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1

Higher order ionospheric propagation effects on GPS radio occultation signals  

NASA Astrophysics Data System (ADS)

With the increasing number of remote sensing satellites using the GPS radio occultation technique for atmospheric sounding, the estimation of higher order ionospheric effects and their mitigation have become relevant and important. Due to long ionospheric limb paths, GPS signals are strongly affected by ionospheric refraction during radio occultation. Standard dual-frequency GPS measurements may be used to estimate the first order term of the refractive index. However, non-linear terms such as the second and third order ionospheric terms and ray path bending effects are not considered in occultation measurements so far. Analysing selected CHAMP-GPS occultation events different higher order ionospheric terms are estimated and their effects on dual-frequency range estimation and total electron content (TEC) estimation are discussed. We have found that the separation between the GPS L1 and L2 ray paths exceeds the kilometer level during occultation for a vertical TEC level of more than 160 TEC units. Corresponding errors in the GPS dual-frequency range estimation and TEC estimation are found to exceed the meter and 10 TEC units level, respectively.

Hoque, M. Mainul; Jakowski, N.

2010-07-01

2

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

-dimentional coordinate corrections, computed in the CF reference system show high diurnal variability, caused6. Coordinate solution shift due to 2-nd order ionospheric effect The second-order ionospheric path, IRI2007 values for TEC and the height of ionospheric maximum, and International Geomagnetic Reference

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

The effect of the 2nd order ionosphere correction on GPS orbits and station positions  

Microsoft Academic Search

The Global Positioning System (GPS) transmits two frequencies, allowing users to correct for the first-order ionospheric signal group delay (or phase advance) that can be as large as 100 meters on L1 frequency. The second-order ionospheric term, caused by the Faraday rotation effect induced by the Earth magnetic field, is about 1000 times smaller and usually ignored. Implementation of the

S. Kedar; G. A. Hajj; A. Komjathy; B. D. Wilson; W. I. Bertiger

2004-01-01

5

Second-order ionospheric effects on satellite radio occultation observations and their impact on atmospheric studies  

NASA Astrophysics Data System (ADS)

This dissertation describes the development of first-of-a-kind mathematical models that both quantify higher-order ionospheric effects and their impact on Global Positioning System radio occultation (GPS/RO) data products. We develop new and innovative models to: a) remove the second-order ionospheric effect from Total Electron Content (TEC) estimations; b) quantify the second-order ionospheric delay in GPS/RO signal propagation using the Faraday phenomenon; c) quantify the vertical distribution of the first- and second-order ionospheric residual effects on GPS/RO data products; and d) retrieve improved atmospheric water vapour profiles. For the first time we combine GPS/RO measurements with space-based gravity missions to characterize the response of the GPS/RO-derived atmospheric parameters to the Earth's gravity anomalies. Independently, we implement these mathematical models in a new GPS/RO processing software package to investigate, for the first time, the impact of higher-order ionospheric residual effects on ionospheric and atmospheric products. We observe that under low solar activity, the second-order ionospheric residual effect introduces: a) slowly varying positive systematic biases of ˜1-3 TECU on TEC estimations as function of occultation time; b) maximum negative systematic biases of ˜0.35 N-units on atmospheric refractivity close to the Earth's surface; c) negative systematic biases of ˜0.5 K close to the Earth's surface, which decrease with altitude and above 26 km become positive, peaking at ˜2.0 K at 50 km and d) negative systematic biases of ˜0.08 mbar on the water vapour pressure. Further studies reveal that the second-order ionospheric residual effect increases non-linearly with solar variability, oscillating between +/-3 mm (at Rz12=2) and +/-15 mm (at Rz12=114), whereas its value increases with increasing latitude. The first-order ionospheric residual effect arising from the geometrical splitting of the dual-frequency GPS radiowave signals is ˜2-3 orders of magnitude smaller than the second-order ionospheric residual effect, with the potential of increasing in magnitude at high solar activity. A series of sensitivity studies show that the LEO velocity uncertainties affect the GPS/RO bending angle accuracy more than the Doppler shift uncertainties. Finally, we find that the Earth's gravity anomalies can introduce negative systematic biases on the atmospheric temperature profiles of up to ˜0.5 K close to the Earth's surface. This dissertation demonstrates the simplicity, innovation, effectiveness and importance of our proposed mathematical models on the future of GPS/RO atmospheric remote sensing.

Vergados, Panagiotis

6

Effects of modelling higher-order ionospheric terms on global GPS solutions  

NASA Astrophysics Data System (ADS)

Higher order ionospheric effects arise both from the expansion of the refractive index of the ionosphere as a series and from signal bending due to gradients in refractive index. There is an approximately eleven year variation in the electron content of the ionosphere due to the solar cycle. This means that systematic errors with a trend over several years are possible. Presented here are comparisons of the effects on the GPS reference frame and/or coordinates from modeling variations of the second and third order ionospheric refractive index terms. Results from an experimental implementation of the higher-order bending terms are also outlined. In particular, we perform periodic analysis and noise analysis of differenced coordinate time series and find that that higher-order ionospheric effects do not appear to contribute to the power-law noise typically seen in GPS coordinate time series. However, neglecting higher order ionospheric terms may bias station velocities and also tropospheric zenith delays at low latitudes.

Petrie, E. J.; King, M.; Moore, P.; Lavallee, D. A.

2010-12-01

7

A Review of Higher Order Ionospheric Refraction Effects on Dual Frequency GPS  

Microsoft Academic Search

Higher order ionospheric effects are increasingly relevant as precision requirements on GPS data and products increase. The\\u000a refractive index of the ionosphere is affected by its electron content and the magnetic field of the Earth, so the carrier\\u000a phase of the GPS L1 and L2 signals is advanced and the modulated code delayed. Due to system design the polarisation is

Elizabeth J. Petrie; Manuel Hernández-Pajares; Paolo Spalla; Philip Moore; Matt A. King

2011-01-01

8

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

9

Higher-Order Ionospheric Effects on the GPS Reference Frame and GPS velocities  

NASA Astrophysics Data System (ADS)

We present time series over the period of a complete solar cycle (1995 - 2008) showing the influence of the second and third order ionospheric terms on the GPS reference frame. We include a comparison of the differences found when using either a tilted dipole model or the International Geomagnetic Reference Field (IGRF) for the magnetic field component of the second order term. We examine reference frame translation, rotation, and scale change and velocity effects. We find relatively small differences between the dipole and IGRF solutions, reaching their maximum at ionospheric maximum. For both approaches the reference frame effect is most significant in the Z-translation, where it varies from < 1mm at solar minimum up to 10-15mm at times of peak ionospheric activity. The impact on the other reference frame parameters is much less significant. The mathematical formulation is as outlined in Fritsche et al. (2005). The GPS processing was performed using a modified version of the GAMIT software using a global network of stations, and includes recent developments such as improved tropospheric mapping functions and antenna phase centre corrections. The Total Electron Content (TEC) was obtained from IONEX files. Finally, we present preliminary data showing the effects on the above of including a simple model of ionospheric bending of GPS signals, as suggested by Hoque & Jakowski(2008).

Petrie, E. J.; King, M. A.; Moore, P.; Lavallée, D. A.

2009-04-01

10

Higher-order ionospheric effects on the GPS observables and means of modeling them  

NASA Technical Reports Server (NTRS)

Based on relaistic modeling of the electron density of the ionosphere and using a dipole moment approximation for the earth magnetic field, we are able to estimate the effect of the ionosphere on the Global Positioning Systems (GPS) signal for a ground user. The lowest-order (1/f(exp 2)) effect, which is of the order of .1 - 30 meters of zenith group delay, is subtracted out by forming a linear combination of the dual frequencies of the GPS signal. One is left with second- (1/f(exp 3)) and third-order (1/f(exp 4)) effects which are estimated typically to be approximately 0 - 2 cm, and approximately 0 - 2 mm at zenith respectively, depending on the time of day, time of year, the solar cycle and the relative geometry of the magnetic field and the line of sight. Given the total electron content along a line of sight, we derive an approximation to the second-order term which is accurate to approximately 90% within the magnetic dipole moment model; this approximation can be used to reduce the second-order term to the millimeter level, thus potentially improving precise positioning in space and on the ground. The induced group delay, or phase advance, due to second- and third-order effects are examined for two ground receivers located at equatorial and mid-latitude regions tracking several GPS satellites.

Bassiri, Sassan; Hajj, George A.

1993-01-01

11

Distribution and mitigation of higher-order ionospheric effects on precise GNSS processing  

NASA Astrophysics Data System (ADS)

Higher-order ionospheric effects (I2+) are one of the main limiting factors in very precise Global Navigation Satellite Systems (GNSS) processing, for applications where millimeter accuracy is demanded. This paper summarizes a comprehensive study of the I2+ effects in range and in GNSS precise products such as receiver position and clock, tropospheric delay, geocenter offset, and GNSS satellite position and clock. All the relevant higher-order contributions are considered: second and third orders, geometric bending, and slant total electron content (dSTEC) bending (i.e., the difference between the STEC for straight and bent paths). Using a realistic simulation with representative solar maximum conditions on GPS signals, both the effects and mitigation errors are analyzed. The usage of the combination of multifrequency L band observations has to be rejected due to its increased noise level. The results of the study show that the main two effects in range are the second-order ionospheric and dSTEC terms, with peak values up to 2 cm. Their combined impacts on the precise GNSS satellite products affects the satellite Z coordinates (up to +1 cm) and satellite clocks (more than ±20 ps). Other precise products are affected at the millimeter level. After correction the impact on all the precise GNSS products is reduced below 5 mm. We finally show that the I2+ impact on a Precise Point Positioning (PPP) user is lower than the current uncertainties of the PPP solutions, after applying consistently the precise products (satellite orbits and clocks) obtained under I2+ correction.

Hernández-Pajares, Manuel; Aragón-Ángel, Àngela; Defraigne, Pascale; Bergeot, Nicolas; Prieto-Cerdeira, Roberto; García-Rigo, Alberto

2014-04-01

12

A Review of Higher Order Ionospheric Refraction Effects on Dual Frequency GPS  

NASA Astrophysics Data System (ADS)

Higher order ionospheric effects are increasingly relevant as precision requirements on GPS data and products increase. The refractive index of the ionosphere is affected by its electron content and the magnetic field of the Earth, so the carrier phase of the GPS L1 and L2 signals is advanced and the modulated code delayed. Due to system design the polarisation is unaffected. Most of the effect is removed by expanding the refractive index as a series and eliminating the first term with a linear combination of the two signals. However, the higher order terms remain. Furthermore, transiting gradients in refractive index at a non-perpendicular angle causes signal bending. In addition to the initial geometric bending term, another term allows for the difference that the curvature makes in electron content along each signal. Varying approximations have been made for practical implementation, mainly to avoid the need for a vertical profile of electron density. The magnetic field may be modelled as a tilted co-centric dipole, or using more realistic models such as the International Geomagnetic Reference Field. The largest effect is from the second term in the expansion of the refractive index. Up to several cm on L2, it particularly affects z-translation, and satellite orbits and clocks in a global network of GPS stations. The third term is at the level of the errors in modelling the second order term, while the bending terms appear to be absorbed by tropospheric parameters. Modelling improvements are possible, and three frequency transmissions will allow new possibilities.

Petrie, Elizabeth J.; Hernández-Pajares, Manuel; Spalla, Paolo; Moore, Philip; King, Matt A.

2011-05-01

13

Estimate of higher order ionospheric errors in GNSS positioning  

NASA Astrophysics Data System (ADS)

Precise navigation and positioning using GPS/GLONASS/Galileo require the ionospheric propagation errors to be accurately determined and corrected for. Current dual-frequency method of ionospheric correction ignores higher order ionospheric errors such as the second and third order ionospheric terms in the refractive index formula and errors due to bending of the signal. The total electron content (TEC) is assumed to be same at two GPS frequencies. All these assumptions lead to erroneous estimations and corrections of the ionospheric errors. In this paper a rigorous treatment of these problems is presented. Different approximation formulas have been proposed to correct errors due to excess path length in addition to the free space path length, TEC difference at two GNSS frequencies, and third-order ionospheric term. The GPS dual-frequency residual range errors can be corrected within millimeter level accuracy using the proposed correction formulas.

Hoque, M. Mainul; Jakowski, N.

2008-10-01

14

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

15

Ionospheric scintillation in Brazil: Analyses and Effects on GNSS Positioning  

NASA Astrophysics Data System (ADS)

Ionosphere has a great influence on GNSS (Global Navigation Satellite System) signals and its behavior depends on several variables: local time, geographic location, seasons and solar activity. Besides, there are ionospheric irregularities that also affect the GNSS signal propagation, as the ionospheric scintillation. The ionospheric scintillation can be described as a fast change in phase and amplitude of GNSS signal, caused by irregularities of electron density. Scintillation can degrade or cause the GNSS signal lost. Due to these described factors, one can say that the ionosphere can cause important effects on GNSS positioning. It can degrade the coordinate accuracy obtained by GNSS positioning methods. In this paper the goal is to evaluate the ionospheric effect, in special the ionospheric scintillation in different regions of Brazil, and its effects on GNSS Point Positioning. In order to evaluate the days where the scintillation was more significant it is used a database (http://200.145.185.118/cigala/index.php) from CIGALA (Concept for Ionospheric Scintillation Mitigation for Professional GNSS in Latin America) project (http://cigala.galileoic.org/). Using these data it is possible to obtain information about ionospheric scintillation in different GNSS stations in Brazil. It is possible to correlate the data according to time, season and other factors that can contribute to scintillation analysis. In 2013 must occur an intense solar activity, which can intensify the ionospheric effects, and consequently ionospheric scintillation, mainly in Brazil region, where the scintillation index is already intense. Preliminary evaluations, showed larger values of S4 (scintillation index) in Brazil. For example, in October 2012, it was obtained S4 values larger than 1 in several epochs. This causes severe effects in GNSS Positioning. In this paper, the results of GNSS positioning under ionosphere scintillation effects in different regions of Brazil will be presented.

Alves, D. B.; Souza, J. S.; Silva, H. D.

2013-05-01

16

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

17

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

18

A review of ionospheric effects on Earth-space propagation  

Microsoft Academic Search

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

J. A. Klobuchar

1984-01-01

19

EVLA Memo 118 Ionospheric Effects and Imaging  

E-print Network

Ionospheric electron density variations cause a time and position variable refraction of sources seen through­based technique of [2], [1] developed for use at 74 MHz is described with recent enhancements of low frequency. The shading shows the relative index of refraction and the lines show the effects on the apparent direction

Groppi, Christopher

20

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

21

Ionospheric disturbances produced by chemical releases and the resultant effects on short-wave ionospheric propagation  

NASA Astrophysics Data System (ADS)

As an effective means to actively modify the ionosphere, chemical releases can produce artificial ionospheric holes as a consequence of ionization reduction, which can have a great impact on radio wave propagation. To investigate the morphology control of ionospheric holes by various chemical releases and the resultant effects on radio wave propagation, a quantitative numerical model is developed on the basis of the approximate solutions of the diffusion equation of single-point release in uniform atmosphere. While single-point release produces ellipsoidal ionospheric holes, multipoint release can produce other types of ionospheric holes (such as parabola-like tubular ones), which is strongly dependent on changes in the release species, release altitude, and mass of released neutral gas. Releases of both H2O and SF6 can produce ionospheric holes with a similar spatial extent, but the latter tends to result in clearer boundaries and more pronounced electron density reductions. In addition, either an increase in released amount or releases at higher altitudes can lead to a broader hole. To evaluate the effects of an ionospheric hole on radio wave propagation, three-dimensional ray tracing simulations are performed. The ellipsoidal ionospheric holes can act as a lens focusing and bending radio waves, leading to multiple wave reflections inside the holes. In contrast, in the paraboloid tubular ionospheric holes, the rays can penetrate the disturbed region or reflect back, showing a strong dependence on radio frequency. It is well demonstrated that chemical releases can efficiently give rise to artificial ionospheric disturbances and thus modify ionospheric propagation of radio waves.

Hu, Yaogai; Zhao, Zhengyu; Zhang, Yuannong

2011-07-01

22

Effects of tropospheric and ionospheric refraction errors in the utilization of GEOS-C altimeter data  

NASA Technical Reports Server (NTRS)

The effects of tropospheric and ionospheric refraction errors are analyzed for the GEOS-C altimeter project in terms of their resultant effects on C-band orbits and the altimeter measurement itself. Operational procedures using surface meteorological measurements at ground stations and monthly means for ocean surface conditions are assumed, with no corrections made for ionospheric effects. Effects on the orbit height due to tropospheric errors are approximately 15 cm for single pass short arcs (such as for calibration) and 10 cm for global orbits of one revolution. Orbit height errors due to neglect of the ionosphere have an amplitude of approximately 40 cm when the orbits are determined from C-band range data with predominantly daylight tracking. Altimeter measurement errors are approximately 10 cm due to residual tropospheric refraction correction errors. Ionospheric effects on the altimeter range measurement are also on the order of 10 cm during the GEOS-C launch and early operation period.

Goad, C. C.

1977-01-01

23

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

24

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

25

Ionospheric Effect on a GNSS Radio Occultation Climate Data Record  

NASA Astrophysics Data System (ADS)

Radio occultation (RO) is widely considered to be an observation technique that is particularly well suited for establishing a long-term stable global climate record of density, temperature and bending angle profiles in the 8-30 km height range of the atmosphere. To measure profiles in this height range the ionospheric effect on the RO signals must be eliminated. This ionospheric correction is not perfect and is the most challenging noise source affecting GPS radio occultation temperature profiles in the upper stratosphere. The ionosphere introduces random noise on individual temperature profiles that can affect weather forecasting applications. More serious for climate monitoring are systematic bending angle and resulting temperature biases that change with the solar cycle. We have found a strong correlation between these bending angle biases and F10.7 solar flux values. We have also found a diurnal signal which shows stronger bending angle biases during the day than at night. While the ionosphere is expected to be the main source of these diurnal effects, additional neutral atmospheric influence due to tides cannot be ruled out and needs further investigation. With different GNSS signals and improving receiver technology ionospheric correction in RO processing will evolve in the future. We will also investigate if tracking of the stronger L2C GPS signal could introduce a bias between past and future GNSS observations. This presentation will discuss ways to quantify and limit the ionospheric effect on the RO climate record.

Rocken, C.; Schreiner, W.; Sokolovskiy, S.; Hunt, D.

2008-12-01

26

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

27

Study of the March 31, 2001 magnetic storm effects on the ionosphere using GPS data  

Microsoft Academic Search

Despite the fact that much has been learned about the Sun–Earth relationship during disturbed conditions, understanding the effects of magnetic storms on the neutral and ionized upper atmosphere is still one of the most challenging topics remaining in the physics of this atmospheric region. In order to investigate the magnetospheric and ionospheric–thermospheric coupling processes, many researchers are taking advantage of

M. Fedrizzi; E. R. de Paula; R. B. Langley; A. Komjathy; I. S. Batista; I. J. Kantor

2005-01-01

28

Study of the March 31, 2001 magnetic storm effects on the ionosphere using GPS data  

Microsoft Academic Search

Despite the fact that much has been learned about the Sun Earth relationship during disturbed conditions, understanding the effects of magnetic storms on the neutral and ionized upper atmosphere is still one of the most challenging topics remaining in the physics of this atmospheric region. In order to investigate the magnetospheric and ionospheric thermospheric coupling processes, many researchers are taking

M. Fedrizzi; E. R. de Paula; R. B. Langley; A. Komjathy; I. S. Batista; I. J. Kantor

2005-01-01

29

Study of magnetic storm effects on the ionosphere using GPS data  

Microsoft Academic Search

Despite the fact that much has been learned about Sun-Earth relationship during disturbed conditions, understanding the effects of magnetic storms on the neutral and ionized upper atmosphere is still one of the most challenging topics remaining in the physics of this atmospheric region. In order to investigate the magnetospheric and ionospheric-thermospheric coupling processes, many researchers are taking advantage of the

M. Fedrizzi; E. R. de Paula; I. J. Kantor; I. S. Batista; R. B. Langley; A. Komjathy

2004-01-01

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

EVLA Memo 117 Ionospheric Effects and Calibration  

E-print Network

refraction on VLA observations at 327 MHz. The field­based technique of [3], [1] developed for use at 74 MHz NRAO 1 Abstract Ionospheric electron density variations cause time and position variable refraction although some artifacts remain. Examples are shown using the Obit (http

Groppi, Christopher

32

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

33

Ionospheric scintillation effects on VHF-UHF communication systems  

Microsoft Academic Search

Periods of intense ionospheric scintillations were analyzed in order to provide information for the design and evaluation of the performance of satellite communication links. Scintillation data were available for the auroral and equatorial regions. The amplitude fluctuations are described by cumulative amplitude distributions and show good agreement with the Nakagami m-distribution. A Rayleigh distribution appears to describe the worst case

H. E. Whitney

1976-01-01

34

Solar and lunar ionospheric electrodynamic effects during stratospheric sudden warmings  

NASA Astrophysics Data System (ADS)

Both solar and lunar atmospheric tides are believed to drive ionospheric electrodynamic effects during stratospheric sudden warmings (SSWs), but their relative importance is not well understood. In this study, long-term records (1958-2007) of the geomagnetic field are analyzed to determine the average solar (S) and lunar (L) ionospheric current systems for SSW and non-SSW periods. It is found that the L current intensity is enhanced during SSWs approximately by 75%, while the relative change in the S current intensity is much smaller (~10%). Nonetheless, absolute changes are comparable in the S and L current intensities. At the magnetic equator, semidiurnal perturbations produced by S and L currents reinforce or cancel each other depending on the phase of the moon, creating lunar-dependent recurrent onset in the total effect. These results indicate that both S and L contributions need to be considered to understand ionospheric variability during SSWs.

Yamazaki, Yosuke

2014-11-01

35

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

36

Modeling of multiple effects of atmospheric tides on the ionosphere: An examination of possible coupling  

E-print Network

be considered. We use Sami2 is Another Model of the Ionosphere to test a set of electrodynamicClick Here for Full Article Modeling of multiple effects of atmospheric tides on the ionosphere ionosphere S. L. England,1 T. J. Immel,1 J. D. Huba,2 M. E. Hagan,3 A. Maute,3 and R. DeMajistre4 Received 10

California at Berkeley, University of

37

Ionospheric effects of sudden stratospheric warmings in eastern Siberia region  

NASA Astrophysics Data System (ADS)

Ionospheric effects observed in Russia's Asia region during sudden stratospheric warmings (SSWs) in the winters 2008/2009 and 2012/2013 corresponding to both extreme solar minimum and moderate solar maximum conditions have been examined. To detect the ionospheric effects which must have been induced by the SSWs, we have carried out a joint analysis of total electron content (TEC) global ionospheric maps (GIM), MLS (Microwave Limb Sounder, EOS Aura) measurements of vertical temperature profiles, as well as NCEP/NCAR and UKMO Reanalysis data. It has been revealed for the first time that during strong SSWs the amplitude of diurnal variation of TEC decreases nearly by half in the mid-latitude ionosphere. Besides, the intensity of TEC deviations from the background level increases during SSWs. It has also revealed that during SSW peak the midday TEC maximum considerably decreases, and the night/morning TEC increases compared to quiet days. The pattern of TEC response to SSW is shown to be identical for both quiet and disturbed geophysical conditions.

Polyakova, A. S.; Chernigovskaya, M. A.; Perevalova, N. P.

2014-12-01

38

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

39

Ionospheric storm effects at subauroral latitudes - A case study  

NASA Technical Reports Server (NTRS)

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.; Brace, L. H.; Mayr, H. G.; Carignan, G. R.; Killeen, T. L.

1991-01-01

40

Orbital barium CRRES injection - effective source of ionospheric wavelike disturbances  

NASA Astrophysics Data System (ADS)

Spectral analysis of artificial wavelike disturbances (WD) in ionospheric parameters is presented. The sources of WD are barium clouds injections in Combined Release and Radiation Effects Satellite (CRRES) perigee experiments. Plasma concentration pulsations are found in the ionospheric F2 layer maximum over Havana (Cuba) at distances 1500-2500 km from the barium injection. It was found that for the spectral component with 10 min period, the delay (relative to injection moment) corresponded to WD propagation velocity in 323-390 m/s band and depended on the specific injection conditions. It was shown that in every experiment the WD effective propagation velocity in the terminator region correlated with the sunlit part of the trajectory from the injection point to Havana. When comparing this WD type with WD's of other origins (from earthquakes, high-altitude explosions and solar terminator), it was shown that purposeful injection in the ionosphere of even a small barium quantity with orbital velocity in terminator region might be the effective means for generation or amplification of natural WD.

Ruzhin, Yu. Ya.; Oraevsky, V. N.; Depueva, A. Kh.; Perez, H.; Palasio, L.

41

Seismo-Electromagnetic Effects Observed by DEMETER in the Ionosphere  

NASA Astrophysics Data System (ADS)

The French micro-satellite DEMETER was launched on June 29, 2004 on a polar and circular orbit with an altitude of 700 km. One of its main scientific objectives is to detect in the ionosphere, anomalous variations of electromagnetic waves, particle fluxes or thermal plasma parameters which could be related to seismic activity. If it is shown that such perturbations are real and systematic, they could be considered as short-term precursors, occurring between a few hours and a few days before the quake. There are several hypotheses to explain the generation mechanism of these phenomena (wave emissions from the Earth's crust, piezo- or tribo-electric effects, emissions of radioactive gas or metallic ions, propagation of acoustic-gravity waves, .). The payload of the micro-satellite allows to measure waves in a broad frequency range and also important plasma parameters (ion composition, electron density and temperature, energetic particles). The scientific payload is composed of several sensors: - Three electric and three magnetic sensors (6 components of the electromagnetic field to investigate from DC up to 3.5 MHz), - A Langmuir probe, - An ion spectrometer, and, - An energetic particle analyzer. There are two modes of operation: (i) a survey mode to record low bit rate data all around the Earth, and (ii) a burst mode to record high bit rate data above seismic regions. The telemetry is received in Toulouse and sent to the DEMETER mission center in Orléans where data and plots are processed (http://demeter.cnrs-orleans.fr). After eighteen months of operation, the paper will present significant events recorded when the satellite is close in time and in space to earthquakes. The main purpose of the project is to perform a statistical analysis with many events in order to determine the main characteristics of the seismo-electromagnetic effects and methods which are currently operative will be explained.

Parrot, M.

2005-12-01

42

Springtime Effects In Mesosphere and Ionosphere Over Kazakhstan Region  

NASA Astrophysics Data System (ADS)

The ionospheric density obtained from foF2 in the vertical sounding iono- grams, emission rate and rotation temperature of O2 (0-1) measured by the MORTI instrument over Kazakhstan region, Almaty (43.25N, 76.92E) during the period of February-April 2000 have been analyzed to study springtime effects in the mesosphere and ionosphere. The disturbances in the emission rate and temper- ature are evident from February 29 to March 12 with increase in their magnitudes during time interval considered (E = 200R, T = 80K). Later the emission rate shows the lower values without returning to the intensity observed in Febru- ary. The periodogram method and COPHASE technique have been used to assess the statistically significant oscillations present in the data, estimate azimuth, hor- izontal phase speed and wavelength for all harmonics extracted from the time series. The results indicate that the horizontal phase speeds lie between 38 and 1515 m/s, the horizontal wave lengths are always greater than 250 km, and the periods of waves lie between 45 and 499 min. The azimuths of the wave propaga- tion are different from day to day as an instability in their values. There exists an increase in the amplitudes of the emission rate and temperature perturbations dur- ing the time interval considered on March 10 with a maximum of about 27% in the emission rate and 4% in the rotation temperature. The fluctuating component of the ionospheric critical frequency (foF2) obtained as a difference between the current foF2 values and an ionospheric background level ( a climatological behavior) shows a negative disturbance which appears simultaneously with the sharp increase in the mesospheric emission rate and temperature on March 10 as if it would be a depletion in electron density. Duration of this negative ionospheric disturbance is about 24 hrs, and foF2 = 25%. The variations in horizontal components of the Earth's magnetic field H recorded at the "Alma-Ata" magnetic observatory show a regular quiet-time behavior during these March days (March 9, Ki = 10; March 10, Ki = 17; March 11, Ki = 19; March 12, Ki = 23;March13, Ki = 12).

Aushev, V. M.; Gordienko, G. I.; Pogoreltsev, A. I.; Shepherd, M. G.

43

Venus dayside ionospheric conditions: Effects of ionospheric magnetic field and solar EUV flux  

Microsoft Academic Search

The Venus ionosphere is influenced by both solar EUV and solar wind conditions. Using in situ measurements of solar EUV flux, we investigate the extent of the EUV-contributed modulation of dayside conditions as measured by the Pioneer Venus orbiter Langmuir probe experiment. We use data from the low altitude dayside ionosphere (150-200 km altitude, 0600-1800 local solar time), normalized by

R. C. Elphic; L. H. Brace; R. F. Theis; C. T. Russell

1984-01-01

44

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

45

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

46

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

47

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

48

Effects of inferring unobserved thermospheric and ionospheric state variables by using an Ensemble Kalman Filter on global ionospheric specification and forecasting  

NASA Astrophysics Data System (ADS)

paper demonstrates the significance of ion-neutral coupling to ionospheric data assimilation for ionospheric specification and forecast. Ensemble Kalman Filter (EnKF) is used to assimilate synthetic electron density profiles sampled according to the Formosa Satellite 3/Constellation Observing System for Meteorology, Ionosphere, and Climate into the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM). The combination of the EnKF and first-principles TIEGCM allows a self-consistent treatment of thermosphere and ionosphere coupling in the data assimilation and forecast. Because thermospheric variables affect ionospheric electron densities, different combinations of an observed ionospheric state variable (electron density), and unobserved ionospheric and thermospheric state variables (atomic oxygen ion density, neutral temperature, winds, and composition) are included as part of the EnKF state vector in experiments. In the EnKF, the unobserved state variables are estimated and made dynamically and chemically consistent with the observed state variable, thus improving the performance of the data assimilation system. The impact on ensemble forecast is further examined by initializing the TIEGCM with the assimilation analysis. The main findings are the following: (1) by incorporating ion-neutral coupling into the EnKF, the ionospheric electron density analysis, and forecast can be considerably improved. (2) Thermospheric composition is the most significant state variable that affects ionospheric analysis and forecast. (3) Thermospheric variables have a much longer impact on ionospheric forecast (>24 h) than ionospheric variables (2 to 3 h). (4) In the TIEGCM, the effect of assimilating electron densities is not completely transmitted to the forecast step unless the densities of ion species are estimated.

Hsu, Chih-Ting; Matsuo, Tomoko; Wang, Wenbin; Liu, Jann-Yenq

2014-11-01

49

Effects of geomagnetic storm on GPS ionospheric scintillations at Sanya  

NASA Astrophysics Data System (ADS)

The effects of geomagnetic storm on GPS ionospheric scintillations are studied here using GPS scintillation data recorded at Sanya (18.3°N, 109.5°E; geomagnetic: 7.6°N, 180.8°E), the southmost station in the Chinese longitude region. GPS scintillation/TEC and DMSP data are utilized to show the development of irregularities during the period year 2005 (solar minimum). Statistical analysis of K planetary index (Kp) and amplitude scintillation index (S4) indicates that most storms of the year did not trigger the scintillation occurrence at Sanya. However, cases of scintillation occurring during moderate and strong storm (Dst<-100) periods show clearly that the development of irregularities producing scintillations can be triggered by geomagnetic storms during the low scintillation occurrence season. The effects (trigger or not trigger/inhibit) depend on the maximum dDst/dt determined local time sector, and can be explained by the response of the equatorial vertical drift velocities to magnetospheric and ionospheric disturbance electric fields. For station Sanya, the maximum dDst/dt determined local time is near the noon (or post-midnight) sector for most storms of the year 2005, which inhibited (or did not trigger) the post-sunset (or post-midnight) scintillation occurrence and then led to the phenomena that the statistical results presented.

Li, Guozhu; Ning, Baiqi; Zhao, Biqiang; Liu, Libo; Liu, J. Y.; Yumoto, K.

2008-05-01

50

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

E-print Network

Ionospheric effects upon a satellite navigation system at Mars Michael Mendillo,1 Xiaoqing Pi,2 satellites at Mars. Using recent results from the radio science experiment on board the Mars Global Surveyor (MGS) spacecraft and a photochemical model of Mars' ionosphere, we study the total electron content

Mendillo, Michael

51

Season Variation of Ionosphere Effects of geomagnetic Storms at different Latitudes of East Asia  

Microsoft Academic Search

The most important factors governing the variations of the ionosphere at the time of the geomagnetic storm include a change in electron composition and the circulation system of neutral wind, which depends substantially on the season. Besides, the difference of the geographic and magnetic coordinates complicates the picture of disturbances and leads to a longitudinal dependence of ionospheric effects of

O. M. Pirog; N. M. Polekh; K. G. Ratovsky; G. A. Zherebtsov; V. F. Smirnov; J. K. Shi; X. Wang

2004-01-01

52

On the effect of near-equatorial thunderstorms on the global distribution of ionospheric potential  

E-print Network

On the effect of near-equatorial thunderstorms on the global distribution of ionospheric potential examination of the hypothesis that electric currents flowing up from thunderstorms to the ionosphere (also thunderstorm regions over equatorial Asia/Oceania, Africa and the Americas. We compare the local time variation

Michigan, University of

53

Effect of local inhomogeneity of the ionosphere on the propagation of ULF radio waves  

Microsoft Academic Search

The Stratton-Chu integral equation is used to solve the electrodynamic problem concerning the propagation of ULF waves in an inhomogeneous spherical earth-ionosphere cavity. The effect of the local inhomogeneity of the ionosphere is taken into account in the framework of the Born approximation of perturbation theory. An analysis is made of perturbation variations of the vertical electric component of the

A. P. Nikolaenko

1984-01-01

54

Ionospheric range-rate effects in satellite-to-satellite tracking  

Microsoft Academic Search

Ionospheric range and range rate corrections in satellite-to-satellite tracking were investigated and the magnitude of errors that have to be considered for communications between satellites and related experiments was defined. The major causes of the sudden and sometimes large variations apparent in the ionospheric range and range rate corrections along the satellite arc are the geometric effects of the raypath

R. B. Bent; J. R. Lipofsky; S. K. Llewellyn; P. E. Schmid

1978-01-01

55

Effect of atmospheric tides on the morphology of the quiet time, postsunset equatorial ionospheric anomaly  

E-print Network

Effect of atmospheric tides on the morphology of the quiet time, postsunset equatorial ionospheric of atmospheric tides on the morphology of the quiet time, postsunset equatorial ionospheric anomaly, J. Geophys of magne- tospheric origin, but this report will only focus upon the quiet-time state of this system. [3

California at Berkeley, University of

56

Nightside ionosphere of Mars: Modeling the effects of crustal magnetic fields and electron pitch angle distributions on electron impact  

E-print Network

Nightside ionosphere of Mars: Modeling the effects of crustal magnetic fields and electron pitch, and S. W. Bougher (2009), Nightside ionosphere of Mars: Modeling the effects of crustal magnetic fields 2009; accepted 3 August 2009; published 20 November 2009. [1] The night side ionosphere of Mars

California at Berkeley, University of

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

A first look at the effects of ionospheric signal bending on a globally processed GPS network  

NASA Astrophysics Data System (ADS)

This study provides a first attempt at quantifying potential signal bending effects on the GPS reference frame, coordinates and zenith tropospheric delays (ZTDs). To do this, we homogeneously reanalysed data from a global network of GPS sites spanning 14 years (1995.0-2009.0). Satellite, Earth orientation, tropospheric and ground station coordinate parameters were all estimated. We tested the effect of geometric bending and dTEC bending corrections, which were modelled at the observation level based, in part, on parameters from the International Reference Ionosphere 2007 model. Combined, the two bending corrections appear to have a minimal effect on site coordinates and ZTDs except for low latitude sites. Considering five days (DOY 301-305, 28 October-1 November 2001) near ionospheric maximum in detail, they affect mean ZTDs by up to ~1.7 mm at low latitudes, reducing to negligible levels at high latitudes. Examining the effect on coordinates in terms of power-spectra revealed the difference to be almost entirely white noise, with noise amplitude ranging from 0.3 mm (high latitudes) to 2.4 mm (low latitudes). The limited effect on station coordinates is probably due to the similarity in the elevation dependence of the bending term with that of tropospheric mapping functions. The smoothed z-translation from the GPS reference frame to ITRF2005 changes by less than 2 mm, though the effect combines positively with that from the second order ionospheric refractive index term. We conclude that, at the present time, and for most practical purposes, the geometric and dTEC bending corrections are probably negligible at current GPS/reference frame precisions.

Petrie, Elizabeth J.; King, Matt A.; Moore, Philip; Lavallée, David A.

2010-08-01

59

Swarm Modelling studies of the magnetic effect of low-latitude ionospheric F region currents  

NASA Astrophysics Data System (ADS)

High-resolution magnetic field measurements of the CHAMP satellite have provided evidence that there are considerable currents flowing at F region altitude even during the night when Hall and Pedersen conductivities are very small. The plasma pressure gradient (Lühr et al., 2003) and the Earth's gravity (Maus and Lühr, 2006) have been suggested as dominant forces driving these currents. In order to assess the impact of such currents at low and mid latitudes on Swarm magnetic field measurements, an ESA-sponsored model study was performed. With the help of the Coupled Thermosphere-Ionosphere-Plasmasphere (CTIP) model representative ionospheric conditions were simulated. Based on this "simulated world" environment the distribution of the various current types was calculated and the magnetic effects along representative Swarm orbits estimated. The results are largely consistent with the propositions derived from CHAMP observations. For the first time, the spatial and local time distribution of the F region currents has been made visible on global scale. On the night side, strongest currents are found in the height range 300 to 600 km. Under solar maximum conditions magnetic effects of the order of 5 nT are obtained. With the help of the simulated environment it is possible to investigate the different current components independently. A very promising result is that the magnetic effect of the plasma pressure gradient currents can effectively be corrected by the approach proposed by Lühr et al. (2003).

Stolle, C.; Lühr, H.; Förster, M.; Aylward, A.; Spain, T.; Aruliah, A.; Haagmans, R.; Plank, G.

2009-04-01

60

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.

61

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

Microsoft Academic Search

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

T. Joseph Fitzgerald; Paul E. Argo; Robert C. Carlos

1997-01-01

62

Investigations into the properties, conditions and effects of the ionosphere  

NASA Astrophysics Data System (ADS)

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 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.

Bussey, R. M.; Fremouw, E. J.; Reinisch, B. W.; Szuszczewicz, E. P.

1988-01-01

63

Ionospheric physics  

SciTech Connect

Advances in all areas of ionospheric research are reviewed for the 1987-1990 time period. Consideration is given to the equatorial ionosphere, the midlatitude ionosphere and plasmasphere, the auroral ionosphere, the polar ionosphere and polar wind, ionospheric electrodynamic inputs, plasma waves and irregularities, active experiments, ionospheric forecasting, and coupling the ionosphere with other regions.

Sojka, J.J. (USAF, Geophysics Laboratory, Hanscom AFB, MA (United States))

1991-01-01

64

A theory of ionospheric response to upward-propagating tides: Electrodynamic effects and tidal mixing effects  

NASA Astrophysics Data System (ADS)

The atmospheric tide at ionospheric heights is composed of those locally generated and those propagated from below. The role of the latter in producing the variability of the daytime ionosphere is examined using the National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General Circulation Model. The impact of upward-propagating tides is evaluated by running simulations with and without tidal forcing at the lower boundary (approximately 96 km), which imitates the effect of tides from below. When migrating diurnal and semidiurnal tides at the lower boundary is switched on, the intensity of E region currents and the upward velocity of the equatorial F region vertical plasma drift rapidly increase. The low-latitude ionospheric total electron content (TEC) first increases, then gradually decreases to below the initial level. The initial increase in the low-latitude TEC is caused by an enhanced equatorial plasma fountain while the subsequent decrease is due to changes in the neutral composition, which are characterized by a global-scale reduction in the mass mixing ratio of atomic oxygen O1. The results of further numerical experiments indicate that the mean meridional circulation induced by dissipating tides in the lower thermosphere is mainly responsible for the O1 reduction; it acts like an additional turbulent eddy and produces a "mixing effect" that enhances net downward transport and loss of O1. It is stressed that both electrodynamic effects and mixing effects of upward-propagating tides can be important in producing the variability of ionospheric plasma density. Since the two mechanisms act in different ways on different time scales, the response of the actual ionosphere to highly variable upward-propagating tides is expected to be complex.

Yamazaki, Yosuke; Richmond, Arthur D.

2013-09-01

65

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

66

Space Weather Topics at Ionospheric Effects Symposium 2008  

NASA Astrophysics Data System (ADS)

The ionosphere has captured the interest of scientists and communications specialists for many years. Research has been intrinsically applications oriented since Guglielmo Marconi identified an ionized region within the upper atmosphere that acted like a high-altitude mirror reflecting radio waves so that long-distance communication could be achieved. His successful transatlantic radio transmissions early in the twentieth century heralded the beginning of an era of wireless communications. Eager to capitalize on this, civilian and military industries sponsored research to better understand the ionosphere. These endeavors established that the ionosphere exhibits considerable variability, with significant changes associated with ionospheric storms that are driven by solar disturbances. This variability, now termed space weather, also introduces changes in radio propagation conditions that can disrupt various radio systems, such as high-frequency and satellite communications, the Global Positioning System, radar, and specialized surveillance methods.

Goodman, John

2008-08-01

67

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

68

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

NASA Astrophysics Data System (ADS)

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

69

Ionospheric refraction effects on orbit determination using the orbit determination error analysis system  

NASA Technical Reports Server (NTRS)

The influence of ionospheric refraction on orbit determination was studied through the use of the Orbit Determination Error Analysis System (ODEAS). The results of a study of the orbital state estimate errors due to the ionospheric refraction corrections, particularly for measurements involving spacecraft-to-spacecraft tracking links, are presented. In current operational practice at the Goddard Space Flight Center (GSFC) Flight Dynamics Facility (FDF), the ionospheric refraction effects on the tracking measurements are modeled in the Goddard Trajectory Determination System (GTDS) using the Bent ionospheric model. While GTDS has the capability of incorporating the ionospheric refraction effects for measurements involving ground-to-spacecraft tracking links, such as those generated by the Ground Spaceflight Tracking and Data Network (GSTDN), it does not have the capability to incorporate the refraction effects for spacecraft-to-spacecraft tracking links for measurements generated by the Tracking and Data Relay Satellite System (TDRSS). The lack of this particular capability in GTDS raised some concern about the achievable accuracy of the estimated orbit for certain classes of spacecraft missions that require high-precision orbits. Using an enhanced research version of GTDS, some efforts have already been made to assess the importance of the spacecraft-to-spacecraft ionospheric refraction corrections in an orbit determination process. While these studies were performed using simulated data or real tracking data in definitive orbit determination modes, the study results presented here were obtained by means of covariance analysis simulating the weighted least-squares method used in orbit determination.

Yee, C. P.; Kelbel, D. A.; Lee, T.; Dunham, J. B.; Mistretta, G. D.

1990-01-01

70

The Pedersen current carried by electrons: Effects on magnetosphere-ionosphere coupling  

NASA Astrophysics Data System (ADS)

Observations by the EISCAT Svalbard radar show that electron temperatures Te in the cusp electrojet reach up to about 4000 K. The heat is tapped and converted from plasma convection in the near Earth space by a Pedersen current that is carried by electrons due to the presence of irregularities and their demagnetising effect. The heat is transfered to the neutral gas by collisions. In order to enhance Te to such high temperatures the maximally possible dissipation at 50 % demagnetisation must nearly be reached. The effective Pedersen conductances are found to be enhanced by up to 60 % compared to classical values. Conductivities and conductances respond significantly to variations of the electric field strength E, and "Ohm's law" for the ionosphere becomes non-linear for large E.

Buchert, Stephan

71

Ionospheric range-rate effects in satellite-to-satellite tracking  

NASA Technical Reports Server (NTRS)

Ionospheric range and range rate corrections in satellite-to-satellite tracking were investigated and the magnitude of errors that have to be considered for communications between satellites and related experiments was defined. The major causes of the sudden and sometimes large variations apparent in the ionospheric range and range rate corrections along the satellite arc are the geometric effects of the raypath and the curved ionosphere, and the localized perturbations in electron density along the satellite-to-satellite line of sight. Ionospheric tracking errors are greatly effected by the following parameters, whose influence was thoroughly investigated: satellite height, height of maximum electron density, localized ionospheric perturbations and gradients, and electron density variations with diurnal, day-to-day, seasonal, and solar cycle patterns. The results point to the need of using a sophisticated modeling approach incorporating daily solar data, and where possible actual ionospheric measurements as update information. Simulations were performed for satellites at various heights: Apollo, Geos, and Nimbus tracked by ATS-6; and in two different geometric configurations: coplanar and perpendicular orbits.

Bent, R. B.; Lipofsky, J. R.; Llewellyn, S. K.; Schmid, P. E.

1978-01-01

72

Ionosphere Activity Effects on Anthropogenic VLF Wave measured by DEMETER and Application to Earth Electromagnetic Survey  

NASA Astrophysics Data System (ADS)

Very Low Frequency (VLF) signal from the world-wide powerful VLF stations network, for navigation and military communication is commonly used for ground level electromagnetic survey in geophysics because part of the recorded signal is of internal origin, from induction in the Earth. This VLF signal has been observed also at satellite altitude during the DEMETER mission. The VLF electromagnetic field is recorded on the 15 - 20 kHz frequency band by the ICE et IMSC sensors on-board the spacecraft and provide simultaneously the electric and magnetic component of the electromagnetic signal. The waves transmitted by the ground-based VLF antennas propagate in free space and may pass through the ionosphere, depending on ionosphere properties or orientation of the wave vector relative to the Earth magnetic field. They can only cross the ionosphere and reach the satellite in the case of low ionosphere activities. The ionization varies according to time of day or season and it has been shown that man made VLF waves can precipitate radiation belt energetic electrons into the ionosphere. We study the effect of the interaction between VLF wave transmitted from ground and the ionosphere to analyze the contribution of ionosphere to the signal measured by DEMETER. We calculate the electromagnetic field of the VLF antennas placed on the surface of the Earth and transmitted through the ionosphere up to the satellite as a function of earth electrical resistivity. To compare with the data, we define the ratio between the electric and magnetic field that we call wave impedance. The comparison between the theoretical and observed impedance allows to deduce the average resistivity of the earth for shallow depth from the satellite data.

Leye, P. O.; Tarits, P.

2012-04-01

73

Physics of planetary ionospheres  

NASA Technical Reports Server (NTRS)

The fundamental physical and chemical processes in an idealized planetary ionosphere are considered as a general abstraction, with actual planetary ionospheres representing special cases. After describing the structure of the neutral atmospheres (the barosphere, the thermosphere, and the exosphere) and noting the principal ionizing radiations responsible for the formation of planetary ionospheres, a detailed study is made of the thermal structure of these ionospheres and of the chemical processes and plasma-transport processes occurring in them. The features of equilibrium and realistic models of planetary ionospheres are discussed, and an attempt is made to determine the extent of these ionospheres. Considering the ionosphere as a plasma, a plasma kinetic approach is developed for determining the effects of interactions between individual particles and waves in this plasma. The use of remote-sensing radio techniques and direct measurement or in situ techniques is discussed. Finally, the observed properties of the ionospheres of the Earth, Mars, Venus, and Jupiter are reviewed.

Bauer, S. J.

1973-01-01

74

Effect of solar Coronal Mass Ejections on the ionosphere  

NASA Astrophysics Data System (ADS)

The influence of solar processes on the state of near-earth space is constantly the object of serious study. First of all the solar radiation affects the parameters of the ionosphere and ionizing processes in it. The basic level indicator of the ionized particles is the critical frequency f0F2 of the reflection of radio signal during sounding of ionosphere. Understanding of the role of Coronal Mass Ejections (CME) in global solar-terrestrial processes allow us to put up the problem about their possible influence on near Earth’ processes and ionosphere behavior. Earlier the authors proposed the procedure of the detection the influence of CMEs on the differential parameters of the upper ionosphere Deltaf0F2 as more sensitive in comparison with the traditional methods. First results were based on the data of regular observations of critical frequency f0F2 during the cycle of solar activity (1975-1986). To verify the relationship discovered we used in the proposed study the data of critical frequency f0F2, determined from uniform ionograms obtained with the modern digital Ionosonde CADI. This ionosonde is installed at the landfill NIRFI "Vasilsursk" (near Nizhny Novgorod), and working program of regular observations allowed to obtain ionograms at least once in 1 minutes. The accuracy of determining the critical frequency was less than ± 50 kHz. There are many examples of time coincidence between the periods of CMEs existence and negative deflection in Deltaf0F2 behaviour.

Sheiner, Olga; Fridman, Vladimir; Rakhlin, Alexander; Pershin, Alexsander; Vybornov, Feodor

75

Ionization effects due to solar flare on terrestrial ionosphere  

NASA Technical Reports Server (NTRS)

Sudden frequency deviation ionospheric disturbances related to the flares of May 18 and 19, 1973 were observed from the NASA/MSFC high frequency Doppler sounder array system in Huntsville, Alabama. The results are compared with those observed at Table Mountain near Boulder, Colorado and at the University of Hawaii.

Wu, S. T.; Tan, A.

1976-01-01

76

Manifestation of seismo-ionospheric effect outside of eartquakes preparation zone  

NASA Astrophysics Data System (ADS)

We have researched the large-scale abnormal disturbances of the low-latitude ionosphere, which are taking place under quiet geomagnetic conditions, on a background of data on seismic activity with the view of revealing of features of spatial-time variations of a low-latitude ionosphere during the periods of the raised seismic activity. The daily variations of foF2 values(deviations of measured foF2 from monthly medians) at the ionospheric stations were analyzed. The data on seismic events of the moderate power (M=4-5)in low-latitude area were used for the purpose of specification of spatial and time scales of ionospheric effect manifestations of earthquakes. Reaction of a low-latitude ionosphere, in some cases strongly pronounced, on processes of earthquake preparation is confirmed, including in the removed centers of earthquakes (on the distances considerably exceeding radius of a zone of earthquake preparation). The ionosphere reaction manifests in development of the expressed disturbances of F2-layer critical frequencies in night, pre-sunrise and evening hours under quiet geomagnetic conditions. The remarkable example of occurrence of abnormal disturbances in a low-latitude ionosphere due to removed centers of earthquakes are the disturbances of F2-layer critical frequencies during the catastrophic Chilean (on May 21, 1960, 1002UT, the main shock magnitude M=8.5) and the Alaska (on March 28, 1964, 0336UT, M=8.3) earthquakes. The maximal distances, on which abnormal disturbances were noted, are 3700 km for the Chilean and 9100 km for the Alaska earthquakes. Displacement of the disturbances in a direction from epicenter areas to the geomagnetic equator was noted: from the south - during the Chilean earthquake and from the north - during the Alaska one. Positive disturbances were marked for three days up to the first shock during the Chilean earthquake, during the Alaska one - for a day; development of negative disturbances were occurred on time in immediate proximity by the moments of the first shocks at local time of the stations. The analysis of variations of F2-layer critical frequencies in low-latitude area (results on the South-American region) has confirmed the conclusion about that groups of earthquakes of the moderate power, rather localized in time and space in low-latitude area, can cause abnormal disturbances of F2-layer critical frequencies in this area of ionosphere which may be similar on amplitude with ionospheric effects of strong earthquakes (variations of foF2 more than 50

Ruzhin, Yuri

77

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

78

Effects of Gravity Waves on the Thermosphere/Ionosphere system simulated by an atmosphere-ionosphere coupled Model  

NASA Astrophysics Data System (ADS)

Behaviors of gravity waves in the thermosphere ionosphere are studied by using a whole atmosphere-ionosphere coupled model (GAIA), in which a whole atmosphere general circulation model (GCM), an ionosphere model and an electrodynamics model are integrated. The whole atmosphere GCM contains the region from the ground surface to the upper thermosphere, so that we can simulate excitation of gravity waves in the lower atmosphere and their upward propagation to the thermosphere. We have recently developed an atmosphere-ionosphere coupled model with high horizontal resolution (about 1 degree longitude by 1degree latitude). In this study, we would like to present a preliminary result obtained by the GAIA simulation. Using this coupled model, we investigate the upward propagation of gravity waves from the lower atmosphere to the thermosphere and its impact on ionospheric variability. In particular, we focus our attention on the relation between the convective activity in the troposphere and the thermosphere/ionosphere variability. Our simulation result indicates that gravity waves with a larger horizontal phase velocity (larger vertical wavelength) can penetrate into the thermosphere and affect the general circulation of the upper atmosphere. The longitudinal distribution of the gravity wave activity in low latitudes of the thermosphere is closely related to the cumulus convective activity in the tropics. The impact of the thermospheric gravity wave on the ionosphere is also discussed.

Miyoshi, Y.; Jin, H.; Fujiwara, H.; Shinagawa, H.

2013-12-01

79

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

80

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

Microsoft Academic Search

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,

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

1990-01-01

81

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

82

Ionospheric effects of rocket exhaust products - Skylab and HEAO-C  

NASA Astrophysics Data System (ADS)

A description is presented of a new computer model of the mesosphere, thermosphere, and ionosphere, taking into account a comparison of computed results with experimental data. The model was developed in the course of a study of ionospheric depletion effects of large rocket launches through the F layer. The computer code uses a two-dimensional array of Eulerian mesh cells in Cartesian coordinates x horizontal (in the geomagnetic meridian plane), and z vertical. The code integrates the chemical/photochemical kinetic equations for 30 individual chemical species in each of 315 cells. Solar radiation, scatter UV, cosmic rays, and precipitating electrons are considered. Diffusion rates are computed for each neutral species under the influence of gravity. The midlatitude ionosphere in connection with the launch of Skylab I on May 14, 1973 is considered, and attention is given to rocket launches and two-dimensional model comparisons.

Zinn, J.; Sutherland, C. D.; Duncan, L. M.; Stone, S. N.

83

Effect of ray and speed perturbations on ionospheric tomography by over-the-horizon radar: A new method  

NASA Astrophysics Data System (ADS)

Most recent methods in ionospheric tomography are based on the inversion of the total electron content measured by ground-based GPS receivers. As a consequence of the high frequency of the GPS signal and the absence of horizontal raypaths, the electron density structure is mainly reconstructed in the F2 region (300 km), where the ionosphere reaches the maximum of ionization, and is not sensitive to the lower ionospheric structure. We propose here a new tomographic method of the lower ionosphere, based on the full inversion of over-the-horizon (OTH) radar data. Previous studies using OTH radar for ionospheric tomography inverted only the leading edge echo curve of backscatter ionograms. The major advantage of our methodology is taking into account, numerically and jointly, the effect that the electron density perturbations induce not only in the speed of electromagnetic waves but also on the raypath geometry. This last point is extremely critical for OTH radar inversions as the emitted signal propagates through the ionosphere between a fixed starting point (the radar) and an unknown end point on the Earth surface where the signal is backscattered. We detail our ionospheric tomography method with the aid of benchmark tests. Having proved the necessity to take into account both effects simultaneously, we apply our method to real data. This is the first time that the effect of the raypath deflection has been quantified and that the ionospheric plasma density has been estimated over the entirety of Europe with an OTH radar.

Roy, Corinna; Occhipinti, Giovanni; Boschi, Lapo; Moliné, Jean-Philippe; Wieczorek, Mark

2014-09-01

84

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

85

Ionospheric effects on C3I satellite communications systems in Greenland  

NASA Astrophysics Data System (ADS)

The effects of polar ionospheric scintillation fading on U.S. military satellite communications systems in Greenland are reviewed. The operational type of satellite communications testing, conducted for the past 10 years to evaluate the feasibility of replacing the traditional HF radio links with satellite communications links is described. Some future plans for the operational use of satellite communications in Greenland are identified.

Johnson, A.; Taagholt, J.

1985-06-01

86

Equivalent ionospheric current systems representing IMF sector effects on the polar geomagnetic field  

NASA Astrophysics Data System (ADS)

Equivalent ionospheric current systems representing IMF sector effects on the geomagnetic field in high latitudes are examined for each of the twelve calendar months by spherical harmonic analyses of geomagnetic hourly data at 13 northern polar stations for seven years. The main feature of obtained equivalent current systems includes circular currents at about 80 deg invariant latitude mostly in the daytime in summer and reversed circular currents at about 70 deg invariant latitude mainly at night in winter. Field-aligned current distributions responsible for equivalent currents, as well as vector distributions of electric fields and ionospheric currents, are approximated numerically from current functions of equivalent current systems by taking assumed distributions of the ionospheric conductivity. Two sets of upward and downward field-aligned current pairs in the auroral region, and also a field-aligned current region near the pole show seasonal variations. Also, ionospheric electric-field propagation along geomagnetic field lines from the summer hemisphere to the winter hemisphere with auroral Hall-conductivity effects may provide an explanation for the winter reversal of sector effects.

Matsushita, S.; Xu, W.-Y.

1982-07-01

87

Ionospheric effects of the missile destruction on 9 December 2009  

NASA Astrophysics Data System (ADS)

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

88

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

89

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

90

Cyclotron resonance effects on stochastic acceleration of light ionospheric ions  

NASA Technical Reports Server (NTRS)

The production of energetic ions with conical pitch angle distributions along the auroral field lines is a subject of considerable current interest. There are several theoretical treatments showing the acceleration (heating) of the ions by ion cyclotron waves. The quasi-linear theory predicts no acceleration when the ions are nonresonant. In the present investigation, it is demonstrated that the cyclotron resonances are not crucial for the transverse acceleration of ions by ion cyclotron waves. It is found that transverse energization of ionospheric ions, such as He(+), He(++), O(++), and O(+), is possible by an Electrostatic Hydrogen Cyclotron (EHC) wave even in the absence of cyclotron resonance. The mechanism of acceleration is the nonresonant stochastic heating. However, when there are resonant ions both the total energy gain and the number of accelerated ions increase with increasing parallel wave number.

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

1982-01-01

91

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

92

The low latitude ionospheric effects of the April 2000 magnetic storm near the longitude 120°E  

NASA Astrophysics Data System (ADS)

In this paper, we report the responses of the low latitude ionosphere near the longitude 120°E to the April 2000 geomagnetic storm using Digisonde data measured at Chungli (25.0°N, 121.2°E, Mag. 13.8°N), Wuhan (30.6°N, 114.4°E, Mag. 19.3°N), and Kokubunji (35.7°N, 139.5°E, Mag. 25.7N). At these three stations, the significant ionospheric responses are near-simultaneous height disturbances after the sudden storm commencement (SSC) on April 6, 2000 and wave-like disturbances in the daytime on April 7. The ionospheric height disturbances in the nighttime after the SSC at these stations are suggested to be caused by the storm related perturbed electric fields, and the followed wave-like disturbances may be caused by storm induced atmospheric gravity waves. The vertical effective winds derived from Digisonde measurements imply the existence of significantly large vertical drifts during this storm, which are in agreement with the perturbed zonal electric fields predicted by the model of Fejer and Scherliess (1997) and Scherliess and Fejer (1997). Finally, the storm time derivations of foF2 from its monthly median level at these stations are used to validate the predication ability of the empirical model of Araujo-Pradere et al. (2002), which has included in the International Reference Ionosphere model IRI2000.

Liu, L.; Wan, W.; Lee, C. C.; Ning, B.; Liu, J. Y.

2004-06-01

93

Frequency characteristics of modification effects of high-power radio waves on the ionospheric F-layer  

Microsoft Academic Search

The paper presents experimental results concerning the effect of artificial ionospheric irregularities on the characteristics of linear-FM signals for vertical and oblique sounding of the ionosphere. The radio-transmitting facility operated at a frequency of 4.8 MHz with a power of 200 MW. The effects observed on the linear-FM ionograms are classified according to the effects of artificial irregularities of different

L. M. Erukhimov; V. A. Ivanov; N. A. Mitiakov; V. P. Uriadov; V. A. Frolov

1987-01-01

94

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

95

The effect of large-scale ionospheric gradients on backscatter ionograms  

Microsoft Academic Search

This paper presents the results of the synthesis of a range of backscatter ionograms using ray tracing through model ionospheres. The backscatter ionograms were obtained by the Jindalee over-the-horizon radar facility at Alice Springs in northern Australia. Sample ionograms obtained during 1990 were used, and the study concentrated on reproducing effects due to sunrise-sunset gradients and the equatorial anomaly. Backscatter

C. J. Russell; P. L. Dyson; Z. Houminer; J. A. Bennett; L. Li

1997-01-01

96

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

NASA Astrophysics Data System (ADS)

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

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

Wright, D. M.; Davies, J. A.; Yeoman, T. K.; Robinson, T. R.; Shergill, H.

2006-03-01

97

Measurements of possible D- and E-region telecommunications effects during ionospheric heating. Final report  

SciTech Connect

For this research project, measurements were made of the effects that heating the ionosphere might have on the passage of radiowaves through the D- and E-regions. The purpose of this work was to simulate the effects of the proposed Solar Power Satellite microwave power beam on the lower ionosphere. The increased electron temperatures produced by the Platteville, Colorado, HF ionospheric heater caused cross-modulation on certain radiowaves when the heater was rapidly modulated (the Luxembourg effect). Small amounts of cross-modulation were detected at four frequencies between 60 kHz and 5 MHz. Attempts were made to detect phase path changes - indicative of electron number density changes - while the heater was slowly cycled on and off. No phase path changes could be seen for radiowaves of frequency 10.2 or 60 kHz. If these results are extrapolated to the powers and frequency of the Solar Power Satellite power beam, then no significant impact from D- and E-region modification on telecommunications services are expected.

Showen, R.L.

1980-02-01

98

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

99

Season Variation of Ionosphere Effects of geomagnetic Storms at different Latitudes of East Asia  

NASA Astrophysics Data System (ADS)

The most important factors governing the variations of the ionosphere at the time of the geomagnetic storm include a change in electron composition and the circulation system of neutral wind, which depends substantially on the season. Besides, the difference of the geographic and magnetic coordinates complicates the picture of disturbances and leads to a longitudinal dependence of ionospheric effects of geomagnetic storms. We analyzed the state of the ionosphere using the data from a network of ionosondes and digisondes located in the longitudinal sector of 90-130°E. This region is of interest because the difference between the geographic and magnetic coordinates there is the largest, and formation of a large-scale structure proceeds at the more high geographic latitudes where ionization very depends from season. We investigated the variations of F2-layer critical frequencies, ionospheric altitudes and the ionospheric disturbance index DfoF2. The average a few quiet days variations of foF2, hF and hmF2 were used as the undisturbed level. We considered geomagnetic storms of a different intensity evolving from May, 2003 till January, 2004. During this period there were marked ten storms, which could be divided into the different season. The prolonged negative disturbances at high and middle latitudes were typical for the summer geomagnetic storms during all disturbed period. The increase of foF2 with a subsequent abrupt decrease of foF2 occurred in the evening after the Dst-index had reached its minimum value. At magnetic latitudes lower 30° the disturbances were mainly positive. The tendency of the disturbance variations maintained in the winter and in the autumn. However at high latitudes the intensive positive disturbances caused by precipitation of auroral fluxes were observed in the evening and night. The received variety of disturbances in different seasons is determined primarily by the illumination conditions of ionosphere and the local time of geomagnetic storm onset. The presented experimental results can be used to testing and the correction of empirical models. This work was done with financial support of the Russian Foundation for Basic Research (grant 02-05-39002).

Pirog, O. M.; Polekh, N. M.; Ratovsky, K. G.; Zherebtsov, G. A.; Smirnov, V. F.; Shi, J. K.; Wang, X.

100

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

101

The effect of 20 May 2012 annular solar eclipse on the ionosphere  

NASA Astrophysics Data System (ADS)

The 20 May 2012 annular solar eclipse crossed the mid-latitude ionosphere of Southeast China, Taiwan, Japan, and America West. The total electron content (TEC) derived from ground-based GPS receivers and frequency shifts recorded by Doppler sounding systems in Taiwan are employed to monitor the eclipse signatures. We compare the two observations on the eclipse day and those recorded 1-5 days before to find the associated eclipse effects. Results show that Doppler shifts yield negative values after the first contact but positive values after the third contact. The TECs variations and their time rate of changes are used to observe simultaneous responses of the ionosphere plasma density and soft Doppler during the annular solar eclipse.

Lo, C.; Liu, J. G.

2012-12-01

102

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

103

High-latitude ionospheric drivers and their effects on wind patterns in the thermosphere  

NASA Astrophysics Data System (ADS)

Winds in the thermosphere are highly important for transporting mass, momentum and energy over the globe. It has been moderately difficult to validate how well models reproduce the winds because of a lack of data. In the high latitude region, the ions and neutrals are strongly coupled when the aurora is present, whereas the coupling is weaker when there is no aurora. In this study, we investigate the ability of the Global Ionosphere Thermosphere Model (GITM) to simulate the meso-scale wind structure over Alaska before and during a substorm. Ten distinct numerical simulations of a substorm event that occurred between 02:00 and 17:00 universal time on November 24, 2012 have been preformed. Using GITM, we are able to highlight both subtle and drastic differences in model results affected by various high-latitude ionospheric drivers. Distinct ionospheric inputs considered as drivers include the Weimer potential patterns using IMF solar wind data coupled with the Fuller-Rowell and Evans auroral patterns, SuperDARN fitted potential pattern data, and changes in ionospheric currents measured by the Auroral Electrojet index. We also consider the effects of the boundary between the neutral wind dynamo calculation and the high-latitude imposed electric potential. Neutral wind velocities measured from Scanning Doppler Imager instruments located at three locations in Alaska are then compared to GITM simulated winds for every distinct run. Each component of the wind is compared individually, as they are driven by different forcing terms. Further, electron densities at 240km as a function of location and time are compared with data from the Poker Flat Incoherent Scatter Radar instrument. We have found that differences in the type of input used to model the substorm can lead to significantly disparate results among each individual run. This points to the need to have accurate specifications of the electric potential and auroral precipitation if the wind is to be fully understood.

Liuzzo, L. R.; Ridley, A. J.; Conde, M.; Hampton, D. L.; Bristow, W. A.; Nicolls, M. J.; Mitchell, E. J.

2013-12-01

104

A re-analysis of the atmospheric and ionospheric effects of the Flixborough explosion  

NASA Astrophysics Data System (ADS)

The ionospheric record of the 1974 cyclohexane vapour cloud explosion (VCE) accident near Flixborough is re-examined in light of a new theory used to describe the acoustic field in the atmosphere and ionosphere caused by explosions on the ground. The reconstructed oblique Doppler sounding records from six radio traces agree remarkably well with experimental results when a ground source explosion yield of 283+/-38tons of TNT is utilized. This result, when compared to the detonation of large hydrocarbon fuel-drop-air clouds, suggests that only 14+/-2tons of cyclohexane was involved in the explosion. Additionally the time of the explosion determined from the model, 15:52:08+/-6, agrees, within the mutual uncertainty, with that determined seismically, 15:52:15.5+/-2 UT. The precision in the value of the yield and accuracy of the time of the explosion validates the model used to describe the propagation of acoustic waves by taking into account expansion, absorption, and non-linear and inhomogeneous effects in the atmosphere and ionosphere.

Krasnov, V. M.; Drobzheva, Ya. V.; Venart, J. E. S.; Lastovicka, J.

2003-07-01

105

Post-flare effects in the lower ionosphere of middle latitudes  

NASA Astrophysics Data System (ADS)

Beginning in the 1960s, records were made of noise from the region around the Polar Star on 29 MHz (Krivsky and Tlamicha, 1960) at the Ondrejov Observatory near Prague. Since the aerial characteristic was not too narrow, radio bursts were received of solar origin (of flares) at the noise level, SCNA effects (sudden cosmic noise absorption) at the time of intensive flare X-emission and in some rare cases, after large proton flares, small absorption effects of a few hours duration (Krivsky, 1969). These post-flare absorption effects in cosmic noise are evidently analogous with PCA effects (polar cap absorption) and are connected with ionospheric absorption of radio cosmic noise, caused by fast particles of subcosmic radiation. The recording of long term absorption effects after large particle flares at European midlatitudes was reported at the beginning of the 1960s. It was then usual to record radio cosmic noise with riometers at frequencies of about 18 MHz in the polar or subpolar regions in an effort to record PCA effects of subcosmic radiation (Hakura, 1968). An attempt was made to record the complex of emissions mentioned as well as the effects in a new frequency range (30 MHz), which did not agree with the ideas of the contemporaneous representatives of the Ionospheric Department of the Geophysical Institute in Prague. In recent years radio cosmic noise has been recorded at the Upice Observatory. These long term after flare effects of cosmic radio noise absorption (AF-CNA) at middle latitudes are reported to the geophysical and ionospheric community for the first time.

Krivsky, L.

1989-09-01

106

Simulations of the effects of vertical transport on the thermosphere and ionosphere using two coupled models  

NASA Astrophysics Data System (ADS)

We have explored the sensitivity of the thermosphere and ionosphere to dynamical forcing from altitudes near the mesopause (˜ 95 km) as recently described by Siskind et al., (2014). We show results from five simulations, all for the year 2009, with the NCAR/Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM). Two simulations were driven with the NCAR Global Scale Wind Model (GSWM) and three used output from the Advanced Level Physics High Altitude (ALPHA) version of the Navy's Operational Global Atmospheric Prediction System (NOGAPS). Use of NOGAPS-ALPHA allows for realistic meteorological variability from the lower atmosphere to propogate up into the TIEGCM, including a rich spectrum of non-migrating tides. We find that the additional vertical transport from these tides causes a significant reduction in the calculated peak electron density of the ionospheric F2 layer (NmF2). The mechanism for this effect is the enhanced downward transport of atomic oxygen to the base of the thermosphere. In turn, this yields a greater relative abundance of N2 and hence, enhanced recombination of ions and electrons. To get improved agreement with observed electron densities, we must reduce (Kzz) by a factor of 5. However, even with lower Kzz, our calculation still underestimates the NmF2 compared with radio occultation observations by the Constellation Observing System for Meterology, Ionosphere and Climate (COSMIC) satellite system. This underestimate of NmF2 may be linked to an overestimate of the non-migrating tides in the coupled TIEGCM-NOGAPS calculations or to uncertainties in the bottom boundary for atomic oxygen in the TIEGCM. We are currently exploring the second hypothesis by actively constraining the bottom boundary of the TIEGCM to observed atomic oxygen values from the NASA TIMED/SABER instrument. Siskind et al., (2014) Simulations of the effects of vertical transport on the thermosphere and ionosphere using two coupled models, J. Geophys. Res., DOI:10.1002/2013JA019116. This work sponsored by the Office of Naval Research.

Drob, Douglas; Siskind, David; Dymond, Kenneth; McCormack, John

2014-05-01

107

Ionospheric modeling  

Microsoft Academic Search

The purpose of this report is to familiarize a user of ionospheric models with the options presently available for ionospheric prediction and specification. Two types of ionospheric models are available: the numerical-phenomenological and theoretical models. From the numerical type, the ITS-78, IONCAP, and Bent models have been discussed. In the theoretical models the main concern is the number of parameters

B. S. Dandekar

1982-01-01

108

Effects of the magnetic storm in April 2000 in the low latitude ionosphere near longitude 120E  

NASA Astrophysics Data System (ADS)

A halo-CME induced interplanetary shock wave that passed the Earth around 1648 UT on April 6, 2000 triggered a geomagnetic storm with a minimum value of about -300 nT in Dst index. In this paper, digisonde data from ionospheric stations at Chungli, Wuhan, and Kokubunji are included to investigate the ionospheric responses of low latitudes near longitude 120 E to this storm. At three low latitudes near longitude 120 E during this storm, the significant ionospheric responses was an anomalous rapid and large increase in the ionospheric heights occurred around the beginning of the main phase, and the lifts in h'F and hmF2 lasted for about 2 hours. The nearsimultaneous ionosphere increase was also observed at Chungli, Taiwan. And a wave like disturbance appeared on daytime of the second day. The near simultaneity of the ionospheric lifts at these stations in the nighttime ionospheric heights after the SSC suggested that an ExB plasma drift due to the storm related perturbed east-west electric fields. The empirical models of storm time equatorial zonal electric fields (Fejer and Scherliess, 1997) attributed those rapid and large lifts to the effect of solar wind-magnetosphere dynamo origin, which penetrate to low latitudes and equatorial regions. The following wave like disturbance was suggested to be caused by storm induced Travelling atmospheric disturbances (TADs). A method developed by Liu et al. (2002) and Luan et al. (2002) was used to derive the vertical effective winds from ionospheric measurements. It also shows that there was a significantly downward and upward vertical drift during the storm, which verifies the existence of the storm related perturbed east-west electric fields. Finally, the ionospheric storm time derivation from its monthly median level at these stations was also used to validate the predication ability of STORM, a storm empirical model of Araujo-Pradere et al. (2001), which is now included in the international reference ionosphere model IRI2000. For this particular storm, the model captures decreases in foF2 ratio better at Kokubunji than at Wuhan. But the positive changes and TID like disturbances are missed by the model.

Liu, L.; Wan, W.; Lee, C.

109

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

110

Irregularities in ionospheric plasma clouds: their evolution and effect on radio communication. Technical report  

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

111

Ionospheric effects during first 2 hours after the "Chelyabinsk" meteorite impact  

NASA Astrophysics Data System (ADS)

In this paper, we analyzed the ionospheric effects within the 100-1500 km ranges from the Chelyabinsk meteorite explosion site from the ISTP SB RAS EKB radar data, and from the IG UB RAS PARUS ionosonde data. Both instruments are located at the Arti Observatory, approximately 200 km north of the supposed explosion location. The ionospheric disturbance caused by the meteorite flyby, explosion, and impact had high dynamics and amplitude. Essential effects, however, were observed at more than 100-200 km from the explosion site, and farther, up to 1500 km. Almost simultaneously with the explosion and for 3 minutes (03:20-03:23 UT), there was a motion away from the radar 400 km southwest of the latter (and approximately 200 km west of the explosion site) at the E-layer height with the characteristic velocities 200 m/s and high spectral width. A short delay of the detected effect at a significant distance from the explosion site also testifies to the hypothesis of a large short-living irregularity formations at the heights of the lower E-layer, with the transversal size of several hundreds of kilometers. The first disturbance in the F-layer was observed 15 minutes after the explosion, and it propagated away from the radar almost radially. The radial disturbances were observed up to about 80-100 minutes. The main disturbances in the F-layer were nearly radial waves with the center close to the explosion site. Analyzing the experimental data allowed us to determine the equivalent ionospheric velocities for individual travel mode. The work was done under financial support of RFBR grant #14-05-00514-a.

Berngardt, Oleg; Kurkin, Vladimir; Zherebtsov, Gelii; Grigorieva, Svetlana; Kusonski, Oleg

112

Night-side effects on the polar ionospheric convection due to a solar wind pressure impulse .  

NASA Astrophysics Data System (ADS)

The Sudden Impulse (SI) of solar wind dynamic pressure of 20 february 2000, 21:03 UT, is investigated by making use of data from WIND, GEOTAIL, POLAR and GOES; ground magnetometer chains (Greenland, IMAGE, CANOPUS); SuperDARN HF radars in both Northern and Southern hemispheres. The main effect of the SI described herein is an enhancement of the ionospheric convection around midnight MLT. We suggest that such an enhancement be due to an increase of the dawn-dusk electric field caused by the SI compression of the magnetospheric tail.

Coco, I.; Amata, E.; Marcucci, M. F.; Villain, J.-P.; Hanuise, C.; Cerisier, J.-C.; St. Maurice, J.-P.; Sato, N.

113

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

114

Effect of double layers on magnetosphere-ionosphere coupling  

NASA Technical Reports Server (NTRS)

The dynamic aspects of auroral current structures are reviewed with emphasis on consequences for models of microscopic turbulence (MT). A number of models of MT are introduced into a large-scale model of Alfven wave propagation to determine the effect of various models on the overall structure of auroral currents. The effect of a double layer (DL) electric field which scales with the plasma temperature and the 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 shown that the DL model is less diffusive than the resistive model, indicating the possibility of narrow intense current structures.

Lysak, Robert L.; Hudson, Mary K.

1987-01-01

115

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

116

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

117

Positive ionospheric storm effects at Latin America longitude during the superstorm of 20-22 November 2003: revisit  

NASA Astrophysics Data System (ADS)

Positive ionospheric storm effects that occurred during the superstorm on 20 November 2003 are investigated using a combination of ground-based Global Positioning System (GPS) total electron content (TEC), and the meridian chain of ionosondes distributed along the Latin America longitude of ~280° E. Both the ground-based GPS TEC and ionosonde electron density profile data reveal significant enhancements at mid-low latitudes over the 280° E region during the main phase of the November 2003 superstorm. The maximum enhancement of the topside ionospheric electron content is 3.2-7.7 times of the bottomside ionosphere at the locations of the ionosondes distributed around the mid- and low latitudes. Moreover, the height of maximum electron density exceeds 400 km and increases by 100 km compared with the quiet day over the South American area from middle to low latitudes, which might have resulted from a continuous eastward penetration electric field and storm-generated equatorward winds. Our results do not support the conclusions of Yizengaw et al. (2006), who suggested that the observed positive storm over the South American sector was mainly the consequence of the changes of the bottomside ionosphere. The so-called "unusual" responses of the topside ionosphere for the November 2003 storm in Yizengaw et al. (2006) are likely associated with the erroneous usage of magnetometer and incomplete data.

Zhao, B.; Wan, W.; Lei, J.; Wei, Y.; Sahai, Y.; Reinisch, B.

2012-05-01

118

Sources of uncertainty in ionospheric modeling: The neutral wind  

NASA Astrophysics Data System (ADS)

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

119

Effect of field-aligned potential drop in a global magnetosphere-ionosphere coupling model  

NASA Technical Reports Server (NTRS)

Effects of field-aligned potential drops on the magnetosphere-ionosphere coupling in a steady state are studied on a global ionospheric scale. It is shown that a constant-current generator can support a larger field-aligned potential drop than a constant voltage generator under similar conditions. The magnetospheric convection pattern is distorted more in the constant current generator case than in the constant voltage generator case. The main difference between a constant current generator and a constant voltage generator is found to lie in their ability to adjust the vorticity of the magnetospheric convection. The results show that a constant current generator allows the vorticity of the magnetospheric convection to adjust so that the field-aligned current can be kept constant under the loading influence of the field-aligned potential. On the other hand, a constant voltage generator by definition cannot adjust the vorticity of the magnetospheric convection to maintain the field-aligned current under the loading influence of the field-aligned potential.

Kan, J. R.; Cao, F.

1988-01-01

120

Measuring lightning-induced ionospheric effects with incoherent scatter radar or with cross-modulation  

NASA Astrophysics Data System (ADS)

Measurements have been made of the ionosphere during lightning storms using the incoherent scatter radar at Arecibo, Puerto Rico. Attempts were made to detect the expected increases in the D-region electron number densities, and possible changes in the plasma line echoes in the F-region. No D-region density changes were detected, to a limit of under 200/cc. This upper limit on possible lightning-induced ionization is not necessarily in conflict with predictions, which are of the same order as this limit and depend on assumptions of the strength and duration of the lightning. Spectral plasma line measurements of the incoherent scatter in the F-region, which are a sensitive indication of E-field variations also did not show any changes associated with individual lightning strikes. An alternative method of searching for D-region changes due to lightning is a cross-modulation or riometer experiment, which is modeled here.

Showen, R. L.; Slingeland, A.

1998-05-01

121

The investigation of man-made modifications of the ionosphere. [effects of detonations and rocket exhaust  

NASA Technical Reports Server (NTRS)

Topics covered include: (1) the application of ionosphere modifications models to the simulation of results obtained when rocket-borne explosives were detonated in the ionosphere; (2) the problem of hypersonic vapor releases from orbiting vehicles; (3) measuring the electron content reduction resulting from the firing of a Centaur rocket in the ionosphere; and (4) the preliminary design of the critical frequency tracker which displays the value of electron concentration at the peak of the F 2 region, in real time.

Bernhardt, P. A.; Darosa, A. V.; Price, K. M.

1980-01-01

122

The Effects of Enhanced Fluxes of Soft Xrays on the Ionospheres and Thermospheres of Venus and Mars  

Microsoft Academic Search

We compare here the effects of enhanced fluxes of soft xrays, such as those measured by the SNOE satellite (e.g., Bailey et al., 1999) on models of the lower thermospheres\\/ionospheres of Venus and Mars. Electron density profiles measured by the Radio Science Experiment on Mars Global surveyor show a lower peak or shoulder below the main peak that is ascribed

J. L. Fox

2003-01-01

123

Exposed high-voltage source effect on the potential of an ionospheric satellite  

NASA Technical Reports Server (NTRS)

A pulsed, high-voltage source, which is able to draw a current from the surrounding plasma, is seen to induce large changes in the potential of an ionospheric satellite (the Iowa Plasma Diagnostics Package flown on Space Shuttle flight STS-51F). This, in turn, may affect the operation of other instruments that use the chassis of the satellite as a ground for electrical circuits. The magnitude of the change in satellite potential is dependent upon both the orientation of the high-voltage source, relative to the plasma flow, and the characteristics of the high-voltage source. When the satellite is grounded to the Shuttle Orbiter, this effect is sufficient to change the potential of the Orbiter by a small, but noticeable, amount.

Tribble, A. C.; D'Angelo, N.; Murphy, G. B.; Pickett, J. S.; Steinberg, J. T.

1988-01-01

124

The effect of ionospheric scintillation on VHF\\/UHF satellite communications  

Microsoft Academic Search

Ionospheric scintillations of the type caused by F-layer irregularities can degrade the performance of satellite communication links at UHF. The degradation is most severe for propagation paths that transit the auroral and equatorial ionospheres. In the present paper, scintillation data obtained in the auroral and equatorial regions are analyzed and the results are applied to the evaluation of the performance

H. E. Whitney; Santimay Basu

1977-01-01

125

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

126

Ionospheric refraction effects on orbit determination using the orbit determination error analysis system  

Microsoft Academic Search

The influence of ionospheric refraction on orbit determination was studied through the use of the Orbit Determination Error Analysis System (ODEAS). The results of a study of the orbital state estimate errors due to the ionospheric refraction corrections, particularly for measurements involving spacecraft-to-spacecraft tracking links, are presented. In current operational practice at the Goddard Space Flight Center (GSFC) Flight Dynamics

C. P. Yee; D. A. Kelbel; T. Lee; J. B. Dunham; G. D. Mistretta

1990-01-01

127

Simulation study of ionospheric response to the annular eclipse on May 21, 2012  

NASA Astrophysics Data System (ADS)

It is widely accepted that the ionosphere varies significantly during a solar eclipse. Previous ionospheric observations have indicated that reduction in solar EUV and X-ray radiation results in significant decrease of electron densities. In addition, some studies have suggested that neutral wind variations and neutral composition changes caused by local cooling of the neutral atmosphere indirectly affect the ionosphere. However, effects of the atmospheric processes on the ionospheric variations have not been fully understood. The annular solar eclipse on May 21, 2012 passed over Japan provided us with a good opportunity for studying the ionospheric variations during a solar eclipse. A number of ionospheric data have been obtained at various observatories in Japan. In order to quantitatively study variations in the ionosphere and atmosphere during the solar eclipse, we used the whole atmosphere-ionosphere coupled model (GAIA), and compared the simulation results with the observed data of the ionosphere. The results indicate that electron density decrease is primarily caused by reduction in solar EUV/X-ray radiation, but that neutral atmospheric variations driven by cooling of the atmosphere during the solar eclipse also play an important role in the electron density variations.

Shinagawa, H.; Miyoshi, Y.; Jin, H.; Matsumura, M.; Fujiwara, H.; Tsugawa, T.; Kubo, Y.; Murata, T.

2012-12-01

128

Source, propagation, and effects of lightning in the Earth-ionosphere system  

NASA Astrophysics Data System (ADS)

The capabilities of the World Wide Lightning Location Network (WWLLN) are expanded to enable research of the source, propagation, and effects of lightning in the Earth-ionosphere system. The main expansion of the network capability is the measurement of the very low frequency radiated energy from lightning; the radiated stroke energy is one to one related to the canonical peak current measurements of other ground based networks. Stroke energy is used to develop a model of the network relative detection efficiency; this internal model rates the coverage capabilities of the network compared to the networks best regional coverage. The last dataset developed and discussed is the clustering of the lightning locations into both flashes and the active lightning regions of thunderstorms. These three capabilities of the network allow tracing the effects of lightning and thunderstorms from their source, to a proxy for the global electric circuit and to the magnetosphere. The source of lightning is investigated in two regimes: within thunderstorms and between thunderstorms. Within thunderstorms the time between flashes is found to be proportional to the resulting flash energy for differing thunderstorms, regions, and seasons. Between thunderstorms the lightning energy is shown to differ between land and ocean, with oceanic thunderstorms producing stronger and fewer strokes. The propagation of the radiated energy is measured using the lightning as a probe of attenuation along the different propagation paths. Attenuation is seen to have an asymmetry with magnetic azimuth: eastward moving waves are attenuated less than westward moving waves. The attenuation asymmetry is complimentary to the observed asymmetry in whistler and radio energy emitted through the ionosphere into the magnetosphere. Thunderstorm clusters are used to estimate the total upward current contribution of thunderstorms to the global electric circuit. It is shown that WWLLN can provide one of the first continuous global measurements of this current to the global electric circuit.

Hutchins, Michael L.

129

Thunderstorm coupling to the magnetosphere and associated ionospheric effects. Semiannual Report, 1 November 1991-30 April 1992  

SciTech Connect

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, U.S.

1992-01-01

130

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

NASA Astrophysics Data System (ADS)

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.

Fitzgerald, T. Joseph; Argo, Paul E.; Carlos, Robert C.

1997-03-01

131

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

132

Ionospheric refraction effects on TOPEX orbit determination accuracy using the Tracking and Data Relay Satellite System (TDRSS)  

NASA Technical Reports Server (NTRS)

This investigation concerns the effects on Ocean Topography Experiment (TOPEX) spacecraft operational orbit determination of ionospheric refraction error affecting tracking measurements from the Tracking and Data Relay Satellite System (TDRSS). Although tracking error from this source is mitigated by the high frequencies (K-band) used for the space-to-ground links and by the high altitudes for the space-to-space links, these effects are of concern for the relatively high-altitude (1334 kilometers) TOPEX mission. This concern is due to the accuracy required for operational orbit-determination by the Goddard Space Flight Center (GSFC) and to the expectation that solar activity will still be relatively high at TOPEX launch in mid-1992. The ionospheric refraction error on S-band space-to-space links was calculated by a prototype observation-correction algorithm using the Bent model of ionosphere electron densities implemented in the context of the Goddard Trajectory Determination System (GTDS). Orbit determination error was evaluated by comparing parallel TOPEX orbit solutions, applying and omitting the correction, using the same simulated TDRSS tracking observations. The tracking scenarios simulated those planned for the observation phase of the TOPEX mission, with a preponderance of one-way return-link Doppler measurements. The results of the analysis showed most TOPEX operational accuracy requirements to be little affected by space-to-space ionospheric error. The determination of along-track velocity changes after ground-track adjustment maneuvers, however, is significantly affected when compared with the stringent 0.1-millimeter-per-second accuracy requirements, assuming uncoupled premaneuver and postmaneuver orbit determination. Space-to-space ionospheric refraction on the 24-hour postmaneuver arc alone causes 0.2 millimeter-per-second errors in along-track delta-v determination using uncoupled solutions. Coupling the premaneuver and postmaneuver solutions, however, appears likely to reduce this figure substantially. Plans and recommendations for response to these findings are presented.

Radomski, M. S.; Doll, C. E.

1991-01-01

133

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

NASA Astrophysics Data System (ADS)

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

134

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

SciTech Connect

Simultaneous ground-based observations of narrowband and broadband VLF radio waves and of cloud-to-ground lightning were made at widely spaced locations during the 1987 Wave-Induced Particle Precipitation (WIPP) campaign, conducted from Wallops Island, Virginia. Based on these observations, the first case study has been made of the relationships among located cloud-to-ground (CG) lightning flashes, whistlers, and associated ionospheric effects during a substorm particle injection event. This event took place 2 days after the strongest geomagnetic storm of 1987, during a reintensification in geomagnetic activity that did not affect the high rate of whistlers observed at Faraday Station, Antarctica. At the time of the injection event, several intense nighttime thunderstorms were located over Long Island and the coast of New England, between 400 km northwest and 600 km north of the region geomagnetically conjugate to Faraday. About two thirds of the CG flashes that were detected in these thunderstorms during the hour following the injection event onset were found to be causatively associated with whistlers received at Faraday. During the same period the amplitude of the 24.0-kHz signal from the NAA transmitter in Cutler, Maine, propagating over the thunderstorm centers toward Wallops Island was repeatedly perturbed in a manner characteristic of previously reported VLF signatures of transient and localized ionization enhancements at D region altitudes. Though such enhancements may have been caused by whistler-induced bursts electron precipitation from the magnetosphere, the data in this case are insufficient to establish a clear connection between the NAA amplitude perturbations and the Faraday Station whistlers. In view of the proximity of the NAA great circle path to the storm center, having the lower ionosphere by intense radiation from lightning may also have played a role in the observed VLF perturbations.

Rodriguez, J.V.; Inan, U.S. (Stanford Univ., CA (United States)); Li, Y.Q.; Holzworth, R.H. (Univ. of Washington, Seattle (United States)); Smith, A.J. (British Antarctic Survey (NERC), Cambridge (United Kingdom)); Orville, R.E. (New York State Univ., Albany (United States)); Rosenberg, T.J. (Univ. of Maryland, College Park (United States))

1992-01-01

135

Progress in Observation-Based Ionospheric Modeling  

Microsoft Academic Search

Models for the ionospheric component of space weather are needed for a wide range of applications. For example, any remote sensing techniques that use radio waves traveling through the ionosphere, looking up from the ground or down from space, must correct for the retarding, refractive, and scintillation effects of the ionospheric plasma. Two types of models are used for this

Dieter Bilitza; Bodo Reinisch; Jan Lastovicka

2008-01-01

136

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

137

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

138

Integrated Research Plan April 1, 2008 "Effects of Ionospheric-Magnetospheric  

E-print Network

and at nightside auroral latitudes inject these ionospheric source plasmas outward along magnetic field lines of the solar wind interaction, and is powered mainly by the solar EUV energy absorbed in the F layer [e

Lotko, William

139

A brief review of ionospheric scintillation fading effects as observed in NASA satellite tracking and data acquisition networks.  

NASA Technical Reports Server (NTRS)

Discussion of some results of the effects of ionospheric irregularities on NASA satellite tracking and data acquisition operations. Ionospheric scintillation fading produced by irregularities has been observed at 136 MHz (vhf), 400 MHz (uhf), 1550 MHz (L-band) and 1700 to 2200 MHz (S-band). Details of these observations are presented. Vhf scintillation effects are evident in both auroral and equatorial regions. Fading effects decrease with increasing radio frequency in the auroral region. The same frequency dependence for fading is not observed in the equatorial region. Although there is a seasonal and diurnal character to scintillation in the equatorial region, fading effects are usually more severe than in the auroral region for a given radio frequency. Space diversity measurements indicate that reasonable solutions for vhf telemetry problems are available for either region. Space diversity should provide a solution for microwave frequencies as well. Ionospheric fading amplitude for 1700 MHz is relatively small in the auroral region. In the equatorial region amplitude fading levels for 1550-MHz signals from ATS-5 are often much larger than expected. Observations of the Apollo Lunar Surface Experiment Package (ALSEP) operating at 2300 MHz observed near the geomagnetic equator show fading peaks in excess of 15 dB.

Golden, T. S.

1972-01-01

140

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

141

Effects of large-scale irregularities of the ionosphere in the propagation of decametric radio waves  

Microsoft Academic Search

A numerical experiment is used to study the simultaneous influence of regular space-time gradients and large-scale traveling ionospheric disturbances (TIDs) as manifested in the angular and Doppler characteristics of decametric-wave propagation. Conditions typical for middle latitudes are chosen as the ionospheric models: conditions under which large-scale TIDs in the F2-layer evolve on the background of winter or equinox structures of

T. S. Kerblai; E. M. Kovalevskaia

1985-01-01

142

Effects of solar activity variations on the low latitude topside nighttime ionosphere  

Microsoft Academic Search

We have studied the topside nighttime ionosphere of the low latitude region using data obtained from DMSP F15, ROCSAT-1, KOMPSAT-1, and GUVI on the TIMED satellite for the period of 2000–2004, during which solar activity decreased from its maximum. As these satellites operated at different altitudes, we were able to discriminate altitude dependence of several key ionospheric parameters on the

S. M. Park; H. Kim; S. Min; J. Lee; H. Kil; L. J. Paxton; S.-Y. Su; K. W. Min

2008-01-01

143

Ionospheric range-rate effects in satellite-to-satellite tracking  

Microsoft Academic Search

Investigation of ionospheric range and range-rate corrections in satellite-to-satellite tracking were investigated. Major problems were cited and the magnitude of errors that have to be considered for communications between satellites and related experiments was defined. The results point to the need of using a sophisticated modeling approach incorporating daily solar data, and where possible actual ionospheric measurements as update information,

J. R. Lipofsky; R. B. Bent; S. K. Llewellyn; P. E. Schmid

1977-01-01

144

Improving Klobuchar Type Ionospheric Delay Model using 2D GPS TEC over China  

NASA Astrophysics Data System (ADS)

In Global Positioning System GPS the 8 parameter Klobuchar type ionospheric delay model is broadcast to predicts the global vertical TEC distribution at a given time period for real-time correcting the ionospheric effect on for single frequency GPS measurements The Klobuchar type ionospheric delay model which originally comes from Bent Model is a simple but utility model It adopts trigonometric cosine function to describe the characteristics of ionospheric diurnal variation The reliability for TEC prediction by means of large scale variation can be guaranteed Due to the Klobuchar model is completed in early 1980s confined to the technology of that era the parameters and the model type were not so accurate It needs to be updated and validated for common global and or regional users Using the original Klobuchar model over 60 of the ionosphere delay effects can be corrected generally at present In order to improve the result a new type of the model needs to be developed which is more suitable for TEC correlation of regional and global area For this target after taking the short comes of current models into considerations we increased the number of the original model parameters from 8 to 14 Then use the ionospheric TEC data by Chinese GPS network we evaluated and checked the parameters settings basing on Least Square fitting method It -s showed that the accuracy of the new Klobuchar Model is improved greatly Key Words GPS TEC Ionosphere Klobuchar Model the ionosphere delays correcting models

Han, Ling; Zhang, Hongping; Huang, Yidan; Wang, Mingyuan; Zhu, Wenyao; Ping, Jingsong

145

Ionospheric Predictions with the International Reference ionosphere: Recent Improvements  

NASA Astrophysics Data System (ADS)

The International Reference Ionosphere (IRI) is a widely used tool for the many space weather related application that involve the propagation of electromagnetic waves through the ionosphere and therefore require correction for the retarding and refractive effect the ionosphere has on these waves. IRI is acknowledged as the data-based ionospheric standard by many international organizations (COSPAR, URSI, ISO, ECSS). This presentation will report on the latest improvements of the IRI model with special emphasis on the accurate description of variations with solar activity. Efforts are underway to improve the IRI electron density and ion composition models for very low solar activities similar to the levels experienced during the recent extended solar minimum. First results will be presented and discussed including comparisons with TOPEX-Jason Vertical Ionospheric Electron Content (VIEC) data and the variation of the data-model difference over the solar cycle.

Bilitza, Dieter; Brown, Steven; Beckley, Brian

2013-04-01

146

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

NASA Astrophysics Data System (ADS)

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

147

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

148

Ionospheric chemical releases  

NASA Technical Reports Server (NTRS)

Ionospheric plasma density irregularities can be produced by chemical releases into the upper atmosphere. F-region plasma modification occurs by: (1) chemically enhancing the electron number density; (2) chemically reducing the electron population; or (3) physically convecting the plasma from one region to another. The three processes (production, loss, and transport) determine the effectiveness of ionospheric chemical releases in subtle and surprising ways. Initially, a chemical release produces a localized change in plasma density. Subsequent processes, however, can lead to enhanced transport in chemically modified regions. Ionospheric modifications by chemical releases excites artificial enhancements in airglow intensities by exothermic chemical reactions between the newly created plasma species. Numerical models were developed to describe the creation and evolution of large scale density irregularities and airglow clouds generated by artificial means. Experimental data compares favorably with theses models. It was found that chemical releases produce transient, large amplitude perturbations in electron density which can evolve into fine scale irregularities via nonlinear transport properties.

Bernhardt, Paul A.; Scales, W. A.

1990-01-01

149

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

150

Springtime effects in the mesosphere and ionosphere observed at northern midlatitudes  

NASA Astrophysics Data System (ADS)

Nighttime volume emission rates and rotational temperatures, obtained from simultaneous observations of molecular oxygen and hydroxyl airglow at Almaty (43.25°N, 76.92°E) and Sierra-Nevada (37.2°N, 356.7°E), along with ionospheric density derived from foF2 in the vertical sounding ionograms over Almaty are analysed to study the variability and coupling of parameters observed in the upper mesosphere and ionosphere during the period of February - April, 2000. Ionospheric critical frequency measurements and airglow observations by the Mesopause Rotational Temperature Imager (MORTI) at Almaty and the Spectral Airglow Temperature Imager (SATI) at Sierra-Nevada Observatories show an increase in long-period planetary wave (PW) activity from the end of February until the middle of March, 2000. Very good agreement was found in the temporal variations of emission rates and rotational temperatures from March 1-15, 2000 measured at the Almaty and Sierra-Nevada sites. Similar perturbations could also be seen in the ionospheric critical frequency (?foF2) obtained as a difference between current foF2 values and an ionospheric background level. The perturbations observed have been interpreted employing the Met office stratospheric model results. Latitudinal structure of a quasi 5-day wave was identified, for which the first-symmetric-mode amplitude and symmetric behaviour of phase are in good agreement with theoretical prediction. The analysis of the Met office stratospheric data indicate the presence of westward-propagating PW with periods of ˜5 and 10 days during the period of interest. The temporal correlation between planetary scale oscillations observed in the datasets examined (ionospheric, optical and meteorological) suggest dynamical coupling with the stratosphere. A negative disturbance in ?foF2 of ˜25% observed 1 day before a sharp increase in the MORTI mesospheric rotational temperature registered on March 10 at Almaty, is also discussed in the context of the possible stratosphere/mesosphere/ionosphere coupling.

Aushev, V. M.; Fedulina, I. N.; Gordienko, G. I.; López-González, M. J.; Pogoreltsev, A. I.; Ryazapova, S. Sh.; Shepherd, M. G.

2006-05-01

151

Contribution of ionospheric irregularities to the error of dual-frequency GNSS positioning  

NASA Astrophysics Data System (ADS)

This paper investigates the third-order residual range error in the dual-frequency correction of ionospheric effects on satellite navigation. We solve the two-point trajectory problem using the perturbation method to derive second-approximation formulas for the phase path of the wave propagating through an inhomogeneous ionosphere. It is shown that these formulas are consistent with the results derived from applying perturbation theory directly to the eikonal equation. The resulting expression for the phase path is used in calculating the residual range error of dual-frequency global positioning system (GPS) observations, in view of second- and third-order terms. The third-order correction includes not only the quadratic correction of the refractive index but also the correction for ray bending in an inhomogeneous ionosphere. Our calculations took into consideration that the ionosphere has regular large-scale irregularities, as well as smaller-scale random irregularities. Numerical examples show that geomagnetic field effects, which constitute a second-order correction, typically exceed the effects of the quadratic correction and the regular ionospheric inhomogeneity. The contribution from random irregularities can compare with or exceed that made by the second-order correction. Therefore, random ionospheric irregularities can make a significant (sometimes dominant) contribution to the residual range error.

Kim, B. C.; Tinin, M. V.

2007-03-01

152

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

153

Estimation of ionospheric electric fields, ionospheric currents, and field-aligned currents from ground magnetic records  

Microsoft Academic Search

An approximate method of separating the effects of ionospheric currents from those of field-aligned currents in ground magnetic perturbations observed in high latitudes is developed. The distribution of ionospheric electric fields can also be estimated. The procedure includes the following steps: (1) the calculation of the equivalent ionospheric current function on the basis of magnetic H and D component records

Y. Kamide; A. D. Richmond; S. Matsushita

1981-01-01

154

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

NASA Astrophysics Data System (ADS)

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

155

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

156

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

157

Ionospheric range-rate effects in satellite-to-satellite tracking  

NASA Technical Reports Server (NTRS)

Investigation of ionospheric range and range-rate corrections in satellite-to-satellite tracking were investigated. Major problems were cited and the magnitude of errors that have to be considered for communications between satellites and related experiments was defined. The results point to the need of using a sophisticated modeling approach incorporating daily solar data, and where possible actual ionospheric measurements as update information, as a simple median model cannot possibly account for the complex interaction of the many variables. The findings provide a basis from which the residual errors can be estimated after ionospheric modeling is incorporated in the reduction. Simulations were performed for satellites at various heights: Apollo, Geos, and Nimbus tracked by ATS-6; and in two different geometric configurations: coplanar and perpendicular orbits.

Lipofsky, J. R.; Bent, R. B.; Llewellyn, S. K.; Schmid, P. E.

1977-01-01

158

Ionospheric effects on GPS signals in the Arctic region using early GPS data from Thule, Greenland  

NASA Astrophysics Data System (ADS)

Thule, Greenland, is near the magnetic North Pole, and therefore any high-speed GPS data recorded there are of great potential import in specifying the severity of ionospheric effects on modern commercial navigation and ranging systems that must transit the polar latitudes. While there have now been many sets of GPS receiver data recorded at high latitudes, including GPS-IGS data routinely taken from Thule, Greenland, virtually all of these data have not been recorded at a high enough rate to measure the actual amplitude and phase scintillation effects. One notable exception is very early data taken from Thule, in the late 1980s and early 1990s, a period of high solar activity where data were taken from a L1/L2 dual-frequency receiver having the capability of tracking only one GPS satellite at a time, on both the L1 and the L2 channels with a data sampling rate of 20 Hz. The receiver phase-locked loop bandwidth was 16 Hz; thus, the sampling rate was not fast enough to insure that all the spectral components up to the receiver bandwidth were measured. We report on a new analysis of these "old" data illustrating that the rapid rates of change in total electron content (TEC) and high values of the amplitude scintillation index, S4, reported from these data are very relevant today with the advent of modern civilian aircraft routinely flying in the polar latitudes. For instance, we see a very high correlation between individual amplitude fades on the GPS L1 and L2 channels, indicating that users who suffer instantaneous signal loss on one frequency may not be able to use the secondary frequency to recover the GPS signal modulation, since it, too, will suffer an almost identical fade. Also, the occurrence of large, rapid changes in TEC, previously reported from these high-speed Thule GPS data, has been confirmed and may limit precise positioning in the polar cap latitudes.

El-Arini, M. B.; Secan, J.; Klobuchar, J. A.; Doherty, P. H.; Bishop, G.; Groves, K.

2009-02-01

159

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

160

Effects of field-aligned potential drops on region-2 currents, shielding, and the decoupling of magnetospheric and ionospheric flows  

NASA Astrophysics Data System (ADS)

It is technically difficult to include field-aligned potential drops in simulations of inner-magnetospheric electric fields, because the potential drops are most important in thin, intense sheets of Birkeland current, which are hard to resolve accurately on a large-scale grid. However, we have found a highly idealized situation that can be treated almost completely analytically, with the numerical work confined to solving a 1D differential equation. The calculation is set up as follows: (i) in the zero-order configuration, the inner edge of the plasma-sheet ions is circular, and the ions near the inner edge all gradient/curvature-drift west at the same angular rate; (ii) the convection potential is a small perturbation, in the sense that ExB drift near the inner edge is slow compared to gradient/curvature drift; (iii) the field-aligned potential drop is proportional to the density of field-aligned current; (iv) we look for steady-state solutions. The results indicate that the field-aligned potential drop has the following effects: (i) it decreases the total region-2 current but spreads it out in latitude; (ii) it reduces the efficiency with which the inner edge shields the inner magnetosphere from magnetospheric convection; (iii) it causes particles on the magnetospheric portions of field lines near the inner edge to ExB drift zonally at different rates than particles in the topside ionosphere. Results from these quasi-analytic calculations will be compared with compared with Rice Convection Model simulations of the same idealized physical situation.

Wolf, R.; Sazykin, S. Y.

2013-12-01

161

Electron densities and temperatures in the Venus ionosphere Effects of solar EUV, solar wind pressure and magnetic field  

NASA Technical Reports Server (NTRS)

The Venus ionosphere is influenced by variations in both solar EUV flux and solar wind conditions. On the dayside the location of the topside of the ionosphere, the ionopause, is controlled by solar wind dynamic pressure. Within the dayside ionosphere, however, electron density is affected mainly by solar EUV variations, and is relatively unaffected by solar wind variations and associated magnetic fields induced within the ionosphere. The existence of a substantial nightside ionosphere of Venus is thought to be due to the rapid nightward transport of dayside ionospheric plasma across the terminator. Typical solar wind conditions do not strongly affect this transport and consequently have little direct influence on nightside ionospheric conditions, except on occasions of extremely high solar wind dynamic pressure. However, both nightside electron density and temperature are affected by the presence of magnetic field, as in the case of ionospheric holes.

Elphic, R. C.; Russell, C. T.; Brace, L. H.

1985-01-01

162

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

163

The effect of the solar cycle on the maintenance of the nightside ionosphere of Venus  

Microsoft Academic Search

Pioneer Venus radio occultation measurements of the nightside ionosphere of Venus collected from 1979 to 1986 have made it possible to study its behavior at times of both solar maximum and solar minimum. Although some solar maximum measurements are similar in nature to those observed at solar minimum, which have an average peak density of about 7 à 10³ cm⁻³,

Arvydas J. Kliore; Janet G. Luhmann; Martina H. G. Zhang

1991-01-01

164

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

165

Comparison of Ionospheric and Thermospheric Effects During Two High Speed Stream Events  

NASA Astrophysics Data System (ADS)

We analyze two CIR-HSS events during ascending phase of the current solar cycle. The first event occurred on 8-12 May 2012 and was characterized by a large CIR and intense High Intensity Long Duration Continuous Auroral Activity (HILDCAA). Long-duration moderate geomagnetic storm (Dst ~ -50 nT) occurred during this event. The second event on 29 April - 4 May 2011 had a large CIR and extended HSS, but weaker geomagnetic activity. We focus on understanding differences and similarities of the magnetosphere-ionosphere-thermosphere coupling during these two events. We will use a suite of ground-based and satellite measurements to create a comprehensive picture of the events. Evolution of the polar cap convection pattern is analyzed based on SuperDARN data. DMSP/SSUSI far ultraviolet measurements provide information on airglow intensity and characteristics of the F-region of the dusktime ionosphere. The GPS total electron content (TEC) database and JPL's Global Ionospheric Maps (GIM) are used to study vertical TEC (VTEC) for different local times and latitude ranges. We discuss dynamics of VTEC above individual ground GPS sites with respect to local time and latitude ranges. We analyze the TIMED/SABER zonal flux of nitric oxide (NO) infrared cooling radiation and auroral heating throughout the events. Global dynamics of the column density ratio ?O/N2 is studied based on TIMED/GUVI measurements. Our results will advance understanding of the ionosphere-thermosphere response to external forcing and help future forecasting efforts.

Verkhoglyadova, O. P.; Tsurutani, B.; Mannucci, A. J.; Paxton, L.; Mlynczak, M. G.; Hunt, L. A.; Echer, E.

2013-12-01

166

Doppler shift observations of severe tropospheric weather effects in the ionosphere  

Microsoft Academic Search

Tropospheric severe weather events are regarded as an important natural source of infrasound. They influence the ionosphere through the upward propagating waves. Due to temperature profile in the lower atmosphere, the infrasonic waves are focused upwards and most of the radiated energy can propagate to the upper atmosphere. Detection of infrasonic waves requires sampling in short intervals or preferably continuous

T. Sindelarova; D. Buresova; J. Lastovicka; J. Chum

2007-01-01

167

Quiet time solar illumination effects on the fluxes and characteristic energies of ionospheric outflow  

Microsoft Academic Search

We report on the characteristic energy, intensity, and flow rate of escaping ionospheric ions as a function of solar illumination. The data presented here were acquired with the Toroidal Ion Mass-Angle Spectrograph (TIMAS) instrument on the Polar satellite at altitudes of 6000 to 9000 km, during solar minimum. To obtain uniform coverage under various solar illumination conditions, data were restricted

W. K. Peterson; H. L. Collin; O. W. Lennartsson; A. W. Yau

2006-01-01

168

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

169

Solar cycle dependence of nightside field-aligned currents: Effects of dayside ionospheric conductivity on the solar wind-magnetosphere-ionosphere coupling  

NASA Astrophysics Data System (ADS)

the present study we observationally address the role of ionospheric conductivity 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 conductivity. We statistically examine how, under fixed external conditions, the intensities of the R1 and R2 currents and their demarcation latitude depend on solar activity (F10.7). An emphasis is placed on nightside FACs in the dark hemisphere. The result shows that for fixed ranges of interplanetary electric field, the nightside FACs are more intense for higher solar activity irrespective of their polarities or local times. It is also found that the R1-R2 pair, therefore the auroral oval, moves equatorward as the solar activity increases. For both current intensity and latitude, the dependence on F10.7 is more sensitive at smaller F10.7 and it levels off 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 F10.7. It is expected from force balance 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 presumably affects the energy transport from the solar wind to the magnetosphere, although its details still remain to be understood. We conclude that the ionospheric conductivity plays an active role in the solar wind-magnetosphere-ionosphere coupling.

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

2014-01-01

170

Effects Of The Ionosphere On Ground-Based Detection Of The Global 21 CM Signal From The Cosmic Dawn And The Dark Ages  

E-print Network

Detection of global HI 21 cm signal from the Cosmic Dawn and the Epoch of Reionization is the key science driver for several ongoing ground-based and future ground/space based experiments. The crucial spectral features in the global 21cm signal (turning points) occurs at low radio frequencies < 100 MHz. In addition to the human-generated RFI (Radio Frequency Interference), Earth's ionosphere drastically corrupts low-frequency radio observations from the ground. In this paper, we examine the effects of time-varying ionospheric refraction, absorption and thermal emission at these low radio frequencies and their combined effect on any ground-based global 21cm experiment. It should be noted that this is the first study of the effect of a dynamic ionosphere on global 21cm experiments. Our results indicate that the spectral features in the global 21cm signal below 100 MHz cannot be detected from the ground under even "quiet" night-time ionospheric conditions. Any attempt to calibrate the ionospheric effect will ...

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

2014-01-01

171

Electron densities and temperatures in the Venus ionosphere. Effects of solar EUV, solar wind pressure and magnetic field  

Microsoft Academic Search

The Venus ionosphere is influenced by variations in both solar EUV flux and solar wind conditions. On the dayside the location of the topside of the ionosphere, the ionopause, is controlled by solar wind dynamic pressure. Within the dayside ionosphere, however, electron density is affected mainly by solar EUV variations, and is relatively unaffected by solar wind variations and associated

R. C. Elphic; C. T. Russell; L. H. Brace

1985-01-01

172

Electron densities and temperatures in the Venus ionosphere Effects of solar EUV, solar wind pressure and magnetic field  

Microsoft Academic Search

The Venus ionosphere is influenced by variations in both solar EUV flux and solar wind conditions. On the dayside the location of the topside of the ionosphere, the ionopause, is controlled by solar wind dynamic pressure. Within the dayside ionosphere, however, electron density is affected mainly by solar EUV variations, and is relatively unaffected by solar wind variations and associated

R. C. Elphic; C. T. Russell; L. H. Brace

1985-01-01

173

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

174

A new global ionospheric model  

NASA Technical Reports Server (NTRS)

A new global ionospheric model was successfully implemented. The daytime portion of this model provides one-way ionospheric range corrections that compare favorably with those derived from the Mariner Venus/Mercury S- and X-band dual frequency Doppler data. For elevation angles, gamma higher than 30 deg and solar zenith angle less than 80 deg, this model provides calibrations accurate to a few centimeters. The calibrations provided by the nighttime model are also very reasonable. It is interesting to note that the daytime ionospheric calibrations derived from the current calibration scheme, DIEN/TIEN, are fairly close to those given by the new global model, especially in the temporal variations and thus the Doppler effects. The comparison between the nighttime model and DIEN/TIEN was based on the one-way ionospheric range corrections for three passes near the Mariner 9 encounter with Mars in 1971. They can differ by over 30%.

Yip, K. W.; Vonroos, O. H.

1975-01-01

175

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

176

Electron gyroharmonic effects in ionization and electron acceleration during high-frequency pumping in the ionosphere.  

PubMed

Optical emissions and incoherent scatter radar data obtained during high-frequency electromagnetic pumping of the ionospheric plasma from the ground give data on electron energization in an energy range from 2 to 100 eV. Optical emissions at 4278 A from N2+ that require electrons with energies above the 18 eV ionization energy give the first images ever of pump-induced ionization of the thermosphere. The intensity at 4278 A is asymmetric around the ionospheric electron gyroharmonic, being stronger above the gyroresonance. This contrasts with emissions at 6300 A from O(1D) and of electron temperature enhancements, which have minima at the gyroharmonic but have no apparent asymmetry. This direct evidence of pump-induced ionization contradicts previous indirect evidence, which indicated that ionization is most efficiently produced when the pump frequency was below the gyroharmonic. PMID:17155639

Gustavsson, B; Leyser, T B; Kosch, M; Rietveld, M T; Steen, A; Brändström, B U E; Aso, T

2006-11-10

177

Assessment and Mitigation of Ionospheric Residual Errors in GPS Radio Occultation Retrievals  

NASA Astrophysics Data System (ADS)

Atmospheric soundings derived from Global Positioning System radio occultations (GPSRO) have the potential to be global climate benchmark observations of significant value to the global climate observing system. Past studies comparing refractivity and temperature retrievals from different GPSRO satellite platforms have demonstrated the very high precision of the measurements. However, such studies do not provide an upper bound on any systematic errors that might exist in the retrievals. One possibly significant error source for stratospheric retrievals comes from the Earth’s ionosphere. To remove the ionospheric contribution to the GPSRO measurements, a linear combination of the bending angles from the two GPS frequencies is typically used. However, due to raypath separation from the two GPS signals as well as higher-order frequency dependency of the refractive index, not all the ionospheric effects will be eliminated with this procedure. Uncorrected ionospheric diurnal- and solar-cycle variability could have an undesirable impact on the interpretation of stratospheric trends inferred from GPSRO. In this talk, we will provide an assessment of the ionospheric residual errors using three-dimensional raytracing through the USC/JPL Global Assimilative Ionosphere Model (GAIM) and discuss a new approach towards mitigating the ionospheric residual errors.

Ao, C. O.; Mannucci, A.; Pi, X.; Iijima, B. A.

2009-12-01

178

A study of the ionogram derived effective scale height around the ionospheric hmF2  

Microsoft Academic Search

The diurnal, seasonal, and solar activity variations of the ionogram derived scale height around the ionospheric F-layer peak (Hm) are statistically analyzed at Wuhan (114.4° E, 30.6° N) and the yearly variations of Hm are also investigated for Wuhan and 12 other stations where Hm data are available. Hm, as a measure of the slope of the topside electron number

L. Liu; W. Wan; B. Ning

2006-01-01

179

The effect of ˜27 day solar rotation on ionospheric F2 region peak densities (NmF2)  

NASA Astrophysics Data System (ADS)

Ionospheric F2 region peak electron densities (NmF2) observed from 11 ionosonde stations in the East Asian-Australian sector from 1969 to 1986 have been used to investigate the effect of ˜27 day solar rotation on the ionosphere. These stations were located from the magnetically equatorial regions to the middle latitudes in both hemispheres. We found that, averaged over all stations and for 18 years, the normalized standard deviation of the midday ˜27 day variations of NmF2 was 8% and that of the midnight variations was 10%. We applied different data analysis methods, including Fourier transform, band-pass filter, and multiple linear regression analysis, to determine quantitatively the sources of the observed ˜27 day variations of NmF2 and their relative contributions to these variations. Our results show that the ˜27 day variations in solar radiation and geomagnetic activity, caused by solar rotation, are the main drivers of the ionospheric ˜27 day variations. They accounted for more than 85% of the variations seen in the NmF2 ˜27 day variation, and their contributions became about 95% at higher latitudes. At geomagnetically low latitudes, the contribution of the ˜27 day variation in solar EUV radiation was greater than that of the ˜27 day variation in geomagnetic activity. However, the contribution from geomagnetic activity became more significant and was even larger than the contribution of solar radiation at higher latitudes, especially at midnight. At all latitudes the correlation between the ˜27 day variations of NmF2 and solar radiation was evidently positive, whereas that between NmF2 and geomagnetic activity was positive at geomagnetically low latitudes and became negative at higher middle latitudes. We did not found large seasonal or solar cycle changes in the ˜27 day variations of NmF2. These variations, however, did show significant differences between the two hemispheres.

Ma, Ruiping; Xu, Jiyao; Wang, Wenbin; Lei, Jiuhou

2012-03-01

180

Jovian magnetosphere-ionosphere current system characterized by diurnal variation of ionospheric conductance  

NASA Astrophysics Data System (ADS)

We developed a new numerical model of the Jovian magnetosphere-ionosphere coupling current system in order to investigate the effects of diurnal variation of ionospheric conductance. The conductance is determined by ion chemical processes that include the generation of hydrogen and hydrocarbon ions by solar EUV radiation and auroral electrons precipitation. The model solves the torque equations for magnetospheric plasma accelerated by the radial currents flowing along the magnetospheric equator. The conductance and magnetospheric plasma then change the field-aligned currents (FACs) and the intensity of the electric field projected onto the ionosphere. Because of the positive feedback of the ionospheric conductance on the FAC, the FAC is the maximum on the dayside and minimum just before sunrise. The power transferred from the planetary rotation is mainly consumed in the upper atmosphere on the dayside, while it is used for magnetospheric plasma acceleration in other local time (LT) sectors. Further, our simulations show that the magnetospheric plasma density and mass flux affect the temporal variation in the peak FAC density. The enhancement of the solar EUV flux by a factor of 2.4 increases the FAC density by 30%. The maximum density of the FAC is determined not only by the relationship between the precipitating electron flux and ionospheric conductance, but also by the system inertia, i.e., the inertia of the magnetospheric plasma. A theoretical analysis and numerical simulations reveal that the FAC density is in proportion to the planetary angular velocity on the dayside and to the square of the planetary angular velocity on the nightside. When the radial current at the outer boundary is fixed at values above 30 MA, as assumed in previous model studies, the peak FAC density determined at latitude 73°-74° is larger than the diurnal variable component. This result suggests large effects of this assumed radial current at the outer boundary on the system.

Tao, Chihiro; Fujiwara, Hitoshi; Kasaba, Yasumasa

2010-02-01

181

Ionospheric bending correction for GNSS radio occultation signals  

NASA Astrophysics Data System (ADS)

Ionospheric propagation effects on Global Navigation Satellite Systems (GNSS) signals are the most pronounced during radio occultation due to long ionospheric travel paths of the received signal on low Earth orbiting satellites. Inhomogeneous plasma distribution and anisotropy cause higher-order nonlinear refraction effects on GNSS signals which cannot be fully removed through a linear combination of dual-frequency observables. In this paper, higher-order ionospheric effects due to straight line of sight (LOS) propagation assumption such as the excess path length of the signal in addition to the LOS path and the total electron content difference between the curved path and the LOS path have been investigated for selected GPS-CHAMP occultation events. Based on simulation studies we have derived correction formulas for computing raypath bending effects as functions of signal frequency, tangential height of the raypath, ionospheric parameters such as the maximum ionization and total electron content. If these parameters are known, the proposed correction method is able to correct on an average about 65-80% bending errors of GNSS occultation signals.

Hoque, M. M.; Jakowski, N.

2011-12-01

182

Effects of a solar wind pressure pulse in the magnetosphere and in the ionosphere  

NASA Astrophysics Data System (ADS)

On 17 July 2005, an earthward bound north-south oriented magnetic cloud and its sheath were observed by the Advanced Composition Explorer (ACE), the Solar and Heliospheric Observatory (SoHO), and the Wind solar wind monitors. A steplike increase of the solar wind dynamic pressure was related to the leading edge of the sheath. A timing analysis between the three spacecraft revealed that this front was not aligned with GSE y axis, but tilted by an angle of about 55° towards the x axis. Hence, the first contact with the magnetosphere occured on the dawnside rather than at the subsolar point. Fortunately, Cluster, Double Star 1, and Geotail happened to be distributed close to the magnetopause in this region, which made it possible to closely monitor the motion of the magnetopause. When the pressure pulse impacted the magnetosphere, the magnetopause was perceived first to move inward and then immediatelly correct the overshoot by slightly expanding again such that it ended up between the Cluster constellation with Double Star 1 inside the magnetosphere and Geotail in the magnetosheath. In the ionosphere, the AE index showed a relatively weak enhancement with a peak of less than 200 nT. This enhancement lasted for about 10 minutes and coincided with the inward and subsequent outward motion of the magnetopause observed by the magnetospheric spacecraft. The ground-based International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometer network was also located on the dawn side during the arrival of the pressure pulse. The 1-D equivalent currents showed a peak of eastward current in the region covered by IMAGE, where the westward electrojet generally dominates at that time. After 10 minutes, the region of weakening eastward current was divided in two by the recovering westward electrojet. The 2-D equivalent currents further revealed that while the region of eastward current expanded from the east, the recovery of the westward electrojet began from the western edge of IMAGE field-of-view. We suggest that these observations could be interpreted as a temporary and local reversal of the direction of the plasma sheet convection due to the compression of the magnetosphere.

Juusola, Liisa; Andreeova, Katerina; Palmroth, Minna; Amm, Olaf

2010-05-01

183

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

184

Solar System Ionospheres  

NASA Astrophysics Data System (ADS)

This article reviews our understanding of the ionospheres in the solar system. It provides some basic information on the sources and sinks of the ionospheric plasma, its dynamics, the energetics and the coupling to the neutral atmosphere. Ionospheres in the solar system are reviewed and comparative ionospheric topics are discussed.

Witasse, O.; Cravens, T.; Mendillo, M.; Moses, J.; Kliore, A.; Nagy, A. F.; Breus, T.

185

Solar System Ionospheres  

Microsoft Academic Search

This article reviews our understanding of the ionospheres in the solar system. It provides some basic information on the sources\\u000a and sinks of the ionospheric plasma, its dynamics, the energetics and the coupling to the neutral atmosphere. Ionospheres\\u000a in the solar system are reviewed and comparative ionospheric topics are discussed.

O. Witasse; T. Cravens; M. Mendillo; J. Moses; A. Kliore; A. F. Nagy; T. Breus

2008-01-01

186

Solar System Ionospheres  

Microsoft Academic Search

This article reviews our understanding of the ionospheres in the solar system. It provides some basic information on the sources\\u000a and sinks of the ionospheric plasma, its dynamics, the energetics and the coupling to the neutral atmosphere. Ionospheres\\u000a in the solar system are reviewed and comparative ionospheric topics are discussed.

O. Witasse; T. Cravens; M. Mendillo; J. Moses; A. Kliore; A. F. Nagy; T. Breus

187

Solar System Ionospheres  

NASA Astrophysics Data System (ADS)

This article reviews our understanding of the ionospheres in the solar system. It provides some basic information on the sources and sinks of the ionospheric plasma, its dynamics, the energetics and the coupling to the neutral atmosphere. Ionospheres in the solar system are reviewed and comparative ionospheric topics are discussed.

Witasse, O.; Cravens, T.; Mendillo, M.; Moses, J.; Kliore, A.; Nagy, A. F.; Breus, T.

2008-08-01

188

The ionosphere and the Latin America VLF Network Mexico (LAVNet-Mex) station  

NASA Astrophysics Data System (ADS)

In order to detect and study the ionospheric response to solar flares (transient high energy solar radiation), we have constructed a radio receiver station at Mexico City, which is part of the “Latin American Very low frequency Network” (LAVNet-Mex). This station extends to the northern hemisphere the so called “South American VLF Network”. LAVNet is able to detect small changes in the amplitude and phase of VLF electromagnetic waves (generated by strong transmitters located all around the world) which are affected by changes of the lowest layer of the ionosphere, where these waves are “reflected”. In this way, LAVNet is an excellent tool to study the dynamics of the lower ionospheric layers. In this work we present a technical description and show the capabilities of the new LAVNet-Mex station. Moreover, as an example of its performance, we present the analysis of the ionospheric effects of two solar flares detected on October 16, 2010 and June 7, 2011.

Borgazzi, A.; Lara, A.; Paz, G.; Raulin, J. P.

2014-08-01

189

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

190

Ionospheric effects of earthquakes in Japan in March 2011 obtained from observations of lightning electromagnetic radio signals  

NASA Astrophysics Data System (ADS)

Manifestations of disturbances in the lower ionosphere caused by a complex series of earthquakes (the strong earthquakes with M = 7.3 and M = 9 - known as M9 Tohoku EQ - and the subsequent aftershocks) that occurred near the Japanese island of Honshu have been considered with the use of monitoring measurements of the amplitude of lightning electromagnetic signals (atmospherics) received at Yakutsk. Some data of one-point lightning location systems have been compared with the data of the WWLLN network. The analysis of hourly values variation of the atmospheric amplitude passing over the earthquake epicenters shows that during the initial period (the strong earthquakes on 9 March and 11 March) a typical pattern of variations was observed. It was manifested in the increased amplitude after both earthquakes. There were also possible precursors in the form of the increase in amplitude 12-14 days before the events. Though the focuses of these earthquakes were very close to each other, the registration of both precursors may indicate that both of the lithospheric processes developed to a certain extent independently. During all the days of the atmospheric amplitude enhancement the quasi-periodic variation trains were recorded. Together with the delay of earthquake effects relative to the time of the events, they may testify in favor of transferring the energy of lithospheric processes into the lower ionosphere by means of atmospheric gravity waves.

Mullayarov, V. A.; Argunov, V. V.; Abzaletdinova, L. M.; Kozlov, V. I.

2012-10-01

191

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

192

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

193

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

194

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

195

GEOPHYSICAL RESEARCH LETTERS, VOL. 28, NO. 11, PAGES 2149-2152, JUNE 1, 2001 Effect of solar soft X-rays on the lower ionosphere  

E-print Network

GEOPHYSICAL RESEARCH LETTERS, VOL. 28, NO. 11, PAGES 2149-2152, JUNE 1, 2001 Effect of solar soft X-rays on the lower ionosphere Stanley C. Solomon High Altitude Observatory, National Center for Atmospheric Research by the American Geophysical Union. Paper number 2001GL012866. 0094-8276/01/2001GL012866$05.00 flux below 25 nm

Bailey, Scott

196

Effects of lightning and sprites on the ionospheric potential, and threshold effects on sprite initiation, obtained using an analog model of the global atmospheric electric circuit  

NASA Astrophysics Data System (ADS)

A quantitative model of the global atmospheric electric circuit has been constructed using the PSpice electrical engineering software package. Currents (˜1 kA) above thunderstorms and electrified rain/shower clouds raise the potential of the ionosphere (presumed to be an equipotential surface at 80 km altitude) to ˜250 kV with respect to the Earth's surface. The circuit is completed by currents flowing down through the fair-weather atmosphere in the land/sea surface and up to the cloud systems. Using a model for the atmospheric conductivity profile, the effects of both negative and positive cloud-to-ground (CG) lightning discharges on the ionospheric potential have been estimated. A large positive CG discharge creates an electric field that exceeds the breakdown field from the ionosphere down to ˜74 km, thereby forming a halo, a column sprite, and some milliseconds later, from ˜67 km down to ˜55 km at ˜60 ms after the discharge, a "carrot" sprite. Estimates are made of the return stroke current and the thundercloud charge moment change of a +CG discharge required to exceed the threshold breakdown field, or the threshold field for creating and sustaining negative or positive streamers. The values for breakdown at 80 km altitude are 35 kA and 350 C.km, (Coulomb.kilometers), respectively, and those at 70 km altitude are 45 kA and 360 C.km, respectively. The different temporal and spatial developments of the mesospheric electric field distinguishing between column and carrot sprites agree with the latest deductions from recent observations. The current flowing in the highly conducting sprite reduces the ionospheric potential by ˜1 V.

Rycroft, M. J.; Odzimek, A.

2010-06-01

197

The effects of lightning and sprites on the ionospheric potential, and threshold effects on sprite initiation, obtained using a PSpice model  

NASA Astrophysics Data System (ADS)

A quantitative model of the global atmospheric electric circuit has been constructed using the PSpice electrical engineering software package. Currents (~ 1 kA) above thunderstorms and electrified rain/shower clouds raise the potential of the ionosphere, which is presumed to be an equipotential surface at 80 km altitude, to ~ 250 kV with respect to the Earth's surface. The circuit is completed by currents flowing down through the fair weather atmosphere, in the land/sea surface and up to the cloud systems. Using a model for the atmospheric conductivity profile (Rycroft et al., JASTP, 2007), the effects of both negative and positive cloud-to-ground (CG) lightning discharges ion the ionospheric potential have been estimated. A large positive CG discharge creates an electric field which exceeds the breakdown field from the ionosphere down to ~ 74 km, so forming a halo and a column sprite, and, some ms later, from ~ 67 km down to ~ 55 km at ~ 60 ms after the discharge, thereby forming a "carrot" sprite. Estimates are made of the return stroke current and the thundercloud charge moment change (CMC) for a +CG discharge required to exceed the threshold breakdown field, or the threshold field for creating and sustaining negative or positive streamers. The values for breakdown at 80 km altitude are 35 kA and 350 C.km, respectively, and 45 kA and 360 C.km at 70 km altitude. The different temporal and spatial developments of the mesospheric electric field distinguishing between column and carrot sprites agree with the latest deductions from from recent observations. A current flowing in the highly conducting sprite reduces the ionospheric potential by ~ 1 V.

Rycroft, Michael J.; Odzimek, Anna

2010-05-01

198

Effects of lightning and sprites on the ionospheric potential, and threshold effects on sprite initiation, obtained using an analog model of the global atmospheric electric circuit  

NASA Astrophysics Data System (ADS)

A quantitative model of the global atmospheric electric circuit has been constructed using the PSpice electrical engineering software package. Currents (˜1 kA) above thunderstorms and electrified rain/shower clouds raise the potential of the ionosphere (presumed to be an equipotential surface at 80 km altitude) to ˜250 kV with respect to the Earth's surface. The circuit is completed by currents flowing down through the fair-weather atmosphere in the land/sea surface and up to the cloud systems. Using a model for the atmospheric conductivity profile, the effects of both negative and positive cloud-to-ground (CG) lightning discharges on the ionospheric potential have been estimated. A large positive CG discharge creates an electric field that exceeds the breakdown field from the ionosphere down to ˜74 km, thereby forming a halo, a column sprite, and some milliseconds later, from ˜67 km down to ˜55 km at ˜60 ms after the discharge, a “carrot” sprite. Estimates are made of the return stroke current and the thundercloud charge moment change of a +CG discharge required to exceed the threshold breakdown field, or the threshold field for creating and sustaining negative or positive streamers. The values for breakdown at 80 km altitude are 35 kA and 350 C.km, (Coulomb.kilometers), respectively, and those at 70 km altitude are 45 kA and 360 C.km, respectively. The different temporal and spatial developments of the mesospheric electric field distinguishing between column and carrot sprites agree with the latest deductions from recent observations. The current flowing in the highly conducting sprite reduces the ionospheric potential by ˜1 V.

Rycroft, M. J.; Odzimek, A.

2010-06-01

199

Seismo-ionospheric effects associated with 'Chelyabinsk' meteorite during the first 25 minutes after its fall  

E-print Network

This paper presents the properties of ionospheric irregularities elongated with Earth magnetic field during the first 25 minutes after the fall of the meteorite 'Chelyabinsk' experimentally observed with EKB radar of Russian segment of the SuperDARN. It is shown that 40 minutes before meteor fall the EKB radar started to observe powerful scattering from irregularities elongated with the Earth magnetic field in the F-layer. Scattering was observed for 80 minutes and stopped 40 minutes after the meteorite fall. During 9-15 minutes after the meteorite fall at ranges 400-1200 km from the explosion site a changes were observed in the spectral and amplitude characteristics of the scattered signal. This features were the sharp increase in the Doppler frequency shift of the scattered signal corresponding to the Doppler velocities about 600 m/s and the sharp increase of the scattered signal amplitude. This allows us to conclude that we detected the growth of small-scale ionospheric irregularities elongated with the Ea...

Berngardt, Oleg I

2014-01-01

200

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

201

The Ptolemaic Approach to Ionospheric Electrodynamics  

NASA Astrophysics Data System (ADS)

The conventional treatment of ionospheric electrodynamics (as expounded in standard textbooks and tutorial publications) consists of a set of equations, plus verbal descriptions of the physical processes supposedly represented by the equations. Key assumptions underlying the equations are: electric field equal to the gradient of a potential, electric current driven by an Ohm's law (with both electric-field and neutral-wind terms), continuity of current then giving a second-order elliptic differential equation for calculating the potential; as a separate assumption, ion and electron bulk flows are determined by ExB drifts plus collision effects. The verbal descriptions are in several respects inconsistent with the equations; furthermore, both the descriptions and the equations are not compatible with the more rigorous physical understanding derived from the complete plasma and Maxwell's equations. The conventional ionospheric equations are applicable under restricted conditions, corresponding to a quasi-steady-state equilibrium limit, and are thus intrinsically incapable of answering questions about causal relations or dynamic developments. Within their limited range of applicability, however, the equations are in most cases adequate to explain the observations, despite the deficient treatment of plasma physics. (A historical precedent that comes to mind is that of astronomical theory at the time of Copernicus and for some decades afterwards, when the Ptolemaic scheme could explain the observations at least as well if not better than the Copernican. Some of the verbal descriptions in conventional ionospheric electrodynamics might be considered Ptolemaic also in the more literal sense of being formulated exclusively in terms of a fixed Earth.) I review the principal differences between the two approaches, point out some questions where the conventional ionospheric theory does not provide unambiguous answers even within its range of validity (e.g., topside and bottomside boundary conditions on electrodynamics), and illustrate with some simple examples of how a neutral-wind dynamo really develops.

Vasyliunas, V. M.

2010-12-01

202

Predictions and observations of HF radio propagation in the northerly ionosphere: The effect of the solar flares and a weak CME in early January 2014.  

NASA Astrophysics Data System (ADS)

We have previously reported on a significant new multi-national project to provide improved predictions and forecasts of HF radio propagation for commercial aircraft operating on trans-polar routes. In these regions, there are limited or no VHF air-traffic control facilities and geostationary satellites are below the horizon. Therefore HF radio remains important in maintaining communications with the aircraft at all times. Space weather disturbances can have a range of effects on the ionosphere and hence HF radio propagation - particularly in the polar cap. While severe space weather effects can lead to a total loss of communications (i.e. radio blackout), less intense events can still cause significant disruption. In this paper we will present the effect of a series of M and X class solar flares and a relatively weak CME on HF radio performance from 6 to 13 January 2014. This is an interesting interval from the point of view of HF radio propagation because while the solar effects on the ionosphere are significant, except for an interval of approximately 12 hours duration, they are not so intense as to produce a complete radio blackout on all paths. Observations of the signal-to-noise ratio, direction of arrival, and time of flight of HF radio signals on six paths (one entirely within the polar cap, three trans-auroral, and two sub-auroral) will be presented together with riometer measurements of the ionospheric absorption. Global maps of D-region absorption (D-region absorption prediction, DRAP) inferred from satellite measurements of the solar wind parameters will be compared with the HF and riometer observations. In addition, a ray-tracing model using a realistic background ionosphere and including localised features found in the ionospheric polar cap (e.g. polar patches and arcs) will be used to model the expected and observed HF radio propagation characteristics.

Hallam, Jonathan; Stocker, Alan J.; Warrington, Mike; Siddle, Dave; Zaalov, Nikolay; Honary, Farideh; Rogers, Neil; Boteler, David; Danskin, Donald

2014-05-01

203

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

204

The effect of the solar cycle on the maintenance of the nightside ionosphere of Venus  

NASA Technical Reports Server (NTRS)

The behavior of the Venus nightside ionosphere at solar maximum and solar minimum is discussed based on Pioneer Venus radio occultation measurements. Although some solar maximum measurements are similar to those observed at minimum, which have an average peak density of about 7000/cu cm, others show much higher peak densities, reaching values of about 40,000/cu cm. These elevated peak densities also occur at higher altitudes. The integrated electron column densities for these measurements indicate the presence of substantial ionization above the main peak. The magnitudes of both the peak density and the integrated content above the peak are anticorrelated with the solar wind dynamic pressure, indicating that these enhancements during solar maximum are due to transterminator transport of O(+) ions from the dayside. The resulting ionization peak can be many times the concentration produced by energetic electron fluxes impacting the neutral atmosphere on the nightside.

Kliore, Arvydas J.; Luhmann, Janet G.; Zhang, Martina H. G.

1991-01-01

205

Effects of magnetic anomalies discovered at Mars on the structure of the Martian ionosphere and solar wind interaction as follows from radio occultation experiments  

NASA Astrophysics Data System (ADS)

The slopes of the electron density profiles obtained by radio occultation experiments at Mars revealed different variations with solar zenith angle in comparison with behavior of the electron density profiles in the magnetic field free ionosphere of Venus. The results obtained by the Mars-Global-Surveyor (MGS) spacecraft show the existence of highly variable and very localized magnetic fields of crustal origin at Mars. Addressing the difference between the ionosphere at Venus and Mars, the scale heights of electron density profiles obtained by radio occultation methods onboard Mariner 9 and Viking 1 are analyzed at altitudes higher than the topside boundary of the photoequilibrium region in the magnetic field-free ionosphere. The local increase of the mean scale height in the altitude region 180-250 km is assumed to be either an effect of a nonhorizontal magnetic field associated with the magnetic anomalies or diffusive equilibrium in the magnetic field free ionosphere. The areas where the scale height of electron density profile is increased in comparison with average one have been selected. The angle between the magnetic field measured by MGS MAG/ER at altitudes 120-250 km and local zenith direction is investigated throughout these selected areas.

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

2000-07-01

206

The Ionospheres of Europa, Ganymede, and Callisto  

NASA Astrophysics Data System (ADS)

The U.S. Galileo spacecraft, which has been in orbit around Jupiter since December, 1995, has provided opportunities to collect s-band radio occultation data using the 70 meter antennas of the NASA/JPL Deep Space Net(DSN) at Goldstone, California, Madrid, Spain, and Canberra, Australia. To date, four occultations and one near-occultation by Europa (J2) have been observed. They have shown the presence of electron plasma having a density near the surface of 10,000 to 20,000 cm-3 (Kliore, et al., Science, 277, 1997). If the underlying neutral atmosphere is assumed to consist of H2O or O2, the maximum neutral density near the surface can be inferred to be about 108 cm-3. Ganymede (J3) has also been observed five times by Galileo radio occultation. The results are almost entirely negative, with only one measurement out of ten yielding a possible observation of an ionosphere having a maximum density of about 5,000 cm-3 at an altitude of about 16 km. The failure to observe an ionosphere on Ganymede is at first glance surprising, in view of the detection of oxygen and hydrogen above its surface (c.f., Hall, et al., Astrophys. J., 499, 1998; Barth, et al., GRL, 24, 1997), and it was thought to be due to the shielding effect of Ganymede's magnetic field upon the impinging particles from Jupiter's magnetosphere. Callisto has occulted Galileo four times, and these observations have produced some interesting results. Of the eight individual measurements , two are negative, and six are positive. Two of those six, show unmistakable classic ionospheric layers, having peak electron densities of 15,000 to 20,000 cm-3 . A closer examination of all of these results has revealed a plausible reason for why some observations yield positive results , and some do not. It appears that in order for an ionosphere to be observed, the trailing hemisphere of the satellite must be in sunlight. In that way, the atmosphere created by sputtering effects of the Jovian magnetosphere can be ionized by solar EUV to produce an observable ionosphere. The research described in this paper has been conducted at the Jet Propulsion Laboratory and the University of Michigan with support from NASA contracts and grants

Kliore, A. J.; Anabtawi, A.; Nagy, A. F.

2001-12-01

207

Ray trace calculation of ionospheric propagation at lower frequencies  

NASA Astrophysics Data System (ADS)

The Raytrace/Ionospheric Conductivity and Electron Density-Bent-Gallagher model has been revised to make it applicable to ionospheric propagation at low radio frequencies (0.5-5.0 MHz), where the ionosphere and magnetic anisotropy drastically alter propagation paths and provide a severe test of propagation model algorithms. The necessary revisions are discussed, and the model is applied to the problem of ionospheric penetration from a source below the ionosphere to a receiver above the ionosphere. It is necessary to include the electron collision frequency in the Appleton-Hartree index of refraction in order to permit ionospheric penetration for radio frequencies below the maximum plasma frequency (e.g., whistler modes). The associated reformulation of the ray trace equations for a complex index of refraction is straightforward. Difficulties with numerical methods are cited for the lowest frequencies, and future improvements are indicated.

Reilly, Michael H.

2006-10-01

208

Magnetosphere-ionosphere coupling during CME events  

NASA Astrophysics Data System (ADS)

A series of CMEs during 07-12 November 2004 produced a rare super double geomagnetic storm with three positive initial phases. The response of the magnetosphere and ionosphere to the CMEs and geomagnetic storms is studied using Cluster and ground-based (ESR, EISCAT and Jicamarca radars and magnetometer) observations and modelling. The observations provide a good example of the magnetosphere-ionosphere coupling through prompt penetration electric field (PPEF). The strongest PPEF ever recorded (on 09 November 2004) appears to be generated in the magnetosphere by vxB effect, which is mapped to the high latitude ionosphere along the geomagnetic field lines and promptly penetrated to low latitudes. The high latitude ionosphere over the ESR radar responded directly to the CMEs mainly through particle precipitation that resulted in strong ionisation and thermal expansion of the ionosphere. The low-mid latitude ionosphere responded after the onset of the main phase of the geomagnetic storm. Modelling studies indicate that the PPEF in the presence of an equatorward neutral wind can produce positive ionospheric storms at low-mid latitudes though PPEF on its own is unlikely to produce positive ionospheric storms.

Nanan, Balan; Vijaya Lekshmi, D.; Alleyne, Hugo

209

Verification of ionospheric sensors  

Microsoft Academic Search

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

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

2001-01-01

210

Effects of a strong ICME on the Martian ionosphere as detected by Mars Express and Mars Odyssey  

NASA Astrophysics Data System (ADS)

We present evidence of a substantial ionospheric response to a strong interplanetary coronal mass ejection (ICME) detected by the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) on board the Mars Express (MEX) spacecraft. A powerful ICME impacted the Martian ionosphere beginning on 5 June 2011, peaking on 6 June, and trailing off over about a week. This event caused a strong response in the charged particle detector of the High-Energy Neutron Detector (HEND) on board the Odyssey spacecraft. The ion mass spectrometer of the Analyzer of Space Plasmas and Energetic Atoms instrument on MEX detected an increase in background counts, simultaneous with the increase seen by HEND, due to the flux of solar energetic particles (SEPs) associated with the ICME. Local densities and magnetic field strengths measured by MARSIS and enhancements of 100 eV electrons denote the passing of an intense space weather event. Local density and magnetosheath electron measurements and remote soundings show compression of ionospheric plasma to lower altitudes due to increased solar wind dynamic pressure. MARSIS topside sounding of the ionosphere indicates that it is extended well beyond the terminator, to about 116° solar zenith angle, in a highly disturbed state. This extension may be due to increased ionization due to SEPs and magnetosheath electrons or to plasma transport across the terminator. The surface reflection from both ionospheric sounding and subsurface modes of the MARSIS radar was attenuated, indicating increased electron content in the Mars ionosphere at low altitudes, where the atmosphere is dense.

Morgan, D. D.; Diéval, C.; Gurnett, D. A.; Duru, F.; Dubinin, E. M.; Fränz, M.; Andrews, D. J.; Opgenoorth, H. J.; Ulu?en, D.; Mitrofanov, I.; Plaut, J. J.

2014-07-01

211

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

212

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

213

Effects of a solar wind dynamic pressure increase in the magnetosphere and in the ionosphere  

NASA Astrophysics Data System (ADS)

On 17 July 2005, an earthward bound north-south oriented magnetic cloud and its sheath were observed by the ACE, SoHO, and Wind solar wind monitors. A steplike increase of the solar wind dynamic pressure during northward interplanetary magnetic field conditions was related to the leading edge of the sheath. A timing analysis between the three spacecraft revealed that this front was not aligned with the GSE y-axis, but had a normal (-0.58,0.82,0). Hence, the first contact with the magnetosphere occurred on the dawnside rather than at the subsolar point. Fortunately, Cluster, Double Star 1, and Geotail happened to be distributed close to the magnetopause in this region, which made it possible to closely monitor the motion of the magnetopause. After the pressure front had impacted the magnetosphere, the magnetopause was perceived first to move inward and then immediately to correct the overshoot by slightly expanding again such that it ended up between the Cluster constellation with Double Star 1 inside the magnetosphere and Geotail in the magnetosheath. Coinciding with the inward and subsequent outward motion, the ground-based magnetic field at low latitudes was observed to first strengthen and then weaken. As the magnetopause position stabilised, so did the ground-based magnetic field intensity, settling at a level slightly higher than before the pressure increase. Altogether the magnetopause was moving for about 15 min after its first contact with the front. The high latitude ionospheric signature consisted of two parts: a shorter (few minutes) and less intense preliminary part comprised a decrease of AL and a negative variation of PC. A longer (about ten minutes) and more intense main part of the signature comprised an increase of AU and a positive variation of PC. Measurements from several ground-based magnetometer networks (210 MM CPMN, CANMOS, CARISMA, GIMA, IMAGE, MACCS, SuperMAG, THEMIS, TGO) were used to obtain information on the ionospheric E×B drift. Before the pressure increase, a configuration typical for the prevailing northward IMF conditions was observed at high latitudes. The preliminary signature coincided with a pair of reverse convection vortices, whereas during the main signature, mainly westward convection was observed at all local time sectors. Afterwards, the configuration preceding the pressure increase was recovered, but with slightly enhanced convection. Based on the timing analysis, the existence of the preliminary signature coincided with the passage of the oblique pressure front, whereas during the main signature the front was already well past Earth. The main signature existed during the time the magnetopause was observed to move. As the position stabilised, also the signature disappeared.

Juusola, L.; Andréeová, K.; Amm, O.; Kauristie, K.; Milan, S. E.; Palmroth, M.; Partamies, N.

2010-10-01

214

The effect of the solar cycle on the maintenance of the nightside ionosphere of Venus  

SciTech Connect

Pioneer Venus radio occultation measurements of the nightside ionosphere of Venus collected from 1979 to 1986 have made it possible to study its behavior at times of both solar maximum and solar minimum. Although some solar maximum measurements are similar in nature to those observed at solar minimum, which have an average peak density of about 7 {times} 10{sup 3} cm{sup {minus}3}, others show much higher peak densities, reaching values of about 4 {times} 10{sup 4} cm{sup {minus}3}. These elevated peak densities also occur at higher altitudes. The integrated electron column densities for these measurements are also much higher, indicating the presence of substantial ionization above the main peak. The magnitudes of both the peak density and the integrated content above the peak are anticorrelated with the solar wind dynamic pressure, leading to the interpretation that these enhancements during solar maximum are due to transterminator transport of O{sup +} ions from the dayside when the solar wind dynamic pressure is low enough to permit a sufficiently high dayside ionopause. The resulting ionization peak can be many times the concentration produced by energetic electron fluxes impacting the neutral atmosphere on the nightside, which apparently form the remaining source of the nightside peak at such times during solar maximum, when transterminator flow is cut off by high solar wind pressure depressing the dayside ionopause, and during solar minimum, when the ionopause is always depressed.

Kliore, A.J. (California Inst. of Tech., Pasadena (USA)); Luhmann, J.G. (Univ. of California, Los Angeles (USA)); Zhang, M.H.G. (Austrian Academy of Sciences, Graz (Austria))

1991-07-01

215

Ionospheric specification from GPS data and the RIBG ionospheric propagation model  

Microsoft Academic Search

Global Positioning System (GPS) data for phase delay differential between L1 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),

Michael H. Reilly; Malkiat Singh

1997-01-01

216

Ionospheric irregularities and storm-induced equatorial and high-latitude effects at the anomaly crest region  

NASA Astrophysics Data System (ADS)

IEC information received through VHF RB measurements has been analyzed over the anomaly crest region of Guwahati (92° E, 26° N, 15° N geo.mag) along with a few low/low-mid latitude observations for understanding the roles of influx of plasma to anomaly crest regions, from equatorward and poleward processes during geomagnetically disturbed situations. The conditions leading to inflow of plasma to equatorial anomaly crest region or inhibition of such processes have been described in the paper through systematic analysis of disturbed day (free from sudden commencements) ionospheric electron content (IEC) variations at different temporal situtions. The storm-induced effects in relation to the development of the above conditions have also been examined for moderate and moderately severe isolated storm cases. Finally the paper deals with a few severe storms. The storm-triggered IEC features indicate inhibition or suppression of plasma dumping process at anomaly crests, through equatorial anomaly phenomenon. During winter and many equinoxial storms, the compression effect pushes this station away from the region where effective dumping of ionization from the equator is expected. Diffusion of plasma from the polar region to the crest area has also been observed through penetration of the eastward electric field during many disturbed situations. Depletion of noontime density during winter and equinoxial months and enhancement of the same during summer geomagnetically active situations are examined through anomaly compression (or inhibition) process as well as plasma replenishment through the equatorward wind.

Devi, M.; Barbara, A. K.; Barman, M.

1996-03-01

217

The ionospheres of Ganymede and Callisto from Galileo radio occultations  

NASA Astrophysics Data System (ADS)

The U.S. Galileo spacecraft, which has been in orbit around Jupiter since December, 1995, has provided opportunities to collect s-band radio occultation data using the 70 meter antennas of the NASA/JPL Deep Space Net(DSN) at Goldstone, California, Madrid, Spain, and Canberra, Australia. Ganymede (J3) has been observed five times by Galileo radio occultation. The results are almost entirely negative, with only one measurement out of ten yielding a possible observation of an ionosphere having a maximum density of about 5,000 cm-3 at an altitude of about 16 km. The failure to observe an ionosphere on Ganymede is at first glance surprising, in view of the detection of oxygen and hydrogen above its surface (c.f., Hall, et al., Astrophys. J., 499, 1998; Barth, et al., GRL, 24, 1997), and it was thought to be due to the shielding effect of Ganymede's magnetic field upon the impinging particles from Jupiter's magnetosphere. Callisto has occulted Galileo four times, and these observations have produced some interesting results. Of the eight individual measurements , two are negative, and six are positive. Two of those six show unmistakable classic ionospheric layers, having peak electron densities of 15,000 to 20,000 cm-3 . A closer examination of all of these results has revealed a plausible reason for why some observations yield positive results , and some do not. It appears that in order for an ionosphere to be observed, the trailing hemisphere of the satellite must be in sunlight. In that way, the atmosphere created by sputtering effects of the Jovian magnetosphere can be ionized by solar EUV to produce an observable ionosphere. The research described in this paper has been conducted at the Jet Propulsion Laboratory and the University of Michigan with support from NASA contracts and grants.

Kliore, A. J.; Anabtawi, A.; Nagy, A. F.; Galileo Radio Propagation Science Team

2001-11-01

218

Effects of solar eclipse on the electrodynamical processes of the equatorial ionosphere: a case study during 11 August 1999 dusk time total solar eclipse over India  

Microsoft Academic Search

The effects on the electrodynamics of the equatorial E- and F-regions of the ionosphere, due to the occurrence of the solar eclipse during sunset hours on 11 August 1999, were investigated in a unique observational campaign involving ground based ionosondes, VHF and HF radars from the equatorial location of Trivandrum (8.5° N; 77° E; dip lat. 0.5° N), India. The

R. Sridharan; C. V. Devasia; N. Jyoti; Diwakar Tiwari; K. S. Viswanathan; K. S. V. Subbarao

2002-01-01

219

Ionospheric redistribution during geomagnetic storms  

NASA Astrophysics Data System (ADS)

The abundance of plasma in the daytime ionosphere is often seen to grow greatly during geomagnetic storms. Recent reports suggest that the magnitude of the plasma density enhancement depends on the UT of storm onset. This possibility is investigated over a 7year period using global maps of ionospheric total electron content (TEC) produced at the Jet Propulsion Laboratory. The analysis confirms that the American sector exhibits, on average, larger storm time enhancement in ionospheric plasma content, up to 50% in the afternoon middle-latitude region and 30% in the vicinity of the high-latitude auroral cusp, with largest effect in the Southern Hemisphere. We investigate whether this effect is related to the magnitude of the causative magnetic storms. Using the same advanced Dst index employed to sort the TEC maps into quiet and active (Dst<-100 nT) sets, we find variation in storm strength that corresponds closely to the TEC variation but follows it by 3-6h. For this and other reasons detailed in this report, we conclude that the UT-dependent peak in storm time TEC is likely not related to the magnitude of external storm time forcing but more likely attributable to phenomena such as the low magnetic field in the South American region. The large Dst variation suggests a possible system-level effect of the observed variation in ionospheric storm response on the measured strength of the terrestrial ring current, possibly connected through UT-dependent modulation of ion outflow.

Immel, T. J.; Mannucci, A. J.

2013-12-01

220

Properties of ionospheric irregularities as derived by GNSS scintillation monitors  

NASA Astrophysics Data System (ADS)

Ionospheric influence on the GNSS satellite signals delay, phase and amplitude changes can be deduced from information about various drifting ionospheric density structures. Large and small scale irregularities of electron concentration in the ionosphere determine the changes of the propagating signal. This is the main source of problems for satellite positioning systems that has not been satisfactory solved yet. We present a case study of ionospheric irregular structures patterns during geomagnetic storm event occurred on 5th and 6th April 2010, measured by GPS monitors set on Svalbard and other diagnostic tools. For purpose of comparison we included data of quiet ionosphere period as reference point. Analysis of spatial and temporal phase gradients has been used as a basic tool for calculations of the properties of ionospheric electron concentration irregularities. The properties derived depend on the model of propagation of waves in the ionosphere. We validated estimated properties of ionospheric irregularities using additional measurements. Purpose of this investigation is to recognize ionospheric scintillation diffraction pattern, provide relation between phase measurements and properties of ionospheric irregularities for further forecasting and mitigation of ionospheric effects.

Stevanovic, Djordje; Grzesiak, Marcin

221

Arrival of a tongue of ionization in the nightside polar ionosphere and effects on GPS scintillation  

NASA Astrophysics Data System (ADS)

In this case study we present findings of Global Positioning System (GPS) scintillation in relation to the arriving front of a tongue of ionization in the nightside polar cap over Svalbard. We find almost no amplitude and some phase scintillation in relation to the leading density gradient, which is interpreted as "false" refractive scintillation due to suboptimal data detrending, as opposed to diffractive scintillation from decametre-to-kilometre-scale irregularities. During active geomagnetic conditions, high-density plasma may convect into and across the polar cap. The plasma may be segmented into F region polar cap patches upon entry in the cusp/cleft region, or it may form a continuous tongue of ionization when no such segmentation occurs. Large-scale ionospheric plasma structures such as polar cap patches may contain decametre- to kilometre-scale irregularities, particularly at the edges. Irregularities of these scale sizes cause problems for global navigation satellite system (GNSS) signals, causing amplitude and phase variations known as scintillations. A drawback of most high-latitude GNSS scintillation studies is the use of a 0.1 Hz detrending filter cutoff frequency, which in the literature has been shown to cause "false" phase scintillation. In the literature, much of the high-latitude scintillation research is statistically oriented and concerns polar cap patches. Scintillation directly in relation to ionization tongues is far less studied. We present findings of GPS scintillation in relation to the arriving front of a tongue of ionization on 31 October 2011 in the nightside polar cap over Svalbard, using GPS scintillation and total electron content (TEC) monitors, the EISCAT Svalbard Radar (ESR), and an optical all-sky airglow imager. To our knowledge, this is the first study presenting such detailed multi-instrument data of scintillation in the Svalbard region as well as taking into account the problems of a 0.1 Hz detrending cutoff filter.

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

2014-05-01

222

Effects of a Parallel Electric Field and the Geomagnetic Field in the Topside Ionosphere on Auroral and Photoelectron Energy Distributions  

NASA Technical Reports Server (NTRS)

The consequences of electric field acceleration and an inhomogencous magnetic field on auroral electron energy distributions in the topside ionosphere are investigated. The one- dimensional, steady state electron transport equation includes elastic and inelastic collisions, an inhomogencous magnetic field, and a field-aligned electric field. The case of a self-consistent polarization electric field is considered first. The self-consistent field is derived by solving the continuity equation for all ions of importance, including diffusion of 0(+) and H(+), and the electron and ion energy equations to derive the electron and ion temperatures. The system of coupled electron transport, continuity, and energy equations is solved numerically. Recognizing observations of parallel electric fields of larger magnitude than the baseline case of the polarization field, the effect of two model fields on the electron distribution function in investigated. In one case the field is increased from the polarization field magnitude at 300 km to a maximum at the upper boundary of 800 km, and in another case a uniform field is added to the polarization field. Substantial perturbations of the low energy portion of the electron flux are produced: an upward directed electric field accelerates the downward directed flux of low-energy secondary electrons and decelerates the upward directed component. Above about 400 km the inhomogencous magnetic field produces anisotropies in the angular distribution of the electron flux. The effects of the perturbed energy distributions on auroral spectral emission features are noted.

Min, Q.-L.; Lummerzheim, D.; Rees, M. H.; Stamnes, K.

1993-01-01

223

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

224

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

SciTech Connect

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{approx}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. [Advanced Wireless Communications Research Center and Research Station on Seismo Electromagnetics, University of Electro-Communications, 1-5-1 Chofugaoka, Chofu Tokyo 182-8585 (Japan)

2010-10-20

225

Ionospheric responses to the October 2003 superstorm: Longitude/local time effects over equatorial low and middle latitudes  

NASA Astrophysics Data System (ADS)

Ionospheric responses to the major magnetic storm disturbances of October 2003 are investigated using database selected in the Brazilian and Japanese-Asian longitude sectors. Data obtained from latitudinally spaced digisondes in the equatorial and low-latitude sites in Brazil and from the Asian and Japanese ionosonde network, the total electron content data from the extensive Japanese GPS receiver chain, and magnetometer data from the Pacific equatorial electrojet stations are analyzed during the period 28-31 October. Prompt penetrating (PP) dawn-dusk polar cap electric fields produce large F region plasma uplift on the dayside and eveningside, while the associated westward electric field on the nightside produces large downdraft of the F region plasma, and causes development of westward electrojet current, observed for the first time. Episodes of PP electric field effects appear to be of larger intensity over Brazil than over Asian longitudes. Equatorial anomaly, development due to undershielding as well as overshielding electric fields, was observed in the Brazilian and in the Asian sectors. Disturbance dynamo electric field causes large nighttime F layer uplifts that are modulated by strong meridional winds in both sectors. The disturbance electric field local time variation patterns are compared with the results of recent global model (MTIEGCM) simulation by Richmond et al. (2003) and validated in some cases. Transients of transequatorial winds, flipping direction from southward to northward, in the widely separated longitude sectors, were diagnosed to be present toward the final recovery phase of the storm. These results are presented and discussed in this paper.

Abdu, Mangalathayil A.; Maruyama, Takashi; Batista, Inez S.; Saito, Susumo; Nakamura, Maho

2007-10-01

226

Lower Ionosphere Response to Solar Activity Forcing  

NASA Astrophysics Data System (ADS)

There are two basic channels of solar activity impact on the lower ionosphere (ionosphere below 90-100 km). The first one is through changes of solar electromagnetic ionizing radiation, solar EUV and X-ray flux; particularly the X-ray flux can change by orders of magnitude both during the 11-year solar cycle and strong solar flares. The other channel is via variable solar wind and its interplanetary magnetic field (IMF), which cause geomagnetic storms and other space weather/climate phenomena including variability of penetrating/precipitating high-energy particle flux and via modulation of galactic cosmic rays by IMF. The lower ionosphere response to solar forcing has been studied for more than 50 years by various ground-based methods and with the use of in-situ rocket measurements. In this review the sources of solar activity impact on the lower ionosphere and methods used for investigating lower ionosphere response will be summarized and selected results will be presented. It should be stressed that during strong events of solar origin the electron density in the lower ionosphere may be enhanced by more than an order of magnitude.

Lastovicka, Jan

2012-07-01

227

Radar Ionospheric Impact Mitigation  

Microsoft Academic Search

New ionospheric modeling technology is being developed to improve correction of ionospheric impacts on the performance of ground-based space-surveillance radars (SSRs) in near-real-time. These radars, which detect and track space objects, can experience significant target location errors due to ionospheric delay and refraction of the radar signals. Since these radars must detect and track targets essentially to the radar horizon,

G. Bishop; D. Decker; C. Baker

2006-01-01

228

Self-Consistent Magnetosphere-Ionosphere Coupling  

NASA Technical Reports Server (NTRS)

A self-consistent ring current (RC) model has been developed that couples electron and ion magnetospheric dynamics with the calculation of the electric field. Two new features were taken into account in order to close the self-consistent magnetosphere-ionosphere coupling loop. First, in addition to the RC ions, we have solved an electron kinetic equation in our model. Second, using the relation of Galand and Richmond, we have calculated the height integrated ionospheric conductances as a function of the precipitated high energy magnetospheric electrons and ions that are produced by our model. To validate the results of our model we simulate the magnetic storm of May 2, 1986, a storm that has been comprehensively studied by Fok et al., and have compared our results with different theoretical approaches. The self-consistent inclusion of the hot electrons and their effect on the conductance results in deeper penetration of the magnetospheric electric field. In addition, a slight westward rotation of the potential pattern (compared to previous self-consistent results) is evident in the inner magnetosphere. These effects change the hot plasma distribution, especially by allowing increased access of plasma sheet ions and electrons to low L shells.

Six, N. Frank (Technical Monitor); Khazanov, G. V.; Newman, T. S.; Liemohn, M. W.; Fok, M. C.; Spiro, R. W.

2002-01-01

229

42 CFR 2.61 - Legal effect of order.  

Code of Federal Regulations, 2012 CFR

...2012-10-01 false Legal effect of order. 2.61 Section 2.61...CONFIDENTIALITY OF ALCOHOL AND DRUG ABUSE PATIENT RECORDS Court Orders Authorizing Disclosure and Use § 2.61 Legal effect of order. (a) Effect. An...

2012-10-01

230

42 CFR 2.61 - Legal effect of order.  

...2014-10-01 false Legal effect of order. 2.61 Section 2.61...CONFIDENTIALITY OF ALCOHOL AND DRUG ABUSE PATIENT RECORDS Court Orders Authorizing Disclosure and Use § 2.61 Legal effect of order. (a) Effect. An...

2014-10-01

231

42 CFR 2.61 - Legal effect of order.  

Code of Federal Regulations, 2013 CFR

...2013-10-01 false Legal effect of order. 2.61 Section 2.61...CONFIDENTIALITY OF ALCOHOL AND DRUG ABUSE PATIENT RECORDS Court Orders Authorizing Disclosure and Use § 2.61 Legal effect of order. (a) Effect. An...

2013-10-01

232

42 CFR 2.61 - Legal effect of order.  

Code of Federal Regulations, 2011 CFR

...2011-10-01 false Legal effect of order. 2.61 Section...PROVISIONS CONFIDENTIALITY OF ALCOHOL AND DRUG ABUSE PATIENT RECORDS...Disclosure and Use § 2.61 Legal effect of order. (a) Effect. An order of a...

2011-10-01

233

42 CFR 2.61 - Legal effect of order.  

Code of Federal Regulations, 2010 CFR

...2010-10-01 false Legal effect of order. 2.61 Section...PROVISIONS CONFIDENTIALITY OF ALCOHOL AND DRUG ABUSE PATIENT RECORDS...Disclosure and Use § 2.61 Legal effect of order. (a) Effect. An order of a...

2010-10-01

234

Modeling the global positioning system signal propagation through the ionosphere  

NASA Technical Reports Server (NTRS)

Based on realistic modeling of the electron density of the ionosphere and using a dipole moment approximation for the Earth's magnetic field, one is able to estimate the effect of the ionosphere on the Global Positioning System (GPS) signal for a ground user. The lowest order effect, which is on the order of 0.1-100 m of group delay, is subtracted out by forming a linear combination of the dual frequencies of the GPS signal. One is left with second- and third-order effects that are estimated typically to be approximately 0-2 cm and approximately 0-2 mm at zenith, respectively, depending on the geographical location, the time of day, the time of year, the solar cycle, and the relative geometry of the magnetic field and the line of sight. Given the total electron content along a line of sight, the authors derive an approximation to the second-order term which is accurate to approximately 90 percent within the magnetic dipole moment model; this approximation can be used to reduce the second-order term to the millimeter level, thus potentially improving precise positioning in space and on the ground. The induced group delay, or phase advance, due to second- and third-order effects is examined for two ground receivers located at equatorial and mid-latitude regions tracking several GPS satellites.

Bassiri, S.; Hajj, G. A.

1992-01-01

235

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

236

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

237

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

238

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

239

Integrity monitoring in real-time precise point positioning in the presence of ionospheric disturbances  

NASA Astrophysics Data System (ADS)

Ionospheric disturbances are characterized as fast and random variability in the ionosphere. Those phenomena are difficult to predict, detect and model. Occurrence of some strong ionospheric disturbances can cause, inter alia degradation and interruption of GNSS signals. Therefore they are especially harmful for real-time applications, as for example Precise Point Positioning (PPP) in real time, where one of the most important requirements is to ensure the high level of reliability. In such applications verification and confirmation of a high trust degree towards the estimated coordinates is a very critical issue. In one of the previous papers (K. Wezka, 2012 -Identification of system performance parameters and their usability) two sets of parameters have been proposed for enhance reliability of the PPP. The first one for data quality control (QC) of the raw GNSS observations and the second one for examination of the quality, robustness and performance of various processing approaches (strategies). To the second group the following parameters has been proposed: accuracy, precision, availability, integrity and convergence time. In consideration of perturbation of GNSS signal resulting from sudden ionospheric disturbances, one of the most important demands is effective autonomous integrity monitoring. The poster presents first preliminary results of the applicability of the proposed parameters in order to ensure the high level of reliability/integrity of GNSS observations and positioning results under the presence of strong ionospheric anomalies. The data-set from continuously operated GNSS station located at high latitude, where ionospheric disturbances occur more frequently, were used for the analysis. Various selected Receiver Autonomous Integrity Monitoring (RAIM) approaches for quality control of the GNSS observables are applied to the data sets recorded under different (low/quite and high) ionospheric activities. Based on those analyses the usability of the proposed parameters is verified.

Wezka, K.; Galas, R.

2013-12-01

240

The structure of the Venus ionosphere  

NASA Technical Reports Server (NTRS)

The morphology and temporal variability of the Venus ionosphere are characterized, reviewing the results of recent theoretical investigations, observations, and in situ measurements, especially by the Pioneer Venus Orbiter (PVO). Consideration is given to the Pioneer mission and orbit evolution, early radio occultation profiles of ionospheric N(e), the mean structure and thermal balance of the ionosphere, the ion composition and its dawn-dusk asymmetry, the small-scale spatial structure on the nightside, latitudinal and seasonal variations, solar-cycle effects, suprathermal electrons and superthermal ions, and the global configuration and stability of the ionopause. Data from a single PVO passage through the ionotail are discussed in detail, examining the implications for ion escape and the solar-cycle and short-term variability. The differences among the terrestrial, Martian, and Venusian ionospheres are outlined; the PVO data base is described; and the sources of measurement error are indicated.

Brace, L. H.; Kliore, A. J.

1991-01-01

241

Magnetic Fluctuations in the Martian Ionosphere  

NASA Technical Reports Server (NTRS)

The Martian ionosphere is influenced by both the solar wind and the regional magnetic fields present in the Martian crust. Both influences ought to cause time variable changes in the magnetic fields present in the ionosphere. I report observations of these magnetic field fluctuations in the Martian ionosphere. I use data from the Mars Global Surveyor magnetometer instrument. By using data from the aerobraking low altitude passes (approx. 200 km) I find that there are numerous fluctuations both near and far from the strong crustal sources. Using data from the 400 km altitude mapping phase (which is near the topside of the primary ionosphere), I look at the comparative strength of the fluctuations relative to the solar wind and temporal variations. I discuss which wave modes and instabilities could be contributing to these fluctuations. I also discuss the implications of these fluctuations for understanding energy transfer in the Martian system and the effects on atmospheric escape.

Espley, Jared

2010-01-01

242

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

243

The Ionosphere and the Latin America Very Low Frequency Network Mexico (LAVNet-Mex)  

NASA Astrophysics Data System (ADS)

The radiation emitted by the most energetic transient events in the solar system, solar flares, covers a wide range of wavelengths, from radio waves to gamma rays. When the transient excess of high energy radiation produced by solar flares reach the Earth environment, the upper layers of the Earth atmosphere are affected and highly disturbed. The dynamics (particularly the conductivity) of the ionosphere, is altered during solar explosive events. In order to detect and study the ionospheric response to the transient solar radiative input, we have constructed a VLF receiver station: the `Latin American Very low frequency Network at Mexico' (LAVNet-Mex), which extends to the northern hemisphere the South American VLF Network. LAVNet-Mex detects electromagnetic waves generated by strong transmitters located around the world. These waves travel inside the Earth-Ionosphere waveguide, along the Great Circle Path formed between the emitter and the observer. By observing changes in the phase and amplitude of these waves, it is possible to study the dynamics of the lower layer of the ionosphere during solar eruptive events. In this work we present preliminary results of the analysis of the effects of solar flares (class M and X) occurred in 2012 and that were observed by LAVNet-Mex. We explore the relationship between VLF signals coming from different paths during these solar burst to infer the degree of correlation that can exist between different sectors of the ionosphere.

Borgazzi, A.; Lara, A.; Santiago, A.

2013-05-01

244

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

NASA Astrophysics Data System (ADS)

Orbiting ground penetrating radars (GPRs) as the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) and the Shallow Radar (SHARAD) currently operating on Mars need a fine ionospheric correction in order to deliver products useful for geological investigations. Ionosphere influence can be assessed using a new approach based on the finite-difference time-domain (FDTD) method. The proposed work aims to underline the errors introduced by a not perfect knowledge of the ionosphere electron density profile on the transmitted chirp signal. Such effect has a great impact on the data inversion process that aims to estimate the permittivity of the subsurface detected interfaces. Data inversion is accomplished by evaluating, via a two channels approach, quantities related to crust attenuation, surface/subsurface geometry and power scattered by the detected interfaces. The final product delivered after SAR processing is highly dependent on the ionosphere compensation. Ionosphere phase related distortions have been theoretically modelled using the Chapman density function. They introduce an S/N and a side lobe level (SLL) degradation after matched filtering along with a delay and a pulse shape distortion. Since several data acquired over smooth surfaces do not present a pulse shape verifying the backscattering models introduced for MARSIS and SHARAD and based on Kirchhoff approximation it is important to provide a different approach for the ionosphere compensation in order to obtain more reliable products. Not perfectly compensated data would provide erroneous power levels and a wrong geometric interpretation jeopardizing the entire data inversion process. The finite-difference time-domain (FDTD) method can be used to study the propagation of a MARSIS/SHARAD chirp signal into a plasma modelled according to a desired electron density profile adding a new important benefit to the simulation methods available to understand GPR signals in this context. A 1D-FDTD code is enough to model both plasma and collision frequencies. Using the simulator some recently proposed Martian multi-peak electron density profiles similar to Chapman's one have been synthetized. The Chapman model is then used during matched filtering, as on MARSIS/SHARAD data, to compensate the distortions introduced by the ionosphere underlining the eventual presence of uncompensated residuals quantified in terms of S/N loss, SLL degradation and pulse shape distortion. Such work will be highly useful to produce new ionosphere compensation schemes providing more reliable data to be employed in the data inversion procedure.

Restano, Marco; Picardi, Giovanni; Seu, Roberto

2013-04-01

245

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

246

Ionospheric responses to the October 2003 superstorm: Longitude\\/local time effects over equatorial low and middle latitudes  

Microsoft Academic Search

Ionospheric responses to the major magnetic storm disturbances of October 2003 are investigated using database selected in the Brazilian and Japanese-Asian longitude sectors. Data obtained from latitudinally spaced digisondes in the equatorial and low-latitude sites in Brazil and from the Asian and Japanese ionosonde network, the total electron content data from the extensive Japanese GPS receiver chain, and magnetometer data

Mangalathayil A. Abdu; Takashi Maruyama; Inez S. Batista; Susumo Saito; Maho Nakamura

2007-01-01

247

submitted to Journal of Geophysical Research 2013JA018867 Estimating the Effects of Ionospheric Plasma on Solar-Wind/Magnetosphere  

E-print Network

-ionosphere system is controlled by the amount of magnetic-field-line reconnection between the solar wind magnetic-field strength and same mass density) collisionless plasmas, the reconnection rate R is given by R in the plasmas near the reconnection site and B is the magnetic-field strength in the plasmas near

Lotko, William

248

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

249

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

250

Study of ionospheric models for satellite orbit determination  

NASA Technical Reports Server (NTRS)

Means of improving the accuracy of the ionospheric correction of two empirical ionospheric models, the Bent (Schmid et al. 1973) and international reference ionosphere (IRI) models, have been evaluated. An improved IRI topside formula is found to minimize the tendency for the electron density profile to decrease too sharply with increasing altitude, and is shown to produce results which compare well with satellite data and ground-based incoherent scatter measurements. A model for the effective parabolic thickness is proposed for the bottomside. Comparison with results from a Meteosat tracking exercise demonstrates that the present changes improve the overall accuracy of ionospheric delays calculated using the two models.

Bilitza, D.; Rawer, K.; Pallaschke, S.

1988-01-01

251

Magnetosphere-Ionosphere coupling through the auroral acceleration region  

NASA Technical Reports Server (NTRS)

An important form of coupling between the magnetosphere and the ionosphere occurs through acceleration mechanisms operative in the high altitude ionosphere on magnetic field lines connecting to the auroral zone. Energetic ion mass spectrometer data from within these auroral acceleration regions are presented to illustrate the characteristics of the mechanisms. Observations of ionospheric plasmas in the ring current, the distant plasma sheet, and the magnetotail lobes are shown illustrating the extent of their circulation and the importance of their contribution to the plasma in each regime. Finally the precipitating plasmas in the auroral region and the extent and peculiar effects of the 0(+) component of that precipitation on the ionosphere are illustrated.

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

1981-01-01

252

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

253

The long-term behavior of the main peak of the dayside ionosphere of venus during solar cycle 21 and its implications on the effect of the solar cycle upon the electron temperature in the main peak region  

Microsoft Academic Search

One hundred four measurements of the peak electron density in the dayside ionosphere of Venus (solar zenith angle (SZA) <80°), along with 11 Venera 9-10 measurements, were analyzed in order to establish the response of the dayside peak to the varying solar EUV flux over the maximum to minimum phase of solar cycle 21 (December 1979 to December 1986). The

Arvydas J. Kliore; Luke F. Mullen

1989-01-01

254

Modification of conductivity due to acceleration of the ionospheric medium  

NASA Astrophysics Data System (ADS)

A quantitative division of the ionosphere into dynamo and motor regions is performed on the base of empirical models of space distributions of ionospheric parameters. Pedersen and Hall conductivities are modified to represent an impact of acceleration of the medium because of Ampére's force. It is shown that the currents in the F2 layer are greatly reduced for processes of a few hours duration. This reduction is in particular important for the night-side low-latitude ionosphere. The International Reference Ionosphere model is used to analyze the effect quantitatively. This model gives a second high conducting layer in the night-side low-latitude ionosphere that reduces the electric field and equatorial electrojets, but intensifies night-side currents during the short-term events. These currents occupy regions which are much wider than those of equatorial electrojets. It is demonstrated that the parameter ?d=?P+?H?H/?P that involves the integral Pedersen and Hall conductances ?P, ?H ought to be used instead of the local Cowling conductivity ?C in calculations of the electric current density in the equatorial ionosphere. We may note that Gurevich et al. (1976) derived a parameter similar to ?d for more general conditions as those which we discuss in this paper; a more detailed description of this point is given in Sect. 6. Both, ?d and ?C, appear when a magnetic field line is near a nonconducting domain which means zero current through the boundary of this domain. The main difference between ?d and ?C is that ?d definition includes the possibility for the electric current to flow along a magnetic field line in order to close all currents which go to this line from neighboring ones. The local Cowling conductivity ?C corresponds to the current closure at each point of a magnetic field line. It is adequate only for a magnetic field line with constant local conductivity at the whole line when field-aligned currents do not exist because of symmetry, but ?C=?d in this case. So, there is no reason to use the local Cowling conductivity while the Cowling conductance ?C=?P+?H2/?P is a useful and well defined parameter.

Denisenko, V. V.; Biernat, H. K.; Mezentsev, A. V.; Shaidurov, V. A.; Zamay, S. S.

2008-07-01

255

Ionosphere TEC disturbances before strong earthquakes: observations, physics, modeling (Invited)  

NASA Astrophysics Data System (ADS)

The phenomenon of the pre-earthquake ionospheric disturbances is discussed. A number of typical TEC (Total Electron Content) relative disturbances is presented for several recent strong earthquakes occurred in different ionospheric conditions. Stable typical TEC deviations from quiet background state are observed few days before the strong seismic events in the vicinity of the earthquake epicenter and treated as ionospheric earthquake precursors. They don't move away from the source in contrast to the disturbances related with geomagnetic activity. Sunlit ionosphere approach leads to reduction of the disturbances up to their full disappearance, and effects regenerate at night. The TEC disturbances often observed in the magnetically conjugated areas as well. At low latitudes they accompany with equatorial anomaly modifications. The hypothesis about the electromagnetic channel of the pre-earthquake ionospheric disturbances' creation is discussed. The lithosphere and ionosphere are coupled by the vertical external electric currents as a result of ionization of the near-Earth air layer and vertical transport of the charged particles through the atmosphere over the fault. The external electric current densities exceeding the regular fair-weather electric currents by several orders are required to produce stable long-living seismogenic electric fields such as observed by onboard measurements of the 'Intercosmos-Bulgaria 1300' satellite over the seismic active zones. The numerical calculation results using the Upper Atmosphere Model demonstrate the ability of the external electric currents with the densities of 10-8-10-9 A/m2 to produce such electric fields. The sumulations reproduce the basic features of typical pre-earthquake TEC relative disturbances. It is shown that the plasma ExB drift under the action of the seismogenic electric field leads to the changes of the F2 region electron number density and TEC. The upward drift velocity component enhances NmF2 and TEC and the downward component decreases it, while horizontal components redistribute plasma in the horizontal plane around the source. The UAM calculations also show that the external electric currents of the seismic origin generate the small disturbances of the neutral atmosphere with the characteristics of the internal gravity waves but they don't influence noticeably on the relative pre-earthquake TEC disturbances.

Namgaladze, A. A.

2013-12-01

256

Trans-Ionospheric High Frequency Signal Ray Tracing  

NASA Astrophysics Data System (ADS)

All electromagnetic radiation undergoes refraction as it propagates through the atmosphere. Tropospheric refraction is largely governed by interaction of the radiation with bounded electrons; ionospheric refraction is primarily governed by free electron interactions. The latter phenomenon is important for propagation and refraction of High Frequency (HF) through Extremely High Frequency (EHF) signals. The degree to which HF to EHF signals are bent is dependent upon the integrated refractive effect of the ionosphere: a result of the signal's angle of incidence with the boundaries between adjacent ionospheric regions, the magnitude of change in electron density between two regions, as well as the frequency of the signal. In the case of HF signals, the ionosphere may bend the signal so much that it is directed back down towards the Earth, making over-the-horizon HF radio communication possible. Ionospheric refraction is a major challenge for space-based geolocation applications, where the ionosphere is typically the biggest contributor to geolocation error. Accurate geolocation requires an algorithm that accurately reflects the physical process of a signal transiting the ionosphere, and an accurate specification of the ionosphere at the time of the signal transit. Currently implemented solutions are limited by both the algorithm chosen to perform the ray trace and by the accuracy of the ionospheric data used in the calculations. This paper describes a technique for adapting a ray tracing algorithm to run on a General-Purpose Graphics Processing Unit (GPGPU or GPU), and using a physics-based model specifying the ionosphere at the time of signal transit. This technique allows simultaneous geolocation of significantly more signals than an equivalently priced Central Processing Unit (CPU) based system. Additionally, because this technique makes use of the most widely accepted numeric algorithm for ionospheric ray tracing and a timely physics-based model of the ionosphere instead of the typically used climatologically derived one, we assert that this technique improves geolocation accuracy.

Wright, S.; Gillespie, R. J.

2012-09-01

257

The Venus ionosphere  

NASA Technical Reports Server (NTRS)

Physical properties of the Venus ionosphere obtained by experiments on the US Pioneer Venus and the Soviet Venera missions are presented in the form of models suitable for inclusion in the Venus International Reference Atmosphere. The models comprise electron density (from 120 km), electron and ion temperatures, and relative ion abundance in the altitude range from 150 km to 1000 km for solar zenith angles from 0 to 180 deg. In addition, information on ion transport velocities, ionopause altitudes, and magnetic field characteristics of the Venus ionosphere, are presented in tabular or graphical form. Also discussed is the solar control of the physical properties of the Venus ionosphere.

Bauer, S. J.; Brace, L. M.; Taylor, H. A., Jr.; Breus, T. K.; Kliore, A. J.

1985-01-01

258

On the convergence of ionospheric constrained precise point positioning (IC-PPP) based on undifferential uncombined raw GNSS observations.  

PubMed

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

259

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

260

Radiophysical and radio astronomical diagnostics of ionospheric effects induced by a ground-based infrasonic transmitter (preliminary results)  

Microsoft Academic Search

We present results of preliminary studies aimed at detection of weak ionospheric disturbances induced by acoustic emission\\u000a of a ground-based controlled transmitter. Radio astronomical and radiophysical facilities based on the decameter radio telescope\\u000a URAN-3 were used in these experiments. Three methods were applied in this study: occultation of the disturbed region by radio\\u000a emission from discrete cosmic sources, scattering of

V. V. Koshovy

1999-01-01

261

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

262

Non-Uniform Plasma Discharges in Near Earth Space Environment and Ionosphere to Troposphere Responses  

Microsoft Academic Search

Most earth weather and ionosphere-space environment coupling studies separate the problems into distinct groups. Heliosphere to solar wind - solar storm activity to ionospheric coupling - thermosphere and mid- altitude to the ionosphere and electrical effects such as elves and sprites and thunderstorms in another group - additionally mid and high latitude weather systems are many times separated also. The

J. M. McCanney

2009-01-01

263

Improving Klobuchar Type Ionospheric Delay Model using 2D GPS TEC over China  

Microsoft Academic Search

In Global Positioning System GPS the 8 parameter Klobuchar type ionospheric delay model is broadcast to predicts the global vertical TEC distribution at a given time period for real-time correcting the ionospheric effect on for single frequency GPS measurements The Klobuchar type ionospheric delay model which originally comes from Bent Model is a simple but utility model It adopts trigonometric

Ling Han; Hongping Zhang; Yidan Huang; Mingyuan Wang; Wenyao Zhu; Jingsong Ping

2006-01-01

264

Use of IRI to Model the Effect of Ionosphere Emission on Earth Remote Sensing at L-Band  

NASA Technical Reports Server (NTRS)

Microwave remote sensing in the window at 1.413 GHz (L-band) set aside for passive use only is important for monitoring sea surface salinity and soil moisture. These parameters are important for understanding ocean dynamics and energy exchange between the surface and atmosphere, and both NASA and ESA plan to launch satellite sensors to monitor these parameters at L-band (Aquarius, Hydros and SMOS). The ionosphere is an important source of error for passive remote sensing at this frequency. In addition to Faraday rotation, emission from the ionosphere is also a potential source of error at L-band. As an aid for correcting for emission, a regression model is presented that relates ionosphere emission to the integrated electron density (TEC). The goal is to use TEC from sources such as TOPEX, JASON or GPS to obtain estimates of emission over the oceans where the electron density profiles needed to compute emission are not available. In addition, data will also be presented to evaluate the use of the IRI for computing emission over the ocean.

Abraham, Saji; LeVine, David M.

2004-01-01

265

a Study on the Radio Propagation in the Korean Ionosphere  

Microsoft Academic Search

The effects of the ionosphere on the radio wave propagation are scattering of radio waves, attenuation, angle error, ranging error, and time delay. If ionospheric conditions are suitable, the charged particles can remove energy from radio waves and thus attenuate the signal. Also, a radio wave traveling a path along which the electron density is not constant undergoes changes in

Seok-Hee Bae; Kyu-Hong Choi; Jai-Rim Yuk; Hong-Ik Kim; Kyoung W. Min

1992-01-01

266

Measurements and Modeling of Ionosphere-Plasmasphere Transport  

Microsoft Academic Search

A fundamental aspect of the coupling between Earth's ionosphere and inner magnetosphere is the flow of ionospheric plasma that supplies material to the plasmasphere. Using global observations of the He+ column abundance made by the IMAGE Extreme Ultraviolet Imager, we investigate refilling of the plasmasphere after erosion events associated with geomagnetic storms. To minimize the confounding effects of phenomena other

B. R. Sandel; M. H. Denton

2005-01-01

267

Mechanisms of Ionospheric Mass Ejection  

NASA Technical Reports Server (NTRS)

Ionospheric outflows are directly responsive to solar wind disturbances, particularly in the dayside auroral cusp or cleft regions. Inputs of both electromagnetic energy (Poynting flux) and kinetic energy (particle precipitation) are closely correlated with these outflows. We assess the importance of processes thought to drive ionospheric outflows. These begin with the diffuse effects of photoionization and thermal equilibrium of the ionospheric topside, enhancing Jeans' escape, with ambipolar diffusion and acceleration. Auroral outflows begin with dayside reconnexion and resultant field-aligned currents and driven convection. These produce plasmaspheric plumes, collisional heating and wave-particle interactions, centrifugal acceleration, and auroral acceleration by parallel electric fields, including enhanced ambipolar fields from electron heating by precipitation particles. Solar wind energy dissipation is concentrated by the geomagnetic field into auroral regions with an amplification factor of 10-100, enhancing heavy species plasma and gas escape from gravity, and providing more current carrying capacity. Internal plasmas thus enable electromagnetic driving via coupling to the plasma and neutral gas. We assess the importance of each of these processes in terms of local escape flux production as well as global outflow, and suggest methods for their implementation within multi-species global simulation codes. We conclude by assessing outstanding obstacles to this objective.

Moore, Thomas Earle; Khazanov, George V.; Hannah, Mei-Ching; Glocer, Alex

2010-01-01

268

Seismo-Ionospheric Precursors  

NASA Astrophysics Data System (ADS)

Large earthquakes are often preceded or accompanied by signals of a different nature: electric, electromagnetic, or luminous, although seismic waves are the most obvious manifestation. Recently, seismo-ionospheric phenomena have received considerable discussions. To investigate possible seismo-ionospheric precursors, we statistically examine the relationship between electron density variations at the ionospheric F2 peak observed by a local ionosonde and 184 earthquakes with magnitude 5.0 or larger, which occurred in 170 days during 1994~1999 in the Taiwan area. Results demonstrate that the electron density abnormally decreases during the afternoon period, 1200~1800 LT, within 5 days before the earthquakes. The odds of the earthquakes with the precursor increasing in the earthquake magnitude but decreasing in the range between the epicenter and the ionosonde confirm the existence of an imminent seismo-ionospheric precursor.

Liu, J.; Chen, Y.; Chuo, Y.

2003-12-01

269

Modeling Ionospheric Electrodynamics (Invited)  

NASA Astrophysics Data System (ADS)

We present modeling results of ionospheric electrodynamics using the 3D NRL ionosphere model SAMI3. Recently, SAMI3 has been upgraded to solve the potential equation that determines the electrostatic potential from the ionospheric conductances (Pedersen and Hall) and drivers: neutral wind, gravity, and parallel current systems. We present results showing the impact of different neutral wind models (e.g., HWM93, HWM07, TIMEGCM) on the dynamics of the low- to mid-latitude ionosphere, as well as the Region 1 and 2 current systems. We point out issues and concerns with obtaining an accurate specification of the global electric field within the context of existing models.(with J. Krall, G. Joyce, S. Slinker, and G. Crowley). Research supported by NASA and ONR

Huba, J. D.

2009-12-01

270

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

271

Ionospheric and geomagnetic effects of the solar eclipse of 18 March 1988 in East Asia  

NASA Astrophysics Data System (ADS)

A chain of observational stations running parallel to the path of totality has been used to obtain ionograms, electron-content measurements, magnetograms, and microbarograph recordings of the effects of the March 18, 1988 solar eclipse's transit through Southeast Asia. Depletions of f0E and f0F1 are noted, and electron density-height profiles reveal a deeply hollowed-out electron-density valley over the 200-300 km altitude range. The equatorial anomally diffusion process was substantially reduced. As a result of the electron density depletion in the E-region at the magnetic equator, the northward movement of S(q) current electrons was halted. Direct evidence is obtained for the production of acoustic gravity waves by the moving bow wave front of the solar eclipse.

Walker, G. O.; Li, T. Y. Y.; Wong, Y. W.; Kikuchi, T.; Huang, Y. N.

1991-02-01

272

Radar Ionospheric Impact Mitigation  

NASA Astrophysics Data System (ADS)

New ionospheric modeling technology is being developed to improve correction of ionospheric impacts on the performance of ground-based space-surveillance radars (SSRs) in near-real-time. These radars, which detect and track space objects, can experience significant target location errors due to ionospheric delay and refraction of the radar signals. Since these radars must detect and track targets essentially to the radar horizon, it is necessary to accurately model the ionosphere as the radar would observe it, down to the local horizon. To correct for spatial and temporal changes in the ionosphere the model must be able to update in near-real-time using ionospheric sensor data. Since many radars are in isolated locations, or may have requirements to operate autonomously, an additional required capability is to provide accurate ionospheric mitigation by exploiting only sensor data from the radar site. However, the model must also be able to update using additional data from other types of sensors that may be available. The original radar ionospheric mitigation approach employed the Bent climatological model. This 35-year-old technology is still the means employed in the many DoD SSRs today. One more recent approach used capabilities from the PRISM model. PRISM technology has today been surpassed by `assimilative models' which employ better physics and Kalman filtering techniques. These models are not necessarily tailored for SSR application which needs to optimize modeling of very small regions using only data from a single sensor, or very few. The goal is to develop and validate the performance of innovative and efficient ionospheric modeling approaches that are optimized for the small regions applicable to ground-based radar coverage (radius of ~2000 km at ionospheric altitudes) and somewhat beyond. These approaches must adapt a continuous modeling scheme in near-real-time to be consistent with all observational data that may become available, and degrade gracefully toward a climatological representation in the absence of data. In this presentation we will discuss the issues for improving correction of ionospheric impacts on SSRs, some of the capabilities and limitations of current models, and the requirements and goals for new modeling technologies.

Bishop, G.; Decker, D.; Baker, C.

2006-12-01

273

Dayside Ionospheric Superfountain  

NASA Technical Reports Server (NTRS)

The Dayside Ionospheric Super-fountain modified SAMI2 code predicts the uplift, given storm-time electric fields, of the dayside near-equatorial ionosphere to heights of over 800 kilometers during magnetic storm intervals. This software is a simple 2D code developed over many years at the Naval Research Laboratory, and has importance relating to accuracy of GPS positioning, and for satellite drag.

Tsurutani, Bruce T.; Verkhoglyadova, Olga P.; Mannucci, Anthony J.

2010-01-01

274

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.

275

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

276

Characterisation of residual ionospheric errors in bending angles using GNSS RO end-to-end simulations  

NASA Astrophysics Data System (ADS)

Global Navigation Satellite System (GNSS) radio occultation (RO) is an innovative meteorological remote sensing technique for measuring atmospheric parameters such as refractivity, temperature, water vapour and pressure for the improvement of numerical weather prediction (NWP) and global climate monitoring (GCM). GNSS RO has many unique characteristics including global coverage, long-term stability of observations, as well as high accuracy and high vertical resolution of the derived atmospheric profiles. One of the main error sources in GNSS RO observations that significantly affect the accuracy of the derived atmospheric parameters in the stratosphere is the ionospheric error. In order to mitigate the effect of this error, the linear ionospheric correction approach for dual-frequency GNSS RO observations is commonly used. However, the residual ionospheric errors (RIEs) can be still significant, especially when large ionospheric disturbances occur and prevail such as during the periods of active space weather. In this study, the RIEs were investigated under different local time, propagation direction and solar activity conditions and their effects on RO bending angles are characterised using end-to-end simulations. A three-step simulation study was designed to investigate the characteristics of the RIEs through comparing the bending angles with and without the effects of the RIEs. This research forms an important step forward in improving the accuracy of the atmospheric profiles derived from the GNSS RO technique.

Liu, C. L.; Kirchengast, G.; Zhang, K. F.; Norman, R.; Li, Y.; Zhang, S. C.; Carter, B.; Fritzer, J.; Schwaerz, M.; Choy, S. L.; Wu, S. Q.; Tan, Z. X.

2013-09-01

277

The netlander ionosphere and geodesy experiment  

Microsoft Academic Search

The NEtlander Ionosphere and Geodesy Experiment (NEIGE) of the Netlander Mission to Mars has two series of scientific objectives: (1) to determine Mars orientation parameters in order to obtain information about the interior of Mars and about the seasonal mass exchange between atmosphere and ice caps; and (2) to determine the total electron content (TEC) and the scintillation of radio

J.-P. Barriot; V. Dehant; W. Folkner; J.-C. Cerisier; A. Ribes; J. Benoist; T. Van Hoolst; P. Defraigne; R. Warnant; R. A. Preston; L. Romans; S. Wu; A. W. Wernik

2001-01-01

278

Unusual electron density profiles observed by Cassini radio occultations in Titan's ionosphere: Effects of enhanced magnetospheric electron precipitation?  

NASA Astrophysics Data System (ADS)

The Cassini radio science facility provided 13 occultation electron density profiles of Titan during the period of 2006 and 2009. This paper presents the results of all of these occultation observations. It shows that ten of the observed electron density profiles are similar, but three are significantly different. The number of observations is relatively small for meaningful statistical conclusions, but it is shown, using the corresponding measured electron spectra, that the three anomalous profiles in the ionospheric peak regions are likely to be the result of unusually intense electron precipitation events.

Kliore, A. J.; Nagy, A. F.; Cravens, T. E.; Richard, M. S.; Rymer, A. M.

2011-11-01

279

Ionospheric Effects of the X-Ray Flares of September 24, 2011 According to Oblique Sounding Data  

NASA Astrophysics Data System (ADS)

We present the results of observations of a sudden wideband attenuation of short radio waves and Doppler-shift variations of the signals from broadcast stations on oblique sounding paths in the Eurasian longitudinal sector during a series of X-ray flares that occurred on September 24, 2011. The results of modeling of the electron-density profiles in the lower ionosphere based on measurements of attenuation of short waves on the Moscow—Rostov-on-Don path at a frequency of 9996 kHz of the standard-time RWM station during the most powerful flare that occurred on September 24, 2011 at 09:40 UT are given.

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

2014-10-01

280

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

281

Characteristics of High Latitude Ionosphere Scintillations  

NASA Astrophysics Data System (ADS)

As we enter a new solar maximum period, global navigation satellite systems (GNSS) receivers, especially the ones operating in high latitude and equatorial regions, are facing an increasing threat from ionosphere scintillations. The increased solar activities, however, also offer a great opportunity to collect scintillation data to characterize scintillation signal parameters and ionosphere irregularities. While there are numerous GPS receivers deployed around the globe to monitor ionosphere scintillations, most of them are commercial receivers whose signal processing mechanisms are not designed to operate under ionosphere scintillation. As a result, they may distort scintillation signal parameters or lose lock of satellite signals under strong scintillations. Since 2008, we have established and continuously improved a unique GNSS receiver array at HAARP, Alaska. The array contains high ends commercial receivers and custom RF front ends which can be automatically triggered to collect high quality GPS and GLONASS satellite signals during controlled heating experiments and natural scintillation events. Custom designed receiver signal tracking algorithms aim to preserve true scintillation signatures are used to process the raw RF samples. Signal strength, carrier phase, and relative TEC measurements generated by the receiver array since its inception have been analyzed to characterize high latitude scintillation phenomena. Daily, seasonal, and solar events dependency of scintillation occurrence, spectral contents of scintillation activities, and plasma drifts derived from these measurements will be presented. These interesting results demonstrate the feasibility and effectiveness of our experimental data collection system in providing insightful details of ionosphere responses to active perturbations and natural disturbances.

Morton, Y.

2012-12-01

282

Ionospheric Specifications for SAR Interferometry (ISSI)  

NASA Technical Reports Server (NTRS)

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

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

2013-01-01

283

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

284

Evaluation of Inversion Methods Applied to Ionospheric ro Observations  

NASA Astrophysics Data System (ADS)

The new technique of radio-occultation can be used to study the Earth's ionosphere. The retrieval processes of ionospheric profiling from radio occultation observations usually assume spherical symmetry of electron density distribution at the locality of occultation and use the Abel integral transform to invert the measured total electron content (TEC) values. This pa-per presents a set of ionospheric profiles obtained from SAC-C satellite with the Abel inversion technique. The effects of the ionosphere on the GPS signal during occultation, such as bending and scintillation, are examined. Electron density profiles are obtained using the Abel inversion technique. Ionospheric radio occultations are validated using vertical profiles of electron con-centration from inverted ionograms , obtained from ionosonde sounding in the vicinity of the occultation. Results indicate that the Abel transform works well in the mid-latitudes during the daytime, but is less accurate during the night-time.

Rios Caceres, Arq. Estela Alejandra; Rios, Victor Hugo; Guyot, Elia

285

Deriving the effective scale height in the topside ionosphere based on ionosonde and satellite in situ observations  

NASA Astrophysics Data System (ADS)

scale height is a valuable key parameter measuring the shape of the profile of plasma density in the F2 layer ionosphere. Currently, the data of Chapman scale height are routinely derived from ionogram observations at many ionosonde stations in terms of the SAO explorer software. In this report, we collected the in situ observations of plasma density at altitudes around 600 km from the ROCSAT-1 satellite and of simultaneous F peak parameters from an ionosonde operated at Wuhan (30.6°N, 114.4°E), a low-latitude station in central China, to estimate the topside plasma density profiles by using the Chapman ? function and further retrieve Chapman scale height. Evident solar cycle, seasonal variation, and local time variation are presented in the retrieved Chapman scale height over Wuhan. The climatological features of the derived Chapman scale height are significantly different from those from the ground-based ionograms. Such significant discrepancy suggests that further improvements are required in the present extrapolating topside electron density profiles from ionosonde observations. Furthermore, the attempt to constructing plasma density profiles through combining ionosonde and satellite in situ observations provides a new way to reanalyze observations from different sources and normalize plasma density recorded at varying altitudes to specified altitudes, which is critical and more convenient for ionospheric climatology studies.

Liu, Libo; Huang, He; Chen, Yiding; Le, Huijun; Ning, Baiqi; Wan, Weixing; Zhang, Hui

2014-10-01

286

Ionospheric sources for molecular ion outflow  

NASA Astrophysics Data System (ADS)

Mass-resolved satellite observations have established the presence of molecular ions in the low-altitude magnetosphere, outer magnetosphere, and ring current. Associated molecular outflows originate from the auroral zone F-region ionosphere and, while normally several orders of magnitude less intense than the well-known O+ outflow, are perhaps more closely tied to intense geomagnetic disturbances. Molecular outflow is also fundamentally different from O+ outflow, since molecular ions must first be generated in large quantities in the F-region, and then are subject to very short recombination lifetimes as they escape. Owing to observational difficulties, very little detailed information exists on the generation, energization, and upward transport of molecular ions. Furthermore, the basic geographic and geomagnetic activity dependence of the ionospheric source and higher altitude outflow are only loosely constrained. This research synthesizes both observations and models to gain a better understanding of molecular ion generation and upflow, and the basic characteristics of the ionospheric molecular source during geomagnetic storms. To illustrate ionospheric dynamics associated with published satellite observations of molecular upflow, a 2D ionospheric model is driven by boundary conditions consistent with observed field-aligned currents. These simulations provide detailed information about expected species-dependent ion densities, temperatures, fluxes, and associated transients. Similar model results are also compared against PFISR radar estimates of molecular ions generated by auroral arc activity. A detailed case study of the 24-25 Sept. 1998 geomagnetic storm is presented in which the EISCAT ESR and Tromso radars suggested enhancements in F-region molecular ions and Polar satellite simultaneously observed moleculars in the magnetosphere. Finally, data from Sondrestrom and EISCAT radars during multiple storms are combined in an attempt to build a statistical picture of the latitude and magnetic local time dependence of the ionospheric molecular source. Connections of this source with satellite observations of molecular outflow are also discussed.

Zettergren, M. D.; Peterson, W. K.; Blelly, P. F.; Alcayde, D.; Semeter, J. L.

2012-12-01

287

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

288

Large-order behavior and nonperturbative effects  

NASA Astrophysics Data System (ADS)

We consider the energy-dependence of the large-order behavior of forward scattering amplitudes in theories having explicit mass parameters and instanton solutions. We show that in weak coupling theories the exponential part of the Espinosa-Ringwald type cross section can be determined by taking the minimum element of the perturbative series, suggesting that the series is asymptotic. This observation enables us to calculate the nonperturbative cross section by the perturbation of the Borel transform overline?(b) about the instanton-anti-instanton singularity. The anomalous cross section in the standard model using the leading energy-dependent overline?(b) is presented.

Lee, Taekoon

1995-02-01

289

Rocket studies of the lower ionosphere  

NASA Technical Reports Server (NTRS)

The earth's ionosphere in the altitude range of 50 to 200 km was investigated by rocket-borne sensors, supplemented by ground-based measurement. The rocket payloads included mass spectrometers, energetic particle detectors, Langmuir probes and radio propagation experiments. Where possible, rocket flights were included in studies of specific phenomena, and the availability of data from other experiments greatly increased the significance of the results. The principal ionospheric phenomena studied were: winter anomaly in radiowave absorption, ozone and molecular oxygen densities, mid-latitude sporadic-E layers, energetic particle precipitation at middle and low latitudes, ionospheric instabilities and turbulence, and solar eclipse effects in the D and E regions. This document lists personnel who worked on the project, and provides a bibliography of resultant publications.

Bowhill, Sidney A.

1990-01-01

290

Ionospheric RF lidar  

NASA Astrophysics Data System (ADS)

A new diagnostic consisting of a high-power RF or microwave transmitter and a ground-based lidar system is proposed for probing the ionosphere at heights of 80-200 km. The high-power transmitter creates energetic electrons in the ionosphere, which excite molecules to higher energy levels. These excited molecules become targets for a laser ranging system by resonantly absorbing and reradiating light at specific wavelengths. A laser pulse tuned to a specific transition wavelength is fired from a ground-based laser, and the reradiated light is detected by a ground-based light collector. A study of atmospheric species for ranging was performed, and the most suitable species were found to be N2 and N2(+). A laser whose output is matched exactly to the vibrational-rotational spectrum of ionospheric N2 is proposed as the lidar master oscillator instead of a tunable due laser.

Fukuchi, T.; Wong, A. Y.; Wuerker, R. F.

1990-12-01

291

Responses of the equatorial ionosphere of Vietnam to the solar flare of April 3, 2010  

NASA Astrophysics Data System (ADS)

This report presents the results of ionospheric responses to the solar flare of April 3, 2010 observed over Ho Chi Minh city during period from April 3 to April 9, 2010. The results shows that the magnetic storm created enhancement of foF2 and TEC mainly, i.e.negative storm. The positive phase appeared weakly and only in nighttime. The positive phase of the ionospheric storm appears after 4 hours as a response to the magnetic storm. The most dominant effect on the disturbances during this event is the ionospheric dynamo. During the recovery phase, there is a positive phase at 12 UT on April 9, the foF2 values dropped and h’F2 values increased suddenly, but the TEC values not decreased respectively. It suggests that the efforts must be concentrated on the magnetic-ionospheric disturbance dynamo signature at equatorial region in order to better understand the circulation of the various currents generated during this type of long period geomagnetic storms.

Hoang, Thai Lan

292

Handling cycle slips in GPS data during ionospheric plasma bubble events  

NASA Astrophysics Data System (ADS)

During disturbed ionospheric conditions such as the occurrence of plasma bubbles, the phase and amplitude of the electromagnetic waves transmitted by GPS satellites undergo rapid fluctuations called scintillation. When this phenomenon is observed, GPS receivers are more prone to signal tracking interruptions, which prevent continuous measurement of the total electron content (TEC) between a satellite and the receiver. In order to improve TEC monitoring, a study was conducted with the goal of reducing the effects of signal tracking interruptions by correcting for "cycle slips," an integer number of carrier wavelengths not measured by the receiver during a loss of signal lock. In this paper, we review existing cycle-slip correction methods, showing that the characteristics associated with ionospheric plasma bubbles (rapid ionospheric delay fluctuations, data gaps, increased noise, etc.) prevent reliable correction of cycle slips. Then, a reformulation of the "geometry-free" model conventionally used for ionospheric studies with GPS is presented. Geometric information is used to obtain single-frequency estimates of TEC variations during momentary L2 signal interruptions, which also provides instantaneous cycle-slip correction capabilities. The performance of this approach is assessed using data collected on Okinawa Island in Japan during a plasma bubble event that occurred on 23 March 2004. While an improvement in the continuity of TEC time series is obtained, we question the reliability of any cycle-slip correction technique when discontinuities on both GPS legacy frequencies occur simultaneously for more than a few seconds.

Banville, S.; Langley, R. B.; Saito, S.; Yoshihara, T.

2010-12-01

293

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

294

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

295

Ionized Columns between Thunderstorms and the Ionosphere  

Microsoft Academic Search

It is shown that, if electrons of relativistic energies are generated within thunder- storms and then 'run away' upward above the thunderclouds, their range is probably only a few kilometers; their ionizing effects are therefore localized. Calculations indicate, however, that the bremsstrahlung produced during the stoppage of the electrons can create ionized columns extending to ionospheric heights (about 100 kin).

R. K. COLE

1966-01-01

296

Low Frequency Rada Sounding Through Martian Ionosphere  

NASA Technical Reports Server (NTRS)

In remote radar sounding, it is highly desirable to operate at low frequencies to improve depth of penetration. For spaceborne sounders, the lowest operating frequency is limited by the effect of the ionosphere due to significant dispersion of the radar waves at near plasma frequency.

Safaeinili, A.; Jordan, R.

2000-01-01

297

Evaluation of ionospheric profilers using topside sounding data  

NASA Astrophysics Data System (ADS)

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

298

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

299

Response of migrating tides to the stratospheric sudden warming in 2009 and their effects on the ionosphere studied by a whole atmosphere-ionosphere model GAIA with COSMIC and TIMED/SABER observations  

NASA Astrophysics Data System (ADS)

This paper compares results from a whole atmosphere-ionosphere coupled model, GAIA, with the COSMIC and TIMED/SABER observations during the 2008/2009 northern winter season. The GAIA model has assimilated meteorological reanalysis data by a nudging method. The comparison shows general agreement in the major features from the stratosphere to the ionosphere including the growth and decay of the major stratospheric sudden warming (SSW) event in 2009. During this period, a pronounced semidiurnal variation in the F region electron density and its local-time phase shift similar to the previous observations are reproduced by the model and COSMIC observation. The model suggests that the electron density variation is caused by an enhanced semidiurnal variation in the E × B drift, which is probably related to an amplified semidiurnal migrating tide (SW2) in the lower thermosphere. The model and TIMED/SABER observation show that the SW2 tide amplifies at low latitudes from the stratosphere to the thermosphere as well as the phase variation. Possible mechanisms for the SW2 variability in the low latitude stratosphere could be the change of its propagation condition, especially the (2, 2) mode, due to changing zonal background wind and meridional temperature gradient, and/or an enhancement of its source due to redistribution of stratospheric ozone. Present results also show a prominent long-term variation of the terdiurnal migrating component (TW3) in the ionosphere and atmosphere.

Jin, H.; Miyoshi, Y.; Pancheva, D.; Mukhtarov, P.; Fujiwara, H.; Shinagawa, H.

2012-10-01

300

21 CFR 12.38 - Effective date of an order.  

Code of Federal Regulations, 2010 CFR

...Effective date of an order. 12.38 Section 12.38 Food and Drugs FOOD AND DRUG ADMINISTRATION...Commissioner may issue a final order covering all the drug or device products...more than one final order covering different drug or device...

2010-04-01

301

21 CFR 12.38 - Effective date of an order.  

Code of Federal Regulations, 2013 CFR

...Effective date of an order. 12.38 Section 12.38 Food and Drugs FOOD AND DRUG ADMINISTRATION...Commissioner may issue a final order covering all the drug or device products...more than one final order covering different drug or device...

2013-04-01

302

21 CFR 12.38 - Effective date of an order.  

Code of Federal Regulations, 2011 CFR

...Effective date of an order. 12.38 Section 12.38 Food and Drugs FOOD AND DRUG ADMINISTRATION...Commissioner may issue a final order covering all the drug or device products...more than one final order covering different drug or device...

2011-04-01

303

21 CFR 12.38 - Effective date of an order.  

...Effective date of an order. 12.38 Section 12.38 Food and Drugs FOOD AND DRUG ADMINISTRATION...Commissioner may issue a final order covering all the drug or device products...more than one final order covering different drug or device...

2014-04-01

304

21 CFR 12.38 - Effective date of an order.  

Code of Federal Regulations, 2012 CFR

...Effective date of an order. 12.38 Section 12.38 Food and Drugs FOOD AND DRUG ADMINISTRATION...Commissioner may issue a final order covering all the drug or device products...more than one final order covering different drug or device...

2012-04-01

305

Observations of Midlatitude Ionospheric  

Microsoft Academic Search

Using data from the available networks of GPS receivers (CORS and FAA WAAS), observations of rapid drops in TEC (as much as 14 meters of ionospheric delay or 84 TECu within 100 seconds) have been observed in mid-latitudes during major geomagnetic storms. Investigations of these TEC drops have suggested that the drops were due to what appeared to be \\

T. F. Dehel; A. J. Mannucci; A. Komjathy; X. Pi

2004-01-01

306

Seismo-Ionospheric Phenomena  

NASA Astrophysics Data System (ADS)

Ionospheric F-region disturbances and anomalous foEs increases were separately observed within a few days before two great earthquakes in geomagnetic and solar quiet conditions. The ionospheric foF2 decreased from its monthly median at Wakkanai, 290 km north of the epicenter from 3 days before the M 7.8 earthquake onset of July 12, 1993 in the northern Japan to 3 days after it. Anomalous foEs increases above 7 MHz were observed at Shigaraki, 100 km northeast of the epicenter in the daytime on January 15, 1995 before the M 7.2 Hyogoken-nambu earthquake onset of January 17, 1995. The F-region disturbances before the earthquake is discussed in terms of the ionospheric vertical movements caused by a seismo electric field on the assumption of the global ionosphere-earth seismo current system. The anomalous foEs increases before the earthquake onset could be, caused by unknown super-volt seismo discharges since there was no thunderstorm cloud over the observatories

Ondoh, Tadanori

307

The Venus ionosphere  

Microsoft Academic Search

Physical properties of the Venus ionosphere obtained by experiments on the US Pioneer Venus and the Soviet Venera missions are presented in the form of models suitable for inclusion in the Venus International Reference Atmosphere. The models comprise electron density (from 120 km), electron and ion temperatures, and relative ion abundance in the altitude range from 150 km to 1000

S. J. Bauer; L. M. Brace; H. A. Taylor Jr.; T. K. Breus; A. J. Kliore

1985-01-01

308

The Dayside Ionospheric \\  

Microsoft Academic Search

Prompt penetration electric fields (PPEFs) and the consequential dayside ionospheric superfountain (DIS) are reviewed. An example of O + uplift to ~840 km altitude at ~0940 local time (DMSP F15) during the superstorm of 30 October 2003 is illustrated. The SAMI-2 model is modified to incorporate intense superstorm electric fields. With an inclusion of a ~4 mV\\/m eastward electric field,

B. T. Tsurutani; A. Saito; O. P. Verkhoglyadova; A. J. Mannucci; M. A. Abdu; T. Araki; W. D. Gonzalez; T. Tsuda; K. Yumoto

2006-01-01

309

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

310

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

311

Response-Order Effect in Likert-Type Scales.  

ERIC Educational Resources Information Center

The importance of the presentation order of items on Likert-type scales was studied. It was proposed that subjects tend to choose the first alternative acceptable to them from among the response categories, so that a primacy effect can be predicted. The effects of reversing the order of the response scale on the latent factor structure underlying…

Chan, Jason C.

312

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

313

A numerical study of atmospheric signals in the Earth-ionosphere electromagnetic cavity with the Transmission Line Matrix method  

NASA Astrophysics Data System (ADS)

The effect of the Earth-ionosphere electromagnetic cavity on the spectrum of an atmospheric signal generated by a broadband electrical current source is analyzed numerically by means of the Transmission Line Matrix (TLM) method. Two new TLM meshes are developed, one with transmission lines connected in parallel and the other with connections in series. The equations describing propagation through these parallel or series meshes are equivalent to the Maxwell equations for TEr or TMr modes in the spherical Earth-ionosphere cavity, respectively. The numerical algorithm obtains Schumann resonance frequencies very close to the experimental ones, confirming that this methodology is a valid numerical tool for predicting these resonances on other planets and moons. Finally, the TEr and TMr modes with a higher order than the Schumann resonances are also analyzed, finding that the effect of atmospheric conductivity is to shift the peak frequencies toward higher values than the eigenfrequencies corresponding to the lossless system. For daytime conditions, these peak frequencies appear around 2, 4, 6, 8… kHz, connected to an effective aboveground ionosphere height of approximately 75 km. In the night region, the shift is slightly smaller and the effective ionosphere height is around 85 km in agreement with smaller values in the conductivity profile.

Morente, Juan A.; Portí, Jorge A.; Besser, Bruno P.; Salinas, Alfonso; Lichtenegger, Herbert I. M.; Navarro, Enrique A.; Molina-Cuberos, Gregorio J.

2006-10-01

314

Near real-time monitoring of the ionosphere using dual frequency GPS data in a Kalman filter approach  

Microsoft Academic Search

The ionosphere is an important source of errors for the GPS signals that travel through the ionosphere on their way to the ground-based receivers by introducing a frequency dependent path delay proportional to the total electron content (TEC) along the signal path. For dual-frequency GPS receivers, the ionospheric effects can be accounted for by taking advantage of the dispersive nature

Adela Anghel; Adina Astilean; Tiberiu Letia; Attila Komjathy

2008-01-01

315

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

316

Emissions of ionospheric Alfvén resonator and ionospheric conditions  

NASA Astrophysics Data System (ADS)

We analyze continuous magnetic observations of ionospheric Alfvén resonator (IAR) emissions at mid-latitude observatory Mondy. The measurements were by a LEMI-30 search-coil magnetometer covering the period from March 2010 to May 2011. The results are compared with data from simultaneous ionospheric sounding data and International Reference Ionosphere (IRI-2012) model parameters. The large amount of observational data allowed us to inspect the daily and seasonal variations in some morphological characteristics of the emissions as well as their relationship to ionospheric conditions. The main factor affecting the duration of the emission is how long the lower ionosphere stays in Earth's shadow. We demonstrate a close inverse correlation between the diurnal and seasonal IAR frequency variations, on the one hand, and changes in the ionospheric critical frequency, f0F2, on the other. Additionally, the expected emission frequency scale calculated with the IRI-2012 model is in good agreement with the values measured from the emission spectrograms.

Potapov, A. S.; Polyushkina, T. N.; Dovbnya, B. V.; Tsegmed, B.; Rakhmatulin, R. A.

2014-11-01

317

Development and error analysis of nonlinear ionospheric removal algorithm for ionospheric electron density determination using broadband RF data  

NASA Astrophysics Data System (ADS)

The first documented, empirical comparisons are provided of four methods to retrieve total electron content (TEC) that use broadband, impulsive events detected by satellite in the lower very high frequency range (20-150 MHz). The four TEC retrieval methods are the quasi-longitudinal approximation (i.e., Taylor expansion) of the Appleton-Hartree (A-H) dispersion relation to the first and second orders, as well as the nonlinear ionospheric removal algorithm (NIRA) that utilizes the A-H dispersion equation directly to model the propagation of an electromagnetic wave through the ionosphere. NIRA solves not only for TEC between the ground source and satellite, but also for higher-order ionospheric terms, such as electron density, ionospheric thickness, and angle between wave vector and magnetic field. Regimes of validity for each TEC retrieval method are analyzed by comparison of the parameters retrieved from synthetic data with a known ionosphere and from RF FORTE satellite data measurements of a ground-based broadband transmitter. Results include a comparison between TEC and infinite frequency time of arrival (to) determined by NIRA and determined by using the first- and second-order terms from the Taylor expansion of the A-H equation. Plasma density, ionospheric thickness, and angle between magnetic field and wave vector as determined by the two NIRA methods are also compared.

Lay, E. H.; Close, S.; Colestock, P.; Bust, G.

2011-02-01

318

Investigation of Electron Density Profile in the Lowest Ionosphere by SRP-4 rocket experiment  

NASA Astrophysics Data System (ADS)

The radio wave propagation characteristic in the lower ionosphere is important because of its effect on commercial radio communication, navigation, and broadcast services. The electron density is of primary interest in this region because the high ion-neutral collision frequencies result in radio wave absorption. Previous studies have examined the electron density profile and structure of the ionosphere using the rocket and satellite measurements. The standard International Reference Ionosphere (IRI) model gives the estimated electron density profile based on the measurements, but no sufficient measurements have been accumulated below 65 km to estimate the model ionosphere to lower altitudes. In order to investigate the ionization structure in the altitude below 90 km by means of MF-band signals propagation, the Alaska rocket SRP-4 experiments has been carried out. The rocket was launched at 12:08 LT on March 18, 2002 at Poker Flat Research Range. The apex of rocket trajectory was about 89 km. We observed three different signals, CHENA (257 kHz), KFAR (660 kHz) and KCBF (820 kHz), transmitted from navigation and broadcast stations near Fairbanks, Alaska. Three signals were successfully observed from an altitude 0 km - 89 km during the ascent flight. The intensity of 257 kHz signal decreases steeply at an altitude higher than 65 km and reflects perfectly at about 75 km. The altitudes of perfect reflection of 660 kHz and 820 kHz signals are about 79 km and about 81 km, respectively. The approximate electron density profile can be determined from the comparison between these experimental results and propagation characteristics calculated by the full wave method. We will get the most probable electron density profile in the lowest ionosphere below 65 km.

Ishisaka, K.; Okada, T.; Hawkins, J. G.; Murakami, S.; Miyake, T.; Nagano, I.; Matsumoto, H.

2002-12-01

319

Pressure-driven and ionosphere-driven modes of magnetospheric interchange instability  

NASA Astrophysics Data System (ADS)

A general stability criterion for magnetospheric interchange instability, which includes an ionospheric destabilizing contribution, is derived for an arbitrary finite-? magnetospheric model satisfying the magnetohydrostatic force balance. The derivation is based on the magnetospheric energy principle. Unperturbed field-aligned currents in finite-? nonaxisymmetric magnetospheric models are assumed to close via diamagnetic currents in the magnetosphere or in the ionosphere. By exploiting the limit of a very large perpendicular wave number and the eikonal representation for the perpendicular plasma displacement, the magnetospheric interchange mode is shown to be compressible. In this limit the kink mode makes no contribution to the change in the magnetospheric potential energy. By using magnetospheric flux coordinates, the explicit form of the magnetospheric potential energy change is calculated for interchange perturbations, which do not bend magnetospheric magnetic fields. For a nonaxisymmetric finite-? magnetospheric model, a combined effect of the pressure gradient and field line curvature, not only in the meridional plane but also in the plane parallel to the longitudinal direction, is responsible for pressure-driven interchange instability. For an axisymmetric, north-south symmetric and low-? magnetospheric model, in which the magnetic field is approximated by a dipole field, the m = 1 or m = 2 ionosphere-driven mode, where m is the azimuthal mode number, has an upper critical equatorial ? value for instability in the order of 1. Thus a substantial region of the inner magnetosphere or the near-Earth magnetosphere may be unstable against ionosphere-driven interchange instability caused by a horizontal plasma displacement on the spherical ionospheric surface.

Miura, Akira

2009-02-01

320

Satellite measurement of ionospheric-induced vhf distortion  

SciTech Connect

BLACKBEARD is a satellite RF experiment designed to study distortion and interference effects on transient transionospheric VHF signals. RF distortion will be characterized by a frequency-coherence bandwidth for different ionospheric conditions. Limitations of broad-band measurements from the frequency-coherence bandwidth of the ionosphere and broadcast interference signals will be established through these studies. Distinction between multi-path distortion resulting from large scale, coherent perturbations and small scale, random perturbations to the ionosphere will be emphasized. Ionospheric transfer function models, trans-ionospheric signal predictions, and coherence bandwidth predictions will be tested and optimized with these measurements. A global data base for both broadcast and lightning interference will also derive from these studies. This database will form the basis for interference feature extraction, signal typing, and possible neural network cataloging. The specific missions of the BLACKBEARD experiment include: perform broad-band VHF measurements of transient signals originating from a controlled pulsed ground beacon, to characterize broad-band ionospheric distortion, perform narrow-band VHF measurements of cw signals from a multi-chord interferometry ground beacon array, to characterize ionospheric structure contributing to transmission distortion, and survey power envelopes of lightning and man-made interference in selectable VHF bands, for background rejection purposes. BLACKBEARD is part of the ALEMS soft x-ray measurement satellite, a small satellite system designed for a PEGASUS launch into a 70{degrees} inclination, low earth orbit in late 1992.

Armstrong, W.T.; Murphy, T.; Roussel-Dupre, R.; Carter, M.J.; Blevins, B.

1992-01-01

321

Satellite measurement of ionospheric-induced vhf distortion  

SciTech Connect

BLACKBEARD is a satellite RF experiment designed to study distortion and interference effects on transient transionospheric VHF signals. RF distortion will be characterized by a frequency-coherence bandwidth for different ionospheric conditions. Limitations of broad-band measurements from the frequency-coherence bandwidth of the ionosphere and broadcast interference signals will be established through these studies. Distinction between multi-path distortion resulting from large scale, coherent perturbations and small scale, random perturbations to the ionosphere will be emphasized. Ionospheric transfer function models, trans-ionospheric signal predictions, and coherence bandwidth predictions will be tested and optimized with these measurements. A global data base for both broadcast and lightning interference will also derive from these studies. This database will form the basis for interference feature extraction, signal typing, and possible neural network cataloging. The specific missions of the BLACKBEARD experiment include: perform broad-band VHF measurements of transient signals originating from a controlled pulsed ground beacon, to characterize broad-band ionospheric distortion, perform narrow-band VHF measurements of cw signals from a multi-chord interferometry ground beacon array, to characterize ionospheric structure contributing to transmission distortion, and survey power envelopes of lightning and man-made interference in selectable VHF bands, for background rejection purposes. BLACKBEARD is part of the ALEMS soft x-ray measurement satellite, a small satellite system designed for a PEGASUS launch into a 70{degrees} inclination, low earth orbit in late 1992.

Armstrong, W.T.; Murphy, T.; Roussel-Dupre, R.; Carter, M.J.; Blevins, B.

1992-09-01

322

Ionospheric refraction corrections in the GTDS for satellite-to-satellite tracking data  

Microsoft Academic Search

In satellite-to-satellite tracking (SST) geographic as well as diurnal ionospheric effects must be contended with, for the line of sight between satellites can cross a day-night interface or lie within the equatorial ionosphere. These various effects were examined and a method of computing ionospheric refraction corrections to range and range rate measurements with sufficient accuracy were devised to be used

G. Nesterczuk; J. K. Kozelsky

1976-01-01

323

Ionospheric Alfvén resonator response to remote earthquakes  

NASA Astrophysics Data System (ADS)

The ionospheric Alfvén resonances (IARs) are an interesting wave phenomenon well described in the literature. The IAR formation region is located between two bends of the plasma density profile: in the lower part of the ionospheric F region and at altitudes of about 1000-3000 km. In this region, Alfvén waves are entrapped and form standing waves. The quality factor of the resonator can attain a value of 5-10. We studied local IAR features using data of the Borok Geophysical Observatory (58°N, 38° E) and found that the ionospheric Alfvén resonances observed as geomagnetic pulsations at frequencies of a few hertz respond to remote seismic events. There are different kinds of the seismic wave effect on the IARs mode: sometimes the oscillations arise after an earthquake moment, in other cases they sharply decay, and sometimes they abruptly change their intensity. Among possible mechanisms of the earthquake action on the ionosphere acoustic and electromagnetic waves emerged by a seismic shock are discussed. The work was supported by the RFBR grants 09-05-00048 and 10-05-00661.

Potapov, Alexander S.; Dovbnya, Boris V.; Tsegmed, Battuulai

2010-05-01

324

Configuration of the upper boundary of the ionosphere  

NASA Astrophysics Data System (ADS)

Variations of the upper boundary of the ionosphere (UBI) are investigated based on three sources of information: (i) ionosonde-derived parameters: critical frequency foF2, propagation factor M3000F2, and sub-peak thickness of the bottomside electron density profile; (ii) total electron content (TEC) observations from signals of the Global Positioning System (GPS) satellites; (iii) model electron densities of the International Reference Ionosphere (IRI*) extended towards the plasmasphere. The ionospheric slab thickness is calculated as ratio of TEC to the F2 layer peak electron density, NmF2, representing a measure of thickness of electron density profile in the bottomside and topside ionosphere eliminating the plasmaspheric slab thickness of GPS-TEC with the IRI* code. The ratio of slab thickness to the real thickness in the topside ionosphere is deduced making use of a similar ratio in the bottomside ionosphere with a weight Rw. Model weight Rw is represented as a superposition of the base-functions of local time, geomagnetic latitude, solar and magnetic activity. The time-space variations of domain of convergence of the ionosphere and plasmasphere differ from an average value of UBI at ˜1000 km over the earth. Analysis for quiet monthly average conditions and during the storms (September 2002, October-November 2003, November 2004) has shown shrinking UBI altitude at daytime to 400 km. The upper ionosphere height is increased by night with an ‘ionospheric tail’ which expands from 1000 km to more than 2000 km over the earth under quiet and disturbed space weather. These effects are interposed on a trend of increasing UBI height with solar activity when both the critical frequency foF2 and the peak height hmF2 are growing during the solar cycle.

Gulyaeva, Tamara L.

2007-06-01

325

Predictions of the effects of Mars's encounter with comet C/2013 A1 (Siding Spring) upon metal species in its ionosphere  

NASA Astrophysics Data System (ADS)

The infall of dust from the coma of comet C/2013 A1 (Siding Spring) and its subsequent ablation in the atmosphere of Mars has the potential to affect the abundances of metal species in the atmosphere and ionosphere. We develop relationships between properties of the dust population in the coma and densities of metal species in the atmosphere and ionosphere. These can be used to predict the abundances of metal species in the atmosphere and ionosphere during the encounter. Given postencounter observations of the atmosphere and ionosphere, they can also be used to infer relevant cometary properties. Although current predictions suggest that the influx of cometary dust will be comparable to the sporadic background, the higher entry speed involved, which leads to a greater production rate of ions during ablation, means that metal ion abundances may be enhanced during and after the encounter.

Withers, Paul

2014-10-01

326

Multi-station observation of ionospheric irregularities over South Africa during strong geomagnetic storms  

NASA Astrophysics Data System (ADS)

This paper presents results pertaining to the response of the mid-latitude ionosphere to strong geomagnetic storms that occurred from 31 March to 02 April 2001 and 07-09 September 2002. The results are based on (i) Global Positioning Systems (GPSs) derived total electron content (TEC) variations accompanying the storm, (ii) ionosonde measurements of the ionospheric electrodynamic response towards the storms and (iii) effect of storm induced travelling ionospheric disturbances (TIDs) on GPS derived TEC. Ionospheric data comprising of ionospheric TEC obtained from GPS measurements, ionograms, solar wind data obtained from Advanced Composition Explorer (ACE) and magnetic data from ground based magnetometers were used in this study. Storm induced features in vertical TEC (VTEC) have been obtained and compared with the mean VTEC of quiet days. The response of the mid-latitude ionosphere during the two storm periods examined may be characterised in terms of increased or decreased level of VTEC, wave-like structures in VTEC perturbation and sudden enhancement in hmF2 and h?F. The study reveals both positive and negative ionospheric storm effects on the ionosphere over South Africa during the two strong storm conditions. These ionospheric features have been mainly attributed to the travelling ionospheric disturbances (TIDs) as the driving mechanism for the irregularities causing the perturbations observed. TEC perturbations due to the irregularities encountered by the satellites were observed on satellites with pseudo random numbers (PRNs) 15, 17, 18 and 23 between 17:00 and 23:00 UT on 07 September 2002.

Amabayo, Emirant Bertillas; Cilliers Pierre, J.

2013-03-01

327

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

2015-01-01

328

The Dayside Ionospheric  

Microsoft Academic Search

Prompt penetration electric fields (PPEFs) and the consequential dayside ionospheric superfountain (DIS) are reviewed. An example of O+ uplift to ~840 km altitude at ~0940 local time (DMSP F15) during the superstorm of 30 October 2003 is illustrated. The SAMI-2 model is modified to incorporate intense superstorm electric fields. With an inclusion of a ~4 mV\\/m eastward electric field, SAMI-2*

B. T. Tsurutani; A. Saito; O. P. Verkhoglyadova; A. J. Mannucci; M. A. Abdu; T. Araki; W. D. Gonzalez; B. A. Iijima; G. S. Lakhina; H. McCreadie; J. H. A. Sobral; T. Tsuda; K. Yumoto; V. M. Vasyliunas

2006-01-01

329

Comparison between ionospheric convection vortices and the associated equivalent currents  

Microsoft Academic Search

The equivalent current pattern derived from CANOPUS, NRCAN\\/GSC and MACCS magnetometers has been compared with the ionospheric convection pattern observed by SuperDARN HF radars. The discrepancies between the equivalent convection (EQC) and the SuperDARN-observed convection (SDC) patterns are explained in terms of the effect of day-night photoionization conductance gradient and the coupling between field-aligned currents (FACs) and ionospheric conductances. In

J. Liang; L. Benkevitch; G. J. Sofko; A. V. Koustov

2004-01-01

330

2-dimensional FDTD simulations of plasma wave propagations in the ionosphere  

NASA Astrophysics Data System (ADS)

We developed a 2-dimensional FDTD simulation code which can treat wave propagations in magnetized plasma. Though we need to perform full particle simulations in order to recognize accurate characteristics of waves propagating in space plasma, FDTD simulations can be performed with much less computer resources than those necessary for full particle simulations, in memories as well as cpu times. Since space plasma is magnetized, it is necessary to incorporate the dielectric tensor with anisotropy and dispersibility in FDTD simulation code, in order to calculate the electromagnetic field in space plasma. We use PLRC method to formulization FDTD scheme to reduce numerical errors. In FDTD simulations, it is essential that how to realize an effective absorbing boundary. We developed PML absorbing boundary condition with anisotropy and dispersibility, and succeeded to realize very effective absorbind boundary. According to the rocket observations, we can receive MF radio wave above the dense ionospheric layer whose density is larger than those corresponding to cutoff frequency of MF radio wave. We consider that this is because the thickness of the ionopheric layer is smaller than the wavelength of MF radio wave, the density of ionospheric layer is not constant in the horizontal plane. We have been analyzing the characteristics of MF wave propagation in the ionospher with Full-wave method. In the Full-wave method, since the electron density profile is assumed to change in one-dimensional corrsponding to the alititude, we can only treat one-dimensional electron density profiles. In this study, therefore, we performed a series of FDTD simulations of MF wave propagations in ionospheres with several types of electron density distributions in the horizontal plane, such as electron dense cloud, sporadic layer, etc., and studied the relation between spatial scale of ionospheric layer and MF radio wavelength. In addition, we performed a FDTD simulation of MF radio wave propagations with the ionospheric layer model which is estimated by Full-wave analysis of S-310-37 sounding rocket observations. S-310-37 sonding rocket was launched at USC (Uchinoura Space Center, Kagoshima) in Jan. 2007. We are going to compare FDTD simulation results, Full-wave analysis and rocket observations, and study the influence of electron density profile on the propagation characterictics of MF radio wave in the ionosphere.

Miyake, T.; Yoshino, S.; Okada, T.; Ishisaka, K.

2007-12-01

331

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

332

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

NASA Astrophysics Data System (ADS)

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.

1984-09-01

333

Dark Solitons in Optical Fibers with Higher Order Effects  

Microsoft Academic Search

We consider the higher order nonlinear Schrödinger (HNLS) equation, which governs the nonlinear wave propagation in optical fibers with higher order effects. Lax pair associated with the integrable HNLS equation for the pulse propagation in normal dispersion regime of the fiber media is constructed with the help of Ablowitz-Kaup-Newell-Segur method. Using Hirota bilinear method, dark soliton solution is explicitly derived.

K. Nakkeeran

2002-01-01

334

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

335

The near-equatorial terminator ionosphere of Saturn  

NASA Astrophysics Data System (ADS)

The Cassini orbiter has provided 12 opportunities for three-frequency radio occultations of the rings, atmosphere, and ionosphere of Saturn between May and September of 2005. By virtue of being optimized for the ring observations, these occultations provided measurements of the Saturnian ionosphere in a range of latitudes from about 7 deg. S to about 5 deg.N, and solar zenith angles of about 85 deg. to 95 deg., near both the dawn and dusk terminators. The dawn ionospheres have peak densities about a factor of 5 lower than their dusk counterparts, possibly indicating the depleting effect of water molecules migrating from the rings, while on the night side. The search for a ring ionosphere has also been carried out, and its results will be reported.

Kliore, A. J.; Nagy, A. F.; Anabtawi, A.; Asmar, S. W.

2005-12-01

336

Low-latitude ionosphere dynamics as deduced from meridional ionosonde chain: Ionospheric ceiling  

NASA Astrophysics Data System (ADS)

Interest in the equatorial anomaly in the ionosphere has been focused mostly on f_oF_2, and not much attention was paid to h_mF_2 except for the time rate of change of it in connection with the vertical plasma drift velocity. There have been few climatological studies on h_mF_2 variations associated with development of the equatorial anomaly. In this paper, we revisit the equatorial anomaly in terms of height variations. For this purpose, we analyzed scaled ionogram parameters from three stations located along the magnetic meridian that is a primary component of Southeast Asia low-latitude ionospheric network (SEALION); one at the magnetic equator and the others at conjugate off-equatorial latitudes near 10 degrees magnetic latitude. The daytime h_mF_2 was investigated for each season during the solar minimum period, 2006-2007 and 2009. The peak height increased for approximately 3 hr after sunrise at all locations, as expected from the daytime upward E×B drift. The apparent upward drift ceased before noon at the magnetic equator, while the layer continued to increase at the off-equatorial latitudes, reaching altitudes higher than the equatorial height around noon. The noon time restricted layer height at the magnetic equator did not depend much on the season, while the maximum peak height at the off-equatorial latitudes largely varied with season. The daytime specific limiting height of the equatorial ionosphere was termed ionospheric ceiling. Numerical modeling using the SAMI2 code reproduced the features of the ionospheric ceiling quite well. Dynamic parameters provided by the SAMI2 modeling were investigated and it was shown that the ionospheric ceiling is another aspect of the fountain effect, in which increased diffusion of plasma at higher altitudes has a leading role.

Maruyama, Takashi; Uemoto, Junpei; Tsugawa, Takuya; Supnithi, Pornchai; Ishii, Mamoru; Komolmis, Tharadol

337

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

338

Self-Consistent Magnetosphere-Ionosphere Coupling: Theoretical Studies  

NASA Technical Reports Server (NTRS)

A self-consistent ring current (RC) model has been developed that couples electron and ion magnetospheric dynamics with the calculation of the electric field. Two new features were taken into account in order to close the self-consistent magnetosphere- ionosphere coupling loop. First, in addition to the RC ions, we solve an electron kinetic equation in our model. Second, using the relation of Galand and Richmond [2001], we calculate the height integrated ionospheric conductances as a function of the precipitated high energy magnetospheric electrons and ions that are produced by our code. To validate the results of our model we simulate the magnetic storm of May 2, 1986, a storm that has has been comprehensively studied, and compare our results with different theoretical approaches. The self-consistent inclusion of the hot electrons and, their effect on the conductance results in deeper penetration of the magnetospheric electric field. In addition, a slight westward rotation of the potential pattern (compared to previous self-consistent results) is evident in the inner magnetosphere. This changes the hot plasma distribution, especially by allowing increased access of plasma sheet ions and electrons to low L shells.

Khazanov, G. V.; Newman, T. S.; Liemohn, M. W.; Fok, M.-C.; Spiro, R. W.; Six, N. Frank (Technical Monitor)

2002-01-01

339

Chemical depletion of the ionosphere  

NASA Technical Reports Server (NTRS)

A theoretical study of the chemical and gas dynamical processes resulting from the release of reactive gases into the daytime ionosphere is discussed. Only point releases, such as from an explosion or a pulsed jet, are considered. Some scientific uses of the artificial reduction of the ionospheric plasma are considered.

Bernhardt, P. A.; Darosa, A. V.; Park, C. G.

1977-01-01

340

Mass spectrometry in ionospheric research.  

PubMed

Mass spectrometry played a key role in the development of the understanding of the earth's ionosphere. Of primary importance was its use for in situ atmospheric measurements of the ion and neutral composition of the atmosphere. Mass spectrometry has also played an essential role in the laboratory measurement of critical ionospheric molecular processes. Examples of both are given. PMID:17099890

Ferguson, Eldon E

2007-01-01

341

D-region ionosphere response to the total solar eclipse of 22 July 2009 deduced from ELF-VLF tweek observations in the Indian sector  

Microsoft Academic Search

Study of total solar eclipse effect on D-region ionosphereRare observation of tweek radio atmospherics during total solar eclipseSolar eclipse time D-region ionosphere modulation studied from tweeks observation

Rajesh Singh; B. Veenadhari; Ajeet K. Maurya; Morris B. Cohen; Sushil Kumar; R. Selvakumaran; P. Pant; Abhay K. Singh; Umran S. Inan

2011-01-01

342

Ionospheric total electron content estimation for single-frequency global positioning system receivers  

NASA Astrophysics Data System (ADS)

The ionosphere delays transmissions from the Global Positioning System (GPS) as well as those from other satellite systems. At the GPS frequencies (L-Band), this delay is directly proportional to the total ionospheric electron content (TEC) along the line-of-sight to the satellite. Classified receivers have access to 2 frequencies, to allow them to measure this delay through the difference in the ionospheric effect at the 2 frequencies, but commercial, single-frequency receivers had no direct method for estimating the ionospheric delay; thay have had to rely on a TEC prediction. Two methods are described for single-frequency GPS receivers to estimate the ionospheric TEC directly. These methods take advantage of the dispersive nature of the ionosphere at L-Band frequencies, which causes a phase advance of the carrier that is opposite to the group delay of the GPS code and data.

Smith, Carey A.

343

Response of the ionosphere to the Baltic Sea earthquake of 21 September 2004  

NASA Astrophysics Data System (ADS)

GPS observations of the European permanent network were used to identify seismo-ionospheric precursors of Baltic Sea earthquake of 21 September 2004. It is a very rare event for this region of Europe (magnitude of about 5.0). This value is the threshold for the occurrence of seismic effects in the ionosphere. In total electron content (TEC) data over the region of the earthquake, a specific ionospheric anomaly appeared one day before the earthquake was detected. The ionospheric variability had a positive sign with an enhancement of about 4-5 TECU (1 TECU = 1016 electrons/m2) relative to the non-disturbed state of the ionosphere. The anomaly had a duration of 4-5 hours in the day time. The special size of this anomaly was about 1000 km. The characteristic parameters of the anomaly show that it can be associated with ionospheric precursors of an earthquake.

Krankowski, Andrzej; Zakharenkova, Irina E.; Shagimuratov, Irk I.

2006-03-01

344

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

345

Auroral and photoelectron fluxes in cometary ionospheres  

NASA Astrophysics Data System (ADS)

The analytical yield spectrum method has been used to ascertain photoelectron and auroral electron fluxes in cometary ionospheres, with a view to determining the effects of cometocentric distances, solar zenith angle, and solar minimum and maximum conditions. Auroral electron fluxes are thus calculated for monoenergetic and observed primary electron spectra; auroral electrons are found to make a larger contribution to the observed electron spectrum than EUV-generated photoelectrons. Good agreement is established with extant theoretical works.

Bhardwaj, A.; Haider, S. A.; Spinghal, R. P.

1990-05-01

346

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

347

INSPIRE: Ionosphere Radio Experiments  

NSDL National Science Digital Library

This site, courtesy of Interactive NASA Space Physics Ionosphere Radio Experiments (INSPIRE,) monitors atmospheric sounds that are largely caused by lightning at radio frequencies. The page allows you to listen in on sferics, tweeks, whistlers and other strangely named sounds. This research is in an experimental stage, the site states: "This is an experimental resource. We hope to maintain the VLF audio stream 24 hours a day with infrequent interruptions for maintenance. However, we can't guarantee that it will be available all the time. Let us know if you encounter problems." This is an interesting resource for those interested in atmospheric science or space study.

Philips, Tom

2009-03-25

348

Higher-Order Effects Induced Optical Solitons in Fiber  

Microsoft Academic Search

In this paper, we study the existence conditions of the soliton solutions induced by considering the higher-order effects such as the third-order dispersion (TOD), self-steepening (SS), and self-frequency shift arising from stimulated Raman scattering (SRS) simultaneously in optical soliton communication. Based on the Jacobian expansion method, we successfully obtain bright and dark solitons. The results shows that the resultant inclusion

Yang Qin; Dai Chao-Qin; Zhang Jie-Fang

2005-01-01

349

The Second-Order Talbot Effect with Entangled Photon Pairs  

E-print Network

The second-order Talbot effect is analyzed for a periodic object illuminated by entangled photon pairs in both the quantum imaging and quantum lithography configurations. The Klyshko picture is applied to describe the quantum imaging scheme, in which self-images of the object that may or may not be magnified can be observed nonlocally in the photon coincidences but not in the singles count rate. In the quantum lithography setup, we find that the second-order Talbot length is half that of the classical first-order case, thus the resolution may be improved by a factor of two.

Luo, Kai-Hong; Chen, Xi-Hao; Liu, Qian; Xiao, Min; Wu, Ling-An

2009-01-01

350

Second-order Talbot effect with entangled photon pairs  

NASA Astrophysics Data System (ADS)

The second-order Talbot effect is analyzed for a periodic object illuminated by entangled photon pairs in both the quantum imaging and quantum lithography configurations. The Klyshko picture is applied to describe the quantum imaging scheme, in which self-images of the object that may or may not be magnified can be observed nonlocally in the photon coincidences but not in the singles count rate. In the quantum lithography setup, we find that the second-order Talbot length is half that of the classical first-order case, thus the resolution may be improved by a factor of 2.

Luo, Kai-Hong; Wen, Jianming; Chen, Xi-Hao; Liu, Qian; Xiao, Min; Wu, Ling-An

2009-10-01

351

The Second-Order Talbot Effect with Entangled Photon Pairs  

E-print Network

The second-order Talbot effect is analyzed for a periodic object illuminated by entangled photon pairs in both the quantum imaging and quantum lithography configurations. The Klyshko picture is applied to describe the quantum imaging scheme, in which self-images of the object that may or may not be magnified can be observed nonlocally in the photon coincidences but not in the singles count rate. In the quantum lithography setup, we find that the second-order Talbot length is half that of the classical first-order case, thus the resolution may be improved by a factor of two.

Kai-Hong Luo; Jianming Wen; Xi-Hao Chen; Qian Liu; Min Xiao; Ling-An Wu

2009-09-24

352

Second-order Talbot effect with entangled photon pairs  

SciTech Connect

The second-order Talbot effect is analyzed for a periodic object illuminated by entangled photon pairs in both the quantum imaging and quantum lithography configurations. The Klyshko picture is applied to describe the quantum imaging scheme, in which self-images of the object that may or may not be magnified can be observed nonlocally in the photon coincidences but not in the singles count rate. In the quantum lithography setup, we find that the second-order Talbot length is half that of the classical first-order case, thus the resolution may be improved by a factor of 2.

Luo Kaihong; Chen Xihao; Liu Qian; Wu Lingan [Laboratory of Optical Physics, Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190 (China); Wen Jianming; Xiao Min [Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701 (United States)

2009-10-15

353

New Method for Solving Inductive Electric Fields in the Ionosphere  

NASA Astrophysics Data System (ADS)

We present a new method for calculating inductive electric fields in the ionosphere. It is well established that on large scales the ionospheric electric field is a potential field. This is understandable, since the temporal variations of large scale current systems are generally quite slow, in the timescales of several minutes, so inductive effects should be small. However, studies of Alfven wave reflection have indicated that in some situations inductive phenomena could well play a significant role in the reflection process, and thus modify the nature of ionosphere-magnetosphere coupling. The input to our calculation method are the time series of the potential part of the ionospheric electric field together with the Hall and Pedersen conductances. The output is the time series of the induced rotational part of the ionospheric electric field. The calculation method works in the time-domain and can be used with non-uniform, time-dependent conductances. In addition no particular symmetry requirements are imposed on the input potential electric field. The presented method makes use of special non-local vector basis functions called Cartesian Elementary Current Systems (CECS). This vector basis offers a convenient way of representing curl-free and divergence-free parts of 2-dimensional vector fields and makes it possible to solve the induction problem using simple linear algebra. The new calculation method is validated by comparing it with previously published results for Alfven wave reflection from uniformly conducting ionosphere.

Vanhamäki, H.

2005-12-01

354

Evaluation of six ionospheric models as predictors of TEC  

SciTech Connect

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

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

1990-05-03

355

Ionospheric Signatures of Plasmaspheric Tails  

NASA Astrophysics Data System (ADS)

We present direct comparisons between GPS maps of total electron content (TEC) over the North American continent with Millstone Hill radar observations of storm enhanced density and low and high-altitude satellite measurements of the perturbation of the outer plasmasphere during the March 31, 2001 geomagnetic storm. We find that storm enhanced density (SED) [Foster, J. Geophys. Res., 98, 1675, 1993] and plumes of greatly-elevated TEC result from the erosion of the outer plasmasphere by penetration jet electric fields. Boundaries of the SED/TEC plumes identified at low altitude map directly onto the magnetospheric determination of the boundaries of the plasmapause and plasmaspheric tail determined by EUV imaging from the IMAGE spacecraft. Ground-based GPS observations and radar scans are used to present 2-D snapshots of the ionospheric SED, while DMSP overflights identify the magnetospheric boundaries and mechanisms which contribute to these events. During this event, sunward-convecting plumes of high-TEC plasmaspheric material span the continent from New England to the Canadian Yukon and are responsible for significant ionospheric space weather effects including steep TEC gradients [Vo and Foster, J. Geophys. Res., 106, 21555, 2001] and the occurrence of mid-latitude radio scintillation. Characteristics of the SED/TEC plumes/tails for the March 31, 2001 event are. TEC ~100 TECu; F-region (300 km - 1000 km altitude) sunward velocity ~1000 m/s; sunward flux ~ 5*E24 ions s-1. Total transport to dayside magnetopause/merging region (3-hr event) is ~ 5*E28 ions.

Foster, J. C.; Coster, A. J.; Erickson, P. J.; Goldstein, J.; Rich, F. J.

2002-05-01

356

The effect of the 135.6 nm emission originated from the ionosphere on the TIMED/GUVI O/N2 ratio  

NASA Astrophysics Data System (ADS)

The column number density ratio of atomic oxygen to molecular nitrogen (O/N2 ratio) provided by the Global Ultraviolet Imager (GUVI) onboard the Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED) satellite has been used as a diagnostic of the thermospheric neutral composition. However, a recent study claimed that the GUVI O/N2 ratio is not a pure thermospheric parameter in low latitudes during periods of low geomagnetic activity. This study quantifies the O/N2 ratio contamination by the ionosphere using the GUVI observations and model ionosphere acquired from 31 August to 2 September 2002. During this period, the local time of the GUVI observation was near 1500 and the average Kp index was 2°. The 135.6 nm emission originated from the ionosphere is estimated using the electron density profiles provided by the Utah State University-Global Assimilation of Ionospheric Measurements model. Our results show that the 135.6 nm emission originated from the equatorial ionization anomaly (EIA) contributes 5 ~ 10% to the total 135.6 nm intensity and O/N2 ratio. The EIA feature and longitudinal wave patterns in the GUVI 135.6 nm intensity maps are identified above an altitude of 300 km and show a good agreement with those in the F region plasma density. However, the EIA feature and longitudinal wave patterns do not appear in the GUVI 135.6 nm intensity maps below an altitude of 300 km and in the GUVI N2 Lyman-Birge-Hopfield band intensity maps in any altitude. These observations indicate that the longitudinal wave patterns in the GUVI O/N2 ratio represent the ionospheric phenomenon.

Kil, H.; Lee, W. K.; Shim, J.; Paxton, L. J.; Zhang, Y.

2013-02-01

357

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

358

Modeling of Ionosphere Effects of Geomagnetic Storm Sequence on September 9-14, 2005 in View of Solar Flares and Dependence of Model Input Parameters from AE-and Kp-indices  

NASA Astrophysics Data System (ADS)

Earlier by Klimenko et al., 2009 under carrying out the calculations of the ionospheric effects of storm sequence on September 9-14, 2005 the model input parameters (potential difference through polar caps, field-aligned currents of the second region and particle precipitation fluxes and energy) were set as function of Kp-index of geomagnetic activity. The analyses of obtained results show that the reasons of quantitative distinctions of calculation results and observations can be: the use of 3 hour Kp-index at the setting of time dependence of model input parameters; the dipole approach of geomagnetic field; the absence in model calculations the effects of the solar flares, which were taken place during the considered period. In the given study the model input parameters were set as function of AE-and Kp-indices of geomagnetic activity according to different empirical models and morphological representations Feshchenko and Maltsev, 2003; Cheng et al., 2008; Zhang and Paxton, 2008. At that, we taken into account the shift of field-aligned currents of the second region to the lower latitudes as by Sojka et al., 1994 and 30 min. time delay of variations of the field-aligned currents of second region relative to the variations of the potential difference through polar caps at the storm sudden commencement phase. Also we taken into account the ionospheric effects of solar flares. Calculation of ionospheric effects of storm sequence has been carried out with use of the Global Self-Consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) developed in WD IZMIRAN (Nam-galadze et al., 1988). We carried out the comparison of calculation results with experimental data. This study is supported by RFBR grant 08-05-00274. References Cheng Z.W., Shi J.K., Zhang T.L., Dunlop M. and Liu Z.X. Relationship between FAC at plasma sheet boundary layers and AE index during storms from August to October, 2001. Sci. China Ser. E-Tech. Sci., 2008, Vol. 51, No. 7, 842-848. Feshchenko E.Yu., Maltsev Yu.P. Relations of the polar cap voltage to the geophysical activity. Physics of Auroral Phenomena: XXVI Annual Seminar (February 25-28, 2003): Proc./PGI KSC RAS. Apatity, 2003, 59-61. Klimenko M.V., Klimenko V.V., Ratovsky K.G., and Goncharenko L.P. Numerical modeling of ionospheric parameters during sequence of geomagnetic storms on September 9-14, 2005. Physics of Auroral Phenomena: XXXII Annual Seminar (March 3-6, 2009): Proc./PGI KSC RAS. Apatity, 2009, 162-165. Namgaladze A.A., Korenkov Yu.N., Klimenko V.V., Karpov I.V., Bessarab F.S., Surotkin V.A., Glushenko T.A., Naumova N.M. Global model of the thermosphere-ionosphere-protonosphere system. Pure and Applied Geophysics (PAGEOPH), 1988, Vol. 127, No. 2/3, 219-254. Sojka J.J., Schunk R.W., Denig W.F. Ionospheric response to the sustained high geomagnetic activity during the March '89 great storm. J. Geophys. Res., 1994, Vol. 99, No. A11, 21341-21352. Zhang Y., Paxton L.J. An empirical Kp-dependent global auroral model based on TIMED/GUVI FUV data. J. Atmos. Solar-Terr. Phys., 2008, Vol. 70, 1231-1242.

Klimenko, Maxim; Klimenko, Vladimir; Ratovsky, Konstantin; Goncharenko, Larisa

359

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

360

Quantifying and Modeling Birth Order Effects in Autism  

PubMed Central

Autism is a complex genetic disorder with multiple etiologies whose molecular genetic basis is not fully understood. Although a number of rare mutations and dosage abnormalities are specific to autism, these explain no more than 10% of all cases. The high heritability of autism and low recurrence risk suggests multifactorial inheritance from numerous loci but other factors also intervene to modulate risk. In this study, we examine the effect of birth rank on disease risk which is not expected for purely hereditary genetic models. We analyzed the data from three publicly available autism family collections in the USA for potential birth order effects and studied the statistical properties of three tests to show that adequate power to detect these effects exist. We detect statistically significant, yet varying, patterns of birth order effects across these collections. In multiplex families, we identify V-shaped effects where middle births are at high risk; in simplex families, we demonstrate linear effects where risk increases with each additional birth. Moreover, the birth order effect is gender-dependent in the simplex collection. It is currently unknown whether these patterns arise from ascertainment biases or biological factors. Nevertheless, further investigation of parental age-dependent risks yields patterns similar to those observed and could potentially explain part of the increased risk. A search for genes considering these patterns is likely to increase statistical power and uncover novel molecular etiologies. PMID:22039484

Turner, Tychele; Pihur, Vasyl; Chakravarti, Aravinda

2011-01-01

361

Effect of reaction order on stability of planar detonation waves  

NASA Astrophysics Data System (ADS)

We examine the multi-dimensional linear and non-linear stability of planar detonation waves for one-step Arrhenius rate with arbitrary reaction order. A normal mode analysis with an iterative shooting method is used in linear stability. Results show that the effect of decreasing the reaction order is roughly equivalent to increasing the activation energy, or decreasing the heat release and overdrive. Both the one- and two-dimensional linear stability spectra consist of a larger number of unstable modes at lower reaction order. Bifurcation to non-oscillatory modes occurs at slightly lower activation energy or higher heat release and overdrive for lower reaction order. Thus overall, a lower reaction order results in more unstable waves. Numerical simulations, using a Weighted Essentially Non-Oscillatory scheme, show that activation energy has a stronger effect on cell regularity than the reaction order. It has been suggested that a relationship may exist between transverse wavelength from multi-dimensional linear stability analysis and cell sizes. Our computations confirm previous numerical results that show that the most unstable transverse wavelengths from linear stability analysis are comparable with the minimum channel width in which one full cell is observed in numerical simulations. Wider computations show that cells, which appear regular and periodic in narrow channel computations, become irregular. The average cell size approaches a consistent limit corresponding to an even larger size.

Liang, Z.; Khastoo, B.; Bauwens, L.

2005-02-01

362

Longitudinal Variability in the Geomagnetically Quiescent Ionosphere  

NASA Astrophysics Data System (ADS)

We report on the effects of nonmigrating tides on the Earth's upper atmosphere based upon calculations made with the National Center for Atmospheric Research (NCAR) thermosphere-ionosphere- mesosphere-electrodynamics general circulation model (TIME-GCM) and global-scale wave model (GSWM). We extend the results reported by Hagan et al. (2007) who demonstrated that longitude variations in IMAGE satellite airglow brightness measurements associated with equatorial ionization anomaly peak densities can be attributed to longitudinally variable nonmigrating zonal wind tides which modulate the E-region dynamo and produce electric field effects that map into the F-region aloft. We explore the local time, altitude and seasonal variability of these nonmigrating tidal components in the TIME-GCM along with viable sources of excitation, including latent heat release associated with raindrop formation in deep convective towers in the tropical troposphere as parameterized in the GSWM. We also assess the reliability of our TIME-GCM predictions via comparison with accessible observations of the quiescent ionosphere. Hagan, M.E., A. Maute, R. G. Roble, A. D. Richmond, T. J. Immel, and S. L. England, (2007), Connections between deep tropical clouds and the Earths ionosphere, Geophys. Res. Lett., in press.

Hagan, M. E.; Maute, A.; Roble, R. G.; Richmond, A. D.

2007-12-01

363

Three-dimensional multifluid simulations of ionospheric loss at Mars from nominal solar wind conditions to magnetic cloud events  

Microsoft Academic Search

conditions. Ionospheric losses on the order of 1025 O2 + ions per second are found for quiet solar wind conditions. This is of the same order as that estimated from Phobos 2 measurements. Varying the orientation of Mars' magnetic anomalies relative to the incident solar wind direction leads to only minor variation in the ionospheric loss rates of O2 +

E. M. Harnett; R. M. Winglee

2006-01-01

364

Effects of the geomagnetic asymmetry of flux-tube integrated neutral winds to the Rayleigh-Taylor instability in equatorial ionosphere  

NASA Astrophysics Data System (ADS)

Neutral winds play an important role in the develop-ment of Rayleigh-Taylor instability which is very associated with the occurrence of irregularities in the equatorial and low-latitude regions. For example, eastward winds would make for the development of R-T instability and meridional winds suppress the development of R-T insta-bility. In this work, we investigate effects of the geomagnetic asymmetry of neutral winds to the flux-tube integrated R-T instability in equatorial ionosphere. The flux-tube integrated lin-ear growth rate of R-T instability were estimated and considering the ambient electric fields and asymmetry of neutral winds between North-South hemispheres, and the integrated growth rates were compared which were get with and without the neutral wind, including the zonal and meridional wind. Effects of the longitudinal distribution of the meridional winds on the inte-grated growth rate are investigated also. It is shown that the zonal and meridional wind could significantly affect the growth rates and the meridional winds could decrease the integrated growth rate, respectively. The longitudinal variation of occurrence of irregularities would be related with the global distribution of meridional wind. Reference: Sultan, P.J., Linear theory and modeling of the Rayleigh-Taylor instability leading to the occurrence of equatorial spread F, J. Geophys. Res., 1996, 101(A12), 26875-26891 Basu, B., On the linear theory of equato-rial plasma instability: Comparison of different descriptions, J. Geophys. Res., 2002, 107(A8), 1199, doi: 10.1029/2001JA000317

Luo, Weihua; Xu, Jisheng; Tian, Mao

365

The Ionosphere and Ocean Altimetry  

NASA Technical Reports Server (NTRS)

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

Lindqwister, Ulf J.

1999-01-01

366

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

NASA Astrophysics Data System (ADS)

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

367

Second-order Talbot effect with entangled photon pairs  

Microsoft Academic Search

The second-order Talbot effect is analyzed for a periodic object illuminated by entangled photon pairs in both the quantum imaging and quantum lithography configurations. The Klyshko picture is applied to describe the quantum imaging scheme, in which self-images of the object that may or may not be magnified can be observed nonlocally in the photon coincidences but not in the

Kai-Hong Luo; Jianming Wen; Xi-Hao Chen; Qian Liu; Min Xiao; Ling-An Wu

2009-01-01

368

10 CFR 221.34 - Effect of order.  

Code of Federal Regulations, 2012 CFR

...2012-01-01 false Effect of order. 221.34 Section 221.34 Energy DEPARTMENT OF ENERGY OIL PRIORITY SUPPLY OF CRUDE OIL AND PETROLEUM PRODUCTS TO THE DEPARTMENT OF DEFENSE UNDER THE DEFENSE PRODUCTION ACT Administrative Procedures and...

2012-01-01

369

10 CFR 221.34 - Effect of order.  

...2014-01-01 false Effect of order. 221.34 Section 221.34 Energy DEPARTMENT OF ENERGY OIL PRIORITY SUPPLY OF CRUDE OIL AND PETROLEUM PRODUCTS TO THE DEPARTMENT OF DEFENSE UNDER THE DEFENSE PRODUCTION ACT Administrative Procedures and...

2014-01-01

370

10 CFR 221.34 - Effect of order.  

Code of Federal Regulations, 2010 CFR

...2010-01-01 false Effect of order. 221.34 Section 221.34 Energy DEPARTMENT OF ENERGY OIL PRIORITY SUPPLY OF CRUDE OIL AND PETROLEUM PRODUCTS TO THE DEPARTMENT OF DEFENSE UNDER THE DEFENSE PRODUCTION ACT Administrative Procedures and...

2010-01-01

371

10 CFR 221.34 - Effect of order.  

Code of Federal Regulations, 2013 CFR

...2013-01-01 false Effect of order. 221.34 Section 221.34 Energy DEPARTMENT OF ENERGY OIL PRIORITY SUPPLY OF CRUDE OIL AND PETROLEUM PRODUCTS TO THE DEPARTMENT OF DEFENSE UNDER THE DEFENSE PRODUCTION ACT Administrative Procedures and...

2013-01-01

372

10 CFR 221.34 - Effect of order.  

Code of Federal Regulations, 2011 CFR

...2011-01-01 false Effect of order. 221.34 Section 221.34 Energy DEPARTMENT OF ENERGY OIL PRIORITY SUPPLY OF CRUDE OIL AND PETROLEUM PRODUCTS TO THE DEPARTMENT OF DEFENSE UNDER THE DEFENSE PRODUCTION ACT Administrative Procedures and...

2011-01-01

373

Nonmonotone Impulse Effects in Second Order Periodic Boundary Value Problems  

E-print Network

Nonmonotone Impulse Effects in Second Order Periodic Boundary Value Problems Irena Rach°unkov´a and Milan Tvrd´y September 20, 2002 Summary. This paper deals with the nonlinear impulsive periodic boundary. In contrast to previous papers investigating such problems, the monotonicity of the impulse functions Ji, Mi

Rachùnkova, Irena

374

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

375

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

376

AGU: Journal of Geophysical Research geomagnetic ionosphere currents  

E-print Network

fits are shown along-side scatter plots of individual measurements in corrected geomagnetic apexAGU: Journal of Geophysical Research Keywords geomagnetic ionosphere currents Index Terms Ionosphere: Polar cap ionosphere Ionosphere: Current systems Geomagnetism and Paleomagnetism: Rapid time

Michigan, University of

377

Experimentally investigate ionospheric depletion chemicals in artificially created ionosphere  

NASA Astrophysics Data System (ADS)

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 SF6, CCl2F2, and CO2 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 (SF6-, CCl2F2-) intermediary species provide larger reduction of the electron density than the positive ion (CO2+) 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 SF6 and CO2 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

2012-09-01

378

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

379

Hidden order and disorder effects in URu2Si2  

NASA Astrophysics Data System (ADS)

NMR experiments at ambient pressure in URu 2Si 2 demonstrate a linewidth enhancement effect below the hidden order transition temperature T0. We present single-crystal 29Si NMR parameters for various temperatures and for an applied magnetic field perpendicular to the crystal c-axis. By comparing oriented-powder and single-crystal data, we observe that the size of the linewidth enhancement below T0 correlates with the size of the high- T broadening. We measure a 29Si up-field line shift below T0 which indicates the presence of an internal-field average for the entire crystal. This shift also correlates with the high-temperature width. The 101Ru NQR frequency as a function of temperature was also measured. No strong effect on the NQR frequency is observed at T0. Both NMR and NQR measurements suggest a connection between linewidth/disorder effects and the transition to hidden order.

Bernal, O. O.; Moroz, M. E.; Ishida, K.; Murakawa, H.; Reyes, A. P.; Kuhns, P. L.; MacLaughlin, D. E.; Mydosh, J. A.; Gortenmulder, T. J.

2006-05-01

380

Effect of prestrain on coherence length and order parameter  

NASA Astrophysics Data System (ADS)

In this paper, an analytical method is presented for determining the effective coherence length and order parameter in a superconductor. The interaction of the deformations of the crystal lattice with the superconducting condensate is considered. A simplified free energy has been used in the literature to estimate the effect of the prestrain on the coherence length and the order parameter. The exact solutions for three dimensional and plane strain problems are obtained. Based on the linear elastic theory, an extensive analysis is made during the positive and negative prestrain for the isotropic material. The results show that the effect of the prestrain on the superconductivity is appreciable. A comparison is made between three dimensional and two dimensional results, and there is not significant difference between the results for two conditions. These explicit solutions provide a convenient tool for evaluating the superconductivity when the material undergoes the deformation.

Yong, Huadong; Xue, Feng; Zhou, Youhe

2010-11-01

381

Effects of the solar wind electric field and ionospheric conductance on the cross polar cap potential: Results of global MHD modeling  

Microsoft Academic Search

The behavior of the cross polar cap potential, ?PC, under strong solar wind conditions is studied using global MHD simulations. Simulations using two typical values of the ionospheric Pedersen conductance in agreement with others show that the cross polar cap potential is reduced compared to the corresponding potential in the solar wind due to the stagnation of the magnetosheath flow

V. G. Merkine; K. Papadopoulos; G. Milikh; A. S. Sharma; X. Shao; J. Lyon; C. Goodrich

2003-01-01

382

Effects of magnetic anomalies discovered at Mars on the structure of the Martian ionosphere and solar wind interaction as follows from radio occultation experiments  

Microsoft Academic Search

The slopes of the electron density profiles obtained by radio occultation experiments at Mars revealed different variations with solar zenith angle in comparison with behavior of the electron density profiles in the magnetic field free ionosphere of Venus. The results obtained by the Mars-Global-Surveyor (MGS) spacecraft show the existence of highly variable and very localized magnetic fields of crustal origin

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

2000-01-01

383

Macroscopic effects in noncollinear high-order harmonic generation.  

PubMed

We study two-color high-order harmonic generation using an intense driving field and its weak second harmonic, crossed under a small angle in the focus. Employing sum- and difference-frequency generation processes, such a noncollinear scheme can be used to measure and control macroscopic phase matching effects by utilizing a geometrical phase mismatch component, which depends on the noncollinear angle. We further show how spatial phase effects in the generation volume are mapped out into the far field allowing a direct analogy with temporal carrier envelope effects in attosecond pulse generation. PMID:24765964

Heyl, C M; Rudawski, P; Brizuela, F; Bengtsson, S N; Mauritsson, J; L'Huillier, A

2014-04-11

384

Placing order in space: the SNARC effect in serial learning.  

PubMed

The SNARC effect, consisting of a systematic association between numbers and lateralized response, reflects the mental representation of magnitude along a left-to-right mental number line (Dehaene et al. in J Exp Psychol 122:371-396, 1993). Critically, this effect has been reported in the classification of overlearned non-numerical sequences such as letters, days and months (Gevers et al. in Cognition 87:B87-B95, 2003 and Cortex 40:171-172, 2004) suggesting that ordinal, rather than magnitude information, is critical for spatial coding. This study tests the hypothesis of an oriented spatial representation as the privileged way of mentally organizing serial information, by looking for stimulus-response compatibility effects in the processing of a newly acquired arbitrary sequence. Here we report an association between ordinal position of the items and spatial response preference for both order-relevant and order-irrelevant tasks. These results suggest that any ordered information, even when order is not intrinsically relevant to it, is spontaneously mapped in the representational space. This spatial representation is likely to acquire a left-to-right orientation, at least in western cultures. PMID:19888566

Previtali, Paola; de Hevia, Maria Dolores; Girelli, Luisa

2010-03-01

385

An improved high precision ionospheric total electron content modeling using GPS  

Microsoft Academic Search

Space-based radio navigation systems such as the Global Positioning System (GPS) can provide us with a unique opportunity to study the effect of the ionosphere as the signals propagate from the satellites to the GPS receivers. Based on a modified version of the University of New Brunswick's (UNB) DIPOP software package, the authors enhanced the algorithm to model ionospheric total

Attila Komjathy; George H. Born; David N. Anderson

2000-01-01

386

Atmosphere and Ionosphere of Venus from the Mariner V S-Band Radio Occultation Measurement  

Microsoft Academic Search

Measurements of the frequency, phase, and amplitude of the S-band radio signal of Mariner V as it passed behind Venus were used to obtain the effects of refraction in its atmosphere and ionosphere. Profiles of refractivity, temperature, pressure, and density in the neutral atmosphere, as well as electron density in the daytime ionosphere, are presented. A constant scale height was

Arvydas Kliore; Gerald S. Levy; Dan L. Cain; Gunnar Fjeldbo; S. I. Rasool

1967-01-01

387

Line-of-sight electron density gradients as deduced from an empirical ionospheric model  

Microsoft Academic Search

A topside ionospheric model (Bent Ionospheric Model) was developed for an accurate prediction of integrated total electron content (TEC), from a global data acquired for the years 1962 to 1969. In this paper the effects of line-of-sight electron density gradients on ground to satellite measurements are discussed. The results of analyses show that in the presence of increasing density gradients,

G. Nesterczuk; J. K. Kozelsky; J. A. Behuncik

1976-01-01

388

Ionospheric and Birkeland Current Distributions Inferred from the MAGSAT Magnetometer Data  

Microsoft Academic Search

The MAGSAT vector magnetometer data, with the aid of an accurate magnetic field model, have been used to infer ionospheric and field-aligned sheet current density distributions. The MAGSAT spacecraft is uniquely suited for this study because it provides, for the first time from a satellite, simultaneous observations of effects due to both ionospheric and Birkeland current systems. The method emphasized

L. J. Zanetti; W. Baumjohann; T. A. Potemra

1983-01-01

389

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.

390

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

391

Assimilative modeling of low latitude ionosphere  

NASA Technical Reports Server (NTRS)

In this paper we present an observation system simulation experiment for modeling low-latitude ionosphere using a 3-dimensional (3-D) global assimilative ionospheric model (GAIM). The experiment is conducted to test the effectiveness of GAIM with a 4-D variational approach (4DVAR) in estimation of the ExB drift and thermospheric wind in the magnetic meridional planes simultaneously for all longitude or local time sectors. The operational Global Positioning System (GPS) satellites and the ground-based global GPS receiver network of the International GPS Service are used in the experiment as the data assimilation source. 'The optimization of the ionospheric state (electron density) modeling is performed through a nonlinear least-squares minimization process that adjusts the dynamical forces to reduce the difference between the modeled and observed slant total electron content in the entire modeled region. The present experiment for multiple force estimations reinforces our previous assessment made through single driver estimations conducted for the ExB drift only.

Pi, Xiaoqing; Wang, Chunining; Hajj, George A.; Rosen, I. Gary; Wilson, Brian D.; Mannucci, Anthony J.

2004-01-01

392

Higher order and asymmetry effects on saturation of magnetic islands  

SciTech Connect

Higher order asymptotic matching procedure is developed to derive the nonlinear equation for saturated magnetic island with the symmetric profile of the equilibrium current. The theory extends the previous results to include higher order effects such as nonlinear modification of the equilibrium current and asymmetry in the boundary conditions in the outer region. It is shown that due to a finite width of the nonlinear region, the magnitude of the magnetic flux at the rational surface is different from the asymptotic value found from the outer solution, resulting in the suppression of the island growth for higher values of ?{sup ?} parameter.

Smolyakov, A. I. [Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E2 (Canada) [Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E2 (Canada); International Institute for Fusion Science, UMR7345, Aix Marseille Université, CNRS, IIFS-PIIM, Marseille 13397 (France); NRC “Kurchatov Institute,” 1 Kurchatov Sqr., Moscow 123182 (Russian Federation); Poye, A.; Agullo, O.; Benkadda, S. [International Institute for Fusion Science, UMR7345, Aix Marseille Université, CNRS, IIFS-PIIM, Marseille 13397 (France)] [International Institute for Fusion Science, UMR7345, Aix Marseille Université, CNRS, IIFS-PIIM, Marseille 13397 (France); Garbet, X. [CEA, IRFM, F-13108 Saint Paul Lez Durance (France)] [CEA, IRFM, F-13108 Saint Paul Lez Durance (France)

2013-06-15

393

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

394

Investigation of Electron Density Profile in the ionospheric D and E region by Kagoshima rocket experiment  

NASA Astrophysics Data System (ADS)

The radio wave propagation characteristic in the lower ionosphere is important because of its effect on commercial radio communication, navigation, and broadcast services. The electron density is of primary interest in this region because the high ion-neutral collision frequencies result in radio wave absorption. In order to investigate the ionization structure in the ionospheric D and E region by using the propagation characteristics of MF-band and LF-band radio waves, S-310-37 and S-520-23 sounding rocket experiments have been carried out at Uchinoura Space Center (USC). S-310-37 sounding rocket was launched at 11:20 LT on January 16, 2007. The apex of rocket trajectory was about 138 km. Then S-520-23 sounding rocket was launched at 19:20 LT on September 2, 2007. The apex was about 279 km. As a common measurement, these sounding rockets measure the fields intensities and the waveform of radio waves from NHK Kumamoto broadcasting station (873kHz, 500kW) and JJY signals from Haganeyama LF radio station (60kHz, 50kW). The approximate electron density profile can be determined from the comparison between these experimental results and propagation characteristics calculated by the full wave method. We will get the most probable electron density profile in the ionosphere. In presentation, we will show the propagation characteristic of LF/MF radio waves measured by two sounding rocket experiments. Then we will discuss the analysis method and the estimated electron density profile in the ionosphere.

Ashihara, Y.; Ishisaka, K.; Miyake, T.; Okada, T.; Nagano, I.; Abe, T.; Ono, T.

2007-12-01

395

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

396

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

397

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

398

Challenges in Solar System Ionospheres  

Microsoft Academic Search

The solar system contains a robust set of ionospheres among its nine planets, many moons and comets. If one sets aside the transient atmospheres\\/ionospheres of comets, and those of larger bodies with tenuous surface-boundary-exospheres (e.g., Mercury, Moon, Europa, etc.), plus the under-sampled Pluto, then 10 case studies exist for detailed study and comparison (Venus, Earth, Mars, Jupiter & Io, Saturn

M. Mendillo

2001-01-01

399

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

400

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.

401

Polar Kerr effect from chiral-nematic charge order  

NASA Astrophysics Data System (ADS)

We analyze the polar Kerr effect in an itinerant electron system on a square lattice in the presence of a composite charge order proposed for the pseudogap state in underdoped cuprates. This composite charge order preserves discrete translational symmetries, and is "chiral nematic" in the sense that it breaks time-reversal symmetry, mirror symmetries in x and y directions, and C4 lattice rotation symmetry. The Kerr angle ?K in C4-symmetric system is proportional to the antisymmetric component of the anomalous Hall conductivity ?x y-?y x . We show that this result holds when C4 symmetry is broken. We show that in order for ?x y and ?y x to be nonzero the mirror symmetries in x and y directions have to be broken, and that for ?x y-?y x to be nonzero time-reversal symmetry has to be broken. The chiral-nematic charge order satisfies all these conditions, such that a nonzero signal in a polar Kerr effect experiment is symmetry allowed. We further show that to get a nonzero ?K in a one-band spin-fluctuation scenario, in the absence of disorder, one has to extend the spin-mediated interaction to momenta away from (? ,? ) and has to include particle-hole asymmetry. Alternatively, in the presence of disorder, one can get a nonzero ?K from impurity scattering: either due to skew scattering (with non-Gaussian disorder) or due to particle-hole asymmetry in case of Gaussian disorder. The impurity analysis in our case is similar to that in earlier works on Kerr effect in px+i py superconductors, however, in our case, the magnitude of ?K is enhanced by the flattening of the Fermi surface in the "hot" regions, which mostly contribute to charge order.

Wang, Yuxuan; Chubukov, Andrey; Nandkishore, Rahul

2014-11-01

402

Assessment of Ionospheric Impact on LAAS Using WAAS Supertruth Data  

Microsoft Academic Search

In order to reflect the impact of spatial ionospheric gradients on Local Area Augmentation System (LAAS) users, the LAAS Ground Facility (LGF) broadcasts a conservative standard deviation (? vert_iono_gradient or ? vig) for these errors that is included in the calculation of protection levels (bounds on user position errors). However, \\

Ming Luo; Sam Pullen; Dennis Akos; Gang Xie; Seebany Datta-Barua; Todd Walter; Per Enge

403

Observations of ionospheric magnetospheric coupling - DE and Chatanika coincidences  

NASA Technical Reports Server (NTRS)

Observations from several experiments on board the Dynamics Explorer 1 and 2 (DE 1 and 2) spacecraft and ground-based radar measurements from the Chatanika radar are combined in order to examine the details of ionospheric/magnetospheric coupling in the local evening sector. DE 1 and DE 2 were in coplanar polar orbits that provided measurements almost simultaneously in time and magnetically coincident with the Chatanika radar from L = 3 to L = 17. The coupling processes are inferred from the density, temperature, composition, and angular distributions of the low-energy plasma observed from the E region of the ionosphere to magnetospheric altitudes of 2.5 earth radii. Plasma characteristics of the plasmasphere, main trough, auroral zone, and polar cap can be studied in this data set. The observations imply that as L increases, the dominant coupling mechanism between the ionosphere and magnetosphere in the measured energy range changes from equilibrium diffusion to perpendicular acceleration and finally to parallel acceleration.

Green, J. L.; Brace, L. H.; Waite, J. H.; Chappell, C. R.; Chandler, M. O.; Doupnik, J. R.; Richards, P. G.; Heelis, R.; Shawhan, S. D.

1986-01-01

404