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1

Higher order ionospheric propagation effects on GPS radio occultation signals  

Microsoft Academic Search

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

M. Mainul Hoque; N. Jakowski

2010-01-01

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

Higher order ionospheric effects in GNSS positioning in the European region  

NASA Astrophysics Data System (ADS)

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

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

2011-08-01

5

Effects on noise properties of GPS time series caused by higher-order ionospheric corrections  

NASA Astrophysics Data System (ADS)

Higher-order ionospheric (HOI) effects are one of the principal technique-specific error sources in precise global positioning system (GPS) analysis. These effects also influence the non-linear characteristics of GPS coordinate time series. In this paper, we investigate these effects on coordinate time series in terms of seasonal variations and noise amplitudes. Both power spectral techniques and maximum likelihood estimators (MLE) are used to evaluate these effects quantitatively and qualitatively. Our results show an overall improvement for the analysis of global sites if HOI effects are considered. We note that the noise spectral index that is used for the determination of the optimal noise models in our analysis ranged between -1 and 0 both with and without HOI corrections, implying that the coloured noise cannot be removed by these corrections. However, the corrections were found to have improved noise properties for global sites. After the corrections were applied, the noise amplitudes at most sites decreased, among which the white noise amplitudes decreased remarkably. The white noise amplitudes of up to 81.8% of the selected sites decreased in the up component, and the flicker noise of 67.5% of the sites decreased in the north component. Stacked periodogram results show that, no matter whether the HOI effects are considered or not, a common fundamental period of 1.04 cycles per year (cpy), together with the expected annual and semi-annual signals, can explain all peaks of the north and up components well. For the east component, however, reasonable results can be obtained only based on HOI corrections. HOI corrections are useful for better detecting the periodic signals in GPS coordinate time series. Moreover, the corrections contributed partly to the seasonal variations of the selected sites, especially for the up component. Statistically, HOI corrections reduced more than 50% and more than 65% of the annual and semi-annual amplitudes respectively at the selected sites.

Jiang, Weiping; Deng, Liansheng; Li, Zhao; Zhou, Xiaohui; Liu, Hongfei

2014-04-01

6

Effects of nuclear detonations on the ionosphere  

Microsoft Academic Search

During Operation CASTLE, two ionosphere recorders were operated in the Marshall Islands -at Site Elmer, about 200 miles west of Bikini Atoll, and at Rongerik Atoll, about 150 miles east of Bikini -- in order to study the effects of the detonations on the ionosphere. Severe absorption was observed 200 miles west of all multimegaton shots, lasting several hours, presumably

F. B. Daniels; A. K. Harris

1957-01-01

7

Estimating Second Order Ionospheric Delays During GPS-LEO Radio Occultation Observations: An Alternative Approach  

NASA Astrophysics Data System (ADS)

The demand for millimeter accuracy in Global Positioning System (GPS) applications (receiver and precise point positioning) has raised a considerable interest in studying second order ionospheric delays. Unlike first order, second order ionospheric delays are functions of both, the Total Electron Content (TEC), and the geomagnetic field along the integrated signal path between the transmitter (GPS) and the receiver. The standard method of computing second order ionospheric delays makes use of ionosphere (IRI-2007) and magnetic field models (IGRF-10). We propose a different approach in estimating second order ionospheric delays, based solely on dual frequency GPS raw ionospheric excess phase delays. Specifically, our goal is twofold: (1) compute TEC free from second order ionospheric errors and (2) calculate geomagnetic field values along the integrated signal path between a GPS transmitter and a receiver. We apply our method to near-real time observational data provided by the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) Data Analysis and Archive Centre (CDAAC), from which second order ionospheric delays can be realized. Second order ionospheric delays estimated based on our model attains values between -9 mm and 16 mm, which is larger than the values obtained for ground-based GPS observations. Currently, TEC estimations are based on differencing dual frequency GPS ionospheric excess phase delays, without accounting for second order ionospheric effects. We propose an alternative approach according to which we model the observed carrier-phase observables (L1, L2) taking into account the geomagnetic field that is the source of the second order ionospheric effect. Subsequently, by combining linearly the GPS observables we can solve for the TEC that is free from the second order ionospheric affect. In a second step, we compute geomagnetic field values along the integrated signal path between a GPS transmitter and a receiver based on the Faraday rotation effect, taking advantage of the relation between the rotation angle of the polarization plane of the GPS signal and the Earth's magnetic field. We analyze 30 COSMIC ionospheric radio occultation (RO) events in 2006, 2007 and 2008 and show that our results are in a very good agreement with the IGRF-10 model within 0.2% and 9%. We also demonstrate that the weighted mean geomagnetic field along a GPS-LEO integrated signal path during an RO event is conservative, as it has been assumed by many researchers when estimating second order ionospheric delays, but never proven.

Vergados, P.; Pagiatakis, S. D.

2009-05-01

8

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

9

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

10

Solar cosmic ray effects in the lower ionosphere  

NASA Technical Reports Server (NTRS)

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

Shirochkov, A. V.

1989-01-01

11

Influence of the Second-Order Ionospheric Delay on GNSS Geodetic Solutions  

NASA Astrophysics Data System (ADS)

The level of accuracy reached today by reference GNSS technology is in great part a consequence of progress in modelling various contributions to the observables. At the same time, advances in modelling of a single effect will not necessarily lead to improvements in the final result if there exist greater mismodelled contributions from other sources. One of the effects, the importance of which has been recently understood, is the ionospheric effect of second order. The commonly accepted ionosphere-free linear phase combination eliminates the plasma-induced phase delay in GNSS measurements in the approximation of zero magnetic field. However, due to interaction of the GNSS carrier wave, propagating in an ionospheric plasma, with the geomagnetic field a small additional delay is introduced in the phase observable. The magnitude of such a delay is of the order of~1~cm, and it depends on the geographic coordinates of the observer, local time, season, and solar activity. We use International Reference Ionosphere (IRI2007) and International Geomagnetic Reference Field (IGRF2005) models to create worldwide maps of the second-order ionospheric delay and resulting geodetic displacements for different time, seasons, and phases of solar activity cycle. We show that, due to diurnal and seasonal variability of the second-order ionospheric delay, there are apparent oscillations of geocentre position. We demonstrate that the pattern of such oscillations changes with the phase of solar activity cycle. In applications to kinematic and sub-daily static positioning, we demonstrate that due to high horizontal gradients of electron total content during morning and evening hours, taking into account the second-order ionospheric effect becomes meaningful not only for the global, but also for regional networks. In the case of daily static solutions accounting for the second-order ionospheric delay can help improving the solution precision. Based on the results presented we recommend introducing the modelling of the second-order ionospheric delay in routine GNSS processing for global geodetic networks, especially in view of the forthcoming solar activity maximum.

Palamartchouk, K.

2007-12-01

12

Solar rotation effects on the Martian ionosphere  

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

13

Review of radio-frequency, nonlinear effects on the ionosphere  

SciTech Connect

Modification of the ionosphere by high power radio waves in the megahertz band has been intensively investigated over the past two decades. This research has yielded advances in aeronomy, geophysics, and plasma physics with applications to radio communication and has provided a fruitful interaction of radio theorists and experimentalists. There being almost no linear effects of powerful radio waves on the ionosphere, we concentrate on the nonlinear effects. To put the subject in perspective we trace its history beginning in the early 1930s and highlight the important events up to the late 1960s. We then shift to a phenomenological approach and deal in order with ohmic heating, parametric instabilities, self-focusing and kilometer-scale irregularities, meter-scale irregularities, and a collection of recently discovered effects. We conclude with the observation that stronger international cooperation would benefit this research, and describe a list of promising, difficult challenges.

Gordon, W.E.; Duncan, L.M.

1983-01-01

14

Ionospheric Feedback Effects on Magnetosphere-Ionosphere Coupling  

NASA Astrophysics Data System (ADS)

A new interactive M-I coupling model is developed to investigate the dynamic interaction between magnetospheric dispersive waves, compressional modes, and auroral electron precipitations. The model is applied to investigate the geomagnetic electromagnetic pulsations observed in Earth's magnetosphere in terms of magnetospheric waves triggered by field line resonances and ionospheric feedback instability. M-I coupling is included by accounting for the closure of magnetospheric field-aligned currents through Pedersen currents in the ionosphere. The height-integrated Pedersen conductivity is treated as a dynamic parameter by electrodynamically coupling the 2D finite element wave model "TOPO" to the ionospheric ionization model "GLOW". It is shown that both mechanisms can be used to explain many features of auroral arcs such as the periodic intensification, FACs, and electric fields. However, unlike in a field line resonance where the ponderomotive force causes the plasma to move mainly along the field line, the plasma in the feedback instability is distributed either as a bump or a cavity along a field line and leads to a multi-banded structure in the radial direction. The nonlinear feedback instability model can explain the formation of plasma density and electromagnetic perturbations with the same frequency, which disagree with current FLR scenario.

Lu, Jianyong; Wang, Wenbin; Rankin, Robert; Marchand, Richard

15

On the second order statistics for GPS ionospheric scintillation modeling  

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

16

A study of two flares on 8 July 1968 in the light of their ionospheric effects.  

NASA Technical Reports Server (NTRS)

Detailed study of the observed ionospheric effects of the X-ray flare on July 8, 1968, which was of considerable importance both from the ionospheric and solar physics point of view. The associated optical flare was of importance 3B. The ionospheric effects were examined in order to derive a suitable physical model of flare-induced ionization below 100 km, and hence to estimate the spectral characteristics of the ionizing radiations from the observed SID s. The electron loss coefficients below 70 km height calculated from the formula developed in the analysis are in agreement with available data.

Sengupta, P. R.

1971-01-01

17

Ionospheric effects to antenna impedance  

NASA Technical Reports Server (NTRS)

The reciprocity between high power satellite antennas and the surrounding plasma are examined. The relevant plasma states for antenna impedance calculations are presented and plasma models, and hydrodynamic and kinetic theory, are discussed. A theory from which a variation in antenna impedance with regard to the radiated power can be calculated for a frequency range well above the plasma resonance frequency is give. The theory can include photo and secondary emission effects in antenna impedance calculations.

Bethke, K. H.

1986-01-01

18

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

NASA Astrophysics Data System (ADS)

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

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

19

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

20

Ionospheric effects on synthetic aperture radar at VHF  

SciTech Connect

Synthetic aperture radars (SAR) operated from airplanes have been used at VHF because of their enhanced foliage and ground penetration compared to radars operated at UHF. A satellite-borne VHF SAR would have considerable utility but in order to operate with high resolution it would have to use both a large relative bandwidth and a large aperture. The presence of the ionosphere in the propagation path of the radar will cause a deterioration of the imaging because of dispersion over the bandwidth and group path changes in the imaged area over the collection aperture. In this paper we present calculations of the effects of a deterministic ionosphere on SAR imaging for a radar operated with a 100 MHz bandwidth centered at 250 MHz and over an angular aperture of 23{degrees}. The ionosphere induces a point spread function with an approximate half-width of 150 m in the slant-range direction and of 25 m in the cross-range direction compared to the nominal resolution of 1.5 m in both directions.

Fitzgerald, T.J.

1997-02-01

21

Global characteristics of the second-order ionospheric delay error using inversion of electron density profiles from COSMIC occultation data  

NASA Astrophysics Data System (ADS)

It is a well known fact that ionospheric delay error is a predominant factor which influences the positioning accuarcy of GNSS. Although the main part of the first-order ionospheric delay error can be removed by the frequency-dependent behaviors of the ionosphere, the second-order ionospheric delay error must be eliminated to achieve millimetre-scale positioning accuracy. Due to COSMIC occultation providing electron density profiles on the global scale, the paper presents the first-order and the second-order ionospheric delay error analysis on the global scale using the inversion of electron density profiles from COSMIC occultation data during 2009-2011. Firstly, because of the special geographical location of three ISR (incoherent scatter radar), the first-order and the second-order ionospheric delay errors are calculated and discussed; the paper also shows and analyzes the diurnal, seasonal, semi-annual variation of ionospheric delay error with respect to signal direction. Results show that for the L1 signal path, the first-order ionospheric delay error is the largest near the equator, which is circa 7 m; the maximum second-order ionospheric delay error are circa 0.6 cm, 0.8 cm and 0.6 cm respectively for L1 signals coming from the zenith, the north and the south at 10 degree elevation angles. The second-order ionospheric delay error on the L1 signal path from zenith are the symmetry between 15° and ˜15° with respect to magnetic equator, and are nearly zero at the magnetic equator. For the first time, the second-order ionospheric delay error on the global scale is presented, so this research will greatly contribute to analysing the higher-order ionospheric delay error characteristics on the global scale.

Wang, Hu; Wang, Cheng; Wang, JieXian; Dang, YaMing; Bai, GuiXia; Wang, QianXin

2014-01-01

22

Solar rotational effects in the ionosphere and thermosphere  

NASA Astrophysics Data System (ADS)

The solar rotational signal has been detected in several ionospheric datasets including topside densities and temperatures, TEC and foF2, as well as incoherent scatter radar. These previous studies have established that the 27-day solar rotational signal is indeed present in the ionosphere and they typically correlate the variation with solar indices such as F10.7 or sunspot number. However, a comprehensive picture of precisely what spectral bands in the XUV are responsible for modifying which parts of the ionosphere still remains lacking. We analyze the solar rotational signal in several data sets including TOPEX/Jason (TEC), DMSP/SSIES (topside ionosphere), DMSP SSUSI (twilight/nighttime ionosphere profile), and COSMIC (global occultation measurements). These differing measurements provide complementary perspectives into the global and altitudinal response of the ionosphere to the solar rotational signal. The TIE-GCM is used mechanistically to examine the solar rotational effect on both the ionosphere and thermosphere. We examine under what conditions the solar rotational signal is significant on the bottom-side ionosphere.

Talaat, E. R.; Hsieh, S. W.; Smith, D.; Zhu, X.

2011-12-01

23

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

24

SOLAR FLARE EFFECTS IN THE IONOSPHERE  

Microsoft Academic Search

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

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

1967-01-01

25

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

Microsoft Academic Search

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

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

1961-01-01

26

Estimating and Removing Ionospheric Effects From GESS Interferometric SAR Imagery  

NASA Astrophysics Data System (ADS)

Many users of differential interferometry report image artifacts that cannot be attributed to surface deformation or terrain mismodeling. These artifacts are often ascribed to propagation delays due to the atmosphere or ionosphere. When atmospheric (primarily wet troposphere) delays can be ruled out, the ionosphere is usually blamed for the artifacts. There is rarely sufficient knowledge of the ionosphere at the spatial and temporal scales to prove or refute this assumption, however. In present-day, focused-based processing, large-scale ionospheric effects are typically removed in the baseline correction process before image formation. The large-scale mapping envisioned for the Global Earthquake Satellite System (GESS) precludes the use of baseline correction for removing anything other than physical orbit errors. Thus any effects induced by the ionosphere will be present in full measure. The ionosphere is a dispersive medium and produces several frequency-dependent effects on a radar signal, affecting both the resulting single-channel Synthetic Aperture Radar (SAR) imagery and two-channel interferometric imagery in a number of distinct ways. The signal propagation or group delay slows down the radar pulse relative to free space, while the phase delay advances the phase relative to that of free space. The Faraday rotation alters the polarization of the return signal. One may take advantage of the frequency dependence of the group and phase delays to evaluate the magnitude of the ionospheric total electron count (TEC). Global and large-scale ionospheric fluctuations are associated with solar UV excitation, and are modulated diurnally and seasonally. These can cause propagation delays at L-band of typically 10 to 20 meters, but up to a hundred meters and more in rare instances. Intermediate-scale disturbances (tens to hundreds of kilometers in extent) include traveling ionospheric disturbances (TIDs) and gravity waves induced by a variety of phenomena. These can alter the propagation delay by up to 5-10%. Small-scale disturbances (ionospheric "blobs" less than ~10 km in size) may result in scintillation or SAR defocusing but tend to be small in magnitude. Total day-to-day variability can exceed a few meters of delay, or up to 25% of the total delay. We examine two dual-frequency scenarios. In the first, we assume that GESS transmits a chirp waveform at two L-band ( ~1250 MHz) frequencies, each 10 MHz wide, separated by 70 MHz. In the second, we envision an additional C-band antenna transmitting a 10 MHz-wide chirp centered at 5350 MHz. We apply to interferometric SAR concepts similar to those developed for removing ionospheric effects from GPS signals using the GPS dual frequency range and phase observables. Although there are big differences between GPS and SAR, much work appears applicable. These dual-frequency approaches appear to be capable of removing the ionosphere at the level that GESS requires, at least for intermediate- and larger-scale ionospheric features (10 km and up).

Freedman, A. P.; Madsen, S. N.

2002-05-01

27

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

28

Ionospheric Effects from the superbolid exploded over the Chelyabinsk area  

NASA Astrophysics Data System (ADS)

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

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

29

The effects of solar flares on planetary ionospheres  

E-print Network

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

Withers, Paul

30

Effect of Moon phases in riometer absorption and in the ionospheric and geomagnetic parameters  

Microsoft Academic Search

Variations in the frequency of occurrence of riometer absorption, minimum frequency of reflection of the ionospheric F layer, minimum height, and height of maximum electron density of the ionospheric F layer near the solar minimum have been studied. Application of the superposed epoch technique has detected the Moon phase effect on these ionospheric parameters. This effect was: three events per

S. N. Samsonov; V. F. Smirnov; D. G. Baishev; A. A. Toropov; N. G. Skryabin

2007-01-01

31

Effect of Moon phases in riometer absorption and in the ionospheric and geomagnetic parameters  

Microsoft Academic Search

Variations in the frequency of occurrence of riometer absorption, minimum frequency of reflection of the ionospheric F layer, minimum height, and height of maximum electron density of the ionospheric F layer near the solar minimum have been studied. Application of the superposed epoch technique has detected the Moon phase\\u000a effect on these ionospheric parameters. This effect was: three events per

S. N. Samsonov; V. F. Smirnov; D. G. Baishev; A. A. Toropov; N. G. Skryabin

2007-01-01

32

Inelastic scattering effects on photoelectron spectra and ionospheric electron temperature  

Microsoft Academic Search

Three sets of inelastic scattering cross sections have been used by various investigators in energy degradation computations of photoelectrons. The effects of the three sets upon photoelectron spectra in the ionosphere, electron heating rates and temperature, and dayglow emissions are examined for solar minimum and solar maximum conditions. Comparison of individual cross sections shows large differences among the three sets

K. Stamnes; M. H. Rees

1983-01-01

33

Nonlinear Ionospheric Propagation Effects on UHF and VLF Radio Signals  

Microsoft Academic Search

An investigation of nonlinear wave-plasma interactions in the ionosphere causing significant propagation effects on VLF and UHF radio waves has been conducted. Nonlinear scattering of VLF waves off existing density irregularities is shown to be responsible for the observed spectral broadening. When the irregularity scale size does not exceed a few tens of meters, the scattered wave is found to

Keith Michael Groves

1991-01-01

34

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

E-print Network

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

Withers, Paul

35

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

36

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

37

Effects of large zonal plasma drifts on the subauroral ionosphere  

NASA Technical Reports Server (NTRS)

A model of the earth's ionosphere and plasmasphere is used to investigate the effects of an imposed westward plasma drift of maximum velocity 2 km/s. A closed subauroral tube of plasma is considered and the velocity spike persists for 10 min. Ion-neutral frictional heating causes rapid elevation of the F-region O(+) temperature. The F-layer O(+) concentration is decreased due to increased O(+) loss rate and rapid ion flows both upward and downward from the F-region. The upward flux of O(+) through the topside ionosphere can each 5 x 10 exp 9/sq cm/s; when the velocity spike ceases there is a return flow of O(+) that tends to replenish the F-layer. Most of the features revealed by the model for the F-region and topside ionosphere are in accord with observations of subauroral ion drifts. Downward flows that are predicted to be persistently present around the 300 km altitude level appear to agree with observations only occasionally; suggestions are made to resolve this discrepancy.

Sellek, R.; Bailey, G. J.; Moffett, R. J.; Heelis, R. A.; Anderson, P. C.

1991-01-01

38

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

39

Methods of alleviation of ionospheric scintillation effects on digital communications  

NASA Technical Reports Server (NTRS)

The degradation of the performance of digital communication systems because of ionospheric scintillation effects can be reduced either by diversity techniques or by coding. The effectiveness of traditional space-diversity, frequency-diversity and time-diversity techniques is reviewed and design considerations isolated. Time-diversity signaling is then treated as an extremely simple form of coding. More advanced coding methods, such as diffuse threshold decoding and burst-trapping decoding, which appear attractive in combatting scintillation effects are discussed and design considerations noted. Finally, adaptive coding techniques appropriate when the general state of the channel is known are discussed.

Massey, J. L.

1974-01-01

40

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

NASA Astrophysics Data System (ADS)

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

41

Estimating and Removing Ionospheric Effects From GESS Interferometric SAR Imagery  

Microsoft Academic Search

Many users of differential interferometry report image artifacts that cannot be attributed to surface deformation or terrain mismodeling. These artifacts are often ascribed to propagation delays due to the atmosphere or ionosphere. When atmospheric (primarily wet troposphere) delays can be ruled out, the ionosphere is usually blamed for the artifacts. There is rarely sufficient knowledge of the ionosphere at the

A. P. Freedman; S. N. Madsen

2002-01-01

42

Martian Ionospheric Variability as Observed by MARSIS: The Effects of Solar Energetic Particles, Ionizing Radition, Meteors, and Dust Activity  

Microsoft Academic Search

We present evidence for time variability in the martian ionosphere due to solar energetic particles. We also discuss possible ionospheric effects from meteoric material, dust storms, the diurnal ionization cycle, and crustal magnetic fields.

J. R. Espley; W. Farrell; D. A. Brain; D. D. Morgan; M. H. Acuña; B. Cantor; J. Plaut; G. Picardi

2007-01-01

43

Martian Ionospheric Variability as Observed by MARSIS: The Effects of Solar Energetic Particles, Ionizing Radition, Meteors, and Dust Activity  

NASA Astrophysics Data System (ADS)

We present evidence for time variability in the martian ionosphere due to solar energetic particles. We also discuss possible ionospheric effects from meteoric material, dust storms, the diurnal ionization cycle, and crustal magnetic fields.

Espley, J. R.; Farrell, W.; Brain, D. A.; Morgan, D. D.; Acuña, M. H.; Cantor, B.; Plaut, J.; Picardi, G.

2007-03-01

44

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

45

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

46

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

47

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

E-print Network

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

Withers, Paul

48

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

E-print Network

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

Withers, Paul

49

PolInSAR at Low Frequency and Ionospheric Effects  

NASA Astrophysics Data System (ADS)

Global warning is now known to be the major environmental issue mankind will have to face in the next decade. Monitoring of vegetation and biomass is clearly an essential piece of information required at all levels ranging from the scientific studies to understand and forecast, to the political actors and government leaders responsible for drafting remediation policies and evaluating their impact. Microwave remote sensing with the low-frequency SAR technique can provide a useful characterization of forest (spatial coverage, species, density, height...) at a global scale, relying on the all-weather imaging capabilities of SAR linked with the significant penetration of the low-frequency EM wave in the canopy. The published techniques for forest characterization from low frequency SAR data include radiometry inversion, polarimetric inversion based on the anisotropy parameters and PolInSAR Random Volume Over Ground inversion [1]. In this paper, we will more specifically concentrate on the PolInSAR technique and the impact of ionospheric effect on this inversion. PolInSAR at low frequency can be envisioned with two radar platforms flying in formation or as a repeat pass mission. The second alternative is more plausible given the cost and the size of a low frequency SAR instrument. However the two cases will be discussed in the paper. Among the challenges, the following questions need to be addressed: · What is the impact of ionosphere and Faraday rotation on the PolInSAR inversion results? · Is it necessary to correct the data prior to applying the inversion and what is the highest Faraday rotation for which a correction is not necessary? · What is the effect of loss of interferometric coherence and could this be compensated for? · Can the technique provide an estimation of the Faraday rotation or the differential Faraday rotation? · How does ionospheric and calibration effects interact? · What are the implications on a compact polarimetry mode of operation? · Are Faraday rotation-derived estimates of TEC accurate enough to correct for differential phase offsets caused by e.g. phase delay?

Dubois-Fernandez, P.; Angelliaume, S.; Truong-Loi, M.-L.; Freeman, A.; Pottier, E.

2009-04-01

50

The effect of solar illumination on ionospheric outflow composition in the polar cap region  

NASA Astrophysics Data System (ADS)

We use measurements by the CODIF ion spectrometer aboard the Cluster spacecraft, to investigate the composition of upflowing ion beams detected in the magnetospheric lobes during periods of northward IMF. These ion beams consist of ionospheric ions originating from the local polar ionosphere and are accelerated upward by a quasi-static electric field. This field-aligned electric field effectively acts as an extension of the experiment, probing the plasma at the altitude just below the bottom of the acceleration region and accelerating the ions into the energy range accessible by the CODIF detector. In this way it becomes possible to analyze the composition of upflowing ionospheric ions just above the polar ionosphere where ions are usually too cold to be measured by ion detectors due to the spacecraft charging We make a statistical analysis of the change in the composition of upflowing ions as a function of the solar zenith angle at the local ionosphere for a set of ~70 events. We show that the composition undergoes a very distinct regime change around 100° solar zenith angle, which corresponds to the solar terminator at ionospheric altitude. While the H+ density only shows weak variations with the solar zenith angle, the amount of O+ ions sharply decreases around 100° solar zenith angle. This illustrates how the alteration of ionospheric properties by solar illumination can affect the ionospheric upflow composition, and particularly the amount of O+ upflowing from the polar ionosphere. With a very simple model we investigate the implications of these observations on the seasonal variation of the average composition of ionospheric plasma upflowing from the polar ionosphere. Considering both the northern and southern polar regions, we show that the proportion of the polar ionosphere which is sunlit (i.e. below 100° solar zenith angle) varies through the year. Therefore the O+ dependency on solar illumination evidenced by Cluster suggests that ionospheric outflow will exhibit seasonal variations. Due to this seasonal effect, we may expect a higher amount of O+ ions escaping the polar ionosphere during spring/autumn than during winter/summer.

Maes, Lukas; Maggiolo, Romain; Haaland, Stein; Dandouras, Iannis; De Keyser, Johan; Fear, Rob; Fontaine, Dominique

2014-05-01

51

Flare Effects in Mars's Ionosphere Observed by Mars Express Topside Sounding  

NASA Astrophysics Data System (ADS)

Since the beginning of Solar Cycle 24, there have been several strong solar flares, one of which, on 22 September 2011, may have contributed to the safing of the Mars Express Spacecraft. The Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument on board Mars Express, in orbit around Mars, can be used in Active Ionospheric Sounding mode to detect disturbances of the Martian ionosphere. In this presentation, we identify several high-energy particle events at Mars originating in solar flares, including that of 22 September 2011, using in situ particle data from the High-Energy Neutron Detector (HEND). HEND is part of the Gamma Ray Spectrometer on board the Odyssey spacecraft, also in orbit around Mars. Using the timing of the high-energy particle events from HEND, we use MARSIS ionospheric electron density profiles, local electron densities, and surface reflection absorption to track the effect of flare particles on the Martian ionosphere. We incorporate data from the Mars Express particle and plasma instrument ASPERA-3 to show effects on the particle distribution in the ionosphere and to note an extension of the nightside ionosphere to altitudes of several thousand kilometers approximately one day after the particle onset. The flux peak of the 22 September 2011 event coincides with intense spread-F-like echoes near the ionospheric peak and in the "upper layer" ionosphere, implying a predominance of oblique echoes, even in the absence of strong cusplike magnetic topology. As with previous particle events, the nightside surface reflection disappears due to electron collision damping, and the MARSIS Subsurface-mode signal is obscured by noise. During the most intense fluxes of this flare, the peak of the upper layer structure of the Martian ionosphere remains stable, although less pronounced than during less intense fluxes, suggesting a filling-in of undercut or shelflike structures in the electron density profile above the main layer.

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

2012-04-01

52

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

53

The study of the effect of solar eclipses on the ionosphere based on satellite beacon observations  

NASA Astrophysics Data System (ADS)

The ionospheric effect of a solar eclipse was first noticed in 1927 during an English eclipse. In studies of the effects of solar eclipses on the ionosphere by ionosondes during the next 30 years, the obtained results were difficult to interpret. Results obtained after the introduction of additional techniques indicate that the redistribution of ionization due to temperature changes is important, as is recombination. More recently, a more detailed study of the eclipse effects throughout the ionosphere was made possible as a result of the addition of the satellite beacon observations. The present investigation provides a review of the study of eclipse effects on the ionosphere based on satellite beacon observations. Attention is given to early observations, and total and partial solar eclipses over North America, Africa, Australia, and India.

Cohen, E. A.

1984-06-01

54

Monitoring the ionospheric storm effect with multiple instruments in North China: July15-16, 2012 magnetic storm event.  

NASA Astrophysics Data System (ADS)

A major geomagnetic storm occurred on July 15-16, 2012, which is characterized by a long-lasting southward turning of interplanetary geomagnetic field (IMF) for ~30 hours below -10 nT. Prominent large-scale ionospheric disturbances were observed in North China during this extreme space weather event. This study reveals the possibility of using the newly built China seismo-ionospheric ground-based monitoring network (CSGMN) to investigate the ionospheric storm effect during different phase of the storm. As a main part of the CSGMN, the oblique and vertical sounding systems and global position system (GPS) network all observed a moderate and a strong positive storm effects around the noon and the sunset sector on 15 July. The maximum enhancement of parameter peak electron density (NmF2) increased 100% and TEC 60%. The positive phase then is followed by an intense negative storm effect during the entire day on July 16 with NmF2 and TEC fell below 40% of the previous quiet day values. Also, the electron density profiles retrieved from the COSMIC radio occultation measurements were examined and validated with the ground measurements in order to estimate the possibility of its use as an additional data source to study altitude distribution of ionospheric storms. Good agreement has been reached between the ground and satellite occultation measurements even if they are not close. The result here shows that CSGMN can be a very powerful network not only for the seismo-ionospheric study but also in monitoring space weather.

Wang, Min

2014-05-01

55

Ionospheric effect of HF surface wave over-the-horizon radar  

NASA Astrophysics Data System (ADS)

The use of HF surface wave radar as an effective method for inspecting the environment of the ocean in the beyond-the-horizon area has been developing in recent years. However, because the radiating beam of the transmitting antenna is of a certain width and its electromagnetic radiating power propagates not only along the sea surface but also to the upper space, as a result, after interacting with the ionosphere or a scattering object on its path, the backscattered signal then returns to the radar along the radiative path. Thus, if we analyze the echo signal received by the radar, we can obtain some information about the ionosphere. This paper presents a method of sensing the ionosphere using HF ground wave radar, which can give information about the altitude of the ionosphere, Doppler, meteor showers, etc.

Gao, Huotao; Li, Geyang; Li, Yongxu; Yang, Zijie; Wu, Xiongbin

2006-12-01

56

The ``Same Side - Opposite Side Effect'' of the Heliospheric Current Sheet in Ionospheric Negative Storms  

NASA Astrophysics Data System (ADS)

Using 141 CME-interplanetary shock (CME-IPS) events and foF2 from eight ionosonde stations from January 2000 to September 2005, from the statistical results we find that there is a “same side - opposite side effect” in ionospheric negative storms, i.e., a large portion of ionospheric negative disturbances are induced by the same-side events (referring to the CMEs whose source located on the same side of the heliospheric current sheet (HCS) as the Earth), while only a small portion is associated with the opposite-side events (the CMEs source located on the opposite side of the HCS as the Earth); the ratio is 128 vs. 46, and it reaches 41 vs. 14 for the intense ionospheric negative storms. In addition, the ionospheric negative storms associated with the same-side events are often more intense. A comparison of the same-side event (4 April 2000) and the opposite-side event (2 April 2001) shows that the intensity of the ionospheric negative storm caused by the same-side event is higher than that by the opposite-side event, although their initial conditions are quite similar. Our preliminary results show that the HCS has an “impeding” effect to CME-IPS, which results in a shortage of energy injection in the auroral zone and restraining the development of ionospheric negative perturbations.

Li, Z.; Wei, F. S.; Feng, X. S.; Zhao, X. H.

2010-05-01

57

Effects of Geomagnetic effect on Sub-ionospheric VLF-LF Signals Propagation  

NASA Astrophysics Data System (ADS)

Abstract: To investigate the effect of geomagnetic storm on subionospheric VLF-LF signal propagation, we analyze the variation in amplitude of VLF-LF signal using advanced complex continuous wavelet transform techniques. We analyze the VLF signal transmitted form ICV (20.27 kHz) located at Isola di Tavolara (40.55o N, 9.430 E), Italy and DH038 (23.40 kHz) Rhauderfehn (53.040 N, 7.340 E) Germany and one LF signal transmitted form NRK (37.50 kHz) transmitter located at Grindavik (63.510 N, 22.280 E), Iceland. We observed significant absorption in amplitude of these signals during the geomagnetic storm compared to their ambient values for the same period during the adjacent 7 days. The signal strength along their propagation paths was controlled by the storm associated decrease in ionization in the D-region of the ionosphere. Waveguide mode theory calculations show that the elevation of the height of lower ionosphere boundary of Earth-ionosphere waveguide was significantly decreased during this period. Key words: Subionospheric VLF-LF propagation, Complex Wavelet Transform, Geomagnetic activity and Earth-ionosphere waveguide

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

58

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

59

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

60

Effect of a Meteoric Shower on the Ionosphere  

Microsoft Academic Search

OF the various agencies responsible for producing and maintaining ionisation of the ionosphere, bombardment of the upper atmosphere by meteors has been suggested as one. Skellett1 has carried out a calculation of the energy received by the earth due to impact of the meteors and finds that during a meteoric shower it might be so high as a fourteenth of

S. K. Mitra; P. Syam; B. N. Ghose

1934-01-01

61

Low- and mid-latitude ionospheric effects of energetic electrons  

NASA Astrophysics Data System (ADS)

Recent observations revealed events of energetic and relativistic electron enhancements in the Earth’s radiation belt (ERB) occurred on timescales of less than a few hours. As it was shown, so-called "rapid rebuilding" events were caused by substorms. We found that similar enhancements were also seen under the ERB in the forbidden zone. Both phenomena of sudden growth of energetic electrons inside and under the ERB relate to substorm dipolarizations, which result in rapid changes in the configuration of the magnetic field and generation of inductive electric fields. In the previous studies we found very intense fluxes of energetic electrons in the forbidden zone which resulted in substantial abundant ionospheric ionization during strong magnetic storms. Here we analyze enhancements of >30-keV quasi-trapped electrons during a moderate recurrent (CIR/HSS-driven) geomagnetic storm on 22 July 2009. We focus on particular issue of the magnetosphere-ionosphere coupling through the quasi-trapped electrons at low-latitudes. We show that unusually large area in the nighttime ionosphere with increased total electron content (TEC) and prominent elevation of the F-layer at low-latitudes coincides spatially and temporarily with enhanced electron fluxes. Ionizing particles are considered now as an addition source of ionization during recurrent magnetic storms along with generally accepted mechanisms for storm-time TEC increases or so-called positive ionospheric storms.

Suvorova, Alla; Matsumoto, Haruhisa; Kunitsyn, Viacheslav; Andreeva, Elena; Nesterov, Ivan; Dmitriev, Alexei; Huang, Chien-Ming

62

Ionospheric Scintillation Effects on Single and Dual Frequency GPS Positioning  

E-print Network

occurs when the GPS or SBAS satellite signal travels through small-scale irregularities in electron density in the ionosphere, typically in the evening and nighttime in equatorial regions. Frequent scintillation and high rates of change in Total Electron Content (TEC) can cause loss of lock to dual frequency

Stanford University

63

Modeling the effects of secular variation of geomagnetic field orientation on the ionospheric long term trend over the past century  

Microsoft Academic Search

A middle- and low-latitude ionospheric theoretical model is used for the first time to assess the effects of the secular variations of geomagnetic field orientation on ionospheric long-term trends over the past century. It is found that the varied geomagnetic field can produce ionospheric long-term trends in both foF2 and hmF2. Since the amplitudes of geomagnetic field change depend on

Xinan Yue; Libo Liu; Weixing Wan; Yong Wei; Zhipeng Ren

2008-01-01

64

Lunar tidal effects in the electrodynamics of the low latitude ionosphere  

NASA Astrophysics Data System (ADS)

The low latitude ionosphere is highly variable over a large range of temporal and spatial scales even during geomagnetically quiet periods, largely as a result of electrodynamic plasma drift effects. Several recent experimental and modeling studies have investigated the electrodynamic response of the low latitude ionosphere to high latitude and lower atmospheric wave activity, particularly during sudden stratospheric warmings. In this work, we review some recent results on the short-term variability of equatorial vertical plasma drifts measured mostly at the Jicamarca Radio Observatory and their effects on equatorial short-scale spread F irregularities. We show that lunar tidal semidiurnal and diurnal effects, which have been largely ignored in most studies, can play significant roles in low latitude ionospheric variability.

Fejer, Bela G.; Tracy, Brian D.

2013-10-01

65

Electron gyroharmonic effects on ionospheric stimulated Brillouin scatter  

NASA Astrophysics Data System (ADS)

Stimulated Brillouin scattering (SBS) and resonant phenomena are well known in the context of laser fusion, fiber optics, and piezoelectric semiconductor plasmas, as well as in various biological applications. Due to recent advances, active space experiments using high-power high-frequency (HF) radio waves may now produce stimulated Brillouin scattering (SBS) in the ionospheric plasma. The sensitivity of the narrowband SBS emission lines to pump frequency stepping across electron gyroharmonics is reported here for the first time. Experimental observations show that SBS emission sidebands are suppressed as the HF pump frequency is stepped across the second and third electron gyroharmonics. A correlation of artificially enhanced airglow and SBS emission lines excited at the upper hybrid altitude is observed and studied for second gyroharmonic heating. The SBS behavior near electron gyroharmonics is shown to have important diagnostic applications for multilayered, multi-ion component plasmas such as the ionosphere.

Mahmoudian, A.; Scales, W. A.; Bernhardt, P. A.; Isham, B.; Kendall, E.; Briczinski, S. J.; Fuentes, N. E. B.; Vega-Cancel, O.

2014-08-01

66

Effect of small ionospheric irregularities on radio wave absorption  

NASA Technical Reports Server (NTRS)

The ionospheric absorption of a radio wave caused by small-scale irregularities with a gaussian autocorrelation function is calculated for various values of the linear scale height, the radio frequency, the scale size of the irregularities, and the mean-square fractional electron density fluctuations. The absorption is due to scattering of the radio wave into plasma oscillations by the irregularities. It is concluded that the absorption due to such irregularities with a mean-square fractional electron density deviation greater than about 0.000001 exceeds the normal collisional height-integrated absorption. Absorption of this type could play a significant part in heating experiments or in an ionosphere containing naturally occurring irregularities.

Chen, H. C.; Fejer, J. A.

1975-01-01

67

Case Studies of Ionospheric Effects of Stratospheric Sudden Warmings  

NASA Astrophysics Data System (ADS)

Recent studies have shown large variations in low-latitude ionospheric electron density occurring after stratospheric sudden warming event. We use observations of GPS total electron content data in the Western Hemisphere for winters of 2009, 2008, and 2003 to illustrate main features of ionospheric changes related to stratospheric sudden warmings. The common feature in all events is the increase in the electron density during the morning hours and the decrease in the afternoon, related to amplification of 12-hour signature in low-latitude vertical ion drifts. This feature persists for several days after the peak in stratospheric temperature. As stratospheric warming event subsides, the feature shifts to later local times, indicating a phase shift in the 12-hour wave. Non-linear interaction of planetary waves with tides leading to increase in the amplitude of semidiurnal tide at low latitude lower thermosphere and modulation of E-region electric field with subsequent mapping along the magnetic field lines to the F-region is thought to be the primary mechanism responsible for the observed ionospheric response.

Goncharenko, L. P.; Coster, A. J.; Chau, J. L.; Liu, H.; Rideout, W.; Valladares, C. E.

2009-12-01

68

Ionospheric effects of the cosmic gamma ray burst of 29 March 2003  

NASA Astrophysics Data System (ADS)

We present evidence for ionospheric effects caused by the gamma ray burst that originated at a cosmological distance. At the time of the strong cosmic gamma-ray burst of 29 March 2003 (GRB030329) that took place in the nighttime in Japan we observed a transient decrease in the strength of the radio noise coming from extraterrestrial sources (cosmic noise) at 38 MHz. We also observed a sudden field-amplitude decrease of an 8.006 MHz transmission signal recorded at a distance of 690 km from the transmitter. These phenomena are interpreted as a result of an ionospheric absorption enhancement due to transient ionization caused by GRB030329. We also report no appreciable effect on the ionospheric electron column content derived using GPS (Global Positioning System) microwave signals.

Maeda, Koitiro; Tomizawa, Ichiro; Shibata, Takashi F.; Tokimasa, Noritaka; Saito, Akinori; Maruyama, Takashi

2005-09-01

69

Ionospheric Storm Effects above Kharkov during the August 5-6, 2011  

NASA Astrophysics Data System (ADS)

The super strong magnetic storm began at 19:03 UT on August 5, 2011. The geomagnetic activity index Kp during the main storm phase was 8-, Dst = -113 nT. The solar wind radial velocity during the main phase varied within 570 - 620 km s-1. The temperature of solar wind particles increased up to 6.4·105 K and their concentration Nsw ? 1.9·107 m-3. The value of the interplanetary magnetic field (IMF) Bz component was -(15 - 18) nT, the value of the magnetic induction modulus of the IMF equaled 25 - 27 nT. The aurora activity index was AE ? 1740 nT. The value of Akasofu function was ? ? 37 GJ s-1. For the observations of ionospheric storm effects, the Kharkov incoherent scatter radar was used, which is unique source of information about parameters and processes in ionospheric plasma in mid-latitude Europe. The effects of the magnetic storm on August 5 - 6, 2011 were observed in variations of ionosphere parameters confidently. The storm above Kharkov was accompanied by a negative ionosphere disturbance. The electron density in the F2-layer maximum of ionosphere decreased approximately by a factor up to 2 in comparison with the reference day up to 1011 m-3. Next twenty-four hours on 6 August Nm was approximately more on 30 % than in the reference day of 4th August 2011. The F2-layer maximum height in the main phase of the ionospheric storm increased to 513 km. In quiet conditions of 4th August F2-layer was on a height zm ? 315 km. The electron density on heights 200, 250, 300, 350 and 400 km in the moment of the main phase of the ionospheric storm decreased approximately by 85, 91, 82, 61 and 27% accordingly. The electron temperature in the main phase of the ionospheric storm increased approximately by a factor up to 4 and 2.5 at the heights 200 - 250 km, and in the range of heights 300 - 700 km Te increased approximately by a factor up to 1.5 - 1.8 in comparison with the reference day. The ion temperature in considered period also increased approximately on 700 - 1000 K in the range of heights 200 - 250 km. On heights 300 - 700 km Ti increased approximately by a factor up to 1.5. The storm on August 5 - 6, 2011 had adduced to transform of dynamic and heat conditions in ionosphere.

Chernogor, L.; Domnin, I.; Emelyanov, L.; Kharytonova, S.; Lyashenko, M.

2012-04-01

70

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

71

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

72

Effective radius of heating of the lower ionosphere by intense shortwave radiation  

NASA Astrophysics Data System (ADS)

The results of a theoretical analysis of the radial distribution of electron temperature T e in the area of heating of the lower ionosphere by intense shortwave radiation are presented. It was established that effective radius r eff of heating at a certain height may differ significantly from the characteristic radius of illumination of the ionosphere ( a) by radiation at this height. At the boundary of the heating area ( r = r eff ), the characteristic radial scale of T e changes is less than the corresponding scale of changes in the squared amplitude of the radiation electric field, and it is almost independent of the amplitude value; i.e., the formation of a relatively strong T e gradient at such a boundary is a common feature of heating of the lower ionosphere by intense shortwave radiation.

Alpatov, V. V.; Badin, V. I.; Grebnev, I. A.; Deminov, M. G.; Faermak, D. S.

2012-11-01

73

Effects of meteorological forcing on the thermosphere and ionosphere as simulated by numerical models  

NASA Astrophysics Data System (ADS)

The ionosphere-thermosphere system is influenced not only by solar and magnetospheric processes, but also by meteorological variability. Ionospheric observations of total electron content during the current solar cycle have shown that variability associated with meteorological forcing is important during solar minimum, and also can have significant ionospheric effects during solar medium to maximum conditions. Numerical models can be used to help understand the mechanisms that couple the lower and upper atmosphere over the solar cycle. This presentation gives an overview of the different proposed lower to upper atmosphere coupling mechanisms from a modeling perspective. Gravity and planetary waves along with tides play a crucial role in coupling the troposphere and stratosphere to the upper atmosphere. These waves and tides, when they dissipate, alter the background atmosphere which leads to changes in the tidal and planetary wave propagation. Some tides and waves reach the E-region around 100-150 km and change the low latitude plasma drift via the wind-driven electrodynamo. The vertical drift is one factor which determines the low latitude F-region ionosphere structure during the daytime. There is also observational evidence that tides propagate into the upper thermosphere and directly influence the plasma distribution. In addition, numerical simulations have suggested that tides and waves alter the upper thermospheric composition which in turn influences the F-region ionosphere. Including meteorological variability in numerical models increases the ionospheric variability, and enable us to reproduce some of the observed effects of strong meteorological disturbances, e.g, during Stratospheric Sudden Warming periods. We will allude to the need for further model development to improve the numerical model performance when meteorological variability is included.

Maute, Astrid

2014-05-01

74

The effects on the ionosphere of inertia in the high latitude neutral thermosphere  

NASA Technical Reports Server (NTRS)

High-latitude ionospheric currents, plasma temperatures, densities, and composition are all affected by the time-dependent response of the neutral thermosphere to ion drag and Joule heating through a variety of complex feedback processes. These processes can best be studied numerically using the appropriate nonlinear numerical modeling techniques in conjunction with experimental case studies. In particular, the basic physics of these processes can be understood using a model, and these concepts can then be applied to more complex realistic situations by developing the appropriate simulations of real events. Finally, these model results can be compared with satellite-derived data from the thermosphere. We used numerical simulations from the National Center of Atmospheric Research Thermosphere/Ionosphere General Circulation Model (NCAR TIGCM) and data from the Dynamic Explorer 2 (DE 2) satellite to study the time-dependent effects of the inertia of the neutral thermosphere on ionospheric currents, plasma temperatures, densities, and composition. One particular case of these inertial effects is the so-called 'fly-wheel effect'. This effect occurs when the neutral gas, that has been spun-up by the large ionospheric winds associated with a geomagnetic storm, moves faster than the ions in the period after the end of the main phase of the storm. In these circumstances, the neutral gas can drag the ions along with them. It is this last effect, which is described in the next section, that we have studied under this grant.

Burns, Alan; Killeen, Timothy

1993-01-01

75

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

76

The Effects of Solar Flares on Planetary Ionospheres PAUL WITHERS1  

E-print Network

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

Withers, Paul

77

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

78

Effects of Lightning Return Stroke Parameters on Radiated Fields, on the Ground and in the Ionosphere  

NASA Astrophysics Data System (ADS)

We present numerical simulations of lightning return stroke currents and the fields radiated in the Earth-ionosphere waveguide and into the lower ionosphere. Where previous lightning-ionosphere interaction models approximate the return stroke current as constant over the altitude range of the return stroke, we implement a modified transmission line model of the return stroke, with either linear (MTLL) or exponential (MTLE) current decay with altitude. Using this model we investigate the effects of the return stroke rise time ?r, fall time ?f, propagation speed vrs, and terminal altitude h on both the electrostatic and radiated fields. These parameters affect the field amplitudes and waveforms both as measured along the ground and in the lower ionosphere, the latter having implications for sprite initiation, D-region ionization and elve luminosity. In addition, these parameters affect the interpretation of temporal signatures of elves. We present results that demonstrate the effects of each of the four parameters on fields, ionization, and elve luminosity and temporal signature. We further investigate the effects of these parameters on the relationship between peak current Ik and E100, the electric field measured at 100 km range on the ground.

Marshall, R. A.

2012-12-01

79

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

80

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

NASA Astrophysics Data System (ADS)

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

Marshall, R. A.

2014-05-01

81

Planetary ionospheres  

NASA Technical Reports Server (NTRS)

An analogy is drawn between the Eath's ionosphere and the existence of ionospheres around other planets or natural satellites. An ionosphere is defined as a series of layers (D, E, E1, F2) and their characteristics are discussed. Emphasis is on the role of solar wind impacting with the potential ionosphere and the subsequent chemical and diffusion processes that can be observed. Data from the MARINER and PIONEER space programs are cited concerning measured electron density and ionospheric refractivity of extraterrestrial ionospheres, then an attempt is made to model these atmospheres based on Earth ionosphere theory.

Bauer, S. J.

1977-01-01

82

The flywheel effect: Ionospheric currents after a geomagnetic storm  

SciTech Connect

In the period following a geomagnetic storm the high-latitude, magnetospheric-driven convection pattern is normally weak. However, the neutral circulation, set up by ion-neutral momentum coupling during the main phase of the storm, may continue for several hours after the storm has ended. This persistent neutral circulation has the potential to drive Hall currents for some hours. In this paper the authors investigate these flywheel' currents by simulating a storm which occurred on the 23rd of November 1982 using the National Center for Atmospheric Research Thermosphere Ionosphere General Circulation Model (NCAR-TIGCM). The resulting high-latitude, height-integrated Hall currents are dominated by the neutral-wind-driven component for several hours after the end of main phase of the storm. The direction of these currents is reversed from normal. Analysis of the neutral and ion components of this current system indicates that the neutral component may drive as much as 80% of the high-latitude current system immediately after the storm has ended, and may continue to dominate this system for 4 to 5 hours.

Deng, W.; Killeen, T.L.; Burns, A.G. (Univ. of Michigan, Ann Arbor (United States)); Roble, R.G. (National Center for Atmospheric Research, Boulder, CO (United States))

1991-10-01

83

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

84

Ionospheric irregularities and effects on GNSS navigation systems in the polar cap  

NASA Astrophysics Data System (ADS)

In this presentation we describe efforts that are currently ongoing at Svalbard to study ionospheric irregularities and their effects on GNSS navigation systems in the polar cap. We present initial measurements from a series of new multi-constellation TEC and scintillation receivers that we are installing around Svalbard. These data will be compared with multi-instrument observations from EISCAT, SuperDARN, ground-based optics, and sounding rockets.

Oksavik, Kjellmar; van der Meeren, Christer; Moen, Joran I.; Lester, Mark

2013-04-01

85

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.

86

Effects of high-latitude ionospheric electric field variability on global thermospheric Joule heating and mechanical energy transfer rate  

Microsoft Academic Search

Effects of high-latitude ionospheric electric field variability on the Joule heating and mechanical energy transfer rate are investigated by incorporating realistic spatial and temporal characteristics of electric field variability derived from observations into the forcing of a thermosphere ionosphere electrodynamic general circulation model. First, the characteristics of subgrid-scale variability are examined from a spectral analysis of Dynamic Explorer-2 (DE-2) plasma

Tomoko Matsuo

2008-01-01

87

Frequencies and polarizations of ULF waves in the magnetosphere: effects of ionospheric Pedersen and Hall conductances.  

NASA Astrophysics Data System (ADS)

We extended a recently developed Field line Resonance model based on covariant-contravariant formalism to include finite ionospheric conductivities. The nature of our model allows a straightforward incorporation of both Pedersen and Hall conductivities, while earlier studies were restricted to using Pedersen conductance only. In agreement with previous studies we find that Pedersen conductance results primarily in attenuation of the standing wave; its effect on the frequency and polarization of the wave is generally small. In contrast, Hall conductance by itself does not lead dissipation of the wave, but modifies wave's polarization. Thus, including ionospheric Hall conductance is extremely important for realistic modeling polarizations of Ultra Low Frequency wave, which have significance for electron energization in the magnetosphere. We present results applying our new ULF wave model to various background magnetic fields, such as idealized "compressed dipole" and Tsyganenko fields.

Kabin, K.; Rankin, R.; Degeling, A.; Elkington, S.

2008-12-01

88

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

SciTech Connect

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

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

1980-10-01

89

Effect of vertical plasma transport on ionospheric F2-region parameters at equatorial latitude  

NASA Astrophysics Data System (ADS)

The variability of the F2-layer even during magnetically quiet times are fairly complex owing to the effects of plasma transport. The vertical E × B drift velocities (estimated from simplified electron density continuity equation) were used to investigate the seasonal effects of the vertical ion drifts on the bottomside daytime ionospheric parameters over an equatorial latitude in West Africa, Ibadan, Nigeria (Geographic: 7.4°N, 3.9°E, dip angle: 6°S) using 1 year of ionsonde data during International Geophysical Year (IGY) of 1958, that correspond to a period of high solar activity for quiet conditions. The variation patterns between the changes of the vertical ion drifts and the ionospheric F2-layer parameters, especially; foF2 and hmF2 are seen remarkable. On the other hand, we observed strong anti-correlation between vertical drift velocities and h?F in all the seasons. We found no clear trend between NmF2 and hmF2 variations. The yearly average value of upward daytime drift at 300 km altitude was a little less than the generally reported magnitude of 20 ms-1 for equatorial F-region in published literature, and the largest upward velocity was roughly 32 ms-1. Our results indicate that vertical plasma drifts; ionospheric F2-layer peak height, and the critical frequency of F2-layer appear to be somewhat interconnected.

Oyekola, O. S.; Ojo, Akin

90

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

91

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

92

Magnetic field anomalies from seismo-ionospheric effects of 2011 Tohoku earthquake  

NASA Astrophysics Data System (ADS)

Anomalous magnetic variations were observed by ground magnetometers in East Asia area after the 2011 Tohoku earthquake. Some earlier reports showed the seismo-magnetic variations have obvious amplitude around the epicenter, we emphasis here that the variations can still be notable at stations 2000 to 4000 km away from epicenter and we define it as teleseismic magnetic disturbances (TMDs). TMDs appear about 8 min later after the arrival of seismic Rayleigh waves at teleseismic distances, and propagate at a horizontal velocity of 3.9 km/s. The wave-like TMDs last for no longer than 10 minutes, and have a main period of 2.1-3.3 min. TMDs are not generated by direct effects of processes in focal area crust or tsunami waves, instead, their properties consist with the Rayleigh wave model of seismo-ionospheric disturbances. Hence we conclude that the TMDs are the magnetic manifestation of seismotraveling ionospheric disturbances (STIDs), generated by the interaction between the ionosphere and atmosphere through acoustic waves launched by travelling Rayleigh waves. This work was jointly supported by NSFC (40904036, 41274155), China NIBRP (2011CB811405) and Project Supported by the Specialized Research Fund for State Key Laboratories.

Hao, Yongqiang; Xiao, Zuo; Zhang, Donghe

2013-04-01

93

Doppler spectral characteristics of high latitude ionospheric irregularities: Effect on HF radars  

NASA Astrophysics Data System (ADS)

This report considers the Doppler spectral properties of radar signals scattered from high latitude E and F-region ionospheric irregularities. Although the exact mechanism for the production of F-region irregularities is not yet known, it appears that the Doppler shift from these as well as from E-region irregularities is determined by the ionospheric electric field via the E X B/B-squared drift velocity. The width of the backscattered spectra is determined by the viewing angle of the radar relative to the E X B/B-squared drift direction as well as the drift magnitude. Assuming an electrical potential distribution over the Earth's high latitude regions, it has been possible to predict the diurnal variability of the Doppler velocity and width associated with high latitude irregularities. Although some of these predictions agree with previous observations, considerably more knowledge is required of the high latitude potential distribution and its temporal variability. Finally, a novel new technique is proposed whereby through cross spectral analysis the detrimental effects of clutter due to ionospheric irregularities may be eliminated.

Greenwald, R. A.

1981-05-01

94

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

95

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

NASA Astrophysics Data System (ADS)

Stimulated electromagnetic emissions (SEE) are high-frequency radio emissions that are generated during high-power, high-frequency, ordinary mode (O-mode), radiowave heating of the ionosphere. These emissions are particularly useful in ionospheric heating experiments because they provide a way of monitoring space plasma processes remotely and passively. In order to utilize these emissions for diagnostic purposes, it is necessary to understand the space plasma processes involved in their generation. The purpose of these experiments was to observe the responses of a particular component of the SEE, the broad upshifted maximum (BUM), to a variety of heating stimuli in an effort to understand the factors involved in its development. Heating experiments were conducted at the Radiophysical Research Institute SURA Ionospheric Modification Facility in Russia. Experiments consisted of single-pump, two-pump, and single-pump power-stepping experiments. The single-pump and two-pump transmissions were organized into groups of pulses of varying widths and spacings to facilitate the investigation of self-conditioning, preconditioning, and two-pump-interaction conditioning effects. The major findings of these experiments are that the action of a pump can have a conditioning effect on the medium that affects the time development of the BUM. The result of the conditioning process is the formation of an overshoot in the temporal development of the BUM. A residual conditioning effect is sustained after the end of a pump pulse for a period of time (~30 s). The residual conditioning acts as preconditioning for the BUM of a subsequent pump pulse. A second O-mode pump (pump2), at a frequency a few hundred kilohertz above that of the first pump (pump1), is observed to cause additional suppression of the pump1 BUM, implying an enhanced conditioning effect. Time constants for the buildup and decay of the conditioning effects are estimated. During power-stepping experiments, the BUM spectrum was observed to evolve from a weak, narrow spectrum at an effective radiated power (ERP) of ~5 MW, to a strong, broad spectrum with a ramp-like spectral tail at an ERP of ~150 MW. Other features noted during power stepping include (1) strong BUM transients at pump power level transitions, (2) BUM amplitude asymmetry between power-up and power-down sides of a power stepping cycle, (3) reduction of the BUM spectral peak offset from the pump frequency with increasing pump power, and (4) power law dependence of BUM power on pump power (exponent ~2). Results of these experiments are used in an attempt to assess the relevance of small-scale irregularity generation and electron heating mechanisms to the observed conditioning effects.

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

1999-02-01

96

12th International Ionospheric Effects Symposium 13-15 May 2008, Alexandria, VA  

E-print Network

propagation. Among various phenomena of ionosphere, ionospheric scintillation [2] due to electron density irregularities causes deep GPS signal fading. Signal to noise ratio or more precisely carrier to noise density

Stanford University

97

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

NASA Astrophysics Data System (ADS)

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

Klimenko, Maxim; Klimenko, Vladimir

98

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

99

Ionospheric observations during the geomagnetic storm events on 24-27 July 2004: Long-duration positive storm effects  

NASA Astrophysics Data System (ADS)

Ionospheric storms represent large global disturbances of the ionospheric F region electron density in response to geomagnetic storms. In this study, we use a combination of ionospheric total electron content (TEC) global maps and data from in-situ satellite measurements, such as solar wind data from the Advanced Composition Explorer (ACE), the Defense Meteorological Satellite Program (DMSP), and TOPographic EXplorer (TOPEX) and JASON-1 satellites, to investigate the ionospheric response during the geomagnetic storm event on 24-27 July 2004. A chain of ground-based Global Positioning System (GPS) stations and ionosonde measurements across South Africa have been used to give a comprehensive coverage over this midlatitude location. The most pronounced ionospheric effects of the storm occurred at low- and midlatitudes in the Southern hemisphere, with the most significant enhancements, observed on 25 and 27 July, presented here. The DMSP F15 satellite observed a sharp density enhancement over the midlatitudes. Over South Africa, the enhancement on 25 July was about twice as large as that observed on 27 July. The positive storm enhancements on 25 and 27 July both lasted over 7 hours, and can be classified as long-duration positive storm effects. Also, IMF Bz had southward orientation for an extended number of hours (exceeding 9 hours) and could have been the means by which energy was continuously fed into the magnetosphere and ionosphere. In addition, the F region critical frequency (foF2) values observed at two ionosonde stations showed marked positive responses that were associated with an increase in the ionospheric peak height (hmF2).

Ngwira, Chigomezyo M.; McKinnell, Lee-Anne; Cilliers, Pierre J.; Coster, Anthea J.

2012-01-01

100

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.

101

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

102

Ionospheric irregularity physics modelling  

SciTech Connect

Theoretical and numerical simulation techniques have been employed to study ionospheric F region plasma cloud striation phenomena, equatorial spread F phenomena, and high latitude diffuse auroral F region irregularity phenomena. Each of these phenomena can cause scintillation effects. The results and ideas from these studies are state-of-the-art, agree well with experimental observations, and have induced experimentalists to look for theoretically predicted results. One conclusion that can be drawn from these studies is that ionospheric irregularity phenomena can be modelled from a first principles physics point of view. Theoretical and numerical simulation results from the aforementioned ionospheric irregularity areas will be presented.

Ossakow, S.L.; Keskinen, M.J.; Zalesak, S.T.

1982-01-01

103

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

104

Effect of the shear flow in the generation and self-organization of internal gravity wave structures in the dissipative ionosphere  

NASA Astrophysics Data System (ADS)

A linear mechanism for the generation and amplification of internal gravity waves and their further nonlinear dynamics in the stably stratified dissipative ionosphere in the presence of an inhomogeneous zonal wind (shear flow) is studied. For shear flows, the operators of linear problems are non-self-conjugate and the corresponding eigenfunctions are nonorthogonal. Therefore, the canonical modal approach is poorly applicable to study such motions. In this case, the so-called nonmodal mathematical analysis is more adequate. Dynamic equations and equations for the energy transport of internal gravity perturbations in the ionosphere with shear flows are derived on the basis of the nonmodal approach. Exact analytic solutions of linear and nonlinear equations are found. The growth rate of the shear instability of internal gravity waves is determined. It is revealed that perturbations grow in time according to a power law, rather than exponentially. The frequency and wavenumber of the generated internal gravity modes depend on time; hence, a wide spectrum of wave perturbations caused by linear effects (rather than nonlinear turbulent ones) forms in the ionosphere with shear flows. The efficiency of the linear mechanism for the amplification of internal gravity waves during their interaction with the inhomogeneous zonal wind is analyzed. A criterion for the development of the shear instability of such waves in the ionospheric plasma is obtained. It is shown that, in the presence of shear instability, internal gravity waves extract the shear flow energy in the initial (linear) stage of their evolution, due to which their amplitude and, accordingly, energy increase substantially (by an order of magnitude). As the amplitude increases, the mechanism of nonlinear self-localization comes into play and the process terminates with the self-organization of strongly localized solitary nonlinear internal gravity vortex structures. As a result, a new degree of freedom of the system and a new way of the evolution of perturbations in a medium with a shear flow appear. Inductive and viscous dampings limit the lifetime of vortex internal gravity structures in the ionosphere; nevertheless, their lifetime is long enough for them to strongly affect the dynamic properties of the medium. It is revealed on the basis of the analytic solution of a set of time-independent nonlinear dynamic equations that, depending on the velocity profile of the shear flow, the nonlinear internal gravity structures can take the form of a purely monopole vortex, a dipole cyclone-anticyclone pair, a transverse vortex chain, or a longitudinal vortex path against the background of the inhomogeneous zonal wind. The accumulation of such vortices in the ionosphere can result in a strongly turbulent state.

Aburjania, G. D.; Zimbardo, G.; Kharshiladze, O. A.

2012-12-01

105

Mutual Neutralization of Atomic Oxygen Ions Over the Course of the Solar Cycle and Its Effects on Ionospheric Remote Sensing  

NASA Astrophysics Data System (ADS)

Over the past decade, several investigations have used ultraviolet remote sensing to quantify the behavior of the F region of the ionosphere (e.g., TIMED/GUVI, IMAGE/FUV, DMSP/SSUSI). In addition, global ionospheric assimilation systems such as the Global Assimilation of Ionospheric Measurements (GAIM) and the Ionospheric Data Assimilation Three Dimensional (IDA3D) ingest these ultraviolet measurements as part of a comprehensive characterization of the ionosphere. Most of these remote sensing/assimilation techniques rely on measurements of atomic oxygen emission at 135.6 nm, which is primarily due to atomic oxygen ion recombination. There is, however, a second mechanism for generation of 135.6 nm radiance in the F region - Mutual Neutralization - which results from the reaction of oppositely charged oxygen ions. This source is most significant at lower altitudes (250 km or so) where the concentration of neutral atomic oxygen is relatively high. Because of its dependence on the neutral oxygen density, this effect has a significant solar cycle variation and must be accounted for correctly in any studies that use the 135.6 nm radiance data. In this work we provide a characterization of the behavior of mutual neutralization (relative to recombination emission) as a function of solar activity. We also provide assimilation friendly correction mechanisms for the determination of electron densities in the F region.

Comberiate, J.; Demajistre, R.; Schaefer, R. K.; Zhang, Y.; Paxton, L. J.

2011-12-01

106

Utilization of ionosonde data to analyze the latitudinal penetration of ionospheric storm effects  

SciTech Connect

Increased emphasis is placed on global coupling between the magnetosphere, ionosphere, and thermosphere systems, particularly with regard to the penetration of dynamic, chemical, and electrodynamic effects from high to low latitudes during magnetically disturbed periods. An emerging potential exists for latitudinal and longitudinal chains of ionosondes to contribute uniquely to this thrust in ways complementary to the capabilities and shortcomings of other groundbased sensors and satellites. Here is illustrated a methodology to realize the fullest potential of such ionosonde data. Hourly values are fit in latitude using Legendre polynominals, and variations from quiet time values are displayed in latitude - U.T. coordinates using a color graphics method which provides an illuminating illustration of the penetration of ionospheric disturbances in latitude and their dependence on Kp, storm time, and local time. Observed effects are interpreted in terms of plausible electric field, neutral wind, and neutral composition changes during the storm period. Besides reflecting the anticipated southward flows and equatorward extensions in conjunction with magnetically disturbed conditions, the 24-hour average meridional winds exhibit a northward return flow after the magnetic disturbance has relaxed.

Forbes, J.M.; Codrescu, M.; Hall, T.J.

1988-03-01

107

Prompt penetration electric fields (PPEFs) and their ionospheric effects during the great magnetic storm of 30–31 October 2003  

Microsoft Academic Search

We explore the ionospheric effects of prompt penetration electric fields (PPEFs) for a variety of interplanetary magnetic field directions. We use the great magnetic storm of 30–31 October as an example of PPEF effects. For intense southward interplanetary magnetic fields (IMFs), inward plasma sheet convection occurs with the result of magnetospheric ring current formation and an intense magnetic storm. Concurrent

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

2008-01-01

108

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 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

109

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

110

Correction of Ionospheric effects in Coseismic ALOS data of the 2008 Wenchuan (Mw7.9) earthquake  

NASA Astrophysics Data System (ADS)

The Mw7.9 Wenchuan earthquake (12 May 2008) ruptured the middle segment of the Longmenshan (LMS) thrust belt, located at the eastern margin of the Tibetan Plateau. Several research groups have produced maps of the coseismic deformation using ALOS PALSAR data. However, the deformation maps and the estimated fault slip distributions differ significantly from each other in these studies. This difference is mainly because of anomalous InSAR signals, caused by ionospheric effects, which the researchers have dealt with in various different ways or ignored altogether. The ionospheric variations in the Wenchuan coseismic data are unusually strong and affect both the InSAR phase and the azimuth offset tracking measurements. Despite the various research efforts, important questions remain to be adequately addressed, e.g. (1) How do ionospheric effects distort InSAR observations of the coseismic deformation and how can we correct for them in the interferometric phase and azimuth offset measurements? (2) What are the differences between the Wenchuan fault slip models estimated from contaminated and ionospheric-corrected ALOS data? Some researchers have tried to correct for the ionospheric effects seen in the ALOS data using various different methods and external data sources, but their improvements have been very limited. Here we propose a new method utilizing additional interferogram pairs that only include the ionospheric effects, but no coseismic deformation, to remove the ionospheric signals. We applied this method to the InSAR data to produce "ionospheric free" coseismic interferograms and azimuth offset measurements. We validated our InSAR results against GPS measurements, which show that our corrected InSAR data are in a very good agreement with the GPS observations, confirming a successful removal of the ionospheric signals. Out of the 6 parallel ascending ALOS tracks we used to map the coseismic deformation, we find that data from 3 tracks are severely distorted by ionospheric effects. Unfortunately, these are the tracks where the most important fault slip patterns are located, such as the largest surface fault rupture and a transition from pure reverse faulting to a combination of reverse and right-lateral strike slip. This means that previous fault slip models estimated from contaminated ALOS data are likely biased and should be be reevaluated. Beside InSAR data, azimuth offsets often prove to be a useful supplementary information when studying large earthquakes, e.g. for locating the fault rupture. However, until now these data have been mostly ignored in the case of the Wenchuan earthquake due to the strong ionospheric effects. For our final fault model, we combine the corrected ALOS InSAR and azimuth offset data with GPS observations and descending Envisat (both image mode and ScanSAR) data to constrain better the spatial details of the fault slip.

Feng, G.; Jonsson, S.; Hetland, E. A.; Li, Z.

2012-12-01

111

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

112

Birth Order: Reconciling Conflicting Effects  

Microsoft Academic Search

Secular trends in test scores are accurately predicted by trends in aggregate birth orders. The trend data contradict individual-difference analyses that show birth order as a poor predictor of individual test scores. This article demonstrates why the 2 formulations of the problem the individually, distributed birth order analysis and aggregate-pattern analysis-generate different results. A meaningful interpretation is given by the

Robert B. Zajonc; Patricia R. Mullally

1997-01-01

113

Ordered Delinquency: The "Effects" of Birth Order On Delinquency  

PubMed Central

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

Cundiff, Patrick R.

2014-01-01

114

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

PubMed

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

Cundiff, Patrick R

2013-08-01

115

Birth Order: Reconciling Conflicting Effects.  

ERIC Educational Resources Information Center

Introduces the confluence model as a theory specifying the process by which the intellectual environment modifies intellectual development. Using this model, explores the contradiction between prediction of secular trends in test scores by trends in aggregate birth order and the lack of prediction of individual test scores by birth order using…

Zajonc, Robert B.; Mullally, Patricia R.

1997-01-01

116

Ionospheric research  

NASA Technical Reports Server (NTRS)

Data from research on ionospheric D, E, and F, regions are reported. Wave propagation, mass spectrometer measurements, and atmospheric reactions of HO2 with NO and NO2 and NH2 with NO and O2 are summarized.

1975-01-01

117

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

118

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

119

Ionospheric penetration characteristics of ELF waves radiated from a current source in the lithosphere related to seismic activity  

Microsoft Academic Search

Electromagnetic wave radiation from an underground current source related to seismic activity is discussed. In order to estimate the ionospheric effects on the electromagnetic waves associated with the seismic activity, ELF waves in the frequency range from 10 Hz to 1 kHz in the ionosphere radiated from a possible seismic current source modeled as an electric dipole located in the

M. Ozaki; S. Yagitani; I. Nagano; K. Miyamura

2009-01-01

120

Ionospheric refraction correction in radio astronomy  

NASA Astrophysics Data System (ADS)

Using Snell's law in polar coordinates, the ionospheric refraction effects on the declination and right ascension determination are discussed in this paper. A ray tracing method is also given. With the ionospheric data observed in Beijing, the correction of ionospheric refraction is estimated and some useful conclusions are drawn.

Chai, Yan; Han, Wen-Jun

1986-10-01

121

Birth order effects: A reply to Breland  

Microsoft Academic Search

Answers H. M. Breland's assertions concerning birth order effects in verbal achievement. It is argued that if birth order differences in intellectual functioning exist in childhood, they are very slight and exert at most minimal effects on adult functioning.

Carmi Schooler

1973-01-01

122

Lunar tidal effects in the electrodynamics of the low-latitude ionosphere  

NASA Astrophysics Data System (ADS)

We used extensive measurements made by the Jicamarca Unattended Long-Term Investigations of the Ionosphere and Atmosphere (JULIA) and Incoherent Scatter Radar (ISR) systems at Jicamarca, Peru during geomagnetic quiet conditions to determine the climatologies of lunar tidal effects on equatorial vertical plasma drifts. We use, for the first time, the expectation maximization (EM) algorithm to derive the amplitudes and phases of the semimonthly and monthly lunar tidal perturbations. Our results indicate, as expected, lunar tidal effects can significantly modulate the equatorial plasma drifts. The local time and seasonal dependent phase progression has been studied in much more detail than previously and has shown to have significant variations from the average value. The semimonthly drift amplitudes are largest during December solstice and smallest during June solstice during the day, and almost season independent at night. The monthly lunar tidal amplitudes are season independent during the day, while nighttime monthly amplitudes are largest and smallest in December solstice and autumnal equinox, respectively. The monthly and semimonthly amplitudes decrease from early morning to afternoon and evening to morning with moderate to large increases near dusk and dawn. We also examined these perturbation drifts during periods of sudden stratospheric warmings (SSWs). Our results show, for the first time, the enhancements of the lunar semimonthly tidal effects associated with SSWs to occur at night, as well as during the day. Our results also indicate during SSWs, monthly tidal effects are not enhanced as strongly as the semimonthly effects.

Tracy, Brian D.

123

Doppler spectral characteristics of high latitude ionospheric irregularities: Effect on HF radars  

Microsoft Academic Search

This report considers the Doppler spectral properties of radar signals scattered from high latitude E and F-region ionospheric irregularities. Although the exact mechanism for the production of F-region irregularities is not yet known, it appears that the Doppler shift from these as well as from E-region irregularities is determined by the ionospheric electric field via the E X B\\/B-squared drift

R. A. Greenwald

1981-01-01

124

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

125

HF ground scatter from the polar cap: Ionospheric propagation and ground surface effects  

NASA Astrophysics Data System (ADS)

In addition to being scattered by the ionospheric field-aligned irregularities, HF radar signals can be reflected by the ionosphere toward the Earth and then scattered back to the radar by the rugged ground surface. These ground scatter (GS) echoes are responsible for a substantial part of the returns observed by HF radars making up the Super Dual Auroral Radar Network (SuperDARN). While a GS component is conventionally used in studying ionosphere dynamics (e.g., traveling ionospheric disturbances, ULF waves), its potential in monitoring the state of the scattering surface remains largely unexploited. To fill this gap, we investigated diurnal and seasonal variation of the ground echo occurrence and location from a poleward-looking SuperDARN radar at Rankin Inlet, Canada. Using colocated ionosonde information, we have shown that seasonal and diurnal changes in the high-latitude ionosphere periodically modulate the overall echo occurrence rate and spatial coverage. In addition, characteristics of GS from a particular geographic location are strongly affected by the state of the underlying ground surface. We have shown that (1) ice sheets rarely produce detectable backscatter, (2) mountain ranges are the major source of GS as they can produce echoes at all seasons of the year, and (3) sea surface becomes a significant source of GS once the Arctic sea ice has melted away. Finally, we discuss how the obtained results can expand SuperDARN abilities in monitoring both the ionosphere and ground surface.

Ponomarenko, P. V.; St. Maurice, J.-P.; Hussey, G. C.; Koustov, A. V.

2010-10-01

126

Effect of an MLT dependent electron loss rate on the magnetosphere-ionosphere coupling  

NASA Astrophysics Data System (ADS)

As plasma sheet electrons drift earthward, they get scattered into the loss cone due to wave-particle interactions and the resulting precipitation produces auroral conductance. Realistic electron loss is thus important for modeling the magnetosphere - ionosphere (M-I) coupling and the degree of plasma sheet electron penetration into the inner magnetosphere. In order to evaluate the significance of electron loss, we used the Rice Convection Model (RCM) coupled with a force-balanced magnetic field to simulate plasma sheet transport under different electron loss rates and under self-consistent electric and magnetic field. We used different magnitudes of i) strong pitch angle diffusion everywhere electron loss rate (strong rate) and ii) a more realistic loss rate with its MLT dependence determined by wave activity (MLT rate). We found that electron pressure under the MLT rate is larger compared to the strong rate inside L ? 12 RE. The dawn-dusk asymmetry in the precipitating electron energy flux under the MLT rate, with much higher energy flux at dawn than at dusk, agrees better with statistical DMSP observations. High-energy electrons inside L ? 8 RE can remain there for many hours under the MLT rate, while those under the strong rate get lost within minutes. Under the MLT rate, the remaining electrons cause higher conductance at lower latitudes; thus after a convection enhancement, the shielding of the convection electric field is less efficient, and as a result, the ion plasma sheet penetrates further earthward into the inner magnetosphere than under the strong rate.

Gkioulidou, Matina; Wang, Chih-Ping; Wing, Simon; Lyons, Larry R.; Wolf, Richard A.; Hsu, Tung-Shin

2012-11-01

127

Common origin of positive ionospheric storms at middle latitudes and the geomagnetic activity effect at low latitudes  

SciTech Connect

The author looks for a correlation between two different atmospheric effects. They are a positive atmospheric storm (an anomalous increase in the F2 region ionization density), observed at middle latitudes, and the geomagnetic activity effect (the anomalous changes of temperature and gas density seen in the thermosphere), observed at low latitudes. A temporal correlation is sought to test the argument that both of these effects are the result of travelling atmospheric disturbances (TAD). A TAD is a pulselike atmospheric wave thought to be generated by substorm activity, and to propagate with high velocity (600 m/s) from polar latitudes toward equatorial latitudes. The author looks at data from five separate events correlating magnetic, ionospheric, and neutral atmospheric measurements. The conclusion is that there is a positive correlation between magnetic substorm activity at high latitudes, and positive ionospheric storms at middle latitudes and geomagnetic activity at low latitudes. The time correlations are consistent with high propagation speeds between these events. The author also presents arguments which indicate that the middle latitude positive ionospheric storms are not the result of electric field effects.

Proelss, G.W. (Universitaet Bonn (Germany))

1993-04-01

128

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

NASA Technical Reports Server (NTRS)

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

Cole, Keith D.

1993-01-01

129

Plasma and electromagnetic effects in the ionosphere related to the dynamics of charged aerosols in the lower atmosphere  

Microsoft Academic Search

The paper presents a physical model of the electrodynamic effect on the ionosphere of natural and artificial processes that\\u000a occur in the near-Earth atmospheric layer and are accompanied by the transfer of charged aerosols in the atmosphere. These\\u000a processes include the preparation of earthquakes and typhoons, dust storms, and nuclear accidents. The model is based experimentally\\u000a on satellite and ground-based

V. M. Sorokin

2007-01-01

130

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

131

Main ionospheric trough as a boundary layer in the ionosphere  

NASA Astrophysics Data System (ADS)

The mid-latitude electron density trough observed in the topside ionosphere has been shown to be the near-Earth signature of the plasmapause and can provide useful information about the magnetosphere-ionosphere dynamics and morphology. Thus for present the evolution of iono-spheric trough in time and space domain we need some multipoint measurements and different type of measurements techniques. To develop a quantitative model of evolution ionospheric trough features during geomagnetic disturbances the analyse of particle and waves in situ mea-surements and TEC data was carried out. The high resolutions plasma particle diagnostics and wave diagnostics located on board of currently operated satellite DEMETER can give us precisely description of trough signatures and instabilities at define point in space. In particular we will show the temperature and ion drifts manifestation inside ionospheric trough. On the other hand GPS permanent networks such as IGS and EPN provide regular monitoring of the ionosphere in a global scale. Furthermore radio occultation techniques is considered. The radio occultation technique using GPS signals has been proven to be a promising technique to retrieve accurate profiles of the ionospheric electron density with high vertical resolution on a global scale. FormoSat-3/COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) is a joint scientific mission between Taiwan and the U.S.A. The mission placed six small micro-satellites into six different orbits at 700˜800 kilometer above the earth surface. The aim of this paper is to present some general behavior of trough dynamics as well as the fine structures of ionospheric trough and discuss the different type of instability generated inside the trough region from ULF frequency range thru VLF up to HF frequency range. In order to better understand the physical conditions and evolution of ionosphere trough region and describe the coupling between ionosphere and inner magnetosphere the detail examination of geomagnetic storm in January 2005 is presented. As a consequence of different time scales of physical processes occurred in the near Earth environment during geomagnetic disturbances and energy transfer between ionosphere and magnetosphere the examination of ion end electron fluxes inside ionosphere trough are disused.

Rothkaehl, Hanna; Krankowski, Andrzej; Liu, Yann-Yeng; Slominska, Ewa; Czajkowski, Tomasz

132

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

133

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

134

Tsunami Ionospheric warning and Ionospheric seismology  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

135

Predictions of electron temperatures in the Mars ionosphere and their effects on electron densities  

NASA Astrophysics Data System (ADS)

Observations of peak electron densities in the Mars ionosphere are well fit by a simplistic theory that assumes the electron temperature, Te, at the peak remains constant as solar zenith angle, ?, changes. However, Te ought to vary with both altitude and ?. Here we use an existing numerical model of ionospheric energetics, which includes both vertical and diurnal variations in temperatures, to predict that Te at the ionospheric peak is relatively independent of ?. This model accurately predicts the observed dependence of peak electron density on ?, whereas predictions using Viking-based electron temperatures that are held constant with time do not. A simplified analytic model is developed to interpret these results further. It predicts that the difference between electron and neutral temperatures is proportional to the ratio of electron heating rate to electron production rate and proportional to the square root of solar irradiance.

Withers, Paul; Fallows, Kathryn; Matta, Majd

2014-04-01

136

Time and Order Effects on Causal Learning  

ERIC Educational Resources Information Center

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

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

2006-01-01

137

Birth order effects: Not here, not now  

Microsoft Academic Search

A review of birth order effects, which considers previously reported and unreported data and recently hypothesized biases arising from long-term population trends, reveals (a) almost no reliable evidence for birth order effects among males living in the United States in the middle 1960s, and (b) only a marginal increase in such evidence when restrictions on time, place, and sex are

Carmi Schooler

1972-01-01

138

Roughness in lattice ordered effect algebras.  

PubMed

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

139

UHF Radar observations at HAARP with HF pump frequencies near electron gyro-harmonics and associated ionospheric effects  

NASA Astrophysics Data System (ADS)

Results for HF modification experiments at the HAARP facility in Alaska are presented for experiments with the HF pump frequency near third and fourth electron gyro-harmonics. A UHF diagnostic radar with range resolution of 600 m was used to determine time-dependent altitudes of scattering from plasma turbulence during heating experiments. Experiments were conducted with multiple HF frequencies stepped by 20 kHz above and below the gyro-harmonic values. During times of HF heating the HAARP facility has sufficient power to enhance large-scale ionospheric densities in the lower ionosphere (about 150-200 km altitude) and also in the topside ionosphere (above about 350 km). In the lower ionosphere, time-dependent decreases of the altitude of radar scatter result from electron density enhancements. The effects are substantially different even for relatively small frequency steps of 20 kHz. In all cases the time-varying altitude decrease of radar scatter stops about 5-10 km below the gyro-harmonic altitude that is frequency dependent; we infer that electron density enhancements stop at this altitude where the radar signals stop decreasing with altitude. Experiments with corresponding total electron content (TEC) data show that for HF interaction altitudes above about 170 km there is substantial topside electron density increases due to upward electron thermal conduction. For lower altitudes of HF interaction the majority of the thermal energy is transferred to the neutral gas and no significant topside density increases are observed. By selecting an appropriate HF frequency a little greater than the gyro-harmonic value we have demonstrated that the ionospheric response to HF heating is a self-oscillating mode where the HF interaction altitude moves up and down with a period of several minutes. If the interaction region is above about 170 km this also produces a continuously enhanced topside electron density and upward plasma flux. Experiments using an FM scan with the HF frequency increasing near the gyro-harmonic value were conducted. The FM scan rate was sufficiently slow that the electron density was approximately in an equilibrium state. For these experiments the altitude of the HF interaction follows a near straight line downward parallel to the altitude-dependent gyro-harmonic level.

Watkins, Brenton; Fallen, Christopher; Secan, James

140

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

E-print Network

resulting in ranging errors are examined for a potential orbital network of communications and navigational, much in the same way as GPS measurements are used in terrestrial ionospheric physics. INDEX TERMS: 6225-increasing spectrum of civilian and military applications. Illustrated schemati- cally in Figure 1a is the augmented

Mendillo, Michael

141

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

142

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

143

Heater Beam Angle Effect on Simulated Brillouin Scatter in Magnetized Ionospheric Plasma  

NASA Astrophysics Data System (ADS)

High power electromagnetic waves transmitted from HAARP have recently been shown to excite low frequency electrostatic waves by magnetized stimulated Brillouin scatter MSBS near the reflection or upper hybrid resonance regions. The pump wave may excite either electrostatic ion acoustic wave (IA) or electrostatic ion cyclotron wave (EIC) waves. Whether IA and EIC waves are excited depends on the wave propagation relative to the ambient magnetic field. It had been confirmed that only ion acoustic waves are observed for propagation near magnetic zenith while EIC waves can only be observed with more oblique propagation angles. The original discovery of EIC waves excited by the MSBS process considered only a narrow range of heater beam angles. The EIC wave strength in the spectrum was observed to be highly variable and proposed to possibly be near threshold. Also observations of the upshifted EIC waves in the spectrum were almost nonexistent. This was true for cascading of the downshifted EIC lines as well. Those EIC spectrum lines can provide valuable diagnostics for ion composition. This experiment conducted at the 2010 HAARP Summer School aims to look more thoroughly at a broader range of heater beam angle effects on IA and EIC waves generated by MSBS in the F layer ionosphere. The expected results show that the stronger IA and EIC spectrum lines were observed by the O-mode excitation. With increasing tilting angles, there exists a critical heater power beam angle above that EIC modes appear in the lower SEE spectrum. The power spectrum of EIC is more sensitively affected by the power beam angle than the IA spectrum lines. The experiments also aim to observe the second EIC (or even higher) frequency downshifted harmonics generated with increasing tilting angle.

Fu, H.; Bernhardt, P. A.; Scales, W. A.; Briczinski, S. J.; San Antonio, G.; Selcher, C. A.

2010-12-01

144

Birth order effects: A reply to Schooler  

Microsoft Academic Search

Replies to C. Schooler's criticisms regarding birth order studies by presenting evidence to support Breland's contention that birth order effects on verbal achievement do exist, and that these are not caused by either population biases or socioeconomic status differences. (22 ref.)

Hunter M. Breland

1973-01-01

145

Monitoring the ionospheric positioning error with a GNSS dense network  

NASA Astrophysics Data System (ADS)

Local variability in the ionospheric Total Electron Content (TEC) can seriously affect the accuracy of GNSS real-time applications. In relative positioning, users have to compute the vector (called baseline) linking their receiver to a reference station for which the position is accurately known. As long as the ionosphere remains quiet (i.e. a background ionosphere with no local disturbance), the accuracy of relative positioning using phase measurements is of a few cm. The SoDIPE-RTK software developed at the Royal Meteorological Institute of Belgium allows to compute the part of the positioning error only due to the ionosphere (referred later as "ionospheric error") for a given baseline. In practice, baselines considered in this paper are not larger than 40km in order to ensure a successful ambiguity resolution process for both L1 and L2 carriers. More precisely, data analysed in the frame of this work are baselines belonging to the Belgian GPS dense network called Active Geodetic Network (AGN). SoDIPE-RTK has been applied on the whole network during typical ionospheric conditions: quiet, active and stormy. Active conditions refer to disturbed ionosphere due to the occurrence of Traveling Ionospheric Disturbances (TID's) while stormy conditions are relative to extremely disturbed plasma during the occurrence of powerful geomagnetic storms. From this dataset, we extract some descriptive statistics like average, standard deviation, extrema... of the ionospheric error. As expected, this term is centimeter-level during quiet conditions while maximum values are reached during stormy conditions. For a 10km baseline, one can observe ionospheric errors of about 15cm during the occurrence of a winter medium-scale TID (MSTID) and up to 1m during geomagnetic storms. Moreover, the availability of a dense network allows to study the influence of baseline orientation on ionospheric error magnitude. We have analysed two specific cases of moving ionospheric structures: a winter MSTID and an "ionospheric wall" (TEC depletion) caused by an extreme geomagnetic storm. In both cases, equatorwards direction of propagation was clearly visible on polar plots. Indeed, baselines oriented parallel to the direction of propagation of disturbances are more affected by TEC gradients than others. SoDIPE-RTK is therefore a tool which allows not only to assess the effect of ionospheric disturbances on relative positioning but also to monitor propagation patterns of such disturbances while run through a GPS dense network. Finally, we propose a service dedicated to GNSS relative positioning users based on SoDIPE-RTK. Every 15 minutes, each AGN baseline is mapped in a given color ranging from green (quiet conditions) to red (extreme conditions). This easy-to-use application allows registered users to access to local information about current ionospheric conditions on the field.

Wautelet, Gilles; Lejeune, Sandrine; Warnant, René

2010-05-01

146

AM Radio Ionosphere Station: Teacher's Guide  

NSDL National Science Digital Library

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

147

Ionospheric penetration characteristics of ELF waves radiated from a current source in the lithosphere related to seismic activity  

NASA Astrophysics Data System (ADS)

Electromagnetic wave radiation from an underground current source related to seismic activity is discussed. In order to estimate the ionospheric effects on the electromagnetic waves associated with the seismic activity, ELF waves in the frequency range from 10 Hz to 1 kHz in the ionosphere radiated from a possible seismic current source modeled as an electric dipole located in the lithosphere, are precisely computed by using a full-wave analysis. In this calculation, the ionosphere is assumed to be an inhomogeneous and anisotropic medium, and the Earth's crust is assumed to be a homogeneous and isotropic conductive medium. Especially, the effects of the geomagnetic field on the ionospheric wave propagation are precisely considered. The results of the calculations in the frequency range from 10 Hz to 1 kHz show frequency dependence in spatial distributions of the wave intensities due to the geomagnetic field-aligned whistler propagation in the ionosphere and the Earth-ionosphere waveguide propagation. Wave intensities which could be observed on the ground and in the ionosphere are determined by assuming the magnitude of the current moment of a seismic dipole source. In a possible situation, the current moment is estimated to be about 80 A·m/Hz1/2 which generates a detectable wave magnetic field on the ground just above a seismic source. However, if we try to detect it in the ionosphere, the source current moment must be thousands of times more intense.

Ozaki, M.; Yagitani, S.; Nagano, I.; Miyamura, K.

2009-02-01

148

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

149

Ionospheric effects of the March 13, 1989, magnetic storm at low and equatorial latitudes  

Microsoft Academic Search

The great geomagnetic storm of March 13, 1989 caused severely anomalous behavior in the equatorial and low latitude ionosphere in the Brazilian longitude sector. The ionograms over Fortaleza indicated F region upward plasma drifts exceeding 200 m s⁻¹ at 1,830 LT as compared to normal values of 40 m s⁻¹ for this epoch. Large negative phases were observed in foF2

Inez S. Batista; E.R. De Paula; M. A. Abdu; N. B. Trivedi; M. E. Greenspan

1991-01-01

150

Comparison of ionospheric peak parameters derived from different modeling approaches  

NASA Astrophysics Data System (ADS)

Due to the fact that Ionosphere is a dispersive medium, microwave signals travelling through this medium are affected proportional to their frequencies. This effect allows gaining information about the parameters of the ionosphere in terms of Total Electron Content (TEC) or the electron density. There are different approaches for modeling these parameters. Some models are based on physical properties such as the Global Assimilative Ionospheric Model (GAIM). Some are empirical models, e.g. the International Reference Ionosphere (IRI), the NeQuick model, or the Neustrelitz TEC Model (NTCM). Finally some models are based on purely mathematical/statistical approaches. In the mathematical models, the corresponding model parameters are calculated using measurements from different space geodetic techniques or the ionosonde data. This study investigates different approaches for computing the electron density along the ray path. First the mathematical approach developed at Technical University of Berlin (TUB) for global 3D reconstruction of the ionospheric F2-peak parameters is presented. In this approach, the F2-peak parameters, i.e. the maximum electron density and its corresponding height are represented as a function of geographic or geomagnetic longitude, latitude, and height with two sets of spherical harmonic expansions of degree and order 15, which correspond to a spatial resolution of 5° in longitude and 2.5° in latitude. To assess this modeling approach, the estimated F2-peak parameters are compared with the peak parameters derived from several other modeling approaches.

Mahdi Alizadeh, M.; Schuh, Harald

2014-05-01

151

Models of ionospheric VLF absorption of powerful ground based transmitters  

E-print Network

the variability of the ionospheric electron density. We conclude that the global effect of irregularity scattering that the ionospheric electron density profile ass in precipitation of energetic Van Allen electrons. Initial analyses of the contribution of VLF transmitters

152

Model study of the effects of gravity wave dissipation on the thermosphere and ionosphere from deep convection worldwide  

NASA Astrophysics Data System (ADS)

In this paper, we discuss the methods and results of a global modeling study for the effect of deep convection on the thermosphere and ionosphere through the dissipation of atmospheric gravity waves (GWs). The selected time periods are 15-27 June 2009, during the recent extreme solar minimum, and 15-27 June 2000, during the recent solar maximum. The convective plumes which overshot the tropopause are identified from IR images obtained by 5 satellites covering the Earth during each period. We model the excitation of GWs from these plumes, and ray trace them into the thermosphere using our ray trace model which has been upgraded to span the Earth. We then calculate the forcings/heatings/coolings which result when and where these GWs dissipate in the thermosphere. We input these forcings/heatings/coolings into the global TIME-GCM, and re-run the model. In this paper, we discuss these methods and models in detail. We then discuss how the thermosphere and ionosphere responded to the dissipation of these convectively-generated GWs worldwide. We show that the responses propagate westward due to wind filtering by tides in the lower thermosphere. We also show that the neutral temperature and wind perturbations are larger during extreme solar minimum than during solar maximum.

Vadas, Sharon; Liu, Hanli

153

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

154

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

155

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

156

Modelling ionospheric density structures  

NASA Technical Reports Server (NTRS)

Large-scale density structures are a common feature in the high-latitude ionsphere. The structures were observed in the dayside cusp, polar cap, and nocturnal auroral region over a range of altitudes, including the E-region, F-region and topside ionosphere. The origins, lifetimes and transport characteristics of large-scale density structures were studied with the aid of a three-dimensional, time-dependent ionospheric model. Blob creation due to particle precipitation, the effect that structured electric fields have on the ionosphere, and the lifetimes and transport characteristics of density structures for different seasonal, solar cycle, and interplanetary magnetic field (IMF) conditions were studied. The main conclusions drawn are: (1) the observed precipitation energy fluxes are sufficient for blob creation if the plasma is exposed to the precipitation for 5 to 10 minutes; (2) structured electric fields produce structured electron densities, ion temperatures, and ion composition; (3) the lifetime of an F-region density structure depends on several factors, including the initial location where it was formed, the magnitude of the perturbation, season, solar cycle and IMF; and (4) depending on the IMF, horizontal plasma convection can cause an initial structure to break up into multiple structures of various sizes, remain as a single distorted structure, or become stretched into elongated segments.

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

1989-01-01

157

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

158

Estimating the lower ionosphere height and lightning location using multimode “tweek” atmospherics  

NASA Astrophysics Data System (ADS)

There is proposed a new method of estimating the effective ionospheric height of the Earth-ionosphere waveguide and the propagation distance of tweek-atmospherics. It is based on the compensation of waveguide frequency dispersion of a tweek signal, which enables us to improve the accuracy of deducing the cutoff frequencies, especially in the presence of noise. An approach to solve the inverse problem is suggested that reduces the task of finding both the source range and the waveguide cutoff frequencies by using the multimode characteristics of tweeks to an issue of one-dimensional optimization. Based on the numerical modeling of multimode tweek-atmospherics in the Earth-ionosphere waveguide with exponential vertical conductivity profile of the lower ionosphere, it was shown that the accuracy of estimating the effective waveguide height by the new method is good as about 100-400 m for the first and higher order modes. It then allows us to estimate the parameters of vertical conductivity profile of the lower ionosphere for a wide range of source distances from a few hundred to a few thousand kilometers, as long as two or more tweek harmonics can be detected. Preliminary analysis of experimental tweek records show a decrease of the effective height with increasing the mode number, and the scale height of the exponential vertical conductivity profile for the isotropic lower ionosphere model is estimated to be in a range of 0.4-2.5 km.

Shvets, A. V.; Serdiuk, T. M.; Gorishnyaya, Y. V.; Hobara, Y.; Hayakawa, M.

2014-02-01

159

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

160

Effect of the zonal E × B plasma drift on the electron number density in the low-latitude ionospheric F region at high solar activity near the December solstice  

NASA Astrophysics Data System (ADS)

The variations in the electron number density of the ionospheric F2 layer maximum ( NmF2) under the action of the zonal plasma drift in the geomagnetic west-geomagnetic east direction perpendicularly to the electric ( E) and geomagnetic ( B) fields during a geomagnetically quiet period on December 7, 1989, at high solar activity have been studied based on a three-dimensional nonstationary theoretical model of electron number densities and temperatures in the ionospheric F region. Calculated and measured NmF2 values for 12 low-latitude ionospheric sounding stations have been compared. When the zonal E × B plasma drift is ignored, the NmF2 values become smaller by up to a factor of 3 under nighttime conditions in the low-latitude ionosphere. The average effect of the zonal E × B plasma drift on NmF2 in the low-latitude ionosphere is larger during winter nights than under summer nighttime conditions.

Pavlov, A. V.; Pavlova, N. M.

2013-04-01

161

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

162

Ionospheric effects on the F region during the sunrise for the annular solar eclipse over Taiwan on 21 May 2012  

NASA Astrophysics Data System (ADS)

On 21 May 2012 (20:56, Universal Time; UT, on 20 May), an annular solar eclipse occurred, beginning at sunrise over southeast China and moving through Japan, sweeping across the northern Pacific Ocean, and completing its passage over the western United States at sunset on 20 May 2012 (02:49 UT, 21 May). We investigated the eclipse area in Taiwan, using an ionosonde and global positioning system (GPS) satellite measurements. The measurements of foF2, hmF2, bottomside scale height around the peak height (Hm), and slab thickness (B0) were collected at the ionosonde station at Chung-Li Observatory. In addition, we calculated the total electron content (TEC) to study the differences inside and outside the eclipse area, using 3 receivers located at Marzhu (denoted as MATZ), Hsinchu (TNML), and Henchun (HENC). The results showed that the foF2 values gradually decreased when the annularity began and reached a minimum level of approximately 2.0 MHz at 06:30 LT. The hmF2 immediately decreased and then increased during the annular eclipse period. The TEC variations also appeared to deplete in the path of the eclipse and opposite the outside passing area. Further, the rate of change of the TEC values (dTEC / dt measured for 15 min) was examined to study the wave-like fluctuations. The scale height near the F2 layer peak height (Hm) also decreased and then increased during the eclipse period. To address the effects of the annular eclipse in the topside and bottomside ionosphere, this study provides a discussion of the variations between the topside and bottomside ionospheric parameters during the eclipse period.

Chuo, Y. J.

2013-11-01

163

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

164

Ionospheric modification by rocket effluents. Final report  

SciTech Connect

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

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

1980-06-01

165

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

166

On the problem of detection of seismo-ionospheric phenomena by multi-instrumental radiophysical observations  

NASA Astrophysics Data System (ADS)

Analysis of the previous works on lithosphere-ionosphere interactions confirmed the necessity to use simultaneous observations from several independent diagnostics tools in order to raise the reliability of the observed seismo-ionospheric effects. The influence on the ionosphere from below is weaker in comparison with effects of solar or geomagnetic origin. Due to this reason it is very actual the problem of detection of seismo-ionospheric anomalies on the background of strong regular and quasi-regular variation of space weather parameters. For the given research we use integrated processing of the ionospheric data from different sources: total electron content (TEC) data obtained on the basis of regular GPS observations of IGS stations located in Sakhalin and Japan regions, ionospheric E and F2 layers peak parameters, derived from data of Japan ionosonde network and electron density profiles, obtained by FORMOSAT-3/COSMIC radio occultation measurements. As a case-study it was analyzed the Nevelsk earthquake (M 6.2) that took place at the Far East of Russian Federation on August 2, 2007. On July 29, 2007, several days prior to earthquake, the characteristic anomaly was found out as the day-time significant enhancement of TEC at the vicinity of earthquake. This enhancement reached the maximal value of 4-6 TECU in absolute values, that is 40-50% to the background conditions, and it was situated very close to the epicenter position. The noticeable enhancement of F2 peak critical frequency (foF2) was observed over Wakkanai ionosonde. For the evening hours (19-22 LT) it reached the value of 6.8-7.7 MHz whereas monthly median was 5.3-5.7 MHz. This foF2 increase was coincided in time with the appearance of TEC anomaly in TEC maps over the considered region (taken from GIMs IONEX). In order to separate seismo-ionospheric perturbations from geomagnetic disturbances it was done the comparative analysis of the revealed ionospheric effect possibly related with seismic activity and ionosphere changes during geomagnetic storms which took place during July and August of 2007. We acknowledge the University Corporation for Atmospheric Research (UCAR) for providing the COSMIC data, IGS community for GPS permanent data and WDC for Ionosphere, Tokyo, National Institute of Information and Communications Technology (NICT) for ionosonde data. This work was supported by Russian Federation President grant MK-2058.2011.5.

Cherniak, Iurii; Zakharenkova, Irina; Shagimuratov, Irk; Suslova, Olga

2012-07-01

167

Low/Mid-latitude Ionospheric irregularities and scintillation climatology  

NASA Astrophysics Data System (ADS)

Ionospheric scintillation occur when radio signals propagate through an irregular ionosphere (e.g., plasma bubbles). Since plasma bubbles are regions of depleted ion and electron densities, a plasma bubble located on the satellite-to-ground signal path will cause radio signals to fluctuate in phase and amplitude. Ionospheric scintillation data were analyzed in the magnetic latitudinal field-of-view 29° N -13.4° N, observed by a stand-alone SCINDA (Scintillation Network Decision Aid) - GPS receiver at Helwan, Egypt (29.86° N, 31.32° E). A minimum 20° elevation cut off angle has been set in order to minimize the multipath effect. During the enhancing phase of the current solar cycle 24 (years 2010, 2011, 2012 and 2013), the behaviour of the scintillation occurrence were characterized. The seasonal, annual and solar cycle variation of scintillation occurrence is investigated together with the Total Electron Content (TEC), to put in evidence the relation between the electron density gradients and the ionospheric irregularities causing scintillation. This study considers a first step to develop a scintillation climatology over Northern Africa.

Abdallah, Amr; Groves, K. M.; Mahrous, Ayman; Hussein, Fayrouz

168

On the effect of BUM generation enhancement revealed using the scheme of additional heating of ionospheric plasma  

NASA Astrophysics Data System (ADS)

We present measured characteristics of the artificial ionospheric radio emission (AIRE), which were obtained experimentally using additional heating of the ionospheric F-region by O-polarized waves. It is shown that the observed enhancement of intensity of the broad upshifted maximum (BUM) of the AIRE can result from the influence of electrons accelerated in the plasma: esonance region on its generation. An empirical model of the phenomenon observed is developed. It is concluded from experimental results that the BUM has a complex structure and only one of its components produces the above emission enhancement. We show the possibility of using the AIRE in additional heating of ionospheric plasma for diagnostics of artificial ionospheric turbulence and investigation of the features of perturbation propagation along the geomagnetic field lines.

Frolov, V. L.; Erukhimov, L. M.; Komrakov, G. P.; Sergeev, E. N.; Thidé, B.; Bernhardt, P. A.; Wagner, L. S.; Goldstein, J. A.; Selcher, G.

1997-05-01

169

The Impact of Ionospheric Disturbances on High Accuracy Positioning in Brazil  

NASA Astrophysics Data System (ADS)

High positioning accuracy is a key requirement to a number of applications with a high economic impact, such as precision agriculture, surveying, geodesy, land management, off-shore operations. Global Navigation Satellite Systems (GNSS) carrier phase measurement based techniques, such as Real Time Kinematic (RTK), Network-RTK (NRTK) and Precise Point Positioning (PPP), have played an important role in providing centimetre-level positioning accuracy, and become the core of the above applications. However these techniques are especially sensitive to ionospheric perturbations, in particular scintillation. Brazil sits in one of the most affected regions of the Earth and can be regarded as a test-bed for scenarios of the severe ionospheric condition. Over the Brazilian territory, the ionosphere behaves in a considerably unpredictable way and scintillation activity is very prominent, occurring especially after sunset hours. NRTK services may not be able to provide satisfactory accuracy, or even continuous positioning during strong scintillation periods. CALIBRA (Countering GNSS high Accuracy applications Limitations due to Ionospheric disturbances in BRAzil) started in late 2012 and is a project funded by the GSA (European GNSS Agency) and the European Commission under the Framework Program 7 to deliver improvements on carrier phase based high accuracy algorithms and their implementation in GNSS receivers, aiming to counter the adverse ionospheric effects over Brazil. As the first stage of this project, the ionospheric disturbances, which affect the applications of RTK, NRTK or PPP, are characterized. Typical problems include degraded positioning accuracy, difficulties in ambiguity fixing, NRTK network interpolation errors, long PPP convergence time etc. It will identify how GNSS observables and existing algorithms are degraded by ionosphere related phenomena, evaluating the impact on positioning techniques in terms of accuracy, integrity and availability. Through the use of ionospheric estimators such as the TEC (Total Electron Content) fluctuations, I95 index and scintillation parameters (such as S4 and ??), observed positioning degradation has been correlated with ionospheric disturbances in order to characterise the impact. The ultimate objective is to quantify how residual errors remaining in both the double differenced and undifferenced GNSS observables are driven by ionospheric related phenomena. Two different scale GNSS networks have been used in this study. One is a large scale sparse network (Brazilian wide), which is a specialized ionospheric monitoring network, built by the CIGALA project (http://cigala.galileoic.org/); the other is a regional (state of São Paulo) network, which can provide case study data and also ground truth. The outcome of the above characterization study will be discussed in this paper. It will enable and facilitate the development of the mitigation algorithms, which include the screening of contaminated observations, observation de-weighting, enhanced network interpolation and ambiguity fixing strategy.

Yang, L.; Park, J.; Susnik, A.; Aquino, M. H.; Dodson, A.

2013-12-01

170

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

171

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

172

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

173

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

174

Three-dimensional, high resolution, computerized ionospheric tomographic imaging and computational modeling of an artificial ionospheric cavity  

NASA Astrophysics Data System (ADS)

Tomographic techniques use line integral measurements to reconstruct local values of the measured parameter. These techniques have been applied to the ionosphere by using radio transmissions to measure the integral of electron density between a satellite and a chain of ground-based receiving stations. The resultant reconstructions form a two-dimensional map of the electron density in the plane of the satellite/receiver chain. Insufficient quantity of receivers and not having a complete range of accessible look angles with the available receivers are responsible for the non-uniqueness in the reconstructions. The limited look angle problem can be alleviated by making use of alternative data sources such as incoherent scatter radars ( ISR) that provide information on the vertical structure of the electron density. The non-optimal receiver placement problem can be alleviated through the use of sophisticated reconstruction algorithms. The computerized ionospheric tomography (CIT) technique has recently been used to image the artificially modified ionosphere above the Arecibo Observatory (AO) HF heating facility. A total of nine radio beacon receivers forming a three by three matrix were deployed across the entire island of Puerto Rico. The arrangement maximizes the likelihood that several of the receiver-to-satellite lines of sight would intersect the heated region of the ionosphere. Several satellite passes associated with such an intersection occurred, and the resultant tomographic inversions indicate the existence of an electron density cavity approximately 45 kilometers in latitudinal extent. The reduction of electron density in this cavity was typically on the order of 20%. The experimental observations were supported by theoretical work using the open-source SAMI2 ionospheric model. Methods were developed to model both the ohmic heating of the electrons and the suprathermal heating caused by nonlinear effects. Modeled ohmic heating values of 941 K/s match the observed heated temperature profiles. Modeled suprathermal electrons effects on the vibrational temperature of N2 indicate a vibrational/translation temperature differential of 308°K.

Selcher, Craig A.

175

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

176

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

NASA Astrophysics Data System (ADS)

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

Liu, Ningyu; Dwyer, Joseph; Rassoul, Hamid

2013-04-01

177

Probing the lower ionospheric perturbations associated with earthquakes by means of subionospheric VLF/LF propagation  

NASA Astrophysics Data System (ADS)

There have been reports for many years 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 present a possible use of VLF/LF (very low frequency (3-30 kHz)/low frequency (30-300 kHz)) radio sounding of seismo-ionospheric perturbations. In order to avoid the overlapping with my own previous reviews, we first show some pioneering results for the Kobe EQ and 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), medium-distance (6-8 Mm) propagation anomalies, the fluctuation spectra of subionospheric VLF/LF data (the effect of atmospheric gravity waves, 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-electromagnetic study.

Hayakawa, Masashi

2011-12-01

178

Main ionospheric trough as a duct of energy between ionosphere and magnetosphere region  

NASA Astrophysics Data System (ADS)

The mid-latitude electron density trough observed in the topside ionosphere has been shown to be the near-Earth signature of the plasmapause and can provide useful information about the magnetosphere-ionosphere dynamics and morphology. Thus for present the evolution of ionospheric trough in time and space domain we need some multipoint measurements and different type of measurements techniques. To develop a quantitative model of evolution ionospheric trough features during geomagnetic disturbances the analyse of particle and waves in situ measurements and TEC data was carried out. The high resolutions plasma particle diagnostics and wave diagnostics located on board of currently operated satellite DEMETER can give us precisely description of trough signatures and instabilities at define point in space. On the other hand GPS permanent networks such as IGS and EPN provide regular monitoring of the ionosphere in a global scale. The aim of this paper is to present some general behaviour of trough dynamics as well as the fine structures of ionospheric trough and discuss the different type of instability generated inside the trough region from ULF frequency range thru VLF up to HF frequency range. In order to better understand the physical conditions and evolution of ionosphere trough region and describe the coupling between ionosphere and inner magnetosphere the detail examination of geomagnetic storm in January 2005 is presented. As a consequence of different time scales of physical processes occurred in the near Earth environment during geomagnetic disturbances and energy transfer between ionosphere and magnetosphere the examination of ion end electron fluxes inside ionosphere trough are disused.

Rothkaehl, Hanna; Czajkowski, Tomasz; Grzesiak, Marcin; S?omi?ska, Ewa; Wronowski, Roman; S?omi?ski, Jan; Koperski, Piotr; Krankowski, Andrzej

2010-05-01

179

Effect upon universal order of Hubble expansion  

NASA Astrophysics Data System (ADS)

The level of order R in a spherical system of radius r0 with a probability amplitude function ?(x),x=r,?,? obeys R=(1/2)r02I, where I=4?dx| is its Fisher information level. We show that a flat space universe obeying the Robertson-Walker metric has an invariant value of the order as it undergoes either uniform Hubble expansion or contraction. This means that Hubble expansion per se does not cause a loss of universal order as time progresses. Instead, coarse graining processes characterizing decoherence and friction might cause a loss of order. Alternatively, looking backward in time, i.e. under Hubble contraction, as the big bang is approached and the Hubble radius r0 approaches small values, the structure in the amplitude function ?(x) becomes ever more densely packed, increasing all local slopes ?? and causing the Fisher information I to approach unboundedly large values. As a speculation, this ever-well locates the initial position of the universe in a larger, multiverse. We define a measure of order or complexity proportional to the Fisher information. The measure is applied to our flat-space, dust and gas dominated, universe. Despite the universe’s relentless, ever-accelerating Hubble expansion, its level of order is found to remain constant.

Frieden, B. R.; Plastino, A.; Plastino, A. R.

2012-01-01

180

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

181

Venus' nighttime horizontal plasma flow, 'magnetic congestion', and ionospheric hole production  

NASA Technical Reports Server (NTRS)

A simple rectilinear, two-dimensional MHD model is used to investigate the effects of field-aligned plasma loss and cooling on a dense plasma convecting across a weak magnetic field, in order to illumine the Venus nighttime phenomena of horizontal plasma flow, magnetic congestion and ionospheric hole production. By parameterizing field-aligned variations and explicitly solving for cross magnetic field variations, it is shown that the abrupt horizontal enhancements of the vertical magnetic field, as well as sudden decreases of the plasma density to very low values (which are characteristic of ionospheric holes), can be produced in the presence of field-aligned losses.

Grebowsky, J. M.; Mayr, H. G.; Curtis, S. A.; Taylor, H. A., Jr.

1983-01-01

182

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

183

Birth Order Effects among Black College Students  

Microsoft Academic Search

The purpose of this study was to examine the relationship between birth order, vocational choice, choice of college, and selected personality characteristics among Black college students. The 16 Personality Factors Question naire, the Assessment of Career Decision Making, and a research questionnaire were administered to a sample of 231 students enrolled in freshman orientation classes at Grambling State University, Grambling,

Bernita L. Patterson; Howard E. A. Tinsley

1980-01-01

184

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

185

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

186

International reference ionosphere 1990  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

187

Magnetic fluctuations in the Martian ionosphere  

NASA Astrophysics Data System (ADS)

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 ( ~ 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, J. R.

2010-12-01

188

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

189

Ionospheric clutter model for high frequency surface wave radar  

Microsoft Academic Search

The detection performance of a high frequency surface wave radar (HFSWR) system is primarily limited by clutter, especially ionospheric clutter. Therefore, in order to analyze and\\/or simulate the capabilities of an HFSWR system a model for the clutter is required. This paper develops and tests a new radio wave propagation theory to model ionospheric clutter. The model is based on

Maryam Ravan; Raviraj S. Adve

2012-01-01

190

Global ionospheric total electron contents (TECs) during the last two solar minimum periods  

NASA Astrophysics Data System (ADS)

last solar minimum period was anomalously extended and low in EUV irradiance compared with previous solar minima. It can readily be expected that the thermosphere and the ionosphere must be correspondingly affected by this low solar activity. While there have been unanimous reports on the thermospheric changes, being cooler and lower in its density as expected, the ionospheric responses to low solar activity in previous studies were not consistent with each other, probably due to the limited ionospheric observations used for them. In this study, we utilized the measurements of total electron content (TEC) from TOPEX and JASON-1 satellites during the periods of 1992 to 2010, which includes both the last two solar minimum periods, in order to investigate how the ionosphere responded to the extremely low solar activity during the last solar minimum compared with previous solar minimum. Although the global daily mean TECs show negligible differences between the two solar minimum periods, the global TEC maps reveal that there are significant systematic differences ranging from about -30% to +50% depending on local time, latitude, and season. The systematic variations of the ionospheric responses seem to mainly result from the relative effects of reduced solar EUV production and reduced recombination rate due to thermospheric changes during the last solar minimum period.

Jee, Geonhwa; Lee, Han-Byul; Solomon, Stanley C.

2014-03-01

191

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

192

Measured ionospheric Doppler spreading of HF ground backscatter  

NASA Astrophysics Data System (ADS)

Doppler spectra from ionospherically propagated ground backscatter are presented. These spectra show how the ionosphere distorts HF backscatter radio waves by frequency speading. The ground backscatter spectra presented here show that ionospheric Dopper spreading is so ubiquitous that its effect should never be disregarded, even when a narrow azimuth beam radar such as ours is used. Nevertheless, Doppler spreading varies so quickly that it usually pays to wait for it to diminish.

Jones, R. M.; Riley, J. P.; Georges, T. M.

1983-03-01

193

Higher Order Effects in Nonlinear Raman Scattering  

NASA Astrophysics Data System (ADS)

Fully resonant four-wave mixing spectroscopies have been shown to be both highly sensitive and selective under conditions where the extent of homogeneous broadening associated with the excited electronic state is small. Given the restrictive nature of this stipulation such studies have been limited to a number of dilute organic guest-host systems performed at cryogenic temperatures. Extending the range of systems and problems addressable by these spectroscopies through the use of methods that reduce the dependence on well-defined excited electronic states provides the central motivation of this thesis. The approach taken here involves the simultaneous development of resonances with two ground state vibrational levels through interaction with the fifth-order nonlinear susceptibility, chi^{(5)}.. In experiments using toluene and benzene, where the excitation is far from an electronic resonance, one is able to observe signals derived from a five-photon interaction. Through differences in the component selection capabilities of chi^{(5)} and cascaded chi^{(3)} processes one concludes these signals originate from a cascaded mechanism. Calculations of the efficiencies of these processes confirm the experimental observations. Also indicated is the need for the spatial separation of the contributions from these competing pathways as is possible through differences in their respective phase matching conditions. Observation of the desired chi^{(5)} process appears limited by the input intensities attainable with the nanosecond laser system employed here. Estimates indicate the laser intensities attainable with commercially available picosecond technology should produce an increase in the efficiency of the chi^{(5)} process sufficient to allow its detection. Similar studies involving p-nitroaniline, where excitation now approaches an electronic resonance, are limited by a decrease in the absolute intensity of the observed signal. Through the use of an internal standard one observes a decrease in the absolute intensity on the order of 10^6 , of which all but a factor of about 350 can be accounted for as differences in experimental conditions. Concentration studies and line shape analyses confirm the observed relative intensities and allow estimation of the contributions to the third-order susceptibility.

Ivanecky, Joseph Edward, III

194

Characterizing lower ionosphere forcing by a strong lightning stroke using VLF/LF radio wave remote sensing and propagation modeling  

NASA Astrophysics Data System (ADS)

The direct and indirect effects of lightning strokes on the lower ionosphere seen with VLF signal propagation with regard to the generation of Trimpis are well known, e.g. [5]. Additionally to these events with recovery times of the order of seconds disturbance events with long recovery times of the order of minutes to half an hour are observed and related to direct lightning EMP heating of the lower ionosphere [2]. This work discusses remote sensing and modeling of such an event (4th of Nov. 2012, 3:04:27 UT, North Sea) allowing to characterize the disturbance conditions with regard to time development and space extension.

Schmitter, E. D.

2013-09-01

195

Ionosphere around equinoxes during low solar activity  

NASA Astrophysics Data System (ADS)

The seasonal behaviors of the ionosphere have been investigated for several decades, but the differences of the ionosphere between the March and September equinoxes are still an open question. In this analysis we utilize the data of ionospheric electron density (Ne) profiles from Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission radio occultation measurements, total electron density (TEC) from TOPEX and Jason-1, and TEC from Global Positioning System (GPS) receivers as well as global ionosonde measurements of the F2 layer peak electron density (NmF2) to investigate the behaviors of the daytime ionosphere around equinoxes during low solar activity (LSA). The analysis reveals that during LSA the equinoctial asymmetry in ionospheric plasma density is mainly a low-latitude phenomenon. The differences of equinoctial TEC and NmF2 have considerable amplitudes at low latitudes in both hemispheres and less significant at higher latitudes. With increasing altitude, the asymmetry in COSMIC Ne becomes weaker in the Southern Hemisphere, and the northern pronounced asymmetry regions move toward the magnetic equator. The ionospheric equinoctial asymmetry may be considered as a manifestation of the annual variation, whose annual phase significantly shifts away from the solstices. The F layer peak height (hmF2) extracted from COSMIC Ne profiles also shows an equinoctial asymmetry at low latitudes, indicating the existence of equinoctial differences in low-latitude neutral winds, specifically in the Northern Hemisphere. It reveals that, besides the important effect of the neutral wind, other processes should play roles in the forming of the observed equinoctial asymmetry in the ionosphere.

Liu, Libo; He, Maosheng; Yue, Xin'an; Ning, Baiqi; Wan, Weixing

2010-09-01

196

Birth order effects on autism symptom domains  

Microsoft Academic Search

Autism is predominantly genetically determined. Evidence supports familiality of the main sets of behavioral characteristics that define the syndrome of autism; however, possible non-genetic effects have also been suggested. The present study compared levels of autism symptom domains, as measured by the Autism Diagnostic Interview, and useful phrase speech scores between 106 pairs of first- and second-born siblings from multiply affected

Abraham Reichenberg; Christopher Smith; James Schmeidler; Jeremy M. Silverman

2007-01-01

197

Observations of Ionospheric Currents at Mars  

NASA Astrophysics Data System (ADS)

How the solar wind interacts with a planetary object depends upon the object's properties, such as the presence of a magnetic field or an atmosphere. An unmagnetized object cannot stand-off the solar wind unless it possess a substantial atmosphere. Currents can be induced in the ionosphere which act to cancel out the external solar wind magnetic field preventing it from reaching the surface. Here we present observations of such induced currents in the ionosphere of Mars. During aerobraking maneuvers, Mars Global Surveyor made several passes through the ionosphere in the unmagnetized northern hemisphere. From the observed changes in the local magnetic field, we calculate vertical profiles of (predominantly) horizontal ionospheric currents. Given an atmospheric model, we also calculate the ionospheric conductivity and the ionospheric electric fields associated with these currents. These results can give us insights into how external magnetic fields are effectively screened out by induced currents and how induced magnetospheres form around unmagnetized objects. This work is supported in part by NASA's Mars Fundamental Research and Mars Data Analysis Programs.

Fillingim, Matthew; Lillis, R.; Brain, D.

2012-10-01

198

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

199

42 CFR 2.61 - Legal effect of order.  

Code of Federal Regulations, 2011 CFR

...Health PUBLIC HEALTH SERVICE, DEPARTMENT OF HEALTH AND HUMAN SERVICES GENERAL PROVISIONS CONFIDENTIALITY OF ALCOHOL AND DRUG ABUSE PATIENT RECORDS Court Orders Authorizing Disclosure and Use § 2.61 Legal effect of order. (a)...

2011-10-01

200

Birth order matters: the effect of family size and birth order on educational attainment  

Microsoft Academic Search

Using the British Household Panel Survey, we investigate if family size and birth order affect children’s subsequent educational\\u000a attainment. Theory suggests a trade-off between child quantity and “quality” and that siblings are unlikely to receive equal\\u000a shares of parental resources devoted to children’s education. We construct a new birth order index that effectively purges\\u000a family size from birth order and

Alison L. Booth; Hiau Joo Kee

2009-01-01

201

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

202

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

203

Ionospheric effect of HF surface wave over-the-horizon radar  

Microsoft Academic Search

The use of HF surface wave radar as an effective method for inspecting the environment of the ocean in the beyond-the-horizon area has been developing in recent years. However, because the radiating beam of the transmitting antenna is of a certain width and its electromagnetic radiating power propagates not only along the sea surface but also to the upper space,

Huotao Gao; Geyang Li; Yongxu Li; Zijie Yang; Xiongbin Wu

2006-01-01

204

Effects of chemical releases by the STS 3 orbiter on the ionosphere  

Microsoft Academic Search

The Plasma Diagnostics Package, flown aboard STS-3 as part of the first Shuttle payload (OSS-1), recorded the effects of various chemical releases from the Orbiter. Changes in the plasma environment was observed during flash evaporator system releases, water dumps and maneuvering thruster operations. During flash evaporator operations, broadband Orbiter-generated electrostatic noise was enhanced and plasma density irregularities were observed to

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

1985-01-01

205

Effects of chemical releases by the STS3 Orbiter on the ionosphere. Final report  

Microsoft Academic Search

The Plasma Diagnostics Package, flown aboard STS-3 as part of the first Shuttle payload (OSS-1), recorded the effects of various chemical releases from the Orbiter. Changes in the plasma environment was observed during flash evaporator system releases, water dumps and maneuvering thruster operations. During flash evaporator operations, broadband Orbiter-generated electrostatic noise was enhanced and plasma density irregularities were observed to

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

1983-01-01

206

Effects of chemical releases by the STS3 Orbiter on the ionosphere  

Microsoft Academic Search

The Plasma Diagnostics Package, flown aboard STS-3 as part of the first Shuttle payload (OSS-1), recorded the effects of various chemical releases from the Orbiter. Changes in the plasma environment was observed during flash evaporator system releases, water dumps and maneuvering thruster operations. During flash evaporator operations, broadband Orbiter-generated electrostatic noise was enhanced and plasma density irregularities were observed to

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

1983-01-01

207

Analysis of the effect of ionosphere in L-band ALOS interferograms of the Gulf of Corinth in Greece  

NASA Astrophysics Data System (ADS)

A series of L-band PALSAR/ALOS single (HH) and dual (HH-VV) polarisation data over the Gulf of Corinth, Greece, have been acquired. Differential interferograms were calculated from these data. The Gulf of Coring seismic area is also monitored with 6 permanent GPS receivers. For the epochs of PALSAR observations, we extracted from the dual-frequency GPS data the ionospheric delay in the line of sight of each satellite. At some stations equipped with receivers collecting P1 and P2, the absolute delay can be estimated. At all stations, relative delays from L1 and L2 were extracted from the data. We analyze our results and discuss the possible influence of the ionosphere in the differential interferograms as well as in singles (of dual polarisation) images and its weight compared to the tropospheric noise.

Elias, P.; Briole, P.; Herekakis, T.; Belehaki, A.

2009-04-01

208

Role of Ionospheric Plasmas in Earth's Magnetotail  

NASA Technical Reports Server (NTRS)

This tutorial will summarize observations and theories indicating a prominent role of ionospheric plasma in the Earth's magnetotail. At the Global scale, I will argue that it is ionospheric plasma momentum and dynamic pressure that are responsible for the production of plasmoids, through the action of a transient near-Earth neutral or X-line, which serves to release excessive plasma pressure from the magnetotail field. Ionospheric plasma gains the momentum and energy to produce plasmoids and their related effects through its interaction with the solar wind, beginning at the dayside reconnection region and extending across the polar caps through the magnetotail lobes. This distant neutral line can be depicted as a feature much like that found in cometary magnetospheres, where disconnection limits the amount of IMF hung up on the cometary coma. On the other hand, the near-Earth neutral one can be seen as a feature unique to planets with an intrinsic magnetic field and internal source of plasma, the heating of which produces pressures too large to be restrained. Ionospheric plasmas also have other more local roles to play in the magnetotail. The circulation influences the composition of the plasma sheet, and the resultant wave environment, giving rise to reduced wave propagation speeds. Important heavy ion cyclotron resonances, and enhanced finite gyro-radius effects including non-adiabatic particle acceleration. At minimum, the presence of ionospheric plasma must influence the rate of reconnection via its enhanced mass density. Other non-MHD effects of ionospheric plasma presence are likely to be important but need much more investigation to be well understood. The MMS mission is designed to penetrate the subtle diffusion region physics that is involved, and its ability to observe ionospheric plasma involvement in reconnection will contribute significantly toward that goal.

Moore, Thomas E.

2007-01-01

209

Modeling the martian ionosphere  

NASA Astrophysics Data System (ADS)

The accessibility of the Martian atmosphere to spacecraft provides an opportunity to study an ionosphere that differs from our own. Yet, despite the half century of measurements made at Mars, the current state of the neutral atmosphere and its embedded plasma (ionosphere) remains largely uncharacterized. In situ measurements of the neutral and ionized constituents versus height exist only from the two Viking Landers from the 1970s. Subsequent satellite and remote sensing data offer sparse global coverage of the ionosphere. Thermal characteristics of the plasma environment are not well understood. Patchy crustal magnetic fields interact with the Martian plasma in a way that has not been fully studied. Hence, investigating the coupled compositional, thermal and crustal-field-affected properties of the ionosphere can provide insight into comparative systems at Earth and other planets, as well as to atypical processes such as the solar wind interaction with topside ionospheric plasma and associated pathways to escape. Ionospheric models are fundamental tools that advance our understanding of complex plasma systems. A pre-existing one-dimensional model of the Martian ionosphere has been upgraded to include more comprehensive chemistry and transport physics. This new BU Mars Ionosphere Model has been used to study the composition, thermal structure and dynamics of the Martian ionosphere. Specifically: the sensitivity of the abundance of ions to neutral atmospheric composition has been quantified, diurnal patterns of ion and electron temperatures have been derived self-consistently using supra-thermal electron heating rates, and the behavior of ionospheric plasma in crustal field regions was simulated by constructing a two-dimensional ionospheric model. Results from these studies were compared with measurements and show that (1) ion composition at Mars is highly sensitive to the abundance of neutral molecular and atomic hydrogen, (2) lighter ions heat up more efficiently than heavier ones and provide additional heating sources for cooler plasma, and (3) crustal field morphology affects plasma dynamics and structure at Mars in a way that is consistent with observations. Finally, model predictions of ion composition and plasma temperatures are provided for observations to be made by several instruments on board the upcoming 2013 MAVEN orbiter.

Matta, Majd Mayyasi

210

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

211

VHF ionospheric scintillations near the equatorial anomaly crest: solar and magnetic activity effects  

NASA Astrophysics Data System (ADS)

20 dB) mainly occur in the pre-midnight period, and in the post-midnight period, the scintillations are generally moderate (5-10 dB) or weak (<5 dB). The nocturnal scintillation occurrence decreases with the decrease in solar activity from 1989 to 1992. Monthly mean scintillation occurrence changes according to solar activity during E- and D-months but not so during J-months. The effects of magnetic activity on scintillations vary with season and, in general, inhibit the scintillation occurrence in the pre-midnight period and enhance it a little in the post-midnight period, especially after 0300 hours IST (Indian Standard Time). For most of the severe magnetic storms in which Dst goes below -125 nT and the recovery phase starts in the post-midnight to dawn local time sector, strong post-midnight scintillations, which sometimes extend for several hours beyond the local sunrise, are observed.

Kumar, S.; Gwal, A. K.

2000-02-01

212

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

NASA Astrophysics Data System (ADS)

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

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

1983-12-01

213

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

SciTech Connect

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

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

1983-12-01

214

Effects of chemical releases by the STS 3 orbiter on the ionosphere  

NASA Astrophysics Data System (ADS)

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

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

1985-04-01

215

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

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

216

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

217

Anomalous modification of the ionospheric total electron content prior to the 26 September 2005 Peru earthquake  

Microsoft Academic Search

This paper investigates the features of pre-earthquake ionospheric anomalies in the total electron content (TEC) data obtained on the basis of regular GPS observations from the International GNSS Service (IGS) network. For the analysis of the ionospheric effects of the 26 September 2005 Peru earthquake, Global Ionospheric Maps (GIMs) of TEC were used. The possible influence of the earthquake preparation

I. E. Zakharenkova; I. I. Shagimuratov; N. Yu. Tepenitzina; A. Krankowski

2008-01-01

218

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

Microsoft Academic Search

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

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

2006-01-01

219

Modelling the high-latitude ionosphere  

NASA Technical Reports Server (NTRS)

Results of an ionospheric model program are presented which demonstrate the extreme variability of the steady state, daytime, ionospheric F region electron density and ion composition due to both neutral atmospheric changes with solar cycle, season and magnetic activity, and to the effects of ionospheric drifts caused by perpendicular electric fields. Consideration is given to the time history of the ionospheric plasma as it undergoes convective motion due to the combined effects of corotation forces and electromagnetic forces which results from the mapping of the magnetospheric cross tail electric field to the rotating ionosphere. A simple model of the convection pattern is described. The model calculates the net effect of the tendency for the plasma to corotate about the geographic pole and the E sub Bar times B sub Bar velocity induced by a perpendicular electric field mapped to a circle centered about a point 5 deg antisunward of the geomagnetic pole and oriented such that the equipotentials are parallel to the noon midnight meridian. This convection pattern shows the generally accepted features of high latitude convection, but because of the offset between the geographic and geomagnetic poles a marked universal time dependence in these features is predicted.

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

1981-01-01

220

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

NASA Astrophysics Data System (ADS)

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

Boudjada, Mohammed Yahia; Schwingenschuh, Konrad; Al-Haddad, Emad; Parrot, Michel; Galopeau, Patrick H. M.; Besser, Bruno; Stangl, Guenter; Voller, Wolfgang

2012-04-01

221

Total electron content measurements in ionospheric physics  

NASA Astrophysics Data System (ADS)

With the advent of modern global networks of dual-frequency Global Positioning System (GPS), total electron content (TEC) measurements along slant paths connecting GPS receivers and satellites at 22,000 km have become the largest data set available to ionospheric scientists. The TEC can be calculated from the time and phase delay in the GPS signal using the GPS Toolkit, but an unknown bias will remain. In addition, UHF/VHF radio beacons on board low-Earth-orbiting satellites can also be used to measure the electron content. However, the TEC measurements are obtained by integrating TEC differences between slant paths, but also contain biases. It is often necessary to use data assimilative algorithms like the Ionospheric Data Assimilation Three-Dimensional (IDA3D), and to treat both GPS- and LEO-beacon TEC measurements as relative data in order to conduct ionospheric studies.

Garner, T. W.; Gaussiran, T. L., II; Tolman, B. W.; Harris, R. B.; Calfas, R. S.; Gallagher, H.

2008-08-01

222

IGS-global ionospheric maps for accurate computation of GPS single- frequency ionospheric delay-simulation study  

NASA Astrophysics Data System (ADS)

The Ionospheric delay is still one of the largest sources of error that affects the positioning accuracy of any satellite positioning system. This problem could be solved due to the dispersive nature of the Ionosphere by combining simultaneous measurements of signals at two different frequencies but it is still there for single- frequency users. Much effort has been made in establishing models for single- frequency users to make this effect as small as possible. These models vary in accuracy, input data and computational complexity, so the choice between the different models depends on the individual circumstances of the user. From the simulation point of view, the model needed should be accurate with a global coverage and good description to the Ionosphere's variable nature with both time and location. The author reviews some of these established models, starting with the BENT model, the Klobuchar model and the IRI (International Reference Ionosphere) model. Since quiet a long time, Klobuchar model considers the most widely used model ever in this field, due to its simplicity and time saving. Any GPS user could find Klobuchar model's coefficients in the broadcast navigation message. CODE, Centre for Orbit Determination in Europe provides a new set of coefficients for Klobuchar model, which gives more accurate results for the Ionospheric delay computation. IGS (International GPS Service) services include providing GPS community with a global Ionospheric maps in IONEX-format (IONosphere Map Exchange format) which enables the computation of the Ionospheric delay at the desired location and time. The study was undertaken from GPS-data simulation point of view. The aim was to select a model for the simulation of GPS data that gives a good description of the Ionosphere's nature with a high degree of accuracy in computing the Ionospheric delay that yields to better-simulated data. A new model developed by the author based on IGS global Ionospheric maps. A comparison study had been made involving the Klobuchar model with GPS broadcasted coefficients, the Klobuchar model with CODE coefficients and the new established model. The study had proved that the Klobuchar model had a shortcoming side regarding its low accuracy and less detailed des cription for the Ionosphere's behaviour. Using the CODE Klobuchar-styled coefficients in the Klobuchar model will give a better accuracy in computing the delay but it will still give a less detailed description of the ionosphere performance. The use of the global Ionospheric maps from one of the IGS centers gives us higher accuracy in computing the Ionospheric delay and also very detailed description for the ionosphere nature which is essential for the simulation purposes and will end with better simulated GPS data.

Farah, A.

223

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

224

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

225

Ionosphere/microwave beam interaction study. [satellite solar energy conversion  

NASA Technical Reports Server (NTRS)

A solar power satellite microwave power density of 20mw sq cm was confirmed as the level where nonlinear interactions may occur in the ionosphere, particularly at 100 km altitude. Radio wave heating at this altitude, produced at the Arecibo Observatory, yielded negative results for radio wave heating of an underdense ionosphere. Overdense heating produced striations in the ionosphere which may cause severe radio frequency interference problems under certain conditions. The effects of thermal self-focusing are shown to be limited severely geographically. The aspect sensitivity of field-aligned striations makes interference-free regions above magnetic latitude about 60 deg. A test program is proposed to simulate the interaction of the SPS beam with the ionosphere, to measure the effects of the interaction on the ionosphere and on communication and navigation systems, and to interpret the results.

Duncan, L. M.; Gordon, W. E.

1977-01-01

226

Propagation of electromagnetic waves in a structured ionosphere  

SciTech Connect

The ionosphere is a birefringent medium which strongly affects the transmission of very high frequency (vhf) radio signals. These effects must be understood in detail if one wishes to look at the propagation of wide bandwidth coherent signals through the ionosphere. We develop a general perturbative solution of Maxwell`s equations for vhf signals propagating in the ionosphere, subject only to mild restrictions on the ionospheric structure. This solution can be extended to give the propagating field to any desired degree of precision. The case of a laminar ionosphere with harmonic waves is developed in greater detail, and we show how to calculate the ray path in this case. This solution is used to elucidate the effects of refraction on the phase of the signal, and we calculate the spatial- and frequency-coherence functions. The electric field for a laminar ionosphere without waves is analyzed to clarify the physical origins of the terms modifying the signal phase. We then calculate the solution in this case for the Appleton-Hartree model of the ionospheric dielectric function and express the result as a series in inverse powers of frequency. We conclude by calculating the ray path for a model ionosphere using the Appleton-Hartree dielectric function and a parabolic layer for the electron density.

Murphy, T.

1996-06-01

227

Tsunamigenic ionospheric hole  

NASA Astrophysics Data System (ADS)

Traveling ionospheric disturbances generated by an epicentral ground/sea surface motion, ionospheric disturbances associated with Rayleigh-waves as well as post-seismic 4-minute monoperiodic atmospheric resonances and other-period atmospheric oscillations have been observed in large earthquakes. In addition, a giant tsunami after the subduction earthquake produces an ionospheric hole which is widely a sudden depletion of ionospheric total electron content (TEC) in the hundred kilometer scale and lasts for a few tens of minutes over the tsunami source area. The tsunamigenic ionospheric hole detected by the TEC measurement with Global Position System (GPS) was found in the 2011 M9.0 off the Pacific coast of Tohoku, the 2010 M8.8 Chile, and the 2004 M9.1 Sumatra earthquakes. This occurs because plasma is descending at the lower thermosphere where the recombination of ions and electrons is high through the meter-scale downwelling of sea surface at the tsunami source area, and is highly depleted due to the chemical processes.

Kakinami, Yoshihiro; Kamogawa, Masashi; Tanioka, Yuichiro; Watanabe, Shigeto; Riadi Gusman, Aditya; Liu, Jann-Yenq; Watanabe, Yasuyuki; Mogi, Toru

228

Tsunamigenic ionospheric hole  

NASA Astrophysics Data System (ADS)

Traveling ionospheric disturbances generated by an epicentral ground/sea surface motion, ionospheric disturbances associated with Rayleigh-waves as well as post-seismic 4-minute monoperiodic atmospheric resonances and other-period atmospheric oscillations have been observed in large earthquakes. In addition, a giant tsunami after the subduction earthquake produces an ionospheric hole which is widely a sudden depletion of ionospheric total electron content (TEC) in the hundred kilometer scale and lasts for a few tens of minutes over the tsunami source area. The tsunamigenic ionospheric hole detected by the TEC measurement with Global Position System (GPS) was found in the 2011 M9.0 off the Pacific coast of Tohoku, the 2010 M8.8 Chile, and the 2004 M9.1 Sumatra earthquakes. This occurs because plasma is descending at the lower thermosphere where the recombination of ions and electrons is high through the meter-scale downwelling of sea surface at the tsunami source area, and is highly depleted due to the chemical processes.

Kakinami, Yoshihiro; Kamogawa, Masashi; Tanioka, Yuichiro; Watanabe, Shigeto; Gusman, Aditya Riadi; Liu, Jann-Yenq; Watanabe, Yasuyuki; Mogi, Toru

2012-06-01

229

Effects of diffraction by ionospheric electron density irregularities on the range error in GNSS dual-frequency positioning and phase decorrelation  

Microsoft Academic Search

Errors in GPS positioning due to diffraction by ionospheric irregularitiesPhase decorrelation between different GPS frequencies due to diffractionDecrease in correlation for strong scintillation conditions

Vadim E. Gherm; Nikolay N. Zernov; Hal J. Strangeways

2011-01-01

230

Ionospheric Corrections to Tropospheric Retrievals  

NASA Technical Reports Server (NTRS)

Ionosphere affects radio occultations significantly, particularly at stratospheric altitudes. Variations with solar and diurnal cycle are major concerns for observing climate trends. Large scale and small scale ionospheric structure have different impacts. The International Radio Occultation Working Group (CGMS) will benefit from greater participation of the ionospheric community.

Mannucci, A. J.; Ao, C. O.; Iijima, B. A.; Pi, Xiaoqing

2012-01-01

231

Ionospheric effects of major magnetic storms during the international space weather period of September and October 1999: GPS observations, VHF\\/UHF scintillations, and in situ density structures at middle and equatorial latitudes  

Microsoft Academic Search

In this paper we present a study of the ionospheric effects of a halo coronal mass ejection (CME) initiated on the Sun on September 20, 1999, and causing the largest magnetic storm during this month on September 22-23, 1999, with the hourly Dst index being -167 nT at ~2400 UT on September 22. The recurrent CME on October 18 caused

Sunanda Basu; Santimay Basu; C. E. Valladares; H.-C. Yeh; S.-Y. Su; E. MacKenzie; P. J. Sultan; J. Aarons; F. J. Rich; P. Doherty; T. W. Bullett

2001-01-01

232

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

233

Experimental evidence of electromagnetic pollution of ionosphere  

NASA Astrophysics Data System (ADS)

The Earth’s ionosphere responds to external perturbations originated mainly in the Sun, which is the primary driver of the space weather (SW). But solar activity influences on the ionosphere and the Earth's atmosphere (i.e., the energy transfer in the direction of the Sun-magnetosphere-ionosphere-atmosphere-surface of the Earth), though important, is not a unique factor affecting its state - there is also a significant impact of the powerful natural and anthropogenic processes, which occur on the Earth’s surface and propagating in opposite direction along the Earth’s surface-atmosphere-ionosphere-magnetosphere chain. Numerous experimental data confirm that the powerful sources and consumers of electrical energy (radio transmitters, power plants, power lines and industrial objects) cause different ionospheric phenomena, for example, changes of the electromagnetic (EM) field and plasma in the ionosphere, and affect on the state of the Earth atmosphere. Anthropogenic EM effects in the ionosphere are already observed by the scientific satellites and the consequences of their impact on the ionosphere are not currently known. Therefore, it is very important and urgent task to conduct the statistically significant research of the ionospheric parameters variations due to the influence of the powerful man-made factors, primarily owing to substantial increase of the EM energy production. Naturally, the satellite monitoring of the ionosphere and magnetosphere in the frequency range from tens of hertz to tens of MHz with wide ground support offers the best opportunity to observe the EM energy release, both in the global and local scales. Parasitic EM radiation from the power supply lines, when entering the ionosphere-magnetosphere system, might have an impact on the electron population in the radiation belt. Its interaction with trapped particles will change their energy and pitch angles; as a result particle precipitations might occur. Observations of EM emission by multiple low orbiting satellites have confirmed a significant increase in their intensity over the populated areas of Europe and Asia. Recently, there are many experimental evidences of the existence of power line harmonic radiation (PLHR) in the ionosphere. Their spectra consist of succession of 50 (60) Hz harmonics which is accompanied by a set of lines separated by 50 (60) or 100 (120) Hz - the central frequency of which is shifted to high frequency. These lines cover rather wide band - according to the available experimental data, their central frequencies are observed from ~1.5 - 3 kHz up to 15 kHz, and recently the main mains frequencies are also observed. The examples of power line harmonic radiation, which were detected by “Sich-1M”, “Chibis-M” and “Demeter” satellites, have been presented and discussed. The available experimental data, as well as theoretical estimations, allow us with a high degree of certainty to say that the permanent satellite monitoring of the ionospheric and magnetospheric anthropogenic EM perturbations is necessary for: a) objective assessment and prediction of the space weather conditions; b) evaluation of the daily or seasonal changes in the level of energy consumption; c) construction of a map for estimation of near space EM pollution. This study is partially supported by SSAU contract N 4-03/13.

Pronenko, Vira; Korepanov, Valery; Dudkin, Denis

234

Report from ionospheric science  

NASA Technical Reports Server (NTRS)

The general strategy to advance knowledge of the ionospheric component of the solar terrestrial system should consist of a three pronged attack on the problem. Ionospheric models should be refined by utilization of existing and new data bases. The data generated in the future should emphasize spatial and temporal gradients and their relation to other events in the solar terrestrial system. In parallel with the improvement in modeling, it will be necessary to initiate a program of advanced instrument development. In particular, emphasis should be placed on the area of improved imaging techniques. The third general activity to be supported should be active experiments related to a better understanding of the basic physics of interactions occurring in the ionospheric environment. These strategies are briefly discussed.

Raitt, W. J.; Banks, Peter M.; Nagy, A. F.; Chappell, C. R.

1989-01-01

235

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

236

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

237

HF radar ionospheric clutter  

NASA Astrophysics Data System (ADS)

The characteristics of HF radar echoes reflected from ionization irregularities aligned along the lines of force of the Earth's magnetic field are presented. Utilizing experimental radar-ionospheric clutter data acquired at frequencies between HF and UHF, an analysis is made of the amplitude, the cross-sectional area and the angular extent statistics of HF field-aligned echoes. The Doppler frequency variation, the frequency of occurrence and the diurnal and seasonal variation of HF ionospheric backscatter echoes and their correlation with solar-geophysical conditions are also discussed.

Millman, G. H.

1982-08-01

238

Computerized ionospheric tomography  

SciTech Connect

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

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

1990-05-03

239

Birth order effects on young students’ academic achievement  

Microsoft Academic Search

We examine birth order effects on academic achievement for ten-year-old students using data for the entire population of fifth graders in Norway 2007\\/2008. The analysis thus adds to a thin empirical literature focusing on birth order effects among young children. We find that being firstborn confers a significant advantage in families with two, three and four children. The analysis makes

Hans Bonesrønning; Sofia Sandgren Massih

2011-01-01

240

Ionospheric monitoring by the Global Navigation Satellite System (GNSS)  

NASA Astrophysics Data System (ADS)

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

Park, Jihye

241

Large magnetocaloric effect in manganites with charge order  

NASA Astrophysics Data System (ADS)

In this work, we report the magnetocaloric effect (|?SM|), around the charge/orbital ordering transition in the mixed valent manganite Nd0.5Sr0.5MnO3. The magnitude of |?SM| around this first-order transition is around three times larger than that obtained around the second-order transition (ferromagnetic-metallic-to-paramagnetic-insulator) in the same compound. Actually, the magnetocaloric response around the charge-order transition is comparable to pure Gd, the rare earth with the highest magnetocaloric effect. The possibility of an easy tuning of the charge-order transition temperatures in doped manganites opens a way of investigation materials usable in magnetic refrigerators.

Sande, P.; Hueso, L. E.; Miguéns, D. R.; Rivas, J.; Rivadulla, F.; López-Quintela, M. A.

2001-09-01

242

Ionospheric modification during moderate geomagnetic storm at low solar activity  

NASA Astrophysics Data System (ADS)

In this report we present an analysis of the ionospheric response to moderate (Dst<70 nT), 11 October 2008, geomagnetic storm. TEC maps over European region were created on the base of GPS observations provided by IGS/EPN. Strong short-term positive effect was detected near noon of 11 October 2008. The TEC enhancement exceeded 100% on latitudes of 65-35N and was decreased to lower latitudes. The positive effect was associated with large scale traveling disturbance. During storm there was observed the increase and modification of horizontal gradients structure and ionospheric trough had moved to equator, until 57-58 geomagnetic latitudes. The electron density profiles, retrieved from the Formosat-3/COSMIC radio occultation measurements and also measurements from European ionospheric sounding stations (DIAS), were analyzed within the case-study to estimate the altitudinal modification of the ionosphere. The considerable enhancement of the peak electron density was observed in European region during 11-15 UT, it reached the factor of 2.8 in comparison with quiet conditions. The height of the ionospheric F2 layer was risen by 60 km. For graphical demonstration of the observed ionospheric effects global electron density maps were calculated on the base of globally distributed COSMIC RO profiles. Electron density maps for different altitude slices were analyzed. This positive effect was revealed distinctly in RO electron density profiles and products based on these data - ionospheric electron content and global maps of electron density.

Krankowski, A.; Shagimuratov, I.; Zakharenkova, I.; Krypiak-Gregorczyk, A.

2010-12-01

243

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

244

Interplanetary magnetic field variations and the electromagnetic state of the equatorial ionosphere  

NASA Technical Reports Server (NTRS)

The Esq phenomena were selected in order to examine the effect of the interplanetary magnetic field (IMF) on the ionospheric plasma and to obtain insight into the interplanetary ionospheric coupling processes. January-March 1973 interplanetary magnetic field data of Explorer 43, Huancayo ionograms, and surface equatorial magnetograms were used. The IMF observations from Explorer 43 in the form of 15-sec averages were examined around the time of disappearance of the Esq. The IMF z-component was observed to change from a negative to a positive value before the disappearance of the Esq in four events where simultaneous data were available. The general explanation is that the induced electric field becomes westward from a previous eastward direction, coinciding with the IMF z-component reversal. Thus, just before the Esq disappears, the magnetosphere is subjected to the westward electric field. If this field is impressed to the low-latitude ionosphere, the resultant electric field in the equatorial ionosphere changes from eastward (westward) to westward (eastward) in the daytime (nighttime).

Patel, V. L.

1978-01-01

245

Effects of low concentrations of O2 and CO on the ion-clustering reactions in the lower ionosphere of Mars  

NASA Technical Reports Server (NTRS)

It is demonstrated that under conditions which approximate those of the Martian ionosphere traces of CO and O2 can be effectively incorporated in ion clusters via ion-molecule reaction schemes initiated by the CO2(+) ion. For example, when 0.3% CO is added to CO2, (CO)2(+), and /(CO)2CO2/(+) appear as the major cations (584 A radiation, 300 K). In mixtures containing O2 in addition to CO, (CO2,O2+) and /(CO2)2O2/(+) are important species. A recently proposed mechanism to account for the low abundance of CO and O2 in the Martian atmosphere is discussed in the light of these observations.

Sieck, L. W.; Gorden, R., Jr.; Ausloos, P.

1973-01-01

246

Openness to experience, plasticity, and creativity: Exploring lower-order, high-order, and interactive effects  

Microsoft Academic Search

What are creative people like? Openness to experience is important to creativity, but little is known about plasticity, the higher-order factor that subsumes openness. College students (n=189) completed measures of the Big Five and measures of creative cognition (fluency and quality of divergent thinking), everyday creative behaviors, creative achievement, and self-rated creativity. Latent variable models found broad effects of openness

Paul J. Silvia; Emily C. Nusbaum; Christopher Berg; Christopher Martin; Alejandra O’Connor

2009-01-01

247

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

248

Soviet ionospheric modification research  

Microsoft Academic Search

Soviet published literature in ionospheric modification research by high-power radio waves is assessed, including an evaluation of its impact on and applications to future remote-sensing and telecommunications systems. This assessment is organized to place equal emphasis on basic research activities, designed to investigate both the natural geophysical environment and fundamental plasma physics; advanced research programs, such as those studying artificial

L. M. Duncan; H. C. Carlson; F. T. Djuth; J. A. Fejer; N. C. Gerson; T. Hagfors; D. B. Newman Jr.; R. L. Showen

1988-01-01

249

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

250

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

251

Observations of O+ in transit from the ionosphere: The pipeline  

NASA Astrophysics Data System (ADS)

Energetic O+ ions have important dynamic effects on all regions of the magnetosphere including the ring current. Here we discuss some of the dynamical effects. We emphasize observations of O+ populations escaping from the ionosphere under various geomagnetic conditions and their access to the plasma sheet and ring current. We review data establishing that a significant flux of O+ escapes the ionosphere during geomagnetically quiet intervals. Our analysis suggests that most magnetospheric O+ is in transit between the ionosphere and ring current during the quiet intervals before geomagnetic storms.

Peterson, William; Elkington, Scot; Yau, Andrew W.

252

Generation of ion-conic distribution by upgoing ionospheric electrons  

Microsoft Academic Search

Downward currents in auroral regions are commonly measured with amplitudes of 1--5 ..mu..A\\/m². Such currents are likely the result of upgoing thermal ionospheric electrons falling through a field-aligned potential drop on the order of their thermal energyl. Similar distributions of upgoing ionospheric electrons may also occur in regions of diffuse auroral electron precipitation to preserve current continuity in the presence

P. B. Dusenbery; L. R. Lyons

1981-01-01

253

Dilution effects on orbital order in strongly correlated electron systems  

Microsoft Academic Search

Dilution effects in orbital ordered systems with strong electron correlation are studied theoretically. Vacancy-concentration x dependence of the orbital-ordering temperature TOO calculated in the two-representative orbital models, i.e. the eg-orbital model in a three dimensional square lattice and the two-dimensional orbital compass model. Reduction of TOO as a function of x is stronger than that in dilute magnets and is

S. Ishihara; T. Tanaka; M. Matsumoto

2007-01-01

254

Birth-Order Effects in the Academically Talented  

Microsoft Academic Search

Birth-order position was studied among 828 academically talented students from a national sample collected by the Institute for the Academic Advancement of Youth of Johns Hopkins University. When compared to 1990 U.S. Census Bureau data, this sample was disproportionately composed of first-born students. However, much of this birth order effect can be explained by the covariate of family size, with

Wayne D. Parker

1998-01-01

255

Formation and detection of high latitude ionospheric irregularities  

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

256

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

257

ISIS : a formation flying ionospheric seismic imaging experiment  

NASA Astrophysics Data System (ADS)

Today, available techniques for the lithosphere tomography are limited by the number of seismic stations that we can deploy : it is sometimes difficult to access to some remote regions, but foremost the number of stations that are deployable over the oceans is strongly reduced. If we can dispose of some sites on islands (which are all characterized by a strong background noise), and on the measurements on coastal areas borders, it is therefore difficult to inverse the fine structure of the oceanic lithosphere. A promising idea is to use a long known idea, that earthquakes have a measurable impact on the ionosphere. As a matter of fact, the decrease of the atmosphere density with respect to altitude implies an amplification of the Rayleigh waves in the atmosphere, up to a maximum at about 250 km. This effect has been quantified for the Denali earthquake (Ducic et al, 2003) though its impact on the TEC content on the ionosphere. We therefore propose to detect this effect from space, thanks to a spaceborne multistatic SAR. Our concept includes 3 satellites in formation (along the same orbit) in a MEO orbit (about 19000 km). The master satellite payload is a slightly modified SAR, which operates around two main frequencies, in order to allow the computation of the delay induced by ionospheric fluctuations. The two other satellites have a passive payload which is time-synchronized with the master SAR: the use of their crossing rays will allow a 3D reconstruction of the ionosphere. A preliminary design of the space segment proposes an implementation on a MEO-orbit compatible bus, with high peak power capabilities. In order to allow the compatibility of the payload concept with the on-board available power, we have assumed that the satellite will enter in its alert mode on ground request. When an earthquake occurs, we dispose of a ten minutes delay to "wake-up" the satellite. When not in alert mode, its nominal imaging frequency will be reduced to allow the detection of long period phenomena, such as tsunamis.

Mimoun, D.; Lognonné, Ph; Garcia, R.; Occhipinti, G.; Abbondanza, S.

258

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

NASA Technical Reports Server (NTRS)

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

Tan, A.

1990-01-01

259

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

NASA Technical Reports Server (NTRS)

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

Balachandran, N. K.

1983-01-01

260

Origin of ultraviolet emission source in the Jovian ionosphere at the feet of the Io flux tube  

Microsoft Academic Search

A model for an explanation of far ultraviolet (FUV) emissions observed from the Io flux tube footprints at the Jovian ionosphere is presented. An acceleration of electrons and ions of the ionospheric plasma up to sufficient energies for an effective excitation of H2 Lyman and Werner bands is proposed. The neutral particles within the Jovian ionosphere are excited due to

Vladimir E. Shaposhnikov; Valerii V. Zaitsev; Helmut O. Rucker; Galina V. Litvinenko

2001-01-01

261

Observations of Ionospheric Currents at Mars and Venus  

NASA Astrophysics Data System (ADS)

How the solar wind interacts with a planetary object depends upon the object's properties, such as the presence of a magnetic field or an atmosphere. An unmagnetized object cannot stand-off the solar wind unless it possess a substantial atmosphere. Currents can be induced in the ionosphere which act to cancel out the external solar wind magnetic field preventing it from reaching the surface. Here we present observations of such induced currents in the ionospheres of Mars and Venus. During aerobraking maneuvers, Mars Global Surveyor made several passes through the ionosphere of Mars in the unmagnetized northern hemisphere. Likewise, Pioneer Venus Orbiter and Venus Express have passed through the ionosphere of Venus. From the observed changes in the local magnetic field, we calculate vertical profiles of (predominantly) horizontal ionospheric currents. Given an atmospheric model, we also calculate the ionospheric conductivity and the ionospheric electric fields associated with these currents. These results can give us insights into how external magnetic fields are effectively screened out by induced currents and how induced magnetospheres form around unmagnetized objects.

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

2013-12-01

262

Birth Order Effects on Personality and Achievement Within Families  

Microsoft Academic Search

We investigated birth order effects on personality and achievement in four studies (N = 1,022 families) including both stu- dent and adult samples. Control over a wide range of variables was effected by collecting within-family data: Participants compared their siblings (and themselves) on a variety of personality and achievement dimensions. Across four diverse data sets, first-borns were nominated as most

Delroy L. Paulhus; Paul D. Trapnell; David Chen

1999-01-01

263

Satellite observations of an ionospheric acceleration mechanism  

Microsoft Academic Search

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

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

1976-01-01

264

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

265

Pecuniary Effects, Second-Order Conditions, and the LRAC Curve.  

ERIC Educational Resources Information Center

Explores the importance of second-order conditions in the cost-minimization problem confronting the monopsonistic employer of factor inputs. Describes an alternative approach to the presence of pecuniary effects that does not depend on the assumption that firms are monopsonistic in factor markets. (CMK)

Comolli, Paul M.

2000-01-01

266

Presentation order effects on accounting students' ethical judgments  

Microsoft Academic Search

This study presents the results of two experiments that test whether students' judgments about the acceptability of questionable actions are affected by the order in which ethical arguments are presented in the classroom. When ethical arguments are presented sequentially in a group setting, prior research suggests a primacy effect; where the first behavior pattern observed by group members sets the

Randall E. LaSalle

1997-01-01

267

Birth-Order Effects in the Academically Talented.  

ERIC Educational Resources Information Center

Birth-order position was studied among 828 academically talented sixth-grade students. When compared to census data, the sample was disproportionately composed of first-born students. However, this effect was largely explained by the covariate of family size, with small families over represented among the gifted. Other findings indicated no…

Parker, Wayne D.

1998-01-01

268

Ionospheric signatures of Lightning  

NASA Astrophysics Data System (ADS)

The geostationary metrology satellite (GMS) monitors motions of thunderstorm cloud, while the lightning detection network (LDN) in Taiwan and the very high Frequency (VHF) radar in Chung-Li (25.0›XN, 121.2›XE) observed occurrences of lightning during May and July, 1997. Measurements from the digisonde portable sounder (DPS) at National Central University shows that lightning results in occurrence of the sporadic E-layer (Es), as well as increase and decrease of plasma density at the F2-peak and E-peak in the ionosphere, respectively. A network of ground-based GPS receivers is further used to monitor the spatial distribution of the ionospheric TEC. To explain the plasma density variations, a model is proposed.

Hsu, M.; Liu, J.

2003-12-01

269

Comparison of measured and modeled solar EUV flux and its effect on the E-F1 region ionosphere  

NASA Technical Reports Server (NTRS)

Two different photochemical schemes are used to investigate the response of the E-F1 region ionosphere to different solar EUV flux models, and the results are compared with incoherent scatter radar electron density measurements taken at Millstone Hill. The latest EUV flux model (Tobiska, 1991), which incorporates more recent measurements, has generally more flux at short wavelengths compared to the Hinteregger et al. (1981) flux model based on AE-E satellite data. This results in better agreement with the measurements in the E-F1 region and above. The Tobiska flux model gives a smaller E region peak density, due to the influence of low Ly-beta flux in the November 10, 1988 rocket measurements of Woods and Rottman (1990). The photoionization and photoabsorption cross sections of Conway (1988) give results in somewhat better agreement with observations than the cross sections of Torr et al. (1979). For the zenith angles considered (daytime conditions), the Chapman function method for calculating photoabsorption yields results in satisfactory agreement with a more rigorous calculation method using a formula from Rees (1989).

Buonsanto, M. J.; Solomon, S. C.; Tobiska, W. K.

1992-01-01

270

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

271

OVERCOMING IONOSPHERIC SCINTILLATION FOR WORLDWIDE GPS AVIATION  

E-print Network

in the equatorial area, including Brazil and India, is ionospheric scintillation. Due to electron density irregularities inside the ionosphere, transionospheric radio waves interfere constructively and de- structively

Stanford University

272

Bipolar climatology of GPS ionospheric scintillation at solar minimum  

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

273

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

NASA Astrophysics Data System (ADS)

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

Harrison, Giles; Aplin, Karen; Rycroft, Michael

2014-05-01

274

A statistic study of ionospheric solar flare activity indicator  

NASA Astrophysics Data System (ADS)

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

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

275

A statistic study of ionospheric solar flare activity indicator  

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

276

Summary of Sessions: Ionosphere - Thermosphere - Mesosphere Working Group  

NASA Technical Reports Server (NTRS)

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

Spann, J. F.; Bhattacharyya, A.

2006-01-01

277

Computerized Physician Order Entry - effectiveness and efficiency of electronic medication ordering with decision support systems  

PubMed Central

Health political background Computerized physician order entry (CPOE) systems are software to electronically enter medication orders. They can be equipped with tools for decision support (CDS). In Germany, various vendors offer such systems for hospitals and physicians’ offices. These systems have mostly been developed during the last five to ten years. Scientific background CPOE-systems exist since the 1970’s. Usually, clinical decision support is integrated into the CPOE to avoid errors. Research questions This HTA-report aims to evaluate the effectiveness and efficiency of CPOE-/CDS-systems and their ethical, social and legal aspects. Methods The systematic literature search (27 international data bases) yielded 791 abstracts. Following a two-part selection process, twelve publications were included in the assessment. Results All reviews and studies included in the present report show that the use of CPOE-/CDS-systems can lead to a reduction of medication errors. Minor errors can be eliminated almost completely. The effect of CPOE-/CDS-systems on the rate of adverse drug events (ADE) is evaluated in only two primary studies with conflicting results. It is difficult to compare the results of economical studies because they evaluate different settings, interventions and time frames. In addition, the documentation often is not fully transparent. All four studies included measure costs and effects from the perspective of a hospital or hospital affiliation. Concerning social aspects, the literature points at changes regard competing interests of technology and humans that result from the implementation of CPOE-systems. The experience of institutions in which the implementation of CPOE-systems leads to problems showed that the importance of considering the socio-organisational context had partly been underestimated. Discussion CPOE-/CDS-systems are able to reduce the rate of medication errors when ordering medications. The adherence to guidelines, communication, patient care and personnel satisfaction can also be affected positively. However, the literature also reports negative effects, as through the use of CPOE-/CDS-systems new errors can be generated. This makes continuous revisions of the system, as well as data-updates necessary. Concerning the cost-benefit-ratio from the hospital perspective, the two qualitatively best economic studies show contradictory results. Therefore, a positive cost-benefit-ratio for individual hospitals cannot be assumed, particularly as the study results cannot be generalized. Conclusions If the implementation of CPOE-/CDS-systems is well planned and conducted, the system adapted to the needs of the institution and continuously reviewed, and data used are updated on a regular basis, the rate of medication ordering errors can be reduced considerably by using CPOE-/CDS-systems. However, it is not clear how this results in a reduction of ADE. Prospective, systematic multi-centre evaluation-studies with clear methodology are needed, which include an analysis of the user-friendliness and of social and technical aspects of the system. Such studies should evaluate the impact a CPOE-/CDS-system has on ADE-rates and mortality. A detailed description of the system used and of the hospital evaluated is essential. If possible, costs and cost effects should be surveyed and documented transparently. PMID:21289894

Sturzlinger, Heidi; Hiebinger, Cora; Pertl, Daniela; Traurig, Peter

2009-01-01

278

Remote sensing the ionosphere by means of space geodetic techniques  

NASA Astrophysics Data System (ADS)

In the last decade space geodetic techniques, such as Very Long Baseline Interferometry (VLBI), Global Navigation Satellite Systems (GNSS), satellite altimetry missions, and Low Earth Orbiting (LEO) satellites have contributed extensively to remote sensing and modeling of the ionosphere. This paper presents a general overview of the ionospheric investigations using the space geodetic techniques. VLBI is a differential space geodetic technique which is capable of deriving absolute ionosphere parameters, i.e. Vertical Total Electron Content (VTEC) for each station. The VTEC values can be determined by taking advantage of the fact that the slant ionosphere delays are elevation dependent and can be described by an empirical mapping function. Thus VTEC values can be estimated for each station and constant instrumental delays can be separated from these parameters within the adjustment process. The classical input data for development of Global Ionosphere Maps (GIM) are the dual-frequency GNSS observations. GIMs are developed using the GNSS ionospheric observable or the geometry-free linear combination of simultaneous observations at two carriers L1 and L2. In this way along with the geometric term, all frequency-independent effects such as clock offsets and tropospheric delay are eliminated and only the ionospheric refraction and the differential inter-frequency hardware delays of both satellites and receivers remain. However, when studying the ionosphere globally, it should be pointed out that the GNSS stations are in-homogeneously distributed around the world, with large gaps particularly over the oceans; this fact reduces the precision of the GIM over these areas. On the other hand, dual-frequency satellite altimetry missions such as Jason-1 provide information about the ionosphere precisely above the oceans; and furthermore LEO satellites, such as Formosat-3/Cosmic provide well-distributed information of the ionosphere in globe. Combining different techniques for developing the ionospheric maps significantly improves the accuracy and reliability of the developed model, as the combined model uses the advantages of each particular method and provides a more accurate result than the result from each single technique. Depending on whether we want to estimate VTEC in a local, regional or global basis, an appropriate base-function is used. For global representation of VTEC spherical harmonics expansion is most commonly used. To model the ionosphere regionally kriging technique can also be implemented. Kriging is an interpolation technique applied in geostatistics, which uses sample values and a variogram to determine the unknown values at different locations.

Schuh, Harald; Mahdi Alizadeh Elizei, M.; Tierno Ros, Claudia; Todorova, Sonya

2012-07-01

279

Abnormally large magnetospheric electric field on 9 November 2004 and its effect on equatorial ionosphere around the world  

NASA Astrophysics Data System (ADS)

There was a solar event around 1850 UT on 9th November 2004, associated with an abnormally large solar wind flow pressure and large southward interplanetary magnetic field, causing an abnormally large prompt penetration electric field between 1850 and 2100 UT. Abnormally large vertical F-region drifts by Jicamarca backscatter radar were reported associated with the event. The F-region over Jicamarca, Peru (14-16 LT) and Sao Luis, Brazil (16-18 LT) was lifted upward, broken into two portions and the upper one was blown out of the range of the ionosonde. At Fortaleza, an off-equatorial station in Brazil, the F-region was also lifted up but later the foF2 increased due to the flow of ionization from upper layer blown up over the equatorial region. The F-region at Ascension Island (19-21 LT), an off-equatorial station, was lifted up without any deformations till 1915 LT but descended at 1930 LT due to reversal of electric field polarity. At Indian stations, Trivandrum and Waltair (00-02 LT), the F-region was pushed down and later disappeared as a consequence of enhanced westward ionospheric electric field in the night sector. The ionosonde did not receive any echo for a couple of hours till the next sunrise. The F-region at Kototaban (03-05 LT), Indonesia also disappeared after a rapid descend. At Kwajelien (06-08 LT) there was no equatorial type of sporadic-E at 07 to 09 LT due to the westward electric field.

Rastogi, R. G.; Chandra, H.; Condori, Louis; Abdu, M. A.; Reinisch, B.; Tsunoda, R. T.; Prasad, D. S. V. V. D.; Pant, T. K.; Maruyama, T.

2012-10-01

280

Birth-order effects on facets of extraversion  

Microsoft Academic Search

The present study investigated the reasons for inconsistent findings concerning birth-order effects and extraversion. According to Sulloway (1995, 1996), one would expect first-born siblings to rate higher on one of the facets, dominance, and later-born siblings to rate higher on the other facet, sociability. In a within-family design, 96 undergraduate and graduate students rated themselves and their siblings on a

Emma Beck; Katriina L. Burnet; Jane Vosper

2006-01-01

281

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

282

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

283

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

284

Ionospheres of the terrestrial planets  

Microsoft Academic Search

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

R. W. Schunk; A. F. Nagy

1980-01-01

285

Dressed four-wave mixing second-order Talbot effect  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

286

Day-side ionospheric conductivities at Mars  

NASA Astrophysics Data System (ADS)

We present estimates of the day-side ionospheric conductivities at Mars based on magnetic field measurements by Mars Global Surveyor (MGS) at altitudes down to ˜100 km during aerobraking orbits early in the mission. At Mars, the so-called ionospheric dynamo region, where plasma/neutral collisions permit electric currents perpendicular to the magnetic field, lies between 100 and 250 km altitude. We find that the ionosphere is highly conductive in this region, as expected, with peak Pedersen and Hall conductivities of 0.1-1.5 S/m depending on the solar illumination and induced magnetospheric conditions. Furthermore, we find a consistent double peak pattern in the altitude profile of the day-side Pedersen conductivity, similar to that on Titan found by Rosenqvist et al. (2009). A high altitude peak, located between 180 and 200 km, is equivalent to the terrestrial peak in the lower F-layer. A second and typically much stronger layer of Pedersen conductivity is observed between 120 and 130 km, which is below the Hall conductivity peak at about 130-140 km. In this altitude region, MGS finds a sharp decrease in induced magnetic field strength at the inner magnetospheric boundary, while the day-side electron density is known to remain high as far down as 100 km. We find that such Titan-like behaviour of the Pedersen conductivity is only observed under regions of strongly draped magnetospheric field-lines, and negligible crustal magnetic anomalies below the spacecraft. Above regions of strong crustal magnetic anomalies, the Pedersen conductivity profile becomes more Earth-like with one strong Pedersen peak above the Hall conductivity peak. Here, both conductivities are 1-2 orders of magnitude smaller than the above only weakly magnetised crustal regions, depending on the strength of the crustal anomaly field at ionospheric altitudes. This nature of the Pedersen conductivity together with the structured distribution of crustal anomalies all over the planet should give rise to strong conductivity gradients around such anomalies. Day-side ionospheric conductivities on Mars (in regions away from the crustal magnetic anomalies) and Titan seem to behave in a very similar manner when horizontally draped magnetic field-lines partially magnetise a sunlit ionosphere. Therefore, it appears that a similar double peak structure of strong Pedersen conductivity could be a more general feature of non-magnetised bodies with ionised upper atmospheres, and thus should be expected to occur also at other non-magnetised terrestrial planets like Venus or other planetary bodies within the host planet magnetospheres.

Opgenoorth, H. J.; Dhillon, R. S.; Rosenqvist, L.; Lester, M.; Edberg, N. J. T.; Milan, S. E.; Withers, P.; Brain, D.

2010-08-01

287

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

288

Transient (approximately equals 10 s) VLF amplitude and phase perturbations due to lightning-induced electron precipitation into the ionosphere (the Trimpi effect)  

NASA Astrophysics Data System (ADS)

This paper describes certain characteristics and statistics of the Trimpi effect, as observed near to and equatorward of the Antarctic Peninsula region, inferred using data from specially designed narrowband OPAL (Omega Phase and Amplitude Logger) receivers deployed in 1989 at Faraday and Halley stations, Antarctica. The amplitude and phase of signals from four Omega VLF transmitters were recorded in each Omega segment (8 segments per 10 s). A 12 month data set was scanned for Trimpi events which, however, were observed on only three of the eight paths, namely Hawaii-Faraday, Argentina-Faraday, and Argentina-Halley, due to inadequate signal-noise ratio on the other paths. The great majority of the approximately 3500 observed events occurred at night. For the all-sea, Hawaii-Faraday path at night, with a single mode dominant at the receiver, lightning-induced electron precipitation (LEP) was inferred to be occurring up to approximately 1.8 Mm from Faraday. A scatter plot of Trimpi amplitude versus phase for this path is interpreted to infer that LEP regions responsible for the events occurred mostly in the L-range 2-3, with the horizontal size of an affected region in the ionosphere being typically 50 km latitudinally and 200 km longitudinally.

Smith, A. J.; Cotton, P. D.; Robertson, J. S.

1993-05-01

289

Effect of Under-Resolved Grids on High Order Methods  

NASA Technical Reports Server (NTRS)

There has been much discussion on verification and validation processes for establishing the credibility of CFD simulations. Since the early 1990s, many of the aeronautical and mechanical engineering related reference journals mandated that any accepted articles in numerical simulations (without known solutions to compared with) need to perform a minimum of one level of grid refinement and time step reduction. Due to the difficulty in analysis, the effect of under-resolved grids and the nonlinear behavior of available spatial discretizations, are scarcely discussed in the literature. Here, an under-resolved numerical simulation is one where the grid spacing being used is too coarse to resolve the smallest physically relevant scales of the chosen continuum governing equations that are of interest to the numerical modeler. With the advent of new developments in fourth-order or higher spatial schemes, it has become common to regard high order schemes as more accurate, reliable and require less grid points. The danger comes when one tries to perform computations with the coarsest grid possible while still hoping to maintain numerical results sufficiently accurate for complex flows, and especially, data-limited problems. On one hand, high order methods when applies to highly coupled multidimensional complex nonlinear problems might have different stability, convergence and reliability behavior than their well studied low order counterparts, especially for nonlinear schemes such as TVD, MUSCL with limiters, ENO, WENO and discrete Galerkin. On the other hand, high order methods involve more operation counts and systematic grid convergence study can be time consuming and prohibitively expansive. At the same time it is difficult to fully understand or categorize the different nonlinear behavior of finite discretizations, especially at the limits of under-resolution when different types of bifurcation phenomena might occur, depending on the combination of grid spacings, time steps, initial conditions and numerical treatments of boundary conditions.

Yee, H. C.; Sjoegreen, B.; Mansour, Nagi (Technical Monitor)

2001-01-01

290

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

NASA Astrophysics Data System (ADS)

A small group at METU has been developing data driven models in order to forecast some critical parameters, which affect the communication and navigation systems, since 1990. The background on the subjects supports new achievements in terms of theoretical and experimental basis contributing the COST 296 WG2 activities. This work mentions the representative contributions. (i) A method has been proposed for the assessment of HF Channel Availability under ionospheric disturbances. Signal to Noise Ratio (SNR), Doppler Spread and Modified Power Delay Spread were considered. The study relates the modem performance to ionospheric disturbances. Ionospheric disturbance was characterised by Disturbance Storm Type (DST) index. Radar data including Effective Multipath Spread, Composite Doppler Spread and SNR values were obtained from the experiment conducted between Leicester UK (52.63° N; 1.08° W) and Uppsala, Sweden (59.92° N; 17.63° E) in the year 2001. First, joint probability density function (PDF) of SNR, Doppler Spread, and Effective Multipath Spread versus DST were considered. It was demonstrated by determining the conditional PDFs, and by using Bayes' Theorem, that there were dependencies between DST and the above mentioned parameters [Sari, 2006]. Thus, it is concluded that the availability of the HF channel is a function of DST. As examples of modem characterizations, Military Standards were considered. Given a magnetic condition, the modem availability was calculated. The model developed represents the ionospheric HF channel, and it is based on a stochastic approach. Depending on the new experimental data, the conditional PDFs could be updated continuously. The HF channel availability under various ionospheric Space Weather (SW) conditions can be determined using the model. The proposed method is general and can include other indices as well. The method can also be applied to a variety of other processes. (ii) The effects of space weather conditions on the variation of group range and line-of-sight Doppler velocity of the HF Radar echo signal were investigated. HF radar system under ionospheric disturbances has been identified globally and some operational suggestions have been presented. It is possible for the HF radar operator to estimate the possible skip distance and possible single hop group ranges for the given frequencies of 11 MHz and 14 MHz [Buyukpabuscu, 2007]. (iii) The measurements over the HF band during the 29 March 2006 total solar eclipse in Antalya (36° N; 30° E) Turkey was conducted from the channel occupancy and atmospheric noise points of view. The whole HF band ranging from 1 to 30 MHz has been swept using 10 kHz peak and 200 Hz average detectors of a certified EMI receiver equipped with a calibrated active monopole antenna. The changes in the atmospheric noise during the eclipse were reported [Tulunay, 2006]. The model based, theoretical and experimental works mentioned are promising and have potential for future research and developments. References Buyukpabuscu S.O. (2007), System Identification with Particular Interest On The High Frequency Radar Under Ionospheric Disturbances, MS Thesis, Electrical and Electronics Eng., Middle East Technical Univ., Ankara, Turkey, February 2007. Sari M.O. (2006), A New Approach For The Assessment Of Hf Channel Availability Under Ionospheric Disturbances, MS Thesis, Electrical and Electronics Eng., Middle East Technical Univ., Ankara, Turkey, September 2006. Tulunay E., E. M. Warrington, Y. Tulunay, Y. Bahad?rlar, A.S. Türk, R. Çaputçu, T. Yap?c? , E.T. ?enalp (2006), Propagation Related Measurements during Three Solar Eclipses in Turkey, IET 10th International Conference on Ionospheric Radio Systems & Techniques, IRST 2006, 18-21 July 2006, London, UK.

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

2009-04-01

291

Geometric modulation: A more effective method of steerable ELF/VLF wave generation with continuous HF heating of the lower ionosphere  

NASA Astrophysics Data System (ADS)

ELF/VLF radio waves (300 Hz-30 kHz) are difficult to generate with practical antennae, because of their extraordinarily long (10-1000 km) wavelengths, and the lossy nature of the Earth's surface at these frequencies. ELF/VLF waves have been successfully generated via amplitude modulated (AM) HF (2-10 MHz) heating of the lower ionosphere. Through the temperature-dependent conductivity of the lower ionospheric plasma, a patch of the ionospheric current becomes a large radiating `antenna'. We implement a new method of ELF/VLF wave generation, herein named `geometric modulation', involving scanning the HF heating beam in a geometric pattern without modulating its power. Utilizing results from the upgraded 3.6 MW radiated HAARP HF antenna array, we show that geometric modulation can enhance ELF/VLF wave generation by up to ~11 dB over the conventional AM method. Geometric modulation also allows directional launching of the signal into the Earth-ionosphere waveguide, forming an unprecedented steerable large-element ELF/VLF ionospheric phased array.

Cohen, M. B.; Inan, U. S.; Golkowski, M. A.

2008-06-01

292

TEC Fluctuations Map - pilot phase of the new IGS Ionospheric Product  

NASA Astrophysics Data System (ADS)

Since 1998 Ionospheric Working Group of the International GNSS Service has been creating the reliable global VTEC maps. Currently the ionospheric maps are generated with 2 hour time resolution and show the mean state of the Total Electron Content for this period.They cannot demonstrate the whole dynamic of the electron concentration especially during the storm-time periods for the equatorial region and at high latitudes. However, in the last few years the number of the permanent GNSS station around North Geomagnetic Pole increased systematically and nowadays it is possible to create the map of ionospheric variability for this region. Importance of this topic has turned up in the latest IGS Ionosphere Working Group resolution passed during the International GNSS Service Workshop 2012. At the beginning 2013 the IGS is planning to start the pilot phase of the new ionospheric product - TEC Fluctuations map, which are generated at GRL/UWM Center in Olsztyn. The maps are created based on phase observations from over 150 permanent GNSS stations belong to IGS/EPN, PBO and POLENET Networks located over 45th degree of the north geomagnetic latitude. In order to estimate the level of the ionospheric variability ROT Index is used. The presentation shows the applied algorithm, the example maps for different ionospheric conditions and plans. In the future other IGS Ionosphere Associate Analysis Centers will also create maps of ionospheric variability for routine generation IGS combined product.

Sieradzki, Rafal; Krankowski, Andrzej

2013-04-01

293

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

294

A relationship between solar proton events, ionospheric uplift observed at VLF and negative ionospheric storms  

NASA Astrophysics Data System (ADS)

Three consecutive magnetic storms during the month of September 1982 were found to be associated with solar proton events (SPE) observed over a number of high latitude VLF propagation paths. The penetration of solar protons into the auroral zone produced a marked reduction in reflection height at night for high latitude VLF paths resulting in a reduced diurnal phase shift. This effect has been known for some 50 years. However in this paper, a previously unidentified response is described consisting of an increase in the night 90 km reflection height over middle latitude and transequatorial VLF paths. Solar protons do not penetrate to these latitudes and this slight increase in VLF reflection height was associated with typical negative ionospheric storm effects in the F2 region. Dynamics at the 90 km base of the night ionosphere are little known and difficult to investigate except at VLF. These results are the first to suggest a response of the night ionospheric base to events leading to the well known negative ionospheric storm seen at greater heights. Such negative storms seen in the F2 region have been associated with an equatorward wind surge and change in neutral atmospheric chemistry driven by joule heating in the auroral zone produced by solar proton precipitation.

Lynn, K. J. W.

2013-12-01

295

Effective orbital ordering in multiwell optical lattices with fermionic atoms  

NASA Astrophysics Data System (ADS)

We consider the behavior of Fermi atoms on optical superlattices with two-well structure for each node. Fermions on such lattices serve as an analog simulator of the Fermi-type Hamiltonian. We derive a mapping between fermion quantum ordering in the optical superlattices and the spin-orbital physics developed for degenerate d-electron compounds. The appropriate effective spin-orbital model appears to be a modification of the Kugel-Khomskii Hamiltonian. We show how different ground states of this Hamiltonian correspond to particular spin-pseudospin arrangement patterns of fermions on the lattice. The dependence of the fermion arrangement on phases of complex hopping amplitudes is illustrated.

Belemuk, A. M.; Chtchelkatchev, N. M.; Mikheyenkov, A. V.

2014-08-01

296

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

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

297

Second-order nonlinear optical effects of spin currents.  

PubMed

Pure spin currents carry information in spintronics and signify novel quantum spin phenomena such as topological insulators. Measuring pure spin currents, however, is difficult since they have no direct electromagnetic induction. Noticing that a longitudinal spin current, in which electrons move along their spin directions, is a chiral quantity, we envisage that it has a chiral sum-frequency optical effect. A systematic symmetry analysis confirms this idea and reveals the second-order optical effects of general spin currents with unique polarization dependence. Microscopic calculations based on the eight-band model of III-V compound semiconductors show that the susceptibility is sizable under realistic conditions. These findings form a basis for "seeing" spin currents where and while they flow with standard nonlinear optical spectroscopy, providing a toolbox to explore a wealth of physics connecting spins and photons. PMID:20867405

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

2010-06-25

298

GPS Remote sensing of seismic waves in the Ionosphere: interpretation and modeling with realistic seismic sources and Solid Earth/atmospheric/ionospheric models. (Invited)  

NASA Astrophysics Data System (ADS)

With the development of dense GPS networks, observations of seismic waves in the ionosphere are now common and reported almost systematically after quakes with magnitude larger than 7.5. They are associated to integrated perturbations in the ionospheric electron density at altitude between 250 and 350 km, in contrary to Doppler observations, related to the vertical electrons velocities at altitudes between 150 and 200 km. The observed waves are either acoustic waves, generated by the vertical displacement of the Earth surface near the epicenter and propagating over regional distances (up to about one thousand km) in the atmosphere or acoustic-Rayleigh waves generated by the Rayleigh surface wave front at tele-seismic distance of several thousands km. These waves are observed above the atmospheric cutoff, in contrary to tsunami-induced gravity waves, observed also in the ionosphere but below the Brunt-Väisälä frequency. The modeling of these waves requests not only the modeling of the solid-earth/atmosphere coupling problems but also the one of the atmosphere/ionosphere coupling. It is then mandatory to consider the variability in space and time of the atmosphere and ionosphere (e.g. density, temperature, ions and electron density), as well as magnetic field, in order to model the observed electronic content perturbations. This variability is illustrated by the computation of normal modes of the coupled earth/atmosphere/ionosphere system. This allows us to show the variability of these normal modes in term of eigen-frequencies, atmospheric velocity amplitudes and ionospheric electron perturbation with respect to different conditions in latitude, longitude, local time, month and F10.7 indice. We then present several observations (including after the 5/12/2008 Wenchuan, 12/26/2004 Sumatra-Andaman and 9/25/2003 Tokachi-Oki earthquakes). These observations show clearly the two different types of waves described above, as well as their sensitivity to the observation conditions, especially in term of inclination of the sounding path between the ground receivers and GPS satellites. The observed noise is discussed, including aliasing and multi-pathing effects. These observations are then modeled and the misfit between observed and modeled waveforms are discussed. We especially analyze the crustal, atmospheric and ionospheric effects, as well as the limitation in the models and modeling (e.g. non linearity, heat diffusion and ion-neutral interactions in the atmospheric wave modeling). A special focus is finally given to the modeling of the source, as the later is either smaller than the radiated waves for Rayleigh waves and much larger for the acoustic waves, due to the differences in the propagation speeds (3.5 km/s versus 0.33 km/s). Perspectives are finally given, both in term of future modeling effort or in term of observation efforts, either with better GPS observing systems based on phase array antenna, or with possible space remote sensing techniques.

Lognonne, P.; Rolland, L. M.; Astafyeva, E.; Kherani, A.; Occhipinti, G.; Coisson, P.

2010-12-01

299

Beyond the Linear-Order Relativistic Effect in Galaxy Clustering: Second-Order Gauge-Invariant Formalism  

E-print Network

We present the second-order general relativistic description of the observed galaxy number density in a cosmological framework. The observed galaxy number density is affected by the volume and the source effects, both of which arise due to the mismatch between physical and observationally inferred quantities such as the redshift, the angular position, the volume, and the luminosity of the observed galaxies. These effects are computed to the second order in metric perturbations without choosing a gauge condition or adopting any restrictions on vector and tensor perturbations, extending the previous linear-order calculations. Paying particular attention to the second-order gauge transformation, we explicitly isolate unphysical gauge modes and construct second-order gauge-invariant variables. Moreover, by constructing second-order tetrads in the observer's rest frame, we clarify the relation between the physical and the parametrized photon wavevectors. Our second-order relativistic description will provide an es...

Yoo, Jaiyul

2014-01-01

300

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

301

Attenuation of lightning-produced sferics in the Earth-ionosphere waveguide and low-latitude ionosphere  

NASA Astrophysics Data System (ADS)

We compare radio atmospherics (sferics) detected by the World Wide Lightning Location Network (WWLLN) to very low frequency (VLF) whistler waves observed in the low-latitude ionosphere by the Vector Electric Field Instrument of the Communications/Navigation Outage Forecasting System (C/NOFS) satellite. We also model the propagation of these sferics through the Earth-ionosphere waveguide to the subsatellite point using the Long-Wavelength Propagation Capability software and compare this result to the same C/NOFS data set. This unprecedentedly expansive data set allows comparison to theory and prior observation of VLF radio wave propagation in the Earth-ionosphere waveguide and low-latitude ionosphere. We show that WWLLN and C/NOFS observe the well-known effect of variable attenuation with direction within the Earth-ionosphere waveguide. Propagation within the ionosphere is also examined, and a lack of attenuation above 400 km is observed. Finally, in comparison to recent works using Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) data by Fiser et al. and Chum et al., we find that C/NOFS successfully detects whistlers with comparable amplitudes at much greater distances, compared to those reported for DEMETER.

Burkholder, Brian S.; Hutchins, Michael L.; McCarthy, Michael P.; Pfaff, Robert F.; Holzworth, Robert H.

2013-06-01

302

Forecasting Space Weather in the Upper Atmosphere and Ionosphere (Invited)  

NASA Astrophysics Data System (ADS)

The feasibility of performing meaningful forecasts of the state of the thermosphere and ionosphere depends on the time scales of interest. Whether accomplished using empirical models derived from climatological information, or using numerical models describing the physics and dynamics of the coupled system, the reality of any forecast is dependent on the specification of the initial state, and the knowledge of the parameters that will impact it in the future. The zero-time forecast, or nowcast, is eminently possible, and basic systems have been implemented operationally using data assimilation techniques. This is considerably more advanced with respect to the ionosphere, because there are more ionospheric data currently available. But a fully coupled thermosphere is crucial for accomplishing accurate ionospheric specification and forecast, because the ionosphere responds strongly to thermospheric drivers, and because the effects of changing thermospheric dynamics are persistent. The prospects for short term (less than an hour) forecasts are also good. The 30 to 90 minute delay between measurements near the Sun-Earth L1 saddle point, and the arrival of solar wind and interplanetary field perturbations at the magnetopause, can be exploited to predict the effects of geomagnetic disturbances on the thermosphere-ionosphere. Lower atmosphere meteorology fields are sufficiently known and change slowly on these time scales, as do solar irradiance drivers (except during flares) so the boundary conditions to full-physics numerical models can be specified. The initial state of the system can be effectively characterized by data assimilation models. Sophisticated physical models using efficient parallel algorithms are available. Therefore, there are no fundamental obstacles to implementation of short-term thermosphere-ionosphere forecasting, only programmatic or technical ones. On longer time scales, magnetospheric forecasting is contingent on meaningful prediction of the solar wind and interplanetary magnetic field. Significant progress has been made on the former, but the latter remains extremely difficult, due to the lack of knowledge of solar magnetic field configuration during eruptive events. Therefore, forecasting thermosphere-ionosphere parameters when driven by magnetospheric storms, on time scales of one to several days, remains a speculative activity. In this paper, we will present simulations demonstrating the capabilities of a thermosphere-ionosphere model employed in a prognostic mode. Model initialization using fields obtained from data assimilation schemes will be demonstrated, and the interplay of their persistence with ionospheric dynamics described.

Solomon, S. C.

2013-12-01

303

Preseismic Lithosphere-Atmosphere-Ionosphere Coupling  

NASA Astrophysics Data System (ADS)

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

Kamogawa, Masashi

304

Ionospheric responses to two large geomagnetic storms over Japanese and Indian longitude sectors  

NASA Astrophysics Data System (ADS)

The physical processes including the prompt penetration electric field, disturbance dynamo originated electric field, disturbed thermospheric winds and composition changes can play a significant role in restructuring the equatorial, low, mid and high-latitude ionosphere during storm-time. However, it has not yet been revealed that the contribution of individual physical processes, their interactions and impacts on that restructuring (Maruyama et al., 2005) is primarily due to the lack of continuous observational facilities. In this present research, the electric field (measured indirectly) and thermospheric wind (derived from an empirical disturbance wind model) components are effectively utilized as alternate database to ascertain the individual role of physical processes by studying the ionospheric response over Japanese and Indian longitude sectors during two geomagnetic storms occurring on 31 March, 2001 and 20 November, 2003 using ground (ionospheric parameters scaled from ionosondes and global ionospheric maps of total electron content measured by the ground-based GPS receivers) and satellite-borne (in-situ electron density data measured by the Planar Longmuir Probe onboard CHAMP satellite) measurements. It has been found that the equatorial ionization anomaly is expanded and intensified during the main phase of these two storms, which is believed to be caused by the prompt penetration electric field according to the current theory. In addition, the storm associated thermospheric wind is propagating equatorward (with an average velocity of ˜230 m/s) during the recovery phase of these two storms that is responsible for a height rise in the virtual height of the F-layer (h'F) starting from mid to low and equatorial latitudes with a consistent time delay. The empirical model derived winds corroborate the equatorward propagation, suggesting that this wind model data could be used as an alternate database particularly during the space weather events in order to discuss the global dynamical state of the ionosphere. Further, an important observation is that the ionospheric irregularities are found in the electron densities in the form of depletions nearly at anomaly crest region (˜23°N) as measured by the CHAMP satellite over the Japanese longitude sector during the main phase of the 20 November, 2003 storm during the pre mid night period that correspond to the time of rapid decrease (˜-30-35 nT/h) in Sym-H index due to prompt penetration of eastward electric fields into the low latitudes.

Uma, G.; Brahmanandam, P. S.; Kakinami, Yoshihiro; Dmitriev, A.; Latha Devi, N. S. M. P.; Uday Kiran, K.; Prasad, D. S. V. V. D.; Rama Rao, P. V. S.; Niranjan, K.; Seshu Babu, Ch.; Chu, Y. H.

2012-01-01

305

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

306

Linear mode conversion in inhomogeneous magnetized plasmas during ionospheric  

E-print Network

facilitate acceleration of fast energetic electrons, resulting in observed enhanced airglow. INDEX TERMS Science: Ionospheric propagation (2487); 2411 Ionosphere: Electric fields (2712); 2439 Ionosphere of initial density inhomogeneities in the ionosphere which leads to the thermal self-focusing instability

Rubloff, Gary W.

307

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

308

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

309

Characteristics of the global ionospheric electron density during the extreme solar minimum condition  

NASA Astrophysics Data System (ADS)

The last solar minimum period between the cycles 23 and 24 was anomalously low and lasted long compared with previous solar minimums. The resulting solar irradiance received in the Earth’s upper atmosphere was extremely low and therefore it can readily be expected that the upper atmosphere should be greatly affected by this low solar activity. There were several studies on this effect but many of them was on the thermosphere (Solomon et al., 2010; Emmert et al., 2010). According to these studies, the thermospheric temperature was cooler and the density was lower than the previous solar minimum periods. The low solar irradiance during the last solar minimum should also affect the ionosphere, not only via the lower ion-electron production due to the lower EUV radiation but also through the interactions with the thermosphere that was already influenced by the low solar irradiance. In this study, we utilized the measurements of total electron content (TEC) from the TOPEX and JASON satellites during the periods of 1992 to 2010, which includes the last two solar minimums, in order to investigate the differences between the ionospheric behaviors during the two minimum conditions. Initially the levels of the global ionization will be examined during these minimum periods and then further discussions will be continued on the details of the ionospheric behavior such as the seasonal and storm-time variations.

Jee, G.

2010-12-01

310

Birth Order Matters: The Effect of Family Size and Birth Order on Educational Attainment  

Microsoft Academic Search

We use unique retrospective family background data from the 2003 British Household Panel Survey to explore the degree to which family size and birth order affect a child's subsequent educational attainment. Theory suggests a trade off between child quantity and 'quality'. Family size might adversely affect the production of child quality within a family. A number of arguments also suggest

Alison L. Booth; Hiau Joo Kee

2005-01-01

311

Birth Order Matters: The Effect of Family Size and Birth Order on Educational Attainment  

Microsoft Academic Search

We use unique retrospective family background data from the 2003 wave of the British Household Panel Survey to explore the degree to which family size and birth order affect a child’s subsequent educational attainment. Theory suggests a trade off between child quantity and ‘quality’. Family size might adversely affect the production of child quality within a family. A number of

Alison L Booth; Hiau Joo Kee

2006-01-01

312

Birth Order Matters: The Effect of Family Size and Birth Order on Educational Attainment  

Microsoft Academic Search

We use unique retrospective family background data from the 2003 wave of the British Household Panel Survey to explore the degree to which family size and birth order affect a child’s subsequent educational attainment. Theory suggests a trade off between child quantity and ‘quality’. Family size might adversely affect the production of child quality within a family. A number of

Alison Booth; Hiau Joo Kee

2005-01-01

313

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

314

Adapting empirical ionosphere models to experimental data  

NASA Astrophysics Data System (ADS)

Empirical electron density models, like the International Reference Ionosphere (IRI) and the NeQuick, have been conceived to reproduce the climatological behavior of the ionosphere. To improve the specification of the three-dimensional electron density of the ionosphere for current conditions, different techniques based on the NeQuick adaptation to experimental data have been developed. As a first step, a procedure to ingest GPS-derived vertical total electron content (TEC) maps into the model has been developed using the concept of effective parameter to define the model input Az (ionization level). To consider the possibility of implementing nearreal-time applications, an electron density retrieval method based on direct ingestion of slant TEC data into NeQuick model has been developed. Afterwards, to further improve the model electron density profile formulation, a technique for simultaneously adapting the NeQuick model to TEC data and ionosondes peak parameters has also been proposed. In the present paper, after reviewing the methods developed to update the NeQuick with experimental data, an indication about how to apply the same techniques to IRI will be given.

Nava, Bruno; Coïsson, Pierdavide; Radicella, Sandro M.

315

Formation and evolution of the ionospheric plasma density shoulder and its relationship to the superfountain effects investigated during the 6 November 2001 great storm  

NASA Astrophysics Data System (ADS)

This study investigates the 6 November 2001 great storm's impact on the topside ionosphere utilizing data from the onboard TOPEX/Poseidon-NASA altimeter, Defense Meteorological Satellite Program-Special Sensor Ions, Electrons and Scintillation instruments and ACE interplanetary observatory. A set of field-aligned profiles demonstrate the storm evolution, caused by the precursor and promptly penetrating interplanetary eastward electric (E) fields, and strong equatorward winds reducing chemical loss, during the long-duration negative BZ events. At daytime-evening, the forward fountain experienced repeated strengthening, as the net eastward E field suddenly increased. The resultant symmetrical equatorial anomaly exhibited a continuous increase, while the energy inputs at both auroral regions were similar. In both hemispheres, by progressing poleward, a midlatitude shoulder exhibiting increased plasma densities, a plasma-density dropoff (steep gradient) and a plasma depletion appeared. These features were maintained while the reverse fountain operated. At the dropoff, elevated temperatures indicated the plasmapause. Consequently, the plasma depletion was the signature of plasmaspheric erosion. In each hemisphere, an isolated plasma flow, supplying the minimum plasma, was detected at the shoulder. Plasmaspheric compression, due to the enhanced E fields, could trigger this plasma flow. Exhibiting strong longitudinal variation at evening-nighttime, the shoulder increased 306% over the southeastern Pacific, where the nighttime Weddell Sea Anomaly (WSA) appeared before the storm. There, the shoulder indicated the storm-enhanced equatorward section of the quiet time WSA. Owing to the substantial equatorward plasmapause movement, a larger poleward section of the quiet time WSA eroded away, leaving a large depletion behind. This study reports first these (northern, southern) plasma flows and dramatic storm effects on a nighttime WSA.

Horvath, Ildiko; Lovell, Brian C.

2008-12-01

316

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

317

Response of the Equatorial Ionosphere to Major Magnetic Storms During the Current Solar Maximum Phase  

Microsoft Academic Search

The generalized response of the equatorial ionosphere to major magnetic storms is discussed in the context of recently observed storm induced effects on VHF\\/UHF scintillation, total electron content (TEC) of the ionosphere and satellite insitu measurements of ion density and ion drifts. The scintillation data are obtained from AFRL's network of ground stations that monitor geostationary satellite signals and TEC

S. Basu; P. Sultan; C. Valladares; H. Yeh; S. Su

2001-01-01

318

ANALYSIS OF IONOSPHERIC CONTRIBUTIONS TO THE DOPPLER SHIFTS OF CW SIGNALS FROM ARTIFICIAL EARTH SATELLITES  

Microsoft Academic Search

Radio signals from artificial earth satellites propagated through the earth's ionosphere are subjected to phase delay, refraction, and attenuation. These effects cause .uncertainties in the determination of the vacuum Doppler shift of CW signals. To understand the nature of these ionospheric contributions to the Doppler shift, a theoretical expression for the refracted Doppler shift that is an inverse power series

A. J. Tucker; B. M. Fannin

1968-01-01

319

Auroral ionosphere Joule heating as a reason of the upper thermosphere overheating in the Jupiter and Saturn systems  

NASA Astrophysics Data System (ADS)

All giant planets in the Solar System and particularly Saturn and Jupiter are known to have an upper neutral atmosphere far hotter than it is expected from solar extreme ultraviolet heating alone. While the measured exospheric temperatures on Saturn and Jupiter are close to 500 K and to 1100 K - 2000 K, respectively, the solar heating alone can provide an exospheric temperature only about 200 K. Two main energy deposition mechanisms are discussed in the literature to resolve this contradictions: (1) the gravitation wave dissipation in the upper atmosphere, and (2) the auroral thermosphere Joule heating by the Pedersen ionospheric currents. The ionospheric currents are associated with the field-aligned currents generated due to the magnetosphere-ionosphere slipping. Here we focus on the second mechanism. To improve the accuracy of the numerical estimations we derived the analytic formulas, which describe the dependence of the auroral energy flux on the planetary magnetic field strength, as well as on the solar wind plasma ram pressure, and on the breaking of magnetospheric plasma corotation. The last effect is essential for Jupiter, where the main oval is driven internally at Alvenic radius. We pay attention to the general physical phenomena, which may be only slightly influenced/modified by the specific atmospheric composition and photochemical ionospheric reactions. One of the most important energy inputs to the polar upper atmosphere is Joule heating by the ionospheric Pedersen currents. We estimate it to be ~3.0 TW for Saturn and about 1000 times more (3500 TW) for Jupiter. That represents a significant energy input to Saturn’s and Jupiter’s thermospheres. It is more than an order of magnitude larger as compared to the globally averaged solar input. Therefore, Joule heating may be reasonably appealed for the explanation of the observed high thermosphere temperatures by Saturn (~400-600 K) and Jupiter (1200 K).

Alexeev, Igor; Belenkaya, Elena; Khodachenko, Maxim; Grigoryan, Maria

320

VLF propagation in the earth-ionosphere waveguide channel  

NASA Astrophysics Data System (ADS)

Papers are presented on such topics as the effect of inhomogeneous wind on the propagation of acoustic-gravity waves; electromagnetic waves in a narrow spherical cavity with anisotropic impedance walls; ionospheric anisotropy during nighttime VLF propagation at low latitudes; degenerate eigenvalues in an impedance waveguide; the method of cross sections in the theory of VLF propagation in the irregular earth-anisotropic ionospheric waveguide; and the effect of properties of a high-latitude earth-ionosphere waveguide on the group and phase delays of radio signals singly reflected from the ionosphere. Also considered are mean-field modes in a waveguide channel in the presence of vertical disturbance; the field of a vertical electric dipole above a piecewise-homogeneous surface of the earth; resonance effects at the boundary of two inhomogeneous dielectric half-spaces; the relationship between ULF noise and global electrical-storm activity; and the determination of the parameters of ionospheric wave disturbances from an analysis of sickle-shaped features on ionograms.

Giunninen, E. M.

321

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

322

Ionospheric detection of gravity waves induced by tsunamis  

Microsoft Academic Search

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

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

2005-01-01

323

Higher order QCD effects for Higgs boson studies at colliders  

NASA Astrophysics Data System (ADS)

The Standard Model (SM) of Particle Physics predicts the existence of a fundamental scalar particle, the Higgs boson. The corresponding Higgs field is responsible for the breaking of the electroweak symmetry, and so far it remains undiscovered. It is one of the top priorities of current and future accelerator experiments to detect the Higgs, or rule out its existence. Identifying the Higgs sector requires precise theoretical predictions for many Higgs boson production and decay channels. In this thesis, we focus on next-to-leading-order (NLO) calculations for two important processes: the first is pp ? H + 2 jets at the CERN Large Hadron Collider (LHC). The second is the gammagamma ? H ? bb process at the photon collider mode of operation of the International Linear Collider (MC). For the pp ? H + 2 jets process, we compute certain virtual NLO Quantum Chromodynamics (QCD) corrections to the Higgs production through gluon fusion. In particular, we use a bootstrap approach to calculate the one-loop Higgs + 4 partons amplitudes H qqQQ and Hqqgg analytically, for configurations with equal number of positive and negative helicities ("MHV"). The coupling of the Higgs boson to gluons is treated by an effective interaction in the limit of large top quark mass. The Higgs field is split into a complex field and its complex conjugate, simplifying calculations significantly. The cut-containing parts of the amplitudes are obtained using (generalized) unitarity, while the rational pieces are obtained by recursion relations. Throughout this process, only on-shell amplitudes are used. As a consequence, the method is very efficient and gives compact final answers. Using our results, we can compute the color-singlet piece of the gluon fusion-vector boson fusion interference at one-loop, as well as one loop amplitudes with a pseudoscalar instead of a scalar Higgs. We have verified the correctness of our expressions using a number of nontrivial checks and comparisons with previous calculations in the literature. For the gammagamma ? H ? bb process at a photon collider, we study the interference between the resonant and continuum (gammagamma ? bb) amplitudes. We take into account the virtual gluon exchange between the final state quarks and calculate the one loop corrections to the effective peak height for the case of a light (mH < 160 GeV) Higgs boson. We find that the interference is destructive, depends on the mass of the Higgs and the scattering angle but is only 0.1--0.2%, smaller by an order of magnitude to the experimental accuracy at a photon collider.

Sofianatos, Georgios

324

Monitoring and modeling of ionospheric characteristics in the framework of European COST 296 Action MIERS  

NASA Astrophysics Data System (ADS)

The Mitigation of Ionospheric Effects on Radio Systems COST 296 Action is devoted to the mitigation of ionospheric effects on radio systems. It creates a platform for sharing of data, algorithms, models, and jointly developed advanced technologies, the processing chain from measurements, through algorithms, to operational knowledge. This initiative creates a unique possibility for national groups to consolidate the design of a product required for their own activity and for European assessments in the ionosphere and telecommunication area. An important part of the action is to stimulate and integrate many national and international activities which provide tools for global and regional ionospheric monitoring and modeling. The work includes the near-Earth space plasma monitoring, modeling and forecasting, and a study of the upper atmosphere climate. Well-defined terms of reference include developing ground-based and space-borne monitoring techniques and parameters describing the state of ionospheric plasma, maintaining and extending the flow of real-time and retrospective ionospheric monitoring data to databases. To obtain adequate, high-quality information, special attention is paid to the data ingestion and assimilation in constructing ionospheric models of different spatial and time scale perturbations, as well as storms, small variations, and irregularities. The physical origin of atmospheric/ionospheric effects and their signatures and parameters are investigated. Identification criteria are studied and formulated.

Stanislawska, Iwona; Lastovicka, Jan; Bourdillon, Alain; Zolesi, Bruno; Cander, Ljiljana R.

2010-02-01

325

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

326

Multiple scattering Sunyaev-Zeldovich signal - I. Lowest order effect  

NASA Astrophysics Data System (ADS)

Future high-resolution, high-sensitivity Sunyaev-Zeldovich (SZ) observations of individual clusters will allow us to study the dynamical state of the intracluster medium (ICM). To exploit the full potential of this new observational window, it is crucial to understand the origin of different contributions to the total SZ signal. Here, we investigate the signature caused by multiple scatterings at lowest order of the electron temperature. Previous analytic discussions of this problem used the isotropic scattering approximation, which even for the simplest cluster geometries is rather rough. We take a step forward and consistently treat the anisotropy of the ambient radiation field caused by the first scattering. We show that the multiple scattering SZ signal directly probes line-of-sight anisotropies of the ICM, thereby delivering a new set of SZ observables which could be used for 3D cluster-profile reconstruction. The multiple scattering signal should furthermore correlate spatially with the cluster's X-ray and SZ polarization signals, an effect that could allow enhancing the detectability of this contribution.

Chluba, J.; Dai, L.; Kamionkowski, M.

2014-01-01

327

Beyond the linear-order relativistic effect in galaxy clustering: Second-order gauge-invariant formalism  

NASA Astrophysics Data System (ADS)

We present the second-order general relativistic description of the observed galaxy number density in a cosmological framework. The observed galaxy number density is affected by the volume and the source effects, both of which arise due to the mismatch between physical and observationally inferred quantities such as the redshift, the angular position, the volume, and the luminosity of the observed galaxies. These effects are computed to the second order in metric perturbations without choosing a gauge condition or adopting any restrictions on vector and tensor perturbations, extending the previous linear-order calculations. Paying particular attention to the second-order gauge transformation, we explicitly isolate unphysical gauge modes and construct second-order gauge-invariant variables. Moreover, by constructing second-order tetrads in the observer's rest frame, we clarify the relation between the physical and the parametrized photon wave vectors. Our second-order relativistic description will provide an essential tool for going beyond the power spectrum in the era of precision measurements of galaxy clustering. We discuss potential applications and extensions of the second-order relativistic description of galaxy clustering.

Yoo, Jaiyul; Zaldarriaga, Matias

2014-07-01

328

Ionospheric Refraction Corrections in the GTDS for Satellite-To-Satellite Tracking Data  

NASA Technical Reports Server (NTRS)

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 in orbit determinations. The Bent Ionospheric Model is used for SST refraction corrections. Making use of this model a method of computing corrections through large ionospheric gradients was devised and implemented into the Goddard Trajectory Determination System. The various considerations taken in designing and implementing this SST refraction correction algorithm are reported.

Nesterczuk, G.; Kozelsky, J. K.

1976-01-01

329

Electron precipitation and related aeronomy of the Jovian thermosphere and ionosphere  

SciTech Connect

Voyager ultraviolet spectrometer (UVS) measurements provided the first unassailable evidence for particle precipitation in the Jovian atmosphere. Strong Lyman and Werner band emissions at high latitudes indicate particle precipitation energy fluxes of about 10 ergs cm/sup -2/ s/sup -1/. On the other hand dayglow Lyman and Werner emissions at mid- and low-latitudes may indicate additional particle precipitation fluxes on the order of 0.3 ergs cm/sup -2/ s/sup -1/ at all latitudes. Such particle precipitation can have signficant aernomical effects on the Jovian thermosphere and ionosphere. A one-dimensional theoretical model is used to study these effects for the case of electron precipitation, although ion precipitation produces similar effects. Diffusion equations are solved for all the major neutral species and for H/sup +/, and photochemical solutions are given for short lived ions. These and ionospheric components of the model are coupled with the electron and ion energy equations and a two-stream electron transport code that calculates the energy depostion of precipitating electrons (considered to be the precipitating particles) and photoelectrons. An independent calculation of the vertical neutral temperature is also obtained. The results of the model calculations can be broadly categorized as effects of electron precipitation (1) on the neutral composition and temperature of the thermosphere, and (2) on the composition and structure of the ionosphere. Auroral electron precipitation by 10-keV electrons with a total energy flux of 10 ergs cm/sup -2/ s/sup -1/ produces 4.7 x 10/sup 11/ H atoms cm/sup -2/ s/sup -1/ and 5 ergs cm/sup -2/ s/sup -1/ of heat, over 2 orders of magnitude larger than solar EUV processes that produce 3.3 x 10/sup 9/ H atoms cm/sup -2/ s/sup -1/ and 0.03 ergs cm/sup -2/ s/sup -1/ of heat.

Waite, J.H. Jr.; Cravens, T.E.; Kozyra, J.; Nagy, A.F.; Atreya, S.K.; Chen, R.H.

1983-08-01

330

Ionospheric Profiling using GPS/MET Data  

NASA Technical Reports Server (NTRS)

A report on ionospheric profiling using GPS and MET data is presented. A description of the GPS occultation technique, some examples of GPS/MET data products, the data processing system and a preliminary validation of ionospheric profiles is discussed.

Hajj, George; Romans, Larry

1996-01-01

331

Ionospheric Transmission Losses Associated with Mars-orbiting Radars  

NASA Technical Reports Server (NTRS)

There are a number of obstacles to radar sounding of the deep Martian subsurface from orbit, including signal losses from the medium conductivity, layer reflective losses, and ground clutter. Another adverse process is signal loss as radio waves propagate through the ionospheric plasma medium. The ionosphere is a plasma consisting of free electrons, ions and neutrals that can effectively damp/attenuate radar signals via electrodneutral collisions. The effect is most severe for transmissions at lower frequencies, which, unfortunately, are also favorable transmissions for deep penetration into the subsurface.

Farrell, W. M.

2005-01-01

332

Language and Age Effects in Children's Processing of Word Order  

ERIC Educational Resources Information Center

We compare the processing of transitive sentences in young learners of a strict word order language (English) and two languages that allow noun omissions and many variant word orders: Turkish, a case-marked language, and Mandarin Chinese, a non case-marked language. Children aged 1-3 years listened to simple transitive sentences in the typical…

Candan, Ayse; Kuntay, Aylin C.; Yeh, Ya-ching; Cheung, Hintat; Wagner, Laura; Naigles, Letitia R.

2012-01-01

333

Molecular ordering at electrified interfaces: Template and potential effects  

PubMed Central

Summary A combination of cyclic voltammetry and in situ scanning tunneling microscopy was employed to examine the adsorption and phase transition of 1,1’-dibenzyl-4,4’-bipyridinium molecules (abbreviated as DBV2+) on a chloride-modified Cu(111) electrode surface. The cyclic voltammogram (CV) of the Cu(111) electrode exposed to a mixture of 10 mM HCl and 0.1 mM DBVCl2 shows three distinguishable pairs of current waves P1/P’1, P2/P’2, and P3/P’3 which are assigned to two reversible electron transfer steps, representing the reduction of the dicationic DBV2+ to the corresponding radical monocationic DBV+• (P1/P’1) and then to the uncharged DBV0 (P3/P’3) species, respectively, as well as the chloride desorption/readsorption processes (P2/P’2). At positive potentials (i.e., above P1) the DBV2+ molecules spontaneously adsorb and form a highly ordered phase on the c(p × ?3)-precovered Cl/Cu(111) electrode surface. A key element of this DBV2+ adlayer is an assembly of two individual DBV2+ species which, lined up, forms a so-called “herring-bone” structure. Upon lowering the electrode potential the first electron transfer step (at P1) causes a phase transition from the DBV2+-related herring-bone phase to the so-called "alternating stripe" pattern built up by the DBV+• species following a nucleation and growth mechanism. Comparison of both observed structures with those found earlier at different electrode potentials on a c(2 × 2)Cl-precovered Cu(100) electrode surface enables a clear assessment of the relative importance of adsorbate–substrate and adsorbate–adsorbate interactions, i.e., template vs self-assembly effects, in the structure formation process of DBV cations on these modified Cu electrode surfaces. PMID:25298791

Wandelt, Klaus

2014-01-01

334

Ionospheric Erosion by Alfven Waves  

NASA Astrophysics Data System (ADS)

Using observations from the FAST small explorer spacecraft we present fields and plasma observations above the dayside auroral oval showing the erosion of ionospheric plasmas from the topside ionosphere by the action of Alfven waves. Using interferometric techniques the waves are shown to approximately obey the expected dispersion for Alfven waves with transverse scales extending from greater than electron inertial lengths down to ion gyro-radii. Measurements of the plasma density where these waves are observed show that over latitudinal widths exceeding 100 km total depletion of the cold ionospheric plasma can occur. The plasma within these depleted regions or cavities is composed of magnetosheath ion and electron distributions and upgoing transversely accelerated ions and downgoing field-aligned electrons distributed as conics and field-aligned beams respectively. Poynting flux observations on the density gradients comprising the cavity walls show that these waves are directed downwards and focused inwards towards regions of lower density. The wave phase velocity measurement in the plasma frame, while subject to significant uncertainty, is directed transversely outwards from the cavity. These observations suggest a feedback model for Alfven wave focusing and ion heating on density gradients that can lead to intense ion outflow from the ionosphere and subsequent depletion of ionospheric plasmas.

Chaston, C. C.; Genot, V.; Bonnell, J. W.; Carlson, C.; McFadden, J.; Ergun, R.; Strangeway, R.; Lund, E.; Hwang, K.

2005-12-01

335

Effects of word frequency on individual-item and serial order retention: Tests of the order-encoding view  

Microsoft Academic Search

The orderencoding view of the word frequency effect proposes that low-frequency (LF) items attract more attention to the encoding\\u000a of individual-item information than do high-frequency (HF) items, but at the expense of order encoding (DeLosh & McDaniel,\\u000a 1996). When combined with the assumption that free recall of unrelated words is organized according to their original order\\u000a of presentation, this view

Paul S. Merritt; Edward L. DeLosh; Mark A. McDaniel

2006-01-01

336

Global ionospheric dynamics and electrodynamics during geomagnetic storms (Invited)  

NASA Astrophysics Data System (ADS)

Globally distributed total electron content (TEC) data has become an important tool for exploring the consequences of storm-time electrodynamics. Magnetosphere-ionosphere coupling during the main phase is responsible for the largest ionospheric effects observed during geomagnetic storms, mediated by global scale electrodynamics. Recent research using case studies reveals a complex picture of M-I coupling and its relationship to interplanetary drivers such as the solar wind electric field. Periods of direct coupling exist where the solar wind electric field is strongly correlated with prompt penetration electric fields, observed as enhanced vertical plasma drifts or an enhanced electrojet in the daytime equatorial ionosphere. Periods of decoupling between low latitude electric fields and the solar wind electric field are also observed, but the factors distinguishing these two types of response have not been clearly identified. Recent studies during superstorms suggest a role for the transverse (y-component) of the interplanetary magnetic field, which affects magnetospheric current systems and therefore may affect M-I coupling, with significant ionospheric consequences. Observations of the global ionospheric response to a range of geomagnetic storm intensities are presented. Scientific understanding of the different factors that affect electrodynamic aspects of M-I coupling are discussed.

Mannucci, A. J.; Tsurutani, B.; Verkhoglyadova, O. P.; Komjathy, A.; Butala, M. D.

2013-12-01

337

The Schumann resonance eigenmodes in the Earth's ionosphere observed by Chibis-M microsatellite  

NASA Astrophysics Data System (ADS)

The Schumann resonance (SR) occurs due to the global thunderstorm activity in the Earth-ionosphere cavity. The first five eigenmodes of the SR are 7.8, 14.3, 20.8, 27.3 and 33.8 Hz. This effect is well observed from ground-based electromagnetic (EM) sensors. However, the results of published numerical simulations show that the penetration depth into the ionosphere of EM fields, related to SR, is limited to 50-70 km for electric field and 120-240 km for magnetic field. From this follows, that SR can hardly ever be detected by the low Earth orbiting satellites. In spite of this fact, SR has been found for the first time in data collected by the Communications/Navigation Outage Forecasting System (C/NOFS) satellite [Simoes et al., 2011]. C/NOFS observed SR signals in the altitude range 400-850 km at local night time, from three orthogonal pairs of 20 m tip-to-tip electric field double probes. The SR spectral density is about 0.3 (?V/m)/Hz1/2, which is almost 3 orders of magnitudes lower than usually observed on the Earth's surface. As well, the SR harmonics were observed by Russian Chibis-M microsatellite in 2013, also at local night time. The Chibis-M satellite has mass ~40kg and was launched on January 24, 2012, at 23:14 UTC from the cargo ship 'Progress M-13M' to circular orbit with altitude ~500 km and inclination ~52° . One of the mission goals is to study the plasma wave processes related to solar-magnetosphere-ionosphere-atmosphere connections in ULF-VLF range. The Chibis-M EM field sensors were developed and designed in Lviv Centre of Institute for Space Research, Ukraine. The electric field antenna of Chibis-M has very short base, ~0.42 m, nevertheless the SR eigenfrequencies were reliably detected. The measured spectral density of first SR peak is about 0.5 (?V/m)/Hz1/2, which is very close to value, obtained by C/NOFS satellite. The fact of SR registration in the ionosphere suggests that the Earth-ionosphere waveguide should be described as a leaky cavity for ELF wave propagation. Perhaps the SR detection in ionosphere at local night can be explained by decreasing of plasma density in shadow zone. Thus, at study of ELF waves propagation, the model of the Earth-ionosphere structure should be refined. Simoes, F. A., R. F. Pfaff, H. T. Freudenreich, Satellite observations of Schumann resonances in the Earth's ionosphere, Geophys. Res. Lett., 38, L22101, doi:10.1029/2011GL049668, 2011.

Dudkin, Denys

2014-05-01

338

Effects observed in the equatorial and low latitude ionospheric F-region in the Brazilian sector during low solar activity geomagnetic storms and comparison with the COSMIC measurements  

NASA Astrophysics Data System (ADS)

The main objective of the present investigation has been to compare the ionospheric parameters (NmF2 and hmF2) observed by two ground-based ionospheric sounders (one at PALMAS- located near the magnetic equator and the other at Sao Jose dos Campos-located in the low-latitude region) in the Brazilian sector with that by the satellite FORMOSAT-3/COSMIC radio occultation (RO) measurements during two geomagnetic storms which occurred in December 2006 and July 2009. It should be pointed out that in spite of increasing the latitude (to 10°) and longitude (to 20°) around the stations; we had very few common observations. It has been observed that both the peak electron density (NmF2) and peak height (hmF2) observed by two different techniques (space-borne COSMIC and ground-based ionosondes) during both the geomagnetic storm events compares fairly well (with high correlation coefficients) at the two stations in the Brazilian sector. It should be pointed out that due to equatorial spread F (ESF) in the first storm (December 2006) and no-reflections from the ionosphere during nighttime in the second storm (July 2009), we had virtually daytime data from the two ionosondes.

Sahai, Y.; de Jesus, R.; Fagundes, P. R.; Selhorst, C. L.; de Abreu, A. J.; Tulasi Ram, S.; Aragon-Angel, A.; Pillat, V. G.; Abalde, J. R.; Lima, W. L. C.; Bittencourt, J. A.

2012-11-01

339

Comparative statistical and spectral studies of seismic and non-seismic sub-ionospheric VLF anomalies  

NASA Astrophysics Data System (ADS)

We present a comparative study of seismic and non-seismic sub-ionospheric VLF anomalies. Our method is based on parameter variations of the sub-ionospheric VLF waveguide formed by the surface and the lower ionosphere. The used radio links working in the frequency range between 10 and 50 kHz, the receivers are part of the European and Russian networks. Various authors investigated the lithopsheric-atmospheric-ionospheric coupling and predicted the lowering of the ionosphere over earthquake preparation zones [1]. The received nighttime signal of a sub-ionospheric waveguide depends strongly on the height of the ionospheric E-layer, typically 80 to 85 km. This height is characterized by a typical gradient of the electron density near the atmospheric-ionospheric boundary [2]. In the last years it has been turned out that one of the major issues of sub-ionospheric seismo-electromagnetic VLF studies are the non-seismic influences on the links, which have to be carefully characterized. Among others this could be traveling ionospheric disturbances, geomagnetic storms as well as electron precipitation. Our emphasis is on the analysis of daily, monthly and annual variations of the VLF amplitude. To improve the statistics we investigate the behavior and typical variations of the VLF amplitude and phase over a period of more than 2 years. One important parameter considered is the rate how often the fluctuations are falling below a significant level derived from a mean value. The temporal variations and the amplitudes of these depressions are studied for several years for sub-ionospheric VLF radio links with the receivers in Graz and Kamchatka. In order to study the difference between seismic and non-seismic turbulences in the lower ionosphere a power spectrum analysis of the received signal is performed too. We are especially interested in variations T>6 min which are typical for atmospheric gravity waves causing the lithospheric-atmospheric-ionospheric coupling [3]. All measured and derived VLF parameters are compared with VLF observations several weeks before an earthquake (e.g. L'Aquila, Italy, April 6, 2009) and with co- and post-seismic phenomena. It is shown that this comparative study will improve the one parameter seismo-electromagnetic VLF methods. References: [1] A. Molchanov, M. Hayakawa: Seismo-Electromagnetics and related Phenomena: History and latest results, Terrapub, 2008. [2] S. Pulinets, K. Boyarchuk: Ionospheric Precursors of Earthquakes, Springer, 2004 [3] A. Rozhnoi et al.: Observation evidences of atmospheric Gravity Waves induced by seismic activity from analysis of subionospheric LF signal spectra, National Hazards and Earth System Sciences, 7, 625-628, 2007.

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

2013-04-01

340

10 CFR 221.34 - Effect of order.  

Code of Federal Regulations, 2011 CFR

...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 Sanctions §...

2011-01-01

341

10 CFR 221.34 - Effect of order.  

Code of Federal Regulations, 2012 CFR

...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 Sanctions §...

2012-01-01

342

10 CFR 221.34 - Effect of order.  

Code of Federal Regulations, 2013 CFR

...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 Sanctions §...

2013-01-01

343

10 CFR 221.34 - Effect of order.  

...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 Sanctions §...

2014-01-01

344

10 CFR 221.34 - Effect of order.  

Code of Federal Regulations, 2010 CFR

...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 Sanctions §...

2010-01-01

345

Ordering Effects in NbC and TaC  

NASA Technical Reports Server (NTRS)

By means of transmission electron microscopy and electron diffraction, evidence has been obtained for the existence of long range carbon atom ordering in single-crystal niobium carbide that has a carbon-to-metal ratio close to the integral composition Nb6C5. The ordering, which gives rise to superlattice and domain structures similar to those observed in V6C5, appears, however, only in samples that have been cooled slowly through the order-disorder temperature of 1025 C. In TaC of similar composition, the ordering, although present, remains very imperfect even after the crystals are subjected to the same thermal treatment. The results are interpreted in terms of the electronic structure of the transition metal carbides as it is currently understood, and their relevance to the mechanical properties of NbC and TaC are discussed.

Venables, J. D.; Meyerhoff, M. H.

1972-01-01

346

The development of approaches for ionosphere irregularities modeling on the base of GNSS data  

NASA Astrophysics Data System (ADS)

The ionosphere plays an important role in GNSS applications because it influences on the radio wave propagation through out. The ionosphere delay is the biggest error source for satellite navigation systems, but it can be directly measured and mitigated with using dual frequency GNSS receivers. However GNSS signal fading due to electron density gradients and irregularities in the ionosphere can decrease the operational availability of navigation system. There were developed several models in order to represent ionospheric fluctuations and scintillation activity under different geophysical conditions, but they were calibrated with data sets, that do not include GNSS derived data. It is very actual to develop empirical or semi-empirical model based on GNSS derived measurements which can represent strong ionosphere fluctuation events. In this work we use the data provided by the existing permanent GNSS network in order to produce information and products that can be used to investigate and formalize dependences of ionospheric fluctuation indices on the space weather conditions and to determine the background levels. Our investigation is based on the classical approach when Rate of TEC (ROT), detrended rate of line-of-sight TEC change and ROTI - indexes are calculated from GPS measurements. For analysis there are produced the daily dependences of the ROTI index as a function of geomagnetic local time on the variable grid and averaging parameters. The paper presents the statistical and correlation dependences between sets of geomagnetic indices and parameters that characterized the ionosphere irregularities activity for period of 2010 - 2013 years.

Cherniak, Iurii; Krankowski, Andrzej; Zakharenkova, Irina; Shagimuratov, Irk

347

Io-Jupiter interaction: Alfvén wave propagation and ionospheric Alfvén resonator  

NASA Astrophysics Data System (ADS)

A linear, one-dimensional gyrofluid code has been used to determine the characteristics of propagating Alfvén waves and the ionospheric Alfvén resonator on a Jupiter-Io flux tube. This model includes electron inertia, electron pressure gradient, and finite ion gyroradius effects, as well as the displacement current correction to prevent the Alfvén velocity from exceeding the speed of light. A quasi-steady Vlasov code provides realistic density profiles along the flux tube as input parameters for the gyrofluid model. In this paper, we demonstrate that the majority of the wave energy from an initial pulse with a long wavelength (˜0.1 RJ) is unable to reach Jupiter's ionosphere without wave breaking, phase mixing, and/or other nonlinear processes; however, a significant energy flux may be transferred via high-frequency, small-wavelength waves to the ionosphere. The waves that reach the ionosphere stimulate an ionospheric Alfvén resonator which is generated between the ionospheric boundary and the first velocity peak of the Alfvén phase speed. The ionospheric density and scale height play important roles to determine the resonant frequency. The eigenfrequency decreases with increasing scale height and with increasing ionospheric density. The fundamental frequency and higher harmonics of the Alfvén resonator are comparable to the observed reoccurring frequency of S bursts between a few and hundreds of Hz. On the basis of this information, we suggest the Alfvén resonator as the likely driver explaining multiple occurrences of S bursts.

Su, Yi-Jiun; Jones, S. T.; Ergun, R. E.; Bagenal, F.; Parker, S. E.; Delamere, P. A.; Lysak, R. L.

2006-06-01

348

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

349

Equatorial ionosphere semiannual oscillation investigated from Schumann resonance measurements on board the C/NOFS satellite  

NASA Astrophysics Data System (ADS)

of Schumann resonance signatures in the equatorial ionosphere offers remote sensing capabilities for the investigation of tropospheric and space weather effects in the ionosphere. Schumann resonances are electromagnetic oscillations in the earth-ionosphere cavity produced by lightning activity. Analysis of AC electric field measurements gathered by the Communications/Navigation Outage Forecasting System satellite reveals a semiannual pattern in Schumann resonance data recorded during nighttime in the equatorial ionosphere. This pattern observed in the Schumann resonance amplitude is expected to help validate—or at least constrain—potential mechanisms proposed to explain the semiannual oscillation observed in different geophysical records, such as those reported in a variety of tropospheric, ionospheric/thermospheric, and magnetospheric observations.

Simões, Fernando; Pfaff, Robert; Freudenreich, Henry; Klenzing, Jeffrey; Rowland, Douglas; Bromund, Kenneth; Kepko, Larry; Le, Guan; Liebrecht, Maria Carmen; Martin, Steven; Uribe, Paulo

2013-11-01

350

Metrology and ionospheric observation standards  

NASA Astrophysics Data System (ADS)

Accuracy and ionospheric observation validity are urgent trends nowadays. WMO, URSI and national metrological and standardisation services bring forward requirements and descriptions of the ionospheric observation means. Researches in the sphere of metrological and standardisation observation moved to the next level in the Russian Federation. Fedorov Institute of Applied Geophysics (IAG) is in charge of ionospheric observation in the Russian Federation and the National Technical Committee, TC-101 , which was set up on the base of IAG- of the standardisation in the sphere. TC-101 can be the platform for initiation of the core international committee in the network of ISO The new type of the ionosounde “Parus-A” is engineered, which is up to the national requirements. “Parus-A” calibration and test were conducted by National metrological Institute (NMI) -D.I. Mendeleyev Institute for Metrology (VNIIM), signed CIMP MRA in 1991. VNIIM is a basic NMI in the sphere of Space weather (including ionospheric observations), the founder of which was celebrated chemist and metrologist Dmitriy I. Mendeleyev. Tests and calibration were carried out for the 1st time throughout 50-year-history of ionosonde exploitation in Russia. The following metrological characteristics were tested: -measurement range of radiofrequency time delay 0.5-10 ms; -time measurement inaccuracy of radio- frequency pulse ±12mcs; -frequency range of radio impulse 1-20 MHz ; -measurement inaccuracy of radio impulse carrier frequency± 5KHz. For example, the sound impulse simulator that was built-in in the ionosounde was used for measurement range of radiofrequency time delay testing. The number of standards on different levels is developed. - “Ionospheric observation guidance”; - “The Earth ionosphere. Terms and definitions”.

Panshin, Evgeniy; Minligareev, Vladimir; Pronin, Anton

351

Third Order Nonlinear Optical Effects in Some Polybenzidines  

NASA Astrophysics Data System (ADS)

Third order nonlinear optical properties of organic compounds with pi electron delocalization are currently receiving much attention in view of potential applications in switching and optical information processing. Polymers of Benzidine were synthesized by hydrogen peroxide reaction catalyzed by horseradish peroxidase enzyme. The polymerization reaction was carried out at room temperature in a monophasic organic solvent with a small amount of water at pH 7.5. The technique of Degenerate Four Wave Mixing with picosecond and nanosecond pulses was employed to measure the third order susceptibility chi^{(3) } of polybenzidine. The observed values for chi^{(3)} are of order 10^{-9} to 10 ^{-8} esu. In order to understand the origin of these high values of chi^ {(3)}, we measured the real and imaginary components of chi^{(3)} . Investigation of total energy transmission as a function of incident intensity and fluence at 532 nm for picosecond and nanosecond laser pulses using a frequency doubled Nd:YAG laser indicates reverse saturable absorption. The experiments are carried out for the sample in solution in Dimethyl Sulfoxide and Methanol (DMSO:MeOH) 4:1 ratio. As we observe the nanosecond and picosecond curves to be superimposed for intensity dependence and not for fluence, we conclude that the third order nonlinearity is predominantly due to two photon absorption. Values for Im chi ^{(3)} determined by our experiments are of order 10^{-9} to 10^{-8} esu. We measure the real part of chi^{(3)} by optical Kerr gate technique. The value is about one order lower compared to the imaginary component. In view of the reverse saturable absorption characteristics observed for the samples, the material is a good candidate for applications in optical power limiting.

Cheng, Chi Fai

352

Generation of ion-conic distribution by upgoing ionospheric electrons  

SciTech Connect

Downward currents in auroral regions are commonly measured with amplitudes of 1--5 ..mu..A/m/sup 2/. Such currents are likely the result of upgoing thermal ionospheric electrons falling through a field-aligned potential drop on the order of their thermal energyl. Similar distributions of upgoing ionospheric electrons may also occur in regions of diffuse auroral electron precipitation to preserve current continuity in the presence of the loss of the precipitating electrons to the ionosphere. The drift velocity of the upgoing electrons is sufficient to excite electrostatic ion-cyclotron waves. In addition to being in Landau resonance with the upgoing electrons, these waves cyclotron resonate with the upgoing thermal ions with a parallel energy of several eV. Calculated qusi-linear diffusion rates using measured wave spectra indicate the resonant ions can be heated to perpendicular energies on the order of 100 times the initial ion thermal energy. Comparison with auroral particle observations, both at low altitude (approx.1500 km) and higher altitude (approx.6000 km) shows that ion-conic distributions can readily be explained by such quasi-linear diffusion. The results imply that conic distributions should not occur simultaneously with the keV electron precipitation associated with discrete arcs in regions of upward current but should occur in regions of upgoing ionospheric electrons which may include regions near the edges of auroral arcs and regions of diffuse auroral electron precipitation.

Dusenbery, P.B.; Lyons, L.R.

1981-09-01

353

Titan's upper atmospheric structure and ionospheric composition  

NASA Astrophysics Data System (ADS)

This Dissertation investigates the density structure of the neutral upper atmosphere and the composition of the ionosphere of Titan through Cassini observations. The highly extended atmosphere of Titan consists primarily of N2, CH4, and H2. The focus is on data extracted from the Ion and Neutral Mass Spectrometer (INMS) and the Cassini Plasma Spectrometer (CAPS) instruments onboard Cassini. The INMS, which is fundamentally a quadrupole mass spectrometer, measures the abundance of neutral and ion components with masses of 1--8 and 12--99 Da. The CAPS instrument consists of three subsystems of which the Ion Beam Spectrometer (CAPS-IBS) is used in this study to derive mass spectra of thermal ions up to 400 Da. in mass in Titan's ionosphere. From measurements of molecular nitrogen in Titan's upper atmosphere an atmospheric scale height is derived implying an effective temperature. From an analysis of 29 targeted flybys of Titan we find that the thermosphere is isothermal from an altitude of 1050 km to the exobase height with an average effective temperature of 153 K. The scale height, and hence the effective temperature, is found to be highly variable. We assess this variability against the relevant geospatial, solar, and magnetospheric parameters to determine which are highly correlated to the effective temperatures. Titan's thermospheric temperature is found to be controlled by variations in the magnetospheric plasma environment. No correlation is found to exist with respect to geospatial parameters (i.e., latitude or longitude) and anti-correlation is found with solar parameters implying that Titan's nightside is hotter than its dayside. Furthermore, Titan's thermosphere is found to respond to plasma forcings on timescales less than one Titan day. To investigate the composition of Titan's ionosphere we present a 1D photochemical model of Titan's dayside ionosphere constrained by Cassini measurements. We show that the production of the primary products of photoionization match the INMS data to within 20%. The major ions, CH+5,C2H+ 5 , and HCNH+, are discussed at length and an investigation of the processes controlling their modeled densities is presented. We then present the ion density profiles for the major hydrocarbons in the C3--C6 groups and the major nitrogen-containing ions up to the C4 group. We find that significant chemistry in the nitrogen containing hydrocarbons is missing from previous models and suggest pathways for the growth of these molecules. We also find that the chemistry of Titan's ionosphere is not necessarily dominated by proton exchange processes and that significant molecular growth should be expected through associative ion-molecule reactions. The composition of the ions observed by the Ion Beam Spectrometer (CAPS-IBS) are analyzed with a specific emphasis on those larger than benzene (C 6H6). The CAPS-IBS mass spectra are found to have several peaks corresponding to ions having up to 14 carbon atoms with significant densities and masses up to 400 Da. Fits to the high mass ion spectra determine that each observed peak grouping must contain more than one ion of substantial density possibly indicating some degree of nitrogen incorporation. We compare the high mass ion spectra to various laboratory experiments which have produced large hydrocarbons or tholins through plasma processing of N2, CH4, and various simple hydrocarbons. We conclude from these comparisons that it is likely that Titan's ionospheric chemistry proceeds to higher mass through the reactions of C2 hydrocarbons and nitrogen containing hydrocarbons. Density profiles of the C8--C13 groups are presented from the CAPS-IBS data which show a region of initiation at altitudes above 1050 km and below 1200 km followed by a stagnation and drop-off at the lowest altitudes. We present modeled density profiles of the ions in the C6 and larger groups using an empirical model.

Westlake, Joseph H.

354

The HERO project: Rocket experiments in the artificially heated ionosphere  

NASA Astrophysics Data System (ADS)

Heating experiments will be carried out near Tromsoe, Norway: very powerful radio-waves transmitted upwards into the ionosphere give rise to artificially induced modifications of the natural ionospheric plasma. Many of these modification effects can be followed and interpreted by ground based diagnostic installations such as the EISCAT incoherent scatter facility. Some, however, require in situ methods. Therefore heating rocket (HERO) measurements will complement the ground based observations, gathering data on the modified F region plasma. The planned four payloads are described briefly.

Rose, G.

1980-06-01

355

Ionospheric imaging using computerized tomography  

SciTech Connect

Computerized tomography (CT) techniques can be used to produce a two-dimensional image of the electron density in the ionosphere. The CT problem requires that the measured data be the line integral through the medium of the unknown parameter; transionospheric satellite beacon total electron content data recorded simultaneously at multiple ground stations fulfill this requirement. In this paper the CT problem is formulated as it applies to ionospheric imaging and limitations of the technique are investigated. Simulations are performed assuming a 1000-km-altitude polar-orbiting satellite and both five and three ground stations; the results demonstrate the feasibility of this technique. 14 references.

Austen, J.R.; Franke, S.J.; Liu, C.H.

1988-06-01

356

Radar Soundings of the Ionosphere of Mars  

NASA Astrophysics Data System (ADS)

We report the first radar soundings of the ionosphere of Mars with the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) instrument on board the orbiting Mars Express spacecraft. Several types of ionospheric echoes are observed, ranging from vertical echoes caused by specular reflection from the horizontally stratified ionosphere to a wide variety of oblique and diffuse echoes. The oblique echoes are believed to arise mainly from ionospheric structures associated with the complex crustal magnetic fields of Mars. Echoes at the electron plasma frequency and the cyclotron period also provide measurements of the local electron density and magnetic field strength.

Gurnett, D. A.; Kirchner, D. L.; Huff, R. L.; Morgan, D. D.; Persoon, A. M.; Averkamp, T. F.; Duru, F.; Nielsen, E.; Safaeinili, A.; Plaut, J. J.; Picardi, G.

2005-12-01

357

Ordered Effects of Technology Education Units on Higher-Order Critical Thinking Skills of Middle School Students  

ERIC Educational Resources Information Center

In this quasi-experimental quantitative study, 105 eighth grade students at a suburban middle school in New York State participated in a seven month-long project involving the ordered effects of the technology education units of Lego[R] Mindstorms(TM) NXT Robotics System, Digital Storytelling with Microsoft Windows Movie Maker, and the Marble Maze…

Mojica, Kern D.

2010-01-01

358

Ionospheric parameter analysis techniques and anomaly identification in periods of ionospheric perturbations  

NASA Astrophysics Data System (ADS)

In the present paper we suggest intellectual techniques intended for the analysis of ionospheric parameters. These techniques are directed at studying dynamic processes in the "magnetosphere-ionosphere" system during perturbations. Using the combination of the wavelet transform and neural networks, the authors have developed a technique of approximating the time variation of ionospheric parameters. This technique allows us to make data predictions and detect anomalies in the ionosphere. Multiscale component approximations of the critical frequency of the ionosphere layer F2 were constructed. These approximations can be presented in the following form: begin{center} c_{l,k+m} (t) = varphi_m(3) Bigl (sum_i omega(3_{mi}) varphi_i(2) Bigl (sum_j omega(2_{ij}) varphi_j(1) Bigl (sum_k omega(1_{jk}) c_{l,k} (t) Bigr ) Bigr ) Bigr ) , where c_{l,k} = bigl < f , Psi_{l,k} bigr > ; Psi_{l,k} (t) = 2(l/2) Psi (2(l) t - k) is the wavelet basis; omega(1_{jk}) are the weighting coefficients of the neuron j of the network input layer; omega(2_{ij}) are the weighting coefficients of the neuron i of the network hidden layer; omega(3_{mi}) are the weighting coefficients of the neuron m of the network output layer; varphi(1_j) (z) = varphi(2_i) (z) = (1)/(1+exp(-z))) ; varphi(3_m) (z) = x*z+y . The coefficients c_{l,k} can be found as a result of transforming the original function f into the space with the scale l . In order to obtain the approximations of the time variation of data, neural networks can be united in groups. In the paper we have suggested a multicomponent time variation model of ionospheric parameters, which makes it possible to perform the analysis of the ionospheric dynamic mode, receive predictions about parameter variations, and detect anomalies in periods of perturbations. The multicomponent model also allows us to fill missing values in critical frequency data taking into account diurnal and seasonal variations. Identification of the model is based on combining the wavelet transform with autoregressive integrated moving average methods. The general expression of the multicomponent model is f_0 (t) = sum_{mu = /line{1,M}} sum_{k = /line{1,N_1(mu}}) s_{l,k}(mu) (t) b_{l,k}(mu) (t) , where s_{l,k}(mu) (t) = sum_{q=1}(p_l(mu)) gamma_{l,q}(mu) w(mu_{l,k-q}) (t) - sum_{n=1}(h_l(mu)) theta_{l,n}(mu) alpha(mu_{l,k-n}) (t) is the estimated value of the mu -th component, p_l(mu) is the autoregressive model order of the mu -th component, gamma_{l,q}(mu) are the autoregressive parameters of the mu -th component, w_{l,k}(mu) (t) = nabla(nu(mu)) beta_{l,k}(mu) (t) , nu(mu) is the difference order of the mu -th component, beta_{l,k}(mu) are the decomposition coefficients of the mu -th component, h_l(mu) , theta_{l,k}(mu) are the model orders and moving average parameters of the mu -th component model, alpha(mu_{l,k}) are the residual errors of the mu -th component model, M is the number of characteristic components, N_l(mu) is the length of the mu -th component, b_{l,k}(mu) is the wavelet basis of the mu -th component, l is the scale. Using these techniques we have obtained the approximation of the ionospheric critical frequency time variation for regions located in Kamchatka and Magadan. The analysis of the quiet variation of the parameters was performed, the 5-hour prediction was made, and anomalies occurring in periods of increased solar activity and prior to strong earthquakes in Kamchatka were discovered in the ionosphere. The developed methods are useful for studying the properties of ionospheric perturbations, obtaining information about various parameters of ionospheric plasma irregularities and the dynamic mode of these parameters.

Mandrikova, Oksana; Polozov, Yury; Fetisova Glushkova, Nadejda; Shevtsov, Boris

359

Magnetospheres of Planets and Moons: Links to Their Ionospheres. (Invited)  

NASA Astrophysics Data System (ADS)

The phrase “magnetosphere-ionosphere coupling” has become almost hackneyed in the terrestrial context, but plays an important role in the terrestrial system and must also be emphasized in the context of planetary- and moon-magnetospheres because the underlying principles are similar in all systems. This talk will introduce only two intriguing aspects of the coupling problem for planets and moons. In describing the first topic, we note that, especially for the gas giants Jupiter and Saturn, much of the evidence of magnetosphere-ionosphere coupling is obtained from auroral imaging. In images of Jupiter’s polar ionosphere, bright auroral spots are found to link magnetically to the moons Io, Europa and Ganymede. The spots give evidence of intense field-aligned currents generated near the equator in the interaction between the moons and the flowing plasma of Jupiter’s magnetosphere. The currents must penetrate through regions of impedance mismatch near the upper and lower boundaries of Jupiter’s equatorial plasma torus in order to close in the planetary ionosphere. There is some evidence that the signal propagates through the strong gradient of plasma density at the boundary of the plasma torus by converting into a striated structure that guides high frequency waves. As well, at Io, the interaction has been found to generate localized intense electron fluxes observed to flow along and antiparallel to the magnetic field near the equator. These bidirectional beams are probably accelerated by parallel electric fields near the ionospheric ends of the flux tube, but how the accelerated electrons reach the equator has not been explained. It seems likely that their presence there requires that the (parallel) electric fields in the Jovian ionosphere vary either temporally at high frequency or spatially on short transverse length scales. The full explanation has not yet been developed. As a second example of the role of magnetosphere-ionosphere coupling in planetary systems, we turn to an MHD simulation of the mini-magnetosphere of Ganymede carried out by X. Jia (2010). The significance of the ionosphere in the simulation is that, as the inner plasma boundary, it affects the flow and the dynamics of the entire system. The mathematical reason for the result is evident: differential equations have different solutions for different boundary conditions, but the dramatic changes that arise throughout the entire volume of the magnetosphere as the inner boundary condition is slightly modified may be both surprising and illuminating.

Kivelson, M. G.

2010-12-01

360

Effect of order fluid models on flue gas streamer dynamics  

NASA Astrophysics Data System (ADS)

The present paper shows that in the case of a micro-discharge modelling using the hydrodynamics assumption, the second order fluid model involving the complete electron momentum conservation equation must be used in order to better quantify the radical formation in a micro-discharge applied to air pollution control. The present results show large differences in the micro-discharge parameters (such as velocity and electron density) between the three tested hydrodynamics models: the classical first order model using the local electric field approximation and two second order models using the local energy approximation with or without the drift-diffusion approximation. The tests have been carried out in the case of a wire-to-plane corona reactor filled with a typical flue gas (76% N2, 12% CO2, 6% O2, 6% H2O) at atmospheric pressure and ambient temperature. The simulation of the micro-discharge dynamics is performed using a 1.5D numerical streamer model coupled with a simple chemical kinetics model involving 31 species (charged and neutral particles in their fundamental or metastable state) reacting following 29 selected chemical reactions.

Eichwald, O.; Ducasse, O.; Merbahi, N.; Yousfi, M.; Dubois, D.

2006-01-01

361

Investigation of the dynamics of the ionosphere in the range of the Northern Lights using the EISCAT ionospheric radar  

NASA Astrophysics Data System (ADS)

The interaction between polar ionosphere and magnetosphere, as well as the effects of high electric fields in the F region were investigated. Measurements with the EISCAT ionospheric radar and magnetometers allowed the determination of conductivity and electric fields in the range of the magnetic Ps6 pulsations. An electrostatic model for the Ps6 structures was developed. It was verified that the approximation of Maxwell-Boltzmann velocity distributions of the ions in the F region is acceptable for the interpretation of the measured Thomson scattering spectra. Ion temperature increases by up to a factor 10 can be explained by ohmic heating due to electric fields.

Buchert, Stephan Christoph

1988-07-01

362

Effects of language dominance on item and order memory in free recall, serial recall and order reconstruction.  

PubMed

Spanish-English bilinguals (N = 144) performed free recall, serial recall and order reconstruction tasks in both English and Spanish. Long-term memory for both item and order information was worse in the less fluent language (L2) than in the more fluent language (L1). Item scores exhibited a stronger disadvantage for the L2 in serial recall than in free recall. Relative order scores were lower in the L2 for all three tasks, but adjusted scores for free and serial recall were equivalent across languages. Performance of English-speaking monolinguals (N = 72) was comparable to bilingual performance in the L1, except that monolinguals had higher adjusted order scores in free recall. Bilingual performance patterns in the L2 were consistent with the established effects of concurrent task performance on these memory tests, suggesting that the cognitive resources required for processing words in the L2 encroach on resources needed to commit item and order information to memory. These findings are also consistent with a model in which item memory is connected to the language system, order information is processed by separate mechanisms and attention can be allocated differentially to these two systems. PMID:24303779

Francis, Wendy S; Baca, Yuzeth

2014-11-01

363

Imaging meso-scale ionospheric structures  

NASA Astrophysics Data System (ADS)

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

Burston, Robert

2012-06-01

364

43 CFR 4.1128 - Effect of initial order or decision.  

Code of Federal Regulations, 2013 CFR

...2013-10-01 2013-10-01 false Effect of initial order or decision. 4.1128...Special Rules Applicable to Surface Coal Mining Hearings and Appeals Evidentiary Hearings § 4.1128 Effect of initial order or decision. An...

2013-10-01

365

43 CFR 4.1128 - Effect of initial order or decision.  

Code of Federal Regulations, 2010 CFR

...2010-10-01 2010-10-01 false Effect of initial order or decision. 4.1128...Special Rules Applicable to Surface Coal Mining Hearings and Appeals Evidentiary Hearings § 4.1128 Effect of initial order or decision. An...

2010-10-01

366

43 CFR 4.1128 - Effect of initial order or decision.  

Code of Federal Regulations, 2011 CFR

...2011-10-01 2011-10-01 false Effect of initial order or decision. 4.1128...Special Rules Applicable to Surface Coal Mining Hearings and Appeals Evidentiary Hearings § 4.1128 Effect of initial order or decision. An...

2011-10-01

367

43 CFR 4.1128 - Effect of initial order or decision.  

Code of Federal Regulations, 2012 CFR

...2012-10-01 2011-10-01 true Effect of initial order or decision. 4.1128...Special Rules Applicable to Surface Coal Mining Hearings and Appeals Evidentiary Hearings § 4.1128 Effect of initial order or decision. An...

2012-10-01

368

Review of critical velocity experiments in the ionosphere  

NASA Technical Reports Server (NTRS)

Observations relevant to Alfven's Critical Velocity Effect, of the several shaped-charge releases in the ionosphere are compared with three generations of a macroscopic model of these releases. Good agreement is found with experiments which have reported a low ion yield, but major discrepancies remain with the Porcupine experiment which has the largest yield yet reported.

Torbert, R. B.

1990-01-01

369

Ionospheric Threats to Space-Based Augmentation System Development  

E-print Network

of light in vacuum, f is the signal frequency and the integral is of the number density of electrons N over sets the author illustrates the large absolute values of total electron content (TEC), to which GPS the effect of these highly irregular periods of ionospheric activity by considering the approach WAAS has

Stanford University

370

Acceleration of electrons in Titan's ionosphere  

NASA Astrophysics Data System (ADS)

A consideration of the acceleration mechanism which supplies the fast electrons to the source of Saturnian kilometric radiation (SKR) and an interpretation of the recently reported observational indications of the influence of Titan on the SKR are presented. The proposed mechanism operates by the effect of the different magnetization of the electrons and ions in Titan's ionosphere which in the course of Titan's motion through the Saturnian magnetic field causes the creation of a charge-separation electric field. This field has a component parallel to the magnetic field and accelerates part of the ionospheric electrons (called “runaway electrons”). The performed estimates show that the mechanism accelerates the runaway electrons up to an energy of ˜5 keV. The power of the acceleration mechanism is sufficient for SKR generation and also for the ultraviolet luminescence of Titan's atmosphere. The weakening of the SKR when Titan passes on the dayside of Saturn is due to a decrease of the magnetic field strength near the dayside magnetopause, when the Moon escapes the Saturnian magnetosphere, as well as due to the break in the magnetic connection between the electron acceleration region on Titan and the SKR sources. The latter prevents the penetration of the accelerated electrons into the radiation generation region. When Titan is on the nightside of Saturn, it enters into shell L˜14, which is stretched owing to the ring current. In this case, the electrons that accelerated in the ionosphere of Titan can reach the nightside SKR sources and activate them and therefore being the reason for the Titan influence on the SKR.

Zaitsev, V. V.; Shaposhnikov, V. E.; Khodachenko, M. L.; Rucker, H. O.; Panchenko, M.

2010-03-01

371

Ionospheric imaging using computerized tomography  

Microsoft Academic Search

Computerized tomography (CT) techniques can be used to produce a two-dimensional image of the electron density in the ionosphere. The CT problem requires that the measured data be the line integral through the medium of the unknown parameter; transionospheric satellite beacon total electron content data recorded simultaneously at multiple ground stations fulfill this requirement. In this paper the CT problem

Jeffrey R. Austen; Steven J. Franke; C. H. Liu

1988-01-01

372

Magnetospheric-ionospheric Poynting flux  

NASA Technical Reports Server (NTRS)

Over the past three years of funding SRI, in collaboration with the University of Texas at Dallas, has been involved in determining the total electromagnetic energy flux into the upper atmosphere from DE-B electric and magnetic field measurements and modeling the electromagnetic energy flux at high latitudes, taking into account the coupled magnetosphere-ionosphere system. This effort has been very successful in establishing the DC Poynting flux as a fundamental quantity in describing the coupling of electromagnetic energy between the magnetosphere and ionosphere. The DE-B satellite electric and magnetic field measurements were carefully scrutinized to provide, for the first time, a large data set of DC, field-aligned, Poynting flux measurement. Investigations describing the field-aligned Poynting flux observations from DE-B orbits under specific geomagnetic conditions and from many orbits were conducted to provide a statistical average of the Poynting flux distribution over the polar cap. The theoretical modeling effort has provided insight into the observations by formulating the connection between Poynting's theorem and the electromagnetic energy conversion processes that occur in the ionosphere. Modeling and evaluation of these processes has helped interpret the satellite observations of the DC Poynting flux and improved our understanding of the coupling between the ionosphere and magnetosphere.

Thayer, Jeffrey P.

1994-01-01

373

Effects observed in the Latin American sector ionospheric F region during the intense geomagnetic disturbances in the early part of November 2004  

NASA Astrophysics Data System (ADS)

The Sun was very active in the early part of November 2004. During the period of 8-10 November 2004, intense geomagnetic disturbances with two superstorms were observed. In this paper, we have investigated the generation and suppression of equatorial ionospheric irregularities and the daytime changes in the F region electron density in the Latin American sector during the period of intense geomagnetic disturbances. We present the ionospheric sounding observations carried out at Manaus and Sao Jose dos Campos, Brazil, during this geomagnetically disturbed period. Also, GPS observations obtained from several stations in Brazil, Argentina, and St. Croix, U.S. Virgin Islands, during the disturbed period are presented. During the main phase of the first superstorm, around the prereversal enhancement time (night of 7-8 November), prompt penetration of electric field was observed and the presence of equatorial ionospheric irregularities was detected from St. Croix, U.S. Virgin Islands (in the northern hemisphere) to Bahia Blanca, Argentina (in the southern hemisphere). The ionospheric sounding observations at Manaus indicate inhibition of prereversal enhancement on the nights of 9-10 and 10-11 November, possibly due to the disturbed thermospheric winds or disturbance electric fields. Virtually no phase fluctuations on the nights of 9-10 and 10-11 November were observed in the Latin American sector. During the daytime on 8 November, the vertical total electron content (VTEC) observations show a negative storm phase at Porto Alegre (Brazil) and Bahia Blanca (Argentina). Again during the daytime on 10 November, the VTEC observations show a negative storm phase from Brasilia (Brazil) to Bahia Blanca. These negative storm phases are associated with a decrease in the O/N2 ratio. During the daytime on 9 November, the VTEC observations show a positive storm phase extending from St. Croix to Porto Alegre, and again on 10 November, VTEC observations show a positive storm phase. These positive storm phases observed are possibly due to changes in large-scale wind circulation and an increase in the O/N2 ratio.

Sahai, Y.; Becker-Guedes, F.; Fagundes, P. R.; de Jesus, R.; de Abreu, A. J.; Paxton, L. J.; Goncharenko, L. P.; Brunini, C.; Gende, M.; Ferreira, A. S.; Lima, N. S.; Guarnieri, F. L.; Pillat, V. G.; Bittencourt, J. A.; Candido, C. M. N.

2009-03-01

374

Further insights into interaction of lightning electromagnetic pulse with the ionosphere  

NASA Astrophysics Data System (ADS)

Somu et al. (2012) examined effective ionoshpheric reflection heights for wideband electric fields produced by consecutive return strokes within the same lightning flash. The reflection heights were estimated from the delay of the first sky wave relative to the ground wave in electric field records. It was shown that in many cases the reflection height tended to decrease with stroke order. In this study, we will quantify this effect by considering the occurrence of different patterns of reflection height changes within individual flashes, under both daytime and nighttime conditions. Further, we will show that the observed difference in reflection heights for first and subsequent strokes cannot be explained by the difference in frequency content of first and subsequent return-stroke currents. FDTD calculations for the simulated daytime ionosphere show that the delay of the first sky wave relative to the ground wave is essentially the same for source current waveforms typical for first and subsequent strokes. Additionally, we will examine (1) changes in reflection height as a function of preceding return-stroke peak current and preceding interstroke interval, (2) correlation between magnitudes of first sky wave and ground wave, and (3) effect on the ionospheric reflection height of compact intracloud discharges (CIDs). Acknowledgements: This research was supported in part by NSF and DARPA. NLDN data were provided by Vaisala (J.A. Cramer and W. Brooks). Reference: Somu V.B., V.A. Rakov, M.A. Haddad, and S.A. Cummer, "Ionospheric reflection heights for wideband electric fields produced by consecutive return strokes within the same lightning flash", Abstract AE43A-0241, presented at 2012 Fall Meeting, AGU, San Francisco, Calif., December 3-7, 2012,

Somu, V. B.; Rakov, V. A.; Cummer, S. A.

2013-12-01

375

Upper limits to the nightside ionosphere of Mars  

NASA Technical Reports Server (NTRS)

The nightside ionosphere of Mars could be produced by electron precipitation or by plasma transport from the dayside, by analogy to the Venus, but few measurements are available. We report here model calculations of upper limits to the nightside ion densities on Mars that would be produced by both mechanisms. For the auroral model, we have adopted the downward traveling portions of the electron spectra measured by the HARP instrument on the Soviet Phobos spacecraft in the Martian plasma sheet and in the magnetotail lobes. For the plasma transport case, we have imposed on a model of the nightside thermosphere, downward fluxes of O(+), C(+), N(+), NO(+) and O2(+) that are near the maximum upward fluxes that can be sustained by the dayside ionosphere. The computed electron density peaks are in the range (1.3 - 1.9) x 10 exp 4/cu cm at altitudes of 159 to 179 kin. The major ion for all the models is O2(+), but significant differences in the composition of the minor ions are found for the ionospheres produced by auroral precipitation and by plasma transport. The calculations reported here provide a guide to the data that should be acquired during a future aeronomy mission to Mars, in order to determine the sources of the nightside ionosphere.

Fox, J. L.; Brannon, J. F.; Porter, H. S.

1993-01-01

376

Traveling Ionospheric Disturbances Observed by Midlatitude SuperDARN Radars  

NASA Astrophysics Data System (ADS)

Medium Scale Traveling Ionospheric Disturbances (MSTIDs) are wave-like perturbations of the F-region ionosphere with horizontal wavelengths on the order of 100-250 km and periods between ~15 - 60 min, and are generally thought to be the ionospheric manifestation of Atmospheric Gravity Waves (AGWs). High-latitude MSTIDs have been studied using SuperDARN radars since 1989, and are typically attributed to auroral sources and propagated by the Earth Reflected Wave (ERW) mode. Tropospheric sources and earthquakes are also known to be sources of MSTIDs. Observations of MSTIDs using both mid- and high- latitude SuperDARN radars are presented. North American radar data from November 2010 - November 2011 were searched for signatures of MSTIDs. Initial results suggest that MSTIDs are observed at high latitudes primarily in the fall/winter months, which is consistent with published results. This search also reveals that mid-latitude MSTIDs often appear concurrently with high-latitude MSTIDs and share similar wave parameters. During the fall/winter months, SuperDARN mid-latitude MSTIDs appear more often than high-latitude MSTIDs, likely due to calmer ionospheric conditions at mid-latitudes. In the springtime, SuperDARN-observed MSTIDs are less likely to be seen at high-latitudes, but still appear at mid-latitudes. Selected events are analyzed for wave parameters using the Multiple Signal Classification (MUSIC) technique.

Frissell, N. A.; Baker, J. B.; Ruohoniemi, J. M.; West, M. L.; Bristow, W. A.

2012-12-01

377

Recent Advances in Ionospheric Modeling Using the USU GAIM Data Assimilation Models  

NASA Astrophysics Data System (ADS)

The ionospheric plasma distribution at low and mid latitudes has been shown to display both a background state (climatology) and a disturbed state (weather). Ionospheric climatology has been successfully modeled, but ionospheric weather has been much more difficult to model because the ionosphere can vary significantly on an hour-by-hour basis. Unfortunately, ionospheric weather can have detrimental effects on several human activities and systems, including high-frequency communications, over-the-horizon radars, and survey and navigation systems using Global Positioning System (GPS) satellites. As shown by meteorologists and oceanographers, the most reliable weather models are physics-based, data-driven models that use Kalman filter or other data assimilation techniques. Since the state of a medium (ocean, lower atmosphere, ionosphere) is driven by complex and frequently nonlinear internal and external processes, it is not possible to accurately specify all of the drivers and initial conditions of the medium. Therefore physics-based models alone cannot provide reliable specifications and forecasts. In an effort to better understand the ionosphere and to mitigate its adverse effects on military and civilian operations, specification and forecast models are being developed that use state-of-the-art data assimilation techniques. Over the past decade, Utah State University (USU) has developed two data assimilation models for the ionosphere as part of the USU Global Assimilation of Ionospheric Measurements (GAIM) program and one of these models has been implemented at the Air Force Weather Agency for operational use. The USU-GAIM models are also being used for scientific studies, and this should lead to a dramatic advance in our understanding of ionospheric physics; similar to what occurred in meteorology and oceanography after the introduction of data assimilation models in those fields. Both USU-GAIM models are capable of assimilating data from a variety of data sources, including in situ electron densities from satellites, bottomside electron density profiles from ionosondes, total electron content (TEC) measurements between ground receivers and the GPS satellites, occultation data from satellite constellations, and ultraviolet emissions from the ionosphere measured by satellites. We will present the current status of the model development and discuss the employed data assimilation technique. Recent examples of the ionosphere specifications obtained from our model runs will be presented with an emphasis on the ionospheric plasma distribution during the current low solar activity conditions. Various comparisons with independent data will also be shown in an effort to validate the models.

Scherliess, L.; Thompson, D. C.; Schunk, R. W.

2009-12-01

378

A Comprehensive Method for GNSS Data Quality Determination to Improve Ionospheric Data Analysis  

PubMed Central

Global Navigation Satellite Systems (GNSS) are now recognized as cost-effective tools for ionospheric studies by providing the global coverage through worldwide networks of GNSS stations. While GNSS networks continue to expand to improve the observability of the ionosphere, the amount of poor quality GNSS observation data is also increasing and the use of poor-quality GNSS data degrades the accuracy of ionospheric measurements. This paper develops a comprehensive method to determine the quality of GNSS observations for the purpose of ionospheric studies. The algorithms are designed especially to compute key GNSS data quality parameters which affect the quality of ionospheric product. The quality of data collected from the Continuously Operating Reference Stations (CORS) network in the conterminous United States (CONUS) is analyzed. The resulting quality varies widely, depending on each station and the data quality of individual stations persists for an extended time period. When compared to conventional methods, the quality paramet