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1

Artificial periodic irregularities in the lower ionosphere, atmospheric waves and sporadic E-layer  

Microsoft Academic Search

The long-term researches have shown that artificial periodic irregularities (API) created in the ionosphere plasma are a good means for the ionosphere diagnostics. In the report we present the new applications of the API technique for experimental studies of the lower ionosphere, atmospheric waves and sporadic E-layers. The applications are based on the new so-called two-frequency method of the API

Nataliya V. Bakhmetieva; M. N. Egerev; A. V. Tolmacheva; V. D. Vyakhirev

2010-01-01

2

Artificial Ionospheric Layers during Pump Frequency Stepping Near the 4th Gyroharmonic at HAARP  

NASA Astrophysics Data System (ADS)

We report on artificial descending plasma layers created in the ionosphere F region by high-power high-frequency (HF) radio waves from High-frequency Active Auroral Research Program at frequencies f0 near the fourth electron gyroharmonic 4fce. The data come from concurrent measurements of the secondary escaping radiation from the HF-pumped ionosphere, also known as stimulated electromagnetic emission, reflected probing signals at f0, and plasma line radar echoes. The artificial layers appeared only for injections along the magnetic field and f0>4fce at the nominal HF interaction altitude in the background ionosphere. Their average downward speed ˜0.5km/s holds until the terminal altitude where the local fourth gyroharmonic matches f0. The total descent increases with the nominal offset f0-4fce.

Sergeev, E.; Grach, S.; Shindin, A.; Mishin, E.; Bernhardt, P.; Briczinski, S.; Isham, B.; Broughton, M.; LaBelle, J.; Watkins, B.

2013-02-01

3

Artificial ionospheric mirrors for radar applications  

NASA Astrophysics Data System (ADS)

Recognition of performance limitations associated with traditional skywave over-the-horizon (OTH) HF radars has led a number of investigators to propose the creation of an Artificial Ionospheric Mirror (AIM) in the upper atmosphere, in order to reflect ground-based radar signals for OTH surveillance. The AIM is produced by beaming sufficient electromagnetic power to the lower ionosphere (around 70 km) to enhance the in situ ionization level to 10(exp 7) to 10(exp 8) electrons/cu cm, thereby providing an ionized layer capable of reflecting radar frequencies of 5 to 90 MHz. A baseline AIM system concept and an associated performance evaluation are presented, based upon the relevant ionization and propagation physics and in the context of air surveillance for the cruise missile threat. Results of the subject indicate that a system using this concept would both complement and enhance the performance of the existing skywave OTH radars.

Short, Robert D.; Wallace, Tom; Stewart, Clayton V.; Lallement, Pierre; Koert, Peter

1990-10-01

4

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 Schrödinger 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.

5

Chapman-Layers Ionospheric Model for Mars.  

National Technical Information Service (NTIS)

A numerical model (CLIMM) is developed that adopts functions of two Chapman layers to compute Mars ionospheric electron densities at given local solar zenith angle and height. Electron density profiles derived from Mars Global Survey (MGS)-to-Earth radio ...

A. J. Mannucci C. Ao C. D. Edwards D. S. Kahan G. A. Hajj G. A. Hajj J. L. Callas L. J. Romans S. W. Asmar X. Pi

2008-01-01

6

Modeling of artificial plasma 'bubble' in ionosphere  

NASA Astrophysics Data System (ADS)

Results of a combination of radio-crossing and in situ measurements of plasma density in an artificial plasma 'bubble' in the ionosphere are presented. A shaped charge barium injection was made at a short distance (not greater than 50 m) to plasma diagnostics on the rocket. After injection the rocket passed through an expanding plasma shell. Plasma density depletion inside was more than one order and plasma enhancements on the boundary about 3-5 times that of the background. When the rocket passed the shell and traveled 2.1 km an abrupt drop of telemetry signal level was registered, though the plasma density was not more than 3000 s/cu m.

Oraevskii, V. N.; Ruzhin, Iu. Ia.; Skomarovskii, V. S.; Korobeinikov, V. G.; Kashirin, A. I.; Khriukin, V. I.

1992-12-01

7

Studies of the Lower Ionosphere using Artificial Periodic Irregularities  

NASA Astrophysics Data System (ADS)

Artificial periodic irregularities (API) created in the ionosphere plasma are used for the iono-sphere diagnostics. We present a new applications of API technique for experimental studies of the electron density in the lower ionosphere, atmospheric waves and sporadic E-layers. The applications are based on the new so-called two-frequency method of the API creation. The main results of the ionosphere studies carried out in 2006-2009 by the API technique using SURA heating facility are presented. API are formed in the field of a powerful standing radio wave produced by interference of the incident wave and reflected one by the ionosphere (V.V. Belikovich, E.A. Benediktov, N.V. Bakhmet'eva, A.V. Tolmacheva, Ionospheric Research by Means of Artificial Periodic Irregularities-Katlenburg-Lindau, Germany. 2002. Copernicus GmbH. ISBN 3-936586-03-9). The spatial period of the irregular structure is equal to the standing wavelength ? or the one-half the powerful wavelength ?/2. Ionosphere diagnostics is carried out in the API relaxation (or decay) stage by their sounding of probing radio pulses. The two frequency method bases upon the API creation and the scattering of the probe waves from API at two different frequencies i.e., having different spatial periods of the quasi periodic struc-ture. In the E -region of the ionosphere API are formed as a result of the diffusion redistribution of the ionosphere plasma in the field of the powerful wave. Relaxation of the periodic structure is specified by the ambipolar diffusion process. The API relaxation time is ? = (K 2 Da )-1 where K = 2?/? and Da is the ambipolar diffusion rate. It means that API having different spatial scales destroys with different time scales ? . The API spatial scale depends on the refractive in-dex n that is determined by the electron density N. It is shown the ratio of API relaxation times ? at two frequencies f1 and f2 , measured at the same heights, is connected with the frequencies ratio and the refractive index ratio as ? = ?1 /?2 = (f2 /f1 ) · (n2 /n2 ). The measurement of the 2 2 2 1 ?(h) dependence makes it possible to determine electron density profile N(h). The profile is used for determination of the neutral temperature and density, the turbulent velocity and also the sporadic E -layer parameters. Plasma vertical velocity V was determined by measuring the phase of the probe radio waves scattered from API after switching off the power heating facility, i.e., at the API relaxation stage. The velocity and N(h) data have been used for estimation the total density metallic ions and the effective recombination rate at the sporadic E -layer height. The measured vertical velocity shift was about 10-4 c-1 - 3.5 · 10-3 c-1 . The shift can be caused by acoustic gravity waves and is sufficient for collecting of metal ions in sporadic E -layer. The waves with periods of 10-180 min have been found by the spectral analysis applied to the scat-tered signals characteristics. The temporal variations of the electron density 10-30% in the Es-layer were observed in some occasions. It is possible they connected with patch structure of the sporadic E -layer. One of the API application is a determination of the masses of the predominant metallic ions at the sporadic E -layer height. It is based on the experimental ob-servation that height dependence of the API relaxation time ? (h) has a local maximum at the sporadic E -layer location. The long-lived metallic ions cause the growth of the API relaxation time ? . We have obtained that the observed by API technique sporadic E -layers at the height of 95-110 km contained Ca+ and F e+ ions predominantly and the total density of the metallic percentage wise the electron density reached 60-90% sometimes. Acknowledgments. The work has been supported by RFBR grants No. 08-02-97036 and 09-05-00450.

Bakhmetieva, Nataliya V.; Egerev, Mikhael N.; Tolmacheva, Ariadna V.; Vyakhirev, Valeriy D.

8

Novel artificial optical annular structures in the high latitude ionosphere over EISCAT  

Microsoft Academic Search

The EISCAT low-gain HF facility has been used repeatedly to produce artificially stimulated optical emissions in the F-layer ionosphere over northern Scandinavia. On 12 November 2001, the high-gain HF facility was used for the first time. The pump beam zenith angle was moved in 3° steps along the north-south meridian from 3°N to 15°S, with one pump cycle per position.

M. T. Rietveld; A. Senior; A. J. Kavanagh; B. Isham; F. Honary

2004-01-01

9

Artificial Ionospheric Heating Experiments Conducted by a Magnetosphere-Ionosphere Coupling Model  

NASA Astrophysics Data System (ADS)

This presentation discusses computational dynamics and results of artificial heating in the ionosphere. The results are then compared to experiments including a geophysical experiment conducted at the Polar Aeronomy and Radio Science Summer School (PARS) in conjunction with the High Frequency Active Auroral Research Program (HAARP) The computational model includes the following terms: ion inertia, Ohm's law (Hall term, electron pressure term, electron neutral and electron ion collisions), ionization, recombination, electron energy (heat advection, conduction, heating through ionization, ohmic heating, gravity, energy loss to neutrals and ions), as well as parameterized collisions frequencies, and a height resolved neutral atmosphere. Atmospheric conditions for the time of the experiment (plasma density, temperature, etc) are used as initial conditions. The power and frequency of the heater facility are then used to compute the heating of the ionosphere. Data processing for the experiment and model are ongoing.

Stevens, R. J.; Otto, A.; Krzykowski, M.; Solie, D.

2007-12-01

10

System concept and analysis of an Artificial Ionospheric Mirror (AIM) radar  

NASA Astrophysics Data System (ADS)

Recognition of performance limitations associated with traditional skywave over-the-horizon (OTH) high frequency (HF) radars has led a number of investigators to propose the creation of an Artificial Ionospheric Mirror (AIM) in the upper atmosphere, in order to reflect ground-based radar signals for OTH surveillance. The AIM is produced by beaming sufficient electromagnetic power to the lower ionosphere (around 70 km) to enhance the in situ ionization level to 10(exp 7) to 10(exp 8) electrons/cu cm, thereby providing an ionized layer capable of reflecting radar frequencies of 30 to 90 MHz. This paper presents a baseline AIM system concept and an associated performance evaluation, based upon the relevant ionization and propagation physics and in the context of air surveillance for the cruise missile threat. Results of the subject study indicate that a system using this concept would both complement and enhance the performance of the existing skywave OTH radars.

Short, Robert D.; Stewart, Clayton V.; Wallace, Tom; Lallement, Pierre; Koert, Peter

1990-08-01

11

Interaction of oblique wave beam with ionospheric layer F2  

NASA Astrophysics Data System (ADS)

Interaction of a powerful obliquely incident wave beam of decameter radio waves with the ionospheric F2 layer is analyzed. Much like the linear case, propagation through the natural anti-waveguide layer F2 splits the initial beam. Some part of its energy leaks through the ionospheric layer, the other part goes back along a downward trajectory. However, nonlinearity leads to further stratification of the ionospheric layer. A new feature, in comparison with the linear case, is appearing a narrow waveguide beneath the F2 layer maximum which traps a small part of the beam energy. We study the relationship between these parts of the wave field in a simplified model of parabolic F2 layer, with nonlinearity caused by thermal plasma expulsion from the high field intensity region. Analytical results are supplemented with numerical estimates of the effects.

Molotkov, I. A.; Atamaniuk, B.; Popov, A. V.

2013-06-01

12

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

13

First EISCAT measurement of electron-gas temperature in the artificially heated D-region ionosphere  

Microsoft Academic Search

The ionospheric electron gas can be heated artificially by a powerful radio wave. According to our modeling, the maximum effect of this heating occurs in the D-region where the electron temperature can increase by a factor of ten. Ionospheric plasma parameters such as Ne,Te and Ti are measured by EISCAT incoherent scatter radar on a routine basis. However, in the

A. Kero; T. Bösinger; P. Pollari; E. Turunen; M. Rietveld

2000-01-01

14

Observations of radiation from an electron beam artificially injected into the ionosphere  

Microsoft Academic Search

This paper reports the observations of waves generated by a controlled beam of particles artificially injected into the ionosphere and magnetosphere. The measurements were made during the Electron Echo 1 experiment, in which an electron accelerator was carried to a height of 350 km in the ionosphere from Wallops Island, Virginia, on an Aerobee 350 sounding rocket. It injected into

D. G. Cartwright; P. J. Kellogg

1974-01-01

15

Variation in the Secondary Layer of the Mars Ionosphere  

NASA Astrophysics Data System (ADS)

We investigate variations in the structure of the secondary plasma layer (M1) in the Mars ionosphere that arise from changes in the solar irradiance and the solar zenith angle; we compare to similar variations in the primary (M2) layer of the ionosphere. We analyze the altitude and peak number density of both layers in the Mars Global Surveyor (MGS) dayside electron density profiles. We also employ these observations as new constraints to test a photochemical model of the Mars ionosphere. We find that the variations in the M1 layer are very similar to those of the M2 layer. The peak electron density of the M1 layer has the same dependence on the solar zenith angle as that of the M2 layer, and is consistent with an ideal Chapman layer. The altitude of the M1 layer rises with increasing solar zenith angle, though more slowly than the M2 layer. Periodic changes in electron density are present a both peaks, which follow changes in the solar irradiance due to the rotation of the sun. A one-dimensional photochemical model is used to simulate an electron density profile for each day during a six month stretch of MGS observations. The model's ability to reproduce observations depends strongly on the representation of electron temperature. Observations are matched most closely by simulations in which the electron temperature at the peaks remains constant with time.

Fallows, Kathryn; Girazian, Zachary; Matta, Majd; Withers, Paul

2013-04-01

16

Meteor layers in the Martian ionosphere: Observations and Modelling  

NASA Astrophysics Data System (ADS)

Observations by the radio science experiments MaRS on Mars Express and VeRa on Venus Express revealed the appearance of additional electron density layers in the Martian and Venu-sian ionosphere below the common secondary layers in some of the ionospheric profiles. This may be an indicator for the signature of meteoric particles in the Martian atmosphere. There are two main sources of meteoric flux into planetary atmospheres: the meteoroid stream com-ponent whose origin is related to comets, and the sporadic meteoroid component which has its source in body collisions i.e. in the Kuiper belt or the asteoroid belt. This paper will present the detection status for the Martian meteor layers in MaRS electron density profiles and the first steps towards modelling this feature. The presented meteor layer model will show the influence of the sporadic meteoric component on the Martian ionosphere. Input param-eters to this model are the ablation profiles of atomic Magnesium and Iron in the Martian atmosphere caused by sporadic meteoric influx, the neutral atmosphere which is taken from the Mars Climate Database and electron density profiles for an undisturbed ionosphere from a simple photochemical model. The meteor layer model includes the effects of molecular and eddy diffusion processes of metallic species and contains chemical reaction schemes for atomic Magnesium and Iron. It calculates the altitude-density-profiles for several metallic species on the basis of Mg and Fe in chemical equilibrium by analytical solution of the reaction equations. A first comparison of model and observed meteoric structures in the Martian ionosphere will be presented.

Peter, Kerstin; Molina Cuberos, Gregorio J.; Witasse, Olivier; Paetzold, Martin

17

Modelling of pump-induced artificial ion upwelling in the upper ionosphere at EISCAT  

NASA Astrophysics Data System (ADS)

Pumping the ionosphere with high-frequency high-power radio waves enhances the F-region electron temperature by a few thousand Kelvin and sometimes the ion temperature by a few hundred Kelvin. Ionospheric pumping leads to a number of well-established phenomena, for example, field-aligned plasma irregularities, plasma resonances and artificial optical emissions. We report on novel observations of artificial ionospheric ion upwelling on the topside and down welling on the bottom side during controlled ionospheric modification experiments at EISCAT. Simultaneous radar observations of electron and ion temperature allow us to model the accelerating forces on the ions. The dominant force appears to be ambipolar diffusion in agreement with the natural occurrence of ion outflow.

Kosch, Michael; Rietveld, Michael; Ogawa, Yasunobu; Fujii, Ryoichi

18

An analysis of pump-induced artificial ionospheric ion upwelling at EISCAT  

NASA Astrophysics Data System (ADS)

Ion outflow from the high-latitude ionosphere is a well-known phenomenon and an important source of plasma for the magnetosphere. It is also well known that pumping the ionosphere with high-power high-frequency radio waves causes electron heating. On a few occasions, this has been accompanied by artificially induced ion upwelling. We analyze such a controlled experiment at EISCAT up to 600 km altitude. The pump-enhanced electron temperatures reached up to ˜4000 K above 350 km, and ion upwelling reached up to ˜300 m/s above 500 km altitude. The pump-induced electron pressure gradient can explain the ion velocity below 450 km. Between 450 and 600 km the electron pressure gradient correlates equally with ion acceleration and ion velocity, which represents the transition altitude to free ion acceleration. The electron gas pressure gradient can explain ion upwelling, at least up to 600 km altitude. In addition, such active experiments open the possibility to estimating the F layer ion-neutral collision frequency and neutral density with altitude from ground-based observations.

Kosch, M. J.; Ogawa, Y.; Rietveld, M. T.; Nozawa, S.; Fujii, R.

2010-12-01

19

Self-consistent Powerful Radio-wave Absorption by Artificial Ionosphere Turbulence  

NASA Astrophysics Data System (ADS)

The numerical simulations of non-linear Schrodinger equation in inhomogeneous plasma layer with pumping and damping are carried out to investigate the influence of self-consistent incident powerful electromagnetic wave absorption in the regions of plasma turbulence excitation to reflection index dynamics. The damping of electromagnetic wave is taking into account by including in the set of equations (Kochetov A.V., Mironov V. A., Terina G.I., Strong Turbulence Effects in Artificially Disturbed Ionosphere, Adv. Space.Res. 2002,vol.29, No.9, p.1369) imaginary part of plasma dielectric permitivity in the vicinity of wave reflection point in the regions with strong electromagnetic field. The large range of damping parameters: threshold, decrement; different amplitude dependence, including hysteretic one, is studied, in particular, in correlation to (V. D. Shapiro, V. I. Shevchenko, Handbook of Plasma Physics, Eds. A. A. Galeev, R N. Sudan, Elsevier, 1984, vol.2, p.119). It is obtained for some regimes that the calculated reflection index dynamics agrees qualitatively to the experimental results (B. Thide, E. N. Sergeev, S. M. Grach,T. B. Leyser, T. D. Carrozi, Competition between Langmuir and upper hybrid turbulence in an HF pumped ionosphere, Phys. Rev. Lett., 2005, vol. 95, no.25, p. 255002). The work is supported in part by Russian Foundation for Basic Research by the grant No. 06-02-17334.

Kochetov, Andrey; Menkova, Uliya; Grach, Savely

20

Observations and effects of artificial density layers on oblique high-frequency backscatter  

NASA Astrophysics Data System (ADS)

An improved method of estimating ground-scattered power using high-frequency (HF) ray tracing techniques that overcomes the limitations of the derivation presented by Bristow and Greenwald (1995) is presented. The improved method is applied toward identifying the effects of an artificial ionospheric density layer on measured ground scatter power. The presence of artificial density layers induced at the High Frequency Active Auroral Research Program (HAARP) station in Gakona, Alaska, are observed through the ground-scattered power received by the Kodiak Super Dual Auroral Radar Network (SuperDARN) HF radar. The location and physical dimensions of the artificial layers are estimated by simulating radar returns using HF ray tracing through a model ionosphere that includes a model artificial density layer. Simulation results of ground-scattered power as a function of range are compared to the measured ground-scattered power as a function of range during a time period when artificial layers were evident in ionogram data. It is shown that a model artificial density layer based on research by Pedersen et al. (2009) produces simulation results that approximate the mean of the measured results.

Theurer, T. E.; Bristow, W. A.

2012-04-01

21

Operational ionospheric model as a component of SSA physical layer  

NASA Astrophysics Data System (ADS)

Space Situation Awareness (SSA) it is the need of now-casting and predictive knowledge of space events, conditions and space system configuration. The surveillance systems implemented to give space system and object characterization needs fusion in physical layer the information related among others to weather conditions in space and from ground-based sensors. The models of environmental elements make it possible to provide current and forecast conditions and their impact on implemented infrastructure are crucial for SSA issues. The operational models of the ionosphere are the example of the such important issue. In the paper the single station operational ionospheric model is discussed together with its regional mapping and updating methodology to fulfill SSA regional telecommunication infrastructure requirements.

Stanislawska, Iwona; Klos, Zbigniew

22

Studying the features of transport processes in the upper ionosphere by means of HF-induced artificial ionosphere turbulence  

NASA Astrophysics Data System (ADS)

We analyze some possibilities of experimental determination of the velocity at which the artificial plasma disturbances, induced in the regions of resonance interactions between a HF powerful wave and the F-region ionospheric plasma, spreads along a geomagnetic field line. The diagnostics of these disturbances is based on the used of the stimulated electromagnetic emission (SEE) HF-induced in the ionosphere disturbed volume. The experimental results discussed here were obtained in measurements at the Sura heating facility (Nizhnii Novgorod, Russia) in 1996 - 2003 employing the so-called additional pumping scheme. In such a scheme radiation of one from three module of the Sura facility is used as a diagnostic wave inducing diagnostic SEE (DSEE). Variations in characteristics of the DSEE are a result of influence of turbulence induced by the second powerful wave (pump wave, PW), which is radiated at another frequency and used here as an external source of plasma disturbances. Thus, two spaced disturbed volumes are formed in the ionosphere F-region. The temporal delay between the appearance of PW-produced disturbances at DSEE generation level and the time of switching on the PW allows to estimate their spread velocity along geomagnetic field lines. Results of the performed measurements have unambiguously shown that the spread velocity was usually higher than the ion thermal velocity (VTi ? 10^5 cm/s under conditions of measurements). In many cases, this velocity was close to and sometimes even much higher than the electron thermal velocity VTe ? 2\\cdot10^7 cm/s. It is important to note that pumping during a time interval of 50 - 100 ms at the effective radiated power of about of 50 MW is sufficient to produce visible changes in DSEE intensity. Taking into account the experimental data obtained, it can be assumed that we deal here with field-aligned flows of thermal and suprathermal electron HF-induced in the ionosphere disturbed volume. These electron flows, due to short-circuit currents induced simultaneously, can stimulate the appearance of secondary ionosphere disturbances in a region whose size is much larger than the resonance interaction region. Generation of artificial irregularities in such a large ionosphere region has been recently confirmed in satellite tomography experiments performed at the Sura facility in August 2002. The work was supported by RFBR Grant %No. 02-02-17475 and CRDF Grant %No. RPO-1334.

Frolov, V.; Sergeev, E.

23

Propagation of artificially excited Langmuir waves in the ionosphere  

Microsoft Academic Search

The MPAE heater near Tromso, Norway was used to excite parametric decay instabilities in the ionosphere, which then were observed by means of the EISCAT radar. During unfavorable geophysical conditions the heater power may not be sufficient to exceed the threshold of excitation for wavelengths matched to the observing radar. Evidence is presented that during such conditions instabilities of longer

H. Kohl; H. Kopka; P. Stubbe; C. Lahoz

1987-01-01

24

Photometric instrument for studies of ionospheric artificial airglow emission caused by antropogenous disturbances  

NASA Astrophysics Data System (ADS)

One of informative methods of ionospheric processes data acquisition is based on registration of artificial airglow emission. In fact, artificial modifications of the ionosphere by powerful decameter radiowaves cause airglow emission on waves lengths 1270, 630, 557.7, 427.8 nm. In these experiments airglow emission were found at long expositions only as the registration systems of low sensitivity were used. It has allowed investigating the stages when developing of thermal parametric instabilities mechanism contribute mainly into the electron acceleration. The increase of artificial airglow emission at 557.7 nm was caused by impulses with 5 ms duration that corresponds to times of development of pondermotive parametric instability of ionosphere. That effect was found for the first time at the Kazan State University in collabora-tion with NIRFI (N. Novgorod) [Gumerov R.I., Kapkov V.B. et al. //Radiophysics and Quant. Electronics. 1999. Vol 42. P. 463.]. A new mobile photometric instrument equipped with a high-sensitive photometer and CCD-camera, system of GPS time-synchronization, system of "SURA"-channel review by HF-receiver, and systems of experimental data automatic registration by computer was engineered in the Kazan University. One makes possible the investigation of physical processes at the ionosphere disturbed by powerful radioemission, injections of chemically active substances and plasmas beams. The authors gratefully acknowledge Russian Foundation for Basic Research (Grant No 08-02-01188) for the financial support.

Nasyrov, Igor; Gumerov, Rustam; Nasyrov, Albert; Nikonenkov, Andrey

25

Characterization of propagation and communication properties of the natural and artificially disturbed ionosphere  

NASA Astrophysics Data System (ADS)

This basic research project, conducted during the period starting 12 Sept. 1990 and ending 12 Dec. 1994, studied the effects of natural and artificial ionospheric disturbances on HF and VHF propagation and communication. This project was reasonably divided into two parts where each stood by itself; VHF meteor scatter investigation and HF ionospheric modification studies. In addition to these two studies, a third study was later added to the project to include a Joint Electromagnetic Warfare Center (JEWC) electromagnetic wave propagation and signal loss study. Each of these studies are addressed independently within this final report.

Reinisch, Bobo W.; Sales, Gary S.; Brent, Ronald; Ostergaard, Jens; Huang, Yuming; Li, Eric; Newbury, Steven

1995-05-01

26

Evolution and dynamics of ionospheric intermediate layers above Arecibo Observatory  

NASA Astrophysics Data System (ADS)

The research presented in this dissertation focuses on the formation, evolution, and morphology of midlatitude intermediate layers. This work explores layer morphology using three distinct techniques: in-situ rocket measurements, incoherent scatter radar observations, and a first principles numerical model. The rocket and radar data are from the 1998 Coqui II rocket campaign. This data set is then used in conjunction with the numerical model, which was conceived, developed, and validated as a tool for studying nighttime ionospheric E- region dynamics during the course of this research. The first portion of the research utilizes data provided by instruments aboard a sounding rocket. Neutral wind and plasma density measurements of a weak layer allow the first exploration of the density structure and wind field morphology of an intermediate layer. Coupled with simultaneous data from the Arecibo Observatory (AO), the upleg and downleg density profiles enable the first detailed investigation of the horizontal extent and variation of an intermediate layer. Next, the nightly variability of intermediate layer structure is examined using data from the Arecibo Observatory taken during the three month period of the Coqui II rocket campaign. The numerous layer observations permit a study of the effects of geomagnetic activity on layer development, and provide a qualitative understanding of nightly variability in the lower ionosphere. A numerical model, consisting of three independent phases, explores specific aspects of layer morphology. Phase I calculates the apparent nighttime E- region vertical ion velocities from a time sequence of density profiles. Phase II investigates layer formation due to a static neutral wind field. In- situ measured winds are used to initialize the model and the results are compared to the observed density profiles. Phase III employs time-varying neutral winds to explore the coupling between metallic ion transport and local neutral wind variations. For the first time, the relative metallic ion transport efficiency of meridional versus zonal neutral winds is explored as a function of wave parameters and time. Phase III also investigates layer morphology resulting from the application of the complete horizontal wind field as specified by the empirical model known as the Horizontal Wind Model, HWM-93.

Bishop, Rebecca Lynn

2001-11-01

27

Ionospheric observations of F region artificial plasma turbulence, modified by powerful X-mode radio waves  

NASA Astrophysics Data System (ADS)

We study the influence of additional X-mode heating of the ionospheric plasma on the features of artificial ionospheric turbulence, induced in the ionospheric F region by O-mode waves over the ``Sura'' heating facility (Nizhny Novgorod, Russia). The X heating is shown to suppress the generation of HF plasma turbulence resulting from the development of both the parametric decay and thermal parametric instabilities. Typical times of variations in the turbulence intensity change from <=0.1 s to ~10 s, strongly depending on the heating scheme. Aftereffects of the X heating last up to 30-60 s. We distinguish at least three types of phenomena, according to the observed typical times of the processes, and discuss possible reasons for each of them.

Frolov, V. L.; Kagan, L. M.; Sergeev, E. N.; Komrakov, G. P.; Bernhardt, P. A.; Goldstein, J. A.; Wagner, L. S.; Selcher, C. A.; Stubbe, P.

1999-06-01

28

The ionosphere of Mars: modeling the photochemical dominated region and subjacent meteor layers  

NASA Astrophysics Data System (ADS)

The dayside ionosphere of Mars can be divided into several regions. The photochemical dominated regime includes the main peak M2, mainly formed by solar EUV and the lower peak M1, formed by X-ray and impact ionization by solar photo-electrons. The ionospheric topside often contains a "bulge", an accumulation of electrons above the main peak and a diffusion region, where molecular diffusion dominates the photochemical ionospheric processes. An ionopause can be formed by the interaction of the planetary ionosphere with the solar wind. Sporadic layers of additional electron density (Fig. 1 and Fig. 2) have been identified below M1 in MaRS (Mars Express) and MGS radio science observations. In situ measurements in the Earth atmosphere revealed accumulations of metallic ions in the lower ionospheric region. A meteoroidic origin for this phenomenon is now generally accepted. In situ measurements of metallic ions in the ionosphere of Mars do not exist. A 1D photochemical model for the general ionosphere (IonA, Ionization in Atmospheres) is combined with a model for the meteor layers to study the influence of meteoroids on the ionosphere of Mars. This paper shall present a general comparison between IonA model results and MaRS ionospheric observations. Selected MaRS observations shall be modeled with a combination of IonA and the meteor layer model to gain a deeper understanding of the photochemical processes at this ionospheric altitude region.

Peter, K.; Molina-Cuberos, G.; Witasse, O.; Pätzold, M.

2012-09-01

29

On the {open_quotes}caviton{close_quotes} signal, scattered by artificial ionospheric turbulence  

SciTech Connect

The results of experimental investigations of the {open_quotes}cavitron{close_quotes} signal (CS), scattered by artificial ionospheric turbulence are presented at the vertical sounding by short radiopulses. The dependences of the amplitude and the appearance time of CS on the power of the heating transmitter, the frequency of the probing one, and the virtual height of scattering are considered. The periodic generation of CS was observed with periods of changing from fractions of a second up to several seconds.

Terina, G.I. [Radiophysical Research Institute, Nizhny Novgorod (Russian Federation)

1994-12-01

30

Last studies of artificial airglow emission of ionospheric plasma at the  

Microsoft Academic Search

Experimental results of September 2007 on artificial airglow emission at 557.7 nm [green line, the radiation of atomic oxygen level O(1 S), the excitation threshold 4.17 eV, radiation lifetime 0.7 s)] and 630 nm [red line, the radiation of atomic oxygen level O(1 D), the excitation threshold 1.96.17 eV, radiation lifetime ˜ 100 s)] during HF pumping of the ionosphere

Igor Nasyrov; Savely Grach; Nasyrov Albert; Gumerov Rustam; Klimenko Vladimir

2008-01-01

31

On the {open_quotes}caviton{close_quotes} signal, scattered by artificial ionospheric turbulence  

Microsoft Academic Search

The results of experimental investigations of the {open_quotes}cavitron{close_quotes} signal (CS), scattered by artificial ionospheric turbulence are presented at the vertical sounding by short radiopulses. The dependences of the amplitude and the appearance time of CS on the power of the heating transmitter, the frequency of the probing one, and the virtual height of scattering are considered. The periodic generation of

Terina

1994-01-01

32

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

33

Generation of artificial magnetic pulsations in the Pc1 frequency range by periodic heating of the Earth’s ionosphere: indications of ionospheric Alfvén 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 0.1–3 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. Bösinger; T. Pashin; A. Kero; P. Pollari; P. Belyaev; M. Rietveld; T. Turunen; J. Kangas

2000-01-01

34

Analytical method for determining the location of ionospheric and atmospheric layers from radio occultation data  

NASA Astrophysics Data System (ADS)

We generalize the fundamental principle of the radio-occultation method for studying the atmospheres and ionospheres of planets and the Earth. The criterion containing the necessary and sufficient condition under which the tangential point, at which the refractive-index gradient is normal to the ray trajectory coincides with the radio-ray perigee, is obtained. The method for determining the location and parameters of ionospheric and ionospheric layers, which is based on the relationship between the amplitudes and phases of the analytic functions determined from variations in the phase path (eikonal) and intensity of the radio-occultation signal, is proposed. This method yields qualitative and quantitative estimations of the value of the spatial displacement of the ionospheric or ionospheric layer with respect to the radio-ray perigee and allows one to determine the altitude and inclination of the ionospheric layer. The developed method is, in particular, required for determining the location and inclination of the wind-shear region and the direction of propagation of internal waves in the ionosphere and the atmosphere. This method is simpler and more accurate than the back-propagation, radio-holographic method which was previously used for determining the location of the ionospheric irregularities.

Pavelyev, A. G.; Zhang, K.; Wang, C. S.; Liou, Y. A.; Kuleshov, Yu.

2012-08-01

35

Simulation of Self-consistent Radio Wave Artificial Ionospheric Turbulence Pumping and Damping  

NASA Astrophysics Data System (ADS)

The numerical simulations of the action of self-consistent incident powerful electromagnetic wave absorption arising in the regions of artificial plasma turbulence excitation at formation, saturation and relaxation stages of turbulent structures (Kochetov, A.V., Mironov, V.A., Te-rina, G.I., Bubukina V. N, Physica D, Nonlinear phenomena, 2001, 152-153, 723) to reflection index dynamics are carried out. The nonlinear Schrüdinger equation in inhomogeneous plasma layer with incident electromagnetic wave pumping and backscattered radiation damping (Ko-chetov, et al, Adv. Space Res., 2002, 29, 1369 and 2006, 38, 2490) is extended with the imagi-nary part of plasma dielectric constant (volume damping), which is should be taken into account in strong electromagnetic field plasma regions and results the energy transformation from elec-tromagnetic waves to plasma ones at resonance interaction (D.V. Shapiro, V.I. Shevchenko, in Handbook of Plasma Physics 2, eds. A.A Galeev, R.N. Sudan. Elsevier, Amsterdam, 1984). The volume damping reproduces the basic energy transformation peculiarities: hard excitation, nonlinearity, hysteresis (A.V. Kochetov, E. Mjoelhus, Proc. of IV Intern. Workshop "SMP", Ed. A.G. Litvak, Vol.2, N. Novgorod, 2000, 491). Computer modeling demonstrates that the amplitude and period of reflection index oscillations at the formation stage slowly depend on damping parameters of turbulent plasma regions. The transformation from complicated: quasi-periodic and chaotic dynamics, to quasi-stationary regimes is shown at the saturation stage. Transient processes time becomes longer if the incident wave amplitude and nonlinear plasma response increase, but damping decreases. It is obtained that the calculated reflection and absorption index dynamics at the beginning of the saturation stage agrees qualitatively to the experimental results for ionosphere plasma modification study (Thide B., E.N. Sergeev, S.M. Grach, et. al., Phys. Rev. Lett., 2005, 95, 255002). The work was supported in part by RFBR grant 09-02-01150-a.

Kochetov, Andrey

36

Biomimetic layer-by-layer assembly of artificial nacre.  

PubMed

Nacre is a technologically remarkable organic-inorganic composite biomaterial. It consists of an ordered multilayer structure of crystalline calcium carbonate platelets separated by porous organic layers. This microstructure exhibits both optical iridescence and mechanical toughness, which transcend those of its constituent components. Replication of nacre is essential for understanding this complex biomineral, and paves the way for tough coatings fabricated from cheap abundant materials. Fabricating a calcitic nacre imitation with biologically similar optical and mechanical properties will likely require following all steps taken in biogenic nacre synthesis. Here we present a route to artificial nacre that mimics the natural layer-by-layer approach to fabricate a hierarchical crystalline multilayer material. Its structure-function relationship was confirmed by nacre-like mechanical properties and striking optical iridescence. Our biomimetic route uses the interplay of polymer-mediated mineral growth, combined with layer-by-layer deposition of porous organic films. This is the first successful attempt to replicate nacre, using CaCO(3). PMID:22828626

Finnemore, Alexander; Cunha, Pedro; Shean, Tamaryn; Vignolini, Silvia; Guldin, Stefan; Oyen, Michelle; Steiner, Ullrich

2012-07-24

37

On the physical mechanism of the ionospheric storms in the F2-layer  

NASA Astrophysics Data System (ADS)

AE-C satellite data on the neutral thermospheric composition and temperature along with the ground-based ionospheric sounding data at Winnipeg, Boulder, and Havana were used to analyze the physcial mechanism of F2-layer parameter variations during the ionospheric storm on January 25, 1974. Rishbeth's isobaric F2-layer concept concerning a negative F2-layer storms is analyzed. The observed negative as well as positive n(e)mF2 variations during January 25, 1974 storm period may be explained within the scope of the current F2-region theory without taking into account additional processes proposed by Rishbeth.

Mikhailov, A. V.; Terekhin, Iu. L.; Skoblin, M. G.; Mikhailov, V. V.

1992-10-01

38

Generalized expressions for variations in critical frequencies, electron densities and altitudes of the ionospheric layers.  

National Technical Information Service (NTIS)

We develop generalized mathematical expressions for time and space variations of peak electron densities of the ionospheric D, E, F1 and F2 layers as well as corresponding variations in the altitudes of the electron density peaks in each of these layers. ...

E. C. Njau

1990-01-01

39

Simultaneous observations of radio wave phase and intensity variations for locating the plasma layers in the ionosphere  

Microsoft Academic Search

A new method is introduced to locate the layered structures in the ionosphere based on simultaneous observations of radio wave temporal intensity and phase variations in trans-ionospheric satellite-to-satellite links. The method determines location of the tangent point on the trans-ionospheric ray trajectory where gradient of refractivity is perpendicular to the ray trajectory and the influence of a layered structure on

Y. A. Liou; A. G. Pavelyev

2006-01-01

40

First EISCAT measurement of electron-gas temperature in the artificially heated D-region ionosphere  

NASA Astrophysics Data System (ADS)

The ionospheric electron gas can be heated artificially by a powerful radio wave. According to our modeling, the maximum effect of this heating occurs in the D-region where the electron temperature can increase by a factor of ten. Ionospheric plasma parameters such as Ne,Te and Ti are measured by EISCAT incoherent scatter radar on a routine basis. However, in the D-region the incoherent scatter echo is very weak because of the low electron density. Moreover, the incoherent scatter spectrum from the D-region is of Lorentzian shape which gives less information than the spectrum from the E- and F-regions. These make EISCAT measurements in the D-region difficult. A combined EISCAT VHF-radar and heating experiment was carried out in November 1998 with the aim to measure the electron temperature increase due to heating. In the experiment the heater was switched on/off at 5 minute intervals and the integration time of the radar was chosen synchronously with the heating cycle. A systematic difference in the measured autocorrelation functions was found between heated and unheated periods.

Kero, A.; Bösinger, T.; Pollari, P.; Turunen, E.; Rietveld, M.

2000-09-01

41

A method for improving plasma temperature estimates from incoherent scatter analysis during artificial ionospheric modification experiments  

NASA Astrophysics Data System (ADS)

Spectral features in incoherent scatter data, such as those caused by the purely growing mode (PGM), can often be strongly enhanced during the first few seconds of artificial ionospheric heating experiments, such as those carried out using the high-power European Incoherent Scatter HF heater at Tromsø. These features, often referred to as "overshoot" effects, are indicators of turbulent non-Maxwellian plasma, and the analysis of these spectra using standard incoherent scatter data analysis software leads to a poor estimation of the plasma parameters (particularly electron and ion temperature) during RF heating experiments. In this study, a procedure is developed to derive a more reliable estimate of plasma temperature during periods when the incoherent scatter spectrum is affected by contamination from the PGM. This is achieved by removing the PGM from the measured spectrum and then analyzing the modified spectrum using standard software. The results are compared to those obtained from the analysis of the original, contaminated spectra. It is found that the differences between the results obtained from the corrected and uncorrected spectra are strongly proportional to the magnitude of the PGM feature. We also show that the bulk temperatures during the remainder of the "heater on" period after the overshoot can generally be estimated reliably by the standard analysis software, though with some important exceptions. These results are important since the plasma temperatures play a crucial role in governing thermal conduction processes, and their correct estimation is thus very important to understanding the underlying physical processes which occur during ionospheric heating.

Vickers, H.; Robinson, T.; McCrea, I. W.

2010-11-01

42

Radar observations of the overdense ionospheric ionization created by the artificial electron beam in the 'Zarnitza-2' experiment  

NASA Astrophysics Data System (ADS)

This work contains an analysis of experimental radar data obtained in the 'Zarnitza-2' experiment when the artificial electron beam was injected into the ionosphere below 100 km. The signals observed just after switching off the electron gun are interpreted as radio echoes of overdense secondary ionization produced by the beam. The size of the secondary ionization torch is estimated and distributions of ionization over the cross-section of the torch are calculated and represented at different time moments, taking into account the motion of the rocket. The azimuth dependence of the echo amplitudes is discussed. The obtained Doppler velocity distribution can be interpreted as a height profile of ionospheric winds.

Zhulin, I. A.; Kustov, A. V.; Uspenskii, M. V.; Miroshnikova, T. V.

1980-09-01

43

Study of the ionosphere of Mars: application and limitations of the Chapman-layer model  

NASA Astrophysics Data System (ADS)

The study of data from Viking, Mars Global Surveyor and Mars Express missions is enabling a rapid progress in the knowledge of ionosphere of Mars. Although the Earth's ionosphere is a reference is necessary to note that Mars doesn't have a global magnetic field to form a magnetosphere and the composition of his atmosphere is very different from the case of the Earth. Therefore, the effect of solar wind on the atmosphere, chemical reactions and ionization processes are very different in the two planets. For this reason there may be doubts about the applicability of terrestrial ionospheric models to the ionosphere of Mars. In a first step in this line of study we have applied the Chapman layer model to a significant number of radio-occultation data obtained by the Mars Global Surveyor mission to check the validity range for the fit of the electron density profiles. We also analyze the status of the ionosphere under different conditions of latitude, longitude, time of observation, Martian seasons and solar activity to compare these results with the characteristics and variations in the Earth's ionosphere.

Sanchez-Cano, B.; Herraiz, M.; Rodriguez-Caderot, G.; Radicella, S. M.

2011-11-01

44

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

45

Planetary and tidal wave-type oscillations in the ionospheric sporadic E layers over Tehran region  

NASA Astrophysics Data System (ADS)

It is believed that in the lower ionosphere, particularly in the ionospheric sporadic E (Es) layers (90-130 km), the planetary and tidal wave-type oscillations in the ionized component indicate the planetary and tidal waves in the neutral atmosphere. In the present work, the presence of wave-type oscillations, including planetary and tidal waves in the ionospheric sporadic E layers over Tehran region is examined. Data measured by a digital ionosonde at the ionospheric station of the Institute of Geophysics, University of Tehran, from July 2006 to June 2007 are used to investigate seasonal variations of planetary and tidal waves activities. For the purpose of accurate comparison between different seasons, wavelet transform is applied to time series of foEs and h?Es, namely, the critical frequency and virtual height of Es layers, respectively. The results show that the sporadic E layers over Tehran region are strongly under the influence of upward propagation of waves from below. More specifically, among diverse range of periodicities in the sporadic E layers, we found that diurnal (24 hours) and semidiurnal (12 hours) oscillations in all seasons for both parameters. Moreover, terdiurnal (8 hours) tide-like variation is observed during spring and summer for foEs parameter and summer and winter for h?Es. Furthermore, the results show that diurnal tidal waves obtain their maximum activities during autumn and winter seasons, and their activities decrease during the late spring and summer. In addition, periods of about 2, 4, 6, 10, 14, and 16 days in our observation verifies the hypothesis of upward propagation of planetary waves from lower atmosphere to the ionosphere. Moreover, planetary waves have their maximum activities during equinox.

Karami, K.; Ghader, S.; Bidokhti, A. A.; Joghataei, M.; Neyestani, A.; Mohammadabadi, A.

2012-04-01

46

Monitoring of sporadic plasma layers in the lower ionosphere in the communication link satellite-to-satellite  

Microsoft Academic Search

Method of global monitoring of sporadic plasma layers in the lower ionosphere is developed. In-vestigations were carried out by use of analysis of the amplitude and phase components of radio holograms obtained during the radio occultation missions CHAMP, FORMOSAT-3. Sporadic amplitude scintillation observed in RO experiments contain important information concerning the seasonal, geographical, and temporal distributions of the ionospheric disturbances

Alexander Pavelyev; Stanislav Matyugov; Jens Wickert; Yuei An Liou; Oleg Yakovlev

2010-01-01

47

Flux-lattice melting in artificially layered superconductors  

NASA Astrophysics Data System (ADS)

We apply a previously described lowest-Landau-level formalism to treat flux-lattice melting in artificially layered superconductors, using Monte Carlo methods. For a pin-free layered system, the model predicts a single phase transition with simultaneous ordering both within one layer and between layers. The melting curve calculated using this model agrees reasonably well with experiments of Koorevaar et al. on NbGe/Ge multilayers.

Hwang, Ing-Jye; ŠáŠik, R.; Stroud, D.

1996-11-01

48

Artificially stacked atomic layers: toward new van der Waals solids.  

PubMed

Strong in-plane bonding and weak van der Waals interplanar interactions characterize a large number of layered materials, as epitomized by graphite. The advent of graphene (G), individual layers from graphite, and atomic layers isolated from a few other van der Waals bonded layered compounds has enabled the ability to pick, place, and stack atomic layers of arbitrary compositions and build unique layered materials, which would be otherwise impossible to synthesize via other known techniques. Here we demonstrate this concept for solids consisting of randomly stacked layers of graphene and hexagonal boron nitride (h-BN). Dispersions of exfoliated h-BN layers and graphene have been prepared by liquid phase exfoliation methods and mixed, in various concentrations, to create artificially stacked h-BN/G solids. These van der Waals stacked hybrid solid materials show interesting electrical, mechanical, and optical properties distinctly different from their starting parent layers. From extensive first principle calculations we identify (i) a novel approach to control the dipole at the h-BN/G interface by properly sandwiching or sliding layers of h-BN and graphene, and (ii) a way to inject carriers in graphene upon UV excitations of the Frenkell-like excitons of the h-BN layer(s). Our combined approach could be used to create artificial materials, made predominantly from inter planar van der Waals stacking of robust bond saturated atomic layers of different solids with vastly different properties. PMID:22731861

Gao, Guanhui; Gao, Wei; Cannuccia, E; Taha-Tijerina, Jaime; Balicas, Luis; Mathkar, Akshay; Narayanan, T N; Liu, Zhen; Gupta, Bipin K; Peng, Juan; Yin, Yansheng; Rubio, Angel; Ajayan, Pulickel M

2012-07-02

49

Daytime dependence of disturbances of ionospheric Es-layers connected to earthquakes  

NASA Astrophysics Data System (ADS)

In the present work variations of the semi-transparency of the sporadic E-layer of the ionosphere due to seismic activities are studied. The semi-transparency Q is determined by the blanketing frequency fbEs and the characteristic frequency foEs, Q = (foEs - fbEs)/fbEs. At low values of the blanketing frequency fbEs, the critical frequency foEs does not describe the maximum ionisation density of the Es-layer, as the critical frequencies of regular ionospheric layers (e.g. foF2) do, but it describes the occurrence of small-scall (tenths of meters) inhomogeneities of the ionisation density along the vertical in the layer. The maximum ionisation density of the sporadic layer is proportional to the square of fbEs. In the case of vertical ionospheric sounding, the sporadic layer becomes transparent for signals with frequencies larger than fbEs. Investigations showed that about three days before an earthquake an increase of the semi-transparency interval is observed during sunset and sunrise. In the present work, analogous results are found for data of the vertical sounding stations "Tokyo" and "Petropavlovsk-Kamchatsky". Using the method of superposition of epoches, more than 50 earthquakes with magnitudes M > 5, depths h < 40 km, and distances between the station and the epicenter R < 300 km are considered in case of the vertical sounding station "Tokyo". More than 20 earthquakes with such parameters were analysed in case of the station "Petropavlovsk-Kamchatsky". Days with strong geomagnetic activity were excluded from the analysis. According to the station "Petropavlovsk-Kamchatsky" about 1-3 days before earthquakes, an increase of Es-spread is observed a few hours before midnight. This increase is a sign of large-scale inhomogeneities in the sporadic layers.

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

2012-04-01

50

Ionospheric modification by radio waves: An overview and novel applications  

Microsoft Academic Search

High-power high-frequency radio waves, when beamed into the Earth's ionosphere, can heat the plasma by particle collisions in the D-layer or generate wave-plasma resonances in the F-layer. These basic phenomena have been used in many research applications. In the D-layer, ionospheric currents can be modulated through conductance modification to produce artificial ULF and VLF waves, which propagate allowing magnetospheric research.

M. J. Kosch

2008-01-01

51

Excitation of artificial airglow by high power radio waves from the SURA ionospheric heating facility  

SciTech Connect

The SURA facility for generation of high power radio waves, located near the village of Vasil'sursk USSR, operates between 4.5 and 9.0 MHz and has a maximum effective radiated power (ERP) of 300 MW. Nonlinear interactions between the HF radio waves and F-layer plasma occur near the electromagnetic wave reflection point. Energetic electrons are accelerated out of the interaction regions by the electrostatic waves. Ambient oxygen atoms collisionally excited by these suprathermal electrons yield enhanced airglow. Low-light-level, optical measurements were made at SURA during September 1990. Images of enhanced red-line (630 nm) emissions were recorded during radio wave transmissions at 4.786, 5.455, and 5.828 MHz. The antenna radiation pattern, ionospheric irregularities, and the magnetic field orientation affected the shape of the observed airglow structures. The airglow clouds drifted across the night sky, disappeared, and reformed at the zenith of the antenna array. This has been interpreted in terms of radio beam refraction in drifting plasma irregularities and bifurcation when the beam is split between two density cavities. Subject to clear skies, the authors experience indicates that the low-light-level-imaging technique is a reliable method to study large scale irregularities and electron acceleration with high-power HF transmitting facilities.

Bernhardt, P.A.; Scales, W.A. (Naval Research Lab., Washington, DC (United States)); Grach, S.M.; Keroshtin, A.N.; Kotik, D.S.; Polyakov, S.V. (Radiophysical Research Inst., Novgorod (USSR))

1991-08-01

52

Layered Structures and Internal Waves in the Ionosphere and Atmosphere as Seen from GPS Occultation Data  

NASA Astrophysics Data System (ADS)

High-precision signals emitted by GPS satellites create favourable conditions both for monitoring of the atmosphere and ionosphere and for investigation of the radio wave propagation effects. Comparative theoretical and experimental analysis of the phase and amplitude variations of the GPS radio-holograms discovered a relationship which relates the refraction attenuation, the phase path excess acceleration and Doppler frequency via a classical dynamics equationtype. The advantages of the introduced relationship consist in: (1) a possibility to separate the layered structure and turbulence contributions to RO signal; (2) a possibility to estimate the absorption in the atmosphere by dividing the refraction attenuations found from amplitude and phase data; (3) a possibility to locate the tangent point in the atmosphere with accuracy in the distance from the standard position of of about ±100 km. The suggested method has a general importance because it may be applied for analysis in the trans-ionospheric satellite-to-Earth links. We showed also that the amplitude variations of GPS occultation signals are very sensitive sensors to the internal waves in the atmosphere. The sensitivity of the amplitude method is inversely proportional to the square of the vertical period of the internal wave, indicating high sensitivity of the amplitude data to the wave structures with small vertical periods in the 0.8-4 km interval. Combined analysis of the amplitude and phase of radio occultation signal allows one to determine with high level of reliability the main characteristics of the atmospheric and ionospheric layeres including the vertical distribution of the refractivity, electron density and their gradients. A possibility exists to measure important parameters of the internal waves: the intrinsic phase speed, the horizontal wind perturbations and, under some assumptions, the intrinsic frequency as functions of height in the atmosphere. A new technique has been applied to measurements provided during CHAllenging Minisatellite Payload (CHAMP) and the Formosa Satellite-3 and Constellation Observing System for Meteorology, Ionosphere, and Climate (FORMOSAT-3/COSMIC) radio occultation (RO) missions.

Pavelyev, Alexander; Pavelyev, Alexander; Gubenko, Vladimir; Wickert, Jens; Liou, Yuei An

53

Peculiarities of the development and saturation of artificial ionospheric turbulence during a high-power disturbing transmission  

SciTech Connect

The peculiarities of the wide-band anomalous attenuation of radio waves reflected in a region of the ionosphere disturbed by a high-power pumping wave are investigated experimentally. It is shown that saturation of the anomalous attenuation sets with an increase in the radiation power: its intensity and time of development are stabilized. This indicates the saturation of the magnitude and spectrum of small-scale artificial inhomogeneities responsible for the effect of anomalous attenuation. The weakening of this effect in the process of development of large-scale artificial inhomogeneities is described. The results of an investigation of the initial stage of self-action of a high-power radio wave under the conditions of cyclic operation of the high-power transmitter are given.

Berezin, I.V.; Boiko, G.N.; Volkov, V.M.; Zyuzin, V.A.; Komrakov, G.P.; Leonov, A.M.; Maresov, A.N.; Ryzhov, V.A.; Solynin, V.A.

1987-12-01

54

Identification and localization of layers in the ionosphere using the eikonal and amplitude of radio occultation signals  

NASA Astrophysics Data System (ADS)

Conditions for communication, navigation, and remote sensing in the ionosphere and atmosphere depend strongly on the ionospheric impact on the radio waves propagation. By use of the CHAllenge Minisatellite Payload (CHAMP) radio occultation (RO) data a description of different types of the ionospheric contributions to the RO signals at the altitudes 30-90 km of the RO ray perigee is introduced and compared with results of measurements obtained earlier in the communication link satellite-to-Earth at frequency 1.5415 GHz. An analytical model is introduced for description of the radio waves propagation in a stratified medium consisting of sectors having the spherically symmetric distributions of refractivity. Model presents analytical expressions for the phase path and refractive attenuation of radio waves. Model is applied for analysis of the radio waves propagation effects along a prolonged path including the atmosphere and two parts of the ionosphere. Model explains significant amplitude and phase variations at the altitudes 30-90 km of the RO ray perigee as connected with influence of the inclined ionospheric layers. An innovative eikonal acceleration technique is described and applied for the identification of the inclined ionospheric layers contributions and their location. Possibility to separate the influence of layered structures from contributions of irregularities and turbulence is analyzed.

Pavelyev, A. G.; Zhang, K.; Wickert, J.; Schmidt, T.; Liou, Y.-A.; Gubenko, V. N.; Pavelyev, A. A.; Salimzjanov, R. R.; Kuleshov, Y.

2011-03-01

55

The Formation and Vertical Movement of Dense Ionized Layers in the Ionosphere Due to Neutral Wind Shears  

Microsoft Academic Search

This paper analyzes Dungey's wind-shear mechamsm for the formation of sporadic E layers and the extension of this mechanism, proposed by the author, which causes vertical transport of ionospheric ionization. Approximate equations are derived to describe quasi-steady ionized layers in which forces due to wind shear in the neutral atmosphere are balanced by the effects of pressure gradients and recombination.

W. I. Axford

1963-01-01

56

Research of short-period variations of virtual height of ionosphere layers  

NASA Astrophysics Data System (ADS)

Some results of research of non-uniform structure of an ionosphere (generally for day time conditions) by digital ionosonde "Cyclon" are presented. The virtual height measurements were made by method with the increased accuracy. The technique of multipulse sounding realized on ionosonde "Cyclon" allows getting of the altitude accuracy up to 300 m. Such accuracy, in turn, enables to investigate more thin elements of non-uniform structure of the ionosphere. All measurements of reflection heights (generally from F layer) were made at fixed frequencies concern to quiet day time conditions for several day in August 2008 and February 2010. Measurements were carried out with a one-minute periodicity at ten frequencies in range of 3-3.45 MHz in August and 2.5-4.2 MHz in February. The analysis of time series of virtual heights (on the fixed working frequencies) was performed by an estimation of power spectral density on the basis of algorithm of multiple signal classification (MUSIC). The given method spectral estimation concerns to a class of the spectral methods based on the analysis of own values of an autocorrelation matrix. It provides the best characteristics of the resolution and estimation of frequencies in comparison with autoregressive method and Prony's method, is especial at low signal to noise ratio when these methods are not capable to resolve relatives on frequency of a sinusoid or other narrow-band spectral components. For series of measurements in August with one-minute periodicity the spectral analysis has revealed the basic the period of 15-20 minutes (both for F layer and for Es layer). Except for the basic period in spectra there are peaks at T 10, 35, 180 minutes (for F layer) and T 6 minutes (for Es layer). There are no predominant variations among the more short-period fluctuations.

Akchurin, Adel; Bochkarev, Vladimir

57

GPS observations of the ionospheric F2-layer behavior during the 20th November 2003 geomagnetic storm over South Korea  

NASA Astrophysics Data System (ADS)

The ionospheric F2-layer peak density (NmF2) and its height (hmF2) are of great influence on the shape of the ionospheric electron density profile Ne (h) and may be indicative of other physical processes within the ionosphere, especially those due to geomagnetic storms. Such parameters are often estimated using models such as the semiempirical international reference ionosphere (IRI) models or are measured using moderately priced to expensive instrumentation, such as ionosondes or incoherent scatter radars. Global positioning system (GPS) observations have become a powerful tool for mapping high-resolution ionospheric structures, which can be used to study the ionospheric response to geomagnetic storms. In this paper, we describe how 3-D ionospheric electron density profiles were produced from data of the dense permanent Korean GPS network using the tomography reconstruction technique. These profiles are verified by independent ionosonde data. The responses of GPS-derived parameters at the ionospheric F2-layer to the 20th November 2003 geomagnetic storm over South Korea are investigated. A fairly large increase in the electron density at the F2-layer peak (the NmF2) (positive storm) has been observed during this storm, which is accompanied by a significant uplift in the height of the F2 layer peak (the hmF2). This is confirmed by independent ionosonde observations. We suggest that the F2-layer peak height uplift and NmF2 increase are mainly associated with a strong eastward electric field, and are not associated with the increase of the O/N2 ratio obtained from the GUVI instruments aboard the TIMED satellite. It is also inferred that the increase in NmF2 is not caused by the changes in neutral composition, but is related to other nonchemical effects, such as dynamical changes of vertical ion motions induced by winds and E × B drifts, tides and waves in the mesosphere/lower thermosphere region, which can be dynamically coupled upward to generate ionospheric perturbations and oscillations.

Jin, Shuanggen; Luo, O. F.; Park, P.

2008-12-01

58

Properties of ionospheric gyroechoes in the presence of a sporadic E-layer  

NASA Astrophysics Data System (ADS)

Generation and properties of ionospheric gyroechoes in the presence of a thin sporadic E-layer are investigated theoretically. Full wave analysis is used to calculate the transmission coefficients of model Es-layers. The intensification of the echo and the decrease in its virtual height at the onset of the Es-layer are explained in terms of mode coupling, the phenomena of which are shown to be more complicated than expected by Ellis (1960). A mechanism is also found of producing gyroechoes when an otherwise totally blanketing flat type Es-layer is present. When the maximum plasma frequency is so high that the whistler mode can propagate within the Es-layer at frequencies relevant to the gyroecho, the layer may be transparent for the extraordinary mode. Penetration of the ordinary wave becomes impossible, and the 0X0-reflection and ordinary F-trace can no longer be registered. Thus, the gyrotrace may be caused by the XXX-reflection only, and the resulting polarization on the ground is extraordinary.

Jalonen, L.; Nygren, T.; Turunen, T.

1981-10-01

59

Study of Ionospheric Perturbations in D-Layer Using Awesome VLF Receiver Data at Tashkent Station  

NASA Astrophysics Data System (ADS)

One VLF receiver and two SuperSID receivers were provided to Uzbekistan IHY cite by Stanford University and are operating in Tashkent, under the International Heliophysical Year (IHY). The results obtained at Tashkent IHY station are applied to earthquake electromagnetic precursors, lightning, and solar flares and to ionospheric disturbances originating from gamma ray flares of Soft Gamma-Ray Repeaters connected with evolution of strongly magnetized neutron stars believed as magnetars. Regular monitoring of the D-layer of ionosphere over Central Asia territory has been performed on the permanent basis. Few Solar flare events are observed during February in 2010-2011 years and the analysis showed that there is simultaneous correlation between the times of change of amplitude of the waves and the Solar flares. Features of the lightning discharge generated by radio atmospherics are studied and its effectiveness in D-region ionosphere diagnostics is explained. Assuming that earthquakes (EQs) can be preceded by the electromagnetic signals in the VLF bands detectable from ground-based measurements we have studied VLF amplitude anomalies related to the earthquakes occurred in 2009-2010 years with magnitude more than 5 on the path way from the VLF transmitters to the Tashkent station. For analysing narrowband data we have used the Nighttime Fluctuation (NF) method paying attention to the data obtained during the local nighttime (18:00 LT-06:00 LT). The amplitude data are analysed only for the reason that perturbations are identified more clearly in the amplitude data than in phase data. The mean nighttime amplitude (or trend) and normalized trend are found to increase significantly before the EQ with the same tendency as the NF and normalized NF. The obtained results have revealed a fine agreement with VLF amplitude anomalies observed in Tashkent VLF station during the strong earthquakes occurred on the path way from the transmitters to the receiver. Some of the initial results obtained from the preliminary analysis are presented to show the probing potentiality of VLF waves in ionosphere studies.

Ahmedov, Bobomurat

2012-07-01

60

Auroral ionospheric signatures of the plasma sheet boundary layer in the evening sector  

SciTech Connect

The authors report on particles and fields observed during Defense Meteorological Satellite Program (DMSP) F9 and DE 2 crossings of the polar cap/auroral oval boundary in the evening MLT sector. Season-dependent, latitudinally narrow regions of rapid, eastward plasma flows were encountered by DMSP near the poleward boundary of auroral electron precipitation. Ten DE 2 orbits exhibiting electric field spikes that drive these plasma flows were chosen for detailed analysis. The boundary region is characterized by pairs of oppositely-directed, field-aligned current sheets. The more poleward of the two current sheets is directed into the ionosphere. Within this downward current sheet, precipitating electrons either had average energies of a few hundred eV or were below polar rain flux levels. Near the transition to upward currents, DE 2 generally detected intense fluxes of accelerated electrons and weak fluxes of ions, both with average energies between 5 and 12 keV. In two instances, precipitating ions with energies >5 keV spanned both current sheets. Comparisons with satellite measurements at higher altitudes suggest that the particles and fields originated in the magnetotail inside the distant reconnection region and propagated to Earth through the plasma sheet boundary layer. Auroral electrons are accelerated by parallel electric fields produced by the different pitch angle distributions of protons and electrons in this layer interacting with the near-Earth magnetic mirror. Electric field spikes driving rapid plasma flows along the poleward boundaries of intense, keV electron precipitation represent ionospheric responses to the field-aligned currents and conductivity gradients. The generation of field-aligned currents in the boundary layer may be understood qualitatively as resulting from the different rates of earthward drift for electrons and protons in the magnetotail`s current sheet. 45 refs., 7 figs., 2 tabs.

Burke, W.J.; Machuzak, J.S.; Maynard, N.C. [Phillips Lab., Hanscom Air Force Base, MA (United States); Basinska, E.M.; Erickson, G.M. [Boston Univ., MA (United States); Hoffman, R.A.; Slavin, J.A. [Goddard Space Flight Center, Greenbelt, MD (United States); Hanson, W.B. [Univ. of Texas, Dallas, Richardson, TX (United States)

1994-02-01

61

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

62

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

63

On artificial construction of multilayered ceramics superstructure by layer-by-layer deposition processes  

NASA Astrophysics Data System (ADS)

Artificial construction of multilayered ceramics has been paid much attention as a promising method for designing new functional ceramics, including higher T(c) oxide superconductors. In the present study, preparation of (Bi-Sr-Cu-O)/(Ca-Cu-O) multilayered films were investigated by two methods: a plasma-controlled magnetron sputtering and a quadruple-target ac sputtering. The designed layer periodicity agreed well with that measured by the low-angle X-ray scattering. Other attempts to construct multilayered ceramic structures by layer-by-layer deposition processes are also described for comparison. Furthermore, essential problems for improving the processes are discussed.

Yoshimoto, Mamoru; Koinuma, Hideomi; Takeuchi, Kou

64

The influence of artificial electron heating on plasma irregularities in the lower ionosphere  

NASA Astrophysics Data System (ADS)

It is known small-scale ionospheric irregularities below the homopause level are generated by the neutral air turbulence. Usually an approximation of isothermality Te = Ti = Tn is valid for the lower ionosphere, especially, at middle latitudes. However, the approximation may be broken due to electron heating by powerful radio waves. In the report we consider theoretically reaction of ionospheric irregularities created by the neutral turbulence on the increasing of electron temperature Te due to the radio wave action. For this aim, expressions for the irregularity spectrum, the mean-square level of the plasma density fluctuations, and the radar backscatter cross-section per unit volume have been obtained. Using the expressions we have calculated the spectral form, the rms fluctuation level, and the cross-section ? for the case of the mid-latitude ionosphere at an altitude near 100 km when the ratio of the electron to ion temperature Te /Ti increased from 1 to 10. The spectrum has corresponded to the inertial range of turbulence, the rms level has been estimated for irregularity length-scales smaller than 500 m, and ? has been evaluated for the diagnostic radar frequencies from 5 to 50 MHz and the vertical direction of antenna beam. It was shown that an increase in Te produces a decrease in both the fluctuation level and the backscatter cross-section. In our calculations this level reduced from 6.2 to 4.8 %; the cross-section ? from 1.28×10-8 to 9.06×10-9 m-1 at 5 MHz and from 1.25×10-11 to 8.93×10-12 m-1 at 50 MHz. The rise in Te has also resulted in an increase in the spectral slope (for the approximation of spectrum by a power law k -p , the index p took values from 1.62 to 2.34). These changes are explained by a decrease in the cut-off wavenumber in the irregularity spectrum resulted from an increase in the ambipolar diffusivity due to the rise in Te .

Kyzyurov, Yurij; Chernogor, Leonid F.

65

Monitoring of sporadic plasma layers in the lower ionosphere in the communication link satellite-to-satellite  

NASA Astrophysics Data System (ADS)

Method of global monitoring of sporadic plasma layers in the lower ionosphere is developed. In-vestigations were carried out by use of analysis of the amplitude and phase components of radio holograms obtained during the radio occultation missions CHAMP, FORMOSAT-3. Sporadic amplitude scintillation observed in RO experiments contain important information concerning the seasonal, geographical, and temporal distributions of the ionospheric disturbances and de-pend on solar activity. The geographical and seasonal distributions of sporadic layers in the lower ionosphere as function of solar activity in the period 2002-2008 years is obtained. The general number of RO events with strong amplitude variations can be used as an indicator of the ionospheric activity. We found that during 2001-2008 the daily averaged S4 index measured during CHAllenging Minisatellite Payload (CHAMP) mission depends essentially on solar ac-tivity. The maximum occurred in January 2002, minimum has been observed in summer 2008. Different temporal behavior of S4 index has been detected for polar (with latitude greater than 55 degrees) and low latitude (moderate and equatorial) regions. For polar regions S4 index is slowly decreasing with solar activity. In the low latitude areas S4 index is sharply oscillat-ing, depending on the solar ultraviolet emission variations. The geographical distribution of S4 index variations indicates different origin of ionospheric plasma disturbances in polar and low latitude areas. Origin of the plasma disturbances in the polar areas may be connected with influence of solar wind, the ultraviolet emission of the Sun may be the main cause of the ionospheric irregularities in the low latitude zone. Analysis reveals global oscillations of S4 index with the periods of 5-7 months. Analysis of these oscillations may provide additional connection with solar activity. Therefore, the S4 index of RO signal is important radio physical indicator of solar activity.

Pavelyev, Alexander; Matyugov, Stanislav; Wickert, Jens; Liou, Yuei An; Yakovlev, Oleg

66

Nocturnal Stratification of the Ionospheric F-layer over Karachi, Pakistan during Solar Cycle 22 (1986-96)  

NASA Astrophysics Data System (ADS)

This study has been carried out employing the ionospheric data of Karachi (24.95o N, 67.14o E) for a complete Solar Cycle-22 (1986-96), acquired by means of Digisonde DGS-256. The visual observations of data as shown that some times Nocturnal Ionospheric Stratification at Karachi do occur. However, Nocturnal Ionospheric Stratification is very rare in middle and lower latitudes (TAN and HUANG, 1985). Therefore, the present study is undertaken. Only the night-time F-layer Stratification cases have been included in this study. It is revealed that the Nocturnal Stratification in F-layer at Karachi is mainly a post-midnight phenomenon, under both magnetically quite and disturbed conditions. Though it may occur on pre and post -midnight periods, its occurrence in all the seasons is frequent (95%) in post mid-night period 0215-0500 LT . Only 5% cases were observed in pre mid-night period 2200-0000 LT. Its occurrence during Solar Maximum (1989-90) is significantly greater than at the two solar minimum i.e. 1986-87 and 1995-96. However, its maximum occurrence is observed in 1992 i.e. 2 years after the solar maximum. The seasons in order of its maximum occurrence are Winter, Equinoxes and Summer. Even in Winter its occurrence is observed to be the highest in the month of January. Nocturnal Ionospheric Stratification at Karachi may and may not occur on a TID (Traveling Ionospheric Disturbances) night, irrespective of the fact whether the night is magnetically quite and disturbed. This shows that the nocturnal Stratification is not caused by a TID as reported by TA N and HUANG (1985) over Wuchang (30.5o N, 11.4o E), China. Moreover, Karachi does not lie under any of the zones of particle precipitation described by BOSS and SMITH (1980). Therefore, a future study on the cause of Nocturnal Ionospheric Stratification is clearly required.

Zafar, H.; Zaidi, S.

67

The amplitude fluctuations of the radio wave scattered from a thick ionospheric layer with weak irregularities  

Microsoft Academic Search

The signal received at the ground from a satellite or radio star shows small fluctuations of both phase and amplitude, which are produced by irregularities of refractive index in the ionosphere. The amplitude fluctuations are much the easier to measure and this paper examines theoretically what can be learned about the ionosphere from a study of amplitude fluctuations alone. The

K. G. Budden

1965-01-01

68

A two-layer model of the ionosphere using Global Positioning System data  

NASA Astrophysics Data System (ADS)

We present a new approach to model the Ionosphere based on GPS data. Previous authors have used models with an unique shell. In this case we have included a second shell to account for the distribution of the electrons in the outer part of the Ionosphere. We have analyzed the ionospheric electron content of a region above 30 degrees in declination in different conditions of ionospheric activity using the Kalman filter. The data used has been obtained from the International GPS Service for Geodynamics (IGS) network. Simultaneously we have studied the receiver and transmitter differential biases showing the effects of neglecting the outer part of the Ionosphere in the model. It appears a systematic variations for the receivers—depending on its latitude—not for the satellites.

Juan, J. Miguel; Rius, Antonio; Hernández-Pajares, Manuel; Sanz, Jaume

69

Interferometric temperature measurements in the F2 ionospheric layer during the June 20, 1990 earthquake in Iran  

NASA Astrophysics Data System (ADS)

Results are presented of Doppler temperature measurements in the F2 ionospheric layer, carried out near Ashkhabad (Turkmenistan) during an earthquake in Iran on June 20, 1990. Results indicate a significant temperature increase (by about 350 K) in F2 temperature, observed in the northern and the southern directions, at locations which were nearly equidistant from the earthquake focus. An estimate is made of the energy necessary for the measured temperature increase.

Akmamedov, Kh.

1993-02-01

70

Causes of longitude-latitudinal variations in the ionospheric F2-layer maximum in summer nighttime conditions}\\  

NASA Astrophysics Data System (ADS)

[1] The causes of longitudinal and latitudinal variations in the F2-layer maximum in the summer nighttime ionosphere at middle, subauroral, and auroral latitudes are investigated. To do this the following problems are solved in sequence. The longitudinal variations in hmF2 are studied in the belt of invariant latitudes between 40° and 65° according to the Intercosmos 19 satellite data. It is shown that the longitudinal effect in the quiet ionosphere is rather stable but differs by its character in the Southern and Northern hemispheres. Considerable discrepancies between Intercosmos 19 data and International Reference Ionosphere (IRI) model are detected at high latitudes. On the basis of the longitudinal variations in hmF2 using the servo model of the ionosphere and the Mass Spectrometer Incoherent Scatter thermosphere model, variations in the vertical drift velocity, W, caused by neutral wind are calculated. In terms of the Tikhonov regularization method, the approach to a solution of the inverse problem on deriving meridional and zonal components of the neutral wind from the longitudinal variations in W is developed. A comparison with the Horizontal Wind Model (HWM) neutral wind model is performed and an attempt to correct this model for the considered conditions is made. Estimation of the contribution of the neutral wind, composition and temperature into longitudinal and latitudinal variations in hmF2 is performed. The causes of the asymmetry between the Northern and Southern hemispheres are discussed.

Karpachev, A. T.; Gasilov, N. A.

2006-02-01

71

Modeling of Sporadic Layers Meteoritic in Origin in the Mars' Ionosphere  

NASA Astrophysics Data System (ADS)

Recent measurements of the Martian ionosphere has revealed the existence of low altitude layers at altitudes ranging from 70 and 90 km, well below the main photoionospheric peak. These peaks were detected by radio science experiments both Mars Global Surveyor (in 71 of 56000 profiles, [1]) and Mars Express (in 75 of 465 profiles, [2]). The presence of these layers was not limited to specific times of the day, longitude or latitude. Previous theoretical models [3,4] predicted the existence of a constant low altitude layer, with a maximum density of the same order of magnitude compared with the recent observations. Long-live metallic ions coming from meteoroid particles can increase the concentration of electrons. However, the models are not able to explain the huge variability of the observations. Similar layers have been observed in the Earth's atmosphere, especially during strong meteor shower and it is well known that they contain metallic ions coming from the ablation of extraterrestrial dust. Here we present a model of the vertical density profile of metallic species (magnesium and iron) between 60 and 120 km altitude. The model includes ablation of meteoroids, metal diffusion in the atmosphere, photoionization of neutrals by ultraviolet photons, and the chemistry of ions and neutrals including charge exchange between neutrals and ions. We have found that the presence of Mg and Fe reduces the concentration of the most abundant atmospheric ions and also increase the concentration of electrons below 90 km of altitude. Model results are compared with some selected electron density profiles observed by Mars Express in order to understand the existence of this sporadic layer. We obtain that in some conditions a low altitude layer can be formed which compared relatively well with the observations, even under steady state scenarios. However dynamic models or high meteoroid fluxes, i.e. meteor showers, are required to explain fully the observations. [1] Withers et al. (2008), J. Geophys. Res. 113, A12314. [2] Patzold et al. (2005), Science 310, 837-838. [3] Pesnell et al. (2000), J. Geophys. Res.105, 1695. [4] Molina-Cuberos et al. (2003), Planet. and Space Sci. 51, 239

Molina-Cuberos, G. J.; Peter, K.; Witasse, O. G.; Nuñez, M. J.; Paetzold, M.

2011-12-01

72

Recent Incoherent Scatter Radar Results with Artificial Ionospheric Heating at EISCAT  

NASA Astrophysics Data System (ADS)

During the last few years the solar minimum has made many HF heater-induced phenomena difficult to excite, particularly those where the heater frequency needs to be near or below the O-mode penetration frequency. This condition is even more difficult to meet at night. Consequently the types of experiments performed have been more mesospheric or D region heating experiments, more daytime F region experiments and X-mode heating of the F region. Experiments where electron temperature modulation of the D region affects mesospheric dust charging and thereby the backscatter cross-section of irregularities in the neutral gas, have been particularly fruitful in unraveling the physical processes involved. Four radars covering HF (8 MHz) to UHF (933 MHz) have been used to measure the effects at the various scales. X-mode transmission has also produced, at times, surprisingly strong heating in the F region. This allows us to extend some experiments to lower density conditions, as well as giving us more input to models of the ionospheric energy balance. Some highlights from these and other experiments will be shown.

Rietveld, Michael

2010-05-01

73

Meteoric ion layers in the ionospheres of venus and mars: Early observations and consideration of the role of meteor showers  

NASA Astrophysics Data System (ADS)

Layers of metal ions produced by meteoroid ablation have been known in Earth's ionosphere for decades, but have only recently been discovered at Venus and Mars. Here we report the results of a search for meteoric layers in earlier datasets from Venus and Mars. We find 13 candidates at Venus in Mariner 10, Venera 9/10, and Pioneer Venus Orbiter data that augment the 18 previously identified in Venus Express data. We find 8 candidates at Mars in Mariner 7 and Mariner 9 data that augment the 71 and 10 previously identified in Mars Global Surveyor and Mars Express data, respectively. These new findings extend the ranges of conditions under which meteoric layers have been observed, support studies of the temporal variability of meteoric layers, and (for Venus) independently confirm the existence of meteoric layers. One of the proposed causes of temporal variations in the occurrence rate of meteoric layers is meteor showers. This possibility is controversial, since meteor showers have minimal observed effect on meteoric layers in Earth's ionosphere. In order to aid progress towards a resolution of this issue, we present a series of tests for this hypothesis.

Withers, Paul; Christou, A. A.; Vaubaillon, J.

2013-10-01

74

Annual and semiannual variations in the ionospheric F2-layer: II. Physical discussion  

NASA Astrophysics Data System (ADS)

The companion paper by Zou et al. shows that the annual and semiannual variations in the peak F2-layer electron density (NmF2) at midlatitudes can be reproduced by a coupled thermosphere-ionosphere computational model (CTIP), without recourse to external influences such as the solar wind, or waves and tides originating in the lower atmosphere. The present work discusses the physics in greater detail. It shows that noon NmF2 is closely related to the ambient atomic/molecular concentration ratio, and suggests that the variations of NmF2 with geographic and magnetic longitude are largely due to the geometry of the auroral ovals. It also concludes that electric fields play no important part in the dynamics of the midlatitude thermosphere. Our modelling leads to the following picture of the global three-dimensional thermospheric circulation which, as envisaged by Duncan, is the key to explaining the F2-layer variations. At solstice, the almost continuous solar input at high summer latitudes drives a prevailing summer-to-winter wind, with upwelling at low latitudes and throughout most of the summer hemisphere, and a zone of downwelling in the winter hemisphere, just equatorward of the auroral oval. These motions affect thermospheric composition more than do the alternating day/night (up-and-down) motions at equinox. As a result, the thermosphere as a whole is more molecular at solstice than at equinox. Taken in conjunction with the well-known relation of F2-layer electron density to the atomic/molecular ratio in the neutral air, this explains the F2-layer semiannual effect in NmF2 that prevails at low and middle latitudes. At higher midlatitudes, the seasonal behaviour depends on the geographic latitude of the winter downwelling zone, though the effect of the composition changes is modified by the large solar zenith angle at midwinter. The zenith angle effect is especially important in longitudes far from the magnetic poles. Here, the downwelling occurs at high geographic latitudes, where the zenith angle effect becomes overwhelming and causes a midwinter depression of electron density, despite the enhanced atomic/molecular ratio. This leads to a semiannual variation of NmF2. A different situation exists in winter at longitudes near the magnetic poles, where the downwelling occurs at relatively low geographic latitudes so that solar radiation is strong enough to produce large values of NmF2. This circulation-driven mechanism provides a reasonably complete explanation of the observed pattern of F2 layer annual and semiannual quiet-day variations.

Rishbeth, H.; Müller-Wodarg, I. C. F.; Zou, L.; Fuller-Rowell, T. J.; Millward, G. H.; Moffett, R. J.; Idenden, D. W.; Aylward, A. D.

2000-08-01

75

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

76

Relationship between vertical ExB drift and F2-layer characteristics in the equatorial ionosphere at solar minimum conditions  

NASA Astrophysics Data System (ADS)

Equatorial and low-latitude electrodynamics plays a dominant role in determining the structure and dynamics of the equatorial and low-latitude ionospheric F-region. Thus, they constitute essential input parameters for quantitative global and regional modeling studies. In this work, hourly median value of ionosonde measurements namely, peak height F2-layer (hmF2), F2-layer critical frequency (foF2) and propagation factor M(3000)F2 made at near equatorial dip latitude, Ouagadougou, Burkina Faso (12oN, 1.5oW; dip: 1.5oN) and relevant F2-layer parameters such as thickness parameter (Bo), electron temperature (Te), ion temperature (Ti), total electron content (TEC) and electron density (Ne, at the fixed altitude of 300 km) provided by the International Reference Ionosphere (IRI) model for the longitude of Ouagadougou are contrasted with the IRI vertical drift model to explore in detail the monthly climatological behavior of equatorial ionosphere and the effects of equatorial vertical plasma drift velocities on the diurnal structure of F2-layer parameters. The analysis period covers four months representative of solstitial and equinoctial seasonal periods during solar minimum year of 1987 for geomagnetically quiet-day. We show that month-by-month morphological patterns between vertical E×B drifts and F2-layer parameters range from worst to reasonably good and are largely seasonally dependent. A cross-correlation analysis conducted between equatorial drift and F2-layer characteristics yield statistically significant correlations for equatorial vertical drift and IRI-Bo, IRI-Te and IRI-TEC, whereas little or no acceptable correlation is obtained with observational evidence. Assessment of the association between measured foF2, hmF2 and M(3000)F2 illustrates consistent much more smaller correlation coefficients with no systematic linkage. In general, our research indicates strong departure from simple electrodynamically controlled behavior.

Oyekola, Oyedemi S.

2012-07-01

77

First artificially induced modulation of PMSE using the EISCAT heating facility  

Microsoft Academic Search

A coordinated experiment involving ionospheric heating and VHF observations of polar mesosphere summer echoes (PMSE) has recently been conducted at the EISCAT facility near Tromsø, Norway. We have demonstrated for the first time that ionospheric heating can influence VHF radar returns associated with PMSE. Artificially elevating the electron temperatures within the PMSE layer has been shown to reduce the echo

Phillip B. Chilson; Evgenia Belova; Michael T. Rietveld; Sheila Kirkwood; Ulf-Peter Hoppe

2000-01-01

78

Excitation of artificial airglow by high power radio waves from the SURA ionospheric heating facility  

Microsoft Academic Search

The SURA facility for generation of high power radio waves, located near the village of Vasil'sursk USSR, operates between 4.5 and 9.0 MHz and has a maximum effective radiated power (ERP) of 300 MW. Nonlinear interactions between the HF radio waves and F-layer plasma occur near the electromagnetic wave reflection point. Energetic electrons are accelerated out of the interaction regions

P.A. Bernhardt; W. A. Scales; S. M. Grach; A. N. Keroshtin; D. S. Kotik; S. V. Polyakov

1991-01-01

79

Formation of artificially-layered superconducting materials by pulsed-laser deposition.  

National Technical Information Service (NTIS)

Artificially-layered structures, consisting of (Sr,Ba,Ca)CuO(sub 2) layers in the tetragonal, (open quotes)infinite layer(close quotes) crystal structure, have been grown by pulsed-laser deposition. Superlattice chemical modulation is observed for structu...

D. P. Norton B. C. Chakoumakos J. D. Budai

1994-01-01

80

Times of development and relaxation of artificial small-scale irregularities  

SciTech Connect

For the interpretation of results of studies of high-power shortwave action on the ionospheric F-layer plasma in the complex temporal regime of the pump wave radiation, it is necessary to know the characteristics of development and relaxation of the spectrum of the artificial ionospheric turbulence in the small-scale range. Results of the experimental studies are considered, and a comparison is made between the times of development and relaxation of artificial small-scale irregularities and their spectral charcteristics under the action of high-power radio waves at frequencies of 4.785 and 2.95 MHz on the ionospheric F-layer.

Belikovich, V.V.; Erukhimov, L.M.; Zyuzin, V.A.; Korobkov, Yu.S.; Maksimenko, O.M.; Nasyrov, A.M.; Sergeev, E.N.; Frolov, V.L.; Shavin, P.B.

1988-09-01

81

F3-LAYER Seasonal Variations Near the Southern Crest of the Equatorial Ionospheric Anomaly as a Function of Solar Cycle  

NASA Astrophysics Data System (ADS)

The occurrence of an additional F3-layer has been reported at Brazilian, Indian and Asian sectors by several investigators. In this paper, we report F3-layer seasonal variations carried out at São José dos Campos (23.2 S, 45.0 W; dip latitude 17.6 S), near the southern crest of the equatorial ionospheric anomaly (EIA), Brazil, as a function of solar cycle. The period from September 2000 to August 2001 is used as representative of high solar activity (HSA) and the period from January 2006 to December 2006 as representative of low solar activity (LSA). This investigation shows that the frequency of occurrence of the F3-layer during HSA is 11 times more than during LSA.

Fagundes, P. R.; Klausner, V.; Bittencourt, J. A.; Sahai, Y.; Abalde, J. R.

2011-12-01

82

Formation of artificially-layered high-temperature superconductors using pulsed-laser deposition  

SciTech Connect

Pulsed-laser deposition has been used to synthesize artificially-layered high-temperature superconductors. Novel thin-film SrCu0{sub 2}/BaCu0{sub 2} superlattices have been synthesized which superconduct at temperatures as high as 70 K. These results demonstrate that pulsed-laser deposition and epitaxial stabilization can be effectively used to engineer artificially-layered thin-film materials.

Norton, D.P.; Chakoumakos, B.C.; Budai, J.D.

1995-03-01

83

Signature of 3-4 day planetary waves in the equatorial ionospheric F layer height and medium frequency radar winds over Tirunelveli (8.7oN)  

NASA Astrophysics Data System (ADS)

Signature of 3-4 day planetary waves in the equatorial ionospheric F layer height and medium frequency radar winds over Tirunelveli (8.7oN) S. Sathishkumar1, R. Dhanya1, K. Emperumal1, D. Tiwari2, S. Gurubaran1 and A. Bhattacharyya2 1. Equatorial Geophysical Research Laboratory, Indian Institute of Geomagnetism, Tirunelveli, India 2. Indian Institute of Geomagnetism, Navi Mumbai, India Email: sathishmaths@gmail.com Abstract The equatorial atmosphere-ionosphere system has been studied theoretically and observationally in the past. In the equatorial atmosphere, oscillations with periods of 3-4 days are often observed in the medium frequency (MF) radar over Tirunelveli (8.7oN, 77.8oE, 1.34oN geomag. lat.). Earlier observations show the clear evidence that these waves can propagate from the stratosphere to ionosphere. A digital ionosonde has been providing useful information on several ionospheric parameters from the same site. Simultaneous observations of mesospheric winds using medium frequency radar and F-layer height (h'F) from ionosonde reveal that the 3-4 day wave was evident in both the component during the 01 June 2007 and 31 July 2007. The 3-4 day wave could have an important role in the day to day variability of the equatorial ionosphere evening uplift. Results from an extensive analysis that is being carried out in the direction of 3-4 day wave present in the ionosphere will be presented.

Sundararaman, Sathishkumar

84

Selective reduction of layers at low temperature in artificial superlattice thin films  

PubMed Central

Reduction and oxidation in transition-metal oxides are keys to develop technologies related to energy and the environment. Here we report the selective topochemical reduction observed when artificial superlattices with transition-metal oxides are treated at a temperature below 300 °C with CaH2. [CaFeO2]m/[SrTiO3]n infinite-layer/perovskite artificial superlattice thin films were obtained by low-temperature reduction of [CaFeO2.5]m/[SrTiO3]n brownmillerite/perovskite artificial superlattice thin films. By the reduction only the CaFeO2.5 layers in the artificial superlattices were reduced to the CaFeO2 infinite layers whereas the SrTiO3 layers were unchanged. The observed low-temperature reduction behaviors strongly suggest that the oxygen ion diffusion in the artificial superlattices is confined within the two-dimensional brownmillerite layers. The reduced artificial superlattice could be reoxidized, and thus, the selective reduction and oxidation of the constituent layers in the perovskite-structure framework occur reversibly.

Matsumoto, Kazuya; Haruta, Mitsutaka; Kawai, Masanori; Sakaiguchi, Aya; Ichikawa, Noriya; Kurata, Hiroki; Shimakawa, Yuichi

2011-01-01

85

Aperture Synthesis for HF Radio Signals Propagated Via the F Layer of the Ionosphere.  

National Technical Information Service (NTIS)

A portable high-frequency (HF) radio aperture up to 70 km in length was synthesized by receiving ionospherically propagated signals in a DC-3 airplane. By thus moving a small antenna rapidly over a long distance, a narrow receiving beam width (high azimut...

J. T. Lynch

1970-01-01

86

Layered Structures and Internal Waves in the Ionosphere and Atmosphere as Seen from GPS Occultation Data  

Microsoft Academic Search

High-precision signals emitted by GPS satellites create favourable conditions both for monitoring of the atmosphere and ionosphere and for investigation of the radio wave propagation effects. Comparative theoretical and experimental analysis of the phase and amplitude variations of the GPS radio-holograms discovered a relationship which relates the refraction attenuation, the phase path excess acceleration and Doppler frequency via a classical

Alexander Pavelyev; Vladimir Gubenko; Jens Wickert; Yuei An Liou

2008-01-01

87

Models of ionization by low-energy particles in the ionospheric D, E and F layers  

Microsoft Academic Search

Consideration is given to ionospheric ionization by corpuscular streams and cosmic-ray particles with near-orbital and suborbital velocities. Expressions for the vertical profiles of the electron production rate are derived for cases of fully anisotropic, isotropic and general distributions of penetrating particles from the upper hemisphere, and simplified versions of these formulas are presented. Simplified and complete models of the interaction

P. Velinov

1982-01-01

88

Using ULF Waves Artificially Excited by the SPEAR High Power Radar as Diagnostics for Probing the High Latitude Ionospheric Alfven Resonator  

NASA Astrophysics Data System (ADS)

The SPEAR high power radar facility located in the vicinity of Longyearbyen on Spitsbergen has been utilised to artificially excite ULF waves through the modulated heating of the Polar electrojet. The high power radar beam interacts with the plasma in the D- and E-regions leading to oscillations in the local conductivity. This leads to the radiation of Alfven waves along field lines into the magnetosphere. It has been shown that a narrow flux tube can be tagged by the presence of these waves and field aligned plasma acceleration caused by the complex interaction of the artificial ULF waves with the upper boundary of the ionospheric Alfven resonator (IAR). Recent experiments with SPEAR have focussed on investigating the IAR, which acts a resonant cavity partially trapping ULF waves. These techniques are designed to stimulate one of the resonant harmonics of this cavity in order to improve the efficiency of the process which causes the electron acceleration at the upper boundary of the IAR. This interaction may be fundamentally important to the natural formation of aurora. Measurements of the SPEAR-induced ULF waves made by a set of induction coil magnetometers newly deployed on Spitsbergen will be presented. The observations will be discussed in the context of the ionospheric conditions required for the heating process to successfully excite ULF waves and the nature of the IAR cavity on these occasions.

Wright, D. M.; Yeoman, T. K.; Thomas, C.; Robinson, T. R.; Engebretson, M.; Lessard, M.

2007-12-01

89

Perspective ground-based method for diagnostics of the lower ionosphere and the neutral atmosphere  

NASA Astrophysics Data System (ADS)

We present a new perspective ground-based method for diagnostics of the ionosphere and atmosphere parameters. The method uses one of the numerous physical phenomena observed in the ionosphere illuminated by high-power radio waves. It is a generation of the artificial periodic irregularities (APIs) in the ionospheric plasma. The APIs were found while studying the effects of ionospheric high-power HF modification. It was established that the APIs are formed by a standing wave that occurs due to interference between the upwardly radiated radio wave and its reflection off the ionosphere. The API studies are based upon observation of the Bragg backscatter of the pulsed probe radio wave from the artificial periodic structure. Bragg backscatter occurs if the spatial period of the irregularities is equal to half a wavelength of the probe signal. The API techniques makes it possible to obtain the following information: the profiles of electron density from the lower D-region up to the maximum of the F-layer; the irregular structure of the ionosphere including split of the regular E-layer, the sporadic layers; the vertical velocities in the D- and E-regions of the ionosphere; the turbulent velocities, turbulent diffusion coefficients and the turbopause altitude; the neutral temperatures and densities at the E-region altitudes; the parameters of the internal gravity waves and their spectral characteristics; the relative concentration of negative oxygen ions in the D-region. Some new results obtained by the API technique are discussed .

Bakhmetieva, N. V.; Grigoriev, G. I.; Tolmacheva, A. V.

90

Global characteristics of occurrence of an additional layer in the ionosphere observed by COSMIC/FORMOSAT-3  

NASA Astrophysics Data System (ADS)

Global observations of electron density profile (EDP) from the COSMIC/FORMOSAT-3 satellites were used to investigate, for the first time, the additional stratification of the F2 layer over the equatorial ionosphere on a global scale, which is called F3 layer. The F3 layer in EDP was recognized through the altitude differential profile featured by two maxima existing from 220 km to the peak height of the electron density. There were ˜9,400 cases of F3 layer selected out of ˜448, 000 occultation events at low and equatorial areas during the period of April 2006-September 2010. Statistical results show that the highest occurrence of F3 layer appears at dip latitude 7˜8°/-7˜-8° for Northern/Southern Hemisphere and is more pronounced during summer months at 10:00-14:00 LT. The occurrence also has a clear longitude dependence during boreal summer, with relatively higher occurrence at -80˜-100°, -20˜20°, 80˜120° and -160˜-170° longitudes, that is possibly associated with the wavenumber-3 diurnal tide (DE3). The results support the principle of the F3 layer proposed by Balan et al. (1998), which in turn validate the accuracy of the retrieval of the COSMIC EDP data.

Zhao, Biqiang; Wan, Weixing; Yue, Xinan; Liu, Libo; Ren, Zhipeng; He, Maosheng; Liu, Jing

2011-01-01

91

Physical characteristics and occurrence rates of meteoric plasma layers detected in the Martian ionosphere by the Mars Global Surveyor Radio Science Experiment  

Microsoft Academic Search

Low-altitude plasma layers are present in 71 of 5600 electron density profiles from the Martian ionosphere obtained by the Mars Global Surveyor Radio Science experiment. These layers are produced by the ablation of meteoroids and subsequent ionization of meteoric atoms. The mean altitude of the meteoric layer is 91.7 +\\/- 4.8 km. The mean peak electron density in the meteoric

Paul Withers; M. Mendillo; D. P. Hinson; K. Cahoy

2008-01-01

92

Seasonal and solar cycle dependence of F3-layer near the southern crest of the equatorial ionospheric anomaly  

NASA Astrophysics Data System (ADS)

The occurrence of an additional F3-layer has been reported at Brazilian, Indian and Asian sectors by several investigators. In this paper, we report for the first time the seasonal variations of F3-layer carried out near the southern crest of the equatorial ionospheric anomaly (EIA) at São José dos Campos (23.2°S, 45.0°W; dip latitude 17.6°S - Brazil) as a function of solar cycle. The period from September 2000 to August 2001 is used as representative of high solar activity (HSA) and the period from January 2006 to December 2006 as representative of low solar activity (LSA). This investigation shows that during HSA there is a maximum occurrence of F3-layer during summer time and a minimum during winter time. However, during LSA, there is no seasonal variation in the F3-layer occurrence. Also, the frequency of occurrence of the F3-layer during HSA is 11 times more than during LSA.

Fagundes, P. R.; Klausner, V.; Bittencourt, J. A.; Sahai, Y.; Abalde, J. R.

2011-08-01

93

Excitation of guided ELF-VLF waves through modification of the F2 ionospheric layer by high-power radio waves  

NASA Astrophysics Data System (ADS)

The possibility of controlled excitation of ELF-VLF electromagnetic waves through modification of the F2 ionospheric layer by high-power high-frequency emission is demonstrated in a natural experiment by using the Sura midlatitude heating facility. The excited low-frequency waves can be used to explore the near-Earth space and stimulate the excitation of a magnetospheric maser.

Markov, G. A.; Belov, A. S.; Komrakov, G. P.; Parrot, M.

2012-03-01

94

The Production of Free Electrons in the Ionospheric D Layer by Solar and Galactic Cosmic Rays and the Resultant Absorption of Radio Waves  

Microsoft Academic Search

The behavior of the D layer under bombardment by solar and galactic cosmic rays of energy greater than a few Mev is discussed. In particular, the variation with incident particle flux of the ionospheric parameters that determine the equilibrium electron density is deduced by means of the measurements of mid-day and mid-night absorption of cosmic radio noise corre- sponding to

William Webber

1962-01-01

95

Three-Dimensional Simulation of the Coupled Perkins and Es-Layer Instabilities in the Nighttime Midlatitude Ionosphere  

NASA Astrophysics Data System (ADS)

Plasma density structures and associated irregularities in the nighttime midlatitude ionospheric E and F regions are frequently observed as frontal structures elongated from northwest to southeast (NW-SE) in the northern hemisphere. The frontal structures and the coupling process between the E and F regions are studied with a three-dimensional numerical model which can simulate two instability mechanisms: Perkins instability in the F region and sporadic-E (Es)-layer instability in the E region, both of which have directional preference which can account for the NW-SE structure. Applying sinusoidal perturbation on an Es layer, it is confirmed that the fastest growth of the coupled instability occurs when the unstable conditions on NW-SE perturbation are satisfied in both regions. The perturbation of F-region integrated conductivity grows much faster than the isolated Perkins instability. The predominant process in the coupled system depends on the ratio of integrated Hall to Pedersen conductivity. A larger Hall conductivity given by an Es layer is important for growth of the coupled instability as well as the Es-layer instability itself. NW-SE structure in the E region can be formed from random perturbation regardless of the F-region condition. When the F region is unstable on NW-SE perturbation, however, the Es-layer instability is reinforced through the coupling process, and the NW-SE structure is formed in both regions with a common scale length which is attributed to the Perkins instability. We conclude that (1) the Es-layer instability plays a major role in seeding NW-SE structure in the F region, and the Perkins instability is required to amplify its perturbation, and (2) the coupling process has a significant effect on the scale of the Es-layer perturbation rather than the growth speed of the Es-layer instability.

Yokoyama, T.; Hysell, D. L.; Otsuka, Y.; Yamamoto, M.

2008-12-01

96

Two-dimensional Model of the Ionospheric Alfven Resonator With Active Ionosphere  

NASA Astrophysics Data System (ADS)

This paper presents results from a multi-fluid nonlinear model of low-altitude flux tubes. It represents a significant improvement over previously published models, cf. [Sydorenko, Rankin, and Kabin, 2008]. The ionosphere is considered as a finite thickness highly-collisional plasma layer with multiple ion species. Pedersen conductivity is accounted for and motion of electrons and ions inside the ionosphere is omitted. Following [Schunk, 1996], the temperatures of the plasma components are found as a result of a competition between heating and collisional losses. The electron and ion densities are obtained from their continuity equations, with ionization sources and recombination sinks accounted for. The allowance for variation of temperature affects collision frequencies and densities of the plasma components, thus modifying the conductivity. The multi-fluid model is used to study the ionospheric feedback instability [Lysak, 1991]. In this case, the source of heating is the electric current of an Alfven wave and the temperatures, densities, and conductivity are calculated self-consistently. Another application of the model to be discussed is the excitation of Alfven waves by a convection current in the ionosphere, where the ionospheric conductivity changes with time, similar to experiments on artificial heating of the ionosphere. In these simulations, the conductivity profile is a prescribed function of space and time, which in general can be constrained using experimental data on ionospheric heating. Lysak, R. L. (1991), J. Geophys. Res., 96, 1553. Schunk, R. W., (Editor), STEP: Handbook of Ionospheric Models, Utah State Univ., Logan, Utah, 1996. Sydorenko, D., R. Rankin, and K. Kabin (2008), J. Geophys. Res., 113, A10206, doi:10.1029/2008JA013579.

Sydorenko, D.; Rankin, R.

2010-12-01

97

Synoptic-scale nonlinear stationary magnetized Rossby waves in the ionospheric E-layer  

SciTech Connect

Magnetized Rossby waves are produced by a dynamo electric field and represent the ionospheric generalization of tropospheric Rossby waves in a rotating atmosphere with a spatially inhomogeneous geomagnetic field. They are described by the modified Charney-Obukhov equation with a Poisson-bracket convective nonlinearity. This type of equation has solutions in the form of synoptic-scale nonlinear solitary dipole vortex structures of 1000-3000 km in diameter. With the use of equivalence conditions, various stationary nonlinear solutions are obtained and investigated analytically. The basic characteristics of stationary vortex structures for magnetized Rossby waves are investigate000.

Kaladze, T. D. [Tbilisi State University, I. Vekua Institute of Applied Mathematics (Georgia); Horton, W. [University of Texas at Austin, Institute for Fusion Studies (United States)

2006-12-15

98

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

99

Coordinated optical and radar observations of ionospheric pumping for a frequency pass through the second electron gyroharmonic at HAARP  

Microsoft Academic Search

On 4 February 2005, the High-frequency Active Auroral Research Program (HAARP) facility was operated in O and X mode while pointing into the magnetic zenith to produce artificial optical emissions in the ionospheric F layer. The pump frequency was set to 2.85 MHz to ensure passing through the second electron gyroharmonic of the decaying ionosphere. Optical recordings at 557.7 and

M. J. Kosch; T. Pedersen; E. Mishin; S. Oyama; J. Hughes; A. Senior; B. Watkins; B. Bristow

2007-01-01

100

Envelope solitons of electromagnetic spin waves in an artificial layered multiferroic  

NASA Astrophysics Data System (ADS)

The nonlinear wave properties of an artificial multiferroic medium consisting of a ferroelectric layer and a ferromagnetic layer have been studied. The simultaneous effect of wave nonlinearities of both layers on the formation and propagation of envelope solitons has been analyzed. It has been shown that bright envelope solitons of electromagnetic spin waves can appear in such a medium owing to the wave nonlinearity of ferroelectric layer. In order to confirm the theoretical results, the coefficients of the nonlinear Schrödinger equation have been calculated and this equation has been solved numerically.

Cherkasskii, M. A.; Kalinikos, B. A.

2013-08-01

101

Formation of artificially-layered high-temperature superconductors using pulsed-laser deposition.  

National Technical Information Service (NTIS)

Pulsed-laser deposition has been used to synthesize artificially-layere dhigh-temperature superconductors. Novel thin-film SrCu0(sub 2)/BaCu0(sub2) superlattices have been synthesized which superconduct at temperatures as high as 70 K. These results demon...

D. P. Norton B. C. Chakoumakos J. D. Budai

1995-01-01

102

Formation and properties of novel artificially-layered cuprate superconductors using pulsed-laser deposition.  

National Technical Information Service (NTIS)

Pulsed-laser deposition and epitaxial stabilization have been effectively used to engineer artificially-layered thin-film materials. Novel cuprate compounds have been synthesized using the constraint of epitaxy to stabilize (Ca,Sr)CuO(sub 2)/(Ba,Ca,Sr)CuO...

D. P. Norton B. C. Chakoumakos J. D. Budai

1996-01-01

103

Understanding Layer Promotion and Its Relationship to Melting in Krypton on Graphite Using Artificial Constraints  

Microsoft Academic Search

Constant particle number, density and temperature (N, ?, T) Molecular-Dynamics simulations are used to study second layer promotion and melting in a complete monolayer of krypton deposited onto a graphite substrate. In order to study the vertical behavior of the system and its relationship to melting, artificial horizontal constraints are introduced and their effects are systematically monitored. We find that

E. J. Chamberlin; M. W. Roth

104

An artificial negotiating agent modeling approach embedding dynamic offer generating and cognitive layer  

Microsoft Academic Search

In this paper, a dynamic offer generating unit and cognitive layer are suggested for artificial agents based negotiation systems. For this purpose, first, adaptive time and behavior dependent tactics are developed taking advantages from time continuity and dynamics aspects (features) integrated in their modeling. Then, a negotiation strategy (bilateral over single issue) based on these two tactics is suggested. Second,

Arash Bahrammirzaee; Amine Chohra; Kurosh Madani

2011-01-01

105

Artificial retardation of barotropic waves in layered ocean models  

SciTech Connect

The effect of reducing the barotropic gravity wave speed in a layered ocean model in order to gain computational speed is explored. In theory the error in the propagation of baroclinic gravity waves typically is less than 3% for a reduction of the external gravity speed by one order of magnitude. This is confirmed in a numerical experiment. For baroclinic Rossby waves, the phase speed error is even less. The barotropic response is limited to the reduced radius of deformation. The method, which we will refer to as gravity wave retardation, is therefore applicable only for oceanic flows where the barotropic mode is of minor importance. It is demonstrated that the method gives very good results for the baroclinic flow of an equatorial jet, spinup of a midlatitude ocean and flow over a midoceanic ridge. The method can be considered as an alternative to multilayer reduced gravity models, and has the advantage that bottom topography can be included. 24 refs., 15 figs.

Jensen, T.G. [Colorado State Univ., Fort Collins, CO (United States)]|[Danish Hydraulic Inst., Horsholm (Denmark)

1996-06-01

106

Observations and model calculations of the F3 layer in the Southeast Asian equatorial ionosphere  

NASA Astrophysics Data System (ADS)

To clarify the characteristics of the F3 layer with a focus on magnetic latitude dependence and the relationship to the equatorial anomaly, we performed statistical analysis of F3 layer occurrences using the ionosonde chain data in a magnetic meridional plane in Southeast Asia and performed model calculations. From comparison of the observational and model calculation results, it was found that the field-aligned diffusion of plasma acts to make the F3 layer prominent in the magnetic low-latitude region while acting to decrease the peak density of the F3 layer near the magnetic equator. The magnetic latitude dependence of the F3 layer formation comes not only from the meridional neutral wind effect but also from the field-aligned diffusion effect. The model calculations revealed that the F3 peak corresponds to the electron density-enhanced region associated with the equatorial anomaly. This relationship is consistent with the suggestion that the field-aligned diffusion acts to make the F3 layer prominent in the magnetic low-latitude region since the fundamental factors for generation of the equatorial anomaly are also E × B drift and field-aligned downward diffusion. It is suggested that the local time and magnetic latitudinal variations of the F3 layer result from those of the electron density-enhanced region associated with the equatorial anomaly.

Uemoto, Jyunpei; Maruyama, Takashi; Ono, Takayuki; Saito, Susumu; Iizima, Masahide; Kumamoto, Atsushi

2011-03-01

107

Evidence for the geographic control of additional layer formation in the low-latitude ionosphere  

NASA Astrophysics Data System (ADS)

Ionograms recorded from four ionosonde stations along the Western Pacific (WestPac) chain (about 122°E geographic, 192°E geomagnetic) are employed to study the occurrence of an additional layer at F-region altitudes during the 1-15 March 1998 WestPac campaign. It was found that the appearance of the additional layer at the local noontime hours is a typical phenomenon at Parepare (4°S geographic, 14.8°S geomagnetic). The additional layer was not clearly observed at Cebu (0.4°S geomagnetic) and Manila (3.7°N geomagnetic), and was not observed at Chung-Li (14.2°N geomagnetic) during the campaign. Furthermore, the additional layer was not seen from any of the station on 11 March 1998, a magnetically disturbed day. These results indicate that the fountain effect (produced by E×B motion) plays an important role in the formation of the additional layer. However, they also suggest the dynamics of the layer formation are in some way influenced by the location of the station relative to the geographic equator.

Hsiao, C. C.; Liu, J. Y.; Tsunoda, R. T.; Fukao, S.; Saroso, S.; Nozaki, K.; Badillo, V. L.; Berkey, F. T.; Chen, S. W.; Yamamoto, M.

108

The polar-ionosphere phenomena induced by high-power radio waves from the spear heating facility  

Microsoft Academic Search

We present the results of experimental studies of specific features in the behavior of small-scale artificial field-aligned irregularities (AFAIs) and the DM component in the spectra of stimulated electromagnetic emission (SEE). Analysis of experimental data shows that AFAIs in the polar ionosphere are generated under different background geophysical conditions (season, local time, the presence of sporadic layers in the E

N. F. Blagoveshchenskaya; T. D. Borisova; V. A. Kornienko; A. S. Janzhura; A. S. Kalishin; T. R. Robinson; T. K. Yeoman; D. M. Wright; L. J. Baddeley

2008-01-01

109

Artificial dispersion via high-order homogenization: magnetoelectric coupling and magnetism from dielectric layers  

PubMed Central

We investigate a high-order homogenization (HOH) algorithm for periodic multi-layered stacks. The mathematical tool of choice is a transfer matrix method. Expressions for effective permeability, permittivity and magnetoelectric coupling are explored by frequency power expansions. On the physical side, this HOH uncovers a magnetoelectric coupling effect (odd-order approximation) and artificial magnetism (even-order approximation) in moderate contrast photonic crystals. Comparing the effective parameters' expressions of a stack with three layers against that of a stack with two layers, we note that the magnetoelectric coupling effect vanishes while the artificial magnetism can still be achieved in a centre-symmetric periodic structure. Furthermore, we numerically check the effective parameters through the dispersion law and transmission property of a stack with two dielectric layers against that of an effective bianisotropic medium: they are in good agreement throughout the low-frequency (acoustic) band until the first stop band, where the analyticity of the logarithm function of the transfer matrix () breaks down.

Liu, Yan; Guenneau, Sebastien; Gralak, Boris

2013-01-01

110

A statistical model for Martian ionosphere  

NASA Astrophysics Data System (ADS)

A statistical model for Martian ionosphere is reported. This model is composed by inputs from two means of data assembly. One is so-called Double Quasi-Chapman Layer (QCL) method, by dividing the Martian ionosphere into two parts which can be described sufficiently by a QCL separately; the other is to analyze all observations by EOF method and a "background" ionosphere is therefore defined. The model can give a quite good ionosphere that represent the "average" status of Martian ionosphere, and can be a good "background" Martian ionosphere for other researches. Both MGS radio occultation dataset and MARSIS/MEX ionogram gallery are used to develop this model.

Wang, Jing-Song; Wang, Xiao-Dong; Mao, Tian

111

Creating a two-layered augmented artificial immune system for application to computer network intrusion detection  

NASA Astrophysics Data System (ADS)

Computer network security has become a very serious concern of commercial, industrial, and military organizations due to the increasing number of network threats such as outsider intrusions and insider covert activities. An important security element of course is network intrusion detection which is a difficult real world problem that has been addressed through many different solution attempts. Using an artificial immune system has been shown to be one of the most promising results. By enhancing jREMISA, a multi-objective evolutionary algorithm inspired artificial immune system, with a secondary defense layer; we produce improved accuracy of intrusion classification and a flexibility in responsiveness. This responsiveness can be leveraged to provide a much more powerful and accurate system, through the use of increased processing time and dedicated hardware which has the flexibility of being located out of band.

Judge, Matthew G.; Lamont, Gary B.

2009-05-01

112

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

113

Comparison of peak characteristics of F2 ionospheric layer over Tehran region at a low solar activity period with IRI-2001 and IRI-2007 models predictions  

NASA Astrophysics Data System (ADS)

In the present work values of peak electron density (NmF2) and height of F2 ionospheric layer (hmF2) over Tehran region at a low solar activity period are compared with the predictions of the International Reference Ionosphere models (IRI-2001 and IRI-2007). Data measured by a digital ionosonde at the ionospheric station of the Institute of Geophysics, University of Tehran from July 2006 to June 2007 are used to perform the calculations. Formulations proposed by Shimazaki (1955) and Bilitza et al. (1979) are utilized to calculate the hmF2. The International Union of Radio Science (URSI) and International Radio Consultative Committee (CCIR) options are employed to run the IRI-2001 and IRI-2007 models. Results show that both IRI-2007 and IRI-2001 can successfully predict the NmF2 and hmF2 over Tehran region. In addition, the study shows that predictions of IRI-2007 model with CCIR coefficient has closer values to the observations. Furthermore, it is found that the monthly average of the percentage deviation between the IRI models predictions and the values of hmF2 and NmF2 parameters are less than 10% and 21%, respectively.

Karami, Kh.; Ghader, S.; Raeen, A.

2011-09-01

114

Estimating Deliverability in Multi-Layered Gas Reservoirs Using Artificial Intelligence  

NASA Astrophysics Data System (ADS)

In this research, an artificial intelligence (AI) model has been created to estimate the production rate of each layer in a multi-layered gas reservoir using static properties such as those obtained from well logging, in addition to dynamic properties such as pressure. This approach will be helpful in several reservoir engineering applications, such as understanding layers' depletion, or targeting specific layers for workover. It could also be used for PLT analysis where the measured PLT values are compared to the expected values and a variance analysis could be performed. Data were collected from more than 100 wells in a certain reservoir spanning over four fields. They were combined in related input variables and fed to the AI model for learning purposes. To compare different AI methods, the data were fed to 5 methods, namely ANFIS, MLP, RBF, SVM, and GRNN, and results were optimized for each method. Between the tested AI methods, SVM and GRNN performed best as shown by a low mean absolute percentage error and a very high correlation coefficient. This research shows promising use for AI methods in estimating production rate from each layer in a multi-layered gas reservoir.

Al-Arfaj, Malik Khalid

115

Feasibility of generating an artificial burst in a turbulent boundary layer, phase 2  

NASA Astrophysics Data System (ADS)

Various drag accounts for about half of the total drag on commercial aircraft at subsonic cruise conditions. Two avenues are available to achieve drag reduction: either laminar flow control or turbulence manipulation. The present research deals with the latter approach. The primary objective of Phase 2 research was to investigate experimentally the feasibility of substantially reducing the skin-friction drag in a turbulent boundary layer. The method combines the beneficial effects of suction and a longitudinally ribbed surface. At a sufficiently large spanwise separation, the streamwise grooves act as a nucleation site causing a focusing of low-speed streaks over the peaks. Suction is then applied intermittently through longitudinal slots located at selected locations along those peaks to obliterate the low-speed regions and to prevent bursting. Phase 2 research was divided into two tasks. In the first, selective suction from a single streamwise slot was used to eliminate either a single burst-like event or a periodic train of artificially generated bursts in laminar and turbulent boundary layers that develop on a flat plate towed in a water channel. The results indicate that equivalent values of the suction coefficient as low as 0.0006 were sufficient to eliminate the artificially generated bursts in a laminar boundary layer.

Gad-El-Hak, Mohamed

1989-03-01

116

Artificially layered PbTiO3/BaTiO3 superlattices  

NASA Astrophysics Data System (ADS)

Artificially layered superlattices of ferroelectric oxides provide an appealing route for the tailoring of materials to particular applications [1] by taking advantage of electrostatics, strain and more exotic interactions between different materials at interfaces [2]. First principles calculations [3] suggest that the piezoelectric properties can be enhanced at certain ratios of layer thicknesses in the PbTiO3/BaTiO3 superlattice system. We have fabricated high quality artificially layered PbTiO3/BaTiO3 superlattices on SrTiO3 substrates (with SrRuO3 electrodes) using an off-axis RF magnetron sputtering technique, allowing us to perform a range of experiments, including x-diffraction, electrical measurements and atomic force microscopy. We will discuss our experimental results and their relationship with the theoretical expectations for this system and highlight the potential of using a superlattice approach to create enhanced materials for piezoelectric applications. References [1] M. Dawber, N. Stucki, C. Lichtensteiger, S. Gariglio, P. Ghosez and J.-M. Triscone, Advanced Materials, 19, 4153 (2007). [2] E. Bousquet, M. Dawber, N. Stucki, C. Lichtensteiger, P. Hermet, S.Gariglio, J.-M. Triscone, and P. Ghosez, Nature, 452, 732 (2008). [3] V. R. Cooper and K. M. Rabe, Phys. Rev. B 79, 180101 (R) (2009)

Ziegler, Benedikt; Callori, Sara; Sinsheimer, John; Dawber, Matthew

2010-03-01

117

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

118

A multi-layered backpropagation artificial neural network algorithm for UV spectral classification  

NASA Astrophysics Data System (ADS)

In this paper we present an application of an artificial neural network model based on a multi-layered backpropagation algorithm for spectral classification of UV data from the International Ultraviolet Explorer (IUE) low dispersion spectra reference atlas. The model used is similar to that of von Hippel et al. (1994), and is found to reduce the classification error as compared to the recently reported results on the same data set (Gulati et al. 1994b). The improved version of the network is much simpler in structure and the training time is reduced by a factor of almost 20. Such networks will prove very useful in efficient classification of large databases

Mukherjee, Soma; Bhattacharya, Ujjwal; Parui, S. K.; Gupta, Ranjan; Gulati, Ravi K.

1996-09-01

119

Development of a low cost high precision three-layer 3D artificial compound eye.  

PubMed

Artificial compound eyes are typically designed on planar substrates due to the limits of current imaging devices and available manufacturing processes. In this study, a high precision, low cost, three-layer 3D artificial compound eye consisting of a 3D microlens array, a freeform lens array, and a field lens array was constructed to mimic an apposition compound eye on a curved substrate. The freeform microlens array was manufactured on a curved substrate to alter incident light beams and steer their respective images onto a flat image plane. The optical design was performed using ZEMAX. The optical simulation shows that the artificial compound eye can form multiple images with aberrations below 11 ?m; adequate for many imaging applications. Both the freeform lens array and the field lens array were manufactured using microinjection molding process to reduce cost. Aluminum mold inserts were diamond machined by the slow tool servo method. The performance of the compound eye was tested using a home-built optical setup. The images captured demonstrate that the proposed structures can successfully steer images from a curved surface onto a planar photoreceptor. Experimental results show that the compound eye in this research has a field of view of 87°. In addition, images formed by multiple channels were found to be evenly distributed on the flat photoreceptor. Additionally, overlapping views of the adjacent channels allow higher resolution images to be re-constructed from multiple 3D images taken simultaneously. PMID:24104115

Zhang, Hao; Li, Lei; McCray, David L; Scheiding, Sebastian; Naples, Neil J; Gebhardt, Andreas; Risse, Stefan; Eberhardt, Ramona; Tünnermann, Andreas; Yi, Allen Y

2013-09-23

120

Characteristics of the Lower Thermosphere and Ionospheric D Region Deduced From High Time-Resolution Sporadic E-Layer Data During the Solar Eclipse of August 1, 2008  

NASA Astrophysics Data System (ADS)

The digital ionosonde at Sodankylä Geophysical Observatory, Finland, is performing continuous high time resolution soundings since the beginning of IPY in 2007. During the partial solar eclipse which occurred on first of August, 2008, a stable sporadic E layer was observed with the ionosonde. Using the time development of the recorded echo power of the sporadic E trace at different frequencies as a constraint, we analyse the underlying lower thermospheric and ionospheric D-region characteristics, by applying a detailed coupled ion and neutral chemistry model SIC (Sodankyla Ion Chemistry model), together with modeling of the radio wave propagation and absorption. Use of a simplified ion chemistry model is compared with the use of the SIC model. While the expected effect of the solar eclipse on E-layer critical frequency cannot be seen due to the existence of the sporadic E layer, ionisation in the D-region is consistent with the variation of solar radiation during the eclipse.

Enell, C.; Turunen, E.; Kero, A.; Ulich, T.; Tapaninen, O.; Kaaretkoski, H.; Karppinen, T.

2008-12-01

121

Harnessing competition in artificially layered ferroelectric superlattices to engineer enhanced piezoelectrics  

NASA Astrophysics Data System (ADS)

First principles calculations by Cooper and Rabe (V. R. Cooper and K.M. Rabe, Phys. Rev. B 79, 180101 (R) (2009)), predicted that in PbTiO3/BaTiO3 superlattices an enhancement of the d33 piezoelectric coefficient could be achieved at a particular ratio of the thickness of the constituent layers. We have fabricated high quality artificially layered PbTiO3/BaTiO3 superlattices on SrTiO3 substrates (with SrRuO3 bottom electrodes) using an off-axis RF magnetron sputtering technique, allowing us to perform x-ray diffraction, electrical measurements and atomic force microscopy on this system. The experimental results confirm the prediction from first principles calculations, and we apply a Landau theory model as a useful bridge between the first principles predictions and experimental results at elevated temperature. In this work we have demonstrated that by finely balancing competing material properties in artificial heterostructures, desirable properties that exceed those of the parent compounds can be achieved.

Dawber, Matthew; Ziegler, Benedikt; Callori, Sara; Sinsheimer, John; Cooper, Valentino; Yusufaly, Tahir; Rabe, Karin M.; Chandra, Premala

2011-03-01

122

Formation and properties of novel artificially-layered cuprate superconductors using pulsed-laser deposition  

SciTech Connect

Pulsed-laser deposition and epitaxial stabilization have been effectively used to engineer artificially-layered thin-film materials. Novel cuprate compounds have been synthesized using the constraint of epitaxy to stabilize (Ca,Sr)CuO{sub 2}/(Ba,Ca,Sr)CuO{sub 2} superconducting superlattices in the infinite layer structure. Superlattice chemical modulation can be observed from the x-ray diffraction patterns for structures with SrCuO{sub 2} and (Ca, Sr)CuO{sub 2} layers as thin as a single unit cell ({approximately}3. 4 {angstrom}). X-ray diffraction intensity oscillations, due to the finite thickness of the film, indicate that (Ca,Sr)CuO{sub 2} films grown by pulsed-laser deposition are extremely flat with a thickness variation of only {approximately}20 {angstrom} over a length scale of several thousand angstroms. This enables the unit-cell control of (Ca, Sr)CuO{sub 2} film growth in an oxygen pressure regime in which in situ surface analysis using electron diffraction is not possible. With the incorporation of BaCuO{sub 2} layers, superlattice structures have been synthesized which superconduct at temperatures as high as 70 K. Dc transport measurements indicate that (Ca, Sr)CuO{sub 2}/BaCuO{sub 2} superlattices are two dimensional superconductors with the superconducting transition primarily associated with the BaCuO{sub 2} layers. Superconductivity is observed only for structures with BaCuO{sub 2} layers at least two unit cells thick with {Tc} decreasing as the (Ca,Sr)CuO{sub 2} layer thickness increases. Normalized resistance in the superconducting region collapse to the Ginzburg-Landau Coulomb gas universal resistance curve consistent with the two-dimensional vortex fluctuation model.

Norton, D.P.; Chakoumakos, B.C.; Budai, J.D.

1996-03-01

123

Artificially layered PbTiO3/CaTiO3 superlattices  

NASA Astrophysics Data System (ADS)

It has been shown that in artificially layered PbTiO3/SrTiO3 superlattices, a form of improper ferroelectricity occurs where the rotations of the oxygen octahedra at the interfaces couple with the polar mode and increase the ferroelectric polarization of the material when the layers are very thin. PbTiO3/CaTiO3 superlattices grown on SrTiO3 substrates are also highly likely to display this kind of behavior, as the CaTiO3 ground state is dominated by rotational distortions. This system should also play host to a competition between in-plane ferroelectricity (as CaTiO3 is subjected to a large tensile strain when grown on SrTiO3) and out-of-plane ferroelectricity (the usual result when in PbTiO3 is grown on SrTiO3). Using off-axis RF magnetron sputtering, we have produced high quality superlattices of PbTiO3/CaTiO3 with various layer thicknesses on SrTiO3 substrates with SrRuO3 bottom electrodes. The samples were analyzed using x-ray diffraction, electrical measurements, and atomic force microscopy. Our experimental results reveal a fascinating transition region at certain ratios of the relative layer thicknesses.

Sinsheimer, John; Benkara, Youcef; Daley, Jonathan; Callori, Sara; Dawber, Matthew

2011-03-01

124

Planetary Ionospheres  

Microsoft Academic Search

\\u000a The paper presents a summary of the lectures on planetary ionospheres given at NASA’s 1st Asia Pacific School on International Heliophysical Year conducted at Indian Institute of Astrophysics,\\u000a Kodaikanal, India during 10–22 December 2007. Following an introduction, the paper describes the structure of the ionospheres,\\u000a theory of Earth’s ionosphere including the effects of diffusion, neutral wind and electric field, and

Nanan Balan

2010-01-01

125

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

126

Trends in the F2 ionospheric layer due to long-term variations in the Earth's magnetic field  

Microsoft Academic Search

The Earth's magnetic field presents long-term variations with changes in strength and orientation. Particularly, changes in the dip angle (I) and, consequently, in the sin(I)cos(I) factor, affect the thermospheric neutral winds that move the conducting plasma of the ionosphere. In this way, a lowering or lifting of the F2-peak (hmF2) is induced together with changes in foF2, depending on season,

Ana G. Elias

2009-01-01

127

Tantalum as a buffer layer in diamond-like carbon coated artificial hip joints.  

PubMed

The acid resistance of tantalum coated and uncoated human hip joint prostheses was studied with commercial CrCoMo acetabular cups. The samples were exposed to 10% HCl solution and the quantities of dissolved Cr, Co, and Mo were measured with proton-induced X-ray emission (PIXE). The absolute quantities were obtained with the use of Cr and Se solution standards. Tantalum coatings (thicknesses 4-6 microm) were prepared in vacuum with magnetron sputtering. Tantalum coating decreased the corrosion rate by a factor of 10(6). As a spinoff from recent wear tests on artificial hip joints it was shown that tantalum has excellent mechanical properties as an intermediate layer of diamond-like carbon (DLC) coatings. When tantalum was tested together with DLC on three metal-on-metal hip joint pairs in a hip simulator, no observable defects occurred during 15 million walking cycles with a periodic 50-300-kg load (Paul curve). PMID:12808604

Kiuru, Mirjami; Alakoski, Esa; Tiainen, Veli-Matti; Lappalainen, Reijo; Anttila, Asko

2003-07-15

128

Statistical study of relationship between medium-scale traveling ionospheric disturbance and sporadic E layer activities in summer night over Japan  

NASA Astrophysics Data System (ADS)

We investigate the relationship between medium-scale traveling ionospheric disturbance (MSTID) and sporadic E (Es) layer activities in summer nights by analyzing total electron content (TEC) data obtained from a global positioning system (GPS) network in Japan and ionosonde data obtained at Kokubunji, Japan during May-August in 2001-2005. MSTID activity is defined as , where [delta]I is standard deviation of the TEC perturbations over Kokubunji within 1 h, and is the background TEC. By analyzing nighttime-averaged (19-02 LT) values of MSTID activity and Es layer parameters, we find that the MSTID activity is closely correlated with f0Es and f0Es-fbEs. This result suggests that MSTID and the spatial structures of Es layer could be generated by an electro-dynamical coupling process between the Es layer and F region through polarization electric fields. Furthermore, we suggest that the appearance of the Es layer in the summer hemisphere could play an important role in generating MSTIDs in both hemispheres.

Otsuka, Y.; Tani, T.; Tsugawa, T.; Ogawa, T.; Saito, A.

2008-12-01

129

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

130

DECAMETER AND METER WAVELENGTH RADAR STUDIES OF ARTIFICIAL PLASMA CLOUDS IN THE LOWER IONOSPHERE. I. THERMODYNAMIC PROPERTIES OF THE ATMOSPHERE DISCERNED FROM BLAST WAVE MEASUREMENTS  

Microsoft Academic Search

A series of cesium-seeded explosive bursts in the 90- to 110-km altitude region have been observed with meter and decameter wave radar. Detailed measurements of contact surface expansion, undulation, and stabilization have been used to acquire estimates of the altitude dependence of atmospheric pressure and density in the lower ionosphere. It has been found that events in the development of

John R. Davis; John C. Moore

1970-01-01

131

Artificial disturbances of the ionosphere over the Millstone Hill Incoherent Scatter Radar from dedicated burns of the space shuttle orbital maneuver subsystem engines  

NASA Astrophysics Data System (ADS)

Two ionospheric modification experiments were carried out over the incoherent scatter radar (ISR) located at Millstone Hill, Massachusetts. These experiments are part of the Shuttle Ionospheric Modification with Pulsed Localized Exhaust (SIMPLEX) program at the Naval Research Laboratory. The experiments use 10-s burns of the dual orbital maneuver subsystem (OMS) engines to produce the injection of high-speed molecules in the ionosphere near 380 km altitude. Charge exchange between the high-speed exhaust molecules and the ambient oxygen ions yields molecular ion beams that disturb the natural state of the ionosphere. Radar scatter provides measurements of the ion velocity distributions and plasma turbulence that result from the ion beam interactions. Ground-based observations with the University of Massachusetts Digisonde record the ionospheric density depressions resulting from recombination of the molecular ions with electrons. Prompt signatures of nonequilibrium ion distributions in the OMS engine plume are seen in the data taken during the SIMPLEX III and IV experiments for the space shuttle flights STS-108 and STS-110, respectively. The SIMPLEX III observations are much weaker than those during SIMPLEX IV. These differences are primarily attributed to the changes in the viewing directions for the radar beam. During SIMPLEX IV, the radar is looking more downstream from the exhaust injection and the stimulation of plasma turbulence is seen with the ISR for over 30 s at distances up to 200 km from the burn altitude along the radar beam. Strong backscatter in the radar spectra is attributed to ion acoustic waves driven by the pickup ion beams. Both experiments provide large-scale cavities detected by the Digisonde for up to 20 min after the engine burn. These cavities are the result of ion-electron recombination of the pickup ions.

Bernhardt, Paul A.; Erickson, Philip J.; Lind, Frank D.; Foster, John C.; Reinisch, Bodo W.

2005-05-01

132

The effect of layer-by-layer chitosan-hyaluronic acid coating on graft-to-bone healing of a poly(ethylene terephthalate) artificial ligament.  

PubMed

Surface coating with an organic layer-by-layer self-assembled template of chitosan and hyaluronic acid on a poly(ethylene terephthalate) (PET) artificial ligament was designed for the promotion and enhancement of graft-to-bone healing after artificial ligament implantation in a bone tunnel. The results of in vitro culturing of MC3T3-E1 mouse osteoblastic cells supported the hypothesis that the layer-by-layer coating of chitosan and hyaluronic acid could promote the cell compatibility of grafts and could promote osteoblast proliferation. A rabbit extra-articular tendon-to-bone healing model was used to evaluate the effect of this kind of surface-modified stainless artificial ligament in vivo. The final results proved that this organic compound coating could significantly promote and enhance new bone formation at the graft-bone interface histologically and, correspondingly, the experimental group with coating had significantly higher biomechanical properties compared with controls at 8 weeks (P < 0.05). PMID:21255485

Li, Hong; Ge, Yunsheng; Zhang, Pengyun; Wu, Lingxiang; Chen, Shiyi

2011-01-21

133

Cluster observations and numerical modeling of energy-dispersed ionospheric H+ ions bouncing at the plasma sheet boundary layer  

NASA Astrophysics Data System (ADS)

The Cluster mission offers a unique opportunity to investigate the origin of the energy-dispersed ion structures frequently observed at 4.5-5 R E altitude in the auroral region. We present a detailed study of the 14 February 2001 northern pass, characterized by the successive observation by three spacecraft of a series of energy-dispersed structures at ˜72-75° ILAT in a region of poleward convection. Equatorward, the satellites also observed a localized, steady, and intense source of outflowing energetic (3-10 keV) H+ and O+ ions. These substructures were modeled by launching millions of H+ ions from this ionospheric source and following them through time-dependent electric and magnetic fields obtained from a global MHD simulation of this event. Despite the complexity of ion orbits, the simulations showed that a large number of ions returned to the Cluster location, poleward of their source, in a number of adjacent or overlapping energy-latitude substructures with the correct dispersion. The first dispersed echo was unexpectedly generated by “half-bouncing” ions that interacted with the current sheet to return to the same hemisphere. The time-shifted observations made by two Cluster (SC1 and SC3) spacecrafts were correctly reproduced. Almost all the ions returning to the spacecraft underwent a ˜2-5 keV nonadiabatic acceleration at each interaction with the current sheet in a very confined resonant region. This acceleration explains the overall energy increase from one structure to the next. This event confirms the importance of the ionospheric source in populating bouncing ion clusters within the magnetosphere, even at high latitudes.

Bosqued, J. M.; Ashour-Abdalla, M.; Umeda, T.; El Alaoui, M.; Peroomian, V.; Frey, H. U.; Marchaudon, A.; Laakso, H.

2009-04-01

134

Propagation in the ionosphere, B  

NASA Astrophysics Data System (ADS)

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 activity level forecasts are reviewed. The goal is to design automatic decision aids which allow skilled personnel to adapt to systems operation and interpret the output from computer programs or experimental techniques. In the future, an artificial intelligence system might replace human operators in selecting and using the models and experimental techniques to best advantage.

Cannon, Paul S.

1994-09-01

135

Ionospheric Change and Solar EUV Irradiance  

NASA Astrophysics Data System (ADS)

The ionosphere has been quantitatively monitored for the past six solar cycles. The past few years of observations are showing trends that differ from the prior cycles! Our good statistical relationships between the solar radio flux index at 10.7 cm, the solar EUV Irradiance, and the ionospheric F-layer peak density are showing indications of divergence! Present day discussion of the Sun-Earth entering a Dalton Minimum would suggest change is occurring in the Sun, as the driver, followed by the Earth, as the receptor. The dayside ionosphere is driven by the solar EUV Irradiance. But different components of this spectrum affect the ionospheric layers differently. For a first time the continuous high cadence EUV spectra from the SDO EVE instrument enable ionospheric scientists the opportunity to evaluate solar EUV variability as a driver of ionospheric variability. A definitive understanding of which spectral components are responsible for the E- and F-layers of the ionosphere will enable assessments of how over 50 years of ionospheric observations, the solar EUV Irradiance has changed. If indeed the evidence suggesting the Sun-Earth system is entering a Dalton Minimum periods is correct, then the comprehensive EVE solar EUV Irradiance data base combined with the ongoing ionospheric data bases will provide a most fortuitous fiduciary reference baseline for Sun-Earth dependencies. Using the EVE EUV Irradiances, a physics based ionospheric model (TDIM), and 50 plus years of ionospheric observation from Wallops Island (Virginia) the above Sun-Earth ionospheric relationship will be reported on.

Sojka, J. J.; David, M.; Jensen, J. B.; Schunk, R. W.

2011-12-01

136

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

137

The polar-ionosphere phenomena induced by high-power radio waves from the spear heating facility  

Microsoft Academic Search

We present the results of experimental studies of specific features in the behavior of small-scale artificial field-aligned\\u000a irregularities (AFAIs) and the DM component in the spectra of stimulated electromagnetic emission (SEE). Analysis of experimental\\u000a data shows that AFAIs in the polar ionosphere are generated under different background geophysical conditions (season, local\\u000a time, the presence of sporadic layers in the E

N. F. Blagoveshchenskaya; T. D. Borisova; V. A. Kornienko; A. S. Janzhura; A. S. Kalishin; T. R. Robinson; T. K. Yeoman; D. M. Wright; L. J. Baddeley

2008-01-01

138

Boriding response of AISI W1 steel and use of artificial neural network for prediction of borided layer properties  

Microsoft Academic Search

In the present study, boriding response of AISI W1 steel and prediction of boride layer properties were investigated by using artificial neural network (ANN). Boronizing heat treatment was carried out in a solid medium consisting of Ekabor-I powders at 850–1050 °C at 50 °C intervals for 1–8 h. The substrate used in this study was AISI W1. The presence of

Kenan Genel; Ibrahim Ozbek; Akif Kurt; Cuma Bindal

2002-01-01

139

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.

140

Superconductivity in SrCuO2-BaCuO2 Superlattices: Formation of Artificially Layered Superconducting Materials.  

PubMed

Pulsed-laser deposition was used to synthesize artificially layered high-temperature superconductors. Thin-film compounds were formed when the constraint of epitaxy was used to stabilize SrCuO(2)-BaCuO(2) superlattices in the infinite layer structure. Using this approach, two new structural families, Ba(2)Srn-1,Cun+1 O2n+2+delta and Ba(4)Srn-1 Cun+3O2n+6+delta have been synthesized; these families superconduct at temperatures as high as 70 kelvin. PMID:17811410

Norton, D P; Chakoumakos, B C; Budai, J D; Lowndes, D H; Sales, B C; Thompson, J R; Christen, D K

1994-09-30

141

Attenuation of radio signals by the ionosphere of Mars: Theoretical development and application to MARSIS observations  

Microsoft Academic Search

We investigate the ionospheric conditions required to explain Mars Express Mars Advanced Radar for Subsurface and Ionosphere Sounding topside radar sounder observations of ionospheric attenuation in excess of 13 dB at 5 MHz during solar energetic particle events. We develop theoretical expressions for the attenuation caused by a layer of ionospheric plasma in cases of high, intermediate, and low radio

Paul Withers

2011-01-01

142

Intrathoracic esophageal replacement in the dog with the use of an artificial esophagus composed of a collagen sponge with a double-layered silicone tube  

Microsoft Academic Search

Objectives: Intrathoracic esophageal replacement with an artificial esophagus is considered difficult. We attempted to replace the intrathoracic esophagus with an artificial esophagus composed of a collagen sponge with a double-layered silicone tube and examined the state of host tissue regeneration. Methods: A 5-cm long gap was created in the intrathoracic esophagus in 9 dogs and repaired by interposition of our

Yasumichi Yamamoto; Tatsuo Nakamura; Yasuhiko Shimizu; Kazuya Matsumoto; Yukinobu Takimoto; Tetsuya Kiyotani; Takashi Sekine; Hiroki Ueda; Yu Liu; Nobushige Tamura

1999-01-01

143

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

144

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

145

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

146

First artificially induced modulation of PMSE using the EISCAT Heating Facility  

NASA Astrophysics Data System (ADS)

A coordinated experiment involving ionospheric heating and VHF observations of polar mesosphere summer echoes (PMSE) has recently been conducted at the EISCAT facility near Tromsø, Norway. We have demonstrated for the first time that ionospheric heating can influence VHF radar returns associated with PMSE. Artificially elevating the electron temperatures within the PMSE layer has been shown to reduce the echo power. Based on this and other results from the experiment, it is suggested that the observed reduction in PMSE power is related to an enhancement of the electron diffusivity through the heating.

Chilson, Philip B.; Belova, Evgenia; Rietveld, Michael T.; Kirkwood, Sheila; Hoppe, Ulf-Peter

147

Ionosphere/thermosphere heating determined from dynamic magnetosphere-ionosphere/thermosphere coupling  

NASA Astrophysics Data System (ADS)

Ionosphere/thermosphere heating driven by magnetospheric convection is investigated through a three-fluid inductive (including Faraday's law) approach to describing magnetosphere-ionosphere/thermosphere coupling, for a 1-D stratified ionosphere/thermosphere in this initial study. It is shown that the response of the ionosphere/thermosphere and thus the heating is dynamic and height-dependent. The heating is essentially frictional in nature rather than Joule heating as commonly assumed. The heating rate reaches a quasi-steady state after about 25 Alfvén travel times. During the dynamic period, the heating can be enhanced and displays peaks at multiple times due to wave reflections. The dynamic heating rate can be more than twice greater than the quasi-steady state value. The heating is strongest in the E-layer but the heating rate per unit mass is concentrated around the F-layer peak height. This implies a potential mechanism of driving O+ upflow from O+ rich F-layer. It is shown that the ionosphere/thermosphere heating caused by the magnetosphere-ionosphere coupling can be simply evaluated through the relative velocity between the plasma and neutrals without invoking field-aligned currents, ionospheric conductance, and electric field. The present study provides understanding of the dynamic magnetosphere-ionosphere/thermosphere coupling from the ionospheric/thermospheric view in addition to magnetospheric perspectives.

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

2011-09-01

148

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.

149

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

150

Tsunamis warning from space :Ionosphere seismology  

SciTech Connect

Ionosphere is the layer of the atmosphere from about 85 to 600km containing electrons and electrically charged atoms that are produced by solar radiation. Perturbations - layering affected by day and night, X-rays and high-energy protons from the solar flares, geomagnetic storms, lightning, drivers-from-below. Strategic for radio-wave transmission. This project discusses the inversion of ionosphere signals, tsunami wave amplitude and coupling parameters, which improves tsunami warning systems.

Larmat, Carene [Los Alamos National Laboratory

2012-09-04

151

Layer-by-layer hyaluronic acid-chitosan coating promoted new collagen ingrowth into a poly(ethylene terephthalate) artificial ligament in a rabbit medical collateral ligament (MCL) reconstruction model  

Microsoft Academic Search

The ideal artificial ligament graft should have favorable biocompatibility to facilitate cell adhesion, proliferation, and collagen regeneration. In this present study, surface modification was performed on a poly(ethylene terephthalate) (PET) artificial ligament graft by layer-by-layer (LBL) self-assembly coating of hyaluronic acid (HA) and chitosan (CS). The surface characterization of the ligament was examined using scanning electron microscopy, atomic force microscopy,

Hong Li; Jia Jiang; Yunsheng Ge; Jialing Xu; Pengyun Zhang; Wei Zhong; Shiyi Chen

2012-01-01

152

F layer postsunset height rise due to electric field prereversal enhancement: 2. Traveling planetary wave ionospheric disturbances and their role on the generation of equatorial spread F  

Microsoft Academic Search

This paper investigates the role played by traveling planetary wave ionospheric disturbances (TPWIDs) on the modulation of the electric field prereversal enhancement (PRE) amplitude, near-sunset hours, in the equatorial ionosphere, and their influence on the day-to-day equatorial spread F (ESF) variability. We show that ``fresh'' (ESF) day-to-day variability is closely related with the postsunset height rise due to the electric

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

2009-01-01

153

F layer postsunset height rise due to electric field prereversal enhancement: 2. Traveling planetary wave ionospheric disturbances and their role on the generation of equatorial spread F  

Microsoft Academic Search

This paper investigates the role played by traveling planetary wave ionospheric disturbances (TPWIDs) on the modulation of the electric field prereversal enhancement (PRE) amplitude, near-sunset hours, in the equatorial ionosphere, and their influence on the day-to-day equatorial spread F (ESF) variability. We show that “fresh” (ESF) day-to-day variability is closely related with the postsunset height rise due to the electric

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

2009-01-01

154

Hygroscopic behavior and liquid-layer composition of aerosol particles generated from natural and artificial seawater  

Microsoft Academic Search

Sea-salt aerosol (SSA) particles affect the Earth's radiative balance and moderate heterogeneous chemistry in the marine boundary layer. Using conventional and environmental transmission electron microscopes (ETEM), we investigated the hygroscopic growth and liquid-layer compositions of particles generated from three types of aqueous salt solutions: sodium chloride, laboratory-synthesized seawater (S-SSA particles), and natural seawater (N-SSA particles). Three levels of morphological change

Matthew E. Wise; Evelyn J. Freney; Corey A. Tyree; Jonathan O. Allen; Scot T. Martin; Lynn M. Russell; Peter R. Buseck

2009-01-01

155

Prediction of mining subsidence under thin bedrocks and thick unconsolidated layers based on field measurement and artificial neural networks  

NASA Astrophysics Data System (ADS)

The deformation characteristics of subsidence and movement induced by mining under thin bedrocks and thick unconsolidated layers are researched using field measurement and the prediction method of artificial neural networks (ANN). Firstly, the occurrence characteristics of thin bedrock and thick unconsolidated layers were analyzed in a research coal field. Based on the measured data, the characteristics of ground movement show that the surface subsidence deformation of mining under thin bedrock is more intensive than that of mining under normal thickness bedrock. Such is evident through the settlement time concentrating, the maximum surface subsidence being greater than the thickness of coal seam, the distribution of ground movement and deformation being concentrated, the range extension being wide, the active period being intensive and concentrated, the surface damage being very serious, and the crack development being significant. A quantitative prediction method is made on mining subsidence under thin bedrocks and thick unconsolidated layers by means of ANN. The improved neural network was used for modeling and predicting the mining subsidence. The ANN output can reflect the change trend of ground movement and deformation. The forecasting results are in good agreement with the real observation results.

Yang, Weifeng; Xia, Xiaohong

2013-03-01

156

Pregnancies following artificial insemination with spermatozoa from problem stallion ejaculates processed by single layer centrifugation with Androcoll-E.  

PubMed

Some stallions produce ejaculates of low quality and/or low fertility when used for artificial insemination (AI). The purpose of these five case studies was to use Single Layer Centrifugation (SLC) to select the best spermatozoa from 'problem' ejaculates for subsequent use in AI. Sperm quality, in terms of motility, morphology and chromatin integrity, was improved in the SLC-selected samples compared to the corresponding uncentrifuged samples, with the exception of one stallion thought to have ampullary stasis. In this stallion, neither the incidence of spermatozoa with detached heads nor the proportion of damaged chromatin was decreased by SLC, in contrast to previous results. Pregnancies were obtained after using SLC-selected spermatozoa from the five stallions for AI, indicating that the spermatozoa were functional after SLC. Overall, the results suggest that SLC may be useful when preparing AI doses from some 'problem' ejaculates. PMID:21114793

Morrell, J M; Mari, G; Kútvölgyi, G; Meurling, S; Mislei, B; Iacono, E; Rodriguez-Martinez, H

2010-11-30

157

Hygroscopic behavior and liquid-layer composition of aerosol particles generated from natural and artificial seawater  

NASA Astrophysics Data System (ADS)

Sea-salt aerosol (SSA) particles affect the Earth's radiative balance and moderate heterogeneous chemistry in the marine boundary layer. Using conventional and environmental transmission electron microscopes (ETEM), we investigated the hygroscopic growth and liquid-layer compositions of particles generated from three types of aqueous salt solutions: sodium chloride, laboratory-synthesized seawater (S-SSA particles), and natural seawater (N-SSA particles). Three levels of morphological change were observed with the ETEM as the laboratory-generated particles were exposed to increasing relative humidity (RH). The first level, onset of observable morphological changes, occurred on average at 70, 48, and 35% RH for the NaCl, S-SSA, and N-SSA particles, respectively. The second level, rounding, occurred at 74, 66, and 57% RH for NaCl, S-SSA, and N-SSA particles, respectively. The third level, complete deliquescence, occurred at 75% RH for all particles. Collected ambient SSA particles were also examined. With the exception of deliquescence, they did not exhibit the same hygroscopic characteristics as the NaCl particles. The ambient particles, however, behaved most similarly to the synthesized and natural SSA particles, although the onset of morphological change was slightly higher for the S-SSA particles. We used energy-dispersive X-ray spectrometry to study the composition of the liquid layer formed on the S-SSA and N-SSA particles. The layer was enriched in Mg, S, and O relative to the solid particle core. An important implication of these results is that MgSO4-enriched solutions on the surface of SSA particles may be the solvents of many heterogeneous reactions.

Wise, Matthew E.; Freney, Evelyn J.; Tyree, Corey A.; Allen, Jonathan O.; Martin, Scot T.; Russell, Lynn M.; Buseck, Peter R.

2009-02-01

158

On anomalous temperature dependence of HC2? in natural and artificial layer superconductors  

NASA Astrophysics Data System (ADS)

Anomalous temperature dependence of the perpendicular critical field HC2?(T) of layered transition metal dichalcogenide MX2 with and without pyridine intercalation and that of Nb/Al2O3 superlattice are consistent with the theory of Maekawa, Ebisawa and Fukuyama (MEF) [S. Maekawa, H. Ebisawa, H. Fukuyama, J. Phys. Soc. Jpn. 52 (1983) 1352] based on the weak Anderson localization. For the pure conductor 2H-NbSe2, however, the anomalous HC2?(T) is to originate from the anisotropies in the Fermi surface and energy gap through the effect of nonlocality.

Ikebe, M.; Fujishiro, H.; Obi, Y.; Fujimori, H.; Morohashi, S.

1999-05-01

159

Interaction of an Artificially Thickened Boundary Layer with a Vertically Mounted Pitching Airfoil  

NASA Astrophysics Data System (ADS)

Wind energy represents a large portion of the growing market in alternative energy technologies and the current landscape has been dominated by the more prevalent horizontal axis wind turbine. However, there are several advantages to the vertical axis wind turbine (VAWT) or Darrieus type design and yet there is much to be understood about how the atmospheric boundary layer (ABL) affects their performance. In this study the ABL was simulated in a wind tunnel through the use of elliptical shaped vortex generators, a castellated wall, and floor roughness elements as described in the method of Counihan (1967) and then verified its validity by hot wire measurement of the mean velocity profile as well as the turbulence intensity. The motion of an blade element around a vertical axis is approximated through the use of a pitching airfoil. The wake of the airfoil is investigated through hot wire anemometry in both uniform flow and in the simulated boundary layer both at Re = 1.37x10^5 based on the chord of the airfoil.

Hohman, Tristen; Smits, Alexander; Martinelli, Luigi

2011-11-01

160

Some results of synchronous experimental study of artificial F-spread at radiophysical test sites in nizhny novgorod province  

NASA Astrophysics Data System (ADS)

We show some results of experiments on synchronous sounding of the ionosphere by short-wave signals at the Radiophysical Research Institute’s test site in Zimenki and Vasil’sursk, Nizhniy Novgorod province, during ionospheric modification by high-power short radiowaves from transmitters of the “Sura” facility in Vasil’sursk. In the course of experiments we proved directly the decisive role of large-scale inhomogeneities of the ionospheric plasma with dimensions of from several kilometers to several dozens of kilometers in the formation of artificial F- spread. The small-scale inhomogeneities with dimensions smaller than 1 km, which are localized in a relatively thin layer near the reflection level of a high-power short radiowave, emerged only at sounding waves, propagating (reflected) in the immediate vicinity of the center of the heating region.

Alimov, V. A.; Vybornov, F. I.; Erukhimov, L. M.; Komrakov, G. P.; Mityakov, N. A.; Rakhlin, A. V.

1997-06-01

161

Artificial vision by multi-layered neural networks: neocognitron and its advances.  

PubMed

The neocognitron is a neural network model proposed by Fukushima (1980). Its architecture was suggested by neurophysiological findings on the visual systems of mammals. It is a hierarchical multi-layered network. It acquires the ability to robustly recognize visual patterns through learning. Although the neocognitron has a long history, modifications of the network to improve its performance are still going on. For example, a recent neocognitron uses a new learning rule, named add-if-silent, which makes the learning process much simpler and more stable. Nevertheless, a high recognition rate can be kept with a smaller scale of the network. Referring to the history of the neocognitron, this paper discusses recent advances in the neocognitron. We also show that various new functions can be realized by, for example, introducing top-down connections to the neocognitron: mechanism of selective attention, recognition and completion of partly occluded patterns, restoring occluded contours, and so on. PMID:23098752

Fukushima, Kunihiko

2012-10-05

162

Artificial pinning centers using the barrier layer of ordered nanoporous alumina templates  

NASA Astrophysics Data System (ADS)

The barrier layer of self-ordered anodized aluminium oxide, which is grown from an aluminium foil, has been revealed by a selective chemical etching of the remaining aluminium. The surface obtained in this way consists of a triangular lattice of bumps with 100nm spacing, and heights of approximately 50nm. Using this surface as a template for controlling the pinning in thin superconducting films, superconducting Nb was deposited with different thicknesses and under different deposition angles. The evaporation under a 30° angle shows an asymmetric pinning potential composed of two triangular lattices having different pinning strengths. Matching effects are observed up to 1T. Matching effects are also maintained at relatively low temperature.

Hallet, X.; Mátéfi-Tempfli, S.; Mátéfi-Tempfli, M.; Michotte, S.; Piraux, L.; Vanacken, J.; Moshchalkov, V. V.

2009-03-01

163

Trends in the ionospheric E and F regions over Europe  

Microsoft Academic Search

Continuous observations in the ionospheric E and F regions have been regularly carried out since the fifties of this century at many ionosonde stations. Using these data from 31 European stations long-term trends have been derived for different parameters of the ionospheric E layer (h' E, foE), F1 layer (foF1) and F2 layer (hmF2,foF2). The detected trends in the E

J. Bremer

1998-01-01

164

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

165

Electron cyclotron harmonic resonances in high-frequency heating of the ionosphere  

NASA Astrophysics Data System (ADS)

Electron acceleration by upper hybrid waves under cyclotron harmonic resonance interaction is studied. Theory is formulated; the analytical solutions in the second and fourth harmonic cyclotron resonance cases are obtained, and in the third harmonic case, a first order differential equation governing the evolution of the electron energy is derived. The theory is applied for explaining the generation of artificial ionization layers observed in high-frequency (HF) ionospheric heating experiments. The upper hybrid waves are assumed to be excited parametrically by the O-mode HF heating wave. As the decay mode is the lower hybrid wave, the excited upper hybrid waves have wavelengths ranging from 0.25 to 0.5 m, which are short enough to effectively incorporate the finite Larmour radius effect for the harmonic cyclotron resonance interactions as well as have a frequency bandwidth of about 20 kHz, which provides an altitude region of about 10 km for continuous harmonic cyclotron resonance interaction between electrons and descending waves in the slightly inhomogeneous geomagnetic field. The numerical results on electron acceleration show that electron fluxes with energies larger than 14 eV are generated in the three harmonic cases. These energetic electrons cause impact ionizations, which are descending to form artificial ionization layers at the bottom of the ionospheric F region.

Kuo, Spencer P.

2013-09-01

166

A short-term ionospheric forecasting empirical regional model (IFERM) to predict the critical frequency of the F2 layer during moderate, disturbed, and very disturbed geomagnetic conditions over the European area  

NASA Astrophysics Data System (ADS)

A short-term ionospheric forecasting empirical regional model (IFERM) has been developed to predict the state of the critical frequency of the F2 layer (foF2) under different geomagnetic conditions. IFERM is based on 13 short term ionospheric forecasting empirical local models (IFELM) developed to predict foF2 at 13 ionospheric observatories scattered around the European area. The forecasting procedures were developed by taking into account, hourly measurements of foF2, hourly quiet-time reference values of foF2 (foF2QT), and the hourly time-weighted accumulation series derived from the geomagnetic planetary index ap, (ap(?)), for each observatory. Under the assumption that the ionospheric disturbance index ln(foF2/foF2QT) is correlated to the integrated geomagnetic disturbance index ap(?), a set of statistically significant regression coefficients were established for each observatory, over 12 months, over 24 h, and under 3 different ranges of geomagnetic activity. This data was then used as input to compute short-term ionospheric forecasting of foF2 at the 13 local stations under consideration. The empirical storm-time ionospheric correction model (STORM) was used to predict foF2 in two different ways: scaling both the hourly median prediction provided by IRI (STORM_foF2MED,IRI model), and the foF2QT values (STORM_foF2QT model) from each local station. The comparison between the performance of STORM_foF2MED,IRI, STORM_foF2QT, IFELM, and the foF2QT values, was made on the basis of root mean square deviation (r.m.s.) for a large number of periods characterized by moderate, disturbed, and very disturbed geomagnetic activity. The results showed that the 13 IFELM perform much better than STORM_foF2,sub>MED,IRI and STORM_foF2QT especially in the eastern part of the European area during the summer months (May, June, July, and August) and equinoctial months (March, April, September, and October) under disturbed and very disturbed geomagnetic conditions, respectively. The performance of IFELM is also very good in the western and central part of the Europe during the summer months under disturbed geomagnetic conditions. STORM_foF2MED,IRI performs particularly well in central Europe during the equinoctial months under moderate geomagnetic conditions and during the summer months under very disturbed geomagnetic conditions. The forecasting maps generated by IFERM on the basis of the results provided by the 13 IFELM, show very large areas located at middle-high and high latitudes where the foF2 predictions quite faithfully match the foF2 measurements, and consequently IFERM can be used for generating short-term forecasting maps of foF2 (up to 3 h ahead) over the European area.

Pietrella, M.

2012-02-01

167

Resonant scattering of radio waves in the high-latitude lower ionosphere  

Microsoft Academic Search

A resonant-scattering investigation was carried out in the nighttime high-latitude lower ionosphere during February-March 1978 in the Monchegorsk region. Ionospheric plasma was artificially disturbed by a transmitter continuously emitting linear polarized radio waves at a frequency of 3.3 MHz and an effective power of about 10 MW. Two standing waves were produced in the ionosphere as a result of magnetoionic

V. K. Galaidych; S. I. Maretynenko; V. A. Misiura; L. A. Piven; I. A. Sergienko; V. G. Somov; L. F. Chernogor

1985-01-01

168

Nanostructure characterization of Ni and B layers as artificial pinning centers in multilayered MgB2/Ni and MgB2/B superconducting thin films  

NASA Astrophysics Data System (ADS)

Research on the MgB2/Ni and MgB2/B multilayer films fabricated by an electron beam (EB) evaporation technique have been extensively carried out. The critical current density, Jc of MgB2/Ni and MgB2/B multilayer films in parallel fields has been suggested to be higher than that of monolayer MgB2 film due to introducing the artificial pinning centers of nano-sized Ni and B layers. Nanostructure characterization of the artificial pinning centers in the multilayer films were examined by transmission electron microscopy (TEM) and scanning TEM (STEM-energy dispersive X-ray spectroscopy (STEM-EDS))-EDS to understand the mechanism of flux pinning. The growth of columnar MgB2 grains along the film-thickness direction was recognized in the MgB2/Ni multilayer film, but not in the MgB2/B multilayer film. Nano-sized Ni layers were present as crystalline epitaxial layers which is interpreted that Ni atoms might be incorporated into the MgB2 lattice to form (Mg,Ni)B2 phase. On the other hand, nano-sized B layers were amorphous layers. Crystalline (Mg,Ni)B2 layers worked more effectively than amorphous B-layers, providing higher flux-pinning force that resulted in higher Jc of the MgB2/Ni multilayer film than the MgB2/B multilayer film.

Sosiati, H.; Hata, S.; Doi, T.; Matsumoto, A.; Kitaguchi, H.; Nakashima, H.

2013-05-01

169

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 Tromsø are presented. As a result of the interaction between the high power pump waves and upper hybrid waves in the ionosphere, field-aligned electron density irregularities are artificially excited. Observations of these structures with the CUTLASS coherent HF radars and the EISCAT incoherent UHF radar exhibit

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

2006-01-01

170

Artificial optical emissions in the high-latitude thermosphere induced by powerful radio waves: An observational review  

NASA Astrophysics Data System (ADS)

High-power high-frequency radio waves beamed into the ionosphere with O-mode polarization cause plasma turbulence, which can accelerate electrons. These electrons collide with the F-layer neutrals causing artificial optical emissions identical to the natural aurora. The brightest optical emissions are O( 1D) 630 nm, with a threshold of ˜2 eV, and O( 1S) 557.7 nm, with a threshold of ˜4.2 eV. The optical emissions give direct evidence of electron acceleration by plasma turbulence, the non-Maxwellian electron energy spectrum as well as the morphology of the accelerating region with high spatial resolution. HF pumping of the ionosphere also causes bulk electron temperature enhancements, but these alone are not sufficient to explain the optical emissions. We review the published radar and optical observations of high-latitude pump-induced artificial optical emissions and introduce new data.

Kosch, M. J.; Pedersen, T.; Rietveld, M. T.; Gustavsson, B.; Grach, S. M.; Hagfors, T.

171

Wave-like perturbations in the ionospheric F2-layer observed after the Ms8.1 Samoa earthquake of September 29, 2009  

NASA Astrophysics Data System (ADS)

A study of the critical frequency foF2 variations after the large earthquake (Ms = 8.1) which occurred on 29 September, 2009 in the region of Samoa Islands in the Pacific Ocean is carried out using data of the ionospheric station of Kwajalein. The epicenter of the earthquake was located at about 184 km southwest from Apia (the capital of West Samoa). It was found that wave-like perturbations of foF2 were observed for ˜3 h above the station (located approximately 3560 km northwest from the epicenter). The amplitude of the disturbance was as large as ˜20% of the average magnetic quiet day foF2 values. A comparison of the observed perturbations of foF2 with the ones detected at Stanford ionospheric station after the Alaska earthquake of 28 March 1964 (Ms = 8.4) showed a close similarity of the wave-like perturbations of foF2 in both cases.

Hegai, V. V.; Legen'Ka, A. D.; Kim, V. P.; Georgieva, K.

2011-06-01

172

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

173

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

174

The lipophilicity of artificial and natural sweeteners estimated by reversed-phase thin-layer chromatography and computed by various methods  

Microsoft Academic Search

The chromatographic behavior of some artificial and natural sweeteners was established by reverse phase high performance thin-layer chromatography (RP-HPTLC) on RP-18, RP-18W, RP-8, CN and NH2 stationary phases. The mobile phases were mixtures of acetonitrile–water in different proportions of volume, chosen to create a suitable migration during the chromatographic process. The lipophilicity was described through different chromatographic descriptors such as

Rodica Domnica Briciu; Agata Kot-Wasik; Andrzej Wasik; Jacek Namie?nik; Costel Sârbu

2010-01-01

175

Predicted and measured slant ionospheric electron content  

NASA Astrophysics Data System (ADS)

The total electron content (TEC) is used to indicate the ionisation of the ionosphere. TEC is a quantity with concern for telecommunications, detection systems, track, position, flight control and other systems that use transionospheric signals, because the ionospheric layer affects the mentioned signals. In this work, the slant ionospheric electron content (SIEC) was modelled. The proposed method uses ‘auxiliary’ station that is determined over the slant link on terrestrial surface projection. This allows to obtain TEC between two points. Two models were considered, viz.: (i) the international reference ionosphere (IRI) and (ii) Chapman layer with scale height equal to atomic oxygen scale height (CHO). The validity of the TEC calculated by both ionospheric models was checked with SIEC measurements obtained with geosynchronous satellites signals, for Boulder ATS/6 and Palehua ATS/6 links considering solstices and equinox, in low, moderate and high solar activity periods. In general, in both links, the deviations between predictions and measurements were lower than 30% for about 10 14 h per day. In general, best model predictions are obtained during daylight hours. The results suggest that additional studies for other links and solar activity are required.

Cabrera, Miguel. A.; Ezquer, R. G.; Radicella, S. M.

2005-11-01

176

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

177

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

178

A Snapshot of the Polar Ionosphere.  

National Technical Information Service (NTIS)

This paper presents a picture of the north polar F layer and topside ionosphere obtained primarily from three satellites (Alouette 2, ISIS 1, ISIS 2), that passed over the region within a time interval of ca. 50 min on 25 April 1971, a magnetically quiet ...

J. H. Whitteker L. H. Brace E. J. Maier J. R. Burrows W. H. Dodson

1975-01-01

179

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

180

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

181

A clear view of the multifaceted dayside ionosphere of Mars  

NASA Astrophysics Data System (ADS)

By examining electron density profiles from the Mars Express Radio Science Experiment MaRS, we show that the vertical structure of the dayside ionosphere of Mars is more variable and more complex than previously thought. The top of the ionosphere can be below 250 km (25% occurrence rate) or above 650 km (1%); the topside ionosphere can be well-described by a single scale height (10%) or two/three regions with distinct scale heights (25% or 10%), where those scale heights range between tens and hundreds of kilometers; the main layer of the ionosphere can have a sharply pointed (5%), flat-topped (6%), or wavy (8%) shape, in contrast to its usual Chapman-like shape; a broad increase in electron density is detected at 160-180 km (10%); a narrow increase in electron density is sometimes found in strongly-magnetized regions; and an additional layer is present between the M1 and M2 layers (3%).

Withers, Paul; Fallows, Kathryn; Girazian, Zachary; Matta, Majd; Häusler, Bernd; Hinson, David; Tyler, Len; Morgan, David; Pätzold, Martin; Peter, Kerstin; Tellmann, Silvia; Peralta, Javier; Witasse, Oliver

2012-09-01

182

Power variation analysis of echo signals from ionospheric reflectors  

NASA Astrophysics Data System (ADS)

A series of Power Virtual Height measurements (PVH) of radio echoes reflected from the ionosphere were acquired at a given frequency during the period 3-22 January 2008 with the purpose of studying the slow fading variations through time of the ionospheric channel. To obtain PVH data, an ionospheric vertical sounding system was suitably adapted to work at a single fixed frequency. PVH measurements were recorded between two routine ionospheric vertical soundings, providing a data type that enables evaluation of fading fluctuation through time. The time stability of the ionospheric layers is determined by analyzing the level of the received signal power within a chosen threshold. In this paper the fading behaviour and its characteristics are described, considering only temporal periodicity above 0.5 s. In a further analysis a relation is demonstrated between the recorded fading and the time stability of the signal within a fixed interval of values.

Bianchi, C.; Baskaradas, J. A.; Pietrella, M.; Sciacca, U.; Zuccheretti, E.

2013-03-01

183

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 VHF–UHF communications as well

Smita Dubey; Rashmi Wahi; A. K. Gwal

2006-01-01

184

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

185

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.

186

Ionospheric Anomalies in the Polar Cap and at Mid-Latitudes Revealed by Digital Ionosondes and GPS Receivers  

Microsoft Academic Search

Intensification of the magnetosphere-ionosphere coupling during magnetic storms driven by coronal mass ejections (CMEs) or corotating interaction regions (CIRs) lead to extreme disturbances in density and height of ionospheric plasma layers. Dramatic enhancements of the ionospheric density and plasma content (TEC) appear in mid-latitude ionosphere and extend into the polar cap in the form of continuous tongue of ionization and\\/or

D. Pokhotelov; T. P. Jayachandran; J. W. MacDougall; C. N. Mitchell

2009-01-01

187

Specific Plasma Ionospheric Excitations Modes in the Ionosphere Produced by Space Vehicle Launch and RE Entry and Natural Phenomena  

NASA Astrophysics Data System (ADS)

SPECIFIC PLASMA IONOSPHERIC EXCITATIONS MODES IN THE IONOSPHERE PRODUCED BY SPACE VEHICLE LAUNCH AND RE ENTRY AND NATURAL PHENOMENA We have examined both experimentally and theoretically the formation and excitation of highly well defined specific wave forms of plasma excitation in the D, E, F(1) and F(2) and sometimes G layers of the earth?s ionosphere. In our formal study period from October 1989 until December 1996, we measured 41 distinct events out of a possible 73 events utilizing ground based sensitive T1050 magnetometers. In five cases more than two to three stations were displayed and detected the same ionospheric excitations. Sometimes background noise was high and dominated the signals, but under good measurement conditions signals appeared to be 50 to 70 dbm over the background noise floor. Specific frequencies of the D-layer appeared around 5.2 to 6.52 Hz and E layer excitations were from 10.48 to 12.8 Hz. Sometimes an F double peak appeared around 15 to 17 Hz as excited by space shuttle activity and delta rockets and in several cases, large scale volcanism. A theoretical model has been developed which describes sustained long duration and long range coherent plasma excitation modes which occur when the ionospheric layers are shock excited. Alfven-like velocities of propogation are calculated in these ionospheric layer. Some Schumann resonates were observed from 7 to 8 Hz.

Rauscher, E. A.; van Bise, W. L.

2001-10-01

188

Artificial Particle Precipitation Technique Using HAARP-Generated VLF Waves.  

National Technical Information Service (NTIS)

A new ground-based experimental technique is described, which is designed to optimize artificial precipitation of magnetospheric electrons at high latitudes, due to man-made VLF waves. High-latitude ionospheric modification facilities may be used to modul...

D. Gallagher J. Bortnik M. J. Kosch R. Esposito T. Pedersen

2006-01-01

189

Gyroharmonic features of the hf-induced ionospheric irregularities  

NASA Astrophysics Data System (ADS)

Gyroharmonic features of the different-scale artificial plasma-density irregularities excited by HF modification of the ionospheric F2 region under conditions where the frequency of the O-mode pump wave is close to the fourth gyroharmonic frequency of electrons in the pump wave—plasma interaction region are considered.

Frolov, V. L.; Bolotin, I. A.; Komrakov, G. P.; Vertogradov, G. G.; Vertogradov, V. G.; Vertogradova, E. G.; Akchurin, A. D.; Bochkarev, V. V.; Dresher, A. M.; Zykov, E. Yu.; Katypov, R. R.; Petrova, I. R.; Yusupov, K. M.; Kunitsyn, V. E.; Padokhin, A. M.; Kurbatov, G. A.

2012-11-01

190

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

191

Studying characteristics of the large-scale ionospheric irregularities induced by high-power HF radio emission with GPS diagnosis  

NASA Astrophysics Data System (ADS)

We present the results of experimental studies of artificial large-scale irregularities of the ionospheric electron number density with dual-frequency GPS diagnosis. The total electron content was analyzed in the GPS signal trajectory when the satellites passed over the heated region. Spectral composition of the observed variations was determined by wavelet analysis. Characteristic scales of artificial irregularities of the electron number density in the F layer are estimated. It is experimentally proved that the irregularities remain for at least 15-20 min after the transmitter is switched off. A more confident excitation and increased intensity of the irregularities were also confirmed when the beam was inclined south of the magnetic-zenith direction.

Ryabov, A. V.; Grach, S. M.; Shindin, A. V.; S. Kotik, D.

2011-12-01

192

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

193

Investigations on structural and multiferroic properties of artificially engineered lead zirconate titanate-cobalt iron oxide layered nanostructures  

NASA Astrophysics Data System (ADS)

Mutiferroics are a novel class of next generation multifunctional materials, which display simultaneous magnetic, electric, and ferroelastic ordering, have drawn increasing interest due to their multi-functionality for a variety of device applications. Since, very rare single phase materials exist in nature this kind of properties, an intensive research activity is being pursued towards the development of new engineered materials with strong magneto-electric (ME) coupling. In the present investigation, we have fabricated polycrystalline and highly oriented PbZr0.53,Ti0.47O3--CoFe 2O4 (PZT/CFO) artificially multilayers (MLs) engineered nanostructures thin films which were grown on Pt/TiO2/SiO2/Si and La 0.5Sr0.5CoO3 (LSCO) coated (001) MgO substrates respectively, using the pulsed laser deposition technique. The effect of various PZT/CFO sandwich configurations having 3, 5, and 9 layers, while maintaining similar total PZT and CFO thickness, has been systematically investigated. The first part of this thesis is devoted to the analysis of structural and microstructure properties of the PZT/CFO MLs. X-ray diffraction (XRD) and micro Raman analysis revealed that PZT and CFO were in the perovskite and spinel phases respectively in the all layered nanostructure, without any intermediate phase. The TEM and STEM line scan of the ML thin films showed that the layered structure was maintained with little inter-diffusion near the interfaces at nano-metric scale without any impurity phase, however better interface was observed in highly oriented films. Second part of this dissertation was dedicated to study of the dielectric, impedance, modulus, and conductivity spectroscopies. These measurements were carried out over a wide range of temperatures (100 K to 600 K) and frequencies (100 Hz to 1 MHz) to investigate the grain and grain boundary effects on electrical properties of MLs. The temperature dependent dielectric and loss tangent illustrated step-like behavior and relaxation peaks near the step-up characteristic respectively. The Cole-Cole plots indicate that the most of the dielectric response came from the bulk (grains) MLs below 300 K, whereas grain boundaries and electrode-MLs effects prominent at elevated temperature. The dielectric loss relaxation peaks shifted to higher frequency side with increase in temperature, finally above 300 K, it went out experimental frequency window. Our Cole-Cole fitting of dielectric loss spectra indicated marked deviation from the ideal Debye type of relaxation which is more prominent at elevated temperature. Master modulus spectra support the observation from impedance spectra, it also indicate that the difference between C g and Cgb are higher compared to polycrystalline MLs indicating less effects of grain boundary in highly oriented MLs. We have explained these electrical properties of MLs by Maxwell-Wagner type contributions arising from the interfacial charge at the interface of the MLs structure. Three different types of frequency dependent conduction process were observed at elevated temperature (>300 K), which well fitted with the double power law, sigma(o) = sigma(0) + A 1on1 + A 2on2, it indicates conduction at: Low frequency (<1 kHz) may be due to long range ordering (frequency independent), mid frequency (<10 kHz) may be due to short range hopping, and high frequency (<1 MHz) due to the localized relaxation hopping mechanism. The last part of the thesis is devoted to the study of the multiferroic and magnetoelectric properties of the ML thin films. Both polycrystalline and highly oriented films showed well saturated ferroelectric and ferromagnetic hysteresis loops at room temperature. Temperature dependence of ferroelectric properties showed that polarization slowly decreases from 300 K to 200 K, with complete collapse of polarization at ˜ 100 K, but there was complete recovery of the polarization during heating, which was repeatable over many different experiments. At the same time, in the same temperature interval the remanent magnetization of the MLs showed slo

Ortega Achury, Nora Patricia

194

Current status of closed-form Green's functions in layered media composed of natural and artificial materials  

Microsoft Academic Search

This paper provides an overview of the development of closed-form Green's functions in planar multilayered structures, with an emphasis given to the discrete complex image method (DCIM). In addition to the review of the materials in the literature, the latest developments on DCIM and its applications to artificial materials are also discussed.

M. I. Aksun; Aytac Alparslan; K. A. Michalski

2009-01-01

195

Two-frequency method of the ionospheric diagnostics by API technique  

NASA Astrophysics Data System (ADS)

We present a new way of the investigation of the electron density in the ionospheric E-region, turbulent events and sporadic E-layers using the artificial periodic irregularities (API). API are created in the field of the power standing wave formed by the interference of the incident wave and reflected one by the ionosphere. The spatial period of the irregular periodic structure is equal to the standing wavelength ? or the one-half of the power wavelength ?/2. Physical process dominating on the E-region heights and specifying API decay (relaxation) after the pumping turning off is the ambipolar diffusion process. The API method of the ionosphere diagnostics is connected with an observation of Bragg scattered signals (probe waves) from the artificial periodic structure of the ionospheric plasma on the API relaxation stage (V.V. Belikovich, E.A. Benediktov, N.V. Bakhmet'eva, A.V. Tolmacheva, Ionospheric Research by Means of Artificial Periodic Irregularities, Katlenburg-Lindau, Germany, Copernicus GmbH, 2002, pp. 1-160). The new two-frequency method is based upon the scattering of probe waves from API formed by the power radiation at two frequencies and having therefore different spatial periods. In this case the API relaxation time depends on both ambipolar diffusion rate D and spatial scale of the irregular structure ?. Measuring the ratio of the relaxation time of scattered signals on two frequencies one can determine the height profile of the electron density N(h) and its fine structure. Mathematical simulation made for two frequencies 4.7 and 5.6 MHz shown that electron density in the range of values (2 · 104 -1.8 · 105 ) cm-3 can be defined. The two-frequency API technique has been applied to N(h)-profile measurement in 2006, 2007 using the SURA heating facility (56.13 N, 46.15 E). The API formation and their sounding by probe radio waves of X-polarization were carried out by rotation at frequency of 4.7 MHz and 5.6 MHz. The effective radiated power was about 70 MW at the first frequency and 15 MW at the second one. The session of the measurement of the API relaxation time at each frequency was continued 15 s. During one minute two session of the pumping at each frequency were carried out. During the first 3 s of the session ionosphere was pumped by X-polarized powerful radio wave and API were formed. The pumping period was followed by 12-s pause. Probing pulses with 30-µc duration and a 50 Hz repetition rate were radiated at the same frequency. The amplitude and phase of the scattered signals from the virtual height range 50-750 km were recorded. N(h)-profiles in a height range 95-115 km were obtained. It has appeared the method to consider the fine structure of the profile, to determine even the electron density of sporadic E-layers, which are not registered standard ionosonde. The error of the N(z)-profile determination by API two-frequency method should not be exceeded 10%. The work has been supported by Russian Foundation for Basic Research Grants No. 05-05-64304 and No 05-05-64111.

Bakhmetieva, Nataliya V.; Belikovich, Vitold V.; Tolmacheva, Ariadna V.

196

The field of a radio signal in the case of the simultaneous existence of two sporadic-E layers in the ionosphere  

NASA Astrophysics Data System (ADS)

The paper presents an analysis of signal amplitude recorded at two frequencies (12 and 20 MHz) on a Santiago de Cuba-Havana radio channel during the simultaneous appearance of several sporadic-E layers on oblique-sounding ionograms obtained at the median point of the channel. It is shown that the dependence of the amplitude of the 12-MHz signal on the altitude of the reflecting sporadic-E layer is mainly determined by absorption variations. For the 20-MHz signal, the presence of a lower sporadic-E layer with high screening frequencies can lead to a decrease in signal amplitude in the case of reflection from the upper sporadic-E layer.

Kerblai, T. S.; Nosova, G. N.; Palacio, L.; Melendez, B.

1988-02-01

197

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

198

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

199

Global satellite monitoring of the atmosphere and ionosphere  

Microsoft Academic Search

The possibilities of monitoring the atmosphere and ionosphere along satellite-to-satellite radio occultation paths are considered.\\u000a A relation between the amplitude and the phase of the signal sounding the medium is substantiated. Owing to this relation,\\u000a it is possible to separate the influence of layered and wave structures from the influence of turbulence in the atmosphere\\u000a and ionosphere. The possibility to

A. G. Pavelyev; S. S. Matyugov; O. I. Yakovlev

2008-01-01

200

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

201

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

202

Plasma irregularities associated with artificially created dusty plasmas during active space experiments  

NASA Astrophysics Data System (ADS)

It is well known that natural dust layers in the earth's mesosphere produce radar echoes. For example, one class of these radar echoes are referred to a Polar Mesopheric Summer Echoes PMSE and they are a well investigated phenomena and are a direct consequence of the sub-visible charged dust that exists at altitudes above visible noctilucent cloud NLC regions. The charging of electrons in the background plasma onto an irregular dust background results in electron irregularities that scatter the radar signals. Recent and upcoming active space ex-periments artificially create dust layers in the earth's ionosphere in a controlled manner to investigate the creation, evolution, dynamics, and charging of dust layers in the near earth space environment. A critically important process to be investigated during these experiments is the generation of plasma irregularities. Currently plasma irregularity generation in artificially created dust clouds in the space environment is a much less well understood and investigated issue even though it may have important consequences for the understanding of irregularities associated with natural dust layers. This presentation will address some of the physical pro-cesses expected to be important to generation of plasma irregularities during the early time phase after creation of an artificial dust cloud in the earth's ionosphere during an active release of dust in space. First, parameter regimes and their relevance to plasma irregularity generation during recent and upcoming space experiments will be discussed. Several possible physical mechanisms for generation of plasma irregularities will then be discussed. These include in-homogeneities in the boundary layer of the cloud as well as streaming of the dust particles relative to the background plasma. Next, computational plasma models will be described that may be used for investigating early time evolution after expansion of an artificial dust cloud in the ionosphere. These models will then be used to investigate the electrodynamics and possible plasma irregularity generation mechanisms after creation of an artificial dust cloud. Finally, some predictions will be made on the most important relevant processes for upcoming space experiments that may lead to radar signatures.

Scales, Wayne; Fu, Haiyang; Bordikar, Maitrayee

203

F3 layer during penetration electric field  

Microsoft Academic Search

The occurrence of an additional layer, called F3 layer, in the equatorial ionosphere at American, Indian, and Australian longitudes during the super double geomagnetic storm of 7–11 November 2004 is presented using observations and modeling. The observations show the occurrence, reoccurrence, and quick ascent to the topside ionosphere of unusually strong F3 layer in Australian longitude during the first super

N. Balan; S. V. Thampi; K. Lynn; Y. Otsuka; H. Alleyne; S. Watanabe; M. A. Abdu; B. G. Fejer

2008-01-01

204

On the estimation of quasi-instantaneous frequency modulation of HF signals propagated through the ionosphere  

NASA Astrophysics Data System (ADS)

Three methods for estimating the ionospheric frequency modulation of HF skywave signals are compared. In (1), the instantaneous frequency is obtained by taking the time derivative of the phase of the signal; the two other methods involve autoregressive modeling using (2) the Burg algorithm of Ulrich and Bishop (1975) or (3) the Marple (1980) algorithm. High-quality signals propagated via a sporadic E-layer and backscattered by the sea surface are digitally perturbed with a known frequency modulation, and the efficiencies of the methods in recovering the perturbation is compared. It is found that, for a number of statistical averages greater than four, the standard deviations of the difference between the estimated and the theoretical perturbation are of the same order of magnitude for the three methods, but that (3) yields a less biased estimate. The wave height obtained after removing the artificial modulation is recovered with an accuracy of about 10 percent.

Gauthier, F.; Bourdillon, A.; Parent, J.

1990-03-01

205

A newly developed three-layer agarose microcapsule for a promising biohybrid artificial pancreas: Rat to mouse xenotransplantation  

Microsoft Academic Search

We examined the effectiveness of an improved version of a three-layer agarose microcapsule in islet xenotransplantation. The microcapsule is composed of a mixture of 5% agarose and 5% polystyrene sulfonic acid. The other two outer layers are polybrene and carboxymethyl cellulose. The agarose\\/polystyrene sulfonic acid membrane is for the purpose of immunoisolation, suppression of complement activity and reinforcement of the

T. Tun; K. Inoue; H. Hayashi; T. Aung; Y.-J. Gu; R. Doi; H. Kaji; Y. Echigo; W.-J. Wang; H. Setoyama; M. Imamura; S. Maetani; N. Morikawa; H. Iwata; Y. Ikada

1996-01-01

206

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

207

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

208

Simultaneous ionospheric variability on Earth and Mars  

NASA Astrophysics Data System (ADS)

Ionospheric physics deals with the basic structure and variability of plasma within the upper atmospheres of the Earth and planets. Comparative studies foster both exploration and synthesis within diverse settings. In this paper we examine observations of the ionospheric profiles on Mars obtained on 9-27 March 1999 by the radio science experiment onboard the Mars Global Surveyor satellite, and compare their day-to-day variability with same-day observations on Earth. Using photochemical-equilibrium arguments applicable to the peak electron density layer on Mars and the E-layer on Earth, we find basic agreement in scaling laws between the planets, and in the details of correlations with simultaneous solar flux variations during a period of pronounced solar activity. We ascribe the residual variabilities (larger on Mars than Earth) to both observational uncertainties and to nonsolar mechanisms in need of further study on both planets.

Mendillo, Michael; Smith, Steven; Wroten, Joei; Rishbeth, Henry; Hinson, David

2003-12-01

209

New results of ionospheric and atmospheric researches by the API technique  

NASA Astrophysics Data System (ADS)

Artificial periodic irregularities API are created in the ionosphere illuminated by a high power HF radio wave A standing radio wave is produced as a result of the interference of the incident wave with the reflected wave from the ionosphere The API diagnostics is based upon observation of Bragg backscattering of pulsed probe radio waves from the artificial periodic structure The experiments were carried out using the Sura heating facility 56 1 N 46 1 E Studies throughout sunset-to-sunrise hours were showing the sunset-to-sunrise asymmetry of the height-temporal dependencies of the amplitude and relaxation time of the API scattered signals The phenomena are caused by the D-region features The asymmetry may be well described by a model involving a single-ion species O 2 - which allows found variations in the number density of the atomic and excited oxygen molecules and shows a significant increase in the atomic-oxygen density during sunrise The two-layer stratification of the D-region was found in the observations of April 2004 2005 The electron density shows a minimum at a height h quad approx 75 km Similar phenomena were sometimes observed in the sunset-to-sunrise experiments Investigations of sporadic E-layers and their irregular structure have continued In frame of these studies the molecular masses of the predominant metallic ions and the total ion densities including both metallic and atmospheric NO and O 2 ions were determined Also we suggest a new way of

Belikovich, V. V.; Bakhmetieva, N. V.; Rietveld, M.; Tolmacheva, A. V.

210

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

211

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

212

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

213

Detection of ionospheric Alfvén resonator signatures in the equatorial ionosphere  

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

214

Layer-by-layer hyaluronic acid-chitosan coating promoted new collagen ingrowth into a poly(ethylene terephthalate) artificial ligament in a rabbit medical collateral ligament (MCL) reconstruction model.  

PubMed

The ideal artificial ligament graft should have favorable biocompatibility to facilitate cell adhesion, proliferation, and collagen regeneration. In this present study, surface modification was performed on a poly(ethylene terephthalate) (PET) artificial ligament graft by layer-by-layer (LBL) self-assembly coating of hyaluronic acid (HA) and chitosan (CS). The surface characterization of the ligament was examined using scanning electron microscopy, atomic force microscopy, and energy-dispersive X-ray spectroscopy. The results of in vitro culturing of human foreskin fibroblast cells supported the hypothesis that the LBL coating of CS-HA could promote the cell proliferation and adhesion on the sheets. A rabbit medical collateral ligament reconstruction model was used to evaluate the effect of this LBL coating in vivo. The final results proved that this LBL coating could significantly promote and enhance new collagen formation among the graft fibers. On the basis of these results, we conclude that such CS-HA assembly coating could enhance PET graft biocompatibility in vitro and in vivo, and a CS-HA-coated PET graft has considerable potential as a desirable substitute for ligament reconstruction. PMID:23565685

Li, Hong; Jiang, Jia; Ge, Yunsheng; Xu, Jialing; Zhang, Pengyun; Zhong, Wei; Chen, Shiyi

2012-08-13

215

Structure of the Dayside Martian Upper Ionosphere from MEX MARSIS Topside Soundings  

NASA Astrophysics Data System (ADS)

The MARSIS Active Ionospheric Sounder on board the Mars Express spacecraft takes radar soundings of the Martian topside ionosphere. The ionospheric trace typically has a hook or cusp shape near the maximum plasma frequency in the ionosphere, indicating that the sounding wave is traveling through a region where its frequency is just below the ionospheric maximum. This kind of structure can also occur at frequencies well below the maximum, where it is sometimes reduced to a discountinuous change in the slope of the ionospheric trace. Cusp-like features at sounding frequencies below the ionospheric maximum have been interpreted as indicative of ionospheric layers above the main layer, variously attributed to waves, instabilities, or the transition from a photochemical- to a transport-dominated ionosphere; previous work on the generation of this phenomenon has been inconclusive. In this study, we continue this work by studying the correlation of the frequency of the slope discontinuity to the maximum ionospheric plasma frequency. We use standard inversion techniques to study the altitude of the discontinuity as a function of the solar zenith angle. Finally, for a few long-lived cases, we follow the evolution of the cusp-like or discontinuous feature. These results will tell us whether this layer is caused by processes in photochemical equilibrium, whether the altitude and density of the high-altitude structure are correlated with properties of the ionosphere at lower altitudes, and how these structures evolve in density and altitude, thus giving us definitive information about the morphology and dynamics of the Martian upper ionosphere.

Morgan, D. D.; Gurnett, D. A.; Modolo, R.; Nielsen, E.; Nemec, F.; Duru, F.

2011-12-01

216

Natural electromagnetic ULF noise due to fluctuations of ionospheric currents  

NASA Astrophysics Data System (ADS)

An origin of natural electromagnetic noise observed on the ground surface in the frequency range 10-4-10-2 Hz was examined. Following a recent paper by Surkov and Hayakawa (2007), a flicker noise or 1/f noise, provided by random currents, is treated as a possible source of the ULF electromagnetic noise. In contrast to the cited paper, MHD wave incident on the ionosphere and neutral gas flow in the altitude range of conducting E layer of the ionosphere are considered to be a candidate mechanism for random current fluctuations, which in turn produce random electromagnetic fluctuations in the atmosphere. The main emphasis is on the flicker noise provided by the wind-driven ionospheric currents, which is assumed to be steady, uniform, and isotropic random fields inside the ionosphere. A correlation radius of random ionospheric fields is supposed to be controlled by neutral gas transfer and by acoustic/gravity wave propagation inside the E layer. A correlation matrix and power spectra of the random electromagnetic fields on the ground surface were calculated. The predicted spectral index of the power spectrum of the ULF magnetic noise was found to be 3, which is consistent with ground-based observations. The experimental data were demonstrated to be sandwiched between two theoretical lines, which correspond to daytime and nighttime ionospheric parameters.

Surkov, V. V.; Hayakawa, M.

2008-11-01

217

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

218

Ionospheric precursors for the crustal earthquakes in Italy  

NASA Astrophysics Data System (ADS)

Crustal earthquakes with moderate magnitude M=5.0-6.0 observed in Italy for the period 1995-2002 were used to check if the earlier obtained relationships for middle-term ionospheric precursors are valid for these type of earthquakes. The ionospheric precursors are based on the observed variations of the sporadic E-layer parameters (h'Es, fbEs, foEs) and foF2 at the ionospheric station Rome. Empirical dependencies for the seismo-ionospheric disturbances relating the earthquake magnitude and the epicentric distance are obtained and they have been shown to be similar to those obtained earlier in other seismic regions of the world.

Perrone, L.; Zolesi, B.; Korsunova, L.

2009-04-01

219

Unusual topside ionospheric density response to the November 2003 superstorm  

NASA Astrophysics Data System (ADS)

We use observations from a variety of different ground- and space-based instruments, including ionosonde, ground- and space-based Global Positioning System (GPS) receivers, magnetometers, and solar wind data from the Advanced Composition Explorer (ACE), to examine the response of the ionospheric F2-layer height during the November 2003 superstorm. We found that the topside ionosphere responded unusually to the 20 November 2003 severe storm compared to behavior observed in a number of previous storms. While ground-based GPS receivers observed a large enhancement in dayside TEC, the low-Earth orbiting (˜400 km) CHAMP satellite did not show any sign of dayside TEC enhancement. The real-time vertical density profiles, constructed from ground-based GPS TEC using a tomographic reconstruction technique, clearly revealed that the ionospheric F2-layer peak height had been depressed down to lower altitudes. Ionospheric F-layer peak height (hmF2) from the nearby ionosonde stations over Europe also showed that the dayside F2-layer peak height was below 350 km, which is below the orbiting height of CHAMP. The vertical E × B drift (estimated from ground-based magnetometer equatorial electrojet delta H) showed strong dayside downward drifts, which may be due to the ionospheric disturbance dynamo electric field produced by the large amount of energy dissipation into high-latitude regions. This storm demonstrates that data from LEO satellites varies widely among different superstorms.

Yizengaw, E.; Moldwin, M. B.; Komjathy, A.; Mannucci, A. J.

2006-02-01

220

Unusual topside ionospheric density response to the November 2003 superstorm  

NASA Astrophysics Data System (ADS)

We use observations from a variety of different ground and space-based instruments, including ionosonde, ground and space-based Global Positioning System (GPS) receivers, magnetometers, and the solar wind data from the Advanced Composition Explorer (ACE), to examine the response of the ionospheric F2-layer height during the November 2003 superstorm. We found that the topside ionosphere responded unusually to the November 20, 2003 severe storm. While ground-based GPS receivers observed a large enhancement in dayside TEC, the Low-Earth orbiting (~400 km) CHAMP satellite did not show any sign of dayside TEC enhancement. The real-time vertical density profiles, constructed from ground based GPS TEC using a tomographic reconstruction technique, clearly revealed that the ionospheric F2-layer peak height had been depressed down to lower altitudes. Ionospheric F-layer peak height (hmF2) from the nearby ionosonde stations over Europe also showed that the dayside F2-layer peak height was below 350 km, which is below the orbiting height of CHAMP, on 20 November 2003. The vertical E x B drift (estimated from ground-based magnetometer equatorial electrojet delta H) did show dayside strong downward drifts, which may be attributed to the ionospheric disturbance dynamo electric field produced by the large amount of energy dissipation into high latitude regions. This storm demonstrates that care has to be taken in interpreting data from LEO satellites.

Yizengaw, E.; Moldwin, M. B.; Mannucci, A. J.; Komjathy, A.

2005-12-01

221

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

222

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

223

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

224

The influence of high speed plasma streams on the ionospheric plasma  

Microsoft Academic Search

As shown by statistical investigations, high speed plasma streams (HSPS) in the solar wind cause direct ionospheric effects in the D- and Es-layers at auroral and subauroral latitudes due to increasing precipitation of high energetic particles as well as indirect effects in the F2-region at high, middle and equatorial latitudes caused by auroral heating processes. The ionospheric effects increase with

J. Bremer

1996-01-01

225

GPS tomography for analysing storm density anomalies in mid-latitude ionosphere  

Microsoft Academic Search

During magnetic storms dramatic changes in the solar wind pressure combined with appropriate orientation of the interplanetary magnetic field lead to the intensification of magnetosphereionosphere coupling which causes sudden inputs of the solar wind energy into the ionosphere. This results in extreme disturbances of the height and density of ionospheric layers during the main phase of magnetic storms. The tomographic

Dimitry Pokhotelov; Cathryn Mitchell; Paul Spencer; Nathan Smith; Chris Budd

2008-01-01

226

Irregularities Associated with Artificially Created Dusty Plasmas in the near Earth Space Environment  

NASA Astrophysics Data System (ADS)

A natural dust layer formed by tons of meteoric dust spans the altitude range between 80 and 100 kilometers of the earth’s upper mesosphere and lower thermosphere which forms Noctilucent Clouds NLCs. These dust layers are charged due to collection of electrons and ions from the earth’s ionosphere. Polar Mesospheric Summer Echoes are radar echoes which result from scattering from the irregularities in the electron density above the NLC altitude. An alternate approach to understanding natural dust layers is to perform active space experiments in which a dust cloud is artificially created in a controlled manner in the upper atmosphere. The goal of Charged Aerosol Release Experiment (CARE) is to investigate similarity in plasma irregularity associated with natural and artificial dust layers. This presentation will address some of the physical processes expected to be important during the early time phase after creation of an artificial dust cloud in the earth’s ionosphere. Of major importance will be the production of plasma irregularities which may lead to radar echoes and the possibility of their relationship to PMSEs observed from natural dusty space plasmas. The objective is to investigate the production of electron irregularities due to growth of plasma instabilities driven by inhomogeneities in the boundary between the background plasma and the expanding charged dust layer. First, a two dimensional plasma simulation model will be described that may be used for examining early time evolution after expansion of an artificial dust cloud across the magnetic field in the ionosphere. The model considers a three species system with fluid electrons and ions and Particle-In-Cell PIC charged dust grains in which the dust charge on the grains varies in time according to the standard charging model. The electrons are magnetized and the algorithm incorporates the parallel electron dynamics while the ions are assumed to be unmagnetized. Simulations runs were made to study irregularities with different dust densities, radii, and expansion speed and inclination angle of magnetic field with respect to dust expansion direction. The mechanism is shown to effectively generate irregularities for early times after localized release dust for the parameter regimes of upcoming space experiments.

Bordikar, M. R.; Scales, W.; Mahmoudian, A.; Fu, H.

2009-12-01

227

Collocation method using artificial viscosity for solving stiff singularly perturbed turning point problem having twin boundary layers  

Microsoft Academic Search

A numerical scheme is proposed to solve singularly perturbed two-point boundary value problems with a turning point exhibiting twin boundary layers. The scheme comprises a B-spline collocation method on a uniform mesh, which leads to a tridiagonal linear system. Asymptotic bounds are established for the derivative of the analytical solution of a turning point problem. The analysis is done on

Mohan K. Kadalbajoo; Puneet Arora; Vikas Gupta

2011-01-01

228

Modeling deflection basin using artificial neural networks with cross-validation technique in backcalculating flexible pavement layer moduli  

Microsoft Academic Search

Through the new technological developments, for highway maintenance engineering the structural capacity of pavement is to be determined using non-destructive techniques. Up to now various methodologies have been applied based on the surface deflection bowl obtained under either a known moving wheel load or devices such as falling weight deflectometer. Backcalculating pavement layer moduli are well-accepted procedures in the evaluation

Mehmet Saltan

2008-01-01

229

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

230

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

231

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

232

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

233

Assesment of SIRGAS Ionospheric Maps errors based on a numerical simulation  

NASA Astrophysics Data System (ADS)

SIRGAS (Sistema de Referencia Geocéntrico para las Américas) is responsible of the International Terrestrial Reference Frame densification in Latin America and the Caribbean, which is realized and maintained by means of a continuously operational GNSS network with more than 200 receivers. Besides, SIRGAS uses this network for computing regional maps of the vertical Total Electron Content (TEC), which are released to the community through the SIRGAS web page (www.sirgas.org). As other similar products (e.g.: Global Ionospheric Maps (GIM) computed by the International GNSS Service), SIRGAS Ionospheric Maps (SIM) are based on a thin layer ionospheric model, in which the whole ionosphere is represented by one spherical layer of infinitesimal thickness and equivalent vertical TEC, located at a fixed height above the Earth's surface (tipycally between 350 and 450 km). This contribution aims to characterize the errors introduced in the thin layer ionospheric model by the use of a fixed and, sometimes, inappropiated ionospheric layer height. Particular attention is payed to the propagation of these errors to the estimation of the vertical TEC and to the estimation of the GNSS satellites and receivers Inter-Frequency Biases (IFB). The work relies upon a numerical simulation performed with an empirical model of the Earth's ionosphere, which allows creating a realistic but controlled ionospheric scenario, and then evaluates the errors that are produced when the thin layer model is used to reproduce those ionospheric scenarios. The error assessment is performed for the Central and the northern part of the South American continents, where largest errors are expected because the combined actions of the Appleton Anomaly of the ionosphere and the South-Atlantic anomaly of the geomagnetic field.

Brunini, Claudio; Emilio, Camilion; Francisco, Azpilicueta

2010-05-01

234

Ionospheric modification by high-power radio waves  

SciTech Connect

Powerful, high-frequency radio waves have been used to temporarily modify the ionosphere. Thermal and parametric interactions have led to a diverse range of observed phenomena, including generation of density striations and artificial spread-F, enhancements of electron plasma waves, production of extrathermal electron fluxes and enhanced airglow, modification of the D-region temperature and densities, wideband signal attenuation, and self-focusing and scattering of the electromagnetic waves. The physics of ionospheric modification by high-power radio waves is reviewed in the context of our current theoretical understanding; disturbance generation mechanisms are qualitatively described. In addition, results of recent experiments are summarized in which ionospheric irregularities are generated and their evolution and decay processes investigated in detail. The effects and potential controlled applications of these HF ionospheric modifications for various RF systems studies are discussed. The C/sup 3/I scientific community provides an important motivation for these ionospheric modification studies; their increased interaction and active participation in experimental design and interpretation are encouraged.

Duncan, L.M.

1981-04-01

235

Day-side ionospheric conductivities at Mars  

NASA Astrophysics Data System (ADS)

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

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

2010-08-01

236

The permeability of SPION over an artificial three-layer membrane is enhanced by external magnetic field  

PubMed Central

Background Sensorineural hearing loss, a subset of all clinical hearing loss, may be correctable through the use of gene therapy. We are testing a delivery system of therapeutics through a 3 cell-layer round window membrane model (RWM model) that may provide an entry of drugs or genes to the inner ear. We designed an in vitro RWM model similar to the RWM (will be referred to throughout the paper as RWM model) to determine the feasibility of using superparamagnetic iron oxide (Fe3O4) nanoparticles (SPION) for targeted delivery of therapeutics to the inner ear. The RWM model is a 3 cell-layer model with epithelial cells cultured on both sides of a small intestinal submucosal (SIS) matrix and fibroblasts seeded in between. Dextran encapsulated nanoparticle clusters 130 nm in diameter were pulled through the RWM model using permanent magnets with flux density 0.410 Tesla at the pole face. The SIS membranes were harvested at day 7 and then fixed in 4% paraformaldehyde. Transmission electron microscopy and fluorescence spectrophotometry were used to verify transepithelial transport of the SPION across the cell-culture model. Histological sections were examined for evidence of SPION toxicity, as well to generate a timeline of the position of the SPION at different times. SPION also were added to cells in culture to assess in vitro toxicity. Results Transepithelial electrical resistance measurements confirmed epithelial confluence, as SPION crossed a membrane consisting of three co-cultured layers of cells, under the influence of a magnetic field. Micrographs showed SPION distributed throughout the membrane model, in between cell layers, and sometimes on the surface of cells. TEM verified that the SPION were pulled through the membrane into the culture well below. Fluorescence spectrophotometry quantified the number of SPION that went through the SIS membrane. SPION showed no toxicity to cells in culture. Conclusion A three-cell layer model of the human round window membrane has been constructed. SPION have been magnetically transported through this model, allowing quantitative evaluation of prospective targeted drug or gene delivery through the RWM. Putative in vivo carrier superparamagnetic nanoparticles may be evaluated using this model.

Mondalek, Fadee G; Zhang, Yuan Yuan; Kropp, Bradley; Kopke, Richard D; Ge, Xianxi; Jackson, Ronald L; Dormer, Kenneth J

2006-01-01

237

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

238

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

239

Ionospheric threats to the integrity of airborne GPS users  

NASA Astrophysics Data System (ADS)

The Global Positioning System (GPS) has both revolutionized and entwined the worlds of aviation and atmospheric science. As the largest and most unpredictable source of GPS positioning error, the ionospheric layer of the atmosphere, if left unchecked, can endanger the safety, or "integrity," of the single frequency airborne user. An augmentation system is a differential-GPS-based navigation system that provides integrity through independent ionospheric monitoring by reference stations. However, the monitor stations are not in general colocated with the user's GPS receiver. The augmentation system must protect users from possible ionosphere density variations occurring between its measurements and the user's. This study analyzes observations from ionospherically active periods to identify what types of ionospheric disturbances may cause threats to user safety if left unmitigated. This work identifies when such disturbances may occur using a geomagnetic measure of activity and then considers two disturbances as case studies. The first case study indicates the need for a non-trivial threat model for the Federal Aviation Administration's Local Area Augmentation System (LAAS) that was not known prior to the work. The second case study uses ground- and space-based data to model an ionospheric disturbance of interest to the Federal Aviation Administration's Wide Area Augmentation System (WAAS). This work is a step in the justification for, and possible future refinement of, one of the WAAS integrity algorithms. For both WAAS and LAAS, integrity threats are basically caused by events that may be occurring but are unobservable. Prior to the data available in this solar cycle, events of such magnitude were not known to be possible. This work serves as evidence that the ionospheric threat models developed for WARS and LAAS are warranted and that they are sufficiently conservative to maintain user integrity even under extreme ionospheric behavior.

Datta-Barua, Seebany

240

layer  

Microsoft Academic Search

This paper analyzes the propagation of a cohesive crack through a reinforcement layer and gives a solution that can be used for any specimen and loading condition. Here it faces the case of a reinforced prismatic beam loaded at three points. Reinforcement is represented by means of a free-slip bar bridging the cracked section, anchored at both sides of the

Gonzalo Ruiz

241

Three-dimensional Reconstruction of Ionosphere/Plasmasphere using GNSS measurements  

NASA Astrophysics Data System (ADS)

The dispersion of the ionosphere pertaining to the microwave signals allows gaining information about this medium. Among different systems observing the ionosphere, space geodetic techniques have turned into a promising tool for monitoring and modeling the ionospheric parameters in terms of Total Electron Content (TEC) or electron density along the ray path. The relevant input data for modeling ionospheric parameters is the ionospheric observable (L4) and is formed from the phase-smoothed code pseudorange obtained from dual-frequency Global Navigation Satellite Systems measurements. The L4 is related to the ionospheric electron density using adequate profile function. Within this study, we apply a combination of the multi-layer Chapman profile function for the bottom-side and topside ionosphere, and a separate profile function for the plasmasphere. As a first step of this study, we assume the plasmaspheric contribution to be known, and concentrate only on the ionospheric part. To model the ionospheric electron density in globe, the parameters of electron density, i.e. the maximum electron density, and its corresponding height are modeled using two sets of spherical harmonics expansion. The coefficients of two sets of spherical harmonics expansions are obtained through recursive parameter estimation technique applying appropriate constraints.

Mahdi Alizadeh, M.; Schuh, Harald; Schmidt, Michael

2013-04-01

242

Ionospheric holography. I - The holographic interpretation of ionospheric data. II - The analysis of a set of ionospheric holograms  

NASA Astrophysics Data System (ADS)

Various techniques for ionospheric holography are considered, and it is shown that the recording of both amplitude and phase of the downcoming signal is technically possible and is preferable to the recording of amplitude or intensity only. It is also shown that the 40 MHz radio transmissions from satellites may be simply recorded in the form of one-dimensional Gabor holograms; in addition, a bench study on a test object has revealed that useful reconstructions may be obtained from records showing weak to moderate scintillation. An experiment is described in which a received satellite signal was recorded on photographic film in the form of a hologram, which was analyzed using a laser and an optical bench. The relation of the optical focal length to the height of the scatterer is derived, and it is shown that there are scatterers at all heights in the ionosphere, with a concentration in the E region. It is also found that the model of the ionosphere as a relatively thin layer of irregularly spaced scatterers is a great oversimplification.

Rogers, G. L.; Ireland, W.

1980-04-01

243

Radio Sounding of the Martian and Venusian Ionospheres  

NASA Astrophysics Data System (ADS)

The Mars Express Radio Science Experiment MaRS and the radio science experiment Vera on Venus Express sound the ionospheres of Mars and Venus, respectively, at two frequencies in the microwave band and cover altitudes from the base of the ionosphere at 80 km (100 km at Venus) to the ionopause at altitudes between 300 km and 600 km. In general, both ionospheres consists of a lower layer M1 (V1 at Venus) at about 110 km (115 km), and the main layer M2 (V2) at about 135 km (145 km) altitude, both formed mainly by solar radiation at X-ray and EUV, respectively. The specific derivation and interpretation of the vertical electron density profiles at two radio frequencies from radio sounding is demonstrated in detail. Cases of quiet and disturbed ionospheric electron density profiles and cases of potential misinterpretations are presented. The behavior of the peak densities and peak altitudes of both ionospheres as a function of solar zenith angle and phase of the solar cycle as seen with Mars Express and Venus Express will be compared with past observations, models and conclusions.

Paetzold, M.; Haeusler, B.; Bird, M. K.; Peter, K.; Tellmann, S.; Tyler, G. L.; Withers, P.

2011-12-01

244

Calculation of ray paths in the ionosphere using an analytic raytracing technique  

NASA Astrophysics Data System (ADS)

A method for tracing rays in the ionosphere using analytic solutions to approximate path varying ionospheric potentials is outlined in this report. Using the ionospheric parameters generated by IONCAP and approximating the E-F2 and ground-E layer potential wells by a scaled Morse potential and a linear potential respectively, known solutions to these potentials are promoted to final ray paths by using methods developed for solving the time dependent Schroedinger equation. The computer code necessary to fit the potentials, connect the solutions at the E layer peak, and trace arbitrarily launched rays is described.

Yukon, Stanford P.

1986-07-01

245

A method to correct HF skywave backscattered signals for ionospheric frequency modulation  

NASA Astrophysics Data System (ADS)

A method is described to correct HF signals reflected by the ionosphere and backscattered by the sea surface for ionospheric frequency modulation, which produces spectral-line smearing. The statistical mean of the time derivative of the phase of the signal, weighted by the signal energy, is proposed as an estimator of this modulation. The accuracy of the estimator is measured and the efficiency of the signal processing is tested by synthetically contaminating high-quality signals obtained via sporadic E-layer propagation. Examples of data corrected for F2-layer ionospheric perturbations are shown.

Parent, Jacques; Bourdillon, Alain

1988-01-01

246

Auroral radar backscatter at off-perpendicular aspect angles due to enhanced ionospheric refraction  

NASA Astrophysics Data System (ADS)

This paper studies the effect of ionospheric refraction upon auroral radar backscatter under conditions where the aspect angle appears far from ideal, i.e., when the unrefracted ray path trajectory is at least a few degrees from the perpendicular to the Earth's magnetic field. It is found that wave trapping by curved electron density layers can cause ionospheric refraction as large as 20 deg, even at 150 MHz. This suggests that many so-called off-orthogonal VHF echoes are in reality due to backscattering at near-orthogonal aspect angles, the discepancy arising from increased ionospheric refraction by curved or tilted layers.

Uspensky, M. V.; Williams, P. J. S.; Romanov, V. I.; Pivovarov, V. G.; Sofko, G. J.; Koehler, J. A.

1994-09-01

247

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.

248

Eects of geomagnetic storms on the ionosphere and atmosphere  

Microsoft Academic Search

A geomagnetic storm is a complex process: its various features act at dierent heights. In the F2 layer the midlatitude eect is basically an ionospheric response to storm-induced changes in the neutral atmosphere, which are primarily a consequence of a strong Joule heating in the auroral thermosphere. At lower heights the role of ionization and photochemical processes increases due to

A. D. Danilov; J. Lastovicka

2001-01-01

249

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

250

Investigation of the Ionospheric Short-term Variability.  

National Technical Information Service (NTIS)

Both the total electron content of the ionosphere (TEC) and the critical frequency of the F2 layer (foF2) exhibit large day-to-day variations during quiet and active geomagnetic periods. It is of great interest to ascertain whether good correlation exists...

Z. Houminer G. Shaviv

1997-01-01

251

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

252

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

253

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

254

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

255

Solar cycle modulation of Titan's ionosphere  

NASA Astrophysics Data System (ADS)

During the six Cassini Titan flybys T83-T88 (May 2012 to November 2012) the electron density in the ionospheric peak region, as measured by the radio and plasma wave science instrument/Langmuir probe, has increased significantly, by 15-30%, compared to previous average. These measurements suggest that a long?term change has occurred in the ionosphere of Titan, likely caused by the rise to the new solar maximum with increased EUV fluxes. We compare measurements from TA, TB, and T5, from the declining phase of solar cycle 23 to the recent T83-T88 measurements during cycle 24, since the solar irradiances from those two intervals are comparable. The peak electron densities normalized to a common solar zenith angle Nnorm from those two groups of flybys are comparable but increased compared to the solar minimum flybys (T16-T71). The integrated solar irradiance over the wavelengths 1-80nm, i.e., the solar energy flux, Fe, correlates well with the observed ionospheric peak density values. Chapman layer theory predicts that Nnorm?Fek, with k=0.5. We find observationally that the exponent k=0.54±0.18. Hence, the observations are in good agreement with theory despite the fact that many assumptions in Chapman theory are violated. This is also in good agreement with a similar study by Girazian and Withers (2013) on the ionosphere of Mars. We use this power law to estimate the peak electron density at the subsolar point of Titan during solar maximum conditions and find it to be about 6500cm-3, i.e., 85-160% more than has been measured during the entire Cassini mission.

Edberg, N. J. T.; Andrews, D. J.; Shebanits, O.; Ågren, K.; Wahlund, J.-E.; Opgenoorth, H. J.; Cravens, T. E.; Girazian, Z.

2013-08-01

256

Daytime F Layer Trough.  

National Technical Information Service (NTIS)

The trough in the daytime winter F layer ionization is a fundamental feature of ionospheric-magnetospheric convection causing depletions of an order of magnitude in the electron density at the F layer maximum near midday. As observed by a world-wide array...

J. A. Whalen

1988-01-01

257

Artificial construction of the layered Ruddlesden-Popper manganite La2Sr2Mn3O10 by reflection high energy electron diffraction monitored pulsed laser deposition.  

PubMed

Pulsed laser deposition has been used to artificially construct the n = 3 Ruddlesden-Popper structure La(2)Sr(2)Mn(3)O(10) in epitaxial thin film form by sequentially layering La(1-x)Sr(x)MnO(3) and SrO unit cells aided by in situ reflection high energy electron diffraction monitoring. The interval deposition technique was used to promote two-dimensional SrO growth. X-ray diffraction and cross-sectional transmission electron microscopy indicated that the trilayer structure had been formed. A site ordering was found to differ from that expected thermodynamically, with the smaller Sr(2+) predominantly on the R site due to kinetic trapping of the deposited cation sequence. A dependence of the out-of-plane lattice parameter on growth pressure was interpreted as changing the oxygen content of the films. Magnetic and transport measurements on fully oxygenated films indicated a frustrated magnetic ground state characterized as a spin glass-like magnetic phase with the glass temperature T(g) ? 34 K. The magnetic frustration has a clear in-plane (ab) magnetic anisotropy, which is maintained up to temperatures of 150 K. Density functional theory calculations suggest competing antiferromagnetic and ferromagnetic long-range orders, which are proposed as the origin of the low-temperature glassy state. PMID:22463768

Palgrave, Robert G; Borisov, Pavel; Dyer, Matthew S; McMitchell, Sean R C; Darling, George R; Claridge, John B; Batuk, Maria; Tan, Haiyan; Tian, He; Verbeeck, Jo; Hadermann, Joke; Rosseinsky, Matthew J

2012-04-24

258

Qualitative and quantitative high performance thin layer chromatography analysis of Calendula officinalis using high resolution plate imaging and artificial neural network data modelling.  

PubMed

Calendula officinalis, commonly known Marigold, has been traditionally used for its anti-inflammatory effects. The aim of this study was to investigate the capacity of an artificial neural network (ANN) to analyse thin layer chromatography (TLC) chromatograms as fingerprint patterns for quantitative estimation of chlorogenic acid, caffeic acid and rutin in Calendula plant extracts. By applying samples with different weight ratios of marker compounds to the system, a database of chromatograms was constructed. A hundred and one signal intensities in each of the HPTLC chromatograms were correlated to the amounts of applied chlorogenic acid, caffeic acid, and rutin using an ANN. The developed ANN correlation was used to quantify the amounts of 3 marker compounds in calendula plant extracts. The minimum quantifiable level (MQL) of 610, 190 and 940ng and the limit of detection (LD) of 183, 57 and 282ng were established for chlorogenic, caffeic acid and rutin, respectively. A novel method for quality control of herbal products, based on HPTLC separation, high resolution digital plate imaging and ANN data analysis has been developed. The proposed method can be adopted for routine evaluation of the phytochemical variability in calendula extracts. PMID:24070490

Agatonovic-Kustrin, S; Loescher, Christine M

2013-09-01

259

Artificial Construction of the Layered Ruddlesden-Popper Manganite La2Sr2Mn3O10 by Reflection High Energy Electron Diffraction Monitored Pulsed Laser Deposition  

PubMed Central

Pulsed laser deposition has been used to artificially construct the n = 3 Ruddlesden–Popper structure La2Sr2Mn3O10 in epitaxial thin film form by sequentially layering La1–xSrxMnO3 and SrO unit cells aided by in situ reflection high energy electron diffraction monitoring. The interval deposition technique was used to promote two-dimensional SrO growth. X-ray diffraction and cross-sectional transmission electron microscopy indicated that the trilayer structure had been formed. A site ordering was found to differ from that expected thermodynamically, with the smaller Sr2+ predominantly on the R site due to kinetic trapping of the deposited cation sequence. A dependence of the out-of-plane lattice parameter on growth pressure was interpreted as changing the oxygen content of the films. Magnetic and transport measurements on fully oxygenated films indicated a frustrated magnetic ground state characterized as a spin glass-like magnetic phase with the glass temperature Tg ? 34 K. The magnetic frustration has a clear in-plane (ab) magnetic anisotropy, which is maintained up to temperatures of 150 K. Density functional theory calculations suggest competing antiferromagnetic and ferromagnetic long-range orders, which are proposed as the origin of the low-temperature glassy state.

2012-01-01

260

Ionospheric modification using relativistic electron beams  

NASA Astrophysics Data System (ADS)

The recent development of comparatively small electron linear accelerators (linacs) now makes possible a new class of ionospheric modification experiments using beams of relativistic electrons. These experiments can potentially provide much new information about the interactions of natural relativistic electrons with other particles in the upper atmosphere, and it may also make possible new forms of ionization structures extending down from the lower ionosphere into the largely un-ionized upper atmosphere. The consequences of firing a pulsed 1 A, 5 Mev electron beam downwards into the upper atmosphere are investigated. If a small pitch angle with respect to the ambient geomagnetic field is selected, the beam produces a narrow column of substantial ionization extending down from the source altitude to altitudes of approximately 40 to 45 km. This column is immediately polarized by the natural middle atmosphere fair weather electric field and an increasingly large potential difference is established between the column and the surrounding atmosphere. In the regions between 40 to 60 km, this potential can amount to many tens of kilovolts and the associated electric field can be greater than the field required for breakdown and discharge. Under these conditions, it may be possible to initiate lightning discharges along the initial ionization channel. Filamentation may also occur at the lower end to drive further currents in the partially ionized gases of the stratosphere. Such discharges would derive their energy from the earth-ionosphere electrical system and would be sustained until plasma depletion and/or electric field reduction brought the discharge under control. It is likely that this artificially-triggered lightning would produce measurable low-frequency radiation.

Banks, Peter M.; Fraser-Smith, Anthony C.; Gilchrist, B. E.

1990-10-01

261

Frequency modulation ionospheric pumping at EISCAT: New results  

NASA Astrophysics Data System (ADS)

In November 2011 a new capability of the EISCAT HF ionospheric pump facility was deployed, namely, frequency modulation. The pump frequency was ramped linearly over 300 kHz in 18 minutes. Experiments were performed at a variety of frequency ranges, including the 4th and 5th electron gyro-harmonics in the F-layer ionosphere. The EISCAT UHF radar observed pump frequency-dependent electron temperature enhancements, minimising on the electron gyro-harmonic frequency which are consistent with previous experiments. Novel results include pump frequency-dependent ion temperature enhancements as well as strong plasma density enhancements, which maximise for pump frequencies above the electron gyro-harmonics.

Kosch, Michael; Pedersen, Todd; Rietveld, Michael; Senior, Andrew; Bryers, Carl; Wu, Jun; Xu, Bin

2012-07-01

262

Limitations and possible improvements of ionospheric models for radio propagation  

NASA Astrophysics Data System (ADS)

Factors that affect the applicability of ionospheric models used in connection with ground-to-ground HF propagation are discussed. Most such models are based on monthly medians of hourly observations by a worldwide network of ionosondes. Plots are given of diurnal variation of f0F2, ray paths for two frequencies (4.5 and 4.9 MHz) in a sunrise model ionosphere, observed and computed zenith angle during sunrise, and a comparison of overhead electron density profile with computed profile and true reflection heights for sunrise models, and other significant parameters. Sporadic E-layer tilts are considered.

Paul, A. K.

263

Introducing a disturbance ionosphere index  

NASA Astrophysics Data System (ADS)

Although ionospheric perturbations such as traveling ionospheric disturbances have a strong impact on Global Navigation Satellite Systems (GNSS) and other space-based radio systems, the description of individual perturbations is difficult. To overcome this problem, it is suggested to use a disturbance ionosphere index (DIX) that describes the perturbation degree of the ionosphere in a less specific form as a proxy. Although such an index does not describe the exact propagation conditions at the measurement site, the estimated index number indicates the probability of a potential impact on radio systems used in communication, navigation, and remote sensing. The definition of such a DIX must take into account the following major requirements: relevance to practical needs, objective measure of ionospheric conditions, easy and reproducible computation, and availability of a reliable database. Since the total electron content has been shown in many publications to act as an outstanding parameter for quantifying the range error and also the strength of ionospheric perturbations, we propose a DIX that is based on GNSS measurements. To illustrate the use of the index, recent storms monitored in 2011 and the Halloween storm are discussed. The proposed index is a robust and objective measure of the ionospheric state, applicable to radio systems which are impacted by a highly variable perturbed ionosphere.

Jakowski, N.; Borries, C.; Wilken, V.

2012-01-01

264

Ionospheres of the terrestrial planets  

Microsoft Academic Search

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

R. W. Schunk; A. F. Nagy

1980-01-01

265

Plasma temperatures in Saturn's ionosphere  

Microsoft Academic Search

We have calculated self-consistent electron and ion temperatures in Saturn's ionosphere using a series of coupled fluid and kinetic models developed to help interpret Cassini observations and to examine the energy budget of Saturn's upper atmosphere. Electron temperatures in the midlatitude topside ionosphere during solar maximum are calculated to range between 500 and 560 K during the Saturn day, approximately

Luke Moore; Marina Galand; Ingo Mueller-Wodarg; Roger Yelle; Michael Mendillo

2008-01-01

266

CORISS Observations of Ionospheric Scintillation  

Microsoft Academic Search

Rapid fluctuations in radio occultation (RO) signal to noise ratios and phase can signify the presence of fine scale ionospheric density irregularities along the occultation ray path. While such signatures are clearly identifiable in 1 Hz observations that are typically made at ionospheric tangent altitudes, high-rate (50 Hz) data is required to sample the full range of irregularity scale sizes

P. R. Straus; R. L. Bishop; R. G. Caton; K. M. Groves; C. S. Carrano

2009-01-01

267

GIM-TEC adaptive ionospheric weather assessment and forecast system  

NASA Astrophysics Data System (ADS)

The Ionospheric Weather Assessment and Forecast (IWAF) system is a computer software package designed to assess and predict the world-wide representation of 3-D electron density profiles from the Global Ionospheric Maps of Total Electron Content (GIM-TEC). The unique system products include daily-hourly numerical global maps of the F2 layer critical frequency (foF2) and the peak height (hmF2) generated with the International Reference Ionosphere extended to the plasmasphere, IRI-Plas, upgraded by importing the daily-hourly GIM-TEC as a new model driving parameter. Since GIM-TEC maps are provided with 1- or 2-days latency, the global maps forecast for 1 day and 2 days ahead are derived using an harmonic analysis applied to the temporal changes of TEC, foF2 and hmF2 at 5112 grid points of a map encapsulated in IONEX format (?87.5°:2.5°:87.5°N in latitude, ?180°:5°:180°E in longitude). The system provides online the ionospheric disturbance warnings in the global W-index map establishing categories of the ionospheric weather from the quiet state (W=±1) to intense storm (W=±4) according to the thresholds set for instant TEC perturbations regarding quiet reference median for the preceding 7 days. The accuracy of IWAF system predictions of TEC, foF2 and hmF2 maps is superior to the standard persistence model with prediction equal to the most recent 'true' map. The paper presents outcomes of the new service expressed by the global ionospheric foF2, hmF2 and W-index maps demonstrating the process of origin and propagation of positive and negative ionosphere disturbances in space and time and their forecast under different scenarios.

Gulyaeva, T. L.; Arikan, F.; Hernandez-Pajares, M.; Stanislawska, I.

2013-09-01

268

Nonlinear dynamic processes in modified ionospheric plasma  

NASA Astrophysics Data System (ADS)

Presented work is a contribution to the experimental and theoretical study of nonlinear effects arising on ionospheric plasma under the action of powerful radio emission (G.I. Terina, J. Atm. Terr. Phys., 1995, v.57, p.273; A.V. Kochetov et. al., Advances in Space Research, 2002, in press). The experimental results were obtained by the method of sounding of artificially disturbed ionosphere by short radio pulses. The amplitude and phase characteristics of scattered signal as of "caviton" type (CS) (analogy of narrow-band component of stimulation electromagnetic emission (SEE)) as the main signal (MS) of probing transmitter are considered. The theoretical model is based on numerical solution of driven nonlinear Shrödinger equation (NSE) in inhomogeneous plasma. The simulation allows us to study a self-consistent spatial-temporal dynamics of field and plasma. The observed evolution of phase characteristics of MS and CS qualitatively correspond to the results of numerical simulation and demonstrate the penetration processes of powerful electromagnetic wave in supercritical (in linear approach) plasma regions. The modeling results explain also the periodic generation of CS, the travel CS maximum down to density gradient, the aftereffect of CS. The obtained results show the excitation of strong turbulence and allow us to interpret CS, NC and so far inexplicable phenomena as "spikes" too. The work was supported in part by Russian Foundation for Basic Research (grants Nos. 99-02-16642, 99-02- 16399).

Kochetov, A.; Terina, G.

269

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 (±20º), 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

270

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

271

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

272

On spread-F in the ionosphere before earthquakes  

NASA Astrophysics Data System (ADS)

Occurrence probability of the ionospheric spread-F in connection with earthquakes is analyzed. The F-layer is not close to the Earth (˜400 km), but in situ data could be obtained either by ionospheric sounders or by satellites. Data from the two Japanese ionospheric stations Kokubunji and Akita have been analyzed to find out long-term (a few weeks) variations of spread-F before and after earthquakes. Earthquakes with magnitudes M>5 were taken into account. Only time intervals where geomagnetic variations are weak have been analyzed. It is shown that the probability of spread-F observations starts to decrease approximately 40 days before earthquakes, presents a minimum about 10 days before and then takes 1 month to recover the background level (therefore this increase lasts about 3 weeks after earthquakes). This effect exists if the distance between epicenters and the sounding station is less than 500 km.

Liperovskaya, E. V.; Liperovsky, V. A.; Silina, A. S.; Parrot, M.

2006-01-01

273

Ionospheric irregularities and their potential impact on synthetic aperture radars  

NASA Astrophysics Data System (ADS)

Accumulating data are making it increasingly evident that major plasma irregularities populate substantial portions of the ionosphere. In contrast with these findings, satellite-borne synthetic aperture radar (SAR) systems tacitly assume that the ionosphere is uniformly layered and unchanging under the orbiting SAR. Analysis of plasma irregularity structures measured directly on the S3-4 satellite shows that this assumption is readily violated near the nighttime equator during the occurrence of spread F and at high-latitudes on a nearly 24-hour basis. The irregularities can be very intense, covering scale sizes from meters to hundreds of kilometers. Associated along-track phase path calculations point to a potentially serious problem in SAR imaging integrity in restricted ionospheric space-time domains.

Szuszczewicz, E. P.; Rodriguez, P.; Mango, S.; Singh, M.

1983-10-01

274

Ionospheric precursors to large earthquakes: A case study of the 2011 Japanese Tohoku Earthquake  

NASA Astrophysics Data System (ADS)

Researchers have reported ionospheric electron distribution abnormalities, such as electron density enhancements and/or depletions, that they claimed were related to forthcoming earthquakes. In this study, the Tohoku earthquake is examined using ionosonde data to establish whether any otherwise unexplained ionospheric anomalies were detected in the days and hours prior to the event. As the choices for the ionospheric baseline are generally different between previous works, three separate baselines for the peak plasma frequency of the F2 layer, foF2, are employed here; the running 30-day median (commonly used in other works), the International Reference Ionosphere (IRI) model and the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIE-GCM). It is demonstrated that the classification of an ionospheric perturbation is heavily reliant on the baseline used, with the 30-day median, the IRI and the TIE-GCM generally underestimating, approximately describing and overestimating the measured foF2, respectively, in the 1-month period leading up to the earthquake. A detailed analysis of the ionospheric variability in the 3 days before the earthquake is then undertaken, where a simultaneous increase in foF2 and the Es layer peak plasma frequency, foEs, relative to the 30-day median was observed within 1 h before the earthquake. A statistical search for similar simultaneous foF2 and foEs increases in 6 years of data revealed that this feature has been observed on many other occasions without related seismic activity. Therefore, it is concluded that one cannot confidently use this type of ionospheric perturbation to predict an impending earthquake. It is suggested that in order to achieve significant progress in our understanding of seismo-ionospheric coupling, better account must be taken of other known sources of ionospheric variability in addition to solar and geomagnetic activity, such as the thermospheric coupling.

Carter, B. A.; Kellerman, A. C.; Kane, T. A.; Dyson, P. L.; Norman, R.; Zhang, K.

2013-09-01

275

Ionospheric Remote Sensing with the Ionospheric Occultation Experiment (IOX)  

NASA Astrophysics Data System (ADS)

The Ionospheric Occultation Experiment (IOX) is a dual-frequency GPS receiver with a single Earth-limb viewing antenna. Ionospheric remote sensing is possible during occultation events in which the line of sight to a GPS satellite being tracked by IOX sets through the Earth's limb. IOX is one of four experiments to be flown as part of the United States Air Force Space Test Program's PICOSat mission, currently scheduled for launch in August of this year. PICOSat will be placed into a 67 degree inclination, 800 km altitude orbit, enabling IOX to make ionospheric measurements at all local times under near-solar maximum conditions over the course of its mission. The IOX instrument will be described together with anticipated characteristics of the data expected to be obtained from this mission. Plans for data analysis and scientific studies will be discussed. These include (1) cross-validation of UV ionospheric remote sensing techniques through comparisons with data from sensors on TIMED and DMSP F16 (both of which are also expected to launch sometime this summer); (2) potential observations of equatorial scintillations using an occultation sensor; (3) evaluation of aspects of the occultation data relevant to space weather prediction or assimilation into ionospheric specification models; and (4) detailed analysis of ionospheric structures through enhanced ionospheric tomography. Enhanced ionospheric tomography evaluations are possible through a combination of IOX data with ground-based observations of a dual-frequency beacon that is one of the other three experiments on PICOSat. Ground-based receiver chains will provide information on horizontal structures which can be combined with occultation measurements of vertical structure to provide a more complete picture of the local ionosphere than is possible with beacon measurements alone, as has been done on previous missions.

Straus, P. R.; Bernhardt, P. A.

2001-05-01

276

Focusing of HF radio-waves by ionospheric ducts  

NASA Astrophysics Data System (ADS)

This paper presents the first direct observations of HF focusing induced by natural and artificial ionospheric ducts along with a simple theoretical model. The experiments were conducted by injecting HF radio-waves using the Ionospheric Research Instrument of the High Frequency Active Auroral Research Program located in Gakona, Alaska and detecting them with instruments on the overflying French micro-satellite DEMETER. The latter observed a multiple frequency band structure, which is characteristic of a strong HF signal exceeding the detector's saturation level. Analysis of the O+ density measured by DEMETER along its orbit shows that the strong radio signal coincides with the presence of a “negative” duct in the ionosphere. “Negative” refers to the presence of a plasma density depletion with the peak depletion located near the center of the duct. Such ducts induce changes in the index of refraction leading to the focusing of HF waves in a manner equivalent to a “thick” plasma lens. Examination of the data along with a simple plasma lens model indicates the presence of focal node(s) in the vicinity of the overflying satellite. Two examples, one corresponding to focusing by a natural duct and one by an artificial one are presented.

Milikh, G. M.; Vartanyan, A.; Papadopoulos, K.; Parrot, M.

2011-08-01

277

Modification of equatorial ionospheric electric fields during some major magnetic storms  

NASA Astrophysics Data System (ADS)

Geomagnetic field measurements at equatorial and off-equatorial low latitude stations have been used, in recent years, to study the variations in the daytime equatorial ionospheric electric fields caused by prompt penetration of a magnetospheric electric field into the low latitude ionosphere during periods of undershielding or overshielding. Changes in the daytime equatorial ionospheric electric fields produced by disturbance dynamo effects may also contribute to the observed magnetic field variations. However, at nighttime, due to low electrical conductivity of the ionosphere, changes in the equatorial ionospheric electric field are not expected to contribute significantly to the residual geomagnetic variations after removal of ring current contributions. On some magnetically disturbed days when ground observations have yielded significant negative excursions of the residual magnetic field variations at nighttime, magnetic field measurements made by CHAMP satellite around the dip equator close to the longitude region of the ground obsevations, have shown some unexpected results. An important consequence of variation in the post-sunset equatorial ionospheric electric field due to magnetic activity and the resultant change in the height of the equatorial F layer, is either suppression or enhancement of the growth of equatorial plasma bubbles and associated equatorial spread F irregularities. Observations of ionospheric scintillations caused by these irregularities have also been used to obtain information about changes in the equatorial ionospheric electric fields during some major magnetic storms.

Bhattacharyya, Archana; Alex, S.; Luehr, Hermann; Stolle, Claudia; Tiwari, Diwakar

278

Studies of the high latitude ionospheric convection  

NASA Astrophysics Data System (ADS)

The electrostatic potential distribution in the high latitude ionosphere is representative of the response of the ionosphere magnetosphere system to drivers in the solar wind and conditions in the interplanetary medium. The cross polar cap potential drop, used as a single parameter to describe the global distribution of electrostatic potential, often serves as an input driver for various magnetospheric and space weather models. For a given solar wind condition the cross polar cap potential drop derived from satellite measurements of the electric field, or ion drift in the ionosphere, are observed to have a significant variation, often on the order of thirty percent or greater. Such a large variability could influence the uncertainty of results from models that utilize this electrostatic potential drop as an input, so a further understanding of the sources and organization of these uncertainties will improve the specification itself and the confidence limits of the observations. Sources of this variability are investigated using two years (2000-2001) of ionospheric plasma flow data provided by the DMSP F13 and F15 satellites to calculate the cross polar cap potential drop, along with solar wind data from the ACE satellite in order to explore the behavior of this potential in response to a wide range of interplanetary magnetic field (IMF) conditions during southward IMF (BZ ? 0). A variety of IMF conditions are examined to show how the stability of the IMF and the solar wind speed over both short and long time periods affects variations in the cross polar cap potential drop. The most interesting discovery is that, even during steady state IMF conditions, the largest amount of variability is caused by the displacement of the satellite track with respect to the extrema in potential at the center of the two convection cells in the high-latitude region, especially when the displacement is caused by substorm activity. Included is a study of the average properties of the electrostatic potential drop and its relationship to particle precipitation boundaries across the ionospheric projection of the low latitude boundary layer and the interplanetary electric field.

Drake, Kelly Ann

279

Microscopic study of an artificial grain boundary Josephson junction in a BiSrCaCuO thin film formed on a SrTiO3(110) substrate using a MgO buffer layer  

Microsoft Academic Search

An artificial grain boundary Josephson junction in a BiSrCaCuO thin film was fabricated on an off-oriented SrTiO3(110) substrate using a MgO buffer layer, and was investigated using a transmission electron microscope (TEM). The MgO buffer layer was oriented with a (110) plane parallel to the (110) plane of the 5-deg off-oriented SrTiO3 substrate. The BiSrCaCuO film was grown with the

Junji Tanimura; Tetsuya Takami; Ken'ichi Kuroda; Osamu Wada; Masayuki Kataoka; Kazuyoshi Kojima; Tetsuo Ogama

1993-01-01

280

Lightning induced brightening in the airglow layer  

Microsoft Academic Search

This report describes a transient luminosity observed at the altitude of the airglow layer (about 95 km) in coincidence with a lightning flash in a tropical oceanic thunderstorm directly beneath it. This event provides new evidence of direct coupling between lightning and ionospheric events. This luminous event in the ionosphere was the only one of its kind observed during an

W. L. Boeck; O. H. Vaughan Jr.; R. Blakeslee; B. Vonnegut; M. Brook

1992-01-01

281

Three-Dimensional Ionospheric Model Using Observed Ionospheric Parameters.  

National Technical Information Service (NTIS)

An electron density model, which permits a three-dimensional specification of the ionospheric structure, has been developed. The model generates realistic electron density profiles in the altitude range from 100 to 800 km by making use of selected ionosph...

C. M. Rush D. Miller

1973-01-01

282

Artificial Limbs  

MedlinePLUS

... you are missing an arm or leg, an artificial limb can sometimes replace it. The device, a prosthesis, ... activities such as walking, eating, or dressing. Some artificial limbs let you function nearly as well as before.

283

Sweeteners - artificial  

MedlinePLUS

... in carbonated low-calorie beverages and other products. Neotame is an artificial sweetener used in many diet ... lifetime. The artificial sweeteners aspartame, acesulfame K, saccharin, neotame, and sucralose are all FDA approved. Aspartame is ...

284

Resonance scattering of radio waves in the acoustically disturbed ionosphere  

SciTech Connect

It is known that acoustic waves are excited in the atmosphere for a variety of reasons, including seismic oscillations of the earth's surface as a result of earthquakes, volcanic eruptions, explosions, and in the operation of other powerful sources of natural or artificial origin. When sound waves are sufficiently intense, they can create disturbances in the electron density at ionospheric heights. In this paper, we consider the properties of radio wave scattering off such disturbances created by infrasound waves, i.e., we consider Mandel'shtam-Brillouin scattering in the ionosphere. The authors discuss the possibility of a radiophysical enhancement of the effect connected with the phenomenon of resonance scattering of the radiowaves off the disturbances created in the medium by the acoustic wave.

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

1987-11-01

285

Very Low Frequency (VLF) studies of Ionospheric/Magnetospheric Electromagnetic phenomena in Indian Low Latitude Region using AWESOME Receivers  

NASA Astrophysics Data System (ADS)

Ground based observations of whistler mode ELF/VLF (300 Hz 30 kHz) waves are considered as an important remote sensing tool for the investigation of upper atmosphere and magnetosphere. These VLF waves find their origin in various natural and artificial phenomena, the natural sources include thunderstorms, lightning and associated phenomena. Despite of the fact that conjugate region of India having less lightning activity as it lies in Indian Ocean and also the height of the magnetic field lines connecting the conjugate regions lies in the ionosphere/atmosphere, lot of interesting VLF activity through the magnetosphere is observed in Indian low latitude region. Sub-ionospheric VLF transmissions propagating inside the Earth-ionosphere wave-guide is also being widely used for investigating sudden ionospheric perturbations in lower part of the ionosphere. For this purpose we propose to monitor VLF signals continuously at several locations in Indian sector with the help of AWESOME VLF receivers from Stanford University. AWESOME receivers are capable of collecting both broadband (used for the study of natural signals) and narrowband (sub-ionospheric VLF signals corresponding to VLF transmitters) data. The obtained data will enable us to understand the generation and propagation mechanism of radio atmospherics from lightning flashes, magnetospheric whistlers, VLF emissions and other naturally occurring phenomena. Narrowband sub- ionospheric VLF signals and ground based geomagnetic data in Indian low latitude region will help us to study sudden ionospheric disturbances associated with transient phenomena like solar flares, geomagnetic storms, cosmic gamma-ray flares, etc.

Singh, R.; Veenadhari, B.; Alex, S.

2006-11-01

286

Assimilation of Remote Ionospheric Measurements: Towards a Global Ionospheric Monitor  

NASA Astrophysics Data System (ADS)

Explosive growth in the availability of ionospheric measurements from ground and space provide a fundamentally new opportunity to image the ionosphere as never before. As examples, ground receiver TEC, occultation TEC, space-based whole-Earth UV disc emission, in-situ measurements of electron density, and ground based ionosonde measurements of both bottom-side profiles and critical parameters are all highly desirable and plentiful. However, these disparate measurements must be blended together carefully, each having its own unique capabilities and challenges. Towards this end, we have developed the Global Assimilative Ionospheric Model (GAIM). Utilizing two separate complementary assimilation approaches, such observations are intelligently combined with prior climatological knowledge to yield the best estimate of the current ionospheric state. The first, a variation of the Kalman filter recursive estimation approach, is optimized to produce the best fit ionosphere with emphasis in regions of higher data density relying on a climatological background to assist in regions of sparse data. The second, a 4-dimensional variational approach (4DVAR) instead adjusts physical driver estimates (thermospheric densities and winds, electric fields, and solar radiation intensity in our case) to smoothly match incoming data and spread its influence in a physically consistent manner. For ionospheric data in particular, estimation of these ionospheric drivers is of paramount importance, as the ionosphere is a heavily dissipative system, and forecast without proper drivers is nearly impossible. In this presentation, we shall explore results of merging ground-based GPS and occultation TEC measurements and evaluate the system performance in various solar conditions.

Mandrake, L.; Wilson, B. D.; Mannucci, T.

2005-12-01

287

Analysis and improvement of ionospheric thin shell model used in SBAS for China region  

NASA Astrophysics Data System (ADS)

The most frequently used mapping function for converting slant total electron content (STEC) to vertical total electron content (VTEC) uses a simplified ionospheric single layer model in satellite based augmentation system (SBAS). Aiming at ionospheric single layer model altitude variation, we analyzed the statistical characteristic of mapping function in systemic approach particular for the region of China, and then experimental mapping function was proposed. The experimental mapping function is used in SBAS ionospheric correction and the precision of vertical correction is compared with standard mapping function. The results show that conversion factor errors depend on latitude, time and elevation, experimental mapping function is helpful to the vertical TEC estimation and may improve the precision of SBAS ionospheric refraction correction especially for the low latitude region of China.

Huang, Z.; Yuan, H.

2013-06-01

288

Physical Model of Earthquake Ionospheric Precursors (Invited)  

NASA Astrophysics Data System (ADS)

The GPS derived ionospheric TEC (Total Electron Content) disturbances before earthquakes were discovered in the last years using global and regional TEC maps, TEC measurements over individual stations as well as measurements along individual GPS satellite passes. For strong mid-latitudinal earthquakes the seismo-ionospheric anomalies look like local TEC enhancements or decreases located in the vicinity of the forthcoming earthquake epicenter. Such structures are generated in the ionosphere for several days prior to the main shock. The amplitude of plasma modification reaches the value of 30-90% relative to the non-disturbed level. The zone of the anomaly maximum manifestation extends larger than 1500 km in latitude and 3500-4000 km in longitude. In case of strong low-latitudinal earthquakes there are effects related with the modification of the equatorial F2-region anomaly: deepening or filling of the ionospheric electron density trough over the magnetic equator. The possible physical mechanism which can cause such anomalies has been proposed. We consider that the most probable reason of the NmF2 and TEC disturbances observed before the earthquakes is the vertical drift of the F2-region ionospheric plasma under the influence of the zonal electric field of seismogenic origin related with the vertical transportation of the injected aerosols and radioactive particles. In the middle latitudes the upward electromagnetic drift, created by the eastward electric field, leads to the increase of the NmF2 and TEC due to the plasma transportation to the regions with lower concentration of the neutral molecules and, consequently, with lower loss rate of dominating ions O+ in the ion-molecular reactions. The electric field of the opposite direction (westward) creates the opposite - negative - effect in NmF2 and TEC. In the low latitude regions (near the geomagnetic equator) the increase of the eastward electric field leads to the deepening of the equatorial anomaly minimum (“trough” over the magnetic equator in the latitudinal distribution of electron concentration) due to the intensification of the fountain-effect. To check this hypothesis, the model calculations have been carried out with the use of the UAM (Upper Atmosphere Model) - the global numerical model of the Earth’s upper atmosphere. The electric potential distribution at the near-epicenter region boundary required for the electric field maintenance has been proposed. The upper atmosphere state, presumably foregone a strong earthquake, has been modeled by means of switching-on of additional sources of the electric field in the UAM electric potential equation which was solved numerically jointly with all other UAM equations (continuity, momentum and heat balance) for neutral and ionized gases. The efficiency of the proposed mechanism has been investigated by means of model calculations of the ionosphere response to the action of zonal electric field produced by seismogenic sources located at the middle and low latitudes. The results of the corresponding numerical model calculations of the electric field and its effects in the ionospheric F2-layer and plasmasphere have been presented. They have revealed a fine agreement with TEC anomalies observed before strong earthquakes at the middle and low latitudes both in spatial scales and in amplitude characteristics.

Namgaladze, A. A.

2010-12-01

289

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.

290

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

291

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

292

Monitoring and Imaging Ionospheric Total Electron Content Without the Thin-Shell Approximation  

Microsoft Academic Search

The thin-shell model of the ionosphere relies on the coarse approximation that ionospheric electron density is non-negligible only in the vicinity of a specified reference height (typically the peak of the F-layer). The utility of this approximation resides primarily in the ease with which measurements of slant total electron content (TEC) may be converted into estimates of vertical TEC: if

L. Sparks

2008-01-01

293

Ionospheric scintillation: A brief review  

NASA Astrophysics Data System (ADS)

Irregular diffraction of radio signals by the global ionosphere is studied to predict scintillation using easily measured geophysical parameters. Using a network of equatorial stations it was possible to measure and model the average scintillation characteristics and to relate them to geophysical parameters such as solar flux and geomagnetic indices. Typical models for various stations are shown, including the variations of scintillation as predicted and as measured. The scintillation in auroral regions and the phase distortion caused by the ionosphere are also discussed.

Mullen, J. P.; Aarons, J.; MacKenzie, E. M.

294

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

295

Nighttime ionosphere thermosphere coupling observed during an intense geomagnetic storm  

NASA Astrophysics Data System (ADS)

The electrodynamics of the ionosphere in the tropical region presents various scientific aspects, which remain subject of intensive investigations and debates by the scientific community. During the year 2002, in a joint project between the Universidade do Vale do Paraíba (UNIVAP) and Universidade Luterana do Brasil (ULBRA), a chain of three Canadian Advanced Digital Ionosondes (CADIs) was established nearly along the geomagnetic meridian direction, for tropical ionospheric studies, such as, changes and response due to geomagnetic disturbances and thermosphere ionosphere coupling and the generation and dynamics of ionospheric irregularities, in the Brazilian sector. The locations of the three ionosondes stations are São José dos Campos (23.2°S, 45.9°W, dip latitude 17.6°S under the southern crest of equatorial ionospheric anomaly), Palmas (10.2°S, 48.2°W, dip latitude 5.5°S near the magnetic equator) and Manaus (2.9°S, 60.0°W, dip latitude 6.4°N between the geographic and geomagnetic dip equators). It should be pointed out that Palmas and Manaus are located on the opposite sides of the magnetic equator but both are south of the geographic equator. The three CADIs work in time-synchronized mode and obtain ionograms every 5 min. This configuration of the ionospheric sounding stations allowed us to study the F-region dynamics during geomagnetically disturbed period in the meridional direction. Just after the installation and testing of the three CADIs, on September 05, 2002 a coronal mass ejection (CME) left the Sun and about 2 days after the CME left the Sun, it reached the Earth’s magnetosphere and complex and multi step events took place during the period September 07 09. In the study we note that the equatorial stations located north (Manaus, dip latitude 6.4°N) and south (Palmas, dip latitude 5.5°S) of the dip equator presented significant F-layer height asymmetries during the storm main phase. In addition, the low-latitude station SJC (dip latitude 17.6°S) presented decrease in the F-layer densities (negative phase), whereas Palmas presented increase in the F-layer densities (positive phase) during the main phase. This was followed by positive phase at both the stations. During the first night of the recovery phase a strong formation and evolution of large-scale ionospheric irregularities (equatorial spread-F (ESF)) was observed, but on the second night of the recovery phase, there was strong and almost simultaneous sporadic E (Es) formation at all three stations. During the presence of Es, spread-F formation is not observed, indicating the suppression of spread-F, possibly by sporadic E.

Fagundes, P. R.; Muella, M. T. A. H.; Bittencourt, J. A.; Sahai, Y.; Lima, W. L. C.; Guarnieri, F. L.; Becker-Guedes, F.; Pillat, V. G.; Ferreira, A. S.; Lima, N. S.

296

Spacelab-2 plasma depletion experiments for ionospheric and radio astronomical studies  

NASA Astrophysics Data System (ADS)

The Spacelab-2 Plasma Depletion Experiments were a series of studies to examine Shuttle-induced perturbations in the ionosphere and their application to ground-based radio astronomy. The Space Shuttle Challenger fired its orbital maneuvering subsystem engines, releasing large amounts of exhaust molecules that caused the electrons and ions in earth's upper atmosphere to chemically recombine, thereby creating so-called 'ionospheric holes'. Two burns conducted over New England produced ionospheric peak depletions ranging from 25 to 50 percent, affected the ionosphere over a 200-kilometer altitude range, and covered 1 to 2 deg of latitude. Optical emissions associated with the hole spanned an area of several hundred thousand square kilometers. A third burn was conducted over a low-frequency radio observatory in Hobart, Australia, to create an 'artificial window' for ground-based observations at frequencies normally below the natural ionospheric cutoff (penetration) frequency. The Hobart experiment succeeded in making high-resolution observations at 1.7 megahertz through the induced ionospheric hole.

Mendillo, M.; Baumgardner, J.; Allen, D. P.; Foster, J.; Holt, J.

1987-11-01

297

Spacelab-2 plasma depletion experiments for ionospheric and radio astronomical studies.  

PubMed

The Spacelab-2 Plasma Depletion Experiments were a series of studies to examine shuttle-induced perturbations in the ionosphere and their application to ground-based radio astronomy. The space shuttle Challenger fired its orbital maneuvering subsystem engines on 30 July and 5 August 1985, releasing large amounts of exhaust molecules (water, hydrogen, and carbon dioxide) that caused the electrons and ions in Earth's upper atmosphere to chemically recombine, thereby creating so-called "ionospheric holes." Two burns conducted over New England produced ionospheric peak depletions ranging from 25 to 50 percent, affected the ionosphere over a 200-kilometer altitude range, and covered 1 degrees to 2 degrees of latitude. Optical emissions associated with the hole spanned an area of several hundred thousand square kilometers. A third burn was conducted over a low-frequency radio observatory in Hobart, Australia, to create an "artificial window" for ground-based observations at frequencies normally below the natural ionospheric cutoff (penetration) frequency. The Hobart experiment succeeded in making high-resolution observations at 1.7 megahertz through the induced ionospheric hole. PMID:17744364

Mendillo, M; Baumgardner, J; Allen, D P; Foster, J; Holt, J; Ellis, G R; Klekociuk, A; Reber, G

1987-11-27

298

Global Imaging Monitor of the Ionosphere (GIMI): a far-ultraviolet imaging experiment on ARGOS  

NASA Astrophysics Data System (ADS)

The Global Imaging Monitor of the Ionosphere (GIMI) is one of several remote-sensing instruments under development for flight on the Air Force Space Test Program's P91-1 Advanced Research and Global Observation Satellite, planned for launch in 1997. The primary objective of GIMI is to map and monitor the ionospheric O+ and electron density on a global basis, by means of wide-field imaging of ionospheric far-ultraviolet emissions. it will also be used to detect and characterize local perturbations of the ionosphere due to natural and artificial events. Atomic nitrogen in the upper atmosphere will be measured by nitric oxide nightglow emissions resulting from its combination with atomic oxygen. Observations of stellar occultations by Earth's atmosphere will be used to measure the neutral density distributions of N2 and O2. Other objectives are to map and monitor the ultraviolet background in near-Earth space due to ionospheric and airglow emissions and extraterrestrial sources, and to obtain all-sky surveys of celestial point and diffuse sources. GIMI consists of two wide-field imaging cameras sensitive in three far- and extreme-UV spectral ranges (75 - 110 nm, 131 - 160 nm, and 131 - 200 nm), selected for their utility in day and night ionospheric and neutral atmospheric remote sensing. The GIMI sensors are based on electron-bombarded CCD arrays, with opaque alkali halide photocathodes and Schmidt or all-reflective optical systems.

Carruthers, George R.; Seeley, Timothy D.

1996-11-01

299

Ionospheric Sounding Measurements and Geomagnetic Field Variations at Tamanrasset Observatory  

NASA Astrophysics Data System (ADS)

The ionosphere is ionized upper part of the atmosphere, extending upward from 60 km altitude above the Earth's surface. It is subdivided in three main layers labeled D, E and F. In this work, we want to analyze the temporal variation of the electronic density of these ionospheric layers. We want to focus particularly on the F2 layer. The analysis of the ionograms obtained from the ionospheric vertical soundings done at the Tamanrasset ionosonde station, allows to derive the critical frequencies and the virtual heights of all the ionospheric layers. The electronic density of the F2 layer is then obtained starting from the determination of its critical frequency (f0F2). The ionograms obtained from measurements made during the year 1956 and from the continuous soundings covering years 1992 to 1994 are used to compute the electronic density. The obtained results clearly show that the amplitude of this electronic density is much higher for year 1956 than for the years 1992 to 1994. This is mainly related to the solar activity which was in its ascending phase during the year 1956 and close to the maximum of the solar cycle 19. The solar activity for the 1992-1994 time interval was in its descending phase, close to the minimum of the solar cycle 22. Applying a Fourier Transform to these data sets highlights peaks corresponding to the well known harmonics of 1 year, 6 months, 27 days, 24 hours and their subharmonics. The wavelet analysis shows an interesting fractal behavior of the temporal variations of the electronic density and of the geomagnetic field. A good correlation between the two phenomena has been observed. The comparison of the results of the Ebro ((40.82N, 0.49E), Spain) and Tamanrasset (TAM(22.79N, 5.53E), Algeria) observatory data shows interesting longitudinal/latitudinal effects.

Ali, Moulayali; Zaourar, Naima; Abdessalem, Abtout; Mohamed, Hamoudi

2010-05-01

300

Artificial plasma cusp generated by upper hybrid instabilities in HF heating experiments at HAARP  

NASA Astrophysics Data System (ADS)

High Frequency Active Auroral Research Program digisonde was operated in a fast mode to record ionospheric modifications by the HF heating wave. With the O mode heater of 3.2 MHz turned on for 2 min, significant virtual height spread was observed in the heater off ionograms, acquired beginning the moment the heater turned off. Moreover, there is a noticeable bump in the virtual height spread of the ionogram trace that appears next to the plasma frequency (~ 2.88 MHz) of the upper hybrid resonance layer of the HF heating wave. The enhanced spread and the bump disappear in the subsequent heater off ionograms recorded 1 min later. The height distribution of the ionosphere in the spread situation indicates that both electron density and temperature increases exceed 10% over a large altitude region (> 30 km) from below to above the upper hybrid resonance layer. This "mini cusp" (bump) is similar to the cusp occurring in daytime ionograms at the F1-F2 layer transition, indicating that there is a small ledge in the density profile reminiscent of F1-F2 layer transitions. Two parametric processes exciting upper hybrid waves as the sidebands by the HF heating waves are studied. Field-aligned purely growing mode and lower hybrid wave are the respective decay modes. The excited upper hybrid and lower hybrid waves introduce the anomalous electron heating which results in the ionization enhancement and localized density ledge. The large-scale density irregularities formed in the heat flow, together with the density irregularities formed through the parametric instability, give rise to the enhanced virtual height spread. The results of upper hybrid instability analysis are also applied to explain the descending feature in the development of the artificial ionization layers observed in electron cyclotron harmonic resonance heating experiments.

Kuo, Spencer; Snyder, Arnold

2013-05-01

301

Turbulent spreading of artificial periodic inhomogeneities in the lower ionsphere  

SciTech Connect

We discuss the turbulent relaxation of artificial periodic electron density inhomogeneities (lattices) under conditions characteristic of the D region of the ionosphere. For uniform, isotropic turbulence, the relaxation time is determined by the mean square velocity of turbulent motion and the scale of the inhomogeneity.

Gershman, B.N.; Ruzhov, Y.A.

1984-04-01

302

Whistler wave-induced ionospheric plasma turbulence: Source mechanisms and remote sensing  

NASA Astrophysics Data System (ADS)

We report a series of experiments conducted at Arecibo Observatory in the past, aimed at the investigation of 40.75 kHz whistler wave interactions with ionospheric plasmas and the inner radiation belts at L=1.35. The whistler waves are launched from a Naval transmitter (code-named NAU) operating in Aguadilla, Puerto Rico at the frequency and power of 40.75 kHz and 100 kW, respectively. Arecibo radar, CADI, and optical instruments were used to monitor the background ionospheric conditions and detect the induced ionospheric plasma effects. Four-wave interaction processes produced by whistler waves in the ionosphere can excite lower hybrid waves, which can accelerate ionospheric electrons. Furthermore, whistler waves propagating into the magnetosphere can trigger precipitation of energetic electrons from the radiation belts. Radar and optical measurements can distinguish wave-wave and wave-particle interaction processes occurring at different altitudes. Electron acceleration by different mechanisms can be verified from the radar measurements of plasma lines. To facilitate the coupling of NAU-launched 40.75 kHz whistler waves into the ionosphere, we can rely on naturally occurring spread F irregularities to serve as ionospheric ducts. We can also use HF wave-created ducts/artificial waveguides, as demonstrated in our earlier Arecibo experiments and recent Gakona experiments at HAARP. The newly constructed Arecibo HF heater will be employed in our future experiments, which can extend the study of whistler wave interactions with the ionosphere and the magnetosphere/radiation belts as well as the whistler wave conjugate propagation between Arecibo and Puerto Madryn, Argentina.

Pradipta, R.; Rooker, L. A.; Whitehurst, L. N.; Lee, M. C.; Ross, L. M.; Sulzer, M. P.; Gonzalez, S.; Tepley, C.; Aponte, N.; See, B. Z.; Hu, K. P.

2013-10-01

303

Studying the Lunar Ionosphere with SELENE Radio Science Experiment  

NASA Astrophysics Data System (ADS)

Lunar ionosphere is generally thought to be as thin as 1 cm-3; the process that will prevent the accumulation of newly produced ions near the lunar surface is the impingement of the solar wind magnetic field on the lunar surface, which induces an electric field that sweeps away ions. In harmony with this prediction, most of the radio occultation experiments performed with radio stars failed to detect the lunar ionosphere. Radio occultation experiments conducted with the Soviet Luna 19 and 22 spacecraft, on the other hand, detected large electron densities near the dayside lunar surface. Vyshlov (1974) obtained peak electron densities of 500--1000 cm-3 at heights of 5--10 km, with a gradual decrease at higher altitudes with a scale height of 10--30 km. The measured densities are difficult to explain theoretically, and thus the generation mechanism of the lunar ionosphere is a major issue, with even the validity of the previous observations still under debate. If a thick lunar ionosphere exists, possible mechanisms to maintain the ionized layer are the effect of the remnant magnetic field which stands off the solar wind magnetic field, certain processes that enhance the neutral gas concentration, or charged dust grains that are lifted up by the near-surface electric field. The electron density profiles above the lunar surface are being observed by radio occultation during the SELENE (KAGUYA) mission using sub-satellites. The systematic measurements will establish the morphology of the lunar ionosphere and reveal its dependence on various conditions, thereby providing clues to the generation mechanism. The S-band (2.2GHz) and X-band (8.5GHz) signals transmitted by the Vstar sub- satellite is received at the Usuda Deep Space Center in Japan. The most serious error source is the temporal variation in the terrestrial ionosphere during measurements. In the region where the contribution of the lunar ionosphere is virtually absent, i.e. at altitudes above ~100 km, a gradual variation caused by the terrestrial ionosphere is observed. This variation is extrapolated into the near-moon portion and subtracted from the observed one, thereby eliminating the influence of the terrestrial ionosphere to some extent. In addition to this method, we also use the Rstar sub- satellite, which transmits coherent two signals in S-band, to measure the terrestrial ionosphere during the lunar occultation of Vstar; the subtraction of the Rstar's measurement from the Vstar's measurement gives the lunar ionosphere. The opportunities of the latter method are rather limited, however. More than 100 measurements using Vstar and more than 10 measurements using Rstar and Vstar have been conducted during the first half of the mission. Although the error due to the fluctuation of the terrestrial ionosphere is rather significant, there seems to be a tendency that the electron density increases on the morning side of the moon.

Imamura, T.; Iwata, T.; Yamamoto, Z.; Mochizuki, N.; Kono, Y.; Matsumoto, K.; Liu, Q.; Noda, H.; Hanada, H.; Oyama, K.; Nabatov, A.; Futaana, Y.; Saito, A.; Ando, H.

2008-12-01

304

Fading in the HF ionospheric channel and the role of irregularities  

NASA Astrophysics Data System (ADS)

It is well known that the ionosphere affects radio wave propagation especially in the high frequency (HF) range. HF radio waves reflected by the ionosphere can reach considerable distances, often with changes in amplitude, phase, and frequency. The ionosphere is a dispersive in frequency and time, bi-refractive, absorbing medium, in which multipath propagation due to traveling irregularities is very frequent. The traveling irregularities undulate the reflecting ionospheric layer, introducing variations in signal amplitude (fading). In this multipath time variant channel fading is mainly considered, even though it is not the sole effect. Echo signals from a single reflection, as in ionospheric vertical sounding (VIS) techniques, are affected by a certain degree of variability even in quiet ionospheric conditions. In this work the behavior of the ionospheric channel is studied and characterized by observing the power variation of received echoes using the VIS technique. Multipath fading was analyzed quantifying the power variation of the signal echo due to irregularities on a temporal scale from 0.5 to 256 s. An experimental set-up derived from an ionosonde was implemented and the analysis was performed employing a special numerical algorithm operating off-line on the acquired time sequence of the signal. The gain-loss of the irregularity shapes are determined in some special cases.

Bianchi, C.; Baskaradas, J. A.; Pezzopane, M.; Pietrella, M.; Sciacca, U.; Zuccheretti, E.

2013-08-01

305

Downward Mapping of Equatorial Ionospheric Electric Fields.  

National Technical Information Service (NTIS)

The problem of downward mapping of equatorial ionospheric electric fields is studied in two dimensions. Numerical solutions are shown and are compared with the corresponding ones for high latitudes. It is found that ionospheric electric fields can map dow...

W. D. Gonzalez S. L. G. Dutra A. L. C. Gonzalez A. E. C. Pereira

1985-01-01

306

Ionospheric Perturbations and Schumann Resonance Data.  

National Technical Information Service (NTIS)

The properties of the first Schumann resonance mode are examined experimentally and theoretically to determine the influence of ionospheric disturbance events upon the electromagnetic earth-ionosphere cavity. On the experimental side, a phase-sensitive tr...

P. H. Nelson

1967-01-01

307

Plasma sheet boundary layer  

Microsoft Academic Search

The plasma sheet boundary layer is a temporally variable transition region located between the magnetotail lobes and the central plasma sheet. We have made a survey of these regions by using particle spectra and three-dimensional velocity-space distributions sampled by the ISEE 1 LEPEDEA. Ion composition measurements obtained by the Lockhead ion mass spectrometers indicate that ionospheric ions play a crucial

T. E. Eastman; L. A. Frank; W.K. Peterson; W. Lennartsson

1984-01-01

308

MSI Student Project to Investigate Ionospheric Disturbances  

Microsoft Academic Search

Students at the City University of New York are designing a CubeSat, CUNYSAT-1 with the scientific objective of investigating ionospheric disturbances. Using GPS signals, scintillation measurements obtain signals from GPS satellites and are widely used for measuring rapid disturbances of the ionospheric charge densities (ionospheric scintillations). The ionospheric scintillation experiment will include a 12-channel L1 C\\/A code GPS receiver collecting

V. Shekoyan; P. Marchese; S. Austin; M. Peck; C. Watkins; M. Vittadello

2009-01-01

309

Formation and evolution of dusty plasma structures in the ionosphere  

NASA Astrophysics Data System (ADS)

A self-consistent model of the formation and evolution of dusty plasma structures in the ionosphere has been developed. The effect of the initial distributions of dust particles, as well as condensation and absorption of water molecules by dust particles, on the formation of noctilucent clouds and polar mesosphere summer echoes has been demonstrated. The possibility of the formation of a layered structure of noctilucent clouds has been illustrated.

Dubinskii, A. Yu.; Popel, S. I.

2012-09-01

310

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

311

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

312

Ionospheric Signatures Associated with the 21 February 2008 Svalbard Earthquake  

NASA Astrophysics Data System (ADS)

Previous studies have used different methods to search for a correlation between earthquakes and ionospheric perturbations, including VLF/LF propagation, TEC data, and data from the DEMETER satellite. This study looks for ionospheric disturbances associated with the 21 February 2008 Svalbard earthquake using the EISCAT Svalbard radar(ESR). This earthquake had a moment magnitude of 6.0 and occurred during the International Polar Year(IPY) 2007-2008. As part of the IPY-ICESTAR project the ESR ran continuously during a full year from March 2007 to February 2008, and therefore we have continuous measurements from the time of the earthquake. This is a unique opportunity to study the effects of an earthquake in the ionosphere. From the EISCAT radar, information about electron density, electron temperature, ion temperature and vertical ion velocity, together with the uncertainties of these, for a range of different altitudes, are determined. In this study the main focus has been on a search for signatures in the D-layer electron density. In addition a search for signatures in VLF signals is carried out. Different theories, as enhanced radon emission from the ground and acoustic gravity waves, have been proposed to explain the cause of possible ionospheric signatures associated with earthquakes. The results obtained will be used to test these theories.

Bjoland, L.; Østgaard, N.; Oksavik, K.; Atakan, K.

2012-04-01

313

Gyrotropic waves in the mid-latitude ionosphere  

NASA Astrophysics Data System (ADS)

The propagation of electromagnetic ULF perturbations in the thin conductive ionospheric layer in the magnetic meridian plane is considered. The dispersion relation for the waves propagating in the horizontal direction is obtained accounting for the influence of the conjugate ionosphere. The dependence of the phase velocity and absorption coefficient as the function of the wave frequency and magnetic field inclination are found. It is shown that in the frequency range 0.001 1 Hz the phase velocity increases from a few units to a few tenths of km/s depending on the frequency and so far follows the approximate dependence ?. The phase velocity decreases with the increase in the magnetic field inclination. The propagation of quasi-harmonic and unipolar impulses of gyrotropic waves in the horizontal direction is analyzed. The dependence of their characteristics on the values of conductivity tensor components and on the magnetic field inclination is evaluated. The generation of gyrotropic waves by the electromagnetic field of atmospheric origin in the presence of ionospheric inhomogeneities is considered. The calculation of the power spectra of the geomagnetic field oscillations at the ground level is carried out. The dependence of the spectrum on the magnetic field inclination is obtained. Some features of geophysical phenomena, associated with propagation of gyrotropic waves in the low ionosphere are discussed.

Sorokin, V. M.; Pokhotelov, O. A.

2005-07-01

314

A new algorithm for improved ionospheric electron density modeling  

SciTech Connect

This paper presents an algorithm that allows physical, time-dependent, ionospheric models to reproduce the measured F2 peak electron density (NmF2). The algorithm uses the measured NmF2 to adjust the entire altitude density profile in the model as it steps in time. Thus the algorithm provides an internal constraint to the electron density in addition to the usual initial and boundary constraints. If the plasma temperatures are also well modeled, the new algorithm allows a faithful reproduction of electron density profiles throughout the entire F2 layer to high altitudes. The algorithm offers a simple method of parameterizing electron density profiles from incoherent scatter radars and also extending bottom side measurements into the topside ionosphere. The improved accuracy of the model electron density will allow more accurate studies of ionospheric emissions, energy budget, and minor species densities. There may be other non-ionospheric physical systems where a similar algorithm could be applied. Any system where remote sensing measurements provide internal constraints would be a candidate. 14 refs., 2 figs.

Richards, P.G.; Torr, D.G. [Univ. of Alabama, Huntsville, AL (United States); Hagan, M.E. [NCAR, Boulder, CO (United States)] [and others

1995-06-01

315

Interplanetary Radio Transmission Through Serial Ionospheric and Material Barriers  

SciTech Connect

A usual first principle in planning radio astronomy observations from the earth is that monitoring must be carried out well above the ionospheric plasma cutoff frequency (~5 MHz). Before space probes existed, radio astronomy was almost entirely done above 6 MHz, and this value is considered a practical lower limit by most radio astronomers. Furthermore, daytime ionization (especially D-layer formation) places additional constraints on wave propagation, and waves of frequency below 10-20 MHz suffer significant attenuation. More careful calculations of wave propagation through the earth s ionosphere suggest that for certain conditions (primarily the presence of a magnetic field) there may be a transmission window well below this assumed limit. Indeed, for receiving extraterrestrial radiation below the ionospheric plasma cutoff frequency, a choice of VLF frequency appears optimal to minimize loss. The calculation, experimental validation, and conclusions are presented here. This work demonstrates the possibility of VLF transmission through the ionosphere and various subsequent material barriers. Implications include development of a new robust communications channel, communications with submerged or subterranean receivers / instruments on or offworld, and a new approach to SETI.

Fields, David [ORNL; Kennedy, Robert G [ORNL; Roy, Kenneth I [ORNL; Vacaliuc, Bogdan [ORNL

2013-01-01

316

An empirical model of ionospheric foE over Wuhan  

NASA Astrophysics Data System (ADS)

Daytime half-hourly values of the critical frequency of the ionospheric E-layer, foE, obtained at Wuhan Ionospheric Observatory (geographic 114.4°E, 30.6°N; 45.2°dip), China, during the whole interval of 1957- 1991 and 1999-2004 have been used to develop an empirical model. The model, including variations with local time, day number and solar cycle, is in agreement with the observations. A comparison between our model and IRI and Titheridge's model has also been made. Statistically, our model gives a better performance than IRI and Titheridge's model because data set is obtained with our own station. Both the IRI and Titheridge's model overestimate foE especially in May to September months. Combing with past investigations, we suggest that overestimation of ionospheric parameters by IRI may be a common feature in East Asia. This result is very helpful for both the correction of IRI in East Asia and the development of Chinese Reference Ionosphere (CRI) model.

Yue, X.; Wan, W.; Liu, L.; Ning, B.

2006-03-01

317

A new midlatitude ionosphere electrodynamics coupling model (MIECO): Latitudinal dependence and propagation of medium-scale traveling ionospheric disturbances  

NASA Astrophysics Data System (ADS)

In order to study nighttime medium-scale traveling ionospheric disturbances (MSTIDs), we have developed a new midlatitude ionosphere electrodynamics coupling model (MIECO) which can model the coupling process between the E and F regions with dipole magnetic field lines. Using the new model, MSTID structure is reproduced from random perturbation on an Es layer by the coupled Perkins and sporadic-E (Es)-layer instabilities in a wide latitudinal range. A typical wavelength of ˜150 km, larger amplitude, and smaller MSTID's tilt angles at lower latitudes are consistent with observations. It is shown that the polarization process in the E region driven by neutral winds is essentially important for the full development of MSTIDs as well as the seeding of NW-SE perturbation in the F region.

Yokoyama, Tatsuhiro; Hysell, David L.

2010-04-01

318

The role of planetary waves in the atmosphere-ionosphere interactions  

NASA Astrophysics Data System (ADS)

The main mechanism of interaction between lower neutral atmosphere and ionosphere are the upward propagating atmospheric planetary waves. In the Institute of Solar-Terrestrial Physics RAS the experimental investigations of the interaction between different atmospheric layers from the stratosphere up to ionospheric E- and F-regions were carried out. The long-term database of some midlatitude upper atmosphere parameters was used (the horizontal thermosphere/ionosphere wind, the minimal vertically reflected from the ionosphere radio-frequency fmin, total ozone content, stratospheric temperature). The seasonal variations and significant non-zonality (longitudinal dependence) of the quasi-periodical structure were revealed. The influence of solar and geomagnetic activity periodicities from above and stratospheric thermo-baric field from below on the upper atmosphere processes is evaluated. In spite of significant changeability of planetary waves in the atmosphere-ionosphere system (from day to day, seasonal, from year to year, with solar cycle etc.) there are some similarities for the different atmospheric layers. The empirical model for the lower thermosphere wind field quasi-periodical structure was constructed. It is shown that increasing of planetary waves (wave-numbers 1 and 2) activity leads to the decreasing of the prevailing zonal wind velocity. We consider the atmosphere-ionosphere planetary waves as indicators of the complex disturbances in the Sun-Earth system and important element of upper atmosphere climate.

Kokourov, Victor D.; Vergasova, Galina V.; Kazimirovsky, Edward S.

2004-12-01

319

Trends in the ionospheric E and F regions over Europe  

NASA Astrophysics Data System (ADS)

Continuous observations in the ionospheric E and F regions have been regularly carried out since the fifties of this century at many ionosonde stations. Using these data from 31 European stations long-term trends have been derived for different parameters of the ionospheric E layer (h' E, foE), F1 layer (foF1) and F2 layer (hmF2, foF2). The detected trends in the E and F1 layers (lowering of the E region height h'E; increase of the peak electron densities of the E and F1 layers, foE and foF1) are in qualitative agreement with model predictions of an increasing atmospheric greenhouse effect. In the F2 region, however, the results are more complex. Whereas in the European region west of 30° E negative trends in hmF2 (peak height of the F2 layer) and in the peak electron density (foF2) have been found, in the eastern part of Europe (east of 30° E) positive trends dominate in both parameters. These marked longitudinal differences cannot be explained by an increasing greenhouse effect only, here probably dynamical effects in the F2 layer seem to play an essential role.

Bremer, J.

1998-08-01

320

Ionospheric signatures of magnetospheric convection  

NASA Astrophysics Data System (ADS)

The average patterns of ionospheric convection observed with the Chatanika incoherent scatter radar, when mapped along magnetic field lines to the equatorial plane, delineate regions of earthward convection within the magnetotail that either proceed sunward to the dayside magnetopause (where reconnection with the IMF can occur) or that join the antisunward circulation along the magnetospheric flanks at dusk and dawn. An examination of summer and winter ionospheric convection patterns in terms of the corresponding magnetospheric circulation patterns shows that ionospheric ionization troughs at dusk and dawn are associated with the sunward convection of low density plasma from the night sector, and that plasma in the vicinity of the dawn and dusk electric field reversals circulates at high latitudes away from the solar ionization source at noon. Plasma exiting from the polar cap is convected away from midnight in the equatorward portion of the regions of sunward convection at auroral latitudes.

Foster, J. C.

1984-02-01

321

Artificial intelligence  

SciTech Connect

This book presents papers on artificial intelligence. Topics considered include knowledge engineering, expert systems, applications of artificial intelligence to scientific reasoning, planning and problem solving, error recovery in robots through failure reason analysis, programming languages, natural language, speech recognition, map-guided interpretation of remotely-sensed imagery, and image understanding architectures.

Firschein, O.

1984-01-01

322

Artificial Intelligence.  

ERIC Educational Resources Information Center

|Overview of the artificial intelligence (AI) field provides a definition; discusses past research and areas of future research; describes the design, functions, and capabilities of expert systems and the "Turing Test" for machine intelligence; and lists additional sources for information on artificial intelligence. Languages of AI are also…

Thornburg, David D.

1986-01-01

323

Study of Nightitme enhancement of ionospheric parameters  

NASA Astrophysics Data System (ADS)

In the present work ionospheric electron content (IEC) as well as critical frequency of F2-layer (foF2) data from three locations (low, mid and high) latitudes have been used to study the anomalous nighttime F-region during low to moderate solar activity period i.e. from January 2006 to December 2010. Our results show that at high and mid latitude locations percentage of enhancement with IEC and foF2 is maximum during winter, whereas at low latitude location maximum percentage of enhancement with both the parameters is maximum during equinox. Out of 1176 number of enhancements for IEC, 661 enhancements occurred during pre-midnight hours and 515 occurred during post-midnight hours. Although for foF2 parameter out of 948 enhancements, 457 enhancements occurred during pre-midnight hours and 491 enhancements occurred during post-midnight hours.

Sardar, Nuzhat

2012-07-01

324

Artificial blood  

PubMed Central

Artificial blood is a product made to act as a substitute for red blood cells. While true blood serves many different functions, artificial blood is designed for the sole purpose of transporting oxygen and carbon dioxide throughout the body. Depending on the type of artificial blood, it can be produced in different ways using synthetic production, chemical isolation, or recombinant biochemical technology. Development of the first blood substitutes dates back to the early 1600s, and the search for the ideal blood substitute continues. Various manufacturers have products in clinical trials; however, no truly safe and effective artificial blood product is currently marketed. It is anticipated that when an artificial blood product is available, it will have annual sales of over $7.6 billion in the United States alone.

Sarkar, Suman

2008-01-01

325

The effects of modification of a high-latitude ionosphere by high-power HF radio waves. Part 1. Results of multi-instrument ground-based observations  

Microsoft Academic Search

We present the results of multi-instrument experiments related to studying the phenomena in the high-latitude ionosphere affected by high-power radio waves using the EISCAT technical facilities. It was found for the first time that strong small-scale artificial field-aligned irregularities (AFAIs) are excited when the ionospheric F region is heated by a high-power HF radio wave with X-mode polarization near the

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

2011-01-01

326

The effects of modification of a high-latitude ionosphere by high-power HF radio waves. Part 1. Results of multi-instrument ground-based observations  

Microsoft Academic Search

We present the results of multi-instrument experiments related to studying the phenomena in the high-latitude ionosphere affected\\u000a by high-power radio waves using the EISCAT technical facilities. It was found for the first time that strong small-scale artificial\\u000a field-aligned irregularities (AFAIs) are excited when the ionospheric F region is heated by a high-power HF radio wave with X-mode polarization near the

N. F. Blagoveshchenskaya; f T. D. Borisova; T. K. Yeoman; M. T. Rietveld

2011-01-01

327

Simulations of Ionospheric Storms using a Coupled Magnetosphere-Ionosphere-Thermosphere Model  

NASA Astrophysics Data System (ADS)

The Coupled Magnetosphere Ionosphere Thermosphere (CMIT) model combines the Lyon-Fedder-Mobarry (LFM) global magnetospheric simulation model with the NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model. It simulates the interaction of the magnetosphere and ionosphere in the auroral regions by imposing energetic particle fluxes derived from the magnetospheric current system on the thermosphere-ionosphere model, and using the ionospheric conductance calculated by the three-dimensional interactive thermosphere-ionosphere model as the inner boundary condition of the magnetospheric MHD calculation. New advances in the CMIT model include the imposition of neutral wind forcing on the magnetosphere-ionosphere current system, and the inclusion of global ionospheric electrodynamics. We describe simulations of ionospheric changes during geomagnetic disturbances performed using the CMIT model, driven both by measured solar wind parameters upstream of the magnetosphere and by heliospheric models, and discuss new directions in coupled geospace model development.

Solomon, S. C.

2005-12-01

328

Long-lived artificial ion clouds in the earth's ionosphere  

SciTech Connect

The authors report on two observations made over the Caribbean during the summer of 1991 of barium ion cloud releases, ten hours after the clouds were released. One release was made in the morning twilight, and one in the evening twilight, and each was observed again in the following twilight period by a low light level TV imager and a TV spectrograph onboard a Russian research vessel. These observations were very surprising at the time, but the authors present arguments as to why in retrospect they may not be so unusual in practise. Such cloud releases may provide very sensitive tests of ionspheric convection models.

Milinevsky, G.P. (Kiev Univ., Ukraine (Russian Federation)); Kashirin, A.I. (NPO Typhoon, Obninsk (Russian Federation)); Romanovsky, Yu.A. (Institute of Applied Geophysics, Moscow (Russian Federation)); Stenbaek-Nielson, H.C. (Univ. of Alaska, Fairbanks (United States)); Kelley, M.C. (Cornell Univ., Ithaca, NY (United States))

1993-06-07

329

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

330

Using Radio-Induced Aurora to Observe Ionospheric Irregularities  

NASA Astrophysics Data System (ADS)

Two-dimensional images of F- and E- layers have been obtained using the technique called radio-induced aurora (RIA). This technique makes the plasma layers glow in the ionosphere glow when being stimulated by high power radio waves. Normally the irregularities in the ionosphere do not radiate strong enough visible emissions to be observed from the ground. Experiments at Arecibo Observatory in Puerto Rico and the SURA facility in Russia have shown that the plasma structures can be made to glow at 630.0 nm, 557.7 nm and other wavelengths by illuminating them by HF radio waves with effective radiated powers of 80 megawatts. The regions of the sporadic-E layers that have electron densities greater than the critical density for reflection of the radio waves emit electrons that collide with and excite atmospheric atomic oxygen and molecular nitrogen. A charge-coupled-device (CCD) imager located on the ground is used to capture images of the glowing E and F-region structures. The camera exposure- times were in the range of 15 to 45 seconds. The images obtained using this technique show a wide variety of both field-aligned and wind-aligned irregularities. Some layers cover the antenna pattern cone illuminated by the radio wave beam. Other layers show strong modulations by both plasma and neutral instabilities. Two-dimensional computer simulations of the coupling between neutral winds, electric fields and the ion layers simulate the structure in the images.

Bernhardt, P.; Gondarenko, N.; Guzdar, P.; Huba, J.; Ossakow, S.; Djuth, F.; Tepley, C.; Sulzer, M.; Kagan, L.; Kelley, M.

331

A Campaign to Study Equatorial Ionospheric Phenomena over Guam  

NASA Astrophysics Data System (ADS)

With the development of a series of ground-based and space-based experiments, the United States Air Force Academy (USAFA) is in the process of planning a campaign to investigate the relationship between equatorial ionospheric plasma dynamics and a variety of space weather effects, including: 1) ionospheric plasma turbulence in the F region, and 2) scintillation of radio signals at low latitudes. A Digisonde Portable Sounder DPS-4 will operate from the island of Guam (with a magnetic latitude of 5.6° N) and will provide measurements of ionospheric total electron content (TEC), vertical drifts of the bulk ionospheric plasma, and electron density profiles. Additionally, a dual-frequency GPS TEC/scintillation monitor will be located along the Guam magnetic meridian at a magnetic latitude of approximately 15° N. In campaign mode, we will combine these ground-based observations with those collected from space during USAFA's FalconSAT-3 and FalconSAT-5 low-earth orbit satellite missions, the first of which is scheduled to be active over a period of several months beginning in the 2007 calendar year. The satellite experiments are designed to characterize in situ irregularities in plasma density, and include measurements of bulk ion density and temperature, minority-to- majority ion mixing ratios, small scale (10 cm to 1 m) plasma turbulence, and ion distribution spectra in energy with sufficient resolution for observations of non-thermalized distributions that may be associated with velocity- space instabilities. Specific targets of investigation include: a) a comparison of plasma turbulence observed on- orbit with spread F on ionograms as measured with the Digisonde, b) a correlation between the vertical lifting of the ionospheric layer over Guam and the onset of radio scintillation activity along the Guam meridian at 15° N magnetic latitude, and c) a correlation between on-orbit turbulence and ionospheric scintillation at 15° N magnetic latitude. These relationships may provide further clues into understanding the trigger mechanisms responsible for instigating disturbances in the ionospheric plasma, thus resulting in a turbulent radio propagation medium that may cause outages of radio based communication and navigation systems.

Habash Krause, L.; Balthazor, R.; Dearborn, M.; Enloe, L.; Lawrence, T.; McHarg, M.; Petrash, D.; Reinisch, B. W.; Stuart, T.

2007-05-01

332

Tomographic estimation of the ionosphere using terrestrial GPS sensors  

NASA Astrophysics Data System (ADS)

The ionosphere is a region of partially ionized plasma in Earth's upper atmosphere distributed in layers of varying free electron density. The free electrons change the local index of refraction causing radio waves propagating in the ionosphere to be delayed and bent. Trans-ionospheric propagation of GPS radio signals transmitted from satellites provides observations, in a tomographic sense, of the electron density field by measuring the amount of delay and/or bending. Tomographic estimation of the ionosphere is attractive for two reasons: one, the number of measurements grows as the product of the number of transmitters and receivers whereas for in situ techniques the number grows linearly in the number of sensors; two, the smoothing function of the integral operator makes the measurements most sensitive to large scale structure. A three-dimensional tomographic inversion algorithm is implemented as a real time process ingesting live measurements from a network of dual frequency GPS reference receivers. The tomographic inversion technique is based on a state space model encompassing ionospheric parameters as well as certain measurement biases in the GPS satellite transmitters and reference receivers. Three different state space models were constructed using discrete spectra, separable lattice wavelets, and a hybrid of separable and non-separable two-dimensional wavelets. The primary purpose of the real-time estimator is to provide an ionospheric model for correcting range delay errors on GPS measurements to differentially improve the position solution for aviation applications. Specifically, the Federal Aviation Administration is developing the Wide Area Augmentation System (WAAS) for GPS where positioning accuracy on the order of ones of meters is coupled with a six second time to alarm in the aircraft. In this application the real-time estimator ingests measurements from the GPS reference receiver network, applies the tomographic inversion to form an ionospheric model and transmits that model through a low bandwidth broadcast data link to the aircraft. Further, the estimator must provide a confidence interval for each and every correction to protect the navigation solution. Indeed this latter function is the most ambitious and critical in safety of life operations such as precision approach.

Hansen, Andrew Jakob

2002-09-01

333

Equatorial ionospheric irregularities produced by the Brazilian ionospheric modification experiment (BIME)  

SciTech Connect

On two separate evenings in September 1982, rockets were launched into the bottomside equatorial F{sub 2} region off the coast of Natal, Brazil, to inject chemicals, consisting of mainly H{sub 2}O and CO{sub 2}, to create a hole in ionization. The chemicals were injected near the height where the density gradient was steepest, and at a time when the F{sub 2} region was rising rapidly to see whether plasma bubble irregularities could be generated from instabilities triggered by the ionization hole. On both occasions, hole-induced depletions in total electron content (TEC) of more than 10{sup 16} el/m{sup 2} were observed over horizontal distances of at least 60 km from the chemical injection point. The eastward drifts of these artificial depletions were observed by the time difference in the TEC features observed at various TEC monitoring stations, and from the changing range of oblique ionosonde echoes observed by an ionosonde located 300 km magnetically east of the chemical release point. Their subsequent evolution into plasma bubble irregularities was demonstrated from the observations of spread F echoes, strong amplitude scintillation, and TEC depletion at distances of from 300 to 500 km eastward of the release points. The fact that similar behavior of the ionosphere was observed during the evenings of both rocket chemical releases, and on no other nights of the campaign, is strong evidence of successful artificial generation of bubble irregularities by chemical injection into the bottomside F{sub 2} region.

Klobuchar, J.A. (Air Force Geophysics Lab., Hanscom Air Force Base, MA (USA)); Abdu, M.A. (Instituto de Pesquisas Espaciais, Sao Jose dos Campos (Brazil))

1989-03-01

334

Artificial urushi.  

PubMed

A new concept for the design and laccase-catalyzed preparation of "artificial urushi" from new urushiol analogues is described. The curing proceeded under mild reaction conditions to produce the very hard cross-linked film (artificial urushi) with a high gloss surface. A new cross-linkable polyphenol was synthesized by oxidative polymerization of cardanol, a phenol derivative from cashew-nut-shell liquid, by enzyme-related catalysts. The polyphenol was readily cured to produce the film (also artificial urushi) showing excellent dynamic viscoelasticity. PMID:11763444

Kobayashi, S; Uyama, H; Ikeda, R

2001-11-19

335

Ionospheric Heating by Hydromagnetic Waves  

Microsoft Academic Search

The rate of energy dissipation per umt volume is investigated for hydromagnetic waves traveling downward through the ionosphere. A calculation of the heating rate is made, based on assumptions as to the amplitude and Fourier spectrum of the hydromagnetic waves. It is argued in a general way that the peak heating rate due to hydromagnetic waves occurs near 175 kilometers.

A. J. Dessler

1959-01-01

336

Ionospheric mapping computer contouring techniques  

NASA Astrophysics Data System (ADS)

Established methods of generating uniform grids of scalar quantities from irregularly disposed known values are applied to the development of regional maps of ionospheric characteristics for individual instants of time. Figure-of-merit comparisons are presented to show the general superiority of one particular technique. Ways of supplementing measured input values with 'screen-point' synthesized data are outlined.

Samardjiev, T.; Bradley, P. A.; Cander, Lj. R.; Dick, M. I.

1993-09-01

337

Thermosphere and Ionosphere of Venus.  

National Technical Information Service (NTIS)

Our knowledge of the upper atmosphere and ionosphere of Venus and its interaction with the solar wind has advanced dramatically over the last decade, largely due to the data obtained during the Pioneer Venus mission and to the theoretical work that was mo...

T. E. Cravens

1992-01-01

338

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

339

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

340

Artificial Aerosols.  

National Technical Information Service (NTIS)

This volume contains the technical proceedings of the Workshop on Artificial Aerosols held in Vail, Colorado, June 19-20, 1979. The workshop reviewed the state-of-the-art of chemically, aerodynamically or pyrotechnically produced aerosols and identified f...

A. Deepak L. H. Ruhnke

1980-01-01

341

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

342

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

343

Prediction and analysis of the cathode catalyst layer performance of proton exchange membrane fuel cells using artificial neural network and statistical methods  

Microsoft Academic Search

A mathematical model was developed to investigate the cathode catalyst layer (CL) performance of a proton exchange membrane fuel cell (PEMFC). A numerous parameters influencing the cathode CL performance are implemented into the CL agglomerate model, namely, saturation and eight structural parameters, i.e., ionomer film thickness covering the agglomerate, agglomerate radius, platinum and carbon loading, membrane content, gas diffusion layer

N. Khajeh-Hosseini-Dalasm; S. Ahadian; K. Fushinobu; K. Okazaki; Y. Kawazoe

2011-01-01

344

Interplanetary drivers of ionospheric prompt penetration electric fields  

NASA Astrophysics Data System (ADS)

In this paper we discussed the penetration effects of common interplanetary magnetic cloud (MC) structures like sheath region, both sheath and magnetic cloud boundary layer (MCBL), MC body, and shock-running into a preceding MC on the equatorial ionosphere during intense (SYM-H ?-100 nT) geomagnetic storms. Using solar wind data obtained from the ACE and WIND spacecraft, we have identified these four types of MC structures responsible for the electric field penetration events detected by Jicamarca incoherent scatter radar. After elimination of the propagation delay, the observations show that the equatorial electric field (EEF) was changed immediately following the arrival of solar wind disturbance. Moreover, the duration of EEF corresponded well with that of the corresponding MC structure interval. We suggest that identifying the solar wind structures associated with penetration electric field may shed light on the understanding of the penetration processes and further help exploring their effects on the ionospheric plasma.

Guo, Jianpeng; Feng, Xueshang; Zuo, Pingbing; Zhang, Jie; Wei, Yong; Zong, Qiugang

2011-01-01

345

Artificial Development  

Microsoft Academic Search

Artificial Development is a field of Evolutionary Computation inspired by the developmental processes and cellular growth\\u000a seen in nature. Multiple models of artificial development have been proposed in the past, which can be broadly divided into\\u000a those based on biochemical processes and those based on a high level grammar. Two of the most important aspects to consider\\u000a when designing a

Arturo Chavoya

2009-01-01

346

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

347

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

348

Extreme Space Weather: Storm Enhanced Density in the Ionosphere and Magnetosphere  

NASA Astrophysics Data System (ADS)

During geomagnetic storms the equilibrium of production and loss which maintains average ionospheric characteristics is greatly perturbed. High-latitude disturbance electrodynamics penetrates to the equator and dayside ionospheric total electron content (TEC) is greatly enhanced as solar-produced plasma is uplifted into regions of decreased ion-neutral collision-induced recombination. During extreme events dayside mid-latitude TEC can exceed 200 TECu (1 TECu = 1.E16 electrons m-2). At higher altitudes, interactions in the plasmasphere boundary layer involving hot ring current particles and the outer regions of the cold plasmasphere (the high-altitude extent of the mid-latitude ionosphere) lead to the formation of a broad sub-auroral polarization stream (SAPS) flow channel which transports high-TEC plasma poleward and noonward to the ionospheric footprint of the cusp and onto polar cap magnetic field lines. These high-TEC storm enhanced density (SED) plumes mirror the erosion of the outer plasmasphere. This overall process produces large TEC and TEC gradients at ionospheric heights and significantly impacts magnetospheric processes and particle precipitation effects as the heavy ionospheric SED ions are injected into the magnetosphere, altering both the progression of storm development and subsequent inner magnetosphere/ring current characteristics. In this talk we investigate the processes and physical causes of extreme SED plumes originating in the North American longitude sector.

Foster, J. C.; Coster, A. J.; Erickson, P. J.; Rideout, W.

2011-12-01

349

Electromagnetic Measurements of the Ionosphere at the Ionospheric Station of Rome. EUROCAP Program.  

National Technical Information Service (NTIS)

The project is a continuation of previous EURO CAP PROGRAM agree-ent with the European Research Office. Continuous ionospheric vertical soundings (every hour, every day) have been performed at the ionospheric station of Rome during the period from Novembe...

1995-01-01

350

Observations of aspect sensitive RF-enhanced incoherent backscatter in the polar cap ionosphere  

Microsoft Academic Search

RF-induced plasma instabilities give rise to characteristic spectral enhancements in incoherent scatter spectra. The aspect sensitivity of these enhancements provides valuable information regarding the physical processes that occur within the RF-affected ionospheric patch. These direction-dependent signatures exhibit significant variability and help shed light on possible coupling between artificial field-aligned irregularities generated at the upper-hybrid height and RF-induced instabilities excited near

Ranvir Dhillon; T. R. Robinson; Timothy K. Yeoman

2010-01-01

351

Coherent omnipresent fluctuations in the ionosphere  

NASA Astrophysics Data System (ADS)

Incoherent Scatter Radar power observations at Arecibo, Millstone Hill, and the Poker Flat AMISR have revealed the continuous presence of Coherent Omnipresent Fluctuations in the Ionosphere (COFIs) with periods ranging from roughly 30 to 60 minutes and apparent vertical wavelengths increasing with altitude from tens to hundreds of km. Upon high-pass filtering of the radar power profile and electron concentration data, the COFIs are seen unambiguously and ubiquitously in Arecibo results from 22-23 March 2004, 5-6 June, 21-25 September, and 17-20 November 2005, as well as in Millstone Hill results from 4 October to 4 November 2002. The COFIs are strong throughout the F-region, often spanning altitudes of 160 km to above 500 km, and are detected day and night in the F2-layer (above ˜ 200 km). In fact, the COFIs are seen at every time and altitude that there is sufficient plasma to produce a radar echo. The COFIs also are observed at Poker Flat, although the poor signal-to-noise ratio over segments of the data makes it difficult to determine whether or not they are always present. The consistent detection of the COFIs, along with the longitudinal alignment and large latitudinal spread of the observation sites suggests that these waves always are present over at least a major portion of the northern hemisphere. This phenomenon appears to have been reported in Total Electron Concentration (TEC) maps of the ionosphere over much of North America as well as in airglow images from Arecibo and many other mid-latitude sites around the world. These observations give us insight into the horizontal properties of the waves. Although Medium Scale Traveling Ionospheric Disturbances (MSTIDs) generally are associated with aurorally generated acoustic-gravity waves (AGWs), the properties of the COFIs may suggest otherwise. Other possible source mechanisms are presented; notably a possible link to oscillations in the solar wind and magnetosphere is described. Consistent fluctuations with periods of about an hour have been observed in magnetic field measurements taken at geosynchronous altitudes by the Geostationary Operational Environmental Satellites (GOES)-10 and -12 satellites that may be linked to the COFIs. Concurrent solar wind data from ACE are presented in an attempt to find a more primary source of the COFIs. Both the AGW and magnetospheric explanations for the COFIs are discussed, along with arguments for and against each scenario.

Livneh, Dorey Joseph

352

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

353

Symmetry and asymmetry of ionospheric weather at magnetic conjugate points for two midlatitude observatories  

NASA Astrophysics Data System (ADS)

Variations of the ionospheric weather W-index for two midlatitude observatories, namely, Grahamstown and Hermanus, and their conjugate counterpart locations in Africa are studied for a period from October 2010 to December 2011. The observatories are located in the longitude sector, which has consistent magnetic equator and geographic equator so that geomagnetic latitudes of the line of force are very close to the corresponding geographic latitudes providing opportunity to ignore the impact of the difference of the gravitational field and the geomagnetic field at the conjugate points on the ionosphere structure and dynamics. The ionosondes of Grahamstown and Hermanus provide data of the critical frequency (foF2), and Global Ionospheric Maps (GIM) provide the total electron content (TECgps) along the magnetic field line up to the conjugate point in the opposite hemisphere. The global model of the ionosphere, International Reference Ionosphere, extended to the plasmasphere altitude of 20,200 km (IRI-Plas) is used to deliver the F2 layer peak parameters from TECgps at the magnetic conjugate area. The evidence is obtained that the electron gas heated by day and cooled by night at the summer hemisphere as compared with the opposite features in the conjugate winter hemisphere testifies on a reversal of plasma fluxes along the magnetic field line by the solar terminator. The ionospheric weather W-index is derived from NmF2 (related with foF2) and TECgps data. It is found that symmetry of W-index behavior in the magnetic conjugate hemispheres is dominant for the equinoxes when plasma movement along the magnetic line of force is imposed on symmetrical background electron density and electron content. Asymmetry of the ionospheric storm effects is observed for solstices when the plasma diffuse down more slowly into the colder winter hemisphere than into the warmer summer hemisphere inducing either plasma increase (positive phase) or decrease (negative phase of W-index) in the ionospheric and plasmaspheric plasma density.

Gulyaeva, T. L.; Arikan, F.; Stanislawska, I.; Poustovalova, L. V.

2013-11-01

354

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

355

Atypical nighttime spread-F structure observed near the southern crest of the ionospheric equatorial ionization anomaly  

NASA Astrophysics Data System (ADS)

An atypical nighttime spread-F structure is observed at or above the F-layer, near the crest of the ionospheric equatorial ionization anomaly region (EIA). This ionospheric atypical spread-F phenomenon was observed using two closed spaced (~115 km) ionospheric soundings stations located in Sao Jose dos Campos (23.21 S, 45.97 W) and Cachoeira Paulista (22.70 S, 45.01W), Brazil, in a low-latitude station (near the southern crest of the EIA region), during nighttime, low solar activity, and quiet geomagnetic conditions. This structure, in the initial phase, appears as a faint spread-F trace above or at the F2-layer peak height. After a few minutes, it develops into a strong spread-F trace, and afterwards, it moves to altitudes below to the F2-layer peak heights. Finally, the atypical nighttime F-layer trace structure may remain for a while between the F-layer bottom side and peak height or can move to an altitude above the F-layer peak height, and then it disappears. In order to have a comprehensive view of the ionospheric environment characterizing the phenomenon under study, complementary GPS data were used to investigate the ionosphere environment conditions, during both events. The 6 GPS stations used in this study are distributed from near the equatorial region to low latitudes.

Fagundes, Paulo Roberto

2012-07-01

356

Tiny Ionospheric Photometer Science Program and Mission Operations on COSMIC  

Microsoft Academic Search

The Tiny Ionospheric Photometer (TIP) sensors aboard the Constellation Observing System for Meterology, Ionosphere and Climate (COSMIC) spacecraft comprise a suite of six nadir-viewing ultraviolet photometers for characterizing the Earth's nightside ionosphere. The TIP instruments complement the ionospheric capabilities of the GPS occultation experiment (GOX) by characterizing horizontal ionospheric density gradients. These photometers target OI~135.6~nm emission produced by ionospheric O+

S. A. Budzien; K. F. Dymond; D. H. Chua; C. Coker

2006-01-01

357

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

358

Ionospheric behaviour during storm recovery phase  

NASA Astrophysics Data System (ADS)

Intensive ionospheric research, numerous multi-instrumental observations and large-scale numerical simulations of ionospheric F region response to magnetic storm-induced disturbances during the last several decades were primarily focused on the storm main phase, in most cases covering only a few hours of the recovery phase following after storm culmination. Ionospheric behaviour during entire recovery phase still belongs to not sufficiently explored and hardly predictable features. In general, the recovery phase is characterized by an abatement of perturbations and a gradual return to the "ground state" of ionosphere. However, observations of stormy ionosphere show significant departures from the climatology also within this phase. This paper deals with the quantitative and qualitative analysis of the ionospheric behaviour during the entire recovery phase of strong-to-severe magnetic storms at middle latitudes for nowadays and future modelling and forecasting purposes.

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

2012-04-01

359

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

360

Ionospheric manifestations of wavelike disturbances in the atmosphere and ionosphere observed by radio tomography  

Microsoft Academic Search

Wavelike disturbances are quite often observed in the atmosphere and ionosphere These events can be caused by the influence from atmosphere and space by oscillations of the Earth surface and other phenomena In the atmosphere and ionosphere these wavelike phenomena appear as alternating areas of enhanced and depleted density in the atmosphere or electron concentration in the ionosphere In the

V. Kunitsyn; R. Ahmedov; E. Andreeva; M. Nazarenko; S. Suraev

2006-01-01

361

Investigation of the Accuracy of Ionospheric Models at Mid-Latitudes: Examining Ionospheric Metrics  

Microsoft Academic Search

The electron density specification of the ionosphere is the key parameter supporting many operational products. To assess the accuracy of tools based on space weather models of the ionosphere one must know the accuracy of the underlining models. We are developing a software\\/database package to assess the accuracy of ionospheric models. The package will be placed at the Community Coordinated

V. Eccles; J. J. Sojka; S. Gonzalez; T. J. Fuller-Rowell; M. Howsden

2004-01-01

362

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

363

The ionosphere under extremely prolonged low solar activity  

NASA Astrophysics Data System (ADS)

A critical question in ionospheric physics is the state of the ionosphere and relevant processes under extreme solar activities. The solar activity during 2007-2009 is extremely prolonged low, which offers us a unique opportunity to explore this issue. In this study, we collected the global ionosonde measurements of the F2 layer critical frequency (foF2), E layer critical frequency (foE), and F layer virtual height (h?F) and the total electron content (TEC) maps produced by the Jet Propulsion Laboratory, which were retrieved from dual-frequency GPS receivers distributed worldwide, to investigate the ionospheric phenomena during solar minimum of cycle 23/24, particularly the difference in the ionosphere between solar minima of cycle 23/24 and the preceding cycles. The analysis indicates that the moving 1 year mean foF2 at most ionosonde stations and the global average TEC went to the lowest during cycle 23/24 minimum. The solar cycle differences in foF2 minima display local time dependence, being more negative during the daytime than at night. Furthermore, the cycle difference in daytime foF2 minima is about -0.5 MHz and even reaches to around -1.2 MHz. In contrast, a complex picture presents in global h?F and foE. Evident reduction exists prevailingly in the moving 1 year mean h?F at most stations, while no huge differences are detected at several stations. A compelling feature is the increase in foE at some stations, which requires independent data for further validation. Quantitative analysis indicates that record low foF2 and low TEC can be explained principally in terms of the decline in solar extreme ultraviolet irradiance recorded by SOHO/SEM, which suggests low solar EUV being the prevailing contributor to the unusual low electron density in the ionosphere during cycle 23/24 minimum. It also verifies that a quadratic fitting still reasonably captures the solar variability of foF2 and global average TEC at such low solar activity levels.

Liu, Libo; Chen, Yiding; Le, Huijun; Kurkin, Vladimir I.; Polekh, Nelya M.; Lee, Chien-Chih

2011-04-01

364

Generation mechanisms for magnetosphere-ionosphere current systems deduced from a three-dimensional MHD simulation of the solar wind-magnetosphere-ionosphere coupling processes  

SciTech Connect

Mechanisms that generate the field-aligned current (FAC) systems in the magnetosphere-ionosphere coupling scheme by virtue of the solar wind-magnetosphere interaction are investigated with a three-dimensional magnetohydrodynamic (MHD) simulation. As a simulation scheme, the finite volume total variation diminishing (TVD) scheme on an unstructured grid system is employed for precise calculations of the ionospheric region. In the ionosphere, the divergence of the Pederson and Hall currents is matched with FAC, mainly assuming uniform conductivity. The present calculation reproduces the traditional region 1 and 2 currents in the polar ionosphere, for both the northward and southward interplanetary magnetic fields (IMFs). The calculated magnitude of the region 1 current becomes large on the dayside, in agreement with observational results. For the northward IMF, NBZ currents that dominate the entire polar cap are obtained, with a maximum on the dayside. This current is totally absent in the southward IMF result. Corresponding to the FACs, the northward IMF results in multicell convection in the polar ionosphere, and the southward IMF results in two-cell convection. On the evening side, the calculated region 1 currents flow almost along the field lines away from the Earth toward the magnetospheric low-latitude boundary layer (LLBL), then flow up the magnetopause across the field lines to high latitudes.

Tanaka, T. [Communications Research Laboratory, Tokyo (Japan)

1995-07-01

365

The high-latitude ionosphere: Geophysical basis  

NASA Astrophysics Data System (ADS)

This introductory lecture summarizes concepts of the ionosphere and the magnetosphere that are fundamental to our understanding of high-latitude ionosphere. It begins with the basic theory of the ionosphere, particularly the processes of production and loss which lead to the existence of a permanent ionosphere and render the upper atmosphere electrically conducting. The structure of the magnetosphere, which strongly affects the polar regions because of coupling along the geomagnetic field lines, is then reviewed, including the form of the magnetosphere, and the plasma and energetic particles that are contained within the magnetosphere.

Hargreaves, J. K.

1988-09-01

366

Ionospheric imaging of the southern crest of the Equatorial Ionization Anomaly over Brazil  

NASA Astrophysics Data System (ADS)

A four-dimensional time-dependent tomographic algorithm, named Multi Instrument Data Analysis System (MIDAS), is used to image the equatorial and low-latitude ionosphere over the central-eastern sides of the Brazilian territory. From differential phase data obtained by a chain of ground-based GPS receiver the total electron content (TEC) is estimated and then, together with a modeled ionosphere from International Reference Ionosphere (IRI) model, the electron density distribution is reconstructed and the parameters of the F2-peak layer are accessed from the images. This paper presents the first study of ionospheric tomography using real dual-frequency data from the Brazilian Network for Continuous GPS Monitoring (RBMC). Ionospheric F2- peak electron density (NmF2) accessed from the images are compared to concurrent measurements from three ionosondes installed across Brazil. One year of data during the solar maximum period from March/2001 to February/2002 is used to analyze the seasonal and hourly variation of the F2-layer peak density. The accuracy with which MIDAS images the electron density during geomagnetic quiet periods is investigated through its correlation and deviation with the ionosonde and IRI model data, respectively. The main aspects of the reconstruction results at the equatorial ionization anomaly (EIA) region over Brazil are highlighted and discussed.

Muella, Marcio; De Paula, Eurico; Batista, Inez S.; Mitchell, Cathryn; Paes, Ricardo R.

2012-07-01

367

Tomographic imaging of the equatorial and low-latitude ionosphere over central-eastern Brazil  

NASA Astrophysics Data System (ADS)

A four-dimensional time-dependent tomographic algorithm, named Multi Instrument Data Analysis System (MIDAS), is used to image the equatorial and low-latitude ionosphere over the central-eastern sides of the Brazilian territory. From differential phase data obtained by a chain of ground-based GPS receiver the total electron content (TEC) is estimated and then, together with a modeled ionosphere from International Reference Ionosphere (IRI) model, the electron density distribution is reconstructed and the parameters of the F2-peak layer are accessed from the images. This paper presents the first study of ionospheric tomography using real dual-frequency data from the Brazilian Network for Continuous GPS Monitoring (RBMC). Ionospheric F2-peak electron density (NmF2) accessed from the images are compared to concurrent measurements from three ionosondes installed across Brazil. One year of data during the solar maximum period from March/2001 to February/2002 is used to analyze the seasonal and hourly variation of the F2-layer peak density. The accuracy with which MIDAS images the electron density during geomagnetic quiet periods is investigated through its correlation and deviation with the ionosonde and IRI model data, respectively. The main aspects of the reconstruction results at the equatorial ionization anomaly (EIA) region over Brazil are highlighted and discussed.

Muella, M. T. A. H.; de Paula, E. R.; Mitchell, C. N.; Kintner, P. M.; Paes, R. R.; Batista, I. S.

2011-02-01

368

The ionospheric focused heating experiment  

Microsoft Academic Search

The Ionospheric Focused Heating rocket was launched on May 30, 1992. The sounding rocket carried an instrument and chemical payload along a trajectory that crossed the intersection of the beams from the 430-MHz incoherent scatter radar and the 5.1-MHz high-power radio wave facility near Arecibo. The release of 30 kg of CFâBr into the F region at 285 km altitude

P.A. Bernhardt; C. L. Siefring; P. Rodriguez; D. G. Haas; M. M. Baumback; H. A. Romero; D. A. Solin; F. T. Djuth; L. M. Duncan; D. E. Hunton; C. J. Pollock; M. P. Sulzer; C. A. Tepley; L. S. Wagner; J. A. Goldstein

1995-01-01

369

Climatology of ionospheric slab thickness  

Microsoft Academic Search

. The ionospheric slab thickness defined as a ratio of the total electron content (TEC) to the F-region peak electron density (NmF2) has been analysed during the solar maximum (1981) and minimum (1985) phases of an intense, the 21st, solar cycle. Hourly values of TEC and NmF2 collected at Hawaii (low-latitude), Boulder (mid-latitude) and Goosebay (high-latitude) are used in the

B. Jayachandran; T. N. Krishnankutty; T. L. Gulyaeva

2004-01-01

370

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

371

Ionospheric Imaging from Geostationary Orbit  

Microsoft Academic Search

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

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

2001-01-01

372

Real-time HF ray tracing through a tilted ionosphere  

NASA Astrophysics Data System (ADS)

High-frequency (HF) direction-finding (DF) systems measure the angles of arrival of signals at selected frequencies. With this information, ray tracing can accurately determine the location of the HF transmitters if the three-dimensional (3-D) electron density (Ne) distribution between the DF site and the transmitters is known. The usual approach is to use an ionospheric model like the International Reference Ionosphere (IRI) as a proxy for the density distribution. We describe a more realistic approach developed in cooperation with Codem Systems in Merrimack, New Hampshire. A collocated digisonde at the DF site measures the vertical electron density profile and the local ionospheric tilt, providing, in real time, the inputs for the construction of the 3-D Ne distribution. The vertical profile is automatically obtained from the Automated Real Time Ionogram Scaler with True Height (ARTIST)-scaled ionogram and the local tilt from the sky maps recorded after each ionogram. The characteristics of each layer, for example, critical frequencies and peak heights, are expressed as a function of latitude ? and longitude ?. In the neighborhood of the DF site each characteristic, for example, foF2, is given as foF2(?, ?) = foF2m (1 + C7?? + C8??) (1 + C??? + C???). The coefficients C7 and C8 for any given azimuth direction are determined with the use of the Union Radio Scientifique Internationale/CCIR coefficients (which are also used in IRI), and the calculation of C? and C? makes use of the measured ionospheric tilt data; foF2m is the local, measured foF2 value. When the measured density profile and tilt data are available, the derived 3-D density distribution represents the instantaneous ionosphere structure near the site. The numerical ray tracing includes the effects of the magnetic field and properly treats the spitze effect, making the ray-tracing program especially useful for small distances. Ray tracing through simulated tilts shows that the differences in ground distances for one-hop high-frequency (HF) propagation vary from about 1 to 100 km depending on the assumed tilts and distances. Operational tests for distances up to approximately 100 km have demonstrated good results in determining the transmitter location in real time and have illustrated the importance of using the actual ionospheric profiles and tilts in the ray tracing.

Huang, Xueqin; Reinisch, Bodo W.

2006-10-01

373

No Two Ionospheric Storms Are the Same ..... Nonsense!  

NASA Astrophysics Data System (ADS)

The study of ionospheric disturbances was initiated in the paper "Note on Kennelly-Heaviside Layer Observations During a Magnetic Storm" by Hafstad and Tuve in 1929. A remarkable degree of progress followed, first from the discovery of morphologies during individual case studies, and then from the statistical treatment of large numbers of ionospheric storms at many sites. By the end of 1950s (as the first space probes were being launched), the pioneers of aeronomy (e.g., Martyn, Sato, Matsushita) had analyzed many hundreds of ionospheric storms, reported on their effects, and offered theoretical explanations for the patterns observed. Data from satellites dominated the field during the 1960s to 1980s, producing a coherent picture of morphologies, physical mechanisms and models at most latitudes. With the advent of Space Weather in the 1990s, the field reverted to case study methods only, and new diagnostics (e.g., GPS and IMAGE) gave the impression that new patterns were being discovered and that new ideas were needed to explain them. Indeed, new names (for individual storm events, storm patterns and causative processes) now dominate the field. In many ways, this is a giant step backwards in that the potential for applications to technological systems is offered as sufficient reason to re-cast knowledge gained via the traditional methods of science. A self-perpetuating series of case studies now propels solar- terrestrial-physics via the theme that only one storm at a time can be understood. In this paper, evidence is offered to show that 80 years of study of ionospheric storms has been productive, and that the onset of a new solar cycle in 2009 should not be sufficient to warrant yet another period of re-discovery of solar- terrestrial physics. Rather, new diagnostics from the ground, and crucially needed satellite observations within the ionosphere-thermosphere system, can add to our knowledge if efforts are made to build upon past results, not just re-describe them with better observing systems. As an example, the analysis of 206 ionospheric storms from solar cycle 20 are used to demonstrate the existence of "geophysically comparable sites" --- locations where theory would suggest coherence of storm-time effects in both hemispheres. Long- term ionosonde data show that well understood fundamental processes yield statistical agreement at such locations. Moreover, small departures from coherence then point to subtle differences in mechanisms that add to our overall understanding of the geospace system.

Mendillo, M.

2008-12-01

374

Dynamic Ionosphere Cubesat Experiment (DICE)  

NASA Astrophysics Data System (ADS)

The Dynamic Ionosphere Cubesat Experiment (DICE) mission has been selected for flight under the NSF "CubeSat-based Science Mission for Space Weather and Atmospheric Research" program. The mission has three scientific objectives: (1) Investigate the physical processes responsible for formation of the midlatitude ionospheric Storm Enhanced Density (SED) bulge in the noon to post-noon sector during magnetic storms; (2) Investigate the physical processes responsible for the formation of the SED plume at the base of the SED bulge and the transport of the high density SED plume across the magnetic pole; (3) Investigate the relationship between penetration electric fields and the formation and evolution of SED. The mission consists of two identical Cubesats launched simultaneously. Each satellite carries a fixed-bias DC Langmuir Probe (DCP) to measure in-situ ionospheric plasma densities, and an Electric Field Probe (EFP) to measure DC and AC electric fields. These measurements will permit accurate identification of storm-time features such as the SED bulge and plume, together with simultaneous co-located electric field measurements which have previously been missing. The mission team combines expertise from ASTRA, Utah State University/Space Dynamics Laboratory (USU/SDL), Embry-Riddle Aeronautical University and Clemson University.

Crowley, G.; Fish, C. S.; Bust, G. S.; Swenson, C.; Barjatya, A.; Larsen, M. F.

2009-12-01

375

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

376

Numerical models of the Martian coupled thermosphere and ionosphere  

NASA Astrophysics Data System (ADS)

Two and three dimensional models of the Martian upper atmosphere and ionosphere have been developed to study the dynamics, temperature and composition of its neutral and plasma regimes. Three major neutral species - CO2, N2 and O are considered, together with a number of minor species CO, NO, Ar, O2, and O3. The density distributions of the ion species CO2(+), N2(+), O(+), CO(+), NO(+), Ar(+), and O2(+) are also calculated explicitly. The models solve the time-dependent momentum, energy, continuity and three constituent composition equation self-consistently. The ionosphere is also calculated self-consistency including solar production, chemical sources and sinks and transports. Minor species chemistry and transport are included as well as a comprehensive radiation scheme, including radiative transport between the atmospheric layers. It has been found that the absorption of solar infra-red radiation must be included in order to maintain the temperature of the Martian mesopause. It has also been found that consideration of the day to night compositional variation is necessary for an accurate analysis of the heat conduction and viscosity terms. The models predictions have been compared with experimental observations, mainly from the VIKING space mission, with generally good agreement for major and minor neutral species, and for the ionospheric constituents.

Winchester, C.; Rees, D.

1995-04-01

377

The polar cusp and its ionospheric footprint: Dynamics and transients  

NASA Astrophysics Data System (ADS)

The magnetopause, the boundary layer between the solar wind and the Earth's magnetosphere, is not closed as we have long thought. Transfers of energy, particles and momentum from the solar wind to the magnetosphere actually take place. In the Earth's magnetosphere, the polar cusps are two key regions where the solar wind particles have direct access to the magnetosphere and the polar ionosphere. The ionospheric footprint of the polar cusp is highly dynamic because its location and behavior depend directly on the external conditions (interplanetary magnetic field and solar wind pressure). The cusp dynamics has been studied by means of ground- based and satellite-borne instrumentation. The theory of magnetic reconnection has been successful in explaining entry of solar wind particles into the magnetosphere. Observations indicate that the reconnection process is not steady but rather sporadic or pulsed. The consequences of transient injections of solar wind particles into the dayside high-latitude ionosphere and the associated strong convection electric fields are observed, modeled and discussed.

Pitout, Frederic

2002-12-01

378

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

Microsoft Academic Search

The formation of a volume grating in the near-equator regions of ionosphere due to a high power radio wave is investigated. The radio wave, launched from a ground based transmitter, forms a standing wave pattern below the critical layer, heating the electrons in a space periodic manner. The thermal conduction along the magnetic lines of force inhibits the rise in

Rohtash Singh; A. K. Sharma; V. K. Tripathi

2011-01-01

379

The Relation of Radio SkyWave Transmission to Ionosphere Measurements  

Microsoft Academic Search

A simple, rapid, graphical method is given for obtaining maximum usable frequencies and effective reflection heights of radio waves, from vertical-incidence measurements of the critical frequencies and virtual heights of the various layers in the ionosphere. The method consists of the use of \\

N. Smith

1939-01-01

380

Global Characteristics of the Equatorial Anomaly of the low Latitude Ionosphere Observed by IMAGE\\/FUV  

Microsoft Academic Search

The Equatorial Anomaly (EA) of the low latitude ionosphere has been studied extensively since its discovery by Nanba and Maeda (1939) and Appleton (1946). The EA is produced basically by the uplift of the F-layer plasma at the magnetic equator by zonal electric fields, which subsequently enhances the density of the plasma at the base of field lines on both

E. Sagawa; T. J. Immel; H. U. Frey; S. B. Mende

2003-01-01

381

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

382

Ionosphere disturbances observed throughout Southeast Asia of the superstorm of 20-22 November 2003  

Microsoft Academic Search

Ionospheric disturbances in the Southeast Asian region during the super magnetic storm of 20-22 November 2003 were investigated through an ionosonde chain and a GPS network assisted by the space-borne instruments. At early stage of the storm in the postsunset sector, large enhancements in the critical frequency of F 2 layer and total electron content were observed at northern crest

B. Zhao; W. Wan; K. Tschu; K. Igarashi; T. Kikuchi; K. Nozaki; S. Watari; G. Li; L. J. Paxton; L. Liu; B. Ning; J.-Y. Liu; S.-Y. Su; Harold P. Bulanon

2008-01-01

383

Venus: Ionosphere and Atmosphere as Measured by Dual-Frequency Radio Occultation of Mariner V  

Microsoft Academic Search

Venus has daytime and nighttime ionospheres at the positions probed by radio occultation. The main layers are thin by terrestrial standards, with the nighttime peak concentration of electrons being about two orders of magnitude below that of the daytime peak. Above the nighttime peak were several scale-height regimes extending to a radius of at least 7500, and probably to 9700,

1967-01-01

384

A Novel Conventional Vehicle-Mounted Broadband HF Ionospheric Vertical Sounding Antenna  

Microsoft Academic Search

In ionospheric vertical sounding, an antenna with 1 ~ 20 MHz detection frequency range is enough because F2 layer critical frequency is usually lower than 20MHz, and the antenna gain requirements are relatively low because of the strong vertical sounding echoes. Besides, stable impedance, and vertical main lobe of radiation in the whole sounding frequency range are also required. This

Bo Bai; Ming Yao; Xiaohua Deng

2011-01-01

385

Ionospheric Anomalies in the Polar Cap and at Mid-Latitudes Revealed by Digital Ionosondes and GPS Receivers  

NASA Astrophysics Data System (ADS)

Intensification of the magnetosphere-ionosphere coupling during magnetic storms driven by coronal mass ejections (CMEs) or corotating interaction regions (CIRs) lead to extreme disturbances in density and height of ionospheric plasma layers. Dramatic enhancements of the ionospheric density and plasma content (TEC) appear in mid-latitude ionosphere and extend into the polar cap in the form of continuous tongue of ionization and/or isolated plasma patches. These ionospheric anomalies affect propagation of radio waves and microwave GPS signals and can be detected by various ground-based instruments. Using few CIR- and CME- driven geomagnetic storms of the last solar maximum as examples it will be demonstrated how the ionospheric anomalies evolve globally in time and space during the storms. The tomographic 4D inversions of the GPS data acquired by ground network of dual-frequency GPS receivers will be compared with the measurements of plasma drift and density obtained by digital ionosondes which now compose the Canadian High Arctic Ionospheric Network (CHAIN).

Pokhotelov, D.; Jayachandran, T. P.; MacDougall, J. W.; Mitchell, C. N.

2009-05-01

386

Present and Future IGS Ionospheric Products  

NASA Astrophysics Data System (ADS)

The purpose of this paper is, on one hand, to show the present performance of the combined final and rapid IGS global ionosphere maps (GIMs), and on the other hand to inform the geodetic community on new product - predicted IGS GIMs. In addition, information on future development of IGS ionospheric products will be also presented. Nowadays, the Ionosphere Working Group of IGS generates three types of ionospheric products: final, rapid and predicted, respectively. There are currently four IGS Associate Analysis Centres (IAACs) for the ionospheric products: CODE (Center for Orbit Determination in Europe, University of Berne, Switzerland), ESA/ESOC (European Space Operations Center of ESA, Darmstadt, Germany), JPL (Jet Propulsion Laboratory, Pasadena, U.S.A) and gAGE/UPC (Technical University of Catalonia, Barcelona, Spain). These centres provide ionosphere maps computed with different approaches. Their maps are uploaded to IGS Ionosphere Product Coordinator, who computes official IGS combined products. Since January 2008, this coordination is carried out by the GRL/UWM (Geodynamics Research Laboratory of the University of Warmia and Mazury in Olsztyn, Poland). The IGS GIMs are provided in Ionosphere Exchange (IONEX) format with spatial resolution of 5.0 degrees in longitude and 2.5 degrees in latitude, and temporal resolution of 2 hours. Latency of the final and rapid GIMs is 10 days and 1 day, respectively. In November 2009, the IGS Iono WG started to generate predicted ionospheric products 1 and 2 days in advance (requested for ESA's SMOS mission). These new IGS products are currently based on predicted ionosphere maps prepared by UPC and ESA. During period of more than 10 years of continuous IGS ionosphere operation, the techniques used by the IAACs and the strategies of combination have improved in such a way that the combined IGS GIMs are now significantly more accurate and robust. Future plans include, among others, increasing temporal resolution to 1 hour and studies on taking advantage of COSMIC occultation data.

Krankowski, Andrzej; Wielgosz, Pawel; Hernández-Pajares, Manuel; García-Rigo, Alberto

2010-05-01

387

Artificial Biochemistry  

Microsoft Academic Search

We model chemical and biochemical systems as collectives of interacting stochastic automata, with each automaton representing\\u000a a molecule that undergoes state transitions. In this artificial biochemistry, automata interact by the equivalent of the law of mass action. We investigate several simple but intriguing automata collectives\\u000a by stochastic simulation and by ODE analysis.

Luca Cardelli

2009-01-01

388

Artificial receptors.  

PubMed

Herein I will provide a brief overview of artificial receptors with emphasis on molecularly imprinted polymers (MIPs) and their applications. Alternative techniques to produce artificial receptors such as in silico designed and modelled polymers as well as different receptors designed using libraries of more or less natural composition will also be mentioned. Examples of these include aptamers and bio-nanocomposites. The physical presentation of the receptors is important and may depend on the application. Block polymerization of MIPs and grinding to particles of suitable size used to be the preferred technique, but today beaded materials can be produced in sizes down to nanobeads and also nanofibers can be used to increase available surface area and thereby capacity. For sensor applications it may be attractive to include the artificial receptors in surface coatings or in membrane structures. Different composite designs can be used to provide additional desirable properties. MIPs and other artificial receptors are gaining rapidly increasing attention in very shifting application areas and an attempt to provide a systematic account for current applications has been made with examples from separation, solid-phase extraction, analysis, carbohydrate specific experiments, and MIPs-directed synthesis. PMID:17985098

Danielsson, Bengt

2008-01-01

389

Nighttime thermospheric/ionospheric coupling in tropical region  

NASA Astrophysics Data System (ADS)

Thermospheric/ionospheric coupling during quiet and disturbed periods is one of the important topics of aeronomic studies, especially in tropical region. It is important to know how the neutral wind affects the spatial and temporal F-layer ionospheric plasma density and height variations and the magnitude of electric field generated by the interaction between neutral atmosphere and ionosphere. In this investigation, we will present the nighttime thermospheric meridional winds during quiet and disturbed periods using two equatorial stations, Palmas (10.2 S, 48.2 W, dip latitude 5.7 S) and Manaus (2.9 S, 60.0 W, dip latitude 6.4 N), and one low latitude station, São José dos Campos (23.2 S, 45.9 W, dip latitude 17.6 S), in the Brazilian sector. The meridional winds have been derived using the semi-empirical servo model and F-region height (hpF2 and h'F) variations data. The coefficients of diffusion, recombination and loss rate required in the servo equations are calculated using MSIS model. The results obtained are compared with a semi-empirical global horizontal wind model HWM-90. Also, some of the results are compared with the observational results, from a low latitude station in the Brazilian sector, using an OI 630 nm Fabry-Perot interferometer published earlier. These comparisons are used to check the validity of the method in calculating the velocity and direction of the meridional winds over the equatorial and low-latitude regions. It should be mentioned that the present study assumes a great importance in better understanding of the thermosphere-ionosphere system behavior and response during geomagnetically disturbed conditions.

Muella, Mtah; Fagundes, P. R.; Bittencourt, J. A.; Sahai, Y.; Becker-Guedes, F.; Lima, Wlc; Abalde, J. R.; Pillat, V. G.

390

GPS-study of Ionospheric TEC variations induced by powerful HF-heating.  

NASA Astrophysics Data System (ADS)

The studies of the influence of powerful HF radio waves on the ionosphere revealed strong heating of the ionospheric plasma and generation of artificial irregularities in the ionospheric electron density with the scale sizes from fractions of meter to dozens of kilometers near the reflection height of the powerful radio wave. These irregularities have a considerable effect on the parameters of VHF/UHF/L-band radio waves propagating through the heated area of the ionosphere. The aim of this work is to report the experimental results on the influence of the electron density perturbations caused by HF heating in the dayside midlatitude ionosphere on GPS signals. The experiments were carried out at the Sura heater (Radio Physical Research Institute, N. Novgorod, Russia) in March, 2009. The effective radiated power of the heater was up to 80MW. Different modulations of effective radiated power were applied, in particular, square-wave modulations with periods of 1, 6, 10 and 15 minutes. Variations in the total electron content (TEC) proportional to the reduced phases of navigational signals were studied for those satellite passes, when the rays linking these satellites with the ground receiver intersected the heated region during the periods of heating. We show that the wavelet spectrum of GPS TEC variations contains spectral components (main modulation frequency and its harmonics) corresponding to the modulation and timing of HF-heating when the ionospheric penetration points of the tracked GPS-satellites fall within the heated area. Examples are presented of identification of the heating-induced variations in TEC along the satellite-to-receiver ray, including the determination of amplitude and time characteristics of these variations. The work was supported by the Russian Foundation for Basic Research (grants nos. 08-02-00171, 08-05-00676). The authors are grateful to the staff of the Sura facility for their help in experiments.

Padokhin, Artem M.; Kunitsyn, Viacheslav E.; Vasiliev, Alexey E.; Kurbatov, Gregory A.; Frolov, Vladimir L.; Komrakov, Georgy P.

2010-05-01

391

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

392

Antarctic Peninsula troposphere-stratosphere-ionosphere coupling (APTIC) and conjugate events investigation  

NASA Astrophysics Data System (ADS)

Researches of troposphere-stratosphere-ionosphere coupling are based on idea of the strong influence of the long- and short-term solar activity variations on the polar terrestrial climate and the asymmetry in the energy deposition from the magnetosphere into the polar ionospheres. The solar activity variations produce changeable impact on magnetosphere and polar ionosphere in both hemispheres. Results of this impact are (1) differences in the ozone concentrations in the Antarctic and Arctic stratosphere due to different forcing in spring; (2) different planetary wave activity; (3) different gravity wave flux intensity depended on strengths of the weather frontal cyclones activity. The study of upper atmosphere in both hemispheres is necessary to better understand various physical mechanisms responsible for the energy transfer from the Sun into atmosphere and ionosphere as well as reverse flux from troposphere to geospace. A simultaneous consideration of phenomena occurring over both polar regions is very important for understanding of these processes. The solution of the problem of energy exchange between neutral atmosphere and geospace plasma is need in study of industrial EM pollution from Earth surface to geospace. A corresponding work must promote modeling space weather on satellite heights and earthquake prediction using ionosphere parameters changes. A determinative significance of Antarctic Peninsula is caused by following features: (1) Antarctic Peninsula is situated near an extremely cyclonic active region - Drake Passage, (2) only this region in Antarctica is magnetically conjugated to industrial area in Northern hemisphere, and (3) this region contains many Antarctic stations which are good equipped by devices to study weather and climate, ozone layer, ionosphere and magnetic field. Last years weather observations at Vernadsky station show that up to 60 atmospheric frontal cyclones (with pressure variation more 20 millibars) swept over Antarctic Peninsula during year. Therefore this region is the most appropriate to study ionosphere impact of troposphere induced AGW. These features produced the scientific goal of the project APTIC. It is to explore the response of the ionosphere to strong weather systems sweeping the Antarctic Peninsula sector and identify energy transfer mechanisms. Main task of the project consists in research of the energy exchange processes between lower (troposphere) and upper atmosphere and EM impact of weather front (cyclone) on ionosphere over Antarctic Peninsula as well as in conjugate region (east coast of the USA). Multipositional study of the powered atmosphere cyclone fronts on Antarctic Peninsula to ionosphere, magnetosphere and conjugate region using three (and more in future) automatic meteo-mag-receivers (MMR) is a new direction of researches. Main scientific objectives of APTIC project are (1) study of the travelling ionosphere disturbances (TID) within F2-layer hights; (2) study of macroscale atmosphere wavelike processes: tides, planetary waves and their image in ozone layer; (3) study of the impact of troposphere disturbances to ozone layer and ionosphere; (4) search the possible influence of sharp changes and longtime trend in ozone layer to troposphere and climate; (5) study of the spatial-temporal structure of frontal weather systems, their moving velocity and direction; (6) search of the time variations (shift) in the geomagnetic substorm development using long-distance chain (Frei-Palmer-Vernadsky-Rothera); (7) study of the spatial corelation of resonance geomagnetic micropulsation; (8) study of the polarisation structure of geomagnetic micropulsation.

Milinevsky, G.

2005-04-01

393

Ionospheric and Geomagnetic Activity Investigated Using Oblique Sounding Comparisons With an HF Radio Propagation Model  

NASA Astrophysics Data System (ADS)

Oblique HF sounder paths over ~2000km have been operating between New Zealand and Australia for a number of years. The maximum observed frequencies (MOF) are compared with predictions from the climatological HF radio skywave propagation model used by IPS. Variations from predicted median (MUF),lower (OWF) and upper decile frequencies may be interpreted in terms of ionospheric and geomagnetic activity and the effectiveness of parameterisation of ionospheric support for HF by the T-index examined. Closely spaced multiple paths provide opportunities to investigate small scale F2 layer structures.

Neudegg, D.; Layoun, M.; Hutchinson, S.

2008-12-01

394

A new method for the determination of real height and electron content of the ionosphere  

NASA Astrophysics Data System (ADS)

A method for determining the ionospheric real height is presented. The method involves the lumination technique and requires only two or three data points for calculations. Results using this method for the real height of the F2 layer were found to be in good agreement with those obtained using the parabolic conventional methods. The method can also be used to obtain the vertical distribution of the electron density in the height region between the beginning of the ionosphere and the beginning of the F2 region. Examples of calculations are presented, including the total electron content above Baghdad, Iraq for July 1983 and January 1984.

Abdulla, S. A.; Ishak, R. A.; Shibeb, N. A.

1988-02-01

395

Ionospheric streams at altitudes below 14RE  

NASA Astrophysics Data System (ADS)

The properties of ionospheric ion streams flowing away from Earth into the magnetotail between 2 Re and 14 Re are studied from ISEE-2 data. General agreement between these observations and those at lower and larger distances is found, indicating that the plasma sheet is enriched with ionospheric ions at all distances.

Orsini, S.; Candidi, M.

1985-09-01

396

VLF phase and amplitude: daytime ionospheric parameters  

Microsoft Academic Search

Experimental observations of the daytime variations of VLF phase and amplitude over a variety of long subionospheric paths have been found to be satisfactorily modelled with a D-region ionosphere, described by the two traditional parameters, H? and ? (being measures of the ionospheric height and the rate of increase of electron density with height, respectively). This VLF radio modelling uses

Wayne M. McRae; Neil R. Thomson

2000-01-01

397

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

398

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

399

Ionospheric Limitations on Attainable Satellite Potential  

Microsoft Academic Search

Artiticial satellites orbiting in the ionosphere normally tend to acquire a slight negative charge due to the high velocity of the electrons relative to the ion and satellite veloci- ties. (At very high altitudes where the ionospheric electron concentrations are small, and in the presence of solar radiation, satellites tend to have a small positive charge due to the photo-

1961-01-01

400

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

401

Ionosphere Statistical Tomography based on the Backscattering  

Microsoft Academic Search

The ionosphere statistical tomography is studied here only the back scattering is taken into account. For a spaceborne radar system, ionosphere tomography based on the back scattering will be convenient compared with that based on the forward scattering, because for the first case the ground receiver system setting will be not needed anymore. So the detection cost will be cut

Fang Li

2010-01-01

402

GPS Array as a Sensor of Lithosphere, Troposphere and Ionosphere  

NASA Astrophysics Data System (ADS)

The Japanese dense array of GPS receivers (GEONET) started operation in 1993, and is currently composed of ~1200 stations. GPS (or GNSS in general) receivers can be compared to a Swiss army knife: it could be used not only for positioning (a knife) but also for various purposes, e.g. remote sensing of tropospheric water vapor or ionospheric electrons (screw driver, tin opener etc). Dense GPS arrays have been found extremely useful for variety of geophysical studies. In this lecture, I briefly review their historical achievements, recent highlights, and future perspectives. In Japan, first generation GPS stations were implemented in 1993 (the Kanto-Tokai region) and 1994 (nationwide) by GSI, Japan. Shortly after the launch, they successfully caught coseismic crustal movement of several major earthquakes, the 1994 October Shikotan (Mw8.3), the 1994 December Sanriku (Mw7.6), and the 1995 January Kobe (Mw7.0) earthquakes. These earthquakes accelerated the densification of the GPS network, achieving 1000 in the number of stations within the following 2-3 years. In addition to coseismic jumps, important discoveries continued in 1990s, e.g. large-scale afterslip of interplate thrust earthquakes and slow slip events (SSE). Later it was shown that tilt- and strainmeter can better observe short-term SSEs, and InSAR can draw more detailed maps of coseismic crustal movements. Now GPS array is recognized as a good tool to measure crustal movement with high temporal resolution and stability and with moderate sensitivity and spatial resolution. GPS data are also useful to study hydrosphere. Seasonal crustal movements in Japan mainly reflect changes in hydrological loads. Multipath signatures in GPS data also provide useful information on the environment around the antenna, e.g. soil moisture, snow depth and vegetation. I will compare the snow depth record over a winter inferred by analyzing GPS multipath signatures, and observed by a conventional apparatus. GPS can also measure precipitable water vapor (PWV) of troposphere. After intense feasibility studies of GPS meteorology in 1990s, PWV information from GEONET has been routinely assimilated in the operational mesoscale model of the Japan Meteorological Agency since 2009. It is found useful in predicting localized heavy rainfalls that often attack Japan in summer. It is fairly easy to measure ionospheric total electron content (TEC) by using phase differences between L1 and L2 carriers from GPS satellites. Applications of GPS for upper atmospheric studies started for ionospheric disturbances of space weather origins. In 2003, clear coseismic ionospheric disturbances of the Tokachi-Oki earthquake were found, and the GPS-TEC technique has been extensively used to study ionospheric disturbances of solid earth origins, e.g. earthquakes and volcanic eruptions. There are also several recent examples of artificial ionospheric disturbances caused by rocket launches and passage of ballistic missiles from North Korea above NE Japan. In the last part of the lecture, I summarize what the GPS array saw before, during and after the 2011 Tohoku-Oki earthquake. The topic covers not only pre-, co- and postseismic crustal movements, but also results of high-rate sampling, and possible detection of precursory changes in ionospheric TEC immediately before the earthquake.

Heki, K.

2011-12-01

403

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

404

High-resolution station-based diurnal ionospheric total electron content (TEC) from dual-frequency GPS observations  

NASA Astrophysics Data System (ADS)

electron content (TEC) estimates derived from Global Navigation Satellite System (GNSS) signal delays provide a rich source of information about the Earth's ionosphere. Networks of Global Positioning System (GPS) receivers data can be used to represent the ionosphere by a Global Ionospheric Map (GIM). Data input for GIMs is dual-frequency GNSS-only or a mixture of GNSS and altimetry observations. Parameterization of GNSS-only GIMs approaches the ionosphere as a single-layer model (SLM) to determine GPS TEC models over a region. Limitations in GNSS-only GIM TEC are due largely to the nonhomogenous global distribution of GPS tracking stations with large data gaps over the oceans. The utility of slant GPS ionospheric-induced path delays for high temporal resolution from a single-station data rate offers better representation of TEC over a small region. A station-based vertical TEC (TECV) approach modifies the traditional single-layer model (SLM) GPS TEC method by introducing a zenith angle weighting (ZAW) filter to capture signal delays from mostly near-zenith satellite passes. Comparison with GIMs shows the station-dependent TEC (SD-TEC) model exhibits robust performance under variable space weather conditions. The SD-TEC model was applied to investigate ionospheric TEC variability during the geomagnetic storm event of 9 March 2012 at midlatitude station NJJJ located in New Jersey, USA. The high temporal resolution TEC results suggest TEC production and loss rate differences before, during, and after the storm.

?epni, Murat S.; Potts, Laramie V.; Miima, John B.

2013-09-01

405

Statistical Study of ULF Pc 1-2 Wave Propagation Characteristics in the High Latitude Ionospheric Waveguide  

NASA Astrophysics Data System (ADS)

It is well-documented that the ionospheric cavity bounded by the E and F2 layers acts as a waveguide for geomagnetic pulsations. Using data from a five-station search-coil magnetometer array in the Antarctic (ordered poleward: Halley Bay, AGO P2, South Pole, AGO P1, AGO P5), a study is made of ULF Pc 1-2 geomagnetic pulsations in the 0.1-1.0 Hz range to examine their spectral wave power attenuation during propagation through the ionospheric waveguide. Here we present results from a statistical study of over 100 events showing that Pc 1-2 geomagnetic pulsations exhibit well-defined poleward ducting behavior in the ionospheric waveguide as well as significant spectral power loss during poleward propagation, which suggests that Pc 1-2 waves are injected into the lower latitude ionosphere and guided through the ducting layer. Through the use of spectrograms and wave power attenuation plots, we show both qualitatively and quantitatively how these behaviors are affected by specific ionospheric conditions connected to the timing of the event with regard to magnetic local time. It is also examined in a statistical way how wave spectral power attenuation is related to sunlit conditions, which are thought to contribute to the ionospheric conductivity.

Young, M.; Lessard, M.; Kim, H.; Argall, M.

2009-05-01

406

Technique for measuring ionospheric irregularities generated by high-power oblique HF heating of the F-region  

SciTech Connect

A new technique for investigating the changes in the small to medium scale structure of the F-layer of the ionosphere is developed using the existing capabilities of the University of Lowell Center for Atmospheric Research Digisonde 256 vertical ionospheric sounder. When the ionosphere is heated by a high power HF transmitter operating in an oblique radar or communications mode the formation of irregularities has been observed. The development of these irregularities is described in terms of an index of ionospheric roughness which is shown to correlate very well with the natural formation of spread-F. These measurements are relatively simple and can be carried out from a site directly below the heated region.

Sales, G.S.; Reinisch, B.W.; Ralls, J.A.

1990-08-01

407

Measured ionospheric distortion of HF ground-backscatter spectra  

NASA Astrophysics Data System (ADS)

Skywave-radar measurements of backscatter from land are used to estimate some statistical properties of the ionospheric distortion encountered by sea-state radars. It is confirmed that samples of the path spectrum P(omega) are normally distributed and uncorrelated in frequency, and the first two moments of P(omega) and their spatial and temporal correlation, for quiet F-layer daytime propagation are estimated. An empirical relation connects the equivalent width of P(omega) and expected errors in estimating ocean wave height.

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

1986-04-01

408

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

409

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

410

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

411

Development of a campaign to study equatorial ionospheric phenomena over Guam  

NASA Astrophysics Data System (ADS)

The United States Air Force Academy (USAFA) is in the process of developing a series of ground-based and space-based experiments to investigate the equatorial ionosphere over Guam and the southern crest of the Equatorial Appleton Anomaly over New Guinea. On the ground the Digital Ionospheric Sounder (University of Massachusetts, Lowell DPS-4 unit) and a dual-frequency GPS TEC/scintillation monitor will be used to investigate ionospheric phenomena in both campaign and long-term survey modes. In campaign mode, we will combine these observations with those collected from space during USAFA's FalconSAT-3 and FalconSAT-5 low Earth orbit satellite missions, which will be active over a period of several years beginning in the first quarter of the 2007 calendar year. Additionally, we will investigate the long-term morphology of key ionospheric characteristics useful for driving the International Reference Ionosphere, such as critical frequencies (f oE, f oF1, f oF2, etc.), the M(3000) F2 parameter (the maximum useable frequency for a signal refracted within the F2 layer and received on the ground at a distance of 3000 km away), and a variety of other characteristics. Specific targets of investigation include: (a) a comparison of TEC observed by the GPS receiver with those calculated by IRI driven by DPS-4 observations, (b) a comparison of plasma turbulence observed on-orbit with ionospheric conditions as measured from the ground, and (c) a comparison between topside ionospheric satellite in situ measurements of plasma density during an overpass of a Digisonde versus the calculated value based on extrapolation of the electron density profiles using Digisonde data and a topside ?-Chapman function. This last area of investigation is discussed in detail in this paper.

Habash Krause, L.; Balthazor, R.; McHarg, M. G.; Reinisch, B. W.

2008-08-01

412

Artificial neural network based induction motor design  

Microsoft Academic Search

This paper presents an artificial neural network based designing for induction motors. Based on the actual design data for various types of induction motors, three-layered artificial neural networks have been trained to give better solutions for the fundamental quantities and parameters of individual induction motor. After training, selected quantities have been estimated quite accurately from the input data which is

Takashi Hiyama; Masahiro Ikeda; Takaaki Nakayama

2000-01-01

413

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

414

Ionospheric photoelectrons: comparing Earth, Venus, Mars and Titan  

Microsoft Academic Search

Earth, Venus, Mars and Titan are all objects with significant atmospheres and ionospheres. Ionospheric studies at the Earth first revealed the presence of ionospheric photoelectrons, a product of the principal ionization process for the ionosphere, i.e. photoionization from solar EUV and X rays. Recent space missions with suitable instrumentation have also revealed similar photoelectrons at Venus, Mars and Titan. The

Andrew Coates; Anne Wellbrock; Sharon Tsang; Rudy Frahm; David Winningham; Stas Barabash; Rickard Lundin; Dave Young; Frank Crary

2010-01-01

415

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

416

Artificial Rheotaxis  

NASA Astrophysics Data System (ADS)

Self propelled colloids realize a controlled realization of an artificial bacterium. However living systems present a range of advanced properties such as the migration in gradients, or taxis, based on complex conformational change of proteins. For example, rheotaxis, the directed movement of an organism resulting from a fluid flow, has been reported notably for fish, e.g. salmon, or spermatozoa. Here, we present experimental observations of artificial rheotaxis, i.e. upstream migration of self propelled particles in the presence of a flow. We will present a simple model to account for this surprising effect. In the absence of biological component, this effect is intriguing and questions the ingredients at stake in the living matter.

Palacci, Jeremie; Sacanna, Stefano; Hanson, Kasey; Vatchinsky, Adrian; Pine, David; Chaikin, Paul

2013-03-01

417

Innovative development and application of models for weakly ionized ionospheric plasmas. Final report, 15 May 1990-30 November 1993  

SciTech Connect

Artificial modifications of the ionosphere through chemical releases and ionospheric heating experiments are examined with models of chemistry and transport to advance understanding of ion chemistry of the upper atmosphere. The specific releases investigated were the SF6 released of the CRRES-at-Kwajalein rocket campaign and the CO2 releases of the Red Air I program. Both the SF6 and CO2 releases experienced freezing or clustering of the molecules. This must be accounted for in the composition and airglow observations. In addition, HF heating effects in the E and F region were examined through modeling of energy deposition and resulting chemistry. NO sub x production in a HF ionospheric heater beam is estimated and compared with natural sources of NO sub x. Global effects of HF operation are very small but the local effects can be large enough to permit observable modulation to this environment.

Eccles, J.V.; Hingst, J.; Armstrong, R.

1993-11-01

418

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 (60-72°N, 88-152°E) 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 (66.8°N, 123.3°E), and a drastic decrease in the F2 layer critical frequency (foF2) up to 54% of the quite one over subauroral Yakutsk station (62°N, 129.7°E). 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

419

Measurements of the E- and F-Region Post-Sunset Ionosphere  

NASA Astrophysics Data System (ADS)

The GPS occultation method of ionospheric remote sensing has been shown to provide a means to obtain information about the low-density post-sunset E-region, particularly under conditions when sharp sporadic-E layers are present. Since E-region conductivity is a key factor in the development of low-latitude dynamo electric fields and the associated uplift of the equatorial ionosphere known as the pre-reversal enhancement, occultation data provide a mechanism for investigating the coupling between E-region densities and the dynamics of the higher altitude F-region. We present initial results of case studies involving E-region densities inferred from the Ionospheric Occultation Experiment (IOX) and the CHAMP GPS occultation sensors and measures of the F-region plasma state obtained from nearly coincident datasets (in-situ densities on DMSP and density profiles inferred from UV remote sensors on NASA's TIMED missions and the DMSP F16 spacecraft).

Straus, P. R.; Bishop, R.; Crowley, G.

2006-12-01