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1

Artificial ionospheric layers during pump frequency stepping near the 4th gyroharmonic at HAARP.  

PubMed

We report on artificial descending plasma layers created in the ionosphere F region by high-power high-frequency (HF) radio waves from High-frequency Active Auroral Research Program at frequencies f(0) near the fourth electron gyroharmonic 4f(ce). The data come from concurrent measurements of the secondary escaping radiation from the HF-pumped ionosphere, also known as stimulated electromagnetic emission, reflected probing signals at f(0), and plasma line radar echoes. The artificial layers appeared only for injections along the magnetic field and f(0)>4f(ce) at the nominal HF interaction altitude in the background ionosphere. Their average downward speed ~0.5 km/s holds until the terminal altitude where the local fourth gyroharmonic matches f(0). The total descent increases with the nominal offset f(0)-4f(ce). PMID:23432261

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

2013-02-01

2

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

3

Geometric Aspects of Artificial Ionospheric Layers Driven by High-Power HF-Heating  

NASA Astrophysics Data System (ADS)

We have generalized earlier developed multi-scale dynamic model for the creation and propagation of artificial plasma layers in the ionosphere [Eliasson et al, 2012] by including two dimensional effects in the horizontal direction. Such layers were observed during high-power high frequency HF heating experiments at HAARP [Pedersen et al., 2010]. We have numerically investigated the importance of different angles of incidence of ordinary mode waves on the Langmuir turbulence and the resulting electron acceleration that leads to the formation of artificial ionospheric layers. It was shown that the most efficient electron acceleration and subsequent ionization is obtained at angles between magnetic zenith and the vertical, where strong Langmuir turbulence dominates over weak turbulence. A role played by the heating wave propagation near caustics was also investigated. Eliasson, B. et al. (2012), J. Geophys. Res. 117, A10321, doi:10.1029/2012JA018105. Pedersen, T., et al. (2010), Geophys. Res. Lett., 37, L02106, doi:10.1029/2009GL041895.

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

2013-12-01

4

Experimentally investigate ionospheric depletion chemicals in artificially created ionosphere  

NASA Astrophysics Data System (ADS)

A new approach for investigating ionosphere chemical depletion in the laboratory is introduced. Air glow discharge plasma closely resembling the ionosphere in both composition and chemical reactions is used as the artificially created ionosphere. The ionospheric depletion experiment is accomplished by releasing chemicals such as SF6, CCl2F2, and CO2 into the model discharge. The evolution of the electron density is investigated by varying the plasma pressure and input power. It is found that the negative ion (SF6-, CCl2F2-) intermediary species provide larger reduction of the electron density than the positive ion (CO2+) intermediary species. The negative ion intermediary species are also more efficient in producing ionospheric holes because of their fast reaction rates. Airglow enhancement attributed to SF6 and CO2 releases agrees well with the published data. Compared to the traditional methods, the new scheme is simpler to use, both in the release of chemicals and in the electron density measurements. It is therefore more efficient for investigating the release of chemicals in the ionosphere.

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

2012-09-01

5

Experimentally investigate ionospheric depletion chemicals in artificially created ionosphere  

SciTech Connect

A new approach for investigating ionosphere chemical depletion in the laboratory is introduced. Air glow discharge plasma closely resembling the ionosphere in both composition and chemical reactions is used as the artificially created ionosphere. The ionospheric depletion experiment is accomplished by releasing chemicals such as SF{sub 6}, CCl{sub 2}F{sub 2}, and CO{sub 2} into the model discharge. The evolution of the electron density is investigated by varying the plasma pressure and input power. It is found that the negative ion (SF{sub 6}{sup -}, CCl{sub 2}F{sub 2}{sup -}) intermediary species provide larger reduction of the electron density than the positive ion (CO{sub 2}{sup +}) intermediary species. The negative ion intermediary species are also more efficient in producing ionospheric holes because of their fast reaction rates. Airglow enhancement attributed to SF{sub 6} and CO{sub 2} releases agrees well with the published data. Compared to the traditional methods, the new scheme is simpler to use, both in the release of chemicals and in the electron density measurements. It is therefore more efficient for investigating the release of chemicals in the ionosphere.

Liu Yu; Cao Jinxiang; Wang Jian; Zheng Zhe; Xu Liang; Du Yinchang [CAS Key Laboratory of Basic Plasma Physics, Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

2012-09-15

6

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

7

Diagnostics of artificial ionospheric disturbances by method of pulse sounding  

Microsoft Academic Search

Experimental results of diagnostics of artificial disturbances in the ionosphere by means of sounding by short probing radio pulses are presented Experiments were carried out at the heating facilities Zimenki and Sura in Nizhny Novgorod region Russia Different parameters of the artificially disturbed ionosphere were derived from characteristic analysis of the observed signals caviton signal G I Terina J Atm

G. I. Terina

2006-01-01

8

Artificially created holes in the ionosphere  

NASA Technical Reports Server (NTRS)

The artificial creation of ionospheric holes by the release of highly reactive molecules into the F region is investigated. Through ion-atom interchange or charge transfer reactions, H2 or H2O reacts with O(+) to form OH(+) or H2O(+), respectively, which subsequently dissociatively recombines with electrons at a very rapid rate. The diffusion of H2 is also modified by chemical loss to the ambient atomic oxygen atmosphere. The limited spatial and temporal extent of the hole-making process allows several approximations to be made which permit three-dimensional analytic solutions of the continuity equations for the released particles, the O(+) and e(-) densities, and the intermediary molecular ions. A versatile formalism is developed whereby the hole-making capability of virtually any spatial-temporal configuration of released particles can be determined by convolving a set of destruction operators which can be viewed as Green's functions for the problem. As a specific application of the techniques developed, the modification of a winter nighttime ionosphere is described by simulating the release of 1000 kg of water vapor near a height of 300 km.

Mendillo, M.; Forbes, J. M.

1978-01-01

9

Evolution of Artificial Plasma Inhomogeneities in the Earth's Ionosphere  

NASA Astrophysics Data System (ADS)

The authors generalize for the first time in the literature the data concerning plasma clouds injection in the ionosphere. The difussion and drift of the plasma clouds in the magnetic fields are discussed in detail with taking account of real parameters of the ionosphere, the initial configuration of plasma and for arbitrary orientation of the artificial inhomogeneities. The works on modeling of the dispersion processes in the ionosphere are generalized. A comparison analysis of the experimental data and theoretical results has been given. The book is designed for specialists in the area of ionospheric physics and Near -Earth cosmic space. It can be usefull for students and doctorands in radiophysics, geophysics and radiocommunications.

Filipp, N. D.; Oraevskij, V. N.; Blaunshtein, N. Sh.; Ruzhin, Iu. Ya.

1986-10-01

10

Observation of artificial ionospheric irregularities on Doppler complex ``Spectr''  

NASA Astrophysics Data System (ADS)

At present there is a growing interest to research irregularities at the ionosphere both natural and artificial origin. This research has not only fundamental, but also practical importance for the questions connected with the radio wave propagation. This paper reports the results of our first experiments on registration as radio broadcast signals passed through the disturbed region of the ionosphere ( in this case, we received signals of Moscow exact time station at a frequency of 4996 kHz ) and a powerful radio wave signals used to heat the ionosphere (this method called self-scattering method when the pump wave creates artificial ionospheric irregularities and is scattered on them). Excitation of artificial ionospheric irregularities carried out using heating facility "Sura" , located 100 km eastward of Nizhny Novgorod (coordinates : f = 56,15 N , l = 46.1 E ). Receiving equipment was located in the Kazan (Volga ) Federal University , about 170 km eastward of Sura. Experiment which results are discussed in this paper was carried out from 19 to 22 March 2012. We used the window Fourier transform to analyze the change of radio wave spectrum with time. Quasi-periodic variations with significant amplitude were detected. The periods were equal or multiple to exposure period. The generation of artificial ionospheric disturbances by powerful radio emission of complex “Sura” can be cause of this variation which carries information about the excitation (gain) of internal gravity waves during periodic heating of the ionosphere by powerful HF radio waves.

Petrova, Inna; Latypov, Ruslan; Bochkarev, Vladimir

11

Morphology of meteoric plasma layers in the ionosphere of Mars  

E-print Network

Morphology of meteoric plasma layers in the ionosphere of Mars as observed by the Mars Global Radio Science data #12;Meteoric Plasma Layer EUV layer X-ray layer Meteoric layer Layer at 90 km Observations · 71 meteoric plasma layers in 5600 MGS profiles 5217R00A 4353T31A 3176Q39A 0350E42B #12

Withers, Paul

12

Artificial plasma jet in the ionosphere  

NASA Astrophysics Data System (ADS)

The dynamics of an artificially injected plasma beam in the near-earth space are analyzed in terms of the beam structure, its propagation across the magnetic field, and the resulting wave phenomena (Porcupine Project, flight 4, March 31, 1979). Out of the four ejectable canisters attached to the main payload, two were instrumented by the U.S., one by the USSR (the Xenon plasma beam experiment), and one by West Germany (carrying a barium ion jet experiment). The propagation of the plasma seems to occur in three stages, with high-frequency broad-band oscillations mainly localized in the 'core' of the jet, while low-frequency oscillations were spatially separated from it. The generation region of LF oscillations was found to be much wider than the jet core. As a result of the interaction between the plasma beam and the ambient medium a heating of electrons, up to energies of about 20 eV, associated with LF noise was observed. The behavior of high-energy ions and the observed HF wave phenomena need further analysis.

Haerendel, G.; Sagdeev, R. Z.

13

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

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

14

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

15

Artificial ionosphere turbulence features related to short-pulse modifications of ionosphere F2-region  

NASA Astrophysics Data System (ADS)

We present some experimental results concerning the features of artificial ionosphere turbulence AIT excited in the ionosphere F 2 -region by HF short-pulse tau p 25 ms -- 3 s powerful O-mode radio waves Measurements were carried out at the Sura heating facility in 2002 -- 2005 employing an additional pumping scheme In such a scheme one from three modules of the Sura facility is used to radiate a diagnostic wave which produces a diagnostic stimulated electromagnetic emission d-SEE The second powerful wave pump wave PW which is radiated by another two Sura modules is used as an external source of intensive plasma disturbances Propagating along geomagnetic field lines and changing conditions of d-SEE generation these disturbances are responsible for appearance of variations in d-SEE characteristics Because in the additional pumping scheme two separated in height disturbed volumes are produced in the ionosphere F 2 -region it allows to study an influence of different turbulence component on features of interaction of HF powerful radio wave with ionosphere plasma as well as to estimate a value of disturbance velocity along geomagnetic field lines It has been found that in d-SEE temporal evolution four stages can be derived 1 emission intensity decreasing in 5 -- 10 ms after the PW switch on 2 following growth of emission intensity in 20 -- 40 ms after the PW switch on which can be continued 10 -- 100 ms after PW switch off 3 following fast for le 100 ms relaxation of PW-induced emission intensity 4 slower

Frolov, V. L.; Nedzvetski, D. I.; Sergeev, E. N.

16

Anomalous dc resistivity and double layers in the auroral ionosphere  

SciTech Connect

There are at least four candidate instabilities which might account for anomalous dc rereresistivity in the auroral ionosphere. These are: the ion-acoustic instability, the Buneman instability, the ion-cyclotron instability and double layers. Results are reported of computer simulations of these four instabilities which suggest that double layers are most likely to be responsible for sistivity in the auroral zone.

Kindel, J.M.; Barnes, C.; Forslund, D.W.

1980-01-01

17

Model of Optical Emissions and Artificial Ionization Produced by Ionospheric HF-Heating  

NASA Astrophysics Data System (ADS)

Using the upgraded HAARP transmitter capabilities Pedersen et al., [2010] demonstrated for the first time the formation and control of artificial ionospheric layers by resonant F-region heating. The paper presents a model of the underlying physics based on preheating the electrons at the upper hybrid resonance followed by acceleration at the plasma resonant layer by the ensuing Langmuir turbulence. A number of component models are integrated in a novel numerical scheme to address the issue. A multi-grid approach based on propagation and the generalized Zakharov equations is used to study the formation of the Langmuir turbulence at the F-region peak. Super-thermal formation of electron tails is modeled by using a test particle approach as well as the solution of the diffusion equation in velocity space. A transport model including elastic and inelastic processes is used to study ionization and optical emissions. The model addresses several issues related to Artificial Plasma Layers, including thresholds for artificial ionization structure and the speed of the descending ionization front. The model results are compared with available observations. The work was supported by DARPA via a subcontract with BAE Systems, and by the ONR MURI Grant. Pedersen T., et al. Geophys. Res. Lett., 36, doi:10.1029/2009GL040047, 2009.

Milikh, G. M.; Elliason, B.; Shao, X.; Sharma, S.; Chang, C.; Mishin, E. V.; Papadopoulos, K.

2011-12-01

18

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

19

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

20

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

21

Effects of artificially modified ionospheres on HF propagation: Negative Ion Cation Release Experiment 2 and CRRES Coqui experiments  

Microsoft Academic Search

We report the results of measurements obtained in conjunction with a series of high-altitude chemical release experiments of effects of artificially modified ionospheres upon high-frequency, ionospherically reflected radio paths. Computer simulations indicate that under optimum conditions, ionospheric modifications induced by chemical releases could perturb or even disrupt a communication channel; our experiments corroborate this but also indicate that it is

T. Joseph Fitzgerald; Paul E. Argo; Robert C. Carlos

1997-01-01

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

Laboratory simulation of ionospheric double-layers  

NASA Technical Reports Server (NTRS)

A mechanism for double-layer formation in partially- or fully-ionized plasmas is described, founded on beam-plasma interaction: RF growth along the beam excites a rectified, ponderomotive electric field, which in turn causes charge separation. Laboratory studies of the mechanism are described.

Crawford, F. W.; Levine, J. S.; Ilic, D. B.

1979-01-01

24

Weak double layers in the auroral ionosphere  

NASA Technical Reports Server (NTRS)

Previous work on the evolution of weak double layers in a hydrogen plasma was extended to include H(+) and O(+) with relative drift. The relative drift between hydrogen and oxygen ions due to a quasi-static parallel electric field gives rise to a strong linear fluid instability which dominates the ion-acoustic mode at the bottom of the auroral acceleration region. This ion-ion instability can modify ion distributions at lower altitudes and the subsequent nonlinear evolution of weak double layers at higher altitudes in the ion-acoustic regime. Ion hole formation can occur for smaller relative electron-ion drifts than seen in previous simulations, due to the hydrogen-oxygen two-stream instability. This results in local modification of the ion distributions in phase space, and a partial filling of the valley between the hydrogen and oxygen peaks, which would be expected at higher altitudes on auroral field lines. The observed velocity diffusion does not necessarily preclude ion hole and double layer formation in hydrogen in the ion-acoustic regime. These simulation results are consistent with the experimentally measured persistence of separate hydrogen and oxygen peaks, and the observation of weak double layers above an altitude of 3000 km on auroral field lines.

Hudson, M. K.; Crystal, T. L.; Lotko, W.; Barnes, C.

1987-01-01

25

Characterization of the lower layer in the dayside Venus ionosphere  

NASA Astrophysics Data System (ADS)

The dayside Venus ionosphere consists of two layers: the V2 layer at 141 km, produced by solar extreme ultraviolet (EUV) photons, and the V1 layer at 127 km, produced by solar soft X-rays. The influence of solar zenith angle (SZA) and solar irradiance has been well characterized for the V2 layer, but not the V1 layer, where previous efforts were limited by data scarcity and incomplete SZA coverage. Here we use over 200 radio occultation profiles from Venus Express to characterize how the V1 peak altitude, peak density, and morphology respond to changes in SZA and solar activity. The V1 and V2 peak altitudes do not vary with SZA, and both peak electron densities vary with SZA in a Chapman-like manner. These results imply that the thermal structures of the atmosphere and ionosphere between 141 km and 127 km vary little with SZA. Also, the V1 peak density increases more with solar activity than the V2 peak density and the V1 morphology can change much more than the V2 morphology. These results are due to the soft X-ray flux increasing relative to the EUV flux as solar activity increases.

Girazian, Zachary; Withers, Paul; Paetzold, Martin; Tellmann, Silvia; Peter, Kerstin

2014-11-01

26

A sporadic layer in the Venus lower ionosphere of meteoric origin M. Patzold,1  

E-print Network

A sporadic layer in the Venus lower ionosphere of meteoric origin M. Pa¨tzold,1 S. Tellmann,1 B. Ha meteor layer electron densities increase with decreasing solar zenith angle. Layer shapes are symmetric in the Venus lower ionosphere of meteoric origin, Geophys. Res. Lett., 36, L05203, doi:10.1029/ 2008GL035875. 1

Mendillo, Michael

27

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

NASA Astrophysics Data System (ADS)

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

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

28

Generation of Artificial Ionospheric Irregularities in the Midlatitude Ionosphere Modified by High-Power High-Frequency X-Mode Radio Waves  

NASA Astrophysics Data System (ADS)

We consider the properties of the artificial ionospheric irregularities excited in the ionospheric F 2 region modified by high-power high-frequency X-mode radio waves. It is shown that small-scale (decameter) irregularities are not generated in the midlatitude ionosphere. The intensity of irregularities with the scales l ? ?50 m to 3 km is severalfold weaker compared with the case where the irregularities are excited by high-power O-mode radio waves. The intensity of the larger-scale irregularities is even stronger attenuated. It is found that the generation of large-scale ( l ? ?5-10 km) artificial ionospheric irregularities is enhanced at the edge of the directivity pattern of a beam of high-power radio waves.

Frolov, V. L.; Bolotin, I. A.; Komrakov, G. P.; Pershin, A. V.; Vertogradov, G. G.; Vertogradov, V. G.; Vertogradova, E. G.; Kunitsyn, V. E.; Padokhin, A. M.; Kurbatov, G. A.; Akchurin, A. D.; Zykov, E. Yu.

2014-11-01

29

Patch antennas with new artificial magnetic layers  

E-print Network

A new type of high-impedance surfaces (HIS) has been introduced by C.R. Simovski et al. recently. In this paper, we propose to use such layers as artificial magnetic materials in the design of patch antennas. The new HIS is simulated and patch antennas partially filled by these composite layers are measured in order to test how much the antenna dimensions can be reduced. In order to experimentally investigate the frequency behavior of the material, different sizes of the patches are designed and tested with the same material layer. Also the height of the patch is changed in order to find the best possible position for minimizing the antenna size. This composite layer of an artificial magnetic material has made the antenna smaller while keeping the bandwidth characteristics of the antenna about the same. About 40% of size reduction has been achieved.

M. Ermutlu; C. R. Simovski; M. Karkainen; P. Ikonen; A. A. Sochava; S. A. Tretyakov

2005-04-11

30

Modeling of self-consistent artificial radiowave ionospheric turbulence pumping and damping  

NASA Astrophysics Data System (ADS)

The numerical simulations of the action of self-consistent powerful radiowave absorption arising in the regions of artificial plasma turbulence excitation at formation, saturation and relaxation stages of the turbulence structures (Kochetov, A.V., Mironov, V.A., et. al., Physica D, Nonlinear phenomena, 2001, 152-153, 723) to refection index dynamics are carried out. The nonlinear Schr"odinger equation in inhomogeneous plasma layer with incident electromagnetic wave pumping and backscattered radiation damping (Kochetov, et al, Adv. Space Res., 2002, 29, 1369 and 2006, 38, 2490) is extended with the imaginary part of plasma dielectric constant, which results the energy transformation from electromagnetic wave to plasma one 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 modeling reproduces the basic energy transformation peculiarities: hard excitation, non-linearity, hysteresis (A.V. Kochetov, E. Mjølhus, Proc. of IV Intern. Workshop ``SMP,'' Ed. A.G. Litvak, Vol.2, N. Novgorod, 2000, 491) and demonstrates 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).

Kochetov, Andrey

2011-11-01

31

Evolution and dynamics of ionospheric intermediate layers above Arecibo Observatory  

NASA Astrophysics Data System (ADS)

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

Bishop, Rebecca Lynn

2001-11-01

32

Artificial modification of the ionosphere by launches of rockets which insert space vehicles into orbit  

NASA Astrophysics Data System (ADS)

Results are presented from vertical (ionogram) and inclined (frequency and signal strength variations of reference shortwave stations) probing of artificial ionospheric disturbances (AIDs) formed by powerful rockets during the active portion of their flight. Experimental data obtained over the course of several dozen rocket launches are generalized. The processes of evolution of an AID initiated by shock-acoustic waves are studied theoretically and experimentally, together with questions of shortwave radio scattering on such disturbances.

Nagorskii, P. M.; Tarashchuk, Yu. E.

1993-10-01

33

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

34

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

E-print Network

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 SaÃ? o Luis. Experimental evidence for the F3 layer has been observed in ionograms recorded at Fortaleza and these were

Boyer, Edmond

35

TRANSIENT LAYERS IN THE TOPSIDE IONOSPHERE OF MARS Andrew James Kopf  

E-print Network

path length near the peak in the density profile, where ne/z = 0. 2. Two ionograms that show the presence of a second layer above the main ionospheric layer. Ionogram (A) has a cusp with a vertex, which well above the peak of the main layer. Ionogram (B) has a step without a cusp-shaped vertex, which

Gurnett, Donald A.

36

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

37

Temporal behaviour of artificial small-scale ionospheric irregularities: Review of experimental results  

NASA Astrophysics Data System (ADS)

Features of artificial small-scale ionospheric irregularities (ASI) induced at F-region heights by powerful HF waves are discussed. The investigations presented here were performed during the past two decades at the Zimenki and Sura heating facilities, located at middle latitudes near Nizhniy Novgorod, Russia, as well as at the Gissar facility located at a lower latitude near Dushanbe, Tadzhikistan. The measurements were made by a variety of diagnostic methods employing artificial field-aligned scattering of HF and VHF radio waves, sounding of the disturbed region by means of low-power probing waves and testing of the artificial turbulence by means of stimulated electromagnetic emission (SEE). The dependence of ASI on such parameters as transverse scale length of the artificial irregularities, their location in the disturbed region, the power of the heating wave, the duration of HF radiation, geophysical conditions, aftereffects of the preceding modification, and the schedule of heater operation is considered for both the development stage after pump turn-on and the decay stage after pump turn-off. The temporal evolution of ASI spectral characteristics during the heater period is discussed. An empirical model for the ASI, based on the data available, was elaborated and verified by computer simulation of SEE generation.

Frolov, V. L.; Erukhimov, L. M.; Metelev, S. A.; Sergeev, E. N.

1997-12-01

38

Sporadic E ionization layers observed with radar imaging and ionospheric modification  

NASA Astrophysics Data System (ADS)

Sporadic E ionization layers have been observed in the daytime subauroral ionospheric E layer by a 30 MHz radar in Alaska. The radar detects coherent backscatter from meter-scale field-aligned plasma density irregularities. The irregularities were generated by ionospheric modification—by the emission of strong HF electromagnetic waves directly beneath the layers—making the layers visible to the radar. Aperture-synthesis methods are used to generate imagery of the layers from the radar data. The layers are patchy, with patches organized along fronts spaced by tens of kilometers and propagating slowly toward the southwest. Similar, naturally occurring layers are commonly observed at middle latitudes at night in the absence of ionospheric modification. That the patchy layers can be found at high magnetic latitudes during the day argues that they are most likely produced through the interaction of the ionospheric layer with neutral atmospheric waves and instabilities. Attenuation of the radar echoes when the HF emission frequency exceeded the third harmonic of the electron gyrofrequency was observed and is discussed.

Hysell, D. L.; Munk, J.; McCarrick, M.

2014-10-01

39

Frequency characteristics of modification effects of high-power radio waves on the ionospheric F-layer  

Microsoft Academic Search

The paper presents experimental results concerning the effect of artificial ionospheric irregularities on the characteristics of linear-FM signals for vertical and oblique sounding of the ionosphere. The radio-transmitting facility operated at a frequency of 4.8 MHz with a power of 200 MW. The effects observed on the linear-FM ionograms are classified according to the effects of artificial irregularities of different

L. M. Erukhimov; V. A. Ivanov; N. A. Mitiakov; V. P. Uriadov; V. A. Frolov

1987-01-01

40

Characterization of propagation and communication properties of the natural and artificially disturbed ionosphere. Final report, September 1990-December 1994  

SciTech Connect

This basic research project, conducted during the period starting 12 September 1990 and ending 12 December 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, B.W.; Sales, G.S.; Brent, R.; Ostergaard, J.; Huang, Y.

1995-05-01

41

Simulation of vertical incidence ionograms by ray tracing method in the presence of replacement layer and ionospheric trough  

Microsoft Academic Search

Theoretical ionograms in the presence of a replacement layer and an ionospheric trough are calculated using the ray tracing method. A versatile ionospheric model is applied. Two examples are given where the traces in the ionogram produced by oblique reflections at a horizontal electron density gradient show anomalous behavior. In one case the high frequency part and in the other

T. Nygren

1977-01-01

42

Effects of artificially modified ionospheres on HF propagation: Negative Ion Cation Release Experiment 2 and CRRES Coqui experiments  

NASA Astrophysics Data System (ADS)

We report the results of measurements obtained in conjunction with a series of high-altitude chemical release experiments of effects of artificially modified ionospheres upon high-frequency, ionospherically reflected radio paths. Computer simulations indicate that under optimum conditions, ionospheric modifications induced by chemical releases could perturb or even disrupt a communication channel; our experiments corroborate this but also indicate that it is very difficult to actualize such disruptions. Our experiments have shown that an ionospheric depletion, in which the electron density hole forms a huge radio frequency lens, generates new modes which, however, do not significantly affect a communications system. Under optimum path geometry a signal strength decrease of 10 dB or more is possible for several tens of minutes. Enhancements, such as those produced by barium releases, act as reflecting mirrors that can create a large shadow zone on the ground and block off significant amounts of energy. We measured signal strength decreases of up to 20 dB.

Fitzgerald, T. Joseph; Argo, Paul E.; Carlos, Robert C.

1997-03-01

43

Effects of artificially modified ionospheres on HF propagation: Negative Ion Cation Release Experiment 2 and CRRES Coqui experiments  

SciTech Connect

We report the results of measurements obtained in conjunction with a series of high-altitude chemical release experiments of effects of artificially modified ionospheres upon high-frequency, ionospherically reflected radio paths. Computer simulations indicate that under optimum conditions, ionospheric modifications induced by chemical releases could perturb or even disrupt a communication channel; our experiments corroborate this but also indicate that it is very difficult to actualize such disruptions. Our experiments have shown that an ionospheric depletion, in which the electron density hole forms a huge radio frequency lens, generates new modes which, however, do not significantly affect a communications system. Under optimum path geometry a signal strength decrease of 10 dB or more is possible for several tens of minutes. Enhancements, such as those produced by barium releases, act as reflecting mirrors that can create a large shadow zone on the ground and block off significant amounts of energy. We measured signal strength decreases of up to 20 dB.{copyright} 1997 American Geophysical Union

Fitzgerald, T.J.; Argo, P.E.; Carlos, R.C. [Los Alamos National Laboratory, Los Alamos, New Mexico (United States)] [Los Alamos National Laboratory, Los Alamos, New Mexico (United States)

1997-03-01

44

Gyroharmonic Features of Generation of Artificial Irregularities Hf-Induced in the Ionospheric F_2 Region  

NASA Astrophysics Data System (ADS)

In the report, basing on experimental data obtained at the SURA heating facility [1-4], we consider gyroharmonic features of generation of artificial irregularities HF-induced in the ionospheric F _{2} region. In [5] it was revealed that, when the pump wave frequency (f _{PW}) is slightly above the 4th electron gyro harmonic frequency (4f_{ce}) in the ionosphere disturbed volume, spectra of signals field-aligned scattered from irregularities with l_? ? 10 - 20 m had widths up to DeltaF ? 10 Hz in comparison with DeltaF ? 0.5 Hz, when the f _{PW} was below 4f_{ce}. Obtained in our experiments data have shown that the scattering from decameter irregularities consists of two components (narrow- and wideband) distinguished by their spectral characteristics, relaxation times, and dependence on f _{PW}. The narrowband component is related to scattered signals when f _{PW} is outside the gyro harmonic frequency range. The wideband component is observed at deltaf = f_{PW} - 4f_{ce} ? 0 - 150 kHz and shows well-pronounced gyro features; it has the maximum width (up to 10 Hz) at deltaf_{m} ? 20 - 60 kHz, where the BUM component in SEE spectra has the greatest intensity. A typical growth time for the wideband component is of the same order of magnitude as the growth time of decameter irregularities (0.3 - 0.5 s); its typical decay time is of about 0.4 - 0.9 s, which is much shorter of the decay time for decameter irregularities. It is significant that at the decay stage the fast narrowing of the wideband component spectra is observed. In [4] it was observed short-term decreases in TEC of about 0.03 - 0.05 TECU when a sounding wave crossed the magnetic zenith region in the ionosphere disturbed volume. According to [6] such TEC variations can be produced by generation of super small-scale striations with l_? ? 10 - 20 sm. Basing on obtained experimental data it may be concluded that not only the generation of small-scale irregularities with l_? < 50 m, but the generation of medium- and larger-scale irregularities with scale-lengths from 100 m to a few km has also gyro properties. It means that the generation of high-frequency plasma waves exerts some influence on development of these irregularities, most likely through the generation of small-scale striations. The work was supported by RFBR grants (## 12-05-00312, 13-02-12074, 13-02-12241) and by the scientific program “Geophysics”. References: 1. V.L. Frolov, et al. // Radiophys. Quant. Electron., Engl. Transl., 2000. V. 43(6), p. 446. 2. Kagan, L.M., et al. // J. Radiophysics and Radio Astronomy, 11(3), 221-242, 2006. 3. Frolov V.L., et al. // Radiophys. Quant. Electron., Engl. Transl., 2008. Vol. 51(5), p. 367. 4. Frolov V.L., et al. // Radiophys. Quant. Electron., Engl. Transl., 2012. Vol.55(6), p. 357. 5. Ponomarenko et al. // J. Geophys. Res., 1999. Vol. 104, No. A5, p. 10,081. 6. Gurevich and Zybin. // Phys. Lett. A. 2006. Vol. 358, p.159.

Frolov, Vladimir; Akchurin, Adel; Bolotin, Ilya; Zykov, Evgeniy; Vertogradov, Gennadiy

45

Generation of Artificial Ionospheric Irregularities by the Modification of the Earth's Middle-Latitude Ionosphere by X-Mode Powerful HF Radio Waves  

NASA Astrophysics Data System (ADS)

Basing on experimental data obtained at the SURA heating facility by modification of the Earth’s middle-latitude ionosphere, we consider in the report some peculiarities of the generation of artificial plasma density irregularities when X-mode powerful waves (PW) are used for ionosphere pumping [1]. Experiments were carried out during 2008 - 2012 under quite ionospheric conditions (Sigma K_p = 10 - 30). Analysis of obtained experimental data has shown that: 1) In our measurements the generation of small-scale irregularities with l{_?} {?} 10 - 20 m is not observed in contrast to analogous measurements conducted at the EISCAT-heater [2,3]. 2) The generation of irregularities with l{_?} {?} 50 m - 3 km is mainly observed in evening and night hours. In these conditions their intensity is by 3 to 4 times below in comparison with the O-mode pumping. During day hours these irregularities are not detected due to both strong PW energy absorption in the lower ionosphere and forming a defocusing lens at altitudes of 130 - 150 km [4]. 3) The generation of irregularities with l{_?} {?} 5 - 10 km is only observed in evening and night hours. In these conditions their intensity is by 10 times below in comparison with the O-mode pumping. 4) The generation of the irregularities with l{_?} {?} 50 m is observed only when the PW reflects in the ionospheric F _{2} region. 5) Under day-time conditions the defocusing lens is forming at altitudes of about of 130 - 150 km when the ionosphere is pumping both X- and O- mode powerful waves [4]. Its horizontal size is determined by the HF beam. In our experiments [1] it was revealed that the stronger generation of irregularities with scale-lengths l{_?} {?} 5 - 10 km is observed at the HF beam edge where the effective radiated power is of about 0.1 P _{max}. Such a “beam-edge” effect is also observed when the ionosphere is modified by O-mode PW. The enhancement of irregularity generation at the HF beam edge was considered in [5]. The work was supported by RFBR grants (## 12-05-00312, 13-02-12074, 13-02-12241, 14-05-31445, 14-05-00855, 14-05-10069), grant MK-2670.2014.5, and by the scientific program “Geophysics”. References: 1. Frolov et al. // Radiophys. Quant. Electron., Engl. Transl., 2013 (submitted for publication). 2. Blagovethshenskaya N.F., et al. // Geophys. Res. Lett., 2011. Vol. 38, L08802, doi:10.1029/2011GL046724. 3. Blagoveshchensraya N.F. et al. // J. Atmos. Sol.-Terr. Phys., 2013. Vol. 105-106, p. 231. 4. Boiko G.N. et al. // Radiophys. Quant. Electron., Engl. Transl., 1985. Vol. 28, No. 8, p. 960. 5. Kuo S., et al. // Geophys. Res. Lett., 2010. Vol. 37, L01101, doi:10.1029/2009GL041471.

Frolov, Vladimir; Padokhin, Artem; Kunitsyn, Viacheslav; Akchurin, Adel; Bolotin, Ilya; Zykov, Evgeniy; Vertogradov, Gennadiy

46

Simultaneous observations of thin ion layers and the ionospheric electric field over Sondrestrom  

NASA Astrophysics Data System (ADS)

We present the results of a series of incoherent-scatter radar experiments conducted at Sondrestrom, a high-latitude station (invariant latitude, 73.9°) over the period August 1994 through August 1998. A novel radar mode was employed that allowed simultaneous observation of the structure of thin ion layers along the geomagnetic meridian and of the accompanying ionospheric electric field; however, only layers with peak densities exceeding ~1×105cm-3 could be detected. Layers were observed during 31 out of 85 experiments for a total of 43 distinct events. The overall objective of this investigation was to examine the limits of the current theory of layer formation. Several features are evident in the data: (1) individual layers tend to be ``patchy'' in both a spatial and a temporal sense; (2) the direction of the ionospheric electric field when layers were observed is consistent with theory, but for northwesterly fields the layers form ~10 km lower than expected; (3) variation in a layer's altitude along the geomagnetic meridian can often be correlated to corresponding variation in the direction of the electric field; (4) layers tend to appear when the electric field suddenly changes in direction, magnitude, or both and then remain steady; and (5) layers often disappear from the field of view despite the continued existence of a favorable electric field. We suggest that the altitude discrepancy alluded to in item 2 may result from a systematic error in the model for ion-neutral collision frequency widely employed in studies of thin metallic-ion layers. We also suggest that horizontal drift of layer structures may play an important role in explaining items 4 and 5, which are otherwise difficult to reconcile with the prevailing theory.

Bedey, David F.; Watkins, Brenton J.

2001-05-01

47

Unifying Undergraduate Artificial Intelligence Robotics: Layers Of Abstraction Over Two Channels  

E-print Network

Unifying Undergraduate Artificial Intelligence Robotics: Layers Of Abstraction Over Two Channels Annapolis, Maryland 21402 Abstract From a Computer Science and Artificial Intelligence perspec- tive based on these ideas. Introduction Modern Artificial Intelligence Robotics education treats the field

Crabbe, Frederick

48

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

49

Anomalous Behavior of D-Layer Preparation Time of the Ionosphere Due to Earthquakes as observed from Malda (India)  

SciTech Connect

The anomalous behavior of D-layer preparation time of the ionosphere are observed only before, during and after the earthquakes, which took place in the neighbouring region by monitoring the Very Low Frequency (VLF) signal using Gyrator II loop antenna. The anomalies were also observed in the sunrise terminator times during seismically active days. These anomalous behavior may be due to the Lithosphere-Ionosphere coupling. These anomalies may be a precursor of earthquake.

Chatterjee, Achintya K.; Nandy, Nilmadhab; Bari, Md. Washimul; Choudhury, Asit K. [Indian Centre for Space Physics (Malda Branch), Atul Market, Malda, West Bengal, Inda, 732101 (India)

2010-10-20

50

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

51

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

Microsoft Academic Search

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

W. I. Axford

1963-01-01

52

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

53

Observations of the artificially injected Porcupine xenon ion beam in the ionosphere  

NASA Astrophysics Data System (ADS)

Results are given of ion beam injection experiments performed in the auroral ionosphere in connection with the German Sounding Rocket Project Porcupine. A heavy (xenon) ion beam was injected into the collisionless ionospheric plasma approximately perpendicular to the ambient magnetic field at altitudes from 190 km to about 450 km. The beam propagates nearly undistorted across the plasma because it is essentially depolarized; at the same time the beam is not current neutralized. This unexpected behavior poses the interconnected problems of how the beam manages to become charge neutralized, how current closure is maintained, and what is the mechanism of depolarization.

Haeusler, B.; Treumann, R. A.; Bauer, O. H.; Haerendel, G.; Bush, R.

1986-01-01

54

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

NASA Astrophysics Data System (ADS)

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

Akchurin, Adel; Bochkarev, Vladimir

55

Excitation of the lower oblique resonance by an artificial plasma jet in the ionosphere  

NASA Astrophysics Data System (ADS)

Aboard the Porcupine rockets, bursts of noise were detected in the electron whistler range during the operation of a xenon plasma gun on a package ejected from the main payload. These observations can be interpreted in terms of excitation of the lower oblique resonance by instabilities associated with the motion of the xenon ion beam through the ionospheric plasma.

Thiel, J.; Storey, L. R. O.; Bauer, O. H.; Jones, D.

1984-04-01

56

Variations in the fractal dimension of fluctuations of the ionospheric F2 layer critical frequency  

NASA Astrophysics Data System (ADS)

The 40-year period of observations of short-term variations (with characteristic times of up to 1-2 days) in the critical frequency of the ionospheric F2 layer ( foF2) is analyzed. The continuous (with a step of 1 h) series of fluctuations ( F) of the foF2 critical frequency (with eliminated daily variations) has been calculated using the hourly variations in foF2 at Moscow stations. The fractal dimension (FRH) of the fluctuations, characterizing short-term variations in foF2, has been determined and analyzed on a 30-day interval, using the Higuchi method. It has been established that FRH estimates substantially change in time. The 11-year cycle, which is in antiphase with the solar cycle, and the total annual and semiannual variations, similar to the variations observed in the normalized critical frequency of the E region and in the electron density of the D region, are clearly defined in these changes. Thus, the parameters of fast variations in the ionospheric F2 layer are affected by the phase of the 11-year solar cycle and by the position of the Earth in the orbit or seasonal variations in the atmosphere.

Chertoprud, V. E.; Leshchenko, L. N.; Givishvili, G. V.; Goncharova, E. E.; Ivanov-Kholodny, G. S.

2009-08-01

57

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

58

Ionospheric disturbances in D-layer recorded by VLF receiver at Tashkent IHY station  

NASA Astrophysics Data System (ADS)

Tashkent International Heliophysical Year (IHY) station is a member of Atmospheric Weather Electromagnetic System for Observation, Modeling and Education (AWESOME) network being operated globally to study the ionosphere and the magnetosphere with the help of electromagnetic waves in Very Low Frequency (VLF) band. Regular monitoring of the D- and F-layers of ionosphere over Central Asia territory is being performed on the permanent basis starting year 2008. Solar flare events are permanently observed and the analysis showed that there is simultaneous correlation between the times of change of amplitude of the waves and the Solar flares. Features of the lightning discharge generated by radio atmospherics are studied and its effectiveness in D-region ionosphere diagnostics is explained. We have studied VLF amplitude anomalies related to the earthquakes (EQs) occurred in the recent years with magnitude more than 5 on the path way from the VLF transmitters to the Tashkent station assuming that propagation of VLF ground-based transmitters signals can be perturbed by EQ preparation can be detectable from the ground-based measurements in the VLF bands. For analyzing narrowband data we have used the Nighttime Fluctuation (NF) method paying attention to the data obtained during the local nighttime (20:00 LT-04:00 LT). The mean nighttime amplitude (or trend) and nighttime fluctuation are found to increase significantly before the EQ occurred on the path way from the transmitters to the receiver. The obtained results have revealed an agreement with VLF amplitude anomalies observed in Tashkent VLF station during the strong EQs occurred on the path way from the transmitters to the receiver. Some results are presented to show the probing potentiality of VLF waves to predict short term EQs with high magnitude.

Ahmedov, Bobomurat

59

Comparison of a Multi-Layered Artificial Immune System with a Kohonen Network  

E-print Network

Comparison of a Multi-Layered Artificial Immune System with a Kohonen Network T. Knight and J Networks on some clustering tasks. I. INTRODUCTION Many artificial immune systems (AIS) have been devel is organised as follows. Section II presents a novel multi-layered artificial immune system inspired

Timmis, Jon

60

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

61

An empirical model of the occurrence of an additional layer in the ionosphere from the occultation technique: Preliminary results  

NASA Astrophysics Data System (ADS)

8 year electron density profile (EDP) data from the COSMIC/FORMOSAT-3 satellites radio occultation technique were used to investigate the additional stratification of the F2 (the so-called F3 layer) layer over the equatorial and low-latitude ionosphere on a global scale for both the bottomside and topside ionosphere. The F3 layer was recognized through the altitude differential profile featured by two maxima existing from the selected EDP profile. There were ~37,000 (bottomside) and 25,000 (topside) cases of F3 layer selected out of ~1.27 million occultation events at equatorial and low-latitude areas during the period of April 2006 to August 2014. The statistical results for the bottomside ionosphere resemble that reported in Zhao et al. (2011a), while in the topside the highest occurrence of F3 layer shows a 3-4 h delay depending on the altitude range of the stratification. The magnetic latitude distribution shows different dependence with a tendency to form a single crest toward high altitude. Also, the seasonal variation is weaker in the topside ionosphere compared to the bottomside one, especially in the high altitude. Then we build up an empirical model of the F3 layer occurrence using the bottomside statistics based on empirical orthogonal function (EOF) decomposition as it gets the inherent characters inside the data set and converges quickly. The model well grasps the main features of the F3 occurrence, e.g., the F3 occurrence's sensitivity on the magnetic latitude. Further, in order to accommodate the ground observation a corrected factor was introduced. As F3 layer is an important phenomenon in the low-latitude ionosphere, we have made an attempt to describe its feature with a consecutive function although future work needs to be done for an overall expression of this structure.

Zhao, Biqiang; Zhu, J.; Xiong, B.; Yue, X.; Zhang, M.; Wang, M.; Wan, W.

2014-12-01

62

Modelling of the equatorial ionospheric E-layer based on cos ? index  

NASA Astrophysics Data System (ADS)

Daytime hourly values of the critical frequency of the ionospheric E-layer, f oE, obtained at Ouagadougou Ionospheric Observatory (12.4°N, 1.5°W) in Burkina Faso, West Africa, an equatorial station, during the solar cycle 22 (1985-1995) have been used to develop a model based on solar zenith angle through cos ? index factor using the relation f oE = a (cos ?)n, The average value of the diurnal cos ? index, n, at Ouagadougou was found to be 0.30 for both low and high solar activity. The model was tested with f oE data from Korhogo (9.3°N, 5.4°W) in Cote-d'Ivoire, another equatorial station, and there is good agreement between the model and observations. The validity of the f oE model was also compared with predicted values by IRI-2012 model and good agreement has been observed. The percentage difference, when f oE observed compared with IRI-2012 model, was found to be within f ±10% for both equinoxes and solstices for the two levels of solar activity.

Kazeem, A. K.; Adeniyi, J. O.; Adediji, A. T.

2014-06-01

63

MST radar measurement of ionospheric F region winds: The “layer wind” technique  

NASA Astrophysics Data System (ADS)

We develop an improved application of the mesosphere-stratosphere-troposphere (MST) radar technique for the measurement of winds at ionospheric F region altitudes. While the experiment is basically one of incoherent scatter (IS), which yields very weak signals at the usual operating frequencies of MST radars, we develop an analysis technique that allows the signals to be integrated over the entire F region of the ionosphere to gain sufficient statistical accuracy to compute the "layer wind" accurately. This method is contrasted with the normal IS method of determining winds at discrete heights. The method is applied to data collected with the middle and upper atmosphere radar in Japan, though it is applicable to any MST radar having a comparable or even somewhat smaller power-aperture product and may also be adapted for improved results from mainline IS radars. Using this method, we are able to discuss confidently the geophysical behavior of the wind on individual days, whereas previously we were reluctant to discuss anything but climatological features from data averages.

Oliver, W. L.; Otsuka, Y.; Fukao, S.

1998-07-01

64

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

NASA Astrophysics Data System (ADS)

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

Ahmedov, Bobomurat

2012-07-01

65

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

Microsoft Academic Search

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

Kh. Akmamedov

1993-01-01

66

Two-windows Ionospheric Drift Measurement at Heights 90150 km During Sporadic E-layer Occurrence Using Digisonde DPS-4  

E-print Network

for sounding E and F layers of the ionosphere [Davies, 1990]. Digisonde records an ionogram every 15 minutes, except special campaigns of higher sampling rate. Ionogram autoscaling process "ARTIST" automatically the ionogram sounding). Therefore, sounding frequencies vary from measurement to measurement according

Santolik, Ondrej

67

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

NASA Astrophysics Data System (ADS)

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

Kyzyurov, Yurij; Chernogor, Leonid F.

68

A Response of The Night Ionospheric F Layer To The Passage of Atmospheric Gravity Waves  

NASA Astrophysics Data System (ADS)

Results of experimental studies of a response of the midlatitude nighttime ionospheric F layer to passing atmospheric gravity waves are discussed. Nighttime observations of the F layer were carried out by a digital ionosonde at Almaty (76 55 E, 43 15 N) since June 2000 till May 2001. The ionograms were analyzed for temporal variations of the virtual height (hf(t)) at a series of specific frequencies (the virtual height of a constant electron content), critical frequency of the F-layer (f0F), and height profiles of electron content (N(h) - profiles). A significant part of observations showed defi- nite wave structures on the hf(t) variations observed throughout the entire night, but corresponding f0F variations were less discernible. These hf(t) and f0F variations were always in antiphase. From the h f(t) there was evidence of downward phase propagation of the observed waves. The temporal behavior of the electron content at series of specific heights allowed obtaining height profiles of the wave amplitude (el/m3). A total of 64 height profiles was analyzed. The common shape of these height profiles can be approximated as a parabola with its average thickness (defined at the level of 0.5 maximum amplitude) estimated as 60 km. The altitude of the maximum amplitude was scattered between 200 and 300 km with the most probable value of 240 km (in 62.5% of all events the altitude was ranged between 220 and 260 km). A weak dependence on the magnetic activity was found. During magnetic storms there was a tendency for the maximum amplitude, its altitude, and the thickness of the height amplitude profiles to be larger than those for the quiet magnetic conditions. A sequence of N(h)-profiles calculated for a period of the passing wave showed them to move up and dawn in phase with the passing wave. As the F layer is lifted by the positive surge in gravity wave, the electron content at the F peak decreases, the slab thickness being increased. Subsequently, the opposite happens as hmF falls below its equilibrium value. Such a character of the F layer behavior is remarkably consistent with results of a modeling study of the atmospheric and ionospheric response to a sin- gle short burst of enhanced ion convection at high latitudes (Millward et al. J. Geoph. Res., 1993, v. 98, No. A11, 19173-19179).

Ashkaliev, Ya. F.; Gordienko, G. I.; Jacobi, Ch.; Litvinov, Yu. G.; Vodyannikov, V. V.; Yakovets, A. F.

69

Peculiar features of ionospheric F3 layer during prolonged solar minimum (2007-2009)  

NASA Astrophysics Data System (ADS)

We present the seasonal and local time occurrence of ionospheric F3 layer over Tirunelveli (geographic longitude 77.8°E, geographic latitude 8.7°N, dip 0.7°) during extremely low and prolonged solar activity period (2007-2009). Canadian Advanced Digital Ionosonde observations from this station are used in the present study. We find that the occurrence of F3 layer is nearly 3 times higher during 2009 (˜ 48%) as compared to that during 2007 (˜16%). The increase of this order just within the low solar activity period is unusual. In earlier studies similar increase in F3 occurrence has been reported when solar activity changes from high (F10.7=182) to low (F10.7=72). The other important feature is the presence of postnoon F3 layers which are observed dominantly during summer solstice of 2009. Such occurrence of postnoon F3 layers was nearly absent during summer solstice of the previous solar minimum (1996) over nearby dip equatorial station Trivandrum. We take equatorial electrojet (EEJ) as a proxy for eastward electric field. It is noticed that the EEJ strength and the maximum rate of change of EEJ are higher for F3 days as compared to those on non-F3 days. We find that the peak occurrence of prenoon F3 layer closely coincides with the time of maximum rate of change of EEJ. It is in general accordance with the theory proposed by Balan et al. (1998) that suggests the formation of F3 through vertically upward E × B drift in presence of equatorward neutral wind. The present study reveals that the rate of change of eastward electric field (dE/dt) as well plays an important role in the formation of F3 layer.

Nayak, C. K.; Yadav, V.; Kakad, B.; Sripathi, S.; Emperumal, K.; Pant, T. K.; Bhattacharyya, A.; Jin, Shuanggen

2014-10-01

70

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

71

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

NASA Astrophysics Data System (ADS)

According to the study by Mayer and Jakowski (2009), periods of E layer dominated ionosphere (ELDI) are defined as being characterized by vertical electron density profiles having a maximum density at E layer altitudes. In this paper, characteristics of ELDI intervals have been investigated, focusing on their temporal variations, using field-aligned measurements from the EISCAT and ESR radars during the interval 2009-2011. ELDI events were identified using simple but reasonable criteria, in which a minimal duration was required to exclude possible "fake" events induced by random errors in measurements. It was found that ELDIs were observed more often in winter and earlier spring than other seasons, especially in the auroral zone. The occurrence of ELDI intervals peaks around geomagnetic midnight at auroral latitudes, while it reaches a maximum around geomagnetic local noon at the latitude of the ESR. Our results imply that ELDI intervals appear to be a sporadic rather than a regular phenomenon, in disagreement with previous results inferred from radio occultation measurements. The discrepancy between the typical durations of ELDI events observed by the two radars is remarkable, being 30 min on average at Tromsø but about a half of this at Svalbard. During intervals of ELDI, the mean thicknesses of the E layer are quite close at the two sites, as are the values of HmE and the ratio of NmE / NmF2. Case studies confirm that either extra E layer ionization or F layer density depletion alone could lead to the presence of ELDIs. Based on a careful check on ELDI intervals of various types, however, we suggest that both of them play a critical role in ELDI formation.

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

2014-10-01

72

Ion gyroradius-sized structures and artificial ion conics generated by the Arecibo ionospheric heater  

NASA Astrophysics Data System (ADS)

A model for ionospheric density structures at the O(+) ion gyroradius induced by the Arecibo heater during the recent El Coqui campaign has been developed. We find that (1) these density structures can be accounted for by the parametric decay of the high frequency high power Arecibo heater wave into a low frequency wave with frequency at or near the ion cyclotron frequency and high frequency sideband modes (2) the growth rate of this process peaks at scale sizes corresponding to the O(+) ion gyroradius (3) computed density fluctuations, using a strong turbulence model, associated with the ion cyclotron modes, in the nonlinear regime, are in the range of 2-12% and (4) anisotropic ion-conic-like heating will result from this process. The results of this model are in good agreement with recent El Coqui observations.

Keskinen, M. J.; Rowland, H. L.; Bernhardt, P.

1995-02-01

73

Unifying Undergraduate Artificial Intelligence Robotics: Layers Of Abstraction Over Two Channels  

E-print Network

Unifying Undergraduate Artificial Intelligence Robotics: Layers Of Abstraction Over Two Channels Annapolis, Maryland 21402 Abstract From a Computer Science and Artificial Intelligence perspec- tive to undergraduates. The paper presents an alternative synthesis of the various sub-fields of Artificial Intelligence

Crabbe, Frederick

74

Spaced sensor measurements of artificial airglow emission at 630 nm of ionosphere caused by ``Sura'' facility radiation in November 2013  

NASA Astrophysics Data System (ADS)

Some first results on simultaneous observation artificial airglow emission at 630 nm during HF pumping of the ionosphere by “Sura” facility from two spatial situated experimental sites are reported. The measurements of artificial airglow are usually conducted in red and green lines of atomic oxygen (the radiation of levels O((1) D) and O((1) S) under their excitation by electronic impact) with wave lengths of 630 and 557.7 nm and excitation energy of 1.96 and 4.17 eV accordingly. An enhancement of airglow intensity in the red line is related at present to the electron heating by powerful radio waves. The idea of the experiment was to estimate the heated volume three-dimensional structure and drift motion one. The experiment was carried out in November 2013 at the “Sura” radio facility, situated near Nizhny Novgorod, Russia (geographical coordinates 56.13(o) N, 46.10(o) E, geomagnetic field declination and inclination are ˜ 10.0(o) east and ˜ 71.5(o) , respectively). Conditions of ionosphere were checked by means of "Cady" ionosonde during “Sura” runs. According to the ionospheric conditions, on the 7(th) of November the “Sura” facility operated at frequency 4.540 MHz. At this frequency the effective radiated power was about 120MW. The HF beam width at the “Sura” facility is ˜ 12(o) . A square wave pump modulation of 5 min on, 5 min off, was used. Measurements were carried out in the period from 14:40 to 17:30 UTC. Optical imaging was performed on two spatial experimental sites: “Vasilsursk” (situated about 500 m from antenna system of “Sura” facility); “Raifa” (situated about 170 km from “Sura” facility at the Magnetic Observatory of Kazan Federal University, geographical coordinates 55.93(o) N, 48.75(o) E). They both were fitted out Peltier-cooled front-illuminated bare CCD cameras with 16-bit slow-scan read-out (S1C3). On “Vasilsursk” site the images were binned down to 256× 256 pixels in addition to cooling, in order to increase sensitivity and to reduce noise. A lens giving a ˜ 20(o) field of view was used. Using the stars, the camera look direction was adjusted to be parallel to the pump beam. On “Raifa” site the CCD camera was equipped with parallactic mount and rapid camera lens ZIKAR-2B. The 3 angular degrees wide rapid camera lens line of sight crossed the central ray of the “Sura” antenna pattern at the altitude of 225 km for those experimental conditions. During further “Vasilsursk” site’s experimental data handling and interpretation the “Cyclone” ionosond ionogramms were used. The “Cyclone” ionosonde is situated at “Orekhovka” site of the Kazan Federal University (about 180 km from the Sura facility to the east direction). The “Cyclone” ionosonde held sounding once a minute. The ionogramms data were recalculated to N_{e}(h) - profile by of IRI-2012 model. The plazma resonance area vertical size (the difference between heights of upper hybrid-Bernstein and Langmuir resonanses observation) was calculated by means of the mentioned profile and the World Magnetic Model (WMM-2010). Beside the plazma resonance area size the reflection altitude of the powerful radio wave was calculated by means of the ray tracing method. Some results of data proceeding and interpretation are presented in the report. This work was supported by the Russian Foundation for Basic Research (grants No. 12-02-00513, 13-02-00957, 14-02-31459).

Nasyrov, Igor; Grach, Savely; Gumerov, Rustam; Shindin, Alexey; Kogogin, Denis; Dementiev, Vladislav

75

Results of Experimental and Theoretical Studies of the Atmospheric Turbulence, Internal Gravity Waves and Sporadic-E Layers by Resonant Scattering of Radio Waves on Artificial Periodic Irregularities  

NASA Astrophysics Data System (ADS)

Artificial periodic irregularities (API) formed by the powerful standing radio waves in the ionospheric plasma give the good chance for the lower ionosphere comprehensive studies. In this paper we present some applications of the API technique for experimental studies of sporadic E-layers (E _{s}), internal gravity waves and turbulent events in the lower ionosphere. API are formed in the field of the standing radio wave produced by interference of the incident wave and reflected one from the ionosphere (in more details about the API technique one can see in the book 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 Lambda or one-half the powerful wavelength lambda/2. API diagnostics are carried out at the API relaxation or decay stage by their sounding of probing radio pulses. Based on the measurement of an amplitude and a phase of the API scattered signal their relaxation time and regular vertical plasma velocity are measured. In the E-region of the ionosphere API are formed as a result of the diffusion redistribution of the non-uniformly heated plasma. The relaxation of the periodic structure is specified by the ambipolar diffusion process. The diffusion time is tau=(K (2) D _{a}) (-1) where K=2pi/Lambda and D _{a} is the ambipolar diffusion rate. The atmospheric turbulence causes reduction of the API relaxation time in comparison the diffusion time. Determination of the turbulent velocity is based on this fact. The vertical plasma velocity is determined by measuring the phase of the scattered signal. Atmospheric waves having the periods from 5-10 minutes to 5-6 hours give the contribution to temporal variations of the velocity. Parameters and effects of atmospheric waves and the turbulence on the API relaxation process are presented. Determination of the masses of the predominant metallic ions at the E _{s}-layer height is one of the API applications (Bakhmetieva N.V. and Belikovich V.V. Radiophys. Quantum Electron., 2008, Vol. 51, No 11, pp. 956-969). It is based on the observed fact of the local maximum of the API relaxation time at the sporadic E-layer location. The long-lived metallic ions cause the growth of the API relaxation time tau? at the E _{s}-layer height. It is shown by API technique the sporadic E-layers contain Mg (+) , Ca (+) and Fe (+) ions predominantly at heights of 95-110 km. The new applications are based on the so-called two-frequency method of the API creation and their diagnostics. The method allows one to define the neutral atmosphere and the ionosphere parameters with high accuracy. The main results of the lower ionosphere studies carried out in 2006-2012 by the API technique using the SURA heating facility (56,1 N; 46,15 E) are presented and discussed. We aslo discuss the studies of the HF pumping effects on the formation and parameters of the sporadic E-layers and the modification of the semitransparent E _{s}-layer by the powerful radio wave and diagnostics by the API technique. The work was supported by Russian Foundation for Basic Research under project No 13-02-97067, 13-02-12074 and 13-05-00511.

Bakhmetieva, Nataliya V.; Grigoriev; Tolmacheva, Ariadna V.

76

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

NASA Astrophysics Data System (ADS)

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

Akmamedov, Kh.

1993-02-01

77

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

78

Multiscale modeling and nested simulations of three-dimensional ionospheric plasmas: Rayleigh-Taylor turbulence and nonequilibrium layer dynamics at fine scales  

NASA Astrophysics Data System (ADS)

Multiscale modeling and high resolution three-dimensional simulations of nonequilibrium ionospheric dynamics are major frontiers in the field of space sciences. The latest developments in fast computational algorithms and novel numerical methods have advanced reliable forecasting of ionospheric environments at fine scales. These new capabilities include improved physics-based predictive modeling, nesting and implicit relaxation techniques that are designed to integrate models of disparate scales. A range of scales, from mesoscale to ionospheric microscale, are included in a 3D modeling framework. Analyses and simulations of primary and secondary Rayleigh-Taylor instabilities in the equatorial spread F (ESF), the response of the plasma density to the neutral turbulent dynamics, and wave breaking in the lower region of the ionosphere and nonequilibrium layer dynamics at fine scales are presented for coupled systems (ions, electrons and neutral winds), thus enabling studies of mesoscale/microscale dynamics for a range of altitudes that encompass the ionospheric E and F layers. We examine the organizing mixing patterns for plasma flows, which occur due to polarized gravity wave excitations in the neutral field, using Lagrangian coherent structures (LCS). LCS objectively depict the flow topology and the extracted scintillation-producing irregularities that indicate a generation of ionospheric density gradients, due to the accumulation of plasma. The scintillation effects in propagation, through strongly inhomogeneous ionospheric media, are induced by trapping electromagnetic (EM) waves in parabolic cavities, which are created by the refractive index gradients along the propagation paths.

Mahalov, Alex

2014-09-01

79

25 Years of Ionospheric Modification with the Space Shuttle  

NASA Astrophysics Data System (ADS)

The ionosphere is a low temperature (0.1 eV) plasma layer that surrounds the Earth and affects a wide range of radio systems that involve communications, navigation, and radar. The unmodified ionosphere is in an equilibrium state defined by the balance of production, transport and loss of plasma. The modified ionosphere responds to neutral gas injections with (1) the generation and propagation of plasma waves and (2) the production of plasma irregularities. A single 10 second burn of the on-orbit engines on the Space Shuttle injects 1 GJoule of energy into the upper atmosphere. Injection of hypersonic exhaust vapors from rocket engines pushes the ionosphere out of its equilibrium to yield 20 eV ion beams, launch both neutral and plasma waves, and trigger several instability processes. A wide range of optical emissions, plasma density fluctuations, enhanced temperatures, and changes in composition may be detected during these experiments. Multiple sensors such as instrumented satellites, ground radars, and ground optical instruments are used to determine the extent and lifetime for ionospheric modification. This presentation will focus on experimental data and theoretical discussions of the Space Shuttle Orbital Maneuver Subsystem (OMS) Engines used to modify the upper atmosphere from 1985 to the present. Artificial disturbances in the ionosphere produced by OMS burns have two applications. First, the artificial modification of the ionosphere can provide some control on the radio propagation environment. Second, the man-made disturbances are being produced as proxies to natural disturbances.

Bernhardt, P. A.

2011-12-01

80

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

81

Low-frequency waves and ion heating associated with double layers in the downward current region of the auroral ionosphere  

NASA Astrophysics Data System (ADS)

Recent observations by satellites in the auroral ionosphere have established the presence of strong narrowly localized electric fields parallel to the ambient magnetic field. Physically these fields are formed by two layers of opposite charges in close proximity existing self-consistently in the plasma; this is known as a double layer (DL). The DL field accelerates plasma particles to form beams which excite wave modes and saturate to form electron phase-space holes (EHs). Intense perpendicular heating of ions is concurrently observed, leading to speculations regarding the heating mechanism(s). In this thesis, we address this issue via numerical simulations and analysis. We have performed electrostatic kinetic simulations using the Vlasov-Poisson system of equations for conditions prevalent in the downward current region (DCR) of the auroral ionosphere. The simulations display low-frequency waves, EHs and ion heating, consistent with observations. We determine the relative importance of two proposed mechanisms for ion heating: stochastic heating due to EHs and due to wave-particle interactions at identifiable wave modes. Stochastic heating of ions via EH-ion scattering is estimated to account for approximately 10-15% of the observed increase in ion temperature in regions of intense wave activity. Spectral analysis shows that the energy exchange between waves and ions is concentrated at frequencies and wave numbers associated with nearly perpendicular magnetized ion wave modes and not EHs. We conclude that, in the vicinity of DLs in the DCR of the auroral ionosphere where both intense waves and EHs are present, wave-particle interactions are the principal mechanism of ion heating, with stochastic heating by electron phase-space holes playing a minor role.

Sen, Naresh

2009-06-01

82

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.

83

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

NASA Astrophysics Data System (ADS)

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

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

2011-01-01

84

Mid-latitude magnetically conjugate ionospheric F2-layer during magnetic storm periods. Ph.D. Thesis  

SciTech Connect

Thermospheric winds and penetrating electric fields play important roles in the complex phenomenon of F2-layer magnetic storms. The combined effect of both on the ionosphere can be inferred using a method based on the nonlinear relationship between the neutral winds and the height of the F2-layer. The F2-layer peak electron density depletion on the storm day generally became more pronounced than quiet-time median values during nighttime. The high to low latitude F2-layer electron density depletion is particularly evident at both hemispheres. A simultaneous enhancement of the eastward electric fields at all latitudes suggests an intimate relationship between the peak electron density depletion and the penetrating electric fields during an onset of storm. The behavior of meridional neutral winds during magnetic storm periods at all latitudes has been shown to differ from their quiet-time patterns. Meridional neutral winds during quiet-time for the months considered are usually equatorward during day and night in the summer season, poleward during the day, and slightly equatorward at night during the winter season for both hemispheres. Meridional neutral winds during storm periods generally become equatorward of quiet time values at night and reach their maximum deviation from the quiet time medians near local midnight. Electric fields can be separated from the effects of neutral air dynamics during the onset of magnetic storms. Simultaneous changes from the quiet-time values of hmF2 occurring at one or more pairs of conjugate stations indicate the penetration of zonal electric fields. Different local times of storm onset were examined to show that the penetration of electric fields to mid-latitudes normally occurs near midnight periods. This may be correlated with the currents flowing into the high latitude ionosphere in the evening sector.

Wu, H.Y.

1993-01-01

85

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

Microsoft Academic Search

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

William Webber

1962-01-01

86

Rossby-Khantadze electromagnetic planetary waves driven by sheared zonal winds in the E-layer ionosphere  

NASA Astrophysics Data System (ADS)

Nonlinear simulations of electromagnetic Rossby and Khantadze planetary waves in the presence of a shearless and sheared zonal flows in the weakly ionized ionospheric E-layer are carried out. The simulations show that the nonlinear action of the vortex structures keeps the solitary character in the presence of shearless zonal winds as well as the ideal solutions of solitary vortex in the absence of zonal winds. In the presence of sheared zonal winds, the zonal flows result in breaking into separate multiple smaller pieces. A passively convected scalar field is shown to clarify the transport associated with the vortices. The work shows that the zonal shear flows provide an energy source into the vortex structure according to the shear rate of the zonal winds.

Futatani, S.; Horton, W.; Kahlon, L. Z.; Kaladze, T. D.

2015-01-01

87

Remote sensing of the ionospheric F layer by use of O I 6300-A and O I 1356-A observations  

NASA Technical Reports Server (NTRS)

The possibility of using airglow techniques for estimating the electron density and height of the F layer is studied on the basis of a simple relationship between the height of the F2 peak and the column emission rates of the O I 6300 A and O I 1356 A lines. The feasibility of this approach is confirmed by a numerical calculation of F2 peak heights and electron densities from simultaneous measurements of O I 6300 A and O I 1356 A obtained with earth-facing photometers carried by the Ogo 4 satellite. Good agreement is established with the F2 peak heights estimates from top-side and bottom-side ionospheric sounding.

Chandra, S.; Reed, E. I.; Meier, R. R.; Opal, C. B.; Hicks, G. T.

1975-01-01

88

Chemical depletion of the ionosphere  

NASA Technical Reports Server (NTRS)

A theoretical study of the chemical and gas dynamical processes resulting from the release of reactive gases into the daytime ionosphere is discussed. Only point releases, such as from an explosion or a pulsed jet, are considered. Some scientific uses of the artificial reduction of the ionospheric plasma are considered.

Bernhardt, P. A.; Darosa, A. V.; Park, C. G.

1977-01-01

89

Envelope solitons of electromagnetic spin waves in an artificial layered multiferroic  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

90

Artificial excitation of ELF waves with frequency of Schumann resonance  

NASA Astrophysics Data System (ADS)

We report results from the experiment aimed at the artificial excitation of extremely low-frequency (ELF) electromagnetic waves with frequencies corresponding to the frequency of Schumann resonance. Electromagnetic waves with these frequencies can form a standing pattern inside the spherical cavity formed by the surface of the Earth and the ionosphere. In the experiment the ELF waves were excited by heating the ionosphere with X-mode HF electromagnetic waves generated at the High Frequency Active Auroral Research Program (HAARP) facility in Alaska. The experiment demonstrates that heating of the ionosphere can excite relatively large-amplitude electromagnetic waves with frequencies in the range 7.8-8.0 Hz when the ionosphere has a strong F layer, the frequency of the HF radiation is in the range 3.20-4.57 MHz, and the electric field greater than 5 mV/m is present in the ionosphere.

Streltsov, A. V.; Guido, T.; Tulegenov, B.; Labenski, J.; Chang, C.-L.

2014-11-01

91

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

92

Evaluation of a technique to generate artificially thickened boundary layers in supersonic and hypersonic flows  

NASA Technical Reports Server (NTRS)

The feasibility of using a contoured honeycomb model to generate a thick boundary layer in high-speed, compressible flow was investigated. The contour of the honeycomb was tailored to selectively remove momentum in a minimum of streamwise distance to create an artificially thickened turbulent boundary layer. Three wind tunnel experiments were conducted to verify the concept. Results indicate that this technique is a viable concept, especially for high-speed inlet testing applications. In addition, the compactness of the honeycomb boundary layer simulator allows relatively easy integration into existing wind tunnel model hardware.

Porro, A. R.; Hingst, W. R.; Davis, D. O.; Blair, A. B., Jr.

1991-01-01

93

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

94

Artificially thickened turbulent boundary layers for studying heat transfer and skin friction on rough surfaces  

NASA Astrophysics Data System (ADS)

A technique has been developed to produce artificially thickened boundary layers on a uniformly rough surface which have two-dimensional, equilibrium properties representative of normal behavior at the level of spectra of the longitudinal velocity fluctuations. Skin surface friction coefficients and Stanton numbers are obtained for rough surface boundary layers much thicker than those previously studied. The results provide additional understanding of turbulent shear flow and a basis for testing engineering calculation schemes and design procedures for situations where thick, rough-wall boundary layers are present. The Stanton numbers and skin friction coefficients are shown to be representative of natural behavior because three higher levels of information, as well as the turbulent transport of momentum and heat, are the same as would have existed in naturally developed layers of the same thickness.

Ligrani, P. M.; Moffat, R. J.; Kays, W. M.

1983-06-01

95

Magnetic structure of Tb-Fe films with an artificially layered structure  

SciTech Connect

The magnetic structure of Tb-Fe films with an artificially layered structure has been investigated by measuring the temperature dependence of the magnetization of the films. Ferrimagnetic coupling between Tb and Fe through the interface was explicitly observed up to about 9-A Tb and 10-A Fe layers. Films with thinner Tb and Fe layers than these thicknesses are composed of only ferrimagnetically coupled Tb-Fe regions. Films with thicker layers of Tb and Fe are composed of ferrimagnetically coupled Tb-Fe, ferromagnetic Fe, ferromagnetic Tb, and/or magnetically compensated Tb regions. The Tb-Fe films exhibit various temperature dependencies of the magnetization corresponding to these magnetic structures.

Yamauchi, K.; Habu, K.; Sato, N.

1988-11-15

96

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

PubMed

We investigate a high-order homogenization (HOH) algorithm for periodic multi-layered stacks. The mathematical tool of choice is a transfer matrix method. Expressions for effective permeability, permittivity and magnetoelectric coupling are explored by frequency power expansions. On the physical side, this HOH uncovers a magnetoelectric coupling effect (odd-order approximation) and artificial magnetism (even-order approximation) in moderate contrast photonic crystals. Comparing the effective parameters' expressions of a stack with three layers against that of a stack with two layers, we note that the magnetoelectric coupling effect vanishes while the artificial magnetism can still be achieved in a centre-symmetric periodic structure. Furthermore, we numerically check the effective parameters through the dispersion law and transmission property of a stack with two dielectric layers against that of an effective bianisotropic medium: they are in good agreement throughout the low-frequency (acoustic) band until the first stop band, where the analyticity of the logarithm function of the transfer matrix ([Formula: see text]) breaks down. PMID:24101891

Liu, Yan; Guenneau, Sébastien; Gralak, Boris

2013-10-01

97

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

NASA Astrophysics Data System (ADS)

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

Judge, Matthew G.; Lamont, Gary B.

2009-05-01

98

Ionospheric modeling  

Microsoft Academic Search

The purpose of this report is to familiarize a user of ionospheric models with the options presently available for ionospheric prediction and specification. Two types of ionospheric models are available: the numerical-phenomenological and theoretical models. From the numerical type, the ITS-78, IONCAP, and Bent models have been discussed. In the theoretical models the main concern is the number of parameters

B. S. Dandekar

1982-01-01

99

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

100

Natural hazards monitoring and forecast using the GNSS and other technologies of the ionosphere monitoring  

NASA Astrophysics Data System (ADS)

It is well established now that Atmosphere-Ionosphere Coupling is provided through the local changes of the Global Electric Circuit parameters. Main agent - is column conductivity, modulated mainly at the altitudes of the Global Boundary Layer. We demonstrate the ionospheric effects for different types of natural hazards including volcano eruptions, dusty storms from Western Africa, ionospheric effects from tropical hurricanes, multiple earthquakes. We consider the important role of air ionization from natural (natural ground radioactivity and galactic cosmic rays) and artificial sources (nuclear weapon tests in atmosphere and underground, nuclear power stations and other nuclear enterprises emergencies). We rise also important question that such effects of the ionosphere variability are not taken into account by any ionospheric model and their correct recognition is important not only from the point of view the disasters monitoring but for navigation itself because the magnitude of the ionospheric effects sometimes exceeds the effects from strong magnetic storms and other severe space weather conditions. Some effects like ionospheric effects from tropical hurricanes have more complex physical nature including the formation of streams of neutral atmosphere over the hurricane eye and formation of the strong positive plasma concentration anomaly at the altitude near 1000 km. Some plasma anomalies registered over the tropical depressions before hurricane formation give hope on predictive capabilities of plasma observations over the tropical depressions.

Pulinets, S. A.; Davidenko, D.

2013-12-01

101

Layer-by-layer assembly of a redox enzyme displayed on the surface of elongated bacteria into a hierarchical artificial biofilm based anode.  

PubMed

To achieve an efficient electron transfer communication between bacteria and electrodes, several strategies including enzyme surface display, bacteria elongation as well as layer-by-layer assembly techniques were used to assemble bacteria, methylene blue, multiwall carbon nanotubes, and carbon papers into hierarchical micro/nano artificial biofilm based bioanodes. PMID:25572527

Xia, Lin; Ravenna, Yehonatan; Alfonta, Lital

2015-01-29

102

A study on ionospheric TEC forecast using genetic algorithm and neural network  

NASA Astrophysics Data System (ADS)

Back propagation artificial neural network (ANN) augmented by genetic algorithm (GA) is introduced to forecast ionospheric TEC with the dual-frequency GPS measurements from the low and high solar activity years in this paper due to ionosphere space characterizing by the highly nonlinear and time-varying with random variations. First, with different number of neurons in the hidden layer, different transfer function and training function, the training performance of network model is analyzed and then optimized network structure is determined. The ionospheric TEC values one hour in advance are forecasted and further the prediction performance of the developed network model is evaluated at the given criterions. The results show that predicted TEC using BP neural network improved by genetic algorithm has good agreement with observed data. In addition, the prediction errors are smaller in middle and high latitudes than in low latitudes, smaller in low solar activity than in high solar activity. Compared with BP Network with three layers structure, Prediction precision of network model optimized by genetic algorithm is further improved. The resolution quality indicate that the proposed algorithm can offer a powerful and reliable alternative to the design of ionospheric TEC forecast technologies, and provide advice for the regional ionospheric TEC maps. Key words: Neural network, Genetic algorithm, Ionospheric TEC, Forecast,

Huang, Zhi; Yuan, Hong

103

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

104

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

105

Some Properties of Long-term Variations of the Oxygen red 630 nm Line Nightglow Intensity and the Ionosphere F2 Layer  

NASA Astrophysics Data System (ADS)

Long-term data sets of total nightglow intensity of the oxygen red 630 0 nm line observed at Abastumani 41 75 o N 42 82 o E and the ionosphere F2 layer critical frequency f 0 F2 observed at Almaty 43 25 o N 76 92 o E during the period of 1957-1993 have been investigated The comparison of the annual mean value of the red line intensity and the ionospheric F2 layer maximum electron density NmF2 reveals the following properties a the dominant long-term variation for both parameters has a characteristic period of 11-year consistent with the solar cycle The amplitude of the red line nightglow intensity deviation from its mean value at the solar maximum minimum phase is greater than that of the NmF2 during the same period of night b The long-term trends of these variations are different for the period following twilight pre-midnight and that after midnight The long-term trend of the red line intensity is about one order of magnitude greater than that of the NmF2 c The second order regression equation with solar indices for NmF2 gives a small increase of the correlation coefficient between the theoretical and observational values The third order regression equation with different solar indices is considered convenient for describing long-term variations in the mean annual red line intensity

Gudadze, N.; Didebulidze, G.; Javakhishvili, G.; Aushev, V.; Shepherd, M.; Vardosanidze, M.

106

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

107

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

108

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

109

Ionospheric modifications in high frequency heating experiments  

NASA Astrophysics Data System (ADS)

Featured observations in high-frequency (HF) heating experiments conducted at Arecibo, EISCAT, and high frequency active auroral research program are discussed. These phenomena appearing in the F region of the ionosphere include high-frequency heater enhanced plasma lines, airglow enhancement, energetic electron flux, artificial ionization layers, artificial spread-F, ionization enhancement, artificial cusp, wideband absorption, short-scale (meters) density irregularities, and stimulated electromagnetic emissions, which were observed when the O-mode HF heater waves with frequencies below foF2 were applied. The implication and associated physical mechanism of each observation are discussed and explained. It is shown that these phenomena caused by the HF heating are all ascribed directly or indirectly to the excitation of parametric instabilities which instigate anomalous heating. Formulation and analysis of parametric instabilities are presented. The results show that oscillating two stream instability and parametric decay instability can be excited by the O-mode HF heater waves, transmitted from all three heating facilities, in the regions near the HF reflection height and near the upper hybrid resonance layer. The excited Langmuir waves, upper hybrid waves, ion acoustic waves, lower hybrid waves, and field-aligned density irregularities set off subsequent wave-wave and wave-electron interactions, giving rise to the observed phenomena.

Kuo, Spencer P.

2015-01-01

110

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

111

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

112

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

NASA Astrophysics Data System (ADS)

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

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

2005-05-01

113

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

114

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

115

Tomographic estimation of the ionosphere using terrestrial GPS sensors  

Microsoft Academic Search

The ionosphere is a region of partially ionized plasma in Earth's upper atmosphere distributed in layers of varying free electron density. The free electrons change the local index of refraction causing radio waves propagating in the ionosphere to be delayed and bent. Trans-ionospheric propagation of GPS radio signals transmitted from satellites provides observations, in a tomographic sense, of the electron

Andrew Jakob Hansen

2002-01-01

116

Photoluminescence quenching and charge transfer in artificial heterostacks of monolayer transition metal dichalcogenides and few-layer black phosphorus.  

PubMed

Transition metal dichalcogenides monolayers and black phosphorus thin crystals are emerging two-dimensional materials that demonstrated extraordinary optoelectronic properties. Exotic properties and physics may arise when atomic layers of different materials are stacked together to form van der Waals solids. Understanding the important interlayer couplings in such heterostructures could provide avenues for control and creation of characteristics in these artificial stacks. Here we systematically investigate the optical and optoelectronic properties of artificial stacks of molybdenum disulfide, tungsten disulfide, and black phosphorus atomic layers. An anomalous photoluminescence quenching was observed in tungsten disulfide-molybdenum disulfide stacks. This was attributed to a direct to indirect band gap transition of tungsten disulfide in such stacks while molybdenum disulfide maintains its monolayer properties by first-principles calculations. On the other hand, due to the strong build-in electric fields in tungsten disulfide-black phosphorus or molybdenum disulfide-black phosphorus stacks, the excitons can be efficiently splitted despite both the component layers having a direct band gap in these stacks. We further examine optoelectronic properties of tungsten disulfide-molybdenum disulfide artificial stacks and demonstrate their great potentials in future optoelectronic applications. PMID:25569715

Yuan, Jiangtan; Najmaei, Sina; Zhang, Zhuhua; Zhang, Jing; Lei, Sidong; M Ajayan, Pulickel; Yakobson, Boris I; Lou, Jun

2015-01-27

117

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

118

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

NASA Astrophysics Data System (ADS)

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

Hu, Yaogai; Zhao, Zhengyu; Zhang, Yuannong

2011-07-01

119

An investigation of the formation patterns of the ionospheric F3 layer in low and equatorial latitudes  

NASA Astrophysics Data System (ADS)

Ionogram traces with the F3 layer in different latitude do not always seem similar. In our work, we tend to describe morphological features of traces with the F3 layer in magnetic low-latitude region and near magnetic equator through the quantitative investigation of the diurnal variation and latitude dependence of two morphologically characteristic parameters - the foF2-to-foF3 ratio and the difference between h?F3 and h?F2 - in geomagnetically quiet period. The distribution of two formation patterns (pattern A and pattern B are defined with increasing F3 peak density and with nearly constant or decreasing F3 peak density respectively as the peak moving upward around the onset of the F3 layer’s occurrence) of the F3 layer is also investigated based on statistics of formation patterns of the F3 layer in Sanya and Kwajalein in 2011. The ideal equinoctial distribution (without the summer-to-winter neutral wind) of those patterns is symmetrical about magnetic equator with pattern A in magnetic low-latitude region and pattern B near magnetic equator. When taking the summer-to-winter neutral wind which resists (enhances) the plasma diffusion to higher latitude in the windward (leeward) into consideration in a solstice, pattern A could be observed near magnetic equator in summer hemisphere and pattern B in magnetic low-latitude region in winter hemisphere compared with the ideal distribution in the equinox.

Zhu, Jie; Zhao, Biqiang; Wan, Weixing; Ning, Baiqi

2013-09-01

120

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

121

Orbital barium CRRES injection - effective source of ionospheric wavelike disturbances  

NASA Astrophysics Data System (ADS)

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

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

122

Some characteristics of large-scale travelling ionospheric disturbances and a relationship between the F2 layer height rises of these disturbances and equatorial pre-sunrise events  

NASA Astrophysics Data System (ADS)

Initially some characteristics of large-scale travelling ionospheric disturbances (LS-TIDs) have been discussed briefly particularly as reported in the early literature. These discussions also involve the literature on the generation of LS-TIDs at times of geomagnetic bays. Secondly, the possibility that LS-TIDs may be responsible for the F2 layer equatorial pre-sunrise height rises is investigated. Tabulations at hourly intervals of h'F at Huancayo and Washington for a Rz max period (1957-1960) have been used to identify height rises. For a three-hour interval at Huancayo h'F levels equal to or greater than 40 km of medians are used to identify the pre-sunrise height rises. Also height rises at Washington, which occurred earlier than those at Huancayo, have been considered for evidence of travelling disturbances. For 40 events analysed using geomagnetic bays and Washington height rises, a few hours before they occur at Huancayo, indicate the statistical significance of an association with LS-TIDs. Similar results of statistical significance have been obtained using Washington events and bays on average 34 h before 46 Huancayo events. These delays ranged from 29 h to 38 h. The results indicate that bays which occur the day before are responsible for LS-TIDs which encircle the earth.

Bowman, G. G.; Mortimer, I. K.

2010-07-01

123

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

Microsoft Academic Search

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

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

2012-01-01

124

Tsunamis warning from space :Ionosphere seismology  

SciTech Connect

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

Larmat, Carene [Los Alamos National Laboratory

2012-09-04

125

Anomalous variations in the ionospheric F 2-layer structure at geomagnetic midlatitudes of the Southern and Northern hemispheres at the transition from summer to winter conditions under low solar activity  

NASA Astrophysics Data System (ADS)

The structure and dynamics of the ionosphere and plasmasphere at low solar activity under quiet geomagnetic conditions on January 15 17, 1985, and July 10 13, 1986, over Millstone Hill station and Argentine Islands ionosonde, the locations of which are approximately magnetically conjugate, have been theoretically calculated. The detected correction of the model input parameters makes it possible to coordinate the measured and calculated anomalous variations in the electron density NmF2 at the height hmF2 of the ionospheric F2 layer over Argentine Islands ionosonde as well as the calculated and measured values of NmF2 and electron temperature at the hmF2 height over Millstone Hill station. It has been shown that vibrationally excited N2 and O2 molecules almost do not influence the formation of the winter anomaly under the conditions of low solar activity. A difference between the influence of electronically excited O+ on N e ions under winter and summer conditions forms not more than 11% of the N e winter anomaly event in the F 2 layer and topside ionosphere. The model without electronically excited O+ ions reduces the duration of the N e winter anomaly event. It has been shown that the seasonal variations in the composition of the neutral atmosphere form mainly the NmF2 winter anomaly event over the Millstone Hill radar at low solar activity.

Pavlov, A. V.; Pavlova, N. M.; Makarenko, S. F.; Shubin, V. N.

2008-06-01

126

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

127

25th anniversary article: Artificial carbonate nanocrystals and layered structural nanocomposites inspired by nacre: synthesis, fabrication and applications.  

PubMed

Rigid biological systems are increasingly becoming a source of inspiration for the fabrication of next generation advanced functional materials due to their diverse hierarchical structures and remarkable engineering properties. Among these rigid biomaterials, nacre, as the main constituent of the armor system of seashells, exhibiting a well-defined 'brick-and-mortar' architecture, excellent mechanical properties, and interesting iridescence, has become one of the most attractive models for novel artificial materials design. In this review, recent advances in nacre-inspired artificial carbonate nanocrystals and layered structural nanocomposites are presented. To clearly illustrate the inspiration of nacre, the basic principles relating to plate-like aragonite single-crystal growth and the contribution of hierarchical structure to outstanding properties in nacre are discussed. The inspiration of nacre for the synthesis of carbonate nanocrystals and the fabrication of layered structural nanocomposites is also discussed. Furthermore, the broad applications of these nacre inspired materials are emphasized. Finally, a brief summary of present nacre-inspired materials and challenges for the next generation of nacre-inspired materials is given. PMID:24338814

Yao, Hong-Bin; Ge, Jin; Mao, Li-Bo; Yan, You-Xian; Yu, Shu-Hong

2014-01-01

128

Solar System Ionospheres  

NASA Astrophysics Data System (ADS)

This article reviews our understanding of the ionospheres in the solar system. It provides some basic information on the sources and sinks of the ionospheric plasma, its dynamics, the energetics and the coupling to the neutral atmosphere. Ionospheres in the solar system are reviewed and comparative ionospheric topics are discussed.

Witasse, O.; Cravens, T.; Mendillo, M.; Moses, J.; Kliore, A.; Nagy, A. F.; Breus, T.

129

Solar System Ionospheres  

Microsoft Academic Search

This article reviews our understanding of the ionospheres in the solar system. It provides some basic information on the sources\\u000a and sinks of the ionospheric plasma, its dynamics, the energetics and the coupling to the neutral atmosphere. Ionospheres\\u000a in the solar system are reviewed and comparative ionospheric topics are discussed.

O. Witasse; T. Cravens; M. Mendillo; J. Moses; A. Kliore; A. F. Nagy; T. Breus

2008-01-01

130

Solar System Ionospheres  

Microsoft Academic Search

This article reviews our understanding of the ionospheres in the solar system. It provides some basic information on the sources\\u000a and sinks of the ionospheric plasma, its dynamics, the energetics and the coupling to the neutral atmosphere. Ionospheres\\u000a in the solar system are reviewed and comparative ionospheric topics are discussed.

O. Witasse; T. Cravens; M. Mendillo; J. Moses; A. Kliore; A. F. Nagy; T. Breus

131

Solar System Ionospheres  

NASA Astrophysics Data System (ADS)

This article reviews our understanding of the ionospheres in the solar system. It provides some basic information on the sources and sinks of the ionospheric plasma, its dynamics, the energetics and the coupling to the neutral atmosphere. Ionospheres in the solar system are reviewed and comparative ionospheric topics are discussed.

Witasse, O.; Cravens, T.; Mendillo, M.; Moses, J.; Kliore, A.; Nagy, A. F.; Breus, T.

2008-08-01

132

Three-layered scaffolds for artificial esophagus using poly(?-caprolactone) nanofibers and silk fibroin: An experimental study in a rat model.  

PubMed

The purpose of this study was to determine the feasibility of an artificial esophagus using a three-layered poly(?-caprolactone) (PCL)-silk fibroin (SF) scaffold in a rat model. The artificial esophagus was a three-layered, hybrid-type prosthesis composed of an outer and inner layer of PCL with a middle layer of SF. After depositing the inner layer of the PCL scaffold by electrospinning, the lyophilized middle SF layer was created. The outer layer of PCL was produced following the same procedure used to make the inner PCL layer. Eleven rats were anesthetized using inhaled anesthesia. Circumferential defects of the cervical esophagus (n?=?11) were created and reconstructed. Groups of rats were sacrificed after the 1st and 2nd weeks. Three rats died of an esophageal fistula and wound infection. No gross evidence of a fistula, perforation, abscess formation, seroma accumulation, or surrounding soft-tissue necrosis was observed in the other rats sacrificed after the 1st and 2nd weeks. The artificial esophagus constructs produced complete healing of the circumferential defects by the 2nd week. The composition of the three-layered artificial esophagus was confirmed histologically to have an outer and inner layer of PCL and a middle layer of SF. The fusion of the PCL-SF scaffold and the regenerative tissue remained intact. Our study proposes a more practical experimental model for studying a three-layered PCL-SF scaffold in the esophagus. However, further studies on circumferential defect reconstruction in a rat model are still required. © 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part A:, 2014. PMID:25294581

Chung, Eun-Jae; Ju, Hyung Woo; Park, Hyun Jung; Park, Chan Hum

2014-10-01

133

Determination of physical properties of planetary sub-surface layers by artificial impacts and penetrometry  

Microsoft Academic Search

In recent years the exploration of planetary bodies by surface probes has entered a new phase of interest. The mechanical properties of the near-surface layers of cometary and planetary bodies, including their strength, texture and layering, are important parameters needed both for a proper physical understanding of these bodies and for the design of lander missions.The strength properties of such

N. I. Kömle; G. Kargl; A. J. Ball

2001-01-01

134

The delayed occurrence of equatorial ionospheric F2 layer post-sunset height decreases following auroral-zone substorm onsets  

NASA Astrophysics Data System (ADS)

Nighttime F2 layer height decreases have been examined for post-sunset intervals at the equatorial station, Huancayo. The analyses involved mainly Rz max years, (1957-1960), although Rz min years (1974-1977) were also used. The data were obtained from tabulations of the ionogram parameters h'F, f[circle, open]F2 and f[circle, open]Es. The height reductions are delayed by more than 7 h following geomagnetic substorm onsets for locations at longitudes to the east. The reduced occurrence of spread-F and f[circle, open]Es enhancements is found to be associated. These enhancements are also recorded at the European station, Dourbes about 4.5 h before the Huancayo enhancements. It is proposed that an LS-TID which propagates in the 80 km sound channel may be involved. Also, the experimental evidence suggests that the westward propagation of the LS-TIDs allows equatorial disturbances to occur at local times (before midnight) which are similar to the times when the LS-TIDs are generated.

Bowman, G. G.; Mortimer, I. K.

2010-02-01

135

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

136

Atmospheric electricity coupling between earthquake regions and the ionosphere  

NASA Astrophysics Data System (ADS)

We propose a mechanism to explain suggested links between seismic activity and ionospheric changes detected overhead. Specifically, we explain changes in the natural extremely low-frequency (ELF) radio noise recently observed in the topside ionosphere aboard the DEMETER satellite at night, before major earthquakes. Our mechanism utilises increased electrical conductivity of surface layer air before a major earthquake, which reduces the surface-ionosphere electrical resistance. This increases the vertical fair weather current, and (to maintain continuity of electron flow) lowers the ionosphere. Magnitudes of crucial parameters are estimated and found to be consistent with observations. Natural variability in ionospheric and atmospheric electrical properties is evaluated, and may be overcome using a hybrid detection approach. Suggested experiments to investigate the mechanism involve measuring the cut-off frequency of ELF "tweeks", the amplitude and phase of very low frequency radio waves in the Earth-ionosphere waveguide, or medium frequency radar, incoherent scatter or rocket studies of the lower ionospheric electron density.

Harrison, R. G.; Aplin, K. L.; Rycroft, M. J.

2010-04-01

137

Stabilization of an injected conducting layer for artificially enhancing drag on orbital debris  

NASA Astrophysics Data System (ADS)

The evolution of a magnetized conducting medium suspended in magnetic and gravitational fields is examined. In this paper some effects of the influence of velocity fields on the linear stability properties of such layers are investigated. A fully compressible, three-dimensional analysis of the layer is described. The relevant equations are derived and then solved by the MagnetoHydroDynamic SPEctral Compressible Linear Stability (MHDSPECLS) algorithm, a Chebyshev collocation code. The code allows for the computation of magnetic and thermal effects. A complete stabilization of the system is found above a critical velocity of approximately 2500 m/s.

Dahlburg, R. B.; Rudakov, L.; Crabtree, C.; Ganguli, G.

2013-12-01

138

Artificial Neural Network Prediction of Stability Numbers for Two-layered Slopes with Associated Flow Rule  

Microsoft Academic Search

The design of earthen embankments is quite often carried out with the use of stability number charts as originally introduced by Taylor. However, such charts are not easily available for the layered soil slopes with the inclusion of pore water pressure and seismic forces. In this paper, a neural network modeling using back propagation technique was done to predict the

Pijush Samui; Bimlesh Kumar

139

Physics of planetary ionospheres  

NASA Technical Reports Server (NTRS)

The fundamental physical and chemical processes in an idealized planetary ionosphere are considered as a general abstraction, with actual planetary ionospheres representing special cases. After describing the structure of the neutral atmospheres (the barosphere, the thermosphere, and the exosphere) and noting the principal ionizing radiations responsible for the formation of planetary ionospheres, a detailed study is made of the thermal structure of these ionospheres and of the chemical processes and plasma-transport processes occurring in them. The features of equilibrium and realistic models of planetary ionospheres are discussed, and an attempt is made to determine the extent of these ionospheres. Considering the ionosphere as a plasma, a plasma kinetic approach is developed for determining the effects of interactions between individual particles and waves in this plasma. The use of remote-sensing radio techniques and direct measurement or in situ techniques is discussed. Finally, the observed properties of the ionospheres of the Earth, Mars, Venus, and Jupiter are reviewed.

Bauer, S. J.

1973-01-01

140

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

NASA Astrophysics Data System (ADS)

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

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

2009-02-01

141

Verification of ionospheric sensors  

Microsoft Academic Search

Ionospheric products from sensors and models were compared to investigate strengths and limitations of each. Total electron content data from computerized ionospheric tomography (CIT) and TOPEX sensors in the Caribbean region in 1997 were compared to estimates produced by models Parameterized Ionospheric Model (PIM) and Raytrace\\/ICED-Bent-Gallagher (RIBG) and global maps from GPS. A 5 total electron content unit (TECU) bias

Clayton Coker; Glenn Kronschnabl; David S. Coco; Gary S. Bust; Thomas L. Gaussiran

2001-01-01

142

Physical mechanisms associated with long-range propagation of the signals from ionospheric heating experiments  

NASA Astrophysics Data System (ADS)

propagation of heater-produced signals has been studied in experiments with the European Incoherent Scatter Scientific Association ionospheric heating facility and with several globally distributed receiving sites by Zalizovski et al. [2009]. Two distinctive components were present in the signals' spectra, and these can be attributed to two modes of propagation of the signals. One of the components is narrowband and stable; it obviously can be associated with the multihop ionospheric propagation of HF waves radiated by the side lobes of the heater's antenna array. Prominent features of the second component are its wider spectral band (up to few tens of hertz) and strong variations in the average Doppler frequency shift and in the power, which in many cases were synchronous at the different receiving sites. These effects are most likely produced by the ionospheric scattering and dynamics within the heater's main beam. The tricky part is to explain how a portion of the HF energy contained in the relatively narrow main beam of the heater is redirected toward the remote receiving locations. We suggest a robust mechanism explaining the long-range propagation of the wideband component of the heater-generated signal based on the theory of scattering from rough surfaces. This mechanism preserves all the observed properties of the remote signals. We show that mountain relief in the vicinity of the heater plays the role of the rough surface causing almost isotropic scattering of the heater's main beam after it is reflected by the ionosphere. Multiple scattering by natural and artificial field-aligned irregularities in the ionospheric layer may be related to the ground-scattered remote signals through its role in spatial redistribution of the heater's radiation.

Zabotin, Nikolay A.; Zavorotny, Valery U.; Rietveld, Michael T.

2014-10-01

143

Sputtered-silica defect layer in artificial opals: tunability of highly transmitted and reflected optical modes  

E-print Network

We propose an original and efficient method to engineer a defect between two well-ordered silica opals by sputtering silica on the top of the first one. As the amount of sputtered silica can be well controlled, it is also the case for the thickness of the layer and consequently for the spectral position of the defect mode. The optical response of these sandwich structures is studied in terms of specular reflection and transmission spectroscopy. Tunable highly transmitted and reflected optical modes are evidenced. The very good agreement between the experimental results and the simulations, run without fitting parameters, demonstrates the almost perfect order of the synthesized structures.

Hong, Phan Ngoc; Coolen, Laurent; Maître, Agnès; Schwob, Catherine

2013-01-01

144

Systematic behavior of semiempirical global ionospheric models in quiet geomagnetic conditions  

Microsoft Academic Search

Semiempirical ionospheric models are widely used in many applications. In this work we analyze the global representation of the vertical total electron content (VTEC) derived from the La Plata single-layer GPS ionospheric model (LPIM), the international reference ionosphere (IRI) model, and the Bent model. To perform this analysis, we compare the output from these models with VTEC determinations from the

A. M. Meza; A. R. Díaz; C. A. Brunini; M. A. Van Zele

2002-01-01

145

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

146

Inverting ionospheric radio occultation measurements using maximum entropy  

Microsoft Academic Search

Practical aspects of the inversion of ionospheric radio occultation data using the Abel transform and its inverse are discussed. The linear inverse transform exhibits poor error propagation characteristics, producing significant artifacts preferentially at low altitudes where they might easily be mistaken for intermediate or sporadic layers in the ionosphere. Tikhonov regularization, which can be viewed as fixed linear filtering, reduces

D. L. Hysell

2007-01-01

147

Sputnik 1 and the First Satellite Ionospheric Experiment  

NASA Astrophysics Data System (ADS)

The world's first scientific space experiment was carried out in 1957 during the flight of the first Artificial Earth Satellite (AES) - Sputnik 1. It was an ionospheric experiment performed at IZMIRAN under the direction of Prof. Ya.L.Alpert (1911-2010). The sunrise and sunset variations in the AES radio signal were recorded in order to determine the distribution of electron density in the topside ionosphere (above the maximum). The experiment demonstrated the capabilities of the satellite radio beacon method, which is now very important and widely used for studying the ionosphere. Our report submitted to the COSPAR General Assembly in Russia describes the history and results of that experiment, as well as some other contributions by Ya.L.Alpert to ionospheric research. Yakov L.Alpert was one of the most famous and influential radiophysicists of his time, the author of many fundamental studies and of a number of classic books on the theory of propagation of electromagnetic waves, interaction of artificial bodies with ionospheric plasmas, ionospheric radio scattering, and the use of satellite radio beacon methods for studying the ionosphere.

Sinelnikov, Vyacheslav; Kuznetsov, Vladimir; Alpert, Svetlana

148

Radio Waves and the Ionosphere  

NSDL National Science Digital Library

In this activity students will discover that when amplitude modulated (AM) radio waves travel from transmitter to a receiver far away, they have to bounce off the underside of the ionosphere and that the waves lose some of their energy each time they are reflected. Students will learn that although this is normally a small amount, it can be several times larger during a solar storm. They also learn that radio signals passing through this layer and bouncing off the ionosphere higher up, have some or all of their intensity absorbed. During this activity students will calculate the percent of change, determine the final percentage of radio wave strength at the receiving station, and will learn that solar flares can cause disruptions in radio waves.

Susan Higley

149

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

Microsoft Academic Search

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

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

2010-01-01

150

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

151

Radar Ionospheric Impact Mitigation  

Microsoft Academic Search

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

G. Bishop; D. Decker; C. Baker

2006-01-01

152

The Ionospheric Peak on the Venus Dayside  

Microsoft Academic Search

Many electron density profiles of the dayside ionosphere of Venus have been measured by the Pioneer Venus orbiter between December 1978 and October 1980, using the dual-frequency radio occultation technique. The peak electron density as a function of solar zenith angle can be described by a simple Chapman layer theory with proper normalization; however, it does not predict adequately the

T. E. Cravens; A. J. Kliore; J. U. Kozyra; A. F. Nagy

1981-01-01

153

Wenchuan Earthquake Ionospheric Precursors: Modeling and Experiment  

NASA Astrophysics Data System (ADS)

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

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

154

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.

155

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

156

Phenomena in the High-Latitude Ionospheric F Region Induced by a HF Heater Wave at Frequencies Near the Fourth Electron Gyroharmonic  

NASA Astrophysics Data System (ADS)

We present the results of multi-instrument studies of the phenomena in the high-latitude ionospheric F region stimulated by high-power HF O-mode radio waves injected towards the magnetic zenith when the ratio of the heater frequency to the cutoff frequency of the F2 layer is near the fourth electron gyroharmonic. Based on the stimulated electromagnetic emission (SEE), spectral observations in the kilohertz and hertz frequency bands of detunings relative to the heater wave frequency, the behaviors of different parameters of the ionospheric plasma and small-scale artificial field-aligned irregularities are compared and analyzed. The coexistence of the thermal (resonance) parametric instability (TPI) and parametric decay (striction) instability (PDI) was found in the vicinity of the fourth gyroresonance harmonic.

Borisova, T. D.; Blagoveshchenskaya, N. F.; Kalishin, A. S.; Kosch, M.; Senior, A.; Rietveld, M. T.; Yeoman, T. K.; Hagstrom, I.

2014-06-01

157

Solar proxies pertaining to empirical ionospheric total electron content models  

Microsoft Academic Search

Solar proxies and indices exhibiting extreme ultraviolet (EUV) irradiance that affects the ionospheric total electron content (TEC) were examined through training an artificial neural network (ANN). A TEC database was constructed from a dense GPS receiver network over Japan from April 1997 to March 2008, covering an entire 11 year solar activity period. In empirical models of upper atmospheric parameters,

Takashi Maruyama

2010-01-01

158

The fine structure of 'caviton' signal scattered by modified ionosphere  

Microsoft Academic Search

The results of experimental study of the spatial and temporal characteristics of ``caviton'' signal (CS) (narrow-band one), scattered by artificially disturbed ionospheric plasma under its sounding by short probing radio pulses are presented. At the heating facilities ``Zimenki'' and ``Sura'' the registration of the time dependencies of CS amplitude and phase at the different virtual heights of scattering with different

G. I. Terina

2004-01-01

159

Anomalies in the Ionosphere around the Southern faults of Haiti near the 2010 Earthquake  

NASA Astrophysics Data System (ADS)

In the last few decades, research on earthquake prediction has resulted in the recognition that there may exist many earthquake precursors in the lithosphere, atmosphere and ionosphere. The ionosphere is naturally perturbed by solar and geomagnetic disturbances and it is difficult to extract the variations connected with earthquakes particularly for the equatorial and high latitude ionosphere. Several researchers have contending theories on the mechanisms associated with pre-earthquake signals. The basic premise is that a thin layer of particles created before earthquakes due to ions originating from the earth's crust travel to the earth's surface and begin radiating from the earth's surface due to strong electric fields Namgaladze et al., [2009]. The ions can then travel from above earth's surface to the ionosphere where they can create ionospheric disturbances. When solar and geomagnetic disturbances can be ruled out, the effects of pre-seismic activities in the ionosphere can be assessed using fluctuations in the ionospheric electron density in the vicinity of fault lines. The Parameterized Ionospheric Model (PIM) is a fast global ionospheric model which produces electron density profiles (EDPs) between 90 and 25000 km altitude, which corresponds to critical altitudes of the ionosphere Daniell et al., [1995]. Since PIM only simulates a statistical mean ionosphere, sudden variations in ionospheric electron density will not be represented in the models, which make PIM ideal for background electron density predictions. The background predictions can then removed from the actual electron density data which could provide means for identifying pre-seismic electron density perturbations.

Cornely, P.; Daniell, R. E.

2013-12-01

160

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

161

A new global version of M(3000)F2 prediction model based on artificial neural networks  

NASA Astrophysics Data System (ADS)

A new version of global empirical model for the ionospheric propagation factor, M(3000)F2 prediction is presented. Artificial neural network (ANN) technique was employed by considering the relevant geophysical input parameters which are known to influence the M(3000)F2 parameter. This new version is an update to the previous neural network based M(3000)F2 global model developed by Oyeyemi et al. (2007), and aims to address the inadequacy of the International Reference Ionosphere (IRI) M(3000)F2 model (the International Radio Consultative Committee (CCIR) M(3000)F2 model). The M(3000)F2 has been found to be relatively inaccurate in representing the diurnal structure of the low latitude region and the equatorial ionosphere. In particular, the existing hmF2 IRI model is unable to reproduce the sharp post-sunset drop in M(3000)F2 values, which correspond to a sharp post-sunset peak in the peak height of the F2 layer, hmF2. Data from 80 ionospheric stations globally, including a good number of stations in the low latitude region were considered for this work. M(3000)F2 hourly values from 1987 to 2008, spanning all periods of low and high solar activity were used for model development and verification process. The ability of the new model to predict the M(3000)F2 parameter especially in the low latitude and equatorial regions, which is known to be problematic for the existing IRI model is demonstrated.

Oronsaye, S. I.; McKinnell, L. A.; Habarulema, J. B.

2014-02-01

162

The Venus ionosphere  

NASA Technical Reports Server (NTRS)

Physical properties of the Venus ionosphere obtained by experiments on the US Pioneer Venus and the Soviet Venera missions are presented in the form of models suitable for inclusion in the Venus International Reference Atmosphere. The models comprise electron density (from 120 km), electron and ion temperatures, and relative ion abundance in the altitude range from 150 km to 1000 km for solar zenith angles from 0 to 180 deg. In addition, information on ion transport velocities, ionopause altitudes, and magnetic field characteristics of the Venus ionosphere, are presented in tabular or graphical form. Also discussed is the solar control of the physical properties of the Venus ionosphere.

Bauer, S. J.; Brace, L. M.; Taylor, H. A., Jr.; Breus, T. K.; Kliore, A. J.

1985-01-01

163

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.

164

Seismo-Ionospheric Precursors  

NASA Astrophysics Data System (ADS)

Large earthquakes are often preceded or accompanied by signals of a different nature: electric, electromagnetic, or luminous, although seismic waves are the most obvious manifestation. Recently, seismo-ionospheric phenomena have received considerable discussions. To investigate possible seismo-ionospheric precursors, we statistically examine the relationship between electron density variations at the ionospheric F2 peak observed by a local ionosonde and 184 earthquakes with magnitude 5.0 or larger, which occurred in 170 days during 1994~1999 in the Taiwan area. Results demonstrate that the electron density abnormally decreases during the afternoon period, 1200~1800 LT, within 5 days before the earthquakes. The odds of the earthquakes with the precursor increasing in the earthquake magnitude but decreasing in the range between the epicenter and the ionosonde confirm the existence of an imminent seismo-ionospheric precursor.

Liu, J.; Chen, Y.; Chuo, Y.

2003-12-01

165

Modeling Ionospheric Electrodynamics (Invited)  

NASA Astrophysics Data System (ADS)

We present modeling results of ionospheric electrodynamics using the 3D NRL ionosphere model SAMI3. Recently, SAMI3 has been upgraded to solve the potential equation that determines the electrostatic potential from the ionospheric conductances (Pedersen and Hall) and drivers: neutral wind, gravity, and parallel current systems. We present results showing the impact of different neutral wind models (e.g., HWM93, HWM07, TIMEGCM) on the dynamics of the low- to mid-latitude ionosphere, as well as the Region 1 and 2 current systems. We point out issues and concerns with obtaining an accurate specification of the global electric field within the context of existing models.(with J. Krall, G. Joyce, S. Slinker, and G. Crowley). Research supported by NASA and ONR

Huba, J. D.

2009-12-01

166

Unusual topside ionospheric density response to the November 2003 superstorm  

Microsoft Academic Search

We use observations from a variety of different ground- and space-based instruments, including ionosonde, ground- and space-based Global Positioning System (GPS) receivers, magnetometers, and solar wind data from the Advanced Composition Explorer (ACE), to examine the response of the ionospheric F2-layer height during the November 2003 superstorm. We found that the topside ionosphere responded unusually to the 20 November 2003

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

2006-01-01

167

Unusual topside ionospheric density response to the November 2003 superstorm  

Microsoft Academic Search

We use observations from a variety of different ground and space-based instruments, including ionosonde, ground and space-based Global Positioning System (GPS) receivers, magnetometers, and the solar wind data from the Advanced Composition Explorer (ACE), to examine the response of the ionospheric F2-layer height during the November 2003 superstorm. We found that the topside ionosphere responded unusually to the November 20,

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

2005-01-01

168

Investigation of the D and E regions of the ionosphere  

NASA Technical Reports Server (NTRS)

Details of an experimental program that investigates the ionosphere using sounding rockets are presented. The investigation is part of a continuing program to gather data on the D and E regions of the ionosphere during periods of recurring natural phenomena that influence these regions. To achieve these ends, four vehicles were launched during the eclipse of the sun on March 7, 1970. Other vehicles totalling 10 in all were launched to investigate transient phenomena such as the sporadic E layer.

Kelly, R. N.; Engelman, A.; Tobey, A. F.

1973-01-01

169

Radar Ionospheric Impact Mitigation  

NASA Astrophysics Data System (ADS)

New ionospheric modeling technology is being developed to improve correction of ionospheric impacts on the performance of ground-based space-surveillance radars (SSRs) in near-real-time. These radars, which detect and track space objects, can experience significant target location errors due to ionospheric delay and refraction of the radar signals. Since these radars must detect and track targets essentially to the radar horizon, it is necessary to accurately model the ionosphere as the radar would observe it, down to the local horizon. To correct for spatial and temporal changes in the ionosphere the model must be able to update in near-real-time using ionospheric sensor data. Since many radars are in isolated locations, or may have requirements to operate autonomously, an additional required capability is to provide accurate ionospheric mitigation by exploiting only sensor data from the radar site. However, the model must also be able to update using additional data from other types of sensors that may be available. The original radar ionospheric mitigation approach employed the Bent climatological model. This 35-year-old technology is still the means employed in the many DoD SSRs today. One more recent approach used capabilities from the PRISM model. PRISM technology has today been surpassed by `assimilative models' which employ better physics and Kalman filtering techniques. These models are not necessarily tailored for SSR application which needs to optimize modeling of very small regions using only data from a single sensor, or very few. The goal is to develop and validate the performance of innovative and efficient ionospheric modeling approaches that are optimized for the small regions applicable to ground-based radar coverage (radius of ~2000 km at ionospheric altitudes) and somewhat beyond. These approaches must adapt a continuous modeling scheme in near-real-time to be consistent with all observational data that may become available, and degrade gracefully toward a climatological representation in the absence of data. In this presentation we will discuss the issues for improving correction of ionospheric impacts on SSRs, some of the capabilities and limitations of current models, and the requirements and goals for new modeling technologies.

Bishop, G.; Decker, D.; Baker, C.

2006-12-01

170

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

171

Travelling ionospheric disturbance over California mid 2000  

NASA Astrophysics Data System (ADS)

In this paper, the GPS data collected by more than 130 permanent GPS stations that belong to the Southern California Integrated GPS Network (SCIGN) around the launch of a Minuteman-II missile on 8 July 2000 (UTC) is processed to reveal traveling ionospheric disturbance (TID) all over the network on average 15 min after the launch. This TID was initially perceived to be excited by the launch itself, but this conclusion is challenged by the propagation direction. This is because this TID seems to travel towards the air force base from where the launch took place, not far away from it. This challenge is based on the assumption that TID is occurring at one single ionospheric altitude. While the nature of ionosphere supports such horizontally-guided propagation, multi-altitude ionospheric pierce points are hypothesized, which would support the suggestion that detected TID is excited by the missile launch itself, despite the apparent reverse direction of propagation. The overall analysis rules out any extra-terrestrial sources like solar flares, or seismic sources like earthquakes, which confirms the conclusion of TID excitation by the launch. There is apparent coherence of the TID for about 45 min and the propagation speed of TID within the layer of ionosphere is calculated to be approximately equal to 1230 m/s. While the usual assumption for TID is that they occur around an altitude of 350 km, such sound speed can only occur at much higher altitudes. Further research is recommended to accurately pinpoint the ionospheric pierce points and develop an algorithm to locate the source of TID in case it is totally unknown.

Hawarey, M.

2006-01-01

172

Estimation of optical turbulence in the atmospheric surface layer from routine meteorological observations: an artificial neural network approach  

NASA Astrophysics Data System (ADS)

The focus of this paper is on the estimation of optical turbulence (commonly characterized by C2n ) near the land-surface using routinely measured meteorological variables (e.g., temperature, wind speed). We demonstrate that an artificial neural network-based approach has the potential to be effectively utilized for this purpose. We use an extensive scintillometer-based C2n dataset from a recent field experiment in Texas, USA to evaluate the accuracy of the proposed approach.

Wang, Yao; Basu, Sukanta

2014-10-01

173

First observation of the anomalous electric field in the topside ionosphere by ionospheric modification over EISCAT  

NASA Astrophysics Data System (ADS)

have developed an active ground-based technique to estimate the steady state field-aligned anomalous electric field (E*) in the topside ionosphere, up to ~600 km, using the European Incoherent Scatter (EISCAT) ionospheric modification facility and UHF incoherent scatter radar. When pumping the ionosphere with high-power high-frequency radio waves, the F region electron temperature is significantly raised, increasing the plasma pressure gradient in the topside ionosphere, resulting in ion upflow along the magnetic field line. We estimate E* using a modified ion momentum equation and the Mass Spectrometer Incoherent Scatter model. From an experiment on 23 October 2013, E* points downward with an average amplitude of ~1.6 ?V/m, becoming weaker at higher altitudes. The mechanism for anomalous resistivity is thought to be low-frequency ion acoustic waves generated by the pump-induced flux of suprathermal electrons. These high-energy electrons are produced near the pump wave reflection altitude by plasma resonance and also result in observed artificially induced optical emissions.

Kosch, M. J.; Vickers, H.; Ogawa, Y.; Senior, A.; Blagoveshchenskaya, N.

2014-11-01

174

Sources of uncertainty in ionospheric modeling: The neutral wind  

NASA Astrophysics Data System (ADS)

neutral wind is a critical input parameter for physics-based ionospheric models, affecting both the height of the F layer and the total electron content. Unfortunately, the currently available models of the thermospheric wind do not seem to represent it very accurately, and this places a serious limitation on the effectiveness of ionospheric modeling and forecasting. We make use of several decades' worth of midlatitude ionosonde observations of the F region peak, in order to compare the effectiveness of several neutral wind models when used as drivers for an ionospheric model. We check the simulation results against the ground truth of the ionosonde observations using the technique of forecast skill scores. We find that with the ionospheric model in use here (the Utah State University Time Dependent Ionospheric Model (TDIM)), a very simple neutral wind pattern outperforms the more complex models. Increases in skill scores as high as 50% are obtained, relative to the reference case of zero wind; also, in some cases, there are similarly large decreases in skill scores. We view this as a sensitivity study, rather than an effort to identify the best wind model in an absolute sense, because any ionospheric model is an assemblage of algorithms, boundary conditions, and drivers that are themselves imperfect. We identify reasons for the large variability in skill scores with respect to season, longitude, and solar cycle level. We close with a brief discussion of other parameters in ionospheric modeling that are similarly uncertain, e.g., a downward electron flux and the Burnside factor.

David, Michael; Sojka, Jan J.; Schunk, Robert W.

2014-08-01

175

Low-latitude ionosphere dynamics as deduced from meridional ionosonde chain: Ionospheric ceiling  

NASA Astrophysics Data System (ADS)

Interest in the equatorial anomaly in the ionosphere has been focused mostly on f_oF_2, and not much attention was paid to h_mF_2 except for the time rate of change of it in connection with the vertical plasma drift velocity. There have been few climatological studies on h_mF_2 variations associated with development of the equatorial anomaly. In this paper, we revisit the equatorial anomaly in terms of height variations. For this purpose, we analyzed scaled ionogram parameters from three stations located along the magnetic meridian that is a primary component of Southeast Asia low-latitude ionospheric network (SEALION); one at the magnetic equator and the others at conjugate off-equatorial latitudes near 10 degrees magnetic latitude. The daytime h_mF_2 was investigated for each season during the solar minimum period, 2006-2007 and 2009. The peak height increased for approximately 3 hr after sunrise at all locations, as expected from the daytime upward E×B drift. The apparent upward drift ceased before noon at the magnetic equator, while the layer continued to increase at the off-equatorial latitudes, reaching altitudes higher than the equatorial height around noon. The noon time restricted layer height at the magnetic equator did not depend much on the season, while the maximum peak height at the off-equatorial latitudes largely varied with season. The daytime specific limiting height of the equatorial ionosphere was termed ionospheric ceiling. Numerical modeling using the SAMI2 code reproduced the features of the ionospheric ceiling quite well. Dynamic parameters provided by the SAMI2 modeling were investigated and it was shown that the ionospheric ceiling is another aspect of the fountain effect, in which increased diffusion of plasma at higher altitudes has a leading role.

Maruyama, Takashi; Uemoto, Junpei; Tsugawa, Takuya; Supnithi, Pornchai; Ishii, Mamoru; Komolmis, Tharadol

176

Generation of Acoustic-Gravity Waves in Ionospheric HF Heating Experiments: Simulating Large-Scale Natural Heat Sources  

NASA Astrophysics Data System (ADS)

In this thesis, we investigate the potential role played by large-scale anomalous heat sources (e.g. prolonged heat wave events) in generating acoustic-gravity waves (AGWs) that might trigger widespread plasma turbulence in the ionospheric layer. The main hypothesis is that, the thermal gradients associated with the heat wave fronts could act as a source of powerful AGW capable of triggering ionospheric plasma turbulence over extensive areas. In our investigations, first we are going to examine a case study of the summer 2006 North American heat wave event. Our examination of GPS-derived total electron content (TEC) data over the North American sector reveals a quite noticeable increase in the level of daily plasma density fluctuations during the summer 2006 heat wave period. Comparison with the summer 2005 and summer 2007 data further confirms that the observed increase of traveling ionospheric disturbances (TIDs) during the summer 2006 heat wave period was not simply a regular seasonal phenomenon. Furthermore, a series of field experiments had been carried out at the High-frequency Active Auroral Research Program (HAARP) facility in order to physically simulate the process of AGW/TID generation by large-scale thermal gradients in the ionosphere. In these ionospheric HF heating experiments, we create some time-varying artificial thermal gradients at an altitude of 200--300 km above the Earth's surface using vertically-transmitted amplitude-modulated 0-mode HF heater waves. For our experiments, a number of radio diagnostic instruments had been utilized to detect the characteristic signatures of heater-generated AGW/TID. So far, we have been able to obtain several affirmative indications that some artificial AGW/TID are indeed being radiated out from the heated plasma volume during the HAARP-AGW experiments. Based on the experimental evidence, we may conclude that it is certainly quite plausible for large-scale thermal gradients associated with severe heat wave events to generate some AGW which might induce widespread plasma turbulence far in space. (Copies available exclusively from MIT Libraries, libraries.mit.edu/docs - docs mit.edu)

Pradipta, Rezy

177

Configuration of the upper boundary of the ionosphere  

NASA Astrophysics Data System (ADS)

Variations of the upper boundary of the ionosphere (UBI) are investigated based on three sources of information: (i) ionosonde-derived parameters: critical frequency foF2, propagation factor M3000F2, and sub-peak thickness of the bottomside electron density profile; (ii) total electron content (TEC) observations from signals of the Global Positioning System (GPS) satellites; (iii) model electron densities of the International Reference Ionosphere (IRI*) extended towards the plasmasphere. The ionospheric slab thickness is calculated as ratio of TEC to the F2 layer peak electron density, NmF2, representing a measure of thickness of electron density profile in the bottomside and topside ionosphere eliminating the plasmaspheric slab thickness of GPS-TEC with the IRI* code. The ratio of slab thickness to the real thickness in the topside ionosphere is deduced making use of a similar ratio in the bottomside ionosphere with a weight Rw. Model weight Rw is represented as a superposition of the base-functions of local time, geomagnetic latitude, solar and magnetic activity. The time-space variations of domain of convergence of the ionosphere and plasmasphere differ from an average value of UBI at ˜1000 km over the earth. Analysis for quiet monthly average conditions and during the storms (September 2002, October-November 2003, November 2004) has shown shrinking UBI altitude at daytime to 400 km. The upper ionosphere height is increased by night with an ‘ionospheric tail’ which expands from 1000 km to more than 2000 km over the earth under quiet and disturbed space weather. These effects are interposed on a trend of increasing UBI height with solar activity when both the critical frequency foF2 and the peak height hmF2 are growing during the solar cycle.

Gulyaeva, Tamara L.

2007-06-01

178

Features of artificial ULF/VLF signals induced by SURA facility under increased solar activity conditions  

NASA Astrophysics Data System (ADS)

It was conducted a comprehensive study of artificial ionospheric signal generation in the ULF/VLF bands at SURA facility during the past four years. We investigated the influence of geomagnetic activity on the characteristics of artificial low-frequency signals in recent years under the background of increasing solar activity. No correlation with variations of Earth's magnetic field was observed for weak geomagnetic disturbances (Kp < 3). It was observed decreasing in the amplitude of signals at frequencies of 3 and 6 Hz, while the VLF signals at frequencies of 2 and 2.6 kHz increased for growth phase of the geomagnetic field perturbations during a small magnetic storms October 7, 2011 (Ki = 4 according to Moscow station). A similar pattern was traced in 2013 during storms March 21 (Kp = 5), May 24-25 (Kp = 5 +) and August 16 (Kp = 5 +). There are two possible reasons for the observed dependence - increasing the absorption of HF and VLF waves in the lower ionosphere, and / or reduction of the critical frequency of the F-layer, usually accompanied by a magnetic storm. The last factor is perhaps the most likely. This dependence was traced more convincingly on May 24-25, when during a storm time SURE had operated from evening until 6:00 MST in the morning. Signal amplitude explicitly followed the F- layer critical frequency variation. Some of the measurements in June 2012 were conducted during a magnetic storm on June 16-18, (Kp = 6). It was also found a decrease in the amplitude of the signal at the rise of the magnetic disturbance. In addition, during the daytime session 18.06.2012 during the recovery phase, it was detected modulation of artificial signals at frequencies 11 and 17 Hz with a period of 30 seconds. Note that the period of 30s is the main period of oscillation of the geomagnetic field line passing through the SURA facility, and more, the periods for torsional and the toroidal oscillation modes of this field line surprising coincidence for SURA geomagnetic latitude. Also the peculiarities were displayed in the polarization of artificial VLF signals during magnetic storms. Typically, the artificial emission is elliptically polarized at all frequencies of VLF signals with a predominance of the left- polarization. During a storm time, it was detected a change in the polarization of artificial VLF emissions. The right polarization becomes predominant. This fact can be associated with changes in ionospheric plasma parameters under a magnetic storm conditions. This work was supported by RFBR grants 13-02-0072 and 13-02-12074.

Kotik, Dmitry; Ryabov, Alexander; Pershin, Alexsander; Ermakova, Elena

179

Ionospheric RF lidar  

NASA Astrophysics Data System (ADS)

A new diagnostic consisting of a high-power RF or microwave transmitter and a ground-based lidar system is proposed for probing the ionosphere at heights of 80-200 km. The high-power transmitter creates energetic electrons in the ionosphere, which excite molecules to higher energy levels. These excited molecules become targets for a laser ranging system by resonantly absorbing and reradiating light at specific wavelengths. A laser pulse tuned to a specific transition wavelength is fired from a ground-based laser, and the reradiated light is detected by a ground-based light collector. A study of atmospheric species for ranging was performed, and the most suitable species were found to be N2 and N2(+). A laser whose output is matched exactly to the vibrational-rotational spectrum of ionospheric N2 is proposed as the lidar master oscillator instead of a tunable due laser.

Fukuchi, T.; Wong, A. Y.; Wuerker, R. F.

1990-12-01

180

Ionosphere-magnetosphere studies using ground based VLF radio propagation technique: an Indian example  

Microsoft Academic Search

Since IGY period (1957-58), natural and artificially produced Very Low Frequency (VLF) elec-tromagnetic radiations are being recorded at large number of ground stations all over the world and on-board satellites to study various radio wave-thermal\\/energetic plasma interactive pro-cesses related to earth's ionosphere-plasmasphere-magnetosphere environment. The terrestrial propagation of these VLF radio waves are primarily enabled through the earth ionosphere wave guide

Subhas Chakravarty

2010-01-01

181

Intercepted signals for ionospheric science  

NASA Astrophysics Data System (ADS)

The ISIS array (Intercepted Signals for Ionospheric Science) is a distributed, coherent software radio array designed for the study of geospace phenomena by observing the scatter of ambient radio frequency (RF) signals. ISIS data acquisition and analysis is performed using the MIDAS-M platform (Millstone Data Acquisition System - Mobile). Observations of RF signals can be performed between HF and L-band using the Array nodes and appropriate antennas. The deployment of the Array focuses on observations of the plasmasphere boundary layer. We discuss the concept of the coherent software radio array, describe the ISIS hardware, and give examples of data from the system for selected applications. In particular, we include the first observations of E region irregularities using the Array. We also present single-site passive radar observations of both meteor trails and E region irregularities using adaptive filtering techniques.

Lind, F. D.; Erickson, P. J.; Coster, A. J.; Foster, J. C.; Marchese, J. R.; Berkowitz, Z.; Sahr, J. D.

2013-05-01

182

The effect of ionospheric scintillation on VHF\\/UHF satellite communications  

Microsoft Academic Search

Ionospheric scintillations of the type caused by F-layer irregularities can degrade the performance of satellite communication links at UHF. The degradation is most severe for propagation paths that transit the auroral and equatorial ionospheres. In the present paper, scintillation data obtained in the auroral and equatorial regions are analyzed and the results are applied to the evaluation of the performance

H. E. Whitney; Santimay Basu

1977-01-01

183

Medium and small-scale ionospheric irregularities detected by GPS radio occultation method  

Microsoft Academic Search

The radio occultation technique is used to study plasma irregularities in the F2 layer ionosphere and below. The data, acquired by the GPS receiver onboard the geophysical research satellite CHAMP for more than three years, allow to study ionospheric irregularities under different geophysical conditions on a global scale. The dual-frequency GPS signals provide a possibility to trace irregularities with a

K. Tsybulya; N. Jakowski

2005-01-01

184

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

185

Stallion spermatozoa selected by single layer centrifugation are capable of fertilization after storage for up to 96?h at 6°C prior to artificial insemination  

PubMed Central

Background One of the challenges faced by equine breeders is ensuring delivery of good quality semen doses for artificial insemination when the mare is due to ovulate. Single Layer Centrifugation (SLC) has been shown to select morphologically normal spermatozoa with intact chromatin and good progressive motility from the rest of the ejaculate, and to prolong the life of these selected spermatozoa in vitro. The objective of the present study was a proof of concept, to determine whether fertilizing ability was retained in SLC-selected spermatozoa during prolonged storage. Findings Sixteen mares were inseminated with SLC-selected sperm doses that had been cooled and stored at 6°C for 48?h, 72?h or 96?h. Embryos were identified in 11 mares by ultrasound examination 16–18?days after presumed ovulation. Conclusion SLC-selected stallion spermatozoa stored for up to 96?h are capable of fertilization. PMID:22788670

2012-01-01

186

In-Situ Transmission Electron Microscopy Probing of Native Oxide and Artificial Layers on Silicon Nanoparticles for Lithium Ion Batteries  

SciTech Connect

Surface modification of silicon nanoparticle via molecular layer deposition (MLD) has been recently proved to be an effective way for dramatically enhancing the cyclic performance in lithium ion batteries. However, the fundamental mechanism as how this thin layer of coating function is not known, which is even complicated by the inevitable presence of native oxide of several nanometers on the silicon nanoparticle. Using in-situ TEM, we probed in detail the structural and chemical evolution of both uncoated and coated silicon particles upon cyclic lithiation/delithation. We discovered that upon initial lithiation, the native oxide layer converts to crystalline Li2O islands, which essentially increases the impedance on the particle, resulting in ineffective lithiation/delithiation, and therefore low coulombic efficiency. In contrast, the alucone MLD coated particles show extremely fast, thorough and highly reversible lithiation behaviors, which are clarified to be associated with the mechanical flexibility and fast Li+/e- conductivity of the alucone coating. Surprisingly, the alucone MLD coating process chemically changes the silicon surface, essentially removing the native oxide layer and therefore mitigates side reaction and detrimental effects of the native oxide. This study provides a vivid picture of how the MLD coating works to enhance the coulombic efficiency and preserve capacity and clarifies the role of the native oxide on silicon nanoparticles during cyclic lithiation and delithiation. More broadly, this work also demonstrated that the effect of the subtle chemical modification of the surface during the coating process may be of equal importance as the coating layer itself.

He, Yang; Piper, Daniela M.; Gu, Meng; Travis, Jonathan J.; George, Steven M.; Lee, Se-Hee; Genc, Arda; Pullan, Lee; Liu, Jun; Mao, Scott X.; Zhang, Jiguang; Ban, Chunmei; Wang, Chong M.

2014-10-27

187

The Ionosphere of Mars: Sources, Variability and Coupling to the Solar Wind  

NASA Astrophysics Data System (ADS)

The ionosphere -thermosphere components of the Mars International Reference Atmosphere (MIRA) represent the upper limits of the planet's atmospheric environment. Above approximately 100 km, the ionospheric domain occurs in a relatively limited altitude region, but one that contains a rich blend of photo- chemical processes and space plasma dynamics. There are two ionospheric layers between 100-150 km, an exosphere that begins near 200 km and an "ionopause" near 350 km that results from the solar wind interaction with ionospheric plasma. The recent discovery of localized magnetic fields (predominately in the southern hemisphere) adds a complexity of ionosphere-magnetosphere-like interactions that needs to be understood. The MIRA Ionospheric Team will be composed of an international group of researchers involved in all aspects of upper atmospheric science at Mars. The proposed effort will involve working with other MIRA groups in the years ahead, and especially with colleagues involved in upcoming satellite missions to Mars.

Mendillo, M.; Kliore, A.

188

Observations of Midlatitude Ionospheric  

Microsoft Academic Search

Using data from the available networks of GPS receivers (CORS and FAA WAAS), observations of rapid drops in TEC (as much as 14 meters of ionospheric delay or 84 TECu within 100 seconds) have been observed in mid-latitudes during major geomagnetic storms. Investigations of these TEC drops have suggested that the drops were due to what appeared to be \\

T. F. Dehel; A. J. Mannucci; A. Komjathy; X. Pi

2004-01-01

189

Seismo-Ionospheric Phenomena  

NASA Astrophysics Data System (ADS)

Ionospheric F-region disturbances and anomalous foEs increases were separately observed within a few days before two great earthquakes in geomagnetic and solar quiet conditions. The ionospheric foF2 decreased from its monthly median at Wakkanai, 290 km north of the epicenter from 3 days before the M 7.8 earthquake onset of July 12, 1993 in the northern Japan to 3 days after it. Anomalous foEs increases above 7 MHz were observed at Shigaraki, 100 km northeast of the epicenter in the daytime on January 15, 1995 before the M 7.2 Hyogoken-nambu earthquake onset of January 17, 1995. The F-region disturbances before the earthquake is discussed in terms of the ionospheric vertical movements caused by a seismo electric field on the assumption of the global ionosphere-earth seismo current system. The anomalous foEs increases before the earthquake onset could be, caused by unknown super-volt seismo discharges since there was no thunderstorm cloud over the observatories

Ondoh, Tadanori

190

The Venus ionosphere  

Microsoft Academic Search

Physical properties of the Venus ionosphere obtained by experiments on the US Pioneer Venus and the Soviet Venera missions are presented in the form of models suitable for inclusion in the Venus International Reference Atmosphere. The models comprise electron density (from 120 km), electron and ion temperatures, and relative ion abundance in the altitude range from 150 km to 1000

S. J. Bauer; L. M. Brace; H. A. Taylor Jr.; T. K. Breus; A. J. Kliore

1985-01-01

191

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

192

Solitons and ionospheric heating  

NASA Technical Reports Server (NTRS)

It is noted that for parameters characterizing the Platteville ionospheric heating facility, the Langmuir wave evolution at the exact reflection point of the heater wave involves an oscillating two-stream instability followed by a collisionally damped three-dimensional soliton collapse. The result gives an alternative explanation for certain experimental observations.

Weatherall, J. C.; Goldman, M. V.; Sheerin, J. P.; Nicholson, D. R.; Payne, G. L.; Hansen, P. J.

1982-01-01

193

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

194

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

195

Emissions of ionospheric Alfvén resonator and ionospheric conditions  

NASA Astrophysics Data System (ADS)

We analyze continuous magnetic observations of ionospheric Alfvén resonator (IAR) emissions at mid-latitude observatory Mondy. The measurements were by a LEMI-30 search-coil magnetometer covering the period from March 2010 to May 2011. The results are compared with data from simultaneous ionospheric sounding data and International Reference Ionosphere (IRI-2012) model parameters. The large amount of observational data allowed us to inspect the daily and seasonal variations in some morphological characteristics of the emissions as well as their relationship to ionospheric conditions. The main factor affecting the duration of the emission is how long the lower ionosphere stays in Earth's shadow. We demonstrate a close inverse correlation between the diurnal and seasonal IAR frequency variations, on the one hand, and changes in the ionospheric critical frequency, f0F2, on the other. Additionally, the expected emission frequency scale calculated with the IRI-2012 model is in good agreement with the values measured from the emission spectrograms.

Potapov, A. S.; Polyushkina, T. N.; Dovbnya, B. V.; Tsegmed, B.; Rakhmatulin, R. A.

2014-11-01

196

Response of topside ionosphere to man-made electromagnetic emissions  

NASA Astrophysics Data System (ADS)

Investigation of electromagnetic measurements in the VLF range, obtained by DEMETER satellite revealed that terrestrial navigational stations are clearly "visible" in the ionosphere. Statistical studies were performed in the frequency range between 10kHz and 20kHz for one component of electric and magnetic field. We used data collected with ICE and IMSC in-struments placed on-board DEMETER. Global maps of man-made emissions show significant ionospheric response. This first satellite from the CNES MYRIADE micro-satellite series was launched on a polar orbit in June 2004 and provides permanent in-situ observations of ionospheric plasma parameters at the altitude of 700 km. As there are now more than five years of operational data a statistical study on both, the bulk ionospheric parameters and electromagnetic emissions, is possible. Since, statistical analysis have shown how easily are detectable man-made signals in the ionosphere, it has implied further studies on other plasma parameters. Using Langmuir probe experiment ISL ("Instrument Sonde de Langmuir") we develop global maps for electron temperature and density. Data are represented in geographic coordinates and averaged over one-month period. We present comparison analysis, that give the statistical background for further studies of noises occurring in the upper layers of ionosphere.

Slominska, Ewa; Rothkaehl, Hanna; Slominski, Jan

197

Integrated Research Plan April 1, 2008 "Effects of Ionospheric-Magnetospheric  

E-print Network

and at nightside auroral latitudes inject these ionospheric source plasmas outward along magnetic field lines of the solar wind interaction, and is powered mainly by the solar EUV energy absorbed in the F layer [e

Lotko, William

198

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

NASA Astrophysics Data System (ADS)

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

Yukon, Stanford P.

1986-07-01

199

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

200

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

201

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

202

BOLAS: A Canadian-US Ionospheric Tether Mission  

NASA Technical Reports Server (NTRS)

Everyday, international broadcasters, ships, and aircraft use a naturally conducting atmospheric layer, the ionosphere, to reflect communications signals over the Earth's horizon. A better understanding of this layer, with its irregularities, instabilities, and dynamics, would improve communications transmission and reception. This atmospheric layer is also a lens that can distort signal transmissions from communications, navigation, and surveillance satellites. The ionosphere over Canada and other high latitude countries can carry large currents and is particularly dynamic, so that a scientific understanding of this layer is critical. The BOLAS (Bistatic Observations using Low Altitude Satellites) mission would characterize reflective and transmissive properties of the ionosphere by flying two satellites, each with identical HF receivers, dipole antennas, particle probes, and GPS receivers. The satellites would be connected by a non-conducting tether to maintain a 100 m separation, and would cartwheel in the orbit plane to spatially survey the ionosphere. The six-month mission would fly in a high inclination, 350 x 600 km orbit, and would be active during passes over the auroral region of Canada. This paper discusses the system requirements and architecture, spacecraft and operations concepts, and mission design, as well as team organization, international cooperation and the scientific and technological benefits that are expected.

Tyc, George; Vigneron, Frank; Jablonski, Alexander; James, H. Gordon; Carrington, Connie; Rupp, Charles

1997-01-01

203

Observations of the effects of meteors on the ionospheres of  

E-print Network

Observations of the effects of meteors on the ionospheres of Venus, Earth and Mars Paul Withers1, A Planetology: Venus-Earth-Mars, ESLAB 2009 ESTEC, The Netherlands #12;Observations of the effects of meteors that affect metal ion layers ­ Meteor showers ­ Sporadic meteoroids ­ Magnetic fields and winds · Status

Withers, Paul

204

Comparison of Ionospheric Observations and Dynamical Predictions of Meteor  

E-print Network

Comparison of Ionospheric Observations and Dynamical Predictions of Meteor Showers at Mars Paul intervals when there are many of these profiles and call them meteor showers We study cometary orbits to identify the parent bodies responsible for the meteor showers #12;Meteoric Layers (MEX) Profile with EUV

Withers, Paul

205

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

206

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. PMID:22463768

2012-01-01

207

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

208

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

209

Oblique sounding of the ionosphere by powerful wave beams  

NASA Astrophysics Data System (ADS)

The article is devoted to modeling the impact on the ionosphere powerful obliquely incident wave beam. The basis of this analysis will be orbital variational principle for the intense wave beams-generalization of Fermat's principle to the case of a nonlinear medium (Molotkov and Vakulenko, 1988a,b; Molotkov, 2003, 2005). Under the influence of a powerful wave beam appears manageable the additional stratification of the ionospheric layer F2. Explicit expressions show how the properties of the test beam, with a shifted frequency, released in the same direction as the beam depend on the intensity of a powerful beam and the frequency shift.

Molotkov, I. A.; Atamaniuk, B.

2011-04-01

210

Ionospheric response to the acoustic gravity wave singularity  

NASA Astrophysics Data System (ADS)

An original model of atmospheric wave propagation from ground sources to the ionosphere in the atmosphere with a realistic high-altitude temperature profile is analyzed. Shaping of a narrow domain with elevated pressure in the resonance region where the horizontal phase wave velocity is equal to the sound velocity is examined theoretically within the framework of linearized Eq.s. Numerical simulations for the model profiles of atmospheric temperature and viscosity confirm analytical result for the special feature of wave fields. The formation of the narrow domain with plasma irregularities in the D and low E ionospheric layers caused by the acoustic gravity wave singularity is discussed.

Savina, Olga N.; Bespalov, Peter A.

2014-11-01

211

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

212

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

213

Observed correlations between interplanetary magnetic field variations and the dynamics of the auroral oval and the high-latitude ionosphere  

Microsoft Academic Search

Flights of the Air Force Cambridge Research Laboratories flying ionospheric laboratory investigated the day sector of the auroral oval under conditions of darkness. Airborne all-sky cameras and a vertical incidence ionospheric sounder were used to follow the time history of the equatorward boundary of the auroral oval and the F layer irregularity zone (Fliz). In the geomagnetic day sector the

C. P. Pike; C.-I. Meng; S.-I. Akasofu; J. A. Whalen

1974-01-01

214

Layers  

NASA Astrophysics Data System (ADS)

The temperature-dependent photoresponse characteristics of MnAl2S4 layers have been investigated, for the first time, by use of photocurrent (PC) spectroscopy. Three peaks were observed at all temperatures. The electronic origin of these peaks was associated with band-to-band transitions from the valence-band states ?4( z), ?5( x), and ?5( y) to the conduction-band state ?1( s). On the basis of the relationship between PC-peak energy and temperature, the optical band gap could be well expressed by the expression E g( T) = E g(0) - 2.80 × 10-4 T 2/(287 + T), where E g(0) was estimated to be 3.7920 eV, 3.7955 eV, and 3.8354 eV for the valence-band states ?4( z), ?5( x), and ?5( y), respectively. Results from PC spectroscopy revealed the crystal-field and spin-orbit splitting were 3.5 meV and 39.9 meV. The gradual decrease of PC intensity with decreasing temperature can be explained on the basis of trapping centers associated with native defects in the MnAl2S4 layers. Plots of log J ph, the PC current density, against 1/ T, revealed a dominant trap level in the high-temperature region. By comparing PC and the Hall effect results, we confirmed that this trap level is a shallow donor 18.9 meV below the conduction band.

Hong, K. J.; Jeong, T. S.; Youn, C. J.

2014-09-01

215

Solitons and ionospheric modification  

NASA Technical Reports Server (NTRS)

The possibility of Langmuir soliton formation and collapse during ionospheric modification is investigated. Parameters characterizing former facilities, existing facilities, and planned facilities are considered, using a combination of analytical and numerical techniques. At a spatial location corresponding to the exact classical reflection point of the modifier wave, the Langmuir wave evolution is found to be dominated by modulational instability followed by soliton formation and three-dimensional collapse. The earth's magnetic field is found to affect the shape of the collapsing soliton. These results provide an alternative explanation for some recent observations.

Sheerin, J. P.; Nicholson, D. R.; Payne, G. L.; Hansen, P. J.; Weatherall, J. C.; Goldman, M. V.

1982-01-01

216

INSPIRE: Ionosphere Radio Experiments  

NSDL National Science Digital Library

This site, courtesy of Interactive NASA Space Physics Ionosphere Radio Experiments (INSPIRE,) monitors atmospheric sounds that are largely caused by lightning at radio frequencies. The page allows you to listen in on sferics, tweeks, whistlers and other strangely named sounds. This research is in an experimental stage, the site states: "This is an experimental resource. We hope to maintain the VLF audio stream 24 hours a day with infrequent interruptions for maintenance. However, we can't guarantee that it will be available all the time. Let us know if you encounter problems." This is an interesting resource for those interested in atmospheric science or space study.

Philips, Tom

2009-03-25

217

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

218

Response of topside ionosphere to man-made electromagnetic emissions  

NASA Astrophysics Data System (ADS)

Investigation of electromagnetic measurements in the VLF range, obtained by DEMETER satellite revealed that terrestrial navigational stations are clearly "visible" in the ionosphere. Statistical studies were performed in the frequency range between 10kHz and 20kHz for one component of electric and magnetic field. We used data collected with ICE and IMSC instruments placed on-board DEMETER. This first satellite from the CNES MYRIADE micro-satellite series was launched on a polar orbit in June 2004 and provides permanent in-situ observations of ionospheric plasma parameters at the altitude of ~700 km. As there are now more than five years of operational data a statistical study on both, the bulk ionospheric parameters and electromagnetic emissions, is possible. Since, statistical analysis have shown how easily are detectable man-made signals in the ionosphere, it has implied further studies on other plasma parameters. Using Langmuir probe experiment ISL ("Instrument Sonde de Langmuir") we develop global maps for electron temperature and density. Data are represented in geographic coordinates and averaged over one-month period. We present comparison analysis, that give the statistical background for further studies of noises occurring in the upper layers of ionosphere.

Slominska, Ewa; Rothkaehl, Hanna; Slominski, Jan; Wiktorowicz, Grzegorz

2010-05-01

219

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

220

Comparing ionospheric models with mid-latitude ionosonde observations  

NASA Astrophysics Data System (ADS)

The purpose of this research work is to validate the ionospheric models (IRI and CHIU) to assess its suitability and usefulness as an operational tool. The ionospheric model is a computer model designed to predict the state of the global ionosphere for 24 h. The scope was limited to conduct comparisons between the predicted F2 layer critical frequencies (f0F2) against observed ionosonde data. The ionospheric prediction model (IPM) was designed to predict by using monthly median sunspot number, while the observation data are taken from two digital ionospheric sounding stations (Okinawa, 26.28N, 127.8E and Wakkanai, 45.38N, 141.66E) which lies within the mid-latitude region of the globe. Analysis of the f0F2 data from stations for year (2001) with high solar activity and year (2004) with low solar activity, four months (March, June, September and December) chosen based primarily on data availability. From results it seen that the ratio between monthly median predicted and observed f0F2 values for each model used in this research work and for the chosen months was nonlinear with local time, so the empirical formula for applying correction factors were determined, these formula can be used to correct the error occurred in predicted f0F2 value.

Al-Ubaidi, Najat M. R.

2009-06-01

221

Anomalous variations in the ionospheric F 2 -layer structure at geomagnetic midlatitudes of the Southern and Northern hemispheres at the transition from summer to winter conditions under low solar activity  

Microsoft Academic Search

The structure and dynamics of the ionosphere and plasmasphere at low solar activity under quiet geomagnetic conditions on\\u000a January 15–17, 1985, and July 10–13, 1986, over Millstone Hill station and Argentine Islands ionosonde, the locations of which\\u000a are approximately magnetically conjugate, have been theoretically calculated. The detected correction of the model input parameters\\u000a makes it possible to coordinate the measured

A. V. Pavlov; N. M. Pavlova; S. F. Makarenko; V. N. Shubin

2008-01-01

222

A post-Pioneer Venus reassessment of the Martian dayside ionosphere as observed by radio occultation methods  

NASA Technical Reports Server (NTRS)

Global characteristics of the dayside ionosphere of Mars were investigated by reanalyzing the electron-density dayside altitude profiles obtained by Mariners 4, 6, 7, and 9 and the Viking 1 and 2. The properties of both the electron density peaks and the topside profiles with the behavior expected for a Chapman layer in the Mars ionosphere were compared with those observed at Venus with the Pioneer Venus. The results yield an improved picture of the solar zenith angle dependences of both the peaks and the scale heights of the ionosphere of Mars, and their comparison with Venus at solar minimum. It is shown that, under similar conditions where the incident solar wind dynamic pressure exceeds the peak ionospheric thermal pressure, the Martian dayside ionosphere peaks at higher altitudes in the flanks and has a greater scale height. Thus, Martian and Venusian ionospheres would present different obstacles to solar wind.

Zhang, M. H. G.; Luhmann, J. G.; Kliore, A. J.; Kim, J.

1990-01-01

223

Cubesat-Based Dtv Receiver Constellation for Ionospheric Tomography  

NASA Astrophysics Data System (ADS)

The Radio Aurora Explorer mission, funded by NSF's Space Weather and Atmospheric Research program, has demonstrated the utility of CubeSat-based radio receiver payloads for ionospheric research. RAX has primarily been an investigation of microphysics of meter-scale ionospheric structures; however, the data products are also suitable for research on ionospheric effects on radio propagation. To date, the spacecraft has acquired (1) ground-based UHF radar signals that are backscattered from meter-scale ionospheric irregularities, which have been used to measure the dispersion properties of meter-scale plasma waves and (2) ground-based signals, directly on the transmitter-spacecraft path, which have been used to measure radio propagation disturbances (scintillations). Herein we describe the application of a CubeSat constellation of UHF receivers to expand the latter research topic for global-scale ionospheric tomography. The enabling factor for this expansion is the worldwide availability of ground-based digital television (DTV) broadcast signals whose characteristics are optimal for scintillation analysis. A significant part of the populated world have transitioned, or soon to be transitioned, to DTV. The DTV signal has a standard format that contains a highly phase-stable pilot carrier that can be readily adapted for propagation diagnostics. A multi-frequency software-defined radar receiver, similar to the RAX payload, can measure these signals at a large number of pilot carrier frequencies to make radio ray and diffraction tomographic measurements of the ionosphere and the irregularities contained in it. A constellation of CubeSats, launched simultaneously, or in sequence over years, similar to DMSPs, can listen to the DTV stations, providing a vast and dense probing of the ionosphere. Each spacecraft can establish links to a preprogrammed list of DTV stations and cycle through them using time-division frequency multiplexing (TDFM) method. An on board program can sort the frequencies and de-trend the phase variations due to spacecraft motion. For a single channel and a spacecraft-DTV transmitter path scan, TEC can be determined from the incremental phase variations for each channel. Determination of the absolute TEC requires knowledge of the absolute phase, i.e., including the number of 2? cycles. The absolute TEC can be determined in the case of multi-channel transmissions from a single tower (most towers house multiple television stations). A CubeSat constellation using DTV transmissions as signals of opportunity is a composite instrument for frontier ionospheric research. It is a novel application of CubeSats to understand the ionospheric response to solar, magnetospheric and upper atmospheric forcing. Combined tomographic measurements of ionospheric density can be used to study the global-scale ionospheric circulation and small-scale ionospheric structures that cause scintillation of trans-ionospheric signals. The data can support a wide range of studies, including Sub-auroral Polarization Streams (SAPS), low latitude plasma instabilities and the generation of equatorial spread F bubbles, and the role of atmospheric waves and layers and sudden stratospheric warming (SSW) events in traveling ionospheric disturbances (TID).

Bahcivan, H.; Leveque, K.; Doe, R. A.

2013-12-01

224

The Ionospheres of Europa, Ganymede, and Callisto  

NASA Astrophysics Data System (ADS)

The U.S. Galileo spacecraft, which has been in orbit around Jupiter since December, 1995, has provided opportunities to collect s-band radio occultation data using the 70 meter antennas of the NASA/JPL Deep Space Net(DSN) at Goldstone, California, Madrid, Spain, and Canberra, Australia. To date, four occultations and one near-occultation by Europa (J2) have been observed. They have shown the presence of electron plasma having a density near the surface of 10,000 to 20,000 cm-3 (Kliore, et al., Science, 277, 1997). If the underlying neutral atmosphere is assumed to consist of H2O or O2, the maximum neutral density near the surface can be inferred to be about 108 cm-3. Ganymede (J3) has also been observed five times by Galileo radio occultation. The results are almost entirely negative, with only one measurement out of ten yielding a possible observation of an ionosphere having a maximum density of about 5,000 cm-3 at an altitude of about 16 km. The failure to observe an ionosphere on Ganymede is at first glance surprising, in view of the detection of oxygen and hydrogen above its surface (c.f., Hall, et al., Astrophys. J., 499, 1998; Barth, et al., GRL, 24, 1997), and it was thought to be due to the shielding effect of Ganymede's magnetic field upon the impinging particles from Jupiter's magnetosphere. Callisto has occulted Galileo four times, and these observations have produced some interesting results. Of the eight individual measurements , two are negative, and six are positive. Two of those six, show unmistakable classic ionospheric layers, having peak electron densities of 15,000 to 20,000 cm-3 . A closer examination of all of these results has revealed a plausible reason for why some observations yield positive results , and some do not. It appears that in order for an ionosphere to be observed, the trailing hemisphere of the satellite must be in sunlight. In that way, the atmosphere created by sputtering effects of the Jovian magnetosphere can be ionized by solar EUV to produce an observable ionosphere. The research described in this paper has been conducted at the Jet Propulsion Laboratory and the University of Michigan with support from NASA contracts and grants

Kliore, A. J.; Anabtawi, A.; Nagy, A. F.

2001-12-01

225

Ionospherically reflected proton whistlers  

NASA Astrophysics Data System (ADS)

We present experimental observations and detailed investigation of the variety of proton whistlers that includes transequatorial and ionospherically reflected proton whistlers. The latter have previously been indicated from numerical modeling of spectrograms. The study is based on six-component ELF wave data from the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite which permits to obtain not only spectrograms displaying the power spectral density but also such wave properties as the polarization, wave normal angle, wave refractive index, and normalized parallel component of the Poynting vector. The explanation of various types of proton whistlers is based on the properties of ion cyclotron wave propagation in a multicomponent magnetoplasma, with special consideration of the effect of ion hybrid resonance reflection. Analysis of experimental data is supplemented by numerical modeling of spectrograms that reproduces the main features of experimental ones. As a self-contained result, we provide conclusive experimental evidences that the region illuminated by a lightning stroke in the Earth-ionosphere waveguide may spread over a distance of 4000 km in both hemispheres.

Vavilov, D. I.; Shklyar, D. R.

2014-12-01

226

Artificial Intelligence.  

ERIC Educational Resources Information Center

This issue of "Information Technology Quarterly" is devoted to the theme of "Artificial Intelligence." It contains two major articles: (1) Artificial Intelligence and Law" (D. Peter O'Neill and George D. Wood); (2) "Artificial Intelligence: A Long and Winding Road" (John J. Simon, Jr.). In addition, it contains two sidebars: (1) "Calculating and…

Information Technology Quarterly, 1985

1985-01-01

227

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

228

Phenomena associated with complex (dusty) plasmas in the ionosphere during high-speed meteor showers  

SciTech Connect

Formation of dusty plasmas in the Earth's ionosphere at 80-120 km altitudes during high-speed meteor showers and its detectable manifestations are discussed. Emphasis is given to ground-based observations such as detection of low-frequency (<50 Hz) ionospheric radio noise, ground-based observations of infrasonic waves, and amplification of the intensity of green radiation at 557.7 nm from a layer at the 110-120 km altitude in the lower ionosphere. The physical processes responsible for these manifestations are considered.

Kopnin, S. I. [Institute for Dynamics of Geospheres, RAS, Moscow 119334 (Russian Federation); Popel, S. I. [Institute for Dynamics of Geospheres, RAS, Moscow 119334 (Russian Federation); Space Research Institute, RAS, Moscow 117997 (Russian Federation); Yu, M. Y. [Department of Physics, Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou 310027, China and Institute for Theoretical Physics I, Ruhr University, D-44780 Bochum (Germany)

2009-06-15

229

Phenomena associated with complex (dusty) plasmas in the ionosphere during high-speed meteor showers  

NASA Astrophysics Data System (ADS)

Formation of dusty plasmas in the Earth's ionosphere at 80-120 km altitudes during high-speed meteor showers and its detectable manifestations are discussed. Emphasis is given to ground-based observations such as detection of low-frequency (<50 Hz) ionospheric radio noise, ground-based observations of infrasonic waves, and amplification of the intensity of green radiation at 557.7 nm from a layer at the 110-120 km altitude in the lower ionosphere. The physical processes responsible for these manifestations are considered.

Kopnin, S. I.; Popel, S. I.; Yu, M. Y.

2009-06-01

230

Terahertz resonant artificial interface layers  

Microsoft Academic Search

Planar metamaterials, so-called metasurfaces, can efficiently be described by a modified transfer matrix formalism, that takes into account anisotropic, conductive interfaces. This method is applied for evaluation of the transmission of THz pulses through different metasurface geometries.

D. Dietze; J. Darmo; M. Martl; K. Unterrainer

2010-01-01

231

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

232

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

233

AGU: Journal of Geophysical Research geomagnetic ionosphere currents  

E-print Network

fits are shown along-side scatter plots of individual measurements in corrected geomagnetic apexAGU: Journal of Geophysical Research Keywords geomagnetic ionosphere currents Index Terms Ionosphere: Polar cap ionosphere Ionosphere: Current systems Geomagnetism and Paleomagnetism: Rapid time

Michigan, University of

234

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

235

Physical Model of Earthquake Ionospheric Precursors (Invited)  

NASA Astrophysics Data System (ADS)

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

Namgaladze, A. A.

2010-12-01

236

Computer simulation of ionospheric radio frequency heating  

NASA Astrophysics Data System (ADS)

Linear and nonlinear absorption of electromagnetic waves in a warm, magnetized, nonuniform plasma is studied using an electromagnetic particle simulation code ZOHAR with either one or two spatial and three velocity dimensions. With fixed ions, finite temperature, and finite wave amplitude, transmission of the ordinary mode to the slow extraordinary wave (Z mode) is found to agree with cold plasma theory for linear conversion, and the interference of mode converted waves is observed. With mobile ions and a parabolic density profile which peaks at the critical layer, the wave electric field is enhanced by a factor of 10 or more near the critical layer where the wave becomes electrostatic, and small-scale density fluctuations (cavitons) are observed, typical of strong Langmuir turbulence. Wave damping and particle acceleration are also observed. Application to ionospheric heating is discussed.

Close, R. A.; Bauer, B. S.; Wong, A. Y.; Langdon, A. B.; Kruer, W. L.

1990-12-01

237

Computer simulation of ionospheric radio frequency heating  

NASA Astrophysics Data System (ADS)

Linear and nonlinear absorption of electromagnetic waves in a warm, magnetized, nonuniform plasma is studied using an electromagnetic particle simulation code (ZOHAR) with either 1 or 2 spatial and 3 velocity dimensions. With fixed ions, finite temperature, and finite wave amplitude, transmission of the ordinary mode to the slow extraordinary wave (Z mode) is found to agree with cold plasma theory for linear conversion, and interference of mode converted waves is observed. With mobile ions and a parabolic density profile which peaks at the critical layer (omega (sub p) = omega), the wave electric field is enhanced (factor of ten or more) near the critical layer where the wave becomes electrostatic, and small scale density fluctuations (cavitons) are observed delta (l) approx. 10 lambda (sub D); delta n/n approx. = 0.1, typical of strong Langmuir turbulence. Wave damping and particle acceleration are also observed. Application to ionospheric heating is discussed.

Close, R. A.; Bauer, B. S.; Wong, A. Y.; Langdon, A. B.; Kruer, W. L.; Mjolhus, E.

1989-12-01

238

A new global ionospheric model  

NASA Technical Reports Server (NTRS)

A new global ionospheric model was successfully implemented. The daytime portion of this model provides one-way ionospheric range corrections that compare favorably with those derived from the Mariner Venus/Mercury S- and X-band dual frequency Doppler data. For elevation angles, gamma higher than 30 deg and solar zenith angle less than 80 deg, this model provides calibrations accurate to a few centimeters. The calibrations provided by the nighttime model are also very reasonable. It is interesting to note that the daytime ionospheric calibrations derived from the current calibration scheme, DIEN/TIEN, are fairly close to those given by the new global model, especially in the temporal variations and thus the Doppler effects. The comparison between the nighttime model and DIEN/TIEN was based on the one-way ionospheric range corrections for three passes near the Mariner 9 encounter with Mars in 1971. They can differ by over 30%.

Yip, K. W.; Vonroos, O. H.

1975-01-01

239

Plasma Interactions in Titan's Ionosphere  

E-print Network

calculations of the thermal electron population (electrons with energies less than 2 eV), and chemical reactions in the ionosphere. The results of these models will be compared to data collected by instruments aboard Cassini. Modeled ion production rates...

Richard, Matthew

2013-05-31

240

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

Microsoft Academic Search

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

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

1992-01-01

241

Effects of large-scale irregularities of the ionosphere in the propagation of decametric radio waves  

Microsoft Academic Search

A numerical experiment is used to study the simultaneous influence of regular space-time gradients and large-scale traveling ionospheric disturbances (TIDs) as manifested in the angular and Doppler characteristics of decametric-wave propagation. Conditions typical for middle latitudes are chosen as the ionospheric models: conditions under which large-scale TIDs in the F2-layer evolve on the background of winter or equinox structures of

T. S. Kerblai; E. M. Kovalevskaia

1985-01-01

242

Phenomena associated with complex (dusty) plasmas in the ionosphere during high-speed meteor showers  

Microsoft Academic Search

Formation of dusty plasmas in the Earth's ionosphere at 80-120 km altitudes during high-speed meteor showers and its detectable manifestations are discussed. Emphasis is given to ground-based observations such as detection of low-frequency (<50 Hz) ionospheric radio noise, ground-based observations of infrasonic waves, and amplification of the intensity of green radiation at 557.7 nm from a layer at the 110-120

S. I. Kopnin; S. I. Popel; M. Y. Yu

2009-01-01

243

Challenges in Solar System Ionospheres  

Microsoft Academic Search

The solar system contains a robust set of ionospheres among its nine planets, many moons and comets. If one sets aside the transient atmospheres\\/ionospheres of comets, and those of larger bodies with tenuous surface-boundary-exospheres (e.g., Mercury, Moon, Europa, etc.), plus the under-sampled Pluto, then 10 case studies exist for detailed study and comparison (Venus, Earth, Mars, Jupiter & Io, Saturn

M. Mendillo

2001-01-01

244

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

245

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

NASA Astrophysics Data System (ADS)

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

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

1987-11-01

246

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

PubMed

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

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

1987-11-27

247

A simulation study with a new residual ionospheric error model for GPS radio occultation climatologies  

NASA Astrophysics Data System (ADS)

In this study, a new model was explored, which corrects for higher order ionospheric residuals in global positioning system (GPS) radio occultation (RO) data. Recently, the theoretical basis of this new "residual ionospheric error model" has been outlined (Healy and Culverwell, 2015). The method was tested in simulations with a one-dimensional model ionosphere. The proposed new model for computing the residual ionospheric error is the product of two factors, one of which expresses its variation from profile-to-profile and from time-to-time in terms of measurable quantities (the L1 and L2 bending angles), the other of which describes the weak variation with altitude. A simple integral expression for the residual error (Vorob'ev and Krasil'nikova, 1994) has been shown to be in excellent numerical agreement with the exact value, for a simple Chapman layer ionosphere. In this case, the "altitudinal" element of the residual error varies (decreases) by no more than about 25% between ~10 and ~100 km for physically reasonable Chapman layer parameters. For other simple model ionospheres the integral can be evaluated exactly, and results are in reasonable agreement with those of an equivalent Chapman layer. In this follow-up study the overall objective was to explore the validity of the new residual ionospheric error model for more detailed simulations, based on modelling through a complex three-dimensional ionosphere. The simulation study was set up, simulating day and night GPS RO profiles for the period of a solar cycle with and without an ionosphere. The residual ionospheric error was studied, the new error model was tested, and temporal and spatial variations of the model were investigated. The model performed well in the simulation study, capturing the temporal variability of the ionospheric residual. Although, it was not possible, due to high noise of the simulated bending angle profiles at mid to high latitudes, to perform a thorough latitudinal investigation of the performance of the model, first positive and encouraging results were found at low latitudes. Furthermore, first application tests of the model on the data showed a reduction on temperature level of the ionospheric residual at 40 km from about -2.2 to -0.2 K.

Danzer, J.; Healy, S. B.; Culverwell, I. D.

2015-01-01

248

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

249

The Faraday Fading of Radio Waves from an Artificial Satellite  

Microsoft Academic Search

Faraday fading of signals from an artificial satellite is analyzed in terms of the dif- ference between the Doppler shifts of the ordinary and extraordina .ry components in the iono- sphere. A procedure is outlined for determining the vertical distribution of electron density in the upper ionosphere. F, xplanations are given for the apparently excessive values of electron content yielded

F. H. Hibberd

1959-01-01

250

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

NASA Astrophysics Data System (ADS)

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

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

251

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

252

Fading in the HF ionospheric channel and the role of irregularities  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

253

Earthquake-Ionosphere Coupling Processes  

NASA Astrophysics Data System (ADS)

After a giant earthquake (EQ), acoustic and gravity waves are excited by the displacement of land and sea surface, propagate through atmosphere, and then reach thermosphere, which causes ionospheric disturbances. This phenomenon was detected first by ionosonde and by HF Doppler sounderin the 1964 M9.2 Great Alaskan EQ. Developing Global Positioning System (GPS), seismogenic ionospheric disturbance detected by total electron content (TEC) measurement has been reported. A value of TEC is estimated by the phase difference between two different carrier frequencies through the propagation in the dispersive ionospheric plasma. The variation of TEC is mostly similar to that of F-region plasma. Acoustic-gravity waves triggered by an earthquake [Heki and Ping, EPSL, 2005; Liu et al., JGR, 2010] and a tsunami [Artu et al., GJI, 2005; Liu et al., JGR, 2006; Rolland, GRL, 2010] disturb the ionosphere and travel in the ionosphere. Besides the traveling ionospheric disturbances, ionospheric disturbances excited by Rayleigh waves [Ducic et al, GRL, 2003; Liu et al., GRL, 2006] as well as post-seismic 4-minute monoperiodic atmospheric resonances [Choosakul et al., JGR, 2009] have been observed after the large earthquakes. Since GPS Earth Observation Network System (GEONET) with more than 1200 GPS receiving points in Japan is a dense GPS network, seismogenic ionospheric disturbance is spatially observed. In particular, the seismogenic ionospheric disturbance caused by the M9.0 off the Pacific coast of Tohoku EQ (henceforth the Tohoku EQ) on 11 March 2011 was clearly observed. Approximately 9 minutes after the mainshock, acoustic waves which propagated radially emitted from the tsunami source area were observed through the TEC measurement (e. g., Liu et al. [JGR, 2011]). Moreover, there was a depression of TEC lasting for several tens of minutes after a huge earthquake, which was a large-scale phenomenon extending to a radius of a few hundred kilometers. This TEC depression may be an ionospheric phenomenon attributed to tsunami, termed tsunamigenic ionospheric hole (TIH) [Kakinami and Kamogwa et al., GRL, 2012]. After the TEC depression accompanying a monoperiodic variation with approximately 4-minute period as an acoustic resonance between the ionosphere and the solid earth, the TIH gradually recovered. In addition, geomagnetic pulsations with the periods of 150, 180 and 210 seconds were observed on the ground in Japan approximately 5 minutes after the mainshock. Since the variation with the period of 180 seconds was simultaneously detected at the magnetic conjugate of points of Japan, namely Australia, field aligned currents along the magnetic field line were excited. The field aligned currents might be excited due to E and F region dynamo current caused by acoustic waves originating from the tsunami. This result implies that a large earthquake generates seismogenic field aligned currents. Furthermore, monoperiodical geomagnetic oscillation pointing to the epicenter of which velocity corresponds to Rayleigh waves occurs. This may occur due to seismogenic arc-current in E region. Removing such magnetic oscillations from the observed data, clear tsunami dynamo effect was found. This result implies that a large EQ generates seismogenic field aligned currents, seismogenic arc-current and tsunami dynamo current which disturb geomagnetic field. Thus, we found the complex coupling process between a large EQ and an ionosphere from the results of Tohoku EQ.

Kamogawa, Masashi

254

Interplanetary Radio Transmission Through Serial Ionospheric and Material Barriers  

SciTech Connect

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

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

2013-01-01

255

Progress in Observation-Based Ionospheric Modeling  

Microsoft Academic Search

Models for the ionospheric component of space weather are needed for a wide range of applications. For example, any remote sensing techniques that use radio waves traveling through the ionosphere, looking up from the ground or down from space, must correct for the retarding, refractive, and scintillation effects of the ionospheric plasma. Two types of models are used for this

Dieter Bilitza; Bodo Reinisch; Jan Lastovicka

2008-01-01

256

Study of ionospheric and tropospheric models  

Microsoft Academic Search

To improve Bent's ionospheric model, the source of the NASA model applied by ESOC when computing the ionospheric refraction correction at radio location of satellites, empirical data were compared with the model and with proposed changes. The most important improvements proposed refer to the shape of the electron density profile and to the ionospheric peak parameters. A saturated relation instead

K. Rawer; D. Bilitza

1985-01-01

257

Ionospheric model assessment using TRANSIT data  

Microsoft Academic Search

Total Electron Content (TEC) measurements derived from observation of polar-orbiting TRANSIT satellites were incorporated into an assessment of the Bent ionospheric model, as implemented for the PAVPAW program. Both temporal and spatial assessments of the ionospheric model were performed. By suitable adaptation of the programs developed for this assessment, similar assessments of other ionospheric models could be performed.

Andrew J. Mazzella Jr.; John G. Casserly; Michael B. Delorey; James R. Hughes

1991-01-01

258

Generic relationships between observational parameters defining ionospheric variability  

NASA Astrophysics Data System (ADS)

It has long been known that travelling ionospheric disturbances (TIDs) are seen as a tilted descending variation in isolines of constant electron density derived from ionograms. This is the descending phase front of what is actually an ascending TID, as originally noted by Hines. What is less known is that this descent results in a time delay between the motion of the ionosphere at the greatest observed height and the arrival of the disturbance at the base of the layer (typically the F2) which in turn causes a temporary a compression of the layer thickness and a temporary increase in maximum electron density (foF2). The tilt in the descending electron density variation is often used as the identifying mark of a TID. This paper points out that the relationships observed between foF2, descending height and layer thickness is not unique to a TID but is a generic relationship observed whenever ionization is driven up and down magnetic field lines. Examples of this broader relationship are given for the equatorial post sunset rise and fall in electron density and in equatorial and middle latitude variations in ionospheric diurnal patterns which may repeat over a number of days. Such patterns are definitely not caused by TIDs.

Lynn, Kenneth; Heitmann, Andrew; Gardener-Garden, Robert

259

Artificial blood  

PubMed Central

Artificial blood is a product made to act as a substitute for red blood cells. While true blood serves many different functions, artificial blood is designed for the sole purpose of transporting oxygen and carbon dioxide throughout the body. Depending on the type of artificial blood, it can be produced in different ways using synthetic production, chemical isolation, or recombinant biochemical technology. Development of the first blood substitutes dates back to the early 1600s, and the search for the ideal blood substitute continues. Various manufacturers have products in clinical trials; however, no truly safe and effective artificial blood product is currently marketed. It is anticipated that when an artificial blood product is available, it will have annual sales of over $7.6 billion in the United States alone. PMID:19742251

Sarkar, Suman

2008-01-01

260

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

261

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

262

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

SciTech Connect

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, E-mail: Wenbo.Tang@asu.edu; Mahalov, Alex, E-mail: Alex.Mahalov@asu.edu [School of Mathematical and Statistical Sciences, Arizona State University, Tempe, Arizona 85287 (United States)] [School of Mathematical and Statistical Sciences, Arizona State University, Tempe, Arizona 85287 (United States)

2014-04-15

263

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

264

Metrology and ionospheric observation standards  

NASA Astrophysics Data System (ADS)

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

Panshin, Evgeniy; Minligareev, Vladimir; Pronin, Anton

265

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

266

Venera-9,-10 and Venera-15,-16 occultation data: proposals for updating a model of Venus ionosphere (VIRA)  

NASA Astrophysics Data System (ADS)

This work aims at obtaining useful properties of Venusian ionosphere by re-examining dual-frequency occultation data from Venera-9,-10,-15, and -16 missions. High precision analysis of Venusian ionosphere was ensured by both high stability and coherence of radio signals with 32 cm and 8 cm wavelengths, and the fact that the 32 cm radio signal is highly sensitive to refraction on layered ionospheric structures. Occultation experiments in Venera-9, -10, -15, and -16 missions covered solar zenith angles between 10 and 90 degrees in daytime, and between 90 and 166 degrees at night. 189 electron density profiles were obtained from the data. These results demonstrate that ionosphere is highly susceptible to changes in solar zenith angles and solar activity levels. Daytime ionosphere is highly variable above 170 km in altitude. Electron density profiles frequently vary from a fully developed ionosphere which has ionopause at 1000 km to a compressed ionosphere with ionopause at 250 km. The main electron profile maximum usually lies within a few kilometres of the 142 km altitude point. The lower maximum is usually located approximately 13 km below. The lower boundary of daytime ionosphere can exist in the 80-100 km interval. We also detected interdependent oscillations of the neutral and ionized medium between 60 and 115 km. Nighttime ionosphere also varies strongly. Electron density profiles may frequently have 2 peaks. The altitude of the main maximum (142 km) is close to that of the daytime ionosphere; the lower peak lies in the 120-130 km interval. No ionization below 110 km was observed. The obtained results can serve to improve our understanding of the properties of Venusian ionosphere and atmosphere. This work is partially supported by Program 22 of the Presidium of RAS.

Gavrik, Anatoly; Kopnina, Tatiana; Bondarenko, Michael; Gavrik, Yury

267

The ionospheres of Ganymede and Callisto from Galileo radio occultations  

NASA Astrophysics Data System (ADS)

The U.S. Galileo spacecraft, which has been in orbit around Jupiter since December, 1995, has provided opportunities to collect s-band radio occultation data using the 70 meter antennas of the NASA/JPL Deep Space Net(DSN) at Goldstone, California, Madrid, Spain, and Canberra, Australia. Ganymede (J3) has been observed five times by Galileo radio occultation. The results are almost entirely negative, with only one measurement out of ten yielding a possible observation of an ionosphere having a maximum density of about 5,000 cm-3 at an altitude of about 16 km. The failure to observe an ionosphere on Ganymede is at first glance surprising, in view of the detection of oxygen and hydrogen above its surface (c.f., Hall, et al., Astrophys. J., 499, 1998; Barth, et al., GRL, 24, 1997), and it was thought to be due to the shielding effect of Ganymede's magnetic field upon the impinging particles from Jupiter's magnetosphere. Callisto has occulted Galileo four times, and these observations have produced some interesting results. Of the eight individual measurements , two are negative, and six are positive. Two of those six show unmistakable classic ionospheric layers, having peak electron densities of 15,000 to 20,000 cm-3 . A closer examination of all of these results has revealed a plausible reason for why some observations yield positive results , and some do not. It appears that in order for an ionosphere to be observed, the trailing hemisphere of the satellite must be in sunlight. In that way, the atmosphere created by sputtering effects of the Jovian magnetosphere can be ionized by solar EUV to produce an observable ionosphere. The research described in this paper has been conducted at the Jet Propulsion Laboratory and the University of Michigan with support from NASA contracts and grants.

Kliore, A. J.; Anabtawi, A.; Nagy, A. F.; Galileo Radio Propagation Science Team

2001-11-01

268

Nanostructured artificial nacre  

Microsoft Academic Search

Finding a synthetic pathway to artificial analogs of nacre and bones represents a fundamental milestone in the development of composite materials. The ordered brick-and-mortar arrangement of organic and inorganic layers is believed to be the most essential strength- and toughness-determining structural feature of nacre. It has also been found that the ionic crosslinking of tightly folded macromolecules is equally important.

Zhiyong Tang; Nicholas A. Kotov; Sergei Magonov; Birol Ozturk

2003-01-01

269

Artificial Life  

Microsoft Academic Search

Artificial Life is the study of man-made systems that exhibit behaviors characteristic of natural living systems. It complements the traditional biological sciences concerned with the analysis of living organisms by attempting to synthesize life-like behaviors within computers and other artificial media. By extending the empirical foundation upon which biology is based beyond the carbon-chain life that has evolved on earth,

Chris Langton

1987-01-01

270

Exploring the ionosphere of Mars  

E-print Network

and ionosphere of Mars NASA 1/26Preamble Techniques Magnetism Structure #12;2/26 This is Mars 0.5 x R-Earth 1 #12;Radio occultation technique 10/26 MGS MARS Antenna on Earth Preamble Techniques Magnetism, no geometric limitations 12/26Preamble Techniques Magnetism Structure #12;Mars is magnetically crazy 13

Withers, Paul

271

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

272

Ionospheric redistribution during geomagnetic storms  

NASA Astrophysics Data System (ADS)

The abundance of plasma in the daytime ionosphere is often seen to grow greatly during geomagnetic storms. Recent reports suggest that the magnitude of the plasma density enhancement depends on the UT of storm onset. This possibility is investigated over a 7year period using global maps of ionospheric total electron content (TEC) produced at the Jet Propulsion Laboratory. The analysis confirms that the American sector exhibits, on average, larger storm time enhancement in ionospheric plasma content, up to 50% in the afternoon middle-latitude region and 30% in the vicinity of the high-latitude auroral cusp, with largest effect in the Southern Hemisphere. We investigate whether this effect is related to the magnitude of the causative magnetic storms. Using the same advanced Dst index employed to sort the TEC maps into quiet and active (Dst<-100 nT) sets, we find variation in storm strength that corresponds closely to the TEC variation but follows it by 3-6h. For this and other reasons detailed in this report, we conclude that the UT-dependent peak in storm time TEC is likely not related to the magnitude of external storm time forcing but more likely attributable to phenomena such as the low magnetic field in the South American region. The large Dst variation suggests a possible system-level effect of the observed variation in ionospheric storm response on the measured strength of the terrestrial ring current, possibly connected through UT-dependent modulation of ion outflow.

Immel, T. J.; Mannucci, A. J.

2013-12-01

273

Ionospheric precursors of earthquakes and Global Electric Circuit  

NASA Astrophysics Data System (ADS)

The electromagnetic coupling between the seismically activated area and the ionosphere is considered within the framework of the Global Electric Circuit (GEC) conception. First we consider the anomalous variations in the ionosphere associated with the earthquake preparation process, their temporal and spatial characteristics using the results from recent publications. Then the GEC conception is presented shortly with main accent put on ionization processes which play key role in the complex chain of physical and chemical interactions changing the electric properties of the planetary boundary layer of atmosphere. We treat this part of troposphere as an open complex system with dissipation where so called “blow up” processes are developed leading to sharp and fast changes of atmospheric parameters including the electric properties of the boundary layer. The new concept named Spatial Scintillation Index is introduced in the last part of the paper. In general, this paper may be considered as a short review of the recent achievements in understanding of the seismo-ionospheric coupling.

Pulinets, Sergey; Davidenko, Dmitry

2014-03-01

274

A refracting radio telescope. [using ionosphere as lens  

NASA Technical Reports Server (NTRS)

Observations of extraterrestrial radio sources at the lower end of the radio frequency spectrum are limited by reflection of waves from the topside ionosphere and by the large size of antenna apertures necessary for the realization of narrow beamwidths. The use of the ionosphere as a lens is considered. The lens is formed by the release of chemicals such as H2 and H2O at the F2-layer peak. These chemicals promote dissociative recombination of O(+) in the ionosphere resulting in a local reduction in plasma density. Gradients in electron density in the vicinity of the gas release tend to focus rays propagating through the depleted region. Preliminary calculations indicate that a lens capable of focusing cosmic radio waves in the 1 to 10 MHz frequency range may be produced by the release of 100 kg of H2 at the peak of the nighttime F layer. The beamwidth of a refracting radio telescope using this lens may be less than 1/5 degree.

Bernhardt, P.; Da Rosa, A. V.

1977-01-01

275

Modification of conductivity due to acceleration of the ionospheric medium  

NASA Astrophysics Data System (ADS)

A quantitative division of the ionosphere into dynamo and motor regions is performed on the base of empirical models of space distributions of ionospheric parameters. Pedersen and Hall conductivities are modified to represent an impact of acceleration of the medium because of Ampére's force. It is shown that the currents in the F2 layer are greatly reduced for processes of a few hours duration. This reduction is in particular important for the night-side low-latitude ionosphere. The International Reference Ionosphere model is used to analyze the effect quantitatively. This model gives a second high conducting layer in the night-side low-latitude ionosphere that reduces the electric field and equatorial electrojets, but intensifies night-side currents during the short-term events. These currents occupy regions which are much wider than those of equatorial electrojets. It is demonstrated that the parameter ?d=?P+?H?H/?P that involves the integral Pedersen and Hall conductances ?P, ?H ought to be used instead of the local Cowling conductivity ?C in calculations of the electric current density in the equatorial ionosphere. We may note that Gurevich et al. (1976) derived a parameter similar to ?d for more general conditions as those which we discuss in this paper; a more detailed description of this point is given in Sect. 6. Both, ?d and ?C, appear when a magnetic field line is near a nonconducting domain which means zero current through the boundary of this domain. The main difference between ?d and ?C is that ?d definition includes the possibility for the electric current to flow along a magnetic field line in order to close all currents which go to this line from neighboring ones. The local Cowling conductivity ?C corresponds to the current closure at each point of a magnetic field line. It is adequate only for a magnetic field line with constant local conductivity at the whole line when field-aligned currents do not exist because of symmetry, but ?C=?d in this case. So, there is no reason to use the local Cowling conductivity while the Cowling conductance ?C=?P+?H2/?P is a useful and well defined parameter.

Denisenko, V. V.; Biernat, H. K.; Mezentsev, A. V.; Shaidurov, V. A.; Zamay, S. S.

2008-07-01

276

Interplanetary drivers of ionospheric prompt penetration electric fields  

NASA Astrophysics Data System (ADS)

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

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

2011-01-01

277

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

278

Low-latitude ionospheric effects of energetic electrons during a recurrent magnetic storm  

NASA Astrophysics Data System (ADS)

study a magnetosphere-ionosphere coupling at low latitudes during a moderate (corotating interaction regions/high-speed solar wind streams-driven) geomagnetic storm on 22 July 2009. Recently, it has been shown that during major (coronal mass ejection-driven) storms, quasi-trapped >30 keV electrons largely enhance below the radiation belt in the forbidden zone and produce an additional ionization in the topside ionosphere. In this work, we examine a case of the recurrent storm when the magnetosphere-ionosphere coupling through the quasi-trapped electrons also may take place. Data from NOAA/Polar-orbiting Operational Environmental Satellite and Japanese Greenhouse gases Observing Satellite were used to identify the forbidden electron enhancement (FEE). We find a positive vertical gradient of the electron fluxes that indicates to the radiation belt as a source of FEE. Using global ionospheric maps, radiotomography reconstructions from beacon data and COSMIC/FORMOSAT-3 radio occultation measurements, we have observed an unusually large area in the nighttime ionosphere with increased total electron content (TEC) and prominent elevation of the F layer at low latitudes that coincides with FEEs spatially and temporarily. Ionizing particles are considered as an addition source of ionization along with generally accepted mechanisms for storm time TEC increase (a positive ionospheric storm). We discuss relative contributions of the FEE and disturbance dynamo electric field in the TEC increases during the storm recovery phase.

Suvorova, A. V.; Huang, C.-M.; Matsumoto, H.; Dmitriev, A. V.; Kunitsyn, V. E.; Andreeva, E. S.; Nesterov, I. A.; Tsai, L.-C.

2014-11-01

279

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

280

The accuracy of ionospheric models with ionosonde observations at mid-latitude region  

NASA Astrophysics Data System (ADS)

The purpose of this paper is to validate the ionospheric models to assess its suitability and usefulness as an operational tool for Iraqi HF-Communication The ionospheric model is a computer model designed to predict the state of the global ionosphere for 24 hours The scope was limited to conduct comparisons between the predicted F2 layer critical frequencies f 0 F 2 against observed ionosonde data An ionospheric prediction model IPM was designed to predict a set of ionospheric parameters by using monthly median sunspot number The observation data were taken for three months only February March and December and it was chosen with high solar activity for 1989 based primarily on data availability from two digital ionospheric sounding DIS stations Al-Battani Iraq 33 34 N 44 45 E Kokubunji Japan 34 54 N 109 49 E which lies within the mid latitude region of the globe Analysis of the f 0 F 2 data showed that there is non linear difference between the IRIC IRIU and CHIU models output and the observed data values from these results the empirical formula for applying correction factors were determined these formula can be used to correct the error occurred in predicted f 0 F 2 value

Al-Ubaidi, N.

281

Observing rapid quasi-wave ionospheric disturbance using amplitude charts  

NASA Astrophysics Data System (ADS)

Data from vertical (quasi-vertical) sounding are traditionally used for determining a number of ionospheric parameters such as critical frequencies of E and F layers, peaks of these layers, and for reconstructing electron density profiles. In this respect, radio sounding is not used to its full capacity. Modern ionosondes provide additional information encoded in ionospheric echoes, including information on reflected-signal amplitude. The time dependence of the amplitude-frequency characteristic of reflected signal has been named "amplitude chart" (A-chart). Ionosondes used by the ISTP SB RAS Geophysical Observatory for constructing A-charts employ the frequency-modulated continuous-wave (FMCW) signal in a range 1.3-15 MHz. One-minute sounding interval allows a more detailed study of dynamic processes in the ionosphere. The ionosonde has a direct digital synthesizer and direct sampling receiver without automatic gain control (AGC). The absence of AGC and the high dynamic range enable determination of the relative field strength at a receiving point and registration of relative long-term variations in reflected-signal amplitude over the entire range of operating frequencies of the ionosonde. We have revealed that the passage of travelling ionospheric disturbances (TID) along with height-frequency distortion modulates amplitude characteristics of signal. The characteristic depth of the modulation reaches 40 dB. The pronounced alternate vertical stripes typical for A-charts are likely to be associated with focusing properties of TID. In order to examine the space-time structure of TID able to induce such a focusing of the radio waves, we performed ray tracing simulations. We used geometrical-optics approximation, took magneto-ionic effects into account and prescribed electron density to be a stratified electron density profile on which an undulating disturbance was superimposed. This work was supported by the RFBR grant ?14-05-00259-?.

Kurkin, Vladimir; Laryunin, Oleg; Podlesnyi, Alexey

282

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

283

Manifestation of seismo-ionospheric effect outside of eartquakes preparation zone  

NASA Astrophysics Data System (ADS)

We have researched the large-scale abnormal disturbances of the low-latitude ionosphere, which are taking place under quiet geomagnetic conditions, on a background of data on seismic activity with the view of revealing of features of spatial-time variations of a low-latitude ionosphere during the periods of the raised seismic activity. The daily variations of foF2 values(deviations of measured foF2 from monthly medians) at the ionospheric stations were analyzed. The data on seismic events of the moderate power (M=4-5)in low-latitude area were used for the purpose of specification of spatial and time scales of ionospheric effect manifestations of earthquakes. Reaction of a low-latitude ionosphere, in some cases strongly pronounced, on processes of earthquake preparation is confirmed, including in the removed centers of earthquakes (on the distances considerably exceeding radius of a zone of earthquake preparation). The ionosphere reaction manifests in development of the expressed disturbances of F2-layer critical frequencies in night, pre-sunrise and evening hours under quiet geomagnetic conditions. The remarkable example of occurrence of abnormal disturbances in a low-latitude ionosphere due to removed centers of earthquakes are the disturbances of F2-layer critical frequencies during the catastrophic Chilean (on May 21, 1960, 1002UT, the main shock magnitude M=8.5) and the Alaska (on March 28, 1964, 0336UT, M=8.3) earthquakes. The maximal distances, on which abnormal disturbances were noted, are 3700 km for the Chilean and 9100 km for the Alaska earthquakes. Displacement of the disturbances in a direction from epicenter areas to the geomagnetic equator was noted: from the south - during the Chilean earthquake and from the north - during the Alaska one. Positive disturbances were marked for three days up to the first shock during the Chilean earthquake, during the Alaska one - for a day; development of negative disturbances were occurred on time in immediate proximity by the moments of the first shocks at local time of the stations. The analysis of variations of F2-layer critical frequencies in low-latitude area (results on the South-American region) has confirmed the conclusion about that groups of earthquakes of the moderate power, rather localized in time and space in low-latitude area, can cause abnormal disturbances of F2-layer critical frequencies in this area of ionosphere which may be similar on amplitude with ionospheric effects of strong earthquakes (variations of foF2 more than 50

Ruzhin, Yuri

284

Photochemistry of Titan's Atmosphere and Ionosphere  

NASA Astrophysics Data System (ADS)

A global-mean model of coupled neutral and ion chemistry on Titan has been developed. Unlike the previous models, the model involves ambipolar diffusion and escape of ions, hydrodynamic escape of light species, and calculates the H2 density near the surface that was assigned previously. We tried to reduce the numbers of species and reactions in the model and remove all species and reactions that weakly affect the observed species. Hydrocarbon chemistry is extended to C12H10 for neutrals and C10H11+ for ions but does not include PAHs. The model involves 386 reactions of 83 neutrals and 33 ions, effects of magnetospheric electrons and cosmic rays. UV absorption by Titan's haze was calculated using the Huygens observations and a code for aggregate particles. Hydrocarbon, nitrile, and ion chemistries are strongly coupled on Titan, and attempt to calculate them separately (e.g. in models of ionospheric composition) may result in significant error. The model densities of various species are typically in good agreement with the observations except vertical profiles in the stratosphere that are steeper than the CIRS limb data. Influx of O+ 106 cm-2 s-1 from Saturn's magnetosphere is sufficient to support CO at the observed level of 50 ppm without a surface source. The ionosphere includes a peak at 80 km formed by the cosmic rays, a steplike layer at 700-900 km and a peak at 1120 km (SZA = 60º). Nighttime densities of major ions agree with the INMS data. Ion chemistry dominates in the production of bicyclic aromatic hydrocarbons (indene and naphthalene) above 750 km. Precipitation rate of the photochemical products by polymerization and condensation is capable to fill the observed lakes and seas for a geologically short period of 10-100 Myr. The model does not support the low C/N ratio observed by the Huygens ACP in Titan's haze.

Krasnopolsky, Vladimir A.

2008-09-01

285

Properties of Regions of ELF Radiation Induced by HF Ionospheric Heating  

NASA Astrophysics Data System (ADS)

ELF wave (30 - 3000 Hz) generation and propagation is an important topic of research affecting many areas of space physics. For example, ELF waves generated by lightning discharges can effectively interact with particles in the Earth's radiation belts. Also, ELF waves can penetrate effectively under water to allow wireless communication with submersible crafts. However, it is difficult to generate ELF waves artificially because of their long wavelengths. In this work, the High Frequency Active Auroral Research Program (HAARP) transmitter array (3.6 MW, 2.75 - 10 MHz) is used to generate ELF waves in a controlled manner through periodic heating of the ionospheric D-layer and subsequent modulation of the conductivity of the auroral electrojet. The low-earth-orbit DEMETER satellite is used to study ELF power distribution as a function of the distance from the source. The spatial power distribution depends on many factors. Some of them can be controlled: the ELF and HF frequencies, direction, and modulation techniques. Other parameters are natural and cannot be directly affected: strength of the electrojet current, plasma density, and so on. Initial studies were conducted on a case by case basis, but now they are complemented by a statistical study of multiple experiments over four years. Three regions of ELF radiation are seen in case studies and in an averaged pattern. The most important feature is a column of radiation into space about the size of the heated region (~50 km) and average field strength of 100-150 uV/m. Total ELF power in the column is estimated to be about 1 W. It is found that the column is displaced by 50 - 100 km to the South from the field line of the source. A full-wave model predicts a column of about the same size, but displaced to the North from the field line by 50 km. In addition, the model enables the identification of different physical mechanisms of wave propagation to the three regions of radiation. In brief, in region 1 (the column) and region 2 (up to 300 km from the source in the horizontal distance) waves reach the satellite directly; while in region 3 waves at first are propagating in the Earth-ionosphere waveguide and then leak to the satellite through the ionosphere. The sizes of regions in observations and modeling are comparable. Raytracing is used to interpret the difference between the position of the column in the observations and full-wave modeling. Full-wave modeling assumes vertically stratified ionospheric density, while ray tracing can be used with more realistic models of plasma density including horizontal gradients. It is shown that a horizontal gradient indeed can explain the bending of the column in observations. Employing simple model with linear horizontal gradient of Log(Ne), it was deduced that density should change by an order magnitude over about 5 degrees in latitude in order for ray trajectories to match observations.

Piddyachiy, D.; Bell, T. F.; Inan, U. S.; Foust, F.; Lehtinen, N. G.; Parrot, M.

2011-12-01

286

NeMars empirical model for the dayside martian ionosphere and its use to validate MARSIS instrument techniques: Possible contribution to the Mars International Reference Ionosphere (MIRI)  

NASA Astrophysics Data System (ADS)

NeMars is an empirical model of the two main electron density layers of the Martian dayside ionosphere [Sánchez - Cano et al., 2013]. It is mainly based on MARSIS AIS data (Active Ionospheric Sounding from the Mars Advanced Radar and Ionospheric Sounding experiment aboard Mars Express mission) and to a lesser extent on radio-occultation data from the Mars Global Surveyor mission. The model starts from Chapman theory, but allows variation of scale height and altitude of the main layer with solar zenith angle, and assumes the predominance of Chapman-like photochemical processes above 200 km of altitude. The model is able to reproduce with good approximation the main characteristics of both ionospheric regions: electron density and peak altitudes, scale heights, shape of the profiles and Total Electron Content (TEC) of the entire ionosphere. These can be computed in a simple and quick way starting from solar zenith angle, solar flux F10.7 (as a proxy of solar activity), and heliocentric distance. TEC is the integral of the electron density along the vertical direction and constitutes a very useful parameter in characterizing the ionosphere. In particular, in the case of Earth, it is critical for satellite communications and navigation. Independent measurements of the Martian TEC derived from MARSIS subsurface sounding data [Mouginot et al., 2008 and Cartacci et al., 2013] can be used to validate TEC estimates produced by NeMars. However, initial comparisons reveal that TEC estimates based on MARSIS AIS data are not consistent with those obtained from MARSIS subsurface sounding data: this is probably due to the fact that MARSIS in AIS mode is a topside sounder, measuring only the properties of the ionosphere above the maximum plasma frequency, while in subsurface mode it provides an integral information on the TEC for the entire ionosphere. In an attempt to face this problem, the NeMars model outputs are being used to simulate the radio-wave propagation, to study the TEC retrieving techniques constrains and limits. In the context of the ongoing efforts for the creation of a Mars International Reference Ionosphere (MIRI), we propose to contribute to this effort making use of the AIS data and the NeMars model of daytime electron density. References: Cartacci et al 2013. Icarus, 223, 423-437. Mouginot et al. Planet. 2008. Space Sci. 56, 917-926. Sánchez - Cano et al., 2013. Icarus, 225, 236-247.

Sanchez-Cano, Beatriz; Witasse, Olivier; Radicella, Sandro M.; Cartacci, Marco; Orosei, Roberto; Herraiz, Miguel; Rodriguez-Caderot, Gracia

287

Preface: International Reference Ionosphere - Progress in Ionospheric Modelling  

NASA Technical Reports Server (NTRS)

The international reference ionosphere (lRI) is the internationally recommended empirical model for the specification of ionospheric parameters supported by the Committee on Space Research (COSPAR) and the International Union of Radio Science (URSI) and recognized by the International Standardization Organization (ISO). IRI is being continually improved by a team of international experts as new data become available and better models are being developed. This issue chronicles the latest phase of model updates as reported during two IRI-related meetings. The first was a special session during the Scientific Assembly of the Committee of Space Research (COSPAR) in Montreal, Canada in July 2008 and the second was an IRI Task Force Activity at the US Air Force Academy in Colorado Springs in May 2009. This work led to several improvements and additions of the model which will be included in the next version, IRI-201O. The issue is divided into three sections focusing on the improvements made in the topside ionosphere, the F-peak, and the lower ionosphere, respectively. This issue would not have been possible without the reviewing efforts of many individuals. Each paper was reviewed by two referees. We thankfully acknowledge the contribution to this issue made by the following reviewers: Jacob Adeniyi, David Altadill, Eduardo Araujo, Feza Arikan, Dieter Bilitza, Jilijana Cander, Bela Fejer, Tamara Gulyaeva, Manuel Hermindez-Pajares, Ivan Kutiev, John MacDougal, Leo McNamara, Bruno Nava, Olivier Obrou, Elijah Oyeyemi, Vadym Paznukhov, Bodo Reinisch, John Retterer, Phil Richards, Gary Sales, J.H. Sastri, Ludger Scherliess, Iwona Stanislavska, Stamir Stankov, Shin-Yi Su, Manlian Zhang, Y ongliang Zhang, and Irina Zakharenkova. We are grateful to Peggy Ann Shea for her final review and guidance as the editor-in-chief for special issues of Advances in Space Research. We thank the authors for their timely submission and their quick response to the reviewer comments and humbly apologize for any delays in the editing process.

Bilitza Dieter; Reinisch, Bodo

2010-01-01

288

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

289

Artificial noses.  

PubMed

The mammalian olfactory system is able to detect many more odorants than the number of receptors it has by utilizing cross-reactive odorant receptors that generate unique response patterns for each odorant. Mimicking the mammalian system, artificial noses combine cross-reactive sensor arrays with pattern recognition algorithms to create robust odor-discrimination systems. The first artificial nose reported in 1982 utilized a tin-oxide sensor array. Since then, however, a wide range of sensor technologies have been developed and commercialized. This review highlights the most commonly employed sensor types in artificial noses: electrical, gravimetric, and optical sensors. The applications of nose systems are also reviewed, covering areas such as food and beverage quality control, chemical warfare agent detection, and medical diagnostics. A brief discussion of future trends for the technology is also provided. PMID:21417721

Stitzel, Shannon E; Aernecke, Matthew J; Walt, David R

2011-08-15

290

Three-layer microfibrous peripheral nerve guide conduit composed of elastin-laminin mimetic artificial protein and poly(L-lactic acid)  

PubMed Central

We developed a microfibrous poly(L-lactic acid) (PLLA) nerve conduit with a three-layered structure to simultaneously enhance nerve regeneration and prevent adhesion of surrounding tissue. The inner layer was composed of PLLA microfiber containing 25% elastin-laminin mimetic protein (AG73-(VPGIG)30) that promotes neurite outgrowth. The thickest middle layer was constructed of pure PLLA microfibers that impart the large mechanical strength to the conduit. A 10% poly(ethylene glycol) was added to the outer layer to prevent the adhesion with the surrounding tissue. The AG73-(VPGIG)30 compositing of an elastin-like repetitive sequence (VPGIG)30 and a laminin-derived sequence (RKRLQVQLSIRT: AG73) was biosynthesized using Escherichia coli. The PLLA microfibrous conduits were fabricated using an electrospinning procedure. AG73-(VPGIG)30 was successfully mixed in the PLLA microfibers, and the PLLA/AG73-(VPGIG)30 microfibers were stable under physiological conditions. The PLLA/AG73-(VPGIG)30 microfibers enhanced adhesion and neurite outgrowth of PC12 cells. The electrospun microfibrous conduit with a three-layered structure was implanted for bridging a 2.0-cm gap in the tibial nerve of a rabbit. Two months after implantation, no adhesion of surrounding tissue was observed, and the action potential was slightly improved in the nerve conduit with the PLLA/AG73-(VPGIG)30 inner layer. PMID:25101261

Kakinoki, Sachiro; Nakayama, Midori; Moritan, Toshiyuki; Yamaoka, Tetsuji

2014-01-01

291

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

292

Dynamics of the midlatitude ionospheric F region at sunrise  

NASA Astrophysics Data System (ADS)

The behavior of the F2 layer at sunrise has been studied based on vertical-incidence ionospheric sounding data in Almaty (76°55'E, 43°15'N). Records with small amplitudes of electron density background fluctuations were selected in order to exactly estimate the onsets of a pronounced increase in the electron density at different altitudes. It has been indicated that the electron density growth rate is a function of altitude; in this case, the growth rate at the F2 layer maximum is much lower than such values at fixed altitudes of ˜30-55 km below the layer maximum. The solar zenith angle (?) and the blanketing layer thickness ( h 0) at the beginning of a pronounced increase in the electron density at altitude h are linearly related to the h value, and these quantities vary within ˜90° < ? < 100° and 180 km < h 0 < 260 km, respectively.

Yakovets, A. F.; Vodyannikov, V. V.; Nurmukhanbetova, K. Zh.; Godrienko, G. I.; Litvinov, Yu. G.

2012-09-01

293

The Ionosphere and the Latin America Very Low Frequency Network Mexico (LAVNet-Mex)  

NASA Astrophysics Data System (ADS)

The radiation emitted by the most energetic transient events in the solar system, solar flares, covers a wide range of wavelengths, from radio waves to gamma rays. When the transient excess of high energy radiation produced by solar flares reach the Earth environment, the upper layers of the Earth atmosphere are affected and highly disturbed. The dynamics (particularly the conductivity) of the ionosphere, is altered during solar explosive events. In order to detect and study the ionospheric response to the transient solar radiative input, we have constructed a VLF receiver station: the `Latin American Very low frequency Network at Mexico' (LAVNet-Mex), which extends to the northern hemisphere the South American VLF Network. LAVNet-Mex detects electromagnetic waves generated by strong transmitters located around the world. These waves travel inside the Earth-Ionosphere waveguide, along the Great Circle Path formed between the emitter and the observer. By observing changes in the phase and amplitude of these waves, it is possible to study the dynamics of the lower layer of the ionosphere during solar eruptive events. In this work we present preliminary results of the analysis of the effects of solar flares (class M and X) occurred in 2012 and that were observed by LAVNet-Mex. We explore the relationship between VLF signals coming from different paths during these solar burst to infer the degree of correlation that can exist between different sectors of the ionosphere.

Borgazzi, A.; Lara, A.; Santiago, A.

2013-05-01

294

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

295

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

296

Saturn's ionosphere: Inferred electron densities  

NASA Technical Reports Server (NTRS)

During the two Voyager encounters with Saturn, radio bursts were detected which appear to have originated from atmospheric lightning storms. Although these bursts generally extended over frequencies from as low as 100 kHz to the upper detection limit of the instrument, 40 MHz, they often exhibited a sharp but variable low frequency cutoff below which bursts were not detected. We interpret the variable low-frequency extent of these bursts to be due to the reflection of the radio waves as they propagate through an ionosphere which varies with local time. We obtain estimates of electron densities at a variety of latitude and local time locations. These compare well with the dawn and dusk densitis measured by the Pioneer 11 Voyager Radio Science investigations, and with model predictions for dayside densities. However, we infer a two-order-of-magnitude diurnal variation of electron density, which had not been anticipated by theoretical models of Saturn's ionosphere, and an equally dramatic extinction of ionospheric electron density by Saturn's rings.

Kaiser, M. L.; Desch, M. D.; Connerney, J. E. P.

1983-01-01

297

Mechanisms of Ionospheric Mass Escape  

NASA Technical Reports Server (NTRS)

The dependence of ionospheric O+ escape flux on electromagnetic energy flux and electron precipitation into the ionosphere is derived for a hypothetical ambipolar pick-up process, powered the relative motion of plasmas and neutral upper atmosphere, and by electron precipitation, at heights where the ions are magnetized but influenced by photo-ionization, collisions with gas atoms, ambipolar and centrifugal acceleration. Ion pick-up by the convection electric field produces "ring-beam" or toroidal velocity distributions, as inferred from direct plasma measurements, from observations of the associated waves, and from the spectra of incoherent radar echoes. Ring-beams are unstable to plasma wave growth, resulting in rapid relaxation via transverse velocity diffusion, into transversely accelerated ion populations. Ion escape is substantially facilitated by the ambipolar potential, but is only weakly affected by centrifugal acceleration. If, as cited simulations suggest, ion ring beams relax into non-thermal velocity distributions with characteristic speed equal to the local ion-neutral flow speed, a generalized "Jeans escape" calculation shows that the escape flux of ionospheric O+ increases with Poynting flux and with precipitating electron density in rough agreement with observations.

Moore, T. E.; Khazanov, G. V.

2010-01-01

298

Mechanisms of Ionospheric Mass Ejection  

NASA Technical Reports Server (NTRS)

Ionospheric outflows are directly responsive to solar wind disturbances, particularly in the dayside auroral cusp or cleft regions. Inputs of both electromagnetic energy (Poynting flux) and kinetic energy (particle precipitation) are closely correlated with these outflows. We assess the importance of processes thought to drive ionospheric outflows. These begin with the diffuse effects of photoionization and thermal equilibrium of the ionospheric topside, enhancing Jeans' escape, with ambipolar diffusion and acceleration. Auroral outflows begin with dayside reconnexion and resultant field-aligned currents and driven convection. These produce plasmaspheric plumes, collisional heating and wave-particle interactions, centrifugal acceleration, and auroral acceleration by parallel electric fields, including enhanced ambipolar fields from electron heating by precipitation particles. Solar wind energy dissipation is concentrated by the geomagnetic field into auroral regions with an amplification factor of 10-100, enhancing heavy species plasma and gas escape from gravity, and providing more current carrying capacity. Internal plasmas thus enable electromagnetic driving via coupling to the plasma and neutral gas. We assess the importance of each of these processes in terms of local escape flux production as well as global outflow, and suggest methods for their implementation within multi-species global simulation codes. We conclude by assessing outstanding obstacles to this objective.

Moore, Thomas Earle; Khazanov, George V.; Hannah, Mei-Ching; Glocer, Alex

2010-01-01

299

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

300

Artificial Sweeteners  

NSDL National Science Digital Library

This Science Update, from Science NetLinks, features an interview with Purdue University psychologist Susie Swithers about new research suggesting that artificial sweeteners may promote overeating. Science Updates are audio interviews with scientists and are accompanied by a set of questions as well as links to related Science NetLink lessons and other related resources.

Science Update;

2004-08-02

301

An observational study of the nightside ionospheres of Mars and Venus with radio occultation methods  

Microsoft Academic Search

An analysis of Mars and Venus nightside electron density profiles obtained with radio occultation methods shows how the nightside ionospheres of both planets vary with solar zenith angle. From previous studies it is known that the dayside peak electron densities at Mars and Venus show a basic similarity in that they both exhibit Chapman layer-like behavior. In contrast, the peak

M. H. G. Zhang; J. G. Luhmann; A. J. Kliore

1990-01-01

302

Ionospheric F-region Drift Measurements, First Results for Winter 2006  

E-print Network

sounding The classical ionosonde transmits vertically an upward propagating pulse of radio wave-of-flight of the signal indicates the virtual height of the reflecting layer, where the frequency of the transmitted pulse of transmitted waves. Transmitted signal illuminates a large area of the ionosphere. Consequently, the receiving

Santolik, Ondrej

303

Anomalous electron density events in the quiet summer ionosphere at solar minimum over Millstone Hill  

E-print Network

that these low values of hmp 2 (seen as a G condition on ionograms) exist in the ionosphere due to a decrease on ionograms, when the critical frequency of the p 2 layer is lower than the critical frequency of the p 1. The result is a low hmax value (below 200 km) observed by ionograms, so that no information is obtainable

Boyer, Edmond

304

Evaluation of ionospheric radiowave absorption from one ionogram of vertical sounding ionosonde  

NASA Astrophysics Data System (ADS)

The new method of absorption evaluation based on one digital ionogram by "Parus-A" ionosonde is presented. The main idea is to replace the time-averaging of amplitudes reflected from an ionosphere signals, with averaging of some “amplitude factor” in a frequency domain. An amplitude factor is determined by taking operating heights for each frequency into account. Regularities of behavior of daily and seasonal variations of amplitude factor repeat the patterns of behavior of the absorption of radio waves defined by many researchers who had worked with the amplitude averaging method. The proposed evaluation algorithm can work in the conditions of the disturbed ionosphere. The limiting factor is the size of the frequency range where a reflection from the same ionospheric layer exists. As a result, the usage of the method on frequencies of E layer in the morning and evening hours is comlicated when the layer is formed. Highly diffused reflections increase dispersion of the frequency series of absorption assessments if night layer F is used. Experimental results are presented with diurnal and seasonal variations in the estimates of absorption based on Moscow ionospheric station data.

Filippov, Mikhail; Danilkin, Nick

305

Mid-latitude ionospheric perturbation associated with the Spacelab-2 plasma depletion experiment at Millstone Hill  

E-print Network

scatter radar at Millstone Hill captured the ionospheric response to the ®ring of the Space Shuttle In a sequence of planned experiments, the orbital maneuvering subsystem (OMS) engines of the Space Shuttle Challenger OMS thrusters near the peak of the F layer on July 30, 1985. Details of the excitation of airglow

Paris-Sud XI, Université de

306

Calculation of atmospheric electric fields penetrating from the ionosphere  

NASA Astrophysics Data System (ADS)

The spatial distributions of electric fields and currents in the Earth’s atmosphere are calculated. Electric potential distributions typical of substorms and quiet geomagnetic conditions are specified in the ionosphere. The Earth is treated as a perfect conductor. The atmosphere is considered as a spherical layer with a given height dependence of electrical conductivity. With the chosen conductivity model and an ionospheric potential of 300 kV with respect to the Earth, the electric field near the ground is vertical and reaches 110 Vm-1. With the 60-kV potential difference in the polar cap of the ionosphere, the electric field disturbances with a vertical component of up to 13 V m-1 can occur in the atmosphere. These disturbances are maximal near the ground. If the horizontal scales of field nonuniformity are over 100 km, the vertical component of the electric field near the ground can be calculated with the one-dimensional model. The field and current distributions in the upper atmosphere can be obtained only from the three-dimensional model. The numerical method for solving electrical conductivity problems makes it possible to take into account conductivity inhomogeneities and the ground relief.

Denisenko, V. V.; Bychkov, V. V.; Pomozov, E. V.

2009-12-01

307

Experimental investigation of ULF/VLF radio wave generation and propagation in the upper atmosphere and ionosphere during EISCAT heating experiment in 2012  

NASA Astrophysics Data System (ADS)

Powerful high frequency radio waves transmitted from high-power HF heating facilities modify the ionospheric plasma. The X-mode HF pump wave generates strong small-scale artificial field aligned irregularities in the F region of the ionosphere when the heater frequency is near or above the critical frequency of F2 layer [Blagoveshchenskaya et al]. One of the tasks of the Russian EISCAT heating campaign in February 2012 was an investigation of the generation and propagation of ULF/VLF signals generated as the result of HF radiation modulation. Despite the numerous attempts of long-range detection of such signals, there are a few successful results. The most reliable and important results were obtained by [Barr et al.] more than 20 years ago. They measured the VLF radio waves in Lindau, Germany at the distance of about 2000 km from EISCAT Heater. We present the results of the ULF/VLF registrations at the same distance during heating campaign of February 2012. The measurements were conducted at Mikhnevo Geohysical Observatory located in 80 km to the south of Moscow and at the distance of about 1900 km from Tromsø. For measurements were used a sensitive receivers with crossed air-coil loop antennas in the frequency range from 800 Hz to 30 kHz in the femtotesla amplitude range. We recorded the radial and azimuthal magnetic component of the signals and from their ratio obtained the mode polarization. The radiated heater frequency was modulated by 517, 1017, 2017, 3017, 4017 and 6017 Hz. It was shown the signals with frequency less than 2 kHz propagate in the QTEM mode, and signals at the frequency from 2 to 4 kHz are in the QTE mode. Observed magnetic field strengths and waveguide polarizations are found to be in line with the predictions of simple waveguide models. Qualitative coincidence of the signals polarization character and its dependence on the frequency specifies adequacy of numerical models and reliability of the data received in campaign 2012. Blagoveshchenskaya N. F., M. T. Rietveld et al. Artificial field-aligned irregularities in the high-latitude F region of the ionosphere induced by an X-mode HF heater wave. // Geophys. Res. Lett. - 2011. V. 38, doi: 10.1029/2011GL046724. Barr, R., P. Stubbe, and H. Kopka, 1991, Long-range detection of VLF radiation produced by heating the auroral electrojet. Radio Science, Volume 26, Number 4, Pages 871-879, July-August 1991

Ryakhovskiy, Iliya; Gavrilov, Boris; Zetzer, Julius; Rietveld, Michael; Poklad, Yuriy; Blagoveshchenskaya, Nataly

308

Study of the equatorial ionosphere behavior over Brazilian region during the last two solar minima  

NASA Astrophysics Data System (ADS)

The recent solar cycle 23-24 presented an unusually deep and long lasting minimum activity period. The impact of this solar minimum on the system magnetosphere-thermosphere-ionosphere has been the subject of several studies. In this study we use the measurements by digisondes installed in the Brazilian sector to investigate the climatology of the ionospheric parameters over Sao Luis (2.33 S degrees, 44.2 W degrees, dip angle: -6.7), an equatorial site, and over Cachoeira Paulista (23S degrees, 45 W degrees, dip angle: -37), a location over the southern crest of the equatorial ionospheric anomaly (EIA). The ionograms were manually scaled in order to extract the ionospheric parameters: hmF2 (the F2 layer peak height, in km) and foF2 (the F2 layer critical frequency, in MHz). The critical frequency is related to the peak electron density of the F2-layer, NmF2, where: NmF2= 1.24 x 1010 (foF2)2 el.m-3. We determine the monthly average values of these parameters to investigate the local time and the seasonal dependence on the solar activity. We also compare the ionospheric behavior during the last two solar minima period: the solar cycle 22-23 (1996) and the solar cycle 23-24 (2008-2009). It is observed that in general the plasma densities and F-region heights are lower in the recent solar minimum, compared to the last one, especially for lower latitude region. In addition, we observe the occurrence of F-region plasma irregularities around local midnight and during post-midnight hours, which present morphological features that are distinct from typical irregularities associated with post sunset equatorial spread-F. We discuss the dependence of the ionospheric behavior on the solar flux.

Nicoli Candido, C. M.; Batista, I. S.

2013-12-01

309

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

310

GPS Array as a Sensor of Lithosphere, Troposphere and Ionosphere  

NASA Astrophysics Data System (ADS)

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

Heki, K.

2011-12-01

311

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

312

Magnetosphere-ionosphere coupling during CME events  

NASA Astrophysics Data System (ADS)

A series of CMEs during 07-12 November 2004 produced a rare super double geomagnetic storm with three positive initial phases. The response of the magnetosphere and ionosphere to the CMEs and geomagnetic storms is studied using Cluster and ground-based (ESR, EISCAT and Jicamarca radars and magnetometer) observations and modelling. The observations provide a good example of the magnetosphere-ionosphere coupling through prompt penetration electric field (PPEF). The strongest PPEF ever recorded (on 09 November 2004) appears to be generated in the magnetosphere by vxB effect, which is mapped to the high latitude ionosphere along the geomagnetic field lines and promptly penetrated to low latitudes. The high latitude ionosphere over the ESR radar responded directly to the CMEs mainly through particle precipitation that resulted in strong ionisation and thermal expansion of the ionosphere. The low-mid latitude ionosphere responded after the onset of the main phase of the geomagnetic storm. Modelling studies indicate that the PPEF in the presence of an equatorward neutral wind can produce positive ionospheric storms at low-mid latitudes though PPEF on its own is unlikely to produce positive ionospheric storms.

Nanan, Balan; Vijaya Lekshmi, D.; Alleyne, Hugo

313

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

314

Ionizations and Drifts in the Ionosphere  

Microsoft Academic Search

Our knowledge of the vertical distribution, and the horizontal irregularities and movements, of electrons in the ionosphere is summarized. The mechanism by which electrons can be moved either by the movement of the surrounding air or by electric fields arising from charges elsewhere in the ionosphere is discussed. The statistical description of a randomly moving distribution function which is commonly

J. A. lrATCLIFFE

1959-01-01

315

Ionospheric true height profiles from oblique ionograms  

Microsoft Academic Search

An improved technique for the reduction of an HF oblique ionogram to an ionospheric true height profile is presented. It is based on a more accurate generalization of the Breit-Tuve theorem to curved earth and ionosphere geometries. The improvement over previous methods is demonstrated by means of calculations on known cases.

Michael H. Reilly; E. O. Hulburt

1985-01-01

316

First measurement of winds in the ionosphere.  

E-print Network

) assumes funding responsi- bility for the Arecibo Observatory. The Cornell-based National Astronomy's ionosphere, scientists realize the telescope's impact for radio and radar astronomy, as well. 19641970 First measurement of winds in the ionosphere. 1971 The National Science Foundation (NSF

Danforth, Bryan Nicholas

317

Development of low latitude ionospheric model  

Microsoft Academic Search

Ionospheric models are needed for aeronomic studies and for predicting ionospheric characteristics for radio system applications. The paper is concerned primarily with the development of a modeling method for constructing electron density profiles with application to low-latitude regions such as the Indian subcontinent where the electron density profiles have strong longitude dependence, particularly during daytime. The method developed is based

Y. V. Somayajulu; A. B. Ghosh

1979-01-01

318

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

319

Investigation of Possible Ionospheric Heating by  

Microsoft Academic Search

Satellite drag analyses have shown that the tempearture of the upper atmosphere of the earth increases during a magnetic storm. It has been suggested that hydromagnetic (hm) waves present in the ionosphere during a magnetic storm may dissipate enough energy to produce the observed heating. The hm wave spectrum in the ionosphere during four magnetic storms was determined by relating

Hydromagnetic Waves

320

Artificial Intelligence in Sports Prediction  

Microsoft Academic Search

This paper presents an extension of earlier work in the use of artificial intelligence for prediction of sporting outcomes. An expanded model is described, as well as a broadening of the area of application of the original work. The model used is a form of multi-layer perceptron and it is presented with a number of features which attempt to capture

Alan Mccabe; Jarrod Trevathan

2008-01-01

321

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

322

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

323

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

NASA Astrophysics Data System (ADS)

Mechanisms that generate the field-aligned current (FAC) systems in the magnetosphere-ionosphere coupling scheme by virtue of the solar wind-magnetosphere interaction are investigated with a three-dimensional magnetohydrodynamic (MHD) simulation. As a simulation scheme, the finite volume total variation diminishing (TVD) scheme on an unstructured grid system is employed for precise calculations of the ionospheric region. In the ionosphere, the divergence of the Pederson and Hall currents is matched with FAC, mainly assuming uniform conductivity. The present calculation reproduces the traditional region 1 and 2 currents in the polar ionosphere, for both the northward and southward interplanetary magnetic fields (IMFs). The calculated magnitude of the region 1 current becomes large on the dayside, in agreement with observational results. For the northward IMF, NBZ currents that dominate the entire polar cap are obtained, with a maximum on the dayside. This current is totally absent in the southward IMF result. Corresponding to the FACs, the northward IMF results in multicell convection in the polar ionosphere, and the southward IMF results in two-cell convection. On the evening side, the calculated region 1 currents flow almost along the field lines away from the Earth toward the magnetospheric low-latitude boundary layer (LLBL), then flow up the magnetopause across the field lines to high latitudes. The region 1 currents in the morning side are similar but opposite in direction. In the noon-midnight meridian (xz) plane, the main part of the region 1 current passes the tailward side of the cusp in the magnetosphere. The region 1 current converges to a very narrow region in the noon-midnight meridian (xz) plane when the IMF is northward, whereas it passes the noon-midnight meridian (xz) plane diverging to wide regions in the x direction when the IMF is southward. These differences are attributed to the efficient current-driving effect (J dot E less than 0) of the high-latitude boundary layer (HLBL) for the southward IMF. The calculated region 2 currents on the evening (morning) side flow toward (away from) the Earth and close in the inner magnetosphere near the equator. The evening region 2 currents flow azimuthally from the inner boundary of the plasma sheet and show a sharp turn toward the Earth at the ring current region where strong drivers are distributed. For the northward IMF, the NBZ current that flows toward (away from) the evening (morning) polar cap ionosphere is connected with currents in the magnetotail. In the NBZ current loop, there is no remarkable driver or load (J dot E greater than 0). In the evening magnetosphere, the NBZ current that flows into the dayside ionosphere passes the low-latitude side of the NBZ current that flows into the nightside ionosphere, then it turns aside to the outward (+y) direction and turns back before reaching the dayside ionosphere. ionospheric conductivity results in a wedge-current-like structure in the evening side. This result indicates that the current generated in the ionosphere cannot be ignored in the magnetosphere-ionosphere current systems.

Tanaka, T.

1995-07-01

324

Comparison of travelling ionospheric disturbance measurements with thermosphere/ionosphere model results  

NASA Astrophysics Data System (ADS)

Comparisons of modeled and measured responses of the ionosphere to the passage of atmospheric gravity waves are made for data recorded by an ionosonde located at Almaty (76°55' E, 43°15' N) from June 2000 until May 2001. Temporal variations of the altitude (hmF) and electron content (NmF) of the F-layer peak are used for comparisons. A significant part of the observations showed well-defined wave structures on the hmF, NmF and other parameter variations observed throughout the entire nights. Both the modeling study and measurements showed that, as the F-layer is lifted by the positive surge in gravity wave, the electron content at the F-layer peak decreases, with the slab thickness being increased as well. Subsequently, the opposite happens as hmF falls below its equilibrium value. Some discrepancy between the model and experimental results related to the phase difference between hmF and NmF variations is revealed.

Ashkaliev, Ya. F.; Gordienko, G. I.; Jacobi, Ch.; Litvinov, Yu. G.; Vodyannikov, V. V.; Yakovets, A. F.

2003-04-01

325

Photochemistry of Titan's Atmosphere and Ionosphere  

NASA Astrophysics Data System (ADS)

A global-mean model of coupled neutral and ion chemistry on Titan has been developed. Unlike the previous models, the model involves ambipolar diffusion and escape of ions, hydrodynamic escape of light species with molecular mass less than 20, and calculates the H2 and CO densities near the surface that were assigned previously. We tried to reduce the numbers of species and reactions in the model and remove all species and reactions that weakly affect balances of the observed atmospheric components. However, all new species observed or derived from the Cassini observations and related reactions are included in the model. Hydrocarbon chemistry is extended to bicyclic aromatic hydrocarbons (up to C12H10 for neutrals and C10H11+ for ions) but does not include PAHs. The model involves 375 reactions of 81 neutrals and 33 ions. Chemistry is driven by the solar UV and EUV photons, magnetospheric electrons, and cosmic rays. Absorption of the solar UV radiation by Titan's haze was calculated using the data on the haze particles from the optical observations at the Huygens probe and a code for the aggregate particles. Hydrocarbon, nitrile, and ion chemistries are strongly coupled on Titan. Therefore the approach in some previous models when at first hydrocarbons, then nitriles, and finally ions were calculated may result in significant error. Similarly, models of ionospheric composition may be in error because they neglect effects of ion reactions on the neutral atmosphere. The model densities of various species are in reasonable agreement with the observations. However, the calculated vertical profiles in the stratosphere are steeper than those retrieved from the CIRS limb observations. The ionosphere includes an E-layer at 700-900 km and F1-layer above 900 km with a peak electron density of 3700 cm-3 at 1120 km (SZA = 60°). A narrow peak at 80 km is due to the cosmic ray ionization. The calculated densities of major ions in the nighttime ionosphere at 1100 km are in good agreement with the observed INMS mass spectrum. Ion chemistry dominates in the production of bicyclic aromatic hydrocarbons (indene and naphthalene) above 750 km. This production peaks at 820 km where [C9H11+] = 450 cm-3. However, the major production of the polymer blocks is in the reaction C6H + C4H2 ? C10H3 which peaks at 440 km. Polymerizations of HC3N and HCN peak at 320 and 220 km, respectively, and the bulk condensation of hydrocarbons occurs below 100 km. Overall, precipitation rate of the photochemical products is equal to 7.5 kg cm-2 Byr-1. Escape rates of methane and hydrogen are 2.2 and 1.5 kg cm-2 Byr-1, respectively. The ion escape is small, and we do not consider nonthermal escape processes in our model. The escape of CH4 and H2 for the age of Titan corresponds to a loss of a methane ocean 0.5 km deep and may be compared to the global-mean depth of the hydrocarbon lakes and seas of ~1 m on Titan. The model does not support the low C/N ratio observed by the Huygens ACP in Titan's haze.

Krasnopolsky, V. A.

2008-05-01

326

Sparse reconstruction algorithm for the computerized ionospheric tomography  

Microsoft Academic Search

A tomographic method is presented for obtaining ionospheric image with highly sparse measurements. The proposed method is based on the sparsity constraint which is applicable to general ionospheric conditions. The ionosphere electron density profile can be reconstructed with high resolution even when the TEC measurements are severely insufficient and the signal-noise ratio is rather low, while the traditional ionospheric tomography

Yanli Liu; Fang Li

2010-01-01

327

Ionospheric effects of rocket exhaust products - Skylab and HEAO-C  

NASA Astrophysics Data System (ADS)

A description is presented of a new computer model of the mesosphere, thermosphere, and ionosphere, taking into account a comparison of computed results with experimental data. The model was developed in the course of a study of ionospheric depletion effects of large rocket launches through the F layer. The computer code uses a two-dimensional array of Eulerian mesh cells in Cartesian coordinates x horizontal (in the geomagnetic meridian plane), and z vertical. The code integrates the chemical/photochemical kinetic equations for 30 individual chemical species in each of 315 cells. Solar radiation, scatter UV, cosmic rays, and precipitating electrons are considered. Diffusion rates are computed for each neutral species under the influence of gravity. The midlatitude ionosphere in connection with the launch of Skylab I on May 14, 1973 is considered, and attention is given to rocket launches and two-dimensional model comparisons.

Zinn, J.; Sutherland, C. D.; Duncan, L. M.; Stone, S. N.

328

The Pioneer 10 radio occultation measurements of the ionosphere of Jupiter  

NASA Technical Reports Server (NTRS)

Data from the Pioneer 10 radio occultation measurements are utilized to study the vertical electron number density distribution in the Jovian ionosphere. The immersion measurements were made at 26 North latitude in the late afternoon local time. The solar zenith angle in this region was 81 deg. Emersion measurements were made at 58 North latitude near the morning terminator where the solar zenith angle was 95 deg. The detectable portion of the Jovian ionosphere consists of a number of layers distributed over an altitude range of more than 3000 km. The maximum density appears to be on the order of 30,000 electrons per cu cm. Assuming that H(+) is the principal ion in the upper portion of the ionosphere yields a topside plasma temperature of 900 plus or minus 400 K.

Fjeldbo, G.; Kliore, A.; Seidel, B.; Sweetnam, D.; Cain, D.

1975-01-01

329

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

330

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

331

Traveling ionospheric disturbances in the Weddell Sea Anomaly associated with geomagnetic activity  

NASA Astrophysics Data System (ADS)

present observations from the Falkland Islands Super Dual Auroral Radar Network radar of the propagation of HF radio waves via the Weddell Sea Ionospheric Anomaly (WSA), a region of enhanced austral summer nighttime ionospheric electron densities covering the southern Pacific and South Americas region. This anomaly is thought to be produced by uplift of the ionosphere by prevailing equatorward thermospheric winds. Of particular interest are perturbations of the WSA-supported propagation, which suggest that during periods of geomagnetic disturbance, the ionospheric layer can be lowered by several tens of kilometers and subsequently recover over a period of 1 to 2 h. Perturbations can appear singly or as a train of two to three events. We discuss possible causes of the perturbations and conclude that they are associated with equatorward propagating large-scale atmospheric waves produced by magnetospheric energy deposition in the auroral or subauroral ionosphere. Changes in high/middle latitude electrodynamics during geomagnetic storms may also account for the perturbations, but further modeling is required to fully understand their cause.

Milan, S. E.; Grocott, A.; Larquier, S.; Lester, M.; Yeoman, T. K.; Freeman, M. P.; Chisham, G.

2013-10-01

332

Modeling and observations of the low latitude ionosphere-plasmasphere system at long deep solar minimum  

NASA Astrophysics Data System (ADS)

The behavior of the low latitude ionosphere-plasmasphere system in American-Brazilian longitudes (30°W-120°W) in three seasons at the long deep solar minimum (2006-2010) is investigated using the theoretical model SUPIM and FORMOSAT-3/COSMIC electron density and GIM-TEC data. The data and model reveal some new aspects primarily for the low solar EUV fluxes. The ionosphere develops as a thin layer in the morning though becomes nearly as strong as that at normal solar minimum at around diurnal maximum (14 LT). However, after sunset the ionosphere-plasmasphere system decays rapidly to become an extremely weak cold system prior to sunrise (05 LT) when the ionosphere contracts to about 1/3rd as strong as that at normal solar minimum, with peak density only about 1.8 × 105 cm-3, half width only about 150 km, and O+/H+ transition height as low as 475 km where the ion densities are only 104 cm-3 and ion temperatures are only 600 K. The mechanical effects of the neutral wind dominate over other processes, which causes the disappearance of the well known winter anomaly in TEC and Nmax, and lowest O+/H+ transition height (˜650 km at 14 LT and 475 km at 05 LT) occurring at around ±15° magnetic latitudes where the mechanical effects optimize. In addition, the ionosphere becomes weakest about 7 months after the solar activity dipped to the lowest level in 2008.

Nanan, B.; Chen, C. Y.; Rajesh, P. K.; Liu, J. Y.; Bailey, G. J.

2012-08-01

333

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

334

Analysis of ionospheric parameters using graphical models  

NASA Astrophysics Data System (ADS)

The main topic of this work is to study the influence of geomagnetic disturbances and solar activity on thermal plasma parameters. We employ multivariate statistic methods applied to long period daily observational data obtained using ionosondes. For the investigation of relationships between time variations of ionosphere parameter F2 layer critical frequency (foF2) and solar radiation flux at 10.7cm wavelength (F10.7 index) we use graphical models [1, 2, 3] which describe and transparently represent the structure of dependence relationships in the time series. We compare this method with a common correlation analysis results and we use it for time delay searching. We consider the structure of pairwise dependence of its individual components, looking for the maximum likelihood estimate of the variance matrix under conditions given by the graphical model. Deviance is used as a test statistics and the particular graphical model is selected by Iterative Proportional Fitting. The data best fit model is computed. First results of such an approach are presented. [1] Whittaker J.: Graphical models in applied multivariate statistics, Wiley, New York, 1990. [2] Jordan M.I.: Graphical models. Statistical, Science 19; 140-155, 2004. [3] Buhl S.: On the existence of maximum likelihood estimators for graphical Gaussian models. Scand. J. Statist. 20, 263-270, 1993.

Podolska, Katerina; Truhlik, Vladimir; Triskova, Ludmila

2010-05-01

335

North-south components of the annual asymmetry in the ionosphere  

NASA Astrophysics Data System (ADS)

retrospective study of the asymmetry in the ionosphere during the solstices is made using the different geospace parameters in the North and South magnetic hemispheres. Data of total electron content (TEC) and global electron content (GEC) produced from global ionospheric maps, GIM-TEC for 1999-2013, the ionospheric electron content (IEC) measured by TOPEX-Jason 1 and 2 satellites for 2001-2012, the F2 layer critical frequency and peak height measured on board ISIS 1, ISIS 2, and IK19 satellites during 1969-1982, and the earthquakes M5+ occurrences for 1999-2013 are analyzed. Annual asymmetry is observed with GEC and IEC for the years of observation with asymmetry index, AI, showing January > July excess from 0.02 to 0.25. The coincident pattern of January-to-July asymmetry ratio of TEC and IEC colocated along the magnetic longitude sector of 270° ± 5°E in the Pacific Ocean is obtained varying with local time and magnetic latitude. The sea/land differences in the F2 layer peak electron density, NmF2, and the peak height, hmF2, gathered with topside sounding data exhibit tilted ionosphere along the seashores with denser electron population at greater peak heights over the sea. The topside peak electron density NmF2, TEC, IEC, and the hemisphere part of GEC are dominant in the South hemisphere which resembles the pattern for seismic activity with dominant earthquake occurrence in the South magnetic hemisphere. Though the study is made for the hemispheric and annual asymmetry during solstices in the ionosphere, the conclusions seem valid for other aspects of seismic-ionospheric associations with tectonic plate boundaries representing zones of enhanced risk for space weather.

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

2014-07-01

336

Galileo radio occultation measurements of Io's ionosphere and plasma wake  

NASA Astrophysics Data System (ADS)

Six radio occultation experiments were conducted with the Galileo orbiter in 1997, yielding detailed measurements of the distribution and motion of plasma surrounding Io. This distribution has two components. One is highly asymmetric, consisting of a wake or tail that appears only on the downstream side and extends to distances as large as 10 Io radii. The other resembles a bound ionosphere and is present within a few hundred kilometers of Io's surface throughout the upstream and downstream hemispheres. Motion of plasma within the wake was measured through cross correlation of data acquired simultaneously at two widely separated terrestrial antennas. Plasma near Io's equatorial plane is moving away from Io in the downstream direction. Its speed increases from 30 kms-1 at a distance of 3 Io radii from the center of Io to 57 kms-1 at 7 Io radii. The latter corresponds to corotation with Jupiter's magnetic field, which suggests that bulk plasma motion rather than wave motion is being observed. Results for the bound ionosphere include vertical profiles of electron density at 10 locations near Io's terminator. The ionosphere is substantial, with the peak density exceeding 50,000 cm-3 at 9 out of 10 locations and reaching a maximum of 277,000 cm-3. The peak density varies systematically with Io longitude, with maxima near the center of the hemispheres facing toward (0°W) and away from (180°W) Jupiter and minima near the center of the downstream (90°W) and upstream (270°W) hemispheres. This pattern may be related to the Alfvénic current system induced by Io's motion through magnetospheric plasma. The vertical extent of the bound ionosphere increases from ~200 km near the center of the upstream hemisphere to ~400 km near the boundary between the leading and trailing hemispheres. There is a close resemblance between one ionospheric profile and a Chapman layer, and the topside scale height implies a plasma temperature of 202+/-14K if Na+ is the principal ion. Two intense volcanic hot spots, Kanehekili and 9606A, may be influencing the atmospheric structure at this location.

Hinson, D. P.; Kliore, A. J.; Flasar, F. M.; Twicken, J. D.; Schinder, P. J.; Herrera, R. G.

1998-12-01

337

Ion Escape from the Ionosphere of Titan  

NASA Technical Reports Server (NTRS)

Ions have been observed to flow away from Titan along its induced magnetic tail by the Plasma Science Instrument (PLS) on Voyager 1 and the Cassini Plasma Spectrometer (CAPS) on Cassini. In both cases, the ions have been inferred to be of ionospheric origin. Recent plasma measurements made at another unmagnetized body, Venus, have also observed similar flow in its magnetic tail. Much earlier, the possibility of such flow was inferred when ionospheric measurements made from the Pioneer Venus Orbiter (PVO) were used to derive upward flow and acceleration of H(+), D(+) and O(+) within the nightside ionosphere of Venus. The measurements revealed that the polarization electric field in the ionosphere produced the principal upward force on these light ions. The resulting vertical flow of H(+) and D(+) was found to be the dominant escape mechanism of hydrogen and deuterium, corresponding to loss rates consistent with large oceans in early Venus. Other electrodynamic forces were unimportant because the plasma beta in the nightside ionosphere of Venus is much greater than one. Although the plasma beta is also greater than one on Titan, ion acceleration is expected to be more complex, especially because the subsolar point and the subflow points can be 180 degrees apart. Following what we learned at Venus, upward acceleration of light ions by the polarization electric field opposing gravity in the ionosphere of Titan will be described. Additional electrodynamic forces resulting from the interaction of Saturn's magnetosphere with Titan's ionosphere will be examined using a recent hybrid model.

Hartle, R.; Sittler, E.; Lipatov, A.

2008-01-01

338

The Ionosphere of Callisto Observed by Galileo Radio Science  

NASA Astrophysics Data System (ADS)

The Galileo Europa Mission (GEM) provided three occultations by Callisto, in addition to the single occultation during the prime mission, which occurred on orbit 9 (C9, June 25, 1997). The new occultations occurred on C20 (May 5, 1999), C22 (Aug. 14, 1999), and C23 (Sept 16, 1999). The C9 occultation observations, which occurred very close to the equator (2 deg and 3 deg South lat.) produced no evidence of ionospheric layers with electron densities exceeding the noise background ( 2,000 cm-3). The C20 observations, made at 18 deg N and S lat., show possible layers of density 2,000 to 5,000 cm-3 between the altitudes of 30 and 70 km. The C22 and C23 exit measurements, at latitudes of 33-34 deg North and solar zenith angles (SZA) of 97.6 and 101.3 deg, also show possible layers of density 5,000 cm-3 at altitudes from 10 to 30 km. However, The C22 and C23 observations, which occurred at 34 deg N latitude and SZA of 78.7 and 82.5 deg, clearly show layers having peak electron densities of 15,000 and 17,000 cm-3 at altitudes of 23 and 46 km, respectively. No significant theoretical analysis and modeling of these results was possible before the abstract deadline, but it appears that the density of neutral O2 at the surface of Callisto that would lead to the observed ionospheric layers must be of the order of 108 cm-3. More results of theoretical modeling will be presented at the meeting. This work was performed at the Jet Propulsion Laboratory, California Institute of Technology, and the Space Physics Research Laboratory, University of Michigan with support of the Galileo Project and NASA.

Kliore, A. J.; Anabtawi, A.; Nagy, A. F.

2000-10-01

339

A Unified Fluid Model for Low-latitude Ionosphere Turbulence Causes Radiowave Scintillations  

NASA Astrophysics Data System (ADS)

Nonlinear dynamics of the low latitudes E-layer simulated with a systems of differential equations describing the neutral wind driven Farley-Buneman instability and the density-gradient-drift instability as rising bubbles and falling higher electron density spikes. The simulations extent earlier nonlinear studies by using empirical models for the atmosphere and ionosphere backgrounds to give realistic local time-altitude parameters within a Python wrapped F90 simulations. New equations that keep both the compressional and rotational ion flows that apply in the lower F layer are analyzed to describe plumes extending to the peak of the F layer. A ray-tracing technique is used to describe the small angle scattering at high frequency [Gigahertz] GNSS signals treated as rays in the turbulent ionospheric plasma.

Hassan, E.; Horton, W.

2012-12-01

340

Perturbations of ionosphere-magnetosphere coupling by powerful VLF emissions from ground-based transmitters  

SciTech Connect

The characteristics of the plasma-wave disturbances stimulated in the near-Earth plasma by powerful VLF radiation from ground-based transmitters are investigated. Radio communication VLF transmitters of about 1 MW in power are shown to produce artificial plasma-wave channels (density ducts) in the near-Earth space that originate in the lower ionosphere above the disturbing emission source and extend through the entire ionosphere and magnetosphere of the Earth along the magnetic field lines. Measurements with the onboard equipment of the DEMETER satellite have revealed that under the action of emission from the NWC transmitter, which is one of the most powerful VLF radio transmitters, the generation of quasi-electrostatic (plasma) waves is observed on most of the satellite trajectory along the disturbed magnetic flux tube. This may probably be indicative of stimulated emission of a magnetospheric maser.

Belov, A. S., E-mail: alexis-belov@yandex.ru; Markov, G. A.; Ryabov, A. O. [Lobachevsky Nizhni Novgorod State University (Russian Federation); Parrot, M. [Environment Physics and Chemistry Laboratory (France)

2012-12-15

341

Ionospheric effects of the missile destruction on 9 December 2009  

NASA Astrophysics Data System (ADS)

report on ionosonde and meteor radar observations made in Sodankylä Geophysical Observatory (SGO, 67°22'N, 26°38'E, Finland) on 9 December 2009, during a test launch of the Russian solid propellant military missile. Due to a technical problem, the missile was self-destroyed around 07 UT at an ionospheric height (near 200 km altitude) over the Kola Peninsula (Russia), at a distance about 500 km to east from the observatory. Products of the explosion were spread into a large area and reached the region of SGO meteor radar observations in about 2 h (around 09 UT). After about 3 h (around 10 UT), a sporadic E layer presumably composed of the remains including long-lived metallic (aluminum and its oxides) ions, was observed near the zenith of the SGO ionosonde. We discuss possible mechanisms accounting for transport of the remains. (1) Since the event occurred during a long-lasting period of extremely low solar and magnetic activity, the ionospheric electric field was unlikely to play a substantial role in the transport of the remains and sporadic E layer formation. (2) The horizontal transport of the remains cannot be explained by the neutral winds based on empirical models. (3) Theoretical estimations suggest that the observed transport could be due to thermospheric turbulence.

Kozlovsky, Alexander; Shalimov, Sergey; Lukianova, Renata; Lester, Mark

2014-05-01

342

Magnetic zenith effect in the ionospheric modification by an X-mode HF heater wave  

NASA Astrophysics Data System (ADS)

We report experimental results aimed at an investigation of the magnetic zenith effect in the high latitude ionosphere F region from ionospheric modification by powerful HF heater wave with X-polarization. The ionospheric modification was produced by the HF heating facility at Tromsø (Norway) using the phased array with a narrow beam with of 6 degrees. Effective radiated power was varied between 450 and 1000 MW. The HF pump wave radiated in different directions relative to the magnetic field from 90 degrees (vertical) to 78 degrees (magnetic zenith) at frequencies near or above the ordinary-mode critical frequency. The response of the ionosphere plasma to the HF pump wave impact was checked by the UHF incoherent scatter radar located in the immediate vicinity of the HF heater. UHF radar was probing the plasma parameters, such as electron density and temperature (Ne and Te), HF-induced plasma and ion lines in the altitude range from 90 to 600 km. It was running in a scanning mode when UHF radar look angles were changed from 74 to 90 degrees by 1 or 2 degree step. It was clearly demonstrated that the strongest heater-induced effects took place in the magnetic field-aligned direction when HF pointing was also to the magnetic zenith. It was found that strong Ne enhancement of up to 80 % along magnetic field (artificial density ducts) were excited only under HF pumping towards magnetic zenith. The width of the artificial ducts comes to only 2 degrees. The Ne increases were accompanied by the Te enhancements of up to about 50 %. Less pronounced Te increases were also observed in the directions of 84 and 90 degrees. Strong Ne enhancements can be accompanied by excitation of strong HF-induced plasma and ion lines. Thus experimental results obtained points to the strong magnetic zenith effect due to self-focusing powerful HF radio wave with X-mode polarization.

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

2013-12-01

343

The ionosphere disturbances observation on the Kharkiv incoherent scatter radar  

NASA Astrophysics Data System (ADS)

he ionosphere plasma characteristics are responding on variations of solar and magnetic activity. The research of an ionosphere structure and dynamics is important as for understanding physics of processes and for radiophysical problems solution. The method incoherent scatter (IS) of radio waves allows determining experimentally both regular variations of the basic parameters ionosphere, and their behavior during perturbation. The equipment and measurement technique, developed by authors, are allows obtaining certain data about behavior of an ionosphere during various origin and intensity ionosphere perturbations. The Institute of Ionsphere IS radar located near Kharkiv, Ukraine (geographic coordinates: 49.6oN, 36.3oE, geomagnetic coordinates: 45.7oN, 117.8oE) was used to observe the processes in the ionosphere. The radar is operate with 100-m zenith parabolic antenna at 158 MHz with peak transmitted power of ~2.0 MW. The double-frequency measuring channel mode with compound sounding signal was employed for experiments. That provided ~ 20-km resolution in range ~100-400 km and ~100-km in range ~200-1100 km. Over a period of series of experiment are obtained data about variations of electron density simultaneous in the heights interval 100-1000 km, including three sun eclipses, two superstrong and a few moderate magnetic storms, as well as disturbance, is caused by powerful rockets starts. During strong geomagnetic storm on November 8-12, 2004 was observed night time increasing of electronic temperature up to 3000 ? and ions temperature up to 2000K. Usually at this time temperature of ions is equal to temperature of electrons. During negative ionosphere storm was observed decreasing of electronic density at maximum F2 layer. The height of a F2 layer maximum was increased by 150 km and 70 km at daytime. The interesting phenomenon - high-power backscatter signal coherent backscatter was observed first time during geogeomagnetic storm 29-30 may 2003. A usually observable spectrum of a dispersing medium has two identical on magnitude of a symmetrical extremum appropriate iono-acoustic waves. From distances 900 - 1300 km is registered high-power, unstable signal with a narrow-band spectrum This signal on the correlation, spectral and temporary characteristics are different both from incoherent scatter signal, and from signals reflected from space vehicles. At night time 9.11.2004 and day time 10.11.2004 anomaly signals - coherent backscatter were observed the same way as. It is derived, that the coherent backscatter was observed during a sharp decreasing of Dst index from approximately -40 up to -130 nTl for May 2003 and from approximately -120 up to -240 nTl for 9 November and from -160 up to -290 nTl 10 November 2004. During both event electron density in maximum F2 is increased. Similar characteristics midlatitude coherent backscatters were observed at Millstone Hill , on Irkutsk IS radar. On EISCAT radars was observed so-called naturally enhanced ion-acoustic lines (NEIAL) with similar spectra and amplitude-temporal characteristics. The radar observations ionosphere plasma response on start of heaviest Russian launch vehicle ?Proton-K? was carried out at 25 December 2006. The distance from the rocket launch site and the site of observations is 2500 km. At heights of 250-320 km, a magnitude of the scattered signal sharply raised up to 2 times as compared to the period before start and in reference day on 21.12.2008 (fig. 3). In launch day is clearly seen there are two disturbed areas. The first disturbance was observed 8 min after rocket start. The calculated apparent velocity of disturbance propagation reached the value of 5.2 km/s. This velocity is typical for slow magneto-hydro-dynamic waves in the ionosphere. The second disturbance was observed 60 min after start. The calculated apparent velocity of disturbance propagation was about 700 m/s. The internal gravity waves propagate with similar velocities at the heights of the ionosphere F layer. The moderate geomagnetic storm in April 2006 occurred on the phase of mi

Cherniak, Iu.; Lysenko, V.

2009-04-01

344

Mass loss of shuttle space suit orthofabric under simulated ionospheric atomic oxygen bombardment  

NASA Technical Reports Server (NTRS)

Many polymeric materials used for thermal protection and insulation on spacecraft degrade significantly under prolonged bombardment by ionospheric atomic oxygen. The covering fabric of the multilayered shuttle space suit is composed of a loose weave of GORE-TEX fibers, Nomex and Kevlar-29, which are all polymeric materials. The complete evaluation of suit fabric degradation from ionospheric atomic oxygen is of importance in reevaluating suit lifetime and inspection procedures. The mass loss and visible physical changes of each test sample was determined. Kapton control samples and data from previous asher and flight tests were used to scale the results to reflect ionospheric conditions at about 220 km altitude. It is predicted that the orthofabric loses mass in the ionosphere at a rate of about 66% of the original orthofabric mass/yr. The outer layer of the two-layer orthofabric test samples shows few easily visible signs of degradation, even when observed at 440X. It is concluded that the orthofabric could suffer significant loss of performance after much less than a year of total exposure time, while the degradation might be undetectable in post flight visual examinations of space suits.

Miller, W. L.

1985-01-01

345

Data verification of a hardware-software complex of sounding an ionosphere and ionosonde DPS-4  

NASA Astrophysics Data System (ADS)

Appeared in recent years, opportunities to use as a source of signals used to determine the parameters of the ionosphere, the spacecraft global navigation satellite systems GLONASS and GPS are not currently in widespread use practices ionospheric wave frequency and radio centers and dispatch services. Given the urgency of the discussed areas of research, long experiment whose purpose is to conduct a comparative analysis of the results of determining the critical frequency of F2-layer of the ionosphere in two ways - vertical sounding (ionosonde DPS-4) and radio translucence track "satellite-the Earth" with signals using GLONASS satellites and GPS was started in 2013. For a comparative analysis of the results the hardware-software complex ionospheric soundings (HSCIS) was located at territory of the Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of the Russian Academy of Sciences. HSCIS product includes a personal computer with it specialized software, a dual-frequency navigation receiver and small receiving antenna. Used in the product receiver developed by NovAtel allows us to receive the signals of the navigation systems GPS/GLONASS and maintain their processing in real time. Location receiver determined autonomously: antenna position - 55.76o N, 37.94o E, coordinates ionosonde DPS-4 - 55.5o N, 37.3o E. In fact, both devices were in close proximity, which it allows for the identity conditions of observation. Both devices operate in real time. Ionosonde DPS- 4 gave the ionosphere parameters every 15 minutes, HSCIS - every minute. Information from both instruments displayed on the screen monitors, and recorded in the memory used by computers. Along with the numerical parameters on the monitor products HSCIS displayed time course of the critical frequency F2- layer of the ionosphere obtained from observations of the nearest navigation satellite. When limiting elevation observations 15o simultaneous use of navigation satellites can reach 23, their average number is 12-15. Ionosphere parameters were determined for each satellite, located within sight of the receiver, using the radio sounding on the track "navigation satellite - terrestrial receiver". HSCIS has a high degree of automation and provides hour continuous operation mode with archiving thematic and service information. For compare we use the results obtained according to navigation satellite, subionospheric points which were closest to the location of the ionosonde DPS- 4. On average, for the month of June the average daily value of relative root-mean-square error was 7 % during the day - 6.65 %, at night - 6.71 %, in July, 8.77 %, 7.34 % and 9.5 %, respectively.

Smirnov, Vladimir; Ruzhin, Yuri; Smirnova, Elena; Skobelkin, Vladimir; Tynyankin, Sergey

346

L-Band Ionosphere Scintillations Observed by A GNSS Receiver Array at HAARP  

NASA Astrophysics Data System (ADS)

As we enter a new solar maximum period, GNSS receivers, especially the ones operating in high latitude and equatorial regions, are facing an increasing threat from ionosphere scintillations. The increased solar activities, however, also offer a great opportunity to collect scintillation data to gain better understandings of scintillation effects on GNSS signals. During the past decade, many GPS receivers have been deployed around the globe to monitor ionosphere scintillations. Most of these GPS receivers are commercial receivers whose tracking mechanisms are not designed to operate under ionosphere scintillation. When strong scintillations occur, these receivers will either generate erroneous outputs or completely lose lock. Even when the scintillation is mild, the tracking loop outputs are not true representation of the signal parameters due the tracking loop transfer function. High quality, unprocessed GNSS receiver front end raw IF samples collected during ionosphere scintillations are necessary to produce realistic scintillation signal parameter estimations. In this presentation, we will update our effort in establishing a unique GNSS receiver array at HAARP, Alaska to collect GPS and GLONASS satellite signals at various stages of the GNSS receiver processing. Signal strength, carrier phase, and relative TEC measurements generated by the receiver array as well as additional on-site diagnostic instrumentation measurements obtained from two active heating experiment campaigns conducted in 2011 will be presented. Additionally, we will also highlight and contrast the artificial heating experiment results with observations of natural scintillation events captured by our receivers using an automatic event trigger mechanism during the past year. These interesting results demonstrate the feasibility and effectiveness of our experimental data collection system in providing insightful details of ionosphere responses to active perturbations and natural disturbances.

Morton, Y.; Pelgrum, W.; van Graas, F.

2011-12-01

347

2-dimensional FDTD simulations of plasma wave propagations in the ionosphere  

NASA Astrophysics Data System (ADS)

We developed a 2-dimensional FDTD simulation code which can treat wave propagations in magnetized plasma. Though we need to perform full particle simulations in order to recognize accurate characteristics of waves propagating in space plasma, FDTD simulations can be performed with much less computer resources than those necessary for full particle simulations, in memories as well as cpu times. Since space plasma is magnetized, it is necessary to incorporate the dielectric tensor with anisotropy and dispersibility in FDTD simulation code, in order to calculate the electromagnetic field in space plasma. We use PLRC method to formulization FDTD scheme to reduce numerical errors. In FDTD simulations, it is essential that how to realize an effective absorbing boundary. We developed PML absorbing boundary condition with anisotropy and dispersibility, and succeeded to realize very effective absorbind boundary. According to the rocket observations, we can receive MF radio wave above the dense ionospheric layer whose density is larger than those corresponding to cutoff frequency of MF radio wave. We consider that this is because the thickness of the ionopheric layer is smaller than the wavelength of MF radio wave, the density of ionospheric layer is not constant in the horizontal plane. We have been analyzing the characteristics of MF wave propagation in the ionospher with Full-wave method. In the Full-wave method, since the electron density profile is assumed to change in one-dimensional corrsponding to the alititude, we can only treat one-dimensional electron density profiles. In this study, therefore, we performed a series of FDTD simulations of MF wave propagations in ionospheres with several types of electron density distributions in the horizontal plane, such as electron dense cloud, sporadic layer, etc., and studied the relation between spatial scale of ionospheric layer and MF radio wavelength. In addition, we performed a FDTD simulation of MF radio wave propagations with the ionospheric layer model which is estimated by Full-wave analysis of S-310-37 sounding rocket observations. S-310-37 sonding rocket was launched at USC (Uchinoura Space Center, Kagoshima) in Jan. 2007. We are going to compare FDTD simulation results, Full-wave analysis and rocket observations, and study the influence of electron density profile on the propagation characterictics of MF radio wave in the ionosphere.

Miyake, T.; Yoshino, S.; Okada, T.; Ishisaka, K.

2007-12-01

348

An Approach to Ionospheric Calibration Bill Erickson  

E-print Network

An Approach to Ionospheric Calibration Bill Erickson University of Tasmania Abstract. I am a low the south coast of Tasmania in the prevailing westerlies of the "Roaring Forties" where the nearest land

Ellingson, Steven W.

349

The structure of the Venus ionosphere  

NASA Technical Reports Server (NTRS)

The morphology and temporal variability of the Venus ionosphere are characterized, reviewing the results of recent theoretical investigations, observations, and in situ measurements, especially by the Pioneer Venus Orbiter (PVO). Consideration is given to the Pioneer mission and orbit evolution, early radio occultation profiles of ionospheric N(e), the mean structure and thermal balance of the ionosphere, the ion composition and its dawn-dusk asymmetry, the small-scale spatial structure on the nightside, latitudinal and seasonal variations, solar-cycle effects, suprathermal electrons and superthermal ions, and the global configuration and stability of the ionopause. Data from a single PVO passage through the ionotail are discussed in detail, examining the implications for ion escape and the solar-cycle and short-term variability. The differences among the terrestrial, Martian, and Venusian ionospheres are outlined; the PVO data base is described; and the sources of measurement error are indicated.

Brace, L. H.; Kliore, A. J.

1991-01-01

350

The upper atmosphere and ionosphere of Mars  

NASA Technical Reports Server (NTRS)

The topics discussed include the following: the dynamic atmosphere of Mars; possible similarities with Earth and Venus; the atmosphere and ionosphere of Mars; solar wind interactions; future approved missions; and possible future mission.

Brace, Larry H.

1992-01-01

351

Ionospheric scintillation in the polar cap  

NASA Astrophysics Data System (ADS)

The state of knowledge of ionospheric scintillation in the polar cap today is compared to the state of knowledge of the equatorial ionosphere a decade ago. Recent airborne measurements made by a team of Avionics Laboratory and Air Force Geophysics Laboratory personnel indicate that the occurrence of scintillation depends on the season and solar flux density. Little dependence of scintillation on magnetic index of day is noted. Nearly simultaneous onsets on scintillation at two aircraft locations 100 km apart indicate a very high ionospheric irregularity velocity in the polar cap. Ionospheric irregularity flow in the polar cap is seen as being away from the noontime auroral oval toward the midnight sector with a two-cell flow back toward the noon sector.

Johnson, A. L.

352

The theory of ionospheric focused heating  

NASA Technical Reports Server (NTRS)

Ionospheric modification by high power radio waves and by chemical releases are combined in a theoretical study of ionospheric focused heating. The release of materials which promote electron-ion recombination creates a hole in the bottomside ionosphere. The ionospheric hole focuses high power radio waves from a ground-based transmitter to give a 20 dB or greater enhancement in power density. The intense radio beam excites atomic oxygen by collisions with accelerated electrons. Airglow from the excited oxygen provides a visible trace of the focused beam. The large increase in the intensity of the radio beam stimulates new wave-plasma interactions. Numerical simulations show that the threshold for the two-plasmon decay instability is exceeded. The interaction of the pump electromagnetic wave with the backward plasmon produces a scattered electromagnetic wave at 3/2 the pump frequency. The scattered wave provides a unique signature of the two-plasmon decay process for ground-based detection.

Bernhardt, P. A.; Duncan, L. M.

1987-01-01

353

Magnetic Fluctuations in the Martian Ionosphere  

NASA Technical Reports Server (NTRS)

The Martian ionosphere is influenced by both the solar wind and the regional magnetic fields present in the Martian crust. Both influences ought to cause time variable changes in the magnetic fields present in the ionosphere. I report observations of these magnetic field fluctuations in the Martian ionosphere. I use data from the Mars Global Surveyor magnetometer instrument. By using data from the aerobraking low altitude passes (approx. 200 km) I find that there are numerous fluctuations both near and far from the strong crustal sources. Using data from the 400 km altitude mapping phase (which is near the topside of the primary ionosphere), I look at the comparative strength of the fluctuations relative to the solar wind and temporal variations. I discuss which wave modes and instabilities could be contributing to these fluctuations. I also discuss the implications of these fluctuations for understanding energy transfer in the Martian system and the effects on atmospheric escape.

Espley, Jared

2010-01-01

354

Space weather. Ionospheric control of magnetotail reconnection.  

PubMed

Observed distributions of high-speed plasma flows at distances of 10 to 30 Earth radii (R(E)) in Earth's magnetotail neutral sheet are highly skewed toward the premidnight sector. The flows are a product of the magnetic reconnection process that converts magnetic energy stored in the magnetotail into plasma kinetic and thermal energy. We show, using global numerical simulations, that the electrodynamic interaction between Earth's magnetosphere and ionosphere produces an asymmetry consistent with observed distributions in nightside reconnection and plasmasheet flows and in accompanying ionospheric convection. The primary causal agent is the meridional gradient in the ionospheric Hall conductance which, through the Cowling effect, regulates the distribution of electrical currents flowing within and between the ionosphere and magnetotail. PMID:25013068

Lotko, William; Smith, Ryan H; Zhang, Binzheng; Ouellette, Jeremy E; Brambles, Oliver J; Lyon, John G

2014-07-11

355

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. PMID:20356731

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

2010-01-01

356

Artificial Skin in Robotics.  

E-print Network

??Artificial Skin - A comprehensive interface for system-environment interaction - This thesis investigates a multifunctional artificial skin as touch sensitive whole-body cover for robotic systems.… (more)

Strohmayr, Michael

2012-01-01

357

Auroral pulsations from ionospheric winds  

NASA Technical Reports Server (NTRS)

The possibility that auroral pulsations are due to oscillatory electrical circuits in the ionosphere that are driven by the negative resistance of jet stream winds is examined. For the condenser plates, the highly conducting surfaces above the edges of the jet stream are postulated. The dielectric constant of the plasma between the plates is quite large. The current that is driven perpendicular to and by the jet stream closes along the plates and through Pedersen currents in the F region above the stream. This closed loop gives the inductance and resistance for the circuit. Periods of oscillation for this circuit appear to be in the range of Pc 1 to Pc 3. In accord with observations, this circuit appears to be able to limit the brightness of pulsations.

Nakada, M. P.

1989-01-01

358

Magnetic Earth Ionosphere Resonant Frequencies  

NASA Technical Reports Server (NTRS)

The Community College Division is pleased to report progress of NASA funded research at West Virginia State College. During this reporting period, the project research group has continued with activities to develop instrumentation capability designed to monitor resonant cavity frequencies in the atmospheric region between the Earth's surface and the ionosphere. In addition, the project's principal investigator, Dr. Craig Spaniol, and NASA technical officer, Dr. John Sutton, have written and published technical papers intended to expand the scientific and technical framework needed for project research. This research continues to provide an excellent example of government and education working together to provide significant research in the college environment. This cooperative effort has provided many students with technical project work which compliments their education.

Spaniol, Craig

1994-01-01

359

Solar illumination of the ionosphere during nighttime  

NASA Astrophysics Data System (ADS)

Considerations of the geometry of the earth's shadow are used to show that a considerable part of the ionosphere on the nighttime side of the earth is actually illuminated by the sun. It is found that, at F-region heights (about 300 km), about 30 percent of the so-called 'nighttime' ionosphere is illuminated by the sun. At a height of about 1000 km, the nighttime hemisphere is half illuminated, the sun being above the horizon at this height.

Guliaev, R. A.; Guliaeva, T. L.

1984-04-01

360

Can Ionospheric Sounding Help Tsunami Warning Systems ?  

Microsoft Academic Search

A series of ionospheric anomalies following the Sumatra tsunami has been recently reported in the scientific literature (e.g., Liu et al. 2006; DasGupta et al. 2006; Occhipinti et al. 2006). Similar anomalies were also observed after the tsunamigenic earthquake in Peru in 2001 (Artru et al., 2005). All these anomalies show the signature in the ionosphere of tsunami-generated internal gravity

G. Occhipinti; P. Lognonné; A. Komjathy; E. A. Kherani; F. Crespon; A. Mannucci

2007-01-01

361

Electrodynamics of Ionosphere–Thermosphere Coupling  

Microsoft Academic Search

\\u000a An overview of ionosphere-thermosphere electrodynamic coupling is presented. Collisions between the charged and neutral constituents\\u000a of the upper atmosphere couple their respective dynamics and energetics. Magnetic stresses readily transfer momentum and energy\\u000a over long distances along geomagnetic-field lines, accompanied by electric fields and currents. Consequently, the E and F regions of the ionosphere are strongly coupled, and momentum is transferred

Arthur D. Richmond

362

Excitation of a magnetospheric maser through modification of the Earth's ionosphere by high-power HF radio emission from a ground-based transmitter  

SciTech Connect

A method for controlled excitation of a magnetospheric maser through the production of artificial density ducts by high-power HF radio emission from the Earth's surface has been proposed and implemented in an in-situ experiment. Artificial density ducts allow one to affect the maser resonator system and the excitation and propagation of low-frequency electromagnetic waves in a disturbed magnetic flux tube. The experimental data presented here were obtained at the mid-latitude Sura heating facility. The characteristics of electromagnetic and plasma disturbances at outer-ionosphere altitudes were measured using the onboard equipment of the DEMETER satellite as it passed through the magnetic flux tube rested on the region of intense generation of artificial ionospheric turbulence.

Markov, G. A., E-mail: markov@rf.unn.ru; Belov, A. S., E-mail: alexis-belov@yandex.ru [Lobachevsky Nizhni Novgorod State University (Russian Federation); Frolov, V. L.; Rapoport, V. O. [Radiophysical Research Institute (Russian Federation); Parrot, M. [Environment Physics and Chemistry Laboratory (France)

2010-01-15

363

Ionospheric Signatures of Plasmaspheric Tails  

NASA Astrophysics Data System (ADS)

We present direct comparisons between GPS maps of total electron content (TEC) over the North American continent with Millstone Hill radar observations of storm enhanced density and low and high-altitude satellite measurements of the perturbation of the outer plasmasphere during the March 31, 2001 geomagnetic storm. We find that storm enhanced density (SED) [Foster, J. Geophys. Res., 98, 1675, 1993] and plumes of greatly-elevated TEC result from the erosion of the outer plasmasphere by penetration jet electric fields. Boundaries of the SED/TEC plumes identified at low altitude map directly onto the magnetospheric determination of the boundaries of the plasmapause and plasmaspheric tail determined by EUV imaging from the IMAGE spacecraft. Ground-based GPS observations and radar scans are used to present 2-D snapshots of the ionospheric SED, while DMSP overflights identify the magnetospheric boundaries and mechanisms which contribute to these events. During this event, sunward-convecting plumes of high-TEC plasmaspheric material span the continent from New England to the Canadian Yukon and are responsible for significant ionospheric space weather effects including steep TEC gradients [Vo and Foster, J. Geophys. Res., 106, 21555, 2001] and the occurrence of mid-latitude radio scintillation. Characteristics of the SED/TEC plumes/tails for the March 31, 2001 event are. TEC ~100 TECu; F-region (300 km - 1000 km altitude) sunward velocity ~1000 m/s; sunward flux ~ 5*E24 ions s-1. Total transport to dayside magnetopause/merging region (3-hr event) is ~ 5*E28 ions.

Foster, J. C.; Coster, A. J.; Erickson, P. J.; Goldstein, J.; Rich, F. J.

2002-05-01

364

Electric Field in a Double Layer and the Imparted Momentum  

Microsoft Academic Search

It is shown that the net momentum delivered by the large electric field inside a one-dimensional double layer is zero. This is demonstrated through an analysis of the momentum balance in the double layer at the boundary between the ionosphere and the aurora cavity. For the recently observed double layer in a current-free plasma expanding along a divergent magnetic field,

A. Fruchtman

2006-01-01

365

Space weather phenomena in the equatorial ionosphere  

NASA Astrophysics Data System (ADS)

Our increasing dependence on space-based technological systems requires that we understand the factors that determine "space weather", which affects the operation of satellites as well as space-based communication and navigation systems. The latter are particularly vulnerable to conditions in the dip equatorial ionosphere where geometry of the geomagnetic field creates conditions for the growth of certain plasma instabilities, which produce sub-kilometer scale structure in the ionospheric plasma that are capable of scattering VHF and higher frequency radio waves. The phenomenon of the equatorial plasma bubble (EPB) that occurs in the postsunset equatorial and low latitude ionosphere is therefore an important component of space weather in this region. Forecasting of this space weather phenomenon involves not only the identification of ambient conditions responsible for the day-to-day variation in its occurrence and spatial structure during magnetically quiet periods but also understanding the influence of solar variability on these conditions. This paper discusses briefly our present understanding of the role played by certain parameters of the equatorial ionosphere in the development of EPBs and the influence of solar activity on the equatorial ionosphere, in the context of its role in the generation of ionospheric irregularities that may be detrimental to the operation of space-based communication and navigation systems.

Bhattacharyya, Archana

2013-03-01

366

Lower Ionosphere Response to Solar Activity Forcing  

NASA Astrophysics Data System (ADS)

There are two basic channels of solar activity impact on the lower ionosphere (ionosphere below 90-100 km). The first one is through changes of solar electromagnetic ionizing radiation, solar EUV and X-ray flux; particularly the X-ray flux can change by orders of magnitude both during the 11-year solar cycle and strong solar flares. The other channel is via variable solar wind and its interplanetary magnetic field (IMF), which cause geomagnetic storms and other space weather/climate phenomena including variability of penetrating/precipitating high-energy particle flux and via modulation of galactic cosmic rays by IMF. The lower ionosphere response to solar forcing has been studied for more than 50 years by various ground-based methods and with the use of in-situ rocket measurements. In this review the sources of solar activity impact on the lower ionosphere and methods used for investigating lower ionosphere response will be summarized and selected results will be presented. It should be stressed that during strong events of solar origin the electron density in the lower ionosphere may be enhanced by more than an order of magnitude.

Lastovicka, Jan

2012-07-01

367

Radar Ionogram with Oblique Ionospheric Echo  

NASA Technical Reports Server (NTRS)

This plot, called an ionogram, shows data from sounding Mars' ionosphere with the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS). The horizontal axis is the frequency of the pulse. The left vertical axis is the time delay after transmitting the pulse, with time increasing downward. The right vertical axis is a conversion of time delay to distance, showing the apparent range to the reflection point. The intensity of the received signal at any given frequency and apparent range is indicated by the color, with dark blue being the least intense and green being the most intense.

The green echo at an apparent range of about 800 kilometers (497 miles) from 2.5 to 5.5 megahertz is the reflected signal from the surface of Mars. The curved bright green feature with an apparent range varying from about 600 to 750 kilometers (373 to 466 miles) at frequencies from about 0.7 to 1.8 megahertz is the echo from the top side of the ionosphere. A second echo of the ionosphere, at an apparent range of about 100 kilometers (62 miles) is labeled 'Oblique ionospheric echo.' Such echoes are believed to come from distorted structures in the ionosphere caused by the magnetic fields in the crust of Mars.

MARSIS is an instrument on the European Space Agency's Mars Express orbiter. NASA and the Italian Space Agency jointly funded the instrument.

2005-01-01

368

Storm Signatures and Irregularities in the Equatorial Ionosphere Observed by Using FORMOSAT-3/COSMIC (Invited)  

NASA Astrophysics Data System (ADS)

This paper reports that fluctuations in the vertical electron density triggering by magnetic storms and irregularities of S4 scintillations in the equatorial ionosphere probed by FORMOSAT-3/COSMIC (F3/C). For the storm study, the electron density profiles derived by the F3/C RO (radio occultation) in high-, mid- and low-latitudes during the quiet time and disturbed periods are subdivided into four sectors, noon, dusk, midnight, and dawn, to find wavy characteristics. The wavelet transformation is further applied to examine the profiles before and during the storm period. Above 300km, the ionosphere becomes very structured, and the amplitude in fluctuations of 15~30km wavelength significantly enhances during the storm period, especially high latitude region. The concurrence in changes of the geomagnetic index and the ionospheric density suggest that penetration electric fields and energy inputs at high latitudes play important roles. On the other hand, the F3/C RO provides an excellent opportunity to monitor three-dimensional structures and dynamics of the ionospheric scintillations during the low solar activity year of 2007-2013. Measurements of the global F3/C S4 index are subdivided and examined in various latitudes, longitudes, altitudes, and seasons. The F-region scintillations in the equatorial and low-latitude ionosphere start around post-sunset period and often persist till post-midnight hours (0300 MLT, magnetic local time) during the March and September equinox as well as December Solstice seasons. The E-region scintillations reveal a clear solar zenith effect and yield pronounced intensities in mid-latitudes during the Summer Solstice seasons, which are well correlated with occurrences of the sporadic E-layer. Finally, impact of the F3/C follow-on, FORMOSAT-7/COSMIC-2, mission on ionospheric space weather monitoring will be briefed.

Liu, J. G.; Chen, L.; Hsu, R.; Lee, I.; Chang, G.; Yu, S.; Liu, T.

2013-12-01

369

Advanced specification of electron density and temperature in the IRI ionosphere plasmasphere model  

NASA Astrophysics Data System (ADS)

A plasmasphere extension has been incorporated in the International Reference Ionosphere, IRI*, using the Russian standard model of the ionosphere, SMI, at altitudes from 1000 km to the plasmapause (?36,000 km). The IRI model has been improved using global space time statistics of the half-width of the topside ionosphere estimated from ISIS1, ISIS2, and IK19 satellite observations. Chebishev orthogonal polynomial approximations of the topside half-width of the electron-density profile, normalized to the F2-layer peak height for the ranges of geomagnetic latitude, local time, and solar activity, are incorporated in the IRI electron-density profile. Comparison of the Chebishev model of the topside half-width and its standard deviation with IRI-Bent and ISIS/IK19 data demonstrates an improvement of the IRI-Bent model using the new anchor point in the topside ionosphere. Extension of IRI ionospheric electron temperature towards the plasmasphere is made with a revised model for the electron temperature in the upper ionosphere and plasmasphere. The previous model equation is modified to produce height variations in accord with recent theory and observations. Field-aligned profiles then depend on three parameters, which are determined as a function of latitude by fitting the modified equation to satellite data at heights of 400 10,000 km. This leads to a new global model giving Te as a function of height, latitude, local time and season, with first-order corrections for changes with solar flux and magnetic activity. Estimates of the ion temperature Ti are also obtained. Results represent a mean of current experimental data, and give smooth, physically realistic variations under all conditions.

Gulyaeva, T. L.; Titheridge, J. E.

2006-01-01

370

Simulations of Atmospheric Neutral Wave Coupling to the Ionosphere  

NASA Astrophysics Data System (ADS)

The densities in the E- and F-layer plasmas are much less than the density of background neutral atmosphere. Atmospheric neutral waves are primary sources of plasma density fluctuations and are the sources for triggering plasma instabilities. The neutral atmosphere supports acoustic waves, acoustic gravity waves, and Kelvin Helmholtz waves from wind shears. These waves help determine the structure of the ionosphere by changes in neutral density that affect ion-electron recombination and by neutral velocities that couple to the plasma via ion-neutral collisions. Neutral acoustic disturbances can arise from thunderstorms, chemical factory explosions and intentional high-explosive tests. Based on conservation of energy, acoustic waves grow in amplitude as they propagate upwards to lower atmospheric densities. Shock waves can form in an acoustic pulse that is eventually damped by viscosity. Ionospheric effects from acoustic waves include transient perturbations of E- and F-Regions and triggering of E-Region instabilities. Acoustic-gravity waves affect the ionosphere over large distances. Gravity wave sources include thunderstorms, auroral region disturbances, Space Shuttle launches and possibly solar eclipses. Low frequency acoustic-gravity waves propagate to yield traveling ionospheric disturbances (TID's), triggering of Equatorial bubbles, and possible periodic structuring of the E-Region. Gravity wave triggering of equatorial bubbles is studied numerically by solving the equations for plasma continuity and ion velocity along with Ohms law to provide an equation for the induced electric potential. Slow moving gravity waves provide density depressions on bottom of ionosphere and a gravitational Rayleigh-Taylor instability is initiated. Radar scatter detects field aligned irregularities in the resulting plasma bubble. Neutral Kelvin-Helmholtz waves are produced by strong mesospheric wind shears that are also coincident with the formation of intense E-layers. An atmospheric model for periodic structures with Kelvin-Helmholtz (KH) wavelengths is used to show the development of quasi-periodic structures in the E-layer. For the model, a background atmosphere near 100 km altitude with a scale height of 12.2 km is subjected to a wind shear profile varying by 100 m/s over a distance of 1.7 km. This neutral speed shear drives the KH instability with a growth time of about 100 seconds. The neutral KH wave is a source of plasma turbulence. The E-layer responds to the KH-Wave structure in the neutral atmosphere as an electrodynamic tracer. The plasma flow leads to small scale plasma field aligned irregularities from a gradient drift, plasma interchange instability (GDI) or a Farley-Buneman, two-stream instability (FBI). These irregularities are detected by radar scatter as quasi-periodic structures. All of these plasma phenomena would not occur without the initiation by neutral atmospheric waves.

Siefring, C. L.; Bernhardt, P. A.

2005-12-01

371

Oblique Sounding and Modeling of the Ionospheric HF Channel  

NASA Astrophysics Data System (ADS)

We present the results of experimental studies of the distance-frequency and amplitude-frequency characteristics of the ionospheric HF channel on mid-latitude paths of oblique chirp sounding. It is shown that the maximum observed frequencies (MOFs) are subject to short-period variations with the quasi-periods from 30 min to 2 h.The amplitude of the MOF variations reaches 2 MHz and can increase up to 5 8 MHz on the Cyprus—Rostov-on-Don one-hop path in the sunrise-sunset time. It is established that the MOF fluctuations are accompanied by pronounced “cusp” features occurring in the upper rays and moving with time to the region of shorter delays, i.e., from lower to higher frequencies. The amplitude-frequency characteristics of individual propagation modes undergo deep fluctuations (up to 20 30 dB)whose quasi-period and depth depend on the frequency. It is shown that the appearance of fluctuations is caused by interference of the unresolved rays within the limits of one propagation mode. Based on the modeling, it is shown that “cusps” in oblique-sounding ionograms are due to the influence of traveling ionospheric disturbances (TIDs). The TID parameters are estimated. It is shown that conditions of the formation of “ cusps” in the distance-frequency characteristics depend on the TID amplitude, the wavelength of the disturbance wave, and the direction of its phase front with respect to the propagation path. The effect of quasi-regular frequency modulation of the Pedersen mode with a period of 250 300 kHz on the Cyprus-Rostov-on-Don chirp-sounding path is found. Altitude stratification of the ionosphere near the F-layer maximum, which is responsible for the focusing and defocusing of the Pedersen mode, is estimated. It is established that the stratification scale amounts to approximately 200 250 m.

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

2005-06-01

372

Ionospheric climatology derived from gps occultation observations made by the ionospheric occultation experiment  

Microsoft Academic Search

The ionospheric occultation experiment (IOX) is a GPS occultation sensor with an ionospheric mission focus. IOX measurements of GPS L1 and L2 carrier phase during Earth limb views of setting GPS satellites are used together with the Abel transform to determine vertical profiles of electron density from which F-region peak parameters are determined. Data from a four and a half

Paul Straus

2005-01-01

373

Ionospheric specification from GPS data and the RIBG ionospheric propagation model  

Microsoft Academic Search

Global Positioning System (GPS) data for phase delay differential between L1 and L2 frequencies are analyzed by a model in which the combined effect of hardware and phase ambiguity terms is represented by a constant for each receiver-satellite path and the ionospheric contribution is represented by the RIBG model (ray trace through the combined ICED (ionospheric conductivity and electron density),

Michael H. Reilly; Malkiat Singh

1997-01-01

374

Forecast of ionospheric disturbances using a high-resolution atmosphere-ionosphere coupled model  

NASA Astrophysics Data System (ADS)

Space weather forecasts are about to enter a stage incorporating numerical forecasts based on realistic numerical simulation, in addition to conventional methods used by forecasters to make predictions based on observational data and experience. At the National Institute of Information and Communications Technology (NICT) of Japan, we have developed an atmosphere-ionosphere coupled model, which includes the whole neutral atmosphere and the ionosphere. The model is called GAIA (Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy). The present version has spatial resolution of about 1 degree in horizontal direction. In addition, we are also developing a high-resolution regional ionospheric model, which has a horizontal resolution of about 10 km.We plan to combine GAIA and the regional model to reproduce mesoscale ionospheric phenomena, such as plasma bubbles and SED (storm enhanced density). The model will be a useful tool for space weather forecast. We will report previous results, and a plan for the new model.

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

375

Heat balance of the ionosphere - Implications for the International Reference Ionosphere  

NASA Technical Reports Server (NTRS)

Theoretical considerations can be helpful tools in modeling ionospheric parameters in regions and for times where not enough experimental data are available. This study asks whether results of heat balance calculations should be introduced to supplement the data base for the International Reference Ionosphere. The present status of the theoretical understanding is discussed and the influence of the following unresolved or neglected times are examined: (1) electron heating rate, (2) electron cooling by fine structure excitation of atomic oxygen, and (3) height-dependent Coulomb Logarithm. The ambiguity introduced by these terms leads to up to 30 percent uncertainty in the electron temperature of the lower ionosphere. The electron temperature in the upper ionosphere is largely determined by heat conduction from above and depends critically on the conditions assumed at the boundary between ionosphere and plasmasphere.

Bilitza, D.

1985-01-01

376

First modulation of high-frequency polar mesospheric summer echoes by radio heating of the ionosphere  

NASA Astrophysics Data System (ADS)

The first high-frequency (HF, 8 MHz) observations of the modulation of polar mesospheric summer echoes (PMSE) by artificial radio heating of the ionosphere are presented and compared to observations at 224 MHz and model predictions. The experiments were performed at the European Incoherent Scatter facility in northern Norway. It is shown that model results are in qualitative and partial quantitative agreement with the observations, supporting the prediction that with certain ranges of ice particle radii and concentration, PMSE at HF radar wavelengths can be enhanced by heating due to the dominance of dust charging over plasma diffusion.

Senior, A.; Mahmoudian, A.; Pinedo, H.; La Hoz, C.; Rietveld, M. T.; Scales, W. A.; Kosch, M. J.

2014-08-01

377

Observation of radio-wave-induced red hydroxyl emission at low altitude in the ionosphere.  

PubMed

We report the discovery of radio-wave-induced red emission of OH Meinel rotation-vibrational bands at 629.79 nm. These are the first measurements of artificial aurora below 100 km. We believe that the 629.79-nm OH emission was due to radio-wave focusing by sporadic ionization clouds near 80-85 km altitude, thus giving a technique to visualize the low-altitude sporadic ionization and providing insight into ionospheric interactions at these low altitudes. PMID:15783973

Kagan, L M; Nicolls, M J; Kelley, M C; Carlson, H C; Belikovich, V V; Bakhmet'eva, N V; Komrakov, G P; Trondsen, T S; Donovan, E

2005-03-11

378

Artificial symbiogenesis.  

PubMed

Symbiosis is the phenomenon in which organisms of different species live together in close association, resulting in a raised level of fitness for one or more of the organisms. Symbiogenesis is the name given to the process by which symbiotic partners combine and unify-forming endosymbioses and then potentially transferring genetic material-giving rise to new morphologies and physiologies evolutionarily more advanced than their constitutents. In this article we begin by using the NKC model of coevolution to examine endosymbiosis and its effect on the evolutionary performance of the partners involved. We are then able to suggest the conditions under which endosymbioses are more likely to occur and why; we find they emerge between organisms within a window of their respective "chaotic gas regimes" and hence that the association represents a more stable state for the partners. The conditions under which gene transfer is more likely to represent an advantage for such endosymbionts are then examined within the same model. We find that, providing a suitable pathway exists, such a process can lead to a more efficient genetic configuration for the symbionts within a window that overlaps that in which endosymbioses occur. Finally, the results are used as grounds for implementing symbiogenesis within artificial evolutionary multiagent systems. PMID:8925499

Bull, L; Fogarty, T C

1995-01-01

379

Artificial Intelligence Daniel Polani  

E-print Network

Artificial Intelligence Daniel Polani Artificial Intelligence ­ p.1/26 Is it AI? 1. text editor 2 12. Turing test contenders Artificial Intellige The Turing Test: is partner human or not? See: e.g. [Saygin et al., 2000] Artificial Intelligence ­ p.3/26 The Turing Test II

Polani, Daniel

380

Artificial Intelligence Adversarial Search  

E-print Network

Artificial Intelligence Adversarial Search Readings: Chapter 6 of Russell & Norvig. Artificial Rybka. Artificial Intelligence ­ p.2/25 Games vs. Search problems "Unpredictable" opponent: Solution, poker, scrabble nuclear war Artificial Intelligence ­ p.3/25 Tic-Tac-Toe XX XX X X X XX MAX (X) MIN (O

Srinivasan, Padmini

381

The Metal Oxide Space Clouds (MOSC) Experiment: High Frequency (HF) Signatures and Interactions with the Ambient Ionosphere  

NASA Astrophysics Data System (ADS)

With support from the NASA sounding rocket team, AFRL performed two separate 5 kg releases of samarium metal vapor in the lower F-region near Kwajalein Atoll in May 2013. A fraction of the samarium subsequently ionized forming a plasma cloud that persisted for tens of minutes to hours in the post-sunset period. Numerous sensors were used to characterize the clouds including the ALTAIR incoherent scatter radar, multiple GPS and optical instruments, satellite radio beacons, and a dedicated network of high frequency (HF) radio links. The primary objectives of the experiments were to understand the dynamics, evolution and chemistry of Sm atoms in the earth's upper atmosphere. Sm is predicted to both photo-ionize and chemi-ionize through charge exchange with neutral oxygen (O). Ionization rates and loss reactions are not well known. A secondary objective was to understand the interaction of an artificial plasma cloud with the low latitude ionosphere during the pre-reversal enhancement period leading up to the post-sunset development of large-scale Rayleigh-Taylor instability. It was initially hoped that the introduction of the artificial plasma might be sufficient to quench the development of the instability by maintaining high conductivity within the affected flux tubes. Modeling results showed that this result was unlikely due to the relatively small amount of material being released. However, it appeared possible that the presence of SmO+ near the bottomside of the F-region might be capable of reducing the formation of short-scale irregularities within the larger Rayleigh-Taylor 'bubbles'. Indeed, preliminary results indicate that the artificial layers, positioned at 170 and 180 km respectively, did interact with the overlying F region and in at least one case, cause a decrease in the short-scale component of the natural irregularity spectrum. The results suggest that it may be possible to mitigate the formation of low-latitude irregularities responsible for radio wave scintillation with a MOSC-based approach.

Groves, K. M.; Caton, R. G.; Pedersen, T. R.; Parris, R. T.; Su, Y.; Cannon, P. S.; Jackson-booth, N. K.; Angling, M. J.; Retterer, J. M.

2013-12-01

382

An observational study of the nightside ionospheres of Mars and Venus with radio occultation methods  

SciTech Connect

An analysis of Mars and Venus nightside electron density profiles obtained with radio occultation methods shows how the nightside ionospheres of both planets vary with solar zenith angle. From previous studies it is known that the dayside peak electron densities at Mars and Venus show a basic similarity in that they both exhibit Chapman layer-like behavior. In contrast, the peak altitudes at mars behave like an ideal Chapman layer on the dayside, whereas the altitude of the peak at Venus is fairly constant up to the terminator. The effect of major dust storms can also be seen in the peak altitudes at Mars. All Venus nightside electron density profiles show a distinct main peak for both solar minimum and maximum, whereas many profiles from the nightside of Mars do not show any peak at all. This suggests that the electron density in the Mars nightside ionosphere is frequently too low to be detected by radio occultation. On the Pioneer Venus orbiter, disappearing ionospheres were observed near solar maximum in the in-situ data when the solar wind dynamic pressure was exceptionally high. This condition occurs because the high solar wind dynamic pressure decreases the altitude of the ionopause near the terminator below {approximately}250 km, thus reducing the normal nightward transport of dayside ionospheric plasma. On the basis of the Venus observations, one might predict that if a positive correlation of nightside peak density with dynamic pressure was found, it could mean that transport from the dayside is the only significant source for the nightside ionosphere of Mars. The lack of a correlation would imply that the precipitation source at Mars is quite variable.

Zhang, M.H.G. (Austrian Academy of Sciences, Graz (Austria)); Luhmann, J.G. (Univ. of California, Los Angeles (United States)); Kliore, A.J. (Jet Propulsion Lab., Pasadena, CA (United States))

1990-10-01

383

Role of the atmospheric gravity waves in lithosphere-ionosphere coupling and in generation of the ionospheric earthquake precursors  

NASA Astrophysics Data System (ADS)

Up to the present days there are no well-distinguished physical mechanisms of lithosphere-ionosphere interaction and generation of the ionospheric earthquake precursors. Several hypothetical possibilities have been suggested in the literature: (i) electric currents are generated in the lithosphere during earthquake preparation phase, the electromagnetic emission of these currents influences the ionosphere; (ii) ionosphere responds to the seismogenic variations of air conductivity and related variation of fair-weather electric field; (iii) lithosphere and ionosphere are coupled via middle-scale atmospheric gravity waves (AGW) traveling upwards to the ionospheric heights and producing the effects known as traveling ionospheric disturbances (TID). In spite of great quantity of observations of ionospheric earthquake precursors, there is a lack of appropriate experimental data: such kind of data that will help us to choose between mentioned hypotheses. Our research is devoted to the studying and verification of AGW-mechanism of seismo-ionospheric effects. The original data have been provided by synchronous measurements of atmospheric pressure variations and ionospheric plasma variations carried out in seismically active Chiba area in Japan during the year 2003. Seismogenic AGW with period about 1 hour has been selected from the broad spectra of pressure variations. Correlated ionospheric response has been detected by means of subionospheric VLF/LF propagation. Cross-analysis of barometric and ionospheric parameters has been done in order to recognize the process of AGW-coupling between perturbations at surface and ionospheric levels.

Lizunov, G.; Hayakawa, M.; Hattori, K.; Mayakawa, Sh.

384

First results from the Cassini radio occultations of the Titan ionosphere  

NASA Astrophysics Data System (ADS)

The first four sets of radio occultations of the Titan's ionosphere were obtained by the Cassini spacecraft between March 2006 and May 2007. These occultations occurred at middle and high latitudes, at solar zenith angles from about 86° to 96°. The main ionospheric peak was seen, as expected from modeling and previous observations, near 1200 km, with a density of about 1-3 × 103 cm-3. A consistent ledge near 1000 km was also seen, and one of the polar observations found a significant (˜3 × 103 cm-3) layer in the region of 500-600 km. This layer also is seen in other observations with a density varying from about 0.7 to 1.7 × 103 cm-3, suggesting a variable production source (or sources) for this peak.

Kliore, Avydas J.; Nagy, Andrew F.; Marouf, Essam A.; French, Richard G.; Flasar, F. Michael; Rappaport, Nicole J.; Anabttawi, Aseel; Asmar, Sami W.; Kahann, Daniel S.; Barbinis, Elias; Goltz, Gene L.; Fleischman, Don U.; Rochblatt, David J.

2008-09-01

385

Ionospheric behavior over Europe during the solar eclipse of 3 October 2005  

NASA Astrophysics Data System (ADS)

An annular eclipse occurred over Europe in the morning hours of 3 October 2005. The well-defined obscuration function of the solar radiation during the eclipse provided a good opportunity to study the ionospheric/thermospheric response to solar radiation changes. Since the peak electron density behavior of the ionospheric F2 layer follows the local balance of plasma production, loss and transport, the ionospheric plasma redistribution processes significantly affect the shape of the electron density profile. These processes are discussed here based on a comparison of vertical incidence sounding (VS) and vertical total electron content (TEC) data above-selected ionosonde stations in Europe. The equivalent slab thickness, derived with a time resolution of 10 min, provides relatively good information on the variation of the electron density profile during the eclipse. The computations reveal an increased width of the ionosphere around the maximum phase. As indicated by the available measurements over Spain, the photo production is significantly reduced during the event leading to a slower increase of the total ionization in comparison with the neighboring days. The supersonic motion of the Moon's cool shadow through the atmosphere may generate atmospheric gravity waves that propagate upward and are detectable as traveling ionospheric disturbances at ionospheric heights. High-frequency (HF) Doppler shift spectrograms were recorded during the eclipse showing a distinct disturbance along the eclipse path. Whereas the ionosonde measurements at the Ebro station/Spain in the vicinity of the eclipse path reveal the origin of the wave activity in the lower thermosphere below about 180 km altitude, the similar observations at Pruhonice/Czech Republic provide arguments to localize the origin of the abnormal waves in the middle atmosphere well below the ionospheric heights. Although ionosonde and HF Doppler measurements show enhanced wave activity, the TEC data analysis does not, which is an indication that the wave amplitudes are too small for detecting them via this interpolation method. The total ionization reduces up to about 30% during the event. A comparison with similar observations from the solar eclipse of 11 August 1999 revealed a quite different ionospheric behavior at different latitudes, a fact that needs further investigation.

Jakowski, N.; Stankov, S. M.; Wilken, V.; Borries, C.; Altadill, D.; Chum, J.; Buresova, D.; Boska, J.; Sauli, P.; Hruska, F.; Cander, Lj R.

2008-04-01

386

Mid-latitude ionospheric perturbation associated with the Spacelab-2 plasma depletion experiment at Millstone Hill  

NASA Astrophysics Data System (ADS)

Elevation scans across geomagnetic mid latitudes by the incoherent scatter radar at Millstone Hill captured the ionospheric response to the firing of the Space Shuttle Challenger OMS thrusters near the peak of the F layer on July 30, 1985. Details of the excitation of airglow and the formation of an ionospheric hole during this event have been reported in an earlier paper by Mendillo et al.. The depletion (factor sim2) near the 320 km Shuttle orbital altitude persisted for sim35 min and then recovered to near normal levels, while at 265 km the density was reduced by a factor of sim6; this significant reduction in the bottomside F-region density persisted for more than 3 hours. Total electron content in the vicinity of the hole was reduced by more than a factor of 2, and an oscillation of the F-region densities with 40-min period ensued and persisted for several hours. Plasma vertical Doppler velocity varied quasi-periodically with a sim80-min period, while magnetic field variations observed on the field line through the Shuttle-burn position exhibited a similar sim80-min periodicity. An interval of magnetic field variations at hydromagnetic frequencies (sim95 s period) accompanied the ionospheric perturbations on this field line. Radar observations revealed a downward phase progression of the 40-min period density enhancements of -1.12° km-1, corresponding to a 320-km vertical wavelength. An auroral-latitude geomagnetic disturbance began near the time of the Spacelab-2 experiment and was associated with the imposition of a strong southward IMF Bz across the magnetosphere. This created an additional complication in the interpretation of the active ionospheric experiment. It cannot be determined uniquely whether the ionospheric oscillations, which followed the Spacelab-2 experiment, were related to the active experiment or were the result of a propagating ionospheric disturbance (TID) launched by the enhanced auroral activity. The most reasonable conclusion is that the ionospheric oscillations were a result of the coincident geomagnetic disturbance. The pronounced depletion of the bottomside ionosphere, however, accentuated the oscillatory behavior during the interval following the Shuttle OMS burn.

Foster, J. C.; Holt, J. M.; Lanzerotti, L. J.

2000-01-01

387

Thermosphere-ionosphere coupling: An experiment in interactive modeling  

SciTech Connect

The National Center for Atmospheric Research thermosphere general circulation model (TGCM) is utilized to perform a series of controlled experiments aimed at better understanding the interactive coupling between ionospheric plasma densities and thermospheric neutral winds. The experiments are simple and controlled so as to facilitate identification of governing mechanisms. The interaction is accomplished by parameterizing the F layer peak height (h{sub m}F{sub 2}) in an empirical ionospheric model in terms of the meridional wind ({upsilon}{sub south}) and forcing h{sub m}F{sub 2} and {upsilon}{sub south} to remain mutually coupled in a dynamical calculation. Interactive computations are performed where the TGCM is driven by 30-kV and 90-kV cross polar cap potentials and are compared with corresponding reference simulations where h{sub m}F{sub 2} is constrained to a balance height near 280 km with a small ({approximately}20 km) diurnal variation. Mutual coupling between h{sub m}F{sub 2} and {upsilon}{sub south} is found to be weak during the daytime when the F layer exhibits a broad vertical structure. At night, when the F{sub 2} layer is more localized, the neutral dynamical structure is dependent on whether h{sub m}F{sub 2} is significantly above or below the altitude (approximately 275-300 km) at which ion drag effectively competes with viscosity in the neutral momentum balance. At Arecibo during both levels of high-latitude forcing, the premidnight elevation (+75 km) of h{sub m}F{sub 2} relative to a nighttime balance height of approximately 290 km is accompanied by an increase ({approximately}50 m s{sup {minus}1}) in the zonal wind above 250 km relative to the noninteractive simulation. A much smaller effect, characterized by an 8-hour periodicity spanning 24 hours, is seen in the meridional wind component.

Forbes, J.M. (Boston Univ., MA (United States)); Roble, R.G. (National Center for Atmospheric Research, Boulder, CO (United States))

1990-01-01

388

Study of Correlationships between Main Ionospheric Parameters by Stochastic Modeling  

NASA Astrophysics Data System (ADS)

We employ multivariate statistic methods applied to long period daily observational data for find out time shifts between fundamental ionospheric parameters. The F2 layer critical frequency (foF2), Kp index, and solar radiation flux at 10.7cm (F10.7 index), and relative sunspot number R as indicators of phase of solar cycle as studied time series was used. As a paralel observed series was utilized E10.7 (Solar EUV index based on F10.7) and TEC series. The foF2 data series measured from mid-latitude ionosonde stations was used. For investigation of relationships between time and geographic variations of parameters studied we employ the method of the conditional independence graphical models (CIG) which describing and transparently representing structure of dependence relationships in the time series. This method appears useful for studying the correlationships between fundamental ionospheric parameters and can be applied even in the case when classical parametric methods are not convenient, e.g. for non-continuous time series etc. We consider the structure of pairwise dependence of its individual components, looking for the maximum likelihood estimate of the variance matrix under conditions given by the graphical model. The CIG method allowed implementation of additional time series variables into previous model. Simultaneously we used clasical stochastic model. The data best fit relationship model is computed.

Podolská, K.; Truhlík, V.; T?ísková, L.

2012-04-01

389

The blast wave of the Shuttle plume at ionospheric heights  

SciTech Connect

The main engine burn (MEB) of the Space Shuttle deposits {approximately} 2 x 10{sup 12} joules of explosive energy and {approximately} 3 x 10{sup 5} kg of exhaust in almost horizontal flight at 105-110 km altitude during the period 300-550 s into the ascent. This extremely robust perturbation provides a potential active-excitation source for a variety of geophysical processes, including (1) the effects of aurora-like localized heating on the generation of gravity waves in the thermosphere, (2) the ducting mechanisms for long-period infrasound in the upper atmosphere, (3) dynamo effects associated with transient charge separation, (4) interactions with ambient midlatitude current systems at E-layer heights, and (5) effects in the Earth-ionosphere waveguide of transient electron-density perturbations in the D-region. The sine qua non of such an agenda is to gain a quantitative understanding of the near-field behavior of the MEB exhaust-plume`s quasi-cylindrical expansion, which generates a blast wave propagating away from the explosion. The authors report on observed electron-density signatures of this blast wave as manifested on lines-of-sight (LOSs) from a very-long-baseline interferometer (VLBI) illuminated by 137-MHz beacon signals from the MARECS-B satellite. They also compare the observations to a preliminary three-dimensional neutral-air acoustic model coupled to the ionospheric electron density. 7 refs., 5 figs., 1 tab.

Li, Y.Q.; Jacobson, A.R.; Carlos, R.C.; Massey, R.S.; Taranenko, Y.N.; Wu, G. [Los Alamos National Lab., NM (United States)] [Los Alamos National Lab., NM (United States)

1994-12-01

390

The blast wave of the Shuttle plume at ionospheric heights  

NASA Astrophysics Data System (ADS)

The main engine burn (MEB) of the Space Shuttle deposits ˜2×1012 joules of explosive energy and ˜3×105 kg of exhaust in almost horizontal flight at 105-110 km altitude during the period 300-550 s into the ascent. This extremely robust perturbation provides a potential active-excitation source for a variety of geophysical processes, including (1) the effects of aurora-like localized heating on the generation of gravity waves in the thermosphere, (2) the ducting mechanisms for long-period infrasound in the upper atmosphere, (3) dynamo effects associated with transient charge separation, (4) interactions with ambient midlatitude current systems at E-layer heights, and (5) effects in the Earth-ionosphere waveguide of transient electron-density perturbations in the D-region. The sine qua non of such an agenda is to gain a quantitative understanding of the near-field behavior of the MEB exhaust-plume's quasi-cylindrical expansion, which generates a blast wave propagating away from the explosion. We report on observed electron-density signatures of this blast wave as manifested on lines-of-sight (LOSs) from a very-long-baseline interferometer (VLBI) illuminated by 137-MHz beacon signals from the MARECS-B satellite. We also compare the observations to a preliminary three-dimensional neutral-air acoustic model coupled to the ionospheric electron density.

Li, Y. Q.; Jacobson, A. R.; Carlos, R. C.; Massey, R. S.; Taranenko, Y. N.; Wu, G.

1994-12-01

391

Regional Validation of Jason2 Dual-Frequency Ionosphere Delays  

Microsoft Academic Search

In this study, we validated the Jason-2 (J2) dual-frequency ionosphere delay measurements in terms of vertical total electron content (VTEC) in the Geophysical Data Record (GDR) with the coarse resolution JPL Global Ionospheric Maps (GIM), the regional ionospheric maps generated by the Crustal Motion Observation Network of China (CMONOC), and the Jason-1 (J1) interleaved tandem mission (with J2) ionosphere delay

Kuo-Hsin Tseng; C. K. Shum; Yuchan Yi; Chunli Dai; Hyongki Lee; Dieter Bilitza; Attila Komjathy; C. Y. Kuo; Jinsong Ping; Michael Schmidt

2010-01-01

392

Ray trace calculation of ionospheric propagation at lower frequencies  

Microsoft Academic Search

The Raytrace\\/Ionospheric Conductivity and Electron Density-Bent-Gallagher model has been revised to make it applicable to ionospheric propagation at low radio frequencies (0.5-5.0 MHz), where the ionosphere and magnetic anisotropy drastically alter propagation paths and provide a severe test of propagation model algorithms. The necessary revisions are discussed, and the model is applied to the problem of ionospheric penetration from a

Michael H. Reilly

2006-01-01

393

Ray trace calculation of ionospheric propagation at lower frequencies  

Microsoft Academic Search

The Raytrace\\/Ionospheric Conductivity and Electron Density–Bent-Gallagher model has been revised to make it applicable to ionospheric propagation at low radio frequencies (0.5–5.0 MHz), where the ionosphere and magnetic anisotropy drastically alter propagation paths and provide a severe test of propagation model algorithms. The necessary revisions are discussed, and the model is applied to the problem of ionospheric penetration from a

Michael H. Reilly

2006-01-01

394

A study of the ionogram derived effective scale height around the ionospheric hmF2  

Microsoft Academic Search

The diurnal, seasonal, and solar activity variations of the ionogram derived scale height around the ionospheric F-layer peak (Hm) are statistically analyzed at Wuhan (114.4° E, 30.6° N) and the yearly variations of Hm are also investigated for Wuhan and 12 other stations where Hm data are available. Hm, as a measure of the slope of the topside electron number

L. Liu; W. Wan; B. Ning

2006-01-01

395

Thermospheric wind during a storm-time large-scale traveling ionospheric disturbance  

Microsoft Academic Search

A prominent large-scale traveling ionospheric disturbance (LSTID) was observed in Japan during the major magnetic storm (Dst ~ -358 nT) of 31 March 2001. It was detected as enhancements of the 630-nm airglow and foF2, GPS-TEC variations, and a decrease in F-layer virtual height at 1700-1900 UT (0200-0400 LT). It moved equatorward with a speed of ~600 m\\/s. The decrease

K. Shiokawa; Y. Otsuka; T. Ogawa; S. Kawamura; M. Yamamoto; S. Fukao; T. Nakamura; T. Tsuda; N. Balan; K. Igarashi; G. Lu; A. Saito; K. Yumoto

2003-01-01

396

Coupling of the Auroral and Polar Ionosphere to the Solar Wind During the Extended Solar Minimum  

NASA Astrophysics Data System (ADS)

The response of the auroral and polar ionospheres to prevailing solar wind corotating interaction regions (CIR) has been monitored to an unprecedented extent during the International Polar Year (IPY) and beyond by two incoherent scatter radars. These two radars are located at Svalbard, the EISCAT Svalbard Radar (ESR) and at Poker Flat, the Poker Flat Incoherent Scatter Radar (PFISR). Each radar attempted to operate "24/7" with at least a 10-minute cadence for the entire IPY beginning 1 March 2007 and ending 29 February 2008. The radars achieved an impressive 80% of their target. Indeed PFISR continues to operate in this aggressive mode. During the one year IPY interval over 50 CIRs occurred. Each led to a solar wind-magnetosphere-ionosphere/thermosphere event. Each of these lasted from one to three days. ESR and PFISR were operating for about 40 of the CIRs. Hence, an extensive ionospheric response data-base has been collected in both the polar and auroral regions for these events. These events have very repeatable and significant impact on the ionosphere. Once the CIR begins the F-layer ion temperature is increased and temperatures continues to be elevated for several days. The heating is seen in two forms: an overall increase in temperature by more than 20%, as well as frequent episodes of dramatic heating that lead to short lived ion temperature enhancements up to a factor of 2. The observations also show how the F-layer height and density respond to these drivers. Using the extended PFISR observation mode the electric field is also observed. The electric field is enhanced during these CIR events indicating coupling from the solar wind-magnetosphere has been made to the ionosphere. Joule heating estimates are also able to confirm the heating observations. During times of dramatic heating, the auroral E-region enhancements are a further indication of coupling to the magnetosphere. We present an overview of the CIR morphology from the ionospheric perspective of the solar wind-magnetosphere coupling with the ionosphere. This study is based on observations made at two locations, one in the polar-cusp region (ESR) and the other in the auroral-dayside equatorward of cusp region (PFISR).

Sojka, Jan J.; Schunk, Robert; Nicolls, Michael; van Eyken, Anthony; Heinselman, Craig

397

Plasma Density and Electro-Magnetic Field Perturbations Hf-Induced in the Outer Ionosphere: Review of Experimental Results  

NASA Astrophysics Data System (ADS)

In the report we consider features of plasma density and electro-magnetic field perturbations induced in the Earth’s outer ionosphere by modification of F _{2} region by O-mode powerful HF radio waves radiated by the SURA heating facility. Experiments presented were carried out in 2005 - 2010. Plasma density perturbations were detected at altitudes of about of 700 km by instruments onboard the French DEMETER satellite when it intersected the disturbed magnetic flux tube. The formation of artificial HF-induced plasma density ducts in the outer ionosphere is a central discovery, which was made during the SURA-DEMETER experiments [1,2]. Analysis of experimental data available makes it possible to formulate ducts features and point out the conditions under which the formation of such ducts takes place. 1. Under night conditions ducts are characterized by the increased plasma density in the range from 20% to 80% relatively to its background value. As this takes place, the excess in the plasma ion component is due to O (+) ions dominating at altitudes of about 700 km, whereas the densities of lower mass H (+) and He ({+) } ions typically decrease by a percentage amount that is much more the relative increase in the density of O (+) ions. The duct formation was never observed under daytime conditions. According to [3] the HF-induced ducts were observed by ionosphere pumping in morning and evening hours but in these cases their intensity was no more than a few percentages. 2. The size of the ducts along the satellite orbits is of about 80 - 100 km. It is a reason why such ducts can be observed only if the minimal distance between the satellite and the center of the heated flux tube is less than 50 km. 3. The formation of ducts is observed only if the effective radiated power is more than 40 MW. For the SURA facility, to heat the ionosphere at higher efficiency due to the “magnetic-zenith effect”, the HF beam is often inclined by 12 - 16(°) southward. 4. The pump wave frequency should be no less than 0.5 - 0.7 MHz below the F _{2} layer critical frequency f _{0F2}. In the opposed case the penetration of the radiated power behind the F _{2} ionospheric layer can take place [4]. 5. Strong variations of the electron temperature are observed inside the ducts, at the same time the ion temperature is unchanged. 6. A feature of the ducts is the presence of strong electro-magnetic field fluctuations in a frequency range from a few Hz to tens of kHz [1,5]. 7. It was revealed that the formation of the ducts in the outer ionosphere can stimulate the precipitation of energetic electrons with E ? 100 keV from the Earth’s radiation belts [6]. The work was supported by RFBR grants (## 12-05-00312, 13-02-12074, 13-02-12241) and by the scientific program “Geophysics”. References: 1. Rapoport V.O., V.L. Frolov, G.P. Komrakov, et al. // Radiophysics and Quantum Electronics, 2007. Vol. 50(8), p. 645. 2. Frolov V.L., V.O. Rapoport, G.P. Komrakov, et. al. // JETP Letters, 2008. Vol. 88, No. 12, p. 790. 3. Frolov V.L., I.A. Bolotin, V.O. Rapoport, et. al. // XXIV All-Russian conference “Radio Wave Propagation”. Irkutsk, 2014 (submitted for publication). 4. Frolov V.L., N.A. Mityakov, E.A. Shorokhova, M. Parrot. // Radiophysics and Quantum Electronics, 2013. Vol. 56(6), p. 325. 5. Rapoport V.O., V.L. Frolov, S.V. Polyakov, et al. // J. Geophys. Res., 2010. Vol. 115, A10322, doi:10.1029/2010JA015484. 6. Markov G.A., A.S. Belov, V.L. Frolov, et al. // JETPh, 2010. Vol. 138, No. 6(12), p. 1037.

Frolov, Vladimir; Rauch, Jean-Louis; Parrot, Michel; Rapoport, Victor; Shorokhova, Elena

398

Ionospheric calibration for single frequency altimeter measurements  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

399

Temporal variations of ionospheric parameters derived from electron density profiles at high latitudes  

NASA Astrophysics Data System (ADS)

The ionosphere in the high latitude zone shows similar features to those of middle latitudes but additional factors make it more irregular and variable. The ionosonde, the basic technique for studying the ionosphere, has limitations when it is used at high latitudes avoiding to get a complete information from the ionograms. However the advent of moder sounders permits to produce better ionograms and to gather more information on the ionosphere. This study presents the diurnal and seasonal variations of ionospheric parameters derived from electron density profiles obtained at high latitudes for different solar activity conditions. The day-to-day variability is also examined. The database includes hourly values obtained at selected stations of the Northern and Southern hemispheres. The parameters analyzed are: the F2 peak parameters (foF2 and hmF2), the scale height at the F2 layer (Hm), the integrated total electron content (ITEC) and the equivalent slab thickness (EST).The results presented can be used to extract some properties of the electron density profiles at high latitudes in order to improve the IRI model for this latitudinal region.

Estela Mosert, Marta; McKinnell, Lee-Anne; Magdaleno, Sergio; Jadur, Camilo Alberto

400

Nighttime increases in ionosphere electron content (a statistical and experimental study)  

NASA Astrophysics Data System (ADS)

Variations of nighttime ionosphere total electron content (TEC) have been studied using the Faraday rotation angle data obtained at middle latitudes (Almaty, Kazakhstan) from the geostationary satellite ETS-II during the years 1985-1986. Critical frequency values of the ionosphere F2-layer shown in the vertical sounding ionograms measured at Alma-Ata station (43.25/°N, 76.92/°E) have been used throughout the study. Morphological and statistical analyses are used to investigate the anomalous nighttime increases (ANI) in TEC that occurred during the years. The ANI events are looked at in terms of their amplitude and probability of occurrence, and their duration and peak time. Special features in the events are found to interpret the ANI as a travelling ionosphere disturbance. By examining the hourly, nightly values foF2 and TEC over the two years it has been suggested that the ANI events exist on an ionosphere background which contains regular quasi-periodical oscillations in the period range of 4-30 days.

Gordienko, G. I.; Zachateiskiy, D. E.; Kaliev, M. Z.; Mukasheva, S. N.; Vodyannikov, V. V.

2001-04-01

401

Kilometer-sized waves in electron density in the Venusian nightside ionosphere  

NASA Technical Reports Server (NTRS)

As periapsis of the Pioneer Venus Orbiter (PVO) descended into the lower nightside ionosphere of Venus in the Fall of 1992, wave-like ionospheric density strucutures began to appear on some of the volt-ampere characteristics of the Orbiter Electron Temperature Probe. The number of such events is insufficient to fully define their morphology but enough to provide an indication of the wave amplitudes, scale sizes, occurrence altitudes, and local time variation. The density variations were quasi-sinudoidal, with wavelengths of the order of 1 km along the nearly horizontal trajectory near periapsis. Nearly all of the wave events were encountered within an altitude band lying between 140 and 160 km, a region containing the steep negative N(sub e) gradient just above the ionospheric peak. The waves generally did not fill the occurrence band but were seen primarily as isolated events on curves taken intermittently as PVO crossed through the band. Peak-to-trough amplitudes (delta N/N) were in the range of 5% to 50%. The latitudinal extent of the waves could not be resolved because volt-ampere curves were obtained only intermittent, however, their occurrence on both inbound and outbound passages through the wave band suggests that the waves sometimes exist in layers that extend over at least 15 deg of latitude. The generation mechanism for these waves is unknown, but we suspect that it involves the steep density gradient that separates the main nightside ionosphere from the tenuous, and probably rapidly flowing plasma above.

Brace, Larry H.

1993-01-01

402

Hemispheric, seasonal and latitudinal dependence of storm-time ionosphere during low solar activity period  

NASA Astrophysics Data System (ADS)

Analysis of the seasonal, hemispheric and latitudinal variation of the ionospheric F2 peak during periods of disturbed geomagnetic conditions in 2011, a year of low solar activity, had been studied using hourly data obtained from low- and mid-latitude ionosonde stations. Our results showed an enhancement in F2-layer maximum electron density (NmF2) at daytime over low latitudes. For the mid-latitude stations, NmF2 depletion pre-dominates the daytime and overturned at nighttime. In general, the variation in terms of magnitude is higher in the low-latitude than at mid-latitude. The nighttime decrease in NmF2 is accompanied by a corresponding F2 peak height (hmF2) increase and overturned at daytime. The hmF2 response during the equinoctial months is lower than the solstices. NmF2 shows distinct seasonal, hemispheric and latitudinal dependence in its response. Appearance of a significant ionospheric effect in southern hemisphere is higher than in the northern hemisphere, and is more pronounced in the equinoxes at low latitudes. At mid-latitudes, the ionospheric effect is insignificant at both hemispheres. A negative ionospheric response dominates the whole seasons at the mid-latitude except for March equinox. The reverse is the case for the hmF2 observation. The amplitudes of both the NmF2 and hmF2 increase with increasing latitude and maximize in the southern hemisphere in terms of longitude.

Adekoya, B. J.; Adebesin, B. O.

2014-12-01

403

Control of equatorial ionospheric morphology by atmospheric tides  

Microsoft Academic Search

A newly discovered 1000-km scale longitudinal variation in ionospheric densities is an unexpected and heretofore unexplained phenomenon. Here we show that ionospheric densities vary with the strength of non-migrating, diurnal atmospheric tides that are, in turn, driven mainly by weather in the tropics. A strong connection between tropospheric and ionospheric conditions is unexpected, as these upward propagating tides are damped

T. J. Immel; E. Sagawa; S. L. England; S. B. Henderson; M. E. Hagan; S. B. Mende; H. U. Frey; C. M. Swenson; L. J. Paxton

2006-01-01

404

A review of ionospheric effects on Earth-space propagation  

Microsoft Academic Search

A short description is given of each ionospheric total electron content (TEC) effect upon radio waves, along with a representative value of the magnitude of each of these effects under normal ionospheric conditions. A discussion is given of the important characteristics of average ionospheric TEC behavior and the temporal and spatial variability of TEC. Radio waves undergo several effects when

J. A. Klobuchar

1984-01-01