Solar energetic particles (SEPs) affect the solar-terrestrial space environment and become a very important aspect in space weather research. In this work, we numerically investigate the transport processes of SEPs in three-dimensional interplanetary magnetic field, with an emphasis on the longitudinal distribution of SEPs in the heliosphere. We confirm our previous finding that there exists an east-west longitudinal asymmetry in the SEP intensities, i.e., with the same longitude separations between the solar source centers and the magnetic footpoint of the observer, the fluxes of SEP events originating from solar sources located on the eastern side of the nominal magnetic footpoint of the observer are systematically larger than those of the SEP events originating from sources located on the western side. We discuss the formation mechanism of this phenomenon, and conclude that the longitudinally asymmetric distribution of SEPs results from the east-west azimuthal asymmetry in the topology of the heliospheric magnetic field as well as the effects of perpendicular diffusion on the transport of SEPs in the heliosphere. Our results will be valuable to understanding Sun-Earth relations and useful for space weather forecasting.
The turbulence and spatial nonuniformity of the guide magnetic field cause two competitive effects, namely, the scattering effect and the adiabatic focusing effect, respectively. In this work, we numerically solve the five-dimensional Fokker-Planck transport equation to investigate the radial evolutions of these important effects undergone by the solar energetic particles (SEPs) propagating through interplanetary space. We analyze the interplay process between the scattering and adiabatic focusing effects in the context of three-dimensional propagation, with special attention to the scenario o…
The concept of energetic particle reservoirs, essentially based on the assumption of the presence of outer reflecting boundaries/magnetic mirrors or diffusion barriers (deterministic) rather than on the effect of particle diffusive propagation (stochastic) in magnetic turbulence, has been used for decades to describe the space-extended decay phases of energetic particle events within the fields of space physics, solar physics, and plasma physics. Using five-dimensional time-dependent Fokker-Planck transport equation simulations, in this work we demonstrate that the so-called particle reservoir…
Observations of energetic neutral atoms (ENAs) are a fruitful tool for remote diagnosis of the plasma in the heliosphere and its vicinity. So far, instruments detecting ENAs from the heliosphere were configured for observations of hydrogen atoms. Here, we estimate emissions of ENAs of the heavy chemical elements helium, oxygen, nitrogen, and neon. A large portion of the heliospheric ENAs is created in the inner heliosheath from neutralized interstellar pick-up ions (PUIs). We modeled this process and calculated full-sky intensities of ENAs for energies 0.2-130 keV/nuc. We found that the larges…
A recent study by Opher et al. (2015) suggested the heliosphere has a "croissant" shape, where the heliosheath plasma is confined by the toroidal solar magnetic field. The "croissant" heliosphere is in contrast to the classically accepted view of a comet-like tail. We investigate the effect of the "croissant" heliosphere model on energetic neutral atom (ENA) maps. Regardless of the existence of a split tail, the confinement of the heliosheath plasma should appear in ENA maps. ENA maps from the Interstellar Boundary Explorer (IBEX) have shown two high latitude lobes with excess ENA flux at high…
Parallel Diffusion Coefficient of Energetic Charged Particles in the Inner Heliosphere from the Turbulent Magnetic Fields Measured by Parker Solar Probe
Observations of the energetic neutral atoms (ENAs) of heliospheric origin by IBEX differ from expectations based on heliospheric models. It was proposed that the structure of the heliosphere may be similar to the "two-stream" model derived in 1961 by Parker for the case of strong interstellar magnetic field. Using MHD simulations, we examine possible structure of the heliosphere for a wide range of interstellar magnetic field strengths, with different choices of interstellar medium and solar wind parameters. For the model heliospheres, we calculate the fluxes of ENAs created in the inner helio…
Solar flare accelerated electrons escaping into the interplanetary space and seen as type III solar radio bursts are often detected near the Earth. Using numerical simulations we consider the evolution of energetic electron spectrum in the inner heliosphere and near the Earth. The role of Langmuir wave generation, heliospheric plasma density fluctuations, and expansion of magnetic field lines on the electron peak flux and fluence spectra is studied to predict the electron properties as could be observed by Solar Orbiter and Solar Probe Plus. Considering various energy loss mechanisms we show t…
We propose a model for interpreting highly variable ion composition ratios in solar energetic particles (SEP) events recently observed by Parker Solar Probe (PSP) at $0.3 - 0.45$ astronomical unit. We use numerical simulations to calculate SEP propagation in a turbulent interplanetary magnetic field with a Kolmogorov power spectrum from large scale down to the gyration scale of energetic particles. We show that when the source regions of different species are offset by a distance comparable to the size of the source regions, the observed energetic particle composition He/H can be strongly vari…
Several concepts for heliospheric missions operating at heliocentric distances far beyond Earth orbit are currently investigated by the scientific community. The mission concept of the Interstellar Probe (McNutt et al. 2018), e.g., aims at reaching a distance of 1000 au away from the Sun within this century. This would allow the coming generation to obtain a global view of our heliosphere from an outside vantage point by measuring the Energetic Neutral Atoms (ENAs) originating from the various plasma regions. It would also allow for direct sampling of unperturbed interstellar medium, and for m…
Observations of energetic neutral atoms (ENAs) allow for remote sensing of plasma properties in distant regions of the heliosphere. So far, most of the observations have concerned only hydrogen atoms. In this paper, we present perspectives for observations of helium energetic neutral atoms (He ENAs). We calculated the expected intensities of He ENAs created by the neutralization of helium ions in the inner heliosheath and through the secondary ENA mechanism in the outer heliosheath. We found that the dominant source region for He ENAs is the inner heliosheath. The obtained magnitudes of intens…
Large solar proton events (SPEs) affect the solar-terrestrial space environment and become a very important aspect in space weather research. In this work, we statistically investigate 78 solar proton events of 1996-2011 and find that there exists a longitudinally asymmetric distribution of flare sources of the solar proton events observed near 1 AU, namely, with the same longitude separation between magnetic field line footpoint of observer and flare sources, the number of the solar proton events originating from sources located at eastern side of the nominal magnetic footpoint of observer is…
Interstellar neutral hydrogen (ISN H) gas penetrates freely the heliopause. Inside the inner heliosheath, the charge-exchange interaction of this gas with the shocked solar wind and pickup ions creates energetic neutral atoms (ENAs). ISN H is strongly depleted inside the termination shock but a fraction reaches the Earth's orbit. In these regions of the heliosphere, ISN H is the source population for interstellar pickup ions and for the heliospheric backscatter glow. The Globally Distributed Flux (GDF) of ENAs created in the inner heliosheath has been sampled directly by Interstellar Boundary …
Signatures of Reconnection and a Split Heliospheric Tail in High-Energy Energetic Neutral Atoms
Boston University（波士顿大学）；University of Maryland, College Park（马里兰大学帕克分校）；Academy of Athens（雅典学院）；University of Michigan（密歇根大学）；University of Arizona（亚利桑那大学）；Southwest Research Institute（西南研究院）；Johns Hopkins University（约翰斯·霍普金斯大学）；HSE University（俄罗斯高等经济大学）；Lomonosov Moscow State University（莫斯科国立大学）；University of Alabama in Huntsville（阿拉巴马大学亨茨维尔分校）
Solar Orbiter strives to unveil how the Sun controls and shapes the heliosphere and fills it with energetic particle radiation. To this end, its Energetic Particle Detector (EPD) has now been in operation, providing excellent data, for just over a year. EPD measures suprathermal and energetic particles in the energy range from a few keV up to (near-) relativistic energies (few MeV for electrons and about 500 MeV/nuc for ions). We present an overview of the initial results from the first year of operations and we provide a first assessment of issues and limitations. During this first year of op…
The Interstellar Boundary Explorer (IBEX) spacecraft is providing the first all-sky maps of the energetic neutral atoms (ENAs) produced by charge-exchange between interstellar neutral \HI\ atoms and heliospheric solar wind and pickup ions in the heliosphere boundary regions. The 'edge' of the interstellar cloud presently surrounding the heliosphere extends less than 0.1 pc in the upwind direction, terminating at an unknown distance, indicating that the outer boundary conditions of the heliosphere could change during the lifetime of the IBEX satellite. Using reasonable values for future outer h…
Solar Electron Beam -- Langmuir Wave Interactions and How They Modify Solar Electron Beam Spectra: Solar Orbiter Observations of a Match Made in the Heliosphere
Solar Orbiter观测表明，太阳电子束与朗缪尔波的共振波粒相互作用导致约10和50keV处电子能谱出现特定拐点特征，该结论获数值模拟支持且可推广至更广日心距。
Understanding the time-dependent relationship between the Sun's variability and cosmic rays (GCR) is essential for developing predictive models of energetic radiation in space. When traveling inside the heliosphere, GCRs are affected by magnetic turbulence and solar wind disturbances which result in the so-called solar modulation effect. To investigate this phenomenon, we have performed a data-driven analysis of the temporal dependence of the GCR flux over the solar cycle. With a global statistical inference of GCR data collected in space by AMS-02 and PAMELA on monthly basis, we have determin…
A large data set of 78 solar proton events observed near the Earth's orbit during 1996-2011 is investigated. An East-West longitudinal (azimuthal) asymmetry is found to exist in the distribution of flare sources of solar proton events. With the same longitudinal separation between the flare sources and the magnetic field line footpoint of observer, the number of the solar proton events originating from solar sources located on the eastern side of the nominal magnetic footpoint of observer is larger than the number of the solar proton events from solar sources located on the western side. We em…
Tracking a solar energetic eruption and associated energetic particles from Sun to spacecraft
University of Turku（图尔库大学）；Turku Collegium for Science, Medicine and Technology, University of Turku（图尔库科学与技术医学学院，图尔库大学）；University of Graz（格拉茨大学）；Leibniz Institute for Astrophysics Potsdam (AIP)（波茨坦莱布尼茨天体物理研究所 (AIP)）；LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS（拉格朗日天体物理学实验室，巴黎天文台，巴黎文理研究大学，索邦大学，巴黎西岱大学，塞吉-蓬图瓦兹大学，法国国家科学研究中心）
Solar Orbiter is a joint ESA-NASA mission planed for launch in October 2018. The science payload includes remote-sensing and in-situ instrumentation designed with the primary goal of understanding how the Sun creates and controls the heliosphere. The spacecraft will follow an elliptical orbit around the Sun, with perihelion as close as 0.28 AU. During the late orbit phase the orbital plane will reach inclinations above 30 degrees, allowing direct observations of the solar polar regions. The Energetic Particle Detector (EPD) is an instrument suite consisting of several sensors measuring electro…
Galactic Cosmic Rays and Solar Energetic Particles in Cis-Lunar Space: Need for contextual energetic particle measurements at Earth and supporting distributed observations
Observations from Parker Solar Probe's first five orbits are used to investigate the helioradial evolution of probability density functions (PDFs) of fluctuations of magnetic field components, between \(\sim 28\) - 200 \(\rs\). Transformation of the magnetic field vector to a local mean-field coordinate system permits examination of anisotropy relative to the mean magnetic field direction. Attention is given to effects of averaging-interval size. It is found that PDFs of the perpendicular fluctuations are well approximated by a Gaussian function, with the parallel fluctuations less so: kurtose…
Aims. A model of heliosheath density and energy spectra of alpha-particles and He+ ions carried by the solar wind is developed. Neutralization of heliosheath He+ ions, mainly by charge exchange (CX) with neutral interstellar H and He atoms, gives rise to ~0.2 - ~100 keV fluxes of energetic neutral He atoms (He ENA). Such fluxes, if observed, would give information about plasmas in the heliosheath and heliospheric tail. Methods. Helium ions crossing the termination shock (TS) constitute suprathermal (test) particles convected by (locally also diffusing through) hydrodynamically calculated backg…
In the outer heliosphere, beyond the solar wind termination shock, it is expected that the warped heliospheric current sheet forms a region of closely-packed, multiple, thin current sheets. Such a system may be subject to the ion-kinetic tearing instability, and hence generate magnetic islands and hot populations of ions associated with magnetic reconnection. Reconnection processes in this environment have important implications for local particle transport, and for particle acceleration at reconnection sites and in turbulence. We study this complex environment by means of three-dimensional hy…
Recent modelling of solar energetic particles (SEPs) propagation through the heliospheric turbulence, also discussed in this workshop, has investigated the role of the pitch-angle scattering and the perpendicular transport in spreading particles in heliolongitude, as shown by multi-spacecraft measurements (STEREO A/B, ACE, SOHO, etc.) at 1 AU in various energy ranges. In some events the first-order pitch-angle anisotropy of the particles distribution is not-negligible. We calculate the average perpendicular displacement due to the gradient/curvature drift in an inhomogeneous turbulence account…
The shape of the solar wind bubble within the interstellar medium, the so-called heliosphere, has been explored over six decades. As the Sun moves through the surrounding partially-ionized medium, neutral hydrogen atoms penetrate the heliosphere, and through charge-exchange with the supersonic solar wind, create a population of hot pick-up ions (PUIs). The Termination Shock (TS) crossing by Voyager 2 (V2) data demonstrated that the heliosheath (HS) (the region of shocked solar wind) pressure is dominated by suprathermal particles. Here we use a novel magnetohydrodynamic model that treats the f…
Understanding the outer heliospheric interface is a major challenge, especially in the light of recent observations by the IBEX and Voyager missions. We present further details on a new required theoretical correction that has been identified as substantial in a recent paper, the so-called source depletion effect. These results complement and expand earlier calculations of transit-time delays by presenting global skymaps of Energetic Neutral Atoms (ENAs) calculated with the depletion correction, comparing them with skymaps calculated without these corrections. Our results demonstrate that the …
We propose that magnetic reconnection at the heliopause only occurs where the interstellar magnetic field points nearly anti-parallel to the heliospheric field. By using large-scale magnetohydrodynamic (MHD) simulations of the heliosphere to provide the initial conditions for kinetic simulations of heliopause (HP) reconnection we show that the energetic pickup ions downstream from the solar wind termination shock induce large diamagnetic drifts in the reconnecting plasma and stabilize non-anti-parallel reconnection. With this constraint the MHD simulations can show where HP reconnection most l…
The solar wind (SW) and local interstellar medium (LISM) are turbulent media. Their interaction is governed by complex physical processes and creates heliospheric regions with significantly different properties in terms of particle populations, bulk flow and turbulence. Our knowledge of the solar wind turbulence \nature and dynamics mostly relies on near-Earth and near-Sun observations, and has been increasingly improving in recent years due to the availability of a wealth of space missions, including multi-spacecraft missions. In contrast, the properties of turbulence in the outer heliosphere…
Ensemble Modeling of the Solar Wind Flow with Boundary Conditions Governed by Synchronic Photospheric Magnetograms. I. Multi-point Validation in the Inner Heliosphere
The pickup protons originate as a result of the ionization of hydrogen atoms in the supersonic solar wind, forming the suprathermal component of protons in the heliosphere. While picked by the heliospheric magnetic field and convected into the heliosheath, the pickup protons may suffer the stochastic acceleration by the solar wind turbulence in the region from the Sun up to the heliospheric termination shock, where they can also experience the shock-drift acceleration or the reflection from the cross-shock potential. These processes create a high-energy "tail" in the pickup ion energy distribu…
Global models of the heliosphere are critical tools used in the interpretation of heliospheric observations. There are several three-dimensional magnetohydrodynamic (MHD) heliospheric models that rely on different strategies and assumptions. Until now only one paper has compared global heliosphere models, but without magnetic field effects. We compare the results of two different MHD models, the BU and Moscow models. Both models use identical boundary conditions to compare how different numerical approaches and physical assumptions contribute to the heliospheric solution. Based on the differen…
The injection, propagation and arrival of solar energetic particles (SEPs) during eruptive solar events is an important and current research topic of heliospheric physics. During the largest solar events, particles may have energies up to a few GeVs and sometimes even trigger ground-level enhancements (GLEs) at Earth. We study the first GLE-event of solar cycle 24, from 17th May 2012, using data from multiple spacecraft (SOHO, GOES, MSL, STEREO-A, STEREO-B and MESSENGER). These spacecraft are located throughout the inner heliosphere, at heliocentric distances between 0.34 and 1.5 astronomical …
The Interstellar Boundary Explorer (IBEX) has now operated in space for 7 years and returned nearly continuous observations that have led to scientific discoveries and reshaped our entire understanding of the outer heliosphere and its interaction with the local interstellar medium. Here we extend prior work, adding the 2014-2015 data for the first time, and examine, validate, initially analyze, and provide a complete 7-year set of Energetic Neutral Atom (ENA) observations from ~0.1 to 6 keV. The data, maps, and documentation provided here represent the 10th major release of IBEX data and inclu…
The aim of this study is to generate maps of the hard X-ray emission produced by energetic electrons in a solar flare and compare them with observations. The ultimate goal is to test the viability of the combined MHD/test-particle approach for data-driven modelling of active events in the solar corona and their impact on the heliosphere. Based on an MHD model of X-class solar flare observed on the 8th of September 2017, we calculate trajectories of a large number of electrons and protons using the relativistic guiding-centre approach. Using the obtained particle trajectories, we deduce the spa…
We study the solar energetic particle (SEP) event associated with the 2012 July 23 extreme solar storm, for which STEREO and the spacecraft at L1 provide multi-point remote sensing and in situ observations. The extreme solar storm, with a superfast shock and extremely enhanced ejecta magnetic fields observed near 1 AU at STEREO A, was caused by the combination of successive coronal mass ejections (CMEs). Meanwhile, energetic particles were observed by STEREO and near-Earth spacecraft such as ACE and SOHO, suggestive of a wide longitudinal spread of the particles at 1 AU. Combining the SEP obse…
Evolution and Impact of Switchbacks Throughout the Heliosphere
Space Sciences Laboratory, University of California, Berkeley（加州大学伯克利分校空间科学实验室）；Department of Physics, Auburn University（奥本大学物理系）；Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles（加州大学洛杉矶分校地球、行星与空间科学系）；Department of Physics, The University of Texas at Austin（德克萨斯大学奥斯汀分校物理系）；Astronomy and Space Physics Department, National Taras Shevchenko University of Kyiv（基辅国立塔拉斯舍甫琴科大学天文与空间物理系）；Department of Climate and Space Sciences and Engineering, University of Michigan（密歇根大学气候与空间科学与工程系）；Center for Astrophysics, Harvard & Smithsonian（哈佛-史密森尼天体物理中心）；LPC2E, CNRS/University of Orléans/CNES（CNRS/奥尔良大学/CNES LPC2E）；Southwest Research Institute（西南研究院）；University of Maryland College Park（马里兰大学帕克分校）；Department of Physics, Imperial College London（伦敦帝国理工学院物理系）；Institute for Plasma Science and Technology (ISTP), CNR（CNR等离子体科学与技术研究所）；Max Planck Institute for Solar System Research（马克斯·普朗克太阳系统研究所）
Power-law distributions are a near universal feature of energetic particle spectra in the heliosphere. Anomalous Cosmic Rays (ACRs), super-Alfvénic ions in the solar wind and the hardest energetic electron spectra in flares all have energy fluxes with power-laws that depend on energy $E$ approximately as $E^{-1.5}$. We present a new model of particle acceleration in systems with a bath of merging magnetic islands that self-consistently describes the development of velocity-space anisotropy parallel and perpendicular to the local magnetic field and includes the self-consistent feedback of press…
We investigate the solar phenomena associated with the origin of the solar energetic particle (SEP) event observed on 2013 April 11 by a number of spacecraft distributed in the inner heliosphere over a broad range of heliolongitudes. We use Extreme UltraViolet (EUV) and white-light coronagraph observations from the Solar Dynamics Observatory (SDO), the SOlar and Heliospheric Observatory (SOHO) and the twin Solar TErrestrial RElations Observatory spacecraft (STEREO-A and STEREO-B) to determine the angular extent of the EUV wave and coronal mass ejection (CME) associated with the origin of the S…
Solar Energetic Particles (SEPs), a major component of space weather, propagate through the interplanetary medium strongly guided by the Interplanetary Magnetic Field (IMF). In this work, we analyse the implications a flat Heliospheric Current Sheet (HCS) has on proton propagation from SEP release sites to the Earth. We simulate proton propagation by integrating fully 3-D trajectories near an analytically defined flat current sheet, collecting comprehensive statistics into histograms, fluence maps and virtual observer time profiles within an energy range of 1--800 MeV. We show that protons exp…
Energetic Particle Acceleration and Transport: Interplanetary Coronal Mass Ejections and Shocks
National Observatory of Athens, IAASARS（雅典国家天文台）；California Institute of Technology（加州理工学院）；University of Arizona（亚利桑那大学）；Department of Astrophysical Sciences, Princeton University（普林斯顿大学天体物理科学系）；European Space Agency (ESA), European Space Astronomy Centre (ESAC)（欧洲空间局（ESA），欧洲空间天文中心（ESAC））；Universidad de Alcalá, Space Research Group (SRG-UAH)（阿尔卡拉大学，空间研究小组（SRG-UAH））；The Johns Hopkins University, Applied Physics Laboratory（约翰斯·霍普金斯大学，应用物理实验室）；Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel（基尔大学实验与应用物理研究所）；National Key Laboratory of Deep Space Exploration/School of Earth and Space Sciences, University of Technology and Science of China（中国科学技术大学深空探测全国重点实验室/地球与空间科学学院）；Institute of Physics, University of Graz（格拉茨大学物理研究所）；NASA, Goddard Space Flight Center（美国国家航空航天局戈达德太空飞行中心）；Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室）；University of New Hampshire（新罕布什尔大学）；Southwest Research Institute（西南研究院）；CAS Center for Excellence in Comparative Planetology, University of Science and Technology of China（中国科学院比较行星学卓越创新中心，中国科学技术大学）
本综述利用多航天器多点多仪器观测，结合Solar Orbiter与Parker Solar Probe的近太阳高能粒子测量，研究行星际日冕物质抛射和激波对高能粒子加速与传输的作用，以解决相关未决问题。
Increased and Varied Radiation during the Sun's Encounters with Cold Clouds in the last 10 million years
Boston University（波士顿大学）；University of Arizona（亚利桑那大学）；Harvard University（哈佛大学）；University of Maryland, College Park（马里兰大学帕克分校）；Okinawa Institute of Science and Technology Graduate University（冲绳科学技术大学院大学）；California Institute of Technology（加州理工学院）；Columbia University（哥伦比亚大学）；Smithsonian Astrophysical Observatory（史密森尼天体物理台）；National and Kapodistrian University of Athens（雅典国家卡波蒂斯坦大学）
