Search Publications
Wave-Number Spectra and Intermittency in the Terrestrial Foreshock Region
Glassmeier, K. -H.; Narita, Y.; Treumann, R. A.
Wave-number spectra of magnetic field fluctuations are directly determined in the terrestrial foreshock region (upstream of a quasiparallel collisionless shock wave) using four-point Cluster spacecraft measurements. The spectral curve is characterized by three ranges reminiscent of turbulence: energy injection, inertial, and dissipation range. The…
Measurement of the Electric Fluctuation Spectrum of Magnetohydrodynamic Turbulence
Bale, S. D.; Horbury, T. S.; Reme, H. +2 more
Magnetohydrodynamic (MHD) turbulence in the solar wind is observed to show the spectral behavior of classical Kolmogorov fluid turbulence over an inertial subrange and departures from this at short wavelengths, where energy should be dissipated. Here we present the first measurements of the electric field fluctuation spectrum over the inertial and…
Gamma-Ray Constraint on Galactic Positron Production by MeV Dark Matter
Bertone, Gianfranco; Beacom, John F.; Bell, Nicole F.
The Galactic positrons, as observed by their annihilation gamma-ray line at 0.511 MeV, are difficult to account for with astrophysical sources. It has been proposed that they are produced instead by dark matter annihilation or decay in the inner Galactic halo. To avoid other constraints, these processes are required to occur “invisibly,” such that…
Spatial Correlation of Solar-Wind Turbulence from Two-Point Measurements
Dasso, S.; Matthaeus, W. H.; Smith, C. W. +3 more
Interplanetary turbulence, the best studied case of low frequency plasma turbulence, is the only directly quantified instance of astrophysical turbulence. Here, magnetic field correlation analysis, using for the first time only proper two-point, single time measurements, provides a key step in unraveling the space-time structure of interplanetary …
Weak Compressible Magnetohydrodynamic Turbulence in the Solar Corona
Chandran, Benjamin D. G.
This Letter presents a calculation of the power spectra of weakly turbulent Alfvén waves and fast magnetosonic waves (“fast waves”) in low-β plasmas. It is shown that three-wave interactions transfer energy to high-frequency fast waves and, to a lesser extent, high-frequency Alfvén waves. High-frequency waves produced by MHD turbulence are a promi…
Drift-Kinetic Alfvén Waves Observed near a Reconnection X Line in the Earth's Magnetopause
Balogh, A.; Reme, H.; Goldstein, M. L. +7 more
We identify drift-kinetic Alfvén waves in the vicinity of a reconnection X line on the Earth’s magnetopause. The dispersive properties of these waves have been determined using wavelet interferometric techniques applied to multipoint observations from the Cluster spacecraft. Comparison of the observed wave dispersion with that expected for drift-k…
Ion-Pressure Equations Derived from Measurements in Space
Stasiewicz, K.
Cluster measurements at the bow shock, the magnetosheath, and the magnetospheric boundary layer are used to derive ion-pressure equations for hot anisotropic plasmas. It is demonstrated that both perpendicular and parallel ion pressures are well approximated by polybaric expressions ∝NγBκ, where N is the plasma density, B is …
Proper Orthogonal Decomposition of Solar Photospheric Motions
Vecchio, A.; Carbone, V.; Veltri, P. +5 more
The spatiotemporal dynamics of the solar photosphere is studied by performing a proper orthogonal decomposition (POD) of line of sight velocity fields computed from high resolution data coming from the MDI/SOHO instrument. Using this technique, we are able to identify and characterize the different dynamical regimes acting in the system. Low-frequ…
MeV Dark Matter: Has It Been Detected?
Silk, Joseph; Hooper, Dan; Paul, Jacques +2 more
We discuss the possibility that the recent detection of 511keV γ rays from the galactic bulge, as observed by INTEGRAL, is a consequence of low mass (1 100 MeV) particle dark matter annihilations. We discuss the type of halo profile favored by the observations as well as the size of the annihilation cross section needed to account for the signal. …
Structure of the Magnetic Reconnection Diffusion Region from Four-Spacecraft Observations
André, M.; Khotyaintsev, Y.; Vaivads, A. +6 more
Magnetic reconnection leads to energy conversion in large volumes in space but is initiated in small diffusion regions. Because of the small sizes of the diffusion regions, their crossings by spacecraft are rare. We report four-spacecraft observations of a diffusion region encounter at the Earth's magnetopause that allow us to reliably distinguish…