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

NASA Astrophysics Data System (ADS)

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

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



Ionospheric effects of magnetic storm observed by means of oblique sounding of artificial ionospheric turbulence  

NASA Astrophysics Data System (ADS)

Results of experimental studies of the influence of the artificial ionospheric turbulence (AIT) on HF propagation are presented. Ionospheric modification and the creation of a scatterer was produced by powerful radio emission of the SURA heating facility (Nizhny Novgorod region). For diagnostics of the AIT were used the Russian chirp sounders network and HF Doppler radar. The reception of scattered signals was carried out in the Rostov-Don on the oblique V-type antenna oriented to the SURA heating facility. It is investigated ionospheric effects of magnetic storm during August 17-22, 2003 accompanied a period of the experiment. It is shown that ionospheric effects of the magnetic storm observed by means of Doppler frequency shift (DFS) measurements signals scattered from artificial small-scale field-aligned irregularities correlate well with the behavior of the southward component Bz of the interplanetary magnetic field and with variations in the geomagnetic field near the Earth surface. It has been found that at heights of the mid-latitude ionospheric F region under undisturbed conditions the electric field and the drift velocity of irregularities correspond to the typical values about 1 mV m-1 and 20 m s-1, respectively. During magnetic storm these values increase up to values of about 8.6 mV m-1 and 186 m s-1, which better correspond to the values typical for the high-latitude ionosphere. It is found that in the magnetically-disturbed period sporadically appearing trains with quasi-periodical modulation of DFS for the scattered signal with a period of ˜ 40-60 s and amplitude reaching 2 Hz were observed. The relation of the quasi-periodical oscillations of the DFS for the scattered signal to the presence of magnetohydrodynamics waves excited during a magnetic storm is considered. It is concluded that use HF Doppler radar for AIT sounding is of interest for diagnostics of wave processes in the ionosphere and magnetosphere. The conditions of formation of the HF signal field in the upper ionosphere have been studied using the diagnostics of the ionospheric channel by means of radio wave aspect scattering from artificial small-scale field-aligned irregularities. It has been shown that at long-distance paths the Es-layer may play the key role in formation in the upper ionosphere of the radio wave field at frequencies exceeding maximum usable frequency (MUF) of the standard hop propagation via the ionosphere F region. Modeling of oblique sounding ionogram on long-distance path in presence of the "lateral" signal received due to artificial field-aligned scattering is carried out.

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


The HERO project: Rocket experiments in the artificially heated ionosphere  

NASA Astrophysics Data System (ADS)

Heating experiments will be carried out near Tromsoe, Norway: very powerful radio-waves transmitted upwards into the ionosphere give rise to artificially induced modifications of the natural ionospheric plasma. Many of these modification effects can be followed and interpreted by ground based diagnostic installations such as the EISCAT incoherent scatter facility. Some, however, require in situ methods. Therefore heating rocket (HERO) measurements will complement the ground based observations, gathering data on the modified F region plasma. The planned four payloads are described briefly.

Rose, G.



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

Microsoft Academic Search

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

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



Main ionospheric trough as a boundary layer in the ionosphere  

NASA Astrophysics Data System (ADS)

The mid-latitude electron density trough observed in the topside ionosphere has been shown to be the near-Earth signature of the plasmapause and can provide useful information about the magnetosphere-ionosphere dynamics and morphology. Thus for present the evolution of iono-spheric trough in time and space domain we need some multipoint measurements and different type of measurements techniques. To develop a quantitative model of evolution ionospheric trough features during geomagnetic disturbances the analyse of particle and waves in situ mea-surements and TEC data was carried out. The high resolutions plasma particle diagnostics and wave diagnostics located on board of currently operated satellite DEMETER can give us precisely description of trough signatures and instabilities at define point in space. In particular we will show the temperature and ion drifts manifestation inside ionospheric trough. On the other hand GPS permanent networks such as IGS and EPN provide regular monitoring of the ionosphere in a global scale. Furthermore radio occultation techniques is considered. The radio occultation technique using GPS signals has been proven to be a promising technique to retrieve accurate profiles of the ionospheric electron density with high vertical resolution on a global scale. FormoSat-3/COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) is a joint scientific mission between Taiwan and the U.S.A. The mission placed six small micro-satellites into six different orbits at 700˜800 kilometer above the earth surface. The aim of this paper is to present some general behavior of trough dynamics as well as the fine structures of ionospheric trough and discuss the different type of instability generated inside the trough region from ULF frequency range thru VLF up to HF frequency range. In order to better understand the physical conditions and evolution of ionosphere trough region and describe the coupling between ionosphere and inner magnetosphere the detail examination of geomagnetic storm in January 2005 is presented. As a consequence of different time scales of physical processes occurred in the near Earth environment during geomagnetic disturbances and energy transfer between ionosphere and magnetosphere the examination of ion end electron fluxes inside ionosphere trough are disused.

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


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



Microsoft Academic Search

Radio signals from artificial earth satellites propagated through the earth's ionosphere are subjected to phase delay, refraction, and attenuation. These effects cause .uncertainties in the determination of the vacuum Doppler shift of CW signals. To understand the nature of these ionospheric contributions to the Doppler shift, a theoretical expression for the refracted Doppler shift that is an inverse power series

A. J. Tucker; B. M. Fannin



Physics studies in Artificial Ionospheric Mirror (AIM) related phenomena. Final report, 26 August 1987-31 August 1989  

SciTech Connect

This document reports on the progress made and final results of a study into the fundamental physics of electromagnetic induced ionization in the lower ionosphere (60 - 80 km), using a ground based radiation source. The technique of remotely controlled ionization can be used to create a layered region of ionization and to then use the Artificial Ionospheric Mirror (AIM) to reflect HF/VHF signals for over the horizon communications and radar applications. The objective of the study was to identify the basic physics issues controlling RF breakdown phenomena and to develop an understanding of those issues sufficient for performing quantitative prediction of AIM characteristics and the impact of those characteristics on the reflecting wave. Results of the study indicate that AIM is a viable concept and has the potential of providing important benefits over more traditional communication/radar technology.

Short, R.; Ali, A.; Lallement, P.; Koert, P.; Papadopoulos, D.



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



Three-dimensional, high resolution, computerized ionospheric tomographic imaging and computational modeling of an artificial ionospheric cavity  

NASA Astrophysics Data System (ADS)

Tomographic techniques use line integral measurements to reconstruct local values of the measured parameter. These techniques have been applied to the ionosphere by using radio transmissions to measure the integral of electron density between a satellite and a chain of ground-based receiving stations. The resultant reconstructions form a two-dimensional map of the electron density in the plane of the satellite/receiver chain. Insufficient quantity of receivers and not having a complete range of accessible look angles with the available receivers are responsible for the non-uniqueness in the reconstructions. The limited look angle problem can be alleviated by making use of alternative data sources such as incoherent scatter radars ( ISR) that provide information on the vertical structure of the electron density. The non-optimal receiver placement problem can be alleviated through the use of sophisticated reconstruction algorithms. The computerized ionospheric tomography (CIT) technique has recently been used to image the artificially modified ionosphere above the Arecibo Observatory (AO) HF heating facility. A total of nine radio beacon receivers forming a three by three matrix were deployed across the entire island of Puerto Rico. The arrangement maximizes the likelihood that several of the receiver-to-satellite lines of sight would intersect the heated region of the ionosphere. Several satellite passes associated with such an intersection occurred, and the resultant tomographic inversions indicate the existence of an electron density cavity approximately 45 kilometers in latitudinal extent. The reduction of electron density in this cavity was typically on the order of 20%. The experimental observations were supported by theoretical work using the open-source SAMI2 ionospheric model. Methods were developed to model both the ohmic heating of the electrons and the suprathermal heating caused by nonlinear effects. Modeled ohmic heating values of 941 K/s match the observed heated temperature profiles. Modeled suprathermal electrons effects on the vibrational temperature of N2 indicate a vibrational/translation temperature differential of 308°K.

Selcher, Craig A.


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


Spread E, F layer ionospheric clutter identification in range-Doppler map for HFSWR  

Microsoft Academic Search

Wide range covering, strong intensity, time-variant, fluctuation and irregular distribution of the spread E, F layer ionospheric clutter badly affects the system performance of High Frequency Surface Wave Radar (HFSWR). A spread E, F layer ionospheric clutter identification method is proposed based on the region segmentation results and region characteristics of the clutter. First of all, convolution template is used

Yang Li; Ning Zhang; Qiang Yang



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

NASA Astrophysics Data System (ADS)

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

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



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

NASA Technical Reports Server (NTRS)

In two barium releases made over the Caribbean during the summer of 1991, the ion cloud was observed to last more than 10 hours. Observations were made with a low light level TV imager and a TV spectrograph operated onboard a Russian research vessel conducting ionospheric research and participating in the NASA-CRRES mission. The two clouds were observed near the release region for 15 to 25 minutes during the twilight following the initial release. One of the releases was made during evening twilight and the ion cloud reappeared the following morning, while the other was a morning release and the late-time observations made the next evening. The observations are highly surprising since, generally, it has been assumed that the ion cloud would dissipate within a few hours. However, the long life time appears consistent with current knowledge about dissipative processes. The long lifetime of barium ion clouds may provide for the most sensitive experimental testing of ionospheric convection models, a possibility with clear implications for future barium release experiments.

Milinevskij, G. P.; Kashirin, A. I.; Romanovskij, Yu. A.; Stenbaek-Nielsen, H. C.; Kelley, M. C.



Relaxation Time of Artificial Periodic Irregularities of the Ionospheric Plasma and Diffusion in the Inhomogeneous Atmosphere  

NASA Astrophysics Data System (ADS)

We consider diffusion of the ionospheric-plasma irregularities as applied to the problem of experimental determination of the lower-ionosphere parameters by artificial periodic irregularities of the electron number density. A rigorous solution to the problem of diffusion of one-dimensional plasma irregularities in a weakly ionized medium, whose diffusion coefficient exponentially decreases with the altitude, is obtained. The Green's function for this problem is found. Three parameters are taken into account in the solution, namely, the size of the region occupied by the irregularities, the size of the irregularities, and a typical spatial scale of the e-fold decrease in the diffusion coefficient. Theoretical relaxation times of the irregularities as functions of these parameters are analyzed. Calculated relaxation times are compared with the times measured in the observation of the artificial periodic irregularities created by the SURA facility. Calculated relaxation times of these irregularities are in good agreement with the observed values.

Grigor'ev, G. I.; Bakhmet'eva, N. V.; Tolmacheva, A. V.; Kalinina, E. E.



Predicting the ionospheric F layer using neural networks  

NASA Astrophysics Data System (ADS)

A new neural network (NN) based ionospheric model for the bottomside electron density profile over Grahamstown, South Africa (33.3°S, 26.5°E) has been developed and is referred to as the LAM model. This paper discusses the development of the F layer contribution to the LAM model. Archived data from the Grahamstown ionospheric station have been presented to various NNs, which have been trained to predict the parameters required to produce an electron density profile. Since the dataset was only made up of Grahamstown data, the model is currently a single station model. The input space designed for the F layer contribution to the LAM model consisted of various combinations of the following parameters: day number (DN), hour (HR), a measure of the solar activity, and a measure of the magnetic activity. The solar activity input was represented by a 2-month running mean value of the sunspot number (R2), while the magnetic activity variable was represented by either a 24-hour or 48-hour running mean of the magnetic ak value (A8 or A16). The outputs from the NNs were the peak parameters and Chebyshev coefficients required to describe the shape and location of the F profile. This paper also discusses how NNs have been employed to provide an effective mechanism for determining the probability of the existence of an F1 layer. An F1 layer can exist in one of the following three states; F1 exists, no F1, or F1 exists in L condition state. A special NN was trained to provide the probability of F1 layer existence in each of these states. An L algorithm is applied to determine the shape and location of the profile under L condition state. In addition, a smoothing technique was designed to deal with discontinuities across the F1-F2 boundary. It is shown that the NN-based LAM model can successfully predict descriptions for the shape and location of the average profile for a given input set, and, in addition, that NNs can be employed to provide solutions to previously difficult prediction tasks such as the probability of F1 layer existence.

McKinnell, Lee-Anne; Poole, Allon W. V.



Layer structure of the Venus daytime ionosphere from Venera-15,-16 radio occultation  

NASA Astrophysics Data System (ADS)

Up to now more than five hundred radio occultation experiments had been carried out by different missions to research physical properties of the Venus ionosphere. The purpose of this report is to show new properties of the Venus daytime ionosphere reanalyzing Venera-15,-16 dual-frequency occultation data. The high coherence and stability of radio signals of Venera- 15,-16 at wave lengths 32 cm and 8 cm, along with the fact, that the refractive amplification at 32 cm in the ionosphere exceeds by factor 6 the refractive amplification at 13 cm used by others researches, have allowed to perform analysis of radiophysical parameters in the Venus ionosphere more accurate. Progress in the radiovision theory and up-to-date digital processing techniques have provided an opportunity to discover unknown layered structure of the Venus daytime ionosphere. We offer the new technique of the data analysis that allows us to separate influence of noise, ionosphere and atmosphere on the radio occultation results. We point out that significant gradient variations in the vertical distribution of the electron density are observed in the region of maximum electron density of the daytime ionosphere at altitudes of 150-175 km. That testifies layered structure of this part of the Venus ionosphere. The results of data analysis reveal the regular existence of the ionospheric layers in the bottom daytime ionosphere at altitudes from 80 up to 115 km. The bottom border of the ionosphere part can vary in the range of 80-100 km, and gradients of the electron density show strong variability. We detect the wave structure in the top atmosphere and in the bottom ionosphere at altitudes from 60 up to 115 km as well. It is difficult to obtain correct electron density in the region, where we have detected the new ionospheric layers. Relative errors of the electron density are greater than 100% at altitudes between 80 and 120 km. The bottom part of the ionosphere is more variable, than overlying area of the main maximum of the daytime ionosphere. It is difficult to explain such layered structures of the Venus daytime ionosphere by means of existing model of the photochemical equilibrium.

Gavrik, Anatoly


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

NASA Technical Reports Server (NTRS)

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

Cole, Keith D.



Biomimetic layer-by-layer assembly of artificial nacre  

NASA Astrophysics Data System (ADS)

Nacre is a technologically remarkable organic-inorganic composite biomaterial. It consists of an ordered multilayer structure of crystalline calcium carbonate platelets separated by porous organic layers. This microstructure exhibits both optical iridescence and mechanical toughness, which transcend those of its constituent components. Replication of nacre is essential for understanding this complex biomineral, and paves the way for tough coatings fabricated from cheap abundant materials. Fabricating a calcitic nacre imitation with biologically similar optical and mechanical properties will likely require following all steps taken in biogenic nacre synthesis. Here we present a route to artificial nacre that mimics the natural layer-by-layer approach to fabricate a hierarchical crystalline multilayer material. Its structure-function relationship was confirmed by nacre-like mechanical properties and striking optical iridescence. Our biomimetic route uses the interplay of polymer-mediated mineral growth, combined with layer-by-layer deposition of porous organic films. This is the first successful attempt to replicate nacre, using CaCO3.

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



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.



Thermal response of the F region ionosphere in artificial modification experiments by HF radio waves  

NASA Technical Reports Server (NTRS)

The thermal response of the nighttime F region ionosphere to local heating by HF radio waves has been observed with the incoherent scatter radar at Arecibo, Puerto Rico. The observations consist of high-resolution space and time variation of the electron temperature as a high-power HF transmitter is switched on and off with a period 240 s. As soon as the HF transmitter is turned on, the electron temperature begins to rise rapidly in a narrow altitude region near 300 km, below the F2 layer peak. The electron temperature perturbation subsequently spreads over a broader altitude region. The observations are compared with the anticipated thermal response of the ionosphere based on numerical solutions of the coupled time-dependent heat conduction equations for the electron and composite ion gases and are found to be in good agreement over the entire altitude region covered by the observations.

Mantas, G. P.; Lahoz, C. H.; Carlson, H. C., Jr.



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.



Ionospheric correction for spaceborne single-frequency GPS based on single layer model  

NASA Astrophysics Data System (ADS)

A modified ionospheric correction method and the corresponding approximate algorithm for spaceborne single-frequency Global Positioning System (GPS) users are proposed in this study. Single Layer Model (SLM) mapping function for spaceborne GPS was analyzed. SLM mapping functions at different altitudes were calculated. Ionospheric Pierce Point (IPP) trajectories of the dlft station (An IGS station located at the longitude of 4°23'15.22''E and the latitude of 51°59'9.63''N, in the TU Delft University, The Netherlands.) and the GRACE satellite were computed with the corresponding single layer height of 350 and 500 km, respectively. The Klobuchar model was used to compute ionospheric delays for the dlft station, and modified Klobuchar model, together with scale factors, was used to compute the fractional ionospheric corrections above the GRACE altitudes. Calculation results were validated using dual-frequency observations. The study shows that the single layer height needs to be changed from 350 to 500 km according to the altitude of GRACE. Approximate forms of Earth angle and slant factor developed for modified Klobuchar model are applicable to GRACE, with accuracy adequate to preserve the essential elements required to compute ionospheric delays. Results show that the Klobuchar model is effective for ground GPS, and the modified Klobuchar model corrects more than 80% on average of the ionospheric delays for spaceborne single-frequency GPS.

Yang, Xia; Li, Jiancheng; Zhang, Shoujian



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 October 2008; accepted 29 October 2008; published 12 March 2009. [1] The Venus Express Radio Science (VeRa) experiment aboard Venus Express has detected, by means of radio occultation, distinct, low-lying layers

Mendillo, Michael


Planetary ionospheres  

NASA Technical Reports Server (NTRS)

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

Bauer, S. J.



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.



Enhanced intervalley scattering in artificially stacked double-layer graphene  

NASA Astrophysics Data System (ADS)

We fabricated artificially stacked double-layer graphene by sequentially transferring graphene grown by chemical vapor deposition. The double-layer graphene was characterized by Raman spectroscopy and transport measurements. A weak localization effect was observed for different charge carrier densities and temperatures. The obtained intervalley scattering rate was unusually high compared to normal Bernal-stacked bilayer or single-layer graphene. The sharp point defects, local deformation, or bending of graphene plane required for intervalley scattering from one Dirac cone to another seemed to be enhanced by the artificially stacked graphene layers.

Iqbal, M. Z.; Kelekçi, Özgür; Iqbal, M. W.; Jin, Xiaozhan; Hwang, Chanyong; Eom, Jonghwa



Effects of the Earth's Ionosphere on HF Radio Astronomy from Artificial Satellites  

Microsoft Academic Search

A theoretical analysis of the effects of the ionosphere on HF observations from satellite-borne radio telescopes is presented. The primary effect investigated is the focusing effect of the ionosphere on incoming cosmic noise. This effect was computed according to the Hamiltonian equations for a ray path in a general magnetoionic medium, assuming the ionosphere to be a nonhomogenous, nonisotropic, magnetoionic

M. D. Grossi; K. M. Strom; S. E. Strom



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


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

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



In-situ observations of intermediate layers in the night time ionosphere  

NASA Astrophysics Data System (ADS)

Night time ionospheric electron density profiles have been obtained using impedance and Langmuir probe techniques showing the presence of intermediate layers. Four sounding rockets were launched in July of 2003 at Wallops Island, VA and two more were launched in August of 2004 from Kwajalein atoll, Marshall Islands. Although these rocket campaigns were conducted at different latitudes they both indicated a patchy spatial structure. All six flights used essentially the same plasma impedance probe but the later campaign included a sweeping Langmuir probe. More emphasis is given to the data from the later campaign, "Scattering Layer in the Bottomside Equatorial F-region Ionosphere" investigation, which was a part of the NASA EQUIS II campaign. Electron density from this data set is analyzed using Balmain's theory for a short antenna in a cold magnetoplasma and compared with data from the sweeping Langmuir probe.

Gregory, J.; Swenson, C. M.; Humphries, S.; Fish, C.; Carlson, C.; Barjatya, A.



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

NASA Astrophysics Data System (ADS)

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

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



A digest of electrodynamic coupling and layer instabilities in the nighttime midlatitude ionosphere  

NASA Astrophysics Data System (ADS)

The basic elements of electrodynamic coupling and positive feedback between a sporadic E (Es) layer and the F layer of the nighttime midlatitude ionosphere are briefly described. This coupled system is interesting because each layer, in isolation, can be unstable to perturbations in vertical displacement (i.e., the so-called Es layer and Perkins instabilities). The two processes are similar generically and can be referred to as layer instabilities. Moreover, both have maximum growth rates when frontal perturbations are aligned northwest to southeast in azimuth (northern hemisphere), which leads to interactive behavior with positive feedback because the polarization electric fields that arise from both processes are in phase and additive. Consequently, the growth rates of both instabilities are enhanced by their mutual presence; the largest enhancement, however, occurs in the structuring of the F layer. Some of the interesting aspects of coupled-system behavior are described and discussed.

Tsunoda, Roland T.


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


Some distinctive features in the behavior of small-scale artificial ionospheric irregularities at mid-and high latitudes  

NASA Astrophysics Data System (ADS)

We present the results of experimental studies of some features in the behavior of small-scale artificial irregularities (SSAIs) at mid-and high latitudes based on the “Sura” and EISCAT/HEATING HF facilities. Observations were performed by the method of aspect scattering using a network of diagnostic paths having a common reception point located near St. Petersburg. We found that an extremely long duration of the second (slow) stage of SSAI relaxation of up to 5 min occurs in the evening hours when the ionosphere above the “Sura” facility is illuminated by the Sun, but the solar terminator travels through the magnetically conjugated ionosphere. The conjecture is made that the processes initiated by the terminator are mostly responsible for secondary ionospheric turbulence maintaining the irregularities above “Sura.” A drastic increase in the Doppler spectra width of the scattered signals is revealed when the magnetically conjugate point of the ionosphere is located on the shade side of the terminator, but the ionosphere above the “Sura” facility is still lighted. It is assumed that the “ run away” of photoelectrons from the day to the night side could reduce the threshold of excitation of artificial irregularities, leading to an increase in their intensity. The presence of fairly intense scattered signals was detected from the “Sura” and EISCAT/HEATING experimental results both under conditions of pulsed HF heating after continuous heater-on periods and cycled HF heating by short pulses. In the case of pulsed heating by short pulses with duration ?p < 100 ms and average radiated power Pa below the threshold power Pthr of the SSAI generation cutoff the irregularities can be maintained due only to striction parametric instabilities. The excitation of irregularites under the cycled HF pumping with the pulse duration ?p = 384 ms for Pa comparable with Pthr was detected. The aspect-angle dependence, or the so-called magnetic zenith effect, was found in the SSAI intensity. The residual turbulence aftereffects played a significant role in the SSAI development.

Blagoveshchenskaya, N. F.; Borisova, T. D.; Kornienko, V. A.; Frolov, V. L.; Rietveld, M. T.; Brekke, A.



Comparative study of polar ionospheric F layer observations with IRI in both hemispheres  

NASA Astrophysics Data System (ADS)

Based on the good geographic locations of magnetic conjugate between Chinese Zhongshan Station in Antarctic and Svalbard Station in Arctic, with the convenient share of International Polar Year (IPY, 2007-2008) radar data, the characteristics of F layer ionosphere in both hemispheres are compared. The main work of this paper can be concluded as follows: 1. The study on diurnal variations of F layer ionosphere in both Antarctic and Arctic As for foF2, there are magnetism noon phenomena in the Autumn of Zhongshan and Spring of Svalbard. And at equinox, the changing range is much bigger than in other seasons. As for hmF2, at equinox, the diurnal variation has an asymmetric "W" shape, whose changing range is much wider. The changing range in summer is relatively small and smooth. And compared with other seasons, the hmF2 in Zhongshan and Svalbard are much similar in shape, yet the average height of Zhongshan is higher than that of Svalbard. 2. The study on comparison between observations and IRI in both Antarctic and Arctic. In summer, the foF2 observations in Zhongshan and Svalbard fit the IRI model much better. It is possibly explained by the reason that the IRI model is largely based on the observations at lower altitude which best consider the solar radiation. Similar, in polar zone the sun is most active in summer and plays a vital part in affecting the ionosphere environment. In winter, the comparison results are the worst. IRI model can not reflect the change of peak value after the noon. It because the sun is always under the horizon for most of time in winter which results in the lack of solar radiation. The auroral particle precipitation is mostly affecting the F layer at equinox and in winter, but not well included in the IRI model. Besides, the hmF2 forecasted is larger than the observations.

He, Fang; Zhang, Beichen


Field-aligned and field-perpendicular velocities in the ionospheric F2-layer  

NASA Technical Reports Server (NTRS)

The correlation between variations in the components of the ionospheric F2-layer parallel and perpendicular to the geomagnetic field is theoretically examined. The servo model of Rishbath (1967) is used as a basis for further calculations. The equations involved are presented in full and results are given for various assumed conditions. The response of the model to both steplike and periodic perturbations of the perpendicular component is considered along with the effects of winds and the Coriolis force. Arecibo and Malvern data are reviewed on the basis of theoretically predicted behavior.

Rishbeth, H.; Ganguly, S.; Walker, J. C. G.



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.



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


Characteristics of layers, waves and turbulence in the atmosphere and ionosphere as estimated by GPS space radio-holography  

NASA Astrophysics Data System (ADS)

The spatial, seasonal and geographical distrubutions of the intensity of layers, turbulence and internal waves at different altitudes in the atmosphere and ionosphere of the Earth are presented. The results have been obtained on the base of locality principle using a new phase acceleration-intensity method for analysis of the GPS radio occultation signals. This methodology has been applied to mesearements of the inclination and altitude of ionospheric layers. Obtained information has been used for estimation of the front orientation, internal frequency and phase speed of the internal waves in the ionosphere and neutral atmosphere. A new index of the ionospheric activity as measured from the phase of radio waves passed through the ionosphere is introduced and its high correlation with S4 scintillation index is established. This correlation indicates the significant influence of ionospheric layers on variations of characteristics of radio waves in transionospheric communication links. Specially for the troposphere the geographical distribution of the weak total absorption (about of 1-2 db) of the radio waves at GPS frequencies in the Earth atmosphere corresponding to influence of the oxygen and water vapor in the troposphere is measured with accuracy better than 0.1 db. Obtained results expanded the applicable domain of the GPS space radio-holography for global investigation of the natural processes in the atmosphere and ionosphere as function of solar activity and space weather effects. The new phase acceleration-intensity method is also a basic tool which can be applied for data analysis of future planetary radio occultation missions

Pavelyev, Alexander; Gubenko, Vladimir; Matyugov, Stanislav; Pavelyev, Alexey


Characterization of Artificial Guidestars Generated in the Mesospheric Sodium Layer  

NASA Technical Reports Server (NTRS)

Using a 10 W average power sum-frequency laser, we have generated resonant fluorescence beacons in the mesospheric sodium layer and are currently evaluating them for use as an artificial guidestar for atmospheric compensation using adaptive optics. Two flashlamp pumped Nd:YAG lasers operating at 1.064 and 1.319 microns are mixed in a lithium triborate crystal to produce 589 nm light at 840 Hz. The laser emits 47.5 microsec mode-locked pulse trains at 11-14 mJ per pulse and is tuned to the sodium resonance transition with intracavity etalons.

Jelonek, M. P.; Fugate, R. Q.; Lange, W. J.; Slavin, A. C.; Ruane, R. E.; Cleis, R. A.



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

NASA Technical Reports Server (NTRS)

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

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



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.



Generation of 'artificial' bursts in a turbulent boundary layer  

NASA Technical Reports Server (NTRS)

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

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



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

NASA Astrophysics Data System (ADS)

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

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



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.


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


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.



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

NASA Astrophysics Data System (ADS)

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

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



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

SciTech Connect

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

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



Seasonal variation of the ionospheric F2-layer intensity at midlatitudes during the solar cycle 23  

NASA Astrophysics Data System (ADS)

We investigate the seasonal variation of the ionospheric F2-layer intensity at midlatitudes during the solar cycle 23. The occurrence of larger daytime electron density in winter than in summer is called as seasonal anomaly or winter anomaly. The seasonal anomaly occurs mainly at midlatitudes and is more pronounced in the northern hemisphere than in the southern hemisphere. We investigate the variation of the seasonal anomaly with solar cycle and local time by analyzing the radio occultation measurements from FORMOSAT-3/COSMIC satellites during the solar minimum period (2007-2008) and from the CHAMP satellite during the solar maximum period (2001-2002). The vertical electron density profiles obtained from COSMIC and CHAMP will be compared with those observed by the Incoherent Scatter Radar at Millstone Hill. The hemispheric difference in the seasonal anomaly will also be investigated by using the ionosonde measurements of the F-peak electron density at Osan in Korea and Darwin in Australia. We discuss the combined effects of the neutral composition and the global annual asymmetry on the creation of the seasonal anomaly.

Lee, W.; Kil, H.; Wu, Q.; Chung, J.; Cho, S.; Park, J.



Using the radial basis function neural network to predict ionospheric critical frequency of F2 layer over Wuhan  

NASA Astrophysics Data System (ADS)

Neural networks (NNs) have been applied to ionospheric predictions recently. This paper uses radial basis function neural network (RBF-NN) to forecast hourly values of the ionospheric F2 layer critical frequency( f oF 2), over Wuhan (30.5N, 114.3E), China. The false nearest neighbor method is used to determine the embedding dimension, and the principal component analysis (PCA) is used to reduce noise and dimension. The whole study is based on a sample of about 26,000 observations of f oF 2 with 1-h time resolution, derived during the period from January 1981 to December 1983. The performance of RBF-NN is estimated by calculating the normalized root-mean-squared (NRMSE) error, and its results show that short-term predictions of f oF 2 are improved.

Liu, Dan-Dan; Yu, Tao; Wang, Jing-Song; Huang, Cong; Wan, Wei-Xing



27/10/2010 12:42AGU: Modification of midlatitude ionospheric parameters in the F2 layer by persistent highspeed solar wind streams Page 1 of 1  

E-print Network

27/10/2010 12:42AGU: Modification of midlatitude ionospheric parameters in the F2 layer:// Keywords F layer HSS ionosphere Index Terms Space Weather: Corotating streams Ionosphere: Ionosphere/magnetosphere interactions Abstract Modification of midlatitude

Ulich, Thomas


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

SciTech Connect

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

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



Anomalous Enhancement of Ionospheric F2 layer critical frequency and Total Electron Content over Low Latitudes before three recent major Earthquakes of China  

NASA Astrophysics Data System (ADS)

This paper reports unusual variations in the ionospheric Total electron Content (TEC) and the critical frequency of the F2 layer (foF2) few days before the main shock of three major earthquakes (magnitude greater than 6 on Rector Scale). Epicenters of these earthquakes are distributed in China. Ionospheric data, recorded by a network of ionosonde and GPS receivers at Delhi (28.6N, 77.2E) Bhopal (23.29N, 77.46E) and Trivandrum (8.4N, 76.6E) are analyzed for finding the seismo-ionospheric signatures of these major earthquakes recently occurred in China. The results clearly indicate large enhancements in foF2 and TEC on geomagnetic quiet days, observed mainly at a low latitude station Delhi, which is nearest to the earthquake epi-centers. This anomalous behavior of foF2 and TEC appeared 1 to 4 days before the main shock and especially during 1100 -1700 LT. However the ionospheric foF2 and TEC variability at equatorial station, Trivandrum and equatorial anomaly station, Bhopal did not show any significant changes, thereby indicating the localized nature of such unusual ionospheric vari-ations. The observed results suggest that the unusual enhancements of ionospheric foF2 and TEC over Delhi few days before the main shock of each earthquake are most possibly due to seismo-ionospheric link.

Sharma, Kavita


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

NASA Astrophysics Data System (ADS)

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

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



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: 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


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

NASA Astrophysics Data System (ADS)

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

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



Behavior of parameters of the ionospheric F2 layer at the turn of the Centuries: 1. critical frequency  

NASA Astrophysics Data System (ADS)

The available massifs of experimental data on the critical frequency of the ionospheric F2 layer, foF2, covering the first decade of the new century, are considered. On the basis of studying these massifs, a conclusion is drawn that the scatter of foF2 values (measured by the standard deviation (SD)) relative to the dependence on solar activity has grown substantially over recent decades as compared to the period 1958-1979. The possible causes of the SD increase are considered. It is shown that the foF2 values for the period 1998-2010 decreased as compared to the period 1958-1979 by an average of 0.6 MHz which gives an estimate of the foF2 trend of ˜-0.03 MHz per year. Linear trends in foF2 for some ionospheric stations are analyzed. It is obtained that, in spite of the scatter in the data, it is possible to obtain statistically significant trends for each considered situation (day and postsunset period in summer and winter). At the same time, the winter negative trends (˜-0.052 MHz per year) are approximately a factor of 2 higher than the summer ones (˜-0.024 MHz per year). Comparisons with the trends obtained for earlier periods show that the negative trend in foF2 increased substantially towards the first decade of our century.

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



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



Remote sensing of natural and artificial variations in the Earth-ionosphere cavity via very low frequency  

NASA Astrophysics Data System (ADS)

In this article we present results from very low frequency (VLF) observations of transient and intermittent phenomena in the Earth-ionosphere waveguide. The scientific objectives are remote localisation and characterisation of short time disturbances. The VLF amplitude and phase variations aid to physically investigate the atmospheric media from the Earth's surface up to the lower ionosphere (~ 70-90 km, D- and E-region) which is part of propagation channels for satellite communications and navigational applications. We consider two common types of anomalies in the waveguide, these events are associated with (i) solar flares and (ii) geomagnetic storms. We conclude that with a continuous operating VLF receiver network a service for lower atmospheric channel monitoring / characterisation can be established.

Eichelberger, H. U.; Leitgeb, E.; Prattes, G.; Schwingenschuh, K.; Biagi, P. F.; Maggipinto, T.; Rozhnoi, A.; Solovieva, M.; Besser, B. P.; Stachel, M.; Jernej, I.; Aydogar, O.



Anomalous enhancement of ionospheric F2 layer critical frequency and total electron content over low latitudes before three recent major earthquakes in China  

NASA Astrophysics Data System (ADS)

This paper reports unusual variations in the ionospheric total electron content (TEC) and the critical frequency of the F2 layer (foF2) a few days before the main shock of three major earthquakes (M > 6). Epicenters of these earthquakes are distributed in China. Ionospheric data, recorded by an Indian network of ionosonde and GPS receivers at Delhi (28.6°N, 77.2°E), Bhopal (23.29°N, 77.46°E), and Trivandrum (8.4°N, 76.6°E) are analyzed to find seismoionospheric signatures of three recent major earthquakes in China. The results clearly indicate large enhancements in foF2 and TEC on geomagnetic quiet days, observed mainly at a low-latitude station in Delhi, which is nearest to the earthquake epicenters. The anomalous behavior of foF2 and TEC appeared 1-4 days before the main shock and especially during 1100-1700 LT. However, the ionospheric foF2 and TEC variability at the equatorial station Trivandrum and equatorial anomaly station Bhopal did not show any significant changes, thereby indicating the localized nature of such unusual ionospheric variations. The observed results suggest that the unusual enhancements of ionospheric foF2 and TEC over Delhi a few days before the main shock of each earthquake are most likely due to a seismoionospheric link.

Sharma, Kavita; Dabas, R. S.; Sarkar, S. K.; Das, R. M.; Ravindran, Sudha; Gwal, A. K.



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, Robotics often appears as a collection of disjoint, some- times antagonistic sub-fields. The lack robotics, and shows how these traditional sub-fields fit in to the whole. Finally, it presents a curriculum

Crabbe, Frederick


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, Robotics often appears as a collection of often disjoint, sometimes antagonistic sub-fields. The lack robotics, and shows how these traditional sub-fields fit in to the whole. Finally, it presents a curriculum

Crabbe, Frederick


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.



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.



Annual and semiannual variations in the ionospheric F2-layer. I. Modelling  

E-print Network

and semiannual variations of F2-layer electron density (NmF2) and height (hmF2) have been compared of hmF2. Some features of the F2-layer, not reproduced by the present version of CTIP, are attributed in summer by vibrationally excited molecular nitrogen, and the semiannual variation in hmF2, which may

Paris-Sud XI, Université de


Excitation of guided ELF-VLF waves through modification of the F{sub 2} ionospheric layer by high-power radio waves  

SciTech Connect

The possibility of controlled excitation of ELF-VLF electromagnetic waves through modification of the F{sub 2} ionospheric layer by high-power high-frequency emission is demonstrated in a natural experiment by using the Sura midlatitude heating facility. The excited low-frequency waves can be used to explore the near-Earth space and stimulate the excitation of a magnetospheric maser.

Markov, G. A.; Belov, A. S.; Komrakov, G. P. [Lobachevsky State University (Russian Federation); Parrot, M. [Environmental Physics and Chemistry Laboratory (France)



Soviet ionospheric modification research  

Microsoft Academic Search

Soviet published literature in ionospheric modification research by high-power radio waves is assessed, including an evaluation of its impact on and applications to future remote-sensing and telecommunications systems. This assessment is organized to place equal emphasis on basic research activities, designed to investigate both the natural geophysical environment and fundamental plasma physics; advanced research programs, such as those studying artificial

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



Optimization of parameters of an artificial aerosol layer for radiation frost protection  

Microsoft Academic Search

Data are presented on losses from frosts in the Southern Federal Region of Russia. Problems are considered of optimization\\u000a for radiation frost protection, based on production of artificial smoke layers and fogs. Studies of infrared radiation attenuation\\u000a by aerosol of different dispersion and simulation of aerosol turbulent diffusion show that, within the atmospheric transmittance\\u000a window, a sufficient greenhouse effect can

A. M. Abshaev; Kh. Zh. Malkarov



An Artificial Immune Network with Multi-layered B Cells Architecture  

NASA Astrophysics Data System (ADS)

This paper describes an artificial immune network with multi-layered B cells architecture. It is not our concern to reproduce with confidence any immune phenomenon, but to show that immune concepts can be used to develop powerful computational tools for engineering applications. As an important result of our model based on multi-layered B cells architecture, the network is capable of creating better immune response and describing pattern category for arbitrary sequences of analog (gray-scale, continuous valued) input patterns, as well as binary input patterns.

Sun, Wei-Dong; Tang, Zheng; Tamura, Hiroki; Ishii, Masahiro



E-print Network

. The irregular boundary defined by the cusps and steps gives the maximum electron density of the second layer, ne defined peak in the density profile. 3. A spectrogram that shows the transient variations in the electron the occurrence probability, the middle panel gives the maximum electron density, and the bottom panel gives

Gurnett, Donald A.


Phase-Space Model for Correlated Double Layers, Bipolar Structures, and VLF Saucer Generation in the Auroral Ionosphere  

NASA Astrophysics Data System (ADS)

Recent observations by the FAST satellite have provided high-time-resolution measurements of three interrelated phenomena in the downward current region of the auroral ionosphere: intense parallel electric fields (e.g. double layers) localized to tens of Debye lengths(Ergun et al., PRL) 87, 045003 (2001).; drifting localized bipolar field structures interpreted in terms of electron phase-space holes(Ergun et al., GRL), 25, 2042 (1998).; and intense quasi-electrostatic whistler emissions (VLF saucers) originating on the same field lines as the bipolar structures.(Ergun et al., Electron phase-space holes in the VLF saucer source region, GRL), in press (2001). Numerical simulations and theoretical modeling suggest how these observations may be related. 1-D open-boundary Vlasov simulations show that a density depression in an equipotential plasma carrying a field-aligned current can produce a strong localized parallel electric field (i.e., a potential jump) characteristic of a classical double layer. The electrons accelerated by this field interact with a low-velocity population on the high-potential side to produce a series of electron phase space holes propagating away from the potential ramp. Multi-dimensional (magnetized) PIC and Vlasov simulations of the two-stream instability show that electron phase-space holes initially develop coherence perpendicular to B, thus forming ``tubes'' in phase space. However, these tubes later become unstable due to a resonant interaction of electrostatic whistlers (or lower-hybrid waves) with vibrational modes of the phase-space tubes.(Newman et al., PRL), 86, 1239 (2001). The whistler waves generated by this instability may be the source of the observed VLF saucers.

Newman, David L.



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

NASA Technical Reports Server (NTRS)

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

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



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.



Production of Double-Layered Metal Nanocups for Artificial Nanospace of Biomolecular Reaction  

NASA Astrophysics Data System (ADS)

Nanocups (NCs), sub-micrometer semispherical bowls consisting of two different nanometer-thick metals on inner and outer layers, have been fabricated to mimic a localized nano-scale biochemical reaction environment for reactive biomolecules. Homogeneous polystyrene beads were used as a cast of the NCs, placed on a Si substrate, dried, and processed by oxygen plasma etching until the desired diameters and gaps among neighboring bead casts. For the fabrication of Au/Ni double-layered NCs, Au and Ni were sequentially deposited on upper halves of the bead surfaces by thermal evaporation with nanometer-order thickness control. The polystyrene casts were removed completely by UV-ozone oxidization reaction, and Au/Ni double-layered NCs were fabricated on a Si substrate. To orient the holes of the fabricated NCs to top for the substrate, poly(dimethylsiloxane) (PDMS) sol was dropped on the NCs placed on the Si substrate, hardened, and peeled off from the substrate, and then the NCs were placed on the PDMS surface with those holes turned-up. To examine the selective interaction of biomolecules on the inner layer of NCs as the artificial nanospace for biomolecular reactions, a thiolated target DNA was immobilized onto the inner layer of a Au/Ni NC as a model. The target DNA was labeled through hybridization reaction using small Au nanoparticles (NPs) on which a complementary probe DNA was immobilized. Both the surface-specific immobilization of the target DNA on the Au layer of the NC and the specific hybridization in NC nanospaces were confirmed by direct observations after those reactions using field emission scanning electron microscopy (FE-SEM), indicating that the inside of the fabricated NCs can be used as the artificial nanospace for studying localized biomolecular reactions.

Kim, Hyonchol; Hayashi, Masahito; Terazono, Hideyuki; Takei, Hiroyuki; Yasuda, Kenji



Mirror symmetry of ions and electron temperature variations within the dusty dynamo layer of the auroral ionosphere  

NASA Astrophysics Data System (ADS)

Quasi-periodic (consisting of a dozen electro-thermal structures, ETS) variations of ionospheric parameters during April, 10 and March, 23 1988 substorms were investigated using the data of EISCAT radars in Tromso. These variations were measured at the lower edge of dynamo-layer 106 km and include the ion and electron temperature, electron density and ionospheric electric field; all data were smoothed out using moving average with optimal lag window. It was shown that: 1) ETS clusters are observed when value of the electric field is < 10 mV/m and average electron density is about (5-10)*10 (4) /sm (3) , 2) For each ETS the envelop demonstrate the so called mirror symmetry, that is antiphased variations of the ion and electron temperature (when Ti increases and Te decreases), 3) The symmetry breaks when the electric field is larger than FB instability threshold (15-20 mVm), 4) The periods of these variations is in the range of 3-10 min, 5) The self-similarity of the scales is observed: smaller scales are included into the larger scales, 6) Temperature variations were accompanied by the electric field variations with amplitude of 4-7 mV/m, 7) Large scale structures (and sometimes dyads formed by two subsequent structures) were accompanied by the electric field rotation up to the whole circle. Specific ETS and plasma parameters variations can be interpreted as a result of Ekman-type instability in the dusty plasma of the dynamo layer. The mirror symmetry of plasma temperature variations is an evidence of a partial blocking of energy transfer between the ions and electrons at low values of the external electric field (below FB instability threshold) because the main energy in such a kind of plasma is attributed to dusty macro-particles (Fortov et al., 2010). Under these conditions the time scale of the dust particle energy variations are considerably larger than the corresponding scales of the temperature variations. According to our previous results (Timofeev et al, 2009-2013) the coherent increase of correlation coefficient (CC) of plasma temperature time variations and smoothed value of the electric field means that the CC can be used as an indicator of the ETS "rigidity" (hence the energy and charge of macro-particles). We used this coherence to estimate the time scale of the macro-particles energy growth (during preliminary phase of March 23, 1988 substorm) and get values of 12-19 min. In the present study we used the same event to estimate the time scale of the plasma temperatures mirror variations and obtained that they are at least 2-3 times shorter. Such a difference in the time scale determines the ETS formation. Finally, after FB instability excitation the electrons can quickly exchange their energy with plasmons, so that the mirror symmetry in temperature variations breaks down.

Timofeev, Evgeny; Kangas, Jorma; Vallinkoski, Matti


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.



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

NASA Technical Reports Server (NTRS)

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

Gad-El-hak, Mohamed



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


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

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



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


Pregnancy rates after artificial insemination with cooled stallion spermatozoa either with or without Single Layer Centrifugation.  


A successful outcome after artificial insemination with cooled semen is dependent on many factors, the sperm quality of the ejaculate being one. Previous studies have shown that spermatozoa with good motility, normal morphology, and good chromatin integrity can be selected by means of colloid centrifugation, particularly single layer centrifugation (SLC) using species-specific colloids. The purpose of the present study was to conduct an insemination trial with spermatozoa from "normal" ejaculates, i.e., from stallions with no known fertility problem, to determine whether the improvements in sperm quality seen in SLC-selected sperm samples compared with uncentrifuged controls in laboratory tests are reflected in an increased pregnancy rate after artificial insemination. In a multicentre study, SLC-selected sperm samples and uncentrifuged controls from eight stallions were inseminated into approximately 10 mares per treatment per stallion. Ultrasound examination was carried out approximately 16 days after insemination to detect an embryonic vesicle. The pregnancy rates per cycle were 45% for controls and 69% for SLC-selected sperm samples, which is statistically significant (P < 0.0018). Thus, the improvement in sperm quality reported previously for SLC-selected sperm samples is associated with an increase in pregnancy rate, even for ejaculates from stallions with no known fertility problem. PMID:25159661

Morrell, J M; Richter, J; Martinsson, G; Stuhtmann, G; Hoogewijs, M; Roels, K; Dalin, A-M



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


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



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)



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

Microsoft Academic Search

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

Ana G. Elias



Effects of artificial sea film slick upon the atmospheric boundary layer structure  

NASA Astrophysics Data System (ADS)

Organic surface-active compounds accumulate at the ocean-atmosphere boundary, influencing several air-sea interaction processes. In coastal areas with high biological activity this accumulation frequently becomes visible as mirrorlike patches ("slicks") on the sea surface. The artificial surface films of oleyl alcohol and vegetable oil were produced in the Black Sea coastal zone (one site was located near Gelendjik and another was near Crimea coast) to investigate its influence on energy and gas exchange between atmosphere and sea surface under different meteorological conditions. The atmospheric turbulence measurements during the passage of an artificial sea slick are compared with similar measurements without a sea slick. The effects of the slick are modifications of roughness length z0, and a possible increase in mean wind speed. In the mean, during the passage of the slick, the roughness length decreased while the mean wind speed appeared to increase. For the spectral comparison we compared the wind field over the sea during the time the film slick was in the vicinity of the measurement site with the wind field observed after the slick had passed. The cross-spectral density was computed between horizontal velocity and vertical velocity (Reynolds stress) and between atmospheric temperature and vertical velocity (heat flux). The introduction of the sea film slick, with its damping and suppression of capillary waves, appears to completely destroy the atmospheric turbulence generation. When a slick is present, the U-W phase angle and Reynolds stress spectrum for the atmosphere appear to be completely unaffected by undulating sea surface directly below the sensors. Spectral and wavelet analysis of the atmospheric surface layer characteristics showed a significant correlation between the processes on the sea surface and the atmospheric boundary layer. An intensification of change processes in the vicinity of the windward slick boundary are detected. It may be connected with the formation of internal boundary layer over the slick. Gas exchange, in this case desorption of CO2 was determined before and after formation of the artificial surface film. In the one experiment performed inhibition of exchange was significant when the film was present. These results demonstrate the importance of observing small-scale atmospheric processes near the sea surface. It is strongly recommended that this technique be exploited to its fullest to enhance our understanding of the small-scale processes at the air-sea boundary. The experiments have confirmed the influence of surface-active compounds, including oil pollution, which have been significantly changed the state of the sea surface, the processes in the atmospheric turbulent layer.The results also have important implications on ocean remote sensing applications. The work was supported by RFBR (grant 08-05-00099, grant 08-05-00890).

Repina, Irina; Artamonov, Arseniy; Malinovsky, Vladimir; Chechin, Dmitriy



Introduction to the Ionosphere Alan Aylward  

E-print Network

#12;The Ionosphere Structure and Formation of the Ionosphere Structure The F2 layer peak (hmF2) occurs. In contrast to the F1 region, the F2 layer is maintained at night. The E region is strongest at daytime hmF2


Ionospheric foF2 morphology and response of F2 layer height over Jicamarca during different solar epochs and comparison with IRI-2012 model  

NASA Astrophysics Data System (ADS)

Diurnal, seasonal and annual foF2 variability and the response of the F2-layer height over Jicamarca (11.9 °S, 76.8 °W, 1 °N dip) during periods of low (LSA), moderate (MSA) and high (HSA) solar activities was investigated. The relative standard deviation ( V R ) was used for the analysis. The F2-layer critical frequency pre-noon peak increases by a factor of 2 more than the post-noon peak as the solar activity increases. The variability coefficient ( V R ) is lowest during the day (7-16%) for the three solar epochs; increases during nighttime (20-26%, 14-26%, and 10-20%, respectively for the LSA, MSA and HSA years); and attained highest magnitude during sunrise (21-27%, 24-27%, and 19-30%, respectively in similar order). Two major peaks were observed in V R - the pre-sunrise peak, which is higher, and the post-sunset peak. Generally, the variability increases as the solar activity decreases. Annually, V R peaks within 23-24%, 19-24% and 15-24% for the LSA, MSA, and HSA periods, respectively. The ionospheric F2-layer height rises to the higher level with increasing solar activity. The foF2 comparison results revealed that Jicamarca is well represented on the IRI-2012 model, with an improvement on the URSI option. The importance of vertical plasma drift and photochemistry in the F2-layer was emphasized.

Adebesin, B. O.; Adekoya, B. J.; Ikubanni, S. O.; Adebiyi, S. J.; Adebesin, O. A.; Joshua, B. W.; Olonade, K. O.



Generation of zonal flow and magnetic field by coupled internal-gravity and alfvén waves in the ionospheric E-layer  

NASA Astrophysics Data System (ADS)

Nonlinear dynamics of coupled internal-gravity (IG) and alfven electromagnetic planetary waves in the weakly ionized ionospheric E-layer is investigated. Under such coupling new type of alfven waves is revealed. It is shown that such short wavelength turbulence of IG and alfvén waves is unstable with respect to the excitation of low-frequency and large-scale perturbations of the zonal flow and magnetic field. A set of coupled equations describing the nonlinear interaction of coupled IG and alfven waves with zonal flows is derived. The nonlinear mechanism of the instability is driven by the advection of vorticity and is based on the parametric excitation of convective cells by finite-amplitude coupled IG and alfven waves leading to the inverse energy cascade toward the longer wavelength. The growth rates of the corresponding instability and the conditions for driving them are determined. The possibility of generation of the intense mean magnetic field is shown.

Kaladze, Tamaz; Kahlon, Laila


Zonal flows and magnetic fields driven by large-amplitude Rossby-Alfvén-Khantadze waves in the E-layer ionosphere  

NASA Astrophysics Data System (ADS)

waves and vortices in the weakly ionized ionospheric E layer are dominated by the Hall conductivity that couples the Rossby and Alfvén dynamics giving rise to what are called Rossby-Alfvén-Khantadze electromagnetic structures. At finite amplitudes we show that the nonlinearities in the dynamics generate sheared zonal-flow velocities and zonal magnetic field fluctuations. The zonal-flow mechanism is based on the parametric excitation of the zonal variations through three-wave mode coupling in the planetary-scale waves. The coupled dynamics of the nonlinear 3-D incompressible flows and the magnetic field fluctuations are derived and used to derive the structure and growth rates for the zonal flows and zonal magnetic fields. Large-amplitude planetary waves are shown to drive up magnetic fluctuations up to 100 nT.

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



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.



Ionospheric research  

NASA Technical Reports Server (NTRS)

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



Compliant layer bearings in artificial joints. Part 2: simulator and fatigue testing to assess the durability of the interface between an elastomeric layer and a rigid substrate.  


Artificial joints have been much improved since their introduction but they still have a limited lifetime. In an attempt to increase their life by improving the lubrication acting within these prostheses, compliant layered polyurethane (PU) joints have been devised. These joints mimic the natural synovial joint more closely by promoting fluid film lubrication. In this study, tests were performed on compliant layer joints to determine their ability to function under a range of conditions. Both static and dynamic compression tests were undertaken on compliant artificial hip joints of two different radial clearances. Friction tests were also performed before and after static loading. In addition to this, knee wear tests were conducted to determine the suitability of a compliant layer in these applications. In the knee tests, variations in experimental testing conditions were investigated using both active and passive rotation and severe malalignment of the tibial inserts. The static compression tests together with the friction studies suggest that a small radial clearance is likely to result in 'grabbing' contact between the head and cup. The larger radial clearance (0.33 microm) did not exhibit these problems. The importance of the design of the compliant layer joints was highlighted with delamination occurring on the lateral bearings during the knee wear studies. The bearings with a layer 2 mm thick performed better than the bearings with a layer 3 mm thick. Tests conducted on flat PU bearings resulted in no delamination; therefore, it was concluded that the layer separation was caused by design issues rather than by material issues. It was found that, with careful material choice, consideration of design, and effective manufacturing techniques, the compliant layer joint functioned well and demonstrated durability of the union between the hard and soft layers. These results give encouragement for the suitability of these joints for clinical use. PMID:19239063

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



The influence of electron density gradient direction on gradient-drift instabilities in the E-layer of the ionosphere  

E-print Network

We show that the dispersion relation for gradient-drift and Farley-Buneman instabilities within the approximation of the two-fluid MHD should contain the terms which are traditionally supposed to be small. These terms are caused by taking into account divergence of particles velocity and electron density gradient along the magnetic field direction. It is shown that at heights below 115km the solution of the dispersion relation transforms into standard one, except the situations, when the electron density gradient is parallel to magnetic field or wave-vector. In these cases the traditionally neglected summands to the growth rate of the irregularities becomes significant. The additional terms depend on relative directions of electron density gradient, magnetic field and mean velocities. This leads to the different instability growth conditions at equatorial and high-latitude regions of the ionosphere. The obtained results do not contradict with the experimental data.

Berngardt, O I



Plasma and electromagnetic effects in the ionosphere related to the dynamics of charged aerosols in the lower atmosphere  

Microsoft Academic Search

The paper presents a physical model of the electrodynamic effect on the ionosphere of natural and artificial processes that\\u000a occur in the near-Earth atmospheric layer and are accompanied by the transfer of charged aerosols in the atmosphere. These\\u000a processes include the preparation of earthquakes and typhoons, dust storms, and nuclear accidents. The model is based experimentally\\u000a on satellite and ground-based

V. M. Sorokin



AM Radio Ionosphere Station: Teacher's Guide  

NSDL National Science Digital Library

In this activity students will monitor the ionosphere by using an amplitude modulated (AM) radio to track solar storms and other changes in ionosphere reflectivity. They will discover that above the earth's surface a layer of charged particles called the ionosphere is capable of reflecting radio waves and that the reflectivity properties of the ionosphere can be changed dramatically by solar activity. In order to detect and study some of these changes, students will use the radio to listen for changes in background noise and the appearance of distant stations, learning that a simple everyday device can let them detect invisible changes in their environment caused by solar activity.


Ionospheric signatures of Lightning  

NASA Astrophysics Data System (ADS)

The geostationary metrology satellite (GMS) monitors motions of thunderstorm cloud, while the lightning detection network (LDN) in Taiwan and the very high Frequency (VHF) radar in Chung-Li (25.0›XN, 121.2›XE) observed occurrences of lightning during May and July, 1997. Measurements from the digisonde portable sounder (DPS) at National Central University shows that lightning results in occurrence of the sporadic E-layer (Es), as well as increase and decrease of plasma density at the F2-peak and E-peak in the ionosphere, respectively. A network of ground-based GPS receivers is further used to monitor the spatial distribution of the ionospheric TEC. To explain the plasma density variations, a model is proposed.

Hsu, M.; Liu, J.



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

NASA Astrophysics Data System (ADS)

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

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



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



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.



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.



Radio Tomography and Imaging of Ionospheric Disturbances Caused by Active Experiments  

NASA Astrophysics Data System (ADS)

We present the results of the radiotomographic imaging of the artificial ionospheric disturbances obtained in the experiments on the modification of the midlatitude ionosphere by powerful HF radiowaves carried out during last decade at the Sura heating facility. The experiments were conducted using both O- and X- mode radiowaves at frequencies lower than critical frequency of the ionospheric F2 layer both in daytime and nighttime ionosphere. Various schemes of the radiation of the heating wave were used including square wave modulation of the effective radiated power (ERP) at various frequencies and power stepping. Radio transmissions of the low- (Parus/Tsikada) and high-orbital (GPS/GLONASS) navigational satellites received at the mobile network of receiving sites were used for the remote sensing of the heated area of the ionosphere. We study the variations in TEC caused by HF heating showing that the GNSS TEC spectra often contain frequency components corresponding to the modulation periods of the ERP of the heating wave. The manifestations of the heating-induced variations in TEC are most prominent in the area of magnetic zenith of the pumping wave. In this work we also present the radiotomographic reconstructions of the spatial structure of the disturbed area of the ionosphere corresponding to the directivity pattern of the heater as well as the spatial structure of the wave-like disturbances, which are possibly AGWs, diverging from the heated area of the ionosphere. We also compare the effects obsereved during artificial heating experiments with those obsereved during rocket launches and powerful industiral explosions. The possibility of generation of electromagnetic waves by moving wave-like structures in ionosphere (like AGWs induced by HF-heating observed in our experiments) is also addressed in this work. The authors acknowledge the support of the Russian Foundation for Basic Research (grants ? 13-05-01122, 14-05-31445, 14-05-00855, 14-05-10069), grants of the President of Russian Federation (MK-2670.2014.5) and Lomonosov Moscow State University Program of Development.

Kunitsyn, Viacheslav; Padokhin, Artem; Andreeva, Elena; Tereshchenko, Evgeny; Nesterov, Ivan; Vladimir Frolov, S.


Effect of Moon phases in riometer absorption and in the ionospheric and geomagnetic parameters  

Microsoft Academic Search

Variations in the frequency of occurrence of riometer absorption, minimum frequency of reflection of the ionospheric F layer, minimum height, and height of maximum electron density of the ionospheric F layer near the solar minimum have been studied. Application of the superposed epoch technique has detected the Moon phase effect on these ionospheric parameters. This effect was: three events per

S. N. Samsonov; V. F. Smirnov; D. G. Baishev; A. A. Toropov; N. G. Skryabin



Effect of Moon phases in riometer absorption and in the ionospheric and geomagnetic parameters  

Microsoft Academic Search

Variations in the frequency of occurrence of riometer absorption, minimum frequency of reflection of the ionospheric F layer, minimum height, and height of maximum electron density of the ionospheric F layer near the solar minimum have been studied. Application of the superposed epoch technique has detected the Moon phase\\u000a effect on these ionospheric parameters. This effect was: three events per

S. N. Samsonov; V. F. Smirnov; D. G. Baishev; A. A. Toropov; N. G. Skryabin



A general elastohydrodynamic lubrication analysis of artificial hip joints employing a compliant layered socket under steady state rotation.  


A general numerical methodology was developed in the present study to analyse the elastohydrodynamic lubrication problem of a compliant layered socket against a rigid ball under steady state rotation representing flexion and extension during walking, with particular reference to artificial hip joint replacements. The general numerical methodology consisted of using the Newton-Raphson method to solve the Reynolds equation, simultaneously with the full elasticity equation using the finite element method in combination with the fast Fourier transform technique. Two specific types of acetabular cup were considered, one with ultra-high molecular weight polyethylene used in current total hip joint replacements, and one with polyurethane proposed for compliant layered 'cushion form bearings' for future developments. The film thickness and the pressure distribution for both cups were obtained under a wide range of operating conditions. The predicted central or average film thicknesses within the contact conjunction were compared with those estimated from various simplified theories available in the literature. A simple analytical methodology was consequently established to estimate the lubricating film thickness in a compliant layered socket, based on the corresponding ball-on-plane model and the consideration of the curvature effect. PMID:15532994

Wang, F C; Liu, F; Jin, Z M



Experimental and theoretical study of artificial plasma layers produced by two intersecting beams in a chamber  

NASA Technical Reports Server (NTRS)

The work done on the Bragg scattering of electromagnetic waves by microwave produced plasma layers is reported. Also summarized is the work accomplished on the propagation of high power microwave pulses in an air breakdown environment. Ongoing work on the theoretical model and numerical results of pulse propagation in air is also presented as are the results of studying the decay of plasma density and temperature.

Kuo, S. P.; Zhang, Y. S.



Reactivity surveillance in a nuclear reactor by using a layered artificial neural network  

SciTech Connect

Layered neural networks, which are a class of models based on neuronal computation in biological systems, are applied to the task of reactivity monitoring in a nuclear reactor to improve the safety and the reliability of the operating plant. Training is done with a maximum likelihood method, which is suitable for on-line training. Operational data from the Fast Breeder Test Reactor are used to study its performance. The adaptability of the network to slow variations in the system parameters and its ability to learn in a noisy environment are studied.

Arul, A.J. (Indira Gandhi Centre for Atomic Research, Tamil Nadu (India). Reactor Physics Div.)



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


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

Fukushima, Kunihiko



LIFDAR: A Diagnostic Tool for the Ionosphere  

NASA Astrophysics Data System (ADS)

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

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



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

NASA Astrophysics Data System (ADS)

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

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



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)



Magnetospheric-ionospheric changes caused by flights of space vehicles  

NASA Astrophysics Data System (ADS)

The process of formation and disappearance of an ionospheric “hole” in the F2 layer caused by the ejection of water molecules during the flight of a space vehicle has been considered using the method of computational experiment based on the mathematical ionospheric-magnetospheric model in a coordinate system fixed on the magnetic force line of the Earth.

Ishanov, S. A.; Levanov, E. I.; Medvedev, V. V.; Zalesskaya, V. A.; Zharkova, Yu. S.



Ionosphere around equinoxes during low solar activity  

NASA Astrophysics Data System (ADS)

The seasonal behaviors of the ionosphere have been investigated for several decades, but the differences of the ionosphere between the March and September equinoxes are still an open question. In this analysis we utilize the data of ionospheric electron density (Ne) profiles from Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission radio occultation measurements, total electron density (TEC) from TOPEX and Jason-1, and TEC from Global Positioning System (GPS) receivers as well as global ionosonde measurements of the F2 layer peak electron density (NmF2) to investigate the behaviors of the daytime ionosphere around equinoxes during low solar activity (LSA). The analysis reveals that during LSA the equinoctial asymmetry in ionospheric plasma density is mainly a low-latitude phenomenon. The differences of equinoctial TEC and NmF2 have considerable amplitudes at low latitudes in both hemispheres and less significant at higher latitudes. With increasing altitude, the asymmetry in COSMIC Ne becomes weaker in the Southern Hemisphere, and the northern pronounced asymmetry regions move toward the magnetic equator. The ionospheric equinoctial asymmetry may be considered as a manifestation of the annual variation, whose annual phase significantly shifts away from the solstices. The F layer peak height (hmF2) extracted from COSMIC Ne profiles also shows an equinoctial asymmetry at low latitudes, indicating the existence of equinoctial differences in low-latitude neutral winds, specifically in the Northern Hemisphere. It reveals that, besides the important effect of the neutral wind, other processes should play roles in the forming of the observed equinoctial asymmetry in the ionosphere.

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



Sporadic-E ionospheric clutter suppression in HF surface-wave radar  

Microsoft Academic Search

The unwanted radar echoes from the ionosphere are collectively called ionospheric clutter. It has proved to be the greatest impediment to achieving consistently good performance in long-range detection of surface vessels and sea state monitoring for HF surface wave radar (HFSWR). Ionospheric clutter can mask target\\/sea echoes having similar Doppler shifts. Main characteristics of sporadic-E ionospheric clutter (Es-layer clutter) are

Wan Xianrong; Cheng Feng; Ke Hengyu



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


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

NASA Astrophysics Data System (ADS)

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

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



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

NASA Astrophysics Data System (ADS)

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

Harrison, Giles; Aplin, Karen; Rycroft, Michael



Solving the non-linear model of the electron density of the ionosphere  

NASA Astrophysics Data System (ADS)

Precise and high precision ionosphere models are important for modern satellite navigation and positioning systems. In most cases, the ionosphere models are based on pure mathematical approaches, e.g. by applying spherical harmonic expansions for the vertical total electron content. In order to achieve a deeper understanding of the complex phenomena within the ionosphere, physical conditions have to be considered and introduced. The physics-motivated Chapman function is very efficient for describing the vertical structure of the electron density. Introducing the Chapman function and a plasmasphere layer, the vertical distribution of the electron density can be described by five parameters altogether, namely (1) the F2 peak electron density (NmF2), (2) the peak height (hmF2), (3) the topside scale height (HF2), (4) the plasmasphere basic density (NP) and (5) the scale height (HP). In our approach, each of these parameters is decomposed into an initial part, derived from a given ionosphere model or other initial assumptions, and an unknown correction term. Exploiting the localizing property of B-spline base functions, the latter is modeled as a series expansion in terms of tensor products of three one-dimensional endpoint-interpolating B-splines depending on latitude, longitude and time, respectively. Considering the necessary linearization of the exponential terms of the Chapman and the plasmaspheric layer, the unknown model coefficients are solved by an appropriate parameter estimation procedure using an iterative algorithm. In this contribution we focus on the numerical solution of the linearized model. This includes a closer view on the iterative method, the regularization scheme and the convergence analysis. Due to complexity of the problem, the topside scale height HF2 is expanded in a first step to test the adjustment approach. Data gaps are artificially created to investigate inhomogeneous data availability. In this case proper prior information and regularization are needed to ensure the convergence of the system.

Liang, W.; Schmidt, M.; Dettmering, D.; Hugentobler, U.; Limberger, M.



Ionosphere tomography based on spaceborne SAR  

NASA Astrophysics Data System (ADS)

Two models of ionosphere tomography based on spaceborne SAR (Synthetic Aperture Radar) are proposed. For HF-SAR the signal with sweeping frequency lower than the characteristic frequency of ionosphere will be scatted during the ionosphere propagation and completely reflected at a corresponding height. The ionospheric electron density isolines looked as series of random surfaces can be reconstructed from the HF-SAR echoes by using the inverse scattering technique for layered rough surfaces and the method of moment (MoM). The numerical simulation show that due to the MoM can provide a full wave solution, the ionosphere tomography with high resolution can be obtained as long as enough sampling data of HF-SAR echoes are used. For VHF/UHF/P/L-band SAR the TEC (Total Electron Content) can be obtained from the SAR echoes scattered by some strong point targets (such as the calibrators, etc.) appeared in the SAR imaged ground region, and the ionosphere tomography can be performed by CT technique.

Li, Lianlin; Li, Fang



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.



Diurnal and seasonal variation of F2-layer ionospheric parameters at equatorial ionization anomaly crest region and their comparison with IRI-2001  

NASA Astrophysics Data System (ADS)

Diurnal and seasonal variations of critical frequency of ionospheric F2-region ‘foF2’ and the height of peak density ‘hmF2’ are studied using modern digital ionosonde observations of equatorial ionization anomaly (EIA) crest region, Bhopal (23.2°N, 77.6°E, dip 18.5°N), during solar minimum period 2007. Median values of these parameters are obtained at each hour using manually scaled data during different seasons and compared with the International Reference Ionosphere-2001 model predictions. The observations suggest that on seasonal basis, the highest values of foF2 are observed during equinox months, whereas highest values of hmF2 are obtained in summer and lowest values of both foF2 and hmF2 are observed during winter. The observed median and IRI predicted values of foF2 and hmF2 are analyzed with upper and lower bound of inter-quartile range (IQR) and it is find out that the observed median values are well inside the inter-quartile range during the period of 2007. Comparison of the recorded foF2 and hmF2 values with the IRI-2001 output reveals that IRI predicted values exhibit better agreement with hmF2 as compared to foF2. In general, the IRI model predictions show some agreement with the observations during the year 2007. Therefore it is still necessary to implement improvements in order to obtain better predictions for EIA regions.

Yadav, Sneha; Dabas, R. S.; Das, Rupesh M.; Upadhayaya, A. K.; Sharma, Kavita; Gwal, A. K.



Biophysical investigations of the structure and function of the tear fluid lipid layers and the effect of ectoine. Part B: artificial lipid films.  


The tear fluid lipid layer is present at the outermost part of the tear film which lines the ocular surface and functions to maintain the corneal surface moist by retarding evaporation. Instability in the structure of the tear fluid lipid layer can cause an increased rate of evaporation and thus dry eye syndrome. Ectoine has been previously shown to fluidize lipid monolayers and alter the phase behavior. In the current study we have investigated the effect of ectoine on the artificial tear fluid lipid layer composed of binary and ternary lipid mixtures of dipalmitoyl phosphatidylcholine (DPPC), cholesteryl esters and tri-acyl-glycerols. The focus of our study was mainly the structural and the biophysical aspects of the artificial tear fluid lipid layer using surface activity studies and topology analysis. The presence of ectoine consistently causes an expansion of the pressure-area isotherm indicating increased intermolecular spacing. The topology studies showed the formation of droplet-like structures due to the addition of ectoine only when tri-acyl-glycerol is present in the mixture of DPPC and chol-palmitate, similar to the natural meibomian lipids. Consequently, the hypothesis of an exclusion of tri/di-acyl-glycerol from the meibomian lipid film in the presence of ectoine in the subphase is confirmed. A model describing the effect of ectoine on meibomian lipid films is further presented which may have an application for the use of ectoines in eye drops as a treatment for the dry eye syndrome. PMID:24853656

Dwivedi, Mridula; Brinkkötter, Marc; Harishchandra, Rakesh Kumar; Galla, Hans-Joachim



International reference ionosphere 1990  

NASA Technical Reports Server (NTRS)

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

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



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.



HICO and RAIDS Experiment Payload - Remote Atmospheric and Ionospheric Detection System (RAIDS)  

NASA Technical Reports Server (NTRS)

The HICO and RAIDS Experiment Payload - Remote Atmospheric and Ionospheric Detection System (HREP-RAIDS) experiment will provide atmospheric scientists with a complete description of the major constituents of the thermosphere (layer of the Earth's atmosphere) and ionosphere (uppermost layer of the Earth's atmosphere), global electron density profiles at altitudes between 100 - 350 kilometers.

Budzien, Scott



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.



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.



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.



Propagation of electromagnetic waves in a structured ionosphere  

SciTech Connect

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

Murphy, T.



Ionospheric irregularity physics modelling  

SciTech Connect

Theoretical and numerical simulation techniques have been employed to study ionospheric F region plasma cloud striation phenomena, equatorial spread F phenomena, and high latitude diffuse auroral F region irregularity phenomena. Each of these phenomena can cause scintillation effects. The results and ideas from these studies are state-of-the-art, agree well with experimental observations, and have induced experimentalists to look for theoretically predicted results. One conclusion that can be drawn from these studies is that ionospheric irregularity phenomena can be modelled from a first principles physics point of view. Theoretical and numerical simulation results from the aforementioned ionospheric irregularity areas will be presented.

Ossakow, S.L.; Keskinen, M.J.; Zalesak, S.T.



Remote Radio Imaging of E- and F-Region Irregularities Using Computerized Ionospheric Tomography  

NASA Astrophysics Data System (ADS)

The plasma structures in the ionosphere can be sporadic E-layers found between 100 and 120 km altitude or spread-F irregularities between 200 and 600 km altitude. The spatial and temporal variations in electron density have been associated with both neutral and plasma instabilities driven by neutral winds, electric fields and gravity. To resolve some of the issues concerning sporadic-E and spread-F occurrence, the Naval Research Laboratory has engaged in a program called Coherent Electromagnetic Radio Tomography (CERTO) where radio beacons are placed in space for tomographic imaging of the plasma layers. Working with the University of Kyoto in Japan, CERTO beacons were used during the the second Sporadic-E Experiment over Kyushu (SEEK2). The SEEK2 Rocket Campaign occurred on 3 August 2002, and the Dual Band Beacon (DBB) transmitted to Ground Receivers providing unique data on E-Region electron densities. The beacons continuous radiated unmodulated signals at 149.988 and 399.968 MHz. Analysis was completed for four sets of beacon data to provide the first two-dimensional image of a sporadic E-layer. The rocket beacon technique was shown to be an excellent tool to study Sporadic-E layers because absolute TEC accuracy of 0.01 TEC Units can be easily obtained. Tri Band versions of the CERTO beacons are currently scheduled for launch on the C/NOFS, NPSat1, and the six COSMIC satellites. These satellites will be in inclinations of 15, 35 and 70 degrees, respectively at altitudes from 375 to 800 km. Computer simulations have been conducted to generate electron densities from the NRL SAMI3 model and localized simulations of ionospheric bubbles. The total electron content (TEC) derived from the artificial electron data has been used to test CIT algorithms. With proper receiver placement, electron density images of the F-region can be produced using computerized ionospheric tomography with better than 10 kilometer spatial resolution. The CERTO beacons on satellite will provide a global data base for ionospheric measurements that will be available to the international scientific community.

Bernhardt, P.; Siefring, C.; Selcher, C.; Kamalabadi, F.; Bust, G.; Yamamoto, M.; Fukao, S.


Modeling the martian ionosphere  

NASA Astrophysics Data System (ADS)

The accessibility of the Martian atmosphere to spacecraft provides an opportunity to study an ionosphere that differs from our own. Yet, despite the half century of measurements made at Mars, the current state of the neutral atmosphere and its embedded plasma (ionosphere) remains largely uncharacterized. In situ measurements of the neutral and ionized constituents versus height exist only from the two Viking Landers from the 1970s. Subsequent satellite and remote sensing data offer sparse global coverage of the ionosphere. Thermal characteristics of the plasma environment are not well understood. Patchy crustal magnetic fields interact with the Martian plasma in a way that has not been fully studied. Hence, investigating the coupled compositional, thermal and crustal-field-affected properties of the ionosphere can provide insight into comparative systems at Earth and other planets, as well as to atypical processes such as the solar wind interaction with topside ionospheric plasma and associated pathways to escape. Ionospheric models are fundamental tools that advance our understanding of complex plasma systems. A pre-existing one-dimensional model of the Martian ionosphere has been upgraded to include more comprehensive chemistry and transport physics. This new BU Mars Ionosphere Model has been used to study the composition, thermal structure and dynamics of the Martian ionosphere. Specifically: the sensitivity of the abundance of ions to neutral atmospheric composition has been quantified, diurnal patterns of ion and electron temperatures have been derived self-consistently using supra-thermal electron heating rates, and the behavior of ionospheric plasma in crustal field regions was simulated by constructing a two-dimensional ionospheric model. Results from these studies were compared with measurements and show that (1) ion composition at Mars is highly sensitive to the abundance of neutral molecular and atomic hydrogen, (2) lighter ions heat up more efficiently than heavier ones and provide additional heating sources for cooler plasma, and (3) crustal field morphology affects plasma dynamics and structure at Mars in a way that is consistent with observations. Finally, model predictions of ion composition and plasma temperatures are provided for observations to be made by several instruments on board the upcoming 2013 MAVEN orbiter.

Matta, Majd Mayyasi


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



Tsunami Ionospheric warning and Ionospheric seismology  

NASA Astrophysics Data System (ADS)

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

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



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

Microsoft Academic Search

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

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



Ionospheric modification during moderate geomagnetic storm at low solar activity  

NASA Astrophysics Data System (ADS)

In this report we present an analysis of the ionospheric response to moderate (Dst<70 nT), 11 October 2008, geomagnetic storm. TEC maps over European region were created on the base of GPS observations provided by IGS/EPN. Strong short-term positive effect was detected near noon of 11 October 2008. The TEC enhancement exceeded 100% on latitudes of 65-35N and was decreased to lower latitudes. The positive effect was associated with large scale traveling disturbance. During storm there was observed the increase and modification of horizontal gradients structure and ionospheric trough had moved to equator, until 57-58 geomagnetic latitudes. The electron density profiles, retrieved from the Formosat-3/COSMIC radio occultation measurements and also measurements from European ionospheric sounding stations (DIAS), were analyzed within the case-study to estimate the altitudinal modification of the ionosphere. The considerable enhancement of the peak electron density was observed in European region during 11-15 UT, it reached the factor of 2.8 in comparison with quiet conditions. The height of the ionospheric F2 layer was risen by 60 km. For graphical demonstration of the observed ionospheric effects global electron density maps were calculated on the base of globally distributed COSMIC RO profiles. Electron density maps for different altitude slices were analyzed. This positive effect was revealed distinctly in RO electron density profiles and products based on these data - ionospheric electron content and global maps of electron density.

Krankowski, A.; Shagimuratov, I.; Zakharenkova, I.; Krypiak-Gregorczyk, A.



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.



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


Electrical responses of artificial DNA nanostructures on solution-processed In-Ga-Zn-O thin-film transistors with multistacked active layers.  


We propose solution-processed In-Ga-Zn-O (IGZO) thin-film transistors (TFTs) with multistacked active layers for detecting artificial deoxyribonucleic acid (DNA). Enhanced sensing ability and stable electrical performance of TFTs were achieved through use of multistacked active layers. Our IGZO TFT had a turn-on voltage (V(on)) of -0.8 V and a subthreshold swing (SS) value of 0.48 V/decade. A dry-wet method was adopted to immobilize double-crossover DNA on the IGZO surface, after which an anomalous hump effect accompanying a significant decrease in V(on) (-13.6 V) and degradation of SS (1.29 V/decade) was observed. This sensing behavior was attributed to the middle interfaces of the multistacked active layers and the negatively charged phosphate groups on the DNA backbone, which generated a parasitic path in the TFT device. These results compared favorably with those reported for conventional field-effect transistor-based DNA sensors with remarkable sensitivity and stability. PMID:23211212

Jung, Joohye; Kim, Si Joon; Yoon, Doo Hyun; Kim, Byeonghoon; Park, Sung Ha; Kim, Hyun Jae



Tsunamigenic ionospheric hole  

NASA Astrophysics Data System (ADS)

Traveling ionospheric disturbances generated by an epicentral ground/sea surface motion, ionospheric disturbances associated with Rayleigh-waves as well as post-seismic 4-minute monoperiodic atmospheric resonances and other-period atmospheric oscillations have been observed in large earthquakes. In addition, a giant tsunami after the subduction earthquake produces an ionospheric hole which is widely a sudden depletion of ionospheric total electron content (TEC) in the hundred kilometer scale and lasts for a few tens of minutes over the tsunami source area. The tsunamigenic ionospheric hole detected by the TEC measurement with Global Position System (GPS) was found in the 2011 M9.0 off the Pacific coast of Tohoku, the 2010 M8.8 Chile, and the 2004 M9.1 Sumatra earthquakes. This occurs because plasma is descending at the lower thermosphere where the recombination of ions and electrons is high through the meter-scale downwelling of sea surface at the tsunami source area, and is highly depleted due to the chemical processes.

Kakinami, Yoshihiro; Kamogawa, Masashi; Tanioka, Yuichiro; Watanabe, Shigeto; Riadi Gusman, Aditya; Liu, Jann-Yenq; Watanabe, Yasuyuki; Mogi, Toru


Tsunamigenic ionospheric hole  

NASA Astrophysics Data System (ADS)

Traveling ionospheric disturbances generated by an epicentral ground/sea surface motion, ionospheric disturbances associated with Rayleigh-waves as well as post-seismic 4-minute monoperiodic atmospheric resonances and other-period atmospheric oscillations have been observed in large earthquakes. In addition, a giant tsunami after the subduction earthquake produces an ionospheric hole which is widely a sudden depletion of ionospheric total electron content (TEC) in the hundred kilometer scale and lasts for a few tens of minutes over the tsunami source area. The tsunamigenic ionospheric hole detected by the TEC measurement with Global Position System (GPS) was found in the 2011 M9.0 off the Pacific coast of Tohoku, the 2010 M8.8 Chile, and the 2004 M9.1 Sumatra earthquakes. This occurs because plasma is descending at the lower thermosphere where the recombination of ions and electrons is high through the meter-scale downwelling of sea surface at the tsunami source area, and is highly depleted due to the chemical processes.

Kakinami, Yoshihiro; Kamogawa, Masashi; Tanioka, Yuichiro; Watanabe, Shigeto; Gusman, Aditya Riadi; Liu, Jann-Yenq; Watanabe, Yasuyuki; Mogi, Toru



Ionospheric Corrections to Tropospheric Retrievals  

NASA Technical Reports Server (NTRS)

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

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



In situ transmission electron microscopy probing of native oxide and artificial layers on silicon nanoparticles for lithium ion batteries.  


Surface modification of silicon nanoparticles 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 of how this thin layer of coating functions is not known, which is 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 reactions and detrimental effects of the native oxide. This study provides a vivid picture of how the MLD coating works to enhance the Coulombic efficiency, preserves capacity, and clarifies the role of the native oxide on silicon nanoparticles during cyclic lithiation and delithiation. More broadly, this work also demonstrates that the effect of the subtle chemical modification of the surface during the coating process may be of equal importance to the coating layer itself. PMID:25347792

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



Report from ionospheric science  

NASA Technical Reports Server (NTRS)

The general strategy to advance knowledge of the ionospheric component of the solar terrestrial system should consist of a three pronged attack on the problem. Ionospheric models should be refined by utilization of existing and new data bases. The data generated in the future should emphasize spatial and temporal gradients and their relation to other events in the solar terrestrial system. In parallel with the improvement in modeling, it will be necessary to initiate a program of advanced instrument development. In particular, emphasis should be placed on the area of improved imaging techniques. The third general activity to be supported should be active experiments related to a better understanding of the basic physics of interactions occurring in the ionospheric environment. These strategies are briefly discussed.

Raitt, W. J.; Banks, Peter M.; Nagy, A. F.; Chappell, C. R.



Experimental results from the HERO project - In situ measurements of ionospheric modifications using sounding rockets  

NASA Astrophysics Data System (ADS)

The HEating ROcket project HERO comprised the first in situ experiments to measure artificial ionospheric modifications at F layer heights set up by radio waves transmitted from the Heating facility at Ramfjord near Tromso in northern Norway. Four instrumented payloads were launched on sounding rockets from Andoya Rocket Range during the autumn of 1982 into a sunlit ionosphere with the sun close to the horizon. The payloads recorded modifications, in particular, the presence of electron plasma waves near the reflection level of the heating wave. The amplitude and phase of the three components of the electric and magnetic fields of the heating wave were measured simultaneously as a function of altitude. Coherent spectra of the three electric field components of the locally generated electron plasma waves were obtained in a 50-kHz-wide band. At the same time quasi-continuous measurements were made on several fixed frequencies from 4 kHz to 16 kHz below the heating frequency and in the VLF-range using linear dipole antennas. Moreover, measurements were made of electron temperature, suprathermal electrons, and local electron density along the rocket trajectory. The experimental results are presented and discussed.

Rose, G.; Grandal, B.; Neske, E.; Ott, W.; Spenner, K.; Holtet, J.; Maseide, K.; Troim, J.



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.



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


Study on the microstructure of thin-layer facade plasters of thermal insulating system during artificial weathering  

Microsoft Academic Search

Investigations involving the influence of simulate weathering on the microstructure of thin-layer plasters laid on foamed polystyrene are reported. In order to examine internal changes, two kinds of properties were examined in time per 100 cycles during 400 cycles. One of the properties is an open porosity connected with pore structure tested by the mercury intrusion method (MIP), and total

Jerzy Bochen



Computerized ionospheric tomography  

SciTech Connect

In this paper the background of computerized tomography (CT) and its application to the ionosphere is reviewed. CT techniques, using only total electron content (TEC) data, can be used to reconstruct a two-dimensional image of the electron density in the ionosphere. The limitations of this technique are discussed and examples showing the limitations and capabilities are presented. Simulation results for two applications are presented: imaging the high latitude trough, and the correction of tracking radar range rate errors. Some possible extensions of the technique are presented.

Austen, J.R.; Raymund, T.D.; Klobuchar, J.A.; Stalker, J.; Liu, C.H.



HF radar ionospheric clutter  

NASA Astrophysics Data System (ADS)

The characteristics of HF radar echoes reflected from ionization irregularities aligned along the lines of force of the Earth's magnetic field are presented. Utilizing experimental radar-ionospheric clutter data acquired at frequencies between HF and UHF, an analysis is made of the amplitude, the cross-sectional area and the angular extent statistics of HF field-aligned echoes. The Doppler frequency variation, the frequency of occurrence and the diurnal and seasonal variation of HF ionospheric backscatter echoes and their correlation with solar-geophysical conditions are also discussed.

Millman, G. H.



Temporal modulations of the longitudinal structure in F2 peak height in the equatorial ionosphere as  

E-print Network

layer peak height (hmF2) in the equatorial ionosphere. For this study, electron density profiles, Ionosphere, and Climate (COSMIC) are fitted with a twolayer Chapman function to determine hmF2. The hmF2 structure in hmF2 could thus be attributed to the interaction of DE3 with a 5 day planetary wave. Citation

California at Berkeley, University of


The main ionospheric trough in the East Asian region: Observation and modeling  

Microsoft Academic Search

Research results concerning the main ionospheric trough (MIT) in the afternoon sector are present. Data are used from the meridional chain of stations located in the East Asian region. The analysis of ionospheric storms with different intensities reveals that the depletion in the F2 layer ionization in the afternoon\\/evening sector can be observed in the subauroral latitudes in the storm

O. M. Pirog; N. M. Polekh; E. B. Romanova; A. V. Tashchilin; G. A. Zherebtsov



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

SciTech Connect

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

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



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



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.



Day-side ionospheric conductivities at Mars  

NASA Astrophysics Data System (ADS)

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

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



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.



Wet model of Saturn's ionosphere: Water from the rings  

NASA Technical Reports Server (NTRS)

Current theoretical models of Saturn's ionosphere are difficult to reconcile with the ionospheric electron density profiles obtained from the Pioneer and Voyager radio occultation observations and the large diurnal variation of maximum ionospheric electron density deduced from studies of Saturn lightning discharges. A model of Saturn's ionosphere is proposed in which water plays a major role as a minor constituent present by virtue of downward diffusion from an external source. This model of the Saturn ionosphere is a classical 'F2' type layer resulting from the photodissociative production of H(+) from H2 and rapid chemical loss due to a series of charge exchange reactions with water. A planet-wide influx of about 4x10 to the 7th power molecules/sec/sq cm of water from the rings is consistent with the observed ionospheric electron densities and estimates of influx due to micrometeoride bombardment of the rings. An enhanced influx of water occurs at latitudes (-38 deg, +44 deg) magnetically connected to the inner edge of Saturn's B ring which results from an electromagnetic erosion process contributing substantially to the (local) upper atmosphere water content. Present day influx at these latitudes is possibly as large as 2x10 to the 9th power molecules/sec/sq cm.

Connerney, J. E. P.; Waite, J. H.




E-print Network

in the equatorial area, including Brazil and India, is ionospheric scintillation. Due to electron density irregularities inside the ionosphere, transionospheric radio waves interfere constructively and de- structively

Stanford University


Radio Sounding of the Martian and Venusian Ionospheres  

NASA Astrophysics Data System (ADS)

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

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



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

NASA Astrophysics Data System (ADS)

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

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



Modelling ionospheric density structures  

NASA Technical Reports Server (NTRS)

Large-scale density structures are a common feature in the high-latitude ionsphere. The structures were observed in the dayside cusp, polar cap, and nocturnal auroral region over a range of altitudes, including the E-region, F-region and topside ionosphere. The origins, lifetimes and transport characteristics of large-scale density structures were studied with the aid of a three-dimensional, time-dependent ionospheric model. Blob creation due to particle precipitation, the effect that structured electric fields have on the ionosphere, and the lifetimes and transport characteristics of density structures for different seasonal, solar cycle, and interplanetary magnetic field (IMF) conditions were studied. The main conclusions drawn are: (1) the observed precipitation energy fluxes are sufficient for blob creation if the plasma is exposed to the precipitation for 5 to 10 minutes; (2) structured electric fields produce structured electron densities, ion temperatures, and ion composition; (3) the lifetime of an F-region density structure depends on several factors, including the initial location where it was formed, the magnitude of the perturbation, season, solar cycle and IMF; and (4) depending on the IMF, horizontal plasma convection can cause an initial structure to break up into multiple structures of various sizes, remain as a single distorted structure, or become stretched into elongated segments.

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



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



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


Flare Effects in Mars's Ionosphere Observed by Mars Express Topside Sounding  

NASA Astrophysics Data System (ADS)

Since the beginning of Solar Cycle 24, there have been several strong solar flares, one of which, on 22 September 2011, may have contributed to the safing of the Mars Express Spacecraft. The Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument on board Mars Express, in orbit around Mars, can be used in Active Ionospheric Sounding mode to detect disturbances of the Martian ionosphere. In this presentation, we identify several high-energy particle events at Mars originating in solar flares, including that of 22 September 2011, using in situ particle data from the High-Energy Neutron Detector (HEND). HEND is part of the Gamma Ray Spectrometer on board the Odyssey spacecraft, also in orbit around Mars. Using the timing of the high-energy particle events from HEND, we use MARSIS ionospheric electron density profiles, local electron densities, and surface reflection absorption to track the effect of flare particles on the Martian ionosphere. We incorporate data from the Mars Express particle and plasma instrument ASPERA-3 to show effects on the particle distribution in the ionosphere and to note an extension of the nightside ionosphere to altitudes of several thousand kilometers approximately one day after the particle onset. The flux peak of the 22 September 2011 event coincides with intense spread-F-like echoes near the ionospheric peak and in the "upper layer" ionosphere, implying a predominance of oblique echoes, even in the absence of strong cusplike magnetic topology. As with previous particle events, the nightside surface reflection disappears due to electron collision damping, and the MARSIS Subsurface-mode signal is obscured by noise. During the most intense fluxes of this flare, the peak of the upper layer structure of the Martian ionosphere remains stable, although less pronounced than during less intense fluxes, suggesting a filling-in of undercut or shelflike structures in the electron density profile above the main layer.

Morgan, D. D.; Gurnett, D. A.; Duru, F.; Dubinin, E.; Fraenz, M.; Opgenoorth, H.; Withers, P.; Mitrofanov, I.; Plaut, J. J.



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



Venus Ionosphere and Solar Wind Interaction  

NASA Astrophysics Data System (ADS)

Venus Express, which was inserted into orbit in mid-2006, has added significantly to the knowledge gained from Pioneer Venus from 1978 to 1992. This observational database interpreted in terms of modern multi-fluid codes and hybrid simulations has deepened our understanding of Earth’s very different twin sister planet. Furthermore, the very different orbits of VEX and PVO has allowed the more complete mapping of the volume of space around the planet. Now the bow shock has been probed over its full surface, the ionosphere mapped everywhere, and the tail studied from the ionosphere to 12 Venus radii. Some unexpected discoveries have been made. The exospheric hydrogen at Venus, unlike that at Mars, does not produce ion-cyclotron waves, perhaps because the stronger gravity of Venus produces a smaller geocorona. The solar wind interaction drapes the magnetic field around the planet, and a strong layer of magnetic field builds up at low altitudes. While the layer does not appear to penetrate into the dayside atmosphere (perhaps diffusing only slowly through the low atmosphere), it does appear to dip into the atmosphere at night. Surprisingly, over the poles, this layer is most strongly seen when the IMF BY component has a positive Y-component in Venus-Solar-Orbital coordinates. Multi-fluid simulations show that this result is consistent with the pressure of significant ion densities of ions with quite different mass which causes magnetic polarity control of the ion flow over the terminators. Reconnection is found in the tail close to the planet, and the structure of the outer tail found by PVO is confirmed to exist in the inner tail by VEX. When combined, the VEX and PVO Data provide a very comprehensive picture of the physics of the solar wind interaction with the ionosphere of Venus.

Russell, C. T.; Luhmann, Janet G.; Ma, Yingjuan; Zhang, Tielong; Villarreal, M.


Ionospheric modification using relativistic electron beams  

NASA Technical Reports Server (NTRS)

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

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



Ionospheric Transmission Losses Associated with Mars-orbiting Radars  

NASA Technical Reports Server (NTRS)

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

Farrell, W. M.



Ionospheres of the terrestrial planets  

Microsoft Academic Search

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

R. W. Schunk; A. F. Nagy



On the effect of BUM generation enhancement revealed using the scheme of additional heating of ionospheric plasma  

NASA Astrophysics Data System (ADS)

We present measured characteristics of the artificial ionospheric radio emission (AIRE), which were obtained experimentally using additional heating of the ionospheric F-region by O-polarized waves. It is shown that the observed enhancement of intensity of the broad upshifted maximum (BUM) of the AIRE can result from the influence of electrons accelerated in the plasma: esonance region on its generation. An empirical model of the phenomenon observed is developed. It is concluded from experimental results that the BUM has a complex structure and only one of its components produces the above emission enhancement. We show the possibility of using the AIRE in additional heating of ionospheric plasma for diagnostics of artificial ionospheric turbulence and investigation of the features of perturbation propagation along the geomagnetic field lines.

Frolov, V. L.; Erukhimov, L. M.; Komrakov, G. P.; Sergeev, E. N.; Thidé, B.; Bernhardt, P. A.; Wagner, L. S.; Goldstein, J. A.; Selcher, G.



Imaging meso-scale ionospheric structures  

NASA Astrophysics Data System (ADS)

The accuracy and capacity to resolve meso-scale structures of a four dimensional ionospheric imaging algorithm in the circumstance of data from dense networks of permanent GNSS ground receiver stations were investigated. Simulation studies were conducted in order to be able to assess the performance of the algorithm over the entire imaged region. The Multi-instrument Data Assimilation Software (MIDAS) algorithm was used for this purpose. Simulated input data in Receiver Independent Exchange Format (RINEX) were produced by calculating slant Total Electron Content (sTEC) values for satellite to receiver raypaths through an artificially generated ionosphere. Modeling these signals including Differential Code Biases (DCBs) and noise had negligible impact on the output from the imaging algorithm when compared with modeled signals that included neither. Comparing the output from MIDAS using a range of grid definitions show that finer grids have improved capacity to resolve meso-scale structures in the input model but over all are less accurate than coarser grids. The greatest errors occur in low-data regions of the grid and where structures in the input have the greatest gradients in vertical Total Electron Content (vTEC). A good compromise between the conflicting needs of resolution and accuracy is given by a grid defined with 2° × 2° latitude by longitude local horizontal grid divisions.

Burston, Robert



Hardware and software complex monitoring the Earth ionosphere  

NASA Astrophysics Data System (ADS)

The complex structure of the propagation medium, as well as continuous change in time ionospheric plasma parameters affect the propagation of radio waves. Therefore, objectives of the study processes in the ionosphere associated with both the practical tasks of ensuring stable operation of radiocommunication systems and with no less important scientific - research tasks of monitoring near-Earth space. A promising approach to the control of the ionosphere based on the method of radio occultation and to identify the main ionospheric parameters ( total electron content of the critical frequency and height of the ionospheric layer F2) on the results of the reception and signal processing of satellite navigation systems GLONASS and GPS. To solve this problem the theory for solving the inverse problem of radio sounding of the ionosphere on the track satellite–the Earth developed. It based on the use of functional connections parameters probing signals and their propagation medium and the mathematical apparatus of solutions of Fredholm integral equations of the 1st kind, belonging to the class of inverse ill-posed problems of atmospheric refraction. On its basis the continuous monitoring technology designed for the reconstruction of the spatiotemporal structure of the ionosphere and solving operational control and the total electron content of the ionosphere by radio translucence method with using radio navigation satellite system GPS/GLONASS. Based on developed technology of continuous monitoring an automated hardware and software complex intended for determining the parameters of altitude distribution of the electron density of the ionosphere of the Earth designed. It uses the information of the navigation satellite system GPS/GLONASS and works in real time. Automated hardware-software system designed based on dual-frequency receiver firm NovAtel, operating signals navigation satellite systems GPS/GLONASS. The complex allows determine the parameters of the Earth's ionosphere by radio translucence method on track satellite – the Earth simultaneously 10-20 azimuthal directions over the territory, an area of about 3 million square km’s.

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


Methods for Creation and Detection of Ultra-Strong Artificial Ionization in the Upper Atmosphere (Invited)  

NASA Astrophysics Data System (ADS)

The High Frequency Active Auroral Research Program (HAARP) transmitter in Alaska has been used to produce localized regions of artificial ionization at altitudes between 150 and 250 km. High power radio waves tuned near harmonics of the electron gyro frequency were discovered by Todd Pederson of the Air Force Research Laboratory to produce ionosonde traces that looked like artificial ionization layers below the natural F-region. The initial regions of artificial ionization (AI) were not stable but had moved down in altitude over a period of 15 minutes. Recently, artificial ionization has been produced by the 2nd, 3rd, 4th and 6th harmonics transmissions by the HAARP. In march 2013, the artificial ionization clouds were sustained for more the 5 hours using HAARP tuned to the 4 fce at the full power of 3.6 Mega-Watts with a twisted-beam antenna pattern. Frequency selection with narrow-band sweeps and antenna pattern shaping has been employed for optimal generation of AI. Recent research at HAARP has produced the longest lived and denser artificial ionization clouds using HF transmissions at the harmonics of the electron cyclotron frequency and ring-shaped radio beams tailored to prevent the descent of the clouds. Detection of artificial ionization employs (1) ionosonde echoes, (2) coherent backscatter from the Kodiak SuperDARN radar, (3) enhanced ion and plasma line echoes from the HAARP MUIR radar at 400 MHz, (4) high resolution optical image from ground sites, and (5) unique stimulated electromagnetic emissions, and (6) strong UHF and L-Band scintillation induced into trans-ionospheric signals from satellite radio beacons. Future HAARP experiments will determine the uses of long-sustained AI for enhanced HF communications.

Bernhardt, P. A.; Siefring, C. L.; Briczinski, S. J.; Kendall, E. A.; Watkins, B. J.; Bristow, W. A.; Michell, R.



GIM-TEC adaptive ionospheric weather assessment and forecast system  

NASA Astrophysics Data System (ADS)

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

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



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



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.



The Jovian ionospheric E region  

NASA Technical Reports Server (NTRS)

A model of the Jovian ionosphere was constructed, that includes direct photoionization of hydrocarbon molecules. A high-resolution solar spectrum was synthesized from Hinteregger's solar maximum spectrum (F79050N), and high-resolution cross sections for photoabsorption by H2 bands in the range 842 to 1116 A were constructed. Two strong solar lines and about 30 percent of the continuum flux between 912 and 1116 A penetrate below the methane homopause despite strong absorption by CH4 and H2. It is found that hydrocarbons (mainly C2H2 are ionized at a maximum rate of 55/cu cm per sec at 320 km above the ammonia cloud tops. The hydrocarbon ions produced are quickly converted to more complex hydrocarbon ions through reactions with CH4, C2H2, C2H6, and C2H4. It is found that a hydrocarbon ion layer is formed near 320 km that is about 50 km wide with a peak density in excess of 10,000/cu cm.

Kim, Y. H.; Fox, J. L.



Are ionospheric storms the same during different solar cycles?  

NASA Astrophysics Data System (ADS)

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

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



Theory and Observations of Plasma Waves Excited Space Shuttle OMS Burns in the Ionosphere  

Microsoft Academic Search

Measurements of artificial plasma turbulence were obtained during two Shuttle Exhaust Ionospheric Turbulence Experiments (SEITE) conducted during the flights of the Space Shuttle (STS-127 and STS-129). Based on computer modeling at the NRL PPD and Laboratory for Computational Physics & Fluid Dynamics (LCP), two dedicated burns of the Space Shuttle Orbital Maneuver Subsystem (OMS) engines were scheduled to produce 200

P. A. Bernhardt; R. F. Pfaff; P. W. Schuck; D. E. Hunton; M. R. Hairston



Artificial Intelligence.  

ERIC Educational Resources Information Center

Describes kinds of results achieved by computer programs in artificial intelligence. Topics discussed include heuristic searches, artificial intelligence/psychology, planning program, backward chaining, learning (focusing on Winograd's blocks to explore learning strategies), concept learning, constraint propagation, language understanding…

Waltz, David L.



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



Electron gyroharmonic effects on ionospheric stimulated Brillouin scatter  

NASA Astrophysics Data System (ADS)

Stimulated Brillouin scattering (SBS) and resonant phenomena are well known in the context of laser fusion, fiber optics, and piezoelectric semiconductor plasmas, as well as in various biological applications. Due to recent advances, active space experiments using high-power high-frequency (HF) radio waves may now produce stimulated Brillouin scattering (SBS) in the ionospheric plasma. The sensitivity of the narrowband SBS emission lines to pump frequency stepping across electron gyroharmonics is reported here for the first time. Experimental observations show that SBS emission sidebands are suppressed as the HF pump frequency is stepped across the second and third electron gyroharmonics. A correlation of artificially enhanced airglow and SBS emission lines excited at the upper hybrid altitude is observed and studied for second gyroharmonic heating. The SBS behavior near electron gyroharmonics is shown to have important diagnostic applications for multilayered, multi-ion component plasmas such as the ionosphere.

Mahmoudian, A.; Scales, W. A.; Bernhardt, P. A.; Isham, B.; Kendall, E.; Briczinski, S. J.; Fuentes, N. E. B.; Vega-Cancel, O.



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)



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.



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


Linear mode conversion in inhomogeneous magnetized plasmas during ionospheric  

E-print Network

facilitate acceleration of fast energetic electrons, resulting in observed enhanced airglow. INDEX TERMS Science: Ionospheric propagation (2487); 2411 Ionosphere: Electric fields (2712); 2439 Ionosphere of initial density inhomogeneities in the ionosphere which leads to the thermal self-focusing instability

Rubloff, Gary W.


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.



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



Ionospheric Effects from the superbolid exploded over the Chelyabinsk area  

NASA Astrophysics Data System (ADS)

The Chelyabinsk meteorite fall is undoubtedly the most documented in history. Its passage through the atmosphere was recorded by video and photographers, visual observers, infrasonic microphones, seismographs on the ground, and by satellites in orbit. The data of transionospheric sounding by signals from the GPS cluster satellites carried out in the zone of explosion of the Chelyabinsk meteoroid have been analyzed. The analysis has shown that the explosion had a very weak effect on the ionosphere. The observed ionospheric disturbances were asymmetric with respect to the explosion epicenter. The signals obtained were compared both in shape and in amplitude with the known surface explosions for which the diagnostics of the ionospheric effects had been made by radio techniques. Ionospheric effects in the form of acoustic-gravity waves (AGW) produced by 500-600 tons TNT explosions on the ground are detected with confidence both by vertical sounding and by GPS techniques. This allows us to suggest that the reported equivalent of the meteoroid explosion was obviously overestimated. The experiments on the injection of barium vapor (3.3 kg) carried out under similar conditions in the terminator zone revealed the response of the ionosphere in variations of the critical frequencies of the layer at a distance of 1500-2000 km (AGW with a period of 5-10 min). The absence of such ionospheric effects in the remote zone at 1500-1700 km from the epicenter of the bolide explosion in the case under discussion also makes us feel doubtful about the estimated explosion equivalent.

Ruzhin, Yuri; Smirnov, Vladimir; Kuznetsov, Vladimir; Smirnova, Elena


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



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


Interactions with planetary ionospheres and atmospheres - A review  

NASA Technical Reports Server (NTRS)

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

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



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



Ionospheric Profiling using GPS/MET Data  

NASA Technical Reports Server (NTRS)

A report on ionospheric profiling using GPS and MET data is presented. A description of the GPS occultation technique, some examples of GPS/MET data products, the data processing system and a preliminary validation of ionospheric profiles is discussed.

Hajj, George; Romans, Larry



Artificial Intelligence  

E-print Network

This paper is a general overview of the field of artificial Intelligence and of some of the application issues within that field. Its first objective is to try and establish a viable definition for what artificial intelligence is, and to make a...

Appleton, D. S.


Artificial intelligence  

SciTech Connect

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

Firschein, O.



Artificial intelligence  

SciTech Connect

This book presents the papers given at a symposium on expert systems and artificial intelligence. Topics considered at the symposium included knowledge representation, industrial expert systems, knowledge bases, computer-aided design, computer-aided manufacturing, mathematical logic, robots, flexible manufacturing systems, decision-making in computer-aided planning, computerized control systems, artificial intelligence applied systems, computerized simulation, and natural language.

Ponomaryov, V.M.



Movements of the mid-latitude ionospheric trough  

Microsoft Academic Search

The mid-latitude trough, often called the main trough, is defined to be the circumpolar region at about L=4 where the night-time electron concentration of the F-layer is anomalously low. It can be considered as the boundary region between the mid-latitude and the polar ionospheres. A description is provided of a method by which an ionosonde, normally operating at vertical incidence,

A. S. Rodger; M. Pinnock



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


Ionospheric Erosion by Alfven Waves  

NASA Astrophysics Data System (ADS)

Using observations from the FAST small explorer spacecraft we present fields and plasma observations above the dayside auroral oval showing the erosion of ionospheric plasmas from the topside ionosphere by the action of Alfven waves. Using interferometric techniques the waves are shown to approximately obey the expected dispersion for Alfven waves with transverse scales extending from greater than electron inertial lengths down to ion gyro-radii. Measurements of the plasma density where these waves are observed show that over latitudinal widths exceeding 100 km total depletion of the cold ionospheric plasma can occur. The plasma within these depleted regions or cavities is composed of magnetosheath ion and electron distributions and upgoing transversely accelerated ions and downgoing field-aligned electrons distributed as conics and field-aligned beams respectively. Poynting flux observations on the density gradients comprising the cavity walls show that these waves are directed downwards and focused inwards towards regions of lower density. The wave phase velocity measurement in the plasma frame, while subject to significant uncertainty, is directed transversely outwards from the cavity. These observations suggest a feedback model for Alfven wave focusing and ion heating on density gradients that can lead to intense ion outflow from the ionosphere and subsequent depletion of ionospheric plasmas.

Chaston, C. C.; Genot, V.; Bonnell, J. W.; Carlson, C.; McFadden, J.; Ergun, R.; Strangeway, R.; Lund, E.; Hwang, K.



Low- and mid-latitude ionospheric effects of energetic electrons  

NASA Astrophysics Data System (ADS)

Recent observations revealed events of energetic and relativistic electron enhancements in the Earth’s radiation belt (ERB) occurred on timescales of less than a few hours. As it was shown, so-called "rapid rebuilding" events were caused by substorms. We found that similar enhancements were also seen under the ERB in the forbidden zone. Both phenomena of sudden growth of energetic electrons inside and under the ERB relate to substorm dipolarizations, which result in rapid changes in the configuration of the magnetic field and generation of inductive electric fields. In the previous studies we found very intense fluxes of energetic electrons in the forbidden zone which resulted in substantial abundant ionospheric ionization during strong magnetic storms. Here we analyze enhancements of >30-keV quasi-trapped electrons during a moderate recurrent (CIR/HSS-driven) geomagnetic storm on 22 July 2009. We focus on particular issue of the magnetosphere-ionosphere coupling through the quasi-trapped electrons at low-latitudes. We show that unusually large area in the nighttime ionosphere with increased total electron content (TEC) and prominent elevation of the F-layer at low-latitudes coincides spatially and temporarily with enhanced electron fluxes. Ionizing particles are considered now as an addition source of ionization during recurrent magnetic storms along with generally accepted mechanisms for storm-time TEC increases or so-called positive ionospheric storms.

Suvorova, Alla; Matsumoto, Haruhisa; Kunitsyn, Viacheslav; Andreeva, Elena; Nesterov, Ivan; Dmitriev, Alexei; Huang, Chien-Ming


Very Low Frequency Remote Sensing of the Ionosphere and Magnetosphere  

NASA Astrophysics Data System (ADS)

This review talk will explore the technique of Very Low Frequency (VLF, 3-30 kHz) remote sensing of the ionosphere and magnetosphere, in which ground-based transmitter beacons (nominally for submarine communications) are used as a probe wave to study the D-region of the ionosphere (60-90 km), a layer is too low for satellites and too high for balloons. Guided efficiently by the Earth-ionosphere waveguide, VLF waves can be used on a global level, to sensitively quantify any ionospheric disturbance in the D-region. These include the impacts of solar flares, lightning heating (both the EMP and the quasi-static field changes), electron precipitation from lightning, and cosmic gamma-ray bursts. We will review many experimental and modeling efforts that have been made over the past several decades, including recent work on the transionospheric absorption of VLF waves from transmitters and lightning radio emissions. We will also review recent international efforts to build a global network of VLF receivers under the umbrella of the United Nations Basic Space Science Initiative.

Cohen, M.



Interplanetary radio transmission through serial ionospheric and material barriers  

NASA Astrophysics Data System (ADS)

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 E.; Kennedy, Robert G.; Roy, Kenneth I.; Vacaliuc, Bogdan



Ionospheric refraction correction in radio astronomy  

NASA Astrophysics Data System (ADS)

Using Snell's law in polar coordinates, the ionospheric refraction effects on the declination and right ascension determination are discussed in this paper. A ray tracing method is also given. With the ionospheric data observed in Beijing, the correction of ionospheric refraction is estimated and some useful conclusions are drawn.

Chai, Yan; Han, Wen-Jun



Simulations of plasma structure evolution in the high-latitude ionosphere  

NASA Technical Reports Server (NTRS)

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

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



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


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

SciTech Connect

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

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



Whistler interaction with field-aligned density irregularities in the ionosphere: Refraction, diffraction, and interference  

NASA Astrophysics Data System (ADS)

Field-aligned density irregularities (FAI) with kilometer-scale sizes transverse to the background magnetic field are a common feature in the ionosphere at all latitudes and local times. In this paper, we investigate the effect of these irregularities on the transionospheric propagation of very low frequency whistler waves and develop a quantitative description of FAI-related effects on whistler propagation through the lower ionosphere. Using an electron magnetohydrodynamics simulation, we provide two applications of our model. First, we show that the presence of kilometer-scale FAI in the ionosphere can reduce the power observed in the equatorial magnetosphere by more than 10 dB in some cases. Second, we demonstrate that multiple FAIs can act as a discrete lens for whistlers, providing a possible means for increasing wave power in artificial whistler ducting experiments.

Woodroffe, J. R.; Streltsov, A. V.



A unified theory of ionosphere-plasmasphere transport of suprathermal electrons  

SciTech Connect

The authors present a model of suprathermal electrons in the ionosphere and plasmasphere based on a solution to the kinetic equation along the entire length of a closed magnetic field line, that is, simultaneously for the two conjugate ionospheres and the plasmasphere. They call this the unified approach. It allows the determination of the distribution in energy and pitch-angle of photoelectrons along the complete length of the field line thereby avoiding the introduction of artificial boundaries between the ionosphere and magnetosphere and, consequently, avoids problem introduced by the uncertainty of these boundary conditions. In addition, it automatically accounts for back-scattered electrons in the atmosphere and plasmasphere, and avoids splitting photoelectrons into a loss-cone and a trapped population. The method is not limited to specific situations such as conjugated sunrise or symmetrical illumination of hemispheres, but is equally applicable to arbitrary illumination conditions.

Khazanov, G.V.; Neubert, T. (Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Oceanic, Atmospheric and Space Science); Gefan, G.D. (Irkutsk Polytechnical Inst., Irkutsk (Russian Federation))



Ionospheric imaging using computerized tomography  

SciTech Connect

Computerized tomography (CT) techniques can be used to produce a two-dimensional image of the electron density in the ionosphere. The CT problem requires that the measured data be the line integral through the medium of the unknown parameter; transionospheric satellite beacon total electron content data recorded simultaneously at multiple ground stations fulfill this requirement. In this paper the CT problem is formulated as it applies to ionospheric imaging and limitations of the technique are investigated. Simulations are performed assuming a 1000-km-altitude polar-orbiting satellite and both five and three ground stations; the results demonstrate the feasibility of this technique. 14 references.

Austen, J.R.; Franke, S.J.; Liu, C.H.



Radar Soundings of the Ionosphere of Mars  

NASA Astrophysics Data System (ADS)

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.

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.



Solar wind erosion of the polar regions of the Mars ionosphere  

NASA Astrophysics Data System (ADS)

Measurements conducted with the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) instrument of the Mars Express spacecraft provide data of plasma fluxes that stream away from the polar regions of the Mars ionosphere with energy spectra whose peak value increases with distance from the planetary surface. The observed energy distribution reveals a velocity boundary layer with ionospheric plasma that is eroded from the polar regions of the Mars ionosphere and that extends in the downstream direction within a geometry similar to that present along the polar flanks of the Venus ionosheath. The direction of motion of the ionospheric particles in those fluxes is close to that of the solar wind velocity and is not also oriented in a transverse direction as would have been expected if they were solely accelerated by the convective electric field of the solar wind. The ionospheric plasma eroded and deviated by the solar wind within the boundary layer forms a region whose shape is compatible with that of the asymmetric Mars plasma halo that was inferred from the X-ray emission lines measured with the reflecting grating spectrometer of the XMM-Newton telescope. The latter emission is interpreted as resulting from thermal dissipative processes associated with the transport of solar wind momentum to the polar upper ionosphere where both plasma populations interact with each other. Different conditions are applicable throughout most of the dayside hemisphere where the enhanced interplanetary magnetic field intensities that are observed within the ionosphere should make the interaction of the oncoming solar wind plasma with the ionospheric material less efficient.

Pérez-de-Tejada, H.; Lundin, R.; Durand-Manterola, H.; Reyes-Ruiz, M.



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



Artificial Satellite  

NASA Astrophysics Data System (ADS)

A man-made object placed in orbit round the Earth or some other celestial body. The first artificial Earth satellite was Sputnik 1, launched by the then Soviet Union, on 4 October 1957. Spherical in shape, and with a mass of 84 kg, it entered an orbit with a perigee altitude of 229 km, an apogee altitude of 947 km and a period of 96 min. Artificial satellites are used for a wide variety of roles,...

Murdin, P.



ALTAIR incoherent scatter observations of the equatorial daytime ionosphere  

NASA Astrophysics Data System (ADS)

The first high-resolution electron density maps of the low-latitude D- and E-region ionosphere in the Pacific sector acquired with ALTAIR UHF measurements are presented. The electron density data were collected in connection with a rocket based common volume experiment described by Friedrich et al. (2006). The observed phenomena in the density maps include E-region density layers of tidal origin, shorter lived layers with small vertical scales, and lower E-region electron density enhancement in response to enhanced X-ray flux.

Kudeki, Erhan; Milla, Marco; Friedrich, Martin; Lehmacher, Gerald; Sponseller, Dale



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

NASA Astrophysics Data System (ADS)

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

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



A Campaign to Study Equatorial Ionospheric Phenomena over Guam  

NASA Astrophysics Data System (ADS)

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

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



Ionospheric imaging using computerized tomography  

Microsoft Academic Search

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

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



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.



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.



Moment expansion for ionospheric range error  

NASA Technical Reports Server (NTRS)

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

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



Reanalysis of Mars ionospheric electron density profiles from Mariner 9  

NASA Astrophysics Data System (ADS)

The Mariner 9 radio occultation experiment acquired 118 profiles of dayside ionospheric electron density from 1971-2. Relative to the MGS dataset, which contains the only electron density profiles for Mars that are readily available to the public today, the Mariner 9 dataset has some unique characteristics. Profiles extend to 300-400 km, thereby probing the topside ionosphere better than the MGS profiles that typically terminate around 200 km. Profiles were acquired during the waning phase of a tremendous dust storm, when the ionospheric peak was 20-30 km higher than normal. Profiles are distributed globally, whereas MGS profiles are poleward of 60 degrees north latitude, and sample solar zenith angles as low as 47 degrees, whereas MGS was limited to 71 degrees and higher. We have digitized the Mariner 9 electron density profiles from their microfilm archive. Here we report on a broad scientific analysis of these profiles. We examine the dependence of electron densities in the M2 and M1 layers on solar zenith angle and flux, how the dust storm affected both peak altitude and ionopause altitude, and the presence of meteoric layers.

Weiner, S. L.; Withers, P.



Effects of large zonal plasma drifts on the subauroral ionosphere  

NASA Technical Reports Server (NTRS)

A model of the earth's ionosphere and plasmasphere is used to investigate the effects of an imposed westward plasma drift of maximum velocity 2 km/s. A closed subauroral tube of plasma is considered and the velocity spike persists for 10 min. Ion-neutral frictional heating causes rapid elevation of the F-region O(+) temperature. The F-layer O(+) concentration is decreased due to increased O(+) loss rate and rapid ion flows both upward and downward from the F-region. The upward flux of O(+) through the topside ionosphere can each 5 x 10 exp 9/sq cm/s; when the velocity spike ceases there is a return flow of O(+) that tends to replenish the F-layer. Most of the features revealed by the model for the F-region and topside ionosphere are in accord with observations of subauroral ion drifts. Downward flows that are predicted to be persistently present around the 300 km altitude level appear to agree with observations only occasionally; suggestions are made to resolve this discrepancy.

Sellek, R.; Bailey, G. J.; Moffett, R. J.; Heelis, R. A.; Anderson, P. C.



Numerical simulation of the plasma thermal disturbances during ionospheric modification experiments at the SURA heating facility  

NASA Astrophysics Data System (ADS)

indent=1cm We present the results of numerical simulation of the near-Earth plasma disturbances produced by resonant heating of the ionospheric F-region by high-power HF radio emission from the SURA facility. The computational model is based on the modified version of the SAMI2 code (release 1.00). The model input parameters are appropriated to the conditions of the SURA-DEMETER experiment. In this work, we study the spatial structure and temporal characteristics of stimulated large-scale disturbances of the electron number density and temperature. It is shown that the stimulated disturbances are observed throughout the ionosphere. Disturbances are recorded both in the region below the pump wave reflection level and in the outer ionosphere (up to 3000 km). At the DEMETER altitude, an increase in the ion number density is stipulated by the oxygen ions O (+) , whereas the number density of lighter H (+) ions decreases. A typical time of the formation of large-scale plasma density disturbances in the outer ionosphere is 2-3 min. After the heater is turned off, the disturbances relaxation time is approximately 30 min. The simulation results are important for planning future promising experiments on the formation of ionospheric artificial density ducts. This work was supported by the Russian Foundation for Basic Research (project No. 12-02-00747-a), and the Government of the Russian Federation (contract No. 14.B25.31.0008).

Belov, Alexey; Huba, J. D.


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.



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

Microsoft Academic Search

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




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



Langmuir probe measurements in the ionosphere  

NASA Astrophysics Data System (ADS)

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

Barjatya, Aroh


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

NASA Astrophysics Data System (ADS)

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

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



Ionospheric response to the entry and explosion of the South Ural superbolide  

NASA Astrophysics Data System (ADS)

The South Ural meteoroid (February 15, 2013; near the city of Chelyabinsk) is undoubtedly the best documented meteoroid in history. Its passage through the atmosphere has been recorded on videos and photographs, visually by observers, with ground-based infrasound microphones and seismographs, and by satellites in orbit. In this work, the results are presented of an analysis of the transionospheric GPS sounding data collected in the vicinity of the South Ural meteoroid site, which show a weak ionospheric effect. The ionospheric disturbances are found to be asymmetric about the explosion epicenter. The received signals are compared, both in shape and amplitude, with the reported ionospheric effects of ground level explosions with radio diagnostics. It is shown that the confident registration of ionospheric effects as acoustic gravity waves (AGWs) by means of vertical sounding and GPS technologies for ground explosions in the range of 0.26-0.6 kt casts doubt on the existing TNT equivalent estimates (up to 500 kt) for the Chelyabinsk event. The absence of effects in the magnetic field and in the ionosphere far zone at distances of 1500-2000 km from the superbolide explosion epicenter also raises a question about the possibility of an overestimated TNT equivalent. An alternative explanation is to consider the superposition of a cylindrical ballistic wave (due to the hypersonic motion of the meteoroid) with spherical shock waves caused by the multiple time points of fragmentation (multiple explosions) of the superbolide as a resulting source of the AGW impact on ionospheric layers.

Ruzhin, Yu. Ya.; Kuznetsov, V. D.; Smirnov, V. M.



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

NASA Astrophysics Data System (ADS)

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

Fagundes, Paulo Roberto



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



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


Ionospheric Feedback Effects on Magnetosphere-Ionosphere Coupling  

NASA Astrophysics Data System (ADS)

A new interactive M-I coupling model is developed to investigate the dynamic interaction between magnetospheric dispersive waves, compressional modes, and auroral electron precipitations. The model is applied to investigate the geomagnetic electromagnetic pulsations observed in Earth's magnetosphere in terms of magnetospheric waves triggered by field line resonances and ionospheric feedback instability. M-I coupling is included by accounting for the closure of magnetospheric field-aligned currents through Pedersen currents in the ionosphere. The height-integrated Pedersen conductivity is treated as a dynamic parameter by electrodynamically coupling the 2D finite element wave model "TOPO" to the ionospheric ionization model "GLOW". It is shown that both mechanisms can be used to explain many features of auroral arcs such as the periodic intensification, FACs, and electric fields. However, unlike in a field line resonance where the ponderomotive force causes the plasma to move mainly along the field line, the plasma in the feedback instability is distributed either as a bump or a cavity along a field line and leads to a multi-banded structure in the radial direction. The nonlinear feedback instability model can explain the formation of plasma density and electromagnetic perturbations with the same frequency, which disagree with current FLR scenario.

Lu, Jianyong; Wang, Wenbin; Rankin, Robert; Marchand, Richard


Meteor impacts, sporadic E layer formation and the incoherent scatter method  

Microsoft Academic Search

A study using incoherent scatter measurements during strong meteor showers, which addresses the many physical processes needed on the way for meteors to thin layers consisting of metals or alkali metals in the ionospheric E region, is reviewed. Meteors are considered to deposit elements which are layered into a broad metallic belt in the ionospheric E region extending over the

Asta Pellinen-Wannberg



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;



Ionospheric limitations to time transfer by satellite  

NASA Technical Reports Server (NTRS)

The ionosphere can contribute appreciable group delay and phase change to radio signals traversing it; this can constitute a fundamental limitation to the accuracy of time and frequency measurements using satellites. Because of the dispersive nature of the ionosphere, the amount of delay is strongly frequency-dependent. Ionospheric compensation is necessary for the most precise time transfer and frequency measurements, with a group delay accuracy better than 10 nanoseconds. A priori modeling is not accurate to better than 25%. The dual-frequency compensation method holds promise, but has not been rigorously experimentally tested. Irregularities in the ionosphere must be included in the compensation process.

Knowles, S. H.



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

NASA Astrophysics Data System (ADS)

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

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



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

NASA Astrophysics Data System (ADS)

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

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



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.



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.



Aerosol growth in Titan's ionosphere through particle charging  

NASA Astrophysics Data System (ADS)

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

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



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.



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

NASA Astrophysics Data System (ADS)

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

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



Electromagnetic Pulse in the Magnetosphere Generated by Impulsive Current near the Lower Boundary of the Ionosphere  

Microsoft Academic Search

A solution to the problem of current spreading is constructed in the case of relaxation of electric charges, which have arisen in the mesosphere for one reason or other. These currents penetrate into the conductive region with anisotropic conductivity of the D- and E-layers of the ionosphere, being transformed to a MHD-wave that propagates into the magnetosphere. Based on this

V. V. Surkov; Yu. I. Galperin



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.



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



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 (;)



Energetics of the ionospheric feedback interaction  

Microsoft Academic Search

The ionospheric feedback instability has been invoked as a possible mechanism for the formation of narrow auroral arcs. This instability can excite eigenmodes of both field line resonances and the ionospheric Alfvén resonator, producing narrow-scale structures. Although the basic dispersion relation of this instability has been discussed for both of these cases, the energetics of this instability has not been

Robert L. Lysak; Yan Song



Effects of nuclear detonations on the ionosphere  

Microsoft Academic Search

During Operation CASTLE, two ionosphere recorders were operated in the Marshall Islands -at Site Elmer, about 200 miles west of Bikini Atoll, and at Rongerik Atoll, about 150 miles east of Bikini -- in order to study the effects of the detonations on the ionosphere. Severe absorption was observed 200 miles west of all multimegaton shots, lasting several hours, presumably

F. B. Daniels; A. K. Harris



Ionospheric calibration from an array signal processing  

E-print Network

of turbulent flow. It obeys a powerlaw with exponent = -11/3. The fluctuations of ionospheric electron density and the array aperture are larger than the ionospheric irregularity scale. The complex gains depend on Station be specified as covariance, structure function or power spectral density The structure function is defined

Langendoen, Koen


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



Polar Ionospheric Imaging at Storm Time  

Microsoft Academic Search

During periods of major geomagnetic storms the polar ionosphere becomes very variable. Ground-based measurements, such as NIMS, GPS or ionosonde data are too sparse to do tomographic imaging, however, combination of these data sources as well as other available measurements, such as satellite- based data, may have the possibility to monitor the structure of the disturbed polar ionosphere. In this

Ping Yin; Cathryn Mitchell; Gary Bust



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.



A Source of Energy for the Ionosphere  

Microsoft Academic Search

THE heat requirement of the equatorial and temperate zone ionosphere is normally about 2 × 1010 cal. sec.-1 (cf. Johnson1). This is because of the loss of heat downwards due to a temperature gradient of about 10° K. km.-1 between 100 and 200 km. altitude. It is the purpose of this communication to suggest that joule heating by ionospheric electric

K. D. Cole



Investigations of the ionosphere by space techniques  

NASA Technical Reports Server (NTRS)

Much of the impetus to ionosphere research since the International Geophysical Year has come from new types of measurement using space vehicles. The key developments are outlined, together with the contributions that they have made to the understanding of the ionosphere.

Bowhill, S. A.



Derivation of a planetary ionospheric storm index  

Microsoft Academic Search

The planetary ionospheric storm index, Wp, is deduced from the numerical global ionospheric GPS-IONEX maps of the vertical total electron content, TEC, for more than half a solar cycle, 1999-2008. The TEC values are extracted from the 600 grid points of the map at latitudes 60° N to 60° S with a step of 5° and longitudes 0° to 345°

T. L. Gulyaeva; I. Stanislawska



Results from Automated Ionospheric Data Analysis for  

E-print Network

Lee* Tetra Tech AMT Sungwook Jung and Minchan Kim Korea Advanced Institute of Science and Technology processing ionospheric data using the automated tool. Pre-existing ionospheric storm data are processed], [3]. If such gradients are not detected by the LAAS ground facility (LGF), users can suffer from

Stanford University


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.



On the problem of detection of seismo-ionospheric phenomena by multi-instrumental radiophysical observations  

NASA Astrophysics Data System (ADS)

Analysis of the previous works on lithosphere-ionosphere interactions confirmed the necessity to use simultaneous observations from several independent diagnostics tools in order to raise the reliability of the observed seismo-ionospheric effects. The influence on the ionosphere from below is weaker in comparison with effects of solar or geomagnetic origin. Due to this reason it is very actual the problem of detection of seismo-ionospheric anomalies on the background of strong regular and quasi-regular variation of space weather parameters. For the given research we use integrated processing of the ionospheric data from different sources: total electron content (TEC) data obtained on the basis of regular GPS observations of IGS stations located in Sakhalin and Japan regions, ionospheric E and F2 layers peak parameters, derived from data of Japan ionosonde network and electron density profiles, obtained by FORMOSAT-3/COSMIC radio occultation measurements. As a case-study it was analyzed the Nevelsk earthquake (M 6.2) that took place at the Far East of Russian Federation on August 2, 2007. On July 29, 2007, several days prior to earthquake, the characteristic anomaly was found out as the day-time significant enhancement of TEC at the vicinity of earthquake. This enhancement reached the maximal value of 4-6 TECU in absolute values, that is 40-50% to the background conditions, and it was situated very close to the epicenter position. The noticeable enhancement of F2 peak critical frequency (foF2) was observed over Wakkanai ionosonde. For the evening hours (19-22 LT) it reached the value of 6.8-7.7 MHz whereas monthly median was 5.3-5.7 MHz. This foF2 increase was coincided in time with the appearance of TEC anomaly in TEC maps over the considered region (taken from GIMs IONEX). In order to separate seismo-ionospheric perturbations from geomagnetic disturbances it was done the comparative analysis of the revealed ionospheric effect possibly related with seismic activity and ionosphere changes during geomagnetic storms which took place during July and August of 2007. We acknowledge the University Corporation for Atmospheric Research (UCAR) for providing the COSMIC data, IGS community for GPS permanent data and WDC for Ionosphere, Tokyo, National Institute of Information and Communications Technology (NICT) for ionosonde data. This work was supported by Russian Federation President grant MK-2058.2011.5.

Cherniak, Iurii; Zakharenkova, Irina; Shagimuratov, Irk; Suslova, Olga



Photoelectron fluxes in the Martian ionosphere  

NASA Technical Reports Server (NTRS)

Calculations are presented of the steady-state photoelectron distribution in the upper atmosphere of Mars, consistent with the neutral upper atmosphere and ionosphere particle concentrations and temperatures measured by Viking 1. Uncertainties in the calculations affect the thermal electron gas heating rate. Major conclusions are that (1) over most of the altitude range of the Martian ionosphere, the steady-state photoelectron flux amplitude is larger than that in the earth's, so that photoelectron-impact-excited airglow on Mars is generally more significant than it is on earth; (2) the steady-state photoelectron energy distribution in the Martian ionosphere is softer and more structured than that in the terrestrial ionosphere; (3) photoelectron impact ionization contributes about 30% to the total ionization rate in the Martian ionosphere; and (4) photoelectron impact excitation contributes 20-30% of the CO2(+) and CO zenith airglow emissions on Mars.

Mantas, G. P.; Hanson, W. B.



GPS based method of ionospheric study  

NASA Astrophysics Data System (ADS)

The GPS ionospheric sounding is a powerful tool for remote sensing of the ionosphere. The GPS signals have provided an unique opportunity to study the short scale length variations in TEC (Total Electron Content) along the signal path in the presence of ionospheric irregularities and scintillations caused by these irregularities. GPS based ionospheric measurement can measure TEC variations smaller than 10-2 TEC unit. This paper presents the observations of real time TEC and scintillation obtained with dual frequency GPS receiver GSV4004A at Bhopal. The receiver is specially configured to measure amplitude and phase scintillation from the L1 frequency GPS signals and ionospheric TEC from the L1 (1575 MHz) and L2 (1227 MHz) frequency GPS signals. The data for TEC and scintillation have been analyzed and the results for the crest of anomaly region (Bhopal) have been discussed.

Gwal, A. K.; Sarkar, S.; Malhotra, K.


Ionospheric modification by rocket effluents. Final report  

SciTech Connect

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

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



Long-term changes in thermospheric composition inferred from a spectral analysis of ionospheric F-region data  

NASA Astrophysics Data System (ADS)

A study of ionospheric data recorded at Slough/Chilton, UK, from 1935 to 2012, has revealed long-term changes in the relative strength of the annual and semi-annual variability in the ionospheric F2 layer critical frequencies. Comparing these results with data from the southern hemisphere station at Stanley in the Falkland Islands between 1945 and 2012 reveals a trend that appears to be anti-correlated with that at Chilton. The behaviour of foF2 is a function of thermospheric composition and so we argue that the observed long-term changes are driven by composition change. The ionospheric trends share some of their larger features with the trend in the variability of the aa geomagnetic index. Changes to the semi-annual/annual ratio in the Slough/Chilton and Stanley data may therefore be attributable to the variability in geomagnetic activity which controls the average latitudinal extent of the auroral ovals and subsequent thermospheric circulation patterns. Changes in ionospheric composition or thermospheric wind patterns are known to influence the height of the F2 layer at a given location. Long-term changes to the height of the F2 layer have been used to infer an ionospheric response to greenhouse warming. We suggest that our observations may influence such measurements and since the results appear to be dependent on geomagnetic longitude, this could explain why the long-term drifts observed in F2 layer height differ between locations.

Scott, C. J.; Stamper, R.; Rishbeth, H.



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.



Application of computerized tomography to the investigation of ionospheric structures  

Microsoft Academic Search

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

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



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



Saturn: atmosphere, ionosphere, and magnetosphere.  


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



The magnetosphere ionosphere system from the perspective of plasma circulation: A tutorial  

NASA Astrophysics Data System (ADS)

This tutorial review examines the role of O+ in the dynamics of magnetosphere ionosphere coupling. The life cycle of an O+ plasma element is considered as it circulates from the mid- to high-latitude ionosphere. Energization and diversion of the convecting plasma element into outflows involves Alfvénic turbulence at the low-altitude base of the cusp and plasmasheet boundary layer and in downward-current “pressure cookers.” Observational evidence indicating that O+ dominates the plasmasheet and ring current during extreme storm intervals is reviewed. The impacts of an O+-enriched plasma on solar wind magnetosphere ionosphere coupling are considered at both the micro and global scales. A synthesis of results from observation, theory and simulations suggests that the presence of O+ in the magnetosphere is both a disruptive and a moderating agent in maintaining the balance between dayside and nightside magnetic merging.

Lotko, W.



New model of Saturn's ionosphere with an influx of water from the rings  

NASA Technical Reports Server (NTRS)

A radically different model of Saturn's ionosphere is proposed in which water plays a major role as a minor constituent present by downward diffusion from an external source. The model ionosphere is a classical F2 type layer resulting from the photodissociative production of H(+) from H2 and rapid chemical loss by a series of charge exchange reactions with water. A planet-wide influx of about 4 x 10 to the 7th molecules/sq cm/s of water from the rings is consistent with the observed ionospheric electron densities. An enhanced influx of water occurs at latitudes (-38, +44 deg) connected magnetically at the inner edge of Saturn's B ring, where an electromagnetic erosion process takes place. The present-day influx at these latitudes may be as large as 2 x 10 to the 9th molecules/sq cm/s.

Connerney, J. E. P.; Waite, J. H.



TIWS: Thermospheric/Ionospheric Wave Studies  

NASA Astrophysics Data System (ADS)

The proposed TIWS Cubesat is instrumented to remotely sense waves in the upper mesosphere using nadir O2 Atmospheric (0-0) band airglow measurements and ionospheric structure with in-situ ion density measurements. The mesospheric airglow observations will provide a brightness perturbation measurement (I’/I) that is directly related to wave amplitudes. The ratio of the P to R branch within the band will provide a measure of the layer brightness rotational temperature, as well as wave amplitudes (T’/T), but phase shifted to the wave amplitude measured by I’/I. In addition to wave amplitudes, vertical wavelengths (?z) are deduced from the phase difference between I’/I and T’/T. Horizontal wavelengths (?x) are measured only when 2-D information is available such as near observatories, but global measurements of amplitude and ?z, from phase, are independent of ?x. TIWS will also be instrumented with a Retarding Potential Analyzer (RPA). The RPA will nominally be operated in a current mode, related to the ion density and density perturbations along the orbit. Additional modes will be designed for the RPA to periodically determine the ion composition and ion temperature, and to provide a burst mode for gathering high-resolution ion density fluctuation measurements in equatorial spread F. The bus for the 3-U satellite will be the Illinisat-2.

Carlson, C.; Swenson, G. R.; Makela, J. J.; Ghosh, A.; Coverstone, V.; Earle, G.



Functional artificial free-standing yeast biofilms  

Microsoft Academic Search

Here we report fabrication of artificial free-standing yeast biofilms built using sacrificial calcium carbonate-coated templates and layer-by-layer assembly of extracellular matrix-mimicking polyelectrolyte multilayers. The free-standing biofilms are freely floating multilayered films of oppositely charged polyelectrolytes and live cells incorporated in the polyelectrolyte layers. Such biofilms were initially formed on glass substrates of circular and ribbon-like shapes coated with thin layers

Svetlana A. Konnova; Mehmet Kahraman; Alsu I. Zamaleeva; Mustafa Culha; Vesselin N. Paunov; Rawil F. Fakhrullin



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.



Ionospheric imaging using computerized tomography  

SciTech Connect

Computerized tomography (CT) techniques can be used to produce a two-dimensional image of the electron density in the ionosphere. The necessary data are transionospheric satellite beacon total electron content (TEC) data recorded simultaneously at multiple ground stations. The ionospheric imaging case presents a difficult problem due to large amounts of missing data. This is a consequence of the locations of the transmitter (in orbit) and receivers (ground-based) and causes the reconstruction algorithm to fail to correctly reconstruct the background density profile. Despite this limitation, a method has been developed which successfully reconstructs the irregularities and variations in the profile. A computer program simulates the data collection and image reconstruction process. This allows the method to be tested with several electron density models, transmitter and receiver locations, and noniterative and iterative reconstruction algorithms. Simulations are performed assuming a 1,000-km-altitude polar-orbiting satellite and several ground stations. The imaged region is 3,500 km wide by 800 km high. A new algorithm, which is a modification of the discrete backprojection algorithm, is developed for use with nonuniform sampling geometries.

Austen, J.R.



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.



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



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:; Markov, G. A.; Ryabov, A. O. [Lobachevsky Nizhni Novgorod State University (Russian Federation); Parrot, M. [Environment Physics and Chemistry Laboratory (France)



Total Artificial Heart  


... NHLBI on Twitter. What Is a Total Artificial Heart? A total artificial heart (TAH) is a device ... the chest to an outside power source. Normal Heart and CardioWest Total Artificial Heart Figure A shows ...


Coupling between tsunamis and ionosphere: ground-based and space-based observation opportunities  

NASA Astrophysics Data System (ADS)

Large scale phenomena as tsunamis propagating through the ocean excite gravity waves that can reach ionospheric heights. The coupling between the ground/ocean and the atmosphere up to the ionosphere opens the possibility to observe in the upper atmosphere the effects of the propagation of tsunamis. During all recent major tsunami events ionospheric waves have been observed by ground GPS networks, satellite altimeters and, recently, also by an airglow imager. During the tsunami event of 11 March 2011 an all-sky camera in Hawaii observes the Internal Gravity Waves (IGW) during about one-and-a-half hours before the arrival of the, while it was crossing the Pacific Ocean in that region. Collocated ionospheric measurements were also done with GNSS sounding and Jason satellite. We present results of assessment studies of ground-based and space-based ionospheric remote sensing for tsunami propagation monitoring. We analyze the cases of airglow imager, Over-The-Horizon (OTH) radar, GPS, radio occultation and GNSS reflectometry. We describe modeling results of IGW excited by a realistic tsunami propagation model through the ocean near Hawaii. The model includes the propagation of the gravity wave in the atmosphere, the coupling between neutral and charged particles in the ionosphere and the production of the airglow emission at 630.0 nm. Synthetic all-sky images are calculated by integration of the emission along rays from the camera location to though the airglow layer. Additional ground-based observations could be provided by (OTH) radars, which operate in High Frequency (HF) band and can be used to monitor the bottomside ionosphere. Synthetic radar measurements computed using HF numerical ray-tracing confirm the possibility to detect IGW excited by tsunamis. The large coverage of OTH radar and its sensitivity to low-altitude plasma anomalies provides a wide range of observation. Additionally, we analyze the capabilities of space-based radio occultation and GNSS reflectometry to detect the gravity waves excited by tsunamis while measuring satellite-to-satellite TEC. All these techniques open new opportunities of oceanic monitoring through ionospheric monitoring to support classic techniques for tsunami detetion and confirm that the ionospheric tsunami monitoring has now reached a state-of-the-art compatible with its implementation in a space mission.

Coisson, Pierdavide; Makela, Jonathan J.; Occhipinti, Giovanni; Astafyeva, Elvira; alam Kherani, Esfhan; Lognonne, Philippe



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



Magnetic fluctuations in the Martian ionosphere  

NASA Astrophysics Data System (ADS)

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 ( ~ 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, J. R.



Propagation studies using a theoretical ionosphere model  

NASA Technical Reports Server (NTRS)

The mid-latitude ionospheric and neutral atmospheric models are coupled with an advanced three dimensional ray tracing program to see what success would be obtained in predicting the wave propagation conditions and to study to what extent the use of theoretical ionospheric models is practical. The Penn State MK 1 ionospheric model, the Mitra-Rowe D region model, and the Groves' neutral atmospheric model are used throughout this work to represent the real electron densities and collision frequencies. The Faraday rotation and differential Doppler velocities from satellites, the propagation modes for long distance high frequency propagation, the group delays for each mode, the ionospheric absorption, and the spatial loss are all predicted.

Lee, M.



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.



Space weather. Ionospheric control of magnetotail reconnection.  


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



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.


An Ionospheric Metric Study Using Operational Models  

NASA Astrophysics Data System (ADS)

One of the outstanding challenges in upgrading ionospheric operational models is quantifying their improvement. This challenge is not necessarily an absolute accuracy one, but rather answering the question, "Is the newest operational model an improvement over its predecessor under operational scenarios?" There are few documented cases where ionospheric models are compared either with each other or against "ground truth". For example a CEDAR workshop team, PRIMO, spent almost a decade carrying out a models comparison with ionosonde and incoherent scatter radar measurements from the Millstone Hill, Massachusetts location [Anderson et al.,1998]. The result of this study was that all models were different and specific conditions could be found when each was the "best" model. Similarly, a National Space Weather Metrics ionospheric challenge was held and results were presented at a National Space Weather meeting. The results were again found to be open to interpretation, and issues with the value of the specific metrics were raised (Fuller-Rowell, private communication, 2003). Hence, unlike the tropospheric weather community, who have established metrics and exercised them on new models over many decades to quantify improvement, the ionospheric community has not yet settled on a metric of both scientific and operational value. We report on a study in which metrics were used to compare various forms of the International Reference Ionosphere (IRI), the Ionospheric Forecast Model (IFM), and the Utah State University Global Assimilation of Ionospheric Measurements Model (USU-GAIM) models. The ground truth for this study was a group of 11 ionosonde data sets taken between 20 March and 19 April 2004. The metric parameter was the ionosphere's critical frequency. The metric was referenced to the IRI. Hence, the study addressed the specific question what improvement does IFM and USU-GAIM have over IRI. Both strengths (improvements) and weaknesses of these models are discussed. These discussions address both scientific merit as well as operational considerations.

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



Observations of Ionospheric Currents at Mars  

NASA Astrophysics Data System (ADS)

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

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



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.



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:; Belov, A. S., E-mail: [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)



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.



Comparison of topside ionospheric profilers for use in modelling and monitoring applications  

NASA Astrophysics Data System (ADS)

Ground-based ionosonde measurements can be used to determine the electron density profile up to the ionospheric density peak, hmF2, only. In order to reconstruct a complete, full-height electron density profile, a model is usually needed for the shape of the topside ionospheric density. Different shapes have been used over the years, most frequently the so-called Chapman- and Epstein-layers. We use topside sounder data to evaluate the quality of the fit obtained by using profiles with different shapes and determine which profile provides the best fit. While the topside sounder database available at the US National Space Science Data Center is quite extensive, it is also very inhomogeneous. Data availability varies widely with local time, day of year, latitude and longitude. Measurements have been obtained over a period spanning more than a full solar cycle but the data coverage is irregular during different levels of solar activity. All these issues cause difficulties in correctly interpreting the results of the data analyses. Also, it must be taken into account that the provided data comes from different satellites, which orbited at different heights. This, too, can cause some biases in the results. These complications are investigated and, if necessary, compensated for. The correlations between the shape of the topside electron density profile and several possible factors that might influence this shape are also investigated. This includes geomagnetic indices (Kp and Dst), solar activity (indicated by F10.7), time of day, day of year and magnetic longitude and latitude. Finally, also the interdependencies of different characteristics of the ionosphere are discussed. For example, if the boundary between the ionosphere and plasmasphere is lower it could be expected that not only the scale height of the topside density changes, but also the shape of the density profile. Results are applied into further improving the RMI ionospheric monitoring service LIEDR (Local Ionospheric Electron Density profile Reconstruction).

Verhulst, Tobias; Stankov, Stan



Effect of vertical plasma transport on ionospheric F2-region parameters at equatorial latitude  

NASA Astrophysics Data System (ADS)

The variability of the F2-layer even during magnetically quiet times are fairly complex owing to the effects of plasma transport. The vertical E × B drift velocities (estimated from simplified electron density continuity equation) were used to investigate the seasonal effects of the vertical ion drifts on the bottomside daytime ionospheric parameters over an equatorial latitude in West Africa, Ibadan, Nigeria (Geographic: 7.4°N, 3.9°E, dip angle: 6°S) using 1 year of ionsonde data during International Geophysical Year (IGY) of 1958, that correspond to a period of high solar activity for quiet conditions. The variation patterns between the changes of the vertical ion drifts and the ionospheric F2-layer parameters, especially; foF2 and hmF2 are seen remarkable. On the other hand, we observed strong anti-correlation between vertical drift velocities and h?F in all the seasons. We found no clear trend between NmF2 and hmF2 variations. The yearly average value of upward daytime drift at 300 km altitude was a little less than the generally reported magnitude of 20 ms-1 for equatorial F-region in published literature, and the largest upward velocity was roughly 32 ms-1. Our results indicate that vertical plasma drifts; ionospheric F2-layer peak height, and the critical frequency of F2-layer appear to be somewhat interconnected.

Oyekola, O. S.; Ojo, Akin


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


Main ionospheric trough as a duct of energy between ionosphere and magnetosphere region  

NASA Astrophysics Data System (ADS)

The mid-latitude electron density trough observed in the topside ionosphere has been shown to be the near-Earth signature of the plasmapause and can provide useful information about the magnetosphere-ionosphere dynamics and morphology. Thus for present the evolution of ionospheric trough in time and space domain we need some multipoint measurements and different type of measurements techniques. To develop a quantitative model of evolution ionospheric trough features during geomagnetic disturbances the analyse of particle and waves in situ measurements and TEC data was carried out. The high resolutions plasma particle diagnostics and wave diagnostics located on board of currently operated satellite DEMETER can give us precisely description of trough signatures and instabilities at define point in space. On the other hand GPS permanent networks such as IGS and EPN provide regular monitoring of the ionosphere in a global scale. The aim of this paper is to present some general behaviour of trough dynamics as well as the fine structures of ionospheric trough and discuss the different type of instability generated inside the trough region from ULF frequency range thru VLF up to HF frequency range. In order to better understand the physical conditions and evolution of ionosphere trough region and describe the coupling between ionosphere and inner magnetosphere the detail examination of geomagnetic storm in January 2005 is presented. As a consequence of different time scales of physical processes occurred in the near Earth environment during geomagnetic disturbances and energy transfer between ionosphere and magnetosphere the examination of ion end electron fluxes inside ionosphere trough are disused.

Rothkaehl, Hanna; Czajkowski, Tomasz; Grzesiak, Marcin; S?omi?ska, Ewa; Wronowski, Roman; S?omi?ski, Jan; Koperski, Piotr; Krankowski, Andrzej



Fractal analysis of RF signals scattered by small-scale ionospheric irregularities  

NASA Astrophysics Data System (ADS)

The fractal dimension as a characteristic of an experimental data series is considered. The correlation integral method is used for dimension calculation. It is shown that by the fractal dimension one can identify a variety of ionospheric processes even when the conventional spectral analysis fails. It is found that the realizations corresponding to volume scattering by natural and artificial irregularities have finite dimension, which is significantly different. A technique for preparing experimental data to be processed by the correlation integral method is developed. The influence of the data sampling rate and signal-to-noise ratio on the dimension is analyzed.

Bulgakov, S. A.; Ponomarenko, P. V.; Yampolsky, Yu. M.



Role of Ionospheric Plasmas in Earth's Magnetotail  

NASA Technical Reports Server (NTRS)

This tutorial will summarize observations and theories indicating a prominent role of ionospheric plasma in the Earth's magnetotail. At the Global scale, I will argue that it is ionospheric plasma momentum and dynamic pressure that are responsible for the production of plasmoids, through the action of a transient near-Earth neutral or X-line, which serves to release excessive plasma pressure from the magnetotail field. Ionospheric plasma gains the momentum and energy to produce plasmoids and their related effects through its interaction with the solar wind, beginning at the dayside reconnection region and extending across the polar caps through the magnetotail lobes. This distant neutral line can be depicted as a feature much like that found in cometary magnetospheres, where disconnection limits the amount of IMF hung up on the cometary coma. On the other hand, the near-Earth neutral one can be seen as a feature unique to planets with an intrinsic magnetic field and internal source of plasma, the heating of which produces pressures too large to be restrained. Ionospheric plasmas also have other more local roles to play in the magnetotail. The circulation influences the composition of the plasma sheet, and the resultant wave environment, giving rise to reduced wave propagation speeds. Important heavy ion cyclotron resonances, and enhanced finite gyro-radius effects including non-adiabatic particle acceleration. At minimum, the presence of ionospheric plasma must influence the rate of reconnection via its enhanced mass density. Other non-MHD effects of ionospheric plasma presence are likely to be important but need much more investigation to be well understood. The MMS mission is designed to penetrate the subtle diffusion region physics that is involved, and its ability to observe ionospheric plasma involvement in reconnection will contribute significantly toward that goal.

Moore, Thomas E.



Case studies of the dynamics of ionospheric ions in the Earth's magnetotail  

NASA Astrophysics Data System (ADS)

This paper presents case studies of the dynamics of the terrestrial ions in the midplasma sheet and inside the lobes (˜17-19 RE). The high time resolution measurements of H+, He+, and O+ ions made on board Cluster show that these ions are massively injected into the tail during substorms/storms from the nightside ionosphere and mainly dispersed by time of flight effects; a single oxygen injection being able to account for over 80% of the oxygen population of the midtail plasma sheet during storm time. Inside the lobes, during disturbed times, ionospheric oxygen ions appear as nearly monoenergetic beams, quasi field-aligned, propagating antisunward from the ionosphere, as expected from the "cleft ion fountain." Most of the time, the ionospheric protons are very cold and their distribution function is not fully measurable by a charged spacecraft. However, we show that protons can, at times, acquire a large drift motion, reach energy larger than 30 eV, and be directly measurable by the CIS spectrometers. This occurs when large disturbances propagate in the plasma sheet boundary layer during both quiet and disturbed periods. We show that the large, variable, Alfvén waves generated by these plasma sheet disturbances modulate the energy of lobe protons and oxygen ions and inject electromagnetic energy, in excess of 15 × 10-3 W/m2, down to the polar cap. Deeper inside the plasma sheet boundary layer, large electric fields associated with the Earthward stream of plasma sheet particles give enough drift energy to a very cold ionospheric proton population to become fully detectable by the Cluster ion spectrometers.

Sauvaud, J.-A.; Louarn, P.; Fruit, G.; Stenuit, H.; Vallat, C.; Dandouras, J.; RèMe, H.; André, M.; Balogh, A.; Dunlop, M.; Kistler, L.; MöBius, E.; Mouikis, C.; Klecker, B.; Parks, G. K.; McFadden, J.; Carlson, C.; Marcucci, F.; Pallocchia, G.; Lundin, R.; Korth, A.; McCarthy, M.



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.



Heating of ionospheric ion beams in inverted-V structures  

NASA Astrophysics Data System (ADS)

Beams of H+, He+, and O+ ions have been observed when the four Cluster satellites crossed the high-latitude plasma sheet boundary layer at ˜4 RE. These beams appear as inverted-V structures in the energy flux time spectrograms. The pitch angles of the beams range from ˜0 to 30° indicating the ions are streaming along the magnetic field out of the ionosphere. The streaming velocity is a few tens of km/s to several hundred km/s, consistent with the beams having gone through a potential drop of several tens of eV to a few keV. These beams are intense with beam to ambient density ratios, ?nb/nT, as large as ˜0.3. The beams are hotter than the ionospheric ion thermal energy, indicating the ions have been heated while accelerated along the magnetic field. We present first results that show the ions tend to be hotter at the peak (several hundred eV) than at the start of the inverted-V structures (a few tens of eV). These results interpreted in terms of a U-shaped potential structure indicate the hottest ions come from the central region where the potential difference is maximum.

Cui, Y. B.; Fu, S. Y.; Parks, G. K.



A Miniature Sweeping Impedance Probe for Ionospheric Plasma Diagnostics  

NASA Astrophysics Data System (ADS)

The impedance of a probe immersed in ionospheric plasma at radio frequencies is an important technique for determining absolute electron density. Building on 50 years of history in developing and flying RF probes for plasma diagnostics at Utah State, a new SIP (Sweeping Impedance Probe) design has been completed which will obtain qualitative improvement over previous instruments in terms of accuracy and sweep rate. This instrument will provide a continuous measurement of the plasma impedance magnitude and phase with an expected accuracy of 1% and 1 degree respectively over the 1 to 20 MHz range. This new SIP will be launched in January 2014 onboard the Auroral Spatial Structures Probe (ASSP) NASA sounding rocket mission using a short monopole probe. The rocket apogee of 600 km will allow the characterization of the plasma in the E and F layers at auroral latitudes and the study of short term and spatial variations along the high-altitude profile of the sounding rocket. Although this SIP design has been developed for a sounding rocket, it can be optimized and miniaturized for Cubesat's and included along other ionospheric diagnostic instruments such as double and Langmuir probes. This presentation is focused on the overall design of the instrument, the tests results for the ASSP instrument and conceptual designs for future CubeSat mission similar to the NSF DICE mission.

Martin-Hidalgo, J.; Swenson, C.



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.



Models of ionospheric VLF absorption of powerful ground based transmitters  

E-print Network

the variability of the ionospheric electron density. We conclude that the global effect of irregularity scattering that the ionospheric electron density profile ass in precipitation of energetic Van Allen electrons. Initial analyses of the contribution of VLF transmitters


Modeling the Electrodynamics of the Low-Latitude Ionosphere.  

National Technical Information Service (NTIS)

The electrodynamics of the Earth's low-latitude ionosphere is dependent on the ionospheric conductivity and the thermospheric neutral density, temperature, and winds present. This two-part study focused on the gravity wave seeding mechanism of equatorial ...

C. S. Wohlwend



Results From YOUTHSAT - Indian experiment in earths thermosphere-ionosphere region.  

NASA Astrophysics Data System (ADS)

It is known that the characterization and modeling of the ionosphere/thermosphere necessitates a comprehensive understanding of the various processes prevailing therein. India’s first, indigenous and dedicated aeronomy satellite 'YOUTHSAT' carrying two Indian payloads - RaBIT (Radio Beacon for Ionospheric Tomography), and LiVHySI (Limb Viewing Hyper Spectral Imager) and one Russian payload SOLRAD, was conceived primarily to address to this aspect and launched on April 20, 2011 in an 818 Km polar orbit from SHAR on ISRO launch vehicle PSLV. The payloads RaBIT and LiVHySI were designed specifically to observe the ionised and neutral components of the upper atmosphere respectively. YOUTHSAT is a small satellite quiet advanced in its class having all the functionalities which are normally associated with a bigger satellite. The rising phase of the 23rd solar cycle was considered to be the best window for various observations from onboard YOUTHSAT. As an Indo Russian endeavour, it was launched with an objective of investigating the terrestrial upper atmosphere vis-a-vis the activity on the sun. RaBIT, an ISRO venture, is a radio beacon emitting coherent radio signal at 150 and 400 MHz frequencies. These are received using a chain of five receivers deployed along the ~76oE meridian at Trivandrum, Bangalore, Hyderabad, Bhopal and Delhi. The receivers estimate the Total Electron Content (TEC) of the ionosphere through the relative phase change of the received radio signals. The TECs thus estimated near simultaneously, are used to generate a tomogram, which gives an Altitude-Latitude distribution of the ionospheric electron density. For YOUTHSAT configuration, the tomogram covers the ionosphere from a few degrees (5-6o) south of Trivandrum to about 3-4o north of Delhi depending upon the satellite elevation. The RaBIT tomography network is by far the longest network existing anywhere in the world, and is unique therefore. Through RaBIT, a unique dataset leading to ionospheric tomograms representing altitude-latitude variation of electron density over the 77oE meridian over the Indian region has been generated around specific times (~10:30 AM/PM). These tomograms have provided, among others: (a) First ever images of the ionospheric nighttime ESF irregularities (b) Quantification of the topside F3 ionospheric layers using Tomography (c) Evidence of wavelike modulations in the overall low and equatorial ionospheric region using tomography (d) Day and night differences in the electron density distribution, (e) Evidence of the presence of the ionospheric top-side layer (f) Modulations in the ionosphere due to space weather activity and (g) Direct evidence of the presence of Travelling Atmospheric Disturbance (TAD). YOUTHSAT recently completed its mission life time of about two years, after having generated a comprehensive set of data on terrestrial upper atmosphere. The YOUTHSAT data are being analysed by various researchers and more results providing a new insight into the upper atmospheric processes are in offing. Some of the important outcomes mentioned above will be discussed in detail.

Tarun Kumar, Pant


Electron-density irregularities in the day-time equatorial ionosphere  

Microsoft Academic Search

Electron-density irregularities have been observed in the day-time equatorial ionosphere using probe experiments carried out in the payloads of two rockets launched near Lima, Peru during Project Condor, 1983. Simultaneous observations of the mesosphere and upper E-region were obtained using the radar at Jicamarca. A layer of mesospheric irregularities is identified as originating in neutral atmosphere turbulence. In the electrojet

L. G. Smith; O. Royrvik



A large-scale traveling ionospheric disturbance during the magnetic storm of 15 September 1999  

Microsoft Academic Search

Using a comprehensive data set and model calculations, we have investigated a prominent large-scale traveling ionospheric disturbance (LSTID) observed in Japan (?37°–16° MLAT) on 15 September 1999, during a recovery phase of sequential storms. The LSTID was detected at 2300–2400 LT (1400–1500 UT) as an enhancement of the 630-nm airglow intensity (50?350 R), a decrease in the F layer virtual

K. Shiokawa; Y. Otsuka; T. Ogawa; N. Balan; K. Igarashi; A. J. Ridley; D. J. Knipp; A. Saito; K. Yumoto



Lower ionospheric sounding by the use of LoranC signals  

Microsoft Academic Search

An investigation is conducted concerning the use of pulsed 100 kHz radio signals, developed for Loran-C navigation systems, in studies of the geophysical characteristics of the lower ionosphere below the E layer. The investigation included an observation of Loran-C signals which were transmitted from a station at Iwo Jima, at a distance of about 1177 km from the receiving station.

A. Iwata; H. Ishikawa



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



A theoretical study of the ionosphere over Zhongshan Station, Antarctica  

Microsoft Academic Search

A three-dimensional, time-dependent model for the polar ionosphere has been developed. The simulation results are applied to the interpretation of the ionospheric F region over Zhongshan Station. The daily variation is obtained for the high-latitude global polar ionosphere NmF2, mainly taking into account the interaction between the solar EUV ionization and the ionospheric convection processes in the polar region. It

B. Zhang; R. Liu; H. Yang; Z. Chen



Experimental evidence of electromagnetic pollution of ionosphere  

NASA Astrophysics Data System (ADS)

The Earth’s ionosphere responds to external perturbations originated mainly in the Sun, which is the primary driver of the space weather (SW). But solar activity influences on the ionosphere and the Earth's atmosphere (i.e., the energy transfer in the direction of the Sun-magnetosphere-ionosphere-atmosphere-surface of the Earth), though important, is not a unique factor affecting its state - there is also a significant impact of the powerful natural and anthropogenic processes, which occur on the Earth’s surface and propagating in opposite direction along the Earth’s surface-atmosphere-ionosphere-magnetosphere chain. Numerous experimental data confirm that the powerful sources and consumers of electrical energy (radio transmitters, power plants, power lines and industrial objects) cause different ionospheric phenomena, for example, changes of the electromagnetic (EM) field and plasma in the ionosphere, and affect on the state of the Earth atmosphere. Anthropogenic EM effects in the ionosphere are already observed by the scientific satellites and the consequences of their impact on the ionosphere are not currently known. Therefore, it is very important and urgent task to conduct the statistically significant research of the ionospheric parameters variations due to the influence of the powerful man-made factors, primarily owing to substantial increase of the EM energy production. Naturally, the satellite monitoring of the ionosphere and magnetosphere in the frequency range from tens of hertz to tens of MHz with wide ground support offers the best opportunity to observe the EM energy release, both in the global and local scales. Parasitic EM radiation from the power supply lines, when entering the ionosphere-magnetosphere system, might have an impact on the electron population in the radiation belt. Its interaction with trapped particles will change their energy and pitch angles; as a result particle precipitations might occur. Observations of EM emission by multiple low orbiting satellites have confirmed a significant increase in their intensity over the populated areas of Europe and Asia. Recently, there are many experimental evidences of the existence of power line harmonic radiation (PLHR) in the ionosphere. Their spectra consist of succession of 50 (60) Hz harmonics which is accompanied by a set of lines separated by 50 (60) or 100 (120) Hz - the central frequency of which is shifted to high frequency. These lines cover rather wide band - according to the available experimental data, their central frequencies are observed from ~1.5 - 3 kHz up to 15 kHz, and recently the main mains frequencies are also observed. The examples of power line harmonic radiation, which were detected by “Sich-1M”, “Chibis-M” and “Demeter” satellites, have been presented and discussed. The available experimental data, as well as theoretical estimations, allow us with a high degree of certainty to say that the permanent satellite monitoring of the ionospheric and magnetospheric anthropogenic EM perturbations is necessary for: a) objective assessment and prediction of the space weather conditions; b) evaluation of the daily or seasonal changes in the level of energy consumption; c) construction of a map for estimation of near space EM pollution. This study is partially supported by SSAU contract N 4-03/13.

Pronenko, Vira; Korepanov, Valery; Dudkin, Denis


Mesoscale ionospheric tomography at the Auroral region  

NASA Astrophysics Data System (ADS)

FMI (Finnish Meteorological Institute) has used observations from the dense GNSS network in Finland for high resolution regional ionospheric tomography. The observation system used in this work is the VRS (Virtual Reference Station) network in Finland operated by Geotrim Ltd. This network contains 86 GNSS ground stations providing two frequency GPS and GLONASS observations with the sampling rate of 1 Hz. The network covers the whole Finland and the sampling of the ionosphere is very good for observing mesoscale ionospheric structures at the Auroral region. The ionospheric tomography software used by FMI is the MIDAS (Multi-Instrument Data Analysis System) algorithm developed and implemented by the University of Bath (Mitchell and Spencer, 2003). MIDAS is a 3-D extension of the 2-D tomography algorithm originally presented by Fremouw et al. (1992). The research at FMI is based on ground based GNSS data collected in December 2006. The impacts of the two geomagnetic storms during the month are clearly visible in the retrieved electron density and TEC maps and they can be correlated with the magnetic field disturbances measured by the IMAGE magnetometer network. This is the first time that mesoscale structures in the ionospheric plasma can be detected from ground based GNSS observations at the Auroral region. The continuous high rate observation data from the Geotrim network allows monitoring of the temporal evolution of these structures throughout the storms. Validation of the high resolution electron density and TEC maps is a challenge as independent reference observations with a similar resolution are not available. FMI has compared the 3-D electron density maps against the 2-D electron density plots retrieved from the observations from the Ionospheric Tomography Chain operated by the Sodankylä Geophysical Observatory (SGO). Additional validation has been performed with intercomparisons with observations from the ground based magnetometer and auroral camera network (MIRACLE), riometers, and the ionosonde station at SGO. This presentation will show the results from the ionospheric tomography research at FMI. References: Fremouw, E., J. Secan and B. Howe (1992): Application of stochastic inverse theory to ionospheric tomography, Radio Sci., 27(5), 721-732. Mitchell, C.N. and Spencer, P.S.J. (2003): A three-dimensional time-dependent algorithm for ionospheric imaging using GPS, Ann. Geophys., 46, 687-696.

Luntama, J.; Kokkatil, G. V.



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


Solar rotation effects on the Martian ionosphere  

NASA Astrophysics Data System (ADS)

present a detailed investigation of the solar rotation effects on the Martian high-latitude (~63°N-81°N) ionosphere using the electron density (Ne) data measured by Mars Global Surveyor and solar XUV and EUV fluxes measured by SOHO under high (2000-2001), medium (2003), and low (2005) solar activity conditions. A fast Fourier transform spectral analysis method is used to estimate the amplitude of the rotation period in these parameters. This method clearly reveals the presence of solar rotation effects in the Martian ionospheric Ne at all altitudes (90-220 km), peak electron density (NmM2), and total electron content under the three solar activity conditions. These effects are in phase with the solar UV fluxes (corrected for the Martian orbit). The period of rotation effect (~26 days) is the same at all altitudes, though its amplitude is strongest at the ionospheric M2 peak (~135-140 km, ~3.5-6% of the mean values) and has a secondary enhancement at the M1 peak (~110-115 km). The effect of solar rotation on the M2 peak is larger during medium solar activity (2003) than during high solar activity (2000-2001). The effect, however, is absent in the ionospheric peak height (hmM2). The rotation effects on Mars are also compared with those on the Earth. Unlike at Mars, the Earth's high-latitude ionosphere shows no clear solar rotation effect, though the effect is observed clearly at lower latitudes.

Venkateswara Rao, N.; Balan, N.; Patra, A. K.



Modelling the high-latitude ionosphere  

NASA Technical Reports Server (NTRS)

Results of an ionospheric model program are presented which demonstrate the extreme variability of the steady state, daytime, ionospheric F region electron density and ion composition due to both neutral atmospheric changes with solar cycle, season and magnetic activity, and to the effects of ionospheric drifts caused by perpendicular electric fields. Consideration is given to the time history of the ionospheric plasma as it undergoes convective motion due to the combined effects of corotation forces and electromagnetic forces which results from the mapping of the magnetospheric cross tail electric field to the rotating ionosphere. A simple model of the convection pattern is described. The model calculates the net effect of the tendency for the plasma to corotate about the geographic pole and the E sub Bar times B sub Bar velocity induced by a perpendicular electric field mapped to a circle centered about a point 5 deg antisunward of the geomagnetic pole and oriented such that the equipotentials are parallel to the noon midnight meridian. This convection pattern shows the generally accepted features of high latitude convection, but because of the offset between the geographic and geomagnetic poles a marked universal time dependence in these features is predicted.

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



Ion clusters and the Venus ultraviolet haze layer  

NASA Technical Reports Server (NTRS)

The daytime ionosphere of Venus is observed between 100 and 500 km altitude with a peak electron concentration of 100,000/cc at 140 km. It is suggested that at altitudes less than 130 km the ion CO2(+)-CO2 is an important ionic constituent of the Venus ionosphere. Below 100 km ion clustering processes combine with the low temperature at the mesopause to form coagulates, giving rise to the ultraviolet haze layer observed. An atmospheric model is presented.

Aikin, A. C.



Modeling scattering from lightning-induced ionospheric disturbances with the discontinuous Galerkin method  

NASA Astrophysics Data System (ADS)

Simulation of the propagation of very low frequency (VLF) waves in the Earth-ionosphere waveguide remains a significant computational challenge as a result of the variable wavelength at these frequencies in the magnetized plasma environment of the lower ionosphere. The discontinuous Galerkin (DG) method is naturally and easily adapted to nonuniform grids and so is ideal for simulation in media where the characteristic length scale varies significantly. We present an automatic procedure based on minimal system realization to incorporate any linear, anisotropic dispersive material in the DG framework, with application to a perfectly matched layer and scattering from strong disturbances in a magnetoplasma. We apply these techniques to modeling of scattering from lightning electromagnetic pulse-induced ionospheric disturbances, calculating the full 3-D scattered VLF wavefields from intense lightning-induced ionospheric perturbations over a large volume. We plot the spatial distribution of the phase and amplitude response as seen by a ground-based receiver over a large area. The results are consistent with previous results from 2-D models, showing maximum received signal strength amplitude perturbations on the order of 0.1 to 0.2 dB for intense vertical discharges under smooth ambient conditions and on the order of 0.5 dB for very intense, repeated horizontal discharges.

Foust, F. R.; Spasojevic, M.; Bell, T. F.; Inan, U. S.



Opportunities investigating the thermosphere/ionosphere system by low Earth orbiting satellite missions (Invited)  

NASA Astrophysics Data System (ADS)

New opportunities for investigating the thermosphere/ionosphere interactions arise from in situ measurements on board low Earth orbiting satellites. Ten years of successful operation of the CHAMP satellite mission at a unique orbit altitude of about 400 km revealed many interesting features of the coupling between the thermosphere and ionosphere and the different atmospheric layers. Examples are the investigations of signatures of stratospheric warming events that are known to change significantly the dynamics of the equatorial ionosphere. It was shown that these modifications are due to an enhancement of lunar tidal effects, e.g. reflected in the thermospheric zonal wind, in the equatorial electroje or in the eastward electric field. Another topic concerns the energy deposit in the F-region though cooling of the thermal electron gas caused by elastic and inelastic processes (Schunk and Nagy, 2009). We find that a significant deposition is present during day at mid latitudes. At low latitudes the energy flux remain important until midnight. Observed heating rates depend on the satellite altitudes, but they are globally available from the CHAMP data. Further enhanced investigations are expected from ESA's three-satellite Swarm mission with a launch planned in 2014. The mission will provide observations of electron density, electron and ion temperature, ion drift and the electric field together with neutral density and winds. High-precision magnetic field observations will allow monitoring ionospheric currents.

Stolle, C.; Park, J.; Luhr, H.



A theoretical model of artificial spread F echoes  

NASA Technical Reports Server (NTRS)

A theoretical model is developed for artificial spread F echoes elicited by irradiating the ionospheric F region with signals from ground-based HF transmitters. Account is taken of the irregularity polarizations, scale length and the magnetic dip angle of the echo. Ray tracing equations are defined for wave propagation in a horizontally stratified ionosphere which has been bathed with HF signals and therefore contains wavelike structures. Irregularities polarized within the meridian plane are found to cause the spread F echoes, while perpendicularly polarized irregularities do not. A magnetic dip angle of 5 deg must be exceeded for the spread F to become strong. The irregularities need scale lengths exceeding 100 m. Modes of operation are identified for inducing the required spread F echoes using ground-based radiotelescopes.

Kuo, S. P.; Kuo, S. C.; Lee, M. C.



Plasma Waves in an Inhomogeneous Ionosphere Carl Caleman  

E-print Network

Plasma Waves in an Inhomogeneous Ionosphere Carl Caleman 8th April 2003 #12;Abstract The inhomogeneity of space plasma is the cause of interesting physical phenomena. The plasma in our ionosphere waves reaches the ionosphere, interacts with the local plasma there, and are reflected back again one



E-print Network

WHISTLER-MODE PROPAGATION IN THE COLLISIONAL IONOSPHERE OF VENUS R. J. Strangeway Institute identified as whistler-mode waves have been observed in the nightside ionosphere of Venus by the Pioneer Venus Orbiter. These waves are propagating in a collisional, weakly magnetized ionosphere, and it has

Strangeway, Robert J.


Development and use of a GPS ionospheric scintillation monitor  

Microsoft Academic Search

Global Positioning System (GPS) satellite signals provide convenient radio beacons for ionospheric studies. Among other propagation phenomena, the ionosphere affects GPS signal propagation through amplitude scintillations that develop after radio waves propagate through ionospheric electron density irregularities. This paper outlines the design, testing, and operation of a specialized GPS receiver to monitor L-band amplitude scintillations: the Cornell scintillation monitor. The

Theodore L. Beach; Paul M. Kintner



Ionospheric Clutter Suppression in HF Surface Wave Radar  

Microsoft Academic Search

The ionospheric clutter has been proved to be one of the dominant clutters degrading the performance of the HF surface-wave radar (HFSWR) severely, so suppressing the ionospheric clutter is a vital part of radar signal processing sequence. In this paper, the spatial characteristics of the ionospheric clutter in a planar array are analyzed, then a new orthogonal projection method with

M. Wu; B. Y. Wen; H. Zhou



Higher order ionospheric propagation effects on GPS radio occultation signals  

Microsoft Academic Search

With the increasing number of remote sensing satellites using the GPS radio occultation technique for atmospheric sounding, the estimation of higher order ionospheric effects and their mitigation have become relevant and important. Due to long ionospheric limb paths, GPS signals are strongly affected by ionospheric refraction during radio occultation. Standard dual-frequency GPS measurements may be used to estimate the first

M. Mainul Hoque; N. Jakowski



Estimating and Removing Ionospheric Effects From GESS Interferometric SAR Imagery  

Microsoft Academic Search

Many users of differential interferometry report image artifacts that cannot be attributed to surface deformation or terrain mismodeling. These artifacts are often ascribed to propagation delays due to the atmosphere or ionosphere. When atmospheric (primarily wet troposphere) delays can be ruled out, the ionosphere is usually blamed for the artifacts. There is rarely sufficient knowledge of the ionosphere at the

A. P. Freedman; S. N. Madsen



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

NASA Astrophysics Data System (ADS)

An atypical nighttime spread-F structure is observed on ionograms at or above the F2 trace, near the crest of the ionospheric equatorial ionization anomaly (EIA) region. This ionospheric atypical spread-F phenomenon was observed using two closed spaced (˜115 km) ionospheric soundings stations located in Sao Jose dos Campos (23.21°S, 45.97°W) and Cachoeira Paulista (22.70°S, 45.01°W), Brazil, in a low-latitude station (near the southern crest of the EIA region), during nighttime, low solar activity, and quiet geomagnetic conditions. This structure, in the initial phase, appears in the ionogram as a faint spread-F trace above or at the F2-layer peak height. After a few minutes, it develops into a strong spread-F trace, and afterwards, it moves to altitudes below the F2-layer peak heights. Finally, the atypical nighttime F-layer trace structure may remain for a while between the F-layer bottom side and peak height or can move to an altitude above the F-layer peak height, and then it disappears. In order to have a comprehensive view of the ionospheric environment characterizing the phenomenon under study, complementary data from six GPS station were used to investigate the ionosphere environment conditions, during both events. The six GPS stations used in this study are distributed from near the equatorial region to low latitudes and provide evidence that the atypical nighttime spread-F structures are not related with large scale equatorial irregularities (plasma bubbles).

Fagundes, P. R.; Bittencourt, J. A.; de Abreu, A. J.; Moor, L. P.; Muella, M. T. A. H.; Sahai, Y.; Abalde, J. R.; Pezzopane, M.; Sobral, J. H. A.; Abdu, M. A.; Pimenta, A. A.; Amorim, D. C. M.



Research on artificial meteor trail emergency communication  

NASA Astrophysics Data System (ADS)

As the particles known as meteors enter the earth's atmosphere, a small fraction of which can form ionized cloud, this ionized cloud has property useful for reflecting electromagnetic wave. Meteor burst communication is a point to point communication technology base on the above principle. Similarly, artificial meteor trail communication establishes “ionized cloud” signal channel by alkali metal ionizing at high-altitude ionosphere to reflect electromagnetic waves. Currently, Meteor burst communication is a mature communication technology with many advantages. However, as a completely uncontrollable natural phenomena, the communication time, duration time, the amount of information transmitted and antenna alignment direction are all uncontrollable. We can only figure out key parameters such as throughput and waiting time within a certain time relying on statistical regularities. Information transmission between specified sites in certain time is impossible to predict accurately. These disadvantages greatly reduce the dependability of meteor trail communication and cannot meet emergency communication’s requirements for real-time, controllable and uninterrupted. Artificial meteor trail emergency communication technology solves the above problems, it’s a reliable emergency telecommunication method. This paper focuses on the necessity and feasibility of artificial meteor trail emergency communication technology, as well as its future application.

Juntao, Liu; Xijun, Yan; Li, Jia


Simultaneous Multi-angle Radar Observations of Langmuir Turbulence Excited by RF Ionospheric Interactions at HAARP  

NASA Astrophysics Data System (ADS)

The high power HAARP HF transmitter is employed to generate and study strong Langmuir turbulence (SLT) in the interaction region of overdense ionospheric plasma. Diagnostics included the Modular UHF Ionospheric Radar (MUIR) sited at HAARP, the SuperDARN-Kodiak HF radar, and HF receivers to record stimulated electromagnetic emissions (SEE). Dependence of diagnostic signals on HAARP HF parameters, including pulselength, duty-cycle, aspect angle, and frequency were recorded. Short pulse, low duty cycle experiments demonstrate control of artificial field-aligned irregularities (AFAI) and isolation of ponderomotive effects. Among the effects observed and studied are: SLT spectra including cascade, collapse, and co-existence spectra and an outshifted plasma line under certain ionospheric conditions. High time resolution studies of the temporal evolution of the plasma line reveal the appearance of an overshoot effect on ponderomotive timescales. Bursty turbulence is observed in the collapse and cascade lines. For the first time, simultaneous multi-angle radar measurements of plasma line spectra are recorded demonstrating marked dependence on aspect angle with the strongest interaction region observed displaced southward of the HF zenith pointing angle. Numerous measurements of the outshifted plasma line are observed. Experimental results are compared to previous high latitude experiments and predictions from recent modeling efforts.

Sheerin, J. P.; Watanabe, N.; Rayyan, N.; Spry, D.; Adham, N.; Watkins, B. J.; Bristow, W. A.; Spaleta, J.; Bernhardt, P. A.



Multi-angle Spectra Evolution of Langmuir Turbulence Excited by RF Ionospheric Interactions at HAARP  

NASA Astrophysics Data System (ADS)

The high power HAARP HF transmitter is employed to generate and study strong Langmuir turbulence (SLT) in the interaction region of overdense ionospheric plasma. Diagnostics included the Modular UHF Ionospheric Radar (MUIR) sited at HAARP, the SuperDARN-Kodiak HF radar, and HF receivers to record stimulated electromagnetic emissions (SEE). Dependence of diagnostic signals on HAARP HF parameters, including pulselength, duty-cycle, aspect angle, and frequency were recorded. Short pulse, low duty cycle experiments demonstrate control of artificial field-aligned irregularities (AFAI) and isolation of ponderomotive effects. Among the effects observed and studied are: SLT spectra including cascade, collapse, and co-existence spectra and an outshifted plasma line under certain ionospheric conditions. High time resolution studies of the temporal evolution of the plasma line reveal the appearance of an overshoot effect on ponderomotive timescales. Bursty turbulence is observed in the collapse and cascade lines. For the first time, simultaneous multi-angle radar measurements of plasma line spectra are recorded demonstrating marked dependence on aspect angle with the strongest interaction region observed displaced southward of the HF zenith pointing angle. Numerous measurements of the outshifted plasma line are observed. Experimental results are compared to previous high latitude experiments and predictions from recent modeling efforts.

Sheerin, J. P.; Rayyan, N.; Watkins, B. J.; Bristow, W. A.; Spaleta, J.; Watanabe, N.; Golkowski, M.; Bernhardt, P. A.



Total electron content measurements in ionospheric physics  

NASA Astrophysics Data System (ADS)

With the advent of modern global networks of dual-frequency Global Positioning System (GPS), total electron content (TEC) measurements along slant paths connecting GPS receivers and satellites at 22,000 km have become the largest data set available to ionospheric scientists. The TEC can be calculated from the time and phase delay in the GPS signal using the GPS Toolkit, but an unknown bias will remain. In addition, UHF/VHF radio beacons on board low-Earth-orbiting satellites can also be used to measure the electron content. However, the TEC measurements are obtained by integrating TEC differences between slant paths, but also contain biases. It is often necessary to use data assimilative algorithms like the Ionospheric Data Assimilation Three-Dimensional (IDA3D), and to treat both GPS- and LEO-beacon TEC measurements as relative data in order to conduct ionospheric studies.

Garner, T. W.; Gaussiran, T. L., II; Tolman, B. W.; Harris, R. B.; Calfas, R. S.; Gallagher, H.



Ionospheric tomography using ADS-B signals  

NASA Astrophysics Data System (ADS)

Numerical modeling has demonstrated that Automatic Dependent Surveillance Broadcast (ADS-B) signals can be used to reconstruct two-dimensional (2-D) electron density maps of the ionosphere using techniques for computerized tomography. Ray tracing techniques were used to determine the characteristics of individual waves, including the wave path and the state of polarization at the satellite receiver. The modeled Faraday rotation was computed and converted to total electron content (TEC) along the raypaths. The resulting TEC was used as input for computerized ionospheric tomography (CIT) using algebraic reconstruction technique. This study concentrated on reconstructing mesoscale structures 25-100 km in horizontal extent. The primary scientific interest of this study was to show that ADS-B signals can be used as a new source of data for CIT to image the ionosphere and to obtain a better understanding of magneto-ionic wave propagation.

Cushley, A. C.; Noël, J.-M.



Whistlers. [in earth ionosphere and magnetosphere  

NASA Technical Reports Server (NTRS)

Theoretical models of ionospheric whistler phenomena are reviewed and compared with experimental data. Whistlers were characterized as lightning discharges through a dispersive medium in 1919, with the first observed appearance of whistler noises detected in telephone communications. Magneto-ionic theory is used to characterize whistlers, with the Appleton-Hartree equations applied to the wave fields arising from lightning interactions with ionospheric plasma. Large values of the refractive index or slow propagation speeds give rise to the whistler mode, i.e., propagation of the wave through plasmas of any density. Propagation through the ionosphere is examined with the Snell's law, and account is taken of absorption and the necessity of obtaining full-wave solutions. Finally, theories are under development to explain the occurrence of ducting, i.e., guiding of the whistler wave by field-aligned plasma density irregularities.

Park, C. G.



Ionosphere/microwave beam interaction study  

NASA Technical Reports Server (NTRS)

The microwave beam of the Solar Power Satellite (SPS) is predicted to interact with the ionosphere producing thermal runaway up to an altitude of about 100 kilometers at a power density threshold of 12 mW/cm sq (within a factor of two). The operation of the SPS at two frequencies, 2450 and 5800 MHz, is compared. The ionosphere interaction is less at the higher frequency, but the tropospheric problem scattering from heavy rain and hail is worse at the higher frequency. Microwave signals from communication satellites were observed to scintillate, but there is some concern that the uplink pilot signal may be distorted by the SPS heated ionosphere. The microwave scintillations are only observed in the tropics in the early evenings near the equinoxes. Results indicate that large phase errors in the uplink pilot signal can be reduced.

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



Impact of Flare Radiation on the Ionosphere  

NASA Astrophysics Data System (ADS)

We study the impact of the solar flare radiation on the low- to mid-latitude ionosphere for a number of flares: 28 Oct 2003, 29 Oct 2003, 4 Nov 2004, and 7 Sept 2005. We use the solar EUV spectrum from the Flare Irradiance Spectral Model (FISM)1; the spectrum considers 10Å bins from 10 -- 1050 Å and a one minute cadence. We use this spectrum in the NRL three-dimensional ionosphere model SAMI3 to obtain the global impact of the flare on the mid- to low-latitude ionosphere. We find that the TEC can increase by ~ 10% which can be as high as ~ 25 TECU. Finally, we compare our results to GPS data and discuss improvements to the model. 1 Chamberlin, P.C., T.N. Woods, and F.G. Eparvier, ILWS Workshop Proc., GOA, 2006. Research supported by ONR.

Slinker, S.; Krall, J.; Huba, J. D.; Warren, H.; Joyce, G.



Can Ionospheric Sounding Help Tsunami Warning Systems ?  

NASA Astrophysics Data System (ADS)

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 waves (IGW) propagating in the neutral atmosphere over oceanic regions. The strong amplification mechanism of atmospheric IGW allows to detect these anomalies when the tsunami is offshore where the see level displacement is still small. In addition, the dense coverage of ionospheric sounding instruments over the oceans increases over time and more instruments will be able to provide ionospheric measurements: i.d., Doppler sounding, over-the-horizon radar (OTH) and space-based GPS data (e.g., COSMIC). Most of the ionospheric anomalies are also deterministic and reproducible by numerical modeling (Occhipinti et al., 2006), this latter will supply an useful help in the estimation of expected anomalies. The sensitivity of altimeters, OTH radar, ground-based and space-based GPS measurements is analyzed in this work by the way of the modeling. The results are used to discuss the role of ionospheric sounding in the future oceanic monitoring and tsunami warning system. [Artru et al., 2005] Geophys. J. Int., 160, 2005 [DasGupta et al., 2006] Earth Planet. Space, 35, 929-959. [Liu et al., 2006] J. Geophys. Res., 111, A05303. [Occhipinti et al., 2006] Geophys. Res. Lett., 33, L20104, 2006

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



Effect of the zonal E × B plasma drift on the electron number density in the low-latitude ionospheric F region at high solar activity near the December solstice  

NASA Astrophysics Data System (ADS)

The variations in the electron number density of the ionospheric F2 layer maximum ( NmF2) under the action of the zonal plasma drift in the geomagnetic west-geomagnetic east direction perpendicularly to the electric ( E) and geomagnetic ( B) fields during a geomagnetically quiet period on December 7, 1989, at high solar activity have been studied based on a three-dimensional nonstationary theoretical model of electron number densities and temperatures in the ionospheric F region. Calculated and measured NmF2 values for 12 low-latitude ionospheric sounding stations have been compared. When the zonal E × B plasma drift is ignored, the NmF2 values become smaller by up to a factor of 3 under nighttime conditions in the low-latitude ionosphere. The average effect of the zonal E × B plasma drift on NmF2 in the low-latitude ionosphere is larger during winter nights than under summer nighttime conditions.

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



HF sideband generation in the ionosphere  

SciTech Connect

The temporal development of sidebands excited near sunrise by two strong HF waves separated by a few hertz is presented. Sidebands are not observed before sunrise when the ionospheric critical frequency is less than the heater frequency. As the ionospheric density increases following sunrise and overdense conditions are established, strong sidebands emerge. Even though these results favor a mechanism which phase modulates the reflected HF wave over one which first downconverts the HF power to ULF before exciting sidebands, it is possible that either mechanism could at times contribute to sideband production. 8 refs.

Noble, S.T.; Gordon, W.E.; Duncan, L.M.; Mccoy, J.E. (Rice Univ., Houston, TX (USA); Los Alamos National Lab., NM (USA); NASA, Johnson Space Center, Houston, TX (USA))



The calculation of ionospheric ray paths  

E-print Network

. 28 ionosphere by using the normal index surface curves. Consider a wave incident upon the stratified medium at an angle W from the vertical. 0 Erect a perpendicular line to the horizontal a distance sinu from 0 the origin 0 of the normal index.... 28 ionosphere by using the normal index surface curves. Consider a wave incident upon the stratified medium at an angle W from the vertical. 0 Erect a perpendicular line to the horizontal a distance sinu from 0 the origin 0 of the normal index...

Koehler, Buford Ray



CIGALA: an FP7 innovative activity to tackle the threat of Ionospheric Scintillation to GNSS operations in Latin America  

NASA Astrophysics Data System (ADS)

Drifting ionospheric electron density irregularities may lead to the scintillation of transionospheric radio waves, as in the case of signals broadcast from artificial satellites. Scintillations can not only degrade signal quality but also cause receiver loss of lock on GNSS satellites, therefore posing a major threat to GNSS based applications demanding high levels of accuracy, availability and integrity, including EGNOS-based applications notably in low latitude areas. The problem is particularly acute in Latin America and will be further amplified with the next solar maximum, predicted for 2013. The CIGALA (Concept for Ionospheric Scintillation Mitigation for Professional GNSS in Latin America) project, led by Septentrio NV and co-funded by the European GNSS Supervisory Authority (GSA) through the European 7th Framework Program, will tackle this problem. The aim of the CIGALA project is to develop ionospheric scintillation mitigation countermeasures to be implemented in Septentrio's professional multi-frequency multi-constellation GNSS receivers and tested in Latin America. The project will leverage research and development activities coordinated between European and Brazilian experts and will involve a wide scale ionospheric measurement and test campaigns that will be conducted in Brazil with the support of several local academic and industrial partners. Details on the objectives, current status, and workflow of the project will be presented and discussed.

Francisco Galera Monico, João.; Bougard, Bruno; Sleewaegen, Jean-Marie; Willems, Tom; Saüt, Carine; Aquino, Marcio; de Franceschi, Giorgiana; Ferreira da Silva, Elcia; Forte, Biagio; Wernik, Andrzej W.



The Artificial Life Roots of Artificial Intelligence  

Microsoft Academic Search

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

Luc Steels; R. Brooks



Design of Artificial Dielectrics for Anti-Reflection-Coatings  

Microsoft Academic Search

With the increasing interest in new artificial materials ranging from meta-materials to photonic bandgap materials there is a growing need for accurate models of artificial materials. We examine the design of a three-layer structure with an artificial dielectric as an anti-reflection-coating on both sides of a dielectric slab. We present a field-equivalent circuit theory to calculate the effective dielectric constant

S. Biber; J. Richter; S. Martius; L.-P. Schmidt



Artificial Intelligence and Robotics  

E-print Network

Since Robotics is the field concerned with the connection of perception to action, Artificial Intelligence must have a central role in Robotics if the connection is to be intelligent. Artificial Intelligence addresses ...

Brady, Michael



Inter-hemispheric imaging of the ionosphere with the upgraded IRI-Plas model during the space weather storms  

NASA Astrophysics Data System (ADS)

International Reference Ionosphere extended to the plasmasphere (IRI-Plas) is upgraded analytically for assimilative mode of operation using GPS-derived Total Electron Content (TEC) for reconstruction of instantaneous ionospheric critical frequency and topside scale height at magnetic conjugate hemisphere. The performance of IRI-Plas code is examined with TECgps retrieved from Global Ionospheric Maps compared with the F2-layer critical frequency at eight ionosonde locations in East Asia region on both hemispheres during the space weather storms at solar maximum (2000) and solar minimum (2006). Missing ionosonde data are completed by cloning of critical frequency. Decomposition of TECgps in electron density profile with IRI-Plas code reveals the opposite relative changes of critical frequency and the topside scale height depending on solar activity. The ionospheric weather W index is computed for the desired locations in conjugate hemispheres and consistent results are obtained indicating the departure of instantaneous values of ionospheric parameters from their respective median varying from quiet state to intense storm.

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



Properties of ionospheric irregularities as derived by GNSS scintillation monitors  

NASA Astrophysics Data System (ADS)

Ionospheric influence on the GNSS satellite signals delay, phase and amplitude changes can be deduced from information about various drifting ionospheric density structures. Large and small scale irregularities of electron concentration in the ionosphere determine the changes of the propagating signal. This is the main source of problems for satellite positioning systems that has not been satisfactory solved yet. We present a case study of ionospheric irregular structures patterns during geomagnetic storm event occurred on 5th and 6th April 2010, measured by GPS monitors set on Svalbard and other diagnostic tools. For purpose of comparison we included data of quiet ionosphere period as reference point. Analysis of spatial and temporal phase gradients has been used as a basic tool for calculations of the properties of ionospheric electron concentration irregularities. The properties derived depend on the model of propagation of waves in the ionosphere. We validated estimated properties of ionospheric irregularities using additional measurements. Purpose of this investigation is to recognize ionospheric scintillation diffraction pattern, provide relation between phase measurements and properties of ionospheric irregularities for further forecasting and mitigation of ionospheric effects.

Stevanovic, Djordje; Grzesiak, Marcin


The current status of the ionospheric observations in NICT  

NASA Astrophysics Data System (ADS)

In Japan, NICT (National Institute of Information and Communications Technology) is in charge of space weather forecasting services as a Regional Warning Center of International Space Environment Service (ISES). Also, we have been operating WDC for Ionosphere since 1957. With help of geospace environment data exchanging among the international cooperation, NICT routinely operates daily space weather forecast service to provide information on nowcasts and forecasts of solar flare, geomagnetic disturbances, solar proton event, and radio-wave propagation conditions in the ionosphere. To monitor the ionospheric condition over Japan, we have been operating domestic ionosonde network We have four station, Wakkanai, Kokubunji, Yamagawa, Okinawa. Also we have an ionospheric observatory in Syowa Station, Antarctica. Also, we are operating south-east Asia low-latitute ionospheric network (SEALION). This is for the purpose of monitoring and forecasting equatorial ionospheric disturbances, especially plasma bubbles. In the present talk, we will introduce our current activities and future perspective of the ionospheric observations in NICT.

Nagatsuma, Tsutomu; Murata, Ken T.; Tsugawa, Takuya; Kato, Hisao; Ishibashi, Hiromitsu



A Technique to Separate Ground and Ionospheric HF Radar Backscatter for Ionospheric Remote Sensing  

NASA Astrophysics Data System (ADS)

The use of High Frequency (HF) radar for ionospheric remote sensing has recently proliferated, as in the case of the growing Super Dual Auroral Radar Network (SuperDARN). However, because of the complexity of ionospheric propagation modes and the fact that individual echoes of ground and ionospheric scatter origin may have similar spectral characteristics, it is often impossible to determine whether an echo is a legitimate ionospheric scatter echo or a spurious ground scatter echo. We have developed a technique that utilizes the statistical distribution of spectral parameters and range and elevation angle of arrival data of ground and ionospheric echoes to identify the origin of an echo with a high degree of confidence. For the two radar stations specifically presented here, the confidence of identification of an echo's origin is 90%. We use data from the Kapuskasing and Saskatoon HF radars for 12 days throughout the year of 2001 and examine the joint distribution of backscatter line-of-sight velocity v and spectral width w. We observe that for v >/= 100 m/s, which is presumably ionospheric scatter, the distribution of line-of-sight velocity decreases exponentially with v for a given value of spectral width. The e-folding velocity is 450 m/s. We extrapolate this distribution to smaller v to obtain the joint distribution of velocity and width in ionospheric scatter, which we subtract from the total distribution to obtain the distribution of velocity and width in ground scatter. These distributions, when normalized, intersect along the line v[m/s] = 60 m/s - 0.4w[m/s]. This line represents the separatrix between ground scatter and ionospheric scatter for these stations. To validate this separatrix, we investigate the distribution of the reflection heights calculated from echo range and elevation angle of arrival data. The distribution of reflection heights for presumed ionospheric and ground scatter are distinctly different and are consistent with the presumed identification. Finally, the separatrix provides a 90% confidence of identification of a particular echo as of ground scatter or ionospheric scatter origin based on the overlap between the respective distributions of spectral parameters. This result is robust, being independent of radar station and season. While the particular values of the separatrix parameters and confidence level may vary for other HF radar stations based on local ionospheric and surface conditions, the technique should be generally applicable.

Blanchard, G.; Sundeen, S.; Baker, K.



An improved model of the lightning electromagnetic field interaction with the D-region ionosphere  

NASA Astrophysics Data System (ADS)

We present an improved time-domain model of the lightning electromagnetic pulse (EMP) interaction with the lower ionosphere. This improved model inherently accounts for the Earth's curvature, includes an arbitrary number of ion species, and uses a convolutional Perfectly Matched Layer (PML) boundary. We apply an improved model of electron heating due to the lightning EMP and electrostatic fields, and we include ionization, attachment, and detachment. In addition to modeling lightning, this model can be used for long-distance VLF wave propagation in the Earth-ionosphere waveguide, heating of the lower ionosphere by VLF transmitters, and heating in the F-region ionosphere by lightning. In this paper we present three initial results of this model. First, we compare results of ionospheric heating and electron density disturbances with and without electron detachment taken into account. We find that detachment is important only for the QE effects on time scales longer than 1 ms. Second, we find a simple explanation for the recently-reported “elve doublets”, which we find are an effect of the rise and fall times of the lightning waveform. In particular, we find that all elves are doublets, and the rise and fall times of the current pulse control the brightness and separation in time of the two successive halves of the elve. Third, we find a similar simple explanation for “ring” sprites, whole columns appear in a circle symmetric around the discharge axis. We find that ring sprites can be initiated for particular current waveforms, where the QE and EMP fields in the mesosphere produce a maximum reduced field away from the discharge axis.

Marshall, R. A.



Longitudinal variations of positive dayside ionospheric storms related to recurrent geomagnetic storms  

NASA Astrophysics Data System (ADS)

have performed an analysis of case events and statistics of positive ionospheric storms in the dayside region of the equatorial ionization anomaly during recurrent geomagnetic storms (RGSs), which dominate in geomagnetic and ionospheric conditions on the declining phase of solar activity in 2004 to 2008. It is shown that total electron content (TEC) has a tendency to minimize before the beginning of RGSs and to peak 3 to 4 days after, i.e., on the RGS recovery phase produced by high-intensity long-duration continuous auroral activity. The maximum of TEC coincides with the maximum of solar wind velocity within high-speed solar wind streams. An analysis of electron content vertical profiles, derived from two independent methods using ionosondes and Constellation Observing System for Meteorology, Ionosphere, and Climate /Formosa Satellite mission-3 radio occultation, showed that in the maximum of an ionospheric storm on 28 March 2008, the F2 layer thickens, NmF2 increases by ~50%, and hmF2 elevates by a few tens of kilometers. The response of positive ionospheric storms to solar, heliospheric, and geomagnetic drivers reveals a prominent longitudinal asymmetry. In the longitudinal range from -90° to 90°, the solar illumination plays a major role, and in the range from 90° to -120°, the influence of heliospheric and geomagnetic drivers becomes significant. The highest correlations of the TEC enhancements with the heliospheric and geomagnetic drivers were found during December-February (r increased from ~0.3 to ~0.5). We speculate that the dynamics controlling this might result from an effect of solar zenith angle, storm time effects of thermospheric ?O/N2 enhancement, and penetrating electric fields of interplanetary and magnetospheric origin.

Dmitriev, A. V.; Huang, C.-M.; Brahmanandam, P. S.; Chang, L. C.; Chen, K.-T.; Tsai, L.-C.



Artificial MusclesArtificial Muscles Douglas ThorDouglas Thor  

E-print Network

Artificial Muscles 3 primary types:3 primary types: Pneumatic Artificial Muscles (PAMs)Pneumatic Artificial Muscles Nanotube Muscles (CNMsCNMs)) AlievAliev,, et alet al. Science 323, 1575 (2009). Science 323, 1575 (2009) #12;Pneumatic Artificial

Fygenson, Deborah Kuchnir


The Evolutionary Emergence Artificial Intelligence  

E-print Network

The Evolutionary Emergence route to Artificial Intelligence Alastair Channon Degree: MSc with a brief discussion. Keywords: Artificial Intelligence, Emergence, Genetic Algorithms, Artificial Life: Inman Harvey Submitted: 2 September 1996 (Minor revisions October 1996) Abstract The artificial

Fernandez, Thomas


Investigation of ionospheric stimulated Brillouin scatter generated at pump frequencies near electron gyroharmonics  

NASA Astrophysics Data System (ADS)

Stimulated Electromagnetic Emissions (SEEs), secondary electromagnetic waves excited by high power electromagnetic waves transmitted into the ionosphere, produced by the Magnetized Stimulated Brillouin Scatter (MSBS) process are investigated. Data from four recent research campaigns at the High Frequency Active Auroral Research Program (HAARP) facility is presented in this work. These experiments have provided additional quantitative interpretation of the SEE spectrum produced by MSBS to yield diagnostic measurements of the electron temperature and ion composition in the heated ionosphere. SEE spectral emission lines corresponding to ion acoustic (IA) and electrostatic ion cyclotron (EIC) mode excitation were observed with a shift in frequency up to a few tens of Hz from the pump frequency for heating near the third harmonic of the electron gyrofrequency 3fce. The threshold of each emission line has been measured by changing the pump wave power. The excitation threshold of IA and EIC emission lines originating at the reflection and upper hybrid altitudes is measured for various beam angles relative to the magnetic field. Variation of strength of MSBS emission lines with pump frequency relative to 3fce and 4fce is also studied. A full wave solution has been used to estimate the amplitude of the electric field at the interaction altitude. The estimated instability threshold using the theoretical model is compared with the threshold of MSBS lines in the experiment and possible diagnostic information for the background ionospheric plasma is discussed. Simultaneous formation of artificial field-aligned irregularities (FAIs) and suppression of the MSBS process is investigated. This technique can be used to estimate the growth time of artificial FAIs which may result in determination of plasma waves and physical process involved in the formation of FAIs.

Mahmoudian, A.; Scales, W. A.; Bernhardt, P. A.; Fu, H.; Briczinski, S. J.; McCarrick, M. J.




E-print Network

ARTIFICIAL INTELLIGENCE: ENGINEERING, SCIENCE, OR SLOGAN? Nils J. Nilsson Artificial Intelligence that artificial intelligence (AI) is primarily concerned with propositional languages for representing knowledge and motor activities (analogous to low-level animal or human vision and muscle control) seems to be quite

Pratt, Vaughan


Encyclopedia of Artificial Intelligence  

E-print Network

Encyclopedia of Artificial Intelligence Juan Ramón Rabuñal Dopico University of A Coruña, Spain of artificial intelligence / Juan Ramon Rabunal Dopico, Julian Dorado de la Calle, and Alejandro Pazos Sierra) -- ISBN 978-1-59904-850-5 (ebook) 1. Artificial intelligence--Encyclopedias. I. Rabunal, Juan Ramon, 1973

Liang, Faming


Meteor matter interaction with the Earth's atmosphere and the ionospheric E-region structure  

NASA Technical Reports Server (NTRS)

The exploration of the ionospheric E region is a pressing problem, both in the applied and fundamental studies. Results are presented of an investigation: (1) to estimate the meteor ionization contribution to the night time E layer and influx; (2) to study the phenomenon of intensive sporadic layer formation following cessation of meteor stream activity; and (3) to access the role of metallic ions of meteor origin in the diurnal and seasonal variations in the occurrence probabilities of midlatitude E sub s. The contribution was evaluated of meteor matter, Lyman radiation and corpuscular particles to the electron concentration of the night E region. Results are discussed.

Alimov, O.



Magnetospheric convection and the high latitude F2 ionosphere. [in the polar regions  

NASA Technical Reports Server (NTRS)

Behavior of the polar ionospheric F-layer as it is convected through the cleft, over the polar cap, and through the night side F-layer trough zone was investigated. Passage through the cleft adds of the order of 200,000 ions/cu cm in the vicinity of the F 2 peak and redistributes the ionization above approximately 400 km altitude to conform with an increased electron temperature. The F-layer is also raised of the order of 20 km in altitude by the convection electric field. In the night soft electron precipitation zone, the layer is lowered in altitude by the convection electric field, and then decays, primarily by chemical recombination, as it convects equatorward and around the dawn side of the earth. In the absence of ionization sources, decay by factors of the order of 100 to 1000 occur prior to entry into the sunlit hemisphere, thus forming the F-layer night trough.

Knudsen, W. C.




Microsoft Academic Search

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

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



Cassini radio occultations of Titan's ionosphere  

NASA Astrophysics Data System (ADS)

We report results on Titan's ionosphere from the Cassini radio occultation of March 26, 2007 (T27), as well as those of March 19, 2006 (T12), and May 20,2006 (T14) . The 2006 occultations occurred at low Southern latitudes of 14.7S, 36.2S, 19.8S, and 21.9S. The 2007 occultation was nearly polar, at latitudes of 81S and 59N. The solar zenith angles for all occultations were near the terminator, ranging from 85 to 95 deg. The ionosphere peak was observed to lie close to an altitude of 1200 km, and the observed peak densities ranged from about 1.2 to 2.0x103 cm-3, which is in fairly good agreement with other Cassini observations and the previous Voyager radio occultation results. Radio occultation observations of the Titan ionosphere are difficult because of its low density and small size, and it was facilitated by the unprecedented Cassini radio science system, which has three frequencies that can operate simultaneously: S-band (2.3 GHz), X-band (8.4 GHz), and Ka-band (32 GHz). In particular, Ka-band hads never been used before to probe Titan's ionosphere, and the signal-to-noise ratios at all frequencies of 42, 54, and 48 dB-Hz., respectively, have never before been achieved.

Kliore, A. J.; Nagy, A. F.; Flasar, F. M.; Schinder, P. J.; French, R. G.; Marouf, E. A.; Rappaport, N. J.; Anabtawi, A.; McGhee, C. A.



Ionospheric Alfvén resonator response to remote earthquakes  

NASA Astrophysics Data System (ADS)

The ionospheric Alfvén resonances (IARs) are an interesting wave phenomenon well described in the literature. The IAR formation region is located between two bends of the plasma density profile: in the lower part of the ionospheric F region and at altitudes of about 1000-3000 km. In this region, Alfvén waves are entrapped and form standing waves. The quality factor of the resonator can attain a value of 5-10. We studied local IAR features using data of the Borok Geophysical Observatory (58°N, 38° E) and found that the ionospheric Alfvén resonances observed as geomagnetic pulsations at frequencies of a few hertz respond to remote seismic events. There are different kinds of the seismic wave effect on the IARs mode: sometimes the oscillations arise after an earthquake moment, in other cases they sharply decay, and sometimes they abruptly change their intensity. Among possible mechanisms of the earthquake action on the ionosphere acoustic and electromagnetic waves emerged by a seismic shock are discussed. The work was supported by the RFBR grants 09-05-00048 and 10-05-00661.

Potapov, Alexander S.; Dovbnya, Boris V.; Tsegmed, Battuulai



Mesoscale ionospheric tomography at the Auroral region  

Microsoft Academic Search

FMI (Finnish Meteorological Institute) has used observations from the dense GNSS network in Finland for high resolution regional ionospheric tomography. The observation system used in this work is the VRS (Virtual Reference Station) network in Finland operated by Geotrim Ltd. This network contains 86 GNSS ground stations providing two frequency GPS and GLONASS observations with the sampling rate of 1

J. Luntama; G. V. Kokkatil



Jupiter's Thermosphere and Ionosphere R. V. Yelle  

E-print Network

9 Jupiter's Thermosphere and Ionosphere R. V. Yelle University of Arizona S. Miller University College, London 9.1 INTRODUCTION Jupiter's upper atmosphere forms the boundary between the lower of molecular energy levels may depart from their local thermodynamic equilibrium (LTE) values. Jupiter shares

Yelle, Roger V.


Global Response to Local Ionospheric Mass Ejection  

NASA Technical Reports Server (NTRS)

We revisit a reported "Ionospheric Mass Ejection" using prior event observations to guide a global simulation of local ionospheric outflows, global magnetospheric circulation, and plasma sheet pressurization, and comparing our results with the observed global response. Our simulation framework is based on test particle motions in the Lyon-Fedder-Mobarry (LFM) global circulation model electromagnetic fields. The inner magnetosphere is simulated with the Comprehensive Ring Current Model (CRCM) of Fok and Wolf, driven by the transpolar potential developed by the LFM magnetosphere, and includes an embedded plasmaspheric simulation. Global circulation is stimulated using the observed solar wind conditions for the period 24-25 Sept 1998. This period begins with the arrival of a Coronal Mass Ejection, initially with northward, but later with southward interplanetary magnetic field. Test particles are launched from the ionosphere with fluxes specified by local empirical relationships of outflow to electrodynamic and particle precipitation imposed by the MIlD simulation. Particles are tracked until they are lost from the system downstream or into the atmosphere, using the full equations of motion. Results are compared with the observed ring current and a simulation of polar and auroral wind outflows driven globally by solar wind dynamic pressure. We find good quantitative agreement with the observed ring current, and reasonable qualitative agreement with earlier simulation results, suggesting that the solar wind driven global simulation generates realistic energy dissipation in the ionosphere and that the Strangeway relations provide a realistic local outflow description.

Moore, T. E.; Fok, M.-C.; Delcourt, D. C.; Slinker, S. P.; Fedder, J. A.



Radar Soundings of the Ionosphere of Mars  

E-print Network

for Subsurface and Ionosphere Sounding) instrument on board the orbiting Mars Express spacecraft. Several types of the local electron density and magnetic field strength. The Mars Express spacecraft (1), currently in orbit cannot be made. Because of geometric constraints imposed by the orbits of Earth and Mars, radio

Gurnett, Donald A.


Importance of Ionospheric Gradients for error Correction  

NASA Astrophysics Data System (ADS)

Importance of Ionospheric Gradients for error Correction R. Ram Prasad1, P.Nagasekhar2 1Sai Spurthi Institute of Technology-JNTU Hyderabad,2Sai Spurthi Institute of Technology-JNTU Hyderabad Email In India, Indian Space Research Organization (ISRO) has established with an objective to develop space technology and its application to various national tasks. To cater to the needs of civil aviation applications, GPS Aided Geo Augmented Navigation (GAGAN) system is being jointly implemented along with Airports Authority of India (AAI) over the Indian region. The most predominant parameter affecting the navigation accuracy of GAGAN is ionospheric delay which is a function of total number of electrons present in one square meter cylindrical cross sectional area in the line of site direction between the satellite and the user on the earth i.e. Total Electron Content (TEC).The irregular distribution of electron densities i.e. rate of TEC variation, causes Ionospheric gradients such as spatial gradients (Expressed in TECu/km) and temporal gradients (Expressed in TECu /minute). Among the satellite signals arriving to the earth in multiple directions, the signals which suffer from severe ionospheric gradients can be estimated i.e. Rate of TEC Index (ROTI) and Rate of TEC (ROT). These aspects which contribute to errors can be treated for improving GAGAN positional accuracy.

Ravula, Ramprasad


Numerical simulations on ion acoustic double layers  

SciTech Connect

A comprehensive numerical study of ion acoustic double layers has been performed for both periodic as well as for 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 potential and the ionospheric Pedersen resistance. It is found that the number of double layers and the associated potential buildup across the system increases with the system length.

Sato, T.; Okuda, H.



Enhancement of EM-Ionosphere interaction through Plasma Lens and Frequency Chirping  

NASA Astrophysics Data System (ADS)

During ionospheric modification, both satellite beacons and sky maps from digital ionosonde measurements have detected large-density perturbation. This perturbation reaches a maximum when the incident HF matches the plasma frequency on the density plateau (or at f_oF2 layer). Experiments and theories are presented which describe how a plasma lens can be created at a lower altitude by pre-conditioning the ionosphere at a lower altitude; the lowering of plasma density at the center of the heated region causes a change in the index of refraction, thereby forming an equivalent ionospheric lens^1. Unlike earlier results obtained at Arecibo Observatory^2 using water molecules injected by a rocket, our concept is simpler and can be repeated many times. Another enhancement of interaction comes from the chirping of the heating frequency such that all the waves converge at the resonant layer at a particular time^3. Work supported by SDSU. ^1 A.Y. Wong, Proceedings of Ionsopheric Interactions Workshop, Santa Fe, NM, April, 2002. ^2 M. Sulzer, private communication. ^3 S. Cowley and E. Valeo, private communication.

Pau, J.; Wong, A. Y.; Rosenthal, G.; Koziar, K. E.; Stone, K.



Medium-scale 4-D ionospheric tomography using a dense GPS network  

NASA Astrophysics Data System (ADS)

The ionosphere above Scandinavia in December 2006 is successfully imaged by 4-dimensional tomography using the software package MIDAS from the University of Bath. The method concentrates on medium-scale structures: between 100 km and 2000 km in horizontal size. The input consists of TEC measurements from the dense GPS network Geotrim in Finland. In order to ensure sufficient vertical resolution of the result, EISCAT incoherent scatter radar data from Tromsø are used as additional input to provide the vertical profile information. The TEC offset of the measurements is unknown, but the inversion procedure is able to determine this automatically. This auto-calibration is shown to work well. Comparisons with EISCAT radar results and with occultation results show that the inversion using EISCAT data for profile information is much better able to resolve vertical profiles of irregular structures than the inversion using built-in profiles. Still, with either method the intensities of irregular structures of sizes near the resolution (about 100 km horizontal size) can be underestimated. Also, the accuracy of the inversion worsens above areas where no receivers are available. The ionosphere over Scandinavia in December 2006 often showed a dense E-layer in early morning hours, which generally disappeared during midday when a dense F-layer was present. On 14 December, a strong coronal mass ejection occurred, and many intense irregularities appeared in the ionosphere, which extended to high altitudes.

van de Kamp, M. M. J. L.



IRI, an International Standard for the Ionosphere  

NASA Astrophysics Data System (ADS)

The International Reference Ionosphere (IRI) is a data-based model of the ionosphere that has been steadily improved and updated by a joint working group of the Committee on Space Research and the International Union of Radio Science. We will report about the most recent IRI workshops and the improvements and additions planned for the next version of the model. In particular new models will be included for the D-region electron density (Friedrich et al., 2002), and for the ion densities (Triskova et al., 2003) the latter based on Atmosphere Explorer C, D, E and Intercosmos 24 data. A correction term will be introduced in the topside electron density model to alleviate problems at high solar activities and high altitudes (Bilitza, 2002). A special IRI task groups is working on an occurrence probability model for spread-F (Abdu et al., 2003) for inclusion in IRI. A quantitative description of ionospheric variability (standard deviation from monthly mean) is the goal of a special IRI task force activity at the International Center for Theoretical Physics (Radicella 2002). We will also report about activities to update IRI with actual measurements and thus obtain a more accurate description of the actual ionosphere. A proposal to make the IRI model the ISO standard for the ionosphere is now pending before the International Standardization Organization (ISO). The IRI homepage is at and a web-interface for computing and plotting IRI parameters can be found at . Abdu, M. A., J. R de Souza, I. S. Batista, and J. H. A. Sobral, Equatorial Spread F statistics and their empirical modeling for the IRI: A regional model for the Brazilian longitude sector, Adv. Space Res., in press, 2003. Triskova, L., V. Truhlik and J. Smilauer, An empirical model of ion composition in the outer ionosphere, Adv. Space Res., in press, 2003 Bilitza, D., A Correction for the IRI Topside Model Based on Alouette/ISIS Data, World Space Congress, Houston, Texas, 2002. Friedrich, M., M. Harrich, R. Steiner, K. M. Torkar, and F.-J. Luebken, The quiet auroral ionosphere and its neutral background, World space congress, Houston, Texas, 2002.

Bilitza, D.; Reinisch, B.; Triskova, L.; Friedrich, M.



The Roles of Artificial Intelligence in Information Systems  

Microsoft Academic Search

By classifying information processing tasks which are suitable for artificial intelligence approaches we determine an architectural structure for large systems. We visualize a three-layer architecture of private applications, mediating information servers, and an infrastructure which provides information resources.

Gio Wiederhold



GNSS station characterisation for ionospheric scintillation applications  

NASA Astrophysics Data System (ADS)

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

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



Isis 1 observations of the high-latitude ionosphere during a geomagnetic storm.  

NASA Technical Reports Server (NTRS)

The Isis 1 satellite has made measurements of several ionospheric and related parameters, and the results of the various measurements have been compared in detail for two north transpolar passes during the geomagnetic storm of February 3, 1969. Simultaneous measurements were made of local electron and ion densities and temperatures, electron density between the satellite and the peak of the F layer, radio noise, and particle fluxes over a wide energy range extending down to 10 eV. Several features of the ionosphere (in particular, enhancements of radio noise, scale height, and plasma temperatures) appear to be due to soft-particle (100 eV to 1 keV) precipitation, which is related to magnetospheric structure as delineated by the observation of more energetic particles. The magnetosheath particles precipitating on the dayside of the polar cap are particularly effective.

Whitteker, J. H.; Hartz, T. R.; Brace, L. H.; Burrows, J. R.; Heikkila, W. J.; Sagalyn, R. C.; Thomas, D. M.



Analysis of the ionosphere/plasmasphere electron content variability during strong geomagnetic storm  

NASA Astrophysics Data System (ADS)

The ionosphere/plasmasphere electron content (PEC) variations during strong geomagnetic storms in November 2004 were estimated by combining of mid-latitude Kharkov incoherent scatter radar observations and GPS TEC data derived from global TEC maps. The comparison between two independent measurements was performed by analysis of the height-temporal distribution for specific location corresponding to the mid-latitudes of Europe. The percentage contribution of PEC to GPS TEC indicated the clear dependence from the time with maximal values (more than 70%) during night-time. During day-time the lesser values (30-45%) were observed for quiet geomagnetic conditions and rather high values of the PEC contribution to GPS TEC (up to 90%) were observed during strong negative storm. These changes can be explained by the competing effects of electric fields and winds, which tend to raise the layer to the region with lower loss rate and movement of the ionospheric plasma to the plasmasphere.

Cherniak, Iu. V.; Zakharenkova, I. E.; Dzubanov, D.; Krankowski, A.



Investigation of mid-latitude ionospheric currents by combined rocket techniques.  

NASA Technical Reports Server (NTRS)

A comprehensive range of neutral atmospheric and simultaneous ionospheric structure measurements were obtained from a Skylark rocket launched at Woomera during evening twilight on a quiet magnetic day. Above 150 km, good agreement was found between the results obtained from three different methods of electric field measurement despite the low field strength (about 1.5 mV/m). In the immediate vicinity of an intense sporadic E layer, the probe measurements indicated large excursions of the electrostatic field amounting to 6.5 mV/m at 105.3 km and 2.7 mV/m at 104.8 km. The calculated ionospheric current system in the vicinity of the rocket trajectory was of similar magnitude to that indicated by local ground-based magnetometers, but was diametrically opposed in direction.

Rees, D.; Dorling, E. B.; Wrenn, G. L.; Aggson, T. L.; Burrows, K.; Haerendel, G.; Rieger, E.; Lloyd, K. H.; Wilson, J. W. G.



Evaluation of COMPASS ionospheric model in GNSS positioning  

NASA Astrophysics Data System (ADS)

As important products of GNSS navigation message, ionospheric delay model parameters are broadcasted for single-frequency users to improve their positioning accuracy. GPS provides daily Klobuchar ionospheric model parameters based on geomagnetic reference frame, while the regional satellite navigation system of China's COMPASS broadcasts an eight-parameter ionospheric model, COMPASS Ionospheric Model(CIM), which was generated by processing data from continuous monitoring stations, with updating the parameters every 2 h. To evaluate its performance, CIM predictions are compared to ionospheric delay measurements, along with GPS positioning accuracy comparisons. Real observed data analysis indicates that CIM provides higher correction precision in middle-latitude regions, but relatively lower correction precision for low-latitude regions where the ionosphere has much higher variability. CIM errors for some users show a common bias for in-coming COMPASS signals from different satellites, and hence ionospheric model errors are somehow translated into the receivers' clock error estimation. In addition, the CIM from the China regional monitoring network are further evaluated for global ionospheric corrections. Results show that in the Northern Hemisphere areas including Asia, Europe and North America, the three-dimensional positioning accuracy using the CIM for ionospheric delay corrections is improved by 7.8%-35.3% when compared to GPS single-frequency positioning ionospheric delay corrections using the Klobuchar model. However, the positioning accuracy in the Southern Hemisphere is degraded due apparently to the lack of monitoring stations there.

Wu, Xiaoli; Hu, Xiaogong; Wang, Gang; Zhong, Huijuan; Tang, Chengpan



Local ionospheric electron density reconstruction from simultaneous ground-based GNSS and ionosonde measurements  

NASA Astrophysics Data System (ADS)

The purpose of the LIEDR (Local Ionospheric Electron Density Reconstruction) system is to acquire and process data from simultaneous ground-based GNSS TEC and digital ionosonde measurements, and subsequently to deduce the vertical electron density distribution in the local ionosphere. LIEDR is primarily designed to operate in real time for service applications, and, if sufficient data from solar and geomagnetic observations are available, to provide short-term forecast as well. For research applications and further development of the system, a post-processing mode of operation is also envisaged. In essence, the reconstruction procedure consists in the following. The high-precision ionosonde measurements are used for directly obtaining the bottom part of the electron density profile. The ionospheric profiler for the lower side (i.e. below the density peak height, hmF2) is based on the Epstein layer functions using the known values of the critical frequencies, foF2 and foE, and the propagation factor, M3000F2. The corresponding bottom-side part of the total electron content is calculated from this profile and is then subtracted from the GPS TEC value in order to obtain the unknown portion of the TEC in the upper side (i.e. above the hmF2). Ionosonde data, together with the simultaneously-measured TEC and empirically obtained O+/H+ ion transition level values, are all required for the determination of the topside electron density scale height. The topside electron density is considered as a sum of the constituent oxygen and hydrogen ion densities with unknown vertical scale heights. The latter are calculated by solving a system of transcendental equations that arise from the incorporation of a suitable ionospheric profiler (Chapman, Epstein, or Exponential) into formulae describing ionospheric conditions (plasma quasi-neutrality, ion transition level). Once the topside scale heights are determined, the construction of the vertical electron density distribution in the entire altitude range is a straightforward process. As a by-product of the described procedure, the value of the ionospheric slab thickness can be easily computed. To be able to provide forecast, additional information about the current solar and geomagnetic activity is needed. For the purpose, observations available in real time -- at the Royal Institute of Meteorology (RMI), the Royal Observatory of Belgium (ROB), and the US National Oceanic and Atmospheric Administration (NOAA) -- are used. Recently, a new hybrid model for estimating and predicting the local magnetic index K has been developed. This hybrid model has the advantage of using both, ground-based (geomagnetic field components) and space-based (solar wind parameters) measurements, which results in more reliable estimates of the level of geomagnetic activity - current and future. The described reconstruction procedure has been tested on actual measurements at the RMI Dourbes Geophysics Centre (coordinates: 50.1N, 4.6E) where a GPS receiver is collocated with a digital ionosonde (code: DB049, type: Lowell DGS 256). Currently, the nominal time resolution between two consecutive reconstructions is set to 15 minutes with a forecast horizon for each reconstruction of up to 60 minutes. Several applications are envisaged. For example, the ionospheric propagation delays can be estimated and corrected much easier if the electron density profile is available at a nearby location on a real-time basis. Also, both the input data and the reconstruction results can be used for validation purposes in ionospheric models, maps, and services. Recent studies suggest that such ionospheric monitoring systems can help research/services related to aircraft navigation, e.g. for development of the ‘ionospheric threat' methodology.

Stankov, S. M.; Warnant, R.; Stegen, K.



Exploring Earth's Ionosphere with CINDI: Bringing an Upper Atmosphere Mission into Pre-College Classrooms  

NASA Astrophysics Data System (ADS)

We will present the Education and Public Outreach work in progress for the joint Air Force/NASA project CINDI (Coupled Ion Neutral Dynamic Investigation), which will launch in early 2004 on a US Air Force C/NOFS (Communications/Navigations Outage Forecast System) Satellite. CINDI, in conjunction with the other instruments on C/NOFS, will study how radio signals sent through the ionosphere are affected by variability with this layer of the atmosphere. The Educational outreach for CINDI is focused on helping students, educators, and the general public better understand the link between the ionosphere and our technological civilization. The ionosphere is typically neglected in pre-college science classes despite its impact on modern society and the substantial resources invested by funding agencies on furthering our understanding of this atmospheric layer. Our approach is to increase student understanding of the terrestrial ionosphere and Sun-Earth connections through strong connections to existing pre-college curricula and standards. We have created a partnership between the William B. Hanson Center for Space Sciences and the Science Education Program within the University of Texas at Dallas (UTD) to produce a quality Educator Guide and a Summer Educator Workshop. A senior graduate student in physics and an experienced middle school educator in UTD's Science Education Master of Science Teaching Program have been partnered to ensure that our the Educator Guide and Workshop will contain both science and pedagogy, and be easily integrated into secondary science classes. The summer 2004 workshop will be offered in the Dallas area, which has a significant population of minority and economically disadvantaged students. We will recruit teachers from districts that serve a large number of underserved/underrepresented students. The Educator Guide and workshop materials will be made available on the CINDI Web site for distribution to a national audience.

Urquhart, M. L.; Hairston, M. R.; Richardson, J. M.; Olson, C.



Modeling magnetospheric plasma; Proceedings of the First Huntsville Workshop on Magnetosphere/Ionosphere Plasma Models, Guntersville, AL, Oct. 14-16, 1987  

NASA Technical Reports Server (NTRS)

The conference presents papers on the global modeling of magnetospheric plasma processes, the modeling of the midlatitude ionosphere and plasmasphere, the modeling of the auroral zone and boundary layer, the modeling of the polar magnetosphere and ionosphere, and the modeling of the plasma sheet and ring current. Particular attention is given to the kinetic approach in magnetospheric plasma transport modeling, self-consistent neutral point current and fields from single particle dynamics, preliminary statistical survey of plasmaspheric ion properties from observations by DE 1/RIMS, and a model of auroral potential structures based on dynamics explorer plasma data. Other topics include internal shear layers in auroral dynamics, quantitative parameterization of energetic ionospheric ion outflow, and open flux merging in an expanding polarcap model.

Moore, T. E. (editor); Waite, J. H., Jr. (editor)



Radio Tomography of Ionospheric Structures (probably) due to Underground-Surface-Atmosphere-Ionosphere Coupling  

NASA Astrophysics Data System (ADS)

Ionospheric radio-tomography (RT) utilizes radio signals transmitted from the global navigational satellite systems (GNSS), including low-orbiting (LO) navigational systems such as Transit, Tsikada, etc., and high-orbiting (HO) navigational systems such as GPS, GLONASS, Galileo, Beidou, etc. The signals that are transmitted from the LO navigational satellites and recorded by ground receiving chains can be inverted for almost instantaneous (5-8 min) 2D snapshots of electron density. The data from the networks of ground receivers that record the signals of the HO satellites are suitable for implementing high-orbital RT (HORT), i.e. reconstructing the 4D distributions of the ionospheric electron density (one 3D image every 20-30 min). In the regions densely covered by the GNSS receivers, it is currently possible to get a time step of 2-4 min. The LORT and HORT approaches have a common methodical basis: in both these techniques, the integrals of electron density along the ray between the satellite and the receiver are measured, and then the tomographic procedures are applied to reconstruct the distributions of electron density. We present several examples of the experiments on the ionospheric RT, which are related to the Underground-Surface-Atmosphere-Ionosphere (USAI) coupling. In particular, we demonstrate examples of RT images of the ionosphere after industrial explosions, rocket launches, and modification of the ionosphere by high-power radio waves. We also show RT cross sections reflecting ionospheric disturbances caused by the earthquakes (EQ) and tsunami waves. In these cases, there is an evident cause-and-effect relationship. The perturbations are transferred between the geospheres predominantly by acoustic gravity waves (AGW), whose amplitudes increase with increasing height. As far as EQ are concerned, the cause of the USAI coupling mechanism is not obvious. It is clear, however, that the regular RT studies can promote the solution of this challenging problem. The single-point measurements (by ionosondes or by isolated receivers) are not amenable to unambiguous interpretation; based on these data, it is impossible to distinguish the contribution of USAI coupling from the ionospheric effects induced by the "ordinary" impacts (the Sun, the solar wind, geomagnetic perturbations, galactic cosmic rays, etc.). In order to localize sources of the ionospheric disturbances, the geophysicist needs information on the spatial structure and dynamics of the ionospheric perturbations. This information (2D-4D RT images) is optimally provided by RT methods. We present examples of the ionospheric disturbances caused by EQs as well as the ionospheric precursors of these EQs in the form of specific ionospheric irregularities: AGW- and soliton-like wave disturbances, which we identified using RT methods. Based on the results of the RT studies in the Alaska and Taiwan regions, we have detected several dozen AGW-related precursors of EQs. These data allow us to attempt to locate the source of these perturbations. We discuss the possibilities and prospects of further research aimed at identifying and analyzing precursors of EQs and establishing the mechanisms of USAI coupling. We are grateful to Northwest Research Associates, Inc., and Dr. L.-C.Tsai for providing raw RT data for Alaska and Taiwan.

Kunitsyn, V.; Nesterov, I.; Andreeva, E.; Rekenthaler, D. A.



The application of artificial electron beams to magnetospheric research  

NASA Technical Reports Server (NTRS)

Scientific and technical progress made in the utilization of electron beams injected from large sounding rockets for the investigation of magnetospheric structure and dynamics and plasma physics is reviewed. Consideration is given to the problem of vehicle neutralization during the generation of electron beams in the ionosphere and the stability and electromagnetic wave emissions of electron beams propagating in space. Optical effects observed during the two Hess artificial aurora experiments, the Minnesota Echo IV and V experiments, the Zarnitsa-1 artificial aurora experiment and the Precede-Excede experiments are discussed, together with atmospheric scattering effects observed during Echo I, II and III, and results of the three experimental programs which have detected and analyzed beams after passage through the distant magnetosphere (the second Hess experiment, ARAKS and the Electron Echo experiments) are presented. Finally, plans for future research are outlined, and a chronology and complete bibliography of the programs conducted to date are included.

Winckler, J. R.



In-situ studies of plasma irregularities in high latitude ionosphere with the ICI-2 sounding rocket within the 4DSpace project  

NASA Astrophysics Data System (ADS)

Ionospheric plasma is often characterized by irregularities, instabilities, and turbulence. Two regions of the ionospheric F-layer are of particular interest: low-latitudes for the equatorial anomaly and electrojet, and high-latitude regions where the most dynamic phenomena occur due to magnetic field lines coupling to the magnetosphere and the solar wind. The spectra of plasma fluctuations in the low-latitude F-layer usually exhibit a power law with a steeper slope at high frequencies [1]. Until recently, there was no clear evidence of the corresponding double slope spectra for plasma fluctuations in the high latitude ionospheric F-layer, and this difference was not well understood. We report the first direct observations of the double slope power spectra for plasma irregularities in the F-layer of the polar ionosphere [2]. The ICI-2 sounding rocket, which intersected enhanced plasma density regions with decameter scale irregularities in the cusp region, measured the electron density with unprecedented high resolution. This 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 gyro-frequency. The double slope spectra are further supported by the results from the ICI-3 sounding rocket. Double slope spectra were not resolved in previous works presumably due to limited resolution of instruments. The study is a part of the 4DSpace initiative for integrated studies of the ionospheric plasma turbulence with multi-point, multi-scale in-situ studies by sounding rockets and satellites, and numerical and analytical models. A brief overview of the 4DSpace initiative is given. [1] M.C. Kelley, The Earth’s Ionosphere Plasma Physics and Electrodynamics (Elsevier, Amsterdam 2009). [2] A. Spicher, W. J. Miloch, and J. I. Moen, Geophys. Res. Lett. 40, (in press, accepted 13.02.2014).

Miloch, Wojciech; Moen, Joran; Spicher, Andres



E-print Network

METEORIC PLASMA LAYERS ON VENUS AND MARS WITHERS ± PATM 2012 ± PAGE 1 OF 33 Table of Contents Cover meteoroids do to ionospheres 2 2 ± Outline of proposed investigation 4 3 ± Available observations of meteoric layers 4 4 ± Available numerical model of meteoric layers 5 5 ± Task A: Comparison of basic observed

Withers, Paul


Small-scale variability in Saturn's lower ionosphere  

NASA Astrophysics Data System (ADS)

We perform and present a wavelet analysis on all 31 Cassini electron density profiles published to date (Nagy, A.F. et al. [2006]. J. Geophys. Res. 111 (A6), CiteID A06310; Kliore, A.J. et al. [2009]. J. Geophys. Res. 114 (A4), CiteID A04315). We detect several discrete scales of variability present in the observations. Small-scale variability (S < 700 km) is observed in almost all data sets at different latitudes, both at dawn and dusk conditions. The most typical scale of variability is 300 km with scales between 200 km and 450 km being commonly present in the vast majority of the profiles. A low latitude dawn/dusk asymmetry is noted in the prevalent scales with the spectrum peaking sharply at the 300 km scale at dusk conditions and being broader at dawn conditions. Compared to dawn conditions the dusk ionosphere also shows more significant variability at the 100 km scale. The 300 km vertical scale is also present in the few available profiles from the northern hemisphere. Early observations from 2005 show a dominant scale at 350 km whereas later in 2007-2008 the spectrum shifts to the shorter scales with the most prominent scale being 300 km. The performed wavelet analysis and the obtained results are independent of assumptions about the nature of the layers and do not require a definition for a "background" electron density profile. In the second part of the paper we present a gravity wave propagation/dissipation model for Saturn's upper atmosphere and compare the wave properties to the characteristics of the observed electron density variability at different scales. The general features observed in the data are consistent with gravity waves being present in the lower ionosphere and causing layering of the ions and the electrons. The wave-driving mechanism provides a simultaneous explanation for several of the properties of the observed variability: (i) lack of variability in the electron density above the predicted region of wave dissipation; (ii) in most cases the peak amplitude of variability occurs within the altitude range for dissipation of gravity waves or below; (iii) shorter scales have smaller amplitudes than the longer scales; (iv) shorter scales are present at lower altitudes whereas longer scales persist to higher altitudes; and (v) several layers often form a system of equally spaced maxima and minima that can be traced over a large altitude range.

Matcheva, Katia I.; Barrow, Daniel J.



Ionospheric effects during first 2 hours after the "Chelyabinsk" meteorite impact  

NASA Astrophysics Data System (ADS)

In this paper, we analyzed the ionospheric effects within the 100-1500 km ranges from the Chelyabinsk meteorite explosion site from the ISTP SB RAS EKB radar data, and from the IG UB RAS PARUS ionosonde data. Both instruments are located at the Arti Observatory, approximately 200 km north of the supposed explosion location. The ionospheric disturbance caused by the meteorite flyby, explosion, and impact had high dynamics and amplitude. Essential effects, however, were observed at more than 100-200 km from the explosion site, and farther, up to 1500 km. Almost simultaneously with the explosion and for 3 minutes (03:20-03:23 UT), there was a motion away from the radar 400 km southwest of the latter (and approximately 200 km west of the explosion site) at the E-layer height with the characteristic velocities 200 m/s and high spectral width. A short delay of the detected effect at a significant distance from the explosion site also testifies to the hypothesis of a large short-living irregularity formations at the heights of the lower E-layer, with the transversal size of several hundreds of kilometers. The first disturbance in the F-layer was observed 15 minutes after the explosion, and it propagated away from the radar almost radially. The radial disturbances were observed up to about 80-100 minutes. The main disturbances in the F-layer were nearly radial waves with the center close to the explosion site. Analyzing the experimental data allowed us to determine the equivalent ionospheric velocities for individual travel mode. The work was done under financial support of RFBR grant #14-05-00514-a.

Berngardt, Oleg; Kurkin, Vladimir; Zherebtsov, Gelii; Grigorieva, Svetlana; Kusonski, Oleg


Sources of the traveling ionospheric disturbances observed by the ionospheric TIDDBIT sounder near Wallops Island on 30 October 2007  

NASA Astrophysics Data System (ADS)

We model the gravity waves (GWs) excited by Tropical Storm (TS) Noel at 0432 UT on 30 October 2007. Using forward ray tracing, we calculate the body forces which result from the saturation and dissipation of these GWs. We then analyze the 59 traveling ionospheric disturbances (TIDs) observed by the TIDDBIT ionospheric sounder at 0400-1000 UT near Wallops Island. These TIDs were located at the bottomside of the F layer at z = 230-290 km, had periods of ?r = 15 to 90 min, horizontal wavelengths of ?H = 100 to 3000 km, and horizontal phase speeds of cH = 140 to 650 m/s. 33 (˜60%) of the TIDs were propagating northwest(NW) and north(N)ward, from the direction of TS Noel 1700-2000 km away. We show that these TIDs were likely GWs. 40% of these GWs had phase speeds larger than 280m/s. This precluded a tropospheric source and suggested mesospheric and thermospheric sources instead. Using reverse ray tracing, we compare the GW locations with the regions of convective overshoot, mesospheric body forces, and thermospheric body forces. We identify 27 of the northwest/northward propagating GWs as likely being secondary GWs excited by thermospheric body forces. Three may have originated from mesospheric body forces, although this is much less likely. None are identified as primary GWs excited directly by TS Noel. 11 of these GWs with cH < 205 m/s likely reflected near the tropopause prior to detection. This secondary GW spectrum peaks at ?H ˜ 100-300 km and cH ˜ 100-300 m/s. To our knowledge, this is the first identification and quantification of secondary GWs from thermospheric body forces.

Vadas, Sharon L.; Crowley, Geoff



Ionospheric scintillation in Brazil: Analyses and Effects on GNSS Positioning  

NASA Astrophysics Data System (ADS)

Ionosphere has a great influence on GNSS (Global Navigation Satellite System) signals and its behavior depends on several variables: local time, geographic location, seasons and solar activity. Besides, there are ionospheric irregularities that also affect the GNSS signal propagation, as the ionospheric scintillation. The ionospheric scintillation can be described as a fast change in phase and amplitude of GNSS signal, caused by irregularities of electron density. Scintillation can degrade or cause the GNSS signal lost. Due to these described factors, one can say that the ionosphere can cause important effects on GNSS positioning. It can degrade the coordinate accuracy obtained by GNSS positioning methods. In this paper the goal is to evaluate the ionospheric effect, in special the ionospheric scintillation in different regions of Brazil, and its effects on GNSS Point Positioning. In order to evaluate the days where the scintillation was more significant it is used a database ( from CIGALA (Concept for Ionospheric Scintillation Mitigation for Professional GNSS in Latin America) project ( Using these data it is possible to obtain information about ionospheric scintillation in different GNSS stations in Brazil. It is possible to correlate the data according to time, season and other factors that can contribute to scintillation analysis. In 2013 must occur an intense solar activity, which can intensify the ionospheric effects, and consequently ionospheric scintillation, mainly in Brazil region, where the scintillation index is already intense. Preliminary evaluations, showed larger values of S4 (scintillation index) in Brazil. For example, in October 2012, it was obtained S4 values larger than 1 in several epochs. This causes severe effects in GNSS Positioning. In this paper, the results of GNSS positioning under ionosphere scintillation effects in different regions of Brazil will be presented.

Alves, D. B.; Souza, J. S.; Silva, H. D.



Measured ionospheric Doppler spreading of HF ground backscatter  

NASA Astrophysics Data System (ADS)

Doppler spectra from ionospherically propagated ground backscatter are presented. These spectra show how the ionosphere distorts HF backscatter radio waves by frequency speading. The ground backscatter spectra presented here show that ionospheric Dopper spreading is so ubiquitous that its effect should never be disregarded, even when a narrow azimuth beam radar such as ours is used. Nevertheless, Doppler spreading varies so quickly that it usually pays to wait for it to diminish.

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



Global Ionospheric Radio Observatory (GIRO): Status and prospective  

Microsoft Academic Search

The Global Ionospheric Radio Observatory (GIRO), http:\\/\\/, acquires and disseminates HF ionospheric sounding data from 64 Digisonde locations in 27 countries. GIRO publishes its 30+ million record holdings over the Internet, provides an interactive read\\/write environment to experts of data interpretation, and forwards real-time data for measurement assimilation and radio propagation and space weather forecast. Of importance to the ionospheric

Ivan A. Galkin; Bodo W. Reinisch



Flow Visualization of Artificially Generated Hairpin Vortices  

NASA Astrophysics Data System (ADS)

To investigate the potential mechanisms for hairpin packet formation in fully turbulent boundary layers, a flow visualization study of artificially generated hairpin vortices in an otherwise laminar boundary layer is performed. The experiments are conducted in a recently constructed free surface water channel at Lafayette College. A new method to artificially generate individual hairpin vortices is employed which utilizes a flexible membrane which is inflated to create transient hemispherical protrusions on a flat plate, zero pressure gradient laminar boundary layer. By controlling the duration of time the membrane protrudes above the wall, a single vortex can be reliably generated. This technique avoids the need for fluid injection in order to ensure uniform particle seeding for subsequent PIV measurements. Multiple generation sites are placed at different streamwise locations to allow hairpins of different maturity to interact. The characteristics of single hairpin vortices will be compared to those described in the literature along with a qualitative analysis of the interaction of two hairpin vortices.

Sabatino, Daniel; Palframan, Mark



Dynamic interactions between ionospheric plasma and spacecraft  

NASA Technical Reports Server (NTRS)

Studies of the interactions between the Space Station Freedom and ionospheric plasma led to an improved understanding of the dynamics of these interactions. Some of the issues related to developing and sustaining arcs in ionospheric conditions are considered. A technique for the estimation of the amplitude and duration of arcs is presented. The technique uses the capacitance of the system to estimate the peak current and then uses the charge stored to estimate the arc duration. As new technologies are implemented on spacecraft, new environmental compatibility issues will arise. Some of the issues related to driving dielectric surfaces with alternating current voltages are considered. The steady state charging criteria is that over an oscillation, the ion charge collected is compensated for by the electron charge collected. This tends to drive the average potential negative so that the dielectric surface is positive for only a small portion of the cycle.

Snyder, David B.



Preseismic Lithosphere-Atmosphere-Ionosphere Coupling  

NASA Astrophysics Data System (ADS)

Preseismic atmospheric and ionospheric disturbances besides preseismic geo-electric potential anomalies and ultra-low-frequency (ULF) geomagnetic variations observed on the ground have been reported. Both the phenomena have been found since the 1980s and a number of papers have been published. Since most of the reported phenomena transiently appear with accompanying quiescence before the mainshock, this prevents us to intuitively recognize a correlation between the anomaly appearance and the earthquake occurrence. Some of them, however, showed that anomalies monotonically grew into the mainshock, of which a variation supports the concept of seismic nucleation process under the pre-earthquake state. For example, Heki [GRL, 2011] reported that ionospheric electron density monotonically enhanced tens of minutes prior to the subduction mega-earthquake. However, this preseismic enhancement is apparent variation attributed to tsunamigenic ionospheric hole [Kakinami and Kamogawa et al, GRL, 2012], namely wide and long-duration depression of ionospheric electron after tsunami-excited acoustic waves reach the ionosphere. Since the tsunamigenic ionospheric hole could be simulated [Shinagawa et al., GRL, 2013], the reported variations are high-possibly pseudo phenomena [Kamogawa and Kakinami, JGR, 2013]. Thus, there are barely a few reports which show the preseismic monotonic variation supported by the concept of the seismic nucleation process. As far as we discuss the preseismic geoelectromagnetical and atmospheric-ionospheric anomalies, preseismic transient events from a few weeks to a few hours prior to the mainshock are paid attention to for the precursor study. In order to identify precursors from a number of anomalies, one has to show a statistical significance of correlation between the earthquake and the anomalies, to elucidate the physical mechanism, or to conduct both statistical and physical approach. Since many speculation of the physical mechanism have been hardly verified so far, a statistical approach has been unique way to promote the research. After the 2000s, several papers showing robust statistical results have arisen. In this paper, we focus on publications satisfying the following identification criteria: 1) A candidate of precursor, namely anomaly, is quantitatively defied. 2) Two time-series of anomalies and earthquake are constructed within the fixed thresholds such as a minimum magnitude, a region, and a lead-time. 3) To obtain a statistical correlation, a statistical process which includes four relations considering all combination among earthquake - no earthquake versus anomaly and no anomalies is applied, e. g., phi correlation. 4) For correlations under various thresholds the results keep consistency. 5) Large anomalies appear before large earthquakes. One of papers based on the identification criteria, which concerns preseismic geoelectrically anomalies, is introduced as an educative example. VAN method in Greece, i. e., Geo-electric potential difference measurement for precursor study in Greece, has been often discussed in the point of view of success and failure performance for practical prediction [Varotsos et al, Springer, 2011] to show a correlation and then less number of papers shows the statistical correlation with satisfying the identification criteria [Geller (ed.), GRL, 1996], so that the phenomena had been controversial. However, recent related study in Kozu-Island, Japan which satisfied the criteria showed the robust correlation [Orihara and Kamogawa et al., PNAS, 2012]. Therefore, the preseismic geoelectric anomalies are expected to be a precursor. Preseismic lithosphere-atmosphere-ionosphere coupling has been intensively discussed [Kamogawa, Eos, 2006]. According to review based on the identification criteria with considering recent publications, plausible precursors have been found, which are tropospheric anomaly [Fujiwara and Kamogawa, GRL, 2004], daytime electron depletion in F region [Liu et al, JGR, 2006], nighttime decrease of background intensity of VLF electromagnetic waves poss

Kamogawa, Masashi


Electric fields in the ionosphere and magnetosphere.  

NASA Technical Reports Server (NTRS)

Review of current techniques for measuring ionospheric and magnetospheric electric fields and existing measurements. Considerable progress in understanding electric fields has been made in the auroral regions where fields originating basically from convection patterns in the magnetosphere and modified by ionospheric interaction have been detected by both the barium ion cloud and double floating probe techniques and have been compared against predictions. The anticorrelation of electric fields and auroral arcs, the establishment of the auroral electrojet currents as Hall currents, the irregular nature of the electric fields, and the reversal of the electric fields between the eastward and westward electrojet regions have been some of the important observations. Recent barium ion cloud observations in the polar cap have indicated that the long assumed electrojet return current across the polar cap does not exist.

Maynard, N. C.



Connection Between the Magnetosphere and Ionosphere  

NASA Technical Reports Server (NTRS)

Two decades of space research have produced ample evidence that particles and fields originating in the active Sun can gain entry into the terrestrial magnetosphere and deposit their energy in the ionosphere and atmosphere. The final link in this solar-terrestrial chain is generically referred to as magnetosphere-ionosphere coupling (MIC). Because of the far-reaching implications of recent discoveries in MIC and because a coherent assessment of them has yet to be made, the principal task is to critically assess these new observations and the new perspectives that they may engender. The MIC topics of interest are roughly grouped according to the scale lengths of the phenomena being treated. This particular choice of groupings is mainly for convenience, with perhaps some suggestion as to the direction of energy cascade from the largest scales down to the smaller scale.



Ionospheric perturbation degree estimates for improving GNSS applications  

NASA Astrophysics Data System (ADS)

Ionosphere can adversely affect accuracy, continuity, availability, and integrity of modern Global Navigation Satellite Systems (GNSS) in different ways. Hence, reliable information on key parameters describing the perturbation degree of the ionosphere is helpful for estimating the potential degradation of the performance of these systems. So, to guarantee the required safety level in aviation, Ground Based Augmentation Systems (GBAS) and Satellite Based Augmentation Systems (SBAS) have been established for detecting and mitigating ionospheric threats in particular due to ionospheric gradients. The paper reviews various attempts and capabilities to characterize the perturbation degree of the ionosphere currently being used in precise positioning and safety of life applications. Continuity and availability of signals are mainly impacted by amplitude and phase scintillations characterized by indices such as S4 or phase noise. To characterize medium and large scale ionospheric perturbations that may seriously affect accuracy and integrity of GNSS, the use of an internationally standardized Disturbance Ionosphere Index (DIX) is recommended. The definition of such a DIX must take into account the practical needs, should be an objective measure of ionospheric conditions and easy and reproducible to compute. A preliminary DIX approach is presented and discussed. Such a robust and easy adaptable index should have a great potential for being used in operational ionospheric weather services and GNSS augmentation systems.

Jakowski, Norbert; Mainul Hoque, M.; Wilken, Volker; Berdermann, Jens; Hlubek, Nikolai


Management and Operations of the National Astronomy and Ionosphere Center  

NSF Publications Database

... Astronomy and Ionosphere Center (NAIC), provides instrumentation for research in radio astronomy ... observing capabilities in radio astronomy, radar astronomy, and atmospheric sciences, and observing ...


Magnetosphere-Ionosphere coupling through the auroral acceleration region  

NASA Technical Reports Server (NTRS)

An important form of coupling between the magnetosphere and the ionosphere occurs through acceleration mechanisms operative in the high altitude ionosphere on magnetic field lines connecting to the auroral zone. Energetic ion mass spectrometer data from within these auroral acceleration regions are presented to illustrate the characteristics of the mechanisms. Observations of ionospheric plasmas in the ring current, the distant plasma sheet, and the magnetotail lobes are shown illustrating the extent of their circulation and the importance of their contribution to the plasma in each regime. Finally the precipitating plasmas in the auroral region and the extent and peculiar effects of the 0(+) component of that precipitation on the ionosphere are illustrated.

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



Joule heating of Io's ionosphere by unipolar induction currents  

NASA Technical Reports Server (NTRS)

Electrical induction in Io's ionosphere, due to the corotating plasma bound to the Jovian magnetosphere, is one possible source for the attainment of the high temperatures suggested by the large scale height of Io's ionosphere. Unipolar induction models are constructed to calculate ionospheric joule heating numerically, whose heating rates lie between 10 to the -9th and 10 to the -8th W/cu m. The binding and coupling of the ionosphere is due to the dense, and possibly ionized, neutral SO2 atmosphere, and there appears to be no need to postulate the existence of an intrinsic Ionian magnetic field in order to retain the observed ionnosphere.

Herbert, F.; Lichtenstein, B. R.



The Structure of the Titan Ionosphere  

NASA Astrophysics Data System (ADS)

Eight vertical profiles of the electron density in Titan's ionosphere were derived from the Cassini radio occultations of March 26, and May28, 2007 (T27 and T31), as well as those of March 19, 2006 (T12), and May 20,2006 (T14) . The 2006 occultations occurred at low Southern latitudes of 14.7S, 36.2S, 19.8S, and 21.9S. The 2007 occultations were nearly polar, at latitudes of 75S and 61N for T27. and 75S and 74N for T31.. The solar zenith angles for all occultations were near the terminator, ranging from 85 to 95 deg. The ionosphere peak was observed to lie close to an altitude of 1200 km, and the observed peak densities ranged from about 1.2 to 2.2 x 103 cm-3, which is in good agreement with other Cassini observations and the previous Voyager radio occultation results. In all measurements, the peak densities are about 30% higher near the dusk terminator, showing the influence of solar EUV. Radio occultation observations of the Titan ionosphere are difficult because of its low density and small size, and it was facilitated by the unprecedented Cassini radio science system, which has three frequencies that can operate simultaneously: S-band (2.3 GHz), X-band (8.4 GHz), and Ka-band (32 GHz). In particular, Ka-band had never been used before to probe Titan's ionosphere, and the signal-to-noise ratios at all frequencies of 42, 54, and 48 dB-Hz., respectively, have never before been achieved. The rsults indicate a clear dusk-dawn asymmetry in peak electron density, with the average dusk densty being about 40% greater than the dawn side. . The dusk profiles also have more structure both above and below the main peak, including a peak at about 500 km. altitude.

Kliore, Arvydas J.; Nagy, A. F.; Flasar, F. M.; Schinder, P. J.; French, R. G.; Marouf, E. A.; Rappaport, N. J.; Anabtawi, A.; McGhee, C. A.; Cassini Radio Science Support Team



Ionospheric Signatures in Radio Occultation Data  

NASA Technical Reports Server (NTRS)

We can extend robustly the radio occultation data record by 6 years (+60%) by developing a singlefrequency processing method for GPS/MET data. We will produce a calibrated data set with profile-byprofile data characterization to determine robust upper bounds on ionospheric bias. Part of an effort to produce a calibrated RO data set addressing other key error sources such as upper boundary initialization. Planned: AIRS-GPS water vapor cross validation (water vapor climatology and trends).

Mannucci, Anthony J.; Ao, Chi; Iijima, Byron A.; Kursinkski, E. Robert



Satellite observations of an ionospheric acceleration mechanism  

Microsoft Academic Search

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

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



Photoelectron escape from the ionosphere of Jupiter  

NASA Technical Reports Server (NTRS)

Photoelectron escape fluxes and ambient electron heating from the Jovian ionosphere are computed as a function of local time and latitude. Several differences for the fluxes expected from a hydrogen atmosphere, rather than a terrestrial type of atmosphere, are described, including an increase in structure in the energy spectra due to the paucity of ionic states entering the photo-ionization processes and lower escape fluxes above 10 eV than were expected from a simple scaling of earth fluxes.

Swartz, W. E.; Reed, R. W.; Mcdonough, T. R.



Anomalous Seismo-ionospheric Perturbations Observed in Sub-ionospheric VLF Signal  

NASA Astrophysics Data System (ADS)

Electromagnetic anomalies have been observed in sub-ionospheric VLF signal before recent earthquakes in Japan on 15 February, 2009, Nicobar Island, India on 10 August, 2009 and Kepulaun Mentawai Region, Indonesia on 16 Aug 2009. VLF signal transmitted from Hawaii, USA North West Cape, Australia is monitored continuously at our ground station Varanasi. Here we have tried to find out ionospheric perturbations revealed by VLF signals prior to the earthquake. We observed a significant enhancement in nighttime fluctuation several days before the earthquake. VLF radio waves show anomalous variations in amplitude from their day to day variability. It is fond that nighttime trend exhibit a significant decrease in amplitude several days before the earthquake. Apart form the decrease in amplitude it is also found that there is sudden enhancement in daytime amplitude, within 48 hours prior to the earthquake. The possible mechanisms for these ionospheric perturbations due to earthquake have been discussed.

Singh, Ashutosh Kumar; Singh, Rajesh; Singh, Abhay Kumar


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

NASA Technical Reports Server (NTRS)

The geomagnetic control of the Earth's atmosphere is well understood. In the F-region and the topside ionosphere, non-electrical forces transport plasma along the magnetic field lines only. In consequence, the worldwide distribution of ionization is strongly dependent on the dip angle. For example, the equatorial anomaly is roughly symmetrical about the dipole equator rather than the geographic. The same appears to be the case in the Jovian ionosphere (Mahajan, 1981). The influence of the magnetic field of Jupiter on its ionization pattern is one of several outstanding topics which need to be studied. Tan (1986) investigated the formation of the equatorial anomaly in the Jovian ionosphere under a centered dipole model. Tan (1988) further studied the effect of the tilt of the Jovian dipole. The results were in broad agreement with those of a diffusive equilibrium model (Tan and Wu, 1981). An off-centered dipole model is constructed and its effects on the ionization pattern are investigated.

Tan, A.



Solar Flare Impacts on Ionospheric Electrodynamics  

NASA Technical Reports Server (NTRS)

The sudden increase of X-ray and extreme ultra-violet irradiance during flares increases the density of the ionosphere through enhanced photoionization. In this paper, we use model simulations to investigate possible additional contributions from electrodynamics, finding that the vertical E X B drift in the magnetic equatorial region plays a significant role in the ionosphere response to solar flares. During the initial stage of flares, upward E X B drifts weaken in the magnetic equatorial region, causing a weakened equatorial fountain effect, which in turn causes lowering of the peak height of the F2 region and depletion of the peak electron density of the F2 region. In this initial stage, total electron content (TEC) enhancement is predominantly determined by solar zenith angle control of photoionization. As flares decay, upward E X B drifts are enhanced in the magnetic equatorial region, causing increases of the peak height and density of the F2 region. This process lasts for several hours, causing a prolonged F2-region disturbance and TEC enhancement in the magnetic equator region in the aftermath of flares. During this stage, the global morphology of the TEC enhancement becomes predominantly determined by these perturbations to the electrodynamics of the ionosphere.

Qian, Liying; Burns, Alan G.; Solomon, Stanley C.; Chamberlin, Phillip C.



Adapting empirical ionosphere models to experimental data  

NASA Astrophysics Data System (ADS)

Empirical electron density models, like the International Reference Ionosphere (IRI) and the NeQuick, have been conceived to reproduce the climatological behavior of the ionosphere. To improve the specification of the three-dimensional electron density of the ionosphere for current conditions, different techniques based on the NeQuick adaptation to experimental data have been developed. As a first step, a procedure to ingest GPS-derived vertical total electron content (TEC) maps into the model has been developed using the concept of effective parameter to define the model input Az (ionization level). To consider the possibility of implementing nearreal-time applications, an electron density retrieval method based on direct ingestion of slant TEC data into NeQuick model has been developed. Afterwards, to further improve the model electron density profile formulation, a technique for simultaneously adapting the NeQuick model to TEC data and ionosondes peak parameters has also been proposed. In the present paper, after reviewing the methods developed to update the NeQuick with experimental data, an indication about how to apply the same techniques to IRI will be given.

Nava, Bruno; Coïsson, Pierdavide; Radicella, Sandro M.


Comparative Ionospheres: All Planets Enjoy Sunshine  

NASA Astrophysics Data System (ADS)

The ionization of a planet's (or moon's) upper atmosphere is caused by energetic photons (EUV and X-rays), augmented by the influx of energetic particles (meteoritic, heliospheric, magnetospheric). The primary structure of an ionosphere, its electron density profile with height Ne(h), results from photochemical processes, with modifications (sometimes dramatically so) due to transport. Typically, the Ne(h) profiles on Venus and Mars conform to photochemical equilibrium, while at Earth both photochemistry and dynamics are needed. For the giant planets, photochemistry alone is unable to match observations. This suggests the need for dynamical processes (winds, E-fields), energetics (e.g., loss via vibrationally-excited molecules), and possible influxes of material (e.g., water products)--- all poorly constrained by observations. Variable solar activity affects all planetary ionospheres, and local plasma instabilities may occur as well. This brief paper provides an overview of known characteristics of planetary ionospheres, and then gives examples of regional and episodic disturbances on Mars as a way to encourage the study of solar-terrestrial planet-relationships (STPR) as a future direction for aeronomy.

Mendillo, M.



A review of artificial intelligence  

Microsoft Academic Search

This paper reviews the field of artificial intelligence focusing on embodied artificial intelligence. It also considers models of artificial consciousness, agent-based artificial intelligence and the philosophical commentary on artificial intelligence. It concludes that there is almost no consensus nor formalism in the field and that the achievements of the field are meager.

E. S. Brunette; R. C. Flemmer; C. L. Flemmer



Season Variation of Ionosphere Effects of geomagnetic Storms at different Latitudes of East Asia  

NASA Astrophysics Data System (ADS)

The most important factors governing the variations of the ionosphere at the time of the geomagnetic storm include a change in electron composition and the circulation system of neutral wind, which depends substantially on the season. Besides, the difference of the geographic and magnetic coordinates complicates the picture of disturbances and leads to a longitudinal dependence of ionospheric effects of geomagnetic storms. We analyzed the state of the ionosphere using the data from a network of ionosondes and digisondes located in the longitudinal sector of 90-130°E. This region is of interest because the difference between the geographic and magnetic coordinates there is the largest, and formation of a large-scale structure proceeds at the more high geographic latitudes where ionization very depends from season. We investigated the variations of F2-layer critical frequencies, ionospheric altitudes and the ionospheric disturbance index DfoF2. The average a few quiet days variations of foF2, hF and hmF2 were used as the undisturbed level. We considered geomagnetic storms of a different intensity evolving from May, 2003 till January, 2004. During this period there were marked ten storms, which could be divided into the different season. The prolonged negative disturbances at high and middle latitudes were typical for the summer geomagnetic storms during all disturbed period. The increase of foF2 with a subsequent abrupt decrease of foF2 occurred in the evening after the Dst-index had reached its minimum value. At magnetic latitudes lower 30° the disturbances were mainly positive. The tendency of the disturbance variations maintained in the winter and in the autumn. However at high latitudes the intensive positive disturbances caused by precipitation of auroral fluxes were observed in the evening and night. The received variety of disturbances in different seasons is determined primarily by the illumination conditions of ionosphere and the local time of geomagnetic storm onset. The presented experimental results can be used to testing and the correction of empirical models. This work was done with financial support of the Russian Foundation for Basic Research (grant 02-05-39002).

Pirog, O. M.; Polekh, N. M.; Ratovsky, K. G.; Zherebtsov, G. A.; Smirnov, V. F.; Shi, J. K.; Wang, X.


Ionospheric responses to two large geomagnetic storms over Japanese and Indian longitude sectors  

NASA Astrophysics Data System (ADS)

The physical processes including the prompt penetration electric field, disturbance dynamo originated electric field, disturbed thermospheric winds and composition changes can play a significant role in restructuring the equatorial, low, mid and high-latitude ionosphere during storm-time. However, it has not yet been revealed that the contribution of individual physical processes, their interactions and impacts on that restructuring (Maruyama et al., 2005) is primarily due to the lack of continuous observational facilities. In this present research, the electric field (measured indirectly) and thermospheric wind (derived from an empirical disturbance wind model) components are effectively utilized as alternate database to ascertain the individual role of physical processes by studying the ionospheric response over Japanese and Indian longitude sectors during two geomagnetic storms occurring on 31 March, 2001 and 20 November, 2003 using ground (ionospheric parameters scaled from ionosondes and global ionospheric maps of total electron content measured by the ground-based GPS receivers) and satellite-borne (in-situ electron density data measured by the Planar Longmuir Probe onboard CHAMP satellite) measurements. It has been found that the equatorial ionization anomaly is expanded and intensified during the main phase of these two storms, which is believed to be caused by the prompt penetration electric field according to the current theory. In addition, the storm associated thermospheric wind is propagating equatorward (with an average velocity of ˜230 m/s) during the recovery phase of these two storms that is responsible for a height rise in the virtual height of the F-layer (h'F) starting from mid to low and equatorial latitudes with a consistent time delay. The empirical model derived winds corroborate the equatorward propagation, suggesting that this wind model data could be used as an alternate database particularly during the space weather events in order to discuss the global dynamical state of the ionosphere. Further, an important observation is that the ionospheric irregularities are found in the electron densities in the form of depletions nearly at anomaly crest region (˜23°N) as measured by the CHAMP satellite over the Japanese longitude sector during the main phase of the 20 November, 2003 storm during the pre mid night period that correspond to the time of rapid decrease (˜-30-35 nT/h) in Sym-H index due to prompt penetration of eastward electric fields into the low latitudes.

Uma, G.; Brahmanandam, P. S.; Kakinami, Yoshihiro; Dmitriev, A.; Latha Devi, N. S. M. P.; Uday Kiran, K.; Prasad, D. S. V. V. D.; Rama Rao, P. V. S.; Niranjan, K.; Seshu Babu, Ch.; Chu, Y. H.



Solar Cycle Variations of the Lower Ionosphere Detected by VLF Remote Sensing  

NASA Astrophysics Data System (ADS)

Stanford University’s Very Low Frequency (VLF) Beacon transmitter resumed its operations at South Pole Station in February 2009 for the purpose of studying the ionospheric effects of energetic particle precipitation. VLF remote sensing (i.e., the measurement of the amplitude and phase of sub-ionospheric signals) is a sensitive tool for measuring ionospheric conductivity (i.e., electron density and temperature), especially at altitudes below 90 km. Using a 6.25 km dipole antenna, the Beacon transmits a 9 kW, 19.4 kHz signal for one minute out of every fifteen minutes. VLF receivers located at sites throughout Antarctica detect the transmitted signal including Palmer, Rothera, and Commandante Ferraz on the Antarctic Peninsula, SANAE in Queen Maud Land, and the Automated Geophysical Observatories (AGO) located inland. By integrating the signal for its 60-second duration, signal-to-noise ratios of >10 dB are typical at Palmer Station. The amplitude and phase measured at the stations depend on the height and conductivity of the D-region ionosphere along the propagation path and hence on the intensity of solar radiation and the intensity of particle precipitation from the polar cap to the subauroral zone. While there have not been significant precipitation events during this extended solar minimum, the amplitude and phase of the Beacon signal still shows a diurnal variation as the day-night terminator exposes different lengths of the propagation path to enhanced daytime ionization as the Earth rotates. The reduced solar activity has resulted in lower overall nighttime D-layer ionization. This appears as deeper diurnal variations in amplitude of the Beacon signal during solar minimum although the effect on the received phase is less predictable. We show comparisons of the amplitude and phase characteristics of the Beacon signal from 2009 with that from its last operating period during the declining phase of the previous solar cycle from 2004-2005 as well as with a sub-ionospheric model of VLF propagation using different ionospheric profiles.

Jin, G.; Spasojevic, M.; Inan, U. S.