A. Osepian - Academia.edu (original) (raw)

Papers by A. Osepian

Research paper thumbnail of Modeling of the D-region behavior in the polar ionosphere during the solar flare of April 5, 2004

Geomagnetism and Aeronomy, 2007

ABSTRACT On the basis of the ion chemistry theoretical model, the impact of a powerful solar flar... more ABSTRACT On the basis of the ion chemistry theoretical model, the impact of a powerful solar flare on variations in the ion composition and electron density in the D region of the polar ionosphere is considered. Good agreemnt between the model profiles of the electron density N e (h) and the experimental data obtained during the flare by the partial reflection method is found. It is shown that the decrease in the effective recombination coefficient observed during disturbances is explained by the depletion of the relative content of the rapidly recombining complex ion clusters.

Research paper thumbnail of Precipitating Protons and Their Role in Ionization of the Polar Ionosphere

Cosmic Research, 2004

Spatial distributions of the electron density in the latitude range 60 ° -90 ° N were calculated ... more Spatial distributions of the electron density in the latitude range 60 ° -90 ° N were calculated on the basis of a physical model of the E and lower F regions of the high-latitude ionosphere using statistical models of auroral proton and electron precipitation. It is shown that precipitating protons can play the key role in the ionization of the E region in the dusk and midnight sectors of the auroral oval. However, quantitative estimates of the contribution of protons to the ionization depend on the used statistical models of electron precipitation.

Research paper thumbnail of Ionization and NO production in the polar mesosphere during high-speed solar wind streams: model validation and comparison with NO enhancements observed by Odin-SMR

Annales Geophysicae, 2015

ABSTRACT Precipitation of high-energy electrons (EEP) into the polar middle atmosphere is a poten... more ABSTRACT Precipitation of high-energy electrons (EEP) into the polar middle atmosphere is a potential source of significant production of odd nitrogen, which may play a role in stratospheric ozone destruction and in perturbing large-scale atmospheric circulation patterns. High-speed streams of solar wind (HSS) are a major source of energization and precipitation of electrons from the Earth's radiation belts, but it remains to be determined whether these electrons make a significant contribution to the odd-nitrogen budget in the middle atmosphere when compared to production by solar protons or by lower-energy (auroral) electrons at higher altitudes, with subsequent downward transport. Satellite observations of EEP are available, but their accuracy is not well established. Studies of the ionization of the atmosphere in response to EEP, in terms of cosmic-noise absorption (CNA), have indicated an unexplained seasonal variation in HSS-related effects and have suggested possible order-of-magnitude underestimates of the EEP fluxes by the satellite observations in some circumstances. Here we use a model of ionization by EEP coupled with an ion chemistry model to show that published average EEP fluxes, during HSS events, from satellite measurements (Meredith et al., 2011), are fully consistent with the published average CNA response (Kavanagh et al., 2012). The seasonal variation of CNA response can be explained by ion chemistry with no need for any seasonal variation in EEP. Average EEP fluxes are used to estimate production rate profiles of nitric oxide between 60 and 100 km heights over Antarctica for a series of unusually well separated HSS events in austral winter 2010. These are compared to observations of changes in nitric oxide during the events, made by the sub-millimetre microwave radiometer on the Odin spacecraft. The observations show strong increases of nitric oxide amounts between 75 and 90 km heights, at all latitudes poleward of 60° S, about 10 days after the arrival of the HSS. These are of the same order of magnitude but generally larger than would be expected from direct production by HSS-associated EEP, indicating that downward transport likely contributes in addition to direct production.

Research paper thumbnail of High-speed solar wind streams and polar mesosphere winter echoes at Troll, Antarctica

Annales Geophysicae, 2015

Research paper thumbnail of Electron density profiles in the quiet lower ionosphere based on the results of modeling and experimental data

Annales Geophysicae, 2012

Abstract The theoretical PGI (Polar Geophysical Institute) model for the quiet lower ionosphere h... more Abstract The theoretical PGI (Polar Geophysical Institute) model for the quiet lower ionosphere has been applied for computing the ionization rate and electron density profiles in the summer and winter D-region at solar zenith angles less than 80 and larger than 99 under steady state conditions. In order to minimize possible errors in estimation of ionization rates provided by solar electromagnetic radiation and to obtain the most exact values of electron density, each wavelength range of the solar spectrum has been divided into ...

Research paper thumbnail of Influence of water vapour on the height distribution of positive ions, effective recombination coefficient and ionisation balance in the quiet lower ionosphere

Annales Geophysicae, 2014

ABSTRACT Mesospheric water vapour concentration effects on the ion composition and electron densi... more ABSTRACT Mesospheric water vapour concentration effects on the ion composition and electron density in the lower ionosphere under quiet geophysical conditions were examined. Water vapour is an important compound in the mesosphere and the lower thermosphere that affects ion composition due to hydrogen radical production and consequently modifies the electron number density. Recent lower-ionosphere investigations have primarily concentrated on the geomagnetic disturbance periods. Meanwhile, studies on the electron density under quiet conditions are quite rare. The goal of this study is to contribute to a better understanding of the ionospheric parameter responses to water vapour variability in the quiet lower ionosphere. By applying a numerical D region ion chemistry model, we evaluated efficiencies for the channels forming hydrated cluster ions from the NO+ and O2+ primary ions (i.e. NO+.H2O and O2+.H2O, respectively), and the channel forming H+(H2O)n proton hydrates from water clusters at different altitudes using profiles with low and high water vapour concentrations. Profiles for positive ions, effective recombination coefficients and electrons were modelled for three particular cases using electron density measurements obtained during rocket campaigns. It was found that the water vapour concentration variations in the mesosphere affect the position of both the Cl2+ proton hydrate layer upper border, comprising the NO+(H2O)n and O2+(H2O)n hydrated cluster ions, and the Cl1+ hydrate cluster layer lower border, comprising the H+(H2O)n pure proton hydrates, as well as the numerical cluster densities. The water variations caused large changes in the effective recombination coefficient and electron density between altitudes of 75 and 87 km. However, the effective recombination coefficient, αeff, and electron number density did not respond even to large water vapour concentration variations occurring at other altitudes in the mesosphere. We determined the water vapour concentration upper limit at altitudes between 75 and 87 km, beyond which the water vapour concentration ceases to influence the numerical densities of Cl2+ and Cl1+, the effective recombination coefficient and the electron number density in the summer ionosphere. This water vapour concentration limit corresponds to values found in the H2O-1 profile that was observed in the summer mesosphere by the Upper Atmosphere Research Satellite (UARS). The electron density modelled using the H2O-1 profile agreed well with the electron density measured in the summer ionosphere when the measured profiles did not have sharp gradients. For sharp gradients in electron and positive ion number densities, a water profile that can reproduce the characteristic behaviour of the ionospheric parameters should have an inhomogeneous height distribution of water vapour.

Research paper thumbnail of Diurnal and Seasonal Variations of the Energy Spectrum of Precipitating Electrons Derived from Electron Concentration Measurement Data Obtained by the Method of Incoherent Scattering of Radio Waves

Research paper thumbnail of Conditions in the magnetosphere and ionosphere during nighttime sudden commencements that develop against a background of disturbances

The spectra of trapped electrons measured in the presence of disturbances are used in determining... more The spectra of trapped electrons measured in the presence of disturbances are used in determining the spectra of electrons that escape during a sudden commencement (SC). For spectral data that take into account seasonal changes in the neutral atmosphere, calculations are made of the rate of ion formation; in addition, on the basis of a simplified six-ion model of the D region, the absorption and electron density profiles are calculated. For those cases where there is good agreement between calculated and experimental values of absorption, the lifetime of particles in the magnetosphere during SCs is determined.

Research paper thumbnail of VLF emission during SC

Research paper thumbnail of Methods for detecting electron fluxes precipitating in the auroral-absorption zone

Research paper thumbnail of Anomalous E-region ion layers in twilight conditions. Experiment and model

Anomalous E-region ion layers in twilight conditions-Experiment and model. Natalia Smirnova, Shei... more Anomalous E-region ion layers in twilight conditions-Experiment and model. Natalia Smirnova, Sheila Kirkwood, Alevtina Osepyan ESA Symposium on European Rocket and Balloon Programmes and Related Research, 12 th, Lillehammer, Norway, 269-272, 1995. ...

Research paper thumbnail of Electron fluxes precipitating into the midlatitude ionosphere

A method is proposed for determining electron fluxes precipitating into the midlatitude ionospher... more A method is proposed for determining electron fluxes precipitating into the midlatitude ionosphere during global magnetic storms. Explorer-45 data are used to calculate the pitch-angle distribution of electrons in the loss cone and to determine the total precipitating flux at L = 3 for different global-storm phases. The electron density profiles and absorption variations calculated using the proposed method are similar to those measured during a global storm.

Research paper thumbnail of A model of the lower auroral ionosphere in calculations of radio-wave propagation characteristics

A model for electron density in the lower polar ionosphere is discussed which was developed in th... more A model for electron density in the lower polar ionosphere is discussed which was developed in the Polar Geophysical Institute. This model was used to calculate the propagation characteristics of decametric waves. It is shown that, during disturbance periods, the auroral ionosphere at heights of 80-100 km has significant screening properties in addition to absorbing properties.

Research paper thumbnail of Recovering of Precipitating Electrons Spectra on the Incoherent Scattering Radar Data

Precipitating electrons are the main ionization source in the polar ionosphere. They determine pr... more Precipitating electrons are the main ionization source in the polar ionosphere. They determine practically all important electrodynamical properties of an ionosphere. So, the form of the spectrum and its time history allows to identify the zone of the precipitating particles source in magnitosphere in different substorm phases. It's worthwhile to note that quantitative estimations of the full energy flow is important for estimation of energy balance in atmosphere, and effects, caused by invasions of the high-energy particles must be taken into account in the study of the middle atmosphere chemistry. Incoherent radars are unique and powerful source for the observation and measurements of an ionosphere electrodynamic parameters. In principle, it is possible to determine the energy spectrum of precipitating electrons on their data. From mathematical point of view the problem of spectrum recovering is a linear integral Fredholm equation of the 1st kind, which is the classical ill-po...

Research paper thumbnail of The interaction of bilingualism and stuttering in an adult

Journal of Communication Disorders

The relation between bilingualism and stuttering was examined in a bilingual adult who stutters. ... more The relation between bilingualism and stuttering was examined in a bilingual adult who stutters. Language ability in English and Afrikaans was assessed through the use of cloze and language proficiency tests. Anticipation, adaptation and consistency of stuttering were investigated. Frequency, distribution and nature of disfluencies on narrative and procedural tasks were analyzed according to a modified version of the Systematic Disfluency Analysis (SDA) . Results indicated that language ability influenced frequency, distribution and nature of disfluencies. The subject was more proficient and stuttered less in his predominant language. Implications for the interaction of language and stuttering were discussed. Clinical strategies for dealing with bilingual stutterers were considered.

Research paper thumbnail of Coefficients of pitch-angle electron diffusion in the radiation belts

The paper examines two approaches to the determination of pitch-angle diffusion coefficients in s... more The paper examines two approaches to the determination of pitch-angle diffusion coefficients in studies of electron precipitation associated with principal-harmonic cyclotron resonance. The approaches are based on different limiting cases of the solution of the diffusion equation. Results obtained with the two approaches are found to be in agreement. A simple procedure, which does not require special computer calculations, is proposed for determining the diffusion coefficients.

Research paper thumbnail of Precipitation of Energetic Electrons into the High-Latitude Atmosphere in the Morning Local Sectors

Research paper thumbnail of Effective recombination coefficients in the D- and E-regions during auroral absorption events

Research paper thumbnail of V. Barabash, A. Osepian, and P. Dalin: Influence of water vapor on the height distribution of positive ions, effective recombination coefficient and ionisation balance in the quiet lower ionosphere. Ann. Geophys. 2014, V. 32, p. 207-222

Research paper thumbnail of Electron density in the auroral zone - Experiment and model

Auroral-absorption data are used to determine the parameters of precipitating electron fluxes and... more Auroral-absorption data are used to determine the parameters of precipitating electron fluxes and to calculate electron density profiles for the disturbances of November 17-18, 1983. Model-determined values of electron density for the 70.5-100.5-km height range are compared with a large volume of experimental N(h) profiles obtained with the EISCAT setup during the period considered. It is concluded that the proposed approach for calculating electron density at different D-region heights is sufficiently accurate.

Research paper thumbnail of Modeling of the D-region behavior in the polar ionosphere during the solar flare of April 5, 2004

Geomagnetism and Aeronomy, 2007

ABSTRACT On the basis of the ion chemistry theoretical model, the impact of a powerful solar flar... more ABSTRACT On the basis of the ion chemistry theoretical model, the impact of a powerful solar flare on variations in the ion composition and electron density in the D region of the polar ionosphere is considered. Good agreemnt between the model profiles of the electron density N e (h) and the experimental data obtained during the flare by the partial reflection method is found. It is shown that the decrease in the effective recombination coefficient observed during disturbances is explained by the depletion of the relative content of the rapidly recombining complex ion clusters.

Research paper thumbnail of Precipitating Protons and Their Role in Ionization of the Polar Ionosphere

Cosmic Research, 2004

Spatial distributions of the electron density in the latitude range 60 ° -90 ° N were calculated ... more Spatial distributions of the electron density in the latitude range 60 ° -90 ° N were calculated on the basis of a physical model of the E and lower F regions of the high-latitude ionosphere using statistical models of auroral proton and electron precipitation. It is shown that precipitating protons can play the key role in the ionization of the E region in the dusk and midnight sectors of the auroral oval. However, quantitative estimates of the contribution of protons to the ionization depend on the used statistical models of electron precipitation.

Research paper thumbnail of Ionization and NO production in the polar mesosphere during high-speed solar wind streams: model validation and comparison with NO enhancements observed by Odin-SMR

Annales Geophysicae, 2015

ABSTRACT Precipitation of high-energy electrons (EEP) into the polar middle atmosphere is a poten... more ABSTRACT Precipitation of high-energy electrons (EEP) into the polar middle atmosphere is a potential source of significant production of odd nitrogen, which may play a role in stratospheric ozone destruction and in perturbing large-scale atmospheric circulation patterns. High-speed streams of solar wind (HSS) are a major source of energization and precipitation of electrons from the Earth's radiation belts, but it remains to be determined whether these electrons make a significant contribution to the odd-nitrogen budget in the middle atmosphere when compared to production by solar protons or by lower-energy (auroral) electrons at higher altitudes, with subsequent downward transport. Satellite observations of EEP are available, but their accuracy is not well established. Studies of the ionization of the atmosphere in response to EEP, in terms of cosmic-noise absorption (CNA), have indicated an unexplained seasonal variation in HSS-related effects and have suggested possible order-of-magnitude underestimates of the EEP fluxes by the satellite observations in some circumstances. Here we use a model of ionization by EEP coupled with an ion chemistry model to show that published average EEP fluxes, during HSS events, from satellite measurements (Meredith et al., 2011), are fully consistent with the published average CNA response (Kavanagh et al., 2012). The seasonal variation of CNA response can be explained by ion chemistry with no need for any seasonal variation in EEP. Average EEP fluxes are used to estimate production rate profiles of nitric oxide between 60 and 100 km heights over Antarctica for a series of unusually well separated HSS events in austral winter 2010. These are compared to observations of changes in nitric oxide during the events, made by the sub-millimetre microwave radiometer on the Odin spacecraft. The observations show strong increases of nitric oxide amounts between 75 and 90 km heights, at all latitudes poleward of 60° S, about 10 days after the arrival of the HSS. These are of the same order of magnitude but generally larger than would be expected from direct production by HSS-associated EEP, indicating that downward transport likely contributes in addition to direct production.

Research paper thumbnail of High-speed solar wind streams and polar mesosphere winter echoes at Troll, Antarctica

Annales Geophysicae, 2015

Research paper thumbnail of Electron density profiles in the quiet lower ionosphere based on the results of modeling and experimental data

Annales Geophysicae, 2012

Abstract The theoretical PGI (Polar Geophysical Institute) model for the quiet lower ionosphere h... more Abstract The theoretical PGI (Polar Geophysical Institute) model for the quiet lower ionosphere has been applied for computing the ionization rate and electron density profiles in the summer and winter D-region at solar zenith angles less than 80 and larger than 99 under steady state conditions. In order to minimize possible errors in estimation of ionization rates provided by solar electromagnetic radiation and to obtain the most exact values of electron density, each wavelength range of the solar spectrum has been divided into ...

Research paper thumbnail of Influence of water vapour on the height distribution of positive ions, effective recombination coefficient and ionisation balance in the quiet lower ionosphere

Annales Geophysicae, 2014

ABSTRACT Mesospheric water vapour concentration effects on the ion composition and electron densi... more ABSTRACT Mesospheric water vapour concentration effects on the ion composition and electron density in the lower ionosphere under quiet geophysical conditions were examined. Water vapour is an important compound in the mesosphere and the lower thermosphere that affects ion composition due to hydrogen radical production and consequently modifies the electron number density. Recent lower-ionosphere investigations have primarily concentrated on the geomagnetic disturbance periods. Meanwhile, studies on the electron density under quiet conditions are quite rare. The goal of this study is to contribute to a better understanding of the ionospheric parameter responses to water vapour variability in the quiet lower ionosphere. By applying a numerical D region ion chemistry model, we evaluated efficiencies for the channels forming hydrated cluster ions from the NO+ and O2+ primary ions (i.e. NO+.H2O and O2+.H2O, respectively), and the channel forming H+(H2O)n proton hydrates from water clusters at different altitudes using profiles with low and high water vapour concentrations. Profiles for positive ions, effective recombination coefficients and electrons were modelled for three particular cases using electron density measurements obtained during rocket campaigns. It was found that the water vapour concentration variations in the mesosphere affect the position of both the Cl2+ proton hydrate layer upper border, comprising the NO+(H2O)n and O2+(H2O)n hydrated cluster ions, and the Cl1+ hydrate cluster layer lower border, comprising the H+(H2O)n pure proton hydrates, as well as the numerical cluster densities. The water variations caused large changes in the effective recombination coefficient and electron density between altitudes of 75 and 87 km. However, the effective recombination coefficient, αeff, and electron number density did not respond even to large water vapour concentration variations occurring at other altitudes in the mesosphere. We determined the water vapour concentration upper limit at altitudes between 75 and 87 km, beyond which the water vapour concentration ceases to influence the numerical densities of Cl2+ and Cl1+, the effective recombination coefficient and the electron number density in the summer ionosphere. This water vapour concentration limit corresponds to values found in the H2O-1 profile that was observed in the summer mesosphere by the Upper Atmosphere Research Satellite (UARS). The electron density modelled using the H2O-1 profile agreed well with the electron density measured in the summer ionosphere when the measured profiles did not have sharp gradients. For sharp gradients in electron and positive ion number densities, a water profile that can reproduce the characteristic behaviour of the ionospheric parameters should have an inhomogeneous height distribution of water vapour.

Research paper thumbnail of Diurnal and Seasonal Variations of the Energy Spectrum of Precipitating Electrons Derived from Electron Concentration Measurement Data Obtained by the Method of Incoherent Scattering of Radio Waves

Research paper thumbnail of Conditions in the magnetosphere and ionosphere during nighttime sudden commencements that develop against a background of disturbances

The spectra of trapped electrons measured in the presence of disturbances are used in determining... more The spectra of trapped electrons measured in the presence of disturbances are used in determining the spectra of electrons that escape during a sudden commencement (SC). For spectral data that take into account seasonal changes in the neutral atmosphere, calculations are made of the rate of ion formation; in addition, on the basis of a simplified six-ion model of the D region, the absorption and electron density profiles are calculated. For those cases where there is good agreement between calculated and experimental values of absorption, the lifetime of particles in the magnetosphere during SCs is determined.

Research paper thumbnail of VLF emission during SC

Research paper thumbnail of Methods for detecting electron fluxes precipitating in the auroral-absorption zone

Research paper thumbnail of Anomalous E-region ion layers in twilight conditions. Experiment and model

Anomalous E-region ion layers in twilight conditions-Experiment and model. Natalia Smirnova, Shei... more Anomalous E-region ion layers in twilight conditions-Experiment and model. Natalia Smirnova, Sheila Kirkwood, Alevtina Osepyan ESA Symposium on European Rocket and Balloon Programmes and Related Research, 12 th, Lillehammer, Norway, 269-272, 1995. ...

Research paper thumbnail of Electron fluxes precipitating into the midlatitude ionosphere

A method is proposed for determining electron fluxes precipitating into the midlatitude ionospher... more A method is proposed for determining electron fluxes precipitating into the midlatitude ionosphere during global magnetic storms. Explorer-45 data are used to calculate the pitch-angle distribution of electrons in the loss cone and to determine the total precipitating flux at L = 3 for different global-storm phases. The electron density profiles and absorption variations calculated using the proposed method are similar to those measured during a global storm.

Research paper thumbnail of A model of the lower auroral ionosphere in calculations of radio-wave propagation characteristics

A model for electron density in the lower polar ionosphere is discussed which was developed in th... more A model for electron density in the lower polar ionosphere is discussed which was developed in the Polar Geophysical Institute. This model was used to calculate the propagation characteristics of decametric waves. It is shown that, during disturbance periods, the auroral ionosphere at heights of 80-100 km has significant screening properties in addition to absorbing properties.

Research paper thumbnail of Recovering of Precipitating Electrons Spectra on the Incoherent Scattering Radar Data

Precipitating electrons are the main ionization source in the polar ionosphere. They determine pr... more Precipitating electrons are the main ionization source in the polar ionosphere. They determine practically all important electrodynamical properties of an ionosphere. So, the form of the spectrum and its time history allows to identify the zone of the precipitating particles source in magnitosphere in different substorm phases. It's worthwhile to note that quantitative estimations of the full energy flow is important for estimation of energy balance in atmosphere, and effects, caused by invasions of the high-energy particles must be taken into account in the study of the middle atmosphere chemistry. Incoherent radars are unique and powerful source for the observation and measurements of an ionosphere electrodynamic parameters. In principle, it is possible to determine the energy spectrum of precipitating electrons on their data. From mathematical point of view the problem of spectrum recovering is a linear integral Fredholm equation of the 1st kind, which is the classical ill-po...

Research paper thumbnail of The interaction of bilingualism and stuttering in an adult

Journal of Communication Disorders

The relation between bilingualism and stuttering was examined in a bilingual adult who stutters. ... more The relation between bilingualism and stuttering was examined in a bilingual adult who stutters. Language ability in English and Afrikaans was assessed through the use of cloze and language proficiency tests. Anticipation, adaptation and consistency of stuttering were investigated. Frequency, distribution and nature of disfluencies on narrative and procedural tasks were analyzed according to a modified version of the Systematic Disfluency Analysis (SDA) . Results indicated that language ability influenced frequency, distribution and nature of disfluencies. The subject was more proficient and stuttered less in his predominant language. Implications for the interaction of language and stuttering were discussed. Clinical strategies for dealing with bilingual stutterers were considered.

Research paper thumbnail of Coefficients of pitch-angle electron diffusion in the radiation belts

The paper examines two approaches to the determination of pitch-angle diffusion coefficients in s... more The paper examines two approaches to the determination of pitch-angle diffusion coefficients in studies of electron precipitation associated with principal-harmonic cyclotron resonance. The approaches are based on different limiting cases of the solution of the diffusion equation. Results obtained with the two approaches are found to be in agreement. A simple procedure, which does not require special computer calculations, is proposed for determining the diffusion coefficients.

Research paper thumbnail of Precipitation of Energetic Electrons into the High-Latitude Atmosphere in the Morning Local Sectors

Research paper thumbnail of Effective recombination coefficients in the D- and E-regions during auroral absorption events

Research paper thumbnail of V. Barabash, A. Osepian, and P. Dalin: Influence of water vapor on the height distribution of positive ions, effective recombination coefficient and ionisation balance in the quiet lower ionosphere. Ann. Geophys. 2014, V. 32, p. 207-222

Research paper thumbnail of Electron density in the auroral zone - Experiment and model

Auroral-absorption data are used to determine the parameters of precipitating electron fluxes and... more Auroral-absorption data are used to determine the parameters of precipitating electron fluxes and to calculate electron density profiles for the disturbances of November 17-18, 1983. Model-determined values of electron density for the 70.5-100.5-km height range are compared with a large volume of experimental N(h) profiles obtained with the EISCAT setup during the period considered. It is concluded that the proposed approach for calculating electron density at different D-region heights is sufficiently accurate.