WorldWideScience

Sample records for polar ionospheric model

  1. Rocket Measurements Within a Polar Cap Arc: Ionospheric Modelling,

    Science.gov (United States)

    1987-11-19

    References Aarons, Jules , Global morphology of ionospheric scintillations, Proc. IEEE, 70, 360, 1982. Banks, P.M., Chapell, C.R., and A.F. Nagy, A new model...penetration of soft electrons into the ionosphere, Planet. Space Sci., 24, 409, 1975. Mantas, George P., Carlson, Herbert C. Jr., and Caesar H. LaHoz

  2. Polar cap arcs from the magnetosphere to the ionosphere: kinetic modelling and observations by Cluster and TIMED

    Directory of Open Access Journals (Sweden)

    R. Maggiolo

    2012-02-01

    Full Text Available On 1 April 2004 the GUVI imager onboard the TIMED spacecraft spots an isolated and elongated polar cap arc. About 20 min later, the Cluster satellites detect an isolated upflowing ion beam above the polar cap. Cluster observations show that the ions are accelerated upward by a quasi-stationary electric field. The field-aligned potential drop is estimated to about 700 V and the upflowing ions are accompanied by a tenuous population of isotropic protons with a temperature of about 500 eV. The magnetic footpoints of the ion outflows observed by Cluster are situated in the prolongation of the polar cap arc observed by TIMED GUVI. The upflowing ion beam and the polar cap arc may be different signatures of the same phenomenon, as suggested by a recent statistical study of polar cap ion beams using Cluster data. We use Cluster observations at high altitude as input to a quasi-stationary magnetosphere-ionosphere (MI coupling model. Using a Knight-type current-voltage relationship and the current continuity at the topside ionosphere, the model computes the energy spectrum of precipitating electrons at the top of the ionosphere corresponding to the generator electric field observed by Cluster. The MI coupling model provides a field-aligned potential drop in agreement with Cluster observations of upflowing ions and a spatial scale of the polar cap arc consistent with the optical observations by TIMED. The computed energy spectrum of the precipitating electrons is used as input to the Trans4 ionospheric transport code. This 1-D model, based on Boltzmann's kinetic formalism, takes into account ionospheric processes such as photoionization and electron/proton precipitation, and computes the optical and UV emissions due to precipitating electrons. The emission rates provided by the Trans4 code are compared to the optical observations by TIMED. They are similar in size and intensity. Data and modelling results are consistent with the scenario of quasi

  3. The Effect of Sub-Auroral Polarization Streams (SAPS) on Ionosphere and Thermosphere during 2015 St. Patrick's Day storm: Global Ionosphere-Thermosphere Model (GITM) Simulations

    Science.gov (United States)

    Guo, J.; Deng, Y.; Zhang, D.; Lu, Y.; Sheng, C.

    2017-12-01

    Sub-Auroral Polarization Streams (SAPS) are incorporated into the non-hydrostatic Global Ionosphere-Thermosphere Model (GITM), revealing the complex effects on neutral dynamics and ion-neutral coupling processes. The intense westward ion stream could enhance the neutral zonal wind within the SAPS channel. Through neutral dynamics the neutrals then divide into two streams, one turns poleward and the other turns equatorward, forming a two-cell pattern in the SAPS-changed wind. The significant Joule heating induced by SAPS also leads to traveling atmospheric disturbances (TAD) accompanied by traveling ionospheric disturbances (TID), increasing the total electron content (TEC) by 2-8 TECu in the mid-latitude ionosphere. We investigate the potential causes of the reported poleward wind surge during the St. Patrick's Day storm in 2015. It is confirmed that Coriolis force on the westward zonal wind can contribute the poleward wind during post-SAPS interval. In addition, the simulations imply that the sudden decrease of heating rate within auroral oval could result in a TAD propagating equatorward, which could also be responsible for the sudden poleward wind surge. This study highlights the complicated effects of SAPS on ion-neutral coupling and neutral dynamics.

  4. Representation of the Auroral and Polar Ionosphere in the International Reference Ionosphere (IRI)

    Science.gov (United States)

    Bilitza, Dieter; Reinisch, Bodo

    2013-01-01

    This issue of Advances in Space Research presents a selection of papers that document the progress in developing and improving the International Reference Ionosphere (IRI), a widely used standard for the parameters that describe the Earths ionosphere. The core set of papers was presented during the 2010 General Assembly of the Committee on Space Research in Bremen, Germany in a session that focused on the representation of the auroral and polar ionosphere in the IRI model. In addition, papers were solicited and submitted from the scientific community in a general call for appropriate papers.

  5. A model of the plasma flow and current in Saturn's polar ionosphere under conditions of strong Dungey cycle driving

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    C. M. Jackman

    2006-05-01

    Full Text Available We propose a simple model of the flow and currents in Saturn's polar ionosphere. This model is motivated by theoretical reasoning, and guided quantitatively by in situ field and flow data from space missions, ground-based IR Doppler measurements, and Hubble Space Telescope images. The flow pattern consists of components which represent (1 plasma sub-corotation in the middle magnetosphere region resulting from plasma pick-up and radial transport from internal sources; (2 the Vasyliunas-cycle of internal plasma mass-loss down the magnetospheric tail at higher latitudes; and (3 the polar Dungey-cycle flow driven by the solar wind interaction. Upstream measurements of the interplanetary magnetic field (IMF indicate the occurrence of both extended low-field rarefaction intervals with essentially negligible Dungey-cycle flow, and few-day high-field compression regions in which the Dungey-cycle voltage peaks at a few hundred kV. Here we model the latter conditions when the Dungey-cycle is active, advancing on previous axi-symmetric models which may be more directly applicable to quiet conditions. For theoretical convenience the overall flow pattern is constructed by adding together two components - a purely rotational flow similar to previous axi-symmetric models, and a sun-aligned twin vortex representing the dawn-dusk asymmetry effects associated with the Vasyliunas-and Dungey-cycle flows. We calculate the horizontal ionospheric current associated with the flow and the field-aligned current from its divergence. These calculations show that a sheet of upward-directed field-aligned current flows at the boundary of open field lines which is strongly modulated in local-time by the Dungey-cycle flows. We then consider implications of the field-aligned current for magnetospheric electron acceleration and aurorae using two plasma source populations (hot outer magnetospheric electrons and cool dense magnetosheath electrons. Both sources display a strong dawn

  6. Polarization of Narrowband VLF Transmitter Signals as an Ionospheric Diagnostic

    Science.gov (United States)

    Gross, N. C.; Cohen, M. B.; Said, R. K.; Gołkowski, M.

    2018-01-01

    Very low frequency (VLF, 3-30 kHz) transmitter remote sensing has long been used as a simple yet useful diagnostic for the D region ionosphere (60-90 km). All it requires is a VLF radio receiver that records the amplitude and/or phase of a beacon signal as a function of time. During both ambient and disturbed conditions, the received signal can be compared to predictions from a theoretical model to infer ionospheric waveguide properties like electron density. Amplitude and phase have in most cases been analyzed each as individual data streams, often only the amplitude is used. Scattered field formulation combines amplitude and phase effectively, but does not address how to combine two magnetic field components. We present polarization ellipse analysis of VLF transmitter signals using two horizontal components of the magnetic field. The shape of the polarization ellipse is unchanged as the source phase varies, which circumvents a significant problem where VLF transmitters have an unknown source phase. A synchronized two-channel MSK demodulation algorithm is introduced to mitigate 90° ambiguity in the phase difference between the horizontal magnetic field components. Additionally, the synchronized demodulation improves phase measurements during low-SNR conditions. Using the polarization ellipse formulation, we take a new look at diurnal VLF transmitter variations, ambient conditions, and ionospheric disturbances from solar flares, lightning-ionospheric heating, and lightning-induced electron precipitation, and find differing signatures in the polarization ellipse.

  7. Determining polar ionospheric electrojet currents from Swarm satellite constellation magnetic data

    DEFF Research Database (Denmark)

    Aakjær, Cecilie Drost; Olsen, Nils; Finlay, Chris

    2016-01-01

    We determine the strength and location of the ionospheric currents responsible for the polar electrojets from magnetic data collected by the Swarm satellite constellation on an orbit-by-orbit basis. The ionospheric currents are modelled using a simple, yet robust, method by a series of line...

  8. A model of the plasma flow and current in Saturn's polar ionosphere under conditions of strong Dungey cycle driving

    Directory of Open Access Journals (Sweden)

    C. M. Jackman

    2006-05-01

    Full Text Available We propose a simple model of the flow and currents in Saturn's polar ionosphere. This model is motivated by theoretical reasoning, and guided quantitatively by in situ field and flow data from space missions, ground-based IR Doppler measurements, and Hubble Space Telescope images. The flow pattern consists of components which represent (1 plasma sub-corotation in the middle magnetosphere region resulting from plasma pick-up and radial transport from internal sources; (2 the Vasyliunas-cycle of internal plasma mass-loss down the magnetospheric tail at higher latitudes; and (3 the polar Dungey-cycle flow driven by the solar wind interaction. Upstream measurements of the interplanetary magnetic field (IMF indicate the occurrence of both extended low-field rarefaction intervals with essentially negligible Dungey-cycle flow, and few-day high-field compression regions in which the Dungey-cycle voltage peaks at a few hundred kV. Here we model the latter conditions when the Dungey-cycle is active, advancing on previous axi-symmetric models which may be more directly applicable to quiet conditions. For theoretical convenience the overall flow pattern is constructed by adding together two components - a purely rotational flow similar to previous axi-symmetric models, and a sun-aligned twin vortex representing the dawn-dusk asymmetry effects associated with the Vasyliunas-and Dungey-cycle flows. We calculate the horizontal ionospheric current associated with the flow and the field-aligned current from its divergence. These calculations show that a sheet of upward-directed field-aligned current flows at the boundary of open field lines which is strongly modulated in local-time by the Dungey-cycle flows. We then consider implications of the field-aligned current for magnetospheric electron acceleration and aurorae using two plasma source populations (hot outer magnetospheric electrons and cool dense magnetosheath electrons. Both sources display a

  9. A new method to reconstruct the ionospheric convection patterns in the polar cap

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    P. L. Israelevich

    1999-06-01

    Full Text Available A new method to reconstruct the instantaneous convection pattern in the Earth's polar ionosphere is suggested. Plasma convection in the polar cap ionosphere is described as a hydrodynamic incompressible flow. This description is valid in the region where the electric currents are field aligned (and hence, the Lorentz body force vanishes. The problem becomes two-dimensional, and may be described by means of stream function. The flow pattern may be found as a solution of the boundary value problem for stream function. Boundary conditions should be provided by measurements of the electric field or plasma velocity vectors along the satellite orbits. It is shown that the convection pattern may be reconstructed with a reasonable accuracy by means of this method, by using only the minimum number of satellite crossings of the polar cap. The method enables us to obtain a reasonable estimate of the convection pattern without knowledge of the ionospheric conductivity.Key words. Ionosphere (modelling and forecasting; plasma convection; polar ionosphere

  10. A new method to reconstruct the ionospheric convection patterns in the polar cap

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    P. L. Israelevich

    Full Text Available A new method to reconstruct the instantaneous convection pattern in the Earth's polar ionosphere is suggested. Plasma convection in the polar cap ionosphere is described as a hydrodynamic incompressible flow. This description is valid in the region where the electric currents are field aligned (and hence, the Lorentz body force vanishes. The problem becomes two-dimensional, and may be described by means of stream function. The flow pattern may be found as a solution of the boundary value problem for stream function. Boundary conditions should be provided by measurements of the electric field or plasma velocity vectors along the satellite orbits. It is shown that the convection pattern may be reconstructed with a reasonable accuracy by means of this method, by using only the minimum number of satellite crossings of the polar cap. The method enables us to obtain a reasonable estimate of the convection pattern without knowledge of the ionospheric conductivity.

    Key words. Ionosphere (modelling and forecasting; plasma convection; polar ionosphere

  11. Possibility of Ionospheric Cause of FACs and Convection Field in the Magnetosphere-Ionosphere System: The Harang Reversal, Premidnight Upward-FAC, and the Ionospheric Hall Polarization Field

    Science.gov (United States)

    Nakamizo, A.; Yoshikawa, A.

    2016-12-01

    Whereas it is generally thought that Birkeland Currents (FACs) are generated in the magnetosphere and that the ionospheric convection reflects the magnetospheric convection, we present a possibility that the ionosphere drives FACs and the convection field in the M-I system. We apply this idea to the Harang Reversal (HR) for demonstration. By using an ionospheric potential solver we calculate the electrostatic field for given distributions of FACs and conductance. The result shows that a conspicuous structure resembling HR is generated even for a symmetric distribution of the R1-type FACs and that the Hall polarization field is produced at the equatorward boundary of the auroral region as the primary currents diverge/converge at the conductance gradient there, which causes the potential deformation (HR). Conventionally HR has been considered to be of the magnetospheric origin, and a ring current model actually produces the corresponding structure in the magnetosphere [e.g., Erickson et al., 1991]. Observationally the divE equivalent to HR is consistent with the premidnight upward-FAC seen in Iijima and Potemra's diagram. A recent theoretical study [Ohtani et al., 2016] proposes that HR is a required structure for the interchange stability of the magnetotail in the presence of the R1 and R2-FAC systems including a premidnight upward-FAC. Returning to our result, the important point is that HR is reproduced at the conductance edge by the ionospheric polarization field, for which the primary field originates from the R1-FACs distributed far from that region. We also suggest: (i) In a more realistic finite ΣA, the total ionospheric polarization is partly released by a FAC, which may be a part of the premidnight upward-FAC. (ii) However, existing simulation models do not allow this type of current closure, and accordingly they may enhance the HR structure in the magnetosphere. This discussion should hold generally and would promote the global M-I coupling studies to the

  12. The polar cliff in the morning sector of the ionosphere

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    G. W. Prölss

    2013-05-01

    Full Text Available By "polar cliff" we mean the steep increase in the ionization density observed in the morning sector of the polar ionosphere. Here the properties of this remarkable feature are investigated. The data set consists of electron density and temperature measurements obtained by the Dynamics Explorer 2 satellite. Only data recorded in the Northern Hemisphere winter are considered (solar zenith angle ≥ 90°. We find that for moderately disturbed conditions, the foot of the polar cliff is located below 60° invariant latitude. Here, within about 4°, the density increases by a factor of 4, on average. The actual location of the polar cliff depends primarily on the level of geomagnetic activity, its associated density increase on geographic longitude and altitude. As to the longitudinal variations, they are attributed to asymmetries in the background ionization density at middle latitudes. Using a superposed epoch type of averaging procedure, mean latitudinal profiles of the polar cliff and the associated electron temperature changes are derived. Since these differ significantly from those derived for the afternoon/evening sector, we conclude that the subauroral ionospheric trough does not extend into the morning sector. As to the origin of the polar cliff in the morning sector, local auroral particle precipitation should play only a secondary role.

  13. A Review of Ionospheric Scintillation Models.

    Science.gov (United States)

    Priyadarshi, S

    This is a general review of the existing climatological models of ionospheric radio scintillation for high and equatorial latitudes. Trans-ionospheric communication of radio waves from transmitter to user is affected by the ionosphere which is highly variable and dynamic in both time and space. Scintillation is the term given to irregular amplitude and phase fluctuations of the received signals and related to the electron density irregularities in the ionosphere. Key sources of ionospheric irregularities are plasma instabilities; every irregularities model is based on the theory of radio wave propagation in random media. It is important to understand scintillation phenomena and the approach of different theories. Therefore, we have briefly discussed the theories that are used to interpret ionospheric scintillation data. The global morphology of ionospheric scintillation is also discussed briefly. The most important (in our opinion) analytical and physical models of scintillation are reviewed here.

  14. The ionospheric impact on GPS performance in southern polar region

    Science.gov (United States)

    Hong, C.-K.; Grejner-Brzezinska, D. A.; Arslan, N.; Willis, M.; Hothem, L.

    2006-01-01

    The primary objective of this paper is to present the results of the study of the effects of varying ionospheric conditions on the GPS signal tracking in the southern polar region. In the first stage of this study, the data collected by the OSU/USGS team in October-November 2003 within the TAMDEF (Transantarctic Mountains Deformation) network were used together with some IGS Antarctic stations to study the effect of severe ionospheric storms on GPS hardware. Note that TAMDEF is a joint USGS/OSU project with the primary objective of measuring crustal motion in the Transantarctic Mountains of Southern Victoria Land using GPS techniques. This study included ten Antarctic stations equipped with different dual-frequency GPS hardware, and the data were evaluated for two 24-hour periods of severe ionospheric storm (2003/10/29) and moderate ionospheric conditions (minor storm of 2003/11/11). The results of this study were presented at the LAG Assembly in Cairns, Australia (Grejner-Brzezinska et al., 2005). Additional tests, in a more controlled environment, were carried out at the US Antarctic station, McMurdo, between January 10 and February 6, 2006, under varying ionospheric conditions, where several different types of receivers were connected to the same antenna located on the rooftop of the Crary Laboratory (the primary test site). In this scenario, each antenna was subject to identical ionospheric effects during each day of the test, and no spatial decorrelation effects were present, as seen in the previous study, due to the spatial separation of the receivers tested. It should be noted, however, that no moderate or severe ionospheric storms occurred during the experiment, so, unfortunately, this type of conditions was not tested here. The test was repeated with different receivers connected to different antenna types; a total of four 5-day sessions were carried out. The following receiver types were used at the primary site: Trimble 5700, Ashtech Z-Surveyor, JNS Euro

  15. Modeling the Ionosphere with GPS and Rotation Measure Observations

    Science.gov (United States)

    Malins, J. B.; Taylor, G. B.; White, S. M.; Dowell, J.

    2017-12-01

    Advances in digital processing have created new tools for looking at and examining the ionosphere. We have combined data from dual frequency GPSs, digital ionosondes and observations from The Long Wavelength Array (LWA), a 256 dipole low frequency radio telescope situated in central New Mexico in order to examine ionospheric profiles. By studying polarized pulsars, the LWA is able to very accurately determine the Faraday rotation caused by the ionosphere. By combining this data with the international geomagnetic reference field, the LWA can evaluate ionospheric profiles and how well they predict the actual Faraday rotation. Dual frequency GPS measurements of total electron content, as well as measurements from digisonde data were used to model the ionosphere, and to predict the Faraday rotation to with in 0.1 rad/m2. Additionally, it was discovered that the predicted topside profile of the digisonde data did not accurate predict faraday rotation measurements, suggesting a need to reexamine the methods for creating the topside predicted profile. I will discuss the methods used to measure rotation measure and ionosphere profiles as well as discuss possible corrections to the topside model.

  16. Ionospheric Modeling for Precise GNSS Applications

    NARCIS (Netherlands)

    Memarzadeh, Y.

    2009-01-01

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

  17. A climatological morphology of ionospheric disturbances at high and polar latitudes

    Directory of Open Access Journals (Sweden)

    Dimitris N. Fotiadis

    2016-01-01

    Full Text Available After a historical introduction on the first well-documented observations of ionospheric phenomena and a review of the current, state-of-the art polar ionospheric studies, a climatological morphology of the irregular F-region plasma structures at high and polar latitudes is being presented, following a feature-aided pattern recognition method. Using the available in three solar cycles hourly foF2 data from 18 ionosonde stations, an ionospheric definition of disturbed conditions, independent of any causative mechanism, is being applied and positive/negative disturbances of duration smaller than 24 hours are sorted out. No latitudinal/longitudinal bins or seasons are defined and disturbances in each month and station are handled separately while four local time intervals of storm commencement are considered, according to solar zenith angle. A median profile per disturbance is produced only when a minimum occurrence probability is satisfied. Non-systematic features are excluded from this analysis by careful selection of the time window under morphological investigation. First, the median profiles of disturbance patterns are fitted to standard distributions and then, if they fail, they are grouped according to their major characteristic features and are described by a dynamic variation envelope along with their distribution in space and time. The present model, while being a non-conditional stand-alone model of ionospheric storms at high and polar latitudes offered to radio users, may complement existing empirical models. Finally, the present model may ultimately reveal cause-effect relationships with geomagnetic field or interplanetary parameters after further correlation studies undertaken in the future.

  18. Preface: International Reference Ionosphere - Progress in Ionospheric Modelling

    Science.gov (United States)

    Bilitza Dieter; Reinisch, Bodo

    2010-01-01

    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

  19. Polar ionospheric responses to solar wind IMF changes

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    Y. Zhang

    2000-06-01

    Full Text Available Auroral and airglow emissions over Eureka (89° CGM during the 1997-98 winter show striking variations in relation to solar wind IMF changes. The period January 19 to 22, 1998, was chosen for detailed study, as the IMF was particularly strong and variable. During most of the period, Bz was northward and polar arcs were observed. Several overpasses by DMSP satellites during the four day period provided a clear picture of the particle precipitation producing the polar arcs. The spectral character of these events indicated excitation by electrons of average energy 300 to 500 eV. Only occasionally were electrons of average energy up to ~1 keV observed and these appeared transitory from the ground optical data. It is noted that polar arcs appear after sudden changes in IMF By, suggesting IMF control over arc initiation. When By is positive there is arc motion from dawn to dusk, while By is negative the motion is consistently dusk to dawn. F-region (anti-sunward convections were monitored through the period from 630.0 nm emissions. The convection speed was low (100-150 m/s when Bz was northward but increased to 500 m/s after Bz turned southward on January 20.Key words: Atmospheric composition and structure (airglow and aurora - Ionosphere (particle precipitation - Magnetospheric Physics (polar cap phenomena

  20. Plasma Irregularity Production in the Polar Cap F-Region Ionosphere

    Science.gov (United States)

    Lamarche, Leslie

    Plasma in the Earth's ionosphere is highly irregular on scales ranging between a few centimeters and hundreds of kilometers. Small-scale irregularities or plasma waves can scatter radio waves resulting in a loss of signal for navigation and communication networks. The polar region is particularly susceptible to strong disturbances due to its direct connection with the Sun's magnetic field and energetic particles. In this thesis, factors that contribute to the production of decameter-scale plasma irregularities in the polar F region ionosphere are investigated. Both global and local control of irregularity production are studied, i.e. we consider global solar control through solar illumination and solar wind as well as much more local control by plasma density gradients and convection electric field. In the first experimental study, solar control of irregularity production is investigated using the Super Dual Auroral Radar Network (SuperDARN) radar at McMurdo, Antarctica. The occurrence trends for irregularities are analyzed statistically and a model is developed that describes the location of radar echoes within the radar's field-of-view. The trends are explained through variations in background plasma density with solar illumination affecting radar beam propagation. However, it is found that the irregularity occurrence during the night is higher than expected from ray tracing simulations based on a standard ionospheric density model. The high occurrence at night implies an additional source of plasma density and it is proposed that large-scale density enhancements called polar patches may be the source of this density. Additionally, occurrence maximizes around the terminator due to different competing irregularity production processes that favor a more or less sunlit ionosphere. The second study is concerned with modeling irregularity characteristics near a large-scale density gradient reversal, such as those expected near polar patches, with a particular focus on

  1. An Ionospheric Metric Study Using Operational Models

    Science.gov (United States)

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

    2006-12-01

    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

  2. Polar ionospheric responses to solar wind IMF changes

    Directory of Open Access Journals (Sweden)

    Y. Zhang

    Full Text Available Auroral and airglow emissions over Eureka (89° CGM during the 1997-98 winter show striking variations in relation to solar wind IMF changes. The period January 19 to 22, 1998, was chosen for detailed study, as the IMF was particularly strong and variable. During most of the period, Bz was northward and polar arcs were observed. Several overpasses by DMSP satellites during the four day period provided a clear picture of the particle precipitation producing the polar arcs. The spectral character of these events indicated excitation by electrons of average energy 300 to 500 eV. Only occasionally were electrons of average energy up to ~1 keV observed and these appeared transitory from the ground optical data. It is noted that polar arcs appear after sudden changes in IMF By, suggesting IMF control over arc initiation. When By is positive there is arc motion from dawn to dusk, while By is negative the motion is consistently dusk to dawn. F-region (anti-sunward convections were monitored through the period from 630.0 nm emissions. The convection speed was low (100-150 m/s when Bz was northward but increased to 500 m/s after Bz turned southward on January 20.

    Key words: Atmospheric composition and structure (airglow and aurora - Ionosphere (particle precipitation - Magnetospheric Physics (polar cap phenomena

  3. General solution for calculating polarization electric fields in the auroral ionosphere and application examples

    Science.gov (United States)

    Amm, O.; Fujii, R.; VanhamäKi, H.; Yoshikawa, A.; Ieda, A.

    2013-05-01

    We devise an approach to calculate the polarization electric field in the ionosphere, when the ionospheric conductances, the primary (modeled) or the total (measured) electric field, and the Cowling efficiency are given. In contrast to previous studies, our approach is a general solution which is not limited to specific geometrical setups, and all parameters may have any kind of spatial dependence. The solution technique is based on spherical elementary current (vector) systems (SECS). This way, we avoid the need to specify explicit boundary conditions for the searched polarization electric field of its potential which would be required if the problem was solved in a differential equation approach. Instead, we solve an algebraic matrix equation, and the implicit boundary condition that the divergence of the polarization electric field vanishes outside our analysis area is sufficient. In order to illustrate our theory, we then apply it to two simple models of auroral electrodynamic situations, the first being a mesoscale strong conductance enhancement in the early morning sector within a relatively weak southward primary electric field, and a morning sector auroral arc with only a weak conductance enhancement, but a large southward primary electric field at the poleward flank of the arc. While the significance of the polarization electric field for maximum Cowling efficiency is large for the first case, it is rather minor for the second one. Both models show that the polarization electric field effect may not only change the magnitude of the current systems but also their overall geometry. Furthermore, the polarization electric field may extend into regions where the primary electric field is small, thus even dominating the total electric field in these regions. For the first model case, the total Joule heating integrated over the analysis area decreases by a factor of about 4 for maximum Cowling efficiency as compared to the case of vanishing Cowling efficiency

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

    Science.gov (United States)

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

    2014-08-01

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

  5. Multi-instrument probing of the polar ionosphere under steady northward IMF

    Directory of Open Access Journals (Sweden)

    S. E. Pryse

    2000-01-01

    Full Text Available Observations are presented of the polar ionosphere under steady, northward IMF. The measurements, made by six complementary experimental techniques, including radio tomography, all-sky and meridian scanning photometer optical imaging, incoherent and coherent scatter radars and satellite particle detection, reveal plasma parameters consistent with ionospheric signatures of lobe reconnection. The optical green-line footprint of the reconnection site is seen to lie in the sunward plasma convection of the lobe cells. Downstream in the region of softer precipitation the reverse energy dispersion of the incoming ions can be identified. A steep latitudinal density gradient at the equatorward edge of the precipitation identifies the general location of an adiaroic boundary, separating the open field lines of polar lobe cells from the closed field of viscous-driven cells. Enhancements in plasma density to the south of the gradient are interpreted as ionisation being reconfigured as it is thrust against the boundary by the antisunward flow of the viscous cells near noon. Each of the instruments individually provides valuable information on certain aspects of the ionosphere, but the paper demonstrates that taken together the different experiments complement each other to give a consistent and comprehensive picture of the dayside polar ionosphere..Key words. Ionosphere (polar ionosphere · Magnetospheric physics (magnetosphere-ionosphere interactions; polar cap phenomena

  6. Multi-instrument probing of the polar ionosphere under steady northward IMF

    Directory of Open Access Journals (Sweden)

    S. E. Pryse

    Full Text Available Observations are presented of the polar ionosphere under steady, northward IMF. The measurements, made by six complementary experimental techniques, including radio tomography, all-sky and meridian scanning photometer optical imaging, incoherent and coherent scatter radars and satellite particle detection, reveal plasma parameters consistent with ionospheric signatures of lobe reconnection. The optical green-line footprint of the reconnection site is seen to lie in the sunward plasma convection of the lobe cells. Downstream in the region of softer precipitation the reverse energy dispersion of the incoming ions can be identified. A steep latitudinal density gradient at the equatorward edge of the precipitation identifies the general location of an adiaroic boundary, separating the open field lines of polar lobe cells from the closed field of viscous-driven cells. Enhancements in plasma density to the south of the gradient are interpreted as ionisation being reconfigured as it is thrust against the boundary by the antisunward flow of the viscous cells near noon. Each of the instruments individually provides valuable information on certain aspects of the ionosphere, but the paper demonstrates that taken together the different experiments complement each other to give a consistent and comprehensive picture of the dayside polar ionosphere..

    Key words. Ionosphere (polar ionosphere · Magnetospheric physics (magnetosphere-ionosphere interactions; polar cap phenomena

  7. Model of traveling ionospheric disturbances

    Directory of Open Access Journals (Sweden)

    Fedorenko Yury P.

    2013-10-01

    Full Text Available A multiscale semi-empirical model of traveling ionospheric disturbances (TIDs is developed. The model is based on the following assumptions: (1 TIDs are generated by acoustic-gravity waves (AGWs and propagate as pressure waves; (2 time intervals between adjacent extrema of atmospheric pressure oscillations in a disturbance source are constant; (3 the pressure extrema propagate from the source up to ~14 000 km at a constant horizontal velocity; (4 the velocity of each extremum is determined only by its number in a TID train. The model was validated using literature data on disturbances generated by about 20 surface and high-altitude nuclear explosions, two volcano explosions, one earthquake and by energetic proton precipitation events in the magnetospheric cusp of the northern hemisphere. Model tests using literature data show that the spatial and temporal TID periods may be predicted with an accuracy of 12%. Adequacy of the model was also confirmed by our observations collected using transionospheric sounding. The following TID parameters: amplitudes, horizontal spatial periods, and a TID front inclination angle in a vertical plane are increasing as the distance between an AGW and the excitation source is increasing. Diurnal and seasonal variability of the TID occurrence, defined as ratio of TID events to the total number of observations for the corresponding period, is not observed. However, the TID occurrence was growing from ~50% in 1987 to ~98% in 2010. The results of other studies asserting that the TID occurrence does not depend on the number of sunspots and magnetic activity are confirmed. The TID occurrence has doubled over the period from 1987 to 2010 indicating increasing solar activity which is not associated with sunspot numbers. The dynamics of spatial horizontal periods was studied in a range of 150–35 000 km.

  8. Comparison of global and regional ionospheric models

    Science.gov (United States)

    Ranner, H.-P.; Krauss, S.; Stangl, G.

    2012-04-01

    Modelling of the Earth's ionosphere means the description of the variability of the vertical TEC (Total Electron Content) in dependence of geographic latitude and longitude, height, diurnal and seasonal variation as well as solar activity. Within the project GIOMO (next Generation near real-time IOnospheric MOdels) the objectives are the identification and consolidation of improved ionospheric modelling technologies. The global models Klobuchar (GPS) and NeQuick (currently in use by EGNOS, in future used by Galileo) are compared to the IGS (International GNSS Service) Final GIM (Global Ionospheric Map). Additionally a RIM (Regional Ionospheric Map) for Europe provided by CODE (Center for Orbit Determination in Europe) is investigated. Furthermore the OLG (Observatorium Lustbühel Graz) regional models are calculated for two test beds with different latitudes and extensions (Western Austria and the Aegean region). There are three different approaches, two RIMs are based on spherical harmonics calculated either from code or phase measurements and one RIM is based on a Taylor series expansion around a central point estimated from zero-difference observations. The benefits of regional models are the local flexibility using a dense network of GNSS stations. Near real-time parameters are provided within ten minutes after every clock hour. All models have been compared according to their general behavior, the ability to react upon extreme solar events and the robustness of estimation. A ranking of the different models showed a preference for the RIMs while the global models should be used within a fall-back strategy.

  9. Present situation of researches on polar ionosphere by C.C.I.R

    International Nuclear Information System (INIS)

    Ishikawa, Saburo

    1974-01-01

    Various subjects of studies made by the sixth research committee of C.C.I.R. (International Radio Consultative Committee) are reported. The C.C.I.R. has not any definite study programme and question concerning polar ionosphere, because it studies and delivers opinion on the techniques and operation of radio communication especially in developing countries. The subjects of study programme by the sixth research committee are as follows: estimation of the intensity and transmission loss of space wave electric field in a zone between 1.5 and 40 MHz, observation of the ionosphere of oblique entrance, scattering propagation of ionosphere, back scattering, fading of signal transmitted through ionosphere, transmission of space waves in the zone between 150 and 1,500 kHz, and effect of ionosphere on space communication. In addition, the following fourteen reports are cited: confirmation of prodromal phenomena of ionosphere disturbances, observation of the ionosphere of oblique entrance, remote propagation with supermode, basic information on forecast, back scattering, side scattering from the ground surface and ionosphere, Esub(s) propagation, scattering propagation, Esub(s) forecast, fading, effect of ionosphere on the transmission between the earth and space, radio noise produced in and above ionosphere, and propagation of standard broadcast wave. (Iwakiri, K.)

  10. Ionospheric Modelling using GPS to Calibrate the MWA. II: Regional Ionospheric Modelling using GPS and GLONASS to Estimate Ionospheric Gradients

    Science.gov (United States)

    Arora, B. S.; Morgan, J.; Ord, S. M.; Tingay, S. J.; Bell, M.; Callingham, J. R.; Dwarakanath, K. S.; For, B.-Q.; Hancock, P.; Hindson, L.; Hurley-Walker, N.; Johnston-Hollitt, M.; Kapińska, A. D.; Lenc, E.; McKinley, B.; Offringa, A. R.; Procopio, P.; Staveley-Smith, L.; Wayth, R. B.; Wu, C.; Zheng, Q.

    2016-07-01

    We estimate spatial gradients in the ionosphere using the Global Positioning System and GLONASS (Russian global navigation system) observations, utilising data from multiple Global Positioning System stations in the vicinity of Murchison Radio-astronomy Observatory. In previous work, the ionosphere was characterised using a single-station to model the ionosphere as a single layer of fixed height and this was compared with ionospheric data derived from radio astronomy observations obtained from the Murchison Widefield Array. Having made improvements to our data quality (via cycle slip detection and repair) and incorporating data from the GLONASS system, we now present a multi-station approach. These two developments significantly improve our modelling of the ionosphere. We also explore the effects of a variable-height model. We conclude that modelling the small-scale features in the ionosphere that have been observed with the MWA will require a much denser network of Global Navigation Satellite System stations than is currently available at the Murchison Radio-astronomy Observatory.

  11. Understanding Transient Forcing with Plasma Instability Model, Ionospheric Propagation Model and GNSS Observations

    Science.gov (United States)

    Deshpande, K.; Zettergren, M. D.; Datta-Barua, S.

    2017-12-01

    Fluctuations in the Global Navigation Satellite Systems (GNSS) signals observed as amplitude and phase scintillations are produced by plasma density structures in the ionosphere. Phase scintillation events in particular occur due to structures at Fresnel scales, typically about 250 meters at ionospheric heights and GNSS frequency. Likely processes contributing to small-scale density structuring in auroral and polar regions include ionospheric gradient-drift instability (GDI) and Kelvin-Helmholtz instability (KHI), which result, generally, from magnetosphere-ionosphere interactions (e.g. reconnection) associated with cusp and auroral zone regions. Scintillation signals, ostensibly from either GDI or KHI, are frequently observed in the high latitude ionosphere and are potentially useful diagnostics of how energy from the transient forcing in the cusp or polar cap region cascades, via instabilities, to small scales. However, extracting quantitative details of instabilities leading to scintillation using GNSS data drastically benefits from both a model of the irregularities and a model of GNSS signal propagation through irregular media. This work uses a physics-based model of the generation of plasma density irregularities (GEMINI - Geospace Environment Model of Ion-Neutral Interactions) coupled to an ionospheric radio wave propagation model (SIGMA - Satellite-beacon Ionospheric-scintillation Global Model of the upper Atmosphere) to explore the cascade of density structures from medium to small (sub-kilometer) scales. Specifically, GEMINI-SIGMA is used to simulate expected scintillation from different instabilities during various stages of evolution to determine features of the scintillation that may be useful to studying ionospheric density structures. Furthermore we relate the instabilities producing GNSS scintillations to the transient space and time-dependent magnetospheric phenomena and further predict characteristics of scintillation in different geophysical

  12. Data ingestion and assimilation in ionospheric models

    Czech Academy of Sciences Publication Activity Database

    Burešová, Dalia; Nava, B.; Galkin, I.; Angling, M.; Stankov, S. M.; Coisson, P.

    2009-01-01

    Roč. 52, 3/4 (2009), s. 235-253 ISSN 1593-5213 R&D Projects: GA ČR GA205/08/1356; GA MŠk OC 091 Institutional research plan: CEZ:AV0Z30420517 Keywords : ionosphere * models * data assimilation * data ingestion Subject RIV: DG - Athmosphere Sciences, Meteorology Impact factor: 0.548, year: 2009

  13. An extended TRANSCAR model including ionospheric convection: simulation of EISCAT observations using inputs from AMIE

    Directory of Open Access Journals (Sweden)

    P.-L. Blelly

    2005-02-01

    Full Text Available The TRANSCAR ionospheric model was extended to account for the convection of the magnetic field lines in the auroral and polar ionosphere. A mixed Eulerian-Lagrangian 13-moment approach was used to describe the dynamics of an ionospheric plasma tube. In the present study, one focuses on large scale transports in the polar ionosphere. The model was used to simulate a 35-h period of EISCAT-UHF observations on 16-17 February 1993. The first day was magnetically quiet, and characterized by elevated electron concentrations: the diurnal F2 layer reached as much as 1012m-3, which is unusual for a winter and moderate solar activity (F10.7=130 period. An intense geomagnetic event occurred on the second day, seen in the data as a strong intensification of the ionosphere convection velocities in the early afternoon (with the northward electric field reaching 150mVm-1 and corresponding frictional heating of the ions up to 2500K. The simulation used time-dependent AMIE outputs to infer flux-tube transports in the polar region, and to provide magnetospheric particle and energy inputs to the ionosphere. The overall very good agreement, obtained between the model and the observations, demonstrates the high ability of the extended TRANSCAR model for quantitative modelling of the high-latitude ionosphere; however, some differences are found which are attributed to the precipitation of electrons with very low energy. All these results are finally discussed in the frame of modelling the auroral ionosphere with space weather applications in mind.

  14. An extended TRANSCAR model including ionospheric convection: simulation of EISCAT observations using inputs from AMIE

    Directory of Open Access Journals (Sweden)

    P.-L. Blelly

    2005-02-01

    Full Text Available The TRANSCAR ionospheric model was extended to account for the convection of the magnetic field lines in the auroral and polar ionosphere. A mixed Eulerian-Lagrangian 13-moment approach was used to describe the dynamics of an ionospheric plasma tube. In the present study, one focuses on large scale transports in the polar ionosphere. The model was used to simulate a 35-h period of EISCAT-UHF observations on 16-17 February 1993. The first day was magnetically quiet, and characterized by elevated electron concentrations: the diurnal F2 layer reached as much as 1012m-3, which is unusual for a winter and moderate solar activity (F10.7=130 period. An intense geomagnetic event occurred on the second day, seen in the data as a strong intensification of the ionosphere convection velocities in the early afternoon (with the northward electric field reaching 150mVm-1 and corresponding frictional heating of the ions up to 2500K. The simulation used time-dependent AMIE outputs to infer flux-tube transports in the polar region, and to provide magnetospheric particle and energy inputs to the ionosphere. The overall very good agreement, obtained between the model and the observations, demonstrates the high ability of the extended TRANSCAR model for quantitative modelling of the high-latitude ionosphere; however, some differences are found which are attributed to the precipitation of electrons with very low energy. All these results are finally discussed in the frame of modelling the auroral ionosphere with space weather applications in mind.

  15. Application of GPS Measurements for Ionospheric and Tropospheric Modelling

    Science.gov (United States)

    Rajendra Prasad, P.; Abdu, M. A.; Furlan, Benedito. M. P.; Koiti Kuga, Hélio

    military navigation. The DOD's primary purposes were to use the system in precision weapon delivery and providing a capability that would help reverse the proliferation of navigation systems in military. Subsequently, it was very quickly realized that civil use and scientific utility would far outstrip military use. A variety of scientific applications are uniquely suited to precise positioning capabilities. The relatively high precision, low cost, mobility and convenience of GPS receivers make positioning attractive. The other applications being precise time measurement, surveying and geodesy purposes apart from orbit and attitude determination along with many user services. The system operates by transmitting radio waves from satellites to receivers on the ground, aircraft, or other satellites. These signals are used to calculate location very accurately. Standard Positioning Services (SPS) which restricts access to Coarse/Access (C/A) code and carrier signals on the L1 frequency only. The accuracy thus provided by SPS fall short of most of the accuracy requirements of users. The upper atmosphere is ionized by the ultra violet radiation from the sun. The significant errors in positioning can result when the signals are refracted and slowed by ionospheric conditions, the parameter of the ionosphere that produces most effects on GPS signals is the total number of electrons in the ionospheric propagation path. This integrated number of electrons, called Total Electron Content (TEC) varies, not only from day to night, time of the year and solar flux cycle, but also with geomagnetic latitude and longitude. Being plasma the ionosphere affects the radio waves propagating through it. Effects of scintillation on GPS satellite navigation systems operating at L1 (1.5754 GHz), L2 (1.2276 GHz) frequencies have not been estimated accurately. It is generally recognized that GPS navigation systems are vulnerable in the polar and especially in the equatorial region during the

  16. Improving the Ionospheric Auroral Conductance in a Global Ring Current Model and the Effects on the Ionospheric Electrodynamics

    Science.gov (United States)

    Yu, Y.; Jordanova, V. K.; McGranaghan, R. M.; Solomon, S. C.

    2017-12-01

    The ionospheric conductance, height-integrated electric conductivity, can regulate both the ionospheric electrodynamics and the magnetospheric dynamics because of its key role in determining the electric field within the coupled magnetosphere-ionosphere system. State-of-the-art global magnetosphere models commonly adopt empirical conductance calculators to obtain the auroral conductance. Such specification can bypass the complexity of the ionosphere-thermosphere chemistry but on the other hand breaks the self-consistent link within the coupled system. In this study, we couple a kinetic ring current model RAM-SCB-E that solves for anisotropic particle distributions with a two-stream electron transport code (GLOW) to more self-consistently compute the height-dependent electric conductivity, provided the auroral electron precipitation from the ring current model. Comparisons with the traditional empirical formula are carried out. It is found that the newly coupled modeling framework reveals smaller Hall and Pedersen conductance, resulting in a larger electric field. As a consequence, the subauroral polarization streams demonstrate a better agreement with observations from DMSP satellites. It is further found that the commonly assumed Maxwellian spectrum of the particle precipitation is not globally appropriate. Instead, a full precipitation spectrum resulted from wave particle interactions in the ring current accounts for a more comprehensive precipitation spectrum.

  17. Improving the Nightside Mid-latitude Ionospheric Density in the Global Ionosphere-Thermosphere Model

    Science.gov (United States)

    Wu, C.; Ridley, A. J.

    2017-12-01

    The ionosphere and plasmasphere interact with each other through upwelling of plasma into the plasmasphere during the day and downwelling of the plasma into the ionosphere during the night. The storage of ion density in the plasmasphere and subsequent downwelling maintains the ion density in the nighttime mid-latitude ionosphere. Global models of the upper atmosphere that do not contain a plasmasphere, but are limited in altitude, such as the Thermosphere Ionosphere Electrodynamics Global Circulation Model (TIEGCM) and the Global Ionosphere-Thermosphere Model(GITM) need a boundary condition that allows for some sort of downwelling to occur. In the TIEGCM, this has been set to a constant downward flux, while GITM has had no downwelling specification at all, which has caused the nighttime mid-latitude densities to be much too low. We present a new boundary condition in GITM, where there is downward ion flux from the upper boundary, allowing the ionosphere to be maintained during the night. This new boundary condition is dependent on the the Disturbance Storm Time (Dst), since, as the activity level increases (i.e., Dst decreases), the plasmasphere is eroded and will not serve to supply the ionosphere at night. Various quiet time and active time comparisons to ionosonde electron density and total electron content data will be presented that show that the ionospheric density in GITM is improved due to this new boundary condition.

  18. The theta aurora and ionospheric flow convection: Polar ultraviolet imager and SuperDARN radar observations

    Science.gov (United States)

    Liou, K.; Ruohoniemi, J. M.; Newell, P. T.; Meng, C. I.

    2003-12-01

    We report results from a case study of the theta aurora that occurred during a magnetic cloud event on November 8, 2000. The interplanetary magnetic field (IMF) was strongly northward for more than 12 hours, while the y-component of IMF changed signs several times. Auroral images from the Ultraviolet Imager on board the Polar satellite show clear instances of theta auroras during the prolonged northward IMF period. This event provides a good opportunity for testing current models of theta aurora generation and evolution. We examine in situ particle data from the DMSP satellites to find magnetospheric source regions responsible for the theta auroras. We also examine ionospheric plasma flow convection data from the SuperDARN radar network to study relationships between the ionospheric plasma flow pattern and the location of the theta auroras. Our results clearly indicate that the theta aurora bar, at least on nightside, was located in a region of anti-sunward convecting flow. This is not consistent with the current view that theta auroras reside in regions of closed field lines and hence in regions of sunward convecting flow. Implication of the new findings will be discussed.

  19. Research on Polarization Cancellation of Nonstationary Ionosphere Clutter in HF Radar System

    Directory of Open Access Journals (Sweden)

    Xingpeng Mao

    2015-01-01

    Full Text Available Oblique projection polarization filter (OPPF can be applied as an effective approach for interference cancellation in high-frequency surface wave radar (HFSWR and other systems. In order to suppress the nonstationary ionosphere clutter further, a novel OPPF based clutter suppressing scheme is proposed in this paper. The polarization and nonstationary characteristic of the clutter are taken into account in the algorithms referred to as range-Doppler domain polarization suppression (RDDPS and the range-time domain polarization suppression (RTDPS method, respectively. The RDDPS is designed for weak ionosphere clutter and implemented in the range-Doppler domain directly, whereas the RTDPS algorithm is designed to suppress the powerful ionosphere clutter with a multisegment estimation and suppression scheme. About 15–23 dB signal to interference ratio (SIR improvement can be excepted when using the proposed method, whereas the targets can be more easily detected in the range-Doppler map. Experimental results demonstrate that the scheme proposed is effective for nonstationary ionosphere clutter and is proven to be a practical interference cancellation technique for HFSWR.

  20. Space weather: Modeling and forecasting ionospheric

    International Nuclear Information System (INIS)

    Calzadilla Mendez, A.

    2008-01-01

    Full text: Space weather is the set of phenomena and interactions that take place in the interplanetary medium. It is regulated primarily by the activity originating in the Sun and affects both the artificial satellites that are outside of the protective cover of the Earth's atmosphere as the rest of the planets in the solar system. Among the phenomena that are of great relevance and impact on Earth are the auroras and geomagnetic storms , these are a direct result of irregularities in the flow of the solar wind and the interplanetary magnetic field . Given the high complexity of the physical phenomena involved (magnetic reconnection , particle inlet and ionizing radiation to the atmosphere) one of the great scientific challenges today is to forecast the state of plasmatic means either the interplanetary medium , the magnetosphere and ionosphere , for their importance to the development of various human activities such as radio , global positioning , navigation, etc. . It briefly address some of the international ionospheric modeling methods and contributions and participation that currently has the space group of the Institute of Geophysics Geophysics and Astronomy (IGA) in these activities of modeling and forecasting ionospheric. (author)

  1. Polar cap hot patches: Enhanced density structures different from the classical patches in the ionosphere

    Science.gov (United States)

    Zhang, Q.-H.; Ma, Y.-Z.; Jayachandran, P. T.; Moen, J.; Lockwood, M.; Zhang, Y.-L.; Foster, J. C.; Zhang, S.-R.; Wang, Y.; Themens, D. R.; Zhang, B.-C.; Xing, Z. Y.

    2017-08-01

    Based on in situ and ground-based observations, a new type of "polar cap hot patch" has been identified that is different from the classical polar cap enhanced density structure (cold patches). Comparing with the classical polar cap patches, which are transported from the dayside sunlit region with dense and cold plasma, the polar cap hot patches are associated with particle precipitations (therefore field-aligned currents), ion upflows, and flow shears. The hot patches may have the same order of density enhancement as classical patches in the topside ionosphere, suggesting that the hot patches may be produced by transported photoionization plasma into flow channels. Within the flow channels, the hot patches have low-energy particle precipitation and/or ion upflows associated with field-aligned currents and flow shears. Corresponding Global Navigation Satellite System (GNSS) signal scintillation measurements indicate that hot patches may produce slightly stronger radio signal scintillation in the polar cap region than classical patches. A new type of polar cap patches, "polar cap hot patches," is identified to differentiate enhanced density structures from classical patches. Hot patches are associated with particle precipitations, ion upflows, field-aligned currents, and shear flows in the polar cap. Hot patches may lead to slightly stronger ionospheric scintillations of GNSS signals in the polar cap region than classical patches.

  2. Geodetic Space Weather Monitoring by means of Ionosphere Modelling

    Science.gov (United States)

    Schmidt, Michael

    2017-04-01

    The term space weather indicates physical processes and phenomena in space caused by radiation of energy mainly from the Sun. Manifestations of space weather are (1) variations of the Earth's magnetic field, (2) the polar lights in the northern and southern hemisphere, (3) variations within the ionosphere as part of the upper atmosphere characterized by the existence of free electrons and ions, (4) the solar wind, i.e. the permanent emission of electrons and photons, (5) the interplanetary magnetic field, and (6) electric currents, e.g. the van Allen radiation belt. It can be stated that ionosphere disturbances are often caused by so-called solar storms. A solar storm comprises solar events such as solar flares and coronal mass ejections (CMEs) which have different effects on the Earth. Solar flares may cause disturbances in positioning, navigation and communication. CMEs can effect severe disturbances and in extreme cases damages or even destructions of modern infrastructure. Examples are interruptions to satellite services including the global navigation satellite systems (GNSS), communication systems, Earth observation and imaging systems or a potential failure of power networks. Currently the measurements of solar satellite missions such as STEREO and SOHO are used to forecast solar events. Besides these measurements the Earth's ionosphere plays another key role in monitoring the space weather, because it responses to solar storms with an increase of the electron density. Space-geodetic observation techniques, such as terrestrial GNSS, satellite altimetry, space-borne GPS (radio occultation), DORIS and VLBI provide valuable global information about the state of the ionosphere. Additionally geodesy has a long history and large experience in developing and using sophisticated analysis and combination techniques as well as empirical and physical modelling approaches. Consequently, geodesy is predestinated for strongly supporting space weather monitoring via

  3. Method to locate the polar cap boundary in the nightside ionosphere and application to a substorm event

    Directory of Open Access Journals (Sweden)

    A. T. Aikio

    2006-08-01

    Full Text Available In this paper we describe a new method to be used for the polar cap boundary (PCB determination in the nightside ionosphere by using the EISCAT Svalbard radar (ESR field-aligned measurements by the 42-m antenna and southward directed low-elevation measurements by the ESR 32 m antenna or northward directed low-elevation measurements by the EISCAT VHF radar at Tromsø. The method is based on increased electron temperature (Te caused by precipitating particles on closed field lines. Since the Svalbard field-aligned measurement provides the reference polar cap Te height profile, the method can be utilised only when the PCB is located between Svalbard and the mainland. Comparison with the Polar UVI images shows that the radar-based method is generally in agreement with the PAE (poleward auroral emission boundary from Polar UVI. The new technique to map the polar cap boundary was applied to a substorm event on 6 November 2002. Simultaneous measurements by the MIRACLE magnetometers enabled us to put the PCB location in the framework of ionospheric electrojets. During the substorm growth phase, the polar cap expands and the region of the westward electrojet shifts gradually more apart from the PCB. The substorm onset takes place deep within the region of closed magnetic field region, separated by about 6–7° in latitude from the PCB in the ionosphere. We interpret the observations in the framework of the near-Earth neutral line (NENL model of substorms. After the substorm onset, the reconnection at the NENL reaches within 3 min the open-closed field line boundary and then the PCB moves poleward together with the poleward boundary of the substorm current wedge. The poleward expansion occurs in the form of individual bursts, which are separated by 2–10 min, indicating that the reconnection in the magnetotail neutral line is impulsive. The poleward expansions of the PCB are followed by latitude dispersed intensifications in the westward electrojet

  4. Long-term analysis of ionospheric polar patches based on CHAMP TEC data

    DEFF Research Database (Denmark)

    Noja, M.; Stolle, Claudia; Park, J.

    2013-01-01

    Total electron content (TEC) from LEO satellites offers great possibility to sound the upper ionosphere and plasmasphere. This paper describes a method to derive absolute TEC observations aboard CHAMP considering multipath effects and receiver differential code bias. The long-term data set of 9...... that enhanced TEC at midlatitudes and low latitudes during December solstice provides a greater possibility to transport high-density plasma to the polar region through the buildup of TOIs. ©2013. American Geophysical Union. All Rights Reserved....

  5. Modeling ionospheric disturbance features in quasi-vertically incident ionograms using 3-D magnetoionic ray tracing and atmospheric gravity waves

    Science.gov (United States)

    Cervera, M. A.; Harris, T. J.

    2014-01-01

    The Defence Science and Technology Organisation (DSTO) has initiated an experimental program, Spatial Ionospheric Correlation Experiment, utilizing state-of-the-art DSTO-designed high frequency digital receivers. This program seeks to understand ionospheric disturbances at scales < 150 km and temporal resolutions under 1 min through the simultaneous observation and recording of multiple quasi-vertical ionograms (QVI) with closely spaced ionospheric control points. A detailed description of and results from the first campaign conducted in February 2008 were presented by Harris et al. (2012). In this paper we employ a 3-D magnetoionic Hamiltonian ray tracing engine, developed by DSTO, to (1) model the various disturbance features observed on both the O and X polarization modes in our QVI data and (2) understand how they are produced. The ionospheric disturbances which produce the observed features were modeled by perturbing the ionosphere with atmospheric gravity waves.

  6. A snapshot of the polar ionosphere. [satellite observation of F layer and topside

    Science.gov (United States)

    Whitteker, J. H.; Brace, L. H.; Maier, E. J.; Burrows, J. R.; Dodson, W. H.; Winningham, J. D.

    1976-01-01

    This paper presents a picture of the north polar F layer and topside ionosphere obtained primarily from three satellites (Alouette 2, ISIS 1, ISIS 2) that passed over the region within a time interval of about 50 min on a magnetically quiet day. The horizontal distribution of electron densities at the peak of the F layer is found to be similar to synoptic results from the IGY. Energetic-particle and ionospheric-plasma data are also presented, and the F-layer data are discussed in terms of these measurements as well as in terms of electric-field and neutral N2 density measurements made by other satellites on other occasions. The major feature observed is a tongue of F-region ionization extending from the dayside across the polar cap, which is accounted for by antisunward drift due to magnetospheric convection. In the F layer and topside ionosphere, the main effect of auroral precipitation appears to be heating and expansion of the topside. A region of low F-layer density appears on the morning side of the polar cap, which may be due to convection and possibly also to enhanced N2 densities.

  7. Saturn's polar ionospheric flows and their relation to the main auroral oval

    Directory of Open Access Journals (Sweden)

    S. W. H. Cowley

    2004-04-01

    Full Text Available We consider the flows and currents in Saturn's polar ionosphere which are implied by a three-component picture of large-scale magnetospheric flow driven both by planetary rotation and the solar wind interaction. With increasing radial distance in the equatorial plane, these components consist of a region dominated by planetary rotation where planetary plasma sub-corotates on closed field lines, a surrounding region where planetary plasma is lost down the dusk tail by the stretching out of closed field lines followed by plasmoid formation and pinch-off, as first described for Jupiter by Vasyliunas, and an outer region driven by the interaction with the solar wind, specifically by reconnection at the dayside magnetopause and in the dawn tail, first discussed for Earth by Dungey. The sub-corotating flow on closed field lines in the dayside magnetosphere is constrained by Voyager plasma observations, showing that the plasma angular velocity falls to around half of rigid corotation in the outer magnetosphere, possibly increasing somewhat near the dayside magnetopause, while here we provide theoretical arguments which indicate that the flow should drop to considerably smaller values on open field lines in the polar cap. The implied ionospheric current system requires a four-ring pattern of field-aligned currents, with distributed downward currents on open field lines in the polar cap, a narrow ring of upward current near the boundary of open and closed field lines, and regions of distributed downward and upward current on closed field lines at lower latitudes associated with the transfer of angular momentum from the planetary atmosphere to the sub-corotating planetary magnetospheric plasma. Recent work has shown that the upward current associated with sub-corotation is not sufficiently intense to produce significant auroral acceleration and emission. Here we suggest that the observed auroral oval at Saturn instead corresponds to the ring of upward

  8. Saturn's polar ionospheric flows and their relation to the main auroral oval

    Directory of Open Access Journals (Sweden)

    S. W. H. Cowley

    2004-04-01

    Full Text Available We consider the flows and currents in Saturn's polar ionosphere which are implied by a three-component picture of large-scale magnetospheric flow driven both by planetary rotation and the solar wind interaction. With increasing radial distance in the equatorial plane, these components consist of a region dominated by planetary rotation where planetary plasma sub-corotates on closed field lines, a surrounding region where planetary plasma is lost down the dusk tail by the stretching out of closed field lines followed by plasmoid formation and pinch-off, as first described for Jupiter by Vasyliunas, and an outer region driven by the interaction with the solar wind, specifically by reconnection at the dayside magnetopause and in the dawn tail, first discussed for Earth by Dungey. The sub-corotating flow on closed field lines in the dayside magnetosphere is constrained by Voyager plasma observations, showing that the plasma angular velocity falls to around half of rigid corotation in the outer magnetosphere, possibly increasing somewhat near the dayside magnetopause, while here we provide theoretical arguments which indicate that the flow should drop to considerably smaller values on open field lines in the polar cap. The implied ionospheric current system requires a four-ring pattern of field-aligned currents, with distributed downward currents on open field lines in the polar cap, a narrow ring of upward current near the boundary of open and closed field lines, and regions of distributed downward and upward current on closed field lines at lower latitudes associated with the transfer of angular momentum from the planetary atmosphere to the sub-corotating planetary magnetospheric plasma. Recent work has shown that the upward current associated with sub-corotation is not sufficiently intense to produce significant auroral acceleration and emission. Here we suggest that the observed auroral oval at Saturn instead corresponds to the ring of

  9. Thermosphere-Ionosphere-Electrodynamics General Circulation Model for the Ionospheric Connection Explorer: TIEGCM-ICON

    Science.gov (United States)

    Maute, Astrid

    2017-10-01

    The NASA Ionospheric Connection explorer (ICON) will study the coupling between the thermosphere and ionosphere at low- and mid-latitudes by measuring the key parameters. The ICON mission will also employ numerical modeling to support the interpretation of the observations, and examine the importance of different vertical coupling mechanisms by conducting numerical experiments. One of these models is the Thermosphere-Ionosphere-Electrodynamics General Circulation Model-ICON (TIEGCM-ICON) which will be driven by tidal perturbations derived from ICON observations using the Hough Mode Extension method (HME) and at high latitude by ion convection and auroral particle precipitation patterns from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE). The TIEGCM-ICON will simulate the thermosphere-ionosphere (TI) system during the period of the ICON mission. In this report the TIEGCM-ICON is introduced, and the focus is on examining the effect of the lower boundary on the TI-system to provide some guidance for interpreting future ICON model results.

  10. ADAPTIVE MODEL REFINEMENT FOR THE IONOSPHERE AND THERMOSPHERE

    Data.gov (United States)

    National Aeronautics and Space Administration — ADAPTIVE MODEL REFINEMENT FOR THE IONOSPHERE AND THERMOSPHERE ANTHONY M. D’AMATO∗, AARON J. RIDLEY∗∗, AND DENNIS S. BERNSTEIN∗∗∗ Abstract. Mathematical models of...

  11. Performance Analysis of Different NeQuick Ionospheric Model Parameters

    Directory of Open Access Journals (Sweden)

    WANG Ningbo

    2017-04-01

    Full Text Available Galileo adopts NeQuick model for single-frequency ionospheric delay corrections. For the standard operation of Galileo, NeQuick model is driven by the effective ionization level parameter Az instead of the solar activity level index, and the three broadcast ionospheric coefficients are determined by a second-polynomial through fitting the Az values estimated from globally distributed Galileo Sensor Stations (GSS. In this study, the processing strategies for the estimation of NeQuick ionospheric coefficients are discussed and the characteristics of the NeQuick coefficients are also analyzed. The accuracy of Global Position System (GPS broadcast Klobuchar, original NeQuick2 and fitted NeQuickC as well as Galileo broadcast NeQuickG models is evaluated over the continental and oceanic regions, respectively, in comparison with the ionospheric total electron content (TEC provided by global ionospheric maps (GIM, GPS test stations and JASON-2 altimeter. The results show that NeQuickG can mitigate ionospheric delay by 54.2%~65.8% on a global scale, and NeQuickC can correct for 71.1%~74.2% of the ionospheric delay. NeQuick2 performs at the same level with NeQuickG, which is a bit better than that of GPS broadcast Klobuchar model.

  12. Evaluation of the performance of DIAS ionospheric forecasting models

    Directory of Open Access Journals (Sweden)

    Tsagouri Ioanna

    2011-08-01

    Full Text Available Nowcasting and forecasting ionospheric products and services for the European region are regularly provided since August 2006 through the European Digital upper Atmosphere Server (DIAS, http://dias.space.noa.gr. Currently, DIAS ionospheric forecasts are based on the online implementation of two models: (i the solar wind driven autoregression model for ionospheric short-term forecast (SWIF, which combines historical and real-time ionospheric observations with solar-wind parameters obtained in real time at the L1 point from NASA ACE spacecraft, and (ii the geomagnetically correlated autoregression model (GCAM, which is a time series forecasting method driven by a synthetic geomagnetic index. In this paper we investigate the operational ability and the accuracy of both DIAS models carrying out a metrics-based evaluation of their performance under all possible conditions. The analysis was established on the systematic comparison between models’ predictions with actual observations obtained over almost one solar cycle (1998–2007 at four European ionospheric locations (Athens, Chilton, Juliusruh and Rome and on the comparison of the models’ performance against two simple prediction strategies, the median- and the persistence-based predictions during storm conditions. The results verify operational validity for both models and quantify their prediction accuracy under all possible conditions in support of operational applications but also of comparative studies in assessing or expanding the current ionospheric forecasting capabilities.

  13. The Near Real Time Ionospheric Model of Latvia

    Science.gov (United States)

    Kaļinka, M.; Zvirgzds, J.; Dobelis, D.; Lazdāns, E.; Reiniks, M.

    2015-11-01

    A highly accurate ionosphere model is necessary to enable a fast and reliable coordinate determination with GNSS in real time. It is a partially ionized atmospheric region ranging up to 1,000 km height, affected by spatial variations, space weather, seasonal and solar cycle dependence. New approaches and algorithms of modelling techniques are sought to provide better solutions in the territory of Latvia. Ionospheric TEC value has large differences in Western Latvia and Eastern Latvia. Actual ionospheric map should be calculated and delivered to the surveyors near real time and published on the WEB. Delivering actual map to rover GNSS devices in a field will provide the surveyors with ionospheric conditions and allow choosing best time for surveying and making geodetic measurements with higher accuracy and reliability.

  14. Basic theory and model calculations of the Venus ionosphere

    Science.gov (United States)

    Nagy, A. F.; Cravens, T. E.; Gombosi, T. I.

    1983-01-01

    An assessment is undertaken of current understanding of the physical and chemical processes that control Venus's ionospheric behavior, in view of the data that has been made available by the Venera and Pioneer Venus missions. Attention is given to the theoretical framework used in general planetary ionosphere studies, especially to the equations describing the controlling physical and chemical processes, and to the current status of the ion composition, density and thermal structure models developed to reproduce observed ionospheric behavior. No truly comprehensive and successful model of the nightside ionosphere has been published. Furthermore, although dayside energy balance calculations yield electron and ion temperature values that are in close agreement with measured values, the energetics of the night side eludes understanding.

  15. Global GPS Ionospheric Modelling Using Spherical Harmonic Expansion Approach

    Directory of Open Access Journals (Sweden)

    Byung-Kyu Choi

    2010-12-01

    Full Text Available In this study, we developed a global ionosphere model based on measurements from a worldwide network of global positioning system (GPS. The total number of the international GPS reference stations for development of ionospheric model is about 100 and the spherical harmonic expansion approach as a mathematical method was used. In order to produce the ionospheric total electron content (TEC based on grid form, we defined spatial resolution of 2.0 degree and 5.0 degree in latitude and longitude, respectively. Two-dimensional TEC maps were constructed within the interval of one hour, and have a high temporal resolution compared to global ionosphere maps which are produced by several analysis centers. As a result, we could detect the sudden increase of TEC by processing GPS observables on 29 October, 2003 when the massive solar flare took place.

  16. On magnetospheric electron impact ionisation and dynamics in Titan's ram-side and polar ionosphere – a Cassini case study

    Directory of Open Access Journals (Sweden)

    G. R. Lewis

    2007-11-01

    Full Text Available We present data from the sixth Cassini flyby of Titan (T5, showing that the magnetosphere of Saturn strongly interacts with the moon's ionosphere and exo-ionosphere. A simple electron ionisation model provides a reasonable agreement with the altitude structure of the ionosphere. Furthermore, we suggest that the dense and cold exo-ionosphere (from the exobase at 1430 km and outward to several Titan radii from the surface can be explained by magnetospheric forcing and other transport processes whereas exospheric ionisation by impacting low energy electrons seems to play a minor role.

  17. SAMI3_ICON: Model of the Ionosphere/Plasmasphere System

    Science.gov (United States)

    Huba, J. D.; Maute, A.; Crowley, G.

    2017-10-01

    The NRL ionosphere/plasmasphere model SAMI3 has been modified to support the NASA ICON mission. Specifically, SAMI3_ICON has been modified to import the thermospheric composition, temperature, and winds from TIEGCM-ICON and the high-latitude potential from AMIE data. The codes will be run on a daily basis during the ICON mission to provide ionosphere and thermosphere properties to the science community. SAMI3_ICON will provide ionospheric and plasmaspheric parameters such as the electron and ion densities, temperatures, and velocities, as well as the total electron content (TEC), peak ionospheric electron density (NmF2) and height of the F layer at NmF2 (hmF2).

  18. Development of ionospheric data assimilation model under geomagnetic storm conditions

    Science.gov (United States)

    Lin, C. C. H.; Chen, C. H.; Chen, W.; Matsuo, T.

    2016-12-01

    This study attempts to construct the ionosphere data assimilation model for both quiet and storm time ionosphere. The model assimilates radio occultation and ground-based GNSS observations of global ionosphere using an Ensemble Kalman Filter (EnKF) software of Data Assimilation Research Testbed (DART) together with the theoretical thermosphere-ionosphere-electrodynamic general circulation model (TIEGCM), developed by National Center for Atmospheric Research (NCAR). Using DART-TIEGCM, we investigate the effects of rapid assimilation-forecast cycling for the 26 September 2011 geomagnetic storm period. Effects of various assimilation-forecast cycles, 60-, 30-, and 10-minutes, on the ionospheric forecast are examined by using the global root-mean-square of observation-minus-forecast (OmF) TEC residuals during the entire storm period. Examinations show that the 10-minutes assimilation cycle could greatly improve the quality of model forecast under the storm conditions. Additionally, examinations of storm-time forecast quality for different high latitude forcing given by Heelis and Weimer empirical models are also performed.

  19. Comparative evaluation of NeQuick and IRI models over Polar Regions

    Science.gov (United States)

    Pietrella, Marco; Nava, Bruno; Pezzopane, Michael; Migoya-Orue, Yenca; Scotto, Carlo

    2016-04-01

    In the framework of the AUSPICIO (AUtomatic Scaling of Polar Ionograms and Cooperative Ionospheric Observations) project, the ionograms recorded at Hobart (middle latitude), Macquarie Island, Livingstone Island and Comandante Ferraz (middle-high latitude) and those recorded at the ionospheric observatories of Casey, Mawson, Davis, and Scott Base (Antarctic Polar Circle), have been taken into account to study the capability of NeQuick-2 and IRI-2012 models in predicting the behavior of the ionosphere, mainly in the polar region. In particular, the applicability of NeQuick-2 and IRI-2012 models was evaluated under two different modes: a) as assimilative models ingesting the foF2 and hmF2 measurements obtained from the electron density profiles provided by the Adaptive Ionospheric Profiler (AIP); b) as climatological models taking as input F10.7 solar activity index. The results obtained from the large number of comparisons made for each ionospheric observatory when NeQuick-2 and IRI-2012 models work according to the two modes above mentioned, reveal that the best description of the ionosphere electron density at the polar regions is provided when peak parameter data are ingested in near-real-time into NeQuick-2 and IRI-2012 models which, indeed, are not always able to represent efficiently the behavior of the ionosphere over the polar regions when operating in long term prediction mode. The statistical analysis results expressed in terms of root mean square errors (r.m.s.e.) for each ionospheric observatory show that, outside the Antarctic Polar Circle (APC), NeQuick-2 performance is better than the IRI-2012 performance; on the contrary, inside the APC IRI-2012 model performs better than NeQuick-2.

  20. The response of ionospheric convection in the polar cap to substorm activity

    Directory of Open Access Journals (Sweden)

    M. Lester

    Full Text Available We report multi-instrument observations during an isolated substorm on 17 October 1989. The EISCAT radar operated in the SP-UK-POLI mode measuring ionospheric convection at latitudes 71°λ-78°λ. SAMNET and the EISCAT Magnetometer Cross provide information on the timing of substorm expansion phase onset and subsequent intensifications, as well as the location of the field aligned and ionospheric currents associated with the substorm current wedge. IMP-8 magnetic field data are also included. Evidence of a substorm growth phase is provided by the equatorward motion of a flow reversal boundary across the EISCAT radar field of view at 2130 MLT, following a southward turning of the interplanetary magnetic field (IMF. We infer that the polar cap expanded as a result of the addition of open magnetic flux to the tail lobes during this interval. The flow reversal boundary, which is a lower limit to the polar cap boundary, reached an invariant latitude equatorward of 71°λ by the time of the expansion phase onset. A westward electrojet, centred at 65.4°λ, occurred at the onset of the expansion phase. This electrojet subsequently moved poleward to a maximum of 68.1°λ at 2000 UT and also widened. During the expansion phase, there is evidence of bursts of plasma flow which are spatially localised at longitudes within the substorm current wedge and which occurred well poleward of the westward electrojet. We conclude that the substorm onset region in the ionosphere, defined by the westward electrojet, mapped to a part of the tail radially earthward of the boundary between open and closed magnetic flux, the "distant" neutral line. Thus the substorm was not initiated at the distant neutral line, although there is evidence that it remained active during the expansion phase. It is not obvious whether the electrojet mapped to a near-Earth neutral line, but at its most poleward, the expanded electrojet does not reach the estimated latitude of the polar cap

  1. Regional 4-D modeling of the ionospheric electron density

    Science.gov (United States)

    Schmidt, M.; Bilitza, D.; Shum, C. K.; Zeilhofer, C.

    2008-08-01

    The knowledge of the electron density is the key point in correcting ionospheric delays of electromagnetic measurements and in studying the ionosphere. During the last decade GNSS, in particular GPS, has become a promising tool for monitoring the total electron content (TEC), i.e., the integral of the electron density along the ray-path between the transmitting satellite and the receiver. Hence, geometry-free GNSS measurements provide informations on the electron density, which is basically a four-dimensional function depending on spatial position and time. In addition, these GNSS measurements can be combined with other available data including nadir, over-ocean TEC observations from dual-frequency radar altimetry (T/P, JASON, ENVISAT), and TECs from GPS-LEO occultation systems (e.g., FORMOSAT-3/COSMIC, CHAMP) with heterogeneous sampling and accuracy. In this paper, we present different multi-dimensional approaches for modeling spatio-temporal variations of the ionospheric electron density. To be more specific, we split the target function into a reference part, computed from the International Reference Ionosphere (IRI), and an unknown correction term. Due to the localizing feature of B-spline functions we apply tensor-product spline expansions to model the correction term in a certain multi-dimensional region either completely or partly. Furthermore, the multi-resolution representation derived from wavelet analysis allows monitoring the ionosphere at different resolutions levels. For demonstration we apply three approaches to electron density data over South America.

  2. Quantitative modelling of the closure of meso-scale parallel currents in the nightside ionosphere

    Directory of Open Access Journals (Sweden)

    A. Marchaudon

    2004-01-01

    Full Text Available On 12 January 2000, during a northward IMF period, two successive conjunctions occur between the CUTLASS SuperDARN radar pair and the two satellites Ørsted and FAST. This situation is used to describe and model the electrodynamic of a nightside meso-scale arc associated with a convection shear. Three field-aligned current sheets, one upward and two downward on both sides, are observed. Based on the measurements of the parallel currents and either the conductance or the electric field profile, a model of the ionospheric current closure is developed along each satellite orbit. This model is one-dimensional, in a first attempt and a two-dimensional model is tested for the Ørsted case. These models allow one to quantify the balance between electric field gradients and ionospheric conductance gradients in the closure of the field-aligned currents. These radar and satellite data are also combined with images from Polar-UVI, allowing for a description of the time evolution of the arc between the two satellite passes. The arc is very dynamic, in spite of quiet solar wind conditions. Periodic enhancements of the convection and of electron precipitation associated with the arc are observed, probably associated with quasi-periodic injections of particles due to reconnection in the magnetotail. Also, a northward shift and a reorganisation of the precipitation pattern are observed, together with a southward shift of the convection shear. Key words. Ionosphere (auroral ionosphere; electric fields and currents; particle precipitation – Magnetospheric physics (magnetosphere-ionosphere interactions

  3. Wave disturbances in the polar ionosphere after a Vitim meteorite burst

    Science.gov (United States)

    Tereshchenko, V. D.; Ogloblina, O. F.; Tereshchenko, V. A.; Chernyakov, S. M.

    On September 24th, 2002, at 16:49 UT in the Mamsko-Chuisk region of the Irkutsk oblast of Russia it was a fall of a big meteorite. The fall was accompanied with light, acoustic, geomagnetic, seismic and mechanical phenomena which were recorded by ground and space means of observations. The meteorite has burst in the air at the altitude of 30 km with coordinates of the burst: 58.23 N, 113.46 E. After 17:00 UT there was recorded a sequence of small disturbances of the geomagnetic field and wavelike changes of amplitude of medium wave radioreflections at heights from 47 till 129 km in Tumanny (Murmansk oblast, Russia; 69.0 N, 35.7 E) which was situated at a distance of 4000 km from a place of the burst. It was gotten that after the burst three types of waves (magnetoacoustic, acoustic-gravitational and infraacoustic) spread in the polar mesosphere and lower ionosphere. Observable disturbances had periods of oscillations about 3-4, 5-6 and more than 9-10 minutes. A similarity characteristics of the wave indignations with analogous ones which were gotten earlier during investigations of effects of the Tungusk meteorite and the American space station "Skylab" falls and also a fact of a registration of a pressure wave on a net of microbarographs of PGI in Apatity permit to maintain that the source of the indignations in the polar ionosphere is the meteorite explosion. The hypothesis about wavequide spreading of atmospheric waves to large distance was confirmed.

  4. Modeling Chinese ionospheric layer parameters based on EOF analysis

    Science.gov (United States)

    Yu, You; Wan, Weixing

    2016-04-01

    Using 24-ionosonde observations in and around China during the 20th solar cycle, an assimilative model is constructed to map the ionospheric layer parameters (foF2, hmF2, M(3000)F2, and foE) over China based on empirical orthogonal function (EOF) analysis. First, we decompose the background maps from the International Reference Ionosphere model 2007 (IRI-07) into different EOF modes. The obtained EOF modes consist of two factors: the EOF patterns and the corresponding EOF amplitudes. These two factors individually reflect the spatial distributions (e.g., the latitudinal dependence such as the equatorial ionization anomaly structure and the longitude structure with east-west difference) and temporal variations on different time scales (e.g., solar cycle, annual, semiannual, and diurnal variations) of the layer parameters. Then, the EOF patterns and long-term observations of ionosondes are assimilated to get the observed EOF amplitudes, which are further used to construct the Chinese Ionospheric Maps (CIMs) of the layer parameters. In contrast with the IRI-07 model, the mapped CIMs successfully capture the inherent temporal and spatial variations of the ionospheric layer parameters. Finally, comparison of the modeled (EOF and IRI-07 model) and observed values reveals that the EOF model reproduces the observation with smaller root-mean-square errors and higher linear correlation co- efficients. In addition, IRI discrepancy at the low latitude especially for foF2 is effectively removed by EOF model.

  5. Ionosphere-thermosphere models at the Community Coordinated Modeling Center

    Science.gov (United States)

    Webb, Phillip A.; Kuznetsova, Masha M.; Hesse, Michael; Rastaetter, Lutz; Chulaki, Anna

    2009-02-01

    One of the ways to address the science needs of the research community and to enable science progress is to provide community access to modern space science models. The Community Coordinated Modeling Center (CCMC) is a multiagency partnership based at the Goddard Space Flight Center that hosts a set of state-of-the-art space science models ranging from the solar atmosphere to the Earth's upper atmosphere. The CCMC provides a Web-based, no-cost, Runs on Request system, by which the interested scientist can readily request simulations for time intervals of interest. CCMC also provides a tailored Web-based visualization interface for the model output, including near-real-time results from select models. Model outputs have been specifically tailored for easy comparison with observational data to facilitate data analysis and model validation. This paper provides an overview of CCMC activities, with an emphasis on the ionosphere-thermosphere models residing there.

  6. Model based Computerized Ionospheric Tomography in space and time

    Science.gov (United States)

    Tuna, Hakan; Arikan, Orhan; Arikan, Feza

    2018-04-01

    Reconstruction of the ionospheric electron density distribution in space and time not only provide basis for better understanding the physical nature of the ionosphere, but also provide improvements in various applications including HF communication. Recently developed IONOLAB-CIT technique provides physically admissible 3D model of the ionosphere by using both Slant Total Electron Content (STEC) measurements obtained from a GPS satellite - receiver network and IRI-Plas model. IONOLAB-CIT technique optimizes IRI-Plas model parameters in the region of interest such that the synthetic STEC computations obtained from the IRI-Plas model are in accordance with the actual STEC measurements. In this work, the IONOLAB-CIT technique is extended to provide reconstructions both in space and time. This extension exploits the temporal continuity of the ionosphere to provide more reliable reconstructions with a reduced computational load. The proposed 4D-IONOLAB-CIT technique is validated on real measurement data obtained from TNPGN-Active GPS receiver network in Turkey.

  7. A Modeling Approach for Earthquake-Ionosphere Coupling

    Science.gov (United States)

    Meng, X.; Komjathy, A.; Verkhoglyadova, O. P.; Savastano, G.; Mannucci, A. J.

    2017-12-01

    We present a newly developed modeling approach for the earthquake-ionosphere coupling process, which extends the capability of Wave Perturbation - Global Ionosphere-Thermosphere Model (WP-GITM) developed originally for tsunami-ionosphere coupling. The new WP-GITM represents an earthquake as a point source at its epicenter, and takes the ground vertical velocity data from seismic measurements as input. The model then solves the neutral density, velocity, and temperature perturbations generated by spherical acoustic-gravity waves and the resulting perturbations in ions and electrons. We apply the model to simulate the near-field ionospheric disturbances during two earthquake events with different local times including the 2011 Tohoku-Oki (local afternoon) and the 2015 Illapel events (local evening). To validate the results, we retrieve receiver-to-satellite total electron content (TEC) perturbations from the simulations and compare them to the corresponding slant TEC perturbations from Global Positioning System (GPS) TEC observations. We find good agreement on magnitudes and arrival times between the simulations and observations and discuss directions of future research.

  8. Space geodetic techniques for global modeling of ionospheric peak parameters

    Science.gov (United States)

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

    The rapid development of new technological systems for navigation, telecommunication, and space missions which transmit signals through the Earth’s upper atmosphere - the ionosphere - makes the necessity of precise, reliable and near real-time models of the ionospheric parameters more crucial. In the last decades space geodetic techniques have turned into a capable tool for measuring ionospheric parameters in terms of Total Electron Content (TEC) or the electron density. Among these systems, the current space geodetic techniques, such as Global Navigation Satellite Systems (GNSS), Low Earth Orbiting (LEO) satellites, satellite altimetry missions, and others have found several applications in a broad range of commercial and scientific fields. This paper aims at the development of a three-dimensional integrated model of the ionosphere, by using various space geodetic techniques and applying a combination procedure for computation of the global model of electron density. In order to model ionosphere in 3D, electron density is represented as a function of maximum electron density (NmF2), and its corresponding height (hmF2). NmF2 and hmF2 are then modeled in longitude, latitude, and height using two sets of spherical harmonic expansions with degree and order 15. To perform the estimation, GNSS input data are simulated in such a way that the true position of the satellites are detected and used, but the STEC values are obtained through a simulation procedure, using the IGS VTEC maps. After simulating the input data, the a priori values required for the estimation procedure are calculated using the IRI-2012 model and also by applying the ray-tracing technique. The estimated results are compared with F2-peak parameters derived from the IRI model to assess the least-square estimation procedure and moreover, to validate the developed maps, the results are compared with the raw F2-peak parameters derived from the Formosat-3/Cosmic data.

  9. High-altitude chemical-release systems for Project BIME (Brazilian Ionospheric Modification Experiments) Project IMS (Ionospheric Modification Studies) Project PIIE (Polar Ionospheric Irregularities Experiment) Project Polar Arcs. Final report, 30 September 1981-30 June 1987

    Energy Technology Data Exchange (ETDEWEB)

    Stokes, C.S.; Murphy, W.J.

    1987-07-31

    Project BIME, a Spread-F observation program involved the launching of two Nike-Black Brant rockets each containing a payload containing Ammonium Nitrate Fuel Oil (ANFO). The rockets were launched from Barriera Do Inferno Launch Site in Natal, Brazil in August of 1982. Project IMS, an F-layer modification experiment involved three launch vehicles. A Nike-Tomahawk and two Sonda III rockets. The Nike-Tomahawk carried a sulfur hexafluoride (SF/sub 6/) payload. One of the Sonda III rockets carried a payload that consisted of an SF/sub 6/ canister and a samarium/strontium thermite canister. The remaining Sonda III carried a payload that consisted of a trifluorobromo methane (CF/sub 3/Br) canister and a samarium thermite canister. The rockets were launched from Wallops Island Launch Facility, Virginia in November of 1984. Project PIIE and Polar Arcs, a program to investigate polar ionospheric irregularities, involved the launch of a Nike-Black Brant rocket which housed one samarium thermite canister and six barium canisters. An attempted launch of the payload was returned in March of 1985, however, launch criteria could not be met and the payload was returned to FRC for storage and refurbishment for launch in 1987. The rocket was launched successfully from Sondrestrom Air Base, Greenland in March of 1987.

  10. Modeling the UT effect in global distribution of ionospheric electric fields

    DEFF Research Database (Denmark)

    Lukianova, R.; Christiansen, Freddy

    2008-01-01

    A new approach for modeling the global distribution of ionospheric electric potentials utilizing high-precision maps of field-aligned currents (FACs) derived from measurements by the Orsted and Magsat satellites as input to a comprehensive numerical scheme is presented. We simulate the universal...... an increase of the daily variation in the cross-polar potential drop (U-PC) at the equinoxes and a decrease at the solstices. Under equinoctial and zero IMF conditions the U-PC can vary by a factor of two, while the convection cells keep their shape. The model predicts that the summer U-PC can be smaller...

  11. High Frequency Backscatter from the Polar and Auroral E-Region Ionosphere

    Science.gov (United States)

    Forsythe, Victoriya V.

    The Earth's ionosphere contains collisional and partially-ionized plasma. The electric field, produced by the interaction between the Earth's magnetosphere and the solar wind, drives the plasma bulk motion, also known as convection, in the F-region of the ionosphere. It can also destabilize the plasma in the E-region, producing irregularities or waves. Intermediate-scale waves with wavelengths of hundreds of meters can cause scintillation and fading of the Global Navigation Satellite System (GNSS) signals, whereas the small-scale waves (lambda processes that generate small-scale plasma waves, and experimentally, by analyzing data collected with the newly-deployed high-southern-latitude radars within the Super Dual Auroral Radar Network (SuperDARN). The theoretical part of this work focuses on symmetry properties of the general dispersion relation that describes wave propagation in the collisional plasma in the two-stream and gradient-drift instability regimes. The instability growth rate and phase velocity are examined under the presence of a background parallel electric field, whose influence is demonstrated to break the spatial symmetry of the wave propagation patterns. In the observational part of this thesis, a novel dual radar setup is used to examine E-region irregularities in the magnetic polar cap by probing the E-region along the same line from opposite directions. The phase velocity analysis together with raytracing simulations demonstrated that, in the polar cap, the radar backscatter is primarily controlled by the plasma density conditions. In particular, when the E-region layer is strong and stratified, the radar backscatter properties are controlled by the convection velocity, whereas for a tilted E-layer, the height and aspect angle conditions are more important. Finally, the fundamental dependence of the E-region irregularity phase velocity on the component of the plasma convection is investigated using two new SuperDARN radars at high southern

  12. Large-scale irregularities of the winter polar topside ionosphere according to data from Swarm satellites

    Science.gov (United States)

    Lukianova, R. Yu.; Bogoutdinov, Sh. R.

    2017-11-01

    An analysis of the electron density measurements ( Ne) along the flyby trajectories over the high-latitude region of the Northern Hemisphere under winter conditions in 2014 and 2016 has shown that the main large-scale structure observed by Swarm satellites is the tongue of ionization (TOI). At the maximum of the solar cycle ( F 10.7 = 160), the average value of Ne in the TOI region at an altitude of 500 km was 8 × 104 cm-3. Two years later, at F 10.7 = 100, Ne 5 × 104 cm-3 and Ne 2.5 × 104 cm-3 were observed at altitudes of 470 and 530 km, respectively. During the dominance of the azimuthal component of the interplanetary magnetic field, the TOI has been observed mainly on the dawn or dusk side depending on the sign of B y . Simultaneous observations of the convective plasma drift velocity in the polar cap show the transpolar flow drift to the dawn ( B y y generation of large-scale irregularities in the polar ionosphere.

  13. Observing and modelling F-region ionospheric dynamics using the OII 7320A emission

    International Nuclear Information System (INIS)

    Carr, S.S.

    1992-01-01

    Limb-scan observations of Doppler line profiles from the (OII) lambda 7320A emission at F-Region altitudes, made with the Fabry-Perot interferometer (FPI) on the Dynamics Explorer-2 (DE-2) spacecraft, were analyzed to provide measurements of the meridional component of the ion convection velocity along the instrument line-of-sight. The DE-2 results presented demonstrate the first spaceborne use of the remote-sensing Doppler technique for measurements of ionospheric convection. The FPI meridional ion drift measurements were compared with nearly simultaneous in situ ion drift measurements from the Retarding Potential Analyzer (RPA) on DE-2. Once allowance is made for the temporal lag between the in situ and remote measurements, the results from the two techniques are found to be in good agreement, within specified experimental errors, giving confidence in the FPI measurements. The spaceborne interferometric technique has future utility for 2-dimensional imaging of polar ionospheric convection. Results from a simulated space-based observing platform, based on the DE-2 technique and an extension of a 7320A aeronomical model, are presented to demonstrate that a large fraction of the entire polar ionospheric convection pattern can be monitored from space during approximately 16-minute polar passes of a suitably-instrumented satellite. In the simulation, the polar-orbiting satellite's FPI system views the 7320A emission at various tangent point altitudes at +/- 45 deg and +/- 135 deg to the satellite velocity vector. By adjusting the horizon scan angle, several swaths of vectors at different horizontal spacing from the satellite can be recovered. Doppler line profiles from the (OII) 7320A emission at F-Region altitudes, made with the FPI at Sondre Stromfjord, Greenland, were analyzed to provide ion drift vectors and temperatures

  14. Modeling Callisto's Ionosphere, Airglow and Magnetic Field Environment

    OpenAIRE

    Hartkorn, Oliver

    2017-01-01

    Previous observations of the Galileo spacecraft and the Hubble Space Telescope indicate that Callisto possesses a neutral atmosphere which is mostly composed of O2 and additionally contains H2O and CO2. The first aim of our study is to constrain density and structure of the atmospheric O2. Based on existent observations and findings, we construct a phenomenological model of Callisto's atmosphere. Then, we use this atmosphere model as input information for an ionosphere model, which ...

  15. Quantitative modeling of the ionospheric response to geomagnetic activity

    Directory of Open Access Journals (Sweden)

    T. J. Fuller-Rowell

    2000-07-01

    Full Text Available A physical model of the coupled thermosphere and ionosphere has been used to determine the accuracy of model predictions of the ionospheric response to geomagnetic activity, and assess our understanding of the physical processes. The physical model is driven by empirical descriptions of the high-latitude electric field and auroral precipitation, as measures of the strength of the magnetospheric sources of energy and momentum to the upper atmosphere. Both sources are keyed to the time-dependent TIROS/NOAA auroral power index. The output of the model is the departure of the ionospheric F region from the normal climatological mean. A 50-day interval towards the end of 1997 has been simulated with the model for two cases. The first simulation uses only the electric fields and auroral forcing from the empirical models, and the second has an additional source of random electric field variability. In both cases, output from the physical model is compared with F-region data from ionosonde stations. Quantitative model/data comparisons have been performed to move beyond the conventional "visual" scientific assessment, in order to determine the value of the predictions for operational use. For this study, the ionosphere at two ionosonde stations has been studied in depth, one each from the northern and southern mid-latitudes. The model clearly captures the seasonal dependence in the ionospheric response to geomagnetic activity at mid-latitude, reproducing the tendency for decreased ion density in the summer hemisphere and increased densities in winter. In contrast to the "visual" success of the model, the detailed quantitative comparisons, which are necessary for space weather applications, are less impressive. The accuracy, or value, of the model has been quantified by evaluating the daily standard deviation, the root-mean-square error, and the correlation coefficient between the data and model predictions. The modeled quiet-time variability, or standard

  16. Ionospheric scintillation forecasting model based on NN-PSO technique

    Science.gov (United States)

    Sridhar, M.; Venkata Ratnam, D.; Padma Raju, K.; Sai Praharsha, D.; Saathvika, K.

    2017-09-01

    The forecasting and modeling of ionospheric scintillation effects are crucial for precise satellite positioning and navigation applications. In this paper, a Neural Network model, trained using Particle Swarm Optimization (PSO) algorithm, has been implemented for the prediction of amplitude scintillation index (S4) observations. The Global Positioning System (GPS) and Ionosonde data available at Darwin, Australia (12.4634° S, 130.8456° E) during 2013 has been considered. The correlation analysis between GPS S4 and Ionosonde drift velocities (hmf2 and fof2) data has been conducted for forecasting the S4 values. The results indicate that forecasted S4 values closely follow the measured S4 values for both the quiet and disturbed conditions. The outcome of this work will be useful for understanding the ionospheric scintillation phenomena over low latitude regions.

  17. Modelling the main ionospheric trough using the Electron Density Assimilative Model (EDAM) with assimilated GPS TEC

    Science.gov (United States)

    Parker, James A. D.; Eleri Pryse, S.; Jackson-Booth, Natasha; Buckland, Rachel A.

    2018-01-01

    The main ionospheric trough is a large-scale spatial depletion in the electron density distribution at the interface between the high- and mid-latitude ionosphere. In western Europe it appears in early evening, progresses equatorward during the night, and retreats rapidly poleward at dawn. It exhibits substantial day-to-day variability and under conditions of increased geomagnetic activity it moves progressively to lower latitudes. Steep gradients on the trough-walls on either side of the trough minimum, and their variability, can cause problems for radio applications. Numerous studies have sought to characterize and quantify the trough behaviour. The Electron Density Assimilative Model (EDAM) models the ionosphere on a global scale. It assimilates observations into a background ionosphere, the International Reference Ionosphere 2007 (IRI2007), to provide a full 3-D representation of the ionospheric plasma distribution at specified times and days. This current investigation studied the capability of EDAM to model the ionosphere in the region of the main trough. Total electron content (TEC) measurements from 46 GPS stations in western Europe from September to December 2002 were assimilated into EDAM to provide a model of the ionosphere in the trough region. Vertical electron content profiles through the model revealed the trough and the detail of its structure. Statistical results are presented of the latitude of the trough minimum, TEC at the minimum and of other defined parameters that characterize the trough structure. The results are compared with previous observations made with the Navy Ionospheric Monitoring System (NIMS), and reveal the potential of EDAM to model the large-scale structure of the ionosphere.

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

    Science.gov (United States)

    Namgaladze, A. A.

    2013-12-01

    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

  19. Cellular automata model of magnetospheric-ionospheric coupling

    Directory of Open Access Journals (Sweden)

    B. V. Kozelov

    2003-09-01

    Full Text Available We propose a cellular automata model (CAM to describe the substorm activity of the magnetospheric-ionospheric system. The state of each cell in the model is described by two numbers that correspond to the energy content in a region of the current sheet in the magnetospheric tail and to the conductivity of the ionospheric domain that is magnetically connected with this region. The driving force of the system is supposed to be provided by the solar wind that is convected along the two boundaries of the system. The energy flux inside is ensured by the penetration of the energy from the solar wind into the array of cells (magnetospheric tail with a finite velocity. The third boundary (near to the Earth is closed and the fourth boundary is opened, thereby modeling the flux far away from the tail. The energy dissipation in the system is quite similar to other CAM models, when the energy in a particular cell exceeds some pre-defined threshold, and the part of the energy excess is redistributed between the neighbouring cells. The second number attributed to each cell mimics ionospheric conductivity that can allow for a part of the energy to be shed on field-aligned currents. The feedback between "ionosphere" and "magnetospheric tail" is provided by the change in a part of the energy, which is redistributed in the tail when the threshold is surpassed. The control parameter of the model is the z-component of the interplanetary magnetic field (Bz IMF, "frozen" into the solar wind. To study the internal dynamics of the system at the beginning, this control parameter is taken to be constant. The dynamics of the system undergoes several bifurcations, when the constant varies from - 0.6 to - 6.0. The Bz IMF input results in the periodic transients (activation regions and the inter-transient period decreases with the decrease of Bz. At the same time the onset of activations in the array shifts towards the "Earth". When the modulus of the Bz IMF exceeds some

  20. Spherical Slepian as a new method for ionospheric modeling in arctic region

    Science.gov (United States)

    Etemadfard, Hossein; Hossainali, Masoud Mashhadi

    2016-03-01

    From the perspective of the physical, chemical and biological balance in the world, the Arctic has gradually turned into an important region opening ways for new researchers and scientific expeditions. In other words, various researches have been funded in order to study this frozen frontier in details. The current study can be seen in the same milieu where researchers intend to propose a set of new base functions for modeling ionospheric in the Arctic. As such, to optimize the Spherical Harmonic (SH) functions, the spatio-spectral concentration is applied here using the Slepian theory that was developed by Simons. For modeling the ionosphere, six International GNSS Service (IGS) stations located in the northern polar region were taken into account. Two other stations were left out for assessing the accuracy of the proposed model. The adopted GPS data starts at DOY 69 (Day of Year) and ends at DOY 83 (totally 15 successive days) in 2013. Three Spherical Slepian models respectively with the maximal degrees of K=15, 20 & 25 were used. Based on the results, K=15 is the optimum degree for the proposed model. The accuracy and precision of the Slepian model are about 0.1 and 0.05 TECU, respectively (TEC Unit=1016 electron/m2). To understand the advantage of this model, it is compared with polynomial and trigonometric series which are developed using the same set of measurements. The accuracy and precision of trigonometric and polynomial models are at least 4 times worse than the Slepian one.

  1. Traveling Ionospheric Disturbances generated by upward propagating gravity waves simulated by a whole atmosphere-ionosphere coupled Model

    Science.gov (United States)

    Miyoshi, Y.; Jin, H.; Fujiwara, H.; Shinagawa, H.

    2017-12-01

    It has been recognized that gravity waves (GWs) play an important role on the momentum and energy budget in the thermosphere/ionosphere. In this study, using a whole atmosphere-ionosphere coupled model (GAIA), behaviors of Traveling Ionospheric Disturbances (TIDs) generated by upward propagating GWs in the thermosphere are investigated. The horizontal resolution of GAIA is 1 degree longitude by 1 degree latitude, which is adequate to simulate large-scale GWs. The GAIA contains the region from the ground surface to the upper thermosphere, so that we can simulate excitation of gravity waves in the lower atmosphere, their upward propagation to the mesosphere and thermosphere, and their impacts on the thermosphere/ionosphere system. The GAIA can simulate TIDs because interaction processes between the ionosphere and neutral atmosphere are included. We focus on seasonal and longitudinal variations of TIDs and their relation to GW activity in the thermosphere. Our results indicate that many TIDs are generated by upward propagating GWs in the thermosphere, and these TIDs propagate equatorward. TIDs are much stronger in winter than in summer. Moreover, day-to-day variability of GW activity in the stratosphere and mesosphere are examined, and their impacts on temporal variability of TIDs are discussed.

  2. Equatorial Ionospheric Response to Different Estimated Disturbed Electric Fields as Investigated Using Sheffield University Plasmasphere Ionosphere Model at INPE

    Science.gov (United States)

    Bravo, M. A.; Batista, I. S.; Souza, J. R.; Foppiano, A. J.

    2017-10-01

    Good ionospheric modeling is important to understand anomalous effects, mainly during geomagnetic storm events. Ionospheric electric fields, thermospheric winds, and neutral composition are affected at different degrees, depending on the intensity of the magnetic disturbance which, in turns, affects the electron density distribution at all latitudes. The most important disturbed parameter for the equatorial ionosphere is the electric field, which is responsible for the equatorial ionization anomaly. Here various electric field measurements and models are analyzed: (1) measured by the Jicamarca incoherent scatter radar (ISR), (2) from Jicamarca Unattended Long-Term studies of the Ionosphere and Atmosphere (JULIA) radar, (3) deduced from magnetometers, (4) calculated from the time variations of the F layer height (dh'F/dt), and (5) deduced from interplanetary electric field determinations. The response of ionospheric parameters foF2 and hmF2 to the electric fields simulated using the Sheffield University Plasmasphere Ionosphere Model version available at Instituto Nacional de Pesquisas Espaciais is compared with observations for two locations, during the geomagnetic storm events of 17-18 April 2002 and 7-10 November 2004. Results are found to be consistent with the observations in such a way that a hierarchy among the different types of drifts used can be established. When no ISR measurements are available, the drifts deduced from magnetometers or measured by the JULIA are best when including the contribution derived from dh'F/dt for the 18-24 LT time interval. However, when none of these drifts are available, drifts inferred from the interplanetary electric field seem to be a good alternative for some purposes.

  3. Ingestion of FORMOSAT-3/COSMIC GPS data into La Plata Ionospheric Model: A preliminary assessment

    Science.gov (United States)

    Conte, J. Federico; Brunini, Claudio

    2017-08-01

    La Plata Ionospheric Model (LPIM; Brunini et al., 2011) has been upgraded to a new stage enabling the ingestion of sTEC values retrieved from GPS receivers on board the FORMOSAT-3 Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) satellites, in order to determine corrections to the global mean values of the ionosphere F2 layer critical frequency, fo F 2 (related to the peak density, Nm F 2) and the F2 layer peak height, hm F 2 .

  4. Statistical Patterns of Ionospheric Convection Derived From Mid-Latitude, High-Latitude, and Polar SuperDARN HF Radar Observations

    Science.gov (United States)

    Thomas, E. G.; Shepherd, S. G.

    2017-12-01

    Global patterns of ionospheric convection have been widely studied in terms of the interplanetary magnetic field (IMF) magnitude and orientation in both the Northern and Southern Hemispheres using observations from the Super Dual Auroral Radar Network (SuperDARN). The dynamic range of driving conditions under which existing SuperDARN statistical models are valid is currently limited to periods when the high-latitude convection pattern remains above about 60° geomagnetic latitude. Cousins and Shepherd [2010] found this to correspond to intervals when the solar wind electric field Esw 0) the high-latitude radars often experience difficulties in measuring convection above about 85° geomagnetic latitude. In this presentation, we introduce a new statistical model of ionospheric convection which is valid for much more dominant IMF Bz conditions than was previously possible by including velocity measurements from the newly constructed tiers of radars in the Northern Hemisphere at midlatitudes and in the polar cap. This new model (TS17) is compared to previous statistical models derived from high-latitude SuperDARN observations (RG96, PSR10, CS10) and its impact on instantaneous Map Potential solutions is examined.

  5. Numerical modelling of the Earth’s ionosphere F region

    Science.gov (United States)

    Ostanin, P. A.; Kulyamin, D. V.; Dymnikov, V. P.

    2017-11-01

    This paper presents the first version of a new INM RAS Earth’s ionosphere F region dynamical model. A complete set of model equations is formulated taking into account all the key physical processes that form the global state of the ionospheric F region (plasma chemistry, ambipolar diffusion, wind transport, drift across magnetic lines). For the numerical solution, a splitting method based on the physical processes and geometric directions is proposed. The first stage of splitting in a quasi-two-dimensional approximation setting with a projection of ambipolar diffusion on the vertical direction is considered. It is numerically implemented stepwise using various difference schemes for three separate model formulations (taking into account diffusion only along the vertical direction, considering a realistic direction of diffusion along the magnetic field excluding and including a mixed derivative term). The applicability, efficiency, conservation, and monotonicity of these numerical methods are analyzed. The first numerical experiments show convergence of the numerical solution to a stationary vertical profile specific to the F region. The greatest consistency with the observed profiles is obtained in the mid-latitudes. Using the thus constructed model it is shown that the electron density profile is most sensitive to the neutral temperature and ionization level with qualitatively different structures of the corresponding modes of variability.

  6. Ionospheric topside models compared with experimental electron density profiles

    Directory of Open Access Journals (Sweden)

    S. M. Radicella

    2005-06-01

    Full Text Available Recently an increasing number of topside electron density profiles has been made available to the scientific community on the Internet. These data are important for ionospheric modeling purposes, since the experimental information on the electron density above the ionosphere maximum of ionization is very scarce. The present work compares NeQuick and IRI models with the topside electron density profiles available in the databases of the ISIS2, IK19 and Cosmos 1809 satellites. Experimental electron content from the F2 peak up to satellite height and electron densities at fixed heights above the peak have been compared under a wide range of different conditions. The analysis performed points out the behavior of the models and the improvements needed to be assessed to have a better reproduction of the experimental results. NeQuick topside is a modified Epstein layer, with thickness parameter determined by an empirical relation. It appears that its performance is strongly affected by this parameter, indicating the need for improvements of its formulation. IRI topside is based on Booker's approach to consider two parts with constant height gradients. It appears that this formulation leads to an overestimation of the electron density in the upper part of the profiles, and overestimation of TEC.

  7. Precipitation and total power consumption in the ionosphere: Global MHD simulation results compared with Polar and SNOE observations

    Directory of Open Access Journals (Sweden)

    M. Palmroth

    2006-05-01

    Full Text Available We compare the ionospheric electron precipitation morphology and power from a global MHD simulation (GUMICS-4 with direct measurements of auroral energy flux during a pair of substorms on 28-29 March 1998. The electron precipitation power is computed directly from global images of auroral light observed by the Polar satellite ultraviolet imager (UVI. Independent of the Polar UVI measurements, the electron precipitation energy is determined from SNOE satellite observations on the thermospheric nitric oxide (NO density. We find that the GUMICS-4 simulation reproduces the spatial variation of the global aurora rather reliably in the sense that the onset of the substorm is shown in GUMICS-4 simulation as enhanced precipitation in the right location at the right time. The total integrated precipitation power in the GUMICS-4 simulation is in quantitative agreement with the observations during quiet times, i.e., before the two substorm intensifications. We find that during active times the GUMICS-4 integrated precipitation is a factor of 5 lower than the observations indicate. However, we also find factor of 2-3 differences in the precipitation power among the three different UVI processing methods tested here. The findings of this paper are used to complete an earlier objective, in which the total ionospheric power deposition in the simulation is forecasted from a mathematical expression, which is a function of solar wind density, velocity and magnetic field. We find that during this event, the correlation coefficient between the outcome of the forecasting expression and the simulation results is 0.83. During the event, the simulation result on the total ionospheric power deposition agrees with observations (correlation coefficient 0.8 and the AE index (0.85.

  8. The use of global ionospheric irregularity models for satellite communications

    Science.gov (United States)

    Pope, J. H.

    1974-01-01

    Scintillation data obtained in the VHF region were used by Fremouw to develop a global scintillation model. An attempt has been made in the present study to improve this model in several respects. One of these is to modify the high latitude term in the model to better represent data obtained in the northern high latitude regions. Another improvement is the extention of the frequency region of validity to the L band and microwave regions. This attempt is based on certain theoretical considerations regarding the effects of distribution in irregularity sizes. Recent satellite in situ measurements indicate that the ionospheric irregularity description is functionally different from that assumed in the past. These satellite measurements are used in connection with the theoretical development to improve the model.

  9. Estimation of Ion temperatures in the Ionosphere using Swarm Langmuir Probe data and a Physics-Based Model

    Science.gov (United States)

    Lomidze, L.; Knudsen, D. J.; Burchill, J. K.; Kouznetsov, A.

    2017-12-01

    Ion temperature is one of the key parameters that provides insight into the thermal balance of the coupled ionosphere-thermosphere system. Together with the temperatures of neutral and electron gases it controls various physical and chemical processes in the upper atmosphere. These include the ion-neutral collision frequencies, chemical reaction rates and plasma scale height, all of which affect the variation and distribution of the electron density. Yet, the modeling of ionospheric ion temperature has received relatively little attention compared to other parameters. The Electric Field Instruments on the European Space Agency's (ESA's) polar orbiting Swarm satellites consist of a pair of Thermal Ion Imagers (TII) and a pair of Langmuir probes (LP) measuring ionospheric plasma parameters at around 500 km. The TII was designed to image ion velocity distribution functions and provide ionospheric electric fields and ion temperatures along the satellites' orbits. Currently, the TII instruments are operating only during limited time intervals, while the measurements of ionospheric electron temperatures and densities are carried out continuously. In this work we estimate the ion temperatures along the orbits of Swarm satellites at low and middle latitudes using a heat balance equation for the ions gas under steady-state conditions. The physics-based ion temperature model assumes ions are heated by the hotter electron gas through elastic Coulomb collisions and cooled by resonance charge transfer collisions with the parent atoms and by elastic collisions with unlike atoms and molecules. The corrected Swarm LP data represent key input parameters for the model. To evaluate the validity of the proposed method, we perform two types of analysis. The first is based on the synthetic (model-generated) inputs by a physics-based ionosphere model which solves the complete ion heat balance equation. In another, the estimates of ion temperatures are obtained using actual data for those

  10. Magnetospheric ion deposition on Titan's ionosphere in hybrid model

    Science.gov (United States)

    Sillanpaa, I.; Johnson, R. E.; Crary, F. J.; Young, D. T.; Kallio, E. J.; Jarvinen, R.

    2010-12-01

    Hybrid modelling allows tracking ion particle in self-consist electromagnetic fields. Titan is a specific case where ion gyromotion plays a significant role in the interaction with the ambient plasma flow. We present hybrid simulation results from a medium-strength magnetospheric flow case. The water-group ions are shown to dominate the energy deposition by particles into Titan's ionosphere, while incident protons and pickup ions deposit about a total of a third of the water-group energy. Neutral collisions for the incident ions were taken into account via stopping cross sections. We show that Titan's neutral exosphere reduces the flux and energy deposit of especially lighter flow ions into Titan's atmosphere. Distribution of impacts and energy deposit by incident watergroup ions onto Titan's exobase.

  11. Separation of O/X Polarization Modes on Oblique Ionospheric Soundings

    Science.gov (United States)

    Harris, T. J.; Cervera, M. A.; Pederick, L. H.; Quinn, A. D.

    2017-12-01

    The oblique-incidence sounder (OIS) is a well-established instrument for determining the state of the ionosphere, with several advantages over vertical-incidence sounders (VIS). However, the processing and interpretation of OIS ionograms is more complicated than that of VIS ionograms. Due to the Earth's magnetic field, the ionosphere is birefringent at radio frequencies and a VIS or OIS will typically see two distinct ionospheric returns, known as the O and X modes. The separation of these two modes on a VIS, using a polarimetric receive antenna, is a well-established technique. However, this process is more complicated on an OIS due to a variable separation in the phase difference between the two modes, as measured between the two arms of a polarimetric antenna. Using a polarimetric antenna that can be rotated and tilted, we show that this variation in phase separation within an ionogram is caused by the variation in incidence angle, with some configurations leading to greater variation in phase separation. We then develop an algorithm for separating O and X modes in oblique ionograms that can account for the variation in phase separation, and we demonstrate successful separation even in relatively difficult cases. The variation in phase separation can also be exploited to estimate the incident elevation, a technique which may be useful for other applications of HF radio.

  12. Longitudinal Structure of the 135.6 NM Ionospheric Emission as Modeled by the Cmam-Uam Model System

    Science.gov (United States)

    Martynenko, O. V.; Fomichev, V. I.; Semeniuk, K.; Beagley, S. R.; Ward, W. E.; McConnell, J. C.

    2012-12-01

    The development of whole atmosphere models extending from the surface up to the ionosphere is a new field which is recently attracting more attention of the geophysical community. One of the primary goals of whole atmosphere modeling is to determine how lower atmosphere dynamical variability would propagate into and affect the upper atmosphere and ionosphere. As the first step toward developing a whole atmosphere model in Canada, the extended Canadian Middle Atmosphere Model (CMAM) has been coupled with Murmansk's ionospheric Upper Atmosphere Model (UAM). To find out whether this model system is capable to capture the effect of the upward penetrating waves generated in the lower atmosphere on the ionospheric structure, it was used to reproduce the longitudinal structure of the 135.6 nm ionospheric emission observed by the IMAGE-FUV imager. These observations show four emission peaks in longitude in the equatorial region at 8 pm local time (and hence 4 peaks in electron/ion density), a pattern which cannot be obtained with the ionospheric model alone. Results obtained with the CMAM-UAM model system show good agreement with the observations. Analysis of the model results also suggests that the main mechanism for generating this longitudinal structure of the ionospheric emission is a modification of the ionospheric electric field in the E-region caused by differences in the diurnal evolution of the zonal wind in different longitudinal sectors due to waves penetrating from the lower atmosphere.

  13. Modeling of the global distribution of ionospheric electric fields based on realistic maps of field-aligned currents

    DEFF Research Database (Denmark)

    Lukianova, R.; Christiansen, Freddy

    2006-01-01

    [1] A new approach for modeling the global distribution of ionospheric electric potentials utilizing high-precision maps of FACs derived from measurements by the Orsted and Champ satellites as input to a comprehensive numerical scheme is presented. The boundary conditions provide a correct...... predicts that the summer cross-polar potentials are smaller than the winter potentials. The value of the ratio depends on the combination of season/IMF B-Y sign. The ratio is found to be greater for the combination of B-Y > 0/southern summer and B-Y value is obtained...

  14. A theory of ionospheric dynamo for complete model of terrestrial space at high and medium latitudes

    International Nuclear Information System (INIS)

    Vardanyan, Yu.S.

    1992-01-01

    A multi-layer model of terrestrial cosmic space at high and medium latitudes is considered in the approximation of infinite conductivity of the Earth taking into account the ambipolar diffusion processes in upper layers of ionosphere. 14 refs

  15. Theory, measurements, and models of the upper atmosphere and ionosphere of Saturn

    Science.gov (United States)

    Atreya, S. K.; Donahue, T. M.; Nagy, A. F.; Waite, J. H., Jr.; Mcconnell, J. C.

    1984-01-01

    The structure and composition of the thermosphere, exosphere, and ionosphere of saturn have been determined from observations at optical and radio wavelengths mainly by instruments aboard Voyager spacecraft. Techniques for determining the vertical profiles of temperature and density and the atmospheric vertical mixing in the upper Saturn atmosphere are discussed. Radio occultation measurements and theoretical models of Saturn's ionosphere are reviewed, and attempts to interpret the measurements using the models are discussed. Finally, mechanisms of thermospheric heating are examined.

  16. Modelling the Main Ionospheric Trough Across the Northern Hemisphere

    National Research Council Canada - National Science Library

    Mitchell, Cathryn

    2004-01-01

    This report results from a contract tasking University of Bath as follows: The contractor will investigate disturbances in the Northern Hemisphere ionosphere using a Multi-instrument data analysis (MIDAS) imaging algorithm...

  17. Global Magnetospheric Simulations: coupling with ionospheric and solar wind models

    Science.gov (United States)

    Lapenta, Giovanni; Olshevskyi, Vyacheslav; Amaya, Jorge; Deca, Jan; Markidis, Stefano; Vapirev, Alexander

    2013-04-01

    We present results on the global fully kinetic model of the magnetosphere of the Earth. The simulations are based on the iPic3D code [1] that treats kinetically all plasma species solving implicitly the equations of motion for electrons and ions, coupled with the Maxwell equations. We present results of our simulations and discuss the coupling at the inner boundary near the Earth with models of the ionosphere and at the outer boundary with models of the arriving solar wind. The results are part of the activities of the Swiff FP7 project: www.swiff.eu [1] Stefano Markidis, Giovanni Lapenta, Rizwan-uddin, Multi-scale simulations of plasma with iPIC3D, Mathematics and Computers in Simulation, Volume 80, Issue 7, March 2010, Pages 1509-1519, ISSN 0378-4754, 10.1016/j.matcom.2009.08.038 [2] Giovanni Lapenta, Particle simulations of space weather, Journal of Computational Physics, Volume 231, Issue 3, 1 February 2012, Pages 795-821, ISSN 0021-9991, 10.1016/j.jcp.2011.03.035.

  18. Influence of the ionospheric model on DCB computation and added value of LEO satellites

    Science.gov (United States)

    Wautelet, Gilles; Lestarquit, Laurent; Loyer, Sylvain; Mercier, Flavien; Perosanz, Félix

    2016-04-01

    In order to compute inter-frequency Differential Code Biases (DCBs), the Geometry-Free combination of a GNSS signal pair needs to be corrected from the ionospheric refraction effect. Such information is obtained using either Global Ionospheric Maps (GIMs) or local models. In this work we investigate the influence of GIMs on the final value and precision of DCB solution. The study covers different ionospheric conditions, ranging from very quiet ionospheric background up to a severe ionospheric storm. In a first step, the Slant Total Electron Content (STEC) between GIMs is assessed as a function of receiver latitude, elevation mask and ionospheric conditions. Then, daily DCBs are estimated using these different GIMs, receiver and satellite contributions being separated using a zero-mean constraint. If the precision of satellite DCBs is clearly dependent on ionospheric conditions and of the observing network, the choice of the GIM seems also to have a non negligible impact. At last, an independent estimation of DCBs is performed using Low Earth Orbit (LEO) observations (such as JASON's GPS data). This solution is compared with our ground network solution and with DCBs coming from the International GNSS Service.

  19. An Ionospheric Es Layer Clutter Model and Suppression in HF Surfacewave Radar

    Directory of Open Access Journals (Sweden)

    Yajun Li

    2013-01-01

    Full Text Available This paper based on a fast implemented multiphase screen method using DFT puts forward an ionospheric Es layer clutter model and uses the newly developed dimensionality reduction space-time adaptive processing- (STAP- JDL algorithm to suppress Es layer clutter, which proves the validity of the proposed model. Firstly, the multiphase screen method was analyzed, and a fast algorithm using DFT was proposed. Then, based on the multiphase screen method and thorough simulation, we reached a conclusion of the high-frequency radio wave propagation’s fluctuation characteristics in the ionosphere. According to the results of the analysis, a new Es layer ionospheric clutter model was established and was compared with the measured data and verification was made. Finally, based on the built clutter model, JDL algorithm was applied to the high-frequency surface wave radar ionospheric clutter suppression, using the measured data to verify the validity of the model and algorithm. The simulation results showed that the built model can show the characteristics of the ionospheric Es layer clutter and that the JDL algorithm can suppress ionospheric Es layer clutter quite effectively.

  20. Coordinated polar spacecraft, geosynchronous spacecraft, and ground-based observations of magnetopause processes and their coupling to the ionosphere

    Directory of Open Access Journals (Sweden)

    G. Le

    2004-12-01

    an indirect cause of the observed Pc5 pulsations. During the same interval, two flux transfer events were also observed in the magnetosphere near the oscillating magnetopause. Their ground signatures were identified in the CANOPUS data. The time delays of the FTE signatures from the Polar spacecraft to the ground stations enable us to estimate that the longitudinal extent of the reconnection X-line at the magnetopause was ~43° or ~5.2 RE. The coordinated in-situ and ground-based observations suggest that FTEs are produced by transient reconnection taking place along a single extended X-line at the magnetopause, as suggested in the models by Scholer (1988 and Southwood et al. (1988. The observations from this study suggest that the reconnection occurred in two different forms simultaneously in the same general region at the dayside magnetopause: 1 continuous reconnection with a pulsed reconnection rate, and 2 transient reconnection as flux transfer events.

    Key words. Magnetospheric physics (Magnetopause, cusp and boundary layers; Magnetosphere-ionosphere interactions; MHD waves and instabilities

  1. Coordinated polar spacecraft, geosynchronous spacecraft, and ground-based observations of magnetopause processes and their coupling to the ionosphere

    Directory of Open Access Journals (Sweden)

    G. Le

    2004-12-01

    indirect cause of the observed Pc5 pulsations. During the same interval, two flux transfer events were also observed in the magnetosphere near the oscillating magnetopause. Their ground signatures were identified in the CANOPUS data. The time delays of the FTE signatures from the Polar spacecraft to the ground stations enable us to estimate that the longitudinal extent of the reconnection X-line at the magnetopause was ~43° or ~5.2 RE. The coordinated in-situ and ground-based observations suggest that FTEs are produced by transient reconnection taking place along a single extended X-line at the magnetopause, as suggested in the models by Scholer (1988 and Southwood et al. (1988. The observations from this study suggest that the reconnection occurred in two different forms simultaneously in the same general region at the dayside magnetopause: 1 continuous reconnection with a pulsed reconnection rate, and 2 transient reconnection as flux transfer events. Key words. Magnetospheric physics (Magnetopause, cusp and boundary layers; Magnetosphere-ionosphere interactions; MHD waves and instabilities

  2. ULF Waves in the Ionospheric Alfven Resonator: Modeling of MICA Observations

    Science.gov (United States)

    Streltsov, A. V.; Tulegenov, B.

    2017-12-01

    We present results from a numerical study of physical processes responsible for the generation of small-scale, intense electromagnetic structures in the ultra-low-frequency range frequently observed in the close vicinity of bright discrete auroral arcs. In particular, our research is focused on the role of the ionosphere in generating these structures. A significant body of observations demonstrate that small-scale electromagnetic waves with frequencies below 1 Hz are detected at high latitudes where the large-scale, downward magnetic field-aligned current (FAC) interact with the ionosphere. Some theoretical studies suggest that these waves can be generated by the ionospheric feedback instability (IFI) inside the ionospheric Alfven resonator (IAR). The IAR is the region in the low-altitude magnetosphere bounded by the strong gradient in the Alfven speed at high altitude and the conducting bottom of the ionosphere (ionospheric E-region) at low altitude. To study ULF waves in this region we use a numerical model developed from reduced two fluid MHD equations describing shear Alfven waves in the ionosphere and magnetosphere of the earth. The active ionospheric feedback on structure and amplitude of magnetic FACs that interact with the ionosphere is implemented through the ionospheric boundary conditions that link the parallel current density with the plasma density and the perpendicular electric field in the ionosphere. Our numerical results are compared with the in situ measurements performed by the Magnetosphere-Ionosphere Coupling in the Alfven Resonator (MICA) sounding rocket, launched on February 19, 2012 from Poker Flat Research Range in Alaska to measure fields and particles during a passage through a discreet auroral arc. Parameters of the simulations are chosen to match actual MICA parameters, allowing the comparison in the most precise and rigorous way. Waves generated in the numerical model have frequencies between 0.30 and 0.45 Hz, while MICA measured

  3. Towards better description of solar activity variation in the International Reference Ionosphere topside ion composition model

    Czech Academy of Sciences Publication Activity Database

    Truhlík, Vladimír; Bilitza, D.; Třísková, Ludmila

    2015-01-01

    Roč. 55, č. 8 (2015), s. 2099-2105 ISSN 0273-1177 R&D Projects: GA MŠk(CZ) LH11123 Institutional support: RVO:68378289 Keywords : ion composition * topside ionosphere * solar activity * empirical model * International Reference Ionosphere Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 1.409, year: 2015 http://www.sciencedirect.com/science/article/pii/S027311771400489X

  4. Polar Plasma at Ganymede: Ionospheric outflow and discovery of the plasma sheet

    Science.gov (United States)

    Collinson, G.; Paterson, W.; Dorelli, J.; Glocer, A.; Sarantos, M.; Wilson, R. J.; Bard, C.

    2017-12-01

    On the 27th of June 1996, the NASA Galileo spacecraft made humanities first flyby of Jupiter's largest moon, Ganymede, discovering that it is unique to science in being the only moon known to possess an internally generated magnetic dynamo field. Although Galileo carried a plasma spectrometer, the Plasma Subsystem (PLS), converting its highly complex raw data stream into meaningful plasma moments (density, temperature, velocity) is extremely challenging, and was only ever performed for the second (out of six) Ganymede flybys. Resurrecting the original Galileo PLS data analysis software, we processed the raw PLS data from G01, and for the first time present the properties of plasmas encountered. Dense, cold ions were observed outflowing from the moon's north pole (presumed to be dominated by H+ from the icy surface), with more diffuse, warmer field-aligned outflows in the lobes. Dropouts in plasma density combined with velocity perturbations either side of this suggest that Galileo briefly crossed the cusps onto closed magnetic field lines. PLS observations show that upon entry into the magnetosphere, Galileo crossed through the plasma sheet, observing plasma flows consistent with reconnection-driven convection, highly energized 105 eV ions, and a reversal in the magnetic field. The densities of plasmas flowing upwards from Ganymede's ionosphere were higher on open "lobe" field lines than on closed field lines, suggesting that the ionospheric source of these plasmas may be denser at the poles, there may be additional acceleration mechanisms at play, or the balance of ions were outside the energy range of PLS.

  5. Evaluation of regional ionospheric grid model over China from dense GPS observations

    Directory of Open Access Journals (Sweden)

    Xin Zhao

    2016-09-01

    Full Text Available The current global or regional ionospheric models have been established for monitoring the ionospheric variations. However, the spatial and temporal resolutions are not enough to describe total electron content (TEC variations in small scales for China. In this paper, a regional ionospheric grid model (RIGM with high spatial-temporal resolution (0.5° × 0.5° and 10-min interval in China and surrounding areas is established based on spherical harmonics expansion from dense GPS measurements provided by Crustal Movement Observation Network of China (CMONOC and the International GNSS Service (IGS. The correlation coefficient between the estimated TEC from GPS and the ionosonde measurements is 0.97, and the root mean square (RMS with respect to Center for Orbit Determination in Europe (CODE Global Ionosphere Maps (GIMs is 4.87 TECU. In addition, the impact of different spherical harmonics orders and degrees on TEC estimations are evaluated and the degree/order 6 is better. Moreover, effective ionospheric shell heights from 300 km to 700 km are further assessed and the result indicates that 550 km is the most suitable for regional ionospheric modeling in China at solar maximum.

  6. Global Ionospheric Modelling using Multi-GNSS: BeiDou, Galileo, GLONASS and GPS.

    Science.gov (United States)

    Ren, Xiaodong; Zhang, Xiaohong; Xie, Weiliang; Zhang, Keke; Yuan, Yongqiang; Li, Xingxing

    2016-09-15

    The emergence of China's Beidou, Europe's Galileo and Russia's GLONASS satellites has multiplied the number of ionospheric piercing points (IPP) offered by GPS alone. This provides great opportunities for deriving precise global ionospheric maps (GIMs) with high resolution to improve positioning accuracy and ionospheric monitoring capabilities. In this paper, the GIM is developed based on multi-GNSS (GPS, GLONASS, BeiDou and Galileo) observations in the current multi-constellation condition. The performance and contribution of multi-GNSS for ionospheric modelling are carefully analysed and evaluated. Multi-GNSS observations of over 300 stations from the Multi-GNSS Experiment (MGEX) and International GNSS Service (IGS) networks for two months are processed. The results show that the multi-GNSS GIM products are better than those of GIM products based on GPS-only. Differential code biases (DCB) are by-products of the multi-GNSS ionosphere modelling, the corresponding standard deviations (STDs) are 0.06 ns, 0.10 ns, 0.18 ns and 0.15 ns for GPS, GLONASS, BeiDou and Galileo, respectively in satellite, and the STDs for the receiver are approximately 0.2~0.4 ns. The single-frequency precise point positioning (SF-PPP) results indicate that the ionospheric modelling accuracy of the proposed method based on multi-GNSS observations is better than that of the current dual-system GIM in specific areas.

  7. Ionospheric conductance distribution and MHD wave structure: observation and model

    Directory of Open Access Journals (Sweden)

    F. Budnik

    Full Text Available The ionosphere influences magnetohydrodynamic waves in the magnetosphere by damping because of Joule heating and by varying the wave structure itself. There are different eigenvalues and eigensolutions of the three dimensional toroidal wave equation if the height integrated Pedersen conductivity exceeds a critical value, namely the wave conductance of the magnetosphere. As a result a jump in frequency can be observed in ULF pulsation records. This effect mainly occurs in regions with gradients in the Pedersen conductances, as in the auroral oval or the dawn and dusk areas. A pulsation event recorded by the geostationary GOES-6 satellite is presented. We explain the observed change in frequency as a change in the wave structure while crossing the terminator. Furthermore, selected results of numerical simulations in a dipole magnetosphere with realistic ionospheric conditions are discussed. These are in good agreement with the observational data.

    Key words. Ionosphere · (Ionosphere · magnetosphere interactions · Magnetospheric physics · Magnetosphere · ionosphere interactions · MHD waves and instabilities.

  8. Ionospheric conductance distribution and MHD wave structure: observation and model

    Directory of Open Access Journals (Sweden)

    F. Budnik

    1998-02-01

    Full Text Available The ionosphere influences magnetohydrodynamic waves in the magnetosphere by damping because of Joule heating and by varying the wave structure itself. There are different eigenvalues and eigensolutions of the three dimensional toroidal wave equation if the height integrated Pedersen conductivity exceeds a critical value, namely the wave conductance of the magnetosphere. As a result a jump in frequency can be observed in ULF pulsation records. This effect mainly occurs in regions with gradients in the Pedersen conductances, as in the auroral oval or the dawn and dusk areas. A pulsation event recorded by the geostationary GOES-6 satellite is presented. We explain the observed change in frequency as a change in the wave structure while crossing the terminator. Furthermore, selected results of numerical simulations in a dipole magnetosphere with realistic ionospheric conditions are discussed. These are in good agreement with the observational data.Key words. Ionosphere · (Ionosphere · magnetosphere interactions · Magnetospheric physics · Magnetosphere · ionosphere interactions · MHD waves and instabilities.

  9. Effects of polar field-aligned currents on the distribution of the electric field and current in the middle and low latitudes ionosphere

    International Nuclear Information System (INIS)

    Maekawa, Koichiro

    1978-01-01

    According to the analysis of the magnetic records from the Triad satellite, it has been found that there are two regions of the field-aligned current of magnetospheric origin along the auroral oval; Region 1 in higher latitude and Region 2 in lower latitude. These currents seem to have important effect on the distribution of electric field and current in the ionosphere, in addition to the Sq electric field and current of ionospheric origin. The global current systems generated by the field-aligned current were calculated, using some simplified ionospheric models. The effect of the field-aligned current on the distribution of electric field and current of the ionosphere at middle and low latitudes was investigated. (Yoshimori, M.)

  10. A kinetic model for runaway electrons in the ionosphere

    Directory of Open Access Journals (Sweden)

    G. Garcia

    2006-09-01

    Full Text Available Electrodynamic models and measurements with satellites and incoherent scatter radars predict large field aligned current densities on one side of the auroral arcs. Different authors and different kinds of studies (experimental or modeling agree that the current density can reach up to hundreds of µA/m2. This large current density could be the cause of many phenomena such as tall red rays or triggering of unstable ion acoustic waves. In the present paper, we consider the issue of electrons moving through an ionospheric gas of positive ions and neutrals under the influence of a static electric field. We develop a kinetic model of collisions including electrons/electrons, electrons/ions and electrons/neutrals collisions. We use a Fokker-Planck approach to describe binary collisions between charged particles with a long-range interaction. We present the essential elements of this collision operator: the Langevin equation for electrons/ions and electrons/electrons collisions and the Monte-Carlo and null collision methods for electrons/neutrals collisions. A computational example is given illustrating the approach to equilibrium and the impact of the different terms (electrons/electrons and electrons/ions collisions on the one hand and electrons/neutrals collisions on the other hand. Then, a parallel electric field is applied in a new sample run. In this run, the electrons move in the z direction parallel to the electric field. The first results show that all the electron distribution functions are non-Maxwellian. Furthermore, runaway electrons can carry a significant part of the total current density, up to 20% of the total current density.

  11. A kinetic model for runaway electrons in the ionosphere

    Directory of Open Access Journals (Sweden)

    G. Garcia

    2006-09-01

    Full Text Available Electrodynamic models and measurements with satellites and incoherent scatter radars predict large field aligned current densities on one side of the auroral arcs. Different authors and different kinds of studies (experimental or modeling agree that the current density can reach up to hundreds of µA/m2. This large current density could be the cause of many phenomena such as tall red rays or triggering of unstable ion acoustic waves. In the present paper, we consider the issue of electrons moving through an ionospheric gas of positive ions and neutrals under the influence of a static electric field. We develop a kinetic model of collisions including electrons/electrons, electrons/ions and electrons/neutrals collisions. We use a Fokker-Planck approach to describe binary collisions between charged particles with a long-range interaction. We present the essential elements of this collision operator: the Langevin equation for electrons/ions and electrons/electrons collisions and the Monte-Carlo and null collision methods for electrons/neutrals collisions. A computational example is given illustrating the approach to equilibrium and the impact of the different terms (electrons/electrons and electrons/ions collisions on the one hand and electrons/neutrals collisions on the other hand. Then, a parallel electric field is applied in a new sample run. In this run, the electrons move in the z direction parallel to the electric field. The first results show that all the electron distribution functions are non-Maxwellian. Furthermore, runaway electrons can carry a significant part of the total current density, up to 20% of the total current density.

  12. A Year-Long Comparison of GPS TEC and Global Ionosphere-Thermosphere Models

    Science.gov (United States)

    Perlongo, N. J.; Ridley, A. J.; Cnossen, I.; Wu, C.

    2018-02-01

    The prevalence of GPS total electron content (TEC) observations has provided an opportunity for extensive global ionosphere-thermosphere model validation efforts. This study presents a year-long data-model comparison using the Global Ionosphere-Thermosphere Model (GITM) and the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM). For the entire year of 2010, each model was run and compared to GPS TEC observations. The results were binned according to season, latitude, local time, and magnetic local time. GITM was found to overestimate the TEC everywhere, except on the midlatitude nightside, due to high O/N2 ratios. TIE-GCM produced much less TEC and had lower O/N2 ratios and neutral wind speeds. Seasonal and regional biases in the models are discussed along with ideas for model improvements and further validation efforts.

  13. A multi-satellite study of accelerated ionospheric ion beams above the polar cap

    Directory of Open Access Journals (Sweden)

    R. Maggiolo

    2006-07-01

    Full Text Available This paper presents a study of nearly field-aligned outflowing ion beams observed on the Cluster satellites over the polar cap. Data are taken at geocentric radial distances of the order of 5–9 RE. The distinction is made between ion beams originating from the polar cusp/cleft and beams accelerated almost along the magnetic field line passing by the spacecraft. Polar cusp beams are characterized by nearly field-aligned proton and oxygen ions with an energy ratio EO+ / EH+, of the order of 3 to 4, due to the ion energy repartition inside the source and to the latitudinal extension of the source. Rapid variations in the outflowing ion energy are linked with pulses/modifications of the convection electric field. Cluster data allow one to show that these perturbations of the convection velocity and the associated ion structures propagate at the convection velocity. In contrast, polar cap local ion beams are characterized by field-aligned proton and oxygen ions with similar energies. These beams show the typical inverted V structures usually observed in the auroral zone and are associated with a quasi-static converging electric field indicative of a field-aligned electric field. The field-aligned potential drop fits well the ion energy profile. The simultaneous observation of precipitating electrons and upflowing ions of similar energies at the Cluster orbit indicates that the spacecraft are crossing the mid-altitude part of the acceleration region. In the polar cap, the parallel electric field can thus extend to altitudes higher than 5 Earth radii. A detailed analysis of the distribution functions shows that the ions are heated during their parallel acceleration and that energy is exchanged between H+ and O+. Furthermore, intense electrostatic waves are observed simultaneously. These observations could be due to an ion-ion two-stream instability.

  14. Ionospheric effects of magnetospheric substorms during SUNDIAL and their modelling

    International Nuclear Information System (INIS)

    Goncharova, E.E.; Kishcha, P.V.; Shashun'kina, V.M.; Telegin, V.A.

    1993-01-01

    Ionospheric effects of substorms are considered using the networks of the vertical probing stations during SUNDIAL periods. Calculations of electron concentration distribution and comparison of calculation results with experimental data are conducted on the basis of the developed technique of simulation of large-scale internal gravitational wave effects

  15. Modeling optical and UV polarization of AGNs. IV. Polarization timing

    Science.gov (United States)

    Rojas Lobos, P. A.; Goosmann, R. W.; Marin, F.; Savić, D.

    2018-03-01

    Context. Optical observations cannot resolve the structure of active galactic nuclei (AGN), and a unified model for AGN was inferred mostly from indirect methods, such as spectroscopy and variability studies. Optical reverberation mapping allowed us to constrain the spatial dimension of the broad emission line region and thereby to measure the mass of supermassive black holes. Recently, reverberation was also applied to the polarized signal emerging from different AGN components. In principle, this should allow us to measure the spatial dimensions of the sub-parsec reprocessing media. Aim. We conduct numerical modeling of polarization reverberation and provide theoretical predictions for the polarization time lag induced by different AGN components. The model parameters are adjusted to the observational appearance of the Seyfert 1 galaxy NGC 4151. Methods: We modeled scattering-induced polarization and tested different geometries for the circumnuclear dust component. Our tests included the effects of clumpiness and different dust prescriptions. To further extend the model, we also explored the effects of additional ionized winds stretched along the polar direction, and of an equatorial scattering ring that is responsible for the polarization angle observed in pole-on AGN. The simulations were run using a time-dependent version of the STOKES code. Results: Our modeling confirms the previously found polarization characteristics as a function of the observer`s viewing angle. When the dust adopts a flared-disk geometry, the lags reveal a clear difference between type 1 and type 2 AGN. This distinction is less clear for a torus geometry where the time lag is more sensitive to the geometry and optical depth of the inner surface layers of the funnel. The presence of a scattering equatorial ring and ionized outflows increased the recorded polarization time lags, and the polar outflows smooths out dependence on viewing angle, especially for the higher optical depth of the

  16. A multi-satellite study of accelerated ionospheric ion beams above the polar cap

    Directory of Open Access Journals (Sweden)

    R. Maggiolo

    2006-07-01

    Full Text Available This paper presents a study of nearly field-aligned outflowing ion beams observed on the Cluster satellites over the polar cap. Data are taken at geocentric radial distances of the order of 5–9 RE. The distinction is made between ion beams originating from the polar cusp/cleft and beams accelerated almost along the magnetic field line passing by the spacecraft. Polar cusp beams are characterized by nearly field-aligned proton and oxygen ions with an energy ratio EO+ / EH+, of the order of 3 to 4, due to the ion energy repartition inside the source and to the latitudinal extension of the source. Rapid variations in the outflowing ion energy are linked with pulses/modifications of the convection electric field. Cluster data allow one to show that these perturbations of the convection velocity and the associated ion structures propagate at the convection velocity.

    In contrast, polar cap local ion beams are characterized by field-aligned proton and oxygen ions with similar energies. These beams show the typical inverted V structures usually observed in the auroral zone and are associated with a quasi-static converging electric field indicative of a field-aligned electric field. The field-aligned potential drop fits well the ion energy profile. The simultaneous observation of precipitating electrons and upflowing ions of similar energies at the Cluster orbit indicates that the spacecraft are crossing the mid-altitude part of the acceleration region. In the polar cap, the parallel electric field can thus extend to altitudes higher than 5 Earth radii. A detailed analysis of the distribution functions shows that the ions are heated during their parallel acceleration and that energy is exchanged between H+ and O+. Furthermore, intense electrostatic waves are observed simultaneously. These observations could be due to an ion-ion two-stream instability.

  17. Update of the Polar SWIFT model for polar stratospheric ozone loss (Polar SWIFT version 2)

    Science.gov (United States)

    Wohltmann, Ingo; Lehmann, Ralph; Rex, Markus

    2017-07-01

    The Polar SWIFT model is a fast scheme for calculating the chemistry of stratospheric ozone depletion in polar winter. It is intended for use in global climate models (GCMs) and Earth system models (ESMs) to enable the simulation of mutual interactions between the ozone layer and climate. To date, climate models often use prescribed ozone fields, since a full stratospheric chemistry scheme is computationally very expensive. Polar SWIFT is based on a set of coupled differential equations, which simulate the polar vortex-averaged mixing ratios of the key species involved in polar ozone depletion on a given vertical level. These species are O3, chemically active chlorine (ClOx), HCl, ClONO2 and HNO3. The only external input parameters that drive the model are the fraction of the polar vortex in sunlight and the fraction of the polar vortex below the temperatures necessary for the formation of polar stratospheric clouds. Here, we present an update of the Polar SWIFT model introducing several improvements over the original model formulation. In particular, the model is now trained on vortex-averaged reaction rates of the ATLAS Chemistry and Transport Model, which enables a detailed look at individual processes and an independent validation of the different parameterizations contained in the differential equations. The training of the original Polar SWIFT model was based on fitting complete model runs to satellite observations and did not allow for this. A revised formulation of the system of differential equations is developed, which closely fits vortex-averaged reaction rates from ATLAS that represent the main chemical processes influencing ozone. In addition, a parameterization for the HNO3 change by denitrification is included. The rates of change of the concentrations of the chemical species of the Polar SWIFT model are purely chemical rates of change in the new version, whereas in the original Polar SWIFT model, they included a transport effect caused by the

  18. An Ionospheric Index Model based on Linear Regression and Neural Network Approaches

    Science.gov (United States)

    Tshisaphungo, Mpho; McKinnell, Lee-Anne; Bosco Habarulema, John

    2017-04-01

    The ionosphere is well known to reflect radio wave signals in the high frequency (HF) band due to the present of electron and ions within the region. To optimise the use of long distance HF communications, it is important to understand the drivers of ionospheric storms and accurately predict the propagation conditions especially during disturbed days. This paper presents the development of an ionospheric storm-time index over the South African region for the application of HF communication users. The model will result into a valuable tool to measure the complex ionospheric behaviour in an operational space weather monitoring and forecasting environment. The development of an ionospheric storm-time index is based on a single ionosonde station data over Grahamstown (33.3°S,26.5°E), South Africa. Critical frequency of the F2 layer (foF2) measurements for a period 1996-2014 were considered for this study. The model was developed based on linear regression and neural network approaches. In this talk validation results for low, medium and high solar activity periods will be discussed to demonstrate model's performance.

  19. Analytical model of the statistical properties of contrast of large-scale ionospheric inhomogeneities.

    Science.gov (United States)

    Vsekhsvyatskaya, I. S.; Evstratova, E. A.; Kalinin, Yu. K.; Romanchuk, A. A.

    1989-08-01

    A new analytical model is proposed for the distribution of variations of the relative electron-density contrast of large-scale ionospheric inhomogeneities. The model is characterized by other-than-zero skewness and kurtosis. It is shown that the model is applicable in the interval of horizontal dimensions of inhomogeneities from hundreds to thousands of kilometers.

  20. CEDAR Electrodynamics Thermosphere Ionosphere (ETI) Challenge for Systematic Assessment of Ionosphere/Thermosphere Models: NmF2, hmF2, and Vertical Drift Using Ground-Based Observations

    Science.gov (United States)

    Shim, J. S.; Kuznetsova, M.; Rastatter, L.; Hesse, M.; Bilitza, D.; Butala, M.; Codrescu, M.; Emery, B.; Foster, B.; Fuller-Rowell, T.; hide

    2011-01-01

    Objective quantification of model performance based on metrics helps us evaluate the current state of space physics modeling capability, address differences among various modeling approaches, and track model improvements over time. The Coupling, Energetics, and Dynamics of Atmospheric Regions (CEDAR) Electrodynamics Thermosphere Ionosphere (ETI) Challenge was initiated in 2009 to assess accuracy of various ionosphere/thermosphere models in reproducing ionosphere and thermosphere parameters. A total of nine events and five physical parameters were selected to compare between model outputs and observations. The nine events included two strong and one moderate geomagnetic storm events from GEM Challenge events and three moderate storms and three quiet periods from the first half of the International Polar Year (IPY) campaign, which lasted for 2 years, from March 2007 to March 2009. The five physical parameters selected were NmF2 and hmF2 from ISRs and LEO satellites such as CHAMP and COSMIC, vertical drifts at Jicamarca, and electron and neutral densities along the track of the CHAMP satellite. For this study, four different metrics and up to 10 models were used. In this paper, we focus on preliminary results of the study using ground-based measurements, which include NmF2 and hmF2 from Incoherent Scatter Radars (ISRs), and vertical drifts at Jicamarca. The results show that the model performance strongly depends on the type of metrics used, and thus no model is ranked top for all used metrics. The analysis further indicates that performance of the model also varies with latitude and geomagnetic activity level.

  1. The local ionospheric modeling by integration ground GPS observations and satellite altimetry data

    Directory of Open Access Journals (Sweden)

    Mohammad Ali Sharifi

    2017-01-01

    Full Text Available The free electrons in the ionosphere have a strong impact on the propagation of radio waves. When the signals pass through the ionosphere, both their group and phase velocity are disturbed. Several space geodetic techniques such as satellite altimetry, low Earth orbit (LEO satellite and very long baseline interferometry (VLBI can be used to model the total electron content. At present, the classical input data for development of ionospheric models are based on dual-frequency GPS observations, However, a major problem with this observation type is the nonuniform distribution of the terrestrial GPS reference stations with large gaps notably over the sea surface and ocean where only some single stations are located on islands, leading to lower the precision of the model over these areas. In these regions the dual-frequency satellite altimeters provide precise information about the parameters of the ionosphere. Combination of GPS and satellite altimetry observations allows making best use of the advantages of their different spatial and temporal distributions. In this study, the local ionosphere modeling was done by the combination of space geodetic observations using spherical Slepian function. The combination of the data from ground GPS observations over the western part of the USA and the altimetry mission Jason-2 was performed on the normal equation level in the least-square procedure and a least-square variance component estimation (LS-VCE was applied to take into account the different accuracy levels of the observations. The integrated ionosphere model is more accurate and more reliable than the results derived from the ground GPS observations over the oceans.

  2. LION: A dynamic computer model for the low-latitude ionosphere

    Directory of Open Access Journals (Sweden)

    J. A. Bittencourt

    2007-11-01

    Full Text Available A realistic fully time-dependent computer model, denominated LION (Low-latitude Ionospheric model, that simulates the dynamic behavior of the low-latitude ionosphere is presented. The time evolution and spatial distribution of the ionospheric particle densities and velocities are computed by numerically solving the time-dependent, coupled, nonlinear system of continuity and momentum equations for the ions O+, O2+, NO+, N2+ and N+, taking into account photoionization of the atmospheric species by the solar extreme ultraviolet radiation, chemical and ionic production and loss reactions, and plasma transport processes, including the ionospheric effects of thermospheric neutral winds, plasma diffusion and electromagnetic E×B plasma drifts. The Earth's magnetic field is represented by a tilted centered magnetic dipole. This set of coupled nonlinear equations is solved along a given magnetic field line in a Lagrangian frame of reference moving vertically, in the magnetic meridian plane, with the electromagnetic E×B plasma drift velocity. The spatial and time distribution of the thermospheric neutral wind velocities and the pattern of the electromagnetic drifts are taken as known quantities, given through specified analytical or empirical models. The model simulation results are presented in the form of computer-generated color maps and reproduce the typical ionization distribution and time evolution normally observed in the low-latitude ionosphere, including details of the equatorial Appleton anomaly dynamics. The specific effects on the ionosphere due to changes in the thermospheric neutral winds and the electromagnetic plasma drifts can be investigated using different wind and drift models, including the important longitudinal effects associated with magnetic declination dependence and latitudinal separation between geographic and geomagnetic equators. The model runs in a normal personal computer (PC and generates color maps illustrating the

  3. TEC ingestion into NeQuick 2 to model the East African equatorial ionosphere

    Science.gov (United States)

    Nigussie, M.; Radicella, S. M.; Damtie, B.; Nava, B.; Yizengaw, E.; Ciraolo, L.

    2012-10-01

    NeQuick 2 ionospheric empirical model depends on global ionospheric coefficients that are estimated from unevenly distributed ionosonde measurements. In regions, like Africa, where very few observational data were available until recently, the model estimated the ionospheric peak parameters by interpolation. When one wants to employ the model to specify the ionosphere where very few data have been used for model development, the performances of the model need careful validation. This study investigates the performances of NeQuick 2 in the East African region by assisting the model with measurements from a single Global Positioning System (GPS) receiver, which has been deployed recently. This can be done by first calculating an effective ionization level that drives NeQuick 2 to compute slant total electron content (sTEC) which fits, in the least square sense, with the measurements taken from a single GPS receiver. We then quantify the performances of NeQuick 2 in reproducing the measured TEC by running the model at four other locations, where GPS stations are available, using the same effective ionization level that we calculated from a single GPS station as a driver of the model. Finally, the performances of the model before and after data ingestion have been investigated by comparing the model results with the experimental sTEC and vertical TEC (vTEC) obtained from the four test stations. Three months data during low solar activity conditions have been used for this study. We have shown that the capability of NeQuick 2, in describing the East African region of the ionosphere, can be improved substantially by data ingestion. We found that the model after ingestion reproduces the experimental TEC better as far as about 620 km away from the reference station than that before adaptation. The statistical comparisons of the performances of the model in reproducing sTEC before and after ingestion are also discussed in this study.

  4. The International Reference Ionosphere 2012 – a model of international collaboration☆

    Directory of Open Access Journals (Sweden)

    Bilitza Dieter

    2014-02-01

    Full Text Available The International Reference Ionosphere (IRI project was established jointly by the Committee on Space Research (COSPAR and the International Union of Radio Science (URSI in the late sixties with the goal to develop an international standard for the specification of plasma parameters in the Earth’s ionosphere. COSPAR needed such a specification for the evaluation of environmental effects on spacecraft and experiments in space, and URSI for radiowave propagation studies and applications. At the request of COSPAR and URSI, IRI was developed as a data-based model to avoid the uncertainty of theory-based models which are only as good as the evolving theoretical understanding. Being based on most of the available and reliable observations of the ionospheric plasma from the ground and from space, IRI describes monthly averages of electron density, electron temperature, ion temperature, ion composition, and several additional parameters in the altitude range from 60 km to 2000 km. A working group of about 50 international ionospheric experts is in charge of developing and improving the IRI model. Over time as new data became available and new modeling techniques emerged, steadily improved editions of the IRI model have been published. This paper gives a brief history of the IRI project and describes the latest version of the model, IRI-2012. It also briefly discusses efforts to develop a real-time IRI model. The IRI homepage is at http://IRImodel.org.

  5. Analysis of the positive ionospheric response to a moderate geomagnetic storm using a global numerical model

    Directory of Open Access Journals (Sweden)

    A. A. Namgaladze

    2000-04-01

    Full Text Available Current theories of F-layer storms are discussed using numerical simulations with the Upper Atmosphere Model, a global self-consistent, time dependent numerical model of the thermosphere-ionosphere-plasmasphere-magnetosphere system including electrodynamical coupling effects. A case study of a moderate geomagnetic storm at low solar activity during the northern winter solstice exemplifies the complex storm phenomena. The study focuses on positive ionospheric storm effects in relation to thermospheric disturbances in general and thermospheric composition changes in particular. It investigates the dynamical effects of both neutral meridional winds and electric fields caused by the disturbance dynamo effect. The penetration of short-time electric fields of magnetospheric origin during storm intensification phases is shown for the first time in this model study. Comparisons of the calculated thermospheric composition changes with satellite observations of AE-C and ESRO-4 during storm time show a good agreement. The empirical MSISE90 model, however, is less consistent with the simulations. It does not show the equatorward propagation of the disturbances and predicts that they have a gentler latitudinal gradient. Both theoretical and experimental data reveal that although the ratio of [O]/[N2] at high latitudes decreases significantly during the magnetic storm compared with the quiet time level, at mid to low latitudes it does not increase (at fixed altitudes above the quiet reference level. Meanwhile, the ionospheric storm is positive there. We conclude that the positive phase of the ionospheric storm is mainly due to uplifting of ionospheric F2-region plasma at mid latitudes and its equatorward movement at low latitudes along geomagnetic field lines caused by large-scale neutral wind circulation and the passage of travelling atmospheric disturbances (TADs. The calculated zonal electric field disturbances also help to create the positive ionospheric

  6. Analysis of the positive ionospheric response to a moderate geomagnetic storm using a global numerical model

    Directory of Open Access Journals (Sweden)

    A. A. Namgaladze

    Full Text Available Current theories of F-layer storms are discussed using numerical simulations with the Upper Atmosphere Model, a global self-consistent, time dependent numerical model of the thermosphere-ionosphere-plasmasphere-magnetosphere system including electrodynamical coupling effects. A case study of a moderate geomagnetic storm at low solar activity during the northern winter solstice exemplifies the complex storm phenomena. The study focuses on positive ionospheric storm effects in relation to thermospheric disturbances in general and thermospheric composition changes in particular. It investigates the dynamical effects of both neutral meridional winds and electric fields caused by the disturbance dynamo effect. The penetration of short-time electric fields of magnetospheric origin during storm intensification phases is shown for the first time in this model study. Comparisons of the calculated thermospheric composition changes with satellite observations of AE-C and ESRO-4 during storm time show a good agreement. The empirical MSISE90 model, however, is less consistent with the simulations. It does not show the equatorward propagation of the disturbances and predicts that they have a gentler latitudinal gradient. Both theoretical and experimental data reveal that although the ratio of [O]/[N2] at high latitudes decreases significantly during the magnetic storm compared with the quiet time level, at mid to low latitudes it does not increase (at fixed altitudes above the quiet reference level. Meanwhile, the ionospheric storm is positive there. We conclude that the positive phase of the ionospheric storm is mainly due to uplifting of ionospheric F2-region plasma at mid latitudes and its equatorward movement at low latitudes along geomagnetic field lines caused by large-scale neutral wind circulation and the passage of travelling atmospheric disturbances (TADs. The calculated zonal electric field disturbances also help

  7. An electrodynamic model of the solar wind interaction with the ionospheres of Mars and Venus

    International Nuclear Information System (INIS)

    Cloutier, P.A.; Daniell, R.E. Jr.

    1979-01-01

    the electrodynamic model for the solar wind interaction with non-magnetic planets (Cloutier and Daniell, Planet. Space Sci. 21, 463, 1973; Daniell and Cloutier, Planet. Space Sci. 25, 621, 1977) is modified to include the effects of non-ohmic currents in the upper ionosphere. The model is then used to calculate convection patterns induced by the solar wind in the ionospheres of Mars and Venus. For Mars the observations of the neutral mass spectrometer or Vikings 1 and 2 provided the neutral atmosphere. Model calculations reproduced the retarding potential analyzer data and indicate that the ionosphere above about 200 km is probably controlled by convection rather than chemistry or diffusion. For Venus a model atmosphere based on Dickenson and Ridley, J. Atmos. Sci. 32, 1219 (1975) and Mayr et al., J. Geophys. Res. 83, 4411 (1978) was used. The resulting model calculations were compared to radio occultation data from Mariners 5 and 10 and Venera 9 which represent extremes in the variability of the upper Cytherean ionosphere. The model calculations are shown to fall within this variation. These results represent the state of the theory immediately prior to the Pioneer-Venus encounter. (author)

  8. Electrodynamic model of atmospheric and ionospheric processes on the eve of an earthquake

    Science.gov (United States)

    Sorokin, V. M.; Ruzhin, Yu. Ya.

    2015-09-01

    Electric field generation and its accompanying phenomena in the atmosphere-ionosphere system have been intensively studied in recent years. This paper considers the results of these studies, which have served as the physical basis for the model of lithosphere-ionosphere coupling. According to our model, the intensive processes in the lower atmosphere and lithosphere have an electrodynamic effect on the ionospheric plasma. The model was used to conduct theoretical studies of plasma and electromagnetic effects accompanying the generation of conduction current in the global circuit. It has been shown that the electrodynamic model of the influence of seismic and meteorological processes on cosmic plasma can serve as a physical basis for a satellite system to monitor earthquake precursors and the catastrophic phase of typhoon development. The model makes it possible to couple the satellite data of electromagnetic and plasma measurements with electrophysical and meteorological characteristics of the lower atmosphere at the stage of earthquake preparation and typhoon initiation. The model suggests that the numerous effects in the cosmic plasma have a single source: a change in the conduction current flowing in the atmosphere-ionosphere circuit.

  9. Model modifications in Schumann resonance intensity caused by a localized ionosphere disturbance over the earthquake epicenter

    Directory of Open Access Journals (Sweden)

    A. P. Nickolaenko

    2006-03-01

    Full Text Available This paper is a further extension of our latest observations and modeling by Hayakawa et al. (2005a, in which we discovered the anomalous behavior of Schumann resonance observed in Japan, in possible association with the Chi-chi earthquake in Taiwan. Schumann resonance intensity changes associated with a localized decrease in the lower ionospheric height over the earthquake epicenter are modeled. The knee model of the vertical conductivity profile of the ionosphere describes the regular Earth-ionosphere cavity, and the modified knee model is introduced for the disturbance. The localized ionosphere modification is of a Gaussian radial dependence; it has a 1-Mm radius, and the decrease reaches 20 km in the lower ionosphere height over the epicenter of the earthquake (Taiwan. The diffraction problem in the Earth-ionosphere cavity with a localized disturbance is resolved by using the Stratton-Chu integral equation. This solution is constructed for the case of natural resonance oscillations driven by independent random sources distributed worldwide. The data of the Optical Transient Detector (OTD are used to introduce the source distribution. A pronounced increase in the intensity of the Schumann resonance is obtained around the fourth mode frequency (up to 20% when thunderstorms are concentrated in Central America. The worldwide distribution of lightning strokes blurs and slightly reduces the effect (15% increase in intensity for the observer in Japan and the localized nonuniformity positioned over Taiwan. A clear qualitative similarity is obtained in relation to the experimental data, indicating that records collected in Japan may be explained by the impact of a localized decrease in the lower ionosphere over the epicenter of the earthquake. It is admitted that the assumed conductivity decrease could only be caused by a severe change in the ionization in the middle atmosphere. It is not in the scope of this paper to discuss the possible mechanism

  10. Asymmetric distribution of the ionospheric electric potential in the opposite hemispheres as inferred from the SuperDARN observations and FAC-based convection model

    DEFF Research Database (Denmark)

    Lukianova, R.; Hanuise, C.; Christiansen, Freddy

    2008-01-01

    We compare the SuperDARN convection patterns with the predictions of a new numerical model of the global distribution of ionospheric electric potentials. The model utilizes high-precision statistical maps of field-aligned currents (FAC) derived from measurements made by polar-orbiting low...... governed by the IMF clock angle and solar zenith angle. We calculate the convection patterns for specific cases caused by the sign of By and season and demonstrate the capability of the FAC-based model reproduce the radar observations. The simulation confirms that the solar zenith angle should be linked...

  11. Ionospheric Alfvén resonator and aurora: Modeling of MICA observations

    Science.gov (United States)

    Tulegenov, B.; Streltsov, A. V.

    2017-07-01

    We present results from a numerical study of small-scale, intense magnetic field-aligned currents observed in the vicinity of the discrete auroral arc by the Magnetosphere-Ionosphere Coupling in the Alfvén Resonator (MICA) sounding rocket launched from Poker Flat, Alaska, on 19 February 2012. The goal of the MICA project was to investigate the hypothesis that such currents can be produced inside the ionospheric Alfvén resonator by the ionospheric feedback instability (IFI) driven by the system of large-scale magnetic field-aligned currents interacting with the ionosphere. The trajectory of the MICA rocket crossed two discrete auroral arcs and detected packages of intense, small-scale currents at the edges of these arcs, in the most favorable location for the development of the ionospheric feedback instability, predicted by the IFI theory. Simulations of the reduced MHD model derived in the dipole magnetic field geometry with realistic background parameters confirm that IFI indeed generates small-scale ULF waves inside the ionospheric Alfvén resonator with frequency, scale size, and amplitude showing a good, quantitative agreement with the observations. The comparison between numerical results and observations was performed by "flying" a virtual MICA rocket through the computational domain, and this comparison shows that, for example, the waves generated in the numerical model have frequencies in the range from 0.30 to 0.45 Hz, and the waves detected by the MICA rocket have frequencies in the range from 0.18 to 0.50 Hz.

  12. Ionospheric detection of tsunami earthquakes: observation, modeling and ideas for future early warning

    Science.gov (United States)

    Occhipinti, G.; Manta, F.; Rolland, L.; Watada, S.; Makela, J. J.; Hill, E.; Astafieva, E.; Lognonne, P. H.

    2017-12-01

    Detection of ionospheric anomalies following the Sumatra and Tohoku earthquakes (e.g., Occhipinti 2015) demonstrated that ionosphere is sensitive to earthquake and tsunami propagation: ground and oceanic vertical displacement induces acoustic-gravity waves propagating within the neutral atmosphere and detectable in the ionosphere. Observations supported by modelling proved that ionospheric anomalies related to tsunamis are deterministic and reproducible by numerical modeling via the ocean/neutral-atmosphere/ionosphere coupling mechanism (Occhipinti et al., 2008). To prove that the tsunami signature in the ionosphere is routinely detected we show here perturbations of total electron content (TEC) measured by GPS and following tsunamigenic earthquakes from 2004 to 2011 (Rolland et al. 2010, Occhipinti et al., 2013), nominally, Sumatra (26 December, 2004 and 12 September, 2007), Chile (14 November, 2007), Samoa (29 September, 2009) and the recent Tohoku-Oki (11 Mars, 2011). Based on the observations close to the epicenter, mainly performed by GPS networks located in Sumatra, Chile and Japan, we highlight the TEC perturbation observed within the first 8 min after the seismic rupture. This perturbation contains information about the ground displacement, as well as the consequent sea surface displacement resulting in the tsunami. In addition to GNSS-TEC observations close to the epicenter, new exciting measurements in the far-field were performed by airglow measurement in Hawaii show the propagation of the internal gravity waves induced by the Tohoku tsunami (Occhipinti et al., 2011). This revolutionary imaging technique is today supported by two new observations of moderate tsunamis: Queen Charlotte (M: 7.7, 27 October, 2013) and Chile (M: 8.2, 16 September 2015). We finally detail here our recent work (Manta et al., 2017) on the case of tsunami alert failure following the Mw7.8 Mentawai event (25 October, 2010), and its twin tsunami alert response following the Mw7

  13. Challenges Handling Magnetospheric and Ionospheric Signals in Internal Geomagnetic Field Modelling

    DEFF Research Database (Denmark)

    Finlay, Chris; Lesur, V.; Thébault, E.

    2017-01-01

    systems in the ionosphere and magnetosphere. In order to fully exploit magnetic data to probe the physical properties and dynamics of the Earth’s interior, field models with suitable treatments of external sources, and their associated induced signals, are essential. Here we review the methods presently...

  14. Assimilative Modeling of Ionospheric Disturbances with FORMOSAT-3/COSMIC and Ground-Based GPS Measurements

    Directory of Open Access Journals (Sweden)

    Xiaoqing Pi

    2009-01-01

    Full Text Available The four-dimensional Global Assimilative Ionospheric Model (GAIM is applied to a study of ionospheric disturbances. The investigation is focused on disturbance features, particularly in the altitude and latitude dimensions, at low latitudes during a geomagnetic storm on 7 August 2006, under solar minimum conditions. The modeling of storm-time ionospheric state (electron density is conducted by assimilating an unprecedented volume of line-of-sight TEC data collected by the Global Positioning System (GPS occultation receivers on board six FORMOSAT-3/COSMIC satellites and geodetic-quality GPS receivers at two hundred globally-distributed ground tracking stations.With a band-limited Kalman filter technique to update the ionospheric state, the assimilative modeling reveals a pronounced enhancement in the equatorial anomaly in the East Asia sector during dusk and evening hours. The disturbance characteristics, obtained by comparing with the quiet conditions prior to the storm also modeled in this study through data assimilation, include lifted F layer and reduced electron density in the equatorial region, enhanced density at the magnetically conjugate anomaly latitudes, and tilted feature of density increase towards higher altitudes at lower latitudes. The characteristics are attributed to the enhanced plasma fountain effect driven by an enhanced eastward zonal electric field. These results enable us to distinguish the storm-time electric field perturbations clearly from other sources during the storm. The possible origins of electric field perturbations are also discussed, including penetration of the magnetospheric electric field and wind dynamo disturbances.

  15. Methodology and consistency of slant and vertical assessments for ionospheric electron content models

    Science.gov (United States)

    Hernández-Pajares, Manuel; Roma-Dollase, David; Krankowski, Andrzej; García-Rigo, Alberto; Orús-Pérez, Raül

    2017-12-01

    A summary of the main concepts on global ionospheric map(s) [hereinafter GIM(s)] of vertical total electron content (VTEC), with special emphasis on their assessment, is presented in this paper. It is based on the experience accumulated during almost two decades of collaborative work in the context of the international global navigation satellite systems (GNSS) service (IGS) ionosphere working group. A representative comparison of the two main assessments of ionospheric electron content models (VTEC-altimeter and difference of Slant TEC, based on independent global positioning system data GPS, dSTEC-GPS) is performed. It is based on 26 GPS receivers worldwide distributed and mostly placed on islands, from the last quarter of 2010 to the end of 2016. The consistency between dSTEC-GPS and VTEC-altimeter assessments for one of the most accurate IGS GIMs (the tomographic-kriging GIM `UQRG' computed by UPC) is shown. Typical error RMS values of 2 TECU for VTEC-altimeter and 0.5 TECU for dSTEC-GPS assessments are found. And, as expected by following a simple random model, there is a significant correlation between both RMS and specially relative errors, mainly evident when large enough number of observations per pass is considered. The authors expect that this manuscript will be useful for new analysis contributor centres and in general for the scientific and technical community interested in simple and truly external ways of validating electron content models of the ionosphere.

  16. Quantitative calculations of helium ion escape fluxes from the polar ionospheres

    International Nuclear Information System (INIS)

    Raitt, W.J.; Schunk, R.W.; Banks, P.M.

    1978-01-01

    Recent experimental measurements of He + outward fluxes have been obtained for winter and summer hemispheres. The observed fluxes indicate an average He + escape flux of 2 x 10 7 cm -2 s -1 in the winter hemisphere and a factor of 10-20 lower in the summer hemisphere. Earlier theoretical calculations had yielded winter fluxes a factor of 4 lower than the measured values and summer fluxes a further factor of 20 below the winter fluxes. We have attempted to reduce this discrepancy between our earlier theoretical model and the experimental observations by improving our theoretical model in the following ways. The helium photoionization cross sections used are accurate to 10%, the latest solar EUV fluxes measured by the Atmosphere Explorer satellites have been incorporated, and the most recent MSIS model of the neutral atmosphere is contained in the model. A range of conditions covering solar cycle, seasonal, and geomagnetic conditions were studied. The results show a maximum He + escape flux of 1.4 x 10 7 cm -2 s -1 for solar maximum, winter, low magnetic activity conditions, which is within the scatter of the measured fluxes. The computed summer He + escape flux is a factor of 20 lower than the winter value, a result which is in reasonable agreement with the summer experimental observations. Possible reasons for the slight discrepancy between theory and experiment in summer are discussed

  17. Nonlinear model of short-scale electrodynamics in the auroral ionosphere

    Directory of Open Access Journals (Sweden)

    J.-M. A. Noël

    2000-09-01

    Full Text Available The optical detection of auroral subarcs a few tens of m wide as well as the direct observation of shears several m/s per m over km to sub km scales by rocket instrumentation both indicate that violent and highly localized electrodynamics can occur at times in the auroral ionosphere over scales 100 m or less in width. These observations as well as the detection of unstable ion-acoustic waves observed by incoherent radars along the geomagnetic field lines has motivated us to develop a detailed time-dependent two-dimensional model of short-scale auroral electrodynamics that uses current continuity, Ohm's law, and 8-moment transport equations for the ions and electrons in the presence of large ambient electric fields to describe wide auroral arcs with sharp edges in response to sharp cut-offs in precipitation (even though it may be possible to describe thin arcs and ultra-thin arcs with our model, we have left such a study for future work. We present the essential elements of this new model and illustrate the model's usefulness with a sample run for which the ambient electric field is 100 mV/m away from the arc and for which electron precipitation cuts off over a region 100 m wide. The sample run demonstrates that parallel current densities of the order of several hundred µA m-2 can be triggered in these circumstances, together with shears several m/s per m in magnitude and parallel electric fields of the order of 0.1 mV/m around 130 km altitude. It also illustrates that the local ionospheric properties like densities, temperature and composition can strongly be affected by the violent localized electrodynamics and vice-versa.Key words: Ionosphere (auroral ionosphere, electric fields and currents, ionosphere-magnetosphere interactions

  18. Nonlinear model of short-scale electrodynamics in the auroral ionosphere

    Directory of Open Access Journals (Sweden)

    J.-M. A. Noël

    Full Text Available The optical detection of auroral subarcs a few tens of m wide as well as the direct observation of shears several m/s per m over km to sub km scales by rocket instrumentation both indicate that violent and highly localized electrodynamics can occur at times in the auroral ionosphere over scales 100 m or less in width. These observations as well as the detection of unstable ion-acoustic waves observed by incoherent radars along the geomagnetic field lines has motivated us to develop a detailed time-dependent two-dimensional model of short-scale auroral electrodynamics that uses current continuity, Ohm's law, and 8-moment transport equations for the ions and electrons in the presence of large ambient electric fields to describe wide auroral arcs with sharp edges in response to sharp cut-offs in precipitation (even though it may be possible to describe thin arcs and ultra-thin arcs with our model, we have left such a study for future work. We present the essential elements of this new model and illustrate the model's usefulness with a sample run for which the ambient electric field is 100 mV/m away from the arc and for which electron precipitation cuts off over a region 100 m wide. The sample run demonstrates that parallel current densities of the order of several hundred µA m-2 can be triggered in these circumstances, together with shears several m/s per m in magnitude and parallel electric fields of the order of 0.1 mV/m around 130 km altitude. It also illustrates that the local ionospheric properties like densities, temperature and composition can strongly be affected by the violent localized electrodynamics and vice-versa.

    Key words: Ionosphere (auroral ionosphere, electric fields and currents, ionosphere-magnetosphere interactions

  19. LF/MF Propagation Modeling for D-Region Ionospheric Remote Sensing

    Science.gov (United States)

    Higginson-Rollins, M. A.; Cohen, M.

    2017-12-01

    The D-region of the ionosphere is highly inaccessible because it is too high for continuous in-situ measurement techniques and too low for satellite measurements. Very-Low Frequency (VLF) signals have been developed and used as a diagnostic tool for this region of the ionosphere and are favorable because of the low ionospheric attenuation rates, allowing global propagation - but this also creates an ill-posed multi-mode propagation problem. As an alternative, Low-Frequency (LF) and Medium-Frequency (MF) signals could be used as a diagnostic tool of the D-region. These higher frequencies have a higher attenuation rate, and thus only a few modes propagate in the Earth-ionosphere waveguide, creating a much simpler problem to analyze. The United States Coast Guard (USCG) operates a national network of radio transmitters that serve as an enhancement to the Global Positioning System (GPS). This network is termed Differential Global Positioning System (DGPS) and uses fixed reference stations as a method of determining the error in received GPS satellite signals and transmits the correction value using low frequency and medium frequency radio signals between 285 kHz and 385 kHz. Using sensitive receivers, we can detect this signal many hundreds of km away. We present modeling of the propagation of these transmitters' signals for use as a diagnostic tool for characterizing the D-region. The Finite-Difference Time-Domain (FDTD) method is implemented to model the groundwave radiated by the DGPS beacons and account for environmental effects, such as changing soil conductivities and terrain. A full wave numerical solver is used to model the skywave component of the propagating signal and specifically to ascertain the reflection coefficients for various ionospheric conditions. Preliminary results are shown and discussed, and comparisons with collected data are presented.

  20. Advanced algorithms for ionosphere modelling in GNSS applications within AUDITOR project

    Science.gov (United States)

    Goss, Andreas; Erdogan, Eren; Schmidt, Michael; Garcia-Rigo, Alberto; Hernandez-Pajares, Manuel; Lyu, Haixia; Nohutcu, Metin

    2017-04-01

    The H2020 project AUDITOR of the European Union started on January 1st 2016, with the participation of several European institutions and universities. The goal of the project is the implementation of a novel precise positioning technique, based on augmentation data in a customized GNSS receiver. Therefore more sophisticated ionospheric models have to be developed and implemented to increase the accuracy in real-time at the user side. Since the service should be available for the public, we use public data from GNSS networks (e.g. IGS, EUREF). The contributions of DGFI-TUM and UPC are focusing on the development of high accuracy GNSS algorithms to provide enhanced ionospheric corrections. This includes two major issues: 1. The existing mapping function to convert the slant total electron content (STEC) measurable by GNSS into the vertical total electron content (VTEC) is based on a so called single layer model (SLM), where all electrons are concentrated on an infinitesimal thin layer with fixed height (between 350 and 450 kilometers). This quantity is called the effective ionospheric height (EIH). An improvement of the mapping function shall be achieved by estimating more realistic numerical values for the EIH by means of a voxel-based tomographic model (TOMION). 2. The ionospheric observations are distributed rather unevenly over the globe and within specific regions. This inhomogeneous distribution is handled by data adaptive B-Spline approaches, with polynomial and trigonometric functions used for the latitude and longitude representations to provide high resolution VTEC maps for global and regional purposes. A Kalman filter is used as sequential estimator. The unknown parameters of the filter state vector are composed of the B-spline coefficients as well as the satellite and receiver DCBs. The resulting high accuracy ionosphere products will be disseminated to the users via downlink from a dedicated server to a receiver site. In this context, an appropriate

  1. A Distributed Web-based Solution for Ionospheric Model Real-time Management, Monitoring, and Short-term Prediction

    Science.gov (United States)

    Kulchitsky, A.; Maurits, S.; Watkins, B.

    2006-12-01

    With the widespread availability of the Internet today, many people can monitor various scientific research activities. It is important to accommodate this interest providing on-line access to dynamic and illustrative Web-resources, which could demonstrate different aspects of ongoing research. It is especially important to explain and these research activities for high school and undergraduate students, thereby providing more information for making decisions concerning their future studies. Such Web resources are also important to clarify scientific research for the general public, in order to achieve better awareness of research progress in various fields. Particularly rewarding is dissemination of information about ongoing projects within Universities and research centers to their local communities. The benefits of this type of scientific outreach are mutual, since development of Web-based automatic systems is prerequisite for many research projects targeting real-time monitoring and/or modeling of natural conditions. Continuous operation of such systems provide ongoing research opportunities for the statistically massive validation of the models, as well. We have developed a Web-based system to run the University of Alaska Fairbanks Polar Ionospheric Model in real-time. This model makes use of networking and computational resources at the Arctic Region Supercomputing Center. This system was designed to be portable among various operating systems and computational resources. Its components can be installed across different computers, separating Web servers and computational engines. The core of the system is a Real-Time Management module (RMM) written Python, which facilitates interactions of remote input data transfers, the ionospheric model runs, MySQL database filling, and PHP scripts for the Web-page preparations. The RMM downloads current geophysical inputs as soon as they become available at different on-line depositories. This information is processed to

  2. Modeling ionospheric foF2 by using empirical orthogonal function analysis

    Science.gov (United States)

    E, A.; Zhang, D.-H.; Xiao, Z.; Hao, Y.-Q.; Ridley, A. J.; Moldwin, M.

    2011-08-01

    A similar-parameters interpolation method and an empirical orthogonal function analysis are used to construct empirical models for the ionospheric foF2 by using the observational data from three ground-based ionosonde stations in Japan which are Wakkanai (Geographic 45.4° N, 141.7° E), Kokubunji (Geographic 35.7° N, 140.1° E) and Yamagawa (Geographic 31.2° N, 130.6° E) during the years of 1971-1987. The impact of different drivers towards ionospheric foF2 can be well indicated by choosing appropriate proxies. It is shown that the missing data of original foF2 can be optimal refilled using similar-parameters method. The characteristics of base functions and associated coefficients of EOF model are analyzed. The diurnal variation of base functions can reflect the essential nature of ionospheric foF2 while the coefficients represent the long-term alteration tendency. The 1st order EOF coefficient A1 can reflect the feature of the components with solar cycle variation. A1 also contains an evident semi-annual variation component as well as a relatively weak annual fluctuation component. Both of which are not so obvious as the solar cycle variation. The 2nd order coefficient A2 contains mainly annual variation components. The 3rd order coefficient A3 and 4th order coefficient A4 contain both annual and semi-annual variation components. The seasonal variation, solar rotation oscillation and the small-scale irregularities are also included in the 4th order coefficient A4. The amplitude range and developing tendency of all these coefficients depend on the level of solar activity and geomagnetic activity. The reliability and validity of EOF model are verified by comparison with observational data and with International Reference Ionosphere (IRI). The agreement between observations and EOF model is quite well, indicating that the EOF model can reflect the major changes and the temporal distribution characteristics of the mid-latitude ionosphere of the Sea of Japan

  3. Spatial correlation structure of the ionosphere predicted by geomagnetic indices and application to global field modelling

    Science.gov (United States)

    Holschneider, M.; Ferrat, K.; Lesur, V.; Stolle, C.

    2017-12-01

    Ionospheric fields are modelled in terms of random structures taking into account a mean behaviour as well as random fluctuations which are described through two point correlation kernels. These kernels are estimated from long time series of numerical simulations from various models. These correlations are best expressed in SM system of coordinates. For the moment we limit ourselves to spatial correlations only in this coordinate system. We study the influence of various indices as possible predictor parameters for these correlations as well as seasonal effects. The various time series of ionospheric fields are stored in a HDF5 database which is accessible via a web interface. The obtained correlation structures serve as prior information to separate external and internal field components from observatory based measurements. We present a model that predicts the correlations as a function of time and some geomagnetic indices. First results of the inversion from observatory data are presented.

  4. The model of beam-plasma discharge in the rocket environment during an electron beam injection in the ionosphere

    International Nuclear Information System (INIS)

    Mishin, E.V.; Ruzhin, Yu.Ya.

    1980-01-01

    The model of beam-plasma discharge in the rocket environment during electron beam injection in the ionosphere is constructed. The discharge plasma density dependence on the neutral gas concentration and the beam parameters is found

  5. Polarization characteristics of standing wave electromagnetic fields at the ionospheric Alfvén resonator lower harmonics: altitude profiles

    Czech Academy of Sciences Publication Activity Database

    Prikner, Karel; Feygin, F. Z.; Raita, T.

    2014-01-01

    Roč. 58, č. 2 (2014), s. 338-341 ISSN 0039-3169 Institutional research plan: CEZ:AV0Z30120515 Keywords : ionospheric Alfvén resonator * EMIC waves * EISCAT measurements Subject RIV: DE - Earth Magnetism, Geodesy, Geography Impact factor: 0.806, year: 2014

  6. Alfven waves in the auroral ionosphere: A numerical model compared with measurements

    International Nuclear Information System (INIS)

    Knudsen, D.J.; Kelley, M.C.; Vickrey, J.F.

    1992-01-01

    The authors solve a linear numerical model of Alfven waves reflecting from the high-latitude ionosphere, both to better understanding the role of the ionosphere in the magnetosphere/ionosphere coupling process and to compare model results with in situ measurements. They use the model to compute the frequency-dependent amplitude and phase relations between the meridional electric and the zonal magnetic fields due to Alfven waves. These relations are compared with measurements taken by an auroral sounding rocket flow in the morningside oval and by the HILAT satellite traversing the oval at local noon. The sounding rocket's trajectory was mostly parallel to the auroral oval, and is measured enhanced fluctuating field energy in regions of electron precipitation. The rocket-measured phase data are in excellent agreement with the Alfven wave model, and the relation between the modeled and the measured by HILAT are related by the height-integrated Pedersen conductivity Σ p , indicating that the measured field fluctuations were due mainly to structured field-aligned current systems. A reason for the relative lack of Alfven wave energy in the HILAT measurements could be the fact that the satellite traveled mostly perpendicular to the oval and therefore quickly traversed narrow regions of electron precipitation and associated wave activity

  7. SAMI2 model results for the quiet time low latitude ionosphere over India

    Science.gov (United States)

    Rao, S. S.; Sharma, Shweta; Pandey, R.

    2018-04-01

    Efficacy of SAMI2 model for the Indian low latitude region around 75°E longitudes has been tested for different levels of solar flux. With a slight modification of the plasma drift velocity the SAMI2 model has been successful in reproducing quiet time ionospheric low latitude features like Equatorial Ionization Anomaly. We have also showed the formation of electron hole in the topside equatorial ionosphere in the Indian sector. Simulation results show the formation of electron hole in the altitude range 800-2500 km over the magnetic equator. Indian zone results reveal marked differences with regard to the time of occurrence, seasonal appearances and strength of the electron hole vis-a-vis those reported for the American equatorial region.

  8. Ionospheric modelling to boost the PPP-RTK positioning and navigation in Australia

    Science.gov (United States)

    Arsov, Kirco; Terkildsen, Michael; Olivares, German

    2017-04-01

    This paper deals with implementation of 3-D ionospheric model to support the GNSS positioning and navigation activities in Australia. We will introduce two strategies for Slant Total Electron Content (STEC) estimation from GNSS CORS sites in Australia. In the first scenario, the STEC is estimated in the PPP-RTK network processing. The ionosphere is estimated together with other GNSS network parameters, such as Satellite Clocks, Satellite Phase Biases, etc. Another approach is where STEC is estimated on a station by station basis by taking advantage of already known station position and different satellite ambiguities relations. Accuracy studies and considerations will be presented and discussed. Furthermore, based on this STEC, 3-D ionosphere modeling will be performed. We will present the simple interpolation, 3-D Tomography and bi-cubic splines as modeling techniques. In order to assess these models, a (user) PPP-RTK test bed is established and a sensitivity matrix will be introduced and analyzed based on time to first fix (TTFF) of ambiguities, positioning accuracy, PPP-RTK solution convergence time etc. Different spatial configurations and constellations will be presented and assessed.

  9. Ion temperature in the outer ionosphere - first version of a global empirical model

    Czech Academy of Sciences Publication Activity Database

    Třísková, Ludmila; Truhlík, Vladimír; Šmilauer, Jan; Smirnova, N. F.

    2004-01-01

    Roč. 34, č. 9 (2004), s. 1998-2003 ISSN 0273-1177 R&D Projects: GA ČR GP205/02/P037; GA AV ČR IAA3042201; GA MŠk ME 651 Institutional research plan: CEZ:AV0Z3042911 Keywords : plasma temperatures * topside ionosphere * empirical models Subject RIV: DG - Athmosphere Sciences, Meteorology Impact factor: 0.548, year: 2004

  10. Monitoring and modeling of ionospheric characteristics in the framework of European COST 296 Action MIERS

    Czech Academy of Sciences Publication Activity Database

    Stanislawska, I.; Laštovička, Jan; Bourdillon, A.; Zolesi, B.; Cander, Lj. R.

    2010-01-01

    Roč. 8, - (2010), S02001/1-S02001/7 ISSN 1542-7390 R&D Projects: GA MŠk OC 091 Grant - others:European Commission(XE) COST296 Institutional research plan: CEZ:AV0Z30420517 Keywords : Ionosphere * monitoring * modeling * COST296 Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 1.833, year: 2010

  11. The International Reference Ionosphere 2012 – a model of international collaboration

    Czech Academy of Sciences Publication Activity Database

    Bilitza, D.; Altadill, D.; Zhang, Y.; Mertens, Ch.; Truhlík, Vladimír; Richards, P.; McKinnell, L.- A.; Reinisch, B.

    2014-01-01

    Roč. 4, 20 February (2014), A07/1-A07/12 ISSN 2115-7251 R&D Projects: GA MŠk(CZ) LH11123 Institutional support: RVO:68378289 Keywords : International Reference Ionosphere * empirical models * plasma parameters * real - time IRI Subject RIV: DG - Athmosphere Sciences, Meteorology Impact factor: 2.558, year: 2014 http://www.swsc-journal.org/articles/swsc/abs/2014/01/swsc130043/swsc130043.html

  12. NUCLEON POLARIZATION IN 3-BODY MODELS OF POLARIZED LI-6

    NARCIS (Netherlands)

    SCHELLINGERHOUT, NW; KOK, LP; COON, SA; ADAM, RM

    1993-01-01

    Just as He-3 --> can be approximately characterized as a polarized neutron target, polarized Li-6D has been advocated as a good isoscalar nuclear target for the extraction of the polarized gluon content of the nucleon. The original argument rests upon a presumed ''alpha + deuteron'' picture of Li-6,

  13. Empirical models of the electron concentration of the ionosphere and their value for radio communications purposes

    International Nuclear Information System (INIS)

    Dudeney, J.R.; Kressman, R.I.

    1986-01-01

    Criteria for the development of ionosphere electron concentration vertical profile empirical models for radio communications purposes are discussed and used to evaluate and compare four contemporary schemes. Schemes must be optimized with respect to quality of profile match, availability and simplicity of the external data required for profile specification, and numerical complexity, depending on the application. It is found that the Dudeney (1978) scheme provides the best general performance, while the Booker (1977) technique is optimized for precision radio wave studies where an observed profile is available. The CCIR (Bradley and Dudeney, 1973) scheme performance is found to be inferior to the previous two, and should be superceded except where mathematical simplicity is prioritized. The International Reference Ionosphere profile is seen to have significant disadvantages with respect to all three criteria. 17 references

  14. Observations and modeling of ionospheric disturbance excited by 2015 Calbuco volcano eruption

    Science.gov (United States)

    Chen, P. C.; Lin, C. C. H.; Chen, C. H.

    2016-12-01

    Volcanic eruptions could trigger acoustic-gravity waves (AGWs) that propagate to the upper atmosphere with increasing oscillation amplitudes. At the ionospheric heights, perturbations in neutrals could affect the plasma through momentum exchanges and lead to disturbances of electron density detectable by dual-frequency observation of GPS. In this study, we observed ionospheric total electron content (TEC) disturbances resulting from the Plinian volcano eruption of Calbuco, Chile in 2015. The eruption event was consist of two major eruptions occurred during 22- 23 April. Observations show clear time rate change of TEC disturbances followed by disturbance oscillations. Spectral analysis of the TEC disturbances indicates two distinguished frequency peaks at 3.7 and 4.4 mHz. To understand the mechanism responsible to the oscillations, we perform theoretical simulations using a nonlinear and non-hyrostatic atmosphere-ionosphere perturbation model. By applying a point source of energy deposition to synthetic the volcano eruption effect in the model, simulations show ion density disturbances with the similar oscillation peak appearing around 3.7 mHz. Comparisons between the detailed simulation results and observations will also be made.

  15. Theoretical modelling of the ionospheric F1-ledge, part 2: Characteristics points

    International Nuclear Information System (INIS)

    Zhang Shunrong; Radicella, S.M.; Huang Xinyu

    1996-01-01

    Ionospheric characteristics relevant to the F1-ledge representation are investigated by using a theoretical ionospheric model and digisonde data. Results indicate that the altitude of the maximum gradient of the electron density with height (base point) is consistent with the height of half maximum density by night, and differences of about 20 km can be seen by day when an intermediate layer appears with the former always higher. It is also pointed out that electron density is particularly sensitive to dynamic processes at that height, where there is no photochemical equilibrium although the photoionization and the chemical loss of the oxygen ions are of the same order of magnitude. The fact that the base point carries information about both F2- and F1-layers suggests a possible use of the parameter in bottom side ionospheric modelling. As the occurrence of the minimum variability of electron density found experimentally in the F1-ledge is concerned, large variabilities of dynamic transport increasing from the F1-ledge height up are considered to be the main cause of the increasing variability with height. Changes due to photoionization and chemical reactions, which increase also with height but with a less degree in the molecular ions dominated region, are considered responsible for the slight variability observed in the upper E region until the minimum is reached at F1 heights. (author). 21 refs, 7 figs

  16. Modeling ionospheric pre-reversal enhancement and plasma bubble growth rate using data assimilation

    Science.gov (United States)

    Rajesh, P. K.; Lin, C. C. H.; Chen, C. H.; Matsuo, T.

    2017-12-01

    We report that assimilating total electron content (TEC) into a coupled thermosphere-ionosphere model by using the ensemble Kalman filter results in improved specification and forecast of eastward pre-reversal enhancement (PRE) electric field (E-field). Through data assimilation, the ionospheric plasma density, thermospheric winds, temperature and compositions are adjusted simultaneously. The improvement of dusk-side PRE E-field over the prior state is achieved primarily by intensification of eastward neutral wind. The improved E-field promotes a stronger plasma fountain and deepens the equatorial trough. As a result, the horizontal gradients of Pedersen conductivity and eastward wind are increased due to greater zonal electron density gradient and smaller ion drag at dusk, respectively. Such modifications provide preferable conditions and obtain a strengthened PRE magnitude closer to the observation. The adjustment of PRE E-field is enabled through self-consistent thermosphere and ionosphere coupling processes captured in the model. The assimilative outputs are further utilized to calculate the flux tube integrated Rayleigh-Taylor instability growth rate during March 2015 for investigation of global plasma bubble occurrence. Significant improvements in the calculated growth rates could be achieved because of the improved update of zonal electric field in the data assimilation forecast. The results suggest that realistic estimate or prediction of plasma bubble occurrence could be feasible by taking advantage of the data assimilation approach adopted in this work.

  17. Associating an ionospheric parameter with major earthquake ...

    Indian Academy of Sciences (India)

    Quasi-static electric field anomaly in the upper ionosphere before an earthquake had been observed as an ionospheric precursor (Gousheva et al. 2009). According to. LAIC model (Lithosphere–Atmosphere–Ionosphere. Coupling model), geochemical, atmospheric and ionospheric parameters are united by a common.

  18. A new global model for the ionospheric F2 peak height for radio wave propagation

    Directory of Open Access Journals (Sweden)

    M. M. Hoque

    2012-05-01

    Full Text Available The F2-layer peak density height hmF2 is one of the most important ionospheric parameters characterizing HF propagation conditions. Therefore, the ability to model and predict the spatial and temporal variations of the peak electron density height is of great use for both ionospheric research and radio frequency planning and operation. For global hmF2 modelling we present a nonlinear model approach with 13 model coefficients and a few empirically fixed parameters. The model approach describes the temporal and spatial dependencies of hmF2 on global scale. For determining the 13 model coefficients, we apply this model approach to a large quantity of global hmF2 observational data obtained from GNSS radio occultation measurements onboard CHAMP, GRACE and COSMIC satellites and data from 69 worldwide ionosonde stations. We have found that the model fits to these input data with the same root mean squared (RMS and standard deviations of 10%. In comparison with the electron density NeQuick model, the proposed Neustrelitz global hmF2 model (Neustrelitz Peak Height Model – NPHM shows percentage RMS deviations of about 13% and 12% from the observational data during high and low solar activity conditions, respectively, whereas the corresponding deviations for the NeQuick model are found 18% and 16%, respectively.

  19. Model Studies of Electrical Coupling Processes in Equatorial Mesosphere and Lower Ionosphere

    Science.gov (United States)

    Tonev, Peter; Velinov, Peter

    2016-07-01

    The quasi-electrostatic response of equatorial lower ionosphere and mesosphere to forcing from below by electrical sources located in the troposphere (e.g. thunderclouds) or at surface (e.g. related to earthquakes) is studied. Such sources generate quasi-static (QS) electric fields in the lower ionosphere and mesosphere which can be large enough in nighttime conditions to cause electron heating, modifications of conductivity and electron density, etc. We demonstrate that this response to the forcing from below highly depends on the geomagnetic latitude determining the magnetic field lines inclination, and thus, the tensor of anisotropic conductivity. Our previous results show that the QS electric fields in the lower nighttime ionosphere above tropospheric sources are much bigger and have larger horizontal extension than those generated at high latitudes by otherwise same conditions. Now we estimate by modeling the electric currents and fields generated at equatorial latitudes in lower ionosphere and mesosphere above electrical charges located in the troposphere or at ground which can have different horizontal dimensions during quiet periods and of their self-consistent effects to electron heating and conductivity. Specific configurations of electric currents and distributions of related electric fields are estimated first by constant (ambient) conductivity. Then, these are evaluated self-consistently with conductivity modification. The electric currents are re-oriented above ~85 km and flow in a narrow horizontal layer where they dense. Respectively, the electric fields and their effect on conductivity have much larger horizontal scale than at middle latitudes (few hundred of kilometers). Sources of large horizontal dimensions, such as mesoscale convective structures and complexes or earthquakes, cause enhancements of electric fields and their effects due to superposition of horizontally reoriented electric currents well above 70 km. In case of thunderstorms these

  20. Lithosphere-Atmosphere-Ionosphere Coupling (LAIC) Model - An Unified Concept for Earthquake Precursors Validation

    Science.gov (United States)

    Pulinets, S.; Ouzounov, D.

    2010-01-01

    The paper presents a conception of complex multidisciplinary approach to the problem of clarification the nature of short-term earthquake precursors observed in atmosphere, atmospheric electricity and in ionosphere and magnetosphere. Our approach is based on the most fundamental principles of tectonics giving understanding that earthquake is an ultimate result of relative movement of tectonic plates and blocks of different sizes. Different kind of gases: methane, helium, hydrogen, and carbon dioxide leaking from the crust can serve as carrier gases for radon including underwater seismically active faults. Radon action on atmospheric gases is similar to the cosmic rays effects in upper layers of atmosphere: it is the air ionization and formation by ions the nucleus of water condensation. Condensation of water vapor is accompanied by the latent heat exhalation is the main cause for observing atmospheric thermal anomalies. Formation of large ion clusters changes the conductivity of boundary layer of atmosphere and parameters of the global electric circuit over the active tectonic faults. Variations of atmospheric electricity are the main source of ionospheric anomalies over seismically active areas. Lithosphere-Atmosphere-Ionosphere Coupling (LAIC) model can explain most of these events as a synergy between different ground surface, atmosphere and ionosphere processes and anomalous variations which are usually named as short-term earthquake precursors. A newly developed approach of Interdisciplinary Space-Terrestrial Framework (ISTF) can provide also a verification of these precursory processes in seismically active regions. The main outcome of this paper is the unified concept for systematic validation of different types of earthquake precursors united by physical basis in one common theory.

  1. Local climatological modeling of ionospheric irregularities detected by GPS in the mid-latitude region

    Science.gov (United States)

    Wautelet, G.; Warnant, R.

    2012-11-01

    Global Positioning System, or GPS, plays an important role in everyday life. More particularly, precise positioning applications constitute a continuously growing sector whose surveyors, civil engineers and more recently farmers represent the principal users. Ionospheric irregularities are considered as the main threat for those applications as their occurrence and their effects on positioning are generally unknown or unmodeled. This paper aims at setting up a local climatological model of such irregularities which can be used as a forecasting tool. The model is based upon a time series of GPS-derived ionospheric irregularities in Belgium covering 10 years of data (period 2002-2011). Our climatological model is twofold: its first component describes the daily variability and is derived from a principal component analysis (PCA) which allows us to retrieve the main patterns of the time series. With the use of low order polynomial and harmonic functions, the second component describes the influence of solar cycle and seasons on irregularity occurrence. Moreover, a statistical autoregressive formulation adapts the model to current conditions. Model validation covers both low and active solar activity periods (years 2008 and 2011) and shows that model accuracy varies with solar conditions and season: values are lower during winter and active solar activity periods, where modeling error can reach up to 60% of the observed value. During summer, model performance is clearly improved, with relative errors generally smaller than 20% for periods of low but also active solar activity.

  2. A new computerized ionosphere tomography model using the mapping function and an application to the study of seismic-ionosphere disturbance

    Science.gov (United States)

    Kong, Jian; Yao, Yibin; Liu, Lei; Zhai, Changzhi; Wang, Zemin

    2016-08-01

    A new algorithm for ionosphere tomography using the mapping function is proposed in this paper. First, the new solution splits the integration process into four layers along the observation ray, and then, the single-layer model (SLM) is applied to each integration part using a mapping function. Next, the model parameters are estimated layer by layer with the Kalman filtering method by introducing the scale factor (SF) γ to solve the ill-posed problem. Finally, the inversed images of different layers are combined into the final CIT image. We utilized simulated data from 23 IGS GPS stations around Europe to verify the estimation accuracy of the new algorithm; the results show that the new CIT model has better accuracy than the SLM in dense data areas and the CIT residuals are more closely grouped. The stability of the new algorithm is discussed by analyzing model accuracy under different error levels (the max errors are 5TECU, 10TECU, 15TECU, respectively). In addition, the key preset parameter, SFγ , which is given by the International Reference Ionosphere model (IRI2012). The experiment is designed to test the sensitivity of the new algorithm to SF variations. The results show that the IRI2012 is capable of providing initial SF values. Also in this paper, the seismic-ionosphere disturbance (SID) of the 2011 Japan earthquake is studied using the new CIT algorithm. Combined with the TEC time sequence of Sat.15, we find that the SID occurrence time and reaction area are highly related to the main shock time and epicenter. According to CIT images, there is a clear vertical electron density upward movement (from the 150-km layer to the 450-km layer) during this SID event; however, the peak value areas in the different layers were different, which means that the horizontal movement velocity is not consistent among the layers. The potential physical triggering mechanism is also discussed in this paper. Compared with the SLM, the RMS of the new CIT model is improved by

  3. Modeling alignment enhancement for solid polarized targets

    Energy Technology Data Exchange (ETDEWEB)

    Keller, D. [University of Virginia, Charlottesville, VA (United States)

    2017-07-15

    A model of dynamic orientation using optimized radiofrequency (RF) irradiation produced perpendicular to the holding field is developed for the spin-1 system required for tensor-polarized fixed-target experiments. The derivation applies to RF produced close to the Larmor frequency of the nucleus and requires the electron spin-resonance linewidth to be much smaller than the nuclear magnetic resonance frequency. The rate equations are solved numerically to study a semi-saturated steady-state resulting from the two sources of irradiation: microwave from the DNP process and the additional RF used to manipulate the tensor polarization. The steady-state condition and continuous-wave NMR lineshape are found that optimize the spin-1 alignment in the polycrystalline materials used as solid polarized targets in charged-beam nuclear and particle physics experiments. (orig.)

  4. Data description and quality assessment of ionospheric electron density profiles for ARPA modeling project. Technical report

    International Nuclear Information System (INIS)

    Conkright, R.O.

    1977-03-01

    This report presents a description of the automated method used to produce electron density (N(h)) profiles from ionograms recorded on 35mm film and an assessment of the resulting data base. A large data base of about 30,000 profiles was required for an ionospheric modeling project. This motivated a search for an automated method of producing profiles. The automated method used is fully described, the resulting data are given a quality grade, and the noon and midnight profiles are presented. Selected portions of this data base are compared with profiles produced by the standard profiling method in use by the Environmental Data Service at Boulder, Colorado

  5. Ionospheric sources for molecular ion outflow

    Science.gov (United States)

    Zettergren, M. D.; Peterson, W. K.; Blelly, P. F.; Alcayde, D.; Semeter, J. L.

    2012-12-01

    Mass-resolved satellite observations have established the presence of molecular ions in the low-altitude magnetosphere, outer magnetosphere, and ring current. Associated molecular outflows originate from the auroral zone F-region ionosphere and, while normally several orders of magnitude less intense than the well-known O+ outflow, are perhaps more closely tied to intense geomagnetic disturbances. Molecular outflow is also fundamentally different from O+ outflow, since molecular ions must first be generated in large quantities in the F-region, and then are subject to very short recombination lifetimes as they escape. Owing to observational difficulties, very little detailed information exists on the generation, energization, and upward transport of molecular ions. Furthermore, the basic geographic and geomagnetic activity dependence of the ionospheric source and higher altitude outflow are only loosely constrained. This research synthesizes both observations and models to gain a better understanding of molecular ion generation and upflow, and the basic characteristics of the ionospheric molecular source during geomagnetic storms. To illustrate ionospheric dynamics associated with published satellite observations of molecular upflow, a 2D ionospheric model is driven by boundary conditions consistent with observed field-aligned currents. These simulations provide detailed information about expected species-dependent ion densities, temperatures, fluxes, and associated transients. Similar model results are also compared against PFISR radar estimates of molecular ions generated by auroral arc activity. A detailed case study of the 24-25 Sept. 1998 geomagnetic storm is presented in which the EISCAT ESR and Tromso radars suggested enhancements in F-region molecular ions and Polar satellite simultaneously observed moleculars in the magnetosphere. Finally, data from Sondrestrom and EISCAT radars during multiple storms are combined in an attempt to build a statistical

  6. Global Three-Dimensional Ionospheric Data Assimilation Model Using Ground-based GPS and Radio Occultation Total Electron Content

    Science.gov (United States)

    Jann-Yenq Liu, Tiger; Lin, Chi-Yen; Matsuo, Tomoko; Lin, Charles C. H.; Tsai, Ho-Fang; Chen, Chao-Yen

    2017-04-01

    An ionospheric data assimilation approach presented here is based on the Gauss-Markov Kalman filter with International Reference Ionosphere (IRI) as the background model and designed to assimilate the total electron content (TEC) observed from ground-based GPS receivers and space-based radio occultation (RO) of FORMOSAT-3/COSMIC (F3/C) or FORMOSAT-7/COSMIC-2 (F7/C2). The Kalman filter consists of the forecast step according to Gauss-Markov process and measurement update step. Observing System Simulation Experiments (OSSEs) show that the Gauss-Markov Kalman filter procedure can increase the accuracy of the data assimilation analysis over the procedure consisting of the measurement update step alone. Moreover, in comparing to F3/C, the dense F7/C2 RO observation can further increase the model accuracy significantly. Validating the data assimilation results with the vertical TEC in Global Ionosphere Maps and that derived from ground-based GPS measurements, as well as the ionospheric F2-peak height and electron density sounded by ionosondes is also carried out. Both the OSSE results and the observation validations confirm that the developed data assimilation model can be used to reconstruct the three-dimensional electron density in the ionosphere satisfactorily.

  7. Analytical modeling of the statistical properties of the contrast of large-scale irregularities of the ionosphere

    Science.gov (United States)

    Vsekhsviatskaia, I. S.; Evstratova, E. A.; Kalinin, Iu. K.; Romanchuk, A. A.

    1989-08-01

    An analytical model is proposed for the distribution of variations of the relative contrast of the electron density of large-scale ionospheric irregularities. The model is characterized by nonzero asymmetry and excess. It is shown that the model can be applied to horizontal irregularity scales from hundreds to thousands of kilometers.

  8. Prediction of global ionospheric VTEC maps using an adaptive autoregressive model

    Science.gov (United States)

    Wang, Cheng; Xin, Shaoming; Liu, Xiaolu; Shi, Chuang; Fan, Lei

    2018-02-01

    In this contribution, an adaptive autoregressive model is proposed and developed to predict global ionospheric vertical total electron content maps (VTEC). Specifically, the spherical harmonic (SH) coefficients are predicted based on the autoregressive model, and the order of the autoregressive model is determined adaptively using the F-test method. To test our method, final CODE and IGS global ionospheric map (GIM) products, as well as altimeter TEC data during low and mid-to-high solar activity period collected by JASON, are used to evaluate the precision of our forecasting products. Results indicate that the predicted products derived from the model proposed in this paper have good consistency with the final GIMs in low solar activity, where the annual mean of the root-mean-square value is approximately 1.5 TECU. However, the performance of predicted vertical TEC in periods of mid-to-high solar activity has less accuracy than that during low solar activity periods, especially in the equatorial ionization anomaly region and the Southern Hemisphere. Additionally, in comparison with forecasting products, the final IGS GIMs have the best consistency with altimeter TEC data. Future work is needed to investigate the performance of forecasting products using the proposed method in an operational environment, rather than using the SH coefficients from the final CODE products, to understand the real-time applicability of the method.

  9. Evaluation of different approaches to modeling the second-order ionospheric delay on GPS measurements

    Science.gov (United States)

    Garcia-Fernandez, M.; Desai, S. D.; Butala, M. D.; Komjathy, A.

    2013-12-01

    This work evaluates various approaches to compute the second order ionospheric correction (SOIC) to Global Positioning System (GPS) measurements. When estimating the reference frame using GPS, applying this correction is known to primarily affect the realization of the origin of the Earth's reference frame along the spin axis (Z coordinate). Therefore, the Z translation relative to the International Terrestrial Reference Frame 2008 is used as the metric to evaluate various published approaches to determining the slant total electron content (TEC) for the SOIC: getting the slant TEC from GPS measurements, and using the vertical total electron content (TEC) given by a Global Ionospheric Model (GIM) to transform it to slant TEC via a mapping function. All of these approaches agree to 1 mm if the ionospheric shell height needed in GIM-based approaches is set to 600 km. The commonly used shell height of 450 km introduces an offset of 1 to 2 mm. When the SOIC is not applied, the Z axis translation can be reasonably modeled with a ratio of +0.23 mm/TEC units of the daily median GIM vertical TEC. Also, precise point positioning (PPP) solutions (positions and clocks) determined with and without SOIC differ by less than 1 mm only if they are based upon GPS orbit and clock solutions that have consistently applied or not applied the correction, respectively. Otherwise, deviations of few millimeters in the north component of the PPP solutions can arise due to inconsistencies with the satellite orbit and clock products, and those deviations exhibit a dependency on solar cycle conditions.

  10. Modelling of optical emissions enhanced by the HF pumping of the ionospheric F-region

    Directory of Open Access Journals (Sweden)

    T. Sergienko

    2012-05-01

    Full Text Available Strong enhancement of the optical emissions with excitation threshold from 1.96 eV (630.0 nm from O(1D up to 18.75 eV (427.8 nm from N2+(1NG have been observed during experiments of the ionosphere modification by high power HF radio waves. Analysis of the optical emission ratios showed clearly that a significant part of the ionospheric electrons have to be accelerated to energies above 30 eV and more in the region where the HF radio wave effectively interacts with the ionospheric plasma. The Monte-Carlo model of electron transport and the optical emission model were used to study the dependence of the optical emission intensity on the acceleration electron parameters. We obtained the following results from analysis of the enhanced intensities of the four optical emissions (630.0, 557.7, 844.6 and 427.8 nm observed in the EISCAT heating experiment on 10 March 2002. The 630.0 emission with an excitation threshold of 1.96 eV is formed predominately by the thermal electrons, where the accelerated electrons play a minor role in the excitation of this emission. In order to explain the experimentally observed intensity ratios, the accelerated electrons must gain energies of more than 60 eV. For accelerated electrons with a power law energy dependence, the efficiency of the optical emission excitation depends on the exponent defining the shape of the electron spectra. However, an agreement with the observed emission intensities is achieved for exponent values not less than zero. Moreover, increasing the exponent to higher values does not affect the emission intensity ratios.

  11. An accurate Kriging-based regional ionospheric model using combined GPS/BeiDou observations

    Science.gov (United States)

    Abdelazeem, Mohamed; Çelik, Rahmi N.; El-Rabbany, Ahmed

    2018-01-01

    In this study, we propose a regional ionospheric model (RIM) based on both of the GPS-only and the combined GPS/BeiDou observations for single-frequency precise point positioning (SF-PPP) users in Europe. GPS/BeiDou observations from 16 reference stations are processed in the zero-difference mode. A least-squares algorithm is developed to determine the vertical total electron content (VTEC) bi-linear function parameters for a 15-minute time interval. The Kriging interpolation method is used to estimate the VTEC values at a 1 ° × 1 ° grid. The resulting RIMs are validated for PPP applications using GNSS observations from another set of stations. The SF-PPP accuracy and convergence time obtained through the proposed RIMs are computed and compared with those obtained through the international GNSS service global ionospheric maps (IGS-GIM). The results show that the RIMs speed up the convergence time and enhance the overall positioning accuracy in comparison with the IGS-GIM model, particularly the combined GPS/BeiDou-based model.

  12. Hierarchical Bayesian modeling of ionospheric TEC disturbances as non-stationary processes

    Science.gov (United States)

    Seid, Abdu Mohammed; Berhane, Tesfahun; Roininen, Lassi; Nigussie, Melessew

    2018-03-01

    We model regular and irregular variation of ionospheric total electron content as stationary and non-stationary processes, respectively. We apply the method developed to SCINDA GPS data set observed at Bahir Dar, Ethiopia (11.6 °N, 37.4 °E) . We use hierarchical Bayesian inversion with Gaussian Markov random process priors, and we model the prior parameters in the hyperprior. We use Matérn priors via stochastic partial differential equations, and use scaled Inv -χ2 hyperpriors for the hyperparameters. For drawing posterior estimates, we use Markov Chain Monte Carlo methods: Gibbs sampling and Metropolis-within-Gibbs for parameter and hyperparameter estimations, respectively. This allows us to quantify model parameter estimation uncertainties as well. We demonstrate the applicability of the method proposed using a synthetic test case. Finally, we apply the method to real GPS data set, which we decompose to regular and irregular variation components. The result shows that the approach can be used as an accurate ionospheric disturbance characterization technique that quantifies the total electron content variability with corresponding error uncertainties.

  13. Numerical modeling of ionospheric parameters from global IMS (International Magnetospheric Study) magnetometer data for the CDAW-6 intervals

    Energy Technology Data Exchange (ETDEWEB)

    Kamide, Y.; Kroehl, H.W.; Hausman, B.A.; McPherron, R.L.; Akasofu, S.

    1983-11-01

    The purpose of this technical report is to present the results of modeling efforts to estimate the distribution of ionospheric electric potential, ionospheric and field-aligned currents, and Joule heating rate from ground-based magnetic records for two intervals; (1) 0600-1800 UT on March 22, 1979, and (2) 1200 UT on March 31 to 0600 UT on April 1, 1979. This global modeling study constitutes one of the major contributions to the Coordinated Data Analysis Workshop (CDAW-6) sponsored by the National Space Science Data Center, NASA.

  14. Simple model for post seismic ionospheric disturbances above an earthquake epicentre and along connecting magnetic field lines

    Directory of Open Access Journals (Sweden)

    R. Marchand

    2008-12-01

    Full Text Available The detection of ionospheric disturbances associated with seismic activity is one of the main objectives of the DEMETER micro-satellite. Its scientific payload provides a comprehensive set of electron and ion measurements. The present work describes a simple model of post-seismic disturbances in the ionosphere above the epicentre. Following a major seism, the neutral atmosphere is assumed to be subject to an acoustic pulse propagating upward, to high altitudes. By coupling this perturbation to the two-dimensional ionospheric model SAMI2 it is then possible to calculate the variations in a number of plasma parameters in the plume region and along connecting magnetic field lines, for an event of representative magnitude. The feasibility of identifying the signature of seismic events from satellite observations is then assessed in view of representative DEMETER measurements and of their natural variability.

  15. Dayside ionosphere of Titan: Impact on calculated plasma densities due to variations in the model parameters

    Science.gov (United States)

    Mukundan, Vrinda; Bhardwaj, Anil

    2018-01-01

    A one dimensional photochemical model for the dayside ionosphere of Titan has been developed for calculating the density profiles of ions and electrons under steady state photochemical equilibrium condition. We concentrated on the T40 flyby of Cassini orbiter and used the in-situ measurements from instruments onboard Cassini as input to the model. An energy deposition model is employed for calculating the attenuated photon flux and photoelectron flux at different altitudes in Titan's ionosphere. We used the Analytical Yield Spectrum approach for calculating the photoelectron fluxes. Volume production rates of major primary ions, like, N2+, N+ , CH4+, CH3+, etc due to photon and photoelectron impact are calculated and used as input to the model. The modeled profiles are compared with the Cassini Ion Neutral Mass Spectrometer (INMS) and Langmuir Probe (LP) measurements. The calculated electron density is higher than the observation by a factor of 2 to 3 around the peak. We studied the impact of different model parameters, viz. photoelectron flux, ion production rates, electron temperature, dissociative recombination rate coefficients, neutral densities of minor species, and solar flux on the calculated electron density to understand the possible reasons for this discrepancy. Recent studies have shown that there is an overestimation in the modeled photoelectron flux and N2+ ion production rates which may contribute towards this disagreement. But decreasing the photoelectron flux (by a factor of 3) and N2+ ion production rate (by a factor of 2) decreases the electron density only by 10 to 20%. Reduction in the measured electron temperature by a factor of 5 provides a good agreement between the modeled and observed electron density. The change in HCN and NH3 densities affects the calculated densities of the major ions (HCNH+ , C2H5+, and CH5+); however the overall impact on electron density is not appreciable ( < 20%). Even though increasing the dissociative

  16. Equatorial ionospheric zonal drift model and vertical drift statistics from UHF scintillation measurements in South America

    Directory of Open Access Journals (Sweden)

    R. E. Sheehan

    2004-09-01

    Full Text Available UHF scintillation measurements of zonal ionospheric drifts have been conducted at Ancon, Peru since 1994 using antennas spaced in the magnetic east-west direction to cross-correlate geo-synchronous satellite signals. An empirical model of average drift over a wide range of Kp and solar flux conditions was constructed from successive two-dimensional fits of drift vs. the parameters and day of year. The model exhibits the typical local time trend of maximum eastward velocity in the early evening with a gradual decrease and reversal in the early morning hours. As expected, velocities at all hours increase with the solar flux and decrease with Kp activity. It was also found that vertical drifts could contribute to the variability of drift measurements to the east of Ancon at a low elevation angle. The vertical drift at the ionospheric intersection to the east can be estimated when combined with nearly overhead observations at Ancon or a similar spaced-antenna site at Antofagasta, Chile. Comparisons on five days with nearly simultaneous measurements of vertical drift by the Julia radar at Jicamarca, Peru show varying agreement with the spaced-antenna estimates. Statistical results from 1997 to 2001 generally agree with radar and satellite studies.

  17. A Model for Negative Ion Chemistry in Titan’s Ionosphere

    Science.gov (United States)

    Mukundan, Vrinda; Bhardwaj, Anil

    2018-04-01

    We developed a one-dimensional photochemical model for the dayside ionosphere of Titan for calculating the density profiles of negative ions under steady-state photochemical equilibrium condition. We concentrated on the T40 flyby of the Cassini orbiter and used the in situ measurements from instruments on board Cassini as input to the model. Using the latest available reaction rate coefficients and dissociative electron attachment cross sections, the densities of 10 anions are calculated. Our study shows CN‑ as the dominant anion, followed by C3N‑, which agrees with the results of previous calculations. We suggest that H‑ could be an important anion in Titan’s ionosphere and is the second most abundant anion at altitudes greater than 1200 km. The main production channel of the major ion CN‑ is the reaction of H‑ with HCN. The H‑ also play a major role in the production of anions C2H‑, C6H‑, and OH‑. We present a comparison of the calculated ion density profiles with the relative density profiles derived using recently reported Cassini CAPS/ELS observations.

  18. The ionospheric eclipse factor method (IEFM) and its application to determining the ionospheric delay for GPS

    DEFF Research Database (Denmark)

    Yuan, Y.; Tscherning, C.C.; Knudsen, Per

    2006-01-01

    A new method for modeling the ionospheric delay using global positioning system (GPS) data is proposed, called the ionospheric eclipse factor method (IEFM). It is based on establishing a concept referred to as the ionospheric eclipse factor (IEF) lambda of the ionospheric pierce point (IPP...

  19. Ionospheric "Volcanology": Ionospheric Detection of Volcano Eruptions

    Science.gov (United States)

    Astafyeva, E.; Shults, K.; Lognonne, P. H.; Rakoto, V.

    2016-12-01

    It is known that volcano eruptions and explosions can generate acoustic and gravity waves. These neutral waves further propagate into the atmosphere and ionosphere, where they are detectable by atmospheric and ionospheric sounding tools. So far, the features of co-volcanic ionospheric perturbations are not well understood yet. The development of the global and regional networks of ground-based GPS/GNSS receivers has opened a new era in the ionospheric detection of natural hazard events, including volcano eruptions. It is now known that eruptions with the volcanic explosivity index (VEI) of more than 2 can be detected in the ionosphere, especially in regions with dense GPS/GNSS-receiver coverage. The co-volcanic ionospheric disturbances are usually characterized as quasi-periodic oscillations. The Calbuco volcano, located in southern Chile, awoke in April 2015 after 43 years of inactivity. The first eruption began at 21:04UT on 22 April 2015, preceded by only an hour-long period of volcano-tectonic activity. This first eruption lasted 90 minutes and generated a sub-Plinian (i.e. medium to large explosive event), gray ash plume that rose 15 km above the main crater. A larger second event on 23 April began at 04:00UT (01:00LT), it lasted six hours, and also generated a sub-Plinian ash plume that rose higher than 15 km. The VEI was estimated to be 4 to 5 for these two events. In this work, we first study ionospheric TEC response to the Calbuco volcano eruptions of April 2015 by using ground-based GNSS-receivers located around the volcano. We analyze the spectral characteristics of the observed TEC variations and we estimate the propagation speed of the co-volcanic ionospheric perturbations. We further proceed with the normal mode summation technique based modeling of the ionospheric TEC variations due to the Calbuco volcano eruptions. Finally, we attempt to localize the position of the volcano from the ionospheric measurements, and we also estimate the time of the

  20. Ionosphere research with a HF/MF cubesat radio instrument

    Science.gov (United States)

    Kallio, Esa; Aikio, Anita; Alho, Markku; Fontell, Mathias; Harri, Ari-Matti; Kauristie, Kirsti; Kestilä, Antti; Koskimaa, Petri; Mäkelä, Jakke; Mäkelä, Miika; Turunen, Esa; Vanhamäki, Heikki; Verronen, Pekka

    2017-04-01

    New technology provides new possibilities to study geospace and 3D ionosphere by using spacecraft and computer simulations. A type of nanosatellites, CubeSats, provide a cost effective possibility to provide in-situ measurements in the ionosphere. Moreover, combined CubeSat observations with ground-based observations gives a new view on auroras and associated electromagnetic phenomena. Especially joint and active CubeSat - ground based observation campaigns enable the possibility of studying the 3D structure of the ionosphere. Furthermore using several CubeSats to form satellite constellations enables much higher temporal resolution. At the same time, increasing computation capacity has made it possible to perform simulations where properties of the ionosphere, such as propagation of the electromagnetic waves in the medium frequency, MF (0.3-3 MHz) and high frequency, HF (3-30 MHz), ranges is based on a 3D ionospheric model and on first-principles modelling. Electromagnetic waves at those frequencies are strongly affected by ionospheric electrons and, consequently, those frequencies can be used for studying the plasma. On the other hand, even if the ionosphere originally enables long-range telecommunication at MF and HF frequencies, the frequent occurrence of spatiotemporal variations in the ionosphere disturbs communication channels, especially at high latitudes. Therefore, study of the MF and HF waves in the ionosphere has both a strong science and technology interests. We introduce recently developed simulation models as well as measuring principles and techniques to investigate the arctic ionosphere by a polar orbiting CubeSat whose novel AM radio instrument measures HF and MF waves. The cubesat, which contains also a white light aurora camera, is planned to be launched in late 2017 (http://www.suomi100satelliitti.fi/eng). The new models are (1) a 3D ray tracing model and (2) a 3D full kinetic electromagnetic simulation. We also introduce how combining of the

  1. Performance evaluation of linear time-series ionospheric Total Electron Content model over low latitude Indian GPS stations

    Science.gov (United States)

    Dabbakuti, J. R. K. Kumar; Venkata Ratnam, D.

    2017-10-01

    Precise modeling of the ionospheric Total Electron Content (TEC) is a critical aspect of Positioning, Navigation, and Timing (PNT) services intended for the Global Navigation Satellite Systems (GNSS) applications as well as Earth Observation System (EOS), satellite communication, and space weather forecasting applications. In this paper, linear time series modeling has been carried out on ionospheric TEC at two different locations at Koneru Lakshmaiah University (KLU), Guntur (geographic 16.44° N, 80.62° E; geomagnetic 7.55° N) and Bangalore (geographic 12.97° N, 77.59° E; geomagnetic 4.53° N) at the northern low-latitude region, for the year 2013 in the 24th solar cycle. The impact of the solar and geomagnetic activity on periodic oscillations of TEC has been investigated. Results confirm that the correlation coefficient of the estimated TEC from the linear model TEC and the observed GPS-TEC is around 93%. Solar activity is the key component that influences ionospheric daily averaged TEC while periodic component reveals the seasonal dependency of TEC. Furthermore, it is observed that the influence of geomagnetic activity component on TEC is different at both the latitudes. The accuracy of the model has been assessed by comparing the International Reference Ionosphere (IRI) 2012 model TEC and TEC measurements. Moreover, the absence of winter anomaly is remarkable, as determined by the Root Mean Square Error (RMSE) between the linear model TEC and GPS-TEC. On the contrary, the IRI2012 model TEC evidently failed to predict the absence of winter anomaly in the Equatorial Ionization Anomaly (EIA) crest region. The outcome of this work will be useful for improving the ionospheric now-casting models under various geophysical conditions.

  2. A comparative Pc1 case study applying two modes of ionospheric Alfvén resonator modeling

    Czech Academy of Sciences Publication Activity Database

    Prikner, Karel; Feygin, F. Z.; Raita, T.

    2010-01-01

    Roč. 54, č. 3 (2010), s. 495-511 ISSN 0039-3169 Grant - others:EU(XE) HPRI 200100132 Institutional research plan: CEZ:AV0Z30120515 Keywords : ionospheric Alfvén resonator * Pc1 pulsations * numerical simulation * EISCAT data * IRI models Subject RIV: DE - Earth Magnetism, Geodesy, Geography Impact factor: 1.123, year: 2010

  3. Modelling the ionosphere of gas-giant exoplanets irradiated by low-mass stars

    Science.gov (United States)

    Chadney, J.; Galand, M.; Unruh, Y.; Koskinen, T.; Sanz-Forcada, J.

    2015-10-01

    The composition and structure of the upper atmosphere of Extrasolar Giant Planets (EGPs) are affected by the high-energy spectrum of the host star from soft X-rays to Extreme UltraViolet (EUV) (0.1-10 nm). This emission depends on the activity level of the star, which is primarily determined by its age [1]. In this study, we focus upon EGPs orbiting K- and M-dwarf stars of different ages. XUV spectra for these stars are constructed using a coronal model [2]. These spectra are used to drive both a thermospheric [3] and an ionospheric model, providing densities of neutral and ion species. Ionisation is included through photo-ionisation and electronimpact processes. The former is calculated by solving the Lambert-Beer law, while the latter is calculated from a supra-thermal electron transport model [4]. Planets orbiting far from the star are found to undergo Jeans escape, whereas close-orbiting planets undergo hydrodynamic escape. The critical orbital distance of transition between the two regimes is dependent on the level of stellar activity. We also find that EGP ionospheres at all orbital distances considered (0.1-1 AU) and around all stars selected (eps Eri, AD Leo, AU Mic) are dominated by the long-lived H+ ion. In addition, planets in the Jeans escape regime also have a layer in which H3 + is the major ion at the base of the ionosphere. For fast-rotating planets, densities of short-lived H3 + undergo significant diurnal variations, their peak value being determined by the stellar X-ray flux. In contrast, densities of longer-lived H+ show very little day/night variability and their value is determined by the level of stellar EUV flux. The H3 + peak in EGPs in the hydrodynamic escape regime under strong stellar illumination is pushed to altitudes below the homopause, where this ion is likely to be destroyed through reactions with heavy species (e.g., hydrocarbons, water). Infrared emissions from H3 + shall also be discussed, as well as the impact of stellar

  4. Response of the Equatorial Ionosphere to the Geomagnetic DP2 current system

    Science.gov (United States)

    Yizengaw, E.; Moldwin, M.; Zesta, E.; Pradipta, R.; Biouele, C. M.; Rabiu, A. B.; Obrou, O.; Bamba, Z.

    2016-12-01

    The response of equatorial ionosphere to the magnetospheric origin DP2 (disturbance polar of the second type) current fluctuations and its impact on the equatorial ionospheric density structure is examined using ground-based multi-instrument observations. The interaction between the solar wind and magnetosphere generates a convection electric field that can penetrate to the ionosphere and cause the DP2 current system. The quasi-periodic DP2 current system, which fluctuates coherently with IMF Bz oscillations, penetrates nearly instantaneously to the dayside equatorial region through the TM0 (zero order transverse magnetic) mode waves in the Earth-ionosphere waveguide and modulates the electrodynamics that are responsible for the complicated nature of dayside ionospheric density variations at the equator. In this paper, using multi-instrument (magnetometers, GPS, radar, and ionosonde) observations, we clearly demonstrated that the high-latitude DP2 current system penetrates to the equator and causes the dayside electrodynamics and ionospheric density to fluctuate coherently with the DP2 current as well as with the IMF Bz component. This clearly indicates that understanding of the quasi-periodic DP2 current systems, such as its source, condition of its penetration to the equatorial region, and the impact it can produce onto the ionospheric density distribution is very important information for the ongoing modeling effort to improve the global ionospheric density structure and scintillation forecasting capability.

  5. Full-wave reflection of lightning long-wave radio pulses from the ionospheric D region: Numerical model

    Science.gov (United States)

    Jacobson, Abram R.; Shao, Xuan-Min; Holzworth, Robert

    2009-03-01

    A model is developed for calculating ionospheric reflection of electromagnetic pulses emitted by lightning, with most energy in the long-wave spectral region (f ~ 3-100 kHz). The building block of the calculation is a differential equation full-wave solution of Maxwell's equations for the complex reflection of individual plane waves incident from below, by the anisotropic, dissipative, diffuse dielectric profile of the lower ionosphere. This full-wave solution is then put into a summation over plane waves in an angular direct Fourier transform to obtain the reflection properties of curved wavefronts. This step models also the diffraction effects of long-wave ionospheric reflections observed at short or medium range (~200-500 km). The calculation can be done with any arbitrary but smooth dielectric profile versus altitude. For an initial test, this article uses the classic D region exponential profiles of electron density and collision rate given by Volland. With even these simple profiles, our model of full-wave reflection of curved wavefronts captures some of the basic attributes of observed reflected waveforms recorded with the Los Alamos Sferic Array. A follow-on article will present a detailed comparison with data in order to retrieve ionospheric parameters.

  6. Climatology and modeling of ionospheric scintillations and irregularity zonal drifts at the equatorial anomaly crest region

    Science.gov (United States)

    Muella, Marcio T. A. H.; Duarte-Silva, Marcelo H.; Moraes, Alison O.; de Paula, Eurico R.; de Rezende, Luiz F. C.; Alfonsi, Lucilla; Affonso, Bruno J.

    2017-11-01

    In this study the climatology of ionospheric scintillations and the zonal drift velocities of scintillation-producing irregularities are depicted for a station located under the southern crest of the equatorial ionization anomaly. Then, the α - μ ionospheric fading model is used for the first- and second-order statistical characterization of amplitude scintillations. In the statistical analyzes, data are used from single-frequency GPS receivers acquired during ˜ 17 years (September 1997-November 2014) at Cachoeira Paulista (22.4° S; 45.0° W), Brazil. The results reveal that the nocturnal occurrence of scintillations follows the seasonal distribution of plasma bubble irregularities observed in the longitudinal sector of eastern South America. In addition to the solar cycle dependence, the results suggest that the occurrence climatology of scintillations is also modulated by the secular variation in the dip latitude of Cachoeira Paulista, since the maximum occurrence of scintillations during the peak of solar cycle 24 was ˜ 20 % lower than that observed during the maximum of solar cycle 23. The dynamics of the irregularities throughout a solar cycle, as investigated from the estimates of the mean zonal drift velocities, presented a good correlation with the EUV and F10.7 cm solar fluxes. Meanwhile, the seasonal behavior showed that the magnitude of the zonal drift velocities is larger during the December solstice months than during the equinoxes. In terms of modeling, the results for the α - μ distribution fit quite well with the experimental data and with the temporal characteristics of fading events independently of the solar activity level.

  7. Modeling diffusion coefficients in binary mixtures of polar and non-polar compounds

    DEFF Research Database (Denmark)

    Medvedev, Oleg; Shapiro, Alexander

    2005-01-01

    The theory of transport coefficients in liquids, developed previously, is tested on a description of the diffusion coefficients in binary polar/non-polar mixtures, by applying advanced thermodynamic models. Comparison to a large set of experimental data shows good performance of the model. Only...

  8. Ionospheric topside sounding.

    Science.gov (United States)

    Calvert, W

    1966-10-14

    Over the past few years, the satellite topside sounders have significantly contributed to the understanding of the upper ionosphere. A great quantity of radio echo data has been accumulated, from which the ionospheric electrondensity distribution can be determined. The topside measurements of electron density essentially agree with similar measurements from the ground, except for an occasional 10-percent discrepancy near the peak of the ionosphere. While horizontal non-uniformity is a likely cause, this discrepancy has not yet been adequately explained. The electron-density scale heights measured at a constant altitude indicate both a higher temperature and a heavier mean ion mass at high latitudes. At low latitudes the topside measurements have shown the detailed latitudinal structure of the equatorial anomaly, demonstrating control by the geomagnetic field. A variety of electron-density irregularities have been studied. Most are greatly elongated along the magnetic field, and produce echoes either by lateral scattering, if they are thin, or by longitudinal ducting, if they are thick. Some of the thick irregularities are continuous between the hemispheres and support conjugate echo propagation. The topside sounders have revealed the complex structure of the ionosphere near the auroral zone and at higher latitudes. At night an east-west trough of greatly reduced electron density occurs equatorward of the auroral zone. At the auroral zone itself the electron density is high and quite variable, both in space and time. The electron density at the polar cap within the auroral zone is often uniform and smooth. Ionospheric irregularities are common in the area of the trough and the auroral zone. Among other satellites, the topside sounders have been used in various plasma studies involving the excitation and propagation of waves. These studies suggest that the ionosphere is an appropriate region for future plasma physics investigations, especially with rocket and

  9. Global Coupled Model Studies of The Jovian Upper Atmosphere In Response To Electron Precipitation and Ionospheric Convection Within The Auroral Region.

    Science.gov (United States)

    Millward, G. H.; Miller, S.; Aylward, A. D.

    The Jovian Ionospheric Model (JIM) is a global three-dimensional model of Jupiter's coupled ionosphere and thermosphere, developed at University College London. Re- cently, the model has been used to investigate the atmospheric response to electron precipitation within the high-latitude auroral region. A series of simulations have been performed in which the model atmosphere is subjected to monochromatic precipitat- ing electrons of varying number flux and initial energy and, in addition, to various degrees of ionospheric convection. The auroral ionospheric conductivity which re- sults is shown to be strongly non-linear with respect to the incoming electron energy, with a maximum observed for incident particles of initial energy 60 KeV. Electrons with higher energies penetrate the thermospheric region completely, whilst electrons of lower energy (say 10 keV) produce ionisation at higher levels in the atmosphere which are less less condusive to the creation of ionospheric conductivity. Studies of the thermospheric winds with the auroral region show that zonal winds (around the auroral oval) can attain values of around 70% of the driving zonal ion velocity. Also the results show that these large neutral winds are limited in vertical extent to the region of large ionospheric conductivity, tailing off markedly at altitudes above this. The latest results from this work will be presented, and the implications for Jovian magnetospheric-ionospheric coupling will be discussed.

  10. Revisit the modeling of the Saturnian ring atmosphere and ionosphere from the "Cassini Grand Finale" results

    Science.gov (United States)

    Tseng, W. L.; Johnson, R. E.; Tucker, O. J.; Perry, M. E.; Ip, W. H.

    2017-12-01

    During the Cassini Grand Finale mission, this spacecraft, for the first time, has done the in-situ measurements of Saturn's upper atmosphere and its rings and provides critical information for understanding the coupling dynamics between the main rings and the Saturnian system. The ring atmosphere is the source of neutrals (i.e., O2, H2, H; Tseng et al., 2010; 2013a), which is primarily generated by photolytic decomposition of water ice (Johnson et al., 2006), and plasma (i.e., O2+ and H2+; Tseng et al., 2011) in the Saturnian magnetosphere. In addition, the main rings have strong interaction with Saturn's atmosphere and ionosphere (i.e., a source of oxygen into Saturn's upper atmosphere and/or the "ring rain" in O'Donoghue et al., 2013). Furthermore, the near-ring plasma environment is complicated by the neutrals from both the seasonally dependent ring atmosphere and Enceladus torus (Tseng et al., 2013b), and, possibly, from small grains from the main and tenuous F and G rings (Johnson et al.2017). The data now coming from Cassini Grand Finale mission already shed light on the dominant physics and chemistry in this region of Saturn's magnetosphere, for example, the presence of carbonaceous material from meteorite impacts in the main rings and each gas species have similar distribution in the ring atmosphere. We will revisit the details in our ring atmosphere/ionosphere model to study, such as the source mechanism for the organic material and the neutral-grain-plasma interaction processes.

  11. Simulations of the September 1987 lower thermospheric tides with the National Center for Atmospheric Research thermosphere-ionosphere general circulation model

    International Nuclear Information System (INIS)

    Fesen, C.G.; Roble, R.G.

    1991-01-01

    The National Center for Atmospheric Research thermosphere-ionosphere general circulation model (TIGCM) was used to simulate incoherent scatter radar observations of the lower thermosphere tides during the first Lower Thermosphere Coupling Study (LTCS) campaign, September 21-26, 1987. The TIGCM utilized time-varying histories of the model input fields obtained from the World Data Center for the LTCS period. These model inputs included solar flux, total hemispheric power, solar wind data from which the cross-polar-cap potential was derived, and geomagnetic K p index. Calculations were made for the semidiurnal ion temperatures and horizontal neutral winds at locations representative of Arecibo, Millstone Hill, and Sondrestrom. The diurnal tides at Sondrestrom were also simulated. Tidal inputs to the TIGCM lower boundary were obtained from the middle atmosphere model of Forbes and Vial (1989). The TIGCM tidal structures are in fair general agreement with the observations. The amplitudes tended to be better simulated than the phases, and the mid- and high-latitude locations are simulated better than the low-latitude thermosphere. This may indicate a need to incorporate coupling of the neutral atmosphere and ionosphere with the E region dynamo in the equatorial region to obtain a better representation of low-latitude thermospheric tides. The model simulations were used to investigate the daily variability of the tides due to the geomagnetic activity occurring during this period. In general, the ion temperatures were predicted to be affected more than the winds, and the diurnal components more than the semidiurnal. The effects are typically largest at high latitudes and higher altitudes, but discernible differences were produced at low latitudes

  12. Ionospheric TEC from the Turkish Permanent GNSS Network (TPGN) and comparison with ARMA and IRI models

    Science.gov (United States)

    Ansari, Kutubuddin; Panda, Sampad Kumar; Althuwaynee, Omar F.; Corumluoglu, Ozsen

    2017-09-01

    The present study investigates the ionospheric Total Electron Content (TEC) variations in the lower mid-latitude Turkish region from the Turkish Permanent GNSS Network (TPGN) and International GNSS Services (IGS) observations during the year 2016. The corresponding vertical TEC (VTEC) predicted by Auto Regressive Moving Average (ARMA) and International Reference Ionosphere 2016 (IRI-2016) models are evaluated to realize their effectiveness over the region. The spatial, diurnal and seasonal behavior of VTEC and the relative VTEC variations are modeled with Ordinary Least Square Estimator (OLSE). The spatial behavior of modeled result during March equinox and June solstice indicates an inverse relationship of VTEC with the longitude across the region. On the other hand, the VTEC variation during September equinox and December solstice including March equinox and June solstice are decreasing with increase in latitude. The GNSS observed and modeled diurnal variation of the VTEC show that the VTEC slowly increases with dawn, attains a broader duration of peak around 09.00 to 12.00 UT, and thereafter decreases gradually reaching minimum around 21.00 UT. The seasonal variation of VTEC shows an annual mode, maxima in equinox and minima in solstice. The average value of VTEC during the June solstice is with slightly higher value than the March equinox though variations during the latter season is more. Moreover, the study shows minimum average value during December solstice compared to June solstice at all stations. The comparative analysis demonstrates the prediction errors by OLSE, ARMA and IRI remaining between 0.23 to 1.17%, 2.40 to 4.03% and 24.82 to 25.79% respectively. Also, the observed VTEC seasonal variation has good agreement with OLSE and ARMA models whereas IRI-VTEC often underestimated the observed value at each location. Hence, the deviations of IRI estimated VTEC compared to ARMA and OLSE models claim further improvements in IRI model over the Turkish region

  13. Interaction of plasma cloud with external electric field in lower ionosphere

    Directory of Open Access Journals (Sweden)

    Y. S. Dimant

    2010-03-01

    Full Text Available In the auroral lower-E and upper-D region of the ionosphere, plasma clouds, such as sporadic-E layers and meteor plasma trails, occur daily. Large-scale electric fields, created by the magnetospheric dynamo, will polarize these highly conducting clouds, redistributing the electrostatic potential and generating anisotropic currents both within and around the cloud. Using a simplified model of the cloud and the background ionosphere, we develop the first self-consistent three-dimensional analytical theory of these phenomena. For dense clouds, this theory predicts highly amplified electric fields around the cloud, along with strong currents collected from the ionosphere and circulated through the cloud. This has implications for the generation of plasma instabilities, electron heating, and global MHD modeling of magnetosphere-ionosphere coupling via modifications of conductances induced by sporadic-E clouds.

  14. Thermospheric tides simulated by the national center for atmospheric research thermosphere-ionosphere general circulation model at equinox

    International Nuclear Information System (INIS)

    Fesen, C.G.; Roble, R.G.; Ridley, E.C.

    1993-01-01

    The authors use the National Center for Atmospheric Research (NCAR) thermosphere/ionosphere general circulation model (TIGCM) to model tides and dynamics in the thermosphere. This model incorporates the latest advances in the thermosphere general circulation model. Model results emphasized the 70 degree W longitude region to overlap a series of incoherent radar scatter installations. Data and the model are available on data bases. The results of this theoretical modeling are compared with available data, and with prediction of more empirical models. In general there is broad agreement within the comparisons

  15. A model study of diurnal behavior of the ionosphere and the protonosphere coupling

    Science.gov (United States)

    Marubashi, K.; Grebowsky, J. M.

    1976-01-01

    A new method to study dynamic behavior of the ionosphere-protonosphere coupling within the plasmasphere is developed and used to calculate ion distributions above 500 km using observed electron densities at 500 km. The method is based on the relation between the total magnetic flux tube content of H(+) above some reference height (e.g., 3000 km) and the H(+) flux at that height, which is uniquely determined by the coupled momentum and continuity equations for the quasi-steady state. The O(+) profile is perturbed from diffusive equilibrium only by ion drag with H(+). The time dependency is taken into account by applying self-consistent boundary conditions which are obtained from the solution of the time-dependent equation for the tube content of H(+). Calculations are carried out for two models. The first model deals with the ion dynamics in a tube of force which rotates with the earth. In the second model, effects of the cross-L plasma drifts are considered. Both models produce diurnal variations of H(+) and O(+) densities near 1000 km similar to observational results.

  16. Unusual Ionospheric Echoes with Velocity and Very Low Special Width Observed by the SuperDARN Radars in the Polar Cap During High Geomagnetic Activity

    National Research Council Canada - National Science Library

    Nishitani, Nozomu

    2004-01-01

    ...) They have a close correlation with geomagnetic activity such that as the Dst index decreases, the radars tend to observe ionospheric echoes with high Doppler velocity and very low spectral width more frequently. (2...

  17. A two-step ionospheric modeling algorithm considering the impact of GLONASS pseudo-range inter-channel biases

    Science.gov (United States)

    Zhang, Rui; Yao, Yi-bin; Hu, Yue-ming; Song, Wei-wei

    2017-12-01

    The Global Navigation Satellite System presents a plausible and cost-effective way of computing the total electron content (TEC). But TEC estimated value could be seriously affected by the differential code biases (DCB) of frequency-dependent satellites and receivers. Unlike GPS and other satellite systems, GLONASS adopts a frequency-division multiplexing access mode to distinguish different satellites. This strategy leads to different wavelengths and inter-frequency biases (IFBs) for both pseudo-range and carrier phase observations, whose impacts are rarely considered in ionospheric modeling. We obtained observations from four groups of co-stations to analyze the characteristics of the GLONASS receiver P1P2 pseudo-range IFB with a double-difference method. The results showed that the GLONASS P1P2 pseudo-range IFB remained stable for a period of time and could catch up to several meters, which cannot be absorbed by the receiver DCB during ionospheric modeling. Given the characteristics of the GLONASS P1P2 pseudo-range IFB, we proposed a two-step ionosphere modeling method with the priori IFB information. The experimental analysis showed that the new algorithm can effectively eliminate the adverse effects on ionospheric model and hardware delay parameters estimation in different space environments. During high solar activity period, compared to the traditional GPS + GLONASS modeling algorithm, the absolute average deviation of TEC decreased from 2.17 to 2.07 TECu (TEC unit); simultaneously, the average RMS of GPS satellite DCB decreased from 0.225 to 0.219 ns, and the average deviation of GLONASS satellite DCB decreased from 0.253 to 0.113 ns with a great improvement in over 55%.

  18. Estimation of energy budget of ionosphere-thermosphere system during two CIR-HSS events: observations and modeling

    Directory of Open Access Journals (Sweden)

    Verkhoglyadova Olga

    2016-01-01

    Full Text Available We analyze the energy budget of the ionosphere-thermosphere (IT system during two High-Speed Streams (HSSs on 22–31 January, 2007 (in the descending phase of solar cycle 23 and 25 April–2 May, 2011 (in the ascending phase of solar cycle 24 to understand typical features, similarities, and differences in magnetosphere-ionosphere-thermosphere (IT coupling during HSS geomagnetic activity. We focus on the solar wind energy input into the magnetosphere (by using coupling functions and energy partitioning within the IT system during these intervals. The Joule heating is estimated empirically. Hemispheric power is estimated based on satellite measurements. We utilize observations from TIMED/SABER (Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry to estimate nitric oxide (NO and carbon dioxide (CO2 cooling emission fluxes. We perform a detailed modeling study of these two similar HSS events with the Global Ionosphere-Thermosphere Model (GITM and different external driving inputs to understand the IT response and to address how well the model reproduces the energy transport. GITM is run in a mode with forecastable inputs. It is shown that the model captures the main features of the energy coupling, but underestimates NO cooling and auroral heating in high latitudes. Lower thermospheric forcing at 100 km altitude is important for correct energy balance of the IT system. We discuss challenges for a physics-based general forecasting approach in modeling the energy budget of moderate IT storms caused by HSSs.

  19. Report from ionospheric science

    International Nuclear Information System (INIS)

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

    1989-01-01

    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

  20. The improved DGR analytical model of electron density height profile and total electron content in the ionosphere

    OpenAIRE

    Radicella, S. M.; Zhang, M. L.

    1995-01-01

    Tests of the analytical model of the electron density profile originally proposed by G, Di Giovanni and S.M. Radicella (DGR model) have shown the need to introduce improvements in order to obtain a model able to reproduce the ionosphere in a larger spectrum of geophysical and time conditions. The present paper reviews the steps toward such progress and presents the final formulation of the model. It gives also a brief re- view of tests of the improved model done by different authors.

  1. Magnetic Field Perturbations from Currents in the Dark Polar Regions During Quiet Geomagnetic Conditions

    DEFF Research Database (Denmark)

    Friis-Christensen, Eigil; Finlay, Chris; Hesse, M.

    2017-01-01

    In the day-side sunlit polar ionosphere the varying and IMF dependent convection creates strong ionospheric currents even during quiet geomagnetic conditions. Observations during such times are often excluded when using satellite data to model the internal geomagneticmain field. Observations from...... the night-side or local winter during quiet conditions are, however, also influenced by variations in the IMF. In this paper we briefly review the large scale features of the ionospheric currents in the polar regions with emphasis on the current distribution during undisturbed conditions. We examine...

  2. Research to Operations of Ionospheric Scintillation Detection and Forecasting

    Science.gov (United States)

    Jones, J.; Scro, K.; Payne, D.; Ruhge, R.; Erickson, B.; Andorka, S.; Ludwig, C.; Karmann, J.; Ebelhar, D.

    Ionospheric Scintillation refers to random fluctuations in phase and amplitude of electromagnetic waves caused by a rapidly varying refractive index due to turbulent features in the ionosphere. Scintillation of transionospheric UHF and L-Band radio frequency signals is particularly troublesome since this phenomenon can lead to degradation of signal strength and integrity that can negatively impact satellite communications and navigation, radar, or radio signals from other systems that traverse or interact with the ionosphere. Although ionospheric scintillation occurs in both the equatorial and polar regions of the Earth, the focus of this modeling effort is on equatorial scintillation. The ionospheric scintillation model is data-driven in a sense that scintillation observations are used to perform detection and characterization of scintillation structures. These structures are then propagated to future times using drift and decay models to represent the natural evolution of ionospheric scintillation. The impact on radio signals is also determined by the model and represented in graphical format to the user. A frequency scaling algorithm allows for impact analysis on frequencies other than the observation frequencies. The project began with lab-grade software and through a tailored Agile development process, deployed operational-grade code to a DoD operational center. The Agile development process promotes adaptive promote adaptive planning, evolutionary development, early delivery, continuous improvement, regular collaboration with the customer, and encourage rapid and flexible response to customer-driven changes. The Agile philosophy values individuals and interactions over processes and tools, working software over comprehensive documentation, customer collaboration over contract negotiation, and responding to change over following a rigid plan. The end result was an operational capability that met customer expectations. Details of the model and the process of

  3. Preliminar modelling of the chemical impact of possible TLEs on the lower ionosphere of Saturn

    Science.gov (United States)

    Gordillo-Vazquez, F. J.; Luque, A.; Dubrovin, D.; Yair, Y.; Price, C.

    2013-09-01

    Lightning on Saturn has been confirmed by radio [1] and optical signal observations [2]. On Earth, lightning activity is accompanied by a diversity of Transient Luminous Events (TLEs) above the thunder clouds in the stratosphere, where crawlers and blue jets take place, and in the mesosphere where elves, sprites, halos and giant blue jets occur. Optical emissions from TLEs are produced by electric breakdown in the mesosphere (50 - 90 km) due to the field generated by the electric charges accumulated in the trophospheric thunder clouds. The existence of powerful lightning on Saturn might produce, as on Earth, elves and other TLE phenomena in the lower ionosphere of Saturn [3]. We have developed a preliminar time-dependent kinetic model to account for the possible chemical disturbances of halo-like TLEs in the night-time mid-latitude H2/He atmosphere of Saturn. In particular, we have quantified the variation of electron and ion densities at different altitudes (650 - 1000 km) above the 1 bar level together with an estimation of the photon emissions associated to the radiative decays of some excited electronic levels of H2 like H2(d3Πu) responsible for the Fulcher bands in the blue optical range and H2(a3Σ+g) that radiatively decays producing ultraviolet blue continuum emission.

  4. PolarTREC—A Model Program for Taking Polar Literacy into the Future

    Science.gov (United States)

    Warburton, J.; Timm, K.; Larson, A. M.

    2009-12-01

    Polar TREC—Teachers and Researchers Exploring and Collaborating, is a three-year (2007-2009) NSF-funded International Polar Year (IPY) teacher professional development program that advances Science, Technology, Engineering, and Mathematics (STEM) education by improving teacher content knowledge and instructional practices through Teacher Research Experiences (TRE) in the Arctic and Antarctic. Leveraging profound changes and fascinating science taking place in the polar regions, PolarTREC broadly disseminates activities and products to students, educators, researchers, and the public, connecting them with the Arctic and Antarctica and sustaining the widespread interest in the polar regions and building on the enthusiasm that was generated through IPY. Central to the PolarTREC Teacher Research Experience Model, over 40 teachers have spent two to eight weeks participating in hands-on research in the polar regions and sharing their experiences with diverse audiences via live events, online multimedia journals, and interactive bulletin boards. The Connecting Arctic/Antarctic Researchers and Educators (CARE) Network unifies learning community members participants, alumni, and others, developing a sustainable association of education professionals networking to share and apply polar STEM content and pedagogical skills. Educator and student feedback from preliminary results of the program evaluation has shown that PolarTREC’s comprehensive program activities have many positive impacts on educators and their ability to teach science concepts and improve their teaching methods. Additionally, K-12 students polled in interest surveys showed significant changes in key areas including amount of time spent in school exploring research activities, importance of understanding science for future work, importance of understanding the polar regions as a person in today’s world, as well as increased self-reported knowledge and interest in numerous science content areas. Building

  5. Modeling transverse heating and outflow of ionospheric ions from the dayside cusp/cleft. 1 A parametric study

    Directory of Open Access Journals (Sweden)

    M. Bouhram

    2003-08-01

    Full Text Available The transport patterns of non-thermal H + and O + field-aligned flows from the dayside cusp/cleft, associated with transverse heating by means of wave-particle interactions and in combination with the poleward motion due to the magnetospheric convection are investigated. This has been accomplished by developing a steady-state, two-dimensional, trajectory-based code. The ion heating is modelled by means of a Monte Carlo technique, via the process of ion cyclotron resonance (ICR, with the electromagnetic left-hand circular polarized component of a broad-band, extremely low-frequency (BBELF turbulence. The altitude dependence of ICR heating from 1000 km to 3 Earth radii (RE is modelled by a power law spectrum, with an index a, and a parameter w0 that is proportional to the spectral density at a referenced gyrofrequency. Because of the finite latitudinal extent of the cusp/cleft, the incorporation of the horizontal convection drift leads to a maximum residence time tD of the ions when being energized. A large set of simulations has been computed so as to study the transport patterns of the H + and O + bulk parameters as a function of tD , a, and w0. Residence time effects are significant in O + density patterns while negligible for H +. When comparing the results with analytical one-dimensional theories (Chang et al., 1986; Crew et al., 1990, we find that mean ion energies and pitch angles at the poleward edge of the heating region are slightly influenced by tD and may be used as a probe of ICR parameters ( a, w0. Conversely, poleward of the heating region, upward velocity and mean energy dispersive patterns depend mainly on tD (e.g. the magnitude of the convection drift with latitudinal profiles varying versus tD . In short, the main conclusion of the paper is that any triplet (tD , a, w0 leads to a unique transport-pattern feature of ion flows associated with a cusp/cleft ionospheric source. In a companion paper, by using high-altitude (1.5–3 RE

  6. Exploring the Cigala/calibra Network Data Base for Ionosphere Monitoring Over Brazil

    Science.gov (United States)

    Vani, B. C.; Galera Monico, J. F.; Shimabukuro, M. H.; Pereira, V. A.; Aquino, M. H.

    2013-12-01

    The ionosphere in Brazil is strongly influenced by the equatorial anomaly, therefore GNSS based applications are widely affected by ionospheric disturbances. A network for continuous monitoring of the ionosphere has been deployed over its territory since February/2011, as part of the CIGALA and CALIBRA projects. Through CIGALA (Concept for Ionospheric Scintillation Mitigation for Professional GNSS in Latin America), which was funded by European Commission (EC) in the framework of the FP7-GALILEO-2009-GSA (European GNSS Agency), the first stations were deployed at Presidente Prudente, São Paulo state, in February 2011. CIGALA was finalized in February 2012 with eight stations distributed over the Brazilian territory. Through CALIBRA (Countering GNSS high Accuracy applications Limitations due to Ionospheric disturbances in BRAzil), which is also funded by the European Commission now in the framework of the FP7-GALILEO-2011-GSA, new stations are being deployed. Some of the stations are being specifically placed according to geomagnetic considerations aiming to support the development of a local scintillation and TEC model. CALIBRA started in November 2012 and will have two years of duration, focusing on the development of improved and new algorithms that can be applied to high accuracy GNSS techniques in order to tackle the effects of ionospheric disturbances. PolarRxS-PRO receivers, manufactured by Septentrio, have been deployed at all stations This multi-GNSS receiver can collect data at rates of up to 100 Hz, providing ionospheric TEC, scintillation parameters like S4 and Sigma-Phi, and other signal metrics like locktime for all satellites and frequencies tracked. All collected data (raw and ionosphere monitoring records) is stored at a central facility located at the Faculdade de Ciências e Tecnologia da Universidade Estadual Paulista (FCT/UNESP) in Presidente Prudente. To deal with the large amount of data, an analysis infrastructure has also been established

  7. Locally adapted NeQuick 2 model performance in European middle latitude ionosphere under different solar, geomagnetic and seasonal conditions

    Science.gov (United States)

    Vuković, Josip; Kos, Tomislav

    2017-10-01

    The ionosphere introduces positioning error in Global Navigation Satellite Systems (GNSS). There are several approaches for minimizing the error, with various levels of accuracy and different extents of coverage area. To model the state of the ionosphere in a region containing low number of reference GNSS stations, a locally adapted NeQuick 2 model can be used. Data ingestion updates the model with local level of ionization, enabling it to follow the observed changes of ionization levels. The NeQuick 2 model was adapted to local reference Total Electron Content (TEC) data using single station approach and evaluated using calibrated TEC data derived from 41 testing GNSS stations distributed around the data ingestion point. Its performance was observed in European middle latitudes in different ionospheric conditions of the period between 2011 and 2015. The modelling accuracy was evaluated in four azimuthal quadrants, with coverage radii calculated for three error thresholds: 12, 6 and 3 TEC Units (TECU). Diurnal radii change was observed for groups of days within periods of low and high solar activity and different seasons of the year. The statistical analysis was conducted on those groups of days, revealing trends in each of the groups, similarities between days within groups and the 95th percentile radii as a practically applicable measure of model performance. In almost all cases the modelling accuracy was better than 12 TECU, having the biggest radius from the data ingestion point. Modelling accuracy better than 6 TECU was achieved within reduced radius in all observed periods, while accuracy better than 3 TECU was reached only in summer. The calculated radii and interpolated error levels were presented on maps. That was especially useful in analyzing the model performance during the strongest geomagnetic storms of the observed period, with each of them having unique development and influence on model accuracy. Although some of the storms severely degraded the

  8. Real-Time Precise Point Positioning (RTPPP) with raw observations and its application in real-time regional ionospheric VTEC modeling

    Science.gov (United States)

    Liu, Teng; Zhang, Baocheng; Yuan, Yunbin; Li, Min

    2018-01-01

    Precise Point Positioning (PPP) is an absolute positioning technology mainly used in post data processing. With the continuously increasing demand for real-time high-precision applications in positioning, timing, retrieval of atmospheric parameters, etc., Real-Time PPP (RTPPP) and its applications have drawn more and more research attention in recent years. This study focuses on the models, algorithms and ionospheric applications of RTPPP on the basis of raw observations, in which high-precision slant ionospheric delays are estimated among others in real time. For this purpose, a robust processing strategy for multi-station RTPPP with raw observations has been proposed and realized, in which real-time data streams and State-Space-Representative (SSR) satellite orbit and clock corrections are used. With the RTPPP-derived slant ionospheric delays from a regional network, a real-time regional ionospheric Vertical Total Electron Content (VTEC) modeling method is proposed based on Adjusted Spherical Harmonic Functions and a Moving-Window Filter. SSR satellite orbit and clock corrections from different IGS analysis centers are evaluated. Ten globally distributed real-time stations are used to evaluate the positioning performances of the proposed RTPPP algorithms in both static and kinematic modes. RMS values of positioning errors in static/kinematic mode are 5.2/15.5, 4.7/17.4 and 12.8/46.6 mm, for north, east and up components, respectively. Real-time slant ionospheric delays from RTPPP are compared with those from the traditional Carrier-to-Code Leveling (CCL) method, in terms of function model, formal precision and between-receiver differences of short baseline. Results show that slant ionospheric delays from RTPPP are more precise and have a much better convergence performance than those from the CCL method in real-time processing. 30 real-time stations from the Asia-Pacific Reference Frame network are used to model the ionospheric VTECs over Australia in real time

  9. A simplified model of polar cap electric fields

    International Nuclear Information System (INIS)

    D'Angelo, N.

    1977-01-01

    A simple-minded 'model' is used in order to visualize the gross features of polar cap electric fields, in particular the 'diode' effect which had emerged already from earlier observations and the asymmetry between the electric fields observed on the dawn and dusk sides of the polar cap, which depends on Bsub(y)

  10. Faraday Rotation of Automatic Dependent Surveillance-Broadcast (ADS-B) Signals as a Method of Ionospheric Characterization

    Science.gov (United States)

    Cushley, A. C.; Kabin, K.; Noël, J.-M.

    2017-10-01

    Radio waves propagating through plasma in the Earth's ambient magnetic field experience Faraday rotation; the plane of the electric field of a linearly polarized wave changes as a function of the distance travelled through a plasma. Linearly polarized radio waves at 1090 MHz frequency are emitted by Automatic Dependent Surveillance Broadcast (ADS-B) devices that are installed on most commercial aircraft. These radio waves can be detected by satellites in low Earth orbits, and the change of the polarization angle caused by propagation through the terrestrial ionosphere can be measured. In this manuscript we discuss how these measurements can be used to characterize the ionospheric conditions. In the present study, we compute the amount of Faraday rotation from a prescribed total electron content value and two of the profile parameters of the NeQuick ionospheric model.

  11. Polar cap patches observed during the magnetic storm of November 2003: observations and modeling

    Directory of Open Access Journals (Sweden)

    C. E. Valladares

    2015-09-01

    Full Text Available We present multi-instrumented measurements and multi-technique analysis of polar cap patches observed early during the recovery phase of the major magnetic storm of 20 November 2003 to investigate the origin of the polar cap patches. During this event, the Qaanaaq imager observed elongated polar cap patches, some of which containing variable brightness; the Qaanaaq digisonde detected abrupt NmF2 fluctuations; the Sondrestrom incoherent scatter radar (ISR measured patches placed close to but poleward of the auroral oval–polar cap boundary; and the DMSP-F13 satellite intersected topside density enhancements, corroborating the presence of the patches seen by the imager, the digisonde, and the Sondrestrom ISR. A 2-D cross-correlation analysis was applied to series of two consecutive red-line images, indicating that the magnitude and direction of the patch velocities were in good agreement with the SuperDARN convection patterns. We applied a back-tracing analysis to the patch locations and found that most of the patches seen between 20:41 and 21:29 UT were likely transiting the throat region near 19:41 UT. Inspection of the SuperDARN velocities at this time indicates spatial and temporal collocation of a gap region between patches and large (1.7 km s−1 line-of-sight velocities. The variable airglow brightness of the patches observed between 20:33 and 20:43 UT was investigated using the numerical Global Theoretical Ionospheric Model (GTIM driven by the SuperDARN convection patterns and a variable upward/downward neutral wind. Our numerical results indicate that variations in the airglow intensity up to 265 R can be produced by a constant 70 m s−1 downward vertical wind.

  12. The combination of satellite observation techniques for sequential ionosphere VTEC modeling

    Science.gov (United States)

    Erdogan, Eren; Limberger, Marco; Schmidt, Michael; Seitz, Florian; Dettmering, Denise; Börger, Klaus; Brandert, Sylvia; Görres, Barbara; Kersten, Wilhelm F.; Bothmer, Volker; Hinrichs, Johannes; Venzmer, Malte; Mrotzek, Niclas

    2016-04-01

    The project OPTIMAP is a joint initiative by the Bundeswehr GeoInformation Centre (BGIC), the German Space Situational Awareness Centre (GSSAC), the German Geodetic Research Institute of the Technical University of Munich (DGFI-TUM) and the Institute for Astrophysics at the University of Göttingen (IAG). The main goal is to develop an operational tool for ionospheric mapping and prediction (OPTIMAP). A key feature of the project is the combination of different satellite observation techniques to improve the spatio-temporal data coverage and the sensitivity for selected target parameters. In the current status, information about the vertical total electron content (VTEC) is derived from the dual frequency signal processing of four techniques: (1) Terrestrial observations of GPS and GLONASS ensure the high-resolution coverage of continental regions, (2) the satellite altimetry mission Jason-2 is taken into account to provide VTEC in nadir direction along the satellite tracks over the oceans, (3) GPS radio occultations to Formosat-3/COSMIC are exploited for the retrieval of electron density profiles that are integrated to obtain VTEC and (4) Jason-2 carrier-phase observations tracked by the on-board DORIS receiver are processed to determine the relative VTEC. All measurements are sequentially pre-processed in hourly batches serving as input data of a Kalman filter (KF) for modeling the global VTEC distribution. The KF runs in a predictor-corrector mode allowing for the sequential processing of the measurements where update steps are performed with one-minute sampling in the current configuration. The spatial VTEC distribution is represented by B-spline series expansions, i.e., the corresponding B-spline series coefficients together with additional technique-dependent unknowns such as Differential Code Biases and Intersystem Biases are estimated by the KF. As a preliminary solution, the prediction model to propagate the filter state through time is defined by a random

  13. The Influence of Magnetosheath Beta and Ionospheric Conductivity in the Structure of the Lobes Near Solstice

    Science.gov (United States)

    Wilder, F. D.; Eriksson, S.; Wiltberger, M. J.

    2017-12-01

    The saturation of the cross-polar cap potential (CPCP) is an unexplained phenomenon in magnetosphere-ionosphere system science. In the present study, we expand upon the Alfvén Wing model of CPCP saturation by investigating its impact on the magnetosphere-ionosphere current system, particularly the cusp-mantle dynamo associated with lobe field lines. In this expansion of the Alfven wing model, the ability of open flux tubes to deform in response to the fluid stress from the magnetosheath is governed by the magnetosheath plasma beta, which in turn reduces the Maxwell stress imposed on the ionospheric plasma to accelerate it against ion-neutral collisional drag. We perform 32 simulations using the Lyon-Fedder-Mobarry (LFM) Magnetohydrodynamic (MHD) model with varying solar wind density and IMF strength, as well as a dipole tilt of 25 degrees to investigate the relative importance of both magnetosheath plasma beta and ionospheric conductivity in the formation of Alfvén wing-like structures and the saturation of the CPCP. We find that the plasma beta in the magnetosheath is different in each hemisphere and dependent on the stagnation point location. We also show that the lobes become more bent in the summer hemisphere with higher ionospheric conductivity. We find that higher ionospheric conductivity also makes the summer hemisphere lobes more sensitive to changes in the magnetosheath beta.

  14. Identifications of the polar cap boundary and the auroral belt in the high-altitude magnetosphere: a model for field-aligned currents

    International Nuclear Information System (INIS)

    Sugiura, M.

    1975-01-01

    By means of the Ogo 5 Goddard Space Flight Center fluxgate magnetometer data the polar cap boundary is identified in the high-altitude magnetosphere by a sudden transition from a dipolar field to a more taillike configuration. It is inferred that there exists a field-aligned-current layer at the polar cap boundary. In the night side magnetosphere the polar cap boundary is identified as the high-latitude boundary of the plasma sheet. The field-aligned current flows downward to the ionosphere on the morning side of the magnetosphere and upward from the ionosphere on the afternoon side. The basic pattern of the magnetic field variations observed during the satellite's traversal of the auroral belt is presented. Currents flow in opposite directions in the two field-aligned-current layers. The current directions in these layers as observed by Ogo 5 in the high-altitude magnetosphere are the same as those observed at low altitudes by the polar-orbiting Triad satellite (Armstrong and Zmuda, 1973). The magnetic field in the region where the lower-latitude field-aligned-current layer is situated is essentially meridional. A model is presented in which two field-aligned-current systems, one at the polar cap boundary and the other on the low-latitude part of the auroral belt, are main []y connected by ionospheric currents flowing across the auroral belt. The existence of field-aligned currents deduced from the Ogo 5 observations is a permanent feature of the magnetosphere. Intensifications of the field-aligned currents and occurrences of multiple pairs of field-aligned-current layers characterize the disturbed conditions of these regions

  15. Dayside ionosphere of Mars: Empirical model based on data from the MARSIS instrument

    Czech Academy of Sciences Publication Activity Database

    Němec, F.; Morgan, D. D.; Gurnett, D. A.; Duru, F.; Truhlík, Vladimír

    2011-01-01

    Roč. 116, - (2011), E07003/1-E07003/14 ISSN 0148-0227 Institutional research plan: CEZ:AV0Z30420517 Keywords : RADIO OCCULTATION MEASUREMENTS * GLOBAL SURVEYOR OBSERVATIONS * MARTIAN IONOSPHERE Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 3.021, year: 2011 http://www.agu.org/pubs/crossref/2011/2010JE003789.shtml

  16. Effective Solar Indices for Ionospheric Modeling: A Review and a Proposal for a Real-Time Regional IRI

    Science.gov (United States)

    Pignalberi, A.; Pezzopane, M.; Rizzi, R.; Galkin, I.

    2018-01-01

    The first part of this paper reviews methods using effective solar indices to update a background ionospheric model focusing on those employing the Kriging method to perform the spatial interpolation. Then, it proposes a method to update the International Reference Ionosphere (IRI) model through the assimilation of data collected by a European ionosonde network. The method, called International Reference Ionosphere UPdate (IRI UP), that can potentially operate in real time, is mathematically described and validated for the period 9-25 March 2015 (a time window including the well-known St. Patrick storm occurred on 17 March), using IRI and IRI Real Time Assimilative Model (IRTAM) models as the reference. It relies on foF2 and M(3000)F2 ionospheric characteristics, recorded routinely by a network of 12 European ionosonde stations, which are used to calculate for each station effective values of IRI indices IG_{12} and R_{12} (identified as IG_{{12{eff}}} and R_{{12{eff}}}); then, starting from this discrete dataset of values, two-dimensional (2D) maps of IG_{{12{eff}}} and R_{{12{eff}}} are generated through the universal Kriging method. Five variogram models are proposed and tested statistically to select the best performer for each effective index. Then, computed maps of IG_{{12{eff}}} and R_{{12{eff}}} are used in the IRI model to synthesize updated values of foF2 and hmF2. To evaluate the ability of the proposed method to reproduce rapid local changes that are common under disturbed conditions, quality metrics are calculated for two test stations whose measurements were not assimilated in IRI UP, Fairford (51.7°N, 1.5°W) and San Vito (40.6°N, 17.8°E), for IRI, IRI UP, and IRTAM models. The proposed method turns out to be very effective under highly disturbed conditions, with significant improvements of the foF2 representation and noticeable improvements of the hmF2 one. Important improvements have been verified also for quiet and moderately disturbed

  17. Role of the magnetospheric and ionospheric currents in the generation of the equatorial scintillations during geomagnetic storms

    Directory of Open Access Journals (Sweden)

    L. Z. Biktash

    2004-09-01

    Full Text Available The equatorial ionosphere parameters, Kp, Dst, AU and AL indices characterized contribution of different magnetospheric and ionospheric currents to the H-component of geomagnetic field are examined to test the geomagnetic activity effect on the generation of ionospheric irregularities producing VLF scintillations. According to the results of the current statistical studies, one can predict near 70% of scintillations from Aarons' criteria using the Dst index, which mainly depicts the magnetospheric ring current field. To amplify Aarons' criteria or to propose new criteria for predicting scintillation characteristics is the question. In the present phase of the experimental investigations of electron density irregularities in the ionosphere new ways are opened up because observations in the interaction between the solar wind - magnetosphere - ionosphere during magnetic storms have progressed greatly. According to present view, the intensity of the electric fields and currents at the polar regions, as well as the magnetospheric ring current intensity, are strongly dependent on the variations of the interplanetary magnetic field. The magnetospheric ring current cannot directly penetrate the equatorial ionosphere and because of this difficulties emerge in explaining its relation to scintillation activity. On the other hand, the equatorial scintillations can be observed in the absence of the magnetospheric ring current. It is shown that in addition to Aarons' criteria for the prediction of the ionospheric scintillations, models can be used to explain the relationship between the equatorial ionospheric parameters, h'F, foF2, and the equatorial geomagnetic variations with the polar ionosphere currents and the solar wind.

  18. Numerical modeling of ionospheric effects in the middle- and low-latitude F region during geomagnetic storm sequence of 9-14 September 2005

    Science.gov (United States)

    Klimenko, M. V.; Klimenko, V. V.; Ratovsky, K. G.; Goncharenko, L. P.; Sahai, Y.; Fagundes, P. R.; de Jesus, R.; de Abreu, A. J.; Vesnin, A. M.

    2011-06-01

    This study presents the Global Self-Consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) numerical simulations of the 9-14 September 2005 geomagnetic storm effects in the middle- and low-latitude ionosphere. Recent modifications to the GSM TIP model include adding an empirical model of high-energy electron precipitation and introducing a high-resolution (1 min) calculation of region 2 field-aligned currents and a cross-cap potential difference. These modifications resulted in better representation of such effects as penetration of the magnetospheric convection electric field to lower latitudes and the overshielding. The model also includes simulation of solar flare effects. Comparison of model results with observational data at Millstone Hill (42.6°N, 71.5°W, USA), Arecibo (18.3°N, 66.8°W, Puerto Rico), Jicamarca (11.9°S, 76.9°W, Peru), Palmas (10.2°S, 48.2°W, Brazil), and San Jose Campos (23.2°S, 45.9°W, Brazil) shows good agreement of ionospheric disturbances caused by this storm sequence. In this paper we consider in detail the formation mechanism of the additional layers in an equatorial ionosphere during geomagnetic storms. During geomagnetic storms, the nonuniform in height zonal electric field is generated at the geomagnetic equator. This electric field forms the additional layers in the F region of equatorial ionosphere.

  19. Infrared polar brightenings on Jupiter. V - A thermal equilibrium model for the north polar hot spot

    Science.gov (United States)

    Halthore, Rangasayi; Burrows, Adam; Caldwell, John

    1988-01-01

    Voyager IRIS instrument records of the IR hydrocarbon emissions from Jupiter's north polar region are presently studied to determine the spatial and other characteristics of the north polar hot spot. Attention is given to a thermal equilibrium model that exploits the asymmetry found in 7.8-micron emission of stratospheric methane with respect to system III longitude in order to estimate stratospheric zonal wind velocity. This model accurately predicts the observed asymmetry in acetylene's 13.6-micron emission; this requires, however, enhanced acetylene abundance in the hot spot, as well as ethane depletion. Energetic charged particles are suggested to be the most probable cause of these effects.

  20. A new ionospheric electron precipitation module coupled with RAM-SCB within the geospace general circulation model

    Science.gov (United States)

    Yu, Yiqun; Jordanova, Vania K.; Ridley, Aaron J.; Albert, Jay M.; Horne, Richard B.; Jeffery, Christopher A.

    2016-09-01

    Electron precipitation down to the atmosphere due to wave-particle scattering in the magnetosphere contributes significantly to the auroral ionospheric conductivity. In order to obtain the auroral conductivity in global MHD models that are incapable of capturing kinetic physics in the magnetosphere, MHD parameters are often used to estimate electron precipitation flux for the conductivity calculation. Such an MHD approach, however, lacks self-consistency in representing the magnetosphere-ionosphere coupling processes. In this study we improve the coupling processes in global models with a more physical method. We calculate the physics-based electron precipitation from the ring current and map it to the ionospheric altitude for solving the ionospheric electrodynamics. In particular, we use the BATS-R-US (Block Adaptive Tree Scheme-Roe type-Upstream) MHD model coupled with the kinetic ring current model RAM-SCB (Ring current-Atmosphere interaction Model with Self-Consistent Magnetic field (B)) that solves pitch angle-dependent electron distribution functions, to study the global circulation dynamics during the 25-26 January 2013 storm event. Since the electron precipitation loss is mostly governed by wave-particle resonant scattering in the magnetosphere, we further investigate two loss methods of specifying electron precipitation loss associated with wave-particle interactions: (1) using pitch angle diffusion coefficients Dαα(E,α) determined from the quasi-linear theory, with wave spectral and plasma density obtained from statistical observations (named as "diffusion coefficient method") and (2) using electron lifetimes τ(E) independent on pitch angles inferred from the above diffusion coefficients (named as "lifetime method"). We found that both loss methods demonstrate similar temporal evolution of the trapped ring current electrons, indicating that the impact of using different kinds of loss rates is small on the trapped electron population. However, for the

  1. Theoretical study of the seasonal behavior of the global ionosphere at solar maximum

    Science.gov (United States)

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

    1989-01-01

    The seasonal behavior of the global ionosphere was studied using a time-dependent three-dimensional physical model (developed by Shunk and his coworkers) of the ionosphere at altitudes between 120 and 800 km. This model accounts for field-aligned diffusion, cross-field electrodynamic drifts both the equatorial region and at high latitudes, interhemispheric flow, thermospheric winds, polar wind escape, energy-dependent chemical reactions, neutral composition changes, ion production due to solar EUV radiation and auroral precipitation, thermal conduction, diffusion-thermal heat flow, and local heating and cooling processes. The model studies were carried out for both June and December solstice conditions at solar maximum and for low geomagnetic activity. The ionospheric features predicted by the model agreed qualitatively with the available measurements.

  2. Beta Regression Finite Mixture Models of Polarization and Priming

    Science.gov (United States)

    Smithson, Michael; Merkle, Edgar C.; Verkuilen, Jay

    2011-01-01

    This paper describes the application of finite-mixture general linear models based on the beta distribution to modeling response styles, polarization, anchoring, and priming effects in probability judgments. These models, in turn, enhance our capacity for explicitly testing models and theories regarding the aforementioned phenomena. The mixture…

  3. Lower thermosphere coupling study: Comparison of observations with predictions of the University College London-Sheffield thermosphere-ionosphere model

    International Nuclear Information System (INIS)

    Fuller-Rowell, T.J.; Rees, D.; Parish, H.F.; Virdi, T.S.; Williams, P.J.S.; Johnson, R.M.

    1991-01-01

    During the first Lower Thermosphere Coupling Study (LTCS), September 21-25 1987, data were recorded from the incoherent scatter radar sites at EISCAT, Millstone Hill, Sondrestrom, and Arecibo. These experimental facilities measured ionospheric parameters (Ne, Te, Ti, and plasma velocity) in the E and the F regions which have been used to determine the E region neutral wind and infer the neutral temperature in the height range 100-150 km. Propagating tides are clearly visible in some of the parameters, and the latitude structure and phase variations with height indicate the presence of at least the (2,2) and (2,4) global tidal Hough modes. The influence of geomagnetic forcing is also clearly present at high latitudes. The University College London-Sheffield University three-dimensional coupled thermosphere-ionosphere model has been used to simulate this period of observation, by imposing tidal forcing at the lower boundary and magnetospheric forcing at high latitudes, in an attempt to interpret and understand the experimental data. Model simulations are able to predict where the signature of a particular tidal mode is likely to be observed in the respective responses of the temperature and wind structure. The numerical simulations predict the range of observed tidal amplitudes at mid and high latitudes, provided the tidal forcing functions imposed near the lower boundary of the model are larger (400 m geopotential height variation) than those inferred from linear tidal models

  4. FDTD Modeling of LEMP Propagation in the Earth-Ionosphere Waveguide With Emphasis on Realistic Representation of Lightning Source

    Science.gov (United States)

    Tran, Thang H.; Baba, Yoshihiro; Somu, Vijaya B.; Rakov, Vladimir A.

    2017-12-01

    The finite difference time domain (FDTD) method in the 2-D cylindrical coordinate system was used to compute the nearly full-frequency-bandwidth vertical electric field and azimuthal magnetic field waveforms produced on the ground surface by lightning return strokes. The lightning source was represented by the modified transmission-line model with linear current decay with height, which was implemented in the FDTD computations as an appropriate vertical phased-current-source array. The conductivity of atmosphere was assumed to increase exponentially with height, with different conductivity profiles being used for daytime and nighttime conditions. The fields were computed at distances ranging from 50 to 500 km. Sky waves (reflections from the ionosphere) were identified in computed waveforms and used for estimation of apparent ionospheric reflection heights. It was found that our model reproduces reasonably well the daytime electric field waveforms measured at different distances and simulated (using a more sophisticated propagation model) by Qin et al. (2017). Sensitivity of model predictions to changes in the parameters of atmospheric conductivity profile, as well as influences of the lightning source characteristics (current waveshape parameters, return-stroke speed, and channel length) and ground conductivity were examined.

  5. The electric wind of Venus: A global and persistent "polar wind"-like ambipolar electric field sufficient for the direct escape of heavy ionospheric ions

    Science.gov (United States)

    Collinson, Glyn A.; Frahm, Rudy A.; Glocer, Alex; Coates, Andrew J.; Grebowsky, Joseph M.; Barabash, Stas; Domagal-Goldman, Shawn D.; Fedorov, Andrei; Futaana, Yoshifumi; Gilbert, Lin K.; Khazanov, George; Nordheim, Tom A.; Mitchell, David; Moore, Thomas E.; Peterson, William K.; Winningham, John D.; Zhang, Tielong L.

    2016-06-01

    Understanding what processes govern atmospheric escape and the loss of planetary water is of paramount importance for understanding how life in the universe can exist. One mechanism thought to be important at all planets is an "ambipolar" electric field that helps ions overcome gravity. We report the discovery and first quantitative extraterrestrial measurements of such a field at the planet Venus. Unexpectedly, despite comparable gravity, we show the field to be five times stronger than in Earth's similar ionosphere. Contrary to our understanding, Venus would still lose heavy ions (including oxygen and all water-group species) to space, even if there were no stripping by the solar wind. We therefore find that it is possible for planets to lose heavy ions to space entirely through electric forces in their ionospheres and such an "electric wind" must be considered when studying the evolution and potential habitability of any planet in any star system.

  6. The Electric Wind of Venus: A global and persistent "polar wind" like ambipolar electric field sufficient for the direct escape of heavy ionospheric ions

    Science.gov (United States)

    Collinson, G.; Frahm, R.; Glocer, A.; Coates, A. J.; Grebowsky, J. M.; Barbash, S.; Fedorov, A.; Futaana, Y.; Gilbert, L.; Khazanov, G. V.; Domagal-Goldman, S. D.; Nordheim, T.; Mitchell, D. L.; Moore, T. E.; Peterson, W.; Winningham, D.; Zhang, T.

    2016-12-01

    Understanding what processes govern atmospheric escape and the loss of planetary water is of paramount importance for understanding how life in the universe can exist. One mechanism thought to be important at all planets is an "ambipolar" electric field that helps ions overcome gravity. We report the discovery and first quantitative extraterrestrial measurements of such a field at the planet Venus. Unexpectedly, despite comparable gravity, we show the field to be five times stronger than in Earth's similar ionosphere. Contrary to our understanding, Venus would still lose heavy ions (including oxygen and all water-group species) to space, even if there were no stripping by the solar wind. We therefore find it is possible for planets to lose heavy ions to space entirely through electric forces in their ionospheres, and such an "electric wind" must be considered when studying the evolution and potential habitability of any planet in any star system

  7. The Electric Wind of Venus: A Global and Persistent Polar Wind -Like Ambipolar Electric Field Sufficient for the Direct Escape of Heavy Ionospheric Ions

    Science.gov (United States)

    Collinson, Glyn A.; Frahm, Rudy A.; Glocer, Alex; Coates, Andrew J.; Grebowsky, Joseph M.; Barabash, Stas; Domagal-Goldman, Shawn D.; Federov, Andrei; Futaana, Yoshifumi; Gilbert, Lin K.; hide

    2016-01-01

    Understanding what processes govern atmospheric escape and the loss of planetary water is of paramount importance for understanding how life in the universe can exist. One mechanism thought to be important at all planets is an ambipolar electric field that helps ions overcome gravity. We report the discovery and first quantitative extraterrestrial measurements of such a field at the planet Venus. Unexpectedly, despite comparable gravity, we show the field to be five times stronger than in Earths similar ionosphere. Contrary to our understanding, Venus would still lose heavy ions (including oxygen and all water-group species) to space, even if there were no stripping by the solar wind. We therefore find that it is possible for planets to lose heavy ions to space entirely through electric forces in their ionospheres and such an electric wind must be considered when studying the evolution and potential habitability of any planet in any star system.

  8. Developing an ionospheric map for South Africa

    Directory of Open Access Journals (Sweden)

    D. I. Okoh

    2010-07-01

    Full Text Available The development of a map of the ionosphere over South Africa is presented in this paper. The International Reference Ionosphere (IRI model, South African Bottomside Ionospheric Model (SABIM, and measurements from ionosondes in the South African Ionosonde Network, were combined within their own limitations to develop an accurate representation of the South African ionosphere. The map is essentially in the form of a computer program that shows spatial and temporal representations of the South African ionosphere for a given set of geophysical parameters. A validation of the map is attempted using a comparison of Total Electron Content (TEC values derived from the map, from the IRI model, and from Global Positioning System (GPS measurements. It is foreseen that the final South African ionospheric map will be implemented as a Space Weather product of the African Space Weather Regional Warning Centre.

  9. Application of a global magnetospheric-ionospheric current model for dayside and terminator Pi2 pulsations

    Science.gov (United States)

    Imajo, S.; Yoshikawa, A.; Uozumi, T.; Ohtani, S.; Nakamizo, A.; Chi, P. J.

    2017-12-01

    Pi2 magnetic oscillations on the dayside are considered to be produced by the ionospheric current that is driven by Pi2-associated electric fields from the high-latitude region, but this idea has not been quantitatively tested. The present study numerically tested the magnetospheric-ionospheric current system for Pi2 consisting of field-aligned currents (FACs) localized in the nightside auroral region, the perpendicular magnetospheric current flowing in the azimuthal direction, and horizontal ionospheric currents driven by the FACs. We calculated the spatial distribution of the ground magnetic field produced by these currents using the Biot-Savart law in a stationary state. The calculated magnetic field reproduced the observational features reported by previous studies; (1) the sense of the H component does not change a wide range of local time sectors at low latitudes; (2) the amplitude of the H component on the dayside is enhanced at the equator; (3) The D component reverses its phase near the dawn and dusk terminators; (4) the meridian of the D-component phase reversal near the dusk terminator is shifted more sunward than that near the dawn terminator; (5) the amplitude of the D component in the morning is larger than that in the early evening. We also derived the global distributions of observed equivalent currents for two Pi2 events. The spatial patterns of dayside equivalent currents were similar to the spatial pattern of numerically derived equivalent currents. The results indicate that the oscillation of the magnetospheric-ionospheric current system is a plausible explanation of Pi2s on the dayside and near the terminator. These results are included in an accepted paper by Imajo et al. [2017JGR, DOI: 10.1002/2017JA024246].

  10. The effect of magnetospheric erosion on mid- and high-latitude ionospheric flows

    International Nuclear Information System (INIS)

    Freeman, M.P.; Southwood, D.J.

    1988-01-01

    We describe simple quasi-global models of ionospheric flow with the aim of elucidating the potential signatures of magnetopause erosion and allied phenomena at ionospheric heights. Erosion implies the addition of flux to the polar cap and consequently a reduction in the latitude of the polar cap boundary. We consider here the possibility of localized erosion over part of the dayside. Systematic turning of the mid-latitude flow can result to the West and East of the erosion region. After erosion, the boundary must eventually return poleward as stress is released on the nightside. We examine the pattern associated with polar cap boundary reconfiguration. This can give rise to substantial equatorward and tailward flows on closed field lines. We conclude by showing data from the SABRE radar system during a period in which spacecraft measurements have shown erosion is occurring. Various features shown in our models are seen. (author)

  11. Ionospheric forecasting model using fuzzy logic-based gradient descent method

    Directory of Open Access Journals (Sweden)

    D. Venkata Ratnam

    2017-09-01

    Full Text Available Space weather phenomena cause satellite to ground or satellite to aircraft transmission outages over the VHF to L-band frequency range, particularly in the low latitude region. Global Positioning System (GPS is primarily susceptible to this form of space weather. Faulty GPS signals are attributed to ionospheric error, which is a function of Total Electron Content (TEC. Importantly, precise forecasts of space weather conditions and appropriate hazard observant cautions required for ionospheric space weather observations are limited. In this paper, a fuzzy logic-based gradient descent method has been proposed to forecast the ionospheric TEC values. In this technique, membership functions have been tuned based on the gradient descent estimated values. The proposed algorithm has been tested with the TEC data of two geomagnetic storms in the low latitude station of KL University, Guntur, India (16.44°N, 80.62°E. It has been found that the gradient descent method performs well and the predicted TEC values are close to the original TEC measurements.

  12. Ionospheric correction for spaceborne single-frequency GPS based ...

    Indian Academy of Sciences (India)

    1972a, b) and. International Reference Ionosphere (IRI) model. (Rawer et al. 1978; Bilitza 1986, 2001; Bilitza and .... studies need to be done on the Klobuchar model for GPS onboard GRACE. SLM mapping functions for ... The concept of the ionospheric single layer model. (SLM) is usually used in ionosphere research, i.e.,.

  13. Effects of electrojet turbulence on a magnetosphere-ionosphere simulation of a geomagnetic storm

    Science.gov (United States)

    Wiltberger, M.; Merkin, V.; Zhang, B.; Toffoletto, F.; Oppenheim, M.; Wang, W.; Lyon, J. G.; Liu, J.; Dimant, Y.; Sitnov, M. I.; Stephens, G. K.

    2017-05-01

    Ionospheric conductance plays an important role in regulating the response of the magnetosphere-ionosphere system to solar wind driving. Typically, models of magnetosphere-ionosphere coupling include changes to ionospheric conductance driven by extreme ultraviolet ionization and electron precipitation. This paper shows that effects driven by the Farley-Buneman instability can also create significant enhancements in the ionospheric conductance, with substantial impacts on geospace. We have implemented a method of including electrojet turbulence (ET) effects into the ionospheric conductance model utilized within geospace simulations. Our particular implementation is tested with simulations of the Lyon-Fedder-Mobarry global magnetosphere model coupled with the Rice Convection Model of the inner magnetosphere. We examine the impact of including ET-modified conductances in a case study of the geomagnetic storm of 17 March 2013. Simulations with ET show a 13% reduction in the cross polar cap potential at the beginning of the storm and up to 20% increases in the Pedersen and Hall conductance. These simulation results show better agreement with Defense Meteorological Satellite Program observations, including capturing features of subauroral polarization streams. The field-aligned current (FAC) patterns show little differences during the peak of storm and agree well with Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) reconstructions. Typically, the simulated FAC densities are stronger and at slightly higher latitudes than shown by AMPERE. The inner magnetospheric pressures derived from Tsyganenko-Sitnov empirical magnetic field model show that the inclusion of the ET effects increases the peak pressure and brings the results into better agreement with the empirical model.

  14. Modeling transverse heating and outflow of ionospheric ions from the dayside cusp/cleft. 1 A parametric study

    Directory of Open Access Journals (Sweden)

    M. Bouhram

    Full Text Available The transport patterns of non-thermal H + and O + field-aligned flows from the dayside cusp/cleft, associated with transverse heating by means of wave-particle interactions and in combination with the poleward motion due to the magnetospheric convection are investigated. This has been accomplished by developing a steady-state, two-dimensional, trajectory-based code. The ion heating is modelled by means of a Monte Carlo technique, via the process of ion cyclotron resonance (ICR, with the electromagnetic left-hand circular polarized component of a broad-band, extremely low-frequency (BBELF turbulence. The altitude dependence of ICR heating from 1000 km to 3 Earth radii (RE is modelled by a power law spectrum, with an index a, and a parameter w0 that is proportional to the spectral density at a referenced gyrofrequency. Because of the finite latitudinal extent of the cusp/cleft, the incorporation of the horizontal convection drift leads to a maximum residence time tD of the ions when being energized. A large set of simulations has been computed so as to study the transport patterns of the H + and O + bulk parameters as a function of tD , a, and w0. Residence time effects are significant in O + density patterns while negligible for H +. When comparing the results with analytical one-dimensional theories (Chang et al., 1986; Crew et al., 1990, we find that mean ion energies and pitch angles at the poleward edge of the heating region are slightly influenced by tD and may be used as a probe of ICR parameters ( a, w0. Conversely, poleward of the heating region, upward velocity and mean energy dispersive patterns depend mainly on tD (e.g. the magnitude of the convection drift with latitudinal profiles varying versus

  15. Observations that polar climate modelers use and want

    Science.gov (United States)

    Kay, J. E.; de Boer, G.; Hunke, E. C.; Bailey, D. A.; Schneider, D. P.

    2012-12-01

    Observations are essential for motivating and establishing improvement in the representation of polar processes within climate models. We believe that explicitly documenting the current methods used to develop and evaluate climate models with observations will help inform and improve collaborations between the observational and climate modeling communities. As such, we will present the current strategy of the Polar Climate Working Group (PCWG) to evaluate polar processes within Community Earth System Model (CESM) using observations. Our presentation will focus primarily on PCWG evaluation of atmospheric, sea ice, and surface oceanic processes. In the future, we hope to expand to include land surface, deep ocean, and biogeochemical observations. We hope our presentation, and a related working document developed by the PCWG (https://docs.google.com/document/d/1zt0xParsFeMYhlihfxVJhS3D5nEcKb8A41JH0G1Ic-E/edit) inspires new and useful interactions that lead to improved climate model representation of polar processes relevant to polar climate.

  16. A model of quasi-free scattering with polarized protons

    International Nuclear Information System (INIS)

    Teodoro, M.R.

    1976-01-01

    A quantitative evaluation, based on a simple model for spin-free coplanar and asymmetric reaction in 16 O, for 215 MeV incoming polarized protons confirms the use of the strong effective polarization of the knocked-out proton by the spin-orbit coupling and of the strong dependence of free, medium energy, proton-proton cross section on the relative orientation of the proton spins. Effective polarizations, momentum distributions and correlation cross sections have been calculated for the 1p sub(1/2), 1 p sub(3/2) and 1s sub(1/2) states in 16 O, using protons totally polarized orthogonal to the scattering plane. Harmonic oscillator and square wells have been used to generate the bound state wave functions, whereas the optical potentials have been taken spin-independent and purely imaginary [pt

  17. Modeling of nonlinear responses for reciprocal transducers involving polarization switching

    DEFF Research Database (Denmark)

    Willatzen, Morten; Wang, Linxiang

    2007-01-01

    Nonlinearities and hysteresis effects in a reciprocal PZT transducer are examined by use of a dynamical mathematical model on the basis of phase-transition theory. In particular, we consider the perovskite piezoelectric ceramic in which the polarization process in the material can be modeled...... by Landau theory for the first-order phase transformation, in which each polarization state is associated with a minimum of the Landau free-energy function. Nonlinear constitutive laws are obtained by using thermodynamical equilibrium conditions, and hysteretic behavior of the material can be modeled...

  18. Observation and Modeling of Storm Generated Acoustic Waves in the Ionosphere Revealed in a Dense Network of GPS Receivers

    Science.gov (United States)

    Walterscheid, R. L.; Azeem, S. I.

    2017-12-01

    Acoustic waves generated in the lower atmosphere may become an important source of variably in the upper atmosphere. Although they are excited with small amplitudes they are minimally subject to viscous dissipation and may reach significant amplitudes at F-region altitudes. A number of studies in the 1970s showed clear signatures in ionosonde data in the infrasonic period range attributable to thunder storm activity. We have examined Total Electron Content data from a dense network of over 4000 ground-based GPS receivers over the continental United States during an outbreak of severe weather, including tornados, over Kansas in May 2015. A sequence of GPS TEC images showed clear Traveling Ionospheric Disturbances (TIDs) in the form of concentric rings moving outward from the center of the storm region. The characteristics of the disturbance (phase speed and frequency) were consistent with acoustic waves in the infrasonic range. We have modeled the disturbance by including a tropospheric heat source representing latent heat release from a large thunderstorm. The disturbance at ionospheric altitudes resembles the observed disturbance in terms of phase speed, frequency and horizontal wavelength. We conclude that the observed TIDs in TEC were caused by an acoustic wave generated by deep convection.

  19. Uncertainty analysis in Titan ionospheric simulated ion mass spectra: unveiling a set of issues for models accuracy improvement

    Science.gov (United States)

    Hébrard, Eric; Carrasco, Nathalie; Dobrijevic, Michel; Pernot, Pascal

    Ion Neutral Mass Spectrometer (INMS) aboard Cassini revealed a rich coupled ion-neutral chemistry in the ionosphere, producing heavy hydrocarbons and nitriles ions. The modeling of such a complex environment is challenging, as it requires a detailed and accurate description of the different relevant processes such as photodissociation cross sections and neutral-neutral reaction rates on one hand, and ionisation cross sections, ion-molecule and recombination reaction rates on the other hand. Underpinning models calculations, each of these processes is parameterized by kinetic constants which, when known, have been studied experimentally and/or theoretically over a range of temperatures and pressures that are most often not representative of Titan's atmosphere. The sizeable experimental and theoretical uncertainties reported in the literature merge therefore with the uncertainties resulting subsequently from the unavoidable estimations or extrapolations to Titan's atmosphere conditions. Such large overall uncertainties have to be accounted for in all resulting inferences most of all to evaluate the quality of the model definition. We have undertaken a systematic study of the uncertainty sources in the simulation of ion mass spectra as recorded by Cassini/INMS in Titan ionosphere during the T5 flyby at 1200 km. Our simulated spectra seem much less affected by the uncertainties on ion-molecule reactions than on neutral-neutral reactions. Photochemical models of Titan's atmosphere are indeed so poorly predictive at high altitudes, in the sense that their computed predictions display such large uncertainties, that we found them to give rise to bimodal and hypersensitive abundance distributions for some major compounds like acetylene C2 H2 and ethylene C2 H4 . We will show to what extent global uncertainty and sensitivity analysis enabled us to identify the causes of this bimodality and to pinpoint the key processes that mostly contribute to limit the accuracy of the

  20. RESULTS OF THE SHORT COMPARATIVE ANALYSIS OF MATHEMATICAL MODELS OF INFLUENCE OF THE IONOSPHERE OF THE EARTH ON ULTRA BROADBAND SIGNALS X-RANGE

    Directory of Open Access Journals (Sweden)

    M. M. Kasperovich

    2015-01-01

    Full Text Available For range portrait formation at usage ultrabroadband linearly frequency-modulated signal in radar it is necessary to consider all distortions of an electromagnetic wave on a radio route. At observation over circumterraneousobjects the signal transits through an ionosphere. The electromagnetic wave in it will be exposed to non-linearity distortions, which transform of signal time structure. It leads to distance error origin. For its compensating it is necessary to use the mathematical model of signal distortions in an ionosphere.

  1. The worldwide ionospheric data base

    Science.gov (United States)

    Bilitza, Dieter

    1989-01-01

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

  2. The thermospheric effects of a rapid polar cap expansion

    Directory of Open Access Journals (Sweden)

    D. W. Idenden

    Full Text Available In a previous publication we used results from a coupled thermosphere-ionosphere-plasmasphere model to illustrate a new mechanism for the formation of a large-scale patch of ionisation arising from a rapid polar cap expansion. Here we describe the thermospheric response to that polar cap expansion, and to the ionospheric structure produced. The response is dominated by the energy and momentum input at the dayside throat during the expansion phase itself. These inputs give rise to a large-scale travelling atmospheric disturbance (TAD that propagates both antisunward across the polar cap and equatorward at speeds much greater than both the ion drifts and the neutral winds. We concentrate only on the initially poleward travelling disturbance. The disturbance is manifested in the neutral temperature and wind fields, the height of the pressure level surfaces and in the neutral density at fixed heights. The thermospheric effects caused by the ionospheric structure produced during the expansion are hard to discern due to the dominating effects of the TAD.

    Key words. Ionosphere (ionosphere · atmosphere interaction; modeling and forecasting; plasma convection.

  3. The thermospheric effects of a rapid polar cap expansion

    Directory of Open Access Journals (Sweden)

    D. W. Idenden

    1998-10-01

    Full Text Available In a previous publication we used results from a coupled thermosphere-ionosphere-plasmasphere model to illustrate a new mechanism for the formation of a large-scale patch of ionisation arising from a rapid polar cap expansion. Here we describe the thermospheric response to that polar cap expansion, and to the ionospheric structure produced. The response is dominated by the energy and momentum input at the dayside throat during the expansion phase itself. These inputs give rise to a large-scale travelling atmospheric disturbance (TAD that propagates both antisunward across the polar cap and equatorward at speeds much greater than both the ion drifts and the neutral winds. We concentrate only on the initially poleward travelling disturbance. The disturbance is manifested in the neutral temperature and wind fields, the height of the pressure level surfaces and in the neutral density at fixed heights. The thermospheric effects caused by the ionospheric structure produced during the expansion are hard to discern due to the dominating effects of the TAD.Key words. Ionosphere (ionosphere · atmosphere interaction; modeling and forecasting; plasma convection.

  4. Correcting ionospheric Faraday rotation for ASKAP

    Science.gov (United States)

    O'Sullivan, Shane; Gaensler, Bryan; Landecker, Tom L.; Willis, Tony

    2012-10-01

    Next-generation polarisation surveys, such as the POSSUM survey on ASKAP, aim to measure weak, statistical, cosmological effects associated with weak magnetic fields, and so will require unprecedented accuracy and stability for measuring polarisation vectors and their Faraday rotation measures (RMs). Ionospheric Faraday rotation (IFR) corrupts polarization observations and cannot be ignored at mid to low frequencies. In aperture-synthesis polarimetry IFR rotates individual visibilities and leads to a loss of coherence and accuracy of polarization angle determination. Through the POSSUM survey science team we have been involved in developing detailed ionospheric prediction software (POSSUM memos #10a,b) that will be used to correct the observed visibilities on ASKAP before imaging to obtain sufficiently accurate polarization and RM data. To provide a stringent test of this software, we propose a continuous 24 hr observing block using the 1.1-3.1 GHz band to monitor the variations caused by the time-variable ionosphere in the polarization angle and RM of a strongly polarized calibrator source, PKS B1903-802. We request a total of 96 hrs (4 x 24 hrs) to monitor the changes in the ionosphere every 3 to 6 months until BETA/ASKAP-12 is taking reliable polarization data.

  5. Modeling the ionosphere-thermosphere response to a geomagnetic storm using physics-based magnetospheric energy input: OpenGGCM-CTIM results

    Directory of Open Access Journals (Sweden)

    Connor Hyunju Kim

    2016-01-01

    Full Text Available The magnetosphere is a major source of energy for the Earth’s ionosphere and thermosphere (IT system. Current IT models drive the upper atmosphere using empirically calculated magnetospheric energy input. Thus, they do not sufficiently capture the storm-time dynamics, particularly at high latitudes. To improve the prediction capability of IT models, a physics-based magnetospheric input is necessary. Here, we use the Open Global General Circulation Model (OpenGGCM coupled with the Coupled Thermosphere Ionosphere Model (CTIM. OpenGGCM calculates a three-dimensional global magnetosphere and a two-dimensional high-latitude ionosphere by solving resistive magnetohydrodynamic (MHD equations with solar wind input. CTIM calculates a global thermosphere and a high-latitude ionosphere in three dimensions using realistic magnetospheric inputs from the OpenGGCM. We investigate whether the coupled model improves the storm-time IT responses by simulating a geomagnetic storm that is preceded by a strong solar wind pressure front on August 24, 2005. We compare the OpenGGCM-CTIM results with low-earth-orbit satellite observations and with the model results of Coupled Thermosphere-Ionosphere-Plasmasphere electrodynamics (CTIPe. CTIPe is an up-to-date version of CTIM that incorporates more IT dynamics such as a low-latitude ionosphere and a plasmasphere, but uses empirical magnetospheric input. OpenGGCM-CTIM reproduces localized neutral density peaks at ~ 400 km altitude in the high-latitude dayside regions in agreement with in situ observations during the pressure shock and the early phase of the storm. Although CTIPe is in some sense a much superior model than CTIM, it misses these localized enhancements. Unlike the CTIPe empirical input models, OpenGGCM-CTIM more faithfully produces localized increases of both auroral precipitation and ionospheric electric fields near the high-latitude dayside region after the pressure shock and after the storm onset

  6. Erratum: Correction to: Effective Solar Indices for Ionospheric Modeling: A Review and a Proposal for a Real-Time Regional IRI

    Science.gov (United States)

    Pignalberi, A.; Pezzopane, M.; Rizzi, R.; Galkin, I.

    2018-01-01

    The sentence that reads as "It has been demonstrated…very disturbed periods." should read as "It has been demonstrated (Mirò Amarante et al. 2007) that the ionosphere shows small scale variations that global or regional empirical models describe hardly, especially for very disturbed periods."

  7. Space weather effects on lower ionosphere: First investigation from Bharati station during 34th Indian scientific expedition to Antarctica

    Science.gov (United States)

    Guha, Anirban; Saha, Kumarjit; De, Barin Kumar; Subrahmanyam, Kandula Venkata; Shreedevi, P. R.

    2017-04-01

    We investigate the solar flare effects on the D-region of the ionosphere with the help of VLF (Very Low Frequency) radio waves using a portable E-field system from Antarctica during the summer period of 34th Indian scientific expedition. Two GPS time synchronized VLF receivers, one located at Bharati, Antarctica (geographical latitude 69.40°S, longitude 76.18°E) and another located at Tripura, India (geographical latitude 23.84°N, longitude 91.28°E) were operated simultaneously to infer common mode changes in the lower ionosphere for a number of solar flares events. The two systems constantly monitored the carrier amplitude and phase of the MSK (Minimum Shift Keying) modulated navy transmitter located in Australia (Callsign: NWC, 19.8 kHz, geographical latitude 21.88°S, longitude 114.13°E), around 5.6 Mm great circle distance from the two receivers. The results are interpreted in terms of Earth-ionosphere wave-guide characteristics. A Long Wave Propagation Capability (LWPC) model study is also performed to infer the changes in the daytime electron density in polar D-region ionosphere during the solar flares. The exponential fit of the modeled electron density change with average X-ray flux change shows an excellent correlation (R2 value 0.95). The exponential fit is utilized to infer the daytime electron density change in the polar ionosphere during solar flare events. The analyses indicate that small solar flares of class 'C' can be very effectively detected with the portable antenna system even if the receiver is located in polar coastal region compared to equatorial region. The expedition results also demonstrate the feasibility of using portable VLF receivers from the coastal stations for monitoring the polar lower ionosphere from Antarctica and open up new opportunities for long term exploration.

  8. Assessing models for ionospheric weather specifications over Australia during the 2004 Climate and Weather of the Sun-Earth-System (CAWSES) campaign

    Science.gov (United States)

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

    2007-09-01

    The Utah State University (USU) Global Assimilation of Ionospheric Measurements (GAIM) program is developing assimilation models to specify ionospheric weather. In this study the Gauss Markov Kalman Filter (GMKF) GAIM model was used. The period 20 March through 19 April 2004, which spanned the Climate and Weather of the Sun-Earth-System (CAWSES) first study period, has been extensively studied to validate the performance of the GAIM model. Although the USU-GAIM model has both regional and global capabilities and can assimilate data from a wide variety of ionospheric observations, for this study the GMKF model was run in a global mode using data only from 162 ground-based GPS slant total electron content (TEC) stations and in situ measurements from three satellites. Using measurements from the 11 ionosonde stations of the Australian Department of Defence sounder network as an independent bottomside ground-truth, the International Reference Ionosphere (IRI), Ionospheric Forecast Model (IFM), and GMKF were compared for (1) monthly mean climatology and (2) the day-to-day weather during the 31 day period. A skill score was developed for the day-to-day weather by defining the IRI as the reference model. IFM is found to be a 10% improvement, while the GMKF is 39% more capable to capture weather variability. However, the study also identifies that this global version of GMKF has difficulty around sunrise, during which time the GMKF performance can be poorer than IRI. Excluding this interval from the skill score analysis increases the GMKF ability to track weather to 48%. The use of more data and different data types should further increase the GMKF's ability to capture weather variations.

  9. Effects of geomagnetic storm on low latitude ionospheric total ...

    Indian Academy of Sciences (India)

    netospheric polar cap region causes a disturbance in geomagnetic field. As a result of this distur- bance, the energy inputs from the magnetosphere to the upper atmosphere can cause a dramatic change in electron density of the F region of the ionosphere. Geomagnetic storms produce large and. Keywords. Ionospheric ...

  10. X-Parameter Based Modelling of Polar Modulated Power Amplifiers

    DEFF Research Database (Denmark)

    Wang, Yelin; Nielsen, Troels Studsgaard; Sira, Daniel

    2013-01-01

    X-parameters are developed as an extension of S-parameters capable of modelling non-linear devices driven by large signals. They are suitable for devices having only radio frequency (RF) and DC ports. In a polar power amplifier (PA), phase and envelope of the input modulated signal are applied...... at separate ports and the envelope port is neither an RF nor a DC port. As a result, X-parameters may fail to characterise the effect of the envelope port excitation and consequently the polar PA. This study introduces a solution to the problem for a commercial polar PA. In this solution, the RF-phase path...... PA for simulations. The simulated error vector magnitude (EVM) and adjacent channel power ratio (ACPR) were compared with the measured data to validate the model. The maximum differences between the simulated and measured EVM and ACPR are less than 2% point and 3 dB, respectively....

  11. Magnetospheric Dynamical and Morphological Response to Multi-species Plasma Supply From the Ionosphere:New Comprehensive 3D PIC Simulation.

    Science.gov (United States)

    Baraka, S. M.; Ben-Jaffel, L.

    2015-12-01

    The outflow of thermal plasma from the high latitude ionosphere to the magnetosphere (polar wind) has been under investigation using observations and statistical studies for four decades in the altitude range from 1000km to ~ 10 Re, yet we are still missing a global and consistent three-dimensional time-dependent picture of the wind system at the interface between the ionosphere and the magnetosphere. Several questions remain unanswered, such as: I) How the ionospheric ions plasma impact the global structure of the magnetosphere. II) What are the energisation processes of that plasma and where they operate (plasma sheet, ring currents). III) What fraction of the supplied plasma returns to the ionosphere and with what properties after a journey in the magnetosphere; etc. Here, we use a spherical symmetric ionospheric model (International reference ionosphere IRI-2007) that we merge with 3D PIC EM Global code to simulate Magnetosphere-ionosphere coupling. Our aim is to investigate the time-dependent content and dynamics of the 3D magnetosphere in response to thermal ions plasma supply from the ionosphere. Following a comprehensive approach, in this first step, we do not consider chemical reactions nor any feedback from the magnetosphere into the ionosphere. Our newly developed 3D PIC model has a finer grid size (0.1-0.2 RE), a H+ to electron mass ratio of up to 100, includes Earth gravity and tilt of the dipole field. Most importantly, the new tool has the capability to consider distinct species with different masses and charges and to follow them in time separately in the simulation box. We present our first results for the content and dynamics of the magnetosphere following H+ and O+ supply from the ionosphere in the conditions of northern IMF of the solar wind.

  12. Data-driven local-scale modeling of ionospheric responses to auroral forcing using incoherent scatter radar and ground-based imaging measurements

    Science.gov (United States)

    Grubbs, G. A., II; Zettergren, M. D.; Samara, M.; Michell, R.; Hampton, D. L.; Lynch, K. A.; Varney, R. H.; Reimer, A.; Burleigh, M.

    2017-12-01

    The aurora encapsulates a wide range of spatial and temporal scale sizes, particularly during active events such as those that exist during substorm expansion. Of interest to the present work are ionospheric responses to magnetospheric forcing at relatively small scales (0.5-20 km), including formation of structured auroral arc current systems, ion frictional heating, upflow, and density cavity formation among other processes. Even for carefully arranged experiments, it is often difficult to fully assess physical details (time evolution, causality, unobservable parameters) associated with these types of responses, thus highlighting the general need for high-resolution modeling efforts to support the observations. In this work, we develop and test a local-scale model to describe effects of precipitating electrons and electric fields on the ionospheric plasma responses using available remote sensing data (e.g. from ISRs and filtered cameras). Our model is based on a 3D multi-fluid/electrostatic ionospheric model, GEMINI (Zettergren et al., 2015), coupled a two-stream electron transport code which produces auroral intensities, impact ionization, and thermal electron heating GLobal airglOW (GLOW; Solomon, 2017). GEMINI-GLOW thus describes both thermal and suprathermal effects on the ionosphere and is driven by boundary conditions consisting of topside ionospheric field-aligned currents and suprathermal electrons. These boundary conditions are constrained using time and space-dependent electric field and precipitation estimates from recent sounding rocket campaigns, ISINGLASS (02 March 2017) and GREECE (03 March 2014), derived from the Poker Flat incoherent scatter radar (PFISR) drifts and filtered EMCCD cameras respectively. Results from these data-driven case studies are compared to plasma parameter responses (i.e. density and temperature) independently estimated by PFISR and from the sounding rockets. These studies are intended as a first step towards a local

  13. Modeling of very low frequency (VLF radio wave signal profile due to solar flares using the GEANT4 Monte Carlo simulation coupled with ionospheric chemistry

    Directory of Open Access Journals (Sweden)

    S. Palit

    2013-09-01

    Full Text Available X-ray photons emitted during solar flares cause ionization in the lower ionosphere (~60 to 100 km in excess of what is expected to occur due to a quiet sun. Very low frequency (VLF radio wave signals reflected from the D-region of the ionosphere are affected by this excess ionization. In this paper, we reproduce the deviation in VLF signal strength during solar flares by numerical modeling. We use GEANT4 Monte Carlo simulation code to compute the rate of ionization due to a M-class flare and a X-class flare. The output of the simulation is then used in a simplified ionospheric chemistry model to calculate the time variation of electron density at different altitudes in the D-region of the ionosphere. The resulting electron density variation profile is then self-consistently used in the LWPC code to obtain the time variation of the change in VLF signal. We did the modeling of the VLF signal along the NWC (Australia to IERC/ICSP (India propagation path and compared the results with observations. The agreement is found to be very satisfactory.

  14. Numerical modelling of electrochemical polarization around charged metallic particles

    Science.gov (United States)

    Bücker, Matthias; Undorf, Sabine; Flores Orozco, Adrián; Kemna, Andreas

    2017-04-01

    We extend an existing analytical model and carry out numerical simulations to study the polarization process around charged metallic particles immersed in an electrolyte solution. Electro-migration and diffusion processes in the electrolyte are described by the Poisson-Nernst-Planck system of partial differential equations. To model the surface charge density, we consider a time- and frequency-invariant electric potential at the particle surface, which leads to the build-up of a static electrical double layer (EDL). Upon excitation by an external electric field at low frequencies, we observe the superposition of two polarization processes. On the one hand, the induced dipole moment on the metallic particle leads to the accumulation of opposite charges in the electrolyte. This charge polarization corresponds to the long-known response of uncharged metallic particles. On the other hand, the unequal cation and anion concentrations in the EDL give rise to a salinity gradient between the two opposite sides of the metallic particle. The resulting concentration polarization enhances the magnitude of the overall polarization response. Furthermore, we use our numerical model to study the effect of relevant model parameters such as surface charge density and ionic strength of the electrolyte on the resulting spectra of the effective conductivity of the composite model system. Our results do not only give interesting new insight into the time-harmonic variation of electric potential and ion concentrations around charged metallic particle. They are also able to reduce incongruities between earlier model predictions and geophysical field and laboratory measurements. Our model thereby improves the general understanding of IP signatures of metallic particles and represents the next step towards a quantitative interpretation of IP imaging results. Part of this research is funded by the Austrian Federal Ministry of Science, Research and Economy under the Raw Materials Initiative.

  15. Modeling Gravitational Waves to Test GR Dispersion and Polarization

    Science.gov (United States)

    Tso, Rhondale; Chen, Yanbei; Isi, Maximilliano

    2017-01-01

    Given continued observation runs from the Laser Interferometer Gravitational-Wave Observatory Scientific Collaboration, further gravitational wave (GW) events will provide added constraints on beyond-general relativity (b-GR) theories. One approach, independent of the GW generation mechanism at the source, is to look at modification to the GW dispersion and propagation, which can accumulate over vast distances. Generic modification of GW propagation can also, in certain b-GR theories, impact the polarization content of GWs. To this end, a comprehensive approach to testing the dispersion and polarization content is developed by modeling anisotropic deformations to the waveforms' phase, along with birefringence effects and corollary consequences for b-GR polarizations, i.e., breathing, vector, and longitudinal modes. Such an approach can be mapped to specific theories like Lorentz violation, amplitude birefringence in Chern-Simons, and provide hints at additional theories to be included. An overview of data analysis routines to be implemented will also be discussed.

  16. Investigating the polar electrojet using Swarm satellite magnetic data

    DEFF Research Database (Denmark)

    Aakjær, Cecilie Drost; Olsen, Nils; Finlay, Chris

    The aim of this study is to investigate the magnetic perturbations caused by the polar electrojets, which are described by means of a model consisting of a series of infinite line currents placed at the height of the ionosphere along QD latitudes. The method is applied to Swarm magnetic scalar...... of the polar electrojets as well as their temporal evolution. In addition, applying the method to data taken by the Swarm satellites Alpha and Beta allows investigating longitudinal differences of the electrojets....

  17. Ionospheric electron heating associated with pulsating auroras: A Swarm survey and model simulation

    Science.gov (United States)

    Liang, Jun; Yang, B.; Donovan, E.; Burchill, J.; Knudsen, D.

    2017-08-01

    In this paper we report a study on the plasma signatures (electron temperature, plasma density, and field-aligned current) of patchy pulsating auroras in the upper F region ionosphere using Swarm satellite data. Via a survey of 38 patch crossing events, we repeatedly identify a strong electron temperature enhancement associated with the pulsating aurora. On average, the electron temperature at Swarm satellite altitudes ( 460 km) increases from 2200 K at subauroral latitudes to a peak of 3000 K within the pulsating auroral patch. This indicates that pulsating auroras may act as an important heating source for the nightside ionosphere. On the other hand, no well-defined trend of plasma density variations associated with pulsating auroras is identified at Swarm altitudes. The field-aligned currents within the pulsating aurora patch are mostly upward, with mean magnitudes on order of 1 μA/m2. We then perform a numerical simulation to explore the potential mechanisms underlying the strong electron heating associated with the pulsating aurora. Via simulations we find that to account for the realistic electron temperature observation in a major portion of our events, pulsating auroras are likely accompanied by substantial magnetospheric heat fluxes around the order of 1010 eV/cm2. We propose that such magnetospheric heat fluxes may be pertinent to one long-hypothesized feature of pulsating auroras, namely, the coexistence of an enhanced low-energy plasma population in magnetic flux tubes threading the pulsating aurora, in addition to the energetic electron precipitation. Via a Swarm survey we repeatedly find a strong electron temperature enhancement associated with the pulsating aurora The field-aligned currents within pulsating auroras are moderately upward, with mean magnitudes on the order of 1e-6 A/m2 To explain the observed electron heating, pulsating auroras are likely accompanied by magnetospheric heat fluxes around 1E+10 eV/cm2/s.

  18. Investigation of the single layer model of GPS ionospheric data processing using IRI-90 and the attached diffusive equilibrium model of plasmaspheric electron density

    Directory of Open Access Journals (Sweden)

    L. Bànyai

    1997-06-01

    Full Text Available The single layer model of GPS ionospheric data processing is compared with the International Reference Ionosphere í 1990 and the attached Diffusive Equilibrium model of Plasmasphere (IRI-90+DEP which proved to be a good supplement to GPS data processing. These models can be used to estimate the single layer height and to improve the mapping function in day-time. The code delays estimated from IRI-90+DEP models are compared with GPS measurements carried out by TurboRogue receiver. These models can be used to estimate the preliminary receiver biases especially in the case of cross-correlation tracking mode. The practical drawback of the IRI-90 model is the sharp discontinuity of the ion components during sunset and sunrise at an elevation of 1000 km, because it also causes a sharp discontinuity in the TEC values computed from the DEP model. The GPS data may be a good source to improve the topside region of the IRI model estimating smooth TEC transition before and after sunrise in the plasmasphere.

  19. Massive Statistics of VLF-Induced Ionospheric Disturbances

    Science.gov (United States)

    Pailoor, N.; Cohen, M.; Golkowski, M.

    2017-12-01

    The impact of lightning of the D-region of the ionosphere has been measured by Very Low Frequency (VLF) remote sensing, and can be seen through the observance of Early-Fast events. Previous research has indicated that several factors control the behavior and occurrence of these events, including the transmitter-receiver geometry, as well as the peak current and polarity of the strike. Unfortunately, since each event is unique due to the wide variety of impacting factors, it is difficult to make broad inferences about the interactions between the lightning and ionosphere. By investigating a large database of lightning-induced disturbances over a span of several years and over a continental-scale region, we seek to quantify the relationship between geometry, lightning parameters, and the apparent disturbance of the ionosphere as measured with VLF transmitters. We began with a set of 860,000 cases where an intense lightning stroke above 150 kA occurred within 300 km of a transmiter-receiver path. To then detect ionospheric disturbances from the large volume of VLF data and lightning incidents, we applied a number of classification methods to the actual VLF amplitude data, and find that the most accurate is a convolutional neural network, which yielded a detection efficiency of 95-98%, and a false positive rate less than 25%. Using this model, we were able to assemble a database of more than 97,000 events, with each event stored with its corresponding time, date, receiver, transmitter, and lightning parameters. Estimates for the peak and slope of each disruption were also calculated. From this data, we were able to chart the relationships between geometry and lightning parameters (peak current and polarity) towards the occurrence probability, perturbation intensity, and recovery time, of the VLF perturbation. The results of this analysis are presented here.

  20. Modeling radio circular polarization in the Crab nebula

    Science.gov (United States)

    Bucciantini, N.; Olmi, B.

    2018-03-01

    In this paper, we present, for the first time, simulated maps of the circularly polarized synchrotron emission from the Crab nebula, using multidimensional state of the art models for the magnetic field geometry. Synchrotron emission is the signature of non-thermal emitting particles, typical of many high-energy astrophysical sources, both Galactic and extragalactic ones. Its spectral and polarization properties allow us to infer key information on the particles distribution function and magnetic field geometry. In recent years, our understanding of pulsar wind nebulae has improved substantially thanks to a combination of observations and numerical models. A robust detection or non-detection of circular polarization will enable us to discriminate between an electron-proton plasma and a pair plasma, clarifying once for all the origin of the radio emitting particles, setting strong constraints on the pair production in pulsar magnetosphere, and the role of turbulence in the nebula. Previous attempts at measuring the circular polarization have only provided upper limits, but the lack of accurate estimates, based on reliable models, makes their interpretation ambiguous. We show here that those results are above the expected values, and that current polarimetric techniques are not robust enough for conclusive result, suggesting that improvements in construction and calibration of next generation radio facilities are necessary to achieve the desired sensitivity.

  1. TEC ingestion into NeQuick 2 to model the topside electron density in the East-African ionosphere

    Science.gov (United States)

    Nigussie, M.; Radicella, S. M.; Damtie, B.; Nava, B.; Yizengaw, E.

    2012-12-01

    This study investigates the performances of the NeQuick 2 empirical model in the East-African region by assisting this model with Global Positioning System (GPS) measurements obtained from a single station. First we calculate an effective ionization level that drives NeQuick 2 to reproduce TEC that fits the least square sense to the measurements. We then quantify the performances of the NeQuick 2 in reproducing the topside in situ ion density observed by Communication/ Navigation Outage Forecast System (C/NOFS) satellite after modifying the model's input parameter. This is done by inputting the effective ionization level calculated from the slant total electron content (sTEC) measurements obtained from the single GPS receiver to the model. The performances of the model before and after data ingestion are then investigated by comparing the model results with the topside in situ ion density observation. One-month data during low solar activity conditions were used in this study. We have shown that the capability of NeQuick 2 to specify the East-African region topside ionosphere has been increased substantially by means of data ingestion. We found that the model after ingestion reproduces the in situ topside ion density observations better as far as about 824 km away from the reference station than that before adaptation. In this study, the statistical comparisons of the performances of the model in reproducing topside in situ ion density observations before and after ingestion are also discussed.

  2. Interstellar extinction and interstellar polarization: old and new models

    OpenAIRE

    Voshchinnikov, N. V.

    2012-01-01

    The review contains an analysis of the observed and model curves of the interstellar extinction and polarization. The observations mainly give information on dust in diffuse and translucent interstellar clouds. The features of various dust grain models including spherical/non-spherical, homogeneous/inhomogeneous particles are discussed. A special attention is devoted to the analysis of the grain size distributions, alignment mechanisms and magnetic field structure in interstellar clouds. It i...

  3. Comparison of the measured and modelled electron densities and temperatures in the ionosphere and plasmasphere during 20-30 January, 1993

    Directory of Open Access Journals (Sweden)

    A. V. Pavlov

    2000-10-01

    Full Text Available We present a comparison of the electron density and temperature behaviour in the ionosphere and plasmasphere measured by the Millstone Hill incoherent-scatter radar and the instruments on board of the EXOS-D satellite with numerical model calculations from a time-dependent mathematical model of the Earth's ionosphere and plasmasphere during the geomagnetically quiet and storm period on 20–30 January, 1993. We have evaluated the value of the additional heating rate that should be added to the normal photoelectron heating in the electron energy equation in the daytime plasmasphere region above 5000 km along the magnetic field line to explain the high electron temperature measured by the instruments on board of the EXOS-D satellite within the Millstone Hill magnetic field flux tube in the Northern Hemisphere. The additional heating brings the measured and modelled electron temperatures into agreement in the plasmasphere and into very large disagreement in the ionosphere if the classical electron heat flux along magnetic field line is used in the model. A new approach, based on a new effective electron thermal conductivity coefficient along the magnetic field line, is presented to model the electron temperature in the ionosphere and plasmasphere. This new approach leads to a heat flux which is less than that given by the classical Spitzer-Harm theory. The evaluated additional heating of electrons in the plasmasphere and the decrease of the thermal conductivity in the topside ionosphere and the greater part of the plasmasphere found for the first time here allow the model to accurately reproduce the electron temperatures observed by the instruments on board the EXOS-D satellite in the plasmasphere and the Millstone Hill incoherent-scatter radar in the ionosphere. The effects of the daytime additional plasmaspheric heating of electrons on the electron temperature and density are small at the F-region altitudes if the modified electron heat flux is

  4. Comparison of the measured and modeled electron densities and temperatures in the ionosphere and plasmasphere during the period 25-29 June 1990

    Science.gov (United States)

    Pavlov, A. V.; Abe, T.; Oyama, K.-I.

    2001-04-01

    We present a comparison of the electron density and temperature behavior measured in the ionosphere by the Millstone Hill incoherent-scatter radar during the period 25-29 June 1990, and in the plasmasphere within the Millstone Hill magnetic field flux tube by the instruments on board of the EXOS-D satellite in the Northern Hemisphere between 02:07:56 UT and 02:11:08 UT on 28 June 1990 with numerical model calculations from a time-dependent mathematical model of the Earth's ionosphere and plasmasphere. We have evaluated the value of the nighttime additional heating rate that should be added to the normal photoelectron heating in the electron energy equation in the plasmasphere region above 5000 km along the magnetic field line to explain the high electron temperature measured by the instruments on board of the EXOS-D satellite. The additional heating brings the measured and modeled electron temperatures into agreement with the plasmasphere and into very large disagreement with the ionosphere if the classical electron heat flux along magnetic field line is used in the model. The approach of Pavlov et al. (Annales Geophysicae 18 (2000) 1257-1272) based on an effective electron thermal conductivity coefficient along the magnetic field line, is used to explain the measured electron temperature in the ionosphere and plasmasphere. This approach leads to a heat flux which is less than that given by the classical Spitzer-Harm theory. The evaluated additional heating of electrons in the plasmasphere and the decrease of the thermal conductivity in the topside ionosphere and the greater part of the plasmasphere allow the model to accurately reproduce the electron temperatures observed by the instruments on board of the EXOS-D satellite in the plasmasphere and the Millstone Hill incoherent-scatter radar in the ionosphere. The resulting effect of vibrationally excited N2 and O2 on NmF2 is the decrease of the calculated daytime NmF2 up to a factor of 2. The modeled electron

  5. World Day ionospheric observations at Millstone Hill

    Science.gov (United States)

    Foster, J. C.; Holt, J. M.; Loriot, G. B.; Oliver, W. L.

    1985-05-01

    A comprehensive program of multistation observations is being pursued on a regular schedule with the aim to provide an adequate data base for the study and modeling of the global ionosphere. A global network of incoherent scatter radars operates monthly on predetermined radar World Days designated on the International Geophysical Calendar. Fully steerable radars at Sondre Stromfjord, Greenland, and Millstone Hill, MA, provide coverage at polar, auroral, and subauroral latitudes, while the facilities at Arecibo, PR, and Jicamarca, Peru monitor the low-latitude and equatorial region. A description is given of the observations conducted with the aid of the MIT Millstone Hill radar facility. Questions of data intercomparison and aspects of data availability are also discussed.

  6. Application of the nudged elastic band method to the point-to-point radio wave ray tracing in IRI modeled ionosphere

    Science.gov (United States)

    Nosikov, I. A.; Klimenko, M. V.; Bessarab, P. F.; Zhbankov, G. A.

    2017-07-01

    Point-to-point ray tracing is an important problem in many fields of science. While direct variational methods where some trajectory is transformed to an optimal one are routinely used in calculations of pathways of seismic waves, chemical reactions, diffusion processes, etc., this approach is not widely known in ionospheric point-to-point ray tracing. We apply the Nudged Elastic Band (NEB) method to a radio wave propagation problem. In the NEB method, a chain of points which gives a discrete representation of the radio wave ray is adjusted iteratively to an optimal configuration satisfying the Fermat's principle, while the endpoints of the trajectory are kept fixed according to the boundary conditions. Transverse displacements define the radio ray trajectory, while springs between the points control their distribution along the ray. The method is applied to a study of point-to-point ionospheric ray tracing, where the propagation medium is obtained with the International Reference Ionosphere model taking into account traveling ionospheric disturbances. A 2-dimensional representation of the optical path functional is developed and used to gain insight into the fundamental difference between high and low rays. We conclude that high and low rays are minima and saddle points of the optical path functional, respectively.

  7. Investigations in Satellite MIMO Channel Modeling: Accent on Polarization

    Directory of Open Access Journals (Sweden)

    Karagiannidis George K

    2007-01-01

    Full Text Available Due to the much different environment in satellite and terrestrial links, possibilities in and design of MIMO systems are rather different as well. After pointing out these differences and problems arising from them, two MIMO designs are shown rather well adapted to satellite link characteristics. Cooperative diversity seems to be applicable; its concept is briefly presented without a detailed discussion, leaving solving particular satellite problems to later work. On the other hand, a detailed discussion of polarization time-coded diversity (PTC is given. A physical-statistical model for dual-polarized satellite links is presented together with measuring results validating the model. The concept of 3D polarization is presented as well as briefly describing compact 3D-polarized antennas known from the literature and applicable in satellite links. A synthetic satellite-to-indoor link is constructed and its electromagnetic behavior is simulated via the FDTD (finite-difference time-domain method. Previous result of the authors states that in 3D-PTC situations, MIMO capacity can be about two times higher than SIMO (single-input multiple-output capacity while a diversity gain of nearly is further verified via extensive FDTD computer simulation.

  8. Investigations in Satellite MIMO Channel Modeling: Accent on Polarization

    Directory of Open Access Journals (Sweden)

    Péter Horváth

    2007-05-01

    Full Text Available Due to the much different environment in satellite and terrestrial links, possibilities in and design of MIMO systems are rather different as well. After pointing out these differences and problems arising from them, two MIMO designs are shown rather well adapted to satellite link characteristics. Cooperative diversity seems to be applicable; its concept is briefly presented without a detailed discussion, leaving solving particular satellite problems to later work. On the other hand, a detailed discussion of polarization time-coded diversity (PTC is given. A physical-statistical model for dual-polarized satellite links is presented together with measuring results validating the model. The concept of 3D polarization is presented as well as briefly describing compact 3D-polarized antennas known from the literature and applicable in satellite links. A synthetic satellite-to-indoor link is constructed and its electromagnetic behavior is simulated via the FDTD (finite-difference time-domain method. Previous result of the authors states that in 3D-PTC situations, MIMO capacity can be about two times higher than SIMO (single-input multiple-output capacity while a diversity gain of nearly 2×3 is further verified via extensive FDTD computer simulation.

  9. Estimating Parameters for the Earth-Ionosphere Waveguide Using VLF Narrowband Transmitters

    Science.gov (United States)

    Gross, N. C.; Cohen, M.

    2017-12-01

    Estimating the D-region (60 to 90 km altitude) ionospheric electron density profile has always been a challenge. The D-region's altitude is too high for aircraft and balloons to reach but is too low for satellites to orbit at. Sounding rocket measurements have been a useful tool for directly measuring the ionosphere, however, these types of measurements are infrequent and costly. A more sustainable type of measurement, for characterizing the D-region, is remote sensing with very low frequency (VLF) waves. Both the lower ionosphere and Earth's ground strongly reflect VLF waves. These two spherical reflectors form what is known as the Earth-ionosphere waveguide. As VLF waves propagate within the waveguide, they interact with the D-region ionosphere, causing amplitude and phase changes that are polarization dependent. These changes can be monitored with a spatially distributed array of receivers and D-region properties can be inferred from these measurements. Researchers have previously used VLF remote sensing techniques, from either narrowband transmitters or sferics, to estimate the density profile, but these estimations are typically during a short time frame and over a narrow propagation region. We report on an effort to improve the understanding of VLF wave propagation by estimating the commonly known h' and beta two parameter exponential electron density profile. Measurements from multiple narrowband transmitters at multiple receivers are taken, concurrently, and input into an algorithm. The cornerstone of the algorithm is an artificial neural network (ANN), where input values are the received narrowband amplitude and phase and the outputs are the estimated h' and beta parameters. Training data for the ANN is generated using the Navy's Long-Wavelength Propagation Capability (LWPC) model. Emphasis is placed on profiling the daytime ionosphere, which has a more stable and predictable profile than the nighttime. Daytime ionospheric disturbances, from high solar

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

    Science.gov (United States)

    Milinevsky, G.

    2005-04-01

    Researches of troposphere-stratosphere-ionosphere coupling are based on idea of the strong influence of the long- and short-term solar activity variations on the polar terrestrial climate and the asymmetry in the energy deposition from the magnetosphere into the polar ionospheres. The solar activity variations produce changeable impact on magnetosphere and polar ionosphere in both hemispheres. Results of this impact are (1) differences in the ozone concentrations in the Antarctic and Arctic stratosphere due to different forcing in spring; (2) different planetary wave activity; (3) different gravity wave flux intensity depended on strengths of the weather frontal cyclones activity. The study of upper atmosphere in both hemispheres is necessary to better understand various physical mechanisms responsible for the energy transfer from the Sun into atmosphere and ionosphere as well as reverse flux from troposphere to geospace. A simultaneous consideration of phenomena occurring over both polar regions is very important for understanding of these processes. The solution of the problem of energy exchange between neutral atmosphere and geospace plasma is need in study of industrial EM pollution from Earth surface to geospace. A corresponding work must promote modeling space weather on satellite heights and earthquake prediction using ionosphere parameters changes. A determinative significance of Antarctic Peninsula is caused by following features: (1) Antarctic Peninsula is situated near an extremely cyclonic active region - Drake Passage, (2) only this region in Antarctica is magnetically conjugated to industrial area in Northern hemisphere, and (3) this region contains many Antarctic stations which are good equipped by devices to study weather and climate, ozone layer, ionosphere and magnetic field. Last years weather observations at Vernadsky station show that up to 60 atmospheric frontal cyclones (with pressure variation more 20 millibars) swept over Antarctic

  11. Ionospheric Digital Database

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The ionosphere is that part of the Earth's atmosphere that results mainly from the photo ionization of the upper atmosphere. Traditionally, the following ionospheric...

  12. Magnetotail processes and their ionospheric signatures

    Science.gov (United States)

    Ferdousi, B.; Raeder, J.; Zesta, E.; Murphy, K. R.; Cramer, W. D.

    2017-12-01

    In-situ observations in the magnetotail are sparse and limited to single point measurements. In the ionosphere, on the other hand, there is a broad range of observations, including magnetometers, auroral imagers, and various radars. Since the ionosphere is to some extent a mirror of plasmasheet processes it can be used as a monitor of magnetotail dynamics. Thus, it is of great importance to understand the coupling between the ionosphere and the magnetosphere in order to properly interpret the ionosphere and ground observations in terms of magnetotail dynamics. For this purpose, the global magnetohydrodynamic model OpenGGCM is used to investigate magnetosphere-ionosphere coupling. One of the key processes in magnetotail dynamics are bursty bulk flows (BBFs) which are the major means by which momentum and energy get transferred through the magnetotail and down to the ionosphere. BBFs often manifested in the ionosphere as auroral streamers. This study focuses on mapping such flow bursts from the magnetotail to the ionosphere along the magnetic field lines for three states of the magnetotail: pre-substorm onset through substorm expansion and during steady magnetospheric convection (SMC) following the substorm. We find that the orientation of streamers in the ionosphere differes for different local times, and that, for both tail and ionospheric signatures, activity increases during the SCM configutation compared to the pre-onset and quiet times. We also find that the background convection in the tail impacts the direction and deflection of the BBFs and the subsequent orientation of the auroral streamers in the ionosphere.

  13. SHOCK WAVE IN IONOSPHERE DURING EARTHQUAKE

    Directory of Open Access Journals (Sweden)

    V.V. Kuznetsov

    2016-11-01

    Full Text Available Fundamentally new model of the shock wave (SW generation in atmosphere and ionosphere during earthquake is proposed. The model proceeds from the idea of cooperative shock water crystallization in a cloud

  14. Upper ionosphere and magnetospheric-ionospheric coupling

    International Nuclear Information System (INIS)

    Manzano, J.R.

    1989-02-01

    After a presentation of the ionospheric physics and of the earth magnetosphere morphology, generation and dynamics, the magnetosphere-ionosphere coupling in quiet and perturbed conditions is discussed. Some summary information about other planetary magnetospheres, particularly Venus and Jupiter magnetospheres, are finally given. 41 refs, 24 figs

  15. Faraday rotation of Automatic Dependent Surveillance Broadcast (ADS-B) signals as a method of ionospheric characterization

    Science.gov (United States)

    Cushley, A. C.; Kabin, K.; Noel, J. M. A.

    2017-12-01

    Radio waves propagating through plasma in the Earth's ambient magnetic field experience Faraday rotation; the plane of the electric field of a linearly polarized wave changes as a function of the distance travelled through a plasma. Linearly polarized radio waves at 1090 MHz frequency are emitted by Automatic Dependent Surveillance Broadcast (ADS-B) devices which are installed on most commercial aircraft. These radio waves can be detected by satellites in low earth orbits, and the change of the polarization angle caused by propagation through the terrestrial ionosphere can be measured. In this work we discuss how these measurements can be used to characterize the ionospheric conditions. In the present study, we compute the amount of Faraday rotation from a prescribed total electron content value and two of the profile parameters of the NeQuick model.

  16. Understanding and forecasting polar stratospheric variability with statistical models

    Directory of Open Access Journals (Sweden)

    C. Blume

    2012-07-01

    Full Text Available The variability of the north-polar stratospheric vortex is a prominent aspect of the middle atmosphere. This work investigates a wide class of statistical models with respect to their ability to model geopotential and temperature anomalies, representing variability in the polar stratosphere. Four partly nonstationary, nonlinear models are assessed: linear discriminant analysis (LDA; a cluster method based on finite elements (FEM-VARX; a neural network, namely the multi-layer perceptron (MLP; and support vector regression (SVR. These methods model time series by incorporating all significant external factors simultaneously, including ENSO, QBO, the solar cycle, volcanoes, to then quantify their statistical importance. We show that variability in reanalysis data from 1980 to 2005 is successfully modeled. The period from 2005 to 2011 can be hindcasted to a certain extent, where MLP performs significantly better than the remaining models. However, variability remains that cannot be statistically hindcasted within the current framework, such as the unexpected major warming in January 2009. Finally, the statistical model with the best generalization performance is used to predict a winter 2011/12 with warm and weak vortex conditions. A vortex breakdown is predicted for late January, early February 2012.

  17. Polar heating in Saturn's thermosphere

    Directory of Open Access Journals (Sweden)

    C. G. A. Smith

    2005-10-01

    Full Text Available A 3-D numerical global circulation model of the Kronian thermosphere has been used to investigate the influence of polar heating. The distributions of temperature and winds resulting from a general heat source in the polar regions are described. We show that both the total energy input and its vertical distribution are important to the resulting thermal structure. We find that the form of the topside heating profile is particularly important in determining exospheric temperatures. We compare our results to exospheric temperatures from Voyager occultation measurements (Smith et al., 1983; Festou and Atreya, 1982 and auroral H3+ temperatures from ground-based spectroscopic observations (e.g. Miller et al., 2000. We find that a polar heat source is consistent with both the Smith et al. determination of T∞~400 K at ~30° N and auroral temperatures. The required heat source is also consistent with recent estimates of the Joule heating rate at Saturn (Cowley et al., 2004. However, our results show that a polar heat source can probably not explain the Festou and Atreya determination of T∞~800 K at ~4° N and the auroral temperatures simultaneously. Keywords. Ionosphere (Planetary ionosphere – Magnetospherica physics (Planetary magnetospheres – Meterology and atmospheric dynamics (Thermospheric dynamics

  18. DMFC anode polarization: Experimental analysis and model validation

    Science.gov (United States)

    Casalegno, A.; Marchesi, R.

    Anode two-phase flow has an important influence on DMFC performance and methanol crossover. In order to elucidate two-phase flow influence on anode performance, in this work, anode polarization is investigated combining experimental and modelling approach. A systematic experimental analysis of operating conditions influence on anode polarization is presented. Hysteresis due to operating condition is observed; experimental results suggest that it arises from methanol accumulation and has to be considered in evaluating DMFC performances and measurements reproducibility. A model of DMFC anode polarization is presented and utilised as tool to investigate anode two-phase flow. The proposed analysis permits one to produce a confident interpretation of the main involved phenomena. In particular, it confirms that methanol electro-oxidation kinetics is weakly dependent on methanol concentration and that methanol transport in gas phase produces an important contribution in anode feeding. Moreover, it emphasises the possibility to optimise anode flow rate in order to improve DMFC performance and reduce methanol crossover.

  19. Polarity-Driven Geometrical Cluster Growth Model of Budding Yeast

    Science.gov (United States)

    Cabral, Reniel B.; Lim, May T.

    We present a polarity-driven activator-inhibitor model of budding yeast in a two-dimensional medium wherein impeding metabolites secretion (or growth inhibitors) and growth directionality are determined by the local nutrient level. We found that colony size and morphological features varied with nutrient concentration. A branched-type morphology is associated with high impeding metabolite concentration together with a high fraction of distal budding, while opposite conditions (low impeding metabolite concentration, high fraction of proximal budding) promote Eden-type patterns. Increasing the anisotropy factor (or polarity) produced other spatial patterns akin to the electrical breakdown under varying electric field. Rapid changes in the colony morphology, which we conjecture to be equivalent to a transition from an inactive quiescent state to an active budding state, appeared when nutrients were limited.

  20. Modeling the Lower Part of the Topside Ionospheric Vertical Electron Density Profile Over the European Region by Means of Swarm Satellites Data and IRI UP Method

    Science.gov (United States)

    Pignalberi, A.; Pezzopane, M.; Rizzi, R.

    2018-03-01

    An empirical method to model the lower part of the ionospheric topside region from the F2 layer peak height to about 500-600 km of altitude over the European region is proposed. The method is based on electron density values recorded from December 2013 to June 2016 by Swarm satellites and on foF2 and hmF2 values provided by IRI UP (International Reference Ionosphere UPdate), which is a method developed to update the IRI model relying on the assimilation of foF2 and M(3000)F2 data routinely recorded by a network of European ionosonde stations. Topside effective scale heights are calculated by fitting some definite analytical functions (α-Chapman, β-Chapman, Epstein, and exponential) through the values recorded by Swarm and the ones output by IRI UP, with the assumption that the effective scale height is constant in the altitude range considered. Calculated effective scale heights are then modeled as a function of foF2 and hmF2, in order to be operationally applicable to both ionosonde measurements and ionospheric models, like IRI. The method produces two-dimensional grids of the median effective scale height binned as a function of foF2 and hmF2, for each of the considered topside profiles. A statistical comparison with Constellation Observing System for Meteorology, Ionosphere, and Climate/FORMOsa SATellite-3 collected Radio Occultation profiles is carried out to assess the validity of the proposed method and to investigate which of the considered topside profiles is the best one. The α-Chapman topside function displays the best performance compared to the others and also when compared to the NeQuick topside option of IRI.

  1. Complex susceptibility of the cage model of polar liquids

    CERN Document Server

    Coffey, W T; Kalmykov, Yu P; Titov, S V

    2003-01-01

    The Langevin equations of motion of the cage model of polar liquids originally proposed by Hill (1963 Proc. Phys. Soc. 82 723) are solved for the first time for the particular case of rotation about a fixed axis, using a newly developed matrix continued fraction method. It is shown that the cage model predicts both the low-frequency Debye relaxation and a pronounced high-frequency (Poley) absorption peak in the far-infrared (FIR) region. The similarity of the equations of motion of the cage model to the equations which arise in the problem of generalizing the Onsager model of polar fluids to include a time-varying applied field suggests that the FIR (Poley) absorption may have its origins in the combined influence of molecular inertia and the torque due to the reaction field in the frequency-dependent version of the Onsager model. The complex susceptibility yielded by the cage model is shown to be in good agreement with experimental data on CH sub 3 Cl that were taken as a typical example. Moreover, a simple ...

  2. Inductive ionospheric solver for magnetospheric MHD simulations

    Directory of Open Access Journals (Sweden)

    H. Vanhamäki

    2011-01-01

    Full Text Available We present a new scheme for solving the ionospheric boundary conditions required in magnetospheric MHD simulations. In contrast to the electrostatic ionospheric solvers currently in use, the new solver takes ionospheric induction into account by solving Faraday's law simultaneously with Ohm's law and current continuity. From the viewpoint of an MHD simulation, the new inductive solver is similar to the electrostatic solvers, as the same input data is used (field-aligned current [FAC] and ionospheric conductances and similar output is produced (ionospheric electric field. The inductive solver is tested using realistic, databased models of an omega-band and westward traveling surge. Although the tests were performed with local models and MHD simulations require a global ionospheric solution, we may nevertheless conclude that the new solution scheme is feasible also in practice. In the test cases the difference between static and electrodynamic solutions is up to ~10 V km−1 in certain locations, or up to 20-40% of the total electric field. This is in agreement with previous estimates. It should also be noted that if FAC is replaced by the ground magnetic field (or ionospheric equivalent current in the input data set, exactly the same formalism can be used to construct an inductive version of the KRM method originally developed by Kamide et al. (1981.

  3. On the origin of the ionosphere at Moon : a study using results from Chandrayaan-I S-band radio occultation experiment and a photochemical model

    Science.gov (United States)

    Kailasam Madathil, Ambili; Bhardwaj, Anil; Choudhary, Raj Kumar

    2016-07-01

    Using Chandrayaan-1 communication link between orbiter and ground (S-band frequency), the presence of ionosphere at Moon has been explored using Radio Occultation technique. Results obtained from the observations conducted between July 30 and August 14, 2009 show evidence for a possible existence of the Ionosphere at Moon. A few seconds before the occultation of Chandrayaan-1 radio signals, extra fluctuation in the rate of change of difference between the theoretically estimated Doppler and observed Doppler was observed. The fluctuation was more pronounced when the probing radio waves were crossing through the day-night terminator. Using standard onion-peeling technique to invert the phase changes in radio signals to the refractivity of the medium, we estimated the bending angle and hence the electron density profiles for the Lunar medium. The estimated electron density near the Lunar surface was of the order of 400 - 1000 cm ^{-3} which decreased monotonically with increasing altitude till about 40 km above the surface where it became negligible. The observed electron density was compared with the results from a model which was developed based on CHACE measurements abroad Moon Impact Probe of Chandrayaan-I. The model included the photo chemical reactions and solar wind interactions of the lunar plasma. We propose that the ionosphere over Moon could have molecular origin with H _{2}O ^{+},CO_{2} ^{+} and H_{3}O ^{+} as dominant ions.

  4. Mapping ionospheric backscatter measured by the SuperDARN HF radars – Part 2: Assessing SuperDARN virtual height models

    Directory of Open Access Journals (Sweden)

    T. K. Yeoman

    2008-05-01

    Full Text Available The Super Dual Auroral Radar Network (SuperDARN network of HF coherent backscatter radars form a unique global diagnostic of large-scale ionospheric and magnetospheric dynamics in the Northern and Southern Hemispheres. Currently the ground projections of the HF radar returns are routinely determined by a simple rangefinding algorithm, which takes no account of the prevailing, or indeed the average, HF propagation conditions. This is in spite of the fact that both direct E- and F-region backscatter and 1½-hop E- and F-region backscatter are commonly used in geophysical interpretation of the data. In a companion paper, Chisham et al. (2008 have suggested a new virtual height model for SuperDARN, based on average measured propagation paths. Over shorter propagation paths the existing rangefinding algorithm is adequate, but mapping errors become significant for longer paths where the roundness of the Earth becomes important, and a correct assumption of virtual height becomes more difficult. The SuperDARN radar at Hankasalmi has a propagation path to high power HF ionospheric modification facilities at both Tromsø on a ½-hop path and SPEAR on a 1½-hop path. The SuperDARN radar at Þykkvibǽr has propagation paths to both facilities over 1½-hop paths. These paths provide an opportunity to quantitatively test the available SuperDARN virtual height models. It is also possible to use HF radar backscatter which has been artificially induced by the ionospheric heaters as an accurate calibration point for the Hankasalmi elevation angle of arrival data, providing a range correction algorithm for the SuperDARN radars which directly uses elevation angle. These developments enable the accurate mappings of the SuperDARN electric field measurements which are required for the growing number of multi-instrument studies of the Earth's ionosphere and magnetosphere.

  5. Diurnal and seasonal occurrence of polar patches

    Directory of Open Access Journals (Sweden)

    A. S. Rodger

    1996-05-01

    Full Text Available Analysis of the diurnal and seasonal variation of polar patches, as identified in two years of HF-radar data from Halley, Antarctica during a period near sunspot maximum, shows that there is a broad maximum in occurrence centred about magnetic noon, not local noon. There are minima in occurrence near midsummer and midwinter, with maxima in occurrence between equinox and winter. There are no significant correlations between the occurrence of polar patches and the corresponding hourly averages of the solar wind and IMF parameters, except that patches usually occur when the interplanetary magnetic field has a southward component. The results can be understood in terms of UT and seasonal differences in the plasma concentration being convected from the dayside ionosphere into the polar cap. In summer and winter the electron concentrations in the polar cap are high and low, respectively, but relatively unstructured. About equinox, a tongue of enhanced ionisation is convected into the polar cap; this tongue is then structured by the effects of the interplanetary magnetic field, but these Halley data cannot be used to separate the various competing mechanisms for patch formation. The observed diurnal and seasonal variation in the occurrence of polar patches are largely consistent with predictions of Sojka et al. (1994 when their results are translated into the southern hemisphere. However, the ionospheric effects of flux transfer events are still considered essential in their formation, a feature not yet included in the Sojka et al. model.

  6. Model for self-polarization and motility of keratocyte fragments

    KAUST Repository

    Ziebert, F.

    2011-10-19

    Computational modelling of cell motility on substrates is a formidable challenge; regulatory pathways are intertwined and forces that influence cell motion are not fully quantified. Additional challenges arise from the need to describe a moving deformable cell boundary. Here, we present a simple mathematical model coupling cell shape dynamics, treated by the phase-field approach, to a vector field describing the mean orientation (polarization) of the actin filament network. The model successfully reproduces the primary phenomenology of cell motility: discontinuous onset of motion, diversity of cell shapes and shape oscillations. The results are in qualitative agreement with recent experiments on motility of keratocyte cells and cell fragments. The asymmetry of the shapes is captured to a large extent in this simple model, which may prove useful for the interpretation of experiments.

  7. 3D modelling of VLF radio wave propagation in terrestrial waveguide allowing for localized large-scale ionosphere perturbation

    Science.gov (United States)

    Soloviev, O.

    2003-03-01

    The problem of radio wave propagation allowing for 3D localized lower ionosphere irregularity appears in accordance with the necessity of the theoretical interpretation of VLF remote sensing data. The various processes in the Earth's crust and in space (earthquakes, magnetic storms, sporadic E-layers, lightning induced electron precipitations, rocket launches, artificial ionosphere heating, nuclear explosions, etc.) may cause different power and size ionospheric disturbances. This paper presents a further development of the numerical-analytical method for 3D problem solving. We consider a vector problem of VLF vertical electric dipole field in a plane Earth-ionosphere waveguide with a localized anisotropic ionosphere irregularity. The possibility of lowering (elevating) of the local region of the upper waveguide wall is taken into account. The field components on the boundary surfaces obey the Leontovich impedance conditions. The problem is reduced to a system of 2D integral equations taking into account the depolarization of the field scattered by the irregularity. Using asymptotic /(kr>>1) integration along the direction perpendicular to the propagation path, we transform this system to a system of 1D integral equations. The system is solved in the diagonal approximation, combining direct inversion of the Volterra integral operator and the subsequent iterations. The proposed method is useful for study of both small-scale and large-scale irregularities. We obtained estimates of the TE field components that originate entirely from field scattering by a 3D irregularity.

  8. FDTD modelling of induced polarization phenomena in transient electromagnetics

    Science.gov (United States)

    Commer, Michael; Petrov, Peter V.; Newman, Gregory A.

    2017-04-01

    The finite-difference time-domain scheme is augmented in order to treat the modelling of transient electromagnetic signals containing induced polarization effects from 3-D distributions of polarizable media. Compared to the non-dispersive problem, the discrete dispersive Maxwell system contains costly convolution operators. Key components to our solution for highly digitized model meshes are Debye decomposition and composite memory variables. We revert to the popular Cole-Cole model of dispersion to describe the frequency-dependent behaviour of electrical conductivity. Its inversely Laplace-transformed Debye decomposition results in a series of time convolutions between electric field and exponential decay functions, with the latter reflecting each Debye constituents' individual relaxation time. These function types in the discrete-time convolution allow for their substitution by memory variables, annihilating the otherwise prohibitive computing demands. Numerical examples demonstrate the efficiency and practicality of our algorithm.

  9. Daytime Ionosphere Retrieval Algorithm for the Ionospheric Connection Explorer (ICON)

    Science.gov (United States)

    Stephan, Andrew W.; Korpela, Eric J.; Sirk, Martin M.; England, Scott L.; Immel, Thomas J.

    2017-10-01

    The NASA Ionospheric Connection Explorer Extreme Ultraviolet spectrograph, ICON EUV, will measure altitude profiles of the daytime extreme-ultraviolet (EUV) OII emission near 83.4 and 61.7 nm that are used to determine density profiles and state parameters of the ionosphere. This paper describes the algorithm concept and approach to inverting these measured OII emission profiles to derive the associated O+ density profile from 150-450 km as a proxy for the electron content in the F-region of the ionosphere. The algorithm incorporates a bias evaluation and feedback step, developed at the U.S. Naval Research Laboratory using data from the Special Sensor Ultraviolet Limb Imager (SSULI) and the Remote Atmospheric and Ionospheric Detection System (RAIDS) missions, that is able to effectively mitigate the effects of systematic instrument calibration errors and inaccuracies in the original photon source within the forward model. Results are presented from end-to-end simulations that convolved simulated airglow profiles with the expected instrument measurement response to produce profiles that were inverted with the algorithm to return data products for comparison to truth. Simulations of measurements over a representative ICON orbit show the algorithm is able to reproduce hmF2 values to better than 5 km accuracy, and NmF2 to better than 12% accuracy over a 12-second integration, and demonstrate that the ICON EUV instrument and daytime ionosphere algorithm can meet the ICON science objectives which require 20 km vertical resolution in hmF2 and 18% precision in NmF2.

  10. Rigorous vectorial modeling for polarized illumination and projection pupil in OPC

    Science.gov (United States)

    Zhang, Qiaolin; Song, Hua; Lucas, Kevin; Ward, Brian; Shiely, James

    2008-05-01

    High NA and Ultra-High NA (NA>1.0) applications for low k1 imaging strongly demand the adoption of polarized illumination as a resolution enhancement technology since proper illumination polarization configuration can greatly improve the image contrast hence pattern printing fidelity and the effectiveness of optical proximity correction (OPC). However, current OPC/RET modeling software can only model the light source polarization of simple types, such as TE, TM, X, Y, or sector polarization with relatively simple configuration. Realistic polarized light used in scanners is more complex than the aforementioned simple ones. As a result, simulation accuracy and quality of the OPC result will be compromised by the simplification of the light source polarization modeling in the traditional approach. With ever shrinking CD error budget in the manufacturing of IC's at advanced technology nodes, more accurate and comprehensive illumination source modeling for lithography simulations and OPC/RET is needed. On the other hand, for polarized illumination to be fully effective, ideally all the components in the optical lithography system should not alter the polarization state of light during its propagation from illuminator to wafer surface. In current OPC modeling tools, it is typically assumed that the amplitude and polarization state of the light do not change as it passes through the projection lens pupil, i.e. the polarization aberration of projection lens pupil is ignored. However, in reality, the projection lens pupil of the scanner does change the amplitude and the polarization state to some extent, and ignorance of projection pupil induced polarization state and amplitude changes will cause CD errors un-tolerable at the 45nm device generation and beyond. We developed an OPC-deployable modeling approach to model arbitrarily polarized light source and arbitrarily polarized projection lens pupil. Based on polarization state vector descriptions of a general illumination

  11. Modelling polarization dependent absorption: The vectorial Lambert-Beer law

    Science.gov (United States)

    Franssens, G.

    2014-07-01

    The scalar Lambert-Beer law, describing the absorption of unpolarized light travelling through a linear non-scattering medium, is simple, well-known, and mathematically trivial. However, when we take the polarization of light into account and consider a medium with polarization dependent absorption, we now need a Vectorial Lambert-Beer Law (VLBL) to quantify this interaction. Such a generalization of the scalar Lambert-Beer law appears not to be readily available. A careful study of this topic reveals that it is not a trivial problem. We will see that the VLBL is not and cannot be a straightforward vectorized version of its scalar counterpart. The aim of the work is to present the general form of the VLBL and to explain how it arises. A reasonable starting point to derive the VLBL is the Vectorial Radiative Transfer Equation (VRTE), which models the absorption and scattering of (partially) polarized light travelling through a linear medium. When we turn off scattering, the VRTE becomes an infinitesimal model for the VLBL holding in the medium. By integrating this equation, we expect to find the VLBL. Surprisingly, this is not the end of the story. It turns out that light propagation through a medium with polarization-dependent absorption is mathematically not that trivial. The trickiness behind the VLBL can be understood in the following terms. The matrix in the VLBL, relating any input Stokes vector to the corresponding output Stokes vector, must necessarily be a Mueller matrix. The subset of invertible Mueller matrices forms a Lie group. It is known that this Lie group contains the ortho-chronous Lorentz group as a subgroup. The group manifold of this subgroup has a (well-known) non-trivial topology. Consequently, the manifold of the Lie group of Mueller matrices also has (at least the same, but likely a more general) non-trivial topology (the full extent of which is not yet known). The type of non-trivial topology, possessed by the manifold of (invertible

  12. Rational Irrationality: Modeling Climate Change Belief Polarization Using Bayesian Networks.

    Science.gov (United States)

    Cook, John; Lewandowsky, Stephan

    2016-01-01

    Belief polarization is said to occur when two people respond to the same evidence by updating their beliefs in opposite directions. This response is considered to be "irrational" because it involves contrary updating, a form of belief updating that appears to violate normatively optimal responding, as for example dictated by Bayes' theorem. In light of much evidence that people are capable of normatively optimal behavior, belief polarization presents a puzzling exception. We show that Bayesian networks, or Bayes nets, can simulate rational belief updating. When fit to experimental data, Bayes nets can help identify the factors that contribute to polarization. We present a study into belief updating concerning the reality of climate change in response to information about the scientific consensus on anthropogenic global warming (AGW). The study used representative samples of Australian and U.S. Among Australians, consensus information partially neutralized the influence of worldview, with free-market supporters showing a greater increase in acceptance of human-caused global warming relative to free-market opponents. In contrast, while consensus information overall had a positive effect on perceived consensus among U.S. participants, there was a reduction in perceived consensus and acceptance of human-caused global warming for strong supporters of unregulated free markets. Fitting a Bayes net model to the data indicated that under a Bayesian framework, free-market support is a significant driver of beliefs about climate change and trust in climate scientists. Further, active distrust of climate scientists among a small number of U.S. conservatives drives contrary updating in response to consensus information among this particular group. Copyright © 2016 Cognitive Science Society, Inc.

  13. Polar Coordinate Lattice Boltzmann Kinetic Modeling of Detonation Phenomena

    International Nuclear Information System (INIS)

    Lin Chuan-Dong; Li Ying-Jun; Xu Ai-Guo; Zhang Guang-Cai

    2014-01-01

    A novel polar coordinate lattice Boltzmann kinetic model for detonation phenomena is presented and applied to investigate typical implosion and explosion processes. In this model, the change of discrete distribution function due to local chemical reaction is dynamically coupled into the modified lattice Boltzmann equation which could recover the Navier—Stokes equations, including contribution of chemical reaction, via the Chapman—Enskog expansion. For the numerical investigations, the main focuses are the nonequilibrium behaviors in these processes. The system at the disc center is always in its thermodynamic equilibrium in the highly symmetric case. The internal kinetic energies in different degrees of freedom around the detonation front do not coincide. The dependence of the reaction rate on the pressure, influences of the shock strength and reaction rate on the departure amplitude of the system from its local thermodynamic equilibrium are probed. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

  14. Climatology of GNSS ionospheric scintillation at high latitudes

    Science.gov (United States)

    Spogli, L.; Alfonsi, L.; de Franceschi, G.; Romano, V.; Aquino, M.; Dodson, A.; Mitchell, C. N.

    2009-12-01

    Under perturbed conditions caused by intense solar wind magnetosphere coupling, the ionosphere may become highly turbulent and irregularities, typically enhancements or depletions of the electron density embedded in the ambient ionosphere, can form. Such irregularities cause diffraction effects, mainly due to the random fluctuations of the refractive index of the ionosphere, on the satellites signals passing through them and consequent perturbations may cause GNSS navigation errors and outages, abruptly corrupting its performance. Due to the morphology of the geomagnetic field, whose lines are almost vertical at high latitude, polar areas are characterized by the presence of significant ionospheric irregularities having scale sizes ranging from hundreds of kilometers down to a few centimeters and with highly dynamic structures. The understanding of the effect of such phenomena is important, not only in preparation for the next solar cycle (24), whose maximum is expected in 2012, but also for a deeper comprehension of the dynamics of the high-latitude ionosphere. We analyze the fluctuations in the carrier frequency of the radio waves received on the ground, commonly referred to as ionospheric amplitude and phase scintillations, to investigate the physical processes causing them. The phase scintillations on GNSS signals are likely caused by ionospheric irregularities of scale size of hundreds of meters to few kilometers. The amplitude scintillations on GNSS signals are caused by ionospheric irregularities of scale size smaller than the Fresnel radius, which is of the order of hundreds of meters for GNSS signals, typically embedded into the patches. The Istituto Nazionale di Geofisica e Vulcanologia (INGV) and the Institute of Engineering Surveying and Space Geodesy (IESSG) of the University of Nottingham manage the same kind of GISTM (GPS Ionospheric Scintillation and TEC Monitor) receivers over the European high and mid latitude regions and over Antarctica. The

  15. Induced polarization of clay-sand mixtures: experiments and modeling

    International Nuclear Information System (INIS)

    Okay, G.; Leroy, P.; Tournassat, C.; Ghorbani, A.; Jougnot, D.; Cosenza, P.; Camerlynck, C.; Cabrera, J.; Florsch, N.; Revil, A.

    2012-01-01

    were performed with a cylindrical four-electrode sample-holder (cylinder made of PVC with 30 cm in length and 19 cm in diameter) associated with a SIP-Fuchs II impedance meter and non-polarizing Cu/CuSO 4 electrodes. These electrodes were installed at 10 cm from the base of the sample holder and regularly spaced (each 90 degree). The results illustrate the strong impact of the Cationic Exchange Capacity (CEC) of the clay minerals upon the complex conductivity. The amplitude of the in-phase conductivity of the kaolinite-clay samples is strongly dependent to saturating fluid salinity for all volumetric clay fractions, whereas the in-phase conductivity of the smectite-clay samples is quite independent on the salinity, except at the low clay content (5% and 1% of clay in volume). This is due to the strong and constant surface conductivity of smectite associated with its very high CEC. The quadrature conductivity increases steadily with the CEC and the clay content. We observe that the dependence on frequency of the quadrature conductivity of sand-kaolinite mixtures is more important than for sand-bentonite mixtures. For both types of clay, the quadrature conductivity seems to be fairly independent on the pore fluid salinity except at very low clay contents (1% in volume of kaolinite-clay). This is due to the constant surface site density of Na counter-ions in the Stern layer of clay materials. At the lowest clay content (1%), the magnitude of the quadrature conductivity increases with the salinity, as expected for silica sands. In this case, the surface site density of Na counter-ions in the Stern layer increases with salinity. The experimental data show good agreement with predicted values given by our Spectral Induced Polarization (SIP) model. This complex conductivity model considers the electrochemical polarization of the Stern layer coating the clay particles and the Maxwell-Wagner polarization. We use the differential effective medium theory to calculate the complex

  16. Ionospheric Correction in Using ALOS PALSAR InSAR Data for Monitoring Permafrost Subsidence associated with an Arctic Tundra Fire

    Science.gov (United States)

    Liao, H.; Meyer, F. J.; Liu, L.

    2017-12-01

    Tundra fires have important ecological impacts on vegetation succession, carbon cycling, and permafrost dynamics. Recent research has demonstrated that SAR Interferometry (InSAR) is a useful tool for quantifying surface subsidence caused by permafrost degradation and tundra fires. Many of these studies have relied on L-band SAR data due to its ability to remain relatively high coherence in the changing Arctic environment. L-band SAR data, however, are susceptive to ionospheric effects. Traditionally, permafrost-related InSAR studies dealt with ionospheric artifacts by either throwing away ionosphere-contaminated data or by fitting and removing low-order polynomial surfaces from affected images. Discarding data samples is always luxurious and risky, as the number of SAR images is limited and the incurred reduction of temporal sampling might hinder the retrieval of important short-term dynamics in active layer and permafrost. Baseline fitting relies on the assumption that ionospheric signals large spatial scales, an assumption that is often violated in polar regions. To improve upon this situation, we propose the integration of the split-spectrum ionospheric correction technique into permafrost-related InSAR processing workflows. We demonstrate its performance for correcting L-band SAR data in permafrost zones. For the Anaktuvuk River fire area, Alaska, 6 out of 15 ALOS-1 PALSAR scenes used by Liu et al. 2014 were found to be contaminated by ionospheric signals. We extracted the ionospheric phase screens for all contaminated data. We derive their power spectra and provide information on the typical magnitudes and spatial structures of identified phase screens. With the ionosphere corrected data we revisit a model that was developed by Liu et.al (2014) to estimate pre-fire and post-fire thaw-season subsidence for the Anaktuvuk River fire region. We will demonstrate that for our area of interest ionospheric correction leads to improvements of the InSAR-based permafrost

  17. LIFDAR: A Diagnostic Tool for the Ionosphere

    Science.gov (United States)

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

    2011-12-01

    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.

  18. Assessment of ionospheric Joule heating by GUMICS-4 MHD simulation, AMIE, and satellite-based statistics: towards a synthesis

    Directory of Open Access Journals (Sweden)

    M. Palmroth

    2005-09-01

    Full Text Available We investigate the Northern Hemisphere Joule heating from several observational and computational sources with the purpose of calibrating a previously identified functional dependence between solar wind parameters and ionospheric total energy consumption computed from a global magnetohydrodynamic (MHD simulation (Grand Unified Magnetosphere Ionosphere Coupling Simulation, GUMICS-4. In this paper, the calibration focuses on determining the amount and temporal characteristics of Northern Hemisphere Joule heating. Joule heating during a substorm is estimated from global observations, including electric fields provided by Super Dual Auroral Network (SuperDARN and Pedersen conductances given by the ultraviolet (UV and X-ray imagers on board the Polar satellite. Furthermore, Joule heating is assessed from several activity index proxies, large statistical surveys, assimilative data methods (AMIE, and the global MHD simulation GUMICS-4. We show that the temporal and spatial variation of the Joule heating computed from the GUMICS-4 simulation is consistent with observational and statistical methods. However, the different observational methods do not give a consistent estimate for the magnitude of the global Joule heating. We suggest that multiplying the GUMICS-4 total Joule heating by a factor of 10 approximates the observed Joule heating reasonably well. The lesser amount of Joule heating in GUMICS-4 is essentially caused by weaker Region 2 currents and polar cap potentials. We also show by theoretical arguments that multiplying independent measurements of averaged electric fields and Pedersen conductances yields an overestimation of Joule heating.

    Keywords. Ionosphere (Auroral ionosphere; Modeling and forecasting; Electric fields and currents

  19. Inferring Polar Ion Outflows from Topside Ionograms

    Science.gov (United States)

    Sojka, J. J.; Rice, D. D.; Eccles, V.; Schunk, R. W.; David, M.; Benson, R. F.; James, H. G.

    2017-12-01

    The high-latitude topside ionosphere is dominated by O+ ions from the F-region peak around 300 km to over 1000 km altitude. The O+ profile shape provides information on the thermal structure, field aligned plasma dynamics, and outflows into the magnetosphere. Topside electron density profiles (EDP) are either obtained from topside sounders or Incoherent Scatter Radars. There is a large archive of topside sounder ionograms and hand scaled EDPs from the Alouette and ISIS satellites between 1962 and 1990. Recent NASA data enhancement efforts have augmented these EDP archives by producing digital topside ionograms both from the 7-track analog telemetry tapes and from 35 mm topside film ionograms. Rice et al [2017] in their 35 mm ionogram recovery emphasized high latitude ionograms taken during disturbed conditions. The figure below contrasts ISIS-II EDPs extracted from 35 mm films before and during a major storm (Dst -200nT) on 9 April 1972 (left panel: quiet period before the storm; right panel: during the peak of the storm). Both satellite passes used for these EDPs were centered on the Resolute Bay location that in 1972 was close to the magnetic pole. They begin at auroral latitudes around 2100 MLT and end on the dayside around 0900MLT. We will present results of how ionospheric models replicate both the quiet and disturbed conditions shown in the figure. Three types of models will be contrasted: an empirical ionosphere (IRI), a physics based ionospheric model (TDIM), and a fluid-based polar-wind model (PW). During the storm pass, when it is expected that substantial heating is present, the ISIS-II topside EDPs provide severe constraints on the usage of these models. These constraints enable estimates of the outflow fluxes as well as the heating that has occurred. The comparisons with the empirical model establish how well the pre-storm topside is modeled and identifies the challenges as the storm magnitude increases. The physics-based TDIM does have storm drivers

  20. Seasonal effects in the ionosphere-thermosphere response to the precipitation and field-aligned current variations in the cusp region

    Directory of Open Access Journals (Sweden)

    A. A. Namgaladze

    1998-10-01

    Full Text Available The seasonal effects in the thermosphere and ionosphere responses to the precipitating electron flux and field-aligned current variations, of the order of an hour in duration, in the summer and winter cusp regions have been investigated using the global numerical model of the Earth's upper atmosphere. Two variants of the calculations have been performed both for the IMF By < 0. In the first variant, the model input data for the summer and winter precipitating fluxes and field-aligned currents have been taken as geomagnetically symmetric and equal to those used earlier in the calculations for the equinoctial conditions. It has been found that both ionospheric and thermospheric disturbances are more intensive in the winter cusp region due to the lower conductivity of the winter polar cap ionosphere and correspondingly larger electric field variations leading to the larger Joule heating effects in the ion and neutral gas temperature, ion drag effects in the thermospheric winds and ion drift effects in the F2-region electron concentration. In the second variant, the calculations have been performed for the events of 28–29 January, 1992 when precipitations were weaker but the magnetospheric convection was stronger than in the first variant. Geomagnetically asymmetric input data for the summer and winter precipitating fluxes and field-aligned currents have been taken from the patterns derived by combining data obtained from the satellite, radar and ground magnetometer observations for these events. Calculated patterns of the ionospheric convection and thermospheric circulation have been compared with observations and it has been established that calculated patterns of the ionospheric convection for both winter and summer hemispheres are in a good agreement with the observations. Calculated patterns of the thermospheric circulation are in a good agreement with the average circulation for the Southern (summer Hemisphere obtained from DE-2 data for IMF

  1. A novel polar-based human face recognition computational model

    Directory of Open Access Journals (Sweden)

    Y. Zana

    2009-07-01

    Full Text Available Motivated by a recently proposed biologically inspired face recognition approach, we investigated the relation between human behavior and a computational model based on Fourier-Bessel (FB spatial patterns. We measured human recognition performance of FB filtered face images using an 8-alternative forced-choice method. Test stimuli were generated by converting the images from the spatial to the FB domain, filtering the resulting coefficients with a band-pass filter, and finally taking the inverse FB transformation of the filtered coefficients. The performance of the computational models was tested using a simulation of the psychophysical experiment. In the FB model, face images were first filtered by simulated V1- type neurons and later analyzed globally for their content of FB components. In general, there was a higher human contrast sensitivity to radially than to angularly filtered images, but both functions peaked at the 11.3-16 frequency interval. The FB-based model presented similar behavior with regard to peak position and relative sensitivity, but had a wider frequency band width and a narrower response range. The response pattern of two alternative models, based on local FB analysis and on raw luminance, strongly diverged from the human behavior patterns. These results suggest that human performance can be constrained by the type of information conveyed by polar patterns, and consequently that humans might use FB-like spatial patterns in face processing.

  2. Model independent analysis of Λ baryon polarizations in Λb→Λl+l- decay

    International Nuclear Information System (INIS)

    Aliev, T.M.; Oezpineci, A.; Savci, M.

    2003-01-01

    We present a model independent analysis of Λ baryon polarizations in the Λ b →Λl + l - decay. The sensitivity of the averaged Λ polarizations to the new Wilson coefficients is studied. It is observed that there exist certain regions of the new Wilson coefficients where the branching ratio coincides with the standard model prediction, while the Λ baryon polarizations deviate from the standard model results remarkably

  3. General method for calculating polarization electric fields produced by auroral Cowling mechanism and application examples

    Science.gov (United States)

    Vanhamäki, Heikki; Amm, Olaf; Fujii, Ryo; Yoshikawa, Aki; Ieda, Aki

    2013-04-01

    The Cowling mechanism is characterized by the generation of polarization space charges in the ionosphere in consequence of a partial or total blockage of FAC flowing between the ionosphere and the magnetosphere. Thus a secondary polarization electric field builds up in the ionosphere, which guarantees that the whole (primary + secondary) ionospheric current system is again in balance with the FAC. In the Earth's ionosphere the Cowling mechanism is long known to operate in the equatorial electrojet, and several studies indicate that it is important also in auroral current systems. We present a general method for calculate the secondary polarization electric field, when the ionospheric conductances, the primary (modeled) or the total (measured) electric field, and the Cowling efficiency are given. Here the Cowling efficiency is defined as the fraction of the divergent Hall current canceled by secondary Pedersen current. In contrast to previous studies, our approach is a general solution which is not limited to specific geometrical setups (like an auroral arc), and all parameters may have any kind of spatial dependence. The solution technique is based on spherical elementary current (vector) systems (SECS). This way, we avoid the need to specify explicit boundary conditions for the searched polarization electric field or its potential, which would be required if the problem was solved in a differential equation approach. Instead, we solve an algebraic matrix equation, for which the implicit boundary condition that the divergence of the polarization electric field vanishes outside our analysis area is sufficient. In order to illustrate the effect of Cowling mechanism on ionospheric current systems, we apply our method to two simple models of auroral electrodynamic situations: 1) a mesoscale strong conductance enhancement in the early morning sector within a relatively weak southward primary electric field, 2) a morning sector auroral arc with only a weak conductance

  4. Modeling optical and UV polarization of AGNs II. Polarization imaging and complex reprocessing

    Czech Academy of Sciences Publication Activity Database

    Marin, F.; Goosmann, R. W.; Gaskell, C.M.; Porquet, D.; Dovčiak, Michal

    2012-01-01

    Roč. 548, December (2012), A121/1-A121/25 ISSN 0004-6361 R&D Projects: GA MŠk LD12010 Institutional support: RVO:67985815 Keywords : actva galaxies * polarization Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 5.084, year: 2012

  5. Electron correlations in narrow energy bands: modified polar model approach

    Directory of Open Access Journals (Sweden)

    L. Didukh

    2008-09-01

    Full Text Available The electron correlations in narrow energy bands are examined within the framework of the modified form of polar model. This model permits to analyze the effect of strong Coulomb correlation, inter-atomic exchange and correlated hopping of electrons and explain some peculiarities of the properties of narrow-band materials, namely the metal-insulator transition with an increase of temperature, nonlinear concentration dependence of Curie temperature and peculiarities of transport properties of electronic subsystem. Using a variant of generalized Hartree-Fock approximation, the single-electron Green's function and quasi-particle energy spectrum of the model are calculated. Metal-insulator transition with the change of temperature is investigated in a system with correlated hopping. Processes of ferromagnetic ordering stabilization in the system with various forms of electronic DOS are studied. The static conductivity and effective spin-dependent masses of current carriers are calculated as a function of electron concentration at various DOS forms. The correlated hopping is shown to cause the electron-hole asymmetry of transport and ferromagnetic properties of narrow band materials.

  6. Experimental model of the electron temperature profile in the ionosphere at middle latitudes, (1)

    International Nuclear Information System (INIS)

    Hirao, K.; Oyama, K.

    1980-01-01

    The measurement of the electron temperature profile has been successively carried out at the Kagoshima Space Center by using identical radio frequency rectification probes onboard rockets launched during about half a solar activity cycle. By using about 30 profiles, an experimental model of the electron temperature profile and its solar activity dependency are proposed. Some particular characteristic points, bottom, 170 km, 220 km and topside, are examined in relation to local time and solar activity. The high electron temperature layer which appears at around 11 o'clock local time in winter is pointed out. The differences between the observed electron temperature and the model atmospheric neutral temperature at the characteristic points in particular are examined in relation to solar activity. The relation obtained at topside can be roughly explained by the variation of energy loss of electrons with solar activity. (author)

  7. Polar-coordinate lattice Boltzmann modeling of compressible flows

    Science.gov (United States)

    Lin, Chuandong; Xu, Aiguo; Zhang, Guangcai; Li, Yingjun; Succi, Sauro

    2014-01-01

    We present a polar coordinate lattice Boltzmann kinetic model for compressible flows. A method to recover the continuum distribution function from the discrete distribution function is indicated. Within the model, a hybrid scheme being similar to, but different from, the operator splitting is proposed. The temporal evolution is calculated analytically, and the convection term is solved via a modified Warming-Beam (MWB) scheme. Within the MWB scheme a suitable switch function is introduced. The current model works not only for subsonic flows but also for supersonic flows. It is validated and verified via the following well-known benchmark tests: (i) the rotational flow, (ii) the stable shock tube problem, (iii) the Richtmyer-Meshkov (RM) instability, and (iv) the Kelvin-Helmholtz instability. As an original application, we studied the nonequilibrium characteristics of the system around three kinds of interfaces, the shock wave, the rarefaction wave, and the material interface, for two specific cases. In one of the two cases, the material interface is initially perturbed, and consequently the RM instability occurs. It is found that the macroscopic effects due to deviating from thermodynamic equilibrium around the material interface differ significantly from those around the mechanical interfaces. The initial perturbation at the material interface enhances the coupling of molecular motions in different degrees of freedom. The amplitude of deviation from thermodynamic equilibrium around the shock wave is much higher than those around the rarefaction wave and material interface. By comparing each component of the high-order moments and its value in equilibrium, we can draw qualitatively the main behavior of the actual distribution function. These results deepen our understanding of the mechanical and material interfaces from a more fundamental level, which is indicative for constructing macroscopic models and other kinds of kinetic models.

  8. Coupled storm-time magnetosphere-ionosphere-thermosphere simulations including microscopic ionospheric turbulence

    Science.gov (United States)

    Merkin, V. G.; Wiltberger, M. J.; Zhang, B.; Liu, J.; Wang, W.; Dimant, Y. S.; Oppenheim, M. M.; Lyon, J.

    2017-12-01

    During geomagnetic storms the magnetosphere-ionosphere-thermosphere system becomes activated in ways that are unique to disturbed conditions. This leads to emergence of physical feedback loops that provide tighter coupling between the system elements, often operating across disparate spatial and temporal scales. One such process that has recently received renewed interest is the generation of microscopic ionospheric turbulence in the electrojet regions (electrojet turbulence, ET) that results from strong convective electric fields imposed by the solar wind-magnetosphere interaction. ET leads to anomalous electron heating and generation of non-linear Pedersen current - both of which result in significant increases in effective ionospheric conductances. This, in turn, provides strong non-linear feedback on the magnetosphere. Recently, our group has published two studies aiming at a comprehensive analysis of the global effects of this microscopic process on the magnetosphere-ionosphere-thermosphere system. In one study, ET physics was incorporated in the TIEGCM model of the ionosphere-thermosphere. In the other study, ad hoc corrections to the ionospheric conductances based on ET theory were incorporated in the conductance module of the Lyon-Fedder-Mobarry (LFM) global magnetosphere model. In this presentation, we make the final step toward the full coupling of the microscopic ET physics within our global coupled model including LFM, the Rice Convection Model (RCM) and TIEGCM. To this end, ET effects are incorporated in the TIEGCM model and propagate throughout the system via thus modified TIEGCM conductances. The March 17, 2013 geomagnetic storm is used as a testbed for these fully coupled simulations, and the results of the model are compared with various ionospheric and magnetospheric observatories, including DMSP, AMPERE, and Van Allen Probes. Via these comparisons, we investigate, in particular, the ET effects on the global magnetosphere indicators such as the

  9. Ionospheric and thermospheric couplings: vertical, latitudinal and longitudinal

    Science.gov (United States)

    Wickwar, V. B.; Carlson, H. C.

    1999-01-01

    The ionosphere, embedded in and tightly coupled to the thermosphere, is strongly influenced by couplings to other geophysical regions. For example, above it, both the magnetosphere and plasmasphere greatly affect the ionosphere by the precipitation of soft and energetic particles, by heat conduction, and by fluxes of thermal particles. Below, the middle atmosphere affects it with upwardly propagating waves (gravity waves, tides, and planetary waves). All the while, polar and auroral regions greatly affect the mid-latitudes by the equatorward penetration of electric fields and winds, and by the equatorward propagation of waves (traveling ionospheric disturbances or TIDs). Exploring these couplings effectively furthers our understanding of at least the dominant processes and interactions that play such an important role in determining the character of this part of the Earths environment. Significant progress during the Solar-Terrestrial Energy Program (STEP) has demanded that the observational, analytical, and theoretical thrusts of the international scientific community be global in all senses. Observationally, this has led to coordinated measurements from many regions, from the poles to the equator, and from ground- and space-based instruments. It has also led to many different instruments, including new ones, measuring an extensive variety of (related) geophysical parameters. Depending on the instrument, measurements have been made continuously or at appropriate intervals to sample different geomagnetic conditions, and diurnal, seasonal, inter-annual, and solar-cycle variations. Extensive analyses have been carried out on these observations. New empirical models have been developed and old ones improved. Theoretical work has led to new and improved first-principles models that are being used to test our understanding of the observations. Our intent is to review this progress and suggest some future directions. Our approach is to illustrate the broad front of

  10. Signals in the ionosphere generated by tsunami earthquakes: observations and modeling suppor

    Science.gov (United States)

    Rolland, L.; Sladen, A.; Mikesell, D.; Larmat, C. S.; Rakoto, V.; Remillieux, M.; Lee, R.; Khelfi, K.; Lognonne, P. H.; Astafyeva, E.

    2017-12-01

    Forecasting systems failed to predict the magnitude of the 2011 great tsunami in Japan due to the difficulty and cost of instrumenting the ocean with high-quality and dense networks. Melgar et al. (2013) show that using all of the conventional data (inland seismic, geodetic, and tsunami gauges) with the best inversion method still fails to predict the correct height of the tsunami before it breaks onto a coast near the epicenter (warning systems. We anticipate that the method could be decisive for mitigating "tsunami earthquakes" which trigger tsunamis larger than expected from their short-period magnitude. These events are challenging to characterize as they rupture the near-trench subduction interface, in a distant region less constrained by onshore data. As a couple of devastating tsunami earthquakes happens per decade, they represent a real threat for onshore populations and a challenge for tsunami early-warning systems. We will present the TEC observations of the recent Java 2006 and Mentawaii 2010 tsunami earthquakes and base our analysis on acoustic ray tracing, normal modes summation and the simulation code SPECFEM, which solves the wave equation in coupled acoustic (ocean, atmosphere) and elastic (solid earth) domains. Rupture histories are entered as finite source models, which will allow us to evaluate the effect of a relatively slow rupture on the surrounding ocean and atmosphere.

  11. Longitudinal Differences in the Low-latitude Ionosphere and in the Ionospheric Variability

    Science.gov (United States)

    Goncharenko, L. P.; Zhang, S.; Liu, H.; Tsugawa, T.; Batista, I. S.; Reinisch, B. W.

    2017-12-01

    Analysis of longitudinal differences in ionospheric parameters can illuminate variety of mechanisms responsible for ionospheric variability. In this study, we aim to 1) quantitatively describe major features of longitudinal differences in peak electron density in the low-latitude ionosphere; 2) examine differences in ionospheric variability at different longitude sectors, and 3) illustrate longitudinal differences in ionospheric response to a large disturbance event, sudden stratospheric warming of 2016. We examine NmF2 observations by a network of ionosondes in the American (30-80W) and Asian (110-170E) longitudinal sectors. Selected instruments are located in the vicinity of EIA troughs (Jicamarca, Sao Luis, Guam, Kwajalein), northern and southern crests of EIA (Boa Vista, Tucuman, Cachoeira Paulista, Okinawa), and beyond EIA crests (Ramey, Yamagawa, Kokubunji). To examine main ionospheric features at each location, we use long-term datasets collected at each site to construct empirical models that describe variations in NmF2 as a function of local time, season, solar flux, and geomagnetic activity. This set of empirical models can be used to accurately describe background ionospheric behavior and serve as a set of observational benchmarks for global circulation models. It reveals, for example, higher NmF2 in the EIA trough in the Asian sector as compared to the American sector. Further, we quantitatively describe variability in NmF2 as a difference between local observations and local empirical model, and find that American sector's EIA trough has overall higher variability that maximizes for all local times during wintertime, while Asian sector trough variability does not change significantly with season. Additionally, local empirical models are used to isolate ionospheric features resulting from dynamical disturbances of different origin (e.g. geomagnetic storms, convective activity, sudden stratospheric warming events, etc.). We illustrate this approach with

  12. Sudden Ionospheric Disturbances (SID)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Sudden ionospheric disturbances (SID) are caused by solar flare enhanced X-rays in the 1 to 10 angstrom range. Solar flares can produce large increases of ionization...

  13. Ionospheric foF2 anomalies during some intense geomagnetic storms

    Directory of Open Access Journals (Sweden)

    R. P. Kane

    2005-10-01

    Full Text Available The global evolutions of foF2 anomalies were examined for three very intense geomagnetic storms, namely the Halloween events of October-November 2003 (Event X, 29–30 October 2003, Dst –401 nT; Event Y, 20–21 November 2003, Dst –472 nT, and the largest Dst storm (Event Z, 13–14 March 1989, Dst –589 nT. For Event X, troughs (negative storms were clearly seen for high northern and southern latitudes. For northern midlatitudes as well as for low latitudes, there were very strong positive effects on 29 October 2003, followed by negative effects the next day. For Event Y, there were no troughs in NH high latitudes for morning and evening hours but there were troughs for night. For midlatitudes and low latitudes, some longitudes showed strong negative effects in the early morning as expected, but some longitudes showed strong positive effects at noon and in the evening hours. Thus, there were many deviations from the model patterns. The deviations were erratic, indicating considerable local effects superposed on general patterns. A disconcerting feature was the presence of strong positive effects during the 24 h before the storm commencement. Such a feature appears only in the 24 h before the geomagnetic storm commencement but not earlier. If genuine, these could imply a prediction potential with a 24-h antecedence. For Event Z (13–14 March 1989, equinox, all stations (all latitudes and longitudes showed a very strong "negative storm" in the main phase, and no positive storms anywhere. Keywords. Ionosphere (Equatorial ionosphereIonospheric disturbances – Mid-latitude IonospherePolar ionosphere

  14. Impact of cosmic rays and solar energetic particles on the Earth’s ionosphere and atmosphere

    Directory of Open Access Journals (Sweden)

    Mateev Lachezar

    2013-03-01

    Full Text Available A brief review of the study during COST Action ES0803 of effects due to cosmic rays (CR and solar energetic particles (SEP in the ionosphere and atmosphere is presented. Models CORIMIA (COsmic Ray Ionization Model for Ionosphere and Atmosphere and application of CORSIKA (COsmic Ray SImulations for KAscade code are considered. They are capable to compute the cosmic ray ionization profiles at a given location, time, solar and geomagnetic activity. Intercomparison of the models, as well as comparison with direct measurements of the atmospheric ionization, validates their applicability for the entire atmosphere and for the different levels of the solar activity. The effects of CR and SEP can be very strong locally in the polar cap regions, affecting the physical-chemical and electrical properties of the ionosphere and atmosphere. Contributions here were also made by the anomalous CR, whose ionization is significant at high geomagnetic latitudes (above 65°–70°. Several recent achievements and application of CR ionization models are briefly presented. This work is the output from the SG 1.1 of the COST ES0803 action (2008–2012 and the emphasis is given on the progress achieved by European scientists involved in this collaboration.

  15. Dust models compatible with Planck intensity and polarization data in translucent lines of sight

    Science.gov (United States)

    Guillet, V.; Fanciullo, L.; Verstraete, L.; Boulanger, F.; Jones, A. P.; Miville-Deschênes, M.-A.; Ysard, N.; Levrier, F.; Alves, M.

    2018-02-01

    Context. Current dust models are challenged by the dust properties inferred from the analysis of Planck observations in total and polarized emission. Aims: We propose new dust models compatible with polarized and unpolarized data in extinction and emission for translucent lines of sight (0.5 Methods: We amended the DustEM tool to model polarized extinction and emission. We fit the spectral dependence of the mean extinction, polarized extinction, total and polarized spectral energy distributions (SEDs) with polycyclic aromatic hydrocarbons, astrosilicate and amorphous carbon (a-C) grains. The astrosilicate population is aligned along the magnetic field lines, while the a-C population may be aligned or not. Results: With their current optical properties, oblate astrosilicate grains are not emissive enough to reproduce the emission to extinction polarization ratio P353/pV derived with Planck data. Successful models are those using prolate astrosilicate grains with an elongation a/b = 3 and an inclusion of 20% porosity. The spectral dependence of the polarized SED is steeper in our models than in the data. Models perform slightly better when a-C grains are aligned. A small (6%) volume inclusion of a-C in the astrosilicate matrix removes the need for porosity and perfect grain alignment, and improves the fit to the polarized SED. Conclusions: Dust models based on astrosilicates can be reconciled with data by adapting the shape of grains and adding inclusions of porosity or a-C in the astrosilicate matrix.

  16. Observed and modelled effects of auroral precipitation on the thermal ionospheric plasma: comparing the MICA and Cascades2 sounding rocket events

    Science.gov (United States)

    Lynch, K. A.; Gayetsky, L.; Fernandes, P. A.; Zettergren, M. D.; Lessard, M.; Cohen, I. J.; Hampton, D. L.; Ahrns, J.; Hysell, D. L.; Powell, S.; Miceli, R. J.; Moen, J. I.; Bekkeng, T.

    2012-12-01

    Auroral precipitation can modify the ionospheric thermal plasma through a variety of processes. We examine and compare the events seen by two recent auroral sounding rockets carrying in situ thermal plasma instrumentation. The Cascades2 sounding rocket (March 2009, Poker Flat Research Range) traversed a pre-midnight poleward boundary intensification (PBI) event distinguished by a stationary Alfvenic curtain of field-aligned precipitation. The MICA sounding rocket (February 2012, Poker Flat Research Range) traveled through irregular precipitation following the passage of a strong westward-travelling surge. Previous modelling of the ionospheric effects of auroral precipitation used a one-dimensional model, TRANSCAR, which had a simplified treatment of electric fields and did not have the benefit of in situ thermal plasma data. This new study uses a new two-dimensional model which self-consistently calculates electric fields to explore both spatial and temporal effects, and compares to thermal plasma observations. A rigorous understanding of the ambient thermal plasma parameters and their effects on the local spacecraft sheath and charging, is required for quantitative interpretation of in situ thermal plasma observations. To complement this TRANSCAR analysis we therefore require a reliable means of interpreting in situ thermal plasma observation. This interpretation depends upon a rigorous plasma sheath model since the ambient ion energy is on the order of the spacecraft's sheath energy. A self-consistent PIC model is used to model the spacecraft sheath, and a test-particle approach then predicts the detector response for a given plasma environment. The model parameters are then modified until agreement is found with the in situ data. We find that for some situations, the thermal plasma parameters are strongly driven by the precipitation at the observation time. For other situations, the previous history of the precipitation at that position can have a stronger

  17. Modeling of the Ionospheric Scintillation and Total Electron Content Observations during the 21 August 2017 Total Solar Eclipse

    Science.gov (United States)

    Datta-Barua, S.; Gachancipa, J. N.; Deshpande, K.; Herrera, J. A.; Lehmacher, G. A.; Su, Y.; Gyuk, G.; Bust, G. S.; Hampton, D. L.

    2017-12-01

    High concentration of free electrons in the ionosphere can cause fluctuations in incoming electromagnetic waves, such as those from the different Global Navigation Satellite Systems (GNSS). The behavior of the ionosphere depends on time and location, and it is highly influenced by solar activity. The purpose of this study is to determine the impact of a total solar eclipse on the local ionosphere in terms of ionospheric scintillations, and on the global ionosphere in terms of TEC (Total Electron Content). The studied eclipse occurred on 21 August 2017 across the continental United States. During the eclipse, we expected to see a decrease in the scintillation strength, as well as in the TEC values. As a broader impact part of our recently funded NSF proposal, we temporarily deployed two GNSS receivers on the eclipse's totality path. One GNSS receiver was placed in Clemson, SC. This is a multi-frequency GNSS receiver (NovAtel GPStation-6) capable of measuring high and low rate scintillation data as well as TEC values from four different GNSS systems. We had the receiver operating before, during, and after the solar eclipse to enable the comparison between eclipse and non-eclipse periods. A twin receiver collected data at Daytona Beach, FL during the same time, where an 85% partial solar eclipse was observed. Additionally, we set up a ground receiver onsite in the path of totality in Perryville, Missouri, from which the Adler Planetarium of Chicago launched a high-altitude balloon to capture a 360-degree video of the eclipse from the stratosphere. By analyzing the collected data, this study looks at the effects of partial and total solar eclipse periods on high rate GNSS scintillation data at mid-latitudes, which had not been explored in detail. This study also explores the impact of solar eclipses on signals from different satellite constellations (GPS, GLONASS, and Galileo). Throughout the eclipse, the scintillation values did not appear to have dramatic changes

  18. Search for Physics Beyond the Standard Model via Positron Polarization Measurements with Polarized $ ^{17} $F.

    CERN Multimedia

    Versyck, S

    2002-01-01

    This proposal aims at measuring the longitudinal polarization of positrons emitted from polarized $^{17} $F~nuclei. The experiment will have a comparable sensitivity to possible right-handed current contributions in the weak interaction as the experiment which was recently carried out with $ ^{107} $In in Louvain-la-Neuve, but will provide a more stringent limit due to the fact that, since $ ^{17} $F decays through a superallowed $\\beta$ -transition, the recoil-order corrections to the allowed approximation can be taken into account very precisely. Furthermore, because $ ^{17} $F decays via a mixed Fermi/Gamow-Teller $\\beta$ -transition, this experiment will also yield a new limit on possible scalar contributions to the weak interaction. While the $^{17}$F beam is being developed, part of the beamtime was used to perform a similar experiment with $^{118}$ Sb. As this isotope decays via a pure GT $\\beta$ -transition, this experiment will yield new limits on the possible presence of both right-handed and tensor...

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

    Science.gov (United States)

    Cornely, P.; Daniell, R. E.

    2013-12-01

    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.

  20. Comparative ionospheres: Terrestrial and giant planets

    Science.gov (United States)

    Mendillo, Michael; Trovato, Jeffrey; Moore, Luke; Müller-Wodarg, Ingo

    2018-03-01

    The study of planetary ionospheres within our solar system offers a variety of settings to probe mechanisms of photo-ionization, chemical loss, and plasma transport. Ionospheres are a minor component of upper atmospheres, and thus their mix of ions observed depends on the neutral gas composition of their parent atmospheres. The same solar irradiance (x-rays and extreme-ultra-violet vs. wavelength) impinges upon each of these atmospheres, with solar flux magnitudes changed only by the inverse square of distance from the Sun. If all planets had the same neutral atmosphere-with ionospheres governed by photochemical equilibrium (production = loss)-their peak electron densities would decrease as the inverse of distance from the Sun, and any changes in solar output would exhibit coherent effects throughout the solar system. Here we examine the outer planet with the most observations of its ionosphere (Saturn) and compare its patterns of electron density with those at Earth under the same-day solar conditions. We show that, while the average magnitudes of the major layers of molecular ions at Earth and Saturn are approximately in accord with distance effects, only minor correlations exist between solar effects and day-to-day electron densities. This is in marked contrast to the strong correlations found between the ionospheres of Earth and Mars. Moreover, the variability observed for Saturn's ionosphere (maximum electron density and total electron content) is much larger than found at Earth and Mars. With solar irradiance changes far too small to cause such effects, we use model results to explore the roles of other agents. We find that water sources from Enceladus at low latitudes, and 'ring rain' at middle latitudes, contribute substantially to variability via water ion chemistry. Thermospheric winds and electrodynamics generated at auroral latitudes are suggested causes of high latitude ionospheric variability, but remain inconclusive due to the lack of relevant

  1. Supersonic plasma flow between high latitude conjugate ionospheres

    International Nuclear Information System (INIS)

    Roesler, G.

    1975-01-01

    The polar wind problem has been investigated for closed field lines in situations where one of the two conjugate ionospheric regions is fully illuminated by the sun and the other darkness (solstices at high latitudes). A supersonic flow between hemispheres is possible; the magnetospheric part of this flow must be symmetric with respect to the equator. The daytime fluxes are proportional to the neutral hydrogen density. Fluxes of the order of 10 8 cm -2 sec -1 are only possible with density considerably higher than given by CIRA models. For stationary solutions higher flow speeds are needed on the dark side than provided from the illuminated side. It is concluded that shock waves with upward velocities of about 5 km/sec would form above the dark ionosphere. This implies a reduction by a factor of 3 to 5 of the plasma influx into the dark hemisphere, whereby F-layer densities of only up to 2 x 10 4 cm -3 can be maintained. (orig.) [de

  2. Modeling optical and UV polarization of AGNs. III. From uniform-density to clumpy regions

    Science.gov (United States)

    Marin, F.; Goosmann, R. W.; Gaskell, C. M.

    2015-05-01

    Context. A growing body of evidence suggests that some, if not all, scattering regions of active galactic nuclei (AGNs) are clumpy. The inner AGN components cannot be spatially resolved with current instruments and must be studied by numerical simulations of observed spectroscopy and polarization data. Aims: We run radiative transfer models in the optical/UV for a variety of AGN reprocessing regions with different distributions of clumpy scattering media. We obtain geometry-sensitive polarization spectra and images to improve our previous AGN models and their comparison with the observations. Methods: We use the latest public version 1.2 of the Monte Carlo code stokes presented in the first two papers of this series to model AGN reprocessing regions of increasing morphological complexity. We replace previously uniform-density media with up to thousands of constant-density clumps. We couple a continuum source to fragmented equatorial scattering regions, polar outflows, and toroidal obscuring dust regions and investigate a wide range of geometries. We also consider different levels of fragmentation in each scattering region to evaluate the importance of fragmentation for the net polarization of the AGN. Results: In comparison with uniform-density models, equatorial distributions of gas and dust clouds result in grayer spectra and show a decrease in the net polarization percentage at all lines of sight. The resulting polarization position angle depends on the morphology of the clumpy structure, with extended tori favoring parallel polarization while compact tori produce orthogonal polarization position angles. In the case of polar scattering regions, fragmentation increases the net polarization unless the cloud filling factor is small. A complete AGN model constructed from the individual, fragmented regions can produce low polarization percentages (<2%), with a parallel polarization angle for observer inclinations up to 70° for a torus half opening angle of 60°. For

  3. Mathematical modelling of ionospheric TEC from Turkish permanent GNSS Network (TPGN) observables during 2009-2017 and predictability of NeQuick and Kriging models

    Science.gov (United States)

    Ansari, Kutubuddin; Panda, Sampad Kumar; Corumluoglu, Ozsen

    2018-03-01

    The present study examines the ionospheric Total Electron Content (TEC) variations in the lower mid-latitude Turkish region from the Turkish permanent GNSS network (TPGN) and International GNSS Services (IGS) observations during the years 2009 to 2017. The corresponding vertical TEC (VTEC) predicted by Kriging and NeQuick-2 models are evaluated to realize their efficacy over the country. We studied the diurnal, seasonal and spatial pattern of VTEC variation and tried to estimate by a new mathematical model using the long term of 9 years VTEC data. The diurnal variation of VTEC demonstrates a normal trend with its gradual enhancement from dawn to attain a peak around 09:00-14.00 UT and reaching the minimum level after 22.00 UT. The seasonal behavior of VTEC indicates a strong semi-annual variation of VTEC with maxima in September equinox followed by March equinox and minima in June solstice followed by December solstice. Also, the spatial variation in VTEC depicts a meaningful longitudinal/latitudinal pattern altering with seasons. It decreases longitudinally from the west to the east during March equinox and June solstice increases with latitude. The comparative analysis among the GNSS-VTEC, Kriging, NeQuick and the proposed mathematical model are evaluated with the help one way ANOVA test. The analysis shows that the null hypothesis of the models during storm and quiet days are accepted and suggesting that all models are statistically significantly equivalent from each other. We believe the outcomes from this study would complement towards a relatively better understanding of the lower mid-latitude VTEC variation over the Turkish region and analogous latitudes over the globe.

  4. The D-Region Ionospheric Response to the 2017 Solar Eclipse

    Science.gov (United States)

    Cohen, M.; McCormick, J.; Gross, N. C.; Higginson-Rollins, M. A.

    2017-12-01

    VLF/LF radio remote sensing (0.5-500 kHz) is an effective means for quantifying the D-region ionosphere (60-90 km altitude). Disturbances in the ionospheric electron density induce changes in the propagation of VLF/LF signals, so a network of transmitters and receivers can effectively "image" a disturbed region. VLF/LF signals can all be detected from 100s-1000s of km away. We utilize Georgia Tech's network of highly-sensitive VLF/LF receivers to quantify the lower ionospheric response to the "Great American Eclipse". Nine of these were deployed and operational across the Continental US, Alaska and Puerto Rico all operated successfully. Each receiver synchronously recorded the full radio spectrum between 0.5-470 kHz. The included figure shows the eclipse track at 80 km altitude with a green swath. The nine operational receivers are shown with blue stars, and operational VLF/LF transmitters in dark red. Gray lines are shown for each great-circle path linking a VLF/LF transmitter to a receiver. This constellation forms a dense spider's-web grid of radio links, with which we can effectively image the disturbed patch of the D-region ionosphere as it moves across the country. In addition, shown in yellow are NDGPS transmitters which lie between 285-325 kHz. The red dots are the 230,000 geolocated lightning strokes during the 90-mintue eclipse pass, each of which emitted an intense VLF/LF impulse. These are also detected by our receivers. We present our observations and comparison with a theoretical model, using a combination of three techniques established by a series of three 2017 journal papers: (1) Polarization measurements of VLF/LF transmitter signals, (2) Lightning-generated VLF sferics detected 1000s of km away, and (3) NDGPS beacons near 300 kHz for shorter-range sounding of a small patch of the ionosphere. We find evidence of large scale ionospheric changes which affect the D-region over the entire continental region with a slowly-varying signal perturbation

  5. Shocklike soliton because of an impinge of protons and electrons solar particles with Venus ionosphere

    Science.gov (United States)

    Moslem, W. M.; Rezk, S.; Abdelsalam, U. M.; El-Labany, S. K.

    2018-04-01

    This paper introduces an investigation of shocklike soliton or small amplitude Double Layers (DLs) in a collisionless plasma, consisting of positive and negative ions, nonthermal electrons, as well as solar wind streaming protons and electrons. Gardner equation is derived and its shocklike soliton solution is obtained. The model is employed to recognize a possible nonlinear wave at Venus ionosphere. The results indicate that the number densities and velocities of the streaming particles play crucial role to determine the polarity and characteristic features (amplitude and width) of the shocklike soliton waves. An electron streaming speed modifies a negative shocklike wave profile, while an ion streaming speed modulates a positive shocklike wave characteristic.

  6. Modeling the Kelvin polarization force actuation of Micro- and Nanomechanical systems

    DEFF Research Database (Denmark)

    Schmid, Silvan; Hierold, C.; Boisen, Anja

    2010-01-01

    Polarization forces have become of high interest in micro- and nanomechanical systems. In this paper, an analytical model for a transduction scheme based on the Kelvin polarization force is presented. A dielectric beam is actuated by placing it over the gap of two coplanar electrodes. Finite...

  7. Λ polarization in an exact fluid dynamical model for heavy-ion collisions

    Directory of Open Access Journals (Sweden)

    Xie Yilong

    2016-01-01

    Full Text Available Λ polarization is calculated in an exact analytical, rotating model based on parameters from a high resolution (3+1D Particle-in-Cell Relativistic hydrodynamics calculation. The polarization is attributed to effects from thermal vorticity and for the first time the effects of the radial and axial acceleration are also studied separately.

  8. (VTEC) in the Ionosphere for GPS Observations

    African Journals Online (AJOL)

    Michael

    2017-12-02

    Dec 2, 2017 ... artificial intelligence for establishing correction models of ionospheric delay. For instance,. Habarulena et al., (2007) used backpropagation neural network to establish a VTEC model of a region comprised of various observations stations. Hu et al., (2014) proposed a hybrid VTEC prediction technique of ...

  9. Characterizing the Meso-scale Plasma Flows in Earth's Coupled Magnetosphere-Ionosphere-Thermosphere System

    Science.gov (United States)

    Gabrielse, C.; Nishimura, T.; Lyons, L. R.; Gallardo-Lacourt, B.; Deng, Y.; McWilliams, K. A.; Ruohoniemi, J. M.

    2017-12-01

    NASA's Heliophysics Decadal Survey put forth several imperative, Key Science Goals. The second goal communicates the urgent need to "Determine the dynamics and coupling of Earth's magnetosphere, ionosphere, and atmosphere and their response to solar and terrestrial inputs...over a range of spatial and temporal scales." Sun-Earth connections (called Space Weather) have strong societal impacts because extreme events can disturb radio communications and satellite operations. The field's current modeling capabilities of such Space Weather phenomena include large-scale, global responses of the Earth's upper atmosphere to various inputs from the Sun, but the meso-scale ( 50-500 km) structures that are much more dynamic and powerful in the coupled system remain uncharacterized. Their influences are thus far poorly understood. We aim to quantify such structures, particularly auroral flows and streamers, in order to create an empirical model of their size, location, speed, and orientation based on activity level (AL index), season, solar cycle (F10.7), interplanetary magnetic field (IMF) inputs, etc. We present a statistical study of meso-scale flow channels in the nightside auroral oval and polar cap using SuperDARN. These results are used to inform global models such as the Global Ionosphere Thermosphere Model (GITM) in order to evaluate the role of meso-scale disturbances on the fully coupled magnetosphere-ionosphere-thermosphere system. Measuring the ionospheric footpoint of magnetospheric fast flows, our analysis technique from the ground also provides a 2D picture of flows and their characteristics during different activity levels that spacecraft alone cannot.

  10. Effects of the Ionosphere on Passive Microwave Remote Sensing of Ocean Salinity from Space

    Science.gov (United States)

    LeVine, D. M.; Abaham, Saji; Hildebrand, Peter H. (Technical Monitor)

    2001-01-01

    Among the remote sensing applications currently being considered from space is the measurement of sea surface salinity. The salinity of the open ocean is important for understanding ocean circulation and for modeling energy exchange with the atmosphere. Passive microwave remote sensors operating near 1.4 GHz (L-band) could provide data needed to fill the gap in current coverage and to complement in situ arrays being planned to provide subsurface profiles in the future. However, the dynamic range of the salinity signal in the open ocean is relatively small and propagation effects along the path from surface to sensor must be taken into account. In particular, Faraday rotation and even attenuation/emission in the ionosphere can be important sources of error. The purpose or this work is to estimate the magnitude of these effects in the context of a future remote sensing system in space to measure salinity in L-band. Data will be presented as a function of time location and solar activity using IRI-95 to model the ionosphere. The ionosphere presents two potential sources of error for the measurement of salinity: Rotation of the polarization vector (Faraday rotation) and attenuation/emission. Estimates of the effect of these two phenomena on passive remote sensing over the oceans at L-band (1.4 GHz) are presented.

  11. Multicomponent Adsorption Model for Polar and Associating Mixtures

    DEFF Research Database (Denmark)

    Nesterov, Igor; Shapiro, Alexander; Kontogeorgis, Georgios M.

    2015-01-01

    The multicomponent potential adsorption theory (MPTA) is revisited in this work for polar and associating systems. MPTA is used in combination with the CPA equation of state. Previous Studies have shown that both MPTA and other theories present difficulties for complex systems. Some of these prob...

  12. The Shock Wave in the ionosphere during an Earthquake

    Directory of Open Access Journals (Sweden)

    Kuznetsov Vladimir

    2016-01-01

    Full Text Available Fundamentally new model of the shock wave (SW generation in atmosphere and ionosphere during earthquake is proposed. The model proceeds from the idea of cooperative shock water crystallization in a cloud.

  13. Ionospheric travelling convection vortices observed by the Greenland magnetometer chain

    DEFF Research Database (Denmark)

    Kotsiaros, Stavros; Stolle, Claudia; Friis-Christensen, Eigil

    2013-01-01

    The Greenland magnetometer array continuously provides geomagnetic variometer data since the early eighties. With the polar cusp passing over it almost every day, the array is suitable to detect ionospheric traveling convection vortices (TCVs), which were rst detected by Friis-Christensen et al...

  14. Theoretical model of a polarization diffractive elements for the light beams conversion holographic formation in PDLCs

    Science.gov (United States)

    Sharangovich, Sergey N.; Semkin, Artem O.

    2017-12-01

    In this work a theoretical model of the holographic formation of the polarization diffractive optical elements for the transformation of Gaussian light beams into Bessel-like ones in polymer-dispersed liquid crystals (PDLC) is developed. The model is based on solving the equations of photo-induced Fredericks transition processes for polarization diffractive elements formation by orthogonally polarized light beams with inhomogeneous amplitude and phase profiles. The results of numerical simulation of the material's dielectric tensor changing due to the structure's formation process are presented for various recording beams' polarization states. Based on the results of numerical simulation, the ability to form the diffractive optical elements for light beams transformation by the polarization holography methods is shown.

  15. Spatial structure of summertime ionospheric plasma near magnetic noon

    Directory of Open Access Journals (Sweden)

    R. W. Sims

    2005-01-01

    Full Text Available Results are presented from a multi-instrument study of the spatial distribution of the summertime, polar ionospheric electron density under conditions of relatively stable IMF Bz<0. The EISCAT Svalbard radar revealed a region of enhanced densities near magnetic noon that, when comparing radar scans from different local times, appeared to be spatially confined in longitude. This was identified as the tongue-of-ionisation (TOI that comprised photoionisation of sub-auroral origin that is drawn poleward into the polar cap by the anti-sunward flow of the high-latitude convection. The TOI was bounded in longitude by high-latitude troughs; the pre-noon trough on the morning side with a minimum near 78° N and the post-noon trough on the afternoon side with a minimum at 80° N. Complementary measurements by radio tomography, the SuperDARN radars, and a DMSP satellite, together with comparisons with earlier modelling work, provided supporting evidence for the interpretation of the density structuring, and highlighted the role of plasma convection in the formation of summertime plasma distribution. Soft particle precipitation played only a secondary role in the modulation of the large summertime densities entering the polar cap.

  16. Spatial structure of summertime ionospheric plasma near magnetic noon

    Directory of Open Access Journals (Sweden)

    R. W. Sims

    2005-01-01

    Full Text Available Results are presented from a multi-instrument study of the spatial distribution of the summertime, polar ionospheric electron density under conditions of relatively stable IMF Bz<0. The EISCAT Svalbard radar revealed a region of enhanced densities near magnetic noon that, when comparing radar scans from different local times, appeared to be spatially confined in longitude. This was identified as the tongue-of-ionisation (TOI that comprised photoionisation of sub-auroral origin that is drawn poleward into the polar cap by the anti-sunward flow of the high-latitude convection. The TOI was bounded in longitude by high-latitude troughs; the pre-noon trough on the morning side with a minimum near 78° N and the post-noon trough on the afternoon side with a minimum at 80° N. Complementary measurements by radio tomography, the SuperDARN radars, and a DMSP satellite, together with comparisons with earlier modelling work, provided supporting evidence for the interpretation of the density structuring, and highlighted the role of plasma convection in the formation of summertime plasma distribution. Soft particle precipitation played only a secondary role in the modulation of the large summertime densities entering the polar cap.

  17. South polar permanent CO2 ice cap presentation in the Global Mars Multiscale Model

    Science.gov (United States)

    Fazel-Rastgar, Farahnaz

    2018-02-01

    The atmospheric influence caused by the Martian permanent south CO2 ice cap is examined to improve the Global Mars Multiscale Model (GM3) to see if it can significantly improve the representation of south polar meteorology. However, the seasonal carbon dioxide ice in the polar regions is presented in the surface ice simulation by the Global Mars Multiscale Model but the model does not produce a permanent south CO2 ice cap, and the physics code must modify to capture the realistic physical such as ice process detail; probably makes a bias in terms of total CO2 ice and meteorological processes in the model aside from ice formation. The permanent south CO2 ice cap in the model can significantly improve the representation of south polar meteorology for example in predicted surface temperatures, surface pressures, horizontal and zonal winds over the south cap and possible initiation of dust storms at south polar region during the southern summer period.

  18. A Study on the Radio Propagation in the Korean Ionosphere

    Directory of Open Access Journals (Sweden)

    Seok-Hee Bae

    1992-06-01

    Full Text Available The effects of the ionosphere on the radio wave propagation are scattering of radio waves, attenuation, angle error, ranging error, and time delay. If ionospheric conditions are suitable, the charged particles can remove energy from radio waves and thus attenuate the signal. Also, a radio wave traveling a path along which the electron density is not constant undergoes changes in direction, position and time of propagation. The present study is based on Korean ionospheric data obtained at the AnYong Radio Research Institute from Jan. 1985 through Oct. 1989. The data are used to simulate the Korean ionosphere following the Chapman law. The effects of the model ionosphere on the radio wave propagation, such as the angle, position error, time delay, and the attenuation, are studies for the various cases of the wave frequency and the altitude.

  19. Influence of Ionospheric Weather on GNSS Radio Occultation Signals

    Science.gov (United States)

    Yue, X.; Schreiner, W. S.; Pedatella, N. M.; Kuo, Y. H.

    2016-12-01

    Transient loss of lock (LOL) is one of the key space weather effects on the Global Navigation Satellite System (GNSS). Based on the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) Global Positioning System (GPS) radio occultation (RO) observations during 2007-2011, we have analyzed the signal cycle slip (CS) occurrence comprehensively and its correlation to the ionospheric weather phenomena such as sporadic E (Es), equatorial F region irregularity (EFI), and the ionospheric equatorial ionization anomaly (EIA). The high vertical resolution of RO observations enables us to distinguish the CS resulting from different ionospheric layers clearly on a global scale. In the E layer, the CS is dominated by the Es occurrence, while in the F layer, the CS is mainly related to the EIA and EFI at low and equatorial latitudes. In the polar region, the CS is primarily related to polar cap electron density gradients. The overall average CS (> 6 cycles) occurrence is 23% per occultation, with the E (50-150 km) and F (150-600 km) layers contributing 8.3% and 14.7%, respectively. Awareness of the effect of the ionospheric weather on the CS of the low-Earth-orbit (LEO)-based GNSS signal could be beneficial to a variety of applications, including the LEO-based GNSS data processing and the corresponding hardware/firmware design.

  20. Modelling Near-IR polarization to constrain stellar wind bow shocks

    Science.gov (United States)

    Neilson, Hilding R.; Ignace, R.; Shrestha, M.; Hoffman, J. L.; Mackey, J.

    2013-06-01

    Bow shocks formed from stellar winds are common phenomena observed about massive and intermediate-mass stars such as zeta Oph, Betelgeuse and delta Cep. These bow shocks provide information about the motion of the star, the stellar wind properties and the density of the ISM. Because bow shocks are asymmetric structures, they also present polarized light that is a function of their shape and density. We present a preliminary work modeling dust polarization from a Wilkin (1996) analytic bow shock model and explore how the polarization changes as a function of stellar wind properties.

  1. Fractional model for heat conduction in polar bear hairs

    Directory of Open Access Journals (Sweden)

    Wang Qing-Li

    2012-01-01

    Full Text Available Time-fractional differential equations can accurately describe heat conduction in fractal media, such as wool fibers, goose down and polar bear hair. The fractional complex transform is used to convert time-fractional heat conduction equations with the modified Riemann-Liouville derivative into ordinary differential equations, and exact solutions can be easily obtained. The solution process is straightforward and concise.

  2. Computer simulations of ionospheric electric fields and currents - final report of the IMS magnetometer project

    Energy Technology Data Exchange (ETDEWEB)

    Kamide, Y.; Kroehl, H.W.

    1985-12-01

    This report summarizes the major results of a five-year research project initiated by the authors who collaborated with as many as 100 scientists from many countries. In this project a numerical algorithm has been developed and improved from which one estimates the global distribution of electric fields and currents in the horizontal ionosphere as well as field-aligned vertical currents in the polar region from ground-based geomagnetic records and a model of ionospheric conductivity. As an important byproduct of the inversion scheme, we infer the distribution of Joule heat production from the ionospheric currents. Crucial tests of the method in accurately reproducing the large-scale measured patterns of electrodynamic parameters in the earth's environment have proved that the method will accurately reproduce inputs (e.g., ground magnetic perturbation vectors) within the numerical limitations of the most probable solutions of second-order differential equations. As these tests proved successful, the scheme was applied to the extensive geomagnetic data sets which were collected as part of the International Magnetospheric Study (IMS) to determine the instantaneous electric field and current patterns which agreed with those obtained by more direct methods, such as radar and satellite measurements.

  3. The impact of aerosols on polarized sky radiance: model development, validation, and applications

    Directory of Open Access Journals (Sweden)

    C. Emde

    2010-01-01

    Full Text Available Although solar radiation initially is unpolarized when entering the Earth's atmosphere, it is polarized by scattering processes with molecules, water droplets, ice crystals, and aerosols. Hence, measurements of the polarization state of radiation can be used to improve remote sensing of aerosols and clouds. The analysis of polarized radiance measurements requires an accurate radiative transfer model. To this end, a new efficient and flexible three-dimensional Monte Carlo code to compute polarized radiances has been developed and implemented into MYSTIC (Monte Carlo code for the phYSically correct Tracing of photons In Cloudy atmospheres. The code has been extensively validated against published benchmark results. The polarized downwelling radiation field is calculated for various aerosol types showing the high sensitivity of polarized ultraviolet radiances to the particle microphysics. Model simulations are compared to ground based measurements and found to be qualitatively in good agreement. Quantitative differences can be attributed to the assumed aerosol models based on the OPAC aerosol database, which does not include exactly the types of aerosols that have been observed. This comparison to the measurements shows that there is a high potential to retrieve information about the aerosol type from polarized radiance measurements.

  4. Ionospheric Impacts on UHF Space Surveillance

    Science.gov (United States)

    Jones, J. C.

    2017-12-01

    Earth's atmosphere contains regions of ionized plasma caused by the interaction of highly energetic solar radiation. This region of ionization is called the ionosphere and varies significantly with altitude, latitude, local solar time, season, and solar cycle. Significant ionization begins at about 100 km (E layer) with a peak in the ionization at about 300 km (F2 layer). Above the F2 layer, the atmosphere is mostly ionized but the ion and electron densities are low due to the unavailability of neutral molecules for ionization so the density decreases exponentially with height to well over 1000 km. The gradients of these variations in the ionosphere play a significant role in radio wave propagation. These gradients induce variations in the index of refraction and cause some radio waves to refract. The amount of refraction depends on the magnitude and direction of the electron density gradient and the frequency of the radio wave. The refraction is significant at HF frequencies (3-30 MHz) with decreasing effects toward the UHF (300-3000 MHz) range. UHF is commonly used for tracking of space objects in low Earth orbit (LEO). While ionospheric refraction is small for UHF frequencies, it can cause errors in range, azimuth angle, and elevation angle estimation by ground-based radars tracking space objects. These errors can cause significant errors in precise orbit determinations. For radio waves transiting the ionosphere, it is important to understand and account for these effects. Using a sophisticated radio wave propagation tool suite and an empirical ionospheric model, we calculate the errors induced by the ionosphere in a simulation of a notional space surveillance radar tracking objects in LEO. These errors are analyzed to determine daily, monthly, annual, and solar cycle trends. Corrections to surveillance radar measurements can be adapted from our simulation capability.

  5. Relationships between the Birkeland currents, ionospheric currents, and electric fields

    International Nuclear Information System (INIS)

    Bleuler, E.; Li, C.H.; Nisbet, J.S.

    1982-01-01

    Calculations are made of the currents and electric fields in the ionosphere by using a global model of the electron densities including conjugate coupling along field lines. Incoherent scatter and rocket measurements of high-latitude electron densities have been used to derive realistic variations of the polar conductivities as a function of magnetic activity. The Birkeland currents have been specified in terms of three indices, the total current into and out of the hemisphere, the ratio of the magnitudes of the currents in the AM and PM sectors, R/sub ap/ , and R 12 , the ratio of the magnitudes of the currents in region 1 and 2. The relationship between these parameters of the Birkeland current systems and the auroral electrojet indices AE, AL, and AU is examined as well as the polar cap potential and the electric field at lower latitudes. The cusp currents have been modeled in relation to the interplanetary magnetic field and calculations are given of their effect on electric field and current patterns. One aim of this study is to produce a mathematical model of the currents, electric fields and energy inputs produced by field aligned currents that is consistent with, and specifiable in terms of, measured geophysical indices

  6. Ionosphere and Radio Communication

    Indian Academy of Sciences (India)

    The upperionosphere is used for radio communication and navigationas it reflects long, medium, as well as short radio waves. Sincesolar radiation is the main cause of the existence of ionosphere,any variation in the radiations can affect the entireradio communication system. This article attempts to brieflyintroduce the ...

  7. Ionosphere and Radio Communication

    Indian Academy of Sciences (India)

    ionosphere is used for radio communication and navigation as it reflects long, medium, as well as short radio waves. Since solar radiation is the main cause of the existence of iono- sphere, any variation in the radiations can affect the entire radio communication system. This article attempts to briefly introduce the readers to ...

  8. Comparison of the measured and modeled electron densities and temperatures in the ionosphere and plasmasphere during 14-16 May 1991

    Science.gov (United States)

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

    2004-01-01

    The electron density and temperature in the ionosphere and plasmasphere measured by the Millstone Hill incoherent-scatter radar and the instruments on board of the EXOS-D satellite are compared with calculations from a time-dependent mathematical model of the Earth's ionosphere and plasmasphere during 14-16 May 1991. Use of [O]/[N2] correction factors with the NRLMSISE-00 model of the neutral atmosphere was found to bring the modeled and measured F-region main peak electron densities into agreement. It was found that the nighttime additional heating rate should be added to the normal photoelectron heating in the electron energy equation, in the nighttime plasmasphere region, in order for the model to reproduce the observed high plasmaspheric electron temperature within the Millstone Hill magnetic field flux tube in the Northern Hemisphere. The additional heating brings the measured and modeled electron temperatures into agreement in the plasmasphere and into a very large disagreement in the ionosphere, if the classical electron heat flux along magnetic field lines is used. An approach of Pavlov et al. (2000, 2001) based on a new effective electron thermal conductivity coefficient along the magnetic field line and the evaluated additional heating of electrons in the plasmasphere is used to explain the observed electron temperature in the ionosphere and plasmasphere. This approach leads to a heat flux which is less than that given by the classical theory. The effects of the additional plasmaspheric heating of electrons on the electron temperature and density are small at the F-region altitudes if the modified electron heat flux is used. We found that the resulting effect of vibrationally excited N2 and O2 on NmF2 is the decrease of the calculated NmF2 by up to a factor of about 2.7 by day and up to a factor of about 2.5 by night. The modeled electron temperature is very sensitive to the electron density, and this decrease in electron density results in an increase of

  9. Global modelling study (GSM TIP of the ionospheric effects of excited N2, convection and heat fluxes by comparison with EISCAT and satellite data for 31 July 1990

    Directory of Open Access Journals (Sweden)

    Yu. N. Korenkov

    1996-12-01

    Full Text Available Near-earth plasma parameters were calculated using a global numerical self-consistent and time-dependent model of the thermosphere, ionosphere and protonosphere (GSM TIP. The model results are compared with experimental data of different origin, mainly EISCAT measurements and simultaneous satellite data (Ne and ion composition. Model runs with varying inputs of auroral FAC distributions, temperature of vibrationally excited nitrogen and photoelectron energy escape fluxes are used to make adjustments to the observations. The satellite data are obtained onboard Active and its subsatellite Magion-2 when they passed nearby the EISCAT station around 0325 and 1540 UT on 31 July 1990 at a height of about 2000 and 2200 km, respectively. A strong geomagnetic disturbance was observed two days before the period under study. Numerical calculations were performed with consideration of vibrationally excited nitrogen molecules for high solar-activity conditions. The results show good agreement between the incoherent-scatter radar measurements (Ne, Te, Ti and model calculations, taking into account the excited molecular nitrogen reaction rates. The comparison of model results of the thermospheric neutral wind shows finally a good agreement with the HWM93 empirical wind model.

  10. Global modelling study (GSM TIP of the ionospheric effects of excited N2, convection and heat fluxes by comparison with EISCAT and satellite data for 31 July 1990

    Directory of Open Access Journals (Sweden)

    J. Smilauer

    Full Text Available Near-earth plasma parameters were calculated using a global numerical self-consistent and time-dependent model of the thermosphere, ionosphere and protonosphere (GSM TIP. The model results are compared with experimental data of different origin, mainly EISCAT measurements and simultaneous satellite data (Ne and ion composition. Model runs with varying inputs of auroral FAC distributions, temperature of vibrationally excited nitrogen and photoelectron energy escape fluxes are used to make adjustments to the observations. The satellite data are obtained onboard Active and its subsatellite Magion-2 when they passed nearby the EISCAT station around 0325 and 1540 UT on 31 July 1990 at a height of about 2000 and 2200 km, respectively. A strong geomagnetic disturbance was observed two days before the period under study. Numerical calculations were performed with consideration of vibrationally excited nitrogen molecules for high solar-activity conditions. The results show good agreement between the incoherent-scatter radar measurements (Ne, Te, Ti and model calculations, taking into account the excited molecular nitrogen reaction rates. The comparison of model results of the thermospheric neutral wind shows finally a good agreement with the HWM93 empirical wind model.

  11. Mathematical analysis of steady-state solutions in compartment and continuum models of cell polarization.

    Science.gov (United States)

    Zheng, Zhenzhen; Chou, Ching-Shan; Yi, Tau-Mu; Nie, Qing

    2011-10-01

    Cell polarization, in which substances previously uniformly distributed become asymmetric due to external or/and internal stimulation, is a fundamental process underlying cell mobility, cell division, and other polarized functions. The yeast cell S. cerevisiae has been a model system to study cell polarization. During mating, yeast cells sense shallow external spatial gradients and respond by creating steeper internal gradients of protein aligned with the external cue. The complex spatial dynamics during yeast mating polarization consists of positive feedback, degradation, global negative feedback control, and cooperative effects in protein synthesis. Understanding such complex regulations and interactions is critical to studying many important characteristics in cell polarization including signal amplification, tracking dynamic signals, and potential trade-off between achieving both objectives in a robust fashion. In this paper, we study some of these questions by analyzing several models with different spatial complexity: two compartments, three compartments, and continuum in space. The step-wise approach allows detailed characterization of properties of the steady state of the system, providing more insights for biological regulations during cell polarization. For cases without membrane diffusion, our study reveals that increasing the number of spatial compartments results in an increase in the number of steady-state solutions, in particular, the number of stable steady-state solutions, with the continuum models possessing infinitely many steady-state solutions. Through both analysis and simulations, we find that stronger positive feedback, reduced diffusion, and a shallower ligand gradient all result in more steady-state solutions, although most of these are not optimally aligned with the gradient. We explore in the different settings the relationship between the number of steady-state solutions and the extent and accuracy of the polarization. Taken together

  12. Artificial electron beams in the magnetosphere and ionosphere

    International Nuclear Information System (INIS)

    Winckler, J.R.

    1990-01-01

    The Plasma Diagnostics Payload of the Echo 7 satellite carried TV cameras and photometers by means of which the luminosity around an electron beam in the polar ionosphere could be studied. It was found that, while the beam Larmor spiral could be clearly seen near 100 km, above this only a column due to suprathermal electrons was observable. At high altitudes, the emission of neutral gas both generated powerful luminosity and substantially reduced accelerator potentials. An analysis of conjugate echoes indicates that inferred magnetospheric electric fields do not map well into the ionosphere, as well as the presence of strong pitch-angle scattering. 11 refs

  13. Modelling dust polarization observations of molecular clouds through MHD simulations

    Science.gov (United States)

    King, Patrick K.; Fissel, Laura M.; Chen, Che-Yu; Li, Zhi-Yun

    2018-03-01

    The BLASTPol observations of Vela C have provided the most detailed characterization of the polarization fraction p and dispersion in polarization angles S for a molecular cloud. We compare the observed distributions of p and S with those obtained in synthetic observations of simulations of molecular clouds, assuming homogeneous grain alignment. We find that the orientation of the mean magnetic field relative to the observer has a significant effect on the p and S distributions. These distributions for Vela C are most consistent with synthetic observations where the mean magnetic field is close to the line of sight. Our results point to apparent magnetic disorder in the Vela C molecular cloud, although it can be due to either an inclination effect (i.e. observing close to the mean field direction) or significant field tangling from strong turbulence/low magnetization. The joint correlations of p with column density and of S with column density for the synthetic observations generally agree poorly with the Vela C joint correlations, suggesting that understanding these correlations requires a more sophisticated treatment of grain alignment physics.

  14. The Quiet Time Ionospheric Source of Ring Current Plasmas in Boundary Related Coordinates

    Science.gov (United States)

    Peterson, W.; Andersson, L.; Collin, H.; Scudder, J.

    2007-05-01

    Almost all of the ring current plasma comes from the plasma sheet, which is in turn supplied by the ionosphere and solar wind. We know that O+ ions from the ionosphere are present in all regions of the magnetosphere at low levels even during geomagnetically quiet intervals. We also know heavy ionospheric ions such as O+ play a role in the evolution of geomagnetic storms, but we are not sure exactly what that role is. Large-scale modeling efforts constrained by observations provide the fastest path forward to increasing our understanding. One of the obstacles to effectively using the extensive information about ion outflow to constrain large-scale magnetospheric models has been the lack of information about the distribution of the ion outflow in relation to large-scale magnetospheric features such as the auroral oval. We have used data from the Polar satellite to determine the average number and energy fluxes of escaping energetic (15 eV < E/q < 33 keV) H+ and O+ ions in boundary related coordinates during geomagnetically quiet times (Dst < -50). The characteristic energy of escaping ions is determined from the ratio of energy and number fluxes. During quiet times, we found that the characteristic energies in the dayside and nightside auroral regions were moderately uniform. Characteristic O+ energies in the dayside and night side auroral zones are 120 and 700 eV respectively. For H+ the energies are 280 eV and 1.2 keV respectively. We found the most energetic and variable characteristic energies in the polar cap region. Comparison with other observations, including those of thermal O+ from Akebono show that the escaping energetic fluxes in the polar cap are a small fraction (2-3%) of those escaping from the auroral zone. If energization processes acting on auroral field lines above our 1 RE observational altitude are important only during geomagnetic storm intervals, the data presented here almost completely characterize the magnetosphere's ionospheric plasma

  15. Modeling charge polarization voltage for large lithium-ion batteries in electric vehicles

    Directory of Open Access Journals (Sweden)

    Yan Jiang

    2013-06-01

    Full Text Available Purpose: Polarization voltage of the lithium-ion battery is an important parameter that has direct influence on battery performance. The paper aims to analyze the impedance characteristics of the lithium-ion battery based on EIS data. Design/methodology/approach: The effects of currents, initial SOC of the battery on charge polarization voltage are investigated, which is approximately linear function of charge current. The change of charge polarization voltage is also analyzed with the gradient analytical method in the SOC domain. The charge polarization model with two RC networks is presented, and parts of model parameters like Ohmic resistance and charge transfer impedance are estimated by both EIS method and battery constant current testing method. Findings: This paper reveals that the Ohmic resistance accounts for much contribution to battery total polarization compared to charge transfer impedance. Practical implications: Experimental results demonstrate the efficacy of the model with the proposed identification method, which provides the foundation for battery charging optimization. Originality/value: The paper analyzed the impedance characteristics of the lithium-ion battery based on EIS data, presented a charge polarization model with two RC networks, and estimated parameters like Ohmic resistance and charge transfer impedance.

  16. Hydrological excitation of polar motion by different variables from the GLDAS models

    Science.gov (United States)

    Winska, Malgorzata; Nastula, Jolanta; Salstein, David

    2017-12-01

    Continental hydrological loading by land water, snow and ice is a process that is important for the full understanding of the excitation of polar motion. In this study, we compute different estimations of hydrological excitation functions of polar motion (as hydrological angular momentum, HAM) using various variables from the Global Land Data Assimilation System (GLDAS) models of the land-based hydrosphere. The main aim of this study is to show the influence of variables from different hydrological processes including evapotranspiration, runoff, snowmelt and soil moisture, on polar motion excitations at annual and short-term timescales. Hydrological excitation functions of polar motion are determined using selected variables of these GLDAS realizations. Furthermore, we use time-variable gravity field solutions from the Gravity Recovery and Climate Experiment (GRACE) to determine the hydrological mass effects on polar motion excitation. We first conduct an intercomparison of the maps of variations of regional hydrological excitation functions, timing and phase diagrams of different regional and global HAMs. Next, we estimate the hydrological signal in geodetically observed polar motion excitation as a residual by subtracting the contributions of atmospheric angular momentum and oceanic angular momentum. Finally, the hydrological excitations are compared with those hydrological signals determined from residuals of the observed polar motion excitation series. The results will help us understand the relative importance of polar motion excitation within the individual hydrological processes, based on hydrological modeling. This method will allow us to estimate how well the polar motion excitation budget in the seasonal and inter-annual spectral ranges can be closed.

  17. Predicting 21st-century polar bear habitat distribution from global climate models

    Science.gov (United States)

    Durner, G.M.; Douglas, D.C.; Nielson, R.M.; Amstrup, Steven C.; McDonald, T.L.; Stirling, I.; Mauritzen, Mette; Born, E.W.; Wiig, O.; Deweaver, E.; Serreze, Mark C.; Belikov, Stanislav; Holland, M.M.; Maslanik, J.; Aars, Jon; Bailey, D.A.; Derocher, A.E.

    2009-01-01

    Projections of polar bear (Ursus maritimus) sea ice habitat distribution in the polar basin during the 21st century were developed to understand the consequences of anticipated sea ice reductions on polar bear populations. We used location data from satellitecollared polar bears and environmental data (e.g., bathymetry, distance to coastlines, and sea ice) collected from 1985 to 1995 to build resource selection functions (RSFs). RSFs described habitats that polar bears preferred in summer, autumn, winter, and spring. When applied to independent data from 1996 to 2006, the RSFs consistently identified habitats most frequently used by polar bears. We applied the RSFs to monthly maps of 21st-century sea ice concentration projected by 10 general circulation models (GCMs) used in the Intergovernmental Panel of Climate Change Fourth Assessment Report, under the A1B greenhouse gas forcing scenario. Despite variation in their projections, all GCMs indicated habitat losses in the polar basin during the 21st century. Losses in the highest-valued RSF habitat (optimal habitat) were greatest in the southern seas of the polar basin, especially the Chukchi and Barents seas, and least along the Arctic Ocean shores of Banks Island to northern Greenland. Mean loss of optimal polar bear habitat was greatest during summer; from an observed 1.0 million km2 in 1985-1995 (baseline) to a projected multi-model mean of 0.32 million km2 in 2090-2099 (-68% change). Projected winter losses of polar bear habitat were less: from 1.7 million km2 in 1985-1995 to 1.4 million km2 in 2090-2099 (-17% change). Habitat losses based on GCM multi-model means may be conservative; simulated rates of habitat loss during 1985-2006 from many GCMs were less than the actual observed rates of loss. Although a reduction in the total amount of optimal habitat will likely reduce polar bear populations, exact relationships between habitat losses and population demographics remain unknown. Density and energetic

  18. Modeling Polarized Emission from Black Hole Jets: Application to M87 Core Jet

    Directory of Open Access Journals (Sweden)

    Monika Mościbrodzka

    2017-09-01

    Full Text Available We combine three-dimensional general-relativistic numerical models of hot, magnetized Advection Dominated Accretion Flows around a supermassive black hole and the corresponding outflows from them with a general relativistic polarized radiative transfer model to produce synthetic radio images and spectra of jet outflows. We apply the model to the underluminous core of M87 galaxy. The assumptions and results of the calculations are discussed in context of millimeter observations of the M87 jet launching zone. Our ab initio polarized emission and rotation measure models allow us to address the constrains on the mass accretion rate onto the M87 supermassive black hole.

  19. Perturbations of gyrosynchrotron emission polarization from solar flares by sausage modes: forward modeling

    Science.gov (United States)

    Reznikova, V. E.; Van Doorsselaere, T.; Kuznetsov, A. A.

    2015-03-01

    We examined the polarization of the microwave flaring emission and its modulation by the fast sausage standing wave using a linear 3D magnetohydrodynamic model of a plasma cylinder. We analyzed the effects of the line-of-sight angle on the perturbations of the gyrosynchrotron intensity for two models: a base model with strong Razin suppression and a low-density model in which the Razin effect was negligible. The circular polarization (Stokes V) oscillation is in phase with the intensity oscillation, and the polarization degree (Stokes V/I) oscillates in phase with the magnetic field at the examined frequencies in both models. The two quantities experience a periodical reversal of their signs with a period equal to half of the sausage wave period when seen at a 90° viewing angle, in this case, their modulation depth reaches 100%.

  20. Whistler Wave Propagation Through the Ionosphere of Venus

    Science.gov (United States)

    Pérez-Invernón, F. J.; Lehtinen, N. G.; Gordillo-Vázquez, F. J.; Luque, A.

    2017-11-01

    We investigate the attenuation of whistler waves generated by hypotetical Venusian lightning occurring at the altitude of the cloud layer under different ionospheric conditions. We use the Stanford full-wave method for stratified media of Lehtinen and Inan (2008) to model wave propagation through the ionosphere of Venus. This method calculates the electromagnetic field created by an arbitrary source in a plane-stratified medium (i.e., uniform in the horizontal direction). We see that the existence of holes in electronic densities and the magnetic field configuration caused by solar wind play an important role in the propagation of electromagnetic waves through the Venusian ionosphere.

  1. Chemistry in the Thermosphere and Ionosphere.

    Science.gov (United States)

    Roble, Raymond G.

    1986-01-01

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

  2. Application of generalized singular value decomposition to ionospheric tomography

    Directory of Open Access Journals (Sweden)

    K. Bhuyan

    2004-11-01

    Full Text Available The electron density distribution of the low- and mid-latitude ionosphere has been investigated by the computerized tomography technique using a Generalized Singular Value Decomposition (GSVD based algorithm. Model ionospheric total electron content (TEC data obtained from the International Reference Ionosphere 2001 and slant relative TEC data measured at a chain of three stations receiving transit satellite transmissions in Alaska, USA are used in this analysis. The issue of optimum efficiency of the GSVD algorithm in the reconstruction of ionospheric structures is being addressed through simulation of the equatorial ionization anomaly (EIA, in addition to its application to investigate complicated ionospheric density irregularities. Results show that the Generalized Cross Validation approach to find the regularization parameter and the corresponding solution gives a very good reconstructed image of the low-latitude ionosphere and the EIA within it. Provided that some minimum norm is fulfilled, the GSVD solution is found to be least affected by considerations, such as pixel size and number of ray paths. The method has also been used to investigate the behaviour of the mid-latitude ionosphere under magnetically quiet and disturbed conditions.

  3. Enhanced ionosphere-magnetosphere data from the DMSP satellites

    International Nuclear Information System (INIS)

    Rich, F.J.; Hardy, D.A.; Gussenhoven, M.S.

    1985-01-01

    The satellites of the Defense Meteorological Satellite Program (DMSP) represent a series of low-altitude (835 km) polar-orbiting satellites. Their primary objective is related to the observation of the tropospheric weather with a high-resolution white light and infrared imaging system. It is also possible to make images of auroras. On a daily basis, information about auroras is used to assist various communication systems which are affected by the ionospheric disturbances associated with auroras. In the past few years, there have been several improvements in the ionospheric monitoring instrumentation. Since the high-latitude ionosphere is connected to the magnetosphere, the DMSP data are used to monitor magnetospheric processes. The instrumentation of the DMSP satellites is discussed, taking into account the data provided by them. 7 references

  4. Study of the polar current systems using the IMS meridian chains of magnetometers. Pt. 1. Alaska meridian chain

    Energy Technology Data Exchange (ETDEWEB)

    Akasofu, S.I.; Ahn, B.H.; Romick, G.J. (Alaska Univ., Fairbanks (USA). Geophysical Inst.)

    1983-12-01

    Magnetic field data from a meridian chain of observatories and the recently developed computer codes constitute a powerful tool in studying substorm current systems in the polar region. In this paper, we summarize some of the results obtained from the IMS Alaska meridian chain of observatories. The basic data are the average daily magnetic field variations for 50 successive days (March 9- April 27, 28) which represent a moderately disturbed period. With the aid of the two computer codes, we obtained the distribution of the following quantities in the polar ionosphere in invariant-MLT coordinates: the total ionospheric current; the Pedersen current; the Hall current; the field-aligned currents; the Pedersen-associated field-aligned currents; the Hall-associated field-aligned currents; the electric potential; the Joule heat production rate; the auroral particle energy injection rate; the total energy dissipation rate. All these quantities are related to each other self-consistently at every point under the initial assumptions used in the computation. By using a model of the magnetosphere, the following quantities in the polar ionosphere are projected onto the equatorial plane and the Y-Z plane at X = -20 Rsub(E): the Pedersen current counterpart; the Hall current counterpart; the electric potential; the Pedersen-associated field-aligned currents; the Hall-associated field-aligned currents. These distributions patterns serve as an important basis for studying the generation mechanisms of substorm current systems and the magnetosphere-ionosphere coupling process.

  5. IPRT polarized radiative transfer model intercomparison project - Three-dimensional test cases (phase B)

    Science.gov (United States)

    Emde, Claudia; Barlakas, Vasileios; Cornet, Céline; Evans, Frank; Wang, Zhen; Labonotte, Laurent C.; Macke, Andreas; Mayer, Bernhard; Wendisch, Manfred

    2018-04-01

    Initially unpolarized solar radiation becomes polarized by scattering in the Earth's atmosphere. In particular molecular scattering (Rayleigh scattering) polarizes electromagnetic radiation, but also scattering of radiation at aerosols, cloud droplets (Mie scattering) and ice crystals polarizes. Each atmospheric constituent produces a characteristic polarization signal, thus spectro-polarimetric measurements are frequently employed for remote sensing of aerosol and cloud properties. Retrieval algorithms require efficient radiative transfer models. Usually, these apply the plane-parallel approximation (PPA), assuming that the atmosphere consists of horizontally homogeneous layers. This allows to solve the vector radiative transfer equation (VRTE) efficiently. For remote sensing applications, the radiance is considered constant over the instantaneous field-of-view of the instrument and each sensor element is treated independently in plane-parallel approximation, neglecting horizontal radiation transport between adjacent pixels (Independent Pixel Approximation, IPA). In order to estimate the errors due to the IPA approximation, three-dimensional (3D) vector radiative transfer models are required. So far, only a few such models exist. Therefore, the International Polarized Radiative Transfer (IPRT) working group of the International Radiation Commission (IRC) has initiated a model intercomparison project in order to provide benchmark results for polarized radiative transfer. The group has already performed an intercomparison for one-dimensional (1D) multi-layer test cases [phase A, 1]. This paper presents the continuation of the intercomparison project (phase B) for 2D and 3D test cases: a step cloud, a cubic cloud, and a more realistic scenario including a 3D cloud field generated by a Large Eddy Simulation (LES) model and typical background aerosols. The commonly established benchmark results for 3D polarized radiative transfer are available at the IPRT website (http

  6. A Fuzzy Computing Model for Identifying Polarity of Chinese Sentiment Words

    Directory of Open Access Journals (Sweden)

    Bingkun Wang

    2015-01-01

    Full Text Available With the spurt of online user-generated contents on web, sentiment analysis has become a very active research issue in data mining and natural language processing. As the most important indicator of sentiment, sentiment words which convey positive and negative polarity are quite instrumental for sentiment analysis. However, most of the existing methods for identifying polarity of sentiment words only consider the positive and negative polarity by the Cantor set, and no attention is paid to the fuzziness of the polarity intensity of sentiment words. In order to improve the performance, we propose a fuzzy computing model to identify the polarity of Chinese sentiment words in this paper. There are three major contributions in this paper. Firstly, we propose a method to compute polarity intensity of sentiment morphemes and sentiment words. Secondly, we construct a fuzzy sentiment classifier and propose two different methods to compute the parameter of the fuzzy classifier. Thirdly, we conduct extensive experiments on four sentiment words datasets and three review datasets, and the experimental results indicate that our model performs better than the state-of-the-art methods.

  7. A Fuzzy Computing Model for Identifying Polarity of Chinese Sentiment Words.

    Science.gov (United States)

    Wang, Bingkun; Huang, Yongfeng; Wu, Xian; Li, Xing

    2015-01-01

    With the spurt of online user-generated contents on web, sentiment analysis has become a very active research issue in data mining and natural language processing. As the most important indicator of sentiment, sentiment words which convey positive and negative polarity are quite instrumental for sentiment analysis. However, most of the existing methods for identifying polarity of sentiment words only consider the positive and negative polarity by the Cantor set, and no attention is paid to the fuzziness of the polarity intensity of sentiment words. In order to improve the performance, we propose a fuzzy computing model to identify the polarity of Chinese sentiment words in this paper. There are three major contributions in this paper. Firstly, we propose a method to compute polarity intensity of sentiment morphemes and sentiment words. Secondly, we construct a fuzzy sentiment classifier and propose two different methods to compute the parameter of the fuzzy classifier. Thirdly, we conduct extensive experiments on four sentiment words datasets and three review datasets, and the experimental results indicate that our model performs better than the state-of-the-art methods.

  8. The polarized structure function of the nucleons with a non-extensive statistical quark model

    Energy Technology Data Exchange (ETDEWEB)

    Trevisan, Luis A. [Departamento de Matematica e Estatistica, Universidade Estadual de Ponta Grossa, 84010-790, Ponta Grossa, PR (Brazil); Mirez, Carlos [Instituto de Ciencia, Engenharia e Tecnologia - ICET, Universidade Federal dos Vales do Jequitinhonha e Mucuri - UFVJM, Campus do Mucuri, Rua do Cruzeiro 01, Jardim Sao Paulo, 39803-371, Teofilo Otoni, Minas Gerais (Brazil)

    2013-05-06

    We studied an application of nonextensive thermodynamics to describe the polarized structure function of nucleon, in a model where the usual Fermi-Dirac and Bose-Einstein energy distribution, often used in the statistical models, were replaced by the equivalent functions of the q-statistical. The parameters of the model are given by an effective temperature T, the q parameter (from Tsallis statistics), and the chemical potentials given by the corresponding up (u) and down (d) quark normalization in the nucleon and by {Delta}u and {Delta}d of the polarized functions.

  9. CDDIS_DORIS_products_ionosphere

    Data.gov (United States)

    National Aeronautics and Space Administration — Ionosphere correction values derived from analysis of Doppler Orbitography by Radiopositioning Integrated on Satellite (DORIS) data. These products are the generated...

  10. Ionosphere monitoring and forecast activities within the IAG working group "Ionosphere Prediction"

    Science.gov (United States)

    Hoque, Mainul; Garcia-Rigo, Alberto; Erdogan, Eren; Cueto Santamaría, Marta; Jakowski, Norbert; Berdermann, Jens; Hernandez-Pajares, Manuel; Schmidt, Michael; Wilken, Volker

    2017-04-01

    Ionospheric disturbances can affect technologies in space and on Earth disrupting satellite and airline operations, communications networks, navigation systems. As the world becomes ever more dependent on these technologies, ionospheric disturbances as part of space weather pose an increasing risk to the economic vitality and national security. Therefore, having the knowledge of ionospheric state in advance during space weather events is becoming more and more important. To promote scientific cooperation we recently formed a Working Group (WG) called "Ionosphere Predictions" within the International Association of Geodesy (IAG) under Sub-Commission 4.3 "Atmosphere Remote Sensing" of the Commission 4 "Positioning and Applications". The general objective of the WG is to promote the development of ionosphere prediction algorithm/models based on the dependence of ionospheric characteristics on solar and magnetic conditions combining data from different sensors to improve the spatial and temporal resolution and sensitivity taking advantage of different sounding geometries and latency. Our presented work enables the possibility to compare total electron content (TEC) prediction approaches/results from different centers contributing to this WG such as German Aerospace Center (DLR), Universitat Politècnica de Catalunya (UPC), Technische Universität München (TUM) and GMV. DLR developed a model-assisted TEC forecast algorithm taking benefit from actual trends of the TEC behavior at each grid point. Since during perturbations, characterized by large TEC fluctuations or ionization fronts, this approach may fail, the trend information is merged with the current background model which provides a stable climatological TEC behavior. The presented solution is a first step to regularly provide forecasted TEC services via SWACI/IMPC by DLR. UPC forecast model is based on applying linear regression to a temporal window of TEC maps in the Discrete Cosine Transform (DCT) domain

  11. Neural-network-based prediction techniques for single station modeling and regional mapping of the foF2 and M(3000F2 ionospheric characteristics

    Directory of Open Access Journals (Sweden)

    T. D. Xenos

    2002-01-01

    Full Text Available In this work, Neural-Network-based single-station hourly daily foF2 and M(3000F2 modelling of 15 European ionospheric stations is investigated. The data used are neural networks and hourly daily values from the period 1964- 1988 for training the neural networks and from the period 1989-1994 for checking the prediction accuracy. Two types of models are presented for the F2-layer critical frequency prediction and two for the propagation factor M(3000F2. The first foF2 model employs the E-layer local noon calculated daily critical frequency (foE12 and the local noon F2- layer critical frequency of the previous day. The second foF2 model, which introduces a new regional mapping technique, employs the Juliusruh neural network model and uses the E-layer local noon calculated daily critical frequency (foE12, and the previous day F2-layer critical frequency measured at Juliusruh at noon. The first M(3000F2 model employs the E-layer local noon calculated daily critical frequency (foE12, its ± 3 h deviations and the local noon cosine of the solar zenith angle (cos c12. The second model, which introduces a new M(3000F2 mapping technique, employs Juliusruh neural network model and uses the E-layer local noon calculated daily critical frequency (foE12, and the previous day F2-layer critical frequency measured at Juliusruh at noon.

  12. Predicting ionospheric scintillation: Recent advancements and future challenges

    Science.gov (United States)

    Carter, B. A.; Currie, J. L.; Terkildsen, M.; Bouya, Z.; Parkinson, M. L.

    2017-12-01

    Society greatly benefits from space-based infrastructure and technology. For example, signals from Global Navigation Satellite Systems (GNSS) are used across a wide range of industrial sectors; including aviation, mining, agriculture and finance. Current trends indicate that the use of these space-based technologies is likely to increase over the coming decades as the global economy becomes more technology-dependent. Space weather represents a key vulnerability to space-based technology, both in terms of the space environment effects on satellite infrastructure and the influence of the ionosphere on the radio signals used for satellite communications. In recent decades, the impact of the ionosphere on GNSS signals has re-ignited research interest into the equatorial ionosphere, particularly towards understanding Equatorial Plasma Bubbles (EPBs). EPBs are a dominant source of nighttime plasma irregularities in the low-latitude ionosphere, which can cause severe scintillation on GNSS signals and subsequent degradation on GNSS product quality. Currently, ionospheric scintillation event forecasts are not being routinely released by any space weather prediction agency around the world, but this is likely to change in the near future. In this contribution, an overview of recent efforts to develop a global ionospheric scintillation prediction capability within Australia will be given. The challenges in understanding user requirements for ionospheric scintillation predictions will be discussed. Next, the use of ground- and space-based datasets for the purpose of near-real time ionospheric scintillation monitoring will be explored. Finally, some modeling that has shown significant promise in transitioning towards an operational ionospheric scintillation forecasting system will be discussed.

  13. Polarization Characteristics Inferred From the Radio Receiver Instrument on the Enhanced Polar Outflow Probe

    Science.gov (United States)

    Danskin, Donald W.; Hussey, Glenn C.; Gillies, Robert G.; James, H. Gordon; Fairbairn, David T.; Yau, Andrew W.

    2018-02-01

    The Radio Receiver Instrument (RRI) on the CAScade, Smallsat, and Ionospheric Polar Explorer/enhanced Polar Outflow Probe (CASSIOPE/e-POP) satellite was used to receive continuous wave and binary phase shift keyed transmissions from a high-frequency transmitter located in Ottawa, ON, Canada during April 2016 to investigate how the ionosphere affects the polarization characteristics of transionospheric high-frequency radio waves. The spacecraft orientation was continuously slewed to maintain the dipole orientation in a plane perpendicular to the direction toward the transmitter, enabling the first in situ planar polarization determination for continuous wave and binary phase shift keyed modulated radio waves from space at times when the wave frequency is at least 1.58 times the plasma frequency. The Stokes parameters and polarization characteristics were derived from the measured data and interpreted using an existing ray tracing model. For the southern part of the passes, the power was observed to oscillate between the two dipoles of RRI, which was attributed to Faraday rotation of the radio waves. For the first time, a reversal in the rate of change of orientation angle was observed where the minimum in modeled Faraday rotation occurred. The reversal point was poleward of the point of closest approach between the satellite and transmitter; this was explained by the variations of total electron content and component of magnetic field along the direction of propagation. The received signals show both quasi-longitudinal (QL) and quasi-transverse characteristics. South of the transmitter the QL regime is dominant. Around the reversal point, a combination of QL and quasi-transverse nature was observed.

  14. Polar clouds and radiation in satellite observations, reanalyses, and climate models

    Science.gov (United States)

    Lenaerts, Jan T. M.; Van Tricht, Kristof; Lhermitte, Stef; L'Ecuyer, Tristan S.

    2017-04-01

    Clouds play a pivotal role in the surface energy budget of the polar regions. Here we use two largely independent data sets of cloud and surface downwelling radiation observations derived by satellite remote sensing (2007-2010) to evaluate simulated clouds and radiation over both polar ice sheets and oceans in state-of-the-art atmospheric reanalyses (ERA-Interim and Modern Era Retrospective-Analysis for Research and Applications-2) and the Coupled Model Intercomparison Project Phase 5 (CMIP5) climate model ensemble. First, we show that, compared to Clouds and the Earth's Radiant Energy System-Energy Balanced and Filled, CloudSat-CALIPSO better represents cloud liquid and ice water path over high latitudes, owing to its recent explicit determination of cloud phase that will be part of its new R05 release. The reanalyses and climate models disagree widely on the amount of cloud liquid and ice in the polar regions. Compared to the observations, we find significant but inconsistent biases in the model simulations of cloud liquid and ice water, as well as in the downwelling radiation components. The CMIP5 models display a wide range of cloud characteristics of the polar regions, especially with regard to cloud liquid water, limiting the representativeness of the multimodel mean. A few CMIP5 models (CNRM, GISS, GFDL, and IPSL_CM5b) clearly outperform the others, which enhances credibility in their projected future cloud and radiation changes over high latitudes. Given the rapid changes in polar regions and global feedbacks involved, future climate model developments should target improved representation of polar clouds. To that end, remote sensing observations are crucial, in spite of large remaining observational uncertainties, which is evidenced by the substantial differences between the two data sets.

  15. The hadronic vacuum polarization contribution to the muon g - 2 in the quark-resonance model

    NARCIS (Netherlands)

    Pallante, E.

    1994-01-01

    The hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon is parametrized by using the quark-resonance model formulated elsewhere. In this context a recent prediction obtained within the ENJL model can be affected by two additional contributions: the next to leading

  16. UAH mathematical model of the variable polarity plasma ARC welding system calculation

    Science.gov (United States)

    Hung, R. J.

    1994-01-01

    Significant advantages of Variable Polarity Plasma Arc (VPPA) welding process include faster welding, fewer repairs, less joint preparation, reduced weldment distortion, and absence of porosity. A mathematical model is presented to analyze the VPPA welding process. Results of the mathematical model were compared with the experimental observation accomplished by the GDI team.

  17. Optical Modeling and Polarization Calibration for CMB Measurements with Actpol and Advanced Actpol

    Science.gov (United States)

    Koopman, Brian; Austermann, Jason; Cho, Hsiao-Mei; Coughlin, Kevin P.; Duff, Shannon M.; Gallardo, Patricio A.; Hasselfield, Matthew; Henderson, Shawn W.; Ho, Shuay-Pwu Patty; Hubmayr, Johannes; hide

    2016-01-01

    The Atacama Cosmology Telescope Polarimeter (ACTPol) is a polarization sensitive upgrade to the Atacama Cosmology Telescope, located at an elevation of 5190 m on Cerro Toco in Chile. ACTPol uses transition edge sensor bolometers coupled to orthomode transducers to measure both the temperature and polarization of the Cosmic Microwave Background (CMB). Calibration of the detector angles is a critical step in producing polarization maps of the CMB. Polarization angle offsets in the detector calibration can cause leakage in polarization from E to B modes and induce a spurious signal in the EB and TB cross correlations, which eliminates our ability to measure potential cosmological sources of EB and TB signals, such as cosmic birefringence. We calibrate the ACTPol detector angles by ray tracing the designed detector angle through the entire optical chain to determine the projection of each detector angle on the sky. The distribution of calibrated detector polarization angles are consistent with a global offset angle from zero when compared to the EB-nulling offset angle, the angle required to null the EB cross-correlation power spectrum. We present the optical modeling process. The detector angles can be cross checked through observations of known polarized sources, whether this be a galactic source or a laboratory reference standard. To cross check the ACTPol detector angles, we use a thin film polarization grid placed in front of the receiver of the telescope, between the receiver and the secondary reflector. Making use of a rapidly rotating half-wave plate (HWP) mount we spin the polarizing grid at a constant speed, polarizing and rotating the incoming atmospheric signal. The resulting sinusoidal signal is used to determine the detector angles. The optical modeling calibration was shown to be consistent with a global offset angle of zero when compared to EB nulling in the first ACTPol results and will continue to be a part of our calibration implementation. The first

  18. Effect of the Ionosphere on Space and Terrestrial Systems

    Science.gov (United States)

    1978-01-01

    of the ionospheric conditions along the path. shown schematically in Figure 1. The energetic par- ticle data were obtained by the Space Sciences Labor ...Adaptive tures, of difficult inclusion in clima - Ionospheric Range Error Correction for tological models. To accommodate then High Accuracy Radars, URSI...that size and a consistent identification in clima - are effervescent from hour to hour. tology, such as the nighttime trough and the plasmapause

  19. Far-field coseismic ionospheric disturbances of Tohoku earthquake

    Czech Academy of Sciences Publication Activity Database

    Krasnov, V. M.; Drobzheva, Ya. V.; Chum, Jaroslav

    2015-01-01

    Roč. 135, December (2015), s. 12-21 ISSN 1364-6826 R&D Projects: GA ČR(CZ) GC15-07281J Institutional support: RVO:68378289 Keywords : earthquake * infrasonic waves * ionospheric disturbances * infrasound triggered by the earthquake * co-seismic ionospheric perturbations * modeling * remote sensing Subject RIV: DG - Athmosphere Sciences, Meteorology Impact factor: 1.463, year: 2015 http://www.sciencedirect.com/science/article/pii/S1364682615300584

  20. High-latitude ionospheric response to a sudden impulse event during northward IMF conditions

    DEFF Research Database (Denmark)

    Moretto, T.; Ridley, A.J.; Engebretson, M.J.

    2000-01-01

    A high-density structure under northward interplanetary magnetic field B-z conditions is identified at the Wind and IMP 8 satellites, both in the solar wind on August 22, 1995. A compression of the magnetosphere is observed by the GOES 7 magnetometer within a few minutes of the pressure increase......-latitude ionospheric potential patterns by means of the assimilative mapping of ionospheric electrodynamics technique. Convection cells in the polar cap are formed and disappear on minute timescales in accordance with previous results. However, the high-latitude ionospheric ground magnetic signature does not match...... the interpretation as events of traveling convection vortices, as has been suggested by past studies....

  1. Validation of measured poleward TEC gradient using multi-station GPS with Artificial Neural Network based TEC model in low latitude region for developing predictive capability of ionospheric scintillation

    Science.gov (United States)

    Sur, D.; Paul, A.

    2017-12-01

    The equatorial ionosphere shows sharp diurnal and latitudinal Total Electron Content (TEC) variations over a major part of the day. Equatorial ionosphere also exhibits intense post-sunset ionospheric irregularities. Accurate prediction of TEC in these low latitudes is not possible from standard ionospheric models. An Artificial Neural Network (ANN) based Vertical TEC (VTEC) model has been designed using TEC data in low latitude Indian longitude sector for accurate prediction of VTEC. GPS TEC data from the stations Calcutta (22.58°N, 88.38°E geographic, magnetic dip 32°), Baharampore (24.09°N, 88.25°E geographic, magnetic dip 35°) and Siliguri (26.72°N, 88.39°E geographic; magnetic dip 40°) are used as training dataset for the duration of January 2007-September 2011. Poleward VTEC gradients from northern EIA crest to region beyond EIA crest have been calculated from measured VTEC and compared with that obtained from ANN based VTEC model. TEC data from Calcutta and Siliguri are used to compute VTEC gradients during April 2013 and August-September 2013. It has been observed that poleward VTEC gradient computed from ANN based TEC model has shown good correlation with measured values during vernal and autumnal equinoxes of high solar activity periods of 2013. Possible correlation between measured poleward TEC gradients and post-sunset scintillations (S4 ≥ 0.4) from northern crest of EIA has been observed in this paper. From the observation, a suitable threshold poleward VTEC gradient has been proposed for possible occurrence of post-sunset scintillations at northern crest of EIA along 88°E longitude. Poleward VTEC gradients obtained from ANN based VTEC model are used to forecast possible ionospheric scintillation after post-sunset period using the threshold value. It has been observed that these predicted VTEC gradients obtained from ANN based VTEC model can forecast post-sunset L-band scintillation with an accuracy of 67% to 82% in this dynamic low latitude

  2. Considering the potential of IAR emissions for ionospheric sounding

    Science.gov (United States)

    Potapov, A. S.; Polyushkina, T. N.; Tsegmed, B.; Oinats, A. V.; Pashinin, A. Yu.; Edemskiy, I. K.; Mylnikova, A. A.; Ratovsky, K. G.

    2017-11-01

    Knowledge of the ionospheric state allows us to adjust the forecasts of radio wave propagation, specify the environment models, and follow the changes of space weather. At present, probing of the ionosphere is produced by radio sounding with ground ionosondes, as well as by raying signals from satellites. We want to draw attention to the possibility of the diagnosis of the ionospheric parameters by detecting ultra-low frequency (ULF) electromagnetic emission generated in the so-called ionospheric Alfvén resonator (IAR). To do this, we present observations of the IAR emission made simultaneously for the first time at three stations using identical induction magnetometers. The stations are within one-hour difference of local time, two of them are mid-latitudinal; the third one is situated in the auroral zone. We compare frequency and frequency difference between adjacent harmonics of the observed multi-band emission with ionospheric parameters measured at the stations using ionosondes and GPS-observations. Diurnal variations of the ionospheric and ULF emission characteristics are also compared. The results show that there is quite a stable correlation between the resonant frequencies of the resonator bands and the critical frequency of the F2 layer of the ionosphere, namely, the frequency of the IAR emission varies inversely as the critical frequency of the ionosphere. This is due to the fact that the frequency of oscillation captured in the resonator is primarily determined by the Alfvén velocity (which depends on the plasma density) in the ionospheric F2 layer. The correlation is high; it varies at different stations, but is observed distinctly along the whole meridian. However, coefficients of a regression equation that connects the ionosphere critical frequency with DSB frequency vary significantly from day to day at all stations. The reason for such a big spread of the regression parameters is not clear and needs further investigation before we are able to

  3. POLAR-PALOOZA Polar Researchers and Arctic Residents Engage, Inform and Inspire Diverse Public Audiences by sharing Polar Science and Global Connections during the International Polar Year, using a New Model of Informal Science Education

    Science.gov (United States)

    Haines-Stiles, G.; Akuginow, E.

    2006-12-01

    (Please note that the POLAR-PALOOZA initiative described in this Abstract is-as of 9/7/2006-"pending" for possible support from NSF and NASA as part of this year's IPY solicitation. Subject to decisions expected by 9/30, this presentation would either be withdrawn, or amplified with specific participants, locations and dates.) Despite the success of well-regarded movies like "March of the Penguins", the polar regions remain a great unknown for most people. Public knowledge about the Arctic and Antarctic, and the critical role of the Poles in the entire Earth system, is nonexistent, incomplete or burdened with misperceptions. The International Polar Years of 2007-2009-and associated "I*Y" science years such as IHY, IYPE and eGY-present a unique opportunity to change this. The people who can best effect this change are those who know the Poles best, through living or working there. Based on innovative but proven models, POLAR-PALOOZA will use three complementary strategies to engage, inform and inspire large public audiences. (1) A national tour, under the working title "Stories from a Changing Planet", will include in-person presentations at science centers, museums, libraries and schools across North America, including Canada and Mexico. The presentations will be augmented by High Definition Video taped on location at the Poles, audio and video podcasts, and special education and outreach activities for targeted audiences. "Stories from a Changing Planet" will provide diverse audiences with an exciting opportunity to meet and interact directly with polar experts, and to appreciate why the Poles and the research done there are directly relevant to their lives. (2) The "HiDef Video Science Story Capture Corps" is a team of professional videographers, using the latest generation of low-cost, high-quality cameras, deployed to both Poles. They will document the work of multiple researchers and projects, rather than focusing on one topic for a single broadcast program

  4. High-latitude ionospheric outflows characterized through analytic formulas

    Science.gov (United States)

    Zeng, W.; Horwitz, J. L.

    2008-12-01

    Recent advances involving multi-fluid treatments have begun to allow the prospect of global magnetospheric models to simulate the dynamics of multiple ion species, such as various ion species originating from sources in the solar wind and terrestrial ionosphere. Such opportunities for the dynamic treatment of ionospheric ions within the magnetosphere portend a need for realistic accessible methods of estimating ionospheric outflows as linked plasma sources for these global models. Toward this end, in this presentation, the results of numerous physics-based simulations of ionospheric plasma outflows under varied driving agents are distilled in terms of relatively compact analytic expressions. The simulations are conducted with the UT Arlington Dynamic Fluid (DyFK) ionospheric plasma transport code. These analytic expressions for O+ and H+ densities, temperatures and flow velocities are obtained at the 3 RE altitudes corresponding to typical inner boundary levels for certain current global magnetospheric models. These O+ and H+ parameters are expressed as functions of precipitation electron energy flux levels, characteristic energy levels of the precipitating electrons, the peak spectral wave densities for low-frequency electrostatic waves which transversely heat ionospheric ions, and solar zenith angle.

  5. A MULTIPLE SCATTERING POLARIZED RADIATIVE TRANSFER MODEL: APPLICATION TO HD 189733b

    Energy Technology Data Exchange (ETDEWEB)

    Kopparla, Pushkar; Yung, Yuk L. [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA (United States); Natraj, Vijay; Swain, Mark R. [Jet Propulsion Laboratory (NASA-JPL), Pasadena, CA (United States); Zhang, Xi [Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ (United States); Wiktorowicz, Sloane J., E-mail: pkk@gps.caltech.edu [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA (United States)

    2016-01-20

    We present a multiple scattering vector radiative transfer model that produces disk integrated, full phase polarized light curves for reflected light from an exoplanetary atmosphere. We validate our model against results from published analytical and computational models and discuss a small number of cases relevant to the existing and possible near-future observations of the exoplanet HD 189733b. HD 189733b is arguably the most well observed exoplanet to date and the only exoplanet to be observed in polarized light, yet it is debated if the planet’s atmosphere is cloudy or clear. We model reflected light from clear atmospheres with Rayleigh scattering, and cloudy or hazy atmospheres with Mie and fractal aggregate particles. We show that clear and cloudy atmospheres have large differences in polarized light as compared to simple flux measurements, though existing observations are insufficient to make this distinction. Futhermore, we show that atmospheres that are spatially inhomogeneous, such as being partially covered by clouds or hazes, exhibit larger contrasts in polarized light when compared to clear atmospheres. This effect can potentially be used to identify patchy clouds in exoplanets. Given a set of full phase polarimetric measurements, this model can constrain the geometric albedo, properties of scattering particles in the atmosphere, and the longitude of the ascending node of the orbit. The model is used to interpret new polarimetric observations of HD 189733b in a companion paper.

  6. Physical bases of the generation of short-term earthquake precursors: A complex model of ionization-induced geophysical processes in the lithosphere-atmosphere-ionosphere-magnetosphere system

    Science.gov (United States)

    Pulinets, S. A.; Ouzounov, D. P.; Karelin, A. V.; Davidenko, D. V.

    2015-07-01

    This paper describes the current understanding of the interaction between geospheres from a complex set of physical and chemical processes under the influence of ionization. The sources of ionization involve the Earth's natural radioactivity and its intensification before earthquakes in seismically active regions, anthropogenic radioactivity caused by nuclear weapon testing and accidents in nuclear power plants and radioactive waste storage, the impact of galactic and solar cosmic rays, and active geophysical experiments using artificial ionization equipment. This approach treats the environment as an open complex system with dissipation, where inherent processes can be considered in the framework of the synergistic approach. We demonstrate the synergy between the evolution of thermal and electromagnetic anomalies in the Earth's atmosphere, ionosphere, and magnetosphere. This makes it possible to determine the direction of the interaction process, which is especially important in applications related to short-term earthquake prediction. That is why the emphasis in this study is on the processes proceeding the final stage of earthquake preparation; the effects of other ionization sources are used to demonstrate that the model is versatile and broadly applicable in geophysics.

  7. A Review of Low Frequency Electromagnetic Wave Phenomena Related to Tropospheric-Ionospheric Coupling Mechanisms

    Science.gov (United States)

    Simoes, Fernando; Pfaff, Robert; Berthelier, Jean-Jacques; Klenzing, Jeffrey

    2012-01-01

    Investigation of coupling mechanisms between the troposphere and the ionosphere requires a multidisciplinary approach involving several branches of atmospheric sciences, from meteorology, atmospheric chemistry, and fulminology to aeronomy, plasma physics, and space weather. In this work, we review low frequency electromagnetic wave propagation in the Earth-ionosphere cavity from a troposphere-ionosphere coupling perspective. We discuss electromagnetic wave generation, propagation, and resonance phenomena, considering atmospheric, ionospheric and magnetospheric sources, from lightning and transient luminous events at low altitude to Alfven waves and particle precipitation related to solar and magnetospheric processes. We review in situ ionospheric processes as well as surface and space weather phenomena that drive troposphere-ionosphere dynamics. Effects of aerosols, water vapor distribution, thermodynamic parameters, and cloud charge separation and electrification processes on atmospheric electricity and electromagnetic waves are reviewed. We also briefly revisit ionospheric irregularities such as spread-F and explosive spread-F, sporadic-E, traveling ionospheric disturbances, Trimpi effect, and hiss and plasma turbulence. Regarding the role of the lower boundary of the cavity, we review transient surface phenomena, including seismic activity, earthquakes, volcanic processes and dust electrification. The role of surface and atmospheric gravity waves in ionospheric dynamics is also briefly addressed. We summarize analytical and numerical tools and techniques to model low frequency electromagnetic wave propagation and solving inverse problems and summarize in a final section a few challenging subjects that are important for a better understanding of tropospheric-ionospheric coupling mechanisms.

  8. Global scale ionospheric irregularities associated with thunderstorm activity

    International Nuclear Information System (INIS)

    Pulinets, Sergey A.; Depuev, Victor H.

    2003-01-01

    The potential difference near 280 kV exists between ground and ionosphere. This potential difference is generated by thunderstorm discharges all over the world, and return current closes the circuit in the areas of fair weather (so-called fair weather current). The model calculations and experimental measurements clearly demonstrate non-uniform latitude-longitude distribution of electric field within the atmosphere. The recent calculations show that the strong large scale vertical atmospheric electric field can penetrate into the ionosphere and create large scale irregularities of the electron concentration. To check this the global distributions of thunderstorm activity obtained with the satellite monitoring for different seasons were compared with the global distributions of ionosphere critical frequency (which is equivalent to peak electron concentration) obtained with the help of satellite topside sounding. The similarity of the obtained global distributions clearly demonstrates the effects of thunderstorm electric fields onto the Earth's ionosphere. (author)

  9. Polarized neutron diffraction - a tool for testing extinction models: application to yttrium iron garnet

    International Nuclear Information System (INIS)

    Bonnet, M.; Delapalme, A.; Becker, P.

    1976-01-01

    This paper shows that polarized neutron experiments, which do not depend on any scale factor, are very dependent on extinction and provide original tests for extinction models. Moon, Koehler, Cable and Child (1972) have formulated the problem and proposed a first-order solution applicable only when the extinction is small. In the first part, some analytical derivations of secondary extinction corrections are discussed, using the formalism of Becker and Coppens (1974). In the second part, the main principles governing polarized neutron diffraction are briefly reviewed, with a special discussion of extinction problems. The method is then applied to the case of yttrium iron garnet (YIG). This experiment shows the technique of polarized neutrons to be very powerful for testing extinction models and for deciding whether the crystal behaves dynamically or kinematically (following Kato's criterion). (Auth.)

  10. Imaging of fast moving electron-density structures in the polar cap

    Directory of Open Access Journals (Sweden)

    C. N. Mitchell

    2007-06-01

    Full Text Available The imaging of fast-moving electron-density structures in the polar cap presents a unique set of challenges that are not encountered in other ionospheric imaging problems. GPS observations of total electron content in the polar cap are sparse compared to other regions in the Northern Hemisphere. Furthermore, the slow relative motion of the satellites across the sky complicates the problem since the velocity of the plasma can be large in comparison and traditional approaches could result in image blurring. This paper presents a Kalman-filter based method that incorporates a forward projection of the solution based on a model plasma drift velocity field. This is the first time that the plasma motion, rather than just integrations of electron density, has been used in an ionospheric imaging algorithm. The motion is derived from the Weimer model of the electric field. It is shown that this novel approach to the implementation of a Kalman filter provides a detailed view of the polar cap ionosphere under severe storm conditions. A case study is given for the October 2003 Halloween storm where verification is provided by incoherent scatter radars.

  11. Fate of Ice Grains in Saturn's Ionosphere

    Science.gov (United States)

    Hamil, O.; Cravens, T. E.; Reedy, N. L.; Sakai, S.

    2018-02-01

    It has been proposed that the rings of Saturn can contribute both material (i.e., water) and energy to its upper atmosphere and ionosphere. Ionospheric models require the presence of molecular species such as water that can chemically remove ionospheric protons, which otherwise are associated with electron densities that greatly exceed those from observation. These models adopt topside fluxes of water molecules. Other models have shown that ice grains from Saturn's rings can impact the atmosphere, but the effects of these grains have not been previously studied. In the current paper, we model how ice grains deposit both material and energy in Saturn's upper atmosphere as a function of grain size, initial velocity (at the "top" of the atmosphere, defined at an altitude above the cloud tops of 3,000 km), and incident angle. Typical grain speeds are expected to be roughly 15-25 km/s. Grains with radii on the order of 1-10 nm deposit most of their energy in the altitude range of 1,700-1,900 km, and can vaporize, depending on initial velocity and impact angle, contributing water mass to the upper atmosphere. We show that grains in this radius range do not significantly vaporize in our model at initial velocities lower than about 20 km/s.

  12. Travelling ionospheric disturbance properties deduced from Super Dual Auroral Radar measurements

    Directory of Open Access Journals (Sweden)

    J. W. MacDougall

    2000-12-01

    Full Text Available Based on modeling of the perturbations in power and elevation angle produced by travelling ionospheric disturbances (TIDs, and observed by the Super Dual Auroral Radar Network, procedures for determining the TID properties are suggested. These procedures are shown to produce reasonable agreement with those properties of the TIDs that can be measured from simultaneous ionosonde measurements. The modeling shows that measurements of angle-of-elevation perturbations by SuperDARN allows for better determination of the TID properties than using only the perturbations of power as is commonly done.Key words: Ionosphere (auroral ionosphere; ionosphere-atmosphere interactions

  13. CP violation, single lepton polarization asymmetry, and polarized CP asymmetry in B→K*l+l- decay in the four-generation standard model

    International Nuclear Information System (INIS)

    Bashiry, V.; Shirkhanghah, N.; Zeynali, K.

    2009-01-01

    In this paper we present a study of CP asymmetry, single lepton polarization asymmetry and polarized CP asymmetry in B→K*l + l - decay within the four-generation standard model. Taking |V t ' s *V t ' b |=0.01, 0.02, 0.03 with phase {60 deg. -120 deg.}, which is consistent with the b→sl + l - rate and the Bs mixing parameter Δm Bs , we find that CP asymmetry, single lepton polarization asymmetry and polarized CP asymmetry are sensitive to the existence of the fourth generation. This can serve as an indirect method to search for new physics effects, in particular, to search for the fourth-generation quarks(t ' ,b ' ) via their indirect manifestations in loop diagrams.

  14. Dynamical model of coherent circularly polarized optical pulse interactions with two-level quantum systems

    International Nuclear Information System (INIS)

    Slavcheva, G.; Hess, O.

    2005-01-01

    We propose and develop a method for theoretical description of circularly (elliptically) polarized optical pulse resonant coherent interactions with two-level atoms. The method is based on the time-evolution equations of a two-level quantum system in the presence of a time-dependent dipole perturbation for electric dipole transitions between states with total angular-momentum projection difference (ΔJ z =±1) excited by a circularly polarized electromagnetic field [Feynman et al., J. Appl. Phys. 28, 49 (1957)]. The adopted real-vector representation approach allows for coupling with the vectorial Maxwell's equations for the optical wave propagation and thus the resulting Maxwell pseudospin equations can be numerically solved in the time domain without any approximations. The model permits a more exact study of the ultrafast coherent pulse propagation effects taking into account the vector nature of the electromagnetic field and hence the polarization state of the optical excitation. We demonstrate self-induced transparency effects and formation of polarized solitons. The model represents a qualitative extension of the well-known optical Maxwell-Bloch equations valid for linearly polarized light and a tool for studying coherent quantum control mechanisms

  15. Cubesat-Based Dtv Receiver Constellation for Ionospheric Tomography

    Science.gov (United States)

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

    2013-12-01

    sort the frequencies and de-trend the phase variations due to spacecraft motion. For a single channel and a spacecraft-DTV transmitter path scan, TEC can be determined from the incremental phase variations for each channel. Determination of the absolute TEC requires knowledge of the absolute phase, i.e., including the number of 2π cycles. The absolute TEC can be determined in the case of multi-channel transmissions from a single tower (most towers house multiple television stations). A CubeSat constellation using DTV transmissions as signals of opportunity is a composite instrument for frontier ionospheric research. It is a novel application of CubeSats to understand the ionospheric response to solar, magnetospheric and upper atmospheric forcing. Combined tomographic measurements of ionospheric density can be used to study the global-scale ionospheric circulation and small-scale ionospheric structures that cause scintillation of trans-ionospheric signals. The data can support a wide range of studies, including Sub-auroral Polarization Streams (SAPS), low latitude plasma instabilities and the generation of equatorial spread F bubbles, and the role of atmospheric waves and layers and sudden stratospheric warming (SSW) events in traveling ionospheric disturbances (TID).

  16. An interatomic potential model for carbonates allowing for polarization effects

    International Nuclear Information System (INIS)

    Birse, S.E.A.; Archer, T.D.; Dove, Martin T.; Cygan, Randall Timothy; Gale, Julian D.; Redern, Simon A.T.

    2003-01-01

    An empirical model for investigating the behavior of CaCO 3 polymorphs incorporating a shell model for oxygen has been created. The model was constructed by fitting to: the structure of aragonite and calcite; their elastic, static and high-frequency dielectric constants; phonon frequencies at the wave vectors (1/2 0 2) and (0 0 0) of calcite; and vibrational frequencies of the carbonate deformation modes of calcite. The high-pressure phase transition between calcite I and II is observed. The potentials for the CO 3 group were transferred to other carbonates, by refitting the interaction between CO 3 and the cation to both the experimental structures and their bulk modulus, creating a set of potentials for calculating the properties of a wide range of carbonate materials. Defect energies of substitutional cation defects were analyzed for calcite and aragonite phases. The results were rationalized by studying the structure of calcite and aragonite in greater detail.

  17. Extreme Ionospheric Gradients Observed in South Korea during the Last Solar Cycle

    Science.gov (United States)

    Jung, S.; Choi, Y.; Kim, M.; Lee, J.

    2012-12-01

    Ground-Based Augmentation Systems (GBAS) support aircraft precision approach and landing by providing differential corrections for Global Navigation Satellite System (GNSS) pseudorange measurements and integrity information to aviation users within several tens of kilometers of GBAS-equipped airports. During the peak of the last solar cycle, extreme ionospheric gradients as large as 412 mm/km at high elevation and 360 mm/km at low elevation were observed in the United States. For a GBAS user at a 200-foot decision height (DH) for Category I precision approach, a spatial gradient of 412 mm/km could cause a residual range error of 8 meters. To predict the maximum position errors that GBAS users might suffer from these ionospheric threats, an ionospheric anomaly "threat model" for GBAS was developed in the Conterminous U.S (CONUS). The threat model issued to simulate worst-case ionospheric errors and develop mitigation strategies under ionospheric disturbances. Ionospheric conditions should be investigated for all regions where GBAS will be fielded in the future. We presents a method to identify ionospheric anomalies that can pose a potential integrity risk to GBAS users and details the study of extreme ionospheric gradients observed in South Korea during the last solar cycle. GPS dual-frequency code and carrier-phase measurements collected from a total of 74 GPS reference stations in South Korea were processed to observe ionospheric anomalies. Precise ionospheric delay estimates are obtained using the simplified truth processing method and ionospheric gradients are computed using the well-known "station pair method". Ionospheric threats can be modeled as a spatially linear semi-infinite wedge moving with constant speed in mid-latitude regions. A total of 22 dates during the last solar maximum period in 2000 - 2004 were investigated to identify ionospheric anomalies occurred in South Korea. Ten of the dates were the days previously chosen to construct the current

  18. Ionospheric scintillation observations

    International Nuclear Information System (INIS)

    Kakane, V.C.K.

    1982-12-01

    Ionospheric scintillation observations made at Legon, Ghana (5.63 deg. N, 0.19 deg. E, dip angle 8.50) during the year 1979 are reported for two geostationary satellites, Marisat and Sirio, transmitting at 257 MHz and 136 MHz, respectively. The night-time scintillation showed a single peak around 2200-3000 hours local time (GMT). Seasonally, Marisat showed a fast decay of scintillation for the months April-June and June-September from around midnight whilst it persisted for the other months January-March and October-December. (author)

  19. Effects of Response Style on the Polarity and Validity of Two-Dimensional Mood Models.

    Science.gov (United States)

    1985-08-01

    bipolar. Journal of Personality and Social Psychology, 37, 345-356. Russell, J.A. (1980). A circumplex model of affect. Journal of Personality and Social...RESOLUTION TEST CHART NATIONAL BUREAU OF STANDARDS- 19 6 3 A ’ EFFECTS OF RESPONSE STYLE ON THE POLARITY AND VALIDITY OF TWO-DIMENSIONAL MOOD MODELS -: N R...hypothesis requires appropriate measures of emotional state. Therefore, this study compared two alternative models for describing emotional states as

  20. Kriging with Unknown Variance Components for Regional Ionospheric Reconstruction

    Directory of Open Access Journals (Sweden)

    Ling Huang

    2017-02-01

    Full Text Available Ionospheric delay effect is a critical issue that limits the accuracy of precise Global Navigation Satellite System (GNSS positioning and navigation for single-frequency users, especially in mid- and low-latitude regions where variations in the ionosphere are larger. Kriging spatial interpolation techniques have been recently introduced to model the spatial correlation and variability of ionosphere, which intrinsically assume that the ionosphere field is stochastically stationary but does not take the random observational errors into account. In this paper, by treating the spatial statistical information on ionosphere as prior knowledge and based on Total Electron Content (TEC semivariogram analysis, we use Kriging techniques to spatially interpolate TEC values. By assuming that the stochastic models of both the ionospheric signals and measurement errors are only known up to some unknown factors, we propose a new Kriging spatial interpolation method with unknown variance components for both the signals of ionosphere and TEC measurements. Variance component estimation has been integrated with Kriging to reconstruct regional ionospheric delays. The method has been applied to data from the Crustal Movement Observation Network of China (CMONOC and compared with the ordinary Kriging and polynomial interpolations with spherical cap harmonic functions, polynomial functions and low-degree spherical harmonic functions. The statistics of results indicate that the daily ionospheric variations during the experimental period characterized by the proposed approach have good agreement with the other methods, ranging from 10 to 80 TEC Unit (TECU, 1 TECU = 1 × 1016 electrons/m2 with an overall mean of 28.2 TECU. The proposed method can produce more appropriate estimations whose general TEC level is as smooth as the ordinary Kriging but with a smaller standard deviation around 3 TECU than others. The residual results show that the interpolation precision of the

  1. Kriging with Unknown Variance Components for Regional Ionospheric Reconstruction.

    Science.gov (United States)

    Huang, Ling; Zhang, Hongping; Xu, Peiliang; Geng, Jianghui; Wang, Cheng; Liu, Jingnan

    2017-02-27

    Ionospheric delay effect is a critical issue that limits the accuracy of precise Global Navigation Satellite System (GNSS) positioning and navigation for single-frequency users, especially in mid- and low-latitude regions where variations in the ionosphere are larger. Kriging spatial interpolation techniques have been recently introduced to model the spatial correlation and variability of ionosphere, which intrinsically assume that the ionosphere field is stochastically stationary but does not take the random observational errors into account. In this paper, by treating the spatial statistical information on ionosphere as prior knowledge and based on Total Electron Content (TEC) semivariogram analysis, we use Kriging techniques to spatially interpolate TEC values. By assuming that the stochastic models of both the ionospheric signals and measurement errors are only known up to some unknown factors, we propose a new Kriging spatial interpolation method with unknown variance components for both the signals of ionosphere and TEC measurements. Variance component estimation has been integrated with Kriging to reconstruct regional ionospheric delays. The method has been applied to data from the Crustal Movement Observation Network of China (CMONOC) and compared with the ordinary Kriging and polynomial interpolations with spherical cap harmonic functions, polynomial functions and low-degree spherical harmonic functions. The statistics of results indicate that the daily ionospheric variations during the experimental period characterized by the proposed approach have good agreement with the other methods, ranging from 10 to 80 TEC Unit (TECU, 1 TECU = 1 × 10 16 electrons/m²) with an overall mean of 28.2 TECU. The proposed method can produce more appropriate estimations whose general TEC level is as smooth as the ordinary Kriging but with a smaller standard deviation around 3 TECU than others. The residual results show that the interpolation precision of the new proposed

  2. Kriging with Unknown Variance Components for Regional Ionospheric Reconstruction

    Science.gov (United States)

    Huang, Ling; Zhang, Hongping; Xu, Peiliang; Geng, Jianghui; Wang, Cheng; Liu, Jingnan

    2017-01-01

    Ionospheric delay effect is a critical issue that limits the accuracy of precise Global Navigation Satellite System (GNSS) positioning and navigation for single-frequency users, especially in mid- and low-latitude regions where variations in the ionosphere are larger. Kriging spatial interpolation techniques have been recently introduced to model the spatial correlation and variability of ionosphere, which intrinsically assume that the ionosphere field is stochastically stationary but does not take the random observational errors into account. In this paper, by treating the spatial statistical information on ionosphere as prior knowledge and based on Total Electron Content (TEC) semivariogram analysis, we use Kriging techniques to spatially interpolate TEC values. By assuming that the stochastic models of both the ionospheric signals and measurement errors are only known up to some unknown factors, we propose a new Kriging spatial interpolation method with unknown variance components for both the signals of ionosphere and TEC measurements. Variance component estimation has been integrated with Kriging to reconstruct regional ionospheric delays. The method has been applied to data from the Crustal Movement Observation Network of China (CMONOC) and compared with the ordinary Kriging and polynomial interpolations with spherical cap harmonic functions, polynomial functions and low-degree spherical harmonic functions. The statistics of results indicate that the daily ionospheric variations during the experimental period characterized by the proposed approach have good agreement with the other methods, ranging from 10 to 80 TEC Unit (TECU, 1 TECU = 1 × 1016 electrons/m2) with an overall mean of 28.2 TECU. The proposed method can produce more appropriate estimations whose general TEC level is as smooth as the ordinary Kriging but with a smaller standard deviation around 3 TECU than others. The residual results show that the interpolation precision of the new proposed

  3. Polarized microwave forward model simulations for tropical storm ...

    Indian Academy of Sciences (India)

    microwave remote sensing of precipitation sys- tems largely depends on the forward radiative transfer model (Petty 2001), which are themselves based on some assumptions and hence are never perfect. The Tropical Rainfall Measuring Mission. (TRMM) satellite was designed to measure preci- pitation with high resolution ...

  4. Dust in the small Magellanic Cloud. 2: Dust models from interstellar polarization and extinction data

    Science.gov (United States)

    Rodrigues, C. V.; Magalhaes, A. M.; Coyne, G. V.

    1995-01-01

    We study the dust in the Small Magellanic Cloud using our polarization and extinction data (Paper 1) and existing dust models. The data suggest that the monotonic SMC extinction curve is related to values of lambda(sub max), the wavelength of maximum polarization, which are on the average smaller than the mean for the Galaxy. On the other hand, AZV 456, a star with an extinction similar to that for the Galaxy, shows a value of lambda(sub max) similar to the mean for the Galaxy. We discuss simultaneous dust model fits to extinction and polarization. Fits to the wavelength dependent polarization data are possible for stars with small lambda(sub max). In general, they imply dust size distributions which are narrower and have smaller mean sizes compared to typical size distributions for the Galaxy. However, stars with lambda(sub max) close to the Galactic norm, which also have a narrower polarization curve, cannot be fit adequately. This holds true for all of the dust models considered. The best fits to the extinction curves are obtained with a power law size distribution by assuming that the cylindrical and spherical silicate grains have a volume distribution which is continuous from the smaller spheres to the larger cylinders. The size distribution for the cylinders is taken from the fit to the polarization. The 'typical', monotonic SMC extinction curve can be fit well with graphite and silicate grains if a small fraction of the SMC carbon is locked up in the grain. However, amorphous carbon and silicate grains also fit the data well. AZV456, which has an extinction curve similar to that for the Galaxy, has a UV bump which is too blue to be fit by spherical graphite grains.

  5. Numerical Model of an Injection-Locked Wideband Frequency Modulator for Polar Transmitters

    NARCIS (Netherlands)

    Bashir, I.; Staszewski, R.B.; Balsara, P.T.

    2017-01-01

    We present a numerical model of a wideband injection-locked frequency modulator used in a polar transmitter for 3G cellular radio application. At the heart of the system is a self-injection-locked oscillator with a programmable linear tuning range of up to 200 MHz at 4-GHz oscillation frequency.

  6. Polarized Airway Epithelial Models for Immunological Co-Culture Studies

    DEFF Research Database (Denmark)

    Papazian, Dick; Würtzen, Peter A; Hansen, Søren Werner Karlskov

    2016-01-01

    of the epithelial response towards environmental antigens and genetic susceptibility, resulting in inflammation and T cell-derived immune responses. In vivo animal models have long been used to study immune homeostasis of the airways but are limited by species restriction and lack of exposure to a natural......Epithelial cells line all cavities and surfaces throughout the body and play a substantial role in maintaining tissue homeostasis. Asthma and other atopic diseases are increasing worldwide and allergic disorders are hypothesized to be a consequence of a combination of dysregulation......-culture models to become powerful tools in the discovery of key molecules dictating immunity and/or tolerance, and for understanding the complex interplay that takes place between mucosa, airway epithelium and resident or infiltrating immune cells. This review focuses on current knowledge and the advantages...

  7. Dependence of model-simulated response to ozone depletion on stratospheric polar vortex climatology

    Science.gov (United States)

    Lin, Pu; Paynter, David; Polvani, Lorenzo; Correa, Gustavo J. P.; Ming, Yi; Ramaswamy, V.

    2017-06-01

    We contrast the responses to ozone depletion in two climate models: Community Atmospheric Model version 3 (CAM3) and Geophysical Fuild Dynamics Laboratory (GFDL) AM3. Although both models are forced with identical ozone concentration changes, the stratospheric cooling simulated in CAM3 is 30% stronger than in AM3 in annual mean, and twice as strong in December. We find that this difference originates from the dynamical response to ozone depletion, and its strength can be linked to the timing of the climatological springtime polar vortex breakdown. This mechanism is further supported by a variant of the AM3 simulation in which the southern stratospheric zonal wind climatology is nudged to be CAM3-like. Given that the delayed breakdown of the southern polar vortex is a common bias among many climate models, previous model-based assessments of the forced responses to ozone depletion may have been somewhat overestimated.

  8. Ionospheric error contribution to GNSS single-frequency navigation at the 2014 solar maximum

    Science.gov (United States)

    Orus Perez, Raul

    2017-04-01

    For single-frequency users of the global satellite navigation system (GNSS), one of the main error contributors is the ionospheric delay, which impacts the received signals. As is well-known, GPS and Galileo transmit global models to correct the ionospheric delay, while the international GNSS service (IGS) computes precise post-process global ionospheric maps (GIM) that are considered reference ionospheres. Moreover, accurate ionospheric maps have been recently introduced, which allow for the fast convergence of the real-time precise point position (PPP) globally. Therefore, testing of the ionospheric models is a key issue for code-based single-frequency users, which constitute the main user segment. Therefore, the testing proposed in this paper is straightforward and uses the PPP modeling applied to single- and dual-frequency code observations worldwide for 2014. The usage of PPP modeling allows us to quantify—for dual-frequency users—the degradation of the navigation solutions caused by noise and multipath with respect to the different ionospheric modeling solutions, and allows us, in turn, to obtain an independent assessment of the ionospheric models. Compared to the dual-frequency solutions, the GPS and Galileo ionospheric models present worse global performance, with horizontal root mean square (RMS) differences of 1.04 and 0.49 m and vertical RMS differences of 0.83 and 0.40 m, respectively. While very precise global ionospheric models can improve the dual-frequency solution globally, resulting in a horizontal RMS difference of 0.60 m and a vertical RMS difference of 0.74 m, they exhibit a strong dependence on the geographical location and ionospheric activity.

  9. The new ionospheric station of Tucumán: first results

    Directory of Open Access Journals (Sweden)

    M. A. Cabrera

    2007-06-01

    Full Text Available An Advanced Ionospheric Sounder, built at the Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy, was installed at Tucumán, Argentina, particularly interesting for its location, near the southern peak of the ionospheric equatorial anomaly. The aim of this installation is to collect a large number of continuous data useful both to study the dynamics of the equatorial ionospheric plasma and to develop reliable regional ionospheric prediction models. Moreover this ionosonde will contribute to the ionospheric database and real time knowledge of Southern Hemisphere ionospheric conditions for space weather applications. The ionosonde is completely programmable and two PCs support the data acquisition, control, storage and on-line processing. In this work the first results, in terms of ionograms and autoscaled characteristics, are presented and briefly discussed.

  10. Polar mesosphere summer echoes during the July 2000 solar protonevent

    Directory of Open Access Journals (Sweden)

    V. Barabash

    2004-03-01

    Full Text Available The influence of the solar proton event (SPE 14–16 July 2000 on Polar Mesosphere Summer Echoes (PMSE is examined. PMSE were observed by the Esrange VHF MST Radar (ESRAD at 67°53'N, 21°06'E. The 30MHz Imaging Riometer for Ionospheric Studies IRIS in Kilpisjärvi (69°30'N, 20°47'E registered cosmic radio noise absorption caused by ionisation changes in response to the energetic particle precipitation. An energy deposition/ion-chemical model was used to estimate the density of free electrons and ions in the upper atmosphere. Particle collision frequencies were calculated from the MSISE-90 model. Electric fields were calculated using conductivities from the model and measured magnetic disturbances. The electric field reached a maximum of 91mV/m during the most intensive period of the geomagnetic storm accompanying the SPE. The temperature increase due to Joule and particle heating was calculated, taking into account radiative cooling. The temperature increase at PMSE heights was found to be very small. The observed PMSE were rather intensive and extended over the 80–90km height interval. PMSE almost disappeared above 86km at the time of greatest Joule heating on 15 July 2000. Neither ionisation changes, nor Joule/particle heating can explain the PMSE reduction. Transport effects due to the strong electric field are a more likely explanation. Key words. Meteorology and atmospheric dynamics (middle atmospheric dynamics, ionosphere (ionospheric disturbances; solar radiation and cosmic ray effects

  11. Atomic polarizations necessary for coherent infrared intensity modeling with theoretical calculations.

    Science.gov (United States)

    Richter, Wagner E; Silva, Arnaldo F; Bruns, Roy E

    2017-04-07

    The inclusion of atomic polarizations for describing molecular electronic structure changes on vibration is shown to be necessary for coherent infrared intensity modeling. Atomic charges from the ChelpG partition scheme and atomic charges and dipoles from Quantum Theory of Atoms in Molecules (QTAIM) were employed within two different models to describe the stretching and bending vibrational intensities of the C-H, C-F, and C=O groups. The model employing the QTAIM parameters was the Charge-Charge Transfer and Dipolar Polarization model (QTAIM/CCTDP), and the model employing the ChelpG charges was the Equilibrium Charge-Charge Flux (ChelpG/ECCF). The QTAIM/CCTDP models result in characteristic proportions of the charge-charge transfer-dipolar polarization contributions even though their sums giving the total intensities do not discriminate between these vibrations. According to the QTAIM/CCTDP model, the carbon monoxide intensity has electronic structure changes similar to those of the carbonyl stretches whereas they resemble those of the CH stretches for the ChelpG/ECCF model.

  12. Modeling of polarization phenomena due to RF sheaths and electron beams in magnetized plasma

    International Nuclear Information System (INIS)

    Faudot, E.

    2005-01-01

    This work investigates the problematic of hot spots induced by accelerated particle fluxes in tokamaks. It is shown that the polarization due to sheaths in the edge plasma in which an electron beam at a high level of energy is injected, can reach several hundreds volts and thus extend the deposition area. The notion of obstructed sheath is introduced and explains the acceleration of energy deposition by the decreasing of the sheath potential. Then, a 2-dimensional fluid modeling of flux tubes in front of ICRF antennae allows us to calculate the rectified potentials taking into account RF polarization currents transverse to magnetic field lines. The 2-dimensional fluid code designed validates the analytical results which show that the DC rectified potential is 50% greater with polarization currents than without. Finally, the simultaneous application of an electron beam and a RF potential reveals that the potentials due to each phenomenon are additives when RF potential is much greater than beam polarization. The density depletion of polarized flux tubes in 2-dimensional PIC (particles in cells) simulations is characterized but not yet explained. (author)

  13. Polarization modeling and predictions for DKIST part 3: focal ratio and thermal dependencies of spectral polarization fringes and optic retardance

    Science.gov (United States)

    Harrington, David M.; Sueoka, Stacey R.

    2018-01-01

    Data products from high spectral resolution astronomical polarimeters are often limited by fringes. Fringes can skew derived magnetic field properties from spectropolarimetric data. Fringe removal algorithms can also corrupt the data if the fringes and object signals are too similar. For some narrow-band imaging polarimeters, fringes change the calibration retarder properties and dominate the calibration errors. Systems-level engineering tools for polarimetric instrumentation require accurate predictions of fringe amplitudes, periods for transmission, diattenuation, and retardance. The relevant instabilities caused by environmental, thermal, and optical properties can be modeled and mitigation tools developed. We create spectral polarization fringe amplitude and temporal instability predictions by applying the Berreman calculus and simple interferometric calculations to optics in beams of varying F/ number. We then apply the formalism to superachromatic six-crystal retarders in converging beams under beam thermal loading in outdoor environmental conditions for two of the world's largest observatories: the 10-m Keck telescope and the Daniel K. Inouye Solar Telescope (DKIST). DKIST will produce a 300-W optical beam, which has imposed stringent requirements on the large diameter six-crystal retarders, dichroic beamsplitters, and internal optics. DKIST retarders are used in a converging beam with F/ ratios between 8 and 62. The fringe spectral periods, amplitudes, and thermal models of retarder behavior assisted DKIST optical designs and calibration plans with future application to many astronomical spectropolarimeters. The Low Resolution Imaging Spectrograph with polarimetry instrument at Keck also uses six-crystal retarders in a converging F / 13 beam in a Cassegrain focus exposed to summit environmental conditions providing observational verification of our predictions.

  14. Ionospheric climatology and weather disturbances: A tutorial

    Science.gov (United States)

    Schunk, R. W.

    The ionosphere can have a detrimental effect on both civilian and military systems, including OTH radars, HF communications, surveillance, and navigation systems that use GPS satellites. In an attempt to mitigate the adverse effects, specification and forecast models are being developed that are based on sophisticated data assimilation techniques. However, the model development represents a significant challenge because the ionosphere is known to display a marked variation with altitude, latitude, longitude, universal time, season, solar cycle, and geomagnetic activity. This variation results from the couplings, time delays, and feedback mechanisms that are inherent in the system as well as from the effects of solar, interplanetary, magnetospheric, and mesospheric processes. The various processes act in concert to define both a background state (climatology) and a disturbed state (weather), which are described in this tutorial. First, a brief description of the background ionospheric state and the physical processes that are responsible for establishing this state is given. The tutorial then focuses on a discussion of weather disturbances and features, the causes of weather, and the status of weather modeling.

  15. Comparison of ionospheric radio occultation CHAMP data with IRI 2001

    Directory of Open Access Journals (Sweden)

    N. Jakowski

    2004-01-01

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

  16. Uplift of Ionospheric Oxygen Ions During Extreme Magnetic Storms

    Science.gov (United States)

    Tsurutani, Bruce T.; Mannucci, Anthony J.; Verkhoglyadova, Olga P.; Huba, Joseph; Lakhina, Gurbax S.

    2013-01-01

    Research reported earlier in literature was conducted relating to estimation of the ionospheric electrical field, which may have occurred during the September 1859 Carrington geomagnetic storm event, with regard to modern-day consequences. In this research, the NRL SAMI2 ionospheric code has been modified and applied the estimated electric field to the dayside ionosphere. The modeling was done at 15-minute time increments to track the general ionospheric changes. Although it has been known that magnetospheric electric fields get down into the ionosphere, it has been only in the last ten years that scientists have discovered that intense magnetic storm electric fields do also. On the dayside, these dawn-to-dusk directed electric fields lift the plasma (electrons and ions) up to higher altitudes and latitudes. As plasma is removed from lower altitudes, solar UV creates new plasma, so the total plasma in the ionosphere is increased several-fold. Thus, this complex process creates super-dense plasmas at high altitudes (from 700 to 1,000 km and higher).

  17. Technical Note: SWIFT - a fast semi-empirical model for polar stratospheric ozone loss

    Science.gov (United States)

    Rex, M.; Kremser, S.; Huck, P.; Bodeker, G.; Wohltmann, I.; Santee, M. L.; Bernath, P.

    2014-07-01

    An extremely fast model to estimate the degree of stratospheric ozone depletion during polar winters is described. It is based on a set of coupled differential equations that simulate the seasonal evolution of vortex-averaged hydrogen chloride (HCl), nitric acid (HNO3), chlorine nitrate (ClONO2), active forms of chlorine (ClOx = Cl + ClO + 2 ClOOCl) and ozone (O3) on isentropic levels within the polar vortices. Terms in these equations account for the chemical and physical processes driving the time rate of change of these species. Eight empirical fit coefficients associated with these terms are derived by iteratively fitting the equations to vortex-averaged satellite-based measurements of HCl, HNO3 and ClONO2 and observationally derived ozone loss rates. The system of differential equations is not stiff and can be solved with a time step of one day, allowing many years to be processed per second on a standard PC. The inputs required are the daily fractions of the vortex area covered by polar stratospheric clouds and the fractions of the vortex area exposed to sunlight. The resultant model, SWIFT (Semi-empirical Weighted Iterative Fit Technique), provides a fast yet accurate method to simulate ozone loss rates in polar regions. SWIFT's capabilities are demonstrated by comparing measured and modeled total ozone loss outside of the training period.

  18. Polarization transfer in inelastic scattering and pionic models of the EMC effect

    International Nuclear Information System (INIS)

    Carey, T.A.; Jones, K.W.; McClelland, J.B.; Moss, J.M.; Rees, L.B.; Tanaka, N.; Bacher, A.D.

    1985-01-01

    The aim of the experiment reported was to make a precise test of the enhanced pion field model in a medium-energy scattering experiment. The quantity probed is the spin-longitudinal response function, a measure of the nuclear pion density which is used explicitly in the pion-excess models of the EMC effect. The point of reference used is deuterium. The spin-dependent response functions for heavy targets and 2 H are compared using identical experimental techniques. The technique of complete polarization transfer is used to separate the spin-longitudinal and spin-transverse response in the continuum. The experiment consisted of precise determinations of the polarization transfer coefficients for 500 MeV protons inelastically scattered from Pb, Ca, and 2 H. The experiment utilized longitudinal, sideways, and normal polarized beams in conjunction with final polarization analysis from the focal-plane polarimeter of the high-resolution spectrometer. Quantities constructed from these data are the longitudinal and transverse spin-flip probabilities. Calculations were performed of the ratio of longitudinal to transverse response functions and of the EMC effect with the same model. No evidence was found for collectivity in the isovector spin-longitudinal response function. 10 refs

  19. Swarm GPS Receiver Performance under the Influence of Ionospheric Scintillation

    Science.gov (United States)

    Ren, Le; Schön, Steffen

    2016-04-01

    The Swarm mission launched on 22 November 2013 is ESA's first constellation of satellites to study the dynamics of the Earth's magnetic field and its interaction with the Earth system. This mission consists of three identical satellites in near-polar orbits , two flying almost side-by-side at an initial altitude of 460 km, the third flying in a higher orbit of about 530 km. Each satellite is equipped with a high precision 8-channels dual-frequency receiver for the precise orbit determination, which is also the essential fundament in order to take full advantage of the data information provided by this constellation, e.g. for the recovery of gravity field. The quality of the final orbit determination depends on the observation data from the receivers. In this contribution, we will analyze the performance of the Swarm on-board receivers, especially under the influence of ionospheric scintillation caused by ionospheric irregularities. This is a prerequisite for high quality satellite positioning as well as a sound study of the ionosphere. Ionospheric scintillation can lead to the phase disturbances, cycle slips or even loss of signal tracking. The RINEX observation data from Swarm Level 1b products are used to analyze the Swarm receiver performance. We will demonstrate the signal strength, code and phase noise, different linear combinations (geometry free, ionosphere free), as well as GDOP values for the 3 Swarm satellites. The first results show that the observation data are severely disturbed and the signals could be lost around the geomagnetic equator and geomagnetic poles where the ionosphere is active. The results also show that the receivers are more stable in those areas after the update in October 2015.

  20. Improving Geoscience Education through the PolarTREC Teacher Research Experience Model (Invited)

    Science.gov (United States)

    Warburton, J.; Timm, K.; Larson, A. M.

    2010-12-01

    Teacher Research Experiences (TRE’s) are not new. For more than a decade, the National Science Foundation (NSF) as well as other federal agencies have been funding programs that place teachers with researchers in efforts to invigorate science education by bringing educators and researchers together through hands-on experiences. Many of the TRE’s are successful in providing a hands-on field experience for the teachers and researchers however many of the programs lack the resources to continue the collaborations and support the growing network of teachers that have had these field experiences. In 2007, NSF provided funding for PolarTREC—Teachers and Researchers Exploring and Collaborating, a program of the Arctic Research Consortium of the U.S. (ARCUS). PolarTREC is a TRE where K-12 teachers participate in polar field research, working closely with scientists as a pathway to improving science education. In just three years, it has become a successful TRE. What makes PolarTREC different than other the teacher research experience programs and how can others benefit from what we have learned? During this presentation, we will share data collected through the program evaluation and on how PolarTREC contributes to the discipline of Science, Technology, Engineering, and Mathematics (STEM) education and pedagogy through a model program conceived and organized according to current best practices, such as pre-research training, mentoring, support for classroom transfer, and long-term access to resources and support. Data shows that PolarTREC’s comprehensive program activities have many positive impacts on educators and their ability to teach science concepts and improve their teaching methods. Additionally, K-12 students polled in interest surveys showed significant changes in key areas including amount of time spent in school exploring research activities, importance of understanding science for future work, importance of understanding the polar regions as a person

  1. Monitoring of ionospheric irregularities with multi-GNSS observations: a new ionosphere activity index and product services

    Science.gov (United States)

    Wang, Ningbo; Li, Zishen; Yuan, Yunbin; Yuan, Hong

    2017-04-01

    and North American regions. The product files are produced on a daily basis with a latency of 3 days. Users now can access these products from the ftp archive of the Chinese Academy of Sciences (CAS, ftp://ftp.gipp.org.cn/product/). These maps can be used for ionospheric weather services, ionospheric irregularity modeling and foresting, as well as other GNSS applications. Although they are provided in a post-processing mode at present, it is expected that the near real-time services will be available since the availability of real-time data streams from the IGS.

  2. The importance of neutral hydrogen for the maintenance of the midlatitude winter nighttime ionosphere: Evidence from IS observations at Kharkiv, Ukraine, and field line interhemispheric plasma model simulations

    Czech Academy of Sciences Publication Activity Database

    Kotov, K. V.; Richards, P. G.; Bogomaz, O. V.; Chernogor, L. F.; Truhlík, Vladimír; Emelyanov, L. Ya.; Chepurnyy, Ya. M.; Domnin, I. F.

    2016-01-01

    Roč. 121, č. 7 (2016), s. 7013-7025 ISSN 2169-9380 Institutional support: RVO:68378289 Keywords : ionosphere * thermosphere * hydrogen * electron density * nighttime Nm F2 enhancement * plasmasphere Subject RIV: DG - Athmosphere Sciences, Meteorology Impact factor: 2.733, year: 2016 http://onlinelibrary.wiley.com/doi/10.1002/2016JA022442/full

  3. Modeling hydrate formation conditions in the presence of electrolytes and polar inhibitor solutions

    International Nuclear Information System (INIS)

    Osfouri, Shahriar; Azin, Reza; Gholami, Reza; Izadpanah, Amir Abbas

    2015-01-01

    Highlights: • A new predictive model is proposed for prediction of hydrate formation pressures. • A new local composition model was used to evaluate water activity in the presence of electrolyte. • MEG, DEG and TEG were used to test ability of the proposed model in the presence of polar inhibitors. • Cage occupancies by methane for the small cage were higher than carbon dioxide for gas mixtures. • The proposed model gives better match with experimental data in mixed electrolyte solutions. - Abstract: In this paper, a new predictive model is proposed for prediction of gas hydrate formation conditions in the presence of single and mixed electrolytes and solutions containing both electrolyte and a polar inhibitor such as monoethylene glycol (MEG), diethylene glycol (DEG) and triethylene glycol (TEG). The proposed model is based on the γ–φ approach, which uses modified Patel–Teja equation of state (VPT EOS) for characterizing the vapor phase, the solid solution theory by van der Waals and Platteeuw for modeling the hydrate phase, the non-electrolyte NRTL-NRF local composition model and Pitzer–Debye–Huckel equation as short-range and long-range contributions to calculate water activity in single electrolyte solutions. Also, the Margules equation was used to determine the activity of water in solutions containing polar inhibitor (glycols). The model predictions are in acceptable agreement with experimental data. For single electrolyte solutions, the model predictions are similar to available models, while for mixtures of electrolytes and mixtures of electrolytes and inhibitors, the proposed model gives significantly better predictions. In addition, the absolute average deviation of hydrate formation pressures (AADP) for 144 experimental data in solutions containing single electrolyte is 5.86% and for 190 experimental data in mixed electrolytes solutions is 5.23%. Furthermore, the proposed model has an AADP of 14.13%, 5.82% and 5.28% in solutions

  4. Mathematical modeling of planar cell polarity signaling in the Drosophila melanogaster wing

    Science.gov (United States)

    Amonlirdviman, Keith

    Planar cell polarity (PCP) signaling refers to the coordinated polarization of cells within the plane of various epithelial tissues to generate sub-cellular asymmetry along an axis orthogonal to their apical-basal axes. For example, in the Drosophila wing, PCP is seen in the parallel orientation of hairs that protrude from each of the approximately 30,000 epithelial cells to robustly point toward the wing tip. Through a poorly understood mechanism, cell clones mutant for some PCP signaling components, including some, but not all alleles of the receptor frizzled, cause polarity disruptions of neighboring, wild-type cells, a phenomenon referred to as domineering nonautonomy. Previous models have proposed diffusible factors to explain nonautonomy, but no such factors have yet been found. This dissertation describes the mathematical modeling of PCP in the Drosophila wing, based on a contact dependent signaling hypothesis derived from experimental results. Intuition alone is insufficient to deduce that this hypothesis, which relies on a local feedback loop acting at the cell membrane, underlies the complex patterns observed in large fields of cells containing mutant clones, and others have argued that it cannot account for observed phenotypes. Through reaction-diffusion, partial differential equation modeling and simulation, the feedback loop is shown to fully reproduce PCP phenotypes, including domineering nonautonomy. The sufficiency of this model and the experimental validation of model predictions argue that previously proposed diffusible factors need not be invoked to explain PCP signaling and reveal how specific protein-protein interactions lead to autonomy or domineering nonautonomy. Based on these results, an ordinary differential equation model is derived to study the relationship of the feedback loop with upstream signaling components. The cadherin Fat transduces a cue to the local feedback loop, biasing the polarity direction of each cell toward the wing tip

  5. Seasonal effects in the ionosphere-thermosphere response to the precipitation and field-aligned current variations in the cusp region

    Directory of Open Access Journals (Sweden)

    A. A. Namgaladze

    Full Text Available The seasonal effects in the thermosphere and ionosphere responses to the precipitating electron flux and field-aligned current variations, of the order of an hour in duration, in the summer and winter cusp regions have been investigated using the global numerical model of the Earth's upper atmosphere. Two variants of the calculations have been performed both for the IMF By < 0. In the first variant, the model input data for the summer and winter precipitating fluxes and field-aligned currents have been taken as geomagnetically symmetric and equal to those used earlier in the calculations for the equinoctial conditions. It has been found that both ionospheric and thermospheric disturbances are more intensive in the winter cusp region due to the lower conductivity of the winter polar cap ionosphere and correspondingly larger electric field variations leading to the larger Joule heating effects in the ion and neutral gas temperature, ion drag effects in the thermospheric winds and ion drift effects in the F2-region electron concentration. In the second variant, the calculations have been performed for the events of 28–29 January, 1992 when precipitations were weaker but the magnetospheric convection was stronger than in the first variant. Geomagnetically asymmetric input data for the summer and winter precipitating fluxes and field-aligned currents have been taken from the patterns derived by combining data obtained from the satellite, radar and ground magnetometer observations for these events. Calculated patterns of the ionospheric convection and thermospheric circulation have been compared with observations and it has been established that calculated patterns of the ionospheric convection for both winter and summer hemispheres are in a good agreement with the observations. Calculated patterns of the thermospheric circulation are in a good agreement with the average circulation for the Southern (summer Hemisphere obtained

  6. Digital ionospheric sounding in the Arctic

    Science.gov (United States)

    Reinisch, B.; Bibl, K.

    1981-01-01

    New ionogram observation techniques were applied at the Goose Bay Ionospheric Observatory (GBIO) in Newfoundland, Canada, and aboard AFGL's Airborne Ionospheric Observatory (AIO), using the Digisonde 128PS system. A receiving array of four crossed-loop antennas at GBIO enabled incidence angle and polarization measurements within the ionogram in addition to the Doppler observations. The Doppler information in the propagation ionograms between the GBIO Digisonde and the moving AIO sounder facilitates the interpreting of different modes of propagation. Software for the AFGL CDC 6600 computer and for a microcomputer was developed for the processing of the digital ionograms. The identification of ordinary and extraordinary echoes in the Goose Bay ionograms greatly simplify the automatic processing of ionograms. Indeed, it became clear that for automatic ionogram trace identification the O and X tagging is a prerequisite. In support of the ESD 414L project an ionogram communicator (ICOM) was added to the GBIO Digisonde providing - via telephone lines - realtime ionogram printouts at the Over-The-Horizon Backscatter Experimental Radar System in Maine. Another Digisonde station was equipped and brought to operation in Keflavik, Iceland, to provide environmental data for the OTH radar operation.

  7. Expanding signaling-molecule wavefront model of cell polarization in the Drosophila wing primordium.

    Science.gov (United States)

    Wortman, Juliana C; Nahmad, Marcos; Zhang, Peng Cheng; Lander, Arthur D; Yu, Clare C

    2017-07-01

    In developing tissues, cell polarization and proliferation are regulated by morphogens and signaling pathways. Cells throughout the Drosophila wing primordium typically show subcellular localization of the unconventional myosin Dachs on the distal side of cells (nearest the center of the disc). Dachs localization depends on the spatial distribution of bonds between the protocadherins Fat (Ft) and Dachsous (Ds), which form heterodimers between adjacent cells; and the Golgi kinase Four-jointed (Fj), which affects the binding affinities of Ft and Ds. The Fj concentration forms a linear gradient while the Ds concentration is roughly uniform throughout most of the wing pouch with a steep transition region that propagates from the center to the edge of the pouch during the third larval instar. Although the Fj gradient is an important cue for polarization, it is unclear how the polarization is affected by cell division and the expanding Ds transition region, both of which can alter the distribution of Ft-Ds heterodimers around the cell periphery. We have developed a computational model to address these questions. In our model, the binding affinity of Ft and Ds depends on phosphorylation by Fj. We assume that the asymmetry of the Ft-Ds bond distribution around the cell periphery defines the polarization, with greater asymmetry promoting cell proliferation. Our model predicts that this asymmetry is greatest in the radially-expanding transition region that leaves polarized cells in its wake. These cells naturally retain their bond distribution asymmetry after division by rapidly replenishing Ft-Ds bonds at new cell-cell interfaces. Thus we predict that the distal localization of Dachs in cells throughout the pouch requires the movement of the Ds transition region and the simple presence, rather than any specific spatial pattern, of Fj.

  8. A rate-equation model for polarized laser-induced fluorescence to measure electric field in glow discharge He plasmas

    International Nuclear Information System (INIS)

    Takiyama, K.; Watanabe, M.; Oda, T.

    1998-01-01

    Possibility of applying polarized laser-induced fluorescence (LIF) spectroscopy for measuring the electric field in a plasma with a large collisional depolarization has been investigated. A rate equation model including the depolarization process was employed to analyze the time evolution of LIF polarization components. The polarized LIF pulse shapes observed in the sheath of a He glow discharge plasma were successfully reproduced, and the electric field distribution was obtained with high accuracy. (author)

  9. Influence of polarization and a source model for dose calculation in MRT

    Energy Technology Data Exchange (ETDEWEB)

    Bartzsch, Stefan, E-mail: s.bartzsch@dkfz.de; Oelfke, Uwe [The Institute of Cancer Research, 15 Cotswold Road, Belmont, Sutton, Surrey SM2 5NG, United Kingdom and Deutsches Krebsforschungszentrum, Im Neuenheimer Feld 280, D-69120 Heidelberg (Germany); Lerch, Michael; Petasecca, Marco [Centre for Medical Radiation Physics, University of Wollongong, Northfields Avenue, Wollongong 2522 (Australia); Bräuer-Krisch, Elke [European Synchrotron Radiation Facility, 6 Rue Jules Horowitz, 38000 Grenoble (France)

    2014-04-15

    Purpose: Microbeam Radiation Therapy (MRT), an alternative preclinical treatment strategy using spatially modulated synchrotron radiation on a micrometer scale, has the great potential to cure malignant tumors (e.g., brain tumors) while having low side effects on normal tissue. Dose measurement and calculation in MRT is challenging because of the spatial accuracy required and the arising high dose differences. Dose calculation with Monte Carlo simulations is time consuming and their accuracy is still a matter of debate. In particular, the influence of photon polarization has been discussed in the literature. Moreover, it is controversial whether a complete knowledge of phase space trajectories, i.e., the simulation of the machine from the wiggler to the collimator, is necessary in order to accurately calculate the dose. Methods: With Monte Carlo simulations in the Geant4 toolkit, the authors investigate the influence of polarization on the dose distribution and the therapeutically important peak to valley dose ratios (PVDRs). Furthermore, the authors analyze in detail phase space information provided byMartínez-Rovira et al. [“Development and commissioning of a Monte Carlo photon model for the forthcoming clinical trials in microbeam radiation therapy,” Med. Phys. 39(1), 119–131 (2012)] and examine its influence on peak and valley doses. A simple source model is developed using parallel beams and its applicability is shown in a semiadjoint Monte Carlo simulation. Results are compared to measurements and previously published data. Results: Polarization has a significant influence on the scattered dose outside the microbeam field. In the radiation field, however, dose and PVDRs deduced from calculations without polarization and with polarization differ by less than 3%. The authors show that the key consequences from the phase space information for dose calculations are inhomogeneous primary photon flux, partial absorption due to inclined beam incidence outside

  10. Low- and mid-latitude ionospheric electric fields during the January 1984 GISMOS campaign

    International Nuclear Information System (INIS)

    Fejer, B.G.; Kelley, M.C.; Senior, C.; De La Beaujardiere, O.; Holt, J.A.; Tepley, C.A.; Burnside, R.; Abdu, M.A.; Sobral, J.H.A.; Woodman, R.F.; Kamide, Y.; Lepping, R.

    1990-01-01

    This paper examines in detail the electrical coupling between the high-, middle, and low-latitude ionospheres during January 17-19, 1984, using interplanetary and high-latitude magnetic field data together with F region plasma drift measurements from the EISCAT, Sondre Stromfjord, Millstone Hill, Saint-Santin, Arecibo, and Jicamarca incoherent scatter radars. The authors study the penetration of both the zonal and meridional electric field components of high-latitude origin into the low-latitude and the equatorial ionospheres. In the dusk sector, a large perturbation of the zonal equatorial electric field was observed in the absence of similar changes at low and middle latitudes in the same longitudinal sector. The observations in the postmidnight sector are used to compare the longitudinal variation of the zonal perturbation electric field with predictions made from global convection models. The results show that the meridional electric field perturbations are considerably more attenuated with decreasing latitude than the zonal fluctuations. As a result, they conclude that variations in the meridional electric field at low latitudes are largely due to dynamo effects. These observations are used to show that the global convection models reproduce a number of characteristics of low-latitude and equatorial electric fields associated with changes in the polar cap potential drop. In addition, they highlight several areas where there is still substantial disagreement between the electric field data and the theoretical results

  11. Evidence of L-mode electromagnetic wave pumping of ionospheric plasma near geomagnetic zenith

    Science.gov (United States)

    Leyser, Thomas B.; James, H. Gordon; Gustavsson, Björn; Rietveld, Michael T.

    2018-02-01

    The response of ionospheric plasma to pumping by powerful HF (high frequency) electromagnetic waves transmitted from the ground into the ionosphere is the strongest in the direction of geomagnetic zenith. We present experimental results from transmitting a left-handed circularly polarized HF beam from the EISCAT (European Incoherent SCATter association) Heating facility in magnetic zenith. The CASSIOPE (CAScade, Smallsat and IOnospheric Polar Explorer) spacecraft in the topside ionosphere above the F-region density peak detected transionospheric pump radiation, although the pump frequency was below the maximum ionospheric plasma frequency. The pump wave is deduced to arrive at CASSIOPE through L-mode propagation and associated double (O to Z, Z to O) conversion in pump-induced radio windows. L-mode propagation allows the pump wave to reach higher plasma densities and higher ionospheric altitudes than O-mode propagation so that a pump wave in the L-mode can facilitate excitation of upper hybrid phenomena localized in density depletions in a larger altitude range. L-mode propagation is therefore suggested to be important in explaining the magnetic zenith effect.

  12. Evidence of L-mode electromagnetic wave pumping of ionospheric plasma near geomagnetic zenith

    Directory of Open Access Journals (Sweden)

    T. B. Leyser

    2018-02-01

    Full Text Available The response of ionospheric plasma to pumping by powerful HF (high frequency electromagnetic waves transmitted from the ground into the ionosphere is the strongest in the direction of geomagnetic zenith. We present experimental results from transmitting a left-handed circularly polarized HF beam from the EISCAT (European Incoherent SCATter association Heating facility in magnetic zenith. The CASSIOPE (CAScade, Smallsat and IOnospheric Polar Explorer spacecraft in the topside ionosphere above the F-region density peak detected transionospheric pump radiation, although the pump frequency was below the maximum ionospheric plasma frequency. The pump wave is deduced to arrive at CASSIOPE through L-mode propagation and associated double (O to Z, Z to O conversion in pump-induced radio windows. L-mode propagation allows the pump wave to reach higher plasma densities and higher ionospheric altitudes than O-mode propagation so that a pump wave in the L-mode can facilitate excitation of upper hybrid phenomena localized in density depletions in a larger altitude range. L-mode propagation is therefore suggested to be important in explaining the magnetic zenith effect.

  13. Loop quantization of the polarized Gowdy model on T{sup 3}: classical theory

    Energy Technology Data Exchange (ETDEWEB)

    Banerjee, Kinjal; Date, Ghanashyam [Institute of Mathematical Sciences, CIT Campus, Chennai-600 113 (India)], E-mail: kinjal@imsc.res.in, E-mail: shyam@imsc.res.in

    2008-05-21

    The vacuum Gowdy models provide much studied, non-trivial midi-superspace examples. Various technical issues within loop quantum gravity can be studied in these models and one can hope to understand singularities and their resolution in the loop quantization. The first step in this program is to reformulate the model in real connection variables in a manner that is amenable to loop quantization. We begin with the unpolarized model and carry out a consistent reduction to the polarized case. Carrying out complete gauge fixing, the known solutions are recovered.

  14. Ionospheric precursors to scintillation activity

    Directory of Open Access Journals (Sweden)

    Paul S.J. Spencer

    2014-03-01

    Full Text Available Ionospheric scintillation is the rapid fluctuation of both phase and amplitude of trans-ionospheric radio waves due to small scale electron density irregularities in the ionosphere. Prediction of the occurrence of scintillation at L band frequencies is needed to mitigate the disruption of space-based communication and navigation systems. The purpose of this paper is to present a method of using tomographic inversions of the ionospheric electron density obtained from ground-based GPS data to infer the location and strength of the post-sunset plasma drift vortex. This vortex is related to the pre-reversal enhancement in the eastwards electric field which has been correlated to the subsequent occurrence of scintillation.

  15. On the Origin of Ionospheric Hiss: A Conjugate Observation

    Science.gov (United States)

    Zhima, Zeren; Chen, Lunjin; Xiong, Ying; Cao, Jinbin; Fu, Huishan

    2017-11-01

    We present a conjugate observation on whistler mode electromagnetic hiss from the low Earth orbit satellite Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) and the high-altitude elliptical orbit spacecraft Time History of Events and Macroscale Interactions during Substorms (THEMIS). The conjugate observation was performed at 14:51:10 to 15:12:00 UT on 15 June 2010, when DEMETER was flying across the L shell region from 1.39 to 2.80 at an altitude of 660 km; meanwhile, THEMIS probes were passing through the L shell region from 1.64 to 1.91 at altitudes from 1.6 to 2.0 RE. The conjugated observations demonstrate similar time-frequency structures between the ionospheric hiss ( 350 to 800 Hz) captured by DEMETER and the plasmaspheric hiss ( 350 to 900 Hz) recorded by THEMIS probes, including similar peak frequencies ( 500 to 600 Hz), similar lower cutoff frequencies ( 350 to 400 Hz), and upper cutoff frequencies ( 730 to 800 Hz). The wave vector analyses show that the ionospheric hiss propagates obliquely downward to the Earth and slightly equatorward with right-handed polarization, suggesting that its source comes from higher altitudes. Ray tracing simulations with the constraint of observations verify that the connection between ionospheric and plasmaspheric hiss is physically possible through wave propagation. This study provides direct observational evidence to support the mechanism that high-altitude plasmaspheric hiss is responsible for the generation of low-altitude ionospheric hiss.

  16. Signatures of mesospheric particles in ionospheric data

    Directory of Open Access Journals (Sweden)

    M. Friedrich

    2009-02-01

    Full Text Available The state of the ionosphere during the 2007 ECOMA/MASS campaign is described by in-situ observations by three sounding rockets launched from the Andøya Rocket Range and by ground based observations. The ground based measurements included the incoherent scatter radar EISCAT near Tromsø (both on UHF and VHF, as well as an MF radar, a meteor radar and an imaging riometer all located in the close vicinity of the rocket range. The pronounced electron density bite-outs seen by two of the rockets could not be detected from the ground, but the associated PMSE (Polar Mesospheric Summer Echoes provide indirect evidence of pronounced perturbations of mesospheric electron densities.

  17. Conformity, Anticonformity and Polarization of Opinions: Insights from a Mathematical Model of Opinion Dynamics

    Directory of Open Access Journals (Sweden)

    Tyll Krueger

    2017-07-01

    Full Text Available Understanding and quantifying polarization in social systems is important because of many reasons. It could for instance help to avoid segregation and conflicts in the society or to control polarized debates and predict their outcomes. In this paper, we present a version of the q-voter model of opinion dynamics with two types of responses to social influence: conformity (like in the original q-voter model and anticonformity. We put the model on a social network with the double-clique topology in order to check how the interplay between those responses impacts the opinion dynamics in a population divided into two antagonistic segments. The model is analyzed analytically, numerically and by means of Monte Carlo simulations. Our results show that the system undergoes two bifurcations as the number of cross-links between cliques changes. Below the first critical point, consensus in the entire system is possible. Thus, two antagonistic cliques may share the same opinion only if they are loosely connected. Above that point, the system ends up in a polarized state.

  18. Effect of Ionosphere on Geostationary Communication Satellite Signals

    Science.gov (United States)

    Erdem, Esra; Arikan, Feza; Gulgonul, Senol

    2016-07-01

    Geostationary orbit (GEO) communications satellites allow radio, television, and telephone transmissions to be sent live anywhere in the world. They are extremely important in daily life and also for military applications. Since, satellite communication is an expensive technology addressing crowd of people, it is critical to improve the performance of this technology. GEO satellites are at 35,786 kilometres from Earth's surface situated directly over the equator. A satellite in a geostationary orbit (GEO) appears to stand still in the sky, in a fixed position with respect to an observer on the earth, because the satellite's orbital period is the same as the rotation rate of the Earth. The advantage of this orbit is that ground antennas can be fixed to point towards to satellite without their having to track the satellite's motion. Radio frequency ranges used in satellite communications are C, X, Ku, Ka and even EHG and V-band. Satellite signals are disturbed by atmospheric effects on the path between the satellite and the receiver antenna. These effects are mostly rain, cloud and gaseous attenuation. It is expected that ionosphere has a minor effect on the satellite signals when the ionosphere is quiet. But there are anomalies and perturbations on the structure of ionosphere with respect to geomagnetic field and solar activity and these conditions may cause further affects on the satellite signals. In this study IONOLAB-RAY algorithm is adopted to examine the effect of ionosphere on satellite signals. IONOLAB-RAY is developed to calculate propagation path and characteristics of high frequency signals. The algorithm does not have any frequency limitation and models the plasmasphere up to 20,200 km altitude, so that propagation between a GEO satellite and antenna on Earth can be simulated. The algorithm models inhomogeneous, anisotropic and time dependent structure of the ionosphere with a 3-D spherical grid geometry and calculates physical parameters of the

  19. Simulation of Ionospheric Response During Solar Eclipse Events

    Science.gov (United States)

    Kordella, L.; Earle, G. D.; Huba, J.

    2016-12-01

    Total solar eclipses are rare, short duration events that present interesting case studies of ionospheric behavior because the structure of the ionosphere is determined and stabilized by varying energies of solar radiation (Lyman alpha, X-ray, U.V., etc.). The ionospheric response to eclipse events is a source of scientific intrigue that has been studied in various capacities over the past 50 years. Unlike the daily terminator crossings, eclipses cause highly localized, steep gradients of ionization efficiency due to their comparatively small solar zenith angle. However, the corona remains present even at full obscuration, meaning that the energy reduction never falls to the levels seen at night. Previous eclipse studies performed by research groups in the US, UK, China and Russia have shown a range of effects, some counter-intuitive and others contradictory. In the shadowed region of an eclipse (i.e. umbra) it is logical to assume a reduction in ionization rates correlating with the reduction of incident solar radiation. Results have shown that even this straightforward hypothesis may not be true; effects on plasma distribution, motion and temperature are more appreciable than might be expected. Recent advancements in ionospheric simulation codes present the opportunity to investigate the relationship between geophysical conditions and geomagnetic location on resulting eclipse event ionosphere. Here we present computational simulation results using the Naval Research Lab (NRL) developed ionospheric modeling codes Sami2 and Sami3 (Sami2 is Another Model of the Ionosphere) modified with spatio-temporal photoionization attenuation functions derived from theory and empirical data.

  20. Polarization in Raman spectroscopy helps explain bone brittleness in genetic mouse models

    Science.gov (United States)

    Makowski, Alexander J.; Pence, Isaac J.; Uppuganti, Sasidhar; Zein-Sabatto, Ahbid; Huszagh, Meredith C.; Mahadevan-Jansen, Anita; Nyman, Jeffry S.

    2014-11-01

    Raman spectroscopy (RS) has been extensively used to characterize bone composition. However, the link between bone biomechanics and RS measures is not well established. Here, we leveraged the sensitivity of RS polarization to organization, thereby assessing whether RS can explain differences in bone toughness in genetic mouse models for which traditional RS peak ratios are not informative. In the selected mutant mice-activating transcription factor 4 (ATF4) or matrix metalloproteinase 9 (MMP9) knock-outs-toughness is reduced but differences in bone strength do not exist between knock-out and corresponding wild-type controls. To incorporate differences in the RS of bone occurring at peak shoulders, a multivariate approach was used. Full spectrum principal components analysis of two paired, orthogonal bone orientations (relative to laser polarization) improved genotype classification and correlation to bone toughness when compared to traditional peak ratios. When applied to femurs from wild-type mice at 8 and 20 weeks of age, the principal components of orthogonal bone orientations improved age classification but not the explanation of the maturation-related increase in strength. Overall, increasing polarization information by collecting spectra from two bone orientations improves the ability of multivariate RS to explain variance in bone toughness, likely due to polarization sensitivity to organizational changes in both mineral and collagen.

  1. Polar angle as a determinant of amphipathic alpha-helix-lipid interactions: a model peptide study.

    Science.gov (United States)

    Uematsu, N; Matsuzaki, K

    2000-10-01

    Various physicochemical properties play important roles in the membrane activities of amphipathic antimicrobial peptides. To examine the effects of the polar angle, two model peptides, thetap100 and thetap180, with polar angles of 100 degrees and 180 degrees, respectively, were designed, and their interactions with membranes were investigated in detail. These peptides have almost identical physicochemical properties except for polar angle. Like naturally occurring peptides, these peptides selectively bind to acidic membranes, assuming amphipathic alpha-helices, and formed peptide-lipid supramolecular complex pores accompanied by lipid flip-flop and peptide translocation. Despite its somewhat lower membrane affinity, thetap100 exhibited higher membrane permeabilization activity, a greater flip-flop rate, as well as more antimicrobial activity due to a higher pore formation rate compared with thetap180. Consistent with these results, the peptide translocation rate of thetap100 was higher. Furthermore, the number of peptides constituting thetap100 pores was less than that of thetap180, and thetap100 pores involved more lipid molecules, as reflected by its cation selectivity. The polar angle was found to be an important parameter determining peptide-lipid interactions.

  2. Modeling and Simulation of Polarization in Internet Group Opinions Based on Cellular Automata

    Directory of Open Access Journals (Sweden)

    Yaofeng Zhang

    2015-01-01

    Full Text Available Hot events on Internet always attract many people who usually form one or several opinion camps through discussion. For the problem of polarization in Internet group opinions, we propose a new model based on Cellular Automata by considering neighbors, opinion leaders, and external influences. Simulation results show the following: (1 It is easy to form the polarization for both continuous opinions and discrete opinions when we only consider neighbors influence, and continuous opinions are more effective in speeding the polarization of group. (2 Coevolution mechanism takes more time to make the system stable, and the global coupling mechanism leads the system to consensus. (3 Opinion leaders play an important role in the development of consensus in Internet group opinions. However, both taking the opinion leaders as zealots and taking some randomly selected individuals as zealots are not conductive to the consensus. (4 Double opinion leaders with consistent opinions will accelerate the formation of group consensus, but the opposite opinions will lead to group polarization. (5 Only small external influences can change the evolutionary direction of Internet group opinions.

  3. Simulation of low-latitude ionospheric response to 2015 St. Patrick's Day super geomagnetic storm using ionosonde-derived PRE vertical drifts over Indian region

    Science.gov (United States)

    Joshi, L. M.; Sripathi, S.; Singh, Ram

    2016-03-01

    In this paper, we present low-latitude ionospheric response over Indian longitude to the recent super geomagnetic storm of 17 March 2015, using the Sami2 is Another Model of the Ionosphere (SAMI2) model which incorporates ionosonde-derived vertical drift impacted by prompt penetration eastward electric field occurring during the evening prereversal enhancement (PRE) in the vertical drift. The importance of this storm is that (1) Dst reaches as low as -228 nT and (2) prompt penetration of eastward electric field coincided with evening hours PRE. The daytime vertical E × B drifts in the SAMI2 model are, however, considered based on Scherliess-Fejer model. The simulations indicate a significant enhancement in F layer height and equatorial ionization anomaly (EIA) in the post sunset hours on 17 March 2015 vis-a-vis quiet day. The model simulations during recovery phase, considering disturbance dynamo vertical E × B drift along with equatorward disturbance wind, indicate suppression of the daytime EIA. SAMI2 simulations considering the disturbance wind during the recovery phase suggest that equatorward wind enhances the ionospheric density in the low latitude; however, its role in the formation of the EIA depends on the polarity of the zonal electric field. Comparison of model derived total electron content (TEC) with the TEC from ground GPS receivers indicates that model does reproduce enhancement of the EIA during the main phase and suppression of the EIA during the recovery phase of the superstorm. However, peculiarities pertaining to the ionospheric response to prompt penetration electric field in the Indian sector vis-a-vis earlier reports from American sector have been discussed.

  4. EMP-002a Phase Shift through the Ionosphere

    Energy Technology Data Exchange (ETDEWEB)

    Soltz, R. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Simons, D. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Fenimore, E. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Wilks, S. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Carey, T. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2015-10-20

    In this note we review the derivation and use of the Ionospheric Transfer Function (ITF) in the DIO- RAMA model to calculate the propagation of a broad band ElectroMagnetic Pulse (EMP) through the Ionosphere in the limit of geometric optics. This note is intended to resolve a misunderstanding between the NDS VVA and EMP modeling teams regarding the appropriate use of the phase and group velocities in DIORAMA. The di erent approaches are documented in EMP-002 note, \\Phase vs. Group" [1], generated by the LLNL DIORAMA VVA team, and the subsequent response from the DIORAMA EMP modeling team' [2].

  5. Hydrodynamical model of anisotropic, polarized turbulent superfluids. I: constraints for the fluxes

    Science.gov (United States)

    Mongiovì, Maria Stella; Restuccia, Liliana

    2018-02-01

    This work is the first of a series of papers devoted to the study of the influence of the anisotropy and polarization of the tangle of quantized vortex lines in superfluid turbulence. A thermodynamical model of inhomogeneous superfluid turbulence previously formulated is here extended, to take into consideration also these effects. The model chooses as thermodynamic state vector the density, the velocity, the energy density, the heat flux, and a complete vorticity tensor field, including its symmetric traceless part and its antisymmetric part. The relations which constrain the constitutive quantities are deduced from the second principle of thermodynamics using the Liu procedure. The results show that the presence of anisotropy and polarization in the vortex tangle affects in a substantial way the dynamics of the heat flux, and allow us to give a physical interpretation of the vorticity tensor here introduced, and to better describe the internal structure of a turbulent superfluid.

  6. Mechanism for the formation of sporadic-E layers in the high-latitude ionosphere

    Energy Technology Data Exchange (ETDEWEB)

    Vlasov, M.N.; Mishin, E.V.; Telegin, V.A.

    1980-09-01

    A model of the collective interaction of precipitating electrons and the ionospheric plasma is used to explain the formation of short-duration sporadic-E layers in the high-latitude ionosphere. The changes produced in electron density by this collective interaction mechanism are considered.

  7. Ionospheric response to the partial solar eclipse of March 29, 2006, according to the observations at Nizhni Novgorod and Murmansk

    Science.gov (United States)

    Belikovich, V. V.; Vyakhirev, V. D.; Kalinina, E. E.; Tereshchenko, V. D.; Chernyakov, S. M.; Tereshchenko, V. A.

    2008-02-01

    The results of observations of the solar eclipse ionospheric effects on March 29, 2006, are presented. The observations were conducted using the partial reflection method near Nizhni Novgorod and the vertical sounding method at the automatic ionospheric station near Murmansk. It has been obtained that the electron density at altitudes of 77 and 91 km decreases by a factor of more than 4; in this case the response of the ionosphere at an altitude of 91 km lags behind the eclipse maximum phase on the Earth by approximately 20 min. It has been established that the eclipse in the E and F1 regions of the polar ionosphere causes a change in the electron density by 15-20%. The delay time of this effect varies from 12 to 24 min depending on the altitude. It has been registered that the reflection virtual altitude at altitudes of the ionospheric F region increases in Murmansk and Nizhni Novgorod.

  8. Effects of Response Style on Polarity and Validity of Two-Dimensional Mood Models

    Science.gov (United States)

    1985-08-01

    A. (1979) Affective space is bipolar. Journal of PersonalitY and Social Psychology, 37, 345-356. RUSSELL, J. A. (1980) A circumplex model of affect...Classification) (U) EFFECTS OF RESPONSE STYLE ON POLARITY AND VALIDITY OF TWO-DIMENSIONAL MOOD MODELS 12. PERSONAL AUTHOR(S) Vickers, Ross R. Jr., & Hervig, Linda...number) "’"T nipolar and bipolar two-dimensional models have been proposed to represent mood. This study showed that a given data set will produce both

  9. Modeling light entangled in polarization and frequency: case study in quantum cryptography

    Science.gov (United States)

    Myers, John M.

    2005-08-01

    With the recognition of a logical gap between experiments and equations of quantum mechanics comes: (1) a chance to clarify such purely mathematical entities as probabilities, density operators, and partial traces-separated out from the choices and judgments necessary to apply them to describing experiments with devices, and (2) an added freedom to invent equations by which to model devices, stemming from the corresponding freedom in interpreting how these equations connect to experiments. Here I apply a few of these clarifications and freedoms to model polarization-entangled light pulses called for in quantum key distribution (QKD). Available light pulses are entangled not only in polarization but also in frequency. Although absent from the simplified models that initiated QKD, the degree of frequency entanglement of polarization-entangled light pulses is shown to affect the amount of key that can be distilled from raw light signals, in one case by a factor of 4/3. Open questions remain, because QKD brings concepts of quantum decision theory, such as measures of distinguishability, mostly worked out in the context of finite-dimensional vector spaces, into contact with infinite-dimensional Hilbert spaces needed to give expression to optical frequency spectra.

  10. Photometry and Multipolar Magnetic Field Modeling of Polars: BY Camelopardalis and FL Ceti

    Directory of Open Access Journals (Sweden)

    P. A. Mason

    2015-02-01

    Full Text Available We present new broad band optical photometry of two magnetic cataclysmic variable stars, the asynchronous polar BY Camelopardalis and the short period polar FL Ceti. Observations were obtained at the 2.1-m Otto Struve Telescope of McDonald Observatory with 3s and 1s integration times respectively. In an attempt to understand the observed complex changes in accretion flow geometry observed in BY Cam, we performed full 3D MHD simulations assuming a variety of white dwarf magnetic field structures. We investigate fields with increasing complexity including both aligned and non-aligned dipole plus quadrupole field components. We compare model predictions with photometry at various phases of the beat cycle and find that synthetic light curves derived from a multipolar field structure are broadly consistent with optical photometry. FL Ceti is observed to have two very small accretion regions at the foot-points of the white dwarf’s magnetic field. Both accretion regions are visible at the same time in the high state and are about 100 degrees apart. MHD modeling using a dipole plus quadrupole field structure yields quite similar accretion regions as those observed in FL Ceti. We conclude that accretion flows calculated from MHD modeling of multi-polar magnetic fields produce synthetic light curves consistent with photometry of these magnetic cataclysmic variables.

  11. Two electric field Monte Carlo models of coherent backscattering of polarized light.

    Science.gov (United States)

    Doronin, Alexander; Radosevich, Andrew J; Backman, Vadim; Meglinski, Igor

    2014-11-01

    Modeling of coherent polarized light propagation in turbid scattering medium by the Monte Carlo method provides an ultimate understanding of coherent effects of multiple scattering, such as enhancement of coherent backscattering and peculiarities of laser speckle formation in dynamic light scattering (DLS) and optical coherence tomography (OCT) diagnostic modalities. In this report, we consider two major ways of modeling the coherent polarized light propagation in scattering tissue-like turbid media. The first approach is based on tracking transformations of the electric field along the ray propagation. The second one is developed in analogy to the iterative procedure of the solution of the Bethe-Salpeter equation. To achieve a higher accuracy in the results and to speed up the modeling, both codes utilize the implementation of parallel computing on NVIDIA Graphics Processing Units (GPUs) with Compute Unified Device Architecture (CUDA). We compare these two approaches through simulations of the enhancement of coherent backscattering of polarized light and evaluate the accuracy of each technique with the results of a known analytical solution. The advantages and disadvantages of each computational approach and their further developments are discussed. Both codes are available online and are ready for immediate use or download.

  12. The Ionospheric-Thermospheric Component of the LWS-Geospace Program

    Science.gov (United States)

    Kintner, P. M.

    2005-05-01

    The Geospace Mission Definition Team report made a persuasive case for investigating the ionosphere-thermosphere system with both LEO in situ instruments and GEO ionospheric imaging. The GMDT science objectives were derived from the Living With a Star Science Architecture Team's consideration of space weather effects that concern society. The two highest priority ionospheric objectives are "Determine the effects of the long and short term variability of the Sun on the global-scale behavior of the ionospheric electron density" and "Determine the solar and geospace causes of small scale density irregularities in the 100-1000 km altitude range". These general objectives were then focused on specific science questions such as "How does the ionosphere-thermosphere system vary in response to changing fluxes of solar extreme ultraviolet radiation?", How does the mid- and low-latitude ionosphere-thermosphere system respond to geomagnetic storms?", and "What are the sources and characteristics of ionospheric irregularities at mid-latitudes?". Since the submission of the GMDT report to NASA, the case for investigating the disturbed mid-latitude ionosphere has become even more compelling. Society has become more vulnerable to ionospheric storms through augmented GPS systems for aviation. The ionospheric response to geomagnetic storms has been shown to extend from the equator through mid-latitudes and across the polar caps and from the F region to the equatorial plane. The total electron content from the peak of the positive-phase to the minima of the negative phase varies by up to one order of magnitude. Simulations have demonstrated that thermospheric transport can carry disturbed O/N2 ratios from the auroral zone to the equator. Density irregularities have been discovered with scale lengths of 100 km to the GPS signal Fresnel length (~ 400m). The GMDT developed a strategy to characterize and understand these phenomena. At low altitudes, within the thermosphere, two

  13. On the mapping of ionospheric convection into the magnetosphere

    International Nuclear Information System (INIS)

    Hesse, M.; Birn, J.; Hoffman, R.A.

    1997-01-01

    Under steady state conditions and in the absence of parallel electric fields, ionospheric convection is a direct map of plasma and magnetic flux convection in the magnetosphere, and quantitative estimates can be obtained from the mapping along magnetic field lines of electrostatic ionospheric electric fields. The resulting magnetospheric electrostatic potential distribution then provides the convection electric field in various magnetospheric regions. We present a quantitative framework for the investigation of the applicability and limitations of this approach based on an analytical theory derived from first principles. Particular emphasis is on the role of parallel electric field regions and on inductive effects, such as expected during the growth and expansive phases of magnetospheric substorms. We derive quantitative estimates for the limits in which either effect leads to a significant decoupling between ionospheric and magnetospheric convection and provide an interpretation of ionospheric convection which is independent of the presence of inductive electric fields elsewhere in the magnetosphere. Finally, we present a study of the relation between average and instantaneous convection, using two periodic dynamical models. The models demonstrate and quantify the potential mismatch between the average electric fields in the ionosphere and the magnetosphere in strongly time-dependent cases that may exist even when they are governed entirely by ideal MHD

  14. Improved estimation of Mars ionosphere total electron content

    Science.gov (United States)

    Cartacci, M.; Sánchez-Cano, B.; Orosei, R.; Noschese, R.; Cicchetti, A.; Witasse, O.; Cantini, F.; Rossi, A. P.

    2018-01-01

    We describe an improved method to estimate the Total Electron Content (TEC) of the Mars ionosphere from the echoes recorded by the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) (Picardi et al., 2005; Orosei et al., 2015) onboard Mars Express in its subsurface sounding mode. In particular, we demonstrate that this method solves the issue of the former algorithm described at (Cartacci et al., 2013), which produced an overestimation of TEC estimates on the day side. The MARSIS signal is affected by a phase distortion introduced by the Mars ionosphere that produces a variation of the signal shape and a delay in its travel time. The new TEC estimation is achieved correlating the parameters obtained through the correction of the aforementioned effects. In detail, the knowledge of the quadratic term of the phase distortion estimated by the Contrast Method (Cartacci et al., 2013), together with the linear term (i.e. the extra time delay), estimated through a radar signal simulator, allows to develop a new algorithm particularly well suited to estimate the TEC for solar zenith angles (SZA) lower than 95° The new algorithm for the dayside has been validated with independent data from MARSIS in its Active Ionospheric Sounding (AIS) operational mode, with comparisons with other previous algorithms based on MARSIS subsurface data, with modeling and with modeling ionospheric distortion TEC reconstruction.

  15. Analysis of ionosphere variability over low-latitude GNSS stations during 24th solar maximum period

    Science.gov (United States)

    Venkata Ratnam, D.; Sivavaraprasad, G.; Latha Devi, N. S. M. P.

    2017-07-01

    Global Positioning System (GPS) is a remote sensing tool of space weather and ionospheric variations. However, the interplanetary space-dependent drifts in the ionospheric irregularities cause predominant ranging errors in the GPS signals. The dynamic variability of the low-latitude ionosphere is an imperative threat to the satellite-based radio communication and navigation ranging systems. The study of temporal and spatial variations in the ionosphere has triggered new investigations in modelling, nowcasting and forecasting the ionospheric variations. Hence, in this paper, the dynamism in the day-to-day, month-to-month and seasonal variability of the ionospheric Total Electron Content (TEC) has been explored during the solar maximum period, January-December 2013, of the 24th solar cycle. The spatial and temporal variations of the ionosphere are analysed using the TEC values derived from three Indian low-latitude GPS stations, namely, Bengaluru, Guntur and Hyderabad, separated by 13-18° in latitude and 77-81° in longitude. The observed regional GPS-TEC variations are compared with the predicted TEC values of the International Reference Ionosphere (IRI-2012 and 2007) models. Ionospheric parameters such as Vertical TEC (VTEC), relative TEC deviation index and monthly variations in the grand-mean of ionosphere TEC and TEC intensity, along with the upper and lower quartiles, are adopted to investigate the ionosphere TEC variability during quiet and disturbed days. The maximum ionospheric TEC variability is found during March and September equinoxes, followed by December solstice while the minimum variability is observed during June solstice. IRI models are in reasonable agreement with GPS TEC but are overestimating during dawn hours (01:00-06:00 LT) as compared to the dusk hours. Higher percentage deviations are observed during equinoctial months than summer over EIA stations, Guntur and Hyderabad. GPS TEC variations are overestimated during dawn hours for all the

  16. Satellite and ground measurements of latitude distribution of upper ionosphere parameters in the region of the main trough of ionization

    International Nuclear Information System (INIS)

    Filippov, V.M.; Alekseev, V.N.; Afonin, V.V.

    1988-01-01

    Results of simultaneous complex measurements of subauroral ionosphere structure at observations of charged-particle precipitation at Interkosmos-19 satellite, electron concentration and temperature at Kosmos-900 satellite, ionosphere parameters and plasma convection at Zhigansk (L∼4) and Jakutsk (L∼3) stations and 630.0 mm line luminescence by scanning photometer at Zhigansk station, carried out on the 26 - 27.03.1979, are presented. It is found, that the through polar edge is formed by low-energy electron precipitations in diffuse auroral zone. It is confirmed by spatial coincidence of diffuse precipitations equatorial boundary, determined by satellite and ground optical measurements, with the ionization main through polar edge, determined by ground ionospherical observation and satellite measurements Ne at Kosmos-900 satellite. Results of these complex experiments show as well, that one of the main mechanisms of main ionospherical through formation may be plasma convection peculiarities within F region at subauroral zone widthes

  17. 3-D Forward modeling of Induced Polarization Effects of Transient Electromagnetic Method

    Science.gov (United States)

    Wu, Y.; Ji, Y.; Guan, S.; Li, D.; Wang, A.

    2017-12-01

    In transient electromagnetic (TEM) detection, Induced polarization (IP) effects are so important that they cannot be ignored. The authors simulate the three-dimensional (3-D) induced polarization effects in time-domain directly by applying the finite-difference time-domain method (FDTD) based on Cole-Cole model. Due to the frequency dispersion characteristics of the electrical conductivity, the computations of convolution in the generalized Ohm's law of fractional order system makes the forward modeling particularly complicated. Firstly, we propose a method to approximate the fractional order function of Cole-Cole model using a lower order rational transfer function based on error minimum theory in the frequency domain. In this section, two auxiliary variables are introduced to transform nonlinear least square fitting problem of the fractional order system into a linear programming problem, thus avoiding having to solve a system of equations and nonlinear problems. Secondly, the time-domain expression of Cole-Cole model is obtained by using Inverse Laplace transform. Then, for the calculation of Ohm's law, we propose an e-index auxiliary equation of conductivity to transform the convolution to non-convolution integral; in this section, the trapezoid rule is applied to compute the integral. We then substitute the recursion equation into Maxwell's equations to derive the iterative equations of electromagnetic field using the FDTD method. Finally, we finish the stimulation of 3-D model and evaluate polarization parameters. The results are compared with those obtained from the digital filtering solution of the analytical equation in the homogeneous half space, as well as with the 3-D model results from the auxiliary ordinary differential equation method (ADE). Good agreements are obtained across the three methods. In terms of the 3-D model, the proposed method has higher efficiency and lower memory requirements as execution times and memory usage were reduced by 20

  18. Classical and quantum theories of the polarization bremsstrahlung in the local electron density model

    International Nuclear Information System (INIS)

    Astapenko, V.A.; Bureeva, L.A.; Lisitsa, V.S.

    2000-01-01

    Classical and quantum theories of polarization bremsstrahlung in a statistical (Thomas-Fermi) potential of complex atoms and ions are developed. The basic assumptions of the theories correspond to the approximations employed earlier in classical and quantum calculations of ordinary bremsstrahlung in a static potential. This makes it possible to study on a unified basis the contribution of both channels in the radiation taking account of their interference. The classical model makes it possible to obtain simple universal formulas for the spectral characteristics of the radiation. The theory is applied to electrons with moderate energies, which are characteristic for plasma applications, specifically, radiation from electrons on the argon-like ion KII at frequencies close to its ionization potential. The computational results show the importance of taking account of the polarization channel of the radiation for plasma with heavy ions

  19. The Second-Order Polarization Propagator Approximation (SOPPA) method coupled to the polarizable continuum model

    DEFF Research Database (Denmark)

    Eriksen, Janus Juul; Solanko, Lukasz Michal; Nåbo, Lina J.

    2014-01-01

    We present an implementation of the Polarizable Continuum Model (PCM) in combination with the Second–Order Polarization Propagator Approximation (SOPPA) electronic structure method. In analogy with the most common way of designing ground state calculations based on a Second–Order Møller-Plesset (MP......2) wave function coupled to PCM, we introduce dynamical PCM solvent effects only in the Random Phase Approximation (RPA) part of the SOPPA response equations while the static solvent contribution is kept in both the RPA terms as well as in the higher order correlation matrix components of the SOPPA...... response equations. By dynamic terms, we refer to contributions that describe a change in environmental polarization which, in turn, reflects a change in the core molecular charge distribution upon an electronic excitation. This new combination of methods is termed PCM-SOPPA/RPA. We apply this newly...

  20. Simulating polar bear energetics during a seasonal fast using a mechanistic model.

    Directory of Open Access Journals (Sweden)

    Paul D Mathewson

    Full Text Available In this study we tested the ability of a mechanistic model (Niche Mapper™ to accurately model adult, non-denning polar bear (Ursus maritimus energetics while fasting during the ice-free season in the western Hudson Bay. The model uses a steady state heat balance approach, which calculates the metabolic rate that will allow an animal to maintain its core temperature in its particular microclimate conditions. Predicted weight loss for a 120 day fast typical of the 1990s was comparable to empirical studies of the population, and the model was able to reach a heat balance at the target metabolic rate for the entire fast, supporting use of the model to explore the impacts of climate change on polar bears. Niche Mapper predicted that all but the poorest condition bears would survive a 120 day fast under current climate conditions. When the fast extended to 180 days, Niche Mapper predicted mortality of up to 18% for males. Our results illustrate how environmental conditions, variation in animal properties, and thermoregulation processes may impact survival during extended fasts because polar bears were predicted to require additional energetic expenditure for thermoregulation during a 180 day fast. A uniform 3°C temperature increase reduced male mortality during a 180 day fast from 18% to 15%. Niche Mapper explicitly links an animal's energetics to environmental conditions and thus can be a valuable tool to help inform predictions of climate-related population changes. Since Niche Mapper is a generic model, it can make energetic predictions for other species threatened by climate change.