Interplanetary Propagation Research Articles

The temporal and spatial development of MeV proton acceleration at interplanetary shocks

Particle events observed in association with interplanetary shocks exhibit a wide variety of different features. In this paper we will demonstrate how these features can be understood in terms of a spatially and temporally varying shock efficiency and the subsequent interplanetary propagation. The examples presented here will show that while the location of the observer relative to the shock is an important factor in determining the event properties, the radial and temporal evolution of the shock also plays an important role. In particular, there are shocks which in a given energy range predominately accelerate particles close to the Sun, while in others the shock efficiency increases as they propagate outward. Another goal of this paper is to demonstrate that the black box model used here is able to fit the data.

Propagation of particles injected from interplanetary shocks: A black box model and its consequences for acceleration theory and data interpretation

Energetic protons in the hundreds of keV to the tens of MeV range frequently are observed in connection with traveling interplanetary shocks. Occasionally, the particle energies can extend up to about 100 MeV. The intensity time profiles at the observer's site are a superposition of the continuous, spatially and temporally variable acceleration at the shock and the subsequent interplanetary propagation. To gain a better understanding of both processes and to derive their relevant parameters, we extend a numerical solution of the model of focused transport to accommodate the shock as a moving source. No assumptions about the acceleration mechanism are made; the shock is treated as a black box. In this paper we introduce the model, discuss its validity, and present model results which have implications for acceleration theory and data interpretation. The main results concerning acceleration and propagation are as follows: (1) In the limit of strong scattering and low particle speeds our model converges toward diffusive shock acceleration. (2) For weak scattering or fast particles, spatial diffusion is an insufficient approximation for particle transport; in this case, the physical consequence is a fast escape from the shock, and the formal consequence is that the standard description of diffusive shock acceleration is insufficient. (3) Because of this fast escape, even a turbulent foreshock region, while it is perfectly capable of keeping 100 keV protons confined to the shock, would allow 10 MeV protons to stream away easily. Important results for data interpretation are as follows: (1) A quasi‐exponential intensity increase upstream of the shock is not necessarily indicative of diffusive shock acceleration. (2) The intensity at the time of shock passage is a crude measure for the local acceleration efficiency as long as it stays constant or continues to rise.

Comment on “Hydrodynamic instability of the heliopause driven by plasma‐neutral charge‐exchange interactions” by Paulett C. Liewer, S. Roy Karmesin, and J.U. Brackbill

Journal of Geophysical Research: Space PhysicsVolume 102, Issue A5 p. 9835-9837 CommentariesFree Access Comment on “Hydrodynamic instability of the heliopause driven by plasma-neutral charge-exchange interactions” by Paulett C. Liewer, S. Roy Karmesin, and J.U. Brackbill H. L. Pauls, H. L. PaulsSearch for more papers by this authorG. P. Zank, G. P. ZankSearch for more papers by this author H. L. Pauls, H. L. PaulsSearch for more papers by this authorG. P. Zank, G. P. ZankSearch for more papers by this author First published: 01 May 1997 https://doi.org/10.1029/97JA00152Citations: 8AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. References Baranov, V. B., Gasdynamics of the solar wind interaction with the interstellar medium, Space Sci. Rev., 52, 89, 1990. Baranov, V. B., Y. G. Malama, Model of the solar wind interaction with the local interstellar medium: Numerical solution of self-consistent problem, J. Geophys. Res., 9815, 157, 1993. Frisch, P. C., Morphology and ionization of the interstellar cloud surrounding the solar system, Science, 265, 1423, 1994. Gurnett, D. A., W. S. Kurth, S. C. Allendorf, R. L. Poynter, Radio emission from the heliopause triggered by an interplanetary shock, Science, 262, 199, 1993. Liewer, P. C., S. R. Karmesin, J. U. Brackbill, The effect of neutrals on the global heliosphere and interplanetary shock propagation time to the heliopause, Proceedings of Solar Wind 8 D. Winterhalter, J. Gosling, S. Habal, W. Kurth, M. Neugebauer, 382AIP, Woodbury, New York, 1996a. Liewer, P. C., S. R. Karmesin, J. U. Brackbill, Hydrodynamical instability of the heliopause driven by plasma-neutral charge-exchange interactions, J. Geophys. Res., 101, 17,119, 1996b. Osterbart, R., H. J. Fahr, A Boltzmann-kinetic approach to describe the entrance of neutral interstellar hydrogen into the heliosphere, Astron. Astrophys., 264, 260, 1992. Pauls, H. L., G. P. Zank, L. L. Williams, Interaction of the solar wind with the local interstellar medium, J. Geophys. Res., 10021, 595, 1995. Zank, G. P., H. L. Pauls, L. L. Williams, D. T. Hall, Multi-dimensional modelling of the solar wind — LISM interaction including neutrals: A Boltzmann approach, Proceedings of Solar Wind 8 D. Winterhalter, J. Gosling, S. Habal, W. Kurth, M. Neugebauer, 382AIP, Woodbury, New York, 1996a. Zank, G. P., H. L. Pauls, L. L. Williams, D. T. Hall, Interaction of the solar wind with the local interstellar medium: A multifluid approach, J. Geophys. Res., 10121, 639, 1996b. Citing Literature Volume102, IssueA51 May 1997Pages 9835-9837 ReferencesRelatedInformation

Shock waves propagation in the turbulent interplanetary plasma

The effect of turbulence on interplanetary shock waves propagation is considered. It is shown that background turbulence results in additional shock wave deceleration, which may be comparable with the deceleration due to plasma sweeping. The turbulent deceleration is connected with the energy losses due to the strong turbulence amplification behind the moving shock front.

Three‐dimensional MHD simulation of the April 14, 1994, interplanetary coronal mass ejection and its propagation to Earth and Ulysses

A three‐dimensional (3‐D), time‐dependent, magnetohydrodynamic (MHD) model is used to simulate the interplanetary propagation of a disturbance that started in the low corona via the destabilization of a southern hemisphere helmet‐streamer on April 14, 1994. A severe geomagnetic storm occurred at Earth, and a forward‐reverse shock structure was detected at Ulysses (3.2 AU) at E30°S60°. The model is initiated at 18Rs (where Rs is the solar radius, 6.95 × 105 km) within the supersonic and super‐Alfvenic region of the solar wind; hence no consideration is given to the disturbance's evolution from ∼ 1Rs to 18Rs. We refer to the interplanetary disturbance as an interplanetary/coronal mass ejection (ICME) to indicate that it may be relevant to what has been referred to in the literature as a CME but is not related to the flux rope or magnetic cloud that has also received much attention.We find that the 3‐D MHD model, with a simple pressure pulse (suggested by Yohkoh soft Xray observations), provides a satisfactory comparison with the SSC timing at Earth and the Ulysses observations.

Modeling the interplanetary propagation of 0.1–20 MeV shock-accelerated protons. I: Effects of the adiabatic deceleration and solar wind convection

The focused transport equation for particle propagation (Roelof, 1969) allows us to model flux and anisotropy profiles when the anisotropy is high for long periods. This equation has been applied to model Energetic Storm Particle events of these characteristics, assuming a source of accelerated protons at the front of the interplanetary shocks (Heras et al., 1992 and 1995). Nevertheless, its application is less accurate for energies below 0.5 MeV since the effects of adiabatic deceleration and solar wind convection are not negligible. We present a numerical code that includes both effects in the transport equation, and we apply different tests to validate it. We shortly discuss the influence of these effects in the flux and anisotropy profiles of Energetic Storm Particle Events.

Modeling the interplanetary propagation of 0.1–20 MeV shock-accelerated protons. II: Energy spectrum and evolution of the injection rate

Long lasting (i.e., > 2 days) transient proton fluxes associated with interplanetary shocks are generated by particle acceleration at the shock front while it is moving outwards from the Sun and expanding. Therefore, the physical conditions under which the particle acceleration takes place, “the efficiency of the process”, change as the shock does. We have evaluated the evolution of this injection rate on different Energetic Storm Particle events, for protons with energies from 91 keV to 20 MeV, by fitting the fluxes and anisotropies observed in their upstream region. The results are discussed in terms of the large-scale structure of the shock and its MHD strength at the point of the front magnetically connected with the observer.

Shock waves propagation in the turbulent interplanetary plasma

Effect of turbulence on interplanetary shock waves propagation is considered. It is shown that background turbulence results in the additional shock wave deceleration which may be comparable with the deceleration due to plasma sweeping. The turbulent deceleration is connected with the energy losses due to the strong turbulence amplification behind the moving shock front.

Shock Waves Propagation in the Turbulent Interplanetary Plasma

AbstractEffect of turbulence on interplanetary shock waves propagation is considered. It is shown that background turbulence results in the additional shock wave deceleration which may be comparable with the deceleration due to plasma sweeping. The turbulent deceleration is connected with the energy losses due to the strong turbulence amplification behind the moving shock front.

Relativistic solar proton events

Energetic solar flare particles contain rich information concerning mechanisms of particle acceleration on the Sun and subsequent transport through turbulent interplanetary space. Even the most energetic particles, in particular protons with kinetic energy above ∼500 MeV, may undergo coronal and interplanetary propagation effects, disturbing their accelerated injection spectrum after release from the solar flare. Relativistic solar proton events are recorded by neutron monitors at ground level. A detailed knowledge of the response of these ground-based detectors to the impact by a beam of protons on the top of the atmosphere is required to analyze these observations. The spectral index of arriving protons can be obtained from the response of the world-wide network of neutron monitors provided their directional anisotropy is known. The spectral index may also by determined from the relative enhancements in count rates of two similar detectors at different altitudes but similar asymptotic cones of acceptances, or from the relative enhancements of two detectors with different spectral sensitivities but at the same location of high latitude. Ground level enhancements from solar flare protons have been recorded at Sanae, Antarctica, since 1971 by two neutron monitors with different sensitivities to primary protons in the rigidity range from ≲1 GV to ∼5 GV. Spectral indexes of about 20 of these more energetic solar flare proton events have been determined from the two detector enhancements recorded at Sanae. These indexes do not show any increase (softening of the relativistic proton spectra) with increasing heliolongitude away from the preferred IMF connection region as was obtained for 20–80 MeV protons. Furthermore, most of the enhanced count rates show fluctuations larger than statistical, indicative of propagation in a mostly turbulent interplanetary magnetic field.

Acceleration and propagation of energetic charged particles in the inner heliosphere

Both particle propagation and acceleration are intimately related to the strength of scattering. I shall review some recent developments in our understanding of interplanetary propagation, in particular the dawn of a solution of the well-known discrepancy problem between mean free paths (mfp) derived from quasi-linear theory (QLT) and from fits to observational data. With this much improved understanding of particle scattering we can re-evaluate our understanding of particle acceleration at interplanetary shocks. Special attention is paid to the model of coupled hydrodynamic wave excitation and ion acceleration at shocks.

Jovian electron propagation in three dimensions of the heliosphere: The Ulysses Investigations

We report investigations of Jovian relativistic electrons in the interplanetary medium that provide new insights into both the physical processes by which the Jovian magnetosphere releases its trapped, relativistic electrons into the interplanetary medium, and the modes of their interplanetary propagation. These studies were dependent on the unique postencounter trajectory for Ulysses. The spacecraft remained close to the radial distance of Jupiter (∼5.2 AU) and moved southward on the duskside by only ∼12° in heliographic latitude and <8° in heliographic azimuth relative to Jupiter for the period of ∼100° days of this study. During this period the nominal Parker spiral interplanetary magnetic field with its alternating polarities sector structure established direct magnetic field line connections frequently between Jupiter and the spacecraft. These unique conditions made it possible to investigate in detail, for approximately four solar rotations, both the Jovian electron burst phenomenon and the continuous, diffusive interplanetary propagation of Jovian electrons. The Jovian electron burst phenomenon in the energy range 1‐20 MeV, with flux increasing up to 50 times the diffusive Jovian electron flux are now discovered to occur in both multiples of the planetary rotation period (∼10 hours) and occasionally in half rotation periods, namely, in sequences of 5‐, 10‐, 20‐, or 40‐hour intervals. Electrons in the burst are shown to stream from the magnetosphere and not the magnetotail to the spacecraft during times when the interplanetary magnetic field vector direction includes both Jupiter and the spacecraft. Over 90% of all electron bursts lasting ≥6 hours occurred during the positive magnetic field sector. The few bursts occurring in a negative sector (<10%) were associated with rapid changes in magnetic field orientation near a sector boundary. We found that the time for these burst sequences corresponded to either the dawnside or the duskside tilt of the magnetic dipole. This dawn‐dusk dipole tilt is in a plane approximately orthogonal to the Sun‐Jupiter line and aligned with the average interplanetary magnetic field direction at ∼5 AU. To interpret these measurements, we assumed that the release mechanism is intermittent reconnection of the interplanetary magnetic field with the opposite polarity of a component of the polar magnetospheric field. These experimental results appeared to exclude some models for electron release such as the magnetic anomaly model where the electrons are released into the magnetotail. The diffusive Jovian electron flux continuously present in the interplanetary medium confirmed the “10‐hour clock” variations of the differential energy spectral index found by Pioneer 10 in 1973. Present evidence indicates that this continuum of Jovian electrons with its 10‐hour rocking spectrum may be associated with the same release mechanism as the electron bursts.

Solar energetic particles in the intermediate region of the heliosphere

Energetic particle increases in the energy range 4 to 130 MeV observed by the Kiel Electron Telescope (KET) during the in-ecliptic part of the ULYSSES mission between 1 and 5.4 AU differ distinctly from their appearance in the inner heliosphere inside 1 AU. Prompt events are rare, and for most of the events velocity dispersion is lacking. The observed intensity-time profiles show poor time relations with optical solar flares. The data is far better organized by the structure of the interplanetary medium with its shocks, tangential discontinuities, corotating interaction regions, heliospheric current sheet crossings (sector boundaries), and coronal mass ejections. Nine particle events are discussed in detail. Spectral information as well as composition measurements are used to determine the source of the particle increases: solar, interplanetary, and Jovian. The few prompt events can be fitted with diffusive interplanetary propagation models, yielding radial mean free paths in the range λr = 0.05 to 0.15 AU. The shock related events are dominant at these intermediate distances, with particularly high intensities of MeV-electrons and > 30 MeV protons at merged or double shocks. A new feature are slowly-varying populations (SVP) with long time scales neither related to prompt events nor to local shock effects.

Solar cosmic rays

The first observations of solar cosmic rays were made simultaneously by many investigators at worldwide cosmic-ray stations in the periods of powerful chromospheric flares on February 28 and March 7, 1942. The discovery of these and the investigation of cosmic-ray solar-daily variations with maximum time near noon led some authors (Richtmyer and Teller, 1948; Alfven, 1949, 1950) to a model of apparent cosmic-ray solar origin. We present here the results of the properties of solar cosmic rays from ground events (experimental and theoretical investigations). We also discuss important information from solar experimental data relating to these ground events observed in September and October 1989 and May 1990. Some experimental evidence of acceleration processes in associated phenomena with flares and long-term (solar cycle) variation of the average flux of solar cosmic rays is discussed as also cornal and interplanetary propagation, and that in the terrestrial magnetosphere. Note that the energy spectrum of solar cosmic rays varied very strongly from one flare to another. What are the causes of these phenomena? What is the nature of chemical and isotopic contents of solar cosmic rays? How can its changes occur in the energy spectrum and chemical contents of solar cosmic rays in the process of propagation? Is it possible to recalculate these parameters to the source? What makes solar cosmic rays rich in heavy nucleus and3He? The important data about electrons, positrons, gamma-quanta and neutrons from flares will be discussed in a subsequent paper (Dorman and Venkatesan, 1992). The question is: What main acceleration mechanism of solar flare and associated phenomena are reliable? These problems are connected with the more general problem on solar flare origin and its energetics. In Dorman and Venkatesan (1993) we will consider these problems as well as the problem of prediction of radiation hazard from solar cosmic rays (not only in space, but also in the Earth's atmosphere too).

Solar and interplanetary shock effects on the flux and anisotropy profiles of an Energetic Storm Particle (ESP) event observed on 23–25 April 1979

A large Energetic Storm Particle event was observed by ISEE-3 between 23 and 25 April 1979. This event was associated with an interplanetary shock which was generated by a solar disappearing filament. Flux and anisotropy profiles in the upstream region of the event have been reproduced by means of a particle propagation model which includes particle injection both at the Sun and at the shock front. Injection at the front takes into account the fact that the IMF connection between the shock and the spacecraft is disrupted by the shock itself. The model, coupled to a 2D MHD time-dependent model, makes it possible for us to study the parameters for the interplanetary propagation of the particles, the injection rates both at the Sun and at the shock front, from near the Sun out to 1 AU.

MHD study of temporal and spatial evolution of simulated interplanetary shocks in the ecliptic plane within 1 AU

We utilize a 21/2-D MHD time-dependent model to perform a parametric study of interplanetary shock propagation to 1 AU. The input conditions are represented by the following variables:(1) initial shock velocity, (2) duration of the driving pulse, and (3) width of the pulse at the near-Sun position (18 solar radii). The total net energy added to the solar wind was calculated for each pulse. The forward shock's travel time to, and the peak dynamic pressure at, 1 AU as a function of location along the shock front have been studied over a range of total input pulse energies from 1029 to 1032 ergs. For input pulses with modest angular width and temporal duration, we find that the propagation of the resulting interplanetary fast forward shock waves depends primarily upon the net input energy. The dependence of the transit time upon energy is a power law with a -1/3 index which corresponds to the classical, piston driven case. Reverse shocks are also formed behind all but the lowest energy shocks. Their properties, although also a function of input energy, depend upon the specific values of the input pulse shock velocity, width and duration. We also briefly discuss the propagation of the shocks out to 1 AU, and the conditions for which the interplanetary shocks depart from being symmetric about the input pulse central meridian due to magnetic and dynamic effects.

Long-term effects of an interplanetary shock on the flux and anisotropy profiles of the associated low-energy particle event

A large energetic storm particle event associated with an interplanetary shock was detected by ISEE-3 on 24 April, 1979. We have studied the effects of this shock on the flux and anisotropy profiles in the upstream region of the particle event, and we have developed a propagation model that permits to reproduce the observations. This model includes particle injection, both at the Sun and at the shock, therefore it allows to study the parameters for the interplanetary propagation of low-energy particles, the particle injection rates, and to relate them to the conditions at the shock front.

Injection and diffusive transport of suprathermal through energetic solar flare protons (35 keV to 20 MeV)

We have investigated the injection and interplanetary propagation of low‐energy protons that originated in a prompt solar particle event on July 20, 1981. The event was highly unusual in that solar flare protons could be seen from suprathermal energies (35 keV) to the energetic particle range (20 MeV). The observations were made in interplanetary space using the low‐energy ion instrument (DFH) and ULEWAT instrument on ISEE 3. At the higher energies, the appearance of the time‐intensity and time‐anisotropy profiles in this event were characteristic of diffusive particle propagation; however, owing to extremely quiet interplanetary conditions, it was possible to observe solar particles down to proton energies well below previous studies. We were able to fit the observed time‐intensity and time‐anisotropy profiles over the entire energy range using a model based on the spherically symmetric Fokker‐Planck equation including convection, diffusion, and adiabatic deceleration. From our model fits we find that (1) the radial interplanetary diffusion coefficient K increases with heliocentric radius r as K = K0 rb, where b is close to 1; (2) the scattering mean free path for protons, λ, increases with particle rigidity P as λ ∝ P(0.22±0.03) over the range between 9 and 160 MV; and (3) at Earth orbit, λ values lie between 0.02 AU (for ∼0.5‐MeV electrons) and 0.17 AU (for protons, 10–20 MeV). Anisotropies in this event are long lasting (>48 hours) owing in part to an extended injection: the lower the energy, the longer the injection lasts. The extended period of injection appears to be evidence for diffusive coronal shock acceleration of protons during this event. Following the solar particle event maximum of intensity, a bidirectional streaming event was observed; during this period the particle anisotropies along with changes in the interplanetary magnetic field give evidence for the passage of a magnetic cloud by ISEE 3.

Coronal and interplanetary transport of solar energetic protons and electrons

We present a new method to separate interplanetary and coronal propagation, starting from intensity variations observed by spaceprobes at different heliolongitudes. In general, a decrease in absolute intensities is observed simultaneously with an increase in temporal delays. The coupling of these two effects can be described by Reid's model of coronal diffusion and can in principle be used to determine the two coronal time constants, diffusion time t c and escape time A. In addition, a least-squares fit method is used to determine the parameters of interplanetary transport, assuming a radial dependence as λ(r) = λ0(r/1 AU)b. The method is applied to the two solar events of 27 December, 1977 and 1 January, 1978 which were observed by the spaceprobes Helios 1, Helios 2, and Prognoz 6. Energetic particle data are analysed for 13–27 MeV protons and ∼-0.5 MeV electrons. For the regions in space encountered during these events the mean free path of electrons is smaller than that of protons. Straight interpolation between the two rigidities leads to a rather flat rigidity dependence λ(P) ∼ P n with n = 0.17–0.25. This contradicts the prediction of a constant mean free path or of the transition to scatter-free propagation below about 100 MV rigidity. In three of the four cases the mean free path of 13–27 MeV protons is of the order 0.17 AU, the mean free path of electrons of the order 0.06 AU. For protons we find b ∼- 0.7 for the exponent of the radial variation.

Observations related to the acceleration, injection, and interplanetary propagation of energetic protons during the solar cosmic ray event on February 16, 1984

Data from the worldwide network of neutron monitors and from the cosmic ray telescopes on IMP 8 have been used to deduce the intensity‐time profiles, the anisotropy‐time profiles, the energy spectra, and the pitch angle distributions of the solar protons near Earth during the solar cosmic ray event on February 16, 1984. In addition, measurements by particle detectors on the GOES 5 and 6 and ICE spacecraft were used in the analysis. The pronounced anisotropy of the particle fluxes, lasting ∼40 min at relativistic energies and more than 2 hours at ∼75 MeV, shows that the propagation of the solar protons in the interplanetary magnetic field (IMF) was practically scatter‐free (mean free path λ ≳ 2 AU) and that the injection of the particles into the IMF at the Sun was time‐extended. Although the analysis of the onset times of the event as a function of the reciprocal of the proton speeds does not clearly exclude a δ‐like acceleration of the flare protons, we infer that the solar protons with 70‐ to 500‐MeV energy were injected into the IMF 4 ± 2 min earlier than the relativistic protons. Proton energy spectra at the Sun over a range from 25 MeV to 10 GeV, as constructed from the solar proton observations at Earth, evolved with time in both amplitude and energy. The time evolution of the energy spectra at the Sun also suggests that the lower‐energy protons were accelerated earliest. These observations are consistent with an acceleration of the protons by a coronal shock.