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1

Higher order ionospheric effects in precise GNSS positioning  

Microsoft Academic Search

With the increasing number of precise navigation and positioning applications using Global Navigation Satellite Systems (GNSS)\\u000a such as the Global Positioning System (GPS), higher order ionospheric effects and their correction become more and more important.\\u000a Whereas the first-order error can be completely eliminated by a linear combination of dual- frequency measurements, the second-\\u000a and third-order residual effects remain uncorrected in

M. Mainul Hoque; N. Jakowski

2007-01-01

2

Mitigation of higher order ionospheric effects on GNSS users in Europe  

Microsoft Academic Search

Current dual-frequency GPS measurements can only eliminate the first-order ionospheric term and may cause a higher-order range\\u000a bias of several centimeters. This research investigates the second-order ionospheric effect for GNSS users in Europe. In comparison\\u000a to previous studies, the electron density profiles of the ionosphere\\/plasmasphere are modeled as the sum of three Chapman\\u000a layers describing electron densities of the ionospheric

M. Mainul Hoque; N. Jakowski

2008-01-01

3

Higher-order ionospheric effects on the GPS reference frame and velocities  

Microsoft Academic Search

We describe how GPS time series are influenced by higher-order ionospheric effects over the last solar cycle (1995–2008) and examine implications for geophysical studies. Using 14 years of globally reprocessed solutions, we demonstrate the effect on the reference frame. Including second- and third-order ionospheric terms causes up to 10 mm difference in the smoothed transformation to the International Terrestrial Reference

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

2010-01-01

4

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

NASA Astrophysics Data System (ADS)

This study examines the impact of the second-order ionospheric effect on radio occultation (RO) data products. We propose a new linear combination between dual frequency GPS observables, which retrieves slant total electron content free from the second-order ionospheric effect. Our STEC values differ from those obtained by independent techniques by a maximum of 3 total electron content units (TECU), depending on the geographic location and geomagnetic activity. Additionally, we suggest an alternative method of computing the second-order ionospheric delay in RO experiments, which does not require the use of geomagnetic and ionospheric models. First estimates show that the second-order ionospheric delay for the RO experiments falls within the range [-10, -8] mm, which is of the same order of magnitude with second-order ionospheric delay estimates from ground-based experiments. Finally, as a by-product of our model, we retrieve weighted mean geomagnetic field values, which we compare with theoretical estimates computed by the International Geomagnetic Reference Field-10 (IGRF-10) model. Our estimations agree with the IGRF-10 model between 0.23% and 7.0%.

Vergados, Panagiotis; Pagiatakis, Spiros D.

2010-07-01

5

Global modeling 2nd-order ionospheric delay and its effects on GNSS precise positioning  

NASA Astrophysics Data System (ADS)

Ionospheric delay is one of the major error sources in GNSS navigation and positioning. Nowadays, the dual-frequency technique is the most widely used in ionospheric refraction correction. However, dual-frequency measurements can only eliminate the first-order term of ionospheric delay, while the effect of the second-order term on GNSS observations may be several centimeters. In this paper, two models, the International Reference Ionosphere (IRI) 2007 and International Geomagnetic Reference Field (IGRF) 11 are used to estimate the second-order term through the integral calculation method. Besides, the simplified single layer ionosphere model in a dipole moment approximation for the earth magnetic field is used. Since the traditional integral calculation method requires large calculation load and takes much time, it is not convenient for practical use. Additionally, although the simplified single layer ionosphere model is simple to implement, it results in larger errors. In this study, second-order term ionospheric correction formula proposed by Hoque (2007) is improved for estimating the second-order term at a global scale. Thus, it is more practicable to estimate the second-order term. More importantly, its results have a higher precision of the sub-millimeter level for a global scale in normal conditions. Compared with Hoque's original regional correction model, which calculates coefficients through polynomial fitting of elevation and latitudes, this study proposes a piece-wise look-up table and interpolation technique to modify Hoque model. Through utilizing a table file, the modified Hoque model can be conveniently implemented in an engineering software package, like as PANDA in this study. Through applying the proposed scheme for the second-order ionospheric correction into GNSS precise positioning in both PPP daily and epoch solutions, the results have shown south-shift characteristics in daily solution at a global scale and periodic change with VTEC daily variation in epoch positioning solution.

Zhang, Hongping; Lv, Haixia; Li, Min; Shi, Chuang

2011-06-01

6

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

NASA Astrophysics Data System (ADS)

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

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

2009-04-01

7

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

Microsoft Academic Search

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

Panagiotis Vergados; Spiros D. Pagiatakis

2011-01-01

8

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

9

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

10

Ionospheric effects due to electrostatic thundercloud fields  

Microsoft Academic Search

Electrostatic thundercloud fields are shown to heat lower ionospheric electrons significantly under night time conditions. The effect is maximized under conditions of higher altitudes of thundercloud charges, larger magnitudes of these charges, and larger scale heights of ambient conductivity profiles. The lower ionospheric conductivity can be modified as a result of the heating by up to one order of magnitude

V. P. Pasko; T. F. Bell

1998-01-01

11

Estimate of higher order ionospheric errors in GNSS positioning  

Microsoft Academic Search

Precise navigation and positioning using GPS\\/GLONASS\\/Galileo require the ionospheric propagation errors to be accurately determined and corrected for. Current dual-frequency method of ionospheric correction ignores higher order ionospheric errors such as the second and third order ionospheric terms in the refractive index formula and errors due to bending of the signal. The total electron content (TEC) is assumed to be

M. Mainul Hoque; N. Jakowski

2008-01-01

12

Triple-Frequency Methods for Correcting Second-Order Ionospheric Delay Error in COMPASS System  

Microsoft Academic Search

A advanced triple-frequency methods for correcting higher order ionospheric refraction error were discussed in this paper since COMPASS system provides three carrier frequencies. Based on the analysis of ionospheric delay error model, the triple-frequency corrected model using COMPASS pseudo-range measurements is presented. The second-order ionospheric effect can be eliminated efficiently, and the instance illustrates the advantages and necessity of second-order

Yaqin Zhao; Xiao Fu

2010-01-01

13

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

Microsoft Academic Search

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

Norbert Jakowski; Michael Danielides; Christoph Mayer; Claudia Borries

2010-01-01

14

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

15

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

16

Triple-Frequency Method for High-Order Ionospheric Refractive Error Modelling in GPS Modernization  

Microsoft Academic Search

New opportunities for the refinement of ionospheric modelling and reduction of the ionospheric error in GPS measurements arise since a third-frequency will be introduced for the modernised GPS system. This paper investigates theoretical models of the ionospheric refractive error. A triple-frequency method of correcting the 1st and 2nd order ionospheric refraction is presented and a triple-frequency ionosphere-free combination method is

Zemin Wang; Yue Wu; Kefei Zhang; Yang Meng

2005-01-01

17

Intercomparison Of Approaches For Modeling Second Order Ionospheric Corrections Using Gnss Measurements  

NASA Astrophysics Data System (ADS)

Correcting GNSS tracking data for the effects of second order ionospheric effects have been shown to cause a southward shift in GNSS-based precise point positioning solutions by as much as 10 mm, depending on the solar cycle conditions. The most commonly used approaches for modeling the higher order ionospheric effect include, (a) the use of global ionosphere maps to determine vertical total electron content (VTEC) and convert to slant TEC (STEC) assuming a thin shell ionosphere, and (b) using the dual-frequency measurements themselves to determine STEC. The latter approach benefits from not requiring ionospheric mapping functions between VTEC and STEC. However, this approach will require calibrations with receiver and transmitter Differential Code Biases (DCBs). We present results from comparisons of the two approaches. For the first approach, we also compare the use of VTEC observations from IONEX maps compared to climatological model-derived VTEC as provided by the International Reference Ionosphere (IRI2012). We consider various metrics to evaluate the relative performance of the different approaches, including station repeatability, GNSS-based reference frame recovery, and post-fit measurement residuals. Overall, the GIM-based approaches tend to provide lower noise in second order ionosphere correction and positioning solutions. The use of IONEX and IRI2012 models of VTEC provide similar results, especially in periods of low solar activity periods. The use of the IRI2012 model provides a convenient approach for operational scenarios by eliminating the dependence on routine updates of the GIMs, and also serves as a useful source of VTEC when IONEX maps may not be readily available.

Garcia Fernandez, M.; Butala, M.; Komjathy, A.; Desai, S. D.

2012-12-01

18

Effects of Ionospheric Thickness on the Ionospheric Feedback Instability, and the Problem of Radar Detection  

NASA Astrophysics Data System (ADS)

In order to facilitate Poker Flat AMISR (PFISR) detection of plasma perturbations attributable to the ionospheric feedback instability (IFI), an ionosphere-centric derivation of the growth rate of the IFI has been carried out that accounts for the non-zero vertical thickness of the ionosphere, and the associated parallel electric field. The magnetosphere is treated as a complex admittance, which is determined by analysis of a long cascade of transmission line sections, terminated above the top boundary of the ionospheric Alfven resonator (IAR) by a matched load. The effect of ionospheric thickness is a significant reduction in the growth rate, especially at frequencies above the fundamental, and for “background” electric fields below about 50 mV/m. These dependencies are explained by the fact that the horizontal wavelength of the unstable mode is reduced as the mode frequency is increased, and as the background electric field is decreased. The effects are enough to require consideration in previous numerical simulations of the IFI, which do not include them. Of importance to the problem of detection, the unstable horizontal wavelength is less than 4 km for electric fields below 50 mV/m. Because the PFISR beam width is two to three kilometers (at 120 km in altitude), this means that the electric field needs be greater than 50 mV/m for PFISR to be able to detect density perturbations associated with the IFI. Since the plasma density tends to be low where/when the electric field is large, appropriate conditions are fairly rare. This may explain why our efforts to detect the IFI have so far not met with success. Growth rate versus frequency for the ionospheric feedback instability, for thin and finite thickness ionosphere.

Cosgrove, R. B.; Doe, R.

2009-12-01

19

The composition of Mars' topside ionosphere: Effects of hydrogen  

NASA Astrophysics Data System (ADS)

one-dimensional model of the Martian ionosphere is used to explore the importance of atomic and molecular hydrogen chemistry in the upper atmosphere and ionosphere. Neutral and ionized H and H2 undergo chemical reactions that lead to the production of the hydrogenated ions: H+, H2+, H3+, OH+, HCO+, ArH+, N2H+, HCO2+, and HOC+. Simulations are conducted for the cases of photochemistry only and photochemistry coupled with transport in order to asses the separate effects of plasma diffusion in the topside ionosphere. For both of these cases, the sensitivity of the ionosphere is tested for (1) molecular hydrogen abundance and (2) reaction rate, k1, for the charge exchange between H+ and H2. Results are reported for midday solar minimum conditions. We find that the ionospheric composition of Mars is sensitive to H2 abundance, but relatively insensitive to the reaction rate, k1. Depending on the conditions simulated, the topside ionosphere can contain appreciable amounts of hydrogenated species such as H3+, OH+, and HCO+. Comparisons are made with Viking ion density measurements as well as with results of other published Mars ionospheric models. Future comparisons with more extensive ion composition will be available when the Mars Atmosphere and Volatile Evolution mission arrives at Mars.

Matta, Majd; Withers, Paul; Mendillo, Michael

2013-05-01

20

Ionospheric Superstorms and Their Effects on Gnss  

NASA Astrophysics Data System (ADS)

The most prominent ionospheric effects produced by intense geomagnetic storms at middle and low-latitudes, such as the dayside ionosphere uplift and anomalously strong TEC increase within the crests of the equatorial ionization anomaly (EIA), were recorded during only a few geomagnetic storms during 2000-2006. Based on observations of ionosphere TEC response to more than 15 geomagnetic storms, we found that combination of intensive dawn-to-dusk electric field and southward IMF Bz seems to be the decisive factor for development of the ionosphere super-storm effects. The main purpose of this study is to extend study of ionosphere superstorms 1995-2006 and to make comparative analysis of ionosphere effects of geomagnetic storms on the operation quality of GPS, since it is known that the Earth's ionosphere changes the phase and amplitude of propagating radio signals. These effects have negative influence on performance of satellite and navigation systems. The Global GPS Network is a set of precise GPS receivers, nowadays widely used for a variety of scientific and real-time applications. GPS measures the group and phase delays of signals, which are proportional to the ionosphere total electron content (TEC) along the path between a satellite and a receiver. The GPS frequency is high enough (more than 1 GHz) for signals not to be affected by the medium, so the system is considered as highly reliable and practi-cally invulnerable. However, recent studies showed that significant errors and failures in the performance of GPS system occur during geomagnetic storms and during large solar flares. For our analysis we selected events that occurred in 1995-2006 and with drop of IMF Bz below 12-15 nT that lasted no less than 3 hours and which consequently led to decrease of Dst index to 120-150 nT. We estimate the quality of GPS functioning from the following parameters: 1) counts omissions in the GPS RINEX files, 2) GPS phase slips estimated from L1 and L2 phase measurements, when TEC derivation exceeds 5 TECU/min, 3) positioning accuracy of GPS receivers. According to the preliminary results, the maximum number of counts' omissions and phase slips corresponds to the events that can be classified as ionospheric storms, i.e. with prominent changes in the ionosphere such as ionosphere dayside uplift and super-fountain effect.

Astafyeva, Elvira; Tatarinov, Pavel; Demyanov, Vyacheslav; Mandea, Mioara; Lognonne, Philippe

21

Ionosphere.  

National Technical Information Service (NTIS)

Significant new studies of the ionosphere have occurred very recently. One line of research has involved precise measurements of the arctic and antarctic ionosphere (in the high latitudes). As a result, new models of the ionosphere based on changes in tim...

G. J. Gassmann

1972-01-01

22

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

23

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

24

Equatorial ionosphere 'fountain- effect' above imminent earthquake epicenter  

NASA Astrophysics Data System (ADS)

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

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

2003-04-01

25

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

26

Ionospheric Effect on a GNSS Radio Occultation Climate Data Record  

Microsoft Academic Search

Radio occultation (RO) is widely considered to be an observation technique that is particularly well suited for establishing a long-term stable global climate record of density, temperature and bending angle profiles in the 8-30 km height range of the atmosphere. To measure profiles in this height range the ionospheric effect on the RO signals must be eliminated. This ionospheric correction

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

2008-01-01

27

The orientation of Titan's dayside ionosphere and its effects on Titan's plasma interaction  

NASA Astrophysics Data System (ADS)

A hybrid particle code has been used to examine how Titan's interaction with Saturn's magnetosphere is effected by the orientation of the dayside ionosphere with respect to the incident magnetospheric flow. The hybrid code self-consistently includes a version of Titan's ionosphere represented by 7 generic ion species, over 40 ion-neutral chemical reactions, ion-neutral collisions and Hall and Pederson conductivities. Emphasis is placed on what effects the orientation angle has on the ion loss rates, ion densities, and the electric and magnetic fields. The results are analyzed and regardless of the orientation angle the ionosphere is found to be within photochemical equilibrium below 1200 km altitude. The ion loss rates and field structures also show little dependence on the orientation of the dayside ionosphere. It is found to first order illumination angle does not have a significant effect on these features of the Titan interaction.

Ledvina, S. A.; Brecht, S. H.; Cravens, T. E.

2012-02-01

28

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

NASA Technical Reports Server (NTRS)

On the basis of in situ measurements of solar EUV flux, an investigation is conducted on the extent of EUV-contributed Venus dayside condition modulation as found in the Pioneer Venus Orbiter's Langmuir probe experiment. In addition, a novel method for Venus EUV flux measurement is introduced which relies on the Langmuir probe sensor's photoelectron emission in regions far above the ionosphere. It is found that while EUV flux strongly affects ionospheric number density, its electron temperature effects are minor. An examination of the role of ionospheric magnetic fields in dayside condition modulation shows that large scale horizontal field presence or absence has no effect on electron number density or temperature at these altitudes, due to the collision domination of ions and the fact that vertical diffusive transport is unimpeded by magnetic fields of the observed magnitudes.

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

1984-01-01

29

On spatial scales of seismo-ionospheric effects  

NASA Astrophysics Data System (ADS)

In the present work disturbances of the ionisation intensity in the E- and F-layers of the ionosphere a few days before earthquakes are investigated using data observed by ionospheric sounding stations in Japan, on Kamchatka, and of Middle Asia. Earthquakes with magnitudes M > 5 and depths H < 80 km are considered. The seismo-ionospheric effects are distinguished from seasonal, geomagnetic, 11-years, and 27-days Solar variations of the ionosphere. Days with high Solar and geomagnetic disturbances are excluded from the analysis. To reveal the statistical seismo-ionospheric effects, the superimposed epoches method is applied. It is shown that an earthquake precursor may be observed for seismic shocks with magnitudes M > 5, when the ionospheric station is situated at a distance from the seismic event not larger than the Dobrovolsky radius R = exp(M) km. It seems that the seismo-ionospheric effects are caused by the Earth crust near the station, and not by processes in the epicenter of the upcoming earthquake.

Liperovskaya, Elena V.; Meister, Claudia-Veronika; Hoffmann, Dieter H. H.; Silina, Alexandra S.

2014-05-01

30

Ionospheric Effects Symposium (IES), 2008. 12th International Ionospheric Effects Symposium, held May 13-15, 2008 in Alexandria, VA.  

National Technical Information Service (NTIS)

The 12th International Ionospheric Effects Symposium (IES2008) was held At the Crowne Plaza Hotel, Old Town, Alexandria, Virginia, May 13-15, 2008. There were approximately 150 papers and posters accepted. Papers that were presented verbally are included ...

D. Byers J. M. Goodman R. McCoy

2008-01-01

31

Effects of UGTs on the ionosphere  

NASA Astrophysics Data System (ADS)

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

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

32

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

33

Driving the TING model with GAIM electron densities: Ionospheric effects on the thermosphere  

NASA Astrophysics Data System (ADS)

In order to study the effects of ionospheric plasma densities on the thermosphere, the electron and O+ densities in the Thermosphere Ionosphere Nested Grid (TING) model were replaced by electron densities from the Global Assimilation of Ionospheric Measurements (GAIM) model at pressure level z = 0 (about 210 ˜ 230 km altitude) and above. This GAIM-derived TING model (G-TING) was then run for the period 1-4 April 2004. The TING model was also run as a stand-alone coupled model (S-TING), without using the GAIM electron densities, for the same period. The resulting thermospheric responses from the two simulations were compared at around the F region peak altitude. There was an extended quiet period during this interval followed by a moderate geomagnetic storm (Kp ˜ 6.0). The ingestion of the GAIM electron densities had little effect on the neutral temperature and composition during the quiet period before the storm, but there were noticeable global effects on the neutral winds, mainly as a result of changes in the ion drag force. During disturbed periods, changed electron densities produced much more significant effects on the global thermosphere. The increased auroral electron densities enhanced the Joule heating rate, in addition to the ion drag, which resulted in significant global changes not only in the neutral winds, but also in the neutral temperature and composition. The results of our study confirm that having correct ionospheric plasma densities is critical to accurately predicting the thermosphere in the coupled thermosphere-ionosphere model.

Jee, G.; Burns, A. G.; Wang, W.; Solomon, S. C.; Schunk, R. W.; Scherliess, L.; Thompson, D. C.; Sojka, J. J.; Zhu, L.

2008-03-01

34

Ionospheric scintillation effects on single frequency GPS  

Microsoft Academic Search

Ionospheric scintillation of Global Positioning System (GPS) signals threatens navigation and military operations by degrading performance or making GPS unavailable. Scintillation is particularly active within, although not limited to, a belt encircling the Earth within 20 degrees of the geomagnetic equator. As GPS applications and users increase, so does the potential for degraded precision and availability from scintillation. We examined

R. A. Steenburgh; C. G. Smithtro; K. M. Groves

2008-01-01

35

Lower Atmosphere Wave Effects on Ionospheric Variability  

NASA Astrophysics Data System (ADS)

The Ionosphere-Thermosphere-Mesosphere (ITM) region is highly variable and has a complex system of drivers including variable solar radiation, geomagnetic activity, and forcing from the lower atmosphere. While magnetospheric forcing dominates the variability at high latitudes in the ionosphere and thermosphere, photochemistry and neutral dynamics play dominant roles in the ITM structure and variability at mid and low latitudes. Waves that originate in the troposphere grow in amplitude as they travel upwards into decreasing density at higher altitudes where they become the most prominent dynamical features of the ITM. The winddriven E-region dynamo generates large-scale electric fields, causing upward plasma drifts that combine with pressure forces and gravity to form the equatorial ionization anomaly in electron density. As a result, variability in E-region winds could translate upwards into the low-latitude ionosphere. The dominant dynamical feature in the E-region is the diurnal tide, and its seasonal, interannual, and daily variability are important factors in understanding the behavior of the ionosphere. The momentum deposition from upward propagating waves is thought to generate the quasibiennial oscillation (QBO) and semiannual oscillation (SAO) in the zonal circulation of the stratosphere and mesosphere. These zonal wind oscillations, in turn, modulate the waves as they propagate upwards, including the migrating and nonmigrating tides. Understanding the behavior of the tides is not only crucial to characterizing mesopause variability but also transport in the region. Momentum deposition by the diurnal tide at low latitudes in the lower thermosphere produces indirect circulations that will transport neutral and ionized constituents both vertically and horizontally to higher latitudes. Recent global observations of the low latitude neutral atmospheric and ionospheric structure revealed by TIMED/SABER, TIMED/GUVI, TOPEX, JASON, COSMIC/FORMOSAT and DMSP allow us to investigate the interplay between the neutral, plasma, and background fields. In this talk we examine the relationship between the variability observed in mesospheric and lower thermospheric dynamical fields to variations observed in the low latitude ionosphere using these long-term global satellite observations.

Talaat, Elsayed; Yee, Jeng-Hwa; Paxton, Larry, , Dr; Demajistre, Robert; Christensen, Andrew; Mlynczak, M. G.; Russell, J. M., III; Zhu, Xun; Sotirelis, Thomas; Kil, Hyosub

36

Effect of Lunar Eclipse on the Ionosphere  

Microsoft Academic Search

FOR some time we have been studying the variation of height of the different layers of the ionosphere at different hours of the day and night by the well-known group-retardation method. The technique of Breit and Tuve1, with the later improvements suggested by Appleton and Builder2, has been adopted for emitting short radio pulses from an aerial system of half-wave

S. S. Banerjee; B. N. Singh

1936-01-01

37

Effects of Nuclear Explosions on the Ionosphere  

Microsoft Academic Search

DURING October 30, 1961, some unusual phenomena occurred in the F-layer of the ionosphere over Lindau\\/Harz which may be ascribed to the explosion of the 50-megaton TNT nuclear bomb at 08 h. 33 m. 33 s. U.T. over Novaya Zemlya. Between the ½-hr. observations at 10 h. 00 m. and 10 h. 30 m. U.T. the critical frequency of the

Walter Dieminger; Harry Kohl

1962-01-01

38

IONOSPHERIC EFFECTS OF HIGH-ALTITUDE NUCLEAR TESTS  

Microsoft Academic Search

Effects of high-altitude U.S. and Russian nuclear explosions in 1962 on ; the phase advances and amplitudes of VLF signals (stations WWVL and NPM) are ; reported and interpreted. The signal fluctuations are correlated with ; ionospheric effects. (T.F.H.);

H. R. Willard; James F. Kenney

1963-01-01

39

Effects of ionospheric conductance in high-latitude phenomena  

NASA Astrophysics Data System (ADS)

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

Benkevitch, Leonid

40

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

Microsoft Academic Search

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

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

2009-01-01

41

Ionospheric modelling for navigation  

NASA Astrophysics Data System (ADS)

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

Aragon Angel, M. A.

42

Physics of natural and HF - induced ionospheric disturbances and their effects on radio communication  

NASA Astrophysics Data System (ADS)

We report a theoretical study of ionospheric disturbances caused by either natural or man-made processes. Thirteen papers published in either technical journals or conference proceedings are compiled in this report, These papers discuss: (1) the identification of the sources of free energy, the optimum conditions for plasma instabilities as the courses of naturally occurring ionospheric irregularities, and (2) the nonlinear effects leading to the HF ionospheric disturbances such as lower hybrid waves, upper hybrid waves, ionospheric irregularities, and geomagnetic field fluctuations.

Lee, M. C.

1985-06-01

43

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

44

Effects of high-latitude drivers on Ionosphere/Thermosphere parameters  

NASA Astrophysics Data System (ADS)

In order to study effects of high-latitude drivers, we compared Ionosphere/Thermosphere (IT) model performance for predicting IT parameters, which were obtained using different models for the high-latitude ionospheric electric potential including Weimer 2005, AMIE (assimilative mapping of ionospheric electrodynamics) and global magnetosphere models (e.g. Space Weather Modeling Framework). For this study, the physical parameters selected are Total Electron Content (TEC) obtained by GPS ground stations, and NmF2 and hmF2 from COSMIC LEO satellites in the selected 5 degree eight longitude sectors. In addition, Ne, Te, Ti, and Tn at about 300 km height from ISRs are considered. We compared the modeled values with the observations for the 2006 AGU storm period and quantified the performance of the models using skill scores. Furthermore, the skill scores are obtained for three latitude regions (low, middle and high latitudes) in order to investigate latitudinal dependence of the models' performance. This study is supported by the Community Coordinated Modeling Center (CCMC) at the Goddard Space Flight Center. The CCMC converted ionosphere drivers from a variety of sources and developed an interpolation tool that can be employed by any modelers for easy driver swapping. Model outputs and observational data used for the study will be permanently posted at the CCMC website (http://ccmc.gsfc.nasa.gov) as a resource for the space science communities to use.

Shim, J.; Kuznetsova, M. M.; Rastaetter, L.; Berrios, D.; Codrescu, M.; Emery, B. A.; Fedrizzi, M.; Foerster, M.; Foster, B. T.; Fuller-Rowell, T. J.; Mannucci, A.; Negrea, C.; Pi, X.; Prokhorov, B. E.; Ridley, A. J.; Coster, A. J.; Goncharenko, L.; Lomidze, L.; Scherliess, L.

2012-12-01

45

Ionospheric effects of the extreme solar activity of February 1986  

NASA Technical Reports Server (NTRS)

During February 1986, near the minimum of the 11 year Solar sunspot cycle, after a long period of totally quiet solar activity (R sub z = 0 on most days in January) a period of a suddenly enhanced solar activity occurred in the minimum between solar cycles 21 and 22. Two proton flares were observed during this period. A few other flares, various phenomena accompanying proton flares, an extremely severe geomagnetic storm and strong disturbances in the Earth's ionosphere were observed in this period of enhanced solar activity. Two active regions appeared on the solar disc. The flares in both active regions were associated with enhancement of solar high energy proton flux which started on 4 February of 0900 UT. Associated with the flares, the magnetic storm with sudden commencement had its onset on 6 February 1312 UT and attained its maximum on 8 February (Kp = 9). The sudden enhancement in solar activity in February 1986 was accompanied by strong disturbances in the Earth's ionosphere, SIDs and ionospheric storm. These events and their effects on the ionosphere are discussed.

Boska, J.; Pancheva, D.

1989-01-01

46

Evaluation of different approaches to modeling the second-order ionospheric delay on GPS measurements  

NASA Astrophysics Data System (ADS)

This work evaluates various approaches to compute the second order ionospheric correction (SOIC) to Global Positioning System (GPS) measurements. When estimating the reference frame using GPS, applying this correction is known to primarily affect the realization of the origin of the Earth's reference frame along the spin axis (Z coordinate). Therefore, the Z translation relative to the International Terrestrial Reference Frame 2008 is used as the metric to evaluate various published approaches to determining the slant total electron content (TEC) for the SOIC: getting the slant TEC from GPS measurements, and using the vertical total electron content (TEC) given by a Global Ionospheric Model (GIM) to transform it to slant TEC via a mapping function. All of these approaches agree to 1 mm if the ionospheric shell height needed in GIM-based approaches is set to 600 km. The commonly used shell height of 450 km introduces an offset of 1 to 2 mm. When the SOIC is not applied, the Z axis translation can be reasonably modeled with a ratio of +0.23 mm/TEC units of the daily median GIM vertical TEC. Also, precise point positioning (PPP) solutions (positions and clocks) determined with and without SOIC differ by less than 1 mm only if they are based upon GPS orbit and clock solutions that have consistently applied or not applied the correction, respectively. Otherwise, deviations of few millimeters in the north component of the PPP solutions can arise due to inconsistencies with the satellite orbit and clock products, and those deviations exhibit a dependency on solar cycle conditions.

Garcia-Fernandez, M.; Desai, S. D.; Butala, M. D.; Komjathy, A.

2013-12-01

47

Effect of horizontal gradients on ionospherically reflected or transionospheric paths using a precise homing-in method  

NASA Astrophysics Data System (ADS)

A homing-in method is presented for determining ionospheric reflected or transionospheric paths between fixed transmitter and receiver locations in the presence of ionospheric gradients or ripples. Both initial elevation and azimuth are automatically adjusted to find the path that arrives exactly at the receiver. The method can be used for any 3D ionospheric model to find precise ray paths and phase and group delays for both magneto-ionic modes. The method takes full account of path location, geomagnetic field orientation and the bending of the ray path resulting from horizontal as well as vertical gradients of electron density. It can also find multiple paths e.g. low and high angle, 1- and 2-hops for both ordinary and extraordinary modes. Examples of its use are given for both terrestrial HF links and Earth to Satellite paths. For paths reflected from the ionosphere, the effect of gradients of both critical frequency and height of maximum electron density are determined and the comparative effect of gradients on high and low angle and 1- and 2-hops paths for both magneto-ionic modes investigated. Path variation with frequency for a fixed link is also studied and the bandwidth of the ionospheric background channel (dispersive bandwidth) and its reciprocal (the pulse rise time), important for wideband digital HF broadcasting or spread spectrum HF communications, is estimated for a range of frequencies, for high- and low-angle rays and 1- and 2-hop paths. For Earth-satellite paths, the effect of the ionosphere and horizontal ionospheric gradients is determined for a range of frequencies and elevation angles. It is shown that the method can also enable the determination of second-order errors in satellite navigation methods, such as GPS, due to ionospheric gradients and the effect of the geomagnetic field.

Strangeways, H. J.

2000-10-01

48

High-order stimulated ionospheric diffuse plasma resonances - Significance for magnetospheric emissions  

NASA Technical Reports Server (NTRS)

The paper presents Alouette 2/ISIS 1 data which furnish evidence for the stimulation of high-order D(n) resonances (n greater than 4) by topside sounders, confirming the prediction of Osherovich (1990) based on an analogy with naturally occurring narrowband magnetospheric emissions. The results indicate that observations of stimulated ionospheric emissions and naturally occurring magnetospheric emissions can be used as complementary data sets to address such fundamental questions as the nature of the excitation mechanism for these emissions and the nature of the waves (i.e., whether the waves predominantly electrostatic or with a significant magnetic component present), and the question of the dominance among the Dn, Dn(+), and Dn(-) resonances and the conditions required for all three to be present at the same time.

Benson, Robert F.; Osherovich, Vladimir A.

1992-01-01

49

High-order stimulated ionospheric diffuse plasma resonances - Significance for magnetospheric emissions  

NASA Astrophysics Data System (ADS)

The paper presents Alouette 2/ISIS 1 data which furnish evidence for the stimulation of high-order D(n) resonances (n greater than 4) by topside sounders, confirming the prediction of Osherovich (1990) based on an analogy with naturally occurring narrowband magnetospheric emissions. The results indicate that observations of stimulated ionospheric emissions and naturally occurring magnetospheric emissions can be used as complementary data sets to address such fundamental questions as the nature of the excitation mechanism for these emissions and the nature of the waves (i.e., whether the waves predominantly electrostatic or with a significant magnetic component present), and the question of the dominance among the Dn, Dn(+), and Dn(-) resonances and the conditions required for all three to be present at the same time.

Benson, Robert F.; Osherovich, Vladimir A.

1992-12-01

50

Lower Atmosphere Effects on Thermospheric and Ionospheric Variability  

NASA Astrophysics Data System (ADS)

The Ionosphere-Thermosphere-Mesosphere (ITM) region is highly variable and has a complex system of drivers including variable solar radiation, geomagnetic activity, and forcing from the lower atmosphere. Waves that originate in the troposphere grow in amplitude as they travel upwards into decreasing density at higher altitudes where they become the most prominent dynamical features of the ITM. Planetary and gravity waves modify the zonal mean temperature and winds through dissipation and momentum deposition. The effects of these waves on the ITM are expected to depend on the level of solar activity. For all types of waves, how high they penetrate into the thermosphere depends on the temperature, wind, and viscosity profiles. Current observations have shown signatures of both gravity waves and planetary waves in upper atmospheric measurements of winds, temperature, and ion density. The momentum deposition from upward propagating waves is thought to generate the quasibiennial oscillation (QBO) and semiannual oscillation (SAO) in the zonal circulation of the stratosphere and mesosphere. These zonal wind oscillations, in turn, modulate the waves as they propagate upwards, including the migrating and nonmigrating tides. Understanding the behavior of the tides is not only crucial to characterizing mesopause variability but also transport in the region. Momentum deposition by the diurnal tide at low latitudes in the lower thermosphere produces indirect circulations that will transport neutral and ionized constituents both vertically and horizontally to higher latitudes. While magnetospheric forcing dominates the variability at high latitudes in the ionosphere and thermosphere, photochemistry and neutral dynamics play dominant roles in the ITM structure and variability at mid and low latitudes. The wind-driven E-region dynamo generates large-scale electric fields, causing upward plasma drifts that combine with pressure forces and gravity to form the equatorial ionization anomaly in electron density. As a result, variability in E-region winds could translate upwards into the low-latitude ionosphere. The dominant dynamical feature in the E-region is the diurnal tide, and its seasonal, interannual, and daily variability are important factors in understanding the behavior of the ionosphere. Recent global observations of the low latitude neutral atmospheric and ionospheric structure revealed by TIMED/SABER, TIMED/GUVI, TOPEX, JASON, and DMSP allow us to investigate the interplay between the neutral, plasma, and background fields. In this talk we examine the relationship between the variability observed in mesospheric and lower thermospheric dynamical fields to variations observed in the low latitude ionosphere using these long-term global satellite observations.

Talaat, E. R.; Yee, J.; Paxton, L.; Demajistre, R.; Christensen, A.; Russell, J.; Mlynczak, M.; Zhu, X.; Sotirelis, T.; Smith, D.

2006-05-01

51

Simulation of PPEF effects in dayside low-latitude ionosphere for the October 30, 2003, Superstorm  

NASA Astrophysics Data System (ADS)

One of the important signatures during strong magnetic storms is prompt penetrating electric fields (PPEFs) into the ionosphere, which causes the dayside ionospheric superfountain (DIS). Interplanetary-ionosphere coupling for the October 30, 2003, superstorm is analyzed by using ACE and ground-based measurements. The relationships between the interplanetary magnetic field Bz component, ionospheric vertical velocities above Jicamarca, and horizontal magnetic field components measured at Huancayo are presented. DIS is associated with uplift, displacement, and enhancement of the equatorial ionospheric anomalies. We apply an extended SAMI-2 ionospheric model to simulate DIS effects above Jicamarca for this superstorm. An agreement between our results and observed ƒ0F2 during the main phase of the storm is reported. It is shown that the PPEF approach and corresponding modeling results capture the main physics of the dayside low-latitude ionospheric response during the first couple hours of the magnetic superstorm.

Verkhoglyadova, Olga P.; Tsurutani, Bruce T.; Mannucci, Anthony J.; Saito, Akinori; Araki, Tohru; Anderson, David; Abdu, M.; Sobral, J. H. A.

52

On the principal factors that determine ionospheric superstorms effects  

NASA Astrophysics Data System (ADS)

Ionosphere response to geomagnetic storms, known as ionospheric storms, is a very interesting geophysical event. The most prominent effects produced by intense geomagnetic storms at middle and low-latitudes is dayside ionosphere uplift with concurrent movements of the equatorial ionization anomaly (EIA) crests and anomalously strong TEC increase within the crests of the EIA. However, such significant dayside ionosphere changes were observed during only a few geomagnetic storms for the previous solar cycle. In connection with that, a very interesting question has been opened: what are the most important reasons for the drastic ionosphere changes to be developed and whether there is a "preferred" geographic longitude for the formation and occurrence of ionosphere superstorm effects? It is known that the primary cause of geomagnetic storms and the dayside ionosphere uplift are dawn-to-dusk electric fields associated with the passage of southward directed IMF Bz. Generally speaking, the electric field is composed of two factors: the solar wind velocity and the southward IMF. It has been empirically shown that intense storms with a peak Dst<-100 nT are primarily caused by large Bz<-10 nT with duration greater than 3 hours (Gonzalez and Tsurutani, Planetary and Space Science, 35, 9, 1987). In addition, the electric fields seem to be modulated by the solar wind ram pressure, so that solar wind density, besides Bz IMF and solar wind velocity, plays an important role in the ring current intensification. For this study, from geomagnetic storms that occurred in 2000-2005, we selected those with sharp decrease of IMF Bz below -12-15 nT of duration about 3 hours and with the consequent drop of Dst index to no more than -120-150 nT. The selected 18 events vary in season by their occurrence and in time by a storm onset, so we can analyze seasonal and longitudinal features of TEC response to geomagnetic storms and discuss possible reasons for the observed difference in TEC response to geomagnetic storms. We used data of the CHAMP and SAC-C satellites along with data of satellite altimeters TOPEX and Jason-1. As a result, we obtained 3-dimensional visualization of the ionosphere plasma redistribution during strong geomagnetic storms and good possibility to study in detail the dayside "super-fountain effect" (SFE). We observed severe enhancements of the equatorial TEC (up to 50-60%) with concurrent traveling of the EIA crests for a distance up to 15° of latitude during the "Halloween storms" of 29-31 October 2003 and during intense geomagnetic storms of 21 October 2001, 6 November 2001, 7-8 September 2002 and 20 November 2003. These events were accompanied by increase of TEC above 715 km 2-3 times compared to quiet-time TEC level. Large enhancements in the equatorial and mid-latitude TEC were observed also during events of 30-31 March 2001, 19-20 April 2002 and 7-8 November 2004. However, TEC response to the other of the selected events was not so well pronounced: generally, we observed formation of the dual-peak EIA structure with concurrent increase of the near-equatorial TEC up to 80 TECU. However, the peaks did not travel far from each other, i.e. were located within their normal position.

Astafyeva, E.; Tatarinov, P.

2009-04-01

53

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

54

Proceedings of the workshop on ionospheric and magnetospheric effects of Satellite Power Systems (SPS)  

Microsoft Academic Search

The Workshop on Ionospheric and Magnetospheric Effects of Satellite Power Systems (SPS) was one of four workshops designed to provide guidance in the formation of a program to assess possible atmospheric effects of an SPS. The scope of the workshop was limited to atmospheric effects originating from the release of rocket propellant emissions into the ionosphere and magnetosphere. Atmospheric effects

Rote

1979-01-01

55

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

NASA Technical Reports Server (NTRS)

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

Smith, Ernest K.; Flock, Warren L.

1993-01-01

56

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

NASA Astrophysics Data System (ADS)

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

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

1993-02-01

57

Effects of ionospheric oxygen on magnetospheric structure and dynamics  

NASA Astrophysics Data System (ADS)

During geomagnetically active times, ionospheric O + can contribute a significant fraction of the magnetospheric mass and energy densities. The global response of Earth's magnetosphere to the presence of ionospheric oxygen is still largely unknown and impossible to examine fully with in situ, single point satellite measurements. Global magnetohydrodynamic (MHD) models provide a picture of this large-scale response to ionospheric outflow. The goal of this dissertation is to examine the behavior and effects of outflowing oxygen in a multi-fluid MHD model by determining (1) how O+ outflow from different regions of the ionosphere contributes to plasma sheet populations and (2) the effect of these oxygen populations on convection and global magnetospheric structure. I implement two empirical outflow models at the inner boundary of the recently-developed Multi-Fluid Lyon-Fedder-Mobarry MHD code and examine the response of the model to various outflow conditions. A model based on data from the Akebono spacecraft (Ebihara et al., 2006) provides a low-energy polar and auroral region outflow, whereas a model based on data from the FAST spacecraft (Strangeway et al., 2005) provides higher-energy outflow confined to the auroral regions. Using the Akebono model outflow, I show that both centrifugal acceleration and pressure gradients accelerate thermal O+ along the magnetic field into the plasma sheet and downtail into the solar wind. I examine O+ and H + plasma sheet populations for different outflow and solar wind conditions. To account for observed densities, nightside outflows must be augmented by polar wind, cusp outflows, or both. O+ outflow in general, and nightside outflow in particular, loads the plasma sheet with O +, inflating the plasma sheet, increasing the width of the tail and distance to the tail x-line, and reducing cross polar cap potential (CPCP). These effects are shown to relate to the width of the magnetosheath, indicating that the reduction in CPCP may be due to changes in the bow shock and magnetosheath that divert the solar wind around the magnetosphere. Finally, I show that during a realistic substorm simulation, the timing and strength of substorms are changed by a global O+ outflow.

Garcia-Sage, Katherine

58

Ionospheric and magnetospheric effects of the solar eclipse in northeastern Russia  

Microsoft Academic Search

In the given report results of complex radiophysical experimental measurements magnetospheric and ionospheric effects of a solar eclipse in northeast of Russia (March, 1988 and June, 1990) are considered. For research materials of ground vertical sounding, data about a condition of a magnetic field and record of signals radio stations are used. It is established, that reaction of an ionosphere

Igor N. Poddelsky; Aleksey I. Poddelsky

2009-01-01

59

Ionospheric space weather effects monitored by simultaneous ground and space based GNSS signals  

Microsoft Academic Search

Ionospheric space weather effects can degrade the performance of global navigation satellite systems (GNSS), i.e. their accuracy, reliability and availability. However, well established ground based and innovative space based GNSS measurements offer the unique chance for a permanent monitoring of the electron density structure of the global ionosphere–plasmasphere system. In this paper we review various types of perturbations in the

N. Jakowski; V. Wilken; S. Schlueter; S. M. Stankov; S. Heise

2005-01-01

60

Some ionospheric storm effects at equatorial and low latitudes  

NASA Astrophysics Data System (ADS)

In this paper, the response of the equatorial and low latitude ionosphere to three intense geomagnetic storms occurred in 2002 and 2003 is reported. For that, critical frequency of F2-layer foF2 and the peak height hmF2 hmF2 for the stations Jicamarca (11.9°S), Ascension Is (7.92°S) and Tucuman (26.9°S) are used. The results show a "smoothing" of the Equatorial Anomaly structure during the development of the storms. Noticeable features are the increases in foF2 before the storm sudden commencement (SC) at equatorial latitudes and the southern crest of the Equatorial Anomaly. In some cases nearly simultaneous increases in foF2 are observed in response to the storm, which are attributed to the prompt electric field. Also, positive effects observed at equatorial and low latitudes during the development of the storm seem to be caused by the disturbance dynamo electric field due to the storm-time circulation. Increases in foF2 above the equator and simultaneous decreases in foF2 at the south crest near to the end of a long-duration main phase are attributed to equatorward-directed meridional winds. Decreases in foF2 observed during the recovery phase of storms are believed to be caused by composition changes. The results indicate that the prompt penetration electric field on the EA is important but their effect is of short lived. More significant ionospheric effects are the produced by the disturbance dynamo electric field. The role of storm-time winds is important because they modify the "fountain effect" and transport the composition changes toward low latitudes.

Mansilla, Gustavo A.

2014-05-01

61

Geomagnetic field effect on the ionospheric contribution to the error of navigation satellite systems  

NASA Astrophysics Data System (ADS)

When using global navigation satellite systems (GNSSs) for high-precision measurements, one should consider high-order errors. The ionospheric second-order error caused by the geomagnetic field is approximately proportional to the total electron content. Therefore, this error can be taken into account by modifying the coefficients in an "ionosphere-free" combination of GNSS measurements at two frequencies. This study checks the approximations underlying this modification. We reveal that these approximations are valid and the results depend weakly on the accuracy of ionospheric parameters used a priori for calculating the coefficients of the modified two-frequency formula. In addition, we investigate how the choice of a model of the Earth's magnetic field affects the second-order ionospheric error.

Tinin, M. V.; Konetskaya, E. V.

2013-11-01

62

Comparison of space weather effects and tectonic activity effects on the ionosphere and levels of their predictability.  

NASA Astrophysics Data System (ADS)

Space weather produces profound effects on the ionosphere at the all levels (from D-region up to the palsmasphere). Except the electron concentration redistribution (what is most often discussed in the literature) we deal with the changes of ion composition, heating of the ionosphere what leads to the scale height vertical profile modification. Serious problems of these effects which have many space and terrestrial technological systems put forward the problem of space weather effects predictability the quality of which in the present moment is not high in different models. Recent years presented the reliable proofs that tectonic activity may produce the local effects within the ionosphere, but their order of magnitude can be the same as during geomagnetic storms, and sometimes even higher. It means that technological systems are prone to the degradation of their quality during disturbed periods. This paper tries to present the comparison of both types of disturbances in terms of their temporal, spatial and dynamic characteristics and to analyze the probability of their forecast.

Pulinets, Sergey; Davidenko, Dmitry

2014-05-01

63

Effects of upward propagating atmospheric waves on day-to-day variations in the upper atmosphere by using an atmosphere-ionosphere coupled model  

NASA Astrophysics Data System (ADS)

Recent observational and modeling studies have revealed that the energy input from the lower atmosphere produces significant spatial and temporal variations in the thermosphere/ionosphere. For example, the CHAMP observation has shown that the distributions of the neutral temper-ature and electron density in the equatorial thermosphere/ionosphere have wave-4 pattern in the longitudinal direction. This wave-4 pattern is considered to originate from non-migrating diurnal tide (DE3) that is excited in the troposphere. However, the physical mechanism of spatial and temporal variations in the thermosphere/ionosphere caused by upward propagating atmospheric waves is not fully understood. In order to investigate the physical mechanism of these variations, we developed an atmosphere-ionosphere coupled model, in which a whole at-mosphere general circulation model (GCM), an ionosphere model and an electrodynamics model are integrated. The whole atmosphere GCM contains the region from the ground surface to the upper thermosphere, so that we can simulate excitation of tides in the lower atmosphere and their upward propagation to the thermosphere. By using the coupled model, we examine effects of tides and Kelvin waves from the lower atmosphere on the variations in the thermo-sphere/ionosphere. Our results show that day-to-day variations in the thermosphere/ionosphere are caused by day-to-day variations of these upward propagating waves. We also discuss further development of the coupled model in the near future.

Miyoshi, Yasunobu; Hidekatsu, Jin; Fujiwara, Hitoshi; Shinagawa, Hiroyuki

64

Foreword: Ionospheric effects on communication and related systems (IES)  

NASA Astrophysics Data System (ADS)

The special section contained in this issue of Radio Science is the second of two which have been developed from papers presented at the 1987 symposium on the Effect of the Ionosphere on Communication, Navigation, and Surveillance Systems (IES 1987). This technical conference was jointly sponsored by the Naval Research Laboratory (NRL), the Office of Naval Research (ONR), the Air Force Geophysics Laboratory (AFGL), and the Army Communications-Electronics Command (USACECOM). The symposium was held in Springfield, Virginia on May 5-7, 1987 in cooperation with the Defense Nuclear Agency (DNA), the Naval Ocean Systems Center (NOSC), the Institute for Telecommunication Sciences (ITS), and the Voice of America (VOA). See the May-June 1988 issue of Radio Science for a more complete foreword (Radio Sci., 23, 209, 1988).

Goodman, John M.; Klobuchar, John A.; Soicher, Haim

1988-07-01

65

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

66

Ionospheric physics  

SciTech Connect

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

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

1991-01-01

67

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

68

Ionospheric correction for Seasat altimeter height measurement  

NASA Technical Reports Server (NTRS)

Descriptions are given of the Faraday rotation technique used by Seasat to measure the ionosphere and the scheme employed in mapping the measurements to the spacecraft location, exploiting the fact that the effect of the ionosphere on signal speed, and therefore on Seasat radar altimeter measurements, is directly proportional to the columnar electron content of the ionosphere. The altimeter ionosphere correction is evaluated through comparison with independent methods, and it is demonstrated that the correction, whose total value can be on the order of 20 cm, is accurate to the 3-5 cm level.

Lorell, J.; Colquitt, E.; Anderle, R. J.

1982-01-01

69

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

NASA Technical Reports Server (NTRS)

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

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

1984-01-01

70

Studies of Ionospheric Structures and Their Effects on Systems.  

National Technical Information Service (NTIS)

This is a comprehensive investigation of the basic ionospheric processes which produce plasma density structuring. The emphasis of the research efforts was on understanding the formation and evolution of large-scale structures and the embedded km-scale ir...

C. E. Valladares M. P. Hagan R. Sheehan E. MacKenzie

2002-01-01

71

Space Weather Topics at Ionospheric Effects Symposium 2008  

NASA Astrophysics Data System (ADS)

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

Goodman, John

2008-08-01

72

The effect of longitudinal conductance variations on the ionospheric prompt penetration electric fields  

NASA Astrophysics Data System (ADS)

Ionospheric prompt penetration electric fields of magnetospheric origin, together with the atmospheric disturbance dynamo, represent the most important parameters controlling the storm-time dynamics of the low and mid-latitude ionosphere. These prompt penetration fields result from the disruption of region-2 field-aligned shielding currents during geomagnetically disturbed conditions. Penetration electric fields con- trol, to a large extent, the generation and development of equatorial spread-F plasma instabilities as well as other dynamic space weather phenomena in the ionosphere equatorward of the auroral zone. While modeling studies typically agree with average patterns of prompt penetration fields, experimental results suggest that longitudinal variations of the ionospheric con- ductivities play a non-negligible role in controlling spread-F phenomena, an effect that has not previously been modeled. We present first results of modeling prompt pene- tration electric fields using a version of the Rice Convection Model (RCM) that allows for longitudinal variations in the ionospheric conductance tensor. The RCM is a first- principles numerical ionosphere-magnetosphere coupling model that solves for the electric fields, field-aligned currents, and particle distributions in the ionosphere and inner/middle magnetosphere. We compare these new theoretical results with electric field observations.

Sazykin, S.; Wolf, R.; Spiro, R.; Fejer, B.

73

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

74

The High-Latitude Ionosphere and Its Effects on Radio Propagation  

NASA Astrophysics Data System (ADS)

The ionosphere is indeed the place where Earth and space come together. Correspondingly, the ionosphere is subject to the details and complexities of both Earth and space. If one is to develop a logical understanding of even a limited portion of the ionosphere, that knowledge will be constructed on a foundation of many facts of nature. Awareness of those facts will in turn be supported by a vast historical array of scientific effort to ascertain the fundamentals of Earth and space that combine to form the ionosphere as we know it. Fortunately for us, R. D. Hunsucker and J. K. Hargreaves have written a book that goes from the Earth up and comes from the Sun down to arrive at a remarkably detailed physical description of the ionosphere and its impact on human activities, especially radio-frequency (RF) communications. The High-Latitude Ionosphere and its Effects on Radio Propagation is a bit of a misnomer, because the book covers many more topics than its title suggests. The authors set the stage by developing a detailed picture of the density, temperature, chemical, neutral, and charge states of the atmosphere-ionosphere system. Basic models of the ionization and recombination processes are presented with supporting mathematics and graphical examples. Concepts such as the Chapman production function are introduced and applied, whereby ionizing solar radiation produces electron-ion pairs. One can then grasp how the so-called D, E, and F layers of the ionosphere are related to the ionization of specific molecular species. Along the way, the authors are careful to introduce the extensive nomenclature of ionospheric descriptors. There is a comfortable relationship of prose, mathematics, and graphical material. Reading this book is a pleasure for the scientifically curious mind.

Moses, Ronald W., Jr.

2004-05-01

75

Ionospheric effects caused by the series of geomagnetic storms of September 9-14, 2005  

NASA Astrophysics Data System (ADS)

This study presents the ionospheric effects caused by the series of geomagnetic storms of September 9-14, 2005. The behavior of different ionospheric parameters over the Yakutsk, Irkutsk, Millstone Hill and Arecibo stations during the considered period have been numerically calculated, using a global self-consistent model of the thermosphere, ionosphere, and protonosphere (GSM TIP) developed at WD IZMI-RAN. The model calculations of disturbances of the ionospheric parameters during storms qualitatively agree with the experimental data at these midlatitude stations. We suggest that the causes of the quantitative differences between the model calculations and the observational data were the use of the 3-hour Kp index of geomagnetic activity and the dipole approximation of geomagnetic field in GSM TIP, with additional contributions from the effects of solar flares which are not considered in GSM TIP.

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

2011-06-01

76

The effects of dynamic ionospheric outflow on the ring current  

NASA Astrophysics Data System (ADS)

The importance of ionospheric O+ on the development of the storm time ring current is recognized but not well understood. The addition of this outflow in global MHD models has the potential to change the magnetic field configuration, particle densities and temperatures, and the convection electric field. This makes including heavy ion outflow in ring current simulations difficult, as this addition cannot be easily decoupled from a host of other changes. This study attempts to overcome this problem by using three coupled models, PWOM, RIM, and BATS-R-US, to drive a ring current model, RAM-SCB. The differences in drivers when outflow is included and is not included are compared to see how outflow changes ring current input. It is found that including this outflow reduces the convection electric field, lowers the plasma sheet number density and temperature, and increases the complexity of the plasma sheet ion composition both temporally and spatially. These changes cause an overall reduction in ring current energy density. Further simulations that attempt to isolate these effects find that the most important change in terms of ring current development is the drop in convection electric field. Local time dependencies of O+ injections are found to be nontrivial as well. Capturing all of these effects requires a whole system, first-principles approach.

Welling, D. T.; Jordanova, V. K.; Zaharia, S. G.; Glocer, A.; Toth, G.

2011-02-01

77

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

78

Geomagnetic effects due to an eclipse-induced low-conductivity ionospheric spot  

NASA Astrophysics Data System (ADS)

The solar eclipse on 11 August 1999 was quite unique due to its totality belt coverage of the territory of central Europe where the facilities for the geophysical monitoring are most dense. Ionospheric and geomagnetic observations during the eclipse allowed us to study the eclipse-induced effects more precisely. A mathematical model based on the classical Ashour-Chapman model is considered to show that the decrease (up to 40%) of the ionospheric total electron content in the region of the totality belt leads finally to geomagnetic disturbances quantitatively dependent on the position of both the quasi-circular spot of the ionospheric conductivity decrease and given geomagnetic observatory location. The model is generalized for the anisotropic ionosphere. The theoretical estimates are compared with observational data from European geomagnetic observatories: Fürstenfeldbruck, Nagycenk, Tihany, and Hurbanovo, the last one being nearby the totality belt.

Hvoždara, M.; Prigancová, A.

2002-12-01

79

Investigating magnetospheric interaction effects on Titan's ionosphere with the Cassini orbiter Ion Neutral Mass Spectrometer, Langmuir Probe and magnetometer observations during targeted flybys  

NASA Astrophysics Data System (ADS)

In the ˜6 years since the Cassini spacecraft went into orbit around Saturn in 2004, roughly a dozen Titan flybys have occurred for which the Ion Neutral Mass Spectrometer (INMS) measured that moon's ionospheric density and composition. For these, and for the majority of the ˜60 close flybys probing to altitudes down to ˜950 km, Langmuir Probe electron densities were also obtained. These were all complemented by Cassini magnetometer observations of the magnetic fields affected by the Titan plasma interaction. Titan's ionosphere was expected to differ from those of other unmagnetized planetary bodies because of significant contributions from particle impact due to its magnetospheric environment. However, previous analyses of these data clearly showed the dominance of the solar photon source, with the possible exception of the nightside. This paper describes the collected ionospheric data obtained in the period between Cassini's Saturn Orbit Insertion in 2004 and 2009, and examines some of their basic characteristics with the goal of searching for magnetospheric influences. These influences might include effects on the altitude profiles of impact ionization by magnetospheric particles at the Titan orbit location, or by locally produced pickup ions freshly created in Titan's upper atmosphere. The effects of forces on the ionosphere associated with both the draped and penetrating external magnetic fields might also be discernable. A number of challenges arise in such investigations given both the observed order of magnitude variations in the magnetospheric particle sources and the unsteadiness of the magnetospheric magnetic field and plasma flows at Titan's (˜20Rs (Saturn Radius)) orbit. Transterminator flow of ionospheric plasma from the dayside may also supply some of the nightside ionosphere, complicating determination of the magnetospheric contribution. Moreover, we are limited by the sparse sampling of the ionosphere during the mission as the Titan interaction also depends on Saturn Local Time as well as possible intrinsic asymmetries and variations of Titan's neutral atmosphere. We use organizations of the data by key coordinate systems of the plasma interaction with Titan's ionosphere to help interpret the observations. The present analysis does not find clear characteristics of the magnetosphere's role in defining Titan's ionosphere. The observations confirm the presence of an ionosphere produced mainly by sunlight, and an absence of expected ionospheric field signatures in the data. Further investigation of the latter, in particular, may benefit from numerical experiments on the inner boundary conditions of 3D models including the plasma interaction and features such as neutral winds.

Luhmann, J. G.; Ulusen, D.; Ledvina, S. A.; Mandt, K.; Magee, B.; Waite, J. H.; Westlake, J.; Cravens, T. E.; Robertson, I.; Edberg, N.; Agren, K.; Wahlund, J.-E.; Ma, Y.-J.; Wei, H.; Russell, C. T.; Dougherty, M. K.

2012-06-01

80

Ionospheric superstorms: Polarization terminator effects in the Atlantic sector  

NASA Astrophysics Data System (ADS)

A combination of the effects of stormtime penetration electric fields, the reduced magnetic field strength in the South Atlantic magnetic anomaly (SAA), and the geographic distortion of the magnetic field in the Atlantic sector influence the characteristics of polarization electric fields which form in the E region conductivity-gradient region at the sunset terminator. These effects lead to a strong localized enhancement of total electron content (TEC) at dusk at low-mid latitudes in the American sector during ionospheric superstorms. The E region electric fields map along field lines to the F region and into the opposite hemisphere. We define the polarization terminator (PT) to be the ensemble of points at a given altitude above the E region for which the shadow height at either end of the magnetic field line equals 100 km. Electric fields associated with polarization charge build-up in the conductivity-gradient region along the PT are directed perpendicular to the magnetic field and increase in magnitude as the PT is approached from the dayside. The configuration of the magnetic field in the Atlantic sector due to the offset of the poles and declination effects near the SAA creates a preferred longitude/Universal Time sector (western Atlantic/21 UT) for the build-up of enhanced disturbance time TEC at lower mid latitudes. During strong storms, DMSP observations reveal that the plasma in the equatorial ionization anomaly (EIA) crests moves westward in lockstep with the PT. Electric fields at the PT sweep up the plasmas of the EIA crests and redistribute it into magnetically-conjugate regions at mid latitudes. This effect is strongest in the western Atlantic sector for northern hemisphere summer conditions.

Foster, J. C.; Erickson, P. J.

2013-10-01

81

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

82

Higher order Josephson effects  

NASA Astrophysics Data System (ADS)

Gaussian linking of superconducting loops containing Josephson junctions with enclosed magnetic fields gives rise to interference shifts in the phase that modulates the current carried through the loop, proportional to the magnitude of the enclosed flux. We generalize these results to higher order linking of a superconducting loop with several magnetic solenoids, and show that there may be interference shifts proportional to the product of two or more fluxes.

Buniy, Roman V.; Kephart, Thomas W.

2010-06-01

83

Solar flare and IMF sector structure effects in the lower ionosphere  

NASA Technical Reports Server (NTRS)

About 1% of all sudden ionospheric disturbances (SIDs) observed at the Panska Ves Observatory (Czechoslovakia), were found to be not of solar-XUV origin. Among them, the very rare SWF events (observed at L = 2.4) of corpuscular origin are the most interesting. The IMF sector structure effects in the midlatitude lower ionosphere are minor in comparison with effects of solar flares, geomagnetic storms, etc. There are two basic types of effects. The first type is a disturbance, best developed in geomagnetic activity, and observed in the night-time ionosphere. It can be interpreted as a response to sector structure related changes of geomagnetic (= magnetospheric) activity. The other type is best developed in the tropospheric vorticity area index and is also observed in the day-time ionosphere in winter. This effect is quietening in the ionosphere as well as troposphere. While the occurrence of the former type is persistent in time, the latter is severely diminished in some periods. All the stratosphere, the 10-mb level temperature and height above Berlin-Tempelhof do not display any observable IMF section structure effect.

Lastovicka, J.

1984-01-01

84

Dayside ionospheric processes and their effect on O+ escape  

NASA Astrophysics Data System (ADS)

It is well known that O+ escape from the ionosphere is a multi-stage process where upwelling thermal (less than 1 eV) O+ ions are energized above escape velocity (10 eV) by various processes above the ionosphere. There has been, however, relatively little investigation of the relative importance of ionospheric processes such as photoionization, convection, motion of the neutral atmosphere, and particle precipitation in determining the magnitude and local time distribution of escaping O+ ions. We use a recently developed large-scale database of upwelling thermal O+ ions observed on the DMSP satellites at 850 km during quiet geomagnetic conditions and the FLIP ionospheric code to investigate the relative importance of these processes in the dayside high latitude ionosphere. Observations have established that the escaping flux of energetic O+ ion outflow associated with the dayside cusp is shifted dawnward from noon where the precipitation of low energy electrons and wave power are at their dayside maxima. The magnitude of the dawnward shift is generally larger than the well-documented, convection-driven, shift in the local time of the cusp as a function of the magnitude and direction of the Y component of the interplanetary magnetic field. Modeling using the FLIP code shows that the dawnward shift is the result of the history of the thermal plasma on magnetic field lines as they rotate into and out of darkness producing a maximum upwelling flux shortly after dawn. The combination of a dawn focused source population and noon focused energization region results in a net dawnward shift in the dayside maximum of escaping energetic O+ during the geomagnetically quiet conditions considered. Our model results also suggest that neutral winds influence the location of the dayside local time maximum of upwelling O+ more than electron precipitation.

(Bill) Peterson, W. K.; Richards, Phil; Redmon, Rob; Andersson, Laila

2012-07-01

85

Investigation of the Ionospheric Fluctuations Caused by Space Weather Effects Using GNSS TEC Measurements  

NASA Astrophysics Data System (ADS)

It is known that GPS radio signals passing through the ionosphere suffer varying degrees of rapid variations of their amplitude and phase - signal scintillations. The scintillations are caused by the presence of wide range of scale size irregularities in the ionosphere. It is very important to estimate scintillation and phase fluctuation effects on GNSS navigation system (GPS/GLONASS) performance and consequently on the precession of the obtained position. Effects of the ionospheric irregularities on the GPS signals can be evaluated by measurements of the differential phase time rate of dual frequency GPS signals. GPS observations carried out at the Arctic IGS (International GNSS Service) stations were used to study the development of TEC fluctuations in the high latitude ionosphere. Standard GPS measurements with 30s sampling rate allow the detection of middle- and large-scale ionospheric irregularities. For detection of ionospheric fluctuations the rate of TEC (ROT, in the unit of TECU/min) at 1 min interval was used. The temporal occurrence of TEC fluctuations is clearly observed in time variations in the dual frequency carrier phase along satellite passes. As a measure of the fluctuation activity level the Rate of TEC Index (ROTI) based on standard deviation of ROT was also used. ROTI was estimated in 10-minute interval. These techniques and IGS data were used to study the occurrence of TEC fluctuations at the northern latitude ionosphere for selected geomagnetic storms occurred at the end of 23rd and beginning of new 24th solar cycles. Results demonstrate that fluctuation activity of GPS signals in the high latitude ionosphere is depended on geomagnetic conditions. Intensity of fluctuations essentially increases during geomagnetic storms. The strongest TEC fluctuations occurred as short time rate of TEC enhancements of a factor of 2-5 relative to the quiet time. During geomagnetic disturbed conditions strong phase fluctuations can register at latitudes low than 65°. GPS observations of the Northern hemisphere were used as a raw data for mapping the irregularities over the North Pole. These maps illustrate the spatial structure of the ionospheric irregularities, so called irregularity oval which position is correlated with the auroral oval. During geomagnetic storms the intensity of the irregularities essentially increases and their location expands toward equator. The study showed that observations of GNSS signal fluctuations activity in the high-latitudinal ionosphere can provide monitoring of the space weather dynamics. This work was supported by the RAS Presidium Program N 22.

Shagimuratov, Irk; Krankowski, Andrzej; Cherniak, Iurii; Ephishov, Ivan; Zakharenkova, Irina; Yakimova, Galina

2013-04-01

86

On the ionosphere calibration in GPS radio occultation measurements  

Microsoft Academic Search

Elimination of the ionospheric contribution to atmospheric delays in GPS radio occultation measurements is a key issue in the retrieval of accurate pressure and temperature profiles above the tropopause. The traditional so-called ``ionosphere-free'' combination of the L1 and L2 phase paths, eliminating the first-order ionospheric effects, is not sufficient because of the nonnegligible bending of the two ray paths. Because

Stig Syndergaard

2000-01-01

87

The worldwide ionospheric data base  

NASA Technical Reports Server (NTRS)

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

Bilitza, Dieter

1989-01-01

88

Simulation of nonlinear effects in ionospheric alfven resonator  

NASA Astrophysics Data System (ADS)

Ionospheric Alfven Resonator (IAR) is the region stretching from the Earth ionosphere to the altitudes of several thousand kilometers. The upper boundary of the IAR corresponds to the strong gradient of Alfven speed at altitude of about several thousand kilometers. IAR affects propagation and absorption of Alfven waves coming from the magnetosphere and is important for magnetosphere-ionosphere coupling. We developed a numerical MHD model of IAR to help with interpretation of data from the future e-POP satellite mission. The model uses dipole coordinates and resolves two dimensions along and across geomagnetic field lines in the meridional plane. Electrons and hydrogen and oxygen ions are represented as cold fluids. In simulation, the IAR eigenmodes (standing shear Alfven waves) are excited by a packet of Alfven waves coming from high altitude. The nonlinear Lorentz force associated with the magnetic field of the IAR oscillations accelerates ions along the geomagnetic field and modifies the plasma density. This force may provide the explanation for the plasma density cavities observed by satellites (Viking, Freja, FAST). In the model, the electrodynamic properties of the medium vary self-consistently in response to the density change, which allows to reproduce self-action of the wave. As the cavity develops, the transverse spatial scale of the IAR oscillations decreases at the regions where the plasma density is nonuniform across the geomagnetic field. This amplifies the wave electric field directed along the geomagnetic field and intensifies the electron acceleration.

Sydorenko, Dmytro; Rankin, Robert; Kabin, Konstantin; Lu, Jianyong

89

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

NASA Technical Reports Server (NTRS)

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

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

1975-01-01

90

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

91

Modeling the Effects of Ionospheric Scintillation on GPS Carrier Phase Tracking  

Microsoft Academic Search

A characterization is given for the behavior of Global Positioning System phase tracking loops in the presence of severe equatorial ionospheric scintillation. The purpose of this work is to develop a simple, general, and realistic scintillation effects model that can be used to improve the scintillation performance of phase tracking loops. The new characterization of scintillation effects proposed herein employs

TODD E. HUMPHREYS; MARK L. PSIAKI; PAUL M. KINTNER

2010-01-01

92

Ionospheric and magnetospheric effects of the solar eclipse in northeastern Russia  

NASA Astrophysics Data System (ADS)

In the given report results of complex radiophysical experimental measurements magnetospheric and ionospheric effects of a solar eclipse in northeast of Russia (March, 1988 and June, 1990) are considered. For research materials of ground vertical sounding, data about a condition of a magnetic field and record of signals radio stations are used. It is established, that reaction of an ionosphere to passage of a lunar shadow is shown in increase minimal and operating heights of reflection of a F-layer (approximately on 20-25 km), reduction of critical frequencies of a F2-layer and in falling concentration of the electron in a maximum of a F- layer (up to 50 % in the maximal phase of an eclipse), usually characteristic for a night ionosphere.

Poddelsky, Igor N.; Poddelsky, Aleksey I.

2009-02-01

93

Effects of a Weak Planetary Field on a Model Venus Ionosphere  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

94

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

95

Effect of TADs on the F-region of Low midlatitude ionosphere during intense geomagnetic storm.  

NASA Astrophysics Data System (ADS)

Effect of TAD's on the F region ionosphere of low-mid latitude ionosphere during three intense storms of20 th Nov,2003(-422nT),30 th Oct 2003(-383nT),07Nov,2004(-373nT)respectively are studued using ionosonde data of Delhi(28ø N 77øE).It has been seen that the electon density profile in the F1 region are greatly influenced by the TAD's presence. Further the pre-existing F1 cusp become better devloped during the passage of TAD's.

Upadhayaya, Arun Kumar; Joshi, Shivani; Singh Dabas, Raj; Das, Rupesh M.; Yadav, Sneha

96

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

97

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

98

Ionospheric disturbance overview  

NASA Technical Reports Server (NTRS)

A program of research and exploratory development was undertaken to assess the potential impact of Satellite Power System operation on the ionosphere. The program relies on the utilization of ground-based ionospheric heating facilities in order to simulate the ionospheric heating that will come from the Satellite Power System. Thus far, the experimental program directed toward assessing telecommunications impacts has received the most attention, and little impact was observed on VLF, LF, and MF operations.

Rush, C. M.

1980-01-01

99

Effects of Proton Precipitation on the Coupled Magnetosphere-Ionosphere-Thermosphere  

NASA Astrophysics Data System (ADS)

The fidelity of simulations of the coupled magnetosphere-ionosphere-thermosphere (CMIT) system is contingent on being able to account for the complex interactions that affect their internal dynamics. To achieve a more complete model of the CMIT system, a causally regulated ion precipitation model has been developed and implemented within the CMIT simulation model that couples the Lyon-Fedder-Mobarry (LFM) global magnetosphere model to the Thermosphere-Ionosphere Electrodynamics General Circulation Model (TIEGCM). MHD variables from LFM are used to determine the distribution and intensity of the number and energy fluxes of ion precipitation. The resulting ion precipitation is then ingested into TIEGCM to determine the effects on the ionosphere-thermosphere. Assuming pitch-angle scattering as the primary mechanism for loss-cone filling and a Maxwellian velocity distribution based on MHD simulation state variables, the precipitating proton number flux is determined by integration of the velocity distribution function over the loss cone; the energy flux is approximated as the average ion energy times the number flux. Precipitation of energetic ions (chiefly protons) from the magnetosphere affects the conductivity of the ionosphere, the electrodynamics of which, in turn, regulates the magnetospheric state. Precipitation of less energetic ions (soft ion precipitation) affects the ionospheric plasma distribution and state, especially in the F region. The implementation of the ion precipitation model in the CMIT simulation is shown to improve the accuracy of the model's predictions and overall performance. For the case study presented here, proton precipitation produces enhancements in the Pedersen conductance in the nightside auroral arc of about 200%, and reduces the cross polar cap potential by 4% and the total field-aligned current flowing into the ionosphere by 12%.

Dunlap-Shohl, W. A.; Zhang, B.; Lotko, W.; Smith, R. H.; Schmitt, P.

2012-12-01

100

The effects of the August 1972 magnetic storms on ionospheric scintillations  

Microsoft Academic Search

A 'worst case' of scintillation activity is presented by the analysis of data of a period of severe magnetic activity, August 3-10, 1972. The effect of the dense ionospheric irregularities produced by these storms on scintillation at high latitudes is viewed as a function of local time and the invariant latitude of the propagation path, as well as magnetic activity.

Jules Aarons; Eileen Martin

1975-01-01

101

Validation of techniques for space based remote sensing of auroral precipitation and its ionospheric effects  

Microsoft Academic Search

Knowledge of the spatial distribution of auroral precipitation and its associated ionospheric effects is important both to scientific studies of the Earth's environment and successful operation of defense and communication systems. Observations with the best spatial and temporal coverage are obtained through remote sensing from space-based platforms. Various techniques have been used, including the detection of visible, ultraviolet and X-ray

R. M. Robinson; R. R. Vondrak

1994-01-01

102

Ionospheric Effects Symposium (IES), 2005, Held in Alexandria, Virginia on May 3-5, 2005.  

National Technical Information Service (NTIS)

The 11th International Ionospheric Effects Symposium (IES2005) was held at the Radison Hotel, Old Town Alexandria, Virginia, May 3-5, 2005. The sponsors were the Office of Naval Research (ONR), the Air Force Office of Scientific Research (AFOSR), the Fede...

D. Byers J. M. Goodman R. McCoy

2005-01-01

103

Ionospheric Effects Symposium, 2002, Held in Alexandria, Virginia on May 7-9, 2002.  

National Technical Information Service (NTIS)

The Tenth International Ionospheric Effects Symposium, IES2002, was held at the Radisson Hotel, Old Town Alexandria, Virginia May 7-9, 2002. Topics at IES2002 were not unlike those at previous symposia, but several special sessions were organized. The spe...

J. M. Goodman

2002-01-01

104

Effects of Ionospheric Trough on the Relationship Between the Ring Current and SAPS  

Microsoft Academic Search

Subauroral polarization streams (SAPS), are usually associated with geomagnetically disturbed times and considered as a manifestation of magnetosphere and ionosphere (M-I) coupling. Previous research results using radar and satellite measurements have revealed many features of the SAPS events. However, the generation mechanism of SAPS is not without dispute. In this paper, we focus on the effects of subauroral trough conductance

Y. Zheng; P. C. Brandt; A. T. Lui; M. Fok

2007-01-01

105

Geomagnetic effects due to an eclipse-induced low-conductivity ionospheric spot  

Microsoft Academic Search

The solar eclipse on 11 August 1999 was quite unique due to its totality belt coverage of the territory of central Europe where the facilities for the geophysical monitoring are most dense. Ionospheric and geomagnetic observations during the eclipse allowed us to study the eclipse-induced effects more precisely. A mathematical model based on the classical Ashour-Chapman model is considered to

M. Hvozdara; A. Prigancová

2002-01-01

106

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

107

Polarization effects of the finite-size low-altitude ionosphere  

NASA Astrophysics Data System (ADS)

We use two-fluid or Hall effect MHD description of weakly-ionized stratified atmosphere to describe several polarization features of the MHD disturbance penetration. We employ a pair of functions for the electric and magnetic field components ratio which can be treated analytically. As an example we derive an approximation to the case of the MHD waves in the Earth's Hall ionosphere and demonstrate its different polarization responses (ellipticity and rotation) for Alfvén and fast magnetosonic modes depending on the Hall region thickness. Neglecting the Hall thickness effect we derive previously obtained, well-known results for the rotation of the polarization plane of the MHD waves (Dungey, 1963; Nishida, 1964; Inoue, 1973; Hughes, 1974; Hughes and Southwood, 1976). The ionospheric effects are more essential for the polarization of the fast magnetosonic waves. The polarization changes of the magnetosonic waves are expressed as a function of i) the ratio (R) of the height-integrated Hall (?_H) and Pedersen (?_p) conductivities (conductances) in the Hall region (85-125 km) and ii) a wave/magnetospheric parameter (A_m) and the ratio A_m/?_p. The wave/magnetospheric parameter A_m depends on the wave frequency and the horizontal scale of the ULF waves. Using standard models IRI 90 and MSIS 86, responses of ULF magnetosonic waves to seasonal/diurnal ionospheric variations at subauroral/middle latitudes are illustrated for arbitrary, but reasonable values of the wave/magnetospheric parameter A_m. The polarization plane rotation for the ULF compressional waves ranges between 0 and ?/2 and reaches the classical ?/2 degree only for special cases. Along with the rotation effect an ellipticity effect has also local time course. These findings suggest a new dissipative mechanism (non-resonant) of transformation of magnetosonic waves into Alfvén modes in the ionosphere. In addition we suggest a physical insight for the MHD wave transformation effects by the ionosphere. These findings should be taken into account for the analysis of various polarization features of the geomagnetic pulsations observed on the ground. Sunrise effect on the polarization of the Pc 3-4 pulsations (Saka et al., 1982), the effect of transformation of pure compressional ULF disturbance in the magnetosphere into transverse wave on ground (Lanzerotti and Tartaglia, 1972) proved to be explained in terms of both the polarization rotation and the ellipticity mechanism by the ionosphere. Simultaneous measurements of the electric and magnetic field of ULF waves at ground and balloon heights have revealed polarizations of opposite handedness (Bering et al., 1995). It is shown that the polarization changes of the magnetosonic wave through a horizontally homogeneous high-latitude ionosphere continue further through the atmosphere and would result in different polarization states for the electric and magnetic fields. The northern (southern) hemisphere ionosphere causes an additional left(right)-hand polarization effect in the ionosphere/atmosphere produced mostly on the ULF wave magnetic field. The opposite handedness of the Pc5 wave polarization recorded at the South Pole by measurements of the ULF electric and magnetic field components (Bering et al., 1995) might be explained as a result of an influence of the ionosphere on the ULF waves of an initially left-hand polarization.

Nenovski, P.

2001-01-01

108

Interplanetary magnetic field effects on high latitude ionospheric convection  

NASA Technical Reports Server (NTRS)

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

Heelis, R. A.

1985-01-01

109

Electron heating and airglow emission due to lightning effects on the ionosphere  

NASA Astrophysics Data System (ADS)

This study is the first attempt to consider lightning effects on the F2 region. Although pulsed electric fields parallel to the geomagnetic field have been observed by every rocket flight over active thunderstorms at thermospheric heights, their existence remains controversial. Predicting the disturbance of ionospheric parameters induced by these electric fields may lead to verifying them using ground-based ionospheric observations. This study is also important for understanding the kinetics of ionospheric plasma disturbed by pulsed parallel electric fields. These fields can accelerate electrons from pulse to pulse. If the pause between flashes is longer than ? en , electrons are scattered by elastic collisions with neutrals and transformed into thermal electrons with a corresponding electron temperature enhancement. Inelastic collisions of electrons with neutrals will become more important with increased energy and, subsequently, the electron energy distribution (EED) can differ from a Maxwellian distribution. The vibrational excitation of N2 is extremely important as a source of inelastic collisions for energy ?2 eV. This vibrational barrier can influence the EED. An electron kinetics model induced by pulsed parallel electric fields in ionospheric plasma is developed here. The accelerated and heated electrons can excite airglow in the F2 region. Excitation of red line emissions is most effective. Red line intensities during thunderstorms are predicted to be much higher than the background intensity. Our model also predicts a significant increase in electron temperature in the F2 region during a strong thunderstorm. Opportunities for observing the ionospheric effects of parallel electric fields induced by lightning are discussed.

Vlasov, Michael N.; Kelley, Michael C.

2009-10-01

110

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

111

Ionospheric effects of the magnetic storm on 18-22 August 2003 according to the data of HF sounding of the artificial ionospheric turbulence  

NASA Astrophysics Data System (ADS)

The results of the experimental studies of the influence on the HF signals characteristics of the artificial ionospheric turbulence (AIT) created by the impact on the ionosphere of the powerful radioemission of the heating facilities SURA (Nizhny Novgorod region of Russia) are presented. The measurements were conducted on 18-22 August 2003 in the evening time (1600-2000 UT) at the linearly frequency modulated (LFM) sounding paths: Khabarovsk-Rostov on Don, Irkutsk-Rostov on Don, and Inskip (England)-Rostov on Don and also at the Moscow-Rostov on Don path by the reception of signals of the RVM precise time stations. It was found that at the presence of a strong sporadic E layer at the Irkutsk-SURA path, there appeared the conditions for the SW signal propagation through the upper ionosphere at the frequencies exceeding the maximum usable frequency of the standard hop-like propagation through the F region. The presence of these signals was detected by descending of radio waves from F region altitudes to the Rostov-on-Don reception point due to their scatter at artificial small-scale magnetically oriented irregularities. Using the measurements of the Doppler shift of the frequency of the signals scattered at AIT, ionospheric effects of the magnetic storm occurred in the period of the experiment were studied. It is shown that during the magnetic storm the electric field and irregularity drift velocity at F region heights over the SURA facility reached values of ~8.6 mV m-1 and 186 m s-1, respectively, that is, the values typical for the high-latitude ionosphere. The relation of the quasiperiodic oscillations of the Doppler frequency of the scattered signal to propagation of magnetohydrodynamics waves excited during a magnetic storm is considered.

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

2004-07-01

112

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

113

VLF bursts in the night ionosphere of Venus - Effects of the magnetic field  

NASA Technical Reports Server (NTRS)

The occurrence rate of bursts at 0.1, 0.73, 5.4, and 30 kHz in the night ionosphere of Venus and factors controlling these bursts are examined. It is found that orientation has little effect on the occurrence rates but that the field strength has a strong effect. A contour map of the 100 Hz occurrences is shown to be similar to earlier maps at higher frequencies which have been corrected for altitude dependence.

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

1988-01-01

114

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

NASA Technical Reports Server (NTRS)

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

Comfort, R. H.

1975-01-01

115

Impact and Mitigation of Ionospheric Space Weather Effects on GNSS Receiver Performance (Invited)  

NASA Astrophysics Data System (ADS)

The Earth's ionosphere is considered to be the single largest source of space weather effects on Global Navigation Satellite System (GNSS) signals and positioning accuracy. Most of the space weather effects leading to ionospheric perturbations on the GNSS signals are either due to dispersion or to scintillation caused by plasma density irregularities. This paper presents some significant results related to the impact and mitigation of ionospheric space weather effects on GNSS receiver performance. The correlation of scintillation occurrence with changes in the solar and interplanetary conditions with the consequential impact on GNSS receiver tracking performance at high latitudes is analysed. Further, an assessment of the GNSS receiver tracking performance under scintillation is presented and the construction of the receiver Phase Locked Loop (PLL) jitter variance maps is proposed. These maps can offer a potentially useful tool to provide users with the prevailing tracking conditions under scintillation over a certain area. They can also be used to help mitigate the effects of scintillation on GNSS positioning. This can be done in association with a strategy that involves using the tracking errors to improve the stochastic model of the observations in the position estimation. Validation strategies and practical aspects as well as limitations in the use of these maps are also discussed in this paper.

Vadakke Veettil, S.; Aquino, M. H.

2013-12-01

116

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

117

Propagation of ULF waves (0.1-1Hz) through the ionosphere including dip angle effect  

NASA Astrophysics Data System (ADS)

An analytic model for the propagation of ultra low frequency (ULF) waves in the Pc1 range (0.1-1Hz) within oblique background magnetic field is developed. By taking a Carte-sian coordinate system, we stratify the area of ULF wave propagation into three regions: the magnetosphere, the thin sheet ionosphere (lies in XY plane) and the insulated atmosphere. The variation of the Alfven speed with height (Z direction) is considered in the present study. The reflection coefficient, wave mode conversion coefficient are derived and the ky (the perpen-dicular wave number for an oblique background magnetic field, B0 in the XZ plane) effect is emphasized. The results show that variation in dip angle can effectively modify the resonant frequency and the growth rate of the Ionospheric Alfven Resonator (IAR) and consequently alter the reflection and transition properties of the Alfven waves. By taking into account the effects of ky, the model also shows that ky plays an important role in affecting the ULF wave propagation and the ratio between ky and kx is important for the wave reflection and ground magnetic signal. Key words: Pc1; dip angle; Ionospheric Alfven Resonator (IAR)

Shi, Run; Zhao, Zhengyu; Zhang, Beichen

118

IONOSPHERIC CORRECTIONS FOR TIMING APPLICATIONS  

Microsoft Academic Search

The group retardation effect of the electrons in the earth's ionosphere can seriously limit the accuracy of time transfer by radio waves relayed via satel- lite. The dual frequency approach used in the GPS satellite system eliminates this potential problem, but other techniques, such as the use of models of the ionosphere, can only partially remove the ionospheric time delay

John A. Klobuchar

119

GPS and ionospheric scintillations  

Microsoft Academic Search

Ionospheric scintillations are one of the earliest known effects of space weather. Caused by ionization density irregularities, scintillating signals change phase unexpectedly and vary rapidly in amplitude. GPS signals are vulnerable to ionospheric irregularities and scintillate with amplitude variations exceeding 20 dB. GPS is a weak signal system and scintillations can interrupt or degrade GPS receiver operation. For individual signals,

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

2007-01-01

120

Cyclotron harmonic effect on the thermal oscillating two-stream instability in the high latitude ionosphere  

NASA Astrophysics Data System (ADS)

A thermal oscillating two-stream instability as the generation mechanism of electron Bernstein/upper hybrid waves by the omicron-mode HF heater wave in the high-latitude ionosphere is investigated. The purely growing decay mode is described by the fluid equations, while the kinetic equations are employed to derive the coupled mode equations of the electron Bernstein/upper hybrid sidebands. It is found that the instability can be excited in the altitude regions both above and below the upper hybrid resonance layer. The parametric excitation of electron Bernstein waves is in general not effective. On the other hand, the upper hybrid sidebands of the instability excited in the 'below' region have been considered by Leyser (1991) to be the pumps for the parametric excitation of downshifted maximum (DM) lines of the stimulated electromagnetic emissions (SEEs) observed in the ionospheric heating experiments. The detail analysis of the proposed work shows that the instability zone of upper hybrid waves below the upper hybrid resonance layer becomes very small when the heater frequency f(sub zero) is operated near three times of the local electron cyclotron frequency f(sub c). Thus the source wave of the DM lines is effectively suppressed. This result explains the phenomenon of quenching of the DM feature in the SEE spectrum as f(sub zero) is adjusted near 3f(sub c) in the ionospheric modification experiments.

Huang, J.; Kuo, S. P.

1994-02-01

121

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

122

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

NASA Astrophysics Data System (ADS)

We have explored the sensitivity of the thermosphere and ionosphere to dynamical forcing from altitudes near the mesopause (~95 km). We performed five simulations, all for the year 2009, with the National Center for Atmospheric Research (NCAR)/Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM). Two simulations were driven with the NCAR Global Scale Wind Model, and three used output from the Advanced Level Physics High Altitude (ALPHA) version of the Navy's Operational Global Atmospheric Prediction System (NOGAPS). Use of NOGAPS-ALPHA allows for realistic meteorological variability from the lower atmosphere to propagate up into the TIEGCM, including a rich spectrum of nonmigrating tides. We find that the additional vertical transport from these tides causes a significant reduction in the calculated peak electron density of the ionospheric F2 layer (NmF2). The mechanism for this effect is the enhanced downward transport of atomic oxygen to the base of the thermosphere. In turn, this yields a greater relative abundance of N2 and hence enhanced recombination of ions and electrons. To get improved agreement with observed electron densities, we must reduce (Kzz) by a factor of 5. However, even with lower Kzz, our calculation still underestimates the NmF2 compared with radio occultation observations by the Constellation Observing System for Meteorology, Ionosphere and Climate satellite system. This underestimate of NmF2 may be linked to an overestimate of the nonmigrating tides in the coupled TIEGCM-NOGAPS calculations or to uncertainties in the bottom boundary for atomic oxygen in the TIEGCM.

Siskind, D. E.; Drob, D. P.; Dymond, K. F.; McCormack, J. P.

2014-02-01

123

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

SciTech Connect

A 2.54 cm diameter conducting electrically isolated Copper sphere is suspended in a low density (10{sup 4} cm{sup -3}), low temperature (T{sub e} = 0.5 eV) Argon plasma, which mimics a spacecraft in an ionospheric plasma. An electron beam with current density of approximately 10{sup -10} A/cm{sup 2} and beam spot of 10.2 cm diameter, which mimics an auroral electron beam, is fired at the sphere while varying the beam energy from 100 eV to 2 keV. The plasma potential in the sheath around the sphere is measured using an emissive probe as the electron beam energy is varied. To observe the effects of the electron beam, the experimental sheath potential profiles are compared to a model of the plasma potential around a spherically symmetric charge distribution in the absence of electron beams. Comparison between the experimental data and the model shows that the sphere is less negative than the model predicts by up to half a volt for beam energies that produce high secondary electron emission from the surface of the sphere. It is shown that this secondary emission can account for changes in potential of spacecraft in the ionosphere as they pass through auroral beams and thus helps to improve interpretations of ionospheric thermal ion distributions.

Siddiqui, M. U. [Department of Engineering Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Gayetsky, L. E.; Mella, M. R.; Lynch, K. A. [Department of Physics and Astronomy, Dartmouth College, Hanover, New Hampshire 03755 (United States); Lessard, M. R. [Space Science Center, University of New Hampshire, Durham, New Hampshire 03824 (United States)

2011-09-15

124

The energetics of Titan's ionosphere  

NASA Astrophysics Data System (ADS)

We have developed a comprehensive model to study the dynamics and energetics of the ionosphere of Titan. We solved the one-dimensional, time-dependent, coupled continuity and momentum equations for several ion species, together with single ion and electron energy equations, in order to calculate density, velocity, and temperature profiles. Calculations were carried out for several cases corresponding to different local times and configurations of the Titan-Saturn system. In our model the effects of horizontal magnetic fields were assumed to be negligible, except for their effect on reducing the electron and ion thermal conductivities and inhibiting vertical transport in the subram region. The ionospheric density peak was found to be at an altitude of about 1100 km, in accordance with earlier model calculations. The ionosphere is chemically controlled below an altitude of about 1500 km. Above this level, ion densities differ significantly from their chemical equilibrium values due to strong upward ion velocities. Heat is deposited in a narrow region around the ionospheric peak, resulting in temperature profiles increasing sharply and reaching nearly constant values of 800-1000 deg K for electrons and 300 deg K for ions in the topside, assuming conditions appropriate for the wake region. In the subram region magnetic correction factors make the electron heat conductivities negligible, resulting in electron temperatures increasing strongly with altitude and reaching values in the order of 5000 deg K at our upper boundary located at 2200 km. Ion chemical heating is found to play an important role in shaping the ion energy balance in Titan's ionosphere.

Roboz, A.; Nagy, A. F.

1994-02-01

125

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

126

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

127

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

Microsoft Academic Search

In global modeling, magnetosphere-ionosphere (MI) coupling physically connects a global magnetospheric (GM) model and a global ionospheric-thermospheric (GIT) model. The field-aligned current from the GM model and the conductance distributions from the GIT model are used in a Poisson equation derived from the ionospheric Ohm's law combined with current continuity to determine the electrostatic potential in the ionosphere. In current

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

2010-01-01

128

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

NASA Astrophysics Data System (ADS)

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

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

129

Effect of double layers on magnetosphere-ionosphere coupling  

NASA Technical Reports Server (NTRS)

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

Lysak, Robert L.; Hudson, Mary K.

1987-01-01

130

Geomagnetic activity effect on the global ionosphere during the 2007-2009 deep solar minimum  

NASA Astrophysics Data System (ADS)

this paper the significant effect of weaker geomagnetic activity during the 2007-2009 deep solar minimum on ionospheric variability on the shorter-term time scales of several days was highlighted via investigating the response of daily mean global electron content (GEC, the global area integral of total electron content derived from ground-based GPS measurements) to geomagnetic activity index Ap. Based on a case during the deep solar minimum, the effect of the recurrent weaker geomagnetic disturbances on the ionosphere was evident. Statistical analyses indicate that the effect of weaker geomagnetic activity on GEC variations on shorter-term time scales was significant during 2007-2009 even under relatively quiet geomagnetic activity condition; daily mean GEC was positively correlated with geomagnetic activity. However, GEC variations on shorter-term time scales were poorly correlated with geomagnetic activity during the solar cycle descending phase of 2003-2005 except under strong geomagnetic disturbance condition. Statistically, the effects of solar EUV irradiance, geomagnetic activity, and other factors (e.g., meteorological sources) on GEC variations on shorter-term time scales were basically equivalent during the 2007-2009 solar minimum.

Chen, Yiding; Liu, Libo; Le, Huijun; Wan, Weixing

2014-05-01

131

Effect of double layers on magnetosphere-ionosphere coupling  

NASA Technical Reports Server (NTRS)

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

Lysak, Robert L.; Hudson, Mary K.

1987-01-01

132

Continual Initialization of The TING Model with GAIM Electron Densities: Ionospheric Effects on The Thermosphere  

NASA Astrophysics Data System (ADS)

We have continually replaced the electron and O+ densities in the Thermosphere Ionosphere Nested Grid (TING) model by the electron densities from the Global Assimilation of Ionospheric Measurements (GAIM) model at pressure level z=-2 (about 165 km altitude) and above during early April 2004. There was an extended quiet period during this interval followed by a moderate geomagnetic storm (K_p ~ 6.0). The ingestion of the GAIM electron densities had little effect on the neutral temperature and composition during the quiet period before the storm, but there was a noticeable global effect on the neutral winds at this time that resulted from changes in ion drag. During disturbed periods, the changed electron densities had large effects on the global thermosphere. Increases in the auroral electron densities enhance the Joule heating rate, which results in considerable increases in the high-latitude neutral temperatures. These temperature increases induce fairly large modification of the global circulation of the neutral atmosphere and thereby affect neutral temperature and composition at low and middle latitudes.

Jee, G.; Burns, A.; Wang, W.; Solomon, S. C.; Schunk, R. W.; Scherliess, L.; Thompson, D. C.; Sojka, J. J.; Zhu, L.

2006-12-01

133

Perturbation effect of the Coulomb drag on the orbital elements of the earth satellite moving in the ionosphere  

NASA Astrophysics Data System (ADS)

The perturbation effects of the Coulomb drag on the orbital elements of the earth satellite moving in the ionosphere are studied. The theoretical results show that the Coulomb drag results in both the secular and periodic variation in the semi-major axis and eccentricity. However, the argument of the perigee exhibits no secular variation, but only periodic variation. The inclination and the ascending node remain no variation. As an example, the secular effects of the Coulomb drag on the semi-major axis and the eccentricity of an ionosphere satellite Alouette (S-27) are calculated in the ionosphere with the mean height 1000 km. It can be shown that the semi-major axis contracts and the eccentricity decreases for the case of the Coulomb drag under the interaction of the ions with the electric field of an earth satellite.

Li, Lin-Sen

2011-04-01

134

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.

Cundiff, Patrick R.

2014-01-01

135

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

136

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

SciTech Connect

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

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

1992-10-22

137

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

138

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

139

Ionospheric Storms — A Review  

Microsoft Academic Search

In this paper, our current understanding and recent advances in the study of ionospheric storms is reviewed, with emphasis\\u000a on the F2-region. Ionospheric storms represent an extreme form of space weather with important effects on ground- and space-based\\u000a technological systems. These phenomena are driven by highly variable solar and magnetospheric energy inputs to the Earth's\\u000a upper atmosphere, which continue to

M. J. Buonsanto

1999-01-01

140

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

SciTech Connect

The ionospheric responses to the solar eclipse of September 23, 1987, in the equatorial anomaly crest region have been investigated by using ionospheric vertical sounding, VLF propagation delay time, and differential Doppler shift data observed at Chungli, which is located near the northern equatorial anomaly crest region. It has been found that temporal variations of the F{sub 1} layer and D region are mainly controlled by local solar radiation. Quantitative analysis of the variations of the F{sub 1} layer critical frequency, F{sub o} F{sub 1}, shows that electrons are removed from the F{sub 1} layer through ionic recombination. However, the temporal variations of f{sub o}F{sub 2} and electron density above 200 km show that the variations o the F{sub 2} layer around the equatorial anomaly region are controlled not by local solar radiation but by solar radiation at the equator. The fountain effect plays an important role even during the solar eclipse. The VLF propagation time delay is controlled by the variations of average path obscuration. Atmospheric gravity waves produced by the moving bow wave front of the solar eclipse are found with a period around 17-23 min and wavelength about 293 km.

Kang Cheng; Yinnnien Huang; Senwen Chen (Ministry of Transportation and Communications, Taipei (Taiwan))

1992-01-01

141

Ionospheric plasma cloud dynamics  

NASA Technical Reports Server (NTRS)

Measurements of the thermospheric neutral wind and ionospheric drift made at Eglin AFB, Florida and Kwajalein Atoll are discussed. The neutral wind measurements at Eglin had little variation over a period of four years for moderate magnetic activity (Kp 4); the ionospheric drifts are small. Evidence is presented that indicates that increased magnetic activity has a significant effect on the neutral wind magnitude and direction at this midlatitude station. The neutral wind at dusk near the equator is generally small although in one case out of seven it was significantly larger. It is described how observations of large barium releases can be used to infer the degree of electrodynamic coupling of ion clouds to the background ionosphere. Evidence is presented that indicates that large barium releases are coupled to the conjugate ionosphere at midlatitudes.

1976-01-01

142

Auroral effects in the D region of the ionosphere. [interactions between auroral particles and electromagnetic fields  

NASA Technical Reports Server (NTRS)

Physical phenomena associated with the interaction between auroral particles and electromagnetic fields, auroral energy flow, and the propagation of auroral effects to low altitudes are discussed in detail. It is concluded that energy deposition of soft auroral X-rays would be negligible at stratospheric altitudes. New data from incoherent backscatter measurements of neutral winds in the auroral region indicate a lack of correlation between stratospheric winds and winds in the auroral ionosphere. Magnetograms are used to show that sector boundary crossings with a time scale of approximately one hour (as opposed to the sector structure itself with a time scale of several days) do not couple effectively with the magnetosphere and are not significant energy inputs to it.

Akasofu, S. I.

1974-01-01

143

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

144

Ionospheric Calibration for Single Frequency Altimeter Measurements.  

National Technical Information Service (NTIS)

This study is a preliminary analysis of the effectiveness (in terms of altimeter calibration accuracy) of various ionosphere models and the Global Positioning System (GPS) to calibrate single frequency altimeter height measurements for ionospheric path de...

W. S. Schreiner, G. H. Born, R. E. Markin

1994-01-01

145

Meteor showers effects in the low terrestrial ionosphere detected at VLF ionosonde and long distance propagation paths  

NASA Astrophysics Data System (ADS)

The effect of Geminids and eta Aquarids meteor showers in the lower ionosphere were observed using two different methods. Low ionosphere group heights measured by a very low frequency ionosonde located south of Brazil indicated an anomalous lowering of the effective reflection height and presented night-time 5 sigma deviation in good correlation with Eta Aquarids stream transit. The group reflection coefficients present a very pronounced variation reaching values 3 sigma below the normal values. Diurnal very low frequency phase variations in two long-distance propagation paths present night-time 7 sigma and 4 sigma phase deviations from the average during the Eta Aquarids shower transit. The Geminids shower effect in the lower ionosphere was detected in two different long distance very low frequency propagation paths: NAA, Culter, U.S.A. - Atibaia, S.P., Brazil presented 5 sigma phase deviation and ARG, Argentina - Atibaia, S.P., Brasil presented 3.5 sigma phase deviation from the average. The geomagnetic activity in the periods covered by this investigation was low and the results obtained are a confirmation through two different techniques of changes in the physical conditions of the low ionosphere by meteor shower.

Vilas-Boas, J. W. S.; Paesleme, N. M.; Piazza, L. R.; Macedomoura, M. S. S.

1984-08-01

146

About the nature of the Night-time Winter Anomaly effect (NWA) in the F-region of the ionosphere  

NASA Astrophysics Data System (ADS)

The Night-time Winter Anomaly (NWA) effect is shown to be a regular phenomenon at the mid-latitude ionosphere in the American and Asian longitude sectors under low solar activity conditions. Total electron content, vertical sounding data as well as topside sounder measurements onboard Alouette indicate a significant higher night-time ionization level in winter than in summer under certain conditions which are discussed in more detail. It is shown that the NWA effect is closely related to the asymmetry of the geographic-geomagnetic relationships in the American and in the Asian longitude sectors, respectively. In the former sector NWA occurs in the northern hemisphere, in the latter in the southern hemisphere. Since the sea-sonal variation of the night-time ionization is similar at conjugated hemispheres, interhemispheric coupling processes are assumed to generate the NWA effect. This idea is consistent with numerical calculations, modelling the system ionosphere-plasmasphere-ionosphere along magnetic flux tubes in the American longitude sector. The model calculations show that interhemispheric fluxes react very sensitive to dynamical forces as f.i. meridional winds in both ionospheres. The derived field-aligned plasma fluxes as well as the resulting higher tube content in December than in June are consistent with the observations.

Jakowski, N.; Förster, M.

1995-05-01

147

Conjugate effects of june 21, 2001 solar eclipse in radio noise of the midlatitude ionosphere  

Microsoft Academic Search

Partially ionized ionosphere plasma is a source of the noise, which can be registered in meter and decimeter wave ranges. The disturbances that changed the physical conditions in the ionosphere are reflected in the noise: solar flares, terminator motion, solar eclipses, sporadic Es, particle precipitation. Trapped particle precipitation appears during the pitch-angle diffusion in the cone of loses under their

S. Musatenko; E. Kurochka; V. Choliy; M. Medvedsky; O. Slipchenko; A. Lastochkin; V. Reshetnyk

2002-01-01

148

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

Microsoft Academic Search

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

R. A. Wolf

1970-01-01

149

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

150

On Es-spread effects in the ionosphere connected to earthquakes  

NASA Astrophysics Data System (ADS)

In the present work, phenomena in the ionosphere are studied, which are connected with earthquakes (16 events) having a depth of less than 50 km and a magnitude M larger than 4. Analysed are night-time Es-spread effects using data of the vertical sounding station Petropavlovsk-Kamchatsky (?=53.0°, ?=158.7°) from May 2004 until August 2004 registered every 15 min. It is found that the maximum distance of the earthquake from the sounding station, where pre-seismic phenomena are yet observable, depends on the magnitude of the earthquake. Further it is shown that 1-2 days before the earthquakes, in the pre-midnight hours, the appearance of Es-spread increases. With a probability of more than 0.95, this increase of Es-spread observations before midnight is not casual.

Liperovskaya, E. V.; Meister, C.-V.; Pokhotelov, O. A.; Parrot, M.; Bogdanov, V. V.; Vasil'Eva, N. E.

2006-08-01

151

Lower ionosphere effect observed during the 30 June 1992 total solar eclipse  

NASA Astrophysics Data System (ADS)

VLF radio signals (12.9 kHz) transmitted from ?-Argentina (43°12'S, 65°24'W) were received in Atibaia, Brazil (23°11 'S, 46°33'W) during the total solar eclipse of 30 June 1992. The surface path of the totality crossed the VLF propagation path in the sunrise transition period causing a phase delay of 6.4 ?s and an amplitude change of 1.3 dB. The ionospheric response to the Sun's obscuration was compared with the phase delays reported for several solar eclipses that occurred from 1966 to 1979. The results are mainly discussed in terms of the length of VLF propagation path affected. Some similarities between a sudden phase anomaly and a reversed eclipse effect are also raised.

Mendes Da Costa, A.; Paes Leme, N. M.; Rizzo Piazza, L.

152

Lower ionosphere effect observed during the 30 June 1992 total solar eclipse  

NASA Astrophysics Data System (ADS)

VLF radio signals (12.9 kHz) transmitted from Omega-Argentina (43 deg 12 minutes S, 65 deg 24 minutes W) were received in Atibaia, Brazil (23 deg 11 minutes S, 46 deg 33 minutes W) during the total solar eclipse of 30 June 1992. The surface path of the totality crossed the VLF propagation path in the sunrise transition period causing a phase delay of 6.4 microsecond and an amplitude change of 1.3 dB. The ionospheric response to the Sun's obscuration was compared with the phase delays reported for several solar eclipses that occurred from 1966 to 1979. The results are mainly discussed in terms of the length of VLF propagation path affected. Some similarities between a sudden phase anomaly and a reversed eclipse effect are also raised.

da Costa, A. Mendes; Leme, N. M. Paes; Piazza, L. Rizzo

1995-01-01

153

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

154

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

SciTech Connect

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

Inan, U.S.

1992-01-01

155

Duration of an ionospheric data assimilation initialization of a coupled thermosphere-ionosphere model  

NASA Astrophysics Data System (ADS)

Initial conditions provide a critical input for accurate numerical forecast models in meteorology and oceanography. In this paper, we address this problem in space weather forecast models of the thermosphere-ionosphere system by using the electron densities from the Global Assimilation of Ionospheric Measurements (GAIM) model to initialize the ionospheric part of the Thermosphere Ionosphere Nested Grid (TING) model. The electron densities from the GAIM-initialized TING model (G-TING) are compared with the output from the stand-alone TING model (S-TING) for geomagnetically quiet and disturbed times in the early April 2004 period in order to observe how long the effects of the initialization would last. Our study shows that the e-folding time of the initialization is about 2 ˜ 3 hours for most conditions, although this result would probably be different if the initialization for the thermosphere is also included. However, this relaxation time displays significant variations with latitude, local time, and height, and it may also depend on the initial electron density differences between G-TING and S-TING. Furthermore, positive (G-TING > S-TING) and negative (G-TING < S-TING) density differences have different time durations of the initialization effects. Our study also indicates that there is little variation of the relaxation time with the geomagnetic activity despite the impact of geomagnetic storms on the thermosphere-ionosphere system.

Jee, G.; Burns, A. G.; Wang, W.; Solomon, S. C.; Schunk, R. W.; Scherliess, L.; Thompson, D. C.; Sojka, J. J.; Zhu, L.

2007-01-01

156

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

SciTech Connect

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

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

1992-01-01

157

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

158

Ionospheric Research.  

National Technical Information Service (NTIS)

The report contains research directed toward the investigation of the lower ionosphere. Specific emphasis was placed on the design, conduction and analysis of rocket-borne A.C. conductivity probes and radio wave propagation experiments. These objectives h...

T. A. Seliga

1968-01-01

159

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

160

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

161

On developing a new ionospheric perturbation index for space weather operations  

Microsoft Academic Search

The ionosphere plays an active role in the complex Sun-Earth relationship and the space weather manifestation. Hence, permanent monitoring of the ionosphere state is required for reliably managing radio systems using ionospheric or trans-ionospheric propagation. In order to efficiently operate and further improve the functionality of such systems, key information on the ionosphere condition is needed, most of all the

N. Jakowski; S. Stankov; S. Schlueter; D. Klaehn

2004-01-01

162

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

163

High Resolution Reconstruction of the Ionosphere for SAR Applications  

NASA Astrophysics Data System (ADS)

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

Minkwitz, David; Gerzen, Tatjana; Hoque, Mainul

2014-05-01

164

Some Geomagnetic and Ionospheric Effects in Antarctica Prior to Storm Sudden Commencements.  

National Technical Information Service (NTIS)

Ionospheric height changes, blackout conditions, and geomagnetic activity for Antarctica in the relatively quiet times (geomagnetically) before storm sudden commencements are investigated. The principal results give evidence for 24-hourly periodicities in...

G. G. Bowman

1966-01-01

165

Sunrise Effects on the Latitudinal Variations of Topside Ionospheric Densities and Scale Heights.  

National Technical Information Service (NTIS)

Ionospheric sunrise represents the transition period between quasi-equilibrium conditions attained during the night and those attained during the day. The arrival of sunrise is manifested by a rapid increase in electron temperatures and a less rapid incre...

H. Soicher

1972-01-01

166

General Overview of the Solar Activity Effects on the Lower Ionosphere.  

National Technical Information Service (NTIS)

Solar activity influences the ionospheric D region. That influence manifests itself both in the form of various solar induced disturbances and in the form of the D region dependence on solar activity parameters (UV-flux, interplanetary magnetic field, sol...

A. D. Danilov

1989-01-01

167

Cooling of the upper atmosphere by enhanced greenhouse gases - Modelling of thermospheric and ionospheric effects  

Microsoft Academic Search

Using the NCAR Thermosphere\\/Ionosphere General Circulation Model, predictions are made that (depending on location and the phase of the solar cycle) the thermospheric temperature should be lowered by 30-40 K and the air density at heights of 200-300 km should be reduced by 20-40 percent, thus increasing the orbital lifetimes of satellites. The height of the ionospheric F2-layer peak should

H. Rishbeth; R. G. Roble

1992-01-01

168

Exploring the influence of ionospheric O+ outflow on magnetospheric dynamics: The effect of outflow intensity  

NASA Astrophysics Data System (ADS)

The ionospheric O+ outflow varies dramatically during geomagnetic activities, but the influence of its initial characteristics on the magnetospheric dynamics has not been well established. To expand a previous study on the impact of ionospheric heavy ions outflow originating from different source regions on the magnetotail dynamics and dayside reconnection rate, this study conducts two idealized numerical experiments with different O+ outflow densities to examine the consequent change in the magnetosphere system, especially on the solar wind-magnetosphere coupling efficiency. Results indicate that a larger O+ outflow is capable of triggering the Kelvin-Helmholtz instability (KHI) on the magnetopause flanks. The subsequent surface waves enhance the solar wind-magnetosphere coupling efficiency by transmitting more solar wind energy into the magnetosphere-ionosphere system, increasing the cross polar cap potential index. This index is initially reduced after the ionospheric mass loading owing to the direct depression in the dayside reconnection rate as commonly reported from earlier literature. The above KHI is generated under steady state solar wind conditions, suggesting that besides the commonly recognized cause, the elevated solar wind speed, ionospheric heavy ions outflow is another potential factor in disturbing the boundary by enhancing the mass density near the magnetopause and thus lowering the threshold for generating KHI. During storms, the increased ionospheric mass source causes an increased probability of KHI, which allows more solar wind plasma into the magnetosphere. This implies there is a possibility of even further nonlinear coupling between the magnetosphere and solar wind.

Yu, Yiqun; Ridley, Aaron J.

2013-09-01

169

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

170

Using Remote Sensing as a Plasma Diagnostic: A Discussion of Techniques Being Used to Probe the Ionosphere in Order to Determine the Energy and Spectral Characteristics of Precipitating Electrons and Protons  

NASA Technical Reports Server (NTRS)

Spectrally resolved global images of the Earth from recent (and planned) missions are being (and will be) used to probe the ionosphere in order to determine the energy characteristics of precipitating electrons and protons. We describe the techniques that are being used, discuss the extent to which they are successful, and envision the approach that future space experiments should take in order to improve on current techniques.

Spann, J.; Parks, G.; Brittnacher, M.; Germany, G.; Mende, S.; Frey, H.; Chenette, D.; Schulz, M.; Petrinec, S.

1999-01-01

171

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

172

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

NASA Astrophysics Data System (ADS)

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

Cole, K. D.

1993-03-01

173

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

174

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

175

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

176

Assessing Ionospheric effects on L-band SAR data: Implications to co-seismic deformation measurements on the Sichuan Eartquake.  

NASA Astrophysics Data System (ADS)

SAR data from the Alos L-band sensor (PALSAR) is an efficient tool for ground surface deformation measurements using both radar interferometry (INSAR) and sub-pixel image correlation. On the recent Sichuan earthquake, these methods were successfully used by several Research teams in order to estimate the deformation field and to detect the surface rupture. The main interest of L-band InSAR is due to the fact that results are less affected by temporal decorrelation than C-band InSAR data, especially in highly vegetated areas. However, the L-band deformation maps are severely hampered by ionospheric contributions to the radar signal. In particular, the azimuth offsets (pixel displacement along the orbit) are affected by "stripes" with amplitudes that could be higher than the deformation signal. In this paper, we propose a methodology for estimating the ionospheric contribution to the InSAR signal based on the azimuth pixel offset. The retrieved ionospheric contribution is then used to compute a correction that can we apply both to the correlogram and interferogram. We therefore propose a joint correction of the azimuth offsets and interferometric phases based on features observed on the correlation image. The proposed method is used to improve our deformation maps on the Sichuan Eartquake.

Raucoules, D.; de Michele, M.

2009-04-01

177

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

178

Imaging the Ionosphere Using Polarimetric SAR and GPS  

NASA Astrophysics Data System (ADS)

In this paper, we will present ionospheric electron content measurements derived from polarimetric data collected using the Phased Array type L-band Synthetic Aperture Radar (PALSAR) onboard the Japanese Advanced Land Observing Satellite (ALOS). The radar measurements of latitudinal features in different regions under various conditions are compared with 2D and 3D assimilative ionsopheric models that ingest GPS data. The comparisons show consistent results between the SAR- and GPS-based techniques. This indicates that GPS-based techniques could be applied to corrections of SAR data, at least to the first order approximation, that are subject to the Faraday rotation and other ionospheric effects. In addition, while GPS measurements collected from global and regional GPS networks are useful to provide large-scale snapshots of ionospheric TEC maps and 3D densities, polarimetric SAR could become a powerful tool to image the ionosphere in much higher resolutions. The potential of SAR-based ionospheric imaging will be discussed that can significantly enhance our capability of investigating outstanding ionospheric research topics.

Pi, X.; Freeman, A.; Chapman, B. D.; Chapin, E.

2008-12-01

179

Magnetic-inclination effects in the spectral resonance structure of the ionospheric Alfvén resonator  

NASA Astrophysics Data System (ADS)

Based on recent developments in the formalism governing the spectral resonance structures (SRS) of the Ionospheric Alfvén resonator (IAR) as observed on the Earth's surface, a numerical code was developed to investigate properties of SRS which can in particular be contributed to magnetic inclination effects. Among the theoretical findings are: 1) SRS is discernible in both orthogonal components, 2) the harmonic structure of SRS is not anymore over frequency equidistantly distributed, 3) the frequency scales of SRS differ in the two normal modes. The theoretically predicted properties could be found in the observations of a low latitude and some of them even in the data of a mid latitude station. The verification, however, is not as straight forward because the predicted effects do not only depend on magnetic inclination but also on the wave angle of the lightning induced electromagnetic wave k-vector with the normal to the magnetic meridian passing through the observation site. So far the formalism is simplified as it deals with a single source situation alone whereas the actual observation is a composite of excitations caused by an average of about 60 flashes of lightning operating all the time, world-wide.

Bösinger, T.; Ermakova, E. N.; Haldoupis, C.; Kotik, D. S.

2009-03-01

180

Ionospheric chemical releases  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

181

Corotation lag of the Jovian atmosphere, ionosphere, and magnetosphere  

SciTech Connect

The authors modify the Jovian ionosphere-magnetosphere coupling model presented by Hill (1979) to include rotational slippage of the neutral atmosphere at ionospheric heights, relative to a frame of reference corotating rigidly with Jupiter. In the modified model, as altitude increases, the drift velocities of neutrals and ions relative to the corotating frame increase from zero at the bottom of the ionosphere to their respective maximum values at the top, and the corotation lag of the magnetosphere is enhanced for a given rate of mass loading of the magnetosphere. The height variations of the drift velocities of neutrals and ions in the ionosphere and the enhancement factor for the corotation lag of the magnetosphere are related to the atmospheric eddy diffusion coefficient at ionospheric heights. On the basis of ionospheric properties deduced from measurements of Pioneer 11, Voyager 1, and Voyager 2, they derive height profiles of ion and neutral drift speed for various possible values of the eddy diffusion coefficient. If they accept the ion injection rate from Io (10{sup 29} ions/s) and the ion transport rate through the Jovian magnetosphere (3 {times} 10{sup 28} ions/s), corresponding to the observed values of the corotation lag of the Io torus ({delta}{omega}{sub I} = 0.04{omega}{sub j}) and the critical distance for magnetospheric corotation (L{sub 0} = 20), respectively, the effective ionospheric conductance is reduced by a factor of the order of 10, resulting in an enhanced corotation lag, for a given rate of mass loading, by the same factor compared to earlier models. The eddy diffusion coefficient in the high-latitude ionosphere is inferred to be {approximately} 10{sup 13} n{sub n}{sup {minus}1/2}m{sup 1/2}/s, or about a factor of 20 larger than the value inferred from Voyager measurements at near-equatorial latitudes.

Huang, T.S.; Hill, T.W. (Rice Univ., Houston, TX (USA))

1989-04-01

182

The effect of ionospheric outflow and magnetospheric composition on the formation and evolution geospace currents  

NASA Astrophysics Data System (ADS)

We address the effect of ionospheric outflow and magnetospheric ion composition on the physical processes that control the development of August 5, 2011 magnetic storm. Simulations using the Space Weather Modeling Framework (SWMF) together with composition measurements from TWINS are used to investigate the global dynamics and energization of ions throughout the magnetosphere during storm time, with a focus on the formation and evolution of the ring current during storm time. For this purpose we include simulations involving multi fluid, multi species and single fluid MHD for the global magnetosphere. We find that multi fluid MHD simulations together polar outflow produce the best results when modeling a storm, in that the modeled Dst shows the highest correlation with the homologous observed quantity. Changing the composition in the inner magnetosphere in a dynamic way alters the total energy density of the magnetosphere, leading to changes in the magnetic field as well as particle trajectories throughout the simulated domain. Adding oxygen to the system leads to a reduction in the CPCP and brings the nightside reconnection line closer to Earth which yields less adiabatic heating. Therefore it reduces the amount of heated plasma that has access to the inner magnetosphere producing a weaker ring current. Oxygen observations from the TWINS spacecraft show intensifications of the ENA emission during the main phase of the storm, well correlated with substorm injection during that time. Synthetic mass separated ENA images reveal similar features, in direct agreement with the observations.

Ilie, R.; Skoug, R. M.; Funsten, H. O.

2013-05-01

183

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

184

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

185

Schumann resonance effects of electrical conductivity perturbations in an exponential atmospheric/ionospheric profile  

NASA Astrophysics Data System (ADS)

An examination of the Schumann resonance effects of conductivity disturbances superimposed on an exponential vertical conductivity profile in the atmosphere is presented. Differential equations are defined for the radial segment of the eigenfunctions of the earth ionosphere system in the case of spherically symmetric, isotropic dielectric of arbitrary radial profile. Integration of the eigenfunctions produces the vertical and tangential electric field components, and thereby the Joule dissipation profile. It is found that the Schumann resonances have a two-level structure in the Joule dissipation profile, with maximum dissipation happening at the mesospheric height of 50 km. A secondary maximum is situated at 90 km. The vertical component of the electric field of the Schumann modes is constant from the ground up to 40 km, then decreases rapidly. Moderate perturbation conductivity enhancements below 65 km lead to depressed Schumann eigenfrequencies, but below 50 km and between 70-85 km causes depressed Q-values. Between 50-70 km and over 85 km, enhanced conductivity increases the Q-values.

Sentman, D. D.

1983-01-01

186

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

Microsoft Academic Search

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

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

1981-01-01

187

Ionospheric scintillation  

Microsoft Academic Search

Available observations of ionospheric scintillation are analyzed to evaluate the adequacy of existing models used for the interpretation of scintillation data. The theoretical models are reviewed and the frequency and propagation geometry dependences predicted by the models are compared with the observations. The models were used to construct scintillation occurrence distribution functions which show that scintillation phenomena significantly affect the

R. K. Crane

1977-01-01

188

Ionospheric irregularities  

Microsoft Academic Search

Extensive experimental and theoretical research has been performed in the last decade to study ionospheric irregularities. These studies have shown that plasma instabilities play a major role in the generation of the irregularities. In this work we describe in detail the recent experimental studies of the E and F region irregularities and also the extensive work on plasma instability theories

B.G. Fejer; M. C. Kelley

1980-01-01

189

Ionospheric Research.  

National Technical Information Service (NTIS)

The Statement of Work for the research to be performed under Contract AF 19(628)-4050 called for research directed toward the investigation of the lower ionosphere. Specific emphasis was placed on the design, conduction and analysis of rocket-borne A. C. ...

T. A. Seliga

1967-01-01

190

HF propagation through actively modified ionospheres  

NASA Astrophysics Data System (ADS)

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

Argo, Paul E.; Fitzgerald, T. Joseph; Wolcott, John H.; Simons, David J.; Warshaw, Steve; Carlson, Ralph

191

Characterising the Ionosphere (La caracterisation de l'ionosphere).  

National Technical Information Service (NTIS)

This report is a compilation of papers from academic and other research institutes that describe ionospheric phenomena and parameters that affect electromagnetic propagation. The report addresses both mid-latitude and high-latitude effects. The first chap...

G. Wyman

2009-01-01

192

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

193

Analysis of FORTE data to extract ionospheric parameters  

NASA Astrophysics Data System (ADS)

The ionospheric transfer function is derived for a spherically symmetric ionosphere with an arbitrary radial electron density profile in the limit where the radio frequencies of interest ? are much larger than the plasma frequency ?pe. An expansion of the transfer function to second order in the parameter X (= ?2pe/?2) is carried out. In this limit the dispersive properties of the ionosphere are manifested as a frequency-dependent time of arrival that includes quadratic, cubic, and quartic terms in 1/?. The coefficients of these terms are related to the total electron content (TEC) along the slant path from transmitter to receiver, the product of TEC and the longitudinal magnetic field strength along the slant path, and refractive bending and higher-order electron density profile effects, respectively. By fitting the time of arrival versus frequency of a transionospheric signal to a polynomial in 1/? it is possible to extract the TEC, the longitudinal magnetic field strength, the peak electron density, and an effective thickness for the ionosphere. This exercise was carried out for a number of transionospheric pulses measured in the VHF by the FORTE satellite receiver and generated by the Los Alamos Portable Pulser. The results are compared with predictions derived from the International Reference Ionosphere and the United States Geological Survey geomagnetic field model.

Roussel-Dupré, Robert A.; Jacobson, Abram R.; Triplett, Laurie A.

2001-01-01

194

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

195

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

196

Calculating Second-Order Effects in MOSFET's  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

197

Hybrid simulations of Venus' ionospheric magnetization states  

NASA Astrophysics Data System (ADS)

The solar wind interaction with the plasma environment of Venus is studied with focus on ionospheric magnetization states using a 3D hybrid simulation code. The plasma environment of Venus was investigated mainly by Pioneer Venus Orbiter (PVO) and the still ongoing Venus Express (VEX) mission. Unlike many other planets, Venus' ionosphere is not shielded by a strong magnetosphere. Hence, data measured by spacecraft like PVO and VEX close to the planet are highly sensitive to solar wind and IMF upstream conditions, which cannot be measured while the spacecraft is inside the magnetosheath region about one hour before and after the closest approach. However, solar wind and IMF are known to change within minutes; ionospheric magnetization states, found by PVO and VEX, are highly dependent on the solar wind upstream pressure and also the magnetic field direction may change rapidly in case of a magnetic sector boundary crossing. When these solar wind induced transition effects occur, the causal change in the solar wind cannot be determined from ionospheric in-situ data. Additionally, with an orbital period of 24 hours, measuring transition timescales of solar wind triggered events is not possible. Our self-consistent simulations aim to provide a global picture of the solar wind interaction with Venus focusing on the effects of upstream fluctuations to the magnetic field in the vicinity of the planet. We use the A.I.K.E.F. (Adaptive Ion Kinetic Electron Fluid) 3D hybrid simulation code to model the entire Venus plasma environment. The simulation grid is refined within the ionosphere in order to resolve strong small-scale gradients of the magnetic field and ion density, a necessity to describe the magnetic field depletion inside the Venus' ionosphere. In contrast to other simulation studies, we apply no boundary conditions for the magnetic field at the planetary surface. Furthermore, we include varying upstream conditions like solar wind velocity and density as well as IMF strength and direction by adjusting these parameters after a first, quasi-stationary state has been reached. This allows for a simulation of dynamic processes like the transition between the magnetized and unmagnetized ionospheric state and fossil fields.

Wiehle, Stefan; Motschmann, Uwe; Fränz, Markus

2013-04-01

198

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

SciTech Connect

The Venus ionosphere is influenced by variations in both solar EUV flux and solar wind conditions. On the dayside the location of the topside of the ionosphere, the ionopause, is controlled by solar wind dynamic pressure. Within the dayside ionosphere, however, electron density is affected mainly by solar EUV variations, and is relatively unaffected by solar wind variations and associated magnetic fields induced within the ionosphere. The existence of a substantial nightside ionosphere of Venus is thought to be due to the rapid nightward transport of dayside ionospheric plasma across the terminator. Typical solar wind conditions do not strongly affect this transport and consequently have little direct influence on nightside ionospheric conditions, except on occasions of extremely high solar wind dynamic pressure. However, both nightside electron density and temperature are affected by the presence of magnetic field, as in the case of ionospheric holes. 12 references.

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

1985-01-01

199

Topside sounder studies of corpuscular radiation effects on the ionosphere during quiet and disturbed conditions  

Microsoft Academic Search

Studies of electron scale heights obtained from topside ionograms lead to the conclusion that energetic particles do not usually affect the ionospheric plasma temperature at heights of 400 or 500 km. During magnetic disturbances, however, the electron scale heights in the region of the South Atlantic magnetic anomaly, but not at other longitudes, appear to be abnormal, possibly as the

J. W. King; P. A. Smith; K. C. Reed; C. Seabrook

1967-01-01

200

Multifrequency Doppler Radar Observations of Electron Gyroharmonic Effects during Electromagnetic Pumping of the Ionosphere  

Microsoft Academic Search

Experimental results of multifrequency HF Doppler radar studies during electromagnetic pumping of the ionosphere from the ground are reported. The Doppler shifts of the radar waves after turn-on of the vertically injected HF pump wave depend on the pump frequency and exhibit, at relatively large reflection altitudes, opposite signs for pump frequencies above or below an electron gyroharmonic. The results

S. Grach; G. Komrakov; M. Yurishchev; B. Thide; T. Leyser; T. Carozzi

1997-01-01

201

Effects of substorm dynamics on magnetic signatures of the ionospheric Alfvén resonator  

NASA Astrophysics Data System (ADS)

Spectral resonance structures (SRS) of the ionospheric Alfvén resonator (IAR) measured by the induction magnetometer at the High Frequency Active Auroral Research Program (HAARP) ionospheric observatory during a substorm on 28 February 2006 are presented. The evolution of IAR SRS is compared to ionospheric parameters measured by the colocated Digisonde, riometer and all-sky imager at HAARP. Initially, the magnetic IAR signatures (spectral resonance structures) exhibited an expected variation that can be attributed to typical diurnal changes in ionospheric structure. At substorm onset, the signatures disappeared because of either a suppression of resonance conditions by substorm-related particle precipitation or enhanced power in the Pc1 spectrum that concealed continuing IAR SRS. After the substorm, the SRS reappeared; however the harmonics had shifted to lower frequencies with tighter frequency spacing. For the first time, we show that this time-dependent behavior in IAR SRS is explained by increased F region densities resulting from electron precipitation. Similarities between observed IAR harmonic frequencies and those calculated with a model suggest that variations in F region density, especially foF2, may often dominate the evolution of IAR eigenfrequencies. This could potentially provide a mechanism for monitoring topside dynamics using IAR SRS.

Parent, Adrienne; Mann, Ian R.; Rae, I. Jonathan

2010-02-01

202

Doppler shift observations of severe tropospheric weather effects in the ionosphere  

Microsoft Academic Search

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

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

2007-01-01

203

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

Microsoft Academic Search

This paper investigates the third-order residual range error in the dual-frequency correction of ionospheric effects on satellite\\u000a navigation. We solve the two-point trajectory problem using the perturbation method to derive second-approximation formulas\\u000a for the phase path of the wave propagating through an inhomogeneous ionosphere. It is shown that these formulas are consistent\\u000a with the results derived from applying perturbation theory

B. C. Kim; M. V. Tinin

2007-01-01

204

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

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

205

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

NASA Astrophysics Data System (ADS)

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

Le, G.; Pfaff, R. F.; Kepko, E. L.; Rowland, D. E.; Bromund, K. R.; Freudenreich, H.; Martin, S. C.; Liebrecht, M. C.; Maus, S.

2010-12-01

206

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.

207

Characteristics of Pi2 Electric Pulsations at the Ionosphere  

NASA Astrophysics Data System (ADS)

At the onset of magnetospheric substorms, impulsive hydromagnetic oscillations occur with period range from 40 to 150 seconds. They are called Pi2 magnetic pulsations and occur globally in the magnetosphere. Pi2 has been studied with arrays of magnetometers on the ground and with in-situ observation by satellites. However Pi2 electric pulsation in the low-latitude ionosphere is not yet clarified sufficiently. Therefore we have focused on measuring Pi2 electric pulsations by an FM-CW radar. In order to detect the ionospheric electric fields we have built an FM-CW (HF) radar at Sasaguri, Fukuoka, Japan (Magnetic Latitude: 23.2 degree, Magnetic Longitude: 199.6 degree). The radar provides us Doppler information of the ionosphere by high-time resolution of 10 sec. When the eastward electric field penetrates into the low- latitude ionosphere, it drifts upward owing to the frozen-in effects of the F-region. In contrast to the penetration of the eastward electric field, the ionosphere drifts downward when the westward electric field penetrates. Thus we can measure the east-west ionospheric electric fields. From our ionospheric radar observation, Pi2 electric pulsation of about 0.2 mV/m amplitude can be identified in nightside at Nov.6, 2003. We also compared the Pi2 with geomagnetic field data obtained from Circum-pan Pacific Magnetic Network (CPMN) stations. As a result, we found a phase lag between the Pi2 electric pulsation and mightside magnetic Pi2 pulsation at Kujyu (KUJ; M. Lat. 23.6 degree, M. Lon. 203.2 degree).

Ikeda, A.; Yumoto, K.; Shinohara, M.; Nozaki, K.; Yoshikawa, A.; Uozumi, T.; Tokunaga, T.; Hirayama, Y.

2007-12-01

208

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

NASA Astrophysics Data System (ADS)

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

Šulic, D.; Nina, A.; Sreckovic, V.

2010-07-01

209

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

NASA Astrophysics Data System (ADS)

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

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

1993-02-01

210

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

PubMed

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

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

2006-11-10

211

Electron Gyroharmonic Effects in Ionization and Electron Acceleration during High-Frequency Pumping in the Ionosphere  

SciTech Connect

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

Gustavsson, B. [Department of Physics and Technology, University of Tromsoe, Tromsoe (Norway); Leyser, T. B. [Swedish Institute of Space Physics, Uppsala (Sweden); Kosch, M. [Department of Communication Systems, Lancaster University, Lancaster (United Kingdom); Rietveld, M. T. [EISCAT Scientific Association, Ramfjordmoen (Norway); Steen, A. [Remspace Inc., Linkoeping (Sweden); Braendstroem, B. U. E. [Swedish Institute of Space Physics, Kiruna (Sweden); Aso, T. [National Institute of Polar Research, Tokyo (Japan)

2006-11-10

212

Electron Gyroharmonic Effects in Ionization and Electron Acceleration during High-Frequency Pumping in the Ionosphere  

Microsoft Academic Search

Optical emissions and incoherent scatter radar data obtained during high-frequency electromagnetic pumping of the ionospheric plasma from the ground give data on electron energization in an energy range from 2 to 100 eV. Optical emissions at 4278 Å from N2+ that require electrons with energies above the 18 eV ionization energy give the first images ever of pump-induced ionization of

B. Gustavsson; T. B. Leyser; M. Kosch; M. T. Rietveld; Å. Steen; B. U. E. Brändström; T. Aso

2006-01-01

213

General overview of the solar activity effects on the lower ionosphere  

NASA Technical Reports Server (NTRS)

Solar activity influences the ionospheric D region. That influence manifests itself both in the form of various solar induced disturbances and in the form of the D region dependence on solar activity parameters (UV-flux, interplanetary magnetic field, solar wind etc.) in quiet conditions. Relationship between solar activity and meteorological control of the D region behavior is considered in detail and examples of strong variations of aeronomical parameters due to solar or meteorological events are given.

Danilov, A. D.

1989-01-01

214

Simulation of equatorial electrojet magnetic effects with the thermosphere-ionosphere-electrodynamics general circulation model  

Microsoft Academic Search

In this work, the magnetic variations simulated by the NCAR thermosphere-ionosphere-electrodynamics general circulation model (TIE-GCM) in the vicinity of the magnetic equator are examined to evaluate the ability of this model to reproduce the major features of the equatorial electrojet (EEJ) as observed on the ground as well as on board low-altitude orbiting satellites. The TIE-GCM simulates electric currents of

V. Doumbia; A. Maute; A. D. Richmond

2007-01-01

215

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

216

An effect of the ionospheric Alfvén resonator on multiband Pc1 pulsations  

NASA Astrophysics Data System (ADS)

. On 2 December 1999, the magnetometer stations in northern Finland registered structured Pc1 activity simultaneously in three distinct frequency bands. Using simultaneous EISCAT radar measurements of the high-latitude ionosphere, we have studied the ionospheric resonator properties during this multiband Pc1 event. The frequencies of the three structured Pc1 bands were found to closely correspond to the second, third and fourth harmonic of the calculated fundamental frequency of the ionospheric Alfvén resonator (IAR). In addition, those frequencies of the three pearl bands that were closest to the exact IAR harmonics were found to have the strongest intensities. The results demonstrate that the resonator can have an important role on ground-based Pc1 activity over a notably large frequency range, favoring transmission of waves with frequencies close to the resonator's eigenfrequencies. Since the frequencies of all three bands correspond to the maximum rather than the minimum of the transmission coefficient, the traditional bouncing wave packet model needs to be revised.

Prikner, K.; Mursula, K.; Kangas, J.; Kerttula, R.; Feygin, F.

2004-02-01

217

Ionospheric and Thermospheric Effects During the Initial Radiative Phase of the Bastille Day Event  

NASA Astrophysics Data System (ADS)

Increases in the solar EUV and X-ray irradiance during a solar flare can produce enhanced ionization and heating in the terrestrial ionosphere. The resulting energetic photoelectrons in turn cause increases in the far ultraviolet (FUV) dayglow (100 - 150 nm). Enhancements of some 50 per cent had previously been detected in OGO-4 nadir-viewing data [C B Opal, Space Research XIII, 797, 1973]. Similar enhancements have now been seen in the FUV limb-viewing dayglow observations from the ARGOS satellite during the Bastille Day flare (July 14, 2000). Because extinction of the FUV dayglow by O2 prevents seeing below 140 km tangent altitude on the limb, increases in the dayglow above that altitude must be caused by the component of the flare spectral irradiance which is deposited there, namely at wavelengths greater than 20 nm. This conclusion is corroborated by the observation of the flare at 30.3 nm made by the SEM instrument on the SOHO satellite. We study this solar-ionospheric connection using a modified version of the NRL solar spectrum as input to the SAMI2 ionospheric model, and also calculate thermospheric heating rates for this event.

Meier, R. R.; Drob, D. P.; Nicholas, A. C.; Bishop, J.; Picone, J. M.; Thonnard, S. E.; Dymond, K. F.; Budzien, S. A.; Lean, J.; Mariska, J. T.; Huba, J. D.; Joyce, G.; Warren, H. P.; Judge, D. L.

2001-05-01

218

Dawn/Dusk Auroras and Propagating Convection Disturbances: Ionospheric Effects of Increasing Solar Wind Ram Pressure  

NASA Astrophysics Data System (ADS)

A dawn/dusk auroral event that occurred on June 27, 1997 has been studied using observations from the WIND and POLAR spacecraft, Antarctic all-sky images, and Greenland magnetometers. The aurora was caused by a gradual (T ~ 90 min), intense (Pram ~ 11 nPa) solar wind ram pressure (\\varrho V2) pulse. Auroral intensities on both dawn and dusk flanks of the auroral oval increased linearly with the pressure increase. The aurora occurred in both diffuse and discrete forms. The energy deposition flux into discrete auroras was calculated to be increased by a factor of ~5 when the ram pressure increased by a factor of ~2 during the event. Propagating convection disturbances in the ionosphere were also detected within the auroras. The convection disturbances appeared in the magnetograms as ~20 min period and ~100 nT amplitude pulsations, which propagated antisunward at a speed of ~11 km/s. This ionospheric speed mapped to the magnetosheath flow speed very well. Mechanisms of the ionospheric responses are suggested to be some form of viscous interaction that occurs on the magnetopause boundary layer (such as the Kelvin-Helmholtz instability) and adiabatic compression.

Zhou, X.; Tsurutani, B. T.; Mende, S. B.; Frey, H. U.; Watermann, J. F.; Sibeck, D. G.; Arballo, J. K.

2001-12-01

219

Dawn/dusk auroras and geomagnetic fluctuations: Ionospheric effects of intense solar wind ram pressure  

NASA Astrophysics Data System (ADS)

A dawn/dusk auroral event has been studied using multiple observations from the Wind and Polar spacecraft, Antarctic all-sky images, and Greenland magnetometers. The aurora was caused by a gradual (T?90 min), intense (maximum of Pram?11 nPa) solar wind ram pressure pulse that occurred on June 27, 1997. The aurora occurred with both diffuse and discrete forms. The energy deposition flux into the discrete auroral structures is calculated to have increased by a factor of ˜5 when the ram pressure increased by a factor of ˜2 during the event. Ionospheric propagating convection disturbances were also detected within the auroral region. The geomagnetic disturbance propagated antisunward in the ionosphere at a speed of ˜11 km s-1 which mapped into the dawnside magnetopause at a speed of ˜405 km s-1. This value is in good agreement with the magnetosheath flow speed. Mechanisms of the ionospheric responses are speculated to be magnetopause perturbations, some form of viscous interaction that occurs on the magnetopause boundary layer (such as the Kelvin-Helmholtz instability), adiabatic compression, or magnetic field shearing.

Zhou, X.-Y.; Frey, H. U.; Watermann, J. F.; Tsurutani, B. T.; Sibeek, D. G.; Mende, S. B.; Arballo, J. K.

220

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

221

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

222

Design of a Thermosphere-Ionosphere Data Assimilation Scheme  

NASA Astrophysics Data System (ADS)

Changes in thermospheric density affect the drag experienced by low-orbiting satellites and hence their orbits, the associated loss in orbit predictability causing difficulties for satellite operators. Space weather is one cause for these density changes, as the associated changes in solar or geomagnetic activity affect the coupled thermosphere-ionosphere system. The ATMOP project (www.atmop.eu) is designed to provide a European capability for nowcasting and forecasting of the thermosphere. One project component is developing a data assimilation scheme to bring real thermospheric and ionospheric observations into a physical model of the thermosphere-ionosphere system, in order to improve the model's representation of thermospheric density. Here we present ongoing work on this data assimilation scheme, including quality control of observations such as total electron content (TEC) maps, the design of the assimilation scheme itself, and prospects for future extensions such as driving the thermosphere-ionosphere model's lower boundary with output from the Met Office's Unified Model, to include lower atmosphere effects on the thermosphere and ionosphere.

Henley, E.; Jackson, D.; Chartier, A. T.; Johnson, D. G.

2012-12-01

223

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

224

HF propagation characteristics of artificial ionospheric layers  

Microsoft Academic Search

Artificial ionospheric layers descending from the background F-region ionosphere can be produced by highpower HF transmissions with effective radiated powers of 10 5 ->10 6 W, especially near harmonics of the electron gyrofrequency. Multiple high-speed DPS-4D ionosondes were utilized to obtain direct and oblique ionospheric soundings from a large number of artificial layers during an experimental campaign at the High

Todd Pedersen; Bodo Reinisch; Vadym Paznukhov; Ryan Hamel

2011-01-01

225

Ionosphere-reflected propagation  

NASA Technical Reports Server (NTRS)

The predictability of those ionospheric parameters relevant to ionosphere-reflected communications is considered along with their optimum utilization. Several excellent original articles and review papers which have been published from time to time dealing with the long term and short term forecasting of ionospheric parameters, radio systems, and modelling needs for ionospheric communications, are covered.

Reddy, B. M.

1979-01-01

226

Activities Report on Ionospheric Observation.  

National Technical Information Service (NTIS)

Sounding rocket electrostatic wave investigations; experiments involving provoked ionospheric disturbances; noctilucent cloud research; and Viking satellite studies of ionosphere-magnetosphere coupling are summarized. Ionospheric modification by stimulate...

1983-01-01

227

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

PubMed

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

Coates, Andrew J

2009-02-28

228

Ionospheric corrections for GPS time transfer  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

229

Ionospheric mapping function for total electron content (TEC) using global positioning system (GPS) data in Malaysia  

Microsoft Academic Search

The ionosphere layer is very important to the communication system. This research involves the determination of total electron content (TEC) in ionosphere based on height in order to determine the appropriate TEC value for Malaysia and for the equitorial region generally. The ionospheric model used is the single layer model based on the Bernese GPS 5.0 Software. The ionosphere TEC

Norsuzila Ya' acob; Mardina Abdullah; Mahamod Ismail; Siti Aminah Bahari; M. K. Ismail

2008-01-01

230

Ionospheric imaging in Africa  

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

231

LETTER: Effects of mobility on ordering dynamics  

NASA Astrophysics Data System (ADS)

Models of ordering dynamics allow us to understand natural systems in which an initially disordered population homogenizes some traits via local interactions. The simplest of these models, with wide applications ranging from evolutionary to social dynamics, are the Voter and Moran processes, usually defined in terms of static or randomly mixed individuals that interact with a neighbor to copy or modify a discrete trait. Here we study the effects of diffusion in Voter/Moran processes by proposing a generalization of ordering dynamics in a metapopulation framework, in which individuals are endowed with mobility and diffuse through a spatial structure represented as a graph of patches upon which interactions take place. We show that diffusion dramatically affects the time to reach the homogeneous state, independently of the underlying network's topology, while the final consensus emerges through different local/global mechanisms, depending on the mobility strength. Our results highlight the crucial role played by mobility in ordering processes and set up a general framework that allows its effect to be studied on a large class of models, with implications in the understanding of evolutionary and social phenomena.

Baronchelli, Andrea; Pastor-Satorras, Romualdo

2009-11-01

232

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

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

233

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

234

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

NASA Astrophysics Data System (ADS)

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

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

2010-10-01

235

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

Microsoft Academic Search

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

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

1995-01-01

236

Effective medium theory of ordering in alloys  

SciTech Connect

This thesis presents the first study of alloy phase stability based on the effective medium theory (EMT) of intermetallic interaction. The systems under study are the noble metal alloys of Cu and Au. EMT theory is applied to Cu-Au system to study the Cu-Au configurational ordering phase diagram and to study the kinetics of Cu{sub 3}Au order-disorder transition. Monte Carlo simulations and mean field theory are the statistical techniques used in the study. The agreements with experimental results are broad, the three stoichiometric composition structures, their order-disorder transition temperatures, the lattice constant, the cohesive energy, the superlattice structure in Cu{sub 50}Cu{sub 50}, the Cu-Au phase diagram, and the anisotropy in structure factor in domain growth in Cu{sub 3}Au. This work also compares EMT with Ising model and results of other methods. The author concludes that EMT is a proper theory for interatomic interactions in intermetallic alloys.

Xi, Z.

1993-12-31

237

Exploring the Effects of Ionospheric Outflow on the Inner Magnetosphere using RAM-SCB  

NASA Astrophysics Data System (ADS)

The Ring current Atmosphere interactions Model with Self-Consistently calculated 3D Mag-netic field (RAM-SCB) has been used to successfully study inner magnetosphere dynamics during different solar wind and magnetosphere conditions. Historically, this numerical model has relied on empirical formulations to provide magnetic field boundary conditions, ionospheric electric potential, and to specify heavy ion composition at the outer boundary. Either empirical models or observations typically specify plasma density and temperature at the boundary. Re-cently, RAM-SCB has been integrated into the Space Weather Modeling Framework, a flexible system that creates real time, two-way coupling between RAM-SCB, the multi-species version of BATS-R-US global MHD and the Polar Wind Outflow Model. Through these couplings, RAM-SCB receives first-principle derived magnetic and plasma boundary conditions as well as convective electric potentials from the SWMF and returns inner magnetosphere plasma pres-sure to correct the MHD solution. This work uses the newly coupled system to explore the relationship between ionospheric outflow and ring current plasma distribution and composition. Data-model comparisons of magnetic field and particle fluxes are used to investigate how well the coupled system represents real world conditions.

Welling, Daniel; Jordanova, Vania; Zaharia, Sorin; Toth, Gabor

238

Effects of background and observational error covariance models on ionospheric data assimilation  

NASA Astrophysics Data System (ADS)

With relatively limited observations, a data assimilation model could build the ionospheric electron density distribution in near real time. In this study, a model based on the Gauss-Markov Kalman filter with the International Reference Ionosphere (IRI) as the background assimilates the two different observations of ground-based GPS TEC (total electron content) and F3/C RO (FORMOSAT-3/COSMIC radio occultation) TEC. Two different background model error covariance, locational-independent and locational-dependent are adopted. The later remains the vertical and horizontal correlation at each location calculates from empirical orthogonal functions (EOFs), while the former models from the same Gaussian function. Here, the satellite slant TEC is used in the model to assimilate the electron density. Several observing system simulation experiments (OSSEs) show that the assimilated electron density by using locational-dependent error covariance has better preference than locational-independent one. Finally, data of incoherent scatter radar and ionosonde are used to valid the data assimilation results.

LIN, C.; Matsuo, T.; Araujo-Pradere, E. A.; Liu, J. G.; Lin, C.

2013-12-01

239

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

240

Towards a Predictive Model of Low Latitude Ionospheric Space Weather  

Microsoft Academic Search

Space weather in the earth's equatorial ionosphere, in the form of rising bubble structures, can have significant effects on space-based satellite communications and navigation system and, as a result, have important societal consequences. For example, the Global Positioning System (GPS) can suffer severe scintillation and fading due to the ionospheric density structures associated with equatorial ionospheric bubbles. The development of

M. Keskinen; S. L. Ossakow; B. G. Fejer

2003-01-01

241

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

242

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

NASA Astrophysics Data System (ADS)

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

Rycroft, M. J.; Odzimek, A.

2010-06-01

243

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

NASA Astrophysics Data System (ADS)

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

Rycroft, M. J.; Odzimek, A.

2010-06-01

244

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

NASA Astrophysics Data System (ADS)

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

Rycroft, Michael J.; Odzimek, Anna

2010-05-01

245

Influence of water vapour on the height distribution of positive ions, effective recombination coefficient and ionisation balance in the quiet lower ionosphere  

NASA Astrophysics Data System (ADS)

Mesospheric water vapour concentration effects on the ion composition and electron density in the lower ionosphere under quiet geophysical conditions were examined. Water vapour is an important compound in the mesosphere and the lower thermosphere that affects ion composition due to hydrogen radical production and consequently modifies the electron number density. Recent lower-ionosphere investigations have primarily concentrated on the geomagnetic disturbance periods. Meanwhile, studies on the electron density under quiet conditions are quite rare. The goal of this study is to contribute to a better understanding of the ionospheric parameter responses to water vapour variability in the quiet lower ionosphere. By applying a numerical D region ion chemistry model, we evaluated efficiencies for the channels forming hydrated cluster ions from the NO+ and O2+ primary ions (i.e. NO+.H2O and O2+.H2O, respectively), and the channel forming H+(H2O)n proton hydrates from water clusters at different altitudes using profiles with low and high water vapour concentrations. Profiles for positive ions, effective recombination coefficients and electrons were modelled for three particular cases using electron density measurements obtained during rocket campaigns. It was found that the water vapour concentration variations in the mesosphere affect the position of both the Cl2+ proton hydrate layer upper border, comprising the NO+(H2O)n and O2+(H2O)n hydrated cluster ions, and the Cl1+ hydrate cluster layer lower border, comprising the H+(H2O)n pure proton hydrates, as well as the numerical cluster densities. The water variations caused large changes in the effective recombination coefficient and electron density between altitudes of 75 and 87 km. However, the effective recombination coefficient, ?eff, and electron number density did not respond even to large water vapour concentration variations occurring at other altitudes in the mesosphere. We determined the water vapour concentration upper limit at altitudes between 75 and 87 km, beyond which the water vapour concentration ceases to influence the numerical densities of Cl2+ and Cl1+, the effective recombination coefficient and the electron number density in the summer ionosphere. This water vapour concentration limit corresponds to values found in the H2O-1 profile that was observed in the summer mesosphere by the Upper Atmosphere Research Satellite (UARS). The electron density modelled using the H2O-1 profile agreed well with the electron density measured in the summer ionosphere when the measured profiles did not have sharp gradients. For sharp gradients in electron and positive ion number densities, a water profile that can reproduce the characteristic behaviour of the ionospheric parameters should have an inhomogeneous height distribution of water vapour.

Barabash, V.; Osepian, A.; Dalin, P.

2014-03-01

246

Bulk photogalvanic effects beyond second order  

NASA Astrophysics Data System (ADS)

Examining the bulk photogalvanic effect (BPE) at nonperturbative laser fields, it is shown that illuminating a thin noncentrosymmetric crystal, quasicrystal, or nanotube the point group of which is Dn>2, C(3,5,…)h, or D(3,5,…)h with a monochromatic linearly polarized field, at practically any orientation, induces a nonvanishing directed current component jz along its polar axis. This is in contrast to the vanishing jz predicted by the commonly employed photogalvanic tensor. Similarly, we discuss the appearance of an angular-dependent jz, already for C(n>2)v and Cn>2, and circular dichroism in the BPE that are not resolved in second order. We suggest the possible observation of these currents in, e.g., thin ?-quartz and LiNbO3:Fe crystals and single-walled chiral carbon nanotubes.

Alon, Ofir E.

2003-03-01

247

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

248

The ultra-fast Kelvin waves in the equatorial ionosphere: observations and modeling  

NASA Astrophysics Data System (ADS)

The main purpose of this study is to investigate the vertical coupling between the mesosphere and lower thermosphere (MLT) region and the ionosphere through ultra-fast Kelvin (UFK) waves in the equatorial atmosphere. The effect of UFK waves on the ionospheric parameters was estimated using an ionospheric model which calculates electrostatic potential in the E-region and solves coupled electrodynamics of the equatorial ionosphere in the E- and F-regions. The UFK wave was observed in the South American equatorial region during February-March 2005. The MLT wind data obtained by meteor radar at São João do Cariri (7.5° S, 37.5° W) and ionospheric F-layer bottom height (h'F) observed by ionosonde at Fortaleza (3.9° S; 38.4° W) were used in order to calculate the wave characteristics and amplitude of oscillation. The simulation results showed that the combined electrodynamical effect of tides and UFK waves in the MLT region could explain the oscillations observed in the ionospheric parameters.

Onohara, A. N.; Batista, I. S.; Takahashi, H.

2013-02-01

249

The effects of interplanetary magnetic field orientation on dayside high-latitude ionospheric convection  

NASA Technical Reports Server (NTRS)

The Atmosphere Explorer C data base of Northern Hemisphere ionospheric convection signatures at high latitudes is examined during times when the interplanetary magnetic field orientation is relatively stable. It is found that when the interplanetary magnetic field (IMF) has its expected garden hose orientation, the center of a region where the ion flow rotates from sunward to antisunward is displaced from local noon toward dawn irrespective of the sign of By. Poleward of this rotation region, called the cleft, the ion convection is directed toward dawn or dusk depending on whether By is positive or negative, respectively. The observed flow geometry can be explained in terms of a magnetosphere solar wind interaction in which merging is favored in either the prenoon Northern Hemisphere or the prenoon Southern Hemisphere when the IMF has a normal sector structure that is toward or away, respectively.

Heelis, R. A.

1984-01-01

250

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

251

Electrodynamics of the Nighttime Equatorial Ionosphere: the Effects of Winds and Waves  

NASA Astrophysics Data System (ADS)

In this paper we present initial results from two sounding rockets designed to study the coupling bewteen neutral winds and electric fields in the equatorial ionosphere. The combined instrumented and chemical release payloads were launched from Kwajalein in September 2004. The rockets carried instruments measuring electric fields, plasma densities, neutral densities, and was accompanied by a TMA release to profile neutral winds. Ground based airglow imagers and were used to determine mesospheric conditions; specifically, the presence of gravity waves. The goal of the experiment was to investigate correlations between the gravity wave wind structure and local electric fields. This coupling is expected to be appreciable at the equator, where the magnetic field is nearly horizontal. Here we present initial results and discuss plans for data analysis.

Gelinas, L. J.; Kelley, M. C.; Clemmons, J.; Larsen, M.; Makela, J.

2004-12-01

252

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

253

Speed-dependent collision effects on radar back-scattering from the ionosphere. [incoherent scatter radar  

NASA Technical Reports Server (NTRS)

The question whether the differences between fluctuation spectra for linearly speed-dependent and speed-independent collision frequencies could account for disagreements between rocket and incoherent scatter estimate was addressed. The basic theory used for computing the fluctuation spectrum is outlined. The speed-dependence of the charge-neutral collision frequency is discussed, with special emphasis on its derivation from the mobility measurements. Various developments of the computer code used for the computation of the fluctuation spectrum are described. The range of values of input parameters typical to the collision-dominated ionosphere are briefly described. The computational results are presented, and the significance and limitation of these results and the future scope of the research are discussed.

Behl, Y. K.; Theimer, O. H.

1982-01-01

254

Birth order effects on autism symptom domains.  

PubMed

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 families. In addition, the intercorrelations between the measures were compared between siblings. The overall mean repetitive behavior total score was significantly higher (worse) in first-born than in second-born siblings. In contrast, first-born siblings had significantly lower (better) useful phrase speech than their younger siblings. Autism social and non-verbal communication scores were significantly correlated in first- and in second-born siblings. However, there was a significant difference in the coefficients between first- and second-born siblings. Performance on the non-verbal communication domain was also significantly and positively correlated with useful phrase speech score in both first- and second-born siblings. It is unclear at this time whether these results are of biologic origin. Nevertheless, the findings suggest that genetic studies in autism using specific levels of familial autism traits as phenotypes should take into account their intercorrelations and birth order effects embedded in the instrument. PMID:17289158

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

2007-03-30

255

Ionospheric characteristics: a review  

SciTech Connect

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

Rich, F.J.

1983-01-01

256

Ionospheric Observation Activities Report.  

National Technical Information Service (NTIS)

Space plasma physics research, particularly high latitude ionospheric phenomena and phenomena related to the interaction of the ionosphere with the magnetosphere and with the neutral atmosphere is summarized. Experiments using sounding rockets, the Viking...

1984-01-01

257

The Effect of the Ionosphere on Communication, Navigation and Surveillance Systems Based on Ionosph eric Effects Symposium held on 5-7 May 1987 in Springfield, Virginia  

NASA Astrophysics Data System (ADS)

Topics addressed include: wideband high frequency and longwave studies, tranionospheric propagation - total electron content, high frequency measurements, ionospheric modification, high frequency models, spacecraft glow, transionospheric propagation - scintillation, and high latitude ionospheric interaction.

Goodman, John M.; Klobuchar, John A.; Joiner, R. G.; Soicher, Haim

258

Investigating ionosphere-thermosphere space weather using ensemble based modeling  

NASA Astrophysics Data System (ADS)

In order to be able to predict ionosphere-thermosphere space weather using numerical models, it is necessary to understand the sources of uncertainty within the model. A major source of uncertainty arises due to inaccurate specification of the external drivers of the ionosphere-thermosphere system. In addition, uncertainties within the ionosphere-thermosphere models themselves, due to the myriad of parameterizations that are utilized, results in further uncertainty in the prediction. One way to help quantify the uncertainty when attempting to predict space weather is to use ensembles of model simulations to better understand the effects of these different sources of uncertainty on the system. This is done in the lower atmospheric community where, for example, ensembles of model runs are used to predict the percent chance that there will be a thunderstorm tomorrow. In this presentation, we examine the effect that uncertainty in the high-latitude drivers has on the upper atmosphere using ensembles of simulations of the Global Ionosphere-thermosphere model. The ensembles are created using results from an analysis of solar wind data from the past 15 years.

Pawlowski, D. J.; Ridley, A. J.; Flegal, J.

2013-12-01

259

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

260

Dynamic processes in the ionosphere during magnetic storms from the Kharkov incoherent scatter radar observations  

NASA Astrophysics Data System (ADS)

[1] Results of studying the ionosphere behavior during several magnetic storms of various intensities are presented. The features of pronounced negative ionospheric disturbances accompanying the severe magnetic storms on 25 September 1998 and 29-30 May 2003 (Kp ? 8) are considered. Among them there are a decrease in the electron density by a factor of 3-4, uplifting of the ionospheric F2 layer by 100-160 km, increase in the temperature of the charged and neutral atmospheric components, and infringement of plasma transfer processes and thermal balance in the ionosphere-plasmasphere system. In the morning of 25 September 1998, an unusual increase in the upward plasma drift velocity was registered. On 29-30 May 2003 during the storm main phase, a depletion of the relative density of hydrogen ions by more than an order of magnitude was observed that could manifest an emptying of the magnetic flux tube over Kharkov. These effects are explained in terms of thermospheric disturbances, Joule heating, particle precipitation, penetration of magnetospheric electric fields to midlatitudes, the shift of the main ionospheric trough and related structures toward the radar latitude, etc. The ionospheric storm on 20-21 March 2003 had two phases. Its strong negative phase proceeded against a background of a minor geomagnetic disturbance (Kp ? 5). The destabilizing impact of the electric field pulse and traveling atmospheric disturbance generated by magnetospheric substorms could be the cause of the change in the storm phase that occurred in the sunset period.

Chernogor, L. F.; Grigorenko, Ye. I.; Lysenko, V. N.; Taran, V. I.

2007-10-01

261

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

262

Data Assimilation Model for the Thermospheric Neutral Winds at Mid- and Low-Latitudes and Its Use for Ionosphere-Thermosphere Studies  

NASA Astrophysics Data System (ADS)

The dynamics of the mid- and low-latitude F region ionosphere and the ionosphere-thermosphere coupling are strongly controlled by thermospheric neutral winds. Consequently, in order to understand various mid- and low-latitude ionospheric phenomena it is vital to have an accurate representation of thermospheric winds. However, up to date, their reliable estimation remains a challenge because of difficulties in both, measurement and modeling. The global sparseness and lack of continuous observations of global thermospheric winds often make empirical wind models to fall short in adequately reproducing even their observed climatology. For the present work a new method was developed to estimate global thermospheric neutral winds by combining ionospheric observations with a Kalman filter technique. First, the neutral wind along the magnetic meridian is obtained by assimilating seasonally averaged COSMIC radio occultation data of F-region ionosphere peak parameters (NmF2 and hmF2) into the Global Assimilation of Ionospheric Measurements Full Physics (GAIM-FP) model. The model, which is based on the Ionosphere Plasmasphere Model (IPM) and an Ensemble Kalman filter, provides 3D electron density throughout the ionosphere together with the magnetic meridional wind required to match the model results with the observed ionospheric parameters. Next, the estimation of global zonal and meridional winds is performed using a separate Kalman filter, based on a physics-based 3D thermospheric neutral wind model and on the GAIM-FP calculated magnetic meridional wind data. The ionospheric drag and ion diffusion velocities, needed for the wind calculation, are also provided by GAIM-FP. As an output the model gives the 3D thermospheric neutral wind field at mid- and low-latitudes in the 110 - 600 km altitude range. The results of our wind decomposition are presented for three different seasons during recent solar minimum and the effects of the neutral wind on longitudinal variations observed in the ionosphere are shown.

Lomidze, L.; Scherliess, L.

2013-12-01

263

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

264

An improved coupling model for the lithosphere-atmosphere-ionosphere system (Invited)  

NASA Astrophysics Data System (ADS)

In order to explain the observed ionospheric TEC variations before strong earthquakes, we have developed a comprehensive model for the lithosphere-atmosphere-ionosphere (LAI) coupling [Kuo et al., 2011]. In our previous model, the dynamo current flows from the lithosphere, through the atmosphere, and into the ionosphere. The TEC variations in the ionosphere are numerically calculated based on NRL SAMI3 code. Nighttime plasma bubbles are generated for large earthquakes. However, the current in the atmosphere is obtained by first solving the electric field ? from ?(??), where the conductivity tensor ? consists of Pedersen and Hall conductivity. The background magnetic field is assumed to be perpendicular to the horizontal plane. In the present paper, we improve the calculation of currents in the atmosphere by solving the current density J directly from the current continuity equation ?J = 0. The currents in the atmosphere can be solved for any arbitrary angle of magnetic field, i.e., any magnetic latitude. The effects of atmospheric currents and electric fields on the ionosphere with lithosphere current source located at low magnetic altitude 15° and middle magnetic altitude 30° are obtained. For upward (downward) atmospheric currents flowing into the ionosphere, the simulation results show that the westward (eastward) electric fields dominate. At magnetic latitude 15°, the upward (downward) current causes the increase (decrease) of TEC, while the upward (downward) current causes the decrease (increase) of TEC at higher magnetic latitude 30°. The dynamo current density required to generate the same amount of TEC variation in the improved model is found to be smaller by a factor of 30 as compared to that obtained in our earlier paper. We also calculate the ionosphere dynamics with imposed zonal westward and eastward electric field based on SAMI3 code. In the nighttime ionosphere, it is found that the westward electric field may trigger two plasma bubbles on the two sides of the imposed electric field region, while a single plasma bubble is formed just above the imposed eastward electric field region.

Lee, L.; Kuo, C.; Huba, J. D.

2013-12-01

265

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

NASA Astrophysics Data System (ADS)

This study presents the modeling of ionospheric response to geomagnetic storms of September 9-14, 2005. We examine the performance of the Global Self-Consistent Model of Thermosphere, Ionosphere and Protonosphere (GSM TIP) and International Reference Ionosphere-2000 (IRI-2000), and compare the modeling predictions with the ionosonde and incoherent scatter radar observations over Yakutsk, Irkutsk, Millstone Hill and Arecibo stations. IRI-2000 predicted well all negative foF2 disturbances. In comparison with IRI-2000, the GSM TIP better reproduced the positive phase observed during the disturbed times. We discuss the possible reasons of the differences between the GSM TIP model calculations, IRI predictions, and the observations.

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

2012-06-01

266

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

267

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

NASA Astrophysics Data System (ADS)

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

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

2010-10-01

268

Ionospheric Challenges for GNSS Based Augmentation Systems  

NASA Astrophysics Data System (ADS)

The ionosphere is a highly dynamic physical phenomenon that presents a variable source of error for Global Navigation Satellite System (GNSS) signals and GNSS based operational systems. The Federal Aviation Administration's (FAA) Wide-Area Augmentation System (WAAS) was designed to enhance the GNSS standard positioning service by providing additional accuracy, availability and integrity that is sufficient for use in commercial aviation. It is the first of a number of planned regional Satellite Based Augmentation Systems (SBAS). Other systems in development include the European EGNOS system, the MSAS system in Japan and the GAGAN system in India. In addition, the South American countries are investigating the feasibility of operating an SBAS system in this region. Much of the WAAS ionospheric research and development focused on defining and mitigating ionospheric challenges characteristic of the mid-latitude regions, where the ionosphere is well studied and relatively quiescent. The EGNOS and MSAS systems will primarily operate under a similarly quiescent mid-latitude ionosphere. SBAS system development in South America, India and other low-latitude regions, however, will have to contend with much more extreme conditions. These conditions include strong spatial and temporal gradients, plasma depletions and scintillation. All of these conditions have a potential to limit SBAS performance in the low latitude regions. This presentation will review the effects that the ionosphere has on the mid-latitude WAAS system. It will present the techniques that are used to mitigate ionospheric disturbances induced on the system during severe geomagnetic activity and it will quantify the effect that this activity has on system performance. The presentation will then present data from the South American Low-latitude Ionospheric Sensor Network (LISN) that can be used to infer the ionospheric effects on SBAS performance in the most challenging low-latitude ionospheric environment. LISN is a network of GNSS receivers and other ionospheric sensors that are in the process of deployment and installation across the western half of South America. Its purpose is to address key questions about the physics of the equatorial ionosphere and to develop forecasting/predictions capabilities concerning the onset of equatorial Spread F. The International Civil Aviation Organization has committed to transition to satellite navigation. This presentation will summarize the effects and the limitations that the ionosphere places on satellite based navigation systems.

Doherty, P.; Valladares, C. E.

2007-12-01

269

Time domain effects of model order reduction  

Microsoft Academic Search

It is suggested that a preliminary and essential step in the design of flight control systems for highly augmented aircraft is obtaining an accurate open-loop dynamics model. Very large-order open-loop state-space models are constructed from analytical and empirical data obtained from knowledge of the vehicle's aerodynamics, propulsion, and structure dynamics. A balancing methodology for reducing a very large-order state-space representation

Robert J. Dudginski; Richard D. Colgren

1988-01-01

270

Effects observed in the ionospheric F region in the east Asian sector 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 a companion paper (hereinafter referred to as paper 1), the effects observed in the F region during the intense geomagnetic disturbances in the early part of November 2004 in the Latin American sector were presented. In the present paper, we investigate the effects observed in the F region during the intense geomagnetic disturbances in the early part of November 2004 in the east Asian sector. We have used the ionospheric sounding observations at Ho Chi Minh City (Vietnam) and Okinawa, Yamagawa, Kokubunji, and Wakkanai (Japan) in the present investigations. Also, GPS observations in the east Asian sector (several longitude zones) have been used to study the effect in the F region during the intense geomagnetic disturbances. The ion density versus latitudinal variations obtained by the DMSP F15 satellite orbiting at about 800 km altitude in the east Asian sector and the magnetic field data obtained at several stations in the Japanese meridian are also presented. Several important features from these observations in both the sectors during this extended period of intense geomagnetic disturbances are presented. The east Asian sector showed very pronounced effects during the second superstorm, which was preceded by two storm enhancements. It should be mentioned that around the beginning of the night on 10 November, ionospheric irregularities propagating from higher midlatitude region to low-latitude region were observed in the Japanese sector. The most intense geomagnetic field H component in that sector was observed on 10 November at L = 2.8, indicating that the auroral oval and the heating got further to low latitudes and the ionospheric irregularities observed in the Japanese sector on this night are midlatitude ionospheric disturbances associated with the second superstorm. The absence of ionospheric irregularities in the Japanese sector during the 8 November superstorm suggests that the magnetosphere-ionosphere system was possibly preconditioned (primed) when the second interplanetary structure impacted the magnetosphere.

Sahai, Y.; Becker-Guedes, F.; Fagundes, P. R.; de Jesus, R.; de Abreu, A. J.; Otsuka, Y.; Shiokawa, K.; Igarashi, K.; Yumoto, K.; Huang, C.-S.; Lan, H. T.; Saito, A.; Guarnieri, F. L.; Pillat, V. G.; Bittencourt, J. A.

2009-03-01

271

Ionospheric Indices Based on GPS TEC  

NASA Astrophysics Data System (ADS)

The solar terrestrial environment is presently characterized by a suite of indices that represent the system's dynamics and indicate the degree of space weather effects. These indices an have extended heritage based on measurements that are well calibrated and readily available. Examples of these are the solar radio flux at 10.7 cm (F10.7), magnetospheric currents inferred from ground-based magnetographs (Dst), and auroral electrojet also based on ground-based magnetograms (AE family of indices). At the present time, the ionosphere's dynamics and response to space weather are not characterized by a "true" ionosphere index. However, since ionospheric plasma variability has a major adverse effect on human space technologies, the creation of such an index may be appropriate. The major adverse effects are associated with radio wave propagation through the ionosphere either communications or navigation. Over the past decade thousands of ground-based dual frequency GPS receivers have been deployed. Each of these measures ionospheric total electron content (TEC) continuously in multiple directions. Hence, with the standardized formatting of these measurements and their near real-time nature, a unique ionospheric data stream exists from which indices can, in principle, be developed. This study is an initial exploration of how a purely ionospheric index could be derived from these GPS TEC data. Regional versus global issues are addressed, as well as diurnal issues.

Noguera, C.; Sojka, J. J.; Thompson, D. C.; Schunk, R. W.

2005-12-01

272

Wide area ionosphere grid modelling in the auroral region  

NASA Astrophysics Data System (ADS)

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

Skone, Susan Helen

273

Cross modulation of whistler mode and HF waves above the HAARP ionospheric heater  

NASA Astrophysics Data System (ADS)

The HF facility of the High Frequency Active Auroral Research Program (HAARP) is employed to generate ELF/VLF radiation by modulation of overhead auroral electrojet currents for magnetospheric wave injection and propagation in the Earth-ionosphere waveguide. HAARP induced ducted magnetospherically amplified whistler mode signals are observed to return to the vicinity of the HF facility and experience cross modulation with simultaneous HF transmissions. The cross modulation effect results from modification of the attenuation properties of the ionospheric medium by HAARP HF waves in the daytime ionosphere. The cross modulation concept is subsequently investigated as a new method for ELF/VLF wave generation with the HAARP heating facility using two co-located HF beams. The new generation method is observed to generate radiation from 630 Hz-37 kHz. Observed amplitudes are an order of magnitude lower than fundamental frequencies generated using conventional AM, but of the same order as AM second harmonics.

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

2009-08-01

274

Paired Comparisons with Order-Effects  

Microsoft Academic Search

Suppose $n$ tea-tasting ladies are asked to compare two brands of brandy. Each lady drinks two cups, one of each brand. The order is determined by coin-tossing. The lady is forced to state whether she prefers the first or the second cup. Thus each lady provides one out of four possible outcomes: which brand did she try first, did she

Willem Schaafsma

1973-01-01

275

Ionospheric effects of the March 1990 magnetic storm: Comparison of theory and measurement  

SciTech Connect

This paper presents a comparison of the measured and modeled inospheric response to magnetic storms at Millstone Hill and Arecibo during March 16-23, 1990. Magnetic activity was low until midday UT on day 18 when Kp reached 6, days 19 and 20 were quiet, but a large storm occurred around midnight UT on day 20 (Kp=7) and it was moderately disturbed (Kp=4) for the remainder of the study period. At Millstone Hill, the daytime peak electron density (NmF{sub 2}) showed only a modest 30% decrease in response to the first storm and recovered to prestorm values before the onset of the second storm. The model reproduces the daytime peak electron density well for this period. However, the severe storm on March 20 caused a factor of 4 depletion in electron density, while the model densities were not greatly affected. The inclusion of vibrationally excited nitrogen (N{sub 2}) in the model was unable to account for the observed large electron density depletions afterward March 20. The storm did not appear to affect the overall magnitude of the electron density at Arecibo very much, but did cause unusual wavelike structure in the peak density and peak height following the storm. The model reproduces the daytime NmF{sub 2} very well for Arecibo, but after sunset the model densities decay too rapidly. This study indicates that successful modeling of severe ionospheric storms will require better definition of the storm time inputs, especially of the neutral atmosphere. 26 refs., 10 figs.

Richards, P.G.; Torr, D.G. [Univ. of Alabama, Huntsville, AL (United States)] [Univ. of Alabama, Huntsville, AL (United States); Buonsanto, M.J.; Sipler, D.P. [Massachusetts Institute of Technology, Westford, MA (United States)] [Massachusetts Institute of Technology, Westford, MA (United States)

1994-12-01

276

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

277

A Unified View of Cloud-to-Ground, Cloud-to-Cloud and Cloud-to-Ionosphere Discharges, Based on Joint Effects of Electric Reconnection and Critical Velocity  

Microsoft Academic Search

This paper attempts to explain recently observed multiple coupling among cloud-to-ground, cloud-to-cloud, and cloud-to-ionosphere discharges on the basis of joint effects of electric reconnection and critical velocity. These observations indicate that the cloud shape and charge distribution is thought to be inclined and extended rather horizontally with a sequence of electrically cusped charge distribution or horizontal double layers in contrast

Hiroshi Kikuchi

2001-01-01

278

DGPS Positioning Improvement by Utilizing the Ionospheric Horizontal Gradient Factor  

NASA Astrophysics Data System (ADS)

The ionospheric horizontal gradient is the variation of electron density with latitude and longitude which can cause the azimuthal deviation of the Global Positioning System (GPS) ray path. The effect of an ionospheric horizontal gradient is more pronounced in the low-latitude region (equatorial) and mid-auroral (trough) or polar regions than at mid-latitudes. In this paper, the positioning improvement in differential GPS (DGPS) by mitigating the ionospheric horizontal gradient has been shown. This ionospheric horizontal gradient factor was obtained from ionospheric tomographic images or contour of Total Electron Content (TEC) from Rutherford Appleton Laboratory (RAL) in the United Kingdom (UK). Since the factor of ionospheric horizontal gradient from RAL UK's TEC contour correlates very well with the factor of ionospheric horizontal gradient from the International Reference Ionosphere (IRI), so the factor of ionospheric horizontal gradient for the ionosphere over the equatorial region was determined from IRI. Then, this factor will be used to show DGPS positioning improvement over the equatorial region. By using the same linear gradient method approach, a significant amount of positioning improvement (15 cm) has been shown over the equatorial region for the DGPS by mitigating the ionospheric horizontal gradient.

Nagarajoo, K.

2011-03-01

279

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 inhomogeneous 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 inhomogeneous 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 O(+) 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 is 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 inhomogeneous 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

280

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

281

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

282

Solar variability and its effect on the ionosphere/thermosphere at low and mid-latitudes obtained from the GAIM-Physics-Based data assimilation model (GAIM-FP)  

NASA Astrophysics Data System (ADS)

Our ability to specify and forecast ionospheric dynamics and weather at low and mid latitudes is strongly limited by our current understanding of solar variability, the coupling processes in the ionosphere-thermosphere system and the coupling between the high and low latitude regions. Furthermore only a limited number of observations are available for a specification of ionospheric dynamics and weather at these latitudes. As shown by meteorologists and oceanographers, the best specification and weather models are physics-based data assimilation models that combine the observational data with our understanding of the physics of the environment. Therefore, we have developed and continue to develop four data assimilation models; two for the ionosphere, one for the high-latitude ionosphere dynamics, and one for the thermosphere. One of these models is the Global Assimilation of Ionospheric Measurements Full-Physics model (GAIM-FP). The model is based on an Ensemble Kalman filter technique and a physics-based model of the ionosphere/plasmasphere (IPM), which covers the altitude range from 90 to 20,000 km, includes six ion species, is based on the International Geomagnetic Reference Field (IGRF), and allows for inter-hemisphere flow. The model can assimilate bottom-side Ne profiles from ionosondes, slant TEC from ground-based GPS stations, in situ Ne from the DMSP satellites, occultation data from several satellites, and line-of-sight UV emissions measured by satellites. As an output the assimilation model provides the 3-dimensional density distribution throughout the ionosphere and information about the physical drivers, including the neutral winds, composition and electric fields. In the current application of the model we have assimilated a multitude of ground- and space-based ionospheric observations during the last solar minimum to specify the effects of solar variability on the low- and mid-latitude ionosphere/thermosphere. The model was used to determine the 3-dimensional ionospheric morphology and the various driving forces. We will present examples of the ionosphere weather and driver specifications obtained from our model runs with an emphasis on its relationship with solar variability.

Scherliess, Ludger; Sojka, Jan J.; Schunk, Robert

2012-07-01

283

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

284

Long-term ionospheric anomaly monitoring for ground based augmentation systems  

NASA Astrophysics Data System (ADS)

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

Jung, Sungwook; Lee, Jiyun

2012-08-01

285

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

NASA Astrophysics Data System (ADS)

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

Hayakawa, M.

2010-10-01

286

Low Latitude Ionosphere Measurements by the Global-scale Observations of the Limb and Disk (GOLD) Mission  

NASA Astrophysics Data System (ADS)

The GOLD Mission of Opportunity will provide answers to key elements of an overarching question for Heliophysics science: what is the global-scale response of the thermosphere and ionosphere to forcing in the integrated Sun-Earth system? GOLD will perform remote-sensing measurements of the Earth's thermosphere and ionosphere, using an ultraviolet imager on board a commercial, geosynchronous satellite. The resulting measurements of the electron densities in the nighttime ionosphere as well as the neutral composition and temperature in the thermosphere, when combined with current modeling capabilities, will advance our understanding of Thermosphere-Ionosphere (T-I) forcing. GOLD will provide the first global- scale "snapshot" of temperature that can be compared with the coincident "snapshot" of composition changes to understand how these two major parameters simultaneously react to the various forcing mechanisms. GOLD will continue observing the same longitudes from the daytime into the night allowing the relationship between presunset conditions in the T-I system and the longitudinal dependence of variations in the ionosphere to be separated. One question that GOLD will address is: do vertical ion drifts, as manifested in the structure of the equatorial anomaly, affect the occurrence of ionospheric irregularities? Solar and geomagnetic forcing produces variations in the structure of the equatorial ionosphere at night (equatorial anomaly) and the occurrence of irregularities within the ionosphere. These ionospheric density variations, with scale sizes ranging from hundreds to tens of km, have profound effects on systems using radio frequencies. Irregularities at low latitudes are produced in the post-sunset ionosphere by the Rayleigh-Taylor (R-T) instability. The growth of these R-T instabilities into large-scale plasma bubbles has an optical signature and is the greatest source of ionospheric irregularities at low latitudes. Simulations of GOLD observations indicate that bubbles on the order of 25 km will be observable. At low latitudes, our understanding is currently based on relatively limited geographic coverage, and even that understanding is not well connected to the global-scale variations/changes. In particular, the longitude dependence of the pre-reversal enhancement in upward E×B drift velocity, which initiates the R-T instability mechanism, is poorly known. The relationships between these vertical E×B drifts, as manifested in the structure of the equatorial anomaly, and the occurrence of ionospheric irregularities will be established using observations from GOLD.

Eastes, R. W.; Anderson, D. N.; McClintock, W. E.; Aksnes, A.; Andersson, L.; Burns, A. G.; Budzien, S. A.; Codrescu, M. V.; Daniell, R. E.; Dymond, K. F.; England, S. L.; Eparvier, F. J.; Harvey, J. E.; Immel, T. J.; Krywonos, A.; Lankton, M. R.; Lumpe, J. D.; Richmond, A. D.; Rusch, D. W.; Siegmund, O. H.; Solomon, S. C.; Strickland, D. J.; Woods, T. N.

2008-12-01

287

Simulation of the Mars Ionosphere Radio Occultation Experiments  

NASA Astrophysics Data System (ADS)

The Mars ionosphere radio occultation experiment between the Chinese YH-1 spacecraft and the Russian Phobos-Grunt spacecraft orbiting Mars will be the first satellite to satellite radio occultation experiment in history, which will achieve high quality ionospheric electron density profiles. The technique used in this experiment is analyzed and introduced. Simulations of the radio occultation have been completed. Forward calculations of the radio wave observable for the ionospheric radio occultation events have been done with the 3D ray tracing method and a simple Chapman ionosphere background model. The backward inversion with the forward calculated radio occultation observation data gives reliable and consistent ionospheric electron density profiles, which show the reliability of the simulation algorithms. With the simulation method, the effects of errors from the radio signal phase measurement and the orbit determination of the satellite on the inversion are analyzed in cases. Results show that phase errors of 5% circle have a negligible effect on the daytime ionosphere radio occultation, and lead to an absolute error of less than 4×;10^8 m3 for nighttime electron density profiles. Orbit errors of the satellite mainly pose a systematic rising or descending to the ionosphere height. The above results show that Sino-Russian cooperative Mars ionosphere radio occultation experiments is expected to achieve high quality Mars ionosphere profiles. Their technique regime can be used for the lunar ionosphere exploring.

Hu, X.; Wu, X. C.; Gong, X. Y.; Wang, X.; Xu, Q. C.

2009-07-01

288

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

NASA Astrophysics Data System (ADS)

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

Herne, D. E.

2009-12-01

289

Dynamic Agents of Magnetosphere-Ionosphere Coupling  

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

290

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

291

Ionospheric calibration for single frequency altimeter measurements  

NASA Technical Reports Server (NTRS)

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

Schreiner, William S.; Born, George H.

1993-01-01

292

Soliton explosion control by higher-order effects.  

PubMed

We numerically study the impact of self-frequency shift, self-steepening, and third-order dispersion on the erupting soliton solutions of the quintic complex Ginzburg-Landau equation. We find that the pulse explosions can be completely eliminated if these higher-order effects are properly conjugated two by two. In particular, we observe that positive third-order dispersion can compensate the self-frequency shift effect, whereas negative third-order dispersion can compensate the self-steepening effect. A stable propagation of a fixed-shape pulse is found under the simultaneous presence of the three higher-order effects. PMID:20517411

Latas, Sofia C V; Ferreira, Mário F S

2010-06-01

293

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

294

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

295

Imaging Ionospheric Fine Structures Using Polarimetric SAR and GPS  

NASA Astrophysics Data System (ADS)

In this paper, we will present Faraday rotation images derived from polarimetric data collected using the Phased Array type L-band Synthetic Aperture Radar (PALSAR) onboard the Japanese Advanced Land Observing Satellite (ALOS). It will be shown that such space-borne radar techniques are capable of capturing 2D ionospheric structures with kilometer to sub-kilometer resolutions. This new capability will be demonstrated with examples of imaging ionospheric perturbations due to space weather and geophysical events, such as auroral arcs, ionospheric irregularities, and traveling ionospheric disturbances. The radar images are also compared with GPS-based measurements and models. While 2D ionospheric TEC maps derived from GPS data or 3D assimilative ionospheric model provide large-scale ionospheric ambient conditions, the rate of TEC measurements also derived from GPS data can be used to detect small-scale ionospheric irregularities that are associated with SAR images. The potential of combining SAR- and GPS-based ionospheric imaging at different spatial scales will be discussed, which can significantly enhance our capability of investigating outstanding ionospheric research topics and supporting mitigation of media effects on SAR.

Pi, X.; Freeman, A.; Chapman, B.

2009-04-01

296

Currents to the ionosphere from thunderstorm generators - A model study  

NASA Technical Reports Server (NTRS)

A computer model (Nisbet, 1983) was used to evaluate the role of thunderstorm clouds in generating the currents necessary for the maintenance of the ionospheric potential. The effects of variations in the breakdown electric field below the lower charge center, heights of the upper and lower charge centers, generator currents and geometry, as well as of the conductivity profile of the cloud, the surrounding air, and the ionosphere, on the currents to the ionosphere were examined. It was shown that the most important single variable controlling the ionospheric current/generator current ratio for both very active storms and for storms that do not produce lightning is the height of the lower active center. The ionospheric conductivity has a negligible effect on the total current to the ionosphere, although it is very important in controlling the electric field and current density waveforms above the cloud.

Nisbet, J. S.

1985-01-01

297

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

298

Parametric Instabilities Generated in the Ionosphere by Intense Radio Waves.  

National Technical Information Service (NTIS)

The earth's ionosphere is, from energetic grounds, one of the few regions where man can apply sufficient energy to modify the environment significantly. The energy content of 100 cubic kilometers of ionospheric plasma is of the order of 10 megawatt-secs. ...

C. Oberman E. Valeo F. Perkins

1972-01-01

299

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

300

Investigating the MLT and L-shell dependence of the ionospheric Alfvén resonator with ground-based magnetic observations  

NASA Astrophysics Data System (ADS)

The ionospheric Alfvén resonator IAR is a natural resonant cavity in the ionosphere formed between two regions of large Alfvén velocity gradients Shear Alfvén waves can become trapped in the cavity through partial reflection at the gradients and a vertical standing wave pattern may develop in the upper ionosphere In the 0 1 to 10 Hz range resonance structures in the dynamic power and polarization spectra of ground magnetometer data are believed to be the fingerprints or proof for the existence of the IAR Previous studies have focused primarily on observations of the magnetic signatures at isolated sites However in an attempt to better understand the global extent of the resonator and its signatures we have performed analysis across a collection of stations in the Canada-U S sector We have investigated the dependence of IAR onset times occurrence rate and eigenfrequency evolution on local time L-shell and sunrise sunset times The relationship between magnetic activity in particular structured Pc1-2 pulsations and resonance features was examined Furthermore we have characterized IAR events using simultaneous induction coil and ionosonde data from the HAARP site near Gakona Alaska in order to determine how ionospheric parameters such as the foF2 electron density peak affect IAR signatures Observational studies of the properties and behaviour of resonant magnetic features are essential in understanding the ionospheric Alfvén resonator and its effect upon magnetosphere-ionosphere coupling and plasma dynamics in

Parent, A.; Mann, I.

301

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

NASA Astrophysics Data System (ADS)

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

Meyer, Stephen; Collier, Andrew; Koen, Etienne

302

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

303

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

NASA Astrophysics Data System (ADS)

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

Restano, Marco; Picardi, Giovanni; Seu, Roberto

2013-04-01

304

The Effect of Solar X-Ray Flares on Earth's Ionosphere as Natural Source for Electromagnetic Noise and Interference  

NASA Astrophysics Data System (ADS)

Solar X-ray flares causing an sudden ionospheric disturbance (SID) affecting on telecommunications and tel-services as natural source for electromagentic noise and interference. Daily X-ray back ground and Flare measured by artificial satellite GOES. X-ray background from 25 April 1983 to 31 December 1996 and X-ray Flare from 1 January 1981 to 31 December 1996 daily average, and Flare index from 1 January 1986 to 31 October 1996, and Sudden Ionospheric Disturbance data from 1 January 1981 to 31 December 1995, were analyzed by the periodogram technique to estimate the short and long term variabilities . The data are obtained from NOAA, Boulder, Colorado,USA. It is found that there are short periodicities such as 26 day period of rotation of sun, and 13, 8.33, 4.17, 2.5 day and long and term periodicities such as 182, 121, 90.99, 72.3, 61, 52 day . Also, 11 eleven year cycle are clear in the total period. The variability of the solar radiation entering the upper atmosphere of the Earth directly affect the state of the upper atmosphere and ionosphere through the excitation and ionization of atoms and molecules, Ionospheric variability significantly impacts ground and space-based communications. And can attenuate, totally absorb, reflect, change direction of propagation, and change phase and amplitude of radio waves.

Mosalam Shaltout, M. A.; Ei-Genedi, S.

305

Effects of causally driven cusp O+ outflow on the storm time magnetosphere-ionosphere system using a multifluid global simulation  

Microsoft Academic Search

It is widely accepted that the ionosphere is an important source of ions in the magnetosphere and until recently this population has largely been neglected from many global simulations. In this study, a causally regulated cusp O+ outflow is added to the multifluid version of the Lyon-Fedder-Mobarry (LFM) global simulation. The cusp outflow algorithm uses empirical relationships to regulate the

O. J. Brambles; W. Lotko; P. A. Damiano; B. Zhang; M. Wiltberger; J. Lyon

2010-01-01

306

Modelling the effects of ionospheric disturbances on quasi-vertically incident ionograms using 3D magneto-ionic raytracing  

Microsoft Academic Search

Ionospheric disturbances are manifest over a large range of spatial and temporal scales. Currently DSTO has a good understanding of these disturbances at the largest scales (> 1000 km and > 15 min) through its network of vertical incident (VI) sounders. However, we are interested in investigating these disturbances at much smaller scale sizes. To this end DSTO has initiated

M. Cervera; T. Harris

2011-01-01

307

Ionospheric convection driven by NBZ currents  

NASA Technical Reports Server (NTRS)

Computer simulations of Birkeland currents and electric fields in the polar ionosphere during periods of northward IMF were conducted. When the IMF z component is northward, an additional current system, called the NBZ current system, is present in the polar cap. These simulations show the effect of the addition of NBZ currents on ionospheric convection, particularly in the polar cap. When the total current in the NBZ system is roughly 25 to 50 percent of the net region 1 and 2 currents, convection in the central portion of the polar cap reverses direction and turns sunward. This creates a pattern of four-cell convection with two small cells located in the polar cap, rotating in an opposite direction from the larger cells. When the Birkeland currents are fixed (constant current source), the electric field is reduced in regions of relatively high conductivity, which affects the pattern of ionospheric convection. Day-night asymmetries in conductivity change convection in such a way that the two polar-cap cells are located within the large dusk cell. When ionospheric convection is fixed (constant voltage source), Birkeland currents are increased in regions of relatively high conductivity. Ionospheric currents, which flow horizontally to close the Birkeland currents, are changed appreciably by the NBZ current system. The principal effect is an increase in ionospheric current in the polar cap.

Rasmussen, C. E.; Schunk, R. W.

1987-01-01

308

Atmospheric winds between 100 and 700 km and their effects on the ionosphere  

Microsoft Academic Search

The global wind system produced at different local times by pressure gradients in the upper atmosphere is calculated using data from Jacchia's model atmosphere. The horizontal wind velocities vary with height, and are of the order of 100 m sec-1 at about 300 km; they depend on ion drag, viscosity and Coriolis forces, but the major importance of ion drag

H. Kohl; J. W. King

1967-01-01

309

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

310

Model of Jovian F Region Ionosphere (Saturnian Ionosphere in Offset Dipole Approximation).  

National Technical Information Service (NTIS)

Researchers investigated the offset effect of Saturn's dipole on its ionosphere. The magnetic field of Saturn is primarily that of a dipole closely aligned to the rotational axis, but displaced northward from the center by a distance approximately equal t...

A. Tan

1991-01-01

311

Order Effects in Children's Gender-Constancy Responses.  

ERIC Educational Resources Information Center

Study examines the Slaby and Frey (1975) gender-constancy interview, which has been widely used in tests of the cognitive-developmental account. Sixty children, aged between 42 and 54 months, were given the interview either in the traditional order or in a reversed order. Order effects were found. Methodological issues are discussed. (Author/BN)

Siegal, Michael; Robinson, Judith

1987-01-01

312

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

Microsoft Academic Search

This study provides a first attempt at quantifying potential signal bending effects on the GPS reference frame, coordinates and zenith tropospheric delays (ZTDs). To do this, we homogeneously reanalysed data from a global network of GPS sites spanning 14 years (1995.0-2009.0). Satellite, Earth orientation, tropospheric and ground station coordinate parameters were all estimated. We tested the effect of geometric bending

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

2010-01-01

313

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

NASA Technical Reports Server (NTRS)

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

Tan, A.

1991-01-01

314

High Order Effects in Cross Section Sensitivity Analysis.  

National Technical Information Service (NTIS)

Two types of high order effects associated with perturbations in the flux shape are considered: Spectral Fine Structure Effects (SFSE) and non-linearity between changes in performance parameters and data uncertainties. SFSE are investigated in Part I usin...

E. Greenspan Y. Karni D. Gilai

1978-01-01

315

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

Microsoft Academic Search

This study provides a first attempt at quantifying potential signal bending effects on the GPS reference frame, coordinates\\u000a and zenith tropospheric delays (ZTDs). To do this, we homogeneously reanalysed data from a global network of GPS sites spanning\\u000a 14 years (1995.0–2009.0). Satellite, Earth orientation, tropospheric and ground station coordinate parameters were all estimated.\\u000a We tested the effect of geometric bending and

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

2010-01-01

316

International reference ionosphere: Recent developments  

NASA Astrophysics Data System (ADS)

An introduction to the history and intentions of the International Reference Ionosphere (IRI) is given and future plans are outlined. The description of the topside electron density profile in the IRI is based on Bent's summary of topside sounder measurements, mainly Alouette. Instead of Bent's tabular form, the IRI has the advantage of an analytical description. Our comparison with AEROS satellite data shows that the IRI model is inaccurate in its description of the latitudinal behavior of the electron density in the topside ionosphere close to the magnetic equator. An improved IRI formula is proposed that closely follows the experimental data. The present IRI is restricted to solar activities reached during the last solar cycle 20. Measurements during the present solar cycle indicate a saturation effect for very high solar activities.

Bilitza, Dieter

1986-05-01

317

Equatorial-PRIMO (Problems Related to Ionospheric Models and Observations)  

NASA Astrophysics Data System (ADS)

We do not fully understand all the relevant physics of the equatorial ionosphere, so that current models do not completely agree with each other and are not able to accurately reproduce observations. To understand the strengths and the limitations of theoretical, time-dependent, low-latitude ionospheric models in representing observed ionospheric structure and variability and to better understand the underlying ionospheric physics and develop improved models, we initiated a multi-year Equatorial-PRIMO workshop at the CEDAR meeting this year. Two sets of ionosphere-plasmasphere models are participated: non self-consistent models including Ionospheric Forecast Model (IFM), Ionosphere-Plasmasphere Model (IPM), Low Latitude Ionospheric Specification Model (LLIONS), Physically Based Model (PBMOD), Global Ionosphere and Plasmasphere (GIP), SAMI2 is Another Model of the Ionosphere (SAMI2) and self-consistent models including SAMI3 is Also a Model of the Ionosphere (SAMI3), Thermosphere-Ionosphere-Electrodynamics general circulation model (TIE-GCM), Thermosphere-Ionosphere-Mesosphere-Electrodynamics general circulation model (TIME-GCM), Global Ionosphere-Thermosphere Model (GITM), the Coupled Thermosphere Ionosphere Plasmasphere Electrodynamics (CTIPe), Integrated Dynamics through Earth’s Atmosphere (IDEA). In order to have fair comparisons, we set the Burnside factor (the collision frequency between O+-O) to 1 and F10.7 to 120. All the models are run under geomagnetic quiet conditions in equinox, June solstice, and December solstice. Diurnal variation of electron density, neutral density, wind velocity, and vertical drifts at Jicamarca longitude at equatorial region from these models will be compared. Currently, of the non self-consistent models, PBMOD, SAMI2 and GIP have been run under these conditions. For the self-consistent models, calculations using CTIPe, GITM and TIE-GCM have been carried out. Furthermore, since the lower boundary conditions can be an important source in reproducing ionospheric variability and causing differences in the models, we implement the Whole Atmosphere Model (WAM) as the lower boundary of CTIPe. The comparisons of CTIPe neutral wind and electron density with and without WAM as lower boundary will help us determine the possibility of testing the same lower boundary conditions in participated models. We present these results and describe our vision of the way forward for Equatorial-PRIMO.

Fang, T.; Anderson, D. N.; Fuller-Rowell, T. J.; Akmaev, R. A.; Codrescu, M.; Millward, G. H.; Sojka, J. J.; Scherliess, L.; Eccles, J. V.; Retterer, J. M.; Huba, J. D.; Joyce, G. R.; Richmond, A. D.; Maute, A. I.; Crowley, G.; Ridley, A. J.; Vichare, G.

2010-12-01

318

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

319

Effect of zonal E × B plasma drift on electron density in the low-latitude ionospheric F region at a solar activity maximum near vernal equinox  

NASA Astrophysics Data System (ADS)

The variations in the density of the ionospheric F2 layer maximum ( NmF2) under the action of the zonal plasma drift perpendicularly to the magnetic ( B) and electric ( E) fields in the direction geomagnetic west-geomagnetic east have been studied using the three-dimensional nonstationary theoretical model of electron and ion densities ( N e and N i ) and temperatures ( T e and T i ) in the low-latitude and midlatitude ionospheric F region and plasmasphere. The method of numerical calculations of N e , N i , T e , and T i , including the advantages of the Lagrangian and Eulerian methods, is used in the model. A dipole approximation of the geomagnetic field ( B), taking into account the non-coincidence of the geographic and geomagnetic poles and differences between the positions of the Earth’s and geomagnetic dipole centers, is accepted in the calculations. The calculated NmF2 and altitudes of the F2 layer maximum ( hmF2) have been compared with these quantities measured at 16 low-latitude ionospheric sounding stations during the geomagnetically quiet period October 11-12, 1958. This comparison made it possible to correct the input model parameters: the NRLMSISE-00 model [O], the meridional component of the neutral wind velocity according to the HWW90 model, and the meridional component of the equatorial plasma drift due to the electric field specified by the empirical model. It has been indicated that the effect of the zonal E × B plasma drift on NmF2 can be neglected under daytime conditions and changes in NmF2 and hmF2 under the action of this drift are insignificant under nighttime conditions north of 25° and south of -26° geomagnetic latitude. The effect of the zonal E × B plasma drift on NmF2 and hmF2 is most substantial in the nightside ionosphere approximately from -20° to 20° geomagnetic latitude, and the neglect of this drift results in an up to 2.4-fold underestimation of NmF2. The found dependence of the effect of the zonal E × B plasma drift on NmF2 and hmF2 on geomagnetic latitude is related to the longitudinal asymmetry of B, asymmetry of the neutral wind about the geomagnetic equator, and changes in the meridional E × B plasma drift at a change in geomagnetic longitude.

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

2007-10-01

320

New electron gyroharmonic effects in HF scatter from pump-excited magnetic field-aligned ionospheric irregularities  

Microsoft Academic Search

Experimental results of resonant high-frequency (HF) scattering from small-scale geomagnetic field-aligned plasma irregularities excited by electromagnetic HF pumping of the ionospheric F region from the Sura radio facility in Russia are reported. These results include the first observations of a minimum in the scattered signal intensity when the pump frequency was near the fourth electron gyroharmonic and of a significant

P. V. Ponomarenko; T. B. Leyser; B. Thidé

1999-01-01

321

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

Microsoft Academic Search

The Vector Electric Field Investigation (VEFI) suite onboard the C\\/NOFS spacecraft includes a sensitive fluxgate magnetometer to measure DC and ULF magnetic fields in the low latitude ionosphere. The instrument includes a DC vector measurement at 1 sample\\/sec with a range of ± 45,000 nT whose primary objective is to provide direct measurements of both VxB and ExB that are

G. Le; R. F. Pfaff; E. L. Kepko; D. E. Rowland; K. R. Bromund; H. Freudenreich; S. C. Martin; M. C. Liebrecht; S. Maus

2010-01-01

322

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.

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

2013-01-01

323

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

PubMed

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

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

2013-01-01

324

Ionospheric ion upwelling in the wake of flux transfer events at the dayside magnetopause  

SciTech Connect

The effects of flux transfer events (FTE) on the dayside auroral ionosphere are studied, using a simple twin-vortex model of induced ionospheric plasma flow. It is shown that the predicted and observed velocities of these flows are sufficient to drive nonthermal plasma in the F region, not only within the newly opened flux tube of the FTE, but also on the closed, or ''old'' open, field lines around it. In fact, with the expected poleward neutral wind, the plasma is more highly nonthermal on the flanks of, but outside, the open flux tube: EISCAT observations indicate that plasma is indeed driven into nonthermal distributions in the regions. The nonthermal plasma is thereby subject to additional upforce due to the resulting ion temperature anisotropy and transient expansion due to Joule heating and also to ion accelerations associated with the FTE field aligned current system. Any upflows produced on closed field lines in the vicinity of the FTE are effectively bunched-up in the ''wake'' of the FTE. Observations from the AMPTE-UKS satellite at the magnetopause reveal ion upflows of energy approx.100 eV flowing out from the ionosphere on closed field lines which are only found in the wake of the FTE. Such flows are also only found shortly after two, out of all the FTEs observed by AMPTE-UKS. The outflow from the ionosphere is two orders of magnitude greater than predicted for the ''classical'' polar wind. It is shown that such ionospheric ion flows are only expected in association with FTEs on the magnetopause which are well removed from the sub-solar point: either towards dusk or, as in the UKS example discussed here, towards dawn. It is suggested that such ionospheric ions will only be observed if the center of the FTE open flux tube passes very close to the satellite.

Lockwood, M.; Smith, M.F.; Farrugia, C.J.; Siscoe, G.L.

1988-06-01

325

International Reference Ionosphere 1990.  

National Technical Information Service (NTIS)

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 condition...

D. Bilitza K. Rawer L. Bossy I. Kutiev K. Oyama

1990-01-01

326

Arecibo Ionospheric Observatory.  

National Technical Information Service (NTIS)

The brochure describes the Arecibo Ionospheric Observatory and the scientific research program being carried there with the world's largest radio-radar telescope. Arecibo is operated by Cornell University with funding provided by the Advanced Research Pro...

D. W. Taylor

1967-01-01

327

Ionospheric Research Using Satellites.  

National Technical Information Service (NTIS)

Results of measurements of electron content, of ionospheric slab thickness and of scintillations from three low latitude stations are presented. The three stations are Nairobi (Kenya), Kingston (Jamaica), and Haifa (Israel). Measurements were made at the ...

J. Mass Z. Houminer

1968-01-01

328

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

329

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

NASA Technical Reports Server (NTRS)

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

Abraham, Saji; LeVine, David M.

2004-01-01

330

Dayside Ionospheric Superfountain  

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

331

Spatial-Temporal Characteristics of Large Scale Disturbances of Electron Density Observed in the Ionospheric F-Region before Strong Earthquakes  

NASA Astrophysics Data System (ADS)

The spatial dimensions and temporal dynamics of large scale disturbances of electron density in the ionospheric F-region during the preparatory phase of destructive earthquakes are estimated. The most appropriate data (as far as the moments of satellite passages are concerned) were selected out of more than 300 investigated cases. In order to demonstrate effects at different latitudes, the cases of high-latitude (Alaska), mid-latitude (Central Italy), and low-latitude (New Zealand) earthquakes were considered. Using the data of external vertical sounding of the ionosphere performed by the Alouette-1 and Interkosmos-19 satellites together with the data of vertical sounding of the ionosphere by ground-based instruments, we get for the first time with reasonable accuracy the spatial characteristics of precursors in the ionosphere. It is shown that seismic ionospheric disturbances are strongly time-dependent before the beginning of the main shock. Seismic ionospheric disturbances are generated weakly several days before the first shock, but at that moment the disturbed region is located not above the epicenter, but rather a little displaced from it. As the moment of the earthquake approaches, the disturbance covers more and more space; moreover, its value also increases. Several hours after the shock the disturbance migrates in the reverse order. Under some conditions, the disturbances may appear not only above epicenter regions. They can be transferred along the magnetic field lines into conjugate regions in the opposite hemisphere.

Pulinets, S. A.; Legen'ka, A. D.

2003-05-01

332

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

333

Implications of Ionospheric Scintillation for GNSS Users in Northern Europe  

Microsoft Academic Search

Extensive ionospheric scintillation and Total Electron Content (TEC) data were collected by the Institute of Engineering Surveying and Space Geodesy (IESSG) in Northern Europe during years of great impact of the solar maximum on GNSS users (2001 2003). The ionospheric TEC is responsible for range errors due to its time delay effect on transionospheric signals. Electron density irregularities in the

Marcio Aquino; Terry Moore; Alan Dodson; Sam Waugh; Jock Souter; Fabiano S. Rodrigues

2005-01-01

334

Accuracy of orbit determination from ionospherically corrupted tracking data  

Microsoft Academic Search

Description of a procedure for correcting the adverse effects of ionospheric tracking-data corruption upon the accuracy of satellite orbit determinations based on these data. Under the proposed procedure, the ionosphere is modeled by a single parameter whose statistical distribution is approximately normal. This parameter is then included in the solution vector, along with the satellite position and velocity. The procedure

P. Norris

1974-01-01

335

Global Ionosphere Thermosphere Model results of the Halloween Storm  

Microsoft Academic Search

The Global Ionosphere Thermosphere Model (GITM) is a new code for examining the upper atmosphere of the Earth. GITM has a flexible grid structure, doesn't assume a hydrostatic equilibrium, and allows a wide variety of ionospheric and thermospheric physics to be easily investigated. We have modeled the October 29-31, 2003 storms with GITM numerous times, to investigate the effects of

A. J. Ridley; Y. Deng; D. Pawlowski; H. Liu

2006-01-01

336

Fast ionospheric feedback instability and substorm onset  

NASA Technical Reports Server (NTRS)

A study suggesting that the Alfven resonator can play an important role in modifying the ionosphere on the time and space scales required to play a significant role in substorm formation is presented. Although the effect of magnetosphere-ionosphere coupling on the onset of substorms has been studied, the effects due to gradients of the Alfven speed along auroral field line were neglected. The large increase of the Alfven speed with altitude above the ionosphere creates an effective resonant cavity, which can lead to fluctuations in the electric and magnetic fields as well as in particle fluxes in the range 0.1 to 1 Hz. Such fluctuations can be observed from the ground as PiB pulsations associated with substorm onset. These fluctuations can be excited by a fast feedback instability, which can grow on time scales much less than the Alfven travel time between the ionosphere and the plasma sheet. The instability enhances the value of both the Pedersen and Hall conductivity, and may play a role in preparing the ionosphere for substorm onset.

Lysak, Robert L.; Grieger, John; Song, Yan

1992-01-01

337

The netlander ionosphere and geodesy experiment  

Microsoft Academic Search

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

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

2001-01-01

338

LEISA: CubeSat for Ionospheric Characterization  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

339

Design of a New Far Ultraviolet Interferometer for Ionospheric Spectroscopy.  

National Technical Information Service (NTIS)

A new far ultraviolet interferometer for ionospheric spectroscopy was designed and tested. The design uses a concave spherical grating in an off-plane Rowland circle configuration. Wave fronts are split into zero and negative first order diffractions, ref...

J. W. Nichols

1990-01-01

340

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.

341

Solar radiation-induced changes in ionospheric height and the Schumann resonance waveguide on different timescales  

NASA Astrophysics Data System (ADS)

This study draws together the available observations in the Schumann resonance frequency range to examine the general issue of sensitivity of ionospheric height variations to changes in ionizing radiation from the Sun on different timescales. Ionospheric height can be formally defined, and two characteristic heights are recognized in the Schumann resonance frequency range. In general, order of magnitude changes in radiation are needed to cause relative changes in ionospheric height as large as 10%, as is the case on both the diurnal and 11-year timescales. Changes in EUV radiation are probably insufficiently strong to account for either the 27-day or the 11-year variation in ionospheric height. More ionization-effective X radiation is needed, but much smaller height changes are expected on the solar rotation timescale because the variations in X radiation on this timescale are only tens of percent and not orders of magnitude. The annual variation in radiation from the Sun is only 7%, with an expected height variation less than 100 m, and this remains to be verified by observations. The general insensitivity of the Schumann resonance cavity to changes in ionizing radiation lends stability to the medium that is valuable toward quantifying absolute changes in the global lightning activity on various timescales within the cavity.

Williams, E. R.; SáTori, G.

2007-04-01

342

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

343

Ionospheric effects near the magnetic equator and the anomaly crest of the Indian longitude zone during a large number of intense geomagnetic storms  

NASA Astrophysics Data System (ADS)

Ionospheric effects of a large number (51) of severe geomagnetic storms are studied using total electron content (TEC) and VHF/UHF scintillation data from Calcutta, situated near the northern crest of equatorial ionization anomaly and equatorial spread-F (ESF) data from Kodaikanal. The susceptibility of the equatorial ionosphere to develop storm time plasma density irregularities responsible for ESF and scintillation is found to be largely modulated by the local times of occurrences of main and recovery phases as seen in the Dst index. While inhibition of premidnight scintillation for lower TEC values compared to the quiet day averages is omnipresent, occurrence of scintillation for enhancements of TEC is largely dependent on initiation time and amplitude of the said deviations. An overall reduction in threshold values of h?F for observing storm induced ESF and scintillation compared to reported quiet time values is noted. The results are discussed in terms of storm time variabilities in electric fields, neutral wind system and composition changes.

Hajra, R.; Chakraborty, S. K.; Dasgupta, A.

2010-11-01

344

Study of cyclone effect in Kamchatka on electron distribution in the ionosphere by satellite tomography in the conditions of low seismicity  

NASA Astrophysics Data System (ADS)

The paper presents the results of investigation of cyclone possible effect on ionosphere parameters. Monitoring of ionosphere state has been carried out by automatic sounding applying low orbital navigational spacecrafts in the conditions of low seismicity. Receiving stations were locating in meridian direction of Kamchatka peninsular in Paratunka, Mil'kovo and Esso villages. It has been shown that during night time cyclone passage (according to local time) on 18.01, 03.02 and 17.02 2013 over Kamchatka, synchronous increase of electron concentration occurred in the region over its epicenter in comparison to the next days without cyclones. With the increase of the latitude, i.e. further from the center of the cyclone, electron concentration decreased in comparision to calm days. The work has been realized within the FEB RAS special-purpose program "Satillite monitoring of the Far East for fundamental researches of FEB RAS" and the project on RAS Presidium Program RAS #12-1-P22-01.

Bogdanov, Vadim; Kaisin*, Alexander; Polyukhova*, Anastasia; Romanov, Alexander; Prikhod'ko, Anna

2014-05-01

345

Plasma interactions in Titan's ionosphere  

NASA Astrophysics Data System (ADS)

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

Richard, Matthew Scott

346

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

347

Robust detection of ionospheric irregularities  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

348

Influence of ionospheric anomalies in the positioning  

NASA Astrophysics Data System (ADS)

GNSS observables depend on the satellite-receiver distance, atmospheric effects, satellite and receiver offsets and phase ambiguities, as well as satellite and receiver equipment delays. GNSS observations specific to a receiver and a satellite (undifferenced observations) can be used to estimate the ionospheric effect. In this study, different procedures are used to estimate the ionospheric delay from GNSS data belonging to permanent GPS stations. In particular, these tests intend to detect ionospheric anomalies under certain conditions in equatorial geographical latitudes. From the Slant Total Electron Content (STEC) estimated between one GPS station and several satellites the contribution of the anomalies is isolated and its amplitude and duration are computed. Finally, an analysis of the possible influence of these anomalies in the positioning estimation is carried out.

Rodriguez-Caderot, G.; Moreno, B.; de Lacy, M. C.

2009-04-01

349

Impact of Ground Level Enhancement from Solar Cosmic Rays on 20 January 2005 - Results for Ozone and Ionosphere Effects  

NASA Astrophysics Data System (ADS)

The influences of major solar proton flare from 20 January 2005 on the ionized and neutral components in the middle atmosphere are analyzed in this work This flare is accompanied by ground level enhancement of solar cosmic rays and strong geomagnetic storm with SSC on 22 January 2005 Kp index reaches 8 Short-term variations along the ozone profiles are discussed Ozone partial pressure measurements from the programme Halogen Occultation Experiment HALOE realized by the Upper Atmospheric Research Satellite UARS are used The GOES-10 satellite obtained the data on high energy protons All energetic intervals 0 8 - 4 MeV 4 - 9 MeV 9 - 15 MeV 15 - 40 MeV 40 - 80 MeV 80 - 165 MeV 165 - 500 MeV are used Cosmic ray data from super neutron monitors Kiel - Germany 54 9 95 6 geomagnetic degree and Potchefstroom - South African Republic -27 3 -90 1 geomagnetic degree are analyzed also Statistical analysis with this big volume of data is accomplished Correlation and cross-correlation analysis between ozone and particle data is made Different behaviors of the ozone response in both hemispheres is obtained on the basis of these computations The ionosphere results for the same period are obtained in the observatory Sofia - Bulgaria by means of A3 method The minimal reflectance frequency fmin which characterizes the state of the lower ionosphere has unusual course For complement the other ionospheric parameters are involved also The present investigation is an example for complex analysis of solar and extra-terrestrial influence in the middle atmosphere

Velinov, P.; Tassev, Y.; Spassov, H.; Tomova, D.

350

The effects of seasonal and diurnal variations in the Earth's magnetic dipole orientation on solar wind-magnetosphere-ionosphere coupling  

NASA Astrophysics Data System (ADS)

The angle ? between the geomagnetic dipole axis and the geocentric solar magnetospheric (GSM) z axis, sometimes called the “dipole tilt,” varies as a function of UT and season. Observations have shown that the cross-polar cap potential tends to maximize near the equinoxes, when on average ? = 0, with smaller values observed near the solstices. This is similar to the well-known semiannual variation in geomagnetic activity. We use numerical model simulations to investigate the role of two possible mechanisms that may be responsible for the influence of ? on the magnetosphere-ionosphere system: variations in the coupling efficiency between the solar wind and the magnetosphere and variations in the ionospheric conductance over the polar caps. Under southward interplanetary magnetic field (IMF) conditions, variations in ionospheric conductance at high magnetic latitudes are responsible for 10-30% of the variations in the cross-polar cap potential associated with ?, but variations in solar wind-magnetosphere coupling are more important and responsible for 70-90%. Variations in viscous processes contribute slightly to this, but variations in the reconnection rate with ? are the dominant cause. The variation in the reconnection rate is primarily the result of a variation in the length of the section of the separator line along which relatively strong reconnection occurs. Changes in solar wind-magnetosphere coupling also affect the field-aligned currents, but these are influenced as well by variations in the conductance associated with variations in ?, more so than the cross-polar cap potential. This may be the case for geomagnetic activity too.

Cnossen, Ingrid; Wiltberger, Michael; Ouellette, Jeremy E.

2012-11-01

351

The Effects of Solar and Ionospheric Parameters on Seasonal Variation of 6300 Angstroms Line Emission at Calcutta  

NASA Astrophysics Data System (ADS)

The purpose of this paper is to find correlation between OI 6300 Å line intensity with solar and ionospheric parameters. A critical study have been made and the following important results are obtained: (i) Solar flare index plays more important role for the emissions of 6300 Å line than other solar parameters. (ii) Intensity of 6300 Å line increases linearly with the increase of solar flare index. (iii) Virtual height plays more important role than critical frequency for the emission of 6300 Å line-intensity. (iv) Possible explanation of this type of variation is also presented.

Midya, S. K.; Chattopadhyay, R.

1996-01-01

352

Review of Ionospheric Effects of Solar Wind Magnetosphere Coupling in the Context of the Expanding Contracting Polar Cap Boundary Model  

NASA Astrophysics Data System (ADS)

This paper reviews the coupling between the solar wind, magnetosphere and ionosphere. The coupling between the solar wind and Earth’s magnetosphere is controlled by the orientation of the Interplanetary Magnetic Field (IMF). When the IMF has a southward component, the coupling is strongest and the ionospheric convection pattern that is generated is a simple twin cell pattern with anti-sunward flow across the polar cap and return, sunward flow at lower latitudes. When the IMF is northward, the ionospheric convection pattern is more complex, involving flow driven by reconnection between the IMF and the tail lobe field, which is sunward in the polar cap near noon. Typically four cells are found when the IMF is northward, and the convection pattern is also more contracted under these conditions. The presence of a strong Y (dawn-dusk) component to the IMF leads to asymmetries in the flow pattern. Reconnection, however, is typically transient in nature both at the dayside magnetopause and in the geomagnetic tail. The transient events at the dayside are referred to as flux transfer events (FTEs), while the substorm process illustrates the transient nature of reconnection in the tail. The transient nature of reconnection lead to the proposal of an alternative model for flow stimulation which is termed the expanding/contracting polar cap boundary model. In this model, the addition to, or removal from, the polar cap of magnetic flux stimulates flow as the polar cap boundary seeks to return to an equilibrium position. The resulting average patterns of flow are therefore a summation of the addition of open flux to the polar cap at the dayside and the removal of flux from the polar cap in the nightside. This paper reviews progress over the last decade in our understanding of ionospheric convection that is driven by transient reconnection such as FTEs as well as by reconnection in the tail during substorms in the context of a simple model of the variation of open magnetic flux. In this model, the polar cap expands when the reconnection rate is higher at the dayside magnetopause than in the tail and contracts when the opposite is the case. By measuring the size of the polar cap, the dynamics of the open flux in the tail can be followed on a large scale.

Lester, M.; Milan, S. E.; Provan, G.; Wild, J. A.

2006-06-01

353

Characteristics of High Latitude Ionosphere Scintillations  

NASA Astrophysics Data System (ADS)

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

Morton, Y.

2012-12-01

354

Ionospheric Specifications for SAR Interferometry (ISSI)  

NASA Technical Reports Server (NTRS)

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

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

2013-01-01

355

USE OF SECOND-ORDER ELECTROSEISMIC EFFECTS IN ELECTRIC PROSPECTING  

Microsoft Academic Search

The second-order electroseismic effects described may be divided into three classes: electroseismic, electromagnetic, and piezoelectric. Application of these effects to prospecting for certain types of geological features such as quartz veins and pegmatites indicates new methods of subsurface exploration. A brief review of methods and procedures is discussed with results of testing over a pegmatite which is not exposed at

N. N. Neyshtadt

1962-01-01

356

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

357

Parametric Instabilities and Ionospheric Modification  

Microsoft Academic Search

Parametric instabilities, excited in the ionosphere by high-power HF transmitters with a frequency below the maximum ionospheric plasma frequency, produce nonlinear energy absorption and enhanced scattering of electromagnetic radiation, which has been detected by the Arecibo Thomson scatter radar. This paper reviews and extends both the linear and nonlinear saturation theory of parametric instabilities within the ionospheric context. The new

F. W. Perkins; C. Oberman; E. J. Valeo

1974-01-01

358

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

359

Detection of ionospheric Alfvén resonator signatures in the equatorial ionosphere  

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

360

Ionospheric sources for molecular ion outflow  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

361

Higher-order effects in polarized proton dynamics  

Microsoft Academic Search

So far, polarized proton beams have never been accelerated to energies higher than 25 GeV. During the acceleration process, the beam polarization is quite undisturbed, when the accelerator is well adjusted, except at first-order depolarizing spin orbit resonances. At some accelerators other effects have been observed but first-order resonances have always been dominant. At these resonances the spin tune plus

G. H. Hoffstaetter; M. Vogt; D. P. Barber

1999-01-01

362

Ionospheric calibration for single frequency altimeter measurements  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

363

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

364

Second-order Talbot effect with entangled photon pairs  

SciTech Connect

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

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

2009-10-15

365

The Role of neutral winds play in Titan's ionospheric dynamics  

NASA Astrophysics Data System (ADS)

This paper will present the latest results of high resolution 3-D hybrid particle code simulations of Titan. The research is focused on understanding the interaction of Titan's ionosphere with Saturn's magnetosphere and the the subsequent ionospheric losses that occur. We test what role neutral winds may play in that interaction. This presentation will address our current research into the Titan's plasma interaction and its effects on Titan's ionosphere. The hybrid particle code HALFSHEL contains a variety of physical and chemical models which will also be discussed. These include a chemistry package that produces the ionosphere on grid resolution of 50 km altitude, as well as the Hall and Pedersen conductivities associated with plasma neutral collisions. The specific simulations to be presented self-consistently evolve the motion of the magnetospheric O+ and several generic ionospheric species.

Ledvina, S. A.; Brecht, S. H.; Bell, J. M.

2013-12-01

366

International Reference Ionosphere -2010  

NASA Astrophysics Data System (ADS)

The International Reference Ionosphere 2010 includes several important improvements and ad-ditions. This presentation introduces these changes and discusses their benefits. The electron and ion density profiles for the bottomside ionosphere will be significantly improved by using more ionosonde data as well as photochemical considerations. As an additional lower iono-sphere parameter IRI-2010 will include the transition height from molecular to cluster ions. At the F2 peak Neural Net models for the peak density and the propagation factor M3000F2, which is related to the F2 peak height, are introduced as new options. At high latitudes the model will benefit from the introduction of auroral oval boundaries and their variation with magnetic activity. Regarding the electron temperature, IRI-2010 now models variations with solar activity. The homepage for the IRI project is at http://IRI.gsfc.nasa.gov/.

Bilitza, Dieter; Reinisch, Bodo

367

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

368

Theory of imperfect magnetosphere-ionosphere coupling  

SciTech Connect

A theory of magnetosphere-ionosphere coupling in the presence of field-aligned potential drops is formulated within the framework of magnetohydrodynamic equations. Our formulation allows the magnetosphere as well as the ionosphere to respond self-consistently to the parallel potential drop along auroral field lines. Equipotential contours are distorted into a V-shaped structure near the convection reversal boundary and S-shaped on the equatorward side, each gives rise to an inverted V precipitation band. The loading effect of the imperfect coupling results in a valley in the electric field profile which occurs equatorward of the convection reversal boundary.

Kan, J.R.; Lee, L.C.

1980-09-01

369

Characterizing Extreme Ionospheric Storms  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

370

Estimation of ionospheric TEC and Faraday rotation for L-band SAR  

NASA Astrophysics Data System (ADS)

Spaceborne synthetic aperture radar (SAR) systems are used to measure geo- and biophysical parameters of the Earth's surface, e.g. for agriculture, forestry and land subsidence investigations. Upcoming SAR sensors such as the Japanese Phased Array L-band Synthetic Aperture Radar (PALSAR) onboard the Advanced Land Observing Satellite (ALOS) exemplify a trend towards lower frequencies and higher range chirp bandwidth in order to obtain additional information with higher geometric resolution. However, the use of large bandwidths causes signal degradation within a dispersive medium such as the ionosphere. Under high solar activity conditions at L-band frequencies, ionosphere-induced path delays and Faraday rotation become significant for SAR applications. Due to ionospheric effects, blind use of a generic matched filter causes inaccuracy when correlating the transmitted with the received signal. Maximum correlation occurs where the length of the matched filter, based on a synthetic chirp model of the transmitted signal, is adjusted to correspond to that of the received signal. By searching for the proper adjustment necessary to reach this maximum, the change in length can be estimated and used to derive variations in the total electron content (TEC) and degree of Faraday rotation within the ionosphere from all range lines in a SAR image.

Jehle, Michael; Rüegg, Maurice; Small, David; Meier, Erich; Nüesch, Daniel

2005-10-01

371

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

372

Effect of impurities on the magnetic ordering in chromium  

SciTech Connect

It is well known that impurities profoundly alter the magnetic properties of chromium. For example, doping with as little as 0.2% vanadium changes the phase transition from weakly first order in pure chromium to second order. While vanadium impurities suppress the Neel temperature {ital T}{sub {ital N}}, doping with manganese dramatically enhances {ital T}{sub {ital N}}. Impurities also change the wave vector of the spin-density wave, which has the order parameter {ital g}. According to the theory of Young and Sokoloff (YS), the first-order transition in pure chromium is caused by a charge-density wave with order parameter {delta}{proportional to}{ital g}{sup 2}. Scattering by impurities suppresses the charge-density wave and drives the transition to second order. In this paper we refine the YS formalism by examining the subtle balance between the spin-density and charge-density terms in the free energy. We find that the first-order transition is destroyed when the concentration of vanadium exceeds about 0.15%, in agreement with experimental measurements. We also study the effect of impurities on the band structure and Neel temperature.

Fishman, R.S. (Department of Physics, SU Station Box 5566, North Dakota State University, Fargo, North Dakota 58105-5566 (United States) Solid State Division, P.O. Box 2008, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)); Liu, S.H. (Solid State Division, P.O. Box 2008, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States))

1992-06-01

373

Maternal age, birth order, and race: differential effects on birthweight  

PubMed Central

Background Studies examining the influence of maternal age and birth order on birthweight have not effectively disentangled the relative contributions of each factor to birthweight, especially as they may differ by race. Methods A population-based, cross-sectional study of North Carolina births from 1999 to 2003 was performed. Analysis was restricted to 510 288 singleton births from 28 to 42 weeks’ gestation with no congenital anomalies. Multivariable linear regression was used to model maternal age and birth order on birthweight, adjusting for infant sex, education, marital status, tobacco use and race. Results Mean birthweight was lower for non-Hispanic black individuals (NHB, 3166 g) compared with non-Hispanic white individuals (NHW, 3409 g) and Hispanic individuals (3348 g). Controlling for covariates, birthweight increased with maternal age until the early 30s. Race-specific modelling showed that the upper extremes of maternal age had a significant depressive effect on birthweight for NHW and NHB (35+ years, p<0.001), but only age less than 25 years was a significant contributor to lower birthweights for Hispanic individuals, p<0.0001. Among all racial subgroups, birth order had a greater influence on birthweight than maternal age, with the largest incremental increase from first to second births. Among NHB, birth order accounted for a smaller increment in birthweight than for NHW and Hispanic women. Conclusion Birth order exerts a greater influence on birthweight than maternal age, with signficantly different effects across racial subgroups.

Swamy, Geeta K; Edwards, Sharon; Gelfand, Alan; James, Sherman A; Miranda, Marie Lynn

2014-01-01

374

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

375

Ordering and disordering effects in confined liquid crystals  

Microsoft Academic Search

Confined liquid crystals exhibit significantly different physical properties from those of a bulk. The confinement could have either ordering or disordering effects on a liquid crystal (LC) phase depending on the topology of the confining surface and on the surface-LC interaction. This dissertation presents a deuteron nuclear magnetic resonance (DNMR) study of confined nCB liquid crystals, focusing on the surface

Tao Jin

2003-01-01

376

Nonlinear high-order effects in stimulated Raman scattering spectrum  

Microsoft Academic Search

A dependence of the stimulated Raman scattering (SRS) of water solutions of HNO3 on the pumping level has been studied. The lines of the fourth and higher order effects were found. The results are treated in the basis of a spectrally uniform model of radiation centres and dependence of the coefficients of nonlinear susceptibility on the pumping.

I. I. Kondilenko; P. A. Korotkov; V. I. Maly

1972-01-01

377

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

378

Ionized Columns between Thunderstorms and the Ionosphere  

Microsoft Academic Search

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

R. K. COLE

1966-01-01

379

Earthquake impact on ionospheric Alfvén resonances  

NASA Astrophysics Data System (ADS)

According to BGO data, it is discovered that ionospheric Alfvén resonances (IARs) observed as geomagnetic pulsations at frequencies of a few hertz arise in response to seismic events. The paper presents examples showing how seismic waves affect the IAR regime. Possible mechanisms of this effect are discussed.

Potapov, A. S.; Dovbnya, B. V.; Tsegmed, B.

2008-04-01

380

Low Frequency Rada Sounding Through Martian Ionosphere  

NASA Technical Reports Server (NTRS)

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

Safaeinili, A.; Jordan, R.

2000-01-01

381

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

382

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

383

The Dayside Ionospheric \\  

Microsoft Academic Search

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

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

2006-01-01

384

The ionospheric disturbance dynamo  

Microsoft Academic Search

The purpose of the present work is to develop a theory of the ionospheric disturbance dynamo and to examine, on the basis of theoretically predicted features, its relevance to the understanding of certain observations. A longitudinally symmetric, time-dependent numerical model of the thermospheric disturbance winds driven by an auroral heating event and the associated electric fields and currents derived for

M. Blanc; A. D. Richmond

1980-01-01

385

Modeling Saturn's Ionosphere: Comparisons with Cassini  

NASA Astrophysics Data System (ADS)

The Saturn-Thermosphere-Ionosphere-Model (STIM) -- a global circulation model -- is used to study parameters in Saturn's ionosphere that affect the location and magnitude of the electron density peak. Past observations from the Pioneer and Voyager spacecraft indicated that the ionosphere had a peak between ˜1900 - 2900 km, with a maximum density ranging from 6000 - 20,000 electrons/cc. Preliminary results from the first occultation by Cassini show an ionospheric peak of somewhat fewer than 10,000 electrons/cc near 1200 km, and a peak of order 1000 electrons/cc near 2500 km. We use STIM to explore parameter space for processes that could lead to the dawn/dusk asymmetries present in the observations. These parameters include: (a) the reaction rate between H+ and vibrationally excited H2, (b) an influx of H20 from the top of the atmosphere, (c) a vertical drift caused by neutral winds and/or an E x B drift forcing plasma along magnetic field lines, and (d) a variation in the location of the turbopause. Support for this work was provided by a grant from the NASA Planetary Atmospheres Program (MM), a NASA Graduate Student Research Proposal grant (LM), and a British Royal Society University Research Fellowship (IMW).

Moore, L.; Mendillo, M.; Mueller-Wodarg, I.

2005-08-01

386

Disturbed Nighttime Ionosphere Observed by KOMPSAT-1  

NASA Astrophysics Data System (ADS)

Korea has launched its first multi-purpose satellite, KOMPSAT-1, on December 21, 1999 into 685 km altitude sun-synchronous polar orbit with the descending node at 22:50 local time. The unique orbital characteristic of the spacecraft is suitable for the global study of upper ionosphere at fixed local time and altitude. Ionospheric Measurement Sensor (IMS), composed of a Langmuir Probe (LP) and the Electron Temperature Probe (ETP), monitored the variation of the nighttime local ionosphere along the satellite track until August 2, 2001. The present paper describes the variation of the mid-latitude ionospheric trough observed by IMS according to the geomagnetic disturbance as well as its possible seasonal variations. It is seen that the trough location moves equatorward and the subauroral temperature enhances as the Kp index increases, as previously reported. While the midlatitude electron density generally increases with Kp, it is seen that the density at the trough decreases with the increasing Kp. In order to study the storm and substorm features, both the Kp and the Dst indices are compared with these activities.

Min, K. W.; Park, S.; Lee, E.

2002-12-01

387

Higher order and asymmetry effects on saturation of magnetic islands  

SciTech Connect

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

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

2013-06-15

388

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

Microsoft Academic Search

A quantitative model of the global atmospheric electric circuit has been constructed using the PSpice electrical engineering software package. Currents (~ 1 kA) above thunderstorms and electrified rain\\/shower clouds raise the potential of the ionosphere, which is presumed to be an equipotential surface at 80 km altitude, to ~ 250 kV with respect to the Earth's surface. The circuit is

Michael J. Rycroft; Anna Odzimek

2010-01-01

389

Ionospheric disturbances under low solar activity conditions  

NASA Astrophysics Data System (ADS)

The paper is focused on ionospheric response to occasional magnetic disturbances above selected ionospheric stations located at middle latitudes of the Northern and Southern Hemisphere under extremely low solar activity conditions of 2007-2009. We analyzed changes in the F2 layer critical frequency foF2 and the F2 layer peak height hmF2 against 27-days running mean obtained for different longitudinal sectors of both hemispheres for the initial, main and recovery phases of selected magnetic disturbances. Our analysis showed that the effects on the middle latitude ionosphere of weak-to-moderate CIR-related magnetic storms, which mostly occur around solar minimum period, could be comparable with the effects of strong magnetic storms. In general, both positive and negative deviations of foF2 and hmF2 have been observed independent on season and location. However positive effects on foF2 prevailed and were more significant. Observations of stormy ionosphere also showed large departures from the climatology within storm recovery phase, which are comparable with those usually observed during the storm main phase. The IRI STORM model gave no reliable corrections of foF2 for analyzed events.

Buresova, D.; Lastovicka, J.; Hejda, P.; Bochnicek, J.

2014-07-01

390

Investigation of Mars' ionospheric response to solar energetic particle events  

NASA Astrophysics Data System (ADS)

We investigate the effects of solar energetic particle (SEP) events on the Martian ionosphere using observations from the Mars Global Surveyor (MGS) Electron Reflectometer (ER) and Radio Science (RS) experiments. Although MGS/ER is not designed to measure solar storm particles, it detects SEPs as increased instrument background. Using this proxy for SEP fluxes near Mars, we compare electron density profiles obtained from the RS experiment during periods of high and low SEP activity. Six case studies show no clear evidence for an increase in the ionospheric electron density between 200 and 100 km altitudes. However, 4 of the 6 events show a small increase in electron density below 100 km altitude during SEP events, suggesting that high-energy (10-20 keV) electrons may cause ionization in the lower ionosphere. We also observe an ˜25% decrease in the ionospheric electron density between ˜100 and ˜120 km altitude for the two strongest events, suggesting that SEPs trigger a process that increases electron loss in this altitude range of the lower ionosphere. However, we cannot be confident from only two events that this effect is caused directly or indirectly by increased SEP fluxes. A statistical study confirms the case study results, but not over all solar zenith angles. Additionally, we observe depletions in the topside ionospheric electron density at some solar zenith angles, which can be explained by compression of the ionosphere by the passing CME.

Ulusen, Demet; Brain, David A.; Luhmann, Janet G.; Mitchell, David L.

2012-12-01

391

Thermosphere-Ionosphere-Magnetosphere Coupling and Mass Outflow - the Magnetosphere/Ionosphere Perspective (Invited)  

NASA Astrophysics Data System (ADS)

Global scale models of the solar wind-magnetosphere-ionosphere interaction have long established history of including magnetosphere-ionosphere coupling through the electrodynamic coupling. Typically this coupling includes closure of field aligned currents from the magnetosphere in the electrostatic ionosphere with the conductances being modified by particle precipitation processes. Recent advances in simulation technology, namely multi-fluid MHD, allow the scope of MI coupling in simulations to include mass outflows from the thermosphere-ionosphere into the magnetosphere. Multiple approaches to addressing this challenge have been developed. In one approach empirical parametrization of the outflow characteristics, namely velocity and flux, are used to include high intensity sources