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1

HF propagation characteristics of artificial ionospheric layers  

Microsoft Academic Search

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

Todd Pedersen; Bodo Reinisch; Vadym Paznukhov; Ryan Hamel

2011-01-01

2

Creation of artificial ionospheric layers using high-power HF waves  

NASA Astrophysics Data System (ADS)

We report the first evidence of artificial ionospheric plasmas reaching sufficient density to sustain interaction with a high-power HF pump beam produced by the 3.6 MW High-Frequency Active Auroral Program (HAARP) transmitter in Gakona, Alaska. The HF-driven ionization process is initiated near the 2nd electron gyroharmonic at 220 km altitude in the ionospheric F region. Once the artificial plasma reaches sufficient density to support interaction with the transmitter beam it rapidly descends as an ionization wave to 150 km altitude. Although these initial artificial layers appear to be dynamic and highly structured, this new ability to produce significant artificial plasma in the upper atmosphere opens the door to a new regime in ionospheric radio wave propagation where transmitter-produced plasmas dominate over the natural ionospheric plasma and may eventually be employed as active components of communications, radar, and other systems.

Pedersen, Todd; Mishin, Evgeny; Kendall, Elizabeth; Mills, Travis; Carlson, H. C.; Snyder, A. L.; Gustavsson, Bjorn

3

Creation of artificial ionospheric layers using high-power HF waves  

NASA Astrophysics Data System (ADS)

We report the first evidence of artificial ionospheric plasmas reaching sufficient density to sustain interaction with a high-power HF pump beam produced by the 3.6 MW High-Frequency Active Auroral Program (HAARP) transmitter in Gakona, Alaska. The HF-driven ionization process is initiated near the 2nd electron gyroharmonic at 220 km altitude in the ionospheric F region. Once the artificial plasma reaches sufficient density to support interaction with the transmitter beam it rapidly descends as an ionization wave to ˜150 km altitude. Although these initial artificial layers appear to be dynamic and highly structured, this new ability to produce significant artificial plasma in the upper atmosphere opens the door to a new regime in ionospheric radio wave propagation where transmitter-produced plasmas dominate over the natural ionospheric plasma and may eventually be employed as active components of communications, radar, and other systems.

Pedersen, T.; Gustavsson, B.; Mishin, E.; Kendall, E.; Mills, T.; Carlson, H. C.; Snyder, A. L.

2010-01-01

4

Numerical modeling of artificial ionospheric layers driven by high-power HF-heating  

NASA Astrophysics Data System (ADS)

We present a multi-scale dynamic model for the creation and propagation of artificial plasma layers in the ionosphere observed during high-power high frequency (HF) heating experiments at HAARP. Ordinary mode electromagnetic waves excite parametric instabilities and strong Langmuir turbulence near the reflection point. The coupling between high frequency electromagnetic and Langmuir waves and low-frequency ion acoustic waves is numerically simulated using a generalized Zakharov equation. The acceleration of plasma electrons is described by a Fokker-Planck model with an effective diffusion coefficient constructed using the simulated Langmuir wave spectrum. The propagation of the accelerated electrons through the non-uniform ionosphere is simulated by a kinetic model accounting for elastic and inelastic collisions with neutrals. The resulting ionization of neutral gas increases the plasma density below the acceleration region, so that the pump wave is reflected at a lower altitude. This leads to a new turbulent layer at the lower altitude, resulting in a descending artificial ionized layer that moves from near 230 km to about 150 km. The modeling results reproduce artificial ionospheric layers produced for similar sets of parameters during the high-power HF experiments at HAARP.

Eliasson, Bengt; Shao, Xi; Milikh, G.; Mishin, E. V.; Papadopoulos, K.

2012-10-01

5

Numerical modeling of artificial ionospheric layers driven by high-power HF-heating  

NASA Astrophysics Data System (ADS)

We present a multi-scale dynamic model for the creation and propagation of artificial plasma layers in the ionosphere observed during high-power high frequency heating experiments at HAARP. Ordinary mode electromagnetic waves excite parametric instabilities and strong Langmuir turbulence near the reflection point. The coupling between high frequency electromagnetic and Langmuir waves and low-frequency ion acoustic waves is numerically simulated using a generalized Zakharov equation. The acceleration of plasma electrons is described by a Fokker-Planck model with an effective diffusion coefficient constructed using the simulated Langmuir wave spectrum. The propagation of the accelerated electrons through the non-uniform ionosphere is simulated by a kinetic model accounting for elastic and inelastic collisions with neutrals. The resulting ionization of neutral gas increases the plasma density below the acceleration region, so that the pump wave is reflected at a lower altitude. This leads to a new turbulent layer at the lower altitude, resulting in a descending artificial ionized layer, that moves from near 230 km to about 150 km. At the terminal altitude, ionization, recombination, and ambipolar diffusion reach equilibrium, so the descent stops. The modeling results reproduce artificial ionospheric layers produced for similar sets of parameters during the high-power HF experiments at HAARP.

Milikh, G. M.; Eliasson, B.; Shao, X.; Mishin, E. V.; Papadopoulos, K.

2012-12-01

6

Numerical modeling of artificial ionospheric layers driven by high-power HF heating  

NASA Astrophysics Data System (ADS)

We present a multi-scale dynamic model for the creation and propagation of artificial plasma layers in the ionosphere observed during high-power high-frequency (HF) heating experiments at HAARP. Ordinary (O) mode electromagnetic (EM) waves excite parametric instabilities and strong Langmuir turbulence (SLT) near the reflection point. The coupling between high-frequency electromagnetic and Langmuir waves and low-frequency ion acoustic waves is numerically simulated using a generalized Zakharov equation. The acceleration of plasma electrons is described by a Fokker-Planck model with an effective diffusion coefficient constructed using the simulated Langmuir wave spectrum. The propagation of the accelerated electrons through the non-uniform ionosphere is simulated by a kinetic model accounting for elastic and inelastic collisions with neutrals. The resulting ionization of neutral gas increases the plasma density below the acceleration region, so that the pump wave is reflected at a lower altitude. This leads to a new turbulent layer at the lower altitude, resulting in a descending artificial ionized layer (DAIL), that moves from near 230 km to about 150 km. At the terminal altitude, ionization, recombination, and ambipolar diffusion reach equilibrium, so the descent stops. The modeling results reproduce artificial ionospheric layers produced for similar sets of parameters during the high-power HF experiments at HAARP.

Eliasson, B.; Shao, X.; Milikh, G.; Mishin, E. V.; Papadopoulos, K.

2012-10-01

7

Laboratory investigation of the boundary layer processes of artificially created ionospheric depletion  

NASA Astrophysics Data System (ADS)

In the work, we have experimentally investigated the boundary layer processes of artificially created ionospheric depletions. Those ionospheric depletions were modeled via releasing attachment chemicals, such as SF6,CF4, and CO2, into the ambient plasmas. Boundary layer of width of electric scale length emerged and separated those plasmas into two regions, the ambient plasmas and the negative ions plasmas. In the localized boundary layer, those fluctuations of the electron density and the floating potential were investigated varying with the plasma pressure and the partial pressure of released chemicals. The electron density decreased sharply that yielded steep density gradients ?ne, and the floating potential increased which generated sheared electron flows. It is found that the magnitude of fluctuating floating potential is proportional to that of the ?ne. Those fluctuations were analyzed in detail using digital spectra analysis techniques. Vortex-like coherent structures were observed in the fluctuations of electrostatic potentials. These coherent frequencies are sensitive to the mass of the negative ions, and all lie in the lower hybrid range. By comparing the experimental results with theoretical predictions, the modes have been identified as the coherent structures resulting from the electron-ion hybrid instability. Our results are important to study the early phase nonlinear evolution of the ionospheric depletion and also may be applied to the plasma sheet boundary layer in where often encounters the narrow electron density gradients and sheared electron flows.

Liu, Yu; Cao, Jinxiang; Xu, Liang; Zhang, Xiao; Wang, Pi; Wang, Jian; Du, Yinchang; Zheng, Zhe

2014-05-01

8

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

NASA Astrophysics Data System (ADS)

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 creation for the ionosphere diagnostic. 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 (Belikovich et al., 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 power wavelength ?/2. Ionosphere diagnostic is carried out in the API relaxation 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 that is having different spatial periods of the quasi periodic structure. In the E-region of the ionosphere API are formed as a result of the diffusion redistribution of the ionosphere plasma. Relaxation of the periodic structure is specified by the ambipolar diffusion process. The API relaxation time depends on the power wavelength and 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 index 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. The measurement of the ?(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 (Belikovich V.V. Radiophys. Quantum Electron., 2006, Vol. 49, No. 9). Vertical velocity 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 maximum. The measured vertical velocity shift was about 5×10-3-10-4 c-1. The shift can be caused by acoustic gravity waves and is sufficient for collecting of metal ions in sporadic E-layer.

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

2010-05-01

9

Artificial ionosphere layers for pumping-wave frequencies near the fourth electron gyroharmonic in experiments at the HAARP facility  

NASA Astrophysics Data System (ADS)

In this paper we consider the action (in the magnetic-zenith direction) of powerful high frequency (HF) radiation of ordinary polarization on the ionosphere F region. We deal with frequencies f 0 > 4 f ce ( f ce is the electron cyclotron frequency) of 1.7 GW equivalent radiated power. This action results in the appearance in the ionosphere of an artificial ionization layer. The layer descends with respect to the basic (unperturbed) layer at a rate of ˜500 m s-1 down to the altitude, where f 0 ? 4 f ce .

Grach, S. M.; Sergeev, E. N.; Shindin, A. V.; Mishin, E. V.; Watkins, B.

2014-02-01

10

Modeling 3D Artificial Ionospheric Ducts  

NASA Astrophysics Data System (ADS)

The injection of powerful HF waves into the ionosphere leads to strong electron heating followed by a depletion of electrons in the heated region. This can create a pressure perturbation which propagates along the entire magnetic field line, enhancing refractive indices and acting as a waveguide to whistler-range waves. These perturbations are known as artificial ducts. Duct formation due to HF heating has previously been studied using a version of Sami2 is Another Model of the Ionosphere (SAMI2) modified to include a flexible source of HF heating. We extend this study to look at the formation of artificial ducts by HF heating in a 3D model using a similarly modified version of SAMI3. We examine how heating over Arecibo can create interhemispheric ducts along magnetic field lines. Acknowledgements: This work was sponsored by the Office of Naval Research.

Zawdie, K. A.; Huba, J. D.; Joyce, G. R.; Wu, T.

2011-12-01

11

Formation of artificial ionospheric ducts  

Microsoft Academic Search

It is well known that strong electron heating by a powerful HF-facility can lead to the formation of electron and ion density perturbations that stretch along the magnetic field line. Those density perturbations can serve as ducts for ELF waves, both of natural and artificial origin. This paper presents the first experimental evidence of plasma modifications associated with ion outflows

G. M. Milikh; K. Papadopoulos; H. Shroff; C. L. Chang; T. Wallace; E. V. Mishin; M. Parrot; J. J. Berthelier

2008-01-01

12

Modeling 3-D artificial ionospheric ducts  

NASA Astrophysics Data System (ADS)

The injection of powerful HF waves into the ionosphere leads to strong electron heating followed by a pressure perturbation, which can drive electrons along the field line to the conjugate side, creating what is known as an artificial duct. The electron temperature along the duct is above the ambient temperature; the electron density is depleted on the heating side and increased on the conjugate side. Duct formation due to HF heating has previously been studied using a modified version of SAMI2 (Sami2 is Another Model of the Ionosphere). We use a similarly modified version of SAMI3 to examine the effects of zonal E × B drifts on interhemispheric ducts created by heating over Arecibo. We found that the longitudinal E × B drifts, particularly those caused by the zonal neutral winds, significantly suppress the effects of HF heating on the conjugate side, reducing the temperature and density increases by about 90% and 75%, respectively.

Zawdie, K. A.; Huba, J. D.; Wu, T.-W.

2013-11-01

13

Artificial periodic irregularities in the auroral ionosphere  

NASA Astrophysics Data System (ADS)

Artificial periodic irregularities (API) are produced in the ionospheric plasma by a powerful standing electromagnetic wave reflected off the F region. The resulting electron-density irregularities can scatter other high-frequency waves if the Bragg scattering condition is met. Such measurements have been performed at mid-latitudes for two decades and have been developed into a useful ionospheric diagnostic technique. We report here the first measurements from a high-latitude station, using the EISCAT heating facility near Tromsø, Norway. Both F-region and lower-altitude ionospheric echoes have been obtained, but the bulk of the data has been in the E and D regions with echoes extending down to 52-km altitude. Examples of API are shown, mainly from the D region, together with simultaneous VHF incoherent-scatter-radar (ISR) data. Vertical velocities derived from the rate of phase change during the irregularity decay are shown and compared with velocities derived from the ISR. Some of the API-derived velocities in the 75-115-km height range appear consistent with vertical neutral winds as shown by their magnitudes and by evidence of gravity waves, while other data in the 50-70-km range show an unrealistically large bias. For a comparison with ISR data it has proved difficult to get good quality data sets overlapping in height and time. The initial comparisons show some agreement, but discrepancies of several metres per second do not yet allow us to conclude that the two techniques are measuring the same quantity. The irregularity decay time-constants between about 53 and 70 km are compared with the results of an advanced ion-chemistry model, and height profiles of recorded signal power are compared with model estimates in the same altitude range. The calculated amplitude shows good agreement with the data in that the maximum occurs at about the same height as that of the measured amplitude. The calculated time-constant agrees very well with the data below 60 km but is larger above 60 km by a factor of up to 2 at 64 km. The comparisons with the model are considered to be a good basis for more refined comparisons. Acknowledgements. This work has been supported by the UK Particle-Physics and Astronomy Research Council. The assistance of the director and staff of the EISCAT Scientific Association, the staff of the Norsk Polarinstitutt and the director and staff of the Swedish Institute of Space Physics is gratefully acknowledged. In addition the authors would like to thank Professor Evgeny Tereshchenko of the Polar Geophysical Institute in Mumansk, Russia and Dr Tuomo Nygrén of the University of Oulu, Finland for provision of data from EISCAT special program time during the November 1995 campaign. Topical Editor D. Alcaydé thanks E. J. Fremouw and another referee for their help in evaluating this paper.--> Correspondence to: I. K. Walker-->

Rietveld, M. T.; Turunen, E.; Matveinen, H.; Goncharov, N. P.; Pollari, P.

1996-12-01

14

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

15

Simulation study of the influence of the ionospheric layer height in the thin layer ionospheric model  

NASA Astrophysics Data System (ADS)

This work aims to contribute to the understanding of the influence of the ionospheric layer height (ILH) on the thin layer ionospheric model (TLIM) used to retrieve ionospheric information from the GNSS observations. Particular attention is paid to the errors caused on the estimation of the vertical total electron content ( vTEC) and the GNSS satellites and receivers inter-frequency biases (IFB), by the use of an inappropriate ILH. The work relies upon numerical simulations performed with an empirical model of the Earth's ionosphere: the model is used to create realistic but controlled ionospheric scenarios and the errors are evaluated after recovering those scenarios with the TLIM. The error assessment is performed in the Central and the northern part of the South American continents, a region where large errors are expected due to the combined actions of the Appleton Anomaly of the ionosphere and the South-Atlantic anomaly of the geomagnetic field. According to this study, there does not exist a unique ILH that cancels the vTEC error for the whole region under consideration. The ILH that cancels the regional mean vTEC error varies with the solar activity and season. The latitude-dependent conversion error propagates to the parameters of the model used to represent the latitudinal variation on the vTEC on the ionospheric layer, and to the IFB, when these values are simultaneously estimated from the observed sTEC. Besides, the ILH that cancels the regional mean vTEC error is different from the one that cancels the IFB error and the difference between both ILH varies with the solar activity and season.

Brunini, Claudio; Camilion, Emilio; Azpilicueta, Francisco

2011-09-01

16

Main ionospheric trough as a boundary layer in the ionosphere  

Microsoft Academic Search

The mid-latitude electron density trough observed in the topside ionosphere has been shown to be the near-Earth signature of the plasmapause and can provide useful information about the magnetosphere-ionosphere dynamics and morphology. Thus for present the evolution of iono-spheric trough in time and space domain we need some multipoint measurements and different type of measurements techniques. To develop a quantitative

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

2010-01-01

17

Model for artificial ionospheric duct formation due to HF heating  

NASA Astrophysics Data System (ADS)

Strong electron heating by the injection of highly powerful HF waves can lead to the formation of ionospheric plasma density perturbations that stretch along the magnetic field lines. Those density perturbations can serve as ducts for guiding natural and artificial ELF/VLF waves. This paper presents a theoretical model of duct formation due to HF heating of the ionosphere. The model is based on the modified SAMI2 code, and is validated by comparison with two well documented experiments. One experiment, conducted at the SURA heating facility, used the low orbit satellite DEMETER as a diagnostic tool to measure the electron and ion temperature and density along the overflying satellite orbit close to the magnetic zenith of the HF-heater. The second experiment, conducted at the EISCAT HF facility and diagnosed by the EISCAT Incoherent Scatter Radar, measured the vertical profiles of the electron and ion temperature between 150-600 km. The model agrees well with the observations, and provides a new understanding of the processes during ionospheric modification.

Milikh, G. M.; Demekhov, A. G.; Papadopoulos, K.; Vartanyan, A.; Huba, J. D.; Joyce, G.

2010-04-01

18

Artificial field-aligned irregularities in the nightside auroral ionosphere  

NASA Astrophysics Data System (ADS)

Experimental results from two Tromsø HF heating experiments in the nightside high latitudinal F region are examined. Bi-static scatter measurements of HF diagnostic signals were carried out on the London Tromsø St. Petersburg and Pori Tromsø St. Petersburg paths using a Doppler spectral method. The properties and behaviour of artificial field-aligned small-scale irregularities (striations) in the nightside high latitudinal F-region in course of the Tromsø ionospheric modification experiments are studied. Experimental studies have been performed by the use of phased array 1 with a beamwidth of 6° instead of 12 14° in phased array 2, more often used in Tromsø ionospheric modification experiments. The comparison between two experiments carried out in the same background geophysical conditions, shows the strongest striations in the field-aligned position of the heater beam. Possible explanation for this angular dependence is self-focusing of HF pump waves on striations causing the energy to be distributed asymmetrically. A principal question related to HF heating experiments is how is the disturbed auroral ionosphere modified. The results obtained on two paths simultaneously have shown that the strong heater-induced striations were observed along with natural ones. Velocities of heater-induced striations were quite different at different parts of the heated volume. It is suggested that the heater-induced striations can be grouped in two patches at different heights possibly due to the temperature-gradient-driven instability.

Blagoveshchenskaya, N. F.; Borisova, T. D.; Kornienko, V. A.; Leyser, T. B.; Rietveld, M. T.; Thidé, B.

2006-01-01

19

Lightning-induced intensification of the ionospheric sporadic E layer.  

PubMed

A connection between thunderstorms and the ionosphere has been hypothesized since the mid-1920s. Several mechanisms have been proposed to explain this connection, and evidence from modelling as well as various types of measurements demonstrate that lightning can interact with the lower ionosphere. It has been proposed, on the basis of a few observed events, that the ionospheric 'sporadic E' layer--transient, localized patches of relatively high electron density in the mid-ionosphere E layer, which significantly affect radio-wave propagation--can be modulated by thunderstorms, but a more formal statistical analysis is still needed. Here we identify a statistically significant intensification and descent in altitude of the mid-latitude sporadic E layer directly above thunderstorms. Because no ionospheric response to low-pressure systems without lightning is detected, we conclude that this localized intensification of the sporadic E layer can be attributed to lightning. We suggest that the co-location of lightning and ionospheric enhancement can be explained by either vertically propagating gravity waves that transfer energy from the site of lightning into the ionosphere, or vertical electrical discharge, or by a combination of these two mechanisms. PMID:15944700

Davis, C J; Johnson, C G

2005-06-01

20

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

21

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

NASA Astrophysics Data System (ADS)

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

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

2004-07-01

22

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

23

Quasi-Stationary Global Auroral Ionospheric Model: E-layer  

NASA Astrophysics Data System (ADS)

E-layer Auroral Ionospheric Model (E-AIM) is developed to provide temporal and spatial density distribution of the main ionosphere neutral species (NO, N(4S),N(2D)), and ions (N2+, NO+,O2+,O+) in the altitude range from 90 to 150 km. NRLMSISE-00 model [Picone et al., JGR 2003] is used for neutral atmosphere content and temperature determination, that is the input for the E-AIM model. The E-AIM model based on chemical equilibrium state in E-layer that reaches in chemical reactions between ionospheric species considering solar radiation ionization source, superposed with sporadic precipitation of magnetospheric electrons. The chemical equilibrium state in each location under specific solar and geomagnetic activity conditions reaches during numerical solution of the continuity equations for the neutrals and ions using the high-performance Gear method [Gear, 1971] for ordinary differential equation (ODE) systems. Applying the Gear method for solving stiff ODE system strongly reduce the computation time and machine resources comparing to widely used methods and provide an opportunity to calculate the global spatial E-layer ion content distribution. In contrast to the mid-latitude ionosphere, structure and dynamics of the auroral zone ionosphere (? ? 60-75° MLat) associated not only with shortwave solar radiation. Precipitating magnetospheric particle flux is the most important ionization source and is the main cause of E-layer disturbances. Precipitated electrons with initial energies of 1 - 30 keV influence the auroral ionosphere E-layer. E-AIM model can estimate ionization rate corresponds to auroral electron precipitation in two different ways: 1. with direct electron flux satellite data; 2. with differential energy spectrum reconstructed from OVATION-Prime empirical model [Newell, JGR 2009] average values, that allows to estimate ionosphere ion content for any time and location in the auroral zone. Comparison of E-AIM results with direct ionospheric observations (ionosonde, incoherent scatter radar) show good agreement of electron concentration vertical distribution values.

Nikolaeva, Vera; Gordeev, Evgeny; Kotikov, Andrey; Makarova, Ludmila; Shirochkov, Aleksander

2014-05-01

24

A Chapman-Layers Ionospheric Model for Mars  

Microsoft Academic Search

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 occultation measurements collected during 1998 through 2005 are used to fit the model. The present model does not include variations with solar extreme

Xiaoqing Pi; Charles D. Edwards; George A. Hajj; Chi Ao; Larry J. Romans; John L. Callas; Anthony J. Mannucci; Sami W. Asmar; Daniel S. Kahan

2008-01-01

25

Attenuation of high-frequency radio waves in the low ionosphere at high latitudes when the ionosphere is artificially perturbed by powerful radio emission  

Microsoft Academic Search

We have discovered a significant (up to 60% and more) attenuation of the intensity of high frequency probe signals received from the low nighttime ionosphere at high altitudes. The reason for the attenuation is that the ionosphere is being influenced by powerful shortwave radio emission. The Polar Geophysical Institute (PGI) was set up so that powerful shortwave radiation could artificially

S. I. Martynenko; V. A. Misyura; V. G. Simov; L. F. Chernogor; A. S. Shemet

1983-01-01

26

A sporadic third layer in the ionosphere of Mars.  

PubMed

The daytime martian ionosphere has been observed as a two-layer structure with electron densities that peak at altitudes between about 110 and 130 kilometers. The Mars Express Orbiter Radio Science Experiment on the European Mars Express spacecraft observed, in 10 out of 120 electron density profiles, a third ionospheric layer at altitude ranges of 65 to 110 kilometers, where electron densities, on average, peaked at 0.8 x 10(10) per cubic meter. Such a layer has been predicted to be permanent and continuous. Its origin has been attributed to ablation of meteors and charge exchange of magnesium and iron. Our observations imply that this layer is present sporadically and locally. PMID:16272118

Pätzold, M; Tellmann, S; Häusler, B; Hinson, D; Schaa, R; Tyler, G L

2005-11-01

27

Viscous Forces in Velocity Boundary Layers around Planetary Ionospheres.  

PubMed

A discussion is presented to examine the role of viscous forces in the transport of solar wind momentum to the ionospheric plasma of weakly magnetized planets (Venus and Mars). Observational data are used to make a comparison of the Reynolds and Maxwell stresses that are operative in the interaction of the solar wind with local plasma (planetary ionospheres). Measurements show the presence of a velocity boundary layer formed around the flanks of the ionosphere where the shocked solar wind has reached super-Alfvénic speeds. It is found that the Reynolds stresses in the solar wind at that region can be larger than the Maxwell stresses and thus are necessary in the local acceleration of the ionospheric plasma. From an order-of-magnitude calculation of the Reynolds stresses, it is possible to derive values of the kinematic viscosity and the Reynolds number that are suitable to the gyrotropic motion of the solar wind particles across the boundary layer. The value of the kinematic viscosity is comparable to those inferred from studies of the transport of solar wind momentum to the earth's magnetosphere and thus suggest a common property of the solar wind around planetary obstacles. Similar conditions could also be applicable to velocity boundary layers formed in other plasma interaction problems in astrophysics. PMID:10511515

Pérez-De-Tejada

1999-11-01

28

Incoherent scatter observations of an artificially modified ionosphere  

NASA Technical Reports Server (NTRS)

The 'experiment of opportunity' to test incoherent scatter radar techniques for the diagnostic study of a chemically induced modification of the ionosphere occasioned by the launch of the HEAO-C satellite is described. The optimal utilization of a steerable incoherent scatter radar for a short duration event is examined. The choice of keeping the antenna fixed to obtain good control data and excellent time resolution along a given direction versus scanning the antenna to obtain mixed spatial and temporal morphologies is discussed. Results for fixed position measurements, elevation scans, ion-drift, and total electron content are presented. The first unambiguous observations of a gas expansion 'snowplow effect' is reported along with the derivation of local and height-integrated plasma recombination rates and the full spatial, temporal, and dynamical morphologies of a large-scale ionospheric hole.

Wand, R. H.; Mendillo, M.

1984-01-01

29

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

30

Propagation of artificially excited Langmuir waves in the ionosphere  

SciTech Connect

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 wavelengths are produced that cannot be seen by the radar immediately, but that become observable after they have propagated for some distance and changed their wavelength according to the dispersion relation. 6 references.

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

1987-08-01

31

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

32

First results of artificial stimulation of the ionospheric Alfvén resonator at 78°N  

NASA Astrophysics Data System (ADS)

On 2 December 2005 a modulated X-mode ionospheric modification experiment was carried out using the Space Plasma Exploration by Active Radar (SPEAR) high power facility on Svalbard (78.15°N, 16.05°E), with the intention of artificially stimulating the Ionospheric Alfvén Resonator (IAR). A modulation frequency of 3 Hz was superimposed on a 20 minute on/off cycle. Local ionograms showed an E region ionosphere of sufficient plasma density for the SPEAR beam to strongly interact with the low-altitude ionospheric plasma. The Barentsburg pulsation magnetometer monitored the resulting wave activity in the 0.5-5 Hz frequency range. Clear enhancements of the spectral power at 3 Hz were observed in the D component data, when SPEAR was transmitting and there was little natural Pc1 wave activity. During part of the interval, when high power substorm-associated Pc1 waves occurred, the polarisation of the artificially-stimulated wave rotated from the D to the H component.

Scoffield, H. C.; Yeoman, T. K.; Robinson, T. R.; Baddeley, L. J.; Dhillon, R. S.; Wright, D. M.; Raita, T.; Turunen, T.

2006-10-01

33

Investigation of natural and artificial stimulation of the Ionospheric Alfven Resonator at high latitude  

NASA Astrophysics Data System (ADS)

Experimental verification of the existence of the Ionospheric Alfven resonator IAR was first provided with the identification of spectral resonance structures in mid-latitude induction magnetometer data in the frequency range 0 1 - 10 Hz Since that time the IAR has been identified at high latitudes and both natural and artificial stimulations of the IAR have been studied Artificial stimulation of the IAR allows the particle acceleration processes which occur at the Alfven velocity peak at the upper boundary of the IAR to be explored an important process in auroral particle acceleration and magnetosphere-ionosphere coupling Here recent progress in the experimental investigation of the high latitude IAR during both passive and active experiments will be reviewed

Yeoman, T. K.; Scoffield, H. C.; Wright, D. M.; Baddeley, L. J.

34

Observations and model calculations of an additional layer in the topside ionosphere above Fortaleza, Brazil  

Microsoft Academic Search

Calculations using the Sheffield University plasmasphere ionosphere model have shown that under certain conditions an additional layer can form in the low latitude topside ionosphere. This layer (the F3 layer) has subsequently been observed in ionograms recorded at Fortaleza in Brazil. It has not been observed in ionograms recorded at the neighbouring station São Luis. Model calculations have shown that

B. Jenkins; G. J. Bailey; M. A. Abdu; I. S. Batista; N. Balan

1997-01-01

35

Coupling of magnetopause-boundary layer to the polar ionosphere  

SciTech Connect

The authors develop a model which seeks to explain ultraviolet auroral images from the Viking satellite which show periodic bright regions which resemble [open quotes]beads[close quotes] or [open quotes]pearls[close quotes] aligned along the postnoon auroral oval. ULF geomagnetic pulsations observed in the cusp region are also addressed by this model. The model addresses plasma dynamics in the low-latitude boundary layer and interactions with the polar ionosphere by means of field-aligned current. The Kelvin-Helmholtz instability can develop in the presence of driven plasma flow, which can lead to the formation and growth of plasma vortices in the boundary layer. The finite conductivity of the earth ionosphere causes these vortices to decay. However regions of enhanced field-aligned power density in the postnoon auroral oval can be associated with field-aligned current filaments and boundary layer vortices. These structures may explain the observed bright spots. The authors also discuss the frequency spectrum and the polarization state of the pulsations.

Wei, C.Q.; Lee, L.C. (Univ. of Alaska, Fairbanks (United States))

1993-04-01

36

Ionosphere.  

National Technical Information Service (NTIS)

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

G. J. Gassmann

1972-01-01

37

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

38

Airborne studies of equatorial F layer ionospheric irregularities  

SciTech Connect

Radio wave and optical experiments were conducted onboard a U.S. Air Force research aircraft in March 1977 and March 1978 at low magnetic latitudes to investigate the effects of F region electron density amplitude. Scintillation measurements were used to monitor the development and motion of F region 6300-A O I airglow depletions, spread F, and scintillation producing irregularities that are all associated with low-density bubbles in the postsunset equatorial ionosphere. The 6300-A airglow depletions are the bottomside signature of low plasma density within the bubbles. Examples of multiple airglow depletions and their relation to variations in the F layer virtual height (h'F) and to the occurrence of amplitude scintillations on 250-MHz satellite signals are described. Estimates of the average bottomside electron density, from simultaneous ionosonde measurements and 6300-A airglow intensities, show electron density decreases of approx.66% within the bubbles. These decreases are approximately the same for bubbles observed at the magnetic equator and near Ascension Island (18 /sup 0/S magnetic latitude). The measurements at Ascension Island show that airglow depletions extend away from the magnetic equator into the southern 6300-A intertropical arc. Variations in the maximum poleward extent of airglow depletions and of associated ionospheric irregularities that give rise to amplitude scintillations were observed. These latitudinal variations are interpreted, using field line mapping considerations, as variations in the maximum altitude of plasma bubbles over the magnetic equator. A north-south flight confirms that the overall pattern of airglow depletions and associated ionospheric irregularities extends continuously across the magnetic equator to +-15/sup 0/ magnetic latitude.

Weber, E.J.; Buchau, J.; Moore, J.G.

1980-09-01

39

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

40

Model of Artificial Ionospheric Ducts due to the HF-heating  

NASA Astrophysics Data System (ADS)

The presence of field aligned density striations plays a critical role in the propagation of whistler waves in the ionosphere. Such density structures have often been observed to extend over distances covering entire magnetic field lines, trapping, channeling and reflecting whistler waves between conjugate regions. The possibility for artificially creating such trans-hemispheric ducts was first discussed by Perrine et al. [2006]. They showed that long term (> 15 minutes) continuous HF-heating of the F-region by powerful ionospheric heaters such as HAARP generates a strong thermal wave in the ionospheric and magnetospheric plasma. This thermal wave propagates along the magnetic field line through the topside ionosphere and magnetosphere, driving ion outflows, displacing the ambient plasma and leading to the formation of density ducts. Two recent experiments detected large scale ducts caused by the HF-heating. One experiment was conducted at HAARP and used the low orbit satellite DEMETER as a diagnostic tool [Milikh et al., 2008]. The experiment shows in situ detected plasma ducts with the spatial scale of a few tens kilometers. Another heating experiment was conducted at the EISCAT HF facility and used UHF radar as a diagnostic tool [Rietveld et al., 2003]. As a result vertical profiles of electron and ion temperature were obtained in the height range 150-600 km. It is the objective of this paper to present the first detailed model of the formation of ionospheric ducts due to HF-heating. The model is checked against the observations made at EISCAT. The results show a good agreement between the model and observations. Milikh, G.M., K. Papadopoulos, et al. (2008), Geophys. Res. Lett, 35, doi:10.1029/2008GL034630. Perrine, R.P., G.M. Milikh, K. Papadopoulos, et al., Radio Sci. (2006), 41, doi:10.1029/2005RS003371. Rietveld, M.T., M.J. Kosch, et al., J. Geophys. Res. (2003), 108, doi:10.1029/2002JA009543.

Vartanyan, A.; Milikh, G. M.; Demekhov, A. G.; Papadopoulos, K.; Huba, J.; Joyce, G. R.

2009-12-01

41

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

42

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

NASA Technical Reports Server (NTRS)

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

Cole, Keith D.

1993-01-01

43

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

2012-01-01

44

Biomimetic layer-by-layer assembly of artificial nacre  

NASA Astrophysics Data System (ADS)

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 CaCO3.

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

2012-07-01

45

Influence of layered structure of the lower ionosphere on nonmonotonic spectrum behavior of ELF atmospheric noise  

SciTech Connect

The authors present studies related to resonance phenomena occurring between and within different layers in the ionosphere, and the effect these resonances can have on the amplitude of extremely low frequency (ELF) wave propagation through the ionosphere. They follow several model problems to illustrate the impact of theses effects.

Molchanov, O.A. [Institute of Physics of the Earth, Moscow (Russian Federation)] [Institute of Physics of the Earth, Moscow (Russian Federation); [Univ. of Electro-Communications, Chofu (Japan); Nickolaenko, A.P. [Institute of Radio Astronomy, Kharkov (Ukraine)] [Institute of Radio Astronomy, Kharkov (Ukraine); Rafalsky, V.A. [Institute of Radio Astronomy, Kharkov (Ukraine)] [Institute of Radio Astronomy, Kharkov (Ukraine); [Univ. of Electro-Communications, Chofu (Japan); Schecotov, A.Yu. [IZMIRAN, Moscow (Russian Federation)] [IZMIRAN, Moscow (Russian Federation); Hayakawa, M. [Univ. of Electro-Communications, Chofu (Japan)] [Univ. of Electro-Communications, Chofu (Japan)

1994-11-15

46

Artificial ducts caused by HF heating of the ionosphere by HAARP  

NASA Astrophysics Data System (ADS)

We report on satellite observations of plasma density enhancements (ducts) in the topside ionosphere during four HAARP/BRIOCHE campaigns during 2009-2010. Artificial ducts, caused by high-power HF radio wave injections from the HAARP transmitter toward the magnetic zenith, are detected by the DEMETER and DMSP satellites on a regular basis when there is a perceptible ionospheric F2 peak density. Overall, the plasma density enhancements detected between 0930 and 1230 LT varied from 3-13%, while those during ˜1730-2215 LT were typically 15-40%. We also used a modified SAMI2 model to study the artificial ducts' mechanism driven by HF electron heating in the bottomside F2 region. The heating builds up the plasma pressure, thus pushing plasma along the magnetic field. The simulation results performed for the input parameters similar to the conditions of the heating experiments are in fair agreement with the pertinent observations. The ducts seem to be produced most efficiently for heating frequencies quite close to the critical frequency foF2.

Vartanyan, A.; Milikh, G. M.; Mishin, E.; Parrot, M.; Galkin, I.; Reinisch, B.; Huba, J.; Joyce, G.; Papadopoulos, K.

2012-10-01

47

Thin Ionospheric Layers Retrieved from Galileo Radio Occultations: Forcing by Gravity Waves?  

Microsoft Academic Search

Measurements of Jupiter's ionosphere from the first Galileo radio-occultation have indicated the presence of thin electron layers below the main broad ``F-type'' peak. At ingress (24(deg) S) the SNR was sufficently large to retrieve two layers just below the 10-nbar level ~ 75 km apart having widths ~ 40 km. We suggest that these layers are driven by vertically propagating

F. M. Flasar; P. J. Schinder; D. P. Hinson

1996-01-01

48

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

49

Physical mechanism and statistics of occurrence of an additional layer in the equatorial ionosphere  

Microsoft Academic Search

A physical mechanism and the location and latitudinal extent of an additional layer, called the F3 layer, that exists in the equatorial ionosphere are presented. A statistical analysis of the occurrence of the layer recorded at the equatorial station Fortaleza (4øS, 38øW; dip 9øS) in Brazil is also presented. The F3 layer forms during the morning-noon period in that equatorial

N. Balan; I. S. Batista; M. A. Abdu; J. MacDougall; G. J. Bailey

1998-01-01

50

Magnetospheric waves and the atmosphere-ionosphere layer  

Microsoft Academic Search

A novel approach to the issue of what effect the ionosphere and atmosphere have on magnetospheric phenomena, an approach that provides explicit boundary conditions for coupled hydromagnetic waves and makes it possible to give an explicit solution to the pulsation problem within a particularly simple configuration, is presented. It is shown that, consistent with well-known observations, the amplitude of resonantly

E. Hameiri; M. G. Kivelson

1991-01-01

51

Planetary ionospheres  

NASA Technical Reports Server (NTRS)

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

Bauer, S. J.

1977-01-01

52

Doppler frequency variations in the field-aligned scattering of VHF waves by artificial irregularities of the ionosphere  

Microsoft Academic Search

Measurements of the DoppIer shift of the frequency spectrum in the field-aligned scattering of radio waves by artificial irregularities induced in the F region of the ionosphere by the action of high-power high-frequency radio radiation have been carried out at high and very-high frequencies [ 1-8]. In those studies the authors have obtained the values of the frequency shifts corresponding

A. V. Korovin; A. M. Nasyrov; E. V. Proskurin; N. N. Yagnov

1982-01-01

53

Response of the M1 Layer of the Mars Ionosphere to Solar Variability  

NASA Astrophysics Data System (ADS)

We investigate the response of the two main plasma layers of the ionosphere of Mars to changes in incident ionizing solar flux, with a focus on the highly variable secondary layer. We determine the altitude, number density, and vertical width of both layers in 5600 Mars Global Surveyor (MGS) electron density profiles, and analyze the variation in these parameters with the solar zenith angle. We also compare these parameters to changes in the incident EUV and soft X-ray solar flux as represented by the Solar Irradiance Platform (SIP) model. We find that the low-altitude, secondary layer, (M1), responds to changes in the solar flux and solar zenith angle in a manner similar to that of the primary layer of the ionosphere, (M2). One significant difference is the vertical width of the M1 layer, which increases with increasing peak electron density, whereas the width of M2 layer does not appear strongly correlated with the density of the layer. We also use a one-dimensional photochemical model to simulate the Mars ionosphere each day during a six month stretch of MGS observations, with daily SIP irradiances as input. Both layers of the simulated electron density profiles exhibit many of the same responses to solar zenith angle and incident solar flux as seen in the MGS data. However, the simulations do not show an increase in the vertical width of the M1 layer as the peak number density increases.

Fallows, K.; Girazian, Z. R.; Matta, M. M.; Withers, P.

2012-12-01

54

The sheath/ionosphere boundary layer at Venus  

NASA Technical Reports Server (NTRS)

At Venus the interaction of the shocked solar wind and cold planetary ions takes place in the dayside mantle. The shocked solar wind is a warm, drifting Maxwellian plasma whereas the planetary plasma is cold; the plasma in the mantle is strongly magnetized. The coexistence of these two populations is unstable, and it leads to wave excitations that organize the energy and momentum exchange between the shocked solar wind and the plasma of planetary origin. The source of the free energy is the solar wind. The intensive wave activity seen in the 100 Hz channel of the wave instrument onboard the Pioneer-Venus Orbiter in the dayside mantle region of Venus can be identified as almost electrostatic VLF waves excited by the kinetic branch of the modified two-stream lower hybrid instability. The waves interact with the particles, and the planetary plasma is heated and accelerated outside the ionosphere, close to its upper boundary. This way solar wind scavenges the ionosphere, and planetary ions leave the planetary magnetosphere. A portion of the wave energy is capable of penetrating directly into the ionosphere and heating it.

Szego, K.; Shapiro, V. D.; Ride, S. K.; Nagy, A. F.; Shevchenko, V. I.

1995-01-01

55

Ionospheric F2-Layer Semi-Annual Variation in Middle Latitude by Solar Activity  

NASA Astrophysics Data System (ADS)

We examine the ionospheric F2-layer electron density variation by solar activity in middle latitude by using foF2 observed at the Kokubunji ionosonde station in Japan for the period from 1997 to 2008. The semi-annual variation of foF2 shows obviously in high solar activity (2000-2002) than low solar activity (2006-2008). It seems that variation of geomagnetic activity by solar activity influences on the semi-annual variation of the ionospheric F2-layer electron density. According to the Lomb-Scargle periodogram analysis of foF2 and Ap index, interplanetary magnetic field (IMF) Bs (IMF Bz <0) component, solar wind speed, solar wind number density and flow pressure which influence the geomagnetic activity, we examine how the geomagnetic activity affects the ionospheric F2-layer electron density variation. We find that the semi-annual variation of daily foF2, Ap index and IMF Bs appear clearly during the high solar activity. It suggests that the semi-annual variation of geomagnetic activity, caused by Russell-McPherron effect, contributes greatly to the ionospheric F2-layer semi-annual electron density variation, except dynamical effects in the thermosphere.

Park, Yoon-Kyung; Kwak, Young-Sil; Ahn, Byung-Ho; Park, Young-Deuk; Cho, Il-Hyun

2010-12-01

56

Variability of an additional layer in the equatorial ionosphere over Fortaleza  

Microsoft Academic Search

The day-to-day variations (or the weather) of an additional layer, called the F3 layer, that has been predicted to exist at altitudes above the F2 peak in the equatorial ionosphere are studied through ionosonde observations and theoretical modeling. The ionograms recorded in 1995 at the equatorial station Fortaleza (4°S, 38°W dip angle 9°S) in Brazil show the occurrence of the

N. Balan; I. S. Batista; M. A. Abdu; S. Watanabe; J. MacDougall

2000-01-01

57

On the coupling of layer instabilities in the nighttime midlatitude ionosphere  

Microsoft Academic Search

There are two plasma-structuring mechanisms that are known to operate at night in the midlatitude ionosphere, the Perkins instability (Perkins, 1973) in the F region, and the more recently discovered sporadic-E layer (EsL) instability (Cosgrove and Tsunoda, 2002) in the E region. Both are layer processes, whose coupled response has been shown to be more unstable than either by itself

Roland T. Tsunoda

2006-01-01

58

Influence of the atmospheric surface layer on the penetration of the electric field from the earth's surface into the ionosphere  

NASA Astrophysics Data System (ADS)

In the used model, the quasistationary electric field in the atmosphere of the Earth is obtained by solving the conductivity equation. The penetration characteristics of the electric field from the Earth's surface into the ionosphere depend on both atmospheric and ionosphere conductivity. The ionosphere is taken into account by setting a special condition on the upper boundary of the atmosphere. The influence of the atmospheric surface layer with a reduced conductivity on the penetration of the electric field from the surface of the Earth into the ionosphere is analyzed.

Pomozov, E. V.

2014-01-01

59

Formation mechanism of additional layers above regular F2 layer in the near-equatorial ionosphere during quiet period  

NASA Astrophysics Data System (ADS)

Earlier the model studies demonstrated that equatorial F2 layer stratification and an additional F3 layer appear in simulation results only by taking into account zonal electric field. Nanan Balan concluded that F3 layer forms during morning-noon period, when the ionization processes dominate over chemical losses and when there is a large upward flow of ionization due to the combined effect of E×B drift and neutral wind. Our recent studies specify that during geomagnetic storms, a non-uniform in height zonal electric fields at the geomagnetic equator form the additional layers above regular F2 layer. In this paper, we consider the formation mechanism of the additional layers in a near-equatorial ionosphere during quiet geomagnetic conditions. This study presents the comparison of the GSM TIP numerical simulations and observation data of Intercosmos-19 satellite. We confirmed that the non-uniform in height vertical plasma drifts form the additional layers at the geomagnetic equator.

Klimenko, M. V.; Klimenko, V. V.; Karpachev, A. T.

2012-12-01

60

Regular changes in the critical frequency of the F 2 layer of the quiet midlatitude ionosphere  

Microsoft Academic Search

A method for constructing the empirical model of the F2 layer critical frequency (foF2) under magnetically quiet conditions, aimed at analyzing disturbances of any nature, is proposed. This method has been analyzed,\\u000a and typical features of regular changes in foF2 of the quiet ionosphere and day-to-day foF2 variability are analyzed using the data from Irkutsk and Slough stations as an

M. G. Deminov; G. A. Zherebtsov; O. M. Pirog; V. N. Shubin

2009-01-01

61

Regular changes in the critical frequency of the F2 layer of the quiet midlatitude ionosphere  

Microsoft Academic Search

A method for constructing the empirical model of the F2 layer critical frequency ( foF2) under magnetically quiet conditions, aimed at analyzing disturbances of any nature, is proposed. This method has been analyzed, and typical features of regular changes in foF2 of the quiet ionosphere and day-to-day foF2 variability are analyzed using the data from Irkutsk and Slough stations as

M. G. Deminov; G. A. Zherebtsov; O. M. Pirog; V. N. Shubin

2009-01-01

62

Coherent structure generated in the boundary layer of a laboratory-created ionospheric depletion  

NASA Astrophysics Data System (ADS)

Laboratory experiments have been conducted to simulate the boundary processes of ionospheric depletion. The ionospheric depletion was modeled through releasing depletion chemical (SF6) into the ambient plasmas. These plasmas were segregated into two regions by a boundary layer of width electric scale length. In the localized boundary layer, the electron density decreased sharply that yielded steep density gradients. Meanwhile, the floating potential increased in the time scales of the lower hybrid (LH) period, which produced strong sheared electron flows. The shear frequency ?s=VE/LE, which characterizes the sheared flow, is much larger than the LH frequency ?LH. A coherent structure was observed when the floating potential fluctuations were analyzed using digital spectral analysis techniques. Comparison with the theory indicated that the structure is driven by the electron-ion hybrid instability which is generated owing to the nonlinear coupling between the electron density gradient and the sheared electron flow. Our results are important to study the early phase nonlinear evolution of the ionospheric depletion, especially in the development of plasma irregularities and turbulence in the boundary layer.

Liu, Yu; Cao, Jinxiang; Xu, Liang; Zhang, Xiao; Wang, Pi; Wang, Jian; Du, Yinchang; Zheng, Zhe

2014-03-01

63

Resonant scattering of energetic electrons in the plasmasphere by monotonic whistler-mode waves artificially generated by ionospheric modification  

NASA Astrophysics Data System (ADS)

Modulated high-frequency (HF) heating of the ionosphere provides a feasible means of artificially generating extremely low-frequency (ELF)/very low-frequency (VLF) whistler waves, which can leak into the inner magnetosphere and contribute to resonant interactions with high-energy electrons in the plasmasphere. By ray tracing the magnetospheric propagation of ELF/VLF emissions artificially generated at low-invariant latitudes, we evaluate the relativistic electron resonant energies along the ray paths and show that propagating artificial ELF/VLF waves can resonate with electrons from ~ 100 keV to ~ 10 MeV. We further implement test particle simulations to investigate the effects of resonant scattering of energetic electrons due to triggered monotonic/single-frequency ELF/VLF waves. The results indicate that within the period of a resonance timescale, changes in electron pitch angle and kinetic energy are stochastic, and the overall effect is cumulative, that is, the changes averaged over all test electrons increase monotonically with time. The localized rates of wave-induced pitch-angle scattering and momentum diffusion in the plasmasphere are analyzed in detail for artificially generated ELF/VLF whistlers with an observable in situ amplitude of ~ 10 pT. While the local momentum diffusion of relativistic electrons is small, with a rate of < 10-7 s-1, the local pitch-angle scattering can be intense near the loss cone with a rate of ~ 10-4 s-1. Our investigation further supports the feasibility of artificial triggering of ELF/VLF whistler waves for removal of high-energy electrons at lower L shells within the plasmasphere. Moreover, our test particle simulation results show quantitatively good agreement with quasi-linear diffusion coefficients, confirming the applicability of both methods to evaluate the resonant diffusion effect of artificial generated ELF/VLF whistlers.

Chang, S. S.; Ni, B. B.; Bortnik, J.; Zhou, C.; Zhao, Z. Y.; Li, J. X.; Gu, X. D.

2014-05-01

64

An investigation of the double layers caused by space vehicles moving through the ionosphere  

NASA Astrophysics Data System (ADS)

On the basis of non-steady-state nonlinear coupling equations of high-frequency field, density disturbance and potential, the evolution of double layers in the wake region of space vehicles moving through the ionosphere is numerically simulated in the non-static limit case. The results show that the interactions among plasmas, the vehicle and high-frequency electromagnetic waves radiated from the antenna system of the vehicle can lead to the formation of double layers. It is shown that the double layer is a nonlinear entity-caviton. Potential disturbance far away from the vehicle and the peak value of potential near the vehicle in the double layer are obvious. This is very important for detecting space vehicles with a stealth characteristic and preventing space vehicles from being harmed by double layers.

Liu, Sanqiu; Liao, Jingjing

2010-10-01

65

Observations of filamentary field-aligned current coupling between the magnetospheric boundary layer and the ionosphere  

NASA Technical Reports Server (NTRS)

A distinct class of dayside high-latitude magnetic pulsations can be identified from the spatial characteristics of the disturbance field. These pulsations exhibit traveling radial patterns such as would result from moving filaments of field-aligned current interacting with the ionosphere to produce cells of Hall current and vortexlike plasma flow. Time intervals containing a series of continuous multiple vortices are investigated here. The vortices occur on the boundary between sunward and antisunward ionospheric plasma convection. Low altitude DMSP satellite particle measurements indicate that the vortices are on magnetic field lines which map to the inner edge of the magnetospheric low latitude boundary layer. No repetitive solar wind disturbance (e.g., pressure variations) appears to be associated with the events, suggesting that the vortices are related to a local magnetospheric instability. No strong correlation between interplanetary field conditions and the detection of vortices is found.

Clauer, C. R.; Mchenry, M. A.; Friis-Christensen, E.

1990-01-01

66

Effect of double layers on magnetosphere-ionosphere coupling  

NASA Technical Reports Server (NTRS)

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

Lysak, Robert L.; Hudson, Mary K.

1987-01-01

67

Rocket/Radar Investigation of Lower Ionospheric Electrodynamics Associated with Intense Midlatitude Sporadic-E Layers  

NASA Technical Reports Server (NTRS)

Sporadic layers, which appear in the region from 100 km to 120 km are thought to be formed by convergent Pedersen drifts induced by altitude gradients in the zonal neutral wind. In this altitude region NO+ and 02+ are the major ions produced by photoionization and charge exchange of atmospheric and ionospheric species. The relative composition of atmospheric ions and meteoric ions in sporadic layers is important in determining their persistence, the time scales for formation, and the electrical conductivity of the layers. This rocket investigation will include a diagnosis of the neutral wind field and the electric field distribution. Coupled with ion composition measurements we will be able to expose the relevant formation mechanisms and the electrodynamic consequences of their existence. A rocket trajectory has been chosen to provide substantial horizontal sampling of the layer properties and knowledge of the horizontal gradients in composition and density are essential to determine the polarization electric fields that may be associated with ionospheric layers. The University of Texas at Dallas (UTD) is responsible for designing, building, and operating the ion mass spectrometers included on these rockets. The following provides a summary of the UTD accomplishments in the second year of the project as well as a description of the plans for the third year's activities. The UTD mass spectrometer acronym has been coined as PRIMS for Puerto Rico Ion Mass Spectrometer.

Heelis, R. A.

1998-01-01

68

Effect of double layers on magnetosphere-ionosphere coupling  

NASA Technical Reports Server (NTRS)

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

Lysak, Robert L.; Hudson, Mary K.

1987-01-01

69

Generation of 'artificial' bursts in a turbulent boundary layer  

NASA Technical Reports Server (NTRS)

In an effort to better understand the physics and structure of coherent events in a turbulent boundary layer, an attempt is made to produce 'artificial' bursts. These are generated in a unique turbulent boundary layer, developed on a flat plate towed in an 18-m water channel, and thus with negligible freestream turbulence. The burst-like events are produced by either withdrawing near-water fluid from two minute holes separated in the spanwise direction, or by pitching a miniature delta wing that is flush-mounted to the wall. Either of these two actions generates a hairpin-like vortex and low-speed streak that resemble naturally occurring structures. The resulting sequence of events that occur at a given location can be controlled at will, thus allowing detailed examination via phase-locked measurements and flow visualization. In this paper, the artificial bursts are compared with natural, random bursts, using flow visualization and hot-film signals. Detailed quantitative data on topographical details and dynamical significance of the bursting structure will be addressed in a forthcoming article.

Gad-El-hak, M.; Hussain, A. K. M. F.

1986-01-01

70

Shear flow driven Rossby-Khantadze electromagnetic planetary vortices in the ionospheric E-layer  

NASA Astrophysics Data System (ADS)

A system of equations describing the nonlinear interaction of coupled Rossby-Khantadze electromagnetic waves with a sheared zonal flow in the Earth's ionospheric E-layer is obtained. For the linear regime the corresponding region of phase velocities is analyzed and the appropriate stability condition of zonal flow is deduced. It is shown that the sheared zonal flow may excite solitary vortical structures in the form of a row of counter-rotating vortices whose amplitudes decrease with the increase of the zonal flow parameter. This conclusion is consistent with the stabilizing idea of a sheared zonal flow. The possibility of an intense magnetic-field generation is shown.

Kaladze, T. D.; Kahlon, L. Z.; Horton, W.; Pokhotelov, O.; Onishchenko, O.

2014-04-01

71

Ionospheric anomaly due to seismic activities - Part 2: Evidence from D-layer preparation and disappearance times  

Microsoft Academic Search

We show evidences for anomalous ionospheric behaviour in the signal of Indian navy VLF transmitting station named VTX due to earthquakes in the South Asian region. We concentrate on the variation of the D-layer preparation time (DLPT) and D-layer disappearance time (DLDT) in a period of sixteen months and study their average behaviors. We identify those days in which DLPT

S. K. Chakrabarti; S. Sasmal

2010-01-01

72

Numerical simulation of the F2-layer stratification and appearance of the F3 and G layers in the equatorial ionosphere: The morphology of the phenomena  

NASA Astrophysics Data System (ADS)

This work is devoted to a numerical simulation of the equatorial ionosphere, performed using the GSM TIP model completed with a new block for calculating the electric field. It has been indicated that the usage of the wind system calculated according to the MSIS-90 model makes it possible to reproduce the electromagnetic drift velocities at the equator, the effect of the F2-layer stratification, and the appearance of the F3 layer in the equatorial ionosphere. The calculations performed using the modified GSM TIP model made it possible to detect a maximum in the electron density vertical profile at an altitude of ˜1000 km, formed by H+ ions, which we called the G layer. If this layer actually exists, it can be observed during sounding the low-latitude ionosphere from satellites during dark time of day.

Klimenko, M. V.; Klimenko, V. V.

2011-10-01

73

Mechanisms of stratification of the F2 layer and formation of the F3 and G layers in the equatorial ionosphere  

NASA Astrophysics Data System (ADS)

The paper is dedicated to the studies of formation mechanisms of additional layers in the equatorial ionosphere carried out using numerical simulations with use of the Global Self-Consistent Model of the Thermosphere, Ionosphere, and Protonosphere (GSM TIP) modified in the part of the solution of the electric field equation in the Earth's ionosphere. Calculations were preformed for quiet geomagnetic conditions using the MSIS-90 model for the calculation of thermospheric parameters. The obtained spatio-temporal pattern of thermospheric circulation and the variations in the dynamo electric field obtained on its basis make it possible to reproduce the stratification effect of the F2 layer and the appearance of the F3 layer in the equatorial ionosphere due to the action of the nonuniform in height zonal electric field at the geomagnetic equator. On the basis of the earlier presented results of calculations using the modified GSM TIP model, the appearance of a maximum in the vertical profile of the electron density at a height of ˜1000 km formed by H+ ions, which we called the G layer, has been predicted. Numerical simulations showed that this layer is formed by the meridional component of the thermospheric wind and is related to the formation of the nighttime midlatitude maximum at heights of the ionospheric F region.

Klimenko, M. V.; Klimenko, V. V.

2012-05-01

74

Two-frequency method of the ionospheric diagnostics by API technique  

Microsoft Academic Search

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

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

2008-01-01

75

A comparative sporadic-E layer study between two mid-latitude ionospheric stations  

NASA Astrophysics Data System (ADS)

Hourly systematic measurements of the highest frequency reflected by the sporadic-E layer (foEs) recorded from January 1976 to June 2009 at the ionospheric stations of Rome (Italy, 41.8°N, 12.5°E) and Gibilmanna (Italy, 37.9°N, 14.0°E) were considered to carry out a comparative study between the sporadic E layer (Es) over Rome and Gibilmanna. Different statistical analysis were performed taking into account foEs observations near the periods of minimum and maximum solar activity. The results reveal that: (1) independently from the solar activity, Es develops concurrently over extended regions in space, instead of being a spatially limited layer which is transported horizontally by neutral winds over a larger area; especially during summer months, when an Es layer is present at Rome, there is a high probability that an Es layer is also present over Gibilmanna, and vice versa; (2) Es layer lifetimes of 1-5 h were found; in particular, Es layers with lifetimes of 5 h both over Gibilmanna and Rome are observed with highest percentages of occurrence in summer ranging between 80% and 90%, independently from the solar activity; (3) latitudinal effects on Es layer occurrence emerge mostly for low solar activity during winter, equinoctial, and summer months, when Es layers are detected more frequently over Gibilmanna rather than Rome; (4) when the presence of an Es layer over Rome and Gibilmanna is not simultaneous, Es layer appearance both over Rome and Gibilmanna confirms to be a locally confined event, because drifting phenomena from Rome to Gibilmanna or vice versa have not been emphasized.

Pietrella, M.; Pezzopane, M.; Bianchi, C.

2014-07-01

76

EISCAT incoherent scatter radar measurements of artificial ionospheric modification at sub-ms time scales  

NASA Astrophysics Data System (ADS)

Efficient generation of ELF/VLF waves through the modulation of ionospheric currents requires reliable measurements of the modulated current for different heater parameters. Incoherent scatter radar (ISR) measurements of modified plasma densities/temperatures would be ideal in quantifying the heating and cooling cycles in response to modulated heating by high-power HF waves. Considering the ms time scales of ELF/VLF generation processes, it is necessary to resolve the heating and cooling cycles at sub-ms time scales. Such measurements using ISRs have largely been avoided due to the common knowledge that the instrument requires minutes of integration. We present herein the results of an epoch averaging experiment using EISCAT that provides 0.2 ms resolution ISR power measurements as a function of phase into the HF heater ON and OFF cycle. In ELF/VLF generation, it is the electron temperature (Te) modulation that results in the modulation of electron collision frequency/mobility and therefore the electrojet modulation. Assuming a reliable electron collision frequency for transport as a function of Te, it is necessary to measure Te and electron density (Ne) simultaneously to predict the ionospheric current modulation. This is possible if (1) two incoherent scatter radars operating at sufficiently different frequencies are used and if (2) the Debye length and Bragg wavelengths are comparable. For the experiment results presented here, the ionospheric volume modified by the EISCAT heater were probed by both EISCAT UHF and VHF incoherent scatter radars operating at 0.16 m and 0.67 m Bragg wavelengths. Considering Ne=1e9 e/m3 in the D region ionosphere, for electron temperature Te=300 K, the Debye length is 0.38 m, where as for Te=1000 K the Debye length is 0.69 m; these parameters are reasonably appropriate to extract Te/Ne from simultaneous UHF/VHF data. We successfully detected ISR power modulation both in the E and F region heated ionosphere. Our findings are as follows: (1) D region ISR spectral broadenings are identified as evidence of plasma heating from 100 km down to 75 km altitude; (2) During the 1.4 ms ON and 1.4 ms OFF heating cycle at 4 MHz X mode, we successfully detected D region modulations of ISR power, with the modulations never recovering to the non-heated state. This implies a time-scale for heating/cooling greater than several ms or longer; (3)In the F region, the time scale of the development of plasma turbulence is measured to be near 0.3 ms; and the decay is around 0.2 ms. In addition, we will present the results of our ongoing attempts to infer Te and Ne profiles by combining UHF and VHF radar measurements.

Bahcivan, H.; Nicolls, M. J.

2011-12-01

77

Measurements and modelling of intermediate, descending, and sporadic layers in the lower ionosphere: Results and implications for global-scale ionospheric-thermospheric studies  

SciTech Connect

The authors demonstrate that conventional ionosondes can provide long-term observations on intermediate, descending, and transitional layers in the 100-200 km altitude region of the ionosphere. Using 15 consecutive days of observations at Townsville, Australia, during the SUNDIAL campaign of September 1989, they tracked the birth of the layers at altitudes above 150 km and their systematic downward motion to the 110 km region at rates between 4 and 5 km/hr. The observations are compared with NCAR TIGCM simulations, and the results show: (1) that the layering process is identifiable with meridional wind-shear-node convergence of ions; (2) that zonal wind controls of the layers are insignificant under the prevailing conditions; and (3) that electric fields play an important role in the effectiveness of the ion-convergence and downward transport processes at altitudes above 125 km. The measurement and modeling comparisons are the first of a kind, providing insight into the relative roles of winds and electric fields, and opening possibilities for determining the global characteristics of the layers and their cause-effect roles in the dynamics of the lower ionospheric-thermospheric domain.

Wilkinson, P.J.; Szuszczewicz, E.P.; Roble, R.G.

1992-01-24

78

E-layer dominated ionosphere observed by EISCAT/ESR radars during solar minimum  

NASA Astrophysics Data System (ADS)

E-layer dominated ionosphere (ELDI) is referred to vertical profiles having peak density at E-layer altitudes (Mayer and Jakowski, 2009). In this paper, characteristics of ELDI were investigated with the help of field-aligned measurements of EISCAT/ESR radars during 2009-2011. ELDI events were identified with simple but reasonable criterions, in which a minimal duration was required to exclude possible 'fake' events induced by random errors in measurements. It was found that ELDI were observed more often in winter than other seasons. In winter, occurrence of ELDI peaks around mid-night at auroral latitude, while it reaches its maximum around geomagnetic local noon at ESR latitude. Our results imply that ELDI looks like a sporadic rather than a regular phenomenon, being contrary to previous results inferred from radio occultation measurements. Discrepancy in duration of ELDI events observed by the two radars is remarkable, being 30 minutes at TromsØ on average and about a half of it at Svalbard. During the presence of ELDI, average thickness of E-layer exhibits undetectable variations at the two sites, as well as HmE and the ratio of NmE/NmF. Case studies reveal that either extra E-layer ionization possible induced by auroral precipitation or density depletion in F-layer caused by plasma convection alone could lead to the presence of ELDI. We suggest that both them play an important role in ELDI formation.

Cai, Hongtao; Li, Fei; Shen, Ge; Zhan, Weijia; Zhou, Kangjun; McCrea, Ian W.; Ma, Shuying

2014-05-01

79

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

NASA Technical Reports Server (NTRS)

We 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 magnetic local time (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 greater than 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.

Burke, W. J.; Machuzak, J. S.; Maynard, N. C.; Basinska, E. M.; Erickson, G. M.; Hoffman, R. A.; Slavin, J. A.; Hanson, W. B.

1994-01-01

80

The influence of the atmospheric ozone layer on the formation of layer D of the ionosphere at sunrise  

NASA Astrophysics Data System (ADS)

Phase data of 13,6 Khz VLF signal, transmitted from Golfo Nuevo, Argentina (43 S, 65 W), and recorded in Atibaia, SP (23 S, 46 W), together with atmospheric ozone measurements from Dobson spectrophotometers located in Cachoeira Paulista, SP (22 S, 45 W) and Natal, RN (4 S, 36 W) are analyzed. A possible influence of the atmospheric ozone layer on the sunrise of the ionospheric D layer is studied. A reasonably good correlation between fluctuation in the total ozone content over Cachoeira Paulista and the sunrise phase transition of the VLF signal is found. This represents experimental evidence that the solar ultraviolet radiation (in specific wavelengths), which is absorbed in the ozone layer, is mainly responsible for the D layer at these times. Also, these correlations seem to occur, in general, with one day delay in the VLF fluctuation, as compared to those in the ozone, during the first half of the year, and advanced in the second half. This last result suggests an annually recurrent behavior in the horizontal transport of the atmospheric ozone.

Medrano, R. A.; Piazza, L. R.; Abdu, M. A.

1982-07-01

81

Behavior of parameters of the ionospheric F2 layer at the edge of the centuries: 2. Height of the layer  

NASA Astrophysics Data System (ADS)

The trends in the height of the ionospheric F2 layer, hmF2, for the period from the end of the 1990s to the beginning of the 2010s are considered. It is shown that for a majority of the considered situations (time of the day plus season) negative trends are obtained for all stations for which series of initial data satisfying the requirements were found. They vary from -1.2 to -3.1 km per year. The trends in the daytime are slightly higher than in the postsunset period which apparently manifests the influence of the contraction of the upper atmosphere on changes in the hmF2 value.

Danilov, A. D.; Konstantinova, A. V.

2013-07-01

82

Observed Response of the Ionospheric F2–Layer and Lower Thermosphere to Geomagnetic Storms during High Solar Activity  

Microsoft Academic Search

The response of the critical frequency of the ionosphere F2–layer, described by its main Fourier components (daily constant, “diurnal” and “semidiurnal waves”) and the lower thermosphere dynamics to the geomagnetic storms in July 1991 and February 1992 is studied. The daily constant displays a negative response, however, the magnitude of reaction depends on the season and latitude. The amplitudes of

Dora Pancheva; Plamen Mukhtarov

1998-01-01

83

Investigation of natural and artificial stimulation of the ionospheric Alfvén resonator at high latitude  

NASA Astrophysics Data System (ADS)

A brief review is provided of recent progress in understanding the ionospheric Alfvén resonator (IAR) at high latitude. Firstly, naturally occurring resonances of the IAR as detected by pulsation magnetometers in the auroral zone at Sodankylä and in the polar cap at Barentsburg are considered. The characteristics of the IAR in the two regions are broadly similar, although the effects of solar illumination are less clear at the higher latitudes. Secondly we review recent attempts to stimulate the IAR through high-power radio frequency experiments both in the auroral zone at Tromsø with the European Incoherent SCATter (EISCAT) heater, and within the polar cap at Longyearbyen with the Space Plasma Exploration by Active Radar (SPEAR) facility. In the auroral zone at, Tromsø the stimulated IAR has been observed by ground-based magnetometers, and through electron acceleration observed on the FAST spacecraft. At SPEAR in the polar cap, the stimulated IAR has been investigated, with ground magnetometers, with the first results indicative of a positive detection.

Yeoman, T. K.; Scoffield, H. C.; Wright, D. M.; Baddeley, L. J.; Vasilyev, A. N.; Semenova, N. V.

2008-09-01

84

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

SciTech Connect

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

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

1992-10-22

85

Study of Nocturnal Stratification of the Ionospheric F-Layer Over Karachi during Solar CYCLE-22 (1986-96)  

NASA Astrophysics Data System (ADS)

This study has been carried out employing the ionospheric data of Karachi (24.950 N, 67.140 E) for a complete Solar Cycle (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 condition. Though it may occur on pre and post- midnight periods, its occurrence in all seasons is frequent (95 %) in post-midnight period 0215- 0500 LT. Only 5% cases were observed in pre-midnight 0200-000 LT. Its occurrence during Solar Maximum (1989-90) is significantly greater than 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. Nocturnal Stratification occurrence even in Winter 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 b TAN and HUANG (1985) over Wuchang (30.50 N, 11.40 E), China. Moreover, Karachi dose not lie under any of the zones of precipitation described by BOSS and SMITH (1980). Therefore, a future study on the cause of Nocturnal Ionospheric Stratification is clearly required.

Kanwal, Ambreen; Shahrukh Zaidi, Syed; Ara Zafar, Husan

86

Modeling the Arecibo nighttime F{sub 2} layer 2. Ionospheric gradients  

SciTech Connect

The servo model is extended and used to fit horizontal gradients in the F{sub 2} layer height and density and to estimate the zonal Pedersen current and its zonal and meridional gradient. Horizontal gradients were measured from the Arecibo Observatory during the following five nights: August 16-17 and 17-18, 1982; and October 4-5, 5-6, and 9-10, 1983. The model gradients are driven by nonzero current gradients, which are applied as needed to fit the measured gradients in the F{sub 2} peak. The gradient is calculated self-consistently in the model. The divergence of the Pedersen current can be deduced when the current flows zonally and is found to differ from zero. This is a consequence of zonal divergence of the model zonal current. Expressions are derived for the divergence of the Hall current and for the curl of the current in the presence of ionospheric gradients. The vertical vorticity of the F region current is determined from the radar and optical measurements and the mass spectrometer/incoherent scatter (MSIS) neutral densities. Both neutral and plasma motions generate current vorticity equally as expected from the F region dynamo. The measured velocity gradients produce more current gradients and vorticity than the measured conductance gradients. The nighttime current may be irrotational or have constant vorticity. Large current gradients occur in conjunction with observed descents of the F{sub 2} peak height. The gradients are interpreted as due to the midnight pressure bulge at low latitudes. Short-period gravity waves of meteorological origin are ruled out as they were not observed and are limited in their ability to reach ionospheric heights. The harmonic analysis used to obtain horizontal wind gradients is largely unaffected by spatially uniform wind accelerations. Therefore the deduced spatial variations in the measured winds are unlikely to be due to temporal variations. 49 refs., 13 figs.

Melendez-Alvira, D.J. [Naval Research Lab., Washington, DC (United States)] [Naval Research Lab., Washington, DC (United States); Burnside, R.G. [Arecibo Observatory (Puerto Rico)] [Arecibo Observatory (Puerto Rico); Walker, J.C.G. [Univ. of Michigan, Ann Arbor, MI (United States)] [Univ. of Michigan, Ann Arbor, MI (United States)

1994-12-01

87

A New Grid based Ionosphere Algorithm for GAGAN using Data Fusion Technique (ISRO GIVE Model-Multi Layer Data Fusion)  

NASA Astrophysics Data System (ADS)

A New Grid based Ionosphere Algorithm for GAGAN using Data Fusion Technique (ISRO GIVE Model-Multi Layer Data Fusion) Saumyaketu Mishra, Nirmala S, A S Ganeshan ISRO Satellite Centre, Bangalore and Timothy Schempp, Gregory Um, Hans Habereder Raytheon Company Development of a region-specific ionosphere model is the key element in providing precision approach services for civil aviation with GAGAN (GPS Aided GEO Augmented Navigation). GAGAN is an Indian SBAS (Space Based Augmentation System) comprising of three segments; space segment (GEO and GPS), ground segment (15 Indian reference stations (INRES), 2 master control centers and 3 ground uplink stations) and user segment. The GAGAN system is intended to provide air navigation services for APV 1/1.5 precision approach over the Indian land mass and RNP 0.1 navigation service over Indian Flight Information Region (FIR), conforming to the standards of GNSS ICAO-SARPS. Ionosphere being largest source of error is of prime concern for a SBAS. India is a low latitude country, posing challenges for grid based ionosphere algorithm development; large spatial and temporal gradients, Equatorial anomaly, Depletions (bubbles), Scintillations etc. To meet the required GAGAN performance, it is necessary to develop and implement a best suitable ionosphere model, applicable for the Indian region as thin shell models like planar does not meet the requirement. ISRO GIVE Model - Multi Layer Data Fusion (IGM-MLDF) employs an innovative approach for computing the ionosphere corrections and confidences at pre-defined grid points at 350 Km shell height. Ionosphere variations over the Geo-magnetic equatorial regions shows peak electron density shell height variations from 200 km to 500 km, so single thin shell assumption at 350 km is not valid over Indian region. Hence IGM-MLDF employs innovative scheme of modeling at two shell heights. Through empirical analysis the shell heights of 250 km and 450 km are chosen. The ionosphere measurement source for these two shells is obtained through a novel idea of utilizing both the Indian reference equipments (INREEs) residing at each of INRESs. Kriging algorithm is applied to compute the grid vertical delay error and error estimates at the IGP in the designated shell heights. A new approach of data fusion is applied at the vertical IGPs to fuse delays and confidences at 350 km shell height. Ionosphere storm detection algorithm utilizes goodness of fit test to protect the user from irregular behavior of ionosphere. Moreover, IGM-MLDF models the associated uncertainties of reference station failures and edge of storm effects through the under sample threat models to protect a GAGAN user from ionosphere abnormalities getting not monitored by the ground system. The algorithm also takes a conservative yet mathematically correct path of including measurement covariance bound at fusion step due to utilization of similar ionosphere measurements from 2 INREEs. To protect user against depletion threat, based on exhaustive empirical analysis algorithm uses the floor value of 6 for error estimate bound. Based on the data collected over the region, performance analysis of new algorithm is presented in this paper. IGM-MLDF is achieving APV-1/1.5 performance over 75 percentage of Indian land mass for GAGAN users. And this algorithm achieves it without requiring any changes in the user message structure, resulting in ease of GAGAN message usage by all the users, including the legacy users.

Srinivasan, Nirmala; Ganeshan, A. S.; Mishra, Saumyaketu

2012-07-01

88

Sequential learning artificial fuzzy neural networks (SLAFNN) with single hidden layer  

Microsoft Academic Search

In this paper, a sequential orthogonal approach to the building and training of a single hidden layer fuzzy neural network is presented. Sequential learning artificial neural network model proposed by Zhang and Morris (Neural Networks 11 (1) (1998) 65) is modified to tackle fuzzy inputs and crisp outputs and a sequential learning artificial fuzzy neural network model is developed and

S. Rajasekaran; Deepa Suresh; G. A. Vijayalakshmi Pai

2002-01-01

89

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

90

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

91

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

92

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

93

Nonlinear propagation of Rossby-Khantadze electromagnetic planetary waves in the ionospheric E-layer  

SciTech Connect

Nonlinear vortex propagation of electromagnetic coupled Rossby and Khantadze planetary waves in the weakly ionized ionospheric E-layer is investigated with numerical simulations. Large scale, finite amplitude vortex structures are launched as initial conditions at low, mid, and high latitudes. For each k-vector the linear dispersion relation has two eigenmodes corresponding to the slow magnetized Rossby wave and the fast magnetic Khantadze wave. Both waves propagate westward with local speeds of the order of 10–20 m/s for the slow wave and of the order of 500–1000 km/s for the fast wave. We show that for finite amplitudes there are dipole solitary structures emitted from the initial conditions. These structures are neutrally stable, nonlinear states that avoid radiating waves by propagating faster than the corresponding linear wave speeds. The condition for these coherent structures to occur is that their amplitudes are such that the nonlinear convection around the core of the disturbance is faster than the linear wave speed for the corresponding dominant Fourier components of the initial disturbance. The presence of the solitary vortex states is indicative of an initial strong disturbance such as that from a solar storm or a tectonic plate movement. We show that for generic, large amplitude initial disturbances both slow and fast vortex structures propagate out of the initial structure.

Futatani, S. [LMFA-CNRS, École Centrale de Lyon, Université de Lyon, Ecully (France)] [LMFA-CNRS, École Centrale de Lyon, Université de Lyon, Ecully (France); Horton, W. [Applied Research Laboratory, The University of Texas at Austin, Austin, Texas 78758 (United States)] [Applied Research Laboratory, The University of Texas at Austin, Austin, Texas 78758 (United States); Kaladze, T. D. [I. Vekua Institute of Applied Mathematics, Tbilisi State University, 2 University St., 0186 Tbilisi, Georgia (United States) [I. Vekua Institute of Applied Mathematics, Tbilisi State University, 2 University St., 0186 Tbilisi, Georgia (United States); Physics Department, Government College University, Lahore 54000 (Pakistan)

2013-10-15

94

Nonlinear propagation of Rossby-Khantadze electromagnetic planetary waves in the ionospheric E-layer  

NASA Astrophysics Data System (ADS)

Nonlinear vortex propagation of electromagnetic coupled Rossby and Khantadze planetary waves in the weakly ionized ionospheric E-layer is investigated with numerical simulations. Large scale, finite amplitude vortex structures are launched as initial conditions at low, mid, and high latitudes. For each k-vector the linear dispersion relation has two eigenmodes corresponding to the slow magnetized Rossby wave and the fast magnetic Khantadze wave. Both waves propagate westward with local speeds of the order of 10-20 m/s for the slow wave and of the order of 500-1000 km/s for the fast wave. We show that for finite amplitudes there are dipole solitary structures emitted from the initial conditions. These structures are neutrally stable, nonlinear states that avoid radiating waves by propagating faster than the corresponding linear wave speeds. The condition for these coherent structures to occur is that their amplitudes are such that the nonlinear convection around the core of the disturbance is faster than the linear wave speed for the corresponding dominant Fourier components of the initial disturbance. The presence of the solitary vortex states is indicative of an initial strong disturbance such as that from a solar storm or a tectonic plate movement. We show that for generic, large amplitude initial disturbances both slow and fast vortex structures propagate out of the initial structure.

Futatani, S.; Horton, W.; Kaladze, T. D.

2013-10-01

95

Crystallographic structure and superconductive properties of Nb-Ti films with an artificially layered structure  

SciTech Connect

Artificially layered niobium-titanium (Nb-Ti) films with various thickness ratios (3/1--1/3) and periodicities (2--100 A) are made in an argon or in a mixed argon/nitrogen atmosphere by a dc magnetron sputtering method. Films with small periodicities (less than 30 A) have an artificial superlattice structure (ASL) with crystallographic coherence between constituent layers, where Nb and Ti grow epitaxially on the closest planes. The crystallographic structures of films are bcc with the (110) plane parallel to the film for films with the same or a thicker Nb layer than a Ti layer, and hcp with the (001) plane parallel to the film for films with a thinner Nb layer than a Ti layer. Films with large periodicities have an artificial superstructure (ASS) with only periodic stacking of constituent layers. Films deposited in the Ar/N atmosphere also have the artificially layered structures of ASL or ASS. The artificially layered structure is thermally stable at temperatures up to 500 {degree}C. The superconducting properties of the films depend strongly on the periodicity and thickness ratio of Nb and Ti layers. The dependence of the transition temperature on the periodicity and thickness ratio is qualitatively explained by a proximity effect with a three-region model. Films with periodicities less than 20 A, composed of the same or a thicker Nb layer than a Ti layer, show high transition temperatures (above 9.3 K). The highest {ital T}{sub {ital c}} of about 13.6 K is obtained in the film composed of monatomic layers of constituents deposited in an Ar atmosphere including 30 vol % N.

Sato, N. (SONY Corporation, Research Center, 7-35 Kitashinagawa-6, Shinagawa-ku, Tokyo 141, Japan (JP))

1990-06-15

96

Formation of Double Layer-Like Structures in Ionospheric Alfven Resonator  

NASA Astrophysics Data System (ADS)

A two-dimensional numerical multi-fluid MHD model describing excitation of ionospheric Alfvén resonator (IAR) by a shear Alfvén wave is developed. In the model, the plasma consists of hydrogen and oxygen ions and electrons with finite temperatures. The nonlinear Lorentz force of the Alfvén wave, gravity force, and thermal pressure are included. The simulated area extends from the top-side ionosphere up to altitudes of a few Earth radii. The model uses density and temperature profiles typical for high-latitude auroral regions. For cold plasmas, Sydorenko, Rankin, and Kabin (2008) have found that the nonlinear force of standing IAR oscillations can produce deep density cavities in less than one minute that are similar to the ones observed in low-altitude magnetosphere. Here it is shown that at later stages (more than about one minute after the beginning of simulation), thermal pressure effects play an important role: perturbation of the initial equilibrium state by electron and ion flows that are created by the nonlinear Lorentz force amplifies the electric field directed along the geomagnetic field in proportion to the density gradient. Light hydrogen ions are accelerated by this electric field much stronger than the heavy oxygen ions. Eventually, at some locations the hydrogen ion flow speed may approach and even exceed the local sound speed. In this case, simulation reveals double layer-like structures with strong (about 0.1 mV/m) localized electric field directed upward. Evolution of such structures depends on the density and temperature profiles, as well as on the amplitude and frequency of the excited IAR eigenmode. The present study qualitatively supports available satellite measurements of intense parallel electrostatic fields in plasma cavities in the low-altitude magnetosphere [e.g., Chaston et al., 2007]. Chaston, C. C. et al., (2007), J. Geophys. Res., 112, A05215, doi:10.1029/2006JA012007. Sydorenko D., R. Rankin, and K. Kabin (2008), J. Geophys. Res., doi:10.1029/2008JA013579, in press.

Sydorenko, D.; Rankin, R.; Kabin, K.

2008-12-01

97

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

98

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

99

Modeling ray tracing through heating perturbed ionosphere with SAMI2  

NASA Astrophysics Data System (ADS)

We present simulations of high frequency (HF) signals/rays tracing through perturbed ionosphere by combining the NRL ionosphere model [Huba, 2000] and the ray tracing program [Jones, 1966]. We show with modeling that by creating artificial disturbances to the ionosphere, i.e. heating-induced geomagnetic-field-aligned density ducts, the radio signal transmission may be deflected out of its original propagation path and may exit the top ionosphere through the density breach at the F2 peak layer. Our results show the possibility to control or disrupt the communication channels in the future.; The solid line shows deviated ray trace due to F2 layer breach created by heat-induced density ducts. The dashed line shows the original ray path when no disturbances present.

Wu, T.; Huba, J. D.; Bernhardt, P. A.

2012-12-01

100

VLF/LF pulse reflections from layers below the ionospheric D-region  

NASA Astrophysics Data System (ADS)

Long wave ionospheric reflectivity data are described from experiments using a VLF/LF pulse ionosounding system. The sounding technique utilized pulses so short, that even at distances of a few hundred kilometers from the transmitter, ground wave and ionospherically reflected sky wave pulses were received separated in time. Pulse reflection data are shown that strongly suggest the simultaneous presence of at least two discrete reflections from different heights in the daytime ionosphere. The upper reflections are identified with the classical D-region, caused primarily by Lyman alpha radiation, while the low-altitude reflections, which occur from shortly before sunrise to shortly after sunset, are believed to be due to ionization caused by cosmic rays and photodetachment. The variability of the low altitude daytime ionosphere is described from VLF/LF pulse reflection data obtained during different seasons, at mid- and low-geomagnetic latitudes, and over different phases of the solar cycle. The effects of the low altitude ionization on the propagation of long radio waves are estimated.

Rasmussen, J. E.; Kossey, P. A.; Turtle, J. P.

1982-02-01

101

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

102

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.

103

Ionospheric anomaly due to seismic activities - Part 2: Evidence from D-layer preparation and disappearance times  

NASA Astrophysics Data System (ADS)

We show evidences for anomalous ionospheric behaviour in the signal of Indian navy VLF transmitting station named VTX due to earthquakes in the South Asian region. We concentrate on the variation of the D-layer preparation time (DLPT) and D-layer disappearance time (DLDT) in a period of sixteen months and study their average behaviors. We identify those days in which DLPT and DLDT exhibit significant deviations. Separately, we compute the energy release by earthquakes during this period and show that "anomalous VLF" days are associated with anomalous energy release. We find that the anomaly and the deviation of DLPT and DLDTs from the mean are linearly correlated. We discuss the predictability in this approach and compare with the terminator shift approach using the same set of data.

Chakrabarti, S. K.; Sasmal, S.; Chakrabarti, S.

2010-08-01

104

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

Microsoft Academic Search

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)CuO2\\/(Ba,Ca,Sr)CuO2 superconducting superlattices in the infinite layer structure. Superlattice chemical modulation can be observed from the x-ray diffraction patterns for structures with SrCuO2 and (Ca,Sr)CuO2 layers as thin as a single unit

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

1996-01-01

105

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

SciTech Connect

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 structures with SrCuO{sub 2} and (Sr,Ca)CuO{sub 2} layers as thin as a single unit cell ({approximately}3.4 {Angstrom}). In addition, novel thin-film superconductors were formed by using the constraint of epitaxy to stabilize SrCuO{sub 2}/BaCuO{sub 2} superlattices in the infinite layer structure. Using this approach, two new structural families, Ba{sub 2}Sr{sub n-1}Cu{sub n+1} O{sub 2n+2+{gamma}} and Ba{sub 4}Sr{sub n-1}Cu{sub n+3}O{sub 2n+6+{gamma}}, have been synthesized which superconduct at temperatures as high as 70 K. These results represent not only the synthesis of new structural families of superconductors, but also 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. [and others

1994-09-01

106

Ionospheric model-observation comparisons: E layer at Arecibo Incorporation of SDO-EVE solar irradiances  

NASA Astrophysics Data System (ADS)

study evaluates how the new irradiance observations from the NASA Solar Dynamics Observatory (SDO) Extreme Ultraviolet Variability Experiment (EVE) can, with its high spectral resolution and 10 s cadence, improve the modeling of the E region. To demonstrate this a campaign combining EVE observations with that of the NSF Arecibo incoherent scatter radar (ISR) was conducted. The ISR provides E region electron density observations with high-altitude resolution, 300 m, and absolute densities using the plasma line technique. Two independent ionospheric models were used, the Utah State University Time-Dependent Ionospheric Model (TDIM) and Space Environment Corporation's Data-Driven D Region (DDDR) model. Each used the same EVE irradiance spectrum binned at 1 nm resolution from 0.1 to 106 nm. At the E region peak the modeled TDIM density is 20% lower and that of the DDDR is 6% higher than observed. These differences could correspond to a 36% lower (TDIM) and 12% higher (DDDR) production rate if the differences were entirely attributed to the solar irradiance source. The detailed profile shapes that included the E region altitude and that of the valley region were only qualitatively similar to observations. Differences on the order of a neutral-scale height were present. Neither model captured a distinct dawn to dusk tilt in the E region peak altitude. A model sensitivity study demonstrated how future improved spectral resolution of the 0.1 to 7 nm irradiance could account for some of these model shortcomings although other relevant processes are also poorly modeled.

Sojka, Jan J.; Jensen, Joseph B.; David, Michael; Schunk, Robert W.; Woods, Tom; Eparvier, Frank; Sulzer, Michael P.; Gonzalez, Sixto A.; Eccles, J. Vincent

2014-05-01

107

GPS slant total electron content accuracy using the single layer model under different geomagnetic regions and ionospheric conditions  

NASA Astrophysics Data System (ADS)

The use of observations from the Global Positioning System (GPS) has significantly impacted the study of the ionosphere. As it is widely known, dual-frequency GPS observations can provide very precise estimation of the slant Total Electron Content (sTEC—the linear integral of the electron density along a ray-path) and that the precision level is bounded by the carrier-phase noise and multi-path effects on both frequencies. Despite its precision, GPS sTEC estimations can be systematically affected by errors in the estimation of the satellites and receivers by Inter-Frequency Biases (IFB) that are simultaneously determined with the sTEC. Thus, the ultimate accuracy of the GPS sTEC estimation is determined by the errors with which the IFBs are estimated. This contribution attempts to assess the accuracy of IFBs estimation techniques based on the single layer model for different ionospheric regions (low, mid and high magnetic latitude); different seasons (summer and winter solstices and spring and autumn equinoxes); different solar activity levels (high and low); and different geomagnetic conditions (quiet and very disturbed). The followed strategy relies upon the generation of a synthetic data set free of IFB, multi-path, measurement noise and of any other error source. Therefore, when a data set with such properties is used as the input of the IFB estimation algorithms, any deviation from zero on the estimated IFBs should be taken as indications of the errors introduced by the estimation technique. The truthfulness of this assessment work is warranted by the fact that the synthetic data sets resemble, as realistically as possible, the different conditions that may happen in the real ionosphere. The results of this work show that during the high solar activity period the accuracy for the estimated sTEC is approximately of ±10 TECu for the low geomagnetic region and of ±2.2 TECu for the mid-latitude. During low solar activity the accuracy can be assumed to be in the order of ±2 TECu. For the geomagnetic high-disturbed period, the results show that the accuracy is degraded for those stations located over the region where the storm has the strongest impact, but for those stations over regions where the storm has a moderate effect, the accuracy is comparable to that obtained in the quiet period.

Brunini, C.; Azpilicueta, F.

2010-05-01

108

Coherent structures in a turbulent boundary layer. I - Generation of 'artificial' bursts  

NASA Technical Reports Server (NTRS)

In an effort to better understand the physics and structure of coherent events in a turbulent boundary layer, an attempt is made to produce 'artificial' bursts. These are generated in a turbulent boundary layer developed on a flat plate towed in an 18 m water channel and thus with negligible freestream turbulence. The burstlike events are produced by either withdrawing near-wall fluid from two minute holes separated in the spanwise direction or by pitching a miniature delta wing that is flush-mounted to the wall. Either of these two actions generates a hairpinlike vortex and low-speed streak that resemble naturally occurring structures. The resulting sequence of events that occur at a given location can be uniquely controlled, thus allowing detailed examination via phase-locked measurements and flow visualization. In this paper, the proof of concept of artificial burst generation is established by comparing the artificial events with natural, random bursts using flow visualization and hot-film signals.

Gad-El-hak, M.; Fazle Hussain, A. K. M.

1986-01-01

109

Ionospheric chemical releases  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

110

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

NASA Technical Reports Server (NTRS)

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

1989-01-01

111

Polar cap Artificial Auroras  

NASA Astrophysics Data System (ADS)

It is well established that high-power high-frequency radio waves, when beamed into the F-layer ionosphere, accelerate electrons 1-2 orders of magnitude above thermal levels. These electrons collide with the neutral oxygen atoms and nitrogen molecules, which subsequently produce optical emissions identical to those in natural auroras. Artificial optical emissions are one of few methods available to directly detect energetic electrons in the ionosphere. The mechanism of acceleration remains under debate but there is evidence for turbulent upper-hybrid and Langmuir electrostatic waves. Artificial optical emissions have been observed at low latitudes (e.g. Arecibo in Puerto Rico), mid-latitudes (e.g. SURA in Russia), and at high latitudes (e.g. EISCAT in Norway and HAARP in Alaska). The electron accelerating mechanisms are sensitive to the magnetic field aspect angle to the pump beam, hence the need to reproduce the phenomenon at different latitudes. Here we report on the first attempt within the polar cap using the SPEAR facility on Svalbard, where the magnetic dip angle is only 8 degrees. Svalbard also has the unique situation of being under the cusp during the daytime whilst the ground is in total darkness during the winter months. In addition, Svalbard is the only location currently available where in-situ rocket measurements are possible within an artificial aurora. Plans for a future launch are discussed.

Kosch, M.; Pedersen, T.; Robinson, T.

2004-12-01

112

Feasibility of generating an artificial burst in a turbulent boundary layer  

NASA Technical Reports Server (NTRS)

Artificial bursts were generated in laminar and turbulent boundary layers. The burst-like events were produced by withdrawing near-wall fluid from two minute holes separated in the spanwise direction or by pitching a miniature delta wing that was flush-mounted to the wall. Either of these actions generated streamwise vorticity and a low-speed streak that resembled a naturally occurring one. The resulting sequence of events occurred at a given location and at controlled times, allowing detailed examination and comparison with natural, random bursts by means of flow visualization and fast-response probe measurement techniques.

Gad-El-hak, M.

1986-01-01

113

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

114

A Wind-Tunnel Artificially-Thickened Simulated Weakly Unstable Atmospheric Boundary Layer  

NASA Astrophysics Data System (ADS)

A wind-tunnel simulation of an atmospheric boundary layer, artificially thickened as is often used in neutral flow wind-loading studies, has been investigated for weakly unstable stratification, including the effect of an overlying inversion. Rather than using a uniform inlet temperature profile, the inlet profile was adjusted iteratively by using measured downstream profiles. It was found that three cycles are sufficient for there to be no significant further change in profiles of temperature and other quantities. Development to nearly horizontally-homogeneous flow took a longer distance than in the neutral case because the simulated layer was deeper and therefore the length scales larger. Comparisons show first-order and second-order moments quantities are substantially larger than given by `standard forms' in the mixed layer but are close in the surface layer. Modified functions, obtained by matching one to the other, are suggested that amount to an interpolation in the mixed layer between the strongly unstable and the weakly unstable cases.

Hancock, P. E.; Zhang, S.; Hayden, P.

2013-12-01

115

Formation of artificially-layered thin-film compounds using pulsed-laser deposition  

SciTech Connect

Superlattice structures, consisting of SrCuO{sub 2}, (Sr,Ca)CuO{sub 2}, and BaCuO{sub 2} layers in the tetragonal, ``infinite layer`` crystal structure, have been grown by pulsed-laser deposition (PLD). Superlattice chemical modulation is observed for structures with component layers as thin as a single unit cell ({approximately}3.4 {angstrom}), indicating that unit-cell control of (Sr,Ca)CuO{sub 2} growth is possible using conventional pulsed-laser deposition over a wide oxygen pressure regime. X-ray diffraction intensity oscillations, due to the finite thickness of the film, indicate that these films are extremely flat with a thickness variation of only {approximately}20 {angstrom} over a length scale of several thousand angstroms. Using the constraint of epitaxy to grow metastable cuprates in the infinite layer structure, novel high-temperature superconducting structural families have been formed. In particular, epitaxially-stabilized SrCuO{sub 2}/BaCuO{sub 2} superlattices, grown by sequentially depositing on lattice-matched (100) SrTiO{sub 3} from BaCuO{sub 2} and SrCuO{sub 2} ablation targets in a PLD system, show metallic conductivity and superconductivity at {Tc}(onset) {approximately}70 K. These results show that pulsed-laser deposition and epitaxial stabilization have been used to effectively ``engineer`` artificially-layered thin-film materials.

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

1995-04-01

116

First experience on spatial discrimination of large-scale natural elf interference on the example of two-point measurements of the magnetic field of an artificial ionospheric source  

NASA Astrophysics Data System (ADS)

We present the results of an experiment on the generation of extremely low-frequency (ELF) electromagnetic fields at frequencies near the first Schumann resonance upon the ionosphere modification by modulated powerful radio emission. The reception was performed at two sites spaced by 14 km in the distance from “SURA” facility. It was found that the natural noise at different reception sites is highly correlated, which allows one to achieve the noise suppression by about an order of magnitude by subtracting the measurement results. We demonstrate the opportunities of spatial discrimination of the interference upon the two-site reception of the “small-scale” field of an artificial ionospheric source. The directions of future studies and possible applications are discussed.

Polyakov, S. V.; Reznikov, B. I.; Shlyugaev, Yu. V.; Kopytenko, E. A.

2006-12-01

117

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

118

Nano-sized layered Mn oxides as promising and biomimetic water oxidizing catalysts for water splitting in artificial photosynthetic systems.  

PubMed

One challenge in artificial photosynthetic systems is the development of artificial model compounds to oxidize water. The water-oxidizing complex of Photosystem II which is responsible for biological water oxidation contains a cluster of four Mn ions bridged by five oxygen atoms. Layered Mn oxides as efficient, stable, low cost, environmentally friendly and easy to use, synthesize, and manufacture compounds could be considered as functional and structural models for the site. Because of the related structure of these Mn oxides and the catalytic centre of the active site of the water oxidizing complex of Photosystem II, the study of layered Mn oxides may also help to understand more about the mechanism of water oxidation by the natural site. This review provides an overview of the current status of layered Mn oxides in artificial photosynthesis and discuss the sophisticated design strategies for Mn oxides as water oxidizing catalysts. PMID:24727405

Najafpour, Mohammad Mahdi; Heidari, Sima; Amini, Emad; Khatamian, Masoumeh; Carpentier, Robert; Allakhverdiev, Suleyman I

2014-04-01

119

Tunable ferroelectricity in artificial tri-layer superlattices comprised of non-ferroic components.  

PubMed

Heterostructured material systems devoid of ferroic components are presumed not to display ordering associated with ferroelectricity. In heterostructures composed of transition metal oxides, however, the disruption introduced by an interface can affect the balance of the competing interactions among electronic spins, charges and orbitals. This has led to the emergence of properties absent in the original building blocks of a heterostructure, including metallicity, magnetism and superconductivity. Here we report the discovery of ferroelectricity in artificial tri-layer superlattices consisting solely of non-ferroelectric NdMnO(3)/SrMnO(3)/LaMnO(3) layers. Ferroelectricity was observed below 40 K exhibiting strong tunability by superlattice periodicity. Furthermore, magnetoelectric coupling resulted in 150% magnetic modulation of the polarization. Density functional calculations indicate that broken space inversion symmetry and mixed valency, because of cationic asymmetry and interfacial polar discontinuity, respectively, give rise to the observed behaviour. Our results demonstrate the engineering of asymmetric layered structures with emergent ferroelectric and magnetic field tunable functions distinct from that of normal devices, for which the components are typically ferroelectrics. PMID:22990860

Rogdakis, K; Seo, J W; Viskadourakis, Z; Wang, Y; Qune, L F N Ah; Choi, E; Burton, J D; Tsymbal, E Y; Lee, J; Panagopoulos, C

2012-01-01

120

Tunable ferroelectricity in artificial tri-layer superlattices comprised of non-ferroic components  

NASA Astrophysics Data System (ADS)

Heterostructured material systems devoid of ferroic components are presumed not to display ordering associated with ferroelectricity. In heterostructures composed of transition metal oxides, however, the disruption introduced by an interface can affect the balance of the competing interactions among electronic spins, charges and orbitals. This has led to the emergence of properties absent in the original building blocks of a heterostructure, including metallicity, magnetism and superconductivity. Here we report the discovery of ferroelectricity in artificial tri-layer superlattices consisting solely of non-ferroelectric NdMnO3/SrMnO3/LaMnO3 layers. Ferroelectricity was observed below 40 K exhibiting strong tunability by superlattice periodicity. Furthermore, magnetoelectric coupling resulted in 150% magnetic modulation of the polarization. Density functional calculations indicate that broken space inversion symmetry and mixed valency, because of cationic asymmetry and interfacial polar discontinuity, respectively, give rise to the observed behaviour. Our results demonstrate the engineering of asymmetric layered structures with emergent ferroelectric and magnetic field tunable functions distinct from that of normal devices, for which the components are typically ferroelectrics.

Rogdakis, K.; Seo, J. W.; Viskadourakis, Z.; Wang, Y.; Ah Qune, L. F. N.; Choi, E.; Burton, J. D.; Tsymbal, E. Y.; Lee, J.; Panagopoulos, C.

2012-09-01

121

Observations of double layer-like and soliton-like structures in the ionosphere  

NASA Technical Reports Server (NTRS)

Two types of large electric field signatures, individual pulses and pulse trains, were observed on a sounding rocket launched into the afternoon auroral zone on January 21, 1982. The typical electric fields in the individual pulses were 50 mV/m or larger, aligned mostly parallel to B, and the corresponding potentials were at leat 100 mV (kT approximately 0.3 eV). A lower limit of 15 km/sec can be set on the velocity of these structures, indicating that they were not ion acoustic double layers. The pulse trains, each consisting of on the order of 100 pulses, were observed in close association with intense plasma frequency waves. This correlation is consistent with the interpretation of these trains as Langmuir solitons. The pulse trains correlate better with the intensity of the field-aligned currents than with the energetic electron flux.

Boehm, M. H.; Carlson, C. W.; Mcfadden, J.; Mozer, F. S.

1984-01-01

122

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

123

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

124

Two Anomalies in the Ionosphere  

Microsoft Academic Search

DURING the War, many new ionospheric stations were instituted in different parts of the world to serve the operational requirements of the Allied Forces. As a result., there have become available, for the first time, sufficient data to provide a rough general morphological picture of the F2 layer of the ionosphere. A study of these data has disclosed the remarkable

Edward V. Appleton

1946-01-01

125

Nonlinear Plasma Effects in Natural and Artificial Aurora  

SciTech Connect

This report describes common features of natural ('Enhanced') aurora and 'artificial aurora'(AA) created by electron beams injected from sounding rockets. These features cannot be explained solely by col-lisional degradation of energetic electrons, thereby pointing to collisionless plasma effects. The fundamental role in electron beam-ionosphere interactions belongs to Langmuir turbulence. Its development in the (weakly-ionized) ionosphere is significantly affected by electron-neutral collisions, so that the heating and acceleration of plasma electrons proceed more efficiently than in collisionless plasmas. As a result, a narrow layer of enhanced auroral glow/ionization is formed above the standard collisional peak.

Mishin, E. V. [Space Vehicles Directorate, Air Force Research Laboratory, Bedford, MA 01731 (United States)

2011-01-04

126

Nonlinear Plasma Effects in Natural and Artificial Aurora  

NASA Astrophysics Data System (ADS)

This report describes common features of natural (`Enhanced') aurora and `artificial aurora' (AA) created by electron beams injected from sounding rockets. These features cannot be explained solely by col-lisional degradation of energetic electrons, thereby pointing to collisionless plasma effects. The fundamental role in electron beam-ionosphere interactions belongs to Langmuir turbulence. Its development in the (weakly-ionized) ionosphere is significantly affected by electron-neutral collisions, so that the heating and acceleration of plasma electrons proceed more efficiently than in collisionless plasmas. As a result, a narrow layer of enhanced auroral glow/ionization is formed above the standard collisional peak.

Mishin, E. V.

2011-01-01

127

Critical frequencies of E-layer in mid-latitudes and the calculations of electron density profiles in the lower ionosphere  

NASA Astrophysics Data System (ADS)

In this paper, experimental formulas for the critical frequencies of the E-layer in midlatitudes and of the distribution of electron density in the lower ionosphere are found. These formulas are expressed in terms of the sunspot number, the solar zenith angle, and the local time. The results of calculations from them for different years, months, days for both morning and afternoon time, and calculations for propagation of the long radio wave and its absorptions are all in agreement with observational data. In addition, it is possible to calculate the distribution of electron density in the D-region from f(OE) obtained by vertical soundings.

Wang, X.; Huang, Z.

1985-07-01

128

A statistical study of the interplanetary magnetic field control of sporadic E-layer occurrence in the southern polar cap ionosphere  

NASA Astrophysics Data System (ADS)

The influence of the interplanetary magnetic field (IMF) on the occurrence of sporadic E (Es)-layers in the southern polar cap ionosphere has been investigated. We statistically analysed ionogram and Doppler velocity observations made using a HF digital ionosonde located at Casey, Antarctica (66.3°S, 110.5°E 81°S magnetic latitude) during the two summer campaign intervals 1 January to 18 February, and 1 November to 31 December 1997. The ionogram and Doppler velocity measurements were used to determine the Es-occurrence and electric field vectors (assuming E×B/B2 drift), respectively. Concurrent IMF data were obtained from measurements made on board the Wind spacecraft. First, the gross properties of the IMF dependence of Es-formation were obtained: the occurrence rate was higher for negative By and/or positive Bz, and lower for positive By and/or negative Bz. To reconcile these gross properties with the electric field theory of Es-layer formation, the detailed diurnal variation of both Es-occurrence and the ionospheric electric field were obtained for different orientations of the IMF. The main statistical results are that: (1) the By component mainly controls the occurrence of the midnight Es-layers through its influence on the corresponding South West electric field; and (2) the Bz component mainly controls the occurrence of the evening Es-layers. However, the change in the occurrence rate for evening Es-layers was not related to the strength of the associated North West and North East electric fields. The total occurrence of Es-layers depended more on By than on Bz, owing to the dominance of By-controlled midnight Es-layers in the occurrence distribution. Nevertheless, the dependence of Es-occurrence on Bz was important. We suggest that the increase in Es-occurrence for positive Bz might be explained by the intermittent production of lower F-region ionisation by polar showers and squalls, which also increase in frequency and intensity for positive Bz. The importance of metallic ion transport within the ionosphere is also considered.

Wan, W.; Parkinson, M. L.; Dyson, P. L.; Breed, A. M.; Morris, R. J.

1999-12-01

129

Pinning magnetic domain via patterning artificial lattice under amorphous magnetic layer  

NASA Astrophysics Data System (ADS)

A novel method for pinning magnetic domains on pre-formatted pinning sites has been developed for perpendicular magnetic anisotropy magneto-optical (MO) thin film media. The pinning sites were artificial lattices made by patterning a layer of gold grid on the substrate using electron beam lithography. Compared with the work proposed using photo- lithography, our method showed the ability of making smaller pinning domains. Moreover, compared with our previous work using the same electron beam lithography method and creating hole arrays on polymethyl methacrylate, this new method could stand higher film deposition temperatures and avoid the MO films rapid deterioration on a PMMA substrate. In order to investigate the domain pinning behavior we did several different procedures and observed their corresponding domain pinning layouts. Magnetic domains were found to be pinned inside the lattice and resembled the geometric shapes of the lattice. The pinned domains acquired the shape of the lattice. In this article, the star-shaped type of geometry of grid arrays is presented.

Wu, Te-ho; Wu, J. C.; Chen, Bing-Mau; Shieh, Han-Ping D.

1999-03-01

130

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

2012-01-01

131

Parameterized ionospheric model: A global ionospheric parameterization based on first principles models  

Microsoft Academic Search

We describe a parameterized ionospheric model (PIM), a global model of theoretical ionospheric climatology based on diurnally reproducible runs of four physics based numerical models of the ionosphere. The four numerical models, taken together, cover the E and F layers for all latitudes, longitudes, and local times. PIM consists of a semianalytic representation of dimally reproducible runs of these models

R. E. Daniell; L. D. Brown; D. N. Anderson; M. W. Fox; P. H. Doherty; D. T. Decker; J. J. Sojka; R. W. Schunk

1995-01-01

132

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

133

HF-induced airglow structure as a proxy for ionospheric irregularity detection  

NASA Astrophysics Data System (ADS)

The High Frequency Active Auroral Research Program (HAARP) heating facility allows scientists to test current theories of plasma physics to gain a better understanding of the underlying mechanisms at work in the lower ionosphere. One powerful technique for diagnosing radio frequency interactions in the ionosphere is to use ground-based optical instrumentation. High-frequency (HF), heater-induced artificial airglow observations can be used to diagnose electron energies and distributions in the heated region, illuminate natural and/or artificially induced ionospheric irregularities, determine ExB plasma drifts, and measure quenching rates by neutral species. Artificial airglow is caused by HF-accelerated electrons colliding with various atmospheric constituents, which in turn emit a photon. The most common emissions are 630.0 nm O(1D), 557.7 nm O(1S), and 427.8 nm N2+(1NG). Because more photons will be emitted in regions of higher electron energization, it may be possible to use airglow imaging to map artificial field-aligned irregularities at a particular altitude range in the ionosphere. Since fairly wide field-of-view imagers are typically deployed in airglow campaigns, it is not well-known what meter-scale features exist in the artificial airglow emissions. Rocket data show that heater-induced electron density variations, or irregularities, consist of bundles of ~10-m-wide magnetic field-aligned filaments with a mean depletion depth of 6% [Kelley et al., 1995]. These bundles themselves constitute small-scale structures with widths of 1.5 to 6 km. Telescopic imaging provides high resolution spatial coverage of ionospheric irregularities and goes hand in hand with other observing techniques such as GPS scintillation, radar, and ionosonde. Since airglow observations can presumably image ionospheric irregularities (electron density variations), they can be used to determine the spatial scale variation, the fill factor, and the lifetime characteristics of irregularities. Telescopic imaging of airglow is a technique capable of simultaneously determining the properties of ionospheric irregularities at decameter resolution over a range of several kilometers. The HAARP telescopic imager consists of two cameras, a set of optics for each camera, and a robotic mount that supports and orients the system. The camera and optics systems are identical except for the camera lenses: one has a wide-angle lens (~19 degrees) and the other has a telescopic lens (~3 degrees). The telescopic imager has a resolution of ~20 m in the F layer and ~10 m in the E layer, which allows the observation of decameter- and kilometer-scale features. Analysis of telescopic data from HAARP campaigns over the last five years will be presented.

Kendall, E. A.

2013-12-01

134

Regularities and irregularities in the ionosphere  

Microsoft Academic Search

A general survey of ionospheric phenomena is given, in which the regular variations f the E and F 1 layers, as illustrated by their intimate dependence on the Sun's zenith distance, are contrasted with the anomalous behaviour of the F 2 layer. Using results from the world's ionospheric stations such anomalous behaviour is identified as geomagnetic distortion, most probably due

Edward Appleton

1956-01-01

135

Ionization distribution in the F2 layer during the March 16-20 and December 5-10, 1988 SUNDIAL campaign intervals, and its comparison with an empirical high latitude model ionosphere  

NASA Astrophysics Data System (ADS)

Results of coordinated vertical ionization measurements in the F2 layer made during the SUNDIAL March 16-20 and December 5-10, 1988 campaign periods are compared with the values of maximal electron concentrations estimated using an empirical high-latitude model ionosphere described by Besprozvannaia (1986). It is shown that, for both the daytime and the nighttime hours, the average error of the model did not exceed 10-30 percent. However, during nighttime, large differences were occasionally encountered between the experimental and the model values, attributed to faulty determinations of the position and the configuration of the main ionospheric trough.

Besprozvannaia, A. S.; Kishcha, P. V.; Nepomniashchaia, E. V.; Pulinets, S. A.; Shchuka, T. I.

1993-02-01

136

Statistical characteristic of the polar ionospheric scale height around the peak height of F2 layer with observations of the ESR  

NASA Astrophysics Data System (ADS)

The ionospheric scale height around the peak height of F2 layer (HmF2) is a very important parameter defining the profile of topside ionosphere. Based on data of the EISCAT ESR radar, we statistically study the HmF2 at high latitudes. In order to derive the HmF2, a least square method is adopted to fit the electron density profile above F2 layer peak from ESR radar data. The results shows that it is in well agreement between the topside profiles deduced from the fitted HmF2 and the actual measuring topside profile with a range of about 300 km above the peak. Therefore, HmF2 can be used as a constant in above range. In addition, the value of HmF2 is greatly affected by the kp index. When the kp is low, the HmF2 fluctuations are small with a low estimated error. However, the high kp can cause strong fluctuations of HmF2 and large estimated errors. On the other hand, there is not an obvious daily variation of the HmF2 during Polar days or Polar nights. It is mainly affected by the kp index. When there are a day-to-night alternation and a low kp index, an obvious daily variation at high latitudes is observed. There is a maximum at night and a minimum in the day time. But HmF2 is still greatly affected by the kp index. Finally, those observed results are compared with those calculated with IRI model.

Yuan, Zhigang; Qi, Feng; Deng, Xiaohua; Wang, Jingfang

137

Ionospheric research  

NASA Technical Reports Server (NTRS)

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

1975-01-01

138

Ionospheric Research.  

National Technical Information Service (NTIS)

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

T. A. Seliga

1968-01-01

139

Ionosphere research  

NASA Technical Reports Server (NTRS)

A report is presented on on-going research projects in ionospheric studies. The topics discussed are planetary atmospheres, E and F region, D region, mass spectrometer measurements, direct measurements and atmospheric reactions.

1976-01-01

140

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

Microsoft Academic Search

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

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

2008-01-01

141

The detection of the ionospheric irregularities by GNSS signal and the incoherent scatter radio measurements  

NASA Astrophysics Data System (ADS)

The high-latitude ionosphere has a very complicated structure and high dynamics. The ionospheric irregularities can produce scintillations of radio waves that occur predominantly in the ionosphere F-layer. The strong fluctuations can influence on the performance of the different space communication and navigation radio systems. The fluctuations of GPS/GLONASS signals are caused by the ionospheric irregularities with spatial dimensions more than 10 km. These structures can be detected by high potential incoherent scatter radars. It was proposed and carried out at the beginning of June 2012 experiment for a detailed study of the nature of the ionospheric irregularities, influencing on GPS/GLONASS signals parameters, by incoherent scatter and trans-ionospheric radio measurements simultaneously. The EISCAT facilities position provides the unique opportunity to study the ionospheric irregularities' parameters associated with TEC fluctuations and GPS/GLONASS signals scintillations. The EISCAT heating facility provides unique possibility to generate the artificial ionospheric irregularities and to estimate the impact factor of these irregularities on GPS/GLONASS signals transionospheric propagation. In order to detect the ionosphere irregularities it is used the IS radar measurements (electron density and plasma temperatures profiles) and simultaneously registered on EISCAT site amplitude and phase fluctuations in GPS/GLONASS signals by use of the Javad multi-constellation GPS/GLONASS receiver with high samples rate (100 Hz) and special scintillation GPS receiver PolaRxS PRO that dedicated to ionospheric monitoring and space weather applications and provides TEC and S4 scintillation index measurements. The low frequency fluctuations can be directly measured due to the electron density changes along the radio ray path between a GPS/GLONASS satellite and a ground-based receiver on EISCAT site. The raw data (under scintillating conditions) obtained by use of the high samples rate GPS/GLONASS receiver are processed in order to derive the scintillation parameters. The practical aspect of this investigation is a detailed study of nature and impact level of the ionospheric irregularities that can influence on the GPS/GLONASS performance especially at high latitudes and during geomagnetically disturbed period and to obtain new knowledge that may improve the reliability of the global navigation systems in Arctic and Antarctic regions. The authors are grateful to the EISCAT Scientific Association for observing time on the EISCAT facilities within the framework of Peer-reviewed Program.

Cherniak, Iurii; Shagimuratov, Irk; Krankowski, Andrzej; Sieradsky, Rafal; Zakharenkova, Irina; Rietveld, Michael; Kapcia, Jacek

2013-04-01

142

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

143

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.

144

Comparison of Observations of Sporadic-E Layers in the Nighttime and Daytime Mid-Latitude Ionosphere  

NASA Technical Reports Server (NTRS)

A comparison of numerous rocket experiments to investigate mid-latitude sporadic-E layers is presented. Electric field and plasma density data gathered on sounding rockets launched in the presence of sporadic-E layers and QP radar echoes reveal a complex electrodynamics including both DC parameters and plasma waves detected over a large range of scales. We show both DC and wave electric fields and discuss their relationship to intense sporadic-E layers in both nighttime and daytime conditions. Where available, neutral wind observations provide the complete electrodynamic picture revealing an essential source of free energy that both sets up the layers and drives them unstable. Electric field data from the nighttime experiments reveal the presence of km-scale waves as well as well-defined packets of broadband (10's of meters to meters) irregularities. What is surprising is that in both the nighttime and daytime experiments, neither the large scale nor short scale waves appear to be distinctly organized by the sporadic-E density layer itself. The observations are discussed in the context of current theories regarding sporadic-E layer generation and quasi-periodic echoes.

Pfaff, R.; Freudenreich, H.; Rowland, D.; Klenzing, J.; Clemmons, J.; Larsen, M.; Kudeki, E.; Franke, S.; Urbina, J.; Bullett, T.

2012-01-01

145

Ionospheric scintillation  

Microsoft Academic Search

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

R. K. Crane

1977-01-01

146

Ionospheric irregularities  

Microsoft Academic Search

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

B.G. Fejer; M. C. Kelley

1980-01-01

147

Ionospheric Research.  

National Technical Information Service (NTIS)

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

T. A. Seliga

1967-01-01

148

Ionization distribution in the F2 layer during the March 16-20 and December 5-10, 1988 SUNDIAL campaign intervals, and its comparison with an empirical high latitude model ionosphere  

Microsoft Academic Search

Results of coordinated vertical ionization measurements in the F2 layer made during the SUNDIAL March 16-20 and December 5-10, 1988 campaign periods are compared with the values of maximal electron concentrations estimated using an empirical high-latitude model ionosphere described by Besprozvannaia (1986). It is shown that, for both the daytime and the nighttime hours, the average error of the model

A. S. Besprozvannaia; P. V. Kishcha; E. V. Nepomniashchaia; S. A. Pulinets; T. I. Shchuka

1993-01-01

149

"Twisted Beam" SEE Observations of Ionospheric Heating from HAARP  

NASA Astrophysics Data System (ADS)

High power HF radio waves exciting the ionosphere provide aeronomers with a unique space-based laboratory capability. The High-Frequency Active Auroral Research Program (HAARP) in Gakona, Alaksa is the world's largest heating facility, providing effective radiated powers in the gigawatt range. Experiments performed at HAARP have allowed researchers to study many non-linear effects of wave-plasma interactions. Stimulated Electromagnetic Emission (SEE) is of interest to the ionospheric community for its diagnostic purposes. Typical SEE experiments at HAARP have focused on characterizing the parametric decay of the electromagnetic pump wave into several different wave modes such as upper and lower hybrid, ion acoustic, ion-Bernstein and electron-Bernstein. These production modes have been extensively studied at HAARP using traditional beam heating patterns and SEE detection. New results are present from HAARP experiments using a "twisted beam" excitation mode. Unlike traditional heating beams used at HAARP or other heating facilities, the twisted beam attempts to impart orbital angular momentum (OAM) into the heating region. Analysis of twisted beam heating shows that the SEE results obtained are nearly identical to the modes without OAM. One difference in the twisted beam mode is the heating region produced is in the shape of a ring as opposed to the more traditional "solid spot" region. The ring heating pattern may be more conducive to the creation of artificial airglow layers. The results of these runs include artificial layer creation and evolution as pertaining to the twisted beam pattern. The SEE measurements aid the interpretation of the twisted beam interactions in the ionosphere.

Briczinski, S. J.; Bernhardt, P. A.; Pedersen, T. R.; Rodriguez, S.; SanAntonio, G.

2012-12-01

150

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

Microsoft Academic Search

Superlattice structures, consisting of SrCuO2, (Ca,Sr)CuO2, and BaCuO2 layers in the tetragonal, ‘infinite layer’ crystal structure, have been grown by pulsed-laser deposition (PLD). Superlattice chemical modulation is observed for structures with component layers as thin as a single unit cell (? 3.4 Å), indicating that unit-cell control of (Ca,Sr)CuO2 growth is possible using conventional pulsed-laser deposition over a wide oxygen

David P. Norton; B. C. Chakoumakos; D. H. Lowndes; J. D. Budai

1996-01-01

151

Generation of zonal flow and magnetic field by coupled Rossby-Alfvén-Khantadze waves in the Earth's ionospheric E-layer  

NASA Astrophysics Data System (ADS)

It is shown that in the Earth's weakly ionized ionospheric E-layer with the dominant Hall conductivity, a new type of coupled Rossby-Alfvén-Khantadze (CRAK) electromagnetic (EM) planetary waves, attributable by the latitudinal inhomogeneity of both the Earth's Coriolis parameter and the geomagnetic field, can exist. Under such coupling, a new type of dispersive Alfvén waves is revealed. The generation of a sheared zonal flow and a magnetic field by CRAK EM planetary waves is investigated. The nonlinear mechanism of the instability is based on the parametric excitation of a zonal flow by interacting four waves, leading to the inverse energy cascade in the direction of a longer wavelength. A three-dimensional (3D) set of coupled equations describing the nonlinear interaction of pumping CRAK waves and zonal flow is derived. The growth rate of the corresponding instability and the conditions for driving them are determined. It is found that the growth rate is mainly stipulated by Rossby waves but the generation of the intense mean magnetic field is caused by Alfvén waves.

Kaladze, T. D.; Horton, W.; Kahlon, L. Z.; Pokhotelov, O.; Onishchenko, O.

2013-12-01

152

Ionospheric Sounding Measurements and Geomagnetic Field Variations at Tamanrasset Observatory  

Microsoft Academic Search

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

Moulayali Ali; Naima Zaourar; Abtout Abdessalem; Hamoudi Mohamed

2010-01-01

153

Growth kinetics of borided layers: Artificial neural network and least square approaches  

NASA Astrophysics Data System (ADS)

The present study evaluates the growth kinetics of the boride layer Fe 2B in AISI 1045 steel, by means of neural networks and the least square techniques. The Fe 2B phase was formed at the material surface using the paste boriding process. The surface boron potential was modified considering different boron paste thicknesses, with exposure times of 2, 4 and 6 h, and treatment temperatures of 1193, 1223 and 1273 K. The neural network and the least square models were set by the layer thickness of Fe 2B phase, and assuming that the growth of the boride layer follows a parabolic law. The reliability of the techniques used is compared with a set of experiments at a temperature of 1223 K with 5 h of treatment time and boron potentials of 2, 3, 4 and 5 mm. The results of the Fe 2B layer thicknesses show a mean error of 5.31% for the neural network and 3.42% for the least square method.

Campos, I.; Islas, M.; Ramírez, G.; VillaVelázquez, C.; Mota, C.

2007-05-01

154

Solar Wind/Magnetosphere/Ionosphere Coupling and the Temporal and Spatial Evolution of Boundary Layers using Cluster, Polar and other ISTP Satellites  

NASA Technical Reports Server (NTRS)

Our analysis concerns macro and meso-scale aspects of coupling between the IMF and the magnetosphere-ionosphere system, as opposed to the microphysics of determining how electron gyrotropy is broken and merging actually occurs. We correlate observed behaviors at Cluster and at Polar with temporal variations in other regions, such as in the ionosphere as measured by SuperDARN. Addressing problems with simultaneous observations from diverse locations properly constrains our interpretations.

Maynard, Nelson C.

2004-01-01

155

On anomalous temperature dependence of H C2? in natural and artificial layer superconductors  

Microsoft Academic Search

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,

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

1999-01-01

156

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

NASA Astrophysics Data System (ADS)

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 altitude at which the critical frequency {f_{x{F_2}}} of the F 2 layer is equal to the frequency f H of the heating accompanied by an up to 50% increase in the electron temperature. The spatial structure of the artificially perturbed ionospheric F region is examined in detail using an incoherent scatter radar operated in the regime of scanning over elevation angles from 92° to 74° with a 2° step. It is shown that the spatial size of the heated patch strongly depends on the angle of the HF pumping relative to the Earth's magnetic field. The phenomena occurring in the artificially modified ionospheric F region heated at frequencies near the third electron gyroharmonic, i.e., at f H = 3 f ce = f UH, where f UH is the upper-hybrid frequency, are explored on the basis of multi-instrument observation data.

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

2011-02-01

157

Development of New aSi\\/cSi Heterojunction Solar Cells: ACJ-HIT (Artificially Constructed Junction-Heterojunction with Intrinsic Thin-Layer)  

Microsoft Academic Search

A new type of a-Si\\/c-Si heterojunction solar cell, called the HIT (Heterojunction with Intrinsic Thin-layer) solar cell, has been developed based on ACJ (Artificially Constructed Junction) technology. A conversion efficiency of more than 18% has been achieved, which is the highest ever value for solar cells in which the junction was fabricated at a low temperature (<200°C).

Makoto Tanaka; Mikio Taguchi; Takao Matsuyama; Toru Sawada; Shinya Tsuda; Shoichi Nakano; Hiroshi Hanafusa; Yukinori Kuwano

1992-01-01

158

Soviet ionospheric modification research  

SciTech Connect

Soviet published literature in ionospheric modification research by high-power radio waves is assessed, including an evaluation of its impact on and applications to future remote-sensing and telecommunications systems. This assessment is organized to place equal emphasis on basic research activities, designed to investigate both the natural geophysical environment and fundamental plasma physics; advanced research programs, such as those studying artificial ionization processes and oblique high-power radio propagation and practical system applications and operational limitations addressed by this research. The assessment indicates that the Soviet Union sustains high-quality theoretical and experimental research programs in ionospheric modification, with a breadth and level of effort greatly exceeding comparable Western programs. Soviet theoretical research tends to be analytical and intuitive, as compared to the Western emphasis on numerical simulation techniques. The Soviet experimental approach is less exploratory, designed principally to confirm theoretical predictions. Although limited by inferior diagnostic capabilities, Soviet experimental facilities are more numerous, operate on a more regular basis, and transmit radio wave powers exceeding those os Western facilities. Because of its broad scope of activity, the Soviet Union is better poised to quickly exploit new technologies and system applications as they are developed. This panel has identified several key areas of Soviet research activity and emerging technology that may offer long-term opportunities for remote-sensing and telecommunications advantages. However, we have found no results that suggest imminent breakthrough discoveries in these fields.

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

1988-07-01

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

Ionosphere-reflected propagation  

NASA Technical Reports Server (NTRS)

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

Reddy, B. M.

1979-01-01

161

Activities Report on Ionospheric Observation.  

National Technical Information Service (NTIS)

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

1983-01-01

162

HAARP-Induced Ionospheric Ducts  

SciTech Connect

It is well known that strong electron heating by a powerful HF-facility can lead to the formation of electron and ion density perturbations that stretch along the magnetic field line. Those density perturbations can serve as ducts for ELF waves, both of natural and artificial origin. This paper presents observations of the plasma density perturbations caused by the HF-heating of the ionosphere by the HAARP facility. The low orbit satellite DEMETER was used as a diagnostic tool to measure the electron and ion temperature and density along the satellite orbit overflying close to the magnetic zenith of the HF-heater. Those observations will be then checked against the theoretical model of duct formation due to HF-heating of the ionosphere. The model is based on the modified SAMI2 code, and is validated by comparison with well documented experiments.

Milikh, Gennady; Vartanyan, Aram [University of Maryland, College Park, MD, 20742 (United States)

2011-01-04

163

Magnetogravity waves in the ionosphere under conditions of finite conductivity  

NASA Astrophysics Data System (ADS)

We obtain dispersion relations for magnetogravity waves in the ionosphere with allowance for the combined influence of magnetic field, gravity, and finite conductivity within the framework of the hydrodynamic approximation. The required conditions are fulfilled in the ionosphere at altitudes over or about 250 km. The auroral electrojet is considered as a source of magnetogravity waves which are frequently observed as traveling ionospheric disturbances. The contribution of magnetogravity waves to the ionospheric disturbances is determined on the basis of analyzing the data from the vertical sounding of the ionospheric F2 layer and the geomagnetic disturbances along the chosen magnetic meridian and on its sides. The features of the obtained dynamic spectra of magnetogravity waves agree with the characteristic frequencies and velocities determined by the calculated dispersion curves. As a result, we confirm the fact that magnetogravity waves stipulate some traveling ionospheric disturbances and can be used for diagnostics of the ionospheric parameters.

Barkhatov, N. A.; Barkhatova, O. M.; Grigor'ev, G. I.

2012-11-01

164

Ionospheric Instabilities and Shock Capturing Algorithms  

NASA Technical Reports Server (NTRS)

We describe the basic physics of the gradient-drift instability and the collisional Rayleigh-Taylor instability, the two plasma instabilities which dominate the production of small-scale structure in the earth's ionosphere. We then focus our attention on the nonlinear evolution of these instabilities for two particular cases: 1) the recursive bifurcation and "freezing" of artificial ion clouds released in the ionosphere; and 2) equatorial spread F. Finally, we discuss the numerical challenges faced in attempting to numerically simulate these instabilities, and the role played by shock-capturing algorithms therein.

Zalesak, Steven T.

1998-01-01

165

Early time evolution of artificially created dusty space plasmas  

NASA Astrophysics Data System (ADS)

An alternate approach to studying natural dust layers in the earth's upper atmosphere is to perform active space experiments in which a dust cloud is created in a controlled manner. Its evolution can then be more carefully observed and studied and then compared to characteristics of natural dust clouds. Such space experiments are currently under development are planned for the near future. Several important issues to be investigated include dust charging processes, plasma flows, electrodynamic structure, plasma irregularities, and coupling between the neutral components of the upper atmosphere and the dust clouds. Also possibilities of remote sensing plasma processes in these clouds through radar measurements will be studied. This talk 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 principal importance will be the production of plasma irregularities which may lead to radar echoes and the possibility of their relationship to well known radar echoes observed from natural dusty space plasmas. First, a plasma model will be described that may be used for investigating early time evolution after expansion of an artificial dust cloud across the magnetic field in the ionosphere. This model will then be used to investigate the electrodynamics and possible plasma irregularity generation mechanisms after creation of an artificial dust cloud. Finally, possibilities of radar signatures observed from the dust cloud will be considered.

Scales, Wayne

166

MoS2 atomic layers with artificial active edge sites as transparent counter electrodes for improved performance of dye-sensitized solar cells  

NASA Astrophysics Data System (ADS)

A novel MoS2 transparent counter electrode for dye-sensitized solar cells is reported. In order to enhance the catalytic activity of the electrode, active edge sites are created artificially by patterning holes on MoS2 atomic layers. Electrochemical analysis shows that the electrochemical activity is significantly improved after the patterning of holes. The photon-to-electron efficiency of the dye-sensitized solar cells based on MoS2 atomic layer counter electrodes is increased remarkably from 2% to 5.8% after the hole patterning.

Zhang, Jing; Najmaei, Sina; Lin, Hong; Lou, Jun

2014-04-01

167

MoS2 atomic layers with artificial active edge sites as transparent counter electrodes for improved performance of dye-sensitized solar cells.  

PubMed

A novel MoS2 transparent counter electrode for dye-sensitized solar cells is reported. In order to enhance the catalytic activity of the electrode, active edge sites are created artificially by patterning holes on MoS2 atomic layers. Electrochemical analysis shows that the electrochemical activity is significantly improved after the patterning of holes. The photon-to-electron efficiency of the dye-sensitized solar cells based on MoS2 atomic layer counter electrodes is increased remarkably from 2% to 5.8% after the hole patterning. PMID:24695461

Zhang, Jing; Najmaei, Sina; Lin, Hong; Lou, Jun

2014-04-24

168

The ionosphere as a source for magnetospheric ions  

NASA Technical Reports Server (NTRS)

Ion composition measurements within the past several years have shown O(+), He(+), and other ions of terrestrial origin to compose a substantial fraction of the magnetospheric ion population. This review examines (1) observations of topside ionospheric composition, (2) mechanisms for energization and injection of ionospheric ions into the magnetosphere, and (3) observations of ions of ionospheric origin in various regions of the magnetosphere, including the plasmasphere, ring current, magnetotail plasma sheet and lobes, and boundary layer and magnetosheath.

Horwitz, J. L.

1982-01-01

169

Ionospheric characteristics: a review  

SciTech Connect

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

Rich, F.J.

1983-01-01

170

Ionospheric Observation Activities Report.  

National Technical Information Service (NTIS)

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

1984-01-01

171

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

SciTech Connect

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. [Polytechnic Institute of New York University, 6 MetroTech Center, Brooklyn, New York 11201 (United States)] [Polytechnic Institute of New York University, 6 MetroTech Center, Brooklyn, New York 11201 (United States)

2013-09-15

172

Artificial Photosynthesis  

Microsoft Academic Search

One-dimensional channel materials, such as zeolites and mesoporous silicas, are very attractive hosts for the preparation\\u000a and investigation of hierarchically organized structures, presenting a successive ordering from the molecular up to macroscopic\\u000a scale. The focus of this article is on artificial photonic antenna systems and on photocatalytically active layers that have\\u000a been built by incorporating organic dyes, complexes, metal cations

Gion Calzaferri

2010-01-01

173

LIFDAR: A Diagnostic Tool for the Ionosphere  

NASA Astrophysics Data System (ADS)

ITT Corporation proposes a novel system to measure and monitor the ion species within the Earth's ionosphere called Laser Induced Fluorescence Detection and Ranging (LIFDAR). Unlike current ionosphere measurements that detect electrons and magnetic field, LIFDAR remotely measures the major contributing ion species to the electron plasma. The LIFDAR dataset has the added capability to demonstrate stratification and classification of the layers of the ionosphere to ultimately give a true tomographic view. We propose a proof of concept study using existing atmospheric LIDAR sensors combined with a mountaintop observatory for a single ion species that is prevalent in all layers of the atmosphere. We envision the LIFDAR concept will enable verification, validation, and exploration of the physics of the magneto-hydrodynamic models used in ionosphere forecasting community. The LIFDAR dataset will provide the necessary ion and electron density data for the system wide data gap. To begin a proof of concept, we present the science justification of the LIFDAR system based on the model photon budget. This analysis is based on the fluorescence of ionized oxygen within the ionosphere versus altitude. We use existing model abundance data of the ionosphere during normal and perturbed states. We propagate the photon uncertainties from the laser source through the atmosphere to the plasma and back to the collecting optics and detector. We calculate the expected photon budget to determine signal to noise estimates based on the targeted altitude and detection efficiency. Finally, we use these results to derive a LIFDAR observation strategy compatible with operational parameters.

Kia, O. E.; Rodgers, C. T.; Batholomew, J. L.

2011-12-01

174

Infrasonic troposphere-ionosphere coupling in Hawaii  

NASA Astrophysics Data System (ADS)

The propagation of infrasonic waves in the ionospheric layers has been considered since the 1960's. It is known that space weather can alter infrasonic propagation below the E layer (~120 km altitude), but it was thought that acoustic attenuation was too severe above this layer to sustain long-range propagation. Although volcanoes, earthquakes and tsunamis (all surface sources) appear to routinely excite perturbations in the ionospheric F layer by the propagation of acoustic and acoustic-gravity waves through the atmosphere, there are few reports of the inverse pathway. This paper discusses some of the routine ground-based infrasonic array observations of ionospheric returns from surface sources. These thermospheric returns generally point back towards the source, with an azimuth deviation that can be corrected using the wind velocity profiles in the mesosphere and lower thermosphere. However, the seismic excitation in the North Pacific by the Tohoku earthquake ensonified the coupled lithosphere-atmosphere-ionosphere waveguide in the 0.01 - 0.1 Hz frequency band, producing anomalous signals observed by infrasound arrays in Hawaii. These infrasonic signals propagated at curiously high velocities, suggesting that some assumptions on ionospheric sound generation and propagation could be revisited.

Garces, M. A.

2011-12-01

175

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

176

The ionospheric responses in the equatorial anomaly region during the 6-7 April 2000 ionospheric storm  

NASA Astrophysics Data System (ADS)

The great magnetic storm on 6-7 April 2000 generated ionospheric disturbances in the equatorial anomaly region. The ionosonde at Chung-Li (24.9›XN, 121›XE) and the GPS receivers observed the ionosphere during this period. The variations of the ionospheric parameters, NmF2 (plasma density of the F-peak), hmF2 (height of the F-peak) and h­ÝF (minimum virtual height of the F-layer), demonstrate that a traveling atmospheric disturbance (TAD) affects the ionosphere in this region. The simultaneous total electron content (TEC) derived from GPS shows that the crest of equatorial anomaly region moves equatorward. To further understand the causality of ionosphere response, the TIEGCM (Thermosphere/Ionosphere General Circulation Model) has been applied to simulate this event. The agreement and discrepancy between the simulated and observed results will be illustrated and discussed.

Lee, C.; Liu, J.; Chen, M.

2002-05-01

177

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

NASA Astrophysics Data System (ADS)

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

Harrison, Giles; Aplin, Karen; Rycroft, Michael

2014-05-01

178

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

179

Venusian Earthquakes Detection by Ionospheric Sounding  

NASA Astrophysics Data System (ADS)

Thanks to technological advances over the past fifteen years the ionosphere is now a new medium for seismological investigation. As a consequence of density structure in Venus atmosphere, the coupling between solid and fluid part of Venus induce a more significant atmospheric responce to quakes and volcanic eruptions (Lognonné & Johnson, 2007). Equivalent perturbation induced by internal activity has been detected on Earth through their subsequent ionospheric signature imaged by ionospheric tools (Doppler sounding or GPS) (Lognonné et al., 2006, Occhipinti et al., 2010). The strong solid/atmosphere coupling on Venus (Garcia et al., 2005, 2009), the thin ionospheric layer as well as absence of magnetic field present optimal circumstances for a better detection of these signals on Venus than on Earth. Consequently, ionospheric Doppler sounders on-board orbiters or balloons will provide informations on the infrasonic response of the atmosphere/ionosphere to quakes, and will help to constrain the interior structure of Venus through the solid/atmosphere coupling. With this paper we explore the future mission possibility and constrains.

Occhipinti, G.; Lognonne, P.; Garcia, R. F.; Gudkova, T.

2010-12-01

180

Comparisons between the ionospheres of Venus and Mars  

NASA Astrophysics Data System (ADS)

The ionospheres of Venus and Mars are remarkably similar in many ways. The V2 layer at Venus and M2 layer at Mars are produced when extreme ultraviolet solar photons ionize atmospheric CO2. Peak ionospheric densities occur in these layers. The V1 layer at Venus and M1 layer at Mars are produced by deeper penetrating solar soft X-rays and subsequent electron collision ionization. Here we compare the properties of these analogous layers using radio occultation data from the Venus Express spacecraft and the Mars Global Surveyor spacecraft. We compare how the peak altitudes and peak densities of each layer depend on solar zenith angle. We also compare how the peak densities of each layer vary with solar flux. We report the results of our analysis and discuss the implications of our findings with regard to terrestrial planet ionospheres.

Girazian, Z. R.; Tarrh, A.; Fallows, K.; Withers, P.; Haeusler, B.; Paetzold, M.; Tellmann, S.

2012-12-01

181

Ionospheric disturbance overview  

NASA Technical Reports Server (NTRS)

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

Rush, C. M.

1980-01-01

182

Properties of the ULF/VLF Signals Generated by the Sura Facility in the Upper Ionosphere  

NASA Astrophysics Data System (ADS)

The results of studying the generation of low-frequency radiation in the ionosphere affected by high-power modulated HF radiation of the Sura facility are presented. A large amount of data on characteristics of the ULF/VLF artificial signals observed in the night time, which indicate the manifestation of a new generation mechanism not related to the quasistationary ionospheric current modulation effect, have been obtained for the first time at the mid-latitudes. The results of studying the dependence of the signal value on the beam inclination of the pump wave and the distance to the observation point from the facility are presented. It is shown that the signals can be both right- and left-hand polarized depending on the level of geomagnetic activity. The measured time delay of the ULF signal indicates the location of the source at the F-layer maximum. Interpretation of the observed characteristics of artificial low-frequency signals based on a ponderomotive excitation mechanism of the diamagnetic ring current around the HF radiation beam at a modulation frequency agrees with the main results of the experiment.

Kotik, D. S.; Ryabov, A. V.; Ermakova, E. N.; Pershin, A. V.; Ivanov, V. N.; Esin, V. P.

2013-11-01

183

The ionosphere under extremely prolonged low solar activity  

Microsoft Academic Search

Use multidata to explore the ionospheric response to unusual solar activityTEC and the F layer declined to the lowest during cycle 23\\/24 minimumSolar EUV is the prevailing contributor to the unusual low electron density

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

2011-01-01

184

High-latitude E and F region ionospheric predictions  

NASA Technical Reports Server (NTRS)

The physical processes and morphology of the high latitude E and F layers are discussed. The existence and adequacy of models, and features to be included are examined, as well as reliability of ionospheric predictions.

Hunsucker, R. D.; Allen, R.; Argo, P. E.; Babcock, R.; Bakshi, P.; Lund, D.; Matsushita, S.; Smith, G.; Shirochkov, A. V.; Wortham, G.

1979-01-01

185

Ionospheric Prediction and Forecasting Services in Mediterranean Area  

NASA Astrophysics Data System (ADS)

This paper will present the basic approach on ionospheric prediction and forecasting used to provide services in Mediterranean area. Both services based on two ionospheric stations (Geomagnetic Indices Forecasting and Ionospheric Nowcasting Tools - GIFINT project) and one ionospheric station (Cyprus Ionospheric Forecasting Service - CIFS project) rely on background ionosphere described by the Simplified Ionospheric Regional Model (SIRM). In case of GIFINT the update of SIRM model is performed by the critical frequency of the F2 layer (foF2) and the propagation factor (M(3000)F2) values coming from the Rome and Gibilmanna ionospheric stations, while in case of CIFS the update of SIRM model is performed by the foF2 and M(3000)F2 values coming from the Nicosia ionospheric station. Some examples of nowcasting and long term maps for foF2 and M(3000)F2 will be shown. Discussion will be focused on the role of real time updating of the SIRM model.

Pezzopane, Michael; Zolesi, Bruno; Haralambous, Haris; Oikonomou, Christina; Cander, Ljiljana R.

2014-05-01

186

Formation of Striations in Ionospheric Plasma Clouds  

Microsoft Academic Search

It is suggested that a low-frequency 'gradient drift' instability may be important for the formation of striations in barium ion clouds released in the ionosphere above the E layer. The theory predicts that the trailing edge (with respect to the neutrals) of the plasma cloud will be unstable while the leading edge is stable, in qualitative agreement with observations. The

Lewis M. Linson; Joseph B. Workman

1970-01-01

187

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

188

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

NASA Astrophysics Data System (ADS)

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 the reflection height for O-mode-polarized radio waves. This directional dependence of RF-enhanced incoherent radar backscatter has been shown using data from the high-latitude ionosphere, and the significant features included consistent field-aligned signatures that may be related to the presence of artificial field-aligned irregularities. These earlier high-latitude results provided motivation for repeating the investigation in the different geophysical conditions that obtain in the polar cap ionosphere. The Space Plasma Exploration by Active Radar (SPEAR) facility is located within the polar cap and has provided observations of RF-enhanced ion and plasma line spectra recorded by the EISCAT Svalbard UHF incoherent scatter radar system (ESR), which is collocated with SPEAR. We present observations of aspect sensitive E-and F-region SPEAR-induced ion and plasma line enhance-ments from several directions in the magnetic meridian plane, centred on field-aligned. These enhancements indicate excitation of both the purely growing mode and the parametric decay instability, together with sporadic E-layer results that may indicate the presence of cavitons. We note consistent enhancements from field-aligned, vertical and also from 5 degrees south of field-aligned. We attribute the prevalence of vertical scatter to the importance of the Spitze region, and of that from field-aligned to possible wave/irregularity coupling.

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

189

GPS and ionospheric scintillations  

Microsoft Academic Search

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

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

2007-01-01

190

International reference ionosphere 1990  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

191

Ionospheric modelling for navigation  

NASA Astrophysics Data System (ADS)

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

Aragon Angel, M. A.

192

Rocket studies of the lower ionosphere  

NASA Technical Reports Server (NTRS)

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

Bowhill, Sidney A.

1990-01-01

193

Ionospheric Effects of Underground Nuclear Explosions  

NASA Astrophysics Data System (ADS)

Telemetry from the Russian INTERCOSMOS 24 satellite recorded ELF and VLF electromagnetic disturbances in the outer ionosphere from an underground nuclear explosion that was detonated at Novaya Zemlya Island on 24 October 1994. The IC24 satellite observations were obtained at about 900 km altitude within a few degrees of ground zero. The disturbances were interpreted for magnetohydrodynamic excitation of the ionosphere’s E layer by the acoustic wave. Electrons are accelerated along the magnetic force lines to amplify longitudinal currents and magnetic disturbances that may be measured by magnetometers at ground-based observatories and on-board satellites. The underground nuclear test near P’unggye, North Korea on 25 May 2009 provides a further significant opportunity for studying the utility of ionospheric disturbances for characterizing ground zero. Of the seismic, infrasound, hydroacoustic, and radionuclide detection elements of the International Monitoring System (IMS) established by the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO), only the first two elements detected this event. However, the event also appears to have been recorded as a direct traveling ionospheric disturbance (TID) in the slant total electron content (TEC) observations derived from a network of the Global Navigation Satellite System (GNSS) measurements. The TID was observed to distances of at least 600 km from the explosion site propagating with a speed of about 281m/s. Thus, the global distributions and temporal variations of the TEC, may provide important information to help detect and characterize clandestine underground nuclear explosions.

Park, J.; von Frese, R. R.; G-Brzezinska, D. A.; Morton, Y.

2010-12-01

194

Examples of meteorological behavior of the ionosphere  

NASA Astrophysics Data System (ADS)

For some time the network of ionosonde stations in Europe were dense enough to study the meteorological behavior of the ionosphere. Because the electron recombination near the maximum of the F-region ionization is sufficiently small, the maximum electron density and the profile are controlled substantially by dynamic processes. Gravity waves and vertical plasma drift and its vertical gradients change the F-layer ionization significantly. In fixed frequency ionosonde recordings the author has discovered direct oblique echoes from a hole in the ionosphere over the Alps. Maps were drawn to show the meteorological properties of this European Anomaly either as a time development of a cross-section of Europe from northern Germany to Rome, Italy using six stations, or as a sequence of a contour maps of the ionosphere over Europe using ten stations. A short animated movie was produced demonstrating the development of the hole in the ionosphere and its recovery with a curl developing. Even the average behavior of the F-region ionization shows substantial differences with location. In Europe the variations of the local gradients in ionization can be different by a factor of two over two locations separated by 1000 km. This behavior, important for understanding the meteorology of the ionosphere and for precise ionspheric radio predictions, certainly requires intense studies with digital sounders in Europe and at other locations.

Bibl, K.

1989-04-01

195

Direct measurement of interactions between stimulation-responsive drug delivery vehicles and artificial mucin layers by colloid probe atomic force microscopy.  

PubMed

A novel thermo- and pH-sensitive nanogel particle, which is a core-shell structured particle with a poly(N-isopropylacrylamide) (p(NIPAAm)) hydrogel core and a poly(ethylene glycol) monomethacrylate grafted poly(methacrylic acid) (p(MMA-g-EG)) shell, is of interest as a vehicle for the controlled release of peptide drugs. The interactions between such nanogel particles and artificial mucin layers during both approach and separation were successfully measured by using colloid probe atomic force microscopy (AFM) under various compression forces, scan velocities, and pH values. While the magnitudes of the compression forces and scan velocities did not affect the interactions during the approach process, the adhesive force during the separation process increased with these parameters. The pH values significantly influenced the interactions between the nanogel particles and a mucin layer. A large steric repulsive force and a long-range adhesive force were measured at neutral pH due to the swollen p(MMA-g-EG) shell. On the other hand, at low pH values, the steric repulsive force disappeared and a short-range adhesive force was detected, which resulted from the collapse of the shell layer. The nanogel particles possessed a pH response that was sufficient to protect the incorporated peptide drug under the harsh acidic conditions in the stomach and to effectively adhere to the mucin layer of the small intestine, where the pH is neutral. The relationships among the nanogel particle-mucin layer interactions, pH conditions, scan velocities, and compression forces were systemically investigated and discussed. PMID:18312015

Iijima, Motoyuki; Yoshimura, Motoyasu; Tsuchiya, Tadashi; Tsukada, Mayumi; Ichikawa, Hideki; Fukumori, Yoshinobu; Kamiya, Hidehiro

2008-04-15

196

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.

197

Electron Acceleration by High Power Radio Waves in the Ionosphere  

NASA Astrophysics Data System (ADS)

At the highest ERP of the High Altitude Auroral Research Program (HAARP) facility in Alaska, high frequency (HF) electromagnetic (EM) waves in the ionosphere produce artificial aurora and electron-ion plasma layers. Using HAARP, electrons are accelerated by high power electrostatic (ES) waves to energies >100 times the thermal temperature of the ambient plasma. These ES waves are driven by decay of the pump EM wave tuned to plasma resonances. The most efficient acceleration process occurs near the harmonics of the electron cyclotron frequency in earth's magnetic field. Mode conversion plays a role in transforming the ES waves into EM signals that are recorded with ground receivers. These diagnostic waves, called stimulated EM emissions (SEE), show unique resonant signatures of the strongest electron acceleration. This SEE also provides clues about the ES waves responsible for electron acceleration. The electron gas is accelerated by high frequency modes including Langmuir (electron plasma), upper hybrid, and electron Bernstein waves. All of these waves have been identified in the scattered EM spectra as downshifted sidebands of the EM pump frequency. Parametric decay is responsible low frequency companion modes such as ion acoustic, lower hybrid, and ion Bernstein waves. The temporal evolution of the scattered EM spectrum indicates development of field aligned irregularities that aid the mode conversion process. The onset of certain spectral features is strongly correlated with glow plasma discharge structures that are both visible with the unaided eye and detectable using radio backscatter techniques at HF and UHF frequencies. The primary goals are to understand natural plasma layers, to study basic plasma physics in a unique ``laboratory with walls,'' and to create artificial plasma structures that can aid radio communications.

Bernhardt, Paul

2012-10-01

198

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

199

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

200

Ionospheric plasma cloud dynamics  

NASA Technical Reports Server (NTRS)

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

1976-01-01

201

Arecibo Ionospheric Observatory.  

National Technical Information Service (NTIS)

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

D. W. Taylor

1967-01-01

202

Ionospheric Research Using Satellites.  

National Technical Information Service (NTIS)

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

J. Mass Z. Houminer

1968-01-01

203

Ionospheric disturbances under low solar activity conditions  

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

204

Compliant layer bearings in artificial joints. Part 1: the effects of different manufacturing techniques on the interface strength between an elastomeric layer and a rigid substrate.  

PubMed

The premise that elastomeric materials could be used as one or more of the articulating components in both hip and knee prostheses was postulated first by Unsworth and co-workers. It was thought that such materials might have the capacity to mimic natural joint behaviour more closely than the more rigid bearing surfaces commonly in use. A more natural joint function in artificial joints should promote better tribology, with full fluid-film lubrication being the goal. Early tests showed that this objective could potentially be achieved with a judicious choice of materials and carefully controlled manufacturing techniques. This paper (Part 1 of a two-part series) describes and explains the techniques used to verify the material selection as well as to determine the most appropriate manufacturing procedure to obtain a strong and robust interface between the support and bearing material of the prosthesis. Two polycarbonate urethane (PU) materials with different hardness values (Corethane 80A and Corethane 75D) gave sufficient interfacial strength when moulded under optimum conditions. Corethane 80A was used as the soft bearing material while Corethane 75D provided the rigid backing component. Peel tests revealed strong interface bonds, varying with processing conditions between 350 and 862 N. Fourier transform infrared spectroscopy and micro-thermal analysis showed that a fusion bond over 30 microm thick formed at the interface. The results of the range of tests and analyses, which have been used in this study, have provided sufficient evidence to validate the process used to manufacture these components. PMID:18935802

Burgess, I C; Jones, E; Scholes, S C; Unsworth, A

2008-08-01

205

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

206

Dayside Ionospheric Superfountain  

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

207

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

208

Tsunami Ionospheric warning and Ionospheric seismology  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

209

Martian ionosphere as observed by the Viking retarding potential analyzers  

Microsoft Academic Search

The retarding potential analyzers on the Viking landers obtained the first in situ measurements of ions from another planetary ionosphere. Mars has an F⁠ionosphere layer with a peak ion concentration of approximately 10⁵ cm⁻³ just below 130-km altitude, of which approx.90% are Oâ\\/sup +\\/ and 10% COâ\\/sup +\\/. At higher altitudes, O\\/sup +\\/ ions were detected with peak concentration

W.B. Hanson; S. Sanatani; D. R. Zuccaro

1977-01-01

210

Artificially layered films of CuBa{sub 2} (Ca{sub 1{minus}x}Sr{sub x}){sub n{minus}1}Cu{sub n}O{sub y} grown using pulsed laser deposition  

SciTech Connect

We have shown that the pulsed laser deposition technique (PLD) can be successfully used to grow artificially layered films of the CuBa{sub 2}(Ca{sub 1{minus}x}Sr{sub x}){sub n{minus}1}Cu{sub n}O{sub y} compound using only two targets having nominal composition BaCuO{sub y} and (Ca{sub 1{minus}x}Sr{sub x})CuO{sub y}, respectively. n was varied between 2 and 5. We have demonstrated, by a kinematic analysis of the x-ray diffraction spectra that the average random discrete thickness fluctuations which affect both the BaCuO{sub y} and (Ca{sub 1{minus}x}Sr{sub x})CuO{sub y} layers are much smaller than one atomic layer. Such features are confirmed by the appearance of sharp peaks even for the n=2 artificially layered structure where only one (Ca{sub 1{minus}x}Sr{sub x})CuO{sub y} cell is deposited in the stacking sequence. These results show that truly new structures can be obtained by a layer by layer deposition technique with a low interfacial disorder and give strong support to the idea of synthesizing new artificial high T{sub c} structures by the PLD technique.{copyright} {ital 1997 American Institute of Physics.}

Aruta, C.; Balestrino, G.; Martellucci, S.; Paoletti, A.; Petrocelli, G. [INFM-Dipartimento di Scienze e Tecnologie Fisiche ed Energetiche, Universita di Roma Tor Vergata, via della Ricerca Scientifica, 00133 Roma (Italy)] [INFM-Dipartimento di Scienze e Tecnologie Fisiche ed Energetiche, Universita di Roma Tor Vergata, via della Ricerca Scientifica, 00133 Roma (Italy)

1997-01-01

211

On the role of electric field direction in the formation of sporadic E-layers in the southern polar cap ionosphere  

NASA Astrophysics Data System (ADS)

Measurements of the occurrence of sporadic E (Es)-layers and F-region electric fields were obtained with a modern, HF digital ionosonde located at Casey, Antarctica (66.3°S, 110.5°E, 81°S CGM latitude) during the late austral summer of 1995/96. The occurrence of Es-layers was inferred from the presence of appropriate traces in normal swept-frequency ionograms, and the electric fields were inferred from F-region ``drift-mode'' velocities assuming that the plasma convection velocities given by E × B/B2 were measured, on average, by the interferometer. The theory of formation of high-latitude Es-layers predicts that electric fields directed toward the south west (SW) should be particularly effective at producing thin layers in the southern hemisphere. Our measurements made at a true polar cap station are consistent with this expectation, and are contrasted with observations made by incoherent scatter radars in the northern hemisphere, which also show the importance of SW electric fields, whereas the same theory predicts that NW electric fields should be important at northern latitudes. We reconcile the interhemispheric differences with simple calculations of ion convergence driven by the electric fields specified by the IZMIRAN electrodynamic model (IZMEM) in both hemispheres. The importance of the interplanetary magnetic field in the control of high-latitude Es formation is emphasised as an important adjunct to space weather modelling and forecasting.

Parkinson, M. L.; Dyson, P. L.; Monselesan, D. P.; Morris, R. J.

1998-03-01

212

Spatially quasi-sinusoidal medium-scale electron-density irregularities of the F2-layer maximum in the ionosphere at low and equatorial latitudes  

NASA Astrophysics Data System (ADS)

The paper examines the situation when medium-scale electron-density irregularities in the F2-layer maximum in the daytime at low and equatorial latitudes have a quasi-sinusoidal shape along the orbit of the Alouette-1 satellite. These irregularities are manifested on the background of a well-developed equatorial anomaly in the daytime F2-region; the intensity maxima of these irregularities are observed in the region of the anomaly crests.

Fatkullin, M. N.; Zarutskaia, E. V.; Fatkullina, V. A.

1992-02-01

213

Robust detection of ionospheric irregularities  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

214

On spatial scales of seismo-ionospheric effects  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

215

Recent Advances in Mid-latitude Ionosphere/Thermosphere Science  

NASA Astrophysics Data System (ADS)

One of the original reasons for building a National Ionospheric Observatory (now the National Astronomy and Ionospheric Center or NAIC) near Arecibo, Puerto Rico was the location, which is in the best behaved region of the ionosphere. At 30° magnetic latitude and 19° geographic latitude, it is well equatorward of the auroral and sub-auroral zones and poleward of the equatorial anomalies most of the time. The island thus has some of the best weather and space weather on the planet. However, similar to an occasional hurricane striking the island, the ionosphere overhead has occasional ionospheric and thermospheric disturbances. Some of these space weather phenomena, e.g., mesoscale TIDs and unstable sporadic E layers, are endemic to the region and, prior to the advent of airglow imagers and GPS networks, were difficult to visualize using radiowave data alone. Other weather events are caused by infringement on this zone from processes in more active weather regions. For example, neutral waves launched from the auroral oval (large scale TIDs) pass through the region; electric fields penetrate from the solar wind and create both plasma uplifts, causing positive ionospheric storms, and stormenhanced density plumes, coursing through the region. From the south, convective equatorial ionospheric storms create plasma bubbles that can reach mid-latitudes. Examples of data obtained during these phenomena, and possibly more, will be presented and discussed in light of our present understanding.

Kelley, Michael

216

Thermospheric Winds and Their Influence on the Ionosphere (Review).  

National Technical Information Service (NTIS)

New results of observations and theoretical calculations of thermospheric winds in the upper atmosphere above 150 km are presented. The effects of the winds on the ionospheric F2-layer are considered in some detail. Many features of the F-layer behavior a...

R. Ruester

1974-01-01

217

Effect of Lunar Eclipse on the Ionosphere  

Microsoft Academic Search

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

S. S. Banerjee; B. N. Singh

1936-01-01

218

Effects of Nuclear Explosions on the Ionosphere  

Microsoft Academic Search

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

Walter Dieminger; Harry Kohl

1962-01-01

219

IONOSPHERIC CORRECTIONS FOR TIMING APPLICATIONS  

Microsoft Academic Search

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

John A. Klobuchar

220

Ionospheric Corrections to Tropospheric Retrievals  

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

221

Parametric Instabilities and Ionospheric Modification  

Microsoft Academic Search

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

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

1974-01-01

222

Swarm SCARF Dedicated Ionospheric Field Inversion chain  

NASA Astrophysics Data System (ADS)

The geomagnetic daily variation at mid-to-low latitudes, referred to as the geomagnetic Sq field, is generated by electrical currents within the conducting layers of the ionosphere on the dayside of the Earth. It is enhanced in a narrow equatorial band, due to the equatorial electrojet. The upcoming ESA Swarm satellite mission, to be launched end of 2013, will consist of three satellites in low-Earth orbit, providing a dense spatial and temporal coverage of the ionospheric Sq field. A Satellite Constellation Application and Research Facility (SCARF) has been set up by a consortium of research institutions, aiming at producing various level-2 data products during the Swarm mission. The Dedicated Ionospheric Field Inversion (DIFI) chain is a SCARF algorithm calculating global, spherical harmonic models of the Sq field at quiet times. It describes seasonal and solar cycle variations, separates primary and induced magnetic fields based upon advanced 3D-models of the mantle electrical conductivity, and relies on core, lithospheric and magnetospheric field models derived from other SCARF algorithms for removing non-ionospheric fields from the data. The DIFI chain was thoroughly tested on synthetic data during the SCARF preparation phase; it is now ready to be used for deriving models from real Swarm data.

Chulliat, A.; Vigneron, P.; Thébault, E.; Sirol, O.; Hulot, G.

2013-11-01

223

Spatial and temporal evolution of 630. 0 nm airglow enhancement during ionospheric heating experiments  

SciTech Connect

Images of 630.00 nm enhancements have been recorded during the January, 1986 ionospheric heating campaign at Arecibo. The artificial airglow clouds convected eastward, vanished, and then reappeared at the zenith of the HF heater. Occasionally, the airglow patches are bifurcated. The structure and motion of the airglow clouds is an indication of the dynamic behavior of the modified ionosphere. 5 refs., 8 figs.

Bernhardt, P.A.; Duncan, L.M.; Tepley, C.A.; Behnke, R.A.; Sheerin, J.P.

1986-01-01

224

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

225

International Reference Ionosphere -2010  

NASA Astrophysics Data System (ADS)

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

Bilitza, Dieter; Reinisch, Bodo

226

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 940 ng and the limit of detection (LD) of 183, 57 and 282 ng 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

2013-10-10

227

Imidazolium or guanidinium/layered manganese (III, IV) oxide hybrid as a promising structural model for the water-oxidizing complex of Photosystem II for artificial photosynthetic systems.  

PubMed

Photosystem II is responsible for the light-driven biological water-splitting system in oxygenic photosynthesis and contains a cluster of one calcium and four manganese ions at its water-oxidizing complex. This cluster may serve as a model for the design of artificial or biomimetic systems capable of splitting water into oxygen and hydrogen. In this study, we consider the ability of manganese oxide monosheets to self-assemble with organic compounds. Layered structures of manganese oxide, including guanidinium and imidazolium groups, were synthesized and characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction spectrometry, and atomic absorption spectroscopy. The compounds can be considered as new structural models for the water-oxidizing complex of Photosystem II. The overvoltage of water oxidation for the compounds in these conditions at pH = 6.3 is ~0.6 V. These compounds may represent the first step to synthesize a hybrid of guanidinium or imidazole together with manganese as a biomimetic system for the water-oxidizing complex of Photosystem II. PMID:23543329

Najafpour, Mohammad Mahdi; Tabrizi, Mahmoud Amouzadeh; Haghighi, Behzad; Eaton-Rye, Julian J; Carpentier, Robert; Allakhverdiev, Suleyman I

2013-11-01

228

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

229

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

2012-05-01

230

Characterizing Extreme Ionospheric Storms  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

231

Ionospheric manifestations of acoustic-gravity waves under quiet and disturbed conditions  

NASA Astrophysics Data System (ADS)

We present the observation results of wave disturbances in the ionosphere, which are known to be manifestations of atmospheric acoustic-gravity waves (AGWs). The observations have been conducted under quiet and naturally or artificially disturbed conditions by ionosonde and incoherent scatter radar located near Kharkiv, Ukraine. Wave disturbance parameters under quiet conditions were obtained and analysed during geophysical periods including vernal and autumn equinoxes as well as summer and winter solstices. The prevailing oscillation in ionospheric F2- layer had the period of 140 - 200 min and relative amplitude of 0.1 - 0.2. The duration of this oscillation changed from 5 - 7 to 24 hours, depending on a season. The amplitude of fluctuations with other periods was noticeably smaller. The time intervals at which the intensity of incoherent scatter signals varied quasi-periodically in the altitude range from 150 to 300 km were detected. The parameters of these variations were estimated using statistical analysis and bandpass filtering. The periods of wave processes were shown to be of 30 - 120 min, there durations did not exceed of 2 - 6 periods and relative amplitudes usually ranged from 0.03 to 0.15. The phase of oscillations was detected to propagate downwards. The vertical phase velocity of travelling ionospheric disturbances (TIDs) was estimated to be in the range from 50 to 200 m/s and increased with altitude. The observations of the partial solar eclipse on January, 4, 2011 near Kharkiv were used to study the ionospheric parameters in naturally disturbed conditions. The F2-layer critical frequency dropped by a factor of 2.1. The time delay of these variations with respect to the main magnitude of the solar disk obscuration was equal to about 16 minutes. The virtual height of signal reflection near the maximum of the F2-layer ionization increased by 70 km, and the height of the model parabolic layer increased by 10 km. Some decrease in electron density and growth of quasi-periodic variations with periods of about 30 and 60 min were detected at all observable heights during this solar eclipse. The diagnostics of wave processes has been performed during ionospheric modification experiments with EISCAT heater. This heater is at a distance of about 2400 km from Kharkiv incoherent scatter radar. We have detected the TIDs over Kharkiv with periods of 40 - 80 min. The duration of these disturbances has not exceeded 120 - 180 min. The relative amplitudes of the TIDs in electron density ranged from 0.05 to 0.15 and those in electron and ion temperatures were about 0.02 - 0.05. The possible mechanisms for the generation of AGWs and TIDs by high power HF radio waves are sharp thermal gradients at the edge of the heated region and modulation of the ionospheric current systems by periodic high power radio transmission.

Barabash, Vladimir; Chernogor, Leonid; Panasenko, Sergii; Domnin, Igor

2014-05-01

232

Net field-aligned currents observed by Triad. [Coupling of ionosphere with distant magnetosphere  

Microsoft Academic Search

From the Triad magnetometer observation of a step-like level shift in the east--west component of the magnetic field at 800 km altitude, the existence of a net current flowing into or away from the ionosphere in a current layer was inferred. The current direction is toward the ionosphere on the morning side and away from it on the afternoon side.

M. Sugiura; T. A. Potemra

1975-01-01

233

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

234

The Dayside Ionospheric \\  

Microsoft Academic Search

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

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

2006-01-01

235

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

236

Analysis of the backscatter spectrum in an ionospheric modification experiment  

NASA Technical Reports Server (NTRS)

Predictions of the backscatter spectrum, including effects of ionospheric inhomogeneity, are compared with experimental observations of incoherent backscatter from an artificially heated region. Our calculations show that the strongest backscatter echo received is not from the reflection level, but from a region some distance below. Certain asymmetrical features are explained of the up-shifted and down-shifted plasma lines in the backscatter spectrum, and the several satellite peaks accompanying them.

Kim, H.; Crawford, F. W.; Harker, K. J.

1974-01-01

237

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

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

HF modulated ionospheric currents  

NASA Astrophysics Data System (ADS)

The HAARP HF facility is used to modulate the components of the auroral electrojet that flow in the D-region of the ionosphere, creating ELF/VLF radiation which is then measured at a receiver co-located with the HAARP HF antenna. An HF heating model is coupled to a full wave plasma interaction FDTD code to determine the ELF/VLF response of the ionospheric plasma to the modulated HF stimulation. The predicted FDTD fields on the ground are found to be in remarkable agreement with those measured at a receiver co-located with HAARP. The FDTD code also predicts an upwardly propagating whistler mode that is tightly bound to the magnetic field lines.

Payne, J. A.; Inan, U. S.; Foust, F. R.; Chevalier, T. W.; Bell, T. F.

2007-12-01

240

Artificial intelligence  

SciTech Connect

This book is an overview of the field of artificial intelligence. The work emphasizes natural language comprehension and knowledge-based reasoning by computers and analyzes the main difficulties involved in making intelligent programs. Representations of knowledge and reasoning mechanisms are provided and applications of artificial intelligence techniques in the development of expert systems are explored.

Bonnet, A.

1986-01-01

241

The Dayside Ionospheric  

Microsoft Academic Search

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

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

2006-01-01

242

Variability of the ionosphere  

Microsoft Academic Search

Hourly foF2 data from over 100 ionosonde stations during 1967–89 are examined to quantify F-region ionospheric variability, and to assess to what degree the observed variability may be attributed to various sources, i.e., solar ionizing flux, meteorological influences, and changing solar wind conditions. Our findings are as follows. Under quiet geomagnetic conditions (Kp<1), the 1-? (? is the standard deviation)

Jeffrey M. Forbes; Scott E. Palo; Xiaoli Zhang

2000-01-01

243

Magnetosphere-ionosphere coupling  

Microsoft Academic Search

A simple two-dimensional model of the magnetosphere-ionosphere system is discussed in which a localized electromotive force applied across a magnetic field line at t=0 is shown to propagate along the magnetic field with the Alfven velocity. The perpendicular electric field is assumed to reverse direction across the field line. Since the perpendicular electric field is limited in space, the propagation

C. K. Goertz; R. W. Boswell

1979-01-01

244

Study of Ionosphere Propagation at Frequencies from 4 to 64 Mhz.  

National Technical Information Service (NTIS)

Techniques for the recording and analysis of phase variations of pulse modulated ground backscatter data are discussed. It is shown that these techniques are capable of yielding additional information about the characteristics of layers of the ionosphere ...

B. Dueno

1968-01-01

245

F-region Magnetospheric ULF Generation by Modulated Ionospheric Heating  

NASA Astrophysics Data System (ADS)

Current modulation of D/E region ionospheric currents at ULF frequencies results in generation of Shear Alfven Waves injected upwards and guided by the magnetic field lines towards the conjugate ionosphere. Under particular ionospheric conditions frequencies in the PC1 range (.2-6Hz) are reflected by the gradient in the Alfven velocity above the F-region resulting in the well-known Ionospheric Alfven Resonator (IAR) structure. Ground detection of ULF waves due to current modulation on the ground is thus limited to the vicinity of the heated spot since at these frequencies the coupling to the earth ionosphere waveguide is evanescent. Propagation of ULF waves at significant lateral distances requires generation of magnetosonic waves since they are the only mode that propagates isotropically and can thus couple efficiently in the Alfvenic duct. In this paper we present a completely new mechanism to generate magnetosonic waves by modulated ionospheric heating that does not require the presence of electrojet currents. The process relies in anomalous electron heating near the F-region peak by preferably using O-mode upper hybrid heating modulated at ULF Pc-1 frequencies. The modulation in the electron pressure drives a Bxgrad(p) oscillatory current. The resultant field aligned magnetic moment generates predominantly magnetosonic waves that are injected laterally into the Alfvenic duct and can also detected above the F-peak by over-flying satellites over distances larger than spanned by the field lines connecting to heated area. In addition to the concept and analytic results the paper will present simulations results using the ZEUS-MP MHD. Non-uniform grids are used to adapt to non-uniform ionospheric plasma density and thin layer of heating source. The effective heating region is placed at about 200-300 km in altitude (F-layer ionosphere). The modulated heating source is modeled as a source with perturbed density, temperature and magnetic field and it transmits modulated-HF electromagnetic waves into a stable ionosphere. Ratios of perturbed magnetic field and density to their background values are extracted from simulations. Different radiation patterns from different polarization component of magnetic field perturbation are investigated. Effects of different profiles of non-uniform ionospheric plasma density on ULF wave propagation are also studied through simulation. Preliminary experimental evidence of the process will also be presented. This work was sponsored by ONR MURI Grant 5-28828

Papadopoulos, K.; Tesfaye, B.; Shroff, H.; Shao, X.; Milikh, G.; Chang, C.; Wallace, T.; Inan, U.; Piddyachiy, D.

2007-12-01

246

Meteoric Ions in Planetary Ionospheres  

NASA Technical Reports Server (NTRS)

Solar system debris, in the form of meteoroids, impacts every planet. The flux, relative composition and speed of the debris at each planet depends on the planet's size and location in the solar system. Ablation in the atmosphere evaporates the meteoric material and leaves behind metal atoms. During the ablation process metallic ions are formed by impact ionization. For small inner solar system planets, including Earth, this source of ionization is typically small compared to either photoionization or charge exchange with ambient molecular ions. For Earth, the atmosphere above the main deposition region absorbs the spectral lines capable of ionizing the major metallic atoms (Fe and Mg) so that charge exchange with ambient ions is the dominant source. Within the carbon dioxide atmosphere of Mars (and possibly Venus), photoionization is important in determining the ion density. For a heavy planet like Jupiter, far from the sun, impact ionization of ablated neutral atoms by impacts with molecules becomes a prominent source of ionization due to the gravitational acceleration to high incident speeds. We will describe the processes and location and extent of metal ion layers for Mars, Earth and Jupiter, concentrating on flagging the uncertainties in the models at the present time. This is an important problem, because low altitude ionosphere layers for the planets, particularly at night, probably consist predominantly of metallic ions. Comparisons with Earth will be used to illustrate the differing processes in the three planetary atmospheres.

Pesnell, W. D.; Grebowsky, Joseph M.; Vondrak, Richard R. (Technical Monitor)

2001-01-01

247

Ionospheric imaging in Africa  

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

248

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

249

Simulation of ion outflows in the ionosphere  

NASA Astrophysics Data System (ADS)

Ion outflows are observed in the polar region in response to particle precipitation and magnetospheric wave activity. In order to study the ion outflow, we modified the previously developed two-dimensional model of realistic active ionosphere [Sydorenko, 2012] by including ion motion along the geomagnetic field. The new model considers a layer of near-Earth plasma of thickness of a few thousand kilometers. The plasma consists of multiple ion species. Collisions between particles are accounted for everywhere, even at high altitudes where they are negligible. Therefore, unlike in the previous model, the electron and ion dynamics is continuous. Chemical reactions between different ion and neutral species are included. Simulations demonstrate formation of field-aligned ion flows when an intense Alfven wave or electron precipitation perturbs the ionosphere. The significance of the results is discussed in the context of Canadian Space Agency e-POP spacecraft mission. Sydorenko D. and R. Rankin, "Simulation of ionospheric disturbances created by Alfven waves", submitted to Journal of Geophysical Research, 2012.

Sydorenko, D.; Rankin, R.

2012-12-01

250

Ionospheric modification using relativistic electron beams  

NASA Technical Reports Server (NTRS)

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.

1990-01-01

251

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

252

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

253

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

254

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

255

Mass spectrometry in ionospheric research.  

PubMed

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

Ferguson, Eldon E

2007-01-01

256

Hydromagnetic Waves in the Ionosphere  

Microsoft Academic Search

A numerical integration of the hydromagnetic wave equations in the ionosphere has been carried out. Tables and graphs are given for the relations between the field amplitudes above and below the ionosphere and for the power dissipated as a function of altitude. The case of a vertically incident plane monochromatic wave near 45 ø geomagnetic latitude is treated. The results

W. E. Francis; Robert Karplus

1960-01-01

257

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

258

Ionospheric Transmission Losses Associated with Mars-orbiting Radars  

NASA Technical Reports Server (NTRS)

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

Farrell, W. M.

2005-01-01

259

Feedback instability of the ionospheric resonant cavity  

Microsoft Academic Search

The exponential increase of the Alfven speed in the topside ionosphere leads to the formation of a resonant cavity (Lysak, 1988) which has been termed the ionospheric Alfven resonator by Trakhtengertz and Feldstein (1984). These authors primarily considered the situation where the ionospheric Pedersen conductivity is low, while Lysak (1988) considered the opposite limit of the infinite ionospheric conductivity. These

Robert L. Lysak

1991-01-01

260

Ionosphere around equinoxes during low solar activity  

Microsoft Academic Search

The seasonal behaviors of the ionosphere have been investigated for several decades, but the differences of the ionosphere between the March and September equinoxes are still an open question. In this analysis we utilize the data of ionospheric electron density (Ne) profiles from Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission radio occultation measurements, total electron density (TEC)

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

2010-01-01

261

Ionospheric modification by high power radio waves  

Microsoft Academic Search

Investigations using powerful, high frequency (HF) radio waves to temporarily modify the ionosphere are reviewed. Studies of the natural upper atmosphere have been conducted using these controlled, active experiments by observing the ionospheric response to HF induced perturbations. Other basic physics investigations have examined the ionosphere and its properties and behavior as a plasma. Topics examined include ionospheric heating, parametric

L. M. Duncan; W. E. Gordon

1982-01-01

262

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

263

The modulation of sporadic-E layers by Kelvin-Helmholtz billows in the neutral atmosphere  

NASA Astrophysics Data System (ADS)

Modulation of electron densities in ion layers between 90 and 150km altitude has been observed using a number of ionospheric diagnostic measurements including scatter of VHF radar waves, artificially pumped optical emissions, scintillations of satellite beacon transmissions. Kelvin-Helmholtz (K-H) turbulence driven by a sheared wind profile is a strong candidate for the source of these modulations. A two-dimensional numerical model is used to calculate the nonlinear evolution of ion layers in ionosphere near 100 and 120km altitude in response to neutral turbulence driven by a wind shear. The amplitude of a K-H billow is allowed to grow as a linear perturbation on the neutral atmosphere to a level that is 10% of the wind shear. The time dependent model of the ionosphere responds to neutral wind perturbation initially by imposing a quasi-sinusoidal modulation near the altitude of the ion layer. This is followed by compression of the initially stratified layer into structures with the wavelength of the K-H instability. These structures are uniform strips in the meridian perpendicular to the direction of the zonal wind. Near 120km, where the ion gyro frequency (?i) is about equal to the ion collision frequency (?i), the equilibrium solutions are clumps at the altitude of the shear. Near 100km, two stable, rippled layers are produced with a separation of about 1km. The amplitudes of the density modulations in the ion layers vary by as much as 500% throughout the simulation. The simulations illustrate the complex evolution of the ion layer structures from small-amplitude, K-H wind turbulence.

Bernhardt, Paul A.

2002-08-01

264

The Jovian ionospheric E region  

SciTech Connect

The authors have constructed a model of the Jovian ionosphere that includes direct photoionization of hydrocarbon molecules. A high resolution solar spectrum was synthesized from Hinteregger's solar maximum spectrum (F79050N) and high resolution cross sections for photoabsorption by H{sub 2} bands in the range 842 to 1,116 {angstrom} were constructed. Two strong solar lines and about 30% of the continuum flux between 912 and 1,116 {angstrom} penetrate below the methane homopause despite strong absorption by CH{sub 4} and H{sub 2}. They find that hydrocarbons (mainly C{sub 2}H{sub 2}) are ionized at a maximum rate of 55 cm{sup {minus}3}sec{sup {minus}1} at 320 km above the ammonia cloud tops. The hydrocarbon ions produced are quickly converted to more complex hydrocarbon ions through reactions with CH{sub 4}, C{sub 2}H{sub 2}, C{sub 2}H{sub 6}, and C{sub 2}H{sub 4}. They find that a hydrocarbon ion layer is formed near 320 km that is about 50 km wide with a peak density in excess of 1 {times} 10{sup 4} cm{sup {minus}3}.

Kim, Y.H.; Fox, J.L. (State Univ. of New York, Stony Brook (USA))

1991-02-01

265

Ionospheric Climatology Over Millstone Hill  

NASA Astrophysics Data System (ADS)

26 years of incoherent scatter observations over Millstone Hill since 1976 have been analyzed and modeled in order to study the climatological behavior in the local ionosphere-thermosphere system. A bin-fit technique is applied to process and represent the huge volume of data: measurements are binned according to local time, season, and altitude; sorted data in each bin are fitted into an empirical model where solar activity index F107 and geomagnetical activity index Ap are included as keyed inputs [Holt et al., 2002]. This paper focuses on seasonal, semiannual and annual variations and the long-term trend in electron density, electron temperature and ion temperature measurements over a 200-500 km height range of the F2 layer. A clear semiannual variation of the electron density is seen above the F2 peak during the day, as well as at the F2 peak and below during the later afternoon to evening period (16-20LT) . The semiannual variation of the electron temperature persists with minimum at equinox during the night, while the annual variation prevails by day with maximum in summer.

Zhang, S.; Holt, J. M.

2002-05-01

266

Studies of low-latitude ionospheric forcing originating in the lower atmosphere using space-based imaging  

Microsoft Academic Search

A significant portion of the energy and momentum propagating upward from the lower and middle atmosphere to ionospheric heights is carried by atmospheric tides. Since most upwardpropagating tidal waves dissipate in the lower ionosphere, their direct influence on neutral and ion conditions in the main F-layer might be expected to be small. Recently however, a strong correlation between modeled tidal

Thomas Immel

2008-01-01

267

Excitation of the ionospheric resonance cavity by thunderstorms  

NASA Astrophysics Data System (ADS)

Excitation of the middle latitude ionospheric Alfvén resonator (IAR) due to global thunderstorm activity is considered. The lightning discharges in thunderstorm centers are modeled in terms of a stochastic Poisson process. The lightning onset time and the current moment amplitude are supposed to be random values, while the shape of current moment is assumed to be a given function. Electromagnetic TM mode radiated from the lightning discharges penetrates into the ionosphere via mode coupling to the shear Alfvén and magnetosonic wave modes in the E layer of the ionosphere. The ionospheric resonance cavity can trap and accumulate the shear Alfvén wave energy with periods from one second to a few tenths of seconds, thereby exciting the IAR resonances. Using a simplified model of the topside ionosphere, we have analyzed a possibility for the IAR excitation far from the tropical thunderstorm region. The low-frequency power spectra of the IAR on the ground surface is studied both analytically and numerically. It is shown that the IAR power spectra exhibit spectral resonance structure (SRS) only during the nighttime conditions. Furthermore, it is found that the calculated spectra are one or two orders of magnitude lower than that observed at Karimshino station in Kamchatka region. This fact suggests that the SRS is not simply due to stochastic lightning discharge process but that some generation mechanisms for the IAR excitation at middle latitudes might also be operative.

Surkov, V. V.; Molchanov, O. A.; Hayakawa, M.; Fedorov, E. N.

2005-04-01

268

Ionospheric mid-latitude response to solar wind discontinuities  

NASA Astrophysics Data System (ADS)

We have compiled a database of 356 discontinuities detected by both the Advanced Composition Explorer ACE) and Cluster satellites in the solar wind between 2001-2012 and analyzed their ionospheric response. Each discontinuity of the data base is defined by a change of at least 5 nT in less than 5 min in one or more components of the interplanetary magnetic field (IMF). The discontinuities are observed in January-April every year, when Cluster enters the solar wind. The ionospheric effects of solar wind discontinuities are investigated by checking the variations of critical frequencies foF2, the heights of the F layer and the ionospheric plasma dynamics recorded using ground measurement with a time resolution of 15 minutes from mid-latitude digisondes located in Czech Republic. The time delay between solar wind input and the ionospheric response is analyzed using the characteristics and the shape of the ionograms. The geoeffectiveness of the solar wind discontinuities is expressed as correlation between key plasma parameters (e,g, the solar wind velocity, magnetic jump across the discontinuity) and the ionospheric variations. Solar cycle effects are also discussed.

Munteanu, Costel; Mosna, Zbysek; Kouba, Daniel; Echim, Marius

2013-04-01

269

Are ionospheric storms the same during different solar cycles?  

NASA Astrophysics Data System (ADS)

ionosphere's response to geomagnetic storms has been studied since the earliest days of terrestrial space physics. In terms of temporal coverage, the largest data sets used extensively have been from the global network of ionosondes. Many previous investigations examined the behavior of the F layer's maximum electron density (Nmax)—often contrasting the difference seen between storms that occur during solar maximum years versus those during solar minimum years. We report on the first attempt to study systematically the patterns of ionospheric disturbance seen during different solar cycles. We select two midlatitude sites with long-term consistency in data: Wallops Island (Virginia) and Hobart (Tasmania)—stations with comparable geographic and geomagnetic coordinates—but in different hemispheres and widely separated longitude sectors. We compare average ionospheric storm patterns using over 200 moderate to severe geomagnetic storms within each of solar cycle #20 (October 1964 to June 1976) and cycle #23 (May 1996 to December 2008). We compute average patterns of ?Nmax(%), measured with respect to monthly mean conditions, following storm and local time. The overall results show remarkable consistency in characteristic patterns of an ionospheric storm: a short positive phase that occurs during the daytime hours on the first day of a storm, with a prolonged negative phase on subsequent days. Statistical differences occur in the overall magnitudes and longevities of these patterns, consistently showing that cycle #23 had less severe ionospheric storms. An analysis of geomagnetic indices shows that degrees of disturbance were, in fact, lower during solar cycle #23 than cycle #20.

Mendillo, Michael; Narvaez, Clara; Marusiak, Angela G.

2013-10-01

270

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

271

Nighttime Ionosphere Tomographic Reconstruction Observatory  

NASA Astrophysics Data System (ADS)

Ionospheric irregularities, also known as ionospheric bubbles, are transient features of the low and middle latitude ionosphere with important implications for operational systems. Understanding irregularity formation, development, and evolution is vital for efforts within NASA and DoD to forecast scintillation. Irregularity structures have been studied primarily using ground-based systems, though some spaced-based remote and in-situ sensing has been performed. An ionospheric observatory aboard the International Space Station (ISS) would provide new capability to study low- and mid-latitude ionospheric structures on a global scale. By combining for the first time high-sensitivity in-track photometry with vertical ionospheric airglow spectrographic imagery, we demonstrate that high-fidelity optical tomographic reconstruction of bubbles can be performed from the ISS. Ground-based imagery can supplement the tomography by providing all-sky images of ionospheric structures (e.g. bubbles and TIDs) and of signatures of lower atmospheric dynamics, such as gravity waves, that may play a role in irregularity formation. The optical instrumentation can be augmented with additional sensors to provide measurements of scintillation and in situ plasma density, composition, and drifts.

Budzien, S. A.; Stephan, A. W.; Makela, J. J.; Chua, D. H.; Dymond, K.; Coker, C.; Chakrabarti, S.

2011-12-01

272

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

273

Towards forecasting and mapping ionospheric space weather under cost actions  

NASA Astrophysics Data System (ADS)

Past COST projects 238 (PRME) and 251 (IITS) encompassed a variety of efforts to forecast and map the ionospheric plasma response to disturbed geophysical conditions over the European region. In a number of case studies they provided useful guidelines for what could be achieved by different theoretical, empirical and artificial neural network techniques. New COST 271 action on `Effects of the upper atmosphere on terrestrial and Earth-space communications' which began in the early months of the year 2000 is focusing upon efforts to map the ionospheric space weather conditions over Europe in near-real-time and to forecast these conditions a few hours ahead. The purpose of the paper is to present some of the findings from the previous COST 251 study and the plans for the new one (COST 271).

Cander, Lj. R.

274

The Ionosphere and Ocean Altimetry  

NASA Technical Reports Server (NTRS)

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

Lindqwister, Ulf J.

1999-01-01

275

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

National Technical Information Service (NTIS)

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

G. Wyman

2009-01-01

276

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

277

Thermosphere-ionosphere coupling - An experiment in interactive modeling  

NASA Technical Reports Server (NTRS)

Using the NCAR thermosphere general circulation model, a series of controlled experiments is performed to investigate the interactive coupling between ionospheric plasma densities and thermospheric neutral winds. The interaction is accomplished by parameterizing the F layer peak height, h(m)F2, in an empirical ionospheric model in terms of the meridional wind, v(south), and by forcing the h(m)F2 and the v(south) parameters to remain mutually coupled in a dynamical calculation. It was found that mutual coupling between forcing and meridional wind is weak during the daytime when the F layer exhibits a broad vertical structure. At night, when the F2 layer is more localized, the neutral dynamical structure is dependent on whether forcing is significantly above or below the altitude (about 275-300 km) at which ion drag effectively competes with viscosity in the neutral momentum balance.

Forbes, Jeffrey M.; Roble, Raymond G.

1990-01-01

278

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

279

Noinlinear, Coherent, Collective, Resonant Plasma Propagation Modes in the Ionosphere  

NASA Astrophysics Data System (ADS)

We theoretically describe the complex media of the ionospheric resonance system in which we consider longitudinal as well as transverse components of electric and magnetic fields resulting from natural and man-made sources of excitation. The properties of the ionosphere, as a cool, ionized medium, can sustain plasmon and ion acoustic excitation modes, which appear to explain certain of its unique observed properties. These properties involve collective, coherent resonant states that are sustained over long propagation distances and also over relatively long temporal periods with low dispersive losses. Long range and relatively long-lived shock excitation modes are examined which produced by natural and/or man-made phenomena, such as solar flare and other activity.(1) Characteristic frequencies of resonant excitation of the ionospheric layers have been characterized, and we also calculate the speed of some of the unique velocities of signal propagations in these specific ionospheric layers. The characteristics of the micro pulsations in the magnetosphere are also characterized. (1) E.A. Rauscher and W.L Van Bise, Bull. Am. Phys. Soc. EB01, 1300(2002)

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

2002-04-01

280

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

281

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

282

Artificial Paranoia.  

National Technical Information Service (NTIS)

A case of artificial paranoia was synthesized in the form of a computer model. Using the test operations of a teletyped psychiatric interview, clinicians judge the input-output behavior of the model to be paranoid. Formal validation of the model will requ...

K. M. Colby S. Weber F. D. Hilf

1970-01-01

283

Artificial Intelligence.  

ERIC Educational Resources Information Center

Making a machine seem intelligent is not easy. As a consequence, demand has been rising for computer professionals skilled in artificial intelligence and is likely to continue to go up. These workers develop expert systems and solve the mysteries of machine vision, natural language processing, and neural networks. (Editor)

Wash, Darrel Patrick

1989-01-01

284

Study of Large Scale Electromagnetic Field with ``Earth-Ionosphere'' Mode  

NASA Astrophysics Data System (ADS)

With the development of ELF, scientists proposed that ELF technologies be applied to geophysics and earthquake prediction. ELF applied in geophysics, is one kind of electromagnetic methods. Because of the long-range of ELF, We should consider the coupling between ionosphere, air and earth media (called “earth-ionosphere” mode), especially the couple between earth media, and this was not taken in account when ELF only refer to communication. The effect of ionosphere has to be took into account for the “earth-ionosphere” mode for its long-range (several thousand kilometers), and the displacement current in the air should be consider also for its long-range. In a word, ELF applied in geophysics is the study on “earth-ionosphere” mode electromagnetic. We should construct “earth-ionosphere” mode model which include the effect of ionosphere and displacement current in the air, and make new mathematical derivation. However, there are only a few number of publications related to the electromagnetic field of the “earth-ionosphere” mode which including ionosphere, air and earth. In our study, we established the model for “earth-ionosphere” mode. Applied R function method for mathematical derivation, and we deduced the formulas of electric and magnetic field component everywhere. Apply high sampling density Hankel digital filter method for numerical simulation. Adopt integral equation method for 3D numerical simulation. After the mathematical derivation, this article has done some numerical simulation. We obtained the forward results in fixed frequencies and fixed distances in “earth-ionosphere” mode with three layers model. We analyzed the effect of ionosphere and displacement current in the air. After that, we gave out the radio pattern within 2500km with different frequency. We also gave out the boundary of near field, far field and wave-guide field. The effects of the changes of effective resistivity and effective reflection height of the ionosphere on the forward results were considered, and the exponential ionosphere model was established. We also model the EM fields for multi-layer models, especially typical type of continental shield and platform models, and at the end, we carried out 3D numerical simulation with integral equation method. Due to the influence of the ionosphere and displacement current in the air, the “earth-ionosphere” mode electromagnetic field was very different from CSAMT. CSAMT field only has near field zone and far field zone, but “earth-ionosphere” mode EM field has an extra wave-guide zone, where the field behavior is very different from the far field zone. Because the reflection effect of the ionosphere, the attenuation of electromagnetic wave in wave-guide zone is small, that causes we can applied “earth-ionosphere” mode electromagnetic for geophysics prospecting. The effect of the displacement current in the air, result in the electromagnetic wave in the axial direction is greater than equatorial direction, and along with the frequency increase, the effect becomes more evident. The study on the electromagnetic field characteristics of “earth-ionosphere” mode, can furnish the information for resolution, instrument development, data processing and measuring setting.

Quan, L. D.; di, Q.; Yue, W. M.; Sep

2010-12-01

285

The worldwide ionospheric data base  

NASA Technical Reports Server (NTRS)

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

Bilitza, Dieter

1989-01-01

286

Diagnostics of the ionospheric turbulence by wide band radio signals  

NASA Astrophysics Data System (ADS)

Results of the investigations of the time-space structure of the HF-pumped ionospheric volume above the SURA heating facility are presented. The method of investigations is based on mea-surements of the amplitude and phase of pulsed (pulse duration < 200µs and interpulse period 20-200 ms), wide band (˜ 300 kHz) and powerful (Effective Radiated Power ˜ 20-150 MW) radio signals radiated by three SURA transmitter and used for multifrequency sounding of the ionospheric plasma in frequency band up to ˜ 1 MHz. For simultaneous modification of the ionosphere and its diagnostics, technical capabilities of SURA transmitter-receiver system, specially elaborated time-frequency modes of transmitter operation, space diversity three point reception, wide band signal recording, digital filtering, spectral and correlation analysis of the short radio pulses reflected from ionosphere were used. As a result of numerically solved in-verse problem of vertical sounding of the HF-perturbed ionosphere, dynamic behavior of the electron plasma density variations was obtained in the regions close to plasma resonance and upper hybrid resonance of the pump wave. In our experiments the pumping usually leaded to plasma expulsion from the resonance regions. A magnitude of artificial plasma density pertur-bations achieved 0.8% from the background density for pump power about P 60 MW ERP. The methods of a similarity and full correlation analysis were used for pulse signal amplitude processing, which were obtained by diversity three point reception with the receiving aerial separation of 84 m. As a result, novel data on fine structure of the space field of the vertical and horizontal velocities of plasma in the perturbed ionosphere volume with high time (up to 20 ms) and frequency (˜ 1 kHz) resolution are obtained. This frequency resolution can be translated into altitude resolution (˜ 50-100 m) in the ionosphere. The work was supported by RFBR grants 10-02-00642, 09-02-01150 and Federal Special-purpose Program "Scientific and pedagogical personnel of innovative Russia".

Sergeev, Evgeny; Shindin, Alexey; Grach, Savely

287

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

288

Ionospheric data assimilation: recovery of strong mid-latitudinal density gradients  

Microsoft Academic Search

The September 1999 Caribbean Ionospheric Campaign (CIC99), spanning the period 15–17 September 1999, was a period of repeated moderate geomagnetic storms. Both incoherent scatter radar (ISR) and digisonde F-layer measurements were made in the vicinity of Arecibo, Puerto Rico by the Arecibo ISR and Ramey Digisonde, which is one of the Digital Ionospheric Sounding System instruments. These data sets showed

Jan J. Sojka; Donald C. Thompson; Robert W. Schunk; J. Vincent Eccles; Jonathan J. Makela; Michael C. Kelley; Sixto A. González; Nestor Aponte; Terence W. Bullett

2003-01-01

289

Interactions with planetary ionospheres and atmospheres - A review  

NASA Technical Reports Server (NTRS)

The interaction of the solar wind with unmagnetized objects possessing an ionosphere is reviewed, with emphasis on recent developments. Venus, Mars, Titan, comets (including the artificial comet created by AMPTE) and the unusual interplanetary events interpreted as cometesimals are considered. The role of the interplanetary magnetic field and of mass loading in producing the observed interactions are highlighted. Interpretation to date is based largely on an MHD (fluid) treatment, but recent results from the first AMPTE barium release and from recordings made at Venus suggest that finite Larmor radius effects introduce asymmetries in the solar wind interaction.

Saunders, Mark A.; Russell, Christopher T.; Luhmann, Janet G.

1986-01-01

290

Applications of a time-dependent polar ionosphere model for radio modification experiments  

NASA Astrophysics Data System (ADS)

A time-dependent self-consistent ionosphere model (SLIM) has been developed to study the response of the polar ionosphere to radio modification experiments, similar to those conducted at the High-Frequency Active Auroral Research Program (HAARP) facility in Gakona, Alaska. SCIM solves the ion continuity and momentum equations, coupled with average electron and ion gas energy equations; it is validated by reproducing the diurnal variation of the daytime ionosphere critical frequency, as measured with an ionosonde. Powerful high-frequency (HF) electromagnetic waves can drive naturally occurring electrostatic plasma waves, enhancing the ionospheric reflectivity to ultra-high frequency (UHF) radar near the HF-interaction region as well as heating the electron gas. Measurements made during active experiments are compared with model calculations to clarify fundamental altitude-dependent physical processes governing the vertical composition and temperature of the polar ionosphere. The modular UHF ionosphere radar (MUIR), co-located with HAARP, measured HF-enhanced ion-line (HFIL) reflection height and observed that it ascended above its original altitude after the ionosphere had been HF-heated for several minutes. The HFIL ascent is found to follow from HF-induced depletion of plasma surrounding the F-region peak density layer, due to temperature-enhanced transport of atomic oxygen ions along the geomagnetic field line. The lower F-region and topside ionosphere also respond to HF heating. Model results show that electron temperature increases will lead to suppression of molecular ion recombination rates in the lower F region and enhancements of ambipolar diffusion in the topside ionosphere, resulting in a net enhancement of slant total electron content (TEC); these results have been confirmed by experiment. Additional evidence for the model-predicted topside ionosphere density enhancements via ambipolar diffusion is provided by in-situ measurements of ion density and vertical velocity over HAARP made by a Defense Meteorological Satellite Program (DMSP) satellite.

Fallen, Christopher Thomas

291

High latitude artificial periodic irregularity observations with the upgraded EISCAT heating facility  

NASA Astrophysics Data System (ADS)

We present a recently developed ionospheric modification experiment that produces artificial periodic irregularities in the ionosphere and uses them to make observations of the spatiotemporal behaviour of the irregularities. In addition, the method can be used to measure Faraday rotation and vertical velocities. We also introduce a novel experiment that allows monitoring the formation of the irregularities during heating, in addition to observing their decay after heating. The first measurements indicate, contrary to existing theory, that the amplitude of the radar echoes from the periodic irregularities grows faster than they decay. We focus on the API effects in the D- and E-region of the ionosphere.

Vierinen, Juha; Kero, Antti; Rietveld, Michael T.

2013-12-01

292

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

293

Artificial Wetlands  

NSDL National Science Digital Library

Golf courses are known as places of recreation. But some of them could someday double as water treatment facilities. Water hazards on golf courses can be used to control environmental hazards. That's according to Purdue University soil microbiologist Ron Turco. He says the artificial wetlands can also control flooding in surrounding communities, by collecting excess water. This Science Update looks at the research, which leads to these findings and offers links to other resources for further inquiry.

American Association for the Advancement of Science (;)

2005-04-11

294

Study of large-scale irregularities generated in the ionospheric F -region by high-power HF waves  

Microsoft Academic Search

Experimental studies of the features of artificial ionospheric turbulence was performed at the “Sura” heating facility in\\u000a August 1998 using numerous diagnostic tools, such as scintillation, chirp-sounding, backscattering, and stimulated electromagnetic\\u000a emission (SEE) measurements, as well as sounding a HF-disturbed volume (DV) by probing waves. It has been found that generation\\u000a of strong artificial large-scale irregularities (ALSIs), which manifest themselves

V. L. Frolov; V. V. Chugurin; G. P. Komrakov; N. A. Mityakov; E. N. Myasnikov; V. O. Rapoport; E. N. Sergeev; V. P. Uryadov; F. I. Vybornov; V. A. Ivanov; V. V. Shumaev; A. M. Nasyrov; I. A. Nasyrov; K. M. Groves

2000-01-01

295

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

296

Ionospheric Calibration for Single Frequency Altimeter Measurements.  

National Technical Information Service (NTIS)

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

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

1994-01-01

297

Digital Ionospheric Sounding in the Arctic.  

National Technical Information Service (NTIS)

New ionogram observation techniques were applied at the Goose Bay Ionospheric Observatory (GBIO) in Newfoundland, Canada, and aboard AFGL's Airborne Ionospheric Observatory (AIO), using the Digisonde 128PS system. A receiving array of four crossed-loop an...

B. W. Reinisch K. Bibl

1981-01-01

298

Role of the Spore Coat Layers in Bacillus subtilis Spore Resistance to Hydrogen Peroxide, Artificial UV-C, UV-B, and Solar UV Radiation  

Microsoft Academic Search

Spores of Bacillus subtilis possess a thick protein coat that consists of an electron-dense outer coat layer and a lamellalike inner coat layer. The spore coat has been shown to confer resistance to lysozyme and other sporicidal substances. In this study, spore coat-defective mutants of B. subtilis (containing the gerE36 and\\/or cotE::cat mutation) were used to study the relative contributions

PAUL J. RIESENMAN; WAYNE L. NICHOLSON

2000-01-01

299

Beating HF waves to generate VLF waves in the ionosphere  

NASA Astrophysics Data System (ADS)

Beat-wave generation of very low frequency (VLF) waves by two HF heaters in the ionosphere is formulated theoretically and demonstrated experimentally. The heater-induced differential thermal pressure force and ponderomotive force, which dominate separately in the D and F regions of the ionosphere, drive an electron current for the VLF emission. A comparison, applying appropriate ionospheric parameters shows that the ponderomotive force dominates in beat-wave generation of VLF waves. Three experiments, one in the nighttime in the absence of D and E layers and two in the daytime in the presence of D and E layers, were performed. X mode HF heaters of slightly different frequencies were transmitted at CW full power. VLF waves at 10 frequencies ranging from 3.5 to 21.5 kHz were generated. The frequency dependencies of the daytime and nighttime radiation intensities are quite similar, but the nighttime radiation is much stronger than the daytime one at the same radiation frequency. The intensity ratio is as large as 9 dB at 11.5 kHz. An experiment directly comparing VLF waves generated by the beat-wave approach and by the amplitude modulation (AM) approach was also conducted. The results rule out the likely contribution of the AM mechanism acting on the electrojet and indicate that beat-wave in the VLF range prefers to be generated in the F region of the ionosphere through the ponderomotive nonlinearity, consistent with the theory. In the nighttime experiment, the ionosphere was underdense to the HF heaters, suggesting a likely setting for effective beat-wave generation of VLF waves by the HF heaters.

Kuo, Spencer; Snyder, Arnold; Kossey, Paul; Chang, Chia-Lie; Labenski, John

2012-03-01

300

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

301

The International Reference Ionosphere - Climatological Standard for the Ionosphere  

NASA Technical Reports Server (NTRS)

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 since its inception in 1969 with the ever-increasing volume of ionospheric data and with better mathematical descriptions of the observed global and temporal variation patterns. The IRI model has been validated with a large amount of data including data from the most recent ionospheric satellites (KOMPSAT, ROCSAT and TIMED) and data from global network of ionosondes. Several IRI teams are working on specific aspects of the IRI modeling effort including an improved representation of the topside ionosphere with a seamless transition to the plasmasphere, a new effort to represent the global variation of F2 peak parameters using the Neural Network (NN) technique, and the inclusion of several additional parameters in IRI, e.g., spread-F probability and ionospheric variability. Annual IRI workshops are the forum for discussions of these efforts and for all science activities related to IRI as well as applications of the IRI model in engineering and education. In this paper I will present a status report about the IRI effort with special emphasis on the presentations and results from the most recent IRI Workshops (Paris, 2004; Tortosa, 2005) and on the most important ongoing IRI activities. I will discuss the latest version of the IRI model, IRI-2006, highlighting the most recent changes and additions. Finally, the talk will review some of the applications of the IRI model with special emphasis on the use for radiowave propagation studies and communication purposes.

Bilitza, Dieter

2006-01-01

302

Threshold energies in the artificial retina  

Microsoft Academic Search

Laser threshold energies for artificial retinal damage from ultrashort (i.e. less than or equal to 1 ns) laser pulses are investigated as a function of both pulse width and spot size. A piece of film acts as the absorbing layer and is positioned at the focus of the Cain artificial eye (17 mm in water). We performed experiments at the

Dale J. Payne; Richard A. Hopkins; Brent Eilert; Gary D. Noojin; Benjamin A. Rockwell

1998-01-01

303

The Mariner 10 radio occultation measurements of the ionosphere of Venus  

Microsoft Academic Search

Data from the Mariner 10 radio occultation experiment have been utilized to determine the vertical electron density distribution in the ionosphere of Venus. The ingress measurements, which were made at latitude 1.3 deg N on the nightside of the planet, show two distinct layers. The main layer was located at 142 km altitude and had a peak density of 9000

G. Fjeldbo; B. Seidel; D. Sweetnam; T. Howard

1975-01-01

304

A new mapping technique for conversion of slant TEC to vertical TEC based on Computerized Ionospheric Tomography  

NASA Astrophysics Data System (ADS)

The most frequently used mapping function for converting slant TEC to vertical TEC uses a single layer model with the assumption that all free electrons are concentrated in an infinitesimally thick spherical shell at the mean ionospheric height and containing the ionospheric pierce point. Spatial structures present in the ionosphere are not taken into account in such single layer models. A three dimensional mapping algorithm developed by Mannucci et al. (1999) uses three independent constant density slabs stacked vertically to model the electron density with the result of reduction in a level error of the TEC maps. We describe a new approach based on Computerized Ionospheric Tomography (CIT) to convert STEC to VTEC. The new method is independent of any assumption regarding the electron density distribution of the ionosphere. In this method, the ionosphere region of interest is divided in to pixels and TEC is represented as the sum of the integration of empirical functions within the pixels, which are intersected by the path along which TEC is measured. Using a suitable inversion algorithm, the empirical function within each pixel is retrieved from TEC data recorded simultaneously at a meridional chain of GPS receivers. The VTEC values are then easily obtained as the sum of the integration of the empirical functions within each pixel along a vertical path. The CIT method is applied for converting STEC to VTEC using GPS TEC data collected at 12 locations across India since 2003. The stations are aligned along three meridional chains. The vertical TEC values obtained from the CIT method are then compared to VTEC obtained from a single layer model. Results have shown that the CIT can be suitably adapted as a mapping technique, which takes into account the presence of spatial structures in the ionosphere. Keywords: Ionosphere (Indian equatorial and low latitude ionosphere, Vertical Total Electron Content, mapping functions, computerized ionospheric tomography)

Bhuyan, Pradip; Bhuyan, Pradip; Bhuyan, Kalyan

305

Modeling Saturn's Ionosphere: Comparisons with Cassini  

Microsoft Academic Search

The Saturn-Thermosphere-Ionosphere-Model (STIM) -- a global circulation model -- is used to study parameters in Saturn's ionosphere that affect the location and magnitude of the electron density peak. Past observations from the Pioneer and Voyager spacecraft indicated that the ionosphere had a peak between ˜1900 - 2900 km, with a maximum density ranging from 6000 - 20,000 electrons\\/cc. Preliminary results

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

2005-01-01

306

Present and Future IGS Ionospheric Products  

Microsoft Academic Search

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

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

2010-01-01

307

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

308

A comprehensive magnetohydrodynamic model of the Venus ionosphere  

SciTech Connect

The MHD Venus ionospheric model developed by Shinagawa and Cravens (1988) has been improved by including the energy equations for ions and electrons in a self-consistent manner. This new model reproduces observed electron density and magnetic field profiles very well, and the basic MHD processes of the Venus ionosphere, as described by Shinagawa and Cravens (1988), remain virtually unchanged. The results indicate that including energetics does not significantly alter the density and magnetic field profiles. Under unmagnetized conditions, it is necessary to impose heat fluxes for both ions and electrons in order to reproduce the observed plasma temperature profiles, which are consistent with the studies by Cravens et al. (1979, 1980) and Kim et al. (1990). In the magnetized ionosphere, it is likely that a heat source for the ions is present at higher altitudes. On the other hand, the observed very high electron temperatures can be reproduced with a reduced conductivity or with a heat source at high altitudes. It is also found that heating processes do not play a significant role in the dynamics at low altitudes. Thus a nearly supersonic downward velocity layer in the lower ionosphere of Venus, proposed by Cloutuer at al. (1987), is unlikely, suggesting that their flow/field model is not applicable to the solar wind-Venus interaction and other unmagnetized bodies in magnetized plasma flows.

Shinagawa, H. (NASA Marshall Space Flight Center, Huntsville, AL (USA)); Kim, J.; Nagy, A.F. (Univ. of Michigan, Ann Arbor (USA)); Cravens, T.E. (Univ. of Kansas, Lawrence (USA))

1991-07-01

309

Acoustic-gravity waves in the Earth's ionosphere  

NASA Astrophysics Data System (ADS)

Taking into account the existence of charged particles in the Earth's ionosphere the propagation of acoustic-gravity waves is investigated. The influence of the Coriolis force is also taken into account. The weakly ionized ionospheric D, E, and F-layers are considered. The existence of a cut-off frequency at 2[Omega]0 ([Omega]0 is the value of the angular velocity of the Earth's rotation) is noted. It is shown that the linear waves are damped because of the Pedersen conductivity. When the acoustic-gravity waves are excited by external events (volcanic eruptions, earthquakes, lightning strikes, etc.) their amplitudes grow until self-organization of these waves into nonlinear vortex solitary structures is admitted. Taking into account the interaction of the induced ionospheric current with the geomagnetic field the governing nonlinear equations are deduced. The formation of dipole vortex solitary structures of low-frequency internal gravity waves is shown for the stable stratified ionosphere. The dynamic energy equation for such nonlinear structures is obtained. It is shown that nonlinear solitary vortical structures damp due to Joule losses.

Kaladze, T. D.; Pokhotelov, O. A.; Shah, H. A.; Khan, M. I.; Stenflo, L.

2008-09-01

310

First incoherent scatter radar observations of ionospheric heating on the second electron gyro-harmonic  

NASA Astrophysics Data System (ADS)

We report first results from a unique experiment performed at the HIPAS ionospheric modification facility in conjunction with the Poker Flat incoherent scatter radar in Alaska. High-power radio waves at 2.85 MHz, which corresponds to the second electron gyro-harmonic at ~245 km altitude, were transmitted into the nighttime ionosphere. Clear evidence of F-region ionospheric electron temperature enhancements were found, for the first time at this pump frequency, maximizing when the pump frequency is close to the second gyro-harmonic and double resonance. This is consistent with previous pump-enhanced artificial optical observations. We estimate the plasma heating efficiency to be approximately double that for higher pump frequencies.

Kosch, M. J.; Gustavsson, B.; Heinselman, C.; Pedersen, T.; Rietveld, M. T.; Spaleta, J.; Wong, A.; Wang, W.; Mutiso, C.; Bristow, B.; Hughes, J.

2009-12-01

311

Multilayer Model: A New Regional Ionospheric Model For Near Real-Time Applications  

NASA Astrophysics Data System (ADS)

The ionosphere is part of the upper atmosphere which affects electromagnetic waves by its ionization. The resulting propagation delay is frequency dependent, so it can be determined with dual frequency measurements. In case of single frequency users ionospheric models are used to correct the measurements. At the Institute of Geodesy and Geophysics (Vienna University of Technology) a new ionospheric model, labeled Multilayer Model, is under development. It consists of nine horizontal equidistant electron layers within the height range of the F2 layer, where the maximum of the ionization can be found. The remaining ionospheric layers (e.g. the E-layers) are currently not considered. The electron content of each of the nine layers is obtained from a simple model with very few parameters, like the current maximum VTEC and weighting functions to account for the spherical distance between the coordinates of the electron maximum and the IPP-points of interest. All parameters are calculated with hourly time resolution from a combination of global (IGS-stations) and regional GNSS observation data. The Multilayer Model focuses on regional densification of global ionosphere models (e.g. IGS VTEC SH models) by means of a small and easy predictable set of parameters. The final ionospheric TEC grids provided by IGS (International GNSS Service) have a resolution of 2 hours x 5° Longitude x 2.5° Latitude. Daily files can be downloaded from the IGS web page (http://www.igs.org/). IRI (International Reference Ionosphere) is a joint project of the Committee on Space Research (COSPAR) and the International Union of Radio Science (URSI). An empirical standard model of the ionosphere is provided which is based on a worldwide network of ionosondes, incoherent scatter radars and other data sources. In this presentation the VTEC values calculated with the regional Multilayer Model are compared to the results of the IGS global TEC grids and IRI. This comparison covers days with low ionospheric activity as well as days with high ionospheric disturbances over the region of Austria in order to evaluate the new model. In addition the produced IONEX-files of the Multilayer Model are used to evaluate the positioning accuracy achieved by processing tracking data of a regional single-frequency GNSS network.

Magnet, N.; Weber, R.

2012-12-01

312

Variations in the horizontal correlation radius of the ionosphere during a magnetospheric substorm  

NASA Astrophysics Data System (ADS)

A change in the correlation radius of the ionosphere during the magnetospheric substorm of February 14, 2011, which is considered to be 500 km at midlatitudes, has been estimated. The vertical sounding (VS) data from the St. Petersburg and Sodankyla (Finland) observatories, as well as the data of oblique incidence sounding (OIS) at the Sodankyla-St. Petersburg path with a length of 790 km, have been analyzed. A specific feature of the experiment consisted in that the signals of a VS transmitter from Sodankyla were synchronously received at the receiving point on the OIS path in St. Petersburg. The OIS path reflection point is located at a distance of ˜400 km from the VS reflection point. Ionograms typical of the VS and OIS signal reflection points in the ionosphere, the distance between which was slightly smaller than the correlation radius of the ionosphere (500 km), and the data of the Sodankyla and St. Petersburg ionosondes have been compared. It has been indicated that a horizontal correlation radius of 400 km can only be considered acceptable during three disturbance phases: the initial phase before the reconfiguration of the ionosphere; the explosion phase (the disturbance maximum), when only the sporadic Es layer is the reflecting ionospheric layer; and the recovery phase, when a disturbance already ceases and the ionosphere returns to its initial undisturbed state. During other disturbance phases, the correlation radius (if it exists) is much smaller than 400 km.

Blagoveshchenskii, D. V.; Rogov, D. D.; Ulich, T.

2013-04-01

313

Simulations of plasma structure evolution in the high-latitude ionosphere  

NASA Technical Reports Server (NTRS)

The Naval Research Laboratory has recently developed a two-dimensional inertial, electrostatic code which has been successfully applied to the development and evolution of ionospheric structure driven by plasma instabilities. This code models the ionosphere and magnetosphere as a set of horizontal two-dimensional layers which are coupled by the vertical magnetic field lines at high latitudes. It is shown that the development of instability-generated structure can be strongly dependent on this coupling. For example, the influence of magnetospheric coupling on the E x B gradient drift instability is to retard the instability's growth and to isotropize density irregularities. The influence of ionospheric coupling on the Kelvin-Helmholtz instability is to retard its growth and to suppress vortex formation. This paper presents the results of numerical simulations of these instabilities and discusses their application to high-latitude ionospheric structure.

Huba, J. D.; Keskinen, M. J.; Fedder, J. A.; Mitchell, H. G.; Satyanarayana, P.

1988-01-01

314

The response of plasma density to breaking inertial gravity wave in the lower regions of ionosphere  

NASA Astrophysics Data System (ADS)

We present a three-dimensional numerical study for the E and lower F region ionosphere coupled with the neutral atmosphere dynamics. This model is developed based on a previous ionospheric model that examines the transport patterns of plasma density given a prescribed neutral atmospheric flow. Inclusion of neutral dynamics in the model allows us to examine the charge-neutral interactions over the full evolution cycle of an inertial gravity wave when the background flow spins up from rest, saturates and eventually breaks. Using Lagrangian analyses, we show the mixing patterns of the ionospheric responses and the formation of ionospheric layers. The corresponding plasma density in this flow develops complex wave structures and small-scale patches during the gravity wave breaking event.

Tang, Wenbo; Mahalov, Alex

2014-04-01

315

Direct evidence of double-slope power spectra in the high-latitude ionospheric plasma  

NASA Astrophysics Data System (ADS)

We report direct observations of the double-slope power spectra for plasma irregularities in the F layer of the polar ionosphere. The investigation of cusp irregularities ICI-2 sounding rocket, which was launched into the polar cusp ionosphere, intersected enhanced plasma density regions with decameter-scale irregularities. Density measurements at unprecedented high resolution with multi-Needle Langmuir Probes allowed for a detailed study of the plasma irregularities down to kinetic scales. Spectral analysis reveals double-slope power spectra for regions of enhanced fluctuations associated mainly with density gradients, with the steepening of the spectra occurring close to the oxygen gyrofrequency. These findings are further supported with the first results from the ICI-3 rocket, which flew through regions with strong precipitation and velocity shears. Previously, double-slope spectra have been observed in the equatorial ionosphere. The present work gives a direct evidence that the double-slope power spectra can be common in the high-latitude ionosphere.

Spicher, A.; Miloch, W. J.; Moen, J. I.

2014-03-01

316

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

317

The High-Latitude Ionosphere and Its Effects on Radio Propagation  

NASA Astrophysics Data System (ADS)

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

Moses, Ronald W., Jr.

2004-05-01

318

Radar soundings of the ionosphere of Mars.  

PubMed

We report the first radar soundings of the ionosphere of Mars with the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) instrument on board the orbiting Mars Express spacecraft. Several types of ionospheric echoes are observed, ranging from vertical echoes caused by specular reflection from the horizontally stratified ionosphere to a wide variety of oblique and diffuse echoes. The oblique echoes are believed to arise mainly from ionospheric structures associated with the complex crustal magnetic fields of Mars. Echoes at the electron plasma frequency and the cyclotron period also provide measurements of the local electron density and magnetic field strength. PMID:16319123

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

2005-12-23

319

Ionospheric and magnetospheric effects of the solar eclipse in northeastern Russia  

NASA Astrophysics Data System (ADS)

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

Poddelsky, Igor N.; Poddelsky, Aleksey I.

2009-02-01

320

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

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

321

GPS studies of the Ionosphere  

NASA Astrophysics Data System (ADS)

This paper is devoted to the use of GPS receivers to study ionosphere. We focus our presentation on physical phenomena at middle and low latitudes: -equatorial fountain study with GPS -signature of magnetic storms on GPS signal -scintillations -etc. . . Invited talk

Amory, Christine

322

Global morphology of ionospheric scintillations  

Microsoft Academic Search

A radio wave traversing the upper and lower atmosphere of the earth suffers a distortion of phase and amplitude. When it traverses drifting ionospheric irregularities, the radio wave experiences fading and phase fluctuation which vary widely with frequency, magnetic and solar activity, time of day, season, and latitude. This review has the objective to organize the experimental and theoretical studies

J. Aarons

1982-01-01

323

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

324

Ionospheric imaging using computerized tomography  

Microsoft Academic Search

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

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

1988-01-01

325

Robust Detection of Ionospheric Irregularities  

Microsoft Academic Search

The Wide Area Augmentation System (WAAS) will provide real-time differential GPS corrections and integrity information for aircraft navigation use. The most stringent application of this system will be precision approach, where the system guides the aircraft to within a few hundred feet of the ground. Precision approach operations require the use of differential ionospheric corrections. WAAS must incorporate information from

Todd Walter; Andrew Hansen; Juan Blanch; Per Enge; Larry Sparks; Byron Iijima; Bakry El-Arini; Roland Lejeune; Eric Altshuler; Rob Fries; Aleck Chu

326

Magnetospheric-ionospheric Poynting flux  

NASA Technical Reports Server (NTRS)

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

Thayer, Jeffrey P.

1994-01-01

327

Artificial Hydrogenases  

PubMed Central

Decades of biophysical study on the hydrogenase (H2ase) enzymes have yielded sufficient information to guide the synthesis of analogues of their active sites. Three families of enzymes serve as inspiration for this work: the [FeFe]-, [NiFe]-, and [Fe]-H2ases, all of which feature iron centers bound to both CO and thiolate. Artificial H2ases effect the oxidation of H2 of H2 and the reverse reaction, the reduction of protons. These reactions occur via the intermediacy of metal hydrides. The inclusion of amine bases within the catalysts is an important design feature that is emulated in related bioinspired catalysts. Continuing challenges are the low reactivity of H2 towards biomimetic H2ases.

Barton, Bryan E.; Olsen, Matthew T.; Rauchfuss, Thomas B.

2010-01-01

328

The ionospheric outflow feedback loop  

NASA Astrophysics Data System (ADS)

Following a long period of observation and investigation beginning in the early 1970s, it has been firmly established that Earth's magnetosphere is defined as much by the geogenic plasma within it as by the geomagnetic field. This plasma is not confined to the ionosphere proper, defined as the region within a few density scale heights of the F-region plasma density peak. Rather, it fills the flux tubes on which it is created, and circulates throughout the magnetosphere in a pattern driven by solar wind plasma that becomes magnetically connected to the ionosphere by reconnection through the dayside magnetopause. Under certain solar wind conditions, plasma and field energy is stored in the magnetotail rather than being smoothly recirculated back to the dayside. Its release into the downstream solar wind is produced by magnetotail disconnection of stored plasma and fields both continuously and in the form of discrete plasmoids, with associated generation of energetic Earthward-moving bursty bulk flows and injection fronts. A new generation of global circulation models is showing us that outflowing ionospheric plasmas, especially O+, load the system in a different way than the resistive F-region load of currents dissipating energy in the plasma and atmospheric neutral gas. The extended ionospheric load is reactive to the primary dissipation, forming a time-delayed feedback loop within the system. That sets up or intensifies bursty transient behaviors that would be weaker or absent if the ionosphere did not “strike back” when stimulated. Understanding this response appears to be a necessary, if not sufficient, condition for us to gain accurate predictive capability for space weather. However, full predictive understanding of outflow and incorporation into global simulations requires a clear observational and theoretical identification of the causal mechanisms of the outflows. This remains elusive and requires a dedicated mission effort.

Moore, T. E.; Fok, M.-C.; Garcia-Sage, K.

2014-08-01

329

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

330

Moment expansion for ionospheric range error  

NASA Technical Reports Server (NTRS)

On a plane earth, the ionospheric or tropospheric range error depends only on the total refractivity content or zeroth moment of the refracting layer and the elevation angle. On a spherical earth, however, the dependence is more complex; so for more accurate results it has been necessary to resort to complex ray-tracing calculations. A simple, high-accuracy alternative to the ray-tracing calculation is presented. By appropriate expansion of the angular dependence in the ray-tracing integral in a power series in height, an expression is obtained for the range error in terms of a simple function of elevation angle, E, at the expansion height and of the mth moment of the refractivity, N, distribution about the expansion height. The rapidity of convergence is heavily dependent on the choice of expansion height. For expansion heights in the neighborhood of the centroid of the layer (300-490 km), the expansion to N = 2 (three terms) gives results accurate to about 0.4% at E = 10 deg. As an analytic tool, the expansion affords some insight on the influence of layer shape on range errors in special problems.

Mallinckrodt, A.; Reich, R.; Parker, H.; Berbert, J.

1972-01-01

331

Development of a database for the verification of trans-ionospheric remote sensing systems  

NASA Astrophysics Data System (ADS)

Remote sensing systems need verification by means of in-situ data or by means of model data. In the case of ionospheric occultation inversion, ionosphere tomography and other imaging methods on the basis of satellite-to-ground or satellite-to-satellite electron content, the availability of in-situ data with adequate spatial and temporal co-location is a very rare case, indeed. Therefore the method of choice for verification is to produce artificial electron content data with realistic properties, subject these data to the inversion/retrieval method, compare the results with model data and apply a suitable type of “goodness of fit” classification. Inter-comparison of inversion/retrieval methods should be done with sets of artificial electron contents in a “blind” (or even “double blind”) way. The set up of a relevant database for the COST 271 Action is described. One part of the database will be made available to everyone interested in testing of inversion/retrieval methods. The artificial electron content data are calculated by means of large-scale models that are “modulated” in a realistic way to include smaller scale and dynamic structures, like troughs and traveling ionospheric disturbances.

Leitinger, R.

2005-08-01

332

Artificial Ionization and UHF Radar Response Associated with HF Frequencies near Electron Gyro-Harmonics (Invited)  

NASA Astrophysics Data System (ADS)

We present new results from O-mode ionospheric heating experiments at the HAARP facility in Alaska to demonstrate that the magnitude of artificial ionization production is critically dependent on the choice of HF frequency near gyro-harmonics. For O-mode heating in the lower F-region ionosphere, typically about 200 km altitude, artificial ionization enhancements are observed in the lower ionosphere (about 150 - 220 km) and also in the topside ionosphere above about 500 km. Lower ionosphere density enhancements are inferred from HF-enhanced ion and plasma-line signals observed with UHF radar. Upper ionospheric density enhancements have been observed with TEC (total electron content) experiments by monitoring satellite radio beacons where signal paths traverse the HF-modified ionosphere. Both density enhancements and corresponding upward plasma fluxes have also been observed in the upper ionosphere via in-situ satellite observations. The data presented focus mainly on observations near the third and fourth gyro-harmonics. The specific values of the height-dependent gyro-harmonics have been computed from a magnetic model of the field line through the HF heated volume. Experiments with several closely spaced HF frequencies around the gyro-harmonic frequency region show that the magnitude of the lower-ionosphere artificial ionization production maximizes for HF frequencies about 1.0 - 1.5 MHz above the gyro-harmonic frequency. The response is progressively larger as the HF frequency is increased in the frequency region near the gyro-harmonics. For HF frequencies that are initially greater than the gyro-harmonic value the UHF radar scattering cross-section is relatively small, and non-existent or very weak signals are observed; as the signal returns drop in altitude due to density enhancements the HF interaction region passes through lower altitudes where the HF frequency is less than the gyro-harmonic value, for these conditions the radar scattering cross-section is significantly increased and strong signals persist while the high-power HF is present . Simultaneous observations of topside TEC measurements and lower-ionosphere UHF radar observations suggest there is an optimum altitude region to heat the lower F-region in order to produce topside ionosphere density enhancements. The observations are dependent on HF power levels and we show several examples where heating results are only observed for the high-power levels attainable with the HAARP facility.

Watkins, B. J.; Fallen, C. T.; Secan, J. A.

2013-12-01

333

Results of ionospheric observations in Alma-Ata on March 16-20 and December 5-10, 1988  

NASA Astrophysics Data System (ADS)

Results are presented of an analysis of ionospheric conditions observed at the Alma-Ata station suring the SUNDIAL periods March 16-20 and December 5-10, 1988. Data collected for the March 16-20, 1988 period indicate a quiet period of the ionosphere, with changes of critical frequencies in the F2 layer (f0F2) falling within the 20 percent limit, except of a short-time increase in f0F2 values on March 19. During the December 5-10 period, the lower-latitude ionosphere was disturbed more than in March, with weak negative disturbances followed by positive ones.

Burlakova, I. A.; Gordienko, G. I.; Zelenkova, I. A.

1993-02-01

334

Langmuir probe measurements in the ionosphere  

NASA Astrophysics Data System (ADS)

Electric probes have been the primary instruments for the in situ investigation of plasma parameters in the Earth's ionosphere. This dissertation is a compendium of three papers, each dealing with a separate spacecraft that carried one or more instruments based on the electric probe technique. The first paper presents data from the Sudden Atom Layer sounding rocket that carried an RF impedance Probe, a DC fixed-bias Langmuir Probe (DCP), and an Electric Field Probe. The combined dataset indicates a case of payload surface charging, the causes of which are investigated within the paper. A generic circuit, model is developed to analyze payload charging and behavior of Langmuir-type instruments. Our analysis indicates that the anomalous charging event was an outcome of triboelectrification of the payload surface from neutral dust particles present in the Earth's mesosphere. These results suggest caution in interpreting observations from the Langmuir class of instrumentation within dusty environments. The second paper presents data from the Floating Potential Measurement Unit (FPMU) that is deployed on the International Space Station. The FPMU instrument suite consists of three different Langmuir-type probes and a Plasma Impedance Probe (PIP). We first give a brief overview of the instrumentation, and then describe the algorithm used to reduce Langmuir probe I-V curves to plasma parameters. It is shown that the derived temperatures agree well with International Reference Ionosphere (IRI) model, while the derived density matches better with the USU-Global Assimilation of Ionospheric Measurement model. The third paper presents the dataset from the EQUIS II sounding rocket campaign. The rocket payloads carried a PIP, a DCP, and an internally heated Sweeping Langmuir Probe. The ratio of the payload surface area to the cumulative area of the instrument and its guard was about 250. We show that on small sounding rocket payloads the DCP technique of relative electron density measurement is not very accurate. We further show that the ion saturation region analysis of the I-V curve produces absolute ion density that matches very well with the absolute electron density derived from the PIP, and the derived temperatures agree reasonably well with the IRI model.

Barjatya, Aroh

335

Nighttime ionospheric enhancements induced by the occurrence of an evening solar eclipse  

NASA Astrophysics Data System (ADS)

solar eclipse on 15 January 2010 traversed Asia and completed its travel on the Shandong Peninsula in China at sunset. Two vertical incidence ionosondes at Wuhan and Beijing and the oblique incidence ionosonde network in North China were implemented to record the ionospheric response to the solar eclipse. Following the initial electron density decrease caused by the eclipse, the ionosphere was characterized by a strong premidnight enhancement, and a subsequent ionospheric decay, and a ~10 h later postmidnight enhancement. Neither geomagnetic disturbance occurred during the eclipse day nor did obvious nighttime peak appear for the 10 day mean of the F2-layer critical frequency (foF2). The electron density profilogram of the Beijing ionosonde indicates that the two enhancements were the result of the plasma flux downward from the top ionosphere, possibly due to the steep decrease of the ionospheric electron density and plasma temperature during the solar eclipse. The two-dimensional differential foF2 maps present the regional variations of the nighttime electron density peaks and decay. Both the pre- and postmidnight enhancements initially appeared in a belt almost in parallel with the eclipse track and then drifted southward. The different magnitudes of greatest eclipse in the umbra and outside tend to account for the different occurrence times of the plasma flux. The ionospheric decay following the premidnight enhancement is also considered as a consequence of the eclipse shade.

Chen, Gang; Qi, Hao; Ning, Baiqi; Zhao, Zhengyu; Yao, Ming; Deng, Zhongxing; Li, Ting; Huang, Shuo; Feng, Wenchao; Wu, Jianhua; Wu, Chen

2013-10-01

336

Extremely Low Ionospheric Peak Altitudes in the Polar-Hole Region  

NASA Technical Reports Server (NTRS)

Vertical electron-density (N (sub e)) profiles, deduced from newly-available ISIS-II digital ionospheric topside-sounder data, are used to investigate the "polar-hole" region within the winter, nighttime polar cap ionosphere during solar minimum. The hole region is located around 0200 MLT near the poleward side of the auroral oval. Earlier investigations had revealed very low N (sub e) values in this region (down to 200/cu cm near 300 km). In the present study, such low N, values (approx. 100/cu cm) were only found near the ISIS (International Satellite for Ionospheric Study)-II altitude of 1400 km. The peak ionospheric concentration below the spacecraft remained fairly constant (approx. 10 (exp 5)/cu cm across the hole region but the altitude of the peak dropped dramatically. This peak dropped, surprisingly, to the vicinity of 100 km. These observations suggest that the earlier satellite in situ measurements, interpreted as deep holes in the ionospheric F-region concentration, could have been made during conditions of an extreme decrease in the altitude of the ionospheric N (sub e) peak. The observations, in combination with other data, indicate that the absence of an F-layer peak may be a frequent occurrence at high latitudes.

Benson, Robert F.; Grebowsky, Joseph M.

1999-01-01

337

Response of the polar low ionosphere to solar precipitation events along the solar cycle  

NASA Astrophysics Data System (ADS)

In this paper, we present a study of the polar low ionospheric responses to solar energetic particle precipitation events occurred during nighttime for different solar activity conditions. During nighttime, the main source of ion production in the quiescent low ionosphere is the collision between galactic cosmic rays (GCR) and neutral atmosphere constituents. Due to variations in the Interplanetary Magnetic Field (IMF) and solar wind along the solar cycle, the solar activity modulates the GCR fluxes and energy spectrum through the interplanetary magnetic rigidity. In addition, for geomagnetic disturbed periods, solar particles can deeply penetrate into the terrestrial atmosphere (especially in Polar Regions), causing ionization excess in the lower layers of the ionosphere. Based on riometer and neutron monitor measurements obtained in Oulu, Finland (65oN), and along with a low ionospheric empirical model, we had studied the response of the low ionosphere to the occurrence of these events. This study allows us to discuss the nocturnal behavior of the polar low ionosphere along the solar cycle (including its peculiarities during the last minimum), and also define an ionization pattern for quiet and disturbed magnetic periods.

Pacini, A. A.; Fujisawa, M. Y.; Brum, C. G.

2013-05-01

338

Global hybrid model of the solar wind interaction with the Venus ionosphere: ion escape processes  

NASA Astrophysics Data System (ADS)

Comprehensive two-dimensional (2D) global hybrid (particle ions, massless fluid electrons) simulations of the solar wind interaction with the ionosphere of Venus are conducted. We calculate the entire Venus-solar wind interaction region including the ionosphere, ionopause transition layer, magnetosheath, and solar wind regions, by applying boundary-fitted coordinates to the particle-in-cell code. Our model is successful in reproducing several observed features, such as long streamers of ionospheric plasma and detached plasma clouds. In this paper, we investigate the processes in which planetary ions are removed by the solar wind interaction using the comprehensive global hybrid model. While the ion escape process due to the pickup of exospheric particles has been intensively studied by many authors, possible ion loss processes that take place at and below the ionopause, such as viscous process associated with the Kelvin-Helmholtz (K-H) instability, are less well understood. Hence, in this paper, the escape processes are investigated with a particular emphasis placed on the processes occurring at the ionopause. We discuss the relative importance of the escape processes for the case of low solar wind dynamic pressure (unmagnetized ionosphere condition) as well as for the high dynamic pressure case (magnetized ionosphere condition), and show the viscous removal process occurring at the ionopause plays a significant role in the ion escape from Venus. The model also suggests the asymmetrical appearance of ``disappearing nightside ionosphere''.

Terada, N.; Shinagawa, H.; Machida, S.

339

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

NASA Astrophysics Data System (ADS)

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

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

2007-10-01

340

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

341

Shear Alfven Wave Injection in the Magnetosphere by Ionospheric Modifications in the Absence of Electrojet Currents  

NASA Astrophysics Data System (ADS)

A new concept of generating ionospheric currents in the ULF/ELF range with modulated HF heating using ground-based transmitters even in the absence of electrojet currents is presented. The new concept relies on using HF heating of the F-region to modulate the electron temperature and has been given the name Ionospheric Current Drive (ICD). In ICD, the pressure gradient associated with anomalous or collisional F-region electron heating drives a local diamagnetic current that acts as an antenna to inject mainly Magneto-Sonic (MS) waves in the ionospheric plasma. The electric field associated with the MS wave drives Hall currents when it reaches the E region of the ionosphere. The Hall currents act as a secondary antenna that inject waves in the Earth-Ionosphere Waveguide (EIW) below and shear Alfven waves or EMIC waves upwards towards the conjugate regions. The paper presents: (i) Theoretical results using a cold Hall MHD model to study ICD and the generation of ULF/ELF waves by the modulation of the electron pressure at the F2-region with an intense HF electromagnetic wave. The model solves equations governing the dynamics of the shear Alfven and magnetosonic modes, of the damped modes in the diffusive Pedersen layer, and of the weakly damped helicon wave mode in the Hall-dominated E-region. The model incorporates realistic profile of the ionospheric conductivities and magnetic field configuration. We use the model to simulate propagation and dynamics of the low-frequency waves and their injection into the magnetosphere from the HAARP and Arecibo ionospheric heaters. (ii) Proof of principle experiments using the HAARP ionospheric heater in conjunction with measurements by the DEMETER satellite This work is supported by ONR MURI grant and DARPA BRIOCHE Program

Papadopoulos, K.; Eliasson, B.; Shao, X.; Labenski, J.; Chang, C.

2011-12-01

342

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

343

The Venus ionosphere from in situ measurements  

NASA Technical Reports Server (NTRS)

The present characterization of the Venus ionosphere gives attention to features observed by the Pioneer Venus orbiter in situ ionospheric particle measuring instrument over an entire cycle of solar activity. A striking change is noted in the typical ionospheric morphology from solar maximum to minimum. The principal source of ionization in the dayside ionosphere during both solar maximum and minimum is solar EUV radiation, while that in the nightside is a downward flux of O(+) ions that originate in the dayside ionosphere and are transported across the nightside hemisphere by a supersonic ion wind. The dayside ionosphere contains fluxes of suprathermal electrons whose energy spectra are consistent with fluxes originating in EUV photo production.

Knudsen, William C.

1992-01-01

344

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

345

Ionospheric corrections for GPS time transfer  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

346

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

347

An advantage of magnetic index nu to show high local disturbances in ionosphere during quiet day conditions  

Microsoft Academic Search

We analysed data of ionospheric characteristics (foE, foEs, foF2, h'E, h'F2) during 30-day long quiet day conditions (Kp = 0-2) in 2004. We found correlations between high local disturbances in ionosphere during very quiet days and high values of magnetic index nu. The coexistence of E sporadic layer or high local disturbances of the foE during magnetically very quiet days

Beata Dziak-Jankowska; Iwona Stanislawska; Dalia Buresova; Tomasz Ernst; Lukasz Tomasik

2010-01-01

348

Ionospheric assimilation techniques for ARGOS Low-Resolution Airglow and Aurora Spectrograph (LORAAS) tomographically reconstructed equatorial electron density profiles  

Microsoft Academic Search

The LORAAS instrument aboard the ARGOS satellite observes line-of-sight ultraviolet limb intensities from ionosphere and thermosphere airglow. This study uses tomographically reconstructed electron density profiles (EDPs) from the nightside emissions. The ionospheric reconstruction is performed using a two-dimensional O+ 1356Å radiative recombination forward model and discrete inverse theory. The forward model assumes a Chapman layer for the vertical electron density

J. J. Sojka; J. V. Eccles; R. W. Schunk; S. McDonald; S. Thonnard; K. Dymond; R. P. McCoy

2004-01-01

349

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

350

What role does the high latitude ionosphere play in the magnetosphere-ionosphere (MI) coupling?  

Microsoft Academic Search

The high-latitude ionosphere is a conducting boundary of the magnetosphere that closes global magnetospheric current systems. It is also a significant mass source of the plasmasheet. At times the auroral ionosphere is expected to control magnetospheric processes and the magnetospheric particle population. However, its role in the particle interchanges (magnetospheric particle precipitation, ionospheric particle outflow) and in the induced aurora

M. Galand; S. Chakrabarti

2002-01-01

351

International reference ionosphere: Recent developments  

NASA Astrophysics Data System (ADS)

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

Bilitza, Dieter

1986-05-01

352

Investigation of traveling ionospheric disturbances  

NASA Technical Reports Server (NTRS)

Maximum entropy power spectra of the ionospheric electron density were constructed to enable PINY to compare them with the power independently obtained by PINY with in situ measurements of ionospheric electron density and neutral species performed with instrumentation carried by the Atmospheric Explorer (AE) satellite. This comparison corroborated evidence on the geophysical reality of the alleged electron density irregularities detected by the ASTP dual frequency Doppler link. Roughly half of the localized wave structures which are confined to dimensions of 1800 km or less (as seen by an orbiting Doppler baseline) were found to be associated with the larger crest of the geomagnetic anomaly in the Southern (winter) Hemisphere in the morning. The observed nighttime structures are also associated with local peaks in the electron density.

Grossi, M.; Estes, R. D.

1981-01-01

353

Ionosphere as a natural detector for investigations of solar EUV flux variations  

NASA Astrophysics Data System (ADS)

It is proposed a method to determine solar EUV fluxes on the basis of data of ionospheric E-layer critical frequency measurements and of ionospheric activity index calculations. A new solar activity index was elaborated on the base of improved ionization theory in ionospheric E-region. It makes possible to carry out independent estimations of EUV fluxes and reciprocal calibration of EUV measurements, using information on ionospheric E-layer as data of the global natural detector of EUV emission. It is shown, that variations of the upper atmosphere temperature and density does not influence the instrumentation indications, and EUV flux responsible for E-layer ionization, can be determined due to E-layer critical frequency measurements. The new index may serve as a quantitative measure of EUV emission, at least, in lines 97.7 and 102.6 nm. Every mid-latitude ionospheric station may serve as a device for measurements of index “equivalent flux” of EUV. Calibration error of this index is defined by a low error of radiophysical measurements of critical frequencies and is equal to ˜7%. The index allows also to investigate long-term variations and to expand a temporal range of research. The L? flux for almost four cycles of solar activity was calculated due to Slough and Chilton stations data. It is shown that variations of EUV fluxes approximately correspond to the main tendency of activity increase in the period from the 20-th to the 23-day cycle. Analysis of ionospheric index reveals an absence of noticeable long-term trends of EUV emission during 1957 2003 period. Use of this index allows to eliminate contradiction between EUV intensities observed onboard SME and UARS satellites, because fluxes in minima between the 21 and 22 cycles (SME epoch) and between the 22 and 23 cycles (a UARS epoch) are practically identical. In general all EUV cycles are similar to each other and it was not found a significant emission trend.

Nusinov, A. A.

354

Ionosphere Scientific Data Stewardship at NGDC  

NASA Astrophysics Data System (ADS)

The Solar and Terrestrial Physics division of the National Geophysical Data Center's (NGDC) Ionosphere program's primary focus is to optimize the collection, archival, analysis and public dissemination of ionospheric space weather and climatology. Data sets available include real time ionosonde observations, U.S. Total Electron Content (USTEC), D-Region Absorption Prediction (DRAP), Forecasting Ionospheric Scintillation Real-time Tool (FIRST), and DMSP particle sensors and auroral imagery. This paper presents NGDC's data holdings, ionosphere program activities and our vision of scientific data stewardship including topics on next generation web services based access and visualization mechanisms, data qualification, validation and accreditation, and general research and environmental science support.

Bullett, T. W.; Redmon, R. J.; Manley, J.; Conkright, R.; Kihn, E. A.; Prendergast, K.; Elespuru, P.; Horan, K.; Schminky, J.; Denig, W. F.

2009-12-01

355

Ionospheric correction for Seasat altimeter height measurement  

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

356

Sudden ionospheric disturbances in solar cycle 24  

NASA Astrophysics Data System (ADS)

Sudden ionospheric disturbances in solar cycle 24 Within the framework of the UN International Space Weather Initiative, and building upon the achievements of the International Heliophysical Year, the German project SIMONE (Sun Ionosphere MOnitoring NEtwork) operates several SID monitors provided by the University of Stanford. Here we present an overview of sudden ionospheric disturbances recorded since 2006 at the high school Gymnasium Walsrode until to date. The continous measurements allow a detailed comparison of locally measured SIDs with the general trend of solar activity during the current solar maximum. We further show that the measurements reveal specific information on the variable response of the dayside ionosphere to solar flares.

Bothmer, Volker; Bernert, Barbara

2014-05-01

357

Ionospheric instrumentation - A new approach  

NASA Astrophysics Data System (ADS)

A new design criterion is proposed for the realization of receivers suitable for ionospheric research. The goal of this criterion is to extend as much as possible the use of microprocessor-based systems to perform not only data handling and instrumentation control, but also to substitute classical radiotechnical circuitry, i.e., the software receiver approach. The motivations of such effort will be presented and discussed.

Ciraolo, L.; Spalla, P.

358

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

359

Ionospheric disturbances initiated by impact of the Chelyabinsk meteoroid  

NASA Astrophysics Data System (ADS)

It has been demonstrated, that impact of the Chelyabinsk meteoroid on the 15th of February, 2013 caused oscillations of critical plasma frequency of the F2 layer of ionosphere (foF2), but there were no detectable variations of the Earth's magnetic field. Also on tomograms of ionosphere, obtained by GPS stations located along 40 th meridian, wave-like disturbances of electron density at heights 200-700 km have been observed. As followed from ionosondes' measurements foF2 oscillations have been detected tens minutes after a main burst in Irkutsk, Norilsk, Yakutsk and then in Moscow and Europe. This time sequence of beginning of the oscillations could be explained by hypothesis that a source lied on the trajectory of the meteoroid far from Chelyabinsk. Post-impact ballistic plume outgoing to the rarefied layers of the atmosphere and then falling back on the dense layers provides the disturbance transmission in a time of tens minutes at a distance of 1500-2000 km. By numerical modeling a possibility for the plume to be formed has been shown. Also modeling of oscillations in F2-layer initiated by the falling plume has been fulfilled. Calculated amplitudes of density variations are in a good agreement with observable ones. Geomagnetic disturbances generated by the impact have been estimated. They appeared to be too small to be detected by nearby stations.

Kuzmicheva, M.; Losseva, T. V.; Lyakhov, A.

2013-12-01

360

Recent Advances in Studies of Ionospheric Modification Using Rocket Exhaust (Invited)  

NASA Astrophysics Data System (ADS)

Rocket exhaust interacts with the ionosphere to produce a wide range of disturbances. A ten second burn of the Orbital Maneuver Subsystem (OMS) engines on the Space Shuttle deposits over 1 Giga Joule of energy into the upper atmosphere. The exhaust vapors travel at speeds between 4.7 and 10.7 km/s coupling momentum into the ions by both collisions and charge exchange. Long-lived plasma irregularities are formed by the artificial hypersonic “neutral wind” passing through the ionosphere. Charge exchange between the fast neutrals and the ambient ions yields high-speed ion beams that excite electro-static plasma waves. Ground based radar has been used to detect both field aligned irregularities and electrostatic turbulence driven by the Space Shuttle OMS exhaust. Molecular ions produced by the charge exchange with molecules in the rocket exhaust recombine with a time scale of 10 minutes leaving a residual plasma depression. This ionospheric “hole” fills in by ambipolar diffusion leaving a depleted magnetic flux tube. This large scale reduction in Pedersen conductivity can provide a seed for plasma interchange instabilities. For instance, a rocket firing on the bottom side of the ionosphere near the equator can trigger a Rayleigh-Taylor instability that is naturally seen as equatorial Spread-F. The Naval Research Laboratory has been exploring these phenomena with dedicated burns of the Space Shuttle OMS engines and exhaust releases from rockets. The Shuttle Ionospheric Modification with Pulsed Localized Exhaust (SIMPLEX) series of experiments uses ground radars to probe the ionosphere affected by dedicated burns of the Space Shuttle OMS engines. Radars located at Millstone Hill, Massachusetts; Arecibo, Puerto Rico; Jicamarca, Peru; Kwajalein, Marshall Island; and Alice Springs, Australia have participated in the SIMPLEX program. A companion program called Shuttle Exhaust Ionospheric Turbulence Experiment has or will use satellites to fly through the turbulence ionosphere produced by Space Shuttle Exhaust. This program is employing the Air Force Research Laboratory C/NOFS and the Canadian CASSIOPE/EPoP satellites to make in situ measurements of Space Shuttle exhaust effects. Finally, NRL is conducting the Charged Aerosol Release Experiment which employs a solid rocket motor to modify the ionosphere using supersonic particulate injection and dusty plasma formation. Both the theoretic basis for these experiments and as summary of the experimental results will be presented.

Bernhardt, P. A.

2009-12-01

361

Integration of artificial SrTiO 3/BaTiO 3 superlattices on Si substrates using a TiN buffer layer by pulsed laser deposition method  

NASA Astrophysics Data System (ADS)

Epitaxial SrTiO 3(STO)/BaTiO 3(BTO) artificial superlattices, STO, BTO, and (Ba 0.5,Sr 0.5)TiO 3 (BSTO) thin films have been grown on TiN-buffered Si (0 0 1) substrates by pulsed laser deposition method and their dielectric properties were studied. The crystal orientation, epitaxy nature, and microstructure of epitaxial oxide thin films were investigated using X-ray diffraction and transmission electron microscopy. Thin films were prepared with laser fluence of 3 and 2 J/cm 2, repetition rate of 8 and 10 Hz, substrate temperature of 700 and 650 °C for TiN and oxide, respectively. The TiN buffer layer and oxide thin films were grown with cube-on-cube epitaxial orientation relationship of [1 1 0](0 0 1) films?[1 1 0](0 0 1) TiN?[1 1 0](0 0 1) Si. The dielectric constants of BTO, STO, BSTO, and STO/BTO superlattice epitaxial thin films with 1 nm/1 nm periodicity were shown to be as high as 300, 410, 520, and 680 at the frequency of 100 kHz, respectively.

Kim, Tae-Un; Kim, Bo Ram; Lee, Won-Jae; Moon, Jong Ha; Lee, Byung-Teak; Kim, Jin Hyeok

2006-04-01

362

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

NASA Astrophysics Data System (ADS)

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

Namgaladze, A. A.

2013-12-01

363

Aerosol growth in Titan's ionosphere through particle charging  

NASA Astrophysics Data System (ADS)

Observations of Titan's lower thermosphere and ionosphere by Cassini instruments demonstrate the presence of large mass negative ions of a few thousand amu, and the presence of positive ions up to a few hundred amu [1,2]. The mechanisms though responsible for the production of these large ions have so far remained elusive. A recent Titan flyby that probed deeper layers of Titan's thermosphere than usual, revealed a discrepancy in the observed positive ion and electron density, with the electron density lower than the abundance required to satisfy charge balance [3]. The remaining electron density was found in the form of the large mass negative ions. Aerosols can be charged on interaction with electrons and ions, while this charge can affect the particle coagulation, thus, their subsequent growth. Given the above observations we investigate here the potential role of aerosols in Titan's ionosphere and how this interaction affects the aerosol evolution. This investigation is performed with the use of a model that couples between the ionospheric photochemical evolution and the microphysical growth of aerosols in a self-consistent approach. Our results show that particle charging has an important role in the ionosphere. Most of the produced particles in the ionosphere attain a negative charge. Thus, they act as a sink for the free electrons with the remaining free electron densities consistent with the recent Cassini observations. Being negatively charged, the particles repel each other reducing in this way the coagulation rates and the growth of the aerosols. On the other hand, the negatively charged particles attract the abundant positive ions, which results to enhanced collisions between them. The mass added to the particles by the ions leads to an increase in their size and an increase in the resulting mass flux of the aerosols. Our simulated mass per charge spectra provide excellent fits to the observed positive and negative ion spectra from the Cassini Plasma Spectrometer (CAPS) at the large mass end of their range. Thus, we identify the observed large mass positive and negative ions as sub-nm size charged aerosols produced in Titan's ionosphere. [1] A. J. Coates, et al., Geophysical Research Lett. 342, L22103 (2007). [2] J. H. Waite, et al., Science 316, 870 (2007). [3] K. Agren, N. Edberg, J.-E. Wahlund, Geophys. Res. Lett. 39,L10201 (2012).

Lavvas, P.; Yelle, R. V.; Koskinen, T.; Bazin, A.; Vuitton, V.; Vigren, E.; Galand, M. F.; Wellbrock, A.; Coates, A. J.; Wahlund, J.; Crary, F.; Snowden, D. S.

2012-12-01

364

Plasma interactions in Titan's ionosphere  

NASA Astrophysics Data System (ADS)

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

Richard, Matthew Scott

365

Artificial anisotropy and polarizing filters  

NASA Astrophysics Data System (ADS)

The calculated spectral transmittance of a multilayer laser mirror is used to determine the effective index of the single layer equivalent to the multilayer stack. We measure the artificial anisotropy of photoresist thin films whose structure is a one-dimensional, subwavelength grating obtained from interference fringes. The limitation of the theory of the first-order effective index homogenization is discussed. We designed normal-incidence, polarizing coating and a polarization rotator by embedding anisotropic films in simple multilayer structures.

Flory, Francois; Escoubas, Ludovic; Lazarides, Basile

2002-06-01

366

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

367

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

368

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

369

Modulation of the midlatitude ionospheric E region by atmospheric gravity waves through polarization electric field  

Microsoft Academic Search

We have studied coupling between the neutral atmosphere and the ionospheric E region in the midlatitude by combining two numerical simulation models. Atmospheric gravity waves generated in the troposphere propagate through the stratosphere and the mesosphere and can reach the lower thermosphere. When a zonal wind shear that can accumulate a sporadic-E (Es) layer (eastward below and westward above) is

T. Yokoyama; T. Horinouchi; M. Yamamoto; S. Fukao

2004-01-01

370

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.

371

Anomalous attenuation of extraordinary waves in ionosphere heating experiments  

NASA Astrophysics Data System (ADS)

Multiple scattering from artificial irregularities, HF-induced in the ionospheric F region, may cause significant attenuation of both ordinary and extraordinary radio waves in addition to the anomalous absorption of ordinary waves by their conversion into plasma waves. We have confirmed the existence and detailed features of this effect at the Sura heating facility by measurements of the attenuation of the powerful pump wave and weak probing waves of extraordinary polarization. Extraordinary waves are attenuated during heating, 1.5-12 dB below a background (nonheating) attenuation value caused by scattering from natural irregularities. Irregularities involved into the multiple scattering process have geomagnetic field-transverse scales of l? ˜ 0.1-1 km. To determine characteristics of these irregularities, a simple inverse problem solution procedure is implemented.

Zabotin, N. A.; Bronin, A. G.; Zhbankov, G. A.; Frolov, V. L.; Komrakov, G. P.; Mityakov, N. A.; Sergeev, E. N.

2002-12-01

372

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

373

The structure of the Venus ionosphere  

Microsoft Academic Search

Our current knowledge of the spatial structure of the Venus ionosphere and its temporal behavior is reviewed, with emphasis on the more recent Pioneer Venus measurements and analysis not covered in earlier reviews. We will stress the ionosphere structure, since other papers in this issue deal with its dynamics, and its magnetic properties. We also discuss some of the limitations

L. H. Brace; A. J. Kliore

1991-01-01

374

Plasma Temperatures in the Ionosphere of Saturn  

Microsoft Academic Search

Using a one-dimensional version of the Saturn Thermosphere Ionosphere Model (STIM), we perform calculations of the ion and electron temperatures in the ionosphere of Saturn. There are no direct measurements of plasma temperatures in Saturn's atmosphere published to date, but they are often estimated from the topside plasma scale heights of radio occultation measurements of electron density. Based on Pioneer,

Luke Moore; M. Galand; M. Mendillo; I. Müller-Wodarg

2007-01-01

375

Radio beacon studies of ionospheric irregularities  

Microsoft Academic Search

Satellite observations of ionospheric irregularities with dimensions ranging from thousands of kilometers to around 100 meters are discussed. These observations were made using the ATS 6 synchronous satellite. European values for the total columnar electron content and the plasmaspheric columnar electron content are larger than those over the USA. Maps of electron content were used in making corrections for ionospheric

K. Davies

1980-01-01

376

Ionospheric Modeling for Precise GNSS Applications  

Microsoft Academic Search

The main objective of this thesis is to develop a procedure for modeling and predicting ionospheric Total Electron Content (TEC) for high precision differential GNSS applications. As the ionosphere is a highly dynamic medium, we believe that to have a reliable procedure it is necessary to transfer the high temporal resolution GNSS network data into the spatial domain. This objective

Y. Memarzadeh

2009-01-01

377

Ionospheric Alfvén resonator revisited: Feedback instability  

Microsoft Academic Search

The theory of ionospheric Alfvén resonator (IAR) and IAR feedback instability is reconsidered. Using a simplified model of the topside ionosphere, we have reanalyzed the physical properties of the IAR interaction with magnetospheric convective flow. It is found that in the absence of the convective flow the IAR eigenmodes exhibit a strong damping due to the leakage of the wave

Oleg A. Pokhotelov; V. Khruschev; M. Parrot; S. Senchenkov; V. P. Pavlenko

2001-01-01

378

Ionospheric effects due to electrostatic thundercloud fields  

Microsoft Academic Search

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

V. P. Pasko; T. F. Bell

1998-01-01

379

Solitons versus parametric instabilities during ionospheric heating  

NASA Technical Reports Server (NTRS)

Various effects associated with ionospheric heating are investigated by numerically solving the modified Zakharov (1972) equations. It is shown that, for typical ionospheric parameters, the modulational instability is more important than the parametric decay instability in the spatial region of strongest heater electric field. It is concluded that the modulational instability leads to the formation of solitons, as originally predicted by Petviashvili (1976).

Nicholson, D. R.; Payne, G. L.; Downie, R. M.; Sheerin, J. P.

1984-01-01

380

Ionospheric ULF oscillations driven from above Arecibo  

Microsoft Academic Search

Understanding the coupling between the surface of the sun, the solar corona, the solar wind, the Earth's magnetosphere and ionosphere is a major focus of today's space research. Over 20 years ago, detailed observations of the ionospheric electron density at Arecibo revealed short period fluctuations (3 minutes), but their cause was never determined. Also, in the past 20 years a

L. P. Dyrud; R. Behnke; E. L. Kepko; M. Sulzer; S. Zafke

2008-01-01

381

Ionospheric models for Venus and Mars  

NASA Technical Reports Server (NTRS)

The ways in which different models employ the multifluid continuity, momentum, and energy equations to characterize the ionospheres of Mars and Venus on the basis of in situ neutral and ion compositions are discussed. The Venus ionosphere is permeated by large-scale magnetic fields when the solar wind dynamic pressure is high, but is free from such fields under conditions of low solar wind dynamic pressure. Large-scale magnetic fields are nearly always present in the Mars ionosphere. Plasma moves downward on both planets for magnetized conditions, and magnetic flux is carried from the magnetosheath down into the ionosphere. Ohmic dissipation of the currents responsible for the magnetic field takes place deep in the ionospheres of both planets.

Cravens, T. E.

1992-01-01

382

Development of the Global Assimilative Ionospheric Model  

NASA Astrophysics Data System (ADS)

This paper provides an overview of the development of the Global Assimilative Ionospheric Model (GAIM) by a team of investigators from the University of Southern California (USC) and the Jet Propulsion Laboratory (JPL). The USC/JPL GAIM utilizes data assimilation techniques, which are widely used in meteorological applications, for the purpose of monitoring and forecasting Earth's ionosphere. We discuss the general structure of GAIM, which includes a first-principles model of the ionosphere, a series of auxiliary models for the driving forces, a data processing subsystem, and an optimization subsystem. Two techniques for the estimation of electron density and driving forces in the ionosphere are presented: The four-dimensional variational method and the Kalman filter. Some validation methods and results are also presented. These results demonstrate the potential of GAIM in providing accurate specification of the ionosphere.

Wang, Chunming; Hajj, George; Pi, Xiaoqing; Rosen, I. Gary; Wilson, Brian

2004-02-01

383

Ionospheric modification by rocket effluents. Final report  

SciTech Connect

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

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

1980-06-01

384

Delta function excitation of waves in the earth's ionosphere  

NASA Technical Reports Server (NTRS)

Excitation of the earth's ionosphere by delta function current sheets is considered, and the temporal and spatial evolution of wave packets is analyzed for a two-component collisional F2 layer. Approximations of an inverse Fourier-Laplace transform via saddle point methods provide plots of typical wave packets. These illustrate cold plasma wave theory and may be used as a diagnostic tool since it is possible to relate specific features, e.g., the frequency of a modulation envelope, to plasma parameters such as the electron cyclotron frequency. It is also possible to deduce the propagation path length and orientation of a remote radio beacon.

Vidmar, R. J.; Crawford, F. W.; Harker, K. J.

1983-01-01

385

Ionospheric disturbances on December 10, 1988, observed from the Arkhangelsk station  

NASA Astrophysics Data System (ADS)

The paper describes the ionospheric disturbance phenomena on December 10, 1988, recorded at the Arkhangelsk station as part of the SUNDIAL project. On this date, a strong ionospheric substorm was observed which was characterized by a deep trough in the subauroral zone with a polarized jet. A sharp interruption of ionization in the F2 layer in the afternoon hours was observed, as were additional scattered reflections from the trough walls and the corpuscular Es species. Data collected at three stations (Mezen', Arkhangelsk, and Karpogory) made it possible to follow the evolution of the disturbance and its latitudinal distribution.

Kozlov, E. F.; Samorokin, N. I.; Ben'kova, N. P.

1993-02-01

386

Comparison of the topside ionosphere scale height determined by topside sounders model and bottomside digisonde profiles  

NASA Astrophysics Data System (ADS)

Topside ionospheric electron density extrapolation techniques rely on the applied profiler model with different techniques resulting in different profile shape. In all these techniques, the parameter that largely determines the shape of the profile is the scale height. Recently, an empirical model of the topside ionosphere scale height was developed, based on the vertical electron density profiles from the topside sounders onboard Alouette and ISIS satellites. The aim of this paper is to compare the scale height determined by the topside sounders model and bottomside digisonde profiles extrapolated above the maximum of the F layer. Theoretical scale height values, calculated by using the IRI plasma temperature model are also included in the comparison.

Belehaki, A.; Marinov, Pencho; Kutiev, Ivan; Jakowski, Norbert; Stankov, Stanimir

387

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

388

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

389

Application of computerized tomography to the investigation of ionospheric structures  

Microsoft Academic Search

Ionospheric total electron content (TEC) measurements, obtained simultaneously at several locations, can be processed using computerized tomography (CT) algorithms to obtain two-dimensional images of ionospheric electron density. Using TEC data computerized ionospheric tomography (CIT) reconstructs an image of the electron density structures in a vertical slice above the receiving stations. We successfully applied this technique to realistic simulations of ionospheric

T. D. Raymund; J. R. Austen; S.J. Franke; J. A. Klobuchar; J. Stalker

1990-01-01

390

Forecasting Ionospheric Conditions with 4DVAR Assimilation Model  

Microsoft Academic Search

One of main objectives established in 2000 for the development of a global data assimilation model for the Earth's ionosphere was to enable the forecast of ionospheric electron and ion densities. Following the exciting development of Global Assimilative Ionospheric Model (GAIM, also known as the Global Assimilation of Ionospheric Measurements) by two teams, the Utah State University team and the

C. Wang; V. Akopian; X. Pi; A. J. Mannucci

2010-01-01

391

Present and Future IGS Ionosphere Working Group Activities  

Microsoft Academic Search

Nowadays the Ionosphere Working Group of the International GNSS Service (IGS) generates two types of ionospheric products: final and rapid, respectively. This IGS Iono WG started the routine generation of ionosphere vertical total electron content (TEC) maps in June 1998. There are currently four IGS Associate Analysis Centres (IAACs) for ionosphere products: CODE (Center for Orbit Determination in Europe, University

Andrzej Krankowski

2008-01-01

392

The Artificial Life Roots of Artificial Intelligence  

Microsoft Academic Search

Behavior-oriented Artificial Intelligence (AI) is a scientific discipline that studies how behavior of agents emerges and becomes intelligent and adaptive. Success of the field is defined in terms of success in building physical agents that are capable of maximizing their own self-preservation in interaction with a dynamically changing environment. The paper addresses this Artificial Life route toward AI and reviews

Luc Steels; R. Brooks

1994-01-01

393

Aerosol growth in Titan's ionosphere  

PubMed Central

Photochemically produced aerosols are common among the atmospheres of our solar system and beyond. Observations and models have shown that photochemical aerosols have direct consequences on atmospheric properties as well as important astrobiological ramifications, but the mechanisms involved in their formation remain unclear. Here we show that the formation of aerosols in Titan’s upper atmosphere is directly related to ion processes, and we provide a complete interpretation of observed mass spectra by the Cassini instruments from small to large masses. Because all planetary atmospheres possess ionospheres, we anticipate that the mechanisms identified here will be efficient in other environments as well, modulated by the chemical complexity of each atmosphere.

Lavvas, Panayotis; Yelle, Roger V.; Koskinen, Tommi; Bazin, Axel; Vuitton, Veronique; Vigren, Erik; Galand, Marina; Wellbrock, Anne; Coates, Andrew J.; Wahlund, Jan-Erik; Crary, Frank J.; Snowden, Darci

2013-01-01

394

Aerosol growth in Titan's ionosphere.  

PubMed

Photochemically produced aerosols are common among the atmospheres of our solar system and beyond. Observations and models have shown that photochemical aerosols have direct consequences on atmospheric properties as well as important astrobiological ramifications, but the mechanisms involved in their formation remain unclear. Here we show that the formation of aerosols in Titan's upper atmosphere is directly related to ion processes, and we provide a complete interpretation of observed mass spectra by the Cassini instruments from small to large masses. Because all planetary atmospheres possess ionospheres, we anticipate that the mechanisms identified here will be efficient in other environments as well, modulated by the chemical complexity of each atmosphere. PMID:23382231

Lavvas, Panayotis; Yelle, Roger V; Koskinen, Tommi; Bazin, Axel; Vuitton, Véronique; Vigren, Erik; Galand, Marina; Wellbrock, Anne; Coates, Andrew J; Wahlund, Jan-Erik; Crary, Frank J; Snowden, Darci

2013-02-19

395

Saturn: atmosphere, ionosphere, and magnetosphere.  

PubMed

The Cassini spacecraft has been in orbit around Saturn since 30 June 2004, yielding a wealth of data about the Saturn system. This review focuses on the atmosphere and magnetosphere and briefly outlines the state of our knowledge after the Cassini prime mission. The mission has addressed a host of fundamental questions: What processes control the physics, chemistry, and dynamics of the atmosphere? Where does the magnetospheric plasma come from? What are the physical processes coupling the ionosphere and magnetosphere? And, what are the rotation rates of Saturn's atmosphere and magnetosphere? PMID:20299587

Gombosi, Tamas I; Ingersoll, Andrew P

2010-03-19

396

Determination of travelling ionospheric disturbances  

NASA Technical Reports Server (NTRS)

A total of 35 days of Faraday rotation data was obtained from the ATS-6 radio beacon experiment operating with the closely spaced network of Elbert, Table Mountain, and Fort Morgan. The 140-MHz Faraday bandpass data are uncorrelated in the transmission range from 8 to 45 minutes. There are distinct, well correlated, and time-displaced maxima and minima that allow the calculation of the speed and direction of horizontal motions of plane fronts of disturbances in the ionosphere. For some selected events, velocities between 88 and 278 m/sec were obtained.

Degenhardt, W.; Hartmann, G. H.; Davies, K.

1978-01-01

397

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

398

Ionospheric characteristics associated with wave-particle interactions in a SED plume during a super geomagnetic storm  

NASA Astrophysics Data System (ADS)

We report some interesting ionospheric characteristics associated with wave-particle interactions with observations of the ionosonde and co-located incoherent scatter radar (ISR) at Millstone Hill in a storm-enhanced density (SED) plume identified from two-dimensional GPS TEC maps during a super geomagnetic storm on Nov. 20, 2003. Firstly, the digisonde ionogram only contained echoes for scanning frequencies from 6.2 MHz to 9.3 MHz. The lack of echoes at frequencies below 6.2 MHz is attributed to enhancements of sub-ionospheric absorption caused by precipitating RC electrons in the SED plume. Secondly, there was an obvious F1 layer, as well as an Es layer, appearing on the ISR profile, that was not observed by the digisonde due to strong sub-ionospheric absorption. For echoes at frequencies from 6.2 MHz to 9.3 MHz, a comparison of the virtual height obtained from the digisonde ionogram and that derived from the ISR electron density profile, demonstrated that an Es layer appeared with a peak altitude of 123 km. The occurrence of the Es layer is attributed to enhancements of precipitating energetic ion fluxes in the SED plume. Our result suggests that the ionospheric behavior in the SED plume is controlled not only by ionospheric dynamical process but also by precipitating energetic RC ions/ electrons as a consequence of wave-particle interactions in the plasmaspheric plume.

Yuan, Zhigang; Xiong, Ying; Zhang, Shunrong; Deng, Xiaohua; Wang, Jingfang

2013-04-01

399

Investigation of the Application of Artificial Neural Networks to Adaptive Optics Imaging Systems.  

National Technical Information Service (NTIS)

Recurrent and feedforward artificial neural networks are developed as wavefront reconstructors. The recurrent neural network studied is the Hopfield neural network and the feedforward neural network studied is the single layer perceptron artificial neural...

A. H. Suzuki

1991-01-01

400

Observation of Ionospheric Alfvén Resonator Signatures in the Earth's Ionosphere at Low Latitude: Implications for Ionospheric Modeling  

NASA Astrophysics Data System (ADS)

The Communications/Navigation Outage Forecasting System (C/NOFS) satellite investigates the electrodynamics of the equatorial regions using a low inclination (13°) orbit with perigee and apogee of 401 and 867 km, respectively. The satellite is equipped with a three-axis double probe electric field detector that provides continuous DC and AC electric field measurements. Detection of Ionospheric Alfvén Resonator (IAR) signatures by C/NOFS offers unique means for investigating ionospheric electrodynamics, namely MHD (MagnetoHydroDynamic) wave propagation, ionospheric dynamics, aeronomy processes, and the Sun-Earth connection. In this work we present C/NOFS electric field measurements related to IAR signatures, and discuss the wave propagation and resonance mechanisms in the ionosphere. Peculiar electric field data offer new, complementary methodologies for inferring ionospheric electron and ion density profiles, and also contribute to the investigation of ionosphere dynamics. Specifically, IAR spectral signatures measured by C/NOFS allow for improving the International Reference Ionosphere (IRI) model, namely electron density and ion composition.

Ivanov, S.; Simoes, F. A.; Klenzing, J. H.; Pfaff, R. F.; Rowland, D. E.; Bilitza, D.

2011-12-01

401

Artificial Heart Program.  

National Technical Information Service (NTIS)

Contents: The need for artificial heart devices; Basic objective of the artificial heart program; Temporary left ventricular assistance: (a) emergency devices to stabilize the circulation; (b) implantable assist pump; Total implantability: A prerequisite ...

1966-01-01

402

Three-dimensional numerical ray tracing on a phenomenological ionospheric model  

NASA Astrophysics Data System (ADS)

In this paper we present a numerical and step by step ray-tracing method on a phenomenological ionospheric electron density (Ne) model, the TaiWan Ionospheric Model (TWIM), which is constructed from the FormoSat3/Constellation Observing System for Meteorology, Ionosphere and Climate (FS3/COSMIC) ionospheric radio occultation data. With the Earth's magnetic field and horizontal Ne gradient effects included, efficient methods for calculating ray parameters such as the ground range, reflection height, phase path, and group path are presented. The three-dimensional TWIM consists of vertically fitted ?-Chapman-type layers, with distinct F2, F1, E, and D layers, for which the layer parameters such as peak density, peak density height, and scale height are represented by surface spherical harmonics. This way the continuity of Ne and its derivatives is maintained. This is important for practical schemes for providing reliable radio propagation predictions. The methodology is successfully applied to a practical high-frequency transmitter for oblique incidence ray tracing and further evaluated by comparing synthetic vertical ionograms generated by the method with experimental ionosonde observations.

Tsai, L.-C.; Liu, C. H.; Huang, J. Y.

2010-10-01

403

Physical mechanism of ionospheric total electron content perturbations over a seismoactive region  

NASA Astrophysics Data System (ADS)

A mechanism for the total electron content (TEC) perturbation in the ionosphere during seismic activity strengthening is proposed. The spatial distribution of the TEC perturbation is shown to be determined by the joint effect of the following two factors: the heating of the ionosphere by electric current and the plasma drift in the electric field of this current. The TEC perturbation behavior depends on the relationship between these processes. The current arises in a global electric circuit as the EMF, which is related to the dynamics of charged aerosols injected into the atmosphere, and comes into being in atmospheric surface layers. The developed model allows calculation of the spatial TEC distribution in the ionosphere for a prescribed horizontal distribution of the charged aerosol concentration at the Earth's surface.

Ruzhin, Yu. Ya.; Sorokin, V. M.; Yashchenko, A. K.

2014-05-01

404

Recent discoveries of the thermospheres and ionospheres of Venus and Mars (Invited)  

NASA Astrophysics Data System (ADS)

Of all the non-terrestrial ionospheres and thermospheres, those of Venus and Mars have been explored and studied the most, thanks to the Pioneer Venus Orbiter and the Mars Global Surveyor from NASA, and the Venus Express and the Mars Express from ESA. We know that the thermosphere and ionosphere are atmospheric layers strongly influenced by solar wind and solar extreme ultra-violet and soft X-ray flux. This talk will outline the most significant discoveries made recently, which have strong implications on how atmospheres evolve and interact with the Sun. For Venus, there is the sporadic behaviour of the atomic oxygen green line emission, and there is the strong variability of the polar upper atmospheric density. For Mars, there are the responses of the upper atmosphere to solar energetic particle events, the effect of the crustal magnetic field, and the ionospheric vertical structure and boundaries. Finally, this talk will address questions that need to be answered by future missions.

Witasse, O. G.

2013-12-01

405

Observations of ELF signatures arising from space-vehicle disturbances of the ionosphere  

SciTech Connect

The authors report on observations of Extremely Low Frequency (ELF) signatures during exit or reentry of space vehicles through the ionosphere. The two modes regularly observed gave signals that peaked at 5.6 Hz and 11.2 Hz. The evidence points to the lower ionosphere, i.e., the D- and E-layers, as the generator of these signals. The measurements were performed using ground-based multiturn coil sensors located in Reno and San Diego. The nature of these signals is unclear at present but it is surmised that they are detecting either the evanescent fields of hydromagnetic waves traveling in the ionosphere or the oscillating geomagnetic field associated with these hydromagnetic waves.

Dea, J.Y.; Van Bise, W.; Rauscher, E.A.; Boerner, W.

1991-05-01

406

Ionospheric Challenges for GNSS Based Augmentation Systems  

NASA Astrophysics Data System (ADS)

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

Doherty, P.; Valladares, C. E.

2007-12-01

407

The equatorial ionospheric scintillations during geomagnetic storms  

NASA Astrophysics Data System (ADS)

Geomagnetic storms and disturbances are thought to play an important role for initiation of the ionospheric scintillations. Scintillation manifest itself in rapid fluctuation of the phase and intensity of a radio signal that has passed through the Earth's ionosphere, typically on a satellite-to-ground propagation channel. Mechanisms of ionospheric scintillation are better understood than its morphology and serious efforts were made to find the empirical relationships in terms of different geomagnetic indices for their forcasting. Such relationships can help to avoid blackouts and distortions in VLF communication due to ionospheric irregularities. We used the different geomagnetic indices, the ionospheric parameters, and the Bz-component of the interplanetary magnetic field (IMF) to study scintillation activity at the dip latitudes. The relationship between the equatorial ionospheric scintillations and the IMF Bz, Dst, Kp, AU, and AL indices is demonstrated. It is shown that in parallel with much used of Dst- index other indices are also suitable for study of scintillation activity. For example, Kp as planetary index carries information about auroral electrojets also and we can see that no scintillation activity when Kp decreases during positive IMF Bz. This means that the auroral electrojets depicted by the AU, and AL-indices and connected with the field-aligned currents (FAC) are decreased and moved to pole ward. The positive IMF Bz is likely to be the factor that inhibits the equator ward penetration of the high latitude electric field. The negative IMF Bz enhances the auroral electric fields and they can penetrate to the equatorial ionosphere. The examples presented in our study allow us to assume that the southward IMF Bz by the Region 1 FAC can form an additional eastward current system at the equatorial ionosphere. Under these conditions the virtual height h'F rises to high altitudes and when it drops the scintillations can be generated. It may be safely suggested that source of this phenomenon is the solar wind electric field responcible for the auroral and equatorial ionosphere coupling. Other processes such as tides, earthquakes etc. can change the ionospheric height also and may play a role in the generation of the ionospheric scintillations. From a practical point of view, the relationships between the solar wind and the ionospheric parameters can be used for the prediction of scintillations, if one takes into account the time delay between the IMF Bz and the equatorial ionospheric data.

Biktash, L.

408

Artificial life and Piaget.  

PubMed

Artificial life provides important theoretical and methodological tools for the investigation of Piaget's developmental theory. This new method uses artificial neural networks to simulate living phenomena in a computer. A recent study by Parisi and Schlesinger suggests that artificial life might reinvigorate the Piagetian framework. We contrast artificial life with traditional cognitivist approaches, discuss the role of innateness in development, and examine the relation between physiological and psychological explanations of intelligent behaviour. PMID:12691760

Mueller, Ulrich; Grobman, K H.

2003-04-01

409

An experimental and theoretical study of the mean diurnal variation of O/+/, NO/+/, O2/+/, and N2/+/ ions in the mid-latitude F1 layer of the ionosphere  

NASA Technical Reports Server (NTRS)

A theoretical model of the diurnal variations in the compositions of the ions O(+), NO(+), O2(+) and N2(+) in the midlatitude F1 layer is presented and compared with measurements made by AE-C. The theoretical model includes the rate coefficients and branching ratios for the dissociative recombination of NO(+), O2(+) and N2(+) with electrons and the ion-atom interchanges of O(+) with N2 and N2(+) with O. Input parameters to the model comprise measurements of ion and electron temperatures, neutral atmosphere composition, the solar EUV flux and the photoelectron spectrum. In general, model calculations are found to agree with satellite measurements, confirming the major ion sources and sinks of the photochemical model, which has an accuracy of + or - 60%.

Torr, D. G.; Torr, M. R.; Brinton, H. C.; Brace, L. H.; Spencer, N. W.; Hedin, A. E.; Hanson, W. B.; Hoffman, J. H.; Nier, A. O.; Walker, J. C. G.

1979-01-01

410

Numerical simulations on ion acoustic double layers  

Microsoft Academic Search

A numerical study of ion-acoustic double layer in the upper atmosphere has been performed for both periodic and nonperiodic systems by means of one-dimensional particle simulations. For a nonperiodic system, an external battery and a resistance are used to model the magnetospheric convection and the ionospheric Pedersen resistance. It is found that the number of double layers and the associated

T. Sato; H. Okuda

1981-01-01

411