We analyze the Cartwheel coronal mass ejectionʼs (CME; 2008 April 9) trajectory in the low corona... more We analyze the Cartwheel coronal mass ejectionʼs (CME; 2008 April 9) trajectory in the low corona with the ForeCAT model. This complex event presented a significant rotation in the low corona and a reversal in its original latitude direction. We successfully reproduce the observed CME's trajectory (latitude and longitude deflection) and speed. Through a 2 c test, we are able to constrain the CME's mass to (2.3−3.0)×10 14 g and the CME's initial shape. We are able to constrain the expansion of the CME as well: the angular width linearly increases until 2.1 R , and is constant afterward. In order to match the observed latitude, we include a non-radial initial speed of −42 km s −1. Despite allowing the CME to rotate in the model, the magnetic forces of the solar background are not able to reproduce the observed rotation. We suggest that the complex reversal in latitude and the significant rotation of the Cartwheel CME can be justified with an asymmetrical reconnection event that ejected the CME nonradially and also initiated its rotation.
Predicting the impact of coronal mass ejections (CMEs) and the southward component of their magne... more Predicting the impact of coronal mass ejections (CMEs) and the southward component of their magnetic field is one of the key goals of space weather forecasting. We present a new model, the ForeCAT In situ Data Observer (FIDO), for predicting the in situ magnetic field of CMEs. We first simulate a CME using ForeCAT, a model for CME deflection and rotation resulting from the background solar magnetic forces (Kay et al. 2015b). Using the CME position and orientation from ForeCAT, we then determine the passage of the CME over a simulated spacecraft. We model the CME's magnetic field using a force free flux rope and we determine the in situ magnetic profile at the synthetic spacecraft. We show that FIDO can reproduce the general behavior of four observed CMEs. FIDO results are very sensitive to the CME's position and orientation, and we show that the uncertainty in a CME's position and orientation from coronagraph images corresponds to a wide range of in situ magnitudes and even polarities. This small range of positions and orientations also includes CMEs that entirely miss the satellite. We show that two derived parameters (the normalized angular distance between the CME nose and satellite position and the angular difference between the CME tilt and the position angle of the satellite with respect to the CME nose) can be used to reliably determine whether an impact or miss occurs. We find that the same criteria separates the impacts and misses for cases representing all four observed CMEs.
Accurate space weather forecasting requires knowledge of the trajectory of coronal mass ejections... more Accurate space weather forecasting requires knowledge of the trajectory of coronal mass ejections (CMEs), including any deflections close to the Sun or through interplanetary space. Kay et al. (2013) introduced ForeCAT, a model of CME deflection resulting from the background solar magnetic field. For a magnetic field solution corresponding to Carrington Rotation (CR) 2029 (declining phase, April-May 2005), the majority of the CMEs deflected to the Heliospheric Current Sheet (HCS), the minimum in magnetic pressure on global scales. Most of the deflection occurred below 4 R. Here we extend ForeCAT to include a three dimensional description of the deflecting CME. We attempt to answer the following questions: a) Do all CMEs deflect to the magnetic minimum? and b) Does most deflection occur within the first few solar radii (4 R)? Results for solar minimum and declining phase CMEs show that not every CME deflects to the magnetic minimum and that the deflection is typically determined below 2 R. Slow, wide, low mass CMEs in declining phase solar backgrounds with strong magnetic field and magnetic gradients exhibit the largest deflections. Local gradients related to active regions tend to cause the largest deviations from the deflection predicted by global magnetic gradients, but variations can also be seen for CMEs in the quiet sun regions of the declining phase CR. We show the torques due to differential forces along the CME can cause rotation about the CME's toroidal axis.
The acceleration of protons and electrons to high (sometimes GeV/nucleon) energies by solar pheno... more The acceleration of protons and electrons to high (sometimes GeV/nucleon) energies by solar phenomena is a key component of space weather. These solar energetic particle (SEP) events can damage spacecraft and communications, as well present radiation hazards to humans. In depth particle acceleration simulations have been performed for idealized magnetic fields for diffusive acceleration and particle propagation, and at the same time the quality of MHD simulations of CMEs has improved significantly. However, to date these two pieces of the same puzzle have remained largely decoupled. Such structures may contain not just a shock, but also sizable sheath and pileup compression regions behind it, and may vary considerably with longitude and latitude based on the underlying coronal conditions. In this work, we have coupled results from a detailed global 3D MHD time-dependent CME simulation to a global proton acceleration and transport model, in order to study time-dependent effects of SEP acceleration between 1.8 and 8 solar radii in the 2005 13 May CME. We find that the source population is accelerated to at least 100 MeV, with distributions enhanced up to six orders of magnitude. Acceleration efficiency varies strongly along field lines probing different regions of the dynamically evolving CME, whose dynamics is influenced by the large-scale coronal magnetic field structure. We observe strong acceleration in sheath regions immediately behind the shock.
The effects of the highly damped modes in the energy and reaction rates in a plasma are discussed... more The effects of the highly damped modes in the energy and reaction rates in a plasma are discussed. These modes, with wave numbers k≫kD, even being only weakly excited, with less than kBT per mode, make a significant contribution to the energy and screening in a plasma. When the de Broglie wavelength is much less than the distance of closest approach of thermal electrons, a classical analysis of the plasma can be made. It is assumed, in the classical analysis, with ℏ→0, that the energy of the fluctuations ℏω≪kBT. Using the fluctuation-dissipation theorem, the spectra of fluctuations with ℏ≠0 is appreciably decreased. The decrease is mainly for the highly damped modes at high frequencies (∼0.5–3kBT). Reaction rates are enhanced in a plasma due to the screening of the reacting ions. This is taken into account by the Salpeter factor, which assumes slow motion for the ions. The implication of including the highly damped modes (with ℏ≠0) in the nuclear reaction rates in a plasma is discus...
Preface (do read it!) vii textbook is intended for students in physical sciences in later years o... more Preface (do read it!) vii textbook is intended for students in physical sciences in later years of their university training and for beginning graduate students in fields of solar, stellar, (exo-)planetary, and planetary-system sciences. The lecturers at the Summer Schools developed a series of five volumes on Heliophysics (four published in printed form by Cambridge University Press, and one online at the Heliophysics Summer School website) contain in total 1919 pages of text and figures, in 56 topical chapters (see Table 2): Vol. I: Preface ix Table 2: (Continued from the previous page) Chapters and their authors in the Heliophysics book series sorted by theme, not showing introductory chapters. Astro-/heliospheres, interstellar environment, and galactic cosmic rays Preface xi 'Space weather' is the term used to describe an ensemble of changing conditions in the vicinity of Earth and, by extension, any other body in a planetary system, typically occurring on time scales up to a few days. Often, the term is implicitly taken to refer also to the conditions from the solar dynamo outward to the furthest reaches of the heliosphere that are involved in space weather around Earth. Much of what is described in this volume therefore concerns space weather: heliophysics contains the science of space weather. However, where the science of space weather focuses on phenomena that can impact society through short-term variability, this text takes the long view by putting the spotlight on evolutionary changes in the states of star-planet systems. As such, this text does describe the foundational processes of space weather, but is not concerned with the impacts of space weather on technological infrastructure, does not address the challenges of forecasting space weather, and skips coupling mechanisms such as ground-induced currents (GICs) associated with geomagnetic disturbances and ground-level enhancements (GLEs) of energetic particles. This choice of focus is motivated by my desire to introduce the reader to the science of heliophysics from the perspective of habitability on time scales on which stellar and planetary atmospheres change, and indeed up to time scales on which stars and their planets evolve, and to do that in a relatively compact form. As you go through this text, you should realize that many of the processes described here have consequences for society, ranging from system design choices to potentially substantial failures in one or more of the infrastructures that we have come to rely on, including continuous and reliable electric power, positional information, and means of communication. Interruptions in quality or availability of any of these can have substantial consequences that may be costly or life-threatening on scales that may involve single individuals or populations of millions. Descriptions of the impacts of space weather can be found in the Heliophysics books in
It is expected that as the Sun travels through the interstellar medium (ISM), there will be diffe... more It is expected that as the Sun travels through the interstellar medium (ISM), there will be different filtration of Galactic Cosmic Rays (GCR) that affect Earth. The effect of GCR on Earth's atmosphere and climate is still uncertain. Although the interaction with molecular clouds was previously considered, the terrestrial impact of compact cold clouds was neglected. There is overwhelming geological evidence from 60 Fe and 244 Pu isotopes that Earth was in direct contact with the ISM 2-3 million years ago, and the local ISM is home to several nearby cold clouds. Here we show, with a state-of the art simulation that incorporate all the current knowledge about the heliosphere that if the solar system passed through a cloud such as Local Leo Cold Cloud, then the heliosphere which protects the solar system from interstellar particles, must have shrunk to a scale smaller than the Earth's orbit around the Sun (0.22AU). Using a magnetohydrodynamic simulation that includes charge exchange between neutral atoms and ions, we show that during the heliosphere shrinkage, Earth was exposed to a neutral hydrogen density of up to 3000cm-3. This could have had drastic effects on Earth's climate and potentially on human evolution at that time, as suggested by existing data.
We report on the energy dependence of Galactic cosmic rays (GCRs) in the very local interstellar ... more We report on the energy dependence of Galactic cosmic rays (GCRs) in the very local interstellar medium (VLISM) as measured by the Low Energy Charged Particle (LECP) instrument on the Voyager 1 spacecraft. The LECP instrument includes a dual-ended solid-state detector particle telescope mechanically scanning through 360° across eight equally spaced angular sectors. As reported previously, LECP measurements showed a dramatic increase in GCR intensities for all sectors of the ≥211 MeV count rate (CH31) at the Voyager 1 heliopause (HP) crossing in 2012; however, since then the count rate data have demonstrated systematic episodes of intensity decrease for particles around 90° pitch angle. To shed light on the energy dependence of these GCR anisotropies over a wide range of energies, we use Voyager 1 LECP count rate and pulse height analyzer (PHA) data from ≥211 MeV channel together with lower-energy LECP channels. Our analysis shows that, while GCR anisotropies are present over a wide ...
Neutral hydrogen has been shown to greatly impact the plasma flow in the heliosphere and the loca... more Neutral hydrogen has been shown to greatly impact the plasma flow in the heliosphere and the location of the heliospheric boundaries. We present the results of the Solar Wind with Hydrogen Ion Exchange and Large-scale Dynamics (SHIELD) model, a new, self-consistent, kinetic–MHD model of the outer heliosphere within the Space Weather Modeling Framework. The charge exchange mean free path is on the order of the size of the heliosphere; therefore, the neutral atoms cannot be described as a fluid. The numerical code SHIELD couples the MHD solution for a single plasma fluid to the kinetic solution for neutral hydrogen atoms streaming through the system. The kinetic code is based on the Adaptive Mesh Particle Simulator, a Monte Carlo method for solving the Boltzmann equation. The numerical code SHIELD accurately predicts the increased filtration of interstellar neutrals into the heliosphere. In order to verify the correct implementation within the model, we compare the results of the nume...
We present an unprecedented comparison of ∼0.52–55 keV energetic neutral atom (ENA) heliosheath m... more We present an unprecedented comparison of ∼0.52–55 keV energetic neutral atom (ENA) heliosheath measurements, remotely sensed by the Interstellar Boundary Explorer (IBEX) mission and the Ion and Neutral Camera (INCA) on the Cassini mission, with modeled ENAs inferred from interstellar pickup protons that have been accelerated at the termination shock, using hybrid simulations, to assess the pickup ion energetics within the heliosheath. This is the first study to use hybrid simulations that are able to accurately model the acceleration of ions to tens of keV energies, which is essential in order to model ENA fluxes in the heliosheath, covering the full energy range observed by IBEX and CASSINI/INCA. The observed ENA intensities are an average value over the time period from 2009 to the end of 2012, along the Voyager 2 (V2) trajectory. The hybrid simulations upstream of the termination shock, where V2 crossed, are constrained by observations. We report an energy-dependent discrepancy ...
<p>The Voyager spacecraft are the first man-made objects to cross the termi... more <p>The Voyager spacecraft are the first man-made objects to cross the termination shock (TS), where the solar wind becomes sub-fast magnetosonic due to the interaction with the local interstellar medium. Voyager 2 observations revealed that classical single-fluid magnetohydrodynamic (MHD) or multispecies single-fluid MHD models are not sufficient to describe the microstructure of the TS and the observed nonlinear waves downstream the TS. Consequently, more sophisticated physical models, like multifluid, hybrid or fully kinetic solar wind models, are needed to capture nonlinear waves, dispersive shock waves, and ion-ion instabilities, where each ion species (and electrons) can move independently with their own bulk velocities, and the fluctuating parts of the ion velocities are often comparable to the mean velocity of the collective plasma fluid. The multifluid simulation of the TS by Zieger et al. [2015] shows a remarkable agreement with high-resolution Voyager 2 observations, reproducing not only the microstructure of the third TS crossing (TS3) but also the energy partitioning among thermal ions, pickup ions (PUI), and electrons across the shock. It was demonstrated that TS3 is a subcritical dispersive shock wave with low fast magnetosonic Mach number and high plasma ß. Here we present multifluid, hybrid, and particle-in-cell (PIC) simulations of the second TS crossing (TS2) by Voyager 2, which was somewhat stronger than TS3, with an observed compression ratio of 2.2. All three types of simulations confirm the dispersive nature of the TS in agreement with Voyager 2 observations. We conclude that TS2, just as TS3, is a subcritical dispersive shock wave with a soliton (overshoot) at the leading edge of the shock and a quasi-stationary nonlinear wave train downstream of the shock front. We compared the cross-shock electric field in the multifluid, hybrid, and PIC simulations and found a reasonable agreement. We show that the Hall electric field is dominating over the convective and ambipolar electric fields, which indicates that electrons play an important role in the shock transition. Finally, we demonstrate that the microstructure of the termination shock is controlled by dispersion rather than ion reflection, and only slightly affected by reflected solar wind ions in the hybrid and PIC simulations, which validates the multifluid model on fluid scale. The dispersive nature of the termination shock has important implications for the transition and acceleration of PUIs across the termination shock, which is revealed in the PUI distributions in our hybrid [Giacalone et al., 2021] and PIC simulations.</p>
International audienceSIHLA (Spatial/Spectral Imaging of Heliospheric Lyman Alpha pronounced as ‘... more International audienceSIHLA (Spatial/Spectral Imaging of Heliospheric Lyman Alpha pronounced as ‘Scylla’ [e.g. Homer, Odyssey, ~675-725 BCE] investigates fundamental physical processes that determine the interaction of the Sun with the interstellar medium (ISM); the Sun with the Earth; and the Sun with comets and their subsequent evolution. To accomplish these goals, SIHLA studies the shape of the heliosphere and maps the solar wind in 3D; characterizes changes in Earth’s extended upper atmosphere (the hydrogen ‘geocorona’); discovers new comets and tracks the composition changes of new and known ones as they pass near the Sun.SIHLA is a NASA Mission of Opportunity that has just completed its Phase A study (the Concept Study Report or CSR). At the time of the writing of this abstract NASA has not decided whether to fly this small satellite mission or its competitor (GLIDE: PI Prof. Lara Waldrop). SIHLA observes the ion-neutral interactions of hydrogen, the universe’s most abundant element, from the edge of the solar system to the Earth, to understand the fundamental properties that shaped our own home planet Earth and the heliosphere. From its L1 vantage point, well outside the Earth’s obscuring geocoronal hydrogen cloud, SIHLA maps the entire sky using a flight-proven, compact, far ultraviolet (FUV) hyperspectral imager with a Hydrogen Absorption Cell (HAC). The hyperspectral scanning imaging spectrograph (SIS) in combination with the spacecraft roll, creates 4 maps >87% of the sky each day, at essentially monochromatic lines over the entire FUV band (115 to 180nm) at every point in the scan. During half of these daily sky maps, the hydrogen absorption cell (HAC) provides a 0.001nm notch rejection filter for the H Lyman a. Using the HAC, SIHLA builds up the lineshape profile of the H Lyman a emissions over the course of a year. SIHLA’s SIS/HAC combination enables us to image the result of the ion-neutral interactions in the heliosheath, 100 AU away, in the lowest energy, highest density, part of the neutral atom spectrum – H atoms with energies below 10eV.The novel aspects of SIHLA are the scope of the science done within a MoO budget. The SIHLA projected costs were below the $75M cap with a 31.3% reserve for Phase B-D. The re-purposing of a spectrographic that was part of the DMSP SSUSI line (a copy was flown and NASA TIMED/GUVI and as NASA NEAR/NIS). Risk is extremely low in this Class-D mission with all major elements at least at TRL6 at this time.SIHLA has a high potential for discovery. We expect that we will 1) First detection of the hot H atoms produced directly from the ion-neutral interactions at the heliopause; 2) First detection of structures in Interplanetary Medium H emission, 3) First detection of response of the Earth’s extended (out to lunar orbit) geocorona to solar/geomagnetic drivers, 4) New UV-bright comets as they enter the inner solar system.SIHLA is a hyperspectral imager; at every point in the sky SIHLA obtains the entire FUV spectrum. This enables SIHLA to easily flag pixels contaminated by stars; obtain the spectrum of the Earth, viewed as an ‘exoplanet’ and observed the response of the exosphere and the thermosphere to solar/geomagnetic events; detect comets and determine their composition and how it varies at they enter and leave the inner solar system
The Sun blows out the solar wind which propagates into the interplanetary medium and forms the he... more The Sun blows out the solar wind which propagates into the interplanetary medium and forms the heliosphere about 100 AU across. The solar activity causes various types of time-dependent phenomena in the solar wind from long-lived corotating interaction regions to shorter on duration but more extreme events like coronal mass ejections. As these structures propagate outward from the Sun, they evolve and interact with each other and the ambient solar wind. Voyager 1 and 2 provided first unique in-situ measurements of these structures in the outer heliosphere. In particular, Voyager observations in the heliosheath, the outermost region of the heliosphere, showed highly variable plasma flows indicating effects of solar variations extending from the Sun to the heliosphere boundaries. Most surprisingly, Voyager 1 data shows shocks and pressure waves beyond the heliosphere in the interstellar medium. Important questions for the future Interstellar Probe mission are (1) how do the heliosphere boundaries respond to solar variations? (2) how do disturbances evolve in the heliosheath? and (3) how far does the Sun influence extend into the interstellar medium? This talk will review observations and recent modeling efforts demonstrating highly variable and dynamic nature of the global heliosphere in response to disturbances originated in the Sun's atmosphere.
We analyze the Cartwheel coronal mass ejectionʼs (CME; 2008 April 9) trajectory in the low corona... more We analyze the Cartwheel coronal mass ejectionʼs (CME; 2008 April 9) trajectory in the low corona with the ForeCAT model. This complex event presented a significant rotation in the low corona and a reversal in its original latitude direction. We successfully reproduce the observed CME's trajectory (latitude and longitude deflection) and speed. Through a 2 c test, we are able to constrain the CME's mass to (2.3−3.0)×10 14 g and the CME's initial shape. We are able to constrain the expansion of the CME as well: the angular width linearly increases until 2.1 R , and is constant afterward. In order to match the observed latitude, we include a non-radial initial speed of −42 km s −1. Despite allowing the CME to rotate in the model, the magnetic forces of the solar background are not able to reproduce the observed rotation. We suggest that the complex reversal in latitude and the significant rotation of the Cartwheel CME can be justified with an asymmetrical reconnection event that ejected the CME nonradially and also initiated its rotation.
Predicting the impact of coronal mass ejections (CMEs) and the southward component of their magne... more Predicting the impact of coronal mass ejections (CMEs) and the southward component of their magnetic field is one of the key goals of space weather forecasting. We present a new model, the ForeCAT In situ Data Observer (FIDO), for predicting the in situ magnetic field of CMEs. We first simulate a CME using ForeCAT, a model for CME deflection and rotation resulting from the background solar magnetic forces (Kay et al. 2015b). Using the CME position and orientation from ForeCAT, we then determine the passage of the CME over a simulated spacecraft. We model the CME's magnetic field using a force free flux rope and we determine the in situ magnetic profile at the synthetic spacecraft. We show that FIDO can reproduce the general behavior of four observed CMEs. FIDO results are very sensitive to the CME's position and orientation, and we show that the uncertainty in a CME's position and orientation from coronagraph images corresponds to a wide range of in situ magnitudes and even polarities. This small range of positions and orientations also includes CMEs that entirely miss the satellite. We show that two derived parameters (the normalized angular distance between the CME nose and satellite position and the angular difference between the CME tilt and the position angle of the satellite with respect to the CME nose) can be used to reliably determine whether an impact or miss occurs. We find that the same criteria separates the impacts and misses for cases representing all four observed CMEs.
Accurate space weather forecasting requires knowledge of the trajectory of coronal mass ejections... more Accurate space weather forecasting requires knowledge of the trajectory of coronal mass ejections (CMEs), including any deflections close to the Sun or through interplanetary space. Kay et al. (2013) introduced ForeCAT, a model of CME deflection resulting from the background solar magnetic field. For a magnetic field solution corresponding to Carrington Rotation (CR) 2029 (declining phase, April-May 2005), the majority of the CMEs deflected to the Heliospheric Current Sheet (HCS), the minimum in magnetic pressure on global scales. Most of the deflection occurred below 4 R. Here we extend ForeCAT to include a three dimensional description of the deflecting CME. We attempt to answer the following questions: a) Do all CMEs deflect to the magnetic minimum? and b) Does most deflection occur within the first few solar radii (4 R)? Results for solar minimum and declining phase CMEs show that not every CME deflects to the magnetic minimum and that the deflection is typically determined below 2 R. Slow, wide, low mass CMEs in declining phase solar backgrounds with strong magnetic field and magnetic gradients exhibit the largest deflections. Local gradients related to active regions tend to cause the largest deviations from the deflection predicted by global magnetic gradients, but variations can also be seen for CMEs in the quiet sun regions of the declining phase CR. We show the torques due to differential forces along the CME can cause rotation about the CME's toroidal axis.
The acceleration of protons and electrons to high (sometimes GeV/nucleon) energies by solar pheno... more The acceleration of protons and electrons to high (sometimes GeV/nucleon) energies by solar phenomena is a key component of space weather. These solar energetic particle (SEP) events can damage spacecraft and communications, as well present radiation hazards to humans. In depth particle acceleration simulations have been performed for idealized magnetic fields for diffusive acceleration and particle propagation, and at the same time the quality of MHD simulations of CMEs has improved significantly. However, to date these two pieces of the same puzzle have remained largely decoupled. Such structures may contain not just a shock, but also sizable sheath and pileup compression regions behind it, and may vary considerably with longitude and latitude based on the underlying coronal conditions. In this work, we have coupled results from a detailed global 3D MHD time-dependent CME simulation to a global proton acceleration and transport model, in order to study time-dependent effects of SEP acceleration between 1.8 and 8 solar radii in the 2005 13 May CME. We find that the source population is accelerated to at least 100 MeV, with distributions enhanced up to six orders of magnitude. Acceleration efficiency varies strongly along field lines probing different regions of the dynamically evolving CME, whose dynamics is influenced by the large-scale coronal magnetic field structure. We observe strong acceleration in sheath regions immediately behind the shock.
The effects of the highly damped modes in the energy and reaction rates in a plasma are discussed... more The effects of the highly damped modes in the energy and reaction rates in a plasma are discussed. These modes, with wave numbers k≫kD, even being only weakly excited, with less than kBT per mode, make a significant contribution to the energy and screening in a plasma. When the de Broglie wavelength is much less than the distance of closest approach of thermal electrons, a classical analysis of the plasma can be made. It is assumed, in the classical analysis, with ℏ→0, that the energy of the fluctuations ℏω≪kBT. Using the fluctuation-dissipation theorem, the spectra of fluctuations with ℏ≠0 is appreciably decreased. The decrease is mainly for the highly damped modes at high frequencies (∼0.5–3kBT). Reaction rates are enhanced in a plasma due to the screening of the reacting ions. This is taken into account by the Salpeter factor, which assumes slow motion for the ions. The implication of including the highly damped modes (with ℏ≠0) in the nuclear reaction rates in a plasma is discus...
Preface (do read it!) vii textbook is intended for students in physical sciences in later years o... more Preface (do read it!) vii textbook is intended for students in physical sciences in later years of their university training and for beginning graduate students in fields of solar, stellar, (exo-)planetary, and planetary-system sciences. The lecturers at the Summer Schools developed a series of five volumes on Heliophysics (four published in printed form by Cambridge University Press, and one online at the Heliophysics Summer School website) contain in total 1919 pages of text and figures, in 56 topical chapters (see Table 2): Vol. I: Preface ix Table 2: (Continued from the previous page) Chapters and their authors in the Heliophysics book series sorted by theme, not showing introductory chapters. Astro-/heliospheres, interstellar environment, and galactic cosmic rays Preface xi 'Space weather' is the term used to describe an ensemble of changing conditions in the vicinity of Earth and, by extension, any other body in a planetary system, typically occurring on time scales up to a few days. Often, the term is implicitly taken to refer also to the conditions from the solar dynamo outward to the furthest reaches of the heliosphere that are involved in space weather around Earth. Much of what is described in this volume therefore concerns space weather: heliophysics contains the science of space weather. However, where the science of space weather focuses on phenomena that can impact society through short-term variability, this text takes the long view by putting the spotlight on evolutionary changes in the states of star-planet systems. As such, this text does describe the foundational processes of space weather, but is not concerned with the impacts of space weather on technological infrastructure, does not address the challenges of forecasting space weather, and skips coupling mechanisms such as ground-induced currents (GICs) associated with geomagnetic disturbances and ground-level enhancements (GLEs) of energetic particles. This choice of focus is motivated by my desire to introduce the reader to the science of heliophysics from the perspective of habitability on time scales on which stellar and planetary atmospheres change, and indeed up to time scales on which stars and their planets evolve, and to do that in a relatively compact form. As you go through this text, you should realize that many of the processes described here have consequences for society, ranging from system design choices to potentially substantial failures in one or more of the infrastructures that we have come to rely on, including continuous and reliable electric power, positional information, and means of communication. Interruptions in quality or availability of any of these can have substantial consequences that may be costly or life-threatening on scales that may involve single individuals or populations of millions. Descriptions of the impacts of space weather can be found in the Heliophysics books in
It is expected that as the Sun travels through the interstellar medium (ISM), there will be diffe... more It is expected that as the Sun travels through the interstellar medium (ISM), there will be different filtration of Galactic Cosmic Rays (GCR) that affect Earth. The effect of GCR on Earth's atmosphere and climate is still uncertain. Although the interaction with molecular clouds was previously considered, the terrestrial impact of compact cold clouds was neglected. There is overwhelming geological evidence from 60 Fe and 244 Pu isotopes that Earth was in direct contact with the ISM 2-3 million years ago, and the local ISM is home to several nearby cold clouds. Here we show, with a state-of the art simulation that incorporate all the current knowledge about the heliosphere that if the solar system passed through a cloud such as Local Leo Cold Cloud, then the heliosphere which protects the solar system from interstellar particles, must have shrunk to a scale smaller than the Earth's orbit around the Sun (0.22AU). Using a magnetohydrodynamic simulation that includes charge exchange between neutral atoms and ions, we show that during the heliosphere shrinkage, Earth was exposed to a neutral hydrogen density of up to 3000cm-3. This could have had drastic effects on Earth's climate and potentially on human evolution at that time, as suggested by existing data.
We report on the energy dependence of Galactic cosmic rays (GCRs) in the very local interstellar ... more We report on the energy dependence of Galactic cosmic rays (GCRs) in the very local interstellar medium (VLISM) as measured by the Low Energy Charged Particle (LECP) instrument on the Voyager 1 spacecraft. The LECP instrument includes a dual-ended solid-state detector particle telescope mechanically scanning through 360° across eight equally spaced angular sectors. As reported previously, LECP measurements showed a dramatic increase in GCR intensities for all sectors of the ≥211 MeV count rate (CH31) at the Voyager 1 heliopause (HP) crossing in 2012; however, since then the count rate data have demonstrated systematic episodes of intensity decrease for particles around 90° pitch angle. To shed light on the energy dependence of these GCR anisotropies over a wide range of energies, we use Voyager 1 LECP count rate and pulse height analyzer (PHA) data from ≥211 MeV channel together with lower-energy LECP channels. Our analysis shows that, while GCR anisotropies are present over a wide ...
Neutral hydrogen has been shown to greatly impact the plasma flow in the heliosphere and the loca... more Neutral hydrogen has been shown to greatly impact the plasma flow in the heliosphere and the location of the heliospheric boundaries. We present the results of the Solar Wind with Hydrogen Ion Exchange and Large-scale Dynamics (SHIELD) model, a new, self-consistent, kinetic–MHD model of the outer heliosphere within the Space Weather Modeling Framework. The charge exchange mean free path is on the order of the size of the heliosphere; therefore, the neutral atoms cannot be described as a fluid. The numerical code SHIELD couples the MHD solution for a single plasma fluid to the kinetic solution for neutral hydrogen atoms streaming through the system. The kinetic code is based on the Adaptive Mesh Particle Simulator, a Monte Carlo method for solving the Boltzmann equation. The numerical code SHIELD accurately predicts the increased filtration of interstellar neutrals into the heliosphere. In order to verify the correct implementation within the model, we compare the results of the nume...
We present an unprecedented comparison of ∼0.52–55 keV energetic neutral atom (ENA) heliosheath m... more We present an unprecedented comparison of ∼0.52–55 keV energetic neutral atom (ENA) heliosheath measurements, remotely sensed by the Interstellar Boundary Explorer (IBEX) mission and the Ion and Neutral Camera (INCA) on the Cassini mission, with modeled ENAs inferred from interstellar pickup protons that have been accelerated at the termination shock, using hybrid simulations, to assess the pickup ion energetics within the heliosheath. This is the first study to use hybrid simulations that are able to accurately model the acceleration of ions to tens of keV energies, which is essential in order to model ENA fluxes in the heliosheath, covering the full energy range observed by IBEX and CASSINI/INCA. The observed ENA intensities are an average value over the time period from 2009 to the end of 2012, along the Voyager 2 (V2) trajectory. The hybrid simulations upstream of the termination shock, where V2 crossed, are constrained by observations. We report an energy-dependent discrepancy ...
<p>The Voyager spacecraft are the first man-made objects to cross the termi... more <p>The Voyager spacecraft are the first man-made objects to cross the termination shock (TS), where the solar wind becomes sub-fast magnetosonic due to the interaction with the local interstellar medium. Voyager 2 observations revealed that classical single-fluid magnetohydrodynamic (MHD) or multispecies single-fluid MHD models are not sufficient to describe the microstructure of the TS and the observed nonlinear waves downstream the TS. Consequently, more sophisticated physical models, like multifluid, hybrid or fully kinetic solar wind models, are needed to capture nonlinear waves, dispersive shock waves, and ion-ion instabilities, where each ion species (and electrons) can move independently with their own bulk velocities, and the fluctuating parts of the ion velocities are often comparable to the mean velocity of the collective plasma fluid. The multifluid simulation of the TS by Zieger et al. [2015] shows a remarkable agreement with high-resolution Voyager 2 observations, reproducing not only the microstructure of the third TS crossing (TS3) but also the energy partitioning among thermal ions, pickup ions (PUI), and electrons across the shock. It was demonstrated that TS3 is a subcritical dispersive shock wave with low fast magnetosonic Mach number and high plasma ß. Here we present multifluid, hybrid, and particle-in-cell (PIC) simulations of the second TS crossing (TS2) by Voyager 2, which was somewhat stronger than TS3, with an observed compression ratio of 2.2. All three types of simulations confirm the dispersive nature of the TS in agreement with Voyager 2 observations. We conclude that TS2, just as TS3, is a subcritical dispersive shock wave with a soliton (overshoot) at the leading edge of the shock and a quasi-stationary nonlinear wave train downstream of the shock front. We compared the cross-shock electric field in the multifluid, hybrid, and PIC simulations and found a reasonable agreement. We show that the Hall electric field is dominating over the convective and ambipolar electric fields, which indicates that electrons play an important role in the shock transition. Finally, we demonstrate that the microstructure of the termination shock is controlled by dispersion rather than ion reflection, and only slightly affected by reflected solar wind ions in the hybrid and PIC simulations, which validates the multifluid model on fluid scale. The dispersive nature of the termination shock has important implications for the transition and acceleration of PUIs across the termination shock, which is revealed in the PUI distributions in our hybrid [Giacalone et al., 2021] and PIC simulations.</p>
International audienceSIHLA (Spatial/Spectral Imaging of Heliospheric Lyman Alpha pronounced as ‘... more International audienceSIHLA (Spatial/Spectral Imaging of Heliospheric Lyman Alpha pronounced as ‘Scylla’ [e.g. Homer, Odyssey, ~675-725 BCE] investigates fundamental physical processes that determine the interaction of the Sun with the interstellar medium (ISM); the Sun with the Earth; and the Sun with comets and their subsequent evolution. To accomplish these goals, SIHLA studies the shape of the heliosphere and maps the solar wind in 3D; characterizes changes in Earth’s extended upper atmosphere (the hydrogen ‘geocorona’); discovers new comets and tracks the composition changes of new and known ones as they pass near the Sun.SIHLA is a NASA Mission of Opportunity that has just completed its Phase A study (the Concept Study Report or CSR). At the time of the writing of this abstract NASA has not decided whether to fly this small satellite mission or its competitor (GLIDE: PI Prof. Lara Waldrop). SIHLA observes the ion-neutral interactions of hydrogen, the universe’s most abundant element, from the edge of the solar system to the Earth, to understand the fundamental properties that shaped our own home planet Earth and the heliosphere. From its L1 vantage point, well outside the Earth’s obscuring geocoronal hydrogen cloud, SIHLA maps the entire sky using a flight-proven, compact, far ultraviolet (FUV) hyperspectral imager with a Hydrogen Absorption Cell (HAC). The hyperspectral scanning imaging spectrograph (SIS) in combination with the spacecraft roll, creates 4 maps >87% of the sky each day, at essentially monochromatic lines over the entire FUV band (115 to 180nm) at every point in the scan. During half of these daily sky maps, the hydrogen absorption cell (HAC) provides a 0.001nm notch rejection filter for the H Lyman a. Using the HAC, SIHLA builds up the lineshape profile of the H Lyman a emissions over the course of a year. SIHLA’s SIS/HAC combination enables us to image the result of the ion-neutral interactions in the heliosheath, 100 AU away, in the lowest energy, highest density, part of the neutral atom spectrum – H atoms with energies below 10eV.The novel aspects of SIHLA are the scope of the science done within a MoO budget. The SIHLA projected costs were below the $75M cap with a 31.3% reserve for Phase B-D. The re-purposing of a spectrographic that was part of the DMSP SSUSI line (a copy was flown and NASA TIMED/GUVI and as NASA NEAR/NIS). Risk is extremely low in this Class-D mission with all major elements at least at TRL6 at this time.SIHLA has a high potential for discovery. We expect that we will 1) First detection of the hot H atoms produced directly from the ion-neutral interactions at the heliopause; 2) First detection of structures in Interplanetary Medium H emission, 3) First detection of response of the Earth’s extended (out to lunar orbit) geocorona to solar/geomagnetic drivers, 4) New UV-bright comets as they enter the inner solar system.SIHLA is a hyperspectral imager; at every point in the sky SIHLA obtains the entire FUV spectrum. This enables SIHLA to easily flag pixels contaminated by stars; obtain the spectrum of the Earth, viewed as an ‘exoplanet’ and observed the response of the exosphere and the thermosphere to solar/geomagnetic events; detect comets and determine their composition and how it varies at they enter and leave the inner solar system
The Sun blows out the solar wind which propagates into the interplanetary medium and forms the he... more The Sun blows out the solar wind which propagates into the interplanetary medium and forms the heliosphere about 100 AU across. The solar activity causes various types of time-dependent phenomena in the solar wind from long-lived corotating interaction regions to shorter on duration but more extreme events like coronal mass ejections. As these structures propagate outward from the Sun, they evolve and interact with each other and the ambient solar wind. Voyager 1 and 2 provided first unique in-situ measurements of these structures in the outer heliosphere. In particular, Voyager observations in the heliosheath, the outermost region of the heliosphere, showed highly variable plasma flows indicating effects of solar variations extending from the Sun to the heliosphere boundaries. Most surprisingly, Voyager 1 data shows shocks and pressure waves beyond the heliosphere in the interstellar medium. Important questions for the future Interstellar Probe mission are (1) how do the heliosphere boundaries respond to solar variations? (2) how do disturbances evolve in the heliosheath? and (3) how far does the Sun influence extend into the interstellar medium? This talk will review observations and recent modeling efforts demonstrating highly variable and dynamic nature of the global heliosphere in response to disturbances originated in the Sun's atmosphere.
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Papers by Merav Opher