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NASA NTRS1986

Effects of three-dimensional heliospheric structures on cosmic-ray modulation

The theory of cosmic-ray transport in the heliosphere contains four distinct physical processes - diffusion, convection, adiabatic cooling, and drifts. The last of these has only recently been evaluated. Extrapolation of present understanding of the regions near the heliospheric equator to high heliographic latitudes leads to the conclusion that particle drift in the large-scale magnetic field plays an important role in cosmic-ray modulation. The large-scale, three-dimensional structure of the interplanetary magnetic field is therefore very important in understanding cosmic rays. Several key observed modulation effects are summarized, each of which is a natural consequence of drift, but which requires special assumptions if drift plays no role. It is concluded that particle drifts play an important and possibly dominant role in transport in the heliosphere.

Jokipii, J. R.↗

NASA NTRS2007

The Virtual Solar Observatory and the Heliophysics Meta-Virtual Observatory

The Virtual Solar Observatory (VSO) is now able to search for solar data ranging from the radio to gamma rays, obtained from space and groundbased observatories, from 26 sources at 12 data providers, and from 1915 to the present. The solar physics community can use a Web interface or an Application Programming Interface (API) that allows integrating VSO searches into other software, including other Web services. Over the next few years, this integration will be especially obvious as the NASA Heliophysics division sponsors the development of a heliophysics-wide virtual observatory (VO), based on existing VO's in heliospheric, magnetospheric, and ionospheric physics as well as the VSO. We examine some of the challenges and potential of such a "meta-VO."

Gurman, Joseph B.↗

NASA NTRS2014

Anomalous Expansion of Coronal Mass Ejections During Solar Cycle 24 and Its Space Weather Implications

The familiar correlation between the speed and angular width of coronal mass ejections (CMEs) is also found in solar cycle 24, but the regression line has a larger slope: for a given CME speed, cycle 24 CMEs are significantly wider than those in cycle 23. The slope change indicates a significant change in the physical state of the heliosphere, due to the weak solar activity. The total pressure in the heliosphere (magnetic + plasma) is reduced by approximately 40%, which leads to the anomalous expansion of CMEs explaining the increased slope. The excess CME expansion contributes to the diminished effectiveness of CMEs in producing magnetic storms during cycle 24, both because the magnetic content of the CMEs is diluted and also because of the weaker ambient fields. The reduced magnetic field in the heliosphere may contribute to the lack of solar energetic particles accelerated to very high energies during this cycle.

coronal mass ejections↗

NASA NTRS2004

The Sun and the Heliosphere as an Integrated System

This book, for the first time, ties together physical processes across the full scale of the heliosphere. It is about the natural connections that exist between various parts of the system. Therefore, it is mainly cast in terms of those mechanisms and phenomena rather than individual missions in space. However, to give credit, this has only been possible because of the existence of a fleet of deep space missions such as Ulysses, SOHO, and the Voyagers. It is only with them working in concert that a real understanding of the physics can be, and has been achieved. There are fourteen chapters in the book, written by top scientists from around the world. The level of presentation is very high but the authors were given enough space to present understandable introductions, physical discussions, and extensive bibliographies. The book can be of use to average scientists and academicians as well as to specialists.

Poletto, Giannina↗

DOE OSTI2025

Orbital Debris IC Report

We started a simulation campaign in support of our ongoing plasma signatures of small orbital debris project SINTRA program funded by IARPA. This project aims to identify plasma signatures generated by the interaction of small orbital debris (>10cm) with space plasma that can be used for detection, tracking and eventually, develop technologies to remove these small but lethal objects. The small orbital debris problem is increasing exponentially threaten the current and future use of space.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1991

Variations of the cosmic-ray flux with time

The physical foundations of the modulation of the galactic cosmic ray flux by the sun are reviewed and related to heliospheric structure and dynamics. The basic physical effects - diffusion, convection, adiabatic cooling and drifts - are evaluated and shown to be all important. The results of numerical models are briefly presented and compared with observations. Present-day modulation is shown to reflect the combination of diffusion-convection effects and drift effects. The Maunder minimum is conjectured to be a period when a quiet sun and smooth solar wind resulted in the dominance of drift effects.

Jokipii, J. R.↗

NASA NTRS2004

The Magnetic Field in the Outer Heliosphere

One of the great achievements of Parker was the prediction that the solar magnetic field would be drawn into Archimedian spirals as it is carried away from the Sun by the solar wind. This prediction has been amply confirmed by many in situ measurements in the intervening four decades. But, Parker made his prediction for a solar wind that expands into infinite space while we now know that the local interstellar medium (LISM) is far from empty and, in fact, confines the solar wind to a finite volume, known as the heliosphere, that extends to approximately 100 AU in the upstream direction (the solar system is moving through the LISM). Voyagers 1/2, presently at -80 AU, are approaching the upstream boundaries of the heliosphere and returning data on the properties of the magnetic field. This is important for understanding how galactic cosmic rays (GCRs) reach the Earth. Voyagers show that the IMF at 10-80 AU behaves much as Parker predicted - with two important exceptions. This is not surprising since the field is essentially passively advected by the solar wind out to 80 AU. But, new models say that nearer the heliosphere boundaries the field plays a major role in the solar wind-LISM interaction. However, of the many physical ingredients that constitute the outer heliosphere, the magnetic field poses some of the most interesting and difficult numerical modeling problems. Presently, only a few results have been published and much remains to be done. Here I will summarize the expected and measured behavior of the magnetic field at 80 AU. Then I will describe modeling predictions beyond 80 AU: magnetic "tornadoes", polarity envelopes, the Axford-Cranfill effect, inner and outer magnetic walls and more. I will also list what I believe to be important new modeling objectives. Finally, I will speculate on what is happening with the magnetic field near the nose of the heliosphere. My conclusion is that models of GCR modulation rarely incorporate even crudely realistic magnetic fields so it is a wonder that they are as successful as they are and no surprise that there are still important discrepancies between GCR modulation observations and the models.

Suess, S. T.↗

NASA NTRSDate not supplied

Modeling and Impact of Solar Energetic Particles in the Heliosphere and Geospace

Understanding the radiation environment due to solar energetic particles in the heliosphere and the Earth’s magnetosphere is a challenging and practically important task. Exposure to energetic particles often leads to malfunctions and unexpected failures of electronics onboard spacecraft. The most vulnerable are exploratory missions when outside of the Earth’s magnetosphere. Geomagnetic field deflects Solar Energetic Particles (SEPs) moving through geospace though some of these particles propagate to LEO and have a high penetrating capability, thus producing significant radiation hazards for human spaceflight. Solar energetic particles also have an essential effect on the composition and dynamics of the Earth’s atmosphere. Precipitating SEPs enhance the atmospheric concentration of NOx and HOx, which play a crucial role in the ozone balance in the middle atmosphere by destroying odd oxygen through catalytic reactions. Numerical modeling of the radiation environment due to SEPs in the inner heliosphere and geospace is a multifold problem. That includes simulating 1) solar wind dynamics and the interplanetary magnetic field, 2) global modeling of the Earth’s magnetosphere, and 3) modeling transport and acceleration of SEPs in the inner heliosphere and geospace. The lecture will outline the key physical processes that control the behavior of SEPs in the heliosphere and geospace, along with the contemporary numerical methods used for their modeling. It will primarily focus on describing the SEP population in geospace across different altitudes, ranging from Low Earth Orbit (LEO) through Medium Earth Orbit (MEO) and Geostationary Orbit (GEO), up to the magnetopause, while considering the realistic geomagnetic field. Additionally, the lecture will cover how the SEP population in geospace varies in response to geomagnetic activity. This includes the temporal trapping of SEPs in geospace and the reduction of the rigidity cutoff during geomagnetic storms.

solar energetic particles↗

NASA NTRSDate not supplied

Energetic Particles in Geospace: Origin, Dynamics, and Modeling

This presentation explores the origins and dynamics of energetic particles—specifically solar energetic particles (SEPs) and galactic cosmic rays (GCRs) - within the heliosphere and Earth's magnetosphere. We will discuss the fundamental physical processes governing their transport and acceleration in the heliosphere, including interactions with the solar wind and the interplanetary magnetic field. The penetration of these particles into Earth's magnetosphere is examined, emphasizing how the geomagnetic field influences their propagation across the magnetosphere. Key phenomena such as the temporal trapping of SEPs in geospace, reductions in rigidity cutoff during geomagnetic storms, and the enhancement of atmospheric NOx and HOx concentrations - which affect the ozone balance through catalytic reactions—are discussed. The presentation also outlines contemporary numerical modeling techniques used to simulate SEPs and GCRs, providing insights into their complex behaviors under varying geomagnetic conditions.

solar energetic particles↗

NASA NTRS2022

Interplanetary Mesoscale Observatory (InterMeso): A Mission to Untangle Dynamic Mesoscale Structures Throughout the Heliosphere

Mesoscale dynamics are a fundamental process in space physics, but fall within an observational gap of current and planned missions. Particularly in the solar wind, measurements at the mesoscales (100s RE to a few degrees heliographic longitude at 1 au) are crucial for understanding the connection between the corona and an observer anywhere within the heliosphere. Mesoscale dynamics may also be key to revealing the currently unresolved physics regulating particle acceleration and transport, magnetic field topology, and the causes of variability in the composition and acceleration of solar wind plasma. Studies using single-point observations do not allow for investigations into mesoscale solar wind dynamics and plasma variability, nor do they allow for the exploration of the sub-structuring of large-scale solar wind structures like coronal mass ejections (CMEs), co-rotating/stream interaction regions (CIR/SIRs), and the heliospheric plasma sheet. To address this fundamental gap in our knowledge of the heliosphere at these scales, the Interplanetary Mesoscale Observatory (InterMeso) concept employs a multi-point approach using four identical spacecraft in Earth-trailing orbits near 1 au. Varying drift speeds of the InterMeso spacecraft enable the mission to span a range of mesoscale separations in the solar wind, achieving significant and innovative science return. Simultaneous, longitudinally-separated measurements of structures co-rotating over the spacecraft also allow for disambiguation of spatiotemporal variability, tracking of the evolution of solar wind structures, and determination of how the transport of energetic particles is impacted by these variabilities.

solar wind↗

NASA NTRS2022

Interplanetary Mesoscale Observatory (InterMeso): A mission to untangle dynamic mesoscale structures throughout the heliosphere

solar wind↗

NASA NTRS2006

Status of Knowledge after Ulysses and SOHO: Session 2: Investigate the Links between the Solar Surface, Corona, and Inner Heliosphere.

As spacecraft observations of the heliosphere have moved from exploration into studies of physical processes, we are learning about the linkages that exist between different parts of the system. The past fifteen years have led to new ideas for how the heliospheric magnetic field connects back to the Sun and to how that connection plays a role in the origin of the solar wind. A growing understanding these connections, in turn, has led to the ability to use composition, ionization state, the microscopic state of the in situ plasma, and energetic particles as tools to further analyze the linkages and the underlying physical processes. Many missions have contributed to these investigations of the heliosphere as an integrated system. Two of the most important are Ulysses and SOHO, because of the types of measurements they make, their specific orbits, and how they have worked to complement each other. I will review and summarize the status of knowledge about these linkages, with emphasis on results from the Ulysses and SOHO missions. Some of the topics will be the global heliosphere at sunspot maximum and minimum, the physics and morphology of coronal holes, the origin(s) of slow wind, SOHO-Ulysses quadrature observations, mysteries in the propagation of energetic particles, and the physics of eruptive events and their associated current sheets. These specific topics are selected because they point towards the investigations that will be carried out with Solar Orbiter (SO) and the opportunity will be used to illustrate how SO will uniquely contribute to our knowledge of the underlying physical processes.

Suess, Steven↗

NASA NTRS1991

The solar cycle variation of the rates of CMEs and related activity

Coronal mass ejections (CMEs) are an important aspect of the physics of the corona and heliosphere. This paper presents results of a study of occurrence frequencies of CMEs and related activity tracers over more than a complete solar activity cycle. To properly estimate occurrence rates, observed CME rates must be corrected for instrument duty cycles, detection efficiencies away from the skyplane, mass detection thresholds, and geometrical considerations. These corrections are evaluated using CME data from 1976-1989 obtained with the Skylab, SMM and SOLWIND coronagraphs and the Helios-2 photometers. The major results are: (1) the occurrence rate of CMEs tends to track the activity cycle in both amplitude and phase; (2) the corrected rates from different instruments are reasonably consistent; and (3) over the long term, no one class of solar activity tracer is better correlated with CME rate than any other (with the possible exception of type II bursts).

Webb, David F.↗

NASA NTRS1994

The cosmic-ray oxygen and helium spectra measured at Pioneer 10 over the time of the 1987 modulation minimum, and implications for the He/O source ratio

At the time of the recent sunspot minimum in 1987 when the cosmic-ray intensity within the heliosphere was a maximum, Pioneer 10(P10) was at a radial distance of approximately 42 AU. The solar modulation parameter Phi is estimated to have reached a minimum value of approximately 150 MV at P10 at that time, as compared with a minimum value of approximately 500 MV at the Earth. Thus P10 is in a sense effectively approximately 0.7 of the way to the heliospheric modulation boundary whatever its physical distance in astronomical units. Accordingly, the spectra of the various cosmic-ray species are much nearer to the interstellar spectra than any spectra ever before measured. We have therefore examined the penetrating high energy telescope (HET) data from P10 for a 2.5 yr period around 1987 to obtain a statistically accurate spectrum of oxygen nuclei over the energy range from 90 to 450 MeV/nucleon for comparison with a 'reference' interstellar spectrum. A similar spectrum is derived for helium nuclei. These two spectra and their ratios constitute important 'reference' spectra for all of the heavier cosmic-ray nuclei. The cosmic-ray source ratio required to explain the observed He/O ratio, when a full Galactic propagation calculation is carried out including secondary He-4 and He-3 production, is 15.9. The implications of this very low ratio and a comparison with the He/O ratio measured at high energies are discussed.

Webber, W. R.↗

NASA NTRS1983

Propagation of solar disturbances - Theories and models

Recent theoretical developments and construction of several models for the propagation of solar disturbances from the sun and their continuation throughout heliospheric space are discussed. Emphasis centers on physical mechanisms as well as mathematical techniques (i.e., analytical and numerical methods). This outline will lead to a discussion of the state-of-the-art of theoretically based modeling efforts in this area. It is shown that the fundamental theory for the study of propagation of disturbances in heliospheric space is centered around the self-consistent analysis of wave and mass motion within the context of magnetohydrodynamics in which the small scale structures will be modified by kinetic effects. Finally, brief mention is made of some interesting problems for which attention is needed for advancement of the understanding of the physics of large scale propagation of solar disturbances in heliospheric space.

Wu, S. T.↗

NASA NTRS2023

Advancing Solar and Heliospheric Science Through the Ongoing Development and Support of Atomic and Laboratory Plasma Physics

This paper outlines the necessity for the availability, accessibility, and expansion of atomic physics data and analysis tools for the meaningful interpretation of spectroscopic and polarimetric observations. As we move towards observing the Sun at higher spatio-temporal resolutions, and near-continuously at a range of wavelengths, it becomes critical to develop the appropriate atomic data and physics tools to facilitate scientific progress. We recommend the continued improvement and expansion of current databases to support the development of optically-thick/radiative transfer models, evaluate non-thermal and non-equilibrium ionization effects, and quantify uncertainties in atomic and molecular values. A critical longterm goal will require extending and strengthening collaborations across the atomic, solar/heliospheric, and laboratory plasma physics communities through the participation and training of early career scientists. We also recommend establishing funding for a centralized atomic physics resource made up of a comprehensive and user-oriented atomic database and modeling framework.

Y J Rivera↗

NASA NTRS2004

The Magnetic Field in the Outer Heliosphere

Voyager and Pioneer empirical results show that the IMF inside the termination shock behaves much as expected, which is not surprising since the field is essentially passively advected in this region. In contrast, MHD and kinematic models imply the field plays a major role in the dynamics in some regions of the heliosheath. However, of the many physical ingredients that constitute the outer heliosphere, the magnetic field poses some of the most interesting and difficult problems when being incorporated into 3D numerical models. Presently, only a few results have been published and much remains to be done. Nevertheless, there are good reasons to press forward with the MHD models. For example, the detailed nature of the field may be important in determining how galactic cosmic rays gain access to the heliosheath. Here I will briefly review the expected behavior of the magnetic field near the termination shock and in the heliosheath and summarize some of the modeling results. I will also review what I believe to be important modeling objectives. Finally, I will speculate on what might be happening with the magnetic field near the nose of the heliosphere and how this might influence plasma transfer across the heliopause.

Suess, Steve↗

NASA NTRS2023

A Data-driven, Physics-based Transport Model of Solar Energetic Particles Accelerated by Coronal Mass Ejection Shocks Propagating through the Solar Coronal and Heliospheric Magnetic Fields

In an effort to develop computational tools for predicting radiation hazards from solar energetic particles (SEPs), we have created a data-driven physics-based particle transport model to calculate the injection, acceleration, and propagation of SEPs from coronal mass ejection (CME) shocks traversing through the solar corona and interplanetary magnetic fields. The model runs on an input of corona and heliospheric plasma and magnetic field configuration from a magnetohydrodynamic model driven by solar photospheric magnetic field measurements superposed with observed CME shocks determined from coronagraph images. SEP source particles are injected at the shock using the result of diffusive shock acceleration formulation from a characteristic obliquity-dependent injection from a heated solar wind thermal tail population. With several advanced computation techniques involving stochastic simulation and integration, the model obtains the particle intensity at any location in interplanetary space through the rigorous solution to the time-dependent 5D focus transport equation in the phase space that includes perpendicular diffusion. We apply the model to the 2011 November 3 CME event. The calculation results reproduce multispacecraft SEP observations at Earth and STEREO-B reasonably well without normalization of particle flux. The observations at STEREO-A can be reproduced by rescaling particle energy or modified energy dependence of particle diffusion coefficients. This circumsolar SEP event seen by spacecraft at Earth, STEREO-A, and STEREO-B at widely separated longitudes can be explained by diffusive shock acceleration by a single CME shock with a moderate speed.

Solar energetic particles↗