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1

Higher order ionospheric effects on GNSS positioning in the European Region  

Microsoft Academic Search

In addition to the common practice of eliminating the (first order) ionospheric effect, for instance, by the ionosphere-free observable, this work shows a method of accounting for the remaining (higher order) ionosperic effects, which lead to residual range errors (RREs) in GNSS positioning. An investigation on the higher (second and third) order ionospheric effects (Ion2 and Ion3) in the European

Zeynep G. Elmas; Marcio Aquino; Haroldo Marques; Joao F. G. Monico

2010-01-01

2

First estimates of the second-order ionospheric effect on radio occultation observations  

Microsoft Academic Search

This study examines the impact of the second-order ionospheric effect on radio occultation (RO) data products. We propose a new linear combination between dual frequency GPS observables, which retrieves slant total electron content free from the second-order ionospheric effect. Our STEC values differ from those obtained by independent techniques by a maximum of 3 total electron content units (TECU), depending

Panagiotis Vergados; Spiros D. Pagiatakis

2010-01-01

3

Higher order ionospheric effects on GNSS positioning in the European Region  

NASA Astrophysics Data System (ADS)

In addition to the common practice of eliminating the (first order) ionospheric effect, for instance, by the ionosphere-free observable, this work shows a method of accounting for the remaining (higher order) ionosperic effects, which lead to residual range errors (RREs) in GNSS positioning. An investigation on the higher (second and third) order ionospheric effects (Ion2 and Ion3) in the European region during the high and low periods of the solar cycle is presented in this work. Days are selected for analysis in terms of the planetary K index (measure of disturbances in the geomagnetic field), Kp, which provides a reasonable threshold to include and exclude the effect of geomagnetic storms on the state of the ionosphere. The stations analyzed in this work are selected from the International GNSS Service (IGS) network in Europe, with a geographical distribution in terms of latitude (mid and high latitudes, including the auroral region) and longitude. This work investigates RREs due to Ion2 and Ion3 by using the program Rinex_HO (Marques et al. 2007) which estimates these errors and the total electron content (TEC) along line of sight for each receiver/satellite link. It also creates new GPS observation files that are corrected for these higher order ionospheric effects. Thereby it is possible to assess the effect of correcting the GPS observations for the higher order ionospheric terms in the station coordinates estimation. In this paper the precise point positioning (PPP) approach was used for analysis.

Elmas, Zeynep G.; Aquino, Marcio; Marques, Haroldo; Monico, Joao F. G.

2010-05-01

4

Higher order ionospheric effects in GNSS positioning in the European region  

NASA Astrophysics Data System (ADS)

After removal of the Selective Availability in 2000, the ionosphere became the dominant error source for Global Navigation Satellite Systems (GNSS), especially for the high-accuracy (cm-mm) demanding applications like the Precise Point Positioning (PPP) and Real Time Kinematic (RTK) positioning. The common practice of eliminating the ionospheric error, e.g. by the ionosphere free (IF) observable, which is a linear combination of observables on two frequencies such as GPS L1 and L2, accounts for about 99 % of the total ionospheric effect, known as the first order ionospheric effect (Ion1). The remaining 1 % residual range errors (RREs) in the IF observable are due to the higher - second and third, order ionospheric effects, Ion2 and Ion3, respectively. Both terms are related with the electron content along the signal path; moreover Ion2 term is associated with the influence of the geomagnetic field on the ionospheric refractive index and Ion3 with the ray bending effect of the ionosphere, which can cause significant deviation in the ray trajectory (due to strong electron density gradients in the ionosphere) such that the error contribution of Ion3 can exceed that of Ion2 (Kim and Tinin, 2007). The higher order error terms do not cancel out in the (first order) ionospherically corrected observable and as such, when not accounted for, they can degrade the accuracy of GNSS positioning, depending on the level of the solar activity and geomagnetic and ionospheric conditions (Hoque and Jakowski, 2007). Simulation results from early 1990s show that Ion2 and Ion3 would contribute to the ionospheric error budget by less than 1 % of the Ion1 term at GPS frequencies (Datta-Barua et al., 2008). Although the IF observable may provide sufficient accuracy for most GNSS applications, Ion2 and Ion3 need to be considered for higher accuracy demanding applications especially at times of higher solar activity. This paper investigates the higher order ionospheric effects (Ion2 and Ion3, however excluding the ray bending effects associated with Ion3) in the European region in the GNSS positioning considering the precise point positioning (PPP) method. For this purpose observations from four European stations were considered. These observations were taken in four time intervals corresponding to various geophysical conditions: the active and quiet periods of the solar cycle, 2001 and 2006, respectively, excluding the effects of disturbances in the geomagnetic field (i.e. geomagnetic storms), as well as the years of 2001 and 2003, this time including the impact of geomagnetic disturbances. The program RINEX_HO (Marques et al., 2011) was used to calculate the magnitudes of Ion2 and Ion3 on the range measurements as well as the total electron content (TEC) observed on each receiver-satellite link. The program also corrects the GPS observation files for Ion2 and Ion3; thereafter it is possible to perform PPP with both the original and corrected GPS observation files to analyze the impact of the higher order ionospheric error terms excluding the ray bending effect which may become significant especially at low elevation angles (Ioannides and Strangeways, 2002) on the estimated station coordinates.

Elmas, Z. G.; Aquino, M.; Marques, H. A.; Monico, J. F. G.

2011-08-01

5

Latitudinal, solar, and vertical variability of higher-order ionospheric effects on atmospheric parameter retrievals from radio occultation measurements  

Microsoft Academic Search

Models higher-order ionospheric effects in a GPS\\/RO geometryQuantifies, for the first time, the impact of those effects on RO temperaturesEmphasizes the importance of accounting those effects on future RO missions

Panagiotis Vergados; Spiros D. Pagiatakis

2011-01-01

6

6. Coordinate solution shift due to 2-nd order ionospheric effect The second-order ionospheric path-delay was modelled for a worldwide  

E-print Network

, IRI2007 values for TEC and the height of ionospheric maximum, and International Geomagnetic Reference maps of the I2-related positioning correction are presented at the right. 3. Ionosphere, its diurnal by solar radiation. The electron density profile and TEC are highly variable with the change of local time

7

Effects of the active auroral ionosphere on magnetosphere - ionosphere coupling  

Microsoft Academic Search

The thesis is devoted to the effects of electromagnetic coupling between the Earth's magnetosphere and the active auroral ionosphere. The research has been focused, in particular, on the concept of ionospheric feedback instability. The feedback instability arises when localized perturbations in ionospheric conductivity become polarized in the presence of background electric field. Under favorable conditions of low ionospheric conductivity and

Dimitri Pokhotelov

2003-01-01

8

Ionospheric effects during severe space weather events seen in ionospheric service data products  

Microsoft Academic Search

Space weather effects are closely related to complex perturbation processes in the magnetosphere-ionosphere-thermosphere systems, initiated by enhanced solar energy input. To understand and model complex space weather processes, different views on the same subject are helpful. One of the ionosphere key parameters is the Total Electron Content (TEC) which provides a first or-der approximation of the ionospheric range error in

Norbert Jakowski; Michael Danielides; Christoph Mayer; Claudia Borries

2010-01-01

9

Higher-order ionosphere modeling for CODE's next reprocessing activities  

NASA Astrophysics Data System (ADS)

CODE (the Center for Orbit Determination in Europe) is a joint venture between the Astronomical Institute of the University of Bern (AIUB, Bern, Switzerland), the Federal Office of Topography (swisstopo, Wabern, Switzerland), the Federal Agency for Cartography and Geodesy (BKG, Frankfurt am Main, Germany), and the Institut für Astronomische und Phsyikalische Geodäsie of the Technische Universität München (IAPG/TUM, Munich, Germany). It acts as one of the global analysis centers of the International GNSS Service (IGS) and participates in the first IGS reprocessing campaign, a full reanalysis of GPS data collected since 1994. For a future reanalyis of the IGS data it is planned to consider not only first-order but also higher-order ionosphere terms in the space geodetic observations. There are several works (e.g. Fritsche et al. 2005), which showed a significant and systematic influence of these effects on the analysis results. The development version of the Bernese Software used at CODE is expanded by the ability to assign additional (scaling) parameters to each considered higher-order ionosphere term. By this, each correction term can be switched on and off on normal-equation level and, moreover, the significance of each correction term may be verified on observation level for different ionosphere conditions.

Lutz, S.; Schaer, S.; Meindl, M.; Dach, R.; Steigenberger, P.

2009-12-01

10

Higher order moments used in ionospheric scintillation description  

NASA Astrophysics Data System (ADS)

Ionospheric scintillations, caused by small scale fluctuations in the electron density structure, presents one of the most influential factor in transionospheric radio wave propagation and important topic for the mitigation of its effects. Initiating disturbances and distortion in phase and amplitude of the propagating signal, scintillation can significantly affect the GNSS accuracy and cause serious problems to commercial navigation systems. Decades of investigations of the probability distribution of the scintillating signals brought a lot of possible solutions, several of them are widely adopted and are in use this days. Solutions like joint Gaussian distribution of complex signal and Rytov solution seems to work for weak scintillating signals, but still there is not an easy way to derive satisfactory results, leading to need for further investigations [Yeh and Liu, 1982]. The focus of this paper is on the statistical analysis of ionospheric scintillation. We analyze various probability distribution functions of scintillating signals using simulated and real data. The analysis results are presented through higher order moments, dependent on various parameters (scintillation index, phase variance, season, time of the day and solar/magnetic activity). Implementation of higher order moments, skewness and kurtosis, could give more information about the ionospheric irregularities influence on the propagating signal and relation to the time delay of the signal.

Stevanovic, D.; Wernik, A. W.

2013-12-01

11

Solar cosmic ray effects in the lower ionosphere  

NASA Technical Reports Server (NTRS)

The polar cap absorption (PCA) events are the most remarkable geophysical phenomena in the high latitude ionosphere. Their effects are extended on the whole polar region in both hemispheres. The PCA events are caused by the intense fluxes of the solar cosmic rays (SCR) which are generated by the solar proton flares. Entering into the Earth's magnetosphere and ionosphere the SCR fluxes create excessive anomal ionization at the ionospheric heights of 50 to 100 km which exceeds usual undisturbed level of ionization in several orders of magnitude. The PCA events can be considered as catastrophic in relation to the polar ionosphere because all radio systems using ionospheric radio channels ceased to operate during these events. On the other hand the abnormally high level of ionization in the ionospheric D region during the PCA events create excellent opportunities to conduct fruitful aeronomical research for the lower ionosphere. Obvious scientific and practical importance of the PCA events leads to publishing of special PCA catalogues. The ionospheric effects caused by the SCR fluxes were profoundly described in the classical paper (Bailey, 1964). Nevertheless several aspects of this problem were not studied properly. An attempt is made to clarify these questions.

Shirochkov, A. V.

1989-01-01

12

Ionospheric effects during severe space weather events seen in ionospheric service data products  

NASA Astrophysics Data System (ADS)

Space weather effects are closely related to complex perturbation processes in the magnetosphere-ionosphere-thermosphere systems, initiated by enhanced solar energy input. To understand and model complex space weather processes, different views on the same subject are helpful. One of the ionosphere key parameters is the Total Electron Content (TEC) which provides a first or-der approximation of the ionospheric range error in Global Navigation Satellite System (GNSS) applications. Additionally, horizontal gradients and time rate of change of TEC are important for estimating the perturbation degree of the ionosphere. TEC maps can effectively be gener-ated using ground based GNSS measurements from global receiver networks. Whereas ground based GNSS measurements provide good horizontal resolution, space based radio occultation measurements can complete the view by providing information on the vertical plasma density distribution. The combination of ground based TEC and vertical sounding measurements pro-vide essential information on the shape of the vertical electron density profile by computing the equivalent slab thickness at the ionosonde station site. Since radio beacon measurements at 150/400 MHz are well suited to trace the horizontal structure of Travelling Ionospheric Dis-turbances (TIDs), these data products essentially complete GNSS based TEC mapping results. Radio scintillation data products, characterising small scale irregularities in the ionosphere, are useful to estimate the continuity and availability of transionospheric radio signals. The different data products are addressed while discussing severe space weather events in the ionosphere e.g. events in October/November 2003. The complementary view of different near real time service data products is helpful to better understand the complex dynamics of ionospheric perturbation processes and to forecast the development of parameters customers are interested in.

Jakowski, Norbert; Danielides, Michael; Mayer, Christoph; Borries, Claudia

13

Assessments of higher-order ionospheric effects on GPS coordinate time series: A case study of CMONOC with longer time series  

NASA Astrophysics Data System (ADS)

Higher-order ionospheric (HIO) corrections are proposed to become a standard part for precise GPS data analysis. For this study, we deeply investigate the impacts of the HIO corrections on the coordinate time series by implementing re-processing of the GPS data from Crustal Movement Observation Network of China (CMONOC). Nearly 13 year data are used in our three processing runs: (a) run NO, without HOI corrections, (b) run IG, both second- and third-order corrections are modeled using the International Geomagnetic Reference Field 11 (IGRF11) to model the magnetic field, (c) run ID, the same with IG but dipole magnetic model are applied. Both spectral analysis and noise analysis are adopted to investigate these effects. Results show that for CMONOC stations, HIO corrections are found to have brought an overall improvement. After the corrections are applied, the noise amplitudes decrease, with the white noise amplitudes showing a more remarkable variation. Low-latitude sites are more affected. For different coordinate components, the impacts vary. The results of an analysis of stacked periodograms show that there is a good match between the seasonal amplitudes and the HOI corrections, and the observed variations in the coordinate time series are related to HOI effects. HOI delays partially explain the seasonal amplitudes in the coordinate time series, especially for the U component. The annual amplitudes for all components are decreased for over one-half of the selected CMONOC sites. Additionally, the semi-annual amplitudes for the sites are much more strongly affected by the corrections. However, when diplole model is used, the results are not as optimistic as IGRF model. Analysis of dipole model indicate that HIO delay lead to the increase of noise amplitudes, and that HIO delays with dipole model can generate false periodic signals. When dipole model are used in modeling HIO terms, larger residual and noise are brought in rather than the effective improvements.

Jiang, Weiping; Deng, Liansheng; Zhou, Xiaohui; Ma, Yifang

2014-05-01

14

Solar rotation effects on the Martian ionosphere  

NASA Astrophysics Data System (ADS)

We present a detailed investigation of the solar rotation effects on the Martian high-latitude (~63°N-81°N) ionosphere using the electron density (Ne) data measured by Mars Global Surveyor and solar XUV and EUV fluxes measured by SOHO under high (2000-2001), medium (2003), and low (2005) solar activity conditions. A fast Fourier transform spectral analysis method is used to estimate the amplitude of the rotation period in these parameters. This method clearly reveals the presence of solar rotation effects in the Martian ionospheric Ne at all altitudes (90-220 km), peak electron density (NmM2), and total electron content under the three solar activity conditions. These effects are in phase with the solar UV fluxes (corrected for the Martian orbit). The period of rotation effect (~26 days) is the same at all altitudes, though its amplitude is strongest at the ionospheric M2 peak (~135-140 km, ~3.5-6% of the mean values) and has a secondary enhancement at the M1 peak (~110-115 km). The effect of solar rotation on the M2 peak is larger during medium solar activity (2003) than during high solar activity (2000-2001). The effect, however, is absent in the ionospheric peak height (hmM2). The rotation effects on Mars are also compared with those on the Earth. Unlike at Mars, the Earth's high-latitude ionosphere shows no clear solar rotation effect, though the effect is observed clearly at lower latitudes.

Venkateswara Rao, N.; Balan, N.; Patra, A. K.

2014-08-01

15

Ionosphere scintillation effects on navigation systems  

NASA Astrophysics Data System (ADS)

This article deals with the impact of ionospheric electron density inhomogeneities on the functionality of global navigation satellite systems emphasizing positioning errors. The scintillation characteristics of transmitted signals have been obtained using data gathered in measurement campaigns. The effects on a standard receiver are then presented. Positioning errors due to scintillations were shown to be greater than 10 meters in the worst case.

Béniguel, Yannick; Adam, Jean-Pierre; Bourdillon, Alain; Lassudrie-Duchesne, P.

2011-03-01

16

A review of ionospheric effects on Earth-space propagation  

NASA Technical Reports Server (NTRS)

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.

Klobuchar, J. A.

1984-01-01

17

Equatorial ionosphere 'fountain- effect' above imminent earthquake epicenter  

NASA Astrophysics Data System (ADS)

Existence of lithosphere-ionosphere interaction is known for a long time, but it does not mean that the ionospheric morphology above areas of earthquakes preparation is investigated sufficiently well. It was shown that seismo-precursor variations of the atmosphere electricity cause appropriate electric field at the ionospheric heights, which being added to existing natural field may both increase or decrease its action on the ionospheric plasma characteristics: drifts, aeronomy, plasma chemistry, ion composition etc. Anomalous variations appear inside whole ionosphere volume from the lowest boundary of Earth's plasma shell (100 km) up to 1000km and higher. Under fortunate coincidence seismo-precursor electric field can generate natural ionosphere phenomena, 'fountain- effect', leading to Appleton anomaly in the equatorial ionosphere over future earthquake position. Our basic idea is to take into account dependence of the observable effects on a geographical position of the earthquake epicenter. As for low latitudes it is proved by specificity of formation and dynamics of equatorial ionosphere (seismogenic ""fountain" effect , first of all), and also by features of earth crust structure close to the equator (mainly meridionally alongated tectonic faults). Ionospheric effects of low-latitude earthquakes were not investigated separately so far though rather semo-active zones are located namely at low latitudes: India, Peru, Oceania. We used the data of topside sounding of ALOUETTE-1 and ISS-b satellites, and also data of ground-based vertical sounding stationary stations Kodaikanal, Huancayo, Djibouti etc. and records of the total electron content (TEC).

Ruzhin, Yu.; Depueva, A. H.; Devi, M.

2003-04-01

18

Measurements of ionospheric effects on wideband signals at VHF  

SciTech Connect

Radars operating at very high frequency (VHF) have enhanced foliage and ground penetration compared to radars operated at higher frequencies. For example, VHF systems operated from airplanes have been used as synthetic aperture radars (SAR); a satellite-borne VHF SAR would have considerable utility. In order to operate with high resolution it would have to use both a large relative bandwidth and a large aperture. A satellite-borne radar would likely have to operate at altitudes above the maximum density of the ionosphere; the presence of the ionosphere in the propagation path of the radar will cause a deterioration of the performance because of dispersion over the bandwidth. The author presents measurements of the effects of the ionosphere on radar signals propagated from a source on the surface of the Earth and received by instruments on the FORTE satellite at altitudes of 800 km. The author employs signals with a 90 MHz bandwidth centered at 240 MHz with a continuous digital recording period of 0.6 s.

Fitzgerald, T.J.

1998-08-17

19

On the second order statistics for GPS ionospheric scintillation modeling  

NASA Astrophysics Data System (ADS)

Equatorial ionospheric scintillation is a phenomenon that occurs frequently, typically during nighttime, affecting radio signals that propagate through the ionosphere. Depending on the temporal and spatial distribution, ionospheric scintillation can represent a problem in the availability and precision for the Global Navigation Satellite System's users. This work is concerned with the statistical evaluation of the amplitude ionospheric scintillation fading events, namely, level crossing rate (LCR) and average fading duration (AFD). Using ?-? model, the LCR and AFD are validated against experimental data obtained in São José dos Campos (23.1°S; 45.8°W; dip latitude 17.3°S), Brazil, a station located near the southern crest of the ionospheric equatorial ionization anomaly. The amplitude scintillation data were collected between December 2001 and January 2002, a period of high solar flux conditions. The obtained results with the proposed model fitted quite well with the experimental data and performed better when compared to the widely used Nakagami-m model. Additionally, this work discusses the estimation of ? and ? parameters, and the best fading coefficients found in this analysis are related to scintillation severity. Finally, for theoretical situations in which no set of experimental data are available, this work also presents parameterized equations to describe these fading statistics properly.

Oliveira Moraes, Alison; Paula, Eurico Rodrigues; Assis Honorato Muella, Marcio Tadeu; Perrella, Waldecir João.

2014-02-01

20

REVIEWS OF TOPICAL PROBLEMS: Nonlinear effects in the ionosphere  

NASA Astrophysics Data System (ADS)

The review is based in a report presented by the author at the RAS Physical Sciences Division's session in honor of Vitaly L Ginzburg's 90th birthday. It examines the current status of theoretical and experimental research on nonlinear phenomena arising when a powerful radio wave propagates in the ionosphere. The focus is on the modification of the ionosphere under the resonance excitation of natural plasma oscillations by radio waves. The upper-hybrid resonance gives rise to strong upper- and lower-hybrid plasma waves; excites strongly elongated ionospheric irregularities, and induces artificial ionospheric radio emission. Nonlinear processes are found to undergo complete transformation near double resonances, when the upper-hybrid frequency is close to a multiple of the electron gyromagnetic frequency. In the neighborhood of the Langmuir resonance, intense plasma waves and ion-sound waves are excited, electrons are effectively accelerated, and an artificial glow of the ionosphere appears.

Gurevich, A. V.

2007-11-01

21

Plasma jet effects on the ionospheric plasma  

NASA Technical Reports Server (NTRS)

Heavy ion beams were injected into the ionospheric plasma (experiments ARCS 1 and ARCS 2). In ARCS 1, operation of a 25eV argon ion source, mounted on a plasma diagnostic payload, produced an accelerated electron population; broadband electric field turbulence; large, spin synchronized electric field perturbations; and depletions of thermal ions. In ARCS 2, the ion source was deployed upward along the local magnetic field direction away from the diagnostic payload, and observed effects are contained within several meters of the ion source. However, enhanced wave levels near the LHR frequency are observed at distances up to 1 km, as are the injected ions themselves. A measurement of the dominant wavelength of the enhanced waves is consistent with an inference based upon the accelerated electron population seen in ARCS 1. This electron population is not evident during ARCS 2.

Moore, T. E.; Arnoldy, R. L.; Cahill, L. J.; Kintner, P. M.

1983-01-01

22

Nonlinear effects in the ionospheric Alfvén resonator  

Microsoft Academic Search

A two-dimensional nonlinear multi-fluid MHD model of the ionosperic Alfvén resonator is presented. The resonator is excited by a packet of shear Alfvén waves propagating downward toward the ionosphere from high altitudes. It is shown that the nonlinear (ponderomotive) force of standing oscillations in the ionospheric Alfvén resonator creates plasma flows along the geomagnetic field that modify the plasma density

D. Sydorenko; R. Rankin; K. Kabin

2008-01-01

23

Investigation of the seismo-ionospheric effects on the base of GPS/GLONASS measurements  

NASA Astrophysics Data System (ADS)

During last years the monitoring of the ionospheric effects of different origin is carried out mainly with use of Global Navigating Satellite Systems (GPS / GLONASS). By means of measurements of the signals temporal delays it is possible to do the mapping of total electron content (TEC) in a column of unit cross section through the Earth's ionosphere and investigate its temporal evolution depended on the variations of electron concentration (NmF2) in the F2 ionospheric region. In the given report we present results of analysis of spatial-temporal variability of the ionosphere during the earthquake preparation phase for several major earthquakes which took place in Japan. It was revealed that for considered events mainly positive TEC anomalies appeared 1-5 days prior to the earthquake. The enhancement of electron concentration reached the value of 30-70% relative to the quiet geomagnetic conditions. In order to analyze the revealed effects in more details it was additionally involved data of GPS TEC values over GPS stations located at different distances from earthquake epicenters and data of vertical sounding of the ionosphere (NICT database). The hourly values of critical frequency of ionospheric F2 and Es layers were obtained from manually scaled ionograms recorded at Japanese ionospheric sounding stations Wakkanai, Kokubunji and Yamagawa. Acknowledgments. We acknowledge the IGS community for providing GPS permanent data and WDC for Ionosphere, Tokyo, National Institute of Information and Communications Technology (NICT) for providing ionosonde data. This work was supported by Russian Federation President grant MK-2058.2011.5.

Zakharenkova, I.; Cherniak, Iu.; Shagimuratov, I.; Suslova, O.

2012-04-01

24

Ionospheric effects of the solar eclipse of July 31, 1981  

NASA Astrophysics Data System (ADS)

The paper discusses observations of polarization-plane Faraday rotation at a frequency of 40 MHz and radio emission from near-earth space at 550 MHz during the solar eclipse of July 31, 1981. An effort was made to correlate the eclipse with the irregular structure of the ionosphere and changes in the total electron content. The observed effects do not appear to be connected with the eclipse but appear to be due to high solar, geomagnetic, and ionospheric activity.

Musatenko, S. I.; Ivchenko, I. S.; Avramchuk, A. D.; Datsko, E. P.; Maksimenko, O. I.

1987-08-01

25

Effects of UGTs on the ionosphere  

SciTech Connect

In this paper we describe the processes that propagate local effects of underground nuclear tests from the ground into the upper atmosphere, and produce a detectable signal in the ionosphere. Initially, the blast wave from a UGT radially expands, until it reaches the surface of the earth. The wave is both reflected and transmitted at this sharp discontinuity in propagation media. ne reflected wave combines with the incident wave to form an Airy surface,'' at which very strong ripping forces tear the earth apart. This broken region is called the spat zone,'' and is launched into ballistic motion. The resultant ground motion launches an acoustical wave into the atmosphere. This acoustic wave, with overpressures of a few tenths of one percent, propagates upwards at the speed of sound. Assuming purely linear propagation, the path of the acoustic energy can be tracked using raytracing models. Most of the wave energy, which is radiated nearly vertically, tends to propagate into the upper atmosphere, while wave energy radiated at angles greater than about 30 degrees to the vertical will be reflected back to earth and is probably what is seen by most infrasonde measurements.

Argo, P.E.; Fitzgerald, T.J.

1992-01-01

26

Effects of UGTs on the ionosphere  

SciTech Connect

In this paper we describe the processes that propagate local effects of underground nuclear tests from the ground into the upper atmosphere, and produce a detectable signal in the ionosphere. Initially, the blast wave from a UGT radially expands, until it reaches the surface of the earth. The wave is both reflected and transmitted at this sharp discontinuity in propagation media. ne reflected wave combines with the incident wave to form an ``Airy surface,`` at which very strong ripping forces tear the earth apart. This broken region is called the ``spat zone,`` and is launched into ``ballistic motion. The resultant ground motion launches an acoustical wave into the atmosphere. This acoustic wave, with overpressures of a few tenths of one percent, propagates upwards at the speed of sound. Assuming purely linear propagation, the path of the acoustic energy can be tracked using raytracing models. Most of the wave energy, which is radiated nearly vertically, tends to propagate into the upper atmosphere, while wave energy radiated at angles greater than about 30 degrees to the vertical will be reflected back to earth and is probably what is seen by most infrasonde measurements.

Argo, P.E.; Fitzgerald, T.J.

1992-10-01

27

Ionospheric Effects of Underground Nuclear Explosions  

NASA Astrophysics Data System (ADS)

Telemetry from the Russian INTERCOSMOS 24 satellite recorded ELF and VLF electromagnetic disturbances in the outer ionosphere from an underground nuclear explosion that was detonated at Novaya Zemlya Island on 24 October 1994. The IC24 satellite observations were obtained at about 900 km altitude within a few degrees of ground zero. The disturbances were interpreted for magnetohydrodynamic excitation of the ionosphere’s E layer by the acoustic wave. Electrons are accelerated along the magnetic force lines to amplify longitudinal currents and magnetic disturbances that may be measured by magnetometers at ground-based observatories and on-board satellites. The underground nuclear test near P’unggye, North Korea on 25 May 2009 provides a further significant opportunity for studying the utility of ionospheric disturbances for characterizing ground zero. Of the seismic, infrasound, hydroacoustic, and radionuclide detection elements of the International Monitoring System (IMS) established by the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO), only the first two elements detected this event. However, the event also appears to have been recorded as a direct traveling ionospheric disturbance (TID) in the slant total electron content (TEC) observations derived from a network of the Global Navigation Satellite System (GNSS) measurements. The TID was observed to distances of at least 600 km from the explosion site propagating with a speed of about 281m/s. Thus, the global distributions and temporal variations of the TEC, may provide important information to help detect and characterize clandestine underground nuclear explosions.

Park, J.; von Frese, R. R.; G-Brzezinska, D. A.; Morton, Y.

2010-12-01

28

A greenhouse effect in the ionosphere?  

Microsoft Academic Search

Following a suggestion by Roble and Dickenson that increases in the mixing ratios of mesospheric carbon dioxide and methane will cool the thermosphere by about 50 K, this paper examines the consequences for the ionosphre. It is concluded that physical and chemical factors that may affect the ionosphere have not been considered in this analysis and therefore further global monitoring

H. Rishbeth

1990-01-01

29

SOLAR FLARE EFFECTS IN THE IONOSPHERE  

Microsoft Academic Search

content of the ionosphere were observed at four or at five stations, simultaneously with the onset of solar flares on May 21 and 23, 1967. The observations are most readily explained by a large, but brief, enhancement of the solar EUV flux on two occasions. An explanation based on X-ray enhancement only does not appear attractive. Time-correlated values of visual

Owen K. Garriott; Aldo V. da Rosa; Michael J. Davis; O. G. Jr. Villard

1967-01-01

30

Method for Canceling Ionospheric Doppler Effect  

NASA Technical Reports Server (NTRS)

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.

Vessot, R. F. C.

1982-01-01

31

Effects of the Earth's Ionosphere on HF Radio Astronomy from Artificial Satellites  

Microsoft Academic Search

A theoretical analysis of the effects of the ionosphere on HF observations from satellite-borne radio telescopes is presented. The primary effect investigated is the focusing effect of the ionosphere on incoming cosmic noise. This effect was computed according to the Hamiltonian equations for a ray path in a general magnetoionic medium, assuming the ionosphere to be a nonhomogenous, nonisotropic, magnetoionic

M. D. Grossi; K. M. Strom; S. E. Strom

1961-01-01

32

Ionospheric effects on polarimetric and interferometric space-borne SAR  

Microsoft Academic Search

In recent years, both polarimetric and interferometric SAR techniques have provided important scientific results. To be useful for science applications, these techniques require precise phase and amplitude calibration. In order to cover large areas using these techniques, it is necessary to use a space-borne SAR. Due to ionospheric disturbance, a space-borne SAR may not be able to produce data useful

Yunjin Kim; J. van Zyl

1998-01-01

33

The effects of solar flares on planetary ionospheres  

E-print Network

1 The effects of solar flares on planetary ionospheres Paul Withers and Michael Mendillo Boston:00-12:30 AOGS Meeting, Singapore #12;Outline · The Sun, solar cycle, solar flares · Observed effects://apod.nasa.gov/apod/image/0712/solarcycle_soho_big.jpg SOHO images at EUV wavelengths (28.4 nm) #12;5 Solar flares http://www

Withers, Paul

34

Observations of the effects of meteors on the ionospheres of  

E-print Network

Observations of the effects of meteors on the ionospheres of Venus, Earth and Mars Paul Withers1, A Planetology: Venus-Earth-Mars, ESLAB 2009 ESTEC, The Netherlands #12;Observations of the effects of meteors that affect metal ion layers ­ Meteor showers ­ Sporadic meteoroids ­ Magnetic fields and winds · Status

Withers, Paul

35

Thermodynamic effect of the ion sound instability in the ionosphere  

NASA Technical Reports Server (NTRS)

During geomagnetic disturbances when the ring current interacts intensely with the plasmasphere, the plasma of this region undergoes a strong heating due to an ion cyclotron instability. This is followed by the transfer of heat along geomagnetic field lines from the heating region to the ionosphere. One of the results of this process is the formation of non-isothermal region (in which T(sub e) greater than 3.4 T(sub i) at ionospheric heights) caused by a rapid cooling the H(+) ions due to their resonant charge exchange with neutral hydrogen. Heat transfer from the top of the flux tube to the ionosphere is investigated using a hydrodynamic model for the ionosphere-plasmasphere coupling. Field-aligned currents, present in the topside ionosphere, are often accompanied by ion sound turbulence. The turbulence scatters electrons, increasing the total electron collision frequency through wave-particle effects. The influence of wave-particle interactions introduces an anomalous component to the total collision frequency, which modifies substantially the heat conduction coefficient of the plasma. As a result, the plasma is heated more intensely above than below this region of ion sound turbulence.

Khazanov, G. V.; Gombosi, T. I.; Gorbachev, O. A.; Trukhan, A. A.; Miller, R. H.

1994-01-01

36

Effects of ionospheric conductance in high-latitude phenomena  

NASA Astrophysics Data System (ADS)

In this thesis, the relationship between several high-latitude phenomena and the ionospheric conductance in both hemispheres is studied theoretically and experimentally. Theoretically, the high-latitude electrodynamics is studied by considering currents in the magnetosphere-ionosphere system resulting from the ionospheric sheet current redistribution between the conjugate ionospheres. It is shown that strong flow between the conjugate ionospheres, the interhemispheric currents (IHC), can be set up if the conductance distribution is asymmetric in the conjugate ionospheric regions. Such conditions are typical for solstices owing to the differences in the solar illumination. Analytical and numerical modeling shows that IHCs can appear in the regions of strong conductance gradient, more specifically around the solar terminator line, and that the intensity of the IHCs can be comparable to the intensity of the well known Region 1/Region 2 currents. The effect of IHC excitation on observable magnetic perturbations on the ground is investigated. It is shown that in the vicinity of the solar terminator line, the pattern of magnetic perturbation can be such that an apparent equivalent current vortex can be detected. In addition, strong conductance gradients are shown to affect significantly the quality of the ionospheric plasma flow estimates from the ground-based magnetometer data. Experimentally, the effect of the nightside ionospheric conductance on occurrence of substorms, global storm sudden commencement and radar auroras is investigated. To characterize substorm occurrence, new parameters, the derivatives of the classical AE and AO indices, are introduced. It is shown that the seasonal and diurnal variations of these parameters are controlled by the total nightside ionospheric conductance in the conjugate regions. The substorm onsets preferentially occur at low levels of the total conductance, which is consistent with the idea of the substorm triggering through the magnetosphere-ionosphere feedback instability. It is hypothesized that the total conductance affects the global storm onsets as well. To check this idea, the 33-year sudden storm commencement (SSC) data are considered. The semiannual, annual, semidiurnal, and diurnal variations in the SSC occurrence rate are found to be significant and these components exhibit a strong relationship with the total conductance of the high-latitude ionospheres. Finally, the SuperDARN midnight echo occurrence is shown to correlate, for some radars, with the total conductance minima and presumably with electric field maxima, which is consistent with general expectation that the F-region irregularities occur preferentially during times of enhanced electric fields. The gradients of the high-latitude conductance can also lead to significant errors in the plasma convection estimates from the ground-based magnetometers, and to investigate this effect a statistical assessment of the difference between the true plasma convection (SuperDARN) and the magnetometer-inferred equivalent convection direction is performed. The largest differences are found for the transition region between the dark and sunlit ionospheres and in the midnight sector where strong conductance gradients are expected due to particle precipitation. Consideration of regular conductance gradients due to solar illumination improves the agreement between the radar and magnetometer data. Finally, an attempt is made to demonstrate the effects of conductance upon the properties of traveling convection vortices (TCVs). Joint SuperDARN and magnetometer data reveal that there is resemblance between the magnetometer and radar inferred TCV images on a scale of thousands of kilometers. However, on a smaller scale of hundreds of kilometers, significant differences are observed.

Benkevitch, Leonid

37

The Effects of Local Ionospheric Decorrelation on LAAS: Theory and Experimental Results  

E-print Network

increases, the lines of sight will travel through different parts of the ionosphere. For a single frequencyThe Effects of Local Ionospheric Decorrelation on LAAS: Theory and Experimental Results Jock R. I adverse effects of the ionosphere on the millions of GPS users. The introduction of the Global Positioning

Stanford University

38

Dynamical effects of substorms in the middle and lower latitude ionosphere. Ph.D. Thesis  

SciTech Connect

The Earth`s ionosphere, a region of the the upper atmosphere spanning altitudes from approximately 100 to 1000 km, contains a complex pattern of electron densities produced by solar emissions, atmospheric chemistry and dynamical processes. In this dissertation, a plasma disturbance effect is identified in long-term observations, characterized statistically, and analyzed using numerical modeling. Results drawn from the model are subjected to verification using a dedicated observational campaign. The distinctive feature treated is a pattern of diurnal double maxima (DDM) in total electron content (TEC) observations. The observed DDM events have a clear relationship with geomagnetic disturbances known as substorms. A time-dependent ionospheric model is used to simulate observed DDM events over a latitudinal range of +/- 38 deg. (dip latitude), and in two longitude sectors (75 deg. W and 7 deg. E). Modeling results show that TEC DDM patterns can be created by a combined effect of ionospheric F region plasma vertical drifts and highly altitude-dependent chemical loss mechanisms. Modeling studies explore two possible substorm-related dynamical sources for these perturbation: magnetospheric electric field penetration and overshielding effects, or traveling disturbances in the neutral atmosphere. Local time, latitudinal, and longitudinal characteristics of these dynamical perturbations are investigated in order to define global-scale signatures of the ionosphere`s response to substorms. An observational campaign was formulated and conducted to verify model predictions. The techniques included: magnetometer in the auroral zone for indications of substorm activity; incoherent scatter radars, from high to low latitudes near 75 deg. W longitude, to measure ionospheric electron densities, plasma drifts and meridional neutral winds; and all sky CCD cameras and a Fabry-Perot interferometer for 6300 A airglow and neutral winds at a sub-auroral site.

Pi, Xiaoqing

1995-01-01

39

A brief review of “solar flare effects” on the ionosphere  

Microsoft Academic Search

The study of solar flare effects (SFEs) on the ionosphere is having a renaissance. The development of GPS ground and satellite data for scientific use has opened up new means for high time resolution research on SFEs. At present, without continuous flare photon spectra (X rays, EUV, UV, and visible) monitoring instrumentation, the best way to model flare spectral changes

B. T. Tsurutani; O. P. Verkhoglyadova; A. J. Mannucci; G. S. Lakhina; G. Li; G. P. Zank

2009-01-01

40

Modeling the Effects of Ionospheric Scintillations on LEO Satellite Communications  

Microsoft Academic Search

The fading statistics of the received signal caused by ionospheric scintillations for a given Earth station in low-Earth orbit (LEO) satellite communication network are studied using the recently available scintillation model. The path distribution from the Earth station to the satellite and the fading statistics of each path are considered. This time-varying channel model allows engineers to understand the effects

Sheng-Yi Li; C. H. Liu

2004-01-01

41

The Effects of Solar Flares on the Ionospheres of Earth and Mars  

E-print Network

The Effects of Solar Flares on the Ionospheres of Earth and Mars Paul Withers Boston University.10.31 (withers@bu.edu) #12;Solar Flares http://www ionosphere to solar flares taught us a lot about the terrestrial ionosphere - the same will be true for Mars

Withers, Paul

42

Ionospheric Effects Observed by Radio Tomography during Severe Geomagnetic Storms  

NASA Astrophysics Data System (ADS)

The geomagnetic storms are an important element of space weather. As known, the distributions of all ionospheric parameters are determined by the interplay of many complex diverse processes of solar-terrestrial coupling. The intervals of geomagnetic storms are marked by dramatic changes in the dynamics of the ionosphere, whose parameters experience significant disturbances. The ionospheric signatures of geomagnetic perturbations are highly diverse in both spatiotemporal scales, ranging from a few seconds to few days and from a few meters to dozen thousand kilometers, and intensity. The methods of GNSS-based radio tomography (RT) are suitable for diagnosing the spatiotemporal structure of ionospheric disturbances caused by different space-weather factors. GNSS comprise the first-generation satellite navigation systems such as low-orbiting (LO) Russian Tsikada and American Transit satellites and second-generation satellite systems such as high-orbiting GPS and GLONASS constellations. The LORT methods reconstruct two-dimensional (2D) structure of the ionospheric electron density distribution in the vertical (altitude-latitude) plane within a spatial sector spanning a few thousand km and a time interval of 10-15 min. The horizontal and vertical resolution of LORT is typically 15-25 km and 25-30 km, respectively. The HORT methods use radio transmissions from HO satellites recorded at the receiving ground network of the International Geodetic Service (IGS), which currently comprises about 2000 receivers. The HORT methods are capable of reconstructing the four-dimensional (4D) (three spatial coordinates and time) structure of the ionosphere. Generally, HORT has a spatial resolution of 100 km at best and a time step of 60-20 min. In the regions covered by dense receiving networks (e.g., in Europe, Alaska, USA), the resolution can be improved to 30-50 and the time step reduced to 30-10 min. The resolution of 10-30 km in space and up to 2 min in time is only achievable in Japan and California, where the receiving networks are very dense. We present the results of HORT and LORT imaging of the ionosphere during the periods of geomagnetic storms of 2003-2013 in different regions of the world -- in the European part of Russia and North America. Different factors acting during the storm time make the ionosphere complexly structured. Radio tomography reveals multi-extremal distributions of the ionospheric plasma with the spots of enhanced ionization, wall-like steep gradients of electron concentration; a complex structure of the ionization trough with the polar wall shifted equatorwards is observed. Many reconstructions show various wavelike structures, travelling ionospheric disturbances, wave effects caused by corpuscular emissions, etc. We demonstrate the comparisons of radio tomography with the ionosonde measurements. In contrast to the ionosondes, which use short radio waves, the RT methods are suitable for diagnosing the ionosphere even during the periods of strong geomagnetic storms, since absorption can typically be neglected in the RT problems due to the high frequencies used. The work was supported by the Russian Foundation for Basic Research (grants 14-05-00855 and 13-05-01122). We are grateful to the North-West Research Associates (NWRA) for providing the experimental relative TEC data from the RT system in Alaska.

Andreeva, Elena S.; Kunitsyn, Vyacheslav E.; Tereshchenko, Evgeniy D.; Nazarenko, Marina O.; Nesterov, Ivan A.; Tumanova, Yuila S.

2014-05-01

43

Thunderstorm coupling to the magnetosphere and associated ionospheric effects  

NASA Technical Reports Server (NTRS)

This project deals with the coupling of electromagnetic energy released during a thunderstorm to the magnetosphere and the ionosphere. Both the effects of an individual lightning event as well the aggregate of all the lightning events during a thunderstorm are considered. Energy in the very low frequency (VLF) band can play a variety of roles in the magnetospheric and ionospheric physics: generation of plasmaspheric hiss believed to be responsible for the slot region in the radiation belts, generation of lower hybrid waves that can heat ions in the auroral and subauroral regions, precipitation of energetic electrons, ionospheric heating etc. While these phenomena have been identified, and characterized to some extent, the influence and role of thunderstorm energy on the magnetosphere and ionosphere at a global scale is not known. Only recently, simultaneous high resolution (temporal and spatial) data sets from ground based lightning detectors and space and ground based VLF detectors have become available, and thus it has become possible to raise a question of the kind mentioned above and try to answer it quantitatively. Work on the correlation between individual lightning discharges in a thunderstorm as detected by the lightning network and the whistlers observed on the DE-1 satellite continued during this period. Results are summarized.

Inan, Umran S.

1992-01-01

44

Ionospheric storm effects at subauroral latitudes: A case study  

SciTech Connect

An attempt is made to classify ionospheric storm effects at subauroral latitudes according to their presumed origin. The storm of December 7/8, 1982, serves as an example. It is investigated using ionosonde, electron content, and DE 2 satellite data. The following effects are distinguished: (1) positive storm effects caused by traveling atmospheric disturbances, (2) positive storm effects caused by changes in the large-scale thermospheric wind circulation, (3) positive storm effects caused by the expansion of the polar ionization enhancement, (4) negative storm effects caused by perturbations of the neutral gas composition, and (5) negative storm effects caused by the equatorward displacement of the trough region.

Proelss, G.W. (Univ. Bonn (West Germany)); Brace, L.H.; Mayr, H.G. (Goddard Space Flight Center, Greenbelt, MD (USA)); Carignan, G.R.; Killeen, T.L. (Univ. of Michigan, Ann Arbor (USA)); Klobuchar, J.A. (Geophysics Lab., Hanscom AFB, MA (USA))

1991-02-01

45

Improved Ionospheric Correction for DGPS by taking into account the Horizontal Gradient Effect over the Equatorial Region  

NASA Astrophysics Data System (ADS)

Improved Ionospheric Correction for DGPS by taking into account the Horizontal Gradient Effect over the Equatorial Region K Nagarajoo Universiti Tun Hussein Onn Malaysia 86400 Parit Raja Johor Darul Takzim Email: karthi@uthm.edu.my DGPS is a system where the range error at a reference station will be eliminated from the range measurement at the user, which `view' the same satellite, presuming that the satellite's path to both the reference station and the user experience common errors due to the ionosphere, clock errors, multipath etc. In this assumption, the error due to the ionospheric refraction is assumed to be the same for the two closely spaced paths (such as a baseline length between reference station and the user is 10km) and thus the presence of ionospheric horizontal gradient is ignored. If a user's path is exposed to a drastically large ionosphere gradient (i.e., over the equatorial region), the large difference of ionosphere delays between the reference station and the user can result in significant position error for the user. Apart from that, the difference in the elevation angle at the reference and the user that `view' the same satellite to get the range measurement does also introduce some millimetre to centimetre of range difference. The neglect of the effect due to the presence of an ionospheric horizontal gradient and the elevation angle's difference (at both ends of the baseline) will cause a significant amount of error in the final DGPS user positioning. In this work, those two effects have been investigated in order to obtain a more accurate ionospheric correction for DGPS and have been found to be roughly comparable showing that they are both important. By performing ray-tracing calculations (using Jones 3-D Ray Tracing program) with and without a linear horizontal ionosphere gradient, the effects of elevation angle and horizontal gradient have been separated and a final positioning improvement of about 8cm has been shown at the user of a DGPS system over the equatorial region. Empirical models have been introduced to model these variations based on the ray tracing results. This is quite a good positioning improvement at the user location which really needs to be considered in applications such as geophysics, surveying and navigation. The geometric dilution of precision or GDOP factor also has been taken into account to get the best formation (geometry) of stocktickerGPS satellites in order to do the DGPS positional improvement at the user station. Keywords : Ionospheric correction, DGPS, horizontal gradient, GDOP, user positioning improvement

Nagarajoo, Karthigesu

46

Effect of anomalous transport coefficients on the thermal structure of the storm time auroral ionosphere  

NASA Technical Reports Server (NTRS)

By analyzing an observed storm time auroral electron temperature profile it is shown that anomalous transport effects strongly influence the thermal structure of the disturbed auroral ionosphere. Such anomalous transport effects are a consequence of plasma turbulence, the existence of which has been established by a large number of observations in the auroral ionosphere. The electron and composite ion energy equations are solved with anomalous electron thermal conductivity and parallel electrical resistivity coefficients. The solutions are parameterized with respect to a phenomenological altitude-dependent anomaly coefficient A and are compared with an observed storm time electron temperature profile above Chatanika. The calculated temperature profile for the classical case (A = 1) disagrees considerably with the measured profile over most of the altitude range up to 450 km. It is shown that an anomaly coefficient with a sharp peak of the order of 10,000 centered around the F2 peak is consistent with observations.

Fontheim, E. G.; Ong, R. S. B.; Roble, R. G.; Mayr, H. G.; Hoegy, W. H.; Ionson, J. A.; Baron, M. J.; Wickwar, V. B.; Vondrak, R. R.

1978-01-01

47

The wavelet method as an alternative for reducing ionospheric effects from single-frequency GPS receivers  

Microsoft Academic Search

The ionospheric effect is one of the major errors in GPS data processing over long baselines. As a dispersive medium, it is\\u000a possible to compute its influence on the GPS signal with the ionosphere-free linear combination of L1 and L2 observables,\\u000a requiring dual-frequency receivers. In the case of single-frequency receivers, ionospheric effects are either neglected or\\u000a reduced by using a

E. M. de Souza; J. F. G. Monico

2007-01-01

48

Effects of the equatorial ionosphere on L-band Earth-space transmissions  

NASA Technical Reports Server (NTRS)

Ionosphere scintillation can effect satellite telecommunication up to Ku-band. Nighttime scintillation can be attributed to large-scale inhomogeneity in the F-region of the ionosphere predominantly between heights of 200 and 600 km. Daytime scintillation has been attributed to sporadic E. It can be thought of as occurring in three belts: equatorial, high-latitude, and mid-latitude, in order of severity. Equatorial scintillation occurs between magnetic latitudes +/- 25 degrees, peaking near +/- 10 degrees. It commonly starts abruptly near 2000 local time and dies out shortly after midnight. There is a strong solar cycle dependence and a seasonal preference for the equinoxes, particularly the vernal one. Equatorial scintillation occurs more frequently on magnetically quiet than on magnetically disturbed days in most longitudes. At the peak of the sunspot cycle scintillation depths as great as 20 dB were observed at L-band.

Smith, Ernest K.; Flock, Warren L.

1993-01-01

49

Ionospheric effects of magnetospheric substorms during the SUNDIAL periods, and their modeling  

NASA Astrophysics Data System (ADS)

Ionospheric effects associated with magnetospheric substorms were recorded at Soviet ionospheric stations during the March 15-20 and December 5-10, 1988 periods of SUNDIAL, and the data were used to validate the technique of Goncharova et al.(1985) for numerical modeling of internal gravity waves during magnetospheric substorms. Results of comparisons showed good agreement between the measured and calculated electron concentration distributions, indicating that the Goncharova et al. model can be used to correct current models of the ionosphere.

Goncharova, E. E.; Kishcha, P. V.; Shashun'kina, V. M.; Telegin, V. A.

1993-02-01

50

Effects of solar flares on the ionosphere of Mars.  

PubMed

All planetary atmospheres respond to the enhanced x-rays and ultraviolet (UV) light emitted from the Sun during a flare. Yet only on Earth are observations so continuous that the consequences of these essentially unpredictable events can be measured reliably. Here, we report observations of solar flares, causing up to 200% enhancements to the ionosphere of Mars, as recorded by the Mars Global Surveyor in April 2001. Modeling the altitude dependence of these effects requires that relative enhancements in the soft x-ray fluxes far exceed those in the UV. PMID:16497929

Mendillo, Michael; Withers, Paul; Hinson, David; Rishbeth, Henry; Reinisch, Bodo

2006-02-24

51

Effects of ionospheric turbulence on SPS pilot signal  

NASA Technical Reports Server (NTRS)

The spatial variation of the electron density was studied by monitoring the differential Doppler on radio beacons aboard the Navy navigation satellites. The radio frequency heater was used to deposit energy in the F-region ionosphere with the heating frequency above peak plasma frequency. The effects of the solar power satellite power beam on the pilot signal were simulated. It was found that a small depletion was formed in the beam and that there was turbulence in the elctron density up the magnetic field line from the beam. It is suggested that the depletion will not seriously affect the power or pilot beams of the solar power satellite.

Clynch, J. R.

1981-01-01

52

Ionospheric effect of partial solar eclipse of 31 July 1981  

NASA Astrophysics Data System (ADS)

Vertical sounding of the ionosphere before, during, and some time after the eclipse was at 1- and 5-minute intervals. Scintillations of radio signals from artificial satellites were registered at frequencies of 150 MHz (3-channel spaced reception), 40 MHz and 180 MHz (single-channel reception). Slant sounding was along the path Moscow-Kiev in the frequency range from 3.5 to 27.5 MHz. A very strong magnetic storm was registered at the Kiev Magnetic Observatory before the eclipse; this storm which lasted 150 hours was preceded by considerable helioactivity. The solar flares and magnetic storm caused an ionospheric storm with very great delta f(0)F2 deviations. During the eclipse, the usual effect was not registered due to strong helio-geomagnetic activity. The E-region anomalies were observed: a local ionization cloud was formed with a very narrow range of electron concentration, decreasing from the low-frequency end. The F1 layer was formed an hour earlier. The effective recombination coefficient obtained during the period of the eclipse agrees with data from rocket experiments.

Datsko, Y. P.; Kasymova, A. G.; Maksimenko, O. I.

1984-05-01

53

Ionospheric effects upon a satellite navigation system at Mars Michael Mendillo,1  

E-print Network

modeling results and determine the extreme cases for TEC at Mars (i.e., when the planet is at perihelion Planetology: Solar System Objects: Mars; 5435 Planetology: Solid Surface Planets: Ionospheres (2459); 5494Ionospheric effects upon a satellite navigation system at Mars Michael Mendillo,1 Xiaoqing Pi,2

Mendillo, Michael

54

Space weather effects on the Mars ionosphere due to solar flares and  

E-print Network

Space weather effects on the Mars ionosphere due to solar flares and meteors Paul Withers1, Michael dotted line marks time of solar flare No data after X14.4 flare on 15 April NmE increased after M7 properties of solar flares and meteors. Can also determine properties of ionosphere that are involved

Withers, Paul

55

Space weather effects on the Mars ionosphere due to solar flares and meteors  

E-print Network

Space weather effects on the Mars ionosphere due to solar flares and meteors P. Withers (1), M observed two aspects of space weather at Mars. Following solar flares of both moderate to strong magnitude the simultaneous responses of the ionospheres of Earth and Mars to solar flares, highlighting the importance

Withers, Paul

56

Modeling the Earth-ionosphere cavity. Effects of hypothetical earthquake precursors over the Schumann resonance  

NASA Astrophysics Data System (ADS)

Schumann resonances (SR) are global phenomena which occur within the Earth-ionosphere cavity. They are the result of waves propagating several turns around the Earth. Due to the dimensions of the cavity, SR belong to the ELF spectra. The main source of excitation is lightning, and several natural processes do modify the geometry of the cavity and its parameters, like for instance seismo-electromagnetic activity, atmospheric aerosols, solar radiation, etc. Therefore, SR are a promising tool for monitoring (and even forecasting) these natural events. Although several measurements seem to confirm the link between electromagnetic activity and earthquake precursors, the physical mechanisms which produce them are still not clear, and several possibilities have been proposed, like for instance piezoelectric effects on the rocks in the lithosphere, emanation of ionizing gasses like radon, or acoustic gravity waves modifying the properties of the ionosphere in the earthquake preparation zone. However, further measurements combined with analytical models and/or numerical simulations are required in order to better understand the seismo-electromagnetic activity. In this work, the whole Earth-ionosphere electromagnetic cavity has been modeled with 10 km accuracy, by means of Transmission-Line Modeling (TLM) method. Since Schumann resonance parameters depend primarily on the geometry of such cavity, electromagnetic changes produced by earthquake precursors can modify the properties of SR. There is not much quantitative information available about the changes produced by the precursors, either in the lithosphere, atmosphere, or ionosphere. Therefore, different models of the precursors are proposed and their consequences over the SR are evaluated. The so-called Chi-Chi earthquake is employed as a case of study.

Toledo-Redondo, Sergio; Salinas, Alfonso; Fornieles, Jesús; Portí, Jorge

2013-04-01

57

Effects of the Dayside Ionospheric Conductance on Solar Wind-Magnetosphere-Ionosphere Coupling  

NASA Astrophysics Data System (ADS)

In the present study we seek to observationally address the role of ionospheric conductance in the solar wind-magnetosphere coupling in terms of global field-aligned currents (FACs). Solar EUV irradiance changes during a solar cycle, and so does its contribution to the ionospheric conductance. We statistically examine how, for fixed ranges of external driver, the intensities of the R1 and R2 currents and their demarcation latitude depend on solar activity (F10.7). An emphasis is placed on night-side FACs in the dark hemisphere. The result shows that under fixed external conditions, the night-side FACs are more intense for higher solar activity irrespective of their polarities or local time. It is also found that the overall FAC system, therefore the auroral oval, moves equatorward as the solar activity increases. For both current intensity and latitude, the dependence on solar activity is more sensitive for smaller values of F10.7 and it becomes more gradual with increasing F10.7. The intensities of dayside FACs reveal similar F10.7 dependence as expected from the enhancement of the local ionospheric conductance. Interestingly, they also move equatorward with increasing solar activity. We suggest that as the dayside R1 current becomes more intense with increasing solar activity, the magnetosphere shrinks on the day side and expands on the night side. This configurational change of the magnetosphere is considered to affect the energy transport from the solar wind to the magnetosphere, although the details still remain to be understood. We conclude that the ionospheric conductance actively affects the solar wind-magnetosphere-ionosphere coupling.

Ohtani, S.; Wing, S.; Merkin, V. G.; Higuchi, T.

2013-12-01

58

Role of the atmospheric gravity waves in lithosphere-ionosphere coupling and in generation of the ionospheric earthquake precursors  

NASA Astrophysics Data System (ADS)

Up to the present days there are no well-distinguished physical mechanisms of lithosphere-ionosphere interaction and generation of the ionospheric earthquake precursors. Several hypothetical possibilities have been suggested in the literature: (i) electric currents are generated in the lithosphere during earthquake preparation phase, the electromagnetic emission of these currents influences the ionosphere; (ii) ionosphere responds to the seismogenic variations of air conductivity and related variation of fair-weather electric field; (iii) lithosphere and ionosphere are coupled via middle-scale atmospheric gravity waves (AGW) traveling upwards to the ionospheric heights and producing the effects known as traveling ionospheric disturbances (TID). In spite of great quantity of observations of ionospheric earthquake precursors, there is a lack of appropriate experimental data: such kind of data that will help us to choose between mentioned hypotheses. Our research is devoted to the studying and verification of AGW-mechanism of seismo-ionospheric effects. The original data have been provided by synchronous measurements of atmospheric pressure variations and ionospheric plasma variations carried out in seismically active Chiba area in Japan during the year 2003. Seismogenic AGW with period about 1 hour has been selected from the broad spectra of pressure variations. Correlated ionospheric response has been detected by means of subionospheric VLF/LF propagation. Cross-analysis of barometric and ionospheric parameters has been done in order to recognize the process of AGW-coupling between perturbations at surface and ionospheric levels.

Lizunov, G.; Hayakawa, M.; Hattori, K.; Mayakawa, Sh.

59

Ionosphere Effects for Wideband GNSS Signals Grace Xingxin Gao, Seebany Datta-Barua, Todd Walter, and Per Enge  

E-print Network

. A signal traveling through the ionosphere becomes distorted due to varying delay over its bandwidth. WeIonosphere Effects for Wideband GNSS Signals Grace Xingxin Gao, Seebany Datta-Barua, Todd Walter to 1215 MHz, over 25 times the two-sided bandwidth of the GPS C/A code. However, because the ionosphere

Stanford University

60

Ionospheric phenomena before strong earthquakes  

Microsoft Academic Search

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 \\

A. S. Silina; E. V. Liperovskaya; V. A. Liperovsky; C.-V. Meister

2001-01-01

61

An investigation of ionospheric irregularity effects on SIR-B image processing and information extraction  

NASA Technical Reports Server (NTRS)

Ionospheric irregularities and associated effects on space-time synthetic aperture radar (SAR) image processing and information extraction, including sensor calibration, target statistics determination, resolution, distortion, and overall image integrity were investigated.

Szuszczewicz, E. P.; Abdu, M. A.; Sobral, J. H. A.; Jost, J.; Reddy, B. M.; Rino, C.; Robinson, T.; Rodrigues, P.; Singh, M.; Woodman, R.

1984-01-01

62

The effect of finite ionosphere conductivities on axisymmetric toroidal Alfvén wave resonances  

Microsoft Academic Search

Previously developed solutions for pure toroidal mode Alfvén waves with finite ionosphere conductivities are modified to apply both inside and outside the plasmapause. Detailed diagrams are provided to illustrate the effect of realistic ionosphere conductances on the wave-forms. As well as graphs of wave-period, these include: (a) half-wave solutions showing the effect of dipole field distortion and consequent enhancement of

W. Allan; F. B. Knox

1979-01-01

63

Stochastic modelling considering ionospheric scintillation effects on GNSS relative and point positioning  

NASA Astrophysics Data System (ADS)

Global Navigation Satellite Systems (GNSS), in particular the Global Positioning System (GPS), have been widely used for high accuracy geodetic positioning. The Least Squares functional models related to the GNSS observables have been more extensively studied than the corresponding stochastic models, given that the development of the latter is significantly more complex. As a result, a simplified stochastic model is often used in GNSS positioning, which assumes that all the GNSS observables are statistically independent and of the same quality, i.e. a similar variance is assigned indiscriminately to all of the measurements. However, the definition of the stochastic model may be approached from a more detailed perspective, considering specific effects affecting each observable individually, as for example the effects of ionospheric scintillation. These effects relate to phase and amplitude fluctuations in the satellites signals that occur due to diffraction on electron density irregularities in the ionosphere and are particularly relevant at equatorial and high latitude regions, especially during periods of high solar activity. As a consequence, degraded measurement quality and poorer positioning accuracy may result. This paper takes advantage of the availability of specially designed GNSS receivers that provide parameters indicating the level of phase and amplitude scintillation on the signals, which therefore can be used to mitigate these effects through suitable improvements in the least squares stochastic model. The stochastic model considering ionospheric scintillation effects has been implemented following the approach described in Aquino et al. (2009), which is based on the computation of weights derived from the scintillation sensitive receiver tacking models of Conker et al. (2003). The methodology and algorithms to account for these effects in the stochastic model are described and results of experiments where GPS data were processed in both a relative and a point positioning mode are presented and discussed. Two programs have been developed to enable the analyses: GPSeq (currently under development at the FCT/UNESP Sao Paulo State University - Brazil) and PP_Sc (developed in a collaborative project between FCT/UNESP and Nottingham University - UK). The point positioning approach is based on an epoch by epoch solution, whereas the relative positioning on an accumulated solution using a Kalman Filter and the LAMBDA method to solve the Double Differences ambiguities. Additionally to the use of an improved stochastic model, all data processing in this paper were performed using an option implemented in both programs, to estimate, for each observable, an individual ionospheric parameter modelled as a stochastic process, using either the white noise or the random walk correlation models. Data from a network of GPS Ionospheric Scintillation and TEC Monitor (GISTM) receivers set up in Northern Europe as part of the ISACCO project (De Franceschi et al., 2006) were used in the experiments. The point positioning results have shown improvements of the order of 45% in height accuracy when the proposed stochastic model is applied. In the static relative positioning, improvements of the order of 50%, also in height accuracy, have been reached under moderate to strong scintillation conditions. These and further results are discussed in this paper.

da Silva, Heloísa Alves; de Oliveira Camargo, Paulo; Galera Monico, João Francisco; Aquino, Marcio; Marques, Haroldo Antonio; de Franceschi, Giorgiana; Dodson, Alan

2010-05-01

64

Effects of prolonged southward interplanetary magnetic field on low-latitude ionospheric electron density  

NASA Astrophysics Data System (ADS)

The present work describes the low-latitude ionospheric variability during an unusually prolonged (~33 h) geomagnetically disturbed condition that prevailed during 15-16 July 2012. The low-latitude electron density in summer hemisphere, investigated using ground- and satellite-based observations, responded to this by generating strong negative ionospheric storm on 16 July. The maximum electron density on 16 July over Indian low latitudes was reduced by more than 50% compared to that on a geomagnetically quiet day (14 July 2012). In contrast to the extreme reduction in total electron content (TEC) in the Northern Hemisphere, TEC from a winter hemispheric station revealed substantial (~23 total electron content unit, 1 TECU = 1016 el m-2) enhancements on the same day. This contrasting hemispherical response in TEC is suggested to be due to the combined effects of strong interhemispheric and solar-driven day-night winds. Further, very weak equatorial electrojet (EEJ) strength on 16 July indicated that the westward electric field perturbations in the low-latitude ionosphere were possibly due to the disturbance dynamo effect associated with meridional circulation from polar to equatorial latitudes. Interestingly, despite reduction in the integrated EEJ strength on 15 July, the low-latitude electron density showed substantial enhancement, highlighting the significant effect of the positive ionospheric storm on the low-latitude ionosphere. The roles of electrodynamical/neutral-dynamical and compositional disturbances are discussed in view of these observations to understand low-latitude ionospheric response when geomagnetic disturbance persists for longer duration.

Bagiya, Mala S.; Hazarika, Rumajyoti; Laskar, Fazlul I.; Sunda, Surendra; Gurubaran, S.; Chakrabarty, D.; Bhuyan, P. K.; Sridharan, R.; Veenadhari, B.; Pallamraju, D.

2014-07-01

65

Modeling the pre-earthquake electrostatic effect on the F region ionosphere  

NASA Astrophysics Data System (ADS)

This paper presents the results of modeling the ionospheric effect of the seismogenic electrostatic field (SEF) seen at the earth's surface as a perturbation of the vertical atmospheric electrostatic field in the earthquake preparation zone. The SEF distribution at ionospheric altitudes is obtained as an analytical solution of the continuity equation for the electric current density. It is shown that at night, the horizontally large scale SEF can efficiently penetrate into the ionosphere and produce noticeable changes in the horizontal distribution of the F region electron density. The results suggest that the seismogenic electrostatic field could be a possible source for the ionospheric variations observed over Taiwan before the strong Chi Chi earthquake of September 21, 1999.

Kim, V. P.; Liu, J. Y.; Hegai, V. V.

2012-12-01

66

Effects of the June 2011 CME Observed by Mars Express Ionospheric Sounding  

NASA Astrophysics Data System (ADS)

We show the effects of a strong coronal mass ejection on the Martian ionosphere as directly observed by the Active Ionospheric Sounding (AIS) mode of the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) on board the Mars Express spacecraft. We are able to time the onset, peak, and recovery from the CME through in situ background provided by the High-Energy Neutron Detector on board the Mars Odyssey spacecraft and the ASPERA-3 plasma instrument on board Mars Express. Increased electron intensity for the duration of the CME is confirmed by disappearance of the MARSIS AIS surface reflection and disruption of the MARSIS Subsurface mode surface reflection. Local electron density and magnetic field strength measurements from MARSIS AIS show that prior to CME peak intensity, there is compression of the Martian ionosphere accompanied by simultaneous plasma density and magnetic field strength oscillation. At the peak of the CME, the Martian ionosphere is compressed enough to be completely below the orbit of Mars Express. The ionospheric peak, usually detectable by MARSIS AIS remote sounding out to about 100° solar zenith angle, is extended at significant density to solar zenith angles of 113°. The nature of this increase, whether due to increased flow or increased ionization due to particle flux, continues to be a subject of inquiry.

Morgan, D. D.; Gurnett, D. A.; Duru, F.; Dubinin, E.; Fraenz, M.; Opgenoorth, H. J.; Andrews, D. J.; Ulusen, D.; Mitrofanov, I.; Plaut, J. J.

2012-12-01

67

The worldwide ionospheric data base  

NASA Technical Reports Server (NTRS)

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.

Bilitza, Dieter

1989-01-01

68

Ionospheric effects of X-ray source Scorpius XR-1. [on terrestrial radio propagation  

NASA Technical Reports Server (NTRS)

A simple two-ion model was employed to evaluate the ionospheric effects of various nocturnal ionization sources. The model was used to calculate the decay of the electron number density at 90 km with and without illumination by Scorpius XR-1 X rays. Reflection parameters for the determination of the effect of cosmic x-ray sources on radio wave propagation were also obtained. The results obtained in the investigation do not support the proposal made by Anathakrishnan and Ramanathan (1969) that the X-ray source in Scorpius XR-1 affects the nighttime lower ionosphere of the earth.

Poppoff, I. G.; Whitten, R. C.; Willoughby, D. S.

1975-01-01

69

The outer ionospheric effect of the solar eclipse on 31 July 1981 at Mohe  

NASA Astrophysics Data System (ADS)

In this paper the whistler data received at Mohe and the simultaneously observed ionospheric data are used, along with the assumption that the electron density distributions at Northern and Southern Hemispheres are necessarily symmetric, to study the effects of solar eclipse of July 31, 1981 on the whistler dispersion. The electron density profile along the magnetic line of force, the electron content of the magnetic flux, and the equivalence scale height at Mohe during the solar eclipse are also determined. In addition, the outer ionospheric effect of the solar eclipse is also discussed.

He, Y.-W.; Huang, T.-Q.; Zhu, M.-Q.; Su, S.-H.

1985-04-01

70

Local and long-distance effects of meteor showers in the low ionosphere  

NASA Astrophysics Data System (ADS)

The effect of the Geminids and alpha Scorpiids meteor showers in the lower ionosphere have been observed using two different methods. Low ionosphere group heights, measured by a VLF ionosonde located in southern Brazil, indicated significant anomalous lowering of the effective reflection height which was in good correlation with the transit of the alpha Scorpiids stream. The diurnal VLF phase variations over two long-distance propagation paths showed significant phase deviations from the average during the transits of the showers' radiants. Geomagnetic activity during the periods concerned was low and the results obtained using the two different techniques confirm the occurrence of changes in the physical conditions of the low ionosphere produced by meteor showers on local, as well as on long-distance, scales.

Vilas Boas, J. W. S.; Paes Leme, N. M.; Rizzo Piazza, L.; da Costa, A. M.; Macedo Moura, M. S. S.

1986-07-01

71

Local and long-distance effects of meteor showers in the low ionosphere  

NASA Astrophysics Data System (ADS)

The effect of the Geminids and ? Scorpiids meteor showers in the lower ionosphere have been observed using two different methods. Low ionosphere group heights, measured by a VLF ionosonde located in southern Brazil, indicated significant anomalous lowering of the effective reflection height which was in good correlation with the transit of the ? Scorpiids stream. The group reflection coefficients also showed very pronounced correlated variations. The diurnal VLF phase variations over two long-distance propagation paths showed significant phase deviations from the average during the transits of the showers' radiants. Geomagnetic activity during the periods concerned was low and the results obtained using the two different techniques confirm the occurrence of changes in the physical conditions of the low ionosphere produced by meteor showers on local, as well as on long-distance, scales.

Boas, J. W. S. Vilas; Leme, N. M. Paes; Piazza, L. Rizzo; Da Costa, A. M.; Moura, M. S. S. Macedo

1986-07-01

72

Ionospheric Asymmetry Evaluation using Tomography to Assess the Effectiveness of Radio Occultation Data Inversion  

NASA Astrophysics Data System (ADS)

The Multi-Instrument Data Analysis System (MIDAS) algorithm is based on the oceanographic imaging techniques first applied to do the imaging of 2D slices of the ionosphere. The first version of MIDAS (version 1.0) was able to deal with any line-integral data such as GPS-ground or GPS-LEO differential-phase data or inverted ionograms. The current version extends tomography into four dimensional (lat, long, height and time) spatial-temporal mapping that combines all observations simultaneously in a single inversion with the minimum of a priori assumptions about the form of the ionospheric electron-concentration distribution. This work is an attempt to investigate the Radio Occultation (RO) data assimilation into MIDAS by assessing the ionospheric asymmetry and its impact on RO data inversion, when the Onion-peeling algorithm is used. Ionospheric RO data from COSMIC mission, specifically data collected during 24 September 2011 storm over mid-latitudes, has been used for the data assimilation. Using output electron density data from Midas (with/without RO assimilation) and ideal RO geometries, we tried to assess ionospheric asymmetry. It has been observed that the level of asymmetry was significantly increased when the storm was active. This was due to the increased ionization, which in turn produced large gradients along occulted ray path in the ionosphere. The presence of larger gradients was better observed when Midas was used with RO assimilated data. A very good correlation has been found between the evaluated asymmetry and errors related to the inversion products, when the inversion is performed considering standard techniques based on the assumption of spherical symmetry of the ionosphere. Errors are evaluated considering the peak electron density (NmF2) estimate and the Vertical TEC (VTEC) evaluation. This work highlights the importance of having a tool which should be able to state the effectiveness of Radio Occultation data inversion considering standard algorithms, like Onion-peeling, which are based on ionospheric spherical symmetry assumption. The outcome of this work will lead to find a better inversion algorithm which will deal with the ionospheric asymmetry in more realistic way. This is foreseen as a task for future research. This work has been done under the framework of TRANSMIT project (ITN Marie Curie Actions - GA No. 264476).

Shaikh, M. M.; Notarpietro, R.; Yin, P.; Nava, B.

2013-12-01

73

Effects of a Weak Planetary Field on a Model Venus Ionosphere  

NASA Astrophysics Data System (ADS)

There are a number of attributes of the near-Venus space environment and upper atmosphere that remain mysterious, including occasional large polar magnetic field stuctures seen on VEX and nightside ionospheric holes seen on PVO. We have been exploring the consequences of a weak global dipole magnetic field of Venus using results of BATS-R-US MHD simulations. An advantage of these models is that they include the effects on a realistic ionosphere. We compare some of the weak magnetosphere's ionospheric properties with the typical unmagnetized ionsphere case. The results show the differences can be quite subtle for dipole fields less than ~10 nT at the equator, as might be expected. Nevertheless the dipole fields do produce distinctive details, especially in the upper regions.

Luhmann, Janet G.; Ma, Yingjuan; Villarreal, Michaela

2014-05-01

74

Techniques and Tools for Estimating Ionospheric Effects in Interferometric and Polarimetric SAR Data  

NASA Technical Reports Server (NTRS)

The InSAR Scientific Computing Environment (ISCE) is a flexible, extensible software tool designed for the end-to-end processing and analysis of synthetic aperture radar data. ISCE inherits the core of the ROI_PAC interferometric tool, but contains improvements at all levels of the radar processing chain, including a modular and extensible architecture, new focusing approach, better geocoding of the data, handling of multi-polarization data, radiometric calibration, and estimation and correction of ionospheric effects. In this paper we describe the characteristics of ISCE with emphasis on the ionospheric modules. To detect ionospheric anomalies, ISCE implements the Faraday rotation method using quadpolarimetric images, and the split-spectrum technique using interferometric single-, dual- and quad-polarimetric images. The ability to generate co-registered time series of quad-polarimetric images makes ISCE also an ideal tool to be used for polarimetric-interferometric radar applications.

Rosen, P.; Lavalle, M.; Pi, X.; Buckley, S.; Szeliga, W.; Zebker, H.; Gurrola, E.

2011-01-01

75

Plausible effect of atmospheric tides on the equatorial ionosphere observed by the FORMOSAT-3/COSMIC: Three-dimensional electron  

E-print Network

Plausible effect of atmospheric tides on the equatorial ionosphere observed by the FORMOSAT-3 of atmospheric tides on the longitudinal structure of the equatorial ionosphere is observed by the FORMOSAT-3 the magnetic field lines from E-region where longitudinal variations in atmospheric tides affect

California at Berkeley, University of

76

Case study of the 15 July 2000 magnetic storm effects on the ionosphere-driver of the positive ionospheric storm in the winter hemisphere  

Microsoft Academic Search

The ionospheric response to the magnetic storm of 15 July 2000 is investigated using the global total electron content (TEC) maps provided by global positioning system and the measurements of ion density, composition, and drift velocity from the Defense Meteorological Satellite Program (DMSP) F13 and F15 spacecraft. The global TEC maps showed clear seasonal effects that can be characterized by

Hyosub Kil; Larry J. Paxton; Xiaoqing Pi; Marc R. Hairston; Yongliang Zhang

2003-01-01

77

Effects of solar wind dynamic pressure on the ionospheric fluence during the 31 August 2005 storm  

E-print Network

Effects of solar wind dynamic pressure on the ionospheric O+ fluence during the 31 August 2005 solar wind data is contrasted against a case where the solar wind dynamic pressure (Pdyn with the solar wind dynamic pressure. Additionally, changes in Pdyn affect the downward Poynting flux only

78

The Effects of Solar Flares on Planetary Ionospheres PAUL WITHERS1  

E-print Network

The Effects of Solar Flares on Planetary Ionospheres PAUL WITHERS1 and MICHAEL MENDILLO1 1 Center 353 1531) During solar flares, the Sun's X-ray irradiance increases dramatically, often within a few during solar flares. Similar increases in plasma densities during solar flares have been observed

Withers, Paul

79

Ionospheric effects of the missile destruction on 9 December 2009  

NASA Astrophysics Data System (ADS)

We report on ionosonde and meteor radar observations made in Sodankylä Geophysical Observatory (SGO, 67°22'N, 26°38'E, Finland) on 9 December 2009, during a test launch of the Russian solid propellant military missile. Due to a technical problem, the missile was self-destroyed around 07 UT at an ionospheric height (near 200 km altitude) over the Kola Peninsula (Russia), at a distance about 500 km to east from the observatory. Products of the explosion were spread into a large area and reached the region of SGO meteor radar observations in about 2 h (around 09 UT). After about 3 h (around 10 UT), a sporadic E layer presumably composed of the remains including long-lived metallic (aluminum and its oxides) ions, was observed near the zenith of the SGO ionosonde. We discuss possible mechanisms accounting for transport of the remains. (1) Since the event occurred during a long-lasting period of extremely low solar and magnetic activity, the ionospheric electric field was unlikely to play a substantial role in the transport of the remains and sporadic E layer formation. (2) The horizontal transport of the remains cannot be explained by the neutral winds based on empirical models. (3) Theoretical estimations suggest that the observed transport could be due to thermospheric turbulence.

Kozlovsky, Alexander; Shalimov, Sergey; Lukianova, Renata; Lester, Mark

2014-05-01

80

The lower ionosphere effects caused by the tsunami-driven internal gravity waves  

NASA Astrophysics Data System (ADS)

Measurements from the VLF/LF station in Petropavlovsk-Kamchatsky (Russia) were used to observe the response of the lower ionosphere to the tsunami triggered by the 2010 Chili earthquake. This earthquake produced the trans-ocean tsunami, which severely affected the coastal communities of Chile and presented a serious threat for all Pacific Ocean coasts including the far eastern coast of Russia. Disturbances in the phase and amplitude of the VLF signal propagating from the transmitter in Hawaiian Islands were observed during the tsunami wave passage recorded by the Deep-ocean Assessments and Reporting of Tsunamis (DART) bottom pressure stations. The tsunami propagation time from the source to Hawaii Islands was about 14 h and to the coast of Russia about 21 h. The new point discussed here is that we observed a second tsunami and its ionospheric effects which have been missed in the previous observations in the upper ionosphere. Nevertheless, the presence of the second tsunami is confirmed by both the VLF and DART's measurements. The tsunamigenic effects in the ionosphere were compared to the in-situ sea-level DART measurements near Hawaii Islands and not far from Kamchatka. The frequency of the maximum spectral amplitude both for the VLF and DART data was found to be in the range of periods of 8-60 min which corresponds to the period of the internal gravity waves generated by tsunami.

Rozhnoi, Alexander; Solovieva, Maria; Shalimov, Sergei; Levin, Boris; Shevchenko, Georgy; Hayakawa, Masashi

2014-05-01

81

Interplanetary magnetic field effects on high latitude ionospheric convection  

NASA Technical Reports Server (NTRS)

Relations between the electric field and the electric current in the ionosphere can be established on the basis of a system of mathematical and physical equations provided by the equations of current continuity and Ohm's law. For this reason, much of the synthesis of electric field and plasma velocity data in the F-region is made with the aid of similar data sets derived from field-aligned current and horizontal current measurements. During the past decade, the development of a self-consistent picture of the distribution and behavior of these measurements has proceeded almost in parallel. The present paper is concerned with the picture as it applies to the electric field and plasma drift velocity and its dependence on the interplanetary magnetic field. Attention is given to the southward interplanetary magnetic field and the northward interplanetary magnetic field.

Heelis, R. A.

1985-01-01

82

Ionospheric effects of the missile destruction on December 9, 2009  

NASA Astrophysics Data System (ADS)

We report on ionosonde and meteor radar observations made in Sodankyla Geophysical Observatory (SGO, 67N, 27E, Finland) on December 9, 2009 during a test launch of the Russian solid propellant military missile. Because of the technical problem the missile was self-destroyed around 07 UT at ionospheric height (170-260 km) over the Kola Peninsula (Russia), at a distance about 500 km to east from the observatory. Products of the explosion, including long-lived ionized aluminum oxides, were spread into the large area and reached the region of SGO meteor radar observations in about 2 hours (around 09 UT). After about 3 hours (around 10 UT) a sporadic E layer presumably composed of the remains was observed close to the zenith of the SGO ionosonde. We present the data and discuss possible mechanisms accounting for both vertical and horizontal transport of the remains. Theoretical estimations suggest that the observed transport could be likely due to thermospheric turbulence.

Kozlovsky, Alexander; Shalimov, Sergey; Lukianova, Renata

2014-05-01

83

Effects of an atmospheric gravity wave on the midlatitude ionospheric F layer  

SciTech Connect

A modeling study of the atmospheric response to a single short burst of enhanced ion convection at high latitudes, undertaken using the Sheffield/University College London/Space Environment Laboratory coupled ionosphere/thermosphere model, has revealed a large-scale atmospheric gravity wave (AGW) moving equatorward from a source in the dawn sector auroral zone. The wave propagates to midlatitude, perturbing the ionosphere and creating a traveling ionospheric disturbance. Analysis of the interaction between the thermosphere and ionosphere during the passage of the AGW at midlatitudes is undertaken and reveals a complex height-dependent response. At lower altitudes the field-aligned velocity of the ions follows closely the field-aligned wind. Above the F peak, diffusion processes become important and the field-aligned ion velocity shows fluctuations which exceded those in the wind. Changes in N{sub m}F{sub 2} and h{sub m} F{sub 2}, during the interaction, are due to redistribution of plasma alone with changes in production and loss insignificant. As the F layer is lifted by the positive surge in the gravity wave, N{sub m}F{sub 2} decreases, due to a divergence in the ion flux, itself caused by the combination of a divergent neutral wind and an increase in the effects of diffusion with altitude. The slab thickness also increases. Subsequently, the opposite happens as h{sub m}F{sub 2} falls below its equilibrium value. 14 refs., 9 figs., 1 tab.

Millward, G.H.; Moffett, R.J.; Quegan, S. [Univ. of Sheffield (United Kingdom); Fuller-Rowell, T.J. [Univ. of Colorado, Boulder, CO (United States)]|[Nationa Oceanic and Atmospheric Administration, Space Environment Lab., Boulder, CO (United States)

1993-11-01

84

Quasi-static electric fields phenomena in the ionosphere associated with pre- and post earthquake effects  

NASA Astrophysics Data System (ADS)

To prove a direct relationship between the quasi-static electric field disturbances and seismic activity is a difficult, but actual task of the modern ionosphere physics. This paper presents new results on the processing and analysis of the quasi-static electric field in the upper ionosphere (h=800-900 km) observed from the satellite INTERCOSMOS-BULGARIA-1300 over earthquakes' source regions (seismic data of World Data Center, Denver, Colorado, USA). Present research focuses on three main areas (i) development of methodology of satellite and seismic data selecting, (ii) data processing and observations of the quasi-static electric field (iii) study and accumulation of statistics of possible connection between anomalous vertical electric fields penetrating from the earthquake zone into the ionosphere, and seismic activity. The most appropriate data (for satellite orbits above sources of forthcoming or just happened seismic events) have been selected from more than 250 investigated cases.The increase of about 5-10-15 mV/m in the vertical component of the quasi-static electric field observed by INTERCOSMOS-BULGARIA-1300 during seismic activity over Southern Ocean, Greenland Sea, South-Weat Pacific Ocean, Indian Ocean, Central America, South-East Pacific Ocean, Malay Archipelago regions are presented. These anomalies, as phenomena accompanying the seismogenic process, can be considered eventually as possible pre-, co- (coeval to) and post-earthquake effects in the ionosphere.

Gousheva, M.; Danov, D.; Hristov, P.; Matova, M.

2008-02-01

85

Effect of self-absorption on attenuation of lightning and transmitter signals in the lower ionosphere  

NASA Astrophysics Data System (ADS)

The attenuation of VLF signals from lightning and ground-based VLF transmitters during transionospheric propagation has been the subject of recent interest, as discrepancies have been found between satellite data and model calculations. Previous modeling efforts, however, have not considered the self-absorption effect due to nonlinear heating and ionization in the lower ionosphere. A self-consistent model of ionospheric heating is presented here using a time-domain model of VLF wave propagation through the ionosphere. The model is able to estimate the attenuation of signals due to heating below ˜100 km altitude. In this model, the ionospheric state is updated as the fields propagate, leading to changes in collision frequency and electron density, which in turn affect the wave propagation. We use this model for ground-based VLF transmitters at different frequencies, amplitudes, and latitudes (i.e., magnetic dip angle), and for lightning-generated sferics with different amplitudes, at different latitudes, and using a variety of ionospheric density profiles. We find that the inclusion of self-consistent heating causes a change in the transionospherically propagating wave amplitude that varies considerably with the source amplitude and other parameters. Typical values for the heating contribution to wave attenuation are 1-2 dB for VLF transmitters, but greater than 10 dB for large amplitude lightning discharges. An interesting effect is observed for VLF transmitters and low-amplitude lightning, where the signal is actually enhanced due to heating, rather than attenuated, in the direction propagating across the Earth's magnetic field.

Marshall, R. A.

2014-05-01

86

Effect of ionospheric self-conditioning and preconditioning on the broad upshifted maximum component of stimulated electromagnetic emission  

Microsoft Academic Search

Stimulated electromagnetic emissions (SEE) are high-frequency radio emissions that are generated during high-power, high-frequency, ordinary mode (O-mode), radiowave heating of the ionosphere. These emissions are particularly useful in ionospheric heating experiments because they provide a way of monitoring space plasma processes remotely and passively. In order to utilize these emissions for diagnostic purposes, it is necessary to understand the space

L. S. Wagner; P. A. Berhnardt; J. A. Goldstein; C. A. Selcher; V. L. Frolov; E. N. Sergeev

1999-01-01

87

Effective velocity power laws for electron-neutral collision frequencies. [in ionosphere  

NASA Technical Reports Server (NTRS)

Calculations of electron transport coefficients in the ionosphere are simplified if the electron-neutral collision frequency can be expressed as a power law in velocity. A new method for determining the effective power law representation for electron-neutral collision frequencies of arbitrary velocity dependence is presented. This method is applied to ionospheric gases in a model calculation. Comparison with similar results of Schunk and Walker and with exact calculations of transport coefficient correction factors demonstrates this technique to be more accurate than the other. Effective power law indexes are computed for both Banks' and Itikawa's collision frequencies. Relative differences between these indexes are found to be considerably larger than the differences between the collision frequencies themselves; however, the effects on transport calculations are shown to be smaller.

Comfort, R. H.

1975-01-01

88

Optimization of satellite coverage in observing cause and effect changes in the ionosphere, magnetosphere, and solar wind. Master's thesis  

SciTech Connect

Disturbances in the ionosphere sometimes cause adverse effects to communications systems, power grids, etc. on the earth. Currently, very little, if any, lead time is given to warn of an impending problem. If a forecast could be made of ionospheric occurrences, some lead time may be given to appropriate agencies and equipment may be saved. Most changes that occur in the ionosphere are a result of interaction of energy, currents, etc. between the magnetosphere and/or solar wind. Before a forecast can be made, however, improvement of ionospheric models currently in use need to be made. The models currently depict features in various regions of the ionosphere but not always where these features are actually observed. So an improvement to the model is needed to create an accurate baseline condition, or in other words an accurate depiction of the current ionosphere. Models could be improved by inputting real-time data from the ionosphere into the model. This data would come from satellites and/or ground-based stations.

Loveless, M.J.

1993-06-01

89

Magnetic zenith effect in the ionospheric modification by an X-mode HF heater wave  

NASA Astrophysics Data System (ADS)

We report experimental results aimed at an investigation of the magnetic zenith effect in the high latitude ionosphere F region from ionospheric modification by powerful HF heater wave with X-polarization. The ionospheric modification was produced by the HF heating facility at Tromsø (Norway) using the phased array with a narrow beam with of 6 degrees. Effective radiated power was varied between 450 and 1000 MW. The HF pump wave radiated in different directions relative to the magnetic field from 90 degrees (vertical) to 78 degrees (magnetic zenith) at frequencies near or above the ordinary-mode critical frequency. The response of the ionosphere plasma to the HF pump wave impact was checked by the UHF incoherent scatter radar located in the immediate vicinity of the HF heater. UHF radar was probing the plasma parameters, such as electron density and temperature (Ne and Te), HF-induced plasma and ion lines in the altitude range from 90 to 600 km. It was running in a scanning mode when UHF radar look angles were changed from 74 to 90 degrees by 1 or 2 degree step. It was clearly demonstrated that the strongest heater-induced effects took place in the magnetic field-aligned direction when HF pointing was also to the magnetic zenith. It was found that strong Ne enhancement of up to 80 % along magnetic field (artificial density ducts) were excited only under HF pumping towards magnetic zenith. The width of the artificial ducts comes to only 2 degrees. The Ne increases were accompanied by the Te enhancements of up to about 50 %. Less pronounced Te increases were also observed in the directions of 84 and 90 degrees. Strong Ne enhancements can be accompanied by excitation of strong HF-induced plasma and ion lines. Thus experimental results obtained points to the strong magnetic zenith effect due to self-focusing powerful HF radio wave with X-mode polarization.

Blagoveshchenskaya, N. F.; Borisova, T. D.; Haggstrom, I.; Rietveld, M. T.; Yeoman, T. K.

2013-12-01

90

Effects of the Ionosphere on Passive Microwave Remote Sensing of Ocean Salinity from Space  

NASA Technical Reports Server (NTRS)

Among the remote sensing applications currently being considered from space is the measurement of sea surface salinity. The salinity of the open ocean is important for understanding ocean circulation and for modeling energy exchange with the atmosphere. Passive microwave remote sensors operating near 1.4 GHz (L-band) could provide data needed to fill the gap in current coverage and to complement in situ arrays being planned to provide subsurface profiles in the future. However, the dynamic range of the salinity signal in the open ocean is relatively small and propagation effects along the path from surface to sensor must be taken into account. In particular, Faraday rotation and even attenuation/emission in the ionosphere can be important sources of error. The purpose or this work is to estimate the magnitude of these effects in the context of a future remote sensing system in space to measure salinity in L-band. Data will be presented as a function of time location and solar activity using IRI-95 to model the ionosphere. The ionosphere presents two potential sources of error for the measurement of salinity: Rotation of the polarization vector (Faraday rotation) and attenuation/emission. Estimates of the effect of these two phenomena on passive remote sensing over the oceans at L-band (1.4 GHz) are presented.

LeVine, D. M.; Abaham, Saji; Hildebrand, Peter H. (Technical Monitor)

2001-01-01

91

Implementation of Inductive Magnetosphere-Ionosphere Coupling and its Effects on Global MHD Magnetospheric Simulations  

NASA Astrophysics Data System (ADS)

In global modeling, magnetosphere-ionosphere (MI) coupling physically connects a global magnetospheric (GM) model and a global ionospheric-thermospheric (GIT) model. The field-aligned current from the GM model and the conductance distributions from the GIT model are used in a Poisson equation derived from the ionospheric Ohm's law combined with current continuity to determine the electrostatic potential in the ionosphere. In current GM models, this electrostatic potential is mapped to the inner boundary of the GM simulation to determine electrostatic boundary conditions on the electric field and MHD velocity there. Inductive effects and the finite Alfven transit time between the low-altitude GM boundary and the high-altitude GIT boundary (MI gap region) are neglected in this formulation of MI coupling. Using fields and currents derived from Lyon-Fedder-Mobarry GM simulations, and conductance distributions derived from its standalone empirical conductance model in the MI coupling Poisson equation, we have computed the fast Fourier transform of the electrostatic field at the low-altitude LFM simulation boundary as described above, and the FFT of the inductive electric field at the boundary under the assumption that ? 0 ? P vA ? 1, where ? P is the ionospheric Pedersen conductance and vA is the smallest value of the Alfven speed in the MI gap region. In this regime, the complete electric field at the low-altitude simulation boundary includes the usual mapped electrostatic field with an inductive addition for which the finite Alfven transit time and the diversion of field-aligned into polarization currents in the gap region are negligible (Lotko, 2004). By comparing the boundary-averaged spectra of the electrostatic and so-determined inductive fields, we confirm that the purely electrostatic formulation of MI coupling is valid when the MHD state varies on times scales exceeding about 200 s. For faster MHD time variations, the inductive electric field is shown to be larger than the electrostatic field at the low-altitude boundary and is thus non-negligible. For example, inductive corrections are expected to be important for sudden impulse events and substorm-related Pi2 fluctuations. We are currently implementing the inductive MI coupling algorithm of Lotko (2004) in the LFM global simulation. Lotko, W. (2004), Inductive magnetosphere-ionosphere coupling, JASTP 66, 1443-1456.

Xi, S.; Lotko, W.; Zhang, B.; Brambles, O.; Wiltberger, M. J.; Lyon, J.; Merkin, V. G.

2010-12-01

92

Ionospheric effects of rocket exhaust products (HEAO-C, Skylab and SPS-HLLV)  

SciTech Connect

This paper reviews the current state of our understanding of the problem of ionospheric F-layer depletions produced by chemical effects of the exhaust gases from large rockets, with particular emphasis on the Heavy Lift Launch Vehicles (HLLV) proposed for use in the construction of solar power satellites. The currently planned HLLV flight profile calls for main second-stage propulsion confined to altitudes below 124 km, and a brief orbit-circularization maneuver at apogee. The second-stage engines deposit 9 x 10/sup 31/ H/sub 2/O and H/sub 2/ molecules between 56 and 124 km. Model computations show that they diffuse gradually into the ionospheric F region, where they lead to weak but widespread and persistent depletions of ionization and continuous production of H atoms. The orbit-circularization burn deposits 9 x 10/sup 29/ exhaust molecules at about 480-km altitude. These react rapidly with the F2 region 0/sup +/ ions, leading to a substantial (factor-of-three) reduction in plasma density, which extends over a 1000- by 2000-km region and persists for four to five hours. Also described are experimental airglow and incoherent-scatter radar measurements performed in conjunction with the 1979 launch of satellite HEAO-C, together with prelaunch and post-launch computations of the ionospheric effects. Several improvements in the model have been driven by the experimental observations. The computer model is described in some detail.

Zinn, J; Sutherland, D; Stone, S N; Duncan, L M; Behnke, R

1980-10-01

93

A multi-instrument study of high-latitude ionospheric irregularities and their effects on GPS ionospheric scintillation  

NASA Astrophysics Data System (ADS)

Scintillations are rapid amplitude and phase fluctuations of electromagnetic signals. GNSS-based systems may be disturbed by plasma irregularities and structures such as plasma patches (areas of enhanced electron density) and plasma gradients in the ionosphere. When the GNSS radio signals propagate through such areas, in particular gradients, the signals experience scintillations that at best increases positioning errors and at worst may break the receiver's signal lock, potentially resulting in the GNSS receiver losing track of its position. Due to the importance of many GNSS applications, it is desirable to study the scintillation environment to understand the limitations of the GNSS systems. For this study, GPS receiver scintillation and Total Electron Content (TEC) data from high-latitude locations will be combined with several other data sets, including the EISCAT Svalbard Radar (ESR) and allsky cameras to perform a multi-instrument case study of GPS ionospheric scintillations. The EISCAT data provides a means to determine the altitude and density of the F layer, which can then be used to calibrate allsky projections as well as coordinates of ionospheric piercing points of the GPS signals. The focus will be studying any connection between scintillations and polar cap patches; however, other interesting and related findings will also be presented, herein statistical long-timespan studies of GPS TEC and/or scintillation data.

van der Meeren, Christer; Oksavik, Kjellmar; Moen, Jøran; Romano, Vincenzo

2013-04-01

94

The Effect of the Ionospheric Fluctuation to the FASR imaging capability and the Strategy for its Calibration  

NASA Astrophysics Data System (ADS)

The ionospheric irregularities are the major source of uncertainty in image synthesis process of grand-based interferometric radio telescopes under a few GHz. The fluctuation alters both the phase and amplitude of the signals reaching the interferometer elements, and it results in positional shift and distortion of the source structure in the synthesized image, which is very difficult to isolate from the true properties of the source. In general, the ionospheric effect is calibrated for with the observation of guide stars for other low-frequency radio telescopes such as VLA (74MHz) and LOFAR. However, this method is not likely to be effective to FASR due to the low sensitivity of the receiver instrument to observe guide stars. We will present the estimated spatial and temporal characteristics of the small- and medium-scale fluctuation of the ionosphere at the proposed construction site of FASR based on the literature review of the relevant studies, and then discuss the simulation result on its impact on the synthesized beam pattern of the array. Based on these results, we will propose the calibration system of the ionospheric fluctuation for FASR. The system will utilize the information from the slant path TEC measurements from GPS and beacon satellite signals and also the ionospheric model based on physics of the ionospheric waves and turbulence sources and sinks. We will also discuss the possibilities of using the multi-frequency observation capability of the FASR and of collaboration with other solar radio telescopes.

Kawakubo, H.; Ruf, C. S.

2006-05-01

95

Testing Ionospheric Faraday Rotation Corrections in CASA  

NASA Astrophysics Data System (ADS)

The Earth’s ionosphere introduces direction- and time-dependent effects over a range of physical and temporal scales and so is a major source for unmodeled phase offsets for low frequency radioastronomical observations. Ionospheric effects are often the limiting factor to making sensitive radioastronomical measurements to probe the solar corona or coronal mass ejections at low frequencies (< 5 GHz). It has become common practice to use global ionospheric models derived from the Global Positioning System (GPS) to provide a means of externally calibrating low frequency data. We have developed a new calibration algorithm in the Common Astronomy Software Applications (CASA) package. CASA, which was developed to meet the data post-processing needs of next generation telescopes such as the Karl G. Jansky Very Large Array (VLA), did not previously have the capability to mitigate ionospheric effects. This algorithm uses GPS-based global ionosphere maps to mitigate the first and second order ionospheric effects (dispersion delay and Faraday rotation, respectively). We investigated several data centers as potential sources for global ionospheric models and chose the International Global Navigation Satellite System Service data product because data from other sources are generally too sparse to use without additional interpolation schemes. This implementation of ionospheric corrections in CASA has been tested on several sets of VLA observations and all of them showed a significant reduction of the dispersion delay. In order to rigorously test CASA’s ability to mitigate ionospheric Faraday rotation, we made VLA full-polarization observations of the standard VLA phase calibrators J0359+5057 and J0423+4150 in August 2014, using L band (1 ? 2 GHz), S band (2 ? 4 GHz), and C band (4 ? 6 GHz) frequencies in the D array configuration. The observations were 4 hours in duration, beginning near local sunrise. In this paper, we give a general description of how these corrections are implemented as well as discussion of the code’s ability to mitigate the ionospheric effects present in these test observations over a range of times and elevation angles. This work was supported at the University of Iowa by grant ATM09-56901.

Kooi, Jason E.; Moellenbrock, George

2015-04-01

96

Ionospheric effects in uncalibrated phase delay estimation and ambiguity-fixed PPP based on raw observable model  

NASA Astrophysics Data System (ADS)

Zero-difference (ZD) ambiguity resolution (AR) reveals the potential to further improve the performance of precise point positioning (PPP). Traditionally, PPP AR is achieved by Melbourne-Wübbena and ionosphere-free combinations in which the ionosphere effect are removed. To exploit the ionosphere characteristics, PPP AR with L1 and L2 raw observable has also been developed recently. In this study, we apply this new approach in uncalibrated phase delay (UPD) generation and ZD AR and compare it with the traditional model. The raw observable processing strategy treats each ionosphere delay as an unknown parameter. In this manner, both a priori ionosphere correction model and its spatio-temporal correlation can be employed as constraints to improve the ambiguity resolution. However, theoretical analysis indicates that for the wide-lane (WL) UPD retrieved from L1/L2 ambiguities to benefit from this raw observable approach, high precision ionosphere correction of better than 0.7 total electron content unit (TECU) is essential. This conclusion is then confirmed with over 1 year data collected at about 360 stations. Firstly, both global and regional ionosphere model were generated and evaluated, the results of which demonstrated that, for large-scale ionosphere modeling, only an accuracy of 3.9 TECU can be achieved on average for the vertical delays, and this accuracy can be improved to about 0.64 TECU when dense network is involved. Based on these ionosphere products, WL/narrow-lane (NL) UPDs are then extracted with the raw observable model. The NL ambiguity reveals a better stability and consistency compared to traditional approach. Nonetheless, the WL ambiguity can be hardly improved even constrained with the high spatio-temporal resolution ionospheric corrections. By applying both these approaches in PPP-RTK, it is interesting to find that the traditional model is more efficient in AR as evidenced by the shorter time to first fix, while the three-dimensional positioning accuracy of the RAW model outperforms the combination model by about 7.9 % . This reveals that, with the current ionosphere models, there is actually no optimal strategy for the dual-frequency ZD ambiguity resolution, and the combination approach and raw approach each has merits and demerits.

Gu, Shengfeng; Shi, Chuang; Lou, Yidong; Liu, Jingnan

2015-02-01

97

The ionospheric effect of Total solar eclipse of 22 July 2009 in the equatorial anomaly region  

NASA Astrophysics Data System (ADS)

Response of the D and E and F-region of the ionosphere to the total solar eclipse of 22 July 2009 at low latitude, Varanasi (geomagnetic lat = 140 55'N, longitude = 1540 E, dip. angle = 37.30) was investigated using multi-instrument. The solar eclipse started at 05:30:04.4 hrs IST and lasted up to 07:27 hrs IST with totally from 6.25 IST to 6.27 IST in the morning hours at Varanasi. Here we have analyzed narrowband (Amplitude and phase of transmitted signal) as well as broadband (entire VLF signal spectrum) VLF data to find any significant changes in amplitude and/or phase of the signals from various transmitters across the world and any variation from the normal diurnal behavior in ionospheric parameters such as electron density, VLF reflection height. The changes in D-region ionospheric VLF reflection heights and electron density during eclipse have been estimated from tweek analysis. The reflection height increased from ~90 km from the first occurrence of tweek to about 93-94 km at the totality and then decreased to ~89 km at the end of the eclipse. Observations suggest that about 30-40% obscuration of solar disc can lead to the tweeks occurrence which otherwise occur only in the nighttime. A significant increase of 3 dB in the strength of the amplitude of VLF signal of 22.2 kHz transmitted from JJI-Japan is observed around the time of the total solar eclipse (TSE) as compared to a normal day. The modeled electron density height profile of the lower ionosphere depicts linear variation in the electron density with respect to solar radiation as observed by tweek analysis also. We have also used GPS based TEC measurement along with the VHF scintillation to study effect of total solar eclipse. To observe the variability of TEC at Varanasi we have used the VTEC of some selected PRNs and quiet mean VTEC of the same PRN. The percentage change in VTEC (DTEC) compared to quiet mean for each PRN is also plotted to observe the effect. There is considerable reduction in VTEC compared to quiet mean VTEC from all the PRN (Maximum up to 58 % for PRN 24) during the total solar eclipse. Signature of gravity waves in the VTEC variation is also discussed. Scintillations bubbles are also observed during and after the eclipse period indicating irregularities in plasma density. These low latitude ionospheric perturbations on the eclipse day are discussed and compared with other normal days.

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

2012-12-01

98

Influence of ionospheric perturbations in GPS time and frequency transfer  

E-print Network

The stability of GPS time and frequency transfer is limited by the fact that GPS signals travel through the ionosphere. In high precision geodetic time transfer (i.e. based on precise modeling of code and carrier phase GPS data), the so-called ionosphere-free combination of the code and carrier phase measurements made on the two frequencies is used to remove the first-order ionospheric effect. In this paper, we investigate the impact of residual second- and third-order ionospheric effects on geodetic time transfer solutions i.e. remote atomic clock comparisons based on GPS measurements, using the ATOMIUM software developed at the Royal Observatory of Belgium (ROB). The impact of third-order ionospheric effects was shown to be negligible, while for second-order effects, the tests performed on different time links and at different epochs show a small impact of the order of some picoseconds, on a quiet day, and up to more than 10 picoseconds in case of high ionospheric activity. The geomagnetic storm of the 30th...

Pireaux, Sophie; Wauters, Laurence; Bergeot, Nicolas; Baire, Quentin; Bruyninx, Carine; 10.1016/j.asr.2009.07.011

2009-01-01

99

Influence of ionospheric perturbations in GPS time and frequency transfer  

E-print Network

The stability of GPS time and frequency transfer is limited by the fact that GPS signals travel through the ionosphere. In high precision geodetic time transfer (i.e. based on precise modeling of code and carrier phase GPS data), the so-called ionosphere-free combination of the code and carrier phase measurements made on the two frequencies is used to remove the first-order ionospheric effect. In this paper, we investigate the impact of residual second- and third-order ionospheric effects on geodetic time transfer solutions i.e. remote atomic clock comparisons based on GPS measurements, using the ATOMIUM software developed at the Royal Observatory of Belgium (ROB). The impact of third-order ionospheric effects was shown to be negligible, while for second-order effects, the tests performed on different time links and at different epochs show a small impact of the order of some picoseconds, on a quiet day, and up to more than 10 picoseconds in case of high ionospheric activity. The geomagnetic storm of the 30th October 2003 is used to illustrate how space weather products are relevant to understand perturbations in geodetic time and frequency transfer.

Sophie Pireaux; Pascale Defraigne; Laurence Wauters; Nicolas Bergeot; Quentin Baire; Carine Bruyninx; Laurence Wauters; Nicolas Bergeot; Quentin Baire; Carine Bruyninx

100

Regionally based alarm index to mitigate ionospheric scintillation effects for GNSS receivers  

NASA Astrophysics Data System (ADS)

An approach to mitigate the effect of ionospheric scintillation on GNSS (Global Navigation Satellite System) users in the European region using TEC (total electron content) at 1 Hz rate is presented. The TEC in the study is derived using raw GPS (Global Positioning System) observations obtained from the EUREF networks. The study also presents derivation of a geographic mesh-map warning of the expected standard deviation of phase jitter in receiver carrier tracking loops, information which would help to mitigate scintillation effects in GPS software receivers.

Tiwari, R.; Strangeways, H. J.

2015-01-01

101

The formation mechanisms of positive and negative ionospheric storm effects in the F region at high-, mid-and low-latitudes  

NASA Astrophysics Data System (ADS)

Ionospheric storm is associated with the chain of events and phenomena in space environment, beginning at the Sun transmitted through the magnetosphere into the thermosphere-ionosphere system. On the electron density disturbances in the F region the ionospheric storms are classified into positive and negative. In particular a sign of ionospheric disturbances depends on considered latitudes. So in the high-latitude ionosphere the negative effects in electron density are formed most frequently and at mid- and low-latitudes the probability of a positive ionospheric storm increases. Previously performed the theoretical and experimental investigations of positive and negative ionospheric storms allowed to explain many aspects of ionospheric disturbances at different latitudes and their formation mechanisms. However, there are still some important differences and outstanding questions in the formation of these disturbances, which answers can be obtained, for example, using the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP). The GSM TIP model calculation results revealed the role of various mechanisms of ionospheric disturbances at low-, mid- and high-latitudes during geomagnetic storms on September 26-29, 2011. These investigations were supported by RFBR Grant ? 14-05-00578 and RAS Program 22.

Klimenko, Maxim; Klimenko, Vladimir

102

Ionosphere Waves Service - A demonstration  

NASA Astrophysics Data System (ADS)

In the frame of the FP7 POPDAT project the Ionosphere Waves Service was developed by ionosphere experts to answer several questions: How make the old ionosphere missions more valuable? How provide scientific community with a new insight on wave processes that take place in the ionosphere? The answer is a unique data mining service accessing a collection of topical catalogues that characterize a huge number of Atmospheric Gravity Waves, Travelling Ionosphere Disturbances and Whistlers events. The Ionosphere Waves Service regroups databases of specific events extracted by experts from a ten of ionosphere missions which end users can access by applying specific searches and by using statistical analysis modules for their domain of interest. The scientific applications covered by the IWS are relative to earthquake precursors, ionosphere climatology, geomagnetic storms, troposphere-ionosphere energy transfer, and trans-ionosphere link perturbations. In this presentation we propose to detail the service design, the hardware and software architecture, and the service functions. The service interface and capabilities will be the focus of a demonstration in order to help potential end-users for their first access to the Ionosphere Waves Service portal. This work is made with the support of FP7 grant # 263240.

Crespon, François

2013-04-01

103

Irregularities in ionospheric plasma clouds: Their evolution and effect on radio communication  

Microsoft Academic Search

Both satellite radio communications, which travel through the Earth's ionosphere, and high frequency (HF) sky wave circuits, which use the ionosphere as a refracting medium, can be strongly affected by radio wave scintillation. High altitude nuclear explosions cause scintillation (by strongly disturbing the ionosphere) and thus severely degrade satellite radio communications over a large region. Since further atmospheric nuclear tests

J. F. Vesecky; J. W. Chamberlain; J. M. Cornwall; D. A. Hammer; F. W. Perkins

1980-01-01

104

Prompt and delayed effects of solar disturbances in magnetosphere-ionosphere system on March 4-7, 2012  

NASA Astrophysics Data System (ADS)

We analyze prompt and delayed effects of five X-class solar flares observed on March 4-7, 2012 at Siberian and Far Eastern ionospheric stations. The flares were associated with intensification of solar cosmic rays and Earth-directed coronal mass ejections. The prompt effects were caused by EUV, X-rays and relativistic particles. They were observed as increase in the daytime lowest frequency reflected from the ionosphere from 1.5-2 MHz to 4-8 MHz and the disappearance of reflections (complete blackout) from the high-latitude ionosphere. Delayed effects were caused by heliospheric inhomogeneity created by four interacting coronal mass ejections. The inhomogeneity enveloped the Earth’s magnetosphere during 80 hours and triggered two (moderate and strong) magnetic storms accompanied by ionospheric storms. Because of the strong variability of the solar wind and the interplanetary magnetic field in the inhomogeneity, the magnetospheric and ionospheric storms had specific features discussed in our report. The work was supported by the Russian Foundation for Basic Research (grant 13-05-91159 and 13-05-00733) and RF President Grant of Public Support for RF Leading Scientific Schools (NSh-2942.2014.5).

Romanova, Elena; Kurkin, Vladimir; Zolotukhina, Nina; Polekh, Nelya

105

Preface to the Special Issue on Thunderstorm Effects in the Atmosphere-Ionosphere System  

NASA Astrophysics Data System (ADS)

The first summer school of the "Thunderstorm Effects in the Atmosphere-Ionosphere System" (TEA-IS) funded by the European Science Foundation through its Research Network Programme took place in Torremolinos (Spain) on June 17-22, 2012. The meeting gathered almost 100 scientists with different backgrounds (plasma physics, electrical and signal engineering, geophysics, space physics and computational science) coming from 20 countries, both from inside and outside TEA-IS member countries. We very briefly comment here on the five review papers included in this Special Issue of Surveys in Geophysics devoted to the 2012 TEA-IS summer school.

Gordillo-Vázquez, F. J.; Luque, A.

2013-11-01

106

Investigations into the properties, conditions, and effects of the ionosphere. Final report 4 Dec 86-31 Dec 89  

SciTech Connect

The contractor and its subcontractors supported GL/AFSC research in ionospheric physics and its systems effects. Support was provided in the following six categories; laboratory measurements; field measurements, aircraft measurements; rocket, satellite, and Shuttle measurements; analytical and theoretical investigations; and engineering analysis. This report summarizes results on 15 specific topics. These topics included ionospheric characteristics central to operation of HF systems, such as OTH radars; engineering studies of meteor/scatter communication links; effects on transionospheric radio propagation controlled by the total electron content (path integral of electron density) of the ionosphere and its fine structure (which produces radiowave scintillation); optical and ultraviolet effects of the aurora and airglow, as well as laboratory uv studies; and feasibility studies on modifying radio blackout and measuring electron density in the D region..

Fremouw, E.J.; Reinisch, B.W.; Szuszczewica, E.P.

1990-01-15

107

Effect of double layers on magnetosphere-ionosphere coupling  

NASA Technical Reports Server (NTRS)

The Earth's auroral zone contains dynamic processes occurring on scales from the length of an auroral zone field line which characterizes Alfven wave propagation to the scale of microscopic processes which occur over a few Debye lengths. These processes interact in a time-dependent fashion since the current carried by the Alfven waves can excite microscopic turbulence which can in turn provide dissipation of the Alfven wave energy. This review will first describe the dynamic aspects of auroral current structures with emphasis on consequences for models of microscopic turbulence. A number of models of microscopic turbulence will be introduced into a large-scale model of Alfven wave propagation to determine the effect of various models on the overall structure of auroral currents. In particular, the effects of a double layer electric field which scales with the plasma temperature and Debye length is compared with the effect of anomalous resistivity due to electrostatic ion cyclotron turbulence in which the electric field scales with the magnetic field strength. It is found that the double layer model is less diffusive than in the resistive model leading to the possibility of narrow, intense current structures.

Lysak, Robert L.; Hudson, Mary K.

1987-01-01

108

The effects of ionospheric outflow on ICME and SIR driven sawtooth events  

NASA Astrophysics Data System (ADS)

Magnetosphere sawtooth oscillations have been observed during interplanetary coronal mass ejection (ICME) events, when the solar wind conditions are relatively steady, and during periods when the interplanetary magnetic field (IMF) fluctuates between northward and southward, as during interplanetary stream interaction regions (SIR). The impact of ionospheric outflow on the ICME-driven 18 April 2002 and SIR-driven 24 October 2002 sawtooth events is investigated using a multifluid adaptation of the Lyon-Fedder-Mobarry global simulation. The mechanisms that generate the sawtooth oscillations are investigated by comparing a baseline simulation without outflow and a simulation that includes an O+ outflow model. The ionospheric outflow is regulated by a statistical relationship between Alfvénic Poynting flux and O+ ion outflow flux. In the baseline simulation for the 18 April 2002 ICME-driven event, one substorm is observed that is generated by the southward turning of the IMF, after which the magnetosphere-ionosphere system settles into a quasi-steady convection mode. When outflow is included, quasi-periodic substorms are observed suggesting that the sawtooth oscillations are generated internally by the effects of the O+ ions. In contrast, during the 24 October 2002 SIR-driven event, quasi-periodic substorms are generated regardless of whether outflow is included or not. For this event, the generation and triggering of the substorms is controlled by the external driving of the solar wind. For both events, when outflow is included, the signatures of the substorms are more intense and are more noticeable across a wider range of local times than in the baseline simulations.

Brambles, O. J.; Lotko, W.; Zhang, B.; Ouellette, J.; Lyon, J.; Wiltberger, M.

2013-10-01

109

Case study of Bastille Day storm effects on the ionosphere using DMSP ion density measurements and TEC maps  

Microsoft Academic Search

Magnetic storm effects on the ionosphere were investigated using the ion density measurements from the DMSP (Defense Meteorological Satellite Program) F13, 14, and 15 spacecrafts and using total electron content (TEC) maps for a selected interval - the Bastille Day storm of July 15, 2000. During the expansion phase of the storm the negative storm effects developed from the high-latitude

H. Kil; L. J. Paxton; Y. Zhang; M. R. Hariston; X. Pi

2001-01-01

110

The effects of 450 kg surface explosions at the E layer of the ionosphere. Los Alamos Source Region Project  

SciTech Connect

A network of hf ionospheric sounders consisting of two transmitter and two receiver stations was deployed to detect the effects of acoustic waves generated by surface ground motion following an underground nuclear test (UGT) at the Nevada Test Site. The frequency of the transmissions were chosen so that the hf radio waves were totally reflected in the E layer of the ionosphere at an altitude of approximately 100 km. The transmissions were highly stable cw tones at two frequencies separated by 100 kHz so that two altitudes separated by approximately .5 km could be sensed. The network sampled four geographic locations in the ionosphere ranging from almost directly overhead of the UGT out to a horizontal range of 60 km. The ionospheric sounders detected disturbances on all the paths beginning at approximately 325 s after the UGT which persisted for up to 100 s. These disturbances will be described in detail in a later paper. Shortly after the UGT an extended series of ionospheric disturbances were detected which we ascribe to the arrival of acoustic shock waves at the E layer caused by the surface detonation of ordinance with effective yields of 450 kg of high explosive during an unrelated exercise conducted by the U. S. Air Force at a nearby bombing range. The conjunction of these disturbances produced a direct comparison of the effects of UGT`s and surface explosions in the ionosphere. In this paper we describe the effects produced by the surface explosions and interpret the disturbance in terms of diffraction induced by electron density changes accompanying the passage of the acoustic waves from the explosions through the reflection altitudes.

Fitzgerald, T.J.; Carlos, R.C.

1992-10-22

111

Manifestation of the cotton-mouton effect in the ionosphere plasma  

NASA Astrophysics Data System (ADS)

Polarization methods used to sound ionospheric plasma are based on the Faraday and Cotton-Mouton effects. While the Faraday effect (rotation of the polarization plane) covers almost the entire ray path, the Cotton-Mouton effect gives rise to local transformation of circularly polarized waves near a point of orthogonality of the ray and the Earth's magnetic field. Comparison of the input and output polarization of probing electromagnetic waves, emitted by a satellite and received by ground stations, can provide valuable information about local plasma parameters near the orthogonality point. This paper presents a theory of interaction of circular waves near this point based on the quasi-isotropic approximation (QIA) of geometrical optics and describes algorithms that can be used to retrieve local plasma parameters from polarization measurements. Experimental configurations to observe the Cotton-Mouton effect with linearly and arbitrarily polarized receivers are discussed.

Kravtsov, Yu. A.; Naida, O. N.

112

Satellite-based augmentation systems: A novel and cost-effective tool for ionospheric and space weather studies  

NASA Astrophysics Data System (ADS)

Satellite-Based Augmentation Systems (SBASes) are designed to provide additional accuracy and robustness to existing satellite-based radio navigation systems for all phases of a flight. However, similar to navigation systems such as GPS which has proven its worth for the investigation of the ionosphere, the SBASes do have certain advantages. In the present paper, we propose and demonstrate SBAS applicability to ionospheric and space weather research in a novel and cost-effective way. The recent commissioning of the Indian SBAS, named GPS Aided Geo Augmented Navigation (GAGAN), covering the equatorial and low-latitude regions centered around the Indian longitudes provides the motivation for this approach. Two case studies involving different ionospheric behavior over low-latitude regions vindicate the potential of SBAS over extended areas.

Sunda, Surendra; Sridharan, R.; Vyas, B. M.; Khekale, P. V.; Parikh, K. S.; Ganeshan, A. S.; Sudhir, C. R.; Satish, S. V.; Bagiya, Mala S.

2015-01-01

113

Climatology of GNSS ionospheric scintillation at high latitudes  

NASA Astrophysics Data System (ADS)

Under perturbed conditions caused by intense solar wind magnetosphere coupling, the ionosphere may become highly turbulent and irregularities, typically enhancements or depletions of the electron density embedded in the ambient ionosphere, can form. Such irregularities cause diffraction effects, mainly due to the random fluctuations of the refractive index of the ionosphere, on the satellites signals passing through them and consequent perturbations may cause GNSS navigation errors and outages, abruptly corrupting its performance. Due to the morphology of the geomagnetic field, whose lines are almost vertical at high latitude, polar areas are characterized by the presence of significant ionospheric irregularities having scale sizes ranging from hundreds of kilometers down to a few centimeters and with highly dynamic structures. The understanding of the effect of such phenomena is important, not only in preparation for the next solar cycle (24), whose maximum is expected in 2012, but also for a deeper comprehension of the dynamics of the high-latitude ionosphere. We analyze the fluctuations in the carrier frequency of the radio waves received on the ground, commonly referred to as ionospheric amplitude and phase scintillations, to investigate the physical processes causing them. The phase scintillations on GNSS signals are likely caused by ionospheric irregularities of scale size of hundreds of meters to few kilometers. The amplitude scintillations on GNSS signals are caused by ionospheric irregularities of scale size smaller than the Fresnel radius, which is of the order of hundreds of meters for GNSS signals, typically embedded into the patches. The Istituto Nazionale di Geofisica e Vulcanologia (INGV) and the Institute of Engineering Surveying and Space Geodesy (IESSG) of the University of Nottingham manage the same kind of GISTM (GPS Ionospheric Scintillation and TEC Monitor) receivers over the European high and mid latitude regions and over Antarctica. The GISTM receivers consist of NovAtel OEM4 dual-frequency receivers with special firmware specifically able to compute in near real time the amplitude and the phase scintillation from the GPS L1 frequency signals, and the ionospheric TEC (Total Electron Content) from the GPS L1 and L2 carrier phase signals. From this ground-based network, we are able to capture the dynamics of ionospheric plasma in a wide latitudinal range, from auroral to cusp/cap regions, considering the contribution of both hemispheres, in a bi-polar framework. The data collection started in 2001 and is still in progress. The results, obtained by statistically analyzing a large data sample over a wide period, show the effect of ionospheric disturbances on the GNSS signals, evidencing the different contributions of the auroral and the cusp/cap ionosphere and highlighting possible scintillation scenarios over polar regions.

Spogli, L.; Alfonsi, L.; de Franceschi, G.; Romano, V.; Aquino, M.; Dodson, A.; Mitchell, C. N.

2009-12-01

114

Investigating magnetospheric interaction effects on Titan's ionosphere with the Cassini orbiter Ion Neutral Mass Spectrometer, Langmuir Probe  

E-print Network

conditions of 3D models including the plasma interaction and features such as neutral winds. PublishedInvestigating magnetospheric interaction effects on Titan's ionosphere with the Cassini orbiter Ion Keywords: Titan Titan, atmosphere Saturn, satellites a b s t r a c t In the $6 years since the Cassini

California at Berkeley, University of

115

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

NASA Astrophysics Data System (ADS)

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 geomagnetic storm. A comparison of the ordinary and extraordinary modes of HF radio ray paths in quiet and disturbed conditions has been done. We considered in more detail the features of the radio ray paths in the presence of F3 layer in the equatorial ionosphere, the main ionospheric trough and tongue of ionization at high latitudes. It is shown that the results obtained with use of radio propagation and GSM TIP models adequately describe HF radio ray paths in the Earth's ionosphere and can be used in applications. These investigations were carried out at financial support of Russian Foundation for Basic Research (RFBR) - Grant # 12-05-31217 and RAS Program 22.

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

2013-04-01

116

Negative Effect on Electron Density in Midlatitude Ionosphere due to Geomagnetic Disturbances: FORMOSAT-3\\/COSMIC Observations  

Microsoft Academic Search

The ionospheric plasma usually responds drastically to severe space weather conditions, signified by strong magnetic field disturbances in the near-Earth environment. The level of disturbances is often well characterized by global indices such as Kp and Dst. Our statistical studies examine the ionospheric vertical electron density profiles under different levels of geomagnetic activities, as characterized by such indices. The studies

S. W. Tam; C. Chen; K. Wang

2009-01-01

117

Effects of Ionospheric Conductivity on Convective Flow of Plasma in the Magnetosphere  

Microsoft Academic Search

Convective flow of plasma in the magnetosphere is apparently driven by the interaction between the solar wind and the magnetosphere, but the flow pattern is regulated by the ionosphere and by pressure gradients in the magnetospheric plasma. The equations for conservation of ionospheric currents are used here to deduce theoretical flow patterns. The currents caused by the pressure of magnetospheric

R. A. Wolf

1970-01-01

118

Whole Atmosphere-Ionosphere Coupled Model (GAIA) for Space Weather Research  

NASA Astrophysics Data System (ADS)

Space near the Earth, called geospace, is a highly complex system, consisting of the solar wind, the magnetosphere, the ionosphere, and the neutral atmosphere. Those regions have different physical characteristics with different temporal and spatial scales. In particular, the magnetosphere, the ionosphere, and the neutral atmosphere are strongly coupled with each other, and interaction between the regions is nonlinear and extremely complicated. Even within each region, there are strong interactions between physical processes with different temporal and spatial scales. Furthermore, the geospace environment significantly varies as electromagnetic energy and particles from the sun vary. In order to quantitatively understand such a complicated system, it is necessary to model the entire region by including all fundamental processes self-consistently. Various types of global numerical models of geospace have been constructed and used to study space weather disturbances in many institutions in the world. At the National Institute of Information and Communications Technology (NICT) of Japan, a real-time solar wind model, magnetosphere model, and ionosphere-thermosphere model have been developed and used for daily space weather forecast. In addition to the effect of geospace disturbance on the upper atmosphere, recent observations of the ionosphere and the thermosphere have revealed that atmospheric waves generated in the lower atmosphere significantly influence the upper atmosphere, the ionosphere, and possibly the magnetosphere. In order to quantitatively study the effects of the lower atmosphere on the ionosphere, we have developed an atmosphere-ionosphere coupled model, which includes the whole neutral atmosphere and the ionosphere. The model is called GAIA (Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy). Using GAIA, relationship between the ionosphere and the atmosphere is being studied. We plan to incorporate magnetospheric inputs to the polar ionosphere by using a magnetospheric model. We will report the status and future plan of the space environment study using GAIA.

Shinagawa, H.; Jin, H.; Miyoshi, Y.; Fujiwara, H.; Tanaka, T.; Fujita, S.; Terada, K.; Murata, K. T.

2011-12-01

119

Effects of artificially modified ionospheres on HF propagation: Negative Ion Cation Release Experiment 2 and CRRES Coqui experiments  

SciTech Connect

We report the results of measurements obtained in conjunction with a series of high-altitude chemical release experiments of effects of artificially modified ionospheres upon high-frequency, ionospherically reflected radio paths. Computer simulations indicate that under optimum conditions, ionospheric modifications induced by chemical releases could perturb or even disrupt a communication channel; our experiments corroborate this but also indicate that it is very difficult to actualize such disruptions. Our experiments have shown that an ionospheric depletion, in which the electron density hole forms a huge radio frequency lens, generates new modes which, however, do not significantly affect a communications system. Under optimum path geometry a signal strength decrease of 10 dB or more is possible for several tens of minutes. Enhancements, such as those produced by barium releases, act as reflecting mirrors that can create a large shadow zone on the ground and block off significant amounts of energy. We measured signal strength decreases of up to 20 dB.{copyright} 1997 American Geophysical Union

Fitzgerald, T.J.; Argo, P.E.; Carlos, R.C. [Los Alamos National Laboratory, Los Alamos, New Mexico (United States)] [Los Alamos National Laboratory, Los Alamos, New Mexico (United States)

1997-03-01

120

A case study of ionospheric storm effects during long-lasting southward IMF Bz-driven geomagnetic storm  

NASA Astrophysics Data System (ADS)

Multiple instrumental observations including GPS total electron content (TEC), foF2 and hmF2 from ionosondes, vertical ion drift measurements from Communication/Navigation Outage Forecasting System, magnetometer data, and far ultraviolet airglow measured by Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics/Global Ultraviolet Imager (TIMED/GUVI) are used to investigate the profound ionospheric disturbances at midlatitude and low latitude during the 14-17 July 2012 geomagnetic storm event, which was featured by prolonged southward interplanetary geomagnetic field component for about 30 h below -10 nT. In the East Asian/Australian sector, latitudinal profile of TEC variations in the main phase were characterized by three bands of increments and separated by weak depressions in the equatorial ionospheric anomaly (EIA) crest regions, which were caused by the combined effects of disturbance dynamo electric fields (DDEF) and equatorward neutral winds. In the recovery phase, strong inhibition of EIA occurred and the summer crest of EIA disappeared on 16 July due to the combined effects of intrusion of neutral composition disturbance zone as shown by the TIMED/GUVI O/N2 measurements and long-lasting daytime westward DDEF inferred from the equatorial electrojet observations. The transit time of DDEF over the dip equator from westward to eastward is around 2200 LT. In the American longitude, the salient ionospheric disturbances in the summer hemisphere were characterized by daytime periodical intrusion of negative phase for three consecutive days in the recovery phase, preceded by storm-enhanced density plume in the initial phase. In addition, multiple short-lived prompt penetration electric fields appeared during stable southward interplanetary magnetic field (IMF) Bz in the recovery phase and were responsible for enhanced the EIA and equatorial ionospheric uplift around sunset.

Liu, Jing; Liu, Libo; Nakamura, Takuji; Zhao, Biqiang; Ning, Baiqi; Yoshikawa, A.

2014-09-01

121

The effects of solar cycle and latitude dependence on the formation of ionospheric C layer  

NASA Astrophysics Data System (ADS)

The C-layer effect is observed on long distance very low frequency (VLF) signal propagation at sunrise, when the solar illumination line (terminator) makes a small angle (alpha is less than 20 deg) with the propagation path. The effect may be described as an additional phase advance, just after the sunrise normal phase advance, recovering in about 90 minutes. Analysis of different propagation paths shows that the magnitude of the observed effect presents a latitudinal and solar cycle dependence. Data obtained for geomagnetic latitudes ranging 14 deg N to 50 deg S have shown that the C-layer effect seems to be more pronounced at higher latitudes. Finally analysis of data at different phases of the solar cycle suggest that for the period of maximum activity the magnitude of the observed C-layer effect is reduced. These effects may be understood bearing in mind that cosmic radiation is mainly responsible for the ionization of regions below the ionospheric D-layer. It is more intense at higher latitudes and also presents a variation with the solar cycle, being minimum when maximum solar activity occurs. In the analysis, different phenomena which could influence the C-layer effect were taken into account, such as SIDs at sunrise, Forbush decrease, stratwarm and magnetic storms.

Requiakuntz, Vera Lucia

1987-09-01

122

Ionosphere research  

NASA Technical Reports Server (NTRS)

A report is presented on on-going research projects in ionospheric studies. The topics discussed are planetary atmospheres, E and F region, D region, mass spectrometer measurements, direct measurements and atmospheric reactions.

1976-01-01

123

Empirical model of ionospheric storm effects on the F2 layer peak height associated with changes of peak electron density  

NASA Astrophysics Data System (ADS)

An empirical model of storm-time behavior of the ionospheric peak height hmF2 associated with changes of peak electron density NmF2 is inferred from the topside true-height profiles provided by ISIS 1, ISIS 2, IK-19, and Cosmos-1809 satellites for the period of 1969-1987. The topside-derived quiet-time models of the ionospheric peak height hqF2 and peak electron density NqF2 are used as a frame of reference. To harmonize the model with storm and substorm effects induced by large-scale traveling ionospheric disturbances (LSTIDs), constraints are applied to the topside data, excluding their changes deviating above LSTID extreme limits. The degree of disturbance is estimated by the ionospheric weather W index; then, the least squares fitting is applied to the median of log(hm/hq) versus log(Nm/Nq). Anticorrelation between instant changes of hmF2 and NmF2 has a particular seasonal-magnetic latitude structure varying with solar activity that is used for the buildup of the analytical model. The model allows the deduction of the instantaneous hmF2 associated with the assessment or forecast of the respective NmF2. The model is validated with the data of five ground-based ionosondes during severe space weather storms at times of high solar activity (2000) and low solar activity (2006), and results agree reasonably well with the peak parameters derived from an ionogram. The model is incorporated into the coupled International Reference Ionosphere-Plasmasphere (IRI-Plas) code, used in the assimilative mode as the three-dimensional (3-D) interpolator of the GPS-derived total electron content, TECgps.

Gulyaeva, T. L.

2012-02-01

124

A case study of lightning, whistlers, and associated ionospheric effects during a substorm particle injection event  

NASA Technical Reports Server (NTRS)

The relationships among cloud-to-ground (CG) lightning, sferics, whistlers, VLF amplitude perturbations, and other ionospheric phenomena occurring during substorm events were investigated using data from simultaneous ground-based observations of narrow-band and broad-band VLF radio waves and of CG lightning made during the 1987 Wave-Induced Particle Precipitation campaign conducted from Wallops Island (Virginia). Results suggest that the data collected on ionospheric phenomena during this event may represent new evidence of direct coupling of lightning energy to the lower ionosphere, either in conjunction with or in the absence of gyroresonant interactions between whistler mode waves and electrons in the magnetosphere.

Rodriguez, J. V.; Inan, U. S.; Li, Y. Q.; Holzworth, R. H.; Smith, A. J.; Orville, R. E.; Rosenberg, T. J.

1992-01-01

125

Experimental investigation of the ionospheric hysteresis effect on the threshold excitation level of the Stimulated Electromagnetic Emission (SEE) during heating at the second electron gyro-harmonic frequency  

NASA Astrophysics Data System (ADS)

Recent experimental observations of the stimulated electromagnetic emission (SEE) spectrum during heating at the second electron gyro-harmonic show structures ordered by ion gyro-frequency. The proposed generation mechanism considers parametric decay of a pump upper hybrid/electron Bernstein (UH/EB) wave into another UH/EB and a group of neutralized ion Bernstein waves. The presumption of the proposed mechanism is that the pump electromagnetic wave is converted into the UH/EB wave. This conversion process generates field aligned irregularity which exhibits hysteresis effect. The predicted ionospheric hysteresis effect is studied during the PARS 2012 at HAARP. The preliminary results are presented for the first time. Also, experimental study of the effects of 1) the transmitter beam angle and 2) the transmitter frequency offset relative to the second electron gyro-harmonic frequency on the ion gyro-harmonic structures in the SEE spectrum are provided. The aforementioned observations are compared to the predictions of the analytical model. Possible connection of the SEE spectral features and artificially generated ionospheric descending layer is also discussed

Samimi, A.; Scales, W.; Cruz, M.; Isham, B.; Bernhardt, P. A.

2012-12-01

126

High Resolution Reconstruction of the Ionosphere for SAR Applications  

NASA Astrophysics Data System (ADS)

Caused by ionosphere's strong impact on radio signal propagation, high resolution and highly accurate reconstructions of the ionosphere's electron density distribution are demanded for a large number of applications, e.g. to contribute to the mitigation of ionospheric effects on Synthetic Aperture Radar (SAR) measurements. As a new generation of remote sensing satellites the TanDEM-L radar mission is planned to improve the understanding and modelling ability of global environmental processes and ecosystem change. TanDEM-L will operate in L-band with a wavelength of approximately 24 cm enabling a stronger penetration capability compared to X-band (3 cm) or C-band (5 cm). But accompanied by the lower frequency of the TanDEM-L signals the influence of the ionosphere will increase. In particular small scale irregularities of the ionosphere might lead to electron density variations within the synthetic aperture length of the TanDEM-L satellite and in turn might result into blurring and azimuth pixel shifts. Hence the quality of the radar image worsens if the ionospheric effects are not mitigated. The Helmholtz Alliance project "Remote Sensing and Earth System Dynamics" (EDA) aims in the preparation of the HGF centres and the science community for the utilisation and integration of the TanDEM-L products into the study of the Earth's system. One significant point thereby is to cope with the mentioned ionospheric effects. Therefore different strategies towards achieving this objective are pursued: the mitigation of the ionospheric effects based on the radar data itself, the mitigation based on external information like global Total Electron Content (TEC) maps or reconstructions of the ionosphere and the combination of external information and radar data. In this presentation we describe the geostatistical approach chosen to analyse the behaviour of the ionosphere and to provide a high resolution 3D electron density reconstruction. As first step the horizontal structure of the ionosphere is studied in space and time on the base of ground-based TEC measurements in the European region. In order to determine the correlation of measurements at different locations or points of time the TEC measurements are subtracted by a base model to define a stationary random field. We outline the application of the NeQuick model and the final IGS TEC maps as background and show first results regarding the distribution and the stationarity of the resulting residuals. Moreover, the occurred problems and questions are discussed and finally an outlook towards the next modelling steps is presented.

Minkwitz, David; Gerzen, Tatjana; Hoque, Mainul

2014-05-01

127

Ionospheric effects of the solar eclipse of September 23, 1987, around the equatorial anomaly crest region  

Microsoft Academic Search

The ionospheric responses to the solar eclipse of September 23, 1987, in the equatorial anomaly crest region have been investigated by using ionospheric vertical sounding, VLF propagation delay time, and differential Doppler shift data observed at Chungli, (24.91 deg N, 121.24 deg E). It has been found that temporal variations of the F1 layer and D region are mainly controlled

Kang Cheng; Yinn-Nien Huang; Sen-Wen Chen

1992-01-01

128

Effects of ionospheric scintillation on Transit satellite measurement of total electron content  

Microsoft Academic Search

Ionospheric scintillation can affect not only satellite communications but also satellite measurements of the ionosphere, such as the measurements of total electron content (TEC) made using Transit-like signal transmissions. In this work a numerical phase-screen propagation simulation is applied to study the accuracy of the measurement of TEC made with Transit-like signals. To measure TEC, the phase from coherently related

D. L. Knepp

2004-01-01

129

Quasi-static electric fields phenomena in the ionosphere associated with pre- and post earthquake effects  

Microsoft Academic Search

To prove a direct relationship between the quasi-static electric field disturbances and seismic activity is a difficult, but actual task of the modern ionosphere physics. This paper presents new results on the processing and analysis of the quasi-static electric field in the upper ionosphere (h=800-900 km) observed from the satellite INTERCOSMOS-BULGARIA-1300 over earthquakes' source regions (seismic data of World Data

M. Gousheva; D. Danov; P. Hristov; M. Matova

2008-01-01

130

Effects of convection electric field on upwelling and escape of ionospheric O(+)  

NASA Technical Reports Server (NTRS)

A Monte Carlo code is used to explore the full effects of the convection electric field on distributions of upflowing O(+) ions from the cusp/cleft ionosphere. Trajectories of individual ions/neutrals are computed as they undergo multiple charge-exchange collisions. In the ion state, the trajectories are computed in realistic models of the magnetic field and the convection, corotation, and ambipolar electric fields. The effects of ion-ion collisions are included, and the trajectories are computed with and without simultaneous stochastic heating perpendicular to the magnetic field by a realistic model of broadband, low frequency waves. In the neutral state, ballistic trajectories in the gravitational field are computed. The initial conditions of the ions, in addition to ambipolar electric field and the number densities and temperatures of O(+), H(+), and electrons as a function of height in the cusp/cleft region were obtained from the results of Gombosi and Killeen (1987), who used a hydrodynamic code to simulate the time-dependent frictional-heating effects in a magnetic tube during its motion though the convection throat. The distribution of the ion fluxes as a function of height are constructed from the case histories.

Cladis, J. B.; Chiu, Yam T.; Peterson, William K.

1992-01-01

131

Low-latitude ionospheric effects of energetic electrons during a recurrent magnetic storm  

NASA Astrophysics Data System (ADS)

We study a magnetosphere-ionosphere coupling at low latitudes during a moderate (corotating interaction regions/high-speed solar wind streams-driven) geomagnetic storm on 22 July 2009. Recently, it has been shown that during major (coronal mass ejection-driven) storms, quasi-trapped >30 keV electrons largely enhance below the radiation belt in the forbidden zone and produce an additional ionization in the topside ionosphere. In this work, we examine a case of the recurrent storm when the magnetosphere-ionosphere coupling through the quasi-trapped electrons also may take place. Data from NOAA/Polar-orbiting Operational Environmental Satellite and Japanese Greenhouse gases Observing Satellite were used to identify the forbidden electron enhancement (FEE). We find a positive vertical gradient of the electron fluxes that indicates to the radiation belt as a source of FEE. Using global ionospheric maps, radiotomography reconstructions from beacon data and COSMIC/FORMOSAT-3 radio occultation measurements, we have observed an unusually large area in the nighttime ionosphere with increased total electron content (TEC) and prominent elevation of the F layer at low latitudes that coincides with FEEs spatially and temporarily. Ionizing particles are considered as an addition source of ionization along with generally accepted mechanisms for storm time TEC increase (a positive ionospheric storm). We discuss relative contributions of the FEE and disturbance dynamo electric field in the TEC increases during the storm recovery phase.

Suvorova, A. V.; Huang, C.-M.; Matsumoto, H.; Dmitriev, A. V.; Kunitsyn, V. E.; Andreeva, E. S.; Nesterov, I. A.; Tsai, L.-C.

2014-11-01

132

Comparison of dayside current layers in Venus' ionosphere and earth's equatorial electrojet  

NASA Technical Reports Server (NTRS)

The major physical aspects of the equatorial electrojet of Earth and the dayside ionospheric current layers of Venus are compared, viz., the electric current intensity and total current, roles of electric field, pressure and gravity, diffusion time scales, and the Bernouille effect. The largest potential differences, of the order of 10 volts, horizontally across the dayside ionosphere of Venus, have important implications for possible dynamo action in the Venus ionosphere and the application of an electric field from the lower atmosphere or from the solar wind. An upper limit to the horizontal scale of vertical magnetic fields in the Venus ionosphere is estimated thereby for the first time. New upper limits on the velocity in, and thickness of, a possible S layer at Venus are presented. If an S layer exists, it is only for extreme conditions of the solar wind. A mechanism for formation of magnetic ropes in the Venus ionosphere is also proposed.

Cole, Keith D.

1993-01-01

133

Comparison of dayside current layers in Venus' ionosphere and earth's equatorial electrojet  

NASA Astrophysics Data System (ADS)

The major physical aspects of the equatorial electrojet of Earth and the dayside ionospheric current layers of Venus are compared, viz., the electric current intensity and total current, roles of electric field, pressure and gravity, diffusion time scales, and the Bernouille effect. The largest potential differences, of the order of 10 volts, horizontally across the dayside ionosphere of Venus, have important implications for possible dynamo action in the Venus ionosphere and the application of an electric field from the lower atmosphere or from the solar wind. An upper limit to the horizontal scale of vertical magnetic fields in the Venus ionosphere is estimated thereby for the first time. New upper limits on the velocity in, and thickness of, a possible S layer at Venus are presented. If an S layer exists, it is only for extreme conditions of the solar wind. A mechanism for formation of magnetic ropes in the Venus ionosphere is also proposed.

Cole, K. D.

1993-03-01

134

Interball project - some cause-and-effect relationships for investigated magnetosphere-ionosphere processes, clarified by uvsips, ska-3, imap-3 experiments on board the interball-2  

NASA Astrophysics Data System (ADS)

The instruments Magnetometer IMAP-- 3 (STIL-Bulgaria) and SKA-3 (a set of particle detectors - RAN- Russia), operating onboard the Interball -- 2 satellite provide in - situ characteristics of the magnetic field, the distribution functions of the electrons and ions, respectively. The UV spectrometer UVSIPS by remote sensing maps ionospheric auroral characteristics in the magnetic field line foot print in 3 lines: of the atomic oxygen (1304 A, 1356 A) and of the nitrogen (1493 A), thus providing monitoring of the interaction solar wind-magnetosphere-ionosphere. We present co-related results from those experiments, confirming some cause-and-effect physical relationships: solar wind/magnetosheet plasma characteristics, their interactions with the outer regions of the magnetosphere, the active plasma processes, the substorm-type phenomena, the magnetosphere-ionosphere interactions, the plasma convection, the auroral phenomena, the respective auroral and airglow manifestations, etc. The obtained results, such as the relation of the UV line intensity I1304/I1356, the frontiers of the auroral oval, the height and dimensions of the auroral arcs, the space and time relationship between the solar wind and the aurora, the measurements of dayside aurora (the substorm usually starts at the equatorward arc of the oval) and others are presented. In addition, our investigation provokes questions about some phenomena as a challenge for future exploration and theoretical explanations - for example, the phenomenon found at the polar edge of the auroral oval in the postmidnight - morning sectors: field-aligned (FA) high-energy upward electron beams in the energy range 20 - 45 keV at altitudes about 3 RE, accompanied by bi-directional electron FA beams of keV energy. Our partial results show the necessity to proceed with the next stage of complete data processing of all experiments in the project in order to make a good evaluation of the investigated phenomena and to achieve the main aims of Interball project.

Palazov, K.; Bochev, A.; Manev, A.; Getsov, P.; Jekov, J.; Jekov, S.; Mardirosyan, G.; Kusmin; Esmont, N.; Prokhorenko, V.

135

Study of a geomagnetic storm effect on the ionospheric scintillation and total electron content (TEC) over the SCINDA station in Abidjan  

NASA Astrophysics Data System (ADS)

This study investigates the ionospheric effects of the magnetic storm of April 5th, 2010. Using ionospheric data recorded with a SCINDA GPS receiver installed in Abidjan (Lat=5.3o N, Long=3.9o W), an equatorial station, we analyzed the variation of the ionospheric scintillation and the TEC during the storm. The ionospheric scintillation is characterized with the so called scintillation index S4.To reduce the multipath effects on the scintillation,S4 values recorded at elevation angle lower than 30o according to the criteria of Otsuka et al., (2006). The TEC is calibrated using the technique by Carrano et al., (2009). The TEC shows two phases of increasing followed by a depression during the main phase of the storm

Obrou, O. K.; Ackah, J.; Zaka, Z. K.

2010-12-01

136

Effects of plasmaspheric ion heating due to ionospheric and magnetospheric sources  

NASA Technical Reports Server (NTRS)

In an initial study, the He(+) observations from the Retarding Ion Mass Spectrometer on Dynamics Explorer 1 (RIMS/DE 1) was examined for more than 120 transits of the plasmasphere in the fall of 1981. The He(+) to H(+) ratio was determined as it varied spatially over portions of the DE 1 orbit, and its variation with solar and magnetic activities and with local time, focusing specifically on the inner plasmasphere. These variations were compared along the L = 2 field line with calculations made by the Field Line Interhemispheric Plasma (FLIP) code. In a recently submitted paper, the He(+) to H(+) density ratio was examined for all the available data from 1981 to 1984 from the RIMS on DE 1. There are two basic characteristics of the ratio: one is that the ratio decreases with radial distance in the plasmasphere, and the other is the strong dependence of the density ratio on solar activity. In addition to the He(+)/H(+) ratio research, a phenomenon has been studied in the topside ionosphere which relates to the thermal coupling of the ionosphere to the plasmasphere. There is little or no correlation with magnetic and solar activity here. Another study has been directed toward the relation of plasma properties to the density gradients forming the plasmapause. The study has followed a two-pronged approach. First, the observations have been analyzed to determine what happens to the plasma properties across these boundary layers (density gradients). Second, comparisons were made with FLIP model calculations to determine how well the model is able to treat these conditions. Among the significant lessons learned in these studies are two that bear directly on the direction of future investigations in this area. First, composition cannot be viewed independently of thermal structure. Second, solar and magnetic activity effects are real; but the causal relationship between activity and effects is frequently quite complicated because several different processes appear to be operating in different ways and on different time scales. Under these circumstances, large correlation coefficients should not be expected and are not generally found.

Comfort, Richard H.

1996-01-01

137

Ion Internal Excitation and Co++ 2 Reactivity: Effect On The Titan, Mars and Venus Ionospheric Chemistry  

NASA Astrophysics Data System (ADS)

In planetary ionospheres, primary molecular and atomic photoions can be produced with substantial electronic and vibrational internal energy. In some cases, this is known to strongly affect both the rate constants and the branching ratio between the reac- tion products. A previous experimental study (Nicolas et al.) made at the Orsay syn- chrotron radiation facility has shown that many endothermic charge transfer reactions which were not considered in the ionospheric chemistry models of Mars, Venus and Earth have to be included because they are driven by electronic excitation of the parent ions. New measurements on two important reactions for Titan and Mars ionospheres, N+ + CH4 and O+ + CO2, will be presented. Branching ratios between products are very different when the parent atomic ions are prepared in their ground states, N+(3P) and O+(4S), or in their first electronic metastable states N+(1D) and O+(2D or P). 2 As the lifetime of these states are long enough, they survive during the mean time be- tween two collisions in the ionospheric conditions. So, the reactions of these excited states must be included in the ionospheric models. Absolute cross section measurements of the reactivity of stable doubly charged molec- ular ions CO++ and their implications for the Martian ionosphere will also be pre- 2 sented. The molecular dication CO++ production by VUV photoionisation and elec- 2 tron impact in the upper ionosphere of Mars is far from being negligible. However, to determine its concentration, it was necessary to evaluate the major loss channels of these ions. For this purpose, we measured the absolute reaction cross section of the sta- ble dications with CO2, the major neutral species of the Mars ionosphere. CO++ ions 2 were produced either by photoionisation or by electron impact, and a reaction cross section of 45 Å2 with 13CO2 was measured. The reaction leads to charge transfer or to collision induced dissociation. These results were integrated in a model predicting the existence of a CO++ dication layer in the Mars ionosphere. 2 Implications of all these measurements for the ionospheric models are studied in collaboration with O.Witasse (ESA-ESTEC, The Netherlands), J.Lilensten (LPG, France) and P.L.Blelly (CESR, France) who developed a new model for Mars. C. Nicolas, C. Alcaraz, J. Zabka, R. Thissen, and O. Dutuit (submitted to Planet. Space Sci. 2001)

Nicolas, C.; Zabka, J.; Thissen, R.; Dutuit, O.; Alcaraz, C.

138

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

NASA Astrophysics Data System (ADS)

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

Nina, A.; ?adež, V.; Šuli?, D.; Sre?kovi?, V.; Žigman, V.

2012-05-01

139

Space weather effects on the low latitude D-region ionosphere during solar minimum  

NASA Astrophysics Data System (ADS)

The effects of the solar flares and the geomagnetic storms (disturbance storm time ( Dst) < -50 nT) during December 2006 to 2008, a period during the unprecedented solar minimum of solar cycles 23 and 24, have been examined on sub-ionospheric very low frequency (VLF) signals from NWC (19.8 kHz), NPM (21.4 kHz), VTX (18.2 kHz), and NLK (24.8 kHz) transmitters monitored at Suva (18.2° S, 178.4° E), Fiji. Apart from the higher class solar flares (C to X), a solar flare of class B8.5 also produced enhancements both on the amplitude and phase. The amplitude enhancements in NLK, NPM, and NWC signals as a function of peak solar flare X-ray flux in decibel (dB; relative to 1 ?W/m2) shows that the relationship curve is steeper and quite linear between the flare power levels of 0 to 15 dB; below 0 dB, the curve gets less steep and flattens towards -5 dB flare power level, while it also gets less steep above 15 dB and almost flattens above 20 dB. In general, the level of amplitude enhancement for NLK signal is higher than that for NPM and NWC signals for all solar flares. The enhancement in the amplitude and phase of VLF signals by solar flares is due to the increase in the D-region electron density by the solar flare-produced extra ionization. The modeling of VLF perturbations produced by B8.5 and C1.5 classes of solar flares on 29 January 2007 using LWPC (Long Wave Propagation Capability) V2.1 codes show that reflection height ( H') was reduced by 0.6 and 1.2 km and the exponential sharpness factor ( ?) was raised by 0.010 and 0.005 km-1, respectively. Out of seven storms with Dst < -50 nT, only the intense storm of 14 to 16 December 2006 with a minimum Dst of -145 nT has shown a clear reduction in the signal strength of NWC and NPM sub-ionospheric signals due to storm-induced reduction in the D-region electron density.

Kumar, Abhikesh; Kumar, Sushil

2014-12-01

140

Radio Tomography of Ionospheric Structures (probably) due to Underground-Surface-Atmosphere-Ionosphere Coupling  

NASA Astrophysics Data System (ADS)

Ionospheric radio-tomography (RT) utilizes radio signals transmitted from the global navigational satellite systems (GNSS), including low-orbiting (LO) navigational systems such as Transit, Tsikada, etc., and high-orbiting (HO) navigational systems such as GPS, GLONASS, Galileo, Beidou, etc. The signals that are transmitted from the LO navigational satellites and recorded by ground receiving chains can be inverted for almost instantaneous (5-8 min) 2D snapshots of electron density. The data from the networks of ground receivers that record the signals of the HO satellites are suitable for implementing high-orbital RT (HORT), i.e. reconstructing the 4D distributions of the ionospheric electron density (one 3D image every 20-30 min). In the regions densely covered by the GNSS receivers, it is currently possible to get a time step of 2-4 min. The LORT and HORT approaches have a common methodical basis: in both these techniques, the integrals of electron density along the ray between the satellite and the receiver are measured, and then the tomographic procedures are applied to reconstruct the distributions of electron density. We present several examples of the experiments on the ionospheric RT, which are related to the Underground-Surface-Atmosphere-Ionosphere (USAI) coupling. In particular, we demonstrate examples of RT images of the ionosphere after industrial explosions, rocket launches, and modification of the ionosphere by high-power radio waves. We also show RT cross sections reflecting ionospheric disturbances caused by the earthquakes (EQ) and tsunami waves. In these cases, there is an evident cause-and-effect relationship. The perturbations are transferred between the geospheres predominantly by acoustic gravity waves (AGW), whose amplitudes increase with increasing height. As far as EQ are concerned, the cause of the USAI coupling mechanism is not obvious. It is clear, however, that the regular RT studies can promote the solution of this challenging problem. The single-point measurements (by ionosondes or by isolated receivers) are not amenable to unambiguous interpretation; based on these data, it is impossible to distinguish the contribution of USAI coupling from the ionospheric effects induced by the "ordinary" impacts (the Sun, the solar wind, geomagnetic perturbations, galactic cosmic rays, etc.). In order to localize sources of the ionospheric disturbances, the geophysicist needs information on the spatial structure and dynamics of the ionospheric perturbations. This information (2D-4D RT images) is optimally provided by RT methods. We present examples of the ionospheric disturbances caused by EQs as well as the ionospheric precursors of these EQs in the form of specific ionospheric irregularities: AGW- and soliton-like wave disturbances, which we identified using RT methods. Based on the results of the RT studies in the Alaska and Taiwan regions, we have detected several dozen AGW-related precursors of EQs. These data allow us to attempt to locate the source of these perturbations. We discuss the possibilities and prospects of further research aimed at identifying and analyzing precursors of EQs and establishing the mechanisms of USAI coupling. We are grateful to Northwest Research Associates, Inc., and Dr. L.-C.Tsai for providing raw RT data for Alaska and Taiwan.

Kunitsyn, V.; Nesterov, I.; Andreeva, E.; Rekenthaler, D. A.

2012-12-01

141

Counterbalancing for Serial Order Carryover Effects in Experimental Condition Orders  

ERIC Educational Resources Information Center

Reactions of neural, psychological, and social systems are rarely, if ever, independent of previous inputs and states. The potential for serial order carryover effects from one condition to the next in a sequence of experimental trials makes counterbalancing of condition order an essential part of experimental design. Here, a method is proposed…

Brooks, Joseph L.

2012-01-01

142

Effects of ionospheric O{sup +} on the magnetopause boundary wave activity  

SciTech Connect

In this paper we use a multi-fluid magnetohydrodynamic (MHD) model to explore effects of ionospheric O{sup +} ions on the development of the Kelvin-Helmholtz (KH) instability at the flanks of the earth's magnetopause. The model used is the multi-fluid version of the Lyon-Fedder-Mobarry (LFM) global magnetospheric MHD simulation code. We set up a controlled numerical experiment whereby the solar wind speed is slowly increased resulting in building up the velocity shear across the magnetopause. As this happens, the KH waves at the magnetopause flanks increase their intensity. Along with the solar wind velocity ramp-up, we introduce O{sup +} fluid in the plasma sheet and watch its influence on the development of the KH instability. We find that the simulation with the O{sup +} ions present at the magnetopause shows a significantly weaker KH wave activity on both edges of the low-latitude boundary layer than the simulation without oxygen but identical otherwise.

Merkin, V. G. [Center for Space Physics, Boston University, MA (United States)

2011-01-04

143

Effects of the Large June 1975 Meteoroid Storm on Earth's Ionosphere.  

PubMed

The June 1975 meteoroid storm detected on the moon by the Apollo seismometers was the largest ever observed. Reexamination of radio data taken at that time showed that the storm also produced pronounced disturbances on Earth, which were recorded as unique phase anomalies on very low frequency (VLF) radio propagation paths in the low terrestrial ionosphere. Persistent effects were observed for the major storm period (20 to 30 June 1975), including reductions in the diurnal phase variation, advances in the nighttime and daytime phase levels, and reductions in the sunset phase delay rate. Large nighttime phase advances, lasting a few hours, were detected on some days at all VLF transmissions, and for the shorter propagation path they were comparable to solar Lyman alpha daytime ionization. Ion production rates attributable to the meteor storm were estimated to be about 0.6 to 3.0 ions per centimeter cubed per second at the E and D regions, respectively. The storm was a sporadic one with a radiant (that is, the point of apparent origin in the sky) located in the Southern Hemisphere, with a right ascension 1 to 2 hours larger than the sun's right ascension. PMID:17748704

Kaufmann, P; Kuntz, V L; Leme, N M; Piazza, L R; Boas, J W; Brecher, K; Crouchley, J

1989-11-10

144

The long-duration positive storm effects in the equatorial ionosphere over Jicamarca  

NASA Astrophysics Data System (ADS)

The long-duration positive storm (LPS) in the equatorial regions is relatively poorly understood. In this report, we conducted a statistical analysis of the LPS effects in the equatorial ionosphere over Jicamarca (12.0°S, 283.2°E) in 1998-2010. There are 250 geomagnetic storms (minimum Dst < -50 nT) in 1998-2010, but the ionosonde observations at Jicamarca are available only for 204 storms. A total of 46 LPSs are identified in terms of the criterion that the storm time relative deviation of peak density of F2 layer (NmF2) exceeds 25% for more than 6 h. A salient feature is that the occurrence of LPSs tends to decay approximately exponentially on the following days after the main phase of geomagnetic storms. The ratios of the number of equatorial LPSs to that of geomagnetic storms have no obvious dependence on season and solar activity. During the daytime LPSs, the disturbed zonal electric field is mostly westward, as indicated from the geomagnetic field changes in the equatorial American region. For the nighttime LPSs, the significant uplifting of F2 layer caused by an eastward electric field is the most important feature. Therefore, the disturbed electric field should play an essential role in forming the equatorial LPSs.

Kuai, Jiawei; Liu, Libo; Liu, Jing; Zhao, Biqiang; Chen, Yiding; Le, Huijun; Wan, Weixing

2015-02-01

145

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

NASA Astrophysics Data System (ADS)

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

Rozhnoi, A.; Solovieva, M.; Levin, B.; Hayakawa, M.; Fedun, V.

2014-04-01

146

Three-dimensional Martian ionosphere model: II. Effect of transport processes due to pressure gradients  

NASA Astrophysics Data System (ADS)

To study the transport of the ionospheric plasma on Mars, we have included a 3-D multifluid dynamical core in a Martian general circulation model. Vertical transport modifies the ion density above ~160 km on the dayside, especially the ions produced at high altitudes like O+, N+, and C+. Near the exobase, the dayside to nightside flow velocity reaches few hundreds of m/s, due to a large horizontal pressure gradient. Comparison with Mars Express/Analyzer of Space Plasmas and Energetic Atoms-3 measurements between 290 and 500 km suggests that this flow could account for at least 20% of the flow produced by the solar wind. This flow is not sufficient to populate substantially the nightside ionosphere at high altitudes, in agreement with recent observations, because of a strong nightside downward flow produced by vertical pressure gradient. The O2+ and NO+ ion densities on the nightside at low altitudes (~130 km) are modified by this downward flow, compared to simulated densities without ion dynamics, while other ions are lost by chemical reactions. Variability at different time scales (diurnal, seasonal, and solar cycles) are studied. We simulate diurnal and seasonal variations of the ionospheric composition due to the variability of the neutral atmosphere and solar flux at the top of the atmosphere. The ionospheric dynamics are not strongly affected by seasons and solar cycles, and the retroaction of the ionosphere on the neutral atmosphere temperature and velocity is negligible compared to other physical processes below the exobase.

Chaufray, J.-Y.; Gonzalez-Galindo, F.; Forget, F.; Lopez-Valverde, M.; Leblanc, F.; Modolo, R.; Hess, S.; Yagi, M.; Blelly, P.-L.; Witasse, O.

2014-07-01

147

Hf propagation through actively modified ionospheres  

SciTech Connect

We have developed a computer modeling capability to predict the effect of localized electron density perturbations created by chemical releases or high-power radio frequency heating upon oblique, one-hop hf propagation paths. We have included 3-d deterministic descriptions of the depleted or enhanced ionization, including formation, evolution, and drift. We have developed a homing ray trace code to calculate the path of energy propagation through the modified ionosphere in order to predict multipath effects. We also consider the effect of random index of refraction variations using a formalism to calculate the mutual coherence functions for spatial and frequency separations based upon a path integral solution of the parabolic wave equation for a single refracted path through an ionosphere which contains random electron density fluctuations. 5 refs., 8 figs.

Argo, P.E.; Fitzgerald, T.J.; Wolcott, J.H.; Simons, D.J. (Los Alamos National Lab., NM (USA)); Warshaw, S.; Carlson, R. (Lawrence Livermore National Lab., CA (USA))

1990-01-01

148

Ordered delinquency: the "effects" of birth order on delinquency.  

PubMed

Juvenile delinquency has long been associated with birth order in popular culture. While images of the middle child acting out for attention or the rebellious youngest child readily spring to mind, little research has attempted to explain why. Drawing from Adlerian birth order theory and Sulloway's born-to-rebel hypothesis, I examine the relationship between birth order and a variety of delinquent outcomes during adolescence. Following some recent research on birth order and intelligence, I use new methods that allow for the examination of between-individual and within-family differences to better address the potential spurious relationship. My findings suggest that contrary to popular belief, the relationship between birth order and delinquency is spurious. Specifically, I find that birth order effects on delinquency are spurious and largely products of the analytic methods used in previous tests of the relationship. The implications of this finding are discussed. PMID:23719623

Cundiff, Patrick R

2013-08-01

149

Ordered Delinquency: The “Effects” of Birth Order On Delinquency  

PubMed Central

Juvenile delinquency has long been associated with birth order in popular culture. While images of the middle child acting out for attention or the rebellious youngest child readily spring to mind, little research has attempted to explain why. Drawing from Adlerian birth order theory and Sulloway's born to rebel hypothesis I examine the relationship between birth order and a variety of delinquent outcomes during adolescence. Following some recent research on birth order and intelligence, I use new methods that allow for the examination of both between-individual and within-family differences to better address the potential spurious relationship. My findings suggest that contrary to popular belief the relationship between birth order and delinquency is spurious. Specifically, I find that birth order effects on delinquency are spurious and largely products of the analytic methods used in previous tests of the relationship. The implications of this finding are discussed. PMID:23719623

Cundiff, Patrick R.

2014-01-01

150

The Effects of Neutral Inertia on Ionospheric Currents in the High-Latitude Thermosphere Following a Geomagnetic Storm  

NASA Technical Reports Server (NTRS)

Results of an experimental and theoretical investigation into the effects of the time dependent neutral wind flywheel on high-latitude ionospheric electrodynamics are presented. The results extend our previous work which used the National Center for Atmospheric Research Thermosphere/Ionosphere General Circulation Model (NCAR TIGCM) to theoretically simulate flywheel effects in the aftermath of a geomagnetic storm. The previous results indicated that the neutral circulation, set up by ion-neutral momentum coupling in the main phase of a geomagnetic storm, is maintained for several hours after the main phase has ended and may dominate height-integrated Hall currents and field-aligned currents for up to 4-5 hours. We extend the work of Deng et al. to include comparisons between the calculated time-dependent ionospheric Hall current system in the storm-time recovery period and that measured by instruments on board the Dynamics Explorer 2 (DE 2) satellite. Also, comparisons are made between calculated field-aligned currents and those derived from DE 2 magnetometer measurements. These calculations also allow us to calculate the power transfer rate (sometimes called the Poynting flux) between the magnetosphere and ionosphere. The following conclusions have been drawn: (1) Neutral winds can contribute significantly to the horizontal ionospheric current system in the period immediately following the main phase of a geomagnetic storm, especially over the magnetic polar cap and in regions of ion drift shear. (2) Neutral winds drive Hall currents that flow in the opposite direction to those driven by ion drifts. (3) The overall morphology of the calculated field-aligned current system agrees with previously published observations for the interplanetary magnetic field (IMF) B(sub Z) southward conditions, although the region I and region 2 currents are smeared by the TI(ICM model grid resolution. (4) Neutral winds can make significant contributions to the field-aligned current system when B(sub Z) northward conditions prevail following the main phase of a storm, but can account for only a fraction of the observed currents. (5) DE 2 measurements provide a demonstration of "local" (satellite-altitude) flywheel effects. (6) On the assumption that the magnetosphere acts as an insulator, we calculate neutral-wind-induced polarization electric fields of approx. 20-30 kV in the period immediately following the geomagnetic storm.

Deng, W.; Killeen, T. L.; Burns, A. G.; Roble, R. G.; Slavin, J. A.; Wharton, L. E.

1993-01-01

151

Tsunami Ionospheric warning and Ionospheric seismology  

NASA Astrophysics Data System (ADS)

The last decade demonstrated that seismic waves and tsunamis are coupled to the ionosphere. Observations of Total Electron Content (TEC) and airglow perturbations of unique quality and amplitude were made during the Tohoku, 2011 giant Japan quake, and observations of much lower tsunamis down to a few cm in sea uplift are now routinely done, including for the Kuril 2006, Samoa 2009, Chili 2010, Haida Gwai 2012 tsunamis. This new branch of seismology is now mature enough to tackle the new challenge associated to the inversion of these data, with either the goal to provide from these data maps or profile of the earth surface vertical displacement (and therefore crucial information for tsunami warning system) or inversion, with ground and ionospheric data set, of the various parameters (atmospheric sound speed, viscosity, collision frequencies) controlling the coupling between the surface, lower atmosphere and the ionosphere. We first present the state of the art in the modeling of the tsunami-atmospheric coupling, including in terms of slight perturbation in the tsunami phase and group velocity and dependance of the coupling strength with local time, ocean depth and season. We then show the confrontation of modelled signals with observations. For tsunami, this is made with the different type of measurement having proven ionospheric tsunami detection over the last 5 years (ground and space GPS, Airglow), while we focus on GPS and GOCE observation for seismic waves. These observation systems allowed to track the propagation of the signal from the ground (with GPS and seismometers) to the neutral atmosphere (with infrasound sensors and GOCE drag measurement) to the ionosphere (with GPS TEC and airglow among other ionospheric sounding techniques). Modelling with different techniques (normal modes, spectral element methods, finite differences) are used and shown. While the fits of the waveform are generally very good, we analyse the differences and draw direction of future studies and improvements, enabling the integration of lateral variations of the solid earth, bathymetry or atmosphere, finite model sources, non-linearity of the waves and better attenuation and coupling processes. All these effects are revealed by phase or amplitude discrepancies in selected observations. We then present goals and first results of source inversions, with a focus on estimations of the sea level uplift location and amplitude, either by using GPS networks close from the epicentre or, for tsunamis, GPS of the Hawaii Islands.

Lognonne, Philippe; Rolland, Lucie; Rakoto, Virgile; Coisson, Pierdavide; Occhipinti, Giovanni; Larmat, Carene; Walwer, Damien; Astafyeva, Elvira; Hebert, Helene; Okal, Emile; Makela, Jonathan

2014-05-01

152

Initial results from the operation of two argon ion generators in the auroral ionosphere  

NASA Technical Reports Server (NTRS)

Two argon ion generators have been lofted by sounding rockets in order to investigate ion beam dynamics and beam effects on the ionosphere, and auroral electrodynamics during rocket passage over auroral arcs. The ion generators were on a subpayload that was separated from the main payload early in the flight. The main payload conducted the diagnostic measurements during ion beam operations. Evidence of heating of the ionosphere around the subpayload during each ion beam emission is noted.

Erlandson, R. E.; Cahill, L. J., Jr.; Pollock, C. J.; Arnoldy, R. L.; Scales, W. A.

1987-01-01

153

GNSS station characterisation for ionospheric scintillation applications  

NASA Astrophysics Data System (ADS)

Ionospheric scintillations are fluctuations in the phase and amplitude of the signals from GNSS (Global Navigation Satellite Systems) occurring when they cross regions of electron density irregularities in the ionosphere. Such disturbances can cause serious degradation of several aspects of GNSS system performance, including integrity, accuracy and availability. The two indices adopted worldwide to characterise ionospheric scintillations are: the amplitude scintillation index, S4, which is the standard deviation of the received power normalised by its mean value, and the phase scintillation index, ??, which is the standard deviation of the de-trended carrier phase. Collaborative work between NGI and INGV supports a permanent network of GISTM (GPS Ionospheric Scintillation and TEC Monitor) receivers that covers a wide range of latitudes in the northern European sector. Data from this network has contributed significantly to several papers during the past few years (see e.g. De Franceschi et al., 2008; Aquino et al., 2009; Spogli et al., 2009, 2010; Alfonsi et al., 2011). In these investigations multipath effects and noise that contaminate the scintillation measurements are largely filtered by applying an elevation angle threshold. A deeper analysis of the data quality and the development of a more complex filtering technique can improve the results obtained so far. The structures in the environment of each receiver in the network which contaminate scintillation measurements should be identified in order to improve the quality of the scintillation and TEC data by removing error sources due to the local environment. The analysis in this paper considers a data set characterised by quiet ionospheric conditions of the mid-latitude station located in Nottingham (UK), followed by a case study of the severe geomagnetic storm, which occurred in late 2003, known generally as the "Halloween Storm".

Romano, Vincenzo; Spogli, Luca; Aquino, Marcio; Dodson, Alan; Hancock, Craig; Forte, Biagio

2013-10-01

154

Solar Cycle Effects on Equatorial Electrojet Strength and Low Latitude Ionospheric Variability (P10)  

NASA Astrophysics Data System (ADS)

veena_iig@yahoo.co.in The most obvious indicators of the activity of a solar cycle are sunspots, flares, plages, and soon. These are intimately linked to the solar magnetic fields, heliospheric processes which exhibit complex but systematic variations. The changes in geomagnetic activity, as observed in the ground magnetic records follow systematic correspondence with the solar activity conditions. Thus the transient variations in the magnetic field get modified by differing solar conditions. Also the solar cycle influences the Earth causing changes in geomagnetic activity, the magnetosphere and the ionosphere. Daily variations in the ground magnetic field are produced by different current systems in the earth’s space environment flowing in the ionosphere and magnetosphere which has a strong dependence on latitude and longitude of the location. The north-south (Horizontal) configuration of the earth’s magnetic field over the equator is responsible for the narrow band of current system over the equatorial latitudes and is called the Equatorial electrojet (EEJ) and is a primary driver for Equatorial Ionization anomaly (EIA). Equatorial electric fields and plasma drifts play the fundamental roles on the morphology of the low latitude ionosphere and strongly vary during geomagnetically quiet and disturbed periods. Quantitative study is done to illustrate the development process of EEJ and its influence on ionospheric parameters. An attempt is also made to examine and discuss the response of the equatorial electrojet parameters to the fast varying conditions of solar wind and interplanetary parameters.

Veenadhari, B.; Alex, S.

2006-11-01

155

Sources of uncertainty in ionospheric modeling: The neutral wind  

NASA Astrophysics Data System (ADS)

The neutral wind is a critical input parameter for physics-based ionospheric models, affecting both the height of the F layer and the total electron content. Unfortunately, the currently available models of the thermospheric wind do not seem to represent it very accurately, and this places a serious limitation on the effectiveness of ionospheric modeling and forecasting. We make use of several decades' worth of midlatitude ionosonde observations of the F region peak, in order to compare the effectiveness of several neutral wind models when used as drivers for an ionospheric model. We check the simulation results against the ground truth of the ionosonde observations using the technique of forecast skill scores. We find that with the ionospheric model in use here (the Utah State University Time Dependent Ionospheric Model (TDIM)), a very simple neutral wind pattern outperforms the more complex models. Increases in skill scores as high as 50% are obtained, relative to the reference case of zero wind; also, in some cases, there are similarly large decreases in skill scores. We view this as a sensitivity study, rather than an effort to identify the best wind model in an absolute sense, because any ionospheric model is an assemblage of algorithms, boundary conditions, and drivers that are themselves imperfect. We identify reasons for the large variability in skill scores with respect to season, longitude, and solar cycle level. We close with a brief discussion of other parameters in ionospheric modeling that are similarly uncertain, e.g., a downward electron flux and the Burnside factor.

David, Michael; Sojka, Jan J.; Schunk, Robert W.

2014-08-01

156

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

NASA Astrophysics Data System (ADS)

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

Rozhnoi, A.; Solovieva, M.; Levin, B.; Hayakawa, M.; Fedun, V.

2014-10-01

157

Magnetic Field Measurement on the C/NOFS Satellite: Geomagnetic Storm Effects in the Low Latitude Ionosphere  

NASA Technical Reports Server (NTRS)

The Vector Electric Field Investigation (VEFI) suite onboard the Communications/Navigation Outage Forecasting System (C/NOFS) spacecraft includes a sensitive fluxgate magnetometer to measure DC and ULF magnetic fields in the low latitude ionosphere. The instrument includes a DC vector measurement at 1 sample/sec with a range of +/- 45,000 nT whose primary objective is to provide direct measurements of both V x B and E x B that are more accurate than those obtained using a simple magnetic field model. These data can also be used for scientific research to provide information of large-scale ionospheric and magnetospheric current systems, which, when analyzed in conjunction with the C/NOFS DC electric field measurements, promise to advance our understanding of the electrodynamics of the low latitude ionosphere. In this study, we use the magnetic field data to study the temporal and local time variations of the ring currents during geomagnetic storms. We first compare the in situ measurements with the POMME (the POtsdam Magnetic Model of the Earth) model in order to provide an in-flight "calibration" of the data as well as compute magnetic field residuals essential for revealing large scale external current systems. We then compare the magnetic field residuals observed both during quiet times and during geomagnetic storms at the same geographic locations to deduce the magnetic field signatures of the ring current. As will be shown, the low inclination of the C/NOFS satellite provides a unique opportunity to study the evolution of the ring current as a function of local time, which is particularly insightful during periods of magnetic storms. This paper will present the initial results of this study.

Le, Guan; Pfaff, Rob; Kepko, Larry; Rowland, Doug; Bromund, Ken; Freudenreich, Henry; Martin, Steve; Liebrecht, C.; Maus, S.

2010-01-01

158

AM Radio Ionosphere Station: Teacher's Guide  

NSDL National Science Digital Library

In this activity students will monitor the ionosphere by using an amplitude modulated (AM) radio to track solar storms and other changes in ionosphere reflectivity. They will discover that above the earth's surface a layer of charged particles called the ionosphere is capable of reflecting radio waves and that the reflectivity properties of the ionosphere can be changed dramatically by solar activity. In order to detect and study some of these changes, students will use the radio to listen for changes in background noise and the appearance of distant stations, learning that a simple everyday device can let them detect invisible changes in their environment caused by solar activity.

159

Ionospheric specification from GPS data and the RIBG ionospheric propagation model  

NASA Astrophysics Data System (ADS)

Global Positioning System (GPS) data for phase delay differential between Ll and L2 frequencies are analyzed by a model in which the combined effect of hardware and phase ambiguity terms is represented by a constant for each receiver-satellite path and the ionospheric contribution is represented by the RIBG model (ray trace through the combined ICED (ionospheric conductivity and electron density), Bent, and Gallagher ionospheric models). RIBG contains a detailed global empirical climatological ionospheric model of the electron density versus height profile (EDP) from 80 km up to the plasmapause, which is combined with a full three-dimensional ray trace propagation model. Discrete inverse theory (DIT) is used to fit the driving parameters of RIBG to about 2 hours worth of data from a single GPS receiver at various geographical locations. Validity is demonstrated by the ability of the GPS-updated RIBG model to predict independent measurements of (1) vertical total electron content (TEC) over the ocean out to substantial distances from a GPS receiver, often in excess of 2000 km at midlatitudes, and (2) the electron density versus height profile (EDP). Performance variation with magnetic latitude is noted. Flexibility in RIBG to adjust different driving parameters for different parts of the EDP, in order to obtain a best fit of GPS data, benefits the EDP prediction. Implications of this approach for GPS navigation and other radio system applications are discussed.

Reilly, Michael H.; Singh, Malkiat

1997-07-01

160

Ionospheric scintillation monitoring and mitigation using a software GPS receiver  

NASA Astrophysics Data System (ADS)

Scintillations are caused by ionospheric irregularities and affect the amplitude, phase, dispersion, and related parameters of GPS signals. Both L1 and L2 are affected in a somewhat uncorrelated fashion. Adequate understanding of the effects that ionospheric scintillation has on GPS signals is essential in order to produce a GPS receiver that is immune to the degradation of signal caused by these scintillation-related effects. Access to the internal workings of commercial GPS receivers is not provided to users. However, in order to understand, control, and mitigate scintillation effects, it is necessary to have access to tracking loops and associated components such as local oscillator. The software GPS receiver developed by the Center for Remote Sensing, Inc. allows the user to access its internal workings; hence facilitating advanced development of GPS receivers under different conditions. In this paper we present the results of analysis of GPS signals under scintillating conditions. Raw signals under conditions of ionospheric scintillation at Ascension Island have been processed using our software GPS receiver in order to derive the scintillation parameters. The receiver has been configured to provide stable operation during scintillation. We describe the receiver architecture, particularly the portion involving the tracking filters and related components, and demonstrate their performances under scintillating conditions. The software-based approach used by us allows receiver implementations which are suitable for ionospheric monitoring as well as for reliable operation during scintillating conditions. The improved architecture may be used for several other applications.

Ganguly, Suman; Jovancevic, Aleksandar; Brown, Andrew; Kirchner, Michael; Zigic, Slavisa; Beach, Theodore; Groves, Keith M.

2004-02-01

161

The Effects of Magnetic Anomalies Discovered at Mars on the Structure of the Martian Ionosphere and the Solar Wind Interaction as Follows from Radio Occultation Experiments  

NASA Technical Reports Server (NTRS)

The electron density distribution in the ionosphere of nonmagnetic (or weakly magnetized) planet depends not only on the solar ultraviolet intensity, but also on the nature of the SW interaction with this planet. Two scenarios previously have been developed based on the observations of the bow shock crossings and on the electron density distribution within the ionosphere. According to one of them Mars has an intrinsic magnetosphere produced by a dipole magnetic field and the Martian ionosphere is protected from the SW flow except during "overpressure conditions, when the planetary magnetic field can not balance the SW dynamic pressure. In the second scenario the Martian intrinsic magnetic dipole field is so weak that Mars has mainly an induced magnetosphere and a Venus-like SW/ionosphere interaction. Today the possible existence of a sufficiently strong global magnetic field that participates in the SW/Mars interaction can no longer be supported. The results obtained by the Mars-Global-Surveyor (MGS) space-craft show the existence of highly variable, but also very localized magnetic fields of crustal origin at Mars as high as 400-1500 nT. The absence of the large-scale global magnetic field at Mars makes it similar to Venus, except for possible effects of the magnetic anomalies associated with the remnant crustal magnetization. However the previous results on the Martian ionosphere obtained mainly by the radio occultation methods show that there appears to be a permanent existence of a global horizontal magnetic field in the Martian ionosphere. Moreover the global induced magnetic field in the Venus ionosphere is not typical at the solar zenith angles explored by the radio occultation methods. Additional information is contained in the original extended abstract.

Ness, N. F.; Acuna, M. H.; Connerney, J. E. P.; Cloutier, P.; Kliore, A. J.; Breus, T. K.; Krymskii, A. M.; Bauer, S. J.

1999-01-01

162

Development of an ionosphere-atmosphere coupled model for space weather forecast  

NASA Astrophysics Data System (ADS)

The solar-terrestrial system consists of the solar atmosphere, the solar wind, the magneto-sphere, the ionosphere, and the neutral atmosphere. Those regions have different physical characteristics with different temporal and spatial scales. In particular, the magnetosphere, the ionosphere, and the neutral atmosphere are strongly coupled with each other, and inter-action between the regions is nonlinear and extremely complicated. Even within each region, there are strong interactions between different physical processes. Furthermore, the geospace environment significantly varies as electromagnetic energy and particles from the sun vary. In order to quantitatively understand such a complicated system, it is necessary to model the entire region by including all fundamental processes self-consistently. Various types of global numerical models of the geospace have been constructed by many institutions in the world, and used to study and predict geospace disturbances. At the National Institute of Information and Communications Technology (NICT), real-time solar wind, magnetosphere, and ionosphere-thermosphere models have been developed and used for daily space weather forecast. However, recent observations of the ionosphere and the thermosphere have revealed that atmospheric waves generated in the lower atmosphere significantly influence the upper atmosphere, the ionosphere, and possibly the magnetosphere. In order to quantitatively study the effects of the lower atmosphere on the ionosphere, we have developed an ionosphere-atmosphere coupled model, which includes the whole neutral atmosphere and the ionosphere. It is planned that the model is coupled with our magnetosphere and solar MHD models, which will be used for space weather forecast. We will report the status and future plan of our ionosphere-atmosphere coupled modeling.

Shinagawa, Hiroyuki; Jin, Hidekatsu; Miyoshi, Yasunobu; Fujiwara, Hitoshi; Fujita, Shigeru; Tanaka, Takashi; Terada, Naoki; Terada, Kaori

163

Numerical Simulations Of The Effect Of Localised Ionospheric Perturbations On Subionospheric VLF Propagation  

E-print Network

Electron density and temperature changes in the D-region of the ionosphere are sensitively manifested as changes in the amplitude and phase of subionospheric Very Low Frequency (VLF) signals propagating beneath the perturbed region. Disturbances (either in electron density or temperature) in the D region cause significant scattering of VLF waves propagating in the earth-ionosphere waveguide, leading to measurable changes in the amplitude and phase of the VLF waves. We analyze Lightning-induced electron precipitation (LEP) events during period 2008 - 2009 at Belgrade station on subionospheric VLF signals from four transmitters (DHO/23.4 kHz, Germany; GQD/22.1 kHz, UK; NAA/24.0 kHz USA and ICV/20.9 kHz Italy).

Sulic, D; Sreckovic, V

2014-01-01

164

Numerical Simulations Of The Effect Of Localised Ionospheric Perturbations On Subionospheric VLF Propagation  

NASA Astrophysics Data System (ADS)

Electron density and temperature changes in the D-region of the ionosphere are sensitively manifested as changes in the amplitude and phase of subionospheric Very Low Frequency (VLF) signals propagating beneath the perturbed region. Disturbances (either in electron density or temperature) in the D region cause significant scattering of VLF waves propagating in the earth-ionosphere waveguide, leading to measurable changes in the amplitude and phase of the VLF waves. We analyze Lightning-induced electron precipitation (LEP) events during period 2008 - 2009 at Belgrade station on subionospheric VLF signals from four transmitters (DHO/23.4 kHz, Germany; GQD/22.1 kHz, UK; NAA/24.0 kHz USA and ICV/20.9 kHz Italy).

Šulic, D.; Nina, A.; Sreckovic, V.

2010-07-01

165

Ionospheric effects associated with changes in the levels of geomagnetic and solar activities  

NASA Astrophysics Data System (ADS)

The characteristics of the changes in the dynamics of the lower atmosphere processes over Central Asia, associated with processes taking place in the ionosphere and magnetosphere were investigated using data collected during SUNDIAL observation periods March 16-20 and December 5-10, 1988. Results showed that the wind velocity reversals observed at heights between 80 and 100 km were associated with changing levels of geomagnetic and solar activity. Analyses of data collected in the lower atmosphere and the ionosphere during these periods showed the presence of an anomaly in the dynamics of the electron concentration in the F layer after the October 1988 event, characterized by a disturbance of the 27-30-day variation.

Karimov, K. A.; Gainutdinova, R. D.

1993-02-01

166

Exploring the Cigala/calibra Network Data Base for Ionosphere Monitoring Over Brazil  

NASA Astrophysics Data System (ADS)

The ionosphere in Brazil is strongly influenced by the equatorial anomaly, therefore GNSS based applications are widely affected by ionospheric disturbances. A network for continuous monitoring of the ionosphere has been deployed over its territory since February/2011, as part of the CIGALA and CALIBRA projects. Through CIGALA (Concept for Ionospheric Scintillation Mitigation for Professional GNSS in Latin America), which was funded by European Commission (EC) in the framework of the FP7-GALILEO-2009-GSA (European GNSS Agency), the first stations were deployed at Presidente Prudente, São Paulo state, in February 2011. CIGALA was finalized in February 2012 with eight stations distributed over the Brazilian territory. Through CALIBRA (Countering GNSS high Accuracy applications Limitations due to Ionospheric disturbances in BRAzil), which is also funded by the European Commission now in the framework of the FP7-GALILEO-2011-GSA, new stations are being deployed. Some of the stations are being specifically placed according to geomagnetic considerations aiming to support the development of a local scintillation and TEC model. CALIBRA started in November 2012 and will have two years of duration, focusing on the development of improved and new algorithms that can be applied to high accuracy GNSS techniques in order to tackle the effects of ionospheric disturbances. PolarRxS-PRO receivers, manufactured by Septentrio, have been deployed at all stations This multi-GNSS receiver can collect data at rates of up to 100 Hz, providing ionospheric TEC, scintillation parameters like S4 and Sigma-Phi, and other signal metrics like locktime for all satellites and frequencies tracked. All collected data (raw and ionosphere monitoring records) is stored at a central facility located at the Faculdade de Ciências e Tecnologia da Universidade Estadual Paulista (FCT/UNESP) in Presidente Prudente. To deal with the large amount of data, an analysis infrastructure has also been established in the form of a web based software named ISMR Query Tool, which provides a capability to identify specific behaviors of ionospheric activity through data visualization and data mining. Its web availability and user-specified features allow the users to interact with the data through a simple internet connection, enabling to obtain insight about the ionosphere according with their own previous knowledge. Information about the network, the projects and the tool can be found at the FCT/UNESP Ionosphere web portal available at http://is-cigala-calibra.fct.unesp.br/. This contribution will provide an overview of results extracted using the monitoring and analysis infrastructure, explaining the possibilities offered by the ISMR Query Tool to support analysis of the ionosphere as well as the development of models and mitigation techniques to counter the effects of ionospheric disturbances on GNSS.

Vani, B. C.; Galera Monico, J. F.; Shimabukuro, M. H.; Pereira, V. A.; Aquino, M. H.

2013-12-01

167

Ionospheric Effects Caused by 40.75 kHz Whistler-mode Waves over Arecibo  

Microsoft Academic Search

We report Arecibo experiments to investigate interactions of 40.75 kHz whistler-mode emissions with ionospheric plasmas, and the subsequent whistler wave-electron interactions in radiation belts. These whistler-modes originate from the Naval transmitter (NAU) in Puerto Rico, emitting radio waves at a power of 100 kW. Based on our theoretical analyses, we show that NAU emissions are intense enough to excite lower

R. Pradipta; A. Labno; J. A. Cohen; L. M. Burton; M. C. Lee; W. J. Burke; M. P. Sulzer; S. P. Kuo

168

Ionospheric trends in mid-latitudes as a possible indicator of the atmospheric greenhouse effect  

Microsoft Academic Search

Using long-term ionosonde measurements in mid-latitudes (Juliusruh: 54.6 deg N, 13.4 deg E; 1957-1990), the first experimental hints of a decrease of the peak height of the ionospheric F2-layer were found. In contrast to that, the long-term variations of the peak electron densities in the F2-layer, as well as the E-layer, are small. These results qualitatively agree with the predictions

J. Bremer

1992-01-01

169

A laboratory experiment to examine the effect of auroral beams on spacecraft charging in the ionosphere  

Microsoft Academic Search

A 2.54 cm diameter conducting electrically isolated Copper sphere is suspended in a low density (104 cm-3), low temperature (Te = 0.5 eV) Argon plasma, which mimics a spacecraft in an ionospheric plasma. An electron beam with current density of approximately 10-10 A\\/cm2 and beam spot of 10.2 cm diameter, which mimics an auroral electron beam, is fired at the

M. U. Siddiqui; L. E. Gayetsky; M. R. Mella; K. A. Lynch; M. R. Lessard

2011-01-01

170

A laboratory experiment to examine the effect of auroral beams on spacecraft charging in the ionosphere  

Microsoft Academic Search

A 2.54 cm diameter conducting electrically isolated Copper sphere is suspended in a low density (104 cm?3), low temperature (Te = 0.5 eV) Argon plasma, which mimics a spacecraft in an ionospheric plasma. An electron beam with current density of approximately 10?10 A?cm2 and beam spot of 10.2 cm diameter, which mimics an auroral electron beam, is fired at the

M. U. Siddiqui; L. E. Gayetsky; M. R. Mella; K. A. Lynch; M. R. Lessard

2011-01-01

171

Vibrationally excited nitrogen in stable auroral red arcs and its effect on ionospheric recombination  

NASA Technical Reports Server (NTRS)

The time-dependent continuity equations, including diffusion, were solved for the first six energy levels of molecular nitrogen for conditions in the thermosphere corresponding to stable auroral red (SAR) arcs. The results show that molecular nitrogen is excited vibrationally to the degree that the rate constant for the ionospheric loss process, O(+) + N2 yields NO(+) + N, is increased by as much as a factor of 7.6 at F2 region altitudes. It was found that deviations from the energetically equivalent Boltzmann distribution were large, causing the rate constant to be as much as 1.6 times the rate constant calculated for the Boltzmann distribution. These results indicate that SAR arc intensities as small as 58 R can produce noticeable increases in the ionosphere ion-atom interchange reaction rate and hence in the rate of loss of ionospheric electrons. It is suggested that the observed decrease of electron density in the F2 region in SAR arcs can probably be explained by enhanced reaction rates for ion-atom interchange between O(+) and N2 caused by vibrational excitation of molecular nitrogen by electron impact.

Newton, G. P.; Walker, J. C. G.; Meijer, P. H. E.

1974-01-01

172

Modeling the effect of sudden stratospheric warming within the thermosphere-ionosphere system  

NASA Astrophysics Data System (ADS)

This paper presents an investigation of thermospheric and ionospheric response to the sudden stratospheric warming (SSW) event, which took place in January 2009. This period was characterized by low solar and geomagnetic activity. Analysis was carried out within the Global Self-consistent Model of Thermosphere, Ionosphere and Protonosphere (GSM TIP). The experimental data of the atmospheric temperatures obtained by Aura satellite above Irkutsk and ionosonde data over Yakutsk and Irkutsk were utilized as well. SSW event was modeled by specifying the temperature and density perturbations at the lower boundary of the GSM TIP model (80 km altitude). It was shown that by setting disturbances in the form of a stationary planetary perturbation s=1 at the lower boundary of the thermosphere, one could reproduce the negative electron density disturbances in the F region of ionosphere during SSW events. Our scenario for the 2009 SSW event in the GSM TIP allowed to obtain results which are in a qualitative agreement with the observation data.

Bessarab, F. S.; Korenkov, Yu. N.; Klimenko, M. V.; Klimenko, V. V.; Karpov, I. V.; Ratovsky, K. G.; Chernigovskaya, M. A.

2012-12-01

173

Ray-based modeling of lightning-induced ionospheric effects on short range VLF skywave signals  

NASA Astrophysics Data System (ADS)

At locations close (~100-km) to a VLF transmitter, observation of the sky wave signal from the transmitter becomes possible by aligning a proximate magnetic loop antenna to null the ground signal. Previous observations using such an arrangement [e.g., Rodriguez et al. 1992], and [Pasko et al., 2002] show a very high degree of temporal variability in received signal amplitude. Observation of VLF signatures of Early/Fast and Lightning-induced Electron Precipitation (LEP) events under these constraints show an unusual number of remarkably large events, more than ten times larger than a typical long-distance path, and often exhibit non-exponential recovery, or no recovery at all. Because of the large spatial extent of LEP events compared to the sky wave path distances, at least portions of the disturbed region must necessarily be nearly overhead the receiver and/or transmitter and we can employ simple ray tracing techniques to determine the evolution of the scattered field from the ionospheric disturbance over time, taking into account path-length difference, absorption, ground, and ionospheric reflection coefficients and multiple hops. We present several examples of characteristic VLF perturbations observed on short paths, and interpret these in terms of a simple ray-path-based model of the VLF scattering from the lower ionosphere.

Cotts, B. R.; Inan, U. S.

2005-12-01

174

Interaction of Titan's ionosphere with Saturn's magnetosphere.  

PubMed

Titan is the only Moon in the Solar System with a significant permanent atmosphere. Within this nitrogen-methane atmosphere, an ionosphere forms. Titan has no significant magnetic dipole moment, and is usually located inside Saturn's magnetosphere. Atmospheric particles are ionized both by sunlight and by particles from Saturn's magnetosphere, mainly electrons, which reach the top of the atmosphere. So far, the Cassini spacecraft has made over 45 close flybys of Titan, allowing measurements in the ionosphere and the surrounding magnetosphere under different conditions. Here we review how Titan's ionosphere and Saturn's magnetosphere interact, using measurements from Cassini low-energy particle detectors. In particular, we discuss ionization processes and ionospheric photoelectrons, including their effect on ion escape from the ionosphere. We also discuss one of the unexpected discoveries in Titan's ionosphere, the existence of extremely heavy negative ions up to 10000amu at 950km altitude. PMID:19073464

Coates, Andrew J

2009-02-28

175

Time and Order Effects on Causal Learning  

ERIC Educational Resources Information Center

Five experiments were conducted to explore trial order and retention interval effects upon causal predictive judgments. Experiment 1 found that participants show a strong effect of trial order when a stimulus was sequentially paired with two different outcomes compared to a condition where both outcomes were presented intermixed. Experiment 2…

Alvarado, Angelica; Jara, Elvia; Vila, Javier; Rosas, Juan M.

2006-01-01

176

Ionospheric imaging in Africa  

NASA Astrophysics Data System (ADS)

ionospheric specification is necessary for improving human activities such as radar detection, navigation, and Earth observation. This is of particular importance in Africa, where strong plasma density gradients exist due to the equatorial ionization anomaly. In this paper the accuracy of three-dimensional ionospheric images is assessed over a 2 week test period (2-16 December 2012). These images are produced using differential Global Positioning System (GPS) slant total electron content observations and a time-dependent tomography algorithm. The test period is selected to coincide with a period of increased GPS data availability from the African Geodetic Reference Frame (AFREF) project. A simulation approach that includes the addition of realistic errors is employed in order to provide a ground truth. Results show that the inclusion of observations from the AFREF archive significantly reduces ionospheric specification errors across the African sector, especially in regions that are poorly served by the permanent network of GPS receivers. The permanent network could be improved by adding extra sites and by reducing the number of service outages that affect the existing sites.

Chartier, Alex T.; Kinrade, Joe; Mitchell, Cathryn N.; Rose, Julian A. R.; Jackson, David R.; Cilliers, Pierre; Habarulema, John-Bosco; Katamzi, Zama; Mckinnell, Lee-Anne; Matamba, Tshimangadzo; Opperman, Ben; Ssessanga, Nicholas; Giday, Nigussie Mezgebe; Tyalimpi, Vumile; Franceschi, Giorgiana De; Romano, Vincenzo; Scotto, Carlo; Notarpietro, Riccardo; Dovis, Fabio; Avenant, Eugene; Wonnacott, Richard; Oyeyemi, Elijah; Mahrous, Ayman; Tsidu, Gizaw Mengistu; Lekamisy, Harvey; Olwendo, Joseph Ouko; Sibanda, Patrick; Gogie, Tsegaye Kassa; Rabiu, Babatunde; Jong, Kees De; Adewale, Adekola

2014-01-01

177

The dynamics of the Venus ionosphere. II - The effects of the time scale of the solar wind dynamic pressure variations  

NASA Technical Reports Server (NTRS)

The effects on the upper dayside Venus ionosphere of a slow increase in solar wind dynamic pressure are simulated numerically with a one-dimensional (spherically symmetric) Lagrangian hydrodynamical code. The simulation is started with an extended ionosphere in pressure equilibrium with the solar wind at the ionopause. The pressure at the ionopause is gradually increased to five times the initial pressure with rise times of 5, 15, and 30 min. It is found that, for rise times greater than about 10 min, the compression of the ionopause is nearly adiabatic, with the ionopause moving downward at velocities of approximately 1-2 km/sec until it reaches a maximally compressed state, at which time the motion reverses. For short rise times the compression produces a shock wave similar to that occurring in the case of a sudden increase in pressure. The global implications of these processes are discussed within the context of Pioneer Venus observations and future theoretical work on this problem is outlined.

Stein, R. F.; Wolff, R. S.

1982-01-01

178

Roughness in Lattice Ordered Effect Algebras  

PubMed Central

Many authors have studied roughness on various algebraic systems. In this paper, we consider a lattice ordered effect algebra and discuss its roughness in this context. Moreover, we introduce the notions of the interior and the closure of a subset and give some of their properties in effect algebras. Finally, we use a Riesz ideal induced congruence and define a function e(a, b) in a lattice ordered effect algebra E and build a relationship between it and congruence classes. Then we study some properties about approximation of lattice ordered effect algebras. PMID:25170523

Xin, Xiao Long; Hua, Xiu Juan; Zhu, Xi

2014-01-01

179

Investigating the effects of ionospheric electric fields on the equatorial magnetosphere using thin filament simulations  

NASA Astrophysics Data System (ADS)

We adopt a model using a thin filament approximation developed in Chen and Wolf [1999] to simulate flux tube motion in the magnetotail. In this code, a flux tube is treated as a 1D string of mass elements immersed in a static background. Compared to 3D magneto-hydrodynamic (MHD) codes, this 1D code can be run with high accuracy and low numerical diffusion using a large number of grid points. This allows localized waves and oscillations to be resolved that would be difficult to reproduce with 3D MHD simulations. The static background is chosen to be a solution to the MHD force balance equation that emulates a magnetospheric environment. Preliminary results suggest that changes in the ionospheric electric field can produce a tailward propagating Alfven wave that rapidly gains amplitude. This disturbance can become large enough to trigger disruptions in the filament structure near the equator. One motivation for the study is the suggestion that sudden localized convection in the ionosphere is associated with substorm onset and the subsequent expansion phase [Kan and Sun, 1996]. A systematic study of this phenomenon will be presented. Chen, C. X., and R. A. Wolf (1999), Theory of thin filament motion in Earth's magnetotail and its application to bursty bulk flows, J. Geophys. Res., 104(A7), doi: 10.1029/1999JA900005. Kan, J. R., and W. Sun (1996), Substorm expansion phase caused by an intense localized convection imposed on the ionosphere, J. Geophys. Res., 101(A12), doi: 10.1029/96JA02426.

Schutza, A. M.; Toffoletto, F.; Wolf, R.

2013-12-01

180

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

SciTech Connect

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

Basak, Tamal; Pal, S. [S. N. Bose National Centre for Basic Sciences, JD Block, Salt-Lake, Kolkata-700098 (India); Chakrabarti, S. K. [S. N. Bose National Centre for Basic Sciences, JD Block, Salt-Lake, Kolkata-700098 (India); Indian Centre for Space Physics, 43 Chalantika, Garia Station Road, Kolkata-700084 (India)

2010-10-20

181

Magnetosphere-ionosphere-thermosphere coupling: Effect of neutral winds on energy transfer and field-aligned current  

Microsoft Academic Search

The assimilative mapping of ionospheric electrodynamics (AMIE) algorithm has been applied to derive the realistic time-dependent large-scale global distributions of the ionospheric convection and particle precipitation during a recent Geospace Environment Modeling (GEM) campaign period: March 28-29, 1992. The AMIE outputs are then used as the inputs of the National Center for Atmospheric Research thermosphere-ionosphere general circulation model to estimate

G. Lu; A.D. Richmond; B. A. Emery; R. G. Roble

1995-01-01

182

Geomagnetic and sunspot activity associations and ionospheric effects of lightning phenomena at Trivandrum near dip equator  

NASA Astrophysics Data System (ADS)

From a study of thunder/lightning observations in Trivandrum (near dip equator) for selected years between 1853 and 2005, we could find an inverse relation of the same with sunspot activity and associations with enhancements in diurnal range of local geomagnetic declination. The results seem to suggest lightning-associated modulation of E-region dynamo currents in the equatorial ionosphere and the thunderstorm activity near dip equator probably acts as a moderator to regulate electric potential gradient changes in the global electric circuit due to solar activity changes.

Girish, T. E.; Eapen, P. E.

2008-12-01

183

Effects of the large June 1975 meteoroid storm on earth's ionosphere  

NASA Astrophysics Data System (ADS)

The meteoroid storm of June, 1975 generated pronounced disturbances on the earth, recorded as unique phase anomalies on VLF radio-propagation paths in the low terrestrial ionosphere during the June 20-30 period. Large nocturnal phase-advances lasting several hours were detected on several days at all VLF transmissions; they are noted to have been comparable, for the shorter propagation path, to solar Ly-alpha diurnal ionization. The storm was sporadic, with an apparent origin in the sky over the Southern Hemisphere whose right ascension was 1-2 hours larger than that of the sun.

Kaufmann, P.; Kuntz, V. L. R.; Paes Leme, N. M.; Piazza, L. R.; Vilas Boas, J. W. S.

1989-11-01

184

Role of ionospheric conductance in magnetosphere-ionosphere coupling  

NASA Astrophysics Data System (ADS)

Magnetosphere-ionosphere (MI) coupling has been studied for a long time. However, not much work has been done on a systematic understanding of the relation between ionospheric Pedersen conductance, its effect on the evolution and modification of field-aligned currents (FACs), and the influence of conductance and FACs on the formation of parallel electric fields which cause particle precipitation. Though the roles of ionospheric conductance gradients for FACs and parallel electric field evolution are directly related, they are poorly understood. This dissertation advances the understanding of these areas and all results of this study are based on numerical simulations that employ a three-dimensional - two-fluid (ions and neutrals) simulation code. The first part of this dissertation presents a systematic study of the magnetospheric and ionospheric influences on the evolution and modification of FACs with focus on the role of ionospheric Pedersen conductance and its gradients. FACs are typically generated in the magnetosphere and are carried into the ionosphere by Alfven waves. During their reflection from the ionosphere these FACs are modified depending on the magnitude and distribution of ionospheric conductance. For conductance gradients along the polarization of the wave, strong Pedersen currents can be generated which in turn enhance the FAC as well. The second part of this dissertation addresses the properties and evolution of parallel electric fields in an attempt to better understand the formation of discrete auroral arcs in response to the evolution of FACs for predetermined ionospheric conductance patterns. Frequently, auroral acceleration is believed to occur through U or V shaped potentials. Therefore, this part examines the properties of localized parallel electric fields in a uniform magnetic field. It is demonstrated that localized parallel electric fields generate magnetic flux in the absence of source of free energy. It is also shown that parallel electric fields generated in a FAC in the presence of a (anomalous) resistivity represent a load and can provide physical explanation for the auroral acceleration geometry. The results demonstrate that such electric fields can be significantly enhanced by Alfven wave reflection where both magnitude and gradients of the ionospheric conductance are important. The strongly enhanced parallel electric field is associated with magnetic reconnection and modifies the FAC system such that thin current layers (with curls and folds) are observed to be embedded in the large scale current system.

Bhattacharya, Tapas

185

Effects of HF heater-produced ionospheric depletions on the ducting of VLF transmissions: A ray tracing study  

NASA Astrophysics Data System (ADS)

Comprehensive three-dimensional ray tracing studies suggest that local large-scale ionospheric density perturbations caused by the HF heater at Arecibo significantly affect the amount of power from upgoing 28.5 kHz VLF transmissions that couples into plasmaspheric ducts on nearby magnetic field lines. Large density depletions can perturb the ray paths of upgoing VLF to enhance or reduce the total power in a local duct. Under certain conditions, ducted power may be enhanced up to 13 dB or attenuated up to 18 dB. The dependence of this effect on the location and cross-L drift of plasmaspheric ducts and the depth of the heater-induced depletion may explain the difficulty in obtaining consistent experimental observations. Nongeometrical optics effects from the heating and resultant structures on VLF propagation may also affect the ducted power distribution but are outside the scope of ray tracing analysis.

Starks, M. J.

2002-11-01

186

Using WAAS Ionospheric Data to Estimate LAAS Short Baseline Gradients  

E-print Network

the ionosphere, e.g. the GPS satellite broadcast, are delayed with respect to the same signal traveling throughUsing WAAS Ionospheric Data to Estimate LAAS Short Baseline Gradients Seebany Datta-Barua, Todd due to ionospheric effects must be bounded such that integrity is maintained with minimal loss

Stanford University

187

WHISTLER-MODE PROPAGATION IN THE COLLISIONAL IONOSPHERE OF VENUS  

E-print Network

that non-linearities do not modify the wave dispersion since the non-linear force causes a longitudinal ionosphere of Venus. Further, we find that while the waves will heat the bottomside ionosphere, little effect in the nightside ionosphere of Venus cannot be electromagnetic waves caused by atmospheric discharges (lightning

Strangeway, Robert J.

188

GPS and ionospheric scintillations  

NASA Astrophysics Data System (ADS)

Ionospheric scintillations are one of the earliest known effects of space weather. Caused by ionization density irregularities, scintillating signals change phase unexpectedly and vary rapidly in amplitude. GPS signals are vulnerable to ionospheric irregularities and scintillate with amplitude variations exceeding 20 dB. GPS is a weak signal system and scintillations can interrupt or degrade GPS receiver operation. For individual signals, interruption is caused by fading of the in-phase and quadrature signals, making the determination of phase by a tracking loop impossible. Degradation occurs when phase scintillations introduce ranging errors or when loss of tracking and failure to acquire signals increases the dilution of precision. GPS scintillations occur most often near the magnetic equator during solar maximum, but they can occur anywhere on Earth during any phase of the solar cycle. In this article we review the subject of GPS and ionospheric scintillations for scientists interested in space weather and engineers interested in the impact of scintillations on GPS receiver design and use.

Kintner, P. M.; Ledvina, B. M.; de Paula, E. R.

2007-09-01

189

Solitons versus parametric instabilities during ionospheric heating  

NASA Technical Reports Server (NTRS)

Various effects associated with ionospheric heating are investigated by numerically solving the modified Zakharov (1972) equations. It is shown that, for typical ionospheric parameters, the modulational instability is more important than the parametric decay instability in the spatial region of strongest heater electric field. It is concluded that the modulational instability leads to the formation of solitons, as originally predicted by Petviashvili (1976).

Nicholson, D. R.; Payne, G. L.; Downie, R. M.; Sheerin, J. P.

1984-01-01

190

Seismo-ionospheric transfer function: dependence on time, location and other special features  

NASA Astrophysics Data System (ADS)

Large earthquakes are known to generate ionospheric disturbances, called coseismic ionosphere disturbances (CID). Vertical displacements of the ground induce pressure waves in the neutral atmosphere that propagate upward and grow in amplitude by several orders of magnitude as they reach ionospheric heights, since the atmospheric density decreases exponentially with height. Then, an ionospheric perturbation is formed via the collisions between neutral and charged particles. During favourable atmospheric and ionospheric conditions, a 0.1 mm/s ground displacement induced by the passage of Rayleigh surface waves generated by an earthquake of magnitude M8 at teleseismic distance, ionospheric layers can oscillate with velocities of about 10 m/s at around 150-200 km height. Those velocities are easily measurable by HF-Doppler sounder and significant Total Electron Content (TEC) variations (typically 0.1 TECU = 1x10^15 e-/m^3) can also be detected by GPS (Global Positioning System). However, before the emitted from the ground neutral waves reach the ionosphere they evolve due to a variety of effects provided by the propagation medium, i.e. the atmosphere. Therefore, one of the most interesting and important questions is the so-called transfer function for coseismic ionospheric disturbances that provides information on evolution and transformation of the “initial” neutral waves into the ultimate ionospheric response. This study analyzes the peculiarities of the transfer function for seismic waves in the ionosphere with respect to local time, geographical location, solar activity, etc. The variability of the solid Earth-atmosphere coupling is first investigated by estimating the amount of seismic energy injected in the atmosphere under variable atmospheric conditions. We model the atmospheric perturbation excited by an earthquake by summation of the Earth spheroidal normal modes computed for a 1D model of solid Earth surrounded by a realistic atmosphere. Further, through the atmosphere-ionosphere coupling we model the CID. The study is done under variable ionospheric conditions and based on the example of a series of large earthquakes (M>7.0) occurred in 2002-2010.

Astafyeva, E.; Rolland, L. M.; Lognonne, P.

2010-12-01

191

Calculating Second-Order Effects in MOSFET's  

NASA Technical Reports Server (NTRS)

Collection of mathematical models includes second-order effects in n-channel, enhancement-mode, metal-oxide-semiconductor field-effect transistors (MOSFET's). When dimensions of circuit elements relatively large, effects neglected safely. However, as very-large-scale integration of microelectronic circuits leads to MOSFET's shorter or narrower than 2 micrometer, effects become significant in design and operation. Such computer programs as widely-used "Simulation Program With Integrated Circuit Emphasis, Version 2" (SPICE 2) include many of these effects. In second-order models of n-channel, enhancement-mode MOSFET, first-order gate-depletion region diminished by triangular-cross-section deletions on end and augmented by circular-wedge-cross-section bulges on sides.

Benumof, Reuben; Zoutendyk, John A.; Coss, James R.

1990-01-01

192

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

NASA Astrophysics Data System (ADS)

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

Grubor, D. P.; Uli?, D. M. Å.; Žigman, V.

2008-06-01

193

Plasma effects of active ion beam injections in the ionosphere at rocket altitudes  

NASA Technical Reports Server (NTRS)

Data from ARCS rocket ion beam injection experiments are primarily discussed. There are three results from this series of active experiments that are of particular interest in space plasma physics. These are the transverse acceleration of ambient ions in the large beam volume, the scattering of beam ions near the release payload, and the possible acceleration of electrons very close to the plasma generator which produce intense high frequency waves. The ability of 100 ma ion beam injections into the upper E and F regions of the ionosphere to produce these phenomena appear to be related solely to the process by which the plasma release payload and the ion beam are neutralized. Since the electrons in the plasma release do not convect with the plasma ions, the neutralization of both the payload and beam must be accomplished by large field-aligned currents (milliamperes/square meter) which are very unstable to wave growth of various modes.

Arnoldy, R. L.; Cahill, L. J., Jr.; Kintner, P. M.; Moore, T. E.; Pollock, C. J.

1992-01-01

194

Ionospheric characteristics: a review  

SciTech Connect

The ionosphere is important to spacecraft charging because the thermal ions and electrons provide a significant current to a spacecraft surface. Low, mid, and high altitude ionospheric characteristics are discussed.

Rich, F.J.

1983-01-01

195

The Nightside Ionosphere of Venus Under Varying Levels of Solar EUV Flux  

NASA Technical Reports Server (NTRS)

Solar activity varied widely over the 14 year lifetime of the Pioneer Venus Orbiter, and these variations directly affected the properties of the nightside ionosphere. At solar maximum, when solar EUV was largest, the Venus ionosphere was found to extend to highest altitudes and nightward ion transport was the main source of the nightside ionosphere. At solar minimum, nightward ion transport was reduced, and electron precipitation was thought to be the main source. In this study, we have attempted a separation of spatial variations from temporal variations by examining the altitude profiles of the magnetic field, and electron density and temperature for three different solar EUV flux ranges. In the upper ionosphere and near-planet magnetotail (h greater than 1800 km), the solar EUV effects are significant. The electron density decreases about an order of magnitude from high to low EUV flux, while the electron temperature at least doubles. The magnetic field also increases 2 - 3 nT. In the lower ionosphere (200 - 600 km), lower EUV fluxes are associated with slightly reduced density, and higher temperature. These results are in accord with recent entry phase observations, where the electron density measured above the ionospheric density peak is lower than that observed at solar maximum during the early Pioneer Venus mission.

Ho, C. M.; Stangeway, R. J.; Russell, C. T.; Luhmann, J. G.; Brace, L. H.

1993-01-01

196

The nightside ionosphere of Venus under varying levels of solar EUV flux  

NASA Technical Reports Server (NTRS)

Solar activity varied widely over the 14 year lifetime of the Pioneer Venus Orbiter (PVO), and these variations directly affected the properties of the nightside ionosphere. At solar maximum, when solar EUV was largest, the Venus ionosphere was found to extend to highest altitudes and nightward ion transport was the main source of the nightside ionosphere. At solar minimum, nightward ion transport was reduced, and electron precipitation was thought to be the main source. In this study, we have attempted a separation of spatial variations from temporal variations by examining the altitude profiles of the magnetic field, and electron density and temperature for three different solar EUV flux ranges. In the upper ionosphere and near-planet magnetotail (h greater than 1800 km), the solar EUV flux effects are significant. The electron density decreases about an order of magnitude from high to low EUV flux, while the electron temperature at least doubles. The magnetic field also increases 2 - 3 nT. In the lower ionosphere (200 - 600 km), lower EUV fluxes are associated with slightly reduced density, and higher temperature. These results are in accord with recent entry phase observations, where the electron density measured above the ionospheric density peak is lower than that observed at solar maximum during the early Pioneer Venus mission.

Ho, C. M.; Strangeway, R. J.; Russell, C. T.; Luhmann, J. G.; Brace, L. H.

1993-01-01

197

Effect of Earthquakes on Lower Ionosphere as Found by Subionospheric VLF Propagation  

NASA Astrophysics Data System (ADS)

Reliable VLF subionospheric signal effect related to the seismic activity was first reported by Hayakawa et al. (1996 a, b) in association with the great Kobe earthquake. We have analyzed the similar data around 10 other great earthquakes (magnitude M >6), in order to understand the main features of such an effect, and the following characteristics are emerged from our analysis:(a) This effect looks as transient oscillations with 5-10 days period, which are initiated a few days before a large earthquake and relaxed for a few days or weeks after it.(b) It is mainly related to crust earthquakes.(c) It cannot be observed outside the sensitivity zone of VLF transmitter (first Fresnel zone) even for very large earthquakes (M >7)

Hayakawa, M.; Molchanov, O. A.

198

Ionospheric modification by rocket effluents. Final report  

SciTech Connect

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.

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

1980-06-01

199

Magnetospheric control of the bulk ionospheric plasma  

SciTech Connect

The temperature, composition, and circulation of the high-latitude, ionosphere display a marked variation with altitude, latitude, longitude, universal time, season, solar cycle, and geomagnetic activity. This variation is largely a consequence of the effect that magnetospheric electric fields, particle precipitation, and heat flows have on the ionosphere. At F-region altitudes, the entire ionosphere drifts in response to magnetospheric electric fields, with the horizontal drift generally displaying a two-cell pattern of antisunward flow over the polar cap and return flow at lower latitudes. This ionospheric motion, in combination with downward magnetospheric heat flows and ion production due to energetic-particle precipitation, act to produce interesting ionospheric features such as ion and electron temperature hot spots, plasma blobs, localized ionization troughs, and extended tongue of ionization, and anomalous F-region peak altitudes and densities. The time delay for the ionosphere to respond to changing magnetospheric conditions is a strong function of altitude and can be as long as 3 to 4 hours in the upper F-region. The ionosphere's response to changing magnetospheric conditions are described using a time-dependent high-latitude ionospheric model.

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

1987-01-01

200

Earthquake-Ionosphere Coupling Processes  

NASA Astrophysics Data System (ADS)

After a giant earthquake (EQ), acoustic and gravity waves are excited by the displacement of land and sea surface, propagate through atmosphere, and then reach thermosphere, which causes ionospheric disturbances. This phenomenon was detected first by ionosonde and by HF Doppler sounderin the 1964 M9.2 Great Alaskan EQ. Developing Global Positioning System (GPS), seismogenic ionospheric disturbance detected by total electron content (TEC) measurement has been reported. A value of TEC is estimated by the phase difference between two different carrier frequencies through the propagation in the dispersive ionospheric plasma. The variation of TEC is mostly similar to that of F-region plasma. Acoustic-gravity waves triggered by an earthquake [Heki and Ping, EPSL, 2005; Liu et al., JGR, 2010] and a tsunami [Artu et al., GJI, 2005; Liu et al., JGR, 2006; Rolland, GRL, 2010] disturb the ionosphere and travel in the ionosphere. Besides the traveling ionospheric disturbances, ionospheric disturbances excited by Rayleigh waves [Ducic et al, GRL, 2003; Liu et al., GRL, 2006] as well as post-seismic 4-minute monoperiodic atmospheric resonances [Choosakul et al., JGR, 2009] have been observed after the large earthquakes. Since GPS Earth Observation Network System (GEONET) with more than 1200 GPS receiving points in Japan is a dense GPS network, seismogenic ionospheric disturbance is spatially observed. In particular, the seismogenic ionospheric disturbance caused by the M9.0 off the Pacific coast of Tohoku EQ (henceforth the Tohoku EQ) on 11 March 2011 was clearly observed. Approximately 9 minutes after the mainshock, acoustic waves which propagated radially emitted from the tsunami source area were observed through the TEC measurement (e. g., Liu et al. [JGR, 2011]). Moreover, there was a depression of TEC lasting for several tens of minutes after a huge earthquake, which was a large-scale phenomenon extending to a radius of a few hundred kilometers. This TEC depression may be an ionospheric phenomenon attributed to tsunami, termed tsunamigenic ionospheric hole (TIH) [Kakinami and Kamogwa et al., GRL, 2012]. After the TEC depression accompanying a monoperiodic variation with approximately 4-minute period as an acoustic resonance between the ionosphere and the solid earth, the TIH gradually recovered. In addition, geomagnetic pulsations with the periods of 150, 180 and 210 seconds were observed on the ground in Japan approximately 5 minutes after the mainshock. Since the variation with the period of 180 seconds was simultaneously detected at the magnetic conjugate of points of Japan, namely Australia, field aligned currents along the magnetic field line were excited. The field aligned currents might be excited due to E and F region dynamo current caused by acoustic waves originating from the tsunami. This result implies that a large earthquake generates seismogenic field aligned currents. Furthermore, monoperiodical geomagnetic oscillation pointing to the epicenter of which velocity corresponds to Rayleigh waves occurs. This may occur due to seismogenic arc-current in E region. Removing such magnetic oscillations from the observed data, clear tsunami dynamo effect was found. This result implies that a large EQ generates seismogenic field aligned currents, seismogenic arc-current and tsunami dynamo current which disturb geomagnetic field. Thus, we found the complex coupling process between a large EQ and an ionosphere from the results of Tohoku EQ.

Kamogawa, Masashi

201

Effect of Grid Definition and Data Distribution on Accuracy of Ionospheric Imaging  

NASA Astrophysics Data System (ADS)

In tomography, the region to be imaged is divided into a grid and knowledge of the values of a parameter as measured along known paths through the region is used to reconstruct the interior of the region by assigning a value to each voxel of the grid. In the ionospheric case, slant Total Electron Content (sTEC) values for rays passing through the ionosphere can be used. The principle source of such data is recordings from Global Positioning System (GPS) ground receiver stations. Each ray is broken down into pieces, according to the path length within each voxel traversed. Each voxel is assigned an unknown value of electron concentration. A set of simultaneous equations in electron concentration and path length can then be constructed for each ray. In ideal circumstances enough rays from sufficient broadcast points to different receiver points exist so that a unique solution to the set of simultaneous equations can be determined. In practice the solution with the minimum error (usually in a least-squares sense) is found because there is always some error in the input measurements. In the case of the ionosphere and the set of broadcasting GPS satellites and ground based receivers, it is in principle impossible to determine a unique solution even in terms of a minimum error. The geometry is such that the set of simultaneous equations has more unknowns than equations. Hence it is necessary to constrain the solution by some additional method or methods [Bust and Mitchell, 2008]. The solution to this inverse problem is re-calculated for each epoch of interest. The Multi-Instrument Data Assimilation System algorithm developed at the University of Bath, UK, and used at the University of New Brunswick under licence uses empirical Orthogonal Functions (EOFs) to constrain the vertical dimension and spherical harmonics to constrain the locally horizontal dimensions. Two different grid boundaries are tested, using MIDAS. The larger of the two includes two ground receiver stations within it that are excluded from the smaller. (The larger there-by including all northern-hemisphere International Global Navigation Satellite System Service (IGS) permanent stations operating at the time.) It is not clear without testing whether the extra voxels necessary to include these two extra stations offset the benefits of their extra input-data or not, when the MIDAS reconstruction is made. For each grid boundary, runs with 2x2, 3x3 and 4x4, latitude x longitude (in degrees), divisions of the grid are compared with Incoherent Scatter Radar (ISR) data the NmF2 parameter. The results shown demonstrate that in each case tested the extra data improves the results despite the increase in number of grid voxels. Further results show that accuracy in the vertical dimension is worse affected than in the locally horizontal dimensions.

Burston, R.

2011-12-01

202

Numerical modeling of the global ionospheric effects of storm sequence on September 9-14, 2005—comparison with IRI model  

NASA Astrophysics Data System (ADS)

This study presents the modeling of ionospheric response to geomagnetic storms of September 9-14, 2005. We examine the performance of the Global Self-Consistent Model of Thermosphere, Ionosphere and Protonosphere (GSM TIP) and International Reference Ionosphere-2000 (IRI-2000), and compare the modeling predictions with the ionosonde and incoherent scatter radar observations over Yakutsk, Irkutsk, Millstone Hill and Arecibo stations. IRI-2000 predicted well all negative f o F 2 disturbances. In comparison with IRI-2000, the GSM TIP better reproduced the positive phase observed during the disturbed times. We discuss the possible reasons of the differences between the GSM TIP model calculations, IRI predictions, and the observations.

Klimenko, M. V.; Klimenko, V. V.; Ratovsky, K. G.; Goncharenko, L. P.

2012-06-01

203

A GPS/GNSS dense network used to monitor ionospheric positioning error  

NASA Astrophysics Data System (ADS)

GPS/GNSS networks are, for the last few years, quickly expanding their density all over the surface of the globe. The present idea is to use this density in order to assess the effect of ionospheric disturbances on relative positioning but also to monitor their propagation patterns. Local variability in the ionospheric electron density can dramaticaly affect the reliability of GPS/GNSS real time applications. In particular, Traveling Ionospheric Disturbances (TID's) or plasma instability due to geomagnetic storms can induce strong disturbances in relative positioning. It is therefore useful to develop an integrity monitoring service based on a GPS/GNSS dense network. To assess the effects of ionospheric activity on relative positioning, the SoDIPE-RTK software (Software for Determining the Ionospheric Positionning Error on RTK) has been developed at the Royal Meteorological Institute of Belgium. The approach consists in computing the positioning error due to the ionosphere and has been applied, as a proof of concept, on the Belgian dense network. This network called Active Geodetic Network (AGN) is composed of 66 GPS (dual-frequency) stations. In order to ensure a successful ambiguity resolution for both L1 and L2 carriers, baselines larger than 40 km are not taken into account in the analysis. In a first step, we assess the nominal RTK precision for each baseline during quiet ionospheric conditions (i.e. a background of low Total Electron Content (TEC) variability). The observed positioning accuracy is ~1 cm and depends mainly on baseline length and satellite geometry at the two considered stations. In a second step, the impact of two ionospheric events on positioning error (a medium scale TID and a powerful geomagnetic storm) is evaluated. As expected, the study demonstrates that the largest effects are observed during the occurrence of the geomagnetic storm with an ionospheric positioning error reaching 0.9 m. The maximal positioning error observed during the TID is around 0.15 m, depending on baseline orientation. This is due to the fact that the sharpest TEC gradients are observed for baselines oriented parallel to the direction of disturbance propagation. Finally, we propose a web service dedicated to GPS/GNSS relative positioning users based on SoDIPE-RTK. Every 15 minutes, a thematic map is produced showing each AGN baseline in a given color ranging from green (quiet conditions) to red (extreme conditions). This user-friendly application allows registered users to access and visualize current ionospheric conditions in the area covered by the whole network. This service based on the AGN is therefore an useful application of a GPS/GNSS dense network and will be extended to other networks in a near future.

Wautelet, G.; Lejeune, S.; Warnant, R.

2010-12-01

204

Ionospheric Correction Based on Ingestion of Global Ionospheric Maps into the NeQuick 2 Model  

PubMed Central

The global ionospheric maps (GIMs), generated by Jet Propulsion Laboratory (JPL) and Center for Orbit Determination in Europe (CODE) during a period over 13 years, have been adopted as the primary source of data to provide global ionospheric correction for possible single frequency positioning applications. The investigation aims to assess the performance of new NeQuick model, NeQuick 2, in predicting global total electron content (TEC) through ingesting the GIMs data from the previous day(s). The results show good performance of the GIMs-driven-NeQuick model with average 86% of vertical TEC error less than 10 TECU, when the global daily effective ionization indices (Az) versus modified dip latitude (MODIP) are constructed as a second order polynomial. The performance of GIMs-driven-NeQuick model presents variability with solar activity and behaves better during low solar activity years. The accuracy of TEC prediction can be improved further through performing a four-coefficient function expression of Az versus MODIP. As more measurements from earlier days are involved in the Az optimization procedure, the accuracy may decrease. The results also reveal that more efforts are needed to improve the NeQuick 2 model capabilities to represent the ionosphere in the equatorial and high-latitude regions. PMID:25815369

Yu, Xiao; She, Chengli; Zhen, Weimin; Bruno, Nava; Liu, Dun; Yue, Xinan; Ou, Ming; Xu, Jisheng

2015-01-01

205

Ionospheric Correction Based on Ingestion of Global Ionospheric Maps into the NeQuick 2 Model.  

PubMed

The global ionospheric maps (GIMs), generated by Jet Propulsion Laboratory (JPL) and Center for Orbit Determination in Europe (CODE) during a period over 13 years, have been adopted as the primary source of data to provide global ionospheric correction for possible single frequency positioning applications. The investigation aims to assess the performance of new NeQuick model, NeQuick 2, in predicting global total electron content (TEC) through ingesting the GIMs data from the previous day(s). The results show good performance of the GIMs-driven-NeQuick model with average 86% of vertical TEC error less than 10 TECU, when the global daily effective ionization indices (Az) versus modified dip latitude (MODIP) are constructed as a second order polynomial. The performance of GIMs-driven-NeQuick model presents variability with solar activity and behaves better during low solar activity years. The accuracy of TEC prediction can be improved further through performing a four-coefficient function expression of Az versus MODIP. As more measurements from earlier days are involved in the Az optimization procedure, the accuracy may decrease. The results also reveal that more efforts are needed to improve the NeQuick 2 model capabilities to represent the ionosphere in the equatorial and high-latitude regions. PMID:25815369

Yu, Xiao; She, Chengli; Zhen, Weimin; Bruno, Nava; Liu, Dun; Yue, Xinan; Ou, Ming; Xu, Jisheng

2015-01-01

206

Characterization of the Ionosphere Over the Murchison Radio Observatory  

NASA Astrophysics Data System (ADS)

The Murchison Radio Observatory (MRO), home of radio astronomy in Australia, is located in mid-latitude Western Australia. Projects currently under development at the MRO include a low-frequency instrument, the Murchison Widefield Array (MWA). The MWA is an aperture synthesis, imaging array operating over the frequency range 80 to 300 MHz. Signals in this range are subject to distortions caused by the ionosphere. The effects of scintillation and Faraday rotation degrade image quality. Historical measurements and models have long shown that the mid-latitude ionosphere has very low scintillation activity. TEC measurements we have made of the ionosphere over the MRO using high-precision, dual-frequency, GPS systems support this belief. Fine grained measurements (of the order 0.01-0.03 TEC units) have permitted fine-scale ionospheric structure to be resolved. These findings are reported and discussed. We review plans to extend this work with the implementation of mobile solar-powered instrumentation that will permit deployment of various GPS configurations that will collect TEC data during the forthcoming period of expected higher solar activity.

Herne, D.; Lynch, M. J.; Kennewell, J.; Carrano, C. S.; Groves, K.; Coster, A. J.; Oberoi, D.

2011-12-01

207

Ionospheric Anomalies Associated with Large Earthquakes: Tomographic Approach  

NASA Astrophysics Data System (ADS)

Many anomalous electromagnetic phenomena possibly associated with large earthquakes have been reported. TEC (Total Electron Contents) anomaly is one of the most promising phenomena preceding large earthquakes. We investigated statistically TEC anomalies before large earthquakes around Japan region during 1998-2010 and found that that positive anomalies significantly appear 1-5 days before M>=6.0 earthquakes in Japan area. In order to evaluate the previous statistical result, we investigate the 2011 off the Pacific coast of Tohoku Earthquake. GIM-TEC* anomalies exceeding +2 ? appear 3-4 days before the earthquake. The duration is more than 20 hours. This result satisfy the previous statistical results of positive anomalies for M>=6.0 earthquakes in Japan. To understand the mechanism, monitoring of 3D distributions of ionospheric electron density is considered to be effective. In this study, to investigate the three-dimensional structure of ionospheric electron density prior to large earthquake, the neural network based tomographic approach is adapted to GEONET and ionosonde data for the 2011 Off the Pacific Coast of Tohoku Earthquake (Mw9.0). As a result, the reconstructed distribution of electron density was enhanced in sub-ionosphere to over F-region in comparison with 15 days backward median distribution. Moreover the enhanced area seems to be developed to upper ionosphere from sub-ionosphere with time. The tomographic results suggest the existence of some energy influx from the surface associated with seismic activity. Then, in order to understand the relationship of detected phenomenon and earthquake, we performed the tomographic analysis for other earthquakes occurred in Japan. The details will be shown in the presentation.

Hirooka, S.; Hattori, K.; Ichikawa, T.; Han, P.

2013-12-01

208

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

NASA Astrophysics Data System (ADS)

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

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

2010-10-01

209

Ionosphere. [of Jupiter  

NASA Technical Reports Server (NTRS)

The original interest in an ionosphere on Jupiter was generated by the discovery of strong radio-frequency emissions at approximately 20 MHz which were thought to be plasma frequencies associated with Jupiter's ionosphere. The ionosphere of Jupiter provides a means to couple the magnetosphere to the atmosphere by virtue of its high conductivity and collisional interaction with the neutral atmosphere. The Pioneer and Voyager have provided direct measurements of profiles of electron concentration at selected locations on Jupiter. Attention is given to basic principles regarding the characteristics of the Jovian ionosphere, the ionization sources, aspects of ion recombination, ion chemistry, observations of Jupiter's ionosphere, the structure of Jupiter's upper atmosphere, and questions of ionospheric modeling. On the basis of the Pioneer and Voyager observations it appears that Jupiter's ionosphere and thermosphere undergo significant solar cycle changes.

Strobel, D. F.; Atreya, S. K.

1983-01-01

210

Compensation for the effect of the ionosphere on Doppler measurements in the experiments of the satellite-to-satellite tracking type  

NASA Astrophysics Data System (ADS)

The effect of the ionosphere on satellite-to-satellite tracking experiment measurements is analyzed, and a method for the elimination of the ionospheric effect by measuring specific signals at different frequencies is described. While the existing NNSS TRANSIT system, which employs the emission of two coherent signals on the satellite-to-terrestrial receiver path, yields results similar to the present method, its application to satellite-to-satellite tracking requires a greater number of transmitters, thereby increasing technical difficulties and cost. This is especially true in the case of a three-frequency measurement system. The main disadvantage of the method proposed is the greater likelihood of failure, since a main satellite transmitter malfunction will abort the entire experiment. This weakness may be addressed by the use of redundant systems.

Latka, J. K.

211

Magnetic zenith effect and some features of the multifractal structure of the small-scale artificial ionospheric turbulence  

Microsoft Academic Search

We present the results of the experiment on studying the multifractal structure (with inhomogeneity sizes from tens to hundreds\\u000a of meters across the Earth’s magnetic field) of the artificial ionospheric turbulence when the midlatitude ionosphere is affected\\u000a by high-power HF radio waves. The experimental studies were performed on the basis of the “Sura” heating facility with the\\u000a help of radio

V. A. Alimov; F. I. Vybornov; E. N. Myasnikov; A. V. Rakhlin; V. L. Frolov

2009-01-01

212

F layer postsunset height rise due to electric field prereversal enhancement: 1. Traveling planetary wave ionospheric disturbance effects  

Microsoft Academic Search

An ionospheric sounding station is operational at Palmas (10.2°S, 48.2°W, dip latitude 5.5°S), Brazil, since 2002. Observations of F layer virtual height day-to-day variations during evening hours (1800 LT to 2000 LT) show a strong variability, even during geomagnetically quiet periods. From the ionospheric multifrequency virtual height variations (at 3, 4, 5, 6, 7, and 8 MHz), observed from July

P. R. Fagundes; J. A. Bittencourt; J. R. Abalde; Y. Sahai; M. J. A. Bolzan; V. G. Pillat; W. L. C. Lima

2009-01-01

213

Wide area ionosphere grid modelling in the auroral region  

NASA Astrophysics Data System (ADS)

Dual frequency GPS receivers enable the estimation of absolute ionospheric delay and total electron content (TEC) along the signal path. By using a number of reference stations, each equipped with a dual frequency receiver, it is possible to estimate values of the vertical ionospheric delay at a set of designated grid points (in latitude and longitude) on an ionosphere shell. This type of ionosphere delay modelling is employed in wide area differential GPS (WADGPS) networks, where grid accuracies generally depend on the temporal/spatial correlations of TEC. These models can suffer degraded performance in regions, such as the high latitude auroral zone, where spatial gradients and temporal variations of electron density may differ significantly from assumptions. Given that future extensions of WADGPS applications include implementation of safety-critical systems to support air navigation in auroral regions, such as the wide area augmentation system (WAAS - FAA[1994]), it is important to establish the impact of auroral effects on such GPS networks. In the research presented here, a detailed study of auroral effects on GPS is conducted, and performance of the ionosphere grid model is investigated in the auroral region. The development of a Canadian wide area network in 1996, by Natural Resources Canada (NRCan) [Caissy et al., 1996], allowed compilation of an extensive GPS data set from the auroral region. In this thesis, periods of enhanced auroral activity (over Canada) are identified from ground-based magnetometer signatures, using the Canadian Space Agency's CANOPUS MARIA array. Signatures of auroral TEC associated with these disturbances are established using corresponding GPS observations from the NRCan network. A wide area ionosphere grid model is developed, and degraded grid accuracies associated with the auroral features are estimated, under various modelling assumptions. It is observed that grid accuracies are degraded by a factor of 2--5, relative to typical accuracies, during periods of enhanced auroral activity. In order to mitigate these effects, a modified grid algorithm is developed in which auroral disturbances are detected from time series of TEC observations. Model parameters are adjusted, consistent with local ionospheric processes, which allows improvements in the grid performance of 15--25 percent. Detailed analysis of a substorm event is conducted, where the largest degradations in grid accuracies are observed during the substorm expansive phase. The potential of monitoring auroral phenomena using GPS observations from a wide area network is explored briefly.

Skone, Susan Helen

214

Feedback instability of the ionospheric resonant cavity  

SciTech Connect

The exponential increase of the Alfven speed in the topside ionosphere leads to the formation of a resonant cavity (Lysak, 1988) which has been termed the ionospheric Alfven resonator by Trakhtengertz and Feldstein (1984). These authors primarily considered the situation where the ionospheric Pedersen conductivity is low, while Lysak (1988) considered the opposite limit of the infinite ionospheric conductivity. These results have been extended to arbitrary ionospheric conductivity by performing a numerical solution of the cavity dispersion relation, which involves Bessel functions of complex argument and order. These results indicate that the damping of excitations of this resonant cavity is strongest when the ionospheric Pedersen and Alfven conductivities are comparable and that growth is possible for incoming wave boundary conditions. The existence of this cavity leads to a modification of the Alfven wave reflection coefficient at the ionosphere. While this reflection coefficient is independent of frequency at low frequencies, it exhibits structure due to the resonant cavity modes at frequencies around 0.1-1 Hz. These cavity modes can also be excited by feedback instabilities (Sato, 1978; Lysak, 1986), leading to growth rates which are enhanced over the case without the cavity. These waves have maximum growth at short wavelengths, particularly when the background Pedersen conductivity is large. The perturbations associated with these instabilities can lead to structuring of auroral currents during substorms, and may help explain the westward traveling surge.

Lysak, R.L. (Univ. of Minnesota, Minneapolis (USA))

1991-02-01

215

On the effective altitude of the HAARP induced ionospheric ELF\\/VLF current modulation and multi-beam vertical ELF\\/VLF interference  

Microsoft Academic Search

The HF heating facility of the High Frequency Active Auroral Research Program (HAARP) has been used to generate ELF\\/VLF waves via modulated heating of the lower ionosphere for several years. Here we investigate the effective altitude of the modulated electrojet currents as a function of HF frequency and harmonic number of the ELF\\/VLF modulation. In one experiment ELF\\/VLF frequency time

M. Golkowski; M. Cohen; R. C. Moore

2010-01-01

216

A New Ionosphere Tomography Algorithm with Two-Grids Virtual Observations Constraints and 3D Velocity Profile  

NASA Astrophysics Data System (ADS)

Due to the sparsity of world's GNSS stations and limitations of projection angles, GNSS-based ionosphere tomography is a typical ill-posed problem. There are two main ways to solve this problem. Firstly the joint inversion method combining multi-source data is one of the effective ways. Secondly using a priori or reference ionosphere models, e.g., IRI or GIM models, as the constraints to improve the state of normal equation is another effective approach. The traditional way for adding constraints with virtual observations can only solve the problem of sparse stations but the virtual observations still lack horizontal grid constraints therefore unable to fundamentally improve the near-singularity characteristic of the normal equation. In this paper, we impose a priori constraints by increasing the virtual observations in n-dimensional space, which can greatly reduce the condition number of the normal equation. Then after the inversion region is gridded, we can form a stable structure among the grids with loose constraints. We then further consider that the ionosphere indeed changes within certain temporal scale, e.g., two hours. In order to establish a more sophisticated and realistic ionosphere model and obtain the real time ionosphere electron density velocity (IEDV) information, we introduce the grid electron density velocity parameters, which can be estimated with electron density parameters simultaneously. The velocity parameters not only can enhance the temporal resolution of the ionosphere model thereby reflecting more elaborate structure (short-term disturbances) under ionosphere disturbances status, but also provide a new way for the real-time detection and prediction of ionosphere 3D changes. We applied the new algorithm to the GNSS data collected in Europe for tomography inversion for ionosphere electron density and velocity at 2-hour resolutions, which are consistent throughout the whole day variation. We then validate the resulting tomography model using independent GNSS station data, and results using the conventional algorithm (Multiplicative Algebraic Reconstruction Techniques), as well as ionosphere ionosonde data in the study area. Key words Ionosphere Tomography, Grid Constraints, Virtual observations, 3D Ionosphere Velocity Image

Kong, Jian; Yao, Yibin; Shum, Che-Kwan

2014-05-01

217

From Cigala to Calibra: AN Infrastructure for Ionospheric Scintillation Monitoring in Brazil  

NASA Astrophysics Data System (ADS)

The CIGALA (Concept for Ionospheric Scintillation Mitigation for Professional GNSS in Latin America) project was funded by the European Commission (EC) in the framework of the FP7-GALILEO-2009-GSA (European GNSS Agency ) activity. It was concluded in February 2012 but the network of GNSS receivers deployed in Brazil remain in operation, continuously collecting data. One of the aims of the project was to create a data base of ionospheric parameters to help analyze TEC and scintillation effects on GNSS. Details of the project can be found at http://is-cigala-calibra.fct.unesp.br/cigala2/#. Following CIGALA, the CALIBRA (Countering GNSS high Accuracy applications Limitations due to Ionospheric disturbances in BRAzil) project was approved, also funded by the EC/GSA. CALIBRA aims to improve existing algorithms and develop new ones that can be applied to high accuracy GNSS techniques in order to tackle the effects of ionospheric disturbances. Through this project the CIGALA network will be expanded. The objective of this presentation is to give details of the CALIBRA and CIGALA projects, mainly concerning the infrastructure setup in Brazil aiming to study effects related to Ionospheric Scintillation.

Monico, J. G.; Camargo, P. D.; Alves, D. B.; Aquino, M.; Pereira, V. S.; Vani, B.

2013-05-01

218

Ionospherically reflected proton whistlers  

NASA Astrophysics Data System (ADS)

We present experimental observations and detailed investigation of the variety of proton whistlers that includes transequatorial and ionospherically reflected proton whistlers. The latter have previously been indicated from numerical modeling of spectrograms. The study is based on six-component ELF wave data from the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite which permits to obtain not only spectrograms displaying the power spectral density but also such wave properties as the polarization, wave normal angle, wave refractive index, and normalized parallel component of the Poynting vector. The explanation of various types of proton whistlers is based on the properties of ion cyclotron wave propagation in a multicomponent magnetoplasma, with special consideration of the effect of ion hybrid resonance reflection. Analysis of experimental data is supplemented by numerical modeling of spectrograms that reproduces the main features of experimental ones. As a self-contained result, we provide conclusive experimental evidences that the region illuminated by a lightning stroke in the Earth-ionosphere waveguide may spread over a distance of 4000 km in both hemispheres.

Vavilov, D. I.; Shklyar, D. R.

2014-12-01

219

Long-term ionospheric anomaly monitoring for ground based augmentation systems  

NASA Astrophysics Data System (ADS)

Extreme ionospheric anomalies can pose a potential integrity threat to ground-based augmentation of the Global Positioning System (GPS), and thus the development of ionospheric anomaly threat models for each region of operation is essential for system design and operation. This paper presents a methodology for automated long-term ionospheric anomaly monitoring, which will be used to build an ionospheric anomaly threat model, evaluate its validity over the life cycle of the system, continuously monitor ionospheric anomalies, and update the threat model if necessary. This procedure automatically processes GPS data collected from external networks and estimates ionospheric gradients at regular intervals. If ionospheric gradients large enough to be potentially hazardous to users are identified, manual data examination is triggered. This paper also develops a simplified truth processing method to create precise ionospheric delay estimates in near real-time, which is the key to automating the ionospheric monitoring procedure. The performance of the method is examined using data from the 20 November 2003 and 9 November 2004 ionospheric storms. These results demonstrate the effectiveness of simplified truth processing within long-term ionosphere monitoring. From the case studies, the automated procedure successfully identified extreme ionospheric anomalies, including the two worst ionospheric gradients observed and validated previously based on manual analysis. The automation of data processing enables us to analyze ionospheric data continuously going forward and to more accurately categorize ionospheric behavior under both nominal and anomalous conditions.

Jung, Sungwook; Lee, Jiyun

2012-08-01

220

The use of subionospheric VLF/LF propagation for the study of lower ionospheric perturbations associated with earthquakes  

NASA Astrophysics Data System (ADS)

It is recently recognized that the ionosphere is very sensitive to seismic effects, and the detection of ionospheric perturbations associated with earthquakes (EQs), attracts a lot of attention as a very promising candidate for short-term EQ prediction. In this review we propose a possible use of VLF/LF (very low frequency (3-30 kHz)/low frequency (30-300 kHz)) radio sounding of seismo-ionospheric perturbations. We first present the first convincing evidence on the presence of ionospheric perturbations for the disastrous Kobe EQ in 1995. The significant shift in terminator times in the VLF/LF diurnal variation, is successfully interpreted in terms of lowering of the lower ionosphere prior to the EQ, which is the confirmation of seismo-ionospheric perturbations. In order to avoid the overlapping with my own previous reviews [1, 2], we try to present the latest results including the statistical evidence on the correlation between the VLF/LF propagation anomalies (ionospheric perturbations) and EQs (especially with large magnitude and with shallow depth), a case study on the Indonesia Sumatra EQ (wavelike structures in the VLF/LF data), medium-distance (6˜8 Mm) propagation anomalies, the fluctuation spectra of subionospheric VLF/LF data (atmospheric gravity waves effect, the effect of Earth's tides etc.), and the mechanism of lithosphere—atmosphere—ionosphere coupling. Finally, we indicate the present situation of this kind of VLF/LF activities going on in different parts of the globe and we suggest the importance of international collaboration in this seismo-electromagnetics study.

Hayakawa, M.

2010-10-01

221

Interpreting Mars ionospheric anomalies over crustal magnetic field regions using a 2-D ionospheric model  

NASA Astrophysics Data System (ADS)

spatially inhomogeneous, small-scale crustal magnetic fields of Mars influence the escape of planetary atmospheric species and the interaction of the solar wind with the ionosphere. Understanding the plasma response to crustal magnetic field regions can therefore provide insight to ionospheric structure and dynamics. To date, several localized spatial structures in ionospheric properties that have been observed over regions of varying magnetic field at Mars have yet to be explained. In this study, a two-dimensional ionospheric model is used to simulate the effects of field-aligned plasma transport in regions of strong crustal magnetic fields. Resulting spatial and diurnal plasma distributions are analyzed and found to agree with observations from several spacecraft and offer compelling interpretations for many of the anomalous ionospheric behaviors observed at or near regions of strong crustal magnetic fields on Mars.

Matta, Majd; Mendillo, Michael; Withers, Paul; Morgan, Dave

2015-01-01

222

Characterisation of the Ionosphere over the Murchison Radio Observatory, Murchison, Western Australia  

NASA Astrophysics Data System (ADS)

The Murchison Radio Observatory (MRO) is the future home of radio astronomy in Australia. Projects are currently under development at the MRO, including a low-frequency instrument, the Murchison Widefield Array (MWA). The MWA is an aperture synthesis, imaging array that when complete will comprise approximately 8,000 dipole antennas, operating in the frequency range, 80 to 300 MHz. Signals in the frequency range of interest reaching the MWA are subject to distortions caused by the ionosphere. The effects of scintillation and Faraday rotation degrade image quality. Self-calibration techniques compensate for scintillation and in the process, provide accurate relative total electron content (TEC) measures of the ionosphere (milli-TEC). However, to ‘unwind’ Faraday rotation effects, the absolute TEC (aTEC) of the ionosphere must be determined. This step is necessary in order to study processes in space involving magnetism. Over a period of two years, absolute TEC measurements have been made over the MRO using high-precision, dual-frequency GPS systems. Continuous measurements have been performed over the past year and campaign-based measurements prior to that. This paper presents results from those studies, which are providing insights into the nature of the ionosphere over a previously poorly understood, mid-latitude region of the southern hemisphere. This work too, is laying a foundation for the accurate characterisation of the ionosphere over the MRO which is also the possible future site of the Square Kilometre Array (SKA).

Herne, D. E.

2009-12-01

223

Electromagnetically induced second-order Talbot effect  

NASA Astrophysics Data System (ADS)

The electromagnetically induced Talbot effect (EITE) offers a nondestructive and lensless way to image ultracold atoms or molecules (Wen J. M. et al., Appl. Phys. Lett., 98 (2011) 081108). We study an atomic imaging scheme based on the second-order two-photon EITE. Entangled photon pairs are taken as the imaging light to realize coincidence recording. Compared to the previous self-imaging scheme, the present one has the characteristic of imaging nonlocally and of the controllable image variation in size, and thus, it is useful for facilitating the EITE application in imaging techniques.

Qiu, Tianhui; Yang, Guojian; Bian, Qing

2013-02-01

224

Solar cycle effects on the structure of the electron density profiles in the dayside ionosphere of Venus  

NASA Technical Reports Server (NTRS)

Results are presented of observations from the changes in the electron density structure of the dayside ionosphere of Venus that were brought about by changing solar activity. The ionopause height is generally low for values of the solar zenith angle below about 50 deg regardless of the phase in the solar cycle. At solar maximum, and at times of intermediate solar activity, the ionopause height for solar zenith angles greater than about 50 deg is highly variable, ranging from a minimum of about 200 km to a maximum of more than 1000 km. At times of solar minimum the great majority of all ionopause heights for all solar zenith angles are uniformly low, lying between 200 and 300 km. It is argued that the compressed nature of the Venus atmosphere at solar minimum is produced by permeation of the ionosphere by the solar wind magnetic field, which occurs when the solar wind dynamic pressure exceeds the ionospheric plasma pressure.

Kliore, Arvydas J.; Luhmann, Janet G.

1991-01-01

225

Investigations into the properties, conditions, and effects of the ionosphere. Report No. 9, 16 December 1987-31 December 1988  

SciTech Connect

Northwest Research Associates (NWRA), as prime contractor, and its two team subcontractors, Science Applications International Corp. (SAIC) and the University of Lowell Center for Atmospheric Research (ULCAR), provide members of their technical staffs to conduct and support scientific and engineering investigations of the ionosphere. The investigations address ionospheric composition, structure, specification, scintillation and chemistry as well as remote sensing of the ionosphere through ultraviolet sensors. Specific work is carried out under individual Task Requirement Notices (TRNs) written for conduct and/or support of investigations in the following six categories: laboratory measurements; field measurements; aircraft measurements; rocket, balloon, shuttle, and satellite measurements; analytical and theoretical investigations; and scientific and engineering analysis. This report provides a summary of the work performed during the period 16 December 1987 through 31 December 1988.

Biello, G.D.; Fremouw, E.J.; Reinisch, B.W.; Szuszczewicz, E.P.

1989-01-15

226

Dynamic Agents of Magnetosphere-Ionosphere Coupling  

NASA Technical Reports Server (NTRS)

VISIONS sounding rocket mission (VISualizing Ion Outflow via Neutral atom imaging during a Substorm) has been awarded to NASA/GSFC (PI Rowland) in order to provide the first combined remote sensing and in situ measurements of the regions where ion acceleration to above 5 e V is occurring, and of the sources of free energy and acceleration mechanisms that accelerate the ions. The key science question of VISIONS is how, when, and where, are ions accelerated to escape velocities in the auroral zone below 1000 km, following substorm onset? Sources of free energy that power this ion acceleration process include (but not limited) electron precipitation, field-aligned currents, velocity shears, and Alfvenic Poynting flux. The combine effect of all these processes on ionospheric ion outflows will be investigated in a framework of the kinetic model that has been developed by Khazanov et al. in order to study the polar wind transport in the presence of photoelectrons.

Khazanov, George V.; Rowland, Douglas E.; Moore, Thomas E.; Collier, Michael

2011-01-01

227

Joule heating of Io's ionosphere by unipolar induction currents  

NASA Technical Reports Server (NTRS)

Electrical induction in Io's ionosphere, due to the corotating plasma bound to the Jovian magnetosphere, is one possible source for the attainment of the high temperatures suggested by the large scale height of Io's ionosphere. Unipolar induction models are constructed to calculate ionospheric joule heating numerically, whose heating rates lie between 10 to the -9th and 10 to the -8th W/cu m. The binding and coupling of the ionosphere is due to the dense, and possibly ionized, neutral SO2 atmosphere, and there appears to be no need to postulate the existence of an intrinsic Ionian magnetic field in order to retain the observed ionnosphere.

Herbert, F.; Lichtenstein, B. R.

1980-01-01

228

Ionospheric calibration for single frequency altimeter measurements  

NASA Technical Reports Server (NTRS)

This report investigates the potential of using Global Positioning System (GPS) data and a model of the ionosphere to supply a measure of the sub-satellite Total Electron Current (TEC) of the required accuracy (10 TECU rms) for the purpose of calibrating single frequency radar altimeter measurements. Since climatological (monthly mean) models are known to be in error by as much as 50 percent, this work focused on the Parameterized Real-Time Ionospheric Specification Model (PRISM) which has the capability to improve model accuracy by ingesting (adjusting to) in situ ionospheric measurements. A set of globally distributed TEC measurements were generated using GPS data and were used as input to improve the accuracy of the PRISM model. The adjusted PRISM TEC values were compared to TOPEX dual frequency TEC measurements (which are considered truth) for a number of TOPEX sub-satellite tracks. The adjusted PRISM values generally compared to the TOPEX measurements within the 10 TECU accuracy requirements when the sub-satellite track passed within 300 to 400 km of the GPS TEC data or when the track passed through a night time ionosphere. However, when the sub-satellite points were greater than 300 to 400 km away from the GPS TEC data or when a local noon ionosphere was sampled, the adjusted PRISM values generally differed by greater than 10 TECU rms with data excursions from the TOPEX TEC measurements of as much as 40 TECU (an 8 cm path delay error at K band). Therefore, it can be concluded from this analysis that an unrealistically large number of GPS stations would be needed to predict sub-satellite TEC at the 10 TECU level in the day time ionosphere using a model such as PRISM. However, a technique currently being studied at the Jet Propulsion Laboratory (JPL) may provide a means of supplying adequate TEC data to meet the 10 TECU ionospheric correction accuracy when using a realistic number of ionospheric stations. This method involves using global GPS TEC data to estimate a global grid of vertical ionospheric TEC as a function of time (i.e. every one half hour) in a sun-fixed longitude frame. Working in a sun-fixed longitude frame, one is not limited by the spatial decorrelation distance of the ionosphere, but instead is limited more by the temporal correlations of the ionosphere in the sun-fixed frame which are a smaller effect. It is the opinion of the authors that using the global sun-fixed TEC grid data, in particular, ingesting it into PRISM, offers the best possibility of meeting the 10 TECU ionospheric correction accuracy requirement, and should be the subject of further study.

Schreiner, William S.; Born, George H.

1993-01-01

229

DEMETER Observations of Equatorial Plasma Depletions and Related Ionospheric Phenomena  

NASA Astrophysics Data System (ADS)

DEMETER, the first micro-satellite of the CNES MYRIAD program, was launched from Baikonour on June 29, 2004 on a nearly circular, quasi helio-synchronous polar orbit at ~ 715 km altitude. The DEMETER mission focuses primarily on the search for a possible coupling between seismic activity and ionospheric disturbances as well as on the effects of natural phenomena such as tropospheric thunderstorms and man-made activities on the ionosphere. The scientific payload provides fairly complete measurements of the ionospheric plasma, energetic particles above ~ 70 keV, and plasma waves, up to 20 kHz for the magnetic and 3.3 MHz for the electric components. Several studies related to space weather and ionospheric physics have been conducted over the past years. Following a brief description of the payload and the satellite modes of operation, this presentation will focus on a set of results that provide a new insight into the physics of instabilities in the night-time equatorial ionosphere. The observations were performed during the major magnetic storm of November 2004. Deep plasma depletions were observed on several night-time passes at low latitudes characterized by the decrease of the plasma density by nearly 3 orders of magnitude relative to the undisturbed plasma, and a significant abundance of molecular ions. These features can be best interpreted as resulting from the rise of the F-layer above the satellite altitude over an extended region of the ionosphere. In one of the passes, DEMETER was operated in the Burst mode and the corresponding high resolution data allowed for the discovery of two unexpected phenomena. The first one is the existence of high intensity monochromatic wave packets at the LH frequency that develop during the decay phase of intense bursts of broadband LH turbulence. The broadband LH turbulence is triggered by whistlers emitted by lightning from atmospheric thunderstorms beneath the satellite. The second unexpected feature is the detection of a population of super-thermal ionospheric ions with a density of about 2-3% of the thermal ion population. The super- thermal ions appeared to be heated to temperatures of a few eV at times when LH turbulence and monochromatic wave packets are observed while the temperature of the core ion population is not affected. High time resolution plasma density measurements show the presence of strong small scale plasma irregularities in the depletions that scatter the high amplitude whistler waves and may lead to the development of strong LH turbulence and of monochromatic wave packets. The ensuing interaction between these waves and the ambient ions may lead to the formation of a super-thermal tail in the ion distribution function. Ion acceleration by LH turbulence and solitary waves is a commonly observed phenomenon along auroral magnetic field lines but, to our knowledge, this is the first time that a similar process has been observed in the equatorial ionosphere. These findings exemplify a novel coupling mechanism between the troposphere and the ionosphere: Under highly disturbed conditions at times of magnetic storms, part of the energy released by lightning and radiated as whistlers can dissipate in the equatorial ionosphere and produce super-thermal ion populations.

Berthelier, J.; Malingre, M.; Pfaff, R.; Jasperse, J.; Parrot, M.

2008-12-01

230

Prediction of Global Ionospheric TEC Maps: First results on a UPC forecast product  

Microsoft Academic Search

A method for short-term prediction of ionospheric Total Electron Content (TEC) has been developed. It is based on using long time series of IGS Global Ionospheric vertical TEC Maps (GIMs) and the application of Autoregressive (AR) models and Neural Networks (NN). In this work, the IGS ionospheric Working Group products provided by UPC analysis center will be used in order

A. García-Rigo; E. Monte; M. Hernández-Pajares; J. M. Juan; J. Sanz; A. Krankowski; P. Wielgosz

2009-01-01

231

Space weather. Ionospheric control of magnetotail reconnection.  

PubMed

Observed distributions of high-speed plasma flows at distances of 10 to 30 Earth radii (R(E)) in Earth's magnetotail neutral sheet are highly skewed toward the premidnight sector. The flows are a product of the magnetic reconnection process that converts magnetic energy stored in the magnetotail into plasma kinetic and thermal energy. We show, using global numerical simulations, that the electrodynamic interaction between Earth's magnetosphere and ionosphere produces an asymmetry consistent with observed distributions in nightside reconnection and plasmasheet flows and in accompanying ionospheric convection. The primary causal agent is the meridional gradient in the ionospheric Hall conductance which, through the Cowling effect, regulates the distribution of electrical currents flowing within and between the ionosphere and magnetotail. PMID:25013068

Lotko, William; Smith, Ryan H; Zhang, Binzheng; Ouellette, Jeremy E; Brambles, Oliver J; Lyon, John G

2014-07-11

232

Characterization of Ionospheric Scintillation Using Simultaneous Formosat-3/COSMIC Radio Occultation Observations and AFRL SCINDA Ground Scintillation Measurements  

NASA Astrophysics Data System (ADS)

Ionospheric scintillation at low latitudes has been studied using ionospheric radio occultation (RO) measurements by the FORMOSAT-3/COSMIC micro-satellites in conjunction with ground-based data from the Scintillation Network Decision Aid (SCINDA) station at Kwajalein Atoll. The Air Force Research Laboratory has developed the SCINDA network for monitoring low-latitude ionospheric total electron content (TEC) and scintillation associated with equatorial spread F. The network currently consists of sixteen stations distributed around the globe and the data have been used to conduct numerous studies on the characteristics and climatology of equatorial scintillation. The present study focuses on COSMIC RO and SCINDA data during the three COSMIC campaigns in 2006. Radio occultation events are selected by requiring that ionospheric scintillation was detected by the SCINDA VHF scintillation monitor at Kwajalein, and that the occultation ray path intersected the Kwajalein longitude below the satellite altitude, which varied from 500 to 800 km for the six FORMOSAT-3 satellites. In order to exclude tropospheric effects, only GPS signal amplitudes from FORMOSAT-3 with ray path tangent altitudes above 100 km are considered. Locations of ionospheric scintillation are estimated by triangulation using the satellites and the SCINDA ground station. Airglow images at Kwajalein are also used to confirm occurrence of equatorial ionospheric scintillations. For the selected events, large amplitude L1 and L2 scintillations tend to occur at altitudes below 200 km at frequencies around 0.5 Hz. The results are discussed as a potential path toward better specifying the occurrence of equatorial scintillations.

Starks, M. J.; Lin, C. S.; Groves, K. M.; Pedersen, T. R.; Basu, S.; Syndergaard, S.; Rocken, C.

2007-05-01

233

An Ionosphere Estimation Algorithm for WAAS Based on Kriging  

E-print Network

. As such it has been applied to map TEC measurements as well as other ionospheric parameters [10], is a limited amount of Total Electron Content (TEC) measurements. As a consequence, in order to estimate of the ionosphere over the region of interest. Using the thin shell model framework, where each TEC measurement

Stanford University

234

Detection of ionospheric signatures of Solar Proton Events by VLF signal phase and amplitude modification  

NASA Astrophysics Data System (ADS)

Very Low Frequency (VLF) radio waves propagate with little attenuation within the Earth-ionosphere waveguide. Perturbations of the lower ionosphere produce a modification of the geometry of the waveguide, resulting in a disruption of the VLF propagation conditions. Iono-spheric perturbations are caused by either an increased flux of energetic photons and particles, or periodic modifications due to the daily and seasonal cycles of the Earth. Whereas the latter occur with a regular periodicity, the former occur at random. In order to differentiate between the periodic and stochastic ionospheric perturbations it is important to understand the mech-anisms which cause the diurnal and seasonal changes in VLF propagation conditions.Mode theory and FDTD techniques are used to examine the effects of spatial and temporal changes in ionospheric conditions as characterised by Wait's parameters. Data taken from a global array of VLF receivers is used in conjunction with GOES proton flux data along with the Sodankylü a Ion Chemistry model (SIC) to test the validity of the model

Meyer, Stephen; Collier, Andrew; Koen, Etienne

235

A Prediction Model for Solar-Driven Ionospheric Electric Fields at Arbitrary Locations  

NASA Astrophysics Data System (ADS)

In an earlier work [Rothwell and Jasperse, 2006] we derived the global ionospheric electric field produced by the Region-1 and Region-2 currents. Despite the simplifying assumptions in that work of both the dipole and spin axis being aligned perpendicular to the ecliptic plane we found promising agreement with Jicamarca vertical drift data. However, in order to extend the model to arbitrary geographic locations we now take into account 1) the tilt of the magnetic dipole, as well as local IGRF modifications in the B-field, 2) a seasonal, solar-driven ionospheric conductance model which is accurate near the terminators, and 3) the Region-1 and Region-2 currents properly defined in magnetic coordinates. For example, the Region-1 and-2 currents are fixed in the inertial frame so that at a given geographic location there is a daily variation in the ionospheric electric field due to this effect. As in the previous work, Region-1 and Region-2 currents are related, using the Hill-Siscoe transpolar potential model, to the solar wind data as measured at L1 by the ACE satellite. In this way, we intend to build a useful Space Weather Forecasting tool by which the time-dependent, solar-driven ionospheric electric field is defined at any geographic location. Rothwell, P. L., and J. R. Jasperse(2006) Modeling the connection of the global ionospheric electric fields to the solar wind, J. Geophys. Res., 111, A3211, Doi:10.1029/2004JA010992.

Rothwell, P. L.; Jasperse, J. R.; Grossbard, N. J.

2007-12-01

236

A prediction model for solar-driven ionospheric electric fields at arbitrary locations  

NASA Astrophysics Data System (ADS)

In an earlier work [Rothwell and Jasperse, 2006] we derived the global ionospheric electric field produced by the Region-1 and Region-2 currents. Despite the simplifying assumptions in that work of both the dipole and spin axis being aligned perpendicular to ecliptic plane we found significant agreement with Jicamarca vertical drift data. However, in order to extend the model to arbitrary geographic locations we now take into account 1) a nonspin-aligned magnetic dipole, as well as local IGRF modifications in the B-field, 2) a more accurate solardriven ionospheric conductance model, especially near the terminators, and 3) the Region-1 and Region-2 currents properly defined in magnetic coordinates. For example, the Region-1 and-2 currents are fixed in the inertial frame so that at a given geographic location there is a daily variation in the ionospheric electric field due to this effect. As in the previous work, Region-1 and Region-2 currents are related using the Hill-Siscoe transpolar potential model to the solar wind data as measured at L1 by the ACE satellite. In this way, we intend to build a useful Space Weather Forecasting tool by which the time-dependent, solar-driven ionospheric electric field is defined at any geographic location. Rothwell, P. L., and J. R. Jasperse(2006) Modeling the connection of the global ionospheric electric fields to the solar wind, J. Geophys. Res., 111, A3211, Doi:10.1029/2004JA010992.

Rothwell, Paul; Jasperse, John; Grossbard, Neil

237

International reference ionosphere 1990  

NASA Technical Reports Server (NTRS)

The International Reference Ionosphere 1990 (IRI-90) is described. IRI described monthly averages of the electron density, electron temperature, ion temperature, and ion composition in the altitude range from 50 to 1000 km for magnetically quiet conditions in the non-auroral ionosphere. The most important improvements and new developments are summarized.

Bilitza, Dieter; Rawer, K.; Bossy, L.; Kutiev, I.; Oyama, K.-I.; Leitinger, R.; Kazimirovsky, E.

1990-01-01

238

Ionosphere effects of tropical cyclones over the Asian region of Russia according to oblique radio-sounding data  

NASA Astrophysics Data System (ADS)

The possibility of manifestation of tropical cyclones in variations of ionospheric parameters in the zone far removed from the disturbance source region has been studied. The data from frequency analysis by maximal observed frequencies (MOF) for the oblique sounding (OS) signals were used. We revealed 1-5 h time intervals with higher oscillation energetics along the Norilsk-Irkutsk, Magadan-Irkutsk, and Khabarovsk-Irkutsk paths (Eastern Siberia and the Far East of Russia) during equinoctial periods (March, September 2005-2011), in November, 2005 and in summer 2010-2011 for different periods of the solar cycle. These time intervals may be interpreted as a manifestation of large-scale traveling ionospheric disturbances (TIDs) whose sources are atmospheric internal gravity waves. By jointly analyzing ionospheric, heliomagnetic, atmospheric, and satellite data on tropical cyclones (TCs), we attempted to associate the series of the revealed TIDs with ionospheric responses to TCs over the Western North Pacific Ocean during the above periods. A significant increase in wave disturbances on OS paths was established to be noted during active tropical cyclogenesis periods in autumn months. For spring equinox (March, 2005-2011), we also note TID manifestations in MOF time variations under quiet heliomagnetic conditions and in TC absence, but the intensity of these wave disturbances was significantly lower, than that of autumn seasons for various years. We estimated the wavelike disturbance propagation velocity by the delay time of TID passing the medium points of the spaced OS paths.

Chernigovskaya, Marina A.; Kurkin, Vladimir I.; Oinats, Alexey V.; Poddelsky, Igor N.

2014-11-01

239

Ionospheric Effects of Sudden Stratospheric Warming During Moderate-to-High Solar Activity: Case Study of January 2013  

NASA Astrophysics Data System (ADS)

A major and long-lasting sudden stratospheric warming occurred in January 2013 during moderate-to-high solar activity conditions. Analysis of experimental observations of ionospheric parameters during the winter of 2012/13 reveals strong ionospheric disturbances associated with this event. Anomalous variations in vertical ion drift measured at the geomagnetic equator at Jicamarca (12S, 75W) are observed for over 40 days from mid-December 2012 to the end of January 2013. We report strong perturbations in the total electron content (TEC) obtained with global network of GPS receivers. These perturbations maximize in the crests of equatorial ionization anomaly, reach 100% of the background TEC value, exhibit significant longitudinal and hemispheric asymmetry, and last for over 40 days. The magnitude of ionospheric anomalies in both vertical drifts and TEC during the January 2013 SSW is comparable to the anomalies observed during the record-strong SSW of January 2009 that coincided with extreme solar minimum. This observation contrasts with results of numerical simulations that predict a weaker ionospheric response to the tidal forcing during high solar activity due to the higher F-region Pedersen conductivity. The temporal behavior of anomalous variations in both vertical drift and TEC is consistent with the phase change of lunar semidiurnal tide and could result from the superposition of amplified solar and lunar tides.

Goncharenko, L. P.; Chau, J. L.; Condor Patilongo, P. J.; Coster, A. J.; Benkevitch, L. V.

2013-12-01

240

Multifractal behaviour of the ionospheric scintillation index time series over an Indian low latitude station Surat  

NASA Astrophysics Data System (ADS)

The amplitude scintillation information recorded by the GSV4004B GISTM (Global Ionospheric Scintillation TEC Monitor) GPS receiver at an Indian low latitude station Surat (21.16°N, 72.78°E) for 48 months during the years 2009, 2010, 2011 and 2012 are utilized in the present work. Multifractal detrended fluctuation analysis (MF-DFA) have been carried out along with computation of q-order fluctuation function, q-order Hurst exponent, q-order mass exponent and multifractal spectrums for each monthly post-sunset S4 index time series. The non-linear dependence of mass exponent and dependence of q-order Hurst exponent on q-values reflect the existence of nonlinear interaction between different scales and multifractal structure in the system, respectively. The comparison of broadness and shape of spectra with the occurrence of scintillation activities registered in the same period reveal the existence of multifractality/complexity in the turbulent ionosphere, which is influenced by the small-scale intermittency and solar flux indices. The truncation of the spectrum is the evidence of manifestation of small-scale intermittency of the turbulent ionosphere. The higher values of the Hölder exponent ?0, calculated from the spectrum, imply the irregular nature of the underlying process. The present study suggests that, MF-DFA may act as an important non-linear technique for identifying the effect of large and small-scale fluctuations in complex and turbulent ionosphere.

Tanna, H. J.; Pathak, K. N.

2014-03-01

241

Effects of VLF heating of ionosphere on the transmission cone of MF waves propagating from ground to space  

NASA Astrophysics Data System (ADS)

Global maps of VLF-MF waves observed by the low-altitude (~700 km) DEMETER satellite (Parrot et al., 2009) have pointed out localized enhancements of wave energy above the most powerful VLF transmitters and their conjugate regions, both in the 18-25 kHz frequency range (VLF transmitters) and in the 2.-2.5 MHz frequency range (emissions associated with lightning discharges). Under hypothesis made for the computation of the refractive index by the Appleton-Hartree formula, simulations are conducted to estimate the effect of VLF heating on the transmission cone of MF waves propagating from ground to space. The method used consists in the computation of the vertical variations of the Real part of the refractive index n and of the ? attenuation factor (? = ?. Imag(n)/c), with an IRI electron density profile derived from the geophysical parameters of a DEMETER orbit and an hybrid collision frequency model taking into account of theoretical and experimental data. Half-angles of the transmission cone are estimated: first, at the X=1 (X=fpe2/f2) low altitude boundary (where Ordinary mode waves may be converted into Extraordinary mode waves), and second, at the high-altitude X=1 boundary (where Extraordinary mode waves may be converted into Ordinary mode waves). It is shown that enhancements in the collision frequencies, produced by VLF heating at altitudes where the product of the collision frequency ? by the electronic density Ne is maximum (i.e. at altitudes including the low-altitude and the high-altitude X=1 boundaries), open the half angle of the transmission cones for MF waves which cross the ionosphere, and so explain enhancements of wave energy observed in the 2. - 2.5 MHz band above the powerful VLF transmitters and their conjugate regions.

Lefeuvre, F.; Pincon, J.; Parrot, M.

2012-12-01

242

Wenchuan Earthquake Ionospheric Precursors: Modeling and Experiment  

NASA Astrophysics Data System (ADS)

Early it was shown, that for strong middle-latitude earthquakes the effects in Total Electron Content (TEC) and in critical frequency of F2-layer (foF2) look like local changes in electron concentration which maxima are located in immediate proximity from epicenter area. Pre-cursory effects of strong near-equatorial earthquakes might be in the form of deepening and widening of electron concentration minimum over the magnetic equator and displacement of equatorial ionization anomaly crests. The problems of physical explanation of possible forma-tion mechanisms of the seismo-ionospheric effects are under discussion now. In Namgaladze et al., 2009 it has been come out with the assumption, that the most probable formation mech-anism of TEC disturbed areas, observable prior strong earthquakes, is the vertical transport of the F2-region ionospheric plasma under the zonal electric field action. The geomagnetic conjugacy of the earthquake ionospheric precursors and effects in equatorial anomaly which development is controlled by zonal electric field are strong arguments in favor of this hypoth-esis. Besides, the analysis of model calculation results with use of the Global Self-consistent Model of the Thermosphere, Ionosphere, Protonosphere (GSM TIP) in Namgaladze et al., 2009 testifies in favor of this hypothesis. There is a question how such electric fields can arise in the ionosphere prior to earthquakes? Now it is not answer to this question. Therefore, for understanding of formation mechanisms of earthquake ionospheric precursors it is necessary to understand the physics of lithosphere-atmosphere-ionosphere coupling prior to earthquake. Many researchers tried to solve this problem. However, until now there is not common opinion concerning to the lithosphere-atmosphere-ionosphere coupling prior to earthquake. Some ba-sic hypotheses for the explanation of this mechanism have been offered: the Internal Gravity Waves (IGWs) of seismogenic origin with the period 1-3 hours, the IGWs with the period from several minutes up to tens minutes, the seismogenic electric field with amplitude from units up to tens mV/m, the abnormal electromagnetic fields and emissions. However, the appearance of local large-scale seismo-ionospheric anomalies in TEC and foF2 it is possible to explain only by two of the mentioned mechanisms: an atmospheric electric field and/or small-scale IGWs. In this study, we present the numerical calculation results for reproduction of observed changes in the ionosphere prior to strong Wenchuan earthquake. This earthquake has been fixed on 12 May 2008. The geomagnetic activity indices for the period on 1-13 May were low. The calcu-lations of Wenchuan earthquake ionospheric precursors were carried out with use of the GSM TIP model. In calculations, the small-scale IGWs and/or the penetration of vertical electric field are considered as the formation mechanisms of earthquake ionospheric precursors. It was carried out the comparison of calculation results with experimental data of TEC and foF2 at various stations, located in China and nearby areas. The obtained results confirm the proposed mechanisms of seismo-ionospheric effect formation by small-scale IGWs and the penetration of the seismogenic vertical electric field from the atmosphere into the ionosphere. References Namgaladze A.A., Klimenko M.V., Klimenko V.V. and Zakharenkova I.E. Physical Mechanism and Mathematical Simulation of Ionosphere Earthquake Precursors Observed in Total Electron Content. Geomagnetism and Aeronomy, 2009, Vol. 49, 252-262.

Klimenko, Maxim; Klimenko, Vladimir; Zhao, Biqiang; Pulinets, Sergej; Zakharenkova, Irina; Bryukhanov, Valerij

243

HPM absorption caused by self-action phenomenon in the lower ionosphere  

Microsoft Academic Search

HPM may cause many non-linear effects when it propagates in the ionosphere. HPM self-action phenomenon is one of the nonlinear effects which could influence HPM propagation notably. This paper analyses self-action working mechanism and calculates HPM power density in the ionosphere quantitatively. The results have great referable value to HPM propagation research in the ionosphere.

Shao Ying; Niu Zhong-xia; Yang Jian-hong; Xing Zhao-wei; Cao Jin-kun

2005-01-01

244

Model of Jovian F region ionosphere (Saturnian ionosphere in offset dipole approximation)  

NASA Technical Reports Server (NTRS)

Researchers investigated the offset effect of Saturn's dipole on its ionosphere. The magnetic field of Saturn is primarily that of a dipole closely aligned to the rotational axis, but displaced northward from the center by a distance approximately equal to 0.05 R sub S, R sub S being the reference radius of Saturn. This offset effect would manifest itself most prominently between the ionospheric profiles in the Northern and Southern Hemispheres of Saturn.

Tan, A.

1991-01-01

245

Ionospheric response to traveling convection twin vortices  

SciTech Connect

Traveling convection twin vortices have been observed for several years. At ionospheric altitudes, the twin vortices correspond to spatially localized, transient structures embedded in a large-scale background convection pattern. The convection vortices are typically observed in the morning and evening regions. They are aligned predominantly in the east-west direction and have a horizontal extent of from 500-1000 km. Associated with the twin vortices are enhanced electric fields, particle precipitation, and an upward/downward field-aligned current pair. Once formed, the twin vortex structures propagate in the tailward direction at speeds of several km/s, but they weaken as they propagate and only last for about 10-20 minutes. Because these convection structures might have a significant effect on the localized ionosphere, the USU ionospheric model was used to calculate the response of the ionosphere to {open_quotes}representative{close_quotes} traveling convection twin vortices for a range of background conditions. The ionospheric response includes localized temperature enhancements, ion composition changes, non-Maxwellian ion distributions, and plasma upwelling events. The response is transient and the magnitude of the response depends on the background ionosphere conditions and on the characteristics of the twin vortices. 17 refs., 4 figs.

Schunk, R.W.; Zhu, L.; Sojka, J.J. [Utah State Univ., Logan, UT (United States)] [Utah State Univ., Logan, UT (United States)

1994-08-15

246

Saturn's ionosphere - Inferred electron densities  

NASA Astrophysics Data System (ADS)

During the two Voyager encounters with Saturn, radio bursts were detected which appear to have originated from atmospheric lightning storms. Although these bursts generally extended over frequencies from as low as 100 kHz to the upper detection limit of the instrument, 40 MHz, they often exhibited a sharp but variable low frequency cutoff below which bursts were not detected. We interpret the variable low-frequency extent of these bursts to be due to the reflection of the radio waves as they propagate through an ionosphere which varies with local time. We obtain estimates of electron densities at a variety of latitude and local time locations. These compare well with the dawn and dusk densities measured by the Pioneer 11 Voyager Radio Science investigations, and with model predictions for dayside densities. However, we infer a two-order-of-magnitude diurnal variation of electron density, which had not been anticipated by theoretical models of Saturn's ionosphere, and an equally dramatic extinction of ionospheric electron density by Saturn's rings. Previously announced in STAR as N84-17102

Kaiser, M. L.; Desch, M. D.; Connerney, J. E. P.

1984-04-01

247

Saturn's ionosphere: Inferred electron densities  

NASA Technical Reports Server (NTRS)

During the two Voyager encounters with Saturn, radio bursts were detected which appear to have originated from atmospheric lightning storms. Although these bursts generally extended over frequencies from as low as 100 kHz to the upper detection limit of the instrument, 40 MHz, they often exhibited a sharp but variable low frequency cutoff below which bursts were not detected. We interpret the variable low-frequency extent of these bursts to be due to the reflection of the radio waves as they propagate through an ionosphere which varies with local time. We obtain estimates of electron densities at a variety of latitude and local time locations. These compare well with the dawn and dusk densitis measured by the Pioneer 11 Voyager Radio Science investigations, and with model predictions for dayside densities. However, we infer a two-order-of-magnitude diurnal variation of electron density, which had not been anticipated by theoretical models of Saturn's ionosphere, and an equally dramatic extinction of ionospheric electron density by Saturn's rings.

Kaiser, M. L.; Desch, M. D.; Connerney, J. E. P.

1983-01-01

248

Analysis of the effects of ionospheric sampling of reflection points near-path, for high-frequency single-site-location direction finding systems. Master's thesis  

SciTech Connect

This thesis suggests a method to estimate the current value of an ionospheric parameter. The proposed method is based on the known variability of the observed current values near path and utilizes data derived from ionospheric sampling measurements. Analysis of errors is provided in Single-Site-Location High-Frequency Direction Finding (SSL-HFDF), arising from ionospheric irregularities such as Es (sporadic E), ionospheric tilts, and traveling ionospheric disturbances (TIDs). The characteristics of Es, tilts and TIDs for mid-latitudes are summarized in tables. The spatial and temporal coherence of ionospheric variabilities and irregularities is analyzed over the electron density. Practical results, measurements, and studies are presented on SSL-HFDF. A survey of characteristics of the ionosphere in the equatorial region is also provided. Finally, some recommendations are given to maximize the applicability of the proposed method.

Filho, C.A.

1990-12-01

249

Magnetic self-field effects on current collection by an ionospheric bare tether  

NASA Astrophysics Data System (ADS)

It was recently suggested that the magnetic field created by the current of a bare tether strongly reduces its own electron-collection capability when a magnetic separatrix disconnecting ambient magnetized plasma from tether extends beyond its electric sheath. It is here shown that current reduction by the self-field depends on the ratio L*/Lt parameterizing bias and current profiles along the tether (Lt ? tether length, L* ? characteristic length gauging ohmic effects) and on a new dimensionless number Ks involving ambient and tether parameters. Current reduction is weaker the lower Ks and L*/Lt, which depend critically on the type of cross section: Ks varies as R5/3, h2/3R, and h2/3 × 1/4 width for wires, round tethers conductive only in a thin layer, and thin tapes, respectively; L* varies as R2/3 for wires and as h2/3 for tapes and round tethers conductive in a layer (R ? radius, h ? thickness). Self-field effects are fully negligible for the last two types of cross sections whatever the mode of operation. In practical efficient tether systems having L*/Lt low, maximum current reduction in case of wires is again negligible for power generation; for deorbiting, reduction is <1% for a 10 km tether and ˜15% for a 20 km tether. In the reboost mode there are no effects for Ks below some threshold; moderate effects may occur in practical but heavy reboost-wire systems that need no dedicated solar power.

SanmartíN, J. R.; Estes, R. D.

2002-11-01

250

Ionospheric Variability and Storms on Mars  

NASA Technical Reports Server (NTRS)

The goal of this grant was to conduct the first-ever study of ionospheric variability on Mars. To do so, we used data from the Radio Science (RS) experiment onboard the Mars Global Surveyor (MGS) satellite. Dr. David Hinson of the RS team at Stanford University was a most helpful and valuable colleague throughout the studies we conducted. For the initial RS datasets available from the MGS mission, there were no severe storms caused by solar wind activity, so we concentrated on day-to-day effects. This turned out to be a wise approach since understanding "normal variability" had to be done before any claim could be made about "space weather" effects. Our approach was three-fold: (1) select a good dataset for characterization of ionosphere variability at Mars, one for which excellent terrestrial data were also available. This turned out to be the period 9-27 March 1999; (2) once the variability at Mars was described, develop and use a new photochemical model of the martian ionosphere to find the extent to which solar variability on those days caused or contributed to the observed patterns; (3) use the results from the above, together with additional datasets from the MGS/RS experiment, to describe some practical consequences that the martian ionosphere would have upon NASA s proposed navigation and communications systems for Mars. The results of these studies showed that: (a) solar variability is the dominant source of ionospheric variability at Mars (during periods of quiet solar wind), (b) that current models do a good job in portraying such effects at the height of the ionospheric peak electron density, and (c) that ionospheric structure on Mars can affect attempts at precise position-fixing at Mars should relatively high (GPS-like) frequencies not be used in a Mars communications and navigation system.

Mendillo, Michael

2004-01-01

251

On the Convergence of Ionospheric Constrained Precise Point Positioning (IC-PPP) Based on Undifferential Uncombined Raw GNSS Observations  

PubMed Central

Precise Point Positioning (PPP) has become a very hot topic in GNSS research and applications. However, it usually takes about several tens of minutes in order to obtain positions with better than 10 cm accuracy. This prevents PPP from being widely used in real-time kinematic positioning services, therefore, a large effort has been made to tackle the convergence problem. One of the recent approaches is the ionospheric delay constrained precise point positioning (IC-PPP) that uses the spatial and temporal characteristics of ionospheric delays and also delays from an a priori model. In this paper, the impact of the quality of ionospheric models on the convergence of IC-PPP is evaluated using the IGS global ionospheric map (GIM) updated every two hours and a regional satellite-specific correction model. Furthermore, the effect of the receiver differential code bias (DCB) is investigated by comparing the convergence time for IC-PPP with and without estimation of the DCB parameter. From the result of processing a large amount of data, on the one hand, the quality of the a priori ionosphere delays plays a very important role in IC-PPP convergence. Generally, regional dense GNSS networks can provide more precise ionosphere delays than GIM and can consequently reduce the convergence time. On the other hand, ignoring the receiver DCB may considerably extend its convergence, and the larger the DCB, the longer the convergence time. Estimating receiver DCB in IC-PPP is a proper way to overcome this problem. Therefore, current IC-PPP should be enhanced by estimating receiver DCB and employing regional satellite-specific ionospheric correction models in order to speed up its convergence for more practical applications. PMID:24253190

Zhang, Hongping; Gao, Zhouzheng; Ge, Maorong; Niu, Xiaoji; Huang, Ling; Tu, Rui; Li, Xingxing

2013-01-01

252

Using IRI for the computation of ionospheric corrections for altimeter data analysis  

Microsoft Academic Search

Measurements by single-frequency satellite altimeter (Geosat, ERS-1) require a ionospheric correction to account for the signal time delay in the ionosphere. We propose using the International Reference Ionosphere (IRI) for the determina-tion of this time delay. To investigate the effectiveness of an IRI correction, we have compared the IRI values with ionospheric corrections deduced from measurements by the dual-frequency Topex

D. Bilitza; C. Koblinsky; B. Beckley; S. Zia; R. Williamson

1995-01-01

253

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

SciTech Connect

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.

Eccles, V.; Armstrong, R.

1993-05-01

254

The Ionospheric-Thermospheric Component of the LWS-Geospace Program  

Microsoft Academic Search

The Geospace Mission Definition Team report made a persuasive case for investigating the ionosphere-thermosphere system with both LEO in situ instruments and GEO ionospheric imaging. The GMDT science objectives were derived from the Living With a Star Science Architecture Team's consideration of space weather effects that concern society. The two highest priority ionospheric objectives are \\

P. M. Kintner

2005-01-01

255

Preparation of a Database for the Study of Scaling Phenomena in the Ionosphere  

E-print Network

, neutral wind velocity). Its time-scales vary from short periods (minutes ­ e.g., Travelling IonosphericPreparation of a Database for the Study of Scaling Phenomena in the Ionosphere Z. Mosna1,2 , P. The correct forecast of the state of the ionosphere requires understanding of all the effects which influence

Santolik, Ondrej

256

Modification of the low-latitude ionosphere before the 26 December 2004 Indonesian earthquake  

Microsoft Academic Search

This paper investigates the features of pre-earthquake ionospheric anomalies in the total electron content (TEC) data obtained on the basis of regular GPS observations from the IGS network. For the analysis of the ionospheric effects of the 26 December 2004 Indonesian earthquake, global TEC maps were used. The possible influence of the earthquake preparation processes on the main low-latitude ionosphere

I. E. Zakharenkova; A. Krankowski; I. I. Shagimuratov

2006-01-01

257

Impact of lightning on the lower ionosphere of Saturn and possible generation of halos and sprites  

E-print Network

Impact of lightning on the lower ionosphere of Saturn and possible generation of halos and sprites 2014 Accepted 24 June 2014 Available online 3 July 2014 Keywords: Saturn Lightning Ionospheres a b s t r a c t We study the effect of lightning on the lower ionosphere of Saturn. A self-consistent one

Ebert, Ute

258

Effects of chemical releases by the STS-3 Orbiter on the ionosphere  

NASA Technical Reports Server (NTRS)

The Plasma Diagnostics Package, flown aboard STS-3 as part of the first Shuttle payload (OSS-1), recorded the effects of various chemical releases from the Orbiter. Changes in the plasma environment was observed during flash evaporator system releases, water dumps and maneuvering thruster operations. During flash evaporator operations, broadband Orbiter-generated electrostatic noise was enhanced and plasma density irregularities were observed to increase by 3 to 30 times with a spectrum which rose steeply and peaked below 6 Hz. In the case of water dumps, background electrostatic noise was enhanced at frequencies below about 3 kHz and suppressed at frequencies above 2 kHz. Thruster activity also stimulated electrostatic noise with a spectrum which peaked at approximately 0.5 kHz. In addition, ions with energies up to 1 keV were seen during some thruster events.

Pickett, J. S.; Murphy, G. B.; Kurth, W. S.; Goertz, C. K.; Shawhan, S. D.

1983-01-01

259

The Effects of Presentation Order in Multitrial Free Recall.  

ERIC Educational Resources Information Center

The experiment tested the effects of presentation word orders in a multitrial free-recall task. Three types of presentation were used: (1) randomized; (2) constant order; and (3) maintained order (maintenance of subjects order of recall on the subsequent presentation). In addition, the effects of number of recalls per presentation (1 or 3) were…

Maitland, Anthony J.

260

Mitigation and exploitation of the ionosphere: A military perspective  

Microsoft Academic Search

The ionosphere is a critical element in the design and operation of many military RF systems. While judicious engineering choices, such as transmission frequency, can mitigate many ionospheric effects, the research scientist and engineer are being asked to meet ever more demanding operational requirements. These, in turn, require ever more sophisticated situational awareness, mitigation, and exploitation techniques, which are being

Paul S. Cannon

2009-01-01

261

Observing rapid quasi-wave ionospheric disturbance using amplitude charts  

NASA Astrophysics Data System (ADS)

Data from vertical (quasi-vertical) sounding are traditionally used for determining a number of ionospheric parameters such as critical frequencies of E and F layers, peaks of these layers, and for reconstructing electron density profiles. In this respect, radio sounding is not used to its full capacity. Modern ionosondes provide additional information encoded in ionospheric echoes, including information on reflected-signal amplitude. The time dependence of the amplitude-frequency characteristic of reflected signal has been named "amplitude chart" (A-chart). Ionosondes used by the ISTP SB RAS Geophysical Observatory for constructing A-charts employ the frequency-modulated continuous-wave (FMCW) signal in a range 1.3-15 MHz. One-minute sounding interval allows a more detailed study of dynamic processes in the ionosphere. The ionosonde has a direct digital synthesizer and direct sampling receiver without automatic gain control (AGC). The absence of AGC and the high dynamic range enable determination of the relative field strength at a receiving point and registration of relative long-term variations in reflected-signal amplitude over the entire range of operating frequencies of the ionosonde. We have revealed that the passage of travelling ionospheric disturbances (TID) along with height-frequency distortion modulates amplitude characteristics of signal. The characteristic depth of the modulation reaches 40 dB. The pronounced alternate vertical stripes typical for A-charts are likely to be associated with focusing properties of TID. In order to examine the space-time structure of TID able to induce such a focusing of the radio waves, we performed ray tracing simulations. We used geometrical-optics approximation, took magneto-ionic effects into account and prescribed electron density to be a stratified electron density profile on which an undulating disturbance was superimposed. This work was supported by the RFBR grant ?14-05-00259-?.

Kurkin, Vladimir; Laryunin, Oleg; Podlesnyi, Alexey

262

Verification of ionospheric sensors  

NASA Astrophysics Data System (ADS)

Ionospheric products from sensors and models were compared to investigate strengths and limitations of each. Total electron content data from computerized ionospheric tomography (CIT) and TOPEX sensors in the Caribbean region in 1997 were compared to estimates produced by models Parameterized Ionospheric Model (PIM) and Raytrace/ICED-Bent-Gallagher (RIBG) and global maps from GPS. A 5 total electron content unit (TECU) bias was observed in TOPEX. CIT and TOPEX confirmed the location and structure of the equatorial anomaly. A GPS map confirmed the location of the anomaly but did not reproduce structure less than 1000 km in latitude and 1500 km in longitude and underestimated TEC by at least 11 TECU or 25%. PIM positioned the anomaly 13° equatorward of its observed location and greatly underestimated (˜50%) the rise in content over 5°-25°N range. RIBG overestimated the latitudinal extent of the anomaly and underestimated TEC at the peak by 40%. Additional comparisons were made using CIT and ionosonde sensors at midlatitude during the summer of 1998. Fourteen days of TEC, hmF2, NmF2, and half-thickness comparisons showed reasonable agreement between CIT and ionosonde for TEC and NmF2. The hmF2 and half-thickness comparisons were contaminated by noise, which accounted for a significant portion of the ionospheric variation. Daytime cases where CIT overestimated maximum density were attributed to underestimating layer thickness. Finally, TOPEX and multiple GPS sensors were compared to verify regional ionospheric conditions associated with occurrence of nighttime ionospheric depletions in the Caribbean during Combined Ionospheric Campaigns in June of 1998. From 0300 to 0800 UT on June 26, GPS and TOPEX showed elevated nighttime content over the entire Caribbean region. Vertical TEC approached 25 TECU in some places with interspersed depletions, which in some cases evacuated nearly the entire ionospheric content.

Coker, Clayton; Kronschnabl, Glenn; Coco, David S.; Bust, Gary S.; Gaussiran, Thomas L., II

2001-01-01

263

37 CFR 251.57 - Effective date of order.  

Code of Federal Regulations, 2010 CFR

...of Copyright Arbitration Royalty Panels § 251.57 Effective date of order. An order of determination issued by the Librarian under § 251.56 shall become effective 30 days following its publication in the Federal Register , unless an appeal...

2010-07-01

264

Solar wind effect on Joule heating in the high-latitude ionosphere  

NASA Astrophysics Data System (ADS)

The effect of solar wind on several electrodynamic parameters, measured simultaneously by the European Incoherent Scatter (EISCAT) radars in Tromsø (TRO, 66.6° cgmLat) and on Svalbard (ESR, 75.4° cgmLat), has been evaluated statistically. The main emphasis is on Joule heating rate QJ, which has been estimated by taking into account the neutral wind. In addition, a generally used proxy QE, which is the Pedersen conductance times the electric field squared, has been calculated. The most important findings are as follows. (i) The decrease in Joule heating in the afternoon-evening sector due to winds reported by Aikio et al. (2012) requires southward interplanetary magnetic field (IMF) conditions and a sufficiently high solar wind electric field. The increase in the morning sector takes place for all IMF directions within a region where the upper E neutral wind has a large equatorward component and the F region plasma flow is directed eastward. (ii) At ESR, an afternoon hot spot of Joule heating centered typically at 14-15 magnetic local time (MLT) is observed during all IMF conditions. Enhanced Pedersen conductances within the hot spot region are observed only for the IMF Bz + /By- conditions, and the corresponding convection electric field values within the hot spot are smaller than during the other IMF conditions. Hence, the hot spot represents a region of persistent magnetospheric electromagnetic energy input, and the median value is about 3 mW/m2. (iii) For the southward IMF conditions, the MLT-integrated QE for By- is twice the value for By+ at TRO. This can plausibly be explained by the higher average solar wind electric field values for By-.

Cai, L.; Aikio, A. T.; Nygrén, T.

2014-12-01

265

LEISA: CubeSat for Ionospheric Characterization  

NASA Astrophysics Data System (ADS)

The University of New Mexico / Configurable Space Microsystems Innovation and Applications Center (COSMIAC) is designing a highly affordable research satellite called LEISA (Low Earth Ionospheric Spectrum Analyzer) to characterize Ionospheric properties that affect electromagnetic wave propagation. By measuring spectral distortion of both natural and man-made impulses LEISA will measure Total Electron Content (TEC), magnetic field strength, refractive effects, plasma properties, and higher-order electron density profile effects. Additionally, LEISA may shed light on the relationships between lightning effects and thunderstorm weather in the troposphere and the potential relationship between the acoustic/seismic events around thunderstorms and Ionospheric weather. The LEISA design effort has led to a number of innovations that may be relevant to other small science spacecraft. The design is particularly challenging because of the need to implement broadband RF reception from 20-200 MHz as well as to capture and process the resulting signals within a 1u spacecraft (10cm x 10cm x 10cm) with less than 2 watts of average available power. One particular challenge is the deployable electrically small biconic wideband UHF antenna that deploys to approximately 1.5m in length and .5 m in width. The resulting antenna system deploys from a diminutive 500 cubic centimeter volume. The remaining electronics must fit within the remaining 500 cubic centimeters, leading the team to develop a system-on-a-chip (SoC) design using a Xilinx Spartan 6 FPGA. The resulting circuit handles the spectrogram capture as well as all command and data handling functions within an average power footprint of approximately 200mW, reserving energy for analog-to-digital conversion (ADC) during capture events. LEISA builds upon prior work by Los Alamos National Laboratory with FORTE and Cibola Flight Experiment. In addition to being much more affordable, LEISA offers the potential of geo-locating events to within approximately 1km, which is useful for inverting the key scientific findings from collected data. The project provides rich research opportunities for undergraduates including FPGA design, deployable systems, RF design, data analysis, antenna design, digital signal processing, filter design, power reduction techniques, and networking and communications.

Suddarth, S. C.; Vera, A.; Pollard, H.; Burgett, T.; King, B.; Hulem, D.; MacGillivray, J.; Montoya, M.; Stanton, W.; Trujillo, B.; Wilson, S.; Heileman, G.

2012-12-01

266

Feedback instability of the ionospheric resonant cavity  

NASA Technical Reports Server (NTRS)

A model is developed that provides a theoretical basis for previous numerical results showing a feedback instability with frequencies characteristic of Alfven travel times within the region of the large increase of Alfven speed above the ionosphere. These results have been extended to arbitrary ionospheric conductivity by developing a numerical solution of the cavity dispersion relation that involves Bessel functions of complex order and argument. It is concluded that the large contrast between the magnetospheric and ionospheric Alfven speed leads to the formation of resonant cavity modes with frequencies ranging from 0.1 to 1 Hz. The presence of the cavity leads to a modification of the reflection characteristics of Alfven waves with frequencies that compare to the cavity's normal modes.

Lysak, Robert L.

1991-01-01

267

Novel Modeling of Mars' Ionospheric Electrodynamics  

NASA Astrophysics Data System (ADS)

The complex interaction between Mars' unique crustal magnetic fields and upper atmospheric electrons, ions and neutrals leads to the formation of currents in the ionospheric dynamo region (i.e., where electrons are magnetized but ions are collisional). These interactions involve elastic and inelastic collisions between ions, electrons and neutrals in the presence of varying bulk motion, pressures, temperatures and densities. In addition, the inherent inhomogeneities in the crustal field causes open and closed magnetic field regions to be in very close proximity. The resulting 'patchy' ionosphere varies on spatial scales of ? ˜100 km. These conditions make it impossible to derive an analytical solution of these ionospheric currents. Here we present the methodology, validation and preliminary results of a novel model of Mars' ionospheric currents. The model performs three-dimensional, multi-fluid, self-consistent simulations of electrodynamics in the region of Mars' ionosphere (˜75-400 km altitude), where differential motion between ions and electrons occurs. Our work is built upon a multi-fluid plasma dynamic model that tracks three ions species (O2+, CO2+, and O+) and electrons. This method applies equations for conservation of mass, conservation of momentum, charge neutrality, and time-dependent pressure for ion species and electrons while simultaneously solving the generalized Ohm's Law and Maxwell-Ampere equation for the electric and magnetic fields. Incorporated into these equations are the aforementioned collisional interactions between the ions, electrons and neutrals. Our results demonstrate the feasibility of a self-consistent model of Mars' ionospheric electrodynamics, and focus on a thorough and methodic validation of each aspect of the model. Our goal is to build a solid ground for the study of the effects of thermospheric neutral winds, magnetic topologies, and day-night variations on the formation and evolution of ionospheric currents on Mars.

Riousset, J. A.; Paty, C. S.; Lillis, R. J.; Fillingim, M. O.; England, S.; Withers, P.

2011-12-01

268

GBAS ionospheric threat model validation: Characterising ionospheric storms in the Australian region  

NASA Astrophysics Data System (ADS)

Uncorrected ionospheric delay, and its equivalent parameter Total Electron Content (TEC), is the largest source of error for single-frequency GPS applications. In particular, spatial and temporal gradients in TEC provide a non-uniform source of error that is difficult to resolve or correct using simple climatological ionospheric models. Differential or augmented GPS sys-tems suffer increased spatial de-correlation under strong TEC gradients thereby reducing their effective range. The range of anomalous TEC gradients and their effects on GPS augmenta-tion systems, such as GBAS and WAAS, in Conterminus United States (CONUS) has been established. A comparable study of Southern Hemisphere regions, in particular the Australian longitude sector, has not been published. In this study, a validation of the ionospheric threat model within GBAS (Ground-Based Augmentation System) was undertaken in the context of ionospheric storm conditions found in the Australian region. The range of anomalous TEC gradients occurring during ionospheric superstorms over the last solar cycle and their projected impact on a GBAS installation in Australia was quantified. The results are presented in the context of comparable observations from the Northern Hemisphere. Regional characteristics of ionospheric storms in the southern hemisphere, particularly those storm features commonly associated with anomalous TEC gradients, are also presented.

Terkildsen, Michael

269

Positive Phase Ionospheric Storms at Geophysically-Equivalent Sites  

NASA Astrophysics Data System (ADS)

At the longitudes of the dipole tilt, the ionosphere experiences a blend of processes governed by the difference (D) between geomagnetic and geographic latitudes. Magnetosphere-ionosphere coupling is maximized where D is most positive and solar induced photo-chemical processes are strongest where D is most negative. The Dmax cases occur in the North American Atlantic sector and in the Australian sector in the southern hemisphere. At these locations, coupling effects caused by penetration electric fields produce extreme examples of positive phase ionospheric storms. We have studied 206 ionospheric storm periods during solar cycle #20 (1964-1976) using ionosonde data from Wallops Island (VA) and Hobart (Tasmania), augmented by additional observations made in Christchurch (New Zealand). We find that the average patterns of the “dusk effect” that occur early in an ionospheric storm occur consistently at geophysically-equivalent sites with magnitudes that scale with the difference between geomagnetic and geographic latitudes.

Mendillo, M.; Narvaez, C. L.

2009-12-01

270

Plasma interactions in Titan's ionosphere  

NASA Astrophysics Data System (ADS)

The Cassini mission has collected vast amounts of in situ data within the ionosphere of Saturn's moon Titan and has shown the complexity of the interaction of Saturn's magnetospheric plasma with Titan. Models of the interactions have been created; however, none have been able to completely describe the observed phenomena. Most notably, modeled electron densities are much larger than the electron densities observed by instruments aboard the Cassini spacecraft. This thesis will explore the possible causes of this discrepancy between measured and modeled electron densities using models calculating the production of ions due to solar photons and magnetospheric electrons precipitating down magnetic field lines and into the ionosphere, temperature calculations of the thermal electron population (electrons with energies less than 2 eV), and chemical reactions in the ionosphere. The results of these models will be compared to data collected by instruments aboard Cassini. Modeled ion production rates and thermal electron temperature profiles will be shown to be in good agreement with ion production rates derived from data collected by the Ion -- Neutral Mass Spectrometer (INMS) and electron temperatures measured by the Radio and Plasma Wave Science -- Langmuir Probe above 1000 km. Modeled ion mass spectra will be generated near the ionospheric peak and will be compared with the INMS measured mass spectra to examine the effects of chemical loss processes on the ion densities. From this analysis it will be shown that the overabundance of modeled electrons is not caused by over production of ions and that chemical loss processes, predominantly the electron dissociative recombination coefficient of HCNH+, need to be reexamined. After the model has been proven to reproduce accurate profiles of ion production and temperature, ion production profiles will be generated using solar photons and magnetospheric electron fluxes for four canonical cases detailed in the work of Rymer et al. [2009] and a globally averaged model of the neutral densities based on INMS neutral measurements from more than 30 flybys of Titan. These generic profiles can be combined to predict ionospheric observations made by the Cassini spacecraft for a variety of solar zenith angles and magnetospheric conditions.

Richard, Matthew Scott

271

Regional ionospheric TEC modelling; working towards mapping Africa's ionosphere  

Microsoft Academic Search

Currently the available data over the African continent does not allow for the construction of a truly representative ionospheric map for the purposes of long term predictions. In addition, the forecasting of the ionospheric variability over long term is a complicated task. This is because the ionospheric medium is continuously changing, it exhibits behavior that is not easily predictable and

John Bosco Habarulema; Lee-Anne McKinnell; Ben Opperman

2011-01-01

272

Robust detection of ionospheric irregularities  

NASA Technical Reports Server (NTRS)

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.

Walter, T.; Hansen, A.; Blanch, J.; Enge, P.; Mannucci, T.; Pi, X.; Sparks, L.; Iijima, B.; El-Arini, B.; Lejeune, R.; Hagen, M.; Altshuler, E.; Fries, R.; Chu, A.

2000-01-01

273

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

NASA Astrophysics Data System (ADS)

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.

Cornely, P.; Daniell, R. E.

2013-12-01

274

Magnetosphere-ionosphere waves  

NASA Astrophysics Data System (ADS)

Self-consistent electrodynamic coupling of the ionosphere and magnetosphere produces waves with clearly defined properties, described here for the first time. Large scale (ideal) disturbances to the equilibrium, for which electron inertia is unimportant, move in the direction of the electric field at a characteristic speed. This may be as fast as several hundred meters per second or approximately half the E × B drift speed. In contrast, narrow scale (strongly inertial) waves are nearly stationary and oscillate at a specific frequency. Estimates of this frequency suggest periods from several tenths of a second to several minutes may be typical. Both the advection speed and frequency of oscillation are derived for a simple model and depend on a combination of ionospheric and magnetospheric parameters. Advection of large scale waves is nonlinear: troughs in E-region number density move faster than crests and this causes waves to break on their trailing edge. Wavebreaking is a very efficient mechanism for producing narrow (inertial) scale waves in the coupled system, readily accessing scales of a few hundred meters in just a few minutes. All magnetosphere-ionosphere waves are damped by recombination in the E-region, suggesting that they are to be best observed at night and in regions of low ionospheric plasma density. Links with observations, previous numerical studies and ionospheric feedback instability are discussed, and we propose key features of experiments that would test the new theory.

Russell, A. J. B.; Wright, A. N.

2012-01-01

275

Local ionospheric corrections derived from GNSS - A case study with TerraSAR-X  

NASA Astrophysics Data System (ADS)

Germany's synthetic aperture radar (SAR) satellites TerraSAR-X and TanDEM-X belong to the latest generation of radar satellites which have moved radar remote sensing to a new level. Besides being an all weather and all day imaging system, radar remote sensing offers various advanced methods like SAR interferometry or persistent scatterer interferometry that exploit magnitude and phase information of the radar signal. In order to achieve centimeter to millimeter accuracy with these advanced methods, all occurring error contributions (internal signal delay, orbit, troposphere, ionosphere, solid earth tides, loading effects, ...) have to be taken into account by applying appropriate corrections. Within the project DLR@Uni funded by the German Helmholtz Association HGF, an experimental framework at Wettzell station has been set up to perform a detailed analysis of all the corrections required for high resolution radar satellites and to achieve the goal of a 1cm precision level for absolute radar coordinates. This framework involves a 1.5 meter corner reflector (CR), a 1.5 year series of data takes from TerraSAR-X, and it makes use of the multi-sensor environment of Wettzell station. Besides Satellite Laser Ranging (SLR) for orbit assessment and the local geodetic network to control the CR reference coordinates, the Wettzell GNSS receivers are used for generating tropospheric and ionospheric corrections. By comparing the reference radar times (range and azimuth) available from geodetic survey with those from the TerraSAR-X data takes, the quality of the corrections can be investigated. Although often being considered negligible for X-band observations, the conducted experiment has clearly shown the necessity for ionospheric corrections, if the capabilities of current SAR satellites are to be fully exploited. For every TerraSAR-X data take, the ionospheric impact was derived from the geometry-free linear combination of the GNSS measurements and modeled in terms of vertical Total Electron Content (vTEC). By mapping this locally observed ionosphere to the TerraSAR-X range geometry and performing this procedure for each pass, a significant improvement in the comparison of the ranging times was achieved. In particular the 30 seconds temporal sampling of the regional vTEC modeling gives an advantage over the GNSS based global vTEC maps issued by the Center for Orbit Determination in Europe (CODE), which are sampled by 2 hours. Another important element regarding ionospheric corrections is the vertical extent of the ionosphere. Like many other low earth orbiting satellites, TerraSAR-X orbits are still within the ionosphere, and thus a separation into top-side and bottom-side ionosphere is required. For doing so, an approach for estimating the top-side vTEC from the TerraSAR-X dual-frequency GPS receiver data was implemented. As a result, the procedure yields top-side reduction values for the total ionospheric corrections obtained from ground-based GNSS. Although being still experimental, this concept already indicates its usefulness during times of increased ionospheric activity. After considering the ionosphere by the outlined methods and taking into a account all the other contributions for the TerraSAR-X SAR system, a range measurement accuracy of 1 cm was achieved for the CR in Wettzell.

Gisinger, Christoph; Balss, Ulrich; Cong, Xiao Ying; Steigenberger, Peter; Eineder, Michael; Pail, Roland; Hugentobler, Urs

2013-04-01

276

Research Spotlight: IRI model overestimated electron density in ionosphere  

NASA Astrophysics Data System (ADS)

Electron density in the Earth's ionosphere, which affects satellites and communications, is highly variable. Solar activity, which increases and decreases on an approximately 11-year cycle, is a key driver of this ionospheric variability. The most recent solar minimum was unusually prolonged, leading to changes in the ionosphere. Did models accurately capture the effects of the long solar minimum on ionospheric electron density? To find out, Lühr and Xiong compared electron density predictions from the frequently used international reference ionosphere (IRI) model with in situ satellite measurements from Challenging Minisatellite Payload (CHAMP) and Gravity Recovery and Climate Experiment (GRACE) for the years 2000-2009. (Geophysical Research Letters, doi:10.1029/2010GL045430, 2010)

Tretkoff, Ernie

2011-01-01

277

Ionospheric calibration for single frequency altimeter measurements  

NASA Technical Reports Server (NTRS)

This study is a preliminary analysis of the effectiveness (in terms of altimeter calibration accuracy) of various ionosphere models and the Global Positioning System (GPS) to calibrate single frequency altimeter height measurements for ionospheric path delay. In particular, the research focused on ingesting GPS Total Electron Content (TEC) data into the physical Parameterized Real-Time Ionospheric Specification Model (PRISM), which estimates the composition of the ionosphere using independent empirical and physical models and has the capability of adjusting to additional ionospheric measurements. Two types of GPS data were used to adjust the PRISM model: GPS receiver station data mapped from line-of-sight observations to the vertical at the point of interest and a grid map (generated at the Jet Propulsion Laboratory) of GPS derived TEC in a sun-fixed longitude frame. The adjusted PRISM TEC values, as well as predictions by the International Reference Ionosphere (IRI-90), a climatological (monthly mean) model of the ionosphere, were compared to TOPEX dual-frequency TEC measurements (considered as truth) for a number of TOPEX sub-satellite tracks. For a 13.6 GHz altimeter, a Total Electron Content (TEC) of 1 TECU 10(exp 16) electrons/sq m corresponds to approximately 0.218 centimeters of range delay. A maximum expected TEC (at solar maximum or during solar storms) of 10(exp 18) electrons/sq m will create 22 centimeters of range delay. Compared with the TOPEX data, the PRISM predictions were generally accurate within the TECU when the sub-satellite track of interest passed within 300 to 400 km of the GPS TEC data or when the track passed through a night-time ionosphere. If neither was the case, in particular if the track passed through a local noon ionosphere, the PRISM values differed by more than 10 TECU and by as much as 40 TECU. The IRI-90 model, with no current ability to unseat GPS data, predicted TEC to a slightly higher error of 12 TECU. The performance of PRISM is very promising for predicting TEC and will prove useful for calibrating single frequency altimeter height measurements for ionospheric path delay. When adjusted to the GPS line-of-sight data the PRISM URSI empirical model predicted TEC over a day's period to within a global error of 8.60 TECU rms during a nighttime ionosphere and 9.74 TECU rms during the day. When adjusted to the GPS derived TEC grid, the PRISM parametrized model predicted TEC to within an error of 8.47 TECU rms for a nighttime ionosphere and 12.83 TECU rms during the day. However, the grid cannot be considered globally due to the lack of sufficient numbers of GPS stations and large latitude gaps in GPS data. It is the opinion of the authors that using the PRISM model and adjusting to the global sun-fixed TEC grid regenerated with a localized weighted interpolation offers the best possibility of meeting the 10 TECU global rms (or 2 cm at 13.6 GHz) ionosphere range correction accuracy requirement of TOPEX/Poseidon and should be the subject of further study. However, it is clear that the anticipated requirement of 34 TECU global rms for TOPEX/Poseidon Follow-On (corresponding to the TOPEX/Poseidon performance) can not be met with any realizable combination of existing models and data assimilation schemes.

Schreiner, William S.; Born, George H.; Markin, Robert E.

1994-01-01

278

Experimental evidence of electromagnetic pollution of ionosphere  

NASA Astrophysics Data System (ADS)

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 multiple low orbiting satellites have confirmed a significant increase in their intensity over the populated areas of Europe and Asia. Recently, there are many experimental evidences of the existence of power line harmonic radiation (PLHR) in the ionosphere. Their spectra consist of succession of 50 (60) Hz harmonics which is accompanied by a set of lines separated by 50 (60) or 100 (120) Hz - the central frequency of which is shifted to high frequency. These lines cover rather wide band - according to the available experimental data, their central frequencies are observed from ~1.5 - 3 kHz up to 15 kHz, and recently the main mains frequencies are also observed. The examples of power line harmonic radiation, which were detected by “Sich-1M”, “Chibis-M” and “Demeter” satellites, have been presented and discussed. The available experimental data, as well as theoretical estimations, allow us with a high degree of certainty to say that the permanent satellite monitoring of the ionospheric and magnetospheric anthropogenic EM perturbations is necessary for: a) objective assessment and prediction of the space weather conditions; b) evaluation of the daily or seasonal changes in the level of energy consumption; c) construction of a map for estimation of near space EM pollution. This study is partially supported by SSAU contract N 4-03/13.

Pronenko, Vira; Korepanov, Valery; Dudkin, Denis

279

Ionospheric correction of space radar data  

NASA Astrophysics Data System (ADS)

Radar is a critical tool for maintaining knowledge of the many objects in low Earth orbit and thus for maintaining confidence that societies around the world are secure against a variety of space-based threats. It is therefore important to raise awareness that LEO objects are embedded in the envelope of relatively dense plasma that co-rotates with the Earth (ionosphere-plasmasphere system) and thus accurate tracking must correct for the group delay and refraction caused by that system. This paper seeks to promote that awareness by reviewing those effects and high-lighting key issues: the need to customise correction to the altitude of the tracked object and prevailing space weather conditions, that ionospheric correction may be particularly important as an object approaches reentry. The paper outlines research approaches that should lead to better techniques for ionospheric correction and shows how these might be pursued in the context of the EURIPOS initiative.

Hapgood, Mike

2010-06-01

280

Beacon satellite receiver for ionospheric tomography  

NASA Astrophysics Data System (ADS)

We introduce a new coherent dual-channel beacon satellite receiver intended for ionospheric tomography. The measurement equation includes neutral atmosphere and ionosphere propagation effects, relative errors in satellite and receiver clocks, and residual Doppler shifts caused by errors in the satellite ephemeris. We also investigate the distribution of errors for phase curve measurements and the use of phase curve measurements for limited angle tomography using the framework of statistical linear inverse problems. We describe the design of our beacon satellite receiver software and present one possible hardware configuration. Finally, we present results obtained using a network of four newly developed receivers and compare the results with those of an existing ionospheric tomography network at Sodankylä Geophysical Observatory.

Vierinen, J.; Norberg, J.; Lehtinen, M. S.; Amm, O.; Roininen, L.; Väänänen, A.; Erickson, P. J.; McKay-Bukowski, D.

2014-12-01

281

Ionospheric tomography using the FORTE satellite  

SciTech Connect

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.

Murphy, T.C.

1993-08-01

282

COSMIC-2: A Platform for Advanced Ionospheric Observations  

NASA Astrophysics Data System (ADS)

The equatorial component of the COSMIC-2 program will consist of 6 satellites to be flown in a 24 degree inclination/520 km altitude orbit. In addition to the primary GNSS radio occultation (RO) payload, to be provided by JPL, the USAF plans to fly a pair of space weather sensors: a multi-frequency radio beacon and the Velocity, Ion Density and Irregularities (VIDI) in-situ plasma sensor package. Together, these three instruments will provide data to address key issues related to the specification and forecast of ionospheric densities and the instabilities/irregularities associated with ionospheric scintillation. The TriG GNSS receiver will provide a substantial increase in the number of daily ionospheric observations relative to COSMIC-1, both in the RO limb-viewing and overhead geometries. These data will provide a significant improvement of assimilative model capabilities for providing accurate ionospheric specifications in the important equatorial region. In addition, TriG will make routine measurements of ionospheric scintillation at L-band frequencies, as pioneered by the CORISS instrument on C/NOFS. The radio beacon, together with a network of ground receivers, will enable direct measurement of scintillation effects on trans-ionospheric signal propagation across the UHF to S-band frequency spectrum. The VIDI sensors will measure the in-situ density depletions associated with scintillation-producing irregularities. Together, the beacon, TriG, and VIDI will provide an unprecedented ability to map equatorial ionospheric instabilities and their effects. The in-situ package will also provide observations of plasma drifts from which electric fields, the most important physical driver for equatorial ionospheric structure, can be inferred. This will enable advancements in ionospheric models to further improve specifications and forecasts. In addition to discussing ionospheric science and operational support aspects of the COSMIC-2 mission, this presentation will also discuss high level COSMIC-2 programmatic status and plans, particular with respect to the mission sensors.

Straus, P. R.; Betz, D. A.

2013-12-01

283

Effects of time ordering in quantum nonlinear optics  

NASA Astrophysics Data System (ADS)

We study time-ordering corrections to the description of spontaneous parametric down-conversion (SPDC), four-wave mixing (SFWM), and frequency conversion using the Magnus expansion. Analytic approximations to the evolution operator that are unitary are obtained. They are Gaussian preserving, and allow us to understand order-by-order the effects of time ordering. We show that the corrections due to time ordering vanish exactly if the phase-matching function is sufficiently broad. The calculation of the effects of time ordering on the joint spectral amplitude of the photons generated in SPDC and SFWM are reduced to quadrature.

Quesada, Nicolás; Sipe, J. E.

2014-12-01

284

Effects of time ordering in quantum nonlinear optics  

E-print Network

We study time ordering corrections to the description of spontaneous parametric down-conversion (SPDC), four wave mixing (SFWM) and frequency conversion (FC) using the Magnus expansion. Analytic approximations to the evolution operator that are unitary are obtained. They are Gaussian preserving, and allow us to understand order-by-order the effects of time ordering. We show that the corrections due to time ordering vanish exactly if the phase matching function is sufficiently broad. The calculation of the effects of time ordering on the joint spectral amplitude of the photons generated in spontaneous SPDC and SFWM are reduced to quadrature.

Nicolás Quesada; J. E. Sipe

2014-07-25

285

Ionospheric monitoring by the Global Navigation Satellite System (GNSS)  

NASA Astrophysics Data System (ADS)

The ionosphere reacts to geophysical events, such as earthquakes, tsunamis, surface explosions, underground nuclear explosions (UNE), etc. The Global Navigation Satellite System (GNSS) remote sensing (RS) enables monitoring of the ionospheric disturbances excited by these events. The purpose of this dissertation is to use GNSS RS to detect, discriminate, model and monitor ionospheric disturbances induced by earthquakes and UNEs. Ionospheric delay, which can be derived from dual frequency GNSS signals, is converted to the total electron contents (TEC) along the signal path. After eliminating the main trend of TEC by taking the numerical third order horizontal 3-point derivatives, the traveling ionospheric disturbances (TIDs) are isolated. Since a TID can be generated due to various events, the source of TID must be verified. In this dissertation, the characteristics of the TID waves induced by an earthquake and an UNE are examined. The case studies are: (1) M9.0 2011 Tohoku, Japan earthquake, (2) 2006 North Korean UNE, and (3) 2009 North Korean UNE. From these experiments, the TIDs resulting from different types of events were characterized and discriminated due to the different waveform properties. In addition, the epicenter of the point source can be determined by TID observations. In experiment (2), the 2009 North Korean UNE was examined, using data from eleven nearby GNSS stations. Within a few hours from the explosion, the GNSS stations detected the TIDs, whose arrival time for each station formulated the linear model with respect to the distance to the station. TIDs were observed to propagate with speeds of roughly 150 - 400 m/s at stations about 365 km to 1330 km from the explosion site. Considering the wind effect, the wind-adjusted TIDs located the UNE to within about 2.7 km of its seismically determined epicenter. Through the case studies, the distinctive signatures of different events were demonstrated, which suggests the uniqueness of TIDs excited by different types of events. The major contributions of this dissertation is a demonstration of the applicability of GNSS RS to detect and discriminate geophysical events causing TIDs, and its ability to determine the epicenter of the point source.

Park, Jihye

286

Characterizing Extreme Ionospheric Storms  

NASA Astrophysics Data System (ADS)

Ionospheric storms consist of disturbances of the upper atmosphere that generate regions of enhanced electron density typically lasting several hours. Depending upon the storm magnitude, gradients in electron density can sometimes become large and highly localized. The existence of such localized, dense irregularities is a major source of positioning error for users of the Global Positioning System (GPS). Consequently, satellite-based augmentation systems have been implemented to improve the accuracy and to ensure the integrity of user position estimates derived from GPS measurements. Large-scale irregularities generally do not pose a serious threat to estimate integrity as they can be readily detected by such systems. Of greater concern, however, are highly localized irregularities that interfere with the propagation of a signal detected by a user measurement but are poorly sampled by the receivers in the system network. The most challenging conditions have been found to arise following disturbances of large magnitude that occur only rarely over the course of a solar cycle. These extremely disturbed conditions exhibit behavior distinct from moderately disturbed conditions and, hence, have been designated "extreme storms". In this paper we examine and compare the behavior of the extreme ionospheric storms of solar cycle 23 (or, more precisely, extreme storms occurring between January 1, 2000, and December 31, 2008), as represented in maps of vertical total electron content. To identify these storms, we present a robust means of quantifying the regional magnitude of an ionospheric storm. Ionospheric storms are observed frequently to occur in conjunction with magnetic storms, i.e., periods of geophysical activity as measured by magnetometers. While various geomagnetic indices, such as the disturbance storm time (Dst) and the planetary Kp index, have long been used to rank the magnitudes of distinct magnetic storms, no comparable, generally recognized index exists for measuring ionospheric storm magnitudes. Since the level of ionospheric disturbance (as represented, for example, by enhancements or depletions in total electron content) does not always scale directly with the level of geophysical disturbance in a coincident magnetic storm, however, an independent, purely ionospheric storm index is preferable for ranking ionospheric storms by their magnitudes. Our storm magnitude metric is calculated from the standard ?2 goodness-of-fit parameter values associated with estimates of vertical total electron content (derived from observations collected by networks of GPS receivers) on a grid at regularly spaced intervals of geodetic latitude and longitude. It takes into account both the instantaneous magnitude of the storm and its temporal duration.

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

2011-12-01

287

Characteristics of ionospheric storms in East Asia  

NASA Astrophysics Data System (ADS)

???The ionosphere experiences intense response during the geomagnetic storm and it varies with latitude and longitude. The DPS-4 digisonde measurements and GPS-TEC data of ionospheric stations located at different latitudes in the longitudinal sector of 90-130E during 2002 to 2012 were analyzed to investigate the ionospheric effects in the different latitude of East Asia during geomagnetic storm. About 70 geomagnetic storms are selected according to the Dst index and observed data and they are in different seasons and different solar activity levels. A few quiet days’ averages of data before geomagnetic storm were used as the undisturbed level. Results show that for the middle and high latitude, the short-lived positive disturbance associated with the initial phase of the every storm was observed in each season and then the disturbances were negative till the termination of storm. At the low latitude, storm-time disturbances of foF2 have obvious diurnal, seasonal and solar cycle characteristics. Generally, geomagnetic activity will cause foF2 to increase at daytime and decrease at nighttime except for the summer in low solar activity period. The intensity of response of foF2 is stronger at nighttime than that at daytime. The negative ionospheric storm effect is the strongest in summer and the positive ionospheric storm effect is the strongest in winter. In high solar activity period, the diurnal variation of the response of foF2 is very pronounced in each season, and the strong ionospheric response can last several days. In low solar activity period, ionospheric response has very pronounced diurnal variation in winter only. It’s notable that geomagnetic activities occurred at local time nighttime can cause stronger and longer responses of foF2 at the low latitude. All in all, the obvious negative phase ionospheric storms often occurred at the low latitude. Moreover a notable phenomenon was observed for the low latitude, there are the intensive oscillations of foF2 occurring during the main storm phase of enhanced storm in Hainan, and it occurred in the morning generally. For the TEC data, strong disturbances can be observed simultaneously from high latitude to low latitude during the main phase of some storms. Generally strong/weak storms can cause the negative/positive phase storms of TEC in the low latitude and which are obvious in the daytime for the summer and winter and in the period from noon to midnight for the equinox. The differences of the responses of foF2 and TEC are also investigated.

Wang, Xiao; Wang, Guojun; Shi, Jiankui

288

Incoherent radar spectra in the auroral ionosphere in the presence of a large electric field: The effect of O+-O+ Coulomb collisions  

NASA Astrophysics Data System (ADS)

We have used Monte Carlo simulations of O+ velocity distributions in the high latitude F- region to improve the calculation of incoherent radar spectra in auroral ionosphere. The Monte Carlo simulation includes ionneutral, O+-O collisions (resonant charge exchange and polarization interaction) as well as O+-O+ Coulomb self-collisions. At high altitudes, atomic oxygen O and atomic oxygen ion O+ dominate the composition of the auroral ionosphere and consequently, the influence of O+-O+ Coulomb collisions becomes significant. In this study we consider the effect of O+-O+ Coulomb collisions on the incoherent radar spectra in the presence of large electric field (100 mVm-1). As altitude increases (i.e. the ion-to-neutral density ratio increases) the role of O+-O+ Coulomb self-collisions becomes significant, therefore, the one-dimensional, 1-D, O+ ion velocity distribution function becomes more Maxwellian and the features of the radar spectrum corresponding to non-Maxwellian ion velocity distribution (e.g. baby bottle and triple hump shapes) evolve to Maxwellian ion velocity distribution (single and double hump shapes). Therefore, O+-O+ Coulomb self-collisions act to isotropize the 1-D O+ velocity distribution by transferring thermal energy from the perpendicular direction to the parallel direction, however the convection electric field acts to drive the O+ ions away from equilibrium and consequently, non-Maxwellian O+ ion velocity distributions appeared. Therefore, neglecting O+-O+ Coulomb self-collisions overestimates the effect of convection electric field.

Barghouthi, I. A.

2005-06-01

289

Evaluation of ionospheric profilers using topside sounding data  

NASA Astrophysics Data System (ADS)

An operational system for deducing and imaging the vertical distribution of the electron density in the local ionosphere has been recently developed. The electron density profile is deduced from combined ground-based measurements of the total electron content, ionospheric vertical incidence soundings, and empirically obtained values of the O+-H+ ion transition height. The topside profile is permitted to take one of several forms: Exponential, Chapman, or Epstein. An evaluation of the above mentioned ionospheric profilers is needed in order to determine which one of them provides the best representation of the current ionospheric conditions. For this purpose, we use electron density profiles obtained from ionograms recorded by the topside sounders onboard the Alouette and ISIS satellites. Every profile has been fitted with each of the above mentioned theoretical ionospheric profilers and the corresponding approximation errors calculated. The results have been analyzed with respect to local time, geomagnetic latitude, season, magnetic and solar activity, ion transition height, and the ionospheric density peak characteristics. It has been found that, in the majority of cases, the best fit is provided by the exponential profiler, followed by the Chapman profiler. Also, while some influence of the underlying physical drivers on the topside electron density profile is detected, it is the use of ionospheric characteristics that offers more reliable selection criteria for the most appropriate profiler.

Verhulst, T.; Stankov, S. M.

2014-03-01

290

Sputnik 1 and the First Satellite Ionospheric Experiment  

NASA Astrophysics Data System (ADS)

The world's first scientific space experiment was carried out in 1957 during the flight of the first Artificial Earth Satellite (AES) - Sputnik 1. It was an ionospheric experiment performed at IZMIRAN under the direction of Prof. Ya.L.Alpert (1911-2010). The sunrise and sunset variations in the AES radio signal were recorded in order to determine the distribution of electron density in the topside ionosphere (above the maximum). The experiment demonstrated the capabilities of the satellite radio beacon method, which is now very important and widely used for studying the ionosphere. Our report submitted to the COSPAR General Assembly in Russia describes the history and results of that experiment, as well as some other contributions by Ya.L.Alpert to ionospheric research. Yakov L.Alpert was one of the most famous and influential radiophysicists of his time, the author of many fundamental studies and of a number of classic books on the theory of propagation of electromagnetic waves, interaction of artificial bodies with ionospheric plasmas, ionospheric radio scattering, and the use of satellite radio beacon methods for studying the ionosphere.

Sinelnikov, Vyacheslav; Kuznetsov, Vladimir; Alpert, Svetlana

291

Effect of third-order dispersion on dark solitons  

NASA Astrophysics Data System (ADS)

Third-order dispersion has a detrimental effect on dark solitons, leading to resonant generation of growing soliton tails and soliton decay. This effect is shown to be much stronger than that for bright solitons.

Afanasjev, Vsevolod V.; Kivshar, Yuri S.; Menyuk, Curtis R.

1996-12-01

292

Solitons and ionospheric heating  

NASA Technical Reports Server (NTRS)

It is noted that for parameters characterizing the Platteville ionospheric heating facility, the Langmuir wave evolution at the exact reflection point of the heater wave involves an oscillating two-stream instability followed by a collisionally damped three-dimensional soliton collapse. The result gives an alternative explanation for certain experimental observations.

Weatherall, J. C.; Goldman, M. V.; Sheerin, J. P.; Nicholson, D. R.; Payne, G. L.; Hansen, P. J.

1982-01-01

293

Phase perturbation measurements through a heated ionosphere  

NASA Technical Reports Server (NTRS)

High frequency radiowaves incident on an overdense (i.e., HF-frequency penetration frequency) ionosphere produce electron density irregularities. The effect of such ionospheric irregularities on the phase of UHF-radiowaves was determined. For that purpose the phase of radiowaves originating from celestial radio sources was observed with two antennas. The radiosources were chosen such that the line of sight to at least one of the antennas (usually both) passed through the modified volume of the ionosphere. Observations at 430 MHz and at 2380 MHz indicate that natural irregularities have a much stronger effect on the UHF phase fluctuations than the HF-induced irregularities for presently achieved HF-power densities of 20-80 uW/sq m. It is not clear whether some of the effects observed are the result of HF-modification of the ionosphere. Upper limits on the phase perturbations produced by HF-modification are 10 deg at 2380 MHz and 80 deg at 430 MHz.

Frey, A.; Gordon, W. E.

1982-01-01

294

Order Topology and Frink Ideal Topology of Effect Algebras  

E-print Network

In this paper, the following results are proved: (1) $ $ If $E$ is a complete atomic lattice effect algebra, then $E$ is (o)-continuous iff $E$ is order-topological iff $E$ is totally order-disconnected iff $E$ is algebraic. (2) $ $ If $E$ is a complete atomic distributive lattice effect algebra, then its Frink ideal topology $\\tau_{id}$ is Hausdorff topology and $\\tau_{id}$ is finer than its order topology $\\tau_{o}$, and $\\tau_{id}=\\tau_o$ iff 1 is finite iff every element of $E$ is finite iff $\\tau_{id}$ and $\\tau_o$ are both discrete topologies. (3) $ $ If $E$ is a complete (o)-continuous lattice effect algebra and the operation $\\oplus$ is order topology $\\tau_o$ continuous, then its order topology $\\tau_{o}$ is Hausdorff topology. (4) $ $ If $E$ is a (o)-continuous complete atomic lattice effect algebra, then $\\oplus$ is order topology continuous.

Lei Qiang; Wu Junde; Li Ronglu

2009-12-15

295

The Millstone Hill ionospheric model and its application to the May 26-27, 1990, ionospheric storm  

NASA Astrophysics Data System (ADS)

The present study gives an overview of the Millstone Hill ionospheric model, which solves continuity and momentum equations for O+(4S), O2+, NO+, and N+. Photochemical equilibrium is assumed at the lower boundary (120 km in the present study) and for estimation of the ion concentrations of N2+ and the metastable states of O+. Inputs to the model are the ion drifts, electron temperatures, and ion temperatures measured by the Millstone Hill incoherent scatter radar, the Mass Spectrometer Incoherent Scatter 1986 (MSIS-86) neutral atmosphere, the observed electron density at the upper boundary (500 km), and an empirical model for NO. The model is extremely flexible in selection of sets of cross sections, EUV flux models, and models for ionization by secondary photoelectron impact. The Millstone Hill ionospheric model is used to simulate the May 26-27, 1990, ionospheric storm, which has been previously studied by Buonsanto [1995a]. The main feature of this storm is an observed large enhancement in the F region electron density above Millstone Hill, the so-called dusk effect. Results show that the effects of the electric fields and height variations in the neutral wind associated with a traveling atmospheric disturbance played a crucial role in the formation of the observed dusk effect. Advection of higher-density plasma from the south apparently also contributed. Vibrationally excited N2 and O2 are found to be important in simulating the electron density during these disturbed summer solar maximum conditions. It has not been found necessary to change the MSIS-86 neutral density in order to bring about good agreement between the observed and calculated NmF2 and HmF2.

Schlesier, A. C.; Buonsanto, M. J.

1999-10-01

296

Numerical validations of neural-network-based ionospheric tomography for disturbed ionospheric conditions and sparse data  

NASA Astrophysics Data System (ADS)

Three-dimensional ionospheric tomography is effective for investigations of the dynamics of ionospheric phenomena. However, it is an ill-posed problem in the context of sparse data, and accurate electron density reconstruction is difficult. The Residual Minimization Training Neural Network (RMTNN) tomographic approach, a multilayer neural network trained by minimizing an objective function, allows reconstruction of sparse data. In this study, we validate the reconstruction performance of RMTNN using numerical simulations based on both sufficiently sampled and sparse data. First, we use a simple plasma-bubble model representing the disturbed ionosphere and evaluate the reconstruction performance based on 40 GPS receivers in Japan. We subsequently apply our approach to a sparse data set obtained from 24 receivers in Indonesia. The reconstructed images from the disturbed and sparse data are consistent with the model data, except below 200 km altitude. To improve this performance and limit any discrepancies, we used information on the electron density in the lower ionosphere. The results suggest the restricted RMTNN-tomography-assisted approach is very promising for investigations of ionospheric electron density distributions, including studies of irregular structures in different regions. In particular, RMTNN constrained by low-Earth-orbit satellite data is effective in improving the reconstruction accuracy.

Hirooka, S.; Hattori, K.; Takeda, T.

2011-10-01

297

Solar flares induced D-region ionospheric and geomagnetic perturbations  

NASA Astrophysics Data System (ADS)

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 (?) for each class of solar flare (C, M and X) have been estimated. It is found that D-region ionospheric parameters (H/, ?) strongly depend on the local time of flare's occurrence and their classes. The flare time electron density estimated by using H/ and ? 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.

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

298

Model of Jovian F region ionosphere (Jovian ionosphere model in offset dipole approximation)  

NASA Technical Reports Server (NTRS)

The geomagnetic control of the Earth's atmosphere is well understood. In the F-region and the topside ionosphere, non-electrical forces transport plasma along the magnetic field lines only. In consequence, the worldwide distribution of ionization is strongly dependent on the dip angle. For example, the equatorial anomaly is roughly symmetrical about the dipole equator rather than the geographic. The same appears to be the case in the Jovian ionosphere (Mahajan, 1981). The influence of the magnetic field of Jupiter on its ionization pattern is one of several outstanding topics which need to be studied. Tan (1986) investigated the formation of the equatorial anomaly in the Jovian ionosphere under a centered dipole model. Tan (1988) further studied the effect of the tilt of the Jovian dipole. The results were in broad agreement with those of a diffusive equilibrium model (Tan and Wu, 1981). An off-centered dipole model is constructed and its effects on the ionization pattern are investigated.

Tan, A.

1990-01-01

299

Ionospheric Features Diagnosed by Radio Tomography during Strong Geomagnetic Disturbances  

NASA Astrophysics Data System (ADS)

During the periods of geomagnetic storms, the ionosphere has a particularly complicated and rapidly changing structure. Each storm is marked by its own set of specific manifestations, which reflect rearrangement of the dynamical pattern of the ionosphere and strong perturbations in its parameters. The complexity and global scale of the ionospheric processes that occur during the storms call for the nonlocal methods for diagnosing the spatiotemporal structure of the ionospheric disturbances. Here, we present the results of studying the ionospheric structure by the methods of low orbital radio tomography (RT). The ionospheric radio tomography is rapidly developing during the last two decades. Due to the sufficiently high satellite velocity (~7.9 km/s) and, correspondingly, quite fast (compared to the characteristic times of the ionospheric processes) passage of the satellite through the ionospheric region under study, the radio tomographic approach is suitable for making nearly instantaneous (covering an interval of 5-10 min) 2D snapshots of the ionosphere in the altitude-latitude plane. The vertical and horizontal resolution of RT is 30-40 km and 20-30 km, respectively. We consider the ionospheric manifestations of strong geomagnetic storms (1991-2012) in different regions worldwide including the European part of Russia and North America. We note that during the geomagnetic disturbances, the ionosondes frequently show unstable operation. In contrast to the ionosondes that use HF radio waves, the RT methods are suitable for imaging the ionosphere even during severe solar and geophysical disturbances. During the periods of strong perturbations, RT detected various wavelike structures, travelling ionospheric disturbances, and different manifestations of acoustic gravity waves in the ionosphere. Using the RT methods, the wave effects of particle precipitation were analyzed, and plasma flows were estimated. Radio tomographic imaging of the ionosphere during severe disturbances reveals multiextremal spotty patterns with steep wall-like gradients in electron density in the north. Thin enhancements of electron concentration that are elongated by hundreds of kilometers along the magnetic field lines and attain dozens of kilometers in the transversal direction are identified. The complexly structured ionospheric trough with a tilted polar wall shifted towards the equator is revealed. Many RT reconstructions show the ionospheric trough to split. For example, the RT imaging of the storm of March 24-28, 1991 indicates that the ionospheric structures that are normally typical of the subauroral and auroral ionosphere (the troughs and anomalous ionization in the F-region) reached middle latitudes at that time. During the strongest geomagnetic storm on October 30-31, 2003, the ionosphere over the European part of Russia was marked by anomalously high electron concentration; the distribution of electron density in the region of increased ionization was extremely complicated in space and highly variable in time. We are grateful to the North-West Research Associates (NWRA) for providing the experimental data on relative TEC measured at the RT system in Alaska. The work was supported by the Russian Foundation for Basic Research (grants 11-05-01157 and 13-05-01122).

Andreeva, Elena S.; Kunitsyn, Vyacheslav E.; Tereshchenko, Evgeniy D.; Kozharin, Maksim A.; Nazarenko, Marina O.

2013-04-01

300

Acoustic and gravity waves in the neutral atmosphere and the ionosphere, generated by severe storms  

NASA Technical Reports Server (NTRS)

Gravity waves in the neutral atmosphere and their propagation in the ionosphere and the study of infrasonic signals from thunder were investigated. Doppler shifts of the order of 0.1 Hz are determined and they provide high-resolution measurements of the movements in the ionosphere. By using an array of transmitters with different frequencies and at different locations, the horizontal and vertical propagation vectors of disturbances propagating through the ionosphere are determined.

Balachandran, N. K.

1983-01-01

301

Ionospheric Corrections via PIM and Real-Time Data  

E-print Network

We describe a method for removing ionospheric effects from single-frequency radio data a posteriori. This method is based on a theoretical climatological model developed by the USAF, which returns electron density as a function of position and time along the line of sight to the source. Together with a model of the earth's magnetic field, ionospheric delays and Faraday rotation values ensue. If contemoraneous ionospheric data -- GPS TEC observations or ionosonde profiles -- exist, they can be incorporated to update the modeled electron densities.

R. M. Campbell

1999-07-29

302

Chemistry in the Thermosphere and Ionosphere.  

ERIC Educational Resources Information Center

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…

Roble, Raymond G.

1986-01-01

303

Robust GPS carrier tracking under ionospheric scintillation  

NASA Astrophysics Data System (ADS)

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 of the proposed tracking scheme is assessed by using both simulated and real data. Real data have been collected in Vietnam by using a USRP (Universal Software Radio Peripheral) N210 front end connected to a rubidium oscillator. Selected events are exploited in order to challenge the algorithm with strong phase and amplitude variations. Moreover, simulated data have been collected by using the prototype of a digital front end developed by Novatel, namely the 'Firehose'. Since the latter includes a TCXO oscillator, the proposed tracking scheme is also opportunely modified to take in account the clock error contribution. References 1. R.S., Conker, M. B. El-Arini, C. J. Hegarty, and T. Hsiao, Modelling the effects of ionospheric scintillation on GPS/satellite-based augmentation system availability. Radio Sci., 38, 1, 1001, doi: 10.1029/2000RS002604, 2003. 2. B. Bougard et al, 'CIGALA: Challenging the Solar Maximum in Brazil with PolaRxS,' ION GNSS, Portland, Sept. 2011.

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

2013-12-01

304

Inductive-dynamic magnetosphere-ionosphere coupling via MHD waves  

NASA Astrophysics Data System (ADS)

In the present study, we investigate magnetosphere-ionosphere/thermosphere (M-IT) coupling via MHD waves by numerically solving time-dependent continuity, momentum, and energy equations for ions and neutrals, together with Maxwell's equations (Ampère's and Faraday's laws) and with photochemistry included. This inductive-dynamic approach we use is fundamentally different from those in previous magnetosphere-ionosphere (M-I) coupling models: all MHD wave modes are retained, and energy and momentum exchange between waves and plasma are incorporated into the governing equations, allowing a self-consistent examination of dynamic M-I coupling. Simulations, using an implicit numerical scheme, of the 1-D ionosphere/thermosphere system responding to an imposed convection velocity at the top boundary are presented to show how magnetosphere and ionosphere are coupled through Alfvén waves during the transient stage when the IT system changes from one quasi steady state to another. Wave reflection from the low-altitude ionosphere plays an essential role, causing overshoots and oscillations of ionospheric perturbations, and the dynamical Hall effect is an inherent aspect of the M-I coupling. The simulations demonstrate that the ionosphere/thermosphere responds to magnetospheric driving forces as a damped oscillator.

Tu, Jiannan; Song, Paul; Vasyli?nas, Vytenis M.

2014-01-01

305

Satellite observations of an ionospheric acceleration mechanism  

Microsoft Academic Search

A satellite-borne energetic ion mass spectrometer experiment has detected fluxes of O\\/sup +\\/ and H\\/sup +\\/ ions flowing up out of the ionosphere in the auroral and polar regions. The observed ions have energies in the keV range, narrow pitch-angle distributions aligned along the magnetic field direction and peak flux intensities of the order of 10⁸ (cm²-sec-sterad-keV)⁻¹. The observations were

E. G. Shelley; R. D. Sharp; R. G. Johnson

1976-01-01

306

Rotation of the ionospheric electric potential caused by spatial gradients of ionospheric conductivity  

NASA Astrophysics Data System (ADS)

The present study focuses on the relationship between the inhomogeneity of the ionospheric conductivity and the rotation of the ionospheric potential. By applying a simplified version of the Hall-conjugate separation method [Yoshikawa, in preparation] to a global ionospheric potential solver, we analyze calculated potential structures separating them into the primary field and secondary field (the polarization field generated by the Hall effect). Calculations are performed with the following conditions for simplification. Here we call the diagonal and off-diagonal components of the conductivity tensor used in the potential solver SGTT/SGPP and SGTP, respectively, and we regard them as Pedersen and Hall conductivities for the high-latitude region. Besides, we call SGTP 'effective-Hall conductivity' based on its characteristics. (1) The input is a dawn-dusk and day-night symmetric R1-FAC. (2) The basic conductivity distribution is homogeneous in the longitudinal direction with only the latitudinal gradient by solar EUV and equatorial enhancement, no day-night difference and no auroral enhancement. (3) From the basic distribution, SGTP is changed with respect to the fixed SGTT/SGPP with the Hall-Pedersen ratio and offset that are applied globally. It is confirmed that the rotation angle (polarization field) is not so changed when we add only offsets but it becomes larger as the Hall-Pedersen ratio increases. This result is not only consistent with a theoretical prediction [Yoshikawa et al., 2013b] but also provides the fact that the ionospheric internal process, the primary-secondary fields generation process, does affect largely on the potential structure, and eventually on the magnetosphere-ionosphere processes. By combining the previously obtained and current results, we will clarify how the potential structure is actually described by the primary field and secondary field. The results can be applied to qualitatively/quantitatively identify the ionospheric causes of components of potential rotation/asymmetries that cannot be explained only by solar wind-magnetosphere effects.

Nakamizo, A.; Yoshikawa, A.; Ohtani, S.; Ieda, A.; Seki, K.

2013-12-01

307

Methods for Small Scale Ionospheric TEC Mapping from Broadband L-Band SAR Data  

Microsoft Academic Search

Ionospheric propagation effects have a significant impact on the signal properties of low-frequency SAR systems. All effects are a function of the density of free electrons in the ionosphere, integrated along the ray-path of the SAR signal, the so-called total electron content (TEC). Methods based on two-frequency GPS observations allow measuring TEC in the ionosphere with a coarse spatial resolution

Franz Meyer; Richard Bamler; Norbert Jakowski; Thomas Fritz

2006-01-01

308

A statistic study of ionospheric solar flare activity indicator  

NASA Astrophysics Data System (ADS)

According to the Chapman ionization theory, an ionospheric solar flare activity indicator (ISFAI) is given by the solar zenith angle and the variation rate of ionospheric vertical total electron content, which is measured from a global network of dual-frequency GPS receivers. The ISFAI is utilized to statistically analyze the ionospheric responses to 1439 M-class and 126 X-class solar flares during solar cycle 23 (1996-2008). The statistical results show that the occurrence of ISFAI peak increases obviously at 3.2 total electron content unit (TECU)/h (1 TECU = 1016 el m-2) and reaches the maximum at 10 TECU/h during M-class flares and 10 TECU/h and 40 TECU/h for X-class flares. ISFAI is closely correlated with the 26-34 nm extreme ultraviolet flux but poorly related to the 0.1-0.8 nm X-ray flux. The central meridian distance (CMD) of flare location is an important reason for depressing relationship between ISFAI and X-ray Flux. Through the CMD effect modification, the ISFAI has a significant dependence on the X-ray flux with a correlation coefficient of 0.76. The ISFAI sensitivity enables to detect the extreme X-class flares, as well as the variations of one order of magnitude or even smaller (such as for C-class flares). Meanwhile, ISFAI is helpful to the calibration of the X-ray flux at 0.1-0.8 nm observed by GOES during some flares. In addition, the statistical results demonstrate that ISFAI can detect 80% of all M-class flares and 92% for all X-class ones during 1996-2008.

Xiong, Bo; Wan, Weixing; Ning, Baiqi; Ding, Feng; Hu, Lianhuan; Yu, You

2014-01-01

309

Three-dimensional structure of the Martian nightside Ionosphere  

NASA Astrophysics Data System (ADS)

The night side ionosphere of Mars is known to be highly variable: essentially nonexistent in certain regions, while occasionally nearly as strong as the photoionization-produced dayside ionosphere in others. Using a kinetic approach called MarMCET (Mars Monte Carlo Electron Transport) [3], we model the dynamics of precipitating electrons on the nightside of Mars to study the effects of magnetic field geometry and electron precipitation on ionospheric structure over the geographic region with the strongest crustal magnetic field (140°-220°E, 20°-70°S). As input, we use nightside precipitating electron energy spectra and pitch angle distributions from the Mars Global Surveyor (MGS) Magnetometer & Electron Reflectometer (MAG/ER), as well as a vector sum of a typical external tail-lobe magnetic field and crustal magnetic field model. We thus calculate ionization rate in 3 dimensions, both for specific observations and average cases. We find that magnetic topology (via pitch angle distributions) plays an important part in determining peak ionization rates. Also, we see large geographic differences in average precipitating electron spectra, likely due to the dynamical coupling of the rotating planet-fixed crustal field with the draped interplanetary magnetic field. This leads to differences in peak ionization rates of more than 4 orders of magnitude across this region of the Martian nightside (see figure 1). We also see a strong dependence of peak ionization rate on magnetic elevation angle measured at MGS mapping orbit altitude of 400 km, as precipitating fluxes are generally lower in regions of closed magnetic topology where magnetic field is generally horizontal at this altitude.

Lillis, R. J.; Fillingim, M. O.; Brain, D.

2011-12-01

310

Bipolar climatology of GPS ionospheric scintillation at solar minimum  

NASA Astrophysics Data System (ADS)

High-rate sampling data of Global Navigation Satellite Systems ionospheric scintillation acquired by a network of GPS Ionospheric Scintillation and TEC Monitor receivers located in the Svalbard Islands, in Norway and in Antarctica have been analyzed. The aim is to describe the “scintillation climatology” of the high-latitude ionosphere over both the poles under quiet conditions of the near-Earth environment. For climatology we mean to assess the general recurrent features of the ionospheric irregularities dynamics and temporal evolution on long data series, trying to catch eventual correspondences with scintillation occurrence. In spite of the fact that the sites are not geomagnetically conjugate, long series of data recorded by the same kind of receivers provide a rare opportunity to draw a picture of the ionospheric features characterizing the scintillation conditions over high latitudes. The method adopted is the Ground Based Scintillation Climatology, which produces maps of scintillation occurrence and of total electron content relative variation to investigate ionospheric scintillations scenario in terms of geomagnetic and geographic coordinates, interplanetary magnetic field conditions and seasonal variability. By means of such a novel and original description of the ionospheric irregularities, our work provides insights to speculate on the cause-effect mechanisms producing scintillations, suggesting the roles of the high-latitude ionospheric trough, of the auroral boundaries and of the polar cap ionosphere in hosting those irregularities causing scintillations over both the hemispheres at high latitude. The method can constitute a first step toward the development of new algorithms to forecast the scintillations during space weather events.

Alfonsi, Lucilla; Spogli, Luca; De Franceschi, Giorgiana; Romano, Vincenzo; Aquino, Marcio; Dodson, Alan; Mitchell, Cathryn N.

2011-06-01

311

Atmospheric Lithosphere-Ionosphere Charge Exchange (ALICE) for coupling between earthquake regions, clouds and the ionosphere  

NASA Astrophysics Data System (ADS)

Atmospheric Lithosphere-Ionosphere Charge Exchange (ALICE) has been proposed as a mechanism to link seismic activity and ionospheric changes detected overhead, which has been observed in data obtained by the DEMETER spacecraft. The ALICE mechanism can explain changes in the natural extremely low frequency (ELF) radio noise observed by DEMETER nocturnally before major earthquakes. ALICE operates through the vertical fair weather current density of global atmospheric electricity, through the modification of surface layer ionisation rates and the associated current flow to the ionosphere. These ideas are extended here to include possible effects on layer clouds through which the current density passes. Specifically, we estimate possible layer cloud changes for changes in surface layer ionisation known in some earthquakes.

Harrison, Giles; Aplin, Karen; Rycroft, Michael

2014-05-01

312

Summary of Sessions: Ionosphere - Thermosphere - Mesosphere Working Group  

NASA Technical Reports Server (NTRS)

The topics covered by the sessions under the working group on Ionosphere-Thermosphere-Mesosphere dealt with various aspects of the response of the ionosphere-thermosphere coupled system and the middle atmosphere to solar variability. There were four plenary talks related to the theme of this working group, thirteen oral presentations in three sessions and six poster presentations. A number of issues related to effects of solar variability on the ionosphere-thermosphere, observed using satellite and ground-based data including ground magnetometer observations, radio beacon studies of equatorial spread F, and modeling of some of these effects, were discussed. Radar observations of the mesosphere-lower thermosphere region and a future mission to study the coupling of thunderstorm processes to this region, the ionosphere, and magnetosphere were also presented.

Spann, J. F.; Bhattacharyya, A.

2006-01-01

313

A Review of Low Frequency Electromagnetic Wave Phenomena Related to Tropospheric-Ionospheric Coupling Mechanisms  

NASA Technical Reports Server (NTRS)

Investigation of coupling mechanisms between the troposphere and the ionosphere requires a multidisciplinary approach involving several branches of atmospheric sciences, from meteorology, atmospheric chemistry, and fulminology to aeronomy, plasma physics, and space weather. In this work, we review low frequency electromagnetic wave propagation in the Earth-ionosphere cavity from a troposphere-ionosphere coupling perspective. We discuss electromagnetic wave generation, propagation, and resonance phenomena, considering atmospheric, ionospheric and magnetospheric sources, from lightning and transient luminous events at low altitude to Alfven waves and particle precipitation related to solar and magnetospheric processes. We review in situ ionospheric processes as well as surface and space weather phenomena that drive troposphere-ionosphere dynamics. Effects of aerosols, water vapor distribution, thermodynamic parameters, and cloud charge separation and electrification processes on atmospheric electricity and electromagnetic waves are reviewed. We also briefly revisit ionospheric irregularities such as spread-F and explosive spread-F, sporadic-E, traveling ionospheric disturbances, Trimpi effect, and hiss and plasma turbulence. Regarding the role of the lower boundary of the cavity, we review transient surface phenomena, including seismic activity, earthquakes, volcanic processes and dust electrification. The role of surface and atmospheric gravity waves in ionospheric dynamics is also briefly addressed. We summarize analytical and numerical tools and techniques to model low frequency electromagnetic wave propagation and solving inverse problems and summarize in a final section a few challenging subjects that are important for a better understanding of tropospheric-ionospheric coupling mechanisms.

Simoes, Fernando; Pfaff, Robert; Berthelier, Jean-Jacques; Klenzing, Jeffrey

2012-01-01

314

Magnetosphere-ionosphere coupling  

Microsoft Academic Search

A simple two-dimensional model of the magnetosphere-ionosphere system is discussed in which a localized electromotive force applied across a magnetic field line at t=0 is shown to propagate along the magnetic field with the Alfven velocity. The perpendicular electric field is assumed to reverse direction across the field line. Since the perpendicular electric field is limited in space, the propagation

C. K. Goertz; R. W. Boswell

1979-01-01

315

Short-term prediction of the foF2 critical frequency in the high latitude ionosphere for DIAS extending services  

NASA Astrophysics Data System (ADS)

Ionospheric forecasting products and services for Europe are provided routinely by the European Digital upper Atmosphere Server, DIAS (http://dias.space.noa.gr). These include alerts and warnings for upcoming ionospheric storm time disturbances as well as single station and regional ionospheric forecasts up to 24 hours ahead for the middle latitude European region. However, in order to meet the users' requirements, it is planned within the Space Situational Awareness Programme of the European Space Agency the extension of the DIAS forecasting services to cover the whole European region, including Scandinavia. To this effect, the Solar Wind driven autoregression model for Ionospheric short-term Forecast (SWIF) will be applied. In the operational mode, SWIF combines historical and real-time ionospheric observations with solar wind parameters obtained in real time at L1 point from ACE spacecraft through the cooperation of an autoregression forecasting algorithm, namely TSAR with an empirical ionospheric storm time model, namely STIM that is triggered by solar wind disturbances detected by STIM's alert detection algorithm. The ionospheric storm time response is then empirically formulated taken into account the latitude and the local time of the observation point at the storm onset. SWIF's prediction efficiency was recently fully documented for the middle latitude ionosphere. As a first step towards the operational implementation of the SWIF for high latitude ionospheric forecasts, the work presented here includes the evaluation of the SWIF's performance over high latitude locations and under disturbed geophysical conditions based on historical data. For this purpose, all available high latitude foF2 observations obtained during a significant number of selected storm events occurred in the previous as well as the current solar cycle are analyzed in respect with the foF2 reference level and the model's predictions. The results verify the validity of STIM's storm alert detection algorithm for high latitude storm time predictions and drive necessary adjustments in the model's empirical expressions improving SWIF's efficiency to capture the direct response of the high latitude ionosphere to geomagnetic storm activity. The model's prediction efficiency is quantified through relevant metrics' estimations (i.e. RMSE, MRE and relative improvement over climatology).

Tsagouri, Ioanna; Belehaki, Anna

2013-04-01

316

Research on the lunar ionosphere using dual-frequency radio occultation with a small VLBI antenna  

NASA Astrophysics Data System (ADS)

The Vstar in the Japanese lunar SELENE Radio Science experiment was occulted by virtue of the lunar ionosphere. Using the single sub-satellite and the S/X band coherent radio waves, dual-frequency measurements were acquired at a ground receiving station. In order to investigate the variation of ionospheric total electron content (TEC) surrounding the moon, the TEC, including the terrestrial ionosphere, the interplanetary plasma and lunar ionosphere, can be derived from the phase information of the observational data. We update the observation equation and algorithms, calculate the linear fitting trend of the lunar ionosphere from 60 to 30 km above the surface of the moon. The fitting trend is extended from 30 to 0 km above the surface of the moon. The lunar ionosphere is obtained by using the short time trend extrapolation method.

Wang, Zhen; Wang, Na; Ping, Jinsong

2015-04-01

317

Study of the effect of magnetic ordering on order-disorder transitions in binary alloys  

NASA Astrophysics Data System (ADS)

We set up a mean-field approximation in a random Ising model characterized by two order parameters: the local sublattice magnetization and a mean-field occupation variable which act as an order parameter for the order-disorder transition. In the effective model Hamiltonian the two order-parameters are coupled. We solve the coupled equations arising from this to describe the total phase diagram. The exchange energies for FeCo alloys have then been accurately obtained from first-principles based on the technique of orbital peeling and a Monte Carlo analysis using a coupled Metropolis-Kawasaki updating has been carried out. Our results reasonably successfully agree with earlier experimental data.

Jena, Ambika Prasad; Sanyal, Biplab; Mookerjee, Abhijit

2014-06-01

318

Ion resonances and ELF wave production by an electron beam injected into the ionosphere - ECHO 6  

NASA Technical Reports Server (NTRS)

Two effects observed with electron antennas ejected from a sounding rocket launched into the ionosphere in March 1983 carrying electron beam guns are discussed. The sensor packages were ejected and travelled parallel to the vehicle trajectory. Electric potentials were measured between the single probes and a plasma diagnostic package while the gun injected electrons into the ionosphere in perpendicular and parallel 1 kHz directions. Signal pulses over the dc-1250 kHz range were detected. A kHz gun frequency caused a signal that decreased by two orders of magnitude between 45-90 m from the beam field line. However, the signal was detectable at 1 mV/m at 120 m, supporting earlier data that indicated that pulsed electron beams can cause ELF waves in space. Beam injection parallel to the magnetic field produced an 840 Hz resonance that could be quenched by activation of a transverse beam.

Winckler, J. R.; Steffen, J. E.; Malcolm, P. R.; Erickson, K. N.; Abe, Y.; Swanson, R. L.

1984-01-01

319

Grating formation by a high power radio wave in near-equator ionosphere  

SciTech Connect

The formation of a volume grating in the near-equator regions of ionosphere due to a high power radio wave is investigated. The radio wave, launched from a ground based transmitter, forms a standing wave pattern below the critical layer, heating the electrons in a space periodic manner. The thermal conduction along the magnetic lines of force inhibits the rise in electron temperature, limiting the efficacy of heating to within a latitude of few degrees around the equator. The space periodic electron partial pressure leads to ambipolar diffusion creating a space periodic density ripple with wave vector along the vertical. Such a volume grating is effective to cause strong reflection of radio waves at a frequency one order of magnitude higher than the maximum plasma frequency in the ionosphere. Linearly mode converted plasma wave could scatter even higher frequency radio waves.

Singh, Rohtash; Sharma, A. K.; Tripathi, V. K. [Department of Physics, Indian Institute of Technology Delhi, New Delhi-110016 (India)

2011-11-15

320

A Global, Three-Ion Approach to the Ionospheric Outflow Problem  

NASA Astrophysics Data System (ADS)

The terrestrial magnetosphere has three key populations: ionospheric hydrogen, ionospheric oxygen, and solar wind hydrogen. These populations enter the magnetosphere at different locations as the result of different dynamics and evolve independently throughout the system. As such, it is expected that the fraction of these populations that arrive at the ring current will arrive with different energy and density distributions and will contribute to the ring current to different degrees. Contemporary fluid models of the terrestrial magnetosphere neglect at least one of these populations by specifying two fluids or less. Such shortcomings complicate the use of MHD to study the effects of ionospheric outflow on the global system. To address these issues, a new three-ion version of the BATS-R-US global MHD model has been developed. This approach has already been shown to affect cusp dynamics and allow the geomagnetic mass spectrometer effect to manifest clearly between heavy oxygen and light hydrogen. By including all three key populations, it is an effective way to investigate the effects of ionospheric outflow on the magnetosphere and ring current as well as study the balance between ionospheric and solar wind plasma contributions. This work reviews this three-ion approach and focuses on recent results when the three-fluid BATS-R-US is coupled to other first principles codes. The three fluid MHD is one-way coupled to the Ring current Atmosphere interactions Model with Self-Consistent Magnetic field (RAM-SCB) in order to investigate how inner magnetosphere dynamics depend on the evolution of the three key plasma populations and their sources. Both an idealized event with simple solar wind features and a real world event using observed solar wind conditions are studied. Results will be compared to single fluid, multi-species simulations. Finally, initial results when outflow is driven in the MHD code via coupling to the Polar Wind Outflow Model (PWOM) will be shown and compared to results when simple inner boundary conditions dictate the ionospheric source.

Welling, Daniel; Liemohn, Michael; Glocer, Alex; Toth, Gabor; Jordanova, Vania; Zaharia, Sorin

2013-04-01

321

Effects of high-order operators in nonrelativistic Lifshitz holography  

NASA Astrophysics Data System (ADS)

In this paper, we study the effects of high-order operators on the nonrelativistic Lifshitz holography in the framework of the Ho?ava-Lifshitz (HL) theory of gravity, which naturally contains high-order operators in order for the theory to be power-counting renormalizable, and provides an ideal place for such studies. In particular, we show that the Lifshitz spacetime is still a solution of the full theory of the HL gravity. The effects of the high-order operators on the spacetime itself is simply to shift the Lifshitz dynamical exponent. However, while in the infrared the asymptotic behavior of a (probe) scalar field near the boundary is similar to that studied in the literature, it gets dramatically modified in the UV limit, because of the presence of the high-order operators in this regime. Then, according to the gauge/gravity duality, this in turn affects the two-point correlation functions.

Wang, Xinwen; Yang, Jie; Tian, Miao; Wang, Anzhong; Deng, Yanbin; Cleaver, Gerald

2015-03-01

322

Towards a Pan-European network for the mitigation of ionospheric threats (Invited)  

NASA Astrophysics Data System (ADS)

Measurements of signals from Global Navigation Satellite Systems (GNSS) offer the possibility to analyze the spatial and temporal characteristics of the electron density structure in the ionosphere and plasmasphere. Dual frequency ground based measurements are well suited to observe horizontal structures of the electron density and their dynamics whereas space based GNSS measurements can effectively contribute to explore the vertical structure of the ionosphere-plasmasphere ionization. The current data base, covering more than one solar cycle, enabled the development of empirical models of ionospheric key parameters such as the total electron content (TEC), the peak density NmF2 and the corresponding peak density height hmF2. TEC models can directly be used as correction in single frequency GNSS applications. Utilizing well established geodetic networks such as that of the International GNSS Service (IGS), it is discussed how ground based GNSS measurements are used to derive regional and global maps of the vertical TEC in near real time. Actual TEC maps are used for correcting ionospheric range errors in operational single frequency applications, e.g. in space based augmentation systems (SBAS) like WAAS in US and EGNOS in Europe. However, severe space weather conditions lead to perturbations of the ionospheric plasma which in turn can affect the performance of GNSS. These perturbations come at a wide range of spatial and temporal scales and are observed as large scale ionization fronts, medium scale travelling ionospheric disturbances, plasma bubbles and small scale irregularities causing radio scintillations at the receiver level. These disturbances can strongly degrade the accuracy, reliability, integrity and availability of the GNSS. This is especially detrimental for space and ground based augmentation systems which have specific accuracy and availability requirements. Therefore an important use of the measurements of GNSS signals is to assess the threat that space weather can have on GNSS. One possible application is the estimation of the strongest possible influence of the ionosphere. This can then be used as a safety margin to fulfill the high safety requirements of aircrafts landing with GNSS and GBAS. GNSS receivers are a crucial component in countless modern systems, e.g. in telecommunication, navigation, remote sensing and precision timing. Additionally the demands on these systems with respect to accuracy, reliability and safety are permanently growing. Considering the fact that the ionospheric impact cannot be ignored enhanced research activities are required to improve current solutions for correcting or mitigating the ionospheric impact or at least to provide awareness of current threats. It is reported how the current EC funded research project TRANSMIT focuses on bringing together young researchers in this field in order to establish a Pan-European network for Ionospheric Perturbation Detection and Monitoring (IPDM) in the upcoming years. To highlight essential results of these researchers, a prototype solution is being prepared to be accessible via internet (http://swaciweb.dlr.de ).

Jakowski, N.; Hlubek, N.; Sato, H.; Berdermann, J.; Aquino, M. H.

2013-12-01

323

Simultaneous radio interferometer and optical observations of ionospheric structure at the Very Large Array  

NASA Astrophysics Data System (ADS)

Radio astronomers are searching the cosmos for new scientific discoveries at increasingly lower radio frequencies and with larger antenna arrays, but their observations of the sky are blurred by the dynamic ionosphere. At the same time, ionospheric scientists are seeking to understand, at increasingly higher spatial and temporal resolutions, the dynamics that drive the ionosphere and its effects on technological systems. Advancements in radio astronomy at the Very Large Array (VLA) are leading to advancements in ionospheric physics and vice versa. We review some of the ionospheric observations made by the VLA at low frequency. Results from a 2003 summer campaign at the VLA are discussed, during which an all-sky optical camera was used to monitor ionospheric structure during VLA 74-MHz operations. The camera and additional off-site sensors, including ionosondes and incoherent scatter radar, were used to identify the dominant, summer nighttime ionospheric phenomena contributing to VLA signal distortion. Knowledge of the specific phenomena, including their spatial and temporal characteristics, can be used to improve low-frequency, astronomical imaging. Similarly, the VLA observations can be used to investigate ionospheric phenomena in great detail, leading to an improved understanding of ionospheric physics. Key to these findings is the identification of specific ionospheric phenomena using support sensors. Implications for the development of the Long Wavelength Array are discussed.

Coker, Clayton; Thonnard, Stefan E.; Dymond, Kenneth F.; Lazio, T. Joseph W.; Makela, Jonathan J.; Loughmiller, Pamela J.

2009-07-01

324

Advanced spectral analysis of ionospheric waves observed with sparse arrays  

NASA Astrophysics Data System (ADS)

This paper presents a case study from a single, 6h observing period to illustrate the application of techniques developed for interferometric radio telescopes to the spectral analysis of observations of ionospheric fluctuations with sparse arrays. We have adapted the deconvolution methods used for making high dynamic range images of cosmic sources with radio arrays to making comparably high dynamic range maps of spectral power of wavelike ionospheric phenomena. In the example presented here, we have used observations of the total electron content (TEC) gradient derived from Very Large Array (VLA) observations of synchrotron emission from two galaxy clusters at 330MHz as well as GPS-based TEC measurements from a sparse array of 33 receivers located within New Mexico near the VLA. We show that these techniques provide a significant improvement in signal-to-noise ratio (S/N) of detected wavelike structures by correcting for both measurement inaccuracies and wavefront distortions. This is especially true for the GPS data when combining all available satellite/receiver pairs, which probe a larger physical area and likely have a wider variety of measurement errors than in the single-satellite case. In this instance, we found that the peak S/N of the detected waves was improved by more than an order of magnitude. The data products generated by the deconvolution procedure also allow for a reconstruction of the fluctuations as a two-dimensional waveform/phase screen that can be used to correct for their effects.

Helmboldt, J. F.; Intema, H. T.

2014-02-01

325

Modeling seasonal variations of auroral particle precipitation in a global-scale magnetosphere-ionosphere simulation  

E-print Network

Modeling seasonal variations of auroral particle precipitation in a global-scale magnetosphere shown strong seasonal variations in a vast array of magnetosphere-ionosphere parameters, including field of the coupled solar wind-magnetosphere-ionosphere system. In order to account for changes in the solar wind

326

Improved Ionospheric Electrodynamic Models and Application to Calculating Joule Heating Rates  

NASA Technical Reports Server (NTRS)

Improved techniques have been developed for empirical modeling of the high-latitude electric potentials and magnetic field aligned currents (FAC) as a function of the solar wind parameters. The FAC model is constructed using scalar magnetic Euler potentials, and functions as a twin to the electric potential model. The improved models have more accurate field values as well as more accurate boundary locations. Non-linear saturation effects in the solar wind-magnetosphere coupling are also better reproduced. The models are constructed using a hybrid technique, which has spherical harmonic functions only within a small area at the pole. At lower latitudes the potentials are constructed from multiple Fourier series functions of longitude, at discrete latitudinal steps. It is shown that the two models can be used together in order to calculate the total Poynting flux and Joule heating in the ionosphere. An additional model of the ionospheric conductivity is not required in order to obtain the ionospheric currents and Joule heating, as the conductivity variations as a function of the solar inclination are implicitly contained within the FAC model's data. The models outputs are shown for various input conditions, as well as compared with satellite measurements. The calculations of the total Joule heating are compared with results obtained by the inversion of ground-based magnetometer measurements. Like their predecessors, these empirical models should continue to be a useful research and forecast tools.

Weimer, D. R.

2004-01-01

327

Tohoku earthquake shook the ionosphere  

Microsoft Academic Search

The giant 11 March 2011 magnitude 9 Tohoku earthquake not only shook the Earth and caused devastating tsunamis but also rattled the ionosphere, according to a new study. The surface seismic waves and tsunamis triggered waves in the atmosphere. These atmospheric waves propagated upward into the ionosphere, creating ripples in ionized gas nearly 350 kilometers above the Earth. Liu et

Ernie Balcerak

2011-01-01

328

Ionospheres of the terrestrial planets  

Microsoft Academic Search

The theory and observations relating to the ionospheres of the terrestrial planets Venus, the earth and Mars are reviewed. Emphasis is placed on comparing the basic differences and similarities between the planetary ionospheres. The review covers the plasma and electric-magnetic field environments that surround the planets, the theory leading to the creation and transport of ionization in the ionspheres, the

R. W. Schunk; A. F. Nagy

1980-01-01

329

Real-Time Ionospheric Characterization and Modeling  

Microsoft Academic Search

Complete descriptions of spatial and temporal distributions of the ionosphere are obtained using a real-time ionospheric characterization (RTIC) system developed at CRS (and described by Ganguly and Brown, 2001). The system accepts data from various sources, regions, and times, then assimilates these data within the framework of physical ionospheric models, providing a 4-D description of the ionosphere anywhere in the

Suman Ganguly; Andrew Brown

330

Joint Correction of Ionospheric Artifact and Orbital Error in L-band SAR Interferometry  

NASA Astrophysics Data System (ADS)

Synthetic aperture radar interferometry (InSAR) is a powerful technique to measure surface deformation. However, the accuracy of this technique for L-band synthetic aperture radar (SAR) system is largely compromised by ionospheric path delays on the radar signals. The ionospheric effect causes severe ionospheric distortion called azimuth streaking in SAR backscattering intensity images as well as long wavelength phase distortion similar to orbital ramp error. Effective detection and correction of ionospheric phase distortion from L-band InSAR images are necessary to measure and interpret surface displacement accurately. Recently Jung et al.(2012) proposed an efficient method to correct ionospheric phase distortions using the multiple aperture interferometry (MAI) interferogram. In this study, we extend this technique to correct the ionosphere effect in InSAR measurements of interseismic deformation. We present case studies in southern California using L-band ALOS PALSAR data and in-situ GPS measurements and show that the long wavelength noise can be removed by joint correction of the ionospheric artifact and the orbital error. Displacement maps created from 20070715-20091020 ALOS PALSAR pair: (a-b) before and after joint correction of ionospheric artifact and orbital error, and (c) after correction from 2D-polynomial fit Displacement maps created from 20071015-20091020 ALOS PALSAR pair: (a-b) before and after joint correction of ionospheric artifact and orbital error, and (c) after correction from 2D-polynomial fit

Jung, H.; Liu, Z.; Lu, Z.

2012-12-01

331

Using IRI for the computation of ionospheric corrections for altimeter data analysis  

NASA Technical Reports Server (NTRS)

Measurements by single-frequency satellite altimeter (Geosat, ERS-1) require a ionospheric correction to account for the signal time delay in the ionosphere. We propose using the International Reference Ionosphere (IRI) for the determination of this time delay. To investigate the effectiveness of an IRI correction, we have compared the IRI values with ionospheric corrections deduce from measurements by the dual-frequency Topex altimeter. By measuring at two frequencies, the Topex instrument can record (and thus eliminate) the ionospheric influence. We find that IRI agrees with the Topex data much better than the model that is currently used in Geosat data analysis. In particular the earlier model does not represent the equatorial double-peak (equator anomaly) clearly seen in the Topex data. Overall, the use of IRI results in a 30% improvement (over the older model) in the accuracy of ionospheric corrections computed for the first year of the Topex mission.

Bilitza, D.; Koblinsky, C.; Beckley, B.; Zia, S.; Williamson, R.

1995-01-01

332

VLF/LF Radio Sounding of Ionospheric Perturbations Associated with Earthquakes  

PubMed Central

It is recently recognized that the ionosphere is very sensitive to seismic effects, and the detection of ionospheric perturbations associated with earthquakes, seems to be very promising for short-term earthquake prediction. We have proposed a possible use of VLF/LF (very low frequency (3-30 kHz) /low frequency (30-300 kHz)) radio sounding of the seismo-ionospheric perturbations. A brief history of the use of subionospheric VLF/LF propagation for the short-term earthquake prediction is given, followed by a significant finding of ionospheric perturbation for the Kobe earthquake in 1995. After showing previous VLF/LF results, we present the latest VLF/LF findings; One is the statistical correlation of the ionospheric perturbation with earthquakes and the second is a case study for the Sumatra earthquake in December, 2004, indicating the spatical scale and dynamics of ionospheric perturbation for this earthquake.

Hayakawa, Masashi

2007-01-01

333

Solitons and ionospheric modification  

NASA Technical Reports Server (NTRS)

The possibility of Langmuir soliton formation and collapse during ionospheric modification is investigated. Parameters characterizing former facilities, existing facilities, and planned facilities are considered, using a combination of analytical and numerical techniques. At a spatial location corresponding to the exact classical reflection point of the modifier wave, the Langmuir wave evolution is found to be dominated by modulational instability followed by soliton formation and three-dimensional collapse. The earth's magnetic field is found to affect the shape of the collapsing soliton. These results provide an alternative explanation for some recent observations.

Sheerin, J. P.; Nicholson, D. R.; Payne, G. L.; Hansen, P. J.; Weatherall, J. C.; Goldman, M. V.

1982-01-01

334

The Potential of Broadband L-Band SAR Systems for Small Scale Ionospheric TEC Mapping  

Microsoft Academic Search

Ionospheric effects have a significant impact on broadband L -band SAR systems. Range delay, range defocussing and Faraday rotation are the most prominent. All effects are a function of the number of free electrons in the ionosphere, counted along the the ray-path of the SAR signal. Methods based on 2-frequency GPS observations allow to measure the number of free electrons

Franz Meyer; Richard Bamler; Norbert Jakowski; Thomas Fritz

2006-01-01

335

Performance evaluation of selected ionospheric delay models during geomagnetic storm conditions in low-latitude region  

NASA Astrophysics Data System (ADS)

Investigation of space weather effects on GPS satellite navigation systems is very crucial in high-precision positional applications such as aircraft landings and missile guidance, etc. The geomagnetic storms can drastically affect the total electron content (TEC) of the ionosphere even in low latitudes, especially for Indian region as it comes under low-latitude region. Hence, the performance of three prominent ionospheric models is investigated for adverse ionospheric conditions using 17 GPS TEC stations data. The models characterized the ionospheric disturbances due to two magnetic storms well.

Venkata Ratnam, D.; Sarma, A. D.; Satya Srinivas, V.; Sreelatha, P.

2011-06-01

336

Simulation of ion outflows in the ionosphere  

NASA Astrophysics Data System (ADS)

Ion outflows are observed in the polar region in response to particle precipitation and magnetospheric wave activity. In order to study the ion outflow, we modified the previously developed two-dimensional model of realistic active ionosphere [Sydorenko, 2012] by including ion motion along the geomagnetic field. The new model considers a layer of near-Earth plasma of thickness of a few thousand kilometers. The plasma consists of multiple ion species. Collisions between particles are accounted for everywhere, even at high altitudes where they are negligible. Therefore, unlike in the previous model, the electron and ion dynamics is continuous. Chemical reactions between different ion and neutral species are included. Simulations demonstrate formation of field-aligned ion flows when an intense Alfven wave or electron precipitation perturbs the ionosphere. The significance of the results is discussed in the context of Canadian Space Agency e-POP spacecraft mission. Sydorenko D. and R. Rankin, "Simulation of ionospheric disturbances created by Alfven waves", submitted to Journal of Geophysical Research, 2012.

Sydorenko, D.; Rankin, R.

2012-12-01

337

The topside ionospheric effective scale heights (HT) derived with ROCSAT-1 and ground-based Ionosonde observations at equatorial and mid-latitude stations  

NASA Astrophysics Data System (ADS)

In this study, we propose the assimilation of topside in situ electron density data from ROCSAT-1 satellite along with the ionosonde measurements for accurate determination of topside iono-spheric effective scale heights (HT) using -Chapman function. The reconstructed topside elec-tron density profiles using these scale heights exhibit an excellent similitude with Jicamarca Incoherent Scatter Radar (ISR) profiles, and are much better representations than the existing methods of Reinisch-Huang method and/or the empirical IRI-2007 model. The main advan-tage with this method is that it allows the precise determination of the effective scale height (HT) and the topside electron density profiles at a dense network of ionosonde/digisonde sta-tions where no ISR facilities are available. The demonstration of the method is applied by investigating the diurnal, seasonal and solar activity variations of HT over the dip-equatorial station Jicamarca and the mid-latitude station Grahamstown. The diurnal variation of scale heights over Jicamarca consistently exhibits a morning time descent followed by a minimum around 0700-0800 LT and a pronounced maximum at noon during all the seasons of both high and moderate solar activity periods. Further, the scale heights exhibit a secondary maximum during the post-sunset hours of equinoctial and summer months, whereas the post-sunset peak is absent during the winter months. These typical features are further investigated using the topside ion properties obtained by ROCSAT-1 as well as SAMI2 model simulations. The re-sults consistently indicate that the diurnal variation of the effective scale height (HT) does not closely follow the plasma temperature variation and at equatorial latitudes is largely controlled by the vertical ExB drift.

Ram Sudarsanam, Tulasi; Su, Shin-Yi; Liu, C. H.; Reinisch, Bodo

338

The Effect of N2 Photoabsorption Cross Section Resolution on C2H6 Production in Titan’s Ionosphere  

NASA Astrophysics Data System (ADS)

Titan’s rich organic chemistry begins with the photochemistry of only two molecules: N2 and CH4. The details on how higher-order hydrocarbons and nitriles are formed from these molecules have key implications for both the structure and evolution of Titan’s atmosphere, and for its surface-atmosphere interactions. Of high importance is the production of C2H6, which is a sink for CH4, and a main component in the polar lakes. Results of photochemical models, though, may be sensitive to the choice of input parameters, such as the N2 photoabsorption cross section resolution, as previously shown for nitrogen (Liang et al. (2007) ApJL 664, 115-118), and CH4 (Lavvas et al. (2011) Icarus 213, 233-251). Here we investigate the possibility of the same effect on the production rates of C2H6. We modeled production and loss rates, as well as mixing ratio and density profiles between an altitude of 600 and 1600 km for low and high resolution N2 cross sections via a coupled ion-neutral-thermal model (De La Haye et al. (2008) Icarus 197, 110-136; Mandt et al. (2012) JGR 117, E10006). Our results show a clear impact of photoabsorption cross section resolution used on all neutral and ion species contributing to C2H6 production. The magnitude of the influence varies amongst species. Ethane production profiles exhibit a significant increase with better resolution; a factor of 1.2 between 750 and 950 km, and a factor of 1.1 in the total column-integrated production rate. These values are lower limits, as additional reactions involving C2H5 not included in the model may also contribute to the production rates. The clear effect on C2H6 (which is not a parent molecule, nor does it bear nitrogen) may have important implications for other molecules in Titan’s atmosphere as well. The possible non-negligible impact of an isotope of nitrogen may argue for the inclusion of isotopes in photochemical models. For future analysis, development of a more efficient and streamlined model called Planet-INC is underway. This open source model is a high-performance probabilistic planetary model that includes detailed uncertainty analysis capabilities.

Luspay-Kuti, Adrienn; Mandt, Kathleen E.; Plessis, Sylvain; Greathouse, Thomas K.

2014-11-01

339

The ionosphere of Triton  

NASA Technical Reports Server (NTRS)

A model of the atmospheric temperature structure and composition inferred from the Voyager (UVS) solar occultations was used together with a one-dimensional chemical diffusive model to interpret the Voyager Radio Science Spectrometer (RSS) ingress measurements of Triton's electron density. Although N2(+) is the major ion created, N(+) produced by dissociative ionization is the dominant ion. Reaction of thermospheric H2, produced by Lyman-alpha dissociation of CH4 in the lower atmosphere, is the major loss for N(+) ions and maintains these ions in PCSS below 600 km. Solar EUV ionization cannot generate electron densities at the magnitude measured by the RSS experiment and an additional ionization source about 3 x 10 to the 8th ions/sq cm per sec is required. The ionosphere may undergo a transition from PCSS to diffusive control if the N(+) ion production rates were greater than the H2 flux derived from CH4. In this case, the upward flowing H2 is totally converted to H by reaction with N(+) and the remaining N(+) ions recombine radiatively to create an ionosphere under diffusive control above the peak.

Majeed, T.; Mcconnell, J. C.; Strobel, D. F.; Summers, M. E.

1990-01-01

340

MF and HF propagation characteristics of ionospheric ducts  

NASA Astrophysics Data System (ADS)

The propagation of MF and HF radio waves along ionospheric ducts is studied in detail by developing a waveguide model of the ducts and determining power levels of ducted echoes. Distributions of returned echo power have been calculated for ducts with various cross-sections and different depletions in electron density. It is found that field aligned ducts with diameters of the order of several kilometers behave as effective waveguides for both direct and conjugate ducting modes. However, the percentage depletion required for guiding is higher than previous calculations using simplified theory. For direct ducting, there is a clear relationship between the total integrated power across a duct and the electron density gradient and propagation frequency.

Platt, I. G.; Dyson, P. L.

1989-10-01

341

Nodal coordinates for the first-order quadratic Zeeman effect  

Microsoft Academic Search

A method due to Pechukas (1972) and De Leon and Heller (1984) is used to construct a curvilinear coordinate system appropriate to the first-order quadratic Zeeman effect. The method is introduced through the example of the classical Coulomb problem. The curvilinear nodal coordinates in momentum space are shown to be the elliptical cylindrical (or conical) coordinates employed by Herrick (1982)

S. Watanabe; P. F. O'Mahony

1987-01-01

342

Second-Order Effects in Mental Health Treatment  

ERIC Educational Resources Information Center

This article argues that mental health clients are typically processed through a fairly standardized, complex professional system which, in its pursuit of salutary helping'' goals may also be occasioning serious negative second-order effects for its clients. The intent of the present article is to direct attention to the professional implications…

Graziano, Anthony M.; Fink, Robert S.

1973-01-01

343

A quantitative study of ionospheric disturbance characteristics during solar flare events using the SuperDARN Hokkaido radar and solar radiation data  

NASA Astrophysics Data System (ADS)

Ionospheric disturbances during solar flare events have been studied by various kinds of observation instrument in the last few decades. Kikuchi et al. (1985) reported on the positive Doppler shift in the HF Doppler system data during solar flare events, and indicated that there are two possible factors of Doppler shift, i.e., (1) apparent ray path decrease by changing refraction index due to increasing electron densities in the D-region ionosphere, and (2) ray path decrease due to descending reflection point associated with increasing electron density in the F-region ionosphere. In this study, we use the SuperDARN Hokkaido Radar to investigate the detailed characteristics of solar flare effects on ionospheric disturbances. We focus on the positive Doppler shift of ground / sea scatter echoes just before sudden fade-out of echoes. Davies et al. (1962) showed that if the factor (1) is dominant, the Doppler shift should have positive correlation with slant range and negative correlation with elevation angle and frequency. On the other hand, if the factor (2) is dominant, the Doppler shift should have negative correlation with slant range and positive correlation with elevation angle and frequency. While Kikuchi et al. (1985) studied solar flare events and mainly discussed frequency dependence of Doppler shift, we study mainly slant range and elevation angle dependence, for the first time to the best of our knowledge. We found that the factor (1), in other words, increase of electron densities at D-region ionosphere, is dominant during solar flare events. This result is consistent with that of Kikuchi et al. In order to study characteristics of ionospheric disturbance in more detail, we are studying relationship between timing / amplitude of ionospheric disturbance and that of the solar irradiation changes, by comparing the HF radar data with high wavelength resolution irradiation data for X-ray and EUV from RHESSI and SDO satellites. Generally, X-ray radiation becomes more important for the changes in the D-region during solar flare events. Therefore we investigate relationship between X-ray flux changes and electron density variation in the D-region ionosphere intensively. Further, we estimated electron density changes in the ionsosphere by analyzing elevation angle dependence of Doppler shift in radar echoes quantitatively. We are estimating electron density by considering chemical reaction and photoreaction caused by solar radiation. We will compare the two electron density changes deduced from different two ways and evaluate the amplitude of ionospheric disturbance observed by the HF radar. More detailed analysis result will be reported.

Watanabe, D.; Nishitani, N.; Imada, S.

2013-12-01

344

Extraordinary induction heating effect near the first order Curie transition  

NASA Astrophysics Data System (ADS)

While materials with a 1st order Curie transition (TC) are known for the magnetic cooling effect due to the reversibility of their large entropy change, they also have a great potential as a candidate material for induction heating where a large loss power is required under a limited alternating magnetic field. We have carried out a proof-of-concept study on the induction heating effect in 1st order ferromagnetic materials where the temperature is self-regulated at TC. LaFe11.57Si1.43H1.75, a well-known magnetocaloric material, was employed in this study because TC of this compound (319 K) resides in the ideal temperature range for hyperthermia treatment of cancerous cells. It is found that the hysteresis loss of LaFe11.57Si1.43H1.75 increases dramatically near TC due to the magnetic phase coexistence associated with the 1st order magnetic transition. The spontaneous magnetization (Ms) shows a very abrupt decrease from 110 Am2kg-1 at 316 K to zero at 319 K. This large Ms immediately below TC along with the enhanced irreversibility of the hysteresis curve result in a specific absorption rate as large as 0.5 kWg-1 under a field of 8.8 kAm-1 at 279 kHz. This value is nearly an order of magnitude larger than that observed under the same condition for conventional iron oxide-based materials. Moreover, the large heating effect is self-regulated at the 1st order TC (319 K). This proof-of-concept study shows that the extraordinary heating effect near the 1st order Curie point opens up a novel alloy design strategy for large, self-regulated induction heating.

Barati, M. R.; Selomulya, C.; Sandeman, K. G.; Suzuki, K.

2014-10-01

345

Preseismic Lithosphere-Atmosphere-Ionosphere Coupling  

NASA Astrophysics Data System (ADS)

Preseismic atmospheric and ionospheric disturbances besides preseismic geo-electric potential anomalies and ultra-low-frequency (ULF) geomagnetic variations observed on the ground have been reported. Both the phenomena have been found since the 1980s and a number of papers have been published. Since most of the reported phenomena transiently appear with accompanying quiescence before the mainshock, this prevents us to intuitively recognize a correlation between the anomaly appearance and the earthquake occurrence. Some of them, however, showed that anomalies monotonically grew into the mainshock, of which a variation supports the concept of seismic nucleation process under the pre-earthquake state. For example, Heki [GRL, 2011] reported that ionospheric electron density monotonically enhanced tens of minutes prior to the subduction mega-earthquake. However, this preseismic enhancement is apparent variation attributed to tsunamigenic ionospheric hole [Kakinami and Kamogawa et al, GRL, 2012], namely wide and long-duration depression of ionospheric electron after tsunami-excited acoustic waves reach the ionosphere. Since the tsunamigenic ionospheric hole could be simulated [Shinagawa et al., GRL, 2013], the reported variations are high-possibly pseudo phenomena [Kamogawa and Kakinami, JGR, 2013]. Thus, there are barely a few reports which show the preseismic monotonic variation supported by the concept of the seismic nucleation process. As far as we discuss the preseismic geoelectromagnetical and atmospheric-ionospheric anomalies, preseismic transient events from a few weeks to a few hours prior to the mainshock are paid attention to for the precursor study. In order to identify precursors from a number of anomalies, one has to show a statistical significance of correlation between the earthquake and the anomalies, to elucidate the physical mechanism, or to conduct both statistical and physical approach. Since many speculation of the physical mechanism have been hardly verified so far, a statistical approach has been unique way to promote the research. After the 2000s, several papers showing robust statistical results have arisen. In this paper, we focus on publications satisfying the following identification criteria: 1) A candidate of precursor, namely anomaly, is quantitatively defied. 2) Two time-series of anomalies and earthquake are constructed within the fixed thresholds such as a minimum magnitude, a region, and a lead-time. 3) To obtain a statistical correlation, a statistical process which includes four relations considering all combination among earthquake - no earthquake versus anomaly and no anomalies is applied, e. g., phi correlation. 4) For correlations under various thresholds the results keep consistency. 5) Large anomalies appear before large earthquakes. One of papers based on the identification criteria, which concerns preseismic geoelectrically anomalies, is introduced as an educative example. VAN method in Greece, i. e., Geo-electric potential difference measurement for precursor study in Greece, has been often discussed in the point of view of success and failure performance for practical prediction [Varotsos et al, Springer, 2011] to show a correlation and then less number of papers shows the statistical correlation with satisfying the identification criteria [Geller (ed.), GRL, 1996], so that the phenomena had been controversial. However, recent related study in Kozu-Island, Japan which satisfied the criteria showed the robust correlation [Orihara and Kamogawa et al., PNAS, 2012]. Therefore, the preseismic geoelectric anomalies are expected to be a precursor. Preseismic lithosphere-atmosphere-ionosphere coupling has been intensively discussed [Kamogawa, Eos, 2006]. According to review based on the identification criteria with considering recent publications, plausible precursors have been found, which are tropospheric anomaly [Fujiwara and Kamogawa, GRL, 2004], daytime electron depletion in F region [Liu et al, JGR, 2006], nighttime decrease of background intensity of VLF electromagnetic waves poss

Kamogawa, Masashi

346

Seismo-ionospheric coupling appearing as equatorial electron density enhancements observed via DEMETER electron density measurements  

NASA Astrophysics Data System (ADS)

We report the processes and results of statistical analysis on the ionospheric electron density data measured by the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite over a period of 6 years (2005-2010), in order to investigate the correlation between seismic activity and equatorial plasma density variations. To simplify the analysis, three equatorial regions with frequent earthquakes were selected and then one-dimensional time series analysis between the daily seismic activity indices and the equatorial ionization anomaly (EIA) intensity indices, which represent relative equatorial electron density increase, were performed for each region. The statistically significant values of the lagged cross-correlation function, particularly in the region with minimal effects of longitudinal asymmetry, indicate that some of the very large earthquakes with M > 5.0 in the low-latitude region can accompany observable precursory and concurrent EIA enhancements, even though the seismic activity is not the most significant driver of the equatorial ionospheric evolution. The physical mechanisms of the seismo-ionospheric coupling is consistent with our observation, and the possibility of earthquake prediction using the EIA intensity variation is discussed.

Ryu, K.; Lee, E.; Chae, J. S.; Parrot, M.; Pulinets, S.

2014-10-01

347

Global Assimilation of Ionospheric Measurements-Gauss Markov model: Improved specifications with multiple data types  

NASA Astrophysics Data System (ADS)

The Earth's ionosphere is a highly dynamic region that is almost constantly in a state of flux. Solar radiation, geomagnetic activity, chemical reactions, and natural dynamics all act to perturb the state of the ionosphere. The ionosphere changes on time scales of hours to days, with the fine-scale ionospheric structures that are frequently observed lacking in global physics-based models due to time step and spatial resolution constraints. To properly specify the ionosphere, data are needed, thus data assimilation. The Utah State University Global Assimilation of Ionospheric Measurements-Gauss Markov (GAIM-GM) model uses a data assimilation method to correct a physics-based model of the ionosphere using five different data types, divided into nine different data sources. Multiple data types are necessary because the data from any individual data source will not be sufficient for global reconstructions. The GAIM-GM specification (in real time) can then be used to correct for ionospheric propagation delays, thereby improving geolocation and communications. The focus here is to show the quantitative effects that multiple data types have on GAIM-GM ionospheric specifications for a relatively quiet day (19 April) in 2012.

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

2014-12-01

348

New Ethanol Ordering Process Effective March 11, 2013, Ethanol must be ordered through an Ethanol Form in the  

E-print Network

New Ethanol Ordering Process Effective March 11, 2013, Ethanol must be ordered through an Ethanol Services will accept faxed orders for Ethanol. · Monday, March 11, 2013 is the first day the PantherExpress System will accept orders for Ethanol. Requirements · Your PantherExpress System account must be properly

Sibille, Etienne

349

Experimentally investigate ionospheric depletion chemicals in artificially created ionosphere  

SciTech Connect

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

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

2012-09-15

350

Plasma Interactions in Titan's Ionosphere  

E-print Network

calculations of the thermal electron population (electrons with energies less than 2 eV), and chemical reactions in the ionosphere. The results of these models will be compared to data collected by instruments aboard Cassini. Modeled ion production rates...

Richard, Matthew

2013-05-31

351

Solar Flare Impacts on Ionospheric Electrodynamics  

NASA Technical Reports Server (NTRS)

The sudden increase of X-ray and extreme ultra-violet irradiance during flares increases the density of the ionosphere through enhanced photoionization. In this paper, we use model simulations to investigate possible additional contributions from electrodynamics, finding that the vertical E X B drift in the magnetic equatorial region plays a significant role in the ionosphere response to solar flares. During the initial stage of flares, upward E X B drifts weaken in the magnetic equatorial region, causing a weakened equatorial fountain effect, which in turn causes lowering of the peak height of the F2 region and depletion of the peak electron density of the F2 region. In this initial stage, total electron content (TEC) enhancement is predominantly determined by solar zenith angle control of photoionization. As flares decay, upward E X B drifts are enhanced in the magnetic equatorial region, causing increases of the peak height and density of the F2 region. This process lasts for several hours, causing a prolonged F2-region disturbance and TEC enhancement in the magnetic equator region in the aftermath of flares. During this stage, the global morphology of the TEC enhancement becomes predominantly determined by these perturbations to the electrodynamics of the ionosphere.

Qian, Liying; Burns, Alan G.; Solomon, Stanley C.; Chamberlin, Phillip C.

2012-01-01

352

Ionospheric scintillation studies  

NASA Technical Reports Server (NTRS)

The diffracted field of a monochromatic plane wave was characterized by two complex correlation functions. For a Gaussian complex field, these quantities suffice to completely define the statistics of the field. Thus, one can in principle calculate the statistics of any measurable quantity in terms of the model parameters. The best data fits were achieved for intensity statistics derived under the Gaussian statistics hypothesis. The signal structure that achieved the best fit was nearly invariant with scintillation level and irregularity source (ionosphere or solar wind). It was characterized by the fact that more than 80% of the scattered signal power is in phase quadrature with the undeviated or coherent signal component. Thus, the Gaussian-statistics hypothesis is both convenient and accurate for channel modeling work.

Rino, C. L.; Freemouw, E. J.

1973-01-01

353

Variation of ionospheric total electron contents near the equatorial anomaly region during the solar minimum  

Microsoft Academic Search

The ionospheric total electron content (TEC), derived by analyzing dual frequency signals from the Global Positioning System (GPS) recorded near the equatorial anomaly region, Varanasi (geomag. lat. 14 degree 55 minute N, geomag. long.154 degree E) is studied. Specifically, we studied monthly seasonal and annual variations as well as solar and geomagnetic effects on the equatorial ionospheric anomaly (EIA) during

Abhay Kumar Singh; Sanjay Kumar; Francisco Azpilicueta

2008-01-01

354

Features of the Ionosphere Modification Preceding Strong Earthquakes Derived Using GPS TEC Measurements  

Microsoft Academic Search

In the last years the monitoring of the ionospheric effects of different origin is related with using of global navigating system (GPS \\/ GLONASS) signals. By means of measurements of the signal temporal delays it is possible to map total electron content (TEC) of the Earth's ionosphere and investigate its temporal evolution depended on the variations of electron concentration in

A. Krankowski; I. Zakharenkova; I. Shagimuratov

2008-01-01

355

A physical mechanism of positive ionospheric storms at low latitudes and midlatitudes  

Microsoft Academic Search

A physical mechanism of the positive ionospheric storms at low latitudes and midlatitudes is presented through multi-instrument observations, theoretical modeling, and basic principles. According to the mechanism, an equatorward neutral wind is required to produce positive ionospheric storms. The mechanical effects of the wind (1) reduce (or stop) the downward diffusion of plasma along the geomagnetic field lines, (2) raise

N. Balan; K. Shiokawa; Y. Otsuka; T. Kikuchi; D. Vijaya Lekshmi; S. Kawamura; M. Yamamoto; G. J. Bailey

2010-01-01

356

Ionospheric Heating by Radio Waves: Predictions for Arecibo and the Satellite Power Station  

Microsoft Academic Search

The effect of resistive heating by radio waves on ionospheric temperatures, electron densities, and airglow emissions is examined by using numerical ionospheric structure and heat balance codes. Two cases are studied: (1) a 3-GHz, 10-GW microwave beam from a proposed satellite power station and (2) IMW and 3-MW beams of 15-MHz radio waves launched by the Arecibo antenna. By intent,

F. W. Perkins; R. G. Roble

1978-01-01

357

Simultaneous, dual-point, in situ measurements of ionospheric structures using space tethers: TSS-1R observations  

NASA Astrophysics Data System (ADS)

First ever simultaneous, dual-point, in situ measurements of natural ionospheric structures using widely spaced tethered sensors, flying in formation, were made during the reflight of the Tethered Satellite System (TSS-1R) mission. A “target-of-opportunity” observation provided a direct comparison of structured ionospheric irregularity features at two altitudes near the South American geomagnetic equator at approximately 2000 hours local time and at an altitude of ?300 km. With the TSS-1R satellite and space shuttle separated by a vertical distance of 10 km, correlated plasma signatures detected by plasma instruments at each end indicated a strong eastward displacement in the irregularity features and possible growth of steepened features at the higher altitude. Observations made by a SUNDIAL ground station ionosonde located north of the flight path also indicated considerable spread-F activity at the time. A SUNDIAL corrected ionospheric model indicated that the shuttle was flying near the F-peak. Therefore, the strongly correlated in situ observations were most likely associated with irregularities in their early development or modulations near the F-peak due to equatorial spread-F (ESF). While the TSS-1R system was not optimized for dual-point in situ ionospheric measurements, and the tether break eliminated additional equatorial zone observations planned for later in the mission, the results reported here nevertheless indicate that vertically correlated plasma features can exist and can also have strong structural variations as a function of altitude. Such variations need closer examination in order to understand their effects on radiowave scintillation. These observations also demonstrated the feasibility of tethered sensors in the study of ionospheric irregularities using controlled vertical sampling.

Indiresan, R. S.; Gilchrist, B. E.; Basu, S.; Lebreton, J.-P.; Szuszczewicz, E. P.

358

Magnetosphere-ionosphere Dynamic Coupling: Reflection and Transmission for Alfven Waves  

NASA Astrophysics Data System (ADS)

The dynamic coupling between the magnetosphere and ionosphere may be viewed as effected by superposition of propagating magnetohydrodynamic (MHD) perturbations between the two regions. At the boundary between the magnetosphere and ionosphere, some perturbations are reflected, while others are transmitted into the ionosphere and subject to further reflection, transmission and absorption within the ionosphere. It is well known that the Alfven waves are the most efficient means to couple slow variations, which carry substantial momentum, between plasmas that are connected by the magnetic field over a long distance. We investigate the reflection and transmission of an Alfven wave incident from the magnetosphere onto the boundary by analogy to optics. Because magnetized plasmas, even with isotropic temperatures, are highly anisotropic for wave propagation, we generalize the law of reflection and specify Snell's law for each of the three wave modes: incompressible Alfven mode and compressible fast and slow modes, for an incident Alfven wave. Unlike conventional optical systems, the interface between two magnetized plasmas is not solid and momentum and energy may be transferred by compression. In the presence of compressible modes, the Fresnel conditions need substantial modification. We derive the Fresnel conditions, the reflectances and transmittances, and mode generation for incidence parallel to the background magnetic field and speed of sound much smaller than Alfven speed. In this case of parallel propagation, Alfven and fast mode waves themselves are identical and can be distinguished only by the orientation of the velocity and magnetic perturbations relative to the latitudinally inclined magnetic field. An incident wave with perturbations in the azimuthal (magnetospheric toroidal) direction is a pure Alfven mode and generates two Alfven waves (reflected and transmitted). An incident wave with perturbations in the latitudinal (magnetospheric poloidal) direction is a pure fast mode wave and generates four waves (fast and slow modes for both reflection and transmission). The slow modes, needed to balance the fast modes at the boundary in order to satisfy the Fresnel conditions, carry little energy mostly because of their small propagation speed.

Song, P.; Vasyliunas, V. M.

2013-12-01

359

Dayside ionospheric conductivities at Mars  

Microsoft Academic Search

We present estimates of the day-side ionospheric conductivities at Mars based on magnetic field measurements by Mars Global Surveyor (MGS) at altitudes down to ?100km during aerobraking orbits early in the mission. At Mars, the so-called ionospheric dynamo region, where plasma\\/neutral collisions permit electric currents perpendicular to the magnetic field, lies between 100 and 250km altitude. We find that the

Hermann Opgenoorth; Ranvir Dhillon; Lisa Rosenqvist; Mark Lester; Niklas Edberg; Steve Milan; Paul Withers; David Brain

2010-01-01

360

Effective recombination coefficient and solar zenith angle effects on low-latitude D-region ionosphere evaluated from VLF signal amplitude and its time delay during X-ray solar flares  

NASA Astrophysics Data System (ADS)

Excess solar X-ray radiation during solar flares causes an enhancement of ionization in the ionospheric D-region and hence affects sub-ionospherically propagating VLF signal amplitude and phase. VLF signal amplitude perturbation (DeltaA) and amplitude time delay (Deltat) (vis- ´a-vis corresponding X-ray light curve as measured by GOES-15) of NWC/19.8 kHz signal have been computed for solar flares which is detected by us during Jan-Sep 2011. The signal is recorded by SoftPAL facility of IERC/ICSP, Sitapur (22(°) 27'N, 87(°) 45'E), West Bengal, India. In first part of the work, using the well known LWPC technique, we simulated the flare induced excess lower ionospheric electron density by amplitude perturbation method. Unperturbed D-region electron density is also obtained from simulation and compared with IRI-model results. Using these simulation results and time delay as key parameters, we calculate the effective electron recombination coefficient (alpha_{eff}) at solar flare peak region. Our results match with the same obtained by other established models. In the second part, we dealt with the solar zenith angle effect on D-region during flares. We relate this VLF data with the solar X-ray data. We find that the peak of the VLF amplitude occurs later than the time of the X-ray peak for each flare. We investigate this so-called time delay (Deltat). For the C-class flares we find that there is a direct correspondence between Deltat of a solar flare and the average solar zenith angle Z over the signal propagation path at flare occurrence time. Now for deeper analysis, we compute the Deltat for different local diurnal time slots DT. We find that while the time delay is anti-correlated with the flare peak energy flux phi_{max} independent of these time slots, the goodness of fit, as measured by reduced-chi(2) , actually worsens as the day progresses. The variation of the Z dependence of reduced-chi(2) seems to follow the variation of standard deviation of Z along the T_x-R_x propagation path. In other words, for the flares having almost constant Z over the path a tighter anti-correlation between Deltat and phi_{max} was observed.

Basak, Tamal; Chakrabarti, Sandip Kumar

361

Effective recombination coefficient and solar zenith angle effects on low-latitude D-region ionosphere evaluated from VLF signal amplitude and its time delay during X-ray solar flares  

NASA Astrophysics Data System (ADS)

Excess solar X-ray radiation during solar flares causes an enhancement of ionization in the ionospheric D-region and hence affects sub-ionospherically propagating VLF signal amplitude and phase. VLF signal amplitude perturbation (? A) and amplitude time delay (? t) (vis-á-vis corresponding X-ray light curve as measured by GOES-15) of NWC/19.8 kHz signal have been computed for solar flares which is detected by us during Jan-Sep 2011. The signal is recorded by SoftPAL facility of IERC/ICSP, Sitapur (22? 27'N, 87? 45'E), West Bengal, India. In first part of the work, using the well known LWPC technique, we simulated the flare induced excess lower ionospheric electron density by amplitude perturbation method. Unperturbed D-region electron density is also obtained from simulation and compared with IRI-model results. Using these simulation results and time delay as key parameters, we calculate the effective electron recombination coefficient ( ? eff ) at solar flare peak region. Our results match with the same obtained by other established models. In the second part, we dealt with the solar zenith angle effect on D-region during flares. We relate this VLF data with the solar X-ray data. We find that the peak of the VLF amplitude occurs later than the time of the X-ray peak for each flare. We investigate this so-called time delay (? t). For the C-class flares we find that there is a direct correspondence between ? t of a solar flare and the average solar zenith angle Z over the signal propagation path at flare occurrence time. Now for deeper analysis, we compute the ? t for different local diurnal time slots DT. We find that while the time delay is anti-correlated with the flare peak energy flux ? max independent of these time slots, the goodness of fit, as measured by reduced- ? 2, actually worsens as the day progresses. The variation of the Z dependence of reduced- ? 2 seems to follow the variation of standard deviation of Z along the T x - R x propagation path. In other words, for the flares having almost constant Z over the path a tighter anti-correlation between ? t and ? max was observed.

Basak, Tamal; Chakrabarti, Sandip K.

2013-12-01

362

Ionospheric F region effects observed in the American and African sectors during the intense geomagnetic storm of September-October 2012  

NASA Astrophysics Data System (ADS)

This study presents an investigation of geomagnetic disturbance effects on the equatorial, low- and mid-latitude ionospheric F region over the American and African sectors during the intense geomagnetic storm (maximum Kp index of 6.7) that occurred on 30th September, 2012 and 1st October, 2012. In this study digital ionosonde and Global Positioning System (GPS) data are simultaneously utilized from 30th September to 3rd October 2012. The diurnal variability over this four day period observed from both the digital ionosonde and from ground based GPS units can be characterized as quiet, slightly disturbed, and strongly disturbed periods. This time period includes the sudden commencement of the storm (SCS), the main phase (MPS), and the recovery phase of the storm (RPS). During the period of investigation, ionospheric parameters F-region critical frequency (foF2) and minimum F-region virtual height ('hF) were obtained at Jicamarca, São Luís, Fortaleza, Palmas and Port Stanley at the following geographical coordinates, respectively: 12.0ºS 76.8ºW, 2.6ºS 44.2ºW, 3.8ºS 38ºW, 10.2ºS 48.8ºW and 51.6ºS 57.9ºW. In this study, we also used observations of 20 GPS stations located at Greenbelt (39.0ºN, 76.8ºW), Cambridge (38.6ºN, 76.1ºW), Virgin Islands (17.6ºN, 64.6ºW), Eusebio (03.9ºS, 38.4ºW), Iquitos (03.8ºS, 73.3 ºW), Arequipa (16.5ºS, 71.5ºW), Cachoeira Paulista (22.7ºS, 45.0ºW), Copiapo (27.4ºS, 70.4ºW), La Plata (34.9ºS, 57.9ºW), Concepcion (36.8ºS, 73.0ºW), Rio Grande (53.8ºS, 67.8ºW), Dakar (14.7ºN, 17.4ºW), Addis (09.0ºN, 38.8ºE), Cotonou (06.4ºN, 02.5ºE), Libreville (00.4ºN, 09.7ºE), Mbarara (00.6ºS, 30.7ºE), Lusaka (15.4ºS, 28.3ºE), Windhoek (22.6ºS, 17.1ºE), Springbok (29.7ºS, 17.9ºE) and Sutherland (32.4ºS, 20.8ºE). Vertical Total Electron Content (VTEC) and TEC fluctuations (ROT, rate of change of TEC) are calculated from GPS data using the measured Slant Total Electron Content (STEC) records from the 20 GPS receiving stations mentioned above in the American and African sectors. Measurements of scintillations (S4, amplitude scintillation index) are also used in this investigation to study the formation of irregularities. Salient features including the observed aforementioned characteristics will be presented and discussed.

De Jesus, Rodolfo; Gende, Mauricio; Fagundes, Paulo Roberto; Coster, Anthea; Bolaji, Segun; Kavutarapu, Venkatesh; De Abreu, Alessandro; Sobral, J. H. A.; Pillat, Valdir Gil; Batista, Inez S.

363

Application of nonlinear methods to the study of ionospheric plasma  

NASA Astrophysics Data System (ADS)

Most of the processes taking place in the auroral region of Earth's ionosphere are reflected in a variety of dynamic forms of the aurora borealis. In order to study these processes it is necessary to consider temporary and spatial variations of the characteristics of ionospheric plasma. Most traditional methods of classical physics are applicable mainly for stationary or quasi-stationary phenomena, but dynamic regimes, transients, fluctuations, selfsimilar scaling could be considered using the methods of nonlinear dynamics. Special interest is the development of the methods for describing the spatial structure and the temporal dynamics of auroral ionosphere based on the ideas of percolation theory and fractal geometry. The fractal characteristics (the Hausdorff fractal dimension and the index of connectivity) of Hall and Pedersen conductivities are used to the description of fractal patterns in the ionosphere. To obtain the self-consistent estimates of the parameters the Hausdorff fractal dimension and the index of connectivity in the auroral zone, an additional relation describing universal behavior of the fractal geometry of percolation at the critical threshold is applied. Also, it is shown that Tsallis statistics can be used to study auroral ionosphere

Chernyshov, A. A.; Mogilevsky, M. M.; Kozelov, B. V.

2015-01-01

364

Variation of the first cut-off frequency of the Earth-ionosphere waveguide observed by DEMETER  

NASA Astrophysics Data System (ADS)

More than four years of VLF electric field data recorded by DEMETER have been analyzed, in order to monitor the first cut-off frequency (QTM1) of the Earth-ionosphere waveguide, at around 1.6-1.8 kHz. Since losses in a waveguide are maximized right at the cut-off frequency, DEMETER (˜700 km orbit) can detect the minimum of energy of the leaking fields coming from the waveguide. This measurement permits to draw a global map of its value (f1), which is directly related to the effective height of the ionosphere (h) by the relation f1 = c/2h (c is the speed of light). It enables the remote sensing of the D region, which is one of the less known layers of the ionosphere, because it is too low for satellites to orbit inside it and too high for balloons to reach it. The effective height depends mainly on the electron density (Ne) and neutral density (Nn) profiles, which determine the plasma frequency and the electron mobility. The effective height shifts downward 5-10 km in southern warm season in the South Pacific Ocean. Another effect is observed in the Indian and Atlantic Oceans; the effective height decreases its value twice a year, in the area of roughly ±15° from the geomagnetic equator. The main causes for the changes on the effective reflection height are the solar radiation and the thunderstorm activity. However, the observed shifts are more prominent over the oceans, and a possible explanation for this difference could be attributed to i) less polluted conditions above the oceans (aerosols change the atmospheric conductivity and then the global atmospheric electric circuit), ii) the effect of the current associated to the thunderclouds on the bottom of the ionosphere because thunderstorms are much more numerous above land, or iii) ionization by elves because their occurrence is larger above oceans.

Toledo-Redondo, S.; Parrot, M.; Salinas, A.

2012-04-01

365

Higher-order effects in inclusive electron-nucleus scattering  

NASA Astrophysics Data System (ADS)

Higher order corrections in the theory of inclusive scattering of high energy electrons by nuclear matter are studied. They involve at least three nucleons, and are due to: (i) the correlations among the spectator nucleons in matter, and (ii) the Pauli blocking of the scattering of the struck nucleon by a spectator nucleon. Their effect on the cross sections is found to be much smaller than those of the two-nucleon correlation hole and of colour transparency.

Benhar, O.; Fabrocini, A.; Fantoni, S.; Pandharipande, V. R.; Pieper, S. C.; Sick, I.

1995-02-01

366

Ionospheric detection of gravity waves induced by tsunamis  

Microsoft Academic Search

Tsunami waves propagating across long distances in the open-ocean can induce atmospheric gravity waves by dynamic coupling at the surface. In the period range 10 to 20 minutes, both have very similar horizontal velocities, while the gravity wave propagates obliquely upward with a vertical velocity of the order of 50 m s-1, and reaches the ionosphere after a few hours.

Juliette Artru; Vesna Ducic; Hiroo Kanamori; Philippe Lognonné; Makoto Murakami

2005-01-01

367

Microwave Discharge Oxygen Ion Source for Ionospheric Plasma Environment Simulation  

Microsoft Academic Search

In recent years, concern has been raised about the interference phenomena (chemical reaction, sputtering etc.) between ionospheric plasma and high-voltage space systems such as the International Space Station and so on. In order to solve the physical mechanisms of these phenomena and establish the prevention technology, it is important to accumulate experimental data based on ground simulation tests. Therefore we

Hiroshi Hayashi; Mengu Cho; Kazutaka Nishiyama; Hitoshi Kuninaka

2005-01-01

368

Second-order nonlinear optical effects of spin currents  

NASA Astrophysics Data System (ADS)

Pure spin currents, which carry information via spins in lieu of charges, are a key element in spintronics and signify the quantum spin Hall effect. However, they are hardly traceable as they bear neither net magnetization nor net charge currents, notwithstanding many "smoking-gun" evidences. We show that a pure spin current has measurable second-order nonlinear optical effects by symmetry analysis and microscopic calculations. These findings may be exploited for directly "seeing" spin currents in real-time and real-space with standard nonlinear optical spectroscopy.

Wang, Jing; Liu, Ren-Bao; Zhu, Bang-Fen

2011-12-01

369

The synthesis of travelling ionospheric disturbance (TID) signatures in HF radar observations using ray tracing  

E-print Network

The synthesis of travelling ionospheric disturbance (TID) signatures in HF radar observations using-time-intensity plots when travelling ionospheric disturbances (TIDs) are present. These signatures, in particular- iments. Key words. Ionosphere (auroral ionosphere; ionosphere ±atmosphere interactions; ionospheric

Paris-Sud XI, Université de

370

Electric fields in the ionosphere  

NASA Technical Reports Server (NTRS)

F-region drift velocities, measured by incoherent-scatter radar were analyzed in terms of diurnal, seasonal, magnetic activity, and solar cycle effects. A comprehensive electric field model was developed that includes the effects of the E and F-region dynamos, magnetospheric sources, and ionospheric conductivities, for both the local and conjugate regions. The E-region dynamo dominates during the day but at night the F-region and convection are more important. This model provides much better agreement with observations of the F-region drifts than previous models. Results indicate that larger magnitudes occur at night, and that daily variation is dominated by the diurnal mode. Seasonal variations in conductivities and thermospheric winds indicate a reversal in direction in the early morning during winter from south to northward. On magnetic perturbed days and the drifts deviate rather strongly from the quiet days average, especially around 13 L.T. for the northward and 18 L.T. for the westward component.

Kirchhoff, V. W. J. H.

1975-01-01

371

Currents and Electrojets in the Ionosphere of Mars  

NASA Astrophysics Data System (ADS)

How the solar wind interacts with a planetary object depends upon the object's properties such as the presence of a magnetic field or an atmosphere. An unmagnetized object cannot stand-off the solar wind unless it possess a substantial atmosphere which can be ionized by solar radiation creating a conductive ionosphere. Currents can then be induced in the ionosphere; these currents act to cancel out the external solar wind magnetic field preventing it from reaching the surface. Here we present simple analytical calculations of such induced currents in the ionosphere of Mars. We consider currents in the ionospheric dynamo region which can be driven by thermospheric winds as well as currents driven by electric fields (i.e., plasma motion through the neutrals). We include in these estimates the effects of "equatorial-type" electrojets due to vertical conductivity gradients in the presence of horizontal magnetic fields. In addition, we consider "auroral-type" electrojets due to horizontal conductivity gradients resulting from particle precipitation and/or large variations in the magnetic field strength near vertical cusps in strong crustal field regions. The direction of the external driver is important. In some cases, the secondary current adds to the primary current creating electrojets. In other cases, the secondary current can cancel or nearly cancel the primary current resulting in very weak net currents. These results can give us insights into how external magnetic fields are effectively screened out by induced currents and how these induced currents can influence ionospheric dynamics around unmagnetized objects.

Fillingim, Matthew O.; Lillis, Robert; Brain, D. A.

2015-04-01

372

Monitoring the ionosphere during the earthquake on GPS data  

NASA Astrophysics Data System (ADS)

The problem of stability estimation of physical state of an atmosphere attracts a rapt attention of the world community but it is still far from being solved A lot of global atmospheric processes which have direct influence upon all forms of the earth life have been detected The comprehension of cause effect relations stipulating their origin and development is possible only on the basis of long-term sequences of observations data of time-space variations of the atmosphere characteristics which should be received on a global scale and in the interval of altitudes as brand as possible Such data can be obtained only with application satellite systems The latest researches have shown that the satellite systems can be successfully used for global and continuous monitoring ionosphere of the Earth In turn the ionosphere can serve a reliable indicator of different kinds of effects on an environment both of natural and anthropogenic origin Nowadays the problem of the short-term forecast of earthquakes has achieved a new level of understanding There have been revealed indisputable factors which show that the ionosphere anomalies observed during the preparation of seismic events contain the information allowing to detect and to interpret them as earthquake precursors The partial decision of the forecast problem of earthquakes on ionospheric variations requires the processing data received simultaneously from extensive territories Such requirements can be met only on the basis of ground-space system of ionosphere monitoring The navigating systems

Smirnov, V. M.; Smirnova, E. V.

373

Ionospheric mid-latitude response to solar wind discontinuities  

NASA Astrophysics Data System (ADS)

We have compiled a database of 356 discontinuities detected by both the Advanced Composition Explorer ACE) and Cluster satellites in the solar wind between 2001-2012 and analyzed their ionospheric response. Each discontinuity of the data base is defined by a change of at least 5 nT in less than 5 min in one or more components of the interplanetary magnetic field (IMF). The discontinuities are observed in January-April every year, when Cluster enters the solar wind. The ionospheric effects of solar wind discontinuities are investigated by checking the variations of critical frequencies foF2, the heights of the F layer and the ionospheric plasma dynamics recorded using ground measurement with a time resolution of 15 minutes from mid-latitude digisondes located in Czech Republic. The time delay between solar wind input and the ionospheric response is analyzed using the characteristics and the shape of the ionograms. The geoeffectiveness of the solar wind discontinuities is expressed as correlation between key plasma parameters (e,g, the solar wind velocity, magnetic jump across the discontinuity) and the ionospheric variations. Solar cycle effects are also discussed.

Munteanu, Costel; Mosna, Zbysek; Kouba, Daniel; Echim, Marius

2013-04-01

374

Cubesat-Based Dtv Receiver Constellation for Ionospheric Tomography  

NASA Astrophysics Data System (ADS)

The Radio Aurora Explorer mission, funded by NSF's Space Weather and Atmospheric Research program, has demonstrated the utility of CubeSat-based radio receiver payloads for ionospheric research. RAX has primarily been an investigation of microphysics of meter-scale ionospheric structures; however, the data products are also suitable for research on ionospheric effects on radio propagation. To date, the spacecraft has acquired (1) ground-based UHF radar signals that are backscattered from meter-scale ionospheric irregularities, which have been used to measure the dispersion properties of meter-scale plasma waves and (2) ground-based signals, directly on the transmitter-spacecraft path, which have been used to measure radio propagation disturbances (scintillations). Herein we describe the application of a CubeSat constellation of UHF receivers to expand the latter research topic for global-scale ionospheric tomography. The enabling factor for this expansion is the worldwide availability of ground-based digital television (DTV) broadcast signals whose characteristics are optimal for scintillation analysis. A significant part of the populated world have transitioned, or soon to be transitioned, to DTV. The DTV signal has a standard format that contains a highly phase-stable pilot carrier that can be readily adapted for propagation diagnostics. A multi-frequency software-defined radar receiver, similar to the RAX payload, can measure these signals at a large number of pilot carrier frequencies to make radio ray and diffraction tomographic measurements of the ionosphere and the irregularities contained in it. A constellation of CubeSats, launched simultaneously, or in sequence over years, similar to DMSPs, can listen to the DTV stations, providing a vast and dense probing of the ionosphere. Each spacecraft can establish links to a preprogrammed list of DTV stations and cycle through them using time-division frequency multiplexing (TDFM) method. An on board program can sort the frequencies and de-trend the phase variations due to spacecraft motion. For a single channel and a spacecraft-DTV transmitter path scan, TEC can be determined from the incremental phase variations for each channel. Determination of the absolute TEC requires knowledge of the absolute phase, i.e., including the number of 2? cycles. The absolute TEC can be determined in the case of multi-channel transmissions from a single tower (most towers house multiple television stations). A CubeSat constellation using DTV transmissions as signals of opportunity is a composite instrument for frontier ionospheric research. It is a novel application of CubeSats to understand the ionospheric response to solar, magnetospheric and upper atmospheric forcing. Combined tomographic measurements of ionospheric density can be used to study the global-scale ionospheric circulation and small-scale ionospheric structures that cause scintillation of trans-ionospheric signals. The data can support a wide range of studies, including Sub-auroral Polarization Streams (SAPS), low latitude plasma instabilities and the generation of equatorial spread F bubbles, and the role of atmospheric waves and layers and sudden stratospheric warming (SSW) events in traveling ionospheric disturbances (TID).

Bahcivan, H.; Leveque, K.; Doe, R. A.

2013-12-01

375

Multi-instrumental study of the ionosphere in European region  

NASA Astrophysics Data System (ADS)

We present the techniques for the investigation of the spatial-temporal structure of the mid-latitude ionosphere on the base of comprehensive analysis of multi-instrumental satellite and ground-based measurements and demonstrates their application at several case study results. For our analysis we used the ionospheric data provided by European ionosondes network (DIAS), as well as GNSS TEC observations. Manually scaled ionosondes' data are used as a benchmark in our study. Two-dimensional maps of vertical TEC over Europe are created using IGS and EUREF permanent networks. These maps have spatial resolution of 1 deg and temporal resolution of 1 h, for investigation of ionosphere response on special events (geomagnetic storms, solar eclipses, etc) there is possibility to create TEC maps with 5-10 min resolution. The high temporal resolution maps give the possibility to study of spatial gradients of electron density. Joint analysis of GPS TEC and FORMOSAT-3/COSMIC radio occultation data allows us to extract and estimate electron content corresponded to the ionosphere (its bottom and topside parts) and the plasmasphere (h>700 km) for different conditions. Several case-studies of geomagnetic storms were analyzed in order to estimate changes and redistribution of electron content between ionosphere and plasmasphere over Europe. The obtained results were compared with TEC, IEC and PEC estimates retrieved by IRI-Plas Model that has the plasmasphere extension up to 20,000 km (GPS orbit). As a new data source there will be new ionospheric sounding station, located in European mid-latitudes in Olsztyn, Poland, that will start its operation at the end of 2013. One of the possible user of ionospheric products is represented by LOFAR (LOw Frequency Array), a new fully digital radio telescope designed for frequencies between 30 MHz and 240 MHz. To the summer of 2015 three new LOFAR stations will be installed in Poland: Lazy (East of Krakow), Borowiec near Poznan and Baldy near Olsztyn. From one side, operation of LOFAR requires calibration of the ionosphere which at low frequencies varies greatly. From the other hand, LOFAR measurements retrieved from several closely located stations can be used for ionosphere/plasmasphere research.

Zakharenkova, I.; Krankowski, A.; Cherniak, I.; Rothkaehl, H.

2013-12-01

376

Dressed four-wave mixing second-order Talbot effect  

NASA Astrophysics Data System (ADS)

We theoretically demonstrate second-order Talbot effect (SOTE) based on entangled photon pairs. The photon pairs are generated from the spontaneous parametric four-wave mixing (SPFWM) process in a cold atomic medium and can be taken as the imaging light in order to realize coincidence recording. A strong standing wave is used to create the electromagnetically induced grating in the entangled photon pairs channels. By changing the frequency detuning of the standing wave or the other optical fields participating in the process, we can manipulate the contrast of the second-order Talbot image. We use the second-order correlation function and the dressed-state picture to explain the SOTE occurring in the SPFWM process. Moreover, we demonstrate the scheme for SOTE based on the spatially correlated twin beams generated from the SPFWM process with injection. This scheme provides a convenient detection proposal for the SOTE at the cost of the image contrast. Compared to the previous self-imaging schemes, the present schemes have the characteristic of controllable image contrast and of nonlocal imaging, and thus, they might broaden their applications in imaging techniques and find applications in quantum lithography.

Chen, Haixia; Zhang, Xun; Zhu, Dayu; Yang, Chang; Jiang, Tao; Zheng, Huaibin; Zhang, Yanpeng

2014-10-01

377

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

NASA Astrophysics Data System (ADS)

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.

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

2011-12-01

378

High-order multiphoton photoelectric effect at midinfrared laser wavelengths  

SciTech Connect

A theoretical model that predicts the unexpectedly high photocurrents that were reported by Farkas et al. [J. Phys. B 31, L461 (1998)] for the photoelectric effect in gold at midinfrared laser wavelengths (12 {mu}m) is presented. It is shown that the observed effect, a nominally 46-photon process at threshold, is a stepwise and multiple-order process, which is strongly saturated at the moderate laser intensity of about {approx}10 MW/cm{sup 2}. The {approx_equal}30-photon-wide energy spectrum of the observed photoelectron current is due to above threshold photoemission. This relatively efficient above threshold effect is due to laser absorption in the long range Coulombic image surface potential.

Georges, A.T. [Department of Physics, University of Patras, Patras 26500 (Greece)

2002-12-01

379

Storm-induced changes of the topside ionosphere as deduced from incoherent-scatter radars. Master's thesis  

SciTech Connect

Incoherent scatter radar observations from Millstone Hill, Saint Santin, and Arecibo are used to illustrate changes of the topside ionosphere during a geomagnetic storm. These observations consist of electron density, electron and ion temperatures, and ion velocity components parallel and perpendicular to the magnetic field. These parameters can further describe changes in ion composition, electric fields, and neutral winds. Attention is given to a specific storm during the Equinox Transition Study (ETS) of September 1984. In order to isolate the storm effects in the topside ionosphere, a comparison will be made between a disturbed and quiet day. A novel result from this study is the finding of correlated oscillations between parallel and perpendicular ion velocity components which are apparently storm induced. Previously, these oscillations have been observed primarily at night, but now it's noticed that during storm conditions there are prominent oscillations during the day.

Lunn, K.J.

1990-01-01

380

Natural hazards monitoring and forecast using the GNSS and other technologies of the ionosphere monitoring  

NASA Astrophysics Data System (ADS)

It is well established now that Atmosphere-Ionosphere Coupling is provided through the local changes of the Global Electric Circuit parameters. Main agent - is column conductivity, modulated mainly at the altitudes of the Global Boundary Layer. We demonstrate the ionospheric effects for different types of natural hazards including volcano eruptions, dusty storms from Western Africa, ionospheric effects from tropical hurricanes, multiple earthquakes. We consider the important role of air ionization from natural (natural ground radioactivity and galactic cosmic rays) and artificial sources (nuclear weapon tests in atmosphere and underground, nuclear power stations and other nuclear enterprises emergencies). We rise also important question that such effects of the ionosphere variability are not taken into account by any ionospheric model and their correct recognition is important not only from the point of view the disasters monitoring but for navigation itself because the magnitude of the ionospheric effects sometimes exceeds the effects from strong magnetic storms and other severe space weather conditions. Some effects like ionospheric effects from tropical hurricanes have more complex physical nature including the formation of streams of neutral atmosphere over the hurricane eye and formation of the strong positive plasma concentration anomaly at the altitude near 1000 km. Some plasma anomalies registered over the tropical depressions before hurricane formation give hope on predictive capabilities of plasma observations over the tropical depressions.

Pulinets, S. A.; Davidenko, D.

2013-12-01

381

Effect of Under-Resolved Grids on High Order Methods  

NASA Technical Reports Server (NTRS)

There has been much discussion on verification and validation processes for establishing the credibility of CFD simulations. Since the early 1990s, many of the aeronautical and mechanical engineering related reference journals mandated that any accepted articles in numerical simulations (without known solutions to compared with) need to perform a minimum of one level of grid refinement and time step reduction. Due to the difficulty in analysis, the effect of under-resolved grids and the nonlinear behavior of available spatial discretizations, are scarcely discussed in the literature. Here, an under-resolved numerical simulation is one where the grid spacing being used is too coarse to resolve the smallest physically relevant scales of the chosen continuum governing equations that are of interest to the numerical modeler. With the advent of new developments in fourth-order or higher spatial schemes, it has become common to regard high order schemes as more accurate, reliable and require less grid points. The danger comes when one tries to perform computations with the coarsest grid possible while still hoping to maintain numerical results sufficiently accurate for complex flows, and especially, data-limited problems. On one hand, high order methods when applies to highly coupled multidimensional complex nonlinear problems might have different stability, convergence and reliability behavior than their well studied low order counterparts, especially for nonlinear schemes such as TVD, MUSCL with limiters, ENO, WENO and discrete Galerkin. On the other hand, high order methods involve more operation counts and systematic grid convergence study can be time consuming and prohibitively expansive. At the same time it is difficult to fully understand or categorize the different nonlinear behavior of finite discretizations, especially at the limits of under-resolution when different types of bifurcation phenomena might occur, depending on the combination of grid spacings, time steps, initial conditions and numerical treatments of boundary conditions.

Yee, H. C.; Sjoegreen, B.; Mansour, Nagi (Technical Monitor)

2001-01-01

382

Effect of Menu Sign Position on Customer Ordering Times and Number of Food-Ordering Errors  

Microsoft Academic Search

Data were collected to determine if an additional menu sign, visible to restaurant customers as they waited in line to order food, would reduce both the amount of time taken to order food as well as the number of food-ordering errors. An A-B-A-B design was utilized in which ordering times and errors were recorded before the addition of a second

R. Spencer Foster; Michael G. Aamodt; James A. Bodenmiller; Jeffrey G. Rodgers; Robert C. Kovach; Devon A. Bryan

1988-01-01

383

Some Considerations On The Within-the-hour Ionospheric Variability  

Microsoft Academic Search

Users of radar surveillance, satellite navigation and satellite communication systems need to assess and monitor ionospheric effects, which exhibit great temporal and spa- tial variation. On the other hand, any degradation in system performance should be promptly detected and its source identified. Thus the need to know a priori when an ionosperic effect may occur at a certain time or

S. S. Kouris; B. Zolesi

2002-01-01

384

Effectiveness of parallel second order model over second and first order models  

Microsoft Academic Search

The chlorine decay is usually described by the first order model (FOM) due to its easiness, although its weaknesses are well known. In this work, two better models, second order model (SOM) and parallel second order model (PSOM), are compared for their accuracy to predict chlorine residuals for a single dosing scenario. Results showed that SOM model provided a better

Ahmad Jabari Kohpaei; Arumugam Sathasivan; Hanieh Aboutalebi

2011-01-01

385

A Forecasting Ionospheric Real-time Scintillation Tool (FIRST)  

NASA Astrophysics Data System (ADS)

Transionospheric radio waves propagating through an irregular ionosphere with plasma depletions, or "bubbles," are subject to sporadic enhancement and fading commonly referred to as scintillation. Knowledge of the current ionospheric condition allows system operators to distinguish between compromises due to the radio environment and system induced failures, while a forecast of the same provides the opportunity for operators to take appropriate actions to mitigate the effects and optimize service. This paper describes a technique that uses the readily accessible ionospheric characteristic h'F from ground-based ionospheric sounder data near the geomagnetic equator to forecast the occurrence or nonoccurrence of low-latitude scintillation activity in VHF/UHF bands. We illustrate the development of the Forecasting Ionospheric Real-time Scintillation Tool and its real-time capability for forecasting scintillation activity. Finally, we have found that there exists a threshold in the h'F value at 1930 LT that corresponds to the onset of scintillation activity in the Peruvian longitude sector, which is found to decrease with decreasing F10.7 cm fluxes in a linear manner.

Redmon, Robert J.; Anderson, David; Caton, Ron; Bullett, Terence

2010-12-01

386

Global ionospheric dynamics and electrodynamics during geomagnetic storms (Invited)  

NASA Astrophysics Data System (ADS)

Globally distributed total electron content (TEC) data has become an important tool for exploring the consequences of storm-time electrodynamics. Magnetosphere-ionosphere coupling during the main phase is responsible for the largest ionospheric effects observed during geomagnetic storms, mediated by global scale electrodynamics. Recent research using case studies reveals a complex picture of M-I coupling and its relationship to interplanetary drivers such as the solar wind electric field. Periods of direct coupling exist where the solar wind electric field is strongly correlated with prompt penetration electric fields, observed as enhanced vertical plasma drifts or an enhanced electrojet in the daytime equatorial ionosphere. Periods of decoupling between low latitude electric fields and the solar wind electric field are also observed, but the factors distinguishing these two types of response have not been clearly identified. Recent studies during superstorms suggest a role for the transverse (y-component) of the interplanetary magnetic field, which affects magnetospheric current systems and therefore may affect M-I coupling, with significant ionospheric consequences. Observations of the global ionospheric response to a range of geomagnetic storm intensities are presented. Scientific understanding of the different factors that affect electrodynamic aspects of M-I coupling are discussed.

Mannucci, A. J.; Tsurutani, B.; Verkhoglyadova, O. P.; Komjathy, A.; Butala, M. D.

2013-12-01

387

The calculation of ionospheric ray paths  

E-print Network

path calculation by calculating ray paths from a cosmic radio source to a satellite in orbit above the level of the ionosphere. Radiation of this type may be totally reflected by the ionosphere thus making reception on the earth impossible... ray paths with constant frequency and variable angle of propagation and range, parabolic ionosphere of electrons assumed, earth's magnetic field neglected 2- 1 The vertical and lateral deviations of a radio wave propagated in a plane ionosphere...

Koehler, Buford Ray

1967-01-01

388

Day–night, seismic, and solar flare effect on the propagation of 24 kHz sub-ionospheric VLF transmitter signals  

Microsoft Academic Search

The preliminary results of a collaborative study on the amplitude variation of 24kHz sub-ionospheric NAA VLF transmitter signals transmitted from Cutler, Maine (Lat. 44.6°N, Long. 67.2°W) and monitored simultaneously at Budapest (Lat. 47.5°N, Long. 19.17°E), Hungary and Agra (Lat. 27.2°N, Long. 78°E), India are presented. The time segments of the propagation paths are so chosen that they lie in the

Manoj Kumar; Vikram Singh; Birbal Singh; P. Steinbach; J. Lichtenberger; D. Hamar

2006-01-01

389

Comparative statistical and spectral studies of seismic and non-seismic sub-ionospheric VLF anomalies  

NASA Astrophysics Data System (ADS)

We present a comparative study of seismic and non-seismic sub-ionospheric VLF anomalies. Our method is based on parameter variations of the sub-ionospheric VLF waveguide formed by the surface and the lower ionosphere. The used radio links working in the frequency range between 10 and 50 kHz, the receivers are part of the European and Russian networks. Various authors investigated the lithopsheric-atmospheric-ionospheric coupling and predicted the lowering of the ionosphere over earthquake preparation zones [1]. The received nighttime signal of a sub-ionospheric waveguide depends strongly on the height of the ionospheric E-layer, typically 80 to 85 km. This height is characterized by a typical gradient of the electron density near the atmospheric-ionospheric boundary [2]. In the last years it has been turned out that one of the major issues of sub-ionospheric seismo-electromagnetic VLF studies are the non-seismic influences on the links, which have to be carefully characterized. Among others this could be traveling ionospheric disturbances, geomagnetic storms as well as electron precipitation. Our emphasis is on the analysis of daily, monthly and annual variations of the VLF amplitude. To improve the statistics we investigate the behavior and typical variations of the VLF amplitude and phase over a period of more than 2 years. One important parameter considered is the rate how often the fluctuations are falling below a significant level derived from a mean value. The temporal variations and the amplitudes of these depressions are studied for several years for sub-ionospheric VLF radio links with the receivers in Graz and Kamchatka. In order to study the difference between seismic and non-seismic turbulences in the lower ionosphere a power spectrum analysis of the received signal is performed too. We are especially interested in variations T>6 min which are typical for atmospheric gravity waves causing the lithospheric-atmospheric-ionospheric coupling [3]. All measured and derived VLF parameters are compared with VLF observations several weeks before an earthquake (e.g. L'Aquila, Italy, April 6, 2009) and with co- and post-seismic phenomena. It is shown that this comparative study will improve the one parameter seismo-electromagnetic VLF methods. References: [1] A. Molchanov, M. Hayakawa: Seismo-Electromagnetics and related Phenomena: History and latest results, Terrapub, 2008. [2] S. Pulinets, K. Boyarchuk: Ionospheric Precursors of Earthquakes, Springer, 2004 [3] A. Rozhnoi et al.: Observation evidences of atmospheric Gravity Waves induced by seismic activity from analysis of subionospheric LF signal spectra, National Hazards and Earth System Sciences, 7, 625-628, 2007.

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

2013-04-01

390

The International Reference Ionosphere - Climatological Standard for the Ionosphere  

NASA Technical Reports Server (NTRS)

The International Reference Ionosphere (IRI) a joint project of URSI and COSPAR is the defacto standard for a climatological specification of ionospheric parameters. IRI is based on a wide range of ground and space data and has been steadily improved since its inception in 1969 with the ever-increasing volume of ionospheric data and with better mathematical descriptions of the observed global and temporal variation patterns. The IRI model has been validated with a large amount of data including data from the most recent ionospheric satellites (KOMPSAT, ROCSAT and TIMED) and data from global network of ionosondes. Several IRI teams are working on specific aspects of the IRI modeling effort including an improved representation of the topside ionosphere with a seamless transition to the plasmasphere, a new effort to represe