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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

Methods for correcting higher-order ionospheric effects on the positioning and timing of GPS.  

NASA Astrophysics Data System (ADS)

One of the main error sources for positioning and timing in GPS is ionospheric refraction error. At present the dual-frequencies technique has been used for correcting the first-order ionospheric effect. The accuracy of 1 - 10 m for positioning or 3 - 30 ns for timing has been obtained by this technique. However, the second-order ionospheric effect needs to be corrected to reach higher accuracies of centimeters, and the third-order ionospheric effect should be corrected for the accuracies of millimeters. In this paper the methods which can correct not only the first-order but also the second and third-order ionospheric effects are proposed, and both of dual-frequencies technique and dual-polarization technique are used in these methods.

Yang, Kejun

1996-06-01

4

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

NASA Astrophysics Data System (ADS)

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

Vergados, Panagiotis

5

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

Microsoft Academic Search

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

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

2011-01-01

6

Ionospheric Effects of Solar Activity.  

National Technical Information Service (NTIS)

The effects of solar flares on the ionsophere are reviewed in a brief and qualitative fashion. Individual phenomena described include the long-term solar-cycle variability of the ionosphere, sudden ionospheric disturbances, polar-cap absorption events, an...

G. C. Reid

1972-01-01

7

Effects of the active auroral ionosphere on magnetosphere - ionosphere coupling  

Microsoft Academic Search

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

Dimitri Pokhotelov

2003-01-01

8

Ionospheric effects 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

Victor P. Pasko; Umran S. Inan; Timothy F. Bell

1998-01-01

9

Magnetospheric cleft: ionospheric effects  

Microsoft Academic Search

The fluxes of electrons that precipitate through the day side clefts of the magnetosphere are intense enough and deposit their energy at a high enough altitude to heat and ionize the F layer and top side ionosphere substantially. Relevant synoptic results from bottom side and top side sounder measurements are reviewed, and new data from the Isis satellites are presented.

J. H. Whitteker

1976-01-01

10

Comparison of Implementation Strategies of the 2nd-order Ionosphere Correction in GPS Data Processing  

Microsoft Academic Search

The 2nd-order ionospheric delay of the GPS signal has been shown to be a contributing factor to both static and seasonal errors of GPS station positions. Caused by Faraday rotation of the GPS electromagnetic waves traveling through the ionosphere in the presence of the Earth's magnetic field, the effect was demonstrated to contribute a latitude-dependent southward bias of the order

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

2005-01-01

11

IONOSPHERIC EFFECTS ASSOCIATED WITH MAGNETIC DISTURBANCES  

Microsoft Academic Search

A bstractConsideration of ionospheric effects coinciding with magnetic disturbances must, as yet, be qualitative. Discussion in this paper is directed toward elucidating the nature of ionospheric changes coincident with magnetic activity in the temperate and equatorial zones as interpreted from automatic multifrequency ionospheric records. Observations at Kensington (Maryland) during summer are described and illustrated. During summer night, following commencement of

L. V. Berkner; H. W. Wells; S. L. Seaton

1939-01-01

12

Ionospheric effects on Geosat altimeter observations  

Microsoft Academic Search

The presence of free electrons and ions modifies the propagation speed of EM waves. Thus the apparent sea height measured by a radar altimeter such as that on Geosat is influenced by passage through the ionosphere. Here, these ionospheric effects are studied using several methods. A model ionosphere for Westford, MA is constructed from two-frequency observations of GPS satellites. This

Steven Musman; Alice Drew; Bruce Douglas

1990-01-01

13

Ionospheric effects on GPS positioning  

Microsoft Academic Search

Ionospheric scintillation results from a single frequency global positioning system (GPS) receiver have been presented in this paper. Ionospheric scintillation is rapid variation in the amplitude and phase of radio signals caused by irregularities in the ionosphere. Ionosphere contains large amplitude variations over spatial scales from few cm to 100s of km. It is observed that VHFUHF communications as well

Smita Dubey; Rashmi Wahi; A. K. Gwal

2006-01-01

14

A survey of ionospheric effects upon earth-space radio propagation  

Microsoft Academic Search

The frequency dependence is derived and the order of magnitude is presented for various ionospheric effects upon radio waves which have frequencies greater than the penetration frequency of the ionosphere. Among the phenomena considered are phase-path length change, refraction, frequency change, group-path delay, polarization rotation, and absorption. A detailed discussion is given of the mean value and variability of ionospheric

R. S. Lawrence; C. G. Little; H. J. A. CHIVERSt

1964-01-01

15

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

16

A new unequal-weighted triple-frequency first order ionosphere correction algorithm and its application in COMPASS  

NASA Astrophysics Data System (ADS)

As the introduction of triple-frequency signals in GNSS, the multi-frequency ionosphere correction technology has been fast developing. References indicate that the triple-frequency second order ionosphere correction is worse than the dual-frequency first order ionosphere correction because of the larger noise amplification factor. On the assumption that the variances of three frequency pseudoranges were equal, other references presented the triple-frequency first order ionosphere correction, which proved worse or better than the dual-frequency first order correction in different situations. In practice, the PN code rate, carrier-to-noise ratio, parameters of DLL and multipath effect of each frequency are not the same, so three frequency pseudorange variances are unequal. Under this consideration, a new unequal-weighted triple-frequency first order ionosphere correction algorithm, which minimizes the variance of the pseudorange ionosphere-free combination, is proposed in this paper. It is found that conventional dual-frequency first-order correction algorithms and the equal-weighted triple-frequency first order correction algorithm are special cases of the new algorithm. A new pseudorange variance estimation method based on the three carrier combination is also introduced. Theoretical analysis shows that the new algorithm is optimal. The experiment with COMPASS G3 satellite observations demonstrates that the ionosphere-free pseudorange combination variance of the new algorithm is smaller than traditional multi-frequency correction algorithms.

Liu, WenXiang; Mou, WeiHua; Wang, FeiXue

2012-03-01

17

Ionospheric effects of Geosat altimeter observations  

SciTech Connect

The presence of free electrons and ions modifies the propagation speed of electromagnetic waves. Thus the apparent sea height measured by a radar altimeter such as that on board Geosat is influenced by passage through the ionosphere. The authors explore ionospheric effects using several methods. A model ionosphere for Westford, Massachusetts, is constructed from two frequency observations of Global Positioning System satellites. This model is compared with a theoretical calculation, Faraday rotation observations, and the ionospheric correction furnished with the Great geophysical data records. They discuss the influence of the solar cycle, which is important at the moment as a particularly active maximum is approached. Some general remarks on the ionospheric influence on the oceanographic signal observed by a satellite altimeter are also included.

Musman, S.; Drew, A.; Douglas, B. (NOAA, Rockville, MD (United States))

1990-03-15

18

Ionospheric effects on modern electronic systems  

Microsoft Academic Search

A basic overview of ionospheric phenomenology is provided. Some of the modern electronic systems of interest and the extent to which the ionosphere may place limits on design and operation are discussed. The effects of importance to electronic systems are defined, and the effects are discussed by frequency regime: the ELF (<3 kHz), VLF (3-30 kHz), and LF (30-300 kHz)

JOHN M. GOODMAN; Jules Aarons

1990-01-01

19

Ionospheric Effects of Geomagnetic Storms on GNSS based Systems  

Microsoft Academic Search

It is known that ionosphere is the effective indicator of the space weather state. Severe ionospheric perturbations can seriously degrade the performance of Global Navigation Satellite Systems (GNSS). During geomagnetic storms the ionospheric gradients are essentially increased in compare with quiet conditions. Strong ionospheric gradients can caused the deterioration of GPS positioning. In the given report it is presented the

Irk Shagimuratov; Andrzej Krankowski; Irina Zakharenkova; Ivan Karpov; Galina Yakimova

2010-01-01

20

Strong turbulence effects in artificially disturbed ionosphere  

NASA Astrophysics Data System (ADS)

The theoretical and experimental study of strong turbulence effects arising in the ionospheric plasma under the action of powerful radio waves is presented. The theoretical results are obtained by the numerical solution of nonlinear Schrdinger equation (NSE) with driven extension in inhomogeneous plasma, the experimental ones by means of artificial ionospheric turbulence sounding by probing radio pulses. The qualitative agreement of theoretical and experimental results is obtained.

Kochetov, A. V.; Mironov, V. A.; Terina, G. I.

21

IONOSPHERIC EFFECTS OF NUCLEAR EXPLOSIONS  

Microsoft Academic Search

Dieminger and Kohl (Nature, 193: 983(1982)) described some ionospheric ; phenomena observed at Lindau, Germany, on October 30, 1961, following a large ; nuclear explosion at Novaya Zemlya in the arctic. Since the recordings were made ; at 1\\/2-hourly intervals, the precise time of the onset of the disturbance could ; not be pinpointed. For a large part of the

W. J. G. Beynon; E. S. O. Jones

1962-01-01

22

A survey of ionospheric effects on space-based radar  

Microsoft Academic Search

In this survey, we fully review almost all potential ionospheric effects on the performance of space-based radar systems (SBRs), which operate in the ambient ionosphere environment; in particular, we review the use of space-based synthetic aperture radar systems (SARs) for imaging. There are two families of effects involved. One is the effects of the background ionosphere (non-turbulent ionosphere), such as

Zheng-Wen Xu; Jian Wu; Zhen-Sen Wu

2004-01-01

23

Atmospheric effects assessment program: Ionospheric sounding  

NASA Astrophysics Data System (ADS)

This document reports efforts on two main goals: to study the short-term ionospheric variability and to study the effects of this variability on high frequency (HF) skywave field strength. To achieve the first goal, ionospheric soundings are being done at 5-minute intervals at San Diego, CA, and at Logan, UT. This time interval was chosen to adequately resolve variations produced by locally generated gravity waves. To study the effects of short-term ionospheric variability on high frequency communications, a circuit is being established to measure the variability of the received HF signal strength. The chosen circuit will have the transmitter located in Forsyth, MT, and the receiver in Imperial Beach, CA (approximately 20 miles south of NRaD).

Sprague, R. A.

1994-02-01

24

Auroral and polar-cap ionospheric effects on radio propagation  

Microsoft Academic Search

Disturbances in the auroral and polar-cap ionosphere can have profound effects on radio signals traversing the high-latitude ionosphere (defined here as that latitudinal region poleward of approximately 55 corrected geomagnetic latitude). Some effects of the high-latitude ionosphere on polar radio paths were documented as early as the 1930s, but intensive investigations of this ionospheric global region started during the International

Robert D. Hunsucker

1992-01-01

25

Effects of UGTs on the ionosphere  

Microsoft Academic Search

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.

P. E. Argo; T. J. Fitzgerald

1992-01-01

26

Calibration of Ionospheric Effects on VHF Tracking.  

National Technical Information Service (NTIS)

A study is presented of the effects of ionospheric perturbations on VHF tracking, based on a mathematical prediction model or on on-line calibration using auxiliary measurements. It is shown how the stochastic model of a received signal is derived with th...

P. Kohler S. Larcher

1976-01-01

27

Dayside cleft aurora and its ionospheric effects  

Microsoft Academic Search

The existence of an opening on the dayside of the earth's magnetic field through which solar plasma could penetrate was noted by Chapman and Ferraro in 1931, and although observational evidence of its auroral and ionospheric effects accumulated steadily over the years, the dayside cleft (or cusp) was not accepted as a real magnetospheric feature until 1971. The history of

Gordon G. Shepherd

1979-01-01

28

Ionospheric Geo-effectiveness of Magnetic Clouds  

Microsoft Academic Search

We present an analysis of the geo-effectiveness of magnetic clouds and the disturbed solar wind surrounding them. Estimates of the ionospheric Joule heating rates based on two ground magnetic indices and estimates of auroral zone particle heating from polar satellites will be combined to provide a summary of the total geomagnetic heating during magnetic cloud passage. Preliminary estimates suggest that

T. J. Bronder; D. J. Knipp; B. Lynch; T. Zurbuchen; M. G. McHarg; F. K. Chun

2002-01-01

29

Quiet auroral arcs - Ionosphere effect of magnetospheric convection stratification  

Microsoft Academic Search

A detailed study of the mechanism of electromagnetic stratification of the large-scale stationary magnetospheric convection due to a friction of the convective flow in the ionosphere layer was performed. Magnetosphere-ionosphere interaction was taken into account by means of the effective boundary conditions on the ionosphere top and bottom boundaries including the actual height profile of charge particles velocity in the

V. Iu. Trakhtengerts; A. Ia. Feldstein

1984-01-01

30

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

NASA Astrophysics Data System (ADS)

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

Hu, Yaogai; Zhao, Zhengyu; Zhang, Yuannong

2011-07-01

31

Ionospheric effects of magnetopause reconnection observed using ionospheric tomography  

Microsoft Academic Search

This paper presents key signatures in the spatial distribution of ionospheric electron density attributed to solar wind particles injected following magnetopause reconnection. Using established criteria, optical auroral emissions have been used to identify the reconnection process. A simultaneous image of electron density shows an enhanced region with a northward gradient in F-layer peak height that may be linked to dispersion

I. K. Walker; J. Moen; C. N. Mitchell; L. Kersley; P. E. Sandholt

1998-01-01

32

Ionospheric Scintillation Effects on GPS  

NASA Astrophysics Data System (ADS)

. Ionospheric scintillation of Global Positioning System (GPS) signals threatens navigation and military operations by degrading performance or making GPS unavailable. Scintillation is particularly active, although not limited to, a belt encircling the earth within 20 degrees of the geomagnetic equator. As GPS applications and users increases, so does the potential for detrimental impacts from scintillation. We examined amplitude scintillation data spanning seven years from Ascension Island, U.K.; Ancon, Peru; and Antofagasta, Chile in the Atlantic/Americas longitudinal sector at as well as data from Parepare, Indonesia; Marak Parak, Malaysia; Pontianak, Indonesia; Guam; and Diego Garcia, U.K.; in the Pacific longitudinal sector. From these data, we calculate percent probability of occurrence of scintillation at various intensities described by the S4 index. Additionally, we determine Dilution of Precision at one minute resolution. We examine diurnal, seasonal and solar cycle characteristics and make spatial comparisons. In general, activity was greatest during the equinoxes and solar maximum, although scintillation at Antofagasta, Chile was higher during 1998 rather than at solar maximum.

Steenburgh, R. A.; Smithtro, C.; Groves, K.

2007-12-01

33

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

34

Ionospheric Electron Concentration Effects on SAR and INSAR  

Microsoft Academic Search

The launch of ALOS and the high potential expected for the L-band PALSAR motivated us to investigate ionospheric electron concentration effects using JERS L-band SAR data acquired at high latitudes. An important focus of our work was on the identification of ionospheric effects and resulted in methodologies to detect ionospheric effects in single SAR acquisitions as well as in repeat-orbit

Urs Wegmller; Charles Werner; Tazio Strozzi; Andreas Wiesmann

2006-01-01

35

Effect of the topography on the ionosphere: results from the Mars Express MARSIS experiment.  

NASA Astrophysics Data System (ADS)

Active Ionospheric Sounding (AIS) data acquired by the MARSIS instrument on board the Mars Express mission have been used to analyze the effect of the irregular Martian topography on the altitude of the main ionospheric peak. Besides basic parameters, such as heliocentric distance or season, solar activity or solar zenith angle that must be considered when the Martian ionosphere is analyzed, there are other factors that can influence the ionosphere behavior. One of them is the topography. Topography seems to play a role on the Martian ionosphere when regional scale is considered. It has been observed that the main ionospheric peak altitude is higher over large volcanic edifices by as much as 20 km above surrounding areas and lower over impact basins by as much as 15 km below surrounding areas. This behavior, apparently only detected at sub-regional scale, has been found for the most prominent topographic features studied in this work. Correction for the solar zenith angle has been taken into account, in order to remove potential effect due to this parameter. This work examines and evaluates the main variations of the main ionosphere peak altitude found in regions with particular topography. A statistical analysis of the ionosphere deviation over each selected structure is given and special attention is paid to the possible physical mechanisms that can explain this phenomenon. MARSIS data have been downloaded from the ESA planetary science archive and topographic information comes from MOLA instrument on board Mars Global Surveyor mission.

Snchez-Cano, Beatriz; Witasse, Olivier; Herraiz, Miguel; Radicella, Sandro M.

2013-04-01

36

Ionospheric effects on synthetic aperture radar at VHF  

SciTech Connect

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

Fitzgerald, T.J.

1997-02-01

37

Measurements of ionospheric effects on wideband signals at VHF  

SciTech Connect

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

Fitzgerald, T.J.

1998-08-17

38

Ionospheric effects upon a satellite navigation system at Mars  

Microsoft Academic Search

Trans-ionospheric radio propagation effects resulting in ranging errors are examined for a potential orbital network of communications and navigational satellites at Mars. Using recent results from the radio science experiment on board the Mars Global Surveyor (MGS) spacecraft and a photochemical model of Mars' ionosphere, we study the total electron content (TEC) at Mars to investigate how its latitude, local

Michael Mendillo; Xiaoqing Pi; Steven Smith; Carlos Martinis; Jody Wilson; David Hinson

2004-01-01

39

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

40

Ionospheric effects on satellite land mobile systems  

Microsoft Academic Search

Satellite-ground radio systems are now so sensitive that ionospheric changes can disrupt their performance. This paper discusses some satellite-to-ground propagation problems in the UHF and L bands caused by the Earth's ionosphere. Such problems include signal time delay, signal dispersion, Faraday rotation, and scintillation.

Kenneth Davies; Ernest K. Smith

2002-01-01

41

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

42

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

43

Ionosphere layer shape from second-order ATS 6 measurements  

Microsoft Academic Search

electron content value. The second-order component of phase path is primarily due to a truncation of the expansion for refractive index when the satellite is within about 45 of zenith, but it is dominated by ray path bending when the satellite is outside that zone. The second-order value is used to derive scale height at the peak of the

M. L. Heron

1981-01-01

44

Higher-order modes in the earth-ionosphere resonator  

NASA Astrophysics Data System (ADS)

A statistical analysis of mean daily spectral realizations of the Ez component of natural radio noise recorded in the Magadan region in the 50-200 Hz band was carried out. In addition to lower modes of Schumann resonances, the existence of higher-order modes was observed. Phase velocities of ELF propagation in the 8-120 Hz band are calculated on the basis of 20 observed modes of resonant frequencies.

Dolgopolov, S. G.; Osinin, V. F.

1989-08-01

45

Ionospheric and stratopsheric effects of a proton flare during unusual solar activity - 22 November 1977  

Microsoft Academic Search

The effect of the proton flare of 22 November 1977 on the various levels in the middle atmosphere and the bottom-side ionosphere is studied in order to compare synchronous phenomena in the middle atmosphere with phenomena in upper regions and to investigate the response of middle atmosphere to the penetration of high energy solar particles and radiation.

P. Velinov; G. Nestorov; Kh. Spasov; Ts. Dachev; Y. Tasev

1984-01-01

46

SOLAR FLARE EFFECTS IN THE IONOSPHERE  

Microsoft Academic Search

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

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

1967-01-01

47

Ionospheric storm effects at subauroral latitudes: A case study  

Microsoft Academic Search

An attempt is made to classify ionospheric storm effects at subauroral latitudes according to their presumed origin. The storm of December 7\\/8, 1982, serves as an example. It is investigated using ionosonde, electron content, and DE 2 satellite data. The following effects are distinguished: (1) positive storm effects caused by traveling atmospheric disturbances, (2) positive storm effects caused by changes

G. W. Proelss; L. H. Brace; H. G. Mayr; G. R. Carignan; T. L. Killeen; J. A. Klobuchar

1991-01-01

48

Trough in the daytime F layer: A macroscopic effect of ionospheric-magnetospheric convection  

SciTech Connect

The daytime F layer trough is a major result of ionospheric-magnetospheric convection, appearing in the winter high latitude ionosphere as a continuous band thousands of kilometers in extent in which the daytime F layer electron density is depleted, often by an order of magnitude. As observed by a global array of ionospheric sounders during solar maximum, the trough occurs in regions of sunward convection, in the morning corresponding to the dawn cell and in the afternoon corresponding to the dusk cell. The formation of the trough is consistent with the transport of low density nighttime plasma into the day sector where it displaces high density daytime plasma, although other mechanisms such as ion chemical effects may also play a role.

Whalen, J.A.

1990-05-03

49

The ionospheric wind dynamo: Effects of its coupling with different atmospheric regions  

NASA Astrophysics Data System (ADS)

Effects of the ionospheric wind dynamo related to its coupling with different atmospheric regions are reviewed. Early studies showed that height-averaged tidal-like winds of order 30 m/s must be present in the dynamo region (90-200 km height) to produce the observed geomagnetic daily variations. They also indicated that diurnal solar tides drive more current than semidiurnal tides, although the latter are important in explaining the observed electric fields and asymmetries of the currents about the equator. Lunar tidal winds of order 10 m/s in the dynamo region, roughly opposite in phase to the tides at ground level, are required to explain the observed lunar geomagnetic variations. There is strong seasonal and longitudinal variability in lunar geomagnetic variations that indicates similar variability in the lunar tidal winds. Day-to-day variability in ionospheric dynamo effects points to short-term variability in the global winds, probably due to variability in tidal propagation conditions through the middle atmosphere and/or to penetration of planetary waves into the dynamo region. However, attempts to correlate observed upper-mesospheric winds with geomagnetic variations have had only limited success. Searches for two-day variations in geomagnetic data associated with the two-day wave in megospheric winds have not consistently found a significant signal. Suggestions of a 16-day variation in geomagnetic and ionospheric data associated with 16-day planetary waves remain to be verified, as do suggestions of possible associations between the stratospheric quasi-biennial oscillation and geomagnetic variations. Coupling among dynamo electric fields and currents, ionospheric plasma variations, and thermospheric dynamics have been shown to be important in a number of situations. Recently, global simulation models that take these mutual-coupling effects into account have been developed. Coupling between the ionospheric and magnetospheric dynamos is also significant, though the quantitative importance and full implications of the "flywheel" effect, "fossil-wind" effect, and "disturbance-dynamo" effect remain to be determined. Fruitful areas of future research will be the further exploitation of observed geomagnetic and ionospheric phenomena to study tidal and planetary-wave propagation conditions in the middle atmosphere, including possible long-term changes associated with a changing atmospheric state; exploitation of simulation models of coupled thermosphere/ionosphere dynamics and electrodynamics; and further investigation of effects associated with coupling between the ionospheric and magnetospheric dynamos.

Richmond, A. D.

50

Study of topographic effects on the main Martian ionospheric peak with the Mars Express MARSIS instrument  

NASA Astrophysics Data System (ADS)

Active Ionospheric Sounding data (AIS) of MARSIS instrument on board Mars Express mission have been used to analyze the effect of the irregular Martian topography on the electron density and altitude of the main ionospheric peak.

Snchez-Cano, B.; Witasse, O.; Herraiz, M.; Radicella, S. M.; Rodrguez-Caderot, G.

2012-09-01

51

Ionospheric Effects Symposium (8th). Held in Alexandria, Virginia on May 7-9, 1996.  

National Technical Information Service (NTIS)

The Eighth International Ionospheric Effects Symposium, covered many aspects of ionospheric phenomena and emphasized many practical applications in the command and control, communication, navigation, and surveillance areas. Included in the program were cu...

D. Anderson H. Soicher J. A. Klobuchar J. M. Goodman R. McCoy

1996-01-01

52

Ionospheric effects on radio communication and ranging pulses  

Microsoft Academic Search

Transionospheric radio pulses used for communication and ranging purposes are modified by propagation effects arising from dispersion and scattering. To describe these effects quantitatively it is convenient to use the concept of temporal moments. The zeroth temporal moment is proportional to energy flow in the wave and is constant in a dissipationless ionosphere under the forward scatter approximation. The first

K. Yeh; C. Liu

1979-01-01

53

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

54

Ionospheric effects of lightning during the increasing part of solar cycle 22  

Microsoft Academic Search

Fundamental problems concerning the role of lightning and thunderstorms in the ionospheric variations and the precipitation dynamics of energetic radiation belt particles are considered. The ionospheric effects of lightning are investigated for the present solar cycle 22, or during 1986 and 1988. It is concluded that the ionosphere is subjected to direct lightning effects upwards and lightning-induced electron precipitation downward.

P. I. Vellinov; Kh. V. Spasov; S. I. Kolev

1991-01-01

55

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

SciTech Connect

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

Pi, Xiaoqing

1995-01-01

56

Nonlinear Ionospheric Propagation Effects on UHF and VLF Radio Signals  

Microsoft Academic Search

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

Keith Michael Groves

1991-01-01

57

Anomalous radio wave absorption due to ionospheric heating effects  

Microsoft Academic Search

An ionospheric volume in the F layer subjected to high power high frequency illumination is observed to be an effective scattering medium for radio signals. Experimental results are representative of a field-aligned scattering geometry. Scatter of the incident wave into electrostatic waves by these strongly field-aligned density irregularities is considered. This model explains the large decreases in radio wave reflectivity

Kristine N. Graham; J. A. Fejer

1976-01-01

58

Perturbations of the FUV dayglow and ionospheric storm effects  

Microsoft Academic Search

Decreases in the brightness of the FUV dayglow associated with magnetic activity are shown to be spatially correlated with negative ionospheric storms. Both disturbance effects are attributed to decreases in the thermospheric atomic oxygen density. The concurrent enhancement of the molecular species explains why the decrease of the ionization density is much larger than the depression of the dayglow.

G. W. Prlss; J. D. Craven

1998-01-01

59

Ionospheric effects on SAR imaging: a numerical study  

Microsoft Academic Search

There has been an increasing interest in the use of spaceborne very high frequency ultra high frequency (VHF-UHF) synthetic aperture radar (SAR) for measuring forest biomass and for detecting underground facilities. The propagation characteristics of the low-frequency electromagnetic wave are severely affected by the ionosphere. Recently, Faraday rotation effects and SAR image degradation have been studied using an analytical model

Jun Liu; Yasuo Kuga; Akira Ishimaru; Xiaoqing Pi; Anthony Freeman

2003-01-01

60

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

61

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

62

Ionospheric effects for L-band 2-D interferometric radiometry  

Microsoft Academic Search

Ionospheric effects are a potential error source for the estimation of surface quantities such as sea surface salinity, using L-band radiometry. This study is carried out in the context of the SMOS future space mission, which uses an interferometric radiometer. We first describe the way the Faraday rotation angle due to electron content along the observing path varies across the

Philippe Waldteufel; Nicolas Floury; Emmanuel P. Dinnat; Gerard Caudal

2004-01-01

63

Doppler study of ionospheric effects of solar flares  

NASA Astrophysics Data System (ADS)

Ionospheric effects arising during solar flares were studied by the Doppler technique on the Fort Collins-Havana path. An approximate electron density profile is determined on the basis of sudden frequency deviation data. Integrated solar flux is determined for the flare of February 15, 1978 at wavelengths of 100-1030 A.

Vazherkin, V. A.; Laso, B.; Lobachevskii, L. A.; Novikov, V. D.; Odintsova, I. N.

1980-12-01

64

Plasma sheet dynamics - Effects on, and feedback from, the polar ionosphere  

Microsoft Academic Search

The plasma sheet is shown to play a major role in determining the electric fields, currents, and particle precipitation regions in the polar ionosphere and upper atmosphere. In turn, ionospheric effects on electric fields and currents within the magnetotail are potentially important for plasma sheet dynamics. The whole is a particularly complex instance of magnetosphere-ionosphere coupling, not adequately yielding to

V. M. Vasyliunas

1981-01-01

65

Ionospheric Effects Symposium (IES), 2011. 13th International Ionospheric Effects Symposium, held May 17-19, 2011 in Alexandria, VA.  

National Technical Information Service (NTIS)

The 13th International Ionospheric Effects Symposium (IES2011) was held At the Crowne Plaza Hotel, Old Town, Alexandria, Virginia, May 17-19, 2011. There were approx. 175 papers and posters accepted, but because of certain travel restrictions, a somewhat ...

J. M. Goodman J. R. Hansen R. McCoy

2011-01-01

66

Simulations of Tsunami Effects in the F-Region Ionosphere  

NASA Astrophysics Data System (ADS)

Recent observations of F-region electron densities and of total electron content (TEC) have revealed disturbances that appear to be correlated with tsunamis. These observations show large electron density perturbations (~ 100%) and large TEC fluctuations (~ 30%) propagating at speeds of ~ 200 m/s and with a characteristic horizontal wavelength of ~ 300 km to 500 km. Published simulations of tsunami propagation through the atmosphere and subsequent interaction with the ionosphere have revealed striking similarities with the observations. However, important physical processes known to affect gravity wave propagation were not included in these prior analyses, while the ionospheric perturbation models they included were oversimplified. Here we describe numerical simulations of the upward propagation of a spectrum of gravity waves forced by a traveling deformation of the lower boundary and the interaction of these waves with the F-region ionosphere. The tsunami is assumed to travel as a steady-state disturbance at the lower boundary (z=0) with a vertical displacement described by a modified Airy function in the horizontal direction. It travels at the shallow water wave speed of 200 m/s. The horizontal wavenumber spectrum of the tsunami is first calculated and from this the vertical velocity spectrum at the surface is calculated. This spectrum is used to provide the forcing at the lower boundary of a spectral full-wave model. This model describes the propagation of linear, steady-state acoustic-gravity waves in a non-isothermal atmosphere with the inclusion of eddy and molecular diffusion of heat and momentum, ion drag, Coriolis force, and height-dependent mean winds. A steady-state 1-D ionospheric perturbation model including O+, NO+, O2+ and N2+ and electrons is used to calculate the electron density response to the tsunami. Electron density perturbations as a function of height and the total electron content (TEC) are calculated as a function of horizontal position. We perform simulations for an assumed maximum tsunami amplitude of 5 cm. Our simulations show that the effect of molecular diffusion is to strongly damp the waves in the topside (> 300 km altitude) ionosphere. In spite of this, the F-region response is large, with vertical displacements of ~ 2 to 5 km and electron density perturbations of ~ 100%. Mean winds have a profound effect on the ability of the waves to propagate into the F-region ionosphere. The higher frequency gravity waves in the spectrum are Doppler shifted to even higher frequencies for propagation into a headwind, which inhibits the propagation of the disturbance to F-region altitudes. We summarize our simulations by comparison with some ionospheric observations.

Hickey, M. P.; Schubert, G.; Walterscheid, R. L.

2008-12-01

67

Thermal-stress effect in the high-latitude ionosphere  

Microsoft Academic Search

The contribution of heat-flux gradients to the viscosity tensor of the ionospheric plasma (i.e., the thermal-stress effect) is analyzed. It is shown that this effect is manifested most strongly in structures with high ion temperature and low plasma concentration, which are observed in high-latitude ionization troughs. Experimental results indicate that the thermal-stress effect makes a significant contribution to the plasma-pressure

Iu. V. Konikov

1991-01-01

68

Estimation of higher-order ionospheric errors in GNSS positioning using a realistic 3-D electron density model  

NASA Astrophysics Data System (ADS)

The accuracy of the positioning systems such as GPS, GLONASS or Galileo is heavily affected by the presence of the ionosphere. Ionosphere-free dual-frequency algorithms used for positioning applications remove most of the ionospheric error but do not take into account its higher-order terms. In addition, the raypaths and total electron content (TEC) are assumed to be the same for both frequencies. This leads to centimeter-level range errors that can cause millimeter-level errors in positioning. In this paper an accurate estimation of the higher-order ionospheric errors based on a realistic 3-D electron density model is presented. A numerical homing-in ray-tracing algorithm is implemented to rigorously calculate satellite to receiver ray trajectories. The numerical simulations performed showed that higher-order ionospheric residual range errors may reach several centimeters (up to 5 cm) at low and middle latitudes; however, at high latitudes they hardly exceed several millimeters (up to 1 cm).

Kashcheyev, A.; Nava, B.; Radicella, S. M.

2012-08-01

69

Ionospheric scintillation effects on single frequency GPS  

NASA Astrophysics Data System (ADS)

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 amplitude scintillation data spanning 7 years from Ascension Island, U.K.; Ancon, Peru; and Antofagasta, Chile in the Atlantic/American longitudinal sector as well as data from Parepare, Indonesia; Marak Parak, Malaysia; Pontianak, Indonesia; Guam; and Diego Garcia, U.K. in the Pacific longitudinal sector. From these data, we calculate percent probability of occurrence of scintillation at various intensities described by the S4 index. Additionally, we determine Dilution of Precision at 1 min resolution. We examine diurnal, seasonal, and solar cycle characteristics and make spatial comparisons. In general, activity was greatest during the equinoxes and solar maximum, although scintillation at Antofagasta, Chile was higher during 1998 rather than at solar maximum.

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

2008-04-01

70

Ionospheric storm effects at subauroral latitudes: A case study  

SciTech Connect

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

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

1991-02-01

71

Ionospheric effect of Leonid meteor showers at 70 km height  

Microsoft Academic Search

The effect of the Leonid meteor showers in the ionospheric D-region has been investigated through the anomaly revealed in the amplitude record of a low-frequency (LF) signal at 40 kHz. Impulsive ionization due to meteoric particles produced an enhancement and a decrease in the amplitude of the LF signal during the day and night, respectively. From the characteristic durations of

S. K. Sarkar; B. K. de

1985-01-01

72

Planetary Ionospheres  

Microsoft Academic Search

\\u000a The paper presents a summary of the lectures on planetary ionospheres given at NASAs 1st Asia Pacific School on International Heliophysical Year conducted at Indian Institute of Astrophysics,\\u000a Kodaikanal, India during 1022 December 2007. Following an introduction, the paper describes the structure of the ionospheres,\\u000a theory of Earths ionosphere including the effects of diffusion, neutral wind and electric field, and

Nanan Balan

2010-01-01

73

Orbital barium CRRES injection - effective source of ionospheric wavelike disturbances  

NASA Astrophysics Data System (ADS)

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

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

74

Ionospheric Disturbance Effects on IPS signals from MEXART  

NASA Astrophysics Data System (ADS)

We present a study related to the impact by ionospheric disturbances in the radio-signal of sources observed with MEXican Array Radio Telescope (MEXART) from April 20th to May 31th of 2010. Along this time interval, we observed the behavior of radio-signal for the sources: 3C048, 3C144, 3C274, Cas A, Cen A, and 3C405, in a daily basis. We found that there were days in which some of these sources showed slight fluctuations, even when there was no major solar event. We analyzed the time series of each source using a Wavelet tool that allowed us to highlight those periods which can exist in the signal related with these fluctuations. In addition, to characterize and identify ionospheric effects, we have calculated the Total Electron Content (TEC) from Global Positioning System (GPS) data and have taken into account the Dst index for the same period with the purpose of discard effect from geomagnetic storms. We found that the TEC can be used as a potential tool to discriminate between interplanetary scintillation and ionospheric fluctuations in MEXART data.

Rodriguez-Martinez, M.; Perez-Enriquez, R.; Carrillo-Vargas, A.; Lopez-Montes, R.; Araujo-Pradere, E. A.; Casillas-Perez, G.; Lopez Cruz-Abeyro, J.

2011-12-01

75

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

76

Synergistic effects of hot plasma-driven potentials and wave-driven ion heating on auroral ionospheric plasma transport  

SciTech Connect

Transverse acceleration by waves and parallel acceleration by field-aligned electric fields are important processes in the transport of ionospheric ions along auroral field lines. In order to study the transport of ionospheric plasma in this environment we have developed a generalized semikinetic model which combines the tracking of ionospheric ion gyrocenters with a generalized fluid treatment of ionospheric electrons. Large-scale upward and downward directed electric fields are generated within the model by introducing magnetospheric plasma whose components have differing temperature anisotropies. We study the effects of such potentials when combined with the effect of ion heating by a distribution of waves along the flux tube. We find that the combination of wave heating and an upward electric field results in an order of magnitude increase in O{sup +} outflow (compared to a case with an upward electric field and no wave heating). Under these conditions we observe the formation of bimodal conics. When a downward electric field to a case with wave heating, the energy gained by the ions from the waves increases by a factor of 2 or 3 (over the scenario with wave heating and no hot plasma-driven electric field) owing to their slower transit of the heating region. Typically, the velocity distributions under these conditions are toroids and counterstreaming conics. We also find that the upflowing, dense, heated ionospheric plasma acts to reduce the potential set up by the anisotropies in the magnetospheric components. 33 refs., 16 figs., 1 tab.

Brown, D.G.; Horwitz, J.L.; Wilson, G.R. [Univ. of Alabama, Huntsville, AL (United States)

1995-09-01

77

Effect of thermal fluxes of charged particles on the spatial structure of the polar ionosphere  

Microsoft Academic Search

A hydrodynamic model of the convective high-latitude ionosphere is used to study the effect of thermal fluxes of charged particles coming into the ionosphere on spatial distributions of electron and ion temperature as well as on concentrations of charged particles in the F-layer. It is shown that these thermal fluxes can have a considerable effect on the distribution of electron

G. I. Mingaleva; V. S. Mingalev; V. N. Krivilev

1993-01-01

78

Effects of solar flares on the ionosphere of Mars.  

PubMed

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

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

2006-02-24

79

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

80

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

Microsoft Academic Search

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

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

2007-01-01

81

Ionospheric scintillation effects on UHF satellite communications  

Microsoft Academic Search

Naturally induced high altitude ionization will cause signal scintillation effects that are of great importance to the design and deployment of military satellite systems employing frequencies below 1 GHz. The scintillation will result in Rician or Rayleigh signal fading with finite signal decorrelation time and limited coherent bandwidth of the transmission channel

P. A. Kullstam; M. J. Keskinen

2000-01-01

82

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

NASA Astrophysics Data System (ADS)

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

Toledo-Redondo, Sergio; Salinas, Alfonso; Fornieles, Jess; Port, Jorge

2013-04-01

83

Monitoring and forecasting of ionospheric space weathereffects of geomagnetic storms  

Microsoft Academic Search

The response of the ionosphere to solar events is an integral part of space weather. The strongest response occurs during the complex coupling processes during a geomagnetic storm. Its various features act at different heights in the ionosphere and atmosphere and, therefore, both the morphology and the mechanisms and origin of geomagnetic storm effects change from one height region to

J. Lastovicka

2002-01-01

84

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 ionosphereplasmasphere 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

85

The ionospheric effect of atmospheric gravity waves excited prior to strong earthquake  

Microsoft Academic Search

We have computed perturbations in the nighttime mid-latitude F2 region ionosphere that could be produced by internal atmospheric gravity waves generated before strong earthquakes through ionospheric Joule heating due to the seismogenic electric field of short duration. There is a strong anisotropy of the atmospheric gravity wave effect with respect to the imminent earthquake epicentre, the electron density changes being

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

2006-01-01

86

Magnetosphere-Ionosphere Coupling: Effects of E-Region Plasma Turbulence on Ionospheric Conductances  

Microsoft Academic Search

During periods of intense geomagnetic activity, strong electric fields and currents penetrate from the magnetosphere into the high-latitude E region ionosphere where they dissipate a significant fraction of their energy. In this region, electrons are magnetized while ions are demagnetized due to frequent collisions with the neutral atmosphere causing the strong electric fields to generate intense electrojets that excite plasma

Y. S. Dimant; M. M. Oppenheim

2010-01-01

87

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

88

Quantitative description of ionospheric storm effects and irregularities. Proceedings. C4.2 Symposium of COSPAR Scientific Commission C held during the Thirty-first COSPAR Scientific Assembly, Birmingham (UK), 14 - 21 Jul 1996  

Microsoft Academic Search

The following topics were dealt with: ionospheric storm effects and irregularities, quantitative description, geomagnetic activity, substorm disturbances, auroral zone, ion composition, upper transition height, electron densities, ionospheric trough position, interplanetary magnetic field effect, solar cycle variations, stable auroral red arcs, electron temperature, topside ionosphere, F1 region, F2 region, critical frequency, ionospheric models, observed ionospheric response, international reference ionosphere, sunrise conditions,

K. Rawer; D. Bilitza

1997-01-01

89

Dynasonde Measurements of Ionospheric Meteor Effects  

NASA Astrophysics Data System (ADS)

The ionization created when meteoric particles impinge on the upper atmosphere has been studied extensively, both with optical methods and by radar techniques. Traditionally, meteor radars have been configured as dedicated, fixed-frequency systems that operate in the HF/VHF bands and are employed to measure winds and other parameters in the mesosphere-lower thermosphere region. It has long been recognized that ionosondes are capable of detecting meteor ionization although the sparse sounding format of most synoptic instruments does not facilitate a rigorous analysis of meteor ionization effects. Furthermore, most ionosonde-based studies have focused on meteor shower intervals when the meteor ionization is especially prominent (e.g. Chandra et. al., 2001). However, the capabilities of digital ionosondes such as the NOAA dynasonde allow the detailed study of various parameters of the meteor-induced ionization such as amplitude, polarization and spatial location, in addition to the time-of-flight, as a function of time and frequency. In this report, we will examine meteor ionization recorded by dynasondes located at Bear Lake (Utah) and Halley (Antarctica) demonstrating that these ionogram data can be used to distinguish between underdense and overdense meteor ionization. Other characteristics of the meteor-induced ionization, such as spatial location and Doppler velocity will also be presented. The dynasonde operated at the USU Bear Lake Observatory (42 N, 111 W) detects a large flux of meteor echoes and will be the primary source of data for this study. Chandra, H., et. al., Sporadic-E associated with the Leonid meteor shower event of November 1998 over low and equatorial latitudes, Annales. Geophys., 19, 59-69, 2001.

Berkey, F. T.; Sikdar, P.; Fish, C. S.; Jones, O.; Tsai, L.; Yen, C.

2002-12-01

90

Observations of the ionospheric response to the 15 December 2006 geomagnetic storm: Long-duration positive storm effect  

Microsoft Academic Search

The long-duration positive ionospheric storm effect that occurred on 15 December 2006 is investigated using a combination of ground-based Global Positioning System (GPS) total electron content (TEC), TOPEX and Jason-1 TEC, and topside ionosphere\\/plasmasphere TEC, GPS radio occultation, and tiny ionospheric photometer (TIP) observations from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites. This multi-instrument approach provides

N. M. Pedatella; J. Lei; K. M. Larson; J. M. Forbes

2009-01-01

91

Accurate determination of ionospheric effects on satellite-based positioning systems in terms of residual range error  

Microsoft Academic Search

The paper considers determination of ionospheric effects on Navsat and Navstar systems which provide three-dimensional position fixes for navigational and geodetic purposes. The satellite signals propagated through the ionosphere are subjected to phase delay, refraction, and dispersion causing uncertainty in the position determination. These uncertainties were evaluated by approximations of the complex refractive index of the ionosphere: the dual frequency

G. O. Ajayi; A. Hedberg; G. Hamberg

1980-01-01

92

Effects on the Ionosphere Due to Phenomena Occurring Below it  

NASA Astrophysics Data System (ADS)

The terrestrial thermosphere and ionosphere form the most variable part of the Earth's atmosphere. Because our society depends on technological systems that can be affected by thermospheric and ionospheric phenomena, understanding, monitoring and ultimately forecasting the changes of the thermosphere-ionosphere system are of crucial importance to communications, navigation and the exploration of near-Earth space. The reason for the extreme variability of the thermosphere-ionosphere system is its rapid response to external forcing from various sources, i.e., the solar ionizing flux, energetic charged particles and electric fields imposed via the interaction between the solar wind, magnetosphere and ionosphere, as well as coupling from below (``meteorological influences'') by the upward propagating, broad spectrum, internal atmospheric waves (planetary waves, tides, gravity waves) generated in the stratosphere and troposphere. Thunderstorms, typhoons, hurricanes, tornadoes and even seismological events may also have observable consequences in the ionosphere. The release of trace gases due to human activity have the potential to cause changes in the lower and the upper atmosphere. A brief overview is presented concerning the discoveries and experimental results that have confirmed that the ionosphere is subject to meteorological control (especially for geomagnetic quiet conditions and for middle latitudes). D-region aeronomy, the winter anomaly of radiowave absorption, wave-like travelling ionospheric disturbances, the non-zonality and regional peculiarities of lower thermospheric winds, sporadic-E occurrence and structure, spread-F events, the variability of ionospheric electron density profiles and Total Electron Content, the variability of foF2, etc., should all be considered in connection with tropospheric and stratospheric processes. ``Ionospheric weather'', as a part of space weather, (i.e., hour-to-hour and day-to-day variability of the ionospheric parameters) awaits explanation and prediction within the framework of the climatological, seasonal, and solar-cycle variations.

Kazimirovsky, E.; Herraiz, M.; De La Morena, B. A.

2003-03-01

93

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

NASA Astrophysics Data System (ADS)

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

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

2009-04-01

94

Effect of magnetic storm on the state of pre-seismic ionosphere  

NASA Astrophysics Data System (ADS)

The analysis of the ionospheric total electron content (TEC) variations obtained by using the GPS measurements before Hokkaido earthquake (EQ) of September 25, 2003 (M=8.3)is presented. It are used both the observation of Japanese GPS stations and global TEC maps created at the IONEX format to estimate the spatial scale of ionospheric irregularities associated with this EQ and possible geomagnetic storm influence on the pre-seismic plasma anomaly. The pre-seismic behavior of TEC was detected within several days before the main event. Anomaly appeared at the same local time during 5 days prior to the main shock as the local TEC enhancement (plasma cloud) located in the vicinity of the forthcoming EQ epicenter. These structures are generated in ionosphere. During the process of the earthquake approach the amplitude of plasma modification was increased, and it has reached the 85-901500 km in latitudes and 4000 km in longitudes. It is shown that according to its main parameters (locality, affinity with the epicenter, dome-shaped zone of manifestation and time of existence) the detected ionospheric plasma anomaly may be associated to the future seismic activity. The geomagnetic storm took place only one day prior to the main shock. Usually it is appeared at ionosphere as global disturbance (or ionosphere storm). In our case the formation of local positive ionosphere modification become manifest during the period of 5 days preceding the earthquake, i.e. we observe the storm influence effect (on the TEC variations) only for the day of earthquake and one day before to it. It is shown that the general pattern of spatialtemporal TEC variations can be presented as superposition of ionospheric storm effects and the ionosphere anomaly of seismogenic origin. As result, the intensification of the pre-seismic plasma anomaly due to magnetic storm action became visible at ionosphere 18 hours before Hokkaido earthquake.

Ruzhin, Yuri; Shpakovsky, Vitaly; Shagimuratov, Irk; Zakharenkova, Irina

95

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

96

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

SciTech Connect

The sequence nature of the diffuse ionospheric resonances D[sub n] stimulated by topside sounders was discovered by Oya (1970) with n ranging from 1 to 4. Osherovich (1987) organized these observations using his earlier theory which predicted a nonequidistant spectrum with frequencies proportional to n[sup [1/2

Benson, R.F. (NASA Goddard Space Flight Center, Greenbelt, MD (United States)); Osherovich, V.A. (Hughest STX Corp., Lanham, MD (United States))

1992-12-01

97

Ionospheric effects from different seismogenic electric field sources  

Microsoft Academic Search

The results of numerical simulations of the impact of different seismogenic electric field sources on TEC (Total Electron Content) of the ionosphere are presented. The external electric currents flowing between the faults and the ionosphere were used as lower boundary condition for the electric potential equation of the UAM (Upper Atmosphere Model). Different configurations and magnitudes of these currents were

Alexander A. Namgaladze; Oleg V. Zolotov

2011-01-01

98

The effects of SDO-EVE measurements on ionospheric modeling  

NASA Astrophysics Data System (ADS)

Errors associated with ionosphere-thermosphere modeling can be attributed to a number of factors. Very often, they are caused by incomplete information regarding the forcings acting on the system. Empirical statistical models and proxies are used to compensate by making use of correlations between available measurements and quantities of interest. One such measurement, F10.7 index often serves as a proxy for Extreme Ultra Violet photon fluxes. While this approach has worked remarkably well, data from the Solar Dynamics Observatory mission allows us to improve the forcings and the model results. In this study, we investigate several alternatives to the F10 approach. We make use of SDO data and the Solar Radiation Physical Model, as well as TIMED-SEE. The effect on model results is presented and discussed, with the SDO / SRPM combination resulting in the greatest increase in model performance.

Negrea, Catalin; Fuller-Rowell, Timothy; Codrescu, Mihail; Eparvier, Frank; Fontenla, Juan

2013-04-01

99

Lightning Interaction with the Lower Ionosphere: Effects of Mesospheric Ions and Geomagnetic Field  

NASA Astrophysics Data System (ADS)

The interaction between the lightning electromagnetic pulse (EMP) and quasi-electrostatic (QE) fields and the D-region ionosphere has been observed optically in the past 20 years through sprites, elves, and gigantic jets. Very-low-frequency (VLF) measurements have been used to measure direct ionospheric modification, which may comprise electron density changes and/or heating. In the same time period, a number of models have been used to study the lightning-ionosphere interaction. Here, we present new time-domain 2D and 3D models of the lightning-ionosphere interaction, including EMP and QE effects. These spherical-coordinate models include effects of Earth's magnetic field; effects of mesospheric and ionospheric electron and ion densities; and responses to arbitrary lightning amplitudes, waveforms, and orientations. In this paper, we use the new models to investigate the response of the ionosphere under varying conditions. First, we focus on the effects of different mesospheric ion density profiles. Mesospheric ions, for which measurements are nearly nonexistent, serve to reduce the amplitude of the electromagnetic pulse as it propagates towards the ionosphere; high ion densities will reduce the wave electric field enough that it does not exceed the breakdown field in the ionosphere. We demonstrate the relationship between the lightning parameters, ion density profile, and observed elve intensity, and show that elves are suppressed when the ion density is high. Second, we investigate the effects of the geomagnetic field magnitude and orientation on wave propagation in and through the ionosphere. We compare these simulation results with known global lightning distributions and compare to the observed whistler distributions onboard satellites.

Marshall, R. A.; Inan, U. S.

2011-12-01

100

The Search for Ionospheric Effects at 150 MHz with PAPER  

NASA Astrophysics Data System (ADS)

PAPER (the Precision Array to Probe the Epoch of Reionization) is a telescope designed to detect the redshifted hydrogen signal from the early universe. The hydrogen is at a redshift of approximately 6-14, bringing the spin-flip transition of neutral hydrogen from 1.4 GHz to a regime between 100 and 230 GHz. PAPER has a test site with 32 antennas in the Radio Quiet Zone of Green Bank, West Virginia, and a 64-antenna array at the Square Kilometer Array candidate site in the Karoo, South Africa. Astronomical observations at such low frequencies are made more challenging by the refractive properties of the ionosphere. We present the angular shifts in bright source positions (Cyg A, Cas A, Vir A, and Tau A) as probes of the variations in the total electron content (TEC) along the lines of sight between the sources and the 32-element array in Green Bank. With an integration time of 10 seconds, we can probe for the small fluctuations, using the visibilities, that may be the most difficult to calibrate in upcoming experiments and observations. More sensitive probes of longer timescales are also done by imaging the sky with both the 32 and 64-element arrays. Here again, the bright source position stability is used as an indicator of the TEC stability. The wideband nature of the PAPER instrument enables it to probe the effects of a varying TEC over a nearly 100 MHz bandwidth. We compare these measurements to more traditional methods of probing the ionosphere, such as GPS satellites, and we discuss the implications that these measurements will have on experiments aimed at detecting the epoch of reionization.

Gugliucci, Nicole E.; Bradley, R.; PAPER Collaboration

2012-01-01

101

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

NASA Astrophysics Data System (ADS)

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

Yamazaki, Yosuke; Richmond, Arthur D.

2013-09-01

102

Monitoring the ionospheric storm effect with multiple instruments in North China: July 15-16, 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 h 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; Lou, Wenyu; Li, Peng; Shen, Xuhui; Li, Qiang

2013-09-01

103

Ionospheric effects preceded the October 2003 Halloween storm  

Microsoft Academic Search

The goal of this study is to reveal some ionospheric forerunners which occur prior to the expansion phase of any storm or substorm. Another task is to compare variations of two main ionospheric parameters, f0F2 and hmaxF2, on two chains of ionosondes located in Europe and North America during the interval October 16-28, 2003. This interval precedes the Halloween storm

D. V. Blagoveshchensky; J. W. MacDougall; A. V. Pyatkova

2005-01-01

104

Ionospheric Scintillation Effects on Single and Dual Frequency GPS Positioning  

Microsoft Academic Search

The low latitude ionosphere poses a challenge to both GPS users and Satellite-Based Augmentation System (SBAS) providers. Single and dual frequency GPS receivers used in low-latitude regions can suffer from rapid amplitude and phase fluctuations known as scintillation. Scintillation occurs when the GPS or SBAS satellite signal travels through small-scale irregularities in electron density in the ionosphere, typically in the

S. Datta-Barua; P. H. Doherty; T. Dehel; J. A. Klobuchar

105

Ionospheric effects preceding the October 2003 Halloween storm  

Microsoft Academic Search

The goal of this study is to reveal some ionospheric forerunners which occur prior to the expansion phase of any storm or substorm. Another task is to compare variations of two main ionospheric parameters, f0F2 and hmaxF2, on two chains of ionosondes located in Europe and North America during the interval 2628 October 2003. This interval precedes the Halloween storm

D. V. Blagoveshchensky; J. W. MacDougall; A. V. Piatkova

2006-01-01

106

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

107

Ionospheric effects of the solar flares as deduced from global GPS network data  

Microsoft Academic Search

Results derived from analysing the ionosphere response to faint and bright\\u000asolar flares are presented. The analysis used technology of a global detection\\u000aof ionospheric effects from solar flares as developed by the authors, on the\\u000abasis of phase measurements of the total electron content (TEC) in the\\u000aionosphere using an international GPS network. The essence of the method is

L. A. Leonovich; A. T. Altynsev; V. V. Grechnev; E. L. Afraimovich

2001-01-01

108

Magnetic and ionospheric effects of the strong magnetospheric storm of March 13th, 1989 over Italy  

Microsoft Academic Search

SummaryIn March 1989 a series of intense solar events caused relevant effects on the Earth's magnetosphere and ionosphere. Interesting\\u000a phenomena like exceptional brilliant Auroras, total blackouts of the HF radio links and one of the strongest magnetospheric\\u000a and ionospheric storms ever recorded in this century, were observed during this month. In this paper the study of the main\\u000a magnetic and

C. Bianchi; A. De Santis; A. Meloni; B. Zolesi

1992-01-01

109

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

110

Effectiveness of predicting radiowave propagation in the ionosphere based on the IRI-2001 ionospheric model  

NASA Astrophysics Data System (ADS)

The standard deviation of predicting radiowave propagation using the IRI-2001 model is estimated based on the data of oblique-incidence sounding on the England-IZMIRAN (2500 km) and Cyprus-IZMIRAN (2300 km) practically perpendicular paths and vertical radiosounding of the ionosphere at the common point (IZMIRAN) during the period March 2002 2007. The observational period covers a wide range of solar activity values: the sunspot number R varied from 112 at a maximum (2002) to 4.8 at a minimum (2007). The results of an analysis of the complex experimental data, which agree with their description by the IRI-2001 model, completed with the calculations of the electron collision frequency, are presented.

Krasheninnikov, I. V.; Egorov, I. B.; Pavlova, N. M.

2008-08-01

111

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

112

Lightning effect on the lower ionosphere deduced from MF recordings  

NASA Astrophysics Data System (ADS)

Previous studies of direct lightning effect on the ionosphere have been done using VLF signals. These studies shown that the quasi-electrostatic field theory explain most of the observed `early/fast' VLF perturbations. However, some recent results showed that the EMP, produced by the lightning, could also perturb the VLF propagation. This property is even used to monitor the lower ionosphere. During the summer 2004, in the frame of the 2004 Eurosprite campaign, the CEA installed in the centre of France a station to measure the vertical electric field with dipole whip antenna. The measurement is not continuous but triggered when the electric field exceeds a threshold of 3 V/m. The data are dated with GPS. The electric field is digitalised in two bands from few kHz to 1 MHz and from 500 kHz to 10 MHz. Lightning appear on spectrograms of the MF-HF component as a vertical line; furthermore during the night, the numerous radio carriers are horizontal lines. We observe on the spectrograms the fading, and even sometimes the disappearance, of some of the MF radio carriers during several milliseconds a millisecond after lightning. About 4000 cloud to ground lightning, during two months, triggered our system. All these lightning have been associated to lightning localised by Meteorage (the French lightning detection network). All the signals have been digitally filtered around several selected carrier signals from 900 to 1600 kHz. For each of lightning detected and each selected carrier frequency, the characteristics of the fading waveform have been measured: attenuation, duration of this attenuation, onset time, time where the signal is at the most attenuated and recovery time. Using these data, we make statistics and plot the impact map of the fading. Lightning of peak current higher than 60 kA may perturb a zone of a radius larger than 300 km. The shape of the attenuation in function of the distance (from the lightning to the crossing point of the radio carrier path and the ionosphere at 80-90 km) is similar to the shape of the ionisation produced by a lightning by the EMP, in other words with a maximum at 80-90 km of the lightning. The fading of a radio carrier is mainly a function of the electron density and the collision frequency. The collision frequency is directly related to the electron temperature. Previous studies showed that the electron density recovery time to the level before the lightning is 10-100 s while the electron temperature recovery time is 0.1-1 s. The mean duration of the attenuation being ~5 ms, the observed fading is thus mainly controlled by the collision frequency change.

Farges, T.; Blanc, E.; Tanguy, M.

2006-12-01

113

Ionosphere dynamics  

Microsoft Academic Search

Early studies of the ionosphere assumed that isoionic surfaces were substantially horizontal and smooth, and diurnal, seasonal and sunspot variations were worked out on that basis. In recent years, the attention of research workers has turned more and more to the study of irregularities and movements in ionization. Irregularities examined range in size from the order of hundreds of kilometers

G. H. Munro; L. H. Heisler

1963-01-01

114

Theory of thermospheric waves and their ionospheric effects  

NASA Astrophysics Data System (ADS)

The analytical aspects of the internal thermospheric waves (IW) theory development are reviewed. The statement of the problem is discussed: the choice of the boundary and initial conditions. Special attention is paid to the upper boundary, the existence of which is the direct consequence of the molecular free way growth with height. The model equations for long waves are derived which take into account dissipation, spherity and rotation of the earth. The wave disturbance evolution is represented by the mode dynamical variables with the characteristics for thermospheric waveguide vertical structure. Nonlinearity of general hydrothermodynamic system leads to mode interaction. Therefore the mode coefficient functions satisfy the system of equations that generalizes the system of coupled KdV. As part of the manifestations of nonlinearity, the mean field generation problem by the quasiperiodic IW is discussed. The analytical F2-ionosphere effect model is represented. The model is based on the ambipolar diffusion equation. The calculated results of F2 maximum height variations during magnetospheric substorms are compared with the empiric model data.

Leble, S. B.

1988-06-01

115

Theory of thermospheric waves and their ionospheric effects  

NASA Astrophysics Data System (ADS)

The analytical aspects of the internal thermospheric waves (IW) theory development are reviewed. The statement of the problem is discussed: the choice of the boundary and initial conditions. Special attention is paid to the upper boundary, the existence of which is the direct consequence of the molecular free way growth with height. The model equations for long waves are derived which take into account dissipation, spherity and rotation of the earth. The wave disturbance evolution is represented by the mode dynamical variables with the characteristics for thermospheric waveguide vertical structure. Nonlinearity of general hydrothermodynamic system leads to mode interaction. Therefore the mode coefficient functions satisfy the system of equations that generalizes the system of coupled KdV. As part of the manifestations of nonlinearity, the mean field generation problem by the quasiperiodic IW is discussed. The analytical F2-ionosphere effect model is represented. The model is based on the ambipolar diffusion equation. The calculated results of F2 maximum height variations during magnetospheric substorms are compared with the empiric model data.

Leble, S. B.

116

Effects of Soft Electron Precipitation on the Coupled Magnetosphere-Ionosphere-Thermosphere  

NASA Astrophysics Data System (ADS)

Global simulations play an important role in understanding the coupled magnetosphere-ionosphere-thermosphere (MIT) system. The MIT interaction involves both electrodynamic and plasma transport processes, and it is influenced by precipitating particles that deposit both thermal and kinetic energy from the magnetosphere in the ionosphere-thermosphere. Currently, global simulation codes do not include soft electron precipitation, which can significantly influence the thermospheric and ionospheric structure. In this study, two types of causally specified soft electron precipitation, direct-entry cusp and broadband electron precipitation, are implemented in the Coupled Magnetosphere-Ionosphere-Thermosphere (CMIT) model. The direct entry cusp electron precipitation is modeled by specifying the electron thermal flux and temperature in a dynamically determined cusp area. The broadband electron precipitation is regulated by the downward Alfvenic Poynting flux based on empirical relations from Polar and FAST satellite data. Simulation results show that while both types of soft electron precipitation have only minor effects on the ionospheric conductance, they can significantly modify the plasma distribution in the F-region ionosphere and the neutral density in the thermosphere.

Zhang, B.; Lotko, W.; Brambles, O.; Wiltberger, M. J.; Wang, W.; Schmitt, P. J.; Lyon, J.

2011-12-01

117

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

118

The worldwide ionospheric data base  

SciTech Connect

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, D.

1989-04-01

119

Solar Cosmic Rays of July 1961 and Their Ionospheric Effects  

Microsoft Academic Search

The temporal and spatial variations of the energy spectrum of the solar protons of energies 0.5 < E < 60 Mev as observed by the particle detectors in the State University of Iowa satellite Injun i during July 1961 have been studied. The variations in the electron density in the lower ionosphere to be expected from the observed proton flux

B. Maehlum; B. J. O'Brien

1962-01-01

120

Source mechanisms and radio effects of ionospheric plasma  

Microsoft Academic Search

Since October 1, 1991 experimental and theoretical research has been conducted by Prof. Min-Chang Lee and his students at BU and MIT. This research work is aimed at investigating the ionospheric plasma disturbances which can affect significantly the radio wave propagation in communications and space surveillance. The research topics which have been investigated include: (1) A source mechanism leading to

Min-Chang Lee

1992-01-01

121

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

122

A statistical study on the effect of earthquakes on the ionosphere, based on the subionospheric LF propagation data in Japan  

NASA Astrophysics Data System (ADS)

A superimposed epoch analysis has been undertaken, in order to find the correlation of the ionospheric perturbations with seismic activity. We take the wave path from the Japanese LF transmitter (frequency=40 kHz) and an observing station of Kochi (wave path length of 770 km), and a much longer period (of five years) than before, is considered. This subionospheric LF propagation can be called "an integrated measurement" in the sense that any earthquakes in the LF sensitive area just around the great-circle path can influence the observed LF signals, so that we define the "effective magnitude" (Meff) by integrating the total energy from different earthquakes in the sensitive area on a current day and by converting it back into magnitude. A superimposed epoch analysis for the effective magnitude greater than 6.0 has yielded that the ionosphere is definitely disturbed in terms of both amplitude and dispersion, and that these perturbations tend to take place prior to an earthquake. The statistical z-test has also been performed, which has indicated that the amplitude is definitely depleted 2-6 days before the earthquake day and also that the dispersion is very much enhanced during the same period. This statistical study has given strong support to the existence of seismo-ionospheric perturbations for high seismic activity.

Maekawa, S.; Horie, T.; Yamauchi, T.; Sawaya, T.; Ishikawa, M.; Hayakawa, M.; Sasaki, H.

2006-09-01

123

Lunar tidal effects in the electrodynamics of the low latitude ionosphere  

NASA Astrophysics Data System (ADS)

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

Fejer, Bela G.; Tracy, Brian D.

2013-10-01

124

Numerical simulation of the effects of a solar energetic particle event on the ionosphere of Mars  

NASA Astrophysics Data System (ADS)

We investigate the ionospheric effects of a solar energetic particle (SEP) event at Mars, specifically the 29 September 1989 event. We use its energy spectrum and a steady state ionospheric model to simulate vertical profiles of ion and electron densities. The ionospheric response to this large event would have been readily observable. It caused electron densities to exceed 104 cm-3 at 30-170 km, much larger than typically observed below 100 km. It also increased the ionosphere's total electron content by half of its subsolar value and would have caused strong attenuation of radio waves. The simulated attenuation is 462 dB at 5 MHz, which demonstrates that SEP events can cause sufficient attenuation (>13 dB) to explain the lack of surface reflections in some MARSIS topside radar sounder observations. We also develop a complementary generalized approach to the study of the ionospheric effects of SEP events. This approach predicts the threshold intensities at which a SEP event is likely to produce detectable changes in electron density profiles and radio wave attenuation measurements. An event one hundred times less intense than the 29 September 1989 event produces electron densities in excess of 3000 cm-3 at 80 km, which should be measurable by radio occultation observations, and causes sufficient attenuation to eliminate MARSIS surface reflections. However, although enhancements in total electron content have been observed during SEP events, predicted enhancements in low altitude electron density were not confirmed by observations.

Sheel, Varun; Haider, S. A.; Withers, Paul; Kozarev, K.; Jun, I.; Kang, S.; Gronoff, G.; Simon Wedlund, C.

2012-05-01

125

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 6.4105 K and their concentration Nsw ? 1.9107 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

126

Atmospheric effects assessment program: Ionospheric sounding. Final report for period ending October 1993  

SciTech Connect

This document reports efforts on two main goals: (1) to study the short-term ionospheric variability, and (2) to study the effects of this variability on high-frequency (HF) skywave field strength. To achieve the first goal, ionospheric soundings are being done at 5-minute intervals at San Diego, CA, and at Logan, UT. This time interval was chosen to adequately resolve variations produced by locally generated gravity waves. To study the effects of short-term ionospheric variability on high frequency communications, a circuit is being established to measure the variability of the received HF signal strength. The chosen circuit will have the transmitter located in Forsyth, MT, and the receiver in Imperial Beach, CA (approximately 20 miles south of NRaD).

Sprague, R.A.

1994-02-01

127

Simulating the effects of ionospheric current systems on ground infrastructure  

NASA Astrophysics Data System (ADS)

Geomagnetic disturbances produced by magnetospheric-ionospheric currents induce currents in ground technological networks that can cause operational problems for infrastructure such as power systems and pipelines. To assess the geomagnetic hazard to infrastructure a simulation package has been developed to calculate the geomagnetically induced currents (GIC) in these networks. The Simulator can start with either a specified ionospheric current such as the auroral electrojet or geomagnetic data from ground networks. Together with an Earth conductivity model these inputs are used to calculate the electric fields experienced by the ground network. The electric fields are then used as input to a network model to calculate the GIC. This talk describes the methodology of electric field calculations and network modelling. These simulations can be used to determine the GIC experienced during recorded large events or expected during high-risk scenarios and thereby contribute to assessing the risk from space weather disturbances.

Boteler, D.; Trichtchenko, L.; Pirjola, R.

2011-12-01

128

Magnetotelluric source effect due to 3D ionospheric current systems using the complex image method for 1D conductivity structures  

Microsoft Academic Search

The complex image method (CIM) is an efficient tool to calculate the electromagnetic field at the earth's surface produced by 3D ionospheric current systems when the earth has a layered conductivity structure. The calculations are applicable to the estimation of source effects on magnetotelluric data. In this paper CIM is used in connection with some typical high-latitude ionospheric events: a

Ari Viljanen; Risto Pirjola; Olaf Amm

1999-01-01

129

The evolution of scattering equatorial F-region irregularities and resultant effects on trans-ionospheric radio waves  

Microsoft Academic Search

Results from a series of ground and airborne experiments are presented which describe spatial and temporal characteristics of equatorial F-region irregularities and the effect of these irregularities on transionospheric radio propagation. The experiments included UHF amplitude scintillation measurements from the WIDEBAND, MARISAT, and LES-9 satellites, and simultaneous ionospheric measurements from the AFGL Airborne Ionospheric Observatory and the Jicamarca Radar Observatory

H. E. Whitney; J. Aarons; J. Buchau; E. J. Weber; J. P. McClure

1978-01-01

130

Penetration of an electrostatic field from the lithosphere into the ionosphere and its effect on the D-region before earthquakes  

Microsoft Academic Search

The penetration of an electrostatic field, from a source located in the lithosphere into the ionosphere is investigated. The electrostatic problem is solved numerically for a medium with an inhomogeneous anisotropic conductivity coupled to an effective upper boundary condition. The results show that the electric field in the ionosphere D-layer can effectively change the parameters of the lower ionosphere. The

V. V. Grimalsky; M. Hayakawa; V. N. Ivchenko; Yu. G. Rapoport; V. I. Zadorozhnii

2003-01-01

131

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

132

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

133

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

Microsoft Academic Search

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

Jeffrey M. Forbes; Mihail Codrescu; Timothy J. Hall

1988-01-01

134

Calculation of ionospheric effects due to acoustic radiation from an underground nuclear explosion  

Microsoft Academic Search

Within the framework of the ionospheric detection of underground nuclear tests, we have developed an analytic computing technique for the acoustic effect of a confined nuclear explosion on upper layers of the Earth's atmosphere. The relationship (32) is obtained, which relates the nuclear test parameters (depth, explosion yield, and mechanical properties of the rock) to the vertical displacement of the

G. V. Rudenko; A. M. Uralov

1995-01-01

135

Ionospheric refraction effects in slant range profiles of auroral HF coherent echoes  

Microsoft Academic Search

The theory of auroral coherent echoes developed for VHF scattering by Uspensky et al. (1988, 1989) is applied to the interpretation of intensity and Doppler velocity slant range profiles of HF radar aurora. The theoretical model includes the effects of irregularity aspect sensitivity, ionospheric refraction of the radar beam, and the reception of signals from different heights. The predicted profiles

M. V. Uspensky; A. V. Kustov; G. J. Sofko; J. A. Koehler; J. P. Villain; C. Hanuise; J. M. Ruohoniemi; P. J. S. Williams

1994-01-01

136

Combined ionospheric effect due to Forbush decreases and magnetospheric high energy particles at mid-latitudes  

Microsoft Academic Search

After geoactive solar flares the Forbush decrease of galactic cosmic rays and magnetospheric high energy particles can cause opposite ionization effects in the ionospheric D-region at mid-latitudes. This has been shown by the change of the ELF and VLF atmospheric radio noise level and that of the LF absorption. The frequency dependence of these variations has been interpreted by waveguide

G. Satori

1991-01-01

137

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

138

Ionospheric storm effects in the nighttime E region caused by neutralized ring current particles  

Microsoft Academic Search

During magnetic storms an anomalous increase in the ionization density of the nighttime E region is observed at low and middle latitudes. It has been suggested that this effect is caused by the precipitation of neutralized ring current particles. Here a coupled ring current decay-ionosphere model is used to confirm the validity of this explanation.

R. Bauske; S. Nol; G. W. Prlss

1997-01-01

139

IONOSPHERIC EQUATORIAL ANOMALY STUDIES DURING SOLAR STORMS  

Microsoft Academic Search

The ionosphere is the major error source in GNSS receivers. Models for single frequency time delay correction do not work at low geomagnetic latitude regions (20), where the ionosphere has a peculiar behavior, known as the Ionospheric Equatorial Anomaly. In order to study the global behavior of the Ionospheric Equatorial Anomaly, dynamic maps based on IONEX data have been generated.

Alexandre B. V. Oliveira; F. Walter

140

How VLBI Can Contribute To Ionospheric Research  

Microsoft Academic Search

Like other space geodetic techniques VLBI observations are carried out at two distinct frequencies in order to determine ionospheric delay corrections. Each ionospheric delay corresponds to the total electron content (TEC) along the ray path through the ionosphere. Because VLBI is a differential technique the observed ionospheric delays represent the differences of the behaviour of the propagation media above each

T. Hobiger; T. Kondo; H. Schuh

2004-01-01

141

Ionospheric and magnetospheric effects of solar flares monitored by ground-based riometer and magnetometers  

NASA Astrophysics Data System (ADS)

The solar flare incidence follows a behavior similar to the solar cycle activity, which results in periodic disturbances on the Earth's ionosphere and magnetosphere. The correlation of this phenomenon can provide important information about the magnetosphere, the Sun/Earth interaction, as well as events occurring in the ionosphere which can, for instance, generate disturbances in telecommunications, small satellites or even in the space weather. Riometer and magnetometers data analysis can provide useful way for measuring and understanding the effects of solar flare radiation in the ionosphere and magnetosphere. The Solar Flare effect (SFE) is associated with the sudden change of ionospheric currents caused by the extra ionization produced by soft X-ray (0.1 to 9.0 nm) and EUV (9.0 to 100.0 nm) radiation from the solar flare. The objective of this work is to present the correlation of the ionospheric and magnetospheric (H, D, Z) sudden disturbances due to high-intensity solar flares (M and X class), that can emit up to 1032 ergs of energy. For this purpose, analysis were performed for the riometer and magnetometers dedicated to study the Solar-Earth interactions at the Southern Space Observatory (SSO/CRS/INPE -MCT), (29.4 S, 53.8 W, 480m a.s.l), So Martinho da a Serra, RS, Brazil. To identify and investigate the sudden radiation increase caused by the solar flare, the X-ray data (0.1 to 0.8 nm) from GOES Satellites and the EUV data (26.0 to 34.0 nm and 0.1 to 50.0 nm) from the Solar EUV Monitor (SEM) on the SOHO spacecraft are correlated. With the analysis of these ground-based instruments and spacecrafts data, the correlation of the solar activity and the magnetospheric and ionospheric disturbances were performed, as for the Sudden Ionospheric Disturbance (SID) and Magnetic Crochet about 60% D-component variation during a large solar flare was observed.

Ronan Coelho Stekel, Tardelli; Schuch, Nelson Jorge; Echer, Ezequiel; Guarnieri, Fernando; Makita, Kazuo; Espindola Antunes, Cassio; Moro, Juliano; Machado Paulo, Claudio

142

Cyclotron resonance effects on stochastic acceleration of light ionospheric ions  

NASA Astrophysics Data System (ADS)

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

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

1982-09-01

143

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

Microsoft Academic Search

The level of accuracy reached today by reference GNSS technology is in great part a consequence of progress in modelling various contributions to the observables. At the same time, advances in modelling of a single effect will not necessarily lead to improvements in the final result if there exist greater mismodelled contributions from other sources. One of the effects, the

K. Palamartchouk

2007-01-01

144

Electron collisional effects on lower hybrid drift instabilities in the ionosphere  

SciTech Connect

Electron collisional as well as ion collisional effects have a significant effect on the stability analysis of lower hybrid drift modes in the ionosphere. Electron collisions stabilized the modes and cause a density gradient threshold for the instability not previously calculated. This threshold results in restrictions on the interpretation of 155- and 415-MHz backscatter results as being due to lower hybrid drift instabilities and suggests measurements to determine whether the instability can account for the backscatter.

Sperling, J.L.; Goldman, S.R.

1980-07-01

145

Laboratory study of some lightning-induced effects in the ionospheric plasma  

Microsoft Academic Search

Laboratory experiments have been conducted at MIT, using the student-built Versatile Toroidal Facility (VTF), to investigate some ionospheric plasma effects produced by lightning-induced whistler waves. Lower hybrid waves, generated by the lightning-induced whistler waves, can cause a chain of extensive plasma effects, such as the acceleration of electrons and ions and the spectral broadening of plasma waves. Two mechanisms by

M. C. Lee; R. J. Riddolls; D. T. Moriarty

1998-01-01

146

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

SciTech Connect

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

Loveless, M.J.

1993-06-01

147

Ionospheric Scintillation Effects on GPS Receivers during Solar Minimum and Maximum  

Microsoft Academic Search

The ionosphere has practical importance in GPS (Global Positioning System) applications because it influences transionospheric radio wave propagation. Among various phenomena in the ionosphere, ionospheric scintillation is characterized by rapid fluctuation and fading of the received signal intensity due to electron density irregularity inside the ionosphere. Deep signal fading caused by scintillation can lead to loss of lock of the

Jiwon Seo; Todd Walter; Edward Marks; Tsung-Yu Chiou; Per Enge

2007-01-01

148

Magnetic storms and their effects in the lower ionosphere: Differences in storms of various types  

NASA Astrophysics Data System (ADS)

During magnetic storms (MS's) in the ionospheric D region, changes in the electron density and corresponding effects on radiowave propagation are observed. The differences in manifestations of MS's in the lower ionosphere are mainly caused by the time and spatial differences in precipitations of energetic electrons. It is shown that the observed differences in the effects of storms in the D region are related to the differences in the corresponding types of MS's determined by the observed fluxes of energetic electrons ( E 0.1-2 MeV) at L ? 3-8. The storm types are identified by changes in the geomagnetic ap and AE indices and the ap/Dst and AE/ Dst ratios during the recovery phase of a storm.

Sokolov, S. N.

2011-12-01

149

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

Microsoft Academic Search

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

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

1992-01-01

150

Ionospheric Effects of Comet Shoemaker-Levy 9 Impacts with Jupiter  

Microsoft Academic Search

We study the thermosphere and ionosphere effects of the July 1994 Comet P\\/Shoemaker-Levy 9 impacts with Jupiter using a one-dimensional transport model which includes detailed neutral-neutral and ion-neutral chemistry and diffusive vertical transport for a variety of sulfur, nitrogen, and oxygen molecular species observed at the time of the impacts. The model uses a background neutral atmosphere based on the

Ahilleas N. Maurellis; Thomas E. Cravens

2001-01-01

151

Ionospheric Effects of Comet ShoemakerLevy 9 Impacts with Jupiter  

Microsoft Academic Search

We study the thermosphere and ionosphere effects of the July 1994 Comet P\\/ShoemakerLevy 9 impacts with Jupiter using a one-dimensional transport model which includes detailed neutralneutral and ion-neutral chemistry and diffusive vertical transport for a variety of sulfur, nitrogen, and oxygen molecular species observed at the time of the impacts. The model uses a background neutral atmosphere based on the

Ahilleas N Maurellis; Thomas E Cravens

2001-01-01

152

The extreme Halloween 2003 solar flares (and Bastille Day, 2000 Flare), ICMEs, and resultant extreme ionospheric effects: A review  

Microsoft Academic Search

Extreme solar flares can cause extreme ionospheric effects. The Oct 28, 2003 flare caused a ?25 TECU (a total electron content unit is 1016electron\\/m2 column density), or a ?30%, increase in the local noon equatorial ionospheric column density. This enhancement occurred within ?5min. This TEC increase was ?5 times the TEC increases detected for the Oct 29, 2003, Nov 4,

B. T. Tsurutani; A. J. Mannucci; B. Iijima; F. L. Guarnieri; W. D. Gonzalez; D. L. Judge; P. Gangopadhyay; J. Pap

2006-01-01

153

Effects of the ionosphere and solar activity on radio occultation signals: Application to CHAllenging Minisatellite Payload satellite observations  

Microsoft Academic Search

We analyze the ionospheric effect on the phase and amplitude of radio occultation (RO) signal. The introduced theoretical model predicts a correlation between the phase acceleration and intensity variations of RO signal and opens a way to locate layered structures in the propagation medium, in particular, in trans-ionospheric satellite-to-satellite links. For considered CHAllenging Minisatellite Payload (CHAMP) RO events, the locations

A. G. Pavelyev; Y. A. Liou; J. Wickert; T. Schmidt; A. A. Pavelyev; S. F. Liu

2007-01-01

154

Electric fields and conductivity in the nighttime E-region - A new magnetosphere-ionosphere-atmosphere coupling effect  

Microsoft Academic Search

Calculations have been made of the effects of intense poleward-directed electric fields upon the nighttime ionospheric E-region. The results show the Pedersen and Hall conductivities are substantially changed, thereby decreasing the ionospheric electrical load seen by magnetospheric sources. It appears that relatively large electric fields can exist in the absence of accompanying large field-aligned currents, as long as the underlying

P. M. Banks; F. Yasuhara

1978-01-01

155

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

Microsoft Academic Search

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

Tomoko Matsuo

2008-01-01

156

Ionospheric Solar Flare Effects Monitored by the Ground-based GPS Receivers V Theory and Observation  

NASA Astrophysics Data System (ADS)

A theoretical model for monitoring ionospheric solar flare effects by using ground-based receivers of the global positioning system (GPS) has been developed and reviewed in this paper. The physical representations and meanings of two GPS quantities, variations in the total electron content (TEC) and their time rate of changes (rTEC), are examined and discussed. The theoretical and mathematical derivations show that the rTEC practically represent the frequency deviation of the GPS signals. Meanwhile, worldwide ground based GPS receivers are used to derive the TEC and associated rTEC to monitor the ionospheric solar flare effect on 14 July (Bastille Day) 2000. It is found that ionospheric solar flare effects can be observed from pre-dawn to post-dusk regions, and the most pronounced signatures appear in the midday area. The agreement between theoretical predications and observations demonstrates that the GPS TEC is suitable to monitor the overall variations of flare X-ray radiations while the rTEC is capable to detect sudden changes in flare X-ray radiations.

Liu, J. Y.; Lin, C. H.; Tsai, H. F.; Liou, Y. A.

2002-05-01

157

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

158

Supermagnetosonic subsolar magnetosheath jets and their effects: from the solar wind to the ionospheric convection  

NASA Astrophysics Data System (ADS)

It has recently been proposed that ripples inherent to the bow shock during radial interplanetary magnetic field (IMF) may produce local high speed flows in the magnetosheath. These jets can have a dynamic pressure much larger than the dynamic pressure of the solar wind. On 17 March 2007, several jets of this type were observed by the Cluster spacecraft. We study in detail these jets and their effects on the magnetopause, the magnetosphere, and the ionospheric convection. We find that (1) the jets could have a scale size of up to a few RE but less than ~6 RE transverse to the XGSE axis; (2) the jets caused significant local magnetopause perturbations due to their high dynamic pressure; (3) during the period when the jets were observed, irregular pulsations at the geostationary orbit and localised flow enhancements in the ionosphere were detected. We suggest that these inner magnetospheric phenomena were caused by the magnetosheath jets.

Hietala, H.; Partamies, N.; Laitinen, T. V.; Clausen, L. B. N.; Facsk, G.; Vaivads, A.; Koskinen, H. E. J.; Dandouras, I.; Rme, H.; Lucek, E. A.

2012-01-01

159

Ionosphere of venus: first observations of the effects of dynamics on the dayside ion composition.  

PubMed

Bennett radio-frequency ion mass spectrometers have returned the first in situ measurements of the Venus dayside ion composition, including evidence of pronounced structural variability resulting from a dynamic interaction with the solar wind. The ionospheric envelope, dominated above 200 kilometers by O(+), responds dramatically to variations in the solar wind pressure, Which is observed to compress the thermal ion distributions from heights as great as 1800 kilometers inward to 280 kilometers. At the thermal ion boundary, or ionopause, the ambient ions are swept away by the solar wind, such that a zone of accelerated suprathermnal plasma is encountered. At higher altitudes, extending outward on some orbits for thousands of kilometers to the bows shock, energetic ion currents are detected, apparently originating from the shocked solar wind plasma. Within the ionosphere, observations of pass-to-pass differences in the ion scale heights are indicative of the effects of ion convection stimlulated by the solar wind interaction. PMID:17832986

Taylor, H A; Brinton, H C; Bauer, S J; Hartle, R E; Cloutier, P A; Michel, F C; Daniell, R E; Donahue, T M; Maehl, R C

1979-02-23

160

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

161

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, Jran; Romano, Vincenzo

2013-04-01

162

Ionospheric Analysis and Ionospheric Modeling.  

National Technical Information Service (NTIS)

Investigations performed towards the development of improved models of the ionosphere are described. The study was directed at improving existing prediction models of ionospheric parameters. This lead to the development of techniques to update on a global...

D. C. Miller J. Gibbs

1974-01-01

163

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

NASA Astrophysics Data System (ADS)

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

Kawakubo, H.; Ruf, C. S.

2006-05-01

164

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

165

Thermospheric tidal effects on the ionospheric midlatitude summer nighttime anomaly using SAMI3 and TIEGCM  

NASA Astrophysics Data System (ADS)

This paper is the first study to employ a three-dimensional physics-based ionosphere model, SAMI3, coupled with the National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) and Global Scale Wave Model to simulate the mesospheric and lower thermospheric tidal effects on the development of midlatitude summer nighttime anomaly (MSNA). Using this coupled model, the diurnal variation of MSNA electron densities at 300 km altitude is simulated on both June solstice (day of year (DOY) 167) and December solstice (DOY 350) in 2007. Results show successful reproduction of the southern hemisphere MSNA structure including the eastward drift feature of the southern MSNA, which is not reproduced by the default SAMI3 runs using the neutral winds provided by the empirical Horizontal Wind Model 93 neutral wind model. A linear least squares algorithm for extracting tidal components is utilized to examine the major tidal component affecting the variation of southern MSNA. Results show that the standing diurnal oscillation component dominates the vertical neutral wind manifesting as a diurnal eastward wave-1 drift of the southern MSNA in the local time frame. We also find that the stationary planetary wave-1 component of vertical neutral wind can cause diurnal variation of the summer nighttime electron density enhancement around the midlatitude ionosphere.

Chen, C. H.; Lin, C. H.; Chang, L. C.; Huba, J. D.; Lin, J. T.; Saito, A.; Liu, J. Y.

2013-06-01

166

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

NASA Astrophysics Data System (ADS)

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

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

2003-07-01

167

Global Observations of Flux Transfer Events and Their Effects on the Magnetosphere-Ionosphere System.  

NASA Astrophysics Data System (ADS)

Multi-instrument observations of the magnetosphere reveal the nature of direct coupling in the solar wind-magnetosphere-ionosphere system, namely dayside reconnection. A case study during which there was a highly favourable conjunction of an extensive array of spacebourne and ground-based instruments offered an excellent opportunity to study magnetic reconnection in situ, as well as its effects on the magnetosphere and ionosphere. Flux transfer events were observed by Geotail during an extended traversal of the dawn magnetopause. Extensive coverage of the entire dayside high-latitude ionosphere was achieved by all of the northern hemisphere SuperDARN radars, and accurate solar wind time delays were possible due to the position of the IMP8 spacecraft immediately upstream of the Earth's bow shock. The SuperDARN radars in the dawn sector, in the vicinity of Geotail's magnetic footprint, measured temporally varying convection velocities. Low-altitude satellites monitored both the size of the auroral oval and particle precipitation in the cusp footprint. Energy-dispersed cusp ions were detected by the DMSP-F11 spacecraft at the same time that an FTE was measured by the magnetically conjugate Geotail. Analysis of the field and plasma data at Geotail reveals details of the structure and motion of the newly reconnected flux tubes as they convected past the spacecraft. The implied location of magnetopause reconnection will be discussed.

McWilliams, K. A.; Yeoman, T. K.; Sibeck, D. G.; Milan, S. E.; Sofko, G. J.; Nagai, T.; Mukai, T.; Hori, T.

2002-12-01

168

Ionospheric effects on a wide-bandwidth, polarimetric, space-based, synthetic-aperture radar  

SciTech Connect

The earth`s ionosphere consists of an ionized plasma which will interact with any electromagnetic wave propagating through it. The interaction is particularly strong at vhf and uhf frequencies but decreases for higher microwave frequencies. These interaction effects and their relationship to the operation of a wide-bandwidth, synthetic-aperture, space-based radar are examined. Emphasis is placed on the dispersion effects and the polarimetric effects. Results show that high-resolution (wide-bandwidth) and high-quality coherent polarimetrics will be very difficult to achieve below 1 GHz.

Brock, B.C.

1993-01-01

169

Ionospheric effects on a wide-bandwidth, polarimetric, space-based, synthetic-aperture radar  

SciTech Connect

The earth's ionosphere consists of an ionized plasma which will interact with any electromagnetic wave propagating through it. The interaction is particularly strong at vhf and uhf frequencies but decreases for higher microwave frequencies. These interaction effects and their relationship to the operation of a wide-bandwidth, synthetic-aperture, space-based radar are examined. Emphasis is placed on the dispersion effects and the polarimetric effects. Results show that high-resolution (wide-bandwidth) and high-quality coherent polarimetrics will be very difficult to achieve below 1 GHz.

Brock, B.C.

1993-01-01

170

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

NASA Astrophysics Data System (ADS)

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

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

1999-02-01

171

An effort to simulate magnetospheric-ionospheric effects in the presence of seismic phenomena  

NASA Astrophysics Data System (ADS)

The paper describes the Soviet MACS (Magnetospheric-Atmospheric Coupling through Seismoacoustic phenomena) program, in which the effects of simulated earthquakes on processes in the magnetosphere and ionosphere were investigated. Seismic events were simulated by the explosion of large charges containing several hundreds of tons of TNT. Particular consideration is given to data acquired from the blast (288 tons of TNT) in the vicinity of Alma-Ata on November 28, 1981. A scheme describing the effect of the seismic waves on the upper atmosphere is elaborated.

Alperovich, L. S.; Vugmeister, B. O.; Gokhberg, M. B.; Drobzhev, V. I.; Erushchenkov, A. I.; Ivanov, E. A.; Kudriavtsev, V. P.; Kulichkov, S. N.; Krasnov, V. M.; Matveev, A. K.

172

The ionospheric effects of a weak intrinsic magnetic field at Mars  

Microsoft Academic Search

An improved model of the Martian ionosphere which allows the magnetic field to have any direction in the horizontal plane is presented, as well as results of calculations for several different intrinsic magnetic field strengths and directions. When the solar wind dynamic pressure exceeds the Martian ionospheric thermal pressure, the plasma motion is weakly downward throughout the ionosphere for the

H. Shinagawa; T. E. Cravens

1992-01-01

173

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

Microsoft Academic Search

Spectral resonance structures (SRS) of the ionospheric Alfvn 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

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

2010-01-01

174

Geomagnetic storm effect on night-time D-region ionosphere and magnetosphere, as measured by ELF-VLF waves  

NASA Astrophysics Data System (ADS)

Extended solar minima during solar cycle 23 given us opportunity to study quite time D-region ionosphere and to examine all methods of analysis by using ELF-VLF broadband data. Beginning of solar cycle 24 is marked in the year 2010 and year 2011 has observed many geomagnetic storm with Dst >-100 nT. Geomagnetic storm causes severe effect on D-region ionosphere that affects ELF-VLF wave propagation. By accurately analysing ELF-VLF waves different D-region ionospheric parameters such as reflection height and electron density at reflection height can be obtained which are better indicator of storm effect. ELF-VLF waves which are travelling via magnetosphere are also being used to revile information about geomagnetic disturbance on magnetosphere. In the present work, we are investigating the geomagnetic storm effect on low-latitude nighttime D-region ionosphere and overlying magnetosphere by analysing ELF-VLF waves observed at Indian Low latitude stations for selected storm days and its comparison with quite days during year 2011. Further the application of ELF-VLF waves in the studies of lower ionosphere and magnetosphere will be discussed.

Maurya, Ajeet K.; Singh, Rajesh; Singh, Abhay Kumar; Ohya, Hiroyo; Selvakumaran, R.; Veenadhari, Bhasakara; Pant, P.

2012-07-01

175

The nighttime winter anomaly (NWA) effect in the American sector as a consequence of interhemispheric ionospheric coupling  

NASA Astrophysics Data System (ADS)

The nighttime winter anomaly (NWA) effect was observed during solar minimum conditions at the American sector by means of ionospheric electron content and vertical sounding measurements in Havana (Cuba). An effective interhemispheric transport of plasma is suggested to explain enhanced northern nighttime ionization during winter solstice. To elucidate this effect, an adequate physical-numerical model of the coupled system ionosphere-plasmasphere is presented and applied to a corotating tube of plasma at L = 1.5 in the American sector. The NWA can be explained by the theoretically derived higher tube content during the December solstice and, accordingly, by more intense nighttime fluxes from the plasmasphere, compared to the June solstice.

Foerster, M.; Jakowski, N.

176

The nighttime winter anomaly (NWA) effect in the american sector as a consequence of interhemispheric ionospheric coupling  

NASA Astrophysics Data System (ADS)

The nighttime winter anomaly (NWA) effect was observed during solar minimum conditions at the American sector by means of ionospheric electron content and vertical sounding measurements in Havana (Cuba). An effective interhemispheric transport of plasma is suggested to explain enhanced northern nighttime ionization during winter solstice. To elucidate this effect, an adequate physicalnumerical model of the coupled system ionosphere-plasmasphere is presented and applied to a corotating tube of plasma at L=1.5 in the American sector. The NWA can be explained by theoretically derived higher tube content during the December solstice and accordingly by more intense nighttime fluxes from the plasmasphere, compared to the June solstice.

Frster, M.; Jakowski, N.

1988-06-01

177

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

NASA Astrophysics Data System (ADS)

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

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

178

The association of the residual error of dual-frequency Global Navigation Satellite Systems with ionospheric turbulence parameters  

NASA Astrophysics Data System (ADS)

The effects of ionospheric scintillation on the residual error of the dual-frequency Global Navigation Satellite System are investigated. For the ordinary and extraordinary waves the scalar wave equations are obtained to a high-frequency approximation from the Maxwell equations. The solution for these scalar equations to the second-order Rytov approximation made it possible to determine the residual error up to the third order taking into account the ionospheric anisotropy and diffraction effects appearing when the signal is propagating through a turbulent ionospheric plasma. It is shown that the third-order effects, associated with scintillation, that is, with the propagation of the signal through a randomly inhomogeneous ionosphere, can be dominant and exceed second-order effects associated with the influence of the geomagnetic field. We investigate the association of the residual error with such parameters of ionospheric turbulence as the variance, and the inner and outer scales.

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

2009-12-01

179

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

180

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

181

Effects of Solar Activity Variations on Daytime and Nighttime Equatorial Topside Ionosphere  

NASA Astrophysics Data System (ADS)

At middle and low latitudes, the ion composition and temperature data in the topside ionosphere are responsive to changes in the EUV flux. High quality ion composition and temperature data from the Defense Meteorological Satellite Program are used to study solar activity variations on the day (0900 LT) and nighttime (2100 LT) equatorial topside ionosphere near 800 km. Latitudinal variations in the total ion composition, temperature, and relative ion concentrations are studied for spring equinox period (April) in 1991, 1996 and 1999 respectively. These years are respresentative of high, low, and moderate solar activities. Both the day and nighttime profiles show the influence of F10.7 in modulating the observed composition, temperatures and total densities. Data taken near 800 km altitude, for both day and nighttime conditions show that as solar activity decreases, average Ni decreases by an order of magnitude, average Ti decreases by about 400 ^ o K , and the H+/Ni ratio increases from zero to almost 80%. Additionally, the nighttime Ni profiles for high solar activity conditions are characterized by the presence of the Appleton anomaly which is not seen at other times.

Venkatraman, S.; Heelis, R.

2001-12-01

182

Dynamical effects of geomagnetic storms and substorms in the middle-latitude ionosphere: An observational campaign  

NASA Astrophysics Data System (ADS)

An observational campaign was conducted in October 1992 for ~36 hours, at three high- to low-latitude sites near 75W longitude (Sondre Stromfjord, Millstone Hill, and Arecibo). Vector plasma drift velocities are obtained using the incoherent scatter radar technique at each site. Neutral winds were measured using a Fabry-Perot interferometer, and 6300 airglow structures were imaged at the midlatitude site. Electric fields and meridional winds for the period were perturbed when magnetic storms and substorms occurred on the day and night of the campaign. The penetration of magnetospheric electric field and the following interplays between ionospheric electrodynamics and thermospheric wind perturbations in the midlatitude ionosphere are assessed using the multidiagnostic measurements. Evidence for traveling atmospheric disturbances (TADs) and large-scale gravity waves induced by auroral heating effects upon the thermosphere is identified. Diffuse aurora and a stable aurora red (SAR) arc were observed from Millstone Hill during the night of the campaign. The SAR arc moved southward when there were westward electric field perturbations, indicating plasmasphere compression in the postmidnight sector under substorm conditions. The SAR arc location was used to infer the motion of the magnetospheric shielding layer past the Millstone Hill site. Ionospheric F region disturbances in hmF2, NmF2, and total electron content were driven by the observed dynamics, exhibiting a complex mix of wind and electric field perturbations. While standard model episodes of penetration and shielding/overshielding occurred during the daytime event, such unambiguous clarifications were far less obvious during the nighttime event. This is perhaps due to the prolonged period of moderate geomagnetic activity that served as the background conditions for the substorms that occurred during the campaign.

Pi, Xiaoqing; Mendillo, Michael; Hughes, W. Jeffrey; Buonsanto, Michael J.; Sipler, Dwight P.; Kelly, John; Zhou, Qihou; Lu, Gang; Hughes, Terrence J.

2000-04-01

183

Space weather effects on low latitude geomagnetic field and ionospheric plasma response  

NASA Astrophysics Data System (ADS)

Space weather disturbances caused by enhanced stream of solar plasma during solar flares and Coronal Mass ejections (CMEs) are known to disrupt communications, endanger satellite payloads and introduce severe errors in a variety of tracking and positioning systems. The phenomena known as geomagnetic storms are the most obvious features of space weather disturbances. Magnetic storms are fundamental disturbances in the magnetosphere and can significantly increase, or decrease ionopheric electron densities (termed positive or negative storms, respectively). Electric fields originating in the magnetosphere can penetrate to the equatorial and low-latitude ionosphere resulting in vertical motions that restructure the F- region density profiles due to the height dependence of the recombination rate. The effect of space weather related perturbations in electric fields and currents in the equatorial and low latitude magnetic field associated with the changes in magnetospheric convection can be investigated using simultaneous observations from ground as well as ionospheric measurements. The present solar cycle witnessed many solar flares and coronal mass ejections (CMEs) which gave rise to intense geomagnetic storms due to highly active solar environment. The series of X-class solar flares occurred from 2 - 15 April 2001. The geomagnetic field was intermittently disturbed during period due to the CME passages. The geomagnetic storm began on 31 March and 11April 2001 are considered for the present study. These events were selected to study from ground based geomagnetic data, multi satellite data of solar wind and interplanetary parameters. Influence of the magnetospheric storm time electric field changes are estimated by the changes in the equatorial electric field as evidenced by the disturbance parameter of the equatorial electrojet strength and corresponding ionospheric response.

Veenadhari, B.; Alex, S.

184

Stratospheric sudden warming effects on the ionospheric migrating tides during 20082010 observed by FORMOSAT-3/COSMIC  

NASA Astrophysics Data System (ADS)

In this paper, ionospheric electron densities obtained from radio occultation soundings of FORMOSAT-3/COSMIC are decomposed into their various constituent tidal components for studying the stratospheric sudden warming (SSW) effects on the ionosphere during 20082010. The tidal analysis indicates that the amplitudes of the zonal mean and major migrating tidal components (DW1, SW2 and TW3) decrease around the time of the SSW, with phase/time shifts in the daily time of maximum around EIA and middle latitudes. Meanwhile consistent enhancements of the SW2 and nonmigrating SW1 tides are seen after the stratospheric temperature increase. In addition to the amplitude changes of the tidal components, well matched phase shifts of the ionospheric migrating tides and the stratospheric temperatures are found for the three SSW events, suggesting a better indicator of the ionospheric response. Although the conditions of the planetary waves and the mean winds in the middle atmosphere region during the 20082010 SSW events may be different, similar variations of the ionospheric tidal components and their associated phase shifts are found.

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

2013-10-01

185

Prompt penetration electric fields (PPEFs) and their ionospheric effects during the great magnetic storm of 3031 October 2003  

Microsoft Academic Search

We explore the ionospheric effects of prompt penetration electric fields (PPEFs) for a variety of interplanetary magnetic field directions. We use the great magnetic storm of 3031 October as an example of PPEF effects. For intense southward interplanetary magnetic fields (IMFs), inward plasma sheet convection occurs with the result of magnetospheric ring current formation and an intense magnetic storm. Concurrent

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

2008-01-01

186

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

Microsoft Academic Search

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

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

2008-01-01

187

[Effect of ionospheric parameters on the respiratory and cardiac system, function of the brain and higher nervous system activity in healthy people].  

PubMed

Effects of complex ionospheric parameters on the parameters of 4 systems of healthy people: respiration and cardiological systems, functions of brain and central neural activity, were studied. Results indicating the presence of highly significant multiple correlations of these biosystems with the complex of ionospheric parameters were received. PMID:9914846

Lushnov, M S; Kobrin, V P; Bulyko, V I; Malakhov, Iu K

188

Ionospheric effects of the solar flares of September 23, 1998 and July 29, 1999 as deduced from global GPS network data  

Microsoft Academic Search

This paper presents data from first global positioning system (GPS) measurements of global response of the ionosphere to solar flares of September 23, 1998 and July 29, 1999. The analysis used novel technology of a global detection of ionospheric effects from solar flares as developed by one of the authors (Afraimovich, Radio Sci. 35 (2000) 1417). The essence of the

E. L. Afraimovich; A. T. Altyntsev; E. A. Kosogorov; N. S. Larina; L. A. Leonovich

2001-01-01

189

Extreme solar EUV flares and ICMEs and resultant extreme ionospheric effects: Comparison of the Halloween 2003 and the Bastille Day events  

Microsoft Academic Search

Extreme solar flares can cause extreme ionospheric effects. The 28 October 2003 flare caused a ?25 total electron content units (TECU = 1016 el\\/m2 column density), or a ?30%, increase in the local noon equatorial ionospheric column density. The rise in the TEC enhancement occurred in ?5 min. This TEC increase was ?5 times the TEC increases detected for the

B. T. Tsurutani; F. L. Guarnieri; T. Fuller-Rowell; A. J. Mannucci; B. Iijima; W. D. Gonzalez; D. L. Judge; P. Gangopadhyay; A. Saito; T. Tsuda; O. P. Verkhoglyadova; G. A. Zambon

2006-01-01

190

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

191

Source mechanisms and radio effects of ionospheric plasma. Annual report, 1 October 1991-30 September 1992  

SciTech Connect

Since October 1, 1991 experimental and theoretical research has been conducted by Prof. Min-Chang Lee and his students at BU and MIT. This research work is aimed at investigating the ionospheric plasma disturbances which can affect significantly the radio wave propagation in communications and space surveillance. The research topics which have been investigated include: (1) A source mechanism leading to the symmetric lower hybrid sidebands and a low-frequency mode in the upper atmosphere, (2) Characteristics of lightning-induced plasmas, (3) Radio wave-produced plasmas and effects on radio communications, (4) Plasma turbulence and formation of field aligned density fluctuations as ionospheric ducts.

Lee, M.C.

1992-11-01

192

Interplanetary magnetic field By and auroral conductance effects on high-latitude ionospheric convection patterns  

NASA Astrophysics Data System (ADS)

The dependence of the ionospheric electric potential (convection) on the interplanetary magnetic field (IMF) and the ionospheric conductivity is investigated to understand the generation of convection patterns in the framework of the solar wind-magnetosphere-ionosphere (S-M-I) coupling scheme and the merging concept. A numerical magnetohydrodynamic (MHD) simulation is adopted for the study of the present problem. To achieve a high resolution in the ionosphere, the MHD calculation employs the finite volume (FV) total-variation diminishing (TVD) scheme with an unstructured grid system. The two-cell convection patterns reproduced from simulation are shown for several cases under the southward IMF condition during the growth-phase interval. In the investigation of these results, special attention is paid to the analysis of mirror symmetry in the convection patterns with respect to the IMF By. On the dayside in the Northern Hemisphere, IMF By- (By+) generates flow deflection on newly opened field lines toward the dusk (dawn) without a severe violation of the mirror symmetry. While the mirror symmetry of the convection pattern is maintained even on the nightside when the ionospheric conductivity is uniform, it is not maintained on the nightside when the ionospheric conductivity is nonuniform. A realistic ionospheric conductivity modifies the convection pattern in the Northern (Southern) Hemisphere so as to emphasize distinctive features seen for IMF By+ (By-) under a uniform conductivity, and the reproduced convection patterns coincide with the observation quite well including fine signatures on the nightside, both for IMF By- and By+. Because of the nonuniform conductivity, cell centers of convection are shifted to the earlier magnetic local times, and the antisunward flow in the northern polar cap is nearly aligned with noon-midnight meridian for IMF By-, while the flow in the northern polar cap has a significant inclination from prenoon to premidnight for IMF By+. These convection patterns can be understood by considering the effect due to the Hall current closure of the region-1 field-aligned current. The analysis for the dependence of nightside convection on IMF By and ionospheric conductivity shows that the Harang discontinuity is attributed partially to the structure of magnetospheric driver but mainly to the effect of nonuniform auroral conductivity. As a consequence, it is more adequate to say that convection patterns are more or less caused by the synthesized effect of more than one process rather than a single elementary process. Reproduced convection patterns in this paper show a particular coincidence with satellite observations summarized by adopting the pattern-recognition-based approach.

Tanaka, T.

2001-11-01

193

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

194

The E and F region ionospheric response to solar flares. I - Effects of approximations of solar flare EUV fluxes  

Microsoft Academic Search

SOLRAD and many other satellite systems have provided a large data base showing the time-dependent behavior of broadband solar fluxes in the X-ray and EUV spectral regions. Results are presented of tests performed to determine how this information can best be used to predict the effects of a solar flare on the ionosphere. The approach has been to first adopt

J. T. Mariska; E. S. Oran

1981-01-01

195

Source mechanisms and radio effects of ionospheric plasma disturbances. Final report, 1 October 1991-30 September 1994  

SciTech Connect

Research on source mechanisms and radio effects of ionospheric plasma disturbances had been conducted including theories, field experiments at Arecibo Puerto Rico, and laboratory experiments with the Versatile Toroidal Facility (VTF) at MIT Plasma Fusion Center. Several graduate students and undergraduate students participated in the research projects and completed their thesis work under the supervision of Prof. Min-Chang Lee.

Lee

1994-09-30

196

Effect of powerful oblique HF waves on ionospheric D-layer absorption  

NASA Astrophysics Data System (ADS)

A simple model of D-layer ionospheric heating in the presence of strong, high frequency (HF) radio waves is used to predict the anomalous, nonlinear wave absorption due to collisional and recombination effects induced by the indirect signal. It is found that little anomalous absorption occurs until effective radiated power (ERP) approaches 100 dBW; further increases in power of several dB beyond this 100 dBW threshold are frustrated by a comparable increase in self-induced, one-way absorption. This trend of increasing absorption with increasing transmitter ERP has considerable implications for design of communication or radar systems that use ultra-powerful, high-gain HF transmitters.

Bloom, R. M.

1993-04-01

197

Ionosphere-magnetosphere coupling and convection  

NASA Astrophysics Data System (ADS)

Some IMS-associated attempts at quantitative modeling of specific observed ionosphere-magnetosphere events are reviewed, including a theoretical model of convection, algorithms for deducing ionospheric current and electric-field patterns from sets of ground magnetograms and appropriate ionospheric conductivity information, and empirical models of ionospheric conductances, polar-cap potential drops, etc. A few topics in the active research area of magnetic-field-aligned electric fields are reviewed very briefly, particularly magnetic-mirror effects and double layers.

Wolf, R. A.; Spiro, R. W.

1984-09-01

198

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

Microsoft Academic Search

The results of high latitude ionospheric modification experiments utilising the EISCAT heating facility at Troms are presented. As a result of the interaction between the high power pump waves and upper hybrid waves in the ionosphere, field-aligned electron density irregularities are artificially excited. Observations of these structures with the CUTLASS coherent HF radars and the EISCAT incoherent UHF radar exhibit

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

2006-01-01

199

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

Microsoft Academic Search

The ionospheric record of the 1974 cyclohexane vapour cloud explosion (VCE) accident near Flixborough is re-examined in light of a new theory used to describe the acoustic field in the atmosphere and ionosphere caused by explosions on the ground. The reconstructed oblique Doppler sounding records from six radio traces agree remarkably well with experimental results when a ground source explosion

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

2003-01-01

200

Ionospheric effects at low latitudes during the March 22, 1979, geomagnetic storm  

Microsoft Academic Search

This paper investigates the response of the equatorial ionosphere to the neutral atmosphere perturbations produced by the magnetic storm of March 22, 1979. A numerical model of the equatorial ionosphere is used to calculate the maximum electron densities and F layer heights associated with a storm-perturbed neutral atmosphere and circulation model. Possible electric field perturbations due to the storm are

C.G. Fesen; G. Crowley; R. G. Roble

1989-01-01

201

October 29-31, 2003 Storm Effects on Ionospheric Currents and Geomagnetically Induced Currents  

Microsoft Academic Search

A major solar storm in late October 2003 produced significant currents in the ionosphere. These currents resulted in geomagnetically induced currents (GIC) in several electrical power transmission systems. Using equivalent ionospheric currents determined from an international array of magnetometers, an enhanced understanding is obtained of how the two dimensional spatially extended currents vary over the Northern Hemisphere during this period.

D. W. Danskin; D. H. Boteler; L. Trichtchenko; L. McKee; G. Jansen van Beek

2004-01-01

202

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

203

Effect of Interplanetary Magnetic Field on the Equatorial Ionosphere Dynamics in March 1998  

NASA Astrophysics Data System (ADS)

Variations of the equatorial ionosphere height and critical frequency foF2 for Cebu Island (124 deg. E, 10.3 deg N; 2.4 in diplatitude) and Manila (121 deg. E, 14.6 deg. N, 7.3 deg. N in diplatitude) are compared with interplanetary magnetic field data. The ground-based measurements of the critical frequency foF2 Jicamarca are used for study of longitudinal variations during of 10 March 1998 magnetic storm. The subsequently main phase decrease of Dst to - 107 nT was generated by the 3 hour's negative IMF Bz=-18nT. Situation in the polar cusp was determined by 6 hour's negative IMF By = - 20 nT. The critical frequency foF2 decrease in the same way at Cebu Island and Jicamarca from 15.45 UT up to 19 UT but the values of decreases are significantly different at two stations. At Cebu Island (the night sector) the foF2 drops from 8 MHz to 2 MHz. In the day sector at Jicamarca the critical frequency drops from 11.5 MHZ to 9 MHz. These changes were accompanied by a rise of heights of the F-region. It is shown that changes in the ionospheric height at two stations (Cebu and Manila) depend from direction of the Bz IMF. The heights at two stations vary almost identical during northward IMF Bz (quiet period on March 7, 1998) and vary a fairly different way during reorientations of the IMF (disturbance periods on 9 and 12 March 1998). The distinctions between quiet and disturbance periods in heights can reach up to 50-100 km. It can be shown that this effect is the result of direct penetration of electric field from the field-aligned currents (FAC), which connected with DP systems, to equatorial ionosphere. This additional electric field of the FAC carries ions away from the equatorial F2 layer and consequently we observe maximum F2 layer at great heights. Differences between behaviour of heights at the two stations during southward IMF Bz are attributable to location of the electrojet that can be formed by the FAC electric field.

Sizova, L.; Maruyama, T.; Nozaki, K.

204

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

205

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

206

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

207

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

208

Ionospheric Storms A Review  

NASA Astrophysics Data System (ADS)

In this paper, our current understanding and recent advances in the study of ionospheric storms is reviewed, with emphasis on the F2-region. Ionospheric storms represent an extreme form of space weather with important effects on ground- and space-based technological systems. These phenomena are driven by highly variable solar and magnetospheric energy inputs to the Earth's upper atmosphere, which continue to provide a major difficulty for attempts now being made to simulate the detailed storm response of the coupled neutral and ionized upper atmospheric constituents using increasingly sophisticated global first principle physical models. Several major programs for coordinated theoretical and experimental study of these storms are now underway. These are beginning to bear fruit in the form of improved physical understanding and prediction of ionospheric storm effects at high, middle, and low latitude.

Buonsanto, M. J.

1999-04-01

209

On the Observation of Ionospheric Effects Due to Dumping of Trapped Particles.  

National Technical Information Service (NTIS)

Energy considerations lead to the conclusion that the Van Allen belts feed sizable amounts of ionizing energy into the ionosphere by precipitation of particles. Most suspicious, although not clearly unique in importance, are the western slopes of the magn...

G. J. Gassmann C. P. Pike

1966-01-01

210

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

211

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

Microsoft Academic Search

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

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

1992-01-01

212

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

213

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

Microsoft Academic Search

The relationships among cloud-to-ground (CG) lightning, sferics, whistlers, VLF amplitude perturbations, and other ionospheric phenomena occurring during substorm events were investigated using data from simultaneous ground-based observations of narrow-band and broad-band VLF radio waves and of CG lightning made during the 1987 Wave-Induced Particle Precipitation campaign conducted from Wallops Island (Virginia). Results suggest that the data collected on ionospheric phenomena

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

1992-01-01

214

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

Microsoft Academic Search

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

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

2008-01-01

215

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

216

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

NASA Astrophysics Data System (ADS)

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

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

2010-10-01

217

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

218

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

219

Determination of a geomagnetic storm and substorm effects on the ionospheric variability from GPS observations at high latitudes  

NASA Astrophysics Data System (ADS)

The aim of this work is to characterize the ionospheric electron content variability during a standard and simple geomagnetic storm, and substorms during it. The analysis is based on tying the geomagnetic disturbances including the signatures of the current wedge formed during the substorm expansion phase, with the variability of ionospheric vertical total electron content (VTEC) in local time; for this reason the VTEC is computed for complete geographical longitude coverage at subauroral and auroral latitudes. The study is based on the geomagnetic storm befallen on April 6 and 7, 2000 (near the equinox) and the TEC are computed from global positioning system (GPS). The main results can be divided into three groups: (a) when the geomagnetic storm starts between pre-midnight and dawn, a minimum of VTEC is recorded, lasting all the long day (ionospheric storm negative phase); also the nighttime electron content may decrease below the corresponding for quiet days; but near the 60 of geomagnetic latitude the ionization polar tongue can be observed at noon, superimposed to the negative phase; (b) computed by GPS stations placed lower than 50, when the geomagnetic storm starts between dawn and noon the VTEC recorded a positive phase, but if it starts at noon a dusk effect is recorded; those located between 50 and 60 show a sudden increase and later sudden decrease to nocturnal values, (c) when the geomagnetic storm starts between afternoon and sunset, at stations located lower than 50 a dusk effect and an ionospheric negative phase during the next day are recorded, but if the GPS stations are located at higher latitude than 50 the VTEC representation shows the nocturnal end of the ionization polar tongue. Expansion phases of substorms are shown as small VTEC variations recorded for a short time: decreases if the substorm happens between dawn and midday; enhancements during the fall of the ionospheric positive phase. From the comparison with the results obtained by other methods, the GPS analysis proves to be an adequate method for studying globally the ionospheric variability at these latitudes.

Gmez, Luis; Ignacio Sabbione, Juan; Andrea van Zele, Mara; Meza, Amalia; Brunini, Claudio

2007-06-01

220

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

221

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-Dupr, Robert A.; Jacobson, Abram R.; Triplett, Laurie A.

2001-01-01

222

Planetary Ionospheres  

NASA Astrophysics Data System (ADS)

Most planets and many satellites in our solar system are surrounded by envelopes of gravitationally bound gases. The interaction of solar radiation and charged particles of solar wind and planetary magnetospheric origin with these gases produces weak IONIZATION that creates planetary ionospheres embedded within the more dense PLANETARY ATMOSPHERES. Additional sources of ionization which are relat...

Strobel, D.; Murdin, P.

2000-11-01

223

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

NASA Astrophysics Data System (ADS)

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

Nina, A.; ?ade, V.; uli?, D.; Sre?kovi?, V.; igman, V.

2012-05-01

224

Effects of neutral compositions on the ionospheric positive storms during the recovery phase  

NASA Astrophysics Data System (ADS)

The ionosonde measurements over Millstone Hill (42.6N, 71.5W), Wallops Is (37.9N, 75.5W), Eglin Afb (30.4N, 86.7W) and Boulder (40N, 105.3W) along with simultaneous GUVI/TIMED [O]/[N2] density ratio measurements are analyzed to investigate positive storm effects during the recovery phase of the April 2004 magnetic storm. The results show that the peak density NmF2 increases significantly on 4 April, 2004 (the recovery phase) with respect to the quiet reference days, especially over Boulder. It is generally accepted that the daytime positive storm results from dynamic processes (the neutral winds/electric field effects) that lift the F2 layer, decreases the recombination rate, and increases the electron density. However, this can't explain these observed phenomena on 4 April, where hmF2 doesn't present evident changes during this period. In fact during this period we find an evident increase in the simultaneous TIMED/GUVI [O]/[N2] density ratio. We suggest that the thermospheric composition perturbation should contribute largely to the ionospheric positive storms at middle latitudes during the recovery phase of the April 2004 storm.

Lei, J.; Zhang, S.; Zhang, Y.

2005-12-01

225

Effect of the solar wind conditions on the ionospheric equivalent current systems  

NASA Astrophysics Data System (ADS)

We employ a global magnetohydrodynamics (MHD) model, namely the PPMLR-MHD model, to investigate the effect of the solar wind conditions, such as the interplanetary magnetic field (IMF) clock angle, southward IMF magnitude and solar wind speed, on the average pattern of the ionospheric equivalent current systems (ECS). A new method to derive ECS from the MHD model is proposed and applied, which takes account of the oblique magnetic field line effects. The model results indicate that when the IMF is due northward, the ECS are very weak while the current over polar region is stronger than the lower latitude; when the IMF rotates southward, the two-cell current system dominates, the eastward electrojet on the afternoon sector and the westward electrojet on the dawn sector increase rapidly while the westward electrojet is stronger than the eastward electrojet. Under southward IMF, the intensity of the westward electrojet and eastward electrojet both increase with the increase of the southward IMF magnitude and solar wind speed, and the increase is very sharp for the westward electrojet. Furthermore, we compare the geomagnetic perturbations on the ground represented by the simulated average ECS with the observation-based statistical results under similar solar wind conditions. It is found that the model results generally match with the observations, but the underestimation of the eastward equivalent current on the dusk sector is the main limitation of the present model.

Zhang, J. J.; Wang, C.; Tang, B. B.; Li, H.

2013-03-01

226

Magnetic declination and zonal wind effects on longitudinal differences of ionospheric electron density at midlatitudes  

NASA Astrophysics Data System (ADS)

A prominent ionospheric longitudinal variation at midlatitudes, in particular, over the continental US, was found recently. This variation is characterized as a higher east-side electron density in the evening and a higher west-side electron density in the morning, and with clear seasonal and solar activity dependencies. A combined effect of geomagnetic declination and changing zonal winds was proposed to explain it. This paper represents a comprehensive investigation of this effect by examining climatology for both electron density longitudinal differences and the nighttime zonal winds in the eastern US. Electron density is from incoherent scatter radar extra-wide coverage experiments during 1978-2011 over Millstone Hill for which the spatial separation of the data can be up to 50 in longitude. The thermospheric zonal wind is from the on-site Fabry-Perot interferometer measurements during 1989-2001. The observed zonal wind climatology is found to be perfectly consistent with the expectation based on the east-west electron density differences in terms of local time, seasonal, and solar cycle dependencies. The correlation between the zonal wind and the east-west differential ratio is extremely high with an overall correlation coefficient of 0.93. The observed time delay of 3 hours in the response of electron density differences to zonal winds is a marked feature. Thus these results confirm positively the declination-zonal wind mechanism and provide new insight into longitudinal variations at midlatitudes for other geographic sectors.

Zhang, Shun-Rong; Foster, John C.; Holt, John M.; Erickson, Philip J.; Coster, Anthea J.

2012-08-01

227

Refractive index effects on the scatter volume location and Doppler velocity estimates of ionospheric HF backscatter echoes  

NASA Astrophysics Data System (ADS)

Ionospheric EB plasma drift velocities derived from the Super Dual Auroral Radar Network (SuperDARN) Doppler data exhibit systematically smaller (by 20-30%) magnitudes than those measured by the Defence Meteorological Satellites Program (DMSP) satellites. A part of the disagreement was previously attributed to the change in the E/B ratio due to the altitude difference between the satellite orbit and the location of the effective scatter volume for the radar signals. Another important factor arises from the free-space propagation assumption used in converting the measured Doppler frequency shift into the line-of-sight velocity. In this work, we have applied numerical ray-tracing to identify the location of the effective scattering volume of the ionosphere and to estimate the ionospheric refractive index. The simulations show that the major contribution to the radar echoes should be provided by the Pedersen and/or escaping rays that are scattered in the vicinity of the F-layer maximum. This conclusion is supported by a statistical analysis of the experimental elevation angle data, which have a signature consistent with scattering from the F-region peak. A detailed analysis of the simulations has allowed us to propose a simple velocity correction procedure, which we have successfully tested against the SuperDARN/DMSP comparison data set.

Ponomarenko, P. V.; St-Maurice, J.-P.; Waters, C. L.; Gillies, R. G.; Koustov, A. V.

2009-11-01

228

GNSS station characterisation for ionospheric scintillation applications  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

229

Parametric effects in inhomogeneous plasma during injection of electron pulses into the ionosphere  

NASA Astrophysics Data System (ADS)

The injection of electron pulses from the rocket into the ionospheric plasma in the lower hemisphere relative to the initial pitch angles of electrons during the substorm recovery phase provoked the generation of parametric processes (the ARAKS experiment). The electron flux observations, obtained using a wide-angle detector, and the whistler wave emission intensity measurements were compared. A wide-angle detector of electrons was mounted on the rocket, and a broadband wave receiver was installed on a nasal cone separated from the rocket. Bursts of the electron flux and wave emission were observed in pauses between electron pulses. It has been indicated that a clearly defined anisotropy of the observed parametric effects of the pitch angle of injected electron pulses is related to resonance characteristics of a wave emitted by electron fluxes in a magnetized plasma. Precipitation of ring current electrons was caused by a change in the magnetic moment of electrons, trapped by the magnetosphere, in the region of magnetic mirror points in the fields of electrostatic oscillations excited during decay of whistlers.

Izhovkina, N. I.

2009-08-01

230

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

PubMed

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

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

1989-11-10

231

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

232

Statistical study of the effect of solar wind dynamic pressure fronts on the dayside and nightside ionospheric convection  

NASA Astrophysics Data System (ADS)

Over the past few years, the prominent role of solar wind dynamic pressure in enhancing dayside and nightside reconnection and driving-enhanced ionospheric convection has been documented by both ground and spaceborne instruments. For a previous case study of an abrupt increase in solar wind dynamic pressure, Super Dual Auroral Radar Network (SuperDARN) measurements of plasma convection within the dayside polar ionosphere revealed an immediate enhancement of plasma convection. The convection enhancement variation closely follows the variation in solar wind pressure. The dayside enhancement was followed by a nightside convection increase about 40 min later, which has similar variation characteristics as seen on the dayside. We now use SuperDARN flow measurements during a large number of solar wind pressure enhancements to conduct a superposed epoch analysis of the effects of solar wind pressure fronts on the dayside and nightside ionospheric convection. The results for the dayside show an increase of convection for nearly all interplanetary magnetic field (IMF) Bz values. The response is more pronounced and immediate (within minutes) for southward IMF, with a duration of 20-30 min. The response time scales increase to 5-10 min for northward IMF, and the enhanced flows last for 30-50 min. We also find a significant enhancement of nightside convection, particularly for small values of IMF By, that follows about 10-15 min after the dayside response and can last for 40-50 min.

Boudouridis, A.; Lyons, L. R.; Zesta, E.; Weygand, J. M.; Ribeiro, A. J.; Ruohoniemi, J. M.

2011-10-01

233

Using Lightning Waveforms To Probe Thunderstorm's Electromagnetic Effects On The Ionospheric D-Layer  

NASA Astrophysics Data System (ADS)

Previous studies indicated that ionospheric D-layer could be disturbed by electromagnetic activities of the underling thunderstorms, either due to impulsive EM radiation (EMP) produced by intense ground strokes or due to removal of charges by lightning flashes (quasi-static electrical, QE). More recent study by the authors showed that the dominant fluctuations in the D-layer could be attributed to the effects of atmospheric gravity wave (AGW) that was originated by the storm. With time-domain, near-range (100s km), multi-station, and broadband VLF/LF observations from the Los Alamos Sferic Array (LASA), high spatial and temporal resolution detection of the D-layer behavior became feasible. Especially, the simultaneous multi-station measurements provide a chance of probing the D-layer from different directions and at different distances from the effecting storm. Together with the measurement, we also developed a time-domain VLF/LF propagation model, which takes the D-layer electron profile as the dominant parameter. In this study, we compare the measured return stroke waveforms with the model simulation and find the best match between the two, and to retrieve the corresponding D-layer electron profile. Our analysis indicated that additional and static ionization occurred directly above some storms, possibly due to the QE effect (or rather a static electrical effect, SE). In the range of a few hundred km, the altitude of the D-layer was found to continuously descending as one approaching toward the storm, suggesting an EMP effect that occurred nearly continuously.

Shao, X.; Lay, E. H.; Jacobson, A. R.

2011-12-01

234

3D Model of the Martian Ionosphere  

NASA Astrophysics Data System (ADS)

For planets without intrinsic magnetic field like Mars and Venus, the ionosphere is the main obstacle decelerating and deviating the solar wind flow. Therefore, the ionosphere plays an important part in erosion processes associated to Mars-solar wind interaction. Below 180 km, the Martian ionosphere is well described by the photochemical equilibrium. Above 180 km, the transport processes become important. To describe the Martian upper ionosphere, we develop a 3D multi-fluid dynamical core in the LMD Martian general circulation model (GCM) (Forget et al. 1999, Gonzalez-Galindo et al. 2009). This core solves the horizontal and vertical dynamics of the main ionospheric species and their coupling and retroaction on the neutral atmosphere at different seasons. This model will be later coupled to a magnetospheric model in order to describe the Martian ionospheric erosion by the solar wind.

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

2012-04-01

235

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.

236

Effect of the interplanetary magnetic field on the distribution of electric fields in the polar ionosphere  

NASA Astrophysics Data System (ADS)

Heppner (1972), in an analysis of satellite data, observed 12 types of electric-field distributions in the polar ionosphere along the morning-evening meridian. In the present paper it is shown that these distribution types can be described by the analytical model of Uvarov and Barashkov (1984). In this model the excitation of the electric fields is investigated by solving the set of continuity equations for current in three regions (the north and south polar caps and a region outside the caps) with allowance for the magnetic conjugacy of the ionosphere in the two hemispheres.

Uvarov, V. M.; Barashkov, P. D.

1985-08-01

237

Ionospheric effects on the transmission of ultralow-frequency plasma waves.  

PubMed

Measurements of magnetospheric ultralow-frequency plasma waves (period tau, approximately 18 to 150 seconds) on the ground under continuous daylight conditions in the Antarctic and under alternate day-night solar illumination at the conjugate station in Quebec indicate a significant local time dependence in the transmission properties of the ionosphere for waves of these periods. When the Antarctic station is compared with the Quebec station, the tilt (with respect to the ionosphere) of the orientation plane of the waves is observed to be larger at local noon than at local night. PMID:17754378

Lanzerotti, L J; Lie, H P; Tartaglia, N A

1972-11-01

238

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

Microsoft Academic Search

In this paper, we report the responses of the low latitude ionosphere near the longitude 120E to the April 2000 geomagnetic storm using Digisonde data measured at Chungli (25.0N, 121.2E, Mag. 13.8N), Wuhan (30.6N, 114.4E, Mag. 19.3N), and Kokubunji (35.7N, 139.5E, Mag. 25.7N). At these three stations, the significant ionospheric responses are near-simultaneous height disturbances after the sudden storm commencement

Libo Liu; Weixing Wan; C. C. Lee; Baiqi Ning; J. Y. Liu

2004-01-01

239

Ionospheric effects of the acoustic wave above the epicenter of an industrial explosion  

SciTech Connect

Results obtained during two industrial explosions are compared. The appearance of identical minute pulsations in the geomagnetic field is determined. The efficiency of ionospheric action of ground-based explosions with the energy of several hundred tons of TNT is confirmed, together with the dependence of duration of the ionospheric response upon the explosion energy. Dopplergrams are used to reconstruct the time profile of neutral gas velocity in the acoustic perturbation at the reflection point of the probing radio wave at a height of /approximately/200 km.

Drobzhev, V.I.; Zheleznyakov, E.V.; Idrisov, I.K.; Kaliev, M.Z.; Kazakov, V.V.; Krasnov, V.M.; Pelenitsyn, G.M.; Savel'ev, V.L.

1988-06-01

240

High-latitude phenomenological model of auroral precipitation and ionospheric effects  

SciTech Connect

A phenomenological approach was taken to model the behavior of the high latitude ionosphere in support of data generated by spectrophotometric images taken by satellites. The model, based on the collected particle precipitation data, incorporates expressions for the differential energy distribution and spatial extent and temporal variations of auroral electron precipitation in the 0.35 keV- 1 MeV range during substorm events. The applicability of the model is demonstrated by the results of a simulation of the expected responses of a spaceborne X-ray imager such as the one planned for the POLAR spacecraft ionospheric imaging experiment. 28 references.

Miller, K.L.; Vondrak, R.R.

1985-06-01

241

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

NASA Astrophysics Data System (ADS)

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

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

242

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

NASA Astrophysics Data System (ADS)

Spectral resonance structures (SRS) of the ionospheric Alfvn 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

243

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

NASA Astrophysics Data System (ADS)

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

Veenadhari, B.; Alex, S.

2006-11-01

244

Ionospheric Effects associated with the Solar Flare of September 28, 1961  

Microsoft Academic Search

THE purpose of this communication is to direct attention to some ionospheric phenomena observed during the period of the above flare and during the early part of the associated geomagnetic storm that ensued on September 30, 1961. The flare, which was of importance 3+, was first detected around 2200 U.T., and the intensity of the Halpha radiation reached a peak

Kenneth Davies

1962-01-01

245

Lunar-dependent equatorial ionospheric electrodynamic effects during sudden stratospheric warmings  

Microsoft Academic Search

We have used plasma drift and magnetic field measurements during the 2001-2009 December solstices to study, for the first time, the longitudinal dependence of equatorial ionospheric electrodynamic perturbations during sudden stratospheric warmings. Jicamarca radar measurements during these events show large dayside downward drift (westward electric field) perturbations followed by large morning upward and afternoon downward drifts that systematically shift to

M. E. Olson; C. Stolle; H. Lhr; L. P. Goncharenko; K. Yumoto; T. Nagatsuma

2010-01-01

246

Simple Methods for Computing Tropospheric and Ionospheric Refractive Effects on Radio Waves  

Microsoft Academic Search

The paper describes a simple and accurate method for computing ionospheric and tropospheric bending. The only assumptions made are that the refractive gradient is radial and that the refractive index profile can be approximated by a finite number of linear segments whose thickness is small compared with the earth's radius. These assumptions are readily justifiable in all practical cases. Since

S. Weisbrod; L. J. Anderson

1959-01-01

247

Ionospheric effects on synthetic aperture radar at 100 MHz to 2 GHz  

Microsoft Academic Search

Recently, there has been increasing interest in the use of spaceborne synthetic aperture radar (SAR) for measuring forest biomass. However, it is noted that conventional SAR using C-band or higher frequencies cannot penetrate into foliage, and therefore the biomass measurements require longer wavelengths, typically P-band (500 MHz). It is also known that the ionosphere is highly dispersive, causing group delay

Akira Ishimaru; Yasuo Kuga; Jun Liu; Yunjin Kim; Tony Freeman

1999-01-01

248

Ionospheric Effects caused by Electrons precipitated from the Outer Radiation Belt  

Microsoft Academic Search

DURING the period October 1962 to March 1963, there was a disturbance in the ionosphere at the Antarctic station Sanae (70 18' S., 2 22' W.) whenever a high flux of precipitated electrons was observed in the magnetically conjugate area by the satellite Alouette1. Together with Gledhill, we2 have shown that similar disturbances are produced at other stations lying near

D. G. Torr; Marsha R. Torr

1967-01-01

249

Ionospheric effects during the partial solar eclipse of 10 July 1972  

Microsoft Academic Search

Polarization measurements at Fort Monmouth, N.J., using ATS-3 emitted signals and bottomside ionospheric sounding measurements at the subionospheric point were performed during the partial solar eclipse of 10 July 1972. A decrease in the total electron content and the plasma temperature ensued with corresponding diffusive particle fluxes into heights of maximum ionization. The diffusion rate to the height of maximum

H. Soicher; F. J. Jr. Gorman

1973-01-01

250

Ionospheric effects of the gravity wave launched by the September 18, 1974, sudden commencement  

Microsoft Academic Search

A sudden commencement of a geomagnetic storm occurred on September 18, 1974. Later, a traveling ionospheric disturbance was detected by the incoherent scatter radar at Millstone Hill, Massachusetts and Arecibo, Puerto Rico. Measurements of electron temperature vertical distribution, ion temperature, and electron density are given. Based on a time-dependent dynamic model of the thermosphere, characteristics of the thermospheric gravity wave

R. G. Roble; A. D. Richmond; W. L. Oliver; R. M. Harper

1978-01-01

251

Geomagnetic storm effects in the ionospheric E- and F-regions  

NASA Astrophysics Data System (ADS)

Ground-based ionosonde data obtained at Alma-Ata station [?=43.25N, ?=76.92E, ?=33.47N, L=1.44) were analysed to study the ionospheric responses of nine intense (Kp?8, Dst<-100 nT) geomagnetic storms with storm sudden commencement (ssc). The collected data show that the ionospheric responses to the geomagnetic storms are highly complex and variable; however, negative ionospheric disturbances are a common feature of the responses. The occurrence of normal night E2-, E-, F1- and auroral type r (retardation) sporadic Es-layers, which are unusual for Alma-Ata, was observed during most active phase in the Dst index. Employing the International Reference Ionosphere (IRI), the night-time E region electron density Ne was estimated for quiet conditions on the epochs of the storm time periods. A direct comparison of the quiet and storm electron density in the 110-200 km altitude range shows a significant storm-induced increase in Ne that reaches a factor of approximately 10 at the 110 km altitude. The interaction of precipitating energetic neutralised ring current particles with the upper atmosphere during geomagnetic disturbances is assumed to be a possible explanation for the observed night events at this latitude sector.

Gordienko, G. I.; Vodyannikov, V. V.; Yakovets, A. F.

2011-08-01

252

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

National Technical Information Service (NTIS)

This report considers the Doppler spectral properties of radar signals scattered from high latitude E and F-region ionospheric irregularities. Although the exact mechanism for the production of F-region irregularities is not yet known, it appears that the...

R. A. Greenwald

1981-01-01

253

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

254

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

255

Atmosphere-Ionosphere Electrodynamic Coupling  

NASA Astrophysics Data System (ADS)

Numerous phenomena that occur in the mesosphere, ionosphere, and the magnetosphere of the Earth are caused by the sources located in the lower atmosphere and on the ground. We describe the effects produced by lightning activity and by ground-based transmitters operated in high frequency (HF) and very low frequency (VLF) ranges. Among these phenomena are the ionosphere heating and the formation of plasma density inhomogeneities, the excitation of gamma ray bursts and atmospheric emissions in different spectral bands, the generation of ULF/ELF/VLF electromagnetic waves and plasma turbulence in the ionosphere, the stimulation of radiation belt electron precipitations and the acceleration of ions in the upper ionosphere. The most interesting results of experimental and theoretical studies of these phenomena are discussed below. The ionosphere is subject to the action of the conductive electric current flowing in the atmosphere-ionosphere circuit. We present a physical model of DC electric field and current formation in this circuit. The key element of this model is an external current, which is formed with the occurrence of convective upward transport of charged aerosols and their gravitational sedimentation in the atmosphere. An increase in the level of atmospheric radioactivity results in the appearance of additional ionization and change of electrical conductivity. Variation of conductivity and external current in the lower atmosphere leads to perturbation of the electric current flowing in the global atmosphere-ionosphere circuit and to the associated DC electric field perturbation both on the Earth's surface and in the ionosphere. Description of these processes and some results of the electric field and current calculations are presented below. The seismic-induced electric field perturbations produce noticeable effects in the ionosphere by generating the electromagnetic field and plasma disturbances. We describe the generation mechanisms of such experimentally observed effects as excitation of plasma density inhomogeneities, field-aligned currents, and ULF/ELF emissions and the modification of electron and ion altitude profiles in the upper ionosphere. The electrodynamic model of the ionosphere modification under the influence of some natural and man-made processes in the atmosphere is also discussed. The model is based on the satellite and ground measurements of electromagnetic field and plasma perturbations and on the data on atmospheric radioactivity and soil gas injection into the atmosphere.

Sorokin, V. M.; Chmyrev, V. M.

256

The effects of crustal magnetic fields and the pressure balance in the high latitude ionosphere/atmosphere at Mars  

NASA Astrophysics Data System (ADS)

The strongest crustal magnetic fields at Mars are located in certain regions in the Southern hemisphere and lead to the formation of large-scale mini-magnetospheres. In the Northern hemisphere, the crustal fields are rather weak and usually do not prevent direct interaction between the SW and an ionosphere/atmosphere. Exceptions occur in the isolated mini-magnetospheres formed by the crustal anomalies. Electron density profiles derived from radio occultation data obtained by the Radio Science Mars Global Surveyor (MGS) experiment have been compared with the crustal magnetic fields measured by the MGS Magnetometer/Electron reflectometer (MAG/ER) experiment. The effective scale-height of the electron density for two altitude ranges, 145 165 km and 165 185 km have been derived for each of the profiles studied. For the regions outside of the mini-magnetospheres the thermal pressure of the ionospheric plasma for the altitude range 145 185 km has been derived. The pressure balance in the high latitude ionosphere at Mars has been studied. In the Northern hemisphere average pressure at the altitude 160 km p160 is practically independent of SZA. In the Northern hemisphere B2/8? can exceed p160 in half the cases at altitudes 170 180 km, and magnetic forces can drive effective convection. In large scale mini-magnetospheres in the Southern hemisphere the ratio H145 165/H165 185 on average, larger and more variable than in the Northern hemisphere. This suggests that plasma convection at altitudes above 165 km is effective. Within the Martian mini-magnetospheres plasma convection has to be primarily a drift of charged particles across the strong crustal magnetic fields and in this regard Martian mini-magnetospheres are similar to the terrestrial magnetosphere.

Breus, T. K.; Ness, N. F.; Krymskii, A. M.; Crider, D. H.; Acuna, M. H.; Connerney, J. E. P.; Hinson, D.; Barashyan, K. K.

257

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

258

Ionospheric variability over Japan  

NASA Astrophysics Data System (ADS)

The understanding of ionospheric variability is important for the user of ionospheric models. A satellite designer or operator needs to know not only monthly average conditions but also the expected deviations from these mean values. In order to contribute to the studies on ionospheric variability, in this paper values of critical frequencies of F2, F1 and E regions and M(3000)F2 factor measured at 4 Japanese stations are used. Data correspond to equinoxes, solstices, high and low solar activity. Quartiles and median values are used to specify variability, because they have the advantage of being less affected by large deviations that can occur during magnetic storms. The results are similar for the considered stations and show that the highest variability correspond to foF2. For March high solar activity the variability of fof2 decreases during hours of maximum ionisation. The M3000F2 factor, in general, shown low variability. Akita (39.72 N, 140.13 E) showed the highest variability for the three frequencies. Moreover, it can be seen that quartiles are not equidistant from the median value.

Ezquer, R. G.; Mosert, M.; Corbella, R.; Erazu, M.; de La Zerda, L.

259

Generation of artificial magnetic pulsations in the Pc1 frequency range by periodic heating of the Earths ionosphere: indications of ionospheric Alfvn resonator effects  

Microsoft Academic Search

A series of six experiments with the EISCAT HF heater device assisted by the EISCAT (European-Incoherent-Scatter) radar were carried out with the purpose of producing artificial magnetic pulsations in the 0.13 Hz frequency range. In only 3 of the 30 h of experiment time under a variety of ionospheric conditions was an artificial magnetic signal detected by ground-based magnetometers. A

T. Bsinger; T. Pashin; A. Kero; P. Pollari; P. Belyaev; M. Rietveld; T. Turunen; J. Kangas

2000-01-01

260

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; Brndstrm, B U E; Aso, T

2006-11-09

261

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

262

'Geomagnetic Disturbances, Solar Particle Events And Their Effects On The Lower Ionosphere based on Savnet Data  

NASA Astrophysics Data System (ADS)

Measurements performed by the VLF technique, using the South America VLF Network (SAVNET) are presented. The SAVNET project has been involved in the IHY activities (2004-2009) and since then in the International Space Weather Initiative (ISWI) program. Explosive solar events and emission of energetic particles have occurred in August 2011. The impacts on the upper atmosphere were observed through subionospheric propagation anomalies as seen in the temporal variations of the signal amplitude and phase recorded on long VLF-paths. Comparing quiet and disturbed days, the phase exhibited unusual higher values that might be associated with excesses of ionization in the lower ionosphere region. These and other aspects of these geomagnetic disturbances in the ionosphere will be further discussed.

Bertoni, Fernando; Raulin, Jean-Pierre

2012-07-01

263

Ionospheric solar flare effects monitored by the ground-based GPS receivers: Theory and observation  

Microsoft Academic Search

(1) The ionosphere responses to a solar flare observed by using ground-based receivers of the global positioning system (GPS) are investigated in this paper. Two quantities, the total electron content (TEC) and its time rate of change (rTEC), can be derived from the receivers. The theoretical studies show that the rTEC is related to the frequency deviation of the GPS

J. Y. Liu; C. H. Lin; Y. A. Liou

2004-01-01

264

Ionospheric solar flare effects monitored by the ground-based GPS receivers: Theory and observation  

Microsoft Academic Search

The ionosphere responses to a solar flare observed by using ground-based receivers of the global positioning system (GPS) are investigated in this paper. Two quantities, the total electron content (TEC) and its time rate of change (rTEC), can be derived from the receivers. The theoretical studies show that the rTEC is related to the frequency deviation of the GPS signals.

J. Y. Liu; C. H. Lin; H. F. Tsai; Y. A. Liou

2004-01-01

265

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

Microsoft Academic Search

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

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

1991-01-01

266

A high-latitude phenomenological model of auroral precipitation and ionospheric effects  

Microsoft Academic Search

A phenomenological approach was taken to model the behavior of the high latitude ionosphere in support of data generated by spectrophotometric images taken by satellites. The model, based on the collected particle precipitation data, incorporates expressions for the differential energy distribution and spatial extent and temporal variations of auroral electron precipitation in the 0.35 keV- 1 MeV range during substorm

K. L. Miller; R. R. Vondrak

1985-01-01

267

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

Microsoft Academic Search

Measurements have been made of the ionosphere during lightning storms using the incoherent scatter radar at Arecibo, Puerto Rico. Attempts were made to detect the expected increases in the D-region electron number densities, and possible changes in the plasma line echoes in the F-region. No D-region density changes were detected, to a limit of under 200\\/cc. This upper limit on

Robert L. Showen; Alexander Slingeland

1998-01-01

268

Investigation of seismo-ionospheric effects associated with Elazig and Van earthquakes in Turkey  

NASA Astrophysics Data System (ADS)

This report presents the specific features of TEC (total electron content of the ionosphere) behavior associated with earthquakes 08 March 2010 (Elaz?g, Mw 6.1) and devastating earthquake with M 7.3, occurred on 23 October 2011 in Van. For this purpose we used both the GPS TEC data from the nearest to the epicenter GPS-IGS stations and constructed TEC maps over Europe. The favorable circumstance for this analysis was the quiet geomagnetic situation during the period previous to the earthquakes (the sum of Kp didn't exceed 5 for first and less than 15 for second case). The typical anomaly was found out one week prior to Elaz?g earthquake and three days prior to Van earthquake as the day-time significant increase of TEC at the nearest stations up to the value of 50% relative to the background condition. To estimate the spatial dimensions of seismo-ionospheric anomaly the differential mapping method was used. Anomalous TEC enhancement was registered since 10 UT and reached the maximal value of 45-55% at 18-20 UT. So, the seismo-ionospheric anomaly was found out as the cloud-shaped increase of total electron content of the ionosphere, it had a well-defined local character and it was situated in the immediate vicinity of the earthquake epicenter area. Acknowledgments. The authors are grateful to the IGS community for providing GPS permanent data and to the USGS Earthquake Hazards Program for the detailed earthquake information. The research leading to these results has received funding from the European Union Sevenths Framework Program (FP7/20017-2013) under grant agreement No. 263502 - PRE-EARTHQUAKES project.

Shagimuratov, I.; Cherniak, Iu.; Zakharenkova, I.; Tepenitsyna, N.; Yakimova, G.

2012-04-01

269

Effects of the ionospheric convection measured by SuperDARN on the ground electric field at polar station Hornsund  

NASA Astrophysics Data System (ADS)

We investigate the effects of ionospheric convection on the ground-level DC electric field measured at polar station Hornsund (77.00 N, 35.55 E). We use the results of a SuperDARN (SuperDual Auroral Radar Network) potential mapping technique to obtain the electric potential due to the ionospheric convection over Hornsund and we analyse diurnal variations of this potential. These are compared with the diurnal variations of the vertical component of the electric field observed at Hornsund in fair-weather conditions where the effects of low atmosphere global electric field generators have been removed by assuming a diurnal change according to the Carnegie curve. We conclude that a 10 kV change in the overhead convection potential results in an average change of the ground field of 10%. We also conclude that SuperDARN observations and the potential mapping technique can be used for the subtraction of the effects of magnetospheric influences on the atmospheric electricity parameters in polar regions.

Odzimek, Anna; Kubicki, Marek; Lester, Mark; Grocott, Adrian

2013-04-01

270

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

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

271

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

272

Effects of solar activity variations on adiabatic heating and cooling effects in the nighttime equatorial topside ionosphere  

NASA Astrophysics Data System (ADS)

Data from the Defense Meteorological Satellite Program are used to examine solar activity variations in ion temperature measured near 800 km altitude across the nighttime equatorial ionosphere. Evidence for ion cooling and heating by adiabatic expansion and compression are seen during high and moderate solar activity conditions. It is found that these effects are strongly dependent on the location of the O+/H+ transition height. During high solar activity a high transition height moves the region of maximum cooling at the dip equator well above 800 km. The region of maximum heating, however, appears in the winter hemisphere near 800 km, where strong longitude variability is seen, owing to the effects of F region neutral winds. During moderate solar activity conditions the transition height is lowered, bringing the region of maximum cooling closer to 800 km altitude. However, the cooling process is not as strong as that seen during high solar activity periods. The heating effects are also lowered during moderate solar activity periods. At 800 km altitude, only relatively small temperature peaks are seen in the winter hemisphere, closer to the dip equator than those seen during high solar activity periods.

Venkatraman, Sarita; Heelis, Rod

1999-08-01

273

Radio wave propagation in a multiscale inhomogeneous ionosphere  

Microsoft Academic Search

Results of an experimental study of the structure of a multiscale inhomogeneous ionosphere and statistical characteristics of signal propagation are reported. A theory is developed for the propagation of radio signals of arbitrary power and polarization in an ionosphere containing multiscale inhomogeneities. The mechanisms responsible for the formation of nonlinearities in an inhomogeneous ionosphere under the effect of oblique-incidence high-intensity

Gennadii K. Solodovnikov; Viktor I. Novozhilov; Mars N. Fatkullin

1990-01-01

274

Presentation Order Effects in Product Taste Tests.  

ERIC Educational Resources Information Center

|Presentation order in paired-comparison testing was varied to measure the impact of primacy v recency effects on consumer product evaluation. First position preference bias characterized the findings, lending support to the attention decrement hypothesis or a suggested palate desensitization effect on subsequent taste trial behavior. (Author)|

Dean, Michael L.

1980-01-01

275

Ionospheric chemical releases  

SciTech Connect

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 modification by chemical releases excites artificial enhancements in airglow intensities by exothermic chemical reactions between the newly created plasma species. Numerical models have been developed to describe the creation and evolution of large scale (>l km) density irregularities and airglow clouds generated by artificial means. Experimental data compares favorably with these models. In general, we find that chemical releases produce transient, large amplitude perturbations in electron density which can evolve into fine scale irregularities via nonlinear transport processes.

Bernhardt, P.A.; Scales, W.A.

1990-10-01

276

The Ptolemaic Approach to Ionospheric Electrodynamics  

NASA Astrophysics Data System (ADS)

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

Vasyliunas, V. M.

2010-12-01

277

The Electrical Coupling Mechanism in the Ionosphere.  

National Technical Information Service (NTIS)

Since the longitudinal conductivity is at least four orders of magnitude higher than the transverse conductivities in the ionosphere, the geomagnetic field lines are ordinarily assumed to be electrical equipotential lines. With this assumption there would...

D. D. Fang

1967-01-01

278

HIGHER ORDER HARD EDGE END FIELD EFFECTS.  

SciTech Connect

In most cases, nonlinearities from magnets must be properly included in tracking and analysis to properly compute quantities of interest, in particular chromatic properties and dynamic aperture. One source of nonlinearities in magnets that is often important and cannot be avoided is the nonlinearity arising at the end of a magnet due to the longitudinal variation of the field at the end of the magnet. Part of this effect is independent of the longitudinal of the end. It is lowest order in the body field of the magnet, and is the result of taking a limit as the length over which the field at the end varies approaches zero. This is referred to as a ''hard edge'' end field. This effect has been computed previously to lowest order in the transverse variables. This paper describes a method to compute this effect to arbitrary order in the transverse variables, under certain constraints.

BERG,J.S.

2004-09-14

279

Time-dependent studies of the aurora - Effects of particle precipitation on the dynamic morphology of ionospheric and atmospheric properties  

Microsoft Academic Search

Roble's (1975) midlatitude diurnal model of the ionospheric F region is extended to include auroral processes and used to study the coupled time-dependent ionospheric and atmospheric processes associated with auroral events. Primary ionization rates and electron-production spectra due to aurorae are calculated and directly coupled into the secondary electron-transport portion of the ionospheric model; the coupled continuity equations include diffusion

R. G. Roble; M. H. Rees

1977-01-01

280

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 So Joo 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

281

The zonal EB plasma drift effects on the low latitude ionosphere electron density at solar minimum near equinox  

NASA Astrophysics Data System (ADS)

The F2-layer peak density, NmF2, and peak altitude, hmF2, which were observed by 12 ionospheric sounders during the 20 September 1964 geomagnetically quiet time period at solar minimum are compared with those calculated by the three-dimensional time-dependent theoretical model of the Earth's low and middle latitude ionosphere and plasmasphere. The modeled NmF2 are also compared with those measured during the geomagnetically quiet time periods of 12-15, 18-21, and 26 September 1964 to take into account observed day-to-day ionospheric variability. Major features of the data are reproduced by the model if the corrected HWM90 neutral wind is used. The changes in NmF2 due to the zonal EB plasma drift are found to be less than 20% in the daytime low latitude ionosphere. The model, which does not take into account the zonal EB plasma drift, underestimates night-time NmF2 up to the maximum factor of 2 at low geomagnetic latitudes. The night-time increase of NmF2 caused by the zonal EB plasma drift is less pronounced at -20 and 20 geomagnetic latitudes in comparison with that between -10 and 10 geomagnetic latitude. The longitude dependence of the calculated night-time low latitude influence of the zonal EB plasma drift on NmF2 is explained in terms of the longitudinal asymmetry in B (the eccentric magnetic dipole is displaced from the Earth's center and the Earth's eccentric tilted magnetic dipole moment is inclined with respect to the Earth's rotational axis), and the variations of the wind induced plasma drift and the meridional EB plasma drift in geomagnetic longitude. The difference between the hmF2 values calculated by including the effect of zonal EB drift and that obtained when it is excluded does not exceed 19 km in the low latitude ionosphere. Over the geomagnetic equator the zonal EB plasma drift produces the maximum increase in the electron density by a factor of 1.06-1.48 and 1.05-1.30 at 700 and 1000 km altitude, respectively, and this increase is not significant above about 1500 km. Changes in the vertical electron content, VEC, caused by the zonal EB plasma do not exceed 16% during the day, while the value of the night-time VEC is increased up to a factor of 1.4 due to this drift. The maximum effects of the zonal EB plasma drift on the night-time electron density derived from the model results corresponding to solar minimum and maximum are quite comparable.

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

2008-08-01

282

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 0823', Longitude 7745') 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

283

Ionospheric effects of the solar flares of September 23, 1998 and July 29, 1999 as deduced from global GPS network data  

Microsoft Academic Search

This paper presents data from first GPS measurements of global re- sponse of the ionosphere to solar flares of September 23, 1998 and July 29, 1999. The analysis used novel technology of a global detection of iono- spheric effects from solar flares (GLOBDET) as developed by one of the authors (Afraimovich E. L.). The essence of the method is that

284

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

285

Presentation Order Effects in Product Taste Tests  

Microsoft Academic Search

Presentation order in paired-comparison testing was varied to measure the impact of primacy versus recency effects on consumer product evaluations. Overall preference and product rating scores were gathered for 1196 male and female Ss aged 13-49 years in two consumer research studies covering 11 taste tests. First position preference bias characterized the findings, lending support to the attention decrement hypothesis

Michael L. Dean

1980-01-01

286

Ray trace calculation of ionospheric propagation at lower frequencies  

NASA Astrophysics Data System (ADS)

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

Reilly, Michael H.

2006-10-01

287

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

288

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

289

Magnetospheric control of the bulk ionospheric plasma  

SciTech Connect

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

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

1987-01-01

290

Modifying the ionosphere with intense radio waves.  

PubMed

The ionospheric modification experiments provide an opportunity to better understand the aeronomy of the natural ionosphere and also afford the control of a naturally occurring plasma, which will make possible further progress in plasma physics. The ionospheric modification by powerful radio waves is analogous to studies of laser and microwave heating of laboratory plasmas (20). " Anomalous" reflectivity effects similar to the observed ionospheric attenuation have already been noted in plasmas modulated by microwaves, and anomalous heating may have been observed in plasmas irradiated by lasers. Contacts have now been established between the workers in these diverse areas, which span a wide range of the electromagnetic spectrum. Perhaps ionospheric modification will also be a valuable technique in radio communications. PMID:17778050

Utlaut, W F; Cohen, R

1971-10-15

291

Modeling Ionospheric Outflows In Global Models (Invited)  

NASA Astrophysics Data System (ADS)

The magnetosphere contains a significant amount of ionospheric O+, particularly during geomagnetically active times. The presence of this ionospheric plasma has a notable impact on magnetospheric composition and processes. We present our methodology for including an ionospheric mass source into global models, and for tracking the consequences for the space environment system. An overview of our recent efforts is provided. In particular, we illustrate the effect that plasma of ionospheric origin can have on the magnetosphere by simulating extreme geospace events when the fraction of O+ is largest, and contrast those results with simulations of more moderate events. We also compare different techniques of modeling/tracking ionospheric outflow, and explore the implications for the storm-time ring current and magnetospheric magnetic field configuration.

Glocer, A.; Toth, G.; Fok, M. H.; Gombosi, T. I.; Welling, D. T.

2010-12-01

292

Texture effects of circularly ordered fibers.  

PubMed

Powder samples can show pronounced texture effects in X-ray scattering. Here, texture effects are described theoretically for circularly ordered fibers and shown experimentally for a special type of these fibers based on nanostructured silica. The systematic diffraction peak intensity dependences, observed with the tilting of the samples, fit well with the theoretical model proposed and can be used as an efficient detection method for circulite-type mesopore organization. Our investigations clearly emphasize the difficulties encountered in the interpretation of peak intensities in the X-ray scattering analyses because of pronounced texture effects. PMID:15945108

Marlow, Frank; Kleitz, Freddy; Wilczok, Ursula; Schmidt, Wolfgang; Leike, Ines

2005-07-11

293

A new coupled model of the ionosphere-magnetosphere interhemispheric dynamics  

NASA Astrophysics Data System (ADS)

The ionosphere is known to play a key role in the electrodynamics of the magnetosphere, but the interhemispheric asymmetries and the connexions between the two hemispheres along the closed magnetic field lines introduce a new feature, the interhemispheric dynamics, which may have a significant contribution to the overall equilibrium. In order to access this dynamics, we have built a new interhemispheric model of the ionosphere, issued from the TRANSCAR family of ionospheric models (Blelly et al., 2005) and based on a 16-moment approximation. This new code has the ability to be used at all latitudes, and as it was the case for the previous generation, it accounts for the magnetosphere electrodynamics in transport of the ionospheric species along the field lines. However, the core of the new model is the dynamical and consistent coupling of the ionospheric transport to the magnetospheric transport through the development of an interface with the magnetosphere model IMM (Hurtaud et al. 2007), which accounts for the interhemispheric asymmetries in the ionospheric electrodynamics. The TRANSCAR-IMM retroactive coupled system is a pseudo 3D ionosphere-magnetosphere model, coupling a 1D approach along the magnetic field lines (TRANSCAR) and a 2D approach in the magnetic equatorial plane (IMM). It has been ported to a parallel architecture based on the Message Passing Interface (MPI) that allows for the simulation of large computational domains. The system is used to study the seasonal asymmetries between the northern and southern hemispheres, the resulting transport and energy transfer and the coupled effects between the ionosphere and the magnetosphere for many different latitudes and solar illumination conditions. We will present this new model and the initial results we obtain on the interhemispheric dynamics in condition of asymmetries between the two hemispheres.

Amaya, J.; Marchaudon, A.; Peymirat, C.; Blelly, P.-L.

2012-04-01

294

Effects of ionospheric oxygen on the magnetopause boundary waves using a high-resolution multi-fluid MHD model  

NASA Astrophysics Data System (ADS)

Recent advances in numerical modeling of ionospheric oxygen in the magnetosphere have revealed a number of global effects. The presence of the heavy ion component was shown to influence substorm dynamics, plasma sheet pressure and composition, the rate and location of the night side reconnection. One of the effects that has long been argued to take place is the influence of oxygen plasma component on the development of magnetopause boundary waves due to Kelvin-Helmholtz (KH) instability. The argument is that the heavier ions increase the Alfven speed inside the magnetosphere thereby lowering the instability threshold. This argument is based on the linear stability analysis derived for a tangential discontinuity between two incompressible plasmas streaming past each other. However, our previously reported results using the multi-fluid Lyon-Fedder-Mobarry (MFLFM) model (Merkin, 2011) suggested that the presence of oxygen ions actually can stabilize the growth of KH waves in the simulation. In the present work we build upon these earlier results by developing a high-resolution version of the MFLFM model. With this new development we are able to better resolve the Low-Latitude Boundary Layer (LLBL) which appears to play an important role in the development of KH waves, not described by the aforementioned linear analysis. We study the dependence of KH waves on the density and temperature of oxygen ions in the magnetosphere, their effects on the properties of the LLBL, including its width and the degree to which it is populated by oxygen. To explore the wave activity in a more quantitative fashion, we analyze the spectral characteristics of the KH waves, including the spatial distribution and temporal evolution of the wave power. The ultimate question that we seek to answer is whether the ionospheric oxygen stabilizes or makes more intense the magnetopause boundary wave activity and under what conditions this occurs.

Lyon, J.; Merkin, V. G.

2011-12-01

295

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

296

Historical overview of HF ionospheric modification research  

SciTech Connect

Radio waves have inadvertently modified the Earth's ionosphere since the Luxembourg observations of Tellegen in 1933 and perhaps since Marconi in 1901. The history of ionospheric modification by radio waves is reviewed, beginning with Marconi, describing the Luxembourg effect and its explanations, and its early use to deduce the properties of the lower ionosphere in the 1930s. The measurements became more sophisticated in the 1950s, leading to the call for high-power high-frequency modification experiments in the upper ionosphere. Beginning in 1970, radio facilities became available of sufficient powers to induce changes in the ionospheric plasma detectable by a wide array of diagnostic instruments and techniques. A summary of these effects is presented based upon work up to 1990. These studies were originally motivated as a means of better understanding the natural ionosphere using a weak perturbational approach. However, a rich spectrum of nonlinear wave-plasma interactions was quickly discovered and ionospheric modification research became strongly motivated by issues in basic plasma physics. The ionosphere and near-Earth space are now exploited as an exceptional plasma laboratory-without-walls for the study of fundamental plasma processes requiring large spatial or temporal scales. Here we present a brief overview of these processes and phenomena, illustrated using results obtained from the Arecibo ionospheric modification facilities. The lessons learned and phenomena explored thus far offer many opportunities for controlling the ionospheric environment critical to many civilian and military telecommunications systems, both to disrupt systems normally operational and to create new propagation paths otherwise unavailable.

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

1990-10-01

297

Characterization of the Ionosphere Over the Murchison Radio Observatory  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

298

Electron-ion collision effects on the formation of prompt striations in the ionosphere  

NASA Astrophysics Data System (ADS)

Electron-ion collisions have been included in the analysis of electrostatic, purely growing, finite ion-gyroradius, flute instabilities generated by a loss cone distribution of energetic ions in the ionosphere. It is shown that the collisions not only reduce the growth rate below the value predicted by collisionless theory but also result in a second lower growth rate mode not found in collisionless theory. Although the electron-ion collision frequency is larger than the ion-gyrofrequency for the parameters of the Buaro barium release experiment, the growth rate of the linearly most unstable mode is not appreciably modified by the collisions from the value predicted from collisionless theory. Electron-ion collisions have a greater impact on the instability as the electron density is increased. Complete stabilization through electron-ion collisions requires densities in excess of 8.7 x 10 to the 7th per cu cm.

Sperling, J. L.; Krall, N. A.

1981-07-01

299

Analysis and numerical simulation of the effect of ion Pedersen mobility on ionospheric barium clouds  

NASA Astrophysics Data System (ADS)

Several aspects concerning the phenomenology of barium cloud striations still lack a satisfactory explanation. The motivation for the present investigation was an unexplained phenomenon known as 'freezing'. For the purposes of the current study, the term 'freezing' is defined to mean the cessation of bifurcation on the part of a specific ionospheric structure. A description is provided of a mechanism whereby the barium ions, and the local electron density enhancement which they represent, may cease bifurcating. It is attempted to show that the Pedersen leakage mechanism is a viable candidate for the cessation of further bifurcation in barium clouds. In addition, it is found that this mechanism can produce sheets of barium at late times.

Zalesak, S. T.; Fedder, J. A.; Ossakow, S. L.

1983-10-01

300

Observational evidence of sudden stratospheric warming effects on the equatorial ionospheric electric fields  

NASA Astrophysics Data System (ADS)

In this work we present strong evidence that during major sudden stratospheric warming (SSW) events the equatorial ionospheric electric fields exhibit a unique and distinctive daytime pattern. In three out of four major SSW events in the last few years when Jicamarca Radio Observatory (JRO) ExB measurements were available, we have observed an anomalous temporal variation of the equatorial vertical ExB drifts, showing a strong semidiurnal variation. The three events occurred during quiet to moderate magnetic conditions (December 2000, January 2003 and January 2008). The fourth strong SSW event in February 1999 does not show the semidiurnal pattern, but it coincides with a magnetically disturbed period. Our observations consists mainly of incoherent scatter radar (ISR) ExB drifts, JULIA radar drifts from 150-km echoes and data from magnetometers. In the three cases with anomalous ExB behavior, the patterns are observed in the daytime ISR drifts and in JULIA drifts and/or magnetometer data. Previous ExB statistics using more than 35 years of Jicamarca ExB drifts and few years of AE-E satellite data show that quiet ExB variability is particularly large during the December solstice and cannot be explained by other phenomena (such as magnetic activity). As the dayside electrodynamics at equatorial latitude is strongly dependent on neutral wind in the lower thermosphere and therefore driven by tidal influences, observations of semidiurnal anomaly in ExB drifts may indicate tidal modulation during SSW events. Large diurnal and semidiurnal variations could be created in high latitude mesosphere and lower thermosphere in association with SSWs as indicated by TIMEGCM simulations (Liu and Roble, 2002). However, observations of such variations at low latitude is an unexpected finding which might shed new light on sources and mechanisms of quiet-time ionospheric variability.

Chau, J. L.; Fejer, B. G.; Goncharenko, L. P.; Condor, P. J.

2008-12-01

301

Daily ionospheric forecasting service (DIFS) III  

NASA Astrophysics Data System (ADS)

The daily variability of the ionosphere can greatly affect HF or SATCOM communications. HF skywave operators plan frequency schedules months in advance, however, they also require daily knowledge of the ionospheric conditions in order to modify assignments. SATCOM operators also require daily information about the levels of scintillation, which are variations in phase, amplitude, polarisation and angle of arrival that can cause severe degradation of the received signal.

Using a number of ionosonde measurements and geomagnetic and solar values, a Daily Ionospheric Forecasting Service (DIFS) has been developed, which provides HF and SATCOM operators with daily forecasts of predicted ionospheric conditions. The system uses in-house algorithms and an externally developed Global Ionospheric Scintillation Model (GISM) to generate HF and SATCOM forecasts. HF forecasts consist of a past summary and a forecast section, primarily displaying observed values and predicted categories for the Maximum Usable Frequency (MUF), as well as an Ionospheric Correction factor (ICF) that can be fed into the ionospheric propagation prediction tool, WinHF. SATCOM forecasts give predictions of global scintillation levels, for the polar, mid and equatorial latitude regions. Thorough analysis was carried out on DIFS and the results conclude that the service gives good accuracy, with user feedback also confirming this, as well.

Butcher, N.

2005-12-01

302

Peak electron densities in Saturn's ionosphere derived from the low-frequency cutoff of Saturn lightning  

Microsoft Academic Search

Peak electron densities of Saturn's ionosphere determined at all local timesDiurnal variation of densities is 12 orders of magnitudeSolar EUV flux relates to electron densities in Saturn's ionosphere

G. Fischer; D. A. Gurnett; P. Zarka; L. Moore; U. A. Dyudina

2011-01-01

303

Irregular Component of Ionospheric Refraction.  

National Technical Information Service (NTIS)

The effect of small to medium scale ionospheric irregularities on the pointing accuracy of UHF radars is examined for mid- and high-latitude sites. Refraction and range errors are estimated for typical situations as well as their elevation dependence. Exa...

T. J. Elkins

1970-01-01

304

On the information content of ionospheric solar flare effect observations - II. Some model considerations on the interpretation of solar flare effects in the ionosphere  

Microsoft Academic Search

Analysis of records of LF sudden field anomaly (SFA) effects, together ; with the SOLRAD-9 records of the corresponding solar x-ray flare, shows that the ; quasi-phase height interpretation of the SFA effects is justified and that ; relatively simple model assumptions are able to provide a quantitative ; interpretation of these effects and their dependence on solar zenith angle

J. Taubenheim; G. Entzian; R. Knuth; K.-H. Ohle

1974-01-01

305

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

306

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

NASA Astrophysics Data System (ADS)

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

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

2010-10-01

307

VLF heating of the lower ionosphere  

SciTech Connect

A controlled wave-injection experiment with a 28.5 kHz transmitter having a radiated power of 100 kW has revealed evidence of ionospheric heating by the VLF waves. Calculations indicate that the observed effect can be attributed to the absorption of wave energy in the lower ionosphere, which is estimated to result in a 30% enhancement in the collision frequency at 85 km. This process also represents a new means of direct coupling of lightning energy to the lower ionosphere.

Inan, U.S. (Stanford Univ., CA (USA))

1990-05-01

308

Ionospheric Calibration for Low Frequency Arrays  

NASA Astrophysics Data System (ADS)

The Mileura Widefield Array is a next generation low frequency radio array which will be constructed in a radio-quiet zone in Western Australia. One of its primary goals is to observe signatures of the epoch of reionization. However, such measurements require highly accurate calibration of ionospheric effects to ensure precise removal of known foreground sources. We report on the efficacy of ionospheric calibration algorithms that are tailored to low frequency arrays whose spatial extent is less than the scale size of ionospheric disturbances. We also apply the techniques to simulations of EOR observations to estimate the magnitude and statistical properties of residual errors that will affect EOR measurements.

Ting, S. Y.; Doeleman, S. S.; Lonsdale, C. J.; Cappallo, R. J.

2005-12-01

309

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

NASA Astrophysics Data System (ADS)

There have been reports for many years that the ionosphere is very sensitive to seismic effects, and the detection of ionospheric perturbations associated with earthquakes (EQs) attracts a lot of attention as a very promising candidate for short-term EQ prediction. In this review we present a possible use of VLF/LF (very low frequency (3-30 kHz)/low frequency (30-300 kHz)) radio sounding of seismo-ionospheric perturbations. In order to avoid the overlapping with my own previous reviews, we first show some pioneering results for the Kobe EQ and we try to present the latest results including the statistical evidence on the correlation between the VLF/LF propagation anomalies (ionospheric perturbations) and EQs (especially with large magnitude and with shallow depth), medium-distance (6-8 Mm) propagation anomalies, the fluctuation spectra of subionospheric VLF/LF data (the effect of atmospheric gravity waves, the effect of Earth's tides, etc.), and the mechanism of lithosphere-atmosphere-ionosphere coupling. Finally, we indicate the present situation of this kind of VLF/LF activities going on in different parts of the globe and we suggest the importance of international collaboration in this seismo-electromagnetic study.

Hayakawa, Masashi

2011-12-01

310

A kinetic model of the ionospheric return currents  

NASA Astrophysics Data System (ADS)

We present a 1D kinetic model of the collisional low altitude auroral ionosphere: the electrons drift through a gas composed of ions and neutrals under the influence of a parallel electric field. We take into account electron/ion (e/i) and electron/electron (e/e) collisions. A Monte-Carlo method is used to simulate with the electron/neutral (e/n) collisions. In order to take into account the temporal evolution, we introduce a feedback on the electric field. We impose a current density and calculate the corresponding electric field. The current density is divergence free. We show that the Electron Distribution Functions (EDF) are non Maxwellian. We calculate an effective conductivity that takes into account the kinetic effects. The modelled conductivity is larger by 30% than the classical one. This work reveals the importance of kinetic models and gives access to the conductivity profile, which are useful to study the ionospheric currents.

Garcia, G.; Forme, F.

2009-10-01

311

Magnetospheric disturbances associated with the 13 December 2006 solar flare and their ionospheric effects over North-East Asia  

NASA Astrophysics Data System (ADS)

We present an observational study of magnetospheric and ionospheric disturbances during the December 2006 intense magnetic storm associated with the 4?/?3.4 class solar flare. To perform the study we utilize the ground data from North-East Asian ionospheric and magnetic observatories (60-72N, 88-152E) and in situ measurements from LANL, GOES, Geotail and ACE satellites. The comparative analysis of ionospheric, magnetospheric and heliospheric disturbances shows that the interaction of the magnetosphere with heavily compressed solar wind and interplanetary magnetic field caused the initial phase of the magnetic storm. It was accompanied by the intense sporadic E and F2 layers and the total black-out in the nocturnal subauroral ionosphere. During the storm main phase, LANL-97A, LANL 1994_084, LANL 1989-046 and GOES_11 satellites registered a compression of the dayside magnetosphere up to their orbits. In the morning-noon sector the compression was accompanied by an absence of reflections from ionosphere over subauroral ionospheric station Zhigansk (66.8N, 123.3E), and a drastic decrease in the F2 layer critical frequency (foF2) up to 54% of the quite one over subauroral Yakutsk station (62N, 129.7E). At the end of the main phase, these stations registered a sharp foF2 increase in the afternoon sector. At Yakutsk the peak foF2 was 1.9 time higher than the undisturbed one. The mentioned ionospheric disturbances occurred simultaneously with changes in the temperature, density and temperature anisotropy of particles at geosynchronous orbit, registered by the LANL-97A satellite nearby the meridian of ionospheric and magnetic measurements. The whole complex of disturbances may be caused by radial displacement of the main magnetospheric domains (magnetopause, cusp/cleft, plasma sheet) with respect to the observation points, caused by changes in the solar wind dynamic pressure, the field of magnetospheric convection, and rotation of the Earth.

Zolotukhina, N.; Polekh, N.; Kurkin, V.; Pirog, O.; Samsonov, S.; Moiseyev, A.

2012-03-01

312

The effects of Corotating interaction region/High speed stream storms on the thermosphere and ionosphere during the last solar minimum  

NASA Astrophysics Data System (ADS)

Geomagnetic storms at solar minimum are driven by the interaction between high speed streams and low speed streams (Corotating Interactions regions/High Speed StreamsCIR/HSSs- this includes both the CIR part of the storm and the HSS part as both has effects on the thermosphere and ionosphere), rather than by Coronal Mass Ejections (CMEs). Solar minimum storms are generally of smaller amplitude, but they also have other characteristics that affect the response of the thermosphere/ionosphere (TI) system to them. We explore both the background upper atmosphere and the characteristics of these CIR/HSS events in 2008 using both models and data. The model data comparisons were good, showing mid-latitude positive storm effects on NmF2 on the day of the storm and long, extended periods of storm induced changes on the following days. Generally, the version of the NCAR-TIEGCM (National Center for Atmospheric Research-Thermosphere Ionosphere Electrodynamics Model) run with the Heelis convection pattern was in better agreement with the data than the version run with the Weimer convection pattern. We attribute this difference in the response of the two versions of the NCAR-TIEGCM to the fact that the precipitation we associate with the Heelis model has been tuned to better represent observed precipitation over many years, whereas such tuning has just begun for the version of the NCAR-TIEGCM that uses the Weimer model. Physically, the most important conclusion that we draw is the CIR/HSS events can have significant effects on the ionosphere and thermosphere for several days after the CIR has ended. While CIR/HSS events are normally weaker than CME events, the effects of the latter normally disappear in a day or two. Thus the effects of CIR/HSS events may be comparable to those of CME events for some fields, notably neutral density changes.

Burns, A. G.; Solomon, S. C.; Qian, L.; Wang, W.; Emery, B. A.; Wiltberger, M.; Weimer, D. R.

2012-07-01

313

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

314

Equatorial ionospheric bubble precursor  

Microsoft Academic Search

A time-dependent nonlinear three-dimensional model for the evolution of the equatorial bottomside lower ionosphere in the presence of dissipating gravity waves has been developed. From the numerical solution of the model, it is found that large bottomtype F-region ionospheric density perturbations and electric fields can be driven by dissipating gravity waves from tropospheric sources. The spatial distribution of the ionospheric

M. J. Keskinen

2010-01-01

315

Radar Ionospheric Impact Mitigation  

Microsoft Academic Search

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

G. Bishop; D. Decker; C. Baker

2006-01-01

316

Variation of the Martian Ionosphere from Mars Express Ionospheric Sounding  

NASA Astrophysics Data System (ADS)

In its five years of operation, the MARSIS ionospheric sounder on board the Mars Express spacecraft has collected a large data set concerned with variations in the Martian ionosphere. In this paper, we shall review three separate topics addressed by these data. The Martian ionopause, similar to the ionopause at Venus, has been detected and studied using two methods available to MARSIS. In addition to direct detection using the local electron density, the ionopause is occasionally clearly visible is the remote sounding data as a distinct shelf-like structure. We have shown that the ionopause at Mars definitely exists but sporadically and less frequently than at Venus. The second topic to be presented is a multi-instrument detection of flux ropes at Mars. MARSIS is able to detect spacecraft-local magnetic fields when Mars Express is at altitudes below the magnetic pileup boundary. In two cases where the orbit of Mars Express closely coincides with that of Mars Global Surveyor (MGS), a strong magnetic field strength has been observed in the MARSIS data in regions where effects of the crustal magnetic fields are not expected. The MGS magnetometer data have been analyzed by the minimum variance technique to show that the magnetic field rotates in a manner characteristic of a magnetic flux rope. These data have been analyzed together to extract the motion of the flux rope. The third topic is the detection of an enhanced state of fluctuation of the Martian ionosphere in the region near the planetary terminator in regions of strong crustal magnetization. These measurements are based on the ionospheric traces that are the principal product of the MARSIS ionospheric sounder. The variance of the motion of the ionosphere has been computed for approximately 40,000 times during nearly 500 orbits and mapped on the sunward face of Mars. We have found that the enhanced fluctuations show a moderate increase when the solar wind pressure is high and when the solar wind and crustal magnetic fields are oppositely directed. The latter condition suggests that magnetic reconnection may be involved in these near-terminator ionospheric fluctuations.

Morgan, D. D.; Gurnett, D.; Duru, F.; Akalin, F.; Leisner, J. S.; Brain, D. A.

2010-05-01

317

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

318

Global ionospheric total electron content mapping using the global positioning system  

NASA Astrophysics Data System (ADS)

Space-based radio navigation systems such as the Navstar Global Positioning System (GPS) can provide us with a unique opportunity to study the effect of the ionosphere as the signals propagate from the satellites to the GPS receivers. Based on a modified version of UNB's DIPOP software package, I developed an algorithm to produce regional or global total electron content (TEC) maps on an hourly basis using dual frequency-GPS observations from stations of the International GPS Service for Geodynamics (IGS). The algorithm uses a spatial linear approximation of the vertical TEC above each IGS station using stochastic parameters in a Kalman filter estimation to describe the local time and geomagnetic latitude dependence of the TEC. I used a new concept to take into account the temporally and spatially varying ionospheric shell height as opposed to a commonly adopted fixed shell height. I demonstrated that the UNB algorithm was capable of modelling the diurnal variation of TEC even during a geomagnetic storm period. I also have modified the International Reference Ionosphere 1995 (IRI-95) model to update its coefficient sets using the UNB GPS-derived regional ionospheric maps, based on a 5 week long GPS campaign, in order to provide more precise IRI-95-derived ionospheric delay predictions for e.g., single frequency GPS receivers. I enhanced the UNB algorithm to estimate ionospheric model parameters from a global set of GPS stations to independently produce hourly snapshots of the global ionosphere. The previously modified IRI-95 model as a sophisticated interpolator was used between two GPS- derived TEC updates to provide improved IRI-95 ionospheric delay predictions. During the update procedure, I enhanced the IRI-95 model with an empirical plasmaspheric electron content model. Based on 3 days' worth of global GPS data during a medium solar activity period in 1993 (33 IGS stations for each day) there was better than a 9 TECU level (1 sigma) agreement in the TEC on a global scale with TOPEX/Poseidon-derived (T/P) TEC data. For a low solar activity 1995 data set (74 IGS stations for each day), the UNB results showed an agreement with the T/P data at better than the 5 TECU level (1 sigma). The UNB global ionospheric TEC modelling technique in conjunction with the IRI-95 update procedure has been demonstrated to be a viable alternative to provide independently-derived ground-based ionospheric delay corrections for single frequency applications such as single frequency radar altimeter missions.

Komjathy, Attila

319

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

320

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

SciTech Connect

The great geomagnetic storm of March 13, 1989 caused severely anomalous behavior in the equatorial and low latitude ionosphere in the Brazilian longitude sector. The ionograms over Fortaleza indicated F region upward plasma drifts exceeding 200 m s{sup {minus}1} at 1,830 LT as compared to normal values of 40 m s{sup {minus}1} for this epoch. Large negative phases were observed in foF2 over Fortaleza and Cachoeira Paulista and in total electron content measured over Sao Jose dos Campos. The equatorial ionization anomaly was totally absent either because of its anomalous expansion to higher latitudes or because of inhibition of its development on the two nights following the storm. Many anomalous variations in F region peak density and height, occurring simultaneously with sharp variations on H component of magnetic field over Fortaleza and with auroral substorms, give strong evidence of penetration of magnetospheric electric fields to equatorial and low latitudes. Auroral type sporadic E and night E layers are observed after 1,830 LT over Cachoeira Paulista, the latter showing peak electron density of about 6 {times} 10{sup 4} el cm{sup {minus}3}, therefore comparable to the E layer peak density in the morning hours at that station. The Fortaleza ionograms show the presence of the F1 layer at night, a phenomenon that has never been observed over our two stations before. The role played by electric fields penetrating from high to low latitudes, particle precipitation, and composition changes in explaining the observations is discussed.

Batista, I.S.; De Paula, E.R.; Abdu, M.A.; Trivedi, N.B. (Inst. Nacional de Pesquisas Espaciais (Brazil)); Greenspan, M.E. (Boston Univ., MA (United States))

1991-08-01

321

Frequency characteristics of the action of powerful radio-frequency radiation on the ionospheric F layer  

SciTech Connect

The results of an investigation of the effect of artificial ionospheric nonuniformities on the characteristics of LFM signals with vertical and oblique sounding of the ionosphere are presented. A classification of the effects observed on ionograms from vertical and oblique-sounding LFM ionosonde, owing to the effect of artificial nonuniformities of different scale, is given. It was found that powerful beams of radio waves have a characteristic effect on the ionospheric plasma under conditions when moving ionospheric disturbances appear.

Erukhimov, L.M.; Ivanov, V.A.; Mityakov, N.A.; Uryadov, V.P.; Frolov, V.A.; Shumaev, V.V.

1988-03-01

322

VLF heating of the lower ionosphere  

Microsoft Academic Search

A controlled wave-injection experiment with a 28.5 kHz transmitter having a radiated power of 100 kW has revealed evidence of ionospheric heating by the VLF waves. Calculations indicate that the observed effect can be attributed to the absorption of wave energy in the lower ionosphere, which is estimated to result in a 30% enhancement in the collision frequency at 85

Umran S. Inan

1990-01-01

323

DEMETER Observations of Equatorial Plasma Depletions and Related Ionospheric Phenomena  

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

324

Ionospheric Imaging from Geostationary Orbit  

NASA Astrophysics Data System (ADS)

An ultraviolet imager is under development to image the ionosphere and thermosphere from geostationary orbit. The instrument will consist of two telescopes, one with a filter wheel to measure the atomic oxygen airglow emission at 130.4 nm and 135.6 nm and molecular nitrogen Lyman-Birge-Hopfield bands near 142.5 nm. The second telescope will image the atomic oxygen ion resonance multiplet at 83.4 nm. Both telescopes will have a field of regard of 1.5 degrees with resolutions of 0.01 degrees providing spatial coverage of 1500 km x 1500 km with a resolution of 10 km x 10 km. The telescopes will be mounted to a two-axis gimbal to image various regions of the disk and limb of the Earth. This instrument is tentatively planned to fly aboard an Air Force Space Test Program satellite in 2005. The primary science goals of the experiment are to image the nightside ionosphere using measurements of the OI 135.6 nm nightglow produced from radiative recombination of electrons with oxygen ions. These observations will be used to study the variability and dynamics of ionospheric irregularities. Secondary objectives include measurement of vertical profiles of electron density at night on the limb of the Earth and measurement of dayside oxygen ion profiles using the 83.4 nm resonant line. Additional objectives include: measurement of the dayside limb profiles of neutral density; studies of thermospheric heating and geomagnetic storms using observations of disk ratios of oxygen to nitrogen; studies of the morphology of the equator-ward edges of the aurora. It is anticipated that nightside ionospheric images can be obtained within 100 to 1000 seconds to allow high time resolution studies of the space weather effects in the ionosphere.

McCoy, R. P.; Wood, K. S.; Dymond, K. F.; Thonnard, S. E.

2001-05-01

325

Magnetosphere-ionosphere coupling during plasmoid evolution: First results  

SciTech Connect

The influence of magnetosphere-ionosphere coupling on the dynamic evolution of the magnetotail is investigated by a three-dimensional resistive MHD code that includes the effects of the closure of field-aligned currents in a simple resistive model ionosphere. Particular emphasis is on the role of this coupling during substorm evolution and the modification of the latter by the convection driven by the ionospheric electric fields. For comparison, the authors present results from a simulation which uses an infinitely conducting ionosphere but is otherwise identical. Comparison of the two simulations shows that the major impact of magnetosphere-ionosphere communication is an acceleration of magnetotail evolution. Otherwise, phenomena in the two models are qualitatively similar. They conclude that ionospheric effects do not significantly affect substorm associated magnetotail dynamics.

Hesse, M.; Birn, J. (Los Alamos National Lab., NM (USA))

1991-07-01

326

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

NASA Astrophysics Data System (ADS)

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

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

2007-05-01

327

Regional improvement of IRI extracted ionospheric electron density by compactly supported base functions using GPS observations  

NASA Astrophysics Data System (ADS)

The ionospheric electron density provides valuable information as to the ongoing physical processes in this part of the atmosphere and is important parameter to cancel the ionospheric effect in positioning computation. Empirical models such as IRI just provide coarse forecasts of the ionospheric electron density values. Nowadays, GPS and other GNSS systems has become a common tool for analyzing the Earth?s atmosphere. Spherical harmonic expansions are used for global modeling of the ionospheric electron density. Spherical harmonics are global support functions. Furthermore, their efficient application requires regularly distributed data on the globe. In this paper, regional four-dimensional electron density is estimated from IRI and Iranian Permanent GPS Network (IPGN) data in order to improve the empirical models accuracy. The electron density is decomposed into reference and correction parts. The reference part is taken from the IR-I2007 model. Due to the localizing feature of B-spline functions, Euclidean quadratic B-splines and tensor-products is used to model the correction term with respect to longitude, latitude and time. EOFs are used to account for the vertical gradient of the electron density in the correction. Ionosonde direct measurements of ionospheric electron density are used for validating the modeling result.

Amerian, Yazdan; Hossainali, Masoud Mashhadi; Voosoghi, Behzad

2013-01-01

328

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

329

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

NASA Astrophysics Data System (ADS)

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

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

2007-10-01

330

Effects of solar X-ray flares in the E region ionosphere of Mars: First model results  

NASA Astrophysics Data System (ADS)

We have used radio occultation data obtained from Mars Global Surveyor (MGS) at high latitudes (65.3-65.6N, 69.3-69.6N and 76.4-77.5N) to study the effects of X-ray flares and CMEs on Total Electron Content (TEC) in the E region of the Martian ionosphere in response to solar events that occurred on 29 and 31 May 2003 and on 17 January and 13 May 2005. Modeling of flare induced solar X-ray fluxes, ion production rates, electron densities and TEC are carried out, in each case based on GOES data. The estimated TEC values are compared with the in situ MGS observations. It is found that solar flare caused enhancements in the TEC of Mars by a factor of 5. Also, a 3D kinetic solar wind model (Hakamada-Akasofu-Fry Version 2/HAFv.2) is used to predict the arrivals of CME shocks at Mars associated with the flare event of May 2005. These predicted shock arrivals were associated with in situ enhancements in TEC by a factor of 2.

Haider, S. A.; McKenna-Lawlor, S. M. P.; Fry, C. D.; Jain, Rajmal; Joshipura, K. N.

2012-05-01

331

Influence of interplanetary solar wind sector polarity on the ionosphere  

NASA Astrophysics Data System (ADS)

Knowledge of solar sector polarity effects on the ionosphere may provide some clues in understanding of the ionospheric day-to-day variability and "hysteresis" effect on foF2. Ionospheric response to changes in solar sector polarity has not been fully documented previously, partly due to the limitation of observations. In this study, a solar-terrestrial connection ranging from solar sector boundary (SB) crossings, geomagnetic disturbances and ionospheric perturbations has been demonstrated. The increases in interplanetary solar wind speed within three days are seen after SB crossings, while the decreases in solar wind dynamic pressure and magnetic field intensity immediately after SB crossings are confirmed by the superposed epoch analysis results. Furthermore, the interplanetary magnetic field (IMF) Bz component turns from northward to southward in March equinox and June solstice as the Earth passes from a solar sector of outward to inward directed magnetic fields, whereas the reverse situation occurs for the transition from toward to away sectors. The IMF Bz component for the same solar sector polarity has opposite signs between March equinox and September equinox, and also between June solstice and December solstice. In order to know how the ionosphere reacts to the interplanetary solar wind variations linkage of SB crossings, the F2 region critical frequency (foF2) covering about four solar cycles and total electron content (TEC) during 1998-2011 are utilized to extract the related information, revealing that they are not modified significantly and vary within the range of 15% on average. The responses of the ionospheric TEC to SB crossings exhibit complex temporal and spatial variations and have strong dependencies on season, latitude, and solar cycle. This effect is more appreciable in equinoctial months than in solstitial months, which is mainly caused by larger southwardBzcomponents in equinox. In September equinox, latitudinal profile of relative variations of foF2 at noon is featured by depressions at high latitudes and enhancements in low-equatorial latitudes during IMF away sectors. The negative phase of foF2 is delayed at solar minimum relative to it during other parts of solar cycle, which might be associated with the difference in longevity of major interplanetary solar wind drivers perturbing the Earth's environment in different phases of solar cycle.

Liu, Jing; Liu, Libo; Zhao, Biqiang; Wan, Weixing

2012-08-01

332

Ionospheric convection driven by NBZ currents  

NASA Astrophysics Data System (ADS)

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.

1987-05-01

333

Wenchuan Earthquake Ionospheric Precursors: Modeling and Experiment  

NASA Astrophysics Data System (ADS)

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

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

334

Effect upon universal order of Hubble expansion  

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

335

Observations of Ionospheric Currents at Mars  

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

336

Ionospheric response to traveling convection twin vortices  

SciTech Connect

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

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

1994-08-15

337

The high-latitude ionosphere  

Microsoft Academic Search

This paper reviews information on the high-latitude ionosphere derived from the Alouette-ISIS program. It is primarily descriptive and deals mainly with F-region features. Particle effects in the D region and night E ionization are briefly considered. F-region features include the main trough, maxima and minima in electron density in the polar region, and electron-density irregularities revealed by the presence of

D. H. Jelly; L. E. Petrie

1969-01-01

338

Statistical study of Subauroral Polarization Streams (SAPS): Solar wind, ionospheric control and its effect on the thermosphere  

NASA Astrophysics Data System (ADS)

The effects of cross-polar cap potential (CPCP) and subauroral flux tube-integrated conductivity on the spatial distribution of Subauroral Polarization Streams (SAPS) have been investigated by using DMSP observations. For higher flux tube-integrated conductivity the SAPS tend to occur more poleward than for lower conductivity. The CPCP averaged over 15 min prior to the SAPS correlates best with the SAPS peak velocities. The high-latitude CPCP has a stronger effect on SAPS velocities for low integrated conductivity than for high conductivity. With coordinated CHAMP and DMSP observations we have further investigated the relationship between SAPS, ionospheric Hall current (electrojet), upper thermospheric zonal wind, and mass density at subauroral regions in the dusk and premidnight sectors. For comparison, we have also analyzed the same parameters as a function of magnetic latitude (30-80 magnetic latitude) during nonSAPS periods. Both neutral and plasma velocities peak at the same latitude regardless of SAPS occurrence. The neutral wind during SAPS events gets enhanced by a factor of 1.5/1.2 for Kp<4 and 1.3/1.9 for Kp?4 in the Northern/Southern Hemisphere, respectively, as compared to nonSAPS time. The velocity difference between plasma drift and neutral wind is also larger during SAPS period than during nonSAPS period, and the difference tends to increase with increasing geomagnetic activity. The peak latitude of the eastward auroral electrojet appears 1.5 poleward of SAPS during SAPS events, confirming the formation of SAPS equatorward of the high conductivity channel. The upper thermosphere is heated during SAPS periods. As a result we observe a 10% enhanced mass density at 400 km altitude with respect to periods without SAPS. In addition a density anomaly peak occurs collocated with the SAPS, displaced from the electrojet peak. We regard this as an indication for efficient thermospheric heating by ion neutral friction.

Wang, H.; Luhr, H.; Ridley, A. J.; Ma, S.

2011-12-01

339

Solar wind-magnetosphere-ionosphere coupling at Jupiter  

NASA Astrophysics Data System (ADS)

A fundamental property of planetary magnetospheres, which varies from planet to planet, is the dynamical influence of either the solar wind and its embedded interplanetary magnetic field (IMF) or of the rotation of the planet. Jovian magnetospheric dynamics are mainly dominated by the combination of rapid planetary rotation and the outflow of material originating from the moon Io, orbiting deep within the magnetospheric cavity. The outward radial transport of this plasma results in the breakdown of corotation at all local times, which in turn sets up a large-scale magnetosphere-ionosphere coupling current system. The main auroral oval in Jupiter's polar ionosphere appears fixed with respect to the planet, an indication of planetary control, and is understood to be associated with this large-scale magnetosphere-ionosphere coupling, and the transfer of angular momentum from the ionosphere to the middle magnetosphere plasma. Jupiter's polar auroral emissions, however, which include all auroral emission lying poleward of the main auroral oval, are ordered by magnetic local time, indicating external control by the solar wind interaction with the jovian magnetosphere. We have recently considered the flows present in Jupiter's ionosphere in terms of three different flow regimes: the sub-corotational flows associated with the main auroral oval, the Vasyliunas cycle associated with the down-tail loss of plasmoids (predominantly a feature of the dusk-side magnetosphere), and the Dungey-cycle flows which are associated with the interaction of the solar wind and embedded interplanetary magnetic field with the magnetosphere, principally via reconnection. Motivated by this picture, we consider from a theoretical standpoint what the effects of pulsed dayside magnetic reconnection will be at Jupiter. This will generate a twin-vortical flow pattern in the ionosphere across the open-closed field line boundary, associated with a bi-polar (i.e. upward and downward) field-aligned current pair. Here we discuss the conditions under which such currents may be carried in either magnetospheric or cusp plasmas, and consider the consequences for auroral emissions at UV and X-ray wavelengths.

Bunce, E. J.

340

The E and F Region Ionospheric Response to Solar Flares: 1. Effects of Approximations of Solar Flare EUV Fluxes  

Microsoft Academic Search

SOLRAD and many other satellite systems have provided a large data base showing the time-dependent behavior of broadband solar fluxes in the X ray and EUV spectral regions. These bands are broad in the sense that one band may contain many ionospherically important spectral lines. We present results of tests performed to determine how this information can best be used

John T. Mariska; Elaine S. Oran

1981-01-01

341

Thermal ion flows in the topside auroral ionosphere and the effects of low-altitude, transverse acceleration  

Microsoft Academic Search

Topside ionospheric profiles are used to study the upward field-aligned flow of thermal O(+) at high latitudes. On the majority of the field lines outside the plasmasphere, the mean flux is approximately equal to the mean polar wind measured by spacecraft at greater altitudes. This is consistent with the theory of thermal light ion escape supported, via charge exchange, by

M. Lockwood

1982-01-01

342

Major magnetic storm of March 13-14, 1989 and associated ionosphere effects. (Reannouncement with new availability information)  

Microsoft Academic Search

The geomagnetic storm of March 1989 was the largest geomagnetic storm of the decade and one of the largest of the century. The authors review many of the `high-latitude` ionospheric observations that were made during this storm. Most of the data presented here comes from the polar-orbiting satellites of the Defense Meteorological Satellite Program (DMSP) series. A review of the

F. J. Rich; W. F. Denig

1993-01-01

343

Source mechanisms and radio effects of ionospheric plasma. Annual report, 1 October 1991-30 September 1992  

Microsoft Academic Search

Since October 1, 1991 experimental and theoretical research has been conducted by Prof. Min-Chang Lee and his students at BU and MIT. This research work is aimed at investigating the ionospheric plasma disturbances which can affect significantly the radio wave propagation in communications and space surveillance. The research topics which have been investigated include: (1) A source mechanism leading to

1992-01-01

344

The Utah State University GaussMarkov Kalman filter of the ionosphere: The effect of slant TEC and electron density profile data on model fidelity  

Microsoft Academic Search

The Utah State University (USU) GaussMarkov Kalman filter (GMKF) of the ionosphere uses the Ionosphere Forecast Model (IFM) to provide the background ionosphere, and a Kalman filter using GaussMarkov relaxation to specify deviations from this background. The USU GMKF can assimilate up to four different types of data: total electron content (TEC) determined from various ground stations and global positioning

D. C. Thompson; L. Scherliess; J. J. Sojka; R. W. Schunk

2006-01-01

345

Ionospheric convection driven by NBZ currents  

SciTech Connect

Computer simulations of Birkeland currents and electric fields in the polar ionosphere during periods of northward interplanetary magnetic field (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% 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. The effects of varying ionospheric conductivity were studied by considering both a constant voltage source and a constant current source. Conductivity gradients due to seasonal and local time variations in solar production were considered, as well as gradients due to electron precipitation. 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. Copyright American Geophysical Union 1987.

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

1987-05-01

346

Ionospheric and geomagnetic radiowave interference. (Latest citations from the INSPEC database). Published Search  

SciTech Connect

The bibliography contains citations concerning ionospheric radiowave propagation and scattering, atmospheric radio noise, radiofrequency interference, and ionospheric electron density profile. Radio signal attenuation and interference, mechanisms of ionospheric propagation, magnetospheric phenomena, seasonal and phase variations, and multipath effects are also presented. (Contains a minimum of 124 citations and includes a subject term index and title list.)

NONE

1995-01-01

347

Ionospheric and geomagnetic radiowave interference. (Latest citations from the INSPEC database). Published Search  

SciTech Connect

The bibliography contains citations concerning ionospheric radiowave propagation and scattering, atmospheric radio noise, radiofrequency interference, and ionospheric electron density profile. Radio signal attenuation and interference, mechanisms of ionospheric propagation, magnetospheric phenomena, seasonal and phase variations, and multipath effects are also presented. (Contains 50-250 citations and includes a subject term index and title list.) (Copyright NERAC, Inc. 1995)

NONE

1996-04-01

348

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

349

Radiowave Imaging of Ionospheric Electron Dynamics  

Microsoft Academic Search

This dissertation is a study of disturbances in the polar ionosphere. A relative ionospheric opacity meter (riometer) is a radio frequency instrument that enables the remote sensing of ionospheric disturbances by recording variations in the cosmic radio noise power received at a terrestrial antenna. The Imaging Riometer for Ionospheric Studies (IRIS) produces images of relative ionospheric opacity. In the ionosphere,

Gregory Hugh van Bavel

1998-01-01

350

Upper Atmosphere and Ionosphere of Mars  

Microsoft Academic Search

It is argued that the single-layer ionosphere at 125 kilometers discovered in the Mariner IV occultation experiment is an F1 region coinciding with the ultraviolet photoionization peak. The CO2 density there must be of the order of 1011 molecules per cubic centimeter. Such a density is consistent with the properties of the lower atmosphere by Mariner IV and the temperature

T. M. Donahue

1966-01-01

351

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

352

A study of the magnetosphere-ionosphere-thermosphere coupling and its impact on lower latitude ionosphere  

NASA Astrophysics Data System (ADS)

The Coupled Magnetosphere-Ionosphere-Thermosphere CMIT model is the geospace component of the Center for Integrated Space weather Modeling CISM suite of Sun-to Earth models The CMIT model includes the Lyon-Fedder-Mobarry LFM global MHD code and the National Center for Atmospheric Research NCAR -Thermosphere- Ionosphere-Electrodynamic Global Circulation Model TIEGCM These two models are coupled by exchanging information about electric fields particle precipitation ionospheric conductance and neutral-wind -generated field-aligned currents at high latitudes The CMIT model has been run to simulate the geospace response to the April 2004 geomagnetic storm We investigate global neutral wind variations during the storm changes in the dynamo field induced by these variations and their effects on ionospheric F region electron densities Large changes are seen in these fields during this storm

Wang, W.; Solomon, S. C.; Wiltberger, M.; Burns, A. G.; Richmond, A. D.; Foster, B. T.; Killeen, T. L.; Lyon, J. G.

353

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

SciTech Connect

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

Filho, C.A.

1990-12-01

354

Novel Modeling of Mars' Ionospheric Electrodynamics  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

355

Ionosphere plasma radio-noises and magnetosphere alfven resonator  

NASA Astrophysics Data System (ADS)

Observations of the ionosphere noises during direct or magnetically conjugated solar eclipses on 1999, 2001, 2002, 2003 let us conclude that one of the effects of the solar eclipse is appearance of ionosphere radionoise quasi-periodic burst trains. The train starts within ten seconds after radio-noise impulse and lasts up to 5 min. The same type trains may be detected in the absence of the eclipse but 5-10 times more rarely (once per 3-5 hours of measurements). The possible explanation of trains arising consists in forming of the magnetosphere Alfven resonator after warming of the ionosphere by the energetic particles precipitated from the magnetosphere into both magnetically conjugated points. The movement of the total eclipse phase from the morning terminator to the evening terminator is the strong source of the Alfven waves. Precipitations may be caused by wave-particle interaction in the top point of the force tube. It is known that during eclipse the ionization sources in E-region of ionosphere appears. So, schematic explanation of the phenomena is: lunar shadow in the ionosphere -> ionosphere irregularity -> Alfven wave -> wave-particle interaction -> precipitations into both hemispheres of ionosphere -> impedances violation -> creation of ionosphere resonator plate -> appearance of magnetosphere Alfven resonator -> precipitation feeds resonator plates. From out measurements follows that at 100 km altitude (E-region of ionosphere) plate size is > 10 km and the resonance frequency of plate oscillations or frequency of the diffuse precipitation may be estimated as 0,20 - 0,60 Hz. For 5 min resonator gets completely exhausted. All particles precipitate into ionosphere and ionosphere resonator plate disappears.

Musatenko, S.; Musatenko, Yu.; Kurochka, E.; Choliy, V.; Lastochkin, A.; Slipchenko, O.

356

Changes in the Earth's magnetic field over the past century: Effects on the ionosphere-thermosphere system and solar quiet (Sq) magnetic variation  

NASA Astrophysics Data System (ADS)

We investigated the contribution of changes in the Earth's magnetic field to long-term trends in the ionosphere, thermosphere, and solar quiet (Sq) magnetic variation using the Coupled Magnetosphere-Ionosphere-Thermosphere (CMIT) model. Simulations with the magnetic fields of 1908, 1958, and 2008 were done. The strongest differences occurred between ~40S-40N and ~100W-50E, which we refer to as the Atlantic region. The height and critical frequency of the F2 layer peak, hmF2 and foF2, changed due to changes in the vertical E B drift and the vertical components of diffusion and transport by neutral winds along the magnetic field. Changes in electron density resulted in changes in electron temperature of the opposite sign, which in turn produced small corresponding changes in ion temperature. Changes in neutral temperature were not statistically significant. Strong changes in the daily amplitude of the Sq variation occurred at low magnetic latitudes due to the northward movement of the magnetic equator and the westward drift of the magnetic field. The simulated changes in hmF2, foF2, and Sq amplitude translate into typical trends of 1 km/decade (night) to 3 km/decade (day), -0.1 to +0.05 MHz/decade, and 5 to 10 nT/century, respectively. These are mostly comparable in magnitude to observed trends in the Atlantic region. The simulated Atlantic region trends in hmF2 and foF2 are ~2.5 times larger than the estimated effect of enhanced greenhouse gases on hmF2 and foF2. The secular variation of the Earth's magnetic field may therefore be the dominant cause of trends in the Atlantic region ionosphere.

Cnossen, Ingrid; Richmond, Arthur D.

2013-02-01

357

Ionospheric feedback effects on the quasi-stationary coupling between LLBL and postnoon\\/evening discrete auroral arcs  

Microsoft Academic Search

We discuss a model for the quasi-stationary coupling between magnetospheric sheared flows in the dusk sector and discrete auroral arcs, previously analyzed for the case of a uniform height-integrated Pedersen conductivity (SigmaP). Here we introduce an ionospheric feedback as the variation of SigmaP with the energy flux of precipitating magnetospheric electrons (?em). One key-component of the model is the kinetic

M. M. Echim; M. Roth; J. de Keyser

2008-01-01

358

Propagation of electromagnetic waves in a structured ionosphere  

SciTech Connect

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

Murphy, T.

1996-06-01

359

Propagation in the Ionosphere, B.  

National Technical Information Service (NTIS)

Sophisticated computer programs or equipment, high frequency systems, satellite to ground systems and meteor burst systems are discussed with respect to ionospheric propagation models. Short term ionospheric forecasts (electron density) and geomagnetic ac...

P. S. Cannon

1994-01-01

360

42 CFR 2.61 - Legal effect of order.  

Code of Federal Regulations, 2012 CFR

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

2012-10-01

361

42 CFR 2.61 - Legal effect of order.  

Code of Federal Regulations, 2011 CFR

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

2011-10-01

362

Considerations of variations in ionospheric field effects in mapping equatorial lithospheric Magsat magnetic anomalies  

Microsoft Academic Search

The longitudinal, seasonal, and altitude-dependent variability of the magnetic field in equatorial latitudes is investigated to determine the effect of these variabilities on the isolation of lithospheric Magsat magnetic anomalies. It was found that the amplitudes of the dawn dip-latitude averages were small compared to the dusk averages, and that they were of the opposite sign. The longitudinal variation in

D. Ravat; W. J. Hinze

1993-01-01

363

Effect of the day night ionospheric conductivity gradient on polar cap convective flow  

Microsoft Academic Search

The electric field data in the polar cap do not display the expected mirror symmetry for positive and negative values of the solar magnetospheric y component of the interplanetary magnetic field, suggesting that an additional effect is squeezing the antisunward flow toward the dawnside of the polar cap. It is shown that a conductivity decrease toward the nightside will produce

G. Atkinson; D. Hutchison

1978-01-01

364

The Martian Ionosphere as seen by the Mars Advanced Radar for Subsurface and Ionosphere Sounding  

NASA Astrophysics Data System (ADS)

The Mars Express spacecraft, inserted into Mars orbit on 25 December 2003, has on board a dual-mode radar sounder, the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS), which was commissioned for service in August 2005. From that time to the present, MARSIS in Active Ionospheric Sounding mode (AIS) has collected over 1 million soundings of the Martian ionosphere on approximately 9000 orbits. These soundings have sampled both day- and nightside ionospheres, during times of solar activity and quiet, and during the various Martian seasons. In this presentation, we shall discuss both important past results and ongoing and projected work. We shall describe how MARSIS electron density profiles can be incorporated with particle precipitation models on the nightside in regions of inhomogeneous crustal magnetic field to better describe observed electron precipitation, generation of Martian aurora, and the formation of the nightside ionosphere. We shall see how MARSIS electron density profiles register the effects of increasing solar activity as we approach the peak of the present solar cycle. Finally, we will show how the ability of MARSIS to sample the plasma frequency in situ can be used to search for plasma escaping the ionosphere of Mars.

Morgan, David D.; Gurnett, Donald; Mitrofanov, Igor; Plaut, Jeffrey; Duru, Firdevs; Lillis, Robert; Andrews, David; Nemec, Frantisek; Fillingim, Matt; Opgenoortn, Hermann; Dubinin, Eduard

2012-07-01

365

Simulated Response of the Magnetosphere-Ionosphere System to Different Forms of Empirically Regulated Ionospheric Outflows  

NASA Astrophysics Data System (ADS)

Empirically derived power-law relations between the locally measured Poynting flux (S) flowing toward the ionosphere and the number flux of ions (F) flowing away from the ionosphere exhibit significant differences that depend on the choice of satellite data samples (Strangeway et al., 2005; Zheng et al., 2005). Such relations attempt to capture in lumped form the causality of electromagnetic power flows into collisionless ion acceleration in the topside ionosphere and low-altitude magnetosphere and the resulting ion outflows -- effects that are otherwise difficult to treat in first-principles fluid models for the field-aligned mass transport. We have implemented a power-law relation of the form F = A*S**b, where A and b are adjustable parameters ultimately constrained by observation, as a low-altitude boundary condition on the LFM global simulation model. This boundary condition allows ions of ionospheric origin to enter the magnetospheric simulation domain and to mix with plasma of solar wind origin in populating the magnetosphere. According to the empirical relation, more ionospheric ions are causally injected into the simulation domain as the Poynting flux through the low-altitude boundary increases. In this paper, we report results from simulations using different values of the parameters A and b to determine the sensitivity of the magnetospheric response to the form of the empirical relation. Simulation diagnostics for the transpolar potential, field-aligned current, ionospheric conductivity, precipitating electron energy flux, and Joule dissipation rate will be presented.

Lotko, W.; Lyon, J.; Melanson, P.; Murr, D.; Wiltberger, M.

2006-12-01

366

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

367

Radioacoustic sensing of the ionosphere  

SciTech Connect

The possibilities of ionospheric diagnostics by radio sensing of disturbances excited in the ionosphere by a monochromatic acoustic wave are analyzed. Numerical estimates of the resonance scattering coefficients for radio waves as a function of the frequency and power of the acoustic waves are obtained for real models of the ionosphere.

Plotkin, V.V.; Izraileva, N.I.

1988-11-01

368

International Reference Ionosphere 2010  

NASA Astrophysics Data System (ADS)

The International Reference Ionosphere (IRI) is an international project sponsored by the Committee on Space research (COSPAR) and the International Union of Radio Science (URSI) that has as its goal the development and improvement of a data-based model of ionospheric densities, temperatures, and velocities using all available and reliable data sources for these ionospheric parameters. The model is widely recognized as the international standard for the specification of ionospheric parameters and recently was accepted by the International Standardization Organization (ISO) as Technical Specification TS 16457. This presentation will discuss the new version of the model, IRI-2010, which includes several important improvements and additions. The electron and ion densities in the lower ionosphere were significantly improved by using a large volume of ionosonde data as well as photochemical considerations. As an additional parameter IRI-2010 includes the transition height from molecular to cluster ions. At the F2 peak Neural Network based models for the peak density and the propagation factor M3000F2, which is related to the F2 peak height, are introduced as new options. For 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.

Bilitza, D.; Reinisch, B. W.; McKinnell, L. A.

2010-12-01

369

Venus nightside ionospheric holes  

NASA Astrophysics Data System (ADS)

Pioneer Venus Orbiter (PVO) measured the ionosphere and atmosphere of Venus for 13 years 10 months yielding a rich data set of archived data from a complement of instruments. One particularly striking feature seen was the occurrence of deep localized nightside ionization depletions commonly called holes. A number of theories have been put forth to explain their observed characteristics, but there is still no consensus on their source. A possibly related phenomenon in the Venus nightside ionosphere is the occurrence of "disappearing" or severely disturbed ionospheres characterized by deep, widespread plasma depletions in almost the entire nightside. This paper reexamines the holes and "disappearing ionospheres" and other characteristics of the nightside ionosphere during solar maximum using a more extensive database than earlier studies. The hole locations, occurrences, and dependencies on solar wind dynamic pressure (Psw) are analyzed, and a comparison is made with earlier studies. It is shown that there is no Psw threshold for holes to occur and at Psw values greater than 9 nPa, hole occurrence decreases while the occurrence of severely disturbed orbits increases, suggesting that holes may evolve into severely disturbed orbits. Other characteristics of the nightside are shown to be influenced by solar wind pressure to varying degrees; for example, the density integrated along the orbit path below the ionopause, and the median density at low altitudes exhibit strong inverse correlation with Psw, while the peak density is nearly independent of Psw.

Hoegy, Walter R.; Grebowsky, Joseph M.

2010-12-01

370

Detection of ionospheric Alfvn 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 Alfvn 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, Alfvn wave propagation, and troposphere-ionosphere-magnetosphere coupling mechanisms.

Simes, 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

371

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

SciTech Connect

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

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

1983-12-01

372

Ionospheric correction of space radar data  

NASA Astrophysics Data System (ADS)

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

Hapgood, Mike

2010-06-01

373

Penetration of magnetospheric electric fields to the equator and their effects on the low-latitude ionosphere during intense geomagnetic storms  

NASA Astrophysics Data System (ADS)

The penetration of magnetospheric electric fields to the magnetic equator has been investigated for two intense magnetic storms that occurred on 31 March 2001 and 6 November 2001. The digital ground magnetic data from equatorial station Tirunelveli (TIR, 0.17S geomagnetic latitude (GML)) and low-latitude station Alibag (ABG, 10.17N GML) have been used to identify the storm time electrojet index, EEJ(Dis), which is the difference of the magnetic field variations between TIR and ABG after removing the quiet day variations. The appearance of enhanced DP 2 currents and counterelectrojets (CEJ) during the main and recovery phases of the magnetic storms is possibly due to prompt penetration of electric fields from the high latitudes. These signatures can be interpreted as a clear indicator of the eastward and westward electric fields at the equator. The observed results suggest that the magnitude of the equatorial ionospheric currents driven by the penetrating electric fields is very sensitive to ionospheric conductivity (which depends on local time). Moreover, the intensity of the DP 2 currents started decreasing during the end of the main phase of the storm despite the large negative southward IMF Bz, indicating the dominance of a well-developed shielding electric field for 1 h. As an effect of penetrating electric fields at the equator, the equatorial ionization anomaly is enhanced during the main phase (because of strong eastward electric field) and is inhibited or reduced due to the strong CEJ (because of westward electric field) during the recovery phase.

Veenadhari, B.; Alex, S.; Kikuchi, T.; Shinbori, A.; Singh, Rajesh; Chandrasekhar, E.

2010-03-01

374

Impact factor for the ionospheric TEC response to solar flare  

NASA Astrophysics Data System (ADS)

As one of the most fast and severest solar eventssolar flare, that mainly are classified according to the peak flux of soft X-rays (1-8 angstrom) measured on the GOES spacecraft, affects the earth's upper atmosphere seriously. During a flare, the Extreme Ultraviolet (EUV) and X-rays emitted from the solar active region ionize the earth's neutral compositions in the altitudes of ionosphere so to make the extra ionospheric ionization that caused the so-called SIDs. Although the increase of electron density during a flare appears in all ionospheric sub-regions, the increase of electron density in the F region due to the extra ionization of EUV radiation is thought to be responsible for a large fraction of the SITEC so that SITEC can be used as an index to represent the response of the ionospheric F region to solar flares. With the advent of GPS satellite beacon methods for measuring the ionospheric TEC, it has become one of the chief parameters for indicating the strength of the flare effects on ionosphere. Through the study of the ionospheric TEC during different solar flares, the different responses of the ionospheric TEC to the same level solar flares classified according to the soft X-ray peak flux have been noted. Statistical analysis shows that besides the solar X-ray peak flux parameter, the parameter of the flare location on solar disc is also related to the effective strength of the ionospheric response to solar flare. In this study, the relationship between the ionospheric TEC enhancement and the flare location, flare X-ray peak level is analyzed statistically and a primary empirical model is obtained for solar flare's space weather forecast.

Zhang, Donghe; Cai, Lei; Hao, Yongqiang; Xiao, Zuo

375

Ionospheric tomography using the FORTE satellite  

SciTech Connect

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

Murphy, T.C.

1993-08-01

376

Deployment of Coherent Ionospheric Doppler Receiver Chain IN EGYPT  

NASA Astrophysics Data System (ADS)

This project was by and between University of Texas at Austin in USA and Helwan University in Egypt in order to conduct joint scientific investigations of the Earth's ionosphere. The parties will develop a network of passive radio instruments to monitor the ionospheric weather associated with the equatorial fountain situated over southern and central Egypt. In order to better understand the spatial and temporal scales over which the equatorial fountain varies, a network of three Coherent Ionospheric Doppler Receiver (CIDR) systems will be deployed in a roughly north-south chain in Egypt. By analyzing the CIDR data set as a function of time and ionospheric drivers, this project will gain valuable new insights into the weather of the equatorial fountain and the radio environment.

Mahrous, A. M.; Garner, T.

2008-05-01

377

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

378

Convective Ionospheric Storms: A Review  

NASA Astrophysics Data System (ADS)

Equatorial spread F (ESF) was discovered almost a century ago using the first radio wave instrument designed to study the upper atmosphere: the ionosonde. The name came from the appearance of reflections from the normally smooth ionosphere, which were spread over the altitude frequency coordinates used by the instrument. Attempts to understand this phenomenon in any depth activated such tools as radars and in situ probes such as rockets and satellites in the 1960s. Over the next 15 years, these tools expanded our experimental understanding enormously, and new nonlinear theoretical methods developed in the late 1970s, which led to proposing a name revision from ESF to convective ionospheric storms. Interest in these phenomena continues, but a new, practical aspect has developed from the associated turbulence effects on communications (transionosphere) and navigation (GPS). The first satellite to specifically investigate this problem and the associated goal of predicting occurrences is under the umbrella of the Communications/Navigation Outage Forecast System (C/NOFS). In contemplating the successful first years of the C/NOFS program, reviewing the state of the art in our knowledge of convective ionospheric storms seems appropriate. We also present some initial results of this satellite program. A major goal of the National Space Weather Program, and of C/NOFS, is predicting these storms, analogous to thunderstorms in the lower atmosphere due to their adverse effects on communication and navigation signals. Although ambitious, predictive capability is a noble and important goal in the current technological age and is potentially within our reach during the coming decade.

Kelley, Michael C.; Makela, Jonathan J.; de La Beaujardire, Odile; Retterer, John

2011-06-01

379

Question order effects in taste testing of beverages  

Microsoft Academic Search

The effect of order position has been demonstrated in marketing research, sometimes compromising survey results. This paper\\u000a studies the influence of order position in product taste trials of carbonated beverages using a sequential monadic design.\\u000a The authors measure attitude ratings across product trials rather than across products to examine the effect of order position\\u000a on preference ratings.

Joe L. Welch; Cathy Owens Swift

1992-01-01

380

Higher order effects in electromagnetic dissociation of neutron halo nuclei  

Microsoft Academic Search

We investigate higher order effects in electromagnetic excitation of neutron halo nuclei using a zero-range model for the neutron-core interaction. In the sudden (or Glauber) approximation all orders in the target-core electromagnetic interaction are taken into account. Small deviations from the sudden approximation are readily calculated. We obtain very simple analytical results and scaling laws for the next-to-leading order effects,

S. Typel; G. Baur

2001-01-01

381

Model simulations of global change in the ionosphere  

Microsoft Academic Search

Observations of secular trends in the E and F1 regions of the ionosphere indicate that electron densities have increased, and that the height of the E-region peak has decreased, during the past several decades. Detection of trends in the upper ionosphere through analysis of F2-layer parameters has been more complex and controversial. In order to facilitate observational detection of long-term

Liying Qian; Stanley C. Solomon; Raymond G. Roble; Timothy J. Kane

2008-01-01

382

Hydrogen Species in the Ionosphere of Mars  

NASA Astrophysics Data System (ADS)

To date, there are only two in situ measurements of the composition of the neutral atmosphere and ionosphere of Mars, those made by the Viking 1 and Viking 2 Landers. On the other hand, models of the Martian ionosphere are plentiful, and most of these models use atmospheric chemistry that is aimed at reproducing the Viking measurements. In these modeling efforts, the atmospheric and ionospheric region of interest centers on the altitudes of the Viking measurements: between ~100 km to ~250 km. The main neutral species detected by Viking were: CO2, N2, Ar, CO, O2, and NO. Atomic Oxygen densities were then inferred from chemical models and only trace detections of atomic and molecular hydrogen were found. Remote spectral measurements later found both H and H2 to dominate the atmosphere above ~250 km. In the work presented here, we build a 1-D ionospheric model that ranges in altitude between 80 and 400 km and includes CO2, CO, O, N2, H2 and H as neutral species. These species are then ionized to produce the primary ions CO2+, CO+, O+, N2+, H2+ and H+. Further reactions with neutrals give rise to the secondary ions: O2+, NO+, OH+, H3+ and HCO+. We allow for two extreme cases of ambipolar diffusion to encompass the effects of induced or crustal magnetic field (B) morphologies: (1) horizontal-B and (2) vertical-B. The first case allows no vertical diffusion in the 1-D model and the second case allows for only vertical diffusion. We find that in the case of no vertical diffusion, the secondary ions HCO+, H3+ and OH+ dominate the topside ionosphere along with O2+. In the case of only vertical diffusion, we find that both HCO+ and O2+ co-dominate the ionosphere. We discuss the implications of these predictions for MAVEN NGIMS observations.

Matta, M. M.; Lollo, A.; Withers, P.; Mendillo, M.

2011-12-01

383

At what energies are second order effects important?  

NASA Astrophysics Data System (ADS)

Over 20 years ago, Byron et al (J. Phys. B (1980) 13, L673) demonstrated that second order effects were important for impact energies as large as 250 eV. In that work, the projectile was treated as a plane wave and the closure approximation was used to perform the sum over intermediate states in the second order term. We have developed a second order distorted wave theory for atomic ionization which does not use closure but instead sums over all intermediate states. We have examined electron impact ionization of hydrogen and helium from the ground state, and found that second order effects are important for impact energies as high as 600 eV and that second order dominates the higher order effects (at least for smaller projectile deflection angles) down to about 100 eV impact energy.

Chen, Zhangjin; Madison, Don H.; Whelan, Colm T.; Walters, H. R. J.

2004-05-01

384

Ionospheric disturbances at the equatorial anomaly crest region during the March 1989 magnetic storms  

SciTech Connect

On March 6, 1989, the largest sunspot group since 1982 came into view as it moved out of the eastern limb of the Sun. It was highly active during March8-18, and a great many transient ionospheric and geomagnetic variations were triggered by this sunspot group. The intensive ionospheric observations at Lunping Observatory and Chungli Ionosphere Station during this period recorded 30 solar flares manifested as shortwave fade-outs, sudden frequency deviations, and solar flare effects and three storm sudden commencement (SSC)-tupe geomagnetic storms, among which the March 13 SSC-type geomagnetic storm triggered an unusually severe ionospheric disturbance. The ionospheric total electron content, the critical frequency of the F{sub 2} layer, f{sub o}F{sub 2}, and the virtual heights at given frequencies all show wavelike up-and-down oscillations of the ionosphere. This oscillatory ionospheric motion is explained as due to the compression and expansion of the plasmasphere.

Yinn-Nien Huang; Kang, Cheng (Telecommunication Training Inst., Taipei, Taiwan (China))

1991-08-01

385

Solar wind drivers for low-latitude ionosphere models during geomagnetic storms  

NASA Astrophysics Data System (ADS)

A prescription for modeling the low-latitude ionosphere under active geomagnetic storm conditions is given, using a set of simple empirical drivers based on parameters of the solar wind. These drivers describe the effects of energy input from the solar wind into the ionosphere, including prompt penetration electric fields and thermospheric heating, thus permitting the ionosphere to be more accurately modeled under these extreme conditions. These drivers are relevant to modeling both the global-scale ambient ionosphere and the plasma instability of the ionosphere. An application of the drivers to modeling the low-latitude ionosphere during the November 2004 storm is presented in a companion paper [Retterer, J.M., Kelley, M.C., Valladares, C., Chau, J., Ilma, R., Gentile, L., Groves, K., 2009. Modeling the low-latitude ionospheric electron density and plasma turbulence in the November 2004 storm period. J. Atmos. Sol.-Terr. Phys., this issue].

Retterer, J. M.; Kelley, M. C.

2010-03-01

386

A review of ionospheric F region theory  

Microsoft Academic Search

Following a brief historical introduction, the paper reviews the types of data which concern ionospheric F region theory. The physical processes which are believed to control the variations of electron density in the F1 and F2 layers are then discussed. Possible explanations of several F region phenomena are presented, together with a brief consideration of magnetic storm effects.

H. Rishbeth

1967-01-01

387

Radio occultation measurements of the lunar ionosphere  

Microsoft Academic Search

Radio occultation measurements by using interplanetary probes is a well known technique to obtain information on planetary atmospheres. To further understand the morphology of the lunar ionosphere we performed radio occultation experiments by using the radio sounding technique. This method mainly consists in the analisys of the effects produced on the radio wave transmitted from the spacecraft to the Earth

S. Pluchino; F. Schillir; E. Salerno; G. Pupillo; G. Maccaferri; P. Cassaro

2008-01-01

388

The ionosphere of Venus  

Microsoft Academic Search

The Venus dayside ionosphere model includes both photochemistry and vertical diffusion. Basic neutral atmosphere and temperature structure were obtained from models by Dickinson and Ridley. A comprehensive study of ion chemistry and diffusion processes used approximations for ion and electron temperature structures. The model accurately reproduces the location of electron density peaks and shows that large mixing ratios of He

D. M. Butler

1975-01-01

389

Ionospheric Research Using Satellites.  

National Technical Information Service (NTIS)

An account is given of the equipment available for ionospheric studies at Nairobi and at the associated stations of Addis Ababa, Asmara and Dar es Salaam. Results are presented for the latitude and diurnal variation of total electron content and scintilla...

A. N. Hunter R. F. Kelleher A. R. Webster

1967-01-01

390

Eye on the Ionosphere  

Microsoft Academic Search

he near-Earth space environment responds directly to the general level of activity on the Sun. During solar minimum, the neutral atmosphere settles to its smallest scale height, the magnetopause expands to its greatest radius (about 13 Earth radii), and ionospheric disturbances are few, occurring weeks or even months apart. During solar maximum, the scale-height of the neutral atmosphere expands such

Jo Ann Joselyn

1999-01-01

391

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

392

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

393

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

NASA Astrophysics Data System (ADS)

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

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

2011-02-01

394

Quasi-analytic models for density bubbles and plasma clouds in the equatorial ionosphere: 2. A simple Lagrangian transport model  

Microsoft Academic Search

The transport equations for the motion of plasma in the equatorial ionosphere are solved using exact solutions for induced electric potentials and deformation of plasma density coordinates. The primary purpose of the quasi-analytic model is to provide an efficient description of the plasma structure in the equatorial ionosphere suitable for investigation of effects on radio wave propagation and ionospheric sensors.

Paul A. Bernhardt

2007-01-01

395

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

396

Chemistry in the Thermosphere and Ionosphere.  

ERIC Educational Resources Information Center

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

Roble, Raymond G.

1986-01-01

397

Chemistry in the Thermosphere and Ionosphere.  

ERIC Educational Resources Information Center

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

Roble, Raymond G.

1986-01-01

398

The effect of ordering on preconditioned conjugate gradients  

Microsoft Academic Search

We investigate the effect of the ordering of the unknowns on the convergence of the preconditioned conjugate gradient method. We examine a wide range of ordering methods including nested dissection, minimum degree, and red-black and consider preconditionings without fill-in. We show empirically that there can be a significant difference in the number of iterations required by the conjugate gradient method

Iain S. Duff; Grard A. Meurant

1989-01-01

399

Bayesian Analysis of Structural Effects in an Ordered Equation System  

Microsoft Academic Search

We describe a new simulation-based algorithm for Bayesian estimation of structural effects in models where the outcome of interest and an endogenous treatment variable are ordered. Our algorithm makes use of a reparameterization, suggested by Nandram and Chen (1996) in the context of a single equation ordered-probit model, which significantly improves the mixing of the standard Gibbs sampler. We illustrate

Mingliang Li; Justin Tobias

2005-01-01

400

Bayesian Analysis of Structural Effects in an Ordered Equation System  

Microsoft Academic Search

We describe a new simulation-based algorithm for Bayesian estimation of structural effects in models where the outcome of interest and an endogenous treatment variable are ordered. Our algorithm makes use of a reparameterization, suggested by Nandram and Chen (1996) in the context of a single equation ordered-probit model, which significantly improves the mixing of the standard Gibbs sampler. We illustrate

Mingliang Li; Justin L. Tobias

2006-01-01

401

Satellite measurement of ionospheric-induced vhf distortion  

SciTech Connect

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

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

1992-01-01

402

Satellite measurement of ionospheric-induced vhf distortion  

SciTech Connect

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

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

1992-09-01

403

Effects of space ordering for light scattering in eye tissues  

Microsoft Academic Search

This paper deals with the problem of calculating the polarization and spatial characteristics of laser radiation scattered by the eye tissues. Multiple scattering effects simultaneously with the degree of near order for scattering particles were taken into account.

Irina L. Maksimova

1999-01-01

404

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

NASA Astrophysics Data System (ADS)

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

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

2006-10-01

405

Connection between Tropospheric Activities and Ionospheric behaviors Simulated by a Whole Atmosphere-Ionosphere Coupled Model  

NASA Astrophysics Data System (ADS)

In This talk, we will introduce an Earths atmosphere-ionosphere coupled model which treats seamlessly the neutral atmospheric region from the troposphere to the thermosphere as well as the thermosphere-ionosphere interaction including the electrodynamics self-consistently. The model is especially useful for the study of vertical connection between the meteorological phenomena and the upper atmospheric behaviors. As an initial simulation using the coupled model, we have carried out a 30-day consecutive run in September. The result reveals that the longitudinal structure of F-region ionosphere varies on day-to-day basis in a highly complex way, and that a clear 4-peak structure of daytime equatorial ionization anomaly (EIA) similar to the recent observations appears as an averaged feature. The simulation reproduces and thus confirms the vertical coupling processes proposed so far with respect to the formation of averaged EIA longitudinal structure, including from the excitation of solar nonmigrating tides in the tropospheric moist convection activity to tidal modulation of ionospheric dynamo electric field which in turn affects EIA generation. The simulation result indicates that not only the ionospheric averaged longitudinal structure but the day-to-day variation can be modulated significantly by the lower atmospheric effect.

Jin, H.; Miyoshi, Y.; Fujiwara, H.; Shinagawa, H.; Terada, K.; Terada, N.; Ishii, M.; Otsuka, Y.; Saito, A.

2010-12-01

406

Major magnetic storm of March 13-14, 1989 and associated ionosphere effects. (Reannouncement with new availability information)  

SciTech Connect

The geomagnetic storm of March 1989 was the largest geomagnetic storm of the decade and one of the largest of the century. The authors review many of the `high-latitude` ionospheric observations that were made during this storm. Most of the data presented here comes from the polar-orbiting satellites of the Defense Meteorological Satellite Program (DMSP) series. A review of the DMSP data shows that most of the high-latitude, top-side ionospheric disturbance occurred on March 13 and 14. The magnitudes of the particle energy flux (ergs cm 2) (1 erg = 10{minus}7 J) and Joule heating were not unusually large for a storm, but the area of the energy deposition, and thus the total energy deposition, was extremely large. At the peak of the storm (minimum in D(st) (disturbance with storm time) and midnight boundary indices) the auroral particle precipitation extended down to magnetic latitudes of 40.1 deg or L = 1.71 while the polar edge of the auroral zone expanded poleward only slightly. The storm was also a period of intense, hemispherically symmetric polar rain fluxes. The auroral electric field was clearly observed down to magnetic latitude of 35 deg. This is consistent with the auroral electrojet (AE) current density and the AE index having a saturation level beyond which the index will increase slowly or not at all as more energy is transferred from the solar wind to the magnetosphere, but the cross polar-cap potential during this storm shows no evidence of saturation. There are only two visible light images from DMSP available near the peak of the storm.

Rich, F.J.; Denig, W.F.

1993-06-30

407

Satellite observations of an ionospheric acceleration mechanism  

Microsoft Academic Search

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

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

1976-01-01

408

Characteristics of absorption and frequency filtration of ULF electromagnetic waves in the ionosphere  

NASA Astrophysics Data System (ADS)

A statistical method for interpreting data from experimental investigations of vertically-propagating electromagnetic ULF waves in the inhomogeneous magnetoactive ionosphere is considered theoretically. Values are obtained for the transmission, reflection and absorption characteristics of ULF waves in a limited ionospheric layer, in order to describe the relation between the frequency of a wave generated at the earth surface and that of a total wave propagating above the ionospheric layer. This relation is used to express the frequency-selective amplitude filtration of ULF waves in the layer. The method is applied to a model of the night ionosphere of mid-geomagnetic latitudes in the form of a plate 1000 km thick. It is found that the relative characteristics of transmission and amplitude loss in the wave adequately describe the frequency selectiveness and wave filtration capacity of the ionosphere. The method is recommended for studies of the structural changes of wave parameters in ionospheric models.

Prikner, K.

409

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

NASA Astrophysics Data System (ADS)

It can be important to determine the correlation of different frequency signals in L band that have followed transionospheric paths. In the future, both GPS and the new Galileo satellite system will broadcast three frequencies enabling more advanced three frequency correction schemes so that knowledge of correlations of different frequency pairs for scintillation conditions is desirable. Even at present, it would be helpful to know how dual-frequency Global Navigation Satellite Systems positioning can be affected by lack of correlation between the L1 and L2 signals. To treat this problem of signal correlation for the case of strong scintillation, a previously constructed simulator program, based on the hybrid method, has been further modified to simulate the fields for both frequencies on the ground, taking account of their cross correlation. Then, the errors in the two-frequency range finding method caused by scintillation have been estimated for particular ionospheric conditions and for a realistic fully three-dimensional model of the ionospheric turbulence. The results which are presented for five different frequency pairs (L1/L2, L1/L3, L1/L5, L2/L3, and L2/L5) show the dependence of diffractional errors on the scintillation index S4 and that the errors diverge from a linear relationship, the stronger are scintillation effects, and may reach up to ten centimeters, or more. The correlation of the phases at spaced frequencies has also been studied and found that the correlation coefficients for different pairs of frequencies depend on the procedure of phase retrieval, and reduce slowly as both the variance of the electron density fluctuations and cycle slips increase.

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

2011-06-01

410

View of Soviet ionospheric modification research  

SciTech Connect

We have reviewed and provided a technical assessment of Soviet research of the past five to ten years in ionospheric modification by high-power radio waves. This review includes a comprehensive survey of Soviet published literature, conference proceedings, and direct discussions with the involved Soviet researchers. The current state of the art for Soviet research in this field is evaluated, identifying areas of potential breakthrough discoveries, and discussing implications of this work for emerging technologies and future applications. This assessment is divided into the categories of basic research, advanced research, and applications. Basic research is further subdivided into studies of the modified natural geophysical environment, nonlinear plasma physics, and polar geophysical studies. Advanced research topics include the generation of artificial ionization mirrors and high-power oblique propagation effects. A separate comparative assessment of Soviet theoretical work also is included in this analysis. Our evaluation of practical and potential applications of this research discusses the utility of ionospheric modification in creating disturbed radio wave propagation environments, and its role in current and future remote-sensing and telecommunications systems. This technical assessment does not include consideration of ionospheric modification by means other than high-power radio waves. The Soviet effort in ionospheric modification sustains theoretical and experimental research at activity levels considerably greater than that found in comparable programs in the West. Notable strengths of the Soviet program are its breadth of coverage, large numbers of scientific participation, theoretical creativity and insight, and its powerful radio wave transmitting facilities.

Duncan, L.M.; Showen, R.L.

1990-10-01

411

Ionospheric Corrections for Shf Satellite Radar Altimetry  

NASA Astrophysics Data System (ADS)

Available from UMI in association with The British Library. Requires signed TDF. To measure the satellite-ocean altitude, a radar altimeter transmits a nadir-directed microwave pulse and times the return of the surface reflection. The intervening free electrons of the ionosphere cause group delay of the pulse resulting in an overestimate of the platform altitude by an amount directly proportional to the sub-satellite electron content. In effect the figure of the ocean surface detected by the altimeter is modulated by the spatial and temporal variation of the ionospheric electron content. A two stage technique has been developed to remove the bias imposed by the ionosphere on altimetric measurements. The first stage generates a prediction of electron content based on ionospheric climatology. The second stage is an adaptive modelling procedure which makes use of data from satellite-ranging radar systems. The first chapter of this thesis gives an introduction to the Earth's ionosphere, describes its effect on radar altimetry and suggests a technique to correct for this influence. Chapter Two reviews previous work in related areas before Chapter Three embarks on a description of the spatial and temporal behaviour of electron content. Chapter Four describes the mathematical sub-models which form the basis of the empirical model and Chapter Five is devoted to the calibration and validation of this model. Chapter Six covers the calculation of the coherence functions of electron content which are crucial for the operation of the adaptive procedure. Chapter Seven compares the new model with one employed for a previous altimeter mission and Chapter Eight summarizes what has gone before and suggests topics for future research.

Leigh, Richard Peter

412

Recency and the Modality Effect in Immediate Ordered Recall  

Microsoft Academic Search

In immediate ordered recall, recency is the improved recall of the last item of a presentation, and the modality effect is the advantage for an acoustic presentation over a subvocalized visual presentation, primarily occurring at the last serial position. Experiment I tested grouped presentations. There was a modality effect for the first item of the last group, even though that

Robert W. Frick

1989-01-01

413

A Nearly Optimal Order Policy to Reduce Bullwhip Effect  

Microsoft Academic Search

An important supply chain research problem is the bullwhip effect caused by information distortion and variation amplification along a supply chain, which can lead to tremendous inefficiencies, such as excessive inventory investment and lost revenues. Motivated by engineering process control methods, this paper proposes a class of order-up-to policies and develops a nearly optimal policy to reduce the bullwhip effect.

H. Liu; K. L. Tsui; F. Tsung

414

International Reference Ionosphere - Climatological Standard for the Ionosphere.  

National Technical Information Service (NTIS)

The International Reference Ionosphere (IRI) a joint project of URSI and COSPAR is the defacto standard for a climatological specification of ionospheric parameters. IRI is based on a wide range of ground and space data and has been steadily improved sinc...

D. Bilitza

2006-01-01

415

Observations of the ionosphere by the Ionosphere Sounding Satellite \\/ISS  

Microsoft Academic Search

The design and electronics of a global ionospheric sounding satellite are described. The satellite missions consisted of studying the global distribution of ionospheric critical frequencies and the virtual range vs frequency characteristics of the sounding echo; study of the global distribution of radio noise intensities and the occurrence frequency of atmospherics; study of such plasma parameters as electron and ion

N. Matuura; R. Nishizaki

1977-01-01

416

Higher-order effects in polarized proton dynamics  

NASA Astrophysics Data System (ADS)

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 or minus one of the orbit tunes is an integer. These beams have usually been investigated by theories which correspondingly lead to an undisturbed polarization during acceleration, except at such resonances. Therefore we speak of ``first-order theories.'' The first frequently used first-order theory is the single resonance model, which is usually used for simulating the acceleration process. Here the equation of spin motion is simplified drastically by dropping all but the dominant Fourier component of the driving term of that differential equation. The second frequently used first-order theory, the linearized spin-orbit motion theory, is also quite crude. It is based on a linearization of the spin and orbit equation of motion with respect to the phase space coordinates and two suitably chosen spin coordinates. Because of linearization this method cannot be used close to resonances but at fixed energies it is a useful tool. It will be shown that the validity of these first-order theories is restricted at Hadron Electron Ring Accelerator (HERA) energies of up to 820 GeV. An overview of the available theories which go beyond the first-order resonances is given and we explain which of these approaches are applicable for the analysis of polarization in the HERA proton ring. Since these theories include more than one Fourier harmonic in the driving term of the equation of motion, we refer to them as ``non-first-order'' or ``higher-order'' theories. Finally, the higher-order effects observed while simulating polarized beams in HERA with these advanced methods are illustrated.

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

1999-11-01

417

Full-Scale Simulations of Ionospheric Langmuir Turbulence  

NASA Astrophysics Data System (ADS)

This brief review is devoted to full-scale numerical modeling of the nonlinear interactions between electromagnetic (EM) waves and the ionosphere, giving rise to ionospheric Langmuir turbulence. A numerical challenge in the full-scale modeling is that it involves very different length- and time-scales. While the EM waves have wavelengths of the order 100 meters, the ionospheric Langmuir turbulence involving electrostatic waves and nonlinear structures can have wavelengths below one meter. A full-scale numerical scheme must resolve these different length- and time-scales, as well as the ionospheric profile extending vertically hundreds of kilometers. To overcome severe limitations on the timestep and computational load, a non-uniform nested grid method has been devised, in which the EM wave is represented in space on a relatively coarse grid with a spacing of a few meters, while the electrostatic wave turbulence is locally resolved on a much denser grid in space at the critical layer where the turbulence occurs. Interpolation and averaging schemes are used to communicate values of the EM fields and current sources between the coarse and dense grids. In this manner, the computational load can be drastically decreased, making it possible to perform full-scale simulations that cover the different time- and space-scales. We discuss the simulation methods and how they are used to study turbulence, stimulated EM emissions, particle acceleration and heating, and the formation of artificial ionospheric plasma layers by ionospheric Langmuir turbulence.

Eliasson, Bengt

2013-03-01

418

Comparison of ionospheric radio occultation CHAMP data with IRI 2001  

NASA Astrophysics Data System (ADS)

GPS radio occultation measurements on board low Earth orbiting satellites can provide vertical electron density profiles of the ionosphere from satellite orbit heights down to the bottomside. Ionospheric radio occultation (IRO) measurements carried out onboard the German CHAMP satellite mission since 11 April 2001 were used to derive vertical electron density profiles (EDPs) on a routine basis. About 150 vertical electron density profiles may be retrieved per day thus providing a huge data basis for testing and developing ionospheric models. Although the validation of the EDP retrievals is not yet completed, the paper addresses a systematic comparison of about 78 000 electron density profiles derived from CHAMP IRO data with the International Reference Ionosphere (IRI 2001). The results are discussed for quite different geophysical conditions, e.g. as a function of latitude, local time and geomagnetic activity. The comparison of IRO data with corresponding IRI data indicates that IRI generally overestimates the upper part of the ionosphere whereas it underestimates the lower part of the ionosphere under high solar activity conditions. In a first order correction this systematic deviation could be compensated by introducing a height dependence correction factor in IRI profiling.

Jakowski, N.; Tsybulya, K.

2004-05-01

419

Effect of third-order dispersion on passive mode locking  

Microsoft Academic Search

The effect of third-order dispersion on the width of mode-locked pulses is investigated analytically and numerically. The pulse width increases monotonically with increasing third-order dispersion as a consequence of the symmetric chirp introduced by it. The chirp broadens the bandwidth and lowers the gain. Computer simulations show the appearance of a resonant sideband that also taxes the gain. Reducing the

H. A. Haus; J. D. Moores; L. E. Nelson

1993-01-01

420

Ionospheric conductivity modulation in ULF pulsations  

NASA Astrophysics Data System (ADS)

Using incoherent scatter radar and magnetometer measurements, we report that during terrestrial magnetic Pc5 pulsations in the afternoon sector, a modulation of particle precipitation and ionospheric conductivities by a factor of 2 occurs in addition to high-amplitude variations of electric and magnetic fields. The event thus seems to be considerably more complicated than previously studied ones where information about conductivities was mostly not available. Our ground-based data set gives us several clues about magnetospheric processes. The origin of the conductivity variations seems to be periodically modulated diffusion of hot electrons into the loss cone that is in turn caused by a ring current instability. The direction of the phase propagation of the observed disturbances is also consistent with the hypothesis of a ring current source. From the ionospheric electron densities we can roughly estimate the equatorial phase space diffusion rate which seems relatively high. In addition, strong electric field and Poynting flux variations suggest that intense coupling to shear Alfvn modes happens in the magnetosphere. The latitudinal variation of power and wave polarization shows features of a field line resonance. Furthermore, power spectral analysis of conductivities, electric and magnetic fields, reveals that there is a turbulent-like background in all three parameters, which is of magnetospheric origin but modified by the ionosphere. The power law slope of the conductivity spectra is comparable to that of the electric field, while the ground magnetic field shows a steeper decrease with frequency because of the shielding of small-scale current structures. A clear anticorrelation between conductivities and the eastward electric field is interpreted as an ionospheric polarization effect, which transmits Alfvn waves from the ionosphere upward. Finally, we show that due to the time-varying conductivities only the handedness (ratio of left- and right-handed components) of the Hall current is very close to that of the magnetic field, while the electric field has a significantly different polarization.

Buchert, Stephan C.; Fujii, R.; Glassmeier, K.-H.

1999-05-01

421

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

422

Morphology of the dayside ionosphere of Venus: Implications for ion outflows  

Microsoft Academic Search

The nightside ionosphere of Venus is formed mostly by day-to-night transport of ions below the ionopause, with a small contribution from precipitation of energetic electrons from the wake. This nightward flux of ions should result in dayside ionospheres that are characterized by smaller electron density scale heights at high altitudes than those that are characteristic of diffusive equilibrium. In order

J. L. Fox

2008-01-01

423

Experimental evidence of AGW generation as possible explanation of lithosphere-ionosphere coupling mechanism  

Microsoft Academic Search

The existence of ionospheric precursors of earthquakes is widely discussed nowadays in numerous papers and monographs. It is a general opinion that for the reliable identification of ionospheric precursors of seismic hazards a problem oriented satellite project is necessary. A couple of such projects DEMETER in France and VARIANT in Ukraine are expected to be launched next year. In order

Y. Yampolski; A. Zalizovski; G. Lizunov; V. Korepanov

2003-01