Implications of fluctuations in the distribution functions of interstellar pick‐up ions for the scattering of low rigidity particles

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95235/1/grl9864.pd

Observed distribution functions of H, He, C, O, and Fe in corotating energetic particle streams: Implications for interplanetary acceleration and propagation

Distribution functions for H, He, C, O, and Fe derived from our IMP 8 measurements of approximately 0.15 to approximately 8 MeV/nucleon particles in three corotating streams observed near earth are shown to have a simple exponential dependence on the particle speed. The e-folding speed, v sub o, is typically 0.01c, is found to be the same for the distribution functions of all elements examined, and varies little from one corotating event to the next. The relative abundances of energetic particles in these events resemble most closely the solar coronal composition and, thus, presumably that of the solar wind. These results may imply that the acceleration of these particles, which occurs in corotating interaction regions at several AU from the sun, is by a statistical process

Acceleration of Galactic Cosmic Rays in the Interstellar Medium

Challenges have arisen to diffusive shock acceleration as the primary means to accelerate galactic cosmic rays (GCRs) in the interstellar medium. Diffusive shock acceleration is also under challenge in the heliosphere, where at least the simple application of diffusive shock acceleration cannot account for observations. In the heliosphere, a new acceleration mechanism has been invented—a pump mechanism, driven by ambient turbulence, in which particles are pumped up in energy out of a low-energy core particle population through a series of adiabatic compressions and expansions—that can account for observations not only at shocks but in quiet conditions in the solar wind and throughout the heliosheath. In this paper, the pump mechanism is applied to the acceleration of GCRs in the interstellar medium. With relatively straightforward assumptions about the magnetic field in the interstellar medium, and how GCRs propagate in this field, the pump mechanism yields (1) the overall shape of the GCR spectrum, a power law in particle kinetic energy, with a break at the so-called knee in the GCR spectrum to a slightly steeper power-law spectrum. (2) The rigidity dependence of the H/He ratio observed from the PAMELA satellite instrument.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98584/1/0004-637X_744_2_127.pd

The case for a common spectrum of particles accelerated in the heliosphere: Observations and theory

In the last decade a significant discovery has been made in the heliosphere: the spectrum of particles accelerated in both the inner heliosphere and in the heliosheath is the same: a power law in particle speed with a spectral index of −5, when the spectrum is expressed as a distribution function; or equivalently, a differential intensity spectrum that is a power law in energy with a spectral index of −1.5. In the inner heliosphere this common spectrum occurs at quite low energies and is most evident in instruments designed to measure suprathermal particles. In the heliosheath, the common spectrum is observed over the full energy range of the Voyager energetic particle instruments, up to energies of ~100 MeV. The remarkable discovery of a common spectrum is compounded by the realization that no traditional acceleration mechanism, i.e., diffusive shock acceleration or stochastic acceleration, can account for the common spectrum. There is thus an opportunity to once again demonstrate the relevance of heliospheric physics by developing a new acceleration mechanism that yields the common spectrum, with the expectation that such a new acceleration mechanism will find broader applications in astrophysics. In this paper, the observations of the common spectrum in the heliosphere are summarized, with emphasis on those that best reveal the conditions in which the acceleration must operate. Then, building on earlier work, a complete derivation is presented of an acceleration mechanism, a pump acceleration mechanism, that yields the common spectrum, and the various subtleties associated with this derivation are discussed. Key Points Particles accelerated in the heliosphere have a common spectrum Traditional acceleration mechanisms do not yield the common spectrum A pump acceleration mechanism does yield the common spectrumPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110081/1/jgra51409.pd

Ionization states of heavy elements observed in the 1974 May 14-15 anomalous solar particle event

The charge states of heavy ions accelerated in the (3)He-Fe rich solar particle event of 1974 May 14-15 are determined using data from the Interplanetary Monitoring Platform-8. In addition to Fe(+11,12) both 0(+5) and Fe(+16,17,18) are also present suggesting variations in coronal temperatures over a range from approximately 400,000 to 5,000,000 K. The presence of 0(+5) and Fe(+16-18) may be explained by a resonant plasma heating mechanism proposed to account for the enhancements of (3)He and Fe

A test for whether or not Voyager 1 has crossed the heliopause

The Voyager 1 spacecraft is currently in the vicinity of the heliopause, which separates the heliosphere from the local interstellar medium. There has been a precipitous decrease in particles accelerated in the heliosphere and a substantial increase in galactic cosmic rays (GCRs). The evidence is unclear, however, as to whether Voyager 1 has crossed the heliopause into the local interstellar medium or remains within the heliosheath. In this Letter we propose a test that will determine whether Voyager 1 has crossed the heliopause: If Voyager 1 remains in the heliosheath, the high densities observed must be due to compressed solar wind, with the consequence that Voyager 1 will encounter another current sheet, where the polarity of the magnetic field reverses. Voyager 1 observations can be used to predict that the next current sheet crossing is likely to occur during 2015. Key Points Voyager 1 is predicted to encounter the heliospheric current sheet again Such an encounter would demonstrate that Voyager 1 remains in the heliosheathPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/108626/1/grl51945.pd

Statistical acceleration of interstellar pick‐up ions in co‐rotating interaction regions

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94615/1/grl9663.pd

Limitations on suprathermal tails of electrons in the lower solar corona

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95261/1/grl9586.pd

Weak pitch angle scattering of few MV rigidity ions from measurements of anisotropies in the distribution function of interstellar pickup H +

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95477/1/grl8632.pd

Unusual composition of the solar wind in the 2–3 May 1998 CME observed with SWICS on ACE

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95193/1/grl11810.pd