The Near-Earth Plasma Environment

An overview of the plasma environment near the earth is provided. We describe how the near-earth plasma is formed, including photo-ionization from solar photons and impact ionization at high latitudes from energetic particles. We review the fundamental characteristics of the earth’s plasma environment, with emphasis on the ionosphere and its interactions with the extended neutral atmosphere. Important processes that control ionospheric physics at low, middle, and high latitudes are discussed. The general dynamics and morphology of the ionized gas at mid- and low-latitudes are described including electrodynamic contributions from wind-driven dynamos, tides, and planetary-scale waves. The unique properties of the near-earth plasma and its associated currents at high latitudes are shown to depend on precipitating auroral charged particles and strong electric fields which map earthward from the magnetosphere. The upper atmosphere is shown to have profound effects on the transfer of energy and momentum between the high-latitude plasma and the neutral constituents. The article concludes with a discussion of how the near-earth plasma responds to magnetic storms associated with solar disturbances.     

Plasma-induced sputtering of an atmosphere

Magnetospheric ions, solar wind ions, and locally produced pick-up ions can impact the atmospheres of objects in the solar system, transferring energy by collisions with atmospheric atoms and molecules. This can result in an expansion of the atmospheric corona with a fraction of the energetic atoms or molecules being lost (sputtered) from the atmosphere. The expanded corona presents a larger target to the incident plasma, which in turn enhances pick-up ion formation and collisional ejection. In this manner a significant flux of atoms or molecules can be lost from an atmosphere, affecting its long-term evolution. This has been shown to be an important process for the dynamics and evolution of the atmosphere of lo, which is bombarded by the Jovian magnetospheric plasma, and for loss of atmosphere from Titan. Sputtering by pick-up ion bombardment has been shown to remove material from the atmosphere of Mars affecting the observed isotope ratios, and energetic O⁺ precipitation affects the Earth's thermosphere. The physics of ion bombardment of a gas which leads to atmospheric sputtering is described here. Analytic expressions derived from transport equations are shown to be useful for estimating the sputtering rate. These are compared to results from transport and Monte-Carlo calculations.     

Solar flares as sources of energetic particles

In this paper a review is presented of the present status of our knowledge of solar flare phenomena with special emphasis on the production of suprathermal particles and their solar effects. Of these energetic particles electrons play an important role since they produce the X-ray and radiobursts observed during many flares. Also, during their slowing down to thermal energies they contribute to the heating of localized regions in the solar atmosphere, through energy exchange with the ambient electrons. Observable radiations of energetic protons, and other nuclei, are produced through nuclear interactions leading to the emissions of gamma-ray lines. Detectable fluxes of these gamma-ray lines are produced only in the most powerful flares. Also the nuclei that enter into deeper layers of the solar atmosphere transfer most of their kinetic energy to the ambient plasma.     

The Solar Wind in the Outer Heliosphere

The solar wind evolves as it moves outward due to interactions with both itself and with the circum-heliospheric interstellar medium. The speed is, on average, constant out to 30 AU, then starts a slow decrease due to the pickup of interstellar neutrals. These neutrals reduce the solar wind speed by about 20% before the termination shock (TS). The pickup ions heat the thermal plasma so that the solar wind temperature increases outside 20–30 AU. Solar cycle effects are important; the solar wind pressure changes by a factor of 2 over a solar cycle and the structure of the solar wind is modified by interplanetary coronal mass ejections (ICMEs) near solar maximum. The first direct evidences of the TS were the observations of streaming energetic particles by both Voyagers 1 and 2 beginning about 2 years before their respective TS crossings. The second evidence was a slowdown in solar wind speed commencing 80 days before Voyager 2 crossed the TS. The TS was a weak, quasi-perpendicular shock which transferred the solar wind flow energy mainly to the pickup ions. The heliosheath has large fluctuations in the plasma and magnetic field on time scales of minutes to days.     

Auroral flares and solar flares

The morphology of development of auroral flares (magnetospheric substorms) for both electron and proton auroras is summarized, based on ground-based as well as rocket-borne and satellite-borne data with specific reference to the morphology of solar flares.The growth phase of an auroral flare is produced by the inflow of the solar wind energy into the magnetosphere by the reconnection mechanism between the solar wind field and the geomagnetic field, thus the neutral and plasma sheets in the magnetotail attaining their minimum thickness with a great stretch of the geomagnetic fluxes into the tail.The onset of the expansion phase of an auroral flare is represented by the break-up of electron and proton auroras, which is associated with strong auroral electrojets, a sudden increase in CNA, VLF hiss emissions and characteristic ULF emissions. The auroral break-up is triggered by the relaxation of stretched magnetic fluxes caused by cutting off of the tail fluxes at successively formed X-type neutral lines in the magnetotail.The resultant field-aligned currents flowing between the tailward magnetosphere and the polar ionosphere produce the field-aligned anomalous resistivity owing to the electrostatic ion-cyclotron waves; the electrical potential drop thus increased further accelerates precipitating charged particles with a result of the intensification of both the field-aligned currents and the auroral electrojet. It seems that the rapid building-up of this positive feedback system for precipitating charged particles is responsible for the break-up of an auroral flare.     

Pickup Ions and Cosmic Rays from Dust in the Heliosphere

The combination of recent observational and theoretical work has completed the catalog of the sources of heliospheric Pickup Ions (PUIs). These PUIs are the seed population for Anomalous Cosmic Rays (ACRs), which are accelerated to high energies at or beyond the Termination Shock (TS). For elements with high First Ionization Potentials (high-FIP atoms: e.g., H, He, Ne, etc.), the dominant source of PUIs and ACRs is from neutral atoms that drift into the heliosphere from the Local Interstellar Medium (LISM) and, prior to ionization, are influenced primarily by solar gravitation and radiation pressure (for H). After ionization, these interstellar ions are pickup up by the solar wind, swept out, and are either accelerated near the TS or beyond it. Elements with low first ionization potentials (low-FIP atoms: e.g., C, Si, Mg, Fe, etc.) are also observed as PUIs by Ulysses and as ACRs by Wind and Voyager. But the low-FIP composition of this additional component reveals a very different origin. Low-FIP interstellar atoms are predominantly ionized in the LISM and therefore excluded from the heliosphere by the solar wind. Remarkably, a low-FIP component of PUIs was hypothesized by Banks (J. Geophys. Res. 76, 4341, 1971) over twenty years prior to its direct detection by Ulysses/SWICS (Geiss et al., J. Geophys. Res. 100(23), 373, 1995) The leading concept for the generation of Inner Source PUIs involves an effective recycling of solar wind on grains near the Sun, as originally suggested by Banks. Voyager and Wind also observe low-FIP ACRs, and a grain-related source appears likely and necessary. Two concepts have been proposed to explain these low-FIP ACRs: the first concept involves the acceleration of the Inner Source of PUIs, and the second involves a so-called Outer Source of PUIs generated from solar wind interaction with the large population of grains in the Kuiper Belt. We review here the observational and theoretical work over the last decade that shows how solar wind and heliospheric grains interact to produce pickup ions, and, in turn, anomalous cosmic rays. The inner and outer sources of pickup ions and anomalous cosmic rays exemplify dusty plasma interactions that are fundamental throughout the cosmos for the production of energetic particles and the formation of stellar systems.     

Shock Acceleration of Ions in the Heliosphere

Energetic particles constitute an important component of the heliospheric plasma environment. They range from solar energetic particles in the inner heliosphere to the anomalous cosmic rays accelerated at the interface of the heliosphere with the local interstellar medium. Although stochastic acceleration by fluctuating electric fields and processes associated with magnetic reconnection may account for some of the particle populations, the majority are accelerated by the variety of shock waves present in the solar wind. This review focuses on “gradual” solar energetic particle (SEP) events including their energetic storm particle (ESP) phase, which is observed if and when an associated shock wave passes Earth. Gradual SEP events are the intense long-duration events responsible for most space weather disturbances of Earth’s magnetosphere and upper atmosphere. The major characteristics of gradual SEP events are first described including their association with shocks and coronal mass ejections (CMEs), their ion composition, and their energy spectra. In the context of acceleration mechanisms in general, the acceleration mechanism responsible for SEP events, diffusive shock acceleration, is then described in some detail including its predictions for a planar stationary shock, shock modification by the energetic particles, and wave excitation by the accelerating ions. Finally, some complexities of shock acceleration are addressed, which affect the predictive ability of the theory. These include the role of temporal and spatial variations, the distinction between the plasma and wave compression ratios at the shock, the injection of thermal plasma at the shock into the process of shock acceleration, and the nonlinear evolution of ion-excited waves in the vicinity of the shock.     

Magnetic storms and associated phenomena

This review will not merely be a précis of the literature in this field though a partial survey is attempted. A critical stand will be taken and a point of view put forward. Experiments to test this point of view and others will be suggested. Several new ideas are introduced.Two broad conditions of the magnetosphere are discussed, the quiet and the disturbed. During the quiet condition, the polar cap F region either glows red or is filled with a family of red auroral arcs parallel roughly to L-contours. Auroras near the auroral zone have an increasing amount of green (5577) coloration. The ionospheric F region exists even in winter over the polar caps despite the absence of solar ionizing radiation or obvious corpuscular bombardment. The red polar glow and the maintenance of the quiet polar winter F region are suggested to be accounted for by the cooling of plasma in the geomagnetic tail. These phenomena consume less than 0.01 of the energy and flux of the solar wind impinging on the magnetosphere. The relevance of dynamo theory to this quiet condition is discussed.During the disturbed condition, many phenomena such as polar magnetic substorms, auroral substorms, the sudden appearance of islands of energetic particles in the magnetosphere, and the rapid acceleration of auroral particles appear to call for the operation of an instability deep in the magnetosphere.The energetics of various facets of geomagnetic disturbance are discussed, and joule dissipation of ionospheric current is found to be a major sink of energy during storms. This causes significant heating of the ionosphere particularly at the site of auroral electrojets. Corpuscular bombardment may consume as much energy, but its heating effect is likely to be less.The stable auroral red arc (SAR-arc) observed equatorwards of normal active aurora during magnetic storms is a major sink of energy of a magnetospheric ring current. It is contended that the ring current generally consists of particles of energy of less than a few keV. It is suggested that the ring current is caused by the irreversible pumping and energisation of plasma from the outer to the inner magnetosphere. This pumping is achieved by the random electrostatic fields associated with the noisy component of geomagnetic disturbance. The SAR-arc must be a major feature of ring current theory.The consumption of energy in polar magnetic and auroral substorms, during a complete storm, is tentatively concluded to be far greater than that of the ring current. The ring current is considered to be a byproduct of magnetic disturbance on higher L-shells.The main phase of a storm should be considered, in storm analysis, as a separate entity from the initial phase, for physically they bear a tenuous and unpredictable relationship to one another. A new system of analysis is proposed in which the onset of geomagnetic noise rather than sudden commencement is taken as the origin of time, both for magnetic and ionospheric storms. This will enable analysis of storms with both gradual and sudden commencements to be made on a common basis.No reliable evidence is found to support the contention that magnetic storms are caused dominantly by neutral H-atoms ejected from the sun. In fact much evidence can be amassed to deny this hypothesis.     

Non-relativistic solar electrons

This review summarizes both the direct spacecraft observations of non-relativistic solar electrons, and observations of the X-ray and radio emission generated by these particles at the Sun and in the interplanetary medium. These observations bear on three physical processes basic to energetic particle phenomena: (1) the acceleration of particles in tenuous plasmas; (2) the propagation of energetic charged particles in a disordered magnetic field, and (3) the interaction of energetic charged particles with tenuous plasmas to produce electromagnetic radiation. Because these electrons are frequently accelerated and emitted by the Sun, mostly in small and relatively simple flares, it is possible to define a detailed physical picture of these processes.In many small solar flares non-relativistic electrons accelerated during flash phase constitute the bulk of the total flare energy. Thus the basic flare mechanism in these flares essentially converts the available flare energy into fast electrons. Non-relativistic electrons exhibit a wide variety of propagation modes in the interplanetary medium, ranging from diffusive to essentially scatter-free. This variability in the propagation may be explained in terms of the distribution of interplanetary magnetic field fluctuations. Type III solar radio burst emission is generated by these electrons as they travel out to 1 AU and beyond. Recent in situ observations of these electrons at 1 AU, accompanied by simultaneous observations of the low frequency radio emission generated by them at 1 AU provide quantitative information on the plasma processes involved in the generation of type III bursts.     

Auroral Plasma Acceleration Above Martian Magnetic Anomalies

Aurora is caused by the precipitation of energetic particles into a planetary atmosphere, the light intensity being roughly proportional to the precipitating particle energy flux. From auroral research in the terrestrial magnetosphere it is known that bright auroral displays, discrete aurora, result from an enhanced energy deposition caused by downward accelerated electrons. The process is commonly referred to as the auroral acceleration process. Discrete aurora is the visual manifestation of the structuring inherent in a highly magnetized plasma. A strong magnetic field limits the transverse (to the magnetic field) mobility of charged particles, effectively guiding the particle energy flux along magnetic field lines. The typical, slanted arc structure of the Earth’s discrete aurora not only visualizes the inclination of the Earth’s magnetic field, but also illustrates the confinement of the auroral acceleration process. The terrestrial magnetic field guides and confines the acceleration processes such that the preferred acceleration of particles is frequently along the magnetic field lines. Field-aligned plasma acceleration is therefore also the signature of strongly magnetized plasma. This paper discusses plasma acceleration characteristics in the night-side cavity of Mars. The acceleration is typical for strongly magnetized plasmas – field-aligned acceleration of ions and electrons. The observations map to regions at Mars of what appears to be sufficient magnetization to support magnetic field-aligned plasma acceleration – the localized crustal magnetizations at Mars (Acuña et al., 1999). Our findings are based on data from the ASPERA-3 experiment on ESA’s Mars Express, covering 57 orbits traversing the night-side/eclipse of Mars. There are indeed strong similarities between Mars and the Earth regarding the accelerated electron and ion distributions. Specifically acceleration above Mars near local midnight and acceleration above discrete aurora at the Earth – characterized by nearly monoenergetic downgoing electrons in conjunction with nearly monoenergetic upgoing ions. We describe a number of characteristic features in the accelerated plasma: The “inverted V” energy-time distribution, beam vs temperature distribution, altitude distribution, local time distribution and connection with magnetic anomalies. We also compute the electron energy flux and find that the energy flux is sufficient to cause weak to medium strong (up to several tens of kR 557.7 nm emissions) aurora at Mars. Monoenergetic counterstreaming accelerated ions and electrons is the signature of field-aligned electric currents and electric field acceleration. The topic is reasonably well understood in terrestrial magnetospheric physics, although some controversy still remains on details and the cause-effect relationships. We present a potential cause-effect relationship leading to auroral plasma acceleration in the nightside cavity of Mars – the downward acceleration of electrons supposedly manifesting itself as discrete aurora above Mars.     

Cosmological Shock Waves

Large-scale structure formation, accretion and merging processes, AGN activity produce cosmological gas shocks. The shocks convert a fraction of the energy of gravitationally accelerated flows to internal energy of the gas. Being the main gas-heating agent, cosmological shocks could amplify magnetic fields and accelerate energetic particles via the multi-fluid plasma relaxation processes. We first discuss the basic properties of standard single-fluid shocks. Cosmological plasma shocks are expected to be collisionless. We then review the plasma processes responsible for the microscopic structure of collisionless shocks. A tiny fraction of the particles crossing the shock is injected into the non-thermal energetic component that could get a substantial part of the ram pressure power dissipated at the shock. The energetic particles penetrate deep into the shock upstream producing an extended shock precursor. Scaling relations for postshock ion temperature and entropy as functions of shock velocity in strong collisionless multi-fluid shocks are discussed. We show that the multi-fluid nature of collisionless shocks results in excessive gas compression, energetic particle acceleration, precursor gas heating, magnetic field amplification and non-thermal emission. Multi-fluid shocks provide a reduced gas entropy production and could also modify the observable thermodynamic scaling relations for clusters of galaxies.     

Interstellar Mapping and Acceleration Probe (IMAP): A New NASA Mission

The Interstellar Mapping and Acceleration Probe (IMAP) is a revolutionary mission that simultaneously investigates two of the most important overarching issues in Heliophysics today: the acceleration of energetic particles and interaction of the solar wind with the local interstellar medium. While seemingly disparate, these are intimately coupled because particles accelerated in the inner heliosphere play critical roles in the outer heliospheric interaction. Selected by NASA in 2018, IMAP is planned to launch in 2024. The IMAP spacecraft is a simple sun-pointed spinner in orbit about the Sun-Earth L1 point. IMAP’s ten instruments provide a complete and synergistic set of observations to simultaneously dissect the particle injection and acceleration processes at 1 AU while remotely probing the global heliospheric interaction and its response to particle populations generated by these processes. In situ at 1 AU, IMAP provides detailed observations of solar wind electrons and ions; suprathermal, pickup, and energetic ions; and the interplanetary magnetic field. For the outer heliosphere interaction, IMAP provides advanced global observations of the remote plasma and energetic ions over a broad energy range via energetic neutral atom imaging, and precise observations of interstellar neutral atoms penetrating the heliosphere. Complementary observations of interstellar dust and the ultraviolet glow of interstellar neutrals further deepen the physical understanding from IMAP. IMAP also continuously broadcasts vital real-time space weather observations. Finally, IMAP engages the broader Heliophysics community through a variety of innovative opportunities. This paper summarizes the IMAP mission at the start of Phase A development.     

Ion Energization and Escape on Mars and Venus

Mars and Venus do not have a global magnetic field and as a result solar wind interacts directly with their ionospheres and upper atmospheres. Neutral atoms ionized by solar UV, charge exchange and electron impact, are extracted and scavenged by solar wind providing a significant loss of planetary volatiles. There are different channels and routes through which the ionized planetary matter escapes from the planets. Processes of ion energization driven by direct solar wind forcing and their escape are intimately related. Forces responsible for ion energization in different channels are different and, correspondingly, the effectiveness of escape is also different. Classification of the energization processes and escape channels on Mars and Venus and also their variability with solar wind parameters is the main topic of our review. We will distinguish between classical pickup and ??mass-loaded?? pickup processes, energization in boundary layer and plasma sheet, polar winds on unmagnetized planets with magnetized ionospheres and enhanced escape flows from localized auroral regions in the regions filled by strong crustal magnetic fields.     

Wave particle interactions as an energy transfer mechanism between different particle species

Recent improvements in experimental techniques and cooperative data analysis efforts have brought a lot of information on the basic mechanisms by which energy can be exchanged between different particle species in the collisionless magnetospheric or solar wind plasmas. Some of these mechanisms are reviewed. A particular emphasis is put on interactions which occur in the equatorial magnetosphere between energetic protons and electromagnetic ultra low frequency (ULF) waves and which are linked with He⁺ ion trapping and heating as well as with field-aligned suprathermal electron beam generation. The process by which ion conic distributions are produced by electrostatic ion cyclotron waves generated at high altitude along auroral field lines by drifting electrons is also discussed.     

Physics of the Solar Wind–Local Interstellar Medium Interaction: Role of Magnetic Fields

The interaction of the solar wind with the local interstellar medium is characterized by the self-consistent coupling of solar wind plasma, both upstream and downstream of the heliospheric termination shock, the interstellar plasma, and the neutral atom component of interstellar and solar wind origin. The complex coupling results in the creation of new plasma components (pickup ions), turbulence, and anomalous cosmic rays, and new populations of neutral atoms and their coupling can lead to energetic neutral atoms that can be detected at 1 AU. In this review, we discuss the interaction and coupling of global sized structures (the heliospheric boundary regions) and kinetic physics (the distributions that are responsible for the creation of energetic neutral atoms) based on models that have been developed by the University of Alabama in Huntsville group.     

Giant Planet Ionospheres and Thermospheres: The Importance of Ion-Neutral Coupling

Planetary upper atmospheres-coexisting thermospheres and ionospheres-form an important boundary between the planet itself and interplanetary space. The solar wind and radiation from the Sun may react with the upper atmosphere directly, as in the case of Venus. If the planet has a magnetic field, however, such interactions are mediated by the magnetosphere, as in the case of the Earth. All of the Solar System’s giant planets have magnetic fields of various strengths, and interactions with their space environments are thus mediated by their respective magnetospheres. This article concentrates on the consequences of magnetosphere-atmosphere interactions for the physical conditions of the thermosphere and ionosphere. In particular, we wish to highlight important new considerations concerning the energy balance in the upper atmosphere of Jupiter and Saturn, and the role that coupling between the ionosphere and thermosphere may play in establishing and regulating energy flows and temperatures there. This article also compares the auroral activity of Earth, Jupiter, Saturn and Uranus. The Earth’s behaviour is controlled, externally, by the solar wind. But Jupiter’s is determined by the co-rotation or otherwise of the equatorial plasmasheet, which is internal to the planet’s magnetosphere. Despite being rapid rotators, like Jupiter, Saturn and Uranus appear to have auroral emissions that are mainly under solar (wind) control. For Jupiter and Saturn, it is shown that Joule heating and “frictional” effects, due to ion-neutral coupling can produce large amounts of energy that may account for their high exospheric temperatures.     

The multifuid solar wind termination shock and its influence on the threedimensional plasma structure upstream and downstream

The solar wind termination shock is described as a multi-fluid phenomenon taking into account the magnetohydrodynamic self-interaction of a multispecies plasma consisting of solar wind ions, pick-up ions and shock-generated anomalous cosmic ray particles. The spatial diffusion of these high energy particles relative to the resulting, pressure-modified solar wind flow structure is described by a coupled system of differential equations describing mass-, momentum-, and energy-flow continuities for all plasma components. The energy loss due to escape of energetic particles (MeV) from the precursor into the inner heliosphere is taken into account. We determine the integrated properties of the anomalous cosmic ray gas and the low-energy solar wind. Also the variation of the compression ratio of the shock structure is quantitatively determined and is related to the pick-up ion energization efficiency and to the mean energy of the downstream anomalous cosmic ray particles. The variation of the resulting shock structure and of the solar wind sheath plasma extent beyond the shock is discussed with respect to its consequences for the LISM neutral gas filtration and the threedimensional shape of the heliosphere.     

Large-scale electric field in the magnetosphere

A review is given on the distribution and origin of the large-scale electric field in the magnetosphere and its influence on the dynamical behavior of the magnetospheric plasma. Following a general discussion on the gross structure of the magnetosphere and its tail, two principal electric field systems are deduced from ground-based geomagnetic variations. One is responsible for the polar substorm, the DP 1 field, which is closely associated with the activation of the auroral electrojet. The other is responsible for the twin current vortices, the DP 2 field, and this represents the general convective system set up in the magnetospheric plasma.The origin of these magnetospheric electric fields is possibly resided in the domain of the solar wind interacting with the outer geomagnetic field. However, the mechanism, in which the energy is transferred, is still quite controversial. Several theories so far proposed are re-examined, and some modification of them are suggested to have a consistent understanding of these two types of electric fields. The effects of electric fields on magnetospheric plasma dynamics are described, such as the formation of the plasmapause, the acceleration and diffusion of energetic particles in the radiation belt.     

Ion Heating and Acceleration During Magnetic Reconnection Relevant to the Corona

The heating and acceleration of ions during magnetic reconnection relevant to coronal heating and flares is explored via particle-in-cell (PIC) simulations and analytic modeling. We show that the dominant heating mechanism of sub-Alvénic ions during reconnection with a guide field, the case of greatest relevance to the corona, results from pickup behavior during the entry into reconnection exhausts, which produces effective thermal speeds of the order of the Alfvén velocity based on the reconnecting magnetic field. There is a mass-to-charge (M/Q) threshold for pickup behavior that favors the heating of high-M/Q ions. Ions below the threshold gain little energy beyond that associated with convective flow. PIC simulations with protons and alphas confirm the pickup threshold. The enhanced heating of high M/Q ions is consistent with observations of abundance enhancements of such ions in impulsive flares. In contrast to anti-parallel reconnection, the temperature increment during ion pickup is dominantly transverse, rather than parallel, to the local magnetic field. The simulations reveal the dominance of perpendicular heating, which is also consistent with observations. We suggest that the acceleration of ions to energies well above that associated with the Alfvén speed takes place during the interaction with many magnetic islands, which spontaneously develop during 3-D guide-field reconnection. The exploration of particle acceleration in a full 3-D multi-island system remains computationally intractable. Instead we explore ion acceleration in a multi-current layer system with low initial β. Ion energy gain takes place due to Fermi reflection in contracting and merging magnetic islands. Particle acceleration continues until the available magnetic free-energy is significantly depleted so that the pressure of energetic ions approaches that of the reconnecting field. Depending on the strength of the ambient guide field and in spite of the low initial plasma β, the dominance of parallel heating can cause significant regions of the plasma to exceed the marginal firehose condition.     

The streaming of solar flare particles and plasma in interplanetary space

A review is given of the features of solar particle emissions which cause various terrestrial disturbances. Three types of corpuscular emissions, namely, solar cosmic rays, energetic storm protons and plasma clouds, are associated with intense solar flares. Outward streaming of the solar wind and of beams of enhanced activity originate from the quiescent solar corona. It is shown that these solar particles propagate through interplanetary space, being modulated in a systematic way by existing magnetic fields. Time variations of solar flare particle flux, and their energy spectrum, are discussed.