics of these waves in the CUTLASS field-of-view. Some ray tracing was carried out to test the applicability of this method. The EISCAT radar facility at Tromsø is well within the CUTLASS field-of-view for these waves and provides a unique opportunity to assess independently the ability of the HF radars to derive gravity wave information. Results from 1st March, 1995, where the EISCAT UHF radar was operating in its CP-1 mode, demonstrate that the radars were in good agreement, especially if one selects the electron density variations measured by EISCAT at around 235 km. CUTLASS and EISCAT gravity wave observations complement each other; the former extends the spatial field of view considerably, whilst the latter provides detailed vertical information about a range of ionospheric parameters.Key words. Ionosphere (ionosphere – atmosphere interactions · Meteorology and atmospheric dynamics (thermospheric dynamics · Radio science (ionospheric propagations

  11. Validation of the CUTLASS HF radar gravity wave observing capability using EISCAT CP-1 data

    Directory of Open Access Journals (Sweden)

    N. F. Arnold

    Full Text Available Quasi-periodic fluctuations in the returned ground-scatter power from the SuperDARN HF radars have been linked to the passage of medium-scale gravity waves. We have applied a technique that extracts the first radar range returns from the F-region to study the spatial extent and characteristics of these waves in the CUTLASS field-of-view. Some ray tracing was carried out to test the applicability of this method. The EISCAT radar facility at Tromsø is well within the CUTLASS field-of-view for these waves and provides a unique opportunity to assess independently the ability of the HF radars to derive gravity wave information. Results from 1st March, 1995, where the EISCAT UHF radar was operating in its CP-1 mode, demonstrate that the radars were in good agreement, especially if one selects the electron density variations measured by EISCAT at around 235 km. CUTLASS and EISCAT gravity wave observations complement each other; the former extends the spatial field of view considerably, whilst the latter provides detailed vertical information about a range of ionospheric parameters.

    Key words. Ionosphere (ionosphere – atmosphere interactions · Meteorology and atmospheric dynamics (thermospheric dynamics · Radio science (ionospheric propagations

  12. CUTLASS HF radar observations of high-velocity E-region echoes

    Directory of Open Access Journals (Sweden)

    M. V. Uspensky

    2001-04-01

    Full Text Available A short event of high-velocity E-region echo observations by the Pykkvibaer HF radar is analysed to study echo parameters and the echo relation to the Farley-Buneman plasma instability. The echoes were detected in several beams aligned closely to the magnetic L-shell direction. Two echo groups were identified: one group corresponded to the classical type 1 echoes with velocities close to the nominal ion-acoustic speed of 400 ms–1 , while the other group had significantly larger velocities, of the order of 700 ms–1 . The mutual relationship between the echo power, Doppler velocity, spectral width and elevation angles for these two groups was studied. Plotting of echo parameters versus slant range showed that all ~700 ms–1 echoes originated from larger heights and distances of 500–700 km, while all ~400 ms–1 echoes came from lower heights and from farther distances; 700–1000 km. We argue that both observed groups of echoes occurred due to the Farley-Buneman plasma instability excited by strong ( ~70 mVm–1 and uniformly distributed electric fields. We show that the echo velocities for the two groups were different because the echoes were received from different heights. Such a separation of echo heights occurred due to the differing amounts of ionospheric refraction at short and large ranges. Thus, the ionospheric refraction and related altitude modulation of ionospheric parameters are the most important factors to consider, when various characteristics of E-region decametre irregularities are derived from HF radar measurements.Key words. Ionosphere (ionospheric irregularities; plasma waves and instabilities; polar ionosphere

  13. Anvendelsesorientering på hf

    DEFF Research Database (Denmark)

    Christensen, Torben Spanget

    2009-01-01

    Med 2005-reformen af de gymnasiale uddannelser blev anvendelsesorientering hf's særlige profilkendetegn. Kravet om anvendelsesorientering er en udfordring til hf-uddannelsen, både i forhold til uddannelsens almene formål og i forhold til den praktiske etablering af anvendelsesorienterede...

  14. First modulation of high-frequency polar mesospheric summer echoes by radio heating of the ionosphere

    Science.gov (United States)

    Senior, A.; Mahmoudian, A.; Pinedo, H.; La Hoz, C.; Rietveld, M. T.; Scales, W. A.; Kosch, M. J.

    2014-08-01

    The first high-frequency (HF, 8 MHz) observations of the modulation of polar mesospheric summer echoes (PMSE) by artificial radio heating of the ionosphere are presented and compared to observations at 224 MHz and model predictions. The experiments were performed at the European Incoherent Scatter facility in northern Norway. It is shown that model results are in qualitative and partial quantitative agreement with the observations, supporting the prediction that with certain ranges of ice particle radii and concentration, PMSE at HF radar wavelengths can be enhanced by heating due to the dominance of dust charging over plasma diffusion.

  15. Monitoring of ionospheric irregularities with multi-GNSS observations: a new ionosphere activity index and product services

    Science.gov (United States)

    Wang, Ningbo; Li, Zishen; Yuan, Yunbin; Yuan, Hong

    2017-04-01

    and North American regions. The product files are produced on a daily basis with a latency of 3 days. Users now can access these products from the ftp archive of the Chinese Academy of Sciences (CAS, ftp://ftp.gipp.org.cn/product/). These maps can be used for ionospheric weather services, ionospheric irregularity modeling and foresting, as well as other GNSS applications. Although they are provided in a post-processing mode at present, it is expected that the near real-time services will be available since the availability of real-time data streams from the IGS.

  16. Improved modeling of midlatitude D-region ionospheric absorption of high frequency radio signals during solar X-ray flares

    Science.gov (United States)

    Schumer, Evelyn A.

    High frequency (HF) radio communication is widely used for real-time, medium to long range communications due to its low cost of operation and maintenance. However, HF communication is strongly dependent on the state of the ionosphere, which is sensitive to solar X-ray flares. The lowest region of the ionosphere, the D-region, is the region in which the majority of the absorption of HF radio wave energy occurs. D-region HF absorption depends on the local electron density, which is enhanced during a solar X-ray flare. HF propagation data obtained during the HF Investigation of D-region Ionospheric Variation Experiment (HIDIVE) and obtained at the Canadian Space Agency NORSTAR riometer in Pinawa, Manitoba, Canada and X-ray flux data, as reported by GOES satellites, are analyzed here for the purpose of validating and improving the performance of two HF absorption models, the operational Space Weather Prediction Center (SWPC) D-region Absorption model and the physical AbbyNormal model. The SWPC D-region absorption model is an empirical model providing real-time global predictions of D-region absorption, and the physical Absorption by the D and E Region of HF Signals with Normal Incidence (AbbyNormal) model is based on simple D-region chemistry and provides near real-time predictions of midlatitude D-region HF absorption. Analysis of the HIDIVE data revealed an absorption dependence on signal frequency of f-1.24 where f is signal frequency, and a Cos 0.9(chi) dependence on solar zenith angle, chi. These relations differ from what is used in the SWPC model, and from these relations, a new empirical model, the Empirical HIDIVE Absorption (EHA) model, is developed. The EHA model can be used to improve the SWPC model performance. NO density data obtained with the Student Nitric Oxide Explorer (SNOE) and during the Halogen Occultation Experiment (HALOE) are used to improve the method by which the AbbyNormal model defines the nitric oxide (NO) profile within the atmosphere

  17. Planetary wave oscillations in the equatorial MLT region and in the E- and F- region of the equatorial ionosphere.

    Science.gov (United States)

    Ramkumar, T.; Gurubaran, S.; Sastri, J.; Rajaram, R.

    The ordered current flows existing in the E and F region of the equatorial ionosphere is believed to be mainly due to the dynamo action of the tidal waves in the neutral winds of the atmosphere. During day times, the emfs induced in the E-region of the ionosphere, because of the high electrical conductivity existing there, are easily mapped on to the F region of the ionosphere through the highly conducting equipotential geomagnetic field lines. So, any changes in the E region electric fie ld due to the perturbations in the tidal winds will produce similar changes in the F region electric field also. Correspondingly the vertical plasma drifts and hence the plasma frequencies in the latter region will show the modulation effects. It is believed that sometimes the lower atmospheric (troposphere and stratosphere) free resonant or any other unstable planetary (period of oscillation varies over a few days to a few tens of days) waves may propagate well above 100 km. These waves then produce current systems through dynamo mechanism or modulate the upward propagating tidal or gravity waves and hence the dynamo currents corresponding to the periods of planetary wave oscillations. In the present paper we present the results on the possible influences of the equatorial mesospheric planetary waves on the equatorial electrojet strength (EEJS), and the equatorial F-region parameters like hpF2 (M3000), h'F, and foF2. For this study, we used the mesospheric wind data obtained with the MF (1.98 MHz) partial reflection radar, located at the Indian dip equatorial site Tirunelveli. The equatorial electrojet strength (EEJS) is obtained by taking the difference of the geomagnetic field variations measured both at the EEJ station Trivandrum and the off EEJ station Alibag. To study the other E and F-region parameters, we used the data obtained- with the ionosonde, located at the EEJ site Kodaikanal. Along with the fast Fourier transform (FFT) technique, we also utilized the wavelet

  18. Solar power satellites and the ionosphere - The effect of high power microwave beams on the ionosphere and the chemical effects due to Heavy-Lift Launch Vehicles

    Science.gov (United States)

    The effects of solar power satellites on the ionosphere are discussed, separated into two categories: (1) passive interactions, in which the ionospheric plasma influences the propagation of the power satellite beam in some way, and in some instances possibly gives rise to co-channel interference through scattering off the beam, and (2) an active inteference, in which ionospheric plasma itself is modified. Strong electron heating from the power satellite beam may produce irregularities in the ionization capable of scattering radio waves of lower frequencies, thereby increasing the potential for broad-band interference. Ionospheric modification may also result from the emission of exhaust effluents from heavy lift launch vehicles, and associated changes in ionospheric chemistry can lead to depletions in ionization at F-region heights. Interference with radio services is briefly discussed.

  19. Extreme Ionospheric Gradients Observed in South Korea during the Last Solar Cycle

    Science.gov (United States)

    Jung, S.; Choi, Y.; Kim, M.; Lee, J.

    2012-12-01

    CONUS threat model. The other 12 dates are newly selected based on two space weather indices, planetary K (Kp) and disturbance, storm time (Dst). An ionospheric gradient of 90.97 mm/km was discovered at 0414UT on November 6, 2001 between stations NAWW and SONC, when PRN 21 was at 20.1° elevation. Most of severe gradients were observed from satellites at low elevation and traveling in a southerly direction of the Korean Peninsula. To locate enhanced-delay regions, we investigate both global ionospheric delay maps generated using the IONosphere MAP Exchange format (IONEX) data provided by International GNSS Service (IGS) and regional delay maps produced using the Korean GPS network stations. To validate observed ionospheric anomaly events, we examine whether similarly large ionospheric gradients are discovered at other nearby station pairs and other satellites whose Ionospheric Pierce Point (IPP) tracks take similar paths. The results from a series of checks support that the equatorial ionospheric anomaly caused severe ionospheric gradients observed from southern stations in South Korea. This study provides a better understanding of ionospheric behavior within the Korean Peninsula under ionospheric storm conditions, and helps investigate the operation and performance of GBAS. Ionospheric threat model developed in each region could be combined into a future global threat model for GBAS.

  20. Radar observations of ionospheric irregularities at Syowa Station, Antarctica: a brief overview

    Directory of Open Access Journals (Sweden)

    T. Ogawa

    1996-12-01

    Full Text Available We briefly overview the radar observations that have been made for 30 years at Syowa Station, Antarctica for studying small-scale electron-density irregularities in the southern high-latitude E- and F-region ionosphere. Some observational results (i.e., long-term variations of radio aurora, Doppler spectra with narrow spectral widths and low Doppler velocities, and simultaneous observations of radar and optical auroras from VHF radars capable of detecting 1.3- to 3-m scale irregularities are presented. A new 50-MHz radar system equipped with phased-antenna arrays began operation in February 1995 to observe two-dimensional behaviours of E-region irregularities. An HF radar experiment also began in February 1995 to explore decameter-scale E- and F-region irregularities in the auroral zone and polar cap. These two radars will contribute to a better understanding of the ionospheric irregularities and ionospheric physics at southern high latitudes.

  1. GPS, Earthquakes, the Ionosphere, and the Space Shuttle

    Science.gov (United States)

    Calais, Eric; Minster, J. Bernard

    1998-01-01

    Sources such as atmospheric or buried explosions and shallow earthquakes producing strong vertical ground displacements are known to produce infrasonic pressure waves in the atmosphere. Because of the coupling between neutral particles and electrons at ionospheric altitudes, these acoustic waves induce variations of the ionospheric electron density. The Global Positioning System provides a way of directly measuring the Total Electron Content in the ionosphere and, therefore. of detecting such perturbations in the upper atmosphere. In this work, we demonstrate the capabilities of the GPS technique to detect ionospheric perturbations caused by the January 17. 1994, M (sub w) =6.7, Northridge earthquake and the STS-58 Space Shuttle ascent. In both cases, we observe a perturbation of the ionospheric electron density lasting for about 30 m, with periods less than 10 m. The perturbation is complex and shows two sub-events separated by about 15 m. The phase velocities and waveform characteristics of the two sub-events lead us to interpret the first arrival as the direct propagation of 2 free wave, followed by oscillatory guided waves propagating along horizontal atmospheric interfaces at 120 km altitude and below.

  2. Improved estimation of Mars ionosphere total electron content

    Science.gov (United States)

    Cartacci, M.; Sánchez-Cano, B.; Orosei, R.; Noschese, R.; Cicchetti, A.; Witasse, O.; Cantini, F.; Rossi, A. P.

    2018-01-01

    We describe an improved method to estimate the Total Electron Content (TEC) of the Mars ionosphere from the echoes recorded by the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) (Picardi et al., 2005; Orosei et al., 2015) onboard Mars Express in its subsurface sounding mode. In particular, we demonstrate that this method solves the issue of the former algorithm described at (Cartacci et al., 2013), which produced an overestimation of TEC estimates on the day side. The MARSIS signal is affected by a phase distortion introduced by the Mars ionosphere that produces a variation of the signal shape and a delay in its travel time. The new TEC estimation is achieved correlating the parameters obtained through the correction of the aforementioned effects. In detail, the knowledge of the quadratic term of the phase distortion estimated by the Contrast Method (Cartacci et al., 2013), together with the linear term (i.e. the extra time delay), estimated through a radar signal simulator, allows to develop a new algorithm particularly well suited to estimate the TEC for solar zenith angles (SZA) lower than 95° The new algorithm for the dayside has been validated with independent data from MARSIS in its Active Ionospheric Sounding (AIS) operational mode, with comparisons with other previous algorithms based on MARSIS subsurface data, with modeling and with modeling ionospheric distortion TEC reconstruction.

  3. Relationship Between the Radio Bursts from the Sun and Ionospheric Propagation

    Science.gov (United States)

    West, Mary Lou; Frissell, N.; Papalos, M.

    2006-12-01

    We are monitoring the sun’s radio activity at 20.1 MHz with a Radio Jove rig, and have begun to monitor the Earth’s ionosphere for HF radio propagation using the worldwide network of beacons set up by the Northern California DX Foundation. These 18 beacons transmit at 14.1, 18.11, 21.15, 24.93, and 28.2 MHz on a 3 minute cadence and allow ham radio operators to judge the radio propagation characteristics to distant lands easily. Although the solar activity cycle is now near its bottom, there are occasional outbursts, some spectacular. August 29, 2006, was such a day, prompting the Radio Jove community to post ten times the usual number of reports to the archive at Goddard Space Flight Center. The next day the Earth’s ionosphere suddenly blossomed with HF openings without any X-ray flares reported. The delay time of 26 hours from the most energetic radio event indicated a velocity of 1600 km/s, normal for a coronal mass ejection. Several other events have also shown delays of about 24 hours from the radio sun to the ionosphere, and are especially noticeable at the higher frequency bands and on the events list of the Space Environment Center of NOAA. The 20.1 MHz monitors may serve as a method to predict radio propagation properties of the ionosphere more quickly than previous methods.

  4. Use of the Hualien, Taiwan, dynasonde for surveillance of HF environmental radio and positioning of transmitting stations

    Science.gov (United States)

    Tsai, L.-C.; Chen, G. H.; Tian, M. H.; Zhang, Y.

    2012-04-01

    Since 2010, a 2nd generation NOAA HF radars, also referred as dynasonde, has been built at Hualien (23.89 N, 121.55 E), Taiwan. The Hualien dynasonde has a new design of ionospheric radar of fully digitizing the complex signal records and using multiple parallel receiver channels for simultaneous measurements of signals from multiple spaced receiving antennas. The Hualien dynasonde utilizes interferometric sounding pulse patterns and a receiving antenna array (including eight receivers connected to different spaced dipole antennas) to receive not only ionospherical echoes but also environmental radio signals. We have applied the Hermite normal form method to solve the phase-measurement aliasing and least squares problem and improve measurements of radio angles of arrival (AOA). The further ray-tracing experiments can be used for the study of radio wave propagation in the ionosphere. In this study we present a numerical and step by step ray-tracing method on a phenomenological ionospheric electron density model, the TaiWan Ionospheric Model (TWIM), which is constructed from the FormoSat3 / Constellation Observing System for Meteorology, Ionosphere and Climate (FS3/COSMIC) ionospheric radio occultation data and global ionosonde foF2 data. The three-dimensional TWIM consists of vertically-fitted α-Chapman-type layers, with distinct F2, F1, E, and D layers, for which the layer parameters such as peak density, peak density height, and scale height are represented by surface spherical harmonics. This way the continuity of Ne and its derivatives is maintained. The methodology is successfully applied to a practical HF transmitter for oblique incidence ray tracing. Then, the AOA data will be used for backward ray tracing in the TWIM model and be used to determine ground-based transmitting station position.

  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. Coupling between tsunamis and ionosphere: ground-based and space-based observation opportunities

    Science.gov (United States)

    Coisson, Pierdavide; Makela, Jonathan J.; Occhipinti, Giovanni; Astafyeva, Elvira; alam Kherani, Esfhan; Lognonne, Philippe

    2012-07-01

    Large scale phenomena as tsunamis propagating through the ocean excite gravity waves that can reach ionospheric heights. The coupling between the ground/ocean and the atmosphere up to the ionosphere opens the possibility to observe in the upper atmosphere the effects of the propagation of tsunamis. During all recent major tsunami events ionospheric waves have been observed by ground GPS networks, satellite altimeters and, recently, also by an airglow imager. During the tsunami event of 11 March 2011 an all-sky camera in Hawaii observes the Internal Gravity Waves (IGW) during about one-and-a-half hours before the arrival of the, while it was crossing the Pacific Ocean in that region. Collocated ionospheric measurements were also done with GNSS sounding and Jason satellite. We present results of assessment studies of ground-based and space-based ionospheric remote sensing for tsunami propagation monitoring. We analyze the cases of airglow imager, Over-The-Horizon (OTH) radar, GPS, radio occultation and GNSS reflectometry. We describe modeling results of IGW excited by a realistic tsunami propagation model through the ocean near Hawaii. The model includes the propagation of the gravity wave in the atmosphere, the coupling between neutral and charged particles in the ionosphere and the production of the airglow emission at 630.0 nm. Synthetic all-sky images are calculated by integration of the emission along rays from the camera location to though the airglow layer. Additional ground-based observations could be provided by (OTH) radars, which operate in High Frequency (HF) band and can be used to monitor the bottomside ionosphere. Synthetic radar measurements computed using HF numerical ray-tracing confirm the possibility to detect IGW excited by tsunamis. The large coverage of OTH radar and its sensitivity to low-altitude plasma anomalies provides a wide range of observation. Additionally, we analyze the capabilities of space-based radio occultation and GNSS

  7. Observation of ionospheric gravity waves induced by the 2011 Tohoku earthquake and tsunami using GPS networks in Japan

    Science.gov (United States)

    Tang, Long; Guo, Bofeng; Zhang, Xiaohong

    2017-04-01

    Recent observation results show the atmospheric gravity waves produced by both tsunami and earthquake can propagate upward to the atmosphere and interact with the plasma at the ionospheric height, leading to the generation of ionospheric disturbances. Carefully analyzing the propagation characteristics of ionospheric disturbances is necessary in order to distinguish the sources. Here, we use the GPS total electron content (TEC) observations in Japan to detect the ionospheric disturbances after the 2011 Tohoku earthquake, respectively. The Tohoku (Japan) earthquake (Mw=9) occurred at 05:46 UT on 11 March 2011 and then triggered powerful tsunami. The fundamental work is to properly isolate the ionospheric disturbances from raw TEC observations. Here, a second-order number difference method is employed to extract disturbance series and analyze the propagation characteristics of the ionospheric disturbances. The results show there are two types of gravity waves in the ionosphere over Japan, which is produced by the tsunami waves and the seismic rupture process, respectively. The earthquake-driven ionospheric gravity waves are distributed around the epicenter (including the areas over and far from the ocean) whereas the tsunami-driven ionospheric gravity waves are observed above the ocean. The earthquake-driven ionospheric gravity waves have different horizontal velocities, including about 210 m/s and 170 m/s, and frequency of about 1.5 mHz. The tsunami-driven ionospheric gravity waves have velocity of about 280 m/s, which are faster than that of the earthquake-driven ionospheric gravity waves, and frequency of about 1.0 mHz. In addition, the tsunami-driven ionospheric gravity waves have similar propagation characteristics in terms of horizontal velocity, direction, travel time, waveform and frequency compared to the tsunami waves causing them. In short, this study distinguishes the tsunami signals in ionosphere from ionospheric disturbances triggered by the earthquake

  8. The worldwide ionospheric data base

    Science.gov (United States)

    Bilitza, Dieter

    1989-01-01

    The worldwide ionospheric data base is scattered over the entire globe. Different data sets are held at different institutions in the U.S., U.S.S.R., Australia, Europe, and Asia. The World Data Centers on the different continents archive and distribute part of the huge data base; the scope and cross section of the individual data holdings depend on the regional and special interest of the center. An attempt is made to pull together all the strings that point toward different ionospheric data holdings. Requesters are provided with the information about what is available and where to get it. An attempt is also made to evaluate the reliability and compatibility of the different data sets based on the consensus in the ionospheric research community. The status and accuracy of the standard ionospheric models are also discussed because they may facilitate first order assessment of ionospheric effects. This is a first step toward an ionospheric data directory within the framework of NSSDC's master directory.

  9. Det anvendelsesorienterede perspektiv på HF

    DEFF Research Database (Denmark)

    Svejgaard, Karin Løvenskjold; Christensen, Torben Spanget

    Rapport fra et projekt, hvor undervisere på hf har arbejdet med at definere og udvikle anvendelsesperspektivet, som er én af formålsformuleringerne i HF-uddanelsen......Rapport fra et projekt, hvor undervisere på hf har arbejdet med at definere og udvikle anvendelsesperspektivet, som er én af formålsformuleringerne i HF-uddanelsen...

  10. Towards Observing Tsunamis in the Ionosphere Using GPS TEC Measurements

    Science.gov (United States)

    Galvan, D. A.; Komjathy, A.; Mannucci, A.; Hickey, M. P.; Schubert, G.; Walterscheid, R. L.; Occhipinti, G.

    2009-12-01

    Recent modeling results and observations have demonstrated that the ionospheric signature of an ocean tsunami can potentially be detected as a traveling ionospheric disturbance (TID) produced by internal gravity waves propagating upward in the atmosphere [e.g., Hickey et al., (2009), Occhipinti et al., (2006)]. These tsunamigenic TID’s have been demonstrated to be present in total electron content (TEC) measurements using ground-based GPS radio signals [e.g., Artru et al., (2005)] and satellite-based altimeter radar [Occhipinti et al., (2006)]. There are many remaining unanswered questions regarding the reliability of detecting tsunamigenic TIDs, including how to distinguish them from TIDs of non-tsunamigenic origin, as well as factors affecting the propagation of internal gravity waves in the ionosphere. We present ongoing research analyzing ground-based GPS TEC observations during multiple known tsunami events. Specifically, fluctuations in TEC are obtained by comparing observed TEC with modeled TEC estimates using JPL’s Global Ionospheric Mapping (GIM) system. These small fluctuations are then band-passed filtered and Fourier analyzed, across multiple GPS satellites and ground stations, to search for wave patterns similar to the coincident ocean tsunami in the same geographic region. Results are discussed in terms of the degree to which a tsunamigenic TID is observed in each case, and the possible causes for failing to observe them. Comparisons between observations and results from theoretical models of tsunamigenic ionospheric wave propagation are also discussed for specific cases.

  11. Physics of the ionosphere ionosfera - atmosfera superior - fisica

    Energy Technology Data Exchange (ETDEWEB)

    Bittencourt, J.A.

    1978-01-01

    A review of the basic concepts of ionospheric physics is presented. The dynamics of the upper neutral atmosphere related to studies of the ionosphere, the formation of the ionosphere, the differences in the various ionospheric layers, physical and chemical processes, ionospheric phenomenon, wave propagation, and a method for measuring ionospheric plasma parameters are presented.

  12. Theory of intense radio waves in an underdense ionosphere: application to solar power satellite transmissions. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Goldman, M V

    1980-11-01

    The instabilities in the F-region plasma are investigated that can be created by the passage of a solar power satellite beam (2.45 Ghz frequency, at a power flux of 23 mW/cm/sup 2/) at frequencies much higher than the cut-off plasma frequency of the ionosphere. The threshold geometry and frequency and intensity scaling laws are calculated for the thermal self-focusing instability, and its saturation level is estimated. The possibility is considered of scaled experiments at HF power to detect the thermal self-focusing instability for an underdense ionosphere. Other experimental possibilities are discussed in terms of the scaling laws. (LEW)

  13. 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) and t...

  14. Measurement and modeling of HF channel directional spread characteristics for northerly paths

    Science.gov (United States)

    Warrington, E. M.; Stocker, A. J.; Siddle, D. R.

    2006-04-01

    The northerly ionosphere is a dynamic propagation medium that causes HF signals reflected from this region to exhibit delay spreads and Doppler shifts and spreads that significantly exceed those observed over midlatitude paths. Since the ionosphere is not perfectly horizontally stratified, the signals associated with each propagation mode may arrive at the receiver over a range of angles in both azimuth and elevation. Such large directional spreads may have a severe impact on radio systems employing multielement antenna arrays and associated signal-processing techniques since the signal environment does not comprise a small number of specular components as often assumed by the processing algorithms. In order to better understand the directional characteristics of HF signals reflected from the northerly ionosphere, prolonged measurements have recently been made over two paths: (1) from Svalbard to Kiruna, Sweden, and (2) from Kirkenes, Norway, to Kiruna. An analysis of these data is presented in this paper. The directional characteristics are summarized, and consideration is given to modeling the propagation effects in the form of a channel simulator suitable for the testing of new equipment and processing algorithms.

  15. Assesment of SIRGAS Ionospheric Maps errors based on a numerical simulation

    Science.gov (United States)

    Brunini, Claudio; Emilio, Camilion; Francisco, Azpilicueta

    2010-05-01

    SIRGAS (Sistema de Referencia Geocéntrico para las Américas) is responsible of the International Terrestrial Reference Frame densification in Latin America and the Caribbean, which is realized and maintained by means of a continuously operational GNSS network with more than 200 receivers. Besides, SIRGAS uses this network for computing regional maps of the vertical Total Electron Content (TEC), which are released to the community through the SIRGAS web page (www.sirgas.org). As other similar products (e.g.: Global Ionospheric Maps (GIM) computed by the International GNSS Service), SIRGAS Ionospheric Maps (SIM) are based on a thin layer ionospheric model, in which the whole ionosphere is represented by one spherical layer of infinitesimal thickness and equivalent vertical TEC, located at a fixed height above the Earth's surface (tipycally between 350 and 450 km). This contribution aims to characterize the errors introduced in the thin layer ionospheric model by the use of a fixed and, sometimes, inappropiated ionospheric layer height. Particular attention is payed to the propagation of these errors to the estimation of the vertical TEC and to the estimation of the GNSS satellites and receivers Inter-Frequency Biases (IFB). The work relies upon a numerical simulation performed with an empirical model of the Earth's ionosphere, which allows creating a realistic but controlled ionospheric scenario, and then evaluates the errors that are produced when the thin layer model is used to reproduce those ionospheric scenarios. The error assessment is performed for the Central and the northern part of the South American continents, where largest errors are expected because the combined actions of the Appleton Anomaly of the ionosphere and the South-Atlantic anomaly of the geomagnetic field.

  16. Back-diffusion plasma generator for ionosphere study

    Science.gov (United States)

    Fang, H. K.; Oyama, K.-I.; Chen, A. B.

    2017-11-01

    To produce ionospheric plasma environments at ground level is essential to get information not only for the development of CubeSat-class spacecraft but also for the design of ionospheric plasma instruments and to confirm their performance. In this paper, we describe the principle of plasma generation and characteristics of the back-diffusion plasma source, which can produce in-lab plasma similar to the Earth’s ionosphere, E and F regions, conditions of electron and ion temperature and density. The ion and electron energy distributions of the plasma generated by a back-diffusion source are measured by means of a cleaned Langmuir probe and gridded particle energy analyzers. The ion motion in front of the source is investigated by a hard-sphere collision model in SIMION software and the simulation results are comparable with the findings of our experiment. Furthermore, plasma densities and ion temperatures at different positions in front of the source are also demonstrated. The back-diffusion source has been accommodated for ionospheric plasma productions in several Asian institutes. The plasma characteristics of the source shown in this paper will benefit space research groups in the development of space plasma instruments.

  17. Physical Layer Definition for a Long-Haul HF Antarctica to Spain Radio Link

    Directory of Open Access Journals (Sweden)

    Rosa Ma Alsina-Pagès

    2016-05-01

    Full Text Available La Salle and the Observatori de l’Ebre (OE have been involved in a remote sensing project in Antarctica for the last 11 years. The OE has been monitoring the geomagnetic activity for more than twenty years and also the ionospheric activity of the last ten years in the Spanish Antarctic Station Juan Carlos I (ASJI (62.7 ° S, 299.6 ° E. La Salle is finishing the design and testing of a low-power communication system between the ASJI and Cambrils (41.0 ° N, 1.0 ° E with a double goal: (i the transmission of data from the sensors located at the ASJI and (ii the performance of an oblique ionospheric sounding of a 12,760 km HF link. Previously, La Salle has already performed sounding and modulation tests to describe the channel performance in terms of availability, Signal-to-Noise Ratio (SNR, Doppler spread and delay spread. This paper closes the design of the physical layer, by means of the channel error study and the synchronization performance, and concludes with a new physical layer proposal for the Oblique Ionosphere Sounder. Narrowband and wideband frames have been defined to be used when the oblique sounder performs as an ionospheric sensor. Finally, two transmission modes have been defined for the modem performance: the High Robustness Mode (HRM for low SNR hours and the High Throughput Mode (HTM for the high SNR hours.

  18. High-latitude HF Doppler observations of ULF waves: 2. Waves with small spatial scale sizes

    Directory of Open Access Journals (Sweden)

    D. M. Wright

    1999-07-01

    Full Text Available The DOPE (Doppler Pulsation Experiment HF Doppler sounder located near Tromsø, Norway (geographic: 69.6°N 19.2°E; L = 6.3 is deployed to observe signatures, in the high-latitude ionosphere, of magnetospheric ULF waves. A type of wave has been identified which exhibits no simultaneous ground magnetic signature. They can be subdivided into two classes which occur in the dawn and dusk local time sectors respectively. They generally have frequencies greater than the resonance fundamentals of local field lines. It is suggested that these may be the signatures of high-m ULF waves where the ground magnetic signature has been strongly attenuated as a result of the scale size of the waves. The dawn population demonstrate similarities to a type of magnetospheric wave known as giant (Pg pulsations which tend to be resonant at higher harmonics on magnetic field lines. In contrast, the waves occurring in the dusk sector are believed to be related to the storm-time Pc5s previously reported in VHF radar data. Dst measurements support these observations by indicating that the dawn and dusk classes of waves occur respectively during geomagnetically quiet and more active intervals.Key words. Ionosphere (auroral ionosphere; ionosphere-magnetosphere interactions · Magnetospheric physics (MHD waves and instabilities

  19. Numerical study of the generation and propagation of ultralow-frequency waves by artificial ionospheric F region modulation at different latitudes

    Directory of Open Access Journals (Sweden)

    X. Xu

    2016-09-01

    Full Text Available Powerful high-frequency (HF radio waves can be used to efficiently modify the upper-ionospheric plasmas of the F region. The pressure gradient induced by modulated electron heating at ultralow-frequency (ULF drives a local oscillating diamagnetic ring current source perpendicular to the ambient magnetic field, which can act as an antenna radiating ULF waves. In this paper, utilizing the HF heating model and the model of ULF wave generation and propagation, we investigate the effects of both the background ionospheric profiles at different latitudes in the daytime and nighttime ionosphere and the modulation frequency on the process of the HF modulated heating and the subsequent generation and propagation of artificial ULF waves. Firstly, based on a relation among the radiation efficiency of the ring current source, the size of the spatial distribution of the modulated electron temperature and the wavelength of ULF waves, we discuss the possibility of the effects of the background ionospheric parameters and the modulation frequency. Then the numerical simulations with both models are performed to demonstrate the prediction. Six different background parameters are used in the simulation, and they are from the International Reference Ionosphere (IRI-2012 model and the neutral atmosphere model (NRLMSISE-00, including the High Frequency Active Auroral Research Program (HAARP; 62.39° N, 145.15° W, Wuhan (30.52° N, 114.32° E and Jicamarca (11.95° S, 76.87° W at 02:00 and 14:00 LT. A modulation frequency sweep is also used in the simulation. Finally, by analyzing the numerical results, we come to the following conclusions: in the nighttime ionosphere, the size of the spatial distribution of the modulated electron temperature and the ground magnitude of the magnetic field of ULF wave are larger, while the propagation loss due to Joule heating is smaller compared to the daytime ionosphere; the amplitude of the electron temperature

  20. Numerical study of the generation and propagation of ultralow-frequency waves by artificial ionospheric F region modulation at different latitudes

    Science.gov (United States)

    Xu, Xiang; Zhou, Chen; Shi, Run; Ni, Binbin; Zhao, Zhengyu; Zhang, Yuannong

    2016-09-01

    Powerful high-frequency (HF) radio waves can be used to efficiently modify the upper-ionospheric plasmas of the F region. The pressure gradient induced by modulated electron heating at ultralow-frequency (ULF) drives a local oscillating diamagnetic ring current source perpendicular to the ambient magnetic field, which can act as an antenna radiating ULF waves. In this paper, utilizing the HF heating model and the model of ULF wave generation and propagation, we investigate the effects of both the background ionospheric profiles at different latitudes in the daytime and nighttime ionosphere and the modulation frequency on the process of the HF modulated heating and the subsequent generation and propagation of artificial ULF waves. Firstly, based on a relation among the radiation efficiency of the ring current source, the size of the spatial distribution of the modulated electron temperature and the wavelength of ULF waves, we discuss the possibility of the effects of the background ionospheric parameters and the modulation frequency. Then the numerical simulations with both models are performed to demonstrate the prediction. Six different background parameters are used in the simulation, and they are from the International Reference Ionosphere (IRI-2012) model and the neutral atmosphere model (NRLMSISE-00), including the High Frequency Active Auroral Research Program (HAARP; 62.39° N, 145.15° W), Wuhan (30.52° N, 114.32° E) and Jicamarca (11.95° S, 76.87° W) at 02:00 and 14:00 LT. A modulation frequency sweep is also used in the simulation. Finally, by analyzing the numerical results, we come to the following conclusions: in the nighttime ionosphere, the size of the spatial distribution of the modulated electron temperature and the ground magnitude of the magnetic field of ULF wave are larger, while the propagation loss due to Joule heating is smaller compared to the daytime ionosphere; the amplitude of the electron temperature oscillation decreases with

  1. Hf på VUC

    DEFF Research Database (Denmark)

    Pless, Mette; Hansen, Niels-Henrik Møller

    Projektets overordnede formål er at kvalificere diskussionen om hf's rolle i uddannelsessystemet med særligt henblik på at belyse søgningen til og gennemførelsen afhf set i lyset af arbejdet med at nå målsætningen om, at mindst 95% af en ungdomsårgang skal gennemføre en ungdomsuddannelse i 2015....... Konkret har forskningsprojektet 3 mål: At afdække hf-kursisternes tidligere uddannelsesforløb og -erfaringer, før de starter på hf på VUC.At afdække, hvordan mødet med uddannelsens studiemiljø opleves af kursisterne, og ikke mindst kursisternes oplevelse af undervisningsformer, lærere mm.At afdække, hvad...... der har fået kursisterne til at søge hf, og hvilke forestillinger de har om hvad de skal bagefter....

  2. Vertical and oblique HF sounding with a network of synchronised ionosondes

    Science.gov (United States)

    Verhulst, Tobias; Altadill, David; Mielich, Jens; Reinisch, Bodo; Galkin, Ivan; Mouzakis, Angelos; Belehaki, Anna; Burešová, Dalia; Stankov, Stanimir; Blanch, Estefania; Kouba, Daniel

    2017-10-01

    A network of ionosondes in Europe has been established to monitor travelling ionospheric disturbances (TIDs) by simultaneously making vertical and oblique incidence HF sounding measurements. This network is the outcome of the Net-TIDE project, a collaboration between European Digisonde operators that have synchronised the sounding schedules of the Digisondes in order to record vertical and oblique ionogram traces simultaneously, and have added Digisonde-to-Digisonde (D2D) fixed frequency oblique-incidence measurements to the measurement schedule. The distances between the observatories involved in the project range from 500 km to over 2000 km. The technical feasibility of this network approach is explored. The challenge for the fixed-frequency D2D skymap measurements is the automatic selection of the sounding frequencies depending on the geometry of the sounding paths, the diurnal and seasonal ionospheric changes, and space weather induced events.

  3. A classification of spectral populations observed in HF radar backscatter from the E region auroral electrojets

    Directory of Open Access Journals (Sweden)

    S. E. Milan

    Full Text Available Observations of HF radar backscatter from the auroral electrojet E region indicate the presence of five major spectral populations, as opposed to the two predominant spectral populations, types I and II, observed in the VHF regime. The Doppler shift, spectral width, backscatter power, and flow angle dependencies of these five populations are investigated and described. Two of these populations are identified with type I and type II spectral classes, and hence, are thought to be generated by the two-stream and gradient drift instabilities, respectively. The remaining three populations occur over a range of velocities which can greatly exceed the ion acoustic speed, the usual limiting velocity in VHF radar observations of the E region. The generation of these spectral populations is discussed in terms of electron density gradients in the electrojet region and recent non-linear theories of E region irregularity generation.

    Key words. Ionosphere (ionospheric irregularities

  4. A classification of spectral populations observed in HF radar backscatter from the E region auroral electrojets

    Directory of Open Access Journals (Sweden)

    S. E. Milan

    2001-02-01

    Full Text Available Observations of HF radar backscatter from the auroral electrojet E region indicate the presence of five major spectral populations, as opposed to the two predominant spectral populations, types I and II, observed in the VHF regime. The Doppler shift, spectral width, backscatter power, and flow angle dependencies of these five populations are investigated and described. Two of these populations are identified with type I and type II spectral classes, and hence, are thought to be generated by the two-stream and gradient drift instabilities, respectively. The remaining three populations occur over a range of velocities which can greatly exceed the ion acoustic speed, the usual limiting velocity in VHF radar observations of the E region. The generation of these spectral populations is discussed in terms of electron density gradients in the electrojet region and recent non-linear theories of E region irregularity generation.Key words. Ionosphere (ionospheric irregularities

  5. 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

  6. Gas-phase reaction studies of dipositive hafnium and hafnium oxide ions: generation of the peroxide HfO2(2+).

    Science.gov (United States)

    Lourenço, Célia; Michelini, Maria del Carmen; Marçalo, Joaquim; Gibson, John K; Oliveira, Maria Conceição

    2012-12-27

    Fourier transform ion cyclotron resonance mass spectrometry was used to characterize the gas-phase reactivity of Hf dipositive ions, Hf(2+)and HfO(2+), toward several oxidants: thermodynamically facile O-atom donor N(2)O, ineffective donor CO, and intermediate donors O(2), CO(2), NO, and CH(2)O. The Hf(2+) ion exhibited electron transfer with N(2)O, O(2), NO, and CH(2)O, reflecting the high ionization energy of Hf(+). The HfO(2+) ion was produced by O-atom transfer to Hf(2+) from N(2)O, O(2), and CO(2), and the HfO(2)(2+) ion by O-atom transfer to HfO(2+) from N(2)O; these reactions were fairly efficient. Density functional theory revealed the structure of HfO(2)(2+) as a peroxide. The HfO(2)(2+) ion reacted by electron transfer with N(2)O, CO(2), and CO to give HfO(2)(+). Estimates were made for the second ionization energies of Hf (14.5 ± 0.5 eV), HfO (14.3 ± 0.5 eV), and HfO(2) (16.2 ± 0.5 eV), and also for the bond dissociation energies, D[Hf(2+)-O] = 686 ± 69 kJ mol(-1) and D[OHf(2+)-O] = 186 ± 98 kJ mol(-1). The computed bond dissociation energies, 751 and 270 kJ mol(-1), respectively, are within these experimental ranges. Additionally, it was found that HfO(2)(2+) oxidized CO to CO(2) and is thus a catalyst in the oxidation of CO by N(2)O and that Hf(2+) activates methane to produce a carbene, HfCH(2)(2+).

  7. Helium implanted AlHf as studied by Ta TDPAC

    Indian Academy of Sciences (India)

    Unknown

    TDPAC; electric field gradient; Hf solute clusters; helium-vacancy complex; defect recovery. 1. Introduction. In recent years a considerable effort has been directed to the behaviour of helium in metals as helium is produced by (n, α) reaction in nuclear materials. Helium atoms are insoluble in metals and are strongly attracted ...

  8. GPS detection of ionospheric perturbations following the January 17, 1994, northridge earthquake

    Science.gov (United States)

    Calais, Eric; Minster, J. Bernard

    1995-01-01

    Sources such as atmospheric or buried explosions and shallow earthquakes producing strong vertical ground displacements produce pressure waves that propagate at infrasonic speeds in the atmosphere. At ionospheric altitudes low frequency acoustic waves are coupled to ionispheric gravity waves and induce variations in the ionoispheric electron density. Global Positioning System (GPS) data recorded in Southern California were used to compute ionospheric electron content time series for several days preceding and following the January 17, 1994, M(sub w) = 6.7 Northridge earthquake. An anomalous signal beginning several minutes after the earthquake with time delays that increase with distance from the epicenter was observed. The signal frequency and phase velocity are consistent with results from numerical models of atmospheric-ionospheric acoustic-gravity waves excited by seismic sources as well as previous electromagnetic sounding results. It is believed that these perturbations are caused by the ionospheric response to the strong ground displacement associated with the Northridge earthquake.

  9. A way to increase the bit ratein ionospheric radio links

    Directory of Open Access Journals (Sweden)

    A. Bourdillon

    2004-06-01

    Full Text Available The aim of this paper is to present a high data rate transmission system through the ionospheric channel in the HF-band (3-30 MHz. The applications expected in this study are image transmitting and real-time videoconferencing. Very high rates are required compared to the standard modems. Therefore, an array processing is performed with a set of antennas whose spatial response differs from one another arranged in a circular array or in a collocated sensor. Synchronization (Zero Crossing Detector and source separation (LMS algorithm resort to classical well-tested techniques involving training sequences. Experimental results are presented for both antenna configurations. These techniques improve data rate, reaching 20 kbits/s within the 6 kHz bandwidth (QAM 64 without coding or interleaving.

  10. A Review of Ionospheric Scintillation Models.

    Science.gov (United States)

    Priyadarshi, S

    This is a general review of the existing climatological models of ionospheric radio scintillation for high and equatorial latitudes. Trans-ionospheric communication of radio waves from transmitter to user is affected by the ionosphere which is highly variable and dynamic in both time and space. Scintillation is the term given to irregular amplitude and phase fluctuations of the received signals and related to the electron density irregularities in the ionosphere. Key sources of ionospheric irregularities are plasma instabilities; every irregularities model is based on the theory of radio wave propagation in random media. It is important to understand scintillation phenomena and the approach of different theories. Therefore, we have briefly discussed the theories that are used to interpret ionospheric scintillation data. The global morphology of ionospheric scintillation is also discussed briefly. The most important (in our opinion) analytical and physical models of scintillation are reviewed here.

  11. Signatures of 3–6 day planetary waves in the equatorial mesosphere and ionosphere

    Directory of Open Access Journals (Sweden)

    B. R. Clemesha

    2006-12-01

    Full Text Available Common periodic oscillations have been observed in meteor radar measurements of the MLT winds at Cariri (7.4° S, 36.5° W and Ascension Island (7.9° S, 14.4° W and in the minimum ionospheric virtual height, h'F, measured at Fortaleza (3.9° S, 38.4° W in 2004, all located in the near equatorial region. Wavelet analysis of these time series reveals that there are 3–4-day, 6–8-day and 12–16-day oscillations in the zonal winds and h'F. The 3–4 day oscillation appeared as a form of a wave packet from 7–17 August 2004. From the wave characteristics analyzed this might be a 3.5-day Ultra Fast Kelvin wave. The 6-day oscillation in the mesosphere was prominent during the period of August to November. In the ionosphere, however, it was apparent only in November. Spectral analysis suggests that this might be a 6.5-day wave previously identified. The 3.5-day and 6.5-day waves in the ionosphere could have important roles in the initiation of equatorial spread F (plasma bubble. These waves might modulate the post-sunset E×B uplifting of the base of the F-layer via the induced lower thermosphere zonal wind and/or the E-region conductivity.

  12. Imaging meso-scale ionospheric structures

    Science.gov (United States)

    Burston, Robert

    2012-06-01

    The accuracy and capacity to resolve meso-scale structures of a four dimensional ionospheric imaging algorithm in the circumstance of data from dense networks of permanent GNSS ground receiver stations were investigated. Simulation studies were conducted in order to be able to assess the performance of the algorithm over the entire imaged region. The Multi-instrument Data Assimilation Software (MIDAS) algorithm was used for this purpose. Simulated input data in Receiver Independent Exchange Format (RINEX) were produced by calculating slant Total Electron Content (sTEC) values for satellite to receiver raypaths through an artificially generated ionosphere. Modeling these signals including Differential Code Biases (DCBs) and noise had negligible impact on the output from the imaging algorithm when compared with modeled signals that included neither. Comparing the output from MIDAS using a range of grid definitions show that finer grids have improved capacity to resolve meso-scale structures in the input model but over all are less accurate than coarser grids. The greatest errors occur in low-data regions of the grid and where structures in the input have the greatest gradients in vertical Total Electron Content (vTEC). A good compromise between the conflicting needs of resolution and accuracy is given by a grid defined with 2° × 2° latitude by longitude local horizontal grid divisions.

  13. Solar Data Assimilation Engine for Ionospheric Forecasts

    Science.gov (United States)

    Fry, C. D.; Eccles, J. V.

    2007-12-01

    The Space Weather Modeling System (SWMS) is a Battlespace Environments Institute (BEI) project that couples space environment models together under the Earth System Modeling Framework, while ensuring that the component models are scalable and portable. BEI is sponsored by the High Performance Computing Modernization Office and managed by Air Force Weather Agency and Naval Research Laboratory. The Hakamada-Akasofu-Fry version 2 (HAFv2) solar wind model and the Global Assimilation of Ionospheric Measurements (GAIM) model are the first two coupled components in the SWMS. Serving as a data assimilation engine, the HAFv2 model uses solar observations to prepare its initial solar wind conditions. Then, the HAFv2 internal algorithms and the initial conditions determine the present and future states of the solar wind conditions at Earth. The outputs of HAFv2 are provided to GAIM to forecast the time-dependent energy input into the high- latitude ionosphere. This presentation describes how the HAFv2 model is being used as a solar data assimilation engine for producing forecasts of solar wind parameters, that then serve as inputs to drive GAIM and other near-Earth space environment models. The overarching goal is to extend the lead time and skill of forecasts of space weather conditions and their corresponding impacts on operational customers.

  14. Some distinctive features in the behavior of small-scale artificial ionospheric irregularities at mid-and high latitudes

    Science.gov (United States)

    Blagoveshchenskaya, N. F.; Borisova, T. D.; Kornienko, V. A.; Frolov, V. L.; Rietveld, M. T.; Brekke, A.

    2007-08-01

    We present the results of experimental studies of some features in the behavior of small-scale artificial irregularities (SSAIs) at mid-and high latitudes based on the “Sura” and EISCAT/HEATING HF facilities. Observations were performed by the method of aspect scattering using a network of diagnostic paths having a common reception point located near St. Petersburg. We found that an extremely long duration of the second (slow) stage of SSAI relaxation of up to 5 min occurs in the evening hours when the ionosphere above the “Sura” facility is illuminated by the Sun, but the solar terminator travels through the magnetically conjugated ionosphere. The conjecture is made that the processes initiated by the terminator are mostly responsible for secondary ionospheric turbulence maintaining the irregularities above “Sura.” A drastic increase in the Doppler spectra width of the scattered signals is revealed when the magnetically conjugate point of the ionosphere is located on the shade side of the terminator, but the ionosphere above the “Sura” facility is still lighted. It is assumed that the “ run away” of photoelectrons from the day to the night side could reduce the threshold of excitation of artificial irregularities, leading to an increase in their intensity. The presence of fairly intense scattered signals was detected from the “Sura” and EISCAT/HEATING experimental results both under conditions of pulsed HF heating after continuous heater-on periods and cycled HF heating by short pulses. In the case of pulsed heating by short pulses with duration τp effect, was found in the SSAI intensity. The residual turbulence aftereffects played a significant role in the SSAI development.

  15. On the collocation between dayside auroral activity and coherent HF radar backscatter

    Directory of Open Access Journals (Sweden)

    J. Moen

    Full Text Available The 2D morphology of coherent HF radar and optical cusp aurora has been studied for conditions of predominantly southward IMF conditions, which favours low-latitude boundary layer reconnection. Despite the variability in shape of radar cusp Doppler spectra, the spectral width criterion of > 220 m s–1 proves to be a robust cusp discriminator. For extended periods of well-developed radar backscatter echoes, the equatorward boundary of the > 220 m s–1 spectral width enhancement lines up remarkably well with the equatorward boundary of the optical cusp aurora. The spectral width boundary is however poorly determined during development and fading of radar cusp backscatter. Closer inspection of radar Doppler profile characteristics suggests that a combination of spectral width and shape may advance boundary layer identification by HF radar. For the two December days studied the onset of radar cusp backscatter occurred within pre-existing 630.0 nm cusp auroral activity and appear to be initiated by sunrise, i.e. favourable radio wave propagation conditions had to develop. Better methods are put forward for analysing optical data, and for physical interpretation of HF radar data, and for combining these data, as applied to detection, tracking, and better understanding of dayside aurora. The broader motivation of this work is to develop wider use by the scientific community, of results of these techniques, to accelerate understanding of dynamic high-latitude boundary-processes. The contributions in this work are: (1 improved techniques of analysis of observational data, yielding meaningfully enhanced accuracy for deduced cusp locations; (2 a correspondingly more pronounced validation of correlation of boundary locations derived from the observational data set; and (3 a firmer physical rationale as to why the good correlation observed should theoretically be expected.

    Key words: Ionosphere (ionospheric

  16. Hf--Co--B alloys as permanent magnet materials

    Energy Technology Data Exchange (ETDEWEB)

    McGuire, Michael Alan; Rios, Orlando; Ghimire, Nirmal Jeevi

    2017-01-24

    An alloy composition is composed essentially of Hf.sub.2-XZr.sub.XCo.sub.11B.sub.Y, wherein 0Hf.sub.2-XZr.sub.XCo.sub.11B.sub.Y, wherein 0.ltoreq.X<2 and 0produce the nanoscale crystalline structure.

  17. Hf--Co--B alloys as permanent magnet materials

    Science.gov (United States)

    McGuire, Michael Alan; Rios, Orlando; Ghimire, Nirmal Jeevi

    2017-01-24

    An alloy composition is composed essentially of Hf.sub.2-XZr.sub.XCo.sub.11B.sub.Y, wherein 0Hf.sub.2-XZr.sub.XCo.sub.11B.sub.Y, wherein 0.ltoreq.X<2 and 0produce the nanoscale crystalline structure.

  18. Kursistbaggrunde på Frederiksberg HF

    DEFF Research Database (Denmark)

    Hansen, Niels-Henrik Møller; Ozmec, Martha Nina

    I denne rapport sættes der fokus på elevernes baggrunde på den 2-årige HF-uddannelse på Frederiksberg HF. Hensigten med rapporten er at beskrive elevernes baggrunde og livssituation samt belyse, hvorledes forskellige baggrunde kan påvirke elevernes trivsel og relation til deres uddannelse på...... Frederiksberg HF....

  19. Tomographic reconstruction of the ionosphere over north America with comparisons to ground-based radar

    Energy Technology Data Exchange (ETDEWEB)

    Pakula, W.A.; Fougere, P.F.; Klobuchar, J.A.; Kuenzler, H.J.; Buonsanto, M.J.

    1995-02-01

    Data collection for the first ground-based ionospheric tomography campaign in North America was conducted over a 48-hour period in mid-November 1991. The data consist of records of ionospheric total electron content (TEC) from a number of passes of the U. S. Navy Navigation Satellite System spacecraft over a chain of ground-based receiving stations. Data collection and reduction techniques are discussed; these include the determination of absolute TEC from the different phase advances induced by the ionosphere in each component of the dual-frequency spacecraft signal. The use of tomographic methods to reconstruct ionospheric electron densities over a two-dimensional (2-D) region of the Earth`s ionosphere at a number of different times is demonstrated. Specifically, two distinct tomographic methods, the algebraic reconstruction technique and a maximum entropy method, are used to mathematically invert the records of TEC. The resulting 2-D contour maps of ionospheric electron density are then compared to similar maps produced by the Millstone Hill incoherent backscatter radar facility located at Westford, Massachusetts. Both qualitative and quantitative measures of agreement among the different reconstructions and the radar maps are presented. The behavior of the ionosphere over the course of the experiment is discussed.

  20. Interplanetary phenomenon, geomagnetic and ionospheric ...

    African Journals Online (AJOL)

    The analysis of the D(foF2) plots appear to show that the storm event is characterized by (i) the occurrence of positive ionospheric storm at the high latitudes and mid latitude stations of Khabarovsk, Yamagawa and Okinawa stations before the beginning of the storm event (ii) Presence of strong negative phase at Manila, ...

  1. Preseismic ionospheric electron enhancements revisited

    Science.gov (United States)

    Heki, Kosuke; Enomoto, Yuji

    2013-10-01

    enhancement of ionospheric Total Electron Content (TEC) immediately before the 2011 Tohoku-oki earthquake (Mw9.0) has been reported by Heki (2011). Critical responses to it often come in two stages; they first doubt the enhancement itself and attribute it to an artifact. Second (when they accept the enhancement), they doubt the significance of the enhancement among natural variability of space weather origin. For example, Kamogawa and Kakinami (2013) attributed the enhancement to an artifact falsely detected by the combined effect of the highly variable TEC under active geomagnetic condition and the occurrence of a tsunamigenic ionospheric hole. Here we closely examine the time series of vertical TEC before and after the 2011 Tohoku-oki earthquake. We first demonstrate that the tsunami did not make an ionospheric hole, and next confirm the reality of the enhancement using data of two other sensors, ionosonde and magnetometers. The amplitude of the preseismic TEC enhancement is within the natural variability, and its snapshot resembles to large-scale traveling ionospheric disturbances. However, distinction could be made by examining their propagation properties. Similar TEC anomalies occurred before all the M ≥ 8.5 earthquakes in this century, suggesting their seismic origin.

  2. Observing Tsunamis in the Ionosphere Using Ground Based GPS Measurements

    Science.gov (United States)

    Galvan, D. A.; Komjathy, A.; Song, Y. Tony; Stephens, P.; Hickey, M. P.; Foster, J.

    2011-01-01

    Ground-based Global Positioning System (GPS) measurements of ionospheric Total Electron Content (TEC) show variations consistent with atmospheric internal gravity waves caused by ocean tsunamis following recent seismic events, including the Tohoku tsunami of March 11, 2011. We observe fluctuations correlated in time, space, and wave properties with this tsunami in TEC estimates processed using JPL's Global Ionospheric Mapping Software. These TEC estimates were band-pass filtered to remove ionospheric TEC variations with periods outside the typical range of internal gravity waves caused by tsunamis. Observable variations in TEC appear correlated with the Tohoku tsunami near the epicenter, at Hawaii, and near the west coast of North America. Disturbance magnitudes are 1-10% of the background TEC value. Observations near the epicenter are compared to estimates of expected tsunami-driven TEC variations produced by Embry Riddle Aeronautical University's Spectral Full Wave Model, an atmosphere-ionosphere coupling model, and found to be in good agreement. The potential exists to apply these detection techniques to real-time GPS TEC data, providing estimates of tsunami speed and amplitude that may be useful for future early warning systems.

  3. Application of HF Radar in Hazard Management

    Directory of Open Access Journals (Sweden)

    Mal Heron

    2016-01-01

    Full Text Available A review is given of the impact that HF radars are having on the management of coastal hazards. Maps of surface currents can be produced every 10–20 minutes which, in real time, improve navigation safety in restricted areas commonly found near ports and harbours. The time sequence of surface current maps enables Lagrangian tracking of small parcels of surface water, which enables hazard mitigation in managing suspended sediments in dredging, in emergency situations where flotsam and other drifting items need to be found, and in pollution control. The surface current measurement capability is used to assist tsunami warnings as shown by the phased-array data from Chile following the Great Tohoku Earthquake in 2011. The newly launched Tsunami Warning Center in Oman includes a network of phased-array HF radars to provide real-time tsunami monitoring. Wind direction maps can be used to locate the position of cold fronts in the open ocean and to monitor the timing and strength of sea-breeze fronts in key locations.

  4. CUTLASS HF radar observations of high-velocity E-region echoes

    Directory of Open Access Journals (Sweden)

    M. V. Uspensky

    Full Text Available A short event of high-velocity E-region echo observations by the Pykkvibaer HF radar is analysed to study echo parameters and the echo relation to the Farley-Buneman plasma instability. The echoes were detected in several beams aligned closely to the magnetic L-shell direction. Two echo groups were identified: one group corresponded to the classical type 1 echoes with velocities close to the nominal ion-acoustic speed of 400 ms1 , while the other group had significantly larger velocities, of the order of 700 ms1 . The mutual relationship between the echo power, Doppler velocity, spectral width and elevation angles for these two groups was studied. Plotting of echo parameters versus slant range showed that all ~700 ms1 echoes originated from larger heights and distances of 500–700 km, while all ~400 ms1 echoes came from lower heights and from farther distances; 700–1000 km. We argue that both observed groups of echoes occurred due to the Farley-Buneman plasma instability excited by strong ( ~70 mVm1 and uniformly distributed electric fields. We show that the echo velocities for the two groups were different because the echoes were received from different heights. Such a separation of echo heights occurred due to the differing amounts of ionospheric refraction at short and large ranges. Thus, the ionospheric refraction and related altitude modulation of ionospheric parameters are the most important factors to consider, when various characteristics of E-region decametre irregularities are derived from HF radar measurements.

    Key words. Ionosphere (ionospheric irregularities; plasma waves and instabilities; polar ionosphere

  5. What can we learn from HF signal scattered from a discrete arc?

    Directory of Open Access Journals (Sweden)

    E. Séran

    2009-05-01

    Full Text Available We present observations of a discrete southward propagating arc which appeared in the mid-night sector at latitudes equatorward of main substorm activity. The arc observations were made simultaneously by the ALFA (Auroral Light Fine Analysis optical camera, the SuperDARN-CUTLASS HF radar and the Demeter satellite during a coordinated multi-instrumental campaign conducted at the KEOPS/ESRANGE site in December 2006. The SuperDARN HF signal which is often lost in the regions of strong electron precipitation yields in our case clear backscatter from an isolated arc of weak intensity. Consequently we are able to study arc dynamics, the formation of meso-scale irregularities of the electron density along the arc, compare the arc motion with the convection of surrounding plasma and discuss the contribution of ionospheric ions in the arc erosion and its propagation.

  6. Multi-frequency HF radar measurements of artificial F-region field-aligned irregularities

    Directory of Open Access Journals (Sweden)

    A. Senior

    2004-01-01

    Full Text Available We present radar backscatter power measurements using the CUTLASS HF radar at Hankasalmi, Finland from F-region field-aligned irregularities induced by HF radio pumping with the EISCAT Heating facility. A novel radar operating mode is used in which the radar frequency is rapidly swept through a number of bands, making use of the varying ionospheric refraction to probe different heights within the heated region. We obtain height profiles of backscatter power which correspond to e-folding scale lengths of around 20km for the mean-square electron density perturbations for pump wave interaction heights in the region of 240-250km in daytime conditions. The results are in agreement with previous measurements made by other techniques. We discuss some problems with the method and suggest improvements for future experiments.

  7. Large discrepancies between garnet Lu-Hf and Sm-Nd isochron ages: the problem of inherited Hf

    Science.gov (United States)

    Raimondo, Tom; Payne, Justin; Hand, Martin; Clark, Chris; Anczkiewicz, Robert

    2017-04-01

    separation and dissolution techniques that preferentially reduce zircon contamination in garnet relative to the untreated whole rock fraction, systematically skewing the Lu-Hf isochron to an apparent age older than the 'true' age. Furthermore, the moderate metamorphic grade of the Walter-Outalpa samples (530 °C; 5 kbar) prevents an appeal to diffusion to explain the large Lu-Hf vs. Sm-Nd age discrepancy. As such, it is concluded that the problem of inherited Hf can produce spuriously old ages that falsely suggest a high closure temperature for the Lu-Hf isotopic system and/or an early onset of garnet nucleation. This should urge caution in the interpretation of Lu-Hf data without consideration of potential inheritance effects.

  8. Predicted and observed characteristics of small-scale field-aligned irregularities generated in the F-region by low power HF heating

    Directory of Open Access Journals (Sweden)

    E. Kolesnikova

    2002-05-01

    Full Text Available Simultaneous HF scattering from the different regions of the heated volume is used to investigate characteristics of the small-scale field-aligned irregularities in the F-region. Time of growth, decay rate and saturation level for different pump powers are deduced from the observations and are compared with their behaviour predicted by the thermal parametric instability model. As a result, the estimates of the density and of the temperature modifications inside of the irregularities are obtained.Key words. Ionosphere (ionospheric irregularities

  9. Directional features of the downshifted peak observed in HF-induced stimulated electromagnetic emission spectra obtained using an interferometer

    Directory of Open Access Journals (Sweden)

    E. D. Tereshchenko

    2006-08-01

    Full Text Available A high frequency (HF ionospheric modification experiment was carried out between 25 September and 8 October 2004, using the EISCAT HF transmitter located near Tromsø, Norway. During this experiment the spectra of the stimulated HF sideband waves (stimulated electromagnetic emission or SEE induced by the HF pump were observed using an interferometer consisting of three spaced receiving antennas with baselines both along and perpendicular to the meridian, and a multi-channel coherent receiver, installed in the vicinity of the HF facility. The transmitter operated at 4040kHz and its antenna beam was scanned to angles of 0°, 7°, 14°, and 21° south from vertical, pausing 4min at each position. This paper focuses on features of the downshifted peak (DP emission, which has not been as thoroughly studied as many of the other SEE spectral features observable within the EISCAT pump frequency range. It was found that the signal-weighted direction of the DP source region remained within 5° of magnetic zenith as the HF beam was tilted between 0 and 21° south of vertical.

  10. The ionospheric response to flux transfer events: the first few minutes

    Directory of Open Access Journals (Sweden)

    A. S. Rodger

    1997-06-01

    Full Text Available We utilise high-time resolution measurements from the PACE HF radar at Halley, Antarctica to explore the evolution of the ionospheric response during the first few minutes after enhanced reconnection occurs at the magnetopause. We show that the plasma velocity increases associated with flux transfer events (FTEs occur first ~100–200 km equatorward of the region to which magnetosheath (cusp precipitation maps to the ionosphere. We suggest that these velocity variations start near the ionospheric footprint of the boundary between open and closed magnetic field lines. We show that these velocity variations have rise times ~100 s and fall times of ~10 s. When these velocity transients reach the latitude of the cusp precipitation, sometimes the equatorward boundary of the precipitation begins to move equatorward, the expected and previously reported ionospheric signature of enhanced reconnection. A hypothesis is proposed to explain the velocity variations. It involves the rapid outflow of magnetospheric electrons into the magnetosheath along the most recently reconnected field lines. Several predictions are made arising from the proposed explanation which could be tested with ground-based and space-based observations.

  11. Coordinated Cluster, ground-based instrumentation and low-altitude satellite observations of transient poleward-moving events in the ionosphere and in the tail lobe

    Directory of Open Access Journals (Sweden)

    M. Lockwood

    Full Text Available During the interval between 8:00–9:30 on 14 January 2001, the four Cluster spacecraft were moving from the central magnetospheric lobe, through the dusk sector mantle, on their way towards intersecting the magnetopause near 15:00 MLT and 15:00 UT. Throughout this interval, the EISCAT Svalbard Radar (ESR at Longyearbyen observed a series of poleward-moving transient events of enhanced F-region plasma concentration ("polar cap patches", with a repetition period of the order of 10 min. Allowing for the estimated solar wind propagation delay of 75 ( ± 5 min, the interplanetary magnetic field (IMF had a southward component during most of the interval. The magnetic footprint of the Cluster spacecraft, mapped to the ionosphere using the Tsyganenko T96 model (with input conditions prevailing during this event, was to the east of the ESR beams. Around 09:05 UT, the DMSP-F12 satellite flew over the ESR and showed a sawtooth cusp ion dispersion signature that also extended into the electrons on the equatorward edge of the cusp, revealing a pulsed magnetopause reconnection. The consequent enhanced ionospheric flow events were imaged by the SuperDARN HF backscatter radars. The average convection patterns (derived using the AMIE technique on data from the magnetometers, the EISCAT and SuperDARN radars, and the DMSP satellites show that the associated poleward-moving events also convected over the predicted footprint of the Cluster spacecraft. Cluster observed enhancements in the fluxes of both electrons and ions. These events were found to be essentially identical at all four spacecraft, indicating that they had a much larger spatial scale than the satellite separation of the order of 600 km. Some of the events show a correspondence between the lowest energy magnetosheath electrons detected by the PEACE instrument on Cluster (10–20 eV and the topside ionospheric enhancements seen by the ESR (at 400–700 km. We suggest that a potential barrier at the

  12. Coordinated Cluster, ground-based instrumentation and low-altitude satellite observations of transient poleward-moving events in the ionosphere and in the tail lobe

    Directory of Open Access Journals (Sweden)

    M. Lockwood

    2001-09-01

    Full Text Available During the interval between 8:00–9:30 on 14 January 2001, the four Cluster spacecraft were moving from the central magnetospheric lobe, through the dusk sector mantle, on their way towards intersecting the magnetopause near 15:00 MLT and 15:00 UT. Throughout this interval, the EISCAT Svalbard Radar (ESR at Longyearbyen observed a series of poleward-moving transient events of enhanced F-region plasma concentration ("polar cap patches", with a repetition period of the order of 10 min. Allowing for the estimated solar wind propagation delay of 75 ( ± 5 min, the interplanetary magnetic field (IMF had a southward component during most of the interval. The magnetic footprint of the Cluster spacecraft, mapped to the ionosphere using the Tsyganenko T96 model (with input conditions prevailing during this event, was to the east of the ESR beams. Around 09:05 UT, the DMSP-F12 satellite flew over the ESR and showed a sawtooth cusp ion dispersion signature that also extended into the electrons on the equatorward edge of the cusp, revealing a pulsed magnetopause reconnection. The consequent enhanced ionospheric flow events were imaged by the SuperDARN HF backscatter radars. The average convection patterns (derived using the AMIE technique on data from the magnetometers, the EISCAT and SuperDARN radars, and the DMSP satellites show that the associated poleward-moving events also convected over the predicted footprint of the Cluster spacecraft. Cluster observed enhancements in the fluxes of both electrons and ions. These events were found to be essentially identical at all four spacecraft, indicating that they had a much larger spatial scale than the satellite separation of the order of 600 km. Some of the events show a correspondence between the lowest energy magnetosheath electrons detected by the PEACE instrument on Cluster (10–20 eV and the topside ionospheric enhancements seen by the ESR (at 400–700 km. We suggest that a potential barrier at the

  13. Measurements of electron density irregularities in the ionosphere of Jupiter by Pioneer 10

    Science.gov (United States)

    Woo, R.; Yang, F.-C.

    1976-01-01

    It is demonstrated that when the frequency spectrum of log amplitude fluctuations is used, the radio-occultation experiment is a powerful tool for detecting, identifying, and studying ionospheric irregularities. Analysis of Pioneer 10 radio-occultation measurements reveals that the Jovian ionosphere possesses electron-density irregularities which are very similar to those found in the earth's ionosphere. This is the first time such irregularities have been found in a planetary ionosphere other than that of the earth. The Pioneer 10 results indicate that the spatial wave-number spectrum of the electron-density irregularities is close to the Kolmogorov spectrum and that the outer scale size is greater than the Fresnel size (6.15 km). This type of spectrum suggests that the irregularities are probably produced by the turbulent dissipation of irregularities larger than the outer scale size.

  14. Radar signal propagation through the ionosphere of Europa

    Science.gov (United States)

    Grima, Cyril; Blankenship, Donald D.; Schroeder, Dustin M.

    2015-11-01

    We review the current state of knowledge of the Europan plasma environment, its effects on radio wave propagation, and its impact on the performance and design of future radar sounders for the exploration of Europa's ice crust. The Europan ionosphere is produced in two independently-rotating hemispheres by photo-ionization of the neutral exosphere and interaction with the Io plasma torus, respectively. This combination is responsible for temporal and longitudinal ionospheric heterogeneities not well constrained by observations. When Europa's ionosphere is active, the maximum cut-off frequency is 1 MHz at the surface. The main impacts on radar signal propagation are dispersive phase shift and Faraday rotation, both a function of the total electron content (up to 4×1015 m-2) and the Jovian magnetic field strength at Europa (~420 nT). The severity of these impacts decrease with increasing center frequency and increase with altitude, latitude, and bandwidth. The 9 MHz channels on the Radar for Icy Moons Exploration (RIME) and proposed Radar for Europa Assessment and Sounding: Ocean to Near-surface (REASON) will be sensitive to the Europan ionosphere. For these or similar radar sounders, the ionospheric signal distortion from dispersive phase shift can be corrected with existing techniques, which would also enable the estimation of the total electron content below the spacecraft. At 9 MHz, the Faraday fading is not expected to exceed 6 dB under the worst conditions. At lower frequencies, any active or passive radio probing of the ice shell exploration would be limited to frequencies above 1-8 MHz (depending on survey configuration) below which Faraday rotation angle would lead to signal fading and detection ambiguity. Radar instruments could be sensitive to neutrals and electrons added in the exosphere from any plume activity if present.

  15. The Influence of the Asymmetric Ionosphere on the Schumann Resonances

    Science.gov (United States)

    Yu, H.; Williams, E. R.

    2015-12-01

    The asymmetric ionosphere is known to affect the behavior of the Earth's Schumann resonances (SR). Several studies have addressed the day-night asymmetry with observation or simulation and showed the contrast in SR amplitude between day and night (Satori et.al 2007, Pechony and Price 2007, Yang et.al., 2006). And distinct perturbations in the ionosphere caused by solar proton events, x-ray emission and earthquake coupling will also produce variations in SRs (Roldugin et.al., 2004, De et al., 2010; Satori et.al., 2015). Considering all these possible variations produced by changes in ionospheric asymmetry, we simulate the SR propagation in an asymmetric cavity including the day-night contribution and the more general perturbation asymmetry using a TDTE (Two Dimensional Telegraph Equation) approach. The change of source position in the asymmetric ionosphere and the size of the perturbation will also affect the SR parameters such as amplitude and modal frequency. The central location of the source in either the daytime or nighttime zone will produce a larger amplitude than other locations in the cavity. For example, the amplitude from a source in the zone with lower electric height (like the daytime region) is larger than the situation with source in region of larger electric height (like nighttime region). The asymmetry(difference on EM amplitude between two regions) will be more distinct when the source is on the terminator between two region than on other position. And when the size of the asymmetric construction is changed, the amplitude and modal frequency will also be changed. The increased size of the zone with lower electric height will produce larger SR amplitudes and decreased modal frequency.

  16. Inter-Hemispheric Differences Due to Ionospheric Asymmetries

    Science.gov (United States)

    Lysak, R. L.; Song, Y.; Waters, C. L.; Sciffer, M. D.; Obana, Y.

    2016-12-01

    The ionospheric conductivity is a critical parameter in the evolution of the global field-aligned current system. The conductivity is produced by both the illumination due to solar ultra-violet radiation and the energy input due to the precipitation of particles. The first effect gives rise to day-night differences in the conductivity, as well as seasonal differences, especially during solstice when one ionosphere is mostly in daylight while the other is mostly dark. During daylight conditions, the large Pedersen conductance leads to a strong reflection of incident Alfvén waves and an enhancement of the field-aligned current. In darkness, Alfvén waves are strongly absorbed and the current decreases. This leads to the so-called "quarter-wave modes" in which a standing Alfvén wave has a node in the electric field in one ionosphere and an anti-node in the other (e.g., Obana et al., 2015). These waves can be observed near the terminator under solstice conditions when one end of the field line is in daylight while the other is in darkness. While the response to solar illumination varies on diurnal time scales, the response of the ionosphere to electron precipitation can be much more rapid. In the presence of a background convection electric field, a localized enhancement of the conductivity due to this precipitation can give rise to a feedback interaction in which the conductivity enhancement and the resulting field-aligned currents can grow. This effect is suppressed in the daylit ionosphere since recombination is faster in the high density region, suggesting that auroral arcs are more prevalent in a dark ionosphere (e.g., Newell et al., 1996). On the other hand, the higher currents resulting in the high-conductivity ionosphere may lead to enhanced parallel electric fields and higher energy precipitation. A similar trade-off may apply in ion outflow regions, since higher density will suppress the ambipolar field necessary to accelerate ions while also providing a

  17. HF propagation results from the Metal Oxide Space Cloud (MOSC) experiment

    Science.gov (United States)

    Joshi, Dev; Groves, Keith M.; McNeil, William; Carrano, Charles; Caton, Ronald G.; Parris, Richard T.; Pederson, Todd R.; Cannon, Paul S.; Angling, Matthew; Jackson-Booth, Natasha

    2017-06-01

    With support from the NASA sounding rocket program, the Air Force Research Laboratory launched two sounding rockets in the Kwajalein Atoll, Marshall Islands in May 2013 known as the Metal Oxide Space Cloud experiment. The rockets released samarium metal vapor at preselected altitudes in the lower F region that ionized forming a plasma cloud. Data from Advanced Research Project Agency Long-range Tracking and Identification Radar incoherent scatter radar and high-frequency (HF) radio links have been analyzed to understand the impacts of the artificial ionization on radio wave propagation. The HF radio wave ray-tracing toolbox PHaRLAP along with ionospheric models constrained by electron density profiles measured with the ALTAIR radar have been used to successfully model the effects of the cloud on HF propagation. Up to three new propagation paths were created by the artificial plasma injections. Observations and modeling confirm that the small amounts of ionized material injected in the lower F region resulted in significant changes to the natural HF propagation environment.

  18. Atmosphere-Ionosphere Coupling via Atmospheric Waves

    Science.gov (United States)

    Koucka Knizova, Petra; Lastovicka, Jan

    2017-04-01

    The Earth atmosphere and ionosphere is complicated and highly variable system which displays oscillations on wide range scales. The most important factor influencing the ionosphere is certainly the solar and geomagnetic activity. However, the processes even in distant regions in the neutral atmosphere cannot be simply neglected. This contribution reviews aspects of ionospheric variability originating in the lower laying atmosphere. It focuses especially on the generation and propagation of the atmospheric waves from their source region up to the heights of the ionosphere. We will show the role of infrasound, gravity waves, tides and planetary waves in the atmosphere-ionosphere coupling. Particularly gravity waves are of high importance for the ionosphere. Recent theoretical and experimental results will briefly be reviewed.

  19. Ionospheric corrections for GPS time transfer

    Science.gov (United States)

    Rose, Julian A. R.; Watson, Robert J.; Allain, Damien J.; Mitchell, Cathryn N.

    2014-03-01

    A real-time ionospheric mapping system is tested to investigate its ability to compensate for the ionospheric delay in single-frequency Global Positioning System (GPS) time transfer over Europe. This technique is compared with two other single-frequency systems: one that does not incorporate any ionospheric correction and one that uses the broadcast Klobuchar model. A dual-frequency technique is also shown as a benchmark. A period in March 2003, during a solar maximum, has been used to display results when the ionospheric delays are large and variable. Data from two European GPS monitoring centers were used to test the time-transfer methods. For averaging times between several minutes and a few hours, the instabilities in the time transfers were dominated by ionospheric effects. The instabilities at longer averaging times were found to be due to clock noise and hardware instabilities. Improvements in time-transfer instabilities are shown by using the ionospheric tomography system.

  20. Finite Temperature Effects on the Evolution of Ionospheric Barium Clouds in the Presence of a Conducting Background Ionosphere.

    Science.gov (United States)

    1984-07-24

    of how far the polarization field produced by the barium cloud maps along the magnetic field (Goldman et. al, *. 1976, Glassman and Sperling, 1983...ionosphere, J. Geophys. Res., 80, 3111, 1975. Glassman , A.J. and J.L. Sperling, Electromagnetic theory of collisional interchange instabilities, J. Geophys...EISENHOWER AVENUE U.S. ARMY MISSILE INTELLIGENCE AGENCY ALEXANDRIA, VA 22333 REDSTONE ARSENAL, AL 35809 O1CY ATTN DACS-BMT J. SHEA 0ICY ATTN JIM

  1. Multiscale Modeling of Ionospheric Irregularities

    Science.gov (United States)

    2014-10-22

    ionospheric dynamics included coupling of neutral fluid, ion gas, electron gas, and electromagnetic equations. 3D Navier- Stokes Equations for Neutral...Scientific Meetings and Conferences • 12th Conference on Space Weather, 95th Annual Meeting of the American Meteorological Soci- ety, Phoenix AZ, 4-8 January...flows and the 3D Navier– Stokes equations for neu- trals. In the current literature, the background neutral flow is usually prescribed and not coupled

  2. High-Latitude Ionospheric Irregularities.

    Science.gov (United States)

    1984-05-10

    Owen, and J. A. Klobuchar , "Recent Studies of the Structure and Morphology of Auroral Zone F- Region Irregularities," Radio Sci., -8, 6, 1167-1180, 1983...We present observations of electron density variations in the F1 region of the ionosphere at two locations near the magnetic equator . Oscillations in...just off the magnetic equator during equatorial spread F conditions. One, a Javalin sounding rocket, was launched by NASA from Natal, Brazil, on 18

  3. 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.

  4. Sudden ionospheric disturbances in solar cycle 24

    Science.gov (United States)

    Bothmer, Volker; Bernert, Barbara

    2014-05-01

    Sudden ionospheric disturbances in solar cycle 24 Within the framework of the UN International Space Weather Initiative, and building upon the achievements of the International Heliophysical Year, the German project SIMONE (Sun Ionosphere MOnitoring NEtwork) operates several SID monitors provided by the University of Stanford. Here we present an overview of sudden ionospheric disturbances recorded since 2006 at the high school Gymnasium Walsrode until to date. The continous measurements allow a detailed comparison of locally measured SIDs with the general trend of solar activity during the current solar maximum. We further show that the measurements reveal specific information on the variable response of the dayside ionosphere to solar flares.

  5. Ionospheric data assimilation and forecasting during storms

    Science.gov (United States)

    Chartier, A.; Matsuo, T.; Anderson, J. L.; Collins, N.; Hoar, T.; Lu, G.; Mitchell, C. N.; Coster, A. J.; Bust, G. S.; Paxton, L. J.

    2016-12-01

    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.

  6. Statistical observations of the MLT, latitude and size of pulsed ionospheric flows with the CUTLASS Finland radar

    Directory of Open Access Journals (Sweden)

    G. Provan

    Full Text Available A study has been performed on the occurrence of pulsed ionospheric flows as detected by the CUTLASS Finland HF radar. These flows have been suggested as being created at the ionospheric footprint of newly-reconnected field lines, during episodes of magnetic flux transfer into the terrestrial magnetosphere (flux transfer events or FTEs. Two years of both high-time resolution and normal scan data from the CUTLASS Finland radar have been analysed in order to perform a statistical study of the extent and location of the pulsed ionospheric flows. We note a great similarity between the statistical pattern of the coherent radar observations of pulsed ionospheric flows and the traditional low-altitude satellite identification of the particle signature associated with the cusp/cleft region. However, the coherent scatter radar observations suggest that the merging gap is far wider than that proposed by the Newell and Meng model. The new model for cusp low-altitude particle signatures, proposed by Lockwood and Onsager and Lockwood provides a unified framework to explain the dayside precipitation regimes observed both by the low-altitude satellites and by coherent scatter radar detection.

    Key words. Magnetospheric physics (magnetosphere · ionosphere interactions; plasma convection; solar wind-magnetosphere interactions

  7. High-latitude observations of impulse-driven ULF pulsations in the ionosphere and on the ground

    Directory of Open Access Journals (Sweden)

    F. W. Menk

    Full Text Available We report the simultaneous observation of 1.6–1.7 mHz pulsations in the ionospheric F-region with the CUTLASS bistatic HF radar and an HF Doppler sounder, on the ground with the IMAGE and SAMNET magnetometer arrays, and in the upstream solar wind. CUTLASS was at the time being operated in a special mode optimized for high resolution studies of ULF waves. A novel use is made of the ground returns to detect the ionospheric signature of ULF waves. The pulsations were initiated by a strong, sharp decrease in solar wind dynamic pressure near 09:28 UT on 23 February 1996, and persisted for some hours. They were observed with the magnetometers over 20° in latitude, coupling to a field line resonance near 72° magnetic latitude. The magnetic pulsations had azimuthal m numbers ~ -2, consistent with propagation away from the noon sector. The radars show transient high velocity flows in the cusp and auroral zones, poleward of the field line resonance, and small amplitude 1.6–1.7 mHz F-region oscillations across widely spaced regions at lower latitudes. The latter were detected in the radar ground scatter returns and also with the vertical incidence Doppler sounder. Their amplitude is of the order of ± 10 ms-1. A similar perturbation frequency was present in the solar wind pressure recorded by the WIND spacecraft. The initial solar wind pressure decrease was also associated with a decrease in cosmic noise absorption on an imaging riometer near 66° magnetic latitude. The observations suggest that perturbations in the solar wind pressure or IMF result in fast compressional mode waves that propagate through the magnetosphere and drive forced and resonant oscillations of geomagnetic field lines. The compressional wave field may also stimulate ionospheric perturbations. The observations demonstrate that HF radar ground scatter may contain important information on small-amplitude features, extending the scope and capability of these radars to

  8. High-latitude observations of impulse-driven ULF pulsations in the ionosphere and on the ground

    Directory of Open Access Journals (Sweden)

    F. W. Menk

    2003-02-01

    Full Text Available We report the simultaneous observation of 1.6–1.7 mHz pulsations in the ionospheric F-region with the CUTLASS bistatic HF radar and an HF Doppler sounder, on the ground with the IMAGE and SAMNET magnetometer arrays, and in the upstream solar wind. CUTLASS was at the time being operated in a special mode optimized for high resolution studies of ULF waves. A novel use is made of the ground returns to detect the ionospheric signature of ULF waves. The pulsations were initiated by a strong, sharp decrease in solar wind dynamic pressure near 09:28 UT on 23 February 1996, and persisted for some hours. They were observed with the magnetometers over 20° in latitude, coupling to a field line resonance near 72° magnetic latitude. The magnetic pulsations had azimuthal m numbers ~ -2, consistent with propagation away from the noon sector. The radars show transient high velocity flows in the cusp and auroral zones, poleward of the field line resonance, and small amplitude 1.6–1.7 mHz F-region oscillations across widely spaced regions at lower latitudes. The latter were detected in the radar ground scatter returns and also with the vertical incidence Doppler sounder. Their amplitude is of the order of ± 10 ms-1. A similar perturbation frequency was present in the solar wind pressure recorded by the WIND spacecraft. The initial solar wind pressure decrease was also associated with a decrease in cosmic noise absorption on an imaging riometer near 66° magnetic latitude. The observations suggest that perturbations in the solar wind pressure or IMF result in fast compressional mode waves that propagate through the magnetosphere and drive forced and resonant oscillations of geomagnetic field lines. The compressional wave field may also stimulate ionospheric perturbations. The observations demonstrate that HF radar ground scatter may contain important information on small-amplitude features, extending the scope and capability of these radars to track

  9. Identifying equatorial ionospheric irregularities using in situ ion drifts

    National Research Council Canada - National Science Library

    R. A. Stoneback; R. A. Heelis

    2014-01-01

    Previous climatological investigations of ionospheric irregularity occurrence in the equatorial ionosphere have utilized in situ measurements of plasma density to identify the presence of an irregularity...

  10. 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

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

    Directory of Open Access Journals (Sweden)

    Y. G. Rapoport

    2017-01-01

    Full Text Available 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

  12. Seasonal and magnetic activity variations of ionospheric electric fields above the southern mid-latitude station, Bundoora, Australia

    Directory of Open Access Journals (Sweden)

    M. L. Parkinson

    Full Text Available We investigate the seasonal, local solar time, and geomagnetic activity variations of the average Doppler velocity measured by an HF digital ionosonde deployed at Bundoora, Australia (145.1° E, 37.7° S, geographic; 49° S magnetic. The Doppler velocities were heavily averaged to suppress the short-term effects (<3 hours of atmospheric gravity waves, and thereby obtain the diurnal variations attributed to the tidally-driven ionospheric dynamo and electric fields generated by magnetic disturbances. The observed seasonal variations in Doppler velocity were probably controlled by variations in the lower thermospheric winds and ionospheric conductivity above Bundoora and in the magnetically conjugate location. The diurnal variations of the meridional (field-perpendicular drifts and their perturbations exhibited a complex structure, and were generally smaller than the variations in the zonal drifts. The latter were basically strongly west-ward during the evening to early morning, and weakly east-ward during the late morning to just past noon. The zonal perturbations were strongly enhanced by increasing geomagnetic activity, and closely resembled the perturbation drifts measured by the incoherent scatter radar (ISR at Millstone Hill (71.5° W, 42.6° N; 57° N. There was also some resemblance between the diurnal variations in the meridional drifts. Overall, the comparisons suggest that with sufficient averaging, Doppler velocities measured with digital ionosondes at mid-latitudes correspond to true ion motions driven by ionospheric electric fields. This is a useful result because apart from the ISRs located in the American-European sector, there are no ground-based instruments capable of measuring electric fields in the mid-latitude ionosphere.

    Key words. Ionosphere (electric fields and currents; ionosphere atmosphere interactions; mid-latitude ionosphere

  13. An unusual geometry of the ionospheric signature of the cusp: implications for magnetopause merging sites

    Directory of Open Access Journals (Sweden)

    G. Chisham

    2002-01-01

    Full Text Available The HF radar Doppler spectral width boundary (SWB in the cusp represents a very good proxy for the equatorward edge of cusp ion precipitation in the dayside ionosphere. For intervals where the Interplanetary Magnetic Field (IMF has a southward component (Bz < 0, the SWB is typically displaced poleward of the actual location of the open-closed field line boundary (or polar cap boundary, PCB. This is due to the poleward motion of newly-reconnected magnetic field lines during the cusp ion travel time from the reconnection X-line to the ionosphere. This paper presents observations of the dayside ionosphere from SuperDARN HF radars in Antarctica during an extended interval ( ~ 12 h of quasi-steady IMF conditions (By ~ Bz < 0. The observations show a quasi-stationary feature in the SWB in the morning sector close to magnetic local noon which takes the form of a 2° poleward distortion of the boundary. We suggest that two separate reconnection sites exist on the magnetopause at this time, as predicted by the anti-parallel merging hypothesis for these IMF conditions. The observed cusp geometry is a consequence of different ion travel times from the reconnection X-lines to the southern ionosphere on either side of magnetic local noon. These observations provide strong evidence to support the anti-parallel merging hypothesis. This work also shows that mesoscale and small-scale structure in the SWB cannot always be interpreted as reflecting structure in the dayside PCB. Localised variations in the convection flow across the merging gap, or in the ion travel time from the reconnection X-line to the ionosphere, can lead to localised variations in the offset of the SWB from the PCB. These caveats should also be considered when working with other proxies for the dayside PCB which are associated with cusp particle precipitation, such as the 630 nm cusp auroral emission.Key words. Ionosphere (plasma convection – Magnetospheric physics (magnetopause, cusp, and

  14. Global evolution and propagation of electric fields associated with Sudden Commencements observed by multi­ple magnetospheric satellites and ionospheric radars

    Science.gov (United States)

    Takahashi, N.; Kasaba, Y.; Shinbori, A.; Nishimura, Y.; Kikuchi, T.; Hori, T.; Nishitani, N.

    2015-12-01

    Sudden commencements (SCs) are triggered by a compression of the dayside magnetosphere, leading to fast mode wave propagation in the equatorial plane. In contrast, the compression induces Alfven waves that propagate toward the dayside polar ionosphere along field lines, and then ionospheric electric fields propagate toward low-latitude ionosphere at speed of light. Several direct observations have provided evidence of the fast mode or Alfven wave propagation, but spatial and temporal evolutions of these propagations are not well known. Moreover, a previous study shows that upward Poynting fluxes transport electromagnetic energy toward the nightside magnetosphere. However, whether such upward Poynting fluxes are launched from the ionosphere or converted from fast mode waves has not been confirmed yet. In this study, we investigate evolution of the electric field in the magnetosphere-ionosphere coupled system using THEMIS, Van Allen Probes, GOES 13 and 15, SuperDARN, and HF Doppler radars. We find 70 SC events occurred from January 2013 to December 2014. The result of event studies shows the time delay of the onsets between dayside and nightside magnetospheric electric fields, which can be explained by the fast mode wave propagation. However, we also find that the SC onset of the nightside electric field (~21 h LT) is 15 s later than that of the midnight one although they are detected in the same L-value, which may suggest a dawn-dusk asymmetry of the electromagnetic energy propagation time in the inner magnetosphere. In the ionosphere, both SuperDARN and HF Doppler radars detect a northward velocity at ~15 h LT about 1 min after that of the dayside magnetospheric electric field, which is consistent with the Alfven velocity from the dayside magnetosphere to the polar ionosphere. We will evaluate the possible propagation path of the electromagnetic energy associated with SCs.

  15. A Multi-frequency Beam-forming HF Radar for Tsunami Detection

    Science.gov (United States)

    Trizna, D. B.

    2007-05-01

    We discuss a new multi-frequency beam-forming HF radar design for robust detection and tracking of tsunami waves from 200 km distances, providing continuous coverage of the tsunami wave pattern after it impinges on the continental shelf. The method works by mapping ocean currents at long range using traditional HF radar method of radial Bragg line Doppler shift measurements. The tsunami is detected by anomalous spatial patterns of higher than normal Bragg-line shifts due to the large orbital wave of the series of tsunami wave crests as they impinge on the continental shelf. An approach using beam forming of 16 or 32 antenna elements provides an update every five minutes or less, while Direction-of-Arrival method systems using just a few antenna elements inherently require of the order of 30 to 60 minutes for a reliable current map. The multi-frequency radar provides a more robust capability than the single frequency HF radar for at least two reasons. First, because the HF channel user spectrum suffers diurnal variability in channel occupancy due to the ionosphere changing with time of day, low frequencies can become contaminated with user noise, so that maximum range for reliable detection not achieved. Under this condition, one would rely on quiet higher HF frequencies that lie above the Maximum Usable Frequency (MUF) for ionospheric reflection propagation. Alternatively, for daylight operation when low frequency utilization can be used to minimize surface wave propagation loss, the sea state might not be sufficiently active to allow long range coverage needed for reliable detection, due to the lack of ocean wave spectral energy at the Bragg-resonant wave frequency. Thus, single- frequency radars, operating in the 4-6 MHz range to minimize propagation losses to achieve long-range coverage, would suffer due to low wind conditions. The multi-frequency HF radar discussed here allows one to dynamically choose the optimum frequency from a set of 8 to 16, as allowed by

  16. Using IRI and GSM TIP model results as environment for HF radio wave propagation model during the geomagnetic storm occurred on September 26-29, 2011

    Science.gov (United States)

    Kotova, D. S.; Klimenko, M. V.; Klimenko, V. V.; Zakharov, V. E.; Ratovsky, K. G.; Nosikov, I. A.; Zhao, B.

    2015-11-01

    This paper analyses the geomagnetic storm on September 26-29, 2011. We compare the calculation results obtained using the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) and IRI-2012 (Bilitza et al., 2014) model with ground-based ionosonde data of stations at different latitudes and longitudes. We examined physical mechanisms responsible for the formation of ionospheric effects during the main phase of geomagnetic storm that occurred at the rising phase of the 24th solar cycle. We used numerical results obtained from IRI-2012 and GSM TIP models as propagation environment for HF signals from an equatorial transmitter during quiet and disturbed conditions. We used the model of HF radio wave propagation developed in I. Kant Baltic Federal University (BFU) that is based on the geometrical optics approximation. We compared the obtained radio paths in quiet conditions and during the main and recovery storm phases and evaluated radio wave attenuation in different media models.

  17. Simulation study of the large-scale modification of the mid-latitude F-layer by HF radio waves with different powers

    Directory of Open Access Journals (Sweden)

    G. I. Mingaleva

    2012-08-01

    Full Text Available A mathematical model of the ionosphere, developed earlier, is applied to investigate the large-scale mid-latitude F-layer modification by HF radio waves with different powers. Simulations are performed for the point with geographic coordinates of the "Sura" heating facility (Nizhny Novgorod, Russia for autumn conditions. The calculations are made for distinct cases, in which the effective absorbed power has different values belonging to the 5–100 MW range, both for nocturnal and daytime conditions. The frequency of powerful HF waves is chosen to be close to the most effective frequency for the large-scale F2-layer modification. The results of modeling indicate that the effective absorbed power can influence considerably the F-layer response to high-power radio waves in the mid-latitude ionosphere.

  18. Fortællingen om hf

    DEFF Research Database (Denmark)

    Klewe, Lars

    2008-01-01

    Artikel i anledning af hf's 40 års jubilæum. Artiklen indeholder blandt andet en redegørelse for en undersøgelse af, hvordan det er gået tre årgange af hf-studenter med hensyn til senere uddannelsesvalg, arbejdsmarkedsplacering mv.......Artikel i anledning af hf's 40 års jubilæum. Artiklen indeholder blandt andet en redegørelse for en undersøgelse af, hvordan det er gået tre årgange af hf-studenter med hensyn til senere uddannelsesvalg, arbejdsmarkedsplacering mv....

  19. Experiments and theory on parametric instabilities excited in HF heating experiments at HAARP

    Energy Technology Data Exchange (ETDEWEB)

    Kuo, Spencer [New York University-Polytechnic School of Engineering, 5 Metrotech Center, Brooklyn, New York 11201 (United States); Snyder, Arnold [NorthWest Research Associates, P.O. Box 530, Stockton Springs, Maine 04981 (United States); Lee, M. C. [Department of Electrical and Computer Engineering, Boston University, Boston, Massachusetts 02215 (United States); Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

    2014-06-15

    Parametric instabilities excited by O-mode HF heater and the induced ionospheric modification were explored via HAARP digisonde operated in a fast mode. The impact of excited Langmuir waves and upper hybrid waves on the ionosphere are manifested by bumps in the virtual spread, which expand the ionogram echoes upward as much as 140 km and the downward range spread of the sounding echoes, which exceeds 50 km over a significant frequency range. The theory of parametric instabilities is presented. The theory identifies the ionogram bump located between the 3.2 MHz heater frequency and the upper hybrid resonance frequency and the bump below the upper hybrid resonance frequency to be associated with the Langmuir and upper hybrid instabilities, respectively. The Langmuir bump is located close to the upper hybrid resonance frequency, rather than to the heater frequency, consistent with the theory. Each bump in the virtual height spread of the ionogram is similar to the cusp occurring in daytime ionograms at the E-F2 layer transition, indicating that there is a small ledge in the density profile similar to E-F2 layer transitions. The experimental results also show that the strong impact of the upper hybrid instability on the ionosphere can suppress the Langmuir instability.

  20. Recent Developments in Ionosphere-Thermosphere Modeling with an Emphasis on Solar Variability

    Science.gov (United States)

    Sojka, J.; Smithtro, C.; Schunk, R.

    The Utah State University modeling developments have led to new results in several areas of ionospheric research. This presentation will present the most recent of these results and their synergisms with both ground-based and satellite-based observations. Particular attention is given to new results associated with solar variability, a central theme to this TIGER symposium. The effect on the ionosphere of differences in solar X-EUV spectra will be demonstrated by studies using the Time Dependent Ionospheric Model (TDIM) while their effect on the coupled thermosphere-ionosphere will be shown using a new model, the Global Average Ionosphere Thermosphere (GAIT) model. How the dayside solar-produced plasma is also an aspect of SAPS, SEDs, Tongues of Ionization, Patches, Polar Wind Jets, and Polar Cap Scintillations, will be described via recent modeling results from a variety of coupled or driven thermosphere, ionosphere, magnetosphere models. The presentation will further the need for improved solar output specification whether via observation or model. These improvements need to be over the flare through solar cycle time scale with particular attention to the short wavelength end of the spectrum.

  1. The new IGS ionospheric product - TEC fluctuation maps and their scientific application

    Science.gov (United States)

    Krankowski, Andrzej; Cherniak, Iurii; Zakharenkova, Irina

    2017-04-01

    The GPS signals fading due to presence of the plasma irregularities in the ionosphere can decrease an operational availability of navigation systems. This effect can be estimated by measuring its impact on phase of the received GPS signal. The new IGS ionospheric fluctuation maps product is based on estimates of the TEC rapid changes. For an overall representation of the spatial evolution of the ionospheric irregularities, which caused the GPS signal fluctuations over the Northern Hemisphere in middle and high latitudes, a daily map of the ROTI index is produced basing on data derived from a representative set of 700 permanent GPS stations. We use the corrected geomagnetic (CGM) coordinates with DGRF/IGRF models. For daily ROTI maps, we averaged and binned all ROTI values collected during 00-24 UT period of a considered day. The grid size is 8 min MLT by 2° MLAT, with the latter covering 50° - 90°. The averaged ROTI value in each MLAT-MLT bin corresponds to probability of the GPS signals phase fluctuations caused by passing of radio signals through the ionospheric irregularities. The resulted ionospheric fluctuation product is represented in the ASCII IONEX-like data format and can be visualized. This data format is described in details. We demonstrate the IGS ionospheric fluctuation map product performance for scientific research application on set of test-cases (geomagnetic storms occurred in the years 2013-2015) for comparative analysis of the resulted daily ROTI maps for quiet and geomagnetically disturbed periods. The intense phase scintillations depicted in the diurnal ROTI maps can provide an important information about development of the severe storm-induced gradients in the ionospheric plasma density, both caused by auroral particle precipitation and plasma flows. It is possible to conclude that IGS ionospheric fluctuation maps product can be effectively used for monitoring of the plasma irregularities with different origin. The independent ground

  2. The mapping of ionospheric TEC for central Russian and European regions on the base of GPS and GLONASS measurements

    Science.gov (United States)

    Shagimuratov, Irk; Cherniak, Iurii; Zakharenkova, Irina; Ephishov, Ivan; Krankowski, Andrzej; Radievsky, Alexander

    2014-05-01

    The total electron content (TEC) is a key parameter not only for space radio communication but also for addressing the fundamental problems of the ionosphere physics and near Earth space. Currently, the main sources of information on the TEC in the global scale are GNSS signals measurements. The spatial-temporal behavior of the ionosphere can be most effectively analyzed using TEC maps. To date, global IGS global ionospheric maps with a resolution of 2.5 degree in latitude and 5 in longitude and a time resolution of 2 h are most widely used. To study the detailed structure of the ionospheric gradients and rapid process as well as for precise positioning task it is necessary to use more precise regional TEC maps. The Regional TEC maps are currently constructed by different research groups for different regions: USA, Europe, Japan etc. The West Department of IZMIRAN research group is a one in Russia who works on the task of regional ionosphere mapping since 2000. It was developed the methodology for obtaining information on the spatial TEC distribution, TEC maps of the ionosphere on the basis of the algorithm for multi-station processing of GNSS observations. Using a set of algorithms and programs, regional TEC maps with a spatial resolution of 1° and a time resolution up to 15 min can be produced. Here is developed the approach to establish the regular online internet service for regional ionosphere mapping of the Western Russia and Eastern Europe. Nowadays the development of GLONASS navigation system is completely finished and it consists of a constellation of more than 24 satellites. It is good perspective for investigations of the ionosphere structure and dynamics on the base of the simultaneous observations of GPS and GLONASS systems. The GLONASS satellites have the inclination about 64 degrees as against GPS satellites with 56. So the GLONASS provides opportunity to study the high latitude ionosphere. The different scale electron density irregularities

  3. 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

  4. 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

  5. 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.

  6. Ionosphere and its Influence on Radio Communications

    Indian Academy of Sciences (India)

    Communications. R S Dabas is at the Radio. Science Division of. National Physical. Laboratory, New Delhi and is responsible for characterization of ionospheric media for radio communication applications. His main area of research is the study of equatorial and low latitude ionosphere. i.e. its properties and dynamics.

  7. Ionospheric F-Region Storms: Unsolved Problems

    Science.gov (United States)

    2006-06-01

    Heaviside layer by the echo- method , Proc. Inst. Radio Eng., 17, 1513-1522, 1929 [8] Kil, H, and L.J. Paxton, Ionospheric disturbances during the magnetic...ionospheric storms, J. Geophys. Res., 107, 10.1029/2001JA900126, 2002 [24] Rishbeth, H., F-region storms and thermospheric dynamics, J. Geomag. Geoelectr

  8. Associating an ionospheric parameter with major earthquake ...

    Indian Academy of Sciences (India)

    With time, ionospheric variation analysis is gaining over lithospheric monitoring in serving precursors for earthquake forecast. The current paper highlights the association of major (Ms ≥ 6.0) and medium (4.0 ≤ Ms > 6.0) earthquake occurrences throughout the world in different ranges of the Ionospheric Earthquake ...

  9. Generation of real-time global ionospheric map based on the global GNSS stations with only a sparse distribution

    Science.gov (United States)

    Li, Zishen; Wang, Ningbo; Li, Min; Zhou, Kai; Yuan, Yunbin; Yuan, Hong

    2017-04-01

    The Earth's ionosphere is part of the atmosphere stretching from an altitude of about 50 km to more than 1000 km. When the Global Navigation Satellite System (GNSS) signal emitted from a satellite travels through the ionosphere before reaches a receiver on or near the Earth surface, the GNSS signal is significantly delayed by the ionosphere and this delay bas been considered as one of the major errors in the GNSS measurement. The real-time global ionospheric map calculated from the real-time data obtained by global stations is an essential method for mitigating the ionospheric delay for real-time positioning. The generation of an accurate global ionospheric map generally depends on the global stations with dense distribution; however, the number of global stations that can produce the real-time data is very limited at present, which results that the generation of global ionospheric map with a high accuracy is very different when only using the current stations with real-time data. In view of this, a new approach is proposed for calculating the real-time global ionospheric map only based on the current stations with real-time data. This new approach is developed on the basis of the post-processing and the one-day predicted global ionospheric map from our research group. The performance of the proposed approach is tested by the current global stations with the real-time data and the test results are also compared with the IGS-released final global ionospheric map products.

  10. Theory and observations of cometary ionospheres

    Science.gov (United States)

    Cravens, T. E.

    The basic physical and chemical processes responsible for the makeup of cometary ionospheres are discussed in the framework of relevant in situ measurements on the Halley and Giacobini-Zinner comets, as well as recent theoretical models of cometary ionospheres. Special attention is given to physical processes responsible for the formation of the contact surface (CS), which is that surface where the magnetic field becomes zero or extremely small and which separates the field-free ionosphere and the magnetized plasma on the outside. Results of in situ observations indicate that the plasma just outside the CS is just as ionospheric in nature as the 'classical' ionospheric plasma residing within this surface. An expression for the magnetic field in this region is derived.

  11. Doppler Spectral Characteristics of High Latitude Ionospheric Irregularities: Effect on HF Radars.

    Science.gov (United States)

    1981-05-01

    DAOP (V) =50090 E-FDLDING DISTANCE OF ARRL E-FIELD(OEGREES) =5 LATITUDE OF POTENTIAL MAXIMUM(DEGREES) =70 OVAL OFFSET<DEGREES) a S MEASUREMENT LATITUDE...DOPPLER WIDT14 CROSS POLAR CAP POTENTIAL DAOP (V) =50000 E-FOLDING DISTANCE OF RRORAL E-FIELD(DEGAEES) =5 LATITUDE OF PDTENTIAL" MPXIMUM(DEGREES) = 70 OVAL...60 -Al1l - jiU 4,1 8.53 12.5 16.3 26.5s 24,#* * U *m U 10 tm 4- U U7 Ito oU LOCAL TIME DOPPLER VELOCITY DOPPLER WIDTH CROSS POLAR CAP POTENTIAL DAOP

  12. Utility of ionosphere and troposphere models for extending the range of high-accuracy GPS

    Science.gov (United States)

    Dodd, David William

    This dissertation studied the use of NOAA real-time ionosphere and troposphere products in extending the range of long-baseline, high-accuracy DGPS for real-time positioning. The question being addressed by this work is; can existing real-time ionosphere and troposphere models reduce the observation uncertainties to the level where they can be used to reliably resolve integer ambiguities, in real-time, over long baselines (>30km). In-house GPS processing software (USM_OTF) was developed to ingest the models and compute epoch-to-epoch, float and fixed ambiguity position solutions. Single baseline processing, ranging from 20 to 740 kin, over several days in four separate sessions (July 2004, January 2005, August 2005 and July 2006) incorporating four regions of the U.S.A. (Michigan, California, Central and the South East), were evaluated. The first session looked at the NOAA real-time troposphere model and the second session looked at the NOAA real-time ionosphere model. The third and fourth sessions looked at the use of both the NOAA real-time ionosphere and troposphere models. Results showed that the NOAA troposphere model reduced the height bias uncertainty by up to 30 cm, under high activity conditions. They also showed that the troposphere model increased the uncertainty standard deviation under these high activity conditions. The results from the first tests of the real-time NOAA ionosphere model showed that, due to satellite coverage issues, it produced worse results than other real-time models. The NOAA model suffered from lack of satellite coverage corrections, especially in areas near the limits of the model, and at the beginning and end of a satellite's flight path. A reduction in satellite numbers lead to weaker geometry and less reliable position solutions. These tests showed that it was better to provide less accurate ionosphere estimates than to leave the satellites out of the solution. These problems were addressed by NOAA prior to the final tests

  13. Saturn: atmosphere, ionosphere, and magnetosphere.

    Science.gov (United States)

    Gombosi, Tamas I; Ingersoll, Andrew P

    2010-03-19

    The Cassini spacecraft has been in orbit around Saturn since 30 June 2004, yielding a wealth of data about the Saturn system. This review focuses on the atmosphere and magnetosphere and briefly outlines the state of our knowledge after the Cassini prime mission. The mission has addressed a host of fundamental questions: What processes control the physics, chemistry, and dynamics of the atmosphere? Where does the magnetospheric plasma come from? What are the physical processes coupling the ionosphere and magnetosphere? And, what are the rotation rates of Saturn's atmosphere and magnetosphere?

  14. 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

  15. Garnet effect on Nd-Hf isotope decoupling: Evidence from the Jinfosi batholith, Northern Tibetan Plateau

    Science.gov (United States)

    Huang, Hui; Niu, Yaoling; Mo, Xuanxue

    2017-03-01

    The initial Nd and Hf isotope ratios of a 420 Ma post-collisional dioritic-granitic batholith from the Northern Tibetan plateau define a negative trend above and orthogonal to the ԐHf(t)-ԐNd(t) terrestrial array. This uncommon trend offers an insight into the origin of the puzzling Nd-Hf isotope decoupling in the crustal rocks. On this trend, samples depleted in heavy rare earth elements (HREEs, i.e., [Dy/Yb]N ≫ 1) deviate most from the terrestrial array whereas samples with flat HREEs (i.e., [Dy/Yb]N ≥ 1) deviate less or plot within the terrestrial array, pointing to the controlling effect of garnet in the magma source. Ancient garnet-bearing residues after melt extraction will have elevated Lu/Hf ratios and can evolve with time to produce high ԐHf(t) at a low ԐNd(t) value. Mixing of melts derived from such source lithologies (high Lu/Hf) with melts possessing a within-terrestrial array Nd-Hf isotopic composition (low Lu/Hf) best explains the observed trend orthogonal to the terrestrial array. The samples from the Jinfosi batholith with the most decoupled Nd-Hf isotope compositions require a larger degree (> 40%) and ancient (i.e., ≥ 1.8 Gyr) previous melt extraction from their source. It follows that the ancient melts with depleted HREEs complementary to those garnet-bearing residues should have low ԐHf values and plot below the terrestrial array, which is indeed shown by some Archean/Paleoproterozic TTGs.

  16. From the Sun to the Earth: impact of the 27-28 May 2003 solar events on the magnetosphere, ionosphere and thermosphere

    Directory of Open Access Journals (Sweden)

    C. Hanuise

    2006-03-01

    Full Text Available During the last week of May 2003, the solar active region AR 10365 produced a large number of flares, several of which were accompanied by Coronal Mass Ejections (CME. Specifically on 27 and 28 May three halo CMEs were observed which had a significant impact on geospace. On 29 May, upon their arrival at the L1 point, in front of the Earth's magnetosphere, two interplanetary shocks and two additional solar wind pressure pulses were recorded by the ACE spacecraft. The interplanetary magnetic field data showed the clear signature of a magnetic cloud passing ACE. In the wake of the successive increases in solar wind pressure, the magnetosphere became strongly compressed and the sub-solar magnetopause moved inside five Earth radii. At low altitudes the increased energy input to the magnetosphere was responsible for a substantial enhancement of Region-1 field-aligned currents. The ionospheric Hall currents also intensified and the entire high-latitude current system moved equatorward by about 10°. Several substorms occurred during this period, some of them - but not all - apparently triggered by the solar wind pressure pulses. The storm's most notable consequences on geospace, including space weather effects, were (1 the expansion of the auroral oval, and aurorae seen at mid latitudes, (2 the significant modification of the total electron content in the sunlight high-latitude ionosphere, (3 the perturbation of radio-wave propagation manifested by HF blackouts and increased GPS signal scintillation, and (4 the heating of the thermosphere, causing increased satellite drag. We discuss the reasons why the May 2003 storm is less intense than the October-November 2003 storms, although several indicators reach similar intensities.

  17. Origin of excess 176Hf in meteorites

    DEFF Research Database (Denmark)

    Thrane, Kristine; Connelly, James; Bizzarro, Martin

    2010-01-01

    with Lu/Hf elemental ratios in meteorites older than similar to 4.56 Ga meteorites unresolved. We attribute (176)Hf excess in older meteorites to an accelerated decay of (176)Lu caused by excitation of the long-lived (176)Lu ground state to a short-lived (176m)Lu isomer. The energy needed to cause...

  18. The ionosphere and thermosphere at southern midlatitudes during the November 1993 ionospheric storm: A comparison of measurement and modeling

    Science.gov (United States)

    Richards, P. G.; Wilkinson, P. J.

    1998-05-01

    A network of ionosondes in the Australian-Japanese region recorded the ionospheric response to a major magnetic storm that occurred near 2400 UT on November 3, 1993, when Kp reached 7. Most stations recorded a positive phase (increase) in NmF2 on November 4 which was well produced by the field line interhemispheric plasma (FLIP) model despite a large relative increase in the model molecular neutral densities. The positive phase appears to be related to a storm-induced large abrupt uplift of the ionospheric peak height (hmF2) that may have been caused by a neutral wind surge or by an electric field. The storm caused large winds to blow from the pole to the equator, raising the measured hmF, by 50-100 km over quiet time values. There was a negative phase (decrease) on November 5 at the higher midlatitude stations but not at the low-latitude stations. The negative phase was not well reproduced by the model. At low latitudes, a short-period wave-like structure was seen in hmF2, NmF2, and equivalent winds. The quiet time equivalent winds in the eastern Australian sector show a pronounced semidiurnal tide signature at all latitudes with a phase shift of about 1 hour for every 15 deg increase in latitude. An algorithm which adjusts the atomic to molecular neutral density ratio by changing the neutral temperature and atomic oxygen density was used to help reproduce the observed electron density. The changes to the standard neutral density ratio were small at Hobart except during the stormy period. At Townsville, the needed changes to the neutral density ratio were generally small at daytime, but large increases were needed at night during quiet periods. The algorithm is unable to uniquely determine whether the changes in neutral density ratio come from changes in temperature or changes in atomic oxygen density. When averaged over the full 14-day campaign, there was good agreement between the modified and standard model neutral temperatures except at the low

  19. Ground-based observations of the auroral zone and polar cap ionospheric responses to dayside transient reconnection

    Directory of Open Access Journals (Sweden)

    J. A. Davies

    Full Text Available Observations from the EISCAT VHF incoherent scatter radar system in northern Norway, during a run of the common programme CP-4, reveal a series of poleward-propagating F-region electron density enhancements in the pre-noon sector on 23 November 1999. These plasma density features, which are observed under conditions of a strongly southward interplanetary magnetic field, exhibit a recurrence rate of under 10 min and appear to emanate from the vicinity of the open/closed field-line boundary from where they travel into the polar cap; this is suggestive of their being an ionospheric response to transient reconnection at the day-side magnetopause (flux transfer events. Simultaneous with the density structures detected by the VHF radar, poleward-moving radar auroral forms (PMRAFs are observed by the Finland HF coherent scatter radar. It is thought that PM-RAFs, which are commonly observed near local noon by HF radars, are also related to flux transfer events, although the specific mechanism for the generation of the field-aligned irregularities within such features is not well understood. The HF observations suggest, that for much of their existence, the PMRAFs trace fossil signatures of transient reconnection rather than revealing the footprint of active reconnection itself; this is evidenced not least by the fact that the PMRAFs become narrower in spectral width as they evolve away from the region of more classical, broad cusp scatter in which they originate. Interpretation of the HF observations with reference to the plasma parameters diagnosed by the incoherent scatter radar suggests that as the PMRAFs migrate away from the reconnection site and across the polar cap, entrained in the ambient antisunward flow, the irregularities therein are generated by the presence of gradients in the electron density, with these gradients having been formed through structuring of the ionosphere in the cusp region in response to transient reconnection

  20. A global scale picture of ionospheric peak electron density changes during geomagnetic storms

    Science.gov (United States)

    Kumar, Vickal V.; Parkinson, Murray L.

    2017-04-01

    Changes in ionospheric plasma densities can affect society more than ever because of our increasing reliance on communication, surveillance, navigation, and timing technology. Models struggle to predict changes in ionospheric densities at nearly all temporal and spatial scales, especially during geomagnetic storms. Here we combine a 50 year (1965-2015) geomagnetic disturbance storm time (Dst) index with plasma density measurements from a worldwide network of 132 vertical incidence ionosondes to develop a picture of global scale changes in peak plasma density due to geomagnetic storms. Vertical incidence ionosondes provide measurements of the critical frequency of the ionospheric F2 layer (foF2), a direct measure of the peak electron density (NmF2) of the ionosphere. By dissecting the NmF2 perturbations with respect to the local time at storm onset, season, and storm intensity, it is found that (i) the storm-associated depletions (negative storm effects) and enhancements (positive storm effects) are driven by different but related physical mechanisms, and (ii) the depletion mechanism tends to dominate over the enhancement mechanism. The negative storm effects, which are detrimental to HF radio links, are found to start immediately after geomagnetic storm onset in the nightside high-latitude ionosphere. The depletions in the dayside high-latitude ionosphere are delayed by a few hours. The equatorward expansion of negative storm effects is found to be regulated by storm intensity (farthest equatorward and deepest during intense storms), season (largest in summer), and time of day (generally deeper on the nightside). In contrast, positive storm effects typically occur on the dayside midlatitude and low-latitude ionospheric regions when the storms are in the main phase, regardless of the season. Closer to the magnetic equator, moderate density enhancements last up to 40 h during the recovery phase of equinox storms, regardless of the local time. Strikingly, high

  1. Quasi-thermal noise and shot noise spectroscopy on a CubeSat in Earth's ionosphere

    Science.gov (United States)

    Maj, Ronald; Cairns, Iver H.

    2017-03-01

    We investigate the practicality of using quasi-thermal noise (QTN) and shot noise spectroscopy on a CubeSat in the Earth's ionosphere and constrain the satellite antenna length for optimal detection of these signals. The voltage spectra predicted for thermal Langmuir waves (QTN) and particle "shot noise" are modeled, and it is shown that the signals detected can provide two very good, independent, passive, in situ methods of measuring the plasma density and temperature in the ionosphere. The impact of the antenna potential ϕ is also discussed, and we show that the negative potential calculated for the ionosphere due to natural current flows has a significant impact on the voltage power level of the shot noise spectrum. The antenna configuration is also shown to play an important role in the shot noise, with a monopole configuration enhancing the spectrum significantly compared with a dipole. Antenna lengths on the order of 20-40 cm are found to be ideal for ionospheric plasma conditions, nicely matching CubeSat sizes and producing detectable thermal Langmuir waves and shot noise at the microvolt level. Further, with a continuous stream of data points at different latitudes and longitudes an orbiting CubeSat can produce a global picture for the ionospheric plasma density and temperature using QTN and shot noise signals. If implemented, especially in a constellation, these data would be more frequent and cover a much greater domain than current ground-based or single-satellite methods. This could lead to improved ionospheric models, such as the empirically based International Reference Ionosphere.

  2. Modeling of the ionospheric perturbations induced by Earthquakes

    Science.gov (United States)

    Occhipinti, G.; Lognonne, P.; Ducic, V.; Artru, J.; Bazin, V.

    2003-04-01

    Technological advances over the past fifteen years have made it possible to detect in the ionosphere not only surface waves generated by Earthquakes but also Tsunamis. The objective of this paper is to model these signals by taking into account all major sources of dissipations within the ionosphere. At high altitudes, a significant coupling is observed between the dynamic and heat equations. Damping is therefore produced by both viscosity and heat diffusion and the standart acoustic theory, even in the viscous case, cannot be used anymore. Such coupling must be explicitly taken into acount in the normal mode equation and in its solution, as well as the radiation of energy above the maximum altitude of the model. We present here preliminary results of this theory. It allows to compute either normal modes or ionospheric velocity field by normal mode summation. The results of our simulations associated to a few quakes are shown. In the viscous case, we compare also synthetics to data obtained by the dense GPS network of California for the Denalli earthquake, by taking into acount all sources of TEC variations and the geometries of GPS satellites to receiver paths.

  3. MONITORING IONOSPHERIC VARIATION FOR A DEFINITE PERIOD TIME IN TURKEY

    Directory of Open Access Journals (Sweden)

    S. Inyurt

    2015-12-01

    Full Text Available Ionosphere has been studied by a number of scientists in recent years. Since GPS observations cannot provide TEC value directly, it can be estimated from combination of observations. In this study TEC values derived from GPS observations were produced variations with two hours increments from the eighth day to fifteenth day in months just after beginning of each season, namely January, April, July and October in 2014 for ZONG TUSAGA-Aktif station and 41 other stations (TUSAGA-Aktif, EUREF, IGS. TEC values computed by the Bernese 5.0 software were compared with the Global Ionosphere Model (GIM TEC values regularly published by Center for Orbit Determination in Europe (CODE and International Reference Ionosphere (IRI-2012 TEC values. As a result of this study, with the comparison of GPS TEC values to GIM TEC values, it has become obvious that GPS TEC values are quite similar to the GIM TEC values. The differences of TEC values derived from GPS TEC and GIM TEC change from 0.91 TECU (January to 1.88 TECU (October. On the other hand, GPS TEC values are also compared with IRI TEC values, and found out that there is a considerable difference between the two TEC values ranging from 6.30 TECU (January to 15.15 TECU (April. Moreover, TEC values derived from GPS measurements are attained similar to GIM TEC, but found to stray from IRI-2012 TEC values remarkably.

  4. Monitoring Ionospheric Variation for a Definite Period Time in Turkey

    Science.gov (United States)

    Inyurt, S.; Mekik, C.; Yildirim, O.

    2015-12-01

    Ionosphere has been studied by a number of scientists in recent years. Since GPS observations cannot provide TEC value directly, it can be estimated from combination of observations. In this study TEC values derived from GPS observations were produced variations with two hours increments from the eighth day to fifteenth day in months just after beginning of each season, namely January, April, July and October in 2014 for ZONG TUSAGA-Aktif station and 41 other stations (TUSAGA-Aktif, EUREF, IGS). TEC values computed by the Bernese 5.0 software were compared with the Global Ionosphere Model (GIM) TEC values regularly published by Center for Orbit Determination in Europe (CODE) and International Reference Ionosphere (IRI-2012) TEC values. As a result of this study, with the comparison of GPS TEC values to GIM TEC values, it has become obvious that GPS TEC values are quite similar to the GIM TEC values. The differences of TEC values derived from GPS TEC and GIM TEC change from 0.91 TECU (January) to 1.88 TECU (October). On the other hand, GPS TEC values are also compared with IRI TEC values, and found out that there is a considerable difference between the two TEC values ranging from 6.30 TECU (January) to 15.15 TECU (April). Moreover, TEC values derived from GPS measurements are attained similar to GIM TEC, but found to stray from IRI-2012 TEC values remarkably.

  5. Products of Dissociative Recombination in the Ionosphere

    Science.gov (United States)

    Cosby, Philip

    1996-01-01

    SRI International undertook a novel experimental measurement of the product states formed by dissociative recombination (DR) of O2(+), NO(+), and N2(+) as a function of both electron energy and reactant ion vibrational level. For these measurements we used a recently developed experimental technique for measuring dissociation product distributions that allows both the branching ratios to be accurately determined and the electronic and rovibrational state composition of the reactant ions to be specified. DR is the dominant electron loss mechanism in all regions of the ionosphere. In this process, electron attachment to the molecular ion produces an unstable neutral molecule that rapidly dissociates. For a molecular ion such as O2(+), the dissociation recombination reaction is (1) O2(+) + e yields O + O + W. The atomic products of this reaction, in this case two oxygen atoms, can be produced in a variety of excited states and with a variety of kinetic energies, as represented by W in Eq. (1). These atoms are not only active in the neutral chemistry of the ionosphere, but are also especially important because their optical emissions are often used to infer in situ concentrations of the parent molecular ion and ambient electron densities. Many laboratory measurements have been made of DR reaction rates under a wide range of electron temperatures, but very little is known about the actual distributions among the final states of the atomic products. This lack of knowledge seriously limits the validity and effectiveness of efforts to model both natural and man-made ionospheric disturbances. Bates recently identified major deficiencies in the currently accepted branching ratios for O2(+) as they relate to blue and green line emission measurements in the nocturnal F-region. During our two-year effort, we partially satisfied our ambitious goals. We constructed and operated a variable pressure, electron-impact ion source and a high pressure, hollow-cathode discharge ion

  6. Geophysical phenomena during an ionospheric modification experiment at Tromsø, Norway

    Directory of Open Access Journals (Sweden)

    N. F. Blagoveshchenskaya

    1998-10-01

    Full Text Available We present an analysis of phenomena observed by HF distance-diagnostic tools located in St. Petersburg combined with multi-instrument observation at Tromsø in the HF modified ionosphere during a magnetospheric substorm. The observed phenomena that occurred during the Tromsø heating experiment in the nightside auroral Es region of the ionosphere depend on the phase of substorm. The heating excited small-scale field-aligned irregularities in the E region responsible for field-aligned scattering of diagnostic HF waves. The equipment used in the experiment was sensitive to electron density irregularities with wavelengths 12–15 m across the geomagnetic field lines. Analysis of the Doppler measurement data shows the appearance of quasiperiodic variations with a Doppler frequency shift, fd and periods about 100–120 s during the heating cycle coinciding in time with the first substorm activation and initiation of the upward field-aligned currents. A relationship between wave variations in fd and magnetic pulsations in the Y-component of the geomagnetic field at Tromsø was detected. The analysis of the magnetic field variations from the IMAGE magnetometer stations shows that ULF waves occurred, not only at Tromsø, but in the adjacent area bounded by geographical latitudes from 70.5° to 68° and longitudes from 16° to 27°. It is suggested that the ULF observed can result from superposition of the natural and heater-induced ULF waves. During the substorm expansion a strong stimulated electromagnetic emission (SEE at the third harmonic of the downshifted maximum frequency was found. It is believed that SEE is accompanied by excitation of the VLF waves penetrating into magnetosphere and stimulating the precipitation of the energetic electrons (10–40 keV of about 1-min duration. This is due to a cyclotron resonant interaction of natural precipitating electrons (1–10 keV with heater-induced whistler waves in the magnetosphere. It is reasonable

  7. Dayside ionospheric convection changes in response to long-period interplanetary magnetic field oscillations: Determination of the ionospheric phase velocity

    Energy Technology Data Exchange (ETDEWEB)

    Saunders, M.A.; Freeman, M.P.; Southwood, D.J.; Cowley, S.W.H. (Imperial College of Science, Technology and Medicine, London (United Kingdom)); Lockwood, M. (Rutherford Appleton Lab., Oxfordshire (United Kingdom)); Samson, J.C. (Univ. of Alberta, Edmonton (Canada)); Farrugia, C.J. (NASA Goddard Space Flight Center, Greenbelt, MD (United States)); Hughes, T.J. (National Research Council of Canada, Ottawa, Ontario (Canada))

    1992-12-01

    Ground magnetic field perturbations recorded by the CANOPUS magnetometer network in the 7 to 13 MLT sector are used to examine how reconfigurations of the dayside polar ionospheric flow take place in response to north-south changes of the IMF. During the 6-hour interval in question IMF B[sub z] oscillates between [plus minus] 7 nT with about a 1-hour period. Corresponding variations in the ground magnetic disturbance are observed which the authors infer are due to changes in ionospheric flow. Cross correlation of the data obtained from two ground stations at 73.5[degrees] magnetic latitude, but separated by [approximately]2 hours in MLT, shows that changes in the flow are initiated in the prenoon sector ([approximately]10 MLT) and then spread outward toward dawn and dusk with a phase speed of [approximately]5 km s[sup [minus]1] over the longitude range [approximately]8 to 12 MLT, slowing to [approximately] 2 km s[sup [minus]1] outside this range. Cross correlating the data from these ground stations with IMP 8 IMF B[sub z] records produces a MLT variation in the ground response delay relative to the IMF which is compatible with these deduced phase speeds. The authors interpret these observations in terms of the ionospheric response to the onset, expansion and decay of magnetic reconnection at the dayside magnetopause.

  8. Variations in ionospheric parameters during periods of minimum and maximum solar activity

    Science.gov (United States)

    Taran, V. I.

    1996-12-01

    Ionospheric investigations in Ukraine are being carried out with uniquely developed incoherent scatter radars. Data on the variations in the electron density and the electron and ion temperatures during periods of low (1994) and high (1989 - 1990) solar activity are presented. The F-layer peak height ranges from 450 at night to 240 km in the daytime; the electron density maximum varies approximately from 0741-3335/38/12A/025/img1 over a cycle of solar activity throughout the winter period. The electron temperature has a maximum afternoon value as the solar activity is high in summer. In the periods of magnetic disturbances, a drop in 0741-3335/38/12A/025/img2 is most frequently observed. In winter, the influence of the sunrise and sunset at the magnetic conjugate point is also observed. An increase in electron temperature, a drop in electron density, and the displacement of the heated region along the magnetic field lines are clearly seen in the ionosphere irradiated by high-power, HF radiation. Longitudinal effects in the ionospheric behaviour were observed in simultaneous measurements in Kharkiv and Millstone Hill (USA).

  9. Ionospheric Effects of X-Ray Solar Bursts in the Brazilian Sector

    Science.gov (United States)

    Becker-Guedes, F.; Takahashi, H.; Costa, J. E.; Otsuka, Y.

    2011-12-01

    When the solar X-ray flux in the interplanetary medium reaches values above a certain threshold, some undesired effects affecting radio communications are expected. Basically, the magnitudes of these effects depend on the X-ray peak brightness and duration, which drive the intensity of the ionosphere response when the associated electromagnetic wave hit the sunlit side of the Earth atmosphere. An important aspect defining the severity of damages to HF radio communications and LF navigation signals in a certain area is the local time when each event takes place. In order to create more accurate warnings referred to possible radio signal loss or degradation in the Brazilian sector, we analyze TEC maps obtained by a GPS network, formed by dual-frequency receivers spread all over the country, to observe ionospheric local changes during several X-ray events in the 0.1-0.8 nm range measured by GOES satellite. Considering the duration, peak brightness, and local time of the events, the final purpose of this study is to understand and predict the degree of changes suffered by the ionosphere during these X-ray bursts. We intend using these results to create a radio blackout warning product to be offered by the Brazilian space weather program named EMBRACE (Estudo e Monitoramento BRAsileiro do Clima Espacial): Brazilian Monitoring and Study of Space Weather.

  10. Ionospheric Responses to Nonlinear Acoustic Waves Generated by Natural Hazard Events

    Science.gov (United States)

    Zettergren, M. D.; Snively, J. B.

    2015-12-01

    Ionospheric total electron content (TEC) fluctuations following large-magnitude earthquakes and resulting tsunamis, e.g. Tohoku in 2011, have been noted in many recent investigations [e.g., Galvan et al., Radio Science, 47(4), 2012]. Earthquakes impact the atmosphere through vertical displacements of the Earth's crust or ocean surfaces producing, as one effect, low-frequency acoustic waves. These waves can achieve significant amplitudes during propagation through the rarefied upper atmosphere, and are capable of driving sizable ionospheric electron density (TEC) fluctuations and electrical currents. Earthquake-generated acoustic waves are readily identifiable in GPS observations as 0.1-2 TECU, 3-5 mHz, oscillations, which are delayed from the quake occurrence by roughly the sound travel time between the ground and ionosphere. In some extreme cases, the onset of acoustic oscillations is concurrent with a persistent, sharp decrease in TEC (~5 TECU) above the epicenter [e.g., Kakinami et al., GRL, 39(13), 2012]. Ionospheric responses to large amplitude acoustic waves are investigated using a coupled atmosphere-ionosphere model [Zettergren and Snively, GRL, 40(20), 2013]. Of particular interest are effects of acoustic wave amplitude and nonlinearity on ionospheric responses, including production of detectable TEC oscillations and longer-lived responses like TEC depletions. The atmospheric dynamics model solves a Navier-Stokes' system of equations and incorporates generation of acoustic waves through acceleration source terms at ground-level. The ionospheric model solves a fluid system of equations for each of the major ionospheric species, and includes an electrostatic description of dynamo currents. The coupled model enables direct computation of observable quantities, such as vertical TEC and magnetic field fluctuations. Here we construct simulation case studies for realistic earthquake events and compare results against published TEC and magnetic field data. This

  11. Localized structure in the cusp and high-latitude ionosphere: a modelling study

    Directory of Open Access Journals (Sweden)

    H. F. Balmforth

    1999-04-01

    Full Text Available The ionospheric signature of a flux transfer event (FTE seen in EISCAT radar data has been used as the basis for a modelling study using a new numerical model of the high-latitude ionosphere developed at the University of Sheffield, UK. The evolution of structure in the high-latitude ionosphere is investigated and examined with respect to the current views of polar patch formation and development. A localized velocity enhancement, of the type associated with FTEs, is added to the plasma as it passes through the cusp. This is found to produce a region of greatly enhanced ion temperature. The new model can provide greater detail during this event as it includes anisotropic temperature calculations for the O+ ions. This illustrates the uneven partitioning of the energy during an event of this type. O+ ion temperatures are found to become increasingly anisotropic, with the perpendicular temperature being substantially larger than the parallel component during the velocity enhancement. The enhanced temperatures lead to an increase in the recombination rate, which results in an alteration of the ion concentrations. A region of decreased O+ and increased molecular ion concentration develops in the cusp. The electron temperature is less enhanced than the ions. As the new model has an upper boundary of 10 000 km the topside can also be studied in great detail. Large upward fluxes are seen to transport plasma to higher altitudes, contributing to the alteration of the ion densities. Plasma is stored in the topside ionosphere and released several hours after the FTE has finished as the flux tube convects across the polar cap. This mechanism illustrates how concentration patches can be created on the dayside and be maintained into the nightside polar cap.Key words. Ionosphere (ionosphere-magnetosphere interactions; polar ionosphere. Magnetospheric physics (magnetopause · cusp and boundary layers

  12. Localized fast flow disturbance observed in the plasma sheet and in the ionosphere

    Directory of Open Access Journals (Sweden)

    R. Nakamura

    2005-02-01

    Full Text Available An isolated plasma sheet flow burst took place at 22:02 UT, 1 September 2002, when the Cluster footpoint was located within the area covered by the Magnetometers-Ionospheric Radars-All-sky Cameras Large Experiment (MIRACLE. The event was associated with a clear but weak ionospheric disturbance and took place during a steady southward IMF interval, about 1h preceding a major substorm onset. Multipoint observations, both in space and from the ground, allow us to discuss the temporal and spatial scale of the disturbance both in the magnetosphere and ionosphere. Based on measurements from four Cluster spacecraft it is inferred that Cluster observed the dusk side part of a localized flow channel in the plasma sheet with a flow shear at the front, suggesting a field-aligned current out from the ionosphere. In the ionosphere the equivalent current pattern and possible field-aligned current location show a pattern similar to the auroral streamers previously obtained during an active period, except for its spatial scale and amplitude. It is inferred that the footpoint of Cluster was located in the region of an upward field-aligned current, consistent with the magnetospheric observations. The entire disturbance in the ionosphere lasted about 10min, consistent with the time scale of the current sheet disturbance in the magnetosphere. The plasma sheet bulk flow, on the other hand, had a time scale of about 2min, corresponding to the time scale of an equatorward excursion of the enhanced electrojet. These observations confirm that localized enhanced convection in the magnetosphere and associated changes in the current sheet structure produce a signature with consistent temporal and spatial scale at the conjugate ionosphere.

  13. Low and Midlatitude Ionospheric Plasma Density Irregularities and Their Effects on Geomagnetic Field

    Science.gov (United States)

    Yokoyama, Tatsuhiro; Stolle, Claudia

    2017-03-01

    Earth's magnetic field results from various internal and external sources. The electric currents in the ionosphere are major external sources of the magnetic field in the daytime. High-resolution magnetometers onboard low-Earth-orbit satellites such as CHAMP and Swarm can detect small-scale currents in the nighttime ionosphere, where plasma density gradients often become unstable and form irregular density structures. The magnetic field variations caused by the ionospheric irregularities are comparable to that of the lithospheric contribution. Two phenomena in the nighttime ionosphere that contribute to the magnetic field variation are presented: equatorial plasma bubble (EPB) and medium-scale traveling ionospheric disturbance (MSTID). EPB is formed by the generalized Rayleigh-Taylor instability over the dip equator and grows nonlinearly to as high as 2000 km apex altitude. It is characterized by deep plasma density depletions along magnetic flux tubes, where the diamagnetic effect produced by a pressure-gradient-driven current enhances the main field intensity. MSTID is a few hundred kilometer-scale disturbance in the midlatitude ionosphere generated by the coupled electrodynamics between the ionospheric E and F regions. The field-aligned currents associated with EPBs and MSTIDs also have significant signatures in the magnetic field perpendicular to the main field direction. The empirical discovery of the variations in the magnetic field due to plasma irregularities has motivated the inclusion of electrodynamics in the physical modeling of these irregularities. Through an effective comparison between the model results and observations, the physical process involved has been largely understood. The prediction of magnetic signatures due to plasma irregularities has been advanced by modeling studies, and will be helpful in interpreting magnetic field observations from satellites.

  14. Reduction in the ionospheric error for a single-frequency GPS timing solution using tomography

    Directory of Open Access Journals (Sweden)

    Cathryn N. Mitchell

    2009-06-01

    Full Text Available

    Abstract

    Single-frequency Global Positioning System (GPS receivers do not accurately compensate for the ionospheric delay imposed upon a GPS signal. They rely upon models to compensate for the ionosphere. This delay compensation can be improved by measuring it directly with a dual-frequency receiver, or by monitoring the ionosphere using real-time maps. This investigation uses a 4D tomographic algorithm, Multi Instrument Data Analysis System (MIDAS, to correct for the ionospheric delay and compares the results to existing single and dualfrequency techniques. Maps of the ionospheric electron density, across Europe, are produced by using data collected from a fixed network of dual-frequency GPS receivers. Single-frequency pseudorange observations are corrected by using the maps to find the excess propagation delay on the GPS L1 signals. Days during the solar maximum year 2002 and the October 2003 storm have been chosen to display results when the ionospheric delays are large and variable. Results that improve upon the use of existing ionospheric models are achieved by applying MIDAS to fixed and mobile single-frequency GPS timing solutions. The approach offers the potential for corrections to be broadcast over a local region, or provided via the internet and allows timing accuracies to within 10 ns to be achieved.



  15. 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.

  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. An inter-hemispheric, statistical study of nightside spectral width distributions from coherent HF scatter radars

    Directory of Open Access Journals (Sweden)

    E. E. Woodfield

    2002-12-01

    Full Text Available A statistical investigation of the Doppler spectral width parameter routinely observed by HF coherent radars has been conducted between the Northern and Southern Hemispheres for the nightside ionosphere. Data from the SuperDARN radars at Thykkvibær, Iceland and Syowa East, Antarctica have been employed for this purpose. Both radars frequently observe regions of high (>200 ms-1 spectral width polewards of low (<200 ms-1 spectral width. Three years of data from both radars have been analysed both for the spectral width and line of sight velocity. The pointing direction of these two radars is such that the flow reversal boundary may be estimated from the velocity data, and therefore, we have an estimate of the open/closed field line boundary location for comparison with the high spectral widths. Five key observations regarding the behaviour of the spectral width on the nightside have been made. These are (i the two radars observe similar characteristics on a statistical basis; (ii a latitudinal dependence related to magnetic local time is found in both hemispheres; (iii a seasonal dependence of the spectral width is observed by both radars, which shows a marked absence of latitudinal dependence during the summer months; (iv in general, the Syowa East spectral width tends to be larger than that from Iceland East, and (v the highest spectral widths seem to appear on both open and closed field lines. Points (i and (ii indicate that the cause of high spectral width is magnetospheric in origin. Point (iii suggests that either the propagation of the HF radio waves to regions of high spectral width or the generating mechanism(s for high spectral width is affected by solar illumination or other seasonal effects. Point (iv suggests that the radar beams from each of the radars are subject either to different instrumental or propagation effects, or different geophysical conditions due to their locations, although we suggest that this result is more likely to

  18. The Jindalee ionospheric sounding system

    Science.gov (United States)

    Earl, G. F.

    The objectives, geometry, and principles of the Jindalee FMCW ionospheric sounding system are described. The system is intended to collect sounding data (backscatter, oblique, vertical incidence) for a synoptic study of propagation conditions; data collection is to operate unattended 24 hours a day; all data are to be calibrated in absolute units; there are to be on-line displays and automated interpretation for real-time frequency management; and data are to be tape-recorded for off-line statistical analysis. The system provides the main radar with real-time propagating advice for the selection of optimum operating frequencies and acquires a synoptic data base for the off-line analysis of propagation conditions. Facilities of the system are located at Mt Everard (20 km northwest of Alice Springs), at Harts Range (100 km northeast of Alice Springs), and at Darwin. Ionograms and ionogram plots after computer cleanup are given.

  19. CDDIS_GNSS_products_ionosphere_rapid

    Data.gov (United States)

    National Aeronautics and Space Administration — Ionosphere Total Electron Content (TEC) grids derived from analysis of Global Navigation Satellite System (GNSS) data. These products are the generated by analysis...

  20. Intense Harmonic Emissions Observed in Saturn's Ionosphere

    Science.gov (United States)

    Sulaiman, A. H.; Kurth, W. S.; Persoon, A. M.; Menietti, J. D.; Farrell, W. M.; Ye, S.-Y.; Hospodarsky, G. B.; Gurnett, D. A.; Hadid, L. Z.

    2017-12-01

    The Cassini spacecraft's first Grand Finale orbit was carried out in April 2017. This set of 22 orbits had an inclination of 63° with a periapsis grazing Saturn's ionosphere, thus providing unprecedented coverage and proximity to the planet. Cassini's Radio and Plasma Wave Science instrument repeatedly detected intense electrostatic waves and their harmonics near closest approach in the dayside equatorial topside ionosphere. The fundamental modes were found to both scale and trend best with the H+ plasma or lower hybrid frequencies, depending on the plasma composition considered. The fine-structured harmonics are unlike previous observations, which scale with cyclotron frequencies. We explore their generation mechanism and show strong evidence of their association with whistler mode waves, consistent with theory. The possibility of Cassini's presence in the ionosphere influencing the resonance and harmonics is discussed. Given their link to the lower hybrid frequency, these emissions may offer clues to constraining Saturn's ionospheric properties.

  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...... and Yeh [1966] have examined the excitation of low-frequency imcompressible waves in an inhomogeneous ionosphere. They find that, below the F-region maximum, there may exist instabilities, the growth rate being given approximately by grho'/rhonu, where g is the gravity, rho is the plasma density, rho......' is its height gradients, and nu is the ion-neutral collision frequency. We have examined the stability of the ionosphere against growth of low-frequency quasielectrostatic waves, taking into account the compressibility of the plasma....

  2. MAVEN Observations of Ionospheric Irregularities at Mars

    Science.gov (United States)

    Fowler, C. M.; Andersson, L.; Shaver, S. R.; Thayer, J. P.; Huba, J. D.; Lillis, R.; Usanova, M. E.; Espley, J.; Ergun, R. E.; Mcfadden, J.; Mahaffy, P. R.; Connerney, J. E. P.; Benna, M.; Elrod, M.; Mitchell, D. L.; Mazelle, C.; Jakosky, B. M.

    2017-11-01

    Ionospheric irregularities associated with horizontal magnetic fields below 200 km altitude are observed at Mars. Plasma density modulations of up to 200% are observed during such events and appear correlated with fluctuations in the magnetic field. The observed fluctuations are likely Doppler shifted and represent spatial structures at length scales of 15-20 km or less. Conditions in the Martian ionosphere below 200 km are synonymous with the terrestrial E region, where ionospheric irregularities have been extensively studied. Interestingly, the irregularities at Mars appear to be electromagnetic in nature, in contrast to the electrostatic nature of irregularities at Earth. It is currently unclear what the primary drivers of these irregularities at Mars are, and further study is needed to explain these important phenomenon within the Martian ionosphere.

  3. CDDIS_GNSS_products_ionosphere_predicted

    Data.gov (United States)

    National Aeronautics and Space Administration — Ionosphere Total Electron Content (TEC) grids derived from analysis of Global Navigation Satellite System (GNSS) data. These products are the generated by analysis...

  4. 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.

  5. 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...

  6. 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.

  7. 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

  8. Conduction Mechanism and Improved Endurance in HfO2-Based RRAM with Nitridation Treatment

    Science.gov (United States)

    Yuan, Fang-Yuan; Deng, Ning; Shih, Chih-Cheng; Tseng, Yi-Ting; Chang, Ting-Chang; Chang, Kuan-Chang; Wang, Ming-Hui; Chen, Wen-Chung; Zheng, Hao-Xuan; Wu, Huaqiang; Qian, He; Sze, Simon M.

    2017-10-01

    A nitridation treatment technology with a urea/ammonia complex nitrogen source improved resistive switching property in HfO2-based resistive random access memory (RRAM). The nitridation treatment produced a high performance and reliable device which results in superior endurance (more than 109 cycles) and a self-compliance effect. Thus, the current conduction mechanism changed due to defect passivation by nitrogen atoms in the HfO2 thin film. At a high resistance state (HRS), it transferred to Schottky emission from Poole-Frenkel in HfO2-based RRAM. At low resistance state (LRS), the current conduction mechanism was space charge limited current (SCLC) after the nitridation treatment, which suggests that the nitrogen atoms form Hf-N-Ox vacancy clusters (Vo +) which limit electron movement through the switching layer.

  9. Ionospheric Modeling for Precise GNSS Applications

    OpenAIRE

    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 the high temporal resolution GNSS network data into the spatial domain. This objective led to the development of a recursive physics-based model for the regular TEC variations and an algorithm for r...

  10. Experiments on the Ionospheric Models in GNSS

    OpenAIRE

    Vinh, La The; Quang, Phuong Xuan; García Rigo, Alberto; Rovira Garcia, Adrià; Ibáñez Segura, Deimos

    2013-01-01

    In GNSS, one of the main error sources of the Standard Positioning Service (SPS) is introduced by the ionosphere. Although this error can be cancelled by combining two signals at different frequencies, most of the single - frequency mass - market receivers do not benefit from this cancel l ation. For that reason, a set of parameter s is included in the navigation message in order to compute the ionospheric delay of any observation by the Klobuchar mod...

  11. Holes: Ionospheric Scintillation, GPS and Imputation

    Science.gov (United States)

    2007-03-01

    by Klobuchar [Parkinson et al., 1996]. 2.3.2 Definition, Characteristics and Models. The situation for scintillation, sadly, is not so simple.Groves...and J. A. Klobuchar (2003), Ionospheric scintillation effects on single and dual frequency gps positioning, in Proceedings of ION GPS/GNSS 2003... Klobuchar (1996), Commercial ionospheric scintillation monitoring receiver development and test results, in Proceedings of the 52nd Annual Meeting of the

  12. Ionospheric shock waves triggered by rockets

    Directory of Open Access Journals (Sweden)

    C. H. Lin

    2014-09-01

    Full Text Available This paper presents a two-dimensional structure of the shock wave signatures in ionospheric electron density resulting from a rocket transit using the rate of change of the total electron content (TEC derived from ground-based GPS receivers around Japan and Taiwan for the first time. From the TEC maps constructed for the 2009 North Korea (NK Taepodong-2 and 2013 South Korea (SK Korea Space Launch Vehicle-II (KSLV-II rocket launches, features of the V-shaped shock wave fronts in TEC perturbations are prominently seen. These fronts, with periods of 100–600 s, produced by the propulsive blasts of the rockets appear immediately and then propagate perpendicularly outward from the rocket trajectory with supersonic velocities between 800–1200 m s−1 for both events. Additionally, clear rocket exhaust depletions of TECs are seen along the trajectory and are deflected by the background thermospheric neutral wind. Twenty minutes after the rocket transits, delayed electron density perturbation waves propagating along the bow wave direction appear with phase velocities of 800–1200 m s−1. According to their propagation character, these delayed waves may be generated by rocket exhaust plumes at earlier rocket locations at lower altitudes.

  13. Robust GPS carrier tracking under ionospheric scintillation

    Science.gov (United States)

    Susi, M.; Andreotti, M.; Aquino, M. H.; Dodson, A.

    2013-12-01

    Small scale irregularities present in the ionosphere can induce fast and unpredictable fluctuations of Radio Frequency (RF) signal phase and amplitude. This phenomenon, known as scintillation, can degrade the performance of a GPS receiver leading to cycle slips, increasing the tracking error and also producing a complete loss of lock. In the most severe scenarios, if the tracking of multiple satellites links is prevented, outages in the GPS service can also occur. In order to render a GPS receiver more robust under scintillation, particular attention should be dedicated to the design of the carrier tracking stage, that is the receiver's part most sensitive to these types of phenomenon. This paper exploits the reconfigurability and flexibility of a GPS software receiver to develop a tracking algorithm that is more robust under ionospheric scintillation. For this purpose, first of all, the scintillation level is monitored in real time. Indeed the carrier phase and the post correlation terms obtained by the PLL (Phase Locked Loop) are used to estimate phi60 and S4 [1], the scintillation indices traditionally used to quantify the level of phase and amplitude scintillations, as well as p and T, the spectral parameters of the fluctuations PSD. The effectiveness of the scintillation parameter computation is confirmed by comparing the values obtained by the software receiver and the ones provided by a commercial scintillation monitoring, i.e. the Septentrio PolarxS receiver [2]. Then the above scintillation parameters and the signal carrier to noise density are exploited to tune the carrier tracking algorithm. In case of very weak signals the FLL (Frequency Locked Loop) scheme is selected in order to maintain the signal lock. Otherwise an adaptive bandwidth Phase Locked Loop (PLL) scheme is adopted. The optimum bandwidth for the specific scintillation scenario is evaluated in real time by exploiting the Conker formula [1] for the tracking jitter estimation. The performance

  14. Compact Reconfigurable HF-UHF Antennas

    National Research Council Canada - National Science Library

    Sarabandi, Kamal

    2004-01-01

    The development of a compact reconfigurable HF-UHF antenna is of great practical importance in mobile military communications where low visibility and high mobility are required Variations of monopole...

  15. LIFDAR: A Diagnostic Tool for the Ionosphere

    Science.gov (United States)

    Kia, O. E.; Rodgers, C. T.; Batholomew, J. L.

    2011-12-01

    ITT Corporation proposes a novel system to measure and monitor the ion species within the Earth's ionosphere called Laser Induced Fluorescence Detection and Ranging (LIFDAR). Unlike current ionosphere measurements that detect electrons and magnetic field, LIFDAR remotely measures the major contributing ion species to the electron plasma. The LIFDAR dataset has the added capability to demonstrate stratification and classification of the layers of the ionosphere to ultimately give a true tomographic view. We propose a proof of concept study using existing atmospheric LIDAR sensors combined with a mountaintop observatory for a single ion species that is prevalent in all layers of the atmosphere. We envision the LIFDAR concept will enable verification, validation, and exploration of the physics of the magneto-hydrodynamic models used in ionosphere forecasting community. The LIFDAR dataset will provide the necessary ion and electron density data for the system wide data gap. To begin a proof of concept, we present the science justification of the LIFDAR system based on the model photon budget. This analysis is based on the fluorescence of ionized oxygen within the ionosphere versus altitude. We use existing model abundance data of the ionosphere during normal and perturbed states. We propagate the photon uncertainties from the laser source through the atmosphere to the plasma and back to the collecting optics and detector. We calculate the expected photon budget to determine signal to noise estimates based on the targeted altitude and detection efficiency. Finally, we use these results to derive a LIFDAR observation strategy compatible with operational parameters.

  16. Brief review of the ionospheric delay models

    Science.gov (United States)

    Zhang, Hong-Ping; Ping, Jin-Song; Zhu, Wen-Yao; Huang, Cheng

    2006-03-01

    Usually, the ionospheric delay models can be sorted as three types - the forecast model, the real-time model and the post-processing model. Different purpose for the application of these models is required to choose one that can be used to correct the ionospheric delay efficiently. Here we compare several ionosphere delay models often used, such as the functional model used for Wide Area Augmentation System (WAAS) - trigonometric series function, polynomial model, and low degree spheric harmonics function. The three models are roughly equivalent to each other in the ionosphere delay correcting for WAAS. The TEC harmonic expansion trend function can be used to analyze the long-trend variations of the ionosphere. The International Ionosphere Reference (IRI) model, as an empirical one, can reach 60 percent of the correcting effect. The Klobuchar model as the GPS broadcast model can also achieve same effect although there are some shortcomings in the parameters setting. This model will be discussed here and some improving methods are presented.

  17. Application of GPS Measurements for Ionospheric and Tropospheric Modelling

    Science.gov (United States)

    Rajendra Prasad, P.; Abdu, M. A.; Furlan, Benedito. M. P.; Koiti Kuga, Hélio

    military navigation. The DOD's primary purposes were to use the system in precision weapon delivery and providing a capability that would help reverse the proliferation of navigation systems in military. Subsequently, it was very quickly realized that civil use and scientific utility would far outstrip military use. A variety of scientific applications are uniquely suited to precise positioning capabilities. The relatively high precision, low cost, mobility and convenience of GPS receivers make positioning attractive. The other applications being precise time measurement, surveying and geodesy purposes apart from orbit and attitude determination along with many user services. The system operates by transmitting radio waves from satellites to receivers on the ground, aircraft, or other satellites. These signals are used to calculate location very accurately. Standard Positioning Services (SPS) which restricts access to Coarse/Access (C/A) code and carrier signals on the L1 frequency only. The accuracy thus provided by SPS fall short of most of the accuracy requirements of users. The upper atmosphere is ionized by the ultra violet radiation from the sun. The significant errors in positioning can result when the signals are refracted and slowed by ionospheric conditions, the parameter of the ionosphere that produces most effects on GPS signals is the total number of electrons in the ionospheric propagation path. This integrated number of electrons, called Total Electron Content (TEC) varies, not only from day to night, time of the year and solar flux cycle, but also with geomagnetic latitude and longitude. Being plasma the ionosphere affects the radio waves propagating through it. Effects of scintillation on GPS satellite navigation systems operating at L1 (1.5754 GHz), L2 (1.2276 GHz) frequencies have not been estimated accurately. It is generally recognized that GPS navigation systems are vulnerable in the polar and especially in the equatorial region during the

  18. Spatial irregularities in Jupiter's upper ionosphere observed by Voyager radio occultations

    Science.gov (United States)

    Hinson, D. P.; Tyler, G. L.

    1982-01-01

    Radio scintillations (at 3.6 and 13 cm) produced by scattering from ionospheric irregularities during the Voyager occultations are interpreted using a weak-scattering theory. Least squares solutions for ionospheric parameters derived from the observed fluctuation spectra yield estimates of (1) the axial ratio, (2) angular orientation of the anisotropic irregularities, (3) the power law exponent of the spatial spectrum of irregularities, and (4) the magnitude of the spatial variations in electron density. It is shown that the measured angular orientation of the anisotropic irregularities indicates magnetic field direction and may provide a basis for refining Jovian magnetic field models.

  19. Anomalous electron density events in the quiet summer ionosphere at solar minimum over Millstone Hill

    Directory of Open Access Journals (Sweden)

    A. V. Pavlo

    1998-04-01

    Full Text Available This study compares the observed behavior of the F region ionosphere over Millstone Hill with calculations from the IZMIRAN model for solar minimum for the geomagnetically quiet period 23-25 June 1986, when anomalously low values of hmF2(<200 km were observed. We found that these low values of hmF2 (seen as a G condition on ionograms exist in the ionosphere due to a decrease of production rates of oxygen ions resulting from low values of atomic oxygen density. Results show that determination of a G condition using incoherent scatter radar data is sensitive both to the true concentration of O+ relative to the molecular ions, and to the ion composition model assumed in the data reduction process. The increase in the O++ N 2 loss rate due to vibrationally excited N2 produces a reduction in NmF2 of typically 5-10% , but as large as 15% , bringing the model and data into better agreement. The effect of vibrationally excited NO+ ions on electron densities is negligible.Key words. Ionosphere (Ion chemistry and composition; Ionosphere-atmosphere interactions; Mid-latitude ionosphere.

  20. On the feasibility of detecting the ionospheric effects of solar energetic particle events at Mars using spacecraft‐spacecraft radio links

    National Research Council Canada - National Science Library

    Withers, Paul

    2016-01-01

    ...) events on the ionosphere of Mars are substantial, but observations have not yet provided quantitative information on the magnitude or vertical distribution of the plasma produced below 100 km by SEP events...

  1. The role of phosphates for the Lu-Hf chronology of meteorites

    Science.gov (United States)

    Debaille, Vinciane; Van Orman, James; Yin, Qing-Zhu; Amelin, Yuri

    2017-09-01

    diffusion processes in phosphate can produce an apparently older Lu-Hf isochron, while this effect will remain negligible in perturbing the Sm-Nd chronology. Our results suggest that only type 3 chondrites with the lowest metamorphic grade and large minerals with minimal diffusive effects are suitable for determination of the Lu-Hf CHUR values and the Lu decay constant respectively.

  2. Overview of Solar Wind-Magnetosphere-Ionosphere-Atmosphere Coupling and the Generation of Magnetospheric Currents

    Science.gov (United States)

    Milan, S. E.; Clausen, L. B. N.; Coxon, J. C.; Carter, J. A.; Walach, M.-T.; Laundal, K.; Østgaard, N.; Tenfjord, P.; Reistad, J.; Snekvik, K.; Korth, H.; Anderson, B. J.

    2017-03-01

    We review the morphology and dynamics of the electrical current systems of the terrestrial magnetosphere and ionosphere. Observations from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) over the three years 2010 to 2012 are employed to illustrate the variability of the field-aligned currents that couple the magnetosphere and ionosphere, on timescales from minutes to years, in response to the impact of solar wind disturbances on the magnetosphere and changes in the level of solar illumination of the polar ionospheres. The variability is discussed within the context of the occurrence of magnetic reconnection between the solar wind and terrestrial magnetic fields at the magnetopause, the transport of magnetic flux within the magnetosphere, and the onset of magnetic reconnection in the magnetotail. The conditions under which the currents are expected to be weak, and hence minimally contaminate measurements of the internally-produced magnetic field of the Earth, are briefly outlined.

  3. ionospheric effects on ionospheric effects on gps signal in low gps

    African Journals Online (AJOL)

    eobe

    position at all different weather around the world [7]–. [9]. Using the GPS dual frequencies receiver system to eliminate ionospheric delays provides a useful tool for .... forecast for the occurrence of 1 - 2 GHz frequency scintillations in the equatorial and low latitude F region using the GPS TEC data [36, 37]. The ionospheric ...

  4. 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.

  5. Southern European ionospheric TEC maps based on Kriging technique to monitor ionosphere behavior

    Science.gov (United States)

    Rodríguez-Bouza, Marta; Paparini, Claudia; Otero, Xurxo; Herraiz, Miguel; Radicella, Sandro M.; Abe, Oladipo E.; Rodríguez-Caderot, Gracia

    2017-10-01

    Global or regional Maps of the ionospheric Total Electron Content (TEC) are an efficient tool to monitor the delay introduced by the ionosphere in the satellite signals. Ionospheric disturbance periods are of particular interest because these conditions can strongly affect satellite navigation range measurements. This work presents post-processing regional vertical TEC maps over Southern Europe ([35°N-50°N] latitude) obtained by applying Kriging interpolation to GPS derived TEC over more than 100 Global Navigation Satellite System (GNSS) stations. These maps are used to study the behavior of the ionosphere during space weather events and their effects. To validate these maps, hereafter called Southern European Ionospheric Maps (SEIMs), their TEC values have been compared with those obtained from EGNOS Message Server (EMS) and with direct experimental TEC data from GNSS stations. Ionospheric space weather events related to geomagnetic storms of March 17th, 2013, February 19th, 2014 and March 17th, 2015 have been selected. To test the methodology, one period of quiet days has been also analyzed. TEC values obtained by SEIMs in the Ionospheric Grid Points (IGPs) defined by EGNOS are very close to those given by EMS and in the period of major geomagnetic storms the difference does not exceed 6 TEC units. These results confirm the good performance of the technique used for obtaining the SEIMs that can be a useful tool to study the ionosphere behavior during geomagnetic storms and their effects in the region of interest.

  6. HF Radio Communication Systems Design Assessment

    Science.gov (United States)

    1980-09-30

    979," Rockwell -WSEA. [37] C. H. Cerva , Notes, "Meeting 17 December 1979, Ft. Huachuca, Arizona,’: Rockwell -WSEA. [38] J. E. Ambrose, Notes, "Fort...34Ionospheric Sounding," February 13, 1980. £53) C. H. Cerva , Memorandum, "Visit to NC-I Navy MARS Station W4USN, NONMC," Rockwell-WSEA, 23 January 1980

  7. "SWING": A European project for a new application of an ionospheric network

    Science.gov (United States)

    Zolesi, B.; Bianchi, C.; Meloni, A.; Baskaradas, J. A.; Belehaki, A.; Altadill, D.; Dalle Mese, E.

    2016-05-01

    The SWING (Short Wave critical Infrastructure Network based on a new Generation high survival radio communication system) is a European project aimed at studying a high survival high-frequency (HF) radio network to link European Critical Infrastructures (ECIs). This system is thought to replace broadband internet communication, maintaining the minimum flux of essential information for the ECIs management and control, in case of wide-scale threats, including terrorist attacks, able to put out of order internet links over the Mediterranean region. SWING is designed to evaluate the threat and increase the security awareness, as well as the level of protection, of analogous and/or interdependent ECIs. In order to meet these goals, SWING was finalized to recognize how and when the internet communication fails and to develop the standard software and hardware tools necessary for implementing communication protocols suited for a reliable and interoperable short-wave (SW) or high-frequency (HF) radio network backup. The internet broadband description and internet failure recognition were taken into consideration in the project but are not treated in this paper. It has been assessed that in case of complete failure of the internet broadband communication fundamental information for the management and control of ECIs over the Mediterranean region can be maintained with a HF network, even in case of moderate ionospheric perturbations.

  8. Recent Advances in Ionospheric Modeling for Mars Exploration using Ground Penetrating Radars

    Science.gov (United States)

    Restano, Marco; Picardi, Giovanni; Seu, Roberto

    2013-04-01

    -FDTD code is enough to model both plasma and collision frequencies. Using the simulator some recently proposed Martian multi-peak electron density profiles similar to Chapman's one have been synthetized. The Chapman model is then used during matched filtering, as on MARSIS/SHARAD data, to compensate the distortions introduced by the ionosphere underlining the eventual presence of uncompensated residuals quantified in terms of S/N loss, SLL degradation and pulse shape distortion. Such work will be highly useful to produce new ionosphere compensation schemes providing more reliable data to be employed in the data inversion procedure.

  9. D region HF radar echoes associated with energetic particle precipitation and pulsating aurora

    Directory of Open Access Journals (Sweden)

    S. E. Milan

    2008-07-01

    Full Text Available Milan et al. (2001 identified a class of narrow, slow-moving HF radar backscatter echoes which originate between altitudes of 80 and 100 km, the ionospheric D- and lower E-regions. These echoes appeared to be associated with the occurrence of pulsating aurora, which are known to be created by energetic electrons capable of penetrating to D region altitudes. In this study we show that these echoes are observed in tandem with enhancements in cosmic noise absorption (auroral absorption, additional evidence that energetic (>30 keV particle precipitation is responsible for generating the irregularities from which a radar can scatter. In addition, we show that the D region backscatter echoes occur predominantly in the post-midnight sector during substorm recovery phase, in common with auroral absorption events and pulsating aurora.

  10. Latitudinal variation of ionospheric slab thickness

    Science.gov (United States)

    Gulyaeva, T. L.; Jayachandran, B.; Krishnankutty, T. N.

    The ionospheric slab thickness τ, defined as a ratio of the total electron content (TEC) to the F-region peak electron density NmF2, is a first order measure of the shape of the electron density profile. In the present study, we use GPS-derived TEC and vertical electron content estimates ITEC from ground-based ionosonde observations together with the corresponding foF2 (F2 layer critical frequency) and hmF2 (F2 layer peak height) at 14 world-wide stations lying at different latitude regions from the geomagnetic equator to north pole. The period of study is during 2001-2002, which is close to the solar maximum phase of the 23rd solar cycle. Hourly values of TEC, ITEC, foF2, hmF2 and τ during the period of study are used to compare τ values from the observation and model predictions using the International Reference Ionosphere extended towards the plasmapause with the plasmasphere option of the Russian standard model of the ionosphere, IRI*. For the three latitudinal zones (high, mid and low latitudes) the IRI* predictions of τ are compared with observed τ values for the bottomside ionosphere (below hmF2), topside ionosphere (between hmF2 and 1000 km), plasmasphere (from 1000 to 20,000 km), and the total height range through the ionosphere and plasmasphere. Significant overestimation of τ has been revealed when using IRI*, particularly for the topside ionosphere at high latitudes. Relation of the topside part of slab thickness with the topside half peak density height above the F2 layer peak provides new characteristic parameter for modeling of the topside shape of electron density profile.

  11. Can Ionospheric Sounding Help Oceanic Monitoring ?

    Science.gov (United States)

    Occhipinti, G.; Lognonne, P.

    2009-05-01

    A series of ionospheric anomalies following the Sumatra tsunami has been reported in the scientific literature (e.g., Liu et al. 2006; DasGupta et al. 2006; Occhipinti et al. 2006). Similar anomalies were also observed after the tsunamigenic earthquake in Peru in 2001 (Artru et al., 2005). All these anomalies show the signature in the ionosphere of tsunami-generated internal gravity waves (IGW) propagating in the neutral atmosphere over oceanic regions. The strong amplification mechanism of atmospheric IGW allows to detect these anomalies when the tsunami is offshore where the see level displacement is still small. In addition, the dense coverage of ionospheric sounding instruments over the oceans increases over time and more instruments will be able to provide ionospheric measurements: i.d., Doppler sounding, over-the-horizon radar (OTH) and space-based GPS data (e.g., COSMIC). Most of the ionospheric anomalies are also deterministic and reproducible by numerical modeling (Occhipinti et al., 2006, 2008) via the ocean/neutral atmosphere/ionosphere coupling mechanism. In addition, the numerical modeling supplies useful helps in the estimation of expected anomalies The sensitivity of altimeters, OTH radar, ground-based and space-based GPS measurements is analyzed in this work by the way of the modeling and data. The results are used to discuss the role of ionospheric sounding in the future oceanic monitoring and tsunami warning system. [Artru et al., 2005] Geophys. J. Int., 160, 2005 [DasGupta et al., 2006] Earth Planet. Space, 35, 929-959. [Liu et al., 2006] J. Geophys. Res., 111, A05303. [Occhipinti et al., 2006] Geophys. Res. Lett., 33, L20104, 2006 [Occhipinti et al., 2008] Geophys. J. Int., 173, 3, 753-1135, 2008.

  12. The Effects of Thunderstorm Static and Quasi-Static Electric Fields on the Lower Ionosphere

    Science.gov (United States)

    Salem, Mohammad Ahmad

    Thunderstorms and their lightning discharges are of great interest to many areas of geophysics and atmospheric electricity. A thunderstorm is an electric generator; it can produce both electrostatic and quasi-electrostatic fields in the overhead atmospheric D region. The D region is the lower part of the ionosphere that extends from about 40-90 km altitude where the electrons and ions are sufficient enough to affect the propagation of radio waves. In contrast to the electrostatic field, the quasi-electrostatic fields can be much stronger in magnitude, but shorter in duration, and can trigger halos. A halo is one type of the transient luminous events (TLEs) and typically appears within 1-2 ms after an intense cloud to ground lightning discharge. It looks like a relatively homogeneous glow in the shape of a pancake that is centered around 75-80 km altitude with a horizontal extent of tens of kilometers and vertical thickness of several kilometers. The goals of this dissertation research are to investigate the electrical effects of thunderstorm electrostatic and quasi-electrostatic fields on the nighttime lower ionosphere, and their covert relation to the formation of atmospheric halos. This work entails numerical and theoretical modeling analyses, and comparison of current theory and simulation results with the actual observations. For the first part of this study we have demonstrated that, under steady state conditions, electrostatic fields of waves are 5 and 2 km, respectively. In the second part of this dissertation, a one-dimensional plasma discharge fluid model is developed to study the response of the nighttime lower ionosphere to the quasi-electrostatic field produced by cloud-to-ground lightning flashes. When the quasi-electrostatic field reaches and exceeds about E k, a halo can be triggered in the lower ionosphere. The modeling results indicate that the ionospheric perturbation is determined by the ambient ionospheric density profile, the charge. moment

  13. Morning sector drift-bounce resonance driven ULF waves observed in artificially-induced HF radar backscatter

    Directory of Open Access Journals (Sweden)

    L. J. Baddeley

    2002-09-01

    Full Text Available HF radar backscatter, which has been artificially-induced by a high power RF facility such as the EISCAT heater at Tromsø, has provided coherent radar ionospheric electric field data of unprecedented temporal resolution and accuracy. Here such data are used to investigate ULF wave processes observed by both the CUTLASS HF radars and the EISCAT UHF radar. Data from the SP-UK-OUCH experiment have revealed small-scale (high azimuthal wave number, m -45 waves, predominantly in the morning sector, thought to be brought about by the drift-bounce resonance processes. Conjugate observations from the Polar CAM-MICE instrument indicate the presence of a non-Maxwellian ion distribution function. Further statistical analysis has been undertaken, using the Polar TIMAS instrument, to reveal the prevalence and magnitude of the non-Maxwellian energetic particle populations thought to be responsible for generating these wave types.Key words. Ionosphere (active experiments; wave-particle interactions Magnetospheric physics (MHD waves and instabilities

  14. Morning sector drift-bounce resonance driven ULF waves observed in artificially-induced HF radar backscatter

    Directory of Open Access Journals (Sweden)

    L. J. Baddeley

    Full Text Available HF radar backscatter, which has been artificially-induced by a high power RF facility such as the EISCAT heater at Tromsø, has provided coherent radar ionospheric electric field data of unprecedented temporal resolution and accuracy. Here such data are used to investigate ULF wave processes observed by both the CUTLASS HF radars and the EISCAT UHF radar. Data from the SP-UK-OUCH experiment have revealed small-scale (high azimuthal wave number, m -45 waves, predominantly in the morning sector, thought to be brought about by the drift-bounce resonance processes. Conjugate observations from the Polar CAM-MICE instrument indicate the presence of a non-Maxwellian ion distribution function. Further statistical analysis has been undertaken, using the Polar TIMAS instrument, to reveal the prevalence and magnitude of the non-Maxwellian energetic particle populations thought to be responsible for generating these wave types.

    Key words. Ionosphere (active experiments; wave-particle interactions Magnetospheric physics (MHD waves and instabilities

  15. 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

  16. Epitaxial growth of HfS2 on sapphire by chemical vapor deposition and application for photodetectors

    Science.gov (United States)

    Wang, Denggui; Zhang, Xingwang; Liu, Heng; Meng, Junhua; Xia, Jing; Yin, Zhigang; Wang, Ye; You, Jingbi; Meng, Xiang-Min

    2017-09-01

    Group IVB transition metal (Zr and Hf) dichalcogenides (TMDs) have been attracting intensive attention as promising candidates in the modern electronic and/or optoelectronic fields. However, the controllable growth of HfS2 monolayers or few layers still remains a great challenge, thus hindering their further applications so far. Here, for the first time we demonstrate the epitaxial growth of high-quality HfS2 with a controlled number of layers on c-plane sapphire substrates by chemical vapor deposition (CVD). The HfS2 layers exhibit an atomically sharp interface with the sapphire substrate, followed by flat, 2D layers with octahedral coordination. The epitaxial relationship between HfS2 and substrate was determined by x-ray diffraction and transmission electron microscopy measurements to be: HfS2 (0 0 0 1) [10-10]||sapphire (0 0 0 1)[1-100]. Moreover, a high-performance photodetector with a high on/off ratio of more than 103 and an ultrafast response rate of 130 µs for the rise and 155 µs for the decay times were fabricated based on the CVD-grown HfS2 layers on sapphire substrates. This simple and controllable approach opens up a new way to produce highly crystalline HfS2 atomic layers, which are promising materials for nanoelectronics.

  17. Lightning in the Ionosphere with C/NOFS

    Science.gov (United States)

    2012-08-25

    loca lightning, electric field, ionosphere , ionospheric plasma, plasma irregularities U U U U Prof. Robert H. Holzworth 206 685 7410 Reset INSTRUCTIONS... ionospheric plasma density irregularities and the occurrence of optical lightning activity; and the observation that lightning electric fields were often the...Geophysical Union, Fall Meeting 2011, abstract #AE21A-0239 On the Relationship between Lightning and Equatorial Ionosphere Density Irregularities , McCarthy

  18. Ionospheric TEC observations from TOPEX satellite

    Energy Technology Data Exchange (ETDEWEB)

    Vladimer, J.A.; Ewell, V.R.; Lee, M.C. [Boston Univ., MA (United States). Electrical, Computer, and Systems Engineering Dept.; Doherty, P.H. [Boston Coll., Newton, MA (United States). Inst. for Science Research; Decker, D.T.; Anderson, D.N.; Klobuchar, J.A. [Phillips Lab., Hanscom AFB, MA (United States). Ionospheric Effects Branch

    1996-12-31

    Variability of Total Electron Content (TEC) in the equatorial anomaly region of the ionosphere can be studied extensively using the results of measurements taken by the NASA/CNES satellite, TOPEX/Poseidon. The NASA radar altimeter (NRA) is the first space-borne dual-frequency altimeter capable of accurately measuring vertical ionospheric TEC below 1,340 km. TOPEX TEC observations have already been used to support results from an ionospheric measurement campaign that was conducted in equatorial anomaly regions of South America by Phillips Laboratory in Spring, 1994. The best agreement in TEC values is seen during intervals of longitudinal proximity of the satellites` paths. The TOPEX over-ocean data can be used as a supplement to land based measurements in applications to ionospheric research at low and middle latitudes. This study focuses on comparisons between TOPEX vertical TEC data and GPS equivalent vertical TEC measurements taken near the East and West coastal regions of South America. Also the Phillips Laboratory Global Parameterized Ionospheric Model (PIM) is utilized in an effort to estimate slant to vertical conversion errors.

  19. Comparison of global and regional ionospheric models

    Science.gov (United States)

    Ranner, H.-P.; Krauss, S.; Stangl, G.

    2012-04-01

    Modelling of the Earth's ionosphere means the description of the variability of the vertical TEC (Total Electron Content) in dependence of geographic latitude and longitude, height, diurnal and seasonal variation as well as solar activity. Within the project GIOMO (next Generation near real-time IOnospheric MOdels) the objectives are the identification and consolidation of improved ionospheric modelling technologies. The global models Klobuchar (GPS) and NeQuick (currently in use by EGNOS, in future used by Galileo) are compared to the IGS (International GNSS Service) Final GIM (Global Ionospheric Map). Additionally a RIM (Regional Ionospheric Map) for Europe provided by CODE (Center for Orbit Determination in Europe) is investigated. Furthermore the OLG (Observatorium Lustbühel Graz) regional models are calculated for two test beds with different latitudes and extensions (Western Austria and the Aegean region). There are three different approaches, two RIMs are based on spherical harmonics calculated either from code or phase measurements and one RIM is based on a Taylor series expansion around a central point estimated from zero-difference observations. The benefits of regional models are the local flexibility using a dense network of GNSS stations. Near real-time parameters are provided within ten minutes after every clock hour. All models have been compared according to their general behavior, the ability to react upon extreme solar events and the robustness of estimation. A ranking of the different models showed a preference for the RIMs while the global models should be used within a fall-back strategy.

  20. Ionospheric Specifications for SAR Interferometry (ISSI)

    Science.gov (United States)

    Pi, Xiaoqing; Chapman, Bruce D; Freeman, Anthony; Szeliga, Walter; Buckley, Sean M.; Rosen, Paul A.; Lavalle, Marco

    2013-01-01

    The ISSI software package is designed to image the ionosphere from space by calibrating and processing polarimetric synthetic aperture radar (PolSAR) data collected from low Earth orbit satellites. Signals transmitted and received by a PolSAR are subject to the Faraday rotation effect as they traverse the magnetized ionosphere. The ISSI algorithms combine the horizontally and vertically polarized (with respect to the radar system) SAR signals to estimate Faraday rotation and ionospheric total electron content (TEC) with spatial resolutions of sub-kilometers to kilometers, and to derive radar system calibration parameters. The ISSI software package has been designed and developed to integrate the algorithms, process PolSAR data, and image as well as visualize the ionospheric measurements. A number of tests have been conducted using ISSI with PolSAR data collected from various latitude regions using the phase array-type L-band synthetic aperture radar (PALSAR) onboard Japan Aerospace Exploration Agency's Advanced Land Observing Satellite mission, and also with Global Positioning System data. These tests have demonstrated and validated SAR-derived ionospheric images and data correction algorithms.

  1. Ranking ICME's efficiency for geomagnetic and ionospheric storms and risk of false alarms

    Science.gov (United States)

    Gulyaeva, T. L.

    2017-11-01

    A statistical analysis is undertaken on ICME's efficiency in producing the geomagnetic and ionospheric storms. The mutually-consistent thresholds for the intense, moderate and weak space weather storms and quiet conditions are introduced with an analytical model based on relations between the equatorial Dst index and geomagnetic indices AE, aa, ap, ap(τ) and the ionospheric Vσ indices. The ionosphere variability Vσ index is expressed in terms of the total electron content (TEC) deviation from the -15-day sliding median normalized by the standard deviation for the 15 preceding days. The intensity of global positive ionospheric storm, Vσp, and negative storm, Vσn, is represented by the relative density of anomalous ±Vσ index occurrence derived from the global ionospheric maps GIM-TEC for 1999-2016. An impact of total 421 ICME events for 1999-2016 on the geomagnetic and ionospheric storms expressed by AE, Dst, aa, ap, ap(τ), Vσp, Vσn indices and their superposition is analyzed using ICME catalogue by Richardson and Cane (2010) during 24 h after the ICME start time t0. Hierarchy of efficiency of ICME → storm relation is established. The ICMEs have a higher probability (22-25%) to be followed by the intense ionospheric and auroral electrojet storms at global and high latitudes as compared to the intense storms at middle and low latitudes (18-20%) and to moderate and weak storms at high latitudes (5-17%). At the same time ICMEs are more effective in producing the moderate storms (24-28%) at the middle and low latitudes as compared to the intense and weak storms at these latitudes (13-22%) and to moderate storms at high latitudes (8-17%). The remaining cases when quiet conditions are observed after ICMEs present higher chance for a false alarm. The risk factor for a false alarm can vary from 18% if the superposition of all indices is considered, to 51-64% for individual AE, Vσp and Vσn indices. The analysis indicates that the mutually-consistent thresholds

  2. Meridian-scanning photometer, coherent HF radar, and magnetometer observations of the cusp: a case study

    Directory of Open Access Journals (Sweden)

    S. E. Milan

    1999-02-01

    Full Text Available The dynamics of the cusp region and post-noon sector for an interval of predominantly IMF By, Bz < 0 nT are studied with the CUTLASS Finland coherent HF radar, a meridian-scanning photometer located at Ny Ålesund, Svalbard, and a meridional network of magnetometers. The scanning mode of the radar is such that one beam is sampled every 14 s, and a 30° azimuthal sweep is completed every 2 minutes, all at 15 km range resolution. Both the radar backscatter and red line (630 nm optical observations are closely co-located, especially at their equatorward boundary. The optical and radar aurora reveal three different behaviours which can interchange on the scale of minutes, and which are believed to be related to the dynamic nature of energy and momentum transfer from the solar wind to the magnetosphere through transient dayside reconnection. Two interpretations of the observations are presented, based upon the assumed location of the open/closed field line boundary (OCFLB. In the first, the OCFLB is co-located with equatorward boundary of the optical and radar aurora, placing most of the observations on open field lines. In the second, the observed aurora are interpreted as the ionospheric footprint of the region 1 current system, and the OCFLB is placed near the poleward edge of the radar backscatter and visible aurora; in this interpretation, most of the observations are placed on closed field lines, though transient brightenings of the optical aurora occur on open field lines. The observations reveal several transient features, including poleward and equatorward steps in the observed boundaries, "braiding" of the backscatter power, and 2 minute quasi-periodic enhancements of the plasma drift and optical intensity, predominantly on closed field lines.Key words. Ionosphere (auroral ionosphere; plasma convection · Magnetospheric physics (magnetopause · cusp · and boundary layers

  3. Phase1 upgrade of the CMS-HF Calorimeter

    CERN Document Server

    Gulmez, Erhan

    2016-01-01

    In this presentation, results of the Phase I upgrade of the CMS Hadron Forward Calorimeter (HF) are discussed. The CMS-HF Calorimeter was using regular PMTs. Cherenkov light produced in the quartz fibers embedded in the iron absorber was read out with the PMTs. However, occasionally, stray muons hitting the PMT windows cause Cherenkov radiation in the PMT itself and produce large signals. These large signals mimic a very high-energy particle and are tagged as important by the trigger. To reduce this problem, PMTs had to be replaced. The four-anode PMTs that were chosen have thinner windows; thereby reducing the Cherenkov radiation in the PMT window. As part of the upgrade, the read-out electronics is to be replaced so that the PMTs are read out in two channels by connecting each pair of anodes to a single channel. Information provided by these two channels will help us reject the false signals due to the stray muons since the Cherenkov radiation in the PMT window is more likely to produce a signal only in one...

  4. Impacts of Temporal-Spatial Variant Background Ionosphere on Repeat-Track GEO D-InSAR System

    Directory of Open Access Journals (Sweden)

    Cheng Hu

    2016-11-01

    Full Text Available An L band geosynchronous synthetic aperture radar (GEO SAR differential interferometry system (D-InSAR will be obviously impacted by the background ionosphere, which will give rise to relative image shifts and decorrelations of the SAR interferometry (InSAR pair, and induce the interferometric phase screen errors in interferograms. However, the background ionosphere varies within the long integration time (hundreds to thousands of seconds and the extensive imaging scene (1000 km levels of GEO SAR. As a result, the conventional temporal-spatial invariant background ionosphere model (i.e., frozen model used in Low Earth Orbit (LEO SAR is no longer valid. To address the issue, we firstly construct a temporal-spatial background ionosphere variation model, and then theoretically analyze its impacts, including relative image shifts and the decorrelation of the GEO InSAR pair, and the interferometric phase screen errors, on the repeat-track GEO D-InSAR processing. The related impacts highly depend on the background ionosphere parameters (constant total electron content (TEC component, and the temporal first-order and the temporal second-order derivatives of TEC with respect to the azimuth time, signal bandwidth, and integration time. Finally, the background ionosphere data at Isla Guadalupe Island (29.02°N, 118.27°W on 7–8 October 2013 is employed for validating the aforementioned analysis. Under the selected background ionosphere dataset, the temporal-spatial background ionosphere variation can give rise to a relative azimuth shift of dozens of meters at most, and even the complete decorrelation in the InSAR pair. Moreover, the produced interferometric phase screen error corresponds to a deformation measurement error of more than 0.2 m at most, even in a not severely impacted area.

  5. On auroral dynamics observed by HF radar: 1. Equatorward edge of the afternoon-evening diffuse luminosity belt

    Directory of Open Access Journals (Sweden)

    M. Uspensky

    2000-12-01

    Full Text Available Observations and modelling are presented which illustrate the ability of the Finland CUTLASS HF radar to monitor the afternoon-evening equatorward auroral boundary during weak geomagnetic activity. The subsequent substorm growth phase development was also observed in the late evening sector as a natural continuation of the preceding auroral oval dynamics. Over an 8 h period the CUTLASS Finland radar observed a narrow (in range and persistent region of auroral F- and (later E-layer echoes which gradually moved equatorward, consistent with the auroral oval diurnal rotation. This echo region corresponds to the subvisual equatorward edge of the diffuse luminosity belt (SEEL and the ionospheric footprint of the inner boundary of the electron plasma sheet. The capability of the Finland CUTLASS radar to monitor the E-layer SEEL-echoes is a consequence of the nearly zero E-layer rectilinear aspect angles in a region 5–10° poleward of the radar site. The F-layer echoes are probably the boundary blob echoes. The UHF EISCAT radar was in operation and observed a similar subvisual auroral arc and an F-layer electron density enhancement when it appeared in its antenna beam.Key words: Ionsophere (ionospheric irregularities · Magnetospheric physics (auroral phenomena; magnetosphere–ionosphere interactions

  6. On auroral dynamics observed by HF radar: 1. Equatorward edge of the afternoon-evening diffuse luminosity belt

    Directory of Open Access Journals (Sweden)

    M. Uspensky

    Full Text Available Observations and modelling are presented which illustrate the ability of the Finland CUTLASS HF radar to monitor the afternoon-evening equatorward auroral boundary during weak geomagnetic activity. The subsequent substorm growth phase development was also observed in the late evening sector as a natural continuation of the preceding auroral oval dynamics. Over an 8 h period the CUTLASS Finland radar observed a narrow (in range and persistent region of auroral F- and (later E-layer echoes which gradually moved equatorward, consistent with the auroral oval diurnal rotation. This echo region corresponds to the subvisual equatorward edge of the diffuse luminosity belt (SEEL and the ionospheric footprint of the inner boundary of the electron plasma sheet. The capability of the Finland CUTLASS radar to monitor the E-layer SEEL-echoes is a consequence of the nearly zero E-layer rectilinear aspect angles in a region 5–10° poleward of the radar site. The F-layer echoes are probably the boundary blob echoes. The UHF EISCAT radar was in operation and observed a similar subvisual auroral arc and an F-layer electron density enhancement when it appeared in its antenna beam.

    Key words: Ionsophere (ionospheric irregularities · Magnetospheric physics (auroral phenomena; magnetosphere–ionosphere interactions

  7. Monitoring the three-dimensional ionospheric electron density ...

    Indian Academy of Sciences (India)

    In this paper, an IRI model assisted GPS-based Computerized Ionospheric Tomography (CIT) technique is developed to inverse the ionospheric electron density (IED) distribution over China. Essentially, an improved algebraic reconstruction technique (IART) is first proposed to reconstruct the ionospheric images with high ...

  8. Influence of the finite ionospheric conductivity on dispersive, nonradiative field line resonances

    Directory of Open Access Journals (Sweden)

    A. Streltsov

    1997-06-01

    Full Text Available The influence of the finite ionospheric conductivity on the structure of dispersive, nonradiative field line resonances (FLRs is investigated for the first four odd harmonics. The results are based on a linear, magnetically incompressible, reduced, two-fluid MHD model. The model includes effects of finite electron inertia (at low altitude and finite electron pressure (at high altitude. The ionosphere is treated as a high-integrated conducting substrate. The results show that even very low ionospheric conductivity (ΣP = 2 mho is not sufficient to prevent the formation of a large-amplitude, small-scale, nonradiative FLR for the third and higher harmonics when the background transverse plasma inhomogeneity is strong enough. At the same time, the fundamental FLR is strongly affected by a state of low conductivity, and when ΣP = 2 mho, this resonance forms only small-amplitude, relatively broad electromagnetic disturbance. The difference in conductivities of northern and southern ionospheres does not produce significant asymmetry in the distribution of electric and magnetic fields along the resonant field line. The transverse gradient of the background Alfvén speed plays an important role in structure of the FLR when the ionospheric conductivity is finite. In cases where the transverse inhomogeneity of the plasma is not strong enough, the low ionospheric conductivity can prevent even higher-harmonic FLRs from contracting to small scales where dispersive effects are important. The application of these results to the formation and temporal evolution of small-scale, active auroral arc forms is discussed.

  9. Low-latitude ionospheric turbulence observed by Aureol-3 satellite

    Directory of Open Access Journals (Sweden)

    Y. Hobara

    2005-06-01

    Full Text Available Using PSD (Power Spectral Density data on electron density and electric field variations observed on board Aureol-3 satellite at low-to-mid-latitude ionosphere we analyze a scale distribution of the ionospheric turbulence in a form k-α, where k is the wave number and α is the spectral index. At first, high-resolution data in the near-equator region for several orbits have been processed. In this case the frequency range is from 6Hz to 100Hz (corresponding spatial scales from 80m to 1.3km, each power spectrum obeys a single power law fairly well, and the mean spectral indices are rather stable with αN=2.2±0.3 and αE=1.8±0.2, for the density and electric field, respectively. Then we produce a statistical study of 96 electric field bursts in the frequency range 10-100Hz from low-time resolution data (filter bank envelope. These bursts concentrate on the side of the Equatorial Anomaly crest (geomagnetic latitude 30-40°. Spectral indices of the bursts vary in the interval αE=2.0-2.5 but are fairly stable in seasons and local times. The electric field power of the burst has rather a large variability but has a relative increase in mean values for the summer and winter, as well as the daytime. The effect of major seismic activities toward the ionospheric turbulence is not conclusive either for the refractive index or for the electric field power. However, the mean value for the electric field power of bursts during seismic periods is larger than that for non seismic periods, and the statistical difference of the mean values is rather significant.

  10. Low-latitude ionospheric turbulence observed by Aureol-3 satellite

    Directory of Open Access Journals (Sweden)

    Y. Hobara

    2005-06-01

    Full Text Available Using PSD (Power Spectral Density data on electron density and electric field variations observed on board Aureol-3 satellite at low-to-mid-latitude ionosphere we analyze a scale distribution of the ionospheric turbulence in a form k, where k is the wave number and α is the spectral index. At first, high-resolution data in the near-equator region for several orbits have been processed. In this case the frequency range is from 6Hz to 100Hz (corresponding spatial scales from 80m to 1.3km, each power spectrum obeys a single power law fairly well, and the mean spectral indices are rather stable with αN=2.2±0.3 and αE=1.8±0.2, for the density and electric field, respectively. Then we produce a statistical study of 96 electric field bursts in the frequency range 10-100Hz from low-time resolution data (filter bank envelope. These bursts concentrate on the side of the Equatorial Anomaly crest (geomagnetic latitude 30-40°. Spectral indices of the bursts vary in the interval αE=2.0-2.5 but are fairly stable in seasons and local times. The electric field power of the burst has rather a large variability but has a relative increase in mean values for the summer and winter, as well as the daytime. The effect of major seismic activities toward the ionospheric turbulence is not conclusive either for the refractive index or for the electric field power. However, the mean value for the electric field power of bursts during seismic periods is larger than that for non seismic periods, and the statistical difference of the mean values is rather significant.

  11. Solar flares induced D-region ionospheric and geomagnetic perturbations

    Science.gov (United States)

    Selvakumaran, R.; Maurya, Ajeet K.; Gokani, Sneha A.; Veenadhari, B.; Kumar, Sushil; Venkatesham, K.; Phanikumar, D. V.; Singh, Abhay K.; Siingh, Devendraa; Singh, Rajesh

    2015-02-01

    The D-region ionospheric perturbations caused by solar flares which occurred during January 2010-February 2011, a low solar activity period of current solar cycle 24, have been examined on NWC transmitter signal (19.8 kHz) recorded at an Indian low latitude station, Allahabad (Geographic lat. 25.75°N, long. 81.85°E). A total of 41 solar flares, including 21 C-class, 19 M-class and 01 X-class, occurred during the daylight part of the NWC-Allahabad transmitter receiver great circle path. The local time dependence of solar flare effects on the change in the VLF amplitude, time delay between VLF peak amplitude and X-ray flux peak have been studied during morning, noon and evening periods of local daytime. Using the Long Wave Propagation Capability code V 2.1 the D-region reference height (H/) and sharpness factor (β) for each class of solar flare (C, M and X) have been estimated. It is found that D-region ionospheric parameters (H/, β) strongly depend on the local time of flare's occurrence and their classes. The flare time electron density estimated by using H/ and β shows maximum increase in the electron density of the order of ~80 times as compared to the normal day values. The electron density was found to increase exponentially with increase in the solar flux intensity. The solar flare effect on horizontal component (H) of the Earth's magnetic field over an equatorial station, Tirunelveli (Geographic lat., 8.7°N, long., 77.8°E, dip lat., 0.4°N), shows a maximum increase in H of ~8.5% for M class solar flares. The increase in H is due to the additional magnetic field produced by the ionospheric electrojet over the equatorial station.

  12. 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.

  13. Ionospheric irregularities in periods of meteorological disturbances

    Science.gov (United States)

    Borchevkina, O. P.; Karpov, I. V.

    2017-09-01

    The results of observations of the total electron content (TEC) in periods of storm disturbances of meteorological situation are presented in the paper. The observational results have shown that a passage of a meteorological storm is accompanied by a substantial decrease in values of TEC and critical frequencies of the ionospheric F2 region. The decreases in values of these ionospheric parameters reach 50% and up to 30% in TEC and critical frequency of the F2 layer, respectively, as compared to meteorologically quiet days. Based on qualitative analysis, it is found that the processes related to formation of local regions of thermospheric heating due to a dissipation of AGW coming into the upper atmosphere from the region of the meteorological disturbance in the lower atmosphere are a possible cause of these ionospheric disturbances.

  14. Imaging magnetospheric boundaries at ionospheric heights

    Science.gov (United States)

    Mendillo, Michael; Baumgardner, Jeffrey; Wroten, Joei; Martinis, Carlos; Smith, Steven; Merenda, Kevin-Druis; Fritz, Theodore; Hairston, Marc; Heelis, Rod; Barbieri, Cesare

    2013-11-01

    all-sky imager (ASI) records atmospheric emissions from zenith to low on the horizon at all azimuths, a region typically spanning millions of square kilometers. Each pixel (with its unique elevation, azimuth, and emission height) can be mapped along B-field lines to the equatorial plane of the magnetosphere. Auroral and subauroral structures and boundaries seen in emission within the ionosphere-thermosphere (I-T) system can thus be related to source regions. For a midlatitude site, this I-T to inner magnetosphere connection typically falls within the L = 2-5 earth radii domain. In this study, we present the first case of a stable auroral red (SAR) arc observed from three widely spaced ASI sites (Europe, North America, New Zealand). SAR arcs are produced during the main and recovery phases of a geomagnetic storm, with emission driven by heat conduction from a very specific location in the magnetosphere—the L value where the plasmapause and the inner edge of the ring current overlap. Using three-site observations, we show that this boundary can be followed for 24 consecutive hours. Simultaneous observations made by three satellites in the Defense Meteorological Satellite Program (DMSP) show that the lowest latitude peak in electron temperature can be used to map the same boundary. A key structure of the inner magnetosphere that cannot be observed continuously from sensors orbiting within the magnetosphere is made continuously visible to ground-based optical systems via effects caused by the drainage of small amounts of ring current energy into the I-T system.

  15. Travelling ionospheric disturbance over California mid 2000

    Directory of Open Access Journals (Sweden)

    M. Hawarey

    2006-01-01

    Full Text Available In this paper, the GPS data collected by more than 130 permanent GPS stations that belong to the Southern California Integrated GPS Network (SCIGN around the launch of a Minuteman-II missile on 8 July 2000 (UTC is processed to reveal traveling ionospheric disturbance (TID all over the network on average 15 min after the launch. This TID was initially perceived to be excited by the launch itself, but this conclusion is challenged by the propagation direction. This is because this TID seems to travel towards the air force base from where the launch took place, not far away from it. This challenge is based on the assumption that TID is occurring at one single ionospheric altitude. While the nature of ionosphere supports such horizontally-guided propagation, multi-altitude ionospheric pierce points are hypothesized, which would support the suggestion that detected TID is excited by the missile launch itself, despite the apparent reverse direction of propagation. The overall analysis rules out any extra-terrestrial sources like solar flares, or seismic sources like earthquakes, which confirms the conclusion of TID excitation by the launch. There is apparent coherence of the TID for about 45 min and the propagation speed of TID within the layer of ionosphere is calculated to be approximately equal to 1230 m/s. While the usual assumption for TID is that they occur around an altitude of 350 km, such sound speed can only occur at much higher altitudes. Further research is recommended to accurately pinpoint the ionospheric pierce points and develop an algorithm to locate the source of TID in case it is totally unknown.

  16. Can Ionospheric Sounding Help Tsunami Warning Systems ?

    Science.gov (United States)

    Occhipinti, G.; Lognonné, P.; Komjathy, A.; Kherani, E. A.; Crespon, F.; Mannucci, A.

    2007-12-01

    A series of ionospheric anomalies following the Sumatra tsunami has been recently reported in the scientific literature (e.g., Liu et al. 2006; DasGupta et al. 2006; Occhipinti et al. 2006). Similar anomalies were also observed after the tsunamigenic earthquake in Peru in 2001 (Artru et al., 2005). All these anomalies show the signature in the ionosphere of tsunami-generated internal gravity waves (IGW) propagating in the neutral atmosphere over oceanic regions. The strong amplification mechanism of atmospheric IGW allows to detect these anomalies when the tsunami is offshore where the see level displacement is still small. In addition, the dense coverage of ionospheric sounding instruments over the oceans increases over time and more instruments will be able to provide ionospheric measurements: i.d., Doppler sounding, over-the-horizon radar (OTH) and space-based GPS data (e.g., COSMIC). Most of the ionospheric anomalies are also deterministic and reproducible by numerical modeling (Occhipinti et al., 2006), this latter will supply an useful help in the estimation of expected anomalies. The sensitivity of altimeters, OTH radar, ground-based and space-based GPS measurements is analyzed in this work by the way of the modeling. The results are used to discuss the role of ionospheric sounding in the future oceanic monitoring and tsunami warning system. [Artru et al., 2005] Geophys. J. Int., 160, 2005 [DasGupta et al., 2006] Earth Planet. Space, 35, 929-959. [Liu et al., 2006] J. Geophys. Res., 111, A05303. [Occhipinti et al., 2006] Geophys. Res. Lett., 33, L20104, 2006

  17. 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.

  18. Ionospheric tomography using the FORTE satellite

    Energy Technology Data Exchange (ETDEWEB)

    Murphy, T.C.

    1993-08-01

    The possibility of obtaining ionospheric profile data via tomographic techniques has elicited considerable interest in recent years. The input data for the method is a set of total electron content measurements along intersecting lines of sight which form a grid. This can conveniently be provided by a fast-moving satellite with a VHF beacon which will generate the multiple paths needed for effective tomography. Los Alamos and Sandia National Laboratories will launch and operate the FORTE satellite for the US Department of Energy, with launch scheduled in 1995. FORTE will provide such a beacon. Additionally, wideband VHF receivers aboard the satellite will allow corraborative measurements of ionospheric profile parameters in some cases.

  19. Using DORIS measurements for ionosphere modeling

    Science.gov (United States)

    Dettmering, Denise; Schmidt, Michael; Limberger, Marco

    2013-04-01

    Nowadays, most of the ionosphere models used in geodesy are based on terrestrial GNSS measurements and describe the Vertical Total Electron Content (VTEC) depending on longitude, latitude, and time. Since modeling the height distribution of the electrons is difficult due to the measurement geometry, the VTEC maps are based on the the assumption of a single-layer ionosphere. Moreover, the accuracy of the VTEC maps is different for different regions of the Earth, because the GNSS stations are unevenly distributed over the globe and some regions (especially the ocean areas) are not very well covered by observations. To overcome the unsatisfying measurement geometry of the terrestrial GNSS measurements and to take advantage of the different sensitivities of other space-geodetic observation techniques, we work on the development of multi-dimensional models of the ionosphere from the combination of modern space-geodetic satellite techniques. Our approach consists of a given background model and an unknown correction part expanded in terms of B-spline functions. Different space-geodetic measurements are used to estimate the unknown model coefficients. In order to take into account the different accuracy levels of the observations, a Variance Component Estimation (VCE) is applied. We already have proven the usefulness of radio occultation data from space-borne GPS receivers and of two-frequency altimetry data. Currently, we test the capability of DORIS observations to derive ionospheric parameters such as VTEC. Although DORIS was primarily designed for precise orbit computation of satellites, it can be used as a tool to study the Earth's ionosphere. The DORIS ground beacons are almost globally distributed and the system is on board of various Low Earth Orbiters (LEO) with different orbit heights, such as Jason-2, Cryosat-2, and HY-2. The last generation of DORIS receivers directly provides phase measurements on two frequencies. In this contribution, we test the DORIS

  20. 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.

  1. Ti-catalyzed HfSiO4 formation in HfTiO4 films on SiO2 studied by Z-contrast scanning electron microscopy

    Directory of Open Access Journals (Sweden)

    Elizabeth Ellen Hoppe

    2013-08-01

    Full Text Available Hafnon (HfSiO4 as it is initially formed in a partially demixed film of hafnium titanate (HfTiO4 on fused SiO2 is studied by atomic number (Z contrast high resolution scanning electron microscopy, x-ray diffraction, and Raman spectroscopy and microscopy. The results show exsoluted Ti is the catalyst for hafnon formation by a two-step reaction. Ti first reacts with SiO2 to produce a glassy Ti-silicate. Ti is then replaced by Hf in the silicate to produce HfSiO4. The results suggest this behavior is prototypical of other Ti-bearing ternary or higher order oxide films on SiO2 when film thermal instability involves Ti exsolution.

  2. Ionospheric Signatures of Tohoku-Oki Tsunami in GPS TEC: Comparisons with Models Near the Epicenter and Far Afield

    Science.gov (United States)

    Galvan, D. A.; Komjathy, A.; Hickey, M. P.; Foster, J. H.; Song, Y.

    2011-12-01

    Ocean tsunamis can produce atmospheric internal gravity waves that propagate to the ionosphere, creating disturbances in ionospheric electron density that travel with the ocean waves below. These traveling ionospheric disturbances (TIDs) can be observed using measurements of total electron content (TEC) between Global Positioning System (GPS) satellites and receivers on the ground. We present observations of ionospheric perturbations caused by multiple tsunami events, including the Tohoku tsunami of March 11, 2011 in regions both near the epicenter and far afield throughout the Pacific Ocean. We have investigated measurements of ionospheric TEC from 1198 GPS receivers in the Japanese GEONET network, dozens of receivers on the Hawaiian Islands, and hundreds more receivers on the west coasts of North and South America. We compare the observed TEC perturbation magnitudes to those produced by the atmosphere-ionosphere coupling model of Hickey et al, 2009. We also compare the position and velocity of the ionospheric gravity wave front with that of the ocean tsunami as estimated by the tsunami sea-surface model of Song, 2007, the Method Of Splitting Tsunami (MOST) model of NOAA, and various observations by Deep-ocean Assessment and Reporting of Tsunamis (DART) buoys. GPS TEC measurements show a TID magnitude in agreement with the atmosphere-ionosphere coupling model, and often aligned with the position of the modeled ocean tsunami wavefront. TIDs from the Tohoku earthquake and tsunami were observed moving away from the epicenter at approximate speeds of 3400 m/s, 1000 m/s and 200-300 m/s, consistent with Rayleigh waves, acoustic waves, and gravity waves, respectively. The gravity wave perturbations, seen as soon as 30 minutes after the earthquake, are mostly between 0.5 to 1.5 TECU, but in some regions were as high as 3 TECU (1 TECU = 10^16 el/m2), representing ~10% of the background TEC. Due to the dense GPS network and high earthquake magnitude, these are the clearest

  3. Ionospheric scintilations over the polish LOFAR station PL610

    Science.gov (United States)

    Pożoga, Mariusz; Rothkaehl, Hanna; Matyjasiak, Barbara; Grzesiak, Marcin; Przepiórka, Dorota

    2017-04-01

    Using polish station PL610 of international LOFAR interferometer we present here observations of ionospheric scintillation over station. Scintillation phenomenon occurs as a result of variations in the refractive index of the medium through which waves are traveling. In particular Earth's ionosphere is strongly variable medium where high density gradients occure. Scintillation measurements may be successfully used to study the irregular structure of the ionosphere. The LOFAR telescope operates at frequencies from 10 to 240 MHz thus provides good opportunity to broad-band study of ionospheric irregularities. During the local mode periods four strong radio sources (LOFAR bright A-team sources) were observed in order to measure ionospheric scintillations.

  4. Decision-aid design factors in connection with HF communication and emitter location disciplines

    Science.gov (United States)

    Goodman, John M.

    1989-09-01

    The advance of microcomputer technology, the growing sophistication of specified propagation models, and the expanding ability to sense the medium and apply that knowledge in real time is leading to an improvement in the prediction of system performance for tactical users. The maturation of artificial intelligence disciplines should provide the user of advanced C3I decision aids an ability to manage the plethora of information more effectively. Critical aspects of the process of developing useful and cost-effective decision aids are identified with emphasis upon the HF medium which is strongly propagation-limited and controlled by variable and often unpredictable phenomena. A major factor in this field of activity is the evolution of self-adaptive system architecture incorporating imbedded Real Time Channel Evaluation (RTCE). In this context, the decision aid is a process which is operationally transparent to the the user but could be user-defined. A key to the development of an adaptive resource management capability is the integration of a set of tools or decision aids which direct the system to compensate for pathological effects by adjustment of system parameters. The approach is ultimately limited by the accuracy with which the ionosphere or the HF channel may be specified. The accepted specification accuracy will determine the design approaches to be followed.

  5. The range split-spectrum method for ionosphere estimation applied to the 2008 Kyrgyzstan earthquake

    Science.gov (United States)

    Gomba, Giorgio; Eineder, Michael

    2015-04-01

    L-band remote sensing systems, like the future Tandem-L mission, are disrupted by the ionized upper part of the atmosphere called ionosphere. The ionosphere is a region of the upper atmosphere composed by gases that are ionized by the solar radiation. The extent of the effects induced on a SAR measurement is given by the electron density integrated along the radio-wave paths and on its spatial variations. The main effect of the ionosphere on microwaves is to cause an additional delay, which introduces a phase difference between SAR measurements modifying the interferometric phase. The objectives of the Tandem-L mission are the systematic monitoring of dynamic Earth processes like Earth surface deformations, vegetation structure, ice and glacier changes and ocean surface currents. The scientific requirements regarding the mapping of surface deformation due to tectonic processes, earthquakes, volcanic cycles and anthropogenic factors demand deformation measurements; namely one, two or three dimensional displacement maps with resolutions of a few hundreds of meters and accuracies of centimeter to millimeter level. Ionospheric effects can make impossible to produce deformation maps with such accuracy and must therefore be estimated and compensated. As an example of this process, the implementation of the range split-spectrum method proposed in [1,2] will be presented and applied to an example dataset. The 2008 Kyrgyzstan Earthquake of October 5 is imaged by an ALOS PALSAR interferogram; a part from the earthquake, many fringes due to strong ionospheric variations can also be seen. The compensated interferogram shows how the ionosphere-related fringes were successfully estimated and removed. [1] Rosen, P.A.; Hensley, S.; Chen, C., "Measurement and mitigation of the ionosphere in L-band Interferometric SAR data," Radar Conference, 2010 IEEE , vol., no., pp.1459,1463, 10-14 May 2010 [2] Brcic, R.; Parizzi, A.; Eineder, M.; Bamler, R.; Meyer, F., "Estimation and

  6. A Probe of Magnetosphere-Ionosphere Coupling using the Propagation Characteristics of Very Low Frequency Signal

    Science.gov (United States)

    Nwankwo, V. U. J.; Chakrabarti, S. K.; Ogunmodimu, O. A.

    2015-12-01

    The amplitude and phase of VLF/LF radio signal are sensitive to changes in the electrical conductivity of the lower ionosphere when propagated in the Earth-ionosphere waveguide. This unique characteristic makes it useful in studying sudden ionospheric disturbances and/or anomaly especially those related to prompt X-ray flux output from solar flares and gamma ray bursts (GRBs). However, strong geomagnetic disturbances and/or storm conditions are known to produce large and global ionospheric disturbances, which can significantly affect VLF radio propagation in the D region ionosphere. Other than X-ray flux enhancement of amplitude and phase, diurnal VLF signature may convey other important information especially those related to geomagnetic disturbance/storm induced ionospheric changes. In this paper, using the data of three propagation paths (at latitudes 40-54), we performed detail analysis of the trend of variations of aspects VLF diurnal signal under varying solar and/or geomagnetic space environmental conditions for identification of possible geomagnetic footprint on the ionosphere. We found that trend of variations significantly reflected the prevailing space weather conditions of various time scales. The `dipping' of the signal diurnal amplitude have shown noteworthy consistency with significantly geomagnetic perturbed and/or storm conditions in the time scale of 1-2 days. We also found that dipping of most MDP signal occurred irrespective of the time (of the day), which an event happened, while those of MBSR, MASS, SRT and SST appear to largely depend on event occurrence time and/or duration. Pre-sunset event had more influence on the SST and MASS (dusk signal), while pre-sunrise event had more influence on the SRT and MBSR (dawn signal), and depending on the duration of the event, impact could be extended to the neighbouring point/component in succession. The induced dipping varied with geomagnetic activity/event intensity and/or duration, as well as the

  7. Impact of the Mt. Pinatubo volcaniceruption on the lower ionosphere andatmospheric waves over Central Europe

    Directory of Open Access Journals (Sweden)

    J. Lastovicka

    2003-06-01

    Full Text Available The very strong volcanic eruption of Mt. Pinatubo in June 1991 directly affected the troposphere and lower and middle stratosphere. Here we look at its effects in the mesopause region as revealed by the radio wave absorption measurements in the lower ionosphere over Central Europe and inferred planetary and gravity wave activity. The gravity wave activity inferred from the nighttime LF radio wave absorption displays an evident enhancement for waves of periods of about 2-3 h coinciding with regional measurements of the optical depth of (volcanic aerosols, while there is no detectable effect for short period waves (T < 1 h. There is no detectable effect in the planetary wave activity inferred from the daytime HF radio wave absorption. As for the absorption itself, the results on the impact of the Mt. Pinatubo eruption do not provide an observable effect.

  8. A review of ionospheric effects on Earth-space propagation

    Science.gov (United States)

    Klobuchar, J. A.

    1984-01-01

    A short description is given of each ionospheric total electron content (TEC) effect upon radio waves, along with a representative value of the magnitude of each of these effects under normal ionospheric conditions. A discussion is given of the important characteristics of average ionospheric TEC behavior and the temporal and spatial variability of TEC. Radio waves undergo several effects when they pass through the Earth's ionosphere. One of the most important of these effects is a retardation, or group delay, on the modulation or information carried on the radio wave that is due to its encounter with the free, thermal electrons in the Earth's ionosphere. Other effects the ionosphere has on radio waves include: radio frequency (RF) carrier phase advance; Doppler shift of the RF carrier of the radio wave; Faraday rotation of the plane of polarization of linearly polarized waves; angular refraction or bending of the radio wave path as it travels through the ionosphere; and amplitude and phase scintillations.

  9. A numerical model of the ionospheric signatures of time-varying magneticreconnection: I. ionospheric convection

    Directory of Open Access Journals (Sweden)

    M. Lockwood

    2004-01-01

    Full Text Available This paper presents a numerical model for predicting the evolution of the pattern of ionospheric convection in response to general time-dependent magnetic reconnection at the dayside magnetopause and in the cross-tail current sheet of the geomagnetic tail. The model quantifies the concepts of ionospheric flow excitation by Cowley and Lockwood (1992, assuming a uniform spatial distribution of ionospheric conductivity. The model is demonstrated using an example in which travelling reconnection pulses commence near noon and then move across the dayside magnetopause towards both dawn and dusk. Two such pulses, 8min apart, are used and each causes the reconnection to be active for 1min at every MLT that they pass over. This example demonstrates how the convection response to a given change in the interplanetary magnetic field (via the reconnection rate depends on the previous reconnection history. The causes of this effect are explained. The inherent assumptions and the potential applications of the model are discussed. Key words. Ionosphere (ionosphere-magnetosphere interactions; plasma convection – Magnetospheric physics (magnetosphere-ionosphere interactions; solar wind-magnetosphere interactions

  10. Contribution of the International Reference Ionosphere to the progress of the ionospheric representation

    Science.gov (United States)

    Bilitza, Dieter

    2017-04-01

    The International Reference Ionosphere (IRI), a joint project of the Committee on Space Research (COSPAR) and the International Union of Radio Science (URSI), is a data-based reference model for the ionosphere and since 2014 it is also recognized as the ISO (International Standardization Organization) standard for the ionosphere. The model is a synthesis of most of the available and reliable observations of ionospheric parameters combining ground and space measurements. This presentation reviews the steady progress in achieving a more and more accurate representation of the ionospheric plasma parameters accomplished during the last decade of IRI model improvements. Understandably, a data-based model is only as good as the data foundation on which it is built. We will discuss areas where we are in need of more data to obtain a more solid and continuous data foundation in space and time. We will also take a look at still existing discrepancies between simultaneous measurements of the same parameter with different measurement techniques and discuss the approach taken in the IRI model to deal with these conflicts. In conclusion we will provide an outlook at development activities that may result in significant future improvements of the accurate representation of the ionosphere in the IRI model.

  11. HF-based clad etching of fibre Bragg grating and its utilization in ...

    Indian Academy of Sciences (India)

    2014-02-09

    Feb 9, 2014 ... of laser dye in dye–ethanol solution. The FBG used in this experiment ... In this case, if the colour produced is different from the colour specified in the dyeing recipe, the manufactured goods ... ing of the concentration of a dye Rh 6G in ethanol solution, based on HF-based etched fibre Bragg grating (FBG) is ...

  12. Real-Time Detection of Tsunami Ionospheric Disturbances with a Stand-Alone GNSS Receiver: A Preliminary Feasibility Demonstration.

    Science.gov (United States)

    Savastano, Giorgio; Komjathy, Attila; Verkhoglyadova, Olga; Mazzoni, Augusto; Crespi, Mattia; Wei, Yong; Mannucci, Anthony J

    2017-04-21

    It is well known that tsunamis can produce gravity waves that propagate up to the ionosphere generating disturbed electron densities in the E and F regions. These ionospheric disturbances can be studied in detail using ionospheric total electron content (TEC) measurements collected by continuously operating ground-based receivers from the Global Navigation Satellite Systems (GNSS). Here, we present results using a new approach, named VARION (Variometric Approach for Real-Time Ionosphere Observation), and estimate slant TEC (sTEC) variations in a real-time scenario. Using the VARION algorithm we compute TEC variations at 56 GPS receivers in Hawaii as induced by the 2012 Haida Gwaii tsunami event. We observe TEC perturbations with amplitudes of up to 0.25 TEC units and traveling ionospheric perturbations (TIDs) moving away from the earthquake epicenter at an approximate speed of 316 m/s. We perform a wavelet analysis to analyze localized variations of power in the TEC time series and we find perturbation periods consistent with a tsunami typical deep ocean period. Finally, we present comparisons with the real-time tsunami MOST (Method of Splitting Tsunami) model produced by the NOAA Center for Tsunami Research and we observe variations in TEC that correlate in time and space with the tsunami waves.

  13. Real-Time Detection of Tsunami Ionospheric Disturbances with a Stand-Alone GNSS Receiver: A Preliminary Feasibility Demonstration

    Science.gov (United States)

    Savastano, Giorgio; Komjathy, Attila; Verkhoglyadova, Olga; Mazzoni, Augusto; Crespi, Mattia; Wei, Yong; Mannucci, Anthony J.

    2017-04-01

    It is well known that tsunamis can produce gravity waves that propagate up to the ionosphere generating disturbed electron densities in the E and F regions. These ionospheric disturbances can be studied in detail using ionospheric total electron content (TEC) measurements collected by continuously operating ground-based receivers from the Global Navigation Satellite Systems (GNSS). Here, we present results using a new approach, named VARION (Variometric Approach for Real-Time Ionosphere Observation), and estimate slant TEC (sTEC) variations in a real-time scenario. Using the VARION algorithm we compute TEC variations at 56 GPS receivers in Hawaii as induced by the 2012 Haida Gwaii tsunami event. We observe TEC perturbations with amplitudes of up to 0.25 TEC units and traveling ionospheric perturbations (TIDs) moving away from the earthquake epicenter at an approximate speed of 316 m/s. We perform a wavelet analysis to analyze localized variations of power in the TEC time series and we find perturbation periods consistent with a tsunami typical deep ocean period. Finally, we present comparisons with the real-time tsunami MOST (Method of Splitting Tsunami) model produced by the NOAA Center for Tsunami Research and we observe variations in TEC that correlate in time and space with the tsunami waves.

  14. HF Interference, Procedures and Tools (Interferences HF, procedures et outils) (CD-ROM)

    National Research Council Canada - National Science Library

    2007-01-01

    ...) on "HF Interference, Procedures and Tools", to address the concerns raised by the potential for unintentional radio interference to be caused by the widespread operation of broadband wire line...

  15. Ionosphere and its Influence on Radio Communications

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 5; Issue 7. Ionosphere and its Influence on Radio Communications. R S Dabas. General Article Volume 5 Issue 7 July 2000 pp 28-43. Fulltext. Click here to view fulltext PDF. Permanent link: http://www.ias.ac.in/article/fulltext/reso/005/07/0028-0043 ...

  16. 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.

  17. Ionospheric irregularities at Antarctic using GPS measurements

    Indian Academy of Sciences (India)

    The purpose of this work is to study the behaviour of the ionospheric scintillation at high latitude during geomagnetically quiet and disturbed conditions which is one of the most relevant themes in the space weather studies. Scintillation is a major problem in navigation application using GPS and in satellite communication at ...

  18. 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.

  19. Ionospheric irregularities at Antarctic using GPS measurements

    Indian Academy of Sciences (India)

    The purpose of this work is to study the behaviour of the ionospheric scintillation at high latitude during geomagnetically quiet and disturbed conditions which is one of the most relevant themes in ... Severe amplitude fading and strong scintillation affect the reliability of GPS navigational system and satellite communication.

  20. The location of the open-closed magnetic field line boundary in the dawn sector auroral ionosphere

    Directory of Open Access Journals (Sweden)

    J. A. Wild

    2004-11-01

    Full Text Available As a measure of the degree of coupling between the solar wind-magnetosphere-ionosphere systems, the rate at which the size of the polar cap (the region corresponding to ionospheric termini of open magnetic flux tubes varies is of prime importance. However, a reliable technique by which the extent of the polar cap might be routinely monitored has yet to be developed. Current techniques provide particularly ambiguous indications of the polar cap boundary in the dawn sector. We present a case study of space- and ground-based observations of the dawn-sector auroral zone and attempt to determine the location of the polar cap boundary using multi-wavelength observations of the ultraviolet aurora (made by the IMAGE FUV imager, precipitating particle measurements (recorded by the FAST, DMSP, and Cluster 1 and 3 satellites, and SuperDARN HF radar observations of the ionospheric Doppler spectral width boundary. We conclude that in the dawn sector, during the interval presented, neither the poleward edge of the wideband auroral UV emission (140-180nm nor the Doppler spectral width boundary were trustworthy indicators of the polar cap boundary location, while narrow band UV emissions in the range 130-140nm appear to be much more reliable.

  1. Exploring the role of ionospheric drivers during the extreme solar minimum of 2008

    Directory of Open Access Journals (Sweden)

    J. Klenzing

    2013-12-01

    Full Text Available During the recent solar minimum, solar activity reached the lowest levels observed during the space age, resulting in a contracted atmosphere. This extremely low solar activity provides an unprecedented opportunity to understand the variability of the Earth's ambient ionosphere. The average E × B drifts measured by the Vector Electric Field Instrument (VEFI on the Communications/Navigation Outage Forecasting System (C/NOFS satellite during this period are found to have several differences from the expected climatology based on previous solar minima, including downward drifts in the early afternoon and a weak to non-existent pre-reversal enhancement. Using SAMI2 (Sami2 is Another Model of the Ionosphere as a computational engine, we investigate the effects of these electrodynamical changes as well as the contraction of the thermosphere and reduced EUV ionization on the ionosphere. The sensitivity of the simulations to wind models is also discussed. These modeled ionospheres are compared to the C/NOFS average topside ion density and composition and Formosa Satellite-3/Constellation Observing System for Meteorology, Ionosphere, and Climate average NmF2 and hmF2. In all cases, incorporating the VEFI drift data significantly improves the model results when compared to both the C/NOFS density data and the F3/C GOX data. Changing the MSIS and EUVAC models produced changes in magnitude, but not morphology with respect to local time. The choice of wind model modulates the resulting topside density and composition, but only the use of the VEFI E × B drifts produces the observed post-sunset drop in the F peak.

  2. Self-consistent Powerful Radio-wave Absorption by Artificial Ionosphere Turbulence

    Science.gov (United States)

    Kochetov, Andrey; Menkova, Uliya; Grach, Savely

    The numerical simulations of non-linear Schrodinger equation in inhomogeneous plasma layer with pumping and damping are carried out to investigate the influence of self-consistent incident powerful electromagnetic wave absorption in the regions of plasma turbulence excitation to reflection index dynamics. The damping of electromagnetic wave is taking into account by including in the set of equations (Kochetov A.V., Mironov V. A., Terina G.I., Strong Turbulence Effects in Artificially Disturbed Ionosphere, Adv. Space.Res. 2002,vol.29, No.9, p.1369) imaginary part of plasma dielectric permitivity in the vicinity of wave reflection point in the regions with strong electromagnetic field. The large range of damping parameters: threshold, decrement; different amplitude dependence, including hysteretic one, is studied, in particular, in correlation to (V. D. Shapiro, V. I. Shevchenko, Handbook of Plasma Physics, Eds. A. A. Galeev, R N. Sudan, Elsevier, 1984, vol.2, p.119). It is obtained for some regimes that the calculated reflection index dynamics agrees qualitatively to the experimental results (B. Thide, E. N. Sergeev, S. M. Grach,T. B. Leyser, T. D. Carrozi, Competition between Langmuir and upper hybrid turbulence in an HF pumped ionosphere, Phys. Rev. Lett., 2005, vol. 95, no.25, p. 255002). The work is supported in part by Russian Foundation for Basic Research by the grant No. 06-02-17334.

  3. A new global model for the ionospheric F2 peak height for radio wave propagation

    Directory of Open Access Journals (Sweden)

    M. M. Hoque

    2012-05-01

    Full Text Available The F2-layer peak density height hmF2 is one of the most important ionospheric parameters characterizing HF propagation conditions. Therefore, the ability to model and predict the spatial and temporal variations of the peak electron density height is of great use for both ionospheric research and radio frequency planning and operation. For global hmF2 modelling we present a nonlinear model approach with 13 model coefficients and a few empirically fixed parameters. The model approach describes the temporal and spatial dependencies of hmF2 on global scale. For determining the 13 model coefficients, we apply this model approach to a large quantity of global hmF2 observational data obtained from GNSS radio occultation measurements onboard CHAMP, GRACE and COSMIC satellites and data from 69 worldwide ionosonde stations. We have found that the model fits to these input data with the same root mean squared (RMS and standard deviations of 10%. In comparison with the electron density NeQuick model, the proposed Neustrelitz global hmF2 model (Neustrelitz Peak Height Model – NPHM shows percentage RMS deviations of about 13% and 12% from the observational data during high and low solar activity conditions, respectively, whereas the corresponding deviations for the NeQuick model are found 18% and 16%, respectively.

  4. Ionospheric plasma disturbances generated by naturally occurring large-scale anomalous heat sources

    Science.gov (United States)

    Pradipta, Rezy; Lee, Min-Chang; Coster, Anthea J.; Tepley, Craig A.; Sulzer, Michael P.; Gonzalez, Sixto A.

    2017-04-01

    We report the findings from our investigation on the possibility of large-scale anomalous thermal gradients to generate acoustic-gravity waves (AGWs) and traveling ionospheric disturbances (TIDs). In particular, here we consider the case of summer 2006 North American heat wave event as a concrete example of such large-scale natural thermal gradients. This special scenario of AGW/TID generation was formulated based on the results of our experiments at the Arecibo Observatory in July 2006, followed by a systematic monitoring/surveillance of total electron content (TEC) fluctuations over North America in 2005-2007 using the MIT Haystack Observatory's Madrigal database. The data from our Arecibo experiments indicate a continual occurrence of intense AGW/TID over the Caribbean on 21-24 July 2006, and the Madrigal TEC data analysis shows that the overall level of TID activity over North America had increased by ∼0.2 TECU during the summer 2006 heat wave event. Our proposed scenario is in agreement with these empirical observations, and is generally consistent with a number of past ionospheric HF heating experiments related to AGW/TID generation.

  5. A new global model for the ionospheric F2 peak height for radio wave propagation

    Directory of Open Access Journals (Sweden)

    M. M. Hoque

    2012-05-01

    Full Text Available The F2-layer peak density height hmF2 is one of the most important ionospheric parameters characterizing HF propagation conditions. Therefore, the ability to model and predict the spatial and temporal variations of the peak electron density height is of great use for both ionospheric research and radio frequency planning and operation. For global hmF2 modelling we present a nonlinear model approach with 13 model coefficients and a few empirically fixed parameters. The model approach describes the temporal and spatial dependencies of hmF2 on global scale. For determining the 13 model coefficients, we apply this model approach to a large quantity of global hmF2 observational data obtained from GNSS radio occultation measurements onboard CHAMP, GRACE and COSMIC satellites and data from 69 worldwide ionosonde stations. We have found that the model fits to these input data with the same root mean squared (RMS and standard deviations of 10%. In comparison with the electron density NeQuick model, the proposed Neustrelitz global hmF2 model (Neustrelitz Peak Height Model – NPHM shows percentage RMS deviations of about 13% and 12% from the observational data during high and low solar activity conditions, respectively, whereas the corresponding deviations for the NeQuick model are found 18% and 16%, respectively.

  6. HF radar and drifter observing system in the Adriatic for fishery management and security

    DEFF Research Database (Denmark)

    Corgnati, Lorenzo; Carlson, Daniel Frazier; Mantovani, Carlo

    2014-01-01

    A HF radar system has been operating since May 2013 in the Southern Adriatic between the Gargano Cape and the Manfredonia Gulf. The system, that has been tested and complemented with drifter launchings during three experiments, produces maps of surface ocean velocities at 2 km resolution every hour....... These data support fishery management as well as search and rescue and pollution mitigation operations. The Manfredonia Gulf is a known nursery area for small pelagic fish (anchovies and sardines), and its dynamics and connectivity properties are very relevant to the study of population dynamics. HF radar...

  7. A modification to the standard ionospheric correction method used in GPS radio occultation

    Directory of Open Access Journals (Sweden)

    S. B. Healy

    2015-08-01

    Full Text Available A modification to the standard bending-angle correction used in GPS radio occultation (GPS-RO is proposed. The modified approach should reduce systematic residual ionospheric errors in GPS radio occultation climatologies. A new second-order term is introduced in order to account for a known source of systematic error, which is generally neglected. The new term has the form κ(a × (αL1(a-αL2(a2, where a is the impact parameter and (αL1, αL2 are the L1 and L2 bending angles, respectively. The variable κ is a weak function of the impact parameter, a, but it does depend on a priori ionospheric information. The theoretical basis of the new term is examined. The sensitivity of κ to the assumed ionospheric parameters is investigated in one-dimensional simulations, and it is shown that κ ≃ 10–20 rad−1. We note that the current implicit assumption is κ=0, and this is probably adequate for numerical weather prediction applications. However, the uncertainty in κ should be included in the uncertainty estimates for the geophysical climatologies produced from GPS-RO measurements. The limitations of the new ionospheric correction when applied to CHAMP (Challenging Minisatellite Payload measurements are noted. These arise because of the assumption that the refractive index is unity at the satellite, made when deriving bending angles from the Doppler shift values.

  8. Investigating the effect of geomagnetic storm and equatorial electrojet on equatorial ionospheric irregularity over East African sector

    Science.gov (United States)

    Seba, Ephrem Beshir; Nigussie, Melessew

    2016-11-01

    . It is also found that prolonged eastward undershielding electric field during the daytime intensified the daytime EEJ magnitude and resulted in strong post-sunset scintillations. We have also observed that the rate of change of BZ (i.e. electric field produced by Faraday's Induction law) and eastward IEFy around the PRE hour is nicely correlated with strong post-sunset scintillations. Moreover, discussions about the causes for the appearance and disappearance of ionospheric scintillation are presented in this paper.

  9. A reassessment of the PRIMO recommendations for adjustments to mid-latitude ionospheric models

    Science.gov (United States)

    David, M.; Sojka, J. J.; Schunk, R. W.

    2012-12-01

    In the late 1990s, in response to the realization that ionospheric physical models tended to underestimate the dayside peak F-region electron density (NmF2) by about a factor of 2, a group of modelers convened to find out why. The project was dubbed PRIMO, standing for Problems Relating to Ionospheric Models and Observations. Five ionospheric models were employed in the original study, including the Utah State University Time Dependent Ionospheric Model (TDIM), which is the focus of the present study. No physics-based explanation was put forward for the models' shortcomings, but there was a recommendation that three adjustments be made within the models: 1) The inclusion of a Burnside factor of 1.7 for the diffusion coefficients; 2) that the branching ratio of O+ be changed from 0.38 to 0.25; and 3) that the dayside ion production rates be scaled upward to account for ionization by secondary photons. The PRIMO recommendations were dutifully included in our TDIM model at Utah State University, though as time went on, and particularly while modeling the ionosphere during the International Polar Year (2007), it became clear that the PRIMO adjustments sometimes caused the model to produce excessively high dayside electron densities. As the original PRIMO study [Anderson et al, 1998] was based upon model/observation comparison over a very limited set of observations from just one station (Millstone Hill, Massachusetts), we have expanded the range of the study, taking advantage of resources that were not available 12 years ago, most notably the NGDC SPIDR Internet data base, and faster computers for running large numbers of simulations with the TDIM model. We look at ionosonde measurements of the peak dayside electron densities at mid-latitudes around the world, across the full range of seasons and solar cycles, as well as levels of geomagnetic activity, in order to determine at which times the PRIMO adjustments should be included in the model, and when it is best not to

  10. 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.

  11. Evaluation of COMPASS ionospheric model in GNSS positioning

    Science.gov (United States)

    Wu, Xiaoli; Hu, Xiaogong; Wang, Gang; Zhong, Huijuan; Tang, Chengpan

    2013-03-01

    As important products of GNSS navigation message, ionospheric delay model parameters are broadcasted for single-frequency users to improve their positioning accuracy. GPS provides daily Klobuchar ionospheric model parameters based on geomagnetic reference frame, while the regional satellite navigation system of China's COMPASS broadcasts an eight-parameter ionospheric model, COMPASS Ionospheric Model(CIM), which was generated by processing data from continuous monitoring stations, with updating the parameters every 2 h. To evaluate its performance, CIM predictions are compared to ionospheric delay measurements, along with GPS positioning accuracy comparisons. Real observed data analysis indicates that CIM provides higher correction precision in middle-latitude regions, but relatively lower correction precision for low-latitude regions where the ionosphere has much higher variability. CIM errors for some users show a common bias for in-coming COMPASS signals from different satellites, and hence ionospheric model errors are somehow translated into the receivers' clock error estimation. In addition, the CIM from the China regional monitoring network are further evaluated for global ionospheric corrections. Results show that in the Northern Hemisphere areas including Asia, Europe and North America, the three-dimensional positioning accuracy using the CIM for ionospheric delay corrections is improved by 7.8%-35.3% when compared to GPS single-frequency positioning ionospheric delay corrections using the Klobuchar model. However, the positioning accuracy in the Southern Hemisphere is degraded due apparently to the lack of monitoring stations there.

  12. High-latitude F region large-scale ionospheric irregularities under different solar wind and zenith angle conditions

    Science.gov (United States)

    Lukianova, R. Yu.; Uvarov, V. M.; Coïsson, P.

    2017-01-01

    A numerical model is used to study systematically the evolution of large scale irregularities depending on the IMF Bz and By components, solar zenith angle (seasonal and daily variation), solar and geomagnetic activity. The model enables to reproduce the 3-D distribution of electron density over the high-latitude F region ionosphere in the altitude range between 130 and 640 km. Since the convection electric field driven by changes in solar wind conditions has an important effect on the high-latitude ionosphere, the rotation of the IMF vector in the Y-Z plane causes a significant redistribution of the ionospheric plasma. Under the southward IMF conditions the plasma density is enhanced over a large portion of the near-pole ionosphere as a tongue of ionization, while the northward IMF leads to a considerable depletion and occurrence of the polar hole. The IMF By polarity is crucial for the shift and extension of the tongue of ionization to the dusk or dawn side. Particle precipitation also plays a role through a localized increase of the electron density mostly within the auroral oval and more pronounced auroral peak. The solar zenith angle, especially its seasonal variation, is the strongest regular factor influencing the electron density magnitude and spatial distribution. In winter, when the polar ionosphere is in darkness, large variations associated with different solar wind condition are more prominent. The daily variation of the zenith angle considerably modifies the Ne within a particular pattern. At a given time, the combined action of the IMF, solar zenith angle, level of solar and geomagnetic activity produces a complicated ionospheric response which can be considered as a superposition of different effects. Quantitative estimates of the ionospheric response to each factor are presented.

  13. Refinement of the supercontinent cycle with Hf, Nd and Sr isotopes

    Directory of Open Access Journals (Sweden)

    Kent C. Condie

    2013-11-01

    External and internal orogens show similar patterns in ɛNd and ɛHf with age suggesting that both juvenile and reworked crustal components are produced in both types of orogens with similar proportions. However, both types of orogens clearly produce more juvenile isotopic signatures in retreating mode than in advancing mode. Many secular changes in ɛHf and ɛNd distributions correlate with the supercontinent cycle. Although supercontinent breakup is correlated with short-lived decreasing ɛHf and ɛNd (≤100 Myr for most supercontinents, there is no isotopic evidence for the breakup of the Paleoproterozoic supercontinent Nuna. Assembly of supercontinents by extroversion is recorded by decreasing ɛNd in granitoids and metasediments and decreasing ɛHf in zircons, attesting to the role of crustal reworking in external orogens in advancing mode. As expected, seawater Sr isotopes increase and seawater Nd isotopes decrease during supercontinent assembly by extroversion. Pangea is the only supercontinent that has a clear isotopic record of introversion assembly, during which median ɛNd and ɛHf rise rapidly for ≤100 Myr. Although expected to increase, radiogenic seawater Sr decreases (and seawater Nd increases during assembly of Pangea, a feature that may be caused by juvenile input into the oceans from new ocean ridges and external orogens in retreating mode. The fact that a probable onset of plate tectonics around 3 Ga is not recorded in isotopic distributions may be due the existence of widespread felsic crust formed prior to the onset of plate tectonics in a stagnant lid tectonic regime, as supported by Nd and Hf model ages.

  14. Optimization of $^{178m2}$/Hf isomer production in spallation reactions at projectile energies up to 100 MeV using STAPRE and ALICE code simulations

    CERN Document Server

    Kirischuk, V I; Khomenkov, V P; Strilchuk, N V; Zheltonozhskij, V A

    2004-01-01

    /sup 178m2/Hf isomer production in different spallation reactions with protons, alpha particles and neutrons at projectile energies up to 100 MeV has been analyzed using both STAPRE and ALICE code simulations. The STAPRE code was used to calculate the isomeric ratios, while the ALICE code was used to simulate the excitation functions of the respective ground states. A number of spallation reactions have been compared taking into account not only /sup 178m2 /Hf isomer productivity but also, first, the isomeric ratios calculated by the STAPRE code; second, the accumulation of the most undesirable Hf isotopes and isomers, such as /sup 172/Hf, /sup 175 /Hf, and /sup 179m/Hf; and, third, the production of other admixtures and by-products that could degrade the quality of the produced /sup 178m2/Hf isomer sources, including all stable Hf isotopes as well. Possibilities and ways of optimizing /sup 178m2/Hf isomer production in spallation reactions at projectile energies up to 100 MeV are discussed. This can be consi...

  15. Comparison of HfCl{sub 4}, HfI{sub 4}, TEMA-Hf, and TDMA-Hf as precursors in early growing stages of HfO{sub 2} films deposited by ALD: A DFT study

    Energy Technology Data Exchange (ETDEWEB)

    Cortez-Valadez, M. [Departamento de Investigación en Física, Universidad de Sonora, Apdo. Postal 5-88, 83190 Hermosillo, Son. (Mexico); Fierro, C.; Farias-Mancilla, J.R. [Instituto de Ingeniería y Tecnología, Departamento de Física y Matemáticas, Universidad Autónoma de Ciudad Juárez, Av. del Charro 450, Cd. Juárez C.P. 32310, Chihuahua (Mexico); Vargas-Ortiz, A. [Universidad Autónoma de Sinaloa, Facultad de Ingeniería Mochis, Ciudad Universitaria, C.P. 81223 Los Mochis, Sinaloa (Mexico); Flores-Acosta, M. [Departamento de Investigación en Física, Universidad de Sonora, Apdo. Postal 5-88, 83190 Hermosillo, Son. (Mexico); Ramírez-Bon, R. [Centro de Investigación y Estudios Avanzados del IPN, Unidad Querétaro, Apdo. Postal 1-798, 76001 Querétaro, Qro. (Mexico); Enriquez-Carrejo, J.L. [Instituto de Ingeniería y Tecnología, Departamento de Física y Matemáticas, Universidad Autónoma de Ciudad Juárez, Av. del Charro 450, Cd. Juárez C.P. 32310, Chihuahua (Mexico); and others

    2016-06-15

    Highlights: • Hafnium oxide growth on Si(100) by atomic layer deposition was simulated. • The interface structure was considered as silicate and silicide. • The interface was studied employing DFT. • TDMA-Hf precursor show better interface stability. - Abstract: The final structure of HfO{sub 2} films grown by atomic layer deposition (ALD) after reaction with OH{sup −} ions has been analyzed by DFT (density functional theory). The interaction of the precursors: HfCl{sub 4} (hafnium tetrachloride), HfI{sub 4} (hafnium tetraiodide), TEMA-Hf (tetrakis-ethylmethylamino hafnium), and TDMA-Hf (tetrakis-dimethylamino hafnium) with HO–H was studied employing the B3LYP (Becke 3-parameter, Lee–Yang–Parr) hybrid functional and the PBE (Perdew–Burke–Ernzerhof) generalized gradient functional. The structural evolution at the Si(100) surface has been analyzed by LDA (local density approximation). The structural parameters: bond length and bond angle, and the vibrational parameters for the optimized structures are also reported. The presence of hafnium silicate at the interface was detected. The infrared spectra and structural parameters obtained in this work agree with previously reported experimental results.

  16. REMPI Spectroscopy of HfF

    CERN Document Server

    Loh, Huanqian; Yahn, Tyler S; Looser, Herbert; Field, Robert W; Cornell, Eric A

    2012-01-01

    The spectrum of electronic states at 30000--33000 cm$^{-1}$ in hafnium fluoride has been studied using (1+1) resonance-enhanced multi-photon ionization (REMPI) and (1+1$'$) REMPI. Six $\\Omega' = 3/2$ and ten $\\Pi_{1/2}$ vibronic bands have been characterized. We report the molecular constants for these bands and estimate the electronic energies of the excited states using a correction derived from the observed isotope shifts. When either of two closely spaced $\\Pi_{1/2}$ electronic states is used as an intermediate state to access autoionizing Rydberg levels, qualitatively distinct autoionization spectra are observed. The intermediate state-specificity of the autoionization spectra bodes well for the possibility of using a selected $\\Pi_{1/2}$ state as an intermediate state to create ionic HfF$^+$ in various selected quantum states, an important requirement for our electron electric dipole moment (eEDM) search in HfF$^+$.

  17. Effects of a “day-time” substorm on the ionosphere and radio propagation

    Science.gov (United States)

    Blagoveshchensky, D.; Kalishin, A.; MacDougall, J.

    2009-11-01

    Propagation mechanisms of lateral (non-great-circle) signals on a high-latitude HF radio path during magnetospheric substorms that occurred in the day-time have been considered. The path is equipped with oblique ionospheric sounding (OIS) from Murmansk to St. Petersburg. The OIS method gives the possibility to determine propagation modes, MOF (maximum observed frequency) values, signal delays, etc. Data of the CUTLASS radar, the IMAGE magnetometer system, the Finnish riometer chain, and the Tromso ionosonde were also used for the analysis. The main results are the following: (1) the lateral signal propagation takes place, as a rule, if the path midpoint is located near the irregularity region that moves sharply from high to low latitudes. The lateral signal propagation appearing during day-time is a new effect. (2) Formation of dense field-aligned irregularities during a substorm leads to decreasing F2MOF values on radio paths. These results can be useful for problems of radiolocation, HF communications and navigation.

  18. Modulational excitation of inhomogeneities in dusty ionospheric plasma

    Science.gov (United States)

    Kopnin, S. I.; Popel, S. I.; Morozova, T. I.

    2015-02-01

    The mechanism for the formation of inhomogeneities of the electron and ion densities in dusty ionospheric plasma as a result of the modulational instability of a pump electromagnetic wave caused by the excitation of dust acoustic perturbations is considered. The inhomogeneities of the electron density produced by the monochromatic radiation of heating facilities at altitudes of 80 and 100 km are estimated numerically. The possibility of excitation of relatively large inhomogeneities of the electron and ion densities δ n e( i)/ n e( i) ≈ 0.05 at altitudes of 80-100 km as a result of modulational interaction is demonstrated. The applicability domains of the method presented in this work are determined.

  19. An explanation of trans-ionospheric pulse pairs

    CERN Document Server

    Wu, H -C

    2016-01-01

    Trans-ionospheric pulse pairs are the most powerful natural radio signals on the Earth and associated with lightning. They have been discovered for two decades by satellites, but their origin still remains elusive. Here we attribute these radio signals to relativistic electrons produced by cloud-to-ground lightning. When these electrons strike the ground, radio bursts are emitted towards space in a narrow cone. This model naturally explains the interval, duration, polarization, coherence and bimodal feature of the pulse pairs. Based on electron parameters inferred from x-ray observation of lightning, the calculated signal intensity agrees with the measurement of satellites. Our results are useful to develop global warning system of storms and hurricane based on GPS satellites.

  20. RFID UHF i HF w bibliotekach

    Directory of Open Access Journals (Sweden)

    Gładysz Bartłomiej

    2015-06-01

    Full Text Available The potential of the innovative Radio Frequency Identification (RFID technology to be applied for support, acceleration and automation of the circulation process of library collection is presented. Technology basics, and hardware and software components are described. Two different radio standards used in libraries are compared. The goal is to present the potential of RFID technology for libraries, to highlight the differences and to build a basis for further consideration of UHF and HF alternatives.

  1. A non-tomographic method for imaging the global ionospheric electron density

    Science.gov (United States)

    Brunini, C.; Meza, A.; Azpilicueta, F.; Schmidt, M.; Nava, B.; Coïson, P.; Radicella, S.

    There are today a variety of approaches for processing dual-frequency GPS observations and to produce global ionospheric maps of TEC. The majority of these researches use ground-based GPS observations from the worldwide tracking network of the International GPS Service. While ground-based ionospheric maps represent a big advance for ionosphere weather, the radial geometry of the ground-based observations limits their capability for providing information on the vertical electron distribution. This limitation can be removed by the introduction of horizontal cuts through the ionosphere, affordable by space-born GPS receivers flying on low-Earth orbiting satellites (e.g. GPS-Met, CHAMP, GRACE, SAC-C). Several empirical models are currently used to describe the electron density distribution in the ionosphere. Among them, the NeQuick model is being used by the ESA EGNOS project for assessment analysis and has been proposed for single-frequency operation in the Galileo project. NeQuick is mostly droved by the two parameters NmF2 and hmF2, whose values are usually computed as function of position and time, using the CCIR climatologic database. Since the CCIR provides monthly averaged values, so significant day-to-day deviations between the actual and predicted TEC can be expected. Therefore, it seems suitable to determine appropriate corrections for the CCIR values in order to better fit the observed TEC. In this contribution we present a non-tomographic method for 3-D imaging of the global electron density distribution that uses the NeQuick model and two-dimensional spherical wavelet expansions for representing the spatial variability of the driving parameters of NeQuick. The coefficients of the wavelet series are computable from TEC observations using parameter estimation methods.

  2. Ionospheric electron density perturbations during the 7-10 March 2012 geomagnetic storm period

    Science.gov (United States)

    Belehaki, Anna; Kutiev, Ivan; Marinov, Pencho; Tsagouri, Ioanna; Koutroumbas, Kostas; Elias, Panagiotis

    2017-02-01

    From 7 to 10 March 2012 a series of magnetospheric disturbances caused perturbations in the ionospheric electron density. Analyzing the interplanetary causes in each phase of this disturbed period, in comparison with the total electron content (TEC) disturbances, we have concluded that the interplanetary solar wind controls largely the ionospheric response. An interplanetary shock detected at 0328UT on 7 March caused the formation of prompt penetrating electric fields in the dayside that transported plasma from the near-equatorial region to higher in attitudes and latitudes forming a giant plasma fountain which is part of the so-called dayside ionospheric super-fountain. The super-fountain produces an increase in TEC which is the dominant effect at middle latitude, masking the effect of the negative storm. Simultaneously, inspecting the TEC maps, we found evidence for a turbulence in TEC propagating southward probably caused by large scale travelling ionospheric disturbances (LSTIDs) linked to auroral electrojet intensification. On 8 March, a magnetospheric sudden impulse at 1130UT accompanied with strong pulsations in all interplanetary magnetic field (IMF) components and with northward Bz component during the growth phase of the storm. These conditions triggered a pronounced directly driven substorm phase during which we observe LSTID. However, the analysis of DMSP satellite observations, provided with strong evidence for Sub-Auroral Polarization Streams (SAPS) formation that erode travelling ionospheric disturbances (TID) signatures. The overall result of these mechanisms can be detected in maps of de-trended TEC, but it is difficult to identify separately each of the sources of the observed perturbations, i.e. auroral electrojet activity and LSTIDs, super-fountain and SAPS. In order to assess the capability of the ionospheric profiler called Topside Sounder Model - assisted Digisonde (TaD model) to detect such perturbations in the electron density, electron

  3. The stabilizing effect of collision-induced velocity shear on the ionospheric feedback instability in Earth's magnetosphere

    Science.gov (United States)

    Sydorenko, D.; Rankin, R.

    2017-07-01

    The feedback instability in the ionospheric Alfvén resonator in Earth's magnetosphere is examined using a two-dimensional multifluid numerical model of coupled ionosphere and magnetosphere. Two simulation configurations are used to demonstrate that the instability occurs under an assumption that is unrealistic for Earth's ionosphere. In the first configuration, a flat sheet height-integrated conducting boundary replaces the ionospheric E layer. In the second configuration, plasma dynamics in a simplified E layer is resolved ignoring ion production, loss, and diffusion. For the same parameters (plasma and neutral density profiles and convection electric field), the instability develops only with the flat sheet boundary. When the E layer is resolved, the variation of ion-neutral collision frequencies with altitude produces vertical shear in the horizontal ion flow velocity. The shear prevents density perturbations from remaining field aligned, causing them to decay rather than grow. It is suggested that the instability cannot occur in Earth's ionosphere because ion-neutral collision frequencies always have a significant variation with altitude through the E layer.

  4. 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.

  5. Ionospheric responses during equinox and solstice periods over Turkey

    Science.gov (United States)

    Karatay, Secil; Cinar, Ali; Arikan, Feza

    2017-11-01

    Ionospheric electron density is the determining variable for investigation of the spatial and temporal variations in the ionosphere. Total Electron Content (TEC) is the integral of the electron density along a ray path that indicates the total variability through the ionosphere. Global Positioning System (GPS) recordings can be utilized to estimate the TEC, thus GPS proves itself as a useful tool in monitoring the total variability of electron distribution within the ionosphere. This study focuses on the analysis of the variations of ionosphere over Turkey that can be grouped into anomalies during equinox and solstice periods using TEC estimates obtained by a regional GPS network. It is observed that noon time depletions in TEC distributions predominantly occur in winter for minimum Sun Spots Numbers (SSN) in the central regions of Turkey which also exhibit high variability due to midlatitude winter anomaly. TEC values and ionospheric variations at solstice periods demonstrate significant enhancements compared to those at equinox periods.

  6. Effects of solar eclipse on the electrodynamical processes of the equatorial ionosphere: a case study during 11 August 1999 dusk time total solar eclipse over India

    Directory of Open Access Journals (Sweden)

    R. Sridharan

    Full Text Available The effects on the electrodynamics of the equatorial E- and F-regions of the ionosphere, due to the occurrence of the solar eclipse during sunset hours on 11 August 1999, were investigated in a unique observational campaign involving ground based ionosondes, VHF and HF radars from the equatorial location of Trivandrum (8.5° N; 77° E; dip lat. 0.5° N, India. The study revealed the nature of changes brought about by the eclipse in the evening time E- and F-regions in terms of (i the sudden intensification of a weak blanketing ES-layer and the associated large enhancement of the VHF backscattered returns, (ii significant increase in h' F immediately following the eclipse and (iii distinctly different spatial and temporal structures in the spread-F irregularity drift velocities as observed by the HF radar. The significantly large enhancement of the backscattered returns from the E-region coincident with the onset of the eclipse is attributed to the generation of steep electron density gradients associated with the blanketing ES , possibly triggered by the eclipse phenomena. The increase in F-region base height immediately after the eclipse is explained as due to the reduction in the conductivity of the conjugate E-region in the path of totality connected to the F-region over the equator along the magnetic field lines, and this, with the peculiar local and regional conditions, seems to have reduced the E-region loading of the F-region dynamo, resulting in a larger post sunset F-region height (h' F rise. These aspects of E-and F-region behaviour on the eclipse day are discussed in relation to those observed on the control day.

    Key words. Ionosphere (electric fields and currents; equatorial ionosphere; ionospheric irregularities

  7. Ionospheric scintillation in Brazil: Analyses and Effects on GNSS Positioning

    Science.gov (United States)

    Alves, D. B.; Souza, J. S.; Silva, H. D.

    2013-05-01

    Ionosphere has a great influence on GNSS (Global Navigation Satellite System) signals and its behavior depends on several variables: local time, geographic location, seasons and solar activity. Besides, there are ionospheric irregularities that also affect the GNSS signal propagation, as the ionospheric scintillation. The ionospheric scintillation can be described as a fast change in phase and amplitude of GNSS signal, caused by irregularities of electron density. Scintillation can degrade or cause the GNSS signal lost. Due to these described factors, one can say that the ionosphere can cause important effects on GNSS positioning. It can degrade the coordinate accuracy obtained by GNSS positioning methods. In this paper the goal is to evaluate the ionospheric effect, in special the ionospheric scintillation in different regions of Brazil, and its effects on GNSS Point Positioning. In order to evaluate the days where the scintillation was more significant it is used a database (http://200.145.185.118/cigala/index.php) from CIGALA (Concept for Ionospheric Scintillation Mitigation for Professional GNSS in Latin America) project (http://cigala.galileoic.org/). Using these data it is possible to obtain information about ionospheric scintillation in different GNSS stations in Brazil. It is possible to correlate the data according to time, season and other factors that can contribute to scintillation analysis. In 2013 must occur an intense solar activity, which can intensify the ionospheric effects, and consequently ionospheric scintillation, mainly in Brazil region, where the scintillation index is already intense. Preliminary evaluations, showed larger values of S4 (scintillation index) in Brazil. For example, in October 2012, it was obtained S4 values larger than 1 in several epochs. This causes severe effects in GNSS Positioning. In this paper, the results of GNSS positioning under ionosphere scintillation effects in different regions of Brazil will be presented.

  8. 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)

  9. Waterhole - An auroral-ionosphere perturbation experiment

    Science.gov (United States)

    Whalen, B. A.; Yau, A. W.; Creutzberg, F.; Pongratz, M. B.

    Preliminary results of the effect of the detonation of 100 kg of high explosives into the field lines of an auroral arc are presented. The payload was rocket-borne to an altitude of 300 km, and caused a depletion of the local ionospheric F region. The explosives were a mixture of the nitromethane and ammonium nitrate, and were housed in the front of the rocket while an instrument package trailed behind. The launch vehicle was a Black Brant X, and created an expanding cloud 40 km in diam. For 130 sec, a hole was cut in the electron precipitation field, and energetic electron precipitation in the hole dropped to background levels. The luminosity of the auroral arc observed by a ground-based scanning photometer decreased by a factor of two, and the ionospheric E region density below the hole decayed at a rate implying a reduction in particle precipitation.

  10. Dynamic interactions between ionospheric plasma and spacecraft

    Science.gov (United States)

    Snyder, David B.

    1995-01-01

    Studies of the interactions between the Space Station Freedom and ionospheric plasma led to an improved understanding of the dynamics of these interactions. Some of the issues related to developing and sustaining arcs in ionospheric conditions are considered. A technique for the estimation of the amplitude and duration of arcs is presented. The technique uses the capacitance of the system to estimate the peak current and then uses the charge stored to estimate the arc duration. As new technologies are implemented on spacecraft, new environmental compatibility issues will arise. Some of the issues related to driving dielectric surfaces with alternating current voltages are considered. The steady state charging criteria is that over an oscillation, the ion charge collected is compensated for by the electron charge collected. This tends to drive the average potential negative so that the dielectric surface is positive for only a small portion of the cycle.

  11. Investigation of ionospheric irregularities by radio holography

    Science.gov (United States)

    Tereshchenko, E. D.; Popov, A. A.; Tereshchenko, A. D.; Khudukon, B. Z.

    Methodological aspects of the design of a radio-holography experiment for the investigation of ionospheric irregularities are considered on the basis of a theoretical examination of the formation of a diffraction field by two coherent satellite signals. The equipment needed to implement such an experiment is described, and results of first observations performed at high latitudes (in the Murmansk region) on February 8, 1978 are examined.

  12. The ionospheric refraction at 38 MHz.

    Science.gov (United States)

    Milogradov-Turin, J.

    The investigation of the observed shift of the North Polar Spur (NPS) at the 38 MHz survey of Milogradov-Turin and Smith (1973) in respect to the position of the NPS on the survey at 408 MHz convolved to the same resolution (Haslam and Salter 1977) has shown that there is no dependence of the NPS position on frequency and that the ionospheric refraction should be larger than believed.

  13. 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.

  14. Ionospheric wave and irregularity measurements using passive radio astronomy techniques

    Science.gov (United States)

    Erickson, W. C.; Mahoney, M. J.; Jacobson, A. R.; Knowles, S. H.

    1988-01-01

    The observation of midlatitude structures using passive radio astronomy techniques is discussed, with particular attention being given to the low-frequency radio telescope at the Clark Lake Radio Observatory. The present telescope operates in the 10-125-MHz frequency range. Observations of the ionosphere at separations of a few kilometers to a few hundreds of kilometers by the lines of sight to sources are possible, allowing the determination of the amplitude, wavelength, direction of propagation, and propagation speed of ionospheric waves. Data are considered on large-scale ionospheric gradients and the two-dimensional shapes and sizes of ionospheric irregularities.

  15. 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

  16. International Reference Ionosphere 2016: From ionospheric climate to real-time weather predictions

    Science.gov (United States)

    Bilitza, D.; Altadill, D.; Truhlik, V.; Shubin, V.; Galkin, I.; Reinisch, B.; Huang, X.

    2017-02-01

    The paper presents the latest version of the International Reference Ionosphere model (IRI-2016) describing the most important changes and improvements that were included with this version and discussing their impact on the IRI predictions of ionospheric parameters. IRI-2016 includes two new model options for the F2 peak height hmF2 and a better representation of topside ion densities at very low and high solar activities. In addition, a number of smaller changes were made concerning the use of solar indices and the speedup of the computer program. We also review the latest developments toward a Real-Time IRI. The goal is to progress from predicting climatology to describing the real-time weather conditions in the ionosphere.

  17. Formation of ionospheric irregularities over Southeast Asia during the 2015 St. Patrick's Day storm

    National Research Council Canada - National Science Library

    Spogli, Luca; Cesaroni, Claudio; Di Mauro, Domenico; Pezzopane, Michael; Alfonsi, Lucilla; Musicò, Elvira; Povero, Gabriella; Pini, Marco; Dovis, Fabio; Romero, Rodrigo; Linty, Nicola; Abadi, Prayitno; Nuraeni, Fitri; Husin, Asnawi; Le Huy, Minh; Lan, Tran Thi; La, The Vinh; Pillat, Valdir Gil; Floury, Nicolas

    2016-01-01

    ...), covering a wide longitudinal sector of the low‐latitude ionosphere. A regional characterization of the storm is provided, identifying the peculiarities of ionospheric irregularity formation...

  18. Equinoctial transitions in the ionosphere and thermosphere

    Directory of Open Access Journals (Sweden)

    A. V. Mikhailov

    2001-07-01

    Full Text Available Equinoctial summer/winter transitions in the parameters of the F2-region are analyzed using ground-based ionosonde and incoherent scatter observations. Average transition from one type of diurnal NmF2 variation to another takes 20–25 days, but cases of very fast (6–10 days transitions are observed as well. Strong day-time NmF2 deviations of both signs from the monthly median, not related to geomagnetic activity, are revealed for the transition periods. Both longitudinal and latitudinal variations take place for the amplitude of such quiet time NmF2 deviations. The summer-type diurnal NmF2 variation during the transition period is characterized by decreased atomic oxygen concentration [O] and a small equatorward thermospheric wind compared to winter-type days with strong poleward wind and increased [O]. Molecular N2 and O2 concentrations remain practically unchanged in such day-to-day transitions. The main cause of the F2-layer variations during the transition periods is the change of atomic oxygen abundance in the thermosphere related to changes of global thermospheric circulation. A possible relationship with an equinoctial transition of atomic oxygen at the E-region heights is discussed.Key words. Atmospheric composition and structure (thermosphere – composition and chemistry – Ionosphere (ionosphere- atmosphere interactions; ionospheric disturbances

  19. The use of ionospheric tomography and elevation masks to reduce the overall error in single-frequency GPS timing applications

    Science.gov (United States)

    Rose, Julian A. R.; Tong, Jenna R.; Allain, Damien J.; Mitchell, Cathryn N.

    2011-01-01

    Signals from Global Positioning System (GPS) satellites at the horizon or at low elevations are often excluded from a GPS solution because they experience considerable ionospheric delays and multipath effects. Their exclusion can degrade the overall satellite geometry for the calculations, resulting in greater errors; an effect known as the Dilution of Precision (DOP). In contrast, signals from high elevation satellites experience less ionospheric delays and multipath effects. The aim is to find a balance in the choice of elevation mask, to reduce the propagation delays and multipath whilst maintaining good satellite geometry, and to use tomography to correct for the ionosphere and thus improve single-frequency GPS timing accuracy. GPS data, collected from a global network of dual-frequency GPS receivers, have been used to produce four GPS timing solutions, each with a different ionospheric compensation technique. One solution uses a 4D tomographic algorithm, Multi-Instrument Data Analysis System (MIDAS), to compensate for the ionospheric delay. Maps of ionospheric electron density are produced and used to correct the single-frequency pseudorange observations. This method is compared to a dual-frequency solution and two other single-frequency solutions: one does not include any ionospheric compensation and the other uses the broadcast Klobuchar model. Data from the solar maximum year 2002 and October 2003 have been investigated to display results when the ionospheric delays are large and variable. The study focuses on Europe and results are produced for the chosen test site, VILL (Villafranca, Spain). The effects of excluding all of the GPS satellites below various elevation masks, ranging from 5° to 40°, on timing solutions for fixed (static) and mobile (moving) situations are presented. The greatest timing accuracies when using the fixed GPS receiver technique are obtained by using a 40° mask, rather than a 5° mask. The mobile GPS timing solutions are most

  20. Hydrogen bond induced HF elimination from photoionized fluorophenol dimers in the gas phase.

    Science.gov (United States)

    Chatterjee, Piyali; Ghosh, Arup K; Chakraborty, Tapas

    2017-02-28

    In this paper, we report finding of a remarkable chemical effect of hydrogen bonding, elimination of hydrogen fluoride (HF) from the hydrogen bonded dimers of 2-fluorophenol (2-FP) and 3-fluorophenol (3-FP), in a supersonic jet expansion upon multi-photon ionization using 4th harmonic wavelength (266 nm) of a Q-switched Nd:YAG laser, and the reaction has been probed by time-of-flight mass spectrometry. No HF elimination is observed to occur by such means from the monomer of 3-FP, but it occurs with a small yield from the monomer of 2-FP. On the other hand, upon dimerization the reaction is triggered on for 3-FP, and for 2-FP it becomes so facile that no intact dimer cation survives and only the HF eliminated product ion appears in the mass spectra. Electronic structure calculation shows that in the cationic ground (D0) state, although the reaction for 2-FP dimer is exothermic, the associated barrier is significantly high (2.75 eV) and for its occurrence, absorption of three photons (2+1 type) is required. However, the reaction is predicted barrierless in the intermediate S1 state of this dimer, and HF loss dimer cation mass peak could appear in the mass spectrum due to an effective two-photon (1+1) ionization process. In the case of 3-FP dimer, the energy barriers both in S1 (neutral) and D0 (ionic) states are high, and it is suggested that for occurrence of HF elimination, dimer cation needs to absorb an additional photon. For facilitation of HF loss from this dimer cation, a rearrangement of the geometry and formation of an intermediate adduct have been suggested, and it is argued that the latter could be produced by nucleophilic attack of the neutral moiety at the ortho site of the cationic counterpart.

  1. Hydrogen bond induced HF elimination from photoionized fluorophenol dimers in the gas phase

    Science.gov (United States)

    Chatterjee, Piyali; Ghosh, Arup K.; Chakraborty, Tapas

    2017-02-01

    In this paper, we report finding of a remarkable chemical effect of hydrogen bonding, elimination of hydrogen fluoride (HF) from the hydrogen bonded dimers of 2-fluorophenol (2-FP) and 3-fluorophenol (3-FP), in a supersonic jet expansion upon multi-photon ionization using 4th harmonic wavelength (266 nm) of a Q-switched Nd:YAG laser, and the reaction has been probed by time-of-flight mass spectrometry. No HF elimination is observed to occur by such means from the monomer of 3-FP, but it occurs with a small yield from the monomer of 2-FP. On the other hand, upon dimerization the reaction is triggered on for 3-FP, and for 2-FP it becomes so facile that no intact dimer cation survives and only the HF eliminated product ion appears in the mass spectra. Electronic structure calculation shows that in the cationic ground (D0) state, although the reaction for 2-FP dimer is exothermic, the associated barrier is significantly high (2.75 eV) and for its occurrence, absorption of three photons (2+1 type) is required. However, the reaction is predicted barrierless in the intermediate S1 state of this dimer, and HF loss dimer cation mass peak could appear in the mass spectrum due to an effective two-photon (1+1) ionization process. In the case of 3-FP dimer, the energy barriers both in S1 (neutral) and D0 (ionic) states are high, and it is suggested that for occurrence of HF elimination, dimer cation needs to absorb an additional photon. For facilitation of HF loss from this dimer cation, a rearrangement of the geometry and formation of an intermediate adduct have been suggested, and it is argued that the latter could be produced by nucleophilic attack of the neutral moiety at the ortho site of the cationic counterpart.

  2. Elve Doublets: The Ionospheric Fingerprints of Compact Intracloud Discharges

    Science.gov (United States)

    da Silva, C. L.; Marshall, R. A.; Pasko, V. P.

    2015-12-01

    Compact intracloud discharges (CIDs) persist to date as one of the most mysterious lightning manifestations. CIDs are known to be the strongest natural sources of radio-frequency radiation on Earth. At VHF frequencies, approximately above 30 MHz, their emitted power is ten times stronger than that of other lightning processes. The well-known strength of CIDs in VHF contrasts with the lack of substantial optical measurements. CID's VLF/LF electric field change waveforms resemble one full cycle of a distorted sine function, with the first half-cycle being (a few times) larger-amplitude and shorter-duration than the second. For this reason CIDs have been dubbed narrow bipolar events (NBEs). NBE waveshapes are strikingly similar to the largest initial breakdown pulses (IBPs) that occur during the earlier stages of a conventional lightning flash, called classic IBPs. The similarity between classic IBP and NBE far-field waveforms, combined with the fact that positive-polarity NBEs frequently appear as the first event in an otherwise regular positive intracloud discharge, may be indicative that the source of these two E-field pulse types share the same physical mechanism inside thunderclouds [da Silva and Pasko, JGR, 120, 4989-5009, 2015]. In this presentation, we introduce a novel way to investigate CIDs. We show evidence that CIDs can produce an unique ionospheric signature, named "elve doublets". These signatures are characterized by a pair of elves separated in time by 80-160 microseconds. Our analysis combines fast photometric elve data, equivalent-transmission-line models to describe the dynamics of CID source currents, and FDTD modeling of electromagnetic wave propagation in the Earth-ionosphere waveguide accounting for its nonlinear interaction with the lower ionosphere [Marshall et al., GRL, 42, 2015, doi:10.1002/2015GL064862]. We show that typical (negative-polarity) CID altitudes, between 14-22 km, explain the time delay observed in elve doublets, where the

  3. Effect of incarcerated HF on the exohedral chemical reactivity of HF@C60.

    Science.gov (United States)

    Vidal, Sara; Izquierdo, Marta; Alom, Shamim; Garcia-Borràs, Marc; Filippone, Salvatore; Osuna, Sílvia; Solà, Miquel; Whitby, Richard J; Martín, Nazario

    2017-10-05

    The first chemical modification on the brand new endohedral HF@C60 is reported. In particular, the isomerization from optically pure (2S,5S)-cis-pyrrolidino[3,4:1,2][60]fullerene 2b to (2S,5R)-trans-pyrrolidino[3,4:1,2][60]fullerene 2b has been studied and compared with empty C60 (2a) and endohedral H2O@C60 (3). The comparative study shows a kinetic order for the isomerization process of H2O@C60 > HF@C60 > C60, thus confirming the effect of the incarcerated species on the zwitterionic intermediate stability.

  4. LU-HF Age and Isotope Systematics of ALH84001

    Science.gov (United States)

    Righter, M.; Lapen, T. J.; Brandon, A. D.; Beard, B. L.; Shafer, J. T.; Peslier, A. H.

    2009-01-01

    Allan Hills (ALH) 84001 is an orthopyroxenite that is unique among the Martian meteorites in having the oldest inferred crystallization age (approx..4.5 to 4.0 Gyr) [e.g., 1-6 and references therein 7]. Its ancient origin makes this stone a critical constraint on early history of Mars, in particular the evolution of different planetary crust and mantle reservoirs. However, because there is significant variability in reported crystallization ages, determination of initial isotope compositions is imprecise making assessment of planetary reservoirs difficult. Here we report a new Lu-Hf mineral isochron age, initial Hf-176/Hf-177 isotope composition, and inferred Martian mantle source compositions for ALH84001 that place constraints on longlived source reservoirs for the enriched shergottite suite of Martian meteorites including Shergotty, Zagami, NWA4468, NWA856, RBT04262, LAR06319, and Los Angeles. Sm-Nd isotope analyses are under way for the same mineral aliquots analyzed for Lu-Hf. The Lu-Hf system was utilized because Lu and Hf are both lithophile and refractory and are not easily redistributed during short-lived thermal pulses associated with shock metamorphism. Moreover, chromite has relatively modest Hf concentrations with very low Lu/Hf ratios [9] yielding tight constraints on initial Hf-176/Hf-177 isotope compositions

  5. A technique for accurately determining the cusp-region polar cap boundary using SuperDARN HF radar measurements

    Directory of Open Access Journals (Sweden)

    G. Chisham

    Full Text Available Accurately measuring the location and motion of the polar cap boundary (PCB in the high-latitude ionosphere can be crucial for studies concerned with the dynamics of the polar cap, e.g. the measurement of reconnection rates. The Doppler spectral width characteristics of backscatter received by the SuperDARN HF radars have been previously used for locating and tracking the PCB in the cusp region. The boundary is generally observed in meridional beams of the SuperDARN radars and appears as a distinct change between low spectral width values observed equatorward of the cusp region, and high, but variable spectral width values observed within the cusp region. To identify the spectral width boundary (SWB between these two regions, a simple algorithm employing a spectral width threshold has often been applied to the data. However, there is not, as yet, a standard algorithm, or spectral width threshold, which is universally applied. Nor has there been any rigorous assessment of the accuracy of this method of boundary determination. This study applies a series of threshold algorithms to a simulated cusp-region spectral width data set, to assess the accuracy of different algorithms. This shows that simple threshold algorithms correctly identify the boundary location in, at the most, 50% of the cases and that the average boundary error is at least ~ 1–2 range gates (~ 1° latitude. It transpires that spatial and temporal smoothing of the spectral width data (e.g. by median filtering, before application of a threshold algorithm can increase the boundary determination accuracy to over 95% and the average boundary error to much less than a range gate. However, this is sometimes at the cost of temporal resolution in the motion of the boundary location. The algorithms are also applied to a year’s worth of spectral width data from the cusp ionosphere, measured by the Halley SuperDARN radar in Antarctica. This analysis highlights the increased accuracy of

  6. A technique for accurately determining the cusp-region polar cap boundary using SuperDARN HF radar measurements

    Directory of Open Access Journals (Sweden)

    G. Chisham

    2003-04-01

    Full Text Available Accurately measuring the location and motion of the polar cap boundary (PCB in the high-latitude ionosphere can be crucial for studies concerned with the dynamics of the polar cap, e.g. the measurement of reconnection rates. The Doppler spectral width characteristics of backscatter received by the SuperDARN HF radars have been previously used for locating and tracking the PCB in the cusp region. The boundary is generally observed in meridional beams of the SuperDARN radars and appears as a distinct change between low spectral width values observed equatorward of the cusp region, and high, but variable spectral width values observed within the cusp region. To identify the spectral width boundary (SWB between these two regions, a simple algorithm employing a spectral width threshold has often been applied to the data. However, there is not, as yet, a standard algorithm, or spectral width threshold, which is universally applied. Nor has there been any rigorous assessment of the accuracy of this method of boundary determination. This study applies a series of threshold algorithms to a simulated cusp-region spectral width data set, to assess the accuracy of different algorithms. This shows that simple threshold algorithms correctly identify the boundary location in, at the most, 50% of the cases and that the average boundary error is at least ~ 1–2 range gates (~ 1° latitude. It transpires that spatial and temporal smoothing of the spectral width data (e.g. by median filtering, before application of a threshold algorithm can increase the boundary determination accuracy to over 95% and the average boundary error to much less than a range gate. However, this is sometimes at the cost of temporal resolution in the motion of the boundary location. The algorithms are also applied to a year’s worth of spectral width data from the cusp ionosphere, measured by the Halley SuperDARN radar in Antarctica. This analysis highlights the increased accuracy of

  7. Temporal distribution characteristics of GNSS ionospheric occultation data and its effects in earthquake-ionosphere anomaly detection

    Directory of Open Access Journals (Sweden)

    Zhao Ying

    2013-01-01

    Full Text Available The temporal distribution characteristics of COSMIC occultation data are analyzed in detail, and the limitations in earthquake-ionosphere anomaly detection caused by the temporal distribution characteristics of COSMIC occultation data are discussed using the example of the Wenchuan earthquake. The results demonstrate that there is no fixed temporal resolution for COSMIC occultation data when compared with other ionospheric observation techniques. Therefore, occultation data cannot currently be independently utilized in research studies but can only be used as a complement to other ionospheric observation techniques for applications with high temporal resolution demands, such as earthquake-ionosphere anomaly detection.

  8. IGS-global ionospheric maps for accurate computation of GPS single- frequency ionospheric delay-simulation study

    Science.gov (United States)

    Farah, A.

    The Ionospheric delay is still one of the largest sources of error that affects the positioning accuracy of any satellite positioning system. This problem could be solved due to the dispersive nature of the Ionosphere by combining simultaneous measurements of signals at two different frequencies but it is still there for single- frequency users. Much effort has been made in establishing models for single- frequency users to make this effect as small as possible. These models vary in accuracy, input data and computational complexity, so the choice between the different models depends on the individual circumstances of the user. From the simulation point of view, the model needed should be accurate with a global coverage and good description to the Ionosphere's variable nature with both time and location. The author reviews some of these established models, starting with the BENT model, the Klobuchar model and the IRI (International Reference Ionosphere) model. Since quiet a long time, Klobuchar model considers the most widely used model ever in this field, due to its simplicity and time saving. Any GPS user could find Klobuchar model's coefficients in the broadcast navigation message. CODE, Centre for Orbit Determination in Europe provides a new set of coefficients for Klobuchar model, which gives more accurate results for the Ionospheric delay computation. IGS (International GPS Service) services include providing GPS community with a global Ionospheric maps in IONEX-format (IONosphere Map Exchange format) which enables the computation of the Ionospheric delay at the desired location and time. The study was undertaken from GPS-data simulation point of view. The aim was to select a model for the simulation of GPS data that gives a good description of the Ionosphere's nature with a high degree of accuracy in computing the Ionospheric delay that yields to better-simulated data. A new model developed by the author based on IGS global Ionospheric maps. A comparison

  9. Characterization of the 1,1-HF Elimination Reaction from the Competition between the 1,1-HF and 1,2-DF Unimolecular Elimination Reactions of CD3CD2CHF2.

    Science.gov (United States)

    Wormack, Leah N; McGreal, Meghan E; McClintock, Corey E; Heard, George L; Setser, D W; Holmes, Bert E

    2015-04-30

    The recombination of CHF2 and C2D5 radicals was used to produce CD3CD2CHF2* molecules with 96 kcal mol(-1) of vibrational energy in a room temperature bath gas. The formation of CD3CD═CHF and CD3CD═CDF was used to identify the 1,2-DF and 1,1-HF unimolecular elimination channels; CD3CD═CDF is formed by isomerization of the singlet-state CD3CD2CF carbene. The total unimolecular rate constant is 1.6 × 10(6) s(-1), and the branching ratio for 1,1-HF elimination is 0.25. Threshold energies of 64 ± 2 and 73 ± 2 kcal mol(-1) were assigned to the 1,2-DF and 1,1-HF reaction channels. The E and Z isomers of 1-fluoropropene were observed for each reaction; approximately 30% of the CD3CD═CDF molecules derived from 1,1-HF elimination retained enough energy to undergo cis-trans isomerization. Electronic structure calculations with density-functional theory were used to characterize the transition-state structures and the H atom migration barrier for CD3CD2CF. Adjustment of the rate constants to account for kinetic-isotope effects suggest that the branching ratio would be 0.20 for 1,1-HF elimination from C2H5CHF2. The results from an earlier study of CD3CHF2 and CH3CHF2 are also reinterpreted to assign a threshold energy of 74 kcal mol(-1) for the 1,1-HF elimination reaction. Because CHF2CHF2* is generated in the photolysis system, the 1,1-and 1,2-HF-elimination reactions of CHF2CHF2* are discussed. The 1,1-HF channel was identified by trapping the CF2HCF carbene with cis-butene-2.

  10. High-aspect-ratio HfC nanobelts accompanied by HfC nanowires: Synthesis, characterization and field emission properties

    Energy Technology Data Exchange (ETDEWEB)

    Tian, Song, E-mail: tiansong22@126.com [State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072 (China); School of Materials Science and Engineering, Chongqing Jiaotong University, Chongqing 400074 (China); Zhang, Yulei; Ren, Jincui; Qiang, Xinfa; Zhang, Shouyang [State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072 (China); Li, Hejun, E-mail: lihejun@nwpu.edu.cn [State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072 (China)

    2017-04-30

    Highlights: • HfC naobelts accompanied by HfC nanowires were synthesized by a catalytic CVD method. • HfC nanobelts as a novel structure of HfC ceramic are reported for the first time. • HfC nanobelts have 100–200 μm in lengths and reach up to 10 μm in widths. • The synthesized product is promising field nanoemitters. - Abstract: As a key refractory carbide, hafnium carbide (HfC) is commonly used as structural materials while the field emission (FE) application of HfC in the field of vacuum microelectronics is almost the only one for functional material purposes. Based on its outstanding physical and chemical characteristics, HfC is identified as a potential candidate with satisfactory mechanical properties and long-term and/or high-temperature FE stability for future applications in high-performance field emitters. However, the development of HfC in various FE applications is hindered because it is not facile to fabricate large-scale low-dimensional HfC field nanoemitters. Herein, High-aspect-ratio HfC nanobelts accompanied by HfC nanowires were synthesized on a large scale by a traditional and simple catalytic chemical vapor deposition (CVD) method. Classical vapor–liquid–solid (VLS) theory was employed to explain the growth of the HfC nanowires and nanobelts along axial direction. The thin HfO{sub 2} shell and thin C layer surrounding the nanostructures might give rise to the diameter fluctuation of HfC nanowires and the width increase of HfC nanobelts in lateral direction. Field emission results show that the high-aspect-ratio HfC nanobelts accompanied by the nanowires are promising field nanoemitters, which exhibit excellent field emission properties with a fairly low turn-on field of ∼1.5 V μm{sup −1} and a low current fluctuation less than ∼10%. This suggests that HfC ceramics with high-aspect-ratio nanostructures are ideal cathode material for various field emission applications.

  11. 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.

  12. Ion Velocity Measurements for the Ionospheric Connections Explorer

    Science.gov (United States)

    Heelis, R. A.; Stoneback, R. A.; Perdue, M. D.; Depew, M. D.; Morgan, W. A.; Mankey, M. W.; Lippincott, C. R.; Harmon, L. L.; Holt, B. J.

    2017-10-01

    The Ionospheric Connections Explorer (ICON) payload includes an Ion Velocity Meter (IVM) to provide measurements of the ion drift motions, density, temperature and major ion composition at the satellite altitude near 575 km. The primary measurement goal for the IVM is to provide the meridional ion drift perpendicular to the magnetic field with an accuracy of 7.5 m s-1 for all daytime conditions encountered by the spacecraft within 15° of the magnetic equator. The IVM will derive this parameter utilizing two sensors, a retarding potential analyzer (RPA) and an ion drift meter (IDM) that have a robust and successful flight heritage. The IVM described here incorporates improvements in the design and operation to produce the most sensitive device that has been fielded to date. It will specify the ion drift vector, from which the component perpendicular to the magnetic field will be derived. In addition it will specify the total ion density, the ion temperature and the fractional ion composition. These data will be used in conjunction with measurements from the other ICON instruments to uncover the important connections between the dynamics of the neutral atmosphere and the ionosphere through the generation of dynamo currents perpendicular to the magnetic field and collisional forces parallel to the magnetic field. Here the configuration and operation of the IVM instrument are described, as well as the procedures by which the ion drift velocity is determined. A description of the subsystem characteristics, which allow a determination of the expected uncertainties in the derived parameters, is also given.

  13. Analysis framework for systematically studying ionospheric response to impulsive events from below

    Science.gov (United States)

    Haaser, Robert A.; Lay, Erin H.; Junor, William

    2017-09-01

    Impulsive phenomena in the Earth's atmosphere produce acoustic and gravity waves which perturb the ionosphere. Such perturbations are often measured using total electron content fluctuations (TEC), derived from ground-based Global Positioning System data. Using TEC data from the Japanese GEONET ground network after the Tōhoku earthquake on 11 March 2011, we demonstrate capabilities of a new framework of methodologies for analyzing ionospheric perturbations. The framework consists of several new techniques: calculating velocity along a single direction to reduce error due to anisotropic propagation, producing normalized bidirectional band-pass spectra that preserve relative timing between various frequencies and allowing a more systematic determination of broadband pulses, and utilizing a wavelet-based technique that considers instantaneous wave phase changes, rather than best fit time differences, to evaluate wave characteristics (speed, direction, and wavelength) within spectral ranges of interest. Using these techniques together decreases subjectivity and reduces errors in attributing fluctuations to given sources. In validating this framework using the Tōhoku case, we consistently identify three kinds of waves: a broad-band pulse (speed: >2000 m/s, max range: >1400 km) arriving in the ionosphere 10-15 min after the quake, acoustic waves following the pulse (period: 3-5 min, speed: 700-1000 m/s, max range: 1400 km) propagating away from the epicenter, consistent with theory and demonstrated in previous studies. This framework also can be applied to other impulsive events in the atmosphere that are more difficult to detect and attribute to sources.

  14. Alfven Waves and Electron Energization and Their Interaction with Auroral Ionospheric Plasma Transport

    Science.gov (United States)

    Jaafari, F. B.; Horwitz, J. L.; Jones, S.; Su, Y.; Zeng, W.

    2008-12-01

    When inertial Alfvén waves propagate along auroral field lines, they involve parallel electric fields which can accelerate auroral electrons. Here, we simulate the propagation of Alfvén waves through O+ and H+ auroral ionosphere-magnetosphere density profiles obtained from the UT Arlington Dynamic Fluid- Kinetic (DyFK) ionospheric plasma transport model. A linear one dimensional gyrofluid code [Jones and Parker, 2003] is used for the Alfvén wave description, incorporating electron inertia, electron pressure gradient and finite ion gyroradius effects. Then, the test particle approach of Su et al. [2004] is used to simulate the response of a distribution of electrons to these Alfvén wave electric fields. These electrons are incorporated into the DyFK model to produce a partially-self-consistent approach to producing the associated ionization and thermal electron heating within the ionosphere-magnetosphere system. Jones, S. T., and S. E. Parker (2003), Including electron inertia without advancing electron flow, J. Comput. Phys., 191, 322. Su, Y.-J., S. T. Jones, R. E. Ergun, and S. E. Parker (2004), Modeling of field-aligned electron bursts by dispersive Alfvén waves in the dayside auroral region, J. Geophys. Res., 109, A11201, doi:10.1029/2003JA010344.

  15. Supermagnetosonic subsolar magnetosheath jets and their effects: from the solar wind to the ionospheric convection

    Directory of Open Access Journals (Sweden)

    H. Hietala

    2012-01-01

    Full Text Available It has recently been proposed that ripples inherent to the bow shock during radial interplanetary magnetic field (IMF may produce local high speed flows in the magnetosheath. These jets can have a dynamic pressure much larger than the dynamic pressure of the solar wind. On 17 March 2007, several jets of this type were observed by the Cluster spacecraft. We study in detail these jets and their effects on the magnetopause, the magnetosphere, and the ionospheric convection. We find that (1 the jets could have a scale size of up to a few RE but less than ~6 RE transverse to the XGSE axis; (2 the jets caused significant local magnetopause perturbations due to their high dynamic pressure; (3 during the period when the jets were observed, irregular pulsations at the geostationary orbit and localised flow enhancements in the ionosphere were detected. We suggest that these inner magnetospheric phenomena were caused by the magnetosheath jets.

  16. Space weather on October 2003 and HF popagation in the Asian and European longitudinal sectors

    Science.gov (United States)

    Kurkin, V. I.; Blagoveshchensky, D. V.; Pirog, O. M.; Stocker, A. J.; Vertogradov, G. G.; Uryadov, V. P.; Warrington, E. M.

    There are presented the results derived from investigating of the HF propagation peculiarities on the subauroral and mid-latitudinal radio paths in the Asian and European longitudinal sectors during the geomagnetic disturbances on October 2003. Intensive negative disturbances of MOF (30-50%) during the moderate disturbance on October 20-22 were marked on the mid-latitudinal paths Khabarovsk-Irkutsk, Magadan-Irkutsk, Khabarovsk-Rostov and Irkutsk-Rostov in the daytime. The signal was not registered on the long paths in the night. During the moderate disturbance from 12 UT to 23 UT on October 24, there were marked an absence of signal passing on the subpolar paths Norilsk- Irkutsk, Dikson-St.Peterburg and Murmansk- St.Peterburg, a abrupt decrease of MOF on the mid-latitudinal paths and an appearance of spread signals off-great circle propagation. It was caused by the strong displacement of the main ionospheric trough (MIT) to the mid latitudes, while according to the data on path Murmansk- St.Peterburg in the quiet time on October 23, the poleward wall of (MIT) was fixing at the invariant latitude 60N during a few hours around midnight. The generation region of ionospheric irregularities in equatorward edge of auroral zone was arrived to the invariant latitude 55N. During the investigated disturbance an increase of MOF was observed 7 hours before to To (the beginning of growth phase) and also 7 hours after Te (the end of growth phase). The strongest ionospheric disturbance was registered on October 29-31, as reaction to two powerful X17.2 and X10 class flares. The displacement of the MIT poleward wall to the invariant latitude 45N resulted in the deep electron density depletion and the absence of signal passing on the subpolar paths in the Asian longitudinal sector on October 29-31. In the European longitudinal sector on the mid-latitudinal path Inskip-Rostov the signals off-great circle propagation were registered in the evening. This testifies about the strong

  17. Sub-auroral flow shear observed by King Salmon HF radar and RapidMAG

    Science.gov (United States)

    Hori, T.; Kikuchi, T.; Tsuji, Y.; Shinbori, A.; Ohtaka, T.; Kunitake, M.; Watari, S.; Nagatsuma, T.; Troshichev, O. A.

    2010-12-01

    We examine in detail the evolution of ionospheric flow shears in the sub-auroral region associated with alternate northward/southward turnings of the IMF. The flow shear structures are often observed in the dusk sector by the SuperDARN King Salmon (KSR) HF radar. Interestingly, some of those show the eastward (westward) flow on the lower (higher) latitude side, respectively, opposite to the typical polarity of the dusk convection cell. In those flow shear events, the IMF has a weak but persistent southward component (~ -1 to -3 nT) before onset of flow shears and following decreases of the southward IMF or even northward turning appear to cause the flow shears. The ground magnetograms provided by the Russian Auroral and Polar Ionospheric Disturbance Magnetometers (RapidMAG) show gradual increases (abrupt declines) of the H-component in association with the increases (decreases) of the merging electric field, respectively, derived from the simultaneous solar wind-IMF observations. The fairly coherent increases (decreases) of the H-component over the wide range of local time (afternoon to evening) indicate development (decay) of the large-scale DP2 current system. A detailed analysis on the 2-D convection structure near the lower latitude edge of the dusk convection cell shows that the ionospheric plasma generally flows westward there and has a larger speed with increasing latitude particularly during increases of the merging electric field. However, once the southward IMF decreases or even shifts to northward and thereby the merging electric field goes down, the region of westward flow moves toward higher latitudes and instead an eastward flow emerges there, forming a flow shear of the counterclockwise sense. This indicates that a downward field-aligned current (FAC), which is the Region-2 (R2) sense on the dusk side, flows into the flow shear region. Subsequently the convection returns to a westward flow again upon increases of the merging electric field due to the

  18. Impact of Galileo on Global Ionosphere Map Estimation

    NARCIS (Netherlands)

    Undetermined, U.

    2006-01-01

    The upcoming GNSS Galileo, with its new satellite geometry and frequency plan, will not only bring many benefits for navigation and positioning but also help to improve ionosphere delay estimation. This paper investigates ionosphere estimation with Galileo and compares it with the results from

  19. Comparison of two views on the structure of ionospheric currents ...

    African Journals Online (AJOL)

    There are two views on the structure of ionospheric currents, here symbolized as VIEW 1 and VIEW 2. The essential difference between them is that VIEW I supports the existence of two ionospheric current layers in the dip equatorial zone as measured by many rockets (Onwumechili,1992b,c). Contrary to the rocket ...

  20. Analysis of ionospheric parameters during Solar events and geomagnetic storms

    Directory of Open Access Journals (Sweden)

    Mandrikova Oksana

    2016-01-01

    Full Text Available The paper shows new methods of analysis of ionospheric and magnetic data applying the models of multicomponent constructions (MCM models developed by the authors. Based on ground station data, the analysis of ionospheric and magnetic data during increased solar activity was carried out.

  1. Probing ionospheric structures using the LOFAR radio telescope

    NARCIS (Netherlands)

    Mevius, M.; van der Tol, S.; Pandey, V.N.; Vedantham, H. K.; Brentjens, M. A.; Bruyn, A. G.; Abdalla, F. B.; Asad, K. M. B.; Bregman, J. D.; Brouw, W. N.; Bus, S.; Chapman, E.; Ciardi, B.; Fernandez, E. R.; Ghosh, A.; Harker, G.; Iliev, I. T.; Jelic, Vibor; Kazemi, S.; Koopmans, L. V. E.; Noordam, J. E.; Offringa, A. R.; Patil, A. H.; Weeren, R. J.; Wijnholds, S.; Yatawatta, S.; Zaroubi, S.

    2016-01-01

    LOFAR is the LOw-Frequency Radio interferometer ARray located at midlatitude (52°53'N). Here we present results on ionospheric structures derived from 29 LOFAR nighttime observations during the winters of 2012/2013 and 2013/2014. We show that LOFAR is able to determine differential ionospheric total

  2. Variability Of Plasma Bubble In The Equatorial Ionosphere At Midnight

    African Journals Online (AJOL)

    There are various types of ionospheric irregularities. Among these is the plasma bubble occurrence. They are most prominent at night time in the equatorial ionosphere. Many of the bubbles drift with approximately the velocity of the background plasma, but it is possible to infer that most bubbles have moved upward at some ...

  3. Ninth Workshop 'Solar Influences on the Magnetosphere, Ionosphere and Atmosphere'

    Science.gov (United States)

    Georgieva, Kayta; Kirov, Boian; Danov, Dimitar

    2017-08-01

    The 9th Workshop "Solar Influences on the Magnetosphere, Ionosphere and Atmosphere" is an international forum for scientists working in the fields of: Sun and solar activity, Solar wind-magnetosphere-ionosphere interactions, Solar influences on the lower atmosphere and climate, Solar effects in the biosphere, Instrumentation for space weather monitoring and Data processing and modelling.

  4. Study of ionospheric anomalies due to impact of typhoon using ...

    Indian Academy of Sciences (India)

    Principal Component Analysis (PCA) and image processing are used to determine Total Electron Content (TEC) anomalies in the F-layer of the ionosphere relating to Typhoon Nakri for 29 May, 2008 (UTC). PCA and image processing are applied to the global ionospheric map (GIM) with transforms conducted for the time ...

  5. Bayesian estimation for ionospheric calibration in radio astronomy

    NARCIS (Netherlands)

    Van der Tol, S.

    2009-01-01

    Radio astronomical observations at low frequencies (< 250 MHz), can be severely distorted by fluctuations in electron density in the ionosphere. The free electrons cause a phase change of electromagnetic waves traveling through the ionosphere. This effect increases for lower frequencies. For this

  6. Ionospheric Electron Densities at Mars: Comparison of Mars Express Ionospheric Sounding and MAVEN Local Measurement

    Czech Academy of Sciences Publication Activity Database

    Němec, F.; Morgan, D. D.; Fowler, C.M.; Kopf, A.J.; Andersson, L.; Gurnett, D. A.; Andrews, D.J.; Truhlík, Vladimír

    in press (2017) E-ISSN 2169-9402 Institutional support: RVO:68378289 Keywords : Mars * ionosphere * MARS IS * Mars Express * MAVEN * radar sounding Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics http://onlinelibrary.wiley.com/doi/10.1002/2017JA024629/full

  7. Propagation Impact on Modern HF (High Frequency) Communications System Design

    Science.gov (United States)

    1986-03-01

    terminal to choose the best frequency. These efforts were aborted in the early 1970s with the expectation of satellite systems. Furthermore, concern...traditional diffic communications and including selectiv connectivity. The frequency selectio ionospheric predic of channel interfe an

  8. Microstructural characterization of as-cast hf-b alloys

    Directory of Open Access Journals (Sweden)

    João Carlos Jânio Gigolotti

    2012-04-01

    Full Text Available An accurate knowledge of several metal-boron phase diagrams is important to evaluation of higher order systems such as metal-silicon-boron ternaries. The refinement and reassessment of phase diagram data is a continuous work, thus the reevaluation of metal-boron systems provides the possibility to confirm previous data from an investigation using higher purity materials and better analytical techniques. This work presents results of rigorous microstructural characterization of as-cast hafnium-boron alloys which are significant to assess the liquid composition associated to most of the invariant reactions of this system. Alloys were prepared by arc melting high purity hafnium (minimum 99.8% and boron (minimum 99.5% slices under argon atmosphere in water-cooled copper crucible with non consumable tungsten electrode and titanium getter. The phases were identified by scanning electron microscopy, using back-scattered electron image mode and X-ray diffraction. In general, a good agreement was found between our data and those from the currently accepted Hafnium-Boron phase diagram. The phases identified are αHfSS and B-RhomSS, the intermediate compounds HfB and HfB2 and the liquide L. The reactions are the eutectic L ⇔ αHfSS + HfB and L ⇔ HfB2 + B-Rhom, the peritectic L + HfB2 ⇔ HfB and the congruent formation of HfB2.

  9. Hf isotope evidence for a hidden mantle reservoir

    DEFF Research Database (Denmark)

    Bizzarro, Martin; Simonetti, A.; Stevenson, R.K.

    2002-01-01

    High-precision Hf isotopic analyses and U-Pb ages of carbonatites and kimberlites from Greenland and eastern North America, including Earth's oldest known carbonatite (3 Ga), indicate derivation from an enriched mantle source. This previously unidentified mantle reservoir-marked by an unradiogenic...... Hf isotopic composition and preserved in the deep mantle for at least 3 b.y.-may account for the mass imbalance in Earth's Hf-Nd budget. The Hf isotopic data presented here support a common mantle source region and genetic link between carbonatite and some oceanic-island basalt volcanoes....

  10. PEMISAHAN Zr – Hf SECARA SINAMBUNG MENGGUNAKAN MIXER SETTLER

    Directory of Open Access Journals (Sweden)

    Dwi Biyantoro

    2017-01-01

    Full Text Available ABSTRAK PEMISAHAN Zr – Hf SECARA SINAMBUNG MENGGUNAKANMIXER SETTLER. Telah dilakukan pemisahanZr – Hf secara sinambung menggunakan pengaduk pengenap (mixer settler 16 stage. Larutan umpan adalah zirkon nitrat dengan kadar Zr = 30786 ppm dan Hf = 499 ppm. Ekstraktan dipakai adalah solven 60 % TBP dalam kerosen dan larutan scrubbingyang dipakai adalah asam nitrat 1 M. Umpan masuk pada stageke 5 dikontakkan secara berlawanan arah dengan solven masuk pada stage ke 16 dan larutan scrubbing masuk pada stage ke 1. Tujuan penelitian ini adalah memisahkan unsur Zr dan Hf dari hasil olah pasir zirkon menggunakan solven TBP dengan alat mixer settler16 stage. Analisis umpan dan hasil proses pemisahan untuk zirkonium (Zr dilakukan dengan menggunakan alat pendar sinar-X, sedangkananalisis unsur hafnium (Hf menggunakan Analisis Pengaktifan Neutron (APN. Parameter penelitian dilakukan dengan variasi keasaman asam nitrat dalam umpan dan variasi waktu pada berbagai laju pengadukan. Hasil penelitian pemisahan unsur Zr dengan Hf diperolehkondisi optimum pada keasaman umpan 4 N HNO3, keseimbangan dicapai setelah 3jam dan laju pengadukan 3300 rpm. Hasil ekstrak  unsur zirkon (Zr diperoleh kadar sebesar 28577 ppm dengan efisiensi 92,76 % serta kadar pengotor hafnium (Hf sebesar 95 ppm. Kata Kunci: pemisahan Zr, Hf, ekstraksi, mixer settler, alat pendar sinar-X, APN. ABSTRACT SEPARATION of Zr - Hf CONTINUOUSLY USE THE MIXER SETTLER. Separation of Zr - Hf continuously using mixer settler 16 stage has been done. The feed solution is zircon nitrate concentration of Zr = 30786 ppm  and Hf = 499 ppm. As the solvent used extractant 60 % TBP in 40 % kerosene. Nitric acid solution used srubbing 1 M. The feed entered into stage to 5 is contacted with solvents direction on the stage to 16 and the scrubbing solution enter the stage to 1. The purpose of this study is to separate Zr and Hf of the results from the process of zircon sand using solvent TBP using 16 stage

  11. A case study of HF radar spectral width in the post midnight magnetic local time sector and its relationship to the polar cap boundary

    Directory of Open Access Journals (Sweden)

    E. E. Woodfield

    Full Text Available The aim of this paper is to advance the current understanding of the spectral width parameter observed by coherent high frequency (HF radars. In particular, we address the relationship of a frequently observed gradient, between low ( < 200 m/s and high ( > 200 m/s spectral width, to magnetospheric boundaries. Previous work has linked this gradient in the spectral width, in the nightside sector of magnetic local time, to the Polar Cap Boundary (PCB, and also to the boundary between the Central Plasma Sheet (CPS and the Plasma Sheet Boundary Layer (PSBL. The present case study investigates the former by comparison with the 630.0 nm optical emission. No suitable data were available to test the second of the two hypotheses. It is found that during the interval in question the spectral width gradient is within the region of the 630.0 nm optical emission. A comparison of coherent and incoherent scatter radar data is also conducted, which indicates that values of high spectral width are typically collocated with elevated F-region electron temperatures. We conclude that the high spectral width region in the interval under study is associated with particle precipitation and also that the spectral width gradient is not a reliable method for locating the PCB.

    Key words. Ionosphere (auroral ionosphere; ionospheric irregularities

  12. Ionospheric radio occultation inversion constrained with the data assimillation

    Science.gov (United States)

    Wu, X.; Hu, X.; Zhang, Y.

    2015-12-01

    Ionospheric radio occultation inversion constrained with the data assimillation Wu Xiaocheng, Hu Xiong, Zhang Yanan National Space Science Center, Chinese Academy of Sciences The assumption that electron density distribution is spherically symmetric, is usually used in the traditional ionospheric radio occultation (IRO) inversion, and it is the main error source of IRO inversion. In order to improve the IRO inversion, many methods were studied. One of them uses known ionosphere background to constrain the inversion of IRO, but it has not been used in the routine processing of observation data, due to that it is difficult to get the proper ionosphere background. Data assimilation can provide accurate electron density on the three dimensional grid, which may be used to constrain the IRO inversion and improve the inversion result. This article assimilates the TEC of ground GPS and IRO observation, and the constrains the IRO inversion. The inversion result is greatly improved. Key Words: Ionospheric radio occultation, Data assimilation, Inversion, GPS

  13. DAASM Project-High Latitude Aircraft HF Propagation Experiment

    Science.gov (United States)

    1975-05-19

    äystemsrESSA eters of High Frequency 5ky-V Tech. HepoH EHL UO-m-Vb. Bibl. K.. et al(1970) Digital Interpreting Goniometrie Ionospheric Sounder. AFCRL...described in detail. It was found that the frequency-averaging technique provided a very efficient and reliable means of cross-spectral estimation, and... reliable method of mode identification. 7. Elkins, T..I. (19731 An Empirical Model of the Polar Ionosphere. Survey in Geophysics, No. 26T

  14. Vertical midscale ionospheric disturbances caused by surface seismic waves based on Irkutsk chirp ionosonde data in 2011-2016

    Science.gov (United States)

    Berngardt, O. I.; Perevalova, N. P.; Podlesnyi, A. V.; Kurkin, V. I.; Zherebtsov, G. A.

    2017-04-01

    Based on the Irkutsk fast monostatic chirp ionosonde data, we made a statistical analysis of ionospheric effects for 28 earthquakes which appeared in 2011-2016 years. These effects are related with surface (Rayleigh) seismic waves far from epicenter. The analysis has shown that nine of these earthquakes were accompanied by vertical midscale ionospheric irregularities (multicusp). To estimate the ionospheric efficiency of the seismic waves, we proposed new index KW. The index estimates the maximal amplitude of the acoustic shock wave generated by given spatial distribution of seismic vibrations and related with maximal spectral power of seismic oscillations. Based on the analysis of experimental data, we have shown that earthquake-related multicusp (5-25 s irregularities) is observed mostly at daytime [07:00-17:00] LST for KW≥4.7. The observations of acoustic waves by GPS technique in the epicenter vicinity (120-600 s irregularities) do not show such a daytime dependence. Based on 24 May 2013 Okhotsk Sea earthquake example, we demonstrated that deep-focus earthquakes can produce strong multicusp far from the epicenter, although do not produce significant GPS ionospheric response in the epicenter vicinity.

  15. Electrodynamics of the Low-Latitude Ionosphere.

    Science.gov (United States)

    Riley, Peter

    We have undertaken a study of the low and mid latitude ionospheric electric field pattern, during both magnetospherically quiet and active periods. Our analysis can be conveniently split into two parts. i.In an effort to study the penetration of magnetospheric electric fields to low latitudes, we have compared Jicamarca F-region vertical drifts for 10 radar-observation periods with the auroral boundary index (ABI). The ABI is the latitude of the equatorward edge of the diffuse aurora at local midnight, as estimated from precipitating-electron fluxes measured from DMSP spacecraft. The periods occurred in the interval January 1984 to June 1991 inclusive and each lasted between 2 and 5 days. We focus on periods that occurred in September 1986, March 1990, and June 1991. In the post-midnight sector, where we expect the penetration to be strongest, we found many examples of correlation; specifically, associated with an ionospheric updraft (implying an eastward electric field) is a strong poleward motion of the auroral boundary. However, we also found a significant number of cases where there was little or no correlation. We conclude that there is only mediocre agreement between the observed Sudden Postmidnight Ionospheric Events (SPIEs) and the ABI. These SPIEs have also been compared with other magnetospheric parameters, namely D_ {rm st} IMF B_{z } and the polar cap potential. D_ {rm st} showed significantly better correlation with the SPIEs. We summarize the proposed models for SPIEs and compare their predictions with the data, concluding that no single model can account for all events. While it is clear that some of these SPIEs can be explained in terms of direct penetration of magnetospheric electric fields, we suggest that the remainder may be due to magnetospherically-generated neutral wind effects. ii. We have constructed a model of the low- and mid-latitude potential distribution, applicable for both quiet and active times. We use the Mass

  16. Ionospheric weather: cloning missed foF2 observations for derivation of variability index

    Directory of Open Access Journals (Sweden)

    T. L. Gulyaeva

    2008-02-01

    Full Text Available A techique for filling the gaps of the missing F2-layer critical frequency is proposed and applied for the derivation of the ionospheric weather index, characterizing the degree of disturbance at each particular station. A daily-hourly analysis of ionosonde observations of foF2 for 16 stations at latitude range 37° to 70° N, longitudes of 10° W to 150° E, is performed during the solar minimum, 2006. Missed ionosonde observations are reconstructed by cloning data of another station. The process of gap filling considers hourly values of the F peak density NmF2 (deduced from foF2, normalized to the respective median, and assumes that this ratio remains the same for the parent and cloned data. It is shown that the correlation coefficient between cloned fcF2 and observed foF2 is greater than 0.75 for the positive and negative ionospheric disturbed days during a year at solar minimum, independent of the distance between the stations in high and middle latitudes. The quiet reference is determined as a running daily-hourly median for 27 days, preceding the day of observation calibrated for a seasonal trend with ITU-R foF2 predictions. The hourly deviation DNmF2 is defined as the logarithm of ratio of NmF2/NmF2med. A segmented logarithmic scale of the ionospheric weather index, W, is introduced, so that W=±1 refers to the quiet state, W=±2 to a moderate disturbance, W=±3 to the ionospheric storm, and W=±4 to the extreme or anomalous conditions. The catalog of the ionospheric disturbances for W exceeding ±2 at least during 3 consecutive hours is produced and presented online at the SRC and IZMIRAN web pages. It is found that the moderate disturbance is a prevailing state of the ionospheric weather for all stations. The stormy conditions comprise 1 to 20% of the times which occur more frequently at high latitudes, by night, during equinox and winter.

  17. Comparison of ionospheric characteristic parameters obtained by ...

    Indian Academy of Sciences (India)

    This paper presents a comparison of ionospheric characteristic parameters obtained by a GPS networkand three ionosondes at Mohe (122.4^◦E, 53.5^◦N, dip angle 70.983^◦N), Zuolingzhen (114.6^◦E, 30.5^◦N, dipangle 46.350^◦N), and Fuke (109.1^◦E, 19.5^◦N, dip angle 27.083^◦N) located in China with an IRI model inthe ...

  18. The International Reference Ionosphere: Model Update 2016

    Science.gov (United States)

    Bilitza, Dieter; Altadill, David; Reinisch, Bodo; Galkin, Ivan; Shubin, Valentin; Truhlik, Vladimir

    2016-04-01

    The International Reference Ionosphere (IRI) is recognized as the official standard for the ionosphere (COSPAR, URSI, ISO) and is widely used for a multitude of different applications as evidenced by the many papers in science and engineering journals that acknowledge the use of IRI (e.g., about 11% of all Radio Science papers each year). One of the shortcomings of the model has been the dependence of the F2 peak height modeling on the propagation factor M(3000)F2. With the 2016 version of IRI, two new models will be introduced for hmF2 that were developed directly based on hmF2 measurements by ionosondes [Altadill et al., 2013] and by COSMIC radio occultation [Shubin, 2015], respectively. In addition IRI-2016 will include an improved representation of the ionosphere during the very low solar activities that were reached during the last solar minimum in 2008/2009. This presentation will review these and other improvements that are being implemented with the 2016 version of the IRI model. We will also discuss recent IRI workshops and their findings and results. One of the most exciting new projects is the development of the Real-Time IRI [Galkin et al., 2012]. We will discuss the current status and plans for the future. Altadill, D., S. Magdaleno, J.M. Torta, E. Blanch (2013), Global empirical models of the density peak height and of the equivalent scale height for quiet conditions, Advances in Space Research 52, 1756-1769, doi:10.1016/j.asr.2012.11.018. Galkin, I.A., B.W. Reinisch, X. Huang, and D. Bilitza (2012), Assimilation of GIRO Data into a Real-Time IRI, Radio Science, 47, RS0L07, doi:10.1029/2011RS004952. Shubin V.N. (2015), Global median model of the F2-layer peak height based on ionospheric radio-occultation and ground-based Digisonde observations, Advances in Space Research 56, 916-928, doi:10.1016/j.asr.2015.05.029.

  19. Pressure induced novel compounds in the Hf-O system from first-principles calculations

    OpenAIRE

    Zhang, Jin; Oganov, Artem R.; Li, Xinfeng; Xue, Kan-Hao; Wang, Zhenhai; Dong, Huafeng

    2015-01-01

    Using first-principles evolutionary simulations, we have systematically investigated phase stability in the Hf-O system at pressure up to 120 GPa. New compounds Hf5O2, Hf3O2, HfO and HfO3 are discovered to be thermodynamically stable at certain pressure ranges and a new stable high-pressure phase is found for Hf2O with space group Pnnm and anti-CaCl2-type structure. Both P62m-HfO and P4m2-Hf2O3 show semimetallic character. Pnnm-HfO3 shows interesting structure, simultaneously containing oxide...

  20. HF Radar Bistatic Measurement of Surface Current Velocities: Drifter Comparisons and Radar Consistency Checks

    OpenAIRE

    Lipa, Belinda; Whelan, Chad; Rector, Bill; Nyden, Bruce

    2009-01-01

    We describe the operation of a bistatic HF radar network and outline analysis methods for the derivation of the elliptical velocity components from the radar echo spectra. Bistatic operation is illustrated by application to a bistatic pair: Both remote systems receive backscattered echo, with one remote system in addition receiving bistatic echoes transmitted by the other. The pair produces elliptical velocity components in addition to two sets of radials. Results are compared with drifter me...

  1. Effects on SuperDARN HF radar echoes of sudden impulses of solar wind dynamic pressure

    Directory of Open Access Journals (Sweden)

    I. Coco

    2005-07-01

    Full Text Available In this work we perform a statistical analysis of the ionospheric echo response observed by six radars of the SuperDARN network in the Northern Hemisphere, over 236 Sudden Impulses (SI of solar wind dynamic pressure events (from 1997 through 2000. For that purpose, we make use of MRS, the Mean Rate of Scattering, as a function of time during the SI event. We classify the events in sudden increases (I events, 144 cases and decreases (D events, 92 cases of the solar wind dynamic pressure. Moreover, we make use of the AE index to define two distinct conditions of the ionosphere under which each event may take place: Quiet and Disturbed. Regarding Quiet conditions, for both I and D events, we find that MRS displays an increase related to the SI time. On the contrary, for Disturbed conditions, D events display an increase in MRS, while I events show a clear dip. The similarity of response for I and D events under Quiet conditions is briefly discussed, but the smaller number of D events does not allow one to further analyse them. As for the I events, a latitudinal analysis shows that the MRS increase for Quiet conditions is seen both at low latitudes (60°–70° Λ and at high latitudes (70°–80° Λ; for Disturbed Is the MRS decrease is stronger at high latitudes. We suggest that the MRS increase for Quiet Is can be due to two different mechanisms: 1 a soft electron precipitation induced by Field Line Resonances (FLR or loss cone instability at lower latitudes; 2 an enlargement of the cusp at higher latitudes, which in turn may induce enhanced particle precipitation. For what concerns Disturbed Is, the MRS decrease can be produced by a higher energy electron precipitation (>1 keV, that enhances the electron density in the E and D regions. This provokes a strong absorbtion of the radio waves in the D region and a higher refraction in the E region, leading to a decrease in MRS, especially at higher latitudes. For I events a further classification

  2. Vertical E × B drift velocity variations and associated low-latitude ionospheric irregularities investigated with the TOPEX and GPS satellite data

    Directory of Open Access Journals (Sweden)

    I. Horvath

    2003-04-01

    Full Text Available With a well-selected data set, the various events of the vertical E × B drift velocity variations at magnetic-equator-latitudes, the resultant ionospheric features at low-and mid-latitudes, and the practical consequences of these E × B events on the equatorial radio signal propagation are demonstrated. On a global scale, the development of a equatorial anomaly is illustrated with a series of 1995 global TOPEX TEC (total electron content maps. Locally, in the Australian longitude region, some field-aligned TOPEX TEC cross sections are combined with the matching Guam (144.86° E; 13.59° N, geographic GPS (Global Positioning System TEC data, covering the northern crest of the equatorial anomaly. Together, the 1998 TOPEX and GPS TEC data are utilized to show the three main events of vertical E × B drift velocity variations: (1 the pre-reversal enhancement, (2 the reversal and (3 the downward maximum. Their effects on the dual-frequency GPS recordings are documented with the raw Guam GPS TEC data and with the filtered Guam GPS dTEC/min or 1-min GPS TEC data after Aarons et al. (1997. During these E × B drift velocity events, the Port Moresby (147.10° E; - 9.40° N, geographic virtual height or h'F ionosonde data (km, which cover the southern crest of the equatorial anomaly in the Australian longitude region, show the effects of plasma drift on the equatorial ionosphere. With the net (D horizontal (H magnetic field intensity parameter, introduced and called DH or Hequator-Hnon-equator (nT by Chandra and Rastogi (1974, the daily E × B drift velocity variations are illustrated at 121° E (geographic in the Australian longitude region. The results obtained with the various data show very clearly that the development of mid-latitude night-time TEC increases is triggered by the westward electric field as the appearance of such night-time TEC increases coincides with the E × B drift velocity reversal. An explanation is offered with the F

  3. VLF and HF Plasma Waves Associated with Spread-F Plasma Depletions Observed on the C/NOFS Satellite

    Science.gov (United States)

    Pfaff, Robert; Freudenreich, H.; Schuck, P.; Klenzing, J.

    2011-01-01

    The C/NOFS spacecraft frequently encounters structured plasma depletions associated with equatorial spread-F along its trajectory that varies between 401 km perigee and 867 km apogee in the low latitude ionosphere. We report two classes of plasma waves detected with the Vector Electric Field Investigation (VEFI) that appear when the plasma frequency is less than the electron gyro frequency, as is common in spread-F depletions where the plasma number density typically decreases below 10(exp 4)/cu cm. In these conditions, both broadband VLF waves with a clear cutoff at the lower hybrid frequency and broadband HF waves with a clear cutoff at the plasma frequency are observed. We interpret these waves as "hiss-type" emissions possibly associated with the flow of suprathermal electrons within the inter-hemispherical magnetic flux tubes. We also report evidence of enhanced wave "transients" sometimes embedded in the broader band emissions that are associated with lightning sferics detected within the depleted plasma regions that appear in both the VLF and HF data. Theoretical implications of these observations are discussed.

  4. Coherent multiple Pc1 pulsation bands: possible evidence for the ionospheric Alfvén resonator

    Directory of Open Access Journals (Sweden)

    F. Z. Feygin

    1994-01-01

    Full Text Available A fair fraction of Pc1 pulsation events observed on the ground includes more than one simultaneous pulsation band. In most such multiband events the bands display different characteristics and, therefore, come from different source regions via horizontal ducting in the ionosphere. However, in this report we identify a new "coherent" subclass of multiband Pc1 events where the pearls of the simultaneous bands have the same group velocities (repetition rates as well as dispersion and other properties, thus implying that the bands are produced by the same source. Studying one example of such a coherent multiband event in more detail, we argue that these events defy an explanation in terms of band splitting by magnetospheric heavy ions because the observed frequency gap between the bands is smaller than would result in such a case. We interpret these events to be due to the frequency dependence of the ionospheric reflection coefficient of Alfvén waves. An oscillatory frequency dependence of the coefficient is a natural consequence of the idea that the ionosphere acts as a resonator for Alfvén waves. We also discuss other predictions of this interpretation.

  5. Coherent multiple Pc1 pulsation bands: possible evidence for the ionospheric Alfvén resonator

    Directory of Open Access Journals (Sweden)

    F. Z. Feygin

    Full Text Available A fair fraction of Pc1 pulsation events observed on the ground includes more than one simultaneous pulsation band. In most such multiband events the bands display different characteristics and, therefore, come from different source regions via horizontal ducting in the ionosphere. However, in this report we identify a new "coherent" subclass of multiband Pc1 events where the pearls of the simultaneous bands have the same group velocities (repetition rates as well as dispersion and other properties, thus implying that the bands are produced by the same source. Studying one example of such a coherent multiband event in more detail, we argue that these events defy an explanation in terms of band splitting by magnetospheric heavy ions because the observed frequency gap between the bands is smaller than would result in such a case. We interpret these events to be due to the frequency dependence of the ionospheric reflection coefficient of Alfvén waves. An oscillatory frequency dependence of the coefficient is a natural consequence of the idea that the ionosphere acts as a resonator for Alfvén waves. We also discuss other predictions of this interpretation.

  6. Measurements and simulation of ionospheric scattering on VHF and UHF radar signals: Channel scattering function

    Science.gov (United States)

    Rogers, Neil C.; Cannon, Paul S.; Groves, Keith M.

    2009-02-01

    The design and operation of transionospheric VHF and UHF radars requires knowledge of amplitude and phase scintillation due to ionospheric scattering. Phase coherence is of particular importance where long coherent integration periods and large bandwidths are required. A thin phase screen, parabolic equation based, Trans-Ionospheric Radio Propagation Simulator (TIRPS) is described. Modeled channel scattering functions (CSFs) are compared to experimental VHF and UHF data derived from the Advanced Research Projects Agency Long-range Tracking and Instrumentation Radar on Kwajalein Island (9.4°N, 166.8°E). TIRPS quantitatively reproduces the experimental results, including the quasi-parabolic profile observed in the measured CSFs under strong turbulence conditions. Variations in the simulated CSF with ionospheric phase screen parameters are also presented. Under conditions of high integrated strength of turbulence (CkL), a low phase spectral index (p = 1), indicating relatively dense small-scale irregularities, produces pronounced range spreading. Conversely, when the spectral index is high (p = 4), indicative of strong focusing/defocusing by large-scale irregularities, there is increased Doppler spreading and, when the outer scale of irregularities is large, a greater likelihood of asymmetry of the CSF about the zero Doppler axis.

  7. Observation and simulation of the ionosphere disturbance waves triggered by rocket exhausts

    Science.gov (United States)

    Lin, Charles C. H.; Chen, Chia-Hung; Matsumura, Mitsuru; Lin, Jia-Ting; Kakinami, Yoshihiro

    2017-08-01

    Observations and theoretical modeling of the ionospheric disturbance waves generated by rocket launches are investigated. During the rocket passage, time rate change of total electron content (rTEC) enhancement with the V-shape shock wave signature is commonly observed, followed by acoustic wave disturbances and region of negative rTEC centered along the trajectory. Ten to fifteen min after the rocket passage, delayed disturbance waves appeared and propagated along direction normal to the V-shape wavefronts. These observation features appeared most prominently in the 2016 North Korea rocket launch showing a very distinct V-shape rTEC enhancement over enormous areas along the southeast flight trajectory despite that it was also appeared in the 2009 North Korea rocket launch with the eastward flight trajectory. Numerical simulations using the physical-based nonlinear and nonhydrostatic coupled model of neutral atmosphere and ionosphere reproduce promised results in qualitative agreement with the characteristics of ionospheric disturbance waves observed in the 2009 event by considering the released energy of the rocket exhaust as the disturbance source. Simulations reproduce the shock wave signature of electron density enhancement, acoustic wave disturbances, the electron density depletion due to the rocket-induced pressure bulge, and the delayed disturbance waves. The pressure bulge results in outward neutral wind flows carrying neutrals and plasma away from it and leading to electron density depletions. Simulations further show, for the first time, that the delayed disturbance waves are produced by the surface reflection of the earlier arrival acoustic wave disturbances.

  8. Conjectured chaotic nature of the ionosphere-magnetosphere coupling in a reconfigurating magnetosphere

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    E. B. Wodnicka

    1996-01-01

    Full Text Available During substorms the magnetic field configuration changes in time; stretching of the magnetosphere during growth phase is followed by its collapse after the onset of the expansion phase. In this study the ionospheric origin oxygen ion dynamics in a time-dependent magnetosphere is analyzed. An induction electric field of several mV/m due to the reconfigurating magnetic field determines the details of the ion extraction from the auroral topside ionosphere. Two regimes of motion are discernible; a regime in regions far from the equatorial plane where the magnetic moment is conserved and a regime near the equatorial plane, in which the motion produces magnetic moment jumps and oscillations. The time spent by the ion in the regions is determined by the initial characteristics of the ion and by the field transition features. Lyapunov characteristic exponents are calculated to estimate the sensitivity of the system to initial conditions. Their values are higher for orbits with chaotic segments compared with the orbits in the static magnetic field and depend on the amplitude of the induced electric field. It follows from the study that the region of chaos usually localized far beyond 10 RE in the plasma sheet is expected to approach closer to the Earth ( r = 6 - 7 RE during substorm associated reconfigurations of the magnetosphere, due to the auroral ionospheric ions.

  9. Topside ionospheric vertical electron density profile reconstruction using GPS and ionosonde data: possibilities for South Africa

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    P. Sibanda

    2011-02-01

    Full Text Available Successful empirical modeling of the topside ionosphere relies on the availability of good quality measured data. The Alouette, ISIS and Intercosmos-19 satellite missions provided large amounts of topside sounder data, but with limited coverage of relevant geophysical conditions (e.g., geographic location, diurnal, seasonal and solar activity by each individual mission. Recently, methods for inferring the electron density distribution in the topside ionosphere from Global Positioning System (GPS-based total electron content (TEC measurements have been developed. This study is focused on the modeling efforts in South Africa and presents the implementation of a technique for reconstructing the topside ionospheric electron density (Ne using a combination of GPS-TEC and ionosonde measurements and empirically o