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G P Zank - One of the best experts on this subject based on the ideXlab platform.
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heliospheric asymmetries due to the action of the Interstellar Magnetic Field
Advances in Space Research, 2009Co-Authors: N V Pogorelov, G P Zank, J W Mitchell, J Heerikhuisen, Iver H. CairnsAbstract:We discuss the asymmetry of the heliospheric discontinuities obtained from the analysis of 3D modeling of the solar wind (SW) interaction with local Interstellar medium (LISM). The flow of charged particles is governed by the ideal MHD equations and the flow of neutral particles is described by the Boltzmann equation. The emphasis is made on the asymmetries of the termination shock (TS) and the heliopause under the combined action of the Interstellar and interplanetary Magnetic Fields (ISMF and IMF) in the presence of neutral hydrogen atoms whose transport through the heliosphere is modeled kinetically, using a Monte Carlo approach. We show that the deflection of neutral hydrogen flow from its original direction in the unperturbed LISM is highly anisotropic and evaluate a possible angle between the hydrogen deflection plane measured in the SOHO SWAN experiment and the plane containing the ISMF and LISM velocity vectors for different ISMF strengths. It is shown that the ISMF of a strength greater than 4 μG can account for the 10 AU difference in the TS heliocentric difference observed during its crossing by the Voyager 1 and Voyager 2 spacecraft, which however results in a larger discrepancy between the calculated and observed velocity distributions. The effect of a strong ISMF on the distribution of plasma quantities in the inner heliosheath and on 2–3 kHz radio emission is discussed.
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three dimensional features of the outer heliosphere due to coupling between the Interstellar and interplanetary Magnetic Fields iii the effects of solar rotation and activity cycle
The Astrophysical Journal, 2009Co-Authors: N V Pogorelov, G P Zank, S N Borovikov, Tatsuki OginoAbstract:We investigate the effects of the 11 year solar cycle and 25 day rotation period of the Sun on the interaction of the solar wind (SW) with the local Interstellar medium (LISM). Our models take into account the partially ionized character of the LISM and include momentum and energy transfer between the ionized and neutral components. We assume that the Interstellar Magnetic Field vector belongs to the hydrogen deflection plane as discovered in the SOHO SWAN experiment. This plane is inclined at an angle of about 60° toward the ecliptic plane of the Sun, as suggested in recent publications relating the local Interstellar cloud properties to the radio emission observed by Voyager 1. It is assumed that the latitudinal extent of the boundary between the slow and fast SW regions, as well as the angle between the Sun's rotation and Magnetic-dipole axes, are periodic functions of time, while the polarity of the Interstellar Magnetic Field changes sign every 11 years at the solar maximum. The global variation of the SW-LISM interaction pattern, the excursions of the termination shock and the heliopause, and parameter distributions in certain directions are investigated. The analysis of the behavior of the wavy heliospheric current sheet in the supersonic SW region shows the importance of neutral atoms on its dynamics.
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heliospheric asymmetries and 2 3 khz radio emission under strong Interstellar Magnetic Field conditions
The Astrophysical Journal, 2009Co-Authors: N V Pogorelov, Iver H. Cairns, J W Mitchell, J Heerikhuisen, G P ZankAbstract:We discuss the asymmetry of the major heliospheric discontinuities obtained from the analysis of three-dimensional modeling of the solar wind interaction with the local Interstellar medium (LISM). The flow of charged particles is governed by the ideal MHD equations and the transport of neutral particles is described by the Boltzmann equation. The emphasis is on the asymmetries of the termination shock (TS) and the heliopause under the combined action of the Interstellar and interplanetary Magnetic Fields (ISMF and IMF) in the presence of neutral hydrogen atoms. It is shown that an ISMF of a strength greater than 4 μG can account for the 10 AU difference in the TS heliocentric distances observed by the Voyager 1 and Voyager 2 spacecraft. We analyze the deflection of neutral hydrogen flow from its original direction in the unperturbed LISM and conclude that it remains within the range measured in the SOHO SWAN experiment. The impact is analyzed of a strong ISMF on the 2-3 kHz radio emission observed by the Voyager spacecraft, using new estimates of the radio emission conditions.
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termination shock asymmetries as seen by the voyager spacecraft the role of the Interstellar Magnetic Field and neutral hydrogen
The Astrophysical Journal, 2007Co-Authors: Nikolai V. Pogorelov, E. C. Stone, V Florinski, G P ZankAbstract:We show that asymmetries of the termination shock due to the influence of the Interstellar Magnetic Field (ISMF) are considerably smaller in the presence of neutral hydrogen atoms, which tend to symmetrize the heliopause, the termination shock, and the bow shock due to charge exchange with charged particles. This leads to a much stronger restriction on the ISMF direction and its strength. We demonstrate that in the presence of the interplanetary Magnetic Field the plane defined by the local Interstellar medium (LISM) velocity and Magnetic Field vectors does not exactly coincide with the plane defined by the Interstellar neutral helium and hydrogen velocity vectors in the supersonic solar wind region, which limits the accuracy of the inferred direction of the ISMF. We take into account the tilt of the LISM velocity vector with respect to the ecliptic plane and show that Magnetic Fields as strong as 3 μG or greater may be necessary to account for the observed asymmetry. Estimates are made of the longitudinal streaming anisotropy of energetic charged particles at the termination shock caused by the nonalignment of the interplanetary Magnetic Field with its surface. By investigating the behavior of interplanetary Magnetic Field lines that cross the Voyager 1 trajectory in the inner heliosheath, we estimate the length of the trajectory segment that is directly connected by these lines to the termination shock. A possible effect of the ISMF draping over the heliopause is discussed in connection with radio emission generated in the outer heliosheath.
Tamas I. Gombosi - One of the best experts on this subject based on the ideXlab platform.
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a strong highly tilted Interstellar Magnetic Field near the solar system
Nature, 2009Co-Authors: Merav Opher, Alouani F Bibi, G Toth, Vladislav V. Izmodenov, J. D. Richardson, Tamas I. GombosiAbstract:Voyager 2, now on the 'Interstellar' leg of its mission, entered the heliosheath, the region just outside the Solar System beyond the solar wind termination shock, in August 2007. The strength and orientation of the Magnetic Fields here are important factors in determining the evolution of gas clouds in the Galaxy, and a new set of Voyager 2 data provides the first in situ measurements of the deflection of the subsonic solar wind plasma flows in the heliosheath. The Field strength in the local Interstellar medium is greater than previous estimates, at 3.7 to 5.5 microgauss. The Field is tilted at 20–30° from the Interstellar medium flow direction and is at an angle of about 30° from the Galactic plane. Although Magnetic Fields have an important role in the evolution of gas clouds in the Galaxy, the strength and orientation of the Field in the Interstellar medium near the heliosphere has been poorly constrained, with previous estimates varying widely and based on indirect observational inferences or modelling. Measurements of the deflection of the solar wind plasma flows in the heliosheath are now used to determine the Magnetic Field strength and orientation in the Interstellar medium. Magnetic Fields play an important (sometimes dominant) role in the evolution of gas clouds in the Galaxy, but the strength and orientation of the Field in the Interstellar medium near the heliosphere has been poorly constrained. Previous estimates of the Field strength range from 1.8–2.5 μG and the Field was thought to be parallel to the Galactic plane1 or inclined by 38–60° (ref. 2) or 60–90° (ref. 3) to this plane. These estimates relied either on indirect observational inferences or modelling in which the Interstellar neutral hydrogen was not taken into account. Here we report measurements of the deflection of the solar wind plasma flows in the heliosheath4 to determine the Magnetic Field strength and orientation in the Interstellar medium. We find that the Field strength in the local Interstellar medium is 3.7–5.5 μG. The Field is tilted ∼20–30° from the Interstellar medium flow direction (resulting from the peculiar motion of the Sun in the Galaxy) and is at an angle of about 30° from the Galactic plane. We conclude that the Interstellar medium Field is turbulent or has a distortion in the solar vicinity.
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Confronting Observations and Modeling: The Role of the Interstellar Magnetic Field in Voyager 1 and 2 Asymmetries
Space Science Reviews, 2009Co-Authors: M. Opher, G Toth, J. D. Richardson, Tamas I. GombosiAbstract:Magnetic effects are ubiquitous and known to be crucial in space physics and astrophysical media. We have now the opportunity to probe these effects in the outer heliosphere with the two spacecraft Voyager 1 and 2. Voyager 1 crossed, in December 2004, the termination shock and is now in the heliosheath. On August 30, 2007 Voyager 2 crossed the termination shock, providing us for the first time in-situ measurements of the subsonic solar wind in the heliosheath. With the recent in-situ data from Voyager 1 and 2 the numerical models are forced to confront their models with observational data. Our recent results indicate that Magnetic effects, in particular the Interstellar Magnetic Field, are very important in the interaction between the solar system and the Interstellar medium. We summarize here our recent work that shows that the Interstellar Magnetic Field affects the symmetry of the heliosphere that can be detected by different measurements. We combined radio emission and energetic particle streaming measurements from Voyager 1 and 2 with extensive state-of-the art 3D MHD modeling, to constrain the direction of the local Interstellar Magnetic Field. The orientation derived is a plane ∼60°–90° from the galactic plane. This indicates that the Field orientation differs from that of a larger scale Interstellar Magnetic Field, thought to parallel the galactic plane. Although it may take 7–12 years for Voyager 2 to leave the heliosheath and enter the pristine Interstellar medium, the subsonic flows are immediately sensitive to the shape of the heliopause. The flows measured by Voyager 2 in the heliosheath indicate that the heliopause is being distorted by local Interstellar Magnetic Field with the same orientation as derived previously. As a result of the Interstellar Magnetic Field the solar system is asymmetric being pushed in the southern direction. The presence of hydrogen atoms tend to symmetrize the solutions. We show that with a strong Interstellar Magnetic Field with our most current model that includes hydrogen atoms, the asymmetries are recovered. It remains a challenge for future works with a more complete model, to explain all the observed asymmetries by V1 and V2. We comment on these results and implications of other factors not included in our present model.
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Confronting Observations and Modeling: The Role of the Interstellar Magnetic Field in Voyager 1 and 2 Asymmetries
Space Science Reviews, 2008Co-Authors: Merav Opher, John D. Richardson, Gabor Toth, Tamas I. GombosiAbstract:Magnetic effects are ubiquitous and known to be crucial in space physics and astrophysical media. We have now the opportunity to probe these effects in the outer heliosphere with the two spacecraft Voyager 1 and 2. Voyager 1 crossed, in December 2004, the termination shock and is now in the heliosheath. On August 30, 2007 Voyager 2 crossed the termination shock, providing us for the first time in-situ measurements of the subsonic solar wind in the heliosheath. With the recent in-situ data from Voyager 1 and 2 the numerical models are forced to confront their models with observational data. Our recent results indicate that Magnetic effects, in particular the Interstellar Magnetic Field, are very important in the interaction between the solar system and the Interstellar medium. We summarize here our recent work that shows that the Interstellar Magnetic Field affects the symmetry of the heliosphere that can be detected by different measurements. We combined radio emission and energetic particle streaming measurements from Voyager 1 and 2 with extensive state-of-the art 3D MHD modeling, to constrain the direction of the local Interstellar Magnetic Field. The orientation derived is a plane ∼60°–90° from the galactic plane. This indicates that the Field orientation differs from that of a larger scale Interstellar Magnetic Field, thought to parallel the galactic plane. Although it may take 7–12 years for Voyager 2 to leave the heliosheath and enter the pristine Interstellar medium, the subsonic flows are immediately sensitive to the shape of the heliopause. The flows measured by Voyager 2 in the heliosheath indicate that the heliopause is being distorted by local Interstellar Magnetic Field with the same orientation as derived previously. As a result of the Interstellar Magnetic Field the solar system is asymmetric being pushed in the southern direction. The presence of hydrogen atoms tend to symmetrize the solutions. We show that with a strong Interstellar Magnetic Field with our most current model that includes hydrogen atoms, the asymmetries are recovered. It remains a challenge for future works with a more complete model, to explain all the observed asymmetries by V1 and V2. We comment on these results and implications of other factors not included in our present model.
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The orientation of the local Interstellar Magnetic Field.
Science, 2007Co-Authors: Merav Opher, E. C. Stone, Tamas I. GombosiAbstract:The orientation of the local Interstellar Magnetic Field introduces asymmetries in the heliosphere that affect the location of heliospheric radio emissions and the streaming direction of ions from the termination shock of the solar wind. We combined observations of radio emissions and energetic particle streaming with extensive three-dimensional magnetohydrodynamic computer simulations of Magnetic Field draping over the heliopause to show that the plane of the local Interstellar Field is ∼60° to 90° from the galactic plane. This finding suggests that the Field orientation in the Local Interstellar Cloud differs from that of a larger-scale Interstellar Magnetic Field thought to parallel the galactic plane.
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Heliosphere in the magnetized local Interstellar medium: Results of a three-dimensional MHD simulation
Journal of Geophysical Research: Space Physics, 1998Co-Authors: Timur Linde, Tamas I. Gombosi, Philip L. Roe, Kenneth G. Powell, Darren L. DezeeuwAbstract:The results of a three-dimensional adaptive magnetohydrodynamic (MHD) model of the interaction of a magnetized solar wind with a magnetized very local Interstellar medium in the presence of neutral Interstellar hydrogen are presented. The interplanetary Magnetic Field is approximated by the Parker spiral, and the direction of the Interstellar Magnetic Field is taken to be arbitrary. It is demonstrated that Magnetic Field interaction has a very pronounced effect on the structure of the global heliosphere. In particular, it is shown that the interaction of the Interstellar wind with the shocked solar wind significantly depends on the direction of the Interstellar Magnetic Field. This effect is mainly manifested in the distances to the heliospheric boundaries and the shape of the heliosphere. Depending on the orientation of the Interstellar Magnetic Field the upstream location of the termination shock is expected to be at 80 ± 10 AU. The termination shock is predicted to be weak in agreement with the available body of observations. It is found that under quiet solar conditions the spiral structure of the interplanetery Magnetic Field remains imprinted in the solar wind far beyond the termination shock. Numerical simulations indicate that Magnetic Fields have a stabilizing effect on the heliopause.
O. Petruk - One of the best experts on this subject based on the ideXlab platform.
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post adiabatic supernova remnants in an Interstellar Magnetic Field parallel and perpendicular shocks
Monthly Notices of the Royal Astronomical Society, 2016Co-Authors: O. Petruk, T Kuzyo, V BeshleyAbstract:Gamma-rays from hadronic collisions are expected from supernova remnants (SNRs) located near molecular clouds. The temperature on the shock interacting with the dense environment quickly reaches $10^5$ K. The radiative losses of plasma become essential in the evolution of SNRs. They decrease the thermal pressure and essentially increase the density behind the shock. The presence of ambient Magnetic Field may considerably alter the behavior of the post-adiabatic SNRs comparing to hydrodynamic scenario. In the present paper, the magneto-hydrodynamic simulations of radiative shocks in Magnetic Field are performed. High plasma compression due to the radiative losses results also in the prominent increase of the strength of the tangential component of Magnetic Field behind the shock and the decrease of the parallel one. If the strength of the tangential Field before the shock is higher than about $3\mathrm{\mu G}$ it prevents formation of the very dense thin shell. The higher the strength of the tangential Magnetic Field the larger the thickness and the lower the maximum density in the radiative shell. Parallel Magnetic Field does not affect the distribution of the hydrodynamic parameters behind the shock. There are almost independent channels of energy transformations: radiative losses are due to the thermal energy, the Magnetic energy increases by reducing the kinetic energy. The large density and high strength of the perpendicular Magnetic Field in the radiative shells of SNRs should result in considerable increase of the hadronic gamma-ray flux comparing to the leptonic one.
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constraints on the local Interstellar Magnetic Field from non thermal emission of sn1006
Astronomy and Astrophysics, 2011Co-Authors: F. Bocchino, M. Miceli, S. Orlando, O. PetrukAbstract:Context. The synchrotron radio morphology of bilateral supernova remnants depends on the mechanisms of particle acceleration and on the viewing geometry. However, unlike X-ray and γ-ray morphologies, the radio emission does not depend on the cut-off region of the parent electron population, making it a simpler and more straightforward tool to investigate the physics of cosmic ray production in supernova remnants (SNRs). Aims. We will use the radio morphology to derive tight constraints on the direction of the local Magnetic Field and its gradient, and on the obliquity dependence of the electron injection efficiency. Methods. We perform a set of 3D MHD simulations describing the expansion of a spherical SNR through a magnetized medium with a non-uniform Magnetic Field. From the simulations, we derive non-thermal radio maps and compare them with observations of the SN1006 remnant. Results. We find that the radio morphology of SN1006 at 1 GHz is best-fitted by a model with quasi-parallel injection efficiency, a Magnetic Field aspect angle of 38 ◦ ± 4 ◦ with the line of sight, and a gradient of the Field strength toward the galactic plane, higher then the expected variations of the large scale Field of the Galaxy. Conclusions. We conclude that the radio limbs of SN1006 are polar caps that do not lie in the plane of sky. The study of the synchrotron radio emission of SNRs is of crucial importance to derive information on the galactic Magnetic Field in the vicinity of the remnants, and to gather more hints on the actual injection efficiency scenario.
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Effects of non-uniform Interstellar Magnetic Field on synch rotron X-ray and inverse-Compton-ray morphology of SNRs
2010Co-Authors: Salvatore Orlando, O. Petruk, Fabrizio Bocchino, Marco Miceli, Piazza Del ParlamentoAbstract:Context. Observations of SNRs in X-ray andγ-ray bands promise to contribute with important informatio n in our understanding of the kinematics of charged particles and Magnetic Fields in th e vicinity of strong non-relativistic shocks and, therefor e, on the nature of galactic cosmic rays. The accurate analysis of SNRs images collected in different energy bands requires the support of theoretical modeling of synchrotron and inverse Compton emission from SNRs. Aims. We develop a numerical code (remlight) to synthesize, from MHD simulations, the synchrotron radio, X-ray and inverse Comptonγ-ray emission originating from SNRs expanding in non-uniform Interstellar medium (ISM) and/or non-uniform Interstellar Magnetic Field (ISMF). As a first application, the code is used to investigate the effects of non-uniform ISMF on the SNR morphology in the non-thermal X-ray andγ-ray bands. Methods. We perform 3D MHD simulations of a spherical SNR shock expanding through a magnetized ISM with a gradient of ambient Magnetic Field strength. The model includes an appro ximate treatment of upstream Magnetic Field amplification an d the effect of shock modification due to back reaction of accelerated cos mic rays, assuming both effects to be isotropic. From the simulations, we synthesize the synchrotron radio, X-ray and inverse Comptonγ-ray emission with the synthesis coderemlight, making different assumptions about the details of acceleration and injectio n of relativistic electrons. Results. A gradient of the ambient Magnetic Field strength induces asy mmetric morphologies in radio, hard X-ray andγ-ray bands independently from the model of electron injection if the gradient has a component perpendicular to the line-of-sight ( LoS). The degree of asymmetry of the remnant morphology depends on the details of the electron injection and acceleration and is different in the radio, hard X-ray, andγ-ray bands. In general, the non-thermal X-ray morphology is the most sensitive to the gradient, showing the highest degree of asymmetry. The ICγ-ray emission is weakly sensitive to the non-uniform ISMF, the degree of asymmetry of the remnant morphology being the lowest in this band.
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Aspect angle for Interstellar Magnetic Field in SN 1006
Monthly Notices of the Royal Astronomical Society, 2009Co-Authors: O. Petruk, G. Dubner, G. Castelletti, F. Bocchino, D. Iakubovskyi, M. G. F. Kirsch, M. Miceli, S. Orlando, I. TelezhinskyAbstract:A number of important processes taking place around strong shocks in supernova remnants (SNRs) depend on the shock obliquity. The measured synchrotron flux is a function of the aspect angle between Interstellar Magnetic Field (ISMF) and the line of sight. Thus, a model of non-thermal emission from SNRs should account for the orientation of the ambient Magnetic Field. We develop a new method for the estimation of the aspect angle, based on the comparison between observed and synthesized radio maps of SNRs, making different assumptions about the dependence of electron injection efficiency on the shock obliquity. The method uses the azimuthal profile of radio surface brightness as a probe for orientation of ambient Magnetic Field because it is almost insensitive to the downstream distribution of Magnetic Field and emitting electrons. We apply our method to a new radio image of SN 1006 produced on the basis of archival Very Large Array and Parkes data. The image recovers emission from all spatial structures with angular scales from a few arcsec to 15 arcmin. We explore different models of injection efficiency and find the following best-fitting values for the aspect angle of SN 1006: φo= 70o± 4.2o if the injection is isotropic, φo= 64o± 2.8o for quasi-perpendicular injection (SNR has an equatorial belt in both cases) and φo= 11o± 0.8o for quasi-parallel injection (polar-cap model of SNR). In the last case, SN 1006 is expected to have a centrally peaked morphology contrary to what is observed. Therefore, our analysis provides some indication against the quasi-parallel injection model.
N V Pogorelov - One of the best experts on this subject based on the ideXlab platform.
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heliospheric asymmetries due to the action of the Interstellar Magnetic Field
Advances in Space Research, 2009Co-Authors: N V Pogorelov, G P Zank, J W Mitchell, J Heerikhuisen, Iver H. CairnsAbstract:We discuss the asymmetry of the heliospheric discontinuities obtained from the analysis of 3D modeling of the solar wind (SW) interaction with local Interstellar medium (LISM). The flow of charged particles is governed by the ideal MHD equations and the flow of neutral particles is described by the Boltzmann equation. The emphasis is made on the asymmetries of the termination shock (TS) and the heliopause under the combined action of the Interstellar and interplanetary Magnetic Fields (ISMF and IMF) in the presence of neutral hydrogen atoms whose transport through the heliosphere is modeled kinetically, using a Monte Carlo approach. We show that the deflection of neutral hydrogen flow from its original direction in the unperturbed LISM is highly anisotropic and evaluate a possible angle between the hydrogen deflection plane measured in the SOHO SWAN experiment and the plane containing the ISMF and LISM velocity vectors for different ISMF strengths. It is shown that the ISMF of a strength greater than 4 μG can account for the 10 AU difference in the TS heliocentric difference observed during its crossing by the Voyager 1 and Voyager 2 spacecraft, which however results in a larger discrepancy between the calculated and observed velocity distributions. The effect of a strong ISMF on the distribution of plasma quantities in the inner heliosheath and on 2–3 kHz radio emission is discussed.
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three dimensional features of the outer heliosphere due to coupling between the Interstellar and interplanetary Magnetic Fields iii the effects of solar rotation and activity cycle
The Astrophysical Journal, 2009Co-Authors: N V Pogorelov, G P Zank, S N Borovikov, Tatsuki OginoAbstract:We investigate the effects of the 11 year solar cycle and 25 day rotation period of the Sun on the interaction of the solar wind (SW) with the local Interstellar medium (LISM). Our models take into account the partially ionized character of the LISM and include momentum and energy transfer between the ionized and neutral components. We assume that the Interstellar Magnetic Field vector belongs to the hydrogen deflection plane as discovered in the SOHO SWAN experiment. This plane is inclined at an angle of about 60° toward the ecliptic plane of the Sun, as suggested in recent publications relating the local Interstellar cloud properties to the radio emission observed by Voyager 1. It is assumed that the latitudinal extent of the boundary between the slow and fast SW regions, as well as the angle between the Sun's rotation and Magnetic-dipole axes, are periodic functions of time, while the polarity of the Interstellar Magnetic Field changes sign every 11 years at the solar maximum. The global variation of the SW-LISM interaction pattern, the excursions of the termination shock and the heliopause, and parameter distributions in certain directions are investigated. The analysis of the behavior of the wavy heliospheric current sheet in the supersonic SW region shows the importance of neutral atoms on its dynamics.
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heliospheric asymmetries and 2 3 khz radio emission under strong Interstellar Magnetic Field conditions
The Astrophysical Journal, 2009Co-Authors: N V Pogorelov, Iver H. Cairns, J W Mitchell, J Heerikhuisen, G P ZankAbstract:We discuss the asymmetry of the major heliospheric discontinuities obtained from the analysis of three-dimensional modeling of the solar wind interaction with the local Interstellar medium (LISM). The flow of charged particles is governed by the ideal MHD equations and the transport of neutral particles is described by the Boltzmann equation. The emphasis is on the asymmetries of the termination shock (TS) and the heliopause under the combined action of the Interstellar and interplanetary Magnetic Fields (ISMF and IMF) in the presence of neutral hydrogen atoms. It is shown that an ISMF of a strength greater than 4 μG can account for the 10 AU difference in the TS heliocentric distances observed by the Voyager 1 and Voyager 2 spacecraft. We analyze the deflection of neutral hydrogen flow from its original direction in the unperturbed LISM and conclude that it remains within the range measured in the SOHO SWAN experiment. The impact is analyzed of a strong ISMF on the 2-3 kHz radio emission observed by the Voyager spacecraft, using new estimates of the radio emission conditions.
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influence of the Interstellar Magnetic Field direction on the shape of the global heliopause
Journal of Geophysical Research, 1998Co-Authors: N V Pogorelov, Takuya MatsudaAbstract:In this paper we study the influence of the angle between the local Interstellar medium velocity and Magnetic Field vectors on the interaction of this medium with the solar wind. Both winds are supposed supersonic. Applicability of the two-shock model of the interaction is discussed. Investigation is performed by numerical solution of the MHD equations for an ideal plasma in the one-fluid approximation.
Nikolai V. Pogorelov - One of the best experts on this subject based on the ideXlab platform.
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LOCAL Interstellar Magnetic Field DETERMINED FROM THE Interstellar BOUNDARY EXPLORER RIBBON
The Astrophysical Journal, 2016Co-Authors: Eric Zirnstein, Herbert O. Funsten, D. J. Mccomas, Jacob Heerikhuisen, George Livadiotis, Nikolai V. PogorelovAbstract:The solar wind emanating from the Sun interacts with the local Interstellar medium (LISM), forming the heliosphere. Hydrogen energetic neutral atoms (ENAs) produced by the solar-Interstellar interaction carry important information about plasma properties from the boundaries of the heliosphere, and are currently being measured by NASA's Interstellar Boundary Explorer (IBEX). IBEX observations show the existence of a "ribbon" of intense ENA emission projecting a circle on the celestial sphere that is centered near the local Interstellar Magnetic Field (ISMF) vector. Here we show that the source of the IBEX ribbon as a function of ENA energy outside the heliosphere, uniquely coupled to the draping of the ISMF around the heliopause, can be used to precisely determine the magnitude (2.93 ± 0.08 μG) and direction (22728 ± 069, 3462 ± 045 in ecliptic longitude and latitude) of the pristine ISMF far (~1000 AU) from the Sun. We find that the ISMF vector is offset from the ribbon center by ~83 toward the direction of motion of the heliosphere through the LISM, and their vectors form a plane that is consistent with the direction of deflected Interstellar neutral hydrogen, thought to be controlled by the ISMF. Our results yield draped ISMF properties close to that observed by Voyager 1, the only spacecraft to directly measure the ISMF close to the heliosphere, and give predictions of the pristine ISMF that Voyager 1 has yet to sample.
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AN ESTIMATE OF THE NEARBY Interstellar Magnetic Field USING NEUTRAL ATOMS
The Astrophysical Journal, 2011Co-Authors: Jacob Heerikhuisen, Nikolai V. PogorelovAbstract:The strength and orientation of the Magnetic Field in the nearby Interstellar medium have remained elusive, despite continual improvements in observations and models. Data from NASA’s Voyager mission and the Solar Wind ANisotropies(SWAN)experimentonboardSolarandHeliosphericObservatory(SOHO)haveplacedobservational constraints on the Magnetic Field, and the more recent Interstellar Boundary Explorer (IBEX) data appear to also bear an imprint of the Interstellar Magnetic Field (ISMF). In this paper, we combine computational models of the heliosphere with data from Voyager, SOHO/SWAN, and IBEX to estimate both the strength and direction of the nearby ISMF. On the basis of our simulations, we find that a Field strength of 2‐3 μG pointing from ecliptic coordinates (220‐224, 39‐44), combined with an Interstellar hydrogen density of ∼0.15 cm −3 , produces results most consistent with observations.
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Draping of the local Interstellar Magnetic Field over the heliopause
Journal of Geophysical Research: Space Physics, 2008Co-Authors: John Mitchell, Iver H. Cairns, Nikolai V. Pogorelov, Gary P. ZankAbstract:[1] A recent theory for radio events at 2–3 kHz observed by the Voyager spacecraft suggests that the emission is generated when shocks associated with global merged interaction regions (GMIRs) enter a region just beyond the heliopause nose that is primed with an enhanced level of superthermal electrons. In this GMIR/priming theory the superthermal electrons are accelerated by lower hybrid waves generated by pick-up ions. For this acceleration to be efficient the pick-up ion ring speed vr and the Alfven speed vA must satisfy the inequality vr/vA ≲ 5, implying that the local Magnetic Field B must be sufficiently large. Here this constraint is used to predict which regions generate radio emission by calculating the draping of the Interstellar Magnetic Field B∞ over the heliopause using the convected Field equations and a gas-dynamic simulation of the solar wind–VLISM interaction. The size and shape of the regions with large ∣B∣ are predicted to depend on the orientation of B∞ relative to the Interstellar flow velocity. For sufficiently perpendicular orientations the high ∣B∣ region is a linear band parallel to B∞ in the plane of the sky, centered near where the surface is closely parallel to B∞, but the band shape is only a ∼10% effect compared with a circular surrounding region. The Magnetic amplification factor increases with decreasing distance to the heliopause nose and increasingly perpendicular orientation of B∞, with factors ≳5 typical within axial and transverse distances to the nose of 5 and 35 AU, respectively. Combining the Magnetic amplification with plausible neutral and plasma parameters, the constraint vr/vA ≲ 5 requires B∞ ≳ 0.06 nT for the GMIR/priming theory to operate within the draping region. A recently proposed constraint, that B be nearly perpendicular to the normal vector to the GMIR surface for effective electron acceleration by the GMIR shock, is also considered. A supporting argument is provided for the previous claim that this constraint predicts strong emission in a band perpendicular to B∞: Calculations show that the shock-accelerated electrons produce significant emission only for distances parallel to B that are small (≈1 AU) compared with the macroscopic regions on the shock where B · ≈ 0. This predicted source orientation agrees well with observations of the source and an independent estimate of the direction of B∞ based on Lyman-α observations. It is argued that the B · ≈ 0 constraint is a natural component of the GMIR/priming theory. The large, relatively circular nature of the draping region where vr/vA ≲ 5 will plausibly lead to the constraint B · ≈ 0 determining the intrinsic source shape in the plane of the sky.
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termination shock asymmetries as seen by the voyager spacecraft the role of the Interstellar Magnetic Field and neutral hydrogen
The Astrophysical Journal, 2007Co-Authors: Nikolai V. Pogorelov, E. C. Stone, V Florinski, G P ZankAbstract:We show that asymmetries of the termination shock due to the influence of the Interstellar Magnetic Field (ISMF) are considerably smaller in the presence of neutral hydrogen atoms, which tend to symmetrize the heliopause, the termination shock, and the bow shock due to charge exchange with charged particles. This leads to a much stronger restriction on the ISMF direction and its strength. We demonstrate that in the presence of the interplanetary Magnetic Field the plane defined by the local Interstellar medium (LISM) velocity and Magnetic Field vectors does not exactly coincide with the plane defined by the Interstellar neutral helium and hydrogen velocity vectors in the supersonic solar wind region, which limits the accuracy of the inferred direction of the ISMF. We take into account the tilt of the LISM velocity vector with respect to the ecliptic plane and show that Magnetic Fields as strong as 3 μG or greater may be necessary to account for the observed asymmetry. Estimates are made of the longitudinal streaming anisotropy of energetic charged particles at the termination shock caused by the nonalignment of the interplanetary Magnetic Field with its surface. By investigating the behavior of interplanetary Magnetic Field lines that cross the Voyager 1 trajectory in the inner heliosheath, we estimate the length of the trajectory segment that is directly connected by these lines to the termination shock. A possible effect of the ISMF draping over the heliopause is discussed in connection with radio emission generated in the outer heliosheath.
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Termination Shock Asymmetries as Seen by the Voyager Spacecraft: The Role of the Interstellar Magnetic Field and Neutral Hydrogen
The Astrophysical Journal, 2007Co-Authors: Nikolai V. Pogorelov, E. C. Stone, V Florinski, Gary P. ZankAbstract:We show that asymmetries of the termination shock due to the influence of the Interstellar Magnetic Field (ISMF) are considerably smaller in the presence of neutral hydrogen atoms, which tend to symmetrize the heliopause, the termination shock, and the bow shock due to charge exchange with charged particles. This leads to a much stronger restriction on the ISMF direction and its strength. We demonstrate that in the presence of the interplanetary Magnetic Field the plane defined by the local Interstellar medium (LISM) velocity and Magnetic Field vectors does not exactly coincide with the plane defined by the Interstellar neutral helium and hydrogen velocity vectors in the supersonic solar wind region, which limits the accuracy of the inferred direction of the ISMF. We take into account the tilt of the LISM velocity vector with respect to the ecliptic plane and show that Magnetic Fields as strong as 3 μG or greater may be necessary to account for the observed asymmetry. Estimates are made of the longitudinal streaming anisotropy of energetic charged particles at the termination shock caused by the nonalignment of the interplanetary Magnetic Field with its surface. By investigating the behavior of interplanetary Magnetic Field lines that cross the Voyager 1 trajectory in the inner heliosheath, we estimate the length of the trajectory segment that is directly connected by these lines to the termination shock. A possible effect of the ISMF draping over the heliopause is discussed in connection with radio emission generated in the outer heliosheath.
