Ordering Cosmic Rays Earth and other planets are constantly bombarded by cosmic rays (charged par... more Ordering Cosmic Rays Earth and other planets are constantly bombarded by cosmic rays (charged particles from the cosmos). The flux of very-high-energy cosmic rays varies according to where we look in the sky. Schwadron et al. (p. 988 , published online 13 February) show that recent measurements of the local interstellar parameters by NASA's Interstellar Boundary Explorer satellite are consistent with observed cosmic ray anisotropies at tera–electron volt energies, implying that local interstellar conditions play a role in ordering very-high-energy cosmic rays in our cosmic vicinity.
The purpose of interstellar probe (ISP) is to follow NASA's exploratory mission to cross... more The purpose of interstellar probe (ISP) is to follow NASA's exploratory mission to cross the heliospheric boundary regions and, for the first time, enter our extra-solar galactic environment. Interstellar probe has therefore captured the imagination of the science community and the public for several decades. In 1999, NASA commissioned a science and technology definition team to address the science and
The Rankine-Hugoniot (R-H) jump conditions at the heliospheric termination shock provide a means ... more The Rankine-Hugoniot (R-H) jump conditions at the heliospheric termination shock provide a means of knitting together the in situ measurements from Voyager 2 (VGR2) with the remote sensing of the heliosheath plasma via energetic neutral atom (ENA) imaging by IBEX and Cassini/INCA. The VGR2 instrument suite has a gap (~1-30 keV) in the ion measurements. While the ENA images (0.2-6 keV and 5-55 keV) fill the VGR2 gap in the pixel containing the VGR2 spacecraft, they do so only in the sense that they provide the ion intensity integrated along the radial line of sight throughout the entire heliosheath. The synthesis we attempt is further complicated by the observational results from all three spacecraft that the non-thermal component of the ion pressure dominates that of the thermal component. We therefore have developed (and applied) a generalized formulation of the R-H conditions that does not invoke an equation of state, but rather can directly ingest the instrumentally-measured non-thermal spectrum. The result is an estimate that the ratio (upstream/downstream) of the non-thermal pressure is ~43%, confirming anew that the termination shock (at least at VGR2) is strongly mediated by non-thermal ions.
The Interstellar Boundary Explorer (IBEX) is a small explorer mission that launched on 19 October... more The Interstellar Boundary Explorer (IBEX) is a small explorer mission that launched on 19 October 2008 with the sole, focused science objective to discover the global interaction between the solar wind and the interstellar medium. IBEX is designed to achieve this objective by answering four fundamental science questions: (1) What is the global strength and structure of the termination shock, (2) How are energetic protons accelerated 12 D.J. McComas et al. at the termination shock, (3) What are the global properties of the solar wind flow beyond the termination shock and in the heliotail, and (4) How does the interstellar flow interact with the heliosphere beyond the heliopause? The answers to these questions rely on energyresolved images of energetic neutral atoms (ENAs), which originate beyond the termination shock, in the inner heliosheath. To make these exploratory ENA observations IBEX carries two ultra-high sensitivity ENA cameras on a simple spinning spacecraft. IBEX's very high apogee Earth orbit was achieved using a new and significantly enhanced method for launching small satellites; this orbit allows viewing of the outer heliosphere from beyond the Earth's relatively bright magnetospheric ENA emissions. The combination of full-sky imaging and energy spectral measurements of ENAs over the range from ∼10 eV to 6 keV provides the critical information to allow us to achieve our science objective and understand this global interaction for the first time. The IBEX mission was developed to provide the first global views of the Sun's interstellar boundaries, unveiling the physics of the heliosphere's interstellar interaction, providing a deeper understanding of the heliosphere and thereby astrospheres throughout the galaxy, and creating the opportunity to make even greater unanticipated discoveries.
Pickup Ion Acceleration at Low-β p Perpendicular Shocks. ... Multiscale hybrid kinetic simulation... more Pickup Ion Acceleration at Low-β p Perpendicular Shocks. ... Multiscale hybrid kinetic simulations of low-β p supercritical shocks demonstrate that pickup ions may be strongly accelerated by shock surfing, also known as multiply reflected ion acceleration. ...
... by the Voyager 2 spacecraft at heliocentric radial distances r from 1 astronomical units (AU)... more ... by the Voyager 2 spacecraft at heliocentric radial distances r from 1 astronomical units (AU) to ... To a first approximation, transport of turbulent fluctuations involves convection and propagation in ... the fluctuating component of the magnetic field, normalized to Alfvén speed units (r is ...
1] Decades of interplanetary measurements of the solar wind and other space plasmas have establis... more 1] Decades of interplanetary measurements of the solar wind and other space plasmas have established that the suprathermal ion intensity distributions (j) are non-Maxwellian and are characterized by high-energy power law tails (j $ E Àk ). Recent analysis by Fisk and Gloeckler of suprathermal ion observations between 1-5 AU demonstrates that a particular differential intensity distribution function emerges universally between $2-10 times the solar wind speed with k $ 1.5. This power law tail is particularly apparent in downstream distributions beyond reverse shocks associated with corotating interaction regions. Similar power law tails have been observed in the downstream flow beyond the termination shock by the Low Energy Charged Particle instrument on both Voyager 1 and Voyager 2. Using kappa distributions with internal energy, density, and bulk flow derived from large-scale magnetohydrodynamic models, we calculate the simulated flux of energetic neutral atoms (ENAs) produced in the heliosheath by charge exchange between solar wind protons and interstellar hydrogen. We then produce simulated ENA maps of the heliosheath, such as will be measured by the Interstellar Boundary Explorer Mission (IBEX). We also estimate the expected signal to noise and background ratio for IBEX. The solar wind suprathermal tail significantly increases the ENA flux within the IBEX energy range, $0.01-6 keV, by more than an order of magnitude at the highest energies over the estimates using a Maxwellian. It is therefore essential to consider suprathermal tails in the interpretation of IBEX ENA images and theoretical modeling of the heliospheric termination shock. Citation: Prested, C., et al. (2008), Implications of solar wind suprathermal tails for IBEX ENA images of the heliosheath,
ABSTRACT In gradual solar energetic particle (SEP) events, protons and heavy ions are often accel... more ABSTRACT In gradual solar energetic particle (SEP) events, protons and heavy ions are often accelerated to >100 MeV/nucleon at a CME-driven shock. In this work, we study particle acceleration at an oblique shock by extending our earlier particle acceleration and transport in heliosphere (PATH) code to include shocks with arbitrary θBN, where θBN is the angle between the upstream magnetic field and the shock normal. Instantaneous particle spectra at the shock front are obtained by solving the transport equation using the total diffusion coefficient κ, which is a function of the parallel diffusion coefficient κ∥ and the perpendicular diffusion coefficient κ⊥. In computing κ∥ and κ⊥, we use analytic expressions derived previously. The particle maximum energy at the shock front as a function of time, the time intensity profiles and particle spectra at 1 AU for five θBN’s are calculated for an example shock.
Ordering Cosmic Rays Earth and other planets are constantly bombarded by cosmic rays (charged par... more Ordering Cosmic Rays Earth and other planets are constantly bombarded by cosmic rays (charged particles from the cosmos). The flux of very-high-energy cosmic rays varies according to where we look in the sky. Schwadron et al. (p. 988 , published online 13 February) show that recent measurements of the local interstellar parameters by NASA's Interstellar Boundary Explorer satellite are consistent with observed cosmic ray anisotropies at tera–electron volt energies, implying that local interstellar conditions play a role in ordering very-high-energy cosmic rays in our cosmic vicinity.
The purpose of interstellar probe (ISP) is to follow NASA's exploratory mission to cross... more The purpose of interstellar probe (ISP) is to follow NASA's exploratory mission to cross the heliospheric boundary regions and, for the first time, enter our extra-solar galactic environment. Interstellar probe has therefore captured the imagination of the science community and the public for several decades. In 1999, NASA commissioned a science and technology definition team to address the science and
The Rankine-Hugoniot (R-H) jump conditions at the heliospheric termination shock provide a means ... more The Rankine-Hugoniot (R-H) jump conditions at the heliospheric termination shock provide a means of knitting together the in situ measurements from Voyager 2 (VGR2) with the remote sensing of the heliosheath plasma via energetic neutral atom (ENA) imaging by IBEX and Cassini/INCA. The VGR2 instrument suite has a gap (~1-30 keV) in the ion measurements. While the ENA images (0.2-6 keV and 5-55 keV) fill the VGR2 gap in the pixel containing the VGR2 spacecraft, they do so only in the sense that they provide the ion intensity integrated along the radial line of sight throughout the entire heliosheath. The synthesis we attempt is further complicated by the observational results from all three spacecraft that the non-thermal component of the ion pressure dominates that of the thermal component. We therefore have developed (and applied) a generalized formulation of the R-H conditions that does not invoke an equation of state, but rather can directly ingest the instrumentally-measured non-thermal spectrum. The result is an estimate that the ratio (upstream/downstream) of the non-thermal pressure is ~43%, confirming anew that the termination shock (at least at VGR2) is strongly mediated by non-thermal ions.
The Interstellar Boundary Explorer (IBEX) is a small explorer mission that launched on 19 October... more The Interstellar Boundary Explorer (IBEX) is a small explorer mission that launched on 19 October 2008 with the sole, focused science objective to discover the global interaction between the solar wind and the interstellar medium. IBEX is designed to achieve this objective by answering four fundamental science questions: (1) What is the global strength and structure of the termination shock, (2) How are energetic protons accelerated 12 D.J. McComas et al. at the termination shock, (3) What are the global properties of the solar wind flow beyond the termination shock and in the heliotail, and (4) How does the interstellar flow interact with the heliosphere beyond the heliopause? The answers to these questions rely on energyresolved images of energetic neutral atoms (ENAs), which originate beyond the termination shock, in the inner heliosheath. To make these exploratory ENA observations IBEX carries two ultra-high sensitivity ENA cameras on a simple spinning spacecraft. IBEX's very high apogee Earth orbit was achieved using a new and significantly enhanced method for launching small satellites; this orbit allows viewing of the outer heliosphere from beyond the Earth's relatively bright magnetospheric ENA emissions. The combination of full-sky imaging and energy spectral measurements of ENAs over the range from ∼10 eV to 6 keV provides the critical information to allow us to achieve our science objective and understand this global interaction for the first time. The IBEX mission was developed to provide the first global views of the Sun's interstellar boundaries, unveiling the physics of the heliosphere's interstellar interaction, providing a deeper understanding of the heliosphere and thereby astrospheres throughout the galaxy, and creating the opportunity to make even greater unanticipated discoveries.
Pickup Ion Acceleration at Low-β p Perpendicular Shocks. ... Multiscale hybrid kinetic simulation... more Pickup Ion Acceleration at Low-β p Perpendicular Shocks. ... Multiscale hybrid kinetic simulations of low-β p supercritical shocks demonstrate that pickup ions may be strongly accelerated by shock surfing, also known as multiply reflected ion acceleration. ...
... by the Voyager 2 spacecraft at heliocentric radial distances r from 1 astronomical units (AU)... more ... by the Voyager 2 spacecraft at heliocentric radial distances r from 1 astronomical units (AU) to ... To a first approximation, transport of turbulent fluctuations involves convection and propagation in ... the fluctuating component of the magnetic field, normalized to Alfvén speed units (r is ...
1] Decades of interplanetary measurements of the solar wind and other space plasmas have establis... more 1] Decades of interplanetary measurements of the solar wind and other space plasmas have established that the suprathermal ion intensity distributions (j) are non-Maxwellian and are characterized by high-energy power law tails (j $ E Àk ). Recent analysis by Fisk and Gloeckler of suprathermal ion observations between 1-5 AU demonstrates that a particular differential intensity distribution function emerges universally between $2-10 times the solar wind speed with k $ 1.5. This power law tail is particularly apparent in downstream distributions beyond reverse shocks associated with corotating interaction regions. Similar power law tails have been observed in the downstream flow beyond the termination shock by the Low Energy Charged Particle instrument on both Voyager 1 and Voyager 2. Using kappa distributions with internal energy, density, and bulk flow derived from large-scale magnetohydrodynamic models, we calculate the simulated flux of energetic neutral atoms (ENAs) produced in the heliosheath by charge exchange between solar wind protons and interstellar hydrogen. We then produce simulated ENA maps of the heliosheath, such as will be measured by the Interstellar Boundary Explorer Mission (IBEX). We also estimate the expected signal to noise and background ratio for IBEX. The solar wind suprathermal tail significantly increases the ENA flux within the IBEX energy range, $0.01-6 keV, by more than an order of magnitude at the highest energies over the estimates using a Maxwellian. It is therefore essential to consider suprathermal tails in the interpretation of IBEX ENA images and theoretical modeling of the heliospheric termination shock. Citation: Prested, C., et al. (2008), Implications of solar wind suprathermal tails for IBEX ENA images of the heliosheath,
ABSTRACT In gradual solar energetic particle (SEP) events, protons and heavy ions are often accel... more ABSTRACT In gradual solar energetic particle (SEP) events, protons and heavy ions are often accelerated to >100 MeV/nucleon at a CME-driven shock. In this work, we study particle acceleration at an oblique shock by extending our earlier particle acceleration and transport in heliosphere (PATH) code to include shocks with arbitrary θBN, where θBN is the angle between the upstream magnetic field and the shock normal. Instantaneous particle spectra at the shock front are obtained by solving the transport equation using the total diffusion coefficient κ, which is a function of the parallel diffusion coefficient κ∥ and the perpendicular diffusion coefficient κ⊥. In computing κ∥ and κ⊥, we use analytic expressions derived previously. The particle maximum energy at the shock front as a function of time, the time intensity profiles and particle spectra at 1 AU for five θBN’s are calculated for an example shock.
Uploads
Papers by G. Zank